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Register a new userALMA CO Observations of Supernova Remnant N63A in the Large Magellanic Cloud: Discovery of Dense Molecular Clouds Embedded within Shock-Ionized and Photoionized Nebulae
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We carried out new $^{12}$CO($J$ = 1-0, 3-2) observations of a N63A supernova remnant (SNR) from the LMC using ALMA and ASTE. We find three giant molecular clouds toward the northeast, east, and near the center of the SNR. Using the ALMA data, we spatially resolved clumpy molecular clouds embedded within the optical nebulae in both the shock-ionized and photoionized lobes discovered by previous H$alpha$ and [S II] observations. The total mass of the molecular clouds is $sim$$800$ $M_{odot}$ for the shock-ionized region and $sim$$1700$ $M_{odot}$ for the photoionized region. Spatially resolved X-ray spectroscopy reveals that the absorbing column densities toward the molecular clouds are $sim$$1.5$-$6.0times10^{21}$ cm$^{-2}$, which are $sim$$1.5$-$15$ times less than the averaged interstellar proton column densities for each region. This means that the X-rays are produced not only behind the molecular clouds, but also in front of them. We conclude that the dense molecular clouds have been completely engulfed by the shock waves, but have still survived erosion owing to their high-density and short interacting time. The X-ray spectrum toward the gas clumps is well explained by an absorbed power-law or high-temperature plasma models in addition to the thermal plasma components, implying that the shock-cloud interaction is efficiently working for both the cases through the shock ionization and magnetic field amplification. If the hadronic gamma-ray is dominant in the GeV band, the total energy of cosmic-ray protons is calculated to be $sim$$0.3$-$1.4times10^{49}$ erg with the estimated ISM proton density of $sim$$190pm90$ cm$^{-3}$, containing both the shock-ionized gas and neutral atomic hydrogen.
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N132D is the brightest gamma-ray supernova remnant (SNR) in the Large Magellanic Cloud (LMC). We carried out $^{12}$CO($J$ = 1-0, 3-2) observations toward the SNR using the Atacama Large Millimeter/submillimeter Array (ALMA) and Atacama Submillimeter Telescope Experiment. We find diffuse CO emission not only at the southern edge of the SNR as previously known, but also inside the X-ray shell. We spatially resolved nine molecular clouds using ALMA with an angular resolution of $5$, corresponding to a spatial resolution of $sim$1 pc at the distance of the LMC. Typical cloud sizes and masses are $sim$2.0 pc and $sim$100 $M_odot$, respectively. High-intensity ratios of CO $J$ = 3-2 / 1-0 $> 1.5$ are seen toward the molecular clouds, indicating that shock-heating has occurred. Spatially resolved X-ray spectroscopy reveals that thermal X-rays in the center of N132D are produced not only behind a molecular cloud, but also in front of it. Considering the absence of a thermal component associated with the forward shock towards one molecular cloud located along the line of sight to the center of the remnant, this suggests that this particular cloud is engulfed by shock waves and is positioned on the near side of remnant. If the hadronic process is the dominant contributor to the gamma-ray emission, the shock-engulfed clouds play a role as targets for cosmic-rays. We estimate the total energy of cosmic-ray protons accelerated in N132D to be $sim$0.5-$3.8 times 10^{49}$ erg as a conservative lower limit, which is similar to that observed in Galactic gamma-ray SNRs.
RX J0046.5$-$7308 is a shell-type supernova remnant (SNR) in the Small Magellanic Cloud (SMC). We carried out new $^{12}$CO($J$ = 1-0, 3-2) observations toward the SNR using Mopra and the Atacama Submillimeter Telescope Experiment. We found eight molecular clouds (A-H) along the X-ray shell of the SNR. The typical cloud size and mass are $sim$10-15 pc and $sim$1000-3000 $M_{odot}$, respectively. The X-ray shell is slightly deformed and has the brightest peak in the southwestern shell where two molecular clouds A and B are located. The four molecular clouds A, B, F, and G have high intensity ratios of $^{12}$CO($J$ = 3-2) / $^{12}$CO($J$ = 1-0) $> 1.2$, which are not attributable to any identified internal infrared sources or high-mass stars. The HI cavity and its expanding motion are found toward the SNR, which are likely created by strong stellar winds from a massive progenitor. We suggest that the molecular clouds A-D, F, and G and HI clouds within the wind-blown cavity at $V_mathrm{LSR} = 117.1$-122.5 km s$^{-1}$ are to be associated with the SNR. The X-ray spectroscopy reveals the dynamical age of $26000^{+1000}_{-2000}$ yr and the progenitor mass of $gtrsim 30$ $M_{odot}$, which is also consistent with the proposed scenario. We determine physical conditions of the giant molecular cloud LIRS 36A using the large velocity gradient analysis with archival datasets of the Atacama Large Millimeter/submillimeter Array; the kinematic temperature is $72^{+50}_{-37}$ K and the number density of molecular hydrogen is $1500^{+600}_{-300}$ cm$^{-3}$. The next generation of $gamma$-ray observations will allow us to study the pion-decay $gamma$-rays from the molecular clouds in the SMC SNR.
