315 research outputs found
GOODS-Herschel: a population of 24 μm dropout sources at z<2
Using extremely deep PACS 100- and 160 μm Herschel data from the GOODS-Herschel program, we identify 21 infrared bright galaxies previously missed in the deepest 24 μm surveys performed by Spitzer/MIPS. These MIPS dropouts are predominantly found in two redshift bins, centred at z ~ 0.4 and ~1.3. Their S_(100)/S_(24) flux density ratios are similar to those of local (ultra-) luminous infrared galaxies (LIRGs and ULIRGs), whose silicate absorption features at 18 μm (at z ~ 0.4) and 9.7 μm (at z ~ 1.3) are shifted into the 24 μm MIPS band at these redshifts. The high-z sub-sample consists of 11 infrared luminous sources, accounting for ~2% of the whole GOODS-Herschel sample and putting strong upper limits on the fraction of LIRGs/ULIRGs at 1.0 43 colour cut selects galaxies with a redshift distribution similar to that of the MIPS dropouts and when combined with a second colour cut, S_(16)/S_8 > 4, isolates sources at 1.0 < z < 1.7. We show that these sources have elevated specific star formation rates (sSFR) compared to main sequence galaxies at these redshifts and are likely to be compact starbursts with moderate/strong 9.7 μm silicate absorption features in their mid-IR spectra. Herschel data reveal that their infrared luminosities extrapolated from the 24 μm flux density are underestimated, on average, by a factor of ~3. These silicate break galaxies account for 16% (8%) of the ULIRG (LIRG) population in the GOODS fields, indicating a lower limit in their space density of 2.0 × 10^(-5) Mpc^(-3). Finally, we provide estimates of the fraction of z < 2 MIPS dropout sources as a function of the 24-, 100-, 160-, 250- and 350 μm sensitivity limits, and conclude that previous predictions of a population of silicate break galaxies missed by the major 24 μm extragalactic surveys have beenoverestimated
A mid-IR study of Hickson Compact Groups II. Multi-wavelength analysis of the complete GALEX-Spitzer Sample
We present a comprehensive study on the impact of the environment of compact
galaxy groups on the evolution of their members using a multi-wavelength
analysis, from the UV to the infrared, for a sample of 32 Hickson compact
groups (HCGs) containing 135 galaxies. Fitting the SEDs of all galaxies with
the state-of-the-art model of da Cunha (2008) we can accurately calculate their
mass, SFR, and extinction, as well as estimate their infrared luminosity and
dust content. We compare our findings with samples of field galaxies,
early-stage interacting pairs, and cluster galaxies with similar data. We find
that classifying the groups as dynamically "old" or "young", depending on
whether or not at least one quarter of their members are early-type systems, is
physical and consistent with past classifications of HCGs based on their atomic
gas content. [...ABRIDGED...] We also examine their SF properties, UV-optical
and mid-IR colors, and we conclude that all the evidence point to an
evolutionary scenario in which the effects of the group environment and the
properties of the galaxy members are not instantaneous. Early on, the influence
of close companions to group galaxies is similar to the one of galaxy pairs in
the field. However, as the time progresses, the effects of tidal torques and
minor merging, shape the morphology and star formation history of the group
galaxies, leading to an increase of the fraction of early-type members and a
rapid built up of the stellar mass in the remaining late-type galaxies.Comment: Accepted for publication in A&A. Figure resolution degraded for arXiv
limits, full resolution paper available at
http://www.physics.uoc.gr/~bitsakis/paperII_bitsakis.pd
On the far-infrared metallicity diagnostics: applications to high-redshift galaxies
In an earlier paper we modeled the far-infrared emission from a star-forming
galaxy using the photoionisation code CLOUDY and presented metallicity
sensitive diagnostics based on far-infrared fine structure line ratios. Here,
we focus on the applicability of the [OIII]88/[NII]122 microns line ratio as a
gas phase metallicity indicator in high redshift submillimetre luminous
galaxies. The [OIII]88/[NII]122 microns ratio is strongly dependent on the
ionization parameter (which is related to the total number of ionizing photons)
as well as the gas electron density. We demonstrate how the ratio of 88/$122
continuum flux measurements can provide a reasonable estimate of the ionization
parameter while the availability of the [NII]205 microns line can constrain the
electron density. Using the [OIII]88/[NII]122 microns line ratios from a sample
of nearby normal and star-forming galaxies we measure their gas phase
