Galaxy Colours

Galaxy Colours

Filters in HyperSuprimeCame on Subaru

Near-infrared filters on VISTA

When we refer to colours we usually mean a combination of these filters to highlight whether a galaxy (or star) spectrum is "red" or "blue". This is also akin to the HR diagram for stars, which uses colours an an indicator of e.g. Temperature.

Combining these you can see how they can be used to understands the SEDs of various objects

Taken from Bowler et al. (2015).

Galaxy colour-magnitude diagram

The most common plot in extragalactic astrophysics, is the colour-magnitude diagram, which plots a colour (blue-red filter) against a magnitude in one of the filters. The y-axis is then the colour and the x-axis is the brightness.

File:Redspiral colourmagnitude.jpg:

Galaxy colour-colour diagram

But you will also see colour-colour diagrams, which are often used to select certain galaxies at certain redshifts as they can pin-point where there are "breaks" in the galaxy spectral energy distribution.

Example of a colour-colour diagram to select high-redshift z>6 galaxies based on their Lyman-break. Taken from Bowler et al. (2015).