101 research outputs found
Spitzer View of Lyman Break Galaxies
Using a combination of deep MID-IR observations obtained by IRAC, MIPS and
IRS on board Spitzer we investigate the MID-IR properties of Lyman Break
Galaxies (LBGs) at z~3, establish a better understanding of their nature and
attempt a complete characterisation of the population. With deep mid-infrared
and optical observations of ~1000 LBGs covered by IRAC/MIPS and from the ground
respectively, we extend the spectral energy distributions (SEDs) of the LBGs to
mid-infrared. Spitzer data reveal for the first time that the mid-infrared
properties of the population are inhomogeneous ranging from those with marginal
IRAC detections to those with bright rest-frame near-infrared colors and those
detected at 24mu MIPS band revealing the newly discovered population of the
Infrared Luminous Lyman Break Galaxies (ILLBGs). To investigate this diversity,
we examine the photometric properties of the population and we use stellar
population synthesis models to probe the stellar content of these galaxies. We
find that a fraction of LBGs have very red colors and large estimated stellar
masses M* > 5x10^10Mo. We discuss the link between these LBGs and
submm-luminous galaxies and we report the detection of rest frame 6.2 and 7.7mu
emission features arising from Polycyclic Aromatic Hydrocarbons (PAH) in the
Spitzer/IRS spectrum of an infrared-luminous Lyman break galaxy at z=3.01.Comment: 4 pages, 2 figures, To appear in the proceedings of IAU Symposioum
245 : Formation and evolution of Galaxies Bulges (CUP
Molecular gas content and high excitation of a massive main-sequence galaxy at z = 3
We present new CO (J = 5-4 and 7-6) and [C I] (3P2-3P1 and 3P1-3P0) emission line observations of the star-forming galaxy D49 at the massive end of the main sequence at z = 3. We incorporate previous CO (J = 3-2) and optical-to-millimetre continuum observations to fit its spectral energy distribution. Our results hint at high-J CO luminosities exceeding the expected location on the empirical correlations with the infrared luminosity. [CI] emission fully consistent with the literature trends is found. We do not retrieve any signatures of a bright active galactic nucleus that could boost the J = 5-4, 7-6 lines in either the infrared or X-ray bands, but warm photon-dominated regions, shocks, or turbulence could in principle do so. We suggest that mechanical heating could be a favourable mechanism able to enhance the gas emission at fixed infrared luminosity in D49 and other main-sequence star-forming galaxies at high redshift, but further investigation is necessary to confirm this explanation. We derive molecular gas masses from dust, CO, and [C I] that all agree within the uncertainties. Given its high star formation rate ~500 Mo yr-1 and stellar mass > 1011.5 Mo, the short depletion timescale of < 0.3 Gyr might indicate that D49 is experiencing its last growth spurt and will soon transit to quiescence.</p
The Interstellar Medium of Quiescent Galaxies and its Evolution With Time
We characterise the basic far-IR (FIR) properties and the gas mass fraction
of massive ( ~ 11.0) quiescent galaxies (QGs) and explore how
these evolve from z = 2.0 to the present day. We use robust, multi-wavelength
(mid- to far-IR and sub-millimetre to radio) stacking ensembles of
homogeneously selected and mass complete samples of log(M*/Msun) > 10.8 QGs. We
find that the dust to stellar mass ratio (Md/M*) rises steeply as a function of
redshift up to z~1.0 and then remains flat at least out to z = 2.0. Using Md as
a proxy of gas mass (Mgas), we find a similar trend for the evolution of the
gas mass fraction (fgas) with z > 1.0 QGs having fgas ~ 7.0% (for solar
metallicity). This fgas is 3 - 10 times lower than that of normal star forming
galaxies (SFGs) at their corresponding redshift but ~3 and ~10 times larger
compared to that of z = 0.5 and local QGs. Furthermore, the inferred gas
depletion time scales are comparable to that of local SFGs and systematically
longer than that of main sequence galaxies at their corresponding redshifts.
