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Analytical Studies of NGC 2571, NGC 6802, Koposov 53 and Be 89 | Astrophysical parameters (age, reddening, distance, radius, luminosity
function, mass function, total mass, relaxation time and mass segregation) have
been estimated for open clusters NGC 2571, NGC 6802, Koposov 53 and Be 89 by
using the Two Micron All Sky Survey (2MASS) photometry. We analyse the
color-magnitude diagrams and stellar radial density profiles. We have found
that NGC 2571 is the youngest one having young main sequence stars while Be 89
is the oldest cluster.
|
Lyman-alpha Forest Tomography of the z>2 Cosmic Web | The hydrogen Ly$\alpha$ forest is an important probe of the $z>2$ Universe
that is otherwise challenging to observe with galaxy redshift surveys, but this
technique has traditionally been limited to 1D studies in front of bright
quasars. However, by pushing to faint magnitudes ($g>23$) with 8-10m large
telescopes it becomes possible to exploit the high area density of
high-redshift star-forming galaxies to create 3D tomographic maps of
large-scale structure in the foreground. I describe the first pilot
observations using this technique, as well discuss future surveys and the
resulting science possibilities for galaxy evolution and cosmology.
|
Strong lensing constraints on modified gravity models | We impose the first strong-lensing constraints on a wide class of modified
gravity models where an extra field that modifies gravity also couples to
photons (either directly or indirectly through a coupling with baryons) and
thus modifies lensing. We use the nonsingular isothermal ellipsoid (NIE)
profile as an effective potential, which produces flat galactic rotation
curves. If a concrete modified gravity model gives a flat rotation curve, then
the parameter $\Gamma$ that characterizes the lensing effect must take some
definite value. We find that $\Gamma = 1.24\pm0.65$ at $1\sigma$, consistent
with general relativity ($\Gamma = 1$). This constrains the parameter space in
some recently proposed models.
|
Reconciling the GRB rate and star formation histories | While there are numerous indications that GRBs arise from the death of
massive stars, the GRB rate does not follow the global cosmic star formation
rate and, within their hosts, GRBs are more concentrated in regions of very
high star formation. We explain both puzzles here. Using the publicly available
VESPA database of SDSS Data Release 7 spectra, we explore a multi-parameter
space in galaxy properties, like stellar mass, metallicity, dust etc. to find
the sub-set of galaxies that reproduce the recently obtained GRB rate by
Wanderman & Piran (2010). We find that only galaxies with present stellar
masses below < 10^{10} Msun and low metallicity reproduce the observed GRB
rate. This is consistent with direct observations of GRB hosts and provides an
independent confirmation of the nature of GRB hosts. Because of the
significantly larger sample of SDSS galaxies, we compute their correlation
function and show that they are anti-biased with respect to the dark matter:
they are in filaments and voids. Using recent observations of massive stars in
local dwarfs we show how the fact that GRB hosts galaxies are dwarfs can
explain the observation that GRBs are more concentrated in regions of high star
formation than SNe. Finally we explain these results using new theoretical
advances in the field of star formation.
|
Constraining dark sector perturbations I: cosmic shear and CMB lensing | We present current and future constraints on equations of state for dark
sector perturbations. The equations of state considered are those corresponding
to a generalized scalar field model and time-diffeomorphism invariant $L(g)$
theories that are equivalent to models of a relativistic elastic medium and
also Lorentz violating massive gravity. We develop a theoretical understanding
of the observable impact of these models. In order to constrain these models we
use CMB temperature data from Planck, BAO measurements, CMB lensing data from
Planck and the South Pole Telescope, and weak galaxy lensing data from
CFHTLenS. We find non-trivial exclusions on the range of parameters, although
the data remains compatible with $w=-1$. We gauge how future experiments will
help to constrain the parameters. This is done via a likelihood analysis for
CMB experiments such as CoRE and PRISM, and tomographic galaxy weak lensing
surveys, focussing in on the potential discriminatory power of Euclid on mildly
non-linear scales.
|
2XMMi J225036.9+573154 - a new eclipsing AM Her binary discovered using
XMM-Newton | We report the discovery of an eclipsing polar, 2XMMi J225036.9+573154, using
XMM-Newton. It was discovered by searching the light curves in the 2XMMi
catalogue for objects showing X-ray variability. Its X-ray light curve shows a
total eclipse of the white dwarf by the secondary star every 174 mins. An
extended pre-eclipse absorption dip is observed in soft X-rays at phi=0.8-0.9,
with evidence for a further dip in the soft X-ray light curve at phi~0.4.
Further, X-rays are seen from all orbital phases (apart from the eclipse) which
makes it unusual amongst eclipsing polars. We have identified the optical
counterpart, which is faint (r=21), and shows a deep eclipse (>3.5 mag in white
light). Its X-ray spectrum does not show a distinct soft X-ray component which
is seen in many, but not all, polars. Its optical spectrum shows Halpha in
emission for a fraction of the orbital period.
|
A general relativistic signature in the galaxy bispectrum: the local
effects of observing on the lightcone | Next-generation galaxy surveys will increasingly rely on the galaxy
bispectrum to improve cosmological constraints, especially on primordial
non-Gaussianity. A key theoretical requirement that remains to be developed is
the analysis of general relativistic effects on the bispectrum, which arise
from observing galaxies on the past lightcone, {as well as from relativistic
corrections to the dynamics}. {As an initial step towards a fully relativistic
analysis of the galaxy bispectrum, we compute for the first time the local
relativistic lightcone effects on the bispectrum,} which come from Doppler and
gravitational potential contributions. For the galaxy bispectrum, the problem
is much more complex than for the power spectrum, since we need the lightcone
corrections at second order. Mode-coupling contributions at second order mean
that relativistic corrections can be non-negligible at smaller scales than in
the case of the power spectrum. In a primordial Gaussian universe, we show that
the local lightcone corrections for squeezed shapes at $z\sim1$ mean that the
bispectrum can differ from the Newtonian prediction by $\gtrsim 10\%$ when the
short modes are $k\lesssim (50\,{\rm Mpc})^{-1}$. These relativistic projection
effects, if ignored in the analysis of observations, could be mistaken for
primordial non-Gaussianity. For upcoming surveys which probe equality scales
and beyond, {all relativistic lightcone effects and relativistic dynamical
corrections should be included} for an accurate measurement of primordial
non-Gaussianity.
|
Redshift-Independent Distances in the NASA/IPAC Extragalactic Database:
Methodology, Content and Use of NED-D | Estimates of galaxy distances based on indicators that are independent of
cosmological redshift are fundamental to astrophysics. Researchers use them to
establish the extragalactic distance scale, to underpin estimates of the Hubble
constant, and to study peculiar velocities induced by gravitational attractions
that perturb the motions of galaxies with respect to the Hubble flow of
universal expansion. In 2006 the NASA/IPAC Extragalactic Database (NED) began
making available a comprehensive compilation of redshift-independent
extragalactic distance estimates. A decade later, this compendium of distances
(NED-D) now contains more than 100,000 individual estimates based on primary
and secondary indicators, available for more than 28,000 galaxies, and compiled
from over 2,000 references in the refereed astronomical literature. This
article describes the methodology, content, and use of NED-D, and addresses
challenges to be overcome in compiling such distances. Currently, 75 different
distance indicators are in use. We include a figure that facilitates comparison
of the indicators with significant numbers of estimates in terms of the
minimum, 25th percentile, median, 75th percentile, and maximum distances
spanned. Brief descriptions of the indicators, including examples of their use
in the database, are given in an Appendix.
|
Feeding Versus Feedback in NGC1068 probed with Gemini NIFS. I.
Excitation | We present emission-line flux distributions and ratios for the inner 200pc of
the narrow-line region of the Seyfert2 galaxy NGC1068, using observations
obtained with the Gemini Near-infrared Integral Field Spectrograph (NIFS) in
the J, H and K bands at a spatial resolution of 10pc and spectral resolution of
5300. The molecular gas emission - traced by the K-band H_2 emission lines -
outlines an off-centered circumnuclear ring with a radius of 100pc showing
thermal excitation. The ionized gas emission lines show flux distributions
mostly outlining the previously known [OIII]5007 ionization bicone. But while
the flux distributions in the HI and HeII emission lines are very similar to
that observed in [OIII], the flux distribution in the [FeII] emission lines is
more extended and broader than a cone close to the nucleus, showing a "double
bowl" or `hourglass" structure". This difference is attributed to the fact that
the [FeII] emission, besides coming from the fully ionized region, comes also
from the more extended partially ionized regions, in gas excited mainly by
X-rays from the active galactic nucleus. A contribution to the [FeII] emission
from shocks along the bicone axis to NE and SW of the nucleus is also supported
by the enhancement of the [FeII](1.2570)/[PII](1.1885) and
[FeII](1.2570)/Pabeta emission-line ratios at these locations and is attributed
to the interaction of the radio jet with the NLR. The mass of ionized gas in
the inner 200pc of NGC1068 is MHII~2.2E4 M_Sun, while the mass of the H2
emitting gas is only M_{H2}~29M_Sun. Taking into account the dominant
contribution of the cold molecular gas, we obtain an estimate of the total
molecular gas mass of Mcold~2E7 M_Sun.
|
Uncorrelated estimates of the primordial power spectrum | We use the localized principle component analysis to detect deviations from
scale invariance of the primordial power spectrum of curvature perturbations.
With the technique we make uncorrelated estimates of the primordial power
spectrum with five wavenumber bins. In the framework of a minimal LCDM model,
using the latest cosmic microwave background data from the WMAP and ACT
experiments we find that more than 95% of the preferred models are incompatible
with the assumption of scale-invariance, but still compatible with a power-law
primordial spectrum. We also forecast the sensitivity and constraints
achievable by the Planck experiment by performing Monte Carlo studies on
simulated data. Planck could significantly improve the constraints on the
primordial power spectrum, especially at small scales by roughly a factor of 4.
|
Rates of Stellar Tidal Disruption | Tidal disruption events occur rarely in any individual galaxy. Over the last
decade, however, time-domain surveys have begun to accumulate statistical
samples of these flares. What dynamical processes are responsible for feeding
stars to supermassive black holes? At what rate are stars tidally disrupted in
realistic galactic nuclei? What may we learn about supermassive black holes and
broader astrophysical questions by estimating tidal disruption event rates from
observational samples of flares? These are the questions we aim to address in
this Chapter, which summarizes current theoretical knowledge about rates of
stellar tidal disruption, and compares theoretical predictions to the current
state of observations.
|
Post-Minkowskian Gravity: Dark Matter as a Relativistic Inertial Effect? | A review is given of the theory of non-inertial frames (with the associated
inertial effects and the study of the non-relativistic limit) in Minkowski
space-time, of parametrized Minkowski theories and of the rest-frame instant
form of dynamics for isolated systems admitting a Lagrangian description. The
relevance and gauge equivalence of the clock synchronization conventions for
the identification of the instantaneous 3-spaces (Euclidean only in inertial
frames) are described. Then this formalism is applied to tetrad gravity in
globally hyperbolic, asymptotically Minkowskian space-times without
super-translations, where the equivalence principle implies the absence of
global inertial frames. The recently discovered York canonical basis,
diagonalizing the York-Lichnerowicz approach, allows to identify the gauge
variables (inertial effects in general relativity) and the tidal ones (the
gravitational waves of the linearized theory) and to clarify the meaning of the
Hamilton equations. The role of the gauge variable ${}^3K$, the trace of the
extrinsic curvature of the non-Euclidean 3-space (the York time not existing in
Newton theory), as a source of inertial effects is emphasized. After the
presentation of preliminary results on the linearization of tetrad gravity in
the family of non-harmonic 3-orthogonal gauges with a free value of ${}^3K$, we
define post-Minkowskian gravitational waves (without post-Newtonian
approximations on the matter sources) propagating in a non-Euclidean 3-space,
emphasizing the non-graviton-like aspects of gravity. It is conjectured that
dark matter may be explained as a relativistic inertial effect induced by
${}^3K$: it would simulate the need to choose a privileged gauge connected with
the observational conventions for the description of matter.
|
Characterizing faint galaxies in the reionization epoch: LBT confirms
two L<0.2L* sources at z=6.4 behind the CLASH/Frontier Fields cluster
MACS0717.5+3745 | We report the LBT/MODS1 spectroscopic confirmation of two images of faint
Lyman alpha emitters at $z=6.4$ behind the Frontier Fields galaxy cluster
MACSJ0717.5+3745. A wide range of lens models suggests that the two images are
highly magnified, with a strong lower limit of mu>5. These are the faintest z>6
candidates spectroscopically confirmed to date. These may be also multiple
images of the same z=6.4 source as supported by their similar intrinsic
properties, but the lens models are inconclusive regarding this interpretation.
To be cautious, we derive the physical properties of each image individually.
Thanks to the high magnification, the observed near-infrared (restframe
ultraviolet) part of the spectral energy distributions and Ly-alpha lines are
well detected with S/N(m_1500)>~10 and S/N(Ly-alpha)~10-15. Adopting mu>5, the
absolute magnitudes, M_1500, and Ly-alpha fluxes, are fainter than -18.7 and
2.8x10^(-18)erg/s/cm2, respectively. We find a very steep ultraviolet spectral
slope beta=-3.0+/-0.5 (F_lambda=lambda^(beta)), implying that these are very
young, dust-free and low metallicity objects, made of standard stellar
populations or even extremely metal poor stars (age<~30Myr, E(B-V)=0 and
metallicity 0.0-0.2 Z/Zsolar). The objects are compact (< 1 kpc^(2)), and with
a stellar mass M* < 10^(8) M_solar. The very steep beta, the presence of the
Ly-alpha line and the intrinsic FWHM (<300 km/s) of these newborn objects do
not exclude a possible leakage of ionizing radiation. We discuss the
possibility that such faint galaxies may resemble those responsible for cosmic
reionization.
|
Sneutrino Inflation with $\alpha$-attractors | Sneutrino inflation employs the fermionic partners of the inflaton and
stabilizer field as right-handed neutrinos to realize the seesaw mechanism for
light neutrino masses. We show that one can improve the latest version of this
scenario and its consistency with the Planck data by embedding it in the theory
of cosmological $\alpha$-attractors.
|
Hot gas heating via magnetic arms in spiral galaxies. The case of M 83 | Reconnection heating has been considered as a potential source of the heating
of the interstellar medium. In some galaxies, significant polarised radio
emission has been found between the spiral arms. This emission has a form of
`magnetic arms' that resembles the spiral structure of the galaxy. Reconnection
effects could convert some of the energy of the turbulent magnetic field into
the thermal energy of the surrounding medium, leaving more ordered magnetic
fields, as is observed in the magnetic arms. Sensitive radio and X-ray data for
the grand-design spiral galaxy M 83 are used for a detailed analysis of the
possible interactions of magnetic fields with hot gas, including a search for
signatures of gas heating by magnetic reconnection effects. Magnetic field
strengths and energies derived from the radio emission are compared with the
parameters of the hot gas calculated from the model fits to sensitive X-ray
spectra of the hot gas emission. The available X-ray data allowed us to
distinguish two thermal components in the halo of M 83. We found slightly
higher average temperatures of the hot gas in the interarm regions, which
results in higher energies per particle and is accompanied by a decrease in the
energy density of the magnetic fields. The observed differences in the energy
budget between the spiral arms and the interarm regions suggest that, similar
to the case of another spiral galaxy NGC 6946, we may be observing hints for
gas heating by magnetic reconnection effects in the interarm regions. These
effects, which act more efficiently on the turbulent component of the magnetic
field, are expected to be stronger in the spiral arms. However, with the
present data it is only possible to trace them in the interarm regions, where
the star formation and the resulting turbulence is low.
