How complex are galaxies?
Methodology
Overview of the research methods used in the paper
Example of the S-curve:
2D manifold embedded in 3D
Compute \(k\)-nearest neighbors
→ edges of a graph
Draw a point
→ find shortest path to all others
Take a radius
→ count number of points in \([r, r+\Delta r]\)
\(r\)
\(\#(<r)\)
\(r\)
\(\#(<r)\)
How well does it perform?
Methodology
- Draw
- \(N\) points
- from \(D\)-sphere
- embed in 14 dimensions
- fill \(14-D\) dims with small (\(<10^{-2}\)) noise
- Measure \(D\) vs. \(N\)
Datasets
Photometric data
- COSMOS 2020 (Weaver+22)
- HAGN (Laigle+19)
14 wide bands
passive/SF split
+ 14 narrow bands
Results
Summary of the key findings and conclusions presented in the paper
COSMOS dataset
COSMOS dataset
HAGN
Both datasets broadly agree
HAGN
w/out noise
HAGN
w/out noise
abs. magnitudes
HAGN
w/out noise
passive only
HAGN
w/out noise
\(10^{10}<M_\star/\mathrm{M_\odot} < 10^{10.5}\)
How complex are galaxies?
How complex are galaxies?
*From wide-band photometry
Galaxies are not that complex
Wide-band photometry is 4-dimensional:
- noise
- redshift
- stellar mass
- SFR
Important to guide dimensionality reduction techniques (UMAP, SOM, VAE)
Physical underlying params?
- halo mass
- local density?
- gravitational shear (Paranjape+18)?
- tidal misalignment (Moon&Lee 24, Cadiou+22)?