70 research outputs found
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
J- and Ks-band Galaxy Counts and Color Distributions in the AKARI North Ecliptic Pole Field
We present the J- and Ks-band galaxy counts and galaxy colors covering 750
square arcminutes in the deep AKARI North Ecliptic Pole (NEP) field, using the
FLoridA Multi-object Imaging Near-ir Grism Observational Spectrometer
(FLAMINGOS) on the Kitt Peak National Observatory (KPNO) 2.1m telescope. The
limiting magnitudes with a signal-to-noise ratio of three in the deepest
regions are 21.85 and 20.15 in the J- and Ks-bands respectively in the Vega
magnitude system. The J- and Ks-band galaxy counts in the AKARI NEP field are
broadly in good agreement with those of other results in the literature,
however we find some indication of a change in the galaxy number count slope at
J~19.5 and over the magnitude range 18.0 < Ks < 19.5. We interpret this feature
as a change in the dominant population at these magnitudes because we also find
an associated change in the B - Ks color distribution at these magnitudes where
the number of blue samples in the magnitude range 18.5 < Ks < 19.5 is
significantly larger than that of Ks < 17.5
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
Infrared luminosity functions of AKARI Sloan Digital Sky Survey galaxies
By cross-correlating the AKARI all-sky survey in six infrared (IR) bands (9, 18, 65, 90, 140 and 160 μm) with the Sloan Digital Sky Survey (SDSS) galaxies, we identified 2357 IR galaxies with a spectroscopic redshift. This is not just one of the largest samples of local IR galaxies, but AKARI provides crucial far-IR (FIR) bands for accurately measuring the galaxy spectral energy distribution (SED) across the peak of the dust emission at > 100 μ m. By fitting modern IR SED models to the AKARI photometry, we measured the total infrared luminosity (L_(IR)) of individual galaxies. Using this L_(IR), we constructed the luminosity functions (LF) of IR galaxies at a median redshift of z= 0.031. The LF agrees well with that at z= 0.0082 (the Revised Bright Galaxy Sample), showing smooth and continuous evolution towards higher redshift LFs measured in the AKARI North Ecliptic Pole (NEP) deep field. By integrating the IR LF weighted by L_(IR), we measured the local cosmic IR luminosity density of Ω_(IR_= (3.8^(+5.8)_(−1.2)) × 10^8 L_⊙ Mpc^(−3). We separate galaxies into active galactic nuclei (AGN), star-forming galaxies (SFG) and composite by using the [N ii]/Hα versus [O iii]/Hβ line ratios. The fraction of AGN shows a continuous increase with increasing L_(IR) from 25 to 90 per cent at 9 10^(11) L_⊙, coinciding with the break of both the SFG and AGN IR LFs. At L_(IR)≤ 10^(11) L_⊙, SFG dominates IR LFs. Only 1.1 ± 0.1 per cent of Ω_(IR) is produced by luminous infrared galaxies (L_(IR) > 10^(11) L_⊙), and only 0.03 ± 0.01 per cent by ultraluminous infrared galaxies (L_(IR) > 10^(12) L_⊙) in the local Universe. Compared with high-redshift results from the AKARI NEP deep survey, we observed a strong evolution of Ω^(SFG)IR^∝ (1 +z)^(4.1±0.4) and Ω^(AGN)IR^∝ (1+z)^(4.1±0.5). Our results show that all of our measured quantities (IR LFs, L^*, Ω^(AGN)IR, Ω^(SFG)IR) show smooth and steady increase from lower redshift (the Revised Bright Galaxy Sample) to higher redshift (the AKARI NEP deep survey)
Number Density Evolution of Ks -band Selected High Redshift Galaxy Populations in the AKARI North Ecliptic Pole Field
We present the number counts of Ks-band selected high redshift galaxy
populations such as extremely red objects (EROs), B, z & K -band selected
galaxies (BzKs) and distant red galaxies (DRGs) in the AKARI NEP field. The
final catalogue contains 308 EROs (Ks<19.0 ; 54 percent are dusty star-forming
EROs and the rest are passive old EROs), 137 star-forming BzKs and 38 passive
old BzKs (Ks<19.0) and 64 DRGs (Ks<18.6). We also produce individual component
source counts for both the dusty star-forming and passive populations. We
compare the observed number counts of the high redshift passively evolving
galaxy population with a backward pure luminosity evolution (PLE) model
allowing different degrees of number density evolution. We find that the PLE
model without density evolution fails to explain the observed counts at faint
magnitudes, while the model incorporating negative density evolution is
consistent with the observed counts of the passively evolving population. We
also compare our observed counts of dusty star-forming EROs with a
phenomenological evolutionary model postulating that the near-infrared EROs can
be explained by the source densities of the far-infrared - submillimetre
populations. Our model predicts that the dusty ERO source counts can be
explained assuming a 25 percent contribution of submillimetre star-forming
galaxies with the majority of brighter Ks -band detected dusty EROs having
luminous (rather than HR10 type ultra-luminous) submillimetre counterparts. We
propose that the fainter Ks>19.5 population is dominated by the sub-millijansky
submillimetre population. We also predict a turnover in in dusty ERO counts
around 19<Ks<20.Comment: (37 pages, 14 figures accepted for publication in The Astrophysical
Journal
Introduction to special section on Recent Advances in the Study of Optical Variability in the Near-Surface and Upper Ocean
Optical variability occurs in the near-surface and upper ocean on very short time and space scales (e.g., milliseconds and millimeters and less) as well as greater scales. This variability is caused by solar, meteorological, and other physical forcing as well as biological and chemical processes that affect optical properties and their distributions, which in turn control the propagation of light across the air-sea interface and within the upper ocean. Recent developments in several technologies and modeling capabilities have enabled the investigation of a variety of fundamental and applied problems related to upper ocean physics, chemistry, and light propagation and utilization in the dynamic near-surface ocean. The purpose here is to provide background for and an introduction to a collection of papers devoted to new technologies and observational results as well as model simulations, which are facilitating new insights into optical variability and light propagation in the ocean as they are affected by changing atmospheric and oceanic conditions
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