|
A spinning supermassive black hole binary model consistent with VLBI
observations of the S5 1928+738 jet | Very Long Baseline Interferometry (VLBI) allows for high-resolution and
high-sensitivity observations of relativistic jets, that can reveal
periodicities of several years in their structure. We perform an analysis of
long-term VLBI data of the quasar S5 1928+738 in terms of a geometric model of
a helical structure projected onto the plane of the sky. We monitor the
direction of the jet axis through its inclination and position angles. We
decompose the variation of the inclination of the inner 2 milliarcseconds of
the jet of S5 1928+738 into a periodic term with amplitude of ~0.89 deg and a
linear decreasing trend with rate of ~0.05 deg/yr. We also decompose the
variation of the position angle into a periodic term with amplitude of ~3.39
deg and a linear increasing trend with rate of ~0.24 deg/yr. We interpret the
periodic components as arising from the orbital motion of a binary black hole
inspiraling at the jet base and derive corrected values of the mass ratio and
separation from the accumulated 18 years of VLBI data. Then we identify the
linear trends in the variations as due to the slow reorientation of the spin of
the jet emitter black hole induced by the spin-orbit precession and we
determine the precession period T_SO=4852+/-646 yr of the more massive black
hole, acting as the jet emitter. Our study provides indications, for the first
time from VLBI jet kinematics, for the spinning nature of the jet-emitting
black hole.
|
Discovery of Balmer Broad Absorption Lines in the Quasar LBQS 1206+1052 | We report the discovery of Balmer broad absorption lines (BALs) in the quasar
LBQS 1206+1052 and present a detailed analysis of the peculiar absorption line
spectrum. Besides Mg II $\lambda \lambda 2796, 2803$ doublet, BALs are also
detected in He I* multiplet at $\lambda \lambda 2946, 3189, 3889$ \AA arising
from metastable helium $2^3S$ level, and in H$\alpha$ and H$\beta$ from excited
hydrogen H I* $n=2$ level, which are rarely seen in quasar spectra. We identify
two components in the BAL troughs of $\Delta v\sim$2000 km s$^{-1}$ width: One
component shows an identical profile in H I*, \hei* and \mgii with its centroid
blueshifted by $-v_{\rm c}\approx 726$ km\ s$^{-1}$. The other component is
detected in \hei* and \mgii with $-v_{\rm c}\approx 1412$ km s$^{-1}$. We
estimate the column densities of H I*, He I*, and Mg II, and compare them with
possible level population mechanisms. Our results favor the scenario that the
Balmer BALs originate in a partially ionized region with a column density of
$N_{\rm H}\sim 10^{21-22}$ cm$^{-2}$ for an electron density of $n_e\sim
10^{6-8} $cm$^{-3}$ via Ly$\alpha$ resonant scattering pumping. The harsh
conditions needed may help to explain the rarity of Balmer absorption line
systems in quasar spectra. With an $i$-band PSF magnitude of 16.50, LBQS
1206+1052 is the brightest Balmer-BAL quasar ever reported. Its high brightness
and unique spectral properties make LBQS 1206+1052 a promising candidate for
follow-up high-resolution spectroscopy, multi-band observations, and long-term
monitoring.
|
When did Population III star formation end? | We construct a theoretical framework to study Population III (Pop III) star
formation in the post-reionization epoch ($z\lesssim 6$) by combining
cosmological simulation data with semi-analytical models. We find that due to
radiative feedback (i.e. Lyman-Werner and ionizing radiation) massive haloes
($M_{\rm halo}\gtrsim 10^{9}\ \rm M_{\odot}$) are the major ($\gtrsim 90$%)
hosts for potential Pop III star formation at $z\lesssim 6$, where dense
pockets of metal-poor gas may survive to form Pop III stars, under inefficient
mixing of metals released by supernovae. Metal mixing is the key process that
determines not only when Pop III star formation ends, but also the total mass,
$M_{\rm PopIII}$, of \textit{active} Pop III stars per host halo, which is a
crucial parameter for direct detection and identification of Pop III hosts.
Both aspects are still uncertain due to our limited knowledge of metal mixing
during structure formation. Current predictions range from early termination at
the end of reionization ($z\sim 5$) to continuous Pop III star formation
extended to $z=0$ at a non-negligible rate $\sim 10^{-7}\ \rm M_{\odot}\
yr^{-1}\ Mpc^{-3}$, with $M_{\rm PopIII}\sim 10^{3}-10^{6}\ \rm M_{\odot}$.
This leads to a broad range of redshift limits for direct detection of Pop III
hosts, $z_{\rm PopIII}\sim 0.5-12.5$, with detection rates $\lesssim 0.1-20\
\rm arcmin^{-2}$, for current and future space telescopes (e.g. HST, WFIRST and
JWST). Our model also predicts that the majority ($\gtrsim 90$%) of the cosmic
volume is occupied by metal-free gas. Measuring the volume filling fractions of
this metal-free phase can constrain metal mixing parameters and Pop III star
formation.
|
Classical transitions with the topological number changing in the early
Universe | We consider classical dynamics of two real scalar fields within a model with
the potential having a saddle point. The solitons of such model are field
configurations that have the form of closed loops in the field space. We study
the formation and evolution of these solitons, in particular, the conditions at
which they could be formed even when the model potential has only one minimum.
These non-trivial field configurations represent domain walls in the
three-dimensional physical space. The set of these configurations can be split
into disjoint equivalence classes. We provide a simple expression for the
winding number of an arbitrary closed loop in the field space and discuss the
transitions that change the winding number. We also show that non-trivial field
configurations could be responsible for the energy density excess that could
evade the CMB constraints but could be important at scales which are
responsible for the formation of galaxies and the massive primordial black
holes.
|
Kinematic groups beyond the Solar neighbourhood with RAVE | We analyse the kinematics of disc stars observed by the RAVE survey in and
beyond the Solar neighbourhood.We detect significant overdensities in the
velocity distributions using a technique based on the wavelet transform.We find
that the main local kinematic groups are large scale features, surviving at
least up to ~1 kpc from the Sun in the direction of anti-rotation, and also at
~700 pc below the Galactic plane.We also find that for regions located at
different radii than the Sun, the known groups appear shifted in the velocity
plane. For example, the Hercules group has a larger azimuthal velocity for
regions inside the Solar circle and a lower value outside. We have also
discovered a new group at (U, V) = (92,-22) km/s in the Solar neighbourhood and
confirmed the significance of other previously found groups. Some of these
trends detected for the first time are consistent with dynamical models of the
effects of the bar and the spiral arms. More modelling is required to
definitively characterise the non-axisymmetric components of our Galaxy using
these groups.
|
A spectroscopic survey of faint, high-galactic latitude red clump stars.
II. The medium resolution sample | Aims. The goal of our survey is to provide accurate and multi-epoch radial
velocities, atmospheric parameters (Teff, log g and [M/H]), distances and space
velocities of faint Red Clump stars. Methods. We recorded high signal-to-noise
(S/N >= 200) spectra of Red Clump stars, over the 4750-5950 Ang range, at a
resolving power 5500. The target stars are distributed over the great circle of
the celestial equator. Radial velocities were obtained via cross-correlation
against IAU radial velocity standards. Atmospheric parameters were derived via
chi^2 fit to a synthetic spectral library. A large number of RC stars from
other surveys were re-observed to check the consistency of our results.
Results. A total of 245 Red Clump stars were observed (60 of them with a second
epoch observation separated in time by about three months), and the results are
presented in an output catalog. None of them is already present in other
surveys of Red Clump stars. In addition to astrometric and photometric support
data from external sources, the catalog provides radial velocities (accuracy
sigma(RV)=1.3 km/s), atmospheric parameters (sigma(Teff)=88 K, sigma(log
g)=0.38 dex and sigma([M/H])=0.17 dex), spectro-photometric distances, (X,Y,Z)
galacto-centric positions and (U,V,W) space velocities.
|
Momentum space sampling of neutrinos in $N$-body simulations | Including massive neutrinos in $N$-body simulations is a challenging task due
to the large thermal velocities of the neutrinos. In particle based codes this
leads to problems of shot-noise due to insufficient sampling of the neutrino
momentum distribution function. In this paper we investigate the benefits and
drawbacks of a scheme first suggested in a paper by Banerjee et al. in which
the initial neutrino distribution is symmetrised in momentum space. We confirm
that this method reduce shot-noise significantly, but we also find that it
generates some spurious power in the neutrino power spectrum at intermediate
and small scales. We speculate that this happens because many neutrinos in the
simulation sample the same underlying dark matter structures while moving
through the simulation. By carefully tuning the number of directions in
momentum space of the initial neutrino distribution we show that some
improvements can be made over the case where initial neutrino directions are
purely random. At redshifts $z\gtrsim 3$ the method works very well, but at
smaller redshifts significant improvements are not possible due to the spurious
power generation.
|
A multiwavelength survey of HI-excess galaxies with surprisingly
inefficient star formation | We present the results of a multiwavelength survey of HI-excess galaxies, an
intriguing population with large HI reservoirs associated with little current
star formation. These galaxies have stellar masses $M_{\star} >10^{10}$
M$_{\odot}$, and were identified as outliers in the gas fraction vs. NUV$-r$
color and stellar mass surface density scaling relations based on the GALEX
Arecibo SDSS Survey (GASS). We obtained HI interferometry with the GMRT, Keck
optical long-slit spectroscopy and deep optical imaging (where available) for
four galaxies. Our analysis reveals multiple possible reasons for the HI excess
in these systems. One galaxy, AGC 10111, shows an HI disk that is
counter-rotating with respect to the stellar bulge, a clear indication of
external origin of the gas. Another galaxy appears to host a Malin 1-type disk,
where a large specific angular momentum has to be invoked to explain the
extreme $M_{\rm HI}$/$M_{\star}$ ratio of 166$\%$. The other two galaxies have
early-type morphology with very high gas fractions. The lack of merger
signatures (unsettled gas, stellar shells and streams) in these systems
suggests that these gas-rich disks have been built several Gyr-s ago, but it
remains unclear how the gas reservoirs were assembled. Numerical simulations of
large cosmological volumes are needed to gain insight into the formation of
these rare and interesting systems.
|
Consistent Higher Derivative Gravitational theories with stable de
Sitter and Anti-de Sitter Backgrounds | In this paper we provide the criteria for any generally covariant, parity
preserving, and torsion free theory of gravity to possess a stable de Sitter
(dS) or anti-de Sitter (AdS) background. By stability we mean the absence of
tachyonic or ghost-like states in the perturbative spectrum that can lead to
classical instabilities and violation of quantum unitarity. While we find that
the usual suspects, the F(R) and F(G) theories, can indeed possess consistent
(A)dS backgrounds, G being the Gauss-Bonnet term, another interesting class of
theories, string-inspired infinite derivative gravity, can also be consistent
around such curved vacuum solutions. Our study should not only be relevant for
quantum gravity and early universe cosmology involving ultraviolet physics, but
also for modifications of gravity in the infra-red sector vying to replace dark
energy .
|
Model Breaking Measure for Cosmological Surveys | Recent observations have led to the establishment of the concordance LCDM
model for cosmology. A number of experiments are being planned to shed light on
dark energy, dark matter, inflation and gravity, which are the key components
of the model. To optimize and compare the reach of these surveys, several
figures of merit have been proposed. They are based on either the forecasted
precision on the LCDM model and its expansion, or on the expected ability to
distinguish two models. We propose here another figure of merit that quantifies
the capacity of future surveys to rule out the LCDM model. It is based on a
measure of the difference in volume of observable space that the future surveys
will constrain with and without imposing the model. This model breaking figure
of merit is easy to compute and can lead to different survey optimizations than
other metrics. We illustrate its impact using a simple combination of
supernovae and BAO mock observations and compare the respective merit of these
probes to challenge LCDM. We discuss how this approach would impact the design
of future cosmological experiments.
|
The IRAM-30m line survey of the Horsehead PDR: I. CF+ as a tracer of C+
and a measure of the Fluorine abundance | C+ is a key species in the interstellar medium but its 158 {\mu}m fine
structure line cannot be observed from ground-based telescopes. Current models
of fluorine chemistry predict that CF+ is the second most important fluorine
reservoir, in regions where C+ is abundant. We detected the J = 1-0 and J = 2-1
rotational lines of CF+ with high signal-to-noise ratio towards the PDR and
dense core positions in the Horsehead. Using a rotational diagram analysis, we
derive a column density of N(CF+) = (1.5 - 2.0) \times 10^12 cm^-2. Because of
the simple fluorine chemistry, the CF+ column density is proportional to the
fluorine abundance. We thus infer the fluorine gas-phase abundance to be F/H =
(0.6 - 1.5) \times 10^-8. Photochemical models indicate that CF+ is found in
the layers where C+ is abundant. The emission arises in the UV illuminated skin
of the nebula, tracing the outermost cloud layers. Indeed, CF+ and C+ are the
only species observed to date in the Horsehead with a double peaked line
profile caused by kinematics. We therefore propose that CF+, which is
detectable from the ground, can be used as a proxy of the C+ layers.
|
New Constraints on the Highest-Energy Cosmic-Ray Electrons and Positrons | At energies above a few TeV, no measurements of the cosmic-ray electron
spectrum exist yet. By considering the similarity of air showers induced by
electrons and gamma rays as seen by ground-based arrays, we use published
limits on isotropic gamma-ray fluxes to place first constraints on the >10 TeV
electron spectrum. We demonstrate that, due the proximity of known sources, the
flux of such electrons (and positrons) can be large. We show how these smoothly
connect to lower-energy positrons measured by PAMELA and relate to exciting new
indications from Fermi.
|
Cosmology with interaction in the dark sector | Unless some unknown symmetry in Nature prevents or suppresses a non-minimal
coupling in the dark sector, the dark energy field may interact with the
pressureless component of dark matter. In this paper, we investigate some
cosmological consequences of a general model of interacting dark matter-dark
energy characterized by a dimensionless parameter $\epsilon$. We derive a
coupled scalar field version for this general class of scenarios and carry out
a joint statistical analysis involving SNe Ia data ({Legacy} and {Constitution}
sets), measurements of baryon acoustic oscillation peak at $z = 0.20$ (2dFGRS)
and $z = 0.35$ (SDSS), and measurements of the Hubble evolution $H(z)$. For the
specific case of vacuum decay ($w = -1$), we find that, although physically
forbidden, a transfer of energy from dark matter to dark energy is favored by
the data.
|
How well do STARLAB and NBODY4 compare? I: Simple models | N-body simulations are widely used to simulate the dynamical evolution of a
variety of systems, among them star clusters. Much of our understanding of
their evolution rests on the results of such direct N-body simulations. They
provide insight in the structural evolution of star clusters, as well as into
the occurrence of stellar exotica. Although the major pure N-body codes
STARLAB/KIRA and NBODY4 are widely used for a range of applications, there is
no thorough comparison study yet. Here we thoroughly compare basic quantities
as derived from simulations performed either with STARLAB/KIRA or NBODY4.
