Jellyfish Galaxies Research Articles

Comparing the interstellar and circumgalactic origin of gas in the tails of jellyfish galaxies

Simulations and observations have found long tails in `jellyfish galaxies', which are commonly thought to originate from ram-pressure stripped gas of the interstellar medium (ISM) in the immediate galactic wake. At larger distances from the galaxy, the long tails have been claimed to form in situ, owing to thermal instability and fast radiative cooling of mixed ISM and intracluster medium (ICM). In this paper, we use magnetohydrodynamical wind tunnel simulations of a galaxy with the arepo code to study the origin of gas in the tails of jellyfish galaxies. To this end, we modelled the galaxy orbit in a cluster by accounting for a time-varying galaxy velocity, ICM density, and the turbulent magnetic field. By tracking gas flows between the ISM, the circumgalactic medium (CGM), and the ICM, we find -- contrary to popular opinion -- that the majority of the gas in the tail originates in the CGM. Prior to the central passage of the jellyfish galaxy in the cluster, the CGM is directly transported to the clumpy jellyfish tail that has been shattered into small cloudlets. After the central cluster passage, gas in the tail originates both from the initial ISM and the CGM, but that from the latter is accreted onto the galactic ISM before being ram-pressure stripped to form filamentary tentacles in the tail. Our simulation shows a declining gas metallicity in the tail as a function of downstream distance from the galaxy. We conclude that the CGM plays an important role in shaping the tails of jellyfish galaxies.

The history of star-forming regions in the tails of six GASP jellyfish galaxies observed with the Hubble Space Telescope (corrigendum)

The history of star-forming regions in the tails of six GASP jellyfish galaxies observed with the Hubble Space Telescope (corrigendum)

Serendipitous Catch of a Giant Jellyfish: An Ionized Nebula around 3C 275.1 with 170 kpc Long Tails

3C 275.1 is a blue quasar at z = 0.55522, hosting powerful outflows and residing in a complex environment. We present a serendipitously detected giant nebula surrounding 3C 275.1, which shows morphological features resembling those of objects known as “jellyfish galaxies,” with extremely long tails of ionized gas extending to 170 kpc in projection. We analyze its optical spectra taken by MUSE on the Very Large Telescope. The brighter part of this giant nebula exceeds 100 kpc, and its rotation curve does not flatten out, making it very different from those of normal spiral galaxies. This system shares some characteristics common to those formed via ram pressure stripping (RPS), yet its long narrow tails and higher ionization are unusual compared to known tails in jellyfish galaxies, not fully consistent with a simple RPS scenario. Our photoionization simulation and the inferred short recombination timescale both suggest that, besides the quasar 3C 275.1, an extra source of ionization is necessary to keep the gas ionized at such a distance from the nucleus, which could be related to RPS, tidal interaction, or active galactic nucleus outflow, providing new evidence of active dynamical interaction of a galaxy with the intracluster medium.

Dark-matter-free Dwarf Galaxy Formation at the Tips of the Tentacles of Jellyfish Galaxies

When falling into a galaxy cluster, galaxies experience a loss of gas due to ram pressure stripping. In particular, disk galaxies lose gas from their disks, and very large tentacles of gas can be formed. Because of the morphology of these stripped galaxies, they have been referred to as jellyfish galaxies. It has been found that star formation is triggered not only in the disk, but also in the tentacles of such jellyfish galaxies. The observed star-forming regions located in the tentacles of those galaxies have been found to be as massive as 3 × 107 M ⊙ and with sizes >100 pc. Interestingly, these parameters in mass and size agree with those of dwarf galaxies. In this work, we make use of the state-of-the-art magnetohydrodynamic (MHD) cosmological simulation IllustrisTNG-50 to study massive jellyfish galaxies with long tentacles. We find that, in the tentacles of TNG-50 jellyfish galaxies, the star formation regions (gas+stars) formed could be as massive as ∼2 × 108 M ⊙. A particular star-forming region was analyzed. This region has a star formation rate of 0.04 M ⊙ yr−1, it is metal-rich, has an average age of 0.46 Gyr, and has a half-mass radius of ∼1 kpc, typical of standard dwarf galaxies. Most importantly, this region is gravitationally self-bound. Overall, we identify a new type of dwarf galaxy being born from the gas tentacles of jellyfish galaxies that, by construction, lacks a dark matter halo.

