3D Light-cone Visualisation

scripts/plot_lightcone_3d.py

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Overview

This script converts each galaxy’s (RA, DEC, z) into a comoving Cartesian position and renders two complementary figures:

1. 3D perspective scatter — a Matplotlib Axes3D scatter on a dark background, coloured by redshift with the turbo colormap. Thin circular rings in the equatorial plane mark comoving distance shells at \(z = 0.1, 0.2, \ldots\).

2. Top-down projection — the same dataset projected onto the \(x\)–\(y\) plane (equatorial comoving coordinates), also coloured by redshift. Because it is a pure 2D scatter, this companion figure is always sharp and well-resolved, complementing the 3D view.

An optional interactive HTML figure (Plotly) can be produced with --interactive.

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Coordinate conversion

Each galaxy at right ascension \(\alpha\), declination \(\delta\), and redshift \(z\) is mapped to comoving Cartesian coordinates:

\[\begin{split}x &= d_C(z)\,\cos\delta\,\cos\alpha \\ y &= d_C(z)\,\cos\delta\,\sin\alpha \\ z_\text{cart} &= d_C(z)\,\sin\delta\end{split}\]

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

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Supported catalogues

Key	FITS file	RA col	DEC col	z col	z range
LS10	~/data/legacysurvey/dr10/sweep/BGS_VLIM_Mstar/ LS10_VLIM_ANY_11.5_…_DATA.fits	RA	DEC	BEST_Z	0.01 – 0.36
GAMA	~/data/GAMA/FULL_CATALOG_PROSPECT_MASSES.fits	RA	DEC	Z	0.002 – 0.50
SDSS	~/data/SDSS/MPA_JHU/full_MERGED.fits	RA	DEC	Z	0.005 – 0.30
DESI_NGC	~/data/DESI/DR1/BGS_ANY_NGC_clustering.dat.fits	RA	DEC	Z	0.01 – 0.50
DESI_SGC	~/data/DESI/DR1/BGS_ANY_SGC_clustering.dat.fits	RA	DEC	Z	0.01 – 0.50

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

# All five surveys, default settings
python scripts/plot_lightcone_3d.py

# DESI NGC + SGC only, up to z = 0.45, 100 000 points per survey
python scripts/plot_lightcone_3d.py \
    --surveys DESI_NGC DESI_SGC --zmax 0.45 --max-points 100000

# Custom viewing angle
python scripts/plot_lightcone_3d.py \
    --surveys DESI_NGC DESI_SGC --elev 25 --azim 30

# Also write an interactive Plotly HTML file
python scripts/plot_lightcone_3d.py \
    --surveys DESI_NGC DESI_SGC --interactive

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Command-line options

Option	Default	Description
--surveys	all five	Space-separated list of catalogue keys. Choices: LS10 GAMA SDSS DESI_NGC DESI_SGC.
--zmax	0.45	Maximum redshift included.
--max-points	100 000	Maximum galaxies per survey (random downsampling when exceeded).
--elev	20.0	Elevation angle for the 3D perspective view [degrees].
--azim	30.0	Azimuth angle for the 3D perspective view [degrees].
--interactive	(flag)	Also write a Plotly interactive HTML alongside the PNG (requires pip install plotly).
--seed	42	Random seed for downsampling.
--output-dir	results/wedgePlots	Directory where output files are written.

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Output files

3D perspective PNG

lightcone_3d_{SURVEYS}_zmax{Z:.2f}.png

Example: lightcone_3d_DESI_NGC+DESI_SGC_zmax0.45.png

Top-down projection PNG

lightcone_topdown_{SURVEYS}_zmax{Z:.2f}.png

Example: lightcone_topdown_DESI_NGC+DESI_SGC_zmax0.45.png

Interactive HTML (optional)

lightcone_3d_{SURVEYS}_zmax{Z:.2f}_interactive.html

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Example outputs

3D perspective — DESI DR1 BGS NGC + SGC

100 000 galaxies per survey placed at their comoving Cartesian positions. The conical footprint of the Northern Galactic Cap (right) and the more isotropic Southern Galactic Cap (left) are clearly distinguishable. Distance shells at \(z = 0.1, 0.2, 0.3, 0.4\) are drawn in the equatorial plane for reference.

3D comoving light cone. Blue–yellow–red: redshift 0 → 0.45 (turbo colormap). The NGC cone (RA = 90°–298°, DEC > 0°) appears as the dominant cluster of points in the upper hemisphere; the SGC fills the southern and equatorial regions.

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Top-down projection — DESI DR1 BGS NGC + SGC

The same dataset projected onto the \(x\)–\(y\) plane (RA-projected comoving coordinates). This 2D view reveals the full sky coverage and the large-scale density contrasts with higher clarity than the 3D scatter.

Top-down projection (\(x\)–\(y\) comoving plane). The partial sky coverage of DESI DR1 BGS is clearly visible: the NGC occupies roughly the upper-left quadrant and the SGC the remaining area. The colour gradient from violet (low-z) to red (high-z) traces the increasing comoving volume with distance.