title
stringlengths 4
245
| abstract
stringlengths 26
3.26k
|
|---|---|
Fisher vs. Bayes : A comparison of parameter estimation techniques for
massive black hole binaries to high redshifts with eLISA | Massive black hole binaries are the primary source of gravitational waves
(GW) for the future eLISA observatory. The detection and parameter estimation
of these sources to high redshift would provide invaluable information on the
formation mechanisms of seed black holes, and on the evolution of massive black
holes and their host galaxies through cosmic time. The Fisher information
matrix has been the standard tool for GW parameter estimation in the last two
decades. However, recent studies have questioned the validity of using the
Fisher matrix approach. For example, the Fisher matrix approach sometimes
predicts errors of $\geq100\%$ in the estimation of parameters such as the
luminosity distance and sky position. With advances in computing power,
Bayesian inference is beginning to replace the Fisher matrix approximation in
parameter estimation studies. In this work, we conduct a Bayesian inference
analysis for 120 sources situated at redshifts of between $0.1\leq z\leq 13.2$,
and compare the results with those from a Fisher matrix analysis. The Fisher
matrix results suggest that for this particular selection of sources, eLISA
would be unable to localize sources at redshifts of $z\lesssim6$. In contrast,
Bayesian inference provides finite error estimations for all sources in the
study, and shows that we can establish minimum closest distances for all
sources. The study further predicts that we should be capable with eLISA, out
to a redshift of at least $z\leq13$, of predicting a maximum error in the chirp
mass of $\lesssim 1\%$, the reduced mass of $\lesssim20\%$, the time to
coalescence of 2 hours, and to a redshift of $z\sim5$, the inclination of the
source with a maximum error of $\sim60$ degrees.
|
Tidal bridge and tidal dwarf candidates in the interacting system Arp194 | Arp194 is a system of recently collided galaxies, where the southern galaxy
(S) passed through the gaseous disc of the northern galaxy (N) which in turn
consists of two close components. This system is of special interest due to the
presence of regions of active star-formation in the bridge between galaxies,
the brightest of which (the region A) has a size of at least 4 kpc. We obtained
three spectral slices of the system for different slit positions at the 6-m
telescope of SAO RAS. We estimated the radial distribution of line-of-sight
velocity and velocity dispersion as well as the intensities of emission lines
and oxygen abundance $12+\log(\mathrm{O/H})$. The gas in the bridge is only
partially mixed chemically and spatially: we observe the O/H gradient with the
galactocentric distances both from S and N galaxies and a high dispersion of
O/H in the outskirts of N-galaxy. Velocity dispersion of the emission-line gas
is the lowest in the star-forming sites of the bridge and exceeds 50-70 km/s in
the disturbed region of N-galaxy. Based on the SDSS photometrical data and our
kinematical profiles we measured the masses of stellar population and the
dynamical masses of individual objects. We confirm that the region A is the
gravitationally bound tidal dwarf with the age of $10^7 - 10^8 $ yr, which is
falling onto the parent S- galaxy. There is no evidence of the significant
amount of dark matter in this dwarf galaxy.
|
The Spectral and Temporal Properties of Transient Sources in Early-Type
Galaxies | We report the spectral and temporal variability properties of 18 candidate
transient and potential transient (TC and PTC) sources detected in deep
multi-epoch Chandra observation of the nearby elliptical galaxies, NGC 3379,
NGC 4278 and NGC 4697. Only one source can be identified with a background
counterpart, leaving 17 TCs + PTCs in the galaxies. Of these, 14 are in the
galaxy field, supporting the theoretical picture that the majority of field
X-ray binaries (XRBs) will exhibit transient accretion for >75% of their
lifetime. Three sources are coincident with globular clusters (GCs), including
two high-luminosity candidate black hole (BH) XRBs, with Lx=5.4E38 erg/s, and
Lx=2.8E39 erg/s, respectively. The spectra, luminosities and temporal behavior
of these 17 sources suggest that the transient population is heterogeneous,
including neutron star (NS) and BH XRBs in both normal and high-rate accretion
modes, and super soft sources containing white dwarf binaries. Our TC and PTC
detections are noticeably fewer that the number expected from the populations
synthesis (PS) models of Fragos et al. (2009), tailored to our new Chandra
pointings of NGC 4278. We attribute this discrepancy to the PS assumption that
the transient population is composed of NS XRBs, as well as differences between
the statistical analysis and error estimates used in the model and our
observations.
|
Extended Schmidt law holds for faint dwarf irregular galaxies | The extended Schmidt law (ESL) is a variant of the Schmidt law which relates
the surface densities of gas and star formation, with the surface density of
stellar mass added as an extra parameter. We empirically investigate for the
first time whether low metallicity faint dwarf irregular galaxies (dIrrs)
follow the ESL. Here we consider the `global' law where surface densities are
averaged over the galactic discs. dIrrs are unique not only because they are at
the lowest end of mass and star formation scales for galaxies, but also because
they are metal-poor compared to the general population of galaxies. Our sample
is drawn from the Faint Irregular Galaxy GMRT Survey (FIGGS) which is the
largest survey of atomic hydrogen in such galaxies. The gas surface densities
are determined using their atomic hydrogen content. The star formation rates
are calculated using GALEX far ultraviolet fluxes after correcting for dust
extinction, whereas the stellar surface densities are calculated using Spitzer
3.6 $\mu$m fluxes. All surface densities are calculated over stellar discs
defined by the 3.6 $\mu$m images. We find dIrrs indeed follow the extended
Schmidt law. The mean deviation of the FIGGS galaxies from the relation is 0.01
dex, with a scatter around the relation of less than half that seen in the
original relation. In comparison, we also show that the FIGGS galaxies are much
more deviant when compared to the `canonical' Kennicutt-Schmidt relation. Our
results help strengthen the universality of the extended Schmidt law,
especially for galaxies with low metallicities. We suggest that models of star
formation in which feedback from previous generations of stars set the pressure
in the ISM, are promising candidates for explaining the ESL. We also confirm
that ESL is an independent relation and not a form of a relation between star
formation efficiency and metallicity.
|
Gravitational corrections to light propagation in a perturbed
FLRW-universe and corresponding weak lensing spectra | When the gravitational lensing of the large-scale structure is calculated
from a cosmological model a few assumptions enter: $(i)$ one assumes that the
photons follow unperturbed background geodesics, which is usually referred to
as the Born-approximation, $(ii)$ the lenses move slowly, $(iii)$ the
source-redshift distribution is evaluated relative to the background quantities
and $(iv)$ the lensing effect is linear in the gravitational potential. Even
though these approximations are small individually they could sum up,
especially since they include local effects such as the Sachs-Wolfe and
peculiar motion, but also non-local ones like the Born-approximation and the
integrated Sachs-Wolfe effect. In this work we will address all points
mentioned and perturbatively calculate the effect on a tomographic cosmic shear
power spectrum of each effect individually as well as all cross-correlations.
Our findings show that each effect is at least 4 to 5 orders of magnitude below
the leading order lensing signal. Finally we sum up all effects to estimate the
overall impact on parameter estimation by a future cosmological weak lensing
survey such as Euclid in a $w$CDM cosmology with parametrisation
$\Omega_\mathrm{m}$, $\sigma_8$,$n_\mathrm{s}$, $h$, $w_0$ and $w_\mathrm{a}$,
using 5 tomographic bins. We consistently find a parameter bias of $10^{-5}$,
which is therefore completely negligible for all practical purposes, confirming
that other effects such as intrinsic alignments and magnification bias will be
the dominant systematic source in future surveys.
|
A Deep Census of Outlying Star Formation in the M101 Group | We present deep, narrowband imaging of the nearby spiral galaxy M101 and its
group environment to search for star-forming dwarf galaxies and outlying HII
regions. Using the Burrell Schmidt telescope, we target the brightest emission
lines of star-forming regions, H$\alpha$, H$\beta$, and [OIII], to detect
potential outlying star-forming regions. Our survey covers $\sim$6 square
degrees around M101, and we detect objects in emission down to an H$\alpha$
flux level of $5.7 \times 10^{-17}$ erg s$^{-1}$ cm$^{-2}$ (equivalent to a
limiting SFR of $1.7 \times 10^{-6}$ $M_\odot$ yr$^{-1}$ at the distance of
M101). After careful removal of background contaminants and foreground M stars,
we detect 19 objects in emission in all three bands, and 8 objects in emission
in H$\alpha$ and [OIII]. We compare the structural and photometric properties
of the detected sources to Local Group dwarf galaxies and star-forming galaxies
in the 11HUGS and SINGG surveys. We find no large population of outlying HII
regions or undiscovered star-forming dwarfs in the M101 Group, as most sources
(93%) are consistent with being M101 outer disk HII regions. Only two sources
were associated with other galaxies: a faint star-forming satellite of the
background galaxy NGC 5486, and a faint outlying HII region near the M101
companion NGC 5474. We also find no narrowband emission associated with
recently discovered ultradiffuse galaxies and starless HI clouds near M101. The
lack of any hidden population of low luminosity star-forming dwarfs around M101
suggests a rather shallow faint end slope (as flat as $\alpha \sim -1.0$) for
the star-forming luminosity function in the M101 Group. We discuss our results
in the context of tidally-triggered star formation models and the interaction
history of the M101 Group.
|
A Search for H I Lyman $\alpha$ Counterparts to Ultra-Fast X-ray
Outflows | Prompted by the H I Ly$\alpha$ absorption associated with the X-ray
ultra-fast outflow at -17,300 $\rm km~s^{-1}$ in the quasar PG~1211+143, we
have searched archival UV spectra at the expected locations of H I Ly$\alpha$
absorption for a large sample of ultra-fast outflows identified in XMM-Newton
and Suzaku observations. Sixteen of the X-ray outflows have predicted H I
Ly$\alpha$ wavelengths falling within the bandpass of spectra from either the
Far Ultraviolet Spectroscopic Explorer or the Hubble Space Telescope, although
none of the archival observations were simultaneous with the X-ray observations
in which UFOs were detected. In our spectra broad features with full-width at
half-maximum of 1000 $\rm km~s^{-1}$ have 2-$\sigma$ upper limits on the H I
column density of generally <$2\times10^{13}~\rm cm^{-2}$. Using grids of
photoionization models covering a broad range of spectral energy distributions,
we find that producing Fe XXVI Ly$\alpha$ X-ray absorption with equivalent
widths $>30$ eV and associated H I Ly$\alpha$ absorption with $\rm
N_{HI}<2\times10^{13}~cm^{-2}$ requires total absorbing column densities $\rm
N_{H}>5\times10^{22}~cm^{-2}$ and ionization parameters log $\xi$ > 3.7.
Nevertheless, a wide range of SEDs would predict observable H I Ly$\alpha$
absorption if ionization parameters are only slightly below peak ionization
fractions for Fe XXV and Fe XXVI. The lack of Ly$\alpha$ features in the
archival UV spectra indicates that either the UFOs have very high ionization
parameters, very hard UV-ionizing spectra, or that they were not present at the
time of the UV spectral observations due to variability.
|
Large-scale HI in nearby radio galaxies (II): the nature of classical
low-power radio sources | An important aspect of solving the long-standing question as to what triggers
various types of Active Galactic Nuclei involves a thorough understanding of
the overall properties and formation history of their host galaxies. This is
the second in a series of papers that systematically study the large-scale
properties of cold neutral hydrogen (HI) gas in nearby radio galaxies. The main
goal is to investigate the importance of gas-rich galaxy mergers and
interactions among radio-loud AGN. In this paper we present results of a
complete sample of classical low-power radio galaxies. We find that extended
Fanaroff & Riley type-I radio sources are generally not associated with
gas-rich galaxy mergers or ongoing violent interactions, but occur in
early-type galaxies without large (> 10^8 M_sun) amounts of extended neutral
hydrogen gas. In contrast, enormous discs/rings of HI gas (with sizes up to 190
kpc and masses up to 2 x 10^10 M_sun) are detected around the host galaxies of
a significant fraction of the compact radio sources in our sample. This
segregation in HI mass with radio source size likely indicates that these
compact radio sources are either confined by large amounts of gas in the
central region, or that their fuelling is inefficient and different from the
fuelling process of classical FR-I radio sources. To first order, the overall
HI properties of our complete sample (detection rate, mass and morphology)
appear similar to those of radio-quiet early-type galaxies. If confirmed by
better statistics, this would imply that low-power radio-AGN activity may be a
short and recurrent phase that occurs at some point during the lifetime of many
early-type galaxies.
|
Nonlinear power spectrum in the presence of massive neutrinos:
perturbation theory approach, galaxy bias and parameter forecasts | Future or ongoing galaxy redshift surveys can put stringent constraints on
neutrinos masses via the high-precision measurements of galaxy power spectrum,
when combined with cosmic microwave background (CMB) information. In this paper
we develop a method to model galaxy power spectrum in the weakly nonlinear
regime for a mixed dark matter (CDM plus finite-mass neutrinos) model, based on
perturbation theory (PT) whose validity is well tested by simulations for a CDM
model. In doing this we carefully study various aspects of the nonlinear
clustering and then arrive at a useful approximation allowing for a quick
computation of the nonlinear power spectrum as in the CDM case. The nonlinear
galaxy bias is also included in a self-consistent manner within the PT
framework. Thus the use of our PT model can give a more robust understanding of
the measured galaxy power spectrum as well as allow for higher sensitivity to
neutrino masses due to the gain of Fourier modes beyond the linear regime.
Based on the Fisher matrix formalism, we find that BOSS or Stage-III type
survey, when combined with Planck CMB information, gives a precision of total
neutrino mass constraint, sigma(m_nu,tot) 0.1eV, while Stage-IV type survey may
achieve sigma(m_nu,tot) 0.05eV, i.e. more than a 1-sigma detection of neutrino
masses. We also discuss possible systematic errors on dark energy parameters
caused by the neutrino mass uncertainty. The significant correlation between
neutrino mass and dark energy parameters is found, if the information on power
spectrum amplitude is included. More importantly, for Stage-IV type survey, a
best-fit dark energy model may be biased and falsely away from the underlying
true model by more than the 1-sigma statistical errors, if neutrino mass is
ignored in the model fitting.
|
Simulations of the Origin and Fate of the Galactic Center Cloud G2 | We investigate the origin and fate of the recently discovered gas cloud G2
close to the Galactic Center. Our hydrodynamical simulations focussing on the
dynamical evolution of the cloud in combination with currently available
observations favor two scenarios: a Compact Cloud which started around the year
1995 and a Spherical Shell of gas, with an apocenter distance within the
disk(s) of young stars and a radius of a few times the size of the Compact
Cloud. The former is able to explain the detected signal of G2 in the
position-velocity diagram of the Br gamma emission of the year 2008.5 and
2011.5 data. The latter can account for both, G2's signal as well as the
fainter extended tail-like structure G2t seen at larger distances from the
black hole and smaller velocities. In contrast, gas stripped from a compact
cloud by hydrodynamical interactions is not able to explain the location of the
detected G2t emission in the observed position-velocity diagrams. This favors
the Spherical Shell Scenario and might be a severe problem for the Compact
Cloud as well as the so-called Compact Source Scenario. From these first
idealized simulations we expect a roughly constant feeding of the supermassive
black hole through a nozzle-like structure over a long period, starting shortly
after the closest approach in 2013.51 for the Compact Cloud. If the matter
accretes in the hot accretion mode, we do not expect a significant boost of the
current activity of Sgr A* for the Compact Cloud model, but a boost of the
average infrared and X-ray luminosity by roughly a factor of 80 for the
Spherical Shell scenario with order of magnitude variations on a timescale of a
few months. The near-future evolution of the cloud will be a sensitive probe of
the conditions of the gas distribution in the milli-parsec environment of the
massive black hole in the Galactic Center.
|
Signatures of First Stars in Galaxy Surveys: Multi-Tracer Analysis of
the Supersonic Relative Velocity Effect and the Constraints from the BOSS
Power Spectrum Measurements | We study the effect of the supersonic relative velocity between dark matter
and baryons on large-scale galaxy clustering and derive the constraint on the
relative velocity bias parameter from the Baryonic Oscillation Spectroscopic
Survey (BOSS) power spectrum measurements. Recent work has shown that the
relative velocity effect may have a dramatic impact on the star formation at
high redshifts, if first stars are formed in minihalos around z~20, or if the
effect propagates through secondary effects to stars formed at later redshifts.
