The Nature of 500 micron Risers I: SMA Observations

TL;DR

This study uses SMA observations to analyze 34 high-redshift dusty star-forming galaxy candidates, revealing that many are multiple sources and that lensing is not the sole cause of their brightness, indicating extremely luminous starburst systems.

Contribution

First high-resolution SMA imaging of 500-riser galaxies, showing significant source blending and quantifying the role of lensing versus multiple sources in their observed brightness.

Findings

24 out of 34 sources have counterparts detected.

At least 35% of bright sources are likely multiple sources.

Remaining sources are extremely luminous with SFRs over 1000 M_sun/yr.

Abstract

We present SMA observations at resolutions from 0.35 to 3 arcseconds of a sample of 34 candidate high redshift dusty star forming galaxies (DSFGs). These sources were selected from the HerMES Herschel survey catalogues to have SEDs rising from 250 to 350 to 500$\mu$m, a population termed 500-risers. We detect counterparts to 24 of these sources, with four having two counterparts. We conclude that the remaining ten sources that lack detected counterparts are likely to have three or more associated sources which blend together to produce the observed Herschel source. We examine the role of lensing, which is predicted to dominate the brightest (F500 $>$ 60mJy) half of our sample. We find that while lensing plays a role, at least 35% of the bright sources are likely to be multiple sources rather than the result of lensing. At fainter fluxes we find a blending rate comparable to, or greater than, the predicted 40%. We determine far-IR luminosities and star formation rates for the non-multiple sources in our sample and conclude that, in the absence of strong lensing, our 500-risers are very luminous systems with L$_{FIR} > 10^{13}$L$_{\odot}$ and star formation rates $> 1000$M$_{\odot}$/yr.