Abstract
Line emission is strongly dependent on the local environmental conditions in which the
emitting tracers reside. In this work, we focus on modelling the CO emission from simulated
giant molecular clouds (GMCs), and study the variations in the resulting line ratios arising
from the emission from the J = 1–0, J = 2–1, and J = 3–2 transitions. We perform a set
of smoothed particle hydrodynamics simulations with time-dependent chemistry, in which
environmental conditions – including total cloud mass, density, size, velocity dispersion,
metallicity, interstellar radiation field (ISRF), and the cosmic ray ionization rate (CRIR) –
were systematically varied. The simulations were then post-processed using radiative transfer
to produce synthetic emission maps in the three transitions quoted above. We find that the
cloud-averaged values of the line ratios can vary by up to ±0.3 dex, triggered by changes in the
environmental conditions. Changes in the ISRF and/or in the CRIR have the largest impact on
line ratios since they directly affect the abundance, temperature, and distribution of CO-rich
gas within the clouds. We show that the standard methods used to convert CO emission to H2
column density can underestimate the total H2 molecular gas in GMCs by factors of 2 or 3,
depending on the environmental conditions in the clouds.
| Item Type: |
Article
|
| Date Type: |
Publication |
| Status: |
Published |
| Schools: |
Physics and Astronomy |
| Subjects: |
Q Science > QB Astronomy |
| Publisher: |
Oxford University Press |
| ISSN: |
0035-8711 |
| Date of First Compliant Deposit: |
15 February 2018 |
| Date of Acceptance: |
12 December 2017 |
| Last Modified: |
26 Apr 2020 13:40 |
| URI: |
http://orca.cf.ac.uk/id/eprint/109135 |
Citation Data
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