The Dwarf Galaxy Population of the Dorado Group Down to [ITAL]M[/ITAL][TINF][ITAL]V[/ITAL][/TINF] ≈ −11

Abstract

We present V and I CCD photometry of suspected low surface brightness dwarf galaxies detected in a survey covering ~2.4 deg2 around the central region of the Dorado group of galaxies. The low surface brightness galaxies were chosen based on their sizes and magnitudes at the limiting isophote of 26 Vμ. The selected galaxies have magnitudes brighter than V ≈ 20 (MV ≈ -11 for an assumed distance to the group of 17.2 Mpc), with central surface brightnesses μ0 > 22.5 V mag arcsec-2, scale lengths h > 2'', and diameters ≥14'' at the limiting isophote. Using these criteria, we identified 69 dwarf galaxy candidates. Four of them are large very low surface brightness galaxies that were detected on a smoothed image, after masking high surface brightness objects. Monte Carlo simulations performed to estimate completeness, photometric uncertainties and to evaluate our ability to detect extended low surface brightness galaxies show that the completeness fraction is, on average, >80% for dwarf galaxies with -17 < MV < -10.5 and 22.5 < μ0 < 25.5 V mag arcsec-2, for the range of sizes considered by us (D ≥ 14''). The V-I colors of the dwarf candidates vary from -0.3 to 2.3 with a peak on V-I = 0.98, suggesting a range of different stellar populations in these galaxies. The projected surface density of the dwarf galaxies shows a concentration toward the group center similar in extent to that found around five X-ray groups and the elliptical galaxy NGC 1132 studied by Mulchaey & Zabludoff, suggesting that the dwarf galaxies in Dorado are probably physically associated with the overall potential well of the group.