Evolu&on of Molecular Gas in Spiral Galaxies How do molecular gas/clouds evolve across spiral arms? Jin Koda (Stony Brook University)

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1 Evolu&on of Molecular Gas in Spiral Galaxies How do molecular gas/clouds evolve across spiral arms? Jin Koda (Stony Brook University)

2 Textbook Picture How do molecular gas/clouds evolve across spiral arms? Atomic à Molecular à Atomic Arm (compression) Molecular H2 Interarm Atomic Background image: Churchwell et al Interarm Atomic

3 Suggested New Picture Arm Molecular H2 Interarm Molecular Koda et al H2 H2 Interarm Molecular

4 M51: CARMA + Nobeyama 45m CO Map GMC Distribu&on CO(1-0) Resolu&on ~160 pc Sensi&vity ~4x10 5 Msun (4sigma) Koda et al. 2009; Schinnerer et al GMC evolu*on Large (arm) à Small (interarm)

5 f mol: : Molecular Frac&on f mol = Σ H2 Σ H2 + Σ HI > 70-80% 10kpc Lidle Azimuthal Change Koda et al. 2009

6 Spurs/Feathers in CO(1-0) Filamentary structures in interarm regions M51 HST (Scoville et al. 2001) Spurs = chains of GMCs CO (1-0) on HST image Koda et al. 2009

7 Dynamically- Driven Evolu&on Mass: GMC on spiral ~ spurs ~ 10 7 M sun Wada & Koda 2004 SPH simula&on Isothermal gas Stellar spiral poten&al Spurs= Remnants of massive GMCs? CO (1-0) on HST image Koda et al. 2009

8 New Picture Evidence in M51 1. Molecular frac&on: only lidle azimuthal change 2. GMCs: large (arm) à small (interarm) 3. Spurs: chains of small GMCs; remnants of large GMCs Arm Molecular H2 Interarm Molecular Strong shear Spur Interarm Molecular

9 CO 2-1/1-0: Systema&c Varia&ons Koda et al Schuster et al CO(1-0) CO(2-1) CO(2-1)/CO(1-0) Spiral arms (mostly downstream) High ra&o ~ Interarm regions Low ra&o ~ M51 Resolu&on ~780pc LVG analysis à x2-3 increases in ρ and/or T The gas stays mostly molecular, but physical condi&ons evolve across spiral arms. Koda et al. 2012; Vlahakis et al. 2013

10 GMC Distribu&on in the MW Large (arm) à Small (interarm) Koda et al Spiral arms from HII regions (radio recombina&on line obs) BU- FCRAO 13 CO Galac&c Ring Survey Jackson et al. 2006

11 l- v Diagram I: Radial trend Example: HI distribu&on The LAB survey (Kalberla et al. 2005) Concentric circles Circular rota&on Koda in prep.

12 l- v Diagram II: Spiral Arms Example: CO distribu&on Steiman- Cameron et al Churchwell et al Robitaille et al. 2012, etc Spiral arms: circular rot. Pineda et al Columbia- CfA survey (Dame e al. 2001) Spiral arms: non- circular Koda in prep.

13 f mol in l- v diagrams b < ±30deg HI HI surface density Σ HI = T dv HI North ( l=0-65deg ) South( l= deg ) The LAB survey Kalberla et al H2 surface density Σ H2 = Xco T dv X CO = CO Columbia- CfA survey Dame e al Molecular frac&on f mol : mol. frac. f mol = Σ H2 Σ H2 + Σ HI Koda in prep.

14 f mol in the MW Molecular frac&on Galac&c radius [kpc] Radial gradient dominant Arm/interarm varia&ons (scaders) - - ~20-30% Koda in prep.

15 Clumpy in sp Growth of Dense Clumps through Spiral Arm 12CO Obs. of l~38deg region with Nobeyama 45m telescope Channel maps: 50 arcmin x 50 arcmin, 15 resolu&on (<0.7pc) Interarm Spiral arm Interarm Poster26 Sawada et al pc or 130pc 90pc

16 Brightness Distribu&on Func&on (BDF) Obs. of l~38deg region with Nobeyama 45m telescope Histogram of brightness temperature Interarm Spiral arm Frac&on of pixels Sawada et al T MB [K] in CO(1-0) ~ column density High T mb gas in spiral arms in the MW

17 Brightness Distribu&on Func&on (BDF) Obs. of l~38deg region with Nobeyama 45m telescope Histogram of brightness temperature Interarm Spiral arm Frac&on of pixels Sawada et al Kainulainen et al T MB [K] in CO(1-0) ~ column density High T mb gas in spiral arms in the MW

18 Brightness Distribu&on Index (BDI) Histogram of brightness temperature Interarm Spiral arm Frac&on of pixels Characterize distribu&on with one parameter Sawada et al (T 0, T 1, T 2, T 3 ) = (3, 5, 10, )

19 Evolu&on Across Spiral Arms BDI calculated in each dl x db = 2x1 deg 2 region BDI Distribu&on Sawada, Hasegawa & Koda 2012 High BDI in spiral arms Dense (or warm) cores developing BU- FCRAO 13 CO Galac&c Ring Survey Jackson et al. 2006

20 Atomic- rich vs Molecular- rich galaxies So far Molecule- rich M51 Atom- rich M33 LMC MW

21 GMC Distribu&on in M33 GMCs mostly on HI spiral arms Not many in interarm regions CO on HI GMC on HI ~1kpc Engargiola et al Central 1-2kpc region more like M51 & MW Tosaki et al. 2011

22 Summary Molecule- dominated galaxies (or regions) New picture: the gas stays molecular from arm through interarm. 1. Molecular frac&on: only lidle azimuthal change 2. GMCs: large (arm) à small (interarm) 3. Spurs: chains of small GMCs; remnants of large GMCs Arm: Molecular ρ and/or T H2 Interarm Molecular Atom- dominated Strong shear Old textbook picture: Atomic à Moleculer à Atomic Spur Interarm Molecular