Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userFirst Detection of Galactic Latitude Dependence of Near-Infrared Diffuse Galactic Light from DIRBE Reanalysis
61
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Observational study on near-infrared (IR) scattering properties of interstellar dust grains has been limited due to its faintness. Using all-sky maps obtained from Diffuse Infrared Background Experiment (DIRBE), we investigate the scattering property from diffuse Galactic light (DGL) measurements at 1.25, 2.2, and 3.5 {mu}m in addition to our recent analyses of diffuse near-IR emission (Sano et al. 2015; Sano et al. 2016). As a result, we first find that the intensity ratios of near-IR DGL to 100 {mu}m emission increase toward low Galactic latitudes at 1.25 and 2.2 {mu}m. The derived latitude dependence can be reproduced by a scattered light model of interstellar dust with a large scattering asymmetry factor g = <cos{theta}> of $0.8^{+0.2}_{-0.3}$ at 1.25 and 2.2 {mu}m, assuming an infinite Galaxy disk as an illuminating source. The derived asymmetry factor is comparable to the values obtained in the optical, but several times larger than that expected from a recent dust model. Since possible latitude dependence of ultraviolet-excited dust emission at 1.25 and 2.2 {mu}m would reduce the large asymmetry factor to the reasonable value, our result may indicate the first detection of such an additional emission component in the diffuse interstellar medium.
rate research
Read More
Near-infrared (IR) diffuse Galactic light (DGL) consists of scattered light and thermal emission from interstellar dust grains illuminated by interstellar radiation field (ISRF). At 1.25 and 2.2um, recent observational study shows that intensity ratios of the DGL to interstellar 100um dust emission steeply decrease toward high Galactic latitudes (b). In this paper, we investigate origin(s) of the b-dependence on the basis of models of thermal emission and scattered light. Combining a thermal emission model with regional variation of the polycyclic aromatic hydrocarbon abundance observed with Planck, we show that contribution of the near-IR thermal emission component to the observed DGL is less than ~20%. We also examine the b-dependence of the scattered light, assuming a plane-parallel Galaxy with smooth distributions of the ISRF and dust density along vertical direction, and assuming a scattering phase function according to a recently developed model of interstellar dust. We normalize the scattered light intensity to the 100um intensity corrected for deviation from the cosecant-b law according to the Planck observation. As the result, the present model taking all the b-dependence of dust and ISRF properties can account for the observed b-dependence of the near-IR DGL. However, uncertainty of the correction for the 100um emission is large and other normalizing quantities may be appropriate for more robust analysis of the DGL.
We report near-infrared (IR) observations of high Galactic latitude clouds to investigate diffuse Galactic light (DGL), which is starlight scattered by interstellar dust grains. The observations were performed at $1.1$ and $1.6,rm{mu m}$ with a wide-field camera instrument, the Multi-purpose Infra-Red Imaging System (MIRIS) onboard the Korean satellite STSAT-3. The DGL brightness is measured by correlating the near-IR images with a far-IR $100,rm{mu m}$ map of interstellar dust thermal emission. The wide-field observation of DGL provides the most accurate DGL measurement achieved to date. We also find a linear correlation between optical and near-IR DGL in the MBM32 field. To study interstellar dust properties in MBM32, we adopt recent dust models with or without $rm{mu m}$-sized very large grains and predict the DGL spectra, taking into account reddening effect of interstellar radiation field. The result shows that observed color of the near-IR DGL is closer to the model spectra without very large grains. This may imply that dust growth in the observed MBM32 field is not active owing to its low density of interstellar medium.
We have conducted B, g, V, and R-band imaging in a 45x40 arcmin^2 field containing part of the high Galactic latitude translucent cloud MBM32, and correlated the intensity of diffuse optical light S_ u(lambda) with that of 100 micron emission S_ u(100um). A chi^2 minimum analysis is applied to fit a linear function to the measured correlation and derive the slope parameter b(lambda)= Delta S_ u(lambda) / Delta S_ u(100um) of the best-fit linear function. Compiling a sample by combining our b(lambda) and published ones, we show that the b(lambda) strength varies from cloud to cloud by a factor of 4. Finding that b(lambda) decreases as S_ u(100um) increases in the sample, we suggest that a non-linear correlation including a quadratic term of S_ u(100um)^2 should be fitted to the measured correlation. The variation of optical depth, which is A_V = 0.16 - 2.0 in the sample, can change b(lambda) by a factor of 2 - 3. There would be some contribution to the large b(lambda) variation from the forward-scattering characteristic of dust grains which is coupled to the non-isotropic interstellar radiation field (ISRF). Models of the scattering of diffuse Galactic light (DGL) underestimate the b(lambda) values by a factor of 2. This could be reconciled by deficiency in UV photons in the ISRF or by a moderate increase in dust albedo. Our b(lambda) spectrum favors a contribution from extended red emission (ERE) to the diffuse optical light; b(lambda) rises from B to V faster than the models, seems to peak around 6000 AA, and decreases towards long wavelengths. Such a characteristic is expected from the models in which the DGL is combined with ERE.
We reanalyze data of near-infrared background taken by Infrared Telescope in Space (IRTS) based on up-to-date observational results of zodiacal light, integrated star light and diffuse Galactic light. We confirm the existence of residual isotropic emission, which is slightly lower but almost the same as previously reported. At wavelengths longer than 2 {mu}m, the result is fairly consistent with the recent observation with AKARI. We also perform the same analysis using a different zodiacal light model by Wright and detected residual isotropic emission that is slightly lower than that based on the original Kelsall model. Both models show the residual isotropic emission that is significantly brighter than the integrated light of galaxies.
Using all-sky maps obtained from COBE/DIRBE at 3.5 and 4.9 um, we present a reanalysis of diffuse sky emissions such as zodiacal light (ZL), diffuse Galactic light (DGL), integrated starlight (ISL), and isotropic residual emission including the extragalactic background light (EBL). Our new analysis, which includes an improved estimate of ISL using the Wide-field Infrared Survey Explorer (WISE) data, enabled us to find the DGL signal in a direct linear correlation between diffuse near-infrared and 100 um emission at high Galactic latitudes (|b| > 35 degree). At 3.5um, the high-latitude DGL result is comparable to the low-latitude value derived from the previous DIRBE analysis. In comparison with models of the DGL spectrum assuming a size distribution of dust grains composed of amorphous silicate, graphite, and polycyclic aromatic hydrocarbon (PAH), the measured DGL values at 3.5 and 4.9 um constrain the mass fraction of PAH particles in the total dust species to be more than ~ 2%. This was consistent with the results of Spitzer/IRAC toward the lower Galactic latitude regions. The derived residual emission of 8.9 +/- 3.4 nW m^{-2} sr^{-1} at 3.5 um is marginally consistent with the level of integrated galaxy light and the EBL constraints from the gamma-ray observations. The residual emission at 4.9 um is not significantly detected due to the large uncertainty in the ZL subtraction, same as previous studies. Combined with our reanalysis of the DIRBE data at 1.25 and 2.2 um, the residual emission in the near-infrared exhibits the Rayleigh-Jeans spectrum.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
