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

YSOs

Result: 18 YSOs!!

C2D: Brooke et al. 2006

Star Formation Activity in the Pipe:Spitzer MIPS/IRAC survey of entire cloud(Frobrich et al. 2009)

1-3 Myr

Covey et al. 2010

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

SFROph = 10 x SFRPipe

But what about GMCs?

The California Molecular Cloud

Lombardi, Lada & Alves 2009 A&A, in press

The California Molecular Cloud

Extent ~

85 pc

Mass = 105 Mo

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 Ak > 1.0

664 M

65 M

Lombardi et al. 2008

Comparing the California and Orion Molecular Clouds

OMC has 10 x as much material at Ak >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 tsf ≈ 2 ± 1 Myr

SFR ~ N(YSOs) / tsf

So N(YSOs) ~ SFR

Ak > 1.0 corresponds to Σgas > 150 M pc-2

SFR is directly proportional to total gas mass at Ak>1.0

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

Proposed Relation Between Density and the SFR

€

M(Ak >1) = M(Ak )dAk1

∞

∫€ €

0 for Ak < 1.0

εobs M(Ak > 1) / tsf for Ak ≥ 1.0

{SFR =

Where:

eobs = SFEobs ≈ 0.23

Σgas ≥ 150 M pc-2

Proposed Relation Between Density and the SFR

€

M(ρ >ρ crit ) = M(ρ )dρρ crit

∞

∫€ €

0 for ρ < ρcrit

εobs M(ρ >ρcrit) / tsf for ρ ≥ ρcrit

{SFR =

Where:

eobs = SFEobs ≈ 0.23

tsf = g tff (rcrit) and ≈ 5 – 10g

ρcrit ≈ 104 mmH cm-3

Proposed Relation Between Density and the SFR

€ €

0 for ρ < ρcrit

εobs M(ρ >ρcrit) / tsf for ρ ≥ ρcrit

{SFR =

Gao & Solomon 2004

Wu et al. 2005

Galaxies

LIR

Milky Way GMCs

SFR ~ MDG

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

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

The End