VLA H I Observations of Gas Stripping in the Virgo Cluster Spiral NGC 4522

By J. Kenney, J. Gorkom, Bernd Vollmer Yale University, Columbia University, Cds, O. Strasbourg. 2004

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We present VLA H I observations at ∼20″ ≃ 1.5 kpc resolution of the highly inclined, H I–deficient Virgo Cluster spiral galaxy NGC 4522, which is one of the clearest and nearest cases of ongoing intracluster medium–interstellar medium (ICM-ISM) stripping. H I is abundant and spatially coincident with the stellar disk in the center, but beyond R = 3 kpc the H I distribution in the disk is sharply truncated, and the only H I is extraplanar and all on the northwest side. Forty percent of the total H I, corresponding to 1.5 × 108 M⊙, is extraplanar and has likely been removed from the galaxy disk by an ICM-ISM interaction. The kinematics and the morphology of the H I appear more consistent with ongoing stripping and less consistent with gas fall-back, which may occur long after peak pressure. Some of the extraplanar gas has line widths (FWZI) of 150 km s-1, including a blueshifted tail of weaker emission, and much of the extraplanar gas exhibits a modest net blueshift with respect to the galaxy's disk rotational velocities, consistent with gas accelerated toward the mean cluster velocity. The southwest side of the galaxy has less H I in the disk but more H I in the halo, suggesting more effective gas removal on the side of the galaxy that is rotating into the ICM wind. In recent simulations of ICM-ISM interactions large surface densities of extraplanar gas like that in NGC 4522 are seen at relatively early stages of active stripping and not during later gas fall-back stages. The galaxy is 3.°3 ≃ 800 kpc from M87, somewhat outside the region of strongest cluster X-ray emission. The ram pressure at this location, assuming a static smooth ICM and standard values for ICM density and galaxy velocity, appears inadequate to cause the observed stripping. We consider the possibility that the ram pressure is significantly stronger than standard values, because of large bulk motions and local density enhancements of the ICM gas, which may occur in a dynamic, shock-filled ICM experiencing subcluster merging. The H I and Hα distributions are similar, with both truncated in the disk at the same radius and H II regions located throughout much of the extraplanar H I. This implies that the star-forming molecular ISM has been effectively stripped from the outer disk of the galaxy along with the H I. The inferred peak stripping rate of ∼10 M⊙ yr-1 is much larger than the galaxy's total star formation rate of ∼0.1 M⊙ yr-1, implying that the rate of triggered star formation due to ICM pressure is presently minor compared with the rate of gas lost as a result of stripping.

Subfields: Astronomy and Astrophysics, Instrumentation

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Citations in the corpus

VLA IMAGING OF VIRGO SPIRALS IN ATOMIC GAS (VIVA). I. THE ATLAS AND THE H i PROPERTIES (2009, methodology): “Kenney et al. (2004) and Vollmer et al. (2004b) present an analysis of the data on NGC 4522, a galaxy far away from M87, yet stripped to well within its optical disk and showing abundant evidence of ongoing stripping.”
On the influence of ram-pressure stripping on the star formation of simulated spiral galaxies (2008, background): “…regions in several cluster late-type galaxies, that show evidence for ram-pressure stripping, but no extended tails of intracluster star-forming regions or clear signatures of interactions with other galaxies (e.g.Cortese et al. 2004; Kenney et al. 2004; Crowl et al. 2005; Cortese et al. 2007).”
BUDHIES II: a phase-space view of H i gas stripping and star formation quenching in cluster galaxies (2015, background): “…of galaxies in clusters have revealed that it is possible to have gas stripping at larger radii than what Gunn & Gott (1972) predict (e.g. Kenney et al. 2004; Tonnesen et al. 2007), due to the presence of non-smooth substructure in the ICM, which translates into scatter in ram-pressure…”
Substructures in hydrodynamical cluster simulations (2008, background): “The stripping also governs the timescale over which galaxy morphology and colours are modified inside galaxy clusters (Abadi et al. 1999; Kenney et al. 2004).”
GAS STRIPPING IN SIMULATED GALAXIES WITH A MULTIPHASE INTERSTELLAR MEDIUM (2009, background): “As discussed in Kenney et al (2004), there are four possibilities for stripping of molecular clouds.”
CAIRNS: The Cluster and Infall Region Nearby Survey. I. Redshifts and Mass Profiles (2003, background): “This weighting is important to remember when comparing our results to, e.g., detailed studies of Virgo galaxies which show ongoing ram pressure stripping and evidence of truncation of star-forming disks (Koopmann & Kenney 2004; Kenney et al. 2004).”
The evolution of substructure - III. The outskirts of clusters (2004, unknown): “Kenney et al. (2004) suggested two possible scenarios to explain its ongoing ICM-ISM stripping: either NGC 4522 is experiencing stripping at this distance due to bulk motions and local density enhancements of the ICM produced by shocks in the ICM, or – since ram-pressure stripping is proportional…”
GASP. I. Gas Stripping Phenomena in Galaxies with MUSE (2017, background): “We note that, although our calculation for JO206 supports ongoing ram-pressure stripping, there are several caveats to be considered (see discussion in, e.g., Kenney et al. 2004 and Jaffé et al. 2015).”
Virgo Galaxies with Long One-sided H I Tails (2007, background): “Several explanations are possible, either the galaxy is affected by viscous turbulent stripping instead of the simple momentum transfer, or the ICM pressure is enhanced due to bulk motions or local clumping of the gas, as it is likely in NGC 4522 (Kenney et al. 2004).”
A REVISED PARALLEL-SEQUENCE MORPHOLOGICAL CLASSIFICATION OF GALAXIES: STRUCTURE AND FORMATION OF S0 AND SPHEROIDAL GALAXIES (2011, background): “Figure 24 shows some of the best evidence for ongoing ram-pressure stripping in the Virgo cluster (adapted from Chung et al. 2007; Kenney et al. 2004, 2008).”
X-ray spectroscopy of the Virgo Cluster out to the virial radius (2011, background): “However, H i imaging surveys have revealed several galaxies falling into the Virgo Cluster that display long H i tails at projected radii of 0.6–1.2 Mpc from the center of the cluster (e.g. Kenney et al. 2004; Chung et al. 2007; Kantharia et al. 2008).”
Environmental Effects on Late‐Type Galaxies in Nearby Clusters (2006, background): “NGC 4522 has Ha, H i, radio continuum, and kinematic properties indicating an ongoing ram pressure event (Kenney & Koopmann 1999; Vollmer et al. 2000, 2004b; Kenney et al. 2004).”
A large H I cloud near the centre of the Virgo cluster (2005, unknown): “…(tidal interactions and ram-pressure stripping by the ICM) have been studied in detail, both theoretically (e.g. Abadi et al. 1999; Quilis et al. 2000; Schulz & Struck 2001; Vollmer et al. 2001) and observationally (e.g. Warmels 1988; Cayatte et al. 1990; Solanes et al. 2001; Kenney et al. 2004).”