ADS: Welikala et al. 2016
ArXiv: Welikala et al. 2016
As part of our collaboration’s work looking into the nature of gravitationally lensed dusty, star forming galaxies discovered in the South Pole Telescope survey, I’ve written a lot about what the background, lensed sources look like, but what about the foreground lensing galaxies and the dark matter haloes they live in? This paper, led by Niraj Welikala, uses data from the Planck and Herschel satellites to show that the foreground lensing galaxies live in environments that are more actively forming stars than random patches of sky, out to distances of about 2Mpc from the lens galaxies.
Niraj determined this by stacking Planck and IRIS data, which spans 220 – 3000GHz, at the locations of the SPT objects, and subtracting the contribution from the background lensed galaxies themselves. This works because Planck has much lower resolution than our other follow-up programs with APEX and Herschel, so Planck picks up emission on much larger spatial scales that isn’t associated with the background galaxies directly.
By looking at the excess emission in Planck, Niraj determines that it’s fully consistent with being associated with the environments around the foreground lensing haloes. Some of the sources responsible for the excess (about 20%) are actually resolved by Herschel, and they have star formation rates of a few hundred solar masses per year; the rest of the excess is probably coming from fainter objects in the neighboring haloes. The results are consistent with simple models of the sources responsible for the Cosmic Infrared Background, and also the relationship between star formation rate and environmental density of galaxies (which reverses around the typical lens redshifts, so that galaxies in more dense regions of space form fewer stars in the nearby universe).