Systematic analysis of jellyfish galaxy candidates in Fornax, Antlia, and Hydra from the S-PLUS survey: a self-supervised visual identification aid

ABSTRACT We study 51 jellyfish galaxy candidates in the Fornax, Antlia, and Hydra clusters. These candidates are identified using the JClass scheme based on the visual classification of wide-field, twelve-band optical images obtained from the Southern Photometric Local Universe Survey. A comprehensive astrophysical analysis of the jellyfish (JClass > 0), non-jellyfish (JClass = 0), and independently organized control samples is undertaken. We develop a semi-automated pipeline using self-supervised learning and similarity search to detect jellyfish galaxies. The proposed framework is designed to assist visual classifiers by providing more reliable JClasses for galaxies. We find that jellyfish candidates exhibit a lower Gini coefficient, higher entropy, and a lower 2D Sérsic index as the jellyfish features in these galaxies become more pronounced. Jellyfish candidates show elevated star formation rates (including contributions from the main body and tails) by $\sim$1.75 dex, suggesting a significant increase in the SFR caused by the ram-pressure stripping phenomenon. Galaxies in the Antlia and Fornax clusters preferentially fall towards the cluster’s centre, whereas only a mild preference is observed for Hydra galaxies. Our self-supervised pipeline, applied in visually challenging cases, offers two main advantages: it reduces human visual biases and scales effectively for large data sets. This versatile framework promises substantial enhancements in morphology studies for future galaxy image surveys.

Introducing the TNG-Cluster simulation: Overview and the physical properties of the gaseous intracluster medium

We introduce the new TNG-Cluster project, an addition to the IllustrisTNG suite of cosmological magnetohydrodynamical simulations of galaxy formation. Our objective is to significantly increase the statistical sampling of the most massive and rare objects in the Universe: galaxy clusters with log(M200c/M⊙) ≳ 14.3 − 15.4 at z = 0. To do so, we re-simulate 352 cluster regions drawn from a 1 Gpc volume that is 36 times larger than TNG300, keeping the IllustrisTNG physical model entirely fixed as well as the numerical resolution. This new sample of hundreds of massive galaxy clusters enables studies of the assembly of high-mass ellipticals and their supermassive black holes (SMBHs), brightest cluster galaxies (BCGs), satellite galaxy evolution and environmental processes, jellyfish galaxies, intracluster medium (ICM) properties, cooling and active galactic nuclei (AGN) feedback, mergers and relaxedness, magnetic field amplification, chemical enrichment, and the galaxy-halo connection at the high-mass end, with observables from the optical to radio synchrotron and the Sunyaev-Zeldovich (SZ) effect, to X-ray emission, as well as their cosmological applications. We present an overview of the simulation, the cluster sample, select comparisons to data, and a first look at the diversity and physical properties of our simulated clusters and their hot ICM.

The history of star-forming regions in the tails of six GASP jellyfish galaxies observed with the Hubble Space Telescope

Aims. In this work, we aim to characterize the stellar populations of star-forming regions detached from the stellar disks of galaxies undergoing ram-pressure stripping. Methods. Using images collected with the WFC3 camera on board of the Hubble Space Telescope, we detected stellar clumps in continuum-subtracted Hα and the ultraviolet (F275W filter); such clumps are often embedded in larger regions (star-forming complexes) detected in the optical (F606W filter). Our sample includes 347 Hα clumps, 851 F275W clumps, and 296 star-forming complexes. We modeled the photometry of these objects in five bands using BAGPIPES to obtain their stellar population parameters. Results. The median mass-weighted stellar ages are 27 Myr for Hα clumps and 39 Myr for F275W clumps and star-forming complexes, but the oldest stars in the complexes can be older than ∼300 Myr which indicates that star formation is sustained for long periods of time. Stellar masses vary from 103.5 to 107.1 M⊙, with star-forming complexes being more massive objects in the sample. Clumps and complexes found further away from the host galaxy are on average younger, less massive, and less obscured by dust. We interpret these trends as due to the effect of ram pressure in different phases of the interstellar medium. Hα clumps form a well-defined sequence in the stellar mass–SFR plane with a slope of 0.73. Some F275W clumps and star-forming complexes follow the same sequence while others stray away from it and passively age. The difference in mean stellar age between a complex and its youngest embedded clump scales with the distance between the clump and the center of the optical emission of the complex, with the most displaced clumps being hosted by the most elongated complexes. This is consistent with a fireball-like morphology, where star formation proceeds in a small portion of the complex while older stars are left behind producing a linear stellar population gradient. The stellar masses of star-forming complexes are consistent with the ones of globular clusters, but their stellar mass surface densities are lower by 2 dex, and their properties are more consistent with the population of dwarf galaxies in clusters.

