On the accuracy of H I observations in molecular clouds. More cold H I than thought?

Result code in IS VaVaI

<a href="https://www.isvavai.cz/riv?ss=detail&h=RIV%2F67985815%3A_____%2F22%3A00556787" target="_blank" >RIV/67985815:_____/22:00556787 - isvavai.cz</a>

Result on the web

<a href="https://doi.org/10.1093/mnras/stac607" target="_blank" >https://doi.org/10.1093/mnras/stac607</a>

DOI - Digital Object Identifier

<a href="http://dx.doi.org/10.1093/mnras/stac607" target="_blank" >10.1093/mnras/stac607</a>

Result language

angličtina

Original language name

On the accuracy of H I observations in molecular clouds. More cold H I than thought?

Original language description

We present a study of the cold atomic hydrogen (H I) content of molecular clouds simulated within the SILCC-Zoom project for solar neighbourhood conditions. We produce synthetic observations of H I at 21 cm, including H I self-absorption (HISA) and observational effects. We find that H I column densities, N-H I, of greater than or similar to 10(22) cm(-2) are frequently reached in molecular clouds with H I temperatures as low as similar to 10 K. Hence, HISA observations assuming a fixed H I temperature tend to underestimate the amount of cold H I in molecular clouds by a factor of 3-10 and produce an artificial upper limit of N-H I around 10(21) cm(-2). We thus argue that the cold H I mass in molecular clouds could be a factor of a few higher than previously estimated. Also, N-H I PDFs obtained from HISA observations might be subject to observational biases and should be considered with caution. The underestimation of cold H I in HISA observations is due to both the large H I temperature variations and the effect of noise in regions of high optical depth. We find optical depths of cold H I around 1-10, making optical depth corrections essential. We show that the high H I column densities (greater than or similar to 10(22) cm(-2)) can in parts be attributed to the occurrence of up to 10 individual HI-H-2 transitions along the line of sight. This is also reflected in the spectra, necessitating Gaussian decomposition algorithms for their in-depth analysis. However, also for a single HI-H-2 transition, N-H I frequently exceeds 10(21) cm(-2), challenging one-dimensional, semi-analytical models. This is due to non-equilibrium chemistry effects and the fact that HI-H-2 transition regions usually do not possess a one-dimensional geometry. Finally, we show that the H I gas is moderately supersonic with Mach numbers of a few. The corresponding non-thermal velocity dispersion can be determined via HISA observations within a factor of similar to 2.

Czech name

—

Czech description

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Type

J_imp - Article in a specialist periodical, which is included in the Web of Science database

CEP classification

—

OECD FORD branch

10308 - Astronomy (including astrophysics,space science)

Project

<a href="/en/project/GA19-15008S" target="_blank" >GA19-15008S: Star formation efficiency in massive star clusters</a><br>

Continuities

I - Institucionalni podpora na dlouhodoby koncepcni rozvoj vyzkumne organizace

Publication year

2022

Confidentiality

S - Úplné a pravdivé údaje o projektu nepodléhají ochraně podle zvláštních právních předpisů

Name of the periodical

Monthly Notices of the Royal Astronomical Society

ISSN

0035-8711

e-ISSN

1365-2966

Volume of the periodical

512

Issue of the periodical within the volume

4

Country of publishing house

GB - UNITED KINGDOM

Number of pages

20

Pages from-to

4765-4784

UT code for WoS article

000779888900004

EID of the result in the Scopus database

2-s2.0-85128744399