Deriving the Physical Structure of High-mass Star Forming Regions Yancy L. Shirley May 2003...
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Transcript of Deriving the Physical Structure of High-mass Star Forming Regions Yancy L. Shirley May 2003...
Deriving the Physical Deriving the Physical Structure of High-mass Star Structure of High-mass Star
Forming RegionsForming Regions
Yancy L. Shirley
May 2003
Collaborators: Neal Evans, Kaisa Young, Dan Jaffe, Claudia Knez, & Jingwen Wu
SF in the Milky WaySF in the Milky Way10101111 stars in the Milky Way stars in the Milky Way
Evidence for SF throughout history of the galaxy Evidence for SF throughout history of the galaxy (Gilmore 2001)(Gilmore 2001)
SF occurs in molecular gasSF occurs in molecular gasMolecular cloud complexes: M < 10Molecular cloud complexes: M < 1077 M M00 (Elmegreen 1986)(Elmegreen 1986)
Isolated Bok globulesIsolated Bok globules M > 1 M M > 1 M00 (Bok & Reilly 1947)(Bok & Reilly 1947)
SF traces spiral structureSF traces spiral structure (Schweizer 1976)(Schweizer 1976)
NASA
M51 Central Region
SF Occurs in Molecular CloudsSF Occurs in Molecular Clouds
Total molecular gas = 1 – 3 x 10Total molecular gas = 1 – 3 x 1099 M Moo
SF occurring throughout MW disk SF occurring throughout MW disk (Combes 1991)(Combes 1991)
SF occurs in isolated & clustered modesSF occurs in isolated & clustered modes
SF occurs within dense molecular coresSF occurs within dense molecular cores
VLT
BHR-71 Pleiades
Lupus
Orion Dense CoresOrion Dense Cores
Lis, et al. 1998VST, IOA U Tokyo
CO J=2-1
High-mass Dense CoresHigh-mass Dense CoresRCW 38
J. Alves & C. Lada 2003
Optical
Near-IR
Blum, Conti, & Damineli 2000
W42
Embedded clusters visible in Near-IR
High-mass Cores : ComplexityHigh-mass Cores : Complexity
S106
Near- IR
Subaru
High-Mass Star FormationHigh-Mass Star Formation
Star with M > 100 MStar with M > 100 Moo appear to exist appear to exist (Kudritzki et al. (Kudritzki et al. 1992):1992): How do massive stars (M > few M How do massive stars (M > few M00) form?) form?
Basic formation mechanism debated:Basic formation mechanism debated:Accretion Accretion (McKee & Tan 2002)(McKee & Tan 2002)
How do you form a star with M > 10 Msun before radiation pressure stops accretion? How do you form a star with M > 10 Msun before radiation pressure stops accretion?
Coalescence Coalescence (Bonnell et al. 1998)(Bonnell et al. 1998)Requires high stellar density: n > 10Requires high stellar density: n > 1044 stars pc stars pc-3-3
Predicts high binary fraction among high-mass starsPredicts high binary fraction among high-mass stars
Theories predict dense core structure & evolution: n(r,t) & v(r,t)Theories predict dense core structure & evolution: n(r,t) & v(r,t)
Observational complications:Observational complications:Farther away than low-mass regions = low resolutionFarther away than low-mass regions = low resolutionDense cores may be forming cluster of stars = SED dominated by most massive Dense cores may be forming cluster of stars = SED dominated by most massive star = SED classification confused!star = SED classification confused!Very broad linewidths consistent with turbulent gasVery broad linewidths consistent with turbulent gas
Potential evolutionary indicators from presence of :Potential evolutionary indicators from presence of :HH22O, CHO, CH33OH masersOH masersHot core Hot core Hyper-compact HII Hyper-compact HII UCHII regions UCHII regions HII HII Star ? Star ?
