Correlation of Structure and Stellar Properties of Galaxies in Stripe 82

Abstract

Establishing a correlation (or lack thereof) between the bimodal color distribution of galaxies and their structural parameters is crucial to understand the origin of bimodality. To achieve that, we have performed a 2D mass-based structural decomposition (bulge+disk) of all disk galaxies (total = 1263) in the Herschel imaging area of the Stripe 82 region using Ks-band images from the VICS82 survey. The scaling relations thus derived are found to reflect the internal kinematics and are employed in combination to select an indubitable set of classical- and pseudo-bulge-hosting disk galaxies. The rest of the galaxies (<20%) are marked as disks with “ambiguous” bulges. Pseudo- and classical bulge–disk galaxies exhibit clear bimodality in terms of all stellar parameters (M *, specific star formation rate, r − K s ). All pseudo-bulge–disk galaxies are blue and star forming, and all classical bulge–disk galaxies are red and quiescent with less than 5% digressions. Ambiguous bulge–disk galaxies are intermediate to pseudo- and classical bulge–disk galaxies in the distribution of all structural and stellar parameters. —based on the placement of bulges on the Kormendy relation—is found to be the most efficient single structural indicator of both bulge type and stellar activity. The placement of ambiguous bulge–disk galaxies on scaling relations and the fundamental plane, in addition to their peculiar stellar properties, suggests that they are dominantly part of the green valley.

On the scaling relations of bulges and early-type galaxies

“…The steepest relation is the general one, for the whole sample, with an observed slope of 2.94 ± 0.21, consistent with other recent studies (e.g. Sachdeva et al 2020, Gao et al 2020, while the intrinsic relation suffering a more important decrease in slope due to the aforementioned biases compared with the separated relations. Gadotti (2009) and Gao et al (2020) performed a multicomponent structural analysis on a large sample of elliptical and disk galaxies, using the Kormendy relation to separate classical and pseudo-bulges.…”

“…Gadotti (2009), Sachdeva et al (2017), Sachdeva et al (2019) and Gao et al (2020) used the Kormendy relation of the eliptical galaxies to classify bulges and found with a high degree of accuracy that pseudo-bulges are the ones which are situated far (more than two or three standard deviations) from the aforementioned relation. Sachdeva et al (2020) defined a new morphology indicator from the Kormendy relation -the relative distance from the ±1σ boundary of the Kormendy relation, and used it to investigate the degree of accuracy of other bulge morphology classifiers (e.g. n b , B/T , concentration index or central velocity dispersion).…”

What is Important? Morphological Asymmetries are Useful Predictors of Star Formation Rates of Star-forming Galaxies in SDSS Stripe 82

“…According to previous studies, the best predictor might be the global Sérsic index (n g ; Bell et al 2012) or velocity dispersion (σ; Wake et al 2012;Cappellari et al 2013;van Dokkum et al 2015;Bluck et al 2020) or central mass density within the half light radius (Kauffmann et al 2003) or Σ 1 (Cheung et al 2012;Fang et al 2013;vanDokkum et al 2014;Woo et al 2015;Barro et al 2017;Whitaker et al 2017). All of the above properties have been associated to varying degrees with the relative importance of the "bulge" or "spheroid" in a galaxy's mass/light distribution (Gadotti 2009;Gao et al 2020;Luo et al 2020;Sachdeva et al 2020;, which is reasonable since this in turn has been linked to black-hole mass (Kormendy & Ho 2013), and thus to AGN quenching. However, among these bulge-linked variables no single one has as yet stood out.…”

Star-dust geometry main determinant of dust attenuation in galaxies

“…Note that the range and representative quality of the full sample is not affected by this selection. In our previous work (Sachdeva et al 2020), we focused on a subset of the total sample (1263 galaxies) to extract multi-component structural parameters in the near-IR range using KS band images from the VICS82 survey (Geach et al 2017). This subset allows us to examine if the structure related findings apply to the distribution of stellar mass or only the bright optical light within a galaxy.…”

“…Utilizing that, Bottrell et al (2019) has computed the detailed set of structural parameters for all galaxies (∼17000) in this area, in optical wavebands. Structural parameters in the infrared (KS band), reflecting the underlying mass distribution, are also available for a subset of the full sample from our earlier work (Sachdeva et al 2020). In addition to that, all defining dust attenuation and stellar parameters are available for these galaxies from GSWLC2 (GALEX-SDSS-WISE Legacy Catalog 2, Salim et al 2018).…”