SDSS DR16 Crossmatch

Galaxy10Crossmatcher (src/astrovision/crossmatcher.py) matches each Galaxy10 position to SDSS DR16 (vizier:V/154/sdss16) with the CDS XMatch service, in batches of 5,000 sources, and caches the result as a compressed CSV.

Key results

17,665

Galaxies matched

objID present · 3″ radius

99.6%

Match rate

of all Galaxy10 images

5,652

With spectroscopic z

SDSS spectra

0.796

Median g−r

all matched galaxies

“5,651 matches” in older descriptions

Some project descriptions quote 5,651 matched galaxies (5,651, about a third of the dataset). That count is the number of galaxies with an absolute magnitude, which requires a spectroscopic redshift; it is not the match rate. The photometric match covers 17,665 galaxies.

Method

Step	Detail
Catalogue	SDSS DR16 photometry via VizieR `V/154/sdss16` (2.97″ is the largest separation retained)
Radius	3.0″ (`radius_as` default), nearest counterpart kept
Colours	u−g, g−r, r−i, i−z, u−r from the five SDSS magnitudes
Populations	blue cloud: u−r < 2.22; red sequence: u−r > 2.55; green valley: in between
Absolute magnitude `Mr`	r minus a distance modulus from cz/H₀ with H₀ = 70 km/s/Mpc; uses `zsp`; galaxies without it get no `Mr`

Populations

Population	Galaxies	Share of matches
Blue cloud	7,357	41.6%
Green valley	3,204	18.1%
Red sequence	7,104	40.2%

Source: data/master_synthesis.csv, column population. Per-class fractions: Morphology Classes page.

Colour discriminates morphology: in pairwise Kolmogorov–Smirnov tests of the g−r distributions, 44 of 45 class pairs differ at p < 0.01 (notebook 05).

Provenance. Model scores in this section are copied from the output cells of the AstroVision notebooks (and, for DINOv2 per-class recall, read from an exported figure). The documentation data pack contains no metrics file for them, so they cannot be re-derived from the pack; the cell of origin is listed for each value in _facts/astrovision/FACTS_INDEX.md §3 and shown when hovering over a number.

Limits of the derived quantities

Mr ignores K-corrections and extinction and assumes a Hubble-flow distance: it is a crude luminosity proxy, valid only for the galaxies with zsp.
The match is positional only; at 3″ some counterparts may be neighbours rather than the target galaxy.
The u−r thresholds are fixed constants in the code (attributed there to Baldry et al. 2004), not fitted to this sample.