1. Outflow, infall, and rotation in high-mass star forming regions
Riccardo Cesaroni
Osservatorio Astrofisico di Arcetri
High-mass vs low-mass: the dividing line
The formation of high-mass stars: accretion vs coalescence
Observations: infall, outflows, and disks
Kinematical evidence supports accretion
≡≫≪ 10M⊙  ′″∼

2. Low-mass vs High-mass
Theory (Shu et al. 1987): star formation from inside-out collapse onto protostar
Two relevant timescales:
accretion  tacc = M*/(dM/dt)
contraction  tKH = GM*/R*L*
Lowmass (< 8 MO): tacc < tKH
Highmass (> 8 MO): tacc > tKH  accretion on ZAMS

4. PROBLEM:
High-mass stars “switch on” still accreting 
 radiation pressure stops accretion 
 stars > 8 MO cannot form!?
SOLUTIONS
Yorke (2003): Kdust< Kcrit  M*/L*
“Reduce’’ L*: non-spherical accretion
“Increase’’ M*: large accretion rates
Reduce Kdust: large grains (coalescence of lower mass stars)

5. Possible models
(Non-spherical) accretion: Behrend & Maeder (2001); Yorke & Sonnhalter (2002); Tan & McKee (2003)
ram pressure > radiation pressure
Coalescence: Bonnell et al. (2004) many
low-mass stars merge into one massive star

6. Implications & predictions
Accretion
infall  disks  outflows
isolated star formation possible
massive stars form at cluster centre:
(dM/dt)  FWHM3 (Shu et al. 1987)
massive stars form with lower mass stars:
t  M*1/4 (Tan & Mc Kee 2003)

7. Implications & predictions
Coalescence
infall, low-mass disks, multiple outflows
isolated star formation impossible
massive stars form at cluster centre:
large n* (108 */pc3 !)  many collisions
massive stars form after lower mass stars

8. best discriminant between models: kinematics of molecular gas
infall: accretion  large accretion rate coalescence  small(?) accretion rate
outflow: accretion  single massive flow coalescence  multiple low-mass flows
rotation: infall+ang. mom. conservation 
 rotating disks (“only’’ in accretion model)

9. best discriminant between models: kinematics of molecular gas
infall: accretion  large accretion rate coalescence  small(?) accretion rate
outflow: accretion  single massive flow coalescence  multiple low-mass flows
rotation: infall+ang. mom. conservation 
 rotating disks (“only’’ in accretion model)

10. best discriminant between models: kinematics of molecular gas
infall: accretion  large accretion rate coalescence  small(?) accretion rate
outflow: accretion  single massive flow coalescence  multiple low-mass flows
rotation: infall+ang. mom. conservation 
 rotating disks (“only’’ in accretion model)

11. best discriminant between models: kinematics of molecular gas
infall: accretion  large accretion rate coalescence  small(?) accretion rate
outflow: accretion  single massive flow coalescence  multiple low-mass flows
rotation: infall+ang. mom. conservation 
 rotating disks (“only’’ in accretion model)

12. Discriminating between models: observations
Observational problems:
IMF  high-mass stars are rare
formation in clusters  confusion
rapid evolution: tacc=20 MO /10-3MOyr-1=2 104yr
large distance: >300 pc, typically a few kpc
parental environment profoundly altered
Advantage:
very luminous (cont. & line) and rich (molecules)!

13. High-mass star
forming region
0.5 pc

14. G
NIR J+H+K
10 pc

15. G
350 micron
0.5 pc
Hunter et al. (2000)

16. Testi et al.
Cesaroni et al.

17. Infall Difficult to reveal: Vff  R-0.5 direct evidence:
red-shifted (self)absorption: ambiguous…
position-velocity plots/channel maps
indirect evidence:
lack of support: Mgas > Mvir
model fit to SED
dM/dt=10-3—10-2 MOyr-1  accretion possible
insufficient resolution: infall on single star?

18. Infall Difficult to reveal: Vff  R-0.5 direct evidence:
red-shifted (self)absorption: ambiguous…
position-velocity plots/channel maps
indirect evidence:
lack of support: Mgas > Mvir
model fit to SED
dM/dt=10-3—10-2 MOyr-1  accretion possible
insufficient resolution: infall on single star?