Hot Cores & UCHII RegionsHot Cores & UCHII Regions
VLA 7mm Cont. BIMA
Hot Cores & UCHII Regions observed in same high-mass regions : W49A
DePree et al. 1997 Wilner et al. 1999
OutlineOutlineWhat is lacking is a fundamental understanding of the What is lacking is a fundamental understanding of the basic properties of the ensemble of high-mass star basic properties of the ensemble of high-mass star forming coresforming cores
Texas survey of high-mass star forming cores:Texas survey of high-mass star forming cores:Plume et al. 1992 & 1997Plume et al. 1992 & 1997 CS line survey CS line survey
Dust Continuum 350 Dust Continuum 350 m Surveym SurveyMueller, Shirley, Evans, & Jacobson 2002, ApJSMueller, Shirley, Evans, & Jacobson 2002, ApJSConstrain n( r ), T ( r )Constrain n( r ), T ( r )High-mass cores associated with HHigh-mass cores associated with H220 maser emission0 maser emission
Arectri catalog of HArectri catalog of H22O maser sourcesO maser sourcesPlume et al. 1992 & 1997Plume et al. 1992 & 1997 CS survey towards (0,0) positionCS survey towards (0,0) position
CS J = 5 - 4 Mapping SurveyCS J = 5 - 4 Mapping SurveyShirley, Evans, Young, Knez, Jaffe 2003, ApJSShirley, Evans, Young, Knez, Jaffe 2003, ApJSDense gas propertiesDense gas properties
CS Dense Core SurveyCS Dense Core SurveyCS J=7-6 detected 104 / 179 cores with H2O masers
Plume et al. 1992
H2O masers trace very dense gas
n > 1010 cm-3 for the 22 GHz 616-523 transition
Low J CO Surveys generally trace lower density gas.
H2O maser positions are known accurately to within a few arcseconds. HII regions and luminous IR sources may not be spatially coincident with dense gas.
Multi-transition study and initial mappingPlume et al. 1997
71 cores detected in CS and C34S J = 2-1, 3-2, 5-4, and 7-6.
21 of the brightest cores mapped in CS 5-4
<R> = 1.0 pc, <Mvir> = 3800 Mo
LVG modeling of multiple CS transitions
CO: Molecular Cloud TracerCO: Molecular Cloud Tracer
Hubble Telescope
CO J=3-2 Emission
NASA, Hubble Heritage TeamCSO
CS & HCN Trace Dense CoresCS & HCN Trace Dense Cores
CO 1-0 CS 2-1 HCN 1-0
Helfer & Blitz 1997
CS LVG ModelsCS LVG Models Initially assumed n( r ) and
T( r ) = CONSTANT 40 sources detected in all 4
CS transitions <log n> = 5.93 (0.23) <log N> = 14.42 (0.49)
2-density component model with a filling factor for the dense component
nhigh ~ 108 cm-3
nlow ~ 104 cm-3
Typically, very high column densities of low density gas required (<log Nlow> = 16.16) with f ~ 0.2
Plume et al. 1997
350 350 m Surveym Survey
5 nights at the CSO 10.4-m telescope5 nights at the CSO 10.4-m telescope
51 high-mass (L51 high-mass (Lbolbol > 100 L > 100 Lsunsun) cores associated with H) cores associated with H22O O
masers (Plume et al. 1992 sample)masers (Plume et al. 1992 sample)850 pc < D < 14 kpc850 pc < D < 14 kpc
All cores also observed in CS5-4 survey All cores also observed in CS5-4 survey (Shirley et al. 2003)(Shirley et al. 2003)
SHARC 350 SHARC 350 m scan maps (4.0 x 2.7 arcmin)m scan maps (4.0 x 2.7 arcmin)mbmb ~ 14 arcsec at 350 ~ 14 arcsec at 350 mm
100 arcsec chop throw100 arcsec chop throw
Mueller, Shirley, Evans, & Jacobson 2002
G9.62+0.10
W43
350 350 m Imagesm ImagesM8E
50,000 AU
W33A
10,000 AU
W28A2 G23.95+0.16
150,000 AU
Mueller et al. 2002
Submm Continuum EmissionSubmm Continuum Emission
Submillimeter continuum emission is Submillimeter continuum emission is optically thinoptically thin. The . The specific intensity along a line-of-sight is given by:specific intensity along a line-of-sight is given by:
Why must we model ?Why must we model ?
