1. 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)

2. 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

3. 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 < 0.15 mags
Mag limits:
14.3 for H, 13.5 for K

4. 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

5. Smoothing Process Image - Background _____________________ Contrast =
1.2’ radius for image
2.0’ radius for smoothing

6. 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

7. What it all looks like… H-Kave from l = 10°-15° H-Kave contrast
K stellar density
K-density contrast

8. Above: Product of density and color contrast.
Below:
MSX image of same field
(l = 10°15°).
Notice the correlation between the dark blue objects on the contrast plot and high absorption areas (dark clouds) in the MSX image.

9. 2MASS three color image of test field.
Also plotted are contours obtained from our selection method for the corresponding area.

10. 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

11. What Now? Develop catalogue of Dark Clouds for publishing
Present work at AAS meeting
Use data on future research missions such as SIRTF

12. THE END

13. 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.