On the scaling relations of bulges and early-type galaxies

Abstract

ABSTRACT Following from our recent work, we present here a detailed structural analysis of a representative sample of nearby spiral and early-type galaxies (ETGs) taken from the Key Insights on Nearby Galaxies: a Far-Infrared Survey with Herschel/ (KINGFISH) / Spitzer Infrared Nearby Galaxies Survey (SINGS) surveys. The photometric parameters of bulges are obtained from bulge-disc decompositions using Galfi data analysis algorithm. The method and corrections for projection and dust effects previously obtained are used to derive intrinsic photometric and structural bulge parameters. We show the main bulge scaling relations and the black hole relations, both observed and intrinsic ones, in B band. We find dust and inclination effects to produce more important changes in the parameters of the Kormendy relation for spiral galaxies, with the respective bulges of late-type galaxies (LTGs) residing on a steeper slope relation than the early-type galaxies (ETGs). We observe that the Kormendy relation in combination with a bulge Sérsic index (nb) threshold does not produce a conclusive morphological separation of bulges. The nb- bulge-to-total flux ratio (B/T) and B/T-stellar mass could be used to discriminate between LTGs and ETGs, while a further use of these parameters to divide bulges with different morphologies is problematic due to overlaps in the two distributions or large spread in values. We confirm the existence of two distinct intrinsic relations between the bulge luminosity (or absolute magnitude) and Sérsic index for LTGs and ETGs, while the relations between the black hole mass (MBH) and bulge luminosity are not found to be statistically different at p<0.05. Within errors, we find statistically similar intrinsic MBH − nb relations for all bulges.