A joint analysis of BLAST 250--500um and LABOCA 870um observations in the Extended Chandra Deep Field South

Preprint
Publisher Website
Google Scholar
  • 12 March 2010
Abstract
We present a joint analysis of the overlapping BLAST 250, 350, 500um, and LABOCA 870um observations (from the LESS survey) of the Extended Chandra Deep Field South. Out to z ~ 3, the BLAST filters sample near the peak wavelength of thermal far-infrared (FIR) emission from galaxies (rest-frame wavelengths ~ 60--200um), primarily produced by dust heated through absorption in star-forming clouds. However, identifying counterparts to individual BLAST sources is very challenging, given the large beams (FWHM 36--60 arcsec). In contrast, the ground-based 870um observations have a significantly smaller 19 arcsec FWHM beam, and are sensitive to higher-redshifts (z ~ 1--5, and potentially beyond) due to the more favourable negative K-correction. In this study we use the LESS data, as well as deep Spitzer and VLA imaging, to identify 125 individual sources that produce significant emission in the BLAST bands. We characterize the temperatures and FIR luminosities for a subset of 73 sources with well-measured submm SEDs and redshift measurements out to z ~ 3. Considering flux-limited sub-samples in each BLAST band, and a dust emissivity index \beta = 2.0, we find a median temperature T = 30K (all bands) as well as median redshifts: z = 1.1 (interquartile range 0.2--1.9) for S_250 > 40 mJy; z = 1.3 (interquartile range 0.6--2.1) for S_350 > 30 mJy; and z = 1.6 (interquartile range 1.2--2.3) for S_500 > 20 mJy. Taking into account the selection effects for our survey (a bias toward detecting lower-temperature galaxies), we find no evidence for evolution in the local FIR-temperature correlation out to z ~ 2.5. Comparing with star-forming galaxy SED templates, about 8% of our sample appears to exhibit significant excesses in the radio and/or mid-IR, consistent with those sources harbouring an AGN. Since our statistical approach differs from most previous studies of submm galaxies, we describe the following techniques in two appendices: our `matched filter' for identifying sources in the presence of point-source confusion; and our approach for identifying counterparts using likelihood ratios. This study is a direct precursor to future joint far-infrared/submm surveys, for which we outline a potential identification and SED measurement strategy.

This publication has 0 references indexed in Scilit: