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We carried out the direct measurement of the fraction of dusty sources in a sample of extremely red galaxies with (R - Ks) > 5.3mag and Ks < 20.2mag, using 24um data from the Spitzer Space Telescope. Combining deep 24um, Ks- and R-band data over an area of 64sq.arcmin in ELAIS N1, we find that 50%+-6% of our ERO sample have measurable 24um flux above the 3sigma flux limit of 40uJy. This flux limit corresponds to a SFR of 12Msun/yr at z~1. The 24um-detected EROs have 24-to-2.2 and 24-to-0.7um flux ratios consistent with infrared luminous, dusty sources at z>1, and an order of magnitude too red to be explained by an infrared quiescent spiral or a pure old stellar population at any redshift. Keck optical spectroscopy of a sample of similarly selected EROs in the FLS field suggests that most of the EROs in ELAIS N1 are probably at z~1. The mean 24um flux (167uJy) of the 24um-detected ERO sample roughly corresponds to the total infrared luminosity of (3-10)x10^(11)Lsun at z=1-1.5, which is similar to that of local LIRGs and ULIGs. The corresponding SFR is ~(50-170)Msun/yr. If the time scale of this starbursting phase is on the order of 10^8yr as inferred for the local LIRGs and ULIGs, the lower limit on the masses of these 24um-detected EROs is (5-20)x10^9Msun. It is plausible that some of the starburst EROs are in the midst of violent transformation to become massive early type galaxies at the epoch of z ~ 1-2., Accepted for publication in ApJ (Spitzer Special Issue)

Context. Wide-field Spitzer surveys allow identification of thousands of potentially high-z submillimeter galaxies (SMGs) through their bright 24 mu m emission and their mid-IR colors. Aims. We want to determine the average properties of such z similar to 2 Spitzer-selected SMGs by combining millimeter, radio, and infrared photometry for a representative IR-flux (lambda(rest) similar to 8 mu m) limited sample of SMG candidates. Methods. A complete sample of 33 sources believed to be starbursts ("5.8 mu m-peakers") was selected in the (0.5 deg(2)) J1046 + 56 field with selection criteria F(24 mu m) > 400 mu Jy, the presence of a redshifted stellar emission peak at 5.8 mu m, and r(Vega)' > 23. The field, part of the SWIRE Lockman Hole field, benefits from very deep VLA/GMRT 20 cm, 50 cm, and 90 cm radio data (all 33 sources are detected at 50 cm), and deep 160 mu m and 70 mu m Spitzer data. The 33 sources, with photometric redshifts similar to 1.5-2.5, were observed at 1.2mm with IRAM-30m/MAMBO to an rms similar to 0.7-0.8mJy in most cases. Their millimeter, radio, 7-band Spitzer, and near-IR properties were jointly analyzed. Results. The entire sample of 33 sources has an average 1.2mm flux density of 1.56 +/- 0.22 mJy and a median of 1.61mJy, so the majority of the sources can be considered SMGs. Four sources have confirmed 4 sigma detections, and nine were tentatively detected at the 3 sigma level. Because of its 24 mu m selection, our sample shows systematically lower F(1.2mm)/F(24 mu m) flux ratios than classical SMGs, probably because of enhanced PAH emission. A median FIR SED was built by stacking images at the positions of 21 sources in the region of deepest Spitzer coverage. Its parameters are T(dust) = 37 +/- 8K, L(FIR) = 2.5 x 10(12) L(circle dot), and SFR = 450 M(circle dot)yr(-1). The FIR-radio correlation provides another estimate of L(FIR) for each source, with an average value of 4.1 x 10(12) L(circle dot); however, this value may be overestimated because of some AGN contribution. Most of our targets are also luminous star-forming BzK galaxies which constitute a significant fraction of weak SMGs at 1.7 less than or similar to z less than or similar to 2.3. Conclusions. Spitzer 24 mu m-selected starbursts and AGN-dominated ULIRGs can be reliably distinguished using IRAC-24 mu m SEDs. Such "5.8 mu m-peakers" with F(24 mu m) > 400 mu Jy have L(FIR) greater than or similar to 10(12) L(circle dot). They are thus z similar to 2 ULIRGs, and the majority may be considered SMGs. However, they have systematically lower 1.2mm/24 mu m flux density ratios than classical SMGs, warmer dust, comparable or lower IR/mm luminosities, and higher stellar masses. About 2000-3000 "5.8 mu m-peakers" may be easily identifiable within SWIRE catalogues over 49 deg(2).

Aims.By combining data from the VIMOS VLT Deep Survey (VVDS) with the Spitzer Wide-area InfraRed Extragalactic survey (SWIRE) we have built the currently largest spectroscopic sample of high redshift galaxies selected in the rest-frame near-infrared. We have obtained 2040 spectroscopic redshifts of galaxies with (m3.6)_AB < 21.5 at 3.6 μ m and 1255 spectroscopic redshifts of galaxies with (m4.5)_AB < 21. These allow us to investigate the clustering evolution of galaxies selected via their rest-frame near-infrared luminosity in the redshift range 0.2 < z < 2.1. Methods: We use the projected two-point correlation function w_p(r_p) to study the three dimensional clustering properties of galaxies detected at 3.6 μ m and 4.5 μ m with the InfraRed Array Camera (IRAC) in the SWIRE survey with measured spectroscopic redshifts from the first epoch VVDS. We compare these properties to those of a larger sample of 16672 SWIRE galaxies for which we have accurate photometric redshifts in the same field. Results: We find that in the 3.6 μ m and 4.5 μ m flux limited samples the apparent correlation length does not change from redshift ~2 to the present. The measured correlation lengths have a mean value of r0 ≃ 3.9±0.5 h-1 Mpc for the galaxies selected at 3.6 μ m and a mean value of r0 ≃ 4.4±0.5 h-1 Mpc for the galaxies selected at 4.5 μ m across the whole redshift range explored. These values are larger than those typicaly found for I-band selected galaxies at I_AB < 24 for which r0 varies from 2.69 h-1 Mpc to 3.63 h-1 Mpc between z = 0.5 to z = 2.1. We find that the difference in correlation length between I-band and 3.6-4.5 μm selected samples decreases with increasing redshift becoming comparable at z ≃ 1.5. We interpret this as evidence that galaxies with older stellar populations and galaxies actively forming stars reside in comparably over-dense environments at epochs earlier than z ≃ 1.5 supporting the recently reported flattening of the color-density relation at high redshift. The increasing difference in correlation length with cosmic time observed between rest-frame UV-optical and near-infrared selected samples could then be an indication that star formation is gradually shifting to lower density regions with decreasing redshift while the older passively evolving galaxies remain in the most over-dense peaks.

