We present Herschel far-IR photometry and spectroscopy as well as ground based CO observations of an intermediate redshift (0.21 < z < 0.88) sample of Herschel-selected (ultra)-luminous infrared galaxies (L_IR > 10^11.5L_sun). With these measurements
we trace the dust continuum, far-IR atomic line emission, in particular [CII],157.7microns, as well as the molecular gas of z~0.3 (U)LIRGs and perform a detailed investigation of the interstellar medium of the population. We find that the majority of Herschel-selected intermediate redshift (U)LIRGs have L_CII/L_FIR ratios that are a factor of about 10 higher than that of local ULIRGs and comparable to that of local normal and high-$z$ star forming galaxies. Using our sample to bridge local and high-z [CII] observations, we find that the majority of galaxies at all redshifts and all luminosities follow a L_CII-L_FIR relation with a slope of unity, from which local ULIRGs and high-z AGN dominated sources are clear outliers. We also confirm that the strong anti-correlation between the L_CII/L_FIR ratio and the far-IR color L_60/L_100 observed in the local Universe holds over a broad range of redshifts and luminosities, in the sense that warmer sources exhibit lower L_CII/L_FIR at any epoch. Intermediate redshift ULIRGs are also characterised by large molecular gas reservoirs and by lower star formation efficiencies compared to that of local ULIRGs. The high L_CII/L_FIR ratios, the moderate star formation efficiencies (L_LIR/L_CO or L_IR/M_gas) and the relatively low dust temperatures of our sample (which are also common characteristics of high-z star forming galaxies with ULIRG-like luminosities) indicate that the evolution of the physical properties of (U)LIRGs between the present day and z > 1 is already significant by z ~ 0.3.
We report the first results from a spectroscopic survey of the [CII] 158um line from a sample of intermediate redshift (0.2<z<0.8) (ultra)-luminous infrared galaxies, (U)LIRGs (LIR>10^11.5 Lsun), using the SPIRE-Fourier Transform Spectrometer (FTS) o
n board the Herschel Space Observatory. This is the first survey of [CII] emission, an important tracer of star-formation, at a redshift range where the star-formation rate density of the Universe increases rapidly. We detect strong [CII] 158um line emission from over 80% of the sample. We find that the [CII] line is luminous, in the range (0.8-4)x10^(-3) of the far-infrared continuum luminosity of our sources, and appears to arise from photodissociation regions on the surface of molecular clouds. The L[CII]/LIR ratio in our intermediate redshift (U)LIRGs is on average ~10 times larger than that of local ULIRGs. Furthermore, we find that the L[CII]/LIR and L[CII]/LCO(1-0) ratios in our sample are similar to those of local normal galaxies and high-z star-forming galaxies. ULIRGs at z~0.5 show many similarities to the properties of local normal and high-z star forming galaxies. Our findings strongly suggest that rapid evolution in the properties of the star forming regions of luminous infrared galaxies is likely to have occurred in the last 5 billion years.
We study the mid- to far-IR properties of a 24um-selected flux-limited sample (S24 > 5mJy) of 154 intermediate redshift (<z>~0.15), infrared luminous galaxies, drawn from the 5MUSES survey. By combining existing mid-IR spectroscopy and new Herschel S
PIRE submm photometry from the HerMES program, we derived robust total infrared luminosity (LIR) and dust mass (Md) estimates and infered the relative contribution of the AGN to the infrared energy budget of the sources. We found that the total infrared emission of galaxies with weak 6.2um PAH emission (EW<0.2um) is dominated by AGN activity, while for galaxies with EW>0.2um more than 50% of the LIR arises from star formation. We also found that for galaxies detected in the 250-500um Herschel bands an AGN has a statistically insignificant effect on the temperature of the cold dust and the far-IR colours of the host galaxy, which are primarily shaped by star formation activity. For star-forming galaxies we reveal an anti-correlation between the LIR-to-rest-frame 8um luminosity ratio, IR8 = LIRL8, and the strength of PAH features. We found that this anti-correlation is primarily driven by variations in the PAHs emission, and not by variations in the 5-15um mid-IR continuum emission. Using the [NeIII]/[NeII] line ratio as a tracer of the hardness of the radiation field, we confirm that galaxies with harder radiation fields tend to exhibit weaker PAH features, and found that they have higher IR8 values and higher dust-mass-weighted luminosities (LIR/Md), the latter being a proxy for the dust temperature (Td). We argue that these trends originate either from variations in the environment of the star-forming regions or are caused by variations in the age of the starburst. Finally, we provide scaling relations that will allow estimating LIR, based on single-band observations with the mid-infrared instrument, on board the upcoming JWST.
