NGC 2523 - Arp 9

Object: NGC 2523, 12.6m, 3' x 1.8', SB(r)bc spiral galaxy at a distance of 160 Mly (49 Mpc) in Camelopardalis. North is up and East to the left, frame is 11.5' x 10'.

Subimages: Unfiltered 24 x 600 sec (4 hrs). Bias/Dark/Flat calibrated. Final FWHM=2.5"
Scope: C11XLT EFL=2970 mm (f/10.5 effective)
Mount: Losmandy G11 with Gemini L4
Camera: ST8XME (0.63"/pixel) set to -35C
Guiding: Self-guide, ExpTime=1s, dithered
Acquisition and processing: MaxIm DL/CCD v4.5
Imaged on: Dec 25, 2006

NGC 2523 is a 140 kly diameter barred spiral galaxy with a prominent inner ring which just encloses the 47 kly long bar. It was catalogued as a "Split Arm" type by Arp, the northern arm clearly forking into two distinct star forming regions. In the paper Dynamical Simulations of NGC 2523 and NGC 4245 [1] this galaxy was used to compare the measured global pattern speed (~ 25 km/s/kpc), to a value obtained via a "sticky particle" model. The global pattern speed is an important parameter of the density wave theory which attempts to explain the abundance and seemingly long lived galaxy spiral patterns. The global pattern speed, which has units of velocity per distance from the nucleus, is the rate at which the density waves travel around the galactic disk. If you could travel at this speed around a galaxy the spiral arms would appear at rest. The above simulation also estimates the corotation radius to be 1.4 times the bar radius. At that radius the stars circulating the galaxy are traveling at the same speed as the density wave, closer in the stars move faster and further out the star move slower.

The faint galaxy 4.5' south of the NGC 2523, next to a double star, is Mailyan 26. In 1973 N. S. Mailyan published a paper [2] listing over 100 dwarf spheroidal galaxies. Unfortunately a revision of the catalog [3] raised doubts that a large fraction of the entries were not dwarf spheroidal but low surface brightness galaxies. From the above image I interpret Mailyan 26 as a low surface brightness spiral. I measure the integrated intensity to be 16.8 +/- 0.2 magnitude, and the angular extent 0.7' x 0.6'. Reference 3 lists the size obtained from the POSS "O" plate as 0.6' x 0.5'.

Mailyan 26, 16.8m, 0.7' x 0.6', low surface brightness spiral galaxy. Crop of linearly stretched unprocessed data (calibrated only) rescaled by 200%.
Note the cluster of very distant galaxies (20.5 to 22nd mag) in the bottom right corner.

[1] P. Treuthardt, H. Salo, R. Buta, accepted for publication in The Astronomical Journal.
[2] N.S. Mialyan, 1973, Astrofizika, 9, 33.
[3] B. F. Madore et al, 1994, Publications of the Astronomical Society of the Pacific, 106, 63-66.