학술논문
A 2-3 mm high-resolution molecular line survey towards the centre of the nearby spiral galaxy NGC 6946
Document Type
Working Paper
Author
Eibensteiner, Cosima; Barnes, Ashley T.; Bigiel, Frank; Schinnerer, Eva; Liu, Daizhong; Meier, David S.; Usero, Antonio; Leroy, Adam K.; Rosolowsky, Erik; Puschnig, Johannes; Lazar, Ilin; Pety, Jérôme; Lopez, Laura A.; Emsellem, Eric; Bešlić, Ivana; Querejeta, Miguel; Murphy, Eric J.; Brok, Jakob den; Schruba, Andreas; Chevance, Mélanie; Glover, Simon C. O.; Gao, Yu; Grasha, Kathryn; Hassani, Hamid; Henshaw, Jonathan D.; Jimenez-Donaire, Maria J.; Klessen, Ralf S.; Kruijssen, J. M. Diederik; Pan, Hsi-An; Saito, Toshiki; Sormani, Mattia C.; Teng, Yu-Hsuan; Williams, Thomas G.
Source
A&A 659, A173 (2022)
Subject
Language
Abstract
The complex physical, kinematic, and chemical properties of galaxy centres make them interesting environments to examine with molecular line emission. We present new $2-4$" (${\sim}75{-}150$ pc at $7.7$ Mpc) observations at 2 and 3 mm covering the central $50$" (${\sim}1.9$ kpc) of the nearby double-barred spiral galaxy NGC 6946 obtained with the IRAM Plateau de Bure Interferometer. We detect spectral lines from ten molecules: CO, HCN, HCO$^+$, HNC, CS, HC$_3$N, N$_2$H$^+$, C$_2$H, CH$_3$OH, and H$_2$CO. We complemented these with published 1mm CO observations and 33 GHz continuum observations to explore the star formation rate surface density ${\Sigma_{\mathrm{SFR}}}$ on 150 pc scales. In this paper, we analyse regions associated with the inner bar of NGC 6946 $-$ the nuclear region (NUC), the northern (NBE), and southern inner bar end (SBE) and we focus on short-spacing corrected bulk (CO) and dense gas tracers (HCN, HCO$^+$, and HNC). We find that HCO$^+$ correlates best with ${\Sigma_{\mathrm{SFR}}}$, but the dense gas fraction ($f_{\mathrm{dense}}$) and star formation efficiency of the dense gas (${\mathrm{SFE_{dense}}}$) fits show different behaviours than expected from large-scale disc observations.The SBE has a higher ${\Sigma_{\mathrm{SFR}}}$, $f_{\mathrm{dense}}$, and shocked gas fraction than the NBE. We examine line ratio diagnostics and find a higher CO(2-1)/CO(1-0) ratio towards NBE than for the NUC. Moreover, comparison with existing extragalactic datasets suggests that using the HCN/HNC ratio to probe kinetic temperatures is not suitable on kiloparsec and sub-kiloparsec scales in extragalactic regions. Lastly, our study shows that the HCO$^+$/HCN ratio might not be a unique indicator to diagnose AGN activity in galaxies.
Comment: 38 pages, 23 figures, accepted for publication in A&A
Comment: 38 pages, 23 figures, accepted for publication in A&A