Jellyfish galaxies with the IllustrisTNG simulations – citizen-science results towards large distances, low-mass hosts, and high redshifts

ABSTRACT We present the ‘Cosmological Jellyfish’ project – a citizen-science classification program to identify jellyfish (JF) galaxies within the IllustrisTNG cosmological simulations. JF are satellite galaxies that exhibit long trailing gas features – ‘tails’ – extending from their stellar body. Their distinctive morphology arises due to ram-pressure stripping (RPS) as they move through the background gaseous medium. Using the TNG50 and TNG100 simulations, we construct a sample of $\sim 80\, 000$ satellite galaxies spanning an unprecedented range of stellar masses, $10^{8.3}{-}10^{12.3}\, \mathrm{M_\odot }$, and host masses, $M_\mathrm{200,c}=10^{10.4}{-}10^{14.6}\, \mathrm{M_\odot }$ back to z = 2. Based on this sample, $\sim 90\, 000$ galaxy images were presented to volunteers in the citizen-science Zooniverse platform, who were asked to determine whether the galaxy image resembles a JF. Based on volunteer votes, each galaxy received a score determining if it is a JF or not. This paper describes the project, the inspected satellite sample, the methodology, and the classification process that resulted in a data set of 5307 visually identified JF galaxies. We find that JF is common in nearly all group- and cluster-sized systems, with the JF fraction increasing with host mass and decreasing with satellite stellar mass. We highlight JF galaxies in three relatively unexplored regimes: low-mass hosts of $M_\mathrm{200,c}\sim 10^{11.5}{-}10^{13}\, \mathrm{M_\odot }$, radial positions within hosts exceeding the virial radius R200, c, and at high redshift up to z = 2. The full data set of our JF scores is publicly available and can be used to select and study JF galaxies in the IllustrisTNG simulations.

The surprising lack of effect from stellar feedback on the gas stripping rate from massive jellyfish galaxies

ABSTRACT We study the role of star formation and stellar feedback in a galaxy being ram pressure (RP) stripped on its infall into a cluster. We use hydrodynamical wind-tunnel simulations of a massive galaxy (Mstar = 1011 M⊙) moving into a massive cluster (Mcluster = 1015 M⊙). We have two types of simulations: with and without star formation and stellar feedback, SF, and radiative cooling (RC), respectively. For each type, we simulate four realizations of the same galaxy: a face-on wind, edge-on wind, 45° angled wind, and a control galaxy not subject to RP. We directly compare the stripping evolution of galaxies with and without star formation. We find that stellar feedback has no direct effect on the stripping process, i.e. there is no enhancement in stripping via a velocity kick to the interstellar medium (ISM) gas. The main difference between RC and SF galaxies is due to the indirect effect of stellar feedback, which produces a smoother and more homogeneous ISM. Hence, while the average gas surface density is comparable in both simulation types, the scatter is broader in the RC galaxies. As a result, at the galaxy outskirts overdense clumps survive in RC simulation, and the stripping proceeds more slowly. At the same time, in the inner disc, underdense gas in the RC holes is removed faster than the smoothly distributed gas in the SF simulation. For our massive galaxy, we therefore find that the effect of feedback on the stripping rate is almost negligible, independent of wind angle.