We construct a large number of star cluster models for various stellar mass
function settings (but without stellar/binary evolution, primordial binaries,
external tidal fields etc), evolve them in parallel with STARLAB/KIRA and
NBODY4, analyse them in a consistent way and compare the averaged results
quantitatively. For this quantitative comparison we develop a bootstrap
algorithm for functional dependencies.
We find an overall excellent agreement between the codes, both for the
clusters' structural and energy parameters as well as for the properties of the
dynamically created binaries. However, we identify small differences, like in
the energy conservation before core collapse and the energies of escaping
stars, which deserve further studies. Our results reassure the comparability
and the possibility to combine results from these two major N-body codes, at
least for the purely dynamical models (i.e. without stellar/binary evolution)
we performed. (abridged)
|
Investigation of the Galactic Bar based on Photometry and Stellar Proper
Motions | A new method for selecting stars in the Galactic bar based on 2MASS infrared
photometry in combination with stellar proper motions from the Kharkiv XPM
catalogue has been implemented. In accordance with this method, red clump and
red giant branch stars are preselected on the color -- magnitude diagram and
their photometric distances are calculated. Since the stellar proper motions
are indicators of a larger velocity dispersion toward the bar and the spiral
arms compared to the stars with circular orbits, applying the constraints on
the proper motions of the preselected stars that take into account the Galactic
rotation has allowed the background stars to be eliminated. Based on a joint
analysis of the velocities of the selected stars and their distribution on the
Galactic plane, we have confidently identified the segment of the Galactic bar
nearest to the Sun with an orientation of 20$^\circ$--25$^\circ$ with respect
to the Galactic center -- Sun direction and a semimajor axis of no more than 3
kpc.
|
The nebular properties of star-forming galaxies at intermediate redshift
from the Large Early Galaxy Astrophysics Census | We present a detailed study of the partial rest-optical
($\lambda_{\mathrm{obs}} \approx 3600-5600\,\r{A}$) spectra of $N = 328$
star-forming galaxies at $0.6 < z < 1.0$ from the Large Early Galaxy
Astrophysics Census (LEGA-C). We compare this sample with low-redshift ($z \sim
0$) galaxies from the Sloan Digital Sky Survey (SDSS), intermediate-redshift
($z \sim 1.6$) galaxies from the Fiber Multi-Object Spectrograph (FMOS)-COSMOS
Survey, and high-redshift ($z \sim 2$) galaxies from the Keck Baryonic
Structure Survey (KBSS). At a lookback time of $6-8\ \mathrm{Gyr}$, galaxies
with stellar masses $\mathrm{log}(\mathrm{M_{\ast}/M_{\odot}}) > 10.25$ appear
remarkably similar to $z \sim 0$ galaxies in terms of their nebular excitation,
as measured using $\mathrm{[O\,III]}\lambda5008 / \mathrm{H}\beta$. There is
some evidence that $0.6 < z < 1.0$ galaxies with lower $\mathrm{M_{\ast}}$ have
higher $\mathrm{[O\,III]}\lambda5008 / \mathrm{H}\beta$ than $z \sim 0$
galaxies and are more similar to less evolved $z \sim 1.6$ and $z \sim 2$
galaxies, which are offset from the $z \sim 0$ locus at all
$\mathrm{M_{\ast}}$. We explore the impact selection effects, contributions
from active galactic nuclei, and variations in physical conditions (ionization
parameter and gas-phase oxygen abundance) have on the apparent distribution of
$\mathrm{[O\,III]}\lambda5008 / \mathrm{H}\beta$ and find somewhat higher
ionization and lower enrichment in $0.6 < z < 1.0$ galaxies with lower
$\mathrm{M_{\ast}}$ relative to $z \sim 0$ galaxies. We use new near-infrared
spectroscopic observations of $N = 53$ LEGA-C galaxies to investigate other
probes of enrichment and excitation. Our analysis demonstrates the importance
of obtaining complete rest-optical spectra of galaxies in order to disentangle
these effects.
|
Probing High-Column Outflows in BALQSOs Using Metastable Helium | Outflows are believed to be ubiquitous and fundamentally important in active
galaxies. Despite their importance, key physical properties of outflows remain
poorly unconstrained; this severely limits study of the acceleration process.
It is especially difficult to constrain the column density since most of the
lines are saturated. However, column densities can be measured using ions that
are expected to be relatively rare in the gas, since they are least likely to
be saturated. Phosphorus, specifically the PV doublet at 1118 and 1128A, is
generally regarded as a useful probe of high column densities because of its
low abundance. We have found that the metastable neutral helium triplet is an
equally valuable probe of high column densities in BALQSOs. The significant
advantage is that it can be observed in the infrared (HeI*10830) and the
optical (HeI*3889) bands from the ground in low-redshift (z<1.2) objects.
We report the discovery of the first HeI*10830 BALQSO FBQS J1151+3822, and
discuss constraints on the column density obtained from the optical and IR HeI*
lines. In addition, a new observation revealing MgII and FeII absorption
provides further constraints, and Cloudy modeling of HeI*, MgII, and FeII
suggests that the difference between LoBALs and FeLoBALs is column density
along the line of sight.
|
PS1-10afx at z=1.388: Pan-STARRS1 Discovery of a New Type of
Superluminous Supernova | We present the Pan-STARRS1 discovery of PS1-10afx, a unique
hydrogen-deficient superluminous supernova (SLSN) at z=1.388. The light curve
peaked at z_P1=21.7 mag, making PS1-10afx comparable to the most luminous known
SNe, with M_u = -22.3 mag. Our extensive optical and NIR observations indicate
that the bolometric light curve of PS1-10afx rose on the unusually fast
timescale of ~12 d to the extraordinary peak luminosity of 4.1e44 erg/s (M_bol
= -22.8 mag) and subsequently faded rapidly. Equally important, the SED is
unusually red for a SLSN, with a color temperature of 6800 K near maximum
light, in contrast to previous H-poor SLSNe, which are bright in the UV. The
spectra more closely resemble those of a normal SN Ic than any known SLSN, with
a photospheric velocity of 11,000 km/s and evidence for line blanketing in the
rest-frame UV. Despite the fast rise, these parameters imply a very large
emitting radius (>5e15 cm). We demonstrate that no existing theoretical model
can satisfactorily explain this combination of properties: (i) a nickel-powered
light curve cannot match the combination of high peak luminosity with the fast
timescale; (ii) models powered by the spindown energy of a rapidly-rotating
magnetar predict significantly hotter and faster ejecta; and (iii) models
invoking shock breakout through a dense circumstellar medium cannot explain the
observed spectra or color evolution. The host galaxy is well detected in
pre-explosion imaging with a luminosity near L*, a star formation rate of 15
M_sun/yr, and is fairly massive (2e10 M_sun), with a stellar population age of
1e8 yr, also in contrast to the dwarf hosts of known H-poor SLSNe. PS1-10afx is
distinct from known examples of SLSNe in its spectra, colors, light-curve
shape, and host galaxy properties, suggesting that it resulted from a different
channel than other hydrogen-poor SLSNe.
|
H-alpha and Free-Free Emission from the WIM | Recent observations have found the ratio of H-alpha to free-free radio
continuum to be surprisingly high in the diffuse ionized ISM (the so-called
WIM), corresponding to an electron temperature of only ~3000K. Such low
temperatures were unexpected in gas that was presumed to be photoionized. We
consider a 3-component model for the observed diffuse emission, consisting of a
mix of (1) photoionized gas, (2) gas that is recombining and cooling, and (3)
cool H I gas. This model can successfully reproduce the observed intensities of
free-free continuum, H-alpha, and collisionally-excited lines such as NII 6583.
To reproduce the low observed value of free-free to H-alpha, the PAH abundance
in the photoionized regions must be lowered by a factor ~3, and ~20% of the
diffuse H-alpha must be reflected from dust grains, as suggested by Wood &
Reynolds (1999).
|
Evolution of the spectral curvature in the ULX Holmberg II X-1 | Ultraluminous X-ray sources (ULXs) are interesting systems as they can host
intermediate mass black holes. Alternatively, ULXs can represent stellar-mass
black holes accreting at super-Eddington rates. Recently spectral curvature or
breaks at energies above a few keV have been detected in high quality ULX
spectra. These spectral features have been taken as evidence against the
intermediate-mass black hole case. In this paper, we report on a new XMM-Newton
observation of the ULX Holmberg II X-1 that also shows a clear spectral break
at approximately 4 keV. This observation was performed during a low luminosity
state of the system and by comparing this new data to a high luminosity state
XMM-Newton observation, we can conclude that the spectral break energy
increases with luminosity. This behaviour is different to a ULX in the Holmberg
IX galaxy,where an opposite trend between the luminosity and the spectral break
energy has been claimed. We discuss mechanisms that could explain this complex
behaviour.
|
Evidence for Multiple Pathways to Deuterium Enhancements in
Protoplanetary Disks | The distributions of deuterated molecules in protoplanetary disks are
expected to depend on the molecular formation pathways. We use observations of
spatially resolved DCN emission from the disk around TW Hya, acquired during
ALMA Science verification with a ~3" synthesized beam, together with comparable
DCO+ observations from the Submillimeter Array, to investigate differences in
the radial distributions of these species and hence differences in their
formation chemistry. In contrast to DCO+, which shows an increasing column
density with radius, DCN is better fit by a model that is centrally peaked. We
infer that DCN forms at a smaller radii and thus at higher temperatures than
DCO+. This is consistent with chemical network model predictions of DCO+
formation from H2D+ at T<30 K and DCN formation from additional pathways
involving CH2D+ at higher temperatures. We estimate a DCN/HCN abundance ratio
of ~0.017, similar to the DCO+/HCO+ abundance ratio. Deuterium fractionation
appears to be efficient at a range of temperatures in this protoplanetary disk.
These results suggest caution in interpreting the range of deuterium fractions
observed in Solar System bodies, as multiple formation pathways should be taken
into account.
|
Damped perturbations in stellar systems: Genuine modes and Landau-damped
waves | This research was stimulated by the recent studies of damping solutions in
dynamically stable spherical stellar systems. Using the simplest model of the
homogeneous stellar medium, we discuss nontrivial features of stellar systems.
Taking them into account will make it possible to correctly interpret the
results obtained earlier and will help to set up decisive numerical experiments
in the future. In particular, we compare the initial value problem versus the
eigenvalue problem. It turns out that in the unstable regime, the Landau-damped
waves can be represented as a superposition of van Kampen modes {\it plus} a
discrete damped mode, usually ignored in the stability study. This mode is a
solution complex conjugate to the unstable Jeans mode. In contrast, the
Landau-damped waves are not genuine modes: in modes, eigenfunctions depend on
time as $\exp (-{\rm i} \omega t)$, while the waves do not have eigenfunctions
on the real $v$-axis at all. However, `eigenfunctions' on the complex
$v$-contours do exist. Deviations from the Landau damping are common and can be
due to singularities or cut-off of the initial perturbation above some fixed
value in the velocity space.
|
AGN Jets and Winds in Polarised Light: The Case of Mrk 231 | We present the results of a multi-frequency, multi-scale radio polarimetric
study with the Very Large Array (VLA) of the Seyfert 1 galaxy and BALQSO, Mrk
231. We detect complex total and polarized intensity features in the source.
Overall, the images indicate the presence of a broad, one-sided, curved outflow
towards the south which consists of a weakly collimated jet with poloidal
inferred magnetic fields, inside a broader magnetized ``wind'' or ``sheath''
component with toroidal inferred magnetic fields. The model of a kpc-scale
weakly collimated jet/lobe in Mrk 231 is strengthened by its C-shaped
morphology, steep spectral index throughout, complexities in the magnetic field
structures, and the presence of self-similar structures observed on the
10-parsec-scale in the literature. The ``wind'' may comprise both nuclear
starburst (close to the core) and AGN winds, where the latter maybe the primary
contributor. Moving away from the core, the ``wind'' component may also
comprise the outer layers (or ``sheath'') of a broadened jet. The inferred
value of the (weakly collimated) jet production efficiency,
$\eta_\mathrm{jet}\sim$0.01 is consistent with the estimates in the literature.
The composite jet and wind outflow in Mrk 231 appears to be low-power and
matter-dominated, and oriented at a small angle to our line of sight.
|
The impact of red giant/AGB winds on AGN jet propagation | Dense stellar winds may mass-load the jets of active galactic nuclei,
although it is unclear what are the time and spatial scales in which the mixing
takes place. We study the first steps of the interaction between jets and
stellar winds, and also the scales at which the stellar wind may mix with the
jet and mass-load it. We present a detailed two-dimensional simulation,
including thermal cooling, of a bubble formed by the wind of a star. We also
study the first interaction of the wind bubble with the jet using a
three-dimensional simulation in which the star enters the jet. Stability
analysis is carried out for the shocked wind structure, to evaluate the
distances over which the jet-dragged wind, which forms a tail, can propagate
without mixing with the jet flow. The two-dimensional simulations point at
quick wind bubble expansion and fragmentation after about one bubble shock
crossing time. Three-dimensional simulations and stability analysis point at
local mixing in the case of strong perturbations and relatively small density
ratios between the jet and the jet dragged-wind, and to a possibly more stable
shocked wind structure at the phase of maximum tail mass flux. Analytical
estimates also indicate that very early stages of the star jet-penetration time
may be also relevant for mass loading. The combination of these and previous
results from the literature suggest highly unstable interaction structures and
efficient wind-jet flow mixing on the scale of the jet interaction height,
possibly producing strong inhomogeneities within the jet. In addition, the
initial wind bubble shocked by the jet leads to a transient, large interaction
surface. The interaction structure can be a source of significant non-thermal
emission.
|
Gas Inflow and Star Formation near Supermassive Black Holes: The Role of
Nuclear Activity | Numerical models of gas inflow towards a supermassive black hole (SMBH) show
that star formation may occur in such an environment through the growth of a
gravitationally unstable gas disc. We consider the effect of nuclear activity
on such a scenario. We present the first three-dimensional grid-based radiative
hydrodynamic simulations of direct collisions between infalling gas streams and
a $4 \times 10^6~\text{M}_\odot$ SMBH, using ray-tracing to incorporate
radiation consistent with an active galactic nucleus (AGN). We assume inflow
masses of $ \approx 10^5~\text{M}_\odot$ and explore radiation fields of 10%
and 100% of the Eddington luminosity ($L_\text{edd}$). We follow our models to
the point of central gas disc formation preceding star formation and use the
Toomre Q parameter ($Q_T$) to test for gravitational instability. We find that
radiation pressure from UV photons inhibits inflow. Yet, for weak radiation
fields, a central disc forms on timescales similar to that of models without
feedback. Average densities of $> 10^{8}~\text{cm}^{-3}$ limit photo-heating to
the disc surface allowing for $Q_T\approx1$. For strong radiation fields, the
disc forms more gradually resulting in lower surface densities and larger $Q_T$
values. Mass accretion rates in our models are consistent with 1%--60% of the
Eddington limit, thus we conclude that it is unlikely that radiative feedback
from AGN activity would inhibit circumnuclear star formation arising from a
massive inflow event.
|
Modelling the chemical enrichment of Population III supernovae: The
origin of the metals in near-pristine gas clouds | The most metal-poor, high redshift damped Lyman-alpha systems (DLAs) provide
a window to study some of the first few generations of stars. In this paper, we
present a novel model to investigate the chemical enrichment of the
near-pristine DLA population. This model accounts for the mass distribution of
the enriching stellar population, the typical explosion energy of their
supernovae, and the average number of stars that contribute to the enrichment
of these DLAs. We conduct a maximum likelihood analysis of these model
parameters using the observed relative element abundances ([C/O], [Si/O], and
[Fe/O]) of the 11 most metal-poor DLAs currently known. We find that the mass
distribution of the stars that have enriched this sample of metal-poor DLAs can
be well-described by a Salpeter-like IMF slope at M > 10 M_sun and that a
typical metal-poor DLA has been enriched by < 72 massive stars (95 per cent
confidence), with masses < 40 M_sun. The inferred typical explosion energy
(E_exp = 1.8^{+0.3}_{-0.2}x10^51 erg) is somewhat lower than that found by
recent works that model the enrichment of metal-poor halo stars. These
constraints suggest that some of the metal-poor DLAs in our sample may have
been enriched by Population II stars. Using our enrichment model, we also infer
some of the typical physical properties of the most metal-poor DLAs. We
estimate that the total stellar mass content is log10(M_*/M_sun) =
3.5^{+0.3}_{-0.4} and the total gas mass is log10(M_gas/M_sun) =
7.0^{+0.3}_{-0.4} for systems with a relative oxygen abundance [O/H] ~ -3.0.
|
Understanding star formation in molecular clouds III. Probability
distribution functions of molecular lines in Cygnus X | Column density (N) PDFs serve as a powerful tool to characterize the physical
processes that influence the structure of molecular clouds. Star-forming clouds
can best be characterized by lognormal PDFs for the lower N range and a
power-law tail for higher N, commonly attributed to turbulence and self-gravity
and/or pressure, respectively. We report here on PDFs obtained from
observations of 12CO, 13CO, C18O, CS, and N2H+ in the Cygnus X North region and
compare to a PDF derived from dust observations with the Herschel satellite.
