• Publications of The Korean Astronomical Society
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• v.32 no.1
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• pp.321-326
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• 2017

We analyzed spectral data of the astrophysical diffuse emission obtained with the low-resolution spectroscopy mode on the AKARI InfraRed Camera (IRC) in the $1.8-5.3{\mu}m$ wavelength region. Advanced reduction methods specialized for slit spectroscopy of diffuse sky spectra have been developed, and a catalog of 278 spectra of the diffuse sky covering a wide range of Galactic and ecliptic latitudes was constructed. Using this catalog, two other major foreground components, the zodiacal light (ZL) and the diffuse Galactic light (DGL), were separated and subtracted by taking correlations with ZL brightness estimated by the DIRBE ZL model and with the $100{\mu}m$ dust thermal emission, respectively. The isotropic emission was interpreted as the extragalactic background light (EBL), which shows significant excess over the integrated light of galaxies at <$4{\mu}m$.

• Publications of The Korean Astronomical Society
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• v.24 no.1
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• pp.1-8
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• 2009

A plane-parallel model of the diffuse Galactic light (DGL) is calculated assuming exponential disks of interstellar dust and OB stars, by solving exactly the radiative transfer equation using an iterative method. We perform a radiative transfer calculation for a model with generally accepted scale heights of stellar and dust distribution and compare the results with those of van de Hulst & de Jong for a constant slab model. We also find that the intensity extrapolated to zero dust optical depth has a negative value, against to the usual expectation.

• Journal of The Korean Astronomical Society
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• v.22 no.2
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• pp.141-160
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• 1989

In order to derive time dependence of the atmospheric diffuse light, which consists of the airglow continuum emission and diffusely scattered radiations of the intergrated starlight, the diffuse Galactic light, and the zodiacal light, we have analyzed the meridian scan observations of the sky brightness at $5,080\;{\AA}$ and $5,300\;{\AA}$. Amplitude of the time-variation becomes larger for lower elevation, and maximum amplitude is found to be about $50\;S_{10}(V)_{G2V}$ at elevation $10^{\circ}$. The atmospheric diffuse radiation attains maximum brightness at around midnight, and afterward it decreases slowly with time. The time-variations for the two wavelengths are similar to each other. The observed brightness distribution of the diffuse light along the zenith distance is fitted to an empirical relation of two parameters. By making the two parameters time-dependent, we describe the spatial and time variations of the atmospheric diffuse light. This enables us to make time dependent correction for the atmospheric diffuse component in the reduction of zodiacal light brightness.

• Publications of The Korean Astronomical Society
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• v.27 no.4
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• pp.353-356
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• 2012

We present new constraints on the cosmic optical background (COB) obtained from an analysis of the Pioneer 10/11 Imaging Photopolarimeter (IPP) data. After careful examination of the data quality, the usable measurements free from the zodiacal light are integrated into sky maps at the blue (${\sim}0.44{\mu}m$) and red (${\sim}0.64{\mu}m$) bands. Accurate starlight subtraction was achieved by referring to all-sky star catalogs and a Galactic stellar population synthesis model down to 32.0 mag. We find that the residual light is separated into two components: one component shows a clear correlation with the thermal $100{\mu}m$ brightness, whilst the other shows a constant level in the lowest $100{\mu}m$ brightness region. The presence of the second component is significant after all the uncertainties and possible residual light in the Galaxy are taken into account, thus it most likely has an extragalactic origin (i.e., the COB). The derived COB brightness is ($(1.8{\pm}0.9){\times}10^{-9}$ and $(1.2{\pm}0.9){\times}10^{-9}\;erg\;s^{-1}\;cm^{-2}\;sr^{-1}\;{\AA}^{-1}$ in the blue and red spectral regions, respectively, or $7.9{\pm}4.0$ and $7.7{\pm}5.8\;nW\;m^{-2}\;sr^{-1}$. Based on a comparison with the integrated brightness of galaxies, we conclude that the bulk of the COB is comprised of normal galaxies which have already been resolved by the current deepest observations. There seems to be little room for contributions from other populations including "first stars" at these wavelengths. On the other hand, the first component of the IPP residual light represents the diffuse Galactic light (DGL)-scattered starlight by the interstellar dust. We derive the mean DGL-to-$100{\mu}m$ brightness ratios of $2.1{\times}10^{-3}$ and $4.6{\times}10^{-3}$ at the two bands, which are roughly consistent with previous observations toward denser dust regions. Extended red emission in the diffuse interstellar medium is also confirmed.

• Journal of The Korean Astronomical Society
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• v.48 no.1
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• pp.57-66
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• 2015

Monte-Carlo radiative models of the diffuse Galactic light (DGL) in our Galaxy are calculated using the dust radiative transfer code MoCafe, which is three-dimensional and takes full account of multiple scattering. The code is recently updated to use a fast voxel traversal algorithm, which has dramatically increased the computing speed. The radiative transfer models are calculated with the generally accepted dust scale-height of 0.1 kpc. The stellar scale-heights are assumed to be 0.1 or 0.35 kpc, appropriate for far-ultraviolet (FUV) and optical wavelengths, respectively. The face-on optical depth, measured perpendicular to the Galactic plane, is also varied from 0.2 to 0.6, suitable to the optical to FUV wavelengths, respectively. We find that the DGL at high Galactic latitudes is mostly due to backward or large-angle scattering of starlight originating from the local stars within a radial distance of r < 0.5 kpc from the Earth. On the other hand, the DGL measured in the Galactic plane is mostly due to stars at a distance range that corresponds to an optical depth of $${\sim_\sim}$$ 1 measured from the Earth. Therefore, the low-latitude DGL at the FUV wavelength band would be mostly caused by the stars located at a distance of $r{\leq}0.5$ kpc and the optical DGL near the Galactic plane mainly originates from stars within a distance range of $1{\leq}r{\leq}2kpc$. We also calculate the radiative transfer models in a clumpy two-phase medium. The clumpy two-phase models provide lower intensities at high Galactic latitudes compared to the uniform density models, because of the lower effective optical depth in clumpy media. However, no significant difference in the intensity at the Galactic plane is found.

