Core-Collapse Supernovae from 9 to 120 Solar Masses Based on Neutrino-powered Explosions

Abstract: Nucleosynthesis, light curves, explosion energies, and remnant masses are calculated for a grid of supernovae resulting from massive stars with solar metallicity and masses from 9.0 to 120 solar masses. The full evolution is followed using an adaptive reaction network of up to 2000 nuclei. A novel aspect of the survey is the use of a one-dimensional neutrino transport model for the explosion. This explosion model has been calibrated to give the observed energy for SN 1987A, using several standard progenitors, and for the Crab supernova using a 9.6 solar mass progenitor. As a result of using a calibrated central engine, the final kinetic energy of the supernova is variable and sensitive to the structure of the presupernova star. Many progenitors with extended core structures do not explode, but become black holes, and the masses of exploding stars do not form a simply connected set. The resulting nucleosynthesis agrees reasonably well with the sun provided that a reasonable contribution from Type Ia supernovae is also allowed, but with a deficiency of light s-process isotopes. The resulting neutron star IMF has a mean gravitational mass near 1.4 solar masses. The average black hole mass is about 9 solar masses if only the helium core implodes, and 14 solar masses if the entire presupernova star collapses. Only 10 over 20 solar masses and some of these are Type Ib or Ic. Some useful systematics of Type IIp light curves are explored.

explosion energy
black hole
core collapse


Phase-space Analysis in the Group and Cluster environment: Time since Infall and Tidal Mass Loss

Abstract: Using the latest cosmological hydrodynamic N-body simulations of groups and clusters, we study how location in phase-space coordinates at z=0 can provide information on environmental effects acting in clusters. We confirm the results of previous authors showing that galaxies tend to follow a typical path in phase-space as they settle into the cluster potential. As such, different regions of phase-space can be associated with different times since first infalling into the cluster. However, in addition, we see a clear trend between total mass loss due to cluster tides, and time since infall. Thus we find location in phase-space provides information on both infall time, and tidal mass loss. We find the predictive power of phase-space diagrams remains even when projected quantities are used (i.e. line-of-sight velocities, and projected distances from the cluster). We provide figures that can be directly compared with observed samples of cluster galaxies and we also provide the data used to make them as supplementary data, in order to encourage the use of phase-space diagrams as a tool to understand cluster environmental effects. We find that our results depend very weakly on galaxy mass or host mass, so the predictions in our phase-space diagrams can be applied to groups or clusters alike, or to galaxy populations from dwarfs up to giants.

group
tidal mass loss
phase-space diagram


Using the Noether symmetry approach to probe the nature of dark energy

Abstract: We propose to use a model-independent criterion based on first integrals of motion, due to Noether symmetries of the equations of motion, in order to classify the dark energy models in the context of scalar field (quintessence or phantom) FLRW cosmologies. In general, the Noether symmetries play an important role in physics because they can be used to simplify a given system of differential equations as well as to determine the integrability of the system. The Noether symmetries are computed for nine distinct accelerating cosmological scenarios that contain a homogeneous scalar field associated with different types of potentials. We verify that all the scalar field potentials, presented here, admit the trivial first integral namely energy conservation, as they should. We also find that the exponential potential inspired from scalar field cosmology, as well as some types of hyperbolic potentials, include extra Noether symmetries. This feature suggests that these potentials should be preferred along the hierarchy of scalar field potentials. Finally, using the latter potentials, in the framework of either quintessence or phantom scalar field cosmologies that contain also a non-relativistic matter(dark matter) component, we find that the main cosmological functions, such as the scale factor of the universe, the scalar field, the Hubble expansion rate and the metric of the FRLW space-time, are computed analytically. Interestingly, under specific circumstances the predictions of the exponential and hyperbolic scalar field models are equivalent to those of the ΛCDM model, as far as the global dynamics and the evolution of the scalar field are concerned. The present analysis suggests that our technique appears to be very competitive to other independent tests used to probe the functional form of a given potential and thus the associated nature of dark energy.

noether symmetry approach
dark energy
cosmological scenario


First all-sky search for continuous gravitational-wave signals from unknown neutron stars in binary systems using Advanced LIGO data

Abstract: Rotating neutron stars can emit continuous gravitational waves, which have not yet been detected. We present a search for continuous gravitational waves from unknown neutron stars in binary systems with orbital period between 15 and 45 days. This is the first time that Advanced LIGO data and the recently developed BinarySkyHough pipeline have been used in a search of this kind. No detections are reported, and upper limits on the gravitational wave amplitude are calculated, which improve the previous results by a factor of 17.

all-sky search
neutron star
gravitational wave


Tests of General Relativity in the Strong Gravity Regime Based on X-Ray Spectropolarimetric Observations of Black Holes in X-Ray Binaries

Abstract: Although General Relativity (GR) has been tested extensively in the weak gravity regime, similar tests in the strong gravity regime are still missing. In this paper we explore the possibility to use X-ray spectropolarimetric observations of black holes in X-ray binaries to distinguish between the Kerr metric and the phenomenological metrics introduced by Johannsen and Psaltis (2011) (which are not vacuum solutions of Einstein's equation) and thus to test the no-hair theorem of GR. To this end, we have developed a numerical code that calculates the radial brightness profiles of accretion disks and parallel transports the wave vector and polarization vector of photons through the Kerr and non-GR spacetimes. We used the code to predict the observational appearance of GR and non-GR accreting black hole systems. We find that the predicted energy spectra and energy dependent polarization degree and polarization direction do depend strongly on the underlying spacetime. However, for large regions of the parameter space, the GR and non-GR metrics lead to very similar observational signatures, making it difficult to observationally distinguish between the two types of models.

general relativity
black hole
x-ray binary


Signatures of X-rays in the early Universe

Abstract: [abridged] With their long mean free paths and efficient heating of the intergalactic medium (IGM), X-rays could have a dramatic impact on the thermal and ionization history of the Universe. We explore this in various signals: (i) Reionization history: including X-rays results in an earlier, more extended reionization. Efficient thermal feedback from X-ray heating could yield an extended, 10 contribution of X-rays to reionization results in a more uniform morphology, though the impact is modest when compared at the same global neutral fraction, xH. However, changes in morphology cannot be countered by increasing the bias of the ionizing sources, making them a robust signature. (iii) The kinetic Sunyaev-Zel'dovich (kSZ) effect: at a fixed reionization history, X-rays decrease the kSZ power at l=3000 by 0.5 microK^2. Our extreme model in which X-rays dominate reionization is the only one that is marginally consistent with upper limits from the South Pole Telescope, assuming no thermal Sunyaev-Zel'dovich (tSZ) - dusty galaxy correlation. Since this extreme model is unlikely, we conclude that there should be a sizable tSZ-dusty galaxy signal. (iv) The cosmic 21cm signal: the impact of X-rays on the 21cm power spectrum during the advanced stages of reionization (xH<0.7) is modest, except in extreme, X-ray dominated models. The largest impact of X-rays is to govern IGM heating. In fact, unless thermal feedback is efficient, the epoch of X-ray heating likely overlaps with the beginning of reionization (xH>0.9). This results in a 21cm power spectrum which is 10-100 times higher than obtained from naive estimates ignoring this overlap. However, if thermal feedback is efficient, the resulting extended epoch between X-ray heating and reionization could provide a clean probe of the matter power spectrum in emission.


Machine Learning meets the redshift evolution of the CMB Temperature

Abstract: We present a model independent and non-parametric reconstruction with a Machine Learning algorithm of the redshift evolution of the Cosmic Microwave Background (CMB) temperature from a wide redshift range z∈[0,3] without assuming any dark energy model, an adiabatic universe or photon number conservation. In particular we use the genetic algorithms which avoid the dependency on an initial prior or a cosmological fiducial model. Through our reconstruction we constrain new physics at late times. We provide novel and updated estimates on the β parameter from the parametrisation T(z)=T_0(1+z)^1-β, the duality relation η(z) and the cosmic opacity parameter τ(z). Furthermore we place constraints on a temporal varying fine structure constant α, which would have signatures in a broad spectrum of physical phenomena such as the CMB anisotropies. Overall we find no evidence of deviations within the 1σ region from the well established ΛCDM model, thus confirming its predictive potential.

redshift evolution
new physics
machine learning


Fab 5: Noncanonical Kinetic Gravity, Self Tuning, and Cosmic Acceleration

Abstract: We investigate circumstances under which one can generalize Horndeski's most general scalar-tensor theory of gravity. Specifically we demonstrate that a nonlinear combination of purely kinetic gravity terms can give rise to an accelerating universe without the addition of extra propagating degrees of freedom on cosmological backgrounds, and exhibit self tuning to bring a large cosmological constant under control. This nonlinear approach leads to new properties that may be instructive for exploring the behaviors of gravity.

nonlinear combination
kinetic gravity term
universe
fab


Storing magnetic fields in pre-collapse cores of massive stars

Abstract: We argue that the radiative zone above the iron core in pre-collapse cores of massive stars can store strong magnetic fields. To reach this conclusion we use the stellar evolutionary code MESA to simulate the evolution of two stellar models with initial masses of 15Mo and 25Mo, and reveal the entropy profile above the iron core just before core collapse. Just above the iron core there is a thin zone with convective shells. We assume that a dynamo in these convective shells amplifies magnetic fields and forms magnetic flux loops. By considering the buoyancy of magnetic flux loops we show that the steep entropy rise in the radiative zone above the dynamo can prevent buoyancy of flux loops with magnetic fields below about 10^13G. When this radiative zone collapses on to the newly born neutron star the converging inflow further amplifies the magnetic fields by a factor of about a hundred. After passing through the stalled shock at about a hundred kilometres from the center, these strong magnetic fields together with instabilities can facilitate the launching of jets that explode the star in the frame of the jittering jets explosion mechanism. Our study further supports the claim for the necessity to include magnetic fields in simulating the explosion of CCSNe.

magnetic field
pre-collapse core
massive star
iron core


Dissipation of dark matter

Abstract: Fluids often display dissipative properties. We explore dissipation in the form of bulk viscosity in the cold dark matter fluid. We constrain this model using current data from supernovae, baryon acoustic oscillations and the cosmic microwave background. Considering the isotropic and homogeneous background only, viscous dark matter is allowed to have a bulk viscosity ≲ 10^7 Pa·s, also consistent with the expected integrated Sachs-Wolfe effect (which plagues some models with bulk viscosity). We further investigate the small-scale formation of viscous dark matter halos, which turns out to place significantly stronger constraints on the dark matter viscosity. The existence of dwarf galaxies is guaranteed only for much smaller values of the dark matter viscosity, ≲ 10^-3 Pa·s.


