2D Light-cone Wedge Plot

scripts/plot_lightcone_wedge.py

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Overview

The wedge plot renders a thin declination slice of a galaxy redshift survey in polar coordinates centred on the observer (Earth):

\[r \;=\; d_C(z) \quad [\text{Mpc}], \qquad \theta \;=\; \alpha \quad [\text{RA, radians}]\]

where \(d_C(z)\) is the comoving distance computed with the Planck 2018 flat ΛCDM cosmology (\(H_0 = 67.4\,\text{km\,s}^{-1}\text{Mpc}^{-1}\), \(\Omega_m = 0.315\)).

The observer sits at the origin; the fan opens to the right. Each galaxy is coloured by its redshift using the turbo colormap. Concentric arcs mark comoving distance milestones and are labelled with both \(d_C\) [Mpc] and the corresponding redshift and lookback time [Gyr].

The script produces:

• Individual wedge for every requested survey, using that survey’s built-in optimal footprint slice (RA range and DEC window) unless the user overrides them.

• Combined wedge (when more than one survey is requested) with each survey shown in a distinct solid colour.

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Supported catalogues

Key	FITS file	RA col	DEC col	z col	Default DEC window
LS10	~/data/legacysurvey/dr10/sweep/BGS_VLIM_Mstar/ LS10_VLIM_ANY_11.5_…_DATA.fits	RA	DEC	BEST_Z	0° ± 3°
GAMA	~/data/GAMA/FULL_CATALOG_PROSPECT_MASSES.fits	RA	DEC	Z	0° ± 3°
SDSS	~/data/SDSS/MPA_JHU/full_MERGED.fits	RA	DEC	Z	0° ± 2°
DESI_NGC	~/data/DESI/DR1/BGS_ANY_NGC_clustering.dat.fits	RA	DEC	Z	35° ± 12°
DESI_SGC	~/data/DESI/DR1/BGS_ANY_SGC_clustering.dat.fits	RA	DEC	Z	0° ± 5°

Quality cuts applied to every catalogue: RA ∈ [0°, 360°], DEC ∈ [−90°, 90°], \(z > 0\), and ZWARNING = 0 where that column exists.

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Usage

Each survey is plotted with its own optimal footprint by default:

# All surveys — individual plots + combined, using per-survey defaults
python scripts/plot_lightcone_wedge.py

# DESI NGC only, dark background
python scripts/plot_lightcone_wedge.py --surveys DESI_NGC --dark

# GAMA G09+G12+G15 fields, dark background
python scripts/plot_lightcone_wedge.py --surveys GAMA --dark

# Equatorial combined: GAMA + SDSS + DESI NGC (explicit DEC requires --force-dec)
python scripts/plot_lightcone_wedge.py \
    --surveys GAMA SDSS DESI_NGC \
    --ra-min 120 --ra-max 240 \
    --dec-center 0 --dec-width 2 --force-dec --dark

# All five surveys, equatorial strip, dark background
python scripts/plot_lightcone_wedge.py \
    --surveys LS10 GAMA SDSS DESI_NGC DESI_SGC \
    --ra-min 120 --ra-max 240 \
    --dec-center 0 --dec-width 2 --force-dec --dark

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Command-line options

Option	Default	Description
--surveys	all five	Space-separated list of catalogue keys to plot. Choices: LS10 GAMA SDSS DESI_NGC DESI_SGC.
--dec-center	0.0	Centre of the DEC slice in degrees. For individual plots this is overridden by each survey’s built-in default unless --force-dec is also set.
--dec-width	2.0	Half-width of the DEC slice in degrees.
--force-dec	(flag)	Apply --dec-center / --dec-width to individual plots too, instead of each survey’s built-in DEC default.
--zmax	0.45	Maximum redshift shown.
--ra-min	0.0	RA lower bound [degrees]. Value 0 signals “use survey default”.
--ra-max	360.0	RA upper bound [degrees]. Value 360 signals “use survey default”.
--max-points	200 000	Maximum number of galaxies plotted per survey (random downsampling applied when exceeded).
--dark	(flag)	Use a dark (#0a0a0a) background instead of white.
--seed	42	Random seed for the downsampling step.
--no-individual	(flag)	Skip the per-survey individual plots; produce only the combined figure.
--no-combined	(flag)	Skip the combined multi-survey figure.
--output-dir	results/wedgePlots	Directory where PNG files are written (created if absent).

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Output files

Individual wedge

wedge_{SURVEY}_zmax{Z:.2f}_dec{DEC:.1f}_w{WIDTH:.1f}_{dark|light}.png

Example: wedge_DESI_NGC_zmax0.45_dec35.0_w12.0_dark.png

Combined wedge

wedge_combined_zmax{Z:.2f}_dec{DEC:.1f}_w{WIDTH:.1f}_{dark|light}.png

Example: wedge_combined_zmax0.45_dec0.0_w2.0_dark.png

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Example outputs

DESI DR1 BGS Northern Galactic Cap

200 000 galaxies from DESI DR1 BGS NGC, declination slice 35° ± 12°, RA = [120°–250°], coloured by redshift.

DESI DR1 BGS NGC — 200 000 galaxies in a 24°-wide declination slice centred at DEC = 35°. The cosmic web is visible as an alternation of dense filaments (bright, yellow–red) and underdense voids (dark gaps).

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GAMA survey

GAMA G09 + G12 + G15 equatorial fields, declination slice 0° ± 3°, RA = [129°–222°].

GAMA — three equatorial fields (G09, G12, G15) separated by survey gaps. The lower galaxy density compared to DESI reflects GAMA’s smaller area and deeper target selection.

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Combined equatorial slice

GAMA + SDSS MPA-JHU + DESI NGC overlaid in a 4°-wide equatorial strip, RA = [120°–240°]. Each survey is drawn in a distinct colour.

Combined wedge. Green: GAMA; pink: SDSS MPA-JHU; blue: DESI DR1 BGS NGC. DESI’s greater depth and area are evident. The three surveys overlap in the G12 and G15 fields (RA ≈ 180°–222°), allowing cross-survey comparisons.