We present observations of the CO[3-2] emission towards two massive and infrared luminous Lyman Break Galaxies at z = 3.21 and z = 2.92, using the IRAM Plateau de Bure Interferometer, placing first constraints on the molecular gas masses (Mgas) of no
n-lensed LBGs. Their overall properties are consistent with those of typical (Main-Sequence) galaxies at their redshifts, with specific star formation rates ~1.6 and ~2.2 Gyr^(-1), despite their large infrared luminosities L_IR ~2-3 x 10^12 Lsun derived from Herschel. With one plausible CO detection (spurious detection probability of 10^(-3)) and one upper limit, we investigate the evolution of the molecular gas-to-stellar mass ratio (Mgas/M*) with redshift. Our data suggest that the steep evolution of Mgas/M* of normal galaxies up to z~2 is followed by a flattening at higher redshifts, providing supporting evidence for the existence of a plateau in the evolution of the specific star formation rate at z > 2.5.
Using Herschel PACS and SPIRE observations as part of the HerMES, we explore the far-IR properties of a sample of mid-IR selected starburst dominated ultra-luminous infrared galaxies (ULIRGs) at z ~ 2. We derive robust estimates of infrared luminosit
ies (L_IR) and dust temperatures (Td) of the population and find that galaxies in our sample range from those that are as cold as high-z sub-millimeter galaxies (SMGs) to those that are as warm as optically faint radio galaxies (OFRGs) and local ULIRGs. We also demonstrate that a significant fraction of our sample would be missed from ground based (sub)mm surveys (850-1200{mu}m) showing that the latter introduce a bias towards the detection of colder sources. Similarly, based on PACS data as part of the PEP project, we construct for the first time the full average SED of a sub-sample of infrared luminous Lyman break galaxies at z ~ 3, and find them to have higher T_d when compared to that of SMGs with comparable L_IR. We conclude that high-z ULIRGs span a wide range of dust temperatures, larger than that seen in local ULIRGs, and that Herschel data provide the means to characterize the bulk of the ULIRG population, free from selection biases introduced by ground based (sub)mm surveys.
Using Herschel PACS and SPIRE observations of Lockman Hole-North and GOODS-N as part of the HerMES project, we explore the far-IR properties of a sample of mid-IR selected starburst dominated ultra-luminous infrared galaxies (ULIRGs) at z ~ 2. The se
lection of the sample is based on the detection of the stellar bump that appears in the SED of star-forming galaxies at 1.6um. We derive robust estimates of infrared luminosities (L_IR) and dust temperatures (T_d) of the population and find that while the luminosities in our sample span less than an order of magnitude (12.24< log(L_IR/Lo) < 12.94), they cover a wide range of dust temperatures (25< T_d < 62 K). Galaxies in our sample range from those that are as cold as high-z sub-millimeter galaxies (SMGs) to those that are as warm as optically faint radio galaxies (OFRGs) and local ULIRGs. Nevertheless, our sample has median T_d=42.3 K, filling the gap between SMGs and OFRGs, bridging the two populations. We demonstrate that a significant fraction of our sample would be missed from ground based (sub)mm surveys (850-1200um) showing that the latter introduce a bias towards the detection of colder sources. We conclude that Herschel} observations, confirm the existence of high-z ULIRGs warmer than SMGs, show that the mid-IR selection of high-z ULIRGs is not T_d-dependent, reveal a large dispersion in T_d of high-z ULIRGs, and provide the means to characterize the bulk of the ULIRG population, free from selection biases introduced by ground based (sub)mm surveys.
