First observations of CN (2–1), HCO+ (3–2) and C2H (3–2) emission lines in the Perseus cluster: constraints on heating mechanisms in the cluster gas
ABSTRACT We present the first observations of emission lines of CN (2–1), HCO+ (3–2) and C2H (3–2) in the Perseus cluster. We observed at two positions: directly at the central galaxy, NGC 1275, and also at a position about 20 arcsec to the east where associated filamentary structure has been shown to have strong CO emission. Clear detections in CN and HCO+ transitions and a weak detection of the C2H transition were made towards NGC 1275, while weak detections of CN and HCO+ were made towards the eastern filamentary structure. Crude estimates of the column densities and fractional abundances (mostly upper limits) as functions of an unknown rotational temperature were made to both sources. These observational data were compared with the outputs of thermal/chemical models previously published by Bayet et al. in an attempt to constrain the heating mechanisms in cluster gas. We find that models in which heating is caused mainly by cosmic rays while other sources of heating are unimportant can account for the molecular observations. This conclusion is consistent with that of Ferland et al. in their study of gas traced by optical and infrared radiation. The cosmic ray heating rate in the regions probed by molecular emissions is required to be at least two orders of magnitude larger than that in the Milky Way.