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One of the most crucial yet poorly constrained parameters in modelling the ionizing emissivity is the escape fraction of photons from star-forming galaxies. Several theoretical and observational studies have been conducted over the past few years, but consensus regarding its redshift evolution has yet to be achieved. We present here the first non-parametric reconstruction of this parameter as a function of redshift from a data-driven reionization model using a Gaussian Process Regression method. Our finding suggests a mild redshift evolution of escape fraction with a mean value of $4\%,7\%,\sim10\%$ at $z=2,6,12$. However, a constant escape fraction of $6-10\%$ at $z\gtrsim 6$ is still allowed by current data and also matches other reionization-related observations. With the detection of fainter high redshift galaxies from upcoming observations of JWST, the approach presented here will be a robust tool to put the most stringent constraint on escape fraction as well as reionization histories., Comment: accepted in MNRAS Letter

We analyse the $f(R)$ gravity in the so-called Jordan frame, as implemented to the isotropic Universe dynamics. The goal of the present study is to show that, according to recent data analyses of the supernovae Ia Pantheon sample, it is possible to account for an effective redshift dependence of the Hubble constant. This is achieved via the dynamics of a non-minimally coupled scalar field, as it emerges in the $f(R)$ gravity. We face the question both from an analytical and purely numerical point of view, following the same technical paradigm. We arrive to establish that the expected decay of the Hubble constant with the redshift $z$ is ensured by a form of the scalar field potential, which remains essentially constant for $z\lesssim0.3$, independently if this request is made a priori, as in the analytical approach, or obtained a posteriori, when the numerical procedure is addressed. Thus, we demonstrate that an $f(R)$ dark energy model is able to account for an apparent variation of the Hubble constant due to the rescaling of the Einstein constant by the $f(R)$ scalar mode., Comment: 6 pages, 3 figures, accepted for publication in MNRAS Letters (manuscript version after the proof corrections)

The homologous collapse from rest of a uniform density sphere under its self gravity is a well-known toy model for the formation dynamics of astronomical objects ranging from stars to galaxies. Equally well-known is that the evolution of the radius with time cannot be explicitly obtained because of the transcendental nature of the differential equation solution. Rather, both radius and time are written parametrically in terms of the development angle $\theta$. We here present an explicit integral solution for radius as a function of time, exploiting methods from complex analysis recently applied to the mathematically-similar 'geometric goat problem'. Our solution can be efficiently evaluated using a Fast Fourier Transform and allows for arbitrary sampling in time, with a simple Python implementation that is $\sim$$100\times$ faster than using numerical root-finding to achieve arbitrary sampling. Our explicit solution is advantageous relative to the usual approach of first generating a uniform grid in $\theta$, since this latter results in a non-uniform radial or time sampling, less useful for applications such as generation of sub-grid physics models., Comment: 4 pages, 3 figures, submitted to MNRAS. Python implementation available at https://gist.github.com/oliverphilcox/559f086f1bf63b23d55c508b2f47bad3

In this letter, we explore the quiescent lives of central galaxies using the SAGE galaxy model and Uchuu dark matter simulation. We ask three questions: (1) How much of a galaxy's life is spent in quiescence? (2) How often do galaxies transition off the main sequence? (3) What is the typical duration of a quiescent phase? We find low and high-mass galaxies spend the highest fraction of their lives in quiescence: 45 \pm 19% for log10(Mstar) < 9.0 (3.68 \pm 1.80 Gyr) and 26 \pm 25% for log10(Mstar) > 11.5 (3.46 \pm 3.30 Gyr), falling to 7 \pm 13% for galaxies in-between (0.82 \pm 1.57 Gyr). Low mass galaxies move in and out of quiescence frequently, 2.8 \pm 1.3 times on average, though only for short periods, 1.49 \pm 1.04 Gyr. This can be traced to the influence of supernova feedback on their quite stochastic evolution. Galaxies of higher mass have fewer quiescent periods, ~0.7 \pm 0.9, and their length increases with mass, peaking at 1.97 \pm 2.27 Gyr. However, our high-mass population comprises star-forming and quiescent galaxies with diverging evolutionary paths, so the actual time may be even longer. These high-mass trends are driven by radio mode feedback from supermassive black holes, which, once active, tend to remain active for extended periods., 5 pages, 3 figures, accepted to MNRAS Letters, open access version see https://doi.org/10.1093/mnrasl/slad031

The origin of Carbon Enhanced Metal-Poor (CEMP-no) stars with low abundances of neutron-capture elements is still unclear. These stars are ubiquitous, found primarily in the Milky Way halo and ultra-faint dwarf galaxies (UFDs). To make a major step forward, we developed a data-calibrated model for Böotes I that simultaneously includes all carbon sources: supernovae and asymptotic giant branch (AGB) stars both from first (Pop III) stars, and subsequent normal star formation (Pop II). We demonstrate that each of these sources leaves a specific chemical signature in the gas, allowing us to identify the origin of present day CEMP-no stars through their location in the A(C)–[Fe/H] diagram. The CEMP stars with A(C) > 6 are predominantly enriched by AGB Pop II stars. We identify a new class of moderate CEMP-s stars with A(C) ∼7 and 0 < [Ba/Fe] < + 1, imprinted by winds from AGB stars. True Pop III descendants are predicted to have A(C) < 6 and a constant [C/Mg] with [Fe/H], in perfect agreement with observations in Böotes I and the Milky Way halo. For the first time we now have a complete picture of the origins of CEMP-no stars which can and will be verified with future observations.