Rayleigh-Jeans approximation fails in outer envelope of Rayleigh-Jeans approximation fails in outer envelope of low-mass coreslow-mass cores
hh/k = 44 K at 350 /k = 44 K at 350 mm
Heating from ISRF is very importantHeating from ISRF is very important in outer envelopes in outer envelopes of coresof cores
Radiative transfer is optically thick at short Radiative transfer is optically thick at short
Observed brightness distribution is convolved with Observed brightness distribution is convolved with complicated beam pattern, scanning, and choppingcomplicated beam pattern, scanning, and chopping
Radiative Transfer ProcedureRadiative Transfer Procedure
nd(r)
L Td(r)
SI(b)
Nearly orthogonal constraints:Nearly orthogonal constraints:
SEDSED Mass x OpacityMass x OpacityI(b)I(b) n(r)n(r)
IterateIteratePhysical Model
n(r) Observations
Gas to
Dust
Radiative
Transfer
Simulate
Obs.
Dust OpacityDust Opacity
OH = Ossenkopf & Henning 1994 coagulated dust grains
Calculated Temperature ProfilesCalculated Temperature Profiles
Mueller et al. 2002
Radiative Transfer ModelsRadiative Transfer Models
Mueller et al. 2002
50,000 AU
Best-fitted Power LawBest-fitted Power Law
Mueller et al. 2002
Single power-law density profiles fit observations
n( r ) = nf (r / rf) –p
p = - dln n/ dln r
Distribution of power law indices
<p> = 1.8 (0.4)
Similar to distribution of low-mass cores modeled by Shirley et al. (2002) & Young et al (2003)
Evolutionary Indicators ?Evolutionary Indicators ?
Mueller et al. 2002
““Standard” IndicatorsStandard” Indicators
Mueller et al. 2002
350 350 m Survey Summarym Survey Summary
Density and Temperature structure of outer envelope Density and Temperature structure of outer envelope characterizedcharacterized
<p> = 1.8 (0.4)<p> = 1.8 (0.4) <n(1000 AU)> is order of magnitude higher than nearby low-<n(1000 AU)> is order of magnitude higher than nearby low-mass star-forming coresmass star-forming cores
Beuther et al.Beuther et al. 1.2mm mapping 69 cores: <p> = 1.6 (0.5) 1.2mm mapping 69 cores: <p> = 1.6 (0.5)Single power law models fit our sampleSingle power law models fit our sample
CAVEAT:CAVEAT: may be contribution from compact components (UCHIIs may be contribution from compact components (UCHIIs or disks) within central beamor disks) within central beam
W3(OH) UCHII may contribute as much as 25% of the central flux assuming W3(OH) UCHII may contribute as much as 25% of the central flux assuming optically thick free-free scaled from 3mm flux optically thick free-free scaled from 3mm flux (Wilner, Welch, & Forster 1995)(Wilner, Welch, & Forster 1995)
<R<Rdecdec> = 0.16 (0.10) pc> = 0.16 (0.10) pc<T<Tisoiso> = 29 (9) K isothermal temperature> = 29 (9) K isothermal temperature
Definitive trends lacking for evolutionary indicatorsDefinitive trends lacking for evolutionary indicatorsExcept perhaps TExcept perhaps Tbol bol vs. Lvs. Lbolbol/L/Lsmmsmm
LLbolbol ranges from 10 ranges from 1033 to 10 to 1066 L Lsunsun
SEDs not well contrained in many cases due to lack of Far-IR SEDs not well contrained in many cases due to lack of Far-IR photometryphotometry
CS J = 5 - 4 SurveyCS J = 5 - 4 Survey
63 high-mass star forming cores associated with H63 high-mass star forming cores associated with H22O O masers mapped at CSO 10.4mmasers mapped at CSO 10.4m
