Search

The low dust temperatures (< 14 K) of Planck Galactic cold clumps (PGCCs) make them ideal targets to probe the initial conditions and very early phase of star formation. TOP-SCOPE is a joint survey program targeting similar to 2000 PGCCs in J = 1-0 transitions of CO isotopologues and similar to 1000 PGCCs in 850 mu m continuum emission. The objective of the TOP-SCOPE survey and the joint surveys (SMT 10 m, KVN 21 m, and NRO 45 m) is to statistically study the initial conditions occurring during star formation and the evolution of molecular clouds, across a wide range of environments. The observations, data analysis, and example science cases for these surveys are introduced with an exemplar source, PGCC G26.53+0.17 (G26), which is a filamentary infrared dark cloud (IRDC). The total mass, length, and mean line mass (M/L) of the G26 filament are similar to 6200 M-circle dot, similar to 12 pc, and similar to 500 M-circle dot pc(-1), respectively. Ten massive clumps, including eight starless ones, are found along the filament. The most massive clump as a whole may still be in global collapse, while its denser part seems to be undergoing expansion owing to outflow feedback. The fragmentation in the G26 filament from cloud scale to clump scale is in agreement with gravitational fragmentation of an isothermal, nonmagnetized, and turbulent supported cylinder. A bimodal behavior in dust emissivity spectral index (beta) distribution is found in G26, suggesting grain growth along the filament. The G26 filament may be formed owing to large-scale compression flows evidenced by the temperature and velocity gradients across its natal cloud.

The low dust temperatures (< 14 K) of Planck Galactic cold clumps (PGCCs) make them ideal targets to probe the initial conditions and very early phase of star formation. TOP-SCOPE is a joint survey program targeting similar to 2000 PGCCs in J = 1-0 transitions of CO isotopologues and similar to 1000 PGCCs in 850 mu m continuum emission. The objective of the TOP-SCOPE survey and the joint surveys (SMT 10 m, KVN 21 m, and NRO 45 m) is to statistically study the initial conditions occurring during star formation and the evolution of molecular clouds, across a wide range of environments. The observations, data analysis, and example science cases for these surveys are introduced with an exemplar source, PGCC G26.53+0.17 (G26), which is a filamentary infrared dark cloud (IRDC). The total mass, length, and mean line mass (M/L) of the G26 filament are similar to 6200 M-circle dot, similar to 12 pc, and similar to 500 M-circle dot pc(-1), respectively. Ten massive clumps, including eight starless ones, are found along the filament. The most massive clump as a whole may still be in global collapse, while its denser part seems to be undergoing expansion owing to outflow feedback. The fragmentation in the G26 filament from cloud scale to clump scale is in agreement with gravitational fragmentation of an isothermal, nonmagnetized, and turbulent supported cylinder. A bimodal behavior in dust emissivity spectral index (beta) distribution is found in G26, suggesting grain growth along the filament. The G26 filament may be formed owing to large-scale compression flows evidenced by the temperature and velocity gradients across its natal cloud.

We report the first map of large-scale (10 pc in length) emission of millimeter-wavelength hydrogen recombination lines (mm-RRLs) toward the giant H II region around the W43-Main young massive star cluster (YMC). Our mm-RRL data come from the IRAM 30 m telescope and are analyzed together with radio continuum and cm-RRL data from the Karl G. Jansky Very Large Array and HCO+ 1-0 line emission data from the IRAM 30 m. The mm-RRLs reveal an expanding wind-blown ionized gas shell with an electron density similar to 70-1500 cm(-3) driven by the WR/OB cluster, which produces a total Ly alpha photon flux of 1.5 x 10(50) s(-1). This shell is interacting with the dense neutral molecular gas in the W43-Main dense cloud. Combining the high spectral and angular resolution mm-RRL and cm-RRL cubes, we derive the two-dimensional relative distributions of dynamical and pressure broadening of the ionized gas emission and find that the RRL line shapes are dominated by pressure broadening (4-55 km s(-1)) near the YMC and by dynamical broadening (8-36 km s(-1)) near the shell's edge. Ionized gas clumps hosting ultra-compact H II regions found at the edge of the shell suggest that large-scale ionized gas motion triggers the formation of new star generation near the periphery of the shell.

