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

z =

Bouwens et al. 2010

z = 0.000

S. Guisard ESO Pipe Nebula Rho Ophiuchi Cloud

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

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

Yield = SFR x Δt 7600 M  8300 M  18 YSOs 200 YSOs N(YSOs) Oph = 10 x N(YSOs) Pipe SFR Oph = 10 x SFR Pipe

But what about GMCs?

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

The California Molecular Cloud Extent ~ 85 pc Mass = 10 5 M o A Bona Fide GMC! Lada, Lombardi & Alves 2009

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

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

Yield = SFR x Δt 7600 M  8300 M  18 YSOs 200 YSOs N(YSOs) Oph = 10 x N(YSOs) Pipe Mass(Oph) = 10 x Mass(Pipe) for A k > M  65 M  Lombardi et al. 2008

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

For these clouds  sf ≈ 2 ± 1 Myr SFR ~ N(YSOs) /  sf So N(YSOs) ~ SFR A k > 1.0 corresponds to Σ gas > 150 M  pc -2 SFR is directly proportional to total gas mass at A k >1.0

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

X 4 x100

0 for A k < 1.0 ε obs M ( A k > 1 ) /  sf for A k ≥ 1.0  SFR = Where:  obs = SFE obs ≈ 0.23 Σ gas ≥ 150 M  pc -2

0 for ρ < ρ crit ε obs M (ρ >ρ crit ) /  sf for ρ ≥ ρ crit  SFR = Where:  obs = SFE obs ≈ 0.23  sf =  ff (  crit )  and  –   crit     m H cm -3

0 for ρ < ρ crit ε obs M (ρ >ρ crit ) /  sf for ρ ≥ ρ crit  SFR = Gao & Solomon 2004 Wu et al Galaxies L IR Milky Way GMCs SFR ~ M DG In external galaxies global star formation rate correlates directly with amount of dense gas

1.- Star Formation Rates in Molecular Clouds of similar mass vary considerably 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 ≈10 4 cm -3 The End

0 for ρ < ρ crit ε obs M (ρ >ρ crit ) /  sf for ρ ≥ ρ crit  SFR = Where:  obs = SFE obs ≈ 0.23  sf =  ff (  crit )  and  –  Gao & Solomon 2004 In external galaxies global star formation rate correlates directly with amount of dense gas Wu et al Galaxies L IR Milky Way GMCs SFR ~ M DG