Andromeda IV (original) (raw)

Irregular Galaxy or Star Cloud Andromeda IV (And IV, PGC 2544), type Irr ?, in Andromeda

[ ](Pics/and4%5Fmb%5Flab.jpg)

RA:

00 : 42.5

Dec:

+40 : 34

Type:

Irr ?

RV:

256 km/s (heliocentric)

Distance:

2900: kly ? 21000 kly ?

Apparent Dimension:

Diameter:

Brightness:

Abs. Mag:

Mass:

Discovered by Van den Bergh in 1972.

Andromeda IV was discovered within a survey by Sidney van der Bergh with the Palomar 48-inch (1.2-meter) Schmidt telescope, together with And I, And II, and And III (see van den Bergh 1972). It was initially classified as dwarf elliptical or spheroidal, then as dwarf irregular galaxy, although already van den Bergh in his discovery paper considers that it might be an old star cloud in the disk of the Andromeda Galaxy, M31.

Investigations of 1991 have indicated that Andromeda IV might be a large, outlying open cluster or star cloud in M31, not an independent galaxy, as its stellar population is probably homogenously young, and it appeared from these measurements that this object participates in M31's galactic rotation (Jones 1993).

Semi-recent re-investitagion with the Hubble Space Telescope (Ferguson, Gallagher and Wyse, 2000) has brought up evidence that, instead, it might be a more remote background galaxy if irregular type, seen through the disk of M31. The moderate surface brightness reported here are consistent with And IV being a small dwarf irregular galaxy, perhaps similar to Local Group dwarfs such as IC 1613and Sextans A. The authors estimate its distance between 5 and 8 Mpc (16 to 26 million light years), which places it well outside the Local Group. It may be associated with another loose group of galaxies containing NGC 784, IC 1727, and UGC 64.

The image in this page was obtained by Matt BenDaniel; it was cropped from a larger image of M31. Matt just caught And IV at the limit of detectability.

References:

• Sidney van den Bergh, 1972. Search for Faint Companions to M31. Astrophysical Journal, Vol. 171, pp. L31-L33 [ADS: 1972ApJ...171L..31V]
• Joseph H. Jones, 1993. CCD photometry of Andromeda IV - Dwarf irregular galaxy or M31 open cluster? Astrophysical Journal, Vol. 105, pp. 933-937 (03/1993) [ADS: 1993AJ....105..933J]
• Annette M. N. Ferguson, J. S. Gallagher, and Rosemary F. G. Wyse, 2000. On the Nature of Andromeda IV. The Astronomical Journal, Volume 120, Issue 2, pp. 821-832 (08/2000) [ADS: 2000AJ....120..821F]

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Hartmut Frommert
Christine Kronberg
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Last Modification: October 6, 2003