HEALPix map file format¶

The HEALPix maps are stored in HDF5 files with one file for each redshift shell. Each map is stored as a single HDF5 dataset in the file’s root group. For descriptions of the available maps see HEALPix map descriptions.

Shell metadata¶

Each file has a Shell group with attributes specifying the extent of the shell:

Attribute name	Meaning
`comoving_inner_radius`	Inner radius of the shell, in comoving Mpc.
`comoving_outer_radius`	Outer radius of the shell, in comoving Mpc.
`nr_files_per_shell`	How many files the maps are split over. This is always 1 in the FLAMINGO data release.

See HEALPix map shell redshifts for a full list of shell redshifts and comoving radii.

Unit system¶

Each file has a HDF5 group Units with attributes specifying the simulation base units used, which are the same as in the snapshots:

Attribute name	Meaning	Value in FLAMINGO
`Unit length in cgs (U_L)`	Simulation base length unit in CGS	\(\mathrm{Mpc}\)
`Unit mass in cgs (U_M)`	Simulation base mass unit in CGS	\(10^{10}\mathrm{M}_{\odot}\)
`Unit time in cgs (U_M)`	Simulation base time unit in CGS	\(\mathrm{Mpc} \mathrm{(km/s)}^{-1}\)
`Unit temperature in cgs (U_M)`	Simulation base temperature unit in CGS	\(\mathrm{K}\)

Map datasets¶

Each map is stored as a one dimensional HDF5 dataset of 64-bit floating point type with one element per pixel. See HEALPix map descriptions for the full list of maps. The map datasets have the following attributes:

Attribute name	Attribute description
`comoving_inner_radius`	Inner radius of the shell, in comoving Mpc.
`comoving_outer_radius`	Outer radius of the shell, in comoving Mpc.
`nside`	HEALPix resolution parameter for the map
`number_of_pixels`	Number of pixels in the map. Equal to the dataset size.
`pixel_ordering_scheme`	HEALPix pixel ordering. Always “ring” in the FLAMINGO data release.
`U_L exponent`	Exponent of the simulation base length unit in the units of this map
`U_M exponent`	Exponent of the simulation base mass unit in the units of this map
`U_T exponent`	Exponent of the simulation base temperature unit in the units of this map
`U_t exponent`	Exponent of the simulation base time unit in the units of this map
`U_I exponent`	Exponent of the current unit (not used in FLAMINGO)

The U_* exponent attributes specify the units of each map the same way as in the snapshots.