On the Star Formation Rates in GMCs with

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On the Star Formation Rates in GMCs with Marco Lombardi, Joao Alves, Jan Forbrich,

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

z = 1 - 10

z = 1 - 10

Bouwens et al. 2010

Bouwens et al. 2010

z = 0. 000

z = 0. 000

S. Guisard ESO Pipe Nebula Rho Ophiuchi Cloud

S. Guisard ESO Pipe Nebula Rho Ophiuchi Cloud

Star Formation Activity in the Pipe: Spitzer MIPS/IRAC survey of entire cloud (Frobrich et

Star Formation Activity in the Pipe: Spitzer MIPS/IRAC survey of entire cloud (Frobrich et al. 2009) Result: 18 YSOs!! YSOs C 2 D: Brooke et al. 2006

Overall star formation activity is insignificant, confined to 0. 2 % of the total

Overall star formation activity is insignificant, confined to 0. 2 % of the total gaseous mass. YSOs 1 -3 Myr Covey et al. 2010 C 2 D: Brooke et al. 2006

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

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

But what about GMCs?

But what about GMCs?

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

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

The California Molecular Cloud A Bona Fide GMC! t~ c p 5 8 n

The California Molecular Cloud A Bona Fide GMC! t~ c p 5 8 n te x E Mass = 105 Mo Lada, Lombardi & Alves 2009

Comparing the California and Orion Molecular Clouds The two clouds are nearly identical in

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

More on Variations in Star Formation Rates in GMCs IRAS Mooney & Solomon 1988

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

664 M 8300 M 65 M 7600 Yield M Lombardi et al. 2008 =

664 M 8300 M 65 M 7600 Yield M Lombardi et al. 2008 = SFR x Δt 200 YSOs 18 YSOs N(YSOs)Oph = 10 x N(YSOs)Pipe Mass(Oph) = 10 x Mass(Pipe) for Ak > 1. 0

Comparing the California and Orion Molecular Clouds The two clouds are nearly identical in

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

SFR is directly proportional to total gas mass at Ak>1. 0 SFR ~ N(YSOs)

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

Star Formation Efficiency is constant within x 4 for the dense gas For 0.

Star Formation Efficiency is constant within x 4 for the dense gas For 0. 5 solar mass stars this translates to <SFE> = 23% ± 13% in the dense gas

Proposed Relation Between Density and the SFR = { 0 εobs M(Ak > 1)

Proposed Relation Between Density and the SFR = { 0 εobs M(Ak > 1) / tsf for Ak < 1. 0 for Ak ≥ 1. 0 Σgas ≥ 150 M pc-2 Where: eobs = SFEobs ≈ 0. 23

Proposed Relation Between Density and the SFR = { 0 for ρ < ρ

Proposed Relation Between Density and the SFR = { 0 for ρ < ρ crit εobs M(ρ >ρcrit) / tsf for ρ ≥ ρcrit ρ crit ≈ 10 4 mm. H cm-3 Where: eobs = SFEobs ≈ 0. 23 tsf = g tff (rcrit) and g ≈ 5 – 10

Proposed Relation Between Density and the SFR = { 0 for ρ < ρ

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

The End 1. - Star Formation Rates in Molecular Clouds of similar mass vary

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