We present high-resolution (sub-parsec) observations of a giant molecular cloud in the nearest star-forming galaxy, the Large Magellanic Cloud. ALMA Band 6 observations trace the bulk of the molecular gas in $^{12}$CO(2-1) and high column density regions in $^{13}$CO(2-1). Our target is a quiescent cloud (PGCC G282.98-32.40, which we refer to as the Planck cold cloud or PCC) in the southern outskirts of the galaxy where star-formation activity is very low and largely confined to one location. We decompose the cloud into structures using a dendrogram and apply an identical analysis to matched-resolution cubes of the 30 Doradus molecular cloud (located near intense star formation) for comparison. Structures in the PCC exhibit roughly 10 times lower surface density and 5 times lower velocity dispersion than comparably sized structures in 30 Dor, underscoring the non-universality of molecular cloud properties. In both clouds, structures with relatively higher surface density lie closer to simple virial equilibrium, whereas lower surface density structures tend to exhibit super-virial line widths. In the PCC, relatively high line widths are found in the vicinity of an infrared source whose properties are consistent with a luminous young stellar object. More generally, we find that the smallest resolved structures (leaves) of the dendrogram span close to the full range of line widths observed across all scales. As a result, while the bulk of the kinetic energy is found on the largest scales, the small-scale energetics tend to be dominated by only a few structures, leading to substantial scatter in observed size-linewidth relationships.
In order to precisely determine temperature and density of molecular gas in the Large Magellanic Cloud, we made observations of optically thin $^{13}$CO($J=3-2$) transition by using the ASTE 10m telescope toward 9 peaks where $^{12}$CO($J=3-2$) clumps were previously detected with the same telescope. The molecular clumps include those in giant molecular cloud (GMC) Types I (with no signs of massive star formation), II (with HII regions only), and III (with HII regions and young star clusters). We detected $^{13}$CO($J=3-2$) emission toward all the peaks and found that their intensities are 3 -- 12 times lower than those of $^{12}$CO($J=3-2$). We determined the intensity ratios of $^{12}$CO($J=3-2$) to $^{13}$CO($J=3-2$), $R^{12/13}_{3-2}$, and $^{13}$CO($J=3-2$) to $^{13}$CO($J=1-0$), $R^{13}_{3-2/1-0}$, at 45$arcsec$ resolution. These ratios were used for radiative transfer calculations in order to estimate temperature and density of the clumps. The parameters of these clumps range kinetic temperature $Tmathrm{_{kin}}$ = 15 -- 200 K, and molecular hydrogen gas density $n(mathrm{H_2})$ = 8$times 10^2$ -- 7$times 10^3$ cm$^{-3}$. We confirmed that the higher density clumps show higher kinetic temperature and that the lower density clumps lower kinetic temperature at a better accuracy than in the previous work. The kinetic temperature and density increase generally from a Type I GMC to a Type III GMC. We interpret that this difference reflects an evolutionary trend of star formation in molecular clumps. The $R^{13}_{3-2/1-0}$ and kinetic temperature of the clumps are well correlated with H$alpha$ flux, suggesting that the heating of molecular gas $n(mathrm{H_2})$ = $10^3$ -- $10^4$ cm$^{-3}$ can be explained by stellar FUV photons.
We carried out $^{12}$CO($J$ = 1-0) observations of the Galactic gamma-ray supernova remnant (SNR) Kesteven 79 using the Nobeyama Radio Observatory 45 m radio telescope, which has an angular resolution of $sim20$ arcsec. We identified molecular and atomic gas interacting with Kesteven 79 whose radial velocity is $sim80$ km s$^{-1}$. The interacting molecular and atomic gases show good spatial correspondence with the X-ray and radio shells, which have an expanding motion with an expanding velocity of $sim4$ km s$^{-1}$. The molecular gas associated with the radio and X-ray peaks also exhibits a high-intensity ratio of CO 3-2/1-0 $>$ 0.8, suggesting a kinematic temperature of $sim24$ K, owing to heating by the supernova shock. We determined the kinematic distance to the SNR to be $sim5.5$ kpc and the radius of the SNR to be $sim8$ pc. The average interstellar proton density inside of the SNR is $sim360$ cm$^{-3}$, of which atomic protons comprise only $sim10$ $%$. Assuming a hadronic origin for the gamma-ray emission, the total cosmic-ray proton energy above 1 GeV is estimated to be $sim5 times 10^{48}$ erg.
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