HUBBLE SPACE TELESCOPEAND HI IMAGING OF STRONG RAM PRESSURE STRIPPING IN THE COMA SPIRAL NGC 4921: DENSE CLOUD DECOUPLING AND EVIDENCE FOR MAGNETIC BINDING IN THE ISM

Abstract

Remarkable dust extinction features in the deep HST V and I images of the face-on Coma cluster spiral galaxy NGC 4921 show in unprecedented ways how ram pressure strips the ISM from the disk of a spiral galaxy. New VLA HI maps show a truncated and highly asymmetric HI disk with a compressed HI distribution in the NW, providing evidence for ram pressure acting from the NW. Where the HI distribution is truncated in the NW region, HST images show a well-defined, continuous front of dust that extends over 90 degrees and 20 kpc. This dust front separates the dusty from dust-free regions of the galaxy, and we interpret it as galaxy ISM swept up near the leading side of the ICM-ISM interaction. We identify and characterize 100 pc-1 kpc scale substructure within this dust front caused by ram pressure, including head-tail filaments, C-shaped filaments, and long smooth dust fronts. The morphology of these features strongly suggests that dense gas clouds partially decouple from surrounding lower density gas during stripping, but decoupling is inhibited, possibly by magnetic fields which link and bind distant parts of the ISM.

Molecular Gas Dominated 50 kpc Ram Pressure Stripped Tail of the Coma Galaxy D100*

“…Such gas lumps decouple from the surrounding diffuse gas and may fall back to the galaxy potential. The same phenomenon, although observed spatially rather than kinematically, has been observed in high resolution optical images of other cluster spirals, which show dense decoupled clouds spatially offset from more diffuse dust which is further downstream (Crowl et al 2005;Abramson & Kenney 2014;Abramson et al 2016;Kenney et al 2015). The velocity field of the stripped ISM may have a large range at any distance.…”

Galaxy Environment in the 3D-HST Fields: Witnessing the Onset of Satellite Quenching at z ∼ 1–2

“…which ram pressure effects have been clearly observed (e.g., Sun et al 2007;Yagi et al 2010;Merluzzi et al 2013;Kenney et al 2015;Fossati et al 2016), and so the lack of significantly shorter quenching times in the higher halo mass bin is consistent with the lack of stripping, and indeed of any strong halomass dependent gas-stripping process. However Balogh et al (2016) find a small halo mass dependence of the quenching times comparing their GEEC2 group sample (M h ∼ 10 13.5 M ⊙ ) to the GCLASS cluster sample (M h > 10 14 M ⊙ ).…”

Globular Clusters and Spur Clusters in NGC 4921, the Brightest Spiral Galaxy in the Coma Cluster

“…Fifth, twisting of the magnetized filaments and the resulting magnetic tension was proposed to explain the features of spurs (outgrowths) in NGC 4921 by Carlqvist (2013, see their Figure 14). Sixth, ram pressure stripping acting on the magnetized filaments was proposed to describe the properties of the spurs in NGC 4921 by Kenney et al (2015). In this scenario, stars form in the dense gas clouds in the arm where magnetic field has permeated.…”

“…However, the spatial resolution in previous simulations was not high enough to investigate the formation of individual star clusters. Recent studies on NGC 4921 spurs by Carlqvist (2013) and Kenney et al (2015) addressed the properties of spurs, noting the presence of stars and star clusters associated with spurs. However, they did not give any photometric properties of the star clusters associated with the spurs.…”

“…Carlqvist (2013) and Kenney et al (2015) studied the morphology of these spurs, but suggested different scenarios to explain their origins. Tikhonov & Galazutdinova (2011) presented VI photometry of star clusters in NGC 4921 and NGC 4923 that were derived from the Hubble Space Telescope (HST)/Advanced Camera for Surveys (ACS) archival images.…”