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The main catalog (Part II of this volume) is composed of 21 columns containing the following data:

Column 1: List of Objects

All objects that are galaxies in the original Shapley-Ames Catalog are listed. They are shown in order of Right Ascension (1950). Since the best available positions are used, the sequence has occasionally been changed from the original SA.

Three SA objects have been omitted because they are not galaxies: NGC 643 is a cluster in SMC, NGC 2149 is a galactic, diffuse nebula, and NGC 6026 is a planetary nebula.

The identification of a few galaxies in the present catalog deserves comment.

NGC 1042: The Shapley-Ames galaxy NGC 1048 is a very faint spiral that clearly does not belong in the catalog. There is, however, a nearby bright spiral, NGC 1042, which should be included. We therefore assume that NGC 1048 in the original SA should read NGC 1042.

NGC 2646: It has been proposed (Seyfert, 1937; Hubble, private notes; RC1; RC2) that the Shapley-Ames galaxy NGC 2646 (BT = 12m.95) should be replaced by the Sa spiral IC 520 (mc = 12m.68). Although the latter galaxy is apparently somewhat brighter, actually both galaxies should have been included. We retain NGC 2646, whose position is correctly given in the original SA, and we list IC 520 in Appendix A among the known galaxies that should have been included by Shapley and Ames.

NGC 4183: The SA lists NGC 4160, but Seyfert's (1937) suspicion that this object is a star has been confirmed by de Vaucouleurs and de Vaucouleurs (RC1). Although the positions leave some discrepancy, the spiral galaxy referred to by Shapley and Ames can only be NGC 4183.

NGC 4342: The nomenclature of NGC 4342 has created considerable confusion in the past (Herzog, 1967). In spite of this, it is possible to relate all relevant observations (position, type, magnitude, velocity) unambiguously to this galaxy. To avoid future confusion, Herzog has proposed that the galaxy be exclusively referred to by its second designation, IC 3256. This has been followed by de Vaucouleurs et al. (RC2), but other recent authors still use the NGC designation (e.g., Nilson, 1973). For historical reasons we retain the designation NGC 4342 here.

NGC 4889: The Shapley-Ames galaxy listed as NGC 4872 is most likely NGC 4889 (Stebbins and Whitford, 1952), which is the brightest member of the Coma cluster.

IC 5179 = IC 5181: The Shapley-Ames galaxy IC 5186 is actually the galaxy IC 5179, which carries also the designation IC 5181 (RC2, p. 337; Corwin, 1977).

New 2: This galaxy is NGC 4507. 1 For historical reasons, we have maintained the designation New 2 of Shapley and Ames.

Two galaxies are designated HA85 (= Harvard Annals, Vol. 85) in the SA. To avoid conlusion, they are listed here as HA85-1 (= A 0509-14) and HA85-2 (= A 1852-45).

The present catalog contains 1246 entries.

Column 2: Alternative Designations for the Shapley-Ames Galaxies

These may prove useful for identification purposes, but completeness was not attempted. For the identification of Markarian objects (``Mark''), the Markarian lists I-X were consulted. We are greatly indebted to Dr. Mira P. Véron for a complete list of certain and probable radio sources (the latter are marked ``?''), which are identified with Shapley-Ames galaxies on the basis of the Catalog of Extragalactic Radio Source Identification (Véron and Véron, 1974; updated version, 1978). Two radio source identifications (with NCC 3689 and NGC 5444) given in the RC2 have not been confirmed.

Columns 3 and 4

The 1950 positions of the galaxies as given by Sandage (1978) or, where not given, from de Vaucouleurs et al. (RC2). For 46 southern galaxies, accurate positions were taken from Holmberg et al. (1974, 1975, 1977, 1978a, 1978b, 1979).

The decimals shown correspond to the accuracy with which the positions are known.

Columns 5 and 6

The Galactic Longitude and Galactic Latitude (1950) as given by de Vaucouleurs et al. (RC2).

Columns 7 and 8

The Supergalactic Longitude and Supergalactic Latitude (1950) as given by de Vaucouleurs et al. (RC2).

