Star formation from (local) molecular clouds to spiral arms. Lee Hartmann University of Michigan

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1 Star formation from (local) molecular clouds to spiral arms Lee Hartmann University of Michigan

2 Structure of molecular clouds Efficiency of star formation Feedback Mechanisms for forming molecular clouds Implications for: observations of distant objects star formation rates IMFs

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4 Taurus: Goldsmith et al CO

5 Taurus: Goldsmith et al CO CO

6 Taurus: Goldsmith et al CO CO

7 Taurus: Goldsmith et al CO CO Fraction of mass in dense regions 10% Fraction of mass in stars 2%

8 Efficiency of star formation:

9 Efficiency of star formation:

10 Efficiency of star formation:

11 Efficiency of star formation:

12 Efficiency of star formation:

13 Structure of molecular clouds most of the mass is at low density

14 Structure of molecular clouds most of the mass is at low density

15 Structure of molecular clouds most of the mass is at low density Efficiency of star formation: low, because only high-density regions form stars... and because of

16 Structure of molecular clouds most of the mass is at low density Efficiency of star formation: low, because only high-density regions form stars... and because of

17 Structure of molecular clouds most of the mass is at low density Efficiency of star formation: low, because only high-density regions form stars... and because of Feedback! (strongly limits cloud lifetimes)

18 Orion Nebula region Megeath et al.

19 Orion Nebula region Megeath et al. Blow-out by ~ 1 Myr

20 Orion Nebula region Megeath et al. Blow-out by B 2-3 Myr Blow-out by ~ 1 Myr

21 Orion Nebula region Megeath et al. Blow-out by B 2-3 Myr Blow-out by ~ 1 Myr

22 Small Green Circles: IR-ex sources, Big Green/Blue Circles: Protostars W5 d=2 kpc 10 pc 24, 8, 4.5 µm Koenig et al. 2008

23 Taurus: low-density regions show magnetic "striations" 12 CO

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25 Low efficiency:

26 Low efficiency: not due to ambipolar diffusion of magnetic fields

27 Low efficiency: not due to ambipolar diffusion of magnetic fields feedback: energy input from massive stars limits cloud lifetimes

28 Low efficiency: not due to ambipolar diffusion of magnetic fields feedback: energy input from massive stars limits cloud lifetimes structured clouds: high density regions small mass/volume filling factors due to

29 Low efficiency: not due to ambipolar diffusion of magnetic fields feedback: energy input from massive stars limits cloud lifetimes structured clouds: high density regions small mass/volume filling factors due to magnetic support of low-density regions (e.g., Price & Bate 2009)

30 Low efficiency: not due to ambipolar diffusion of magnetic fields feedback: energy input from massive stars limits cloud lifetimes structured clouds: high density regions small mass/volume filling factors due to magnetic support of low-density regions (e.g., Price & Bate 2009) gravitational focusing

31 Structure of molecular clouds most of the mass is at low density Efficiency of star formation: low, because of feedback and

32 Structure of molecular clouds most of the mass is at low density Efficiency of star formation: low, because of feedback and

33 Structure of molecular clouds most of the mass is at low density Efficiency of star formation: low, because of feedback and Gravitational focusing- a natural byproduct of the formation mechanisms for molecular clouds

34 Young stars in Orion: most have ages ~ 1-2 Myr ~ 70 pc

35 Young stars in Orion: most have ages ~ 1-2 Myr ~ 70 pc crossing time ~ Myr

36 Young stars in Orion: most have ages ~ 1-2 Myr ~ 70 pc crossing time ~ Myr information not propagated laterally; swept up!

37 Star -forming clouds produced by shocked flows

38 Star -forming clouds produced by shocked flows spiral shocks in galaxies

39 Star -forming clouds produced by shocked flows spiral shocks in galaxies Orion: supernova bubble? 140 pc below galactic plane 12 CO

40 Finite sheet evolution with gravity Burkert & Hartmann 04; piece of bubble wall sheet

41 Finite sheet evolution with gravity Burkert & Hartmann 04; piece of bubble wall sheet how does it know to be in virial equilibrium?

