TheHerschel/HIFI spectral survey of OMC-2 FIR 4 (CHESS)

Abstract

Context. Broadband spectral surveys of protostars offer a rich view of the physical, chemical and dynamical structure and evolution of star-forming regions. The Herschel Space Observatory opened up the terahertz regime to such surveys, giving access to the fundamental transitions of many hydrides and to the high-energy transitions of many other species. Aims. A comparative analysis of the chemical inventories and physical processes and properties of protostars of various masses and evolutionary states is the goal of the Herschel CHEmical Surveys of Star forming regions (CHESS) key program. This paper focusses on the intermediate-mass protostar, OMC-2 FIR 4. Methods. We obtained a spectrum of OMC-2 FIR 4 in the 480 to 1902 GHz range with the HIFI spectrometer onboard Herschel and carried out the reduction, line identification, and a broad analysis of the line profile components, excitation, and cooling. Results. We detect 719 spectral lines from 40 species and isotopologs. The line flux is dominated by CO, H 2 O, and CH 3 OH. The line profiles are complex and vary with species and upper level energy, but clearly contain signatures from quiescent gas, a broad component likely due to an outflow, and a foreground cloud. Conclusions. We find abundant evidence for warm, dense gas, as well as for an outflow in the field of view. Line flux represents 2% of the 7 L luminosity detected with HIFI in the 480 to 1250 GHz range. Of the total line flux, 60% is from CO, 13% from H 2 O and 9% from CH 3 OH. A comparison with similar HIFI spectra of other sources is set to provide much new insight into star formation regions, a case in point being a difference of two orders of magnitude in the relative contribution of sulphur oxides to the line cooling of Orion KL and OMC-2 FIR 4.

On the Nature of the Deeply Embedded Protostar Omc-2 Fir 4

“…The line wings were symmetric and their width and strength increased with the excitation level of the line, suggesting emitting gas that is hot or dense and thus possibly a compact outflow from FIR 4 that contributes to the CO emission. When combining their results with those of Manoj et al (2013), Kama et al (2013) derived a total CO luminosity of ∼0.4 L . If we assume an L bol value of 37 L , the CO luminosity amounts to 1% of the total energy output.…”

“…Both can be interpreted as emission from shocked gas in an outflow. Furthermore, there is evidence in favor of an outflow from far-IR spectra (Manoj et al 2013;Kama et al 2013) in the form of velocity profiles, temperatures, and densities derived from CO lines, although they may contain a contribution from an outflow driven by the nearby protostar OMC-2 FIR 3. These data support the idea that FIR 4 is indeed a protostar, driving a compact outflow.…”

HerschelPlanetary Nebula Survey (HerPlaNS)

“…Absorption lines of OH + have also been detected along several lines of sight in the Galactic ISM towards bright continuum sources, such as the Orion molecular clouds (Gerin et al 2010;Neufeld et al 2010;Gupta et al 2010;Indriolo et al 2012;López-Sepulcre et al 2013) and the massive star-forming region W3 IRS5 . Lines of OH + have also been detected in absorption in the material around young stars (van Dishoeck et al 2011;Benz et al 2013;Kristensen et al 2013;Kama et al 2013) and in the galaxies NGC 4418 and Arp 220 (Rangwala et al 2011;González-Alfonso et al 2013).…”

The HIFI spectral survey of AFGL 2591 (CHESS)

“…AFGL 2591 data were completely reduced with the with the Herschel interactive processing environment 3 (HIPE; Ott 2010), version 8.1, using scripts written by the CHESS data reduction team (Kama et al 2013). After pipelining, the quality of each spectrum was checked and spectral regions with spurious features (spurs) were flagged.…”