Column 9: The Hubble Type and, where applicable, the Luminosity Class

The classification was made by Sandage independently of previous determinations, but following the precepts set out elsewhere (Sandage, 1961, 1975a). The galaxies are classified in the sequence:

- Sa Sb Sc Sd Sm Im
E0 - S0 -
- SBa SBb SBc SBd IBm

with intermediate classes (S0/a, etc.) and a new class, ``Amorphous,'' which replaces Irr (Sandage and Brucato, 1979). A few galaxies, mainly spirals, defy a definite classification. At this writing, some of the galaxies have inadequate plate material and may eventually be found to be normal or to have only minor peculiarities. As there are less than 20 such cases, at least 98 percent of the catalog galaxies can be fitted into the revised Hubble system.

Descriptive terms, such as ``pec'' (= peculiar), ``disrupted,'' ``tidal.'' ``ring'', ``jet'', and ``edge on,'' have been added in several cases. Barred spirals are designated as SB, intermediate types as S/SB.

The presence of an inner ring structure is indicated by (r) following the spiral subclass [e.g., SBab(r)]. Those spirals where the arms spring from the ends of the bar or are traced into the center are indicated by (s). Intermediate cases are designated with (rs). Where no information is given on the presence or absence of an inner ring, no decision could be made. Outer rings surrounding the galaxy are indicated by R preceding the type (e.g., RSa).

The E and S0 galaxies were classified according to their flattening, which, following Hubble, is defined as 10(a-b)/a. The subdivision of S0 galaxies into S01, S02, S03 according to the absence or the presence of dust is explained in Sandage (1961). Note that the subdivisions SB01, SB02, and SB03 in barred spirals refer to the character of the bar and not to the presence of dust, as explained in Sandage (1961).

The spiral and very-late-type galaxies are classified into luminosity classes as originally proposed by van den Bergh (1960a, 1960b, 1960c). The luminosity class of a spiral or Im galaxy is estimated from purely morphological features: the presence of spiral arms, surface brightness, and the degree of order (i.e., the coherence of the pattern and the arm thinness). The earliest class is called ``I,'' the latest class is ``V'' (not represented in the present catalog, but illustrated in the reproductions). Intermediate classes are given, either as half-class steps (e.g., III-IV) or in decimals (e.g., I.8), as explained by Dressler and Sandage (1978). Although the same symbols I-V are adopted as used by van den Bergh, the present classes cannot be assumed to correspond necessarily to his system. In particular, the calibration in absolute magnitude may not be the same. If a calibration of the present luminosity classes in absolute magnitude is attempted from the listed data, it should be remembered that the present catalog represents a magnitude-limited sample. The bias as a function of redshift in such a sample is of course severe (Sandage, Tammann, and Yahil, 1979) and must be accounted for (Tammann, Yahil, and Sandage, 1979).

The reliability of the classification depends on the angular size of the galaxy, the inclination in the case of spiral and Im galaxies, the quality of the available plate material, and strongly on the scale of the plate. A number of large-scale plates were used here for the first time; hence our classes may differ from those assigned by van den Bergh (1960c).

Our classification is rather conservative in the sense that the given types should be in error by not more than a subtype, and the luminosity classes in the mean by not more than half a luminosity class. The errors may be somewhat larger in those cases where small-scale plates had to be used or when the sky survey prints were the only source. Larger than average errors are indicated by ``:'' or ``?'' following the classification in cases where the galaxy may intrinsically defy a simple classification. In cases where the plate material is clearly insufficient, the types are given in parentheses () or brackets [].

Many galaxies were classified independently on plates from different telescopes. A comparison of the types shows that the use of plate material from different telescopes has not introduced systematic errors. The only exceptions are the prints of the Palomar Sky Survey, designated 48 Pr. The classifications from this source could be affected by some systematic errors, especially for galaxies of small angular size. Lower weight should be given to the corresponding types.

The galaxies of the present catalog are separately binned according to type in part III of this volume.

