Colloquium on Jul. 4th, 2019

The clustering of galaxies with pseudo-bulge and classical bulge in the local Universe

Speaker: Lan Wang (NAOC)

Venue: Room 2317, SWIFAR Building

Time: 3:00 PM, Thursday, 4th July, 2019

Abstract: 

We investigate the clustering properties and close neighbour counts for galaxies with different types of bulges and stellar masses. We select samples of ‘classical’ and ‘pseudo’ bulges, as well as ‘bulge-less’ pure disc galaxies, based on the bulge/disc decomposition catalogue of SDSS galaxies provided by Simard et al. (2011). For a given galaxy sample we estimate: the projected two-point cross-correlation function with respect to a spectroscopic reference sample, and the average background-subtracted neighbour count within a projected separation using a photometric reference sample, N_neighbour. We compare the results with the measurements of control samples matched in colour, concentration, and redshift. We find that, when limited to a certain stellar mass range and matched in colour and concentration, all the samples present similar clustering amplitudes and neighbour counts on scales above ∼0.1Mpc. This indicates that neither the presence of a central bulge, nor the bulge type is related to intermediate-to-large scale environments. On smaller scales, in contrast, pseudobulge and pure-disc galaxies similarly show strong excess in close neighbour count when compared to control galaxies, at all masses probed. For classical bulges, small-scale excess is also observed but only for Mstars < 10^10Msun_; at higher masses, their neighbour counts are similar to that of control galaxies at all scales. These results imply strong connections between galactic bulges and galaxy–galaxy interactions in the local Universe, although it is unclear how they are physically linked in the current theory of galaxy formation.