The PDF of 12CO is lognormal for Av~1-30, but is cut for higher Av due to
optical depth effects. The PDFs of C18O and 13CO are mostly lognormal up for
Av~1-15, followed by excess up to Av~40. Above that value, all CO PDFs drop,
most likely due to depletion. The high density tracers CS and N2H+ exhibit only
a power law distribution between Av~15 and 400, respectively. The PDF from dust
is lognormal for Av~3-15 and has a power-law tail up to Av~500. Absolute values
for the molecular line column densities are, however, rather uncertain due to
abundance and excitation temperature variations. Taken the dust PDF face value,
we 'calibrate' the molecular line PDF of CS to the one of the dust and
determined an abundance [CS]/[H2] of 10^-9. The slopes of the power-law tails
of the CS, N2H+, and dust PDFs are consistent with free-fall collapse of
filaments and clumps. A quasi static configuration of filaments and clumps can
possibly also account for the observed N-PDFs, as long as they have a
sufficiently condensed density structure and external ram pressure by gas
accretion is provided. The somehow flatter slopes of N2H+ and CS can reflect an
abundance change and/or subthermal excitation at low column densities.
|
The implications of the surprising existence of a large, massive CO disk
in a distant protocluster | It is not yet known if the properties of molecular gas in distant
protocluster galaxies are significantly affected by their environment as
galaxies are in local clusters. Through a deep, 64 hours of effective on-source
integration with the Australian Telescope Compact Array (ATCA), we discovered a
massive, M_mol=2.0+-0.2x10^11 M_sun, extended, ~40 kpc, CO(1-0)-emitting disk
in the protocluster surrounding the radio galaxy, MRC1138-262. The galaxy, at
z_CO=2.1478, is a clumpy, massive disk galaxy, M_star~5x10^11 M_sun, which lies
250 kpc in projection from MRC1138-262 and is a known H-alpha emitter, HAE229.
HAE229 has a molecular gas fraction of ~30%. The CO emission has a kinematic
gradient along its major axis, centered on the highest surface brightness
rest-frame optical emission, consistent with HAE229 being a rotating disk.
Surprisingly, a significant fraction of the CO emission lies outside of the
UV/optical emission. In spite of this, HAE229 follows the same relation between
star-formation rate and molecular gas mass as normal field galaxies. HAE229 is
the first CO(1-0) detection of an ordinary, star-forming galaxy in a
protocluster. We compare a sample of cluster members at z>0.4 that are detected
in low-order CO transitions with a similar sample of sources drawn from the
field. We confirm findings that the CO-luminosity and FWHM are correlated in
starbursts and show that this relation is valid for normal high-z galaxies as
well as those in overdensities. We do not find a clear dichotomy in the
integrated Schmidt-Kennicutt relation for protocluster and field galaxies. Not
finding any environmental dependence in the "star-formation efficiency" or the
molecular gas content, especially for such an extended CO disk, suggests that
environmentally-specific processes such as ram pressure stripping are not
operating efficiently in (proto)clusters. (abridged)
|
Constraining the Black Hole Mass Spectrum with LISA Observations II:
Direct comparison of detailed models | A number of scenarios have been proposed for the origin of the supermassive
black holes (SMBHs) that are found in the centres of most galaxies. Many such
scenarios predict a high-redshift population of massive black holes (MBHs),
with masses in the range 100 to 100000 times that of the Sun. When the Laser
Interferometer Space Antenna (LISA) is finally operational, it is likely that
it will detect on the order of 100 of these MBH binaries as they merge. The
differences between proposed population models produce appreciable effects in
the portion of the population which is detectable by LISA, so it is likely that
the LISA observations will allow us to place constraints on them. However,
gravitational wave detectors such as LISA will not be able to detect all such
mergers nor assign precise black hole parameters to the merger, due to weak
gravitational wave signal strengths. This paper explores LISA's ability to
distinguish between several MBH population models. In this way, we go beyond
predicting a LISA observed population and consider the extent to which LISA
observations could inform astrophysical modellers. The errors in LISA parameter
estimation are applied with a direct method which generates random sample
parameters for each source in a population realisation. We consider how the
distinguishability varies depending on the choice of source parameters (1 or 2
parameters chosen from masses, redshift or spins) used to characterise the
model distributions, with confidence levels determined by 1 and 2-dimensional
tests based on the Kolmogorov-Smirnov test.
|
Energy Dependent time lags in the Seyfert 1 galaxy NGC 4593 | We investigate the energy-time lag dependence of the source NGC 4593 using
XMM-{\it Newton}/EPIC-pn data. We found that the time lag dependency is linear
in nature with respect to the logarithm of different energy bands. We also
investigate the frequency dependent time lags and identify that at some
frequency range (5 $\times$ 10$^{-5}$ Hz -- 2 $\times$ 10$^{-4}$ Hz) the X-ray
emission is highly coherent, mildly frequency dependent and very strongly
energy dependent. These observations can be explained in the frame work of the
thermal Comptonization process and they indicate a truncated accretion disk
very close to the black hole. We discuss the plausible spectral state to
explain the phenomenon and conclude that the observed properties bear a close
resemblance to the intermediate state or the steep power-law state, found in
galactic black hole sources.
|
Superheavy dark matter through Higgs portal operators | The WIMPzilla hypothesis is that the dark matter is a
super-weakly-interacting and super-heavy particle. Conventionally, the
WIMPzilla abundance is set by gravitational particle production during or at
the end of inflation. In this study we allow the WIMPzilla to interact directly
with Standard Model fields through the Higgs portal, and we calculate the
thermal production (freeze-in) of WIMPzilla dark matter from the annihilation
of Higgs boson pairs in the plasma. The two particle-physics model parameters
are the WIMPzilla mass and the Higgs-WIMPzilla coupling. The two cosmological
parameters are the reheating temperature and the expansion rate of the universe
at the end of inflation. We delineate the regions of parameters space where
either gravitational or thermal production is dominant, and within those
regions we identify the parameters that predict the observed dark matter relic
abundance. Allowing for thermal production opens up the parameter space, even
for Planck-suppressed Higgs-WIMPzilla interactions.
|
Are we seeing accretion flows in a 250kpc-sized Ly-alpha halo at z=3? | Using MUSE on the ESO-VLT, we obtained a 4 hour exposure of the z=3.12 radio
galaxy MRC0316-257. We detect features down to ~10^-19 erg/s/cm^2/arcsec^2 with
the highest surface brightness regions reaching more than a factor of 100
higher. We find Ly-alpha emission out to ~250 kpc in projection from the active
galactic nucleus (AGN). The emission shows arc-like morphologies arising at
150-250 kpc from the nucleus in projection with the connected filamentary
structures reaching down into the circum-nuclear region. The most distant arc
is offset by 700 km/s relative to circum-nuclear HeII 1640 emission, which we
assume to be at the systemic velocity. As we probe emission closer to the
nucleus, the filamentary emission narrows in projection on the sky, the
relative velocity decreases to ~250 km/s, and line full-width at half maximum
range from 300-700 km/s. From UV line ratios, the emission on scales of 10s of
kpc from the nucleus along a wide angle in the direction of the radio jets is
clearly excited by the radio jets and ionizing radiation of the AGN. Assuming
ionization equilibrium, the more extended emission outside of the axis of the
jet direction would require 100% or more illumination to explain the observed
surface brightness. High speed (>300 km/s) shocks into rare gas would provide
sufficiently high surface brightness. We discuss the possibility that the arcs
of Ly-alpha emission represent accretion shocks and the filamentary emission
represent gas flows into the halo, and compare our results with gas accretion
simulations.
|
Three dimensional geometries and the analysis of H II regions | We compare emission line intensities from photoionization models of smooth
and fractal shell geometries for low density H II regions, with particular
focus on the low-ionization diagnostic diagram [N II]/H-alpha vs H-alpha.
Building on previously published models and observations of Barnard's Loop, we
show that the observed range of intensities and variations in the line
intensity ratios may be reproduced with a three dimensional shell geometry. Our
models adopt solar abundances throughout the model nebula, in contrast with
previous one dimensional modeling which suggested the variations in line
intensity ratios could only be reproduced if the heavy element abundances were
increased by a factor of 1.4. For spatially resolved H II regions, the multiple
sightlines that pierce and sample different ionization and temperature
conditions within smooth and fractal shells produce a range of line intensities
that are easily overlooked if only the total integrated intensities from the
entire nebula model are computed. Our conclusion is that inference of H II
region properties, such as elemental abundances, via photoionization models of
one dimensional geometries must be treated with caution and further tested
through three dimensional modeling.
|
Structural diversity of disc galaxies originating in the cold gas inflow
from cosmic webs | Disc galaxies show a large morphological diversity with varying contribution
of three major structural components; thin discs, thick discs, and central
bulges. Dominance of bulges increases with the galaxy mass (Hubble sequence)
whereas thick discs are more prominent in lower mass galaxies. Because galaxies
grow with the accretion of matter, this observed variety should reflect
diversity in accretion history. On the basis of the prediction by the cold-flow
theory for galactic gas accretion and inspired by the results of previous
studies, we put a hypothesis that associates different accretion modes with
different components. Namely, thin discs form as the shock-heated hot gas in
high-mass halos gradually accretes to the central part, thick discs grow by the
direct accretion of cold gas from cosmic webs when the halo mass is low, and
finally bulges form by the inflow of cold gas through the shock-heated gas in
high-redshift massive halos. We show that this simple hypothesis reproduces the
mean observed variation of galaxy morphology with the galaxy mass. This
scenario also predicts that thick discs are older and poorer in metals than
thin discs, in agreement with the currently available observational data.
|
Stellar Archaeology in the Galactic halo with the Ultra-Faint Dwarfs:
VI. Ursa Major II | We present a B, V color-magnitude diagram (CMD) of the Milky Way dwarf
satellite Ursa Major II (UMa II), spanning the magnitude range from V ~ 15 to V
~ 23.5 mag and extending over a 18 {\times} 18 arcmin2 area centered on the
galaxy. Our photometry goes down to about 2 magnitudes below the galaxy's main
sequence turn-off, that we detected at V ~ 21.5 mag. We have discovered a
bona-fide RR Lyrae variable star in UMa II, which we use to estimate a
conservative dereddened distance modulus for the galaxy of (m-M)0 =
17.70{\pm}0.04{\pm}0.12 mag, where the first error accounts for the
uncertainties of the calibrated photometry, and the second reflects our lack of
information on the metallicity of the star. The corresponding distance to UMa
II is 34.7 {\pm} 0.6 ({\pm} 2.0) kpc. Our photometry shows evidence of a spread
in the galaxy subgiant branch, compatible with a spread in metal abundance in
the range between Z=0.0001 and Z=0.001. Based on our estimate of the distance,
a comparison of the fiducial lines of the Galactic globular clusters (GCs) M68
and M5 ([Fe/H]=-2.27 {\pm} 0.04 dex and -1.33 {\pm} 0.02 dex, respectively),
with the position on the CMD of spectroscopically confirmed galaxy members, may
suggest the existence of stellar populations of different metal abundance/age
in the central region of UMa II.
|
Dark photon relic dark matter production through the dark axion portal | We present a new mechanism to produce the dark photon ($\gamma'$) in the
early universe with a help of the axion ($a$) using a recently proposed dark
axion portal. The dark photon, a light gauge boson in the dark sector, can be a
relic dark matter if its lifetime is long enough. The main process we consider
is a variant of the Primakoff process $f a \to f \gamma'$ mediated by a photon,
which is possible with the axion--photon--dark photon coupling. The axion is
thermalized in the early universe because of the strong interaction and it can
contribute to the non-thermal dark photon production through the dark axion
portal coupling. It provides a two-component dark matter sector, and the relic
density deficit issue of the axion dark matter can be addressed by the
compensation with the dark photon. The dark photon dark matter can also address
the reported 3.5 keV $X$-ray excess via the $\gamma' \to \gamma a$ decay.
|
OmegaWINGS: OmegaCAM@VST observations of WINGS galaxy clusters | The Wide-field Nearby Galaxy-cluster Survey (WINGS) is a wide-field
multi-wavelength survey of X-ray selected clusters at z =0.04-0.07. The
original 34'x34' WINGS field-of- view has now been extended to cover a 1 sq.deg
field with both photometry and spectroscopy. In this paper we present the
Johnson B and V-band OmegaCAM/VST observations of 46 WINGS clusters, together
with the data reduction, data quality and Sextractor photometric catalogs.
With a median seeing of 1arcs in both bands, our 25-minutes exposures in each
band typically reach the 50% completeness level at V=23.1 mag. The quality of
the astrometric and photometric accuracy has been verified by comparison with
the 2MASS as well as with SDSS astrometry, and SDSS and previous WINGS imaging.
Star/galaxy separation and sky-subtraction procedure have been tested comparing
with previous WINGS data.
