On the evolution of irradiated turbulence clouds:

A comparative study between modes of triggered star-formation

Background

• Investigate interaction of strong flux of IR (ionizing radiation) with MCs (Molecular Clouds)
• Secondary star formation
• Small molecular clouds can undergo radiation driven implosion
• What about Large molecular clouds?

Evolution of an Irradiated Cloud

• Photo-evaporation time vs free fall time
• Test cloud has a photo-evaporation time ~ 10 free fall times

Method

• SPH code SEREN (open-mp)
• Track location of ionization front from source.
• Material inside is at 8000K - material outside is at 20 K (with some smoothing)

Initial conditions

• mass = 400 solar masses
• radius = 1 pc
• density = 4.9 x 10³/cm³ (uniform)
• T=20 K
• Mach 10 Guassian velocity field with steep power-spectrum P(k) \propto k^{-4} from wave numbers 1 to 8 (but no units )
• t_{ff} = .8 \mbox{Myr} although they quote .27 \mbox{Myr} which might be the dynamical time…?
• Jeans length ~ .34 pc
• Jeans mass ~ 2 solar masses
• So box has 200 jeans masses and a virial parameter of 8 ~ \left ( \frac{M\lambda_J}{R} \right ) ^2?

Evolution

• Simulation was run for .05 Myr and then used as a starting point for runs with irradiation

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1	No ionizing radiation
2	36,000 K
3	47,000 K
4	51,000 K

.25 Myr	.24 Myr
.20 Myr	.1 Myr

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Conclusions

• Turbulence was injected by radiation driven shocks
• Stronger radiation ⇒ stronger turbulence ⇒ faster evolution time ⇒ earlier star formation