GBT21B-324

Deep integration to probe 21-cm emission: a step forward to mapping

Abstract

We propose deep integrations with GBT to measure the average N(HI) in the halo around two nearby star-forming galaxies. This will provide an independent test of the recent claim that high column density cool gas pervades the halos of most galaxies.
Absorption-line work suggests this cool gas has N(H) ~10^19 cm^-2, for N(HI) ~10^17 cm^-2. If true, this cool CGM may represent the main repository of baryons in the universe. Detecting it in emission will provide an important constraint complementary to optical, UV and X-Ray spectroscopy. The GBT is the ideal telescope for such an experiment. But so far this neutral gas has proven difficult to detect in emission, even using the GBT.
In previous GBT observations, we have obtained deep spectra out to ~100 kpc along the principal axes of NGC891 and NGC4565 (Das+2020, ApJ; Das+2021, in prep.). It has resulted in successful detections at each pointing. By comparing the GBT spectra with interferometer maps we find strong evidence for diffuse 21-cm emission. We propose 12 deep spectra probing the CGM along the minor and off axes of NGC4565 and NGC891 to understand the azimuthal distribution of the CGM and better constrain the radial distribution along the minor axes.

Investigators

Name	Institution
Sanskriti Das *	Ohio State University; Stanford University
Amy Sardone	Ohio State University; West Virginia University
Nickolas Pingel	Wisconsin at Madison, University of; Australian National University
Joshua Kingsbury	Ohio State University
D.J. Pisano	Cape Town, University of
Smita Mathur	Ohio State University
Adam Leroy	National Radio Astronomy Observatory; Ohio State University
George Heald	Commonwealth Scientific and Industrial Research Organisation

* indicates the PI