A multi-wavelength view of the Galactic center dust ridge reveals little star formation

¹ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
e-mail: kimmer@mpifr-bonn.mpg.de
² Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, 02138 Cambridge, MA, USA
³ ESO, Alonso de Cordova 3107, Casilla 19001, Santiago 19, Chile
⁴ California Institute of Technology, Cahill Center for Astronomy and Astrophysics, 301-17, Pasadena, CA 91125, USA

Received: 7 March 2012
Accepted: 1 November 2012

Abstract

The Galactic center dust ridge consists of a narrow string of massive condensations, first identified in submillimeter dust continuum emission. To determine whether new high-mass stars are forming in this region, we performed new observations at 870 μm with the Atacama Pathfinder EXperiment (APEX) telescope and at 8.4 GHz with the Very Large Array. We complement our data with recent maser and mid-infrared results. The ridge’s clouds are dark at mid-infrared wavelengths, indicating the presence of cold, high column density material. In combination with existing temperature measurements in the dust ridge, we determine masses of the largest clouds. The results show that the dust ridge contains a very massive reservoir of molecular material. We find five radio continuum sources at 8.4 GHz in the general dust ridge vicinity, but outside of the dust ridge clouds. They are likely all excited by massive young stars, whose properties we constrain. Our observations exclude the existence of zero age main sequence stars with spectral types earlier than B0.5 within the dust ridge clouds. The only indication of ongoing high-mass star formation inside the clouds are class II methanol masers that are found in two of the clouds. Except for a weak water maser, found in previous observations, no signs of star formation are detected in the most massive cloud, M0.25+0.012.