young stellar objects Guido Garay Universidad de Chile Outflows, - - PowerPoint PPT Presentation

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

Outline  Signposts of outflow phenomena and their emission mechanisms.  Characteristics of jets associated with luminous YSO´s.

Aim

Review the current status of our knowledge about the phenomenon of highly collimated ionized flows in high-mass YSOs.

 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. Two main types:

Ionized jets 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

Sν  ν with =(4β-6.2) /(2β-1) for ne  r -β

e.g. Sν  ν0.6 for β=2 Reynolds (1986)

 Elongated morphologies. Angular size along the jet: θν  νγ with  = -2.1/(2β-1)

e.g. θν  ν-0.7 for β=2 Reynolds (1986)

Observed flux density and size dependence with frequency

 Biconical thermal jet S0.7 -0.6

 Cepheus A HW2 jet

Rodriguez et al. (1994)

L = 700 AU

Curiel et al. (2006)

3.6 cm

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(H2O) jet S-0.6 -1.0

Reid et al. 1995 Wilner et al. 1999

• --- : Model of non-uniform synchroton

source

2000 AU

mGauss AU 500 r . 9 ) ( B cm AU 500 r 10 5 . 5 ) ( n

8 . 3 6 . 1 2 er    

               r r

8.4 GHz

see Chen´s talk

1.3 Molecular jets

Highly collimated, high velocity molecular structures. Emission mechanism: Line emission from highly excited (TK  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

• f magnitude in the gas phase due to shocks.

SiO 5-4 SiO 3-2 SiO 1-0

 HH 211 molecular jet

Lee et al. (2007) Hirano et al. (2005)

The highest excitation and highest velocity knots are closely linked to the driving source. Chain of knots.

8000 AU

Molecular jets are usually enclosed within low velocity, low collimation flows. Chen et al. (2012)

IRAS 04166+2706

The EHV range depends on the mass of the driving source. Low mass : V -Vo ~ 25 km s-1 High mass: V -Vo ~ 150 km s-1

Molecular jet (EHV gas)

Santiago-Garcia et al. (2009)

Origin:

Accelerated ambient material?

e.g., prompt entrainment at internal working surfaces in the jet (HH211).

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 low extinctions: optical lines such as H, [O II], [N II], [S II]. Chain of H2 emission knots

Brooks et al. 2003

H2 2.12 m

1.5 pc

At moderate extinctions: near-IR lines such as H2 and [FeII].

H [SII]

HST VLT

HH objects trace ejection events that took place > 105 yrs ago.

HH 111

2.2 Radio knots or lobes

Nature: Working surfaces close (scales of ~ 0.1 pc) to the collimated jet. Free-free emission

• r

Non-thermal emission

Emission

mechanism: from shock excited gas

Which ones dominates? Depends on electron density, ne, and magnetic field, B, within the lobe.

If : ne > ne,th free-free dominates ne < ne,th synchrotron dominates

3 2 1 6 min 2 1 3 3

• r

e, 4 3 4

cm ergs 10 cm 10 n mGauss B 10 2 n

th e,

  

                        E

crit

Density of relativistic electrons Henriksen et al. (1991) Garay et al. (1996) crit crit

0.3 pc

Thermal jet

4.8 GHz

Luminous YSOs in which the radio emission from lobes exhibits negative spectral indices:

Source Luminosity (L) Reference

HH 80-81 1.7x104 Marti et al. (1993) Cepheus A 1.0x104 Garay et al. (1996) IRAS 16547-4247 6.2x104 Garay et al. (2003) G240.31+0.07 MM1 5.0x104 Trinidad (2011)

 IRAS 16547-4247

Highly collimated jet L = 5.3 pc (11´)

 IRAS 18162-2048 HH 80-81

Thermal jet Marti et al. 1993

 Degree of polarization: 10-30%  Polarization vectors  jet axis  B in the direction of the jet B  0.2 mGauss see next talk Carrasco et al. (2010) measured polarization in the central region.

