File Format

The file format used for the velociraptor.observational_data functionality is described below. These files are simple HDF5 files that can be opened using h5py or some other module, and so are easily portable to different systems. They are designed to be both human and machine ‘readable’ to enable maximal re-use throughout many projects.

You are free to write your own reader/writer for this data, but the other sections in this documentation showcase python tools already written to perform such tasks.

HDF5 Fields

The required fields in a file are given here:

file_name.hdf5
├cosmology
│ └9 attributes:
│   ├H0: H0 in km/s/Mpc
│   ├Neff: Effective number of neutrino species
│   ├Ob0: Omega baryons: density of baryonic matter in units of the critical density at z=0.
│   ├Ode0: Omega dark energy: density of dark energy in units of the critical density at z=0.
│   ├Om0: Omega matter: density of matter in units of the critical density at z=0.
│   ├Tcmb0: CMB temperature at z=0
│   ├m_nu: Masses of neutrino species (size 3)
│   ├m_nu_units: Neutrino mass units
│   └name: Name of this cosmology (e.g. WMAP7)
├metadata
│ └6 attributes:
│   ├bibcode: 'Bibcode - available from e.g. ADS'
│   ├citation: 'Short citation (e.g. X et al. 2019)'
│   ├comment: 'Free-text comment describing e.g. IMF choices'
│   ├name: 'Short name that is easily recognised'
│   ├plot_as: 'points' or 'line' - plot as either markers or a line
│   └redshift: 0.0 - floating point number
├x
│ ├2 attributes:
│ │ ├comoving: True/False
│ │ └description: 'Short description of axis, e.g. galaxy stellar mass'
│ └values    [float64: N]
│   └2 attributes:
│     ├unit_registry: Generated by unyt automatically
│     └units: 'String units, e.g. Msun'
└y
   ├2 attributes:
   │ ├comoving: True
   │ └description: 'Short description of axis, e.g. galaxy stellar mass'
   ├scatter  [float64: N (or 2XN), OPTIONAL] - scatter in this dimension.
   │ └2 attributes:
   │   ├unit_registry: Generated by unyt automatically
   │   └units: 'String units, e.g. Msun'
   └values   [float64: N]
   └2 attributes:
      ├unit_registry: Generated by unyt automatically
      └units: 'String units, e.g. Msun'