Column 10: The Source of the Galaxy Type

The following codes have been used:

Number of
Code Source Galaxies

P200 Palomar 200", glass plate 304
C100 Las Campanas 100", glass plate 491
W100 Mount Wilson 100", glass plate 226
W60 Mount Wilson 60", glass plate 160
P48 Palomar 48" -Schmidt, glass plate 6
48 Pr Palomar Sky Survey, paper print 37
C40 D Las Campanas 40", glass plate 12
C40 IT Las Campanas 40", image tube 7
UpS Uppsala Schmidt, glass plate 0
W10 Mount Wilson 10", glass plate 2
CTIO 4m Cerro Tololo 4-meter 1
Total: 1246

Column 11: List of Objects

A repetition of Column 1.

Column 12: The Apparent Blue Magnitude of the Galaxy

The magnitudes are given in the BT system of de Vaucouleurs et al. (RC2). The magnitudes come from the sources listed below and in Table 1:

(i) The RC2.

(ii) Many new source lists have become available that supersede the RC2. Examples are Sandage, 1975b; de Vaucouleurs, 1977; de Vaucouleurs and Corwin, 1977; de Vaucouleurs, Corwin, and Bollinger, 1977; de Vaucouleurs and Bollinger, 1977a, 1977b, 1978.

(iii) V26 and (b - V)0.5 values for E, S0, and a few early-type spiral galaxies, determined photoelectrically by Sandage and Visvanathan (1978), were transformed into the BT system. From galaxies with known (b - V)0.5 and (B - V)T, the relation

(B - V)T = 1.31 (b - V)0.5 + 0m.21

was established. The resulting B26 magnitudes were compared with de Vaucouleurs' BT for 291 galaxies in common. The magnitude difference does not depend on galaxy color (B - V), diameter (D0), or flattening (R25). There is, however, a type-dependent zero-point difference:

(B26 - BT) = -0m.12 for E's, and
(B26 - BT) = -0m.03 for S0's and early-type spirals.

Therefore the B26 magnitudes were corrected by -0m.12, -0m.07, -0m.02, and +0m.03 for E, E/S0, S0/E, and S0 galaxies, respectively. For the few spiral galaxies with B26, a correction of +0.03 was adopted. The agreement between the corrected B26 and BT magnitudes is very satisfactory, since the mean scatter is

sigma(DeltaB) = 0m.19 for E and E/S0, and
sigma(DeltaB) = 0m16 for S0 and S0/E.

For galaxies where the corrected B26 and BT magnitudes are available, a straight mean was adopted as the best value.

(iv) Multiaperture UBV measurements of southern galaxies (mainly spirals) were kindly made available by G. Wegner (1979) before publication. We have followed the precepts of the first approximation, as given in the RC2 (e.g., equation 17a) to derive the logarithmic aperture-diameter ratio xi, which then leads from de Vaucouleurs (1977, table 1) to BT magnitudes. These magnitudes were not originally observed with an aim to derive total magnitudes; the measurements were made with relatively small diaphragms. Therefore, a second approximation to obtain BT is probably not justified. A comparison of these BT values with those of de Vaucouleurs (n = 58) and those derived from Sandage and Visvanathan (n = 50) gives a standard deviation of sigma = 0m.31 and 0m.27, respectively. This suggests the standard deviation of a BT magnitude derived from Wegner's observations to be sigma approx 0m.25. The error is smaller for galaxies observed with larger apertures (xi geq -0.2), i.e. sigma ltapprox 0.2, and somewhat larger for cases where -0.2 > xi > -0.5. (No smaller aperture measurements were considered.) Weight 1 was assigned to cases where xi geq -0.2 and weight 0.5 for smaller values of xi. The Harvard magnitudes reduced to the BT system (as given in RC2, see item 6) have standard deviations of ~ 0m.2 (de Vaucouleurs and Bollinger, 1977a); they were also assigned weight 1. BT values from de Vaucouleurs and his collaborators and from Sandage and Visvanathan were assigned weight 2. With these precepts, a total of 113 magnitudes from Wegner have been incorporated into the catalog.