Chemical abundances along the 1G sequence of the chromosome maps: The Globular Cluster NGC 3201

Abstract: The Hubble Space Telescope (HST) UV Legacy Survey of Galactic Globular Clusters (GCs) has investigated multiple stellar populations by means of the "chromosome map" (ChM) diagnostic tool that maximises the separation between stars with different chemical composition. One of the most challenging features revealed by ChMs analysis is the apparent inhomogeneity among stars belonging to the first population, a phenomenon largely attributed to He variations. However, this explanation is not supported by the uniformity in p-capture elements of these stars. The HST survey has revealed that the GC NGC 3201 shows an exceptionally wide coverage in the Delta(F275W,F814W) parameter of the ChM. We present a chemical abundance analysis of 24 elements in 18 giants belonging to the first population of this GC, and having a wide range in Delta(F275W,F814W). As far as the p-capture elements are concerned, the chemical abundances are typical of 1G stars, as expected from the location of our targets in the ChM. Based on radial velocities and chemical abundances arguments, we find that the three stars with the lowest Delta(F275W,F814W) values are binary candidates. This suggests that, at least those stars could be explained with binarity. These results are consistent with evidence inferred from multi-band photometry that evolved blue stragglers populate the bluest part of the 1G sequence in the ChM. The remaining 15 spectroscopic targets show a small range in the overall metallicity by 0.10 dex, with stars at higher Delta(F275W,F814W) values having higher absolute abundances. We suggest that a small variation in metals and binarity govern the color spread of the 1G in the ChM, and that evolved blue stragglers contribute to the bluest tail of the 1G sequence.

chromosome map
metallicity
chemical abundance


Revisiting Cosmic No-Hair Theorem for Inflationary Settings

Abstract: In this work we revisit Wald's cosmic no-hair theorem in the context of accelerating Bianchi cosmologies for a generic cosmic fluid with non-vanishing anisotropic stress tensor and when the fluid energy momentum tensor is of the form of a cosmological constant term plus a piece which does not respect strong or dominant energy conditions. Such a fluid is the one appearing in inflationary models. We show that for such a system anisotropy may grow, in contrast to the cosmic no-hair conjecture. In particular, for a generic inflationary model we show that there is an upper bound on the growth of anisotropy. For slow-roll inflationary models our analysis can be refined further and the upper bound is found to be of the order of slow-roll parameters. We examine our general discussions and our extension of Wald's theorem for three classes of slow-roll inflationary models, generic multi-scalar field driven models, anisotropic models involving U(1) gauge fields and the gauge-flation scenario.

cosmic no-hair theorem
inflationary setting
gauge field


Scaling regimes in spherical shell rotating convection

Abstract: Rayleigh-Bénard convection in rotating spherical shells can be considered as a simplified analogue of many astrophysical and geophysical fluid flows. Here, we use three-dimensional direct numerical simulations to study this physical process. We construct a dataset of more than 200 numerical models that cover a broad parameter range with Ekman numbers spanning 3× 10^-7≤ E ≤ 10^-1, Rayleigh numbers within the range 10^3 < Ra < 2× 10^10 and a Prandtl number unity. We investigate the scaling behaviours of both local (length scales, boundary layers) and global (Nusselt and Reynolds numbers) properties across various physical regimes from onset of rotating convection to weakly-rotating convection. Close to critical, the convective flow is dominated by a triple force balance between viscosity, Coriolis force and buoyancy. For larger supercriticalities, a subset of our numerical data approaches the asymptotic diffusivity-free scaling of rotating convection Nu∼ Ra^3/2E^2 in a narrow fraction of the parameter space delimited by 6 Ra_c ≤ Ra ≤ 0.4 E^-8/5. Using a decomposition of the viscous dissipation rate into bulk and boundary layer contributions, we establish a theoretical scaling of the flow velocity that accurately describes the numerical data. In rapidly-rotating turbulent convection, the fluid bulk is controlled by a triple force balance between Coriolis, inertia and buoyancy, while the remaining fraction of the dissipation can be attributed to the viscous friction in the Ekman layers. Beyond Ra ≃ E^-8/5, the rotational constraint on the convective flow is gradually lost and the flow properties vary to match the regime changes between rotation-dominated and non-rotating convection. The quantity Ra E^12/7 provides an accurate transition parameter to separate rotating and non-rotating convection.

spherical shell
convection
numerical model


A carefully characterised and tracked Trans-Neptunian survey, the size-distribution of the Plutinos and the number of Neptunian Trojans

Abstract: The Trans-Neptunian Objects (TNOs) may preserve evidence of planet building in their orbital and size-distributions. While all populations show steep size-distributions for large objects, recently relative deficit of Neptunian Trojans and scattering objects with diameters D<100 km were detected. We have investigated this deficit with a 32 square degree survey, detecting 77 TNOs to a limiting r-band magnitude of 24.6. Our Plutinos sample (18 objects in 3:2 mean motion resonance with Neptune) also shows a deficit of D<100 km objects. We reject a single power-law size-distribution and find that the Plutinos favour a divot. The Plutinos are thus added the list of populations with a deficit of D<100 km objects. The fact that three independent samples of three different populations show this trend suggests that it is a real feature, possibly shared by all hot TNO populations as a remnant of "born big" planetesimal formation processes. We surmise the existence of 9000±3000 Plutinos with H_r≤8.66 and 37000^+12000_-10000 Plutinos with H_r≤10.0. Our survey also discovered one temporary Uranian Trojan, one temporary Neptunian Trojans and one stable Neptunian Trojan, from which we derive populations of 110^+500_-100, 210^+900_-200 and 150^+600_-140 , respectively, with H_r≤10.0. The Neptunian Trojans are thus less numerous than the main belt asteroids, which has over 700 asteroids with H_r≤10.0. With such numbers, the temporary Neptunian Trojans cannot be previously stable Trojans that happen to be escaping the resonance now; they must be captured from another reservoir. With three 3:1 and one 4:1 resonators, we add to the growing evidence that the high-order resonances are more populated than expected.

size-distribution
neptunian trojans
neptune


Photon-photon dispersion of TeV gamma rays and its role for photon-ALP conversion

Abstract: The propagation of TeV gamma rays can be strongly modified by B-field induced conversion to axionlike particles (ALPs). We show that, at such high energies, photon dispersion is dominated by background photons - the only example where photon-photon dispersion is of practical relevance. We determine the refractive index for all energies and find that, for fixed energy density, background photons below the pair-production threshold dominate. The cosmic microwave background alone provides an "effective photon mass" of (m_gamma)^2 = -(1.01 neV * E/TeV)^2 for E < 1000 TeV. The extragalactic background light is subdominant, but local radiation fields in the galaxy or the source regions provide significant contributions. Photon-photon dispersion is small enough to leave typical scenarios of photon-ALP oscillations unscathed, but big enough to worry about it case by case.

tev gamma ray
background photon
photon-photon dispersion


The Kepler Pixel Response Function

Abstract: Kepler seeks to detect sequences of transits of Earth-size exoplanets orbiting Solar-like stars. Such transit signals are on the order of 100 ppm. The high photometric precision demanded by Kepler requires detailed knowledge of how the Kepler pixels respond to starlight during a nominal observation. This information is provided by the Kepler pixel response function (PRF), defined as the composite of Kepler's optical point spread function, integrated spacecraft pointing jitter during a nominal cadence and other systematic effects. To provide sub-pixel resolution, the PRF is represented as a piecewise-continuous polynomial on a sub-pixel mesh. This continuous representation allows the prediction of a star's flux value on any pixel given the star's pixel position. The advantages and difficulties of this polynomial representation are discussed, including characterization of spatial variation in the PRF and the smoothing of discontinuities between sub-pixel polynomial patches. On-orbit super-resolution measurements of the PRF across the Kepler field of view are described. Two uses of the PRF are presented: the selection of pixels for each star that maximizes the photometric signal to noise ratio for that star, and PRF-fitted centroids which provide robust and accurate stellar positions on the CCD, primarily used for attitude and plate scale tracking. Good knowledge of the PRF has been a critical component for the successful collection of high-precision photometry by Kepler.

response function
point spread function
jitter
kepler photometry
optical effect


Aharonov-Bohm Radiation

Abstract: A solenoid oscillating in vacuum will pair produce charged particles due to the Aharonov-Bohm (AB) interaction. We calculate the radiation pattern and power emitted for charged scalar particles. We extend the solenoid analysis to cosmic strings, and find enhanced radiation from cusps and kinks on loops. We argue by analogy with the electromagnetic AB interaction that cosmic strings should emit photons due to the gravitational AB interaction of fields in the conical spacetime of a cosmic string. We calculate the emission from a kink and find that it is of similar order as emission from a cusp, but kinks are vastly more numerous than cusps and may provide a more interesting observational signature.

vacuum
particle
cosmic string
aharonov-bohm radiation


Speeding up the universe using dust with pressure

Abstract: We revise the cosmological standard model presuming that matter, i.e. baryons and cold dark matter, exhibits a non-vanishing pressure mimicking the cosmological constant effects. In particular, we propose a scalar field Lagrangian ℒ_1 for matter with the introduction of a Lagrange multiplier as constraint. We also add a symmetry breaking effective potential accounting for the classical cosmological constant problem, by adding a second Lagrangian ℒ_2. Investigating the Noether current due to the shift symmetry on the scalar field, φ→φ+c^0, we show that ℒ_1 turns out to be independent from the scalar field φ. Further we find that a positive Helmotz free-energy naturally leads to a negative pressure without introducing by hand any dark energy term. To face out the fine-tuning problem, we investigate two phases: before and after transition due to the symmetry breaking. We propose that during transition dark matter cancels out the quantum field vacuum energy effects. This process leads to a negative and constant pressure whose magnitude is determined by baryons only. The numerical bounds over the pressure and matter densities are in agreement with current observations, alleviating the coincidence problem. Finally assuming a thermal equilibrium between the bath and our effective fluid, we estimate the mass of the dark matter candidate. Our numerical outcomes seem to be compatible with recent predictions on WIMP masses, for fixed spin and temperature. In particular, we predict possible candidates whose masses span in the range 0.5-1.7 TeV.