We report the first map of large-scale (10 pc in length) emission of millimeter-wavelength hydrogen recombination lines (mm-RRLs) toward the giant H II region around the W43-Main young massive star cluster (YMC). Our mm-RRL data come from the IRAM 30 m telescope and are analyzed together with radio continuum and cm-RRL data from the Karl G. Jansky Very Large Array and HCO+ 1-0 line emission data from the IRAM 30 m. The mm-RRLs reveal an expanding wind-blown ionized gas shell with an electron density similar to 70-1500 cm(-3) driven by the WR/OB cluster, which produces a total Ly alpha photon flux of 1.5 x 10(50) s(-1). This shell is interacting with the dense neutral molecular gas in the W43-Main dense cloud. Combining the high spectral and angular resolution mm-RRL and cm-RRL cubes, we derive the two-dimensional relative distributions of dynamical and pressure broadening of the ionized gas emission and find that the RRL line shapes are dominated by pressure broadening (4-55 km s(-1)) near the YMC and by dynamical broadening (8-36 km s(-1)) near the shell's edge. Ionized gas clumps hosting ultra-compact H II regions found at the edge of the shell suggest that large-scale ionized gas motion triggers the formation of new star generation near the periphery of the shell.

The Columbia University-Universidad de Chile CO Survey of the southern Milky Way is used to separate the CO(1-0) emission of the fourth Galactic quadrant within the solar circle into its dominant components, giant molecular clouds (GMCs). After the subtraction of an axisymmetric model of the CO background emission in the inner southern Galaxy, 92 GMCs are identified, and for 87 of them the twofold distance ambiguity is solved. Their total molecular mass is M(H-2) = 1.14 +/- 0.05 x 10(8) M-circle dot, accounting for around 40% of the molecular mass estimated from an axisymmetric analysis of the H2 volume density in the Galactic disk, M(H-2)(disk) = 3.03 x 10(8) M-circle dot. The large-scale spiral structure in the southern Galaxy, within the solar circle, is traced by the GMCs in our catalog; three spiral arm segments, the Centaurus, Norma, and 3 kpc expanding arm, are analyzed. After fitting a logarithmic spiral arm model to the arms, tangent directions at 310 degrees, 330 degrees, and 338 degrees, respectively, are found, consistent with previous values from the literature. A complete CS(2-1) survey toward IRAS point-like sources with far-IR colors characteristic of ultracompact H II regions is used to estimate the massive star formation rate per unit H-2 mass (MSFR) and the massive star formation efficiency (is an element of) for GMCs. The average MSFR for GMCs is 0.41 +/- 0.06 L-circle dot/M-circle dot, and for the most massive clouds in the Norma arm it is 0.58 +/- 0.09 L-circle dot/M-circle dot. Massive star formation efficiencies of GMCs are, on average, 3% of their available molecular mass.

We present the first results of neutral carbon ([C I](3) P-1-P-3(0) at 492 GHz) and carbon monoxide ((CO)-C-13, J = 1-0) mapping in the Vela Molecular Ridge cloud C (VMR-C) and the G333 giant molecular cloud complexes with the NANTEN2 and Mopra telescopes. For the four regions mapped in this work, we find that [C I] has very similar spectral emission profiles to (CO)-C-13, with comparable line widths. We find that [C I] has an opacity of 0.1-1.3 across the mapped region while the [C I]/(CO)-C-13 peak brightness temperature ratio is between 0.2 and 0.8. The [C I] column density is an order of magnitude lower than that of (CO)-C-13. The H-2 column density derived from [C I] is comparable to values obtained from (CO)-C-12. Our maps show that C I is preferentially detected in gas with low temperatures (below 20 K), which possibly explains the comparable H-2 column density calculated from both tracers (both C I and (CO)-C-12 underestimate column density), as a significant amount of the C I in the warmer gas is likely in the higher energy state transition ([C I](3) P-2-P-3(1) at 810 GHz), and thus it is likely that observations of both the above [C I] transitions are needed in order to recover the total H-2 column density.

