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Register a new userHydrogen recombination near-infrared line mapping of Centaurus A with IRSF/SIRIUS
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Centaurus A (Cen A) is one of the most famous galaxies hosting an active galactic nucleus (AGN), where the interaction between AGN activities and surrounding interstellar and intergalactic media has been investigated. Recent studies reported detections of the H{alpha} emission from clouds in the galactic halo toward the northeast and southwest of the nucleus of Cen A, suggesting that AGN jets may have triggered star formation there. We performed near-infrared line mapping of Cen A with the IRSF 1.4-m telescope, using the narrow-band filter tuned for Pa{beta}, from which we find that the Pa{beta} emission is not detected significantly from either northeast or southwest regions. The upper limit of the Pa{beta}/H{alpha} ratio in the northeast region is compatible with that expected for a typical HII region, in line with the scenario that AGNs have triggered star formation there. On the other hand, the upper limit of Pa{beta}/H{alpha} in the southwest region is significantly lower than that expected for a typical HII region. A possibility to explain the low Pa{beta}/H{alpha} ratio in the southwest region is the scattering of H{alpha} and Pa{beta} photons from the center of Cen A by dust grains in the halo clouds. From the upper limit of Pa{beta}/H{alpha} in the southwest region, we obtain constraints on the dust size distribution, which is found to be compatible with those seen in the interstellar medium of our Galaxy.
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We investigate properties of the interstellar medium (ISM) interacting with shocks around the Galactic supernova remnant IC443, using the results of near-infrared [FeII] and H2 line mapping with the IRSF/SIRIUS. In the present study, we newly performed H2 1-0 S(1) and 2-1 S(1) line mapping with the narrow-band filters tuned for these lines, covering the entire remnant (30x35). Combined with an [FeII] line map, our result shows that the H2 line emission is significantly detected in the southern region, while the [FeII] line emission is detected all over the remnant, suggesting that slow and fast shocks propagate through the southern region and the entire remnant, respectively. In particular, the H2 line emission is relatively strong compared to the [FeII] line emission in the southwestern region, where TeV gamma-ray emission is detected. As the strong H2 line emission indicates the dominance of the dense ISM, this result supports the scenario that the gamma-ray emission is likely to be produced through a heavy interaction between cosmic-ray protons and the dense ISM in the southwestern shell. We also find that the H2 and [FeII] line emissions show an anti-correlated spatial distribution in the same region, suggesting the presence of the clumpy ISM. Such a clumpy morphology of the ISM around IC443 may assist cosmic-ray protons to efficiently interact with large amounts of the ISM protons.
We present the result of near-infrared (near-IR) [Fe II] line mapping of the supernova remnant IC443 with the IRSF/SIRIUS, using the two narrow-band filters tuned for the [Fe II] 1.257 micron and [Fe II] 1.644 micron lines. Covering a large area of 30 x 35, our observations reveal that [Fe II] filamentary structures exist all over the remnant, not only in an ionic shock shell, but also in a molecular shock shell and a central region inside the shells. With the two [Fe II] lines, we performed corrections for dust extinction to derive the intrinsic line intensities. We also obtained the intensities of thermal emission from the warm dust associated with IC443, using the far- and mid-IR images taken with AKARI and Spitzer, respectively. As a result, we find that the [Fe II] line emission relative to the dust emission notably enhances in the inner central region. We discuss causes of the enhanced [Fe II] line emission, estimating the Fe+ and dust masses.
We conducted systematic observations of the H I Br$alpha$ (4.05 $mu$m) and Br$beta$ (2.63 $mu$m) lines in 52 nearby ($z<0.3$) ultraluminous infrared galaxies (ULIRGs) with AKARI. Among 33 ULIRGs wherein the lines are detected, three galaxies show anomalous Br$beta$/Br$alpha$ line ratios ($sim1.0$), which are significantly higher than those for case B (0.565). Our observations also show that ULIRGs have a tendency to exhibit higher Br$beta$/Br$alpha$ line ratios than those observed in Galactic H II regions. The high Br$beta$/Br$alpha$ line ratios cannot be explained by a combination of dust extinction and case B since dust extinction reduces the ratio. We explore possible causes for the high Br$beta$/Br$alpha$ line ratios and show that the observed ratios can be explained by a combination of an optically thick Br$alpha$ line and an optically thin Br$beta$ line. We simulated the H II regions in ULIRGs with the Cloudy code, and our results show that the high Br$beta$/Br$alpha$ line ratios can be explained by high-density conditions, wherein the Br$alpha$ line becomes optically thick. To achieve a column density large enough to make the Br$alpha$ line optically thick within a single H II region, the gas density must be as high as $nsim10^8$ $mathrm{cm}^{-3}$. We therefore propose an ensemble of H II regions, in each of which the Br$alpha$ line is optically thick, to explain the high Br$beta$/Br$alpha$ line ratio.
We present a dust extinction AV map of the Large Magellanic Cloud (LMC) in the H I ridge region using the IRSF near-infrared (IR) data, and compare the AV map with the total hydrogen column density N(H) maps derived from the CO and H I observations. In the LMC H I ridge region, the two-velocity H I components (plus an intermediate velocity component) are identified, and the young massive star cluster is possibly formed by collision between them. In addition, one of the components is suggested to be an inflow gas from the Small Magellanic Cloud (SMC) which is expected to have even lower metallicity gas (Fukui et al. 2017, PASJ, 69, L5). To evaluate dust/gas ratios in the H I ridge region in detail, we derive the AV map from the near-IR color excess of the IRSF data updated with the latest calibration, and fit the resultant AV map with a combination of the N(H) maps of the different velocity components to successfully decompose it into the 3 components. As a result, we find difference by a factor of 2 in AV /N(H) between the components. In additon, the CO-to-H2 conversion factor also indicates difference between the components, implying the difference in the metallicity. Our results are likely to support the scenario that the gas in the LMC H I ridge region is contaminated with an inflow gas from the SMC with a geometry consistent with the on-going collision between the two velocity components.
We report high precision transit photometry of GJ1214b in JHKs bands taken simultaneously with the SIRIUS camera on the IRSF 1.4m telescope at Sutherland, South Africa. Our MCMC analyses show that the observed planet-to-star radius ratios in JHKs bands are R_{rm p}/R_{rm s,J} = 0.11833 pm 0.00077, R_{rm p}/R_{rm s,H} = 0.11522 pm 0.00079, R_{rm p}/R_{rm s,Ks} = 0.11459 pm 0.00099, respectively. The radius ratios are well consistent with the previous studies by Bean et al. (2011) within 1sigma, while our result in Ks band is shallower than and inconsistent at 4sigma level with the previous measurements in the same band by Croll et al. (2011). We have no good explanation for this discrepancy at this point. Our overall results support a flat transmission spectrum in the observed bands, which can be explained by a water-dominated atmosphere or an atmosphere with extensive high-altitude clouds or haze. To solve the discrepancy of the radius ratios and to discriminate a definitive atmosphere model for GJ1214b in the future, further transit observations around Ks band would be especially important.
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