42 Finite sheet evolution with gravity Burkert & Hartmann 04; piece of bubble wall sheet how does it know to be in virial equilibrium? answer: it doesn't

43 Orion A model (Hartmann & Burkert 2007); collapse of finite, massive, elliptical, rotating sheet 13 CO, Bally et al.

44 Orion A model (Hartmann & Burkert 2007); collapse of finite, massive, elliptical, rotating sheet 13 CO, Bally et al.

45 Orion A model (Hartmann & Burkert 2007); collapse of finite, massive, elliptical, rotating sheet 13 CO, Bally et al.

46 Orion A model (Hartmann & Burkert 2007); collapse of finite, massive, elliptical, rotating sheet 13 CO, Bally et al.

47 Orion A model (Hartmann & Burkert 2007); collapse of finite, massive, elliptical, rotating sheet 13 CO, Bally et al.

48 Orion A model (Hartmann & Burkert 2007); collapse of finite, massive, elliptical, rotating sheet 13 CO, Bally et al.

49 Orion A model (Hartmann & Burkert 2007); collapse of finite, massive, elliptical, rotating sheet 13 CO, Bally et al.

50 Global collapse (over ~ 2 Myr) - makes filamentary ridge, Orion Nebula cluster

51 Global collapse (over ~ 2 Myr) - makes filamentary ridge, Orion Nebula cluster

52 Global collapse (over ~ 2 Myr) - makes filamentary ridge, Orion Nebula cluster Short radius of curvature results in extra mass concentrations assemble cluster gas/ stars

53 Orion Nebula cluster- (optical) kinematics of stars and gas: evidence for infall? ΔV vlsr (km/s)) J. Tobin, et al E. Proszkow, F. Adams

54 gravitational focusing: clusters form preferentially at ends of filaments

55 gravitational focusing: clusters form preferentially at ends of filaments can t escape large-scale focusing by gravity

56 Cluster gravitational focusing- any short radius of curvature will do Gutermuth et al.

57 NEED turbulence to generate density fluctuations during cloud formation- must be rapid to compete with global collapse

58 NEED turbulence to generate density fluctuations during cloud formation- must be rapid to compete with global collapse Thin shell Kelvin- Helmholtz cooling (thermal instability) and gravity...

59 F. Heitsch et al. 2007; sheet made by inflows with cooling, gravity

60 F. Heitsch et al. 2007; sheet made by inflows with cooling, gravity

61 Orion Nebula region Megeath et al.

62 Structure of molecular clouds most of the mass is at low density Efficiency of star formation: low, because of feedback and Gravitational focusing- a natural byproduct of the formation mechanisms for molecular clouds: make clusters stars...

63 What about the stellar IMF? N(log m) log M

64 What about the stellar IMF? fragmentation N(log m) log M

65 What about the stellar IMF? fragmentation N(log m) competitive accretion (e.g., Bonnell et al.) log M

66 What about the stellar IMF? fragmentation N(log m) competitive accretion (e.g., Bonnell et al.) log M not clear evidence of variation, though massive clusters near GC suggest slightly flatter upper IMF (Stolte, Figer, etc.)

67 Numerical simulations of competitive accretion in sheets (Hsu et al. 2010); high-mass IMF depends upon amount of accretion, evolution toward Salpeter slope (or beyond?) -1.35

68 Numerical simulations of competitive accretion in sheets (Hsu et al. 2010); high-mass IMF depends upon amount of accretion, evolution toward Salpeter slope (or beyond?) Γ 1 as limiting slope

69 Numerical simulations of competitive accretion in sheets (Hsu et al. 2010); high-mass IMF depends upon amount of accretion, evolution toward Salpeter slope (or beyond?) Γ 1 as limiting slope Similar to star cluster IMF (Fall, Chandar) ; gravitational focussing

70 The local story: Compression

71 The local story: Compression dm(tot)/dt

72 The local story: Compression dm(tot)/dt gravitational focusing feedback (dispersal)

73 The local story: Compression gravitational focusing feedback (dispersal) dm(tot)/dt efficiency

74 The local story: Compression gravitational focusing feedback (dispersal) dm(tot)/dt efficiency

75 How does this work for the molecular "ring"? Jackson et al. Dame 1993, AIPC 278, 267

76 Does star formation follow the H 2 content? Is the SFR low in the molecular "ring"? Or just more diffuse "shielded" gas? Peek 2009, ApJ 698, 1429, from Stahler & Palla 2005

