104.6. Plot histograms and heatmaps

For the Portal Aspect of the Rubin Science Platform at data.lsst.cloud.

Data Release: DP1

Last verified to run: 2025-06-30

Learning objective: Create histograms and heatmaps in the results active chart.

LSST data products: Object table

Credit: Originally developed by the Rubin Community Science team. Please consider acknowledging them if this tutorial is used for the preparation of journal articles, software releases, or other tutorials.

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1. Log in to the Portal aspect of the Rubin Science Platform and execute a query. Go to the Portal’s DP1 Catalogs tab, switch to the ADQL interface. Copy-paste the query below into the box, which will retrieve g- and r-band magnitudes for a sample of extended objects (galaxies) with fluxes greater than 360 nJy. Click “Search”.

SELECT coord_dec, coord_ra,
g_cModelMag,
r_cModelMag,
g_extendedness,
r_extendedness
FROM dp1.Object
WHERE CONTAINS(POINT('ICRS', coord_ra, coord_dec),
CIRCLE('ICRS', 53.0, -28.0, 0.3)) =1
AND g_extendedness = 1
AND r_extendedness = 1
AND g_cModelFlux > 360
AND r_cModelFlux > 360

2. Add a new chart, and choose histogram. The default plot in “Active Charts” panel shows the number of objects as a function of position in the selected region. In the Active Chart panel, click on the “+” button in the upper-left corner of the panel. In the “Add New Chart” pop-up window select “Histogram” as the plot type and enter g_cModelMag as the column (Figure 1). Click “OK”.

Screenshot of the "Add New Chart" pop-up window, set up for a histogram.

Figure 1: The “Add New Chart” pop-up window, set up for a histogram.

3. Delete the default chart. Remove the default plot of coord_ra vs. coord_dec by clicking on the “x” in the upper right corner of the plot.

4. Add a new chart, and choose heatmap. Open the “Add New Chart” pop-up window. Select “Heatmap” as the plot type and enter g_cModelMag for X and the expression g_cModelMag - r_cModelMag for Y (Figure 2). Leave the Color Scale as “Default”. Click “OK”.

Screenshot of the "Add New Chart" pop-up window, set up for a heatmap.

Figure 2: The “Add New Chart” pop-up window, set up for a heatmap.

5. View the histogram and the heatmap. The Active Charts panel now displays a 1-dimensional histogram of the g-band magnitudes at left, and a 2-dimensional histogram (a heatmap) of the g-band magnitude vs. the g-r color at right, as in Figure 3.

Screenshot of the Active Charts showing a 1-d histogram and a 2-d heatamp.

Figure 3: The Active Charts panel displays the g-magnitude histogram and the color-magnitude diagram.