We present first insights into the far-IR properties for a sample of IRAC and MIPS-24um detected Lyman Break Galaxies (LBGs) at z ~ 3, as derived from observations in the northern field of the Great Observatories Origins Survey (GOODS-N) carried out
with the PACS instrument on board the Herschel Space Observatory. Although none of our galaxies are detected by Herschel, we employ a stacking technique to construct, for the first time, the average spectral energy distribution of infrared luminous LBGs from UV to radio wavelengths. We derive a median IR luminosity of L_{IR} = 1.6 x 10^12 Lo, placing the population in the class of ultra luminous infrared galaxies (ULIRGs). Complementing our study with existing multi-wavelength data, we put constraints on the dust temperature of the population and find that for their L_{IR}, MIPS-LBGs are warmer than submm-luminous galaxies while they fall in the locus of the L_{IR}-T_{d} relation of the local ULIRGs. This, along with estimates based on the average SED, explains the marginal detection of LBGs in current sub-mm surveys and suggests that these latter studies introduce a bias towards the detection of colder ULIRGs in the high-z universe, while missing high-z ULIRGS with warmer dust.
We present a multi-wavelength, UV-to-radio analysis for a sample of massive (M$_{ast}$ $sim$ 10$^{10}$ M$_odot$) IRAC- and MIPS 24$mu$m-detected Lyman Break Galaxies (LBGs) with spectroscopic redshifts z$sim$3 in the GOODS-North field (L$_{rm UV}$$>1
.8times$L$^{ast}_{z=3}$). For LBGs without individual 24$mu$m detections, we employ stacking techniques at 24$mu$m, 1.1mm and 1.4GHz, to construct the average UV-to-radio spectral energy distribution and find it to be consistent with that of a Luminous Infrared Galaxy (LIRG) with L$rm_{IR}$=4.5$^{+1.1}_{-2.3}$$times 10^{11}$ L$_{odot}$ and a specific star formation rate (SSFR) of 4.3 Gyr$^{-1}$ that corresponds to a mass doubling time $sim$230 Myrs. On the other hand, when considering the 24$mu$m-detected LBGs we find among them galaxies with L$rm_{IR}> 10^{12}$ L$_{odot}$, indicating that the space density of $zsim$3 UV-selected Ultra-luminous Infrared Galaxies (ULIRGs) is $sim$(1.5$pm$0.5)$times 10^{-5}$ Mpc$^{-3}$. We compare measurements of star formation rates (SFRs) from data at different wavelengths and find that there is tight correlation (Kendalls $tau >$ 99.7%) and excellent agreement between the values derived from dust-corrected UV, mid-IR, mm and radio data for the whole range of L$rm_{IR}$ up to L$rm_{IR}$ $sim$ 10$^{13}$ L$_{odot}$. This range is greater than that for which the correlation is known to hold at z$sim$2, possibly due to the lack of significant contribution from PAHs to the 24$mu$m flux at $zsim$3. The fact that this agreement is observed for galaxies with L$rm_{IR}$ $>$ 10$^{12}$ L$_{odot}$ suggests that star-formation in UV-selected ULIRGs, as well as the bulk of star-formation activity at this redshift, is not embedded in optically thick regions as seen in local ULIRGs and submillimeter-selected galaxies at $z=2$.
We present photometric analysis of deep mid-infrared observations obtained by Spitzer/IRAC covering the fields Q1422+2309, Q2233+1341, DSF2237a,b, HDFN, SSA22a,b and B20902+34, giving the number counts and the depths for each field. In a sample of 75
1 LBGs lying in those fields, 443, 448, 137 and 152 are identified at 3.6microns, 4.5microns, 5.8microns, 8.0microns IRAC bands respectively, expanding their spectral energy distribution to rest-near-infrared and revealing that LBGs display a variety of colours. Their rest-near-infrared properties are rather inhomogeneous, ranging from those that are bright in IRAC bands and exhibit [R]-[3.6] > 1.5 colours to those that are faint or not detected at all in IRAC bands with [R]-[3.6] < 1.5 colours and these two groups of LBGs are investigated. We compare the mid-IR colours of the LBGs with the colours of star-forming galaxies and we find that LBGs have colours consistent with star-foming galaxies at z~3. The properties of the LBGs detected in the 8microns IRAC band (rest frame K-band) are examined separately, showing that they exhibit redder [R]-[3.6] colours than the rest of the population and that IRAC 8microns band can be used as a diagnostic tool, to separate AGN dominated objects from normal star-forming galaxies at z~3
