Publications of the Astronomical Society of Japan (2017), Vol. 00, No. 0 7

Fig. 3. Integrated intensity maps of (a) 12CO, (b) 13CO, and (c) C18O J 1–0 in region A (l 12 to 22 , b 1 to 1 ). The integrated velocity range is = = ◦ ◦ = − ◦ ◦ 50 km s 1 < V < 200 km s 1.Panel(d)showstheSpitzerGLIMPSEimage(blue,3.6µm; green, 5.4 µm; red, 8.0 µm) in the same region. (Color − − LSR − online)

風神FUGIN FOREST Unbiased Galactic plane Imaging survey with Nobeyama 45-m telescope Optical image: Axel Mellinger 1

2019/03/05 formation with ALMA FUGIN: CO observations toward the Giant complex W43: Dense gas and mini-starbursts at the tangential direction of the Scutum Arm 0

Mikito Kohno (Nagoya university D2) K. Tachihara, S. Fujita, A. Ohama, A. Nishimura, M. Hanaoka, Y. Fukui (Nagoya), K. Torii, T. Umemoto, T. Minamidani, M. Matsuo (NRO), N. Kuno, M. Kuriki (Tsukuba), K. Tokuda (NAOJ/Osaka Pref), R. Kiridoshi, T. Onishi (Osaka Pref), Y. Tsuda (Meisei), and FUGIN team 1

NRO45m/FOREST (Red: 12CO J=1–0, Green: 13CO J=1–0, C18O J=1–0) NAOJ ‒1

1

0

12 13 18 Fig. 4. Three-color peak Tmb intensity image of region A: CO (red), CO (green), and C O (blue). (Color online) Spitzer/GLIMPSE+MIPSGAL (Red: 24μm, Green: 8μm, Blue:5.8μm) NASA/JPL-Caltech ‒1 50 48 46 44 42 40 38 36 34 32 30 28 26 24 22 20 18 16 14 12 10 three CO lines, and it is possible to investigate the global intense. The red clouds, which are very bright in 12CO but physical conditions of Galactic GMCs in a way similar to very weak in 13CO and C18O, indicate low optical depth Barnes et al. (2015). In figure 4,denseandwarmregions and high temperature regions. On the other hand, green are shown in white, where all 12CO, 13CO, and C18O are and blue clouds, where 13CO/12CO or C18O/12CO is high, Dense gas and6 high-mass star formationPublications ofin the Astronomicalthe GMC Society of Japan (2018), Vol. 00, No. 0

NGC 6334-6357 (Fukui+18) K km/s

1987IAUS..115....1L Image (Spitzer): 12 grid (a) CO J=2-1 HPBW 10 pc 0 180 360 Red: 24 um 1.2 Vlsr: -30.0 - 4.0 km/s Green : 8 um Contour levels : min 25 K km/s, Step 25 K km/s 1.0 Blue : 3.6 um

0.8

0.6

0.4 Galactic Latitude [degree] (b) Contour levels : min 0.2 K degree, Step 0.4 K degree

GMC

GMC evolution GMC High-mass star 0

-10 Dense gas Vlsr [km/s] Vlsr 100 pc Lada 1987

-20 • What is the origin of the dense gas in the GMC ? Resolution B: 0.45 - 0.97 deg. • How do high-mass formed in the GMC ? 2 353 352 351 K degree Galactic Longitude [degree] 0.0 3.4 6.8

Fig. 4. (a) Integrated intensity map of 12CO J 2–1 obtained with NANTEN2. Purple and black crosses indicate sources (PT08)andOB-type = stars (PT08, Fang et al. 2012), respectively. The final beam sizes after convolution and grid spacing are 90′′ and 30′′,respectively.Theintegrated 1 1 1 velocity range is from 30 to 4 km s− .The1σ noise level is 1.8 K km s− for the velocity interval of 34 km s− .Thelowestcontourandcontour −1 ∼ 12 intervals are 25 K km s− . (b) Galactic longitude–velocity diagram of CO J 2–1. The integrated latitude range is from 0.◦45 to 0.◦97. The velocity 1 = resolution is smoothed to 0.5 km s .The1σ noise level is 0.07 K degree for the latitude interval of 0.◦54. The lowest contour and contour intervals − ∼ are 0.2 K degree and 0.4 K degree, respectively.

the main component and the blueshifted component in the 3.2 NGC 6334

following three regions: l 351.◦0– 351.◦5 (NGC 6334), 12 = Figure 6 shows a CO J 2–1 distribution of the main l 351.◦8–352.◦0 (MC351.9 0.7), and l 352.◦7–353.◦3 = = + = component of the NGC 6334 molecular cloud integrated (NGC 6357). 1 1 between 12 km s− and 2 km s− .Figure7 shows the 12 − Figure 5 shows the CO intensity line ratio of the 12CO distribution for the blueshifted component integrated J 2–1 emission to the J 1–0 emission in the l–b and 1 1 between 20 km s− and 12 km s− .Figure8 shows an = = − − velocity–l diagrams. We convolved the beam size of the overlay of the two components, which indicates a good 12 CO (J 2–1) to 180′′, which is the final beam size of the correspondence between the two velocity components. 12 = CO (J 1–0) data. The clipping levels of figures 5a and 5b 13 = Figure 9a shows the CO J 3–2 distribution of 1 = are 9σ (25 K km s− ) and 3σ (0.3 K degree), respectively. NGC 6334. We identified five 13CO clumps towards the far- The ratio is enhanced to be more than 0.8 in the regions of infrared sub-regions except for II, as listed in table 2.The GM 24, NGC 6334, and NGC 6357 in the main compo- clump boundary is defined at a 75% level of the peak inte- nent. We also note the bridge features toward NGC 6344 grated intensity. We derived the physical parameters using and NGC 6357 show enhancement of the ratio at 8– the 13CO J 3–2 emission (Buckle et al. 2010) under an 1 = 10 km s− . These high ratios suggest that the gas is in a assumption of local thermal equilibrium (LTE). Figure 9b high-excitation state due to heating by the high-mass stars. shows the radio continuum distribution, which traces the

Downloaded from https://academic.oup.com/pasj/advance-article-abstract/doi/10.1093/pasj/psy017/4955196 by guest on 31 March 2018 steep intensity gradient in the 12CO emissions, while G012.820-00.238 is surrounded by molecular gas, especially in the 13CO and C18O emissions. W33 Main is sandwiched by these two H II re- 1 gions. The 45 km s− cloud has diffuse CO emission extended over the present region. The compact emissions at W33 Main and W33 A correspond to the wing features of the outflows (see Section 1 1 3.6 for details), and are thus not related to the 45 km s− cloud. Molecular gas in the 58 km s− cloud is separated into the northern and southern components relative to W33 and the central part corresponding to W33 is weak in the CO emission. There are several clumpy structures embedded at the northern rim of the southern component, which are clearly seen in the 12CO emissions, and these clumps show spatial correlations with radio continuum emissions from the H II regions G012.745- 00.153 and G012.692-00.251 as well as W33 B. In the C18O map in Figure 3(i) and Figure 4(d), W33 B is associated with the strong CO peak. There are several other clumpy molecular structures 1 at the interspace between the northern and southern components of the 58 km s− cloud, forming an arc-like molecular structure which looks surrounding W33. The size of arc-like structure is roughly estimated to be 7 pc. On the other hand, clear associations of molecular clumps with W33 A1 and ∼ W43 (Westerhout 43)W33 Main1 are not recognized. We derived the column densities and masses of the three velocity clouds using the 12CO in- Spitzer, blue: 3.6 μm, green: 8.0 μm, red: 24 μm tegrated intensity maps shown in Figures 3(a)-(c), where we defied the individual clouds by drawing • Parallactic distance 1 (a) contours at 5σ noise levels in the integrated intensity of 8 K km s− for the velocity interval of 10 5.51 kpc 20 1 1 2 km s(Zhang− . Byet al. assuming 2015) a X(CO) factor of 2 10 (K km s− )− cm− (Strong et al. 1988), we esti- × 1 1 1 22 mated• GMC the meancomplex column densities of the 35 km s− , 45 km s− , and 58 km s− clouds as 1.7 10 × 2 22 2 21 2 cm− ,–1.Size7 10: 100cm− pcand 6.2 10 cm− , respectively, with the total molecular masses derived × × W43 Main W43 South as 1.1– 10Mass5M : ,7.11.0101065M , and 3.8 104M . The uncertainty of mass estimation using X-factor × (Nguyen⊙ Luong+2011)× ⊙ × ⊙ is about 30 % (Bolatto et al. 2013). Lin et al. (2016) derived the mean column densities as • Three± high-mass star 22 2 2.5 10 cm− using the infrared dust emission data obtained by Herschel, which is consistent with ×forming regions G30.5 our estimate.– W43 Main – G30.5 N 3.2 C–18OW43 molecular South clump properties 50pc We define C18O molecular clumps using the following procedures in order to investigate the physical 1 1 properties of dense molecular gas belonging to the 35 km s− and 58 km s− clouds corresponding to (b) W43 Main (c) G30.5 (d) W43 South the dust clumps. IRAS 18445-0222 G030.213-00.156 (Bally+2010)1. Search for a peak integrated intensity toward the six dust clumps. Galactic mini-star burst region 3 2. Define a clump boundary as the half level of its peak integrated intensity.

