429 research outputs found
The influence of wavelength, flux, and lensing selection effects on the redshift distribution of dusty, star-forming galaxies
We interpret the large variety of redshift distributions of galaxies found by far-infrared and (sub-)millimeter deep surveys depending on their depth and wavelength using the Bethermin et al. (2012) phenomenological model of galaxy evolution. This model reproduces without any new parameter tuning the observed redshift distributions from 100 μm to 1.4 mm, and especially the increase of the median redshift with survey wavelength. This median redshift varies also significantly with the depth of the surveys, and deeper surveys do necessarily not probe higher redshifts. Paradoxically, at fixed wavelength and flux limit, the lensed sources are not always at higher redshift. We found that the higher redshift of 1.4 mm-selected south pole telescope (SPT) sources compared to other SMG surveys is not only caused by the lensing selection, but also by the longer wavelength. This SPT sample is expected to be dominated by a population of lensed main-sequence galaxies and a minor contribution (∼10%) of unlensed extreme starbursts
The contribution of starbursts and normal galaxies to infrared luminosity functions at z < 2
We present a parameter-less approach to predict the shape of the infrared
(IR) luminosity function (LF) at redshifts z < 2. It requires no tuning and
relies on only three observables: (1) the redshift evolution of the stellar
mass function for star-forming galaxies, (2) the evolution of the specific star
formation rate (sSFR) of main-sequence galaxies, and (3) the double-Gaussian
decomposition of the sSFR-distribution at fixed stellar mass into a
contribution (assumed redshift- and mass-invariant) from main-sequence and
starburst activity. This self-consistent and simple framework provides a
powerful tool for predicting cosmological observables: observed IR LFs are
successfully matched at all z < 2, suggesting a constant or only weakly
redshift-dependent contribution (8-14%) of starbursts to the star formation
rate density. We separate the contributions of main-sequence and starburst
activity to the global IR LF at all redshifts. The luminosity threshold above
which the starburst component dominates the IR LF rises from log(LIR/Lsun) =
11.4 to 12.8 over 0 < z < 2, reflecting our assumed (1+z)^2.8-evolution of sSFR
in main-sequence galaxies.Comment: 7 pages, 4 figures & 1 table. Accepted for publication in ApJL. Minor
typos corrected in v2 following receipt of proof
Measurements of the spectral energy distribution of the cosmic infrared background
The extragalactic background light (EBL) is the relic emission of all
processes of structure formation in the Universe. About half of this
background, called the Cosmic Infrared Background (CIB) is emitted in the
8-1000 microns range, and peaks around 150 microns. It is due to the dust
reemission from star formation processes and AGN emission. The CIB spectral
energy distribution (SED) constraints the models of star formation in the
Universe. It is also useful to compute the opacity of the Universe to the TeV
photons.
We present the different types of measurements of the CIB and discuss their
strengths and weaknesses.
1. The absolute SED was measured by COBE, and by other experiments. These
measurements are limited by the accuracy of the component separation, i.e. the
foreground subtraction.
2. Robust lower limits are determined from the extragalactic number counts of
infrared galaxies. These lower limits are very stringent up to 100 microns. At
larger wavelengths, the rather low angular resolution of the instruments limits
strongly the depth of the number counts. The "stacking" method determines the
flux emitted at a given wavelength by a population detected at another
wavelength, and provides stringent lower limits in the sub-mm range. It is
complementary with other methods based on the statistical analysis of the map
properties like the P(D) analysis.
3. Finally, upper limits can be derived from the high energy spectra of
extragalactic sources. These upper limits give currently good constraints in
the near- and mid-IR.
