Molecular gas dominated 50 kpc ram pressure stripped tail of the Coma galaxy D100

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 H{\alpha}. Our observations with the IRAM 30m telescope reveal in total ~ 10^9 M_sun 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 H{\alpha} 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 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 H{\alpha} surface brightness in ram pressure stripped gas tails, over about 2 dex

Kinematic clues to the origins of starless HI clouds : dark galaxies or tidal debris?

Isolated H i clouds with no optical counterparts are often taken as evidence for galaxy–galaxy interactions, though an alternative hypothesis is that these are primordial ‘dark galaxies’ that have not formed stars. Similarly, certain kinematic features in H i streams are also controversial, sometimes taken as evidence of dark galaxies but also perhaps explicable as the result of harassment. We numerically model the passage of a galaxy through the gravitational field of cluster. The galaxy consists of smoothed particle hydrodynamics particles for the gas and N-bodies for the stars and dark matter, while the cluster includes the gravitational effects of substructure using 400 subhaloes (the effects of the intracluster medium are ignored). We find that harassment can indeed produce long H i streams and these streams can include kinematic features resembling dark galaxy candidates such as VIRGOHI21. We also show that apparent clouds with diameter 100 km s−1 is negligible – making this a very unlikely explanation for the observed clouds in the Virgo cluster with these properties

Ram pressure stripping of tilted galaxies

Ram pressure stripping of galaxies in clusters can yield gas deficient disks. Previous numerical simulations based on various approaches suggested that, except for near edge-on disk orientations, the amount of stripping depends very little on the inclination angle. Following our previous study of face-on stripping, we extend the set of parameters with the disk tilt angle and explore in detail the effects of the ram pressure on the interstellar content (ISM) of tilted galaxies that orbit in various environments of clusters, with compact or extended distributions of the intra-cluster medium (ICM). We further study how results of numerical simulations could be estimated analytically. A grid of numerical simulations with varying parameters is produced using the tree/SPH code GADGET with a modified method for calculating the ISM-ICM interaction. These SPH calculations extend the set of existing results obtained from different codes using various numerical techniques. The simulations confirm the general trend of less stripping at orientations close to edge-on. The dependence on the disk tilt angle is more pronounced for compact ICM distributions, however it almost vanishes for strong ram pressure pulses. Although various hydrodynamical effects are present in the ISM-ICM interaction, the main quantitative stripping results appear to be roughly consistent with a simple scenario of momentum transfer from the encountered ICM. This behavior can also be found in previous simulations. To reproduce the numerical results we propose a fitting formula depending on the disk tilt angle and on the column density of the encountered ICM. Such a dependence is superior to that on the peak ram pressure used in previous simple estimates

Gas stripping in galaxy clusters: a new SPH simulation approach

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. 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. 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. 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.Comment: 18 pages, 23 figures, accepted for publication in A&

Ram pressure drag - the effects of ram pressure on dark matter and stellar disk dynamics

We investigate the effects of ram pressure stripping on gas-rich disk galaxies in the cluster environment. Ram pressure stripping principally effects the atomic gas in disk galaxies, stripping away outer disk gas to a truncation radius. We demonstrate that the drag force exerted on truncated gas disks is passed to the stellar disk, and surrounding dark matter through their mutual gravity. Using a toy model of ram pressure stripping, we show that this can drag a stellar disk and dark matter cusp off centre within it's dark matter halo by several kiloparsecs. We present a simple analytical description of this process that predicts the drag force strength and its dependency on ram pressures and disk galaxy properties to first order. The motion of the disk can result in temporary deformation of the stellar disk. However we demonstrate that the key source of stellar disk heating is the removal of the gas potential from within the disk. This can result in disk thickening by approximately a factor of two in gas-rich disks.Comment: Accepted by MNRAS (Oct 2011) 17 pages, 11 figures, 1 tabl

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

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 $\sim45$ kpc downstream. The velocity dispersion of the ionized gas increases to $\sim80$ km s$^{-1}$ at $\sim20$ 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.Comment: 18 pages, 20 figures, 2 tables, accepted for publication in MNRA

The Carina Flare: What can fragments in the wall tell us?

