Atlas - A Search Service for Images, Spectra, and
Small Source Tables for Datasets Served by IRSA:
Introduction and Instructions
Also available is a Program Interface to Atlas.
IRSA serves many datasets which may consist of images, spectra, small source tables, or light curves. Atlas can be used to search these datasets and provide the results on a single web page.
Each dataset has a homepage with a short description. Generally an all-sky image (or a smaller region) is presented at the top of the homepage in black and white. Often this image is made from 12 micron IRAS Sky Survey Atlas (ISSA) "plates", with a resolution of 0.5 degrees. The color overlays on this image are the footprints of the areas covered by that dataset. Image data are usually displayed as red rectangles overlaid on the sky, yellow dots indicate source lists, and red (or cyan) dots represent spectra. The coordinate system, if displayed, is usually depicted in blue.
How to use this service:
There are three methods for retrieving data through Atlas. You may either click on the image (all-) sky map within an area shown to contain data, or enter a single coordinate (or astronomical object name) in the "Single Object" field, or enter a file name with a table of coordinates (or astronomical object names) in the "Table Upload" field.
If using the image map for searching, keep in mind that the pixel resolution of an all-sky image is often 0.5 degrees; if you require a higher degree of precision you should use the coordinate search method. If entering a position (single or multi-object table upload file), the location information can take the form of coordinates in a variety of formats (see the examples at the bottom of main panel), or can be an object name. If it is the latter, first NED and then SIMBAD are checked to attempt name resolution; once the name is resolved, the celestial coordinates of that object are used for the search query.
Examples of valid input coordinates are provided for each of the Atlas data services, in a variety of coordinate systems. Each example coordinate is separated by a "|" character. Only one is necessary as input in the "Single Object" field (or in the multi-object table listing using "Table Upload"), without the "|" character. The default coordinate system is (RA DEC) Equatorial J2000, in decimal degrees (1st example below).
EXAMPLES OF INPUT
In the 2nd example above, "Local Equatorial J2000 (Equ)" is also known as "sexigesimal" (hours, minutes, seconds; degrees, minutes, seconds). The abbreviation "eq" and "Equ" stands for equinox of the coordinate system; typically equinox is "J2000" (which is the default when the user does not enter the equinox) and of course could also be "B1950", etc.
Multi-Object searching can be performed by selecting the "Table Upload" button and then entering the name of a table on your local file system which contains a list of coordinates or astronomical object names.
Most of IRSA's services allow users to enter single objects or coordinates into a web form, or they can upload a file containing multiple objects and coordinates. The latter method is called "Table Upload," for which IRSA accepts four ASCII table formats:
- IPAC ASCII Column-Aligned (Download template)
- Comma-Separated Values (CSV) or Comma-Delimited (Download template)
- Tab-Delimited (Download template)
- A Simple List of Objects (such as astronomical source names) (Download template)
There are two ways to ensure your tables will work with IRSA's services:
- Run your tables through IRSA's Table Reformat and Validation tool to identify possible errors.
- Read and follow the Using Tables With IRSA Services help document to learn and troubleshoot table formats, including:
- Detailed descriptions of the four acceptable table formats
- A description of how sexagesimal and Galactic coordinates are handled by IRSA services
- Best practices for creating tables
- Troubleshooting solutions for common error messages
- ASCII file with simple name listing
- IPAC table format using object names
- IPAC table format with ra dec positions as well as source names
- IPAC table format with mixture of coord types
- tab-delimited table of positions as well as source names
- comma-delimited table of positions as well as source names
Search Size Constraints
For Atlas datasets which include images, the "Size" search field (in degrees) is adjustable. The maximum search size is listed, and the hard limit is 12.5 degrees. Table 1 below lists all the maximum search sizes for all Atlas collections, in the third column. [The hard limit is due to the fact that the results are displayed as overlays on background 'sky' images. A value of 12.5 degrees is a reasonable limit for the ISSA "plates", the largest background images.]
The checkbox "Images must cover coordinate" allows the user to choose to search for only those images whose footprint on the sky covers the exact input coordinate. If unchecked, all images which overlap the given search area, as determined by location and box size, will be returned.
For Atlas datasets which have catalog or spectral information, the "Source Search Radius" field is provided and can be adjusted for searching. This is a cone search, using a radius where the units can be adjusted using a drop-down menu. The default is half the Size and the maximum is 6.25 degrees.
Next to the "Source Seach Radius" field is the checkbox "Match with image search size". When checked, the search for catalog and spectral information is done using half the value of the "Size" box search (or 6.25 degrees when "Size" is not set); note that the "Source Search Radius" value is overridden in this case.
If searching by location rather than clicking on the sky map, hitting the "Submit" button starts the search.
Multi-Object Search Results
After a Multi-Object search, using Table Upload, the search results are returned in a summary table, collecting the results of each single object search. The table shows the positions of each requested source (ra and dec in decimal degrees); the number of images (N_images), catalog sources (N_srcs) and spectra (N_spectra); a link to the HTML search results page (Result_Link) for each source; and links to data download scripts (Download_Script) for each results set (includes images, catalogs, spectra). The Status column will indicate "ERROR" if a problem was found while searching for data for that source, else "OK" is returned. Note, an empty set of results (no images, catalogs, or spectra found) is a valid result, and therefore "OK" is returned when the search did not find an error.
