GASP

XXVI. HI gas in jellyfish galaxies: The case of JO201 and JO206^⋆

¹ Department of Physics and Electronics, Rhodes University, PO Box 94, Makhanda 6140, South Africa
e-mail: m.ramatsoku@ru.ac.za
² INAF-Osservatorio Astronomico di Cagliari, Via della Scienza 5, 09047 Selargius, CA, Italy
³ INAF-Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
⁴ Kapteyn Astronomical Institute, University of Groningen, Landleven 12, 9747 AV Groningen, The Netherlands
⁵ Department of Astronomy, Columbia University, Mail Code 5246, 550 W 120th Street, New York, NY 10027, USA
⁶ Instituto de Física y Astronomía, Universidad de Valparaíso, Avda. Gran Bretana 1111, Valparaíso, Chile
⁷ Center for Computational Astrophysics, Flatiron Institute, 162 5th Ave, New York, NY 10010, USA
⁸ South African Radio Astronomy Observatory, 2 Fir Street, Black River Park, Observatory 7925, South Africa
⁹ Argelander-Institut fur Astronomie, Auf dem Hugel 71, 53121 Bonn, Germany
¹⁰ National Centre for Radio Astrophysics, Tata Institute of Fundamental Research, Postbag 3, Ganeshkhind, Pune 411 007, India
¹¹ ASTRON, Netherlands Institute for Radio Astronomy, Oude Hoogeveensedijk 4, 7991 PD Dwingeloo, The Netherlands
¹² Department of Astronomy, University of Cape Town, Private Bag X3, Rondebosch 7701, South Africa
¹³ Department of Physics, University of Pretoria, Hatfield, Pretoria 0028, South Africa
¹⁴ Ruhr University Bochum, Faculty of Physics and Astronomy, Astronomical Institute, 44780 Bochum, Germany
¹⁵ Dipartimento di Fisica e Astronomia “Galileo Galilei”, Università di Padova, Vicolo dell’Osservatorio 3, 35122 Padova, Italy

Received: 18 February 2020
Accepted: 2 June 2020

Abstract

We present atomic hydrogen (H I) observations with the Jansky Very Large Array of one of the jellyfish galaxies in the GAs Stripping Phenomena sample, JO201. This massive galaxy (M_* = 3.5 × 10¹⁰ M_⊙) is falling along the line-of-sight towards the centre of a rich cluster (M₂₀₀ ∼ 1.6 × 10¹⁵ M_⊙, σ_cl ∼ 982 ± 55 km s⁻¹) at a high velocity ≥3363 km s⁻¹. Its Hα emission shows a ∼40 kpc tail, which is closely confined to its stellar disc and a ∼100 kpc tail extending further out. We find that H I emission only coincides with the shorter clumpy Hα tail, while no H I emission is detected along the ∼100 kpc Hα tail. In total, we measured an H I mass of M_HI = 1.65 × 10⁹ M_⊙, which is about 60% lower than expected based on its stellar mass and stellar surface density. We compared JO201 to another jellyfish in the GASP sample, JO206 (of a similar mass but living in a ten times less massive cluster), and we find that they are similarly H I-deficient. Of the total H I mass in JO201, about 30% lies outside the galaxy disc in projection. This H I fraction is probably a lower limit since the velocity distribution shows that most of the H I is redshifted relative to the stellar disc and could be outside the disc. The global star formation rate (SFR) analysis of JO201 suggests an enhanced star formation for its observed H I content. The observed SFR would be expected if JO201 had ten times its current H I mass. The disc is the main contributor of the high star formation efficiency at a given H I gas density for both galaxies, but their tails also show higher star formation efficiencies compared to the outer regions of field galaxies. Generally, we find that JO201 and JO206 are similar based on their H I content, stellar mass, and star formation rate. This finding is unexpected considering their different environments. A toy model comparing the ram pressure of the intracluster medium (ICM) versus the restoring forces of these galaxies suggests that the ram pressure strength exerted on them could be comparable if we consider their 3D orbital velocities and radial distances relative to the clusters.