The relative velocity effect has particularly strong signatures in the large
scale clustering of these sources, including the BAO position. Assuming that a
small fraction of stars in low-redshift massive galaxies retain the memory of
the primordial relative velocity effect, galaxy clustering measurements can be
used to constrain the signatures of the first stars. Luminous red galaxies
contain some of the oldest stars in the Universe and are ideally suited to
search for this effect. Using the BOSS power spectrum measurements from the
Sloan Data Release 9, in combination with Planck, we derive the upper limit on
the fraction of the stars sensitive to relative velocity effect f_star<3.3% at
the 95% confidence level in the CMASS galaxy sample. If additional galaxy
sample not sensitive to the effect is available in a given survey, a joint
multi-tracer analysis can be applied to construct a sample-variance cancelling
combination, providing a model-independent way to verify the presence of the
relative velocity effect in the galaxy power spectrum on large scales. Such a
multi-tracer analysis in future galaxy surveys can greatly improve the current
constraint, achieving a 0.1% level in f_star.
|
Supermassive black holes with high accretion rates in active galactic
nuclei: I. First results from a new reverberation mapping campaign | We report first results from a large project to measure black hole (BH) mass
in high accretion rate active galactic nuclei (AGNs). Such objects may be
different from other AGNs in being powered by slim accretion disks and showing
saturated accretion luminosities, but both are not yet fully understood. The
results are part of a large reverberation mapping (RM) campaign using the 2.4-m
Shangri-La telescope at the Yunnan Observatory in China. The goals are to
investigate the gas distribution near the BH and the properties of the central
accretion disks, to measure BH mass and Eddington ratios, and to test the
feasibility of using such objects as a new type of cosmological candles. The
paper presents results for three objects, Mrk 335, Mrk 142 and IRAS F12397+3333
with H$\beta$ time lags relative to the 5100\AA\ continuum of
$10.6^{+1.7}_{-2.9}$, $6.4^{+0.8}_{-2.2}$ and $11.4^{+2.9}_{-1.9}$ days,
respectively. The corresponding BH masses are $(8.3_{-3.2}^{+2.6})\times
10^6M_{\odot}$, $(3.4_{-1.2}^{+0.5})\times 10^6M_{\odot}$ and
$(7.5_{-4.1}^{+4.3})\times 10^6M_{\odot}$, and the lower limits on the
Eddington ratios 0.6, 2.3, and 4.6 for the minimal radiative efficiency of
0.038. Mrk 142 and IRAS F12397+333 (extinction corrected) clearly deviate from
the currently known relation between H$\beta$ lag and continuum luminosity. The
three Eddington ratios are beyond the values expected in thin accretion disks
and two of them are the largest measured so far among objects with RM-based BH
masses. We briefly discuss implications for slim disks, BH growth and
cosmology.
|
Constraining power of cosmological observables: blind redshift spots and
optimal ranges | A cosmological observable measured in a range of redshifts can be used as a
probe of a set of cosmological parameters. Given the cosmological observable
and the cosmological parameter, there is an optimum range of redshifts where
the observable can constrain the parameter in the most effective manner. For
other redshift ranges the observable values may be degenerate with respect to
the cosmological parameter values and thus inefficient in constraining the
given parameter. These are blind redshift ranges. We determine the optimum and
the blind redshift ranges of cosmological observables with respect to the
cosmological parameters: matter density parameter $\Omega_m$, equation of state
parameter $w$ and a modified gravity parameter $g_a$ which parametrizes the
evolution of an effective Newton's constant. We consider the observables:
growth rate of matter density perturbations expressed through $f(z)$ and
$f\sigma_8$, the distance modulus $\mu(z)$, Baryon Acoustic Oscillation
observables $D_V(z) \times \frac{r_s^{fid}}{r_s}$, $H \times
\frac{r_s}{r_s^{fid}}$ and $D_A \times \frac{r_s^{fid}}{r_s}$, $H(z)$
measurements and the gravitational wave luminosity distance. We introduce a new
statistic $S_P^O(z)\equiv \frac{\Delta O}{\Delta P}(z) \cdot V_{eff}^{1/2}$,
including the effective survey volume $V_{eff}$, as a measure of the
constraining power of a given observable $O$ with respect to a cosmological
parameter $P$ as a function of redshift $z$. We find blind redshift spots $z_b$
($S_P^O(z_b)\simeq 0$) and optimal redshift spots $z_s$ ($S_P^O(z_s)\simeq
max$) for these observables with respect to the parameters $\Omega_m$, $w$ and
$g_a$. For $O=f\sigma_8$ and $P=(\Omega_{m},w,g_a)$ we find blind spots at
$z_b\simeq(1,2,2.7)$ respectively and optimal (sweet) spots at
$z_s=(0.5,0.8,1.2)$. Thus probing higher redshifts may be less effective than
probing lower redshifts with higher accuracy.
|
A New Automatic Method to Identify Galaxy Mergers I. Description and
Application to the STAGES Survey | We present an automatic method to identify galaxy mergers using the
morphological information contained in the residual images of galaxies after
the subtraction of a Sersic model. The removal of the bulk signal from the host
galaxy light is done with the aim of detecting the fainter minor mergers. The
specific morphological parameters that are used in the merger diagnostic
suggested here are the Residual Flux Fraction and the asymmetry of the
residuals. The new diagnostic has been calibrated and optimized so that the
resulting merger sample is very complete. However, the contamination by
non-mergers is also high. If the same optimization method is adopted for
combinations of other structural parameters such as the CAS system, the merger
indicator we introduce yields merger samples of equal or higher statistical
quality than the samples obtained through the use of other structural
parameters. We explore the ability of the method presented here to select minor
mergers by identifying a sample of visually classified mergers that would not
have been picked up by the use of the CAS system, when using its usual limits.
Given the low prevalence of mergers among the general population of galaxies
and the optimization used here, we find that the merger diagnostic introduced
in this work is best used as a negative merger test, i.e., it is very effective
at selecting non-merging galaxies. As with all the currently available
automatic methods, the sample of merger candidates selected is contaminated by
non-mergers, and further steps are needed to produce a clean sample. This
merger diagnostic has been developed using the HST/ACS F606W images of the
A901/02 cluster (z=0.165) obtained by the STAGES team. In particular, we have
focused on a mass and magnitude limited sample (log M/M_{O}>9.0,
R_{Vega}<23.5mag)) which includes 905 cluster galaxies and 655 field galaxies
of all morphological types.
|
H3+ and UKIRT: a saga of discovery | This paper relates the history of attempts to detect H3+ in the dense
interstellar medium, from the early 1980's to the successful detection in 1996.
|
Interacting viscous entropy-corrected holographic scalar field models of
dark energy with time-varying G in modified FRW cosmology | We study the entropy-corrected version of the holographic dark energy (HDE)
model in the framework of modified FRW cosmology. We consider a non-flat
universe filled with an interacting viscous entropy-corrected HDE (ECHDE) with
dark matter. We also include the case of variable gravitational constant G in
our model. We obtain the equation of state and the deceleration parameters of
the interacting viscous ECHDE. Moreover, we reconstruct the potential and the
dynamics of the quintessence, tachyon, K-essence and dilaton scalar field
models according to the evolutionary behavior of the interacting viscous ECHDE
model with time-varying G.
|
A New Solution to the Plasma Starved Event Horizon Magnetosphere:
Application to the Forked Jet in M87 | Very Long Baseline Interferometry observations at 86 GHz reveal an almost
hollow jet in M87 with a forked morphology. The detailed analysis presented
here indicates that the spectral luminosity of the central spine of the jet in
M87 is a few percent of that of the surrounding hollow jet $200 -400
\mu\rm{as}$ from the central black hole. Furthermore, recent jet models in
indicate that a hollow "tubular" jet can explain a wide range of plausible
broadband spectra originating from jetted plasma located within $\sim
30\mu\rm{as}$ of the central black hole, including the 230 GHz correlated flux
detected by the Event Horizon Telescope. Most importantly, these hollow jets
from the inner accretion flow have an intrinsic power capable of energizing the
global jet out to kiloparsec scales. Thus motivated, this paper considers new
models of the event horizon magnetosphere (EHM) in low luminosity accretion
systems. Contrary to some models, the spine is not an invisible powerful jet.
It is an intrinsically weak jet. In the new EHM solution, the accreted poloidal
magnetic flux is weak and the background photon field is weak. It is shown how
this accretion scenario naturally results in the dissipation of the accreted
poloidal magnetic flux in the EHM not the accumulation of poloidal flux
required for a powerful jet. The new solution indicates less large scale
poloidal magnetic flux (and jet power) in the EHM than in the surrounding
accretion flow and cannot support significant EHM driven jets.
|
Discovery of New Dwarf Galaxy near The Isolated Spiral Galaxy NGC 6503 | We report the discovery of a new dwarf galaxy (NGC6503-d1) during the Subaru
extended ultraviolet (XUV) disk survey. It is a likely companion of the spiral
galaxy NGC6503. The resolved images, in B, V, R, i, and Halpha, show an
irregular appearance due to bright stars with underlying, smooth and unresolved
stellar emission. It is classified as the transition type (dIrr/dSph). Its
structural properties are similar to those of the dwarfs in the Local Group,
with a V absolute magnitude ~ -10.5, half-light radius ~400 pc, and central
surface brightness ~25.2. Despite the low stellar surface brightness
environment, one HII region was detected, though its Halpha luminosity is low,
indicating an absence of any appreciable O-stars at the current epoch. The
presence of multiple stellar populations is indicated by the color-magnitude
diagram of ~300 bright resolved stars and the total colors of the dwarf, with
the majority of its total stellar mass ~4x10^6 Msun in an old stellar
population.
|
Fractal universe and quantum gravity | We propose a field theory which lives in fractal spacetime and is argued to
be Lorentz invariant, power-counting renormalizable, ultraviolet finite, and
causal. The system flows from an ultraviolet fixed point, where spacetime has
Hausdorff dimension 2, to an infrared limit coinciding with a standard
four-dimensional field theory. Classically, the fractal world where fields live
exchanges energy momentum with the bulk with integer topological dimension.
However, the total energy momentum is conserved. We consider the dynamics and
the propagator of a scalar field. Implications for quantum gravity, cosmology,
and the cosmological constant are discussed.
|
Conformal Invariance, Dark Energy, and CMB Non-Gaussianity | In addition to simple scale invariance, a universe dominated by dark energy
naturally gives rise to correlation functions possessing full conformal
invariance. This is due to the mathematical isomorphism between the conformal
group of certain 3 dimensional slices of de Sitter space and the de Sitter
isometry group SO(4,1). In the standard homogeneous isotropic cosmological
model in which primordial density perturbations are generated during a long
vacuum energy dominated de Sitter phase, the embedding of flat spatial sections
in de Sitter space induces a conformal invariant perturbation spectrum and
definite prediction for the shape of the non-Gaussian CMB bispectrum. In the
case in which the density fluctuations are generated instead on the de Sitter
horizon, conformal invariance of the horizon embedding implies a different but
also quite definite prediction for the angular correlations of CMB
non-Gaussianity on the sky. Each of these forms for the bispectrum is intrinsic
to the symmetries of de Sitter space and in that sense, independent of specific
model assumptions. Each is different from the predictions of single field slow
roll inflation models which rely on the breaking of de Sitter invariance. We
propose a quantum origin for the CMB fluctuations in the scalar gravitational
sector from the conformal anomaly that could give rise to these
non-Gaussianities without a slow roll inflaton field, and argue that conformal
invariance also leads to the expectation for the relation n_S-1=n_T between the
spectral indices of the scalar and tensor power spectrum. Confirmation of this
prediction or detection of non-Gaussian correlations in the CMB of one of the
bispectral shape functions predicted by conformal invariance can be used both
to establish the physical origins of primordial density fluctuations and
distinguish between different dynamical models of cosmological vacuum dark
energy.
|
The age-metallicity relationship in the Small Magellanic Cloud periphery | We present results from Washington CT1 photometry for eleven star fields
located in the western outskirts of the Small Magellanic Cloud (SMC), which
cover angular distances to its centre from 2 up to 13 degrees (~ 2.2 - 13.8
kpc). The colour- magnitude diagrams, cleaned from the unavoidable Milky Way
(MW) and background galaxy signatures, reveal that the most distant dominant
main sequence (MS) stellar populations from the SMC centre are located at an
angular distance of ~ 5.7 deg (6.1 kpc); no sign of farther clear SMC MS is
visible other than the residuals from the MW/background field contamination.
The derived ages and metallicities for the dominant stellar populations of the
western SMC periphery show a constant metallicity level ([Fe/H] = -1.0 dex) and
an approximately constant age value (~ 7-8 Gyr). Their age-metallicity
relationship (AMR) do not clearly differ from the most comprehensive AMRs
derived for almost the entire SMC main body. Finally, the range of ages of the
dominant stellar populations in the western SMC periphery confirms that the
major stellar mass formation activity at the very early galaxy epoch peaked ~
7-8 Gyr ago.
|
The origin of the black hole offset in M31 | Using state-of-the-art high-resolution fully GPU N-body simulations, we
demonstrate for the first time that the infall of a dark matter rich satellite
naturally explains a present black hole offset by sub-parsecs in M31.
Observational data of the tidal features provide stringent constraints on the
initial conditions of our simulations. The heating of the central region of M31
by the satellite via dynamical friction entails a significant black hole offset
after the first pericentric passage. After having reached its maximum offset,
the massive black hole sinks towards the M31 centre due to dynamical friction
and it is determined to be offset by sub-parsecs as derived by observations.
|
Protostellar discs formed from turbulent cores | We investigate the collapse and fragmentation of low-mass, trans-sonically
turbulent prestellar cores, using SPH simulations. The initial conditions are
slightly supercritical Bonnor-Ebert spheres, all with the same density profile,
the same mass (M_O=6.1 Msun) and the same radius (R_O=17,000 AU), but having
different initial turbulent velocity fields. Four hundred turbulent velocity
fields have been generated, all scaled so that the mean Mach number is M=1.
Then a subset of these, having a range of net angular momenta, j, has been
evolved. The evolution of these turbulent cores is not strongly correlated with
j. Instead it is moderated by the formation of filamentary structures due to
converging turbulent flows. A high fraction (~ 82%) of the protostars forming
from turbulent cores are attended by protostellar accretion discs, but only a
very small fraction (~16%) of these discs is sufficiently cool and extended to
develop non-linear gravitational instabilities and fragment.
|
Probing the physicochemical properties of the Leo Ring and the Leo I
group | We present an absorption line study of the physical and chemical properties
of the Leo HI Ring and the Leo I Group as traced by 11 quasar sightlines spread
over a 600 kpc X 800 kpc region. Using HST/COS G130/G160 archival observations
as constraints, we couple cloud-by-cloud, multiphase, Bayesian ionization
modeling with galaxy property information to determine the plausible origin of
the absorbing gas along these sightlines. We search for absorption in the range
600 km/s - 1400 km/s consistent with the kinematics of the Leo Ring/Group. We
find absorption plausibly associated with the Leo Ring towards five sightlines.
