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We present MeerKAT Fornax Survey H Iobservations of NGC 1427A, a blue irregular galaxy with a stellar mass of ∼2 × 109M⊙located near the centre of the Fornax galaxy cluster. Thanks to the excellent resolution (1–6 kpc spatially, 1.4 km s−1in velocity) and H Icolumn density sensitivity (∼4 × 1019to ∼1018cm−2depending on resolution), our data deliver new insights on the long-debated interaction of this galaxy with the cluster environment. We confirm the presence of a broad, one-sided, starless H Itail stretching from the outer regions of the stellar body and pointing away from the cluster centre. We find the tail to have 50% more H I(4 × 108M⊙) and to be 3 times longer (70 kpc) than in previous observations. In fact, we detect scattered H Iclouds out to 300 kpc from the galaxy in the direction of the tail – possibly the most ancient remnant of the passage of NGC 1427A through the intracluster medium of Fornax. Both the velocity gradient along the H Itail and the peculiar kinematics of H Iin the outer region of the stellar body are consistent with the effect of ram pressure given the line-of-sight motion of the galaxy within the cluster. However, several properties cannot be explained solely by ram pressure and suggest an ongoing tidal interaction. This includes: the close match between dense H Iand stars within the disturbed stellar body; the abundant kinematically anomalous H I; and the inversion of the H Ivelocity gradient near the base of the H Itail. We rule out an interaction with the cluster tidal field, and conclude that NGC 1427A is the result of a high-speed galaxy encounter or of a merger started at least 300 Myr ago, where ram pressure shapes the distribution and kinematics of the H Iin the perturbed outer stellar body and in the tidal tails.
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This content will become publicly available on August 1, 2027
A Virgo Environmental Survey Tracing Ionised Gas Emission (VESTIGE): XX. Star formation in the tidal tail of NGC 4254
ALMA12CO(1-0) observations of 42 star-forming regions located outside the disc of the Virgo Cluster galaxy NGC 4254 within an H Igas tail produced during the galaxy’s interaction with another cluster member have revealed the presence of ten giant molecular clouds (GMCs) in four of these regions. All of the GMCs were resolved at the angular resolution of the observations (≃160 pc) and have molecular gas masses ofM(H2)≃(0.8 − 2.0)×106M⊙. These ten clouds are characterised by gas column densities [Σ(H2) ≃ 10 M⊙pc−2] and velocity dispersions [σv(CO) ≃ 3–12 km s−1] respectively lower and comparable to those encountered in similar GMCs in the Milky Way. They follow the relation between the gas column density and the star formation activity (Schmidt law) derived using similar data over the stellar disc of NGC 4254 and other local and Virgo cluster galaxies. With analytic calculations and tuned simulations, we show that these clouds are unstable and thus expected to dissolve on relatively short timescales (∼10–30 Myr). We show that they probably formed after the collapse of dense gas clouds in the H Igas tail stripped during the gravitational interaction that the galaxy suffered several hundreds millions of years ago. The clouds are short-lived and isolated given the low density of the surrounding intracluster medium, which cannot confine the gas expelled by stellar feedback. We discuss the implications of these results in the general context of the fate of stripped gas in hostile cluster environments.
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- Award ID(s):
- 2407821
- PAR ID:
- 10706475
- Author(s) / Creator(s):
- ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; more »
- Publisher / Repository:
- EDP Sciences
- Date Published:
- Journal Name:
- Astronomy & Astrophysics
- Volume:
- 712
- ISSN:
- 0004-6361
- Page Range / eLocation ID:
- A45
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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