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Very Large Array observations of Ammonia in High-mass Star Formation regions

by Xing Lu, Qizhou Zhang, Hauyu Baobab Liu, Junzhi Wang, and Qiusheng Gu, accepted by ApJ May 2014, second issue 01/08/14

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Motivation

  • HMSF in super-dense cores

VLA obs. of NH3 in HMSF

Astro meeting - 19/08

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Motivation

  • HMSF in super-dense cores
    • Super-Jeans density regions (Zhang et al. 2009)

VLA obs. of NH3 in HMSF

Astro meeting - 19/08

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Motivation

  • HMSF in super-dense cores
    • Super-Jeans density regions (Zhang et al. 2009)

VLA obs. of NH3 in HMSF

Astro meeting - 19/08

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Motivation

  • HMSF in super-dense cores
    • Super-Jeans density regions (Zhang et al. 2009)

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  • How are these cores supported?

VLA obs. of NH3 in HMSF

Astro meeting - 19/08

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Motivation

VLA obs. of NH3 in HMSF

Astro meeting - 19/08

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Motivation - Why NH3?

  • Freeze out
    • Zhang et al. 2009 searches for CO, SO, CH3OH and CH3CN between ~220 - 230 GHz
    • The “P1” clump detects only CO

VLA obs. of NH3 in HMSF

Astro meeting - 19/08

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Motivation - Why NH3?

  • Freeze out
    • Zhang et al. 2009 searches for CO, SO, CH3OH and CH3CN between ~220 - 230 GHz
    • The “P1” clump detects only CO
      • Freeze out?
      • Less evolved region?

VLA obs. of NH3 in HMSF

Astro meeting - 19/08

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Motivation - Why NH3?

  • Freeze out
    • Zhang et al. 2009 searches for CO, SO, CH3OH and CH3CN between ~220 - 230 GHz
    • The “P1” clump detects only CO
      • Freeze out?
      • Less evolved region?
  • Temperature
    • Probes excitation temperatures from 10-50 K
    • Signposts evolution, along with linewidth

VLA obs. of NH3 in HMSF

Astro meeting - 19/08

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Motivation - Why NH3?

  • Freeze out
    • Zhang et al. 2009 searches for CO, SO, CH3OH and CH3CN between ~220 - 230 GHz
    • The “P1” clump detects only CO
      • Freeze out?
      • Less evolved region?
  • Temperature
    • Probes excitation temperatures from 10-50 K
    • Signposts evolution, along with linewidth
  • Resolution
    • Most obs. of NH3 are performed with single dishes
    • HMSF regions constrained within 0.1 pc

VLA obs. of NH3 in HMSF

Astro meeting - 19/08

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Motivation - Why NH3?

  • Freeze out
    • Zhang et al. 2009 searches for CO, SO, CH3OH and CH3CN between ~220 - 230 GHz
    • The “P1” clump detects only CO
      • Freeze out?
      • Less evolved region?
  • Temperature
    • Probes excitation temperatures from 10-50 K
    • Signposts evolution, along with linewidth
  • Resolution
    • Most obs. of NH3 are performed with single dishes
    • HMSF regions constrained within 0.1 pc

VLA obs. of NH3 in HMSF

Astro meeting - 19/08

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Observations

  • 62 HMSF targets
    • Picked for luminosity, outflows, known dense NH3

VLA obs. of NH3 in HMSF

Astro meeting - 19/08

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Observations

  • 62 HMSF targets
    • Picked for luminosity, outflows, known dense NH3
      • Biases?

​

VLA obs. of NH3 in HMSF

Astro meeting - 19/08

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Observations

  • 62 HMSF targets
    • Picked for luminosity, outflows, known dense NH3
      • Biases?
  • <3 arcsecond synthesised beam
    • 2kλ smallest uv distance (~25 meters)

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VLA obs. of NH3 in HMSF

Astro meeting - 19/08

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Observations

  • 62 HMSF targets
    • Picked for luminosity, outflows, known dense NH3
      • Biases?
  • <3 arcsecond synthesised beam
    • 2kλ smallest uv distance (~25 meters)
      • Dishes are 25 m each…?

