293 research outputs found
The far infra-red SEDs of main sequence and starburst galaxies
We compare observed far infra-red/sub-millimetre (FIR/sub-mm) galaxy spectral
energy distributions (SEDs) of massive galaxies (
M) derived through a stacking analysis with predictions from
a new model of galaxy formation. The FIR SEDs of the model galaxies are
calculated using a self-consistent model for the absorption and re-emission of
radiation by interstellar dust based on radiative transfer calculations and
global energy balance arguments. Galaxies are selected based on their position
on the specific star formation rate (sSFR) - stellar mass () plane.
We identify a main sequence of star-forming galaxies in the model, i.e. a well
defined relationship between sSFR and , up to redshift . The
scatter of this relationship evolves such that it is generally larger at higher
stellar masses and higher redshifts. There is remarkable agreement between the
predicted and observed average SEDs across a broad range of redshifts
() for galaxies on the main sequence. However, the
agreement is less good for starburst galaxies at , selected here to
have elevated sSFRs the main sequence value. We find that the
predicted average SEDs are robust to changing the parameters of our dust model
within physically plausible values. We also show that the dust temperature
evolution of main sequence galaxies in the model is driven by star formation on
the main sequence being more burst-dominated at higher redshifts.Comment: 20 pages, 13 figures. Accepted to MNRA
Towards a new modelling of gas flows in a semi-analytical model of galaxy formation and evolution
We present an extended version of the semi-analytical model, GalICS. Like its
predecessor, eGalICS applies a post-treatment of the baryonic physics on
pre-computed dark-matter merger trees extracted from an N-body simulation. We
review all the mechanisms that affect, at any given time, the formation and
evolution of a galaxy in its host dark-matter halo. We mainly focus on the gas
cycle from the smooth cosmological accretion to feedback processes. To follow
this cycle with high accuracy we introduce some novel prescriptions: i) a
smooth baryonic accretion with two phases: a cold mode and a hot mode built on
the continuous dark-matter accretion. In parallel to this smooth accretion, we
implement the standard photoionisation modelling to reduce the input gas flow
on the smallest structures. ii) a complete monitoring of the hot gas phase. We
compute the evolution of the core density, the mean temperature and the
instantaneous escape fraction of the hot atmosphere by considering that the hot
gas is in hydrostatic equilibrium in the dark-matter potential well, and by
applying a principle of conservation of energy on the treatment of gas
accretion, supernovae and super massive black hole feedback iii) a new
treatment for disc instabilities based on the formation, the migration and the
disruption of giant clumps. The migration of such clumps in gas-rich galaxies
allows to form pseudo-bulges. The different processes in the gas cycle act on
different time scales, and we thus build an adaptive time-step scheme to solve
the evolution equations. The model presented here is compared in detail to the
observations of stellar-mass functions, star formation rates, and luminosity
functions, in a companion paper
G.A.S. II: Dust extinction in galaxies; Luminosity functions and InfraRed eXcess
19 pages, 18 figures, Accepted by A&AInternational audienceDust is a crucial component of the interstellar medium of galaxies. The presence of dust strongly affects the light produced by stars within a galaxy. As these photons are our main information vector to explore the stellar mass assembly and therefore understand a galaxy's evolution, modeling the luminous properties of galaxies and taking into account the impact of the dust is a fundamental challenge for semi-analytical models.We present the complete prescription of dust attenuation implemented in the new semi-analytical model: G.A.S. This model is based on a two-phase medium originating from a physically motivated turbulent model of gas structuring (G.A.S. I paper). Dust impact is treated by taking into account three dust components: Polycyclic Aromatic Hydrocarbons, Very Small Grains, and Big Grains. All three components evolve in both a diffuse and a fragmented/dense gas phase. Each phase has its own stars, dust content and geometry. Dust content evolves according to the metallicity of it associated phase.The G.A.S. model is used to predict both the UV and the IR luminosity functions from to . Our two-phase ISM prescription catches very well the evolution of UV and IR luminosity functions. We note a small overproduction of the IR luminosity at low redshift (). We also focus on the Infrared-Excess (IRX) and explore its dependency with the stellar mass, UV slope, stellar age, metallicity and slope of the attenuation curves. Our model predicts large scatters for relations based on IRX, especially for the IRX- relation. Our analysis reveals that the slope of the attenuation curve is more driven by absolute attenuation in the FUV band than by disk inclination. We confirm that the age of the stellar population and the slope of the attenuation curve can both shift galaxies below the fiducial star-birth relation in the IRX- diagram
Star formation properties of sub-mJy radio sources
We investigate the star formation properties of ~800 sources detected in one
of the deepest radio surveys at 1.4 GHz. Our sample spans a wide redshift range
(~0.1 - 4) and about four orders of magnitude in star formation rate (SFR). It
