We combine Herschel-Photodetector Array Camera and Spectrometer (PACS) data from the PACS Evolutionary Probe (PEP) program with Spitzer 24 mu m and 16 mu m photometry and ultra deep Infrared ...Spectrograph (IRS) mid-infrared spectra to measure the mid- to far-infrared spectral energy distribution (SED) of 0.7 < z < 2.5 normal star-forming galaxies (SFGs) around the main sequence (the redshift-dependent relation of star formation rate (SFR) and stellar mass). Our very deep data confirm from individual far-infrared detections that z ~ 2 SFRs are overestimated if based on 24 mu m fluxes and SED templates that are calibrated via local trends with luminosity. Galaxies with similar ratios of rest-frame nuL sub(nu)(8) to 8-1000 mu m infrared luminosity (LIR) tend to lie along lines of constant offset from the main sequence. We explore the relation between SED shape and offset in specific star formation rate (SSFR) from the redshift-dependent main sequence. Main-sequence galaxies tend to have a similar nuL sub(nu)(8)/LIR regardless of LIR and redshift, up to z ~ 2.5, and nuL sub(nu)(8)/LIR decreases with increasing offset above the main sequence in a consistent way at the studied redshifts. We provide a redshift-independent calibration of SED templates in the range of 8-60 mu m as a function of Delta log(SSFR) offset from the main sequence. Redshift dependency enters only through the evolution of the main sequence with time. Ultra deep IRS spectra match these SED trends well and verify that they are mostly due to a change in ratio of polycyclic aromatic hydrocarbon (PAH) to LIR rather than continua of hidden active galactic nuclei (AGNs). Alternatively, we discuss the dependence of nuL sub(nu)(8)/LIR on LIR. The same nuL sub(nu)(8)/LIR is reached at increasingly higher LIR at higher redshift, with shifts relative to local by 0.5 and 0.8 dex in log(LIR) at redshifts z ~ 1 and z ~ 2. Corresponding SED template calibrations are provided for use if no stellar masses are on hand. For most of those z ~ 2 SFGs that also host an AGN, the mid-infrared is dominated by the star-forming component.
The complete characterization of the pressure profile of high-redshift galaxy clusters, from their core to their outskirts, is a major issue for the study of the formation of large-scale structures. ...It is essential to constrain a potential redshift evolution of both the slope and scatter of the mass-observable scaling relations used in cosmology studies based on cluster statistics. In this paper, we present the first thermal Sunyaev–Zel’dovich (tSZ) mapping of a cluster from the sample of the New IRAM Kids Arrays (NIKA2) SZ large program that aims at constraining the redshift evolution of cluster pressure profiles and the tSZ-mass scaling relation. We observed the galaxy cluster PSZ2 G144.83+25.11 at redshift z = 0.58 with the NIKA2 camera, a dual-band (150 and 260 GHz) instrument operated at the Institut de Radioastronomie Millimtrique (IRAM) 30-m telescope. We identify a thermal pressure excess in the south-west region of PSZ2 G144.83+25.11 and a high-redshift sub-millimeter point source that affect the intracluster medium (ICM) morphology of the cluster. The NIKA2 data are used jointly with tSZ data acquired by the Multiplexed SQUID/TES Array at Ninety Gigahertz (MUSTANG), Bolocam, and Planck experiments in order to non-parametrically set the best constraints on the electronic pressure distribution from the cluster core (R ~ 0.02R500) to its outskirts (R ~ 3R500). We investigate the impact of the over-pressure region on the shape of the pressure profile and on the constraints on the integrated Compton parameter Y500. A hydrostatic mass analysis is also performed by combining the tSZ-constrained pressure profile with the deprojected electronic density profile from XMM-Newton. This allows us to conclude that the estimates of Y500 and M500 obtained from the analysis with and without masking the disturbed ICM region differ by 65% and 79%, respectively. This work highlights that NIKA2 will have a crucial impact on the characterization of the scatter of the Y500−M500 scaling relation due to its high potential to constrain the thermodynamic and morphological properties of the ICM when used in synergy with X-ray observations of similar angular resolution. This study also presents the typical products that will be delivered to the community for all clusters included in the NIKA2 tSZ Large Program.
