NGC 5121.---S0: Bright nuclear point source. Inner bulge isophotes are
circular but become elliptical at larger radii. No evidence for a bar.
Very LSB disk with no evidence for internal structure.
Nuclear elongated structure (bar?).
March 10/11, 1980
103aD + GG495
A definite spiral pattern surrounds a bulge
and a lens, both burned out in this print of NGC
5121. The spiral features are thin, are tightly
wound, and are not massive, unlike the arms in
the other eight galaxies shown in this panel.
Because the arms are so subtle against the
relatively high surface brightness of the disk
through which they thread, the galaxy was classified
as S0_1_(4)/Sa in the RSA2. But because the
spiral pattern is so pronounced, we now adopt
the classification as very early Sa.
The multiplicity of the spiral pattern differs
from that in the other eight galaxies in this panel.
NGC 5121 has multiple arms, not simply two
symmetrical arms. This galaxy is the earliest of
the Sa multiple-arm spirals (MAS), which later in
the sequence are called filamentary or flocculent
(Elmegreen 1981) spirals. In them, the spiral
patterns are often difficult to trace within a given
arm; there is no given arm because the pattern is
fragmented into many small spiral segments. It is
a local pattern rather than one that has global
coherence (Kormendy and Norman 1979) that
gives rise to the so-called grand design (GD)
galaxies (Elmegreen and Elmegreen 1982),
which have two main, well-defined arms, which
define the large-scale pattern.
Both types of spirals exist from early Sa to
late Sc in the Hubble sequence. We maintain the
distinction throughout this atlas, tracing the
development of each type of arm pattern within
each section of the classification.
NGC 5121 is among the earliest Sa of the
MAS type. MAS-type examples include NGC
4699 (Hubble Atlas, p. 16; panels 78, 87, 118,
S12 here), NGC 2775 (Hubble Atlas, p. 10;
panels 78, 87, S12 here), NGC 1357 (panel 68),
NGC 7377 with its dust arms (panels 75, S14),
NGC 1371 (panels 64, 80, 88, and S3), NGC
6902 (panel 69), and NGC 1350, with its inner
arms in the disk (panels 71, 88, S3).
Extremely low surface brightness dwarf 6' north-following??
Filamentary arms, (R'): 1.1 x 0.95. Similar to NGC 7217.
Very bright center. Arms form (R'): 1.1 x 0.9.
Overexposed center, bright (r) in lens: 0.75 x 0.65, bright (R): 1.2 x 0.95
with knots. Planetary 11' north-following; other low surface brightness
Bright nucleus. Bright envelope. Dark crescent?
HA 88,2 dimensions (0.6 arcmin x 0.6: arcmin. series a') are for the nucleus