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VLA Observations of Stripped Edge-On Virgo Cluster Galaxies
Hugh H. Crowl, Jeffrey D.P. Kenney (Yale University), Jacqueline van Gorkom (Columbia University), Bernd Vollmer (CDS Strasbourg)
Abstract
We present high resolution (15") VLA HI and 1.4 GHz radio continuum observations of five highly inclined, HI deficient, Virgo cluster spiral galaxies. Observations of edge-on galaxies such as these allow us to distinguish extraplanar gas from disk gas. All of our galaxies have truncated H disks, with little or no disk gas beyond a truncation radius. While all the gas disks are truncated, the observations show evidence for a continuum of stripping states: symmetric, truncated gas disks in NGC 4419 and IC 3392 indicate that they were stripped long ago, while the more asymmetric disks in NGC 4402 and NGC 4388 suggest ongoing or more recent stripping, while NGC 4522 is clearly experiencing ongoing stripping. NGC 4402 also shows distinct evidence for an asymmetric extraplanar radio continuum halo and evidence for a small amount of extraplanar HI. Additionally, we have high-resolution BVR images of NGC 4402, showing a remarkable dust lane morphology: at half the optical radius, the dust lane of the galaxy curves up and out of the disk, matching the HI morphology. The optical images of NGC 4402 also show evidence for ongoing dense cloud ablation at the leading edge of the interaction. These observations, which suggest strong ongoing pressure, show that NGC 4402 is in a different environment than the galaxies located at larger cluster radii. Preliminary stellar population results confirm our stripping timescale estimates for these galaxies. Our observations at a range of cluster radii allow us to better understand the interplay between cluster galaxies and the surrounding IGM.

Observations
· VLA C-Array HI and radio continuum observations at 1.4 GHz (~15" Resolution)
· WIYN Tip-Tilt Module (WTTM) imaging in B, V, and R (0.5" - 0.8" Resolution) · WIYN SparsePak IFU observations of outer disk stellar populations.

NGC 4419 WIYN BVR

Extraplanar dust spurs?

Stellar Populations
The stellar populations of the stars in the outer disk can also constrain the stripping history of a galaxy. The strength of the H line is a good indicator of population age.
NGC 4522 NGC 4388 IC 3392 NGC 4419

The HI disks of NGC 4419 and IC 3392 are stripped and quite symmetric. This implies that these galaxies were stripped of their neutral gas a long time (i.e. >1 Gyr) ago.

NGC 4419 HI on R
Extraplanar dust lanes? Extraplanar dust features in the three-color image of NGC 4419 seem to indicate recent disk disturbances, something that would seem to be at odds with the symmetric HI disk. It is possible that we are observing dust falling back onto the disk after a ram pressure event.

NGC 4522 has very strong H absorption and significant H and H absorption, indicating a young stellar population and recent stripping.

NGC 4388 has a moderately strong H line, indicating a fairly recent stripping event.

IC 3392 and NGC 4419 have weak H (compared to their metal lines), indicating an older stellar population and, therefore, that they were stripped of their gas a relatively long time ago.

IC 3392 HI on R

At the HI truncation radii, the dust lanes curve up and away from the plane of the stellar disk. The departure from the disk is more gradual in the west, and more pronounced in the east, similar to the RC and HI distributions.

NGC 4402

HI on R

NGC 4402

WIYN BVR
Differential reddening is visible in this galaxy: north of the disk, significant dust has been pushed up by ram pressure, reddening the stellar light. In the south, the dust has been pushed clear of the stellar disk, revealing the true blue colors of the underlying stellar population. The most remarkable dust features south of the main dust disk are 2 linear dust filaments, shown in the above color image, with widths of ~1-2" (80-150 pc), and lengths of 6.9" (0.5 kpc) in the east and 13.2" (1.0 kpc) in the west. These 2 filaments have nearly the same position angle as each other (-40° in the east and -36° in the west), and as the radio continuum tail, indicating that their morphology is associated with the ICM wind direction.

NGC 4402 has an asymmetric HI profile with a small amount of extraplanar HI.

NGC 4388

HI on R

Triggered star formation can be observed along the southeastern edge of the dust disk.

0.5' 2.5 kpc E

N

NGC 4522 is the only galaxy in our sample that shows a large amount of extraplanar HI close to the disk, a sign that it is being actively stripped.

Galaxy Positions on ROSAT X-Ray Map

NGC 4388 has an asymmetric HI distribution, indicative of a more recent stripping event. Radio Continuum (contours) on Ha (grayscale)