Friday, 28 March 2008

Star formation in BCGs

(Figure 10 of O'Dea et al.,

Upper limits on the mass deposition rate (derived from X-ray emission measurements) vs. star formation rate for brightest cluster galaxies. Filled circles denote the maximum mass deposition rate (assuming no gas heating), while open circles are the rates derived from detailed cooling-flow model fits.

This paper discusses results from a Spitzer survey of 62 brightest cluster galaxies that exhibit optical line emission, specifically the ~50% of those galaxies that show excess infrared emission. While four of these appear to be dominated by AGN, they claim that the remainder show evidence for star formation (from L_IR, CO measurements, and Halpha luminosity). The above figure then appears to show a strong correlation between mass deposition from the ICM and star formation, and therefore such cooling may be the fuel source for the SF activity in these galaxies. Furthermore, the MDR exceeds the SFR, indicating that some reheating mechanism may be at work. It should be noted that all the points in this figure are formally upper limits, so in fact the cooling rate could be entirely consistent with the SFR.

No comments: