We present the first high-resolution map of the cold molecular gas distribution, as traced by CO(2-1) emission with ALMA, in a prominent ram pressure stripped tail. The Norma cluster galaxy ESO 137-001 is undergoing a strong interaction with the surrounding intra-cluster medium and is one of the nearest jellyfish galaxies with a long multi-phase tail. We have mapped the full extent of the tail at 1 ′′ (350 pc) angular resolution and found a rich distribution of mostly compact CO regions extending to nearly 60 kpc in length and 25 kpc in width. In total about 10 9 M ⊙ of molecular gas was detected. The CO features are found predominantly at the heads of numerous small-scale (∼ 1.5 kpc) fireballs (i.e., star-forming clouds with linear streams of young stars extending toward the galaxy) but also of largescale (∼ 8 kpc) super-fireballs, and double-sided fireballs that have additional diffuse ionized gas tails extending in the direction opposite to the stellar tails. The new data help to shed light on the origin of the molecular tail -CO filaments oriented in the direction of the tail with only diffuse associated Hα emission are likely young molecular features formed in situ, whereas other large CO features tilted with respect to the tail may have originated from the densest gas complexes that were pushed gradually away from the disk. The ALMA observations of ESO 137-001, together with observations from HST, Chandra and VLT/MUSE, offer the most complete view of a spectacular ram pressure stripped tail to date.

To investigate the effects the cluster environment has on Late-Type Galaxies (LTGs) we studied HI perturbation signatures for all Abell 1367 LTGs with HI detections. We used new VLA H i observations combined with AGES single dish blind survey data. Our study indicates that the asymmetry between the high-and low-velocity wings of the characteristic double-horn integrated H i spectrum as measured by the asymmetry parameter, A flux , can be a useful diagnostic for ongoing and/or recent HI stripping. 26% of A1367 LTGs have an A flux ratio, more asymmetrical than 3 times the 1σ spread in the A flux ratio distribution of an undisturbed sample of isolated galaxies (2%) and samples from other denser environments (10% to 20%). Over half of the A 1367 LTGs, which are members of groups or pairs, have an A flux ratio larger than twice the 1 σ spread found in the isolated sample. This suggests inter-group/pair interactions could be making a significant contribution to the LTGs displaying such A flux ratios. The study also demonstrates that the definition of the H i offset from the optical centre of LTGs is resolution dependent, suggesting that unresolved AGES H i offsets that are significantly larger than the pointing uncertainties (> 2 σ) reflect interactions which have asymmetrically displaced significant masses of lower density H i, while having minimal impact on the location of the highest density HI in resolved maps. The distribution of A flux from a comparable sample of Virgo galaxies provides a clear indication that the frequency of H i profile perturbations is lower than in A 1367.

We present Very Large Array H i imaging data for a field in the NW of the galaxy cluster Abell 1367 (z= 0.02) in an attempt to probe the effect environment has on the interstellar medium of late‐type spiral galaxies. Several galaxies, like CGCG 097–087, show pronounced tails and asymmetries, and seven out of 10 show significant, several kpc offsets between the H i centroid and the optical. We compare our results against a sample of optically bright, late‐type galaxies (spirals) across the central 1.5 Mpc of the cluster taken from the Arecibo Galaxy Environment Survey. We find that these late‐type spirals are predominantly found in the northern half of the cluster, especially those that are relatively gas rich. We calculate the H i deficiency and find that the expected global trend for the H i deficiency of these spirals to increase with projected proximity to the cluster core, seen in clusters like Coma and Virgo, is not observed. We classified the spirals into four evolutionary states, with the galaxies in each state sharing a similar degree of H i deficiency and optical colour. The common characteristics of the spirals in each evolutionary state suggest they have been subject to similar environmental processes. Many of the spirals in the most common evolutionary state (moderate H i deficiency and blue colour) have an H i intensity maximum which is displaced relative to its optical counterpart. The orientation of these offsets and magnitude of their H i deficiencies together with data from other wavelengths provide observational evidence in support of varying degrees of ram pressure stripping and tidal interaction. In general, our results indicate that the H i discs of bright late‐type galaxies in the central part of the cluster are subject to both gas loss and morphological disturbance as a result of their interaction with the cluster environment. This provides further observational evidence of a more complex environment in Abell 1367 as compared to Virgo and Coma.

We present VLA D‐array H i observations of the RSCG 42 and FGC 1287 galaxy groups, in the outskirts of the Abell 1367 cluster. These groups are projected ∼1.8 and 2.7 Mpc west from the cluster centre. The Arecibo Galaxy Environment Survey provided evidence for H i extending over as much as 200 kpc in both groups. Our new, higher resolution observations reveal that the complex H i features detected by Arecibo are in reality two extraordinary long H i tails extending for ∼160 and 250 kpc, respectively, i.e. among the longest H i structures ever observed in groups of galaxies. Although in the case of RSCG 42 the morphology and dynamics of the H i tail, as well as the optical properties of the group members, support a low‐velocity tidal interaction scenario, less clear is the origin of the unique features associated with FGC 1287. This galaxy displays an exceptionally long ‘dog leg’ H i tail, and the large distance from the X‐ray‐emitting region of Abell 1367 makes a ram‐pressure stripping scenario highly unlikely. At the same time, a low‐velocity tidal interaction seems unable to explain the extraordinary length of the tail and the lack of any sign of disturbance in the optical properties of FGC 1287. An intriguing possibility could be that this galaxy might have recently experienced a high‐speed interaction with another member of the Coma–Abell 1367 Great Wall. We searched for the interloper responsible for this feature and, although we find a possible candidate, we show that without additional observations it is impossible to settle this issue. While the mechanism responsible for this extraordinary H i tail remains to be determined, our discovery highlights how little we know about environmental effects in galaxy groups.