Along three other sightlines, we find absorption likely to be associated with
individual galaxies, intragroup gas, and/or large-scale filamentary structure.
The absorption along these five sightlines is stronger in metal lines than
expected from individual galaxies, indicative of multiple contributions, and of
the complex kinematics of the region. We also identify three sightlines within
a 7-degree X 6-degree field around the Leo Ring, along which we do not find any
absorption. We find that the metallicities associated with the Leo Ring are
generally high, with values between solar and several times solar. The inferred
high metallicities are consistent with the origin of the ring as tidal debris
from a major galaxy merger.
|
Exploring Early and Late Cosmology with Next Generation Surveys | Perturbations from inflation evolve into large scale structure of the late
universe, and encode abundant cosmic structure formation physics. We allow
freedom in the primordial power spectrum, rather than assuming a power law
scale dependence, to study its impact on cosmological parameter determination.
Combining various generations of cosmic microwave background (CMB) data and
galaxy redshift survey data, we investigate the constraints on reconstruction
of the primordial curvature perturbation power spectrum and the late time
cosmology, especially the sum of neutrino masses. We quantify how each
successive generation, in CMB and galaxy surveys, provides significant
improvements, often by factors of several. By using CMB polarization
information over a broad range of angular scales, and galaxy redshift data in
many bins of redshift, one can allow inflationary freedom and still constrain
parameters comparably to assuming power law dependence. The primordial power
spectrum can be reconstructed at the subpercent level in a dozen wavenumber
bins, while simultaneously fitting the sum of neutrino masses to 14 meV.
|
Extreme Variation in Star Formation Efficiency Across a Compact,
Starbursting Disk Galaxy | We report on the internal distribution of star formation efficiency in IRAS
08339+6517 (hereafter IRAS08), using $\sim$200~pc resolution CO(2-1)
observations from NOEMA. The molecular gas depletion time changes by 2
orders-of-magnitude from disk-like values in the outer parts to less than
10$^8$~yr inside the half-light radius. This translates to a star formation
efficiency per free-fall time that also changes by 2 orders-of-magnitude,
reaching 50-100\%, different than local spiral galaxies and typical assumption
of constant, low star formation efficiencies. Our target is a compact, massive
disk galaxy that has SFR 10$\times$ above the $z=0$ main-sequence; Toomre
$Q\approx0.5-0.7$ and high gas velocity dispersion ($\sigma_{mol}\approx
25$~km~s$^{-1}$). We find that IRAS08 is similar to other rotating, starburst
galaxies from the literature in the resolved
$\Sigma_{SFR}\propto\Sigma_{mol}^N$ relation. By combining resolved literature
studies we find that distance from the main-sequence is a strong indicator of
the Kennicutt-Schmidt powerlaw slope, with slopes of $N\approx1.6$ for
starbursts from 100-10$^4$~M$_{\odot}$~pc$^{-2}$. Our target is consistent with
a scenario in which violent disk instabilities drive rapid inflows of gas. It
has low values of Toomre-$Q$, and also at all radii the inflow timescale of the
gas is less than the depletion time, which is consistent with the flat
metallicity gradients in IRAS08. We consider these results in light of popular
star formation theories, in general observations of IRAS08 find the most
tension with theories in which star formation efficiency is a constant. Our
results argue for the need of high spatial resolution CO observations are a
larger number of similar targets.
|
Galactic interstellar sulfur isotopes: A radial $^{32}$S$/$$^{34}$S
gradient? | We present observations of $^{12}$C$^{32}$S, $^{12}$C$^{34}$S,
$^{13}$C$^{32}$S and $^{12}$C$^{33}$S J=2$-$1 lines toward a large sample of
massive star forming regions by using the Arizona Radio Observatory 12-m
telescope and the IRAM\,30-m. Taking new measurements of the carbon
$^{12}$C/$^{13}$C ratio, the $^{32}$S$/$$^{34}$S isotope ratio was determined
from the integrated $^{13}$C$^{32}$S/$^{12}$C$^{34}$S line intensity ratios for
our sample. Our analysis shows a $^{32}$S$/$$^{34}$S gradient from the inner
Galaxy out to a galactocentric distance of 12\,kpc. An unweighted least-squares
fit to our data yields $^{32}$S$/$$^{34}$S = (1.56 $\pm$ 0.17)$\rm D_{\rm GC}$
+ (6.75 $\pm$ 1.22) with a correlation coefficient of 0.77. Errors represent
1$\sigma$ standard deviations. Testing this result by (a) excluding the
Galactic center region, (b) excluding all sources with C$^{34}$S opacities $>$
0.25, (c) combining our data and old data from previous study, and (d) using
different sets of carbon isotope ratios leads to the conclusion that the
observed $^{32}$S$/$$^{34}$S gradient is not an artefact but persists
irrespective of the choice of the sample and carbon isotope data. A gradient
with rising $^{32}$S$/$$^{34}$S values as a function of galactocentric radius
implies that the solar system ratio should be larger than that of the local
interstellar medium. With the new carbon isotope ratios we obtain indeed a
local $^{32}$S$/$$^{34}$S isotope ratio about 10$\%$ below the solar system
one, as expected in case of decreasing $^{32}$S$/$$^{34}$S ratios with time and
increased amounts of stellar processing. However, taking older carbon isotope
ratios based on a lesser amount of data, such a decrease is not seen. No
systematic variation of $^{34}$S$/$$^{33}$S ratios along galactocentric
distance was found.
|
The Black Hole Masses and Eddington Ratios of Type 2 Quasars | Type 2 quasars are an important constituent of active galaxies, possibly
representing the evolutionary precursors of traditionally studied type 1
quasars. We characterize the black hole mass ($M_{\rm BH}$) and Eddington ratio
($L_{\rm bol}/L_{\rm Edd}$) for 669 type 2 quasars selected from the Sloan
Digital Sky Survey, using black hole masses estimated from the $M_{\rm
BH}-\sigma_{\ast}$ relation and bolometric corrections scaled from the
extinction-corrected $ [\rm O~{\scriptsize III}]~ \lambda 5007$ luminosity.
When stellar velocity dispersions cannot be measured directly from the spectra,
we estimate them from the core velocity dispersions of the narrow emission
lines $ \rm [O~{\scriptsize II}]~ \lambda\lambda 3726, 3729$, $ \rm
[S~{\scriptsize II}]~\lambda\lambda 6716, 6731$, and $[ \rm O~{\scriptsize
III}]~ \lambda 5007$, which are shown to trace the gravitational potential of
the stars. Energy input from the active nucleus still imparts significant
perturbations to the gas kinematics, especially to high-velocity, blueshifted
wings. Nonvirial motions in the gas become most noticeable in systems with high
Eddington ratios. The black hole masses of our sample of type 2 quasars range
from $M_{\rm BH}
\approx 10^{6.5} $ to $10^{10.4} \, M_\odot$ (median $10^{8.2} \, M_\odot$).
Type 2 quasars have characteristically large Eddington ratios ($L_{\rm
bol}/L_{\rm Edd}~\approx 10^{-2.9}-10^{1.8}$; median $10^{-0.7}$), slightly
higher than in type~1 quasars of similar redshift; the luminosities of
$\sim$20% of the sample formally exceed the Eddington limit. The high Eddington
ratios may be consistent with the notion that obscured quasars evolve into
unobscured quasars.
|
The Importance of Quantum Pressure of Fuzzy Dark Matter on Lyman-Alpha
Forest | With recent Lyman-alpha forest data from BOSS and XQ-100, some studies
suggested that the lower mass limit on the fuzzy dark matter (FDM) particles is
lifted up to $10^{-21}\,\mathrm{eV}$. However, such a limit was obtained by
$\Lambda$CDM simulations with the FDM initial condition and the quantum
pressure (QP) was not taken into account which could have generated non-trivial
effects in large scales structures. We investigate the QP effects in
cosmological simulations systematically, and find that the QP leads to further
suppression of the matter power spectrum at small scales, as well as the halo
mass function in the low mass end. We estimate the suppressing effect of QP in
the 1D flux power spectrum of Lyman-alpha forest and compare it with data from
BOSS and XQ-100. The rough uncertainties of thermal gas properties in the flux
power spectrum model calculation were discussed. We conclude that more
systematic studies, especially with QP taken into account, are necessary to
constrain FDM particle mass using Lyman-alpha forest.
|
Quiescent Ultra-diffuse galaxies in the field originating from
backsplash orbits | Ultra-diffuse galaxies (UDGs) are the lowest-surface brightness galaxies
known, with typical stellar masses of dwarf galaxies but sizes similar to
larger galaxies like the Milky Way. The reason for their extended sizes is
debated, with suggested internal processes like angular momentum, feedback or
mergers versus external mechanisms or a combination of both. Observationally,
we know that UDGs are red and quiescent in groups and clusters while their
counterparts in the field are blue and star-forming. This dichotomy suggests
environmental effects as main culprit. However, this scenario is challenged by
recent observations of isolated quiescent UDGs in the field. Here we use
$\Lambda$CDM cosmological hydrodynamical simulation to show that isolated
quenched UDGs are formed as backsplash galaxies that were once satellites of
another galactic, group or cluster halo but are today a few Mpc away from them.
These interactions, albeit brief, remove the gas and tidally strip the
outskirts of the dark matter haloes of the now quenched seemingly-isolated
UDGs, which are born as star-forming field UDGs occupying dwarf-mass dark
matter haloes. Quiescent UDGs may therefore be found in non-negligible numbers
in filaments and voids, bearing the mark of past interactions as stripped outer
haloes devoid of dark matter and gas compared to dwarfs with similar stellar
content.
|
The Quasar Luminosity Function at Redshift 4 with Hyper Suprime-Cam Wide
Survey | We present the luminosity function of z=4 quasars based on the Hyper
Suprime-Cam Subaru Strategic Program Wide layer imaging data in the g, r, i, z,
and y bands covering 339.8 deg^2. From stellar objects, 1666 z~4 quasar
candidates are selected by the g-dropout selection down to i=24.0 mag. Their
photometric redshifts cover the redshift range between 3.6 and 4.3 with an
average of 3.9. In combination with the quasar sample from the Sloan Digital
Sky Survey in the same redshift range, the quasar luminosity function covering
the wide luminosity range of M1450=-22 to -29 mag is constructed. It is well
described by a double power-law model with a knee at M1450=-25.36+-0.13 mag and
a flat faint-end slope with a power-law index of -1.30+-0.05. The knee and
faint-end slope show no clear evidence of redshift evolution from those at z~2.
The flat slope implies that the UV luminosity density of the quasar population
is dominated by the quasars around the knee, and does not support the steeper
faint-end slope at higher redshifts reported at z>5. If we convert the M1450
luminosity function to the hard X-ray 2-10keV luminosity function using the
relation between UV and X-ray luminosity of quasars and its scatter, the number
density of UV-selected quasars matches well with that of the X-ray-selected
AGNs above the knee of the luminosity function. Below the knee, the UV-selected
quasars show a deficiency compared to the hard X-ray luminosity function. The
deficiency can be explained by the lack of obscured AGNs among the UV-selected
quasars.
|
Investigating the co-evolution of massive black holes in dual active
galactic nuclei and their host galaxies via galaxy merger simulations | Major galaxy mergers can trigger nuclear activities and are responsible for
high-luminosity quasi-stellar objects /active galactic nuclei (QSOs/AGNs). In
certain circumstances, such mergers may cause dual active galactic nuclei
(dAGN) phenomenon. This study investigates dAGN triggering and evolution of
massive black holes (MBHs) during the merging processes using hydrodynamic code
GADGET-2 to simulate several gas-rich major mergers at redshift $z=2$ and $3$,
respectively. Results reveal that gas-rich major mergers can trigger
significant nuclear activities after the second and third pericentric passages
and the formation of dAGN with significant time duration ($\sim 10 - 390$ Myr).
During the merging processes, galactic bulge evolves with time because of the
rapid star formation in each (or both) galactic centers and initial mixing of
stars in galactic disks due to violent relaxation. MBHs grow substantially due
to accretion and finally merge into a bigger black hole. The growth of galactic
bulges and corresponding increases of its velocity dispersions predate the
growth of MBHs in the dAGN stages. The MBHs in these stages deviate below the
relation between MBH mass and bulge mass (or velocity dispersion), and they
revert to the relation after the final mergers due to the significant accretion
that occurs mostly at a separation less than a few kpc. Then, the two MBHs
merge with each other.
|
Mapping the working of environmental effects in A963 | We qualitatively assess and map the relative contribution of pre-processing
and cluster related processes to the build-up of A963, a massive cluster at
z=0.2 showing an unusually high fraction of star forming galaxies in its
interior. We use Voronoi binning of positions of cluster members on the plane
of the sky in order to map the 2D variations of galaxy properties in the centre
and infall region of A963. We map four galaxy parameters (fraction of star
forming galaxies, specific star formation rate, HI deficiency and age of the
stellar population) based on full SED fitting, 21cm imaging and optical
spectroscopy. We find an extended region dominated by passive galaxies along a
north-south axis crossing the cluster centre, possibly associated with known
filaments of the large-scale structure. There are signs that the passive
galaxies in this region were quenched long before their arrival in the vicinity
of the cluster. Contrary to that, to the east and west of the cluster centre
lie regions of recent accretion dominated by gas rich, actively star forming
galaxies not associated with any substructure or filament. The few passive
galaxies in this region appear to be recently quenched, and some gas rich
galaxies show signs of ongoing ram-pressure stripping. We report the first
tentative observations at 21cm of ongoing ram-pressure stripping at z=0.2, as
well as observed inflow of low-entropy gas into the cluster along filaments of
the large-scale structure. The observed galaxy content of A963 is a result of
strongly anisotropic accretion of galaxies with different properties. Gas rich,
star forming galaxies are being accreted from the east and west of the cluster
and these galaxies are being quenched at r<R200, while the bulk of the
accretion, containing multiple groups, happens along the north-south axis and
brings mostly passive galaxies.
|
Simulations of Axion Minihalos | The axion, motivated as a solution to the strong CP problem, is also a viable
dark matter candidate. We use N-body simulations to study the formation of
substructures from white-noise density fluctuations. The density profiles of
our relaxed axion minihalos can be described by the Navarro-Frenk-White
profile, and the minihalos' concentration number agrees well with a simple,
physically-motivated model. We develop a semi-analytic formula to fit the mass
function from our simulation, which agrees broadly at different redshifts and
only differs at factor of two level from classic halo mass functions. This
analytic mass function allows us to consider uncertainties in the
post-inflation axion scenario, as well as extrapolate our high-redshift
simulations results to the present.
