Article

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

ABSTRACT

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

Full-text

Available from: N. Castro-Rodriguez
  • 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.
    Full-text · Article · Aug 2011 · Astronomy and Astrophysics
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The Herschel Multi-tiered Extragalactic Survey (HerMES) is a legacy programme designed to map a set of nested fields totalling ∼380 deg2. Fields range in size from 0.01 to ∼20 deg2, 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 deg2 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.
    Full-text · Article · Mar 2012 · Monthly Notices of the Royal Astronomical Society
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We have constructed an extended halo model (EHM) which relates the total stellar mass and star-formation rate (SFR) to halo mass (Mh). An empirical relation between the distribution functions of total stellar mass of galaxies and host halo mass, tuned to match the spatial density of galaxies over 0 < z < 2 and the clustering properties at z ∼ 0, is extended to include two different scenarios describing the variation of SFR on Mh. We also present new measurements of the redshift evolution of the average SFR for star-forming galaxies of different stellar masses up to z = 2, using data from the Herschel Multi-tiered Extragalactic Survey for infrared bright galaxies. Combining the EHM with the halo accretion histories from numerical simulations, we trace the stellar mass growth and star-formation history in haloes spanning a range of masses. We find that: (1) the intensity of the star-forming activity in haloes in the probed mass range has steadily decreased from z ∼ 2 to 0; (2) at a given epoch, haloes in the mass range between a few times 1011 M⊙ and a few times 1012 M⊙ are the most efficient at hosting star formation; (3) the peak of SFR density shifts to lower mass haloes over time; and (4) galaxies that are forming stars most actively at z ∼ 2 evolve into quiescent galaxies in today's group environments, strongly supporting previous claims that the most powerful starbursts at z ∼ 2 are progenitors of today's elliptical galaxies.
    Full-text · Article · Mar 2012 · Monthly Notices of the Royal Astronomical Society
Show more