1. Deriving the Physical Structure of High-mass Star Forming Regions Yancy L. Shirley May 2003 Collaborators: Neal Evans, Kaisa Young, Dan Jaffe, Claudia Knez, & Jingwen Wu

2. SF in the Milky Way 10 11 stars in the Milky Way Evidence for SF throughout history of the galaxy (Gilmore 2001) SF occurs in molecular gas Molecular cloud complexes: M < 10 7 M 0 (Elmegreen 1986) Isolated Bok globules M > 1 M 0 (Bok & Reilly 1947) SF traces spiral structure (Schweizer 1976) NASA M51 Central Region

3. SF Occurs in Molecular Clouds Total molecular gas = 1 – 3 x 10 9 M o SF occurring throughout MW disk (Combes 1991) SF occurs in isolated & clustered modes SF occurs within dense molecular cores VLT BHR-71Pleiades Lupus

4. Orion Dense Cores Lis, et al. 1998 VST, IOA U Tokyo CO J=2-1

5. High-mass Dense Cores RCW 38 J. Alves & C. Lada 2003 Optical Near-IR Blum, Conti, & Damineli 2000 W42 Embedded clusters visible in Near-IR

6. High-mass Cores : Complexity S106 Near- IR Subaru

7. High-Mass Star Formation Star with M > 100 M o appear to exist (Kudritzki et al. 1992): How do massive stars (M > few M 0 ) form? Basic formation mechanism debated: Accretion (McKee & Tan 2002) How do you form a star with M > 10 Msun before radiation pressure stops accretion? Coalescence (Bonnell et al. 1998) Requires high stellar density: n > 10 4 stars pc -3 Predicts high binary fraction among high-mass stars Theories predict dense core structure & evolution: n(r,t) & v(r,t) Observational complications: Farther away than low-mass regions = low resolution Dense cores may be forming cluster of stars = SED dominated by most massive star = SED classification confused! Very broad linewidths consistent with turbulent gas Potential evolutionary indicators from presence of : H 2 O, CH 3 OH masers Hot core  Hyper-compact HII  UCHII regions  HII  Star ?

8. Hot Cores & UCHII Regions VLA 7mm Cont. BIMA Hot Cores & UCHII Regions observed in same high- mass regions : W49A DePree et al. 1997Wilner et al. 1999

9. Outline What is lacking is a fundamental understanding of the basic properties of the ensemble of high-mass star forming cores Texas survey of high-mass star forming cores: Plume et al. 1992 & 1997 CS line survey Dust Continuum 350  m Survey Mueller, Shirley, Evans, & Jacobson 2002, ApJS Constrain n( r ), T ( r ) High-mass cores associated with H 2 0 maser emission Arectri catalog of H 2 O maser sources Plume et al. 1992 & 1997 CS survey towards (0,0) position CS J = 5 - 4 Mapping Survey Shirley, Evans, Young, Knez, Jaffe 2003, ApJS Dense gas properties

10. CS Dense Core Survey CS J=7-6 detected 104 / 179 cores with H 2 O masers Plume et al. 1992 H 2 O masers trace very dense gas n > 10 10 cm -3 for the 22 GHz 6 16 -5 23 transition Low J CO Surveys generally trace lower density gas. H 2 O 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 mapping Plume et al. 1997 71 cores detected in CS and C 34 S J = 2-1, 3-2, 5-4, and 7-6. 21 of the brightest cores mapped in CS 5-4 = 1.0 pc, = 3800 M o LVG modeling of multiple CS transitions

11. CO: Molecular Cloud Tracer Hubble Telescope CO J=3-2 Emission NASA, Hubble Heritage Team CSO

12. CS & HCN Trace Dense Cores CO 1-0CS 2-1HCN 1-0 Helfer & Blitz 1997

13. CS LVG Models Initially assumed n( r ) and T( r ) = CONSTANT 40 sources detected in all 4 CS transitions = 5.93 (0.23) = 14.42 (0.49) 2-density component model with a filling factor for the dense component n high ~ 10 8 cm -3 n low ~ 10 4 cm -3 Typically, very high column densities of low density gas required ( = 16.16) with f ~ 0.2 Plume et al. 1997

14. 350  m Survey 5 nights at the CSO 10.4-m telescope 51 high-mass (L bol > 100 L sun ) cores associated with H 2 O masers (Plume et al. 1992 sample) 850 pc < D < 14 kpc All cores also observed in CS5-4 survey (Shirley et al. 2003) SHARC 350  m scan maps (4.0 x 2.7 arcmin)  mb ~ 14 arcsec at 350  m 100 arcsec chop throw Mueller, Shirley, Evans, & Jacobson 2002

15. G9.62+0.10 W43 350  m Images M8E 50,000 AU W33A 10,000 AU W28A2G23.95+0.16 150,000 AU Mueller et al. 2002

16. Submm Continuum Emission Submillimeter continuum emission is optically thin. The specific intensity along a line-of-sight is given by:

17. Why must we model ? Rayleigh-Jeans approximation fails in outer envelope of low-mass cores h /k = 44 K at 350  m Heating from ISRF is very important in outer envelopes of cores Radiative transfer is optically thick at short Radiative transfer is optically thick at short Observed brightness distribution is convolved with complicated beam pattern, scanning, and chopping

18. Radiative Transfer Procedure n d (r) L  T d (r) S  I(b) Nearly orthogonal constraints: SEDMass x Opacity I(b)n(r) Iterate Physical Model n(r) Observations Gas to Dust Radiative Transfer Simulate Obs.