• The Bulletin of The Korean Astronomical Society
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• v.27 no.1
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• pp.28-28
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• 2002

• Publications of The Korean Astronomical Society
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• v.27 no.4
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• pp.217-218
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• 2012

Among the AKARI all-sky survey data, the $9{\mu}m$ diffuse map is crucial to study the polycyclic aromatic hydrocarbon (PAH) emission features on large spatial scales, while the $18{\mu}m$ map is useful to trace hot dust emission. To utilize these advantages, we have improved the AKARI mid-infrared (MIR) all-sky survey diffuse maps. For example, we have established special methods to remove the effects of the ionizing radiation in the South Atlantic Anomaly (SAA) and of the scattered light from the moon. Using improved diffuse map data, we study the properties of PAHs and dust in the Galactic center region associated with high-energy phenomena.

• Publications of The Korean Astronomical Society
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• v.32 no.1
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• pp.59-61
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• 2017

The AKARI 9 and 18 µm diffuse maps reveal the all-sky distribution of the interstellar medium with relatively high spatial resolution of ~6". The zodiacal light is a dominant foreground component in the mid-infrared. Thus, removal of the zodiacal light is a critical issue to study low surface brightness Galactic diffuse emission. We carried out modeling of the zodiacal light based on the Kelsall model which is constructed from the COBE data. In the previous study, only a time-varying component of the zodiacal light brightness was used for determination of the model parameters. However, there remains a residual component of the zodiacal light around the ecliptic plane even after removal with the model. Therefore, instead of using a time-varying component, we use the absolute brightness of the zodiacal light and we find that the new model can better remove the residual component. As a result, the best-fit model parameters are changed from those in the previous study. We discuss the properties of the zodiacal light based on our new result.

• The Bulletin of The Korean Astronomical Society
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• v.38 no.1
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• pp.48.1-48.1
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• 2013

It is known that the diffuse $H{\alpha}$ emission outside of bright H II regions not only are very extended, but also can occur in distinct patches or filaments far from H II regions, and the line ratios of [S II] ${\lambda}6716/H{\alpha}$ and [N II] ${\lambda}6583/H{\alpha}$ observed far from bright H II regions are generally higher than those in the H II regions. These observations have been regarded as evidence against the dust-scattering origin of the diffuse $H{\alpha}$ emission (including other optical lines), and the effect of dust scattering has been neglected in studies on the diffuse $H{\alpha}$ emission. However, as opposed to the previous contention, the expected dust-scattered $H{\alpha}$ halos surrounding H II regions are, in fact, in good agreement with the observed $H{\alpha}$ morphology. We find that the observed line ratios of [S II]/$H{\alpha}$, [N II]/$H{\alpha}$, and He I ${\lambda}5876/H{\alpha}$ in the diffuse ISM accord well with the dust-scattered halos around H II regions, which are photoionized by late O- and/or early B-type stars. We also demonstrate that the $H{\alpha}$ absorption feature in the underlying continuum from the dust-scattered starlight ("diffuse galactic light") and unresolved stars is able to substantially increase the [S II]/$H{\alpha}$ and [N II]/$H{\alpha}$ line ratios in the diffuse ISM.

• Publications of The Korean Astronomical Society
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• v.27 no.4
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• pp.117-122
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• 2012

The interstellar dust grains are formed and supplied to interstellar space from asymptotic giant branch (AGB) stars or supernova remnants, and become constituents of the star- and planet-formation processes that lead to the next generation of stars. Both a qualitative, and a compositional study of this cycle are essential to understanding the origin of the pre-solar grains, the missing sources of the interstellar material, and the chemical evolution of our Galaxy. The AKARI/MIR all-sky survey was performed with two mid-infrared photometric bands centered at 9 and $18{\mu}m$. These data have advantages in detecting carbonaceous and silicate circumstellar dust of AGB stars, and the interstellar polycyclic aromatic hydrocarbons separately from large grains of amorphous silicate. By using the AKARI/MIR All-Sky point source catalogue, we surveyed C-rich and O-rich AGB stars in our Galaxy, which are the dominant suppliers of carbonaceous and silicate grains, respectively. The C-rich stars are uniformly distributed across the Galactic disk, whereas O-rich stars are concentrated toward the Galactic center, following the metallicity gradient of the interstellar medium, and are presumably affected by the environment of their birth place. We will compare the distributions of the dust suppliers with the distributions of the interstellar grains themselves by using the AKARI/MIR All-Sky diffuse maps. To enable discussions on the faint diffuse interstellar radiation, we are developing an accurate AKARI/MIR All-Sky diffuse map by correcting artifacts such as the ionising radiation effects, scattered light from the moon, and stray light from bright sources.