19. Infall Difficult to reveal: Vff  R-0.5 direct evidence:
red-shifted (self)absorption: ambiguous…
position-velocity plots/channel maps
indirect evidence:
lack of support: Mgas > Mvir
model fit to SED
dM/dt=10-3—10-2 MOyr-1  accretion possible
insufficient resolution: infall on single star?

20. Outflow Easy to detect even with low angular resolution
single-dish (>10” i.e. >0.5 pc) CO surveys of UCHIIs, IRAS sources, masers (Shepherd & Churchwell 1996; Zhang et al. 2001; Beuther et al. 2002, etc.), H2 (shocked) 2.2m emission
outflows in high-mass stars do exist
typical parameters: 1 pc, 5—5000 MO ,
10-4—10-2 MO yr-1, dM/dt  L0.7
BUT… are these from the most massive (proto)star?

21. CO(2-1) outflow
&
1mm continuum
Beuther et al. (2002)

22. Outflow Easy to detect even with low angular resolution
single-dish (>10” i.e. >0.5 pc) CO surveys of UCHIIs, IRAS sources, masers (Shepherd & Churchwell 1996; Zhang et al. 2001; Beuther et al. 2002, etc.), H2 (shocked) 2.2m emission
outflows in high-mass stars do exist
typical parms.: 1 pc, MO , MO yr-1
dM/dt  L0.7  continuity from low- to high-mass
BUT… is outflow from one massive (proto)star?

23. CO outflows in YSOs Churchwell (2002)
dM/dt  L0.7

24. Outflow Easy to detect even with low angular resolution
single-dish (>10” i.e. >0.5 pc) CO surveys of UCHIIs, IRAS sources, masers (Shepherd & Churchwell 1996; Zhang et al. 2001; Beuther et al. 2002, etc.), H2 (shocked) 2.2m emission
outflows in high-mass stars do exist
typical parms.: 1 pc, MO , MO yr-1
dM/dt  L0.7  continuity from low- to high-mass
BUT… is outflow from one massive (proto)star?

25.  infall/outflow insufficient to prove model
interferometric (>1” i.e pc) observations of selected targets in CO, HCO+, SiO, etc. (PdBI, OVRO, BIMA, NMA)
“single-dish’’ outflows resolved into (massive & collimated) multiple outflows (Beuther et al. 2002)
precession of outflow complicate interpretation (Shepherd et al. 2000; Gibb et al. 2003)
powering source difficult to identify
 infall/outflow insufficient to prove model

26. CO(2-1)
& mm cont.
Beuther et al.
(2002)
single-dish
(12’’ beam)

27.
Beuther et al.
(2003)
interferometer
(4’’ beam)

28.  infall/outflow insufficient to prove model
interferometric (>1” i.e pc) observations of selected targets in CO, HCO+, SiO, etc. (PdBI, OVRO, BIMA, NMA)
“single-dish’’ outflows resolved into (massive & collimated) multiple outflows (Beuther et al. 2002)
precession of outflow complicate interpretation (Shepherd et al. 2000; Gibb et al. 2003)
powering source difficult to identify
 infall/outflow insufficient to prove model

29. IRAS
Shepherd et al. (2000)
blue lobe
red lobe
H2 knots

30. IRAS
jet in H2 line

31. Cesaroni et al. (in prep.)
IRAS
Cesaroni et al. (in prep.)

32.  infall/outflow insufficient to prove scenario
interferometric (>1” i.e pc) observations of selected targets in CO, HCO+, SiO, etc. (PdBI, OVRO, BIMA, NMA)
“single-dish’’ outflows resolved into (massive & collimated) multiple outflows (Beuther et al. 2002)
precession of outflow complicate interpretation (Shepherd et al. 2000; Gibb et al. 2003)
powering source difficult to identify
 infall/outflow insufficient to prove scenario

