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Cooling Flow Gas in NGC 1275 / PerseusX-ray data have revealed evidence for the infall of typically several hundred solar masses of gas per year in many galaxy clusters, with these COOLING FLOWS focused onto centrally-located gE/cD galaxies (Fabian 1994). However, the fate of this infalling gas is still largely a mystery, as there is little evidence for it at other wavelengths. On average, 10(11) - 10(12) solar masses of material should be deposited in a Hubble time, and some fraction of this material should be found in cool atomic and/or molecular clouds. However, NGC 1275, the gE galaxy at the centre of the rich Perseus cluster, is the ONLY cluster cooling flow galaxy which has been detected in CO (Lazareff et al. 1989; Mirabel et al. 1989; Reuter et al. 1993). NGC 1275 thus presents us with a rare opportunity to learn about the physical conditions of cooling flow gas.
Figure 1. (top) Figure 2. (bottom) To this end, the Canadian TAG awarded us 3 shifts in Nov. 1994 to observe NGC 1275 in CO emission. Our primary goal was to observe in the CO (3-2) line in order to supplement available data in 12CO (2-1) and 12CO (1-0) which Reuter et al. (1993) had already obtained for the inner 20 arcseconds of the galaxy. However, bad weather (Tsys ~ 2000 K !) forced us to switch to receiver A2 for observations of CO (2-1) instead. We therefore observed 13CO (2-1) at the galaxy centre and also obtained a 9-point map in 12CO (2-1) with 7 of the points lying within 20 arcseconds of the galaxy centre and 2 points 40 and 60 arcseconds from the centre. Figure 1 shows the average of 7 x 10-minute scans (obtained in beam-switching mode) for 12CO (2-1) at the galaxy centre, while Figure 2 shows an average of 10 x 10-minute scans for 13CO (2-1) at the same position. These spectra have been binned by 20 channels, giving a velocity resolution of 16 km/s, and are baseline-subtracted. The beam size at 230 GHz is 20 arcsecs, corresponding to 6.8 kpc at the distance of NGC 1275 (Ho = 75 km/s/Mpc). The 12CO detection is quite strong, and 13CO (2-1) is also detected, though these data are noisy and require better baseline subtraction. The 13CO (2-1) data will provide an important constraint for subsequent analysis using a radiative-transfer code. There also seems to be a velocity offset of 50-100 km/s between the 12CO and 13CO emission at this position. Finally, we believe we have made a weak detection of 12CO (2-1) emission as far as 1 arcminute from the galaxy centre, corresponding to ~ 20 kpc. This is still well within the cooling radius of ~ 100-200 kpc however, and it is important to carry out further mapping to determine the CO distribution in this galaxy/cluster. We are currently requesting more time to acquire the CO (3-2) data, at least for the central position. Together with our CO (2-1) data and the maps of Reuter et al. (1993), we should be able to place constraints on the density, kinetic temperature, and CO content of the molecular gas in this most unusual region. These data will thus eventually give us a much better idea of the physical conditions in cooling flow gas, and may shed some light on the nature and final state of the inferred large amounts of infalling material. References: Fabian 1994, ARA&A, 32, 277. Lazareff et al. 1989, ApJ, 336, L13. Mirabel et al. 1989, ApJ, 340, L9. Reuter et al. 1993, A&A, 281, 673. Terry Bridges / RGO / Cambridge / England Judith Irwin / Queens University / Kingston / Ontario / Canada |
