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