77 Does star formation follow the H 2 content? Is the SFR low in the molecular "ring"? Or just more diffuse "shielded" gas? A V ~0.5 in ~ 320 pc Peek 2009, ApJ 698, 1429, from Stahler & Palla 2005

78 Does star formation follow the H 2 content? Is the SFR low in the molecular "ring"? Or just more diffuse "shielded" gas? A V ~0.5 in ~ 160 pc A V ~0.5 in ~ 320 pc Peek 2009, ApJ 698, 1429, from Stahler & Palla 2005

79 12 CO can be seen at low A V ; if more shielding because higher average gas density, a solar neighborhood "molecular cloud" may differ from a molecular ring "cloud" 2007

80 12 CO can be seen at low A V ; if more shielding because higher average gas density, a solar neighborhood "molecular cloud" may differ from a molecular ring "cloud" 12 CO is a column density tracer, not just a density tracer 2007

81 Implications for distant objects:

82 Age "spreads" and "cloud lifetimes" Cep OB2 50 pc 100 µm IRAS dust emission

83 Age "spreads" and "cloud lifetimes" Cep OB2 50 pc ~ 10 Myr-old cluster: supernova/ winds 100 µm IRAS dust emission

84 Age "spreads" and "cloud lifetimes" Cep OB2 50 pc ~ 10 Myr-old cluster: supernova/ winds 100 µm IRAS dust emission ~ 4 Myr-old cluster, H II region

85 Age "spreads" and "cloud lifetimes" Cep OB2 1 Myr-old stars 50 pc ~ 10 Myr-old cluster: supernova/ winds 100 µm IRAS dust emission ~ 4 Myr-old cluster, H II region

86 Age "spreads" and "cloud lifetimes" Cep OB2 1 Myr-old stars 50 pc Extragalactic view: (100 pc) 10 Myr age spread ; H II, H I, CO ~ 10 Myr-old cluster: supernova/ winds 100 µm IRAS dust emission ~ 4 Myr-old cluster, H II region

87 Star formation where gas is compressed by shocks NGC 6946 Hα Ferguson et al. 1998

88 Star formation where gas is compressed by shocks NGC 6946 Hα outer disk spiral shock; not enough material to continue propagating SF Ferguson et al. 1998

89 Star formation where gas is compressed by shocks NGC 6946 Hα outer disk spiral shock; not enough material to continue propagating SF inner disk; potential well, (Q <~ 1), more gas more continuing SF (local feedback) Ferguson et al. 1998

90 Star formation where gas is compressed by shocks NGC 6946 Hα outer disk spiral shock; not enough material to continue propagating SF inner disk; potential well, (Q <~ 1), more gas more continuing SF (local feedback) Ferguson et al dσ/dt Σ eff [v orb - v(pattern)] Σ/t dyn efficiency ~ 2% per cloud, few triggered 10%/orbit one version of the Kennicutt-Schmidt law

91 Gas content and SFR?

92 Gas content and SFR? molecular gas should trace SFR more closely, as it generally traces the densest gas

93 Gas content and SFR? molecular gas should trace SFR more closely, as it generally traces the densest gas high-density molecular tracers should follow the SFR very closely; but this does not address the question of the RATE of formation of dense molecular gas

94 Gas content and SFR? molecular gas should trace SFR more closely, as it generally traces the densest gas high-density molecular tracers should follow the SFR very closely; but this does not address the question of the RATE of formation of dense molecular gas CO is sensitive to column density as well as density; likely to trace different phases in differing regions (and most CO emission comes from non-star forming gas in the solar neighborhood)

95 Structure of molecular clouds: most mass at low ρ Efficiency of star formation ~ few % Feedback + gravitational focusing limit efficiency Molecular clouds formed by large-scale flows; creates turbulent structure necessary for fragmentation into stars distant objects: averaging over cycling of gas star formation rates set by gas content (not just molecular gas) plus rate of compressions gravitational focusing may lead to similar massive star and cluster IMFs, but physics of peak unclear

96 Typical numerical simulations: start with imposed turbulent velocity virial prevents immediate collapse

97 Typical numerical simulations: start with imposed turbulent velocity virial prevents immediate collapse How do clouds "know" to have this level of turbulence, given how the clouds form?