Our work estimates the present-day abundance of axion substructures, as is
necessary for predicting their effect on cosmological microlensing caustics and
pulsar timing. Our calculations suggest that if pulsar timing and microlensing
probes can reach recent sensitivity forecasts, they may be sensitive to the
post-inflation axion dark matter scenario, even when accounting for
uncertainties pertaining to axion strings. For pulsar timing, the most
significant caveat is whether axion minihalos are disrupted by stars, which our
estimates show is mildly important at the most relevant masses. Finally, as our
gravitational simulations are scale invariant, the results can be extended to
models where the dark matter is comprised of other axion-like particles and
even clusters of primordial black holes.
|
Robust Limits from Upcoming Neutrino Telescopes and Implications on
Minimal Dark Matter Models | Experimental developments in neutrino telescopes are drastically improving
their ability to constrain the annihilation cross-section of dark matter. In
this paper, we employ an angular power spectrum analysis method to probe the
galactic and extra-galactic dark matter signals with neutrino telescopes. We
first derive projections for a next generation of neutrino telescope that is
inspired by KM3NeT. We emphasise that such analysis is much less sensitive to
the choice of dark matter density profile. Remarkably, the projected
sensitivity is improved by more than an order of magnitude with respect to the
existing limits obtained by assuming the Burkert dark matter density profile
describing the galactic halo. Second, we analyse minimal extensions to the
Standard Model that will be maximally probed by the next generation of neutrino
telescopes. As benchmark scenarios, we consider Dirac dark matter in $s$- and
$t$-channel models with vector and scalar mediators. We follow a global
approach by examining all relevant complementary experimental constraints. We
find that neutrino telescopes will be able to competitively probe significant
portions of parameter space. Interestingly, the anomaly-free $L_{\mu}-L_{\tau}$
model can potentially be explored in regions where the relic abundance is
achieved through freeze-out mechanism.
|
Bose-Einstein condensation of dark matter solves the core/cusp problem | We analyze the observed properties of dwarf galaxies, which are dark matter
dominated astrophysical objects, by assuming that dark matter is in the form of
a strongly - coupled, dilute Bose - Einstein condensate. The basic
astrophysical properties of the condensate (density profile, rotational
velocity, and mass profile, respectively), are derived from a variational
principle. To test the validity of the model we compare first the tangential
velocity equation of the model with a sample of eight rotation curves of dwarf
galaxies. We find a good agreement between the theoretically predicted rotation
curves (without any baryonic component) and the observational data. The mean
value of the logarithmic inner slope of the mass density profile of dwarf
galaxies is also obtained, and it is shown that the observed value of this
parameter is in agreement with the theoretical results. The predictions of the
Bose - Einstein condensate model are also systematically compared with the
predictions of the standard Cold Dark Matter model. The non-singular density
profiles of the Bose-Einstein condensed dark matter generally show the presence
of an extended core, whose presence is due to the strong interaction between
dark matter particles.
|
Primordial black hole formation by vacuum bubbles II | The discoveries of LIGO/Virgo black holes in recent years have revitalized
the study of primordial black holes. In this work, we investigate a mechanism
where primordial black holes are formed by vacuum bubbles that randomly
nucleate during inflation through quantum tunneling. After inflation, these
bubbles typically run into the ambient radiation fluid with a large Lorentz
factor. In our previous work, we assumed the bubble fields are strongly coupled
to the standard model particles so that the bubble wall is impermeable. Here we
complete this picture by considering bubbles interacting with the fluid only
through gravity. By studying the scenario in several limits, we found that
black holes could form in either subcritical or supercritical regime. Depending
on the model parameters, the resulting mass spectrum of the black holes could
be wide or narrow, and may develop two peaks separated by a large mass range.
With different spectra, these black holes may account for the LIGO/Virgo black
holes, supermassive black holes, and may play an important role in dark matter.
|
A figure of merit for black hole mass measurements with molecular gas | In this work we discuss the technique of using molecular gas kinematics (or
the kinematics of any dynamically cold tracer) to estimate black hole masses.
We present a figure of merit that will be useful in defining future
observational campaigns, and discuss its implications. We show that, in
principle, one can estimate black-hole masses using data that only resolve
scales ~2 times the formal black hole sphere of influence, and confirm this by
reanalysing lower resolution observations of the molecular gas around the black
hole in NGC4526. We go on to discuss the effect that angular resolution,
velocity resolution and the depth of the galaxies potential have on the ability
to estimate black hole masses, and conclude by discussing prospects for the
future. Once ALMA is fully operational, we find that over 10^5 local galaxies
with massive black holes will be observable, and that given sufficient surface
brightness sensitivity one could measure the mass of a >4x10^8 Msun black hole
at any redshift.
|
The ALMA Early Science view of FUor/EXor objects. I. Through the
looking-glass of V2775 Ori | As part of an ALMA survey to study the origin of episodic accretion in young
eruptive variables, we have observed the circumstellar environment of the star
V2775 Ori. This object is a very young, pre-main sequence object which displays
a large amplitude outburst characteristic of the FUor class. We present Cycle-2
band 6 observations of V2775 Ori with a continuum and CO (2-1) isotopologue
resolution of 0.25\as (103 au). We report the detection of a marginally
resolved circumstellar disc in the ALMA continuum with an integrated flux of
$106 \pm 2$ mJy, characteristic radius of $\sim$ 30 au, inclination of
$14.0^{+7.8}_{-14.5}$ deg, and is oriented nearly face-on with respect to the
plane of the sky.
The \co~emission is separated into distinct blue and red-shifted regions that
appear to be rings or shells of expanding material from quasi-episodic
outbursts. The system is oriented in such a way that the disc is seen through
the outflow remnant of V2775 Ori, which has an axis along our line-of-sight.
The $^{13}$CO emission displays similar structure to that of the \co, while the
C$^{18}$O line emission is very weak. We calculated the expansion velocities of
the low- and medium-density material with respect to the disc to be of -2.85 km
s$^{-1}$ (blue), 4.4 km s$^{-1}$ (red) and -1.35 and 1.15 km s$^{-1}$ (for blue
and red) and we derived the mass, momentum and kinetic energy of the expanding
gas. The outflow has an hourglass shape where the cavities are not seen. We
interpret the shapes that the gas traces as cavities excavated by an ancient
outflow. We report a detection of line emission from the circumstellar disc and
derive a lower limit of the gas mass of 3 \MJup.
|
Neutrino effects on the morphology of cosmic large-scale structure | In this work, we propose a powerful probe of neutrino effects on the
large-scale structure (LSS) of the Universe, i.e., Minkowski functionals (MFs).
The morphology of LSS can be fully described by four MFs. This tool, with
strong statistical power, is robust to various systematics and can
comprehensively probe all orders of N-point statistics. By using a pair of
high-resolution N-body simulations, for the first time, we comprehensively
studied the subtle neutrino effects on the morphology of LSS. For an ideal LSS
survey of volume $\sim1.73$ Gpc$^3$/$h^3$, neutrino signals are mainly detected
from void regions with a significant level up to $\thicksim 10\sigma$ and
$\thicksim 300\sigma$ for CDM and total matter density fields, respectively.
This demonstrates its enormous potential for much improving the neutrino mass
constraint in the data analysis of up-coming ambitious LSS surveys.
|
Magnetic fields and cosmic rays in clusters of galaxies | We argue that the observed correlation between the radio luminosity and the
X-ray luminosity in radio emitting galaxy clusters implies that the radio
emission is due to secondary electrons that are produced by p-p interactions
and lose their energy by emitting synchrotron radiation in a strong magnetic
field, B>(8\pi a T_{CMB}^4)^{1/2}\simeq 3\muG. We construct a simple model that
naturally explains the correlation, and show that the observations provide
stringent constraints on cluster magnetic fields and cosmic rays (CRs): Within
the cores of clusters, the ratio beta_{core} between the CR energy (per
logarithmic particle energy interval) and the thermal energy is beta_{core}\sim
2*10^{-4}; The source of these CRs is most likely the cluster accretion shock,
which is inferred to deposit in CRs ~ 0.1 of the thermal energy it generates;
The diffusion time of 100 GeV CRs over scales \gtrsim100 kpc is not short
compared to the Hubble time; Cluster magnetic fields are enhanced by mergers to
\gtrsim 1 % of equipartition, and decay (to <1 muG) on 1 Gyr time scales. The
inferred value of beta_{core} implies that high energy gamma-ray emission from
secondaries at cluster cores will be difficult to detect with existing and
planned instruments.
|
Stellar populations in the ELT perspective | We discuss the impact that the next generation of Extremely Large Telescopes
will have on the open astrophysical problems of resolved stellar populations.
In particular, we address the interplay between multiband photometry and
spectroscopy.
|
SCUBA2 High Redshift Bright Quasar Survey: Far-infrared Properties and
Weak-line Features | We present a submillimetre continuum survey ('SCUBA2 High rEdshift bRight
quasaR surveY', hereafter SHERRY) of 54 high redshift quasars at $5.6<z<6.9$
with quasar bolometric luminosities in a range of (0.2$-$$
5)\times10^{14}\,L_{\odot}$, using the Submillimetre Common-User Bolometer
Array-2 (SCUBA2) on the James Clerk Maxwell Telescope. About 30% (16/54) of the
sources are detected with a typical 850$\mu$m rms sensitivity of 1.2 $\rm
mJy\,beam^{-1}$ ($S\rm _{\nu,850\,\mu m} = 4$-5 mJy, at $>3.5\sigma$). The new
SHERRY detections indicate far-infrared (FIR) luminosities of $\rm
3.5\times10^{12}$ to $\rm 1.4\times10^{13}$ $L_{\odot}$, implying extreme star
formation rates of 90 to 1060 $M_{\odot}$ yr$^{-1}$ in the quasar host
galaxies. Compared with $z =$ 2$-$5 samples, the FIR luminous quasars ($L_{\rm
FIR} > 10^{13}\,L_{\odot}$) are more rare at $z \sim 6$. The
optical/near-infrared (NIR) spectra of these objects show 11% (6/54) of the
sources have weak Ly$\alpha$, emission line features, which may relate to
different sub-phases of the central active galactic nuclei (AGNs). Our SCUBA2
survey confirms the trend reported in the literature that quasars with
submillimeter detections tend to have weaker ultraviolet (UV) emission lines
compared to quasars with nondetections. The connection between weak UV quasar
line emission and bright dust continuum emission powered by massive star
formation may suggest an early phase of AGN-galaxy evolution, in which the
broad line region is starting to develop slowly or is shielded from the central
ionization source, and has unusual properties such as weak line features or
bright FIR emission.
|
A sensitive search for methanol line emission toward evolved stars | We present a sensitive search for methanol line emission in evolved stars at
1 cm, aiming to detect, for the first time, methanol masers in this type of
objects. Our sample comprised post-AGB stars and young planetary nebulae (PNe),
whose mass-loss processes and circumstellar structures resemble those of young
stellar objects (YSOs), where methanol masers are detected. Class I masers were
searched for in 73 objects, whereas Class II ones were searched in 16. No
detection was obtained. The non-detection of Class I methanol masers indicated
that methanol production in dust grains and/or the enhancement of its gas-phase
abundance in the shocked regions of evolved objects are not as efficient as in
YSOs. We suggest that relatively more evolved PNe might have a better
probability of harboring Class II masers.
|
Why the Milky Way's bulge is not only a bar formed from a cold thin disk | By analyzing a N-body simulation of a bulge formed simply via a bar
instability mechanism operating on a kinematically cold stellar disk, and by
comparing the results of this analysis with the structural and kinematic
properties of the main stellar populations of the Milky Way bulge, we conclude
that the bulge of our Galaxy is not a pure stellar bar formed from a
pre-existing thin stellar disk, as some studies have recently suggested. On the
basis of several arguments emphasized in this paper, we propose that the bulge
population which, in the Milky Way, is observed not to be part of the peanut
structure corresponds to the old galactic thick disk, thus implying that the
Milky Way is a pure thin+thick disk galaxy, with only a possible limited
contribution of a classical bulge.
|
COLDz: A High Space Density of Massive Dusty Starburst Galaxies ~1
Billion Years after the Big Bang | We report the detection of CO($J$=2$\to$1) emission from three massive dusty
starburst galaxies at $z$$>$5 through molecular line scans in the NSF's Karl G.
Jansky Very Large Array (VLA) CO Luminosity Density at High Redshift (COLDz)
survey. Redshifts for two of the sources, HDF 850.1 ($z$=5.183) and AzTEC-3
($z$=5.298), were previously known. We revise a previous redshift estimate for
the third source GN10 ($z$=5.303), which we have independently confirmed
through detections of CO $J$=1$\to$0, 5$\to$4, 6$\to$5, and [CII] 158 $\mu$m
emission with the VLA and the NOrthern Extended Milllimeter Array (NOEMA). We
find that two currently independently confirmed CO sources in COLDz are
"optically dark", and that three of them are dust-obscured galaxies at $z$$>$5.
Given our survey area of $\sim$60 arcmin$^2$, our results appear to imply a
$\sim$6-55 times higher space density of such distant dusty systems within the
first billion years after the Big Bang than previously thought. At least two of
these $z$$>$5 galaxies show star-formation rate surface densities consistent
with so-called "maximum" starbursts, but we find significant differences in CO
excitation between them. This result may suggest that different fractions of
the massive gas reservoirs are located in the dense, star-forming nuclear
regions - consistent with the more extended sizes of the [CII] emission
compared to the dust continuum and higher [CII]-to-far-infrared luminosity
ratios in those galaxies with lower gas excitation. We thus find substantial
variations in the conditions for star formation between $z$$>$5 dusty
starbursts, which typically have dust temperatures $\sim$57%$\pm$25% warmer
than starbursts at $z$=2-3 due to their enhanced star formation activity.
|
A Free-Form Lensing Grid Solution for A1689 with New Mutiple Images | Hubble Space Telescope imaging of the galaxy cluster Abell 1689 has revealed
an exceptional number of strongly lensed multiply-imaged galaxies, including
high-redshift candidates. Previous studies have used this data to obtain the
most detailed dark matter reconstructions of any galaxy cluster to date,
resolving substructures ~25 kpc across. We examine Abell 1689 (hereafter,
A1689) non-parametrically, combining strongly lensed images and weak
distortions from wider field Subaru imaging, and we incorporate member galaxies
to improve the lens solution. Strongly lensed galaxies are often locally
affected by member galaxies, however, these perturbations cannot be recovered
in grid based reconstructions because the lensing information is too sparse to
resolve member galaxies. By adding luminosity-scaled member galaxy deflections
to our smooth grid we can derive meaningful solutions with sufficient accuracy
to permit the identification of our own strongly lensed images, so our model
becomes self consistent. We identify 11 new multiply lensed system candidates
and clarify previously ambiguous cases, in the deepest optical and NIR data to
date from Hubble and Subaru. Our improved spatial resolution brings up new
features not seen when the weak and strong lensing effects are used separately,
including clumps and filamentary dark matter around the main halo. Our
treatment means we can obtain an objective mass ratio between the cluster and
galaxy components, for examining the extent of tidal stripping of the luminous
member galaxies. We find a typical mass-to-light ratios of M/L_B = 21 inside
the r<1 arcminute region that drops to M/L_B = 17 inside the r<40 arcsecond
region. Our model independence means we can objectively evaluate the
competitiveness of stacking cluster lenses for defining the geometric
lensing-distance-redshift relation in a model independent way.
|
Determination of HII region metallicity in the context of estimating the
primordial helium abundance | The primordial $^4$He abundance (Y$_p$) is one of the key characteristics of
Primordial Nucleosynthesis processes that occurred in the first minutes after
the Big Bang. Its value depends on the baryon/photon ratio $\eta\equiv
n_b/n_{\gamma}$, and is also sensitive to the relativistic degrees of freedom
which affect the expansion rate of the Universe at the radiation-dominated era.