metallicities and find that their mass metallicity relation is consistent with
the one derived using optical emission lines. Using new, previously
unpublished, Herschel spectroscopic observations of key far-infrared fine
structure lines of the z~3 galaxy HLSW-01 and additional published measurements
of far-infrared fine structure lines of high-z submillimetre luminous galaxies
we derive gas phase metallicities using their [OIII]88/[NII]122 microns line
ratio. We find that the metallicities of these z~3 submm luminous galaxies are
consistent with solar metallicities and that they appear to follow the
mass-metallicity relation expected for z~3 systems.Comment: 10 pages, 7 figures, MNRAS in pres
Dust and gas in star forming galaxies at z~3 - extending galaxy uniformity to 11.5 billion years
We present millimetre dust emission measurements of two Lyman Break Galaxies at z~3 and construct for the first time fully sampled infrared spectral energy distributions (SEDs), from mid-IR to the Rayleigh-Jeans tail, of individually detected, unlensed, UV-selected, main sequence (MS) galaxies at z=3. The SED modelling of the two sources confirms previous findings, based on stacked ensembles, of an increasing mean radiation field with redshift, consistent with a rapidly decreasing gas metallicity in z > 2 galaxies. Complementing our study with CO[3-2] emission line observations, we measure the molecular gas mass (M_H2) reservoir of the systems using three independent approaches: 1) CO line observations, 2) the dust to gas mass ratio vs metallicity relation and 3) a single band, dust emission flux on the Rayleigh-Jeans side of the SED. All techniques return consistent M_H2 estimates within a factor of ~2 or less, yielding gas depletion time-scales (tau_dep ~ 0.35 Gyrs) and gas-to-stellar mass ratios (M_H2/M* ~ 0.5-1) for our z~3 massive MS galaxies. The overall properties of our galaxies are consistent with trends and relations established at lower redshifts, extending the apparent uniformity of star-forming galaxies over the last 11.5 billion years
Herschel-SPIRE-Fourier Transform Spectroscopy of the nearby spiral galaxy IC342
We present observations of the nearby spiral galaxy IC342 with the Herschel
Spectral and Photometric Imaging Receiver (SPIRE) Fourier Transform
Spectrometer. The spectral range afforded by SPIRE, 196-671 microns, allows us
to access a number of 12CO lines from J=4--3 to J=13--12 with the highest J
transitions observed for the first time. In addition we present measurements of
13CO, [CI] and [NII]. We use a radiative transfer code coupled with Bayesian
likelihood analysis to model and constrain the temperature, density and column
density of the gas. We find two 12CO components, one at 35 K and one at 400 K
with CO column densities of 6.3x10^{17} cm^{-2} and 0.4x10^{17} cm^{-2} and CO
gas masses of 1.26x10^{7} Msolar and 0.15x10^{7} Msolar, for the cold and warm
components, respectively. The inclusion of the high-J 12CO line observations,
indicate the existence of a much warmer gas component (~400 K) confirming
earlier findings from H_{2} rotational line analysis from ISO and Spitzer. The
mass of the warm gas is 10% of the cold gas, but it likely dominates the CO
luminosity. In addition, we detect strong emission from [NII] 205microns and
the {3}P_{1}->{3}P_{0} and {3}P_{2} ->{3}P_{1} [CI] lines at 370 and 608
microns, respectively. The measured 12CO line ratios can be explained by
Photon-dominated region (PDR) models although additional heating by e.g. cosmic
rays cannot be excluded. The measured [CI] line ratio together with the derived
[C] column density of 2.1x10^{17} cm^{-2} and the fact that [CI] is weaker than
CO emission in IC342 suggests that [CI] likely arises in a thin layer on the
outside of the CO emitting molecular clouds consistent with PDRs playing an
important role.Comment: 9 pages, 8 figures, accepted for publication in Monthly Notices of
the Royal Astronomical Society (MNRAS
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
A Survey of Atomic Carbon [C I] in High-redshift Main-Sequence Galaxies
We present the first results of an ALMA survey of the lower fine structure
line of atomic carbon [C I](^3P_1\,-\,^{3}P_0) in far infrared-selected
galaxies on the main sequence at in the COSMOS field. We compare our
sample with a comprehensive compilation of data available in the literature for
local and high-redshift starbursting systems and quasars. We show that the [C
I]() luminosity correlates on global scales with the
infrared luminosity similarly to low- CO transitions. We report
a systematic variation of L'_{\rm [C\,I]^3P_1\,-\, ^3P_0}/ as a
function of the galaxy type, with the ratio being larger for main-sequence
galaxies than for starbursts and sub-millimeter galaxies at fixed .
