Radio continuum and CO emission in star-forming galaxies

¹ Istituto di Radioastronomia del CNR, Via Gobetti 101, 40129, Bologna, Italy
² Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125, Firenze, Italy
³ Osservatorio Astronomico di Cagliari, Loc. Poggio dei Pini, Strada 54, 09012 Capoterra (CA), Italy
⁴ Dipartimento di Fisica, Università di Bologna, Via B. Pichat 6/2, 40127 Bologna, Italy

Corresponding author: M. Murgia, murgia@ira.bo.cnr.it

Received: 30 October 2001
Accepted: 23 January 2002

Abstract

We combine the radio continuum images from the NRAO VLA Sky Survey with the CO-line observations from the extragalactic CO survey of the Five College Radio Astronomy Observatory to study the relationship between molecular gas and the star formation rate within the disks of 180 spiral galaxies at 45´´ resolution. We find a tight correlation between these quantities. On average, the ratio between the radio continuum and the CO emission is constant, within a factor of 3, both inside the same galaxy and from galaxy to galaxy. The mean star formation efficiency deduced from the radio continuum corresponds to convert 3.5% of the available molecular gas into stars on a time scale of 10⁸ yr and depends weakly on general galaxy properties, such as Hubble type or nuclear activity. A comparison is made with another similar analysis performed using the H_α luminosity as star formation indicator. The overall agreement we find between the two studies reinforces the use of the radio luminosity as star formation rate indicator not only on global but also on local scales.