25 research outputs found

    Theoretical modelling of two-component molecular discs in spiral galaxies

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    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 50−30050-300 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\left(0.48 \pm 0.01 \right) r_{25}. 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\lesssim 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≳40oi \gtrsim 40^o), 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.Comment: Accepted for publication in A&

    A slow bar in the dwarf irregular galaxy NGC 3741

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    Using the Tremaine-Weinberg method, we measure the speed of the HI bar seen in the disk of NGC 3741. NGC 3741 is an extremely gas rich galaxy with an {H\,{\sc i}} disk which extends to about 8.3 times its Holmberg radius. It is also highly dark matter-dominated. Our calculated value of the pattern speed Ωp\Omega_p is 17.1 ±\pm 3.4 km s−1kpc−1\textrm{s}^{-1}\textrm{kpc}^{-1}. We also find the ratio of the co-rotation radius to the bar semi-major axis to be (1.6 ±\pm 0.3), indicating a slow bar. This is consistent with bar models in which dynamical friction results in a slow bar in dark matter dominated galaxies.Comment: 7 pages, 4 figures, 2 tables Accepted for publlication in MNRA
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