APEX-CHAMP⁺ high-J CO observations of low-mass young stellar objects

IV. Mechanical and radiative feedback^⋆,⋆⋆

¹ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
² Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA
e-mail: Umut.Yildiz@jpl.nasa.gov
³ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
⁴ Max-Planck-Institut für Extraterrestrische Physik (MPE), Giessenbachstrasse 1, 85748 Garching, Germany
⁵ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
⁶ Kavli Institute of Nanoscience, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, The Netherlands
⁷ Kapteyn Institute, University of Groningen, Landleven 12, 9747 AD Groningen, The Netherlands
⁸ ASTRON, Oude Hoogeveensedijk 4, 7991 PD Dwingeloo, The Netherlands
⁹ I. Physikalisches Institut der Universität zu Köln, Zülpicher Strasse 77, 50937 Köln, Germany

Received: 4 July 2014
Accepted: 7 January 2015

Abstract

Context. During the embedded stage of star formation, bipolar molecular outflows and UV radiation from the protostar are important feedback processes. Both processes reflect the accretion onto the forming star and affect subsequent collapse or fragmentation of the cloud.

Aims. Our aim is to quantify the feedback, mechanical and radiative, for a large sample of low-mass sources in a consistent manner. The outflow activity is compared to radiative feedback in the form of UV heating by the accreting protostar to search for correlations and evolutionary trends.

Methods. Large-scale maps of 26 young stellar objects, which are part of the Herschel WISH key program are obtained using the CHAMP⁺ instrument on the Atacama Pathfinder EXperiment (¹²CO and ¹³CO 6−5; E_up ~ 100 K), and the HARP-B instrument on the James Clerk Maxwell Telescope (¹²CO and ¹³CO 3−2; E_up ~ 30 K). The maps have high spatial resolution, particularly the CO 6−5 maps taken with a 9″ beam, resolving the morphology of the outflows. The maps are used to determine outflow parameters and the results are compared with higher-J CO lines obtained with Herschel. Envelope models are used to quantify the amount of UV-heated gas and its temperature from ¹³CO 6−5 observations.

Results. All sources in our sample show outflow activity, with the spatial extent decreasing from the Class 0 to the Class I stage. Consistent with previous studies, the outflow force, F_CO, is larger for Class 0 sources than for Class I sources, even if their luminosities are comparable. The outflowing gas typically extends to much greater distances than the power-law envelope and therefore influences the surrounding cloud material directly. Comparison of the CO 6−5 results with HIFI H₂O and PACS high-J CO lines, both tracing currently shocked gas, shows that the two components are linked, even though the transitions do not probe the same gas. The link does not extend down to CO 3−2. The conclusion is that CO 6−5 depends on the shock characteristics (density and velocity), whereas CO 3−2 is more sensitive to conditions in the surrounding environment (density). The radiative feedback is responsible for increasing the gas temperature by a factor of two, up to 30–50 K, on scales of a few thousand AU, particularly along the direction of the outflow. The mass of the UV heated gas exceeds the mass contained in the entrained outflow in the inner ~3000 AU and is therefore at least as important on small scales.