Eagle Nebula Primer

7/29/2019 Eagle Nebula Primer

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Eagle Nebula Pillars:

From models to observations

5th

International Conference on High Energy Density Laboratory AstrophysicsMarch 10 13, 2004

Marc Pound

University of Maryland

Jave Kane, Bruce Remington, Dmitri Ryutov

Lawrence Livermore National Laboratory

Akira Mizuta, Hideaki Takabe

Institute of Laser Engineering, Osaka University


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How do pillars form?

Pillars (elephant trunks) common

Formation mechanism unclear

Instabilities at cloud interface?

Pre-existing dense cores?

Observations of morphology alone

cannot distinguish between models.


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Formation Mechanism Examples

Ablative Rayleigh-Taylor instability

e.g., Spitzer (1954); Frieman (1954);

Pound (1998); Kane et al. (2001)

see also Tilted Radiation instability

Ryutov et al. (2003)

Shadowing Instability

e.g., Williams (1999)

Dense core/Cometary globule

e.g., Reipurth (1983); Bertoldi & McKee (1990);Lefloch & Lazareff (1994); Williams et al (2001)

In most of these scenarios, the formation

timescale for L ~ 0.5 pc is a few X 105 yr


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Measure received power W as a function offrequency. Antenna temperature T

A= W/k.

Doppler shift gives velocity.

~ 0.2 10'' V ~ 0.1 km/s

CO J=10 is the rimar observational

Horsehead Nebula

0.5 pc

Radiotelescopes


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Datacubes

Can slice cube in multiple ways, take moments, etc.


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CO(J=1-0) Integrated Intensity

Our Data from BIMA array


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What the observations tell us

(model constraints)

Observables

Temperature

Velocity

absolute

gradient

dispersion

line shape

Magnetic Field

Derivables

Density

Mass

Pressure

thermal

turbulent

Column density

Timescales:

Dynamical

Evaporation

... 40 K

... 25 km/s

... 10 km/s/pc

... 1 km/s

... complex

... ??

... 105 cm-3

... 800 Msun

(P/k)... 106 K cm-3

... 108 K cm-3

... 1022

cm-2

... 105 years

... 107

years

See talk by Dmitri Ryutov in

this session


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Geometry of Eagle Nebula


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Our Model

We have developed a

comprehensive 2-D hydrodynamicmodel that includes:

Energy deposition and release due

to the absorption of UV radiation

Recombination of hydrogen

Radiative molecular cooling

Magnetostatic pressure

Geometry/initial conditions based

on Eagle observationsSee Akira Mizuta's

talk in this session.


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The ObjectiveTo go from this...

X, Y, VX

, VY

,

...to this.

X, Y, VZ, F

We need to create synthetic observations

by ''observing'' the model.


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Interferometry and aperture synthesis primer

BIMA millimeter

array

Interferometers measure the Fourier

Transform of the sky brightness distribution,

called the visibility function.

As Earth rotates, antennas pairs trace out

ellipses in the Fourier domain, sampling

different spatial frequencies. Longer

baselines give higher spatial resolution.

Smooth component of emission ''resolved u

v

Example uv coverage


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Steps to create synthetic observations

1) Orient model properly on sky: rotation and inclinationi.2) Taper model brightness according to field of view response

function & mosaic pattern.

3) Sample with actual uvcoverage of observations to create Fourierdomain visibilities.

4) Add noise due to receivers and atmosphere. Note this is done in

the Fourier domain.

5) Grid the visibilities and FFT back to image domain.

6) Deconvolve image with ''dirty'' beam (Airy pattern). This is the

CLEAN algorithm.

'' ''Tools: NEMO dynamics toolbox, MIRIAD interferometry package


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1. Orient model on sky

= 39o (known)

i = 10o (educated guess for Pillar II)


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2. Taper model brightness

Each box corresponds to one field of the mosaic.

The field of view is a Gaussian with FWHM=100''.


