| Abstract |
We present the first results from “Surveying the Whirlpool at Arcseconds with NOEMA” (SWAN), an IRAM Northern Extended Millimetre Array (NOEMA)+30 m large program that maps emission from several molecular lines at 90 and 110 GHz in the iconic nearby grand-design spiral galaxy M 51 at a cloud-scale resolution (∼3″ = 125 pc). As part of this work, we have obtained the first sensitive cloud-scale map of N 2 H + (1–0) of the inner ∼5 × 7 kpc of a normal star-forming galaxy, which we compared to HCN(1–0) and 12 CO(1–0) emission to test their ability in tracing dense, star-forming gas. The average N 2 H + -to-HCN line ratio of our total FoV is 0.20 ± 0.09, with strong regional variations of a factor of ≳2 throughout the disk, including the south-western spiral arm and the center. The central ∼1 kpc exhibits elevated HCN emission compared to N 2 H + , probably caused by AGN-driven excitation effects. We find that HCN and N 2 H + are strongly super-linearily correlated in intensity ( ρ Sp ∼ 0.8), with an average scatter of ∼0.14 dex over a span of ≳1.5 dex in intensity. When excluding the central region, the data are best described by a power law of an exponent of 1.2, indicating that there is more N 2 H + per unit HCN in brighter regions. Our observations demonstrate that the HCN-to-CO line ratio is a sensitive tracer of gas density in agreement with findings of recent galactic studies utilising N 2 H + . The peculiar line ratios present near the AGN and the scatter of the power-law fit in the disk suggest that in addition to a first-order correlation with gas density, second-order physics (such as optical depth, gas temperature) or chemistry (abundance variations) are encoded in the N 2 H + / 12 CO, HCN/ 12 CO, and N 2 H + /HCN ratios. |
| Authors |
Sophia K. Stuber  , J. Pety , E. Schinnerer , Frank Bigiel , A. Usero , Ivana Bešlić , Miguel Querejeta , María J. Jiménez-Donaire , Adam K. Leroy , Jakob S. den Brok , Lukáš Neumann , Cosima Eibensteiner , Yu-Hsuan Teng , Ashley T. Barnes , Mélanie Chevance , Dario Colombo , Daniel A. Dale  , Simon C. O. Glover , Daizhong Liu , Hsi-An Pan
|
| Journal Info |
EDP Sciences | Astronomy & Astrophysics , vol: 680
, pages: L20 - L20
|
| Publication Date |
12/1/2023 |
| ISSN |
0004-6361 |
Type |
article |
| Open Access |
green
|
| DOI |
https://doi.org/10.1051/0004-6361/202348205 |
| Keywords |
Sloan Digital Sky Survey (Score: 0.464227)
|