Recent attempts to detect [OIII] 88$μ$m emission from super-early ($z>10$) galaxy candidates observed by JWST have been unsuccessful. By using zoom-in simulations, we show that these galaxies are faint, and mostly fall below the local metal-poor $\rm [OIII]-SFR$ relation as a result of their low ionization parameter, $U_{\rm ion}\lesssim 10^{-3}$. Such low $U_{\rm ion}$ values are found in galaxies that are in an early assembly stage, and whose stars are still embedded in high-density natal clouds. However, the most luminous galaxy in our sample ($\rm{log}[L_{\rm{[OIII]}}/L_\odot] = 8.4$, $U_{\rm ion} \approx 0.1$) could be detected by ALMA in only $2.8$ hrs., 6 pages, 3 figures, Submitted to MNRAS (comments are welcome)

This paper reports our discovery of the most massive supercluster, termed the King Ghidorah Supercluster (KGSc), at $z=0.50-0.64$ in the Third Public Data Release of the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP PDR3) over 690 deg$^2$, as well as an initial result for a galaxy and dark matter mapping. The primary structure of the KGSc comprises triple broad weak-lensing (WL) peaks over 70 comoving Mpc. Such extensive WL detection at $z>0.5$ can only currently be achieved using the wide-field high-quality images produced by the HSC-SSP. The structure is also contiguous with multiple large-scale structures across a $\sim400$ comoving Mpc scale. The entire field has a notable overdensity ($\delta=14.7\pm4.5$) of red-sequence clusters. Additionally, large-scale underdensities can be found in the foreground along the line of sight. We confirmed the overdensities in stellar mass and dark matter distributions to be tightly coupled and estimated the total mass of the main structure to be $1\times10^{16}$ solar masses, according to the mock data analyses based on large-volume cosmological simulations. Further, upcoming wide-field multi-object spectrographs such as the Subaru Prime Focus Spectrograph may aid in providing additional insights into distant superclusters beyond the 100 Mpc scale., Comment: 5 pages, 5 figures, accepted for publication in MNRAS Letter

The discovery of faint FR~I radio jets in the nearby elliptical galaxy NGC 5322 is reported here using 144 MHz LOFAR image. The jets have an angular extent of $\sim40$ arcmin or a projected physical extent of $\sim350$ kpc. The faint jets remain well collimated and disappear in the intergalactic medium, without any visible hotspot or radio lobes. The jets detected up to $\sim20$ kpc extent at higher frequencies are relatively bright within the optical extent of the galaxy but become faint abruptly outside, where detection is made only in the LOFAR image. The total radio luminosity of the galaxy at 144 MHz is estimated to be $3.7(\pm0.4)\times10^{22}$ W Hz$^{-1}$. The 144 MHz radio luminosity of the faint jets outside the optical extent is estimated to be $7.1(\pm2.0)\times10^{21}$ W Hz$^{-1}$. The extent of the jets for its radio luminosity is abnormally large when compared to the general population of radio galaxies. It makes NGC 5322 a member of a rare population of radio galaxies, previously not detected in other radio surveys. A combined effect of stellar core depletion and low-density environment around the jets, inferred from previous studies in other wave-bands, resulting into weak entrainment of surrounding material to the jets could be responsible for its large size despite a low radio luminosity., Comment: MNRAS submitted; 5 pages, 4 figures; comments welcome

Primordial black holes (PBHs) formed in the early Universe constitute an attractive candidate for dark matter. Within the gaseous environment of the interstellar medium, PBHs with accretion disks naturally launch outflows such as winds and jets. PBHs with significant spin can sustain powerful relativistic jets and generate associated cocoons. Jets and winds can efficiently deposit their kinetic energies and heat the surrounding gas through shocks. Focusing on the Leo T dwarf galaxy, we demonstrate that these considerations can provide novel tests of PBHs over a significant $\sim 10^{-2} M_{\odot} - 10^6 M_{\odot}$ mass range, including the parameter space associated with gravitational wave observations by the LIGO and VIRGO Collaborations. Observing the morphology of emission could allow to distinguish between jet and wind contributions, and hence indirectly detect spinning PBHs., 10 pages, 4 figures

While the cosmic microwave background (CMB) dipole is largely assumed entirely kinematic, there appears evidence that a part of it is primordial. Such possibility arises in models implying a tilt, interpreted as a dark flow, across the observable Universe. The kinematic nature of the entire CMB dipole can be probed using the dipole of cosmic backgrounds from galaxies after the last scattering. The near-IR cosmic infrared background (CIB) spectral energy distribution leads to an amplified dipole compared to the CMB. The CIB dipole is affected by galaxy clustering, decreasing with fainter, more distant galaxies, and by Solar System emissions and Galactic dust, which dominate the net CIB cosmological dipole in the optical/near-IR. We propose a technique that enables an accurate measurement of the kinematic near-IR CIB dipole. The CIB, effectively the integrated galaxy light (IGL), would be reconstructed from resolved galaxies in the forthcoming space-borne wide surveys covering four bands 0.9 to 2.5 micron. The galaxies will be sub-selected from the identified magnitude range where the dipole component from galaxy clustering is below the expected kinematic dipole. Using this technique the dipole can be measured in each of the bands at the statistical signal-to-noise S/N>50--100 with the forthcoming Euclid and Roman surveys, isolating CMB dipole's kinematic nature., MNRAS Letters, in press

We compare the surface brightness profile and morphology of the Galactic Centre Excess (GCE) identified in wide-angle $\gamma$-ray maps from the Fermi-Large Area Telescope to dark matter annihilation predictions derived from high-resolution $\Lambda$CDM magnetohydrodynamic simulations of galaxy formation. These simulations produce isolated, disc-dominated galaxies with structure, stellar populations, gas content, and stellar and halo masses comparable to those of the Milky Way. For a specific choice of annihilation cross-section, they agree well with the Fermi-LAT data over the full observed angular range, $1^{\circ}$ to $15^{\circ}$, whereas their dark-matter only counterparts, lacking any compression of the inner halo by the gravitational effects of the baryons, fail to predict emission as centrally concentrated as observed. These results provide additional support to the hypothesis that the GCE is produced by annihilating dark matter. If, however, it is produced by a different mechanism, they imply a strong upper limit on annihilation rates which can be translated into upper limits on the expected $\gamma$-ray flux not only from the inner Galaxy but also from any substructure, with or without stars, in the Galactic halo., Comment: Accepted to MNRAS letters following minor revision

The cosmological constant is estimated by considering the surface tension of supervoids in a void-dominated cosmic fluid by which we can get a possible source of dark energy. Looking at voids as bubbles, we define the concept of surface tension which is shown to have an almost constant value for supervoids that are enclosed by superclusters. The surface tensions of voids are computed by dimensional method for galaxies and superclusters with different values for each group. At large scale which vast voids are dominant the positive cosmological constants obtained of order $ (\simeq+10^{-52} {\rm m^{-2}} )$, which are very close to those given by $Planck$., 5 pages, 3 figures, 1 table, Title and some figures have been correctedand, published version in MNRASL