IRAS 18447-0229 3. If the area enclosed by the boundary have multiple peaks, define the boundary as a contour of the

G030.404-00.238 10

IRAS 18456-0223 10pc 10pc 10pc Publications of the Astronomical Society of Japan, (2014), Vol. 00, No. 0 15

Spitzer, blue: 3.6 μm, green: 8.0 μmsteep, red: intensity 24 μ gradientm in the 12CO emissions, while G012.820-00.238 is surrounded by molecular gas, especially in the 13CO and C18O emissions. W33 Main is sandwiched by these two H II re- (a) 1 gions. The 45 km s− cloud has diffuse CO emission extended over the present region. The compact emissions at W33 Main and W33 A correspond to the wing features of the outflows (see Section 1 1 3.6 for details), and are thus not related to the 45 km s− cloud. Molecular gas in the 58 km s− cloud is separated into the northern and southern components relative to W33 and the central part corresponding to W33 is weak in the CO emission. There are several clumpy structures embedded at W43 Main W43 Souththe northern rim of the southern component, which are clearly seen in the 12CO emissions, and these clumps show spatial correlations with radio continuum emissions from the H II regions G012.745- 00.153 and G012.692-00.251 as well as W33 B. In the C18O map in Figure 3(i) and Figure 4(d), W33 B is associated with the strong CO peak. There are several other clumpy molecular structures G30.5 1 at the interspace between the northern and southern components of the 58 km s− cloud, forming an arc-like molecular structure which looks surrounding W33. The size of arc-like structure is roughly estimated to be 7 pc. On the other hand, clear associations of molecular clumps with W33 A1 and N ∼ W33 Main1 are50pc not recognized. We derived the column densities and masses of the three velocity clouds using the 12CO in- W43 (Westerhout 43)tegrated intensity maps shown in Figures 3(a)-(c), where we defied the individual clouds by drawing 1 (b) W43 Main (c) G30.5 contours at 5σ noise levels in the integrated intensity of 8 K km s− for the velocity interval of 10 (d) 1 W43 South 20 1 1 2 km s− . By assuming a X(CO) factor of 2 10 (K km s− )− cm− (Strong et al. 1988), we esti- (G29.96-0.02) × IRAS 18445-0222 1 1 1 22 mated the mean column densities of the 35 km s− , 45 km s− , and 58 km s− clouds as 1.7 10 G030.213-00.156 × 2 22 2 21 2 cm− , 1.7 10 cm− and 6.2 10 cm− , respectively, with the total molecular masses derived W43 Main cluster × 7 × N52 bubble 5 1 5 4 as 1.1 10 M ,1.06 10 M , and 3.8 10 M . The uncertainty of mass estimation using X-factor W43-MM1 2 ⊙ ⊙ ⊙ × 4 5 ×8 9 × is about 330 % (Bolatto et al. 2013). Lin et al. (2016) derived the mean column densities as IRAS 18447-0229 ± 22 2 10 2.5 10 cm− using the infrared dust emission data obtained by Herschel, which is consistent with G030.404-00.238 × our estimate. IRAS 18456-0223 10pc 10pc 10pc

18 Fig. 1. (a) Spitzer three color composite image of W43. Blue, green, and red show the Spitzer/IRAC 3.6-µm, Spitzer/IRAC3.2 C 8-µmO (Benjamin molecular et al. clump 2003), and properties • W43 South (G29.96)(Beltran+2013) Spitzer/MIPS• W43 24-µm Main (Carey et al.(Bally+2010) 2009) results. The X marks• indicateG30.5 W43 (Sofue+85, Main (Blum 18) et al. 1999) and W43 South (Wood & Churchwell 1989). (b) Close-up image of W43 Main. The white circles indicate the 51 compact fragments (W43 MM1-MM51) cataloged by Motte– et al.>10 (2003). OB (c)-type Close-up18 stars(UCHII) image of G30.5. (d) Close-up– image of50 W43South. O-type The whitestars crosses indicate the– radioBow continuum shock sources region identified by Condon et al.We (1998). define C O molecular clumps using the following procedures in order to investigate the physical 51 – (10 photon/s) – Five infrared sources 0.1 Myr 1 1 properties(Watson & Hanson of dense 1997) molecular gas belonging to the 35 km s− and 58 km s− clouds corresponding to – 1-6 Myr (Bally+2010) 6 – the1-2 dust10 clumps.L ⦿ 6 – 7-1010 L ⦿ 1. Search for a peak integrated intensity toward the six dust clumps. 2. Define a clump boundary as the half level of its peak integrated intensity. Galactic mini-starbursts region (Bally+2010) 3. If the area enclosed by4 the boundary have multiple peaks, define the boundary as a contour of the 10 Publications of the Astronomical Society of Japan, (2014), Vol. 00, No. 0 15

Spitzer, blue: 3.6 μm, green: 8.0 μm, red: 24 μm (a)

W43 Main W43 South

G30.5

N 50pc Massive cores in W43 Main ALMA IMF large program (b) W43 Main (c) G30.5 (d) W43 South (G29.96-0.02) IRAS 18445-0222

G030.213-00.156

W43 Main cluster 7 N52 bubble 1 6 W43-MM1 2 4 5 8 9 3 IRAS 18447-0229 10

G030.404-00.238

IRAS 18456-0223 10pc 10pc 10pc

Fig. 1. (a) Spitzer three color composite image of W43. Blue, green, and red show the Spitzer/IRAC 3.6-µm, Spitzer/IRAC1.3 mm 8-µ mdust (Benjamin continuum et al. 2003), and Spitzer/MIPS• W43 24-µm (CareyMain et al. 2009)(Bally+2010) results. The X marks indicate W43 Main (Blum et al. 1999) and W43 South (Wood & Churchwell 1989). (b) Close-up image of W43 Main. The white circles indicate the 51 compact fragments (W43 MM1-MM51) cataloged by Motte et al. (2003). (c) Close-up image of G30.5. (d) Close-up– image of W43South. The white crosses indicate theFigure radio continuum 1: High-angular sources resolution identified image by Condon of the W43-MM1 et al. (1998). cloud, revealing a rich population 50 O-type stars of cores. 1.3 mm dust continuum emission,Motte+2018, observed by the ALMA Nature interferometer, Astronomy is presumed to (1051 photon/s) trace the column density of gas, revealing high-density filaments and embedded cores. The filled yellow ellipse on the right represents the angular resolution, and a scale bar is shown. Ellipses outline core boundaries (at half-maximum) as defined by the getsources20 extraction algorithm. – 1-6 Myr (Bally+2010) Core masses span the range from 1M to 100 M , and can therefore be expected to spawn ⇠ ⇠ stars with masses from 0.4M to > 40 M 5 (see Supplementary Table 1). All cores are shown; 6 ⇠ – 7-1010 L ⦿ hashed ellipses indicate the most robust identifications.

Many massive cores in W43-MM1 (Motte+2018) 5

8 Publications of the Astronomical Society of Japan, (2014), Vol. 00, No. 0 15

Spitzer, blue: 3.6 μm, green: 8.0 μm, red: 24 μm (a)

W43 Main W43 South

G30.5

N 50pc Massive cores in W43 Main (b) W43 Main (c) G30.5 1.3(d) mmW43 dust continuumSouth (G29.96-0.02) IRAS 18445-0222

G030.213-00.156

W43 Main cluster 7 N52 bubble 1 6 W43-MM1 2 4 5 8 9 3 IRAS 18447-0229 10

G030.404-00.238

IRAS 18456-0223 10pc 10pc 10pc

Fig. 1. (a) Spitzer three color composite image of W43. Blue, green, and red show the Spitzer/IRAC 3.6-µm, Spitzer/IRACMotte+2018, 8-µm (Benjamin Nature et al. 2003),Astronomy and Spitzer/MIPS• W43 24-µm (CareyMain et al. 2009)(Bally+2010) results. The X marks indicate W43 Main (Blum et al. 1999) and W43 South (Wood & Churchwell 1989). (b) Close-up image of W43 Main. The white circles indicate the 51 compact fragments (W43 MM1-MM51) cataloged by Motte et al. (2003). (c) Close-up image of G30.5. (d) Close-up– image of W43South.50 O-type The white stars crosses indicate the radio continuum sources identified by Condon et al. (1998). (1051 photon/s) A slope of core mass function – 1-6 Myr (Bally+2010) shallower than the IMF 6 – 7-1010 L ⦿

Many massive cores in W43-MM1 (Motte+2018) 6

Figure 2: The W43-MM1 core mass functions: (a) di↵erential form; (b) cumulative form, challenging the relation between the CMF and the IMF. Above the sample 90% completeness limit, estimated to be Mcore = 1.6M (black vertical line), the W43-MM1 CMFs (blue histograms) 0.90 0.96 are well fitted by single power-laws: (a) dN/d log(M) M , and (b) N(>log(M)) M (red / / lines and 1 uncertainties). The error bars on the di↵erential CMF correspond to pN counting statistics. The cumulative CMF in (b) is the more robust, statistically; its 5 global uncertainty ( 0.13, hatched area) is estimated from Monte-Carlo simulations. The W43-MM1 CMF is clearly ± 9, 22 1.35 flatter than the IMF , which in the corresponding mass range has slopes dN/d log(M) M 1.35 9 / and N(>log(M)) M (magenta lines). / FUGIN Galactic Plane3 color CO l-vsurvey diagram Nobeyama 45 m telescope

