SkyView Blog

We are currently in the process of rolling out 5 new surveys including 13 separate bands to enable SkyView users to take advantage of some of the deepest surveys that have been made of the sky. This is the biggest single addition to SkyView’s surveys other than our initial setup twenty years ago. These are surveys made of the GOODS (Great Observatories Origins Deep Survey) regions centered on the Hubble and Chandra Deep Fields. Getting all of the metadata and regression tests set up is taking a while, but users can try out the surveys now at our Version 3.1.0 site. Soon this will be the default.

The surveys we are starting with include:

• A VLA 1.4 GHz survey of the GOODS north field including data from all 4 VLA configurations.
  This data is combined to produce a single image of the field.
• Spitzer MIPS 24 micron data of both the north and south
• Four Spitzer IRAC surveys at 8.0, 5.8, 4.5, and 3.6 microns. Each of the north and south regions is split into two pieces for each wavelength. Only one image is available at 4.5 and 3.6 microns in the southern GOODS region, so that coverage is a little less in those bands.

  These data are provided in FITS files where only a fraction of the file is actually populated. We generated metadata that describes the rectangle inset in the FITS file where there is data. This rectangle is normally rotated with respect to the FITS image axes. We’ve added a new image finder that uses this metadata, skyview.process.imagefinder.RotatedRectangle

For the moment this means that the IRAC data cannot be accessed through SkyView-in-a-Jar but only at our Web site.

• Four HST ACS observations in B, V, I and Z filters. These data are of extremely high resolution and are provided as a set of 18 ~0.25 GB image tiles.

  The full-resolution image tiles are quite large and it takes a fair while to process the full set for a given filter. To make it easy to intercompare this ACS data with lower resolution datasets, we developed SkyView‘s first scheme for hierarchical images where we combined pixels in the original data by factors of two to produce lower resolution data. When a user requests an ACS image, the lowest resolution image that has higher resolution than the user’s request is sampled. SkyView keeps the original data and pixel-combined data at factors of two up to 32. I.e., in our lowest resolution data each pixel is the average of a 32×32 pixel region in the original data — but that’s still better than 1″ per pixel. The standard XMLSurvey class was updated to support hierarchies generally, but so far this has only been used for the ACS.

  The same tiles are used for each resolution. A consequence is that images of large regions (i.e., 0.1 degrees or more) generally render faster since they are typically of lower resolution and can use the smaller files.

• Three Chandra ACIS bands. This includes a soft 0.5-2 keV band, a hard 2-8 keV band and the full 0.5-8 keV band. This represents about 2 megaseconds exposure in the north and 4 megaseconds in the south.

These surveys include what is by far the highest resolution and deepest data in the far IR, optical and X-ray regimes available in SkyView. The resolution of VLA data is only modestly better than for the FIRST data, but the data is much deeper and better sampled. Of course nothing comes for free. The GOODS regions cover only about 0.01% of the sky.

We’ll be adding more GOODS surveys after this initial set — if you have a suggestion or preference please let us know. Currently HST NICMOS data and ground observations from Gemini and the VLT are in the queue.

To try out the new GOODS surveys just go to the V3.1.0 site. You’ll see all of the GOODS surveys listed at the end of the main survey list in their own box — we put them all together rather than breaking them out by regime. You can also use these surveys in the contours and they work very nicely in generating RGB images with each other. When we complete our metadata updates and checks on these data we’ll make 3.1.0 the current version.