Optical Long-Slit Spectroscopy of a Sample of Spiral Galaxies

Transcription

1 PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF THE PACIFIC, 111:1398È1409, 1999 November ( The Astronomical Society of the PaciÐc. All rights reserved. Printed in U.S.A. Optical Long-Slit Spectroscopy of a Sample of Spiral Galaxies K. A. MISSELT,1 GEOFFREY C. CLAYTON,1 AND KARL D. GORDON Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA ; misselt=baton.phys.lsu.edu, gclayton=baton.phys.lsu.edu, gordon=baton.phys.lsu.edu Received 1999 May 18; accepted 1999 July 26 ABSTRACT. We have analyzed long-slit spectra of a sample of 11 spiral galaxies. We identify several disk H II regions in each galaxy and provide classiðcations for the nuclear spectra. We Ðnd seven nuclear H II region galaxies, including four starburst nucleus galaxies, and four LINERs. 1. INTRODUCTION A substantial fraction of the nuclei of spiral galaxies exhibits optical emission lines which indicate nuclear activity (Keel 1983; Ve ron-cetty & Ve ron 1986; Coziol et al. 1994; Ho, Filippenko, & Sargent 1995). Baldwin, Phillips, & Terlevich (1981) and Veilleux & Osterbrock (1987) have proposed an empirical classiðcation of nuclear emissionline regions based on combinations of prominent optical emission lines. When the line ratios [N II] j6584/ha, [SII] jj6716, 6731/Ha, and [O I] j6300/ha are plotted versus [O III] j5007/hb, the three broad classes of nuclear emission-line regions, H II regions, Seyfert galaxies, and low-ionization nuclear emission-line regions (LINERs; Heckman 1980), fall into three distinct regions. Seyfert galaxies and LINERs can be distinguished from nuclear H II regions because they exhibit characteristically higher [N II] j6584/ha (º0.5), [S II] jj6716, 6731/Ha (º0.3), and [O I] j6300/ha (º0.06) line ratios. Seyfert spectra are generally of higher excitation than LINER spectra, and these two groups can be distinguished on the basis of the [O III] j5007/hb line ratio, with the transition being at [O III] j5007/hb D 3 (Veilleux & Osterbrock 1987). The underlying physical basis for the separation of the H II region and active galactic nuclei (AGNs) in the diagnostic diagrams is the principal excitation method, hot young stars versus a power law continuum, respectively (e.g., Koski 1978; Ferland & Osterbrock 1986; Veilleux & Osterbrock 1987; Evans & Dopita 1985). The partially ionized zones, where the low-excitation lines (e.g., [O I] j6300, [N II] jj6548, 6583, [S II] jj6716, 6731) are formed, are relatively extended in regions ionized by power-law continua with a large fraction of high-energy photons. In contrast, in ÈÈÈÈÈÈÈÈÈÈÈÈÈÈÈ 1 Visiting Astronomer, Kitt Peak National Observatory, National Optical Astronomy Observatories, which is operated by the Association of Universities for Research in Astronomy (AURA), Inc., under cooperative agreement with the National Science Foundation. regions ionized by OB stars the partially ionized zones are relatively small or absent. Thus, line ratios involving these low-excitation lines are depressed in H II region nuclei relative to AGNs. The underlying physical distinction between Seyfert galaxies and LINERs is less clear (see Filippenko 1996 for a review). Unusually luminous nuclear H II regions are sometimes called starburst nucleus galaxies (SBNGs; Balzano 1983). Extragalactic disk H II regions are a heterogeneous group, spanning a large range in size, luminosity, and morphology (Kennicutt 1984, 1988; McCall, Rybski, & Shields 1985; Kennicutt, Keel, & Blaha 1989). Studies of the brightest H II regions in spiral galaxies indicate that they have average Ha luminosities of D1039 ergs s~1 and diameters of D500 pc but show a considerable spread about these values with a strong dependence on the morphological type of the parent galaxy. The brightest disk H II regions (giant H II regions) in spirals have Ha luminosities that range from a few times 1037 to 1041 ergs s~1 (Kennicutt 1984, 1988). We have obtained long-slit optical spectroscopy of 11 spiral galaxies in the course of a project to the study the radial distribution of dust and stellar populations of normal spiral galaxies. The galaxies in our sample were selected from the study of nearby, face-on, undisturbed spiral galaxies deðned by de Jong & van der Kruit (1994). Here we present the identiðcation and analysis of disk H II region and nuclear spectra for the galaxies. We have identiðed seven nuclear H II region galaxies, including four SBNGs and four probable LINERs. These are the Ðrst classi- Ðcations available for several of these galaxies. 2. DATA 2.1. Observations and Reduction Long-slit spectra were obtained on four photometric nights in 1998 June at KPNO with the GoldCam spectrometer on the 2.1 m telescope. Observations were carried out 1398

