Andromeda IX

For the star, see 9 Andromedae.

Andromeda IX (And 9) is a dwarf spheroidal satellite of the Andromeda Galaxy. It was discovered in 2004 by resolved stellar photometry from the Sloan Digital Sky Survey (SDSS), by Zucker et al. (2004).^[2] At the time of its discovery, it was the galaxy with the lowest known surface brightness, Σ_V ≃ 26.8mags arcsec⁻² and the faintest galaxy known from its intrinsic absolute brightness.^[2]

Andromeda IX
Observation data (J2000 epoch)
Constellation	Andromeda
Right ascension	00h 52m 53.0s[1]
Declination	+43° 11′ 45″[1]
Redshift	-216 ± ? km/s[1]
Distance	2.50 ± 0.08 Mly (766 ± 25 kpc)[2]
Apparent magnitude (V)	16.2
Characteristics
Type	dE[1]
Notable features	Satellite galaxy M31
Other designations
And IX, PGC 4689222[3]

It was found from data acquired within an SDSS scan along the major axis of M31, on October 5, 2002. Its distance was estimated to be almost exactly the same as that of M31 by McConnacrchie et al. (2005). Star formation history and dust production in Andromeda IX, as the closest satellite to M31, have also been investigated by Abdollahi et al. (2023).^[4]

See also

• List of Andromeda's satellite galaxies