AAS 207th Meeting, 8-12 January 2006
Session 148 Local Benchmarks of Galaxy Evolution
Oral, Wednesday, 10:00-11:30am, January 11, 2006, Delaware B

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[148.04] Stellar Populations of Stripped Spiral Galaxies in the Virgo Cluster

H.H. Crowl (Yale U.)

Clusters play an important role in the evolution of their member galaxies. In the nearby Virgo cluster, we can observe galaxy-galaxy and galaxy-cluster interactions at a level of detail not easily accessible at higher redshift. We present results of an observational study of spiral galaxies in the Virgo Cluster, utilizing optical and UV imaging, HI observations, and optical spectroscopy. These galaxies, many of which have normal stellar distributions and truncated gas disks, are likely the result of ram-pressure stripping by hot cluster gas. Our results indicate that there is a correlation between HI morphology and the age-sensitive Balmer absorption line strength. Specifically, those galaxies with asymmetric HI distributions or extraplanar HI, indicating a recent disturbance by the intra-cluster medium, have the youngest stellar populations in the gas-free outer disk. Observations of both gas and stellar populations allow us to understand when and where galaxies are transformed by gas stripping effects in clusters.

One of the most striking galaxies in our sample is NGC 4522. This galaxy, with a large fraction of its neutral gas displaced to one side of the stellar disk, is one of the best examples of ongoing ram pressure stripping in Virgo. Optical spectroscopy of the outer disk of NGC 4522 (i.e. beyond the sites of active star formation), shows strong H\beta absorption, indicative of a young stellar population and consistent with a recent truncation of star formation in the outer disk. Additionally, we observe strong H\gamma and H\delta absorption, similar to post-starburst k+a galaxies at higher redshift. This suggests that some k+a galaxies observed at higher redshift may be recently stripped cluster spirals.

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