universe
dust
cosmological constant problem


Future Cosmological Constraints from Fast Radio Bursts

Abstract: We consider the possible observation of Fast Radio Bursts (FRBs) with planned future radio telescopes, and investigate how well the dispersions and redshifts of these signals might constrain cosmological parameters. We construct mock catalogues of FRB dispersion measure (DM) data and employ Markov Chain Monte Carlo (MCMC) analysis, with which we forecast and compare with existing constraints in the flat ΛCDM model, as well as some popular extensions that include dark energy equation of state and curvature parameters. We find that the scatter in DM observations caused by inhomogeneities in the intergalactic medium (IGM) poses a big challenge to the utility of FRBs as a cosmic probe. Only in the most optimistic case, with a high number of events and low IGM variance, do FRBs aid in improving current constraints. In particular, when FRBs are combined with CMB+BAO+SNe+H_0 data, we find the biggest improvement comes in the Ω_bh^2 constraint. Also, we find that the dark energy equation of state is poorly constrained, while the constraint on the curvature parameter Ω_k, shows some improvement when combined with current constraints. When FRBs are combined with future BAO data from 21cm Intensity Mapping (IM), we find little improvement over the constraints from BAOs alone. However, the inclusion of FRBs introduces an additional parameter constraint, Ω_bh^2, which turns out to be comparable to existing constraints. This suggest that FRBs provide valuable information about the cosmological baryon density in the intermediate redshift Universe, independent of high redshift CMB data.

cosmology
fast radio bursts
redshift
intergalactic medium


Study of the properties of Cosmic rays and solar X-Ray Flares by balloon borne experiments

Abstract: Indian Centre for Space Physics is engaged in pioneering balloon borne experiments with typical payloads less than 3.5kg. Low cost rubber balloons are used to fly them to a height of about 40km. In a double balloon system, the booster balloon lifts the orbiter balloon to its cruising altitude where data is taken for a longer period of time. In this Paper, we present our first scientific report on the variation of Cosmic Rays and muons with altitude and detection of several solar flares in X-rays between 20keV and 100keV. We found the altitude of the Pfotzer maximum at Tropic of Cancer for cosmic rays and muons and catch several solar flares in hard X-rays. We find that the hard X-ray (> 40keV) sky becomes very transparent above Pfotzer maximum. We find the flare spectrum to have a power-law distribution. From these studies, we infer that valuable scientific research could be carried out in near space using low cost balloon borne experiments. Published in Online version of Indian Journal of Physics.

cosmic ray
balloon borne experiment
space physics


SPH simulations of the induced gravitational collapse scenario of long gamma-ray bursts associated with supernovae

Abstract: We present the first three-dimensional (3D) smoothed-particle-hydrodynamics (SPH) simulations of the induced gravitational collapse (IGC) scenario of long-duration gamma-ray bursts (GRBs) associated with supernovae (SNe). We simulate the SN explosion of a carbon-oxygen core (CO_ core) forming a binary system with a neutron star (NS) companion. We follow the evolution of the SN ejecta, including their morphological structure, subjected to the gravitational field of both the new NS (νNS) formed at the center of the SN, and the one of the NS companion. We compute the accretion rate of the SN ejecta onto the NS companion as well as onto the νNS from SN matter fallback. We determine the fate of the binary system for a wide parameter space including different CO_ core and NS companion masses, orbital periods and SN explosion geometry and energies. We identify, for selected NS nuclear equations-of-state, the binary parameters leading the NS companion, by hypercritical accretion, either to the mass-shedding limit, or to the secular axisymmetric instability for gravitational collapse to a black hole (BH), or to a more massive, fast rotating, stable NS. We also assess whether the binary remains or not gravitationally bound after the SN explosion, hence exploring the space of binary and SN explosion parameters leading to νNS-NS and νNS-BH binaries. The consequences of our results for the modeling of long GRBs, i.e. X-ray flashes and binary-driven hypernovae, are discussed.

gamma-ray burst
supernovae
hypercritical accretion


Wavelet-Bayesian inference of cosmic strings embedded in the cosmic microwave background

Abstract: Cosmic strings are a well-motivated extension to the standard cosmological model and could induce a subdominant component in the anisotropies of the cosmic microwave background (CMB), in addition to the standard inflationary component. The detection of strings, while observationally challenging, would provide a direct probe of physics at very high energy scales. We develop a new framework for cosmic string inference, constructing a Bayesian analysis in wavelet space where the string-induced CMB component has distinct statistical properties to the standard inflationary component. Our wavelet-Bayesian framework provides a principled approach to compute the posterior distribution of the string tension Gμ and the Bayesian evidence ratio comparing the string model to the standard inflationary model. Furthermore, we present a technique to recover an estimate of any string-induced CMB map embedded in observational data. Using Planck-like simulations we demonstrate the application of our framework and evaluate its performance. The method is sensitive to Gμ∼ 5 × 10^-7 for Nambu-Goto string simulations that include an integrated Sachs-Wolfe (ISW) contribution only and do not include any recombination effects, before any parameters of the analysis are optimised. The sensitivity of the method compares favourably with other techniques applied to the same simulations.

string
cosmic microwave background
wavelet transform


Continuum surveys with LOFAR and synergy with future large surveys in the 1-2 GHz band

Abstract: Radio astronomy is entering the era of large surveys. This paper describes the plans for wide surveys with the LOw Frequency ARray (LOFAR) and their synergy with large surveys at higher frequencies (in particular in the 1-2 GHz band) that will be possible using future facilities like Apertif or ASKAP. The LOFAR Survey Key Science Project aims at conducting large-sky surveys at 15, 30, 60, 120 and 200 MHz taking advantage of the wide instantaneous field of view and of the unprecedented sensitivity of this instrument. Four topics have been identified as drivers for these surveys covering the formation of massive galaxies, clusters and black holes using z>6 radio galaxies as probes, the study of the intercluster magnetic fields using diffuse radio emission and Faraday rotation measures in galaxy clusters as probes and the study of star formation processes in the early Universe using starburst galaxies as probes. The fourth topic is the exploration of new parameter space for serendipitous discovery taking advantage of the new observational spectral window open up by LOFAR. Here, we briefly discuss the requirements of the proposed surveys to address these (and many others!) topics as well as the synergy with other wide area surveys planned at higher frequencies (and in particular in the 1-2 GHz band) with new radio facilities like ASKAP and Apertif. The complementary information provided by these surveys will be crucial for detailed studies of the spectral shape of a variety of radio sources (down to sub-mJy sources) and for studies of the ISM (in particular HI and OH) in nearby galaxies.

large survey
ghz band
low frequency array


The spectra of jet bases in FR I radio galaxies: implications for particle acceleration

Abstract: We present accurate, spatially resolved imaging of radio spectra at the bases of jets in eleven low-luminosity (Fanaroff-Riley I) radio galaxies, derived from Very Large Array (VLA) observations. We pay careful attention to calibration and to the effects of random and systematic errors, and we base the flux-density scale on recent measurements of VLA primary amplitude calibrators by Perley Butler (2013). We show images and profiles of spectral index over the frequency range 1.4 - 8.5 GHz, together with values integrated over fiducial regions defined by our relativistic models of the jets. We find that the spectral index decreases (the spectrum flattens) with distance from the nucleus in all of the jets. The mean spectral indices are 0.66 +/- 0.01 where the jets first brighten abruptly and 0.59 +/- 0.01 after they recollimate. The mean change in spectral index between these locations, which is independent of calibration and flux-density scale errors and is therefore more accurately and robustly measured, is -0.067 +/- 0.006. Our jet models associate the decrease in spectral index with a bulk deceleration of the flow from 0.8c to <0.5c. We suggest that the decrease is the result of a change in the characteristics of ongoing particle acceleration. One possible acceleration mechanism is the first-order Fermi process in mildly relativistic shocks: in the Bohm limit, the index of the electron energy spectrum, p, is slightly larger than 2 and decreases with velocity upstream of the shock. This possibility is consistent with our measurements, but requires shocks throughout the jet volume rather than at a few discrete locations. A second possibility is that two acceleration mechanisms operate in these jets: one (with p = 2.32) dominant close to the galactic nucleus and associated with high flow speeds, another (with p = 2.18) taking over at larger distances and slower flow speeds.


Automatic Classification of Variable Stars in Catalogs with missing data

Abstract: We present an automatic classification method for astronomical catalogs with missing data. We use Bayesian networks, a probabilistic graphical model, that allows us to perform inference to pre- dict missing values given observed data and dependency relationships between variables. To learn a Bayesian network from incomplete data, we use an iterative algorithm that utilises sampling methods and expectation maximization to estimate the distributions and probabilistic dependencies of variables from data with missing values. To test our model we use three catalogs with missing data (SAGE, 2MASS and UBVI) and one complete catalog (MACHO). We examine how classification accuracy changes when information from missing data catalogs is included, how our method compares to traditional missing data approaches and at what computational cost. Integrating these catalogs with missing data we find that classification of variable objects improves by few percent and by 15 keeping the computational cost the same.

missing data
variable object
automatic classification


ORIGAMI: Delineating Cosmic Structures with Phase-Space Folds

Abstract: Structures like galaxies and filaments of galaxies in the Universe come about from the origami-like folding of an initially flat three-dimensional manifold in 6D phase space. The ORIGAMI method identifies these structures in a cosmological simulation, delineating the structures according to their outer folds. Structure identification is a crucial step in comparing cosmological simulations to observed maps of the Universe. The ORIGAMI definition is objective, dynamical and geometric: filament, wall and void particles are classified according to the number of orthogonal axes along which dark-matter streams have crossed. Here, we briefly review these ideas, and speculate on how ORIGAMI might be useful to find cosmic voids.


