MaNGA QFitsView Tutorial
This tutorial will use the MaNGA galaxy with PLATE-IFU = 8135-12701. You can download this galaxy yourself with the following rsync command in your terminal:
rsync -avz rsync://data.sdss.org/dr15/manga/spectro/redux/v2_4_3/8135/stack/manga-8135-12701-LOGCUBE.fits.gz LOCAL_PATH
The publicly-available software, QFitsView, by Thomas Ott, offers a powerful way to explore spectroscopic datacubes and even perform on-the-fly analyses like spectral stacking, emission line fitting, and velocity map generation.
QFitsView will work with MaNGA datacubes in either the LOGCUBE (logarithmic wavelength units) or LINCUBE (linear wavelength units) formats. Simply choose “Image Extension” #1 after selecting the desired datacube from the open-file dialog window (note, the default “primary” extension contains only header information, no data, in the MaNGA format, see its datamodel for an overview of all datacube extensions.).
After loading the datacube, QFitsView displays an image of the central wavelength slice in the main panel. The image clipping setting (default: “minmax”) and scaling (default: “linear”) can be set from drop-down menus above. A “logarithmic” scaling makes low surface brightness features more visible. By clicking and dragging the mouse across the main panel, you can adjust the display brightness and color bar (as in image viewers like ds9).
As you move the mouse over the image slice panel, the corresponding spectrum at the cursor location is displayed in the panel below. By pressing the “l” key, you can lock the spectrum display at a specific spaxel. You can then click-and-drag a box on the spectrum to zoom in on a desired wavelength range. Right-click on the mouse to get a menu option to zoom out to the entire spectrum. Press “l” again to unlock the spectral display. (Note: If the spectral display doesn’t update as you move the mouse, try locking and then unlocking by cycling the “l” key).
Instead of displaying the spectrum from the single spaxel underneath the mouse, you can also select circular filled and annular apertures with user-defined sizes. The aperture can be adjusted using drop-down menu and dialog boxes just above the spectral display. QFitsView will display the sum of all spectra falling within the defined aperture by default. You can also choose to display the average or median.
QFitsView enables quite a few advanced, on-the-fly analyses. One of the most useful is an estimated line-flux map. With the spectral display locked, zoom in to a spectral feature of interest, e.g., the Hα line. Select the line’s wavelength extent by holding down the letter “c” while dragging the mouse across the spectral feature. Next you can define the “continuum” level (to be subtracted from the flux in the line region) on both sides of a spectral feature. Define the first continuum region by holding down the letter “x” and dragging the mouse across an appropriate part of the continuum, and repeat this process but press the “v” key to define the second continuum region. The sum of flux in the defined line region, minus the average value from the continuum regions, is then displayed in the image viewing panel. You can redefine the spectral regions by tapping the letter “c” anywhere on the spectral display.
More detailed documentation is available from the QFitsView Documentation page.