.255K The Astrophysical Journal Supplement Series, 79:255-284, 1992 April © 1992. The American Astronomical Society. All rights reserved. Printed in U.S.A. .79. 92ApJS. A SPECTROPHOTOMETRIC ATLAS OF GALAXIES 19 Robert C. Kennicutt, Jr. Steward Observatory, University of Arizona, Tucson, AZ 85721 Received 1991 July 29; accepted 1991 September 11 ABSTRACT Integrated spectra of 55 nearby normal and peculiar galaxies have been compiled into a spectrophotometric atlas. Most observations cover the spectral range 3650-7100 A, with a resolution of 5-8 Â, and sufficient signal- to-noise ratio to measure the prominent emission and absorption features. The spectra have been reduced to a common spectrophotometric scale and are presented as a series of plots, arranged according to morphological and spectral types. A digital version of the data is also available. The general characteristics of the integrated spectra of galaxies are discussed. Subject headings: atlases — galaxies: photometry — galaxies: stellar content — techniques: spectroscopic 1. INTRODUCTION applications. The data from this survey reveal a rich variety of The integrated spectrum of a galaxy is a powerful diagnostic spectral properties among nearby galaxies, which cannot be of its stellar content and evolutionary properties. Early obser- adequately represented by the fragmentary data which are vations by Hubble (1926) and Humason (1931, 1936) pro- available in the literature. Consequently I have compiled the vided some of the first systematic information on the inte- best spectra from the survey into this spectrophotometric atlas grated spectra of nearby galaxies, and this approach was of galaxies. systematized in the famous series of papers by Morgan & The main part of this paper is a set of figures which display Mayall (1957), Morgan (1959), and Morgan & Osterbrock spectra of 55 normal and peculiar galaxies over the 3650-7100 ( 1959). Today integrated spectra provide our primary source Á range, most at resolutions of 5-8 Á, and grouped according of information on the properties of very distant galaxies (e.g., to morphological and spectroscopic types (§3). Each figure is reviews by Dressier & Gunn 1990 and Elfis 1990), but rela- accompanied by a brief discussion of the general spectral prop- tively few comparable observations are available for nearby erties of the individual galaxies, and the main trends which are galaxies (Wells 1972; Dressier & Gunn 1982; Gallagher, Bus- observed along the Hubble sequence and between the different house, & Hunter 1989; Silva 1991 ). While abundant data on types of peculiar galaxies. Most of the discussion in this paper the spectra of the nuclear regions of nearby galaxies are avail- is qualitative, with quantitative analyses deferred to Paper I able, these cannot be directly compared to the observations of and future papers. Other parts of the paper discuss the observa- more distant galaxies, which are made with projected aperture tions, reductions, and spectrophotometric accuracy of the data sizes of several kiloparsecs or more. (§2), and how a digital version of the data may be obtained To address this problem I have obtained truly integrated (§3.5). spectrophotometry for a large and diverse sample of nearby galaxies. The main goals of this survey are to measure the sys- 2. OBSERVATIONS tematic behavior of the nebular emission lines in galaxy spec- The survey was carried out in two stages. Large-aperture, tra, as diagnostics of their star formation rates and ionization moderate-resolution (15-25 Ä) spectrophotometry was ob- mechanisms, and to compare the properties of this nearby sam- tained for 70 galaxies in 1985-1987, using the Intensified Reti- ple with published data for high-redshift systems. The first re- con Scanner (1RS) on the 0.92 m telescope at Kitt Peak Na- sults of this analysis, including emission-line measurements tional Observatory (KPNO). This provided continuum for 80 spiral, irregular, and peculiar galaxies, are presented in energy distributions and emission-line fluxes for a large set of Kennicutt (1992, hereafter Paper I). galaxies, but the spectral resolution of these data was insuffi- During the course of this study it became apparent that high- cient for accurate measurements of weak absorption or emis- quality spectra, with sufficient resolution and signal-to-noise sion features. Subsequently higher resolution (5-7 Ä) data ratio to isolate the primary stellar absorption features, would were obtained for 44 galaxies in 1989-1991, using a long-slit be a valuable resource for other applications, including the drift scanning technique on the Steward Observatory 2.3 m spectroscopic classification of high-redshift galaxies, spectro- telescope. scopic identification of objects detected in radio, infrared, and X-ray surveys, and a variety of rudimentary spectral synthesis 2.1. High-Resolution Spectra Most of the spectra