Hα Morphologies and Environmental Effects in Virgo Cluster Spiral Galaxies

Abstract

We describe the various Hα morphologies of Virgo Cluster and isolated spiral galaxies and associate the Hα morphologies with the types of environmental interactions that have altered the cluster galaxies. The spatial distributions of Hα and R -band emission are used to divide the star formation morphologies of the 52 Virgo Cluster spiral galaxies into several categories: normal (37%), anemic (6%), enhanced (6%), and (spatially) truncated (52%). Truncated galaxies are further subdivided on the basis of their inner star formation rates into truncated/normal (37%), truncated/compact (6%), truncated/anemic (8%), and truncated/enhanced (2%). The fraction of anemic galaxies is relatively small (6%-13%) in both environments, suggesting that starvation is not a major factor in the reduced star formation rates of Virgo spiral galaxies. The majority of Virgo spiral galaxies have their Hα disks truncated (52%), whereas truncated Hα disks are rarer in isolated galaxies (12%). Most of the Hα-truncated galaxies have relatively undisturbed stellar disks and normal to slightly enhanced inner disk star formation rates, suggesting that intracluster medium-interstellar medium (ICM-ISM) stripping is the main mechanism causing the reduced star formation rates of Virgo spiral galaxies. Several of the truncated galaxies are peculiar, with enhanced central star formation rates, disturbed stellar disks, and barlike distributions of luminous H II complexes inside the central 1 kpc but no star formation beyond, suggesting that recent tidal interactions or minor mergers have also influenced their morphology. Two highly inclined Hα-truncated spiral galaxies have numerous extraplanar H II regions and are likely in an active phase of ICM-ISM stripping. Several spiral galaxies have one-sided Hα enhancements at the outer edge of their truncated Hα disks, suggesting modest local enhancements in their star formation rates due to ICM-ISM interactions. Low-velocity tidal interactions and perhaps outer cluster H I accretion seem to be the triggers for enhanced global star formation in four Virgo galaxies. These results indicate that most Virgo spiral galaxies experience ICM-ISM stripping, many experience significant tidal effects, and many experience both.