2 LONG-SLIT SPECTROSCOPY OF SPIRAL GALAXIES 1399 using grating No. 201 with slit widths of 2A (June 26) and 3A (June 27È29), resulting in a spectral range of D3500È10000 A. Resolutions of D12 and D18 A (FWHM) were measured from night sky lines for each slit width, respectively. The D5@ long slit (0A.78 pixel~1) was generally centered on the nucleus of the galaxy at two position angles corresponding to the major and minor axes of the galaxy. Observations were restricted to low air mass in order to minimize light losses due to atmospheric dispersion. The observational data are summarized in Table 1. Basic processing steps, including spectral extraction and calibration, were performed using packages available in IRAF. Flat Ðelds were constructed from exposures of internal quartz lamps taken throughout the night. A residual slit illumination correction was applied to the Ñat Ðelds using twilight sky exposures prior to Ñattening science frames. Exposures of a HeNeAr wavelength calibration source were obtained at each telescope position. The stability of the spectrograph allowed us to globally Ðt a two-dimensional function to wavelength as a function of column and line number to all the HeNeAr exposures. The transformation obtained from this Ðt was subsequently applied to all science frames. One-dimensional spectra were extracted from the two-dimensional spectra at the spatial positions of interest (see Fig. 1). The aperture sizes were generally 10A (D13 pixels) along the spatial direction, although in some cases smaller apertures were used for closely spaced regions. The one dimensional spectra were corrected for telluric O 2 and H O features in the near-ir using observations of the 2 hot standard star BD ] The spectra were Ñuxcalibrated using several observations of spectrophotometric standard stars taken throughout the night and the average KPNO extinction. The accuracy of the calibration was estimated from a comparison of our extracted, calibrated standards with the published spectral energy distributions of the standards. The calibration is good to D12% in the spectral region 4500È9000 A but worsens considerably shortward of 4500 A (D22% at 3500 A ) and longward of 9000 A (D28% at A ) due to the rapidly falling sensitivity of the CCD/ grating combination and the paucity of spectrophotometric standards with data beyond 9000 A, respectively. The signal-to-noise ratio (S/N) was estimated for each spectrum at 5500 A and is reported in Table 4. Since this is the S/N in the continuum, it underestimates the reliability of line measurements for disk H II regions with little continuum but prominent lines. A representative spectrum (NGC 5016 nucleus) with the prominent features labeled is shown in Figure Analysis Line intensities were extracted from the Ñux-calibrated spectra by Ðtting a Gaussian line proðle plus a linear continuum around the lines of interest. Sets of lines that were blended at our instrumental resolution (e.g., [N II] jj6548, 6583]Ha and [S II] jj6713, 6731) were extracted using multiple Gaussian line proðles. Line intensities were extracted in the rest frame of the galaxy. The observed line intensities for individual regions are tabulated in Table 2. Line ratios appropriate for di erentiating between stellar (H II) and nonstellar (AGN) ionizing sources (Veilleux & Osterbrock 1987) were calculated for all regions that had observable Hb emission. Line ratios were corrected for both Galactic foreground extinction and internal extinction. TABLE 1 SUMMARY OF OBSERVATIONS Hubble D Exposure P.A. Galaxy a(j2000)a d(j2000)a Typea (Mpc)a,b E(B[V ) c G UT Date (s) (deg) NGC SAB(rs)bc June , , NGC SA(rs)c June , , NGC SAB(rs)c June , , NGC SA(r)c June , , 95.7 NGC SB(r)c June , , 96.0 NGC SB(r)ab: June June NGC 6246A SAB(r)c pec: June June NGC SB(rs)cd June , , NGC SAB(r)b June , , NGC SAB(rs)c June , 1800, , 104.2, NGC SA(rs)b June , , NOTE.ÈUnits of right ascension are hours, minutes, and seconds, and units of declination are degrees, arcminutes, and arcseconds. a From the NASA Extragalactic Database. b Assuming H \ 75 km s~1 Mpc~1 0 c Galactic foreground reddening from Schlegel et al

3 1400 MISSELT, CLAYTON, & GORDON FIG.1b FIG.1a FIG.1d FIG.1c FIG.1e FIG.1f FIG. 1.ÈGray-scale V -band images from de Jong & van der Kruit (1994) with observed slit positions superposed. Extracted regions are encircled and numbered according to the numbering in Table 1. The bar in the lower right-hand corner indicates 10A on the image. Nuclear identiðcation numbers are not visible due to the brightness of the nuclei.

