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