52 research outputs found
Collision-induced galaxy formation: semi-analytical model and multi-wavelength predictions
A semi-analytic model is proposed that couples the Press-Schechter formalism
for the number of galaxies with a prescription for galaxy-galaxy interactions
that enables to follow the evolution of galaxy morphologies along the Hubble
sequence. Within this framework, we calculate the chemo-spectrophotometric
evolution of galaxies to obtain spectral energy distributions. We find that
such an approach is very successful in reproducing the statistical properties
of galaxies as well as their time evolution. We are able to make predictions as
a function of galaxy type: for clarity, we restrict ourselves to two categories
of galaxies: early and late types that are identified with ellipticals and
disks. In our model, irregulars are simply an early stage of galaxy formation.
In particular, we obtain good matches for the galaxy counts and redshift
distributions of sources from UV to submm wavelengths. We also reproduce the
observed cosmic star formation history and the diffuse background radiation,
and make predictions as to the epoch and wavelength at which the dust-shrouded
star formation of spheroids begins to dominate over the star formation that
occurs more quiescently in disks. A new prediction of our model is a rise in
the FIR luminosity density with increasing redshift, peaking at about , and with a ratio to the local luminosity density about 10 times higher than that in the blue
(B-band) which peaks near .Comment: Minor changes, replaced to match accepted MNRAS versio
Contribution of Galaxies to the Background Hydrogen-Ionizing Flux
We estimate the evolution of the contribution of galaxies to the cosmic
background flux at by means of a semi-analytic model of galaxy
formation and evolution. Such a modelling has been quite successful in
reproducing the optical properties of galaxies. We assume hereafter the
high-redshift damped Lyman- (DLA) systems to be the progenitors of
present day galaxies, and we design a series of models which are consistent
with the evolution of cosmic comoving emissivities in the available near
infrared (NIR), optical, ultraviolet (UV), and far infrared (FIR) bands along
with the evolution of the neutral hydrogen content and average metallicity of
damped Lyman- systems (DLA). We use these models to compute the
galactic contribution to the Lyman-limit emissivity and background flux for . We take into account the absorption of Lyman-limit photons by
HI and dust in the interstellar medium (ISM) of the galaxies. We find that the
background Lyman-limit flux due to galaxies might dominate (or be comparable
to) the contribution from quasars at almost all redshifts if the absorption by
HI in the ISM is neglected. The ISM HI absorption results in a severe
diminishing of this flux--by almost three orders of magnitude at high redshifts
to between one and two orders at . Though the resulting galaxy flux
is completely negligible at high redshifts, it is comparable to the quasar flux
at .Comment: 14 pages, 5 figures, requires mn.sty, accepted for publication in
MNRA
The elliptical colour-magnitude relation as a discriminant between the monolithic and merger paradigms: the importance of progenitor bias
The colour-magnitude relation (CMR) of cluster ellipticals has been widely
used to constrain their star formation histories (SFHs) and to discriminate
between the monolithic and merger paradigms of elliptical galaxy formation. We
investigate the elliptical CMR predicted in the merger paradigm by using a LCDM
hierarchical merger model. We first highlight sections of the literature which
indicate that the traditional use of fixed apertures to derive colours gives a
distorted view of the CMR due to the presence of colour gradients in galaxies.
Fixed aperture observations make the CMR steeper and tighter than it really is.
We then show that the star formation history (SFH) of cluster ellipticals
predicted by the model is quasi-monolithic, with over 95 percent of the total
stellar mass formed before a redshift of 1. The quasi-monolithic SFH produces a
predicted CMR that agrees well at all redshifts with its observed counterpart
once the fixed aperture effect is removed. More importantly, we present
arguments to show that the elliptical-only CMR can be used to constrain the
SFHs of present-day cluster ellipticals only if we believe a priori in the
monolithic collapse model. It is not a meaningful tool for constraining the SFH
in the merger paradigm, because a progressively larger fraction of the
progenitor set of present-day cluster ellipticals is contained in late-type
star forming systems at higher redshift, which cannot be ignored when deriving
the SFHs. Hence, the elliptical-only CMR is not a useful discriminant between
the two competing theories of elliptical galaxy evolution.Comment: replaced with accepted versio
Cooling, Gravity and Geometry: Flow-driven Massive Core Formation
We study numerically the formation of molecular clouds in large-scale
colliding flows including self-gravity. The models emphasize the competition
between the effects of gravity on global and local scales in an isolated cloud.