W43 red：12CO green：13CO Norma blue：C18O Aql spur Scutum AGAL045.121+00.131

W33 AGAL020.081-00.136 W47 W51 Sagi\arius W49

M16 M17 AGAL032.797+00.191 Umemoto+17 FUGIN web https://nro-fugin.github.io ○ Top 25 SFRs with high luminosity Urquhart et al. 2014 Telescope Line Resolution： Period （ ） Noise levels NRO 45 m 12CO(J=1-0) 20” 2014-2017 1.8 K (12CO) (FUGIN) 13CO(J=1-0) (0.5 [email protected] kpc) (W43 : only X-scan) 0.9 K (13CO) C18O(J=1-0) Large scale CO survey to reveal the origin of the dense gas and mini-starbursts in the GMC 7 Result 1 Galactic scale observations of the

8

12CO J=1-0 -30 - 160 km/s

13 CO J=1-0 -30 - 160 km/s

18 C O J=1-0 -30 - 160 km/s

W43

9

12CO J=1-0 W43 GMC -30 - 160 km/s

13 CO J=1-0 -30 - 160 km/s

a

18 C O J=1-0 -30 - 160 km/s

• Tangential direction of the Scutum Arm -> The cross section of the spiral arm W43 • The meeting point of the Long- bar and Scutum Arm (bar-end) (Nguyen Luong+2011, Zhang+ 2014) 10 Publications of the Astronomical Society of Japan, (2014), Vol. 00, No. 0 17

FUGIN 12CO J=1-0

W43

Aquila Spur Norma Arm

W51 Scutum Arm W44

Sagittarius Arm W33

W49 M16 M17 Perseus Arm Rift

Outer (Cygnus) Arm Dashed lines by Reid+16Reid+2016 11

12 1 1 Fig. 2. Upper panel : Integrated intensity map of CO J =1–0 with the velocity range of 30 km s− -160 km s− . Lower panel : Longitude-velocity diagram 12 − of CO J =1–0 with the integrated latitude range of 1◦-+1◦. The white dotted lines indicate the spiral arm at the 1st quadrant from Reid et al. (2016). The − color are adopted as Logarithmic scale. Top-left image shows the view of the Milky Way (NASA/JPL-Caltech/ESO/R. Hurt), and yellow shadow indicates the inner survey area of FUGIN. Results 2 CO spatial distribution and velocity structures of W43 GMC complex

12 steep intensity gradient in the 12CO emissions, while G012.820-00.238 is surrounded by molecular gas, especially in the 13CO and C18O emissions. W33 Main is sandwiched by these two H II re- 1 gions. The 45 km s− cloud has diffuse CO emission extended over the present region. The compact emissions at W33 Main and W33 A correspond to the wing features of the outflows (see Section 1 1 3.6 for details), and are thus not related to the 45 km s− cloud. Molecular gas in the 58 km s− cloud is separated into the northern and southern components relative to W33 and the central part corresponding to W33 is weak in the CO emission. There are several clumpy structures embedded at 12 20 the northern rim of thePublications southern of the component, Astronomical Society which of Japan are, (2014), clearly Vol. 00, seen No. 0 in the CO emissions, and these clumps show spatial correlations with radio continuum emissions from the H II regions G012.745- (a) 12CO J=1-0 00.153 and G012.692-00.251 as well as W33 B. In the C18O map in Figure 3(i) and Figure 4(d), W33 B is associated with the strong CO peak. There are several other clumpy molecular structures 1 at the interspace between the northern and southern components of the 58 km s− cloud, forming an W43 Main arc-like molecular structure whichW43 looks South surrounding W33. The size of arc-like structure is roughly estimated to be 7 pc. On the other hand, clear associations of molecular clumps with W33 A1 and ∼ W33 Main1 are not recognized. G30.5 We derived the column densities and masses of the three velocity clouds using the 12CO in- tegrated intensity maps shown in Figures 3(a)-(c), where we defied the individual clouds by drawing 1 contours at 5σ noise levels in the integratedHPBW intensity of 8 K km s− for the velocity interval of 10 1 20 1 1 2 km s− . By assuming a X(CO) factor of 2 10 (K km s− )− cm− (Strong et al. 1988), we esti- • × Size:13 150 pc 100 pc 1 1 1 22 (b)mated CO J=1-0 the mean column densities of the 35 km s− , 45 km s− , and 58 km s− clouds as 1.7 10 • Connecting of W43 Main and W43 South with 12CO × 2 22 2 21 2 cm− , 1.7 10 cm− and 6.2 10 cm− , respectively, with the total molecular masses derived • Three peaks ×of W43 Main, G30.5, and× W43 South 13 • Totalas 1 .mass1 10 ( 125CO)M ,11.4.0101075M , and 3.8 104M . The uncertainty of mass estimation using X-factor × ⊙ × ⊙ × ⊙ is about 30 % (Bolatto et al. 2013). Lin et al. (2016) derived the mean column densities as ± W43 Main 22 2 W43 South 2.5 10 cm− using the infrared dust emission data obtained by Herschel, which is consistent with × our estimate.

G30.5 3.2 C18O molecular clump properties

We define C18O molecular clumps using the following procedures in order to investigate the physical 1 1 properties of dense molecular gas belonging to the 35 km s− and 58 km s− clouds corresponding to 18 (c) theC dustO J=1-0 clumps. 1. Search for a peak integrated intensity toward the six dust clumps. 2. Define a clump boundary as the half level of its peak integrated intensity. W43 Main 3. If the area enclosed by the boundaryW43 South have multiple peaks, define the boundary as a contour of the 10

G30.5

Fig. 5. Integrated intensity maps of 12CO (a), 13CO (b), and C18O J =1–0 (c) toward W43 obtained with the Nobeyama 45-m telescope. The integrated 1 1 velocity range is from 78 km s− to 120 km s− . The white crosses indicate W43 Main (Blum et al. 1999) and W43 South (Wood & Churchwell 1989). 20 Publications of the Astronomical Society of Japan, (2014), Vol. 00, No. 0

(a) 12CO J=1-0

W43 Main W43 South

G30.5

HPBW

(b) 13CO J=1-0

steep intensity gradient in the 12CO emissions, while G012.820-00.238 is surrounded by molecular gas, especially in the 13CO and C18O emissions. W33 Main is sandwiched by these two H II re- W431 Main gions. The 45 km s− cloud has diffuseW43 CO South emission extended over the present region. The compact emissions at W33 Main and W33 A correspond to the wing features of the outflows (see Section 1 1 3.6 for details), and are thus not related to the 45 km s− cloud. Molecular gas in the 58 km s− cloud is separated into theG30.5 northern and southern components relative to W33 and the central part corresponding to W33 is weak in the CO emission. There are several clumpy structures embedded at the northern rim of the southern component, which are clearly seen in the 12CO emissions, and these clumps show spatial correlations with radio continuum emissions from the H II regions G012.745- 00.153(c) C18 andO J=1-0 G012.692-00.251 as well as W33 B. In the C18O map in Figure 3(i) and Figure 4(d), W33 B is associated with the strong CO peak. There are several other clumpy molecular structures 1 at the interspace between the northern and southern components of the 58 km s− cloud, forming an arc-like molecular structureW43 Main which looks surrounding W33. The size of arc-like structure is roughly W43 South estimated to be 7 pc. On the other hand, clear associations of molecular clumps with W33 A1 and ∼ W33 Main1 are not recognized.

We derived the columnG30.5 densities and masses of the three velocity clouds using the 12CO in- tegrated intensity maps shown in Figures 3(a)-(c), where we defied the individual clouds by drawing 1 contours at 5σ noise levels in the integrated intensity of 8 K km s− for the velocity interval of 10 1 20 1 1 2 km s− . By assuming a X(CO) factor of 2 10 (K km s− )− cm− (Strong et al. 1988), we esti- × 1 1 1 22 • Threemated peaks the of meanW43 columnMain, G30.5, densities and of W43 the 35 South km s− , 45 km s− , and 58 km s− clouds as 1.7 10 × Fig. 5. Integrated intensity maps of 122CO (a), 13CO (b), and22 C18O J2=1–0 (c) toward W43 obtained21 with the2 Nobeyama 45-m telescope. The integrated • Clumpycm1 −structures, 1.71 10 cm− and 6.2 Detailed10 cm− analysis, respectively, of with the total molecular masses derived velocity range is from 78 km s− to 120 km s− .× The white crosses indicate W43 Main (Blum× et al. 1999) and W43 South (Wood & Churchwell 1989). 13 5 65 4 • Total asmass1.1 ( 10CO)M ,1.71.01010 M , andvelocity3.8 10 structuresM . The uncertainty14 of mass estimation using X-factor × ⊙ × ⊙ × ⊙ is about 30 % (Bolatto et al. 2013). Lin et al. (2016) derived the mean column densities as ± 22 2 2.5 10 cm− using the infrared dust emission data obtained by Herschel, which is consistent with × our estimate.