In the last couple of years a population of very massive (M(*) > 10(11) M(circle dot)), high-redshift (z >= 2) galaxies has been identified, but its role in galaxy evolution has not yet been fully understood. Aims. It is necessary to perform a systematic study of high- redshift massive galaxies, in order to determine the shape of the very massive tail of the stellar mass function and determine the epoch of their assembly. Methods. We selected high- z massive galaxies at 5.8 mu m, in the SWIRE ELAIS-S1 field (1 deg(2)). Galaxies with the 1.6 mu m stellar peak redshifted into the IRAC bands (z similar or equal to 1-3, called "IR-peakers") were identified. Stellar masses were derived by means of spectrophotometric fitting and used to compute the stellar mass function (MF) at z = 1-2 and 2-3. A parametric fit to the MF was performed, based on a Bayesian formalism, and the stellar mass density of massive galaxies above z = 2 determined. Results. We present the first systematic study of the very-massive tail of the galaxy stellar mass function at high redshift. A total of 326 sources were selected. The majority of these galaxies have stellar masses in excess of 10(11) M(circle dot) and lie at z > 1.5. The availability of mid-IR data turned out to be a valuable tool to constrain the contribution of young stars to galaxy SEDs, and thus their M(*)/L ratio. The influence of near-IR data and of the chosen stellar library on the SED fitting are also discussed. The z = 2-3 stellar mass function between 10(11) and similar to 10(12) M(circle dot) is probed with unprecedented detail. A significant evolution is found not only for galaxies with M similar to 10(11) M(circle dot), but also in the highest mass bins considered. The comoving number density of these galaxies was lower by more than a factor of 10 at z = 2-3, with respect to the local estimate. SWIRE 5.8 mu m peakers more massive than 1.6 x 10(11) M(circle dot) provide 30-50% of the total stellar mass density in galaxies at z = 2-3.

We construct rest-frame luminosity functions (LFs) at 3.6, 4.5, 5.8, 8 and 24 μm over the redshift range 0 < z < 2 for galaxies and 0 < z < 4 for optical quasi-stellar objects (QSOs), using optical and infrared (IR) data from the Spitzer Wide-area Infrared Extragalactic (SWIRE) Survey. The 3.6- and 4.5-μm galaxy LFs show evidence for moderate positive luminosity evolution up to z~ 1.5, consistent with the passive ageing of evolved stellar populations. Their comoving luminosity density was found to evolve passively, gradually increasing out to z~ 0.5–1 but flattening, or even declining, at higher redshift. Conversely, the 24-μm galaxy LF, which is more sensitive to obscured star formation and/or active galactic nuclei (AGN) activity, undergoes strong positive evolution, with the derived IR energy density and star formation rate (SFR) density ∝ (1 +z)^γ with γ= 4.5^(+0.7)_(−0.6) and the majority of this evolution occurring since z~ 1. Optical QSOs, however, show positive luminosity evolution in all bands, out to the highest redshifts (3 < z < 4). Modelling as L^* ∝ (1 +z)^γ gave γ= 1.3^(+0.1)_(−0.1) at 3.6 μm, γ= 1.0^(+0.1)_(−0.1) at 4.5 μm and stronger evolution at the longer wavelengths (5.8, 8 and 24 μm), of γ~ 3. Comparison of the galaxy LFs to predictions from a semi-analytic model based on cold dark matter (CDM) indicates that an initial mass function (IMF) skewed towards higher mass star formation in bursts compared to locally be preferred. As a result, the currently inferred massive SFRs in distant submm sources may require substantial downwards revision.

We exploit the deep and extended far-IR data sets (at 70, 100 and 160 μm) of the Herschel Guaranteed Time Observation (GTO) PACS Evolutionary Probe (PEP) Survey, in combination with the Herschel Multi-tiered Extragalactic Survey data at 250, 350 and 500 μm, to derive the evolution of the rest-frame 35-, 60-, 90- and total infrared (IR) luminosity functions (LFs) up to z ∼ 4. We detect very strong luminosity evolution for the total IR LF (L_IR ∝ (1 + z)^3.55 ± 0.10) up to z ∼ 2, and ∝ (1 + z)^(1.62 ± 0.51) at 2 < z ≲ 4) combined with a density evolution (∝(1 + z)^(−0.57 ± 0.22) up to z ∼ 1 and ∝ (1 + z)^(−3.92 ± 0.34) at 1 < z ≲ 4). In agreement with previous findings, the IR luminosity density (ρIR) increases steeply to z ∼ 1, then flattens between z ∼ 1 and z ∼ 3 to decrease at z ≳ 3. Galaxies with different spectral energy distributions, masses and specific star formation rates (SFRs) evolve in very different ways and this large and deep statistical sample is the first one allowing us to separately study the different evolutionary behaviours of the individual IR populations contributing to ρIR. Galaxies occupying the well-established SFR–stellar mass main sequence (MS) are found to dominate both the total IR LF and ρIR at all redshifts, with the contribution from off-MS sources (≥0.6 dex above MS) being nearly constant (∼20 per cent of the total ρIR) and showing no significant signs of increase with increasing z over the whole 0.8 < z < 2.2 range. Sources with mass in the range 10 ≤ log(M/M_⊙) ≤ 11 are found to dominate the total IR LF, with more massive galaxies prevailing at the bright end of the high-z (≳2) LF. A two-fold evolutionary scheme for IR galaxies is envisaged: on the one hand, a starburst-dominated phase in which the Super Massive Black Holes (SMBH) grows and is obscured by dust (possibly triggered by a major merging event), is followed by an AGN-dominated phase, then evolving towards a local elliptical. On the other hand, moderately star-forming galaxies containing a low-luminosity AGN have various properties suggesting they are good candidates for systems in a transition phase preceding the formation of steady spiral galaxies.

