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1. ESO 137-002: a large spiral undergoing edge-on ram-pressure stripping with little star formation in the tail

   https://doi.org/10.1093/mnras/stab3280  

   Laudari, Sunil; Jáchym, Pavel; Sun, Ming; Waldron, Will; Chatzikos, Marios; Kenney, Jeffrey; Luo, Rongxin; Nulsen, Paul; Sarazin, Craig; Combes, Françoise; et al (December 2021, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT Ram pressure stripping (RPS) is an important mechanism for galaxy evolution. In this work, we present results from HST and APEX observations of one RPS galaxy, ESO 137-002 in the closest rich cluster Abell 3627. The galaxy is known to host prominent X-ray and H α tails. The HST data reveal significant features indicative of RPS in the galaxy, including asymmetric distribution of dust in the galaxy, dust filaments, and dust clouds in ablation generally aligned with the direction of ram pressure, and young star clusters immediately upstream of the residual dust clouds that suggest star formation (SF) triggered by RPS. The distribution of the molecular gas is asymmetric in the galaxy, with no CO upstream and abundant CO downstream and in the inner tail region. A total amount of ∼5.5 × 109 M⊙ of molecular gas is detected in the galaxy and its tail. On the other hand, we do not detect any active SF in the X-ray and H α tails of ESO 137-002 with the HST data and place a limit on the SF efficiency in the tail. Hence, if selected by SF behind the galaxy in the optical or UV (e.g. surveys like GASP or using the Galex data), ESO 137-002 will not be considered a ‘jellyfish’ galaxy. Thus, galaxies like ESO 137-002 are important for our comprehensive understanding of RPS galaxies and the evolution of the stripped material. ESO 137-002 also presents a great example of an edge-on galaxy experiencing a nearly edge-on RPS wind. 

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2. Tracing the kinematics of the whole ram-pressure-stripped tails in ESO 137-001

   https://doi.org/10.1093/mnras/stad1003  

   Luo, Rongxin; Sun, Ming; Jáchym, Pavel; Waldron, Will; Fossati, Matteo; Fumagalli, Michele; Boselli, Alessandro; Combes, Francoise; Kenney, Jeffrey_D P; Li, Yuan; et al (March 2023, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT Ram pressure stripping (RPS) is an important process to affect the evolution of cluster galaxies and their surrounding environment. We present a large MUSE mosaic for ESO 137-001 and its stripped tails, and study the detailed distributions and kinematics of the ionized gas and stars. The warm, ionized gas is detected to at least 87 kpc from the galaxy and splits into three tails. There is a clear velocity gradient roughly perpendicular to the stripping direction, which decreases along the tails and disappears beyond ∼45 kpc downstream. The velocity dispersion of the ionized gas increases to ∼80 km s−1 at ∼20 kpc downstream and stays flat beyond. The stars in the galaxy disc present a regular rotation motion, while the ionized gas is already disturbed by the ram pressure. Based on the observed velocity gradient, we construct the velocity model for the residual galactic rotation in the tails and discuss the origin and implication of its fading with distance. By comparing with theoretical studies, we interpreted the increased velocity dispersion as the result of the oscillations induced by the gas flows in the galaxy wake, which may imply an enhanced degree of turbulence there. We also compare the kinematic properties of the ionized gas and molecular gas from ALMA, which shows they are co-moving and kinematically mixed through the tails. Our study demonstrates the great potential of spatially resolved spectroscopy in probing the detailed kinematic properties of the stripped gas, which can provide important information for future simulations of RPS. 

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3. ALMA-JELLY. I. High Resolution CO(2–1) Observations of Ongoing Ram Pressure Stripping in NGC 4858 Reveal Asymmetrical Gas Tail Formation and Fallback

   https://doi.org/10.3847/1538-4357/adde47  

   Souchereau, Harrison J; Kenney, Jeffrey_D P; Jáchym, Pavel; Sun, Ming; Cramer, William J; Yagi, Masafumi; Boselli, Alessandro; Brinks, Elias; Combes, Francoise; Cortese, Luca; et al (July 2025, The Astrophysical Journal)

