Halpha surface photometry of galaxies in the Virgo cluster. IV: the current star formation in nearby clusters of galaxies

TL;DR

This study analyzes Halpha imaging of galaxies in the Virgo cluster and nearby superclusters to understand how current star formation correlates with galaxy environment, gas content, and stellar populations.

Contribution

It provides new insights into the relationship between star formation rates, gas deficiency, and environmental effects like ram-pressure stripping in galaxy clusters.

Findings

Star formation rate decreases with proximity to cluster centers for bright galaxies.

Gas deficiency correlates with lower star formation activity in cluster galaxies.

Ram-pressure stripping likely quenches star formation in dense cluster environments.

Abstract

Halpha+[NII] imaging observations of 369 late-type galaxies in the Virgo cluster and in the Coma/A1367 supercluster are analyzed. They constitute an optically selected sample (m_p<16.0) observed with 60% c.a. completeness.These observations provide us with the current (T<10^7 yrs) star formation properties of galaxies. The expected decrease of the star formation rate (SFR),as traced by the Halpha E.W., with decreasing clustercentric projected distance is found only when galaxies brighter than M_p=-19.5 are considered. We also include in our analysis Near Infrared data, providing us with informations on the old (T>10^9yrs) stars. Put together, the young and the old stellar indicators give the ratio of currently formed stars over the stars formed in the past, or "birthrate" parameter b. We also determine the "global gas content" combining HI with CO observations. We define the "gas deficiency" parameter as the logarithmic difference between the gas content of isolated galaxies of a given Hubble type and the measured gas content.For the isolated objects we find that b decreases with increasing NIR luminosity. The gas-deficient objects, primarily members to the Virgo cluster, have their birthrate significantly lower than the isolated objects with normal gas content and of similar NIR luminosity. This indicates that the current star formation is regulated by the gaseous content of spirals.Whatever mechanism (most plausibly ram-pressure stripping) is responsible for the pattern of gas deficiency observed in spiral galaxies members to rich clusters, it also produces the observed quenching of the current star formation.