33. Disks
Circumstellar accretion disks predicted only by accretion model! Any evidence?
Large scale (1 pc)
rotating clumps seen in medium density tracers e.g. NH3 in G (Little et al. 1985)
Small scale (<0.1 pc)
many claims of rotating “disks’’…

34. Disks
Circumstellar accretion disks predicted only by accretion model! Any evidence?
Large scale (1 pc)
rotating clumps seen in medium density tracers e.g. NH3 in G (Little et al. 1985)
Small scale (<0.1 pc)
many claims of rotating “disks’’…

35. CH3OH masers
ATCA, EVN
Ellingsen et al., Walsh et al.
Minier et al.
OH masers
Merlin
outflow sources
Cohen et al. (2003)
SiO & H2O masers
VLA, VLBA
e.g. Orion source I
Greenhill
NIR, mm & cm continuum
BIMA, VLA
jets/outflows in massive stars Hoare et al., Gibb et al.
NH3, C18O, CS, C34S, CH3CN
PdBI, OVRO, BIMA, NMA
UC HIIs, Hot Cores
Keto et al., Cesaroni et al.,
Zhang et al., …

36. CH3OH masers: stellar mass too low; H2 jets parallel to CH3OH spots (De Buizer 2003)
SiO & H2O masers: outflow or disk ?
NIR-cm cont.: confusion between disk and wind emission
Molecular lines: kinematical signature of disk & outflow

37. CH3OH masers
W48
Minier et al. (2000)
M*=6 MO

38. H2O masers
Cep A HW2
Torrelles et al. (1996)

39. SiO & H2O masers: outflow or disk?
CH3OH masers: stellar mass too low; H2 jets parallel to CH3OH spots (De Buizer 2003)
SiO & H2O masers: outflow or disk?
NIR-cm cont.: confusion between disk and wind emission?
Molecular lines: kinematical signature of disk & outflow
core
disk
outflow
outflow

40. G
Shepherd & Kurtz (1999)
2.6mm cont.
disk
CO outflow

41. G
Shepherd & Kurtz (1999)
3.6cm cont. & H2O masers

42. NGC7538S Sandell et al. (2003)

43. Cesaroni et al.; Moscadelli et al.
IRAS
Cesaroni et al.; Moscadelli et al.
M*=7 MO
H2O masers prop. motions

44. Disks & Tori L (LO) Mdisk (MO) Ddisk (AU) M* IRAS20126 104 4 1600 7
G192.16
3 103 15
1000
6-10
NGC7538S
30000
40?
G24.78 (3)
7 105
80-250
20…
G29.96
9 104
300
14000 -
G31.41
3 105
490
16000
B stars
O stars

45. Gibb et al. (2002)
Olmi et al. (2003)
Beltran et al. (2004)

46. Beltran et al. (2004)

47. Beltran et al. (2004)

48. Gibb et al. (2002)
Olmi et al. (2003)

49. Beltran et al. (2004)
1200 AU
Hofner priv comm.

50. Disks & Tori L (LO) Mdisk (MO) Ddisk (AU) M* IRAS20126 104 4 1600 7
G192.16
3 103 15
1000
6-10
NGC7538S
30000 40
G24.78 (3)
7 105
80-250
20…
G29.96
9 104
300
14000 -
G31.41
3 105
490
16000
B stars
O stars

51. Results “Circumcluster’’ (massive) tori in O (proto)stars
Circumstellar (Keplerian) disks in early-B (proto)stars
 Are disks in O (proto)stars short lived?

52. Assuming (dM/dt)acc  (dM/dt)outflow
and Mdisk  M*
disk ioniz.
&
accr. rates
disk life time
B stars
O stars
B stars
O stars

53. Conclusions
Circumstellar (Keplerian) disks in early-B (proto)stars  disk accretion likely
Circumcluster (unstable) tori in O (proto)stars  large accretion rates make them long-lived
ACCRETION SCENARIO MORE LIKELY

55. G45.47+0.05 NH3(2,2) red-shifted absorption Hofner et al. (1999)
systemic
velocity
blue-shifted
emission

56. Fontani et al. (2001)
n  R-2.6

57. CO outflows
in YSOs
Beuther et al. (2002)