(v) Multiapertive UBV measurements for 39 galaxies from Bucknell and Peach (1976) and Godwin et al. (1977) have been reduced to BT magnitudes the same way as the observations by Wegner (see source iv, above). On the average, they are fainter by 0m.07 ± 0m.05 than the weighted mean magnitudes from sources i-iv; this difference was judged to be insignificant and was neglected. The random difference of the magnitudes from source v and the mean from sources i-iv is sigma = 0m.29. If the mean error of the latter is sigma approx 0m.15 to 0m.20, the magnitudes from source v have mean errors of sigma = 0m.2 to 0m.25. We have assigned errors between 0m.2 and 0m.3 to the magnitudes from source v according to the number of observations, the diaphragm size, and the consistency of the individual measurements. Final magnitudes were computed using the corresponding weights and the weights of the magnitudes from sources i (from RC2), ii, iii, and iv.

Number of
Code* Source Galaxies

de Vaucouleurs and collaborators plus Sandage(1975). 552
1) mean from de Vaucouleurs and collaborators and from Sandage and Visvanathan (1978) 245
2) Sandage and Visvanathan (1978) 55
3) weighted mean from de Vaucouleurs and collaborators and from Wegner (1977) 27
4) weighted mean from Sandage and Visvanathan (1978) and from Wegner (1977) 27
5) weighted mean from Wegner (1977) and corrected Harvard magnitude (RC2) 59
8) weighted mean from de Vaucouleurs and collaborators and from Bucknell and Peach (1976) or Godwin et al. (1977)** 18
( ) Harvard magnitude reduced into the BT system (RC2) 256
[ ] uncorrected Harvard magnitude as given in the original Shapley-Ames catalog 7
* Refers to superscript entries in Column 12 of main tabulation in Part II.
** There are also magnitudes availible from Buckell and Peach (1976) or Godwin et at. (1977) for an additional 21 galaxies with superscript 1)-5).

(vi) For a number of galaxies there are still no magnitudes determined from detailed surface photometry or by photoelectric methods. For these galaxies the magnitudes from the original Shapley-Ames catalog were used, after reduction to the BT system. The reduced magnitudes were taken from the RC2, Column 15, upper line (see de Vaucouleurs and Bollinger, 1977a).

(vii) For a few galaxies the original Shapley-Ames magnitudes could not be transformed into the BT system. In these cases the uncorrected, original magnitudes have been used. The uncertainty of these magnitudes is high (~ 0m.4).

No K-correction due to redshift has been applied.

Column 13: Galactic Absorption Calculated from Sandage (1973)

A0 = 0m.132 (cosec b - 1) (for |b| < 50°)
A0 = 0m (for |b| geq 50°).

It should be remembered that the cosec law represents an idealized case. The true Galactic absorption is very patchy and undoubtedly depends on Galactic Longitude. Since the control of the absorption dependence on position is judged to be insufficient for |b| ltapprox 30°, no attempt has been made to apply absorption corrections beyond the cosec law. For some individual galaxies, particularly at lower latitudes, this could well introduce errors of ~ 0.3 magnitude in the absorption correction. The evidence for essentially absorption-free polar caps is strong, however (Sandage, 1973, 1975a; Colomb, Poppel, and Heiles, 1977; Burstein and Heiles, 1978), and use of the adopted absorptions for |b| gtapprox 30° should give negligible systematic errors.

Column 14: Total Internal Absorption

The internal absorption in E, S0, S0/a, and the earliest Sa galaxies was assumed to be zero.

For later-type galaxies the internal absorption was calculated following the principles of Holmberg (1958), who showed that the internal absorption is proportional to cosec i (i = inclination). Approximating cosec i by a/b (where a and b are the major and minor axes of the galaxy), Holmberg expressed the total internal absorption Ai as

Ai = alpha X a/b.

He determined the values of alpha and the maximum values of Ai for edge-on galaxies of different spiral types. However, there are now indications that his maximum values are too large (see Sandage and Tammann, 1976). Therefore, the maximum values have been tentatively reduced here to the upper limits given below. We have adopted interpolated values so as to obtain a smooth transition between the absorption values from the cosec law at small inclinations and the maximum absorption at high inclination (a/b geq 4.7). Our empirical absorption law can be well represented up to Aimax by

Ai = alpha + beta log a/b.