in this atlas were obtained with the Boiler & Chivens (B&C) Spectrograph on the Steward Observatory 1 Visiting Astronomer, Kitt Peak National Observatory, National Opti- cal Astronomical Observatories, which are operated by the Association of 2.3 m telescope. In order to observe very large galaxies (D = Universities for Research in Astronomy, Inc. (AURA), under cooperative 1 '-14') while maintaining high spectral resolution, a narrow agreement with the National Science Foundation. long slit was used, and the galaxy images were trailed across a 255 © American Astronomical Society • Provided by the NASA Astrophysics Data System .255K 256 KENNICUTT Vol. 79 long slit several times during each integration. The spectral spheric dispersion. The blue and red spectra were tied together .79. resolution was dictated by the slit width, while the aperture on by normalizing the mean continuum intensities in the 4950- the sky was defined by the lengths of the slit and the drift scan. 5150 Â overlap region, or in the [O m] A5007 emission line. A total of 44 galaxies were observed with this setup, and spec- Errors of ~5% in the flux scale between regions shortward and 92ApJS. tra for 41 of these are included in the atlas. longward of 5100 Á are possible. This level of uncertainty is 19 The B&C spectrograph was used with a thinned 800 X 800 unimportant for all of the applications in this paper, but it may TI CCD, which was UV-flooded for enhanced blue response. be an important consideration for applications which require Two grating settings were used to cover the full visible spec- the continuum shape to be accurately determined. The overall trum. A 600 gpm grating blazed at 3568 A covered the 3650- accuracy of the spectrophotometry is discussed in detail in 5150 Ä region, and a 400 gpm grating blazed at 7500 Á (with §2.3. 4200 Â blocking filter) covered the 4950-7150 Â region. A 2''5 2.2. Low-Resolution Spectra slit yielded a resolution of 4.5 A in the blue and 7 À in the red. The usable slit length for the observations was approximately Spectra covering the range 3650-6900 Â were obtained for 3Í5; galaxies with diameters along the slit of <2i5 were ob- 70 galaxies during three observing runs in 1987-1989, using served, in order to provide adequate coverage for sky subtrac- the 1RS spectrometer on the KPNO No. 2 0.92 m telescope tion. Several larger, inchned galaxies were measured by align- (f/7.5 focus). The lower resolution of these data ( 10-25 Â) ing the slit with the minor axis, and drift scanning the telescope makes them less useful for general applications, but spectra for along the major axis. The scan lengths were 45 "-800", and the 14 galaxies, mostly strong emission-line galaxies, are included drift rates were adjusted so that the image crossed the slit at in the atlas. least 4 times, to minimize errors due to small variations in drift The 1RS is a dual-beam spectrometer, with an unusual com- speed or transparency. Integration times were 20-60 minutes. bination of a compact image scale and fast camera, which Shot noise from the sky background dominated over CCD make it possible to obtain moderate-resolution spectra with readout noise in all cases. large entrance apertures. All of the observations reported here Each CCD observation contained 130 pixels ( 1 "6 after bin- are fixed pointed measurements, made with a pair of 45 ?5 ning) along the slit. Since the telescope was drifted during the circular apertures, with centers separated by 61 "2 on an east- exposure, however, each pixel of this two-dimensional spec- west line. The galaxies were observed using a 500 gpm grating trum actually is a fine integral of the luminosity distribution, blazed at 5500 À with a WG-360 UV-blocking filter, which averaged along the scan direction, and most direct spatial in- provided photometric coverage over 3700-6900 Á. With the formation is lost. Consequently the data were summed along large apertures, the spectral resolution was modulated by the the slit into one or more one-dimensional sky-subtracted spec- luminosity distributions of the galaxies, ranging from 12 Â tra. Each of these is equivalent to a fixed observation with a FWHM for a point source (such as an emission fine nucleus) rectangular aperture, with dimensions set by the length of the to 25 Á for uniform illumination of the 45" apertures. The drift scan in one direction, and the summation limits (along actual resolution for most of the data is 15-20 À FWHM. the slit) in the perpendicular direction. The aperture limits Additional observations in the blue (3600-5500 Â) were ob- were selected to contain most of the integrated luminosity of tained for approximately half of the program galaxies, using a the galaxies {AID25 = 0.5-1 ), while excluding contamination 400 gpm grating blazed at 8000 Á in second order behind a from bright foreground stars. Although all parts of the galaxy CuS04 filter.