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.
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.
We present first results of a study of the submillimetre (rest frame far-infrared) properties of z~3 Lyman Break Galaxies (LBGs) and their lower-redshift counterparts BX/BM galaxies, based on Herschel-SPIRE observations of the Northern field of the G
reat Observatories Origins Deep Survey (GOODS-N). We use stacking analysis to determine the properties of LBGs well below the current limit of the survey. Although LBGs are not detected individually, stacking the infrared luminous LBGs (those detected with Spitzer at 24 microns yields a statistically significant submm detection with mean flux <S_{250}>= 5.9+/-1.4 mJy confirming the power of SPIRE in detecting UV-selected high-redshift galaxies at submillimetre wavelengths. In comparison, the Spitzer 24 microns detected BX/BM galaxies appear fainter with a stacked value of <S_{250}> = 2.7 +/-0.8 mJy. By fitting the Spectral Energy Distributions (SEDs) we derive median infrared luminosities, L_{IR}, of 2.8x10^{12} Lsun and 1.5x10^{11} Lsun for z~3 LBGs and BX/BMs, respectively. We find that $L_{IR} estimates derived from present measurements are in good agreement with those based on UV data for z~2 BX/BM galaxies, unlike the case for z~3 infrared luminous LBGs where the UV underestimates the true $L_{IR}. Although sample selection effects may influence this result we suggest that differences in physical properties (such as morphologies, dust distribution and extent of star-forming regions) between z ~3 LBGs and z~2 BX/BMs may also play a significant role.
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 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