A recently-proposed algorithm identifies voids in simulations as the regions associated with halos when the initial overdensity field is negated. We apply this method to the real Universe by running a suite of constrained simulations of the 2M++ volume with initial conditions inferred by the BORG algorithm, along with the corresponding inverted set. Our 101 inverted and uninverted simulations, spanning the BORG posterior, each identify ~150,000 "voids as antihalos" with mass exceeding $4.38\times10^{11} \: \mathrm{M_\odot}$ (100 particles) at $z=0$ in a full-sky sphere of radius 155 Mpc/h around the Milky Way. We calculate the size function, volume filling fraction, ellipticity, central density, specific angular momentum, clustering and stacked density profile of the voids, and cross-correlate them with those produced by VIDE on the same simulations. We make our antihalo and VIDE catalogues publicly available., 5 pages, 5 figures; minor revision, matches MNRASL accepted version

With a single training image and using wavelet phase harmonic augmentation, we present polarized Cosmic Microwave Background (CMB) foreground marginalization in a high-dimensional likelihood-free (Bayesian) framework. We demonstrate robust foreground removal using only a single frequency of simulated data for a BICEP-like sky patch. Using Moment Networks we estimate the pixel-level posterior probability for the underlying {E,B} signal and validate the statistical model with a quantile-type test using the estimated marginal posterior moments. The Moment Networks use a hierarchy of U-Net convolutional neural networks. This work validates such an approach in the most difficult limiting case: pixel-level, noise-free, highly non-Gaussian dust foregrounds with a single training image at a single frequency. For a real CMB experiment, a small number of representative sky patches would provide the training data required for full cosmological inference. These results enable robust likelihood-free, simulation-based parameter and model inference for primordial B-mode detection using observed CMB polarization data., Accepted by Monthly Notices of the Royal Astronomical Society Letters. 5 pages with 3 figures (plus 1 page of Supporting Materials with 2 figures)

We present a comparative study of the accuracy and precision of correlation function methods and full-field inference in cosmological data analysis. To do so, we examine a Bayesian hierarchical model that predicts log-normal fields and their two-point correlation function. Although a simplified analytic model, the log-normal model produces fields that share many of the essential characteristics of the present-day non-Gaussian cosmological density fields. We use three different statistical techniques: (i) a standard likelihood-based analysis of the two-point correlation function; (ii) a likelihood-free (simulation-based) analysis of the two-point correlation function; (iii) a field-level analysis, made possible by the more sophisticated data assimilation technique. We find that (a) standard assumptions made to write down a likelihood for correlation functions can cause significant biases, a problem that is alleviated with simulation-based inference; and (b) analysing the entire field offers considerable advantages over correlation functions, through higher accuracy, higher precision, or both. The gains depend on the degree of non-Gaussianity, but in all cases, including for weak non-Gaussianity, the advantage of analysing the full field is substantial., Comment: 6+8 pages, 4+5 figures. Matches MNRAS Letters published version. Appendices provide supplementary information, including calculations of Fisher matrices. Our code and data are publicly available at https://github.com/florent-leclercq/correlations_vs_field

Nested sampling is an important tool for conducting Bayesian analysis in Astronomy and other fields, both for sampling complicated posterior distributions for parameter inference, and for computing marginal likelihoods for model comparison. One technical obstacle to using nested sampling in practice is the requirement (for most common implementations) that prior distributions be provided in the form of transformations from the unit hyper-cube to the target prior density. For many applications - particularly when using the posterior from one experiment as the prior for another - such a transformation is not readily available. In this letter we show that parametric bijectors trained on samples from a desired prior density provide a general-purpose method for constructing transformations from the uniform base density to a target prior, enabling the practical use of nested sampling under arbitrary priors. We demonstrate the use of trained bijectors in conjunction with nested sampling on a number of examples from cosmology., 5 pages, 2 figures, Published as an MNRAS letter

The underlying geometri of spacetime algebra allows one to derive a force by contracting the relativistic generalization of angular momentum, M, with the mass-current, mw, where w is a proper 4-vector velocity. By applying this force to a cosmological object, a repulsive inverse distance-square law is found, which is proportional to the velocity dispersion squared of that structure. It is speculated if this finding may be relevant to the recent suggestion, that such a force may accelerate the expanding universe with no need for a cosmological constant., Comment: 4 pages, no figure, submitted to MNRAS

Recent measurements of the Cosmic Microwave Anisotropies power spectra measured by the Planck satellite show a preference for a closed universe at more than $99 \%$ Confidence Level. Such a scenario is however in disagreement with several low redshift observables, including luminosity distances of Type Ia Supernovae. Here we show that Interacting Dark Energy (IDE) models can ease the discrepancies between Planck and Supernovae Ia data in a closed Universe. Therefore IDE cosmologies remain as very appealing scenarios, as they can provide the solution to a number of observational tensions in different fiducial cosmologies. The results presented here strongly favour broader analyses of cosmological data, and suggest that relaxing the usual flatness and vacuum energy assumptions can lead to a much better agreement among theory and observations., 5 pages, 2 figures, Version accepted for publication in MNRAS letters

The NANOGrav pulsar timing array experiment reported evidence for a stochastic common-spectrum process affecting pulsar timing residuals in its 12.5-year dataset, which might be interpreted as the first detection of a stochastic gravitational wave background (SGWB). I examine whether the NANOGrav signal might be explained by an inflationary SGWB, focusing on the implications for the tensor spectral index $n_T$ and the tensor-to-scalar ratio $r$. Explaining NANOGrav while complying with upper limits on $r$ from BICEP2/Keck Array and Planck requires $r \gtrsim {\cal O}(10^{-6})$ in conjunction with an extremely blue tensor spectrum, $0.7 \lesssim n_T \lesssim 1.3$. After discussing models which can realize such a blue spectrum, I show that this region of parameter space can be brought in agreement with Big Bang Nucleosynthesis constraints for a sufficiently low reheating scale, $T_{\rm rh} \lesssim 100\,{\rm GeV}-1\,{\rm TeV}$. With the important caveat of having assumed a power-law parametrization for the primordial tensor spectrum, an inflationary interpretation of the NANOGrav signal is therefore not excluded., 5 pages, 2 figures. v2: revised conclusions, NANOGrav can in principle be due to an inflationary SGWB provided the reheating temperature is sufficiently (=very) low. References added, version accepted for publication in MNRAS Letters. Comments are welcome

