On the density regime probed by HCN emission

Autor(en)

Gerwyn H. Jones, Paul C. Clark, Simon C. O. Glover, Alvaro Hacar

Abstrakt

HCN J$\, =\,$1$\, -\,$0 emission is commonly used as a dense gas tracer, thought to mainly arise from gas with densities $\mathrm{\sim 10^4\ -\ 10^5\ cm^{-3}}$. This has made it a popular tracer in star formation studies. However, there is increasing evidence from observational surveys of `resolved' molecular clouds that HCN can trace more diffuse gas. We investigate the relationship between gas density and HCN emission through post-processing of high resolution magnetohydrodynamical simulations of cloud-cloud collisions. We find that HCN emission traces gas with a mean volumetric density of $\mathrm{\sim 3 \times 10^3\ cm^{-3}}$ and a median visual extinction of $\mathrm{\sim 5\ mag}$. We therefore predict a characteristic density that is an order of magnitude less than the "standard" characteristic density of $\mathrm{n \sim 3 \times 10^4\ cm^{-3}}$. Indeed, we find in some cases that there is clear HCN emission from the cloud even though there is no gas denser than this standard critical density. We derive luminosity-to-mass conversion factors for the amount of gas at $A_{\rm V} > 8$ or at densities $n > 2.85 \times 10^{3} \: {\rm cm^{-3}}$ or $n > 3 \times 10^{4} \: {\rm cm^{-3}}$, finding values of $\alpha_{\rm HCN} = 6.79, 8.62$ and $27.98 \: {\rm M_{\odot}} ({\rm K \, km \, s^{-1} \, pc^{2}})$, respectively. In some cases, the luminosity to mass conversion factor predicted mass in regions where in actuality there contains no mass.

Organisation(en)

Institut für Astrophysik

Journal

Monthly Notices of the Royal Astronomical Society

Band

520

Seiten

1005-1021

Anzahl der Seiten

17

ISSN

0035-8711

DOI

https://doi.org/10.48550/arXiv.2112.05543

Publikationsdatum

03-2023

Peer-reviewed

Ja

ÖFOS 2012

103004 Astrophysik, 103003 Astronomie

Schlagwörter

Link zum Portal

https://ucrisportal.univie.ac.at/de/publications/d0f618f4-073f-4925-8250-56302e8732c9