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SURVEY OF DUSTY ACTIVE GALACTIC NUCLEI BASED ON THE MID-INFRARED ALL-SKY SURVEY CATALOG
Oyabu, S.,Ishihara, D.,Yamada, R.,Kaneda, H.,Yamagishi, M.,Toba, Y.,Matsuhara, H.,Nakagawa, T.,Malkan, M.,Shirahata, M. The Korean Astronomical Society 2012 天文學論叢 Vol.27 No.4
Many observations have found evidence of the presence of a large number of heavily obscured Active Galactic Nuclei (AGNs). However, the nature of this population is only poorly understood because heavy obscuration by dust prevents one from finding them at optical wavelengths. Mid-infrared AGN searches can overcome this obstacle by penetrating through dust and by detecting direct emission from the dust torus. Thus, we can identify most of the AGN population, including type-2 and buried AGNs. Using the AKARI mid-infrared all-sky survey, we performed an AGN search in the nearby universe. Utilizing the 2MASS photometry, we selected mid-infrared-excess sources and carried out near-infrared spectroscopic observations in the AKARI Phase 3. During these follow-up observations, we have found three galaxies that show strong near-infrared red continuum from hot dust with a temperature of about 500 K, but do not show any AGN features in other wavelengths. The most suitable explanation of near-infrared continuum is the presence of central AGNs. Therefore, we conclude that they are AGNs obscured by dust. We performed X-ray observations of the two galaxies with SUZAKU. No detections in the 0.4-10 keV suggest that the column density may be much higher than $N_H=10^{23.5}cm^{-2}$. Comparing the masses of the host galaxies with those of the SDSS AGNs, we find that the host galaxies of the dusty AGNs discovered with AKARI are less massive populations than those of optically selected AGNs.
A SURVEY OF T TAURI STARS WITH AKARI
Takita, S.,Kataza, H.,Kitamura, Y.,Ueno, M.,Oyabu, S.,Ishihara, D.,Ita, Y. The Korean Astronomical Society 2012 天文學論叢 Vol.27 No.4
We have carried out a survey of T Tauri stars (TTSs) in a 1,800-square-degrees region toward the Taurus-Auriga star forming region with the AKARI Mid-Infrared All-Sky Survey. By combination of AKARI, 2MASS, and UCAC surveys, we created new criteria to chose TTS candidates. We also considered Asymptotic Giant Branch stars and galaxies, which have similar infrared colors, to separate TTSs from these sources. On the basis of our criteria, we find 27 new TTS candidates. To verify our criteria, we performed follow-up observations for them and confirmed that 23 are TTSs.
DETECTION OF THE COSMIC FAR-INFRARED BACKGROUND IN AKARI DEEP FIELD SOUTH
Matsuura, S.,Shirahata, M.,Kawada, M.,Takeuchi, T. T.,Burgarella, D.,Clements, D. L.,Jeong, W.-S.,Hanami, H.,Khan, S. A.,Matsuhara, H.,Nakagawa, T.,Oyabu, S.,Pearson, C. P.,Pollo, A.,Serjeant, S.,Taka IOP Publishing 2011 The Astrophysical journal Vol.737 No.1
<P>We report new limits on the absolute brightness and spatial fluctuations of the cosmic infrared background (CIB) via the AKARI satellite. We carried out observations at 65, 90, 140, and 160 mu m as a cosmological survey in AKARI Deep Field South, which is one of the lowest cirrus regions with a contiguous area of the sky. After removing bright galaxies and subtracting zodiacal and Galactic foregrounds from the measured sky brightness, we successfully measured the CIB brightness and its fluctuations across a wide range of angular scales, from arcminutes to degrees. The measured CIB brightness is consistent with previous results reported from COBE data, but significantly higher than the lower limits at 70 and 160 mu m obtained via Spitzer from the stacking analysis of selected 24 mu m sources. The discrepancy with the Spitzer result is possibly due to a new galaxy population at high redshift obscured by hot dust or unknown diffuse emission. From a power spectrum analysis at 90 mu m, two components were identified: the CIB fluctuations with shot noise due to individual galaxies in a small angular scale from the beam size up to 10 arcminutes, and Galactic cirrus emission dominating at the largest angular scales of a few degrees. The overall shape of the power spectrum at 90 mu m is very similar