The Herschel Multi-Tiered Extragalactic Survey: SPIRE-mm Photometric Redshifts

Monthly Notices of the Royal Astronomical Society (Impact Factor: 5.11). 09/2011; 419(4). DOI: 10.1111/j.1365-2966.2011.19827.x
Source: arXiv


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 500
{\mu}m by the SPIRE instrument on Herschel. From a sample of 63 previously
identified mm-sources with reliable radio identifications in the GOODS-N 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 {\tau} = ({\nu}/{\nu}0)^{\beta}
where {\beta} = +1.8 and {\nu}0 = c/100 {\mu}m. 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 |z|/(1+z) = 0.16 (<
|z| >= 0.51). Including constraints from the radio-far IR correlation the
accuracy is improved to |z|/(1 + z) = 0.15 (< |z| >= 0.45). We estimate the
redshift distribution of mm-selected sources finding a significant excess at z
> 3 when compared to ~ 850 {\mu}m selected samples.

Download full-text


Available from: N. Castro-Rodriguez, Oct 07, 2015
206 Reads
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Establishing the stellar masses (M*), and hence specific star-formation rates (sSFRs) of submillimetre galaxies (SMGs) is crucial for determining their role in the cosmic galaxy/star formation. However, there is as yet no consensus over the typical M* of SMGs. Specifically, even for the same set of SMGs, the reported average M* have ranged over an order of magnitude, from ~5x10^10 Mo to ~5x10^11 Mo. Here we study how different methods of analysis can lead to such widely varying results. We find that, contrary to recent claims in the literature, potential contamination of IRAC 3-8 um photometry from hot dust associated with an active nucleus is not the origin of the published discrepancies in derived M*. Instead, we expose in detail how inferred M* depends on assumptions made in the photometric fitting, and quantify the individual and cumulative effects of different choices of initial mass function, different brands of evolutionary synthesis models, and different forms of assumed star-formation history. We review current observational evidence for and against these alternatives as well as clues from the hydrodynamical simulations, and conclude that, for the most justifiable choices of these model inputs, the average M* of SMGs is ~2x10^11 Mo. We also confirm that this number is perfectly reasonable in the light of the latest measurements of their dynamical masses, and the evolving M* function of the overall galaxy population. M* of this order imply that the average sSFR of SMGs is comparable to that of other star-forming galaxies at z>2, at 2-3 Gyr^-1. This supports the view that, while rare outliers may be found at any M*, most SMGs simply form the top end of the main-sequence of star-forming galaxies at these redshifts. Conversely, this argues strongly against the viewpoint that SMGs are extreme pathological objects, of little relevance in the cosmic history of star-formation.
    Astronomy and Astrophysics 08/2011; 541. DOI:10.1051/0004-6361/201016308 · 4.38 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The Herschel Multi-tiered Extragalactic Survey, HerMES, is a legacy program designed to map a set of nested fields totalling ~380 deg^2. Fields range in size from 0.01 to ~20 deg^2, using Herschel-SPIRE (at 250, 350 and 500 \mu m), and Herschel-PACS (at 100 and 160 \mu m), 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 re-processed optical and ultra-violet radiation from star formation that has been absorbed by dust, and are critical for forming a complete multi-wavelength understanding of galaxy formation and evolution. The survey will detect of order 100,000 galaxies at 5\sigma 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.
    Monthly Notices of the Royal Astronomical Society 03/2012; 424(3). DOI:10.1111/j.1365-2966.2012.20912.x · 5.11 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present a list of 13 candidate gravitationally lensed submillimeter galaxies (SMGs) from 95 square degrees of the Herschel Multi-tiered Extragalactic Survey, a surface density of 0.14\pm0.04deg^{-2}. The selected sources have 500um flux densities (S_500) greater than 100mJy. Gravitational lensing is confirmed by follow-up observations in 9 of the 13 systems (70%), and the lensing status of the four remaining sources is undetermined. We also present a supplementary sample of 29 (0.31\pm0.06deg^{-2}) gravitationally lensed SMG candidates with S_500=80--100mJy, which are expected to contain a higher fraction of interlopers than the primary candidates. The number counts of the candidate lensed galaxies are consistent with a simple statistical model of the lensing rate, which uses a foreground matter distribution, the intrinsic SMG number counts, and an assumed SMG redshift distribution. The model predicts that 32--74% of our S_500>100mJy candidates are strongly gravitationally lensed (mu>2), with the brightest sources being the most robust; this is consistent with the observational data. Our statistical model also predicts that, on average, lensed galaxies with S_500=100mJy are magnified by factors of ~9, with apparently brighter galaxies having progressively higher average magnification, due to the shape of the intrinsic number counts. 65% of the sources are expected to have intrinsic 500micron flux densities less than 30mJy. Thus, samples of strongly gravitationally lensed SMGs, such as those presented here, probe below the nominal Herschel detection limit at 500 micron. They are good targets for the detailed study of the physical conditions in distant dusty, star-forming galaxies, due to the lensing magnification, which can lead to spatial resolutions of ~0.01" in the source plane.
    The Astrophysical Journal 05/2012; 762(1). DOI:10.1088/0004-637X/762/1/59 · 5.99 Impact Factor
Show more