Our analysis also reveals that the average dust temperature (Td) of massive QGs
remains roughly constant ( = 21.0 \pm 2.0K) at least out to z ~ 2.0 and
is substantially colder (~ 10K) compared to that of z > 0 SFGs. This motivated
us to construct and release a redshift-invariant template IR SED, that we use
to make predictions for ALMA observations and to explore systematic effects in
the Mgas estimates of massive, high-z QGs. Finally, we discuss how a simple
model that considers progenitor-bias can effectively reproduce the observed
evolution of Md/M* and fgas. Our results indicate universal initial
interstellar medium conditions for quenched galaxies and a large degree of
uniformity in their internal processes across cosmic time.Comment: Accepted for publication in A&
Automated mining of the ALMA archive in the COSMOS field (A3COSMOS): II. Cold molecular gas evolution out to Redshift 6
We present new measurements of the cosmic cold molecular gas evolution out to redshift 6 based on systematic mining of the ALMA public archive in the COSMOS deep field (A3COSMOS). Our A3COSMOS dataset contains ~700 galaxies (0.3 < z < 6) with high-confidence ALMA detections in the (sub-)millimeter continuum and multi-wavelength spectral energy distributions (SEDs). Multiple gas mass calibration methods are compared and biases in band conversions (from observed ALMA wavelength to rest-frame Rayleigh-Jeans(RJ)-tail continuum) have been tested. Combining our A3COSMOS sample with ~1,000 CO-observed galaxies at 0 < z < 4 (75% at z < 0.1), we parameterize galaxies' molecular gas depletion time and molecular gas to stellar mass ratio (gas fraction) each as a function of the stellar mass, offset from the star-forming main sequence (Delta MS) and cosmic age (or redshift). Our proposed functional form provides a statistically better fit to current data (than functional forms in the literature), and implies a "downsizing" effect (i.e., more-massive galaxies evolve earlier than less-massive ones) and "mass-quenching" (gas consumption slows down with cosmic time for massive galaxies but speeds up for low-mass ones). Adopting galaxy stellar mass functions and applying our function for gas mass calculation, we for the first time infer the cosmic cold molecular gas density evolution out to redshift 6 and find agreement with CO blind surveys as well as semi-analytic modeling. These together provide a coherent picture of cold molecular gas, SFR and stellar mass evolution in galaxies across cosmic time
Physical properties and evolution of (Sub-)millimeter selected galaxies in the galaxy formation simulation Shark
We thoroughly explore the properties of (sub)-millimeter (mm) selected
galaxies (SMGs) in the Shark semi-analytic model of galaxy formation. Compared
to observations, the predicted number counts at wavelengths (lambda) 0.6-2mm
and redshift distributions at 0.1-2mm, agree well. At the bright end (>1mJy),
Shark galaxies are a mix of mergers and disk instabilities. These galaxies
display a stacked FUV-to-FIR spectrum that agrees well with observations. We
predict that current optical/NIR surveys are deep enough to detect bright
(>1mJy) lambda=0.85-2mm-selected galaxies at z<5, but too shallow to detect
counterparts at higher redshift. A James Webb Space Telescope 10,000s survey
should detect all counterparts for galaxies with mJy. We
predict SMG's disks contribute significantly (negligibly) to the rest-frame UV
(IR). We investigate the 01mJy
lambda=0.85-2mm-selected galaxies finding their: (i) stellar masses are
, with the 2mm ones tracing the most massive galaxies
(); (ii) specific star formation rates (SFR) are mildly
(~3-10x) above the main sequence (MS); (iii) host halo masses are , with 2mm galaxies tracing the most massive halos
(proto-clusters); (iv) SMGs have lower dust masses (),
higher dust temperatures (K) and higher rest-frame V-band
attenuation (>1.5) than MS galaxies; (v) sizes decrease with redshift, from
4kpc at z=1 to <1kpc at z=4; (vi) the Carbon Monoxide line spectra of mJy sources peak at 4->3. Finally, we study the contribution of SMGs
to the molecular gas and cosmic SFR density at 01mJy
sources make a negligible contribution at z>3 and z>5, respectively, suggesting
current observations have unveiled the majority of the star formation at
0<z<10.Comment: Accepted for publication in MNRAS. 28 pages, 22 of main text and
figure
A Two-parameter Model for the Infrared/Submillimeter/Radio Spectral Energy Distributions of Galaxies and Active Galactic Nuclei
A two-parameter semi-empirical model is presented for the spectral energy distributions of galaxies with contributions to their infrared-submillimeter-radio emission from both star formation and accretion disk-powered activity. This model builds upon a previous one-parameter family of models for star-forming galaxies, and includes an update to the mid-infrared emission using an average template obtained from Spitzer Space Telescope observations of normal galaxies. Star-forming/active galactic nucleus (AGN) diagnostics based on polycyclic aromatic hydrocarbon equivalent widths and broadband infrared colors are presented, and example mid-infrared AGN fractional contributions are estimated from model fits to the Great Observatories All-Sky LIRG Survey sample of nearby U/LIRGS and the Five mJy Unbiased Spitzer Extragalactic Survey sample of 24 μm selected sources at redshifts 0 ≾ z ≾ 4
ALMA Lensing Cluster Survey: Properties of Millimeter Galaxies Hosting X-ray Detected Active Galactic Nuclei
We report the multi-wavelength properties of millimeter galaxies hosting
X-ray detected active galactic nuclei (AGNs) from the ALMA Lensing Cluster
Survey (ALCS). ALCS is an extensive survey of well-studied lensing clusters
