Abstract

Near-infrared spectroscopy of CO ro-vibrational absorption toward AGN obscurers with JWST/MIRI

Shunsuke BABA (ISAS/JAXA, the University of Tokyo)

Takao NAKAGAWA (ISAS/JAXA)

An obscuring torus is a key element in the active galactic nuclei (AGNs) unified model in which the torus plays an essential role of attenuating the central radiation and dichotomizing AGNs into types 1 and 2. For the verification of the unified model, it is critical to confirm the existence of the torus and to investigate its physical properties. Typical size of obscuring tori is so small (~10 pc) that it is very difficult to make spatially-resolved observations of them in sub-millimeter observations of CO rotational emission lines. Hence we have been promoting near-infrared spectroscopic observations of CO ro-vibrational absorptions (band center 4.7 micron), which are expected to trace warm gas in the molecular tori heated by the central radiation. Those absorption lines can be observed simultaneously and provide us with detailed information of the physical properties of the molecular gas (column density, temperature, and velocity width). In previous researches, Shirahata et al. (2013) conducted high-spectral-resolution observations of the CO absorption band toward the obscured AGN IRAS 08572+3915 with a ground-based telescope Subaru, and Spoon et al. (2004) and Baba et al. (in preparation) studied the absorption with space telescopes Spitzer and AKARI, respectively. These observations have clearly demonstrated the effectiveness of the near-infrared observations of CO in absorption to trace warm gas possibly in the putative molecular tori. However, the size of a sample that ground-based telescopes can observe is highly limited due to the limited wavelength range in the M-band (or redshift of the target) and their relatively shallow detection limits due to very high background. On the other hand, while sensitivities of space telescope (Sitzer and AKARI) are superb, spectral resolving powers of Spitzer and AKARI are insufficient to resolve each rotational level, and detailed analysis is difficult. Hence JWST/MIRI (its medium spectral resolution of R~3000) is a unique opportunity for this study because it can resolve rotational levels of the CO absorption band with superb sensitivity and enables us to study what temperature components of warm gas exist around AGNs and to discuss the geometry of central obscurers.

Mode of presentation: poster