4 LONG-SLIT SPECTROSCOPY OF SPIRAL GALAXIES 1401 FIG.1g FIG.1h FIG.1i FIG.1ÈContinued FIG.1j Both corrections assumed the extinction curve of Cardelli, Clayton, & Mathis (1989) with R \ 3.1. Values for the V Galactic foreground reddening, E(B[V ) (see Table 1), G were taken from the reddening map of Schlegel, Finkbeiner, & Davis (1998). The line ratios were corrected for the internal reddening using the observed Balmer line decrement derived from the observed line ratio, Ha/Hb. An intrinsic line ratio of 2.85 was assumed (case B recombination, n \ e 104 cm~3, and T \ 104 K; Osterbrock 1989). We report the derived reddenings, E(B[V ), for each region in the third I column of Table 3. We have derived Ha luminosities for all regions extracted in our sample. The Ha luminosities were calculated using log L \ 0.4 A(Ha) R E(B [ V ) Ha A(V ) V tot ] log F(Ha) ] 2 log [z(z ] 1)] ] 57.28, where E(B[V ) is the total reddening (Galactic fore- tot ground plus internal derived from the Hb/Ha decrement), F(Ha) is the observed Ha Ñux, and z is the redshift (taken from the NASA Extragalactic Database).2 For those regions without internal reddening determinations, ÈÈÈÈÈÈÈÈÈÈÈÈÈÈÈ 2 The NASA Extragalactic Database is located at nedwww.ipac.caltech.edu.

5 1402 MISSELT, CLAYTON, & GORDON FIG.2a FIG.2b FIG. 2.ÈThe nuclear spectrum of NGC The main features are labeled. E(B[V ) is assumed to be E(B[V ) and the derived Ha tot G luminosity is a lower limit. The derived Ha luminosities are tabulated in Table 4 for all extracted regions. Regions for which only lower limits were calculated are indicated by a º ÏÏ sign. The star formation rates (SFRs) quoted below were derived from the Ha luminosities following Kennicutt (1983): L (Ha) SFR \ 1.12 ] 1041 ergs s~1 M _ yr~1. We emphasize that the Ha luminosities and SFRs should be considered only as rough estimates. In addition to the assumptions used in deriving the SFR (e.g., conversion of Ha to number of Lyman continuum Ñux photons, the slope and cutto mass of the initial mass function; Kennicutt 1983), there are systematic uncertainties associated with the data. Our apertures (10@@ ] 2@@, 10@@ ] 3@@) represent a constant angular size on the sky, corresponding to varying physical sizes depending on the galaxyïs distance. Distances to the galaxies in our sample vary from D11 to 70 Mpc (Table 1) with a mean of 34 Mpc. Within this range of distances, our aperture size of D3@@ ] 10@@ corresponds to physical regions varying from 160 ] 530 pc to 1000 ] 3000 pc. Thus, assuming an average diameter for giant extragalactic H II regions of D500 pc (Kennicutt 1988), our aperture may include only a fraction of the Ha-emitting region for nearby galaxies, whereas several discrete regions may be included in the aperture for more distant galaxies. This e ect could amount to systematic variations in the measured Ha luminosities of factors of 5È10. Since the nuclear Ha-emitting regions should be more centrally condensed (Ho et al. 1997b), this bias should be reduced for the nuclear measurements. Comparisons of our results with other studies (photometric and spectroscopic) are only qualitative owing to di erences in the aperture sizes. We have assumed H 0 \ 75 km s~1 Mpc~1 throughout the analysis. 3. DISCUSSION 3.1. General A large fraction of spiral galaxies shows signs of nuclear activity as inferred from optical emission lines (e.g., Ho et al. 1997a). All of the galactic nuclei in our sample exhibit optical emission lines, and we adopt the classiðcation scheme of Veilleux & Osterbrock (1987), which is based on several line intensity ratios ([O III] j5007/hb, [NII] j6584/ Ha, [SII] jj6716, 6731/Ha, and [O I] j6300/ha), to distinguish between AGNs and nuclear H II region galaxies. The [O I] j6300/ha ratio was of limited use because the [O I] line is faint and was detected in only a few spectra. Diagnostic diagrams for our sample are presented in Figures 3È5. Because all three diagnostic diagrams involve the [O III] j5007/hb ratio, only those regions with measurable Hb and [O III] j5007 lines are plotted. In the cases where no Hb and/or [O III] j5007 lines were measured, a tentative identiðcation can be made based on the single line ratio, [N II] j6584/ha. Although there is some overlap between nuclear H II region galaxies and LINERs in the transition region [0.3 \ log ([N II]j6584/Ha) \ 0.0, LINERs generally have [N II] j6584/ha[0.6 and nuclear H II region galaxies [N II] j6584/ha\0.6 (Coziol 1996; Ve ron, Ve ron-cetty, & GoncÓ alves 1997). We use the Ha luminosity as an indicator of starburst activity; the SBNGs have Ha luminosities between 1040 and 1042 ergs s~1 (Balzano 1983), and we require that L (Ha) º 1040 ergs s~1 for identiðcation as an SBNG.

