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On the Star Formation Rates in GMCs

On the Star Formation Rates in GMCs . with Marco Lombardi, Joao Alves, Jan Forbrich, Gus Munch Kevin Covey & Carlos Roman . z = 1 - 10. Bouwens et al. 2010. z = 0.000. S. Guisard ESO. Pipe Nebula. Rho Ophiuchi Cloud.

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On the Star Formation Rates in GMCs

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  1. On the Star Formation Rates in GMCs with Marco Lombardi, Joao Alves, Jan Forbrich, Gus Munch Kevin Covey & Carlos Roman

  2. z = 1 - 10

  3. Bouwens et al. 2010

  4. z = 0.000

  5. S. Guisard ESO Pipe Nebula Rho Ophiuchi Cloud

  6. Star Formation Activity in the Pipe: Spitzer MIPS/IRAC survey of entire cloud (Frobrich et al. 2009) YSOs Result: 18 YSOs!! C2D: Brooke et al. 2006

  7. Overall star formation activity is insignificant, confined to 0.2 % of the total gaseous mass. 1-3 Myr YSOs Covey et al. 2010 C2D: Brooke et al. 2006

  8. Yield =SFR x Δt 8300 M 7600 M 200 YSOs 18 YSOs N(YSOs)Oph= 10 xN(YSOs)Pipe SFROph = 10 x SFRPipe

  9. But what about GMCs?

  10. The California Molecular Cloud Lombardi, Lada & Alves 2009 A&A, in press

  11. The California Molecular Cloud A Bona Fide GMC! Extent ~ 85 pc Mass = 105 Mo Lada, Lombardi & Alves 2009

  12. Comparing the California and Orion Molecular Clouds YSOs(Orion) > 10 x YSOs(Califoria) SFR(Orion) > 10 x SFR(California) The two clouds are nearly identical in mass & size California Molecular Cloud IRAS Orion Molecular Cloud

  13. More on Variations in Star Formation Rates in GMCs California Molecular Cloud IRAS Mooney & Solomon 1988 ApJL 334, 51 Orion Molecular Cloud SFR(Orion) > 10 x SFR(California)

  14. Yield =SFR x Δt 664 M 8300 M 65 M 7600 M 200 YSOs 18 YSOs Lombardi et al. 2008 N(YSOs)Oph= 10 xN(YSOs)Pipe Mass(Oph)= 10 x Mass(Pipe) for Ak > 1.0

  15. Comparing the California and Orion Molecular Clouds YSOs(Orion) > 10 x YSOs(Califoria) SFR(Orion) > 10 x SFR(California) The two clouds are nearly identical in mass & size OMC has 10 x as much material at Ak >1 mag as the CMC

  16. SFR is directly proportional to total gas mass at Ak>1.0 SFR ~ N(YSOs) / tsf For these clouds tsf ≈ 2 ± 1 Myr So N(YSOs) ~ SFR Ak > 1.0 corresponds to Σgas > 150 M pc-2

  17. Star Formation Efficiency is constant within x4 for the dense gas For 0.5 solar mass stars this translates to <SFE> = 23% ± 13% in the dense gas

  18. Proposed Relation Between Density and the SFR { 0 for Ak < 1.0 εobs M(Ak > 1) / tsf for Ak ≥ 1.0 SFR = Σgas ≥ 150 M pc-2 Where: eobs = SFEobs ≈ 0.23

  19. Proposed Relation Between Density and the SFR { 0 for ρ < ρcrit εobs M(ρ >ρcrit) / tsf for ρ ≥ ρcrit SFR = ρcrit ≈ 104 mmH cm-3 Where: eobs = SFEobs ≈ 0.23 tsf = g tff (rcrit)and g ≈ 5 – 10

  20. Gao & Solomon 2004 Proposed Relation Between Density and the SFR Galaxies { LIR 0 for ρ < ρcrit εobs M(ρ >ρcrit) / tsf for ρ ≥ ρcrit SFR = Wu et al. 2005 Milky Way GMCs SFR ~ MDG In external galaxies global star formation rate correlates directly with amount of dense gas

  21. The End 1.- Star Formation Rates in Molecular Clouds of similar mass vary considerably 2.. - Level of Star Formation correlates directly with total gaseous mass above a threshold column density of Av ≈ 10 mag 3.- The SFR is proportional to the total cloud mass above a critical volume density of n ≈104 cm-3

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