Search

We derive the entire dust extinction (Av) map for the Large Magellanic Cloud (LMC) estimated from the color excess at near-infrared wavelengths. Using the percentile method we recently adopted to evaluate Av distribution along the line of sight, we derive the three-dimensional(3D)Av maps of the three massive star forming regions of N44, N79 and N11 based on the IRSF/SIRIUS point source catalog. The 3D AV maps are compared with the hydrogen column densities N(H) of three different velocity components where one is of the LMC disk velocity and the other two are of velocities lower than the disk velocity. As a result, we obtain 3D dust geometry suggesting that gas collision is on-going between the different velocity components. We also find difference in the timing of the gas collision between the massive star forming regions, which indicates that the gas collision in N44, N79 and N11 occurred later than that in 30 Doradus. In addition, difference by a factor of two in Av/N(H) is found between the velocity components for N44, while significant difference is not found for N79 and N11. From the 3D geometry and Av/N(H) in each star forming region, we suggest that the massive star formation in N44 was induced by an external trigger of tidal interaction between the LMC and the SMC, while that in N79 and N11 is likely to have been induced by internal triggers such as gas converging from the galactic spiral arm and expansion of a supershell although the possibility of tidal interaction cannot be ruled out., 20 pages, 17 figures, accepted for publication in PASJ

The physical origin of the overionized recombining plasmas (RPs) in supernova remnants (SNRs) has been attracting attention because its understanding provides new insight into SNR evolution. However, the process of the overionization, although it has been discussed in some RP-SNRs, is not yet fully understood. Here we report on spatially resolved spectroscopy of X-ray emission from IC~443 with {\it XMM-Newton}. We find that RPs in regions interacting with dense molecular clouds tend to have lower electron temperature and lower recombination timescale. These tendencies indicate that RPs in these regions are cooler and more strongly overionized, which is naturally interpreted as a result of rapid cooling by the molecular clouds via thermal conduction. Our result on IC~443 is similar to that on W44 showing evidence for thermal conduction as the origin of RPs at least in older remnants. We suggest that evaporation of clumpy gas embedded in a hot plasma rapidly cools the plasma as was also found in the W44 case. We also discuss if ionization by protons accelerated in IC~443 is responsible for RPs. Based on the energetics of particle acceleration, we conclude that the proton bombardment is unlikely to explain the observed properties of RPs., 11 pages, 10 figures, 4 tables, accepted for publication in ApJ. arXiv admin note: text overlap with arXiv:1912.08129

We present a new method to evaluate the dust extinction (AV) along the line of sight using the InfraRed Survey Facility (IRSF) near-infrared (NIR) data of the Large Magellanic Cloud (LMC) HI ridge region. In our method, we estimate an AV value for each star from the NIR color excess and sort them from bluer to redder in each line of sight. Using the percentile values of the sorted AV, we newly construct the three-dimensional AV map. We compare the resultant AV map with the total hydrogen column density N(H) traced by velocity-resolved HI and CO observations. In the LMC HI ridge region, Fukui et al. (2017, PASJ, 69, L5) find two velocity components and an intermediate velocity one bridging them. Comparing our three-dimensional AV maps with N(H) maps at the different velocities, we find that the dust geometry is consistent with the scenario of the on-going gas collision between the two velocities as suggested in the previous study. In addition, we find difference by a factor of 2 in AV/N(H) between the two velocity components, which suggests that inflow gas from the Small Magellanic Clouds (SMC) is mixed in this region. As a whole, our results support the triggered star formation in 30 Doradus due to the large-scale gas collision caused by tidal interaction between the LMC and the SMC., 18 pages, 16 figures, accepted for publication in PASJ

Heavily obscured active galactic nuclei (AGNs) are known to show deep silicate absorption features in the mid-infrared (IR) wavelength range of 10--20~$\mu$m. The detailed profiles of the features reflect the properties of silicate dust, which are likely to include information on AGN activities obscured by large amounts of dust. In order to reveal AGN activities obscured by large amounts of dust, we select 115 mid-IR spectra of heavily obscured AGNs observed by Spitzer/IRS, and systematically analyze the composition of silicate dust by spectral fitting using the 10~$\mu$m amorphous and 23~$\mu$m crystalline bands. We find that the main component of the silicate dust obscuring AGNs is amorphous olivine, the median mass column density of which is one order of magnitude higher than those of the minor components of amorphous pyroxene and crystalline forsterite. The median mass fraction of the amorphous pyroxene, $\sim$2\%, is significantly lower than that of the diffuse interstellar medium (ISM) dust in our Galaxy, while the median mass fraction of the crystalline forsterite, $\sim$6\%, is higher than that of the diffuse ISM dust. We also find that the mass fractions of the amorphous pyroxene and the crystalline forsterite positively correlate with each other. The low mass fraction of the amorphous pyroxene suggests that the obscuring silicate dust is newly formed, originating from starburst activities. The relatively high mass fraction of crystalline forsterite implies that the silicate dust is processed in the high temperature environment close to the nucleus and transported to outer cooler regions by molecular outflows. The positive correlation between the mass fractions can be naturally explained considering that amorphous pyroxene is transformed from crystalline forsterite by ion bombardments., Comment: 22 pages, 6 figures, accepted for publication in A&A

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., Comment: 11 pages, 2 figures, accepted for publication in PASJ, typos corrected

We used a data set from AKARI and Herschel images at wavelengths from 7 $\mu$m to 500 $\mu$m to catch the evidence of dust processing in galactic winds in NGC 1569. Images show a diffuse infrared (IR) emission extending from the galactic disk into the halo region. The most prominent filamentary structure seen in the diffuse IR emission is spatially in good agreement with the western H$\alpha$ filament (western arm). The spatial distribution of the $F_\mathrm{350}/F_\mathrm{500}$ map shows high values in regions around the super-star clusters (SSCs) and towards the western arm, which are not found in the $F_\mathrm{250}/F_\mathrm{350}$ map. The color-color diagram of $F_\mathrm{250}/F_\mathrm{350}$-$F_\mathrm{350}/F_\mathrm{500}$ indicates high values of the emissivity power-law index ($\beta_\mathrm{c}$) of the cold dust component in those regions. From a spectral decomposition analysis on a pixel-by-pixel basis, a $\beta_\mathrm{c}$ map shows values ranging from $\sim1$ to $\sim2$ over the whole galaxy. In particular, high $\beta_\mathrm{c}$ values of $\sim2$ are only observed in the regions indicated by the color-color diagram. Since the average cold dust temperature in NGC 1569 is $\sim30$ K, $\beta_\mathrm{c}, Comment: 13 pages, 11 figures, MNRAS accepted for publication