GW190521 challenges our understanding of the late-stage evolution of massive stars and the effects of the pair-instability in particular. We discuss the possibility that stars at low or zero metallicity could retain most of their hydrogen envelope until the pre-supernova stage, avoid the pulsational pair-instability regime and produce a black hole with a mass in the mass gap by fallback. We present a series of new stellar evolution models at zero and low metallicity computed with the Geneva and MESA stellar evolution codes and compare to existing grids of models. Models with a metallicity in the range 0-0.0004 have three properties which favour higher BH masses as compared to higher metallicity models. These are (i) lower mass-loss rates during the post-MS phase, (ii) a more compact star disfavouring binary interaction and (iii) possible H-He shell interactions which lower the CO core mass. We conclude that it is possible that GW190521 may be the merger of black holes produced directly by massive stars from the first stellar generations. Our models indicate BH masses up to 70-75 Msun. Uncertainties related to convective mixing, mass loss, H-He shell interactions and pair-instability pulsations may increase this limit to ~85 Msun., Comment: 6 pages, 3 figures, accepted for publication in MNRAS Letters

Superclusters are a convenient way to partition and characterize the large scale structure of the Universe. In this Letter we explore the advantages of defining superclusters as watershed basins in the divergence velocity field. We apply this definition on diverse datasets generated from linear theory and N-body simulations, with different grid sizes, smoothing scales and types of tracers. From this framework emerges a linear scaling relation between the average supercluster size and the autocorrelation length in the divergence field, a result that holds for one order of magnitude from 10 Mpc/h up to 100 Mpc/h. These results suggest that the divergence-based definition provides a robust context to quantitatively compare results across different observational or computational frameworks. Through its connection with linear theory, it can also facilitate the exploration of how supercluster properties depend on cosmological parameters, paving the way to use superclusters as cosmological probes., 5 pages, 6 figures, accepted for publication in MNRAS Letters

We suggest a crucial direct-observational test for measuring distinction between the standard $\Lambda$CDM model and recently proposed phantom dark energy positive curvature cosmological model. The test is based on the fundamental distance--flux--redshift relation for general Friedmann models. It does not depend on the CMBR data, on the large-scale structure growth models, and also on the value of the Hubble constant $H_0$. Our crucial test can be performed by future gamma-ray burst observations with THESEUS space mission and by using gravitational-wave standard siren observations with modern advanced LIGO--Virgo and also forthcoming LISA detectors., Comment: 4 pages, 1 figure, MNRAS accepted 18.09.2020

The covariant scale-invariant dynamics (SID) theory has recently been proposed as a possible explanation for the observed dynamical discrepancies in galaxies (Maeder & Gueorguiev 2020). SID implies that these discrepancies $-$ commonly attributed to dark matter $-$ arise instead from a non-standard velocity-dependent force that causes two-body near-Keplerian orbits to expand. We show that the predicted expansion of the Earth-Moon orbit is incompatible with lunar laser ranging data at $>200��$. Moreover, SID predicts that the gravitating mass of any object was much smaller in the past. If true, a low-mass red giant star must be significantly older than in standard theory. This would make it much older than the conventional age of the Universe, which however is expected to be similarly old in SID. Moreover, it is not completely clear whether SID truly contains new physics beyond General Relativity, with several previous works arguing that the extra degree of freedom is purely mathematical. We conclude that the SID model is falsified at high significance by observations across a range of scales, even if it is theoretically well formulated., 5 pages, no figures, 1 table. Accepted for publication in the Monthly Notices of the Royal Astronomical Society Letters in this form

We study the 21-cm differential brightness temperature in the presence of primordial helical magnetic fields for redshift $z=10-30$. We argue that the $\alpha$-effect that sets in at earlier time can be helpful in lowering the gas temperature to 3.2 degrees Kelvin at $z=17$. This effect can arise in the early Universe due to some parity violating high energy processes. Using the EDGES (Experiment to Detect the Global Epoch of Reionization Signature) results, we find the upper and lower limits on the primordial magnetic field to be $6\times 10^{-3}~{\rm nG} $ & $5\times 10^{-4}~{\rm nG}$ respectively. We also discuss the effect of Ly$\alpha$ background on the bounds. Our results do not require any new physics in terms of dark matter., Comment: Accepted for publication in MNRAS Letters, 5 pages, 4 figures

Observations of large-scale radio emissions prove the existence of shock accelerated cosmic-ray electrons in galaxy clusters, while the lack of detected $\gamma$-rays limits the acceleration of cosmic-ray protons in galaxy clusters. This challenges our understanding of how diffusive shock acceleration works. In this work, we couple the most updated recipes for shock acceleration in the intracluster medium to state-of-the-art magneto-hydrodynamical simulations of massive galaxy clusters. Furthermore, we use passive tracer particles to follow the evolution of accelerated cosmic-rays. We show that when the interplay between magnetic field topology and the feedback from accelerated cosmic rays is taken into account, the latest developments of particle acceleration theory give results which are compatible with observational constraints., Comment: published by Monthly Notices of the Royal Astronomical Society: Letters, 6 pages, 4 figures

The Fe K_\alpha fluorescent line at 6.4 keV is a powerful probe of the space-time metric in the vicinity of accreting compact objects. We investigated here how some alternative theories of gravity, namely Scalar tensor Theories, that invoke the presence of a non-minimally coupled scalar field and predict the existence of strongly scalarized neutron stars, change the expected line shape with respect to General Relativity. By taking into account both deviations from the general relativistic orbital dynamics of the accreting disk, where the Fe line originates, and the changes in the light propagation around the neutron star, we computed line shapes for various inclinations of the disk with respect to the observer. We found that both the intensity of the low energy tails and the position of the high energy edge of the line change. Moreover we verified that even if those changes are in general of the order of a few percent, they are potentially observable with the next generation of X-ray satellites., Comment: 5 pages, 4 figures, accepted for publication in MNRAS