This relation has the same form as the one derived by Heidmann et al. (1972); but these workers could not determine the value of alpha (the absorption correction of a face-on spiral), and they found, surprisingly, that beta is constant for galaxies of type Sa to Im. Instead, we have adopted the numerical values of alpha for different types of galaxies as given by Holmberg (1958). The alpha-value for Im galaxies was chosen to give a mean internal absorption correction of ~ 0m.3, as suggested by Holmberg (1964).

For the values of log a/b, we have used the values log R25 as given in the RC2 (Column 11). Our adopted values of alpha, beta, and Aimax are:

Galaxy Type alpha beta Aimax

Sa, Sab, Sb 0m.43 1m.34 1m.33
Sbc, Sc, Scd, Sd 0m.28 0m.88 0m.87
Sdm, Sm, Im 0m.14. 0m.44 0m.43

A special problem is posed by the Sa galaxies. Some of them appear to be free of dust, whereas others clearly contain considerable amounts of dust. This makes questionable whether the same internal absorption correction can apply to all Sa galaxies and suggests that Holmberg's high internal absorption corrections apply only to the subsample of Sa galaxies with much dust. For this reason only Sa galaxies with clearly visible dust have been corrected according to the above precepts; for Sa galaxies without any traceable dust, zero internal absorption was adopted, and for the intermediate Sa galaxies only half the correction was applied. In the two latter cases the value of Ai is marked with an asterisk (*).

The uncertainties of the internal absorption corrections are still large. They may well contain systematic errors as large as ~ 0m.5 for highly inclined galaxies, and there may be systematic differences between galaxies of different type due to errors in alpha and beta. In addition, nothing is known about the scatter of individual galaxies about the mean relation. However, we believe that, in general, the internal-absorption-corrected magnitudes are closer to the true luminosity than are the uncorrected magnitudes, because it is clear that some correction is necessary. The mean value of Ai is ~ 0m.5 for spirals and lm galaxies taken as a whole. Clearly then, the mean error of Ai is less than ~ 0m.3.

There are several galaxies, including all those of class Amorphous, for which no correction for internal absorption could be applied.

Column 15: The Apparent Blue Magnitude in the BT system corrected for Galactic and internal absorption

The magnitudes are calculated from the values given in columns 12, 13, and 14.

The magnitudes are shown in brackets [ ] for those galaxies for which no internal absorption correction could be applied.

Column 16: The Absolute Blue Magnitude in the BT system corrected for Galactic and intrinsic absorption

The absolute magnitudes are calculated from the corrected apparent magnitudes (Column 15) and the corrected velocities v0 (Column 20), using an adopted Hubble constant of H0 = 50 km/s/Mpc (Sandage and Tammann, 1976).

The procedure to derive distances to individual galaxies (and hence absolute magnitudes) from the redshift (corrected to the centroid of the Local Group) using a fixed value of H0 is justified by the facts that (1) the random radial velocities are typically leq 50 km/s/Mpc (Sandage and Tammann, 1975; Fisher and Tully, 1975; Tammann et at., 1980), and (2) H (local) appeq H0 (global) (Sandage, Tammann, and Hardy, 1972; Tammann, Yahil, and Sandage, 1981). Even for a field galaxy like NGC 3109 with an exceptionally small radial velocity of v0 = 129 km s-1 the error in the distance introduced by the random component of the radial velocity is leq 40 percent, corresponding to an error of only leq 0m.8 in M. For galaxies with v0 > 500 km/s, a random motion of 50 km s-1 will cause an error in M of only < 0m.2.

The only exceptions where v0 is not a reliable distance indicator are members of galaxian aggregates in which the velocity dispersion is of the same order as the expansion velocity. The two most noteworthy aggregates of this kind are the Local Group and the Virgo Cluster. That they are exceptional in this respect is shown by the fact that the only galaxies with negative v0 so far known are members of these two aggregates. Hence, for galaxies in the Local Group and in the core of the Virgo Cluster (central 6° radius), and for a few additional groups, we have adopted mean distances for the calculation of absolute magnitudes. Table 2 lists those clusters and groups treated in this manner; the member galaxies are identified in the main catalog by capital letters following the M value in Column 16.