3.2 C18O molecular clump properties

We define C18O molecular clumps using the following procedures in order to investigate the physical 1 1 properties of dense molecular gas belonging to the 35 km s− and 58 km s− clouds corresponding to the dust clumps. 1. Search for a peak integrated intensity toward the six dust clumps. 2. Define a clump boundary as the half level of its peak integrated intensity. 3. If the area enclosed by the boundary have multiple peaks, define the boundary as a contour of the 10 Publications of the Astronomical Society of Japan, (2014), Vol. 00, No. 0 5

core Python package for astronomy (Astropy Collaboration 2013), NumPy and SciPy (Walt et al. 2011), Matplotlib (Hunter 2007), IPython (Perez´ et al. 2007), and Montage 3 software. We summarize the observational properties and archival information as Table 4.

3 Results 3.1 Galactic-scale CO distributions and velocity structures of the 1st quadrant with FUGIN

12 Figure 2,3, and 4 upper panels show the integrated intensity map toward the inner (l =10◦–50◦, b = 1◦–1◦) of CO, 13 18 1 − CO, and C O, respectively. The integrated velocity range is from 30 to 160 km s− . The lower panels present the galactic − longitude-velocity diagram where dotted lines indicate the spiral arm from Reid et al. (2016). We find the Norma, Sagittarius, Scutum, Perseus, and Outer (Cygnus) spiral arms. The Aquila rift and Aquila Spur are also found as the local component of the solar neighborhood and the inter-arm region, respectively. The active high-mass star-forming regions and supernova remnant exist in each spiral arms (e.g., W33, M17, M16, W43, W49, W51, and W44). W43 exists in the direction of l =30◦, which contains rich gas from the integrated intensity maps and longitude-velocity diagram of the 1st quadrant. This region is near the tangential point of 24 Publicationsthe of the Scutum Astronomical Arm Societyand the of bar-end Japan, (2014), of the Vol. Milky 00, No. Way 0 (Nguyen-Luong et al. 2011), which consist of many velocity components from 1 18 60 to 120 km s− . We note that dense gas traced by C O (Figure 4) has local distribution compared with the low-density gas traced by 12CO (Figure 2). (a) 12CO J=1-0

3.2 CO distributions toward the W43 giant molecular cloud complex W43 Main W43 South Figure 5 demonstrates the integrated intensity maps of W43 GMC complex, 12CO (a), 13CO (b), and C18O (c), respectively. The 1 integrated velocity range is from 78 to 120 km s− , which correspond to the associated with W43 from the previous IRAM CO J =2-1 observations of Carlhoff et al. (2013). The Xs marks show the center position of W43 Main and W43 South (Blum et al. 1999; Wood & Churchwell 1989). The whole of GMC complex distributes over 150 pc of the Galactic plane. The CO intensity ∼ has peaks at W43 Main, G30.5, and W43 South. Figure 6, 7, and 8 shows the velocity channel maps of 12CO, 13CO, and C18O, respectively. The velocity range is from 66 to 125 1 1 1 G30.5km s− , and the integrated range is 4 km s− . The velocity range of the peak positions is 90-100 km s− of W43 Main, 100-109 1 ∼ 18 km/s of G30.5, and 97-105 km s− of W43 South. We find dense gas trace by C O has clumpy structures over the wide velocity range (Figure 8). 12 Figure 9 presents the longitude-velocity diagram with integrated the latitude of 0.◦4-0.◦4. The CO (low density gas) has broad 1 − 1 velocity width of 40-50 km s− (Figure 8a), which is larger than usually velocity width of the 100 pc size GMC (∆v 10 km s− ) ∼ • Broad velocity(b) 13CO width J=1-0 (30-40 km/s) calculatedlarger than by the Larson’s Larson’s law( law (∆v R0.5:) Larson 1981; Heyer & Brunt 2004). The 13CO is also similar structures of 12CO (Figure 18 ∼ 1 9b). On the other hand, C O (dense gas) has clumpy structures with velocity widths of < 10 km s− . (Figure 9c) Strong turbulent condition in Thethe total GMC molecular complex masses are derived as 1 107 M , 1 107 M , and 2 106 M from 12CO, 13CO, and C18O, ⊙ ⊙ ⊙ W43 Main W43 South 15 ∼ × ∼ × ∼ × respectively. We presented detailed information about the method to calculate the physical properties of the molecular gas at Appendix A. In the next subsection, we focused on the W43 Main, G30.5, and W43 South which correspond to the peaks of C18O dense gas aiming to reveal the origin of the dense gas and high-mass stars.

3.3 W43 Main G30.5 3.3.1 13CO and C18O spatial distributions and the velocity structures 1 1 1 1 We find four different velocity clouds (82 km s− , 94 km s− , 103 km s− , and 115 km s− ), that are likely to be physically associated with the W43 Main cluster. Figure 10 presents the integrated intensity maps of each cloud from 13CO (Figure 10 a-d) and C18O (Figure 10 e-h) emission. The X-mark indicates stellar cluster, and white circles show 51 proto-clusters defined by Motte et al. (2003). 18 1 (c) C O J=1-0 The 82 km s− cloud (Figure 10a,10b) has a peak at (l, b) (30.◦66, 0.◦03), and extends over 20 pc on the western side of 1 ∼ the cluster. The 94 km s− cloud (Figure 10b,10f) is the brightest component and distributes over 20 pc around the cluster. The 13 + two peaks of CO correspond to the W43-MM1 and W43-MM2 ridge identified by using the N2H and SiO emission (Nguyen- W43 Main W43 South 18 1 Luong et al. 2013). In particular, W43-MM2 ridge is the brightest of C O emission (Figure 10f). The 103 km s− cloud (Figure

3 http://montage.ipac.caltech.edu

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12 13 18 Fig. 9. Longitude-velocity diagram of the CO (a), CO (b), and C O (c) J = 1–0 with the integrated latitude range of B = 0.◦4– 0.◦4. − − 24 Publications of the Astronomical Society of Japan, (2014), Vol. 00, No. 0

(a) 12CO J=1-0

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18 12 13 18 Fig. 9. Longitude-velocity• diagram of the CO (a), CO (b), and C O (c) J = 1–0 with the integrated latitude range of B = 0.◦4– 0.◦4. C O has clumpy structures in the GMC − − Detailed analysis of the dense clouds in the GMC complex 16 Results 3 Detailed analysis toward W43 Main, G30.5, and W43 South

17 Publications of the Astronomical Society of Japan, (2014), Vol. 00, No. 0 15

Spitzer, blue: 3.6 μm, green: 8.0 μm, red: 24 μm (a)

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13 18 Fig. 11. Galactic latitude-velocity diagram of CO (a) and C O J = 1–0 (b) integrated over the latitude range from 30.◦7 to 30.◦83. The black boxes show 1 1 the radio recombination line velocity (91.7 km s− ) at (l, b)=(30.◦780, 0.◦020) from Luisi et al (2017), where their resolution is 1.86 km s− 82′′. Fig. 1. (a) Spitzer three color composite image of W43. Blue, green, and red show the Spitzer/IRAC− 3.6-µm, Spitzer/IRAC 8-µm (Benjamin∼ × et al. 2003), and • Four velocity components towardThe W43 yellow dashed Main line indicates the position of W43 Main cluster (Blum et al. 1999) Spitzer/MIPS 24-µm (Carey et al. 2009) results. The X marks indicate W43 Main (Blum et al. 1999) and W43 South (Wood & Churchwell 1989). (b) Close-up •imageRadio of W43 recombination Main. The white circles line indicate velocity the 51 compact at the fragments center (W43 cloud MM1-MM51) cataloged by Motte et al. (2003). (c) Close-up image of G30.5. (d) Close-up image of W43South. The white crosses indicate the radio continuum sources identified by Condon et al. (1998). The three clouds are connected at intermediate velocities 18 Publications of the Astronomical Society of Japan, (2014), Vol. 00, No. 0 15

Spitzer, blue: 3.6 μm, green: 8.0 μm, red: 24 μm (a)

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(a) G30.5 13CO J=1-0 (b) C18O J=1-0 (b) (c) W43 Main G30.5 113 km/s cloud (d) W43 South (G29.96-0.02)103 km/s cloud IRAS 18445-0222

G030.213-00.156

W43 Main cluster 88 km/s cloud 7 N52 bubble 1 6 W43-MM1 2 93 km/s cloud 4 5 8 9 3 IRAS 18447-0229 10

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RRL velocity IRAS 18456-0223 10pc 10pc 10pc