The magnetized and thermally unstable tails of jellyfish galaxies

ABSTRACT Jellyfish galaxies are promising laboratories for studying radiative cooling and magnetic fields in multiphase gas flows. Their long, dense tails are observed to be magnetized, and they extend up to 100 kpc into the intracluster medium (ICM), suggesting that their gas is thermally unstable so that the cold gas mass grows with time rather than being fully dissolved in the hot wind as a result of hydrodynamical interface instabilities. In this paper, we use the arepo code to perform magnetohydrodynamical windtunnel simulations of a jellyfish galaxy experiencing ram-pressure stripping by interacting with an ICM wind. The ICM density, temperature and velocity that the galaxy encounters are time-dependent and comparable to what a real jellyfish galaxy experiences while orbiting the ICM. In simulations with a turbulent magnetized wind, we reproduce observations, which show that the magnetic field is aligned with the jellyfish tails. During the galaxy infall into the cluster with a near edge-on geometry, the gas flow in the tail is fountain-like, implying preferential stripping of gas where the rotational velocity vectors add up with the ram pressure while fall-back occurs in the opposite case. Hence, the tail velocity shows a memory of the rotation pattern of the disc. At the time of the nearest cluster passage, ram-pressure stripping is so strong that the fountain flow is destroyed and instead the tail is dominated by the removal of gas. We show that gas in the tail is very fragmentative, which is a prediction of shattering due to radiative cooling.

Jellyfish galaxies with the IllustrisTNG simulations - No enhanced population-wide star formation according to TNG50

ABSTRACT Due to ram-pressure stripping (RPS), jellyfish galaxies are thought to lose large amounts, if not all, of their interstellar medium. Nevertheless, some, but not all, observations suggest that jellyfish galaxies exhibit enhanced star formation compared to control samples, even in their ram pressure-stripped tails. We use the TNG50 cosmological gravity + magnetohydrodynamical simulation, with an average spatial resolution of 50–200 pc in the star-forming regions of galaxies, to quantify the star formation activity and star formation rates (SFRs) of more than 700 jellyfish galaxies at z = 0–1 with stellar masses $10^{8.3-10.8} \ {\rm M}_\odot$ in hosts with mass $10^{10.5-14.3} \ {\rm M}_\odot$. We extract their global SFRs, the SFRs within their main stellar body versus within the tails, and we follow the evolution of the star formation along their individual evolutionary tracks. We compare the findings for jellyfish galaxies to those of diversely constructed control samples, including against satellite and field galaxies with matched redshift, stellar mass, gas fraction, and host halo mass. According to TNG50, star formation and RPS can indeed occur simultaneously within any given galaxy, and frequently do so. Moreover, star formation can also take place within the ram pressure-stripped tails, even though the latter is typically subdominant. However, TNG50 does not predict elevated population-wide SFRs in jellyfish compared to analogue satellite galaxies with the same stellar mass or gas fraction. Simulated jellyfish galaxies do undergo bursts of elevated star formation along their history but, at least according to TNG50, these do not translate into a population-wide enhancement at any given epoch.

Jellyfish galaxies with the IllustrisTNG simulations – when, where, and for how long does ram pressure stripping of cold gas occur?

ABSTRACT Jellyfish galaxies are prototypical examples of satellite galaxies undergoing strong ram pressure stripping (RPS). We analyse the evolution of 512 unique, first-infalling jellyfish galaxies from the TNG50 cosmological simulation. These have been visually inspected to be undergoing RPS sometime in the past 5 Byr (since z = 0.5), have satellite stellar masses $M_\star ^{\rm sat}\sim 10^{8\!-\!10.5}\, {\rm M}_\odot$, and live in hosts with $M_{\rm 200c}\sim 10^{12\!-\!14.3}\, {\rm M}_\odot$ at z = 0. We quantify the cold gas (T ≤ 104.5 K) removal using the tracer particles, confirming that for these jellyfish, RPS is the dominant driver of cold gas loss after infall. Half of these jellyfish are completely gas-less by z = 0, and these galaxies have earlier infall times and smaller satellite-to-host mass ratios than their gaseous counterparts. RPS can act on jellyfish galaxies over long time-scales of ≈1.5–8 Gyr. Jellyfish in more massive hosts are impacted by RPS for a shorter time span and, at a fixed host mass, jellyfish with less cold gas at infall and lower stellar masses at z = 0 have shorter RPS time spans. While RPS may act for long periods of time, the peak RPS period – where at least 50 per cent of the total RPS occurs – begins within ≈1 Gyr of infall and lasts ≲2 Gyr. During this period, the jellyfish are at host-centric distances ∼0.2–2R200c, illustrating that much of RPS occurs at large distances from the host galaxy. Interestingly, jellyfish continue forming stars until they have lost ≈98 per cent of their cold gas. For groups and clusters in TNG50 $(M_{\rm 200c}^{\rm host}\sim 10^{13\!-\!14.3}\, {\rm M}_\odot)$, jellyfish galaxies deposit more cold gas ($\sim 10^{11\!-\!12}\, {\rm M}_\odot$) into haloes than what exists in them at z = 0, demonstrating that jellyfish, and in general satellite galaxies, are a significant source of cold gas accretion.

