NGC 7814 (HI)
This nearly edge-on galaxy has a striking dust lane across the nucleus
that remains prominent in the NIR.
NGC 7814.---S0/a: Edge-on system. Bright nuclear point source embedded
in a large, luminous, flattened bulge, cut by an obvious dust lane
along the major axis. The disk is very thin and imposed on the much
brighter bulge. There is no evidence for spiral structure, due to the
inclination of the disk. There is no evidence for star formation. Only
the presence of the dust lane prevents a classification of S0.
The nucleus of this galaxy is heavily obscured by a prominent dust lane,
splitting the spatial profile into two peaks (the slit was approximately
perpendicular to the dust lane). We extracted the more prominent of the
two peaks to obtain the spectra shown in Figure 2.
Aug 23/24, 1954
NGC 7814 is one of those centrally important textbook galaxies
where the various components of galactic structure are seen directly
because of the favorable aspect angle of the line of sight. The
central bulge is flattened, but not to the same degree as the
exceedingly thin disk which is the principal feature of NGC 7814. The
bulge light is smooth, giving no indication of recent star formation.
Bulge stars have not collapsed to a disk but retain the
semi-spherical shape of their initial energy of motion. This shape is
determined by the nearly spherical velocity ellipsoid of the
three-dimensional velocity distribution. Evidently, stars were formed
in the bulge in a time that was short compared with the (free-fall)
collapse time of the prototype galaxy gas (of about 10^9^ years);
otherwise, the collapse would have continued until gas-gas collisions
would have dissipated the potential energy of position, creating a
disk with no bulge. (See Chapter 4.)
On the other hand, the paper-thin disk, which is clearly a highly
dissipative structure, must have formed after the bulge because the
gas-gas collisions did occur, dissipating the gravitational energy via
radiation by ordinary atomic processes as the collapse of the
remaining gas proceeded to a plane. This collapse model, after Eggen,
Lynden-Bell, and Sandage (1962), with no dissipation in the halo
formation and strong dissipation in the disk, is almost self-evident,
simply from the form of NGC 7814.
Photometry of the bulge, together with velocity maps of the bulge
rotation, are given by Jarvis and Freeman (1985). Jarvis and Freeman
also discuss the dynamics of bulges as related to the fraction of the
support of the figure due to ordered rotation and the fraction due to
the kinematical filling of the phase space (i.e., concerning the
nature of the velocity ellipsoid, often called pressure support). A
definitive discussion of the surface photometry is by van der Kruit
and Searle (1982).
The galaxy is seen nearly, but not quite, edge on. The parallel
structure in the dust lanes, appearing as the fainter lanes below the
main lane in the print here, shows that we view the thin dust layer
from slightly above the plane on the bottom side of the image here,
seeing part of the plane in silhouette on the near side (bottom)
against the central bulge.
The morphological type is uncertain, of course, because of the
viewing aspect angle. The Sab type is supported by the size of the
central bulge and the absence of visible star formation in the disk,
which is, however, obscured by the dust in the very thin plane. But
the type is not Sc, as the bulge is too large, and there is no
evidence of robust star formation in the disk. The type is not Sa
because of the high dust content.
NGC 7814 was not detected by IRAS, Y89 or ourselves, or in radio
continuum by H87.
A.J., 70, 138, 1965.
Astrofizika, 4, 409, 1968.
Trudy Obs. Leningrad, 26, 48, 1969.
SA(s)ab: (de Vaucouleurs)
Very bright central bulge: 0.5 arcmin x 0.4 arcmin. Outer bulge: 2.0 arcmin x
1.2 arcmin. Strong, thin (0.1 arcmin) dark lane seen edge-on with secondary
layer of dark material.
Lick 13 and Heidelberg Veroff. Vol. 9, 1926 dimensions are for the bright
Interpolated value of B-V(0).
Ritchey, L'Evolution de l'Astrophotographie, S.A.F., Paris, 1929.
Handbuch der Ap. 5, 2, 843, 1933. (Plate 22)
Photograph and Photometry:
Ap. J., 120, 444, 1954.
B.A.N., 16, 1, 1961.
Vol. VIII, Plate 70. 3' x 0.8' in p.a. 132^deg^ Bright; no nucleus or whorls are
discernible, but it is doubtless a spiral seen edgewise. A remarkable, clear-
cut dark lane runs down its entire length. See Abs. Eff. 19 s.n.