Towards a census of high-redshift dusty galaxies with Herschel (original) (raw)
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Towards a census of high-redshift dusty galaxies with Herschel A selection of " 500 µm-risers "
Context. Over the last decade a large number of dusty star forming galaxies has been discovered up to redshift z = 2 − 3 and recent studies have attempted to push the highly-confused Herschel SPIRE surveys beyond that distance. To search for z ≥ 4 galaxies they often consider the sources with fluxes rising from 250 µm to 500 µm (so-called "500 µm-risers"). Herschel surveys offer a unique opportunity to efficiently select a large number of these rare objects, and thus gain insight into the prodigious star-forming activity that takes place in the very distant Universe. Aims. We aim to implement a novel method to obtain a statistical sample of "500 µm-risers" and fully evaluate our selection inspecting different models of galaxy evolution. Methods. We consider one of the largest and deepest Herschel surveys, the Herschel Virgo Cluster Survey. We develop a novel selection algorithm which links the source extraction and spectral energy distribution fitting. To fully quantify selection biases we make end-to-end simulations including clustering and lensing. Results. We select 133 "500 µm-risers" over 55 deg 2 , imposing the criteria: S 500 > S 350 > S 250 , S 250 > 13.2 mJy and S 500 > 30 mJy. Differential number counts are in a fairly good agreement with models, displaying better match than other existing samples. The estimated fraction of strongly lensed sources is 24 +6 −5 % based on models. Conclusions. We present the faintest sample of "500 µm-risers" down to S 250 = 13.2 mJy. We show that noise and weak lensing have an important impact on measured counts and redshift distribution of selected sources. We estimate the flux-corrected star formation rate density at 4 < z < 5 with the "500 µm-risers" and found it close to the total value measured in far-infrared. It indicates that colour selection is not a limiting effect to search for the most massive, dusty z > 4 sources.
2017
Context. Over the last decade a large content of dusty star forming galaxies has been discovered up to redshift z = 2 − 3 and recent studies have attempted to push the highly-confused Herschel SPIRE surveys beyond that distance. To search for z ≥ 4 galaxies they often consider the sources with fluxes rising from 250 µm to 500 µm (so-called "500 µm-risers"). Herschel surveys offer a unique opportunity to efficiently select a large number of these rare objects, and thus gain insight into the prodigious star-forming activity that takes place in the very distant Universe. Aims. We aim to implement a novel method to obtain a statistical sample of "500 µm-risers" and fully evaluate our selection inspecting different models of galaxy evolution. Methods. We consider one of the largest and deepest Herschel surveys, the Herschel Virgo Cluster Survey. We develop a novel selection algorithm which links the source extraction and spectral energy distribution fitting. To fully quantify selection biases we make end-to-end simulations including clustering and lensing. Results. We select 133 "500 µm-risers" over 55 deg 2 , imposing the criteria: S 500 > S 350 > S 250 , S 250 > 13.2 mJy and S 500 >30 mJy. Differential number counts are in a fairly good agreement with models, displaying better match than other existing samples. Our technique allows us to recover ∼ 60% of genuine 500 µm-risers with redshift distribution peaking at z 4. Conclusions. Selecting the "500 µm-risers" that fulfil our criteria is an efficient way to pre-select z 4 galaxies from SPIRE data alone. We show that noise and weak lensing have an important impact on measured counts and redshift distribution of selected sources. We estimate the flux-corrected star formation rate density at 4 < z < 5 with the "500 µm-risers" and found it close to the total value measured in far-infrared. It indicates that colour selection is not a limiting effect to search for the most massive, dusty z > 4 sources.
