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

Detecting Dark Clouds in the Galactic Plane with 2MASS dataBy : Luis MercadoIn collaboration with the part of GLIMPSE team (Christer Watson, Ed Churchwell and Bob Benjamin)

Introduction / BackgroundWhat are Dark Clouds and why study them?Optically thick at visual and IR wavelengthsStar Formation RegionsGLIMPSE & SIRTF Infrared SurveysMSX (8 micron) Showed dark clouds to be thicker than previously believed2MASS 2 Micron All-Sky Survey

2MASS DatabaseImaged entire sky in near infrared with J, H & K filtersUsed data to produce point source catalog with over 300 million sourcesOur selection criteria:Artifact flagsMagnitude errors < 0.15 magsMag limits:14.3 for H, 13.5 for K

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

Smoothing ProcessContrast =Image - Background_____________________Background1.2 radius for image2.0 radius for smoothing

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

What it all looks like

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.

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

Results / ConclusionsDark Clouds are identifiable with 2MASS dataFound technique that proves thisColor excess and stellar density are both used as indicators380 dark clouds were detected in l = 10- 40 range with our techniqueSince we only see foreground stars, information about the clouds is limited

What Now?Develop catalogue of Dark Clouds for publishingPresent work at AAS meetingUse data on future research missions such as SIRTF

THE END

ProblemsLeft: Histogram of # of dark clouds detected vs. galactic longitude. Notice a rise in detections at high longitudes, opposite to what would be expectedRight: 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.