University of Oulu

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.

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

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Author: Kleiner, D.1; Serra, P.1; Maccagni, F. M.1;
Organizations: 1INAF – Osservatorio Astronomico di Cagliari, Via della Scienza 5, 09047 Selargius, CA, Italy
2University of Oulu, Space Physics and Astronomy Unit, Pentti Kaiteran katu 1, 90014 Oulu, Finland
3Institute of Astronomy, Graduate School of Science, The University of Tokyo, 2-21-1 Osawa, Mitaka, Tokyo 181-0015, Japan
4Kapteyn Astronomical Institute, University of Groningen, PO Box 800 9700 AV Groningen, The Netherlands
5INAF – Astronomical Observatory of Capodimonte, Via Moiariello 16, Naples 80131, Italy
6Netherlands Institute for Radio Astronomy (ASTRON), Oude Hoogeveensedijk 4, 7991 PD Dwingeloo, The Netherlands
7Department of Astronomy, Univ. of Cape Town, Private Bag X3, Rondebosch 7701, South Africa
8Inter-University Institute for Data Intensive Astronomy, University of Cape Town, Cape Town, Western Cape 7700, South Africa
9South African Radio Astronomy Observatory, 2 Fir Street, Black River Park, Observatory, Cape Town 7925, South Africa
10Department of Physics and Electronics, Rhodes University, PO Box 94 Makhanda 6140, South Africa
11Argelander-Institut für Astronomie, Auf dem Hügel 71, 53121 Bonn, Germany
12Ruhr University Bochum, Faculty of Physics and Astronomy, Astronomical Institute, 44780 Bochum, Germany
13Dipartimento di Fisica, Università di Cagliari, Cittadella Universitaria, 09042 Monserrato, Italy
14Centre for Space Research, North-West University, Potchefstroom 2520, South Africa
15Department of Physics, University of Pretoria, Private Bag X20, Hatfield 0028, South Africa
16INAF – Istituto di Radioastronomia, Via Gobetti 101, 40129 Bologna, Italy
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 21.3 MB)
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Language: English
Published: EDP Sciences, 2021
Publish Date: 2021-04-29


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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Series: Astronomy and astrophysics
ISSN: 0004-6361
ISSN-E: 1432-0746
ISSN-L: 0004-6361
Volume: 648
Article number: A32
DOI: 10.1051/0004-6361/202039898
Type of Publication: A1 Journal article – refereed
Field of Science: 115 Astronomy and space science
Funding: This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement no. 679627; project name FORNAX). The research of OS is supported by the South African Research Chairs Initiative of the Department of Science and Innovation and the National Research Foundation. KT acknowledges support from IDIA. The work of KMM is supported by JSPS KAKENHI Grant Number of 19J40004. RFP acknowledges financial support from the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement No. 721463 to the SUNDIAL ITN network. AV acknowledges the funding from the Emil Aaltonen foundation. PK is partially supported by the BMBF project 05A17PC2 for D-MeerKAT. AS acknowledges funding from the National Research Foundation under the Research Career Advancement and South African Research Chair Initiative programs (SARChI), respectively. FV acknowledges financial support from the Italian Ministry of Foreign Affairs and International Cooperation (MAECI Grant Number ZA18GR02) and the South African NRF (Grant Number 113121) as part of the ISARP RAIOSKY2020 Joint Research Scheme.
Copyright information: © ESO 2021. Published in this repository with the kind permission of the publisher.