Astronomy Seminar

Astronomy Seminar
Thursday, October 15, 2015
10:00 am, Wilder 202

Allison Kirkpatrick
University of Massachusetts, Amherst

Title: "What Lies Beneath: Dust Obscured Star Formation and Black Hole Growth"

The evolution of massive dusty galaxies is driven internally by AGN growth and star formation, but due to the copious amounts of dust, it is often impossible to observe these processes directly. Instead, we must disentangle information about the inner workings of galaxies from the observed dust emission. Using a large sample of z=0.5-2.8 Ultra Luminous Infrared Galaxies, I quantify the contributions to the dust heating from AGN activity and star formation using deep Spitzer mid-IR spectroscopy. I also explore composite galaxies--those galaxies which show both strong mid-IR star formation and AGN signatures. These galaxies exhibit a clear increase of dust temperature in the far-IR as the AGN grows stronger, indicating that a growing AGN is significantly contributing to LIR, although the galaxy is still strongly star-forming. Furthermore, these composite systems are prevalent even at faint 24 micron flux thresholds, and could be an important source of AGN contamination in any high redshift sample of star forming galaxies, if care is not taken to identify them. I will discuss ways to identify composite galaxies and how to correct infrared luminosities and star formation rates for dust emission heated by an obscured AGN.