1. Osservatorio Astrofisico di Arcetri
Hot Molecular Cores
Riccardo Cesaroni
Osservatorio Astrofisico di Arcetri
The environment of HMCs: the clump
The properties of HMCs: “light’’ & “heavy’’
High-mass star formation: a tentative scenario
G : a benchmark for massive SF
≡≫≪ 10M⊙  ′″∼
(* massiccia  M*>10M⊙  L*>104L⊙  B3-O)

2. HMCs: a (convenient) definition
Observational definition of HMC: region traced by high-excitation lines of exotic (i.e. low-abundance) molecules (CH3CN, HCOOCH3, etc…)
HMCs associated with signposts of massive star formation (UC HIIs, masers, luminous IR sources)
Are HMCs distinct physical entities?

4. HMCs: a (convenient) definition
Observational definition of HMC: region traced by high-excitation lines of exotic (i.e. low-abundance) molecules (CH3CN, HCOOCH3, etc…)
HMCs associated with signposts of massive star formation (UC HIIs, masers, luminous IR sources)
Are HMCs distinct physical entities?

5. The environment of HMCs: the clump
HMCs surrounded by molecular “clumps’’:
Rclump = 10 RHMC ; Mclump= 10 MHMC ; nclump = 0.01 nHMC
D (pc)
M (MO)
nH2 (cm-3)
T (K)
Clump 1
1000
105 30
HMC
0.1
100
107

6. Clump
UC HII
HMC
Core

7. Clump
UC HII
HMC

8. Clump
HMC

9. nR-p with p=1.5-2.5  no break at HMC
 singular isothermal sphere?
Mclump > Mvirial  clumps unstable
Vclump = VHMC  HMCs at rest wrt clumps
TR-q with q=  clumps centrally heated
Clumps might be undergoing inside-out collapse
HMCs are density peaks in clumps
HMCs are T peaks “enlightened’’ by embedded stars

10. HMC
Clump
nH2  R-2.6
Fontani et al. (2002)

11. nR-p with p=1.5-2.5  no break at HMC
 singular isothermal sphere?
Mclump > Mvirial  clumps unstable
Vclump = VHMC  HMCs at rest wrt clumps
TR-q with q=  clumps centrally heated
Clumps might be undergoing inside-out collapse
HMCs are density peaks in clumps
HMCs are T peaks “enlightened’’ by embedded stars

12. Fontani et al. (2002)
sample of 12 Clumps

13. nH2R-p with p=1.5-2.5  no break at HMC
 singular isothermal sphere?
Mclump > Mvirial  clumps unstable
Vclump = VHMC  HMCs at rest wrt clumps
TR-q with q=  clumps centrally heated
Clumps might be undergoing inside-out collapse
HMCs are density peaks in clumps
HMCs are T peaks “enlightened’’ by embedded stars
HMCs are deeply related to clumps

14. nH2R-p with p=1.5-2.5  no break at HMC
 singular isothermal sphere?
Mclump > Mvirial  clumps unstable
Vclump = VHMC  HMCs at rest wrt clumps
TR-q with q=  clumps centrally heated
Clumps might be undergoing inside-out collapse
HMCs are density peaks in clumps
HMCs are T peaks “enlightened’’ by embedded stars
HMCs are deeply related to clumps

15. The stellar content of HMCs
THMC  100 K > Tclump = 30 K  HMCs heated by embedded luminous stars
(sub)mm continuum  mass of gas in HMC
far-IR continuum  luminosity of stars in HMC
Luminosity vs Mass of HMCs:
“light” HMCs (<10-20 MO): few stars, M* > MHMC
“heavy” HMCs (>100 MO ): cluster, Mclust  MHMC

16. Kurtz et al. (2000)

17. M* > MHMC Mcluster  MHMC
Scalo’98
IMF

18. The stellar content of HMCs
THMC  100 K > Tclump = 30 K  HMCs heated by embedded luminous stars
(sub)mm continuum  mass of gas in HMC
far-IR continuum  luminosity of stars in HMC
Luminosity vs Mass of HMCs:
“light” HMCs (<10-20 MO): few stars, M* > MHMC
“heavy” HMCs (>100 MO ): cluster, Mclust  MHMC

19. Examples: “Light’’ HMC with single star
IRAS : Keplerian disk  equilibrium
MHMC = 5 MO; M* = 7 +/- 3 MO
“Heavy’’ HMC with multiple stars
G : 4 UCHIIs  4 B1-O9.5 stars
G : rotation about 2 embedded YSOs ; MHMC > Mdynamic  non-equilibrium  fragmentation over Rcentrifugal ∼ YSOs ∼ RHMC/5

20. M* > MHMC M*=7 MO Keplerian rotation IRAS 20126+4104
Cesaroni et al. (2005)
Moscadelli et al. (2005)
M*=7 MO
Keplerian rotation
M* > MHMC

21. Examples: “Light’’ HMC with single star
IRAS : Keplerian disk  equilibrium
MHMC = 5 MO; M* = 7 +/- 3 MO
“Heavy’’ HMC with multiple stars
G : 4 UCHIIs  4 B1-O9.5 stars
G : rotation about 2 embedded YSOs ; MHMC > Mdynamic  non-equilibrium  fragmentation over Rcentrifugal ∼ YSOs ∼ RHMC/5