13 18 Fig. 14. Galactic latitude-velocity diagram of CO (a) and C O J = 1–0 (b) integrated over the latitude range from 30.◦15 to 30.◦55. The black boxes show 1 1 the radio recombination line velocity ( 102.5 km s− ) at (l,b) (30.◦404, 0.◦238) from Lockman (1989), where their resolution is 4 km s− 3′. Fig. 1. (a) Spitzer three color composite image of W43. Blue,• green,Four andvelocity red show clouds the Spitzer/IRAC toward G30.5 3.6-µm, Spitzer/IRAC 8-µm (Benjamin∼ et al.∼ 2003),− and ∼ × Spitzer/MIPS 24-µm (Carey et al. 2009) results. The X marks• indicateRadio W43recombination Main (Blum et line al. 1999) velocity and W43 at the South center (Wood cloud & Churchwell 1989). (b) Close-up image of W43 Main. The white circles indicate the 51 compact fragments (W43 MM1-MM51) cataloged by Motte et al. (2003). (c) Close-up image of G30.5. (d) Close-up image of W43South. The white crosses indicateThe the radiofour continuum clouds sources are identified connected by Condon et at al. (1998).intermediate velocities19 Publications of the Astronomical Society of Japan, (2014), Vol. 00, No. 0 15

Spitzer, blue: 3.6 μm, green: 8.0 μm, red: 24 μm (a)

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(b) W43 Main (c) G30.5 (a)W43 South 13CO J=1-0 (b) C18O J=1-0 (d) W43 South (G29.96-0.02) 102 km/s cloud IRAS 18445-0222

G030.213-00.156

W43 Main cluster 7 N52 bubble 1 6 W43-MM1 2 4 5 8 9 3 IRAS 18447-0229 10 RRL velocity G030.404-00.238 93 km/s cloud

IRAS 18456-0223 10pc 10pc 10pc 13 Fig. 17. Galactic longitude-velocity diagram of CO J = 1–0 integrated over the latitude range from 30.◦7 to 30.◦83. The black boxes show the H110α radio 1 1 recombination line velocity ( 96.7 km s− ) at (l,b) (29.◦944, 0.◦042) from Lockman (1989), where their resolution is 4 km s− 3′. The blue dotted ∼ ∼ − ∼ × Fig. 1. (a) Spitzer three color composite image of W43. Blue, green, and red show the Spitzer/IRAC 3.6-µm, Spitzer/IRAC• Converging 8-µm (Benjamin two et al. 2003), clouds and at thelines UCHII present the V-shaperegion structure. Spitzer/MIPS 24-µm (Carey et al. 2009) results. The X marks indicate W43 Main (Blum et al. 1999) and W43 South (Wood & Churchwell 1989). (b) Close-up image of W43 Main. The white circles indicate the 51 compact fragments (W43 MM1-MM51) cataloged by Motte et• al.“V (2003).-shape” (c) Close-up structures image of G30.5. around W43 South (d) Close-up image of W43South. The white crosses indicate the radio continuum sources identified by Condon et al. (1998). • Radio recombination line velocity at the center cloud The two clouds are connected at intermediate velocities 20 Discussion 1 CO properties of the W43 GMC complex

21 36 Publications of the Astronomical Society of Japan, (2014), Vol. 00, No. 0

(a) 12CO integrated intensity (b) 13CO integrated intensity (c) C18O integrated intensity 36 Publications of the Astronomical Society of Japan, (2014), Vol. 00, No. 0 Comparison the gas properties with W51 and M17 (a) 12CO integrated intensity (b) 13CO integrated intensity (c) C18O integrated intensity

Fig. 22. Histogram of the integrated intensity of the each pixels in W43, W51, and M17 from 12CO (a), 13CO (b), and C18O J =1–0 (c), respectively. The 1 1 1 frequency is normalized by 47-70 K km s− , 18-27 K km s− , and 2.7-4.0 K km s− , respectively. The clipping levels are adopted as 5σ of the each region.

Fig. 22. (a)Histogram 12CO ofbrightness the integrated temperature intensity of the each pixels(b) in 13 W43,CO W51, brightness and M17 fromtemperature12CO (a), 13CO (b), and(c) C C1818OOJ =brightness1–0 (c), respectively. temperature The 1 1 1 frequency is normalized by 47-70 K km s− , 18-27 K km s− , and 2.7-4.0 K km s− , respectively. The clipping levels are adopted as 5σ of the each region.

(a) 12CO brightness temperature (b) 13CO brightness temperature (c) C18O brightness temperature

LowFig. 23.densityHistogram ofgas the brightness temperature of the each voxels in W43, W51, and M17 from 12CO (a), 13CO (b), and C18O J =1–0 (c), respectively. TheDense gas frequency is normalized by 7.3-9.2 K, 6.7-7.5 K, and 1.9-2.1 K, respectively. The clipping levels are adopted as 5σ of the each region. The 12CO (low density) gas has broad velocity feature

Fig. 23. Histogram18 of the brightness temperature of the each voxels in W43, W51, and M17 from 12CO (a), 13CO (b), and C18O J =1–0 (c), respectively. The 22 Thefrequency C is normalizedO (high by 7.3-9.2 K,density) 6.7-7.5 K, and 1.9-2.1 gas K, respectively. has locally The clipping levels high are adopted brightness as 5σ of the each region. temperature Discussion 2 The origin of dense gas and mini-star burst in the GMC complex

23 28 Publications of the Astronomical Society of Japan, (2014), Vol. 00, No. 0

Bridging features and V-shape structures (a) G30.5 13CO J=1-0 (b) C18OSynthetic J=1-0 observations lse,wihaeitrrtda vdneo lu–lu col- cloud–cloud of evidence segre- star as the for interpreted about are search which components to cluster, cloud us blue–shifted allow and red also using gated would star(s) any This of particles. formation sink the in model sim- “naturally” future also Ideally would happen resolution. ulations higher which at collisions models scale re-run galactic to be would scale di galaxy perform using from to derived and clouds useful models, two be using would analysis It similar neces- models 2015). a scale not al. galaxy et are in Rey-Raposo formed conditions (e.g. those on initial of head representative these sarily a reality undergoing In isolated, clouds collision. two turbulent considered spherical, models initially collision cloud–cloud The 6MODELLIMITATIONS is collision clouds. di the that two that along given sequentially possible latter, is place and the it taking times formed, If snapshot already braking. our have than much stars stage undergone earlier clouds not an velocity at has higher is sepa- between it that are was could or which collision peaks simulations, the M20 our that The than velocity mean models. larger the a in by rated to see similar to- we observations peaks that discernible the those two for showing diagram clearly p–v M20, the wards of middle the over iden- to easier be will between velocities tify. Collisions turbulent clouds. lower the with of clouds spectrum turbulent the to e the illus- to This there resilient feedback. is produced radiative bridge feedback. is broad to diagram the due that this prep). bubbles trates that (in ionised al simulation many et the are Shima in in time published the be At to feedback, radiative and enzo 12. Figure 10 1992PASJ...44..203H 1992PASJ...44..203H 30 113 km/s cloud Publications of the Astronomical Society of Japan, (2014), Vol. 00, No. 0 h otmpnlo iue1 hw h enprofile mean the shows 11 Figure of panel bottom The oe facodcodcliinicuigsa formation star including collision cloud–cloud a of model 103 km/s cloud 6 T. J. Haworth et al. al. et Haworth J. T.

A Haworth+15a 12 OJ10psto–eoiydarmo new a of diagram position–velocity J=1-0 CO ↵ rn matprmtr.Ee better Even parameters. impact erent

88 km/s cloud ↵ rn opnnso the of components erent 93 km/s cloud ↵ cso radiative of ects Habe & Ohta 92

RRL velocity Multiple Cloud-cloud collision scenario can yTrie l 21) u oesteeoespotthe support therefore collision models cloud–cloud Our of (2011). site al. formation a et star be massive Torii to of by concluded site cloud–cloud was young very which feature identifying bridge a broad for M20, this of towards signature potentially instances find scenarios, useful also We other bycollisions. a the reproduced it of not any is broad making is from feature bridge emission a diagrams This intensity broad p–v axis. to lower velocity This by the rise separated diagrams. across spikes give p–v intensity in two models structure collision bridge Cloud–cloud 1) work: this these cloud–cloud from conclusions compare of following We signatures the draw disc. characteristic We collisions. galactic identify and a feedback try in radiative to evolving internal GMC with a line clouds and the turbulent along sight, coincident of number clouds a turbulent for non–interacting diagrams di p–v synthetic of calculated have We 7SUMMAR other degener- with conjunction becomes in signature give diagnostics). useful also the still can then potentially processes (though bridge ate these broad of a which any to If features, rise here. velocity YANDCONCLUSIONS study par- not high In do produce we shocks. can arm spiral outflows traversing ticular in those discussed or signature 3.1.2) H elliptical section leaky the less give scale should in (which large feedback p– gions radiative supernovae, investigate gravity, by to not disrupted due do flows clouds we for example, diagrams For v exhaustive. be case not the not here. is studied which models stars) collision massive the in of ongoing is formation is collision collision the the subject the (i.e. after length unless be cloud field the will radiation along collision sequential ionising cloud-cloud external of an be site to should a it stars, that massive unlikely of formation the triggers collision radiative with simulations work. in subsequent in bridge time ob- feedback the broad still study the is will bridge of We broad evolution sce- feedback. the this radiative time, in despite in least servable which snapshot At in this discernible. 12 at definitely Figure nario, We is in bridge snapshot bubbles. this broad ionised of a multiple of diagram are p–v onset massive there the first the plot time the after which of formation at Myr 3 the star, after feedback. snapshot Myr 2.5 radiative one and include study collision and we fol- stars now, also the of For simulations clouds to the formation the similar and the but 20km/s are low at paper, These colliding this larger, prep). in simu-are (in models ongoing al collision the et cloud–cloud from Shima snapshot of broad a the lations disrupting postprocess e to the we comes bridge into bridge it insight broad when initial feedback the an radiative gain that of To conceivable lived. clumps long is small be it radiative might accelerating 3.1.2), internal primarily section that be (see to Given seems collision. feedback the after 2014). survives (e.g. 2011); al. (e.g. al. et et Torii 2009b); Fukui (e.g. al. et Furukawa by lision ial,teatohsclseaista eepoemay explore we that scenarios astrophysical the Finally, cloud the that premise the on working are we Since signature this long how determined not also have We

