79 research outputs found
AKARI Detections of Hot Dust in Luminous Infrared Galaxies
We present a new sample of active galactic nuclei (AGNs) identified using the
catalog of the AKARI Mid-infrared(MIR) All-Sky Survey. Our MIR search has an
advantage in detecting AGNs that are obscured at optical wavelengths due to
extinction. We first selected AKARI 9micron excess sources with
F(9micron)/F(K_S)>2 where K_S magnitudes were taken from the Two Micron All Sky
Survey. We then obtained follow-up near-infrared spectroscopy with the
AKARI/IRC, to confirm that the excess is caused by hot dust. We also obtained
optical spectroscopy with the Kast Double Spectrograph on the Shane 3-m
telescope at Lick Observatory. On the basis of on these observations, we
detected hot dust with a characteristic temperature of ~500K in two luminous
infrared galaxies. The hot dust is suspected to be associated with AGNs that
exhibit their nonstellar activity not in the optical, but in the near- and
mid-infrared bands, i.e., they harbor buried AGNs. The host galaxy stellar
masses of 4-6 x 10^9 M_sun are small compared with the hosts in
optically-selected AGN populations. These objects were missed by previous
surveys, demonstrating the power of the AKARI MIR All-Sky Survey to widen AGN
searches to include more heavily obscured objects. The existence of multiple
dusty star clusters with massive stars cannot be completely ruled out with our
current data.Comment: 15 pages, 4 figures, to be published in Astronomy & Astrophysic
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Compositions of Dust and Sea Salts in the Dome C and Dome Fuji Ice Cores From Last Glacial Maximum to Early Holocene Based on Ice-Sublimation and Single-Particle Measurements
We analyzed the chemical compositions of dust and seaâsalt particles in the EPICA Dome C (EDC) ice core during 26â7 kyr BP using an iceâsublimation technique and compared the results with existing data of the Dome Fuji (DF) ice core. Combined with ion concentration data, our data suggested similar seaâsalt fluxes in both cores and significantly lower dust flux in the EDC core. The differences in modal size and aspect ratio of dust particles between the two cores support the dominance of Patagonian source suggested by earlier works. The compositions of calcic dust showed major change at ~17 kyr BP, possibly reflecting a relative increase in dust transported via the upper troposphere. The calcium sulfate fraction was higher in the DF core than in the EDC core after ~17 kyr BP, suggesting that higher Patagonian dust contribution to the DF region. Abundant NaCl particles were found in the DF core in comparison with the EDC core from the LGM to early Holocene, possibly because of the high concentration of terrestrial dust in the DF core that reduced acid availability for seaâsalt modification. During the Holocene, the lower NaCl fraction and Clâ/Na+ ratio in the EDC core suggested that most Clâ was lost to the atmosphere from snow at Dome C, while it was preserved at Dome Fuji as NaCl and solid solution.Royal Society
E
Characterization and Improvement of the Image Quality of the Data Taken with the Infrared Camera (IRC) Mid-Infrared Channels onboard AKARI
Mid-infrared images frequently suffer artifacts and extended point spread
functions (PSFs). We investigate the characteristics of the artifacts and the
PSFs in images obtained with the Infrared Camera (IRC) onboard AKARI at four
mid-infrared bands of the S7 (7{\mu}m), S11 (11{\mu}m), L15 (15{\mu}m), and L24
(24 {\mu}m). Removal of the artifacts significantly improves the reliability of
the ref- erence data for flat-fielding at the L15 and L24 bands. A set of
models of the IRC PSFs is also constructed from on-orbit data. These PSFs have
extended components that come from diffraction and scattering within the
detector arrays. We estimate the aperture correction factors for point sources
and the surface brightness correction factors for diffuse sources. We conclude
that the surface brightness correction factors range from 0.95 to 0.8, taking
account of the extended component of the PSFs. To correct for the extended PSF
effects for the study of faint structures, we also develop an image
reconstruction method, which consists of the deconvolution with the PSF and the
convolution with an appropriate Gaussian. The appropriate removal of the
artifacts, improved flat-fielding, and image reconstruction with the extended
PSFs enable us to investigate de- tailed structures of extended sources in IRC
mid-infrared images.Comment: 35 pages, 15 figures, accepted for publication in PAS
Compositions of Dust and Sea Salts in the Dome C and Dome Fuji Ice Cores From Last Glacial Maximum to Early Holocene Based on IceâSublimation and SingleâParticle Measurements