Fluctuations in sky maps of the galaxy redshifts, dubbed as angular redshift fluctuations (ARF), contain precise information about the growth rate of structures and the nature of gravity in the Universe. Specifically, ARF constrain the combination of cosmological parameters $H/H_0\,f\sigma_8(z)$, while being an intrinsically tomographic probe and largely insensitive to many observational systematic errors, all this without requiring the assumption of any redshift-to-distance relation under a given fiducial cosmology. We present the first cosmological constraints derived from ARF by using BOSS LOWZ+CMASS DR12 galaxy samples, obtaining 7\%-accurate constraints on $H/H_0 f\sigma_8(z)$ at more than 20 redshifts over the range $z \in [0.26,0.72]$. Our best-fitting value is $10\%$ larger, but compatible at the $1.4\sigma$ level, than the $\Lambda$CDM expectation set by {\it Planck} observations of the Cosmic Microwave Background (CMB) radiation. Our tomographic measurements, combined with these CMB data, provides one of the strongest constraints on the gravity index $\gamma$, $\gamma=0.44^{+0.09}_{-0.07}$, which lies within $2\sigma$ from the prediction of General Relativity ($\gamma_{\rm GR}\simeq 0.55$)., Comment: 5 pages, 3 figures, matches accepted version in MNRAS letters

We present the conditional HI (neutral hydrogen) Mass Function (HIMF) conditioned on observed optical properties, $M_{\text{r}}$ ($r$-band absolute magnitude) and $C_{\text{ur}}$ ($u-r$ color), for a sample of 7709 galaxies from ALFALFA (40% data release - $\alpha.40$) which overlaps with a common volume in SDSS DR7. Based on the conditional HIMF we find that the luminous red, luminous blue and faint blue populations dominate the total HIMF at the high-mass end, knee and the low-mass end respectively. We use the conditional HIMF to derive the underlying distribution function of $\Omega_{\text{HI}}$ (HI density parameter), $p(\Omega_{\text{HI}})$, in the color-magnitude plane of galaxies. The distribution, $p(\Omega_{\text{HI}})$, peaks in the blue cloud at $M_{\text{r}}^{\text{max}}=$ $-19.25, C_{\text{ur}}^{\text{max}}=1.44$ but is skewed. It has a long tail towards faint blue galaxies and luminous red galaxies. We argue that $p(\Omega_{\text{HI}})$ can be used to reveal the underlying relation between cold gas, stellar mass and the star formation rate (SFR) in an unbiased way; that is the derived relation does not suffer from survey or sample selection., Comment: 5 pages, 3 figures, accepted for publication in MNRAS Letters

We present a semi-analytical description of the relative HD/H2 abundance in the diffuse interstellar medium. We found three asymptotics of the relative HD/H$_2$ abundance for different parts of the medium and their dependence on the physical parameters, namely, number density, intensity of the ultraviolet field, cosmic-ray ionization rate and metallicity. Our calculations are in a good agreement with the full network calculations using Meudon PDR code. We found that in the case of low metallicity and/or higher cosmic ray ionization rate, HD formation rate is significantly enhanced, HD/H2 ratio increases, and the DI/HD transition occurs at a lower penetration depth of UV radiation than the HI/H$_2$ transition. This can explain the observed difference in the HD/H$_2$ abundance between the local and high-redshift measurements., 5 pages, 3 figures, accepted for publication in MNRAS letters

In this letter we present constraints on the scale-dependent "local" type primordial non-Gaussianity, which is described by non-Gaussianity's spectral index $n_{\rm NG}$, from the NRAO VLA Sky Survey and the quasar catalog of the Sloan Digital Sky Survey (SDSS) Data Release 6, together with the SDSS Data Release 12 photo-z sample. Here, we use the auto-correlation analyses of these three probes and their cross-correlation analyses with the cosmic microwave background (CMB) temperature map, and obtain the tight constraint on the spectral index: $n_{\rm NG}=0.2 ^{+0.7}_{-1.0}$ ($1\,\sigma$ C.L.), which shows the first competitive constraint on the running of non-Gaussianity from current large-scale structure clustering data. Furthermore, we also perform the forecast calculations and improve the limit of $n_{\rm NG}$ using the future Euclid mission, and obtain the standard deviation at 68\% confidence level: $\Delta n_{\rm NG}=1.74$ when considering the fiducial value $f_{\rm NL}=3$, which provides the complementary constraining power to those from the CMB bispectrum information., Comment: 6 pages, 2 figures. Accepted by MNRAS Letters

The dwarf satellite galaxies of the Milky Way Crater II and Antlia II have uncommonly low dynamical mass densities, due to their large size and low velocity dispersion. Previous work have failed to identify formation scenarios within the $\Lambda$CDM framework and have invoked cored dark matter haloes, processed by tides. I show that the tidal evolution of $\Lambda$CDM NFW haloes is richer than previously recognised: tidal heating causes the innermost regions of haloes that fall short of the mass-concentration relation to expand significantly, resulting in the formation of giant, kinematically cold satellites like Crater II and Antlia II. Furthermore, while the satellite is reaching apocenter, extra-tidal material can cause an even more inflated appearance. When present, as likely for the larger Antlia II, nominally unbound material can be recognised thanks to its somewhat hotter kinematics and line-of-sight velocity gradient. Contrary to other formation scenarios, Crater II and Antlia II may well have experienced very little mass loss, as in fact hinted by their observed metallicity. If indeed a satellite of NGC1052, tidal evolution of a low-concentration halo may similarly have led to the formation of NGC1052-DF2., Comment: MNRAS Letters submitted, comments welcome

An observer stationary with respect to comoving coordinates of the expanding universe should find the redshift distribution to be isotropic. However, a peculiar motion of the observer would introduce a dipole anisotropy in the observed redshift distribution. Conversely, a dipole anisotropy in observed redshift distribution could be exploited to infer our peculiar motion, or rather of our solar system. We determine here our peculiar velocity by studying the dipole anisotropy in the redshift distribution of a large sample of quasars. The magnitude of the peculiar velocity thus determined turns out to be $2350\pm280$ km s$^{-1}$, not only much larger than 370 km s$^{-1}$ determined from the dipole anisotropy in the Cosmic Microwave Background Radiation (CMBR), but also nearly in an opposite direction. Such large values for peculiar velocity have been found in a couple of radio surveys too, but with a direction along the CMBR dipole. Large genuine differences in the inferred motion, whether in magnitude or direction, are rather disconcerting since a solar peculiar velocity should not depend upon the method of its determination. Such discordant dipoles imply perhaps an anisotropic universe, violating the cosmological principle, a cornerstone of the modern cosmology., Comment: 5 pages, 3 figures, 2 tables, accepted in MNRAS