International audience; We exploit the deep and extended far-IR data sets (at 70, 100 and 160 mu m) of the Herschel Guaranteed Time Observation (GTO) PACS Evolutionary Probe (PEP) Survey, in combination with the Herschel Multi-tiered Extragalactic Survey data at 250, 350 and 500 mu m, to derive the evolution of the rest-frame 35-, 60-, 90-and total infrared (IR) luminosity functions (LFs) up to z similar to 4. We detect very strong luminosity evolution for the total IR LF (L-IR alpha (1 + z)(3.55 +/- 0.10) up to z similar to 2, and. (1 + z) 1.62 similar to 0.51 at 2 \textless z less than or similar to 4) combined with a density evolution ( (1 + z)-0.57 +/- 0.22 up to z similar to 1 and. (1 + z)-3.92 +/- 0.34 at 1 \textless z less than or similar to 4). In agreement with previous findings, the IR luminosity density (.IR) increases steeply to z similar to 1, then flattens between z similar to 1 and z similar to 3 to decrease at z similar to 3. Galaxies with different spectral energy distributions, masses and specific star formation rates (SFRs) evolve in very different ways and this large and deep statistical sample is the first one allowing us to separately study the different evolutionary behaviours of the individual IR populations contributing to.IR. Galaxies occupying the well-established SFR-stellar mass main sequence (MS) are found to dominate both the total IR LF and.IR at all redshifts, with the contribution from off-MS sources (= 0.6 dex above MS) being nearly constant (similar to 20 per cent of the total IR) and showing no significant signs of increase with increasing z over the whole 0.8 \textless z \textless 2.2 range. Sources with mass in the range 10 = log(M/M-circle dot) = 11 are found to dominate the total IR LF, with more massive galaxies prevailing at the bright end of the high-z (greater than or similar to 2) LF. A two-fold evolutionary scheme for IR galaxies is envisaged: on the one hand, a starburst-dominated phase in which the Super Massive Black Holes (SMBH) grows and is obscured by dust (possibly triggered by a major merging event), is followed by an AGN-dominated phase, then evolving towards a local elliptical. On the other hand, moderately star-forming galaxies containing a low-luminosity AGN have various properties suggesting they are good candidates for systems in a transition phase preceding the formation of steady spiral galaxies.

The Herschel Multi-tiered Extragalactic Survey (HerMES) is a legacy programme designed to map a set of nested fields totalling ∼380 deg^2. Fields range in size from 0.01 to ∼20 deg^2, using the Herschel-Spectral and Photometric Imaging Receiver (SPIRE) (at 250, 350 and 500 μm) and the Herschel-Photodetector Array Camera and Spectrometer (PACS) (at 100 and 160 μm), with an additional wider component of 270 deg^2 with SPIRE alone. These bands cover the peak of the redshifted thermal spectral energy distribution from interstellar dust and thus capture the reprocessed optical and ultraviolet radiation from star formation that has been absorbed by dust, and are critical for forming a complete multiwavelength understanding of galaxy formation and evolution. The survey will detect of the order of 100 000 galaxies at 5σ in some of the best-studied fields in the sky. Additionally, HerMES is closely coordinated with the PACS Evolutionary Probe survey. Making maximum use of the full spectrum of ancillary data, from radio to X-ray wavelengths, it is designed to facilitate redshift determination, rapidly identify unusual objects and understand the relationships between thermal emission from dust and other processes. Scientific questions HerMES will be used to answer include the total infrared emission of galaxies, the evolution of the luminosity function, the clustering properties of dusty galaxies and the properties of populations of galaxies which lie below the confusion limit through lensing and statistical techniques. This paper defines the survey observations and data products, outlines the primary scientific goals of the HerMES team, and reviews some of the early results.

We investigate the potential of submm–mm and submm–mm–radio photometric redshifts using a sample of mm-selected sources as seen at 250, 350 and 500μm by the SPIRE instrument on Herschel. From a sample of 63 previously identified mm sources with reliable radio identifications in the Great Observatories Origins Deep Survey North and Lockman Hole North fields, 46 (73 per cent) are found to have detections in at least one SPIRE band. We explore the observed submm/mm colour evolution with redshift, finding that the colours of mm sources are adequately described by a modified blackbody with constant optical depth τ= (ν/nu_0)^β, where β=+1.8 and ν_0=c/100 μm. We find a tight correlation between dust temperature and IR luminosity. Using a single model of the dust temperature and IR luminosity relation, we derive photometric redshift estimates for the 46 SPIRE-detected mm sources. Testing against the 22 sources with known spectroscopic or good quality optical/near-IR photometric redshifts, we find submm/mm photometric redshifts offer a redshift accuracy of |Δz|/(1 +z) = 0.16 (〈|Δz|〉= 0.51). Including constraints from the radio–far-IR correlation, the accuracy is improved to |Δz|/(1 +z) = 0.15 (〈|Δz|〉= 0.45). We estimate the redshift distribution of mm-selected sources finding a significant excess at z > 3 when compared to ∼ 850 μm selected samples.

