ALMA observations towards M83 reveal N2H+ tracing dense gas

@misc{harada2026alma,
  title = {{ALMA observations towards M83 reveal N2H+ tracing dense gas}},
  author = {Nanase Harada and Yuri Nishimura and Toshiki Saito and Mario Tafalla and Jin Koda and Doris Arzoumanian and Sophia K. Stuber and Akihiko Hirota and Yoshimasa Watanabe},
  howpublished = {arXiv},
  year = {2026},
  month = oct,
  doi = {10.48550/arxiv.2610.21142},
  eprint = {2610.21142},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2610.21142},
  note = {CC BY 4.0},
}

TY  - UNPB
TI  - ALMA observations towards M83 reveal N2H+ tracing dense gas
AU  - Nanase Harada
AU  - Yuri Nishimura
AU  - Toshiki Saito
AU  - Mario Tafalla
AU  - Jin Koda
AU  - Doris Arzoumanian
AU  - Sophia K. Stuber
AU  - Akihiko Hirota
AU  - Yoshimasa Watanabe
PY  - 2026
DA  - 2026/10/15
PB  - arXiv
DO  - 10.48550/arxiv.2610.21142
UR  - https://arxiv.org/abs/2610.21142
AB  - Galactic observations have shown that N2H+ intensities preferentially trace star-forming dense molecular gas compared with HCN or HCO+, which are conventionally used as dense-gas tracers in extragalactic studies. In this study, we aim to verify this trend in the nearby star-forming galaxy M83. Using ALMA, we observed the J=1-0 transitions of N2H+ and HCN, along with the 1-mm and 3-mm continuum, and analyzed the archival CO(1-0) data. The data achieved a spatial resolution of 48 pc in the southwestern bar-end region of M83, covering an area of 2.1 kpc x 1.8 kpc. N2H+ and HCN intensities are approximately linearly correlated, indicating that HCN luminosity can still reasonably predict the amount of dense gas as well as N2H+ luminosity does. However, in regions with high column densities, N2H+ becomes a super-linear function of HCN, suggesting that the N2H+ emission is more sensitive to dense gas than HCN. We employed a radiative transfer model that predicts line intensities as a function of column density, adopting parametric column density probability distribution functions (N-PDFs) to describe the underlying column density distribution. The model demonstrates that the observed linear or superlinear trend can be explained by a log-normal distribution only or a log-normal and a power-law tail distribution in the N-PDF. Furthermore, the N2H+ intensity is significantly more sensitive to the power-law tail than the HCN intensity. In addition, our analysis incorporating archival data shows that N2H+ is a less reliable tracer of dense gas in galactic center regions, where warmer temperatures may promote N2H+ destruction.
ER  -