We investigate the impact of dynamical streams and substructure on estimates of the local escape speed and total mass of Milky Way-mass galaxies from modelling the high velocity tail of local halo stars. We use a suite of high-resolution, magneto-hydrodynamical cosmological zoom-in simulations, which resolve phase space substructure in local volumes around solar-like positions. We show that phase space structure varies significantly between positions in individual galaxies and across the suite. Substructure populates the high velocity tail unevenly and leads to discrepancies in the mass estimates. We show that a combination of streams, sample noise and truncation of the high velocity tail below the escape speed leads to a distribution of mass estimates with a median that falls below the true value by $\sim 20 \%$, and a spread of a factor of 2 across the suite. Correcting for these biases, we derive a revised value for the Milky Way mass presented in Deason et al. of $1.29 ^{+0.37}_{-0.47} \times 10^{12}$ $\rm M_{\odot}$., Accepted to the Monthly Notices of the Royal Astronomical Society, Letters, with minor revision

We present an independent cosmic shear analysis of the non-cosmological B-mode distortions within the public first year data from the Dark Energy Survey (DES). We find no significant detection of B-modes in a full tomographic analysis of the primary METACALIBRATION shear catalogue. This is in contrast to the secondary IM3SHAPE shear catalogue, where we detect B- modes at a significance of $\sim 3\sigma$ with a pattern that is consistent with the B-mode signature of a repeating additive shear bias across the survey. We use the COSEBIs statistic to cleanly separate the B-modes from the gravitational lensing signal (E-modes). We find good agreement between the measured E-modes and their theoretical expectation given the DES cosmological parameter constraints., Comment: 5 Pages, 2 Figures

We present a novel method to compress galaxy clustering three-point statistics and apply it to redshift space galaxy bispectrum monopole measurements from BOSS DR12 CMASS data considering a $k$-space range of $0.03-0.12\,h/\mathrm{Mpc}$. The method consists in binning together bispectra evaluated at sets of wave-numbers forming closed triangles with similar geometrical properties: the area, the cosine of the largest angle and the ratio between the cosines of the remaining two angles. This enables us to increase the number of bispectrum measurements for example by a factor of $23$ over the standard binning (from 116 to 2734 triangles used), which is otherwise limited by the number of mock catalogues available to estimate the covariance matrix needed to derive parameter constraints. The $68\%$ credible intervals for the inferred parameters $\left(b_1,b_2,f,\sigma_8\right)$ are thus reduced by $\left(-39\%,-49\%,-29\%,-22\%\right)$, respectively. We find very good agreement with the posteriors recently obtained by alternative maximal compression methods. This new method does not require the a-priori computation of the data-vector covariance matrix and has the potential to be directly applicable to other three-point statistics (e.g. glaxy clustering, weak gravitational lensing, 21 cm emission line) measured from future surveys such as DESI, Euclid, PFS and SKA., Comment: 5 pages, 2 figures, Accepted by MNRAS: Letters

We examine the case of a random isotropic velocity field, in which one of the velocity components (the "radial" component, with magnitude $v_z$) can be measured easily, while measurement of the velocity perpendicular to this component (the "transverse" component, with magnitude $v_T$) is more difficult and requires long-time monitoring. Particularly important examples are the motion of galaxies at cosmological distances and the interpretation of Gaia data on the proper motion of stars in globular clusters and dwarf galaxies. We address two questions: what is the probability distribution of $v_T$ for a given $v_z$, and for what choice of $v_z$ is the expected value of $v_T$ maximized? We show that, for a given $v_z$, the probability that $v_T$ exceeds some value $v_0$ is $p(v_T \ge v_0 | v_z) = {p_z(\sqrt{v_0^2 + v_z^2}})/{p_z(v_z)}$, where $p_z(v_z)$ is the probability distribution of $v_z$. The expected value of $v_T$ is maximized by choosing $v_z$ as large as possible whenever $\ln p_z(\sqrt{v_z})$ has a positive second derivative, and by taking $v_z$ as small as possible when this second derivative is negative., Comment: 6 pages, 4 figures, references and discussion added

Carbon enhanced metal poor (CEMP) stars with low abundances of neutron capture elements (CEMP-no stars) are ubiquitous among metal poor stars in the Milky Way. Recent observations have uncovered their two subgroups that differ in the carbon to magnesium ([C/Mg]) abundance ratio. Here we demonstrate that similar abundance patterns are also present in Milky Way-like galaxies in the EAGLE cosmological hydrodynamical simulation, where these patterns originate from the fact that stars may form from gas enriched predominantly by asymptotic giant branch (AGB) stars or by type-II supernovae. This occurs when stars form in the poorly mixed interstellar medium of Milky Way progenitor galaxies that are undergoing bursty star formation. The CEMP-no stars with lower [C/Mg] form at the onset of a starburst from gas enriched by low metallicity type-II supernovae that power a strong outflow, quenching further star formation. When star formation resumes following cosmological gas accretion, the CEMP-no stars with higher [C/Mg] form, with enrichment by AGB ejecta evident in their higher abundance of barium and lower abundance of magnesium. This suggests that bursty star formation in the progenitors of the Galaxy leaves a permanent imprint in the abundance patterns of CEMP stars., 5 pages, 4 figures, Accepted in MNRAS letters, Comments Welcome

Elucidating the particle physics nature of dark matter (DM) is one of the great challenges in modern science. The current lack of any direct DM detections in the laboratory heightens the need for astrophysical constraints, extending the search to DM models beyond the popular weakly interacting massive particle (WIMP) scenario. We here apply the classical Rees-Ostriker-Silk cooling criterion for galaxy formation to models with ultralight axion DM, also known as fuzzy dark matter (FDM). The resulting constraints provide a heuristic framework for upcoming observations, and our approximate analysis motivates the need for future, self-consistent simulations of FDM structure formation. We use observational constraints for the DM hosts of ultra faint dwarf (UFD) galaxies in the Local Group, together with the redshift constraints for the onset of primordial star formation from the recent EDGES 21-cm cosmology measurement, to illustrate this approach. We find that the existing constraints are straightforward to reconcile with standard $\Lambda$CDM, but disfavour FDM axion masses below $\sim 10^{-21}\,{\rm eV}/c^2$. The future potential for harnessing astrophysical probes of DM particle physics is compelling., Comment: 5 pages, 2 figures, MNRAS Letters: in press

