WALLABY pre-pilot survey: two dark clouds in the vicinity of NGC 1395

Abstract

We present the Australian Square Kilometre Array Pathfinder (ASKAP) WALLABY pre-pilot observations of two ‘dark’ H i sources (with H i masses of a few times 108 $\rm {M}_\odot$ and no known stellar counterpart) that reside within 363 kpc of NGC 1395, the most massive early-type galaxy in the Eridanus group of galaxies. We investigate whether these ‘dark’ H i sources have resulted from past tidal interactions or whether they are an extreme class of low surface brightness galaxies. Our results suggest that both scenarios are possible, and not mutually exclusive. The two ‘dark’ H i sources are compact, reside in relative isolation and are more than 159 kpc away from their nearest H i-rich galaxy neighbour. Regardless of origin, the H i sizes and masses of both ‘dark’ H i sources are consistent with the H i size–mass relationship that is found in nearby low-mass galaxies, supporting the possibility that these H i sources are an extreme class of low surface brightness galaxies. We identified three analogues of candidate primordial ‘dark’ H i galaxies within the TNG100 cosmological, hydrodynamic simulation. All three model analogues are dark matter-dominated, have assembled most of their mass 12–13 Gyr ago, and have not experienced much evolution until cluster infall 1–2 Gyr ago. Our WALLABY pre-pilot science results suggest that the upcoming large area H i surveys will have a significant impact on our understanding of low surface brightness galaxies and the physical processes that shape them.

WALLABY Pre-Pilot Survey: The effects of tidal interaction on radial distribution of color in galaxies of the Eridanus supergroup

“…The key results of this study do not significantly change if we use other parameters like Θ ≡ log[(M * /10 11 M )(d proj /Mpc) −3 ] as the measurement of tidal strength (e.g., Karachentsev et al 2013;Pearson et al 2016;Wong et al 2021).…”

“…The products including velocities, coordinates, Hi total fluxes, and moment maps, were released internally to the WALLABY team. More details about the data can be found in previous WALLABY publications studying the Eridanus fields (For et al 2021;Murugeshan et al 2021;Wong et al 2021).…”

“…We exclude two Hi clouds (Hi dectections with no optical counterparts): WALLABY J033911-222322 and WALLABY J033723-235753, which are studied in detail by Wong et al (2021). The main purpose of this paper is to study how galaxies evolve in the Eridanus supergroup, so we select from the remaining 53 Hi detections using the following criteria: 1) classified as members of any of the three sub-groups by Brough et al (2006) (Section 2.2), or 2) within the escape velocity curve and two virial radii in the phase-space diagram of any of the three sub-groups.…”

Discovery of a bright-dark binary galaxy in a nearby galaxy group

“…However, previous large-area H I surveys have not detected a credible isolated candidate for the dark galaxy [8][9][10] . Even if some previously discovered candidates were later found to be only some almost dark galaxies with deeper optical observation [11][12][13] .…”

The detection of a massive chain of dark HI clouds in the GAMA G23 Field

“…While with increasing sensitivity the number of serendipitous detections of dark clouds or condensations in tidal debris increased (Hibbard et al 2001b,a;Koribalski & Dickey 2004;McKay et al 2004;Koribalski 2004;Koribalski & Manthey 2005;Kilborn et al 2006;English et al 2010), only recently have a substantial number of dark clouds been found in blind H i surveys (cf. Wong et al 2021).…”