Influence of star-forming galaxy selection on the galaxy main sequence

Abstract

Aims. This work aims to determine how the galaxy main sequence (MS) changes using seven different commonly used methods to select the star-forming galaxies within VIPERS data over 0.5 ≤ z < 1.2. The form and redshift evolution of the MS was then compared between selection methods. Methods. The star-forming galaxies were selected using widely known methods: a specific star-formation rate (sSFR); Baldwin, Phillips, and Terlevich (BPT) diagram; a 4000 Å spectral break (D4000) cut; and four colour-colour cuts (near-ultra-violet – V verses r − J (NUVrJ), near-ultra-violet – V verses r − K (NUVrK), u − r, and U − V verses V − J (UVJ)). The main sequences were then fitted for each of the seven selection methods using a Markov chain Monte Carlo forward modelling routine, fitting both a linear main sequence and a MS with a high-mass turnover to the star-forming galaxies. This was done in four redshift bins of 0.50 ≤ z < 0.62, 0.62 ≤ z < 0.72, 0.72 ≤ z < 0.85, and 0.85 ≤ z < 1.20. Results. The slopes of all star-forming samples were found to either remain constant or increase with redshift, and the scatters were approximately constant. There is no clear redshift dependency of the presence of a high-mass turnover for the majority of samples, with the NUVrJ and NUVrK being the only samples with turnovers only at low redshift. No samples have turnovers at all redshifts. Star-forming galaxies selected with sSFR and u − r are the only samples to have no high-mass turnover in all redshift bins. The normalisation of the MS increases with redshift, as expected. The scatter around the MS is lower than the ≈0.3 dex typically seen in MS studies for all seven samples. Conclusions. The lack (or presence) of a high-mass turnover is at least partially a result of the method used to select star-forming galaxies. However, whether a turnover should be present or not is unclear.