to that at longer wavelengths, as observed by Spitzer and the Balloon-borne Large-Aperture Submillimeter Telescope (BLAST). Our power spectrum, with an intermediate angular scale of 10-30 arcminutes, gives a firm upper limit for galaxy clustering, which was found by Spitzer and BLAST. Moreover, the color of the CIB fluctuations, which is obtained by combining our data with the previous results, is as red as ultra-luminous infrared galaxies at high redshift. These galaxies are not likely to provide the majority of the CIB emission at 90 mu m, but are responsible for the fluctuations. Our results provide new constraints on the evolution and clustering properties of distant infrared galaxies and any diffuse emission from the early universe.</P>
The North Ecliptic Pole Wide survey of AKARI: a near- and mid-infrared source catalog
Kim, S. J.,Lee, H. M.,Matsuhara, H.,Wada, T.,Oyabu, S.,Im, M.,Jeon, Y.,Kang, E.,Ko, J.,Lee, M. G.,Takagi, T.,Pearson, C.,White, G. J.,Jeong, W.-S.,Serjeant, S.,Nakagawa, T.,Ohyama, Y.,Goto, T.,Takeuch EDP Sciences 2012 Astronomy and astrophysics Vol.548 No.-
Photometric redshift accuracy in <i>AKARI</i> deep surveys
Negrello, M.,Serjeant, S.,Pearson, C.,Takagi, T.,Efstathiou, A.,Goto, T.,Burgarella, D.,Jeong, W.-S.,Im, M.,Lee, H. M.,Matsuhara, H.,Oyabu, S.,Wada, T.,White, G. Blackwell Publishing Ltd 2009 MONTHLY NOTICES- ROYAL ASTRONOMICAL SOCIETY Vol.394 No.1
<P>ABSTRACT</P><P>We investigate the photometric redshift accuracy achievable with the <I>AKARI</I> infrared data in deep multiband surveys, such as in the North Ecliptic Pole field. We demonstrate that the passage of redshifted polycyclic aromatic hydrocarbons (PAH) and silicate features into the mid-infrared wavelength window covered by <I>AKARI</I> is a valuable means to recover the redshifts of starburst galaxies. To this end, we have collected a sample of ∼60 galaxies drawn from the Great Observatories Origins Deep Survey-North Field with spectroscopic redshift 0.5 ≲<I>z</I><SUB>spec</SUB>≲ 1.5 and photometry from 3.6 to 24 μm, provided by the <I>Spitzer</I>, <I>Infrared Space Observatory</I> and <I>AKARI</I> satellites. The infrared spectra are fitted using synthetic galaxy spectral energy distributions which account for starburst and active nuclei emission. For ∼90 per cent of the sources in our sample, the redshift is recovered with an accuracy |<I>z</I><SUB>phot</SUB>−<I>z</I><SUB>spec</SUB>|/(1 +<I>z</I><SUB>spec</SUB>) ≲ 10 per cent. A similar analysis performed on a set of simulated spectra shows that the <I>AKARI</I> infrared data alone can provide photometric redshifts accurate to |<I>z</I><SUB>phot</SUB>−<I>z</I><SUB>spec</SUB>|/(1 +<I>z</I><SUB>spec</SUB>) ∼ 10 per cent (1σ) at <I>z</I>≲ 2. At higher redshifts, the PAH features are shifted outside the wavelength range covered by <I>AKARI</I> and the photo-<I>z</I> estimates rely on the less prominent 1.6 μm stellar bump; the accuracy achievable in this case on (1 +<I>z</I>) is ∼10–15 per cent, provided that the active galactic nuclei contribution to the infrared emission is subdominant. Our technique is no more prone to redshift aliasing than optical-ultraviolet photo-<I>z</I>, and it may be possible to reduce this aliasing further with the addition of submillimetre and/or radio data.</P>
AKARI OBSERVATION OF THE FLUCTUATION OF THE NEAR-INFRARED BACKGROUND
Matsumoto, T.,Seo, H.J.,Jeong, W.S.,Lee, H.M.,Matsuura, S.,Matsuhara, H.,Oyabu, S.,Pyo, J.,Wada, T. The Korean Astronomical Society 2012 天文學論叢 Vol.27 No.4
We report a search for fluctuations of the sky brightness toward the North Ecliptic Pole with AKARI, at 2.4, 3.2, and $4.1{\mu}m$. The stacked images with a diameter of 10 arcminutes of the AKARI-Monitor Field show a spatial structure on the scale of a few hundred arcseconds. A power spectrum analysis shows that there is a significant excess fluctuation at angular scales larger than 100 arcseconds that cannot be explained by zodiacal light, diffuse Galactic light, shot noise of faint galaxies, or clustering of low-redshift galaxies. These findings indicate that the detected fluctuation could be attributed to the first stars of the universe, i.e., Population III stars.