The first catalogue of spectroscopically confirmed red nuggets at z ∼ 0.7 from the VIPERS survey

Abstract

Context. Red nuggets are a rare population of passive compact massive galaxies thought to be the first massive galaxies that formed in the Universe. First found at z ∼ 3, they are even less abundant at lower redshifts, and it is believed that with time they mostly transformed through mergers into today’s giant ellipticals. The red nuggets that managed to escape this fate can serve as unique laboratories to study the early evolution of massive galaxies. Aims. In this paper we aim to make use of the unprecedented statistical power of the VIMOS Public Extragalactic Redshift Survey to build the largest up-to-date catalogue of spectroscopically confirmed red nuggets at the intermediate redshift 0.5 < z < 1.0. Methods. Starting from a catalogue of nearly 90 000 VIPERS galaxies we selected sources with stellar masses Mstar > 8 × 1010 M⊙ and effective radii Re < 1.5 kpc. From these sources we selected red passive galaxies with old stellar populations based on colour–colour NUVrK diagram, star formation rate values, and verification of their optical spectra. Results. Verifying the influence of the limit of the source compactness on the selection, we found that the sample size can vary by up to two orders of magnitude, depending on the chosen criterion. Using one of the most restrictive criteria with additional checks on their spectra and passiveness, we spectroscopically identified only 77 previously unknown red nuggets. The resultant catalogue of 77 red nuggets is the largest such catalogue built based on the uniform set of selection criteria above the local Universe. The number density calculated on the final sample of 77 VIPERS passive red nuggets per comoving Mpc3 increases from 4.7 × 10−6 at z ∼ 0.61 to 9.8 × 10−6 at z ∼ 0.95, which is higher than values estimated in the local Universe, and lower than the values found at z > 2. It fills the gap at intermediate redshift. Conclusions. A catalogue of red nuggets presented in this paper is a golden sample for future studies of this rare population of objects at intermediate redshift. In addition to covering a unique redshift range and careful selection of galaxies, the catalogue is spectroscopically identified.