Department of Astronomy Center for Radiophysics & Space Research

Feb 2016: The Discovery of a Massive Gas Reservoir in a Starbursting Galaxy that Hosts a Dust-obscured Galactic Nucleus in the Early Universe ~3 Billion Years After the Big Bang

Graduate Student, T.K. Daisy Leung, talks about her recent paper:
"A Massive Molecular Gas Reservoir in the z=2.221 Type-2 Quasar Host Galaxy SMMJ0939+8315 lensed by the Radio Galaxy 3C220.3" by T. K. Daisy Leung & Dominik A. Riechers (The Astrophysical Journal, in press).

My research seeks to improve our current understanding of the environments and the physical mechanisms that trigger star-formation across cosmic time in order to attain a coherent picture on how galaxies and supermassive black holes evolve through the history of the universe. Most of my research is done using observational data obtained with large radio and (sub-)millimeter wavelength interferometric telescopes to investigate the evolution of the gas and dust components in the interstellar medium (the nurseries for stars) of galaxies at cosmological distances. 

An artist's rendition of a supermassive black hole located at the center of a galaxy behind an obscuring dusty torus. (Credits:  NASA/ESA) 

In our recent paper, we use telltale emission from carbon monoxide (CO) molecules to trace the properties of the molecular gas within a gravitationally lensed, dusty, star-forming galaxy (SMMJ0939+8315) which also harbors a voracious galactic black hole at a (comoving) distance of ~18 billion light-years away, and the observed emission was emitted at an epoch only ~3 billion years after the Big Bang (Leung & Riechers 2016; Investigation of the interstellar medium properties of SMMJ0939+8315 is particularly exciting and important as it presents an unique opportunity to peer into the early universe when the most intense bursts of star formation are taking place.

The alignment of two intervening galaxies and their surrounding dark matter acts as cosmic lenses magnifying the light emitted by SMMJ0939+8315.  Our analysis reveals that the observed brightness of SMMJ0939+8315 is magnified by a factor of more than 10 times, making it one of the most apparently luminous dusty sources detected at vast distances away from us.

An overlay image of the lensing-magnified emission from carbon monoxide (white contours) in the interstellar medium of SMMJ0939+8315, indicating the presence of a massive molecular gas reservoir that is responsible for sustaining the intense starbursts.  Red color image shows the lensing configuration of this intricate system as traced by the Hubble Space Telescope. Green color image shows the lensing-distorted emission from the cold dust in SMMJ0939+8315.

Our observations reveal a massive molecular gas reservoir residing in SMMJ0939+8315, which is being converted into young stars at a colossal rate (~500x times faster than the Milky Way). Our findings also suggest that a substantial amount of (the CO-emitting) gas has already been converted into stars and used for feeding the active galactic nucleus (AGN). Hence, we may be witnessing an immediate stage in the evolution of a massive galaxy between a starbursting phase and an unobscured AGN-dominated phase, in which the galactic black hole in this galaxy is growing rapidly. This is a crucial step forward in the understanding of how galaxies evolve in their early phases, as well as providing constraints on cosmological structure formation.

Our observations were obtained with Combined Array for Research in Millimeter-wave Astronomy (CARMA). (Credits: Sean Goebel)

Link to paper: