Cubes vs RSS
The final data product for each MaNGA target comes in two basic forms: Row Stacked Spectra (RSS) and datacubes. To understand the difference between these two formats, it helps to remind ourselves of the MaNGA observing strategy. Instead of only observing each galaxy once, MaNGA observes multiple times with slightly different offsets (dithers) to fill in the gaps between the 2″ wide fibers (there are a few cases where a galaxy was observed on two different plates and these are not combined into a single file). The datacubes resample this data onto a 2-dimensional grid with 0.5? pixels and spatial resolution of 2.5?
The RSS files and datacubes provide information in different formats. For example, in the RSS files, the flux extension is a 2D array of wavelength × number of fibers (number of fibers = IFU size × number of observational pointings). In the datacubes, the flux extension is a 3D array of x-position × y-position × wavelength. Both formats provide wavelength in logarithmic or linear units. For a detailed explanation of data formats, see the data model page.
Which file do I want to use? The answer depends on your goals. If you’re interested in making 2D maps, you may be more interested in using the data cubes that provide data in an intuitive format. However, keep in mind that multiple fibers are used to make a single spaxel, so the uncertainties between spaxels are correlated. In the RSS files, the spectra are independent so the uncertainties are easier to understand. This data format may be better for stacking data from multiple fibers, for example.