$^{13}$CO(J=2--1) and C$^{18}$O(J=2--1) observations of the molecular cloud G285.90+4.53 (Cloud~16) in the Carina Flare supershell (GSH287+04-17) with the APEX telescope are presented. With an algorithm DENDROFIND we identify 51 fragments and compute their sizes and masses. We discuss their mass spectrum and interpret it as being the result of the shell fragmentation process described by the pressure assisted gravitational instability - PAGI. We conclude that the explanation of the clump mass function needs a combination of gravity with pressure external to the shell.Comment: 19 pages, 14 figures, accepted by A&

Ram-pressure stripped radio tail and two ULXs in the spiral galaxy HCG 97b

We report LOFAR and VLA detections of extended radio emission in the spiral galaxy HCG 97b, hosted by an X-ray bright galaxy group. The extended radio emission detected at 144 MHz, 1.4 GHz and 4.8 GHz is elongated along the optical disk and has a tail that extends 27 kpc in projection towards the centre of the group at GHz frequencies or 60 kpc at 144 MHz. Chandra X-ray data show two off-nuclear ultra-luminous X-ray sources (ULXs) with the more distant one being a suitable candidate for an accreting intermediate-mass black hole (IMBH) embedded in an environment with an increased density of molecular gas. Given the observed morphology in optical, CO, and radio continuum, we propose that the galaxy is undergoing ram-pressure stripping and the relativistic plasma accelerated in star-forming regions is transported from the galactic disc by galaxy-intragroup medium interaction. Finally, we also demonstrate that the formation of the radio tail could, in principle, be the result of putative IMBH-induced activity, which could facilitate the stripping or inject the radio plasma via jets.Comment: 15 pages, 11 figures, submitted to MNRAS, comments are welcom

Spectacular Hubble Space Telescope Observations of the Coma Galaxy D100 and Star Formation in Its Ram Pressure-stripped Tail

© 2019. The American Astronomical Society. We present new HST F275W, F475W, and F814W imaging of the region of the Coma cluster around D100, a spiral galaxy with a remarkably long and narrow (60 × 1.5 kpc) ram pressure-stripped gas tail. We find blue sources coincident with the Hα tail, which we identify as young stars formed in the tail. We also determine they are likely to be unbound stellar complexes with sizes of ∼50-100 pc, likely to disperse as they age. From a comparison of the colors and magnitudes of the young stellar complexes with simple stellar population models, we find ages ranging from ∼1 to 50 Myr and masses ranging from 103 to ∼105 M o. We find that the overall rate and efficiency of star formation are low, ∼6.0 × 10-3 M o yr-1 and ∼6 × 10-12 yr-1, respectively. The total Hα flux of the tail would correspond to a star formation rate 7 times higher, indicating that some other mechanism for Hα excitation is dominant. From an analysis of the colors, we track the progression of outside-in star formation quenching in the main body of D100, as well as its apparent companion, S0 D99. Finally, we observe that the dust extinction in the base of the tail has an outer envelope with remarkably smooth and straight edges and linear filamentary substructure strongly suggestive of magnetic fields. These features and the small amount of tail broadening strongly suggest gas cooling restricting broadening and the influence of magnetic fields inhibiting turbulence

Molecular gas and star formation in the Tidal Dwarf Galaxy VCC 2062

The final, definitive version of this paper has been published in A&A, Vol 590, A92, June 2016, doi: 10.1051/0004-6361/201527887. Reproduced with permission from Astronomy & Astrophysics, © ESO.The physical mechanisms driving star formation (SF) in galaxies are still not fully understood. Tidal dwarf galaxies (TDGs), made of gas ejected during galaxy interactions, seem to be devoid of dark matter and have a near-solar metallicity. The latter makes it possible to study molecular gas and its link to SF using standard tracers (CO, dust) in a peculiar environment. We present a detailed study of a nearby TDG in the Virgo Cluster, VCC 2062, using new high-resolution CO(1--0) data from the Plateau de Bure, deep optical imaging from the Next Generation Virgo Cluster Survey (NGVS), and complementary multiwavelength data. Until now, there was some doubt whether VCC 2062 was a true TDG, but the new deep optical images from the NGVS reveal a stellar bridge between VCC 2062 and its parent galaxy, NGC 4694, which is clear proof of its tidal origin. Several high-resolution tracers (\halpha, UV, 8~\mi, and 24~\mi) of the star formation rate (SFR) are compared to the molecular gas distribution as traced by the CO(1-0). Coupled with the SFR tracers, the NGVS data are used with the CIGALE code to model the stellar populations throughout VCC 2062, yielding a declining SFR in the recent past, consistent with the low \halpha/UV ratio, and a high burst strength. HI emission covers VCC 2062, whereas the CO is concentrated near the HI maxima. The CO peaks correspond to two very distinct regions: one with moderate SF to the NE and one with only slightly weaker CO emission but with nearly no SF. Even where SF is clearly present, the SFR is below the value expected from the surface density of the molecular and the total gas as compared to spiral galaxies and other TDGs. After discussing different possible explanations, we conclude that the low surface brightness is a crucial parameter to understand the low SFR.Peer reviewe