98 Typical numerical simulations: start with imposed turbulent velocity virial prevents immediate collapse How do clouds "know" to have this level of turbulence, given how the clouds form? Too much: doesn't collapse, expands; too little, collapse; how to hit the sweet spot?

99 Typical numerical simulations: start with imposed turbulent velocity virial prevents immediate collapse How do clouds "know" to have this level of turbulence, given how the clouds form? Too much: doesn't collapse, expands; too little, collapse; how to hit the sweet spot? can't in general.

100 Typical numerical simulations: start with imposed turbulent velocity virial prevents immediate collapse How do clouds "know" to have this level of turbulence, given how the clouds form? Too much: doesn't collapse, expands; too little, collapse; how to hit the sweet spot? can't in general. However, turbulence IS needed to make stellar fragments...

101 Ages of young associations/clusters

102 Ages of young associations/clusters Fast onset after MC formation!

103 Ages of young associations/clusters Fast onset after MC formation!

104 Ages of young associations/clusters Fast onset after MC formation! <t> << t(cross); clouds swept-up by large scale flows

105 Growth of high-mass power-law tail: doesn t require initial cluster environment dm/dt M 2 dm/dt Bondi-Hoyle: dm/dt M 2 ρ v -3 M 2 log M

106 Orion A: 13 CO (Bally et al.)

107 Ages of young associations/clusters

108 Ages of young associations/clusters Fast onset after MC formation! (because cloud is already collapsing globally)

109 Ages of young associations/clusters Fast onset after MC formation! (because cloud is already collapsing globally)

110 Orion Nebula cluster- kinematics of stars and gas: evidence for infall? ΔV J. Tobin, et al E. Proszkow, F. Adams

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137 Hurray! ONE region not peaking at 1-2 Myr ago... OOPS; NO molecular gas!

138 Hurray! ONE region not peaking at 1-2 Myr ago... OOPS; NO molecular gas!

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140 NO molecular gas!

141 Hsu, Heitsch et al.

142 Compression

143 Compression dm(tot)/dt

144 Compression dm(tot)/dt gravitational focusing feedback (dispersal)

145 Compression gravitational focusing feedback (dispersal) dm(tot)/dt efficiency

146 Compression gravitational focusing feedback (dispersal) dm(tot)/dt efficiency

147 Summary: SFR set by dm(tot)/dt efficiency; Compression (rate of) gravitational focusing (makes low efficiency by feedback possible) feedback (dispersal)

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174 Hurray! ONE region not peaking at 1-2 Myr ago... OOPS; NO molecular gas (only on periphery)

175 Hurray! ONE region not peaking at 1-2 Myr ago... OOPS; NO molecular gas (only on periphery)

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177 NO molecular gas!

178 A popular cloud model:

179 A popular cloud model:

180 A popular cloud model:

181 A popular cloud model:

182 A popular cloud model: Must put in (arbitrary) velocity field with some "large scale" component to make it look like a real cloud

183 Accretion of randomly-placed sink particles in a sheet; does competitive accretion still work? Tina Hsu, LH, Gilberto Gomez, Fabian Heitsch

184 Another popular cloud model: periodic box

185 This model also needs imposed turbulence to make reasonable-looking structure; Another popular cloud model: periodic box

186 Another popular cloud model: periodic box This model also needs imposed turbulence to make reasonable-looking structure; also: eliminates large-scale gravity

187 Sco OB2: quickly emptied by winds, SN de Geus 1992; Preibisch & Zinnecker 99, 02 HI shells ~ 140 pc age ~ 5 Myr age ~ Myr

188 Sco OB2: quickly emptied by winds, SN de Geus 1992; Preibisch & Zinnecker 99, 02 HI shells Oph MC (~ 1 Myr) ~ 140 pc age ~ 5 Myr age ~ Myr

189 Sco OB2: quickly emptied by winds, SN de Geus 1992; Preibisch & Zinnecker 99, 02 Upper Sco HI shells Oph MC (~ 1 Myr) ~ 140 pc age ~ 5 Myr age ~ Myr Ophiuchus molecular cloud

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