FLASH Talks: Casey Lam (UC Berkeley)

Friday, 16 September 2022 1 p.m. — 2 p.m. MST

Online event

Casey Lam (UC Berkeley)
Casey Lam, UC Berkeley
Uncovering the Galactic Black Hole Population with Gravitational Microlensing
There are expected to be 100 million black holes (BHs) in the Milky Way, although until recently mass measurements existed for only two dozen or so in X-ray binary systems. A substantial fraction of the Milky Way's BHs are expected to be isolated. This leaves large uncertainty in the number, masses, velocities, and formation channels of the Galactic BH population. Detection of isolated BHs would enable the comparison of the single vs. binary BH mass distributions, which in turn would enable improved understand of massive star death and BH formation channels. In this talk I will present the analysis of 5 archival isolated BH hole candidates identified via microlensing. Hubble Space Telescope astrometry is jointly analyzed with photometry obtained from ground-based microlensing surveys to measure the masses of the candidates, as well as identify their nature (substellar, stellar, or compact object). One of the five candidates, OGLE-2011-BLG-0462/MOA-2011-BLG-191, is likely a neutron star or low-mass BH. In addition, the full sample of 5 candidates is compared to theoretical expectations on the number and masses of BHs in the Milky Way detectable via microlensing. Given the small sample size, the sample is consistent with the theoretical expectation of 100 million BHs in the Milky Way.
Zhefu Yu, The Ohio State University [**POSTPONED TO A LATER DATE**]
Mapping the Growth of Supermassive Black Holes with the OzDES Reverberation Mapping Project

Accurate mass measurements for supermassive black holes (SMBHs) are critical for understanding their growth over cosmic time. Outside of the local Universe, reverberation mapping (RM) of active galactic nuclei (AGN) is the most accurate method for measuring SMBH masses. RM measures the time lag between the continuum and broad emission line region (BLR) variability of AGN, which gives the virial mass when combined with the broad line width. I will present the latest results from the Dark Energy Survey (DES) - Australian DES (OzDES) RM project, which monitored 735 AGNs for 6 years with weekly photometry and monthly spectroscopy. Our results include some of the highest-quality Mg II lags and a new relationship between the radius of the Mg II BLR radius and the continuum luminosity (R-L relation). I will also describe our latest results on the Hbeta and C IV R-L relation. These R-L relations are extremely important because they are widely used to estimate the masses for large numbers of SMBHs from single-epoch spectra and study the SMBH demographics in a wide range of redshift. I will also present AGN accretion disk size measurements from continuum reverberation mapping, and simulations of the survey strategy of future RM campaigns to maximize the scientific yields.