Galaxies 09: Assembly, Gas Content and Star Formation History of Galaxies

Jeremy Lim
University of Hong Kong

Cool Molecular Gas in Central Cluster Giant Elliptical Galaxies

I briefly review the properties and possible origins of cool molecular gas (as detected in CO) in the central cD (giant elliptical) galaxies of rich clusters in the Local Universe. About 20 such galaxies have now been detected, exhibiting molecular gas masses in the range 10$^{9}$-10$^{11}$ M$_{\odot}$. This is much larger than the molecular gas masses commonly found in low-z field ellipticals, which seldom exceed $\sim$10$^{9}$ M$_{\odot}$ and never $\sim$10$^{10}$ M$_{\odot}$. Also, unlike field ellipticals which usually show a double-horned CO line profile indicative of rotating disks as has been confirmed in all cases well mapped, the CO line profile of central cD galaxies do not show a preferred pattern. All the central cD galaxies detected in molecular gas lie in clusters with strong putative X-ray cooling flows. So far, only one has been well mapped in molecular gas, that of NGC~1275 in the Perseus Cluster. I show that the properties of the molecular gas in this galaxy is consistent with radial free-fall, arguing against cannibalisms (as is believed to be the case in many field ellipticals) but suggesting instead an origin from a X-ray cooling flow.

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