The L'_{\rm [C\,I]^3P_1\,-\, ^3P_0}/ and / mass ratios are similar for main-sequence galaxies and for
local and high-redshift starbursts within a 0.2 dex intrinsic scatter,
suggesting that [C I] is a good tracer of molecular gas mass as CO and dust. We
derive a fraction of %
of the total carbon mass in the atomic neutral phase. Moreover, we estimate the
neutral atomic carbon abundance, the fundamental ingredient to calibrate [C I]
as a gas tracer, by comparing L'_{\rm [C\,I]^3P_1\,-\, ^3P_0} and available
gas masses from CO lines and dust emission. We find lower [C I] abundances in
main-sequence galaxies than in starbursting systems and sub-millimeter
galaxies, as a consequence of the canonical and gas-to-dust
conversion factors. This argues against the application to different galaxy
populations of a universal standard [C I] abundance derived from highly biased
samples.Comment: 14 pages + Appendix. Accepted for publication in ApJ. All the data
tables in Appendix will be also released in electronic forma
Optical integral field spectroscopy of intermediate redshift infrared bright galaxies
The extreme infrared (IR) luminosity of local luminous and ultra-luminous IR
galaxies (U/LIRGs; 11 12,
respectively) is mainly powered by star-formation processes triggered by
mergers or interactions. While U/LIRGs are rare locally, at z > 1, they become
more common, they dominate the star-formation rate (SFR) density, and a
fraction of them are found to be normal disk galaxies. Therefore, there must be
an evolution of the mechanism triggering these intense starbursts with
redshift. To investigate this evolution, we present new optical SWIFT integral
field spectroscopic H{\alpha}+[NII] observations of a sample of 9
intermediate-z (0.2 < z < 0.4) U/LIRG systems selected from Herschel 250{\mu}m
observations. The main results are the following: (a) the ratios between the
velocity dispersion and the rotation curve amplitude indicate that 10-25% (1-2
out of 8) might be compatible with being isolated disks while the remaining
objects are interacting/merging systems; (b) the ratio between un-obscured and
obscured SFR traced by H{\alpha} and LIR, respectively, is similar in both
local and these intermediate-z U/LIRGs; and (c) the ratio between 250{\mu}m and
the total IR luminosities of these intermediate-z U/LIRGs is higher than that
of local U/LIRGs with the same LIR . This indicates a reduced dust temperature
in these intermediate-z U/LIRGs. This, together with their already measured
enhanced molecular gas content, suggests that the interstellar medium
conditions are different in our sample of intermediate-z galaxies when compared
to local U/LIRGs.Comment: Accepted for publication in MNRA
Linking the X-ray and infrared properties of star-forming galaxies at z < 1.5
We present the most complete study to date of the X-ray emission from star formation in high-redshift (median z = 0.7; z −3 in both hard and soft X-ray bands. From the sources which are star formation dominated, only a small fraction are individually X-ray detected and for the bulk of the sample we calculate average X-ray luminosities through stacking. We find an average soft X-ray to infrared ratio of log ?L SX /L IR ? = −4.3 and an average hard X-ray to infrared ratio of log?L HX /L IR ?=−3.8.WereportthattheX-ray/IRcorrelationisapproximatelylinearthrough the entire range of L IR and z probed and, although broadly consistent with the local (z < 0.1) one, it does display some discrepancies. We suggest that these discrepancies are unlikely to be physical, i.e. due to an intrinsic change in the X-ray properties of star-forming galaxies with cosmic time, as there is no significant evidence for evolution of the L X /L IR ratio with redshift. Instead, they are possibly due to selection effects and remaining AGN contamination.
We also examine whether dust obscuration in the galaxy plays a role in attenuating X-rays from star formation, by investigating changes in the L X /L IR ratio as a function of the average dust temperature. We conclude that X-rays do not suffer any measurable attenuation in the host galaxy
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