In this series of papers we explore the evolution of late-type galaxies in the rich cluster Abell 85. In this first paper we revisit the complex dynamical state of A 85 by using independent methods. First, we analyze the galaxy redshift distribution towards A 85 in the whole range 0−40 000 km s −1 , and determine the mean redshifts of the background clusters A 87 and A 89, very close in projection to A 85. Then we search for substructures in A 85 by considering the 2D galaxy distribution of its members (13 000−20 000 km s −1 ) and by applying the kinematical 3D Δ-test to both projected positions and radial velocities. This clearly reveals several substructures: one close to the cluster core and three more projected towards the southeast, along the region where an X-ray filament has been extensively studied. We also analyse the distribution of the brightest blue galaxies across a major fraction of the cluster volume, considering if they are gas-rich or poor. We report a very asymmetric distribution of the blue member galaxies, with most of them to the east and southeast, namely in the region joining the core of A 85 to its farthest substructure in this direction -dubbed the SE clump. By matching our sample of bright blue member galaxies with H i detections reported in the literature, we identify gas-rich and gas-poor ones. As expected, the H i-rich blue galaxies follow the same trend as the parent sample, with most of them projected on the eastern side of the cluster as well. Interestingly no blue objects have been detected in H i up to a projected radius of 2 Mpc in this zone. We finally estimate the ram pressure stripping exerted by the intra-cluster medium as a function of the projected distance from A 85, in order to quantify how important this mechanism might be in sweeping the gas out of the infalling spirals.

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Context. Pre-merger tidal interactions between pairs of galaxies are known to induce significant changes in the morphologies and kinematics of the stellar and interstellar medium components. Large amounts of gas and stars are often found to be disturbed or displaced as tidal debris. This debris then evolves, sometimes forming stars and occasionally forming tidal dwarf galaxies. Here we present results from our H i study of Arp 65, an interacting pair hosting extended H i tidal debris.Aims. In an effort to understand the evolution of tidal debris produced by interacting pairs of galaxies, including in situ star and tidal dwarf galaxy formation, we are mapping H i in a sample of interacting galaxy pairs. The Arp 65 pair is the latest member of this sample to be mapped. Methods.Our resolved H i 21 cm line survey is being carried out using the Giant Metrewave Radio Telescope. We used our H i survey data as well as available SDSS optical, Spitzer infra-red and GALEX UV data to study the evolution of the tidal debris and the correlation of H i with the star-forming regions within it.Results. In Arp 65 we see a high impact pre-merger tidal interaction involving a pair of massive galaxies (NGC 90 and NGC 93) that have a stellar mass ratio of ∼1:3. The interaction, which probably occurred ∼1.0-2.5 × 10 8 yr ago, appears to have displaced a large fraction of the H i in NGC 90 (including the highest column density H i) beyond its optical disk. We also find extended on-going star formation in the outer disk of NGC 90. In the major star-forming regions, we find the H i column densities to be ∼4.7 × 10 20 cm −2 or lower. But no signature of star formation was found in the highest column density H i debris SE of NGC 90. This indicates conditions within the highest density H i debris remain hostile to star formation and it reaffirms that high H i column densities may be a necessary but not sufficient criterion for star formation.

Using VIMOS-IFU observations, we study the interstellar medium (ISM) of two star-forming dwarf galaxies, UM 461 and Mrk 600. Our aim was to search for the existence of metallicity inhomogeneities that might arise from infall of nearly pristine gas feeding ongoing localized star-formation. The IFU data allowed us to study the impact of external gas accretion on the chemical evolution as well as the ionised gas kinematics and morphologies of these galaxies. Both systems show signs of morphological distortions, including cometary-like morphologies. We analysed the spatial variation of 12 + log(O/H) abundances within both galaxies using the direct method (T e ), the widely applied HII-CHI-mistry code, as well as by employing different standard calibrations. For UM 461 our results show that the ISM is fairly well mixed, at large scales, however we find an off-centre and low-metallicity region with 12 + log(O/H) < 7.6 in the SW part of the brightest H ii region, using the direct method. This result is consistent with the recent infall of a low mass metal-poor dwarf or H i cloud into the region now exhibiting the lowest metallicity, which also displays localized perturbed neutral and ionized gas kinematics. Mrk 600 in contrast, appears to be chemically homogeneous on both large and small scales. The intrinsic differences in the spatially resolved properties of the ISM in our analysed galaxies are consistent with these systems being at different evolutionary stages.