The primary MaNGA data products are composed of 3-D reduced data cubes produced by the DRP and 2-D maps of derived quantities produced by the DAP. The 3-D reduced data cubes are constructed from a few tens to a few thousands of individual spectra that have been combined onto a regular grid. The 2-D maps of derived quantities are constructed by analyzing individual or binned groups of spaxels and adding the each quantity at the relevant on-sky location of the spaxel or spaxel group. This page will explain the structure of the raw data (spectra dispersed onto individual CCDs), intermediate data processed through the 2-D (per-exposure) stage of the DRP, final data products processed through the 3-D (per plate) stage of the DRP, intermediate data products constructed during each stage of the DAP analysis, and the final maps and model cubes consolidated from these DAP analysis steps. Additionally, we describe the preimaging data drawn from the NSA reprocessing of the original SDSS imaging survey; this preimaging data is used for the astrometric alignment of the MaNGA spectral imaging.
The default storage format for all MaNGA data (images and cubes) is multi-extension FITS (gzipped to save space). The zeroth extension of such files is blank except for the global header. All extensions of such files are labeled with the EXTNAME header keyword so that they can be read by extension name instead of extension number.
The raw data (identical between MaNGA and eBOSS) is obtained for each of the four cameras individually (b1,b2,r1,r2). Aside from some new keywords, the format is the same as for BOSS raw data. These keywords include:
- Dither position (MGDPOS, values of N,S,E,C). C means no dither; N,S,E are the 3 allowed dither values for the MaNGA dither triangle. (For more details see the MaNGA Observing Strategy paper, Law et al. 2015).
- Dither location (MGDRA, MGDDEC), i.e. offset of the pointing from the nominal center in arcsec of RA and DEC. These are the values actually used by the DRP in determining the astrometric solution.
- PLATETYP='MANGA' or 'APOGEE-2&MANGA', as appropriate (i.e., whether the plate contains only MaNGA holes, or both MaNGA and APOGEE holes for co-observing)
- SRVYMODE='MaNGA stare', 'MaNGA dither', or 'APOGEE-lead' as appropriate. Most galaxy plates are 'MaNGA dither', all-sky plates are 'MaNGA star', and bright-time stellar library plates are 'APOGEE-lead'.
2-D Reduction Pipeline Output
Each exposure through the MaNGA instrument is processed separately through the 2-D Data Reduction Pipeline (DRP) up to and including flux calibration and combination of spectra from individual cameras across the dichroic break.
The structure of these files is loosely based on the BOSS spFrame type files.
That is, they are row-stacked spectra (RSS), two dimensional arrays in which each row corresponds to an individual one-dimensional spectrum.
The following files can (and should) be read using the routine ml_mgframeread.pro.
List of files:
3-D Reduction Pipeline Output
Once a given plate is complete (ie. all of the required sets of dithers are collected), the 3D stage of the DRP extracts the relevant rows for each IFU from the mgCFrame files, computes the astrometric solution of each, and combines the exposures into row-stacked spectra and data cubes.
These output files follow the naming convention [plate]-[ifudesign], which uniquely identifies a given galaxy observation. Note, however, that if a galaxy were to be reobserved on a different plate it would have a different 'plateifu' identifier. 'plateifu' thus uniquely identifies a set of observations, while 'mangaid' uniquely identifies an astronomical target.
In this section NFIBER is taken to mean the number of fibers in a given IFU (e.g., 19, 37, 61, 91 or 127), and NEXP is the number of exposures.
There are two kinds of output files: row-stacked spectra (RSS) that contain each individual spectrum stacked atop each other into into a 2d format, and a data cube that combines individual spectra together into a rectified 3d data cube. RSS files and cubes are provided for all MaNGA dark time targets except the spectrophotometric standard stars on 7-fiber minibundles.
MaNGA adopts the HDUCLASS FITS header extension keyword structure (see https://heasarc.gsfc.nasa.gov/docs/heasarc/ofwg/docs/ofwg_recomm/r8.html) to indicate the type of information contained in the science, error, and mask (i.e., data quality, or DQ) extensions (and the relationship between those extensions). We define HDUCLASS SDSS.
The science extension has HDUCLAS1=IMAGE (for RSS files) or CUBE (for data cubes) and HDUCLAS2=DATA. The ERRDATA and QUALDATA keywords in this extension header point to the error and DQ extensions.
The error extension has HDUCLAS1=IMAGE or CUBE and HDUCLAS2=ERROR. Valid HDUCLAS3 entries are MSE, RMSE, INVMSE, INVRMSE. MaNGA uses INVMSE (i.e., we provide inverse variance). The SCIDATA and QUALDATA keywords in this header point to the science and DQ extensions.
