Object of the Week October 20, 2013 – NGC 450/UGC 807 a discordant galaxy pair in Cet

[Uwe Glahn]

NGC 450 / UGC 807

Cetus

RA: 01 15 30.4
DEC: -00 51 41

Size: 3’ x 2.4’
Mag NGC 450: 11.6v
Mag UGC 807: 15,7b

Discovered by F.W. Herschel in the year 1785 - NGC 450 seems to be a normal SAB(s)cd spiral in the sky. “Hand GoTo friendly” 12’ NE of the 5,7mag bright 38 Cet the galaxy should be visible even with a small 4” aperture telescope.

A second view shows a fainter companion at the NE edge – UGC 807. The different redshift and radial velocity numbers seems to show an unmistakable situation. While NGC 450 is calculated 64 Mio Lj, UGC is around 8 times more distant with 484 Mio Lj (NED). Rubin and Ford (http://articles.adsabs.harvard.edu//full/1983ApJ...271..556R/0000556.000.html?high=51e848784926878) measured their rotational velocities 1983 and concluded that both galaxies are not physically associated.

Moles et all (http://articles.adsabs.harvard.edu//full/1994ApJ...432..135M/0000135.000.html?high=51e848784926878) again studied the galaxy pair 1994 and conclude the opposite. Their studies showed that both galaxies interacting with each other.

Nevertheless the observation of these two “discordant” galaxies seems very interesting. With a brightness of 15,7bmag the fainter UGC should be visible as a faint spot from perhaps 12”-14” range? A 20” showed the UGC as a prominent companion with hints of elongation. The 27” showed the pair as a wonderful object – both galaxies bright and easy.

Aside from the companion NGC 450 sowed some bright HII regions at the eastern edge which should be in reach of a 16”-18” telescope.

SDSS
936

HST
937

sketch with 27" (27", 419x, NELM 6m5+, Seeing III)
938
inverted version (http://www.deepsky-visuell.de/Zeichnungen/NGC450.htm)

And don’t forget…

“Give it a go and let us know!”

Good luck and great viewing!

(sorry for the late post)

[ChristianR]

Hi Uwe,

thanks for the suggestion, I put the object to my list for the next weekend.

I've major doubts to be able to see faint companion with 12";
however, I'll at least try it.

[Steve Gottlieb]

I took at look at this interesting "overlap" pair a couple of years back with Jimi's 48-inch and missed the structure you sketched on the west side of the galaxy.

At 610x this double system is dominated by NGC 450, which appeared bright, large, 2.3' diameter. Sharply concentrated with a relatively large 30" bright core, surrounded by a very large, low surface brightness halo. The halo is slightly asymmetric and more extensive on the west side.

Three faint "stars" are superimposed on the east side of the galaxy; two appear stellar, but the faintest and most westerly object is clearly "soft" at 610x. These are apparently HII knots in the galaxy and the southeast object is listed in NED as UM 311 from the University of Michigan Emission Line Survey. UGC 807 is attached at the NE side of the halo, 1.4' between centers. UGC 807 appeared fairly faint, fairly small, elongated 5:2 SW-NE, 0.7'x0.3', even surface brightness except for a very small brighter nucleus.