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

Detecting Dark Clouds in the Galactic Plane with

2MASS dataBy : Luis Mercado

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

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

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

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

Contrast =Image - Background_____________________

Background

Smoothing Process

1.2’ radius for image

2.0’ radius for smoothing

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

What it all looks like…

H-Kave from l = 10°-15° H-Kave contrast

K stellar density K-density contrast

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.

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

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

What Now?

• Develop catalogue of Dark Clouds for publishing

• Present work at AAS meeting• Use data on future research missions

such as SIRTF

THE END

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.