Detection of an H-alpha Emission Line on a Quasar, RX J1759.4+6638, at z=4.3 with AKARI

We report the detection of an H-alpha emission line in the low resolution spectrum of a quasar, RX J1759.4+6638, at a redshift of 4.3 with the InfraRed Camera (IRC) onboard the AKARI. This is the first spectroscopic detection of an H-alpha emission line in a quasar beyond z=4. The overall spectral energy distribution (SED) of RX J1759.4+6638 in the near- and mid-infrared wavelengths agrees with a median SED of the nearby quasars and the flux ratio of F(Ly-alpha)/F(H-alpha) is consistent with those of previous reports for lower-redshift quasars.Comment: 9pages, 3 figures, Publications of the Astronomical Society of Japan, in pres

An Optical Source Catalog of the North Ecliptic Pole Region

We present a five (u*,g',r',i',z') band optical photometry catalog of the sources in the North Ecliptic Pole (NEP) region based on deep observations made with MegaCam at CFHT. The source catalog covers about 2 square degree area centered at the NEP and reaches depths of about 26 mag for u*, g', r' bands, about 25 mag for i' band, and about 24 mag for z' band (4 sigma detection over an 1 arcsec aperture). The total number of cataloged sources brighter than r'= 23 mag is about 56,000 including both point sources and extended sources. From the investigation of photometric properties using the color-magnitude diagrams and color-color diagrams, we have found that the colors of extended sources are mostly (u*-r') 0.5. This can be used to separate the extended sources from the point sources reliably, even for the faint source domain where typical morphological classification schemes hardly work efficiently. We have derived an empirical color-redshift relation of the red sequence galaxies using the Sloan Digital Sky Survey data. By applying this relation to our photometry catalog and searching for any spatial overdensities, we have found two galaxy clusters and one nearby galaxy group.Comment: 34 pages, 15 figures, 2 tables. Accepted for publication in ApJS. The pdf file with high resolution figures can be downloaded from http://astro.snu.ac.kr/~nhwang/index.files/nep.htm

Near-infrared and Mid-infrared Spectroscopy with the Infrared Camera (IRC) for AKARI

The Infrared Camera (IRC) is one of the two instruments on board the AKARI satellite. In addition to deep imaging from 1.8-26.5um for the pointed observation mode of the AKARI, it has a spectroscopic capability in its spectral range. By replacing the imaging filters by transmission-type dispersers on the filter wheels, it provides low-resolution (lambda/d_lambda ~ 20-120) spectroscopy with slits or in a wide imaging field-of-view (approximately 10'X10'). The IRC spectroscopic mode is unique in space infrared missions in that it has the capability to perform sensitive wide-field spectroscopic surveys in the near- and mid-infrared wavelength ranges. This paper describes specifications of the IRC spectrograph and its in-orbit performance.Comment: 13 pages, 7 figures, accepted for publication on PAS

AKARI infrared imaging of reflection nebulae IC4954 and IC4955

We present the observations of the reflection nebulae IC4954 and IC4955 region with the Infrared Camera (IRC) and the Far-Infrared Surveyor (FIS) on board the infrared astronomical satellite AKARI during its performance verification phase. We obtained 7 band images from 7 to 160um with higher spatial resolution and higher sensitivities than previous observations. The mid-infrared color of the S9W (9um) and L18W (18um) bands shows a systematic variation around the exciting sources. The spatial variation in the mid-infrared color suggests that the star-formation in IC4954/4955 is progressing from south-west to north-east. The FIS data also clearly resolve two nebulae for the first time in the far-infrared. The FIS 4-band data from 65um to 160um allow us to correctly estimate the total infrared luminosity from the region, which is about one sixth of the energy emitted from the existing stellar sources. Five candidates for young stellar objects have been detected as point sources for the first time in the 11um image. They are located in the red S9W to L18W color regions, suggesting that current star-formation has been triggered by previous star-formation activities. A wide area map of the size of about 1 x 1 (deg^2) around the IC4954/4955 region was created from the AKARI mid-infrared all-sky survey data. Together with the HI 21cm data, it suggests a large hollow structure of a degree scale, on whose edge the IC4954/4955 region has been created, indicating star formation over three generations in largely different spatial scales.Comment: 23 pages, 7 figures, accepted for publication in PASJ AKARI special issu

Nature of Infrared Sources in 11 micron Selected Sample from Early Data of the AKARI North Ecliptic Pole Deep Survey

We present the properties of 11 $\mu$m selected sources detected in the early data of the North Ecliptic Pole Deep (NEP-Deep) Survey of AKARI. The data set covers 6 wavelength bands from 2.5 to 11 $\mu$m, with the exposure time of 10 ~ 20 minutes. This field lies within the CFHT survey with four filter bands ($g', r', i',z'), enabling us to establish nearly continuous spectral energy distributions (SEDs) for wavelengths ranging from 0.4 to 11$\mu$m. The main sample studied here consists of 71 sources whose 11$\mu$m AB magnitudes are equal to or brighter than 18.5 (251$\mu$Jy), which is complete to more than 90$\mu$m band has an advantage of sampling star forming galaxies with low to medium redshifts since the prominent PAH feature shifts into this band. As expected, we find that the majority (~68$\mu$m bright sources are star forming galaxies at 0.2 < z < 0.7 with$L_{IR} ~ 10^{10}$--$10^{12} L_{\odot}$ based on the detailed modelling of SEDs. We also find four AGNs lying at various redshifts in the main sample. In addition, we discuss a few sources which have non-typical SEDs of the main sample, including a brown dwarf candidate, a steep power-law source, flat spectrum object, and an early-type galaxy at moderate redshift.Comment: 22 pages, 10 figure

Optical identification of 15 μm sources in the AKARI performance verification field toward the north ecliptic pole

We present the results of optical identifications for 257 mid-infrared sources detected with a deep 15 μm survey over approximately 80 arcmin2 area in the AKARI performance verification field near the North Ecliptic Pole. The 15 μm fluxes of the sources range from 1 mJy down to 40 μJy, approximately one half of which are below 100 μJy. Optical counterparts were searched for within a 200–300 radius in both the BVRi'z' catalog generated by using the deep Subaru/Suprime-cam field, which covers one-third of the performance verification field, and the g'r'i'z' catalog based on observations made with MegaCam at CFHT. We found that the B - R and R - z' colors of sources with successful optical identifications are systematically redder than that of the entire optical sample in the same field. Moreover, approximately 40% of the 15 μm sources show colors with R-L15 > 5, which cannot be explained by the spectral energy distribution (SED) of normal quiescent spiral galaxies, but are consistent with SEDs of redshifted (z > 1) starburst or ultraluminous infrared galaxies. This result indicates that the fraction of the ultraluminous infrared galaxies in our faint 15 μm sample is much larger than that in our brighter 15 μm sources, which is consistent with the evolving mid-infrared luminosity function derived by recent studies based on Spitzer 24 μm deep surveys. Based on an SED fitting technique, the nature of the faint 15 μm sources is further discussed for a selected number of sources with available Ks-band dat