Einstein gravity of a diffusing fluid

Abstract: We discuss Einstein gravity for a fluid consisting of particles interacting with an unidentified environment of some other particles whose dissipative effect is approximated by a diffusion. The environment is described by a time dependent cosmological term which is compensating the lack of the conservation law of the energy momentum of the diffusing fluid. We are interested in a homogeneous flat expanding Universe described by a scale factor a. For a fluid of massless particles at finite temperature we obtain explicit solutions of the diffusion equation which are in the form of a modified Juttner distribution with a time dependent temperature. At later time Universe evolution is described as a diffusion at zero temperature with no equilibration. We find solutions of the diffusion at zero temperature which can be treated as a continuation to a later time of the finite temperature solutions describing an early stage of the Universe. A conservation of the total energy momentum determines the cosmological term up to a constant. The resulting energy momentum inserted into Einstein equations gives a modified Friedmann equation. Solutions of the Friedmann equation depend on the initial value of the cosmological term. The large value of the cosmological constant implies an exponential expansion. If the initial conditions allow a power-like solution for a large time then it must be of the form a≃τ (no deceleration, τ is the cosmic time). The final stage of the Universe evolution is described by a non-relativistic diffusion of a cold dust.

fluid
cosmological term
einstein gravity


FRB event rate counts II — fluence, redshift and dispersion measure distributions

Abstract: We examine how the various observable statistical properties of the FRB population relate back to their fundamental physical properties in a model independent manner. We analyse the flux density and fluence distributions of Fast Radio Bursts (FRBs) as a tool to investigate their luminosity distance distribution and the evolution of their prevalence throughout cosmic history. We examine in detail particular scenarios in which the burst population follows some power of the cosmic star formation rate. FRBs present an important additional measurable over source counts of existing cosmological populations, namely the dispersion measure. Based on the known redshift of FRB121102 (the repeater) we expect at least 50 to the inter-galactic medium and hence it can be used as a proxy for distance. We develop the framework to interpret the dispersion measure distribution, and investigate how the effect of Helium reionization in the intergalactic medium is evident in this distribution. Examination of existing data suggests that the FRB luminosity function is flatter than a critical slope, making FRBs easily detectable to large distances; in this regime the reduction in flux density with distance is outweighed by the increase in the number of bright bursts within the search volume.

redshift
dispersion measure distribution
burst


Studying galaxy cluster morphological metrics with Mock-X

Abstract: Dynamically relaxed galaxy clusters have long played a role in galaxy cluster studies because it is thought their properties can be reconstructed more precisely and with less systematics. As relaxed clusters are desirable, there exist a plethora of criteria for classifying a galaxy cluster as relaxed. In this work, we examine 9 commonly used observational and theoretical morphological metrics extracted from 54,000 Mock-X synthetic X-ray images of galaxy clusters taken from the IllustrisTNG, BAHAMAS and MACSIS simulation suites. We find that the simulated criteria distributions are in reasonable agreement with the observed distributions. Many criteria distributions evolve as a function of redshift, cluster mass, numerical resolution and subgrid physics, limiting the effectiveness of a single relaxation threshold value. All criteria are positively correlated with each other, however, the strength of the correlation is sensitive to redshift, mass and numerical choices. Driven by the intrinsic scatter inherent to all morphological metrics and the arbitrary nature of relaxation threshold values, we find the consistency of relaxed subsets defined by the different metrics to be relatively poor. Therefore, the use of relaxed cluster subsets introduces significant selection effects that are non-trivial to resolve.


Flavor stability analysis of dense supernova neutrinos with flavor-dependent angular distributions

Abstract: Numerical simulations of the supernova (SN) neutrino self-induced flavor conversions, associated with the neutrino-neutrino interactions in the deepest stellar regions, have been typically carried out assuming the "bulb-model". In this approximation, neutrinos are taken to be emitted half-isotropically by a common neutrinosphere. In the recent Ref. <cit.> we have removed this assumption by introducing flavor-dependent angular distributions for SN neutrinos, as suggested by core-collapse simulations. We have found that in this case a novel multi-angle instability in the self-induced flavor transitions can arise. In this work we perform an extensive study of this effect, carrying out a linearized flavor stability analysis for different SN neutrino energy fluxes and angular distributions, in both normal and inverted neutrino mass hierarchy. We confirm that spectra of different nu species which cross in angular space (where F_ν_e=F_ν_x and F_ν̅_e=F_ν̅_x) present a significant enhancement of the flavor instability, and a shift of the onset of the flavor conversions at smaller radii with respect to the case of an isotropic neutrino emission. We also illustrate how a qualitative (and sometimes quantitative) understanding of the dynamics of these systems follows from a stability analysis.

flavor-dependent angular distribution
neutrinosphere
flavor stability analysis


Viable Inflation in Scalar-Gauss-Bonnet Gravity and Reconstruction from Observational Indices

Abstract: In this paper the focus is on inflationary dynamics in the context of Einstein Gauss-Bonnet gravitational theories. We investigate the implications of the slow-roll condition on the slow-roll indices and we investigate how the inflationary dynamical evolution is affected by the presence of the Gauss-Bonnet coupling to the scalar field. For exemplification of our analysis we investigate how the dynamics of inflationary cubic, quartic order and also exponential scalar potentials are affected by the non-trivial Gauss-Bonnet coupling to the scalar field. As we demonstrate it is possible to obtain a viable phenomenology compatible with the observational data, although the canonical scalar field theory with cubic and quartic order potentials does not yield phenomenologically acceptable results. In addition, with regard to the exponential potential example, the Einstein Gauss-Bonnet extension of the single canonical scalar field model has an inherent mechanism that can trigger the graceful exit from inflation. Furthermore we introduce a bottom-up reconstruction technique, in the context of which by fixing the tensor-to-scalar ratio and the Hubble rate as a function of the e-foldings number, one is capable of reproducing the Einstein Gauss-Bonnet theory which generates the aforementioned quantities. We illustrate how the method works by using some relatively simple examples.

scalar field
einstein-gauss-bonnet gravity
inflationary scenario


Uranus and Neptune: Shape and Rotation

Abstract: Both Uranus and Neptune are thought to have strong zonal winds with velocities of several hundred meters per second. These wind velocities, however, assume solid-body rotation periods based on Voyager 2 measurements of periodic variations in the planets' radio signals and of fits to the planets' magnetic fields; 17.24h and 16.11h for Uranus and Neptune, respectively. The realization that the radio period of Saturn does not represent the planet's deep interior rotation and the complexity of the magnetic fields of Uranus and Neptune raise the possibility that the Voyager 2 radio and magnetic periods might not represent the deep interior rotation periods of the ice giants. Moreover, if there is deep differential rotation within Uranus and Neptune no single solid-body rotation period could characterize the bulk rotation of the planets. We use wind and shape data to investigate the rotation of Uranus and Neptune. The shapes (flattening) of the ice giants are not measured, but only inferred from atmospheric wind speeds and radio occultation measurements at a single latitude. The inferred oblateness values of Uranus and Neptune do not correspond to bodies rotating with the Voyager rotation periods. Minimization of wind velocities or dynamic heights of the 1 bar isosurfaces, constrained by the single occultation radii and gravitational coefficients of the planets, leads to solid-body rotation periods of 16.58h for Uranus and 17.46h for Neptune. Uranus might be rotating faster and Neptune slower than Voyager rotation speeds. We derive shapes for the planets based on these rotation rates. Wind velocities with respect to these rotation periods are essentially identical on Uranus and Neptune and wind speeds are slower than previously thought. Alternatively, if we interpret wind measurements in terms of differential rotation on cylinders there are essentially no residual atmospheric winds.

neptune
rotation
planet
uranus
occultation radius


Redshift drift in a pressure-gradient cosmology

Abstract: We derive a redshift drift formula for the spherically symmetric inhomogeneous pressure Stephani universes which are complementary to the spherically symmetric inhomogeneous density Lemaître-Tolman-Bondi models. We show that there is a clear difference between redshift drift predictions for these two models as well as between the Stephani models and the standard ΛCDM Friedmann models. The Stephani models have positive drift values at small redshift and behave qualitatively (but not quantitatively) as the ΛCDM models at large redshift, while the drift for LTB models is always negative. This prediction may perhaps be tested in future telescopes such as European Extremely Large Telescope (EELT), Thirty Meter Telescope (TMT), Giant Magellan Telescope (GMT), and especially, in gravitational wave interferometers DECi-Hertz Interferometer Gravitational Wave Observatory and Big Bang Observer (DECIGO/BBO), which aim at low redshift.


Key Issues Review: Numerical studies of turbulence in stars

Abstract: The numerical simulation of turbulence in stars has led to a rich set of possibilities regarding stellar pulsations, asteroseismology, thermonuclear yields, and formation of neutron stars and black holes. The breaking of symmetry by turbulent flow grows in amplitude as collapse is approached, which insures that the conditions at the onset of collapse are not spherical. This lack of spherical symmetry has important implications for the mechanism of explosion and ejected nucleosynthesis products. Numerical resolution of several different types of three–dimensional (3D) stellar simulations are compared; it is suggested that core collapse simulations may be under-resolved. New physical effects which appear in 3D are summarized. Connections between simulations of progenitor explosion and observations of supernova remnants (SNR) are discussed. Present treatment of boundaries, for mixing regions during He–burning, requires revision.