International audience; We examine the rest-frame far-infrared emission from powerful radio sources with 1.4-GHz luminosity densities of 25 \textless log(L-1.4/W Hz-1) \textless 26.5 in the extragalactic Spitzer First Look Survey field. We combine Herschel/SPIRE flux densities with Spitzer/Infrared Array Camera and Multiband Imaging Photometer for Spitzer infrared data to obtain total (\textlessfile name=”mnr\₁8253\ₘu1.gif” type=”gif”/\textgreaterm) infrared luminosities for these radio sources. We separate our sources into a moderate, 0.4 \textless z \textless 0.9, and a high, 1.2 \textless z \textless 3.0, redshift sub-sample and we use Spitzer observations of a z \textless 0.1 3CRR sample as a local comparison. By comparison to numbers from the Square Kilometre Array (SKA) Simulated Skies, we find that our moderate-redshift sample is complete and our high-redshift sample is 14 per cent complete. We constrain the ranges of mean star formation rates (SFRs) to be 3.4-4.2, 18-41 and 80-581 M-circle dot yr-1 for the local, moderate- and high-redshift samples, respectively. Hence, we observe an increase in the mean SFR with increasing redshift which we can parametrize as similar to(1 + z)Q, where Q = 4.2 +/- 0.8. However, we observe no trends of mean SFR with radio luminosity within the moderate- or high-redshift bins. We estimate that radio-loud active galactic nuclei (AGN) in the high-redshift sample contribute 0.1-0.5 per cent to the total SFR density at that epoch. Hence, if all luminous starbursts host radio-loud AGN we infer a radio-loud phase duty cycle of 0.001-0.005.

Context. Spitzer's wide-field surveys and followup capabilities have allowed a new breakthrough in mid-IR spectroscopy up to redshifts ≥ 2, especially for 24 μm detected sources. Aims. We want to study the mid-infrared properties and the starburst and AGN contributions, of 24 μm sources at z ~ 2, through analysis of mid-infrared spectra combined with millimeter, radio, and infrared photometry. Mid-infrared spectroscopy allows us to recover accurate redshifts. Methods. A complete sample of 16 Spitzer-selected sources (ULIRGs) believed to be starbursts at z ~ 2 (“5.8 μm-peakers”) was selected in the (0.5 deg^2) J1064+56 SWIRE Lockman Hole field (“Lockman-North”). These sources have S_(24µ) > 0.5 mJy, a stellar emission peak redshifted to 5.8 μm, and r'_(Vega) > 23. The entire sample was observed with the low resolution units of the Spitzer/IRS infrared spectrograph. These sources have 1.2 mm observations with IRAM 30 m/MAMBO and very deep 20 cm observations from the VLA. Nine of our sources also benefit from 350 μm observation and detection from CSO/SHARC-II. All these data were jointly analyzed. Results. The entire sample shows good quality IRS spectra dominated by strong PAH features. The main PAH features at 6.2, 7.7, 8.6, and 11.3 μm have high S/N average luminosities of 2.90±0.31, 10.38±1.09, 3.62±0.27, and 2.29±0.26×10^(10) L_☉, respectively. Thanks to their PAH spectra, we derived accurate redshifts spanning from 1.750 to 2.284. The average of these redshifts is 2.017±0.038. This result confirms that the selection criteria of “5.8 μm-peakers” associated with a strong detection at 24 μm are reliable to select sources at z ~ 2. We have analyzed the different correlations between PAH emission and infrared, millimeter, and radio emissions. Practically all our sources are strongly dominated by starburst emission, with only one source showing an important AGN contribution. We have also defined two subsamples based on the equivalent width at 7.7 μm to investigate AGN contributions. Conclusions. Our sample contains strong starbursts and represents a particularly 24 μm-bright class of SMGs. The very good correlation between PAH and far-IR luminosities is now confirmed in high-z starburst ULIRGs. These sources show a small AGN contribution to the mid-IR, around ~20% or less in most cases.

We present spectral energy distributions (SEDs) for 68 Herschel sources detected at 5σ at 250, 350 and 500 μm in the HerMES SWIRE-Lockman field. We explore whether existing models for starbursts, quiescent star-forming galaxies and active galactic nucleus dust tori are able to model the full range of SEDs measured with Herschel. We find that while many galaxies ( 56 per cent) are well fitted with the templates used to fit IRAS, Infrared Space Observatory (ISO) and Spitzer sources, for about half the galaxies two new templates are required: quiescent ('cirrus') models with colder (10-20 K) dust and a young starburst model with higher optical depth than Arp 220. Predictions of submillimetre fluxes based on model fits to 4.5-24 μm data agree rather poorly with the observed fluxes, but the agreement is better for fits to 4.5-70 μm data. Herschel galaxies detected at 500 μm tend to be those with the highest dust masses. © 2010 The Authors. Journal compilation © 2010 RAS.

Using Herschel Photodetector Array Camera (PACS) and Spectral and Photometric Imaging Receiver (SPIRE) observations of Lockman Hole-North and Great Observatories Origins Deep Survey-North (GOODS-N) as part of the Herschel Multi-tiered Extragalactic Survey (HerMES) project, we explore the far-infrared (IR) properties of a sample of mid-IR-selected starburst-dominated ultraluminous infrared galaxies (ULIRGs) at z~ 2. The selection of the sample is based on the detection of the stellar bump that appears in the spectral energy distribution of star-forming galaxies at 1.6 μm. We derive robust estimates of infrared luminosities (LIR) and dust temperatures (Td) of the population and find that while the luminosities in our sample span less than an order of magnitude (12.24 ≤ log(LIR/L·) ≤ 12.94), they cover a wide range of dust temperatures (25 ≤Td≤ 62 K). Galaxies in our sample range from those that are as cold as high-z submillimetre galaxies (SMGs) to those that are as warm as optically faint radio galaxies (OFRGs) and local ULIRGs. Nevertheless, our sample has median Td= 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 (850-1200 μm), 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 Td dependent, reveal a large dispersion in Td 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. © 2010 The Authors. Journal compilation © 2010 RAS.