The most used method of the determination of Y$_p$ is the study of the metal
deficient HII regions located in blue compact dwarf galaxies (BCDs). In this
paper, we discuss in detail various methods of the determination of HII region
metallicity in the context of Y$_p$ analyses. We show that some procedures used
in the methods lead to biases in the metallicity estimates and underestimation
of their uncertainties. We propose a modified method for the metallicity
determination, as well as an additional criterion for selecting objects. We
have selected 69 objects (26 objects with high quality spectra from the
HeBCD+NIR database and 43 objects from the SDSS catalog), for which we estimate
Y and O/H using the proposed method. We have estimated Y$_p=0.2470\pm0.0020$
which is one of the most accurate estimates obtained up to date. Its comparison
with the value Y$_p=0.2470\pm0.0002$ obtained as a result of numerical
modelling of Primordial Nucleosynthesis with the value of $\Omega_b$ taken from
the analysis of the CMB anisotropy (Planck mission), is an important tool for
studying the self-consistency of the Standard cosmological model (a possible
discrepancy between these estimates could be an indicator of a new physics).
The application of the proposed method allows one to more correctly estimate
Y$_p$ and the slope $d$Y/$d$(O/H). Further analysis of the data from the SDSS
catalog can significantly increase the statistics of objects for the regression
analysis, which in turn can refine the Y$_p$ estimate.
|
Simulating cosmological supercooling with a cold atom system II | We perform an analysis of the supercooled state in an analogue of an early
universe phase transition based on a one dimensional, two-component Bose gas
with time-dependent interactions. We demonstrate that the system behaves in the
same way as a thermal, relativistic Bose gas undergoing a first order phase
transition. We propose a way to prepare the state of the system in the
metastable phase as an analogue to supercooling in the early universe. While we
show that parametric resonances in the system can be suppressed by thermal
damping, we find that the theoretically estimated thermal damping in our model
is too weak to suppress the resonances for realistic experimental parameters.
However, we propose that experiments to investigate the effective damping rate
in experiments would be worthwhile.
|
The VMC Survey - VI. Quasars behind the Magellanic system | The number and spatial distribution of confirmed quasi-stellar objects (QSOs)
behind the Magellanic system is limited. This undermines their use as
astrometric reference objects for different types of studies. We have searched
for criteria to identify candidate QSOs using observations from the VISTA
survey of the Magellanic Clouds system (VMC) that provides photometry in the
YJKs bands and 12 epochs in the Ks band. The (Y-J) versus (J-Ks) diagram has
been used to distinguish QSO candidates from Milky Way stars and stars of the
Magellanic Clouds. Then, the slope of variation in the Ks band has been used to
identify a sample of high confidence candidates. These criteria were developed
based on the properties of 117 known QSOs presently observed by the VMC survey.
VMC YJKs magnitudes and Ks light-curves of known QSOs behind the Magellanic
system are presented. About 75% of them show a slope of variation in Ks>10^-4
mag/day and the shape of the light-curve is in general irregular and without
any clear periodicity. The number of QSO candidates found in tiles including
the South Ecliptic Pole and the 30 Doradus regions is 22 and 26, respectively,
with a ~20% contamination by young stellar objects, planetary nebulae, stars
and normal galaxies. By extrapolating the number of QSO candidates to the
entire VMC survey area we expect to find about 1200 QSOs behind the LMC, 400
behind the SMC, 200 behind the Bridge and 30 behind the Stream areas, but not
all will be suitable for astrometry. Further, the Ks band light-curves can help
support investigations of the mechanism responsible for the variations.
|
Stellar Populations in the Central 0.5 pc of the Galaxy I: A New Method
for Constructing Luminosity Functions and Surface-Density Profiles | We present new high angular resolution near-infrared spectroscopic
observations of the nuclear star cluster surrounding the Milky Way's central
supermassive black hole. Using the integral-field spectrograph OSIRIS on Keck
II behind the laser-guide-star adaptive optics system, this spectroscopic
survey enables us to separate early-type (young, 4-6 Myr) and late-type (old,
>1 Gyr) stars with a completeness of 50% down to K' = 15.5 mag, which
corresponds to ~10 \msun for the early-type stars. This work increases the
radial extent of reported OSIRIS/Keck measurements by more than a factor of 3
from 4" to 14" (0.16 pc to 0.56 pc), along the projected disk of young stars.
For our analysis, we implement a new method of completeness correction using a
combination of star-planting simulations and Bayesian inference. We assign
probabilities for the spectral type of every source detected in deep imaging
down to K' = 15.5 mag using information from spectra, simulations, number
counts, and the distribution of stars. The inferred radial surface-density
profiles, $\Sigma(R) \propto R^{-\Gamma}$, for the young stars and late-type
giants are consistent with earlier results ($\Gamma_{early} = 0.93 \pm 0.09$,
$\Gamma_{late} = 0.16 \pm 0.07$). The late-type surface-density profile is
approximately flat out to the edge of the survey. While the late-type stellar
luminosity function is consistent with the Galactic bulge, the
completeness-corrected luminosity function of the early-type stars has
significantly more young stars at faint magnitudes compared to previous surveys
with similar depth. This luminosity function indicates that the corresponding
mass function of the young stars is likely less top-heavy than that inferred
from previous surveys.
|
Recent galaxy mergers and residual star formation of red sequence
galaxies in galaxy clusters | This study explored the GALEX ultraviolet (UV) properties of optical red
sequence galaxies in 4 rich Abell clusters at z \leq 0.1. In particular, we
tried to find a hint of merger-induced recent star formation (RSF) in red
sequence galaxies. Using the NUV - r' colors of the galaxies, RSF fractions
were derived based on various criteria for post-merger galaxies and normal
galaxies. Following k-correction, about 36% of the post-merger galaxies were
classified as RSF galaxies with a conservative criterion (NUV - r' \leq 5), and
that number was doubled (~ 72%) when using a generous criterion (NUV - r' \leq
5.4). The trend was the same when we restricted the sample to galaxies within
0.5xR_{200}. Post-merger galaxies with strong UV emission showed more violent,
asymmetric features in the deep optical images. The RSF fractions did not show
any trend along the clustocentric distance within R_{200}. We performed a
Dressler-Shectman test to check whether the RSF galaxies had any correlation
with the sub-structures in the galaxy clusters. Within R_{200} of each cluster,
the RSF galaxies did not appear to be preferentially related to the clusters'
sub-structures. Our results suggested that only 30% of RSF red sequence
galaxies show morphological hints of recent galaxy mergers. This implies that
internal processes (e.g., stellar mass-loss or hot gas cooling) for the supply
of cold gas to early-type galaxies may play a significant role in the residual
star formation of early-type galaxies at a recent epoch.
|
Accidental Composite Dark Matter | We build models where Dark Matter candidates arise as composite states of a
new confining gauge force, stable thanks to accidental symmetries. Restricting
to renormalizable theories compatible with SU(5) unification, we find 13 models
based on SU(N) gauge theories and 9 based on SO(N). We also describe other
models that require non-renormalizable interactions. The two gauge groups lead
to distinctive phenomenologies: SU(N) theories give complex DM, with
potentially observable electric and magnetic dipole moments that lead to
peculiar spin-independent cross sections; SO(N) theories give real DM, with
challenging spin-dependent cross sections or inelastic scatterings. Models with
Yukawa couplings also give rise to spin-independent direct detection mediated
by the Higgs boson and to electric dipole moments for the electron. In some
models DM has higher spin. Each model predicts a specific set of lighter
composite scalars, possibly observable at colliders.
|
Outflows, Shocks and Coronal Line Emission in a Radio-Selected AGN in a
Dwarf Galaxy | Massive black holes (BHs) in dwarf galaxies can provide strong constraints on
BH seeds, however reliably detecting them is notoriously difficult. High
resolution radio observations were recently used to identify accreting massive
BHs in nearby dwarf galaxies, with a significant fraction found to be
non-nuclear. Here we present the first results of our optical follow-up of
these radio-selected active galactic nuclei (AGNs) in dwarf galaxies using
integral field unit (IFU) data from Gemini-North. We focus on the dwarf galaxy
J1220+3020, which shows no clear optical AGN signatures in its nuclear SDSS
spectrum covering the radio source. With our new IFU data, we confirm the
presence of an active BH via the AGN coronal line [Fe X] and enhanced [O I]
emission coincident with the radio source. Furthermore, we detect broad
H$\alpha$ emission and estimate a BH mass of $M_{\rm BH}=10^{4.9}M_\odot$. We
compare the narrow emission line ratios to standard BPT diagnostics and shock
models. Spatially-resolved BPT diagrams show some AGN signatures, particularly
in [O I]/H$\alpha$, but overall do not unambiguously identify the AGN. A
comparison of our data to shock models clearly indicates shocked emission
surrounding the AGN. The physical model most consistent with the data is an
active BH with a radiatively inefficient accretion flow (RIAF) that both
photoionizes and shock-excites the surrounding gas. We conclude that feedback
is important in radio-selected BHs in dwarf galaxies, and that radio surveys
may probe a population of low accretion-rate BHs in dwarf galaxies that cannot
be detected through optical surveys alone.
|
Discrete Newtonian Cosmology | In this paper we lay down the foundations for a purely Newtonian theory of
cosmology, valid at scales small compared with the Hubble radius, using only
Newtonian point particles acted on by gravity and a possible cosmological term.
We describe the cosmological background which is given by an exact solution of
the equations of motion in which the particles expand homothetically with their
comoving positions constituting a central configuration. We point out, using
previous work, that an important class of central configurations are
homogeneous and isotropic, thus justifying the usual assumptions of elementary
treatments. The scale factor is shown to satisfy the standard Raychaudhuri and
Friedmann equations without making any fluid dynamic or continuum
approximations. Since we make no commitment as to the identity of the point
particles, our results are valid for cold dark matter, galaxies, or clusters of
galaxies. In future publications we plan to discuss perturbations of our
cosmological background from the point particle viewpoint laid down in this
paper and show consistency with much standard theory usually obtained by more
complicated and conceptually less clear continuum methods. Apart from its
potential use in large scale structure studies, we believe that out approach
has great pedagogic advantages over existing elementary treatments of the
expanding universe, since it requires no use of general relativity or continuum
mechanics but concentrates on the basic physics: Newton's laws for
gravitationally interacting particles.
|
Growth of structure in interacting vacuum cosmologies | We examine the growth of structure in three different cosmological models
with interacting dark matter and vacuum energy. We consider the case of
geodesic dark matter with zero sound speed, where the relativistic growing mode
in comoving-synchronous gauge coincides with the Newtonian growing mode at
first order in $\Lambda$CDM. We study corrections to the linearly growing mode
in the presence of interactions and the linear matter growth rate, $f_1$,
contrasting this with the velocity divergence, $f_{rsd}\sigma_8$, observed
through redshift-space distortions. We then derive second-order density
perturbations in these interacting models. We identify the reduced bispectrum
that corresponds to the non-linear growth of structure and show how the shape
of the bispectrum is altered by energy transfer to or from the vacuum. Thus the
bispectrum, or higher-order correlators, might in future be used to identify
dark matter interactions.
|
Description of the evolution of inhomogeneities on a Dark Matter halo
with the Vlasov equation | We use a direct numerical integration of the Vlasov equation in spherical
symmetry with a background gravitational potential to determine the evolution
of a collection of particles in different models of a galactic halo. Such a
collection is assumed to represent a dark matter inhomogeneity which reaches a
stationary state determined by the virialization of the system. We describe
some features of the stationary states and, by using several halo models,
obtain distinctive signatures for the evolution of the inhomogeneities in each
of the models.
|
Gravitational scalar-tensor theory | We consider a new form of theories of gravity in which the action is written
in terms of the Ricci scalar and its first and second derivatives. Despite the
higher derivative nature of the action, the theory is free from ghost under an
appropriate choice of the functional form of the Lagrangian. This model
possesses $2+2$ physical degrees of freedom, namely $2$ scalar degrees and $2$
tensor degrees. We exhaust all such theories with the Lagrangian of the form
$f(R, (\nabla R)^2, \Box R)$, where $R$ is the Ricci scalar, and then show some
examples beyond this ansatz. In course of analysis, we prove the equivalence
between these examples and generalized bi-Galileon theories.
|
Unbinned halo-independent methods for emerging dark matter signals | Halo-independent methods for analyzing direct detection experiments can
provide robust results while making no assumptions about the dark matter halo
in our galaxy. We extend existing methods to the case of unbinned data, which
is especially well suited to emerging dark matter signals with only a few
events in a nearly background-free environment. We show that such methods can
easily be generalized to the case of inelastic or exothermic scattering, and
provide a useful handle on extracting results independent of the halo model
while maximizing the available experimental information.
|
Evolved Massive Stars at Low-metallicity IV. Using 1.6 $\mu$m "H-bump"
to identify red supergiant stars: a case study of NGC 6822 | We present a case study of using a novel method to identify red supergiant
(RSG) candidates in NGC 6822, based on their 1.6 $\mu$m "H-bump". We collected
32 bands of photometric data for NGC 6822 ranging from optical to MIR. By using
the theoretical spectra from MARCS, we demonstrate that there is a prominent
difference around 1.6 $\mu$m ("H-bump") between low-surface-gravity (LSG) and
high-surface-gravity (HSG) targets. Taking advantage of this feature, we
identify efficient color-color diagrams (CCDs) of rzH and rzK to separate HSG
and LSG targets from crossmatching of optical and NIR data. Moreover, synthetic
photometry from ATLAS9 also give similar results. Further separating RSG
candidates from the rest of the LSG candidates is done by using semi-empirical
criteria on NIR CMDs and resulted in 323 RSG candidates. Meanwhile, the
simulation of foreground stars from Besan\c{c}on models also indicates that our
selection criteria is largely free from the contamination of Galactic giants.
In addition to the "H-bump" method, we also use the traditional BVR method as a
comparison and/or supplement, by applying a slightly aggressive cut to select
as much as possible RSG candidates (358 targets). Furthermore, the Gaia
astrometric solution is used to constrain the sample, where 181 and 193 targets
were selected from the "H-bump" and BVR method, respectively. The percentages
of selected targets in both methods are similar as $\sim$60\%, indicating the
comparable accuracy of the two methods. In total, there are 234 RSG candidates
after combining targets from both methods with 140 ($\sim$60\%) of them in
common. The final RSG candidates are in the expected locations on the MIR CMDs,
while the spatial distribution is also coincident with the FUV-selected star
formation regions, suggesting the selection is reasonable and reliable.
|
Experimental study of the $^{30}$Si($^{3}$He,$d$)$^{31}$P reaction and
thermonuclear reaction rate of $^{30}$Si($p$,$\gamma$)$^{31}$P | [Background] Abundance anomalies in some globular clusters, such as the
enhancement of potassium and the depletion of magnesium, can be explained in
terms of an earlier generation of stars polluting the presently observed ones.
It was shown that the potential range of temperatures and densities of the
polluting sites depends on the strength of a few number of critical reaction
rates. The reaction has been identified as one of these important reactions.
[Purpose] The key ingredient for evaluating the thermonuclear reaction rate is
the strength of the resonances which, at low energy, are proportional to their
proton width. Therefore the goal of this work is to determine the proton widths
of unbound 31P states. [Method] States in 31P were studied at the
Maier-Leibnitz-Laboratorium using the one-proton transfer reaction. Deuterons
were detected with the Q3D magnetic spectrometer. Angular distribution and
spectroscopic factors were extracted for 27 states, and proton widths and
resonance strengths were calculated for the unbound states. [Results] Several
unbound states have been observed for the first time in a one-proton transfer
reaction. Above 20 MK, the reaction rate is now entirely estimated from the
observed properties of states. The reaction rate uncertainty from all
resonances other than the resonance has been reduced down to less than a factor
of two above that temperature. The unknown spin and parity of the resonance
dominates the uncertainty in the rate in the relevant temperature range.