The Sextractor photometric catalogues are publicly available at the CDS, and
will be included in the next release of the WINGS database on the VO together
with the OmegaCAM reduced images. These data form the basis for a large ongoing
spectroscopic campaign with AAOmega/AAT and is being employed for a variety of
studies. [abridged]
|
X-Ray Variability and the Inner Region in Active Galactic Nuclei | We present theoretical models of X-ray variability attributable to orbital
signatures from an accretion disk including emission region size,
quasi-periodic oscillations (QPOs) and its quality factor $Q$, and the
emergence of a break frequency in the power spectral density shape. We find a
fractional variability amplitude of $F_{var}\propto M^{-0.4}_{\bullet}$. We
conduct a time series analysis on X-ray light curves ($0.3-10$ keV) of a sample
of active galactic nuclei (AGNs). A statistically significant bend frequency is
inferred in 9 of 58 light curves (16 %) from 3 AGNs for which the break
timescale is consistent with the reported BH spin but not with the reported BH
mass. Upper limits of $2.85 \times 10^7 M_\odot$ in NGC 4051, $8.02 \times 10^7
M_\odot$ in MRK 766 and $4.68 \times 10^7 M_\odot$ in MCG-6-30-15 are inferred
for maximally spinning BHs. For REJ 1034+396, where a QPO at 3733 s was
reported, we obtain an emission region size of $(6 - 6.5) M$ and a BH spin
$a\lesssim$ 0.08. The relativistic inner region of a thin disk, dominated by
radiation pressure and electron scattering is likely to host the orbital
features as the simulated $Q$ ranges from $6.3 \times 10^{-2}$ to $4.25 \times
10^6$, containing the observed $Q$. The derived value of $Q \sim$ 32 for REJ
1034+396 therefore suggests that the AGN hosts a thin disk.
|
Cosmological Aspects of Spontaneous Baryogenesis | We investigate cosmological aspects of spontaneous baryogenesis driven by a
scalar field, and present general constraints that are independent of the
particle physics model. The relevant constraints are obtained by studying the
backreaction of the produced baryons on the scalar field, the cosmological
expansion history after baryogenesis, and the baryon isocurvature
perturbations. We show that cosmological considerations alone provide powerful
constraints, especially for the minimal scenario with a quadratic scalar
potential. Intriguingly, we find that for a given inflation scale, the other
parameters including the reheat temperature, decoupling temperature of the
baryon violating interactions, and the mass and decay constant of the scalar
are restricted to lie within ranges of at most a few orders of magnitude. We
also discuss possible extensions to the minimal setup, and propose two ideas
for evading constraints on isocurvature perturbations: one is to suppress the
baryon isocurvature with nonquadratic scalar potentials, another is to
compensate the baryon isocurvature with cold dark matter isocurvature by making
the scalar survive until the present.
|
On the efficiency of the Blandford-Znajek mechanism for low angular
momentum relativistic accretion | Blandford-Znajek (BZ) mechanism has usually been studied in the literature
for accretion with considerably high angular momentum leading either to the
formation of a cold Keplerian disc, or a hot and geometrically thick
sub-Keplerian flow as described within the framework of ADAF/RIAF. However, in
nearby elliptical galaxies, as well as for our own Galactic centre, accretion
with very low angular momentum is prevalent. Such quasi-spherical strongly
sub-Keplerian accretion has complex dynamical features and can accommodate
stationary shocks. In this letter, we present our calculation for the maximum
efficiency obtainable through the BZ mechanism for complete general
relativistic weakly rotating axisymmetric flow in the Kerr metric. Both shocked
and shock free flow has been studied in detail for rotating and counter
rotating accretion. Such study has never been done in the literature before. We
find that the energy extraction efficiency is low, about 0.1%, and increases by
a factor 15 if the ram pressure is included. Such an efficiency is still much
higher than the radiative efficiency of such optically thin flows. For BZ
mechanism, shocked flow produces higher efficiency than the shock free
solutions and retrograde flow provides a slightly larger value of the
efficiency than that for the prograde flow.
|
RELICS: High-Resolution Constraints on the Inner Mass Distribution of
the z=0.83 Merging Cluster RXJ0152.7-1357 from strong lensing | Strong gravitational lensing (SL) is a powerful means to map the distribution
of dark matter. In this work, we perform a SL analysis of the prominent X-ray
cluster RXJ0152.7-1357 (z=0.83, also known as CL 0152.7-1357) in \textit{Hubble
Space Telescope} images, taken in the framework of the Reionization Lensing
Cluster Survey (RELICS). On top of a previously known $z=3.93$ galaxy multiply
imaged by RXJ0152.7-1357, for which we identify an additional multiple image,
guided by a light-traces-mass approach we identify seven new sets of multiply
imaged background sources lensed by this cluster, spanning the redshift range
[1.79-3.93]. A total of 25 multiple images are seen over a small area of ~0.4
$arcmin^2$, allowing us to put relatively high-resolution constraints on the
inner matter distribution. Although modestly massive, the high degree of
substructure together with its very elongated shape make RXJ0152.7-1357 a very
efficient lens for its size. This cluster also comprises the third-largest
sample of z~6-7 candidates in the RELICS survey. Finally, we present a
comparison of our resulting mass distribution and magnification estimates with
those from a Lenstool model. These models are made publicly available through
the MAST archive.
|
Entropy principle and complementary second law of thermodynamics for
self-gravitating systems | (abbreviated) The statistical mechanics of self-gravitating systems is a
long-held puzzle. In this work, we employ a phenomenological entropy form of
ideal gas, first proposed by White & Narayan, to revisit this issue. By
calculating the first-order variation of the entropy, subject to the mass- and
energy-conservation constraints, we obtain an entropy stationary equation.
Incorporated with the Jeans equation, and by specifying some functional form
for the anisotropy parameter beta, we numerically solve the two equations, and
demonstrate that the velocity anisotropy parameter plays an important role to
attain a density profile that is finite in mass, energy, and spatial extent. If
incorporated again with some empirical density profile from simulations, our
theoretical predictions of the anisotropy parameter, and the radial
pseudo-phase-space density in the outer non-gravitationally degenerate region
of the dark matter halo, agree rather well with the simulation data, and the
predictions are also acceptable in the middle weak-degenerate region of the
dark halo. The second-order variational calculus reveals the seemingly
paradoxical but actually complementary consequence that the equilibrium state
of self-gravitating systems is the global minimum entropy state for the whole
system under long-range violent relaxation, but simultaneously the local
maximum entropy state for every and any small part of the system under
short-range two-body relaxation and Landau damping. This minimum-maximum
entropy duality means that the standard second law of thermodynamics needs to
be re-expressed or generalized for self-gravitating systems. We believe that
our findings, especially the complementary second law of thermodynamics, may
provide crucial clues to the development of the statistical physics of
self-gravitating systems as well as other long-range interaction systems.
|
Preliminary Target Selection for the DESI Quasar (QSO) Sample | The DESI survey will measure large-scale structure using quasars as direct
tracers of dark matter in the redshift range $0.9<z<2.1$ and using quasar
Ly-$\alpha$ forests at $z>2.1$. We present two methods to select candidate
quasars for DESI based on imaging in three optical ($g, r, z$) and two infrared
($W1, W2$) bands. The first method uses traditional color cuts and the second
utilizes a machine-learning algorithm.
|
The impact of clustering and angular resolution on far-infrared and
millimeter continuum observations | Follow-up observations at high-angular resolution of submillimeter galaxies
showed that the single-dish sources are comprised of a blend of several
galaxies. Consequently, number counts derived from low and high angular
resolution observations are in disagreement. This demonstrates the importance
of resolution effects and the need to have realistic simulations to explore
them. We built a new 2deg^2 simulation of the extragalactic sky from the
far-infrared to the submillimeter. It is based on an updated version of the two
star-formation mode galaxy evolution model. Using global galaxy properties, we
use the abundance matching technique to populate a dark-matter lightcone and
thus simulate the clustering. We produce maps and extract the sources, and show
that the limited angular resolution of single-dish instruments have a strong
impact on (sub)millimeter continuum observations. Taking into account these
resolution effects, we are reproducing a large set of observables, including
number counts, redshift distributions, and cosmic infrared background power
spectra. Our simulation describes consistently the number counts from
single-dish telescopes and interferometers. In particular, at 350 and 500 um,
we find that number counts measured by Herschel between 5 and 50 mJy are biased
towards high values by a factor 2, and that redshift distributions are biased
towards low z. We also show that the clustering has an important impact on the
Herschel pixel histogram used to derive number counts from P(D) analysis.
Finally, we demonstrate that the large number density of red Herschel sources
found in observations but not in models could be an observational artifact
caused by the combination of noise, resolution effects, and the steepness of
color and flux density distributions. Our simulation (SIDES) is available at
http://cesam.lam.fr/sides
|
Baryonic acoustic oscillations simulations for the Large Synoptic Survey
Telescope (LSST) | The baryonic acoustic oscillations are features in the spatial distribution
of the galaxies which, if observed at different epochs, probe the nature of the
dark energy. In order to be able to measure the parameters of the dark energy
equation of state to high precision, a huge sample of galaxies has to be used.
The Large Synoptic Survey Telescope will survey the optical sky with 6 filters
from 300nm and 1100nm, such that a catalog of galaxies with photometric
redshifts will be available for dark energy studies. In this article, we will
give a rough estimate of the impact of the photometric redshift uncertainties
on the computation of the dark energy parameter through the reconstruction of
the BAO scale from a simulated photometric catalog.
|
Interplay of super-WIMP and freeze-in production of dark matter | Non-thermalized dark matter is a cosmologically valid alternative to the
paradigm of weakly interacting massive particles. For dark matter belonging to
a $Z_2$-odd sector that contains in addition a thermalized mediator particle,
dark matter production proceeds in general via both the freeze-in and superWIMP
mechanism. We highlight their interplay and emphasize the connection to
long-lived particles at colliders. For the explicit example of a colored
t-channel mediator model we map out the entire accessible parameter space,
cornered by bounds from the LHC, big bang nucleosynthesis and Lyman-alpha
forest observations, respectively. We discuss prospects for the HL- and HE-LHC.
|
New constraints on inelastic dark matter from IceCube | We study the capture and subsequent annihilation of inelastic dark matter
(DM) in the Sun, placing constraints on the DM-nucleon scattering cross section
from the null result of the IceCube neutrino telescope. We then compare such
constraints with exclusion limits on the same cross section that we derive from
XENON1T, PICO and CRESST results. We calculate the cross section for inelastic
DM-nucleon scattering within an extension of the effective theory of DM-nucleon
interactions which applies to the case of inelastic DM models characterised by
a mass splitting between the incoming and outgoing DM particle. We find that
for values of the mass splitting parameter larger than about 200 keV, neutrino
telescopes place limits on the DM-nucleon scattering cross section which are
stronger than the ones from current DM direct detection experiments. The exact
mass splitting value for which this occurs depends on whether DM thermalises in
the Sun or not. This result applies to all DM-nucleon interactions that
generate DM-nucleus scattering cross sections which are independent of the
nuclear spin, including the "canonical" spin-independent interaction. We
explicitly perform our calculations for a DM candidate with mass of 1 TeV, but
our conclusions qualitatively also apply to different masses. Furthermore, we
find that exclusion limits from IceCube on the coupling constants of this
family of spin-independent interactions are more stringent than the ones from a
(hypothetical) reanalysis of XENON1T data based on an extended signal region in
nuclear recoil energy. Our results should be taken into account in global
analyses of inelastic DM models.
|
A nontrivial footprint of standard cosmology in the future observations
of low-frequency gravitational waves | Recent research show that the cosmological components of the Universe should
influence on the propagation of Gravitational Waves (GWs) and even it has been
proposed a new way to measure the cosmological constant using Pulsar Timing
Arrays (PTAs). However, these results have considered very particular cases
(e.g. a de Sitter Universe or a mixing with non-relativistic matter). In this
work we propose an extension of these results, using the Hubble constant as the
natural parameter that includes all the cosmological information and studying
its effect on the propagation of GWs. Using linearized gravity we considered a
mixture of perfect fluids permeating the spacetime and studied the propagation
of GWs within the context of the LCDM model. We found from numerical
simulations that the timing residual of local pulsars should present a
distinguishable peak depending on the local value of the Hubble constant. As a
consequence, when assuming the standard LCDM model, our result predicts that
the region of maximum timing residual is determined by the redshift of the
source. This framework represents a new test for the standard cosmological
model, and it can be used to facilitate the measurements of gravitational wave
by ongoing PTAs projects.
|
The Orion Fingers: Near-IR Adaptive Optics Imaging of an Explosive
Protostellar Outflow | Aims. Adaptive optics images are used to test the hypothesis that the
explosive BN/KL outflow from the Orion OMC1 cloud core was powered by the
dynamical decay of a non-hierarchical system of massive stars. Methods.
Narrow-band H2, [Fe II], and broad-band Ks obtained with the Gemini South
multi-conjugate adaptive optics (AO) system GeMS and near-infrared imager GSAOI
are presented. The images reach resolutions of 0.08 to 0.10", close to the
0.07" diffraction limit of the 8-meter telescope at 2.12 microns. Comparison
with previous AO-assisted observations of sub-fields and other ground-based
observations enable measurements of proper motions and the investigation of
morphological changes in H2 and [Fe II] features with unprecedented precision.
The images are compared with numerical simulations of compact, high-density
clumps moving ~1000 times their own diameter through a lower density medium at
Mach 1000. Results. Several sub-arcsecond H2 features and many [Fe II]
'fingertips' on the projected outskirts of the flow show proper motions of ~300
km/s. High-velocity, sub-arcsecond H2 knots ('bullets') are seen as far as 140"
from their suspected ejection site. If these knots propagated through the dense
Orion A cloud, their survival sets a lower bound on their densities of order
10^7 cm^-3, consistent with an origin within a few au of a massive star and
accelerated by a final multi-body dynamic encounter that ejected the BN object
and radio source I from OMC1 about 500 years ago. Conclusions. Over 120
high-velocity bow-shocks propagating in nearly all directions from the OMC1
cloud core provide evidence for an explosive origin for the BN/KL outflow
triggered by the dynamic decay of a non-hierarchical system of massive stars.
Such events may be linked to the origin of runaway, massive stars.
|
Effects of dust abundance on the far-infrared colours of blue compact
dwarf galaxies | We investigate the FIR properties of a sample of BCDs observed by AKARI. By
utilizing the data at wavelengths of $\lambda =65 \mu$m, 90 $\mu$m, and 140
$\mu$m, we find that the FIR colours of the BCDs are located at the natural
high-temperature extension of those of the Milky Way and the Magellanic Clouds.
This implies that the optical properties of dust in BCDs are similar to those
in the Milky Way. Indeed, we explain the FIR colours by assuming the same grain
optical properties, which may be appropriate for amorphous dust grains, and the
same size distribution as those adopted for the Milky Way dust. Since both
interstellar radiation field and dust optical depth affect the dust
temperature, it is difficult to distinguish which of these two physical
properties is responsible for the change of FIR colours. Then, in order to
examine if the dust optical depth plays an important role in determining the
dust temperature, we investigate the correlation between FIR colour (dust
temperature) and dust-to-gas ratio. We find that the dust temperature tends to
be high as the dust-to-gas ratio decreases but that this trend cannot be
explained by the effect of dust optical depth. Rather, it indicates a
correlation between dust-to-gas ratio and interstellar radiation field.
