The GLASS v1.4.6.3_v2 mocks carry 17% more galaxies than the v1.4.6.3 catalogue they stand in for (60.4 M unit-weight per realisation vs 51.6 M weight-effective), with σ_e matching to 0.2%.
The mocks are therefore under-noised: their noise-dominated error bars are 16% smaller than the data's (0.73× in variance).
Two area conventions
The catalogue's n_eff = 4.957 arcmin⁻² is defined on the footprint mask, sp_validation/cosmo_inference/data/mask/mask_map_footprint_nside_4096.fits (binary nside-4096 map from the HealSparse pixel mask, 2894 deg²) — the area we use for covariances and quote in the papers.
The mock generator uses its own occupied-pixel mask, /n09data/guerrini/glass_mock_v1.4.6.3_v2/mask_nside4096.fits (create_mask.py: nside-4096 pixels containing at least one catalogue galaxy, 2757 deg²).
| catalogue |
galaxies |
n_eff on the footprint mask |
σ_e per component |
UNIONS v1.4.6.3 leak-corrected (/n17data/UNIONS/WL/v1.4.x/v1.4.6.3/unions_shapepipe_cut_struc_2024_v1.4.6.3.fits) |
51.6 M weight-effective |
4.957 |
0.2676 |
GLASS v1.4.6.3_v2 (/n09data/guerrini/glass_mock_v1.4.6.3_v2/results/unions_glass_sim_*_4096.fits) |
60.4 M unit-weight |
5.793 |
0.2682 |
Mock and data galaxies occupy the same pixels (footprints coincide to within 2%), so the count ratio is the whole noise difference: the C_ℓ^BB scatter of the 350 realisations is 0.72× the data covariance, against 0.74 predicted from the counts.
How it happened
make_unions_glass_sim.py (/n17data/sguerrini/sp_validation_copy/glass_mock/) takes the density as --neff, default 6.0905 arcmin⁻², and neither run_glass_mock.sh nor run_glass_mock_local.sh overrides it.
6.09 is the catalogue n_eff from the 2405 deg² era; when the higher-resolution footprint mask moved the area to 2894 deg² the catalogue n_eff became 4.957, but the default did not follow.
6.09 arcmin⁻² on the 2757 deg² occupied-pixel mask gives the 60.4 M galaxies per realisation.
Downstream consequences
- Paper II compares mock scatter against the covariance machinery rerun at the mocks' own noise (CosmoCov with
source_n_gal = 5.793 at area = 2894; NaMaster from the mock count map for C_ℓ^BB) and states the mismatch in the referee response. Not affected beyond that.
- Papers III / IV state that the mocks reproduce the data's number density; the delivered catalogues do not.
A covariance built at the data's n_eff exceeds the mock scatter by 16% in σ from the count mismatch alone.
Paper IV (Fig. 4) reports iNKA error bars 15% above the mocks and OneCovariance within 5–10% of them, and attributes the iNKA gap to non-stationary noise; the count mismatch is a second contribution of the same size and sign. Nothing here quantifies the split.
- Configuration- vs harmonic-space consistency checks calibrated on these mocks are too stringent: scatter measured on mocks with less noise than the data understates what the real catalogue would show.
— Claude on behalf of Cail
The GLASS v1.4.6.3_v2 mocks carry 17% more galaxies than the v1.4.6.3 catalogue they stand in for (60.4 M unit-weight per realisation vs 51.6 M weight-effective), with σ_e matching to 0.2%.
The mocks are therefore under-noised: their noise-dominated error bars are 16% smaller than the data's (0.73× in variance).
Two area conventions
The catalogue's n_eff = 4.957 arcmin⁻² is defined on the footprint mask,
sp_validation/cosmo_inference/data/mask/mask_map_footprint_nside_4096.fits(binary nside-4096 map from the HealSparse pixel mask, 2894 deg²) — the area we use for covariances and quote in the papers.The mock generator uses its own occupied-pixel mask,
/n09data/guerrini/glass_mock_v1.4.6.3_v2/mask_nside4096.fits(create_mask.py: nside-4096 pixels containing at least one catalogue galaxy, 2757 deg²)./n17data/UNIONS/WL/v1.4.x/v1.4.6.3/unions_shapepipe_cut_struc_2024_v1.4.6.3.fits)/n09data/guerrini/glass_mock_v1.4.6.3_v2/results/unions_glass_sim_*_4096.fits)Mock and data galaxies occupy the same pixels (footprints coincide to within 2%), so the count ratio is the whole noise difference: the C_ℓ^BB scatter of the 350 realisations is 0.72× the data covariance, against 0.74 predicted from the counts.
How it happened
make_unions_glass_sim.py(/n17data/sguerrini/sp_validation_copy/glass_mock/) takes the density as--neff, default 6.0905 arcmin⁻², and neitherrun_glass_mock.shnorrun_glass_mock_local.shoverrides it.6.09 is the catalogue n_eff from the 2405 deg² era; when the higher-resolution footprint mask moved the area to 2894 deg² the catalogue n_eff became 4.957, but the default did not follow.
6.09 arcmin⁻² on the 2757 deg² occupied-pixel mask gives the 60.4 M galaxies per realisation.
Downstream consequences
source_n_gal = 5.793atarea = 2894; NaMaster from the mock count map for C_ℓ^BB) and states the mismatch in the referee response. Not affected beyond that.A covariance built at the data's n_eff exceeds the mock scatter by 16% in σ from the count mismatch alone.
Paper IV (Fig. 4) reports iNKA error bars 15% above the mocks and OneCovariance within 5–10% of them, and attributes the iNKA gap to non-stationary noise; the count mismatch is a second contribution of the same size and sign. Nothing here quantifies the split.
— Claude on behalf of Cail