CO Emission from Hercules Cluster Galaxies

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Session 61 -- Properties and Evolution of Clusters of Galaxies
Display presentation, Thursday, 2, 1994, 9:20-6:30

[61.02] CO Emission from Hercules Cluster Galaxies

T.E.Lavezzi, J.M.Dickey (University of Minnesota)

We are studying the feasibility of using the CO $\lambda$1.3 mm and $\lambda$2.6 mm lines for performing Tully-Fisher calculations on galaxies in distant rich clusters. Previous Tully-Fisher calculations have depended on $\lambda$21 cm linewidths. In rich cluster environments, however, the HI disks of spirals are disrupted or even stripped due to interactions with the intergalactic medium. The molecular gas is more tightly bound to the center of the disk, and so CO does not suffer these effects.

Using data obtained with the IRAM-Granada 30-m dish, we detected CO in 13 out of the 32 galaxies searched in the Hercules cluster (z = 0.03). Our detections have a lower gas-mass limit of 0.5 K-km/s or about 4x10$^8$ $M_{sun}$; the strongest detections indicate masses of approximately 2x10$^9$ $M_{sun}$. As these are very weak sources, our integration times went as high as 128 minutes.

Our preliminary findings are that the CO line-centers agree with those of HI to within 2$\sigma$ and the linewidths agree to within 1$\sigma$. This indicates that CO linewidths can be used at least as reliably as HI for distance determinations, which becomes important for those galaxies where reliable HI data is not available, due to environmental effects. Also, we detected CO in four galaxies in which HI has not been seen, allowing us to obtain their distances for the first time.

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