The electromagnetic model of short GRBs, the nature of prompt tails, supernova-less long GRBs and highly efficient episodic accretion

Abstract: Many short GRBs show prompt tails lasting up to hundreds of seconds that can be energetically dominant over the initial sub-second spike. In this paper we develop an electromagnetic model of short GRBs that explains the two stages of the energy release, the prompt spike and the prompt tail. The key ingredient of the model is the recent discovery that an isolated black hole can keep its open magnetic flux for times much longer than the collapse time and, thus, can spin-down electromagnetically, driving the relativistic wind. First, the merger is preceded by an electromagnetic precursor wind. If a fraction of the wind power is converted into pulsar-like coherent radio emission, this may produce an observable radio burst of few milliseconds. At the active stage of the merger, two neutron stars produces a black hole surrounded by an accretion torus in which the amplified magnetic field extracts the rotational energy of the black hole and drives an axially-collimated electromagnetic wind. For observers nearly aligned with the orbital normal this is seen as a classical short GRB. After the accretion of the torus, the isolated black hole keeps the open magnetic flux and drives the equatorially (not axially) collimated outflow, which is seen by an observer at intermediate polar angles as a prompt tail. The tail carries more energy than the prompt spike, but its emission is de-boosted for observers along the orbital normal. Observers in the equatorial plane miss the prompt spike and interpret the prompt tail as an energetic supernova-less long GRB. We also demonstrate that episodic accretion onto the BH of magnetized clouds that carry non-zero magnetic flux can be highly efficient in extracting the spin energy of the BH, producing the outflows with the power exceeding the average accretion power.

supernova-less long grb
episodic accretion
neutron star


Cosmology in a certain vector-tensor theory of gravitation

Abstract: We study relevant cosmological topics in the framework of a certain vector-tensor theory of gravitation (hereafter VT). This theory is first compared with the so-called extended electromagnetism (EE). These theories have a notable resemblance and both explain the existence of a cosmological constant. It is shown that, in EE, a positive dark energy density requires a Lagrangian leading to quantum ghosts, whereas VT is free from these ghosts. On account of this fact, the remainder of the paper is devoted to study cosmology in the framework of VT. Initial conditions, at high redshift, are used to solve the evolution equations of all the VT scalar modes. In particular, a certain scalar mode characteristic of VT -which does not appear in general relativity (GR)- is chosen in such a way that it evolves separately. In other words, the scalar modes of the standard model based on GR do not affect the evolution of the VT characteristic mode; however, this scalar mode influences the evolution of the standard GR ones. Some well known suitable codes (CMBFAST and COSMOMC) have been modified to include our VT initial conditions and evolution equations, which are fully general. One of the resulting codes -based on standard statistical methods- has been used to fit VT predictions and observational evidences about both Ia supernovae and cosmic microwave background anisotropy. Seven free parameters are used in this fit. Six of them are often used in GR cosmology and the seventh one is characteristic of VT. From the statistical analysis it follows that VT seems to be advantageous against GR in order to explain cosmological observational evidences.

certain vector-tensor theory
gravitation
quantum ghost
cosmology


The low-mass population in the young cluster Stock 8: Stellar properties and Initial Mass Function

Abstract: The evolution of HII regions/supershells can trigger a new generation of stars/clusters at their peripheries, with environmental conditions that may affect the initial mass function, disk evolution and star formation efficiency. In this paper we study the stellar content and star formation processes in the young cluster Stock 8, which itself is thought to be formed during the expansion of a supershell. We present deep optical photometry along with JHK and 3.6, 4.5 μm photometry from UKIDSS and Spitzer-IRAC. We use multi-color criteria to identify the candidate young stellar objects in the region. Using evolutionary models, we obtain a median log(age) of 6.5 ( 3.0 Myr) with an observed age spread of 0.25 dex for the cluster. Monte Carlo simulations of the population of Stock 8, based on estimates for the photometric uncertainty, differential reddening, binarity, and variability, indicate that these uncertainties introduce an age spread of 0.15 dex. The intrinsic age spread in the cluster is 0.2 dex. The fraction of young stellar objects surrounded by disk is 35 the Trapezium cluster. The IMF of Stock 8 has a Salpeter- like slope at >0.5 Msun and the IMF flattens and peaks at 0.4 Msun, below which declines into the substellar regime. Although Stock 8 is surrounded by several massive stars, there seems to be no severe environmental effect in the form of IMF due to the proximity of massive stars around the cluster.

young cluster stock
initial mass function
star


An optical test bench for the precision characterization of absolute quantum efficiency for the TESS CCD detectors

Abstract: The Transiting Exoplanet Survey Satellite (TESS) will search for planets transiting bright stars with Ic<13. TESS has been selected by NASA for launch in 2018 as an Astrophysics Explorer mission, and is expected to discover a thousand or more planets that are smaller in size than Neptune. TESS will employ four wide-field optical charge-coupled device (CCD) cameras with a band-pass of 650 nm-1050 nm to detect temporary drops in brightness of stars due to planetary transits. The 1050 nm limit is set by the quantum efficiency (QE) of the CCDs. The detector assembly consists of four back-illuminated MIT Lincoln Laboratory CCID-80 devices. Each CCID-80 device consists of 2048x2048 imaging array and 2048x2048 frame store regions. Very precise on-ground calibration and characterization of CCD detectors will significantly assist in the analysis of the science data obtained in space. The characterization of the absolute QE of the CCD detectors is a crucial part of the characterization process because QE affects the performance of the CCD significantly over the redder wavelengths at which TESS will be operating. An optical test bench with significantly high photometric stability has been developed to perform precise QE measurements. The design of the test setup along with key hardware, methodology, and results from the test campaign are presented.

optical test bench
quantum efficiency
ccd detector


Effects of overlapping sources on cosmic shear estimation: Statistical sensitivity and pixel-noise bias

Abstract: In Stage-IV imaging surveys, a significant amount of the cosmologically useful information is due to sources whose images overlap with those of other sources on the sky. The cosmic shear signal is primarily encoded in the estimated shapes of observed galaxies and thus directly impacted by overlaps. We introduce a framework based on the Fisher formalism to analyze effects of overlapping sources (blending) on the estimation of cosmic shear. For the Rubin Observatory Legacy Survey of Space and Time (LSST), we present the expected loss in statistical sensitivity for the ten-year survey due to blending. We find that for approximately 62 full-depth LSST images, at least 1 overlapping sources. We also find that the statistical correlations between measures of overlapping galaxies and, to a much lesser extent the higher shot noise level due to their presence, decrease the effective number density of galaxies, N_eff, by ∼18 39.4 galaxies per arcmin^2 in r band. We study the impact of varying stellar density on N_eff and illustrate the diminishing returns of extending the survey into lower Galactic latitudes. We extend the Fisher formalism to predict the increase in pixel-noise bias due to blending for maximum-likelihood (ML) shape estimators. We find that noise bias is sensitive to the particular shape estimator and measure of ensemble-average shape that is used, and properties of the galaxy that include redshift-dependent quantities such as size and luminosity.

statistical sensitivity
pixel-noise bias
galaxy


Parity-violating interactions of cosmic fields with atoms, molecules, and nuclei: Concepts and calculations for laboratory searches and extracting limits

Abstract: We propose methods and present calculations that can be used to search for evidence of cosmic fields by investigating the parity-violating effects, including parity nonconservation amplitudes and electric dipole moments, that they induce in atoms. The results are used to constrain important fundamental parameters describing the strength of the interaction of various cosmic fields with electrons, protons, and neutrons. Candidates for such fields are dark matter (including axions) and dark energy, as well as several more exotic sources described by standard-model extensions. Existing parity nonconservation experiments in Cs, Dy, Yb, and Tl are combined with our calculations to directly place limits on the interaction strength between the temporal component, b_0, of a static pseudovector cosmic field and the atomic electrons, with the most stringent limit of |b_0^e| < 7*10^(-15) GeV, in the laboratory frame of reference, coming from Dy. From a measurement of the nuclear anapole moment of Cs, and a limit on its value for Tl, we also extract limits on the interaction strength between the temporal component of this cosmic field, as well as a related tensor cosmic-field component d_00, with protons and neutrons. The most stringent limits of |b_0^p| < 4*10^(-8) GeV and |d_00^p| < 5*10^(-8) for protons, and |b_0^n| < 2*10^(-7) GeV and |d_00^n| < 2*10^(-7) for neutrons (in the laboratory frame) come from the results using Cs. Axions may induce oscillating P- and T-violating effects in atoms and molecules through the generation of oscillating nuclear magnetic quadrupole and Schiff moments, which arise from P- and T-odd intranuclear forces and from the electric dipole moments of constituent nucleons. Nuclear-spin-independent parity nonconservation effects may be enhanced in diatomic molecules possessing close pairs of opposite-parity levels in the presence of time-dependent interactions.


Analyzing the cosmic variance limit of remote dipole measurements of the cosmic microwave background using the large-scale kinetic Sunyaev Zel'dovich effect

Abstract: Due to cosmic variance we cannot learn any more about large-scale inhomogeneities from the primary cosmic microwave background (CMB) alone. More information on large scales is essential for resolving large angular scale anomalies in the CMB. Here we consider cross correlating the large-scale kinetic Sunyaev Zel'dovich (kSZ) effect and probes of large-scale structure, a technique known as kSZ tomography. The statistically anisotropic component of the cross correlation encodes the CMB dipole as seen by free electrons throughout the observable Universe, providing information about long wavelength inhomogeneities. We compute the large angular scale power asymmetry, constructing the appropriate transfer functions, and estimate the cosmic variance limited signal to noise for a variety of redshift bin configurations. The signal to noise is significant over a large range of power multipoles and numbers of bins. We present a simple mode counting argument indicating that kSZ tomography can be used to estimate more modes than the primary CMB on comparable scales. A basic forecast indicates that a first detection could be made with next-generation CMB experiments and galaxy surveys. This paper motivates a more systematic investigation of how close to the cosmic variance limit it will be possible to get with future observations.

variance limit
cosmic microwave background
dipole field


Image recovery with the solar gravitational lens

Abstract: We report on the initial results obtained with an image convolution/deconvolution computer code that we developed and used to study the image formation capabilities of the solar gravitational lens (SGL). Although the SGL of a spherical Sun creates a greatly blurred image, knowledge of the SGL's point-spread function (PSF) makes it possible to reconstruct the original image and remove the blur by way of deconvolution. We discuss the deconvolution process, which can be implemented either with direct matrix inversion or with the Fourier quotient method. We observe that the process introduces a “penalty” in the form of a reduction in the signal-to-noise ratio (SNR) of a recovered image, compared to the SNR at which the blurred image data is collected. We estimate the magnitude of this penalty using an analytical approach and confirm the results with a series of numerical simulations. We find that the penalty is substantially reduced when the spacing between image samples is large compared to the telescope aperture. The penalty can be further reduced with suitable noise filtering, which can yield O(10) or better improvement for low-quality imaging data. Our results confirm that it is possible to use the SGL for imaging purposes. We offer insights on the data collection and image processing strategies that could yield a detailed image of an exoplanet within image data collection times that are consistent with the duration of a realistic space mission.


