First observations of CN(2-1), HCO$^{+}$(3-2) and C$_{2}$H(3-2) emission lines in the Perseus cluster: constraints on heating mechanisms in the cluster gas

TL;DR

This study reports the first detection of specific molecular emission lines in the Perseus cluster, using observations to constrain heating mechanisms, and finds cosmic rays as the dominant heating source in the cluster gas.

Contribution

First observational detection of CN, HCO$^{+}$, and C$_{2}$H lines in the Perseus cluster, providing data to evaluate heating mechanisms in cluster gas.

Findings

Cosmic ray heating can explain molecular observations.

Cosmic ray heating rate is at least 100 times higher than in the Milky Way.

Detected molecular lines suggest cosmic rays dominate cluster gas heating.

Abstract

We present the first observations of emission lines of CN(2-1), HCO$^{+}$(3-2) and C$_{2}$H(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$''$ 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 C$_{2}$H 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 \citet{Baye10c} in an attempt to constrain the heating mechanisms in cluster gas. We find that models in which heating is dominated by cosmic rays can account for the molecular observations. This conclusion is consistent with that of \citet{Ferl09} 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.