Minor Galaxy Interactions: Star Formation Rates and Galaxy Properties

We study star formation in a sample of 1204 galaxies in minor (| \Delta m_z |\geq 2) pairs and compact groups, drawn from the Sloan Digital Sky Survey DataRelease 5 (SDSS DR5). We analyze an analogous sample of 2409 galaxies in major(| \Delta m_z | < 2$) pairs and compact groups to ensure that our selectionreproduces previous results, and we use a ``field'' sample of 65,570 galaxiesfor comparison. Our major and minor pairs samples include only galaxies inspectroscopically confirmed pairs, where the recessional velocity separation$\Delta V < 500$ km/s and the projected spatial separation $\Delta D < 50$kpc/h. The relative magnitude (a proxy for the mass ratio) of the pair is animportant parameter in the effectiveness of the tidally triggered starformation in minor interactions. As expected, the secondary galaxies in minorpairs show evidence for tidally triggered star formation, whereas the primarygalaxies in the minor pairs do not. The galaxy color is also an importantparameter in the effectiveness of triggered star formation in the major galaxypairs. In the major pairs sample, there is a correlation between the specificH$\alpha$ star formation rate (SSFR) and $\Delta D$ in the blue primary andblue secondary galaxies; for the red primary and red secondary galaxies, thereis none. Galaxies in pairs have a higher mean SSFR at every absolute magnitudecompared to matched sets of field galaxies, and the relative increase in meanSSFR becomes larger with decreasing intrinsic luminosity. We also detect asignificantly increased AGN fraction in the pair galaxies compared to matchedsets of field galaxies.Comment: 29 pages, 31 figures, submitted to A