Although the metallicity may also play a role in this correlation, we suggest
that the dust optical depth could regulate the star formation activities, which
govern the interstellar radiation field. We also mention the importance of
submillimetre data in tracing the emission from highly shielded low-temperature
dust.
|
The Accuracy of Weak Lensing Simulations | We investigate the accuracy of weak lensing simulations by comparing the
results of five independently developed lensing simulation codes run on the
same input $N$-body simulation. Our comparison focuses on the lensing
convergence maps produced by the codes, and in particular on the corresponding
PDFs, power spectra and peak counts. We find that the convergence power spectra
of the lensing codes agree to $\lesssim 2\%$ out to scales $\ell \approx 4000$.
For lensing peak counts, the agreement is better than $5\%$ for peaks with
signal-to-noise $\lesssim 6$. We also discuss the systematic errors due to the
Born approximation, line-of-sight discretization, particle noise and smoothing.
The lensing codes tested deal in markedly different ways with these effects,
but they nonetheless display a satisfactory level of agreement. Our results
thus suggest that systematic errors due to the operation of existing lensing
codes should be small. Moreover their impact on the convergence power spectra
for a lensing simulation can be predicted given its numerical details, which
may then serve as a validation test.
|
New parameterization for unified dark matter and dark energy | In this paper we investigate a new phenomenological parameterization for
unified dark matter and dark energy based on the polynomial expansion of the
barotropic equation of state parameter $w$. Our parameterization provides
well-behaving evolution of $w$ for both small and big redshifts as well as in
the far future. The dark fluid described by our parameterization behaves for
big redshifts like a dark matter. Therefore one can parameterize dark energy
and dark matter using a single dark fluid, like in the case of the Chaplygin
gas. Within this parameterization we consider 2 models: one with DE barotropic
parameter fixed to be $-1$ and the second one, where $w \neq -1$ is chosen to
match the best fit to the data. We study main cosmological properties of these
models at the expansion and perturbation levels. Based on Markov chain Monte
Carlo method with currently available cosmic observational data sets, we
constrain these models to determine the cosmological parameters at the level of
background and clustering of matter. We consider the interaction between DM and
DE which directly affects the evolution of matter and its clustering. Our model
appears to be perfectly consistent with the $\Lambda$CDM model, while providing
unification of DE and DM.
|
The Chemistry of the Trailing arm of the Sagittarius Dwarf Galaxy | We present abundances of C, O, Ti, and Fe for eleven M-giant stars in the
trailing tidal arm of the Sagittarius dwarf (Sgr). The abundances were derived
by comparing synthetic spectra with high-resolution infrared spectra obtained
with the Phoenix spectrograph on the Gemini South telescope. The targeted stars
are drawn from two regions of the Sgr trailing arm separated by 66 degrees (5
stars) and 132 degrees (6 stars) from the main body of Sgr. The trailing arm
provides a more direct diagnostic of the chemical evolution of Sgr compared to
the extensively phase-mixed leading arm.
Within our restricted sample of ~2-3 Gyr old stars, we find that the stream
material exhibits a significant metallicity gradient of -(2.4\pm0.3)x10^{-3}
dex / degree (-(9.4\pm1.1)x10^{-4} dex / kpc) away from the main body of Sgr.
The tidal disruption of Sgr is a relatively recently event. We therefore
interpret the presence of a metallicity gradient in the debris as indicative of
a similar gradient in the progenitor. The fact that such a metallicity gradient
survived for almost a Hubble time indicates that the efficiency of radial
mixing was very low in the Sgr progenitor.
No significant gradient is seen to exist in the [alpha/Fe] abundance ratio
along the trailing arm. Our results may be accounted for by a radial decrease
in star formation efficiency and/or radial increase in the efficiency of
galactic wind-driven metal loss in the chemical evolution of the Sgr
progenitor. The [Ti/Fe] and [O/Fe] abundance ratios observed within the stream
are distinct from those of the Galactic halo. We conclude that the fraction of
the intermediate to metal-rich halo population contributed by the recent
dissolution (<3 Gyr) of Sgr-like dwarf galaxies can not be substantial.
|
Where's the Dust?: The Deepening Anomaly of Microwave Emission in NGC
4725 B | We present new Atacama Large Millimeter Array (ALMA) observations towards NGC
4725 B, a discrete, compact, optically-faint region within the star-forming
disk of the nearby galaxy NGC 4725 that exhibits strong anomalous microwave
emission (AME). These new ALMA data include continuum observations centered at
92, 133, 203, and 221 GHz accompanied by spectral observations of the $^{12}$CO
($J=2\rightarrow1$) line. NGC 4725 B is detected in the continuum at all
frequencies, although the detection at 203 GHz is marginal. While molecular gas
is not detected at the exact location of NGC 4725 B, there is molecular gas in
the immediate vicinity (i.e., $\lesssim 100$ pc) along with associated diffuse
8 $\mu$m emission. When combined with existing Very Large Array continuum data
at 1.5, 3, 5.5, 9, 14, 22, 33, and 44 GHz, the spectrum is best fit by a
combination of AME, synchrotron, and free-free emission that is free-free
absorbed below $\sim6$ GHz. Given the strength of the AME, there is
surprisingly no indication of millimeter dust emission associated with NGC 4725
B on $\lesssim$6\arcsec~spatial scales at the sensitivity of the ALMA
interferometric data. Based on the properties of the nearest molecular gas
complex and the inferred star formation rate, NGC 4725 B is consistent with
being an extremely young ($\sim 3-5$ Myr) massive ($\lesssim 10^{5} M_{\odot}$)
cluster that is undergoing active cluster feedback. However, the lack of
millimeter thermal dust emission is difficult to reconcile with a spinning dust
origin of the 30 GHz emission. On the other hand, modeling NGC 4725 B as a new
class of background radio galaxy is also unsatisfactory.
|
Deuterium enrichment of the interstellar grain mantle | We carry out Monte-Carlo simulation to study deuterium enrichment of
interstellar grain mantles under various physical conditions. Based on the
physical properties, various types of clouds are considered. We find that in
diffuse cloud regions, very strong radiation fields persists and hardly a few
layers of surface species are formed. In translucent cloud regions with a
moderate radiation field, significant number of layers would be produced and
surface coverage is mainly dominated by photo-dissociation products such as,
C,CH_3,CH_2D,OH and OD. In the intermediate dense cloud regions (having number
density of total hydrogen nuclei in all forms ~ 2 x 10^4 cm^-3), water and
methanol along with their deuterated derivatives are efficiently formed. For
much higher density regions (~ 10^6 cm^-3), water and methanol productions are
suppressed but surface coverage of CO,CO_2,O_2,O_3 are dramatically increased.
We find a very high degree of fractionation of water and methanol.
Observational results support a high fractionation of methanol but surprisingly
water fractionation is found to be low. This is in contradiction with our model
results indicating alternative routes for de-fractionation of water. Effects of
various types of energy barriers are also studied. Moreover, we allow grain
mantles to interact with various charged particles (such as H^+, Fe^+,S^+ and
C^+) to study the stopping power and projected range of these charged particles
on various target ices.
|
Three-dimensional extinction mapping using Gaussian random fields | We present a scheme for using stellar catalogues to map the three-dimensional
distributions of extinction and dust within our Galaxy. Extinction is modelled
as a Gaussian random field, whose covariance function is set by a simple
physical model of the ISM that assumes a Kolmogorov-like power spectrum of
turbulent fluctuations. As extinction is modelled as a random field, the
spatial resolution of the resulting maps is set naturally by the data
available; there is no need to impose any spatial binning. We verify the
validity of our scheme by testing it on simulated extinction fields and show
that its precision is significantly improved over previous dust-mapping
efforts. The approach we describe here can make use of any photometric,
spectroscopic or astrometric data; it is not limited to any particular survey.
Consequently, it can be applied to a wide range of data from both existing and
future surveys.
|
Hydrogen volume densities in nearby galaxies I - an automated approach | Using a simple model of photodissociated atomic hydrogen on a galactic scale,
it is possible to derive total hydrogen volume densities. These densities,
obtained through a combination of atomic hydrogen, far-ultraviolet and
metallicity data, provide an independent probe of the combined atomic and
molecular hydrogen gas in galactic disks. We present a new, flexible and fully
automated procedure using this simple model. This automated method will allow
us to take full advantage of a host of available data on galaxies in order to
calculate total hydrogen volume densities of giant molecular clouds surrounding
sites of recent star formation. So far this was only possible on a
galaxy-by-galaxy basis using by-eye analysis of candidate photodissociation
regions. We test the automated method by adopting different models for the
dust-to-gas ratio and comparing the resulting densities for M74, including a
new metallicity map of M74 produced by integral field spectroscopy. We test the
procedure against previously published M83 volume densities based on the same
method and find no significant differences. The range of total hydrogen volume
densities obtained for M74 is approximately 5-700 cm-3 . Different dust-to-gas
ratio models do not result in measurably different densities. The cloud
densities presented here add M74 to the list of galaxies analyzed using the
assumption of photodissociated atomic hydrogen occurring near sites of recent
star formation and further solidify the method. For the first time, full
metallicity maps were included in the analysis as opposed to metallicity
gradients. The results will need to be compared to other tracers of the
interstellar medium and photodissociation regions, such as CO and CII, in order
to test our basic assumptions, specifically, our assumption that the HI we
detect originates in photodissociation regions.
|
Helium line emissivities for nebular astrophysics | We present the results of several collisional-radiative models describing
optically-thin emissivities of the main lines in neutral helium formed by
recombination, for a grid of electron temperatures and densities, typical of H
II regions and Planetary Nebulae. Accurate emissivities are required for
example to measure the helium abundance in nebulae and as a consequence its
primordial value. We compare our results with those obtained by previous
models, finding significant differences, well above the target accuracy of one
percent. We discuss in some detail our chosen set of atomic rates and the
differences with those adopted by previous models. The main differences lie in
the treatment of electron and proton collision rates and we discuss which
transitions are least sensitive to the choice of these rates and therefore best
suited to high precision abundance determinations. We have focused our
comparisons on the case B approximation where only He and He$^+$ are
considered, but also present results of full models including the bare nuclei,
photo-excitation and photo-ionisation and either black-body or observed
illuminating spectrum in the case of the Orion nebula, to indicate which
spectral lines are affected by opacity. For those transitions, accurate
radiative transfer calculations should be performed. We provide tables of
emissivities for all transitions within $n \le 5$ and all those between the $n
\le 5$ and $n' \le 25$ states, in the log $T_{\rm e}$ [K]=10$^{3.0(0.1)4.6}$
and log $N_{\rm e}$ [cm$^{-3}$]=10$^{2(0.5)6}$ ranges, and a FORTRAN code to
interpolate to any $T_{\rm e}, N_{\rm e}$ within these ranges.
|
The nuclear dust lane of Circinus: collimation without a torus | In some AGN, nuclear dust lanes connected to kpc-scale dust structures
provide all the extinction required to obscure the nucleus, challenging the
role of the dusty torus proposed by the Unified Model. In this letter we show
the pc-scale dust and ionized gas maps of Circinus constructed using
sub-arcsec-accuracy registration of infrared VLT AO images with optical
\textit{Hubble Space Telescope} images. We find that the collimation of the
ionized gas does not require a torus but is caused by the distribution of dust
lanes of the host galaxy on $\sim$10 pc scales. This finding questions the
presumed torus morphology and its role at parsec scales, as one of its main
attributes is to collimate the nuclear radiation, and is in line with
interferometric observations which show that most of the pc-scale dust is in
the polar direction. We estimate that the nuclear dust lane in Circinus
provides $1/3$ of the extinction required to obscure the nucleus. This
constitutes a conservative lower limit to the obscuration at the central
parsecs, where the dust filaments might get optically thicker if they are the
channels that transport material from $\sim$100 pc scales to the centre.
|
Lupus I Observations from the 2010 Flight of the Balloon-borne Large
Aperture Submillimeter Telescope for Polarimetry | The Balloon-borne Large Aperture Submillimeter Telescope for Polarimetry
(BLASTPol) was created by adding polarimetric capability to the BLAST
experiment that was flown in 2003, 2005, and 2006. BLASTPol inherited BLAST's
1.8 m primary and its Herschel/SPIRE heritage focal plane that allows
simultaneous observation at 250, 350, and 500 {\mu}m. We flew BLASTPol in 2010
and again in 2012. Both were long duration Antarctic flights. Here we present
polarimetry of the nearby filamentary dark cloud Lupus I obtained during the
2010 flight. Despite limitations imposed by the effects of a damaged optical
component, we were able to clearly detect submillimeter polarization on degree
scales. We compare the resulting BLASTPol magnetic field map with a similar map
made via optical polarimetry (The optical data were published in 1998 by J.
Rizzo and collaborators.). The two maps partially overlap and are reasonably
consistent with one another. We compare these magnetic field maps to the
orientations of filaments in Lupus I, and we find that the dominant filament in
the cloud is approximately perpendicular to the large-scale field, while
secondary filaments appear to run parallel to the magnetic fields in their
vicinities. This is similar to what is observed in Serpens South via near-IR
polarimetry, and consistent with what is seen in MHD simulations by F. Nakamura
and Z. Li.
|
Galaxy cluster cores as seen with VLT/MUSE: new strong-lensing analyses
of RX J2129.4+0009, MS 0451.6-0305 & MACSJ2129.4-0741 | We present strong-lensing analyses of three galaxy clusters, RXJ2129.4+0009
(z=0.235), MS0451.6-0305 (z=0.55), and MACSJ2129.4-0741 (z=0.589), using the
powerful combination of Hubble Space Telescope (HST) multi-band observations,
and Multi-Unit Spectroscopic Explorer (MUSE) spectroscopy. In RXJ2129, we newly
spectroscopically confirm 15 cluster members. Our resulting mass model uses 8
multiple image systems as we include a galaxy-galaxy lensing system North-East
of the cluster, and is composed of 71 halos including one dark matter
cluster-scale halo and 2 galaxy-scale halos optimized individually. For MS0451,
we report the spectroscopic identification of 2 new systems of multiple images
in the Northern region, and 112 cluster members. Our mass model uses 16
multiple image systems, and 146 halos, including 2 large-scale halos, and 7
galaxy-scale halos independently optimized. For MACSJ2129, we report the
spectroscopic identification of one new multiple image system at z=4.41, and
newly measure spectroscopic redshifts for 4 cluster members. Our mass model
uses 14 multiple image systems, and is composed of 151 halos, including 2
large-scale halos and 4 galaxy-scale halos independently optimized. Our best
models have rms of 0.29'', 0.6'', 0.74'' in the image plane for RXJ2129,
MS0451, and MACSJ2129 respectively. This analysis presents a detailed
comparison with the existing literature showing excellent agreements, and
discuss specific studies of lensed galaxies, e.g. a group of submilimeter
galaxies at z=2.9 in MS0451, and a bright z=2.1472 red singly imaged galaxy in
MACSJ2129.
|
Dark matter haloes: a multistream view | Mysterious dark matter constitutes about 85% of all mass in the Universe.
Clustering of dark matter plays the dominant role in the formation of all
observed structures on scales from a fraction to a few hundreds of
Mega-parsecs. Galaxies play a role of lights illuminating these structures so
they can be observed. The observations in the last several decades have
unveiled opulent geometry of these structures currently known as the cosmic
web. Haloes are the highest concentrations of dark matter and host luminous
galaxies. Currently the most accurate modeling of dark matter haloes is
achieved in cosmological N-body simulations. Identifying the haloes from the
distribution of particles in N-body simulations is one of the problems
attracting both considerable interest and efforts. We propose a novel framework
for detecting potential dark matter haloes using the field unique for dark
matter -- multistream field. The multistream field emerges at the nonlinear
stage of the growth of perturbations because the dark matter is collisionless.
