The Activation of Galactic Nuclei and Their Accretion Rates Are Linked to the Star Formation Rates and Bulge-types of Their Host Galaxies

Abstract

We use bulge-type classifications of 809 representative SDSS galaxies by Gadotti (2009) to classify a large sample of galaxies into real bulges (classical or elliptical) and pseudobulges using Random Forest. We use structural and stellar population predictors that can easily be measured without image decomposition. Multiple parameters such as the central mass density with 1 kpc, concentration index, Sérsic index and velocity dispersion do result in accurate bulge classifications when combined together. We classify ∼ 44, 500 face-on galaxies above stellar mass of 10 10 M and redshift 0.02 < z < 0.07 into real bulges or pseudobulges with 93 ± 2% accuracy. We show that ∼ 75 − 90% of AGNs identified by the optical line ratio diagnostic are hosted by real bulges. The pseudobulge fraction significantly decreases with AGN signature as the line ratios change from indicating pure star formation (∼ 54 ± 4 %), to composite of star formation and AGN (∼ 18 ± 3%), and to AGN-dominated galaxies (∼ 5 ± 3%). Using the dust-corrected [O III] luminosity as an AGN accretion indicator, and the stellar mass and radius as proxies for a black hole mass, we find that AGNs in real bulges have lower Eddington ratios than AGNs in pseudobulges. Real bulges have a wide range of AGN and star formation activities, although most of them are weak AGNs. For both bulge-types, their Eddington ratios are correlated with specific star formation rates (SSFR). Real bulges have lower specific accretion rate but higher AGN fraction than pseudobulges do at similar SSFRs.

LeMMINGs III. The e-MERLIN legacy survey of the Palomar sample: exploring the origin of nuclear radio emission in active and inactive galaxies through the [O iii] – radio connection

“…Such a break corresponds to the M BH , which roughly separates the BH mass function of local LTGs and ETGs (Davis et al 2014;Greene, Strader & Ho 2020), i.e. pseudo-bulges and bulges (Yesuf et al 2020) and SF-and AGN-dominated sources, respectively (see Kelly & Merloni 2012, Appendix A and Fig. A1).…”

Observational insights on the origin of giant low surface brightness galaxies

“…However, it should be noted that Malin 1, Malin 2 (for a model with two discs), UGC 6614, UGC 1378, and UGC 1922 have Sérsic indices 𝑛 < 2 and their bulges do not look rounder than the discs which could be the main argument for their classification as pseudobulges. It makes the high frequency of AGN activity among gLSBGs even more interesting, since the AGN signatures in the emission line ratios decreases significantly for the galaxies with pseudobulges (Yesuf et al 2020). It could indicate the presence of the current gas supply to the centres of gLSBGs leading to the AGN activity and related to the accretion of material either from a filament or from a gas-rich satellite.…”

Centrally Concentrated H I Distribution Enhances Star Formation in Galaxies

“…We describe the stellar mass distribution using the optical concentration C ≡ R 90 /R 50 (Strateva et al 2001;Kauffmann et al 2003a), where R 90 and R 50 are the radii enclosing 90% and 50% of the r-band Petrosian flux, respectively. Other measures of stellar mass concentration can be contemplated, including the Sérsic (1963) index n, which is available for our sample from Simard et al (2011), the stellar mass surface density within the inner 1 kpc (Fang et al 2013;Yesuf et al 2020), or the surface density within the effective radius (Naab & Trujillo 2006). For convenience and ease of comparison with the literature, we use the concentration parameter C, which is sensitive to the stellar mass distribution out to a relatively large radius.…”