* Astronomy

Title: ALMA Observations of the Submillimeter Dense Molecular Gas Tracers in the Luminous Type-1 Active Nucleus of NGC 7469
Author: Takuma Izumi, Kotaro Kohno, Susanne Aalto, Akihiro Doi, Daniel Espada, Kambiz Fathi, Nanase Harada, Bunyo Hatsukade, Takashi Hattori, Pei-Ying Hsieh, Soh Ikarashi, Masatoshi Imanishi, Daisuke Iono, Sumio Ishizuki, Melanie Krips, Sergio Martín, Satoki Matsu****a, David S. Meier, Hiroshi Nagai, Naomasa Nakai, Taku Nakajima, Kouichiro Nakanishi, Hideko Nomura, Michael W. Regan, Eva Schinnerer, Kartik Sheth, Shuro Takano, Yoichi Tamura, Yuichi Terashima, Tomoka Tosaki, Jean L. Turner, Hideki Umehata, Tommy Wiklind

We present ALMA Cycle 1 observations of the central kpc region of the luminous type-1 Seyfert galaxy NGC 7469 with unprecedented high resolution (0.5" x 0.4" = 165 pc x 132 pc) at submillimeter wavelengths. Utilising the wide-bandwidth of ALMA, we simultaneously obtained HCN(4-3), HCO+(4-3), CS(7-6), and partially CO(3-2) line maps, as well as the 860 m continuum. The region consists of the central ~ 1" component and the surrounding starburst ring with a radius of ~ 1.5"-2.5". Several structures connect these components. Except for CO(3-2), these dense gas tracers are significantly concentrated towards the central ~ 1", suggesting their suitability to probe the nuclear regions of galaxies. Their spatial distribution resembles well those of centimeter and mid-infrared continuum emissions, but it is anti-correlated with the optical one, indicating the existence of dust obscured star formation. The integrated intensity ratios of HCN(4-3)/HCO⁺(4-3) and HCN(4-3)/CS(7-6) are higher at the AGN position than at the starburst ring, which is consistent to our previous findings (submm-HCN enhancement). However, the HCN(4-3)/HCO+(4-3) ratio at the AGN position of NGC 7469 (1.11±0.06) is almost half of the corresponding value of the low-luminosity type-1 Seyfert galaxy NGC 1097 (2.0±0.2), despite the more than two orders of magnitude higher X-ray luminosity of NGC 7469. But the ratio is comparable to that of the close vicinity of the AGN of NGC 1068 (~ 1.5). Based on these results, we speculate that some other heating mechanisms than X-ray (e.g., mechanical heating due to AGN jet) can contribute significantly for shaping the chemical composition in NGC 1097.

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