Spatially resolved self-consistent spectral modelling of jellyfish galaxies from MUSE with FADO: trends with mass and stripping intensity

ABSTRACT We present a spatially resolved stellar population analysis of 61 jellyfish galaxies and 47 control galaxies observed with ESO/MUSE attempting to understand the general trends of the stellar populations as a function of the stripping intensity and mass. This is the public sample from the GASP programme, with 0.01 < z < 0.15 and 8.9 < log (M⋆/M⊙) < 12.0. We apply the spectral population synthesis code fado to fit self-consistently both the stellar and nebular contributions to the spectra of the sources. We present 2D morphological maps for mean stellar ages, metallicities, gas-phase oxygen abundances, and star formation rates for the galaxies with Integrated Nested Laplace Approximation (inla), which is efficient in reconstructing spatial data of extended sources. We find that ‘extreme stripping’ and ‘stripping’ galaxies are typically younger than the other types. Regarding stellar and nebular metallicities, the ‘stripping’ and ‘control passive’ galaxies are the most metal-poor. Based on the phase space for jellyfish cluster members we find trends in ages, metallicities, and abundances with different regions of the diagram. We also compute radial profiles for the same quantities. We find that both the stripping and the stellar masses seem to influence the profiles, and we see differences between various groups and distinct mass bins. The radial profiles for different mass bins present relations already shown in the literature for undisturbed galaxies, i.e. profiles of ages and metallicities tend to increase with mass. However, beyond ∼0.75 effective radius, the ages of the most massive galaxies become similar to or lower than the ages of the lower mass ones.

3D Modeling of the Molecular Gas Kinematics in Optically Selected Jellyfish Galaxies

Cluster galaxies are subject to the ram pressure exerted by the intracluster medium, which can perturb or even strip away their gas while leaving the stars undisturbed. We model the distribution and kinematics of the stars and the molecular gas in four late-type cluster galaxies (JO201, JO204, JO206, and JW100), which show tails of atomic and ionized gas indicative of ongoing ram pressure stripping. We analyze MUSE@VLT data and CO data from the Atacama Large Millimeter Array searching for signatures of radial gas flows, ram pressure stripping, and other perturbations. We find that all galaxies, with the possible exception of JW100, host stellar bars. Signatures of ram pressure are found in JO201 and JO206, which also shows clear indications of ongoing stripping in the molecular disk outskirts. The stripping affects the whole molecular gas disk of JW100. The molecular gas kinematics in JO204 is instead dominated by rotation rather than ram pressure. We also find indications of enhanced turbulence of the molecular gas compared to field galaxies. Large-scale radial flows of molecular gas are present in JO204 and JW100, but more uncertain in JO201 and JO206. We show that our sample follows the molecular gas mass–size relation, confirming that it is essentially independent of environment even for the most extreme cases of stripping. Our findings are consistent with the molecular gas being affected by the ram pressure on different timescales and less severely than the atomic and ionized gas phases, likely because the molecular gas is denser and more gravitationally bound to the galaxy.

