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تسجيل مستخدم جديدUbiquitous ram pressure stripping in the Coma cluster of galaxies
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We report the detection of H$alpha$ trails behind three new intermediate-mass irregular galaxies in the NW outskirts of the nearby cluster of galaxies Abell 1656 (Coma). Hints that these galaxies possess an extended component were found in earlier, deeper H$alpha$ observations carried out with the Subaru telescope. However the lack of a simultaneous $r$-band exposure, together with the presence of strong stellar ghosts in the Subaru images, prevented us from quantifying the detections. We therefore devoted one full night of H$alpha$ observation to each of the three galaxies using the San Pedro Martir 2.1m telescope. One-sided tails of H$alpha$ emission of 10-20 kpc projected size were detected, suggesting an ongoing ram pressure stripping event. We added these 3 new sources of extended ionized gas (EIG) added to the 12 found by Yagi et al. (2010), NGC 4848 (Fossati et al. 2012), and NGC 4921 whose ram pressure stripping is certified by HI asymmetry. This brings the number sources with H$alpha$ trails to 17 gaseous tails out of 27 (63 %) late-type galaxies (LTG) galaxies members of the Coma cluster with direct evidence of ram pressure stripping. The 27 LTG galaxies, among these the 17 with extended H$alpha$ tails, have kinematic properties that are different from the rest of the early-type galaxy (ETG) population of the c ore of the Coma cluster, as they deviate in the phase-space diagram $Delta$V/$sigma$ versus $r/R_{200}$.
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Previous studies have revealed a population of galaxies in galaxy clusters with ram pressure stripped (RPS) tails of gas and embedded young stars. We observed 1.4 GHz continuum and HI emission with the Very Large Array in its B-configuration in two f
ields of the Coma cluster to study the radio properties of RPS galaxies. The best continuum sensitivities in the two fields are 6 and 8 $mu$Jy per 4 beam respectively, which are 4 and 3 times deeper than those previously published. Radio continuum tails are found in 10 (8 are new) out of 20 RPS galaxies, unambiguously revealing the presence of relativistic electrons and magnetic fields in the stripped tails. Our results also hint that the tail has a steeper spectrum than the galaxy. The 1.4 GHz continuum in the tails is enhanced relative to their H$alpha$ emission by a factor of $sim$7 compared to the main bodies of the RPS galaxies. The 1.4 GHz continuum of the RPS galaxies is also enhanced relative to their IR emission by a factor of $sim$2 compared to star-forming galaxies. The enhancement is likely related to ram pressure and turbulence in the tail. We furthermore present HI detections in three RPS galaxies and upper limits for the other RPS galaxies. The cold gas in D100s stripped tail is dominated by molecular gas, which is likely a consequence of the high ambient pressure. No evidence of radio emission associated with ultra-diffuse galaxies is found in our data.
We study galaxies undergoing ram pressure stripping in the Virgo cluster to examine whether we can identify any discernible trend in their star formation activity. We first use 48 galaxies undergoing different stages of stripping based on HI morpholo
gy, HI deficiency, and relative extent to the stellar disk, from the VIVA survey. We then employ a new scheme for galaxy classification which combines HI mass fractions and locations in projected phase space, resulting in a new sample of 365 galaxies. We utilize a variety of star formation tracers, which include g - r, WISE [3.4] - [12] colors, and starburstiness that are defined by stellar mass and star formation rates to compare the star formation activity of galaxies at different stripping stages. We find no clear evidence for enhancement in the integrated star formation activity of galaxies undergoing early to active stripping. We are instead able to capture the overall quenching of star formation activity with increasing degree of ram pressure stripping, in agreement with previous studies. Our results suggest that if there is any ram pressure stripping induced enhancement, it is at best locally modest, and galaxies undergoing enhancement make up a small fraction of the total sample. Our results also indicate that it is possible to trace galaxies at different stages of stripping with the combination of HI gas content and location in projected phase space, which can be extended to other galaxy clusters that lack high-resolution HI imaging.
Ram-pressure stripping (RPS) is a well observed phenomenon of massive spiral galaxies passing through the hot intra-cluster medium (ICM) of galaxy clusters. For dwarf galaxies (DGs) within a cluster, the transformation from gaseous to gas-poor system
s by RPS is not easily observed and must happen in the outskirts of clusters. In a few objects in close by galaxy clusters and the field, RPS has been observed. Since cluster early-type DGs also show a large variety of internal structures (unexpected central gas reservoirs, blue stellar cores, composite radial stellar profiles), we aim in this study to investigate how ram pressure (RP) affects the interstellar gas content and therefore the star-formation (SF) activity. Using a series of numerical simulations, we quantify the dependence of the stripped-off gas on the velocity of the infalling DGs and on the ambient ICM density. We demonstrated that SF can be either suppressed or triggered by RP depending on the ICM density and the DGs mass. Under some conditions, RP can compress the gas, so that it is unexpectedly retained in the central DG region and forms stars. When gas clouds are still bound against stripping but lifted from a thin disk and fall back, their new stars form an ellipsoidal (young) stellar population already with a larger velocity dispersion without the necessity of harassment. Most spectacularly, star clusters can form downstream in stripped-off massive gas clouds in the case of strong RP. We compare our results to observations.
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(Abridged) We perform high resolution 2D hydrodynamical simulations of face-on ram pressure stripping (RPS) of disk galaxies to compile a comprehensive parameter study varying galaxy properties (mass, vertical structure of the gas disk) and covering
a large range of ICM conditions, reaching from high density environments like in cluster centres to low density environments typical for cluster outskirts or groups. We find that the ICM-ISM interaction proceeds in three phases: firstly the instantaneous stripping phase, secondly the dynamic intermediate phase, thirdly the quasi-stable continuous viscous stripping phase. The stripping efficiency depends slightly on the Mach number of the flow, however, the main parameter is the ram pressure. The stripping efficiency does not depend on the vertical structure and thickness of the gas disk. We discuss uncertainties in the classic estimate of the stripping radius of citet{gunn72}, and adapt the estimate used by cite{mori00} for spherical galaxies, (comparison of central pressure with ram pressure). We find that the latter estimate predicts the radius and mass of the gas disk remaining at the end of the second phase very well, and better than the citet{gunn72} criterion. From our simulations we conclude that gas disks of galaxies in high density environments are heavily truncated or even completely stripped, but also the gas disks of galaxies in low density environments are disturbed by the flow and back-falling material, so that they should also be pre-processed.
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