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Register a new userGASP XXVI. HI Gas in Jellyfish Galaxies: The case of JO201 and JO206
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We present HI observations of the jellyfish galaxy, JO201. This massive galaxy (M$_{ast} = 3.5 times 10^{10}$ M$_odot$) is falling along the line-of-sight towards the centre of a rich cluster (M$_{200} sim 1.6 times 10^{15}$ M$_odot$, $sigma_{cl} sim 982$ km/s) at a high velocity $geq$3363 km/s. Its H$alpha$ emission shows a $sim$40 kpc tail confined closely to its stellar disc and a $sim$100 kpc tail extending further out. We find HI emission coinciding only with the shorter clumpy H$alpha$ tail. In total, we measure an HI mass of M$_{rm HI} = 1.65 times 10^{9}$ M$_odot$, 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 similar mass but residing in a 10$times$ less massive cluster), and find that they are similarly HI-deficient. Of the total HI mass in JO201, about 30% lies outside the galaxy disc in projection. This HI fraction is probably a lower limit since most of the HI is redshifted relative to the stellar disc and could be outside the disc. The global star formation rate (SFR) analysis of JO201 suggests that its observed SFR would be expected if it had 10$times$ its current HI mass. The disc is the main contributor of the high star formation efficiency at a given HI 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 HI content, stellar mass and star formation rate. This finding is unexpected considering their different environments. A toy model comparing the ram pressure of the 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.
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We present VLA HI observations of JO206, a prototypical ram-pressure stripped galaxy in the GASP sample. This massive galaxy (M$_{ast} =$ 8.5 $times$ 10$^{10}$ M$_{odot}$) is located at a redshift of $z =$ 0.0513, near the centre of the low-mass galaxy cluster, IIZw108 ($sigma sim575$ km/s). JO206 is characterised by a long tail ($geq$90 kpc) of ionised gas stripped away by ram-pressure. We find a similarly long HI tail in the same direction as the ionised gas tail and measure a total HI mass of $3.2 times 10^{9}$ M$_{odot}$. This is about half the expected HI mass given the stellar mass and surface density of JO206. A total of $1.8 times 10^{9}$ M$_{odot}$ (60%) of the detected HI is in the gas stripped tail. An analysis of the star formation rate shows that the galaxy is forming more stars compared to galaxies with the same stellar and HI mass. On average we find a HI gas depletion time of $sim$0.5 Gyr which is about four times shorter than that of normal spiral galaxies. We performed a spatially resolved analysis of the relation between star formation rate density and gas density in the disc and tail of the galaxy at the resolution of our HI data. The star formation efficiency of the disc is about 10 times higher than that of the tail at fixed HI surface densities. Both the inner and outer parts of JO206 show an enhanced star formation compared to regions of similar HI surface density in field galaxies. The enhanced star formation is due to ram-pressure stripping during the galaxys first infall into the cluster.
X-ray studies of jellyfish galaxies play a crucial role in understanding the interactions between the interstellar medium (ISM) and the intracluster medium (ICM). In this paper, we focused on the jellyfish galaxy JO201. By combining archival Chandra observations, MUSE H$alpha$ cubes, and maps of the emission fraction of the diffuse ionised gas, we investigated both its high energy spectral properties and the spatial correlation between its X-ray and optical emissions. The X-ray emission of JO201 is provided by both the Compton thick AGN (L$_{text{X}}^{0.5-10 text{keV}}$=2.7$cdot$10$^{41}$ erg s$^{-1}$, not corrected for intrinsic absorption) and an extended component (L$_{text{X}}^{0.5-10 , text{keV}}approx$1.9-4.5$cdot$10$^{41}$ erg s$^{-1}$) produced by a warm plasma (kT$approx$1 keV), whose luminosity is higher than expected from the observed star formation (L$_{text{X}}sim$3.8$cdot10^{40}$ erg s$^{-1}$). The spectral analysis showed that the X-ray emission is consistent with the thermal cooling of hot plasma. These properties are similar to the ones found in other jellyfish galaxies showing extended X-ray emission. A point-to-point analysis revealed that this X-ray emission closely follows the ISM distribution, whereas CLOUDY simulations proved that the ionisation triggered by this warm plasma would be able to reproduce the [OI]/H$alpha$ excess observed in JO201. We conclude that the galactic X-ray emitting plasma is originated on the surface of the ISM as a result of the ICM-ISM interplay. This process would entail the cooling and accretion of the ICM onto the galaxy, which could additionally fuel the star formation, and the emergence of [OI]/H$alpha$ excess in the optical spectrum.
