NGC 7469 in Pegasus
November 2022 - Galaxy of the Month
Our challenge this month is the tight galaxy pair in Pegasus catalogued as NGC 7469 or Arp 298. Arp included the pair as part of his double galaxies classification. The brighter of the pair, NGC 7469, was discovered by William Herschel in 1784. The other galaxy in the pair, IC 5283, was found by Bigourdan in 1891 using a 12.4” refractor.
Both galaxies are spirals with NGC 7469 being a barred spiral hosting an AGN of the Seyfert I type. NGC 7469 was one of the 6 galaxies that Carl Seyfert included in his original 1943 paper on Type I Seyfert galaxies. It is also a luminous infrared source (LIRG) with the source powered by a starburst in a circumnuclear ring.
The two galaxies are gravitationally interacting and the interaction appears to have pulled a tidal tail from IC 5283 and also initiated a strong burst of star formation in IC 5283. The interaction may also be the cause of the starburst in NGC 7469. The UV images from GALEX show strong star forming activity in both galaxies and this may be the reason it was included by Markarian in his blue galaxies catalogue. There also appears the be a neutral hydrogen bridge (HI) between the two galaxies.
The pair lies about 200 million light-years away. If they are at this distance then NGC 7469 will be about the same size as our Milky Way galaxy. The galaxies appear to be an isolated pair, i.e. not part of any galaxy group. There was some thought that they might be part of the Pegasus I galaxy group but they have been shown to lie much further away than that group.
The pair were selected to be one of the first targets for the James Webb Space Telescope (JWST). There is also a nice Hubble image of the pair on the ESA/Hubble website.
Two supernovae have been recently found in NGC 7469: SN 2000ft and SN 2008ec (type Ia).
As this galaxy pair is so close together it is going to require high power to separate them. NGC 7469 itself should be fairly easy to see but IC 5283 is much fainter at around 14.8th magnitude so it is going to require a large telescope to find. It is also an edge on galaxy that will make seeing it even harder.
The Night Sky Observer's Guide Vol. 1 suggests that 30cm may be needed to see NGC 7469 and 45cm to see IC 5283 which will appear as not much more than a faint oval patch. The pair do lie in a pretty star field however. Alvin Huey’s observations suggested that with a 55cm (22”) telescope NGC 7469 is very bright but IC 5283 is still no more than a faint streak.
Owen Brazell - Galaxy Section Director