Two speakers! Kate Alexander (Harvard) and Yong Zheng (Columbia University) and

Monday, December 4, 12:05pm
Marlar Lounge 37-252

The Radio Counterpart to GW170817: The First Binary Neutron Star Merger Detected in Gravitational Waves 

Kate Alexander
Harvard University

On 2017 August 17, the long-awaited era of multi-messenger astronomy arrived with the detection of both gravitational waves (GW) and electromagnetic radiation from the same event, GW170817, the merger of two neutron stars in a galaxy 40 Mpc from Earth. Radio observations of compact object mergers provide unique insight, as the longer timescale of radio emission allows for extensive followup and characterization of ejecta energies and the density of surrounding material. I will discuss our ongoing radio monitoring of GW170817, which revealed a relativistic jet pointed away from our line of sight, and compare this event to short gamma-ray bursts. I will also discuss predictions for the future radio evolution of GW170817. With the advent of sensitive facilities like the Karl G. Jansky Very Large Array (VLA) and planning well underway for vastly more powerful wide-field interferometers like the Square Kilometer Array, the study of radio astrophysical transients, including GW counterparts, is poised for dramatic growth.

Detection of Gas Inflows at M33's Disk-Halo Interface
Yong Zheng

Affiliation: Columbia University

The disks of galaxies closely interact with their circumgalactic media (CGM) through the disk-halo interfaces. The disks grow by inflows from the CGM, while the CGM is enriched, stirred, and heated by outflows from the disks. Recent years have seen great breakthroughs in observations of inflows and outflows; however, inflow detections remain rare. In my talk, I will show HST/COS observations of ionized gas inflows at M33’s disk-halo interface. Kinematic modeling of the ionized inflows finds an accretion rate of 2.9 Msun/yr, which is 5-10 times higher than the star-formation rate of M33. We find that the infalling ionized gas could be from the galactic fountain or fall-back material due to a potential M31-M33 interaction in the past. Our work is among the first to unambiguously reveal the existence of disk-wide galactic inflows.