We present first results of a study of the submillimetre (submm) (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 Great 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 μm) 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 submm wavelengths. In comparison, the Spitzer 24 μm 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 2.8 × 10^(12) L_⊙ and 1.5 × 10^(11) L_⊙ for z ~ 3 LBGs and BX/BMs, respectively. We find that LIR 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.

International audience; Using Herschel Photodetector Array Camera (PACS) and Spectral and Photometric Imaging Receiver (SPIRE) observations of Lockman Hole-North and Great Observatories Origins Deep Survey-North (GOODS-N) as part of the Herschel Multi-tiered Extragalactic Survey (HerMES) project, we explore the far-infrared (IR) properties of a sample of mid-IR-selected starburst-dominated ultraluminous infrared galaxies (ULIRGs) at z similar to 2. The selection of the sample is based on the detection of the stellar bump that appears in the spectral energy distribution of star-forming galaxies at 1.6 mu m. 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 \textless= log(L-IR/L-circle dot) \textless= 12.94), they cover a wide range of dust temperatures (25 \textless= T-d \textless= 62 K). Galaxies in our sample range from those that are as cold as high-z submillimetre 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 (850-1200 mu m), 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 spectral energy distributions (SEDs) for 68 Herschel sources detected at 5σ at 250, 350 and 500 μm in the HerMES SWIRE-Lockman field. We explore whether existing models for starbursts, quiescent star-forming galaxies and active galactic nucleus dust tori are able to model the full range of SEDs measured with Herschel. We find that while many galaxies (~56 per cent) are well fitted with the templates used to fit IRAS, Infrared Space Observatory (ISO) and Spitzer sources, for about half the galaxies two new templates are required: quiescent (‘cirrus’) models with colder (10–20 K) dust and a young starburst model with higher optical depth than Arp 220. Predictions of submillimetre fluxes based on model fits to 4.5–24 μm data agree rather poorly with the observed fluxes, but the agreement is better for fits to 4.5–70 μm data. Herschel galaxies detected at 500 μm tend to be those with the highest dust masses.

Using Herschel Photodetector Array Camera (PACS) and Spectral and Photometric Imaging Receiver (SPIRE) observations of Lockman Hole-North and Great Observatories Origins Deep Survey-North (GOODS-N) as part of the Herschel Multi-tiered Extragalactic Survey (HerMES) project, we explore the far-infrared (IR) properties of a sample of mid-IR-selected starburst-dominated ultraluminous infrared galaxies (ULIRGs) at z ~ 2. The selection of the sample is based on the detection of the stellar bump that appears in the spectral energy distribution of star-forming galaxies at 1.6 μm. 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)/L_⊙) ≤ 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 submillimetre 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 (850–1200 μm), 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.

Emission at far-infrared wavelengths makes up a significant fraction of the total light detected from galaxies over the age of Universe. Herschel provides an opportunity for studying galaxies at the peak wavelength of their emission. Our aim is to provide a benchmark for models of galaxy\ud population evolution and to test pre-existing models of galaxies.With the Herschel Multi-tiered Extra-galactic survey, HerMES, we have observed a number of fields of different areas and sensitivity using the SPIRE instrument on Herschel. We have determined the number counts of galaxies down to ∼20 mJy. Our constraints from directly counting galaxies are consistent with, though more precise than, estimates from the BLAST fluctuation analysis. We have found a steep rise in the Euclidean normalised counts

We study the dust properties of galaxies in the redshift range 0.10.5 with L_IR>5x10^{10} L_\odot, appears to be 2-5 K colder than that of AKARI-selected local galaxies with similar luminosities; and the dispersion in T_dust for high-z galaxies increases with L_IR due to the existence of cold galaxies that are not seen among local galaxies. We show that this large dispersion of the L_IR-T_dust relation can bridge the gap between local star-forming galaxies and high-z submillimeter galaxies (SMGs). We also find that three SMGs with very low T_dust (, Comment: 9 pages, 6 figures, To appear in MNRAS

SPIRE, the Spectral and Photometric Imaging REceiver, is the Herschel Space Observatory's submillimetre camera and spectrometer. It contains a three-band imaging photometer operating at 250, 350 and 500 μm, and an imaging Fourier-transform spectrometer (FTS) covering 194–671 μm (447-1550 GHz). In this paper we describe the initial approach taken to the absolute calibration of the SPIRE instrument using a combination of the emission from the Herschel telescope itself and the modelled continuum emission from solar system objects and other astronomical targets. We present the photometric, spectroscopic and spatial accuracy that is obtainable in data processed through the “standard” pipelines. The overall photometric accuracy at this stage of the mission is estimated as 15% for the photometer and between 15 and 50% for the spectrometer. However, there remain issues with the photometric accuracy of the spectra of low flux sources in the longest wavelength part of the SPIRE spectrometer band. The spectrometer wavelength accuracy is determined to be better than 1/10th of the line FWHM. The astrometric accuracy in SPIRE maps is found to be 2 arcsec when the latest calibration data are used. The photometric calibration of the SPIRE instrument is currently determined by a combination of uncertainties in the model spectra of the astronomical standards and the data processing methods employed for map and spectrum calibration. Improvements in processing techniques and a better understanding of the instrument performance will lead to the final calibration accuracy of SPIRE being determined only by uncertainties in the models of astronomical standards.