↵ The lifetimes of broad bridges 1635 rn srpyia ytm:codcodcollisions, cloud–cloud systems: astrophysical erent explain the observational velocity structures 13 13 18 18 Fig. 14.(a)GalacticW43 latitude-velocity South diagramCO of CO J=1-0 (a) and C O J = 1–0 (b) integrated over the latitude(b) range fromC 30O.◦15 J=1-0 to 30.◦55. The black boxes show 1 1 the radio recombination line velocity ( 102.5 km s− ) at (l,b) (30.◦404, 0.◦238) from Lockman (1989), where their resolution is 4 km s− 3′. ∼ ∼ − ∼ × 102 km/s cloud Synthetic observations c 02RS MNRAS RAS, 2012 Downloaded from https://academic.oup.com/mnras/article-abstract/454/2/1634/2892502 by Nagoya University user on 04 March 2019

RRL velocity Haworth+15a Haworth+15b 000 93 km/s cloud ,1–12

ii Haworth+15 ↵ ect re- 24 Figure 1. A schematic of a collision–observer system and a cartoon p–v diagram showing a broad bridge feature. Different colour components in the 13 collision schematic correspond to the different colours on the p–v diagram. Fig. 17. Galactic longitude-velocity diagram of CO J = 1–0 integrated over the latitude range from 30.◦7 to 30.◦83. The black boxes show the H110α radio 1 1 Figure 2. An example CO (J 1 0) p–v diagram of a possible cloud– recombination line velocity ( 96.7 km s− ) at (l,b) (29.◦944, 0.◦042) from Lockman (1989), where their resolution is 4 km s− 3′. The blue dotted = → ∼ ∼ − ∼ × range of different simulations of molecular clouds, including cloud cloud collision towards M20 (Torii et al. 2011). This p–v diagram is produced lines present the V-shape structure. collisions and isolated clouds with radiative feedback. We found using data taken using Mopra and was presented in Haworth et al (2015). that indeed broad bridges appeared in our cloud collision models, but did not arise in any of the simulations of isolated clouds with ra- observer viewing angle in the schematic, the observer sees some diative feedback (though in principle, a broad bridge could possibly redshifted component moving away from them, a blueshifted com- arise given a favourable configuration of gas clouds merely coinci- ponent moving towards them and the intermediate-velocity gas. In dent along the line of sight). Haworth et al. (2015) also compared the p–v diagram, this manifests itself as two peaks along the veloc- the simulated p–v diagrams with observed broad bridge features ity dimension, separated by lower intensity intermediate-velocity towards M20, a site of collision according to Torii et al. (2011). emission – the broad bridge feature. An example of a p–v diagram Broad bridges in p–v diagrams clearly can arise from cloud– with a broad bridge towards in M20, taken with Mopra, is given in cloud collisions; however, it is currently unclear for how long they Fig. 2. should survive. Feedback from winds and the ionizing radiation The intermediate-velocity gas is replenished as long as the col- field of any OB stars that form as well as the conversion of gas lision is still occurring, so in order to remove the broad bridge into stars and the finite lifetime of the collision will presumably feature the collision either needs to end (being fully braked or with limit the amount of time that broad bridge features are visible for. one cloud punching right through the other) or the compressed dense In this paper, we combine a series of analytic arguments with new layer resulting from the smaller cloud needs to be at least partially synthetic observations of cloud collision models, both with and removed. without radiative feedback, to try and address this question. 12 12 Figure 5. CO J=1-0 position–velocity diagrams of the enzo Figure 6. CO J=1-0 position–velocity2.2 Details of diagrams the collision for the feed- models of cloud–cloud collisions. The upper panel is2ANALYTICARGUMENTSREGARDING for a sim- back simulations of Dale et al. From top to bottom the panels are We consider a collision between two clouds in a scenario similar ulation snapshot just prior to the collision (the cloudsTHE are TIME-SCALE just models FOR DISRUPTION J, UP and UQ. to that discussed by Habe & Ohta (1992). One cloud of radius R touching) in the 10 km/s collision model, with both cloudsOF BROAD along BRIDGES 1 collides with a second, larger (R ), cloud at velocity v .Theentirety the line of sight. The middle and lower panels are from the 10 and 2 c In this section, we explore the time for which a broad bridge feature of the small cloud has been compressed after a time approximately 5km/scollisionmodelsrespectivelyatthepointofmaximumcore might survive. There are many processes that might act to remove given by tc R1/vc (this is a lower limit, since it assumes that formation in each model (c.f. 2.1.1). the broad bridge such as the collision being completely braked or the post-collision≈ velocity is small). We work in a frame in which ending as one cloud punches through the other, radiative/mechanical the larger cloud is stationary. After tc the compressed layer is still feedback from massive stars and the conversion of gas into stars. moving with some finite bulk velocity relative to the larger (in our c 2012 RAS, MNRAS 000,1–12 frame, static) cloud, meaning that the broad bridge is still observable for some subsequent time-scale (to be determined below). Our con- 2.1 Preamble: what is the broad bridge siderations here are only very approximate, we do not include the We begin by recapping what the broad bridge feature is in the con- effects of turbulence or instabilities that can arise in a compressive text of a collision. Fig. 1 shows a schematic of a cloud–cloud col- flow (e.g. McLeod & Whitworth 2013). lision, as well as a cartoon of the p–v diagram the observer would see. A smaller cloud (blue) drives into a larger cloud (red). The 2.3 The collision time-scales entirety of the smaller cloud undergoes collision quite quickly, re- sulting in a compressed layer that continues to move into the larger The broad bridge will disappear if the clouds break to the extent that cloud. Between the bulk velocities of the compressed layer and they are no longer separated in velocity by more than half the sum larger cloud, there is intermediate-velocity gas (yellow). For the of their turbulent velocity dispersions. If this happens, then only

MNRAS 454, 1634–1643 (2015) Publications of the Astronomical Society of Japan, (2014), Vol. 00, No. 0 37

(a) 12CO velocity width (mom 2) (b) 13CO velocity width (mom 2) (c) C18O velocity width (mom 2)

Fig. 24. Histogram of the second moment map (velocity width) of the each pixels in W43, W51, and M17 from 12CO (a), 13CO (b), and C18O J =1–0 (c), 1 1 1 respectively. The frequency is normalized by 2.5-4.0 km s− , 2.5-4.0 km s− , and 1.7 km s− , respectively. The clipping levels are adopted as 5σ of the each region. Possible formation scenario in the W43 GMC complex W43 Giant molecular cloud complex 12CO

O-stars

Dense gas (C18O) Cloud motion

~100pc Molecular cloud (13CO)

Cloud-cloud collisions

10 pc b

l ~150 pc Based on the Inoue-san’s slide Fig. 25. Schematic picture of our proposed dense gas and O- scenario of the W43 giant molecular cloud complex. Formation of the dense gas and mini-star bursts produced by cloud-cloud collisions 25 Publications of the Astronomical Society of Japan (2018), Vol. 00, No. 0 7

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30 b=0.23 deg (Tb+20 K)