Global gravity builds up large-scale filaments, while local gravity --
triggered by a combination of strong thermal and dynamical instabilities --
causes cores to form. The dynamical instabilities give rise to a local focusing
of the colliding flows, facilitating the rapid formation of massive
protostellar cores of a few 100 M. The forming clouds do not reach an
equilibrium state, though the motions within the clouds appear comparable to
``virial''. The self-similar core mass distributions derived from models with
and without self-gravity indicate that the core mass distribution is set very
early on during the cloud formation process, predominantly by a combination of
thermal and dynamical instabilities rather than by self-gravity.Comment: 13 pages, 12 figures, accepted by Ap
Merger Histories in Warm Dark Matter Structure Formation Scenario
Observations on galactic scales seem to be in contradiction with recent high
resolution N-body simulations. This so-called cold dark matter (CDM) crisis has
been addressed in several ways, ranging from a change in fundamental physics by
introducing self-interacting cold dark matter particles to a tuning of complex
astrophysical processes such as global and/or local feedback. All these efforts
attempt to soften density profiles and reduce the abundance of satellites in
simulated galaxy halos. In this paper, we explore a somewhat different approach
which consists of filtering the dark matter power spectrum on small scales,
thereby altering the formation history of low mass objects. The physical
motivation for damping these fluctuations lies in the possibility that the dark
matter particles have a different nature i.e. are warm (WDM) rather than cold.
We show that this leads to some interesting new results in terms of the merger
history and large-scale distribution of low mass halos, as compared to the
standard CDM scenario. However, WDM does not appear to be the ultimate
solution, in the sense that it is not able to fully solve the CDM crisis, even
though one of the main drawbacks, namely the abundance of satellites, can be
remedied. Indeed, the cuspiness of the halo profiles still persists, at all
redshifts, and for all halos and sub-halos that we investigated. Despite the
persistence of the cuspiness problem of DM halos, WDM seems to be still worth
taking seriously, as it alleviates the problems of overabundant sub-structures
in galactic halos and possibly the lack of angular momentum of simulated disk
galaxies. WDM also lessens the need to invoke strong feedback to solve these
problems, and may provide a natural explanation of the clustering properties
and ages of dwarfs.Comment: 11 pages, 17 figures, MNRAS submitted, high-res figures can be found
at http://www-thphys.physics.ox.ac.uk/users/AlexanderKnebe/publications.html,
replaced with accepted version (warmon masses corrected!
MoMaF : The Mock Map Facility
We present the Mock Map Facility, a powerful tool to generate mock catalogues
or images from semi-analytically post-processed snapshots of cosmological
N-body simulations. The paper describes in detail an efficient technique to
create such mocks from the GALICS semi-analytic model, providing the reader
with an accurate quantification of the artifacts it introduces at every step.