<D> = 5.3 (3.7) kpc with 28 UCHII regions included<D> = 5.3 (3.7) kpc with 28 UCHII regions included57 peak positions observed in C57 peak positions observed in C3434S J=5-4, 9 in S J=5-4, 9 in 1313CS J=5-4CS J=5-4
Over-sampled On-The-Fly mapsOver-sampled On-The-Fly maps in CS J=5-4in CS J=5-4mbmb ~ 25 arcsec at 245 GHz ~ 25 arcsec at 245 GHz
Median peak integrated intensity S/N = 40Median peak integrated intensity S/N = 4010 arcsec binned maps10 arcsec binned maps
Provide consistent sample from which to determine the Provide consistent sample from which to determine the properties of the deeply embedded phase of high-mass star properties of the deeply embedded phase of high-mass star formationformation
Shirley et al. 2002
CS Rotational TransitionsCS Rotational Transitions
Heavy linear molecule with Heavy linear molecule with many rotational transitions many rotational transitions observable from the groundobservable from the ground
J = 5 - 4 transition good J = 5 - 4 transition good probe of dense gas:probe of dense gas:
bb = 1.98 Debye = 1.98 Debye
nncc(10K) = 8.8 x 10(10K) = 8.8 x 106 6 cmcm-3-3
nneffeff(10K) = 2.2 x 10(10K) = 2.2 x 1066 cm cm-3-3
CS J=5-4 SurveyCS J=5-4 SurveyG19.61-0.23 M8E
S158
S231 W44 S76E
Shirley et al. 2003
CS J=5-4 vs. Dust ContinuumCS J=5-4 vs. Dust Continuum
CS J=5-4 is an excellent tracer of dense gas in high-CS J=5-4 is an excellent tracer of dense gas in high-mass star forming regionsmass star forming regions
Shirley et al. 2003
Deconvolved Size vs. pDeconvolved Size vs. p Convolution of a Gaussian beam pattern with a power law
intensity profile yields a deconvolved source size that varies with p
Shirley et al. 2003
Optical Depth Effect on LinewidthOptical Depth Effect on LinewidthCC3232S is typically optically thick, therefore must use rare S is typically optically thick, therefore must use rare isotope (Cisotope (C3434S) in linewidth sensitive calculationsS) in linewidth sensitive calculations
Shirley et al. 2003
Linewidth-SizeLinewidth-SizeWeak correlation with best fit: Weak correlation with best fit: v ~ rv ~ r0.30.3
CC3434S linewidth 4x larger than predicted linewidth fromS linewidth 4x larger than predicted linewidth from Casselli & Casselli & Myers (1995) Myers (1995) indicating high turbulence: <indicating high turbulence: <v(Cv(C3434S)> = 5.0 (2.0) km/sS)> = 5.0 (2.0) km/s
Shirley et al. 2003
Size, Mass, & PressureSize, Mass, & PressureMedian core size: Median core size: R = 0.32 pcR = 0.32 pc
Alternatively RAlternatively Rnn = 0.40 pc = 0.40 pcMedian projected aspect ratio: Median projected aspect ratio: (a/b) = 1.2(a/b) = 1.2
Median virial mass: Median virial mass: MMvirvir = 920 M = 920 M0 0 corresponding to corresponding to = 0.6 g cm = 0.6 g cm-2-2
Corrections for p and Corrections for p and v broadening necessaryv broadening necessaryMean mass per OB association ~ 440 MMean mass per OB association ~ 440 M00 (Matzner 2002)(Matzner 2002)
Median pressure Median pressure <P/k> = 1.5 x 10<P/k> = 1.5 x 1088 K cm K cm-3-3
Shirley et al. 2003
Virial Mass vs. Dust MassVirial Mass vs. Dust Mass
The virial mass is consistently higher by a factor of 2 to 3 than the mass determined from dust continuum modeling.