We present JVLA-C observations of the HI gas in JO204, one of the most striking jellyfish galaxies from the GASP survey. JO204 is a massive galaxy in the low-mass cluster Abell 957 at z=0.04243. The HI map reveals an extended 90 kpc long ram-pressure stripped tail of neutral gas, stretching beyond the 30 kpc long ionized gas tail and pointing away from the cluster center. The HI mass seen in emission is (1.32 $ pm 0.13) times 10^{9} rm M_{odot}$, mostly located in the tail. The northern part of the galaxy disk has retained some HI gas, while the southern part has already been completely stripped and displaced into an extended unilateral tail. Comparing the distribution and kinematics of the neutral and ionized gas in the tail indicates a highly turbulent medium. Moreover, we observe associated HI absorption against the 11 mJy central radio continuum source with an estimated HI absorption column density of 3.2 $times 10^{20}$ cm$^{-2}$. The absorption profile is significantly asymmetric with a wing towards higher velocities. We modelled the HI absorption by assuming that the HI and ionized gas disks have the same kinematics in front of the central continuum source, and deduced a wider absorption profile than observed. The observed asymmetric absorption profile can therefore be explained by a clumpy, rotating HI gas disk seen partially in front of the central continuum source, or by ram-pressure pushing the neutral gas towards the center of the continuum source, triggering the AGN activity.
Jellyfish are cluster galaxies that experience strong ram-pressure effects that strip their gas. Their H$alpha$ images reveal ionized gas tails up to 100 kpc, which could be hosting ongoing star formation. Here we report the ultraviolet (UV) imaging observation of the jellyfish galaxy JO201 obtained at a spatial resolution $sim$ 1.3 kpc. The intense burst of star formation happening in the tentacles is the focus of the present study. JO201 is the UV-brightest cluster galaxy in Abell 85 ($z sim$ 0.056) with knots and streams of star formation in the ultraviolet. We identify star forming knots both in the stripped gas and in the galaxy disk and compare the UV features with the ones traced by H$alpha$ emission. Overall, the two emissions remarkably correlate, both in the main body and along the tentacles. Similarly, also the star formation rates of individual knots derived from the extinction-corrected FUV emission agree with those derived from the H$alpha$ emission and range from $sim$ 0.01 -to- 2.07 $M_{odot} , yr^{-1}$. The integrated star formation rate from FUV flux is $sim$ 15 $M_{odot} , yr^{-1}$. The unprecedented deep UV imaging study of the jellyfish galaxy JO201 shows clear signs of extraplanar star-formation activity due to a recent/ongoing gas stripping event.
This paper presents a spatially-resolved kinematic study of the jellyfish galaxy JO201, one of the most spectacular cases of ram-pressure stripping (RPS) in the GASP (GAs Stripping Phenomena in Galaxies with MUSE) survey. By studying the environment of JO201, we find that it is moving through the dense intra-cluster medium of Abell 85 at supersonic speeds along our line of sight, and that it is likely accompanied by a small group of galaxies. Given the density of the intra-cluster medium and the galaxys mass, projected position and velocity within the cluster, we estimate that JO201 must so far have lost ~50% of its gas during infall via RPS. The MUSE data indeed reveal a smooth stellar disk, accompanied by large projected tails of ionised (Halpha) gas, composed of kinematically cold (velocity dispersion <40km/s) star-forming knots and very warm (>100km/s) diffuse emission which extend out to at least ~50 kpc from the galaxy centre. The ionised Halpha-emitting gas in the disk rotates with the stars out to ~6 kpc but in the disk outskirts becomes increasingly redshifted with respect to the (undisturbed) stellar disk. The observed disturbances are consistent with the presence of gas trailing behind the stellar component, resulting from intense face-on RPS happening along the line of sight. Our kinematic analysis is consistent with the estimated fraction of lost gas, and reveals that stripping of the disk happens outside-in, causing shock heating and gas compression in the stripped tails.
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