The region of the Virgo Supercluster is delineated here using Dn-sigma distances. The Virgo cluster is apparent as a concentration at SGX = -4 Mpc, SGY = 15 Mpc, but the sampling is sparse enough and the distances are uncertain enough to be sure of the detailed structure. In order to use the same coordinates as SBF, the Dn-sigma and TF distances here have been converted to Mpc by a Hubble constant of 80.
The point size indicates height above the supergalactic plane, large points are at positive SGZ, small points are at negative SGZ. The color of the points shows the redshift of the galaxy in the Sandage, Tammann, Yahil Local Group reference frame. Note that redshift is only used for point color and does not enter into radial distances.
TF distances are now used to show the region of the Virgo Supercluster. The Virgo cluster has pretty much disappeared because spirals have less tendency to cluster than early-type galaxies. There is a very substantial sampling across the region, but no clear pattern of clustering or color (indicating consistent redshifts) except for the large region in Ursa Major (SGX = 6, SGY = 14) where there many galaxies with very similar velocities.
The Virgo Supercluster is at last charted out with the SBF distances. The Virgo cluster is now an obvious concentration of galaxies. Errors in distance give rise to a "Finger of God" extension of a cluster along the line of sight, as is seen in Leo (small points at -0.5, 9.0) and the NGC 5846 group (large points at -13, +19). This extent is consistent with our error estimates, and suggests that the Virgo cluster itself has a substantial spread along the line of sight, since we believe our errors to on the order of 0.5 Mpc in the Virgo core region.
The overlay shows the group membership and names of some of the points displayed here. The Virgo Southern Extension looks like a squirrel tail curving south from the cluster around towards us. The Virgo W cloud is seen as four points at -8, +26, very substantially behind the main cluster. There is also a filament of galaxies stretching from Virgo out to the W cloud, the most prominent member being NGC 4365.
There are occasional discordant points, such as the large, white one at +0.5, +11, but these are generally galaxies which are far above the supergalactic plane whose x, y projection is not a good representation of its true distance.
If you gaze at the SBF map of the supercluster long enough, you start to see constellations, such as the Great Squirrel, comprising the Tail, Body (Virgo core), Head (W cloud), and Arms (Coma I and Ursa Major). Another interesting feature is the Great Crevasse, the apparent division of the Virgo core into two pieces with a gap in between. Although the gap is almost across the line of sight, there are several reasons why we think it may be real (formally it's about 2.8 sigma significant). There is a trend for the southern part of the Virgo core around NGC 4472 to lie in the near part, and the more northern section around NGC 4406 and NGC 4374 to lie in the far part. Also, NGC 4486, M87, lies right in the gap between the two sections. Better measurements will eventually confirm or deny the existence of this bifurcation, but it is clear that the Virgo cluster, including the core, is a dynamically young system.
Incidentally, NGC 4526, the host of SN1994D, is found to be in the near part of the Virgo core. If true, SN1994D, an otherwise bona-fide type Ia supernova, was about 0.5 magnitude brighter than the relation of the CTIO collaboration and Riess, Press, and Kirshner would allow. It appears that SNIa may be good standard candles, but the distribution is certainly not a Gaussian with a dispersion of 0.15 magnitudes, but has an extended tail which is perhaps skewed to the bright end. We also find that SN1972E, in the nearby Centaurus group, is brighter by perhaps 0.5 magnitude than one would guess from a mean SNIa brightness of V = 12.2 in Virgo, and the relative distance between Virgo and Centaurus derived from SBF.
Taking in a larger view, the SBF survey is shown to within about 25 Mpc of our location. Some of the prominent clusters are apparent, such as Virgo, Fornax at -1, -12, and Centaurus at -25, +12.
If you know what you are looking for, the results of the rest of this talk are apparent. Virgo and Fornax are almost equidistant from the Local Group, but Virgo is blue-green (about 1000 km/s) and Fornax is green-yellow (about 1500 km/s). This is the dipole in velocities seen from the Local Group as a result of the Virgo infall. There is also a large region of space centered on the Virgo cluster where there is little change in color, the blue-green mostly indicating 1000 km/s. This is the so-called S-wave distortion of the Hubble diagram, where velocities on the near side of an infall are somewhat large, and velocities on the far side are somewhat small relative to the Hubble flow. Thus, the Virgo infall is obvious in the overall flow pattern, and doesn't depend on the precise velocity of the Virgo core at all.
Another feature which springs to view is that there is an anisotropy in the Hubble constant. In the SGX direction the velocities rapidly climb to pink and white colors, whereas in the SGY direction they do not rise as fast with distance, even allowing for the distortion in velocity from the Virgo infall. This is the local quadrupole distortion of the velocity field, presumably imposed by the tides from distant masses external to the Virgo supercluster.
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