[Conclusion] The remaining source of uncertainty on the reaction rate comes
from the unknown spin and parity of the resonance which can change the reaction
rate by a factor of ten in the temperature range of interest.
|
Molecular gas in two companion cluster galaxies at z=1.2 | We study the molecular gas properties of two star-forming galaxies separated
by 6 kpc in the projected space and belonging to a galaxy cluster selected from
the Irac Shallow Cluster Survey, at a redshift $z=1.2$, i.e., $\sim2$ Gyr after
the cosmic star formation density peak. This work describes the first CO
detection from $1<z<1.4$ star forming cluster galaxies with no reported clear
evidence of AGN. We exploit observations taken with the NOEMA interferometer at
$\sim3$ mm to detect CO(2-1) line emission from the two selected galaxies,
unresolved by our observations. Based on the CO(2-1) spectrum we estimate a
total molecular gas mass $M({\rm H_2})=(2.2^{+0.5}_{-0.4})\times10^{10}$
$M_\odot$ and dust mass $M_{\rm dust}<4.2\times10^8~M_\odot$ for the two
blended sources. The two galaxies have similar stellar masses and a large
relative velocity of $\sim$400 km/s estimated from the CO(2-1) line width.
These findings tend to privilege a scenario where both sources contribute to
the observed CO(2-1). By using the archival Spitzer MIPS flux at 24$\mu$m we
estimate an ${\rm SFR(24\mu m)}=(28^{+12}_{-8})~M_\odot$/yr for each of the two
galaxies. Assuming that the two sources equally contribute to the observe
CO(2-1) our analysis yields a depletion time scale $\tau_{\rm
dep}=(3.9^{+1.4}_{-1.8})\times10^8$ yr, and a molecular gas to stellar mass
ratio $0.17\pm0.13$ for each of two sources, separately. Our results are in
overall agreement with those of other distant cluster galaxies. The two target
galaxies have molecular gas mass and depletion time that are marginally
compatible with, but smaller than those of main sequence field galaxies,
suggesting that the molecular gas has not been refueled enough. Higher
resolution and higher frequency observations will enable us to spatially
resolve the two sources and possibly distinguish between different gas
processing mechanisms.
|
GIARPS High-resolution Observations of T Tauri stars (GHOsT). II.
Connecting atomic and molecular winds in protoplanetary disks | In the framework of the GIARPS High-resolution Observations of T Tauri stars
(GHOsT) project, we aim to characterize the atomic and molecular winds in a
sample of classical T Tauri stars (CTTs) of the Taurus-Auriga region. We
analyzed the flux calibrated [OI] 630 nm and $\rm H_2$ 2.12 $\rm \mu m$ lines
in a sample of 36 CTTs observed at the Telescopio Nazionale Galileo with the
HARPS and GIANO spectrographs. We decomposed the line profiles into different
kinematic Gaussian components and focused on the most frequently detected
component, the narrow low-velocity (v$\rm_p < 20$ $\rm km$ $\rm s^{-1}$)
component (NLVC). We found that the $\rm H_2$ line is detected in 17 sources
($\sim 50 \%$ detection rate), and [OI] is detected in all sources but one. The
NLV components of the $\rm H_2$ and [OI] emission are kinematically linked,
with a strong correlation between the peak velocities and the full widths at
half maximum of the two lines. Assuming Keplerian broadening, we found that the
[OI] NVLC originates from a disk region between 0.05 and 20 au and that of $\rm
H_2$ in a region from 2 and 20 au. We did not find any clear correlation
between v$\rm_p$ of the $\rm H_2$ and [OI] NVLC and the outer disk inclination.
This result is in line with previous studies. Our results suggest that
molecular and neutral atomic emission in disk winds originate from regions that
might overlap, and that the survival of molecular winds in disks strongly
depends on the gas exposure to the radiation from the central star. Our results
demonstrate the potential of wide-band high-resolution spectroscopy in linking
tracers of different manifestations of the same phenomenon.
|
Two Radio Supernova Remnants Discovered in the Outer Galaxy | We report on the discovery of two supernova remnants (SNRs) designated
G152.4-2.1 and G190.9-2.2, using Canadian Galactic Plane Survey data. The aims
of this paper are, first, to present evidence that favours the classification
of both sources as SNRs, and, second, to describe basic parameters (integrated
flux density, spectrum, and polarization) as well as properties (morphology,
line-of-sight velocity, distance and physical size) to facilitate and motivate
future observations. Spectral and polarization parameters are derived from
multiwavelength data from existing radio surveys carried out at wavelengths
between 6 and 92cm. In particular for the source G152.4-2.1 we also use new
observations at 11cm done with the Effelsberg 100m telescope. The interstellar
medium around the discovered sources is analyzed using 1-arcminute line data
from neutral hydrogen (HI) and 45-arcsecond 12CO(J=1-0). G152.4-2.1 is a barrel
shaped SNR with two opposed radio-bright polarized flanks on the North and
South. The remnant, which is elongated along the Galactic plane is evolving in
a more-or-less uniform medium. G190.9-2.2 is also a shell-type remnant with
East and West halves elongated perpendicular to the plane, and is evolving
within a low-density region bounded by dense neutral hydrogen in the North and
South, and molecular (12CO) clouds in the East and West. The integrated radio
continuum spectral indices are -0.65+/-0.05 and -0.66+/-0.05 for G152.4-2.1 and
G190.9-2.2 respectively. Both SNRs are approximately 1 kpc distant, with
G152.4-2.1 being larger (32x30 pc in diameter) than G190.9-2.2 (18x16 pc).
These two remnants are the lowest surface brightness SNRs yet catalogued at
5x10^-23 W m^-2 Hz^-1 sr^-1.
|
Evolution of X-ray cavities | A wide range of recent observations have shown that AGN-driven cavities may
provide the energy source that balances the cooling observed in the centres of
cool-core galaxy clusters. One tool for better understanding the physics of
these cavities is their observed morphological evolution, which is dependent on
such poorly-understood properties as the turbulent density field and the impact
of magnetic fields. Here we combine numerical simulations that include subgrid
turbulence and software that produces synthetic X-ray observations to examine
the evolution of X-ray cavities in the absence of magnetic fields. Our results
reveal an anisotropic size evolution of that is dramatically different from
simplified, analytical predictions. These differences highlight some of the key
issues that must be accurately quantified when studying AGN-driven cavities,
and help to explain why the inferred pV energy in these regions appears to be
correlated with their distance from the cluster center. Interpreting X- ray
observations will require detailed modeling of effects including
mass-entrainment, distortion by drag forces, and pro jection. Current
limitations do not allow a discrimination between purely hydrodynamic and
magnetically-dominated models for X-ray cavities.
|
Black Hole Disks in Galactic Nuclei | Gravitational torques among objects orbiting a supermassive black hole drive
the rapid reorientation of orbital planes in nuclear star clusters (NSCs), a
process known as vector resonant relaxation. In this Letter, we determine the
statistical equilibrium of systems with a distribution of masses, semimajor
axes, and eccentricities. We average the interaction over the apsidal
precession time and construct a Monte Carlo Markov chain method to sample the
microcanonical ensemble of the NSC. We examine the case of NSCs formed by 16
episodes of star formation or globular cluster infall. We find that the massive
stars and stellar mass black holes form a warped disk, while low mass stars
resemble a spherical distribution with a possible net rotation. This explains
the origin of the clockwise disk in the Galactic center and predicts a
population of black holes (BHs) embedded within this structure. The rate of
mergers among massive stars, tidal disruption events of massive stars by BHs,
and BH-BH mergers are highly increased in such disks. The first two may explain
the origin of the observed G1 and G2 clouds, the latter may be important for
gravitational wave detections with LIGO and VIRGO. More generally, black holes
are expected to settle in disks in all dense spherical stellar systems
assembled by mergers of smaller systems including globular clusters.
|
Cold flows and the first quasars | Observations of the most distant bright quasars imply that billion solar mass
supermassive black holes (SMBH) have to be assembled within the first eight
hundred million years. Under our standard galaxy formation scenario such fast
growth implies large gas densities providing sustained accretion at critical or
supercritical rates onto an initial black hole seed. It has been a long
standing question whether and how such high black hole accretion rates can be
achieved and sustained at the centers of early galaxies. Here we use our new
cosmological hydrodynamic simulation (MassiveBlack) covering a volume (0.75
\Gpc)^3 appropriate for studying the rare first quasars to show that steady
high density cold gas flows responsible for assembling the first galaxies
produce the high gas densities that lead to sustained critical accretion rates
and hence rapid growth commensurate with the existence of ~10^9 solar mass
black holes as early as z~7. We find that under these conditions quasar
feedback is not effective at stopping the cold gas from penetrating the central
regions and hence cannot quench the accretion until the host galaxy reaches
M_halo > 10^{12} solar masses. This cold-flow driven scenario for the formation
of quasars implies that they should be ubiquitous in galaxies in the early
universe and that major (proto)galaxy mergers are not a requirement for
efficient fuel supply and growth, particularly for the earliest SMBHs.
|
Possible Transfer of Life by Earth-Grazing Objects to Exoplanetary
Systems | Recently, a 30-cm object was discovered to graze the Earth's atmosphere and
shift into a Jupiter-crossing orbit. We use the related survey parameters to
calibrate the total number of such objects. The number of objects that could
have exported terrestrial microbes out of the Solar System is in the range $2
\times 10^{9}$--$3 \times 10^{11}$. We find that $10^{7}$--$10^{9}$ such
objects could have been captured by binary star systems over the lifetime of
the Solar System. Adopting the fiducial assumption that one polyextremophile
colony is picked up by each object, the total number of objects carrying living
colonies on them upon capture could be $10$--$10^3$.
|
On UV-completion of Palatini-Higgs inflation | We investigate the UV-completion of the Higgs inflation in the metric and the
Palatini formalisms. It is known that the cutoff scales for the perturbative
unitarity of these inflation models become much smaller than the Planck scale
to be consistent with observations. Expecting that the low cutoff scale
originates in the curvature of a field-space spanned by the Higgs fields, we
consider embedding the curved field-space into a higher dimensional flat space
and apply this procedure to the metric-Higgs and the Palatini-Higgs scenarios.
The new field introduced in this way successfully flattens the field-space and
UV-completes the Higgs inflation in the metric formalism. However, in the
Palatini formalism, the new field cannot uplift the cutoff up to the Planck
scale. We also discuss the unavoidable low cutoff in the Palatini formalism in
the context of the local conformal symmetry.
|
High-energy particles and radiation in star-forming regions | Non-thermal particles and high-energy radiation can play a role in the
dynamical processes in star-forming regions and provide an important piece of
the multiwavelength observational picture of their structure and components.
Powerful stellar winds and supernovae in compact clusters of massive stars and
OB associations are known to be favourable sites of high-energy particle
acceleration and sources of non-thermal radiation and neutrinos. Namely, young
massive stellar clusters are likely sources of the PeV (petaelectronvolt)
regime cosmic rays (CRs). They can also be responsible for the cosmic ray
composition, e.g., 22Ne/20Ne anomalous isotopic ratio in CRs. Efficient
particle acceleration can be accompanied by super-adiabatic amplification of
the fluctuating magnetic fields in the systems converting a part of kinetic
power of the winds and supernovae into the magnetic energy through the
CR-driven instabilities. The escape and CR propagation in the vicinity of the
sources are affected by the non-linear CR feedback. These effects are expected
to be important in starburst galaxies, which produce high-energy neutrinos and
gamma-rays. We give a brief review of the theoretical models and observational
data on high-energy particle acceleration and their radiation in star-forming
regions with young stellar population.
|
Maser, infrared and optical emission for late-type stars in the Galactic
plane | Radio astrometric campaigns using VLBI have provided distances and proper
motions for masers associated with young massive stars (BeSSeL survey). The
ongoing BAaDE project plans to obtain astrometric information of SiO maser
stars located in the inner Galaxy. These stars are associated with evolved,
mass-losing stars. By overlapping optical (Gaia), infrared (2MASS, MSX and
WISE) and radio (BAaDE) sources, we expect to obtain important clues on the
intrinsic properties and population distribution of late-type stars. Moreover,
a comparison of the Galactic parameters obtained with Gaia and VLBI can be done
using radio observations on different targets: young massive stars (BeSSeL) and
evolved stars (BAaDE).
|
High density of active galactic nuclei in the outskirts of distant
galaxy clusters | We present a study of the distribution of X-ray detected active galactic
nuclei (AGN) in the five most massive, $M_{500}^{SZ}>10^{14} M_{\odot}$ , and
distant, z$\sim$1, galaxy clusters in the \textit{Planck} and South Pole
Telescope (SPT)\textit{} surveys. The spatial and thermodynamic individual
properties of each cluster have been defined with unprecedented accuracy at
this redshift using deep X-ray observations. This is an essential property of
our sample in order to precisely determine the $R_{500}^{Y_{\textrm x}}$ radius
of the clusters. For our purposes, we computed the X-ray point-like source
surface density in 0.5$R_{500}^{Y_{\textrm x}}$ wide annuli up to a
clustercentric distance of 4$R_{500}^{Y_{\textrm x}}$, statistically
subtracting the background and accounting for the respective average density of
optical galaxies. We found a significant excess of X-ray point sources between
2 and 2.5$R_{500}^{Y_{\textrm x}}$ at the 99.9\% confidence level. The results
clearly display for the first time strong observational evidence of AGN
triggering in the outskirts of high-redshift massive clusters with such a high
statistical significance. We argue that the particular conditions at this
distance from the cluster centre increase the galaxy merging rate, which is
probably the dominant mechanism of AGN triggering in the outskirts of massive
clusters.
|
Solar origins: Place and Chemical Composition | We discuss a chemical evolution model with Z-dependent yields that reproduces
the O/H, C/H, and C/O gradients of the Galactic disk and the chemical history
of the solar vicinity. The model fits the H, He, C, and O abundances derived
from recombination lines of the HII region M17 (including the fraction of C and
O atoms embedded in dust); the protosolar H, He, C, O, and Fe abundances; and
the C/O-O/H, C/Fe-Fe/H, and O/Fe-Fe/H relations derived from stars of the solar
vicinity. The agreement of the model with the protosolar abundances at the
Sun-formation time implies that the Sun originated from a well mixed ISM at a
galactocentric distance of 7.6 $\pm$ 0.8 kpc.
|
Twinlike models for parametrized dark energy | We study cosmological models involving a single real scalar field that has an
equation of state parameter which evolves with cosmic time. We highlight some
common parametrizations for the equation of state as a function of redshift in
the context of twinlike theories. The procedure is used to introduce different
models that have the same acceleration parameter, with the very same energy
densities and pressure in flat spacetime.
|
Toward unbiased estimations of the statefinder parameters | With the use of simulated supernova catalogs, we show that the statefinder
parameters turn out to be poorly and biased estimated by standard cosmography.