Revisiting the Scaling Relations of Black Hole Masses and Host Galaxy Properties

Abstract: New kinematic data and modeling efforts in the past few years have substantially expanded and revised dynamical measurements of black hole masses (Mbh) at the centers of nearby galaxies. Here we compile an updated sample of 72 black holes and their host galaxies, and present revised scaling relations between Mbh and stellar velocity dispersion (sigma), V-band luminosity (L), and bulge stellar mass (Mbulge), for different galaxy subsamples. Our best-fitting power law relations for the full galaxy sample are log(Mbh) = 8.32 + 5.64*log(sigma/200 kms), log(Mbh) = 9.23 + 1.11*log(L/10^11 Lsun), and log(Mbh) = 8.46 + 1.05*log(Mbulge/10^11 Msun). A log-quadratic fit to the Mbh-sigma relation with an additional term of beta_2*[log(sigma/200 kms)]^2 gives beta_2 = 1.68 +/- 1.82 and does not decrease the intrinsic scatter in Mbh. When the early- and late-type galaxies are fit separately, we obtain similar slopes of 5.20 and 5.06 for the Mbh-sigma relation but significantly different intercepts – Mbh in early-type galaxies are about 2 times higher than in late types at a given sigma. Within early-type galaxies, our fits to Mbh(sigma) give Mbh that is about 2 times higher in galaxies with central core profiles than those with central power-law profiles. Our Mbh-L and Mbh-Mbulge relations for early-type galaxies are similar to those from earlier compilations. When the conventional quadrature method is used to determine the intrinsic scatter in Mbh, our dataset shows weak evidence for increased scatter at Mbulge < 10^11 Msun or L_V < 10^10.3 Lsun, while the scatter stays constant for 10^11 < Mbulge < 10^12.3 Msun and 10^10.3 < L_V < 10^11.5 Lsun. A Bayesian analysis indicates a larger sample of Mbh measurements would be needed to detect any statistically significant trend in the scatter with galaxy properties.

black hole
galaxy
stellar velocity dispersion


Directional detection as a strategy to discover Galactic Dark Matter

Abstract: Directional detection of Galactic Dark Matter is a promising search strategy for discriminating genuine WIMP events from background ones. Technical progress on gaseous detectors and read-outs has permitted the design and construction of competitive experiments. However, to take full advantage of this powerful detection method, one need to be able to extract information from an observed recoil map to identify a WIMP signal. We present a comprehensive formalism, using a map-based likelihood method allowing to recover the main incoming direction of the signal and its significance, thus proving its galactic origin. This is a blind analysis intended to be used on any directional data. Constraints are deduced in the (σ_n, m_χ) plane and systematic studies are presented in order to show that, using this analysis tool, unambiguous dark matter detection can be achieved on a large range of exposures and background levels.

galactic dark matter
galactic origin
directional detection


Reconstructing the Last Major Merger of the Milky Way with the H3 Survey

Abstract: Several lines of evidence suggest the Milky Way underwent a major merger at z 2 with a galaxy known as Gaia-Sausage-Enceladus (GSE). Here we use H3 Survey data to argue that GSE entered the Galaxy on a retrograde orbit based on a population of highly retrograde stars with chemistry similar to the largely radial GSE debris. We present the first tailored, high-resolution N-body simulations of the merger. From a grid of 500 simulations we find a GSE with M_*=5×10^8 M_⊙, M_DM=2×10^11 M_⊙ (a 2.5:1 total mass merger) best matches the H3 data. This simulation shows the retrograde GSE stars are stripped from its outer disk early in the merger before the orbit loses significant angular momentum. Despite being selected purely on angular momenta and radial distributions, this simulation reproduces and explains the following empirical phenomena: (i) the elongated, triaxial shape of the inner halo (axis ratios 10:7.9:4.5), whose major axis is at 35 to the plane and connects GSE's apocenters, (ii) the Hercules-Aquila Cloud the Virgo Overdensity, which arise due to apocenter pile-up, (iii) the 2 Gyr lag between the quenching of GSE and the truncation of the age distribution of the in-situ halo, which tracks the 2 Gyr gap between the first and final GSE pericenters. We make the following predictions: (i) the inner halo has a "double-break" density profile with breaks at both 15-18 kpc and 30 kpc, coincident with the GSE apocenters, (ii) the outer halo has retrograde streams containing 10 retrograde (radial) GSE debris originates from its outer (inner) disk – exploiting this trend we reconstruct the stellar metallicity gradient of GSE (-0.04±0.01 dex r_50^-1). These simulations imply GSE delivered 20 (ABRIDGED)


Unifying an asymmetric bounce to the dark energy in Chern-Simons F(R) gravity

Abstract: We propose a cosmological scenario in which the universe undergoes through a non-singular bounce, and after the bounce, it decelerates having a matter-like dominated evolution during some regime of the deceleration era, and finally at the present epoch it evolves through an accelerating stage. Our aim is to study such evolution in the context of Chern-Simons corrected F(R) gravity theory and confront the model with various observational data. Using the reconstruction technique, and in addition by employing suitable boundary conditions, we determine the form of F(R) for the entire possible range of the cosmic time. The form of F(R) seems to unify a non-singular bounce with a dark energy epoch, in particular, from a non-singular bounce to a deceleration epoch and from a deceleration epoch to a late time acceleration era. It is important to mention that the bouncing scenario in the present context is an asymmetric bounce, in particular, the Hubble radius monotonically increases and asymptotically diverges at the late contracting era, while it seems to decrease with time at the present epoch. Such evolution of the Hubble radius leads to the primordial perturbation modes generate at the deep contracting era when all the perturbation modes lie within the horizon. We calculate the scalar and tensor power spectra, and as a result, the primordial observables are found to be in agreement with the latest Planck 2018 constraints. In this regard, the Chern-Simons term seems to have considerable effects on the tensor perturbation evolution, however keeping intact the scalar part of the perturbation with that of in the case of a vacuum F(R) model, and as a result, the Chern-Simons term proves to play an important role in making the observable quantities consistent with the Planck results. Furthermore the theoretical expectation of the dark energy observables are confronted with the Planck+SNe+BAO data.

asymmetric bounce
gravity
primordial perturbation mode


Constraining Extended Gravity Models by S2 star orbits around the Galactic Centre

Abstract: We investigate the possibility to explain theoretically the observed deviations of S2 star orbit around the Galactic Centre using gravitational potentials derived from modified gravity models in absence of dark matter. To this aim, an analytic fourth-order theory of gravity, non-minimally coupled with a massive scalar field is considered. Specifically, the interaction term is given by analytic functions f(R) and f(R,ϕ) where R is the Ricci scalar and ϕ is a scalar field whose meaning can be related to further gravitational degrees of freedom. We simulate the orbit of S2 star around the Galactic Centre in f(R) (Yukawa-like) and f(R,ϕ) (Sanders-like) gravity potentials and compare it with NTT/VLT observations. Our simulations result in strong constraints on the range of gravity interaction. In the case of analytic functions f(R), we are not able to obtain reliable constraints on the derivative constants f_1 and f_2, because the current observations of S2 star indicated that they may be highly mutually correlated. In the case of analytic functions f(R,ϕ), we are able to obtain reliable constraints on the derivative constants f_0, f_R, f_RR, f_ϕ, f_ϕϕ and f_ϕ R. The approach we are proposing seems to be sufficiently reliable to constrain the modified gravity models from stellar orbits around Galactic Centre.


Astronomical photonics in the context of infrared interferometry and high-resolution spectroscopy

Abstract: We review the potential of Astrophotonics, a relatively young field at the interface between photonics and astronomical instrumentation, for spectro-interferometry. We review some fundamental aspects of photonic science that drove the emer- gence of astrophotonics, and highlight the achievements in observational astrophysics. We analyze the prospects for further technological development also considering the potential synergies with other fields of physics (e.g. non-linear optics in condensed matter physics). We also stress the central role of fiber optics in routing and transporting light, delivering complex filters, or interfacing instruments and telescopes, more specifically in the context of a growing usage of adaptive optics.

photonic
infrared interferometry
astronomical instrumentation


A Characteristic Scale for Cold Gas

Abstract: We find that clouds of optically-thin, pressure-confined gas are prone to fragmentation as they cool below ∼10^6 K. This fragmentation follows the lengthscale ∼c_s t_cool, ultimately reaching very small scales (∼0.1pc/n) as they reach the temperature ∼10^4 K at which hydrogen recombines. While this lengthscale depends on the ambient pressure confining the clouds, we find that the column density through an individual fragment N_cloudlet∼10^17cm^-3 is essentially independent of environment; this column density represents a characteristic scale for atomic gas at 10^4 K. We therefore suggest that "clouds" of cold, atomic gas may in fact have the structure of a mist or a fog, composed of tiny fragments dispersed throughout the ambient medium. We show that this scale emerges in hydrodynamic simulations, and that the corresponding increase in the surface area may imply rapid entrainment of cold gas. We also apply it to a number of observational puzzles, including the large covering fraction of diffuse gas in galaxy halos, the broad line widths seen in quasar and AGN spectra, and the entrainment of cold gas in galactic winds. While our simulations make a number of assumptions and thus have associated uncertainties, we show that this characteristic scale is consistent with a number of observations, across a wide range of astrophysical environments. We discuss future steps for testing, improving, and extending our model.

characteristic scale
cold gas
cloud
galactic wind


On light propagation in Swiss-Cheese cosmologies

Abstract: We study the effect of inhomogeneities on light propagation. The Sachs equations are solved numerically in the Swiss-Cheese models with inhomogeneities modelled by the Lemaitre-Tolman solutions. Our results imply that, within the models we study, inhomogeneities may partially mimic the accelerated expansion of the Universe provided the light propagates through regions with lower than the average density. The effect of inhomogeneities is small and full randomization of the photons' trajectories reduces it to an insignificant level.

light propagation
cosmology
swiss-cheese model


Growing dust grains in protoplanetary discs - II. The Radial drift barrier problem

