HEALPix map descriptions¶
This page describes the HEALPix maps computed in spherical shells, including a list of the available quantities and their units.
Some quantities relating to gas particles are smoothed onto the map by converting the particle’s SPH smoothing length to an angular size. See Smoothed maps for details. For other quantities the full contribution from the particle is added to a single pixel and no smoothing is done.
Note
See Integrated lightcones for HEALPix maps of additional, redshift-integrated quantities which were computed in post-processing.
Quantities and units¶
THe HEALPix maps include the following quantities:
Name |
Units |
Smoothed |
Description |
|---|---|---|---|
|
\(10^{10}\mathrm{M}_\odot\) |
No |
Total dynamical mass of the black hole particles in each pixel. |
|
\(-\) |
Yes |
Thermal SZ effect Compton y parameter. Excludes recently heated gas. |
|
\(\mathrm{Mpc}^{-2}\) |
Yes |
Dispersion measure (see note about bug, below). Excludes recently heated gas. |
|
\(10^{10}\mathrm{M}_\odot\) |
No |
Total mass of the dark matter particles in each pixel. |
|
\(-\) |
Yes |
Kinematic SZ effect Doppler b parameter (see note about bug, below). Excludes recently heated gas. |
|
\(10^{10}\mathrm{M}_\odot\) |
No |
Total mass of neutrinos in each pixel. |
|
\(10^{10}\mathrm{M}_\odot\) |
Yes |
Total (SPH smoothed) mass of gas in each pixel. |
|
\(10^{10}\mathrm{M}_\odot\mathrm{Mpc}^{-1}\mathrm{km/s}\) |
No |
Total star formation rate of gas in each pixel. |
|
\(10^{10}\mathrm{M}_\odot\) |
No |
Total mass of star particles in each pixel. |
|
\(10^{10}\mathrm{M}_\odot\) |
No |
Total mass in each pixel, including gas, dark matter, stars, black holes and neutrinos. |
|
\(10^{10}\mathrm{M}_\odot\) |
No |
Total mass of gas in each pixel without smoothing. |
X-ray maps¶
There are also maps of X-ray luminosity in various bands. All X-ray maps are smoothed. There are two types of X-ray maps:
Original X-ray maps output by Swift¶
These maps are available for all observers and to high redshift, but
were computed incorrectly assuming the z=0 UV background at all
redshifts. They have a _FrozenUVB suffix in the
lightconeX.shell_*.hdf5 map files.
Warning
We recommend accessing all X-ray maps via the virtual
datasets in the files lightconeX.shell*.hdf5. The
raw data for the original maps (which suffer from the UVB
issue) are stored in the files
swift_lightconeX.shell*.hdf5 where they do not have
the _FrozenUVB suffix.
Name |
Units |
Description |
|---|---|---|
|
\(10^{10}\mathrm{M}_\odot\mathrm{Mpc}^{-3}\mathrm{(km/s)}^{3}\) |
Total X-ray flux in the eROSITA 2.3 - 8.0 keV band. Assumes z=0 UV background. Excludes recently heated gas. |
|
\(\mathrm{Mpc}^{-3}\mathrm{km/s}\) |
Total X-ray photon flux in the eROSITA 2.3 - 8.0 keV band. Assumes z=0 UV background. Excludes recently heated gas. |
|
\(10^{10}\mathrm{M}_\odot\mathrm{Mpc}^{-3}\mathrm{(km/s)}^{3}\) |
Total X-ray flux in the eROSITA 0.2 - 2.3 keV band. Assumes z=0 UV background. Excludes recently heated gas. |
|
\(\mathrm{Mpc}^{-3}\mathrm{km/s}\) |
Total X-ray photon flux in the eROSITA 0.2 - 2.3 keV band. Assumes z=0 UV background. Excludes recently heated gas. |
|
\(10^{10}\mathrm{M}_\odot\mathrm{Mpc}^{-3}\mathrm{(km/s)}^{3}\) |
Total X-ray flux in the ROSAT 0.5 - 2.0 keV band. Assumes z=0 UV background. Excludes recently heated gas. |
|
\(\mathrm{Mpc}^{-3}\mathrm{km/s}\) |
Total X-ray photon flux in the ROSAT 0.5 - 2.0 keV band. Assumes z=0 UV background. Excludes recently heated gas. |
Recomputed X-ray maps¶
Where lightcone gas particle data are available, we have recomputed
the X-ray maps assuming the correct UV background. These maps are
available for observer 0 in a subset of the L1_m9 variations, and
only for the first ten redshift shells (redshift \(z <
0.5\)). They have a _Recomp suffix in the
lightconeX_shell_*.hdf5 map files.