​

VLA obs. of NH3 in HMSF

Astro meeting - 19/08

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Observations

  • 62 HMSF targets
    • Picked for luminosity, outflows, known dense NH3
      • Biases?
  • <3 arcsecond synthesised beam
    • 2kλ smallest uv distance (~25 meters)
      • Dishes are 25 m each…?
  • NH3 (1,1) and (2,2)
    • Derive kinetic and rotational temperatures

​

VLA obs. of NH3 in HMSF

Astro meeting - 19/08

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Observations

  • 62 HMSF targets
    • Picked for luminosity, outflows, known dense NH3
      • Biases?
  • <3 arcsecond synthesised beam
    • 2kλ smallest uv distance (~25 meters)
      • Dishes are 25 m each…?
  • NH3 (1,1) and (2,2)
    • Derive kinetic and rotational temperatures

​

  • Supreme mapping of HMSF through NH3

VLA obs. of NH3 in HMSF

Astro meeting - 19/08

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Results

  • 3 classifications of morphologies:
    • Hot core / “concentration”
    • Filament
    • Irregular / “dispersed”

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VLA obs. of NH3 in HMSF

Astro meeting - 19/08

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Results

VLA obs. of NH3 in HMSF

Astro meeting - 19/08

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Results

VLA obs. of NH3 in HMSF

Astro meeting - 19/08

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Results

VLA obs. of NH3 in HMSF

Astro meeting - 19/08

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Results - Filaments

  • length / width > 3
  • Consistent VLSR
  • Peaks along the filament
    • Cylindrical collapse
  • Hottest between NH3 peaks

VLA obs. of NH3 in HMSF

Astro meeting - 19/08

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Results - Filaments

  • 5 filament regions converge at a common point
    • “Hub-filament system”
  • Filaments are IR-dark, but the focus is bright
  • Kinematics reveal that the filaments appear to flow towards the focus

VLA obs. of NH3 in HMSF

Astro meeting - 19/08

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Results - Hot cores

  • At the peak, broad linewidths (>5 km/s)
    • Fits accretion motion model from Ulrich 1976
    • Other HMSF molecular lines
      • Strong evidence of an embedded YSO

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VLA obs. of NH3 in HMSF

Astro meeting - 19/08

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Results - Internal heating

  • Infrared sources coincident with temperature peaks
    • Not necessarily coincident with NH3 peaks...

VLA obs. of NH3 in HMSF

Astro meeting - 19/08

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Results - Internal heating

VLA obs. of NH3 in HMSF

Astro meeting - 19/08

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Results - Internal heating

VLA obs. of NH3 in HMSF

Astro meeting - 19/08

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Results - Internal heating

VLA obs. of NH3 in HMSF

Astro meeting - 19/08

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Results - Internal heating

  • Assumption: heating sources are “closely packed” for isotropic radiative heating
    • Derive radial temperature distribution
    • T(rprj) ∝ rprj-α
    • rprj is the projected distance from the center

VLA obs. of NH3 in HMSF

Astro meeting - 19/08

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Results - Internal heating

VLA obs. of NH3 in HMSF

Astro meeting - 19/08

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Results - Internal heating

VLA obs. of NH3 in HMSF

Astro meeting - 19/08

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Results - Internal heating

VLA obs. of NH3 in HMSF

Astro meeting - 19/08

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Results - Internal heating

  • Temperature and NH3 peak are not coincident
  • Masers are slightly offset
    • Anisotropic heating
  • HII region to the west may heat additionally

VLA obs. of NH3 in HMSF

Astro meeting - 19/08

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Additional thoughts

  • Many filaments, few hot cores
    • Evolutionary stage - biases
    • Analyse with masers
  • Southern population?
  • Follow-up obs. with

ALMA (HCO+)

    • Higher resolution

VLA obs. of NH3 in HMSF

Astro meeting - 19/08

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Conclusions

  • Most sources typically contain a NH3 peak, temperature peak and infrared feature coincident.
  • The temperature peak is strongly associated with infrared sources
    • Caused by YSOs
  • Some regions have “uniform” profiles; warm centre, cool envelope
    • Assuming tightly-packed heating sources reveals a radius-temperature power law

VLA obs. of NH3 in HMSF

Astro meeting - 19/08

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Conclusions

  • Results reveal that filamental cores are most likely supported by accretion along the filaments
  • NH3 core properties:
    • R ~ 0.08 pc
    • Δv ~ 1.08 km/s
    • TR ~ 18.1 K
    • Mcore ~ 67 M⊙
      • Higher than low mass sources, yet agree with single dish observations

VLA obs. of NH3 in HMSF

Astro meeting - 19/08