A special problem is posed by the South Polar (or Sculptor) group. A set of uniform plates taken of the late-type candidate members with the Las Campanas 2.5-meter du Pont telescope shows pronounced differences in resolution and hence in distance: NGC 300 is in the foreground, NGC 7793 and probably NGC 253 lie in the background, while NGC 55 and NGC 247 are between. Preliminary distances of these galaxies are listed in Table 2. They are based on the brightness of the brightest blue and M supergiants in these galaxies (Sandage, 1981). The galaxies NGC 24 and NGC 45, which lie in the field of the South Polar Group and at one time were considered to be members, are definitely much more distant and lie, in agreement with their redshift, at a distance of about 10 Mpc.

The greatest uncertainty in the group and cluster assignments in the main catalog is for galaxies of the Virgo Cluster region (VR) between 6° and 10° away from the cluster center. Some of the galaxies in that region may be foreground or background objects. However, in view of the smaller velocity dispersion [sigma(v) = 445 km s-1] of the external region compared with the central cluster core where [sigma(v) = 690 km/s, and considering that the mean velocities of the central core and the outer region are the same to within the errors, most galaxies of the outer region must lie at the same mean distance as the cluster proper.

The distance moduli are given in the preceding table for the two cases where the Hyades modulus is 3.03 and 3.23. The latter value is to be preferred (see van Altena, 1974; Hanson, 1980).

The mean errors of the listed absolute magnitudes for all field galaxies in the catalog are compounded by the mean errors of the apparent magnitudes (~ 0m.2), of the Galactic absorption corrections (~ 0m.15), of the intrinsic absorption corrections (~ 0m.25), and of the corrected velocities (~ 50 km/s, corresponding to < 0m.1), and by the random deviations from an ideal Hubble flow (< 0m.1). Hence, the compounded mean error in absolute magnitude is ltapprox 0m.4.

Group or Cluster Designation <v0> Nr. of SA galaxies (m-Ma (m-Mb Source c

Local Group L 10
M31 24.12 24.32 1
NGC 147 24.12 24.32 1
NGC 185 24.12 24.32 1
NGC 205 24.12 24.32 1
NGC 221 24.12 24.32 1
LMC 18.59 18.79 1
SMC 19.27 19.47 1
M33 24.56 24.76 2
NGC 6822 23.95 24.15 2
IC 5152 (26.0)

South Polar Group S 5
NGC 300 26.7 26.9 3,4,9
NGC 55 27.3 27.5 4
NGC 247 27.3 27.5 4
NGC 7793 27.9 28.1 4
NGC 253 27.9 28.1 4

M81 / NGC 2403 Group N 240±22 7 27.56 27.76 5,6
NGC 5128 Group C 255±25 6 29.0 29.2 7
M101 Group M 368±23 4 29.2 29.4 8,6,7

Virgo Cluster
(a) within 6° V 1026±75 85 31.5 31.7 6
(b) between 6° and
10° from center
VR 1147±93 23 31.5 31.7 6

Fornax Cluster F 1486±76 19 32.4 from<v0>

a (m - M)° corresponding to (m - M) Hyades = 3.03.
b (m - M)° corresponding to (m - M) Hyades = 3.23.
c Sources: 1. Sandage and Tammann, 1971; 2. Sandage and Tammann, 1974a; 3. Graham, 1979; 4. Sandage, 1981; 5. Tammann and Sandage, 1968; 6. Sandage and Tammann, 1976; 7. Tammann, 1977; 8. Sandage and Tammann, 1974b; 9. Melnick, 1978.

Column 17: The Weighted Mean Observed Velocity from all available determinations

Optical and 21-cm observations have been used. Only independent determinations were considered: some authors have published the same observations more than one time (occasionally with minor corrections). In these cases we attempted to exclude all values except the latest.