NGC1052-DF2 was recently discovered as the dark-matter deficient galaxy claimed by van Dokkum et al. (2018a, vD18). However, large uncertainties on its dynamical mass estimate have been pointed out, concerning the paucity of sample, statistical methods and distance measurements. In this work, we discuss the effects of the difference in modeling of the tracer profile of this galaxy on the dynamical mass estimate. To do this, we assume that the tracer densities are modeled with power-law and S\'ersic profiles, and then we solve the spherical Jeans equation to estimate the dynamical mass. Applying these models to kinematic data of globular clusters in NGC1052-DF2, we compare 90 per cent upper limits of dynamical mass-to-light ratios estimated between from this analysis and from vD18. We find that the upper limit obtained by the power-law is virtually the same as the result from vD18, whilst this limit estimated by the S\'ersic is significantly greater than that from vD18, thereby suggesting that NGC1052-DF2 can still be a dark-matter dominated system. Consequently, we propose that dynamical mass estimate of a galaxy is largely affected by not only small kinematic sample but the choice of tracer distributions, and thus the estimated mass still remains quite uncertain., Comment: 5 pages, 3 figures and 2 tables, Accepted for publication in MNRAS Letters

The recent detection of the sky-averaged 21-cm cosmological signal indicates a stronger absorption than the maximum allowed value based on the standard model. One explanation for the required colder primordial gas is the energy transfer between the baryon and dark matter fluids due to non-gravitational scattering. Here, we explore the thermal evolution of primordial gas, collapsing to form Population III (Pop III) stars, when this energy transfer is included. Performing a series of one-zone calculations, we find that the evolution results in stars more massive than in the standard model, provided that the dark matter is described by the best-fit parameters inferred from the 21-cm observation. On the other hand, a significant part of the dark matter parameter space can be excluded by the requirement to form massive Pop III stars sufficiently early in cosmic history. Otherwise, the radiation background needed to bring about the strong Wouthuysen-Field coupling at z >~ 17, inferred to explain the 21-cm absorption feature, could not be builtup. Intriguingly, the independent constraint from the physics of first star formation at high densities points to a similarly narrow range in dark matter properties. This exploratory study has to be followed-up with self-consistent three-dimensional simulations for a more rigorous derivation., 5 pages, 4 figures, accepted to MNRASL

We introduce a new diagnostic for exploring the link between angular momentum and local gravitational instability in galaxy discs. Our diagnostic incorporates the latest developments in disc instability research, is fully consistent with approximations that are widely used for measuring the stellar specific angular momentum, $j_{\star}=J_{\star}/M_{\star}$, and is also very simple. We show that such a disc instability diagnostic hardly correlates with $j_{\star}$ or $M_{\star}$, and is remarkably constant across spiral galaxies of any given type (Sa$\!-\!$Sd), stellar mass ($M_{\star}=10^{9.5}\!-\!10^{11.5}\,\mathrm{M}_{\odot}$) and velocity dispersion anisotropy ($\sigma_{z\star}/\sigma_{R\star}=0\!-\!1$). The fact that $M_{\star}$ is tightly correlated with star formation rate ($\mathrm{SFR}$), molecular gas mass ($M_{\mathrm{mol}}$), metallicity ($12+\log\mathrm{O/H}$) and other fundamental galaxy properties thus implies that nearby star-forming spirals self-regulate to a quasi-universal disc stability level. This proves the existence of the self-regulation process postulated by several star formation models, but also raises important caveats., Comment: MNRAS Letters, in press. Minor revision to match the accepted version (added Fig. 1, Sect. 3.2, the final paragraph of Sect. 4, references and clarifications)

Recent numerical simulations reveal that the isothermal collapse of pristine gas in atomic cooling haloes may result in stellar binaries of supermassive stars with $M_* \gtrsim 10^4\ \mathrm{M}_{\odot}$. For the first time, we compute the in-situ merger rate for such massive black hole remnants by combining their abundance and multiplicity estimates. For black holes with initial masses in the range $10^{4-6} \ \mathrm{M}_{\odot}$ merging at redshifts $z \gtrsim 15$ our optimistic model predicts that LISA should be able to detect 0.6 mergers per year. This rate of detection can be attributed, without confusion, to the in-situ mergers of seeds from the collapse of very massive stars. Equally, in the case where LISA observes no mergers from heavy seeds at $z \gtrsim 15$ we can constrain the combined number density, multiplicity, and coalesence times of these high-redshift systems. This letter proposes gravitational wave signatures as a means to constrain theoretical models and processes that govern the abundance of massive black hole seeds in the early Universe., Accepted for publication in MNRAS: Letters

Observations of high-redshift Type Ia supernovae (SNe~Ia) are used to study the cosmic transparency at optical wavelengths. Assuming a flat $\Lambda$CDM cosmological model based on BAO and CMB results, redshift dependent deviations of SN~Ia distances are used to constrain mechanisms that would dim light. The analysis is based on the most recent Pantheon SN compilation, for which there is a $0.03\pm0.01 {\textrm \,(\rm stat)}$ mag discrepancy in the distant supernova distance moduli relative to the $\Lambda$CDM model anchored by supernovae at $z, Comment: Letter accepted for publication in MNRAS

Gradient pattern analysis (GPA) is a well-established technique for measuring gradient bilateral asymmetries of a square numerical lattice. This paper introduces an improved version of GPA designed for galaxy morphometry. We show the performance of the new method on a selected sample of 54,896 objects from the SDSS-DR7 in common with Galaxy Zoo 1 catalog. The results suggest that the second gradient moment, G2, has the potential to dramatically improve over more conventional morphometric parameters. It separates early from late type galaxies better (\sim 90\%) than the CAS system (C \sim 79\%, A \sim 50\%, S \sim 43\%) and a benchmark test shows that it is applicable to hundreds of thousands of galaxies using typical processing systems., 5 pages, 4 figures. Accepted for publication in MNRAS

