Volume 574, February 2015
|Number of page(s)||8|
|Published online||27 January 2015|
Molecular gas and nuclear activity in early-type galaxies: any link with radio loudness?⋆
1 SISSA-ISAS, via Bonomea 265, 34136 Trieste, Italy
2 Physics Department, The Technion, 32000 Haifa, Israel
3 Physics Department, Faculty of Natural Sciences, University of Haifa, 32000 Haifa, Israel
4 INAF-Istituto di Radio Astronomia, via P. Gobetti 101, 40129 Bologna, Italy
5 INAF-Osservatorio Astrofisico di Torino, via Osservatorio 20, 10025 Pino Torinese, Italy
6 Dipartimento di Fisica e Astronomia, Università di Bologna, via Ranzani 1, 40127 Bologna, Italy
7 Instituto de Astrofísica de Andalucía – CSIC, PO Box 3004, 18008 Granada, Spain
8 Division of Physics, Faculty of Pure and Applied Sciences, University of Tsukuba, Japan
Received: 8 October 2014
Accepted: 2 December 2014
Aims. We want to study the amount of molecular gas in a sample of nearby early-type galaxies (ETGs) that host low-luminosity active galactic nuclei (AGN). We look for possible differences between the radio-loud (RL) and radio-quiet (RQ) AGN.
Methods. We observed the CO(1–0) and CO(2–1) spectral lines with the IRAM 30 m and NRO 45 m telescopes for eight galaxies. They belong to a large sample of 37 local ETGs that host both RQ and RL AGN. We gather data from the literature for the entire sample.
Results. We report the new detection of CO(1–0) emission in four galaxies (UGC 0968, UGC 5617, UGC 6946, and UGC 8355) and CO(2–1) emission in two of them (UGC 0968 and UGC 5617). The CO(2–1)/CO(1–0) ratio in these sources is ~ 0.7 ± 0.2. Considering both the new observations and the literature, the detection rate of CO in our sample is 55± 9%, with no statistically significant difference between the hosts of RL and RQ AGNs. For all the detected galaxies we converted the CO luminosities into the molecular masses, MH2, which range from 106.5 to 108.5 M⊙, without any statistically significant differences between RL and RQ galaxies. This suggests that the amount of molecular gas does not likely set the radio loudness of the AGN. Furthermore, despite the low statistical significance, the presence of a weak trend between the H2 mass with various tracers of nuclear activity (mainly [O III] emission line nuclear power) cannot be excluded.
Key words: galaxies: active / galaxies: elliptical and lenticular, cD / galaxies: nuclei / galaxies: ISM / ISM: molecules
© ESO, 2015
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