Does the stellar disc flattening depend on the galaxy type?

TL;DR

This study investigates how the flatness of stellar discs varies with galaxy type using multi-band 2D decomposition, revealing weak correlations and the influence of bars and bulges on disc thickness across different galaxy classifications.

Contribution

It provides a comprehensive analysis of disc flatness dependence on galaxy type, highlighting the weak correlation with morphological type and the effects of bars and bulges on disc thickness.

Findings

Weak correlation between disc thickness and galaxy type.

1D photometric analysis overestimates disc thickness in bulge-rich galaxies.

Barred galaxies tend to have thicker stellar discs.

Abstract

We analyze the dependence of the stellar disc flatness on the galaxy morphological type using 2D decomposition of galaxies from the reliable subsample of the Edge-on Galaxies in SDSS (EGIS) catalogue. Combining these data with the retrieved models of the edge-on galaxies from the Two Micron All Sky Survey (2MASS) and the Spitzer Survey of Stellar Structure in Galaxies (S$^4$G) catalogue, we make the following conclusions: (1) The disc relative thickness $z_0/h$ in the near- and mid-infrared passbands correlates weakly with morphological type and does not correlate with the bulge-to-total luminosity ratio $B/T$ in all studied bands. (2) Applying an 1D photometric profile analysis overestimates the disc thickness in galaxies with large bulges making an illusion of the relationship between the disc flattening and the ratio $B/T$. (3) In our sample the early-type disc galaxies (S0/a) have both flat and "puffed" discs. The early spirals and intermediate-type galaxies have a large scatter of the disc flatness, which can be caused by the presence of a bar: barred galaxies have thicker stellar discs, on average. On the other hand, the late-type spirals are mostly thin galaxies, whereas irregular galaxies have puffed stellar discs.