Detecting Dark Clouds in the Galactic Plane with 2MASS data

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• Detecting Dark Clouds in the Galactic Plane with
  2MASS data
• By Luis Mercado

In collaboration with the part of GLIMPSE team
(Christer Watson, Ed Churchwell and Bob Benjamin)

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Introduction / Background

• What are Dark Clouds and why study them?
• Optically thick at visual and IR wavelengths
• Star Formation Regions
• GLIMPSE SIRTF
• Infrared Surveys
• MSX (8 micron) Showed dark clouds to be
  thicker than previously believed
• 2MASS 2 Micron All-Sky Survey

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2MASS Database

• Imaged entire sky in near infrared with J, H
  K filters
• Used data to produce point source catalog with
  over 300 million sources
• Our selection criteria
• Artifact flags
• Magnitude errors lt 0.15 mags
• Mag limits
• 14.3 for H, 13.5 for K

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Our Technique

• H-K grid pixels represent average color excess
  over a radius of 1.2
• Stellar density grid pixels represent number of
  stars over radius of 1.2
• Unsharp Masking used Gaussian to smooth image
  and create contrast image

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Smoothing Process
Image - Background
_____________________
Contrast
Background
1.2 radius for image
2.0 radius for smoothing
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Our Technique

• H-K grid pixels represent average color excess
  over a radius of 1.2
• Stellar density grid pixels represent number of
  stars over radius of 1.2
• Unsharp Masking used Gaussian to smooth image
  and create contrast image
• Best technique product of color and density
  contrasts

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What it all looks like
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Above Product of density and color contrast.
Below MSX image of same field (l
1015). Notice the correlation between the dark
blue objects on the contrast plot and high
absorption areas (dark clouds) in the MSX image.
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2MASS three color image of test field. Also
plotted are contours obtained from our selection
method for the corresponding area.
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Results / Conclusions

• Dark Clouds are identifiable with 2MASS data
• Found technique that proves this
• Color excess and stellar density are both used as
  indicators
• 380 dark clouds were detected in
  l 10- 40 range with our technique
• Since we only see foreground stars, information
  about the clouds is limited

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What Now?

• Develop catalogue of Dark Clouds for publishing
• Present work at AAS meeting
• Use data on future research missions such as SIRTF

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• THE END

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Problems
Left Histogram of of dark clouds detected vs.
galactic longitude. Notice a rise in detections
at high longitudes, opposite to what would be
expected
Right Plot of noise and density versus
longitude. Notice the similar behavior. It turns
out noise seems to be proportional to the
density, but in an unexpected way.