Arp 38: not that peculiar
An amateur astrophotographer captured Arp 38, a small edge-on spiral galaxy. Despite Arp's classification as having a low-surface-brightness companion, Hubble data shows the bright spot north of the galaxy's core is merely a bright HII region and star cluster, not a companion galaxy.
Background
- **Arp (Halton Arp)** was an American astronomer who published the *Atlas of Peculiar Galaxies* (1966), a catalog of 338 galaxies that appear unusual in shape, often featuring tidal tails, companion galaxies, or disturbed structure. His catalog became a key reference for studying galaxy interactions and mergers.
- **Arp 38** is entry #38 in that catalog. Arp classified it under "low surface brightness companions," meaning he thought a faint companion galaxy was nearby. The author's own high-resolution image, plus Hubble data, suggests that what Arp called a companion is actually just a bright star-forming region (H II region) inside the galaxy itself — so the galaxy is less "peculiar" than Arp believed.
- The post is from an amateur astrophotographer sharing their deep-sky image and processing notes (telescope: C9.25 Schmidt-Cassegrain, camera: IMX533 sensor). Technical details like "FWHM=4'" and "asinh stretch" describe image sharpness and the mathematical transform used to make faint structures visible on screen.
- "Walking noise" is a common CCD/CMOS artifact — faint vertical or horizontal banding caused by improper calibration frame subtraction.