6 LONG-SLIT SPECTROSCOPY OF SPIRAL GALAXIES 1403 TABLE 2 OBSERVED EMISSION-LINE FLUXESa [O II] [O III] [OIII] HeI [O I] [NII] [N II] [S II] [SII] [S III] [S III] Galaxy Region j3727 Hd Hc Hb j4959 j5007 j5876 j6300 j6548 Ha j6583 j6717 j6731 j9069 j9529 NGC b b NGC b : 1.4: : : b NGC b b NGC b b NGC b : b NGC b : 0.9: b NGC 6246A : b b NGC b : 0.6: :

7 1404 MISSELT, CLAYTON, & GORDON TABLE 2ÈContinued [O II] [OIII] [O III] He I [O I] [NII] [N II] [S II] [S II] [SIII] [S III] Galaxy Region j3727 Hd Hc Hb j4959 j5007 j5876 j6300 j6548 Ha j6583 j6717 j6731 j9069 j b : 0.9: NGC Majorb Minorb NGC b : : NGC b b a In units of 10~15 ergs s~1 cm~2. b Region corresponds to nucleus. FIG. 3.ÈReddening-corrected [O III] j5007/hb vs. [N II] j6584/ha line ratios. The solid line indicates the division between H II regions and AGNs (e.g., Seyfert galaxies and LINERs) following Veilleux & Osterbrock (1987). The dashed line ([O III] j5007/hb \ 3) indicates the separation between Seyfert galaxies ([O III] j5007/hb[3) and LINERs ([O III] j5007/hb\3). Symbol shape as indicated; a Ðlled symbol indicates a line ratio derived from a nuclear spectrum. FIG. 4.ÈReddening-corrected [O III] j5007/hb vs. [S II] jj6716, 6731/Ha line ratios. Symbols and curves as in Fig. 3.

8 LONG-SLIT SPECTROSCOPY OF SPIRAL GALAXIES 1405 TABLE 3 REDDENING-CORRECTED LINE RATIOS [O III] [NII] [S II] [O I] Galaxy Region E(B[V ) a I j5007/hb j6583/ha jj6716, 6731/Ha j6300/ha NGC NGC NGC b b NGC NGC NGC NGC 6246A b b NGC NGC b NGC b b a Internal reddening derived from Ha/Hb ratio and case B recombination theory. b Region corresponds to nucleus. Among the galactic nuclei, only three have both [O III] j5007/hb and [N II] j6584/ha line ratios measured, and we classify all three as nuclear H II regions based on their position in the diagnostic diagrams (see Figs. 3È5). Four other nuclei are tentatively classiðed as nuclear H II regions based on the single line ratio [N II] j6584/ha. Note that of the seven galaxies classiðed as nuclear H II regions, only two are unambiguously so. The remainder may have a weak LINER component; our spectra are not of sufficient resolution to separate a possible LINER component. With sufficient resolution, the line proðles of objects with composite spectra show at least two components, one narrow (nuclear H II region) and one broad (LINER) (Ve ron et al. 1997). The remaining four galaxies in our sample cannot be unambiguously identiðed, although their high [N II] j6584/ Ha line ratios suggest a possible LINER classiðcation. However, the absence of [O I] j6300 emission argues against this classiðcation. A more detailed description of the individual galaxies in our sample is included below. The line ratios of the disk regions are all consistent with

9 1406 MISSELT, CLAYTON, & GORDON TABLE 4 Ha LUMINOSITY AND STAR FORMATION RATES Galaxy Classa Region S/Nb log L Ha c NGC º38.17 H II 2d 110 º º º38.04 H II 6d 58 º38.09 NGC LINERe 3d º º38.37 LINERe 8d º37.82 NGC º39.09 SBNG: 2d º38.84 SBNG: 6d º38.82 NGC º38.93 H IIe 2d 106 º º H IIe 7d 82 º NGC H II/LINERe 2d º º H II/LINERe 7d NGC º º38.38 LINER: 3d 77 º LINER: 5d 47 º º37.99 NGC 6246A SBNG 2d º SBNG 6d NGC LINER: 2d 52 º º º39.24 LINER: 5d 46 º TABLE 4ÈContinued Galaxy Classa Region S/Nb log L Ha c NGC H II/LINERe Majord 68 º38.75 H II/LINERe Minord 55 º38.86 NGC º º º º º39.26 SBNG 