A Download script with ALL the results for all sources is also available; this is a concatenation of the download scripts per source, as one master script. Download scripts use the Unix GNU tool 'wget' for bulk downloads. [WGET HELP]
Clicking a Result_Link brings up a single object search results page; this page is identical to the result if a "Single Object" was used in the search form for that same position.
For reference, the user's table is available. Note, IRSA adds ra and dec coordinates for each source in decimal degrees, if these columns are not provided. The table is also reformatted to IPAC Table Format, if it is not already uploaded as such. The order of the user table sources and the results table summary are the same; the "cnt" (counter) column is the row number of the input user table.
Single Object Search Results
If no data are found for the selected area, a "NOTIFICATION" page is returned stating that the collection does not have data within the input search parameters. If you think there should be data, hit the 'Back' button on your browser to return to the search page and try again with different search criteria, e.g. broaden the search by increasing the Size of the search box and/or radius, or by de-selecting the "Images must cover coordinate" checkbox.
On the results page, data which matched the search criteria will be listed in tabular form as well as being rendered on a background image. (Note that multiple overlays for the exact same position may look like one overlay.) Any source/spectral tables found are listed first, followed by images. You can download or display any of the images listed, download or display the background image, retrieve spectra when they are available, or display source tables.
The results page also contains another search form, which can be used to fine-tune the original search or start a completely new search. Zoom in and out by specifying a smaller or larger search "Size"/"Radius", and then re-submitting the request.
Background images:Table 1 below lists the source of the background images and their characteristics. Most of the background data come from either the IRSA ISSA or 2MASS image collections. ISSA is IRAS data. The images here are at 12 micron. 2MASS images have been made with the Montage mosaic engine, and should be used for visualization only.
For most of the Atlas data collections the results are displayed on a background which is the same size as the requested search size. This allows the user to view the entire requested search area, with the data results overlayed. However, for some Atlas collections visualization of the search results is made clearer by having a larger background size compared to the requested search size. For these data collections, Atlas has a set "background scaling factor" to display the results; the background size is equal to the search size times the background factor. The scaling factors for all collections are also listed Table 1. The Atlas search results page lists the background factor in the lower right of the overlay image, near the 'Background Image' download option.
|Atlas Collection Name||Background Dataset Name||Maximum Allowed Search-Size/Background-Size (deg)||Background Scaling Factor|
|COSMOS||COSMOS Subaru mosaics (B=blue, V=green, i=red); COSMOS front page is SDSS 'i' band||2.0||2.0|
|Cygnus-X||Spitzer IRAC1 (3.6um)||7.0||1.0|
|FIDEL||FIDEL front page and search results page use the FIDEL MIPS data as backdrops: 24um MIPS images for EGS and ECDFS fields, and 70um MIPS image for the GOODS-N field.||0.6||1.5|
|GOODS||2MASS J (1.25 um)||0.6||1.0|
|IUDF||2MASS J (1.25 um)||0.6||1.5|
|SAGE||SAGE front page uses the MIPS 70um SAGE full mosaic; search results are 3-color SAGE MIPS mosaics (24um=blue, 70um=green, 160um=red)||7.0||1.0|
|SAGE-SMC||SAGE-SMC front page uses 3-color Spitzer mosaics (3.6um=blue, 8um=green, 24um=red); search results use Spitzer I1 (3.6um).||12.5||1.0|
|SDWFS||Spitzer IRAC2 (4.5um)||8.0||2.0|
|SERVS||2MASS J (1.25um)||7.1||1.0|
|SIMPLE||Spitzer IRAC1 (3.6um)||0.6||1.5|
|SpUDS||Spitzer IRAC1 (3.6um)||1.0||1.5|
|SWIRE||2MASS J (1.25um)||7.1||1.0|
|GOODS||2MASS J (1.25um)||12.5||1.0|
|LH||2MASS J (1.25um)||7.0||1.0|
ISSA backgrounds have a minimum size of 0.25 degrees.
Bulk Download of data is also available from the results pages, using a wget script. For more information on wget, click here. The script contains a list of all the images, catalogs, and/or spectra returned in the search results.
Small Catalog and/or Spectra results are listed first in the "Table of Sources", if present. If the total is under 6000, the source positions are marked on the background image. There are links to spectra files in the individual tables.
Image results are overlayed on the background sky image and are also individually presented in up to three tables: a master "Image Header Table" below the background image, a "Group" table with keys to the color overlays when images are grouped into separate categories, and a new feature: an interactive, sortable table of "All Images". It is from this last table that you can download and/or display the images. "Cutouts" of the original image are sometimes available, when the original images may be too large. If the "Entire Image" is too large to display, you will see an error message. In this case, display the "Cutout" instead.
The "All Images" table contains the distance of the image center from the requested position. By default, the rows are sorted by distance within each instrument group. You can change the default sorting and select/sort the rows you want by clicking on the Filter Panel (the icon resembling a "funnel").