The first catalogue of spectroscopically confirmed red nuggets at z~0.7 from the VIPERS survey. Linking high-z red nuggets and local relics

Abstract

'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 $z \sim 3$, 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. Those red nuggets which managed to escape this fate can serve as unique laboratories to study the early evolution of massive galaxies. In this paper, we aim to make use of the VIMOS Public Extragalactic Redshift Survey to build the largest up-to-date catalogue of spectroscopically confirmed red nuggets at the intermediate redshift $0.5 8\times10^{10}$ $\rm{M}_{\odot}$ and effective radii $R_\mathrm{e}<1.5$ kpc. Among them, we select red, passive galaxies with old stellar population based on colour--colour NUVrK diagram, star formation rate values, and verification of their optical spectra. Verifying the influence of the limit of the source compactness on the selection, we found that the sample size can vary even 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. Number density calculated on the final sample of 77 VIPERS passive red nuggets per comoving Mpc$^3$ increases from 4.7$\times10^{-6}$ at $z \sim 0.61$ to $9.8 \times 10^{-6}$ at $z \sim 0.95$, which is higher than values estimated in the local Universe, and lower than the ones found at $z>2$. It fills the gap at intermediate redshift.