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Title: Large-scale Spectroscopic Mapping of the ρ Ophiuchi Molecular Cloud Complex. I. The C{sub 2}H-to-N{sub 2}H{sup +} Ratio as a Signpost of Cloud Characteristics

Abstract

We present 2.5-square-degree C{sub 2}H N = 1–0 and N{sub 2}H{sup +} J = 1–0 maps of the ρ Ophiuchi molecular cloud complex. These are the first large-scale maps of the ρ Ophiuchi molecular cloud complex with these two tracers. The C{sub 2}H emission is spatially more extended than the N{sub 2}H{sup +} emission. One faint N{sub 2}H{sup +} clump, Oph-M, and one C{sub 2}H ring, Oph-RingSW, are identified for the first time. The observed C{sub 2}H-to-N{sub 2}H{sup +} abundance ratio ([C{sub 2}H]/[N{sub 2}H{sup +}]) varies between 5 and 110. We modeled the C{sub 2}H and N{sub 2}H{sup +} abundances with 1D chemical models, which show a clear decline of [C{sub 2}H]/[N{sub 2}H{sup +}] with chemical age. Such an evolutionary trend is little affected by temperatures when they are below 40 K. At high density ( n {sub H} > 10{sup 5} cm{sup −3}), however, the time it takes for the abundance ratio to drop at least one order of magnitude becomes less than the dynamical time (e.g., turbulence crossing time of ∼10{sup 5} yr). The observed [C{sub 2}H]/[N{sub 2}H{sup +}] difference between L1688 and L1689 can be explained by L1688 having chemically younger gas in relatively less dense regions.more » The observed [C{sub 2}H]/[N{sub 2}H{sup +}] values are the results of time evolution, accelerated at higher densities. For the relatively low density regions in L1688 where only C{sub 2}H emission was detected, the gas should be chemically younger.« less

Authors:
; ;  [1];  [2];  [3];  [4]
  1. National Astronomical Observatories, Chinese Academy of Sciences, A20 Datun Road, Chaoyang District, Beijing 100012 (China)
  2. Xinjiang Astronomical Observatory, Chinese Academy of Sciences, 150 Science 1-Street, Urumqi 830011 (China)
  3. Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48109 (United States)
  4. Shanghai Astronomical Observatory, Chinese Academy of Sciences, 80 Nandan Road, Shanghai 200030 (China)
Publication Date:
OSTI Identifier:
22663772
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 836; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABUNDANCE; CLOUDS; DENSITY; EMISSION; EVOLUTION; MOLECULAR CLUSTERS; MOLECULES; STARS; TURBULENCE

Citation Formats

Pan, Zhichen, Li, Di, Qian, Lei, Chang, Qiang, Bergin, Edwin A., and Wang, Junzhi, E-mail: panzc@nao.cas.cn, E-mail: dili@nao.cas.cn. Large-scale Spectroscopic Mapping of the ρ Ophiuchi Molecular Cloud Complex. I. The C{sub 2}H-to-N{sub 2}H{sup +} Ratio as a Signpost of Cloud Characteristics. United States: N. p., 2017. Web. doi:10.3847/1538-4357/AA5C33.
Pan, Zhichen, Li, Di, Qian, Lei, Chang, Qiang, Bergin, Edwin A., & Wang, Junzhi, E-mail: panzc@nao.cas.cn, E-mail: dili@nao.cas.cn. Large-scale Spectroscopic Mapping of the ρ Ophiuchi Molecular Cloud Complex. I. The C{sub 2}H-to-N{sub 2}H{sup +} Ratio as a Signpost of Cloud Characteristics. United States. doi:10.3847/1538-4357/AA5C33.
Pan, Zhichen, Li, Di, Qian, Lei, Chang, Qiang, Bergin, Edwin A., and Wang, Junzhi, E-mail: panzc@nao.cas.cn, E-mail: dili@nao.cas.cn. Mon . "Large-scale Spectroscopic Mapping of the ρ Ophiuchi Molecular Cloud Complex. I. The C{sub 2}H-to-N{sub 2}H{sup +} Ratio as a Signpost of Cloud Characteristics". United States. doi:10.3847/1538-4357/AA5C33.
@article{osti_22663772,
title = {Large-scale Spectroscopic Mapping of the ρ Ophiuchi Molecular Cloud Complex. I. The C{sub 2}H-to-N{sub 2}H{sup +} Ratio as a Signpost of Cloud Characteristics},
author = {Pan, Zhichen and Li, Di and Qian, Lei and Chang, Qiang and Bergin, Edwin A. and Wang, Junzhi, E-mail: panzc@nao.cas.cn, E-mail: dili@nao.cas.cn},
abstractNote = {We present 2.5-square-degree C{sub 2}H N = 1–0 and N{sub 2}H{sup +} J = 1–0 maps of the ρ Ophiuchi molecular cloud complex. These are the first large-scale maps of the ρ Ophiuchi molecular cloud complex with these two tracers. The C{sub 2}H emission is spatially more extended than the N{sub 2}H{sup +} emission. One faint N{sub 2}H{sup +} clump, Oph-M, and one C{sub 2}H ring, Oph-RingSW, are identified for the first time. The observed C{sub 2}H-to-N{sub 2}H{sup +} abundance ratio ([C{sub 2}H]/[N{sub 2}H{sup +}]) varies between 5 and 110. We modeled the C{sub 2}H and N{sub 2}H{sup +} abundances with 1D chemical models, which show a clear decline of [C{sub 2}H]/[N{sub 2}H{sup +}] with chemical age. Such an evolutionary trend is little affected by temperatures when they are below 40 K. At high density ( n {sub H} > 10{sup 5} cm{sup −3}), however, the time it takes for the abundance ratio to drop at least one order of magnitude becomes less than the dynamical time (e.g., turbulence crossing time of ∼10{sup 5} yr). The observed [C{sub 2}H]/[N{sub 2}H{sup +}] difference between L1688 and L1689 can be explained by L1688 having chemically younger gas in relatively less dense regions. The observed [C{sub 2}H]/[N{sub 2}H{sup +}] values are the results of time evolution, accelerated at higher densities. For the relatively low density regions in L1688 where only C{sub 2}H emission was detected, the gas should be chemically younger.},
doi = {10.3847/1538-4357/AA5C33},
journal = {Astrophysical Journal},
number = 2,
volume = 836,
place = {United States},
year = {Mon Feb 20 00:00:00 EST 2017},
month = {Mon Feb 20 00:00:00 EST 2017}
}