On the Star Formation Rates in GMCs with Marco Lombardi, Joao Alves, Jan Forbrich, Gus Munch Kevin...
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Transcript of On the Star Formation Rates in GMCs with Marco Lombardi, Joao Alves, Jan Forbrich, Gus Munch Kevin...
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