A MeerKAT view of pre-processing in the Fornax A group

We present MeerKAT neutral hydrogen (H  I ) observations of the Fornax A group, which is likely falling into the Fornax cluster for the first time. Our H  I image is sensitive to 1.4 × 10 19 atoms cm −2 over 44.1 km s −1 , where we detect H  I in 10 galaxies and a total of (1.12 ± 0.02) × 10 9 M ⊙ o...

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Veröffentlicht in:Astronomy and astrophysics (Berlin) 2021-04, Vol.648, p.A32
Hauptverfasser: Kleiner, D., Serra, P., Maccagni, F. M., Venhola, A., Morokuma-Matsui, K., Peletier, R., Iodice, E., Raj, M. A., de Blok, W. J. G., Comrie, A., Józsa, G. I. G., Kamphuis, P., Loni, A., Loubser, S. I., Molnár, D. Cs, Passmoor, S. S., Ramatsoku, M., Sivitilli, A., Smirnov, O., Thorat, K., Vitello, F.
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Sprache:eng
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Zusammenfassung:We present MeerKAT neutral hydrogen (H  I ) observations of the Fornax A group, which is likely falling into the Fornax cluster for the first time. Our H  I image is sensitive to 1.4 × 10 19 atoms cm −2 over 44.1 km s −1 , where we detect H  I in 10 galaxies and a total of (1.12 ± 0.02) × 10 9 M ⊙ of H  I in the intra-group medium (IGM). We search for signs of pre-processing in the 12 group galaxies with confirmed optical redshifts that reside within the sensitivity limit of our H  I image. There are 9 galaxies that show evidence of pre-processing and we classify each galaxy into their respective pre-processing category, according to their H  I morphology and gas (atomic and molecular) scaling relations. Galaxies that have not yet experienced pre-processing have extended H  I discs and a high H  I content with a H 2 -to-H  I ratio that is an order of magnitude lower than the median for their stellar mass. Galaxies that are currently being pre-processed display H  I tails, truncated H  I discs with typical gas fractions, and H 2 -to-H  I ratios. Galaxies in the advanced stages of pre-processing are the most H  I deficient. If there is any H  I , they have lost their outer H  I disc and efficiently converted their H  I to H 2 , resulting in H 2 -to-H  I ratios that are an order of magnitude higher than the median for their stellar mass. The central, massive galaxy in our group (NGC 1316) underwent a 10:1 merger ∼2 Gyr ago and ejected 6.6−11.2 × 10 8 M ⊙ of H  I , which we detect as clouds and streams in the IGM, some of which form coherent structures up to ∼220 kpc in length. We also detect giant (∼100 kpc) ionised hydrogen (H α ) filaments in the IGM, likely from cool gas being removed (and subsequently ionised) from an in-falling satellite. The H α filaments are situated within the hot halo of NGC 1316 and there are localised regions that contain H  I . We speculate that the H α and multiphase gas is supported by magnetic pressure (possibly assisted by the NGC 1316 AGN), such that the hot gas can condense and form H  I that survives in the hot halo for cosmological timescales.
ISSN:0004-6361
1432-0746
DOI:10.1051/0004-6361/202039898