We show that replication effects introduce a negative bias on the clustering
signal -- typically peaking at less than 10 percent around the correlation
length. We also thoroughly discuss how the clustering signal is affected by
finite volume effects, and show that it vanishes at scales larger than about a
tenth of the simulation box size. For the purpose of analysing our method, we
show that number counts and redshift distributions obtained with GALICS and
MOMAF compare well to K-band observations and to the 2dFGRS. Given finite
volume effects, we also show that the model can reproduce the APM angular
correlation function. The MOMAF results discussed here are made publicly
available to the astronomical community through a public database. Moreover, a
user-friendly Web interface (http://galics.iap.fr) allows any user to recover
her/his own favourite galaxy samples through simple SQL queries. The
flexibility of this tool should permit a variety of uses ranging from extensive
comparisons between real observations and those predicted by hierarchical
models of galaxy formation, to the preparation of observing strategies for deep
surveys and tests of data processing pipelines.Comment: 19 pages, 15 Figs, significantly modified version now accepted for
publication in MNRAS. High-resolution version available at
http://galics.cosmologie.fr/papers/momaf.ps.g
Star-Gas Misalignment in Galaxies. I. The Properties of Galaxies from the Horizon-AGN Simulation and Comparisons to SAMI
Recent integral field spectroscopy observations have found that about 11% of galaxies show star-gas misalignment. The misalignment possibly results from external effects such as gas accretion, interaction with other objects, and other environmental effects, hence providing clues to these effects. We explore the properties of misaligned galaxies using Horizon-AGN, a large-volume cosmological simulation, and compare the results with those of the Sydney-AAO Multi-object integral field spectrograph (SAMI) Galaxy Survey. Horizon-AGN can match the overall misalignment fraction and reproduces the distribution of misalignment angles found by observations surprisingly closely. The misalignment fraction is found to be highly correlated with galaxy morphology both in observations and in the simulation: early-type galaxies are substantially more frequently misaligned than late-type galaxies. The gas fraction is another important factor associated with misalignment in the sense that misalignment increases with decreasing gas fraction. However, there is a significant discrepancy between the SAMI and Horizon-AGN data in the misalignment fraction for the galaxies in dense (cluster) environments. We discuss possible origins of misalignment and disagreement.S.K.Y.
acted as the corresponding author and acknowledges support
from the Korean National Research Foundation (NRF2017R1A2A05001116). D.J.K. acknowledges support from
Yonsei University through Yonsei Honors Scholarship. J.J.B.
acknowledges support from an Australian Research Council
Future Fellowship (FT180100231). J.B.H. is supported by an
ARC Laureate Fellowship that funds Jesse van de Sande
and an ARC Federation Fellowship that funded the SAMI
prototype. M.S.O. acknowledges funding support from the
Australian Research Council through a Future Fellowship
(FT140100255). J.v.d.S. is funded under Bland-Hawthorn’s
ARC Laureate Fellowship (FL140100278). Parts of this
research were conducted by the Australian Research Council
Centre of Excellence for All Sky Astrophysics in 3 Dimensions
(ASTRO 3D), through project No. CE170100013. This work
relied on the HPC resources of the Horizon Cluster hosted by
Institut d’Astrophysique de Paris. We warmly thank S.
Rouberol for running the cluster on which the simulation was
post-processed. This work is partially supported by the Spin(e)
grant ANR-13-BS05-0005 of the French Agence Nationale de
la Recherche. The SAMI Galaxy Survey is based on
observations made at the Anglo-Australian Telescope. The
Sydney-AAO Multi-object Integral field spectrograph (SAMI)
was developed jointly by the University of Sydney and the
Australian Astronomical Observatory. The SAMI input catalog
is based on data taken from the Sloan Digital Sky Survey, the
GAMA Survey and the VST ATLAS Survey. The SAMI
Galaxy Survey is supported by the Australian Research
Council Centre of Excellence for All Sky Astrophysics in 3
Dimensions (ASTRO 3D), through project No. CE170100013,
the Australian Research Council Centre of Excellence for Allsky Astrophysics (CAASTRO), through project No.
CE110001020, and other participating institutions. The SAMI
Galaxy Survey website is http://sami-survey.org/
Extragalactic Magnetism with SOFIA (SALSA Legacy Program). VII. A tomographic view of far infrared and radio polarimetric observations through MHD simulations of galaxies
The structure of magnetic fields in galaxies remains poorly constrained,
despite the importance of magnetism in the evolution of galaxies. Radio
synchrotron and far-infrared dust polarization (FIR) polarimetric observations
are the best methods to measure galactic scale properties of magnetic fields in
galaxies beyond the Milky Way. We use synthetic polarimetric observations of a
simulated galaxy to identify and quantify the regions, scales, and interstellar
medium (ISM) phases probed at FIR and radio wavelengths. Our studied suite of
magnetohydrodynamical cosmological zoom-in simulations features
high-resolutions (10 pc full-cell size) and multiple magnetization models. Our
synthetic observations have a striking resemblance to those of observed
galaxies. We find that the total and polarized radio emission extends to
approximately double the altitude above the galactic disk (half-intensity disk
thickness of kpc)
relative to the FIR total and polarized emission that are concentrated in the
disk midplane ( kpc).
