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A blind ATCA HI survey of the Fornax galaxy cluster: properties of the HI detections

Loni, A., Serra, P., Kleiner, D., Cortese, L., Catinella, B., Koribalski, B., Jarrett, T. H., Molnar, D. Cs., Davis, T. A., Iodice, E., Lee-Waddell, K., Loi, F., Maccagni, F. M., Peletier, R., Popping, A., Ramatsoku, M., Smith, M. W .L. and Zabel, N. 2021. A blind ATCA HI survey of the Fornax galaxy cluster: properties of the HI detections. Astronomy and Astrophysics 648 , A31. 10.1051/0004-6361/202039803

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We present the first interferometric blind HI survey of the Fornax galaxy cluster, which covers an area of 15 deg2 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−1 and a 3σ sensitivity of NHI ∼ 2 × 1019 cm−2 and MHI ∼ 2 × 107 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 × 106 to 1.5 × 1010 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⋆  ≲  109 M⊙, indicating that low mass galaxies are more strongly affected throughout their infall towards the cluster. The MHI/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 MHI 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 H2-detected star-forming galaxies. Overall, based on ALMA data, we find a large scatter in H2-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.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Physics and Astronomy
Publisher: EDP Sciences
ISSN: 0004-6361
Date of First Compliant Deposit: 27 January 2021
Date of Acceptance: 26 January 2021
Last Modified: 06 Jan 2022 02:15

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