Galaxy and Mass Assembly: Group and field galaxy morphologies in the star-formation rate – stellar mass plane

¹ National Centre for Nuclear Research, Pasteura 7, 02-093 Warszawa, Poland
e-mail: william.pearson@ncbj.gov.pl
² SRON Netherlands Institute for Space Research, Landleven 12, 9747 AD Groningen, The Netherlands
³ Kapteyn Astronomical Institute, University of Groningen, Postbus 800, 9700 AV Groningen, The Netherlands
⁴ School of Physics, University of New South Wales, NSW 2052, Australia
⁵ Department of Physics and Astronomy, 102 Natural Science Building, University of Louisville, Louisville, KY 40292, USA
⁶ Australian Astronomical Optics, Macquarie University, 105 Delhi Road, North Ryde NSW 2113, Australia
⁷ Astronomy Centre, University of Sussex, Falmer, Brighton BN1 9QH, UK

Received: 13 August 2020
Accepted: 31 December 2020

Abstract

Aims. We study the environment in which a galaxy lies (i.e. field or group) and its connection with the morphology of the galaxy. This is done by examining the distribution of parametric and non-parametric statistics across the star-formation rate (SFR) – stellar mass (M_⋆) plane and studying how these distributions change with the environment in the local universe (z < 0.15).

Methods. We determine the concentration (C), Gini, M₂₀, asymmetry, Gini-M₂₀ bulge statistic (GMB), 50% light radius (r₅₀), total Sérsic index, and bulge Sérsic index (n_Bulge) for galaxies from the Galaxy and Mass Assembly (GAMA) survey using optical images from the Kilo Degree Survey. We determine the galaxy environment using the GAMA group catalogue and split the galaxies into field or group galaxies. The group galaxies are further divided by the group halo mass (M_h)−11 ≤ log(M_h/M_⊙) < 12, 12 ≤ log(M_h/M_⊙) < 13, and 13 ≤ log(M_h/M_⊙) < 14 – and into central and satellite galaxies. The galaxies in each of these samples are then placed onto the SFR-M_⋆ plane, and each parameter is used as a third dimension. We fit the resulting distributions for each parameter in each sample using two two-dimensional Gaussian distributions: one for star-forming galaxies and one for quiescent galaxies. The coefficients of these Gaussian fits are then compared between environments.

Results. Using C and r₅₀, we find that galaxies typically become larger as the group mass increases. This change is greater for larger galaxies. There is no indication that galaxies are typically more or less clumpy as the environment changes. Using GMB and n_Bulge, we see that the star-forming galaxies do not become more bulge or disk dominated as the group mass changes. Asymmetry does not appear to be greatly influenced by environment.