The Neutral Gas Properties of Extremely Isolated Early-type Galaxies III

Abstract

We report on the neutral hydrogen gas content (21 cm emission) of eight extremely isolated early-type galaxies (IEGs) using the Green Bank Telescope. Emission is detected in seven of the eight objects. This paper is the third in a series that collectively present new H i observations for 20 IEGs. Among the 14 H i detections in our observations, eight exhibit a Gaussian-like H i line profile shape, four are double-peaked, one is triple-peaked, and another has a plateaued rectangular shape. Five additional IEGs observed in previous surveys were added to our analysis, bringing the total number of IEGs with H i observations to 25. Of these objects, emission is detected in 19 (76%). The 25 IEGs in our combined study have gas masses that are systematically larger than their luminosity-matched comparison galaxy counterparts. The IEGs presented here follow a trend of increasing gas-richness with bluer B  −  V colors. This correlation is also observed in a comparison sample drawn from the literature composed of loose group and field early-type galaxies. Two IEGs, KIG 164 and KIG 870, exhibit properties highly anomalous for spheroidal systems: luminous ( M B  = −20.5, −20.1) and blue ( B  −  V  = 0.47, 0.48), respectively, with substantial neutral gas, M H i  = 4.1 and 5.5 × 10 9 M ☉ . Other IEG systems may represent early-type galaxies continuing to assemble via quiescent H i accretion from the cosmic web or relaxed merged systems.