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1985Apjs ... 59 ...IW the Astrophysical Journal Supplement Series, 59:1-21,1985 September © 1985. the American Astronomical S IW The Astrophysical Journal Supplement Series, 59:1-21,1985 September .... © 1985. The American Astronomical Society. All rights reserved. Printed in U.S.A. 59 ... A CATALOG OF STELLAR VELOCITY DISPERSIONS. I. 1985ApJS COMPILATION AND STANDARD GALAXIES Bradley C. Whitmore Space Telescope Science Institute Douglas B. McElroy Computer Sciences Corporation1 AND John L. Tonry California Institute of Technology Received 1984 October 23; accepted 1985 February 19 ABSTRACT A catalog of central stellar velocity dispersion measurements is presented, current through 1984 June. The catalog includes 1096 measurements of 725 galaxies. A set of 51 standard galaxies is defined which consists of galaxies with at least three reliable, concordant measurements. We suggest that future studies observe some of these standard galaxies in the course of their observations so that different studies can be normalized to the same system. We compare previous studies with the derived standards to determine relative accuracies and to compute scale factors where necessary. Subject headings: galaxies: internal motions I. INTRODUCTION be flattened by rotation. Results from Whitmore, Rubin, and The ability to make accurate measurements of stellar veloc- Ford (1984) conflict with the Kormendy and Illingworth con- ity dispersions has provided a major catalyst for the study of clusion. galactic structure and dynamics. Several important discoveries While most dispersion profiles are either flat or falling, have resulted from the use of this new tool. For example, a studies of cD galaxies at the center of rich clusters of galaxies correlation between the luminosity of an elliptical galaxy and have shown rising dispersion profiles (Dressier 1979; Carter the central stellar velocity dispersion was discovered by Faber et al 1981). Malumuth and Kirshner (1981) also show that cD and Jackson (1976) and confirmed by several studies (includ- galaxies fall below the Faber-Jackson relation. These results ing Sargent etal 1977; Tonry and Davis 1981a). A similar are consistent with the hypothesis that cD galaxies arise from correlation was found between the luminosity of the bulges of a “special process,” perhaps the cannibalism of nearby com- spiral and SO galaxies and their central velocity dispersion panion galaxies (Ostriker and Tremaine 1975; Hausman and (Whitmore, Kirshner, and Schechter 1979; Whitmore and Ostriker 1978) or the accumulation of tidal debris from other Kirshner 1981; Kormendy and Illingworth 1983; Dressier and galaxies in the cluster (Richstone 1976). Sandage 1983). Several studies have attempted to supply a Several studies have suggested that a rapid rise in the physical explanation for the “Faber-Jackson” relation (Sargent dispersion near the center of galaxies indicates the presence of etal 1911 \ Aaronson, Huchra, and Mould 1979; Terlevich massive black holes in these galaxies (Sargent etal 1978; etal 1981), while others have used the relationship to help Tonry 19846; Dressier 19846). However, other studies determine the distance scale (Schechter 1980; Tonry and (Tremaine and Ostriker 1982; Duncan and Wheeler 1980; Davis 19816; de Vaucouleurs and Olson 1982; Dressier Binney and Mamón 1982; Tonry 1983) have shown that this 1984a). gradient might also be caused by anisotropic dispersion A comparison between the rotation and the velocity disper- tensors. While thorough observations of the rotation and sion in large elliptical galaxies showed that the flattened shape dispersion of several galaxies exist (NGC 596: Wilhams 1981; of these galaxies was not the result of rotation, but instead NGC 3115: Illingworth and Schechter 1982; several galaxies: was probably caused by anisotropic velocity dispersions Kormendy and Illingworth 1982; M31: McElroy 1983; NGC (Illingworth 1977; Schechter and Gunn 1979; Binney 1976, 936; Kormendy 1983), this uncertainty in the orbital motions 1978). However, studies of small ellipticals by Davies etal. of the stars makes the construction of mass models difficult. (1983) and spiral and SO bulges by Kormendy and Illingworth These studies represent only a small sample of the scores of (1982) suggest that these systems are rotating fast enough to papers using stellar velocity dispersions in the past 10 years. Several reviews of the subject are available (Capaccioli 1979; Illingworth 1981; Binney 1982; Kormendy 19826). The cur- rent paper provides a compilation of stellar velocity dispersion 1 Staff member, Space Telescope Science Institute. measurements. Our primary goals are as follows: © American Astronomical Society • Provided by the NASA Astrophysics Data System IW 2 Whitmore, Mcelroy, and tonry .... 59 1. Compile a data base of dispersion measurements for 1. For values with quoted internal errors of less than 10 -1 _1 ... quick reference and use in statistical studies. km s , we adopted an error of 10 km s for computational 2. Compare various studies to determine the relative purposes. While internal errors of only a few km s-1 are now accuracies and normalizing factors. possible, the systematic errors become the dominant uncer- 3. Provide a reference system for the measurement of tainty in these cases. 