Deep 1.1 mm-wavelength imaging of the GOODS-S field by AzTEC/ASTE - II. Redshift distribution and nature of the submillimetre galaxy population

Abstract

We report the results of the counterpart identification and a detailed analysis of the physical properties of the 48 sources discovered in our deep 1.1‐mm wavelength imaging survey of the Great Observatories Origins Deep Survey‐South (GOODS‐S) field using the AzTEC instrument on the Atacama Submillimeter Telescope Experiment. One or more robust or tentative counterpart candidate is found for 27 and 14 AzTEC sources, respectively, by employing deep radio continuum, Spitzer/Multiband Imaging Photometer for Spitzer and Infrared Array Camera, and Large APEX Bolometer Camera 870 μm data. Five of the sources (10 per cent) have two robust counterparts each, supporting the idea that these galaxies are strongly clustered and/or heavily confused. Photometric redshifts and star formation rates (SFRs) are derived by analysing ultraviolet(UV)‐to‐optical and infrared(IR)‐to‐radio spectral energy distributions (SEDs). The median redshift of zmed∼ 2.6 is similar to other earlier estimates, but we show that 80 per cent of the AzTEC–GOODS sources are at z≥ 2, with a significant high‐redshift tail (20 per cent at z≥ 3.3). Rest‐frame UV and optical properties of AzTEC sources are extremely diverse, spanning 10 mag in the i‐ and K‐band photometry (a factor of 104 in flux density) with median values of i= 25.3 and K= 22.6 and a broad range of red colour (i−K= 0–6) with an average value of i−K≈ 3. These AzTEC sources are some of the most luminous galaxies in the rest‐frame optical bands at z≥ 2, with inferred stellar masses M*= (1–30) × 1010 M⊙ and UV‐derived SFRs of SFRUV≳ 101‐3 M⊙ yr−1. The IR‐derived SFR, 200–2000 M⊙ yr−1, is independent of z or M*. The resulting specific star formation rates, SSFR ≈ 1–100 Gyr−1, are 10–100 times higher than similar mass galaxies at z= 0, and they extend the previously observed rapid rise in the SSFR with redshift to z= 2–5. These galaxies have a SFR high enough to have built up their entire stellar mass within their Hubble time. We find only marginal evidence for an active galactic nucleus (AGN) contribution to the near‐IR and mid‐IR SEDs, even among the X‐ray detected sources, and the derived M* and SFR show little dependence on the presence of an X‐ray bright AGN.

Dusty star-forming galaxies at high redshift

“…The p-value itself represents the probability or random coincidence, and generally, a match is considered reliable if p < 0.05 (e.g. Ivison et al, 2002;Pope et al, 2006;Chapin et al, 2009;Yun et al, 2012;Hodge et al, 2013b;Alberts et al, 2013). The p-value is more appropriate for catalogs in which the surface density is low (e.g., ra-dio identifications) and favors counterparts that are brighter than the background population.…”

“…see Carilli & Yun, 1999;Hughes et al, 2002;Aretxaga et al, 2007;Chapin et al, 2009;Yun et al, 2012;Roseboom et al, 2012;Barger et al, 2012;Chen et al, 2013a). These 'millimetric redshifts' are determined from the shape of the far-infrared or submillimeter SED or its colors rather than any properties indicated by its stellar emission characteristics in the optical/near-IR or emission line signatures.…”

“…Beyond the millimeter photometric redshifts work by Aretxaga et al (2007), Chapin et al (2009) compile 28 secure redshift identifications for 1.1 mm-selected DSFGs in GOODS-N and measure a median redshift of z = 2.7 which they claim is statistically distinct from the z = 2.2 mean measured in the Chapman et al sample and z = 2.5 in the Wardlow et al sample. Yun et al (2012) look at the 1.1 mm-detected DSFGs in GOODS-S and exploit the deep multi-wavelength ancillary data to measure redshifts as best as possible in the optical and near-infrared if spectroscopic redshifts do not already exist. Yun et al also show that the millimetric redshift distribution of the sample is nearly identical to the optical/nearinfrared redshift distribution, both of which have a median redshift of z = 2.6 ± 0.1, similar to the median redshift of z = 2.7 ± 0.2 found by Chapin et al (2009).…”

(Sub)millimetre interferometric imaging of a sample of COSMOS/AzTEC submillimetre galaxies

“…4.2). The CO spectralline observations using the Redshift Search Receiver (RSR) on the Large Millimetre Telescope (LMT) performed by Yun et al (2012) yielded a spec-z value of 4.3421 for AzTEC1. Their SMA follow-up observations of C + emission yielded a line detection at z spec = 4.3415, in very good agreement with the CO observations.…”

“…This method robustly takes lower redshift limits into account (e.g. Yun et al 2012). It was assumed that the censored data follow the same distribution as the actual values, and we used the Kaplan-Meier (K-M) method to construct a model of the input data.…”