Galaxy evolution in nearby loose groups – II. Photometric and kinematic characterization of USGC U268 and USGC U376 group members in the Leo cloud★

Abstract

The paper is the second of a series in which we are exploring the co-evolution of galaxies and groups in the Local Universe, adopting a multi-wavelength approach.Here we present the photometric and kinematic characterization of two groups, USGC U268 and USGC U376 (U268 and U376 hereafter) located in different regions of the Leo cloud. We revisit the group membership, using results coming from recent redshift surveys, and we investigate their substructures. U268, composed of 10 catalogued members and 11 new added members, has a small fraction (≈24%) of early-type galaxies (ETGs). U376 has 16 plus 8 new added members, with ≈38% of ETGs. We find the presence of significant substructures in both groups suggesting that they are likely accreting galaxies. U268 is located in a more loose environment than U376. For each member galaxy, broad band integrated and surface photometry have been obtained in far-UV (FUV) and near-UV (NUV) with GALEX, and in u, g, r, i, z (SDSS) bands. H α imaging and 2D high resolution kinematical data have been obtained using PUMA Scanning Fabry-Perot interferometer at the 2.12 m telescope in San Pedro Mártir, (Baja California, México). We improved the galaxy classification and we detected morphological and kinematical distortions that may be connected to either on-going and/or past interaction/accretion events or environmental induced secular evolution. U268 appears more active than U376, with a large fraction of galaxies showing interaction signatures (60% vs. 13%). The presence of bars among late-type galaxies is ≈10% in U268 and ≈29% in U376. The cumulative distribution of (FUV -NUV) colours of galaxies in U268 is significantly different than that in U376 with galaxies in U268 bluer than those in U376. In the (F U V − r vs. M r ) and (N U V − r vs. M r ) planes no members of U268 are found in the 'red sequence', even early-type galaxies lie in the 'blue sequence' or in the 'green valley'. Most (80%) of the early-type members in U376 inhabit the 'red sequence', a large fraction of galaxies, of different morphological types, are located in the 'green valley', while the 'blue sequence' is under-populated with respect to U268.

Galaxy evolution in groups. USGC U268 and USGC U376 in the Leo cloud

“…The best SED-fits of these galaxies have been obtained using SFH typical of Spirals. The higher stellar mass and the smaller virial radius of U376 suggest that it is more evolved than U268, with LGG 225 in between, as also suggested by their Color Magnitude Diagrams (see Marino et al, 2013, their figure 8).…”

“…The SEDs of three Spirals in U376 (NGC 3681, NGC 3684, and NGC 3686) and two in U268 (UGC 5393, NGC 3021), are also well fitted with the SFH assumed in our grid for Irregulars. We note that the 3 Spirals in U376 are located outside of the virial radius of the group (see Figure 6, left panels) and belong to a substructure (Marino et al, 2013, their Fig. 1).…”

“…c Taken from Ramella et al ages of 6 members of U376 for which we compare results from SED-fitting and from SPH simulations with chemo-photometric implementation. We obtained broad band integrated magnitudes (AB system) in FUV (1344 -1786 A) and near-UV (NUV, 1771 -2831Å) from GALEX and in u, g, r, i, and z from Sloan Digital Sky Survey (SDSS) data as described in Marino et al (2013). Figures 2 and 3 show the SEDs of the sample galaxies, arranged by morphological type.…”

“…The best-fit model scaled to the observed fluxes provides an estimate of the current stellar mass, assuming the distances given in Marino et al (2013), and accounting for extinction.…”

“…Marino et al (2013) revisited the group membership and investigated the substructures of two groups, USGC U268 and USGC U376 (U268 and U376 hereafter).…”