PHANGS-JWST First Results: A combined HST and JWST analysis of the nuclear star cluster in NGC 628

分类： 天文学 >> 天文学 提交时间： 2023-02-19

Nils Hoyer Francesca Pinna Albrecht W. H. Kamlah Francisco Nogueras-Lara Anja Feldmeier-Krause Nadine Neumayer Mattia C. Sormani Médéric Boquien Eric Emsellem Anil C. Seth Ralf S. Klessen Thomas G. Williams Eva Schinnerer Ashley T. Barnes Adam K. Leroy Silvia Bonoli J. M. Diederik Kruijssen Justus Neumann Patricia Sánchez-Blázquez Daniel A. Dale

摘要： We combine archival HST and new JWST imaging data, covering the ultraviolet to mid-infrared regime, to morphologically analyze the nuclear star cluster (NSC) of NGC 628, a grand-design spiral galaxy. The cluster is located in a 200 pc x 400 pc cavity, lacking both dust and gas. We find roughly constant values for the effective radius (r_eff ~ 5 pc) and ellipticity ({\epsilon} ~ 0.05), while the S\'ersic index (n) and position angle (PA) drop from n ~ 3 to ~ 2 and PA ~ 130{\deg} to 90{\deg}, respectively. In the mid-infrared, r_eff ~ 12pc, {\epsilon} ~ 0.4, and n ~ 1-1.5, with the same PA ~ 90{\deg}. The NSC has a stellar mass of log10 (M_nsc / M_Sun) = 7.06 +- 0.31, as derived through B-V, confirmed when using multi-wavelength data, and in agreement with the literature value. Fitting the spectral energy distribution, excluding the mid-infrared data, yields a main stellar population's age of (8 +- 3) Gyr with a metallicity of Z = 0.012 +- 0.006. There is no indication of any significant star formation over the last few Gyr. Whether gas and dust were dynamically kept out or evacuated from the central cavity remains unclear. The best-fit suggests an excess of flux in the mid-infrared bands, with further indications that the center of the mid-infrared structure is displaced with respect to the optical center of the NSC. We discuss five potential scenarios, none of them fully explaining both the observed photometry and structure.

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