The Herschel Space Observatory enables us to accurately measure the bolometric output of starburst galaxies and active galactic nuclei (AGN) by directly sampling the peak of their far-infrared (IR) emission. Here we examine whether the spectral energy distribution (SED) and dust temperature of galaxies have strongly evolved over the last 80% of the age of the Universe. We discuss possible consequences for the determination of star-formation rates (SFR) and any evidence for a major change in their star-formation properties. We use Herschel deep extragalactic surveys from 100 to 500 μm to compute total IR luminosities in galaxies down to the faintest levels, using PACS and SPIRE in the GOODS-North field (PEP and HerMES key programs). An extension to fainter luminosities is done by stacking images on 24 μm prior positions. We show that measurements in the SPIRE bands can be used below the statistical confusion limit if information at higher spatial resolution is used, e.g. at 24 μm, to identify “isolated” galaxies whose flux is not boosted by bright neighbors. Below z ~ 1.5, mid-IR extrapolations are correct for star-forming galaxies with a dispersion of only 40% (0.15 dex), therefore similar to z ~ 0 galaxies, over three decades in luminosity below the regime of ultra-luminous IR galaxies (ULIRGs, LIR ≥ 1012 ). This narrow distribution is puzzling when considering the range of physical processes that could have affected the SED of these galaxies. Extrapolations from only one of the 160 μm, 250 μm or 350 μm bands alone tend to overestimate the total IR luminosity. This may be explained by the lack of far-IR constraints around and above ~150 μm (rest-frame) before Herschel on those templates. We also note that the dust temperature of luminous IR galaxies (LIRGs, LIR ≥ 1011 ) around z ~ 1 is mildly colder by 10–15% than their local analogs and up to 20% for ULIRGs at z ~ 1.6 (using a single modified blackbody-fit to the peak far-IR emission with an emissivity index of β = 1.5). Above z = 1.5, distant galaxies are found to exhibit a substantially larger mid- over far-IR ratio, which could either result from stronger broad emission lines or warm dust continuum heated by a hidden AGN. Two thirds of the AGNs identified in the field with a measured redshift exhibit the same behavior as purely star-forming galaxies. Hence a large fraction of AGNs harbor coeval star formation at very high SFR and in conditions similar to purely star-forming galaxies.

We set out to determine the ratio, qIR, of rest-frame 8–1000-μm flux, SIR, to monochromatic radio flux, S1.4 GHz, for galaxies selected at far-infrared (IR) and radio wavelengths, to search for signs that the ratio evolves with redshift, luminosity or dust temperature, Td, and to identify any far-IR-bright outliers – useful laboratories for exploring why the far-IR/radio correlation (FIRRC) is generally so tight when the prevailing theory suggests variations are almost inevitable. We use flux-limited 250-μm and 1.4-GHz samples, obtained using Herschel and the Very Large Array (VLA) in GOODS-North (-N). We determine bolometric IR output using ten bands spanning λobs = 24–1250 μm, exploiting data from PACS and SPIRE (PEP; HerMES), as well as Spitzer, SCUBA, AzTEC and MAMBO. We also explore the properties of an LIR-matched sample, designed to reveal evolution of qIR with redshift, spanning log LIR = 11–12 and z = 0–2, by stacking into the radio and far-IR images. For 1.4-GHz-selected galaxies in GOODS-N, we see tentative evidence of a break in the flux ratio, qIR, at L1.4 GHz ~ 1022.7 W Hz-1, where active galactic nuclei (AGN) are starting to dominate the radio power density, and of weaker correlations with redshift and Td. From our 250-μm-selected sample we identify a small number of far-IR-bright outliers, and see trends of qIR with L1.4 GHz, LIR, Td and redshift, noting that some of these are inter-related. For our LIR-matched sample, there is no evidence that qIR changes significantly as we move back into the epoch of galaxy formation: we find qIR (1+z)γ, where γ = -0.04±0.03 at z = 0–2; however, discounting the least reliable data at z < 0.5 we find γ = -0.26±0.07, modest evolution which may be related to the radio background seen by ARCADE 2, perhaps driven by 1.

We use the Spitzer Wide-area InfraRed Extragalactic Legacy Survey (SWIRE) to explore the specific star-formation activity of galaxies and their evolution near the peak of the cosmic far-infrared (FIR) background at 70 and 160um. We use a stacking analysis to determine the mean FIR properties of well defined subsets of galaxies at flux levels well below the FIR catalogue detection limits of SWIRE and other Spitzer surveys. We tabulate the contribution of different subsets of galaxies to the FIR background at 70um and 160um. These long wavelengths provide a good constraint on the bolometric, obscured emission. The large area provides good constraints at low z and in finer redshift bins than previous work. At all redshifts we find that the specific FIR Luminosity (sLFIR) decreases with increasing mass, following a trend L_FIR/M* propto M_* ^beta with beta =-0.38\pm0.14. This is a more continuous change than expected from the {Delucia2007} semi-analytic model suggesting modifications to the feedback prescriptions. We see an increase in the sLFIR by about a factor of ~100 from 0, v2 Update doesn't change the content of the paper, but now includes data files for the plots Fig 5-13 (all.plotdat, spi.plotdat and ell.plotdat on arXiv package)

Local luminosity functions are fundamental benchmarks for high-redshift galaxy formation and evolution studies as well as for models describing\ud these processes. Determining the local luminosity function in the submillimeter range can help to better constrain in particular the bolometric\ud luminosity density in the local Universe, and Herschel offers the first opportunity to do so in an unbiased way by imaging large sky areas at\ud several submillimeter wavelengths. We present the first Herschel measurement of the submillimeter 0 < z < 0.2 local luminosity function\ud and infrared bolometric (8−1000 μm) local luminosity density based on SPIRE data from the HerMES Herschel key program over 14.7 deg2.\ud Flux measurements in the three SPIRE channels at 250, 350 and 500 μm are combined with Spitzer photometry and archival data. We fit the\ud observed optical-to-submillimeter spectral energy distribution of SPIRE sources and use the 1/Vmax estimator to provide the first constraints on\ud the monochromatic 250, 350 and 500 μm as well as on the infrared bolometric (8−1000 μm) local luminosity function based on Herschel data.\ud We compare our results with modeling predictions and find a slightly more abundant local submillimeter population than predicted by a number\ud of models. Our measurement of the infrared bolometric (8−1000 μm) local luminosity function suggests a flat slope at low luminosity, and the\ud inferred local luminosity density, 1.31+0.24\ud −0.21\ud × 108 L� Mpc−3, is consistent with the range of values reported in recent literature.

