As redshift measurements accumulated in the 1970s and 1980s, it was widely recognized that there was a need to assemble these data into comprehensive catalogs. Beginning with the publication of the CfA redshift survey in 1983 (Huchra et al. 1983), all major redshift surveys (see the Chapter by Strauss in this volume) led to electronically available databases in fairly short order.
Comparable efforts involving redshift-independent distance measurements have been slower in coming. This is largely due to the issue of uniformity. Whereas redshift measurements by different observers rarely exhibit major differences, redshift-independent distances obtained by different observers can, and generally do, differ systematically for any number of reasons. In some cases the origin of such differences is different calibrations of the DI. In others, the calibrations are the same but the input data differ in a subtle way. Finally, the way statistical bias effects are treated (Section 9) often differs among those involved in galaxy distance measurements. For all these reasons, it is not possible simply to go to the published literature, find all papers in which galaxy distances are reported, and lump them together in a single database. Instead, individual data sets must be assembled, their input data and selection criteria characterized, their DI relations recalibrated if necessary, and the final distances brought to a uniform system. Only then can the resultant catalog be relied upon - and even then, caution is required.
The first steps toward assembling homogeneous redshift-distance
catalogs were taken in the late 1980s by David Burstein.
His goal was to combine the then newly-acquired
Dn- data
from the 7-Samurai group (Section 4) with
the extant data on spiral galaxy distances, especially the infrared
TF data obtained by the Aaronson group
(Section 3).
Burstein's efforts produced two electronic
catalogs, the Mark I (1987) and Mark II (1989) Catalogs of Galaxy Peculiar
Velocities. (3)
Burstein's chief
concern was matching the TF and Dn-
distance scales. As there
are, by definition, no galaxies that have both kinds of distances,
this matching could be carried out through a variety of overlapping
approaches. The approach decided upon by Burstein, in consultation
with the other 7 Samurai, was to require the Coma cluster spirals
and ellipticals to have the same mean distances.
Although this procedure was imperfect, the Mark II catalog
was considered reliable enough to be
used in the first major effort to constrain the density parameter
0 by comparing
velocities and densities
(Dekel et al. 1993).
With the publication of a number of large, new TF data sets in the early
1990s, the need for a greatly expanded redshift-distance catalog became
apparent. An important development was the superseding of the majority of the
older infrared TF data, obtained by the Aaronson group, by CCD-based
(R-and I-band) TF data. Han, Mould and coworkers
(Han 1991,
1992;
Han & Mould 1992;
Mould et al. 1991, 1993)
obtained a full-sky cluster
TF sample, based on I -band magnitudes and 21 cm velocity widths,
comprising over 400 galaxies.
Willick (1990,
1991)
and Courteau
(1992;
Courteau et al. 1993)
gathered R-band TF data in the Northern
sky for over 800 galaxies in total. The largest single contribution was that of
Mathewson et
al. (1992)
who published an I-band
TF sample of 1355 galaxies in the Southern sky. Despite
the influx of the new CCD data, one portion of the infrared TF database of
the Aaronson group was not rendered obsolete: the sample of over
300 local (cz
3000 km s-1) galaxies first observed in
the late 1970s and early 1980s
(Aaronson et al. 1982).
This local sample was, however, subjected to a careful reanalysis by
Tormen & Burstein
(1995),
who rederived the H-band magnitudes
using a more homogeneous set of galaxy diameters and
inclinations than was available to the original researchers a decade earlier.
In 1993, a group of astronomers (myself, Burstein, Avishai Dekel,
Sandra Faber, and Stéphane Courteau) began the process
of integrating these TF data and the existing Dn- data into a new
redshift-distance catalog. Our methodology is described in detail
in Willick et al.
(1995,
1996),
and portions of the catalog are presented in
Willick et al. (1997).
The full catalog, known as the
Mark III Catalog of Galaxy Peculiar Velocities,
is quite large (nearly 3000 spirals and over 500 ellipticals,
although this includes several hundred overlaps between data sets)
and is available only electronically, as described in
Willick et al. (1997).
Building upon the foundation laid by Burstein in the Mark I and II catalogs, the Mark III catalog was assembled with special emphasis placed on achieving uniform distances among the separate samples it comprises. Four specific steps were taken toward this goal. First, the raw data in all of the TF samples underwent a uniform set of corrections for inclination and extinction (cf. Section 3.2). Second, the TF relations for each sample were recalibrated using a self-consistent procedure that included correction for selection bias (Section 9). Third, final TF zero points were assigned by requiring that the TF distances of objects common to two or more samples agree in the mean. This step ensures that the different samples are on similar relative distance scales. The global TF zero point was determined by the fully-sky Han-Mould cluster TF sample. (As explained in Section 3, this zero point was such that the distances are given in units of km s-1, not Mpc.) Fourth, the spiral and elliptical distance scales were matched by applying the POTENT algorithm (see the chapter by Dekel in this volume) to each separately, and requiring that they produce statistically consistent velocity fields.
In parallel with the efforts of the Mark III group, similar enterprises have been undertaken by two other groups. Brent Tully has also assembled and recalibrated much of the extant TF data. Riccardo Giovanelli, Martha Haynes, Wolfram Freudling, Luiz da Costa, and coworkers have acquired new I band TF data for ~ 2000 galaxies, and have combined it with the sample of Mathewson et al. 1992). Initial scientific results from each of these efforts have been published (Shaya et al. 1995; Giovanelli et al. 1996; da Costa et al. 1996), and the catalogs themselves will soon become publically available.
New distances for elliptical galaxies, now mostly from
the FP rather than Dn- (Section 4),
continue to be obtained as well. Jorgensen et al. (1995a,b)
have published distances for E and S0 galaxies in 10 clusters out
to 10,000 km s-1. The EFAR group (Burstein, Colless, Davies, Wegner,
and colleagues) are now finishing an FP survey of over 80 groups
and clusters at distances between 7000 and 16,000 km s-1
(Colless et al. 1993;
Wegner et al. 1993,
1996;
Davies et al. 1993).
Implicit in all this ongoing work is that the Mark III catalog,
like its predecessors, is just one step along a path still
being traveled. Just as the Mark III data consists in part
of recalibrated data alreay present in the Mark II, so
will future catalogs incorporate, partially recalibrate,
and expand upon the Mark III.
Of particular note are the distances coming from
the SBF survey of Tonry and coworkers
(Tonry et al. 1997;
cf. Section 5).
The SBF distances are much more accurate
than either TF or Dn- and can provide important checks on them.
Tonry et al. (1997)
have taken initial steps toward
such an intercomparison, and the preliminary results, which
suggest mutally consistent results among SBF, Dn-
, and
TF, are encouraging. Little comparison of SNe and BCG distances
with other DIs has yet been carried out, but will be in the coming
years. It is reasonable
to hope that, by the turn of the century at the latest, the available
redshift-distance catalogs will be superior, in terms of
sky coverage, accuracy, and homogeneity, to the best we have today.