HerMES: CANDIDATE HIGH-REDSHIFT GALAXIES DISCOVERED WITH HERSCHEL /SPIRE
The Astrophysical Journal, 2014
We present a method for selecting z > 4 dusty, star forming galaxies (DSFGs) using Herschel/SPIRE 250/350/500 µm flux densities to search for red sources. We apply this method to 21 deg 2 of data from the HerMES survey to produce a catalog of 38 high-z candidates. Follow-up of the first 5 of these sources confirms that this method is efficient at selecting high-z DSFGs, with 4/5 at z = 4.3 to 6.3 (and the remaining source at z = 3.4), and that they are some of the most luminous dusty sources known. Comparison with previous DSFG samples, mostly selected at longer wavelengths (e.g., 850 µm) and in single-band surveys, shows that our method is much more efficient at selecting high-z DSFGs, in the sense that a much larger fraction are at z > 3. Correcting for the selection completeness and purity, we find that the number of bright (S 500µm ≥ 30 mJy), red Herschel sources is 3.3 ± 0.8 deg −2 . This is much higher than the number predicted by current models, suggesting that the DSFG population extends to higher redshifts than previously believed. If the shape of the luminosity function for high-z DSFGs is similar to that at z ∼ 2, rest-frame UV based studies may be missing a significant component of the star formation density at z = 4 to 6, even after correction for extinction.
Astronomy & Astrophysics, 2019
Aims. We study the statistical properties of dusty star-forming galaxies across cosmic time, such as their number counts, luminosity functions (LF), and the dust-obscured star formation rate density (SFRD). Methods. We used the most recent de-blended Herschel catalogue in the COSMOS field to measure the number counts and LFs at far-infrared (FIR) and sub-millimetre (sub-mm) wavelengths. The de-blended catalogue was generated by combining the Bayesian source extraction tool XID+ and an informative prior derived from the associated deep multi-wavelength photometric data. Results. Through our de-confusion technique and based on the deep multi-wavelength photometric information, we are able to achieve more accurate measurements while at the same time probing roughly ten times below the Herschel confusion limit. Our number counts at 250 μm agree well with previous Herschel studies. However, our counts at 350 and 500 μm are below previous Herschel results because previous Herschel studies...
Herschel unveils a puzzling uniformity of distant dusty galaxies
Astronomy & Astrophysics, 2010
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 since z~2.5. We use Herschel deep extragalactic surveys from 100 to 500um 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). We show that measurements in the SPIRE bands can be used below the statistical confusion limit if information at higher spatial resolution is used 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% (0.15dex), therefore similar to z~0 galaxies. 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 160um, 250um or 350um bands alone tend to overestimate the total IR luminosity. This may be explained by the lack of far-IR constraints around and above ~150um (rest-frame) on local templates. We also note that the dust temperature of luminous IR galaxies around z~1 is mildly colder by 10-15% than their local analogs and up to 20% for ULIRGs at z~1.6. 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 star formation at very high SFR and in conditions similar to purely star-forming galaxies.
The Astrophysical Journal, 2012
The wide-area imaging surveys with the Herschel Space Observatory at submillimeter (sub-mm) wavelengths have now resulted in catalogs of the order of one-hundred-thousand dusty, starburst galaxies. These galaxies capture an important phase of galaxy formation and evolution, but, unfortunately, the redshift distribution of these galaxies, N(z), is still mostly uncertain due to limitations associated with counterpart identification at optical wavelengths and spectroscopic follow-up. We make a statistical estimate of N (z) using a clustering analysis of sub-mm galaxies detected at each of 250, 350 and 500 μm from the Herschel Multi-tiered Extragalactic Survey centered on the Boötes field. We cross-correlate Herschel galaxies against galaxy samples at optical and near-IR wavelengths from the Sloan Digital Sky Survey, the NOAO Deep Wide Field Survey, and the Spitzer Deep Wide Field Survey. We create optical and near-IR galaxy samples based on their photometric or spectroscopic redshift distributions and test the accuracy of those redshift distributions with similar galaxy samples defined with catalogs from the Cosmological Evolution Survey (COSMOS), which has superior spectroscopic coverage. We model the clustering auto-and cross-correlations of Herschel and optical/IR galaxy samples to estimate N (z) and clustering bias factors. The S 350 > 20 mJy galaxies have a bias factor varying with redshift as b(z) = 1.0 +1.0 −0.5 (1 + z) 1.2 +0.3 −0.7. This bias and the redshift dependence is broadly in agreement with galaxies that occupy dark matter halos of mass in the range of 10 12 to 10 13 M. We find that galaxy selections in all three Spectral and Photometric Imaging Receiver (SPIRE) bands share a similar average redshift, with z = 1.8 ± 0.2 for 250 μm selected samples, and z = 1.9 ± 0.2 for both 350 and 500 μm samples, while their distributions behave differently. For 250 μm selected galaxies we find the a larger number of sources with z 1 when compared with the subsequent two SPIRE bands, with 350 and 500 μm selected SPIRE samples having peaks in N (z) at progressively higher redshifts. We compare our clustering-based N(z) results to sub-mm galaxy model predictions in the literature, and with an estimate of N (z) using a stacking analysis of COSMOS 24 μm detections.