Uncertainty in dust opacity may account for difference
Shirley et al. 2003
Cumulative Mass SpectrumCumulative Mass SpectrumSlope of mass spectrum similar to IMF and distribution of OB Slope of mass spectrum similar to IMF and distribution of OB associations associations ~ -1.1 (0.1) ~ -1.1 (0.1) (Massey 1995)(Massey 1995)
9.0
Shirley et al. 2003
Luminosity and MassLuminosity and Mass
Shirley et al. 2003
CS J=5-4 Survey SummaryCS J=5-4 Survey Summary
CS J=5-4 is an excellent tracer of dense gas in high-mass CS J=5-4 is an excellent tracer of dense gas in high-mass star forming coresstar forming cores
Aspect ratios consistent with spherical symmetryAspect ratios consistent with spherical symmetry
Median Median size of 0.32 pcsize of 0.32 pc and median and median virial mass of 920 Mvirial mass of 920 Msunsun
Virial mass a factor of 2 to 3 larger than dust-determined massVirial mass a factor of 2 to 3 larger than dust-determined massCumulative mass spectrumCumulative mass spectrum ~ -0.9 similar to IMF of OB ~ -0.9 similar to IMF of OB associationsassociationsHigh median pressureHigh median pressure of 1.5 x 10 of 1.5 x 1088 K cm K cm-3-3 ameliorates the lifetime ameliorates the lifetime problem for confinement of UCHII regionsproblem for confinement of UCHII regions
L/M is 100x higher than estimates from CO and has a L/M is 100x higher than estimates from CO and has a smaller dispersionsmaller dispersion
L/M L/M 2x higher2x higher for cores with UCHII and/or HII regions for cores with UCHII and/or HII regions
LLbolbol strongly correlates with M strongly correlates with Mvirvir. Combined with low dispersion of . Combined with low dispersion of L/M perhaps indicates that mass of most massive star is related to L/M perhaps indicates that mass of most massive star is related to the mass of the corethe mass of the core
High Mass Pre-protocluster Core?High Mass Pre-protocluster Core?
Have yet to identify initial Have yet to identify initial configuration of high-mass star configuration of high-mass star forming core!forming core!
No unbiased surveys for such No unbiased surveys for such an object made yetan object made yet
Based on dense gas surveys, Based on dense gas surveys, what would a 4500 Mwhat would a 4500 M00, cold , cold
core (T ~ 10K) look like?core (T ~ 10K) look like?
Does this phase exist?Does this phase exist?
Evans et al. 2002
Conclusions & Future WorkConclusions & Future Work
Initial characterization of n( r ) indicates a power law Initial characterization of n( r ) indicates a power law density structure of outer envelopedensity structure of outer envelope
CS J=5-4 traces dense gas properties associated with CS J=5-4 traces dense gas properties associated with star formationstar formation
CS J=7-6 + HCN & HCS J=7-6 + HCN & H1313CN J=3-2 Mapping SurveyCN J=3-2 Mapping Survey (Texas Thesis projects of Jingwen Wu & Claudia Knez)(Texas Thesis projects of Jingwen Wu & Claudia Knez)
Radiative transfer modeling of dense gas & v( r )Radiative transfer modeling of dense gas & v( r )
Combination of Combination of bolometer camera + interferometric dust bolometer camera + interferometric dust continuum imagingcontinuum imaging with radiative transfer modeling is a with radiative transfer modeling is a powerful diagnostic of the density & temperaturepowerful diagnostic of the density & temperature
How much emission is coming from a compact component within central How much emission is coming from a compact component within central beam?beam?SMA & ALMA submm continuum needed!SMA & ALMA submm continuum needed!SOFIA & SIRTF needed to improve SEDSOFIA & SIRTF needed to improve SED