Widefield Arecibo Virgo Extragalactic Survey: II. Characterizing the HI properties and environment of the WAVES South region

Abstract

Context. Galaxy clusters are extreme environments where interactions with the hot intracluster medium drive rapid galaxy evolution. These processes can result in the formation of optically dark gas clouds, as previously observed in Virgo and other clusters. Aims. We investigate the distribution and properties of neutral hydrogen (HI) in two large adjoining regions of the Virgo cluster to understand how the cluster environment influences galaxy transformation. Specifically, we examine the gas content of both star-forming and quiescent populations and search for evidence of gas-loss driven evolution. Methods. We cataloged the 21cm HI Widefield Arecibo Virgo Extragalactic Survey (WAVES) South data using visual and automatic source extraction methods. By combining these results with an optically selected sample, we compared the HI properties of WAVES South with the previously studied VC1 region. To probe gas reservoirs below the nominal detection limit, we performed a stacking analysis of radio spectra across the WAVES South, VC1 and VC2 footprints. Results. We detected 56 HI sources with a median root mean square (rms) noise of 0.8 mJy, including 50 galaxies, two gas clouds (one being optically dark), and the ALFALFA Virgo 7 complex. Our results reveal a significantly lower detection fraction in WAVES South compared to the VC1 region. Stacking showed no new HI detection at a 0.080 mJy rms with a maximum of 157 stacked objects from WAVES South, VC1, and VC2. Conclusions. The lower HI detection fraction suggests that WAVES South is a more dynamically relaxed and evolved environment than the VC1 region. The presence of residual HI in a small subset of early-type galaxies supports a model of dwarf irregular to dwarf elliptical transformation via environmental stripping. Finally, we note a possible evolutionary link between optically dark clouds and recently discovered "blue blobs."