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Register a new userALMA $mathrm{^{13}CO}$(J=1-0) Observations of NGC 604 in M33: Physical Properties of Molecular Clouds
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We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of $mathrm{^{13}CO(J=1-0)}$ line and 104 GHz continuum emission from NGC 604, a giant HII region (GHR) in the nearby spiral galaxy M33. Our high spatial resolution images ( 3.2$times$ 2.4, corresponding to $13 times 10$ pc physical scale) allow us to detect fifteen molecular clouds. We find spatial offsets between the $^{13}CO$ and 104 GHz continuum emission and also detect continuum emission near the centre of the GHR. The identified molecular clouds have sizes ranging from 5-21 pc, linewidths of 0.3-3.0 $mathrm{kms^{-1}}$ and luminosity-derived masses of (0.4-80.5) $times 10^3$ M$_{bigodot}$. These molecular clouds are in near virial equilibrium, with a spearman correlation coefficient of 0.98. The linewidth-size relationship for these clouds is offset from the corresponding relations for the Milky Way and for NGC 300, although this may be an artefact of the dendrogram process.
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We present results of wide-field $^{12}$CO ($J = 2 - 1$) and $^{13}$CO ($J = 2 - 1$) observations toward the Aquila Rift and Serpens molecular cloud complexes (25$^circ < l < 33^circ$ and $1^circ < b < 6^circ$) at an angular resolution of 3$$.4 ($approx$ 0.25 pc) and at a velocity resolution of 0.079 km s$^{-1}$ with the velocity coverage of $-5$ km s$^{-1} < V_{rm LSR} <$ 35 km s$^{-1}$. We found that the $^{13}$CO emission better traces the structures seen in the extinction map and derived the $X_{rm ^{13}CO}$-factor of this region. Applying texttt{SCIMES} to the $^{13}$CO data cube, we identified 61 clouds and derived their masses, radii, and line widths. The line-width-radius relation of the identified clouds basically follows those of nearby molecular clouds. Majority of the identified clouds are close to virial equilibrium although the dispersion is large. By inspecting the $^{12}$CO channel maps by eye, we found several arcs which are spatially extended to 0.2 $-$ 3 degree in length. In the longitude-velocity diagrams of $^{12}$CO, we also found the two spatially-extended components which appear to converge toward Serpens South and W40 region. The existence of two components with different velocities and arcs suggests that large-scale expanding bubbles and/or flows play a role in the formation and evolution of the Serpens South and W40 cloud.
We present the results of ALMA observations in $^{12}$CO($J=2-1$), $^{13}$CO($J=2-1$), and C$^{18}$O($J=2-1$) lines and 1.3 mm continuum emission toward a massive ($sim 10^6 M_{odot}$) giant molecular cloud associated with the giant H II region NGC 604 in one of the nearest spiral galaxy M33 at an angular resolution of 0.44 $times$ 0.27 (1.8 pc $times$ 1.1 pc). The $^{12}$CO and $^{13}$CO images show highly complicated molecular structures composed of a lot of filaments and shells whose lengths are 5 -- 20 pc. We found three 1.3 mm continuum sources as dense clumps at edges of two shells and also at an intersection of several filaments. We examined the velocity structures of $^{12}$CO($J=2-1$) emission in the shells and filaments containing dense clumps, and concluded that expansion of the H II regions cannot explain the formation of such dense cores. Alternatively, we suggest that cloud--cloud collisions induced by an external H I gas flow and the galactic rotation compressed the molecular material into dense filaments/shells as ongoing high-mass star formation sites. We propose that multiple gas converging/colliding events with a velocity of a few tens km s$^{-1}$ are necessary to build up NGC 604, the most significant cluster-forming complex in the Local Group of galaxies.
