1 / 55

Molecular Clouds and Star Formation in the Magellanic Bridge and the SMC

Magellanic Bridge. SMC. LMC. Putman et al. 1998. Molecular Clouds and Star Formation in the Magellanic Bridge and the SMC. Yasuo Fukui, Norikazu Mizuno ( Nagoya University ). Magellanic Bridge. HI connection between the Clouds (LMC-SMC)

kitty
Download Presentation

Molecular Clouds and Star Formation in the Magellanic Bridge and the SMC

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Magellanic Bridge SMC LMC Putman et al. 1998 Molecular Clouds and Star Formation in the Magellanic Bridge and the SMC Yasuo Fukui, Norikazu Mizuno ( Nagoya University )

  2. Magellanic Bridge HI connection between the Clouds (LMC-SMC) M(HI) Bridge ~ 5.5 x 107Msun (Putman et al. 1998) Bridge was pulled from the SMC 0.2 Gyr ago via a tidal encounter between the two Clouds, (e.g., Murai & Fujimoto 1980, Gardiner, Sawa & Fujimoto 1994) Yong Stars in the bridge (6-25 Myr) Blue stars and associations (e.g., Irwin 1990, Grondin 1992, Hambly et al. 1994) Young star formation in the western region ( few Myr ) H filamentary shell (DEM171, Meaburn 1986) Low Metallicity Z ~ 0.08 Zsun Based on C, N, O, Mg, and Si (Rolleston et al. 1999) SMC metallicity Z ~ 0.25 Zsun (e.g., Russel and Dopita 1992)

  3. Irwin et al. 1990

  4. DEM171, caused by a Wolf-Rayet star? Meaburn 1986

  5. Magellanic Bridge Nearby （~ 58 kpc） and extremely low metallicity => understanding evolution of galaxies star formation in the early universe and distant galaxies big bang small galaxies collision & merging giant galaxies H・He Metallicity：low Metallicity =>high In this study, Star formation (molecular clouds) in the Bridge Future of the Bridge

  6. Observation with NANTEN Diameter: 4m Beam size 2.6’ @115GHz ~ 40-50 pc@50-60kpc Velo. Res. 0.1 km/s Band Width 100 km/s Tsys ~ 300 K (SSB) Integration time ~ 20 hours/point 2002 Oct. -2003 July Las Campanas Observatory

  7. Search for CO in the Magellanic Bridge Toward a region of cold atomic hydrogen (Smoker et al. 2000) =>No CO and no stars Kobulnicky & Dickey 1999

  8. Search for CO in the Magellanic Bridge Toward a HI peak with IRAS Source (Muller et al. 2003) The first detection of CO from the Bridge !

  9. -45 -40 Galactic latitude (degree) -35 -30 280 290 300 Galactic longitude (degree) N(HI) > 1021 cm-2 Putman et al. 1998

  10. Clusters and Associations Bica & Schmitt 1995

  11. Search for CO in the Magellanic Bridge with NANTEN HI(Muller er al.) Targets HI and Dust peaks 16 regions40 points IRAS100μm

  12. Results HI 8 CO clouds1-7x103 Msun M(H2) ~2x104 MsunM(HI) ~5x107 Msun IRAS100μm

  13. TCO ~ 10-60 mKdV ~ 1- 4 km/s

  14. SMC SMC

  15. Properties of Molecular clouds in the Bridge are similar to the clouds in the far outer Galaxy (Galactic Warp region) 30 35 25 30 25 20 20 15 15 10 10 5 5 2.5 3 3.5 4 4.5 5 0 1 2 3 4 5 6 Log(Mco) V（km/s） (Nakagawa et al. 2005) with IRAS sources Molecular Clouds in the Bridge V～1.5km/s, Mcloud～ 5000 Msun

  16. Nakagawa et al. （2005） 500 0 z(pc) -500 -1000 Color:HI Red cross:CO -1500 10 14 16 18 20 R(kpc) Galactic Warp

  17. Star Formation in the Bridge (Bica & Schmitt 1995) (Meaburn 1986) HI: Muller et al. 2003

  18. Galaxy collision and formation of Tidal Dwarf Galaxy Braine et al. 2001 TDG: far（20-135 Mpc）, collision of disk galaxies, high metallicity Bridge: near（~ 60 kpc）, collision of small irregulars, low metallicity

  19. Magellanic Bridge evolve into a new dwarf galaxy? （Wiklind 2002 Nature） - Bica & Schmitt (1995) identified 3 clumps D1, D2, D3. - similar to dwarf spheroidals (e.g, Fornax, Draco, Ursa Minor) - D1 has two populous clusters (NGC796, L114) D1 may evolve into a dwarf spheroidal (Bica & Schmitt 1995)

