X-Y Plots

Contents:
+Interacting with X-Y plots
+Plotting catalogs
+Examples of plotting a catalog

Interacting with X-Y plots

One of the most powerful aspects of the x-y plots is its interactivity. If you click on a source in the plot, it is highlighted in other portions of the display - perhaps overplotted on an image or highlighted in a catalog.

You can click and drag to zoom in the plot. This is called "rubber band zoom." You can also use this feature to filter the catalog that is plotted -- this is another aspect of the table filtering covered in another section.

You can change what is plotted by clicking on the gears icon: See the next section.

Plotting catalogs

In either case, letting your mouse hover over a point tells you the values of the point under your cursor, and (if binned) how many points are represented:

To change what is plotted, click on the gears icon in the upper right of the plot window pane: . Configuration options then appear in a pop-up. You can choose a single column to plot against another column -- either start typing a column name into the X and Y boxes, and it will help provide you viable options from the column headings, or click on the "Cols" link to bring up a pop-up with all the columns listed. NOTE THAT you must type in the column name exactly matching the column headings as displayed. By default, it echoes the x and y labels and units from the original table, but you can change this by clicking on the triangles below each entry box (e.g., make the label "SNR in WISE-1" rather than the more cryptic column header "w1snr").

You can also do simple mathematical manipulations. For example, you can plot w1mpro vs. w1mpro-w4mpro. Note that you can reverse the axes such that the brighter objects are at the top of the plot.

You can add or remove the gridlines via the "Grid" checkbox.

If you have few enough points that the plot is not binned, you have additional options in the plot configuration pop-up:

You can plot the points as individual points, points connected by a line, or just a line. You can also specify what column to use for error bars. In this case, the RA in this catalog is in degrees, but the RA errors are in arcseconds. This plot request (shown here) converts the RA errors to degrees before plotting.

You can also restrict what data are plotted in any of several different ways. You can set limits based on the "more options" in the plot options pop-up, or you can use a rubber band zoom, as follows. Click and drag in a sub-region of the plot. The icons in the upper left of the plot change corresponding to what you can do, in this case to these: . They are, from left to right: zoom in on the region you have selected, select the objects in the catalog, and filter the catalog to leave only those objects. If you click on the zoom icon, then the plot axes change to encompass just the sources you have selected. If you click on the select icon, then the plot symbols corresponding to your selection change shape and color, the rows (corresponding to those sources) in the catalog are highlighted in the catalog window pane, and the corresponding objects overplotted on the image in the image window pane change color. If you click on the filter icon, then the catalog view is filtered down, restricted to just those sources you have selected, and the filter notes in the upper left of the plot window (and the upper right of the catalog window) change to remind you that you have a filter applied. Only those sources that pass the filter are shown overlaid on the image(s). (This is the behavior of 'filter', as opposed to 'select'; the former restricts what is shown, the latter just highlights the objects.) For more on filters, see the filter section.

If you move your mouse over any of the points, you will get a pop-up telling you the values corresponding to the point under your cursor. If you click on any of the points, the object(s) corresponding to that point will be highlighted in the overlays in the images shown, and highlighted in the catalog table. This works the other way too - click on a row in the catalog, or an object in the images, and the object will be highlighted in the plot or the catalog or the image.

Want to save a plot to file? At this time, the best way to do that is a screen snapshot. On a Mac, this is accomplished via holding down command, then shift, then 4, then let go and your mouse cursor changes. Hit the space bar to select the window over which your mouse is hovering. Your mouse cursor changes again, and hit the mouse button. A snapshot is then saved to your Desktop, tagged with the date and time.

Examples of plotting catalogs

In a star-forming region defined for this example, we expect that the sources will be dominated by young stars. Stars without circumstellar dust should be at a variety of W1 brightnesses, but all have [W1]-[W4]~0. Background galaxies should be faint and red. Stars with circumstellar dust (e.g., young stars) should be bright and red. Here, we will make a plot, identify a bright and red object in the plot, and find where it is in the WISE images.

1. In the Catalog Search Tool, start a catalog search. Select Project=WISE. Select the AllWISE database, and the AllWISE Source Catalog. Enter a target of IC1396. Pick the cone search method and select 0.5 degrees radius.
2. It may take a few seconds to load and display the catalog. Note that all ~17,500 sources are overplotted on the images on the left and in the plot to the right. The first 100 of the ~17,500 sources are shown in the bottom table, but you can page through all ~17,500. Note that selecting a source in the image makes its corresponding row in the catalog turn green and point in the plot turn yellow; this is all interchangable such that picking a source in one place highlights it in the other places.
3. The plot comes up with an RA/Dec plot by default. Each point represents more than one row of the catalog. Mouse over or click on a point to see how many rows are represented:
4. Click on the expand () icon in the upper right of the plot window to make it big.
5. Click on the gear icon in the upper left of the plot window to change what is plotted.
6. Enter in the x box: w1mpro-w4mpro. This is WISE-1 profile-fitted measurement in magnitudes minus WISE-4 profile-fitted measurement in magnitudes,or [W1]-[W4].
7. Click on the triangle next to "X label/unit/options", and enter "[W1]-[W4]" for the label. Enter "mag" for the unit. Check "grid" to make the grid appear.
8. Enter in the y box: w1mpro
9. Click on the triangle next to "Y label/unit", and enter [W1] for the label. Enter "mag" for the unit. Click on "reverse" to make the brighter objects appear at the top of the plot. Click the "grid" box.
10. Click "Apply."
11. Obtain this plot:
    
    
12. Note that the points are shades of grey, denoting that at least one of the points in the plot is representative of more than one row in the catalog. The legend for how many points correspond to each shade of grey is given in the upper right.
13. Click and drag from corner given approximately by (2,6) to (7,11).
14. The icons in the upper left change after you do this, and we want to zoom on this region. Click on the magnifying glass with a "+" inside.
15. After we zoom, there are few enough points that individual points are shown as blue circles. Where they overlap, the blue appears darker.
16. Find the brightest source near [W1]-[W4]~4.5. Click on that point.
17. Click on "Close" in the upper left to return to the window pane view.
18. The (astrophysically) bright and red object we selected in the plot is highlighted in the overlays on top of the image and in the catalog (though you may need to scroll in the catalog to find the green highlighted line). To find it even more easily, you can click and drag around this point in the plot. Click on the filter icon in the upper left. The plot at this point looks silly, but only that point is left in the overlay of sources on the images and in the catalog list. (If you have been following closely, it should be J213808.44+572647.6.)

Because you can do simple mathematical manipulations when specifying what to plot or use for errors, you can calculate these things on the fly. Load the catalog as in the prior example. Filter it down (spatially or by SNR cuts) to make sure that individual points are shown in the plot.

For the x-axis: Ask it to plot w3mpro-w4mpro. Use sqrt(w3sigmpro^2 + w4sigmpro^2) for the errors. For the y-axis, ask it to plot w1mpro, and use w1sigmpro for the errors. Reverse the y-axis to get bright objects at the top. Obtain a plot something like this, which shows the calculated error bars for each point. Note that the brightest points have small errors, and some of the faintest/reddest sources have large errors in both directions.