Jets from high-mass young stellar objects Guido Garay Universidad de Chile Outflows, Winds and Jets: From young stars to supermassive black holes Charlottesville, March 6, 2012
Aim Review the current status of our knowledge about the phenomenon of highly collimated ionized flows in high-mass YSO s. Outline Signposts of outflow phenomena and their emission mechanisms. Characteristics of jets associated with luminous YSO´s.
Signposts of outflow phenomena and their emission mechanisms. 1. Primary phenomena: Jets Highly collimated, high velocity flows that emanate from young stellar objects. Thought to be the “base” of large scale outflow events (secondary phenomena) like molecular bipolar outflows and HH systems. Ionized jets Two main types: Molecular jets
1.1 Thermal ionized jets Emission mechanism: Free-free emission from (partially) ionized material. Source of ionization: UV photons from shocks produced by the impact of neutral collimated wind on the surrounding high density material. How do we find them?: Detectable as weak radio continuum sources at cm wavelengths. Observational signatures: Distinctive flux density and size dependence with frequency.
Flux density and size dependence with frequency. Flux density. Power law radio continuum spectra with indices near 0.6 S ν ν with =(4 β -6.2) /(2 β -1) for n e r - β e.g. S ν ν 0.6 for β =2 Reynolds (1986) Elongated morphologies. Angular size along the jet: θ ν ν γ with = -2.1/(2 β -1) e.g. θ ν ν -0.7 for β =2 Reynolds (1986)
Cepheus A HW2 jet 3.6 cm S 0.7 -0.6 Rodriguez et al. (1994) L = 700 AU Curiel et al. (2006) Observed flux density and size dependence with frequency Biconical thermal jet
1.2 Non-thermal ionized jets Emission mechanism: Synchrotron emission from relativistic electrons. Electron acceleration: Fermi process in strong shocks produced where the fast collimated wind impact on the surrounding high density material. How do we find them?: Detectable as weak radio continuum sources at cm wavelengths. Observational signatures: Negative spectral indices ( -0.3) Elongated morphologies.
W3(H 2 O) jet 8.4 GHz -1.0 S -0.6 ---- : Model of non-uniform synchroton source 1 . 6 r 2 3 n ( r ) 5 . 5 10 cm er 500 AU 0 . 8 r B ( r ) 9 . 0 mGauss 500 AU 2000 AU see Chen ´ s talk Reid et al. 1995 Wilner et al. 1999
1.3 Molecular jets Highly collimated, high velocity molecular structures. Emission mechanism: Line emission from highly excited (T K 300 K) molecular gas. How do we find Detectable through high angular resolution them?: observations of high excitation lines. Best tracers: CO and SiO. Abundance of SiO is increased by several orders of magnitude in the gas phase due to shocks.
HH 211 molecular jet Chain of knots. The highest excitation and 8000 AU highest velocity SiO 5-4 knots are closely linked to the SiO 3-2 driving source. SiO 1-0 Lee et al. (2007) Hirano et al. (2005)
Molecular jets are usually enclosed within low velocity, low collimation flows. Chen et al. (2012) IRAS 04166+2706 Molecular jet (EHV gas) Santiago-Garcia et al. (2009) The EHV range depends on the mass of the driving source. Low mass : V -V o ~ 25 km s -1 High mass: V -V o ~ 150 km s -1
Accelerated ambient material? e.g., prompt entrainment at internal working surfaces in the jet (HH211). Origin: Bullets? Not yet clear!
2. Secondary phenomena. Signposts of the interaction of collimated wind with ambient cloud, by means of shock waves, away from the driving source. 2.1 Herbig-Haro objects Nature: Large scale (~ several pc) working surfaces within giant outflows. Emission mechanism: Low-excitation shocked gas How do we find them?: Detectable at optical and near IR wavelengths.
Signatures At moderate extinctions: near-IR At low extinctions: optical lines such as H , [O II], [N II], [S II]. lines such as H 2 and [FeII]. H [SII] 1.5 pc H 2 2.12 m VLT Chain of H 2 emission knots HST HH 111 Brooks et al. 2003 HH objects trace ejection events that took place > 10 5 yrs ago.