We report a statistical analysis exploring the origin of the overall low star formation efficiency (SFE) of the Galactic central molecular zone (CMZ) and the SFE diversity among the CMZ clouds using a wide-field HCN $J$=4-3 map, whose optically thin critical density ($sim10^7,mathrm{cm}^{-3}$) is the highest among the tracers ever used in CMZ surveys. Logistic regression is performed to empirically formulate star formation probability of 195 HCN clumps, 13 of which contain star formation signatures. The explanatory parameters in the best-fit model are reduced into the virial parameter $alpha_{mathrm{vir}}$ without significant contribution from other parameters, whereas the performance of the model without $alpha_{mathrm{vir}}$ is no better than that using randomly generated data. The threshold $alpha_{mathrm{vir}}$ is 6, which translates into a volume density ($n_{mathrm{H_2}}$) of $10^{4.6},mathrm{cm}^{-3}$ with the $n_{mathrm{H_2}}$-$alpha_{mathrm{vir}}$ correlation. The scarcity of the low-$alpha_{mathrm{vir}}$ clumps, whose fraction to all HCN clumps is 0.1, can be considered as one of the immediate causes of the suppressed SFE. No correlation between the clump size or mass and star formation probability is found, implying that HCN $J$=4-3 does not immediately trace the mass of star-forming gas above a threshold density. Meanwhile, star-forming and non-star-forming clouds are degenerate in the physical parameters of the CS $mathit{J}$=1-0 clouds, highlighting the efficacy of the HCN $mathit{J}$=4-3 line to probe star-forming regions in the CMZ. The time scale of the high-$alpha_{mathrm{vir}}$ to low-$alpha_{mathrm{vir}}$ transition is $lesssim2$ Myr, which is consistent with the tidal compression and X1/X2 orbit transition models but possibly does not fit the cloud-cloud collision picture.
This {it supplement} paper presents the maps of HCN $J$=4-3, HNC $J$=1-0, $mathrm{H^{13}CN}$ $J$=1-0, and HC$_3$N $J$=10-9 for the Galactic central molecular zone (CMZ), which have been obtained using the Atacama Submillimeter Telescope Experiment and Nobeyama Radio Observatory 45-m telescope. Three-dimensional maps (2-D in space and 1-D in velocity) of the gas kinetic temperature ($T_mathrm{kin}$), hydrogen volume density ($n_mathrm{H_2}$), and fractional abundances of eight molecules (HCN, HNC, $mathrm{HC_3N}$, HCO$^+$, $mathrm{H_2CO}$, SiO, CS, and $mathrm{N_2H^+}$) have been constructed from our and archival data. We have developed a method with hierarchical Bayesian inference for this analysis, which has successfully suppressed the artificial correlations among the parameters created by systematic errors due to the deficiency in the simple one-zone excitation analysis and the calibration uncertainty. The typical values of $T_mathrm{kin}$ and $n_mathrm{H_2}$ are $10^{1.8} $K and $10^{4.2} mathrm{cm}^{-3}$, respectively, and the presence of an additional cold/low-density component is also indicated. The distribution of high-temperature regions is poorly correlated with known active star-forming regions, while a few of them coincide with shocked clouds. Principal component analysis has identified two distinct groups in the eight analyzed molecules: one group with large PC1 and PC2 scores and the other with a large $T_mathrm{kin}$ dependence, which could be explained using two regimes of shock chemistry with fast ($gtrsim 20 mathrm{km,s}^{-1}$) and slow ($lesssim 20 mathrm{km,s}^{-1}$) velocity shocks, respectively. This supports the idea that the mechanical sputtering of dust grains and the mechanical heating play primary roles in the chemical and thermal processes in CMZ clouds.
We present results of the $^{12}$CO (1--0) mosaic observations of the nearby barred-spiral galaxy M83 obtained with the Atacama Large Millimeter/submillimeter Array (ALMA). The total flux is recovered by combining the ALMA data with single-dish data obtained using the Nobeyama 45-m telescope. The combined map covers a $sim$13 kpc$^{2}$ field that includes the galactic center, eastern bar, and spiral arm with a resolution of timeform{2.03} $times$ timeform{1.1} ($sim$45 pc $times$ $sim$25 pc). With a resolution comparable to typical sizes of giant molecular clouds (GMCs), the CO distribution in the bar and arm is resolved into many clumpy peaks that form ridge-like structures. Remarkably, in the eastern arm, the CO peaks form two arc-shaped ridges that run along the arm and exhibit a distinct difference in the activity of star formation: the one on the leading side has numerous HII regions associated with it, whereas the other one on the trailing side has only a few. To see whether GMCs form stars with uniform star formation efficiency (SFE) per free-fall time (SFEff), GMCs are identified from the data cube and then cross-matched with the catalog of HII regions to estimate the star formation rate for each of them. 179 GMCs with a median mass of 1.6 $times$ 10$^{6}$ $M_{odot}$ are identified. The mass-weighted average SFEff of the GMCs is $sim$9.4 $times$ 10$^{-3}$, which is in agreement with models of turbulence regulated star formation. Meanwhile, we find that SFEff is not universal within the mapped region. In particular, one of the arm ridges shows a high SFEff with a mass-weighted value of $sim$2.7 $times$ 10$^{-2}$, which is higher by more than a factor of 5 compared to the inter-arm regions. This large regional variation in SFEff favors the recent interpretation that GMCs do not form stars at a constant rate within their lifetime.
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