To this end, we compute their standard deviations and several bias statistics
on cosmologies near the concordance model, demonstrating that these are very
large, making standard cosmography unsuitable for future and wider compilations
of data. To overcome this issue, we propose a new method that consists in
introducing the series of the Hubble function into the luminosity distance,
instead of considering the usual direct Taylor expansions of the luminosity
distance. Moreover, in order to speed up the numerical computations, we
estimate the coefficients of our expansions in a hierarchical manner, in which
the order of the expansion depends on the redshift of every single piece of
data. In addition, we propose two hybrids methods that incorporates standard
cosmography at low redshifts. The methods presented here perform better than
the standard approach of cosmography both in the errors and bias of the
estimated statefinders. We further propose a one-parameter diagnostic to reject
non-viable methods in cosmography.
|
Galaxy redshift-space bispectrum: the Importance of Being Anisotropic | We forecast the benefits induced by adding the bispectrum anisotropic signal
to the standard, two- and three-point, clustering statistics analysis. In
particular, we forecast cosmological parameter constraints including the
bispectrum higher multipoles terms together with the galaxy power spectrum
(monopole plus quadrupole) and isotropic bispectrum (monopole) data vectors. To
do so, an analytical covariance matrix model is presented. This template is
carefully calibrated on well-known terms of a numerical covariance matrix
estimated from a set of simulated galaxy catalogues. After testing the
calibration using the power spectrum and isotropic bispectrum measurements from
the same set of simulations, we extend the covariance modelling to the galaxy
bispectrum higher multipoles. Using this covariance matrix we proceed to
perform cosmological parameter inference using a suitably generated mock data
vector. Including the bispectrum mutipoles up to the hexadecapole, yields 1-D
$68\%$ credible regions for the set of parameters
$(b_1,b_2,f,\sigma_8,f_\mathrm{NL},\alpha_\perp, \alpha_\parallel)$ tighter by
a factor of 30$\%$ on average for $k_\mathrm{max}=0.09\,h$/Mpc, significantly
reducing at the same time the degeneracies present in the posterior
distribution.
|
Halo collapse: virialization by shear and rotation in dynamical
dark-energy models. Effects on weak-lensing peaks | The evolution of the virial overdensity $\Delta_{\rm vir}$ for $\Lambda$CDM
and seven dynamical dark-energy models is investigated in the extended
spherical collapse model (SCM). Here the virialization process is naturally
achieved by introducing shear and rotation instead of using the virial theorem.
We generalise two approaches proposed in the literature and show that,
regardless of the dark-energy model, the new virialization term can be
calibrated on the peculiar velocity of the shell as measured from Einstein-de
Sitter simulations. The two virialization recipes qualitatively reproduce the
features of the ordinary SCM, i.e., a constant $\Delta_{\rm vir}$ for the EdS
model and time-variation for dark-energy models, but without any mass
dependence. Depending on the actual description of virialization and on the
dark-energy model, the value of $\Delta_{\rm vir}$ varies between 10 and 40
percent. We use the new recipes to predict the surface-mass-density profile of
dark matter haloes and the number of convergence density peaks for LSST- and
Euclid-like weak lensing surveys.
|
Reflection nebulae in the Galactic Center: the case for soft X-ray
imaging polarimetry | The origin of irradiation and fluorescence of the 6.4 keV bright giant
molecular clouds surrounding Sgr A*, the central supermassive black hole of our
Galaxy, remains enigmatic. Testing the theory of a past active period of Sgr A*
requires X-ray polarimetry. In this paper, we show how modern imaging
polarimeters could revolutionize our understanding of the Galactic Center.
Through Monte Carlo modeling, we produce a 4-8 keV polarization map of the
Galactic Center, focusing on the polarimetric signature produced by Sgr B1, Sgr
B2, G0.11-0.11, Bridge E, Bridge D, Bridge B2, MC2, MC1, Sgr C3, Sgr C2, and
Sgr C1. We estimate the resulting polarization, include polarized flux dilution
by the diffuse plasma emission detected toward the GC, and simulate the
polarization map that modern polarimetric detectors would obtain assuming the
performances of a mission prototype. The eleven reflection nebulae investigated
in this paper present a variety of polarization signatures, ranging from nearly
unpolarized to highly polarized (about 77%) fluxes. A major improvement in our
simulation is the addition of a diffuse, unpolarized plasma emission that
strongly impacts soft X-ray polarized fluxes. The dilution factor is in the
range 50% - 70%, making the observation of the Bridge structure unlikely even
in the context of modern polarimetry. The best targets are the Sgr B and Sgr C
complexes, and the G0.11-0.11 cloud. An exploratory observation of a few
hundred kilo-seconds of the Sgr B complex would allow a significant detection
of the polarization and be sufficient to derive hints on the primary source of
radiation. A more ambitious program (few Ms) of mapping the giant molecular
clouds could then be carried out to probe with great precision the turbulent
history of Sgr A*, and place important constraints on the composition and
three-dimensional position of the surrounding gas.
|
The Bright and Dark Sides of High-Redshift starburst galaxies from {\it
Herschel} and {\it Subaru} observations | We present rest-frame optical spectra from the FMOS-COSMOS survey of twelve
$z \sim 1.6$ \textit{Herschel} starburst galaxies, with Star Formation Rate
(SFR) elevated by $\times$8, on average, above the star-forming Main Sequence
(MS). Comparing the H$\alpha$ to IR luminosity ratio and the Balmer Decrement
we find that the optically-thin regions of the sources contain on average only
$\sim 10$ percent of the total SFR whereas $\sim90$ percent comes from an
extremely obscured component which is revealed only by far-IR observations and
is optically-thick even in H$\alpha$. We measure the [NII]$_{6583}$/H$\alpha$
ratio, suggesting that the less obscured regions have a metal content similar
to that of the MS population at the same stellar masses and redshifts. However,
our objects appear to be metal-rich outliers from the metallicity-SFR
anticorrelation observed at fixed stellar mass for the MS population. The
[SII]$_{6732}$/[SII]$_{6717}$ ratio from the average spectrum indicates an
electron density $n_{\rm e} \sim 1,100\ \mathrm{cm}^{-3}$, larger than what
estimated for MS galaxies but only at the 1.5$\sigma$ level. Our results
provide supporting evidence that high-$z$ MS outliers are the analogous of
local ULIRGs, and are consistent with a major merger origin for the starburst
event.
|
Dwarfs or giants? Stellar metallicities and distances in the
Canada-France-Imaging-Survey from $ugrizG$ multi-band photometry | We present a new fully data-driven algorithm that uses photometric data from
the Canada-France-Imaging-Survey (CFIS; $u$), Pan-STARRS 1 (PS1; $griz$), and
Gaia ($G$) to discriminate between dwarf and giant stars and to estimate their
distances and metallicities. The algorithm is trained and tested using the
SDSS/SEGUE spectroscopic dataset and Gaia photometric/astrometric dataset. At
[Fe/H]$<-1.2$, the algorithm succeeds in identifying more than 70% of the
giants in the training/test set, with a dwarf contamination fraction below 30%
(with respect to the SDSS/SEGUE dataset). The photometric metallicity estimates
have uncertainties better than 0.2 dex when compared with the spectroscopic
measurements. The distances estimated by the algorithm are valid out to a
distance of at least $\sim 80$ kpc without requiring any prior on the stellar
distribution, and have fully independent uncertainities that take into account
both random and systematic errors. These advances allow us to estimate these
stellar parameters for approximately 12 million stars in the photometric
dataset. This will enable studies involving the chemical mapping of the distant
outer disc and the stellar halo, including their kinematics using the Gaia
proper motions. This type of algorithm can be applied in the Southern
hemisphere to the first release of LSST data, thus providing an almost complete
view of the external components of our Galaxy out to at least $\sim 80$ kpc.
Critical to the success of these efforts will be ensuring well-defined
spectroscopic training sets that sample a broad range of stellar parameters
with minimal biases. A catalogue containing the training/test set and all
relevant parameters within the public footprint of CFIS is available online.
|
Star and Stellar Cluster Formation: ALMA-SKA Synergies | Over the next decade, observations conducted with ALMA and the SKA will
reveal the process of mass assembly and accretion onto young stars and will be
revolutionary for studies of star formation. Here we summarise the capabilities
of ALMA and discuss recent results from its early science observations. We then
review infrared and radio variability observations of both young low-mass and
high-mass stars. A time domain SKA radio continuum survey of star forming
regions is then outlined. This survey will produce radio light-curves for
hundreds of young sources, providing for the first time a systematic survey of
radio variability across the full range of stellar masses. These light-curves
will probe the magnetospheric interactions of young binary systems, the origins
of outflows, trace episodic accretion on the central sources and potentially
constrain the rotation rates of embedded sources.
|
Gravitational wave astronomy with radio galaxy surveys | In the next decade, new astrophysical instruments will deliver the first
large-scale maps of gravitational waves and radio sources. Therefore, it is
timely to investigate the possibility to combine them to provide new and
complementary ways to study the Universe. Using simulated catalogues
appropriate to the planned surveys, it is possible to predict measurements of
the cross-correlation between radio sources and GW maps and the effects of a
stochastic gravitational wave background on galaxy maps. Effects of GWs on the
large scale structure of the Universe can be used to investigate the nature of
the progenitors of merging BHs, the validity of Einstein's General Relativity,
models for dark energy, and detect a stochastic background of GW. The results
obtained show that the galaxy-GW cross-correlation can provide useful
information in the near future, while the detection of tensor perturbation
effects on the LSS will require instruments with capabilities beyond the
currently planned next generation of radio arrays. Nevertheless, any
information from the combination of galaxy surveys with GW maps will help
provide additional information for the newly born gravitational wave astronomy.
|
From galactic bars to the Hubble tension $-$ weighing up the
astrophysical evidence for Milgromian gravity | Astronomical observations reveal a major deficiency in our understanding of
physics $-$ the detectable mass is insufficient to explain the observed motions
in a huge variety of systems given our current understanding of gravity,
Einstein's General theory of Relativity (GR). This missing gravity problem may
indicate a breakdown of GR at low accelerations, as postulated by Milgromian
dynamics (MOND). We review the MOND theory and its consequences, including in a
cosmological context where we advocate a hybrid approach involving light
sterile neutrinos to address MOND's cluster-scale issues. We then test the
novel predictions of MOND using evidence from galaxies, galaxy groups, galaxy
clusters, and the large scale structure of the Universe. We also consider
whether the standard cosmological paradigm ($\Lambda$CDM) can explain the
observations, and review several previously published highly significant
falsifications of it. Our overall assessment considers both the extent to which
the data agree with each theory and how much flexibility each has when
accommodating the data, with the gold standard being a clear a priori
prediction not informed by the data in question. We also consider some future
tests, including on scales much smaller than galaxies. Our conclusion is that
MOND is favoured by a wealth of data across a huge range of astrophysical
scales, ranging from the kpc scales of galactic bars to the Gpc scale of the
local supervoid and the Hubble tension, which is alleviated in MOND through
enhanced cosmic variance.
|
WIMP isocurvature perturbation and small scale structure | The adiabatic perturbation of dark matter is damped during the kinetic
decoupling due to the collision with relativistic component on sub-horizon
scales. However the isocurvature part is free from damping and could be large
enough to make a substantial contribution to the formation of small scale
structure. We explicitly study the weakly interacting massive particles as dark
matter with an early mater dominated period before radiation domination and
show that the isocurvature perturbation is generated during the phase
transition and leaves imprint in the observable signatures for small scale
structure.
|
Ultraviolet Mg II emission from fast neutral ejecta around Eta Carinae | We present the first images of the nebula around eta Carinae obtained with
HST/WFC3, including a UV image in the F280N filter that traces MgII emission,
plus contemporaneous imaging in the F336W, F658N, and F126N filters that trace
near-UV continuum, [NII], and [FeII], respectively. The F336W and F658N images
are consistent with previous images in these filters, and F126N shows that for
the most part, [FeII] 12567 traces clumpy shocked gas seen in [NII]. The F280N
image, however, reveals MgII emission from structures that have not been seen
in any previous line or continuum images of eta Carinae. This image shows
diffuse MgII emission immediately outside the bipolar Homunculus nebula in all
directions, but with the strongest emission concentrated over the poles. The
diffuse structure with prominent radial streaks, plus an anticorrelation with
ionized tracers of clumpy shocked gas, leads us to suggest that this is
primarily MgII resonant scattering from unshocked, neutral atomic gas. We
discuss the implied structure and geometry of the MgII emission, and its
relation to the Homunculus lobes and various other complex nebular structures.
An order of magnitude estimate of the neutral gas mass traced by MgII is
0.02Msun, with a corresponding kinetic energy around 1e47erg. This may provide
important constraints on polar mass loss in the early phases of the Great
Eruption. We argue that the MgII line may be an excellent tracer of significant
reservoirs of freely expanding, unshocked, and otherwise invisible neutral
atomic gas in a variety of stellar outflows.
|
A Study of Two Diffuse Dwarf Galaxies in the Field | We present optical long-slit spectroscopy and far-ultraviolet to
near-infrared spectral energy distribution fitting of two diffuse dwarf
galaxies, LSBG-285 and LSBG-750, which were recently discovered by the Hyper
Suprime-Cam Subaru Strategic Program (HSC-SSP). We measure redshifts using
H$\alpha$ line emission, and find that these galaxies are at comoving distances
of ${\approx}25$ and ${\approx}41$ Mpc, respectively, after correcting for the
local velocity field. They have effective radii of $r_\mathrm{eff}=1.2$ and 1.8
kpc and stellar masses of $M_\star\approx2$-$3\times10^{7}~M_\odot$. There are
no massive galaxies ($M_\star>10^{10} M_\odot$) within a comoving separation of
at least 1.5 Mpc from LSBG-285 and 2 Mpc from LSBG-750. These sources are
similar in size and surface brightness to ultra-diffuse galaxies, except they
are isolated, star-forming objects that were optically selected in an
environmentally blind survey. Both galaxies likely have low stellar
metallicities $[Z_\star/Z_\odot] < -1.0$ and are consistent with the stellar
mass-metallicity relation for dwarf galaxies. We set an upper limit on
LSBG-750's rotational velocity of ${\sim}50$ km s$^{-1}$, which is comparable
to dwarf galaxies of similar stellar mass with estimated halo masses
$<10^{11}~M_\odot$. We find tentative evidence that the gas-phase metallicities
in both of these diffuse systems are high for their stellar mass, though a
statistically complete, optically-selected galaxy sample at very low surface
brightness will be necessary to place these results into context with the
higher-surface-brightness galaxy population.
|
Numerical modelling of the lobes of radio galaxies in cluster
environments | We have carried out two-dimensional, axisymmetric, hydrodynamic numerical
modelling of the evolution of radio galaxy lobes. The emphasis of our work is
on including realistic hot-gas environments in the simulations and on
establishing what properties of the resulting radio lobes are independent of
the choice of environmental properties and of other features of the models such
as the initial jet Mach number. The simulated jet power we use is chosen so
that we expect the inner parts of the lobes to come into pressure balance with
the external medium on large scales; we show that this leads to the expected
departure from self-similarity and the formation of characteristic central
structures in the hot external medium. The work done by the expanding radio
lobes on the external hot gas is roughly equal to the energy stored in the
lobes for all our simulations once the lobes are well established. We show that
the external pressure at the lobe midpoint is a reasonable estimate of the
internal (lobe) pressure, with only a weak dependence on the environmental
parameters: on the other hand, the predicted radio emission from a source of a
given physical size has a comparatively strong dependence on the environment in
which the lobe resides, introducing an order of magnitude of scatter into the
jet power versus radio luminosity relationship. X-ray surface brightness and
temperature visualizations of our simulations bear a striking resemblance to
observations of some well-studied radio galaxies.