includes both star forming galaxies (SFGs) and active galactic nuclei (AGNs),
further divided into radio-quiet and radio-loud objects. We compare the SFR
derived from the far infrared luminosity, as traced by Herschel, with the SFR
computed from their radio emission. We find that the radio power is a good SFR
tracer not only for pure SFGs but also in the host galaxies of RQ AGNs, with no
significant deviation with redshift or specific SFR. Moreover, we quantify the
contribution of the starburst activity in the SFGs population and the
occurrence of AGNs in sources with different level of star formation. Finally
we discuss the possibility of using deep radio survey as a tool to study the
cosmic star formation history.Comment: 18 pages, 14 figures, 1 table (available in its entirety as ancillary
data
Galaxy stellar mass assembly: the difficulty matching observations and semi-analytical predictions
Semi-analytical models (SAMs) are currently the best way to understand the
formation of galaxies within the cosmic dark-matter structures. While they
fairly well reproduce the local stellar mass functions, correlation functions
and luminosity functions, they fail to match observations at high redshift (z >
3) in most cases, particularly in the low-mass range. The inconsistency between
models and observations indicates that the history of gas accretion in
galaxies, within their host dark-matter halo, and the transformation of gas
into stars, are not well followed. Hereafter, we briefly present a new version
of the GalICS semi-analytical model. We explore the impacts of classical
mechanisms, such as supernova feedback or photoionization, on the evolution of
the stellar mass assembly. Even with a strong efficiency, these two processes
cannot explain the observed stellar mass function and star formation rate
distribution and some other relations. We thus introduce an ad-hoc modification
of the standard paradigm, based on the presence of a \textit{no-star-forming}
gas component, and a concentration of the star-forming gas in galaxy discs. The
main idea behind the existence of the no-star-forming gas reservoir is that
only a fraction of the total gas mass in a galaxy is available to form stars.
The reservoir generates a delay between the accretion of the gas and the star
formation process. This new model is in much better agreement with the
observations of the stellar mass function in the low-mass range than the
previous models, and agrees quite well with a large set of observations,
including the redshift evolution of the specific star formation rate. However,
it predicts a large fraction of no-star-forming baryonic gas, potentially
larger than observed, even if its nature has still to be examined in the
context of the missing baryon problem
Clustering, host halos and environment of z2 galaxies as a function of their physical properties
Using a sample of 25683 star-forming and 2821 passive galaxies at ,
selected in the COSMOS field following the BzK color criterion, we study the
hosting halo mass and environment of galaxies as a function of their physical
properties. Spitzer and Herschel provide accurate SFR estimates for starburst
galaxies. We measure the auto- and cross-correlation functions of various
galaxy sub-samples and infer the properties of their hosting halos using both
an HOD model and the linear bias at large scale. We find that passive and
star-forming galaxies obey a similarly rising relation between the halo and
stellar mass. The mean host halo mass of star forming galaxies increases with
the star formation rate between 30 and 200 M.yr, but flattens
for higher values, except if we select only main-sequence galaxies. This
reflects the expected transition from a regime of secular co-evolution of the
halos and the galaxies to a regime of episodic starburst. We find similar large
scale biases for main-sequence, passive, and starburst galaxies at equal
stellar mass, suggesting that these populations live in halos of the same mass.
We detect an excess of clustering on small scales for passive galaxies and
showed, by measuring the large-scale bias of close pairs, that this excess is
caused by a small fraction () of passive galaxies being hosted by
massive halos ( M) as satellites. Finally,
extrapolating the growth of halos hosting the z2 population, we show that
M M galaxies at z2 will evolve, on average,
into massive (M M), field galaxies in the local
Universe and M M galaxies at z=2 into local,
massive, group galaxies. The most massive main-sequence galaxies and close
pairs of massive, passive galaxies end up in today's clusters.Comment: 18 pages, 16 figures, Accepted by A&
Panchromatic Study of the First Galaxies with Large ALMA Programs
Thanks to deep optical to near-IR imaging and spectroscopy, significant
progress is made in characterizing the rest-frame UV to optical properties of
galaxies in the early universe (z > 4). Surveys with Hubble, Spitzer, and
ground-based facilities (Keck, Subaru, and VLT) provide spectroscopic and
photometric redshifts, measurements of the spatial structure, stellar masses,
and optical emission lines for large samples of galaxies. Recently, the Atacama
Large (Sub) Millimeter Array (ALMA) has become a major player in pushing
studies of high redshift galaxies to far-infrared wavelengths, hence making
panchromatic surveys over many orders of frequencies possible. While past
studies focused mostly on bright sub-millimeter galaxies, the sensitivity of
ALMA now enables surveys like ALPINE, which focuses on measuring the gas and
dust properties of a large sample of normal main-sequence galaxies at z > 4.
