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

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. (2021-04-08)
 
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URL:
https://doi.org/10.1051/0004-6361/202039898

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.
EDP Sciences
08.04.2021

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., … Vitello, F. (2021). A MeerKAT view of pre-processing in the Fornax A group. Astronomy & Astrophysics, 648, A32. https://doi.org/10.1051/0004-6361/202039898

https://rightsstatements.org/vocab/InC/1.0/
© ESO 2021. Published in this repository with the kind permission of the publisher.
https://rightsstatements.org/vocab/InC/1.0/
doi:https://doi.org/10.1051/0004-6361/202039898
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https://urn.fi/URN:NBN:fi-fe2021042927978
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Abstract

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 × 10¹⁹ 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) × 10⁹ 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 H₂-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 H₂-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 H₂, resulting in H₂-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 × 10⁸ 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 (Hα) filaments in the IGM, likely from cool gas being removed (and subsequently ionised) from an in-falling satellite. The Hα filaments are situated within the hot halo of NGC 1316 and there are localised regions that contain H I. We speculate that the Hα 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.

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