  20. Star formation rate in the Magellanic Bridge Mass of CO clouds in the Bridge Mco ~ 1-7×103 Msun similar to Taurus molecular cloud SFR in Taurus molecular cloud N*~ 100, <m*>~ 0.7Msun, τ ~106 yr, M~ 7 ×103 Msun =>1 ×10-8 Msun,star/Msun,cloud /yr SFR estimate from molecular cloud mass SFR ~ 2 ×10-4 Msun/yr SFR estimate from OB association in the Bridge ~ 100 OB association, M* ~ 100 Msun, τ~ 10-25Myr SFR ~ 6 ×10-4 Msun/yr

  21. Very Small Magellanic dwarf galaxy? Star formation is on-going and widespread SFR ~ 2-6×10-4 Msun/yr, a few Gyr ~106 Msun Gravitationally stable system M(HI)~ 5×107Msun => dV ~ 30 km/s dVCO, HI ~ 20-30 km/s Relation with LMC and SMC past collision interval 0.2-1.5 Gyr (e.g., Gardiner et al. 1994, Yoshizawa & Noguchi 2003) Mass ratio Mstar/M(HI) ~ 0.02 ~ low-end for dwarf galaxies (Mateo 1998)

  22. Summary • 8 CO clouds detected in the Magellanic Bridge • - site of star formation • - dust emission trace CO than HI • - close to young associations • - dV~ 2km/s, Mcloud ~ 1-7 × 103 Msun To understand star formation process in the early universe ( low metallicity, HI rich, interacting system, dwarf galaxy ) • New small dwarf galaxy will be formed in the Bridge • - collision of small galaxies also important in forming new galaxy • - SFR~ 2-6×10-4 Msun/yr, gravitationally bound Unique close-by laboratory to study galaxy formation with high resolution and high sensitivity

  23. Small Magellanic Cloud (D ~ 60 kpc) ・Lower metallicity (Dufour 1984) SMC ~ 1/10 Zsun ・Higher gas to dust ratio (Koornneef 1984) 17 times higher than in our galaxy

  24. Taylor et al. (1998) No CO detections Threshold for CO detection in galaxies

  25. Observation with NANTEN • Diameter: 4m • Beam size 2.6 arcmin (@115GHz) • ~ 50 pc@60kpc • Velo. Res. 0.1 km/s • Band Width 100 km/s • Tsys ~ 300 K (SSB) • Total integration time ~ 1 hours • 1998 Oct. -2003 July Las Campanas Observatory

  26. Mizuno et al. 2001

  27. 27 CO clouds identified (10 clouds detected at one observed point. )Mass：6.0×104～9.3×105MsunRadius：35~80 pc Total molecular mass ~4.5×106Msun ~ 0.7 % of HI mass 6.5 ×108Msun (Hindman 1967)

  28. Total molecular mass 5 ×106 Msun < 1% of the total atomic mass

  29. NE region SW region N(HI) ~ ６×1021(cm-2) N(HI) ~ 9×1021(cm-2) 14/20 show a single peak in HI All observed points (51) show multiple peaks in HI

  30. NANTEN & Spitzer Contour: NANTEN Image: Spitzer 3.6(blue), 4.5(green), and 8.0(red) um Spitzer Imaging Survey of the SMC(S3MC) by Bolatto et al.

  31. Properties of molecular clouds in the SMC • Weakness of CO Less C and O abundances => slower CO formation Less dust => faster CO photodissociation • No diffuse CO in the inter-cloud medium CO molecules can only survive in the dense region

  32. Star formation in the SMC • Comparisons of the CO clouds with clusters, associations, and emission nebulae. • SW region --- small, but bright HII regions (e.g., N12, N27) on-going formation of massive stars in large CO clouds • NE region --- large evolved HII region (e.g., N66) smaller CO clouds • Wing region --- small bright HII regions are associated CO clouds

  33. H

  34. Rubio et al. 2004 SIMBA 1.2mm CO(2-1) CO emission arise from high column density clumps ?

  35. (Lequeux et al 1994) In the Galaxy, CO appears at lower distance from the surface of the cloud

  36. Magellanic Bridge SMC LMC Putman et al. 1998

  37. Star formation orange：IRAS 100μm

  38. Yoshizawa & Noguchi 2003

  39. Yoshizawa & Noguchi 2003

  40. Contour:IRAS100μm -74° Declination (J2000) -75° Contour:IRAS100μm 2h20m 2h0m 1h40m Right Ascension (J2000)

  41. ２ １ 3 4 Color :HI (Muller )

  42. Spectra of the HI and CO in the Bridge 1 2 1 V ：1.50km/s V：0.77km/s - HI-CO 4 3 3 4 V ：2.08km/s 線幅：0.91km/s

  43. 検出スペクトル 1 2 線幅：1.50km/s 線幅：0.77km/s - HI -CO - HI -CO 3 4 線幅：0.91km/s 線幅：2.08km/s - HI -CO - HI -CO

  44. 分子雲の広がり　～5点十字観測～ 2’ （35pc）

More Related