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

¹ National Centre for Nuclear Research, Pasteura 7, 02-093 Warszawa, Poland
e-mail: william.pearson@ncbj.gov.pl
² Institute of Astronomy, Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University, Grudziądzka 5, 87-100 Torua, Poland
³ Aix Marseille Univ. CNRS, CNES, LAM, 38 rue Joliot-Curie, 13388 Marseille, France
⁴ INAF – Osservatorio di Astrofisica e Scienza dello Spazio, Via P. Gobetti 93/3, 40129 Bologna, Italy
⁵ Astronomical Observatory of the Jagiellonian University, ul. Orla 171, 30-244 Kraków, Poland

Received: 13 March 2023
Accepted: 29 August 2023

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.