2.2 Radio knots or lobes Nature: Working surfaces close (scales of ~ 0.1 pc) to the collimated jet. Free-free emission Emission from shock excited gas or mechanism: Non-thermal emission Which ones dominates? Depends on electron density, n e , and magnetic field, B, within the lobe. crit If : n e > n e,th free-free dominates crit n e < n e,th synchrotron dominates 1 1 3 2 n 2 4 B E crit 4 e, r 3 min n 2 10 cm - 3 3 6 e, th mGauss 10 cm 10 ergs Henriksen et al. (1991) Density of relativistic electrons Garay et al. (1996)
Luminous YSOs in which the radio emission from lobes exhibits negative spectral indices: Source Luminosity (L ) Reference HH 80-81 1.7x10 4 Marti et al. (1993) Cepheus A 1.0x10 4 Garay et al. (1996) IRAS 16547-4247 6.2x10 4 Garay et al. (2003) G240.31+0.07 MM1 5.0x10 4 Trinidad (2011) IRAS 16547-4247 4.8 GHz 0.3 pc Thermal jet
IRAS 18162-2048 HH 80-81 Carrasco et al. (2010) measured polarization in the central region. Thermal jet Degree of polarization: 10-30% Polarization vectors jet axis B in the direction of the jet B 0.2 mGauss Highly collimated jet L = 5.3 pc (11 ´ ) see next talk Marti et al. 1993
2.3 Molecular bipolar outflows Nature: Ambient molecular gas entrained or swept up by primary jets and winds. Thermal emission Emission from shock excited gas or mechanism: maser emission How do we find them?: Maps of molecular line emission at mm and sub-mm wavelengths. Observational signatures: Strong emission in the wings of the ambient cloud line profile.
Characteristics Few to ten km s -1 (LV outflows) Several tens of km s -1 (HV outflows) Velocities: Hundred km s -1 (EHV outflows) LV outflows Poorly collimated Geometry: HV outflows Moderately collimated EHV outflows Highly collimated Wide range of opening angles interpreted as an evolutionary effect: Outflow-envelope interactions Luminosity increase Early B protostar HC HII UC HII ~10 4 yrs 10 3-4 yrs 10 5 yrs ZAMS Class 0 Class I Class II 10 3-4 yrs 10 2 yrs 10 4 yrs time B5-B3 B1-O8 Early O Arce & Sargent (2006) Beuther & Shepherd (2005)
There is strong correlation between molecular outflow parameters and luminosity of driving source: Momentum rate Cabrit & Bertout 1992 Bontemps et al. 1996 Shepherd & Churchwell 1996 Beuther et al. 2002 Luminosity Similar flow-formation process for stars of all luminosities.
Ionized jets associated with high-mass YSO´s Garay & Lizano (1999) reported a handful of ionized thermal radio jets associated with massive YSOs, all of which have luminosities < 2x10 4 L . Source Lumin. S References (L ) (GHz) (mJy) Cepheus A HW2 1.0x10 4 8 10 0.6 Rodríguez et al. 94 IRAS 20126+4104 1.3x10 4 8 0.2 -- Hofner et al. 99 W75N(B) VLA1 1.5x10 4 8 4 0.7 Torrelles et al. 97 IRAS 18162-2048 1.7x10 4 5 5 0.2 Martí et al. 95
Number of detections has increased during the last decade and detections been made towards progressively more luminous YSOs: Source Lumin. S References (L ) (GHz) (mJy) G35.2-0.7 N 1.6x10 4 9 0.4 >1.3 Gibb et al. 2003 IRAS18089-1732 3.2x10 4 9 1.1 0.58 Zapata et al. 2006 CRL2136-RS4 5.0x10 4 9 0.56 1.2 Menten & Tak 2004 IRAS 16547-4247 6.2x10 4 9 6 0.5 Garay et al. 2003 IRAS 16562-3959 7.0x10 4 9 9 0.85 Guzman et al. 2010 W75N-VLA3 1.4x10 5 9 4.0 0.6 Carrasco et al. 2010 G331.512-0.103 2.2x10 5 9 166 1.1 Bronfman et al. 2008 Jets are found associated with luminous YSOs.
3.1 Characteristics of jets associated with high-mass YSOs High mass loss rates and momentum rates IRAS 16547-4247 ( L = 6 10 4 L ) 4.8 GHz Thermal jet 0.3 pc Derived parameters: Ṁ jet = 8x10 -6 M yr -1 Ṁv = 8x10 -3 M yr -1 km s -1 Garay et al. (2003) Lobes
IRAS 16562-3959 ( L = 7 10 4 L ) Thermal jet 0.07 pc Derived parameters: Ṁ jet = 1.4x10 -6 M yr -1 Ṁv = 7x10 -4 M yr -1 km s -1 n jet = 3x10 5 cm -3 at 1000 AU Guzman et al. (2010) Lobes
High velocities Proper motions: HH 80-81 Difference map Cepheus A HW2 Knots moving at 0.1´´ per year Curiel et al. 2006 Marti et al. (1998) Radio recombination lines : v(FWZP) = 1100 km s-1 Jimenez-Serra et al. (2011) Jet velocities of ~ 500 km s -1
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