Connecting AGN To Host Galaxy Properties

PhD Program

Speaker

Nischal Acharya
DIPC

When

2025/02/10
13:00

Place

CFM Auditorium, Donostia / San Sebastián

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PhD Thesis defense by Nischal Acharya

Supervisors: Silvia Bonoli (DIPC, Ikerbasque)

Galaxy Evolution and Supermassive Black Holes

Supermassive Black Holes (SMBHs) have been established to be at the center of all massive galaxies. Some of these are known to be accreting matter from their host galaxies, dubbed as Active Galactic Nuclei (AGN). It is now known that AGN and their host galaxies coevolve. However, a clear concise does not exist if this coevolution is causal or casual.

This thesis explores the coevolution of these AGN and their host galaxies from largest to the smallest scales. First, utilizing data from the Galaxy and Mass Assembly (GAMA) survey, we compare the large scale environments of 205 Quasars at z < 0.35 against a robust Markov chain Monte Carlos (MCMC) sample of 205,000 inactive galaxies matched in terms of both stellar mass and redshift. The results assert that there is no significant difference between the environment of active and inactive galaxies, implying that stochastic processes are the dominant triggers of AGN at low redshift.

Second, we compare the global and spatially resolved star formation rates (SFR) and specific star formation rates (sSFR) of AGN and non-AGN host galaxies. We compare the properties of 32 X-ray selected AGN using data from the Chandra X-ray Observatory and XMM-Newton survey against a mass matched control sample. Stellar masses and SFR are obtained by fitting Spectral Energy Distributions (SED) of galaxies with 60 optical narrow-band multi-wavelength data from the miniJPAS Survey, which is a 1 deg2 preview of the upcoming Javalambre-Physics of the Accelerated Universe Astrophysical Survey (J-PAS) survey. Our results show that while there are no differences between the global properties of X-ray AGN and non-AGN host galaxies, their sSFR profiles exhibit the exact opposite trend. This suggests that X-ray AGN quench their host galaxies in the central regions, while simultaneously pushing gas to the outskirts of their host galaxy where star formation takes place, for example by compression of gas due to positive feedback.

Following up on the results of our X-ray AGN host galaxies, we examine the radial profiles of Radio AGN host galaxies in the third part of this thesis. We use 12 band optical data from the Javalambre Photometric Local Universe Survey (J-PLUS), which is another prelude to the J-PAS survey covering 3,192 deg2 of the northern sky. Then, we use data from the Low-Frequency Array (LOFAR) survey to cross-match and select a sample of 441 Radio AGN hosts in the J-PLUS field at z < 0.15 and compare their radial profiles against a Baldwin, Phillips & Terlevich (BPT) diagram selected star forming sample. The results corroborate our findings for X-ray AGN, which posit a radially increasing sSFR for Radio
AGN host galaxies. This reaffirms the result that AGN quench their hosts in the center, while enhancing their sSFR on the outskirts of galaxies. Moreover, examining the M∗−MBH scaling relation, we find that highly star forming galaxies lie above scaling relation observed for local galaxies, whereas quenched galaxies like below the local relation, with the average Eddington rate (λEdd) being∼2%.