Please use this identifier to cite or link to this item:
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
ISSN: 0004-6361
1432-0746 (Online)
Alternative Location:
Copyright: 2020 European Southern Observatory
Appears in Collections:Research Papers (A&A)

Files in This Item:
File Description SizeFormat 
2020_Astronomy and Astrophysics_Vol.638_Article No.A66.pdfOpen Access2.65 MBAdobe PDFView/Open
2020_Astronomy and Astrophysics_Vol.638_Article No.A66.epub12.15 MBEPUBView/Open

Items in RRI Digital Repository are protected by copyright, with all rights reserved, unless otherwise indicated.