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 |
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Hauptverfasser: | , , , , , , , , , , , , , , , , , , , , |
Format: | Artikel |
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. |
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ISSN: | 0004-6361 1432-0746 |
DOI: | 10.1051/0004-6361/202039898 |