Searching for the highest redshift sources in 250-500 micron submillimeter surveys

TL;DR

This paper develops a method to identify high-redshift (z>4) submillimeter galaxies using far-infrared peak positions in Herschel/SPIRE and BLAST surveys, incorporating spectral energy distribution modeling and auxiliary data.

Contribution

It introduces a technique combining far-IR peak localization with spectral modeling and prior temperature distributions to statistically select high-redshift galaxy candidates.

Findings

Identified 8 +/- 2 potential z>4 galaxies in the BLAST survey.

Set an upper limit of 17 +/- 4 deg^-2 for z>4 galaxies at S500>45 mJy.

Estimated that 10-85% of 500 micron peak galaxies are at z>4.

Abstract

We explore a technique for identifying the highest redshift (z>4) sources in Herschel/SPIRE and BLAST submillimeter surveys by localizing the position of the far-infrared dust peak. Just as Spitzer/IRAC was used to identify stellar `bump' sources, the far-IR peak is also a redshift indicator; although, the latter also depends on the average dust temperature. We demonstrate the wide range of allowable redshifts for a reasonable range of dust temperatures and show that it is impossible to constraint the redshift of individual objects using solely the position of the far-IR peak. By fitting spectral energy distribution models to simulated Herschel/SPIRE photometry we show the utility of radio and/or far-infrared data in breaking this degeneracy. With prior knowledge of the dust temperature distribution it is possible to obtain statistical samples of high redshift submillimeter galaxy candidates. We apply this technique to the BLAST survey of ECDFS to constrain the number of dusty galaxies at z>4. We find 8 +/- 2 galaxies with flux density ratios of S500>S350; this sets an upper limit of 17 +/- 4 deg-2 if we assume all are at z>4. This is <35% of all 500 micron-selected galaxies down to S500>45 mJy (LIR>2e13Lsun for z>4). Modeling with conventional temperature and redshift distributions estimates the percentage of these 500 micron peak galaxies at z>4 to be between 10-85%. Our results are consistent with other estimates of the number density of very high redshift submillimeter galaxies and follows the decline in the star formation rate density at z>4.