RESEARCH
Determining How AGN Affect the Sizes of Galaxies
The upper panel shows the workflow of this research project, and the lower panel shows an example of the process for an individual galaxy. The three images show the transformation of a B-band galaxy image from dust-free image (left), to dust-attenuated image produced using radiative transfer (center), to the convolved image projected onto the HST 0.06" drizzled pixel scale (right; beam size shown in white). The right-hand image includes background correlated noise that would be observed in the rest-frame B-band at the HST WFC/IR angular resolution. All three images have the same flux scale. The lower right-hand panel shows surface brightness profiles of the dust-unattenuated image (maroon) and the dust-attenuated, PSF-convolved image with noise (pink). The reconstructed surface brightness profile (red) is derived using Sérsic profile fits to the convolved image. The Sérsic profile fits are typically able to account for > ~90% of the light in the dust-attenuated, unconvolved image. The vertical black line shows the best-fitting stellar effective radius at this inclination, 1.5 kpc. The dashed blue line shows the stellar mass surface density profile derived from a two-dimensional projection of the stellar mass particle data.
As a participant of the 2018 Kavli Summer program on Galaxy Formation (https://kspa.soe.ucsc.edu/archives/2018) at the Flatiron Institute, I was able to get my hands dirty with researching galaxy formation physics. Since this isn’t my PhD thesis research I learned a ton about the physics of galaxy formation and the current status of the field.
I collaborated with Rachel Cochrane, Chris Hayward, Daniel Angles-Alcazar, and Jennifer Lotz in understanding how Active Galactic Nuclei (AGN) feedback can affect the observed sizes of galaxies. I conducted SKIRT radiative transfer simulations for a set of FIRE-2 zoom-in galaxy simlations. These galaxy simulations that I analyzed were conducted at a higher resolution than prior simulations and included both a variety of stellar physics and a numerical recipe for black hole accretion. While they do not include the effects of AGN feedback, we can conduct mock observations of these galaxies, as shown in the figure above, to determine how well they align with observational relationships.
We have found that the galaxies start off in relative agreement with the \(R_e-M_\star\) relationship and the \(\Sigma_1-M_\star\) and \(\Sigma_e-M_\star\) relationships at large redshifts. As the galaxies evolve, they begin to diverge from the observational relationships at \(z \sim 2\). From this point on the simulated galaxies are too compact compared to observed galaxies.
We anticipate that including AGN feedback in these simulations will allow material to be heated and prevent accretion into the central region of the galaxy. As a result, the galaxies will be less compact and fall into alignment with the various observational relationships. This hypothesis will be tested with a new suite of galalxy simulations that include the effects of AGN feedback.
A comparison between the measured FIRE-2 galaxy half light radii and the observational van der Wel relationship between the half light radii and the stellar mass of a galaxy.
This figure shows the comparison between the measured density within 1 kpc of the FIRE-2 galaxy and the Barro et. al. \(\Sigma_1-M_\star\) relationship.
Here, we show the comparison between the measured density fo the FIRE-2 galaxies within the half light radius and the Barro et. al. \(\Sigma_e-M_\star\) relationship.
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