19. Dust Opacity OH = Ossenkopf & Henning 1994 coagulated dust grains

20. Calculated Temperature Profiles Mueller et al. 2002

21. Radiative Transfer Models Mueller et al. 2002 50,000 AU

22. Best-fitted Power Law Mueller et al. 2002 Single power-law density profiles fit observations n( r ) = n f (r / r f ) –p p = - dln n/ dln r Distribution of power law indices = 1.8 (0.4) Similar to distribution of low-mass cores modeled by Shirley et al. (2002) & Young et al (2003)

23. Evolutionary Indicators ? Mueller et al. 2002

24. “Standard” Indicators Mueller et al. 2002

25. 350  m Survey Summary Density and Temperature structure of outer envelope characterized = 1.8 (0.4) = 1.8 (0.4) is order of magnitude higher than nearby low-mass star-forming cores is order of magnitude higher than nearby low-mass star-forming cores Beuther et al. 1.2mm mapping 69 cores: = 1.6 (0.5) Single power law models fit our sample CAVEAT: may be contribution from compact components (UCHIIs or disks) within central beam W3(OH) UCHII may contribute as much as 25% of the central flux assuming optically thick free-free scaled from 3mm flux (Wilner, Welch, & Forster 1995) = 0.16 (0.10) pc = 0.16 (0.10) pc = 29 (9) K isothermal temperature = 29 (9) K isothermal temperature Definitive trends lacking for evolutionary indicators Except perhaps T bol vs. L bol /L smm L bol ranges from 10 3 to 10 6 L sun SEDs not well contrained in many cases due to lack of Far-IR photometry

26. CS J = 5 - 4 Survey 63 high-mass star forming cores associated with H 2 O masers mapped at CSO 10.4m = 5.3 (3.7) kpc with 28 UCHII regions included = 5.3 (3.7) kpc with 28 UCHII regions included 57 peak positions observed in C 34 S J=5-4, 9 in 13 CS J=5-4 Over-sampled On-The-Fly maps in CS J=5-4  mb ~ 25 arcsec at 245 GHz Median peak integrated intensity S/N = 40 10 arcsec binned maps Provide consistent sample from which to determine the properties of the deeply embedded phase of high-mass star formation Shirley et al. 2002

27. CS Rotational Transitions Heavy linear molecule with many rotational transitions observable from the ground J = 5 - 4 transition good probe of dense gas:  b = 1.98 Debye n c (10K) = 8.8 x 10 6 cm -3 n eff (10K) = 2.2 x 10 6 cm -3

28. CS J=5-4 Survey G19.61-0.23M8E S158 S231W44S76E Shirley et al. 2003

29. CS J=5-4 vs. Dust Continuum CS J=5-4 is an excellent tracer of dense gas in high- mass star forming regions Shirley et al. 2003

30. Deconvolved 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

31. Optical Depth Effect on Linewidth C 32 S is typically optically thick, therefore must use rare isotope (C 34 S) in linewidth sensitive calculations Shirley et al. 2003

32. Linewidth-Size Weak correlation with best fit:  v ~ r 0.3 C 34 S linewidth 4x larger than predicted linewidth from Casselli & Myers (1995) indicating high turbulence: = 5.0 (2.0) km/s Shirley et al. 2003

33. Size, Mass, & Pressure Median core size: R = 0.32 pc Alternatively R n = 0.40 pc Median projected aspect ratio: (a/b) = 1.2 Median virial mass: M vir = 920 M 0 corresponding to  = 0.6 g cm -2 Corrections for p and  v broadening necessary Mean mass per OB association ~ 440 M 0 (Matzner 2002) Median pressure = 1.5 x 10 8 K cm -3 Shirley et al. 2003

34. Virial 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

35. Cumulative Mass Spectrum Slope of mass spectrum similar to IMF and distribution of OB associations  ~ -1.1 (0.1) (Massey 1995) Shirley et al. 2003

36. Luminosity and Mass Shirley et al. 2003

37. CS J=5-4 Survey Summary CS J=5-4 is an excellent tracer of dense gas in high-mass star forming cores Aspect ratios consistent with spherical symmetry Median size of 0.32 pc and median virial mass of 920 M sun Virial mass a factor of 2 to 3 larger than dust-determined mass Cumulative mass spectrum  ~ -0.9 similar to IMF of OB associations High median pressure of 1.5 x 10 8 K cm -3 ameliorates the lifetime problem for confinement of UCHII regions L/M is 100x higher than estimates from CO and has a smaller dispersion L/M 2x higher for cores with UCHII and/or HII regions L bol strongly correlates with M vir. Combined with low dispersion of L/M perhaps indicates that mass of most massive star is related to the mass of the core

38. High Mass Pre-protocluster Core? Have yet to identify initial configuration of high-mass star forming core! No unbiased surveys for such an object made yet Based on dense gas surveys, what would a 4500 M 0, cold core (T ~ 10K) look like? Does this phase exist? Evans et al. 2002

39. Conclusions & Future Work Initial characterization of n( r ) indicates a power law density structure of outer envelope CS J=5-4 traces dense gas properties associated with star formation CS J=7-6 + HCN & H 13 CN J=3-2 Mapping Survey (Texas Thesis projects of Jingwen Wu & Claudia Knez) Radiative transfer modeling of dense gas & v( r ) Combination of bolometer camera + interferometric dust continuum imaging with radiative transfer modeling is a powerful diagnostic of the density & temperature How much emission is coming from a compact component within central beam? SMA & ALMA submm continuum needed! SOFIA & SIRTF needed to improve SED