Millimeter imaging of submillimeter galaxies in the COSMOS field: redshift distribution

Abstract

We present new IRAM Plateau de Bure interferometer (PdBI) 1.3 mm continuum observations at ∼1.5 resolution of 28 submillimeter galaxies (SMGs), previously discovered with the 870 μm bolometer LABOCA at the APEX telescope from the central 0.7 deg 2 of the COSMOS field. Nineteen out of the 28 LABOCA sources were detected with PdBI at a > ∼ 3σ level of ≈1.4 mJy/beam. A combined analysis of this new sample with existing interferometrically identified SMGs in the COSMOS field yields the following results: i) > ∼ 15%, and possibly up to ∼40% of single-dish detected SMGs consist of multiple sources; ii) statistical analysis of multi-wavelength counterparts to single-dish SMGs shows that only ∼50% have real radio or IR counterparts; iii) ∼18% of interferometric SMGs have either no multi-wavelength counterpart or only a radio-counterpart; and iv) ∼50-70% of z > ∼ 3 SMGs have no radio counterparts (down to an rms of 7-12 μJy at 1.4 GHz). Using the exact interferometric positions to identify the multi-wavelength counterparts allows us to determine accurate photometric redshifts for these sources. The redshift distributions of the combined and the individual 1.1 mm and 870 μm selected samples shows a higher mean and a broader width than those derived in previous studies. This study finds that on average brighter and/or mm-selected SMGs are located at higher redshifts, consistent with previous studies. The mean redshift for the 1.1 mm selected sample (z = 3.1 ± 0.4) is tentatively higher than that for the 870 μm selected sample (z = 2.6 ± 0.4). Based on our nearly complete sample of AzTEC 1.1 mm SMGs in a 0.15 deg 2 area, we infer a higher surface density of z > ∼ 4 SMGs than predicted by current cosmological models. In summary, our findings imply that interferometric identifications at (sub-)millimeter wavelengths are crucial to build statistically complete and unbiased samples of SMGs.

Dusty star-forming galaxies at high redshift

“…Their relative contribution to this plot is given by the large line-filled red square on the right. Chapin et al, 2009) and the red is from AzTEC sources in COSMOS (Smolčić et al, 2012). The solid dark blue histogram represents both spectroscopic and optical photometric redshifts for AzTEC sources in GOODS-S who suggest the distribution is a log-normal in nature with median value z = 2.6 (solid green line).…”

“…One more notable analysis of the 1.1 mm-selected population is summarized by Smolčić et al (2012) who describe interferometric follow-up observations of DSFGs in the COSMOS field. Like the interferometric work on the Laboca CDFS sample from ALMA (summarized in Karim et al, 2013;Hodge et al, 2013b), the Smolčić et al work measures the accuracy of previous counterpart identifications to bolometer-detected sources and identifies submillimeter multiples (see more in § 2.5).…”

Simulated observations of sub-millimetre galaxies: the impact of single-dish resolution and field variance

“…Once multi-wavelength counterparts have been identified, photometric redshifts are derived through fitting an SED to the available photometry, allowing redshift to vary as a free parameter (e.g. Smolčić et al 2012). Whilst observationally inexpensive and thus desirable for large SMG surveys, the errors from photometric redshifts are often significant, and samples are again biased by requiring detection in photometric bands.…”

“…Atacama Large Millimetre Array -ALMA; Plateau de Bure Interferometer -PdBI; Sub-Millimetre Array -SMA) targeted at single-dish detected sources have indicated that the resolution of single-dish telescopes had in some cases blended the sub-mm emission of multiple galaxies into one single-dish source (e.g. Wang et al 2011;Smolčić et al 2012;Hodge et al 2013). Karim et al (2013) showed the effect this blending has on the observed sub-mm number counts, with the single-dish counts derived from the Large APEX (Atacama Pathfinder EXperiment) BOlometer CAmera (LABOCA) Extended Chandra Deep Field-South (ECDFS) Sub-millimetre Survey (LESS; Weiß et al 2009) exhibiting a significant enhancement at the bright end relative to counts derived from the ALMA followup (ALESS).…”

The VLA-COSMOS 3 GHz Large Project: Continuum data and source catalog release

“…), 6 GHz VLA (Myers et al, in prep. ), and the deep multiwavelength X-ray to mm photometry (Scoville et al 2007;Koekemoer et al 2007;Hasinger et al 2007;Capak et al 2007;Sanders et al 2007;Bertoldi et al 2007;Elvis et al 2009;Ilbert et al 2013;McCracken et al 2012;Scott et al 2008;Aretxaga et al 2011;Smolčić et al 2012;Miettinen et al 2015;Civano et al 2016;Laigle et al 2016, Capak et al, in prep. ) and more than 97 000 optical spectroscopic redshifts (Salvato et al, in prep.…”