We analyzed the chemical compositions of dust and seaâsalt particles in the EPICA Dome C (EDC) ice core during 26â7 kyr BP using an iceâsublimation technique and compared the results with existing data of the Dome Fuji (DF) ice core. Combined with ion concentration data, our data suggested similar seaâsalt fluxes in both cores and significantly lower dust flux in the EDC core. The differences in modal size and aspect ratio of dust particles between the two cores support the dominance of Patagonian source suggested by earlier works. The compositions of calcic dust showed major change at ~17 kyr BP, possibly reflecting a relative increase in dust transported via the upper troposphere. The calcium sulfate fraction was higher in the DF core than in the EDC core after ~17 kyr BP, suggesting that higher Patagonian dust contribution to the DF region. Abundant NaCl particles were found in the DF core in comparison with the EDC core from the LGM to early Holocene, possibly because of the high concentration of terrestrial dust in the DF core that reduced acid availability for seaâsalt modification. During the Holocene, the lower NaCl fraction and Clâ/Na+ ratio in the EDC core suggested that most Clâ was lost to the atmosphere from snow at Dome C, while it was preserved at Dome Fuji as NaCl and solid solution
AKARI-CAS --- Online Service for AKARI All-Sky Catalogues
The AKARI All-Sky Catalogues are an important infrared astronomical database
for next-generation astronomy that take over the IRAS catalog. We have
developed an online service, AKARI Catalogue Archive Server (AKARI-CAS), for
astronomers. The service includes useful and attractive search tools and visual
tools.
One of the new features of AKARI-CAS is cached SIMBAD/NED entries, which can
match AKARI catalogs with other catalogs stored in SIMBAD or NED. To allow
advanced queries to the databases, direct input of SQL is also supported. In
those queries, fast dynamic cross-identification between registered catalogs is
a remarkable feature. In addition, multiwavelength quick-look images are
displayed in the visualization tools, which will increase the value of the
service.
In the construction of our service, we considered a wide variety of
astronomers' requirements. As a result of our discussion, we concluded that
supporting users' SQL submissions is the best solution for the requirements.
Therefore, we implemented an RDBMS layer so that it covered important
facilities including the whole processing of tables. We found that PostgreSQL
is the best open-source RDBMS products for such purpose, and we wrote codes for
both simple and advanced searches into the SQL stored functions. To implement
such stored functions for fast radial search and cross-identification with
minimum cost, we applied a simple technique that is not based on dividing
celestial sphere such as HTM or HEALPix. In contrast, the Web application layer
became compact, and was written in simple procedural PHP codes. In total, our
system realizes cost-effective maintenance and enhancements.Comment: Yamauchi, C. et al. 2011, PASP..123..852
Multi-wavelength analysis of 18um-selected galaxies in the AKARI/IRC monitor field towards the North Ecliptic Pole
We present an initial analysis of AKARI 18um-selected galaxies using all 9
photometric bands at 2-24um available in the InfraRed Camera (IRC), in order to
demonstrate new capabilities of AKARI cosmological surveys. We detected 72
sources at 18um in an area of 50.2 arcmin^2 in the AKARI/IRC monitor field
towards the North Ecliptic Pole (NEP). From this sample, 25 galaxies with
probable redshifts z>~ 0.5 are selected with a single colour cut (N2-N3>0.1)
for a detailed SED analysis with ground-based BVRi'z'JK data. Using an SED
radiative transfer model of starbursts covering the wavelength range UV --
submm, we derive photometric redshifts from the optical-MIR SEDs of
18um-selected galaxies. From the best-fit SED models, we show that the IRC
all-band photometry is capable of tracing the steep rise in flux at the blue
side of the PAH 6.2um emission feature. This indicates that the IRC all-band
photometry is useful to constrain the redshift of infrared galaxies,
specifically for dusty galaxies with a less prominent 4000A break. Also, we
find that the flux dip between the PAH 7.7 and 11.2um emission feature is
recognizable in the observed SEDs of galaxies at z~1. By using such a colour
anomaly due to the PAH and silicate absorption features, unique samples of
ULIRGs at z~1, `silicate-break' galaxies, can be constructed from large
cosmological surveys of AKARI towards the NEP, i.e. the NEP-Deep and NEP-Wide
survey. This pilot study suggests the possibility of detecting many interesting
galaxy properties in the NEP-Deep and Wide surveys, such as a systematic
difference in SEDs between high- and low-z ULIRGs, and a large variation of the
PAH inter-band strength ratio in galaxies at high redshifts. [abridged]Comment: Accepted for publication in PASJ, AKARI special issu
The Infrared Camera (IRC) for AKARI - Design and Imaging Performance
The Infrared Camera (IRC) is one of two focal-plane instruments on the AKARI
