CRA Seminar- Dr. Mojegan Azadi

"Hunting for Monsters! Active supermassive black holes identification and their host galaxies' physical properties"

Abstract:

Active galactic nuclei (AGN) are powered by the accretion activity of supermassive black holes residing at the centers of galaxies. While observations propose that growth of AGN and galaxies are globally tied, I investigate whether this connection exists in individual galaxies. I also investigate various AGN selection techniques and star formation rate (SFR) estimates using multi-wavelength data from Chandra, Spitzer and rest-frame optical spectra from the Keck telescope. 

I find that combining multi-wavelength identification techniques provides a complete AGN sample, as each selection method suffers from selection biases. In particular, all selection techniques are biased against identifying AGN in low mass galaxies. Once stellar mass selection biases are taken into account, I find that AGN reside in galaxies with similar physical properties (i.e., SFR) as inactive galaxies. I find that while AGN are prevalent in both star-forming and quiescent galaxies, they are more likely to reside in star-forming galaxies. The probability of fueling an AGN does not strongly depend on SFR for a star-forming galaxy, though it decreases when star formation is shut down in quiescent galaxies. I find no evidence for a strong correlation between SFR of the host galaxy and AGN luminosity. These results indicate that while both AGN and galaxy growth are reliant on the same fuel, enhanced star formation activity does not necessarily go hand-in-hand with increased AGN activity. 

While the star formation activity of galaxies can be traced with various indicators, my investigations indicate that at z~2 a combination of mid-infrared and far-infrared data provide a more reliable SFR estimation than the mid-infrared data alone. I also find that the robustness of UV-based SFRs depends on the extinction correction method used.  I find that about 30% of z ∼ 2 galaxies have SFRs from infrared observations that are elevated relative to the dust corrected UV-based SFR. My investigations show that this infrared excess is not due to any contribution from AGN, and is primarily due to polycyclic aromatic hydrocarbon (PAH) emission.

 

 

Event Details

Date/Time:

  • Date: 
    Thursday, April 12, 2018 - 3:00pm to 4:00pm

For More Information Contact

Prof. Tamara Bogdanovic