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1 Enrique Vázquez-Semadeni Centro de Radioastronomía y Astrofísica, UNAM, México
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EnriqueVázquez-SemadeniCentrodeRadioastronomíayAstrofísica,UNAM,México
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JavierBallesteros-ParedesCentrodeRadioastronomíayAstrofísica,UNAM,México
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Collaborators:
JavierBallesteros-ParedesPedroColínGilbertoGómezAlanWatsonRobiBanerjeeRalfKlessen
STUDENTS:ManuelZamoraAvilés
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Collaborators:
EnriqueVázquez-SemadeniPedroColínGilbertoGómezAlanWatsonRobiBanerjeeRalfKlessen
STUDENTS:ManuelZamoraAvilés
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I.INTRODUCTION
• Withintheturbulentmodelofmolecularcloudsandstarformation(SF),thereexisttwoalternativescenarios:
– “Slow”starformation(Norman&Silk1980;Krumholz&McKee2005;Li&Nakamura2006;Krumholz&Tan2007):• Cloudsareinnearvirialequilibrium,andlastseveraltimestheirfree-falltime.
• Turbulencesupportstheclouds.• Turbulenceisreplenishedbystellarfeedback.• Turbulencemaintainsalowstarformationrate(SFR).
– “Rapid”star formation(Ballesteros-Paredesetal.1999;Elmegreen2000;Klessenetal.2000;Hartmannetal.2001;MacLow&Klessen2004;VSetal.2007,):• Cloudsformbylarge-scalecompressionsand/orinstabilities.• SFoccursrapidly(athighSFR)andcoherently.• StellarfeedbackdisruptsthecloudandterminatesSF.
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• Definingthestarformationefficiencyas
where
then:
“Slow”SF
“Rapid”SF
large Δt, small SFR.
short Δt, large SFR.
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• Thiswork:– Numerically investigate effect of massive-star feedback onparentcloudimmersedindiffuse(WNM)medium:
• SeeManuel Zamora’s poster (this session) for approach to ananalyticalmodel.
• CloudformedbytransoniccompressioninWNM.– Compressiontriggersphasetransitiontocoldmedium(Hennebelle&Pérault1999).
– CloudgrowsbyincorporatingmaterialfromWNM;– Boundedby“phasetransitionfront”.
• AbletofreelyinteractwithWNMenvironment.– Accrete,returnmaterial;– Disperse?
• Subjecttoionizationheating-likestellarfeedback.
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• Numericalmodel:– N-body+AMRhydrodynamicscode(ARTcode,byKravtsovetal.1997;Kravtsov2003).• 256-pcbox.• 4refinementlevels.Equivalentresolution20483.• 0.125pcresolution.
– Stellarparticleformationbydensitythresholdcriterion.• nSF=4x106cm-3.• Mpart~120Msun.
– CoolingfunctionfromKoyama&Inutsuka(2002).
Vázquez-Semadeni et al. 2007.
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• Numericalmodel(cont’d):– Initialvelocityfieldconsistingofoppositely-directedcylindricalstreamswithvelocity6kms-1(Mach#=Ms,inf=0.8)inWNM.
– Superposed initial, low-amplitude turbulent velocity field ofMach#Ms,rmstotriggerinstabilitiesincompressedlayer.• Scale:~cylinderradius.
Converging inflow setup
Lbox
Linflow
Rinf
Ms,inf
Ms,rms
Minf
Ms,inf: Mach number of inflow speed w.r.t. warm gas.
Ms,rms: Mach number of background turbulence in WNM.
Minf: Mass in colliding cylinders = 2 ρ π Rinf
2 Linf
nWNM = 1 cm-3
TWNM = 5000 K cs = 7.4 km s-1
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• Foursimulations:
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• Numericalmodel(cont’d)
– OB-starionization-likeheatingbystellarparticles:• Depositedincellcontainingstellarparticleduring10Myr.• Heating rate taken as free parameter, adjusted to achieve“realistic”HIIregions:
Density Temperature Velocity
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• RunLAF1(Large-amplitudefluctuationswithfeedback)
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• Globalcloudfeaturesandevolution:
– Clouds first appear as atomic, CNM structures (Vázquez-Semadenietal.2006).
– Gravitational contraction sets in globally, bringing columndensity up to molecular-cloud values (Vázquez-Semadeni et al.2007,Heitsch&Hartmann2008).
– Size and mass of clouds determined by scale of dominantcompressionmechanism:• SA simulations: collapse of massive, pancake-shaped cloud ofradius=Rcyl.– Cloudsshapedbycollidinginflows.
• LA simulations: collapse of amorphous, less massive, smallerclouds.– Cloudsshapedbyturbulentfluctuations.
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15 “Central Cloud” in run SAF1 (small fluctuation amplitude with feedback).
20-pc measuring box
16 “Cloud 1” in run LAF1 (Large fluctuation amplitude with feedback).
20-pc measuring box
17 “Cloud 2” in run LAF1 (Large fluctuation amplitude with feedback).
20-pc measuring box
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M(n
>100
cm
-3) [
Msu
n]
Central Cloud, SA
Whole box
10-pc box
No feedback With feedback M
star
[Msu
n]
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M(n
>100
cm
-3) [
Msu
n]
Cloud 1, LA
Whole box
30-pc box
20-pc box
10-pc box
No feedback With feedback
Mst
ar [M
sun]
20
M(n
>100
cm
-3) [
Msu
n]
Cloud 2, LA
Whole box
30-pc box
20-pc box
10-pc box
No feedback With feedback
Mst
ar [M
sun]
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– Suggeststhat,formassiveclouds,
• Total mass (cloud + stars) mainly determined byaccretion,consistentwithFuikuietal.(2009).
• SFinhibitedbyfeedback.
i.e,largerdensegasmassincasewithfeedbackduetoreducedrateofgas-to-starsconversion.
• Apparentlyduetofocusingoffeedbackongasclosesttoformingstarsnext.
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SA, Central cloud
3. SFEisreducedtorealisticvalues
(10-pc box)
Feedback No feedback
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No feedback With feedback
Cloud 1
Cloud 1
Cloud 2
Cloud 2
stellarmasssmallerinthepresenceoffeedback.
LA runs
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4. FactorbywhichSFE is reducedby feedbackdependsonthe cloud mass (at roughly the same size) involved incoherentcollapse.
– Apparently due to short-rangeeffect of feedback vs. long-rangenatureofgravity.• The more extended the infall motions, the less effective thefeedbackindisruptingthem.
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5. SFEcorrelateswithSFR.
“Average” low-mass cloud of Evans et al. 2009 Orion A cloud
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• Caveats:1. Onlyonekindoffeedbackstar(~earlyBstar).– Excessiveforsmallclouds,weakformassiveones.
– May be have non-negligible role in dispersal of small clouds,permanenceoflargeones.
– Work inprogress: considerationofa rangeof feedback-starmasses.
2. Noradiativetransfer;justheatdumping.
3. Nosupernova-likefeedback.– Maygivethe“fatalblow”tolargeclouds.
4. Largeambiguity inmasseswhenone isnot restricted toacertaintracer.
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• Conclusions(cont’d):3. Turbulence does not seem to be able to hold up a large
cloud:– Initialturbulence(fromcloudassembly)dissipatesquickly.
– Stellarfeedbackseemstoolocalized.
– Supersonic “turbulent” linewidths are indicative of globalcontraction. (Hartmann&Burkert2007;Fieldetal.2008;Vázquez-Semadenietal.2008;Heitschetal.2009).