2.3 Molecular bipolar outflows

Nature: Ambient molecular gas entrained or swept up by primary jets and winds. Thermal emission

• r

maser emission

Emission

mechanism: from shock excited gas 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) Hundred km s-1 (EHV outflows) Poorly collimated Moderately collimated Highly collimated

Geometry: Velocities:

 LV outflows  HV outflows  EHV outflows

Wide range of opening angles interpreted as an evolutionary effect:

Class 0 Class I Class II

time

Arce & Sargent (2006)

Early B protostar HC HII UC HII Early O B1-O8 B5-B3 103-4 yrs ~104 yrs 105 yrs 102 yrs 103-4 yrs 104 yrs ZAMS

Beuther & Shepherd (2005)

 Outflow-envelope interactions  Luminosity increase

 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

 Similar flow-formation process for stars of all luminosities.

Luminosity

Garay & Lizano (1999) reported a handful of ionized thermal radio jets associated with massive YSOs, all of which have luminosities < 2x104 L.

Source Lumin.  S  References (L) (GHz) (mJy) Cepheus A HW2 1.0x104 8 10 0.6 Rodríguez et al. 94 IRAS 20126+4104 1.3x104 8 0.2 -- Hofner et al. 99 W75N(B) VLA1 1.5x104 8 4 0.7 Torrelles et al. 97 IRAS 18162-2048 1.7x104 5 5 0.2 Martí et al. 95

 Ionized jets associated with high-mass YSO´s

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 1.6x104 9 0.4 >1.3 Gibb et al. 2003 IRAS18089-1732 3.2x104 9 1.1 0.58 Zapata et al. 2006 CRL2136-RS4 5.0x104 9 0.56 1.2 Menten & Tak 2004 IRAS 16547-4247 6.2x104 9 6 0.5 Garay et al. 2003 IRAS 16562-3959 7.0x104 9 9 0.85 Guzman et al. 2010 W75N-VLA3 1.4x105 9 4.0 0.6 Carrasco et al. 2010 G331.512-0.103 2.2x105 9 166 1.1 Bronfman et al. 2008

 Jets are found associated with luminous YSOs.

Garay et al. (2003)

0.3 pc

Thermal jet Lobes

4.8 GHz  IRAS 16547-4247 (L = 6104 L)

Derived parameters: Ṁjet = 8x10-6 M yr-1 Ṁv = 8x10-3 M yr-1 km s-1

3.1 Characteristics of jets associated with high-mass YSOs  High mass loss rates and momentum rates

Guzman et al. (2010)

0.07 pc

 IRAS 16562-3959 (L = 7104 L)

Thermal jet Lobes

Derived parameters: Ṁjet = 1.4x10-6 M yr-1 Ṁv = 7x10-4 M yr-1 km s-1 njet = 3x105 cm-3 at 1000 AU

Knots moving at 0.1´´ per year HH 80-81

 High velocities

Curiel et al. 2006 Difference map

 Proper motions:

Marti et al. (1998)  Jet velocities of ~ 500 km s-1

 Radio recombination lines : v(FWZP) = 1100 km s-1

Cepheus A HW2

Jimenez-Serra et al. (2011)

Jet luminosity

103 times more luminous and energetic than low-mass jets !

Momentum rate

Rodriguez et al. 2007

High-mass jets Low-mass jets  Jets associated with luminous YSOs are powerful

Velocities : 500 - 1000 km s-1 Sizes : 500 - 2000 AU

Mass loss rates : 10-6 - 10-5 M

yr-1

Momentum rates : 10-3 - 10-2 M

km s-1 yr-1

3.2 Are HMYSO´s with jets associated with molecular bipolar outflows?

Observations show that all high-mass YSO´s associated with jets are also associated with large scale, high velocity collimated molecular outflows.

G331.55-0.11

Bronfman et al. (2008) Garay et al. (2007)

IRAS 16547-4247 IRAS 16562-3959

Guzman et al. (2010)

Mflow ~ 110 M

Systematic surveys have shown that:

Bipolar flow is a common phenomenon toward high-mass

protostellar objects Characteristics of molecular flows associated with high-mass YSOs Velocity : 10 - 100 km s-1 Mass : 50 - 500 M Size : 0.1 - 5 pc Mass outflow rate : 10-4 - 10-3 M yr-1 Momentum rate : 10-3 - 10-1 M km s-1 yr-1  High-mass outflows are 102 – 103 times more massive and energetic than low-mass outflows.

Shepherd & Churchwell 1996 Zhang et al. 2001 Beuther et al. 2002

Ionized jets are, however, rare!

Possible explanations:  Different formation mechanism?  Obscured by bright Hyper Compact HII region?  Short timescale for jet phase? Bipolar outflows in high mass protostar have dynamic ages of 105 yrs > longer than the K-H time of the jet/disk stage of 104 yrs.  jet may turn off and the large scale outflow will still persist as a fossil for a relatively long time.