The Astrophysical Journal, 2013
We combine far-infrared photometry from Herschel (PEP/HERMES) with deep mid-infrared spectroscopy from Spitzer to investigate the nature and the mass assembly history of a sample of 31 Luminous and Ultraluminous Infrared Galaxies at z∼1 and 2 selected in GOODS-S with 24 µm fluxes between 0.2 and 0.5 mJy. We model the data with a self-consistent physical model (GRASIL) which includes a stateof-the-art treatment of dust extinction and reprocessing. We find that all of our galaxies appear to require massive populations of old (> 1 Gyr) stars and, at the same time, to host a moderate ongoing activity of SF (SFR ≤ 100 M ⊙ /yr). The bulk of the stars appear to have been formed a few Gyr before the observation in essentially all cases. Only five galaxies of the sample require a recent starburst superimposed on a quiescent star formation history (SFH). We also find discrepancies between our results and those based on optical-only SED fitting for the same objects; by fitting their observed Spectral Energy Distributions with our physical model we find higher extinctions (by ∆A V ∼ 0.81 and 1.14) and higher stellar masses (by ∆Log(M ⋆ ) ∼ 0.16 and 0.36 dex) for z∼1 and z∼2 (U)LIRGs, respectively. The stellar mass difference is larger for the most dust obscured objects. We also find lower SFRs than those computed from L IR using the Kennicutt relation due to the significant contribution to the dust heating by intermediate-age stellar populations through 'cirrus' emission (∼73% and ∼66% of total L IR for z ∼ 1 and z ∼ 2 (U)LIRGs, respectively).
Herschel-ATLAS: Properties of dusty massive galaxies at low and high redshifts
2014
We present a comparison of the physical properties of a rest-frame 250µm selected sample of massive, dusty galaxies from 0 < z < 5.3. Our sample comprises 29 highredshift submillimetre galaxies (SMGs) from the literature, and 843 dusty galaxies at z < 0.5 from the Herschel -ATLAS, selected to have a similar stellar mass to the SMGs. The z > 1 SMGs have an average SFR of 390 +80 −70 M ⊙ yr −1 which is 120 times that of the low-redshift sample matched in stellar mass to the SMGs (SFR= 3.3 ± 0.2 M ⊙ yr −1 ). The SMGs harbour a substantial mass of dust (1.2 +0.3 −0.2 × 10 9 M ⊙ ), compared to (1.6 ± 0.1) × 10 8 M ⊙ for low-redshift dusty galaxies. At low redshifts the dust luminosity is dominated by the diffuse ISM, whereas a large fraction of the dust luminosity in SMGs originates from star-forming regions. At the same dust mass SMGs are offset towards a higher SFR compared to the low-redshift H-ATLAS galaxies. This is not only due to the higher gas fraction in SMGs but also because they are undergoing a more efficient mode of star formation, which is consistent with their bursty star-formation histories. The offset in SFR between SMGs and low-redshift galaxies is similar to that found in CO studies, suggesting that dust mass is as good a tracer of molecular gas as CO.