with ALMA, covering an area of 133 arcmin over 33 clusters with a 1.2 mm
flux-density limit of 60 (). Utilizing the
archival data of Chandra, we identify three AGNs at 1.06, 2.09, and 2.84
among the 180 millimeter sources securely detected in the ALCS (of which 155
are inside the coverage of Chandra). The X-ray spectral analysis shows that two
AGNs are not significantly absorbed (), while the other shows signs of moderate absorption (). We also perform spectral energy
distribution (SED) modelling of X-ray to millimeter photometry. We find that
our X-ray AGN sample shows both high mass accretion rates (intrinsic 0.5--8 keV
X-ray luminosities of ) and
star-formation rates (). This
demonstrates that a wide-area survey with ALMA and Chandra can selectively
detect intense growth of both galaxies and supermassive black holes (SMBHs) in
the high-redshift universe.Comment: 14 pages, 3 figures, 2 table
Lyman break and ultraviolet-selected galaxies at z ~ 1 - II. PACS 100μm/160μm FIR detections
In this work, we report the Photodetector Array Camera and Spectrometer (PACS) 100 μm/160 μm detections of a sample of 42 GALEX-selected and far-infrared (FIR)-detected Lyman break galaxies (LBGs) at z ~ 1 located in the Cosmic Evolution Survey (COSMOS) field and analyse their ultraviolet (UV) to FIR properties. The detection of these LBGs in the FIR indicates that they have a dust content high enough so that its emission can be directly detected. According to a spectral energy distribution (SED) fitting with stellar population templates to their UV-to-near-IR observed photometry, PACS-detected LBGs tend to be bigger (Reff ~ 4.1 kpc), more massive [log (M*/M⊙) ~ 10.7], dustier [Es(B - V) ~ 0.40], redder in the UV continuum (β ~ -0.60) and UV-brighter [log (LUV/L⊙) ~ 10.1] than PACSundetected LBGs. PACS-detected LBGs at z ~ 1 are mostly disc-like galaxies and are located over the green valley and red sequence of the colour-magnitude diagram of galaxies at their redshift. By using their UV and IR emission, we find that PACS-detected LBGs tend to be less dusty and have slightly higher total star formation rates (SFRs) than other PACS-detected UV-selected galaxies within the same redshift range. As a consequence of the selection effect due to the depth of the FIR observations employed, all our PACS-detected LBGs have total IR luminosities, LIR, higher than 1011 L⊙ and thus are luminous IR galaxies. However, none of the PACS-detected LBGs are in the ultra-luminous IR galaxy (ULIRG) regime, LIR =1012 L⊙, where the FIR observations are complete. The finding of ULIRGs-LBGs at higher redshifts (z ~ 3) suggests an evolution of the FIR emission of LBGs with cosmic time. In an IRX-β diagram, PACS-detected LBGs at z~1 tend to be located around the relation for local starburst similarly to other UV-selected PACS-detected galaxies at the same redshift. Consequently, the dust-correction factors obtained with theirUVcontinuum slope allowus to determine their total SFR, unlike at higher redshifts. However, the dust attenuation derived from UV to NIR SED fitting overestimates the total SFR for most of our PACS-detected LBGs in an age-dependent way: the overestimation factor is higher in younger galaxies. This is likely due to the typical degeneracy between dust attenuation and age in the SED fitting with synthetic templates and highlights the importance of the FIR measurements in the analysis of star-forming galaxies at intermediate redshifts.Generalitat Valenciana PROMETEO-2008/132NASA Office of Space Science NNX09AF08GEuropean Southern Observatory LP175.A-0839Junta de Andalucía TIC-114, P08-TIC-03531Ministerio de Economía y Competitividad AYA2011- 29517-C03-01, AYA2010-22111-C03-02, AYA2010-1516
The Herschel view of the dominant mode of galaxy growth from z=4 to the present day
We present an analysis of the deepest Herschel images in four major extragalactic fields GOODS-North, GOODS-South, UDS and COSMOS obtained within the GOODS-Herschel and CANDELS-Herschel key programs. The picture provided by 10497 individual far-infrared detections is supplemented by the stacking analysis of a mass-complete sample of 62361 star-forming galaxies from the CANDELS-HST H band-selected catalogs and from two deep ground-based Ks band-selected catalogs in the GOODS-North and the COSMOS-wide fields, in order to obtain one of the most accurate and unbiased understanding to date of the stellar mass growth over the cosmic history. We show, for the first time, that stacking also provides a powerful tool to determine the dispersion of a physical correlation and describe our method called "scatter stacking" that may be easily generalized to other experiments. We demonstrate that galaxies of all masses from z=4 to 0 follow a universal scaling law, the so-called main sequence of star-forming galaxies. We find a universal close-to-linear slope of the logSFR-logM* relation with evidence for a flattening of the main sequence at high masses (log(M*/Msun) > 10.5) that becomes less prominent with increasing redshift and almost vanishes by z~2. This flattening may be due to the parallel stellar growth of quiescent bulges in star-forming galaxies. Within the main sequence, we measure a non varying SFR dispersion of 0.3 dex. The specific SFR (sSFR=SFR/M*) of star-forming galaxies is found to continuously increase from z=0 to 4. Finally we discuss the implications of our findings on the cosmic SFR history and show that more than 2/3 of present-day stars must have formed in a regime dominated by the main sequence mode. As a consequence we conclude that, although omnipresent in the distant Universe, galaxy mergers had little impact in shaping the global star formation history over the last 12.5 Gyr
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