Progress have been amazing since the CIB discovery about 15 years ago: the
SED is much better known, and most of it can be accounted for by galaxies
(directly or indirectly). Prospects are also exciting, with fluctuation
analysis with Planck&Herschel, and forthcoming missions.Comment: 9 pages, 1 figure, 1 table, proceedings of invited talk at CRF2010,
DESY Hamburg, Nov 9-12 201
Metal enrichment in a semi-analytical model, fundamental scaling relations, and the case of Milky Way galaxies
Gas flows play a fundamental role in galaxy formation and evolution,
providing the fuel for the star formation process. These mechanisms leave an
imprint in the amount of heavy elements. Thus, the analysis of this metallicity
signature provides additional constraint on the galaxy formation scenario. We
aim to discriminate between four different galaxy formation models based on two
accretion scenarios and two different star formation recipes. We address the
impact of a bimodal accretion scenario and a strongly regulated star formation
recipe. We present a new extension of the eGalICS model, which allows us to
track the metal enrichment process. Our new chemodynamical model is applicable
for situations ranging from metal-free primordial accretion to very enriched
interstellar gas contents. We use this new tool to predict the metallicity
evolution of both the stellar populations and gas phase. We also address the
evolution of the gas metallicity with the star formation rate (SFR). We then
focus on a sub-sample of Milky Way-like galaxies. We compare both the cosmic
stellar mass assembly and the metal enrichment process of such galaxies with
observations and detailed chemical evolution models. Our models, based on a
strong star formation regulation, allow us to reproduce well the stellar mass
to gas-phase metallicity relation observed in the local universe. However, we
observe a systematic shift towards high masses. Our $Mstar-Zg-SFR relation is
in good agreement with recent measurements: our best model predicts a clear
dependence with the SFR. Both SFR and metal enrichment histories of our Milky
Way-like galaxies are consistent with observational measurements and detailed
chemical evolution models. We finally show that Milky Way progenitors start
their evolution below the observed main sequence and progressively reach this
observed relation at z = 0.Comment: 22 pages, 11 figure
The redshift evolution of the distribution of star formation among dark matter halos as seen in the infrared
Recent studies revealed a strong correlation between the star formation rate (SFR) and stellar mass of star-forming galaxies, the so-called star-forming main sequence. An empirical modeling approach (2-SFM) which distinguishes between the main sequence and rarer starburst galaxies is capable of reproducing most statistical properties of infrared galaxies. In this paper, we extend this approach by establishing a connection between stellar mass and halo mass with the technique of abundance matching. Based on a few, simple assumptions and a physically motivated formalism, our model successfully predicts the (cross-)power spectra of the cosmic infrared background (CIB), the cross-correlation between CIB and cosmic microwave background (CMB) lensing, and the correlation functions of bright, resolved infrared galaxies measured by Herschel, Planck, ACT and SPT. We use this model to infer the redshift distribution these observables, as well as the level of correlation between CIB-anisotropies at different wavelengths. We also predict that more than 90% of cosmic star formation activity occurs in halos with masses between 10^11.5 and 10^13.5 Msun. Taking into account subsequent mass growth of halos, this implies that the majority of stars were initially (at z>3) formed in the progenitors of clusters, then in groups at 0.5<z<3 and finally in Milky-Way-like halos at z<0.5. At all redshifts, the dominant contribution to the star formation rate density stems from halos of mass ~10^12 Msun, in which the instantaneous star formation efficiency is maximal (~70%). The strong redshift-evolution of SFR in the galaxies that dominate the CIB is thus plausibly driven by increased accretion from the cosmic web onto halos of this characteristic mass scale
Modeling the connection between ultraviolet and infrared galaxy populations across cosmic times
