AKARI Infrared Camera (IRC) Spectroscopy Observations: Highlights

AKARI Infrared Camera (IRC) Spectroscopy Observations: Highlights Youichi OHYAMA1) and AKARI/IRC team Department of Infrared Astrophysics, Institute of Space and Astronautical Science (ISAS), JAXA, 3-1-1 Yoshinodai, Kanagawa 229-8510, Japan

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The Infrared Camera (IRC) is one of the two instruments on board the AKARI (formerly ASTRO-F; Murakami et al. 2007) satellite. In addition to the imaging mode from 1.8-26.5m for the pointed observation mode of the AKARI, it has a spectroscopic capability in its spectral range (Ohyama et al. 2007). By replacing imaging filters by transmission-type dispersers on the filter wheels, it provides low-resolution (R=20-120) spectroscopy with slits or in the wide imaging FOV (slit-less). The uniqueness of the IRC spectroscopy is the large field of view (~10’ X10’), multi-object spectroscopy with slit-less mode, and the wide and continuous spectral coverage over the entire NIR-MIR range. Before running out of cryogen, the IRC spectroscopy mode has been used in various fields of astronomy. We here present some highlights of the IRC spectroscopy observations to demonstrate its performance and potential. 1.Slit spectroscopy of planetary nebulae (PNe): For diffuse, extended objects, slit spectroscopy is the tool of choice. The spectrum of a PN, NGC 6543, shows many narrow hydrogen/find- structure lines, demonstrating its superb performance of the spectrograph (Ohyama et al. 2007). 2.Slit-less spectroscopic survey of the Large Magellanic Cloud (LMC): With wide-field slit-less spectroscopy capability, investigation on various types of compact sources, including compact HII regions, young stellar objects, and late-type stars, can be made over a large area of the LMC. This study will contribute significantly to understanding of recycling processes of the interstellar medium (ISM), including birth and death of stars. 3.Investigation of the ISM of nearby galaxies with slit spectroscopy: By placing the slit at some interesting locations of nearby, extended galaxies, one can analyze physical conditions of the ISM there. The slit has been located along in-/intra-arm regions of the disk galaxy NGC6946 (Sakon et al. 2007), or at the outer region where the galactic wind blowing from central star- bursting regions causes shock, etc. 4.Slit-less spectroscopy of multiple compact objects embedded within the diffuse ISM of nearby galaxies: Compact sources, like HII regions along spiral arms, can be observed at once spectroscopically, thanks to the wide-field slit-less spectroscopy capability of the IRC. To extract their spectra, one needs to carefully model the background ISM for good subtraction. 5.Revealing a dusty, cold cocoon surrounding hot active nuclei: Powerful active galactic nuclei (AGN) at their very center of luminous infrared galaxies are often hidden deep beneath by a heavy dusty screen. Infrared spectroscopy can be a powerful tool to inspect physical conditions of cold material surrounding the compact, hot nuclei. The NIR/MIR spectroscopy of a powerful infrared galaxy, UGC5101, revealed unexpectedly-prominent absorbing features, providing us with new clues to investigate the onion-like structure made of hot to cold icy/molecular/ionized materials surrounding its AGN core (http://www.ir.isas.jaxa.jp/AKARI /Outreach/results/results_e.html). 6.Accessing redshifted optical spectra of high-z quasars: the IRC is sensitive enough to obtain spectra from faint, distant quasars at z>4 (Oyabu et al. 2007). Infrared spectroscopy from space is essential to study their rest-frame optical spectra of such distant objects, enabling studies of their cosmological evolution. 1 References Murakami, H., et al. 2007, PASJ, 59, 369 Ohyama, Y., et al. 2007, PASJ, 59, 411 Onaka, T., et al. 2007, PASJ, 59, 401 Oyabu, S., et al. 2007, PASJ, 59, 497 Sakon, I., et al. 2007, PASJ, 59, 483