We present first results of a study aimed to constrain the star formation rate and dust content of galaxies at z~2. We use a sample of BzK-selected star-forming galaxies, drawn from the COSMOS ...survey, to perform a stacking analysis of their 1.4 GHz radio continuum as a function of different stellar population properties, after removing AGN contaminants from the sample. Dust unbiased star formation rates are derived from radio fluxes assuming the local radio-IR correlation. The main results of this work are: i) specific star formation rates are constant over about 1 dex in stellar mass and up to the highest stellar mass probed; ii) the dust attenuation is a strong function of galaxy stellar mass with more massive galaxies being more obscured than lower mass objects; iii) a single value of the UV extinction applied to all galaxies would lead to grossly underestimate the SFR in massive galaxies; iv) correcting the observed UV luminosities for dust attenuation based on the Calzetti recipe provide results in very good agreement with the radio derived ones; v) the mean specific star formation rate of our sample steadily decreases by a factor of ~4 with decreasing redshift from z=2.3 to 1.4 and a factor of ~40 down the local Universe. These empirical SFRs would cause galaxies to dramatically overgrow in mass if maintained all the way to low redshifts, we suggest that this does not happen because star formation is progressively quenched, likely starting from the most massive galaxies.
Using Herschel data from the deepest SPIRE and PACS surveys (HerMES and PEP) in COSMOS, GOODS-S and GOODS-N, we examine the dust properties of infrared (IR)-luminous (L
IR > 1010 L) galaxies at 0.1 < ...z < 2 and determine how these evolve with cosmic time. The unique angle of this work is the rigorous analysis of survey selection effects, making this the first study of the star-formation-dominated, IR-luminous population within a framework almost entirely free of selection biases. We find that IR-luminous galaxies have spectral energy distributions (SEDs) with broad far-IR peaks characterized by cool/extended dust emission and average dust temperatures in the 25-45 K range. Hot (T > 45 K) SEDs and cold (T < 25 K), cirrus-dominated SEDs are rare, with most sources being within the range occupied by warm starbursts such as M82 and cool spirals such as M51. We observe a luminosity-temperature (L-T) relation, where the average dust temperature of log L
IR/L ∼ 12.5 galaxies is about 10 K higher than that of their log L
IR/L ∼ 10.5 counterparts. However, although the increased dust heating in more luminous systems is the driving factor behind the L-T relation, the increase in dust mass and/or starburst size with luminosity plays a dominant role in shaping it. Our results show that the dust conditions in IR-luminous sources evolve with cosmic time: at high redshift, dust temperatures are on average up to 10 K lower than what is measured locally (z 0.1). This is manifested as a flattening of the L-T relation, suggesting that (ultra)luminous infrared galaxies (U)LIRGs in the early Universe are typically characterized by a more extended dust distribution and/or higher dust masses than local equivalent sources. Interestingly, the evolution in dust temperature is luminosity dependent, with the fraction of LIRGs with T < 35 K showing a two-fold increase from z ∼ 0 to z ∼ 2, whereas that of ULIRGs with T < 35 K shows a six-fold increase. Our results suggest a greater diversity in the IR-luminous population at high redshift, particularly for ULIRGs.
We present observations of the COJ = 3 arrow right 2 emission toward two massive and infrared luminous Lyman break galaxies (LBGs) at z = 3.21 and z = 2.92, using the IRAM Plateau de Bure ...Interferometer, placing first constraints on the molecular gas masses (M sub(gas)) of non-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 super(-1), despite their large infrared luminosities (L sub(IR) approximate (2-3) x 10 super(12) L sub(middot in circle)) derived from Herschel. With one plausible CO detection (spurious detection probability of 10 super(-3)) and one upper limit, we investigate the evolution of the molecular gas-to-stellar mass ratio (M sub(gas)/Mlo w *) with redshift. Our data suggest that the steep evolution of M sub(gas)/Mlow * 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.