Counting the number of velocity streams in gravitational collapses supplements
our knowledge of spatial clustering. We assume that the virialized haloes have
convex boundaries. Closed and convex regions of the multistream field are hence
isolated by imposing a positivity condition on all three eigenvalues of the
Hessian estimated on the smoothed multistream field. In a single-scale analysis
of high multistream field resolution and low softening length, the halo
substructures with local multistream maxima are isolated as individual halo
sites.
|
The Violent Youth of Bright and Massive Cluster Galaxies and their
Maturation over 7 Billion Years | In this study we investigate the formation and evolution mechanisms of the
brightest cluster galaxies (BCGs) over cosmic time. At high redshift
($z\sim0.9$), we selected BCGs and most massive cluster galaxies (MMCGs) from
the Cl1604 supercluster and compared them to low-redshift ($z\sim0.1$)
counterparts drawn from the MCXC meta-catalog, supplemented by SDSS imaging and
spectroscopy. We observed striking differences in the morphological, color,
spectral, and stellar mass properties of the BCGs/MMCGs in the two samples.
High-redshift BCGs/MMCGs were, in many cases, star-forming, late-type galaxies,
with blue broadband colors, properties largely absent amongst the low-redshift
BCGs/MMCGs. The stellar mass of BCGs was found to increase by an average factor
of $2.51\pm0.71$ from $z\sim0.9$ to $z\sim0.1$. Through this and other
comparisons we conclude that a combination of major merging (mainly wet or
mixed) and \emph{in situ} star formation are the main mechanisms which build
stellar mass in BCGs/MMCGs. The stellar mass growth of the BCGs/MMCGs also
appears to grow in lockstep with both the stellar baryonic and total mass of
the cluster. Additionally, BCGs/MMCGs were found to grow in size, on average, a
factor of $\sim3$, while their average S\'ersic index increased by $\sim$0.45
from $z\sim0.9$ to $z\sim0.1$, also supporting a scenario involving major
merging, though some adiabatic expansion is required. These observational
results are compared to both models and simulations to further explore the
implications on processes which shape and evolve BCGs/MMCGs over the past
$\sim$7 Gyr.
|
CCDM model from quantum particle creation: constraints on dark matter
mass | In this work the results from the quantum process of matter creation have
been used in order to constrain the mass of the dark matter particles in an
accelerated Cold Dark Matter model (Creation Cold Dark Matter, CCDM). In order
to take into account a back reaction effect due to the particle creation
phenomenon, it has been assumed a small deviation $\varepsilon$ for the scale
factor in the matter dominated era of the form $t^{\frac{2}{3}+\varepsilon}$.
Based on recent $H(z)$ data, the best fit values for the mass of dark matter
created particles and the $\varepsilon$ parameter have been found as
$m=1.6\times10^3$ GeV, restricted to a 68.3\% c.l. interval of
($1.5<m<6.3\times10^7$) GeV and $\varepsilon = -0.250^{+0.15}_{-0.096}$ at
68.3\% c.l. For these best fit values the model correctly recovers a transition
from decelerated to accelerated expansion and admits a positive creation rate
near the present era. Contrary to recent works in CCDM models where the
creation rate was phenomenologically derived, here we have used a quantum
mechanical result for the creation rate of real massive scalar particles, given
a self consistent justification for the physical process. This method also
indicates a possible solution to the so called "dark degeneracy", where one can
not distinguish if it is the quantum vacuum contribution or quantum particle
creation which accelerates the Universe expansion.
|
Constraining the Stellar Populations and Star Formation Histories of
Blue Compact Dwarf Galaxies with SED Fits | We discuss and test possible evolutionary connections between Blue Compact
Dwarf galaxies (BCDs) and other types of dwarf galaxies. BCDs provide ideal
laboratories to study intense star formation episodes in low mass dwarf
galaxies, and have sometimes been considered a short-lived evolutionary stage
between types of dwarf galaxies. To test these connections, we consider a
sample of BCDs as well as a comparison sample of nearby galaxies from the Local
Volume Legacy (LVL) survey for context. We fit the multi-wavelength spectral
energy distributions (SED, far-ultra-violet to far-infrared) of each galaxy
with a grid of theoretical models to determine their stellar masses and star
formation properties. We compare our results for BCDs with the LVL galaxies to
put BCDs in the context of normal galaxy evolution. The SED fits demonstrate
that the star formation events currently underway in BCDs are at the extreme of
the continuum of normal dwarf galaxies, both in terms of the relative mass
involved and in the relative increase over previous star formation rates.
Today's BCDs are distinctive objects in a state of extreme star formation which
is rapidly transforming them. This study also suggests ways to identify former
BCDs whose star formation episodes have since faded.
|
Standard Model with a real singlet scalar and inflation | We study the post-inflationary dynamics of the Standard Model Higgs and a
real singlet scalar $s$, coupled together through a renormalizable coupling
$\lambda_{sh}h^2s^2$, in a $Z_2$ symmetric model that may explain the observed
dark matter abundance and/or the origin of baryon asymmetry. The initial values
for the Higgs and $s$ condensates are given by inflationary fluctuations, and
we follow their dissipation and relaxation to the low energy vacua. We find
that both the lowest order perturbative and the non-perturbative decays are
blocked by thermal effects and large background fields and that the condensates
decay by two-loop thermal effects. Assuming instant reheating at $T=10^{16}$
GeV, the characteristic temperature for the Higgs condensate thermalization is
found to be $T_h \sim 10^{14}$ GeV, whereas $s$ thermalizes typically around
$T_s \sim 10^{6}$ GeV. By that time, the amplitude of the singlet is driven
very close to the vacuum value by the expansion of the universe, unless the
portal coupling takes a value $\lambda_{sh}\lesssim 10^{-7}$ and the singlet
$s$ never thermalizes. With these values of the coupling, it is possible to
slowly produce a sizeable fraction of the observed dark matter abundance via
singlet condensate fragmentation and thermal Higgs scattering. Physics also
below the electroweak scale can therefore be affected by the non-vacuum initial
conditions generated by inflation.
|
Long-Term Cyclicities in Phanerozoic Sea-Level Sedimentary Record and
their Potential Drivers (Does the Phanerozoic sea level encode the motion of
solar system in the Milky Way ?) | Cyclic sedimentation has varied at several timescales and this variability
has been geologically well documented at Milankovitch timescales, controlled in
part by climatically (insolation) driven sea-level changes. At the longer (tens
of Myr) timescales connection between astronomical parameters and sedimentation
via cyclic solar-system motions within the Milky Way has also been proposed,
but this hypothesis remains controversial because of the lack of long
geological records. The absence of a physical mechanism that could explain the
connection between climate and astronomy at these longer timescales led to the
explanation of plate motions as the main driver of climate on Earth.
Here we statistically show a prominent and persistent ~36 Myr sedimentary
cyclicity superimposed on two megacycles (~250 Myr) in a relatively
well-constrained sea-level (SL) record of the past 542 Myr (Phanerozoic eon).
Given the possible link between amplitudes of the ~36 and ~250 Myr
cyclicities in SL record and the potential that these periodicities fall into
the frequency band of solar system motions, we suggest an astronomical origin,
and model these periodicities as originating from the path of the solar system
in the Milky Way as vertical and radial periods that modulate the flux of
cosmic rays on Earth. Our finding of the ~36 Myr SL cyclicity lends credibility
to the existing hypothesis about the imprint of solar-system vertical period on
the geological record. The ~250 Myr megacycles are tentatively attributed to a
radial period. However, the tectonic drivers also remain potentially plausible.
The potential existence of a correlation between the modeled astronomical
signal and the geological record may offer an indirect proxy to understand the
structure and history of the Milky Way by providing a 542 Myr long record of
the path of the Sun in our Galaxy.
|
The formation of disks in massive spiral galaxies | The flatness of the rotation curve inside spiral galaxies is interpreted as
the imprint of a halo of invisible matter. Using the deepest observations of
distant galaxies, we have investigated how large disks could have been formed.
Observations include spatially resolved kinematics, detailed morphologies and
photometry from UV to mid-IR. Six Giga-years ago, half of the present-day
spirals had anomalous kinematics and morphologies that considerably affect the
scatter of the Tully Fisher relation. All anomalous galaxies can be modelled
through gas-rich, major mergers that lead to a rebuilt of a new disk. The
spiral-rebuilding scenario is proposed as a new channel to form large disks in
present-day spirals and it accounts for all the observed evolutions since the
last 6 Giga-years. A large fraction of the star formation is linked to merging
events during their whole durations.
|
Self-scattering in protoplanetary disks with dust settling | Scattering of re-emitted flux is considered to be at least partially
responsible for the observed polarisation in the (sub-)millimetre wavelength
range of several protoplanetary disks. Although the degree of polarisation
produced by scattering is highly dependent on the dust model, early studies
investigating this mechanism relied on the assumption of single grain sizes and
simple density distribution of the dust. However, in the dense inner regions
where this mechanism is usually most efficient, the existence of dust grains
with sizes ranging from nanometres to millimetres has been confirmed.
Additionally, the presence of gas forces larger grains to migrate vertically
towards the disk midplane, introducing a dust segregation in the vertical
direction. Using polarisation radiative transfer simulations, we analyse the
dependence of the resulting scattered light polarisation at 350 $\mu$m, 850
$\mu$m, 1.3 mm, and 2 mm on various parameters describing protoplanetary disks,
including the effect of dust grain settling. We find that the different disk
parameters change the degree of polarisation mostly by affecting the anisotropy
of the radiation field, the optical depth, or both. It is therefore very
challenging to deduce certain disk parameter values directly from polarisation
measurements alone. However, assuming a high dust albedo, it is possible to
trace the transition from optically thick to optically thin disk regions. The
degree of polarisation in most of the considered disk configurations is lower
than what is found observationally, implying the necessity to revisit models
that describe the dust properties and disk structure.
|
Determining Cosmology for a Nonlocal Realization of MOND | We numerically determine the cosmological branch of the free function in a
nonlocal metric-based modification of gravity which provides a relativistic
generalization of Milgrom's Modified Newtonian Dynamics. We are able to
reproduce the $\Lambda$CDM expansion history over virtually all of cosmic
history, including the era of radiation domination during Big Bang
Nucleosynthesis, the era of matter domination during Recombination, and most of
the era of vacuum energy domination. The very late period of $0 \leq z <
0.0880$, during which the model deviates from the $\Lambda$CDM expansion
history, is interesting because it causes the current value of the Hubble
parameter to be about 4.5\% larger than it would be for the $\Lambda$CDM model.
This may resolve the tension between inferences of $H_0$ which are based on
data from large redshift and inferences based on Hubble plots.
|
Formation of S0s in extreme environments II: the star-formation
histories of bulges, discs and lenses | Different processes have been proposed to explain the formation of S0s,
including mergers, disc instabilities and quenched spirals. These processes are
expected to dominate in different environments, and thus leave characteristic
footprints in the kinematics and stellar populations of the individual
components within the galaxies. New techniques enable us to cleanly disentangle
the kinematics and stellar populations of these components in IFU observations.
In this paper, we use buddi to spectroscopically extract the light from the
bulge, disc and lens components within a sample of 8 S0 galaxies in extreme
environments observed with MUSE. While the spectra of bulges and discs in S0
galaxies have been separated before, this work is the first to isolate the
spectra of lenses. Stellar populations analysis revealed that the bulges and
lenses have generally similar or higher metallicities than the discs, and the
$\alpha$-enhancement of the bulges and discs are correlated, while those of the
lenses are completely unconnected to either component. We conclude that the
majority of the mass in these galaxies was built up early in the lifetime of
the galaxy, with the bulges and discs forming from the same material through
dissipational processes at high redshift. The lenses, on the other hand, formed
over independent timescales at more random times within the lifetime of the
galaxy, possibly from evolved bars. The younger stellar populations and
asymmetric features seen in the field S0s may indicate that these galaxies have
been affected more by minor mergers than the cluster galaxies.
|
IR Divergence in Inflationary Tensor Perturbations from Fermion Loops | We estimate fermion loop corrections to the two-point correlation function of
primordial tensor perturbations in a slow-roll inflationary background. We
particularly compute an explicit term of one-loop correction from a massless
fermion, and then extend to the complete Interaction Hamiltonian. After that,
we study one-loop corrections contributed by a massive fermion to primordial
tensor fluctuations. The loop correction arisen from a massless fermion field
contains logarithms and thus may constrain the validity of perturbation theory
in inflationary cosmology, but the situation could be relaxed once the
fermion's mass is taken into account. Another one-loop diagram for a massive
fermion which involves one vertex is constrained by a UV cutoff as expected by
quantum field theory. Our result shows that loop corrections of a fermion field
have the same sign as those of a scalar field, and thus implies that the
inclusion of fermion loop corrections may not help to alleviate the issue of IR
divergence in inflationary cosmology.
|
Large-scale cortex-core structure formation in brain organoids | Brain organoids recapitulate a number of brain properties, including neuronal
diversity. However, do they recapitulate brain structure? Using a hydrodynamic
description for cell nuclei as particles interacting initially via an
effective, attractive force as mediated by the respective, surrounding
cytoskeletons, we quantify structure development in brain organoids to
determine what physical mechanism regulates the number of cortex-core
structures. Regions of cell nuclei overdensity in the linear regime drive the
initial seeding for cortex-core structures, which ultimately develop in the
non-linear regime, as inferred by the emergent form of an effective interaction
between cell nuclei and with the extracellular environment, as mediated by a
dynamic cytoskeleton. Individual cortex-core structures then provide a basis
upon which we build an extended version of the buckling without bending
morphogenesis (BWBM) model, with its proliferating cortex and constraining
core, to predict foliations/folds of the cortex in the presence of a
nonlinearity due to cortical cells actively regulating strain. In doing so, we
obtain asymmetric foliations/folds with respect to the trough (sulci) and the
crest (gyri). In addition to laying new groundwork for the design of more
familiar and less familiar brain structures, the hydrodynamic description for
cell nuclei during the initial stages of brain organoid development provides an
intriguing quantitative connection with large-scale structure formation in the
universe.
|
Dusty Quasars at High Redshifts | A population of quasars at z ~ 2 is determined based on dust luminosities
vLv(7.8 um) that includes unobscured, partially obscured, and obscured quasars.
Quasars are classified by the ratio vLv(0.25 um)/vLv(7.8 um) = UV/IR, assumed
to measure obscuration of UV luminosity by the dust which produces IR
luminosity. Quasar counts at rest frame 7.8 um are determined for quasars in
the Bootes field of the NOAO Deep Wide Field Survey using 24 um sources with
optical redshifts from the AGN and Galaxy Evolution Survey (AGES) or infrared
redshifts from the Spitzer Infrared Spectrograph. Spectral energy distributions
are extended to far infrared wavelengths using observations from the Herschel
Space Observatory Spectral and Photometric Imaging Receiver (SPIRE), and new
SPIRE photometry is presented for 77 high redshift quasars from the Sloan
Digital Sky Survey. It is found that unobscured and obscured quasars have
similar space densities at rest frame 7.8 um, but the ratio Lv(100 um)/Lv(7.8
um) is about three times higher for obscured quasars compared to unobscured, so
that far infrared or submm discoveries are dominated by obscured quasars.