Radio emission traces magnetic fields at scales of pc, whereas
FIR emission probes magnetic fields at the smallest scales of our simulations.
These scales are comparable to our spatial resolution and well below the
spatial resolution ( pc) of existing FIR polarimetric measurements.
Finally, we confirm that synchrotron emission traces a combination of the warm
neutral and cold neutral gas phases, whereas FIR emission follows the densest
gas in the cold neutral phase in the simulation. These results are independent
of the ISM magnetic field strength. The complementarity we measure between
radio and FIR wavelengths motivates future multiwavelength polarimetric
observations to advance our knowledge of extragalactic magnetism.Comment: Submitted to ApJ. 32 pages, 15 figure
A simple model for the evolution of super-massive black holes and the quasar population
An empirically motivated model is presented for accretion-dominated growth of
the super massive black holes (SMBH) in galaxies, and the implications are
studied for the evolution of the quasar population in the universe. We
investigate the core aspects of the quasar population, including space density
evolution, evolution of the characteristic luminosity, plausible minimum masses
of quasars, the mass function of SMBH and their formation epoch distribution.
Our model suggests that the characteristic luminosity in the quasar luminosity
function arises primarily as a consequence of a characteristic mass scale above
which there is a systematic separation between the black hole and the halo
merging rates. At lower mass scales, black hole merging closely tracks the
merging of dark halos. When combined with a declining efficiency of black hole
formation with redshift, the model can reproduce the quasar luminosity function
over a wide range of redshifts. The observed space density evolution of quasars
is well described by formation rates of SMBH above . The
inferred mass density of SMBH agrees with that found independently from
estimates of the SMBH mass function derived empirically from the quasar
luminosity function.Comment: 15 pages, 16 figure
The SAMI Galaxy Survey: a statistical approach to an optimal classification of stellar kinematics in galaxy surveys
Large galaxy samples from multi-object IFS surveys now allow for a
statistical analysis of the z~0 galaxy population using resolved kinematics.
However, the improvement in number statistics comes at a cost, with
multi-object IFS survey more severely impacted by the effect of seeing and
lower S/N. We present an analysis of ~1800 galaxies from the SAMI Galaxy Survey
and investigate the spread and overlap in the kinematic distributions of the
spin parameter proxy as a function of stellar mass and
ellipticity. For SAMI data, the distributions of galaxies identified as regular
and non-regular rotators with \textsc{kinemetry} show considerable overlap in
the - diagram. In contrast, visually classified
galaxies (obvious and non-obvious rotators) are better separated in
space, with less overlap of both distributions. Then, we use a
Bayesian mixture model to analyse the observed
- distribution. Below
, a single beta distribution is sufficient
to fit the complete distribution, whereas a second beta
distribution is required above to account
for a population of low- galaxies. While the Bayesian mixture
model presents the cleanest separation of the two kinematic populations, we
find the unique information provided by visual classification of kinematic maps
should not be disregarded in future studies. Applied to mock-observations from
different cosmological simulations, the mixture model also predicts bimodal
distributions, albeit with different positions of the
peaks. Our analysis validates the conclusions from previous
smaller IFS surveys, but also demonstrates the importance of using kinematic
selection criteria that are dictated by the quality of the observed or
simulated data.Comment: 30 pages and 17 figures, accepted for publication in MNRAS. Abstract
abridged for Arxiv. The key figures of the paper are: 3, 7, 8, and 1
- …