The general agreement between optical and 21-cm redshifts and the absence of any significant systematic difference is now well established (Roberts, 1972; Rubin et al., 1976; de Vaucouleurs et al., RC2; Lewis, 1977; Sandage, 1978). The errors in redshifts quoted in the original literature as determined from 21-cm observations are quite consistent with independent 21-cm determinations. Hence, in most cases the errors can be adopted as given in the original source. However, the errors quoted by most optical observers are internal errors. (An exception appears to be Humason's estimated errors of the Mount Wilson velocities in Humason et al., 1956.) For the more extensive lists of optical redshifts having sufficient overlap with independent observations (especially 21-cm data), we determined the true external mean errors. Typically these were found to be about twice the quoted errors (see Sandage, 1978). A similar conclusion was reached by de Vaucouleurs et al. (RC2, table 13), although the mean errors they adopted for different observers are, in some cases, still too small.

For small sets of redshift data where the overlap with independent determinations is insufficient, the true external error was estimated mainly from the spectroscopic dispersion used. The weighted mean velocities were calculated using the adopted mean external errors. Clearly deviating values were excluded.

No zero point corrections were applied to the velocities of any source considered. Such zero point corrections may indeed by necessary for some sources. For instance, Roberts (1972) has proposed that optically determined redshifts with ~ 1200 < v < 2400 km/s are systematically too large by ~ 100 km/s owing to blends of the galaxian and night sky H and K lines, whereas Lewis (1975) has found this effect only in the Lick velocities from Humason et al. (1956). Different zero point corrections have also been applied by de Vaucouleurs et al. (RC2, table 13). In our opinion, this complex problem is not yet Settled. Even if one accepts certain zero point corrections, they would be derived accurately only for spiral and late-type galaxies where the precise 21-cm velocities exist. The present 21-cm data for E and S0 galaxies are not sufficient to define a mean correction for these types. In view of this situation and to avoid a different treatment of galaxies of different type, we have neglected any possible correction.

We have used 430 literature sources or private communications for the velocities. These references contain 3437 velocity determinations for galaxies in the present catalog.

More than five independent redshift determinations are available for 134 galaxies of the Catalog; from two to five determinations exist for 713 galaxies; and the velocity of 394 galaxies rests on only one determination. No redshift data are known for one galaxy (NGC 3285).

The fact that velocity data are available for ~ 99 percent of the catalog galaxies reflects the increasing number of redshift determinations in the years since the end of the Humason-Mayall program in 1956.

Several observers provided prepublication redshift data, as acknowledged at the front of the volume and listed in References A.

Column 18: The Mean Error of the Observed Velocities

The errors are compounded from the assigned errors of the individual. velocity determinations, based generally on an estimate of the external errors of the various observers (e.g., Sandage, 1978, table XII). The mean errors of the catalog are distributed as:

epsilon, km/s n epsilon, km/s n
< 10 239 100-149 80
10-24 251 150-199 24
25-49 293 200-249 17
50-99 338 250-300 3

The median error of the velocities is 40 km/s.

Column 19: The Velocity Corrections Deltav to be applied to the observed velocity to obtain the velocity relative to the centroid of the Local Group

The values are calculated from solution number 2 of Yahil, Tammann, and Sandage (1977):

Deltav = -79 cos l cos b + 296 sin l cos b - 36 sin b.

The listed values Deltav differ from this formula by up to ± 3 km/s because they were computed with a formula in which the coefficients were not rounded off.

Column 20: The Corrected Recession Velocity v0 = v + Deltav relative to the centroid of the Local Group

The true errors are generally the same as those of the uncorrected velocities, except that in some directions the value of Deltav depends strongly on the exact form of the adopted correction formula. In these cases, the remaining uncertainry due to uncertainties in the adopted apex and velocity of the Yahil et al. solution may introduce additional systematic errors of ~ 60 km/s.

Column 21: The Sources for the Redshift Data

Sources in parentheses have been rejected in the calculation of the mean velocity and its mean error. The key for the references is given in Relerences A at the rear of this volume.

1 The original catalog had New 2 = NGC 4517. Further investigation showed that the correct cross-identification for New 2 is NGC 4507. (The NED team). Back.

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