56 research outputs found
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
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
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
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
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&
Illuminating the Dark Side of Cosmic Star Formation II. A second date with RS-NIRdark galaxies in COSMOS
About 12 billion years ago, the Universe was first experiencing light again
after the dark ages, and galaxies filled the environment with stars, metals and
dust. How efficient was this process? How fast did these primordial galaxies
form stars and dust? We can answer these questions by tracing the Star
Formation Rate Density (SFRD) back to its widely unknown high redshift tail,
traditionally observed in the Near-InfraRed (NIR), Optical and UV bands. Thus,
the objects with a high amount of dust were missing. We aim to fill this
knowledge gap by studying Radio Selected NIR-dark (\textit{RS-NIRdark})
sources, i.e. sources not having a counterpart at UV-to-NIR wavelengths. We
widen the sample by Talia et al. (2021) from 197 to 272 objects in the COSMic
evolution Survey (COSMOS) field, including also photometrically contaminated
sources, previously excluded. Another important step forward consists in the
visual inspection of each source in the bands from u* to MIPS-24m.
According to their "environment" in the different bands, we are able to
highlight different cases of study and calibrate an appropriate photometric
procedure for the objects affected by confusion issues. We estimate that the
contribution of RS-NIRdark to the Cosmic SFRD at 3z5 is 10--25
of that based on UV-selected galaxies
Using ALMA to resolve the nature of the early star-forming large-scale structure PLCK G073.4-57.5
Galaxy clusters at high redshift are key targets for understanding matter
assembly in the early Universe, yet they are challenging to locate. A sample of
>2000 high-z candidate structures has been found using Planck's all-sky submm
maps, and a sub-set of 234 have been followed up with Herschel-SPIRE, which
showed that the emission can be attributed to large overdensities of dusty
star-forming galaxies. In order to resolve and characterise the individual
galaxies we targeted the eight brightest SPIRE sources in the centre of the
Planck peak PLCK G073.4-57.5 using ALMA at 1.3 mm, and complemented these
observations with data from IRAC, WIRCam J,K, and SCUBA-2. We detected a total
of 18 millimetre galaxies brighter than 0.3 mJy in 2.4 arcmin^2. The ALMA
source density is 8-30 times higher than average background estimates and
larger than seen in typical 'proto-cluster' fields. We were able to match all
but one of the ALMA sources to a NIR counterpart. The most significant (four)
SCUBA-2 sources are not included in the ALMA pointings, but we find an 8sigma
stacking detection of the ALMA sources in the SCUBA-2 map at 850 um. We derive
photo-z, L_IR, SFR, stellar mass, T_dust, M_dust for all of the ALMA galaxies;
the photo-zs identify two groups each of five sources, at z~1.5 and 2.4. The
two groups show two 'red sequences' (i.e. similar NIR [3.6]-[4.5] colours and
different J-K colours). The majority of the ALMA-detected galaxies are on the
SFR versus stellar mass main sequence, and half of the sample is more massive
than the characteristic stellar mass at the corresponding redshift.
Serendipitous CO line detections in two of the galaxies appear to match their
photometric redshifts at z~1.54. We performed an analysis of star-formation
efficiencies and CO- and mm-continuum-derived gas fractions of our ALMA
sources, combined with a sample of 1<z<3 cluster and proto-cluster members.Comment: 26 pages, revised version, Astronomy & Astrophysics accepte
Ubiquitous Molecular Outflows in z > 4 Massive, Dusty Galaxies II. Momentum-Driven Winds Powered by Star Formation in the Early Universe
Galactic outflows of molecular gas are a common occurrence in galaxies and
may represent a mechanism by which galaxies self-regulate their growth,
redistributing gas that could otherwise have formed stars. We previously
presented the first survey of molecular outflows at z > 4 towards a sample of
massive, dusty galaxies. Here we characterize the physical properties of the
molecular outflows discovered in our survey. Using low-redshift outflows as a
training set, we find agreement at the factor-of-two level between several
outflow rate estimates. We find molecular outflow rates 150-800Msun/yr and
infer mass loading factors just below unity. Among the high-redshift sources,
the molecular mass loading factor shows no strong correlations with any other
measured quantity. The outflow energetics are consistent with expectations for
momentum-driven winds with star formation as the driving source, with no need
for energy-conserving phases. There is no evidence for AGN activity in our
sample, and while we cannot rule out deeply-buried AGN, their presence is not
required to explain the outflow energetics, in contrast to nearby obscured
galaxies with fast outflows. The fraction of the outflowing gas that will
escape into the circumgalactic medium (CGM), though highly uncertain, may be as
high as 50%. This nevertheless constitutes only a small fraction of the total
cool CGM mass based on a comparison to z~2-3 quasar absorption line studies,
but could represent >~10% of the CGM metal mass. Our survey offers the first
statistical characterization of molecular outflow properties in the very early
universe.Comment: ApJ accepted. 25 pages, 16 figures. Data and tables from Papers I and
II available at https://github.com/spt-smg/publicdat
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