We present a fast numerical screened halo model algorithm (CHAM) for modeling non-linear power spectrum for the alternative models to LCDM. This method has three obvious advantages. First of all, it is not being restricted to a specific dark energy/modified gravity model. In principle, all of the screened scalar-tensor theories can be applied. Second, the least assumptions are made in the calculation. Hence, the physical picture is very easily understandable. Third, it is very predictable and does not rely on the calibration from N-body simulation. As an example, we show the case of Hu-Sawicki f(R) gravity. In this case, the typical CPU time with the current parallel Python script (8 threads) is roughly within $10$ minutes. The resulting spectra are in a good agreement with N-body data within a few percentage accuracy up to k~1 h/Mpc., Python script is publicly available at https://github.com/hubinitp/CHAM

Wave dark matter ($\psi \rm{DM}$) composed of extremely light bosons ($m_{\psi} \sim 10^{-22}\,\rm eV$), with quantum pressure suppressing structures below a kpc-scale de Broglie wavelength, has become a viable dark matter candidate. Compared to the conventional free-particle $\psi {\rm DM}$ (${\rm FP} \psi {\rm DM}$), the extreme-axion $\psi \rm{DM}$ model (${\rm EA} \psi {\rm DM}$) proposed by Zhang & Chiueh (2017) features a larger cut-off wavenumber and a broad spectral bump in the matter transfer function. Here we conduct cosmological simulations to compare the halo abundances and assembly histories at $z=4-11$ between three different scenarios: ${\rm FP} \psi {\rm DM}$, ${\rm EA} \psi {\rm DM}$, and cold dark matter (CDM). We show that ${\rm EA} \psi {\rm DM}$ produces significantly more abundant low-mass haloes than ${\rm FP} \psi {\rm DM}$ with the same $m_{\psi}$, and therefore could alleviate the tension in $m_{\psi}$ required by the Ly$\alpha$ forest data and by the kpc-scale dwarf galaxy cores. We also find that, compared to the CDM counterparts, massive ${\rm EA} \psi {\rm DM}$ haloes are on average $3-4$ times more massive at $z=10-11$ due to their earlier formation, undergo a slower mass accretion at $7 \lesssim z \lesssim 11$, and then show a rapidly rising major merger rate exceeding CDM by $\sim 50\%$ at $4 \lesssim z \lesssim 7$. This fact suggests that ${\rm EA} \psi {\rm DM}$ haloes may exhibit more prominent starbursts at $z \lesssim 7$., Comment: 5 pages, 4 figures, only minor updates (accepted for publication in MNRAS letters)

We investigate the evolution of the dark matter density profiles of the most massive galaxy clusters in the Universe. Using a `zoom-in' procedure on a large suite of cosmological simulations of total comoving volume of $3\,(h^{-1}\,\rm Gpc)^3$, we study the 25 most massive clusters in four redshift slices from $z\sim 1$ to the present. The minimum mass is $M_{500} > 5.5 \times 10^{14}$ M$_{\odot}$ at $z=1$. Each system has more than two million particles within $r_{500}$. Once scaled to the critical density at each redshift, the dark matter profiles within $r_{500}$ are strikingly similar from $z\sim1$ to the present day, exhibiting a low dispersion of 0.15 dex, and showing little evolution with redshift in the radial logarithmic slope and scatter. They have the running power law shape typical of the NFW-type profiles, and their inner structure, resolved to $3.8\,h^{-1}$ comoving kpc at $z=1$, shows no signs of converging to an asymptotic slope. Our results suggest that this type of profile is already in place at $z>1$ in the highest-mass haloes in the Universe, and that it remains exceptionally robust to merging activity., 5 pages, 5 figures. Accepted by MNRAS Letters

When it comes to searches for extensions to general relativity, large efforts are being dedicated to accurate predictions for the power spectrum of density perturbations. While this observable is known to be sensitive to the gravitational theory, its efficiency as a diagnostic for gravity is significantly reduced when Solar System constraints are strictly adhered to. We show that this problem can be overcome by studying weigthed density fields. We propose a transformation of the density field for which the impact of modified gravity on the power spectrum can be increased by more than a factor of three. The signal is not only amplified, but the modified gravity features are shifted to larger scales which are less affected by baryonic physics. Furthermore, the overall signal-to-noise increases, which in principle makes identifying signatures of modified gravity with future galaxy surveys more feasible. While our analysis is focused on modified gravity, the technique can be applied to other problems in cosmology, such as the detection of neutrinos, the effects of baryons or baryon acoustic oscillations., 5 pages, 1 figure. Submitted to MNRAS Letters

We present a newly discovered correlation between the wind outflow velocity and the X-ray luminosity in the luminous ($L_{\rm bol}\sim10^{47}\,\rm erg\,s^{-1}$) nearby ($z=0.184$) quasar PDS\,456. All the contemporary XMM-Newton, NuSTAR and Suzaku observations from 2001--2014 were revisited and we find that the centroid energy of the blueshifted Fe\,K absorption profile increases with luminosity. This translates into a correlation between the wind outflow velocity and the hard X-ray luminosity (between 7--30\,keV) where we find that $v_{\rm w}/c \propto L_{7-30}^{\gamma}$ where $\gamma=0.22\pm0.04$. We also show that this is consistent with a wind that is predominately radiatively driven, possibly resulting from the high Eddington ratio of PDS\,456., Comment: 5 pages, 3 figures. Accepted for publication in MNRAS Letter

Combining measurements on the expansion history of the Universe and on the growth rate of cosmic structures is key to discriminate between alternative cosmological frameworks and to test gravity. Recently, Linder (2017) proposed a new diagram to investigate the joint evolutionary track of these two quantities. In this letter, we collect the most recent cosmic growth and expansion rate datasets to provide the state-of-the-art observational constraints on this diagram. By performing a joint statistical analysis of both probes, we test the standard $\Lambda$CDM model, confirming a mild tension between cosmic microwave background predictions from Planck mission and cosmic growth measurements at low redshift ($z1$ will be crucial to discriminate between alternative models., Comment: 5 pages, 3 figures. Accepted for publication in MNRAS letter