Dartmouth Events

Abstract:  We present an X-ray stacking analysis of a sample of 690 low mass galaxies (stellar mass < 10^10 solar masses) that do not contain a previously identified central active galactic nucleus (AGN) with the aim of probing whether these galaxies contain central AGN that would not be detected in standard X-ray surveys. We first show in detail how nearby faint AGN can be identified with multi-wavelength analysis through a case study of Mrk 462. We then draw from the large set of galaxies in SDSS DR7 to create our sample for stacking, and superimpose their Chandra X-ray images to create our stack. We find that the stack has a significant detection at its center, indicating that many of these galaxies produce X-ray emission. We then bin the stack by both stellar mass and star forming rate (SFR) and compare it to relations in the literature for expected X-ray luminosity of high and low mass X-ray binaries to confirm that the X-ray emission from our stack is not solely due to X-ray binaries. After determining that AGNs dominate the X-ray emission from our sample, we compare the luminosity of the stack to an AGN scaling relation between SFR and black hole accretion rate, and find that our stack falls within the scatter.  Finally, we calculate the average Eddington ratio of the stack for a range of black hole occupation fractions to estimate the occupation fraction of the galaxies in our stack.