Star formation rates in isolated galaxies selected from the Two-Micron All-Sky Survey

Abstract

We have considered the star formation properties of 1616 isolated galaxies from the 2MASS XSC selected sample (2MIG) with the FUV GALEX magnitudes. This sample was then compared with corresponding properties of isolated galaxies from the Local Orphan Galaxies catalogue (LOG) and paired galaxies. We found that different selection algorithms define different populations of isolated galaxies. The population of the LOG catalogue, selected from non-clustered galaxies in the Local Supercluster volume, mostly consists of low-mass spiral and late type galaxies. The SSFR upper limit in isolated and paired galaxies does not exceed the value of ~dex(-9.4). This is probably common for galaxies of differing activity and environment (at least at z<0.06). The fractions of quenched galaxies are nearly twice as high in the paired galaxy sample as in the 2MIG isolated galaxy sample. From the behaviour of (S)SFR vs. M_* relations we deduced that the characteristic value influencing evolutionary processes is the galaxy mass. However the environmental influence is notable: paired massive galaxies with logM_*>11.5 have higher (S)SFR than isolated galaxies. Our results suggest that the environment helps to trigger the star formation in the highest mass galaxies. We found that the fraction of AGN in the paired sample is only a little higher than in our isolated galaxy sample. We assume that AGN phenomenon is probably defined by secular galaxy evolution.