1985ApJS stellar velocity dispersions by establishing a set of standard 2. Many authors did not give errors for their measure- galaxies. ments. These measurements were somewhat arbitrarily as- signed error values of 50 km s-1, except for those of Faber and Jackson (1976), which were assigned an error of 20 km s“1, and Schechter and Gunn (1979), which were assigned II. COMPILATION OF STELLAR VELOCITY DISPERSIONS an error of 30 km s-1. Table 1 contains the compilation of central stellar velocity Table 3 shows the source code and various instrumental dispersions through 1984 June 1. It is our intention that this parameters for the different studies. In some cases, the authors catalog be as current and accurate as possible. We intend to used heterogeneous sets of data (different detectors, different update and revise it as more data are made available, and we wavelength regions, etc.). Those studies have multiple entries, shall publish an updated version every few years. Between but to find out precisely which galaxy was done which way in publications a machine-readable magnetic tape version of the such a study, one must refer back to the paper. A blank entry catalog will be available from the Astronomical Data Center in the table means that the authors did not supply that at NASA/Goddard Space Flight Center. Include a blank tape information. An explanation of columns follows: Column (1). and details about the required tape format with any request. —Code for source study. Column (2).—Source study. Column Please direct any corrections, updates, or omissions to the (3).—An indicator of whether the authors measured extended authors. velocity dispersion profiles (Y) or not (N). If only a few Table 1 shows both the value we adopt for the central measurements in the outer regions are available, a Y/N is velocity dispersion (a) and the underlying source measure- entered. Column (4).—The FWHM of the narrowest compari- -1 ments (os). Note that in some cases, a value of zero is reported son line, expressed in km s . This is proportional to the for the velocity dispersion. This means that the study did not instrumental resolution, which is generally defined as an in- measure a central velocity dispersion, just outer ones, often in strumental “velocity dispersion” ainstr = FWHM/2.35. If the the form of extended profiles that do not pass through the FWHM or instrumental dispersion is not given in the paper, center. These studies are included here for completeness. The the stated grating dispersion in Á mm-1 is listed. Columns first column of the table gives the galaxy identification (NGC, (5)-(6).—Width and length of slit used for central dispersion IC, UGC, and miscellaneous). The second column lists the measurement, in arcsec. Columns (7)-(9).—Telescope descrip- Hubble type from de Vaucouleurs, de Vaucouleurs, and Corwin tors. “Size” is the diameter of the primary used, in meters, (1976) or (indicated with an asterisk) Nilson (1973). The third “place” is a code for the observatory, and “det” is a code for column lists the adopted value for the central velocity disper- the detector used (see notes to Table 3). Column (10).—Code sion (km s-1), using scaled values and weighted averages as for the analysis technique used (visual, Fourier quotient, etc., discussed below. Next, individual source measurements, with see notes to Table 3). Column (11).—Number of pixels in quoted errors in parentheses (km s-1), are given. The last spectra. Column (12).—Wavelength range in Â. If available, column contains the source codes for individual measurements the wavelength range and the number of pixels actually used (see Table 3). in the determination of the velocity dispersion are quoted. In Figure 1 shows the comparison of several studies with the other cases the values of these quantities for the raw spectrum standard galaxies (discussed in the next section). These com- are entered. We caution the reader to use the original source parisons led us to adopt scaling factors to bring the source set for their references since these types of uncertainties arise. into better agreement with the standards. We found in general Figure 2 shows a plot of central velocity dispersion as a that a one-parameter least-squares fit (the slope of a line function of morphological type. Of the 725 galaxies in the passing through the origin) was all that was necessary or sample, 597 are classified (see Table 1). The upper panel justified by the data. The only exception was a study by Faber shows the distribution of central velocity dispersions by mor- and Jackson (1976), where both an additive zero-point offset phological type (the points have been artificially distributed in and a non-unit slope were used. The low-resolution spectra the x-direction to reduce overplotting); the lower panel shows (FWHM= 395 km s-1) used in this study probably caused means and the uncertainty in the mean for each type.
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