The CAVITY project. The spatially resolved SFR of galaxies in voids

Abstract

The mass in the Universe is distributed non-uniformly, originating the Large Scale Structure (LSS), characterised by clusters, filaments, walls and voids. Galaxies in voids are bluer, later type, less massive, and have slower evolution than galaxies in denser environments. The effect of the void environment on properties such as star formation rate (SFR) is still under discussion. We tackle this by estimating spatially-resolved SFR from extinction-corrected Halpha luminosities of 220 void galaxies from the CAVITY survey. These observations consist of optical integral field unit data cubes from the PMAS/PPaK spectrograph at Calar Alto Observatory. We measure the continuum-subtracted emission lines to obtain maps of SFR, specific star formation rate (sSFR) and extinction. We assess global properties and radial profiles up to 2 half-light radii. We compare with galaxies in filaments and walls from the CALIFA survey using the same methodology, building a control sample matched in morphology and stellar mass. We find no significant differences in SFR and sSFR, although void galaxies tend to have larger SFR, especially for early spirals. This effect is present for Sa galaxies at all galactocentric distances, and in the outer parts of late-type spirals, evidencing slower transition to quiescence and less evolved discs. Void late-type galaxies have lower extinction. Using extinction normalised by stellar mass surface density as a proxy for gas mass fraction, we find it larger for void early spirals, especially in outer regions. This indicates the effect of the void environment on the transition from star forming to passive.

Figures (13)

• Figure 1: Density distribution of morphological types in the CAVITY parent sample (4866 galaxies) and the selected ones (220 galaxies). The numbers above the bars indicate the number of galaxies in the selected sample of each morphological type.
• Figure 2: Colour-magnitude diagram with the full CAVITY parent sample for galaxies with available Hubble types in Dominguez-Sanchez2018 (grey points) and the selected galaxies (coloured by morphological type).
• Figure 3: Radial profiles and maps of some physical properties of CAVITY54706, one of the Sc galaxies in our sample. The shaded area around them mark the uncertainty, calculated as the standard deviation divided by the square root of the number of pixels taken into account. The red ellipse indicates its half-light radius. The colour bars share scale with their corresponding profile's y-axis. In the left, from top to bottom: Luminosity at the normalisation wavelength ($\lambda=5635$Å) and nebular extinction. In the right column, from top to bottom: extinction-corrected H$\alpha$ luminosity and specific SFR.
• Figure 4: BPT Baldwin1981 and WHaN CidFernandes2010CidFernandes2011 diagnostic diagrams. The dots represent the flux values at the centre (left) or median values at a galactocentric distance of R = 1 HLR (right), coloured by the measurements of EW(H$\alpha$) (top) or by morphological type (bottom). The grey shadow in the left shows the distribution of the values of all pixels of all galaxies. On the right, the blue distribution corresponds to the late type galaxies (LTG; Sa, Sb, Sc or Sd), and the red to the early type galaxies (ETG; E or S0). The transparency of the colour of both morphological distributions is normalised to the total distribution, as in the panels of the left column. The dotted and dashed lines demarcate the limit between star formation and AGN following the criteria of Kauffmann2003 and Kewley2006, respectively. The continuous line differentiates between Seyferts and LINERs Schawinski2007. The dashed-dotted line in the two bottom panels mark delimit the retired galaxies (EW(H$\alpha$) < 3). Measurements below this limit are coloured black in the top panels.
• Figure 5: Global properties coloured by morphological type. Each row shows a different property of each galaxy against their total stellar mass at the left, calculated in Conrado2024, and the density distribution of each morphological type convolved with a gaussian kernel at the right, in the y-axis. The grey straight lines in the top left panel show the SFMS calculated by fitting the Sc and Sd galaxies of this work, derived from H$\alpha$ fluxes (dashed), and of the SFR from stellar population fitting of CALIFA galaxies in Gonzalez-Delgado2016 (dotted). The square dots reference the mean values obtained in Ricciardelli2014, and the contours behind the dots the distribution from Rodriguez2024, both for galaxies in voids. The horizontal dashed lines in the right panels mark the location of the median of each distribution.