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 G24.78+0.08: a benchmark for massive SF ≡≫≪ 10M⊙  ′″∼ (* massiccia  M*>10M⊙  L*>104L⊙  B3-O)

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?

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?

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

Clump UC HII HMC Core

Clump UC HII HMC

Clump HMC

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=0.4-0.5  clumps centrally heated Clumps might be undergoing inside-out collapse HMCs are density peaks in clumps HMCs are T peaks “enlightened’’ by embedded stars

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

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=0.4-0.5  clumps centrally heated Clumps might be undergoing inside-out collapse HMCs are density peaks in clumps HMCs are T peaks “enlightened’’ by embedded stars

Fontani et al. (2002) sample of 12 Clumps

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=0.4-0.5  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

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=0.4-0.5  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

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

Kurtz et al. (2000)

M* > MHMC Mcluster  MHMC Scalo’98 IMF

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

Examples: “Light’’ HMC with single star IRAS20126+4104: Keplerian disk  equilibrium MHMC = 5 MO; M* = 7 +/- 3 MO “Heavy’’ HMC with multiple stars G10.47+0.03: 4 UCHIIs  4 B1-O9.5 stars G31.41+0.31: rotation about 2 embedded YSOs ; MHMC > Mdynamic  non-equilibrium  fragmentation over Rcentrifugal ∼ YSOs ∼ RHMC/5

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

Examples: “Light’’ HMC with single star IRAS20126+4104: Keplerian disk  equilibrium MHMC = 5 MO; M* = 7 +/- 3 MO “Heavy’’ HMC with multiple stars G10.47+0.03: 4 UCHIIs  4 B1-O9.5 stars G31.41+0.31: rotation about 2 embedded YSOs ; MHMC > Mdynamic  non-equilibrium  fragmentation over Rcentrifugal ∼ YSOs ∼ RHMC/5

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

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

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

Examples: “Light’’ HMC with single star IRAS20126+4104: Keplerian disk  equilibrium MHMC = 5 MO; M* = 7 +/- 3 MO “Heavy’’ HMC with multiple stars G10.47+0.03: 4 UCHIIs  4 B1-O9.5 stars G31.41+0.31: rotation about 2 embedded YSOs ; MHMC > Mdynamic  non-equilibrium  fragmentation over Rcentrifugal ∼ YSOs ∼ RHMC/5

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

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

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

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

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 53 ∼ 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

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

Cesaroni et al. (2003)

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

O9.5 + 550 MO Codella et al. (1997) Furuya et al. (2002)

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)

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

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)

Two bipolar outflows: one from “warm’’ core one from HMCs Both outflows are massive: Mout= 10 MO tout= 2 104 yr dMout/dt = 5 10-4 MO/yr

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

HMCs rotate about outflow axis: Mdyn  10 MO < MHMC  100 MO CH3OH masers may trace rotation about 19 MO and 55 MO (= 20MOstar + 30MOgas): spots distribution = Rcentrifugal(HMC) = RHMC/3  circumstellar disks spots velocities = 3 Vrot(HMC)  angular momentum conservation

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.

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