We explore the gas-to-dust mass ratio (M gas/M d) and the CO luminosity-to-M gas conversion factor ( Delta *aCO) of two well-studied galaxies in the Great Observatories Origins Deep Survey North ...field that are expected to have different star-forming modes, the starburst GN20 at z = 4.05 and the normal star-forming galaxy BzK-21000 at z = 1.52. Detailed sampling is available for their Rayleigh-Jeans emission via ground-based millimeter (mm) interferometry (1.1-6.6 mm) along with Herschel PACS and SPIRE data that probe the peak of their infrared emission. Using the physically motivated Draine & Li models, as well as a modified blackbody function, we measure the dust mass (M dust) of the sources and find (2.0+0.7 --0.6 X 109) M for GN20 and (8.6+0.6 --0.9 X 108) M for BzK-21000. The addition of mm data reduces the uncertainties of the derived M dust by a factor of ~2, allowing the use of the local M gas/M d versus metallicity relation to place constraints on the Delta *aCO values of the two sources. For GN20 we derive a conversion factor of Delta *aCO < 1.0 M pc--2 (K km s--1)--1, consistent with that of local ultra-luminous infrared galaxies, while for BzK-21000 we find a considerably higher value, Delta *aCO ~4.0 M pc--2 (K km s--1)--1, in agreement with an independent kinematic derivation reported previously. The implied star formation efficiency is ~25 L /M for BzK-21000, a factor of ~5-10 lower than that of GN20. The findings for these two sources support the existence of different disk-like and starburst star formation modes in distant galaxies, although a larger sample is required to draw statistically robust results.
zCOSMOS is a large-redshift survey that is being undertaken in the COSMOS field using 600 hr of observation with the VIMOS spectrograph on the 8 m VLT. The survey is designed to characterize the ...environments of COSMOS galaxies from the 100 kpc scales of galaxy groups up to the 100 Mpc scale of the cosmic web and to produce diagnostic Information on galaxies and active galactic nuclei. The zCOSMOS survey consists of two parts: (1) zCOSMOS-bright, a magnitude-limited I-band ha < 22.5 sample of about 20,000 galaxies with 0.1 < z < 1.2 covering the whole 1.7 deg super(2) COSMOS ACS field, for which the survey parameters at z similar to 0.7 are designed to be directly comparable to those of the 2dFGRS at z similar to 0.1; and (2) zCOSMOS-deep, a survey of approximately 10,000 galaxies selected through color-selection criteria to have 1.4 < z < 3.0, within the central 1 deg super(2). This paper describes the survey design and the construction of the target catalogs and briefly outlines the observational program and the data pipeline. In the first observing season, spectra of 1303 zCOSMOS-bright targets and 977 zCOSMOS-deep targets have been obtained. These are briefly analyzed to demonstrate the characteristics that may be expected from zCOSMOS, and particularly zCOSMOS-bright, when it is finally completed between 2008 and 2009. The power of combining spectroscopic and photometric redshifts is demonstrated, especially in correctly identifying the emission line in single-line spectra and in determining which of the less reliable spectroscopic redshifts are correct and which are incorrect. These techniques bring the overall success rate in the zCOSMOS-bright so far to almost 90% and to above 97% in the 0.5 < z < 0.8 redshift range. Our zCOSMOS-deep spectra demonstrate the power of our selection techniques to Isolate high-redshift galaxies at 1.4 < z < 3, C and of VIMOS to measure their redshifts using ultraviolet absorption lines.
