Accretion-driven star formation in central dominant galaxies in X-ray clusters

Abstract

We argue that low-mass stars are being formed from the large amounts of gas being accreted by central dominant galaxies in some X-ray clusters. We suggest that low-mass star formation may be favored because the Jeans mass decreases as the ambient pressure increases, and the pressures observed in these accretion flows are four orders of magnitude higher than those in the local interstellar medium. We have calculated the spectra for the inner parts of these galaxies including accretion-driven star formation, and we show that the colors of these galaxies may be affected at an observable level. We suggest observations to search for these color anomalies. The unusual A-type spectrum and blue colors of NGC 1275 may be explained by accretion-driven star formation, as first suggested by Kent and Sargent. The luminosity evolution due to accretion by first brightest cluster galaxies can affect determinations of q/sub 0/ which use these galaxies, although this effect is probably not as large as other evolutionary changes. We speculate that the blue stellar spectra and giant-elliptical light profiles observed in the faint optical extensions around several quasars might indicate that similar star formation is occurring in these quasars, although it is unlikely that they are more » accreting intracluster gas. « less