Reconciling radio relic observations and simulations: The NVSS sample

The diffusive shock acceleration scenario is usually invoked to explain radio relics, although the detailed driving mechanism is still a matter of debate. Our aim is to constrain models for the origin of radio relics by comparing observed relic samples with simulated ones. Here we present a framework to homogeneously extract the whole sample of known radio relics from NVSS so that it can be used for comparison with cosmological simulations. In this way, we can better handle intrinsic biases in the analysis of the radio relic population. In addition, we show some properties of the resulting NVSS sample relics such as the correlation between relic shape and orientation with respect to the cluster. Also, we briefly discuss the typical relic surface brightness and its relation to projected cluster distance and relic angular sizes

Kinematics of the Local Group gas and galaxies in the Hestia simulations

The Local Group (LG) consists of two giant spiral galaxies, the Milky Way (MW) and Andromeda (M31), and several smaller galaxies. The MW and M31 are approaching each other at a radial velocity of about $-109\,$km\,s$^{-1}$. Observational evidence suggests that there is an overall infalling motion of gas and galaxies in the LG, dominated by the dynamics of its two main members. From our perspective, this flow imprints a velocity dipole pattern in the sky when Galactic rotation is removed. We investigate the kinematic properties of gas and galaxies in the LG using a suite of high-resolution simulations performed by the {\sc Hestia} (High-resolution Environmental Simulations of The Immediate Area) collaboration. Our simulations include the correct cosmography surrounding LG-like regions. We build sky maps from the local, Galactic and LG standard of rest reference frames. Our findings show that the establishment of a radial velocity dipole near the preferred barycentre direction is a natural outcome of simulation kinematics for material \textit{outside} the MW virial radius after removing galaxy rotation when the relative radial velocity of MW and M31 is similar to the observed value. These results favour a scenario where gas and galaxies stream towards the LG barycentre, producing the observed velocity dipole.Comment: 3 pages, 3 figures. To appear in the 64th Bulletin of the Argentine Astronomical Society. arXiv admin note: substantial text overlap with arXiv:2210.1558

Cosmological gas accretion history onto the stellar discs of Milky Way-like galaxies in the Auriga simulations -- (I) Temporal dependency

We use the 30 simulations of the Auriga Project to estimate the temporal dependency of the inflow, outflow and net accretion rates onto the discs of Milky Way-like galaxies. The net accretion rates are found to be similar for all galaxies at early times, increasing rapidly up to $\sim 10~\mathrm{M}_\odot \, \mathrm{yr}^{-1}$. After $\sim 6~\mathrm{Gyr}$ of evolution, however, the net accretion rates are diverse: in most galaxies, these exhibit an exponential-like decay, but some systems instead present increasing or approximately constant levels up to the present time. An exponential fit to the net accretion rates averaged over the MW analogues yields typical decay time-scale of $7.2~\mathrm{Gyr}$. The analysis of the time-evolution of the inflow and outflow rates, and their relation to the star formation rate (SFR) in the discs, confirms the close connection between these quantities. First, the inflow$/$outflow ratio stays approximately constant, with typical values of $\dot{M}_\mathrm{out}/ \dot{M}_\mathrm{in} \sim 0.75$, indicating that the gas mass involved in outflows is of the order of 25% lower compared to that involved in inflows. A similar behaviour is found for the SFR$/$inflow rate ratio, with typical values between 0.1 and 0.3, and for the outflow rate$/$SFR which varies in the range $3.5$--$5.5$. Our results show that continuous inflow is key to the SFR levels in disc galaxies, and that the star formation activity and the subsequent feedback in the discs is able to produce mass-loaded galaxy winds in the disc-halo interface.Comment: 21 pages, 15 figure

The three hundred project: thermodynamical properties, shocks and gas dynamics in simulated galaxy cluster filaments and their surroundings

Using cosmological simulations of galaxy cluster regions from The Three Hundred project we study the nature of gas in filaments feeding massive clusters. By stacking the diffuse material of filaments throughout the cluster sample, we measure average gas properties such as density, temperature, pressure, entropy and Mach number and construct one-dimensional profiles for a sample of larger, radially-oriented filaments to determine their characteristic features as cosmological objects. Despite the similarity in velocity space between the gas and dark matter accretion patterns onto filaments and their central clusters, we confirm some differences, especially concerning the more ordered radial velocity dispersion of dark matter around the cluster and the larger accretion velocity of gas relative to dark matter in filaments. We also study the distribution of shocked gas around filaments and galaxy clusters, showing that the surrounding shocks allow an efficient internal transport of material, suggesting a laminar infall. The stacked temperature profile of filaments is typically colder towards the spine, in line with the cosmological rarefaction of matter. Therefore, filaments are able to isolate their inner regions, maintaining lower gas temperatures and entropy. Finally, we study the evolution of the gas density-temperature phase diagram of our stacked filament, showing that filamentary gas does not behave fully adiabatically through time but it is subject to shocks during its evolution, establishing a characteristic z = 0, entropy-enhanced distribution at intermediate distances from the spine of about 1 - 2 $h^{-1}$ Mpc for a typical galaxy cluster in our sample.Comment: 16 pages, 13 figures. Accepted for publication in MNRA