|
The swampland conjecture and the Higgs expectation value | The recently proposed de Sitter swampland conjecture excludes local extrema
of a scalar potential with a positive energy density in a low energy effective
theory. Under the conjecture, the observed dark energy cannot be explained by
the cosmological constant. The local maximum of the Higgs potential at the
symmetric point also contradicts with the conjecture. In order to make the
Standard Model consistent with the conjecture, it has been proposed to
introduce a quintessence field, $Q$, which couples to the cosmological constant
and the local maximum of the Higgs potential. In this paper, we show that such
a modified Higgs potential generically results in a $Q$-dependent Higgs vacuum
expectation value (VEV). The $Q$-dependence of the Higgs VEV induces a
long-range force, which is severely excluded by the tests of the equivalence
principle. Besides, as the quintessence field is in motion, the Higgs VEV shows
a time-dependence, which is also severely constrained by the measurements of
the time-dependence of the proton-to-electron mass ratio. Those constraints
require an additional fine-tuning which is justified neither by the swampland
conjecture nor the anthropic principle. We further show that, even if such an
unjustified fine-tuning condition is imposed at the tree level, radiative
corrections upset it. Consequently, we argue that most of the habitable vacua
in the string landscape are in tension with the phenomenological constraints.
|
The first analytical expression to estimate photometric redshifts
suggested by a machine | We report the first analytical expression purely constructed by a machine to
determine photometric redshifts ($z_{\rm phot}$) of galaxies. A simple and
reliable functional form is derived using $41,214$ galaxies from the Sloan
Digital Sky Survey Data Release 10 (SDSS-DR10) spectroscopic sample. The method
automatically dropped the $u$ and $z$ bands, relying only on $g$, $r$ and $i$
for the final solution. Applying this expression to other $1,417,181$ SDSS-DR10
galaxies, with measured spectroscopic redshifts ($z_{\rm spec}$), we achieved a
mean $\langle (z_{\rm phot} - z_{\rm spec})/(1+z_{\rm spec})\rangle\lesssim
0.0086$ and a scatter $\sigma_{(z_{\rm phot} - z_{\rm spec})/(1+z_{\rm
spec})}\lesssim 0.045$ when averaged up to $z \lesssim 1.0$. The method was
also applied to the PHAT0 dataset, confirming the competitiveness of our
results when faced with other methods from the literature. This is the first
use of symbolic regression in cosmology, representing a leap forward in
astronomy-data-mining connection.
|
Decaying dark matter: a stacking analysis of galaxy clusters to improve
on current limits | We show that a stacking approach to galaxy clusters can improve current
limits on decaying dark matter by a factor $\gtrsim 5-100$, with respect to a
single source analysis, for all-sky instruments such as Fermi-LAT. Based on the
largest sample of X-ray-selected galaxy clusters available to date (the MCXC
meta-catalogue), we provide all the astrophysical information, in particular
the astrophysical term for decaying dark matter, required to perform an
analysis with current instruments.
|
A Comprehensive Study of Ly$\alpha$ Emission in the High-redshift Galaxy
Population | We present an exhaustive census of Lyman alpha (Ly$\alpha$) emission in the
general galaxy population at $3<z<4.6$. We use the Michigan/Magellan Fiber
System (M2FS) spectrograph to study a stellar mass (M$_*$) selected sample of
625 galaxies homogeneously distributed in the range
$7.6<\log{\mbox{M$_*$/M$_{\odot}$}}<10.6$. Our sample is selected from the
3D-HST/CANDELS survey, which provides the complementary data to estimate
Ly$\alpha$ equivalent widths ($W_{Ly\alpha}$) and escape fractions ($f_{esc}$)
for our galaxies. We find both quantities to anti-correlate with M$_*$,
star-formation rate (SFR), UV luminosity, and UV slope ($\beta$). We then model
the $W_{Ly\alpha}$ distribution as a function of M$_{UV}$ and $\beta$ using a
Bayesian approach. Based on our model and matching the properties of typical
Lyman break galaxy (LBG) selections, we conclude that the $W_{Ly\alpha}$
distribution in such samples is heavily dependent on the limiting M$_{UV}$ of
the survey. Regarding narrowband surveys, we find their $W_{Ly\alpha}$
selections to bias samples toward low M$_*$, while their line-flux limitations
preferentially leave out low-SFR galaxies. We can also use our model to predict
the fraction of Ly$\alpha$-emitting LBGs at $4\leqslant z\leqslant 7$. We show
that reported drops in the Ly$\alpha$ fraction at $z\geqslant6$, usually
attributed to the rapidly increasing neutral gas fraction of the universe, can
also be explained by survey M$_{UV}$ incompleteness. This result does not
dismiss reionization occurring at $z\sim7$, but highlights that current data is
not inconsistent with this process taking place at $z>7$.
|
An Ultimate Target for Dark Matter Searches | The combination of S-matrix unitarity and the dynamics of thermal freeze-out
for massive relic particles (denoted here simply by WIMPs) implies a lower
limit on the density of such particles, that provide a (potentially
sub-dominant) contribution to dark matter. This then translates to lower limits
to the signal rates for a variety of techniques for direct and indirect
detection of dark matter. For illustration, we focus on models where
annihilation is s-wave dominated. We derive lower limits to the flux of
gamma-rays from WIMP annihilation at the Galactic center; direct detection of
WIMPs; energetic neutrinos from WIMP annihilation in the Sun; and the effects
of WIMPs on the angular power spectrum and frequency spectrum of the cosmic
microwave background radiation. The results suggest that a variety of
dark-matter-search techniques may provide interesting avenues to seek new
physics, even if WIMPs do not constitute all the dark matter. While the limits
are quantitatively some distance from the reach of current measurements, they
may be interesting for long-range planning exercises.
|
Variation Of The Tully-Fisher Relation As A Function Of The Magnitude
Interval Of A Sample Of Galaxies | In this paper we carry out a preliminary study of the dependence of the
Tully-Fisher Relation (TFR) with the width and intensity level of the absolute
magnitude interval of a limited sample of 2411 galaxies taken from Mathewson \&
Ford (1996). The galaxies in this sample do not differ significantly in
morphological type, and are distributed over an $\sim11$-magnitude interval
($-24.4 < I < -13.0$). We take as directives the papers by Nigoche-Netro et al.
(2008, 2009, 2010) in which they study the dependence of the Kormendy (KR), the
Fundamental Plane (FPR) and the Faber-Jackson Relations (FJR) with the
magnitude interval within which the observed galaxies used to derive these
relations are contained. We were able to characterise the behaviour of the TFR
coefficients $(\alpha, \beta)$ with respect to the width of the magnitude
interval as well as with the brightness of the galaxies within this magnitude
interval. We concluded that the TFR for this specific sample of galaxies
depends on observational biases caused by arbitrary magnitude cuts, which in
turn depend on the width and intensity of the chosen brightness levels.
|
Density Jumps Near the Virial Radius of Galaxy Clusters | Recent simulations have indicated that the dark matter halos of galaxy
clusters should feature steep density jumps near the virial radius. Since the
member galaxies are expected to follow similar collisionless dynamics as the
dark matter, the galaxy density profile should show such a feature as well. We
examine the potential of current datasets to test this prediction by selecting
cluster members for a sample of 56 low-redshift (0.1<z<0.3) galaxy clusters,
constructing their projected number density profiles, and fitting them with two
profiles, one with a steep density jump and one without. Additionally, we
investigate the presence of a jump using a non-parametric spline approach. We
find that some of these clusters show strong evidence for a model with a
density jump. We discuss avenues for further analysis of the density jump with
future datasets.
|
Spin-Spin Interactions in Massive Gravity and Higher Derivative Gravity
Theories | We show that, in the weak field limit, at large separations, in sharp
contrast to General Relativity (GR), all massive gravity theories predict
distance-dependent spin alignments for spinning objects. For all separations GR
requires anti-parallel spin orientations with spins pointing along the line
joining the sources. Hence total spin is minimized in GR. On the other hand,
while massive gravity at small separations ($m_gr \le1.62$) gives the same
result as GR, for large separations ($m_gr>1.62$) the spins become parallel to
each other and perpendicular to the line joining the objects. Namely, the
potential energy is minimized when the total spin is maximized in massive
gravity for large separations. We also compute the spin-spin interactions in
quadratic gravity theories and find that while at large separations GR result
is intact, at small separations, spins become perpendicular to the line joining
sources and anti-parallel to each other.
|
Gravitational Entropy in Szekeres Class I Models | Gravitational entropy is an elusive concept. Various theoretical proposals
have been presented, initially based on Penrose's Weyl Curvature Hypothesis,
and variations of it. A more recent proposal by Clifton, Ellis, and Tavakol
(CET) considered a novel approach by defining such entropy from a Gibbs
equation constructed from an effective stress-energy tensor that emerges from
the 'square root' algebraic decomposition of the Bel-Robinson tensor, the
simplest divergence-less tensor related to the Weyl tensor. Since, so far all
gravitational entropy proposals have been applied to highly restrictive and
symmetric spacetimes, we probe in this paper the CET proposal for a class of
much less idealized spactimes (the Szekeres class I models) capable of
describing the joint evolution of arrays of arbitrary number of structures:
overdensities and voids, all placed on selected spatial locations in an
asymptotic $\Lambda$CDM backgound. By using suitable covariant variables and
their fluctuations, we find the necessary and sufficient conditions for a
positive CET entropy production to be a negative sign of the product of the
density and Hubble expansion fluctuations. To examine the viability of this
theoretical result we examine numerically the CET entropy production for two
elongated over dense regions surrounding a central spheroidal void, all
evolving jointly from initial linear perturbations at the last scattering era
into present day Mpc-size CDM structures. We show that CET entropy production
is positive for all times after last scattering at the precise spatial
locations where structure growth occurs and where the exact density growing
mode is dominant. The present paper provides the least idealized (and most
physically robust) probe of a gravitational entropy proposal in the context of
structure formation.
|
New constraints on the evolution of the stellar-to-dark matter
connection: a combined analysis of galaxy-galaxy lensing, clustering, and
stellar mass functions from z=0.2 to z=1 | Using data from the COSMOS survey, we perform the first joint analysis of
galaxy-galaxy weak lensing, galaxy spatial clustering, and galaxy number
densities. Carefully accounting for sample variance and for scatter between
stellar and halo mass, we model all three observables simultaneously using a
novel and self-consistent theoretical framework. Our results provide strong
constraints on the shape and redshift evolution of the stellar-to-halo mass
relation (SHMR) from z=0.2 to z=1. At low stellar mass, we find that halo mass
scales as Mh M*^0.46 and that this scaling does not evolve significantly with
redshift to z=1. We show that the dark-to-stellar ratio, Mh/M*, varies from low
to high masses, reaching a minimum of Mh/M*~27 at M*=4.5x10^10 Msun and
Mh=1.2x10^12 Msun. This minimum is important for models of galaxy formation
because it marks the mass at which the accumulated stellar growth of the
central galaxy has been the most efficient. We describe the SHMR at this
minimum in terms of the "pivot stellar mass", M*piv, the "pivot halo mass",
Mhpiv, and the "pivot ratio", (Mh/M*)piv. Thanks to a homogeneous analysis of a
single data set, we report the first detection of mass downsizing trends for
both Mhpiv and M*piv. The pivot stellar mass decreases from
M*piv=5.75+-0.13x10^10 Msun at z=0.88 to M*piv=3.55+-0.17x10^10 Msun at z=0.37.
Intriguingly, however, the corresponding evolution of Mhpiv leaves the pivot
ratio constant with redshift at (Mh/M*)piv~27. We use simple arguments to show
how this result raises the possibility that star formation quenching may
ultimately depend on Mh/M* and not simply Mh, as is commonly assumed. We show
that simple models with such a dependence naturally lead to downsizing in the
sites of star formation. Finally, we discuss the implications of our results in
the context of popular quenching models, including disk instabilities and AGN
feedback.
|
Galaxy Clusters Discovered via the Sunyaev-Zel'dovich Effect in the
2500-square-degree SPT-SZ survey | We present a catalog of galaxy clusters selected via their Sunyaev-Zel'dovich
(SZ) effect signature from 2500 deg$^2$ of South Pole Telescope (SPT) data.
This work represents the complete sample of clusters detected at high
significance in the 2500-square-degree SPT-SZ survey, which was completed in
2011. A total of 677 (409) cluster candidates are identified above a
signal-to-noise threshold of $\xi$ =4.5 (5.0). Ground- and space-based optical
and near-infrared (NIR) imaging confirms overdensities of similarly colored
galaxies in the direction of 516 (or 76%) of the $\xi$>4.5 candidates and 387
(or 95%) of the $\xi$>5 candidates; the measured purity is consistent with
expectations from simulations. Of these confirmed clusters, 415 were first
identified in SPT data, including 251 new discoveries reported in this work. We
estimate photometric redshifts for all candidates with identified optical
and/or NIR counterparts; we additionally report redshifts derived from
spectroscopic observations for 141 of these systems. The mass threshold of the
catalog is roughly independent of redshift above $z$~0.25 leading to a sample
of massive clusters that extends to high redshift. The median mass of the
sample is $M_{\scriptsize 500c}(\rho_\mathrm{crit})$ ~ 3.5 x 10$^{14} M_\odot
h^{-1}$, the median redshift is $z_{med}$ =0.55, and the highest-redshift
systems are at $z$>1.4. The combination of large redshift extent, clean
selection, and high typical mass makes this cluster sample of particular
interest for cosmological analyses and studies of cluster formation and
evolution.
|
From global to spatially resolved in low-redshift galaxies | Our understanding of the structure, composition and evolution of galaxies has
strongly improved in the last decades, mostly due to new results based on large
spectroscopic and imaging surveys. In particular, the nature of ionized gas,
its ionization mechanisms, its relation with the stellar properties and
chemical composition, the existence of scaling relations that describe the
cycle between stars and gas, and the corresponding evolution patterns have been
widely explored and described. More recently, the introduction of additional
techniques, in particular Integral Field Spectroscopy, and their use in large
galaxy surveys, have forced us to re-interpret most of those recent results
from a spatially resolved perspective. This review is aimed to complement
recent efforts to compile and summarize this change of paradigm in the
interpretation of galaxy evolution. In particular we cover three particular
aspects not fully covered in detail in recent reviews: (i) the spatially
resolved nature of the ionization properties in galaxies and the confusion
introduced by considering just integrated quantities; (ii) the nature of the
global scaling relations and their relations with the spatially resolved ones;
and (iii) the dependence of the radial gradients and characteristic properties
of the stellar populations and ionized gas on stellar mass and galaxy
morphology. To this end we replicate published results, and present novel ones,
based on the largest compilation of IFS data of galaxies in the nearby universe
to date.
|
On the Energy Spectra of GeV/TeV Cosmic Ray Leptons | Recent observations of cosmic ray electrons from several instruments have
revealed various degrees of deviation in the measured electron energy
distribution from a simple power-law, in a form of an excess around TeV
energies. An even more prominent deviation has been observed in the fraction of
cosmic ray positrons around 100 GeV energies. In this paper we show that the
observed excesses in the electron spectrum may be easily re-produced without
invoking any unusual sources other than the general diffuse Galactic components
of cosmic rays. The primary physical effect involved is the Klein-Nishina
suppression of the electron cooling rate around TeV energies. With a very
reasonable choice of the model parameters characterizing the local interstellar
medium, we can reproduce the most recent observations by Fermi and HESS
experiments. We also find that high positron fraction increasing with energy,
as claimed by the PAMELA experiment, cannot be explained in our model with the
conservative set of the model parameters. We are able, however, to reproduce
the PAMELA results assuming high values of the starlight and interstellar gas
densities, which would be more appropriate for vicinities of supernova
remnants. A possible solution to this problem may be that cosmic rays undergo
most of their interactions near their sources due to the efficient trapping in
the far upstream of supernova shocks by self-generated, cosmic ray-driven
turbulence.
|