The Columbia University-Universidad de Chile CO Survey of the southern Milky Way is used to separate the CO(1-0) emission of the fourth Galactic quadrant within the solar circle into its dominant components, giant molecular clouds (GMCs). After the subtraction of an axisymmetric model of the CO background emission in the inner southern Galaxy, 92 GMCs are identified, and for 87 of them the twofold distance ambiguity is solved. Their total molecular mass is M(H-2) = 1.14 +/- 0.05 x 10(8) M-circle dot, accounting for around 40% of the molecular mass estimated from an axisymmetric analysis of the H2 volume density in the Galactic disk, M(H-2)(disk) = 3.03 x 10(8) M-circle dot. The large-scale spiral structure in the southern Galaxy, within the solar circle, is traced by the GMCs in our catalog; three spiral arm segments, the Centaurus, Norma, and 3 kpc expanding arm, are analyzed. After fitting a logarithmic spiral arm model to the arms, tangent directions at 310 degrees, 330 degrees, and 338 degrees, respectively, are found, consistent with previous values from the literature. A complete CS(2-1) survey toward IRAS point-like sources with far-IR colors characteristic of ultracompact H II regions is used to estimate the massive star formation rate per unit H-2 mass (MSFR) and the massive star formation efficiency (is an element of) for GMCs. The average MSFR for GMCs is 0.41 +/- 0.06 L-circle dot/M-circle dot, and for the most massive clouds in the Norma arm it is 0.58 +/- 0.09 L-circle dot/M-circle dot. Massive star formation efficiencies of GMCs are, on average, 3% of their available molecular mass.

We present the first results of neutral carbon ([C I](3) P-1-P-3(0) at 492 GHz) and carbon monoxide ((CO)-C-13, J = 1-0) mapping in the Vela Molecular Ridge cloud C (VMR-C) and the G333 giant molecular cloud complexes with the NANTEN2 and Mopra telescopes. For the four regions mapped in this work, we find that [C I] has very similar spectral emission profiles to (CO)-C-13, with comparable line widths. We find that [C I] has an opacity of 0.1-1.3 across the mapped region while the [C I]/(CO)-C-13 peak brightness temperature ratio is between 0.2 and 0.8. The [C I] column density is an order of magnitude lower than that of (CO)-C-13. The H-2 column density derived from [C I] is comparable to values obtained from (CO)-C-12. Our maps show that C I is preferentially detected in gas with low temperatures (below 20 K), which possibly explains the comparable H-2 column density calculated from both tracers (both C I and (CO)-C-12 underestimate column density), as a significant amount of the C I in the warmer gas is likely in the higher energy state transition ([C I](3) P-2-P-3(1) at 810 GHz), and thus it is likely that observations of both the above [C I] transitions are needed in order to recover the total H-2 column density.

The formation of high-mass stars is tightly linked to that of their parental clouds. Here, we focus on the high-density parts of W43, a molecular cloud undergoing an efficient event of star formation. Using a column density image derived from Herschel continuum maps, we identify two high-density filamentary clouds, called the W43-MM1 and W43-MM2 ridges. Both have gas masses of 2.1 x 10(4) M-circle dot and 3.5 x 10(4) M-circle dot above > 10(23) cm(-2) and within areas of similar to 6 and similar to 14 pc(2), respectively. The W43-MM1 and W43-MM2 ridges are structures that are coherent in velocity and gravitationally bound, despite their large velocity dispersion measured by the N2H+ (1-0) lines of the W43-HERO IRAM large program. Another intriguing result is that these ridges harbor widespread (similar to 10 pc(2)) bright SiO (2-1) emission, which we interpret to be the result of low-velocity shocks (<= 10 km s(-1)). We measure a significant relationship between the SiO (2-1) luminosity and velocity extent and show that it distinguishes our observations from the high-velocity shocks associated with outflows. We use state-of-the-art shock models to demonstrate that a small percentage (10%) of Si atoms in low-velocity shocks, observed initially in gas phase or in grain mantles, can explain the observed SiO column density in the W43 ridges. The spatial and velocity overlaps between the ridges of high-density gas and the shocked SiO gas suggest that ridges could be forming via colliding flows driven by gravity and accompanied by low-velocity shocks. This mechanism may be the initial conditions for the formation of young massive clusters.