Recomputed maps are available for the following simulations:
L1_m9
fgas+2sigma
fgas-2sigma
fgas-4sigma
fgas-8sigma
Mstar-1sigma
Mstar-1sigma_fgas-4sigma
Jet
Jet_fgas-4sigma
PlanckDCDM12
LS8_fgas-8sigma
NoCooling
Name |
Units |
Description |
|---|---|---|
|
\(10^{10}\mathrm{M}_\odot\mathrm{Mpc}^{-3}\mathrm{(km/s)}^{3}\) |
Total X-ray flux in the eROSITA 2.3 - 8.0 keV band. Excludes recently heated gas. |
|
\(10^{10}\mathrm{M}_\odot\mathrm{Mpc}^{-1}\mathrm{(km/s)}^{3}\) |
Total X-ray flux in the eROSITA 2.3 - 8.0 keV band convolved with eROSITA ARF. Excludes recently heated gas. |
|
\(\mathrm{Mpc}^{-3}\mathrm{km/s}\) |
Total X-ray photon flux in the eROSITA 2.3 - 8.0 keV band. Excludes recently heated gas. |
|
\(\mathrm{Mpc}^{-1}\mathrm{km/s}\) |
Total X-ray photon flux in the eROSITA 2.3 - 8.0 keV band convolved with eROSITA ARF. Excludes recently heated gas. |
|
\(10^{10}\mathrm{M}_\odot\mathrm{Mpc}^{-3}\mathrm{(km/s)}^{3}\) |
Total X-ray flux in the eROSITA 0.2 - 2.3 keV band. Excludes recently heated gas. |
|
\(10^{10}\mathrm{M}_\odot\mathrm{Mpc}^{-1}\mathrm{(km/s)}^{3}\) |
Total X-ray flux in the eROSITA 0.2 - 2.3 keV band convolved with eROSITA ARF. Excludes recently heated gas. |
|
\(\mathrm{Mpc}^{-3}\mathrm{km/s}\) |
Total X-ray photon flux in the eROSITA 0.2 - 2.3 keV band. Excludes recently heated gas. |
|
\(\mathrm{Mpc}^{-1}\mathrm{km/s}\) |
Total X-ray photon flux in the eROSITA 0.2 - 2.3 keV band convolved with eROSITA ARF. Excludes recently heated gas. |
|
\(10^{10}\mathrm{M}_\odot\mathrm{Mpc}^{-3}\mathrm{(km/s)}^{3}\) |
Total X-ray flux in the ROSAT 0.5 - 2.0 keV band. Excludes recently heated gas. |
|
\(10^{10}\mathrm{M}_\odot\mathrm{Mpc}^{-1}\mathrm{(km/s)}^{3}\) |
Total X-ray flux in the ROSAT 0.5 - 2.0 keV band convolved with the ROSAT response function. Excludes recently heated gas. |
|
\(\mathrm{Mpc}^{-3}\mathrm{km/s}\) |
Total X-ray photon flux in the ROSAT 0.5 - 2.0 keV band. Excludes recently heated gas. |
|
\(\mathrm{Mpc}^{-1}\mathrm{km/s}\) |
Total X-ray photon flux in the ROSAT 0.5 - 2.0 keV band convolved with the ROSAT response function. Excludes recently heated gas. |
Exclusion of recently heated gas particles¶
Several of the maps described above, including the X-ray maps, Compton \(y\) parameter, Doppler \(b\) parameter, and dispersion measure were computed using only gas particles which have not been recently heated by AGN. Gas particles are excluded from these maps if they have been AGN heated within the last \(15 \mathrm{Myr}\) and their temperature is between \(10^{-1} \Delta T_{\mathrm{AGN}}\) and \(10^{0.3} \Delta T_{\mathrm{AGN}}\), where \(\Delta T_{\mathrm{AGN}}\) is the AGN feedback heating temperature.
