Physics And Chemistry In UV Illuminated Regions: The Horsehead Case

Guzman, Viviana V.; Pety, Jérôme; Gratier, Pierre; Goicoechea, Javier; Gerin, Maryvonne; Roueff, Evelyne

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https://hdl.handle.net/2142/51074 Copy

Description

Title

Physics And Chemistry In UV Illuminated Regions: The Horsehead Case

Author(s)

• Guzman, Viviana V.
• Pety, Jérôme
• Gratier, Pierre
• Goicoechea, Javier
• Gerin, Maryvonne
• Roueff, Evelyne

Issue Date

2014-06-19

Keyword(s)

Mini-symposium: Astronomical Molecular Spectroscopy in the Age of ALMA

Abstract

Molecular lines are used to trace the structure of the interstellar medium and the physical conditions of the gas in different environments, from protoplanetary disks to high-z galaxies. To fully benefit from the diagnostic power of molecular lines, the formation and destruction paths of the molecules, including the interplay between gas-phase and grain surface chemistry, must be quantitatively understood. Well-defined sets of observations of simple template sources are key to benchmark the theoretical models. In this context the PDR of the Horsehead mane is a particularly interesting case because it has a simple geometry (almost 1D, viewed edge-on) and the density profile across the PDR is well constrained. In this talk, I will summarize our recent results on the ISM physics and chemistry in the Horsehead, from a complete and unbiased line survey at 1, 2 and 3mm performed with the IRAM-30m telescope, where approximately 30 species (plus their isotopologues) are detected with up to 7 atoms. I will show the importance of the interplay between the solid and gas phase chemistry in the formation of (complex) organic molecules, like H$_2$CO, CH$_3$OH, and CH$_3$CN, which reveal that photo-desorption of ices is an efficient mechanism to release molecules into the gas phase. The case of CH$_3$CN is especially surprising, as it is 40 times more abundant in the warm ($T_\mathrm{kin}\sim60$~K) UV-illuminated edge of the nebula, than in the shielded and colder ($T_\mathrm{kin}\sim20$~K) inner layers. I will show that complex molecules, such as HCOOH, CH$_2$CO, CH$_3$CHO, and CH$_3$CCH are easily detected in the PDR. I will also discuss new diagnostics of the UV-illuminated gas, like CF$^+$ (for which we recently resolved its hyperfine structure for the first time), which is observable from the ground, and we propose it can be used as a proxy of C$^+$. I will finish by reporting the first detection of a new molecule, recently confirmed to be the small hydrocarbon C$_3$H$^+$, which shows that photo-erosion of PAHs is needed to explain the enhanced abundance of other small hydrocarbons, like C$_3$H and C$_3$H$_2$.

Publisher

International Symposium on Molecular Spectroscopy

Type of Resource

text

Language

English

Permalink

http://hdl.handle.net/2142/51074

DOI

https://doi.org/10.15278/isms.2014.RF05

Copyright and License Information

Copyright 2014 by the authors. Licensed under a Creative Commons Attribution 4.0 International License. http://creativecommons.org/licenses/by/4.0/

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