The formation of high-mass stars is tightly linked to that of their parental clouds. Here, we focus on the high-density parts of W43, a molecular cloud undergoing an efficient event of star formation. Using a column density image derived from Herschel continuum maps, we identify two high-density filamentary clouds, called the W43-MM1 and W43-MM2 ridges. Both have gas masses of 2.1 x 10(4) M-circle dot and 3.5 x 10(4) M-circle dot above > 10(23) cm(-2) and within areas of similar to 6 and similar to 14 pc(2), respectively. The W43-MM1 and W43-MM2 ridges are structures that are coherent in velocity and gravitationally bound, despite their large velocity dispersion measured by the N2H+ (1-0) lines of the W43-HERO IRAM large program. Another intriguing result is that these ridges harbor widespread (similar to 10 pc(2)) bright SiO (2-1) emission, which we interpret to be the result of low-velocity shocks (<= 10 km s(-1)). We measure a significant relationship between the SiO (2-1) luminosity and velocity extent and show that it distinguishes our observations from the high-velocity shocks associated with outflows. We use state-of-the-art shock models to demonstrate that a small percentage (10%) of Si atoms in low-velocity shocks, observed initially in gas phase or in grain mantles, can explain the observed SiO column density in the W43 ridges. The spatial and velocity overlaps between the ridges of high-density gas and the shocked SiO gas suggest that ridges could be forming via colliding flows driven by gravity and accompanied by low-velocity shocks. This mechanism may be the initial conditions for the formation of young massive clusters.

RX J1713.7-3946 is one of the TeV gamma-ray supernova remnants (SNRs) emitting synchrotron X-rays. The SNR is associated with molecular gas located at similar to 1 kpc. We made new molecular observations toward the dense cloud cores, peaks A, C, and D, in the SNR in the (CO)-C-12(J = 2-1) and (CO)-C-13(J = 2-1) transitions at an angular resolution of 90 ''. The most intense core in (CO)-C-13, peak C, was also mapped in the (CO)-C-12(J = 4-3) transition at an angular resolution of 38 ''. Peak C shows strong signs of active star formation including bipolar outflow and a far-infrared protostellar source, and has a steep gradient with a r(-2.2 +/- 0.4) variation in the average density within radius r. Peak C and the other dense cloud cores are rim-brightened in synchrotron X-rays, suggesting that the dense cloud cores are embedded within or on the outer boundary of the SNR shell. This confirms the earlier suggestion that the X-rays are physically associated with the molecular gas. We present a scenario where the densest molecular core, peak C, survived the blast wave and is now embedded within the SNR. Numerical simulations of the shock-cloud interaction indicate that a dense clump can indeed survive shock erosion, since the shock propagation speed is stalled in the dense clump. Additionally, the shock-cloud interaction induces turbulence and magnetic field amplification around the dense clump that may facilitate particle acceleration in the lower-density inter-clump space leading to enhanced synchrotron X-rays around dense cores.

RX J1713.7-3946 is one of the TeV gamma-ray supernova remnants (SNRs) emitting synchrotron X-rays. The SNR is associated with molecular gas located at similar to 1 kpc. We made new molecular observations toward the dense cloud cores, peaks A, C, and D, in the SNR in the (CO)-C-12(J = 2-1) and (CO)-C-13(J = 2-1) transitions at an angular resolution of 90 ''. The most intense core in (CO)-C-13, peak C, was also mapped in the (CO)-C-12(J = 4-3) transition at an angular resolution of 38 ''. Peak C shows strong signs of active star formation including bipolar outflow and a far-infrared protostellar source, and has a steep gradient with a r(-2.2 +/- 0.4) variation in the average density within radius r. Peak C and the other dense cloud cores are rim-brightened in synchrotron X-rays, suggesting that the dense cloud cores are embedded within or on the outer boundary of the SNR shell. This confirms the earlier suggestion that the X-rays are physically associated with the molecular gas. We present a scenario where the densest molecular core, peak C, survived the blast wave and is now embedded within the SNR. Numerical simulations of the shock-cloud interaction indicate that a dense clump can indeed survive shock erosion, since the shock propagation speed is stalled in the dense clump. Additionally, the shock-cloud interaction induces turbulence and magnetic field amplification around the dense clump that may facilitate particle acceleration in the lower-density inter-clump space leading to enhanced synchrotron X-rays around dense cores.