The CAVITY project: The spatially resolved star formation rate of galaxies in voids

Abstract

The mass in the Universe is distributed non-uniformly, leading to the large scale structure (LSS), characterised by clusters, filaments, walls, and voids. Galaxies in voids have been found to be bluer, of later type, less massive, and to have slower evolution than galaxies in denser large-scale environments. The effect of the void environment on many other evolutionary properties, such as the star formation rate (SFR), is still a topic of discussion. We tackled this problem from a new perspective by estimating the spatially resolved SFR derived from extinction-corrected Hα luminosities of a sample of 220 void galaxies from the Calar Alto Void Integral-field Treasury surveY (CAVITY) project. These observations consist of optical integral field unit data cubes obtained with the PMAS/PPaK spectrograph at the 3.5 m telescope at the Calar Alto Observatory (Almería, Spain). We measured their continuum-subtracted emission lines to obtain the maps of the SFR, specific star formation rate (sSFR), and extinction (AV ). From these values, we assessed the behaviours of the entire galaxies through their global properties, and the spatially resolved information with radial profiles up to two half-light radii. We then compared the results with a sample of galaxies in filaments and walls from the CALIFA survey analysed using the same methodology. We built a control sample matched in morphological type and total stellar mass by taking pairs of each CAVITY galaxy. We find no statistically significant differences in the SFR and sSFR (p ≤ 0.05), although void galaxies tend to have larger SFRs, especially for the early spirals. This effect is present for Sa galaxies at all galactocentric distances (∆ log sSFR [Gyr−1] = 0.25 dex at 1 half light radius, HLR), and it can also be seen in the outer parts (R > 1 HLR) of late-type spirals (∆ log sSFR [Gyr−1] = 0.26 dex at 2 HLR), evidencing a slower transition from star-forming to quiescent and less evolved spiral discs. Additionally, we find void late-type galaxies to have lower extinction (∆ = 0.16 ± 0.06 mag). Using the extinction normalised by the stellar mass surface density as a proxy for the gas mass fraction, we find it to be larger for the void early spirals (by a 5%), especially in their outer regions (23% larger). This indicates the effect of the void environment on the transition stage from star forming to passive.