ALMA Observations of Multiple CO and C Lines toward the Active Galactic Nucleus of NGC 7469: An X-Ray-dominated Region Caught in the Act
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ALMA Observations of Multiple CO and C Lines toward the Active Galactic Nucleus of NGC 7469: An X-Ray-dominated Region Caught in the Act

  • Author(s): Izumi, Takuma
  • Nguyen, Dieu D
  • Imanishi, Masatoshi
  • Kawamuro, Taiki
  • Baba, Shunsuke
  • Nakano, Suzuka
  • Kohno, Kotaro
  • Matsushita, Satoki
  • Meier, David S
  • Turner, Jean L
  • Michiyama, Tomonari
  • Harada, Nanase
  • Martín, Sergio
  • Nakanishi, Kouichiro
  • Takano, Shuro
  • Wiklind, Tommy
  • Nakai, Naomasa
  • Hsieh, Pei-Ying
  • et al.

Published Web Location

https://arxiv.org/abs/2006.09406
No data is associated with this publication.
Abstract

We used the Atacama Large Millimeter/submillimeter Array (ALMA) to map $^{12}$CO($J$ = 1-0), $^{12}$CO($J$ = 2-1), $^{12}$CO($J$ = 3-2), $^{13}$CO($J$ = 2-1), and [CI]($^3P_1$-$^3P_0$) emission lines around the type 1 active galactic nucleus (AGN) of NGC 7469 ($z = 0.0164$) at $\sim 100$ pc resolutions. The CO lines are bright both in the circumnuclear disk (central $\sim 300$ pc) and the surrounding starburst (SB) ring ($\sim 1$ kpc diameter), with two bright peaks on either side of the AGN. By contrast, the [CI]($^3P_1$-$^3P_0$) line is strongly peaked on the AGN. Consequently, the brightness temperature ratio of [CI]($^3P_1$-$^3P_0$) to $^{13}$CO(2-1) is $\sim 20$ at the AGN, as compared to $\sim 2$ in the SB ring. Our local thermodynamic equilibrium (LTE) and non-LTE models indicate that the enhanced line ratios (or CI enhancement) are due to an elevated C$^0$/CO abundance ratio ($\sim 3-10$) and temperature ($\sim 100-500$ K) around the AGN as compared to the SB ring (abundance ratio $\sim 1$, temperature $\lesssim 100$ K), which accords with the picture of the X-ray-dominated Region (XDR). Based on dynamical modelings, we also provide CO(1-0)-to- and [CI]($^3P_1$-$^3P_0$)-to-molecular mass conversion factors at the central $\sim 100$ pc of this AGN as $\alpha_{\rm CO} = 4.1$ and $\alpha_{\rm CI} = 4.4~M_\odot$ (K km s$^{-1}$ pc$^2$)$^{-1}$, respectively. Our results suggest that the CI enhancement is potentially a good marker of AGNs that could be used in a new submillimeter diagnostic method toward dusty environments.

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