The DQ extension has HDUCLAS1=IMAGE or CUBE and HDUCLAS2=QUALITY. MaNGA uses HDUCLAS3=FLAG64BIT, indicating that the DQ extension should be interpreted as a bitmask with up to 64 independent bits available. The SCIDATA and ERRDATA keywords in this header point to the science and error extensions.
In all cases, the dimensionality of the ERROR and QUALITY extensions matches that of the DATA extension.
These are the row-stacked, flux-calibrated fiber spectra for a given galaxy across all exposures. The "LOGRSS" file has logarithmic wavelength sampling from log10(lambda/Angstroms)=3.5589 to 4.0151 (NWAVE=4563 spectral elements). The "LINRSS" file has linear wavelength sampling from 3622.0 to 10353.0 Angstroms (NWAVE=6732 spectral elements). Both files contain one row for each fiber, for a total of NFIBER*NEXP rows.
In brief, these files contain extensions for the flux (in units of 10-17 erg/s/cm2/Angstrom/fiber), the inverse variance, the pixel mask, the pre- and post-pixellized spectral line spread function for each fiber, the wavelength vector, the median spectral resolution (pre- and post-pixellization) as a function of wavelength for the fibers in this IFU, the standard deviation of spectral resolution (pre- and post-pixellization) as a function of wavelength for the fibers in this IFU, a binary table describing the individual exposures that make up the file, and arrays of the effective X and Y positions in arcsec of each fiber (as a function of wavelength) relative to the IFU center.
These are the final 3d data cubes for a given galaxy that combine all fiber spectra across all exposures as described here.
The LOGCUBE data cube has logarithmic wavelength sampling from log10(lambda/Angstroms)=3.5589 to 4.0151 (NWAVE=4563 spectral elements), and 0.5 arcsec spatial pixels (spaxels) for a total size of NX x NY x NWAVE pixels; LINCUBE is the same, except it has linear wavelength sampling from from 3622.0 to 10353.0 Angstroms (NWAVE=6732 spectral elements).
Similar to the RSS files, they contain extensions for the flux (now in units of 10-17 erg/s/cm2/Angstrom/spaxel), inverse variance, pixel mask, per-spaxel line spread function (pre- and post-pixellized versions), wavelength vector, median spectral resolution and standard deviation thereof (pre- and post-pixellized versions), and a binary table describing the individual exposures that make up the file. Additionally, they also include reconstructed broadband 'griz' images created from the spectral data cube, estimates of the reconstructed point source profiles in each of the 'griz' bands, and estimates of the 2d spatial correlation matrices at 'griz' bands.
Data Analysis Pipeline Output
The DAP output primarily consists of two output files, the
MAPS and model
LOGCUBE files, provided for each combination of
MAPS and model
LOGCUBE files provided by the DAP include a
DAPTYPE keyword in the file name. The
DAPTYPE is a short-hand signifying the method used to analyze the DRP
LOGCUBE file. This is a combination of the keywords used to select the spaxel binning approach and the stellar-continuum fitting method. For DR16,
DAPTYPE can have two values:
VOR10-GAU-MILESHC: Spaxels are binned to S/N~10 using the Voronoi binning algorithm (Cappellari & Copin 2003); all binned spectra are treated independently.
HYB10-GAU-MILESHC: The spaxel binning for the stellar-continuum analysis is identical to the
VOR10approach; however, the emission-line and spectral-index measurements are performed on the individual spaxels. Usage notes for the hybrid binning scheme are here.
The advantage of the
VOR10-GAU-MILESHC output is that all measurements are performed at exactly the same spectra. The
HYB10-GAU-MILESHC output is meant to allow for greater spatial resolution for the emission-line analysis and avoid limitations of that analysis by tying it to the S/N of the broadband continuum.
WARNING: Some MAPS file extensions must be corrected to obtain the astrophysically relevant quantities. See Working with MaNGA Data!
