Output Data Products

3DCubeGen produces several types of output files depending on the command and spectrograph used. All output files are FITS format and are gzip-compressed by default.

LVM Cubes

Filename: lvmCube-<name>.fits.gz

Generated by sincube and pipecube.

HDU	Type	Content
0	PrimaryHDU	Flux cube [n_wave, n_y, n_x]. Contains WCS header with RA/Dec (TAN projection) and wavelength (linear, Angstroms) axes.
1	ImageHDU	Error cube [n_wave, n_y, n_x] (if errors: True). Propagated errors from inverse-variance weighting.
2	ImageHDU	Unity array (reserved)
3	ImageHDU	Mask array (reserved)

Key header keywords:

• CRVAL1, CRVAL2 – RA, Dec reference coordinates (deg)

• CD1_1, CD2_2 – pixel scale in RA, Dec (deg/pix)

• CRVAL3, CD3_3, CRPIX3 – wavelength solution (Angstroms)

• CTYPE3: WAVE – air wavelength (linear)

• IFUCON – number of fibers used in reconstruction

• BUNIT – flux units (10^-16 erg/s/cm^2 when flu16: True, otherwise erg/s/cm^2)

LVM Maps

Filename: lvmMap-<name>_<band>.fits.gz

Generated by sinmap and pipemap.

HDU	Type	Content
0 (FLUX)	PrimaryHDU	Flux map [n_y, n_x] in erg/s/cm2. Contains 2D WCS header with RA/Dec (TAN projection).
1 (MAG)	ImageHDU	Magnitude map [n_y, n_x] in AB mag/arcsec2.
2	ImageHDU	Flux error map
3	ImageHDU	Magnitude error map

The <band> suffix corresponds to the photometric filter used:

Band	Description
OII	[OII] 3728 A narrow-band
OIII	[OIII] 5008 A narrow-band
HI	H-alpha 6565 A narrow-band
SII	[SII] 6733 A narrow-band
g	SDSS g broad-band
r	SDSS r broad-band
i	SDSS i broad-band

JPEG Composite Images

Filename: <name>_<type>.jpeg

Generated by pipemap after all seven photometric bands are produced. These are three-color composite images constructed from the magnitude maps.

Available composites:

Type	Channels (R, G, B)	Description
OHS	[SII], H-alpha, [OIII]	Narrow-band emission line composite
OOH	H-alpha, [OIII], [OII]	Narrow-band emission line composite
gri	i, r, g	Broad-band continuum composite
griOOH	Weighted blend	Combined broad-band + narrow-band with configurable weights

LVM RSS (from cube)

Filename: lvmRSS-<name>.fits.gz

Generated by pipecube when cube2rss: True, or manually via rssp_extract() after a sincube run (see DAP Integration Tools). Each non-zero spaxel in the input cube becomes one “fiber” row in the RSS.

HDU	EXTNAME	Status	Content
0	ORIGINAL	Real	Primary header copied from the cube. POSCIRA/POSCIDE are set from the cube’s CRVAL1/CRVAL2. EXPOSURE is hardcoded to 000000 (not recoverable from the cube).
1	FLUX	Real	Flux array [n_spaxels, n_wave] extracted spaxel-by-spaxel from cube HDU 0. Units match the cube (see Flux Units below).
2	IVAR	Real[1]	Inverse variance [n_spaxels, n_wave] computed as 1 / error² from cube HDU 1.
3	MASK	Placeholder	Zero array. No mask information is stored in the cube.
4	WAVE	Real	Wavelength array [1, n_wave] in Angstroms, reconstructed from the cube header keywords CRVAL3, CDELT3/CD3_3, CRPIX3.
5	LSF	Placeholder	Ones array. The line spread function is not preserved in the cube.
6	SKY_EAST	Placeholder	Ones array. Sky spectra are not stored in the cube.
7	SKY_EAST_IVAR	Placeholder	Ones array.
8	SKY_WEST	Placeholder	Ones array.
9	SKY_WEST_IVAR	Placeholder	Ones array.
10	SLITMAP	Real	Binary table. ra/dec are computed from the cube WCS. xpmm/ypmm store the pixel column/row in the cube for back-referencing. Bookkeeping columns (targettype, telescope, ifulabel, etc.) contain generic placeholder strings.

[1]

Requires the cube to have been generated with errors: True. If error propagation was disabled, HDU 1 of the cube is an array of ones and the IVAR extension will contain ones throughout.

MEGARA Outputs

Cube: megCube-<name>.fits / megCube-<name>_<VPH>.fits.gz

The MEGARA cube follows a similar structure to the LVM cube (flux in HDU 0, WCS header) but includes VPH grating information and spectrophotometric calibration metadata in the header.

Spectrum: megSpec-<name>_<VPH>.fits.gz

A 1D extracted spectrum generated by runfulldrp from the reconstructed cube.

VirusP Outputs

Cube: vpCube-<name>.fits

The VirusP cube follows the same structure as the LVM cube (flux in HDU 0 with 3D WCS, error in HDU 1 if enabled). The output is not gzip-compressed by default unless configured otherwise.

Flux Units

The flux unit convention depends on the flu16 parameter:

• flu16: True (default) – flux values are in units of 10^-16 erg/s/cm²/A. The header keyword BUNIT is set to 10^-16 erg/s/cm^2.

• flu16: False – flux values are in native units of erg/s/cm²/A.

The 10^-16 scaling is applied by dividing the flux array by 10^-16, so numerical values in the FITS file are larger and more convenient to work with.