NGC 3631: this is a nearly face-on galaxy, and thus although we
use a very rich catalog, the values of PA and IA are not very well
constrained. We adopt the value of the PA derived in the kinematical
analysis of Knapen (1997). However, the kinematic analysis did not
give a value for the IA, so we adopt the mean of our methods for
this angle, which is in rough average with the photometric values.
NGC 3631. The largest row, as it were splits the spiral arm into two.
The only row in the galaxy NGC 5085 looks similarly (see ).
Remarkably, the spiral on the diametrically opposite side also branches.
NGC 3631 is fairly symmetrical with two major arms and several divisions. It
forms a nearby group together with NGC 3178, NGC 3898, NGC 3953 and NGC 3992 in
Ursa Major. It has had multiple supernova events (Richter & Rosa 1988). The
galaxy is practically face-on. CO seems to be fairly evenly distributed with a
smooth fall-off except in the southern direction where no emission is detected.
No CO is detected beyond 30" from the centre in any of the observed directions.
Feb 4/5, 1981
The grand design nature of the arms in this
striking spiral is evident, as is the larger disorder
(higher geometrical entropy) of the pattern
compared with previous Sbc galaxies of earlier
luminosity classes on the preceding eight panels.
NGC 3631 is the prototype of this later SbcII
The two principal spiral arms begin near the
center and become evident as luminous structures
at the rim of the central, high-surface-brightness
disk. Secondary arms of lower surface
brightness branch outward from these two
principal inner arms.
Bright HII regions are present in all the
arms; the rate of recent star formation is
moderate-to-high. The largest HII regions
coalesce at this angular resolution and have a
combined core diameter at the 3" level. The
redshift of NGC 3631 is v_o = 1238 km/s.
Plate 2 Large Inner Subsystems
=MCG +09-19-047 = Arp 027 = NGC 3631; 10.91m, V_0_=+1162 (RC1),
At the right is a fine superassociation and a straight long subsystem
diverging from the spiral arm. The first one is about 44" or 5000 pc in
= Arp 027 [Note correction to RC2.]
Astrofizika, 6, 367, 1970.
Mem. S.A. Ital., 42, 145, 1972 = Cont. Asiago No. 254.
Astrofizika, 6, 367, 1970.
Obs., 88, 239, 1968.
HII Regions and Distance Modulus:
Ap. J., 194, 559, 1974.
Inf. Bull. Var. S. No. 113, 1965.
IAU Circ. No. 1930, 1965.
Ast. Tsirk. No. 349, 1965.
Inf. Bull. Var. S., No. 113, 1965.
Mem. S.A. Ital., 42, 145, 1971 = Cont. Asiago No. 254.
SA(s)c (de Vaucouleurs), Sc- (Holmberg)
In Arp's class "spiral galaxies in one heavy arm"
"Note straight arm, absorption tube crossing from inside to outside of south
SN 1964a, 1965l
Small, bright nucleus in a bright core: 0.3 arcmin x 0.3 arcmin. 2 main
massive, partially resolved regular arms with some branching.