Abstract: We aim to study the migration of growing dust grains in protoplanetary discs, where growth and migration are tightly coupled. This includes the crucial issue of the radial-drift barrier for growing dust grains. We therefore extend the study performed in Paper I, considering models for grain growth and grain dynamics where both the migration and growth rate depend on the grain size and the location in the disc. The parameter space of disc profiles and growth models is exhaustively explored. In doing so, interpretations for the grain motion found in numerical simulations are also provided. We find that a large number of cases is required to characterise entirely the grains radial motion, providing a large number of possible outcomes. Some of them lead dust particles to be accreted onto the central star and some of them don't. We find then that q<1 is required for discs to retain their growing particles, where q is the exponent of the radial temperature profile T(R) proportional to R^-q. Additionally, the initial dust-to gas ratio has to exceed a critical value for grains to pile up efficiently, thus avoiding being accreted onto the central star. Discs are also found to retain efficiently small dust grains regenerated by fragmentation. We show how those results are sensitive to the turbulent model considered. Even though some physical processes have been neglected, this study allows to sketch a scenario in which grains can survive the radial-drift barrier in protoplanetary discs as they grow.

dust grain
protoplanetary disc
radial-drift barrier


Universality of galactic surface densities within one dark halo scale-length

Abstract: It was recently discovered that the mean dark matter surface density within one dark halo scale length - the radius within which the volume density profile of dark matter remains approximately flat - is constant across a wide range of galaxies. This scaling relation holds for galaxies spanning a luminosity range of 14 magnitudes and the whole Hubble sequence. Here we report that the luminous matter surface density is also constant within one scale length of the dark halo. This means that the gravitational acceleration generated by the luminous component in galaxies is always the same at this radius. Although the total luminous-to-dark matter ratio is not constant, within one halo scale length it is constant. Our finding can be interpreted as a close correlation between the enclosed surface densities of luminous and dark matter in galaxies.


Fuzzy Dark Matter at Cosmic Dawn: New 21-cm Constraints

Abstract: Potential small-scale discrepancies in the picture of galaxy formation painted by the ΛCDM paradigm have led to considerations of modified dark matter models. One such dark matter model that has recently attracted much attention is fuzzy dark matter (FDM). In FDM models, the dark matter is envisaged to be an ultra-light scalar field with a particle mass m_ FDM∼ 10^-22 eV. This yields astronomically large de Broglie wavelengths which can suppress small-scale structure formation and give rise to the observed kpc-sized density cores in dwarf galaxies. We investigate the evolution of the 21-cm signal during Cosmic Dawn and the Epoch of Reionization (EoR) in ΛFDM cosmologies using analytical models. The delay in source formation and the absence of small halos in ΛFDM significantly postpone the Lyα coupling, heating, as well as the reionization of the neutral hydrogen of the intergalactic medium. As a result, the absorption feature in the evolution of the global 21-cm signal has a significantly smaller full width at half maximum (Δ z ≲ 3), than ΛCDM (Δ z ≃ 6). This alone rules out m_ FDM < 6 × 10^-22 eV as a result of the 2σ lower limit Δ z ≳ 4 from EDGES High-Band. As a result, ΛFDM is not a viable solution to the potential small-scale problems facing ΛCDM. Finally, we show that any detection of the 21-cm signal at redshifts z > 14 by interferometers such as the SKA can also exclude ΛFDM models.

cosmic dawn
scalar field
fuzzy dark matter


Gas perturbations in cool cores of galaxy clusters: effective equation of state, velocity power spectra and turbulent heating

Abstract: We present the statistical analysis of X-ray surface brightness and gas density fluctuations in cool cores of ten, nearby and bright galaxy clusters that have deep Chandra observations and show observational indications of radio-mechanical AGN feedback. Within the central parts of cool cores the total variance of fluctuations is dominated by isobaric and/or isothermal fluctuations on spatial scales 10-60 kpc, which are likely associated with slow gas motions and bubbles of relativistic plasma. Adiabatic fluctuations associated with weak shocks constitute less than 10 per cent of the total variance in all clusters. The typical amplitude of density fluctuations is small, 10 per cent or less on scales of 10-15 kpc. Subdominant contribution of adiabatic fluctuations and small amplitude of density fluctuations support a model of gentle AGN feedback as opposed to periodically explosive scenarios which are implemented in some numerical simulations. Measured one-component velocities of gas motions are typically below 100-150 km/s on scales < 50 kpc, and can be up to 300 km/s on 100 kpc scales. The non-thermal energy is < 12 per cent of the thermal energy. Regardless of the source that drives these motions the dissipation of the energy in such motions provides heat that is sufficient to balance radiative cooling on average, albeit the uncertainties are large. Presented results here support previous conclusions based on the analysis of the Virgo and Perseus Clusters, and agree with the Hitomi measurements. With next generation observatories like Athena and Lynx, these techniques will be yet more powerful.


Solar models with accretion. I. Application to the solar abundance problem

Abstract: We generate new standard solar models using newly analyzed nuclear fusion cross sections and present results for helioseismic quantities and solar neutrino fluxes. We discuss the status of the solar abundance problem and investigate whether nonstandard solar models with accretion from the protoplanetary disk might alleviate the problem. We examine a broad range of possibilities, analyzing both metal-enriched and metal-depleted accretion models and exploring three scenarios for the timing of the accretion. Only partial solutions are found: one can bring either the depth of the convective zone or the surface helium abundance into agreement with helioseismic results, but not both simultaneously. In addition, detailed results for solar neutrino fluxes show that neutrinos are a competitive source of information about the solar core and can help constrain possible accretion histories of the Sun. Finally, we briefly discuss how measurements of solar neutrinos from the CN-cycle could shed light on the interaction between the early Sun and its protoplanetary disk.

accretion
solar abundance problem
-neutrino flux


SDSS-IV MaNGA: What Shapes The Distribution Of Metals In Galaxies? Exploring The Roles Of The Local Gas Fraction And Escape Velocity

Abstract: We determine the local metallicity of the ionized gas for more than 9.2× 10^5 star forming regions (spaxels) located in 1023 nearby galaxies included in the SDSS-IV MaNGA IFU survey. We use the dust extinction derived from the Balmer decrement and stellar template fitting in each spaxel to estimate the local gas and stellar mass densities, respectively. We also use the measured rotation curves to determine the local escape velocity (V_esc). We have then analyze the relationships between the local metallicity and both the local gas fraction (μ) and V_esc. We find that metallicity decreases with both increasing μ and decreasing V_esc. By examining the residuals in these relations we show that the gas fraction plays a more primary role in the local chemical enrichment than V_esc. We show that the gas-regulator model of chemical evolution provides a reasonable explanation of the metallicity on local scales. The best-fit parameters for this model are consistent with metal loss caused by momentum-driven galactic outflows. We also argue that both the gas fraction and local escape velocity are connected to the local stellar surface density, which in turn is a tracer of the epoch at which the dominant local stellar population formed


Cosmological constraints from line intensity mapping with interlopers

Abstract: Understanding the formation and evolution of the Universe is crucial for cosmological studies, and the line intensity mapping provides a powerful tool for this kind of study. We propose to make use of multipole moments of redshift-space line intensity power spectrum to constrain the cosmological and astrophysical parameters, such as the equation of state of dark energy, massive neutrinos, primordial non-Gaussianity, and star formation rate density. As an example, we generate mock data of multipole power spectra for H-alpha 6563AA, [OIII] 5007AA and [OII] 3727AA measured by SPHEREx experiment at z=1 considering contaminations from interloper lines, and use Markov Chain Monte Carlo (MCMC) method to constrain the parameters in the model. We find a good fitting result of the parameters compared to their fiducial values, which means that the multipole power spectrum can effectively distinguish signal and interloper lines, and break the degeneracies between parameters, such as line mean intensity and bias. We also explore the cross power spectrum with CSST (Chinese Space Station Telescope) spectroscopic galaxy survey in the constraints. Since more accurate fitting results can be obtained by including measurements of the emission lines at higher redshifts out to z=3 at least and cross-correlations between emission lines can be involved, the line intensity mapping is expected to offer excellent results in future cosmological and astrophysical studies.

line intensity mapping
interloper
redshift


Simulations of the Microwave Sky

Abstract: We create realistic, full-sky, half-arcminute resolution simulations of the microwave sky matched to the most recent astrophysical observations. The primary purpose of these simulations is to test the data reduction pipeline for the Atacama Cosmology Telescope (ACT) experiment; however, we have widened the frequency coverage beyond the ACT bands to make these simulations applicable to other microwave background experiments. Some of the novel features of these simulations are that the radio and infrared galaxy populations are correlated with the galaxy cluster populations, the CMB is lensed by the dark matter structure in the simulation via a ray-tracing code, the contribution to the thermal and kinetic Sunyaev-Zel'dovich (SZ) signals from galaxy clusters, groups, and the IGM has been included, and the gas prescription to model the SZ signals matches the most recent X-ray observations. Regarding the contamination of cluster SZ flux by radio galaxies, we find for 148 GHz (90 GHz) only 3 of halos have their SZ decrements contaminated at a level of 20 find the contamination levels higher for infrared galaxies. However, at 90 GHz, less than 20 their SZ decrements filled in at a level of 20 20 decrements filled in at a level of 50 a population of very high flux infrared galaxies, which are likely lensed sources, contribute most to the SZ contamination of very massive clusters at 90 and 148 GHz. These simulations are publicly available and should serve as a useful tool for microwave surveys to cross-check SZ cluster detection, power spectrum, and cross-correlation analyses.