Turbulence in the tail of a jellyfish galaxy

ABSTRACT When galaxies move through the intracluster medium (ICM) inside galaxy clusters, the ram pressure of the ICM can strip the gas from galaxies. The stripped gas forms tails on the trailing side. These galaxies are hence dubbed ‘jellyfish galaxies’. ESO 137-001 is a quintessential jellyfish galaxy located in the nearest rich cluster, the Norma cluster. Its spectacular multiphase tail has complex morphology and kinematics both from the imprinted galaxy’s interstellar medium (ISM) and as a result of the interactions between the stripped gas and the surrounding hot plasma, mediated by radiative cooling and magnetic fields. We study the kinematics of the multiphase tail using high-resolution observations of the ionized and the molecular gas in the entire structure. We calculate the velocity structure functions in moving frames along the tail and find that turbulence driven by Kelvin–Helmholtz (KH) instability quickly overwhelms the original ISM turbulence and saturates at ∼30 kpc. There is also a hint that the far end of the tail has possibly started to inherit pre-existing large-scale ICM turbulence likely caused by structure formation. Turbulence measured by the molecular gas is generally consistent with that measured by the ionized gas in the tail but has a slightly lower amplitude. Most of the measured turbulence is below the mean free path of the hot ICM (∼11 kpc). Using warm/cool gas as a tracer of the hot ICM, we find that the isotropic viscosity of the hot plasma must be suppressed below 0.01 per cent Spitzer level.

UV and Hα HST Observations of Six GASP Jellyfish Galaxies

Star-forming, Hα-emitting clumps are found embedded in the gaseous tails of galaxies undergoing intense ram pressure stripping in galaxy clusters, so-called jellyfish galaxies. These clumps offer a unique opportunity to study star formation under extreme conditions, in the absence of an underlying disk and embedded within the hot intracluster medium. Yet, a comprehensive, high-spatial-resolution study of these systems is missing. We obtained UVIS/Hubble Space Telescope (HST) data to observe the first statistical sample of clumps in the tails and disks of six jellyfish galaxies from the GASP survey; we used a combination of broadband (UV to I) filters and a narrowband Hα filter. HST observations are needed to study the sizes, stellar masses, and ages of the clumps and their clustering hierarchy. These observations will be used to study the clump scaling relations and the universality of the star formation process, and to verify whether a disk is irrelevant, as hinted at by results from jellyfish galaxies. This paper presents the observations, data reduction strategy, and some general results based on the preliminary data analysis. The high spatial resolution of UVIS gives an unprecedentedly sharp view of the complex structure of the inner regions of the galaxies and of the substructures in the galaxy disks. We found clear signatures of stripping in regions very close in projection to the galactic disk. The star-forming regions in the stripped tails are extremely bright and compact and we did not detect a significant number of star-forming clumps in regions where MUSE did not detect any. The paper finally presents the development plan for the project.

GASP. XLV. Stellar Bars in Jellyfish Galaxies: Analysis of Ionized Gas and Stellar Populations

Stellar bars have been found to substantially influence the properties of stellar populations in galaxies, affecting their ability to form stars. While this can be easily seen when studying galaxies in relatively isolated environments, such type of analysis requires a higher degree of complexity when cluster galaxies are considered, due to the variety of interactions that can potentially occur in these denser environments. We use IFU MUSE data from the GASP survey to study the combined effect of the presence of a stellar bar and ram pressure, on spatially resolved properties of stellar populations. We have analyzed spatially resolved indicators of both recent star formation rates (SFRs) and average stellar population ages to check for signatures of anomalous central star formation activity, also taking into account the possible presence of nuclear activity. We found an increase in central SFR in ram-pressure-affected galaxies when compared with unperturbed ones. The most extreme cases of increased SFR and central rejuvenation occur in barred galaxies that are at advanced stages of ram pressure stripping. For low-mass barred galaxies affected by ram pressure, the combined effect is the systematic enhancement of the star formation activity as opposed to the case of high-mass galaxies, which present both enhancement and suppression. Barred galaxies that present suppression of their star formation activity also present signatures of nuclear activity. Our results indicate that the combined effect of the presence of a bar and strong perturbation by ram pressure is able to trigger the central star formation activity and probably ignite nuclear activity.