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3. Sample with actual uv coverage

Dirty Beam

Core is elliptical

Gaussian


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5. Grid and FFT

Note sidelobe response.


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6. & 7. Deconvolve and restore

Voila!


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Comparison

Densest region of model, n(H2) ~ 103

cm-3

, isrecovered by interferometer. This is about the

critical density for excitation of CO.

Dense region not large enough, however.Let's zoom in for a closer look...


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Closer Comparison

Put the model twice as close and reprocess.

Zoom in on Pillar II.

Similarity is intriguing


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Successes

Basic shape reproduced

Correct final densities reproduced:

n(H2) = 103 105 cm-3

Correct velocity gradient reproduced:

VY sini~ 3 km/s/pc,

compare with 2.2 km/s/pc in Pillar IICaveats

No radiative transfer brightness assumed proportional to

mass in pixel.

Comparing 2D model to integrated 3D datacube need a full

3D or cylindrical model to examine velocity fieldand pillar

substructure.


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Summary

Our model can adequately represent much of the real input

astrophysics of the Eagle.

Physical properties of pillars reproduced.

We have a good technique for creating realistic synthetic

observations from model data.

We also have ``cometary'' models ready to be subjected to

the same technique.

Use synthetic observations to identify best models. Use bestmodels to design laser experiment.

Models applicable to many astronomical objects. We have

good data already for Eagle, Horsehead, and Pelican

nebulae.Hubble/NICMOS


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Advertisement

The Combined Array for Research in Millimeter-wave Astronomy

(CARMA)

Merger of BIMA and OVRO mm arrays atnew high site. Operational in mid-2005.

Order of magnitude improvement in imaging fidelity over

existing arrays.


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T i h R l i h T l I bili


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Testing the Rayleigh-Taylor Instability

No change in gor inclinationi, can match data.

A classic RT spike (incompressible, semi-infinite layer thickness) in

free fall under pseudo-gravity ghas velocity of form:V(X) V

0= [ 2 g( X X

0)]1/2

A i ith th R l i h T l I t bilit !


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Again with the Rayleigh-Taylor Instability!

Classic RT has constant density, therefore constant

column density (# emitters along line of sight).

Data show large variations in H2column density (clumpiness).

Th BIMA Milli t A


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The BIMA Millimeter Array

Observations at =1 and 3 mm

Earth-rotation aperture synthesis

Ten 6.1 meter dishes

Interferometric baselines as long

as 2 km

Resolution of 0.2'' at 1 mm

Compact configuration for

mapping large-scale structure

4 configurations like VLA

Mosaicing large fields

Premier imaging millimeter-


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How long will the Horsehead last?

evaporation timescale

tevap

= M / (dM/dt)

mass loss rate due to photoionization

dM/dt = 2r2 cim

pn

i

Lyman continuum absorbed in layer comparable to cloud radius

ni= (L

LyC/ 4

B)1/2 r-1/2 d-1

tevap

~ 5 Myr

...plug in the numbers, turn crank...


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High Contrast Amateur Photo

There is a bend or "kink" in the Horsehead

Horsehead Nebula


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Horsehead NebulaV = 8 15 km/s

Horsehead Nebula


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CO(J=1-0) Integrated Intensity

Horsehead Nebula


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Centroid Velocitycontours: 0.5 km/s

Velocity Dispersioncontours: 0.15 km/s

Molecular clouds


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Molecular clouds

Agglomerations of molecular material

with masses 102

to 106

Msun

Located primarily in galactic spiral arms

Where stars form

Dominated by turbulence

Clumpy structure

Temperatures ~ few X 10K

Volume densities ~ 103 107cm-3

Primarily H2

with traces of:

CO 10 4

dust 10 2

Bell Labs

10 pc

Orion GMC

Complications


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Complications

Eagle pillars appear to be in a very late stage of RT

evolution, after the bubble has burst. Horsehead appears to be in early stage, but nearby star

formation history unclear.

Magnetic fields

Eagle Nebula Primer

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