NGC 3945 RLBT+..-Double barred (Kormendy 1979, 1982; Wozniak et al. 1995; Erwin
& Sparke 1999, 2003; Erwin 2004) galaxy with prominent outer ring. Exhibits
complicated kinematic structure. The rotational velocity has local minima around
18", then rises toward smaller radii and reaches a local maximum around 8"
before it falls off to the center. The dispersion profile has very strong local
minima-drops from ~=150 km s^-1^ to ~=110 km s^-1^-at r ~= 8" but then rises
again toward the center. This galaxy shows exceptionally strong h_3_ moments of
up to ~=0.25 which are anti-correlated with velocity in the inner region but
become positively correlated at about 20". The h_4_ moments are similarly strong
(up to 0.2) with significant central depression. The LOSVDs do show significant
low velocity shoulders at radii between 2" < parallel r parallel < 10" which is
indicative of a distinct kinematic component (see Section 5.7). The minor axis
profile also shows a local depression in velocity dispersion but at r ~= 3.5",
the central dip in h_4_ is seen as well. We measure slight rotation (i ~= +/- 25
km s^-1^) along the observed position angle of i = 64^deg^ and a significant
central offset of the velocity (~=40 km s^-1^). The major axis velocity profile
shows that a slit position offset of 1" is sufficient to explain the central
velocity peak. A visual inspection of the preacquisition image confirmed that
such an offset was indeed present (about 0.6").
NGC 3945. Strong outer ring produces extreme Type II profile; the inclination
has been updated using a high-quality r-band image from the WFC of the 2.5-m INT
(INT-WFC, La Palma; Erwin et al., in preparation).
NGC 3945 (double bar + inner disk): Kormendy (1979,1982a) and
Wozniak et al. (1995). See Erwin & Sparke (1999) and Erwin & Sparke
(2003); for a detailed study of the inner disk, see Erwin et al. (2003).
Wozniak et al. (1995) suggested this galaxy might be triply barred
(it is listed as such by Moiseev 2001); however, Erwin & Sparke (1999)
used HST images to show that it was double-barred, with a large inner
disk dominating the region between the two bars. Similar bar-disk-bar
systems are NGC 3368, NGC 4785, and NGC 7187.
Feb 1/2, 1981
NGC 3945 is a premiere example and a
prototype of the SB0_2_ subclass of barred S0
galaxies. The central bulge is flattened, its major
axis aligned with the major axis of the external
ring, as is common for this form, repeatedly
discussed. The fuzzy indistinct bar, shown well in
the insert, terminates on the moderately sharp
edge of the disk. A fully detached (at least at high
luminosity levels) external ring surrounds the
inner regions. Although there are intensity variations
around the outer ring, the ring can be
traced over its complete circumference.
PGC 037258 = NGC 3945. Type = RLBR+.., S_T_ = Rb (b = Buta, Catalogue of
Northern Ringed Galaxies, in preparation).
SB(rs)0+ (de Vaucouleurs)
Very small, bright nucleus in an inner lens: 0.43 arcmin x 0.15 arcmin on a
faint bar: 0.95 arcmin x 0.25 arcmin with small blobs. Faint (R):
4.5 arcmin x 2.0 arcmin on POSS.
All dimensions are for the bright part only.