Gas phase Elemental abundances in Molecular cloudS (GEMS) I. The prototypical dark cloud TMC 1

Author(s)

A. Fuente, D. G. Navarro, P. Caselli, M. Gerin, C. Kramer, E. Roueff, T. Alonso-Albi, R. Bachiller, S. Cazaux, B. Commercon, R. Friesen, S. Garcia-Burillo, B. M. Giuliano, J. R. Goicoechea, P. Gratier, A. Hacar, Jimenez-Serra, J. Kirk, Fernando A. Lattanzi, J. C. Loison, J. Malinen, N. Marcelino, R. Martin-Domenech, G. Munoz-Caro, J. Pineda, M. Tafalla, B. Tercero, D. Ward-Thompson, S. P. Trevino-Morales, P. Riviere-Marichalar, O. Roncero, T. Vidal, M. Y. Ballester

Abstract

GEMS is an IRAM 30 m Large Program whose aim is determining the elemental depletions and the ionization fraction in a set of prototypical star-forming regions. This paper presents the first results from the prototypical dark cloud Taurus molecular cloud (TMC) 1. Extensive millimeter observations have been carried out with the IRAM 30 m telescope (3 and 2 mm) and the 40 m Yebes telescope (1.3 cm and 7 mm) to determine the fractional abundances of CO, HCO

⁺, HCN, CS, SO, HCS

⁺, and N

₂H

⁺ in three cuts which intersect the dense filament at the well-known positions TMC 1-CP, TMC 1-NH3, and TMC 1-C, covering a visual extinction range from A

_V ~ 3 to ~20 mag. Two phases with differentiated chemistry can be distinguished: (i) the translucent envelope with molecular hydrogen densities of 1-5 × 10

³ cm

^-3; and (ii) the dense phase, located at A

_V > 10 mag, with molecular hydrogen densities >10

⁴ cm

^-3. Observations and modeling show that the gas phase abundances of C and O progressively decrease along the C

⁺/C/CO transition zone (A

_V ~ 3 mag) where C/H ~ 8 × 10

^-5 and C/O ~ 0.8-1, until the beginning of the dense phase at A

_V ~ 10 mag. This is consistent with the grain temperatures being below the CO evaporation temperature in this region. In the case of sulfur, a strong depletion should occur before the translucent phase where we estimate an S/ H ~ (0.4-2.2) × 10

^-6, an abundance ~7-40 times lower than the solar value. A second strong depletion must be present during the formation of the thick icy mantles to achieve the values of S/H measured in the dense cold cores (S H ~ 8 × 10

^-8). Based on our chemical modeling, we constrain the value of ζ

_H

₂

to ~(0.5-1.8) × 10

^-16 s

^-1 in the translucent cloud.

Organisation(s)

Department of Astrophysics

External organisation(s)

Observatorio Astronómico Nacional (OAN-IGN), Max-Planck-Institut für Plasmaphysik, Centre National De La Recherche Scientifique (CNRS), Sorbonne Université, Paris Observatory, École Normale Supérieure, Paris , Université Paris IV - Paris-Sorbonne, Université Paris XIII, Instituto de Radioastronomía Milimétrica (IRAM), Delft University of Technology, Leiden University, École normale supérieure de Lyon (ENS Lyon), Université Claude-Bernard-Lyon-I, National Radio Astronomy Observatory, Charlottesville, Instituto de Física Corpuscular (IFIC), Spanish National Research Council (CSIC), Université Bordeaux, University of Warwick, University of Helsinki, Universität zu Köln, Harvard University, Harvard-Smithsonian Center for Astrophysics, Smithsonian National Museum of Natural History, University of Central Lancashire, Chalmers University of Technology, Universidade Federal de Juiz de Fora

Journal

Astronomy & Astrophysics

Volume

624

No. of pages

25

ISSN

1432-0746

DOI

https://doi.org/10.1051/0004-6361/201834654

Publication date

04-2019

Peer reviewed

Yes

Austrian Fields of Science 2012

103004 Astrophysics

Keywords

ASJC Scopus subject areas

Astronomy and Astrophysics, Space and Planetary Science

Portal url

https://ucrisportal.univie.ac.at/en/publications/6578163e-83ed-42f5-9c0a-1be2eb57b705