Covering ~49 square degrees in 6 separate fields, the Spitzer Wide-area InfraRed Extragalactic (SWIRE) Legacy survey has the largest area among Spitzer’s “wedding cake” suite of extragalactic surveys. SWIRE is thus optimized for studies of large scale structure, population studies requiring excellent statistics, and searches for rare objects. We discuss the search for high redshift ultraluminous infrared galaxies (ULIRGs) with SWIRE. We have selected complete samples of F_(24μm) > 200 μJy, optically faint, candidate high redshift (z>1) ULIRGs, based on their mid-infrared spectral energy distributions (SEDs). These can be broadly categorized as star formation (SF)-dominated, based on the presence of a clear stellar peak at rest frame 1.6μm redshifted into the IRAC bands, or AGN-dominated if the SED rises featureless into the mid-infrared. AGN-dominated galaxies strongly dominate at the brightest 24μm fluxes, while SF-dominated objects rise rapidly in frequency as F_(24) drops, dominating the sample below 0.5 mJy. We derive photometric redshifts and luminosities for SFdominated objects sampling the z~1.2-3 range. Luminosity functions are being derived and compared with submm-selected samples at similar redshifts. The clustering, millimeter and IR spectral properties of the samples have also been investigated.

We use a simple optical/infrared photometric selection of high redshift QSOs which identifies a Lyman Break in the optical and requires a red IRAC color to distinguish QSOs from common interlopers. We find 100 U-dropout (z ~ 3) QSO candidates with r′ < 22 within 11.2 deg^2 in the ELAIS-N1 & ELAIS-N2 fields in the Spitzer Wide-area Infrared Extragalactic (SWIRE) Legacy Survey. Spectroscopy of 10 candidates shows that they are all QSOs with 2.83 < z < 3.44. We use detailed simulations which incorporate variations in QSO SEDs, IGM transmission and imaging depth to derive a completeness of 85- 90% between 3.0 < z < 3.4. The resulting luminosity function is two magnitudes fainter than SDSS and, when combined with those data, gives a faint end slope β = 1.62±0.18, consistent with measurements at z < 2 and steeper than initial measurements at the same redshift.

We study the ultraviolet to far-infrared (hereafter UV-to-IR) SEDs of a sample of intermediate-redshift (0.2 ≤ z ≤ 0.7) UV-selected galaxies from the ELAIS N1 and ELAIS N2 fields by fitting a multi-wavelength data set to a library of GRASIL templates. Star formation related properties of the galaxies are derived from the library of models by using Bayesian statistics. We find a decreasing presence of galaxies with low attenuation and low total luminosity as redshift decreases, which does not hold for high total luminosity galaxies. In addition, the dust attenuation of low-mass galaxies increases as redshift decreases, and this trend seems to disappear for galaxies with M_* ≥ 10^(11) M_⊙. This result is consistent with a mass-dependent evolution of the dust-to-gas ratio, which could be driven by a mass-dependent efficiency of star formation in star-forming galaxies. The specific star formation rates (SSFR) decrease with increasing stellar mass at all redshifts, and for a given stellar mass the SSFR decreases with decreasing redshift. The differences in the slope of the M^*-SSFR relation found between this work and others at similar redshift could be explained by the adopted selection criteria of the samples, which for a UV-selected sample, favors blue, star-forming galaxies.

By combining the VVDS with the SWIRE data, we have built the currently largest spectroscopic sample of galaxies selected in the rest-frame near-infrared. These allow us to investigate, for the first time using spectroscopic redshifts, the clustering evolution of galaxies selected from their rest-frame near-infrared luminosity in the redshift range 0.2, 11 pages, 8 figures. Accepted for publication in A&A

We present the SEDs of a hard X-ray selected sample containing 136 sources with F_(2-10 keV) > 10^(-14) erg cm^(-2) s^(-1); 132 are AGNs. The sources are detected in a 1 deg^2 area of the XMM-Newton Medium Deep Survey where optical data from the VVDS and CFHTLS and infrared data from the SWIRE survey are available. Based on a SED fitting technique we derive photometric redshifts with σ(1 + z) = 0.11 and 6% of outliers and identify AGN signatures in 83% of the objects. This fraction is higher than derived when a spectroscopic classification is available. The remaining 17^(+9)_(-6)% of AGNs show star-forming galaxy SEDs (SF class). The sources with AGN signatures are divided in two classes, AGN1 (33^(+6)_(-1)%) and AGN2 (50^(+6)_(-11)%). The AGN1 and AGN2 classes include sources whose SEDs are fitted by type 1 and type 2 AGN templates, respectively. On average, AGN1s show soft X-ray spectra, consistent with being unabsorbed, while AGN2s and SFs show hard X-ray spectra, consistent with being absorbed. The analysis of the average SEDs as a function of X-ray luminosity shows a reddening of the infrared SEDs, consistent with a decreasing contribution from the host galaxy at higher luminosities. The AGNs in the SF classes are likely obscured in the mid-infrared, as suggested by their low L_(3-20 μm)/L^(corr)_(0.5-10 keV) ratios. We confirm the previously found correlation for AGNs between the radio luminosity and the X-ray and the mid-infrared luminosities. The X-ray-radio correlation can be used to identify heavily absorbed AGNs. However, the estimated radio fluxes for the missing AGN population responsible for the bulk of the background at E > 10 keV are too faint to be detected even in the deepest current radio surveys.