THE QUEST FOR DUSTY STAR-FORMING GALAXIES AT HIGH REDSHIFT Z 4
We exploit the continuity equation approach and the 'main sequence' star-formation timescales to show that the observed high abundance of galaxies with stellar masses a few 10 10 M ⊙ at redshift z 4 implies the existence of a galaxy population featuring large star formation rates (SFRs) ψ 10 2 M ⊙ yr −1 in heavily dust-obscured conditions. These galaxies constitute the high-redshift counterparts of the dusty star-forming population already surveyed for z 3 in the far-IR band by the Herschel space observatory. We work out specific predictions for the evolution of the corresponding stellar mass and SFR functions out to z ∼ 10, elucidating that the number density at z 8 for SFRs ψ 30 M ⊙ yr −1 cannot be estimated relying on the UV luminosity function alone, even when standard corrections for dust extinction based on the UV slope are applied. We compute the number counts and redshift distributions (including galaxy-scale gravitational lensing) of this galaxy population, and show that current data from AzTEC-LABOCA, SCUBA-2 and ALMA-SPT surveys are already digging into it. We substantiate how an observational strategy based on a color preselection in the far-IR or (sub-)mm band with Herschel and SCUBA-2, supplemented by photometric data via on-source observations with ALMA, can allow to reconstruct the bright end of the SFR functions out to z 8. In parallel, such a challenging task can be managed by exploiting current UV surveys in combination with (sub-)mm observations by ALMA and NIKA2 and/or radio observations by SKA and its precursors.
Galaxy evolution from deep multi-wavelength infrared surveys: a prelude to Herschel
Arxiv preprint arXiv: …, 2009
Context. Studies of the generation and assembly of stellar populations in galaxies largely benefit from far-IR observations, considering that the IR flux is a close prior to the rate of star formation (the bulk of which happens in dust-obscured environments). At the same time, major episodes of nuclear AGN accretion are also dust-obscured and visible in the IR. Aims. At the end of the Spitzer cryogenic mission and the onset of the Herschel era, we review our current knowledge of galaxy evolution at IR wavelengths, and model it to achieve as far as a complete view of the evolution of cosmic sources. We also develop new tools for the analysis of background fluctuations to constrain source counts in regimes of high confusion, as it happens for the Herschel sub-mm surveys. Methods. We analysed a wide variety of new data on galaxy evolution and high-redshift source populations from Spitzer cosmological surveys, and confront them with complementary data from mm ground-based observations and constraints from the far-IR diffuse radiation, as well as preliminary results from Herschel surveys. Results. These data confirm earlier indications about a very rapid increase in galaxy volume emissivity with redshift up to z ≃ 1 [ρ(z) ∝ (1 + z) 4 ], the fastest evolution rate observed for galaxies at any wavelengths. The observed Spitzer counts require a combination of fast evolution for the dominant population and a bumpy spectrum with substantial PAH emission at z ∼ 1 to 2. Number counts at long wavelengths (70 through 1100 µm) confirm these results. All the present data require that the fast observed evolution from z=0 to 1 flattens around redshift 1 and then keeps approximately constant up to z ≃ 2.5 at least. Our estimated redshift-dependent bolometric comoving energy density keeps lower at z 1.5 than some previously published results based on either large extinction corrections, or large spectral extrapolations. Conclusions. The present-day IR/sub-mm data provide evidence of a distinct population of very luminous galaxies becoming dominant at z > 1. Their cosmological evolution, peaking around z ≃ 2, shows a faster decay with cosmic time than lower luminosity systems, whose maximal activity is set around z ≃ 1, then supporting an earlier phase of formation for the most luminous and massive galaxies. From a comparison of our results on the comoving IR emissivity with recent estimates of the redshift-dependent stellar mass functions of galaxies, we find that the two agree well with each other if we assume standard recipes for star formation (a universal Salpeter IMF) and standard fractions (∼ 20 − 30%) for the contribution of obscured AGN accretion. Systematic exploitation of the forthcoming Herschel survey data will be important for confirming all this.