Context. The evolution of galaxies depends on their interaction with the surrounding environment. Ultra-diffuse galaxies (UDGs) have been found in large numbers in clusters. We detected a few star-forming blobs in the VESTIGE survey, located at ∼5 kpc from a UDG, namely NGVS 3543, in association with an HI gas cloud AGC 226178, suggesting a recent interaction between this low-surface-brightness system and the surrounding cluster environment. Aims. We use a complete set of multi-frequency data including deep optical, UV, and narrow-band Hα imaging and HI data to understand the formation process that gave birth to this peculiar system. Methods. For this purpose, we measured (i) the multi-wavelength radial surface brightness profiles of NGVS 3543 and compared them to the predictions of spectro-photometric models of galaxy evolution in rich clusters; and (ii) the aperture photometry of the blue regions in the vicinity of NGVS 3543 in order to determine their age and stellar mass. Results. Comparisons of the observations with evolutionary models indicate that NGVS 3543 has undergone a ram-pressure stripping that peaked ∼100 Myr ago, transforming a blue gas-rich UDG into a red gas-poor UDG. Star formation has taken place in the ram pressure stripped gas, the mass of which is ∼108 M⊙, forming star complexes with a typical age of ∼20 Myr and a stellar mass of ∼104 M⊙. Conclusions. These results suggest that we are observing for the first time the ongoing transformation of a gas-rich UDG into a red and quiescent UDG under the effect of a ram-pressure stripping event. The same process could explain the lack of star-forming UDGs in rich environments observed in several nearby clusters.

Context. Malin 1 is the largest known low surface brightness (LSB) galaxy, the archetype of so-called giant LSBs. The structure and the origin of such galaxies are still poorly understood, especially due to the lack of high-resolution kinematics and spectroscopic data. Aims. We use emission lines from spectroscopic observations of Malin 1 aiming to bring new constraints on the internal dynamics and star formation history of Malin 1. Methods. We have extracted a total of 16 spectra from different regions of Malin 1 and calculated the rotational velocities of these regions from the wavelength shifts and star formation rates from the observed Hα emission line fluxes. We compare our data with existing data and models for Malin 1. Results. For the first time we present the inner rotation curve of Malin 1, characterized in the radial range r < 10 kpc by a steep rise in the rotational velocity up to at least ∼350 km s −1 (with a large dispersion), which had not been observed previously. We use these data to study a suite of new mass models for Malin 1. We show that in the inner regions dynamics may be dominated by the stars (although none of our models can explain the highest velocities measured) but that at large radii a massive dark matter halo remains necessary. The Hα fluxes derived star formation rates are consistent with an early-type disk for the inner region, and with the level found in extended UV galaxies for the outer parts of the giant disk of Malin 1. We also find signs of high metallicity but low dust content for the inner regions.

Using a compilation of Hα fluxes for 384 star-forming galaxies detected during the Virgo Environmental Survey Tracing Ionised Gas Emission (VESTIGE), we study several important scaling relations linking the star formation rate, specific star formation rate, stellar mass, stellar mass surface density, and atomic gas depletion timescale for a complete sample of galaxies in a rich environment. The extraordinary sensitivity of the narrow-band imaging data allows us to sample the whole dynamic range of the Hα luminosity function, from massive galaxies (M star 10 11 M ) to dwarf systems (M star 10 6 M ), where the ionised gas emission is due to the emission of single O-early B stars. This extends previous works to a dynamic range in stellar mass and star formation rate (10 −4 S FR 10 M yr −1 ) that has never been explored so far. The main-sequence relation derived for all star-forming galaxies within one virial radius of the Virgo cluster has a slope comparable to that observed in other nearby samples of isolated objects, but its dispersion is about three times larger (∼ 1 dex). The dispersion is tightly connected to the available amount of HI gas, with gas-poor systems located far below objects of similar stellar mass, but with a normal HI content. When measured on unperturbed galaxies with a normal HI gas content (HI − de f ≤ 0.4), the relation has a slope a=0.92±0.06, an intercept b = -1.57±0.06 (at a pivot point of log M star = 8.451 M ), and a scatter σ 0.40, and it has a constant slope in the stellar mass range 10 6 M star 3 × 10 11 M . The specific star formation rate of HI-poor galaxies is significantly lower than that of HI-rich systems of similar stellar mass, while their atomic gas consumption timescale τ HI is fairly similar, in particular, for objects of stellar mass 10 7 M star 10 9 M . We compare these observational results to the prediction of models expressly tuned to reproduce the effects induced by the interaction of galaxies with their surrounding environment. The observed scatter in the main-sequence relation can be reproduced only after a violent and active stripping process such as ram-pressure stripping that removes gas from the disc (outer parts first) and quenches star formation on short (< 1 Gyr) timescales. This rules out milder processes such as starvation. This interpretation is also consistent with the position of galaxies of different star formation activity and gas content within the phase-space diagram. We also show that the star-forming regions that formed in the stripped material outside perturbed galaxies are located well above the main-sequence relation drawn by unperturbed systems. These extraplanar HII regions, which might be at the origin of ultra-compact dwarf galaxies (UCDs) and other compact sources typical in rich environments, are living a starburst phase lasting only 50 Myr. They later become quiescent systems.

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 M star > 8×10 10 M ⊙ and effective radii R e < 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 Mpc 3 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.

Although it is now recognized that low surface brightness galaxies (LSBs) constitute a large fraction of the number density of galaxies, many of their properties are still poorly known. Based on only a few studies, LSBs are often considered to be “dust poor”, that is, with a very low amount of dust. For the first time, we use a large sample of LSBs and high surface brightness galaxies (HSBs) with deep observational data to study the variation of stellar and dust properties as a function of the surface brightness-surface mass density. Our sample consists of 1631 galaxies that were optically selected (with ugrizy-bands) at z < 0.1 from the North Ecliptic Pole (NEP) Wide field. We used the large multiwavelength set of ancillary data in this field ranging from UV to the far-infrared wavelengths. We measured the optical size and the surface brightness of the targets and analyzed their spectral energy distribution using the CIGALE fitting code. Based on the average r-band surface brightness (μ̄e), our sample consists of 1003 LSBs (μ̄e > 23 mag arcsec−2) and 628 HSBs (μ̄e ≤ 23 mag arcsec−2). We found that the specific star formation rate and specific infrared luminosity (total infrared luminosity per stellar mass) remain mostly flat as a function of surface brightness for both LSBs and HSBs that are star forming, but these characteristics decline steeply when the LSBs and HSBs are quiescent galaxies. The majority of LSBs in our sample have negligible dust attenuation (< 0.1 mag), and only about 4% of them show significant attenuation, with a mean V-band attenuation of 0.8 mag. We found that the LSBs with a significant attenuation also have a high r-band mass-to-light ratio (M/Lr > 3 M⊙/L⊙), making them outliers from the linear relation of surface brightness and stellar mass surface density. These outlier LSBs also show similarity to the extreme giant LSBs from the literature, indicating a possibly higher dust attenuation in giant LSBs. This work provides a large catalog of LSBs and HSBs as well as detailed measurements of several optical and infrared physical properties. Our results suggest that the dust content of LSBs is more varied than previously thought, with some of them having significant attenuation that makes them fainter than their intrinsic value. With these results, we will be able to make predictions on the dust content of the population of LSBs and how the presence of dust will affect their observations from current and upcoming surveys like JWST and LSST.