   Abstract We present new CO(2–1) observations (resolution ∼1″ = 460 pc) of the Coma cluster jellyfish galaxy NGC 4858 obtained from the ALMA-JELLY large program. Analyzing this data alongside complimentary Subaru Hαand Hubble Space Telescope (F600LP / F350LP) observations, we find numerous structural and kinematic features indicative of the effects from strong, inclined ram pressure, including an asymmetric inner gas tail. We estimate a highly inclined disk-wind angle of ${\varphi }_{\text{DW}}=75_{-27}^{+10}$. By subtracting a simple circular velocity model, we find (1): gas clumps that are being accelerated by ram pressure, and (2): signatures of gas clumps that had been previously pushed out of the disk but are now falling inward. We also discuss head-tail morphologies in star complexes within the stellar disk that appear to be ram pressure stripping (RPS)-influenced. Lastly, we compare this galaxy to state-of-the-art galaxy “wind tunnel” simulations. We find that this galaxy is one of the best nearby examples of strong and inclined ram pressure gas stripping, and of gas that is perturbed by ram pressure but not fully stripped and falls back. We emphasize the importance of torques due to ram pressure in highly inclined interactions, which help drive gas inward on the side rotating against the wind, contributing to the formation of asymmetric inner RPS tails. 

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4. ESO 137–001: A jellyfish galaxy model

   https://doi.org/10.1051/0004-6361/202450435  

   Vollmer, B; Sun, M; Jachym, P; Fossati, M; Boselli, A (December 2024, Astronomy & Astrophysics)

   Ram-pressure stripping of the spiral galaxy ESO 137−001 within the highly dynamical intracluster medium (ICM) of the Norma cluster lead to spectacular extraplanar CO, optical, Hα, UV, and X-ray emission. The Hαand X-ray tails extend up to 80 kpc from the galactic disk. We present dynamical simulations of the ram-pressure stripping event, and investigate the physics of the stripped gas and its ability to form stars. We also use these simulations to predict H Imaps and to constrain the orbit of ESO 137−001 within the Norma cluster. Special care was taken for the stripping of the diffuse gas. In a new approach, we analytically estimate the mixing between the intracluster and interstellar media. Different temporal ram-pressure profiles and the ICM-ISM mixing rate were tested. Three preferred models show most of the observed multiwavelength characteristics of ESO 137−001. Our highest-ranked model best reproduces the CO emission distribution, velocity for distances of ≲20 kpc from the galactic disk, and the available near-ultraviolet (NUV) observations. The second and third preferred models best reproduce the available X-ray and Hαobservations of the gas tail, including the Hαvelocity field. The angle between the direction of the galaxy’s motion and the plane of the galactic disk is between 60° and 75°. Ram-pressure stripping thus occurs more face-on. The existence of a two-tailed structure is a common feature in our models, and is due to the combined action of ram pressure and rotation together with the projection of the galaxy on the sky. Our modeling of the Hαemission caused by ionization through thermal conduction is consistent with observations. We predict the H Iemission distributions for the different models. Based on the 3D velocity vector derived from our dynamical model, we derive a galaxy orbit, which is close to unbound. We argue that ram pressure is enhanced by a factor of ∼2.5 compared to that expected for an orbit in an unperturbed spherical ICM. This increase can be obtained in two ways: an increase in the ICM density or a moving ICM opposite to the motion of the galaxy within the cluster. In a strongly perturbed galaxy cluster, such as the Norma cluster, with an off-center ICM distribution, the two possibilities are probable and plausible. 

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5. MUSE sneaks a peek at extreme ram-pressure stripping events – V. Towards a complete view of the galaxy cluster A1367

   https://doi.org/10.1093/mnras/stac345  

   Pedrini, Alex; Fossati, Matteo; Gavazzi, Giuseppe; Fumagalli, Michele; Boselli, Alessandro; Consolandi, Guido; Sun, Ming; Yagi, Masafumi; Yoshida, Michitoshi (March 2022, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT We present an analysis of the kinematics and ionization conditions in a sample composed of seven star-forming galaxies undergoing ram-pressure stripping in the A1367 cluster, and the galaxy ESO137–001 in the Norma cluster. MUSE observations of two new galaxies in this sample, CGCG097–073 and CGCG097–079, are also presented. This sample is characterized by homogeneous integral field spectroscopy with MUSE and by a consistent selection based on the presence of ionized gas tails. The ratio [O i]/H α is consistently elevated in the tails of these objects compared to what observed in unperturbed galaxy discs, an ubiquitous feature which we attribute to shocks or turbulent phenomena in the stripped gas. Compact star-forming regions are observed in only $$\approx 50 {{\ \rm per\ cent}}$$ of the tails, implying that specific (currently unknown) conditions are needed to trigger star formation inside the stripped gas. Focusing on the interface regions between the interstellar and intracluster medium, we observe different line ratios that we associate to different stages of the stripping process, with galaxies at an early stage of perturbation showing more prominent signatures of elevated star formation. Our analysis, thus, demonstrates the power of a well selected and homogeneous sample to infer general properties arising from ram-pressure stripping inside local clusters. 

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