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Fig. 6. Horizontal cuts of the CO-line brightness at v 95 km s 1 at b = − = 0. 45 and 0. 23. Note the sharp intensity rise at the western edge. The − ◦ + ◦ trianglesSuper indicate the longitudes-sonic of G29.96, flows G30.5, and W 43 Main.across the spiral arms (Sofue+85, 18b) 8 2 PublicationsPublications of the the Astronomical Astronomical Society Society of Japan of(2018), Japan Vol.(2018), 00, No. 0 Vol. 00, No. 0

intensities with those at 330 MHz considering the missing Millimeter/submillimeter Array (ALMA) high-resolution maps (Egusa et al. 2018; Hirota et al. 2018). flux in the VLA map. The structural relation between H II regionsGas and flow molec- The emission measure of the responsiblePublications ionized gas of is the Astronomicalular clouds has Society been one of Japan of the major(2018), subjects Vol. 00, of No. star 0 11 3 6 formation mechanics in the Galaxy, such as cloud–cloud

estimated to be EM 7 10 pc cm− for an assumed FaceDownloaded from https://academic.oup.com/pasj/advance-article-abstract/doi/10.1093/pasj/psy106/5127361 by Nagoya University user on 22 October 2018 -on location of W43 ∼ × 4 collisions (McKee & Ostriker 2007). However, spatially- electron temperature of Te 10 K(Sofue1985Figure). The10 elec-b shows a map of fmol, and figures 10c and 10d resolved relations between individual H II regions and dark = 3 tron density is, then, estimated to be n are8cm horizontal− for an cross-sections at b 0◦.5 and vertical at e ∼ clouds in external =+ seem not to have been studied assumed line-of-sight depth equal to the verticall 29 extent◦.5 and of L 30◦.5, respectively.yet. We here focus The on figures individual show H II thatregions the and their Downloaded from https://academic.oup.com/pasj/advance-article-abstract/doi/10.1093/pasj/psy094/5096753 by guest on 15 September 2018 = 2 morphological relation with their associated dark clouds in 100 pc. The H II mass is calculated to be MmolecularmHneL W fraction is saturated in the GMA and GMC at ∼ 4 2 ∼ ∼ M 83. We will show that their morphology is similar to the 2 10 M ,whichis 3 10− times the molecularfml 0.8–0.9. mass. ⊙ cometary cone structure modeled for G30.5 in the Galaxy. × Fig. 1. 12CO(∼J 1–0)× intensity map (gray) of the molecular≥ bow shock This yields the thermal energy= density, or internal pressure, . (MBS) G30.5 in the Galaxy overlaid on a 10 GHz continuumThe horizontal map (con- cross-sectionIn order to explain at theb morphology,0◦5 (figure we propose10b) qualitative 11 3 = II of the H II gastours) of pint (Sofuen ete al.kT2018e ), which1.1 forms10 a− concaveshowserg arccm with a− sudden. respect to increasemodels of basedfmol onmaking theories of a bow sharp shocks molecular and expanded H W43.Thicklinesindicatecalculatedbowsfor∼ ∼ × R 25, 50, and 75 pc. Downloaded from https://academic.oup.com/pasj/advance-article-abstract/doi/10.1093/pasj/psy094/5096753 by guest on 15 September 2018 bow = regions. We may considerThe scale represents two possible 50 pc at the sources distance of to 5.5front ionize kpc. coincident the gas with the MBS front. This fact shows that

in the continuum bow. One possible mechanismthe H isI gas ioniza- is transformed to H2 by the shock compression tion by UV illumination from inside by OBat stars the inMBS W 43, front. 2 Extragalactic giant cometary H II regions Fig. 7. Theoretical bow-shock front for standoff distance RS 25,(GCH) and molecular bow shocks (MBS) and the other is shock-induced ionization by theThe inflowing separate structure= between CO and H I is under- 50, and 75 pc centered on W 43 at (X, Y) (0, 0) pc, overlaid onWe the examine optical images taken from the STScI and 12supersonic flow by the Galactic shock wave.= I CO(J 1–0) map. stood by transitionNASA of H webto sites H of2 Mat 83 the in λ438, MBS 502, edge and 657 in nma bands, = The first, probably most likely, mechanismshort is ionization timescale. Theobserved transverse with HST. velocity We adopt of the the inflow nucleus positionof at from inside (the downstream side) by UV photons from h m .s . 1 H I gas is on the orderRA of δ13V 37(V00 8 andV Dec)sin p 2930◦51 km′56′′ s0(Sofue&− . 1–0) intensity map, where the curve for 50 pc represents= = rot − p = ∼− OB stars in W 43. This postulates the standardThen formation the transitionWakamatsu time is estimated1994) and toa distance be t ofλ 4.5/δ MpcV (Thim3 et al. the observed MBS shape well, in agreement with the above2003). Figure 3 shows an HST image of M 83 at 657 nm, mechanism of an H II region around an OB star5 cluster. ∼ ∼ 10 yr, where λ where10 pcGCHs is theassociated width with of dark the bow-shapedtransition features theoreticalThe radius ofestimation a steady-state of RS (well-evolved)54 pc. We× H emphasizeII region is that∼ the ∼ region, which may(MBSs) be approximated are marked by white by the arcs. width Figure 4 ofshows the the same, Fig. 5. (Top) Velocity–latitude diagram at G30.513. The contours are bow-shockgiven by model can represent the observedmolecular BS. shapes andbut as a supplement for the outer region. drawn every 3 K, starting at 3 K. (Bottom) Schematic view of relative The identification of MBS GCH was obtained by eye- dimensions of the MBS well, if W 43 andThe its constantly surrounding high molecular fraction of+ fmol 0.8–0.9 line-of-sight motion of the MBS’s tangent ridge. identification as follows (numerical identification∼ might be near the Galactic planedesirable, manifests but is far the beyond global the highscope ofmolecular the present skills in dense molecular cloud1/3 is the triggering source of the shock. 3NUV fraction in the innerimaging Galaxy. astronomy). A study First, of galactic-scaleit was easy to findf H II regions FullRH II discussion of the, bow-shock formation mechanism(5) mol where m˙ is the mass injection rate into the shock front, and ≃ 4πnineαr and open clusters using each of the three color photographs ! Fig. 2."Illustration of the molecular bow and GCHvariation concave to theindicated central Fig.fmol 8. (Top)0.8–0.9 Illustration at R of the4 cross-sectionkpc within and the flow lines through the in interstellar gas clouds in galactic spiral shock waves,(e.g.,∼ red for H II regions and∼ blue for OB clusters), as well is approximated by OB proposed for the W 43 SF complexmolecular in the 4 kpc disk arm in of thicknessMBS. The arched50 shape pc (Sofue is formed & by Nakanishi the bow shock and hydraulic jump • Superthe Galaxy- (Sofuesonic et al. 2018 ).flow The small insert across shows an illustration the for as arm assisted by theencountering color-coded image as inserted in the figure 3. dense gas (W43 Main) including analyses of a number of dark-cloud bows foundin the z direction.∼± (Bottom) The same, but seen face-on. The molecular a wavy sequential star formation, discussed later.2016). Then, a search for associated dark lanes and clouds was bow is formed around a giant cometary H II region, concave to the central inwhere nearbyNUV spiralis the UV galaxies, photon number will be radiated presented by the in OB a separateobtained, and young, therefore bright, SF/H II regions are m˙ MMBS/τ. (4) -> Molecular bow structuresOB stars. formed Similar dark bows by and giantthe H II cones Galactic are commonly observedshock compression ∼ stars and α M 834 (NGC10 5236).13 cm Assuming3 s 1 is that the dark recombination clouds in optical almost always associated with dark clouds. We excluded paper (Y. Sofuer in preparation).− − − in star-forming spiral arms of external galaxies (Y.SofueFig. in preparation). 11. (Top) Face-on location of the 4 kpc molecular arm near W 43 at ∼images× represent molecular clouds, we name them MBSs. too faint or diffuse H II regions, which are either associated rate. If we assume that the luminosity of the central cluster adistanceof5.5kpc,adoptedfromZhangetal.(2014). The thick and Here, τ d/V and d 10 pc is the width of the MBS, Vw is We also show that MBSs are generally associated with giant with diffuse clouds or not associated with dark clouds. is comparable to the far-infrared luminosity,5Discussion1.23 point out that similar giant cometary H II regionsnarrow with arrows Hα- indicate the gas flow and radial velocity,26 respectively. = ∼ cometary H II regions (GCH) on their down-streamL sides, By pairing an H II region and a dark cloud, their mor- Gas compression∼ × at the bow head(Bottom) Chronological region passage of the W 43 group (t 0y)ingalactic the wind velocity from the central body, and is replaced by 7 10 L , of dustwhich clouds may alternatively in the central be called 10 giantpc of H WII cone 43 (GHC). (Lin brightphological rim relation are often was looked observed into in in detail galactic individually. shock wave arms = 1 3 3.3 Giant⊙ cometary H II region with5.1 brightFormation rim mechanism of a galactic bow rotation at Vrot through the Galactic shock wave corotating at the pattern Vw σ v 10 km s− , and ρ 30 H cm− is the ambient gas et al. 2016), andTherefore, that an the MBS ionized and a GCH make density one single is setn of ofIn external most cases, galaxies an H II region (Y. Sofue is surrounded in preparation). by an arc of ∼ ∼ ∼ shock i speed Vp of the spiral potential. The sketch is in the corotating system objects.3 So, they may be often referred to as either MBS dark lane in such a way that the H II region is lopsided and density in the outskirts of the GMA taken as the logarithmic Figurene 28cmshows− from a positional the continuum coincidence EM, then of the we 10 have GHz con-Another hypothesis attributes the originat toVp ram. pres- ∼ ∼ or GCH. open to the interarm direction, whileI the other, brigher side 3 3 We first assume that the 4 kpc arm is the H H2 spiral mean of the H I (8 H cm− ) and molecular (100 H cm− ) tinuumRH II 130 bow pc. structureThe morphology with and the energetics molecular (luminosity) bow of atindi- G30.5,sureis facing by a the concave inflowing bow-shaped gas dark from+ lane, the as upstream illustrated side. The ∼ arm defined by Sofue and Nakanishi (2016) as Arm No. 4, By the2 bow shock and the hydraulic jump, the gas is Thus, W 43vidual is luminous H II regions enough and OB clusters to blow have off been most studied of by ramin figure pressure2. Thus is a discovered estimated lopsided to be HpIIextregion andmHn apre#v 7 densities. The inflow gas velocity is given by (Vrot Vp)sin p while the continuum is slightly inside the MBS. The radio optical imaging of M 83 using thewhich Hubble is Space identical Tele- tomolecular the Scutum11 arc are arm here3 of identified Sato et as al. a GCH (20141 and),= an MBS,also accelerated∼ in the z direction, and is lifted to higher z. 1 − the ambient H II gas to radius 100 pc. However, the 10− erg cm− for #v 10 km s− . Here, the pre-shock 30 km s− ,whereVrot and Vp are the rotation velocity bow is also clearlyscope (HST) visible (Chandar on the et∼ al. 2,2010 7,, and2014and;Liuetal. 5 W GHz 43 Main, maps2013; West, using×assuming and that G30.5 a dark MBS cloud are is a∼ molecular located cloud. along According to the loss of angular momentum by the inter- expanding H II gas is blocked by the dense molecular gas gas density was estimated by H I density observed toward ∼ Blair et al. 2014; Whitmore et al. 2011). High-resolution The GCH and MBS are generally located on the down- and pattern speed of the spiral arm, respectively, and p the Bonn 100 m telescope (Altenhoff etthis al. 1979 arm. ;Reichetal. action with the slowly rotating spiral potential at Vp, the blowing from themolecular upstream gas distribution side in the in Galactic M 83 has shock been extensively wave. streamG30.2 sides0.2 of using dark lanes the H ofI spiralmap arms.by Bihr Each et GCH al. (2015) to be Since there is no∼ parallax+ for W 43 Main3 and G30.5, rotation velocity, Vrot, of the shocked gas is decelerated. is the pitch angle of the arm. Inserting these values into 1990This) counter-flow and onobserved the compresses in 330 the CO MHz line the emissions, map H II sphere byand detailed Subrahmanyan to comparativekeep its n andispre sheathedNH I/ insideL 40H an MBS, cm− and,where the innerL wall100 of pc an is the line-of- studies on H II regions are obtained usingthere Atacama remains Large a possibilityMBS∼ coincides that∼ withW 43 the is outer far ( front9 kpc) of2 the and∼ H II regionThis results in a bow-like behavior in the v, b diagram equation (3), we obtain RS 54 pc. Gossradius ( smaller1996) than usingRH theII.Theobservedstandoffdistance VLA. Spectral indices betweenRS sight 10 depth and NH I 100 ∼M pc− is the H I column after ∼ G30.5 near ( 5 kpc), or vice versa. However,∼ the⊙ fact that (figure 5). In figure 7 we present the bow-shock shapes calculated and50 2.7 of theGHz MBS indicate can thus that be naturally the emission explained is thermal by such∼ (Sofuesubtraction of the extended background. Thus the inflowing ∼ the MBS has a clear arc structure concave to W 43 may The velocity gradient (figure 4) at the bow front is 12 a compressed radius of the H II region excited by W 43. On gas pressure is sufficient to heat and partially ionize the gas for RS 25, 50, and 75 pc overlaid on the CO(J 1985), which is also confirmed by comparing the 10 GHz 1 = = the contrary, on the downstream side of W 43be the taken gas flowsas evidenceat thethat bow they shock. are physically Note also interacting. that the pressureas large is compa- as 5 to 10 km s− per 10 pc, or 50 to 1∼− 1 − ∼ ∼− So, we assume here that both W 43 Main and the MBS are 100 km s− kpc− . This is significantly greater than the away from W 43 causing suppressed ram pressure, so that rable to the internal pressure by the molecular− gas in the on the same side, and, further, with the near2 side closer to11 radial3 velocity gradient due to Galactic rotation, which is the H II gas expands farther into the inter-arm region. GMA of pmol 2mHnH2 σv /2 7 10− erg cm− for σ v ∼ ∼ × ∼ 1 1 G29.96 (West) in the same GMA.1 on the order of 10 km s− kpc− . Thus, the velocity jump As a consequence, a giant cometary H II region showing 10 km s− , so that it can compress the molecular gas in the ∼− a lopsided cone of ionized gas open to the downstreamBased on this assumption,GMA stacked we at consider the Galactic a possible shock insce- the potentialcan be reasonably well. attributed to a specific change in the local side is produced inside the MBS, as illustratednario in figureto explain8. theThe kinematics morphology and of three-dimensional the MBS and continuumflow bow velocities remind around the BS. In fact, the radio continuum bow representingmolecular the H II structurerim us of of the the G30.5 cometary MBS. H AsII regions illustrated of in scales,According which to the scenario proposed here, W 43 and its is observed slightly inside the MBS in figurefigure2. We11, also the upstreamare considered gas at velocity to be producedV1 is accelerated by interactionmolecular of H II gas complex were formed prior to the encounter of toward the spiral potential well, where the gas is shocked, the gas in the BS. This means, in turn, that the SF and

