Surface photometry of emission-line galaxies in low density regions

Abstract

Detailed B and R surface photometry is performed for 139 faint emission-line galaxies (ELGs) and for 2 non-ELGs. They are a subsample of the ELG sample selected by Popescu et al. (1996, 1998) towards four nearby voids. We derived the isophotal and integral photometric parameters and radial surface brightness (SB) profiles. Our sample consists mostly of low luminosity (), small linear size ( = 6.0 kpc) ( H 0 = 75 km s -1 Mpc -1 ) and blue ( = 0.93) galaxies. About 83% of the studied ELGs belong to the class of Blue Compact Galaxies (BCGs); others are luminous Starburst Nucleus Galaxies (SBNs) and a few interacting pairs. 72% of the ELGs possess a single dominant HII region, while the remaining 28% show multiple knots. Furthermore 71% of the ELGs show regular outer isophotes, and the remaining 29% reveal disturbed outer morphologies. We performed the SB profile decomposition by means of disentangling the underlying stellar disk and the excess light above the exponential disk. We classified the profiles into 5 types: pure disk profiles (21% of studied 139 ELGs); profiles that show both disk and bulge/nucleus/HII knot components (37%); profiles that have central light depression (13%); non-disky (concave) profiles (7%); and almost unresolved (quasi-stellar) images and stellar SB profiles (22%). Popescu et al. ((1997) found that most of the studied ELGs follow the spatial distribution of “normal” galaxies from the CfA Redshift Survey. 15 ELGs and 1 non-ELG were classified as being well isolated and are distributed within nearby ( 0.033) voids. We found that these isolated ELGs are almost all dwarf galaxies with , they show similar luminosities and colours as the nearby non-isolated ELGs. For 8 of 15 isolated ELGs an underlying LSBG has been detected. The underlying disks of isolated ELGs tend to be larger and of lower SB, than the disks of non-isolated ELGs (of the same total blue flux).