Gasp

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⊙, σcl ∼ 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 MHI = 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.

The High Molecular Gas Content, and the Efficient Conversion of Neutral into Molecular Gas, in Jellyfish Galaxies

“…Black dots are H I deficient galaxies in Virgo from Corbelli et al (2012): filled symbols and empty symbols represent H 2 masses derived with constant or metallicity-dependent a CO . Finally, considering depletion times, we note that in Ramatsoku et al (2020), for JO201 and JO206, we found that H I depletion times are much shorter than the average value found in galaxy disks, apparently implying a very efficient star formation (as far as H I is concerned) and/or a low H I content for their SFR. Evaluating the global (H I + H 2 ) depletion time for the three galaxies where we have both measurements, it turns out that within the galaxy disk the estimated depletion time is in agreement with literature values (Leroy et al 2008) only for the JO206 galaxy, while JO201 and JW100 have unusually long depletion times, unless we assume extremely low values for the a CO .…”

“…Having established that molecular gas is abundantly present in jellyfish galaxies, we now proceed to evaluate the proportion of the different gas phases within the galaxy disk to better characterize the star-forming cycle. Three of our galaxies (Ramatsoku et al 2019(Ramatsoku et al , 2020T. Deb et al 2020, in preparation) also possess an estimate of the H I gas content (preliminary from MeerKat data for JW100), while for the fourth one (JO204) this has been hampered by H I absorption due to the presence of a continuum source at the center of the galaxy (Deb et al 2020).…”

“…For the JO206 galaxy we had to recalculate the mass within the disk using the disk definition adopted here. Vulcani et al (2018); molecular gas masses within the galaxy disk assuming different a CO and, in parenthesis, the molecular gas to stellar mass fractions in the disk; molecular gas to stellar mass fractions in the stripped tail; H 2 depletion times; H I masses within the disk from Ramatsoku et al (2019Ramatsoku et al ( , 2020 and T. Deb et al (2020, in preparation);…”

“…The GASP survey 9 (Poggianti et al 2017b) has started exploring the effects of environmental interactions on nearby (z 0.05) cluster/group galaxies thanks to a dedicated VLT MUSE Large Program (GAs Stripping Phenomena in galaxies with MUSE, P. I. B. Poggianti) mainly tracing the ionized gas, but complementary data sets at different wavelengths are being collected and have started offering a clear view on all the connected gas phases (see also George et al 2018;Poggianti et al 2019;Ramatsoku et al 2019Ramatsoku et al , 2020Deb et al 2020). In particular, in Moretti et al (2018) we observed with the APEX telescope 4 GASP galaxies detecting molecular gas both in the galaxy disks and in the ionized gas tails.…”

GASP XXIX – unwinding the arms of spiral galaxies via ram-pressure stripping

“…This large sample has facilitated the opportunity to observe many new aspects and effects of RPS, including the possibility that RPS can funnel the gas into the central region of the galaxy, triggering and fuelling the AGN (Poggianti et al 2017a), and the widespread evidence of in-situ star formation in the tails (Poggianti et al 2019a). One of the most heavily studied jellyfish galaxies of the GASP survey to date has been JO201, analysed both individually in Bellhouse et al (2017Bellhouse et al ( , 2019, George et al (2018George et al ( , 2019, and Ramatsoku et al (2020) and as part of wider studies (Poggianti et al 2017a;Moretti et al 2018;Vulcani et al 2018;Radovich et al 2019). JO201 is a massive galaxy falling into the massive cluster Abell 85 at supersonic speeds close to the line of sight towards the observer, exhibiting signs of extreme near-face-on RPS.…”