We present measurements of the spatial clustering of ultraluminous infrared galaxies in two redshift intervals, 1.51. Adopting plausible models for the growth of DM haloes with redshift, then the haloes hosting the 2, ASP conference series. To appear in the conference proceedings for "At the edge of the Universe", Sintra, Portugal, October 2006. Six pages, one figure

Spectra have been obtained with the Infrared Spectrograph (IRS) on the Spitzer Space Telescope for 20 sources in the Lockman Hole field of the SWIRE survey. The sample is divided between sources with indicators of an obscured AGN, based primarily on X-ray detections of optically faint sources, and sources with indicators of a starburst, based on optical and near-infrared spectral energy distributions (SEDs), which show a luminosity peak from stellar photospheric emission. Ten of the 11 AGN sources have IRS spectra that show silicate absorption or are power laws; only one AGN source shows PAH emission features. All nine of the sources showing starburst SEDs in the near-infrared show PAH emission features in the IRS spectra. Redshifts are determined from the IRS spectra for all nine starbursts (1.0 < z < 1.9) and 8 of the 11 AGNs (0.6 < z < 2.5). Classification as AGN because of an X-ray detection, the classification as AGN or starburst derived from the photometric SED, and the IRS spectroscopic classification as AGN (silicate absorption) or starburst (PAH emission) are all consistent in 18 of 20 sources. The surface density for starbursts that are most luminous in the mid-infrared is less than that for the most luminous AGNs within the redshift interval 1.7 ≾ z ≾ 1.9. This result implies that mid-infrared source counts at high redshift are dominated by AGNs for f_ν(24 μm) ≳ 1.0 mJy.

We present details of the discovery of XLSS J022303.0−043622, a z= 1.2 cluster of galaxies. This cluster was identified from its X-ray properties and selected as a z > 1 candidate from its optical/near-infrared (IR) characteristics in the XMM Large-Scale Structure Survey (XMM-LSS). It is the most distant system discovered in the survey to date. We present ground-based optical and near-IR observations of the system carried out as part of the XMM-LSS survey. The cluster has a bolometric X-ray luminosity of 1.1 ± 0.7 × 10^44 erg s^−1 , fainter than most other known z > 1 X-ray selected clusters. In the optical it has a remarkably compact core, with at least a dozen galaxies inside a 125 kpc radius circle centred on the X-ray position. Most of the galaxies within the core, and those spectroscopically confirmed to be cluster members, have stellar masses similar to those of massive cluster galaxies at low redshift. They have colours comparable to those of galaxies in other z > 1 clusters, consistent with showing little sign of strong ongoing star formation. The bulk of the star formation within the galaxies appears to have ceased at least 1.5 Gyr before the observed epoch. Our results are consistent with massive cluster galaxies forming at z > 1 and passively evolving thereafter. We also show that the system is straightforwardly identified in Spitzer/IRAC 3.6- and 4.5-μm data obtained by the Spitzer Wide-area Infrared Extragalactic (SWIRE) survey emphasizing the power and utility of joint XMM and Spitzer searches for the most distant clusters.

We address the question of how to deal with confusion limited surveys in the mid-infrared domain by using informations from higher frequency observations over the same sky regions. Such informations, once applied to apparently extended mid-infrared sources, which are indeed ``blends'' of two or more different sources, allow us to disentangle the single counterparts and to split the measured flux density into different components. We present the application of this method to the 24 micron Spitzer archival data in the GOODS-EN1 test field, where apparently extended, ``blended'' sources constitute about 20% of a reliable sample of 983 sources detected above the 5-sigma threshold down to 23 microJy. As higher frequency data-set we have considered the public IRAC images and catalogues on the same field. We show that the 24 micron sample is almost unbiased down to ~40 microJy and the careful application of the deblending procedure does not require any statistical completeness correction (at least at the flux level considered). This is probed by direct comparison of our results with those of Chary et al. (2004), who analysed the same data-set through extensive Monte Carlo simulations. The deblending procedure reduces of about 30% the confusion limit of the MIPS 24 micron survey, allowing one to obtain reliable source counts down to ~40 microJy. The extrapolation of the source counts down to fainter fluxes suggests that our 24 micron sample is able to resolve ~62% of the cosmic background down to a flux level of 38 microJy., Comment: 10 pages, submitted to MNRAS on July 2005

We discuss optical associations, spectral energy distributions and photometric redshifts for SWIRE sources in the ELAIS-N1 area and the Lockman Validation Field. The band-merged IRAC (3.6, 4.5, 5.8 and 8.0 mu) and MIPS (24, 70, 160 mu) data have been associated with optical UgriZ data from the INT Wide Field Survey in ELAIS-N1, and with our own optical Ugri data in Lockman-VF. The spectral energy distributions of selected ELAIS sources in N1 detected by SWIRE, most with spectroscopic redshifts, are modelled in terms of a simple set of galaxy and quasar templates in the optical and near infrared, and with a set of dust emission templates (cirrus, M82 starburst, Arp 220 starburst, and AGN dust torus) in the mid infrared. The optical data, together with the IRAC 3.6 and 4.5 mu data, have been used to determine photometric redshifts. For galaxies with known spectroscopic redshifts there is a notable improvement in the photometric redshift when the IRAC data are used, with a reduction in the rms scatter from 10% in (1+z) to 7%. The photometric redshifts are used to derive the 3.6 and 24 mu redshift distribution and to compare this with the predictions of models. For those sources with a clear mid infrared excess, relative to the galaxy starlight model used for the optical and near infrared, the mid and far infrared data are modelled in terms of the same dust emission templates. The proportions found of each template type are: cirrus 31%, M82 29%, Arp 220 10%, AGN dust tori 29%. The distribution of the different infrared sed types in the L_{ir}/L_{opt} versus L_{ir} plane, where L_{ir} and L_{opt} are the infrared and optical bolometric luminosities, is discussed., Comment: Accepted for publication by Astronomical Journal, 21 figures (5 in colour). Fig 3 available at http://astro.ic.ac.uk/~mrr/