The COSMOS Spitzer survey (S-COSMOS) is a Legacy program (Cycles 2+3) designed to carry out a uniform deep survey of the full 2 deg(2) COSMOS field in all seven Spitzer bands (3.6, 4.5, 5.6, 8.0, ...24.0, 70.0, and 160.0 km). This paper describes the survey parameters, mapping strategy, data reduction procedures, achieved sensitivities to date, and the complete data set for future reference. We show that the observed infrared backgrounds in the S-COSMOS field are within 10% of the predicted background levels. The fluctuations in the background at 24 urn have been measured and do not show any significant contribution from cirrus, as expected. In addition, we report on the number of asteroid detections in the low Galactic latitude COSMOS field. We use the Cycle 2 S-COSMOS data to determine preliminary number counts, and compare our results with those from previous Spitzer Legacy surveys (e.g., SWIRE, GOODS). The results from this "first analysis" confirm that the S-COSMOS survey will have sufficient sensitivity with IRAC to detect 6L* disks and spheroids out to z unk 3, and with MIPS to detect ultraluminous starbursts and AGNs out to z 6 3 at 24 km and out to z 6 1.5-2 at 70 and 160 km.
We compare the average star formation (SF) activity in X-ray selected AGN hosts with a mass-matched control sample of inactive galaxies, including both star forming and quiescent sources, in the ...0.5 < z < 2.5 redshift range. Recent observations carried out by PACS, the 60−210 μm photometric camera on board the Herschel Space Observatory, in GOODS-S, GOODS-N and COSMOS allow us to obtain an unbiased estimate of the far-IR luminosity, and hence of the SF properties, of the two samples. Accurate AGN host stellar mass estimates are obtained by decomposing their total emission into the stellar and the nuclear components. We report evidence of a higher average SF activity in AGN hosts with respect to the control sample of inactive galaxies. The level of SF enhancement is modest (~0.26 dex at ~3σ confidence level) at low X-ray luminosities (LX ≲ 1043.5 erg s-1) and more pronounced (0.56 dex at > 10σ confidence level) in the hosts of luminous AGNs. However, when comparing to star forming galaxies only, AGN hosts are found broadly consistent with the locus of their “main sequence”. We investigate the relative far-IR luminosity distributions of active and inactive galaxies, and find a higher fraction of PACS detected, hence normal and highly star forming systems among AGN hosts. Although different interpretations are possible, we explain our findings as a consequence of a twofold AGN growth path: faint AGNs evolve through secular processes, with instantaneous AGNaccretion not tightly linked to the current total SF in the host galaxy, while the luminous AGNs co-evolve with their hosts through periods of enhanced AGN activity and star formation, possibly through major mergers. While an increased SF activity with respect to inactive galaxies of similar mass is expected in the latter, we interpret the modest SF offsets measured in low-LX AGN hosts as either a) generated by non-synchronous accretion and SF histories in a merger scenario or b) due to possible connections between instantaneous SF and accretion that can be induced by smaller scale (non-major merger) mechanisms. Far-IR luminosity distributions favour the latter scenario.
The inner 20 x 20 arcmin super(2) of the COSMOS field was imaged at 250 GHz (1.2 mm) to an rms noise level of similar to 1 mJy per 11" beam using the Max-Planck Millimeter Bolometer Array (MAMBO-2) ...at the IRAM 30 m telescope. We detect 15 sources at significance between 4 and 7 a, 11 of which are also detected at 1.4 GHz with the VLA with a flux density >24 mu Jy (3 sigma ). We Identify 12 more lower significance mm sources based on their association with faint radio sources. We present the multifrequency Identifications of the MAMBO sources, including VLA radio flux densities, optical and near-infrared identifications, as well as the XMM-Newton X-ray detection for two of the mm sources. We compare radio and optical photometric redshifts and briefly describe the host galaxy morphologies. The colors of the identified optical counterparts suggest most of them to be high-redshift (z similar to 2-3) star-forming galaxies. At least three sources appear lensed by a foreground galaxy. We highlight some MAMBO sources that do not show obvious radio counterparts. These sources could be dusty starburst galaxies at redshifts >3.5. The 250 GHz source areal density in the COSMOS field is comparable to that seen in other deep mm fields.
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