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The Intermediate Velocity Clouds

Bot. C, Cambresy L., Boulanger F., Egret D.
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Introduction
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The Intermediate Velocity Clouds (IVC) are clouds of neutral gas that move in unexpected directions and with unusual velocities with respect to the normal rotation of the rest of our Galaxy. They are detected with the 21cm emission of atomic hydrogen. Some also show significant dust emission but not all of them. The idea is to separate 2 populations in the IVCs: the dust rich ones, and the dust poor ones, with the underlying idea that their origin is different.


Science Aspects
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- The study needs to be done on the whole sky to understand the spatial distribution of these two populations

- The study needs first to identify regions of excess in the ionised or atomic hydrogen maps. This is the equivalent to a source extraction but for extended emission.

-The main core of the study relies on map comparisons at different wavelengths and with different resolutions.

-To detect the IR emission of the IVC, the first step is to remove the foreground emission, using HI data.

-The infrared contribution detected for the IVC will have to be compared to the Halpha emission to check if there is no contamination by the warm interstellar medium.

-The intercomparison of the different maps leads to a classification of the IVCs in two groups (dust poor IVC and dust rich IVC).

- The spatial distribution of the two groups is displayed.

- The data has to be allsky surveys in the far infrared (dust emission), in the 21cm line (atomic hydrogen emission) and in the Halpha line (ionised hydrogen emission), like COBE/DIRBE, Leiden-Dwingeloo/IAR HI survey and SHASSA respectively.


VO Aspects
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Data:

The study would be using the DIRBE far infrared emission allsky survey to trace the dust abundances, the combined surveys of IAR and Leiden-Dwingeloo in HI and the SHASSA survey for the Halpha emission. All these data are public, except the IAR HI survey, but it is expected to be released on a medium time scale (in the comming years). The data will also be compared to the existing catalogs of IVCs in the literature (through Vizier).

Tools:

- extended source extractor. 
- image manipulation tool (simple operations: +,-,*,/,...)
- image convolution tool (to degrade the resolution of maps previously to intercomparison.)
- plotting tool allowing pixel to pixel maps scatterplots with simple fittings, and the possibility to select regions of interest in the plot. This could be a simple adaptation of the VOPlot tool.

VO need
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This SRM proposal is a typical example of what the studies on the extended emission would be with the Virtual Observatory. The gain of the VO is in efficiency, but the main interest of this SRM is that all the requirements for this study are generic tools that can be used in completely different contexts. Furthermore, this study is chosen to be an allsky study, that is dealing with large amounts of data, and it is therefore an example of the kind of problems will have to be solved and the tools  that will be needing with the forthcoming large projects on extended emission (Planck, Herschel, ALMA, ...).