x-cigale: fitting AGN/galaxy SEDs from X-ray to infrared

• Published in: Monthly notices of the Royal Astronomical Society 2020-01, Vol.491 (1), p.740-757
• Main Authors: Yang(杨光), G, Boquien, M, Buat, V, Burgarella, D, Ciesla, L, Duras, F, Stalevski, M, Brandt, W N, Papovich, C
• Format: Article
• Language: English
• Subjects: Astrophysics; Physics; Sciences of the Universe
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/stz3001

Code Investigating GALaxy Emission (cigale) is a powerful multiwavelength spectral energy distribution (SED) fitting code for extragalactic studies. However, the current version of cigale is not able to fit X-ray data, which often provide unique insights into active galactic nucleus (AGN) intrinsic power. We develop a new X-ray module for cigale, allowing it to fit SEDs from the X-ray to infrared (IR). We also improve the AGN fitting of cigale from UV-to-IR wavelengths. We implement a modern clumpy two-phase torus model, skirtor. To account for moderately extincted type 1 AGNs, we implement polar-dust extinction. We publicly release the source code (named ‘x-cigale’). We test x-cigale with X-ray detected AGNs in SDSS, COSMOS, and AKARI-NEP. The fitting quality (as indicated by reduced χ2) is good in general, indicating that x-cigale is capable of modelling the observed SED from X-ray to IR. We discuss constrainability and degeneracy of model parameters in the fitting of AKARI-NEP, for which excellent mid-IR photometric coverage is available. We also test fitting a sample of AKARI-NEP galaxies for which only X-ray upper limits are available from Chandra observations, and find that the upper limit can effectively constrain the AGN SED contribution for some systems. Finally, using x-cigale, we assess the ability of Athena to constrain the AGN activity in future extragalactic studies.