3.3 Why are ionized jets rare?

To answer this question Guzman (2011) undertook an unbiased search for jets towards HMYSO´s.

ATCA survey of jets toward luminous massive proto-stellar

• bjects candidates of harboring jets.

Selection criteria:

 Luminous HMYSO´s (L > 2104 L)  Positive radio continuum spectral indices  Underluminous in radio

Results: 38% Collimated ionized winds 38% Hyper compact HII regions 24% Ultracompact HII regions From the rate of occurence of jets in the sample:

Jet phase in high-mass protostars last for ~2104 yrs.

3.4 Relationship between ionized jets and bipolar molecular

• utflows.

 Hint for a common origin of jets in YSO´s of all luminosities.

Jet luminosity Momentum rate

Low-mass jets High-mass jets

There is a strong correlation between jet radio luminosity and momentum rate of molecular bipolar outflow:

3.5 The large scale environments of HMYSO´s with jets.

Dust continuum observations show that HMYSO´s with jets are found within structures with distinctive physical parameters.

1 pc

1.2 mm 0.87 mm

IRAS 16547-4247

1 pc

1.2 mm 0.87 mm

IRAS 16562-3959

R= 0.23 pc; Md =1.3x103 M R= 0.16 pc; Md =9.1x102 M

 HMYSO´s with jets are associated with massive and dense cores. R ~ 0.25 pc Md ~ 2x103 M n(H2) ~ 2x105 cm-3 N(H2) ~ 5x1023 cm-2 Td ~ 35 K Density depends with radius as n ∝ r –p, with <p>=1.7

Mueller et al. 2002 Hatchell & van der Tak 2003 Williams et al. 2005

 Density structure.

 MDC´s with jets are highly centrally condensed

 Physical parameters.

Optically  thick lines Optically  thin lines

large scale infalling motions

MDC´s with jets are undergoing large scale inflow motions with intense mass infall rate



Vinf ~1 km s-1 Minf ~ 1x10-3 M yr-1 IRAS 16547-4247

 Dynamical state.

Summary of our current knowledge about ionized jets associated with HMYSO´s

 Jets are found associated with high-mass YSOs (up to luminosities of 2x105 L).  They are 103 times more energetic and luminous than low-mass jets.  They have lifetimes of 3x104 yr (this makes them rare).  They are associated with massive and energetic bipolar molecular outflows.  They are located in the central region of massive and dense cores exhibiting infalling motions with high-mass infall rates.

Many open questions …

Still far from understanding the details of the jet phenomena. The momentum rate of the jet is typically only 10% of the momentum rate of the molecular outflow. Guzman et al. (2012)  Which is ionization fraction of the jets?  How are the jets launched and collimated?

Disk wind? X-wind? Hoop stress? Jet launching zone : 10 AU (10 mas at 1 kpc) Jet acceleration/collimation zones: 10-100 AU (10-100 mas at 1 kpc)

 How is the angular momentum transferred from the accretion disk to the jet?  Do jets rotate?

Investigate the morphology & kinematics of the outflowing molecular gas at scales of 10 AU.

 What determines the opening angle in high-mass outflows? Which is the strength and geometry of magnetic fields?

 Sub-arcsec angular resolution  High-fidelity  High spectral resolution

Of course, the instrument of choice is ALMA!

To answer these questions we need to probe jets with:  High spatial resolution (< 10 AU)  High sensitivity  High velocity resolution (v ~ 0.1 km s-1)

End

Arce & Goodman (2002)

 Which is the driving mechanism of massive outflows?

Magnetically diverted flows? Fiege & Henriksen (1996) Momentum driven by highly collimated jets? Masson & Chernin (1993)

• Investigate the morphology and kinematics of the molecular

gas at scales of 1000 AU .

Entrainment by turbulent Jet?

 Observational consideration

yr M M

SUN H K 3 4

20 10 7

 

           Kelvin-Helmholtz time Massive stars spend short time in the pre-main sequence:

3

20 003 . ) (

 

         

SUN

M M M N Rate of massive star formation in the Galaxy:

6

20 200 ) ( ) (

  

            

SUN H K PMS

M M M N M N 

 Massive protostars are very rare

How many massive protostars we expect to see in our Galaxy?