satellite. It is designed for wide-field deep imaging and low-resolution
spectroscopy in the near- to mid-infrared (1.8--26.5um) in the pointed
observation mode of AKARI. IRC is also operated in the survey mode to make an
all-sky survey at 9 and 18um. It comprises three channels. The NIR channel
(1.8--5.5um) employs a 512 x 412 InSb array, whereas both the MIR-S
(4.6--13.4um) and MIR-L (12.6--26.5um) channels use 256 x 256 Si:As impurity
band conduction arrays. Each of the three channels has a field-of-view of about
10' x 10' and are operated simultaneously. The NIR and MIR-S share the same
field-of-view by virtue of a beam splitter. The MIR-L observes the sky about
$25' away from the NIR/MIR-S field-of-view. IRC gives us deep insights into the
formation and evolution of galaxies, the evolution of planetary disks, the
process of star-formation, the properties of interstellar matter under various
physical conditions, and the nature and evolution of solar system objects. The
in-flight performance of IRC has been confirmed to be in agreement with the
pre-flight expectation. This paper summarizes the design and the in-flight
operation and imaging performance of IRC.Comment: Publications of the Astronomical Society of Japan, in pres
The AKARI/IRC Mid-Infrared All-Sky Survey
Context : AKARI is the first Japanese astronomical satellite dedicated to
infrar ed astronomy. One of the main purposes of AKARI is the all-sky survey
performed with six infrared bands between 9 and 200um during the period from
2006 May 6 to
2007 August 28. In this paper, we present the mid-infrared part (9um and 18um
b ands) of the survey carried out with one of the on-board instruments, the
Infrar ed Camera (IRC). Aims : We present unprecedented observational results
of the 9 and 18um AKARI al l-sky survey and detail the operation and data
processing leading to the point s ource detection and measurements. Methods :
The raw data are processed to produce small images for every scan and point
sources candidates, above the 5-sigma noise level per single scan, are der
ived. The celestial coordinates and fluxes of the events are determined
statisti cally and the reliability of their detections is secured through
multiple detect ions of the same source within milli-seconds, hours, and months
from each other. Results : The sky coverage is more than 90% for both bands. A
total of 877,091 s ources (851,189 for 9um, 195,893 for 18um) are confirmed and
included in the cur rent release of the point source catalogue. The detection
limit for point source s is 50mJy and 90mJy for the 9um and 18um bands,
respectively. The position accu racy is estimated to be better than 2".
Uncertainties in the in-flight absolute flux calibration are estimated to be 3%
for the 9um band and 4% for the 18um ban d. The coordinates and fluxes of
detected sources in this survey are also compar ed with those of the IRAS
survey and found to be statistically consistent.Comment: Accepted for publication in AandA AKARI special issu
Fe II Emission in 14 Low-Redshift Quasars: I - Observations
We present the spectra of 14 quasars with a wide coverage of rest wavelengths
from 1000 to 7300 A. The redshift ranges from z = 0.061 to 0.555 and the
luminosity from M_{B} = -22.69 to -26.32. We describe the procedure of
generating the template spectrum of Fe II line emission from the spectrum of a
narrow-line Seyfert 1 galaxy I Zw 1 that covers two wavelength regions of
2200-3500 A and 4200-5600 A. Our template Fe II spectrum is semi-empirical in
the sense that the synthetic spectrum calculated with the CLOUDY
photoionization code is used to separate the Fe II emission from the Mg II
line. The procedure of measuring the strengths of Fe II emission lines is
twofold; (1) subtracting the continuum components by fitting models of the
power-law and Balmer continua in the continuum windows which are relatively
free from line emissions, and (2) fitting models of the Fe II emission based on
the Fe II template to the continuum-subtracted spectra. From 14 quasars, we
obtained the Fe II fluxes in five wavelength bands, the total flux of Balmer
continuum, and the fluxes of Mg II, Halpha, and other emission lines, together
with the full width at half maxima (FWHMs) of these lines. Regression analysis
was performed by assuming a linear relation between any two of these
quantities. Eight correlations were found with a confidence level higher than
99%. The fact that six of these eight are related to FWHM or M_{BH} may imply
that M_{BH} is a fundamental quantity that controls Gamma or the spectral
energy distribution (SED) of the incident continuum, which in turn controls the
Fe II emission. Furthermore, it is worthy of noting that Fe II(O1)/Fe II(U1) is
found to tightly correlate with Fe II(O1)/Mg II, but not with Fe II(U1)/Mg II.Comment: 50 pages, 10 figures, accepted for publication in Ap
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