Bias and scatter in the Hubble diagram from cosmological large-scale structure

Abstract: An important part of cosmological model fitting relies on correlating distance indicators of objects (for example type Ia supernovae) with their redshift, often illustrated on a Hubble diagram. Comparing the observed correlation with a homogeneous model is one of the key pieces of evidence for dark energy. The presence of cosmic structures introduces a bias and scatter, mainly due to gravitational lensing and peculiar velocities, but also due to smaller non-linear relativistic contributions which are more difficult to account for. For the first time we perform ray tracing onto halos in a relativistic N-body simulation. Our simulation is the largest that takes into account all leading-order corrections from general relativity in the evolution of structure, and we present a novel methodology for working out the non-linear projection of that structure onto the observer's past light cone. We show that the mean of the bias in the Hubble diagram is indeed as small as expected from perturbation theory. However, the distribution of sources is significantly skewed with a very long tail of highly magnified objects and we illustrate that the bias of cosmological parameters strongly depends on the function of distance which we consider.

hubble diagram
relativistic n-body simulation
bias


A New Approach to Systematic Uncertainties and Self-Consistency in Helium Abundance Determinations

Abstract: Tests of big bang nucleosynthesis and early universe cosmology require precision measurements for helium abundance determinations. However, efforts to determine the primordial helium abundance via observations of metal poor H II regions have been limited by significant uncertainties. This work builds upon previous work by providing an updated and extended program in evaluating these uncertainties. Procedural consistency is achieved by integrating the hydrogen based reddening correction with the helium based abundance calculation, i.e., all physical parameters are solved for simultaneously. We include new atomic data for helium recombination and collisional emission based upon recent work by Porter et al. and wavelength dependent corrections to underlying absorption are investigated. The set of physical parameters has been expanded here to include the effects of neutral hydrogen collisional emission. Because of a degeneracy between the solutions for density and temperature, the precision of the helium abundance determinations is limited. Also, at lower temperatures (T ≲13,000 K) the neutral hydrogen fraction is poorly constrained resulting in a larger uncertainty in the helium abundances. Thus the derived errors on the helium abundances for individual objects are larger than those typical of previous studies. The updated emissivities and neutral hydrogen correction generally raise the abundance. From a regression to zero metallicity, we find Y_p as 0.2561 ±0.0108, in broad agreement with the WMAP result. Tests with synthetic data show a potential for distinct improvement, via removal of underlying absorption, using higher resolution spectra. A small bias in the abundance determination can be reduced significantly and the calculated helium abundance error can be reduced by ∼25

helium abundance
big bang nucleosynthesis
neutral hydrogen
broad agreement
systematic correction


Tensor to scalar ratio and large scale power suppression from pre-slow roll initial conditions

Abstract: We study corrections to the power spectra of curvature and tensor perturbations and the tensor-to-scalar ratio in single field slow roll inflation due to initial conditions imprinted by a fast-roll stage prior to slow roll. For a wide range of initial inflaton kinetic energy, this stage lasts only a few e-folds and merges smoothly with slow-roll leading to non-Bunch-Davies initial conditions for modes that exit the Hubble radius during slow roll. We describe a program that yields the dynamics in the fast-roll stage while matching to the slow roll stage independent of the inflationary potentials. Corrections to the power spectra are encoded in a transfer function 𝒯_α(k). We obtain 𝒯_α(k) to leading order in a Born approximation valid for modes of observational relevance today. A fit yields 𝒯_α(k) =1+ A_αk^-pcos[2πω k/H_sr+φ_α], with 1.5 ≲ p ≲ 2, ω≃ 1 and H_sr the Hubble scale during slow roll inflation, where curvature and tensor perturbations feature the same p,ω for a wide range of initial conditions. These corrections lead to both a suppression of the quadrupole and oscillatory features in both P_R(k) and r(k_0) with a period of the order of the Hubble scale during slow roll inflation. The results are independent of the specific inflationary potentials, depending solely on the ratio of kinetic to potential energy κ and the slow roll parameters to leading order. For a wide range of κ and the values of ϵ_V;η_V corresponding to the upper bounds from Planck, we find that the low quadrupole is consistent with the results from Planck, and the oscillations in r(k_0) could be observable if the modes corresponding to the quadrupole and the pivot scale crossed the Hubble radius a few e-folds after the onset of slow roll.

roll
initial condition
tensor-to-scalar ratio


High Performance Lyot and PIAA Coronagraphy for Arbitrarily shaped Telescope Apertures

Abstract: Two high performance coronagraphic approaches compatible with segmented and obstructed telescope pupils are described. Both concepts use entrance pupil amplitude apodization and a combined phase and amplitude focal plane mask to achieve full coronagraphic extinction of an on-axis point source. While the first concept, named Apodized Pupil Complex Mask Lyot Coronagraph (APCMLC), relies on a transmission mask to perform the pupil apodization, the second concept, named Phase-Induced Amplitude Apodization complex mask coronagraph (PIAACMC), uses beam remapping for lossless apodization. Both concepts theoretically offer complete coronagraphic extinction (infinite contrast) of a point source in monochromatic light, with high throughput and sub-lambda/D inner working angle, regardless of aperture shape. The PIAACMC offers nearly 100 imposed by first principles. The steps toward designing the coronagraphs for arbitrary apertures are described for monochromatic light. Designs for the APCMLC and the higher performance PIAACMC are shown for several monolith and segmented apertures, such as the apertures of the Subaru Telescope, Giant Magellan Telescope (GMT), Thirty Meter Telescope (TMT), the European Extremely Large Telescope (E-ELT) and the Large Binocular Telescope (LBT). Performance in broadband light is also quantified, suggesting that the monochromatic designs are suitable for use in up to 20 telescopes.

telescope aperture
coronagraph
phase-induced amplitude apodization


Why is the nuclear symmetry energy so uncertain at supra-saturation densities?

Abstract: Within the interacting Fermi gas model for isospin asymmetric nuclear matter, effects of the in-medium three-body interaction and the two-body short-range tensor force due to the ρ meson exchange as well as the short-range nucleon correlation on the high-density behavior of the nuclear symmetry energy are demonstrated respectively in a transparent way. Possible physics origins of the extremely uncertain nuclear symmetry energy at supra-saturation densities are discussed.

nuclear symmetry energy
supra-saturation density
nuclear matter


Is there another coincidence problem at the reionization epoch?

Abstract: The cosmological coincidences between the matter and radiation energy densities at recombination as well as between the densities of matter and the cosmological constant at present time are well known. We point out that moreover the third intersection between the energy densities of radiation and the cosmological constant coincides with the reionization epoch. To quantify the statistical relevance of this concurrence, we compute the Bayes factor between the concordance cosmology with free Thomson scattering optical depth and a model for which this parameter is inferred from imposing a match between the time of density equality and the epoch of reionization. This is to characterize the potential explanatory gain if one were to find a parameter-free physical connection. We find a very strong preference for such a concurrence on the Jeffreys scale from current cosmological observations. We furthermore discuss the effect of choice of priors, changes in reionization history, and free sum of neutrino masses. We also estimate the impact of adding intermediate polarization data from the Planck High Frequency Instrument and prospects for future 21 cm surveys. In the first case, preference for the correlation remains substantial, whereas future data may give results more decisive in pro or substantial in contra. Finally, we provide a discussion on different interpretations of these findings. In particular, we show how a connection between the star-formation history and the cosmological background dynamics can give rise to this concurrence.

coincidence problem
reionization epoch
cosmological constant


Modified Entropic Force

Abstract: The theory of statistical thermodynamics tells us the equipartition law of energy does not hold in the limit of very low temperatures. It is found the Debye model is very successful in explaining the experimental results for most of the solid objects. Motivated by this fact, we modify the entropic force formula which is proposed very recently. Since the Unruh temperature is proportional to the strength of gravitational field, so the modified entropic force formula is an extension of the Newtonian gravity to weak field. On the contrary, General Relativity extends Newtonian gravity to strong field case. Corresponding to Debye temperature, there exists a Debye acceleration g_D. It is found the Debye acceleration is g_D=10^-15N kg^-1. This acceleration is very much smaller than the gravitational acceleration 10^-4N kg^-1 which is felt by the Neptune and the gravitational acceleration 10^-10N kg^-1 felt by the Sun. Therefore, the modified entropic force can be very well approximated by the Newtonian gravity in the solar system and in the Galaxy. With this Debye acceleration, we find the current cosmic speeding up can be explained without invoking any kind of dark energy.

equipartition law
experimental result
gravity
dark energy
modified entropic force


Pinning down the mass of Kepler-10c: the importance of sampling and model comparison

Abstract: Initial RV characterisation of the enigmatic planet Kepler-10c suggested a mass of ∼17 M_⊕, which was remarkably high for a planet with radius 2.32 R_⊕; further observations and subsequent analysis hinted at a (possibly much) lower mass, but masses derived using RVs from two different spectrographs (HARPS-N and HIRES) were incompatible at a 3σ-level. We demonstrate here how such mass discrepancies may readily arise from sub-optimal sampling and/or neglecting to model even a single coherent signal (stellar, planetary, or otherwise) that may be present in RVs. We then present a plausible resolution of the mass discrepancy, and ultimately characterise Kepler-10c as having mass 7.37_-1.19^+1.32 M_⊕, and mean density 3.14^+0.63_-0.55 g cm^-3.


The lamppost model: effects of photon trapping, the bottom lamp and disc truncation

Abstract: We study the lamppost model, in which the primary X-ray sources in accreting black-hole systems are located symmetrically on the rotation axis on both sides of the black hole surrounded by an accretion disc. We show the importance of the emission of the source on the opposite side to the observer. Due to gravitational light bending, its emission can increase the direct (i.e., not re-emitted by the disc) flux by as much as an order of magnitude. This happens for near to face-on observers when the disc is even moderately truncated. For truncated discs, we also consider effects of emission of the top source gravitationally bent around the black hole. We also present results for the attenuation of the observed radiation with respect to that emitted by the lamppost as functions of the lamppost height, black-hole spin and the degree of disc truncation. This attenuation, which is due to the time dilation, gravitational redshift and the loss of photons crossing the black-hole horizon, can be as severe as by several orders of magnitude for low lamppost heights. We also consider the contribution to the observed flux due to re-emission by optically-thick matter within the innermost stable circular orbit.

lamppost model
disc truncation
radiation


A relativistic signature in large-scale structure

Abstract: In General Relativity, the constraint equation relating metric and density perturbations is inherently nonlinear, leading to an effective non-Gaussianity in the dark matter density field on large scales - even if the primordial metric perturbation is Gaussian. Intrinsic non-Gaussianity in the large-scale dark matter overdensity in GR is real and physical. However, the variance smoothed on a local physical scale is not correlated with the large-scale curvature perturbation, so that there is no relativistic signature in the galaxy bias when using the simplest model of bias. It is an open question whether the observable mass proxies such as luminosity or weak lensing correspond directly to the physical mass in the simple halo bias model. If not, there may be observables that encode this relativistic signature.

relativistic signature
effective non-gaussianity
matter density field
galaxy bias