Photometric and clustering properties of hydrodynamical galaxies in a cosmological volume: results at z=0

In this work, we present results for the photometric and clustering properties of galaxies that arise in a LambdaCDM hydrodynamical simulation of the local universe. The present-day distribution of matter was constructed to match the observed large scale pattern of the IRAS 1.2-Jy galaxy survey. Our simulation follows the formation and evolution of galaxies in a cosmological sphere with a volume of ~130^3 (Mpc/h)^3 including supernova feedback, galactic winds, photoheating due to an uniform meta-galactic background and chemical enrichment of the gas and stellar populations. However, we do not consider AGNs. In the simulation, a total of ~20000 galaxies are formed above the resolution limit, and around 60 haloes are more massive than ~10^14 M_sun. Luminosities of the galaxies are calculated based on a stellar population synthesis model including the attenuation by dust, which is calculated from the cold gas left within the simulated galaxies. Environmental effects like colour bi-modality and differential clustering power of the hydrodynamical galaxies are qualitatively similar to observed trends. Nevertheless, the overcooling present in the simulations lead to too blue and overluminous brightest cluster galaxies (BCGs). To overcome this, we mimic the late-time suppression of star formation in massive halos by ignoring recently formed stars with the aid of a simple post-processing recipe. In this way we find luminosity functions, both for field and group/cluster galaxies, in better agreement with observations. Specifically, the BCGs then follow the observed luminosity-halo mass relation. However, in such a case, the colour bi-modality is basically lost, pointing towards a more complex interplay of late suppression of star formation than what is given by the simple scheme adopted.Comment: Typos corrected. Replaced to match published version. 12 pages, 12 figures. To appear in MNRA

Cosmic Structure and Dynamics of the Local Universe

We present a cosmography analysis of the Local Universe based on the recently released Two-Micron All-Sky Redshift Survey (2MRS). Our method is based on a Bayesian Networks Machine Learning algorithm (the Kigen-code) which self-consistently samples the initial density fluctuations compatible with the observed galaxy distribution and a structure formation model given by second order Lagrangian perturbation theory (2LPT). From the initial conditions we obtain an ensemble of reconstructed density and peculiar velocity fields which characterize the local cosmic structure with high accuracy unveiling nonlinear structures like filaments and voids in detail. Coherent redshift space distortions are consistently corrected within 2LPT. From the ensemble of cross-correlations between the reconstructions and the galaxy field and the variance of the recovered density fields we find that our method is extremely accurate up to k ~ 1 h Mpc^-1 and still yields reliable results down to scales of about 3-4 h^-1 Mpc. The motion of the local group we obtain within ~ 80 h^-1 Mpc (v_LG=522+-86 km s^-1, l_LG=291^o +- 16^o, b_LG=34^o+-8^o) is in good agreement with measurements derived from the CMB and from direct observations of peculiar motions and is consistent with the predictions of LambdaCDM.Comment: 6 pages, 5 figures; accepted at MNRAS after minor correction

The three hundred project: thermodynamical properties, shocks and gas dynamics in simulated galaxy cluster filaments and their surroundings

Using cosmological simulations of galaxy cluster regions from THE THREE HUNDRED project we study the nature of gas in filaments feeding massive clusters. By stacking the diffuse material of filaments throughout the cluster sample, we measure average gas properties such as density, temperature, pressure, entropy and Mach number and construct one-dimensional profiles for a sample of larger, radially-oriented filaments to determine their characteristic features as cosmological objects. Despite the similarity in velocity space between the gas and dark matter accretion patterns onto filaments and their central clusters, we confirm some differences, especially concerning the more ordered radial velocity dispersion of dark matter around the cluster and the larger accretion velocity of gas relative to dark matter in filaments. We also study the distribution of shocked gas around filaments and galaxy clusters, showing that the surrounding shocks allow an efficient internal transport of material, suggesting a laminar infall. The stacked temperature profile of filaments is typically colder towards the spine, in line with the cosmological rarefaction of matter. Therefore, filaments are able to isolate their inner regions, maintaining lower gas temperatures and entropy. Finally, we study the evolution of the gas density-temperature phase diagram of our stacked filament, showing that filamentary gas does not behave fully adiabatically through time but it is subject to shocks during its evolution, establishing a characteristic z = 0, entropy-enhanced distribution at intermediate distances from the spine of about 1 − 2 h−1 Mpc for a typical galaxy cluster in our sample

