The density structure of the L1157 molecular outflow

DOI: 
10.1093/mnras/stu2311
Publication date: 
01/02/2015
Main author: 
Gómez-Ruiz A.I.
IAA authors: 
Busquet G.
Authors: 
Gómez-Ruiz A.I., Codella C., Lefloch B., Benedettini M., Busquet G., Ceccarelli C., Nisini B., Podio L., Viti S.
Journal: 
Monthly Notices of the Royal Astronomical Society
Publication type: 
Article
Volume: 
446
Pages: 
3346-3355
Number: 
Abstract: 
We present a multiline CS survey towards the brightest bow-shock B1 in the prototypical chemically active protostellar outflow L1157. We made use of (sub-)mm data obtained in the framework of the Chemical HErschel Surveys of Star forming regions and Astrochemical Surveys at IRAM (ASAI) key science programs. We detected 12C32S, 12C34S, 13C32S, and 12C33S emissions, for a total of 18 transitions, with Eu up to ~180 K. The unprecedented sensitivity of the survey allows us to carefully analyse the line profiles, revealing high-velocity emission, up to 20 km s-1 with respect to the systemic. The profiles can be well fitted by a combination of two exponential laws that are remarkably similar to what previously found using CO. These components have been related to the cavity walls produced by the ~2000 yr B1 shock and the older (~4000 yr) B2 shock, respectively. The combination of low- and high-excitation CS emission was used to properly sample the different physical components expected in a shocked region. Our CS observations show that this molecule is highlighting the dense, nH<inf>2</inf> = 1-5 × 105 cm-3, cavity walls produced by the episodic outflow in L1157. In addition, the highest excitation (E<inf>u</inf> ≥ 130 K) CS lines provide us with the signature of denser (1-5 × 106 cm-3) gas, associated with a molecular reformation zone of a dissociative J-type shock, which is expected to arise where the precessing jet impacting the molecular cavities. The CS fractional abundance increases up to ~10-7 in all the kinematical components. This value is consistent with what previously found for prototypical protostars and it is in agreement with the prediction of the abundances obtained via the chemical code Astrochem. © 2014 The Authors.
Database: 
WOK
SCOPUS
ADS
URL: 
https://ui.adsabs.harvard.edu/#abs/2015MNRAS.446.3346G/abstract
ADS Bibcode: 
2015MNRAS.446.3346G
Keywords: 
ISM: molecules; Molecular data; Radio lines: ISM; Stars: formation; Submillimetre: ISM