Title:	Theoretical modelling of two-component molecular discs in spiral galaxies
Authors:	Patra, Narendra Nath
Keywords:	molecular data ISM: molecules galaxies: kinematics and dynamics galaxies: spiral galaxies: structure
Issue Date:	Jun-2020
Publisher:	EDP Sciences for European Southern Observatory
Citation:	Astronomy & Astrophysics, 2020, Vol.638, Article No. A66
Abstract:	As recent observations of the molecular discs in spiral galaxies point to the existence of a diffuse, low-density thick molecular disc along with the prominent thin one, we investigate the observational signatures of this thick disc by theoretically modelling two-component molecular discs in a sample of eight nearby spiral galaxies. Assuming a prevailing hydrostatic equilibrium, we set up and solved the joint Poisson’s-Boltzmann equation to estimate the three-dimensional distribution of the molecular gas and the molecular scale height in our sample galaxies. The molecular scale height in a two-component molecular disc is found to vary between 50 and 300 pc, which is higher than what is found in a single-component disc. We find that this scale height can vary significantly depending on the assumed thick disc molecular gas fraction. We also find that the molecular gas flares as a function of the radius and follows a tight exponential law with a scale length of (0.48 ± 0.01)r25. We used the density solutions to produce the column density maps and spectral cubes to examine the ideal observing conditions to identify a thick molecular disc in galaxies. We find that unless the molecular disc is an edge-on system and imaged with a high spatial resolution (≲100 pc), it is extremely hard to identify a thick molecular disc in a column density map. The spectral analysis further reveals that at moderate to high inclination (i ≳ 40°), spectral broadening can fictitiously introduce the signatures of a two-component disc into the spectral cube of a single-component disc. Hence, we conclude that a low inclination molecular disc imaged with high spatial resolution would serve as the ideal site for identifying the thick molecular disc in galaxies.
Description:	Open Access
URI:	http://hdl.handle.net/2289/7495
ISSN:	0004-6361 1432-0746 (Online)
Alternative Location:	https://ui.adsabs.harvard.edu/abs/2020A%26A...638A..66P/abstract https://arxiv.org/abs/2004.13056 https://doi.org/10.1051/0004-6361/201936483
Copyright:	2020 European Southern Observatory
Appears in Collections:	Research Papers (A&A)

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