A blind ATCA H i survey of the Fornax galaxy cluster: Properties of the H i detections

A. Loni, P. Serra, D. Kleiner, L. Cortese, B. Catinella, B. Koribalski, T. H. Jarrett, D. Cs Molnar, T. A. Davis, E. Iodice, K. Lee-Waddell, F. Loi, F. M. MacCagni, R. Peletier, A. Popping, M. Ramatsoku, M. W.L. Smith, N. Zabel

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We present the first interferometric blind HI survey of the Fornax galaxy cluster, which covers an area of 15 deg out to the cluster virial radius. The survey has a spatial and velocity resolution of 67″ × 95″(∼6 × 9 kpc at the Fornax cluster distance of 20 Mpc) and 6.6 km s and a 3σ sensitivity of N ∼2 × 10 cm and M ∼2 × 10 M , respectively. We detect 16 galaxies out of roughly 200 spectroscopically confirmed Fornax cluster members. The detections cover about three orders of magnitude in HI mass, from 8 × 10 to 1.5 × 10 M . They avoid the central, virialised region of the cluster both on the sky and in projected phase-space, showing that they are recent arrivals and that, in Fornax, HI is lost within a crossing time, ∼2 Gyr. Half of these galaxies exhibit a disturbed HI morphology, including several cases of asymmetries, tails, offsets between HI and optical centres, and a case of a truncated HI disc. This suggests that these recent arrivals have been interacting with other galaxies, the large-scale potential or the intergalactic medium, within or on their way to Fornax. As a whole, our Fornax HI detections are HI-poorer and form stars at a lower rate than non-cluster galaxies in the same M range. This is particularly evident at M 10 M , indicating that low mass galaxies are more strongly affected throughout their infall towards the cluster. The M/M ratio of Fornax galaxies is comparable to that in the Virgo cluster. At fixed M , our HI detections follow the non-cluster relation between M and the star formation rate, and we argue that this implies that thus far they have lost their HI on a timescale 1-2 Gyr. Deeper inside the cluster HI removal is likely to proceed faster, as confirmed by a population of HI-undetected but H-detected star-forming galaxies. Overall, based on ALMA data, we find a large scatter in H-to-HI mass ratio, with several galaxies showing an unusually high ratio that is probably caused by faster HI removal. Finally, we identify an HI-rich subgroup of possible interacting galaxies dominated by NGC 1365, where pre-processing is likely to have taken place.

Original languageEnglish
Article numberA31
Number of pages18
JournalAstronomy & Astrophysics
Publication statusPublished - 1 Apr 2021


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