compressed, and decelerated to velocity V2.Thevelocity molecular complex W 43 are being affected by the inflowing direction is bent suddenly at the front and, accordingly, the gas from the upstream side. projected line-of-sight (LSR) velocity is decelerated from Although we assumed a spiral structure, we comment up- to downstream sides. on a possible effect of the Galactic bar. The noncircular Non-circular gas motion3306 F. Renaud around et al. the long-bar Renaud+2015

W43

• W43 exists at the meeting Figurepoint 12. ofPositions the of thelong cloud- progenitorsbar and of the Scutum cloud–cloud collision, Arm 30 Myr (left) and 15 Myr (right) before the instant showed in Fig. 11.The‘P1’object is formed along the edge of the bar, while the other one (‘P2’) originates from a beads-on-a-string structure in one spiral arm. The two meet at the extremity • The collision frequency hasof high the bar. Thenear progenitor the ‘P2’ bar is itself-end the result region. of the collision of smaller clouds that occur between the two moments pictured here. The Scutum-Cruxand Norma spiral arms are visually identified with those of the real Galaxy, only for the sake of clarity. The label ‘bar edge’ points to elongated gas structures associated with the bar, i.e. not spirals. Cloud agglomeration near the bar-end region 27

Figure 13. Tangential velocity of the gas surrounding the cloud–cloud Figure 14. Schmidt–Kennicutt diagram of all the clouds in the simulation, merger shown in Fig. 11,comparedtothatofa‘control’cloudwhichhasnot highlighting the progenitors and their merger of the cloud–cloud collision experienced any recent interaction. Distances and velocities are computed discussed in the text. Surface densities are computed using the dense phase 3 in the reference frame of the cloud centre of mass. The merger exhibits a only (>2000 cm− ) at the scale of 50 pc. The dashes lines indicate power- rapid rotation (with a complex behaviour in the central 3pc),inducedby law fits to all the clouds, and the solid lines show the average values. ∼ the cloud–cloud interaction, while the rotation of the control cloud is several 3 times slower. above 2000 cm− , we find that, before the collision, P1 is among the most massive clouds (2 106 M ), while P2 is closer to average further into the high-mass tail of the initial mass function (IMF), (4 105 M ). Their Mach× numbers⊙ are comparable with that of or it could reflect a real change in the IMF towards a statistically the× bulk of⊙ the clouds, i.e. in the transonic regime ( 0.8 at the significant increase in the ratio of high- to low-mass stars. scale of 24 pc). After the P1–P2 collision, most of the≈ clouds in Fig. 14 shows a Schmidt–Kennicutt diagram of the pre- and the simulation have fragmented further and formed their star clus- post-collision stages, comparing the progenitors and the merger to ters. This translates into a mild shift of the Schmidt–Kennicutt 2 all the clouds in the simulation. By applying a density selection relation towards higher surface densities of gas and SFR. The rem- nant of the P1–P2 collision weights 5 106 M (in dense gas), 2 Note that we use this approach to minimize the numerical noise and the and yields a higher Mach number than its× progenitors⊙ ( 1.3). This effect of star formation stochasticity, which becomes significant at the scale translates in the Schmidt–Kennicutt diagram as the merger≈ hosting of individual clouds in our simulation. By using a density threshold and thus focusing on the densest regions of molecular clouds ( 5–10pc),our a more efficient star formation (i.e. a shorter gas depletion time) ∼ method differs from observational methods where a beam of fixed size is than average. This confirms the predictions of Renaud, Kraljic & used, which explains slight differences in the normalization of the relations Bournaud (2012) that supersonic turbulence increases the efficiency shown in Fig. 14 and the literature. See Kraljic et al. (2014)foramore of the conversion of gas into stars or in other words, decreases the observation-oriented approach. gas depletion time (see also Kraljic et al. 2014). We note that such

MNRAS 454, 3299–3310 (2015) Summary

• We carried out the CO survey toward the Giant molecular cloud complex W43 with the FUGIN project • W43 exists near the meeting point of the long-bar and spiral arm • The dense gas distribute at W43 Main, G30.5, and W43-South. • 12CO has broad velocity feature (30-40 km/s) • Three high-mass star forming regions has multiple velocity components connecting with bridging features • The 12CO (low density) gas has broad velocity feature and the C18O (high density) gas has locally high brightness temperature • Possible cloud agglomeration near the bar-end region

Possible the origin of the dense gas and mini-starburst produced by cloud-cloud collisions at bar-end region 28