Kevin C. Cooke
To understand how massive galaxies came to be, we must understand how their star formation rich pasts are affected due to non-stellar processes such as the supermassive black holes in the hearts of galaxies. When a supermassive black hole actively accretes interstellar gas, the surrounding material becomes luminous across the electromagnetic spectrum and is visible as an object called an active galactic nucleus (AGN), or a quasar in the most luminous cases. This energetic output has a tremendous effect on the host galaxy, warming the gas in a process called AGN feedback. AGN feedback is a model commonly cited as the method that a star-forming, gas-rich galaxy transitions to a non-star-forming, gas-poor galaxy.
To address how AGN affect their host's star formation, I will present results from a recently uncovered subtype of quasar, called `cold quasars'. These galaxies host a luminous AGN at their hearts but still retain a cold gas component which we can detect in the far-infrared. These galaxies are observed in the rare moment when an AGN is active but has yet to finish excavating the cold gas from the host, continuing to host star formation rates of ~100s of solar masses per year, hundreds of times more active than our own Milky Way Galaxy. I present new results using a cold quasar detected using the SOFIA far-infrared telescope. Using this new data from SOFIA along with optical observations using the Sloan Digital Sky Survey and additional infrared data from the Spitzer and Herschel space telescopes, we fit a collection of stellar and black hole models to the data. Using these fits, we discuss the importance of cold quasars toward the understanding of these rare and energetic galaxies.
When a supermassive black hole actively accretes interstellar gas, the surrounding material becomes luminous across the electromagnetic spectrum and is visible as an object called an active galactic nucleus (AGN), or called a quasar in the most luminous cases. The energetic output from AGN has a tremendous effect on the host galaxy, warming the gas in a process called AGN feedback. AGN feedback is a model commonly cited as the method that a star-forming, gas-rich galaxy transitions to a non-star-forming, gas-poor galaxy.
To address how AGN affect their host's star formation, I will present results from a subtype of quasar, called `cold quasars'. These galaxies host a luminous AGN at their hearts but still retain a cold gas component which we can detect in the far-infrared. These galaxies are observed in the rare moment when an AGN is active but has yet to finish excavating the cold gas from the host, continuing to host star formation rates of ~100s of solar masses per year, hundreds of times more active than our own Milky Way Galaxy. I present new results using a cold quasar detected using the SOFIA far-infrared telescope to better estimate the star formation in a cold quasar. Seen in Figure 2, we observe a cold quasar in the far-infrared using the SOFIA telescope. The far-infrared is where light is re-emitted from interstellar gas after it has been warmed by star formation. Seen in the right of Fig.2 is what the galaxy looks like in the optical, which is effectively a point source of light due to the high luminosity of the AGN at its center.
Using this new data from SOFIA along with optical observations using the Sloan Digital Sky Survey and additional infrared data from the Spitzer and Herschel space telescopes, we fit a collection of stellar and black hole models to the data (Figure 3). Using these fits, we find that the inclusion of just one extra datapoint tracing the peak of far-infrared emission can better constrain the star formation estimate by nearly a factor of two! This galaxy in particular is best fit with a star-formation rate of 95 solar masses per year, nearly 50 times the Milky Way's star formation (estimated to be ~2 solar masses per year).
To constrain the black hole growth rate, we use the archival X-ray and optical emission data from the XMM-Newton X-ray Observatory satellite and the Sloan Digital Sky Survey respectively. This black hole mass growth rate is similarly found using a model fitting procedure to the total emission in these wavelength ranges. In Figure 4, we find that the stellar mass and black hole mass are growing in lockstep and the galaxy is at the lower mass end of a similar luminous AGN comparison sample. We find that cold quasars represent an early stage of AGN feedback and are a useful laboratory for understanding how star formation and active supermassive black holes can co-exist before the star formation is shut down.