Ultraviolet imaging observations of three jellyfish galaxies: star formation suppression in the centre and ongoing star formation in stripped tails

ABSTRACT Spiral galaxies undergo strong ram-pressure effects when they fall into the galaxy cluster potential. As a consequence, their gas is stripped to form extended tails within which star formation can happen, giving them the typical jellyfish appearance. The ultraviolet imaging observations of jellyfish galaxies provide an opportunity to understand ongoing star formation in the stripped tails. We report the ultraviolet observations of the jellyfish galaxies JW39, JO60, JO194 and compare with observations in optical continuum and Hα. We detect knots of star formation in the disc and tails of the galaxies and find that their UV and Hα flux are well correlated. The optical emission line ratio maps of these galaxies are used to identify for every region the emission mechanism, due to either star formation, LINER or a mix of the two phenomena. The star-forming regions in the emission line maps match very well with the regions having significant UV flux. The central regions of two galaxies (JW39, JO194) show a reduction in UV flux which coincides with composite or LINER regions in the emission line maps. The galaxies studied here demonstrate significant star formation in the stripped tails, suppressed star formation in the central regions and present a possible case of accelerated quenching happening in jellyfish galaxies.

LoTSS Jellyfish Galaxies. IV. Enhanced Star Formation on the Leading Half of Cluster Galaxies and Gas Compression in IC3949

With Mapping Nearby Galaxies at APO integral field spectroscopy, we present a resolved analysis of star formation for 29 jellyfish galaxies in nearby clusters, identified from radio continuum imaging taken by the Low Frequency Array. Simulations predict enhanced star formation on the “leading half” (LH) of galaxies undergoing ram pressure stripping, and in this work we report observational evidence for this elevated star formation. The dividing line (through the galaxy center) that maximizes this star formation enhancement is systematically tied to the observed direction of the ram-pressure-stripped tail, suggesting a physical connection between ram pressure and this star formation enhancement. We also present a case study on the distribution of molecular gas in one jellyfish galaxy from our sample, IC3949, using Atacama Large Millimeter/submillimeter Array CO J = 1 − 0, HCN J = 1 − 0, and HCO+ J = 1 − 0 observations from the ALMA MaNGA Quenching and Star Formation Survey. The H2 depletion time (as traced by CO) in IC3949 ranges from ∼1 Gyr in the outskirts of the molecular gas disk to ∼11 Gyr near the galaxy center. IC3949 shows a clear region of enhanced star formation on the LH of the galaxy where the average depletion time is ∼2.7 Gyr, in line with the median value for the galaxy on the whole. Dense gas tracers, HCN and HCO+, are only detected at the galaxy center and on the LH of IC3949. Our results favor a scenario in which ram pressure compresses the interstellar medium, promoting the formation of molecular gas that in turn fuels a localized increase of star formation.

A GMOS/IFU Study of Jellyfish Galaxies in Massive Clusters

Jellyfish galaxies are an intriguing snapshot of galaxies undergoing ram pressure stripping (RPS) in dense environments, showing spectacular star-forming knots in their disks and tails. We study the ionized gas properties of five jellyfish galaxies in massive clusters with Gemini GMOS/Integral Field Unit observations: MACSJ0916-JFG1 (z = 0.330), MACSJ1752-JFG2 (z = 0.353), A2744-F0083 (z = 0.303), MACSJ1258-JFG1 (z = 0.342), and MACSJ1720-JFG1 (z = 0.383). “Baldwin, Phillips, and Terlevich” diagrams show that star formation, active galactic nuclei (AGNs), or mixed effects are ionizing gas in these galaxies. Radial velocity distributions of ionized gas seem to follow disk rotation of galaxies, with the appearance of a few high-velocity components in the tails as a sign of RPS. Mean gas velocity dispersion is lower than 50 km s−1 in most star-forming regions except near AGNs or shock-heated regions, indicating that the ionized gas is dynamically cold. Integrated star formation rates (SFRs) of these galaxies range from 7 M ⊙ yr−1 to 35 M ⊙ yr−1, and the tail SFRs are from 0.6 M ⊙ yr−1 to 16 M ⊙ yr−1, which are much higher than those of other jellyfish galaxies in the local universe. These high SFR values imply that RPS triggers intense star formation activity in these extreme jellyfish galaxies. The phase-space diagrams demonstrate that the jellyfish galaxies with higher stellar masses and higher host cluster velocity dispersion are likely to have more enhanced star formation activity. The jellyfish galaxies in this study have similar gas kinematics and dynamical states to those in the local universe, but they show a much higher SFR.