Combining observations across different wavelengths into a single, panchromatic
picture of galaxy formation and evolution is currently and in the future an
important focus of the astronomical community.Comment: 4 pages, 2 figures. Submitted to Proceedings IAU Symposium No. 341,
201
The Main Sequences of Star-Forming Galaxies and Active Galactic Nuclei at High Redshift
We provide a novel, unifying physical interpretation on the origin, the average shape, the scatter, and the cosmic evolution for the main sequences of starforming galaxies and active galactic nuclei at high redshift z 1. We achieve this goal in a model-independent way by exploiting: (i) the redshift-dependent SFR functions based on the latest UV/far-IR data from HST/Herschel, and re- lated statistics of strong gravitationally lensed sources; (ii) deterministic evolutionary tracks for the history of star formation and black hole accretion, gauged on a wealth of multiwavelength observations including the observed Eddington ratio distribution. We further validate these ingredients by showing their consistency with the observed galaxy stellar mass functions and AGN bolometric luminosity functions at different redshifts via the continuity equation approach. Our analysis of the main sequence for high-redshift galaxies and AGNs highlights that the present data are consistently interpreted in terms of an in situ coevolution scenario for star formation and black hole accretion, envisaging these as local, time coordinated processes
Genesis of the dusty Universe: modeling submillimetre source counts
We model the evolution of IR galaxies using a phenomenological approach to
match the observed source counts at different IR wavelengths. We introduce a
new algorithm for reproducing source counts based on direct integration of
probability distributions rather than Monte-Carlo sampling. We construct a
simple model for the evolution of the luminosity function and the colour
distribution of IR galaxies which utilizes a minimum number of free parameters.
Moreover we analyze how each of these parameters is constrained by
observational data. The model is based on pure luminosity evolution and adopts
the Dale & Helou SED templates. We find that the 850um source counts and their
redshift distribution depend strongly on the shape of the luminosity evolution
function, but only weakly on the details of the SEDs. We derive the best-fit
evolutionary model using the 850um counts and redshift distribution as
constraints. Moreover our best-fit shows a flattening of the faint end of the
luminosity function towards high redshifts and requires a colour evolution
which implies the typical dust temperatures of objects with the same
luminosities to decrease with redshift. We compare our best-fit model to
observed source counts at shorter and longer wavelengths which indicates our
model reproduces the 70um and 1100um source counts remarkably well, but
under-produces the counts at intermediate wavelengths. Analysis reveals that
the discrepancy arises at low redshifts, indicating that revision of the
adopted SED library towards lower dust temperatures (at a fixed infrared
luminosity) is required. This modification is equivalent to a population of
cold galaxies existing at low redshifts, as also indicated by recent Herschel
results, which are underrepresented in IRAS sample. We show that the modified
model successfully reproduces the source counts in a wide range of IR and submm
wavelengths.Comment: 21 pages, 11 figures, 2 tables. Accepted for publication in MNRAS.
Supplementary information could be found at
http://www.strw.leidenuniv.nl/genesis
The Cosmic Far-Infrared Background Buildup Since Redshift 2 at 70 and 160 microns in the COSMOS and GOODS fields
The Cosmic Far-Infrared Background (CIB) at wavelengths around 160 {\mu}m
corresponds to the peak intensity of the whole Extragalactic Background Light,
which is being measured with increasing accuracy. However, the build up of the
CIB emission as a function of redshift, is still not well known. Our goal is to
measure the CIB history at 70 {\mu}m and 160 {\mu}m at different redshifts, and
provide constraints for infrared galaxy evolution models. We use complete deep
Spitzer 24 {\mu}m catalogs down to about 80 {\mu}Jy, with spectroscopic and
photometric redshifts identifications, from the GOODS and COSMOS deep infrared
surveys covering 2 square degrees total. After cleaning the Spitzer/MIPS 70
{\mu}m and 160 {\mu}m maps from detected sources, we stacked the far-IR images
at the positions of the 24 {\mu}m sources in different redshift bins. We
measured the contribution of each stacked source to the total 70 and 160 {\mu}m
light, and compare with model predictions and recent far-IR measurements made
with Herschel/PACS on smaller fields. We have detected components of the 70 and
160 {\mu}m backgrounds in different redshift bins up to z ~ 2. The contribution
to the CIB is maximum at 0.3 <= z <= 0.9 at 160{\mu}m (and z <= 0.5 at 70
{\mu}m). A total of 81% (74%) of the 70 (160) {\mu}m background was emitted at
z < 1. We estimate that the AGN relative contribution to the far-IR CIB is less
than about 10% at z < 1.5. We provide a comprehensive view of the CIB buildup
at 24, 70, 100, 160 {\mu}m. IR galaxy models predicting a major contribution to
the CIB at z < 1 are in agreement with our measurements, while our results
discard other models that predict a peak of the background at higher redshifts.
Our results are available online http://www.ias.u-psud.fr/irgalaxies/ .Comment: Accepted in Astronomy & Astrophysic
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