Compton \(y\) parameter¶
The Compton \(y\) parameter maps are computed by accumulating the following dimensionless quantity for each gas particle which crosses the lightcone:
\(\Delta y = \frac{\sigma_\text{T} k_\text{B}}{m_\text{e}c^2} \frac{m_\text{g} n_\text{e} T}{\Omega_\text{pixel}^2 d_\text{A}^2 \rho}\)
where \(m_\text{g}\) is the particle’s mass, \(\Omega_\text{pixel}\) is the solid angle of a healpix pixel and \(d_\text{A}\) is the angular diameter distance to the observer. Excludes gas recently heated by AGN.
Doppler \(b\) parameter¶
Warning
Due to a bug, the contribution of each particle to the Doppler \(b\) parameter maps incorrectly included an extra factor of \(a\). In the data release this has been approximately corrected using the expansion factor at the shell mid point.
The Doppler \(b\) parameter maps were intended to be computed by accumulating the following dimensionless quantity for each gas particle which crosses the lightcone:
\(\Delta b = \frac{n_\text{e} m_\text{g} \sigma_\text{T} v_\text{r}}{\Omega_\text{pixel}^2 d_\text{A}^2 \rho c}\)
where \(v_\text{r}\) is the particle’s radial velocity relative to the observer. Excludes gas recently heated by AGN.
Dispersion measure¶
Warning
Due to a bug, the contribution of each particle to the dispersion measure maps incorrectly omitted a factor of \(a\). In the data release this has been approximately corrected using the expansion factor at the shell mid point.
The dispersion measure maps were intended to be computed by accumulating the following quantity for each gas particle which crosses the lightcone:
\(\Delta \text{DM} = \frac{n_\text{e} m_\text{g} a}{\Omega_\text{pixel}^2 d_\text{A}^2 \rho}\)
where \(a\) is the expansion factor at which the particle crossed the lightcone. Excludes gas recently heated by AGN.
Convolved X-ray Maps¶
The convolved X-ray maps (e.g. XrayErositaLowConvolvedPhotons) are
constructed in the same way as the Intrinsic X-ray maps, except
that the emitted photon energy is convolved with the effective area of
the detector belonging to the telescope of the corresponding energy
band (e.g. section 3.1 of McDonald et al (2026) .)
Convolved maps in the ROSAT (0.5-2.0 keV) band adopt the effective
area information from the publicly available ROSAT on-axis response
function
. The maps in the eROSITA-high (2.3 - 8.0 keV band) and eROSITA-low
(0.2 - 2.3 keV) utilise the survey-averaged eROSITA auxiliary
response files,
specifically those for telescope model (TM) 8, which excludes TM5 and
TM7 as they suffer from light leakage (Predehl et al (2021).)
Smoothed maps¶
Gas particles in the FLAMINGO simulations have an associated SPH smoothing length, so quantities derived from the gas can be smoothed onto the HEALPix maps. When a gas particle crosses the lightcone its angular smoothing length is computed as:
where \(h\) is the particle’s smoothing length and \(r\) is the distance from the observer at which the particle crossed the lightcone. A gas particle with an angular smoothing length \(\theta_\text{h}\) will update all pixels within an angular radius
where \(\gamma\) is the number of smoothing lengths at which the SPH kernel falls to zero. If \(\theta_\text{s}\) is smaller than the maximum angular radius of any HEALPix pixel then no smoothing is done and the full contribution of the particle to the map is added to a single pixel. Otherwise, we distribute the particle’s contribution over multiple pixels weighted by a 2D projected smoothing kernel.
The projected kernel is computed using equation 30 of Price (2007):
Here, \(q^2 = q^2_{xy} + q^2_{z}\), \(R = h\gamma\) is the radius where the SPH kernel reaches zero, and \(W(q)\) is the Wendland C2 kernel used in FLAMINGO’s SPH implementation. The contribution to the map from a particle is distributed between all pixels with centres within an angular radius \(\theta_s\) of the particle, weighted by the projected kernel and normalized such that the total contribution to the map is the same as in the un-smoothed case.