Using a phenomenological approach, we self-consistently model the redshift evolution of the ultraviolet (UV) and infrared (IR) luminosity functions across cosmic time, as well as a range of observed IR properties of UV-selected galaxy population. This model is an extension of the 2SFM (2 star-formation modes) formalism, which is based on the observed "main-sequence" of star-forming galaxies, i.e. a strong correlation between their stellar mass and their star formation rate (SFR), and a secondary population of starbursts with an excess of star formation. The balance between the UV light from young, massive stars and the dust-reprocessed IR emission is modeled following the empirical relation between the attenuation (IRX for IR excess hereafter) and the stellar mass, assuming a scatter of 0.4\,dex around this relation. We obtain a good overall agreement with the measurements of the IR luminosity function up to z~3 and the UV luminosity functions up to z~6, and show that a scatter on the IRX-M relation is mandatory to reproduce these observables. We also naturally reproduce the observed, flat relation between the mean IRX and the UV luminosity at LUV>109.5 L⊙. Finally, we perform predictions of the UV properties and detectability of IR-selected samples and the vice versa, and discuss the results in the context of the UV-rest-frame and sub-millimeter surveys of the next decade
The early early type: discovery of a passive galaxy at z=3
We present the discovery of a massive, quiescent galaxy at z=2.99. We have
obtained a HST/WFC3 spectrum of this object and measured its redshift from the
detection of a deep 4000A break consistent with an old population and a high
metallicity. By stellar population modeling of both its grism spectrum and
broad-band photometry, we derive an age of ~0.7 Gyr, implying a formation
redshift of z>4, and a mass >10^11 Msun. Although this passive galaxy is the
most distant confirmed so far, we find that it is slightly less compact than
other z>2 early-types of similar mass, being overall more analogous to those
z~1.6 field early-type galaxies. The discovery of this object shows that
early-type galaxies are detectable to at least z=3 and suggests that the
diversity of structural properties found in z=1.4-2 ellipticals to earlier
epochs could have its origin in a variety of formation histories among their
progenitors.Comment: 6 pages, 4 figures, 1 table. Accepted for publication in The
Astrophysical Journal Letter
The contribution of starbursts and normal galaxies to IR luminosity functions and the molecular gas content of the Universe at z<2
We present a parameter-less approach capable of predicting
the shape of the infrared luminosity function at redshifts z ≤2. It relies on
three observables: (1) the redshift evolution of the stellar mass function
for star-forming galaxies, (2) the evolution of the specific star formation
rate of main-sequence galaxies, and (3) the double-Gaussian decomposition
of the specific star formation rate distribution at fixed stellar mass
into the contributions (assumed to be redshift- and mass-invariant) from
main-sequence and starburst activity.
Using this self-consistent and simple framework, we identify the contributions
of main-sequence and starburst activity to the global infrared luminosity
function and find a constant or only weakly redshift-dependent
contribution (8–14%) of starbursts to the star formation rate density at
z ≤2. Over the same redshift range, we also infer the evolution of the
cosmic abundance of molecular gas in star-forming galaxies, based on the
relations between star formation rate and molecular gas mass followed by
normal and starburst galaxies
A method for setting upper limits to the extragalactic background light with Fermi-LAT and TeV observations of blazars
We propose a method for setting upper limits to the extragalactic background
light (EBL). Our method uses simultaneous {\em Fermi}-LAT and ground-based TeV
observations of blazars and is based on the assumption that the intrinsic
spectral energy distribution (SED) of TeV blazars lies below the extrapolation
of the {\em Fermi}-LAT SED from GeV to TeV energies. By extrapolating the {\em
Fermi}-LAT spectrum, which for TeV blazars is practically unattenuated by
photon-photon pair production with EBL photons, a firm upper limit on the
intrinsic SED at TeV energies is provided. The ratio of the extrapolated
spectrum to the observed TeV spectrum provides upper limits to the optical
depth for the propagation of the TeV photons due to pair production on the EBL,
which in turn sets firm upper limits to EBL models. We demonstrate our method
using simultaneous observations from {\em Fermi}-LAT and ground-based TeV
telescopes of the blazars \object{PKS 2155-304} and \object{1ES 1218+304}, and
show that high EBL density models are disfavored. We also discuss how our
method can be optimized and how {\em Fermi} and X-ray monitoring observations
of TeV blazars can guide future TeV campaigns, leading to potentially much
stronger constraints on EBL models.Comment: 15 pages, 4 figures. Accepted by ApJ Letter
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