64 research outputs found
Recommended from our members
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 km\,s.
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 . After 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 . 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 inflowoutflow ratio stays approximately constant, with typical values of
, 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 SFRinflow rate
ratio, with typical values between 0.1 and 0.3, and for the outflow rateSFR
which varies in the range --. 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
Cosmological gas accretion history on to the stellar discs of Milky Way-like galaxies in the Auriga simulations – II. The inside–out growth of discs
We investigate the growth of stellar discs in Milky Way-mass galaxies using the magnetohydrodynamical simulations of the Auriga Project in a full cosmological context. We focus on the gas accretion process along the discs, calculating the net, infall and outflow rates as a function of galactocentric distance, and investigate the relation between them and the star formation activity. The stellar distributions of around 70 per cent of the simulated galaxies exhibit an ‘inside–out’ pattern, with older (younger) stellar populations preferentially located in the inner (outer) disc regions. In all cases, we find a very tight correlation between the infall, outflow, and net accretion rates, as well as between these three quantities and the star formation rate. This is because the amount of gas which is ultimately available for star formation in each radial ring depends not only on the infall rates, but also on the amount of gas leaving the disc in outflows, which directly relates to the local star formation level. Therefore, any of these rates can be used to identify galaxies with inside–out growth. For these galaxies, the correlation between the dominant times of accretion/star formation and disc radius is well fitted by a linear function. We also find that, when averaged over galaxies with formation histories similar to the Milky Way, the simulated accretion rates show a similar evolution (both temporally and radially integrated) to the usual accretion prescriptions used in chemical evolution models, although some major differences arise at early times and in the inner disc regions
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 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
- …