Quasar source counts for these samples are determined for comparison to the
number of submm sources that have been discovered with the SCUBA-2 camera at z
~ 2 using the Lv(100 um)/Lv(7.8 um) results together with the Bootes 7.8 um
counts, and we find that only ~ 5% of high redshift submm sources are quasars,
including even the most obscured quasars. Illustrative source counts are
predicted to z = 10, and we show that existing SCUBA-2 850 um surveys or 2 mm
surveys with the Goddard-IRAM Superconducting 2 Millimeter Observer (GISMO)
survey camera should already have detected sources at z ~ 10 if quasar and
starburst luminosity functions remain the same from z = 2 until z = 10.
|
The SCUBA-2 Cosmology Legacy Survey: 850um maps, catalogues and number
counts | We present a catalogue of nearly 3,000 submillimetre sources detected at
850um over ~5 square degrees surveyed as part of the James Clerk Maxwell
Telescope (JCMT) SCUBA-2 Cosmology Legacy Survey (S2CLS). This is the largest
survey of its kind at 850um, probing a meaningful cosmic volume at the peak of
star formation activity and increasing the sample size of submillimetre
galaxies selected at 850um by an order of magnitude. We describe the wide 850um
survey component of S2CLS, which covers the key extragalactic survey fields:
UKIDSS-UDS, COSMOS, Akari-NEP, Extended Groth Strip, Lockman Hole North, SSA22
and GOODS-North. The average 1-sigma depth of S2CLS is 1.2 mJy/beam,
approaching the SCUBA-2 850um confusion limit, which we determine to be ~0.8
mJy/beam. We measure the single dish 850um number counts to unprecedented
accuracy, reducing the Poisson errors on the differential counts to
approximately 4% at S_850~3mJy. With several independent fields, we investigate
field-to-field variance, finding that the number counts on 0.5-1 degree scales
are generally within 50% of the S2CLS mean for S_850>3mJy, with scatter
consistent with the Poisson and estimated cosmic variance uncertainties,
although there is a marginal (2-sigma) density enhancement in the GOODS-North
field. The observed number counts are in reasonable agreement with recent
phenomenological and semi-analytic models. Finally, the large solid angle of
S2CLS allows us to measure the bright-end counts: at S_850>10mJy there are
approximately ten sources per square degree, and we detect the distinctive
up-turn in the number counts indicative of the detection of local sources of
850um emission and strongly lensed high-redshift galaxies. Here we describe the
data collection and reduction procedures and present calibrated maps and a
catalogue of sources; these are made publicly available.
|
Colors of Ellipticals from GALEX to Spitzer | Multi-color photometry is presented for a large sample of local ellipticals
selected by morphology and isolation. The sample uses data from GALEX, SDSS,
2MASS and Spitzer to cover the filters NUV, ugri, JHK and 3.6mum. Various
two-color diagrams, using the half-light aperture defined in the 2MASS J
filter, are very coherent from color to color, meaning that galaxies defined to
be red in one color are always red in other colors. Comparison to globular
cluster colors demonstrates that ellipticals are *not* composed of a single
age, single metallicity (e.g., [Fe/H]) stellar population, but require a
multi-metallicity model using a chemical enrichment scenario. Such a model is
sufficient to explain two-color diagrams and the color-magnitude relations for
all colors using only metallicity as a variable on a solely 12 Gyrs stellar
population with no evidence of stars younger than 10 Gyrs. The [Fe/H] values
that match galaxy colors range from -0.5 to +0.4, much higher (and older) than
population characteristics deduced from Lick/IDS line-strength system studies,
indicating an inconsistency between galaxy colors and line indices values for
reasons unknown. The NUV colors have unusual behavior signaling the rise and
fall of the UV upturn with elliptical luminosity. Models with BHB tracks can
reproduce this behavior indicating the UV upturn is strictly a metallicity
effect.
|
Search for Extra-Tidal RR Lyrae Stars in Milky Way Globular Clusters
From Gaia DR2 | We used extra-tidal RR Lyrae stars to study the dynamics of Galactic globular
clusters and know how effects like dynamical friction and tidal disruption
affect these clusters. The Gaia DR2 catalog for RR Lyrae stars (Clementini et
al. 2018) is used along with the proper motions and tidal radii data for the
globular clusters compiled from literature. A sample of 56 Galactic globular
clusters is analyzed. Out of these 56 Galactic globular clusters, only 11 have
extra-tidal RR Lyrae stars. However, only two clusters, namely, NGC 3201 and
NGC 5024, have enough extra-tidal RR Lyrae stars to draw interesting
conclusions. NGC 3201 has 13 extra-tidal RR Lyrae stars which are
asymmetrically distributed around its center with more number of stars in its
trailing zone than its leading part. We conclude that these asymmetrical tidal
tails are due to the combined effect of tidal disruption and the stripped
debris from the cluster. On the other hand, NGC 5024 has 5 extra-tidal RR Lyrae
stars, four of them are concentrated in a region which is at a distance of
about 3 times the tidal radius from its center. These may be the stars that are
being ripped apart from the cluster due to tidal disruption. The presence of
these extra-tidal RR Lyrae stars in the clusters can be an indication that more
cluster stars are present outside their tidal radii which may be revealed by
deep wide field CMDs of the clusters.
|
Inflation with Non-minimal Gravitational Couplings and Supergravity | We explore in the supergravity context the possibility that a Higgs scalar
may drive inflation via a non-minimal coupling to gravity characterised by a
large dimensionless coupling constant. We find that this scenario is not
compatible with the MSSM, but that adding a singlet field (NMSSM, or a variant
thereof) can very naturally give rise to slow-roll inflation. The inflaton is
necessarily contained in the doublet Higgs sector and occurs in the D-flat
direction of the two Higgs doublets.
|
3XMM J185246.6+003317: another low magnetic field magnetar | We study the outburst of the newly discovered X-ray transient 3XMM
J185246.6+003317, re-analysing all available XMM-Newton, observations of the
source to perform a phase-coherent timing analysis, and derive updated values
of the period and period derivative. We find the source rotating at
P=11.55871346(6) s (90% confidence level; at epoch MJD 54728.7) but no evidence
for a period derivative in the 7 months of outburst decay spanned by the
observations. This translates in a 3sigma upper limit for the period derivative
of Pdot<1.4x10^{-13} s/s, which, assuming the classical magneto-dipolar braking
model, gives a limit on the dipolar magnetic field of B_dip<4.1x10^{13} G . The
X-ray outburst and spectral characteristics of 3XMM J185246.6+003317 confirms
the identification as a magnetar, but the magnetic field upper limit we derive
defines it as the third "low-B" magnetar discovered in the past three years,
after SGR 0418+5729 and Swift J1822.3-1606. We have also obtained an upper
limit to the quiescent luminosity (< 4x10^{33} erg/s), in line with the
expectations for an old magnetar. The discovery of this new low field magnetar
reaffirms the prediction of about one outburst per year from the hidden
population of aged magnetars.
|
What to expect from dynamical modelling of galactic haloes | Many dynamical models of the Milky Way halo require assumptions that the
distribution function of a tracer population should be independent of time
(i.e., a steady state distribution function) and that the underlying potential
is spherical. We study the limitations of such modelling by applying a general
dynamical model with minimal assumptions to a large sample of galactic haloes
from cosmological $N$-body and hydrodynamical simulations. Using dark matter
particles as dynamical tracers, we find that the systematic uncertainties in
the measured mass and concentration parameters typically have an amplitude of
25% to 40%. When stars are used as tracers, however, the systematic
uncertainties can be as large as a factor of $2-3$. The systematic
uncertainties are not reduced by increasing the tracer sample size and vary
stochastically from halo to halo. These systematic uncertainties are mostly
driven by underestimated statistical noise caused by correlated phase-space
structures that violate the steady state assumption. The number of independent
phase-space structures inferred from the uncertainty level sets a limiting
sample size beyond which a further increase no longer significantly improves
the accuracy of dynamical inferences. The systematic uncertainty level is
determined by the halo merger history, the shape and environment of the halo.
Our conclusions apply generally to any spherical steady-state model.
|
Quantifying Non-parametric Structure of High-redshift Galaxies with Deep
Learning | At high redshift, due to both observational limitations and the variety of
galaxy morphologies in the early universe, measuring galaxy structure can be
challenging. Non-parametric measurements such as the CAS system have thus
become an important tool due to both their model-independent nature and their
utility as a straightforward computational process. Recently, convolutional
neural networks (CNNs) have been shown to be adept at image analysis, and are
beginning to supersede traditional measurements of visual morphology and
model-based structural parameters. In this work, we take a further step by
extending CNNs to measure well known non-parametric structural quantities:
concentration ($C$) and asymmetry ($A$). We train CNNs to predict $C$ and $A$
from individual images of $\sim 150,000$ galaxies at $0 < z < 7$ in the CANDELS
fields, using Bayesian hyperparameter optimisation to select suitable network
architectures. Our resulting networks accurately reproduce measurements
compared with standard algorithms. Furthermore, using simulated images, we show
that our networks are more stable than the standard algorithms at low
signal-to-noise. While both approaches suffer from similar systematic biases
with redshift, these remain small out to $z \sim 7$. Once trained, measurements
with our networks are $> 10^3$ times faster than previous methods. Our approach
is thus able to reproduce standard measures of non-parametric morphologies and
shows the potential of employing neural networks to provide superior results in
substantially less time. This will be vital for making best use of the large
and complex datasets provided by upcoming galaxy surveys, such as Euclid and
Rubin-LSST.
|
Considerations for the Observability of Kinematically Offset Binary AGN | The gravitational waves from Massive black-hole (MBH) binaries are expected
to be detected by pulsar timing arrays in the next few years. While they are a
promising source for multimessenger observations as binary AGN, few convincing
candidates have been identified in electromagnetic surveys. One approach to
identifying candidates has been through spectroscopic surveys searching for
offsets or time-dependent offsets of broad emission lines (BLs), which may be
characteristic of Doppler shifts from binary orbital motion. In this study, we
predict the parameter space of MBH binaries that should be kinematically
detectable. There is a delicate trade-off between requiring binary separations
to be large enough for BL regions to remain attached to one of the AGN, but
also small enough such that their orbital velocity is detectable. We find that
kinematic signatures are only observable for the lower-mass secondary AGN, for
binaries with total-masses above about $10^8 M_\odot$, and separations between
0.1 and 1 pc. We motivate our usage of a kinematic-offset sensitivity of $10^3$
km/s, and a sensitivity to changing offsets of $10^2$ km/s. With these
parameters, and an Eddington ratio of 0.1, we find that 0.5% of binaries have
detectable offsets, and only 0.03% have detectable velocity changes. Overall,
kinematic binary signatures should be expected in fewer than one in $10^4$ AGN.
Better characterizing the intrinsic variability of BLs is crucial to
understanding and vetting MBH binary candidates. This requires multi-epoch
spectroscopy of large populations of AGN over a variety of timescales.
|
ATOMS: ALMA Three-millimeter Observations of Massive Star-forming
regions-IX. A pilot study towards IRDC G034.43+00.24 on multi-scale
structures and gas kinematics | We present a comprehensive study of the gas kinematics associated with
density structures at different spatial scales in the filamentary infrared dark
cloud, G034.43+00.24 (G34). This study makes use of the H13CO+ (1-0) molecular
line data from the ALMA Three-millimeter Observations of Massive Star-forming
regions (ATOMS) survey, which has spatial and velocity resolution of 0.04 pc
and 0.2 km/s, respectively. Several tens of dendrogram structures have been
extracted in the position-position-velocity space of H13CO+, which include 21
small-scale leaves and 20 larger-scale branches. Overall, their gas motions are
supersonic but they exhibit the interesting behavior where leaves tend to be
less dynamically supersonic than the branches. For the larger-scale, branch
structures, the observed velocity-size relation (i.e., velocity
variation/dispersion versus size) are seen to follow the Larson scaling
exponent while the smaller-scale, leaf structures show a systematic deviation
and display a steeper slope. We argue that the origin of the observed
kinematics of the branch structures is likely to be a combination of turbulence
and gravity-driven ordered gas flows. In comparison, gravity-driven chaotic gas
motion is likely at the level of small-scale leaf structures. The results
presented in our previous paper and this current follow-up study suggest that
the main driving mechanism for mass accretion/inflow observed in G34 varies at
different spatial scales. We therefore conclude that a scale-dependent combined
effect of turbulence and gravity is essential to explain the star-formation
processes in G34.
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On the physical mechanisms governing the cloud lifecycle in the Central
Molecular Zone of the Milky Way | We apply an analytic theory for environmentally-dependent molecular cloud
lifetimes to the Central Molecular Zone of the Milky Way. Within this theory,
the cloud lifetime in the Galactic centre is obtained by combining the
time-scales for gravitational instability, galactic shear, epicyclic
perturbations and cloud-cloud collisions. We find that at galactocentric radii
$\sim 45$-$120$ pc, corresponding to the location of the '100-pc stream', cloud
evolution is primarily dominated by gravitational collapse, with median cloud
lifetimes between 1.4 and 3.9 Myr. At all other galactocentric radii, galactic
shear dominates the cloud lifecycle, and we predict that molecular clouds are
dispersed on time-scales between 3 and 9 Myr, without a significant degree of
star formation. Along the outer edge of the 100-pc stream, between radii of 100
and 120 pc, the time-scales for epicyclic perturbations and gravitational
free-fall are similar. This similarity of time-scales lends support to the
hypothesis that, depending on the orbital geometry and timing of the orbital
phase, cloud collapse and star formation in the 100-pc stream may be triggered
by a tidal compression at pericentre. Based on the derived time-scales, this
should happen in approximately 20 per cent of all accretion events onto the
100-pc stream.
|
The Planetary Nebula Luminosity Function at the Dawn of Gaia | The [O III] 5007 Planetary Nebula Luminosity Function (PNLF) is an excellent
extragalactic standard candle. In theory, the PNLF method should not work at
all, since the luminosities of the brightest planetary nebulae (PNe) should be
highly sensitive to the age of their host stellar population. Yet the method
appears robust, as it consistently produces < 10% distances to galaxies of all
Hubble types, from the earliest ellipticals to the latest-type spirals and
irregulars. It is therefore uniquely suited for cross-checking the results of
other techniques and finding small offsets between the Population I and
Population II distance ladders. We review the calibration of the method and
show that the zero points provided by Cepheids and the Tip of the Red Giant
Branch are in excellent agreement. We then compare the results of the PNLF with
those from Surface Brightness Fluctuation measurements, and show that, although
both techniques agree in a relative sense, the latter method yields distances
that are ~15% larger than those from the PNLF. We trace this discrepancy back
to the calibration galaxies and argue that, due to a small systematic error
associated with internal reddening, the true distance scale likely falls
between the extremes of the two methods. We also demonstrate how PNLF
measurements in the early-type galaxies that have hosted Type Ia supernovae can
help calibrate the SN Ia maximum magnitude-rate of decline relation. Finally,
we discuss how the results from space missions such as Kepler and Gaia can help
our understanding of the PNLF phenomenon and improve our knowledge of the
physics of local planetary nebulae.
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