The Three Hundred project: galaxy cluster mergers and their impact on the stellar component of brightest cluster galaxies

Using the data set of the three hundred project, i.e. a suite of 324 hydrodynamical resimulations of cluster-sized haloes, we study galaxy cluster mergers and their effect on colour and luminosity changes of their brightest cluster galaxies (BCG). We track the main progenitor of each halo at z = 0 and search for merger situations based on its mass accretion history, defining mergers as very rapid increases in the halo mass. Based upon the evolution of the dynamical state of the cluster we define a pre- and post-merger phase. We create a list of all these events and statistically study their mass ratio and time-scales, with the former verifying that all instances are in fact major mergers. By comparing to a control sample of clusters without mergers, we study the effect mergers have on the stellar component of the BCG. Analysing the mass, age, and metallicity of the BCG stellar particles, we find that the stellar content of BCGs grows significantly during mergers and, even though the main growth mechanism is the accretion of older stars, there is even a burst in star formation induced by the merger. In our simulations, BCGs in mergers form in median around 70 per cent more stars than those normally growing, although this depends on the radius considered for defining the BCG. Regarding observable properties, we see an increase in SDSS-u luminosity of 20 per cent during mergers, accompanied by a slightly slower increase of the galaxy g − r colour as compared to the control sample

SDSS-III Baryon Oscillation Spectroscopic Survey data release 12 : galaxy target selection and large-scale structure catalogues

The Baryon Oscillation Spectroscopic Survey (BOSS), part of the Sloan Digital Sky Survey (SDSS) III project, has provided the largest survey of galaxy redshifts available to date, in terms of both the number of galaxy redshifts measured by a single survey, and the effective cosmological volume covered. Key to analysing the clustering of these data to provide cosmological measurements is understanding the detailed properties of this sample. Potential issues include variations in the target catalogue caused by changes either in the targeting algorithm or properties of the data used, the pattern of spectroscopic observations, the spatial distribution of targets for which redshifts were not obtained, and variations in the target sky density due to observational systematics. We document here the target selection algorithms used to create the galaxy samples that comprise BOSS. We also present the algorithms used to create large-scale structure catalogues for the final Data Release (DR12) samples and the associated random catalogues that quantify the survey mask. The algorithms are an evolution of those used by the BOSS team to construct catalogues from earlier data, and have been designed to accurately quantify the galaxy sample. The code used, designated mksample, is released with this paper.Publisher PDFPeer reviewe

The clustering of galaxies in the SDSS-III Baryon Oscillation Spectroscopic Survey : baryon acoustic oscillations in the Data Releases 10 and 11 Galaxy samples

We present a one per cent measurement of the cosmic distance scale from the detections of the baryon acoustic oscillations (BAO) in the clustering of galaxies from the Baryon Oscillation Spectroscopic Survey, which is part of the Sloan Digital Sky Survey III. Our results come from the Data Release 11 (DR11) sample, containing nearly one million galaxies and covering approximately 8500 square degrees and the redshift range 0.2 < z < 0.7. We also compare these results with those from the publicly released DR9 and DR10 samples. Assuming a concordance Λ cold dark matter (ΛCDM) cosmological model, the DR11 sample covers a volume of 13 Gpc3 and is the largest region of the Universe ever surveyed at this density. We measure the correlation function and power spectrum, including density-field reconstruction of the BAO feature. The acoustic features are detected at a significance of over 7σ in both the correlation function and power spectrum. Fitting for the position of the acoustic features measures the distance relative to the sound horizon at the drag epoch, rd, which has a value of rd,fid = 149.28 Mpc in our fiducial cosmology. We find DV = (1264 ± 25 Mpc)(rd/rd,fid) at z = 0.32 and DV = (2056 ± 20 Mpc)(rd/rd,fid) at z = 0.57. At 1.0 per cent, this latter measure is the most precise distance constraint ever obtained from a galaxy survey. Separating the clustering along and transverse to the line of sight yields measurements at z = 0.57 of DA = (1421 ± 20 Mpc)(rd/rd,fid) and H = (96.8 ± 3.4 km s−1 Mpc−1)(rd,fid/rd). Our measurements of the distance scale are in good agreement with previous BAO measurements and with the predictions from cosmic microwave background data for a spatially flat CDM model with a cosmological constant.Publisher PDFPeer reviewe