Letter to the Editor

Mapping the cold molecular gas in a cooling flow cluster: Abell 1795

LERMA, Observatoire de Paris, 61, Av. de l'Observatoire, 75014 Paris, France

Corresponding author: P. Salomé, philippe.salome@bspm.fr

Received: 31 October 2003
Accepted: 16 December 2003

Abstract

Cold molecular gas is found in several clusters of galaxies (Edge [CITE]; Salomé & Combes [CITE]): single dish telescope observations in CO(1–0) and CO(2–1) emission lines have revealed the existence of large amounts of cold gas (up to ~10¹¹ ) in the central region of cooling flow clusters. We present here interferometric observations performed with the IRAM Plateau de Bure interferometer in Abell 1795. Comparison with IRAM 30 m data shows the cold gas detected is extended suggesting a cooling flow origin. The CO features identified are very similar to the structures observed in H_α and with the star forming regions observed through UV continuum excess. A large fraction of the cold gas is not centered on the central cD, but located near brightest X-ray emitting regions along the North–West orientated radio lobe. The cold gas kinematics is consistent with the optical nebulosity behaviour in the very central region. It is not in rotation around the central cD: a velocity gradient shows the cold gas might be cooled gas from the intra-cluster medium being accreted by the central galaxy. The optical filaments, aligned with the cD orbit, are intimately related to the radio jets and lobes. The material fueling the star formation certainly comes from the deposited gas, cooling more efficiently along the edge of the radio lobes. Even if some heating mechanisms are present, these millimetric observations show that an effective cooling to very low temperatures indeed occurs and is probably accelerated by the presence of the radio source.