Abstract. We present results of a method for an automatic search for H  shells in 3D data cubes and apply it to the Leiden-Dwingeloo H  survey of the northern Milky Way. In the 2nd Galactic quadrant, where identifications of structures are not substantially influenced by overlapping, we find nearly 300 structures. The Galactic distribution of shells has an exponential profile in the radial direction with a scale length of σ gsh = 3 kpc. In the z direction, one half of the shells are found at distances smaller than 500 pc. We also calculate the energies necessary to create the shells: there are several structures with energies greater than 10E SN but only one with an energy exceeding 100E SN . Their size distribution, corrected for distance effects, is approximated by a power-law with an index α = 2.1. Our identifications provide a lower limit to the filling factor of shells in the outer Milky Way: f 2D = 0.4 and f 3D = 0.05.

We have discovered large amounts of molecular gas, as traced by CO emission, in the ram pressure stripped gas tail of the Coma cluster galaxy D100 (GMP 2910), out to large distances of about 50 kpc. D100 has a 60 kpc long, strikingly narrow tail which is bright in X-rays and Hα. Our observations with the IRAM 30m telescope reveal in total ∼ 10 9 M ⊙ of H 2 (assuming the standard CO-to-H 2 conversion) in several regions along the tail, thus indicating that molecular gas may dominate its mass. Along the tail we measure a smooth gradient in the radial velocity of the CO emission that is offset to lower values from the more diffuse Hα gas velocities. Such a dynamic separation of phases may be due to their differential acceleration by ram pressure. D100 is likely being stripped at a high orbital velocity 2200 km s −1 by (nearly) peak ram pressure. Combined effects of ICM viscosity and magnetic fields may be important for the evolution of the stripped ISM. We propose D100 has reached a continuous mode of stripping of dense gas remaining in its nuclear region. D100 is the second known case of an abundant molecular stripped-gas tail, suggesting that conditions in the ICM at the centers of galaxy clusters may be favorable for molecularization. From comparison with other galaxies, we find there is a good correlation between the CO flux and the Hα surface brightness in ram pressure stripped gas tails, over ∼ 2 dex.

We present semianalytic and numerical models that take into account the effect of radiative cooling on the hydrodynamics of the matter reinserted by strong stellar winds and supernovae within the volume occupied by young, massive, and compact super stellar clusters. We first corroborate the location of the threshold line in the plane of mechanical energy input rate versus cluster size found by Silich et al. This line separates clusters that are able to drive a quasi-adiabatic or strongly radiative wind from those in which catastrophic cooling occurs within the cluster volume. Then we show that clusters above the threshold line exhibit a bimodal behavior in which the central, densest zones cool rapidly and accumulate the injected matter to eventually feed further generations of star formation, while the outer zones are still able to drive a stationary wind. The results are presented as a series of universal dimensionless diagrams, from which one can infer the sizes of the two zones, the fraction of the deposited mass that goes into each, and the mechanical luminosity of the resultant winds for clusters of all sizes and energy input rates, regardless the assumed adiabatic terminal speed (V A;1 ).

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.

Abstract.We present an N-body computer code -aimed at studies of galactic dynamics -with a CPU-efficient algorithm for a continuous (i.e. time-dependent) stellar mass-loss. First, we summarize available data on stellar mass-loss and derive the long-term (20 Gyr) dependence of mass-loss rate of a coeval stellar population. We then implement it through a simple parametric form into a particle-mesh code with stellar and gaseous particles. We perform several tests of the algorithm reliability and show an illustrative application: a 2D simulation of a disk galaxy, starting as purely stellar but evolving as two-component due to gradual mass-loss from initial stars and to star formation. In a subsequent paper we will use the code to study changes that are induced in galactic disks by the continuous gas recycling compared to the instantaneous recycling approximation, especially the changes in star formation rate and radial inflow of matter.

Aims. The influence of a time-varying ram pressure on spiral galaxies in clusters is explored with a new simulation method based on the N-body SPH/tree code GADGET. Methods. We have adapted the code to describe the interaction of two different gas phases, the diffuse hot intracluster medium (ICM) and the denser and colder interstellar medium (ISM). Both the ICM and ISM components are introduced as SPH particles. As a galaxy arrives on a highly radial orbit from outskirts to cluster center, it crosses the ICM density peak and experiences a time-varying wind. Results. Depending on the duration and intensity of the ISM-ICM interaction, early and late type galaxies in galaxy clusters with either a large or small ICM distribution are found to show different stripping efficiencies, amounts of reaccretion of the extra-planar ISM, and final masses. We compare the numerical results with analytical approximations of different complexity and indicate the limits of the Gunn & Gott simple stripping formula. Conclusions. Our investigations emphasize the role of the galactic orbital history to the stripping amount. We discuss the contribution of ram pressure stripping to the origin of the ICM and its metallicity. We propose gas accumulations like tails, filaments, or ripples to be responsible for stripping in regions with low overall ICM occurrence.

Using the hydrodynamic code ZEUS, we perform 2D simulations to determine the fate of the gas ejected by massive stars within super star clusters. It turns out that the outcome depends mainly on the mass and radius of the cluster. In the case of less massive clusters, a hot high-velocity ($1000 km s À1 ) stationary wind develops and the metals injected by supernovae are dispersed to large distances from the cluster. On the other hand, the density of the thermalized ejecta within massive and compact clusters is sufficiently large as to immediately provoke the onset of thermal instabilities. These deplete, particularly in the central densest regions, the pressure and the pressure gradient required to establish a stationary wind, and instead the thermally unstable parcels of gas are rapidly compressed, by a plethora of repressurizing shocks, into compact high-density condensations. Most of these are unable to leave the cluster volume and thus accumulate to eventually feed further generations of star formation. The simulations cover an important fraction of the parameter space, which allows us to estimate the fraction of the reinserted gas that accumulates within the cluster and the fraction that leaves the cluster as a function of the cluster mechanical luminosity, the cluster size, and heating efficiency.

The removal of gas by ram pressure stripping of galaxies is treated by a purely kinematic description. The solution has two asymptotic limits: if the duration of the ram pressure pulse exceeds the period of vertical oscillations perpendicular to the galactic plane, the commonly used quasi-static criterion of Gunn & Gott is obtained which uses the maximum ram pressure that the galaxy has experienced along its orbit. For shorter pulses the outcome depends on the time-integrated ram pressure. This parameter pair fully describes the gas mass fraction that is stripped from a given galaxy. This approach closely reproduces results from SPH simulations. We show that typical galaxies follow a very tight relation in this parameter space corresponding to a pressure pulse length of about 300 Myr. Thus, the Gunn & Gott criterion provides a good description for galaxies in larger clusters. Applying the analytic description to a sample of 232 Virgo galaxies from the GoldMine database, we show that the ICM provides indeed the ram pressures needed to explain the deficiencies. We also can distinguish current and past strippers, including objects whose stripping state was unknown.