22. Cesaroni et al. (1998); Hofner (pers. comm.)
UC HII
HMC
B0.5 B0 B1

23. Beltran et al. (2005); Hofner et al. (in prep.)
HC HII or wind
HMC
CH3CN(12-11)

24. Beltran et al. (2005); Hofner et al. (in prep.)
NH3 red-shifted
NH3 blue-shifted
NH3 bulk
CH3CN(12-11)

25. Examples: “Light’’ HMC with single star
IRAS : Keplerian disk  equilibrium
MHMC = 5 MO; M* = 7 +/- 3 MO
“Heavy’’ HMC with multiple stars
G : 4 UCHIIs  4 B1-O9.5 stars
G : rotation about 2 embedded YSOs ; MHMC > Mdynamic  non-equilibrium  fragmentation over Rcentrifugal ∼ YSOs ∼ RHMC/5

26. A possible scenario for high-mass SF
Unstable clump: tff=105 yr
Clump
nR-2
Mclump > Mvirial

27. A possible scenario for high-mass SF
Unstable clump: tff=105 yr
Inside-out collapse: dMaccr/dt=Mclump/tff=10-2 MO/yr
infalling
Clump
nR-2
nR-3/2

28. A possible scenario for high-mass SF
Unstable clump: tff=105 yr
Inside-out collapse: dMaccr/dt=Mclump/tff=10-2 MO/yr
Rotation of core with rotation period=105 yr
infalling
Clump
nR-2
nR-3/2
rotating
Core

29. A possible scenario for high-mass SF
Unstable clump: tff=105 yr
Inside-out collapse: dMaccr/dt=Mclump/tff=10-2 MO/yr
Rotation of core with rotation period=105 yr
Fragmentation over Rcentrifugal=RHMC/5=0.01 pc
infalling
Clump
nR-2
nR-3/2
rotating
Core
rotating disks

30. A possible scenario for high-mass SF
Unstable clump: tff=105 yr
Inside-out collapse: dMaccr/dt=Mclump/tff=10-2 MO/yr
Rotation of core with rotation period=105 yr
Fragmentation over Rcentrifugal=RHMC/5=0.01 pc
Formation of HMC with ∼ 100 stars
(dMaccr/dt)star= 10-2 MO /yr /100 =
= 10-4 MO/yr over tSF=tff=105 yr
infalling
Clump
nR-3/2
nR-2
rotating
HMC
circumstellar disks

31. Speculation versus Observations: the G24.78+0.08 star forming region
Group of UCHIIs and masers of various types, surrounded by molecular clump:
RClump= 0.6 pc ; MClump= 5000 MO ;
TClump= 30 K
Clump with nR-1.8 and MClump> Mvirial

32. Cesaroni et al. (2003)

33. T=30 K T=120 K Codella et al. (1997) Furuya et al. (2002)
Cesaroni et al. (2003)
T=30 K
T=120 K

34. O MO
Codella et al. (1997)
Furuya et al. (2002)

35. Two massive cores:
one “warm’’ core (30 K)
one hot core
The hot core splits into 2 HMCs with
T=120 K, M=100 MO:
1 HMC with embedded UC HII region (O9.5 star)
1 HMC with mid-IR source (GLIMPSE)

36. Beltran et al. (2004,2005)
Furuya et al. (2002)

37. Two massive cores:
one “warm’’ core (30 K)
one hot core
The hot core splits into 2 HMCs with
T=120 K, M=100 MO:
1 HMC with embedded UC HII region (O9.5 star)
1 HMC with mid-IR source (GLIMPSE)

38. Two bipolar outflows:
one from “warm’’ core
one from HMCs
Both outflows are massive:
Mout= 10 MO
tout= yr
dMout/dt = MO/yr

39. Moscadelli et al. (in prep.)
Beltran et al. (2004,2005)
Furuya et al. (2002)
Forster & Caswell (1989)
Moscadelli et al. (in prep.)
Mdyn= 19 MO
Mdyn= 55 MO

40. HMCs rotate about outflow axis:
Mdyn  10 MO < MHMC  100 MO
CH3OH masers may trace rotation about MO and 55 MO (= 20MOstar + 30MOgas):
spots distribution = Rcentrifugal(HMC) = RHMC/3  circumstellar disks
spots velocities = 3 Vrot(HMC)  angular momentum conservation

41. Conclusions for G24.78+0.08: Unstable clump? YES  tclump= tff =105yr
High-mass star formation? YES (UCHIIs, masers)
Rotating HMCs? YES  tHMC = toutf = 5 104yr
Centrifugally supported disks? YES  M* =20MO
The proposed scenario seems to work! BUT…
5. NO infall detected!?! Why that???
Infall confined in small region, close to HMC
Outflows “spoil’’ infall signatures
Infall halted by centrifugal forces
In fact, see Keto et al., Sollins et al., Zhang et al., etc.

42. Conclusion
High-mass star formation could proceed through inside-out collapse of pc-scale clumps and subsequent (centrifugal) fragmentation of rotating, massive cores