MAPS files are the primary output file from the DAP and provide 2D "maps" (i.e., images) of DAP measured properties. The shape and astrometric World Coordinate System (WCS, provided in the
MAPS header) of these images identically match that of a single wavelength channel in the corresponding DRP
LOGCUBE file. Most properties are provided in groups of three fits extensions:
[property]: the measurement value
[property]_IVAR: the measurement uncertainty stored as the inverse variance
[property]_MASK: a corresponding bit mask for each pixel
Extensions can either be a single 2D image (
HDUCLAS1= 'IMAGE') or they can have a series of images that are organized along the third dimension (
HDUCLAS1= 'CUBE'). For the latter, each image is said to be in a specific "channel". For example, each Gaussian-fitted emission-line flux is provided in a single channel in the
EMLINE_GFLUX extension, one channel per fitted emission line. The header of extensions with multiple channels provide the names of the quantities in each channel using header keyword
n is the 1-indexed number of the channel. Similarly, because the spectral-index measurements can be in units of either angstroms, magnitudes, or unitless, the header of the spectral-index extensions also include the units using header keywords
Un. If possible with your software package of choice, it is better to select the extension and channel based on its name, not its extension or channel number, in case the detailed numbering changes in future releases. An example of how to do this using python is provided in the MaNGA tutorials.
Internally, the DAP performs all spectral fitting on the binned spectra (termed as such even if a bin only contains a single spaxel) after they have been corrected for Galactic extinction (see here). Therefore, e.g., the output emission-line fluxes have been corrected for Galactic extinction. However, the models and binned spectra in the output model cube files (see below) are reverted to their reddened values for direct comparison with the DRP
LOGCUBE files provide the binned spectra and the best-fitting model spectrum for each spectrum that was successfully fit. These files are useful for detailed assessments of the model parameters because they allow you to return to the spectra and compare the model against the data. The DAP fits the spectra in two stages, one to get the stellar kinematics and the second to determine the emission-line properties. The emission-line module (used for all binning schemes) fits both the stellar continuum and the emission lines at the same time, where the stellar kinematics are fixed by the first fit. The difference between the stellar-continuum fit during the first and second fit are provided by the
EMLINE_BASE extension of this file. I.e., if you want to get the stellar-continuum models from the first fit, you calculate:
stellar_continuum = MODEL - EMLINE - EMLINE_BASE
WARNING: In the HYB binning case, the binned spectra provided in the model cube files are from the Voronoi binning step; however, the emission-line models are fit to the individual spaxels. See discussion of special considerations for the HYB binning case here.
An example of how to plot the model
LOGCUBE data is provided by the MaNGA Tutorials; the example also demonstrates how to effectively use the provided masks.
The DAP analyzes the data via a series of modules, one for each of its primary analysis steps. Each of these modules writes a "reference" file; when re-executed, the DAP will skip the associated analysis step and use the relevant data from the file to continue and complete the remaining steps. The two main DAP output files consolidate and reformat the results from the suite of reference files; however, not all of the properties from the references files are included. We will continue to include further properties in the main output files, as needed/desired. In the meantime, these reference files are provided for users that want the data not included in the
MAPS or model
The names of the reference files follows a concatenation of the analysis keywords used in each analysis steps. The relevant keywords are:
[rdxqakey]: the reduction assessments made of the DRP cube file,
[binkey]: the binning method performed on the DRP spectra,
[sckey]: the stellar-continuum fitting method,
[elmkey]: the emission-line passband database used to calculate the emission-line moments,
[elfkey]: the emission-line fitting method, and
[sikey]: the spectral-index database used to calculate the spectral indices.
[binkey]-[sckey] is currently the same as the
The reference files produced by the DAP are as follows:
- Analysis Step: 1
- Data Model: manga-RDXQAKEY
- Python Class: ReductionAssessments
- Analysis Step: 2
- Data Model: manga-RDXQAKEY-BINKEY
- Python Class: SpatiallyBinnedSpectra
- Analysis Step: 3
- Data Model: manga-RDXQAKEY-DAPTYPE
- Python Class: StellarContinuumModel
- Analysis Step: 4
- Data Model: manga-RDXQAKEY-DAPTYPE-ELMKEY
- Python Class: EmissionLineMoments
- Analysis Step: 5
- Data Model: manga-RDXQAKEY-DAPTYPE-ELFKEY
- Python Class: EmissionLineModel
- Analysis Step: 6
- Data Model: manga-RDXQAKEY-DAPTYPE-ELFKEY-ELMKEY
- Python Class: EmissionLineMoments
- Analysis Step: 7
- Data Model: manga-RDXQAKEY-DAPTYPE-ELFKEY-SIKEY
- Python Class: SpectralIndices
SDSS Legacy Imaging
MaNGA requires that broadband imaging data for target galaxies be available for the DRP to use to register astrometric solutions against and to estimate achieved S/N depth. We use the NASA Sloan Atlas (NSA) re-reduction of the SDSS imaging data, and we provide FITS postage stamps of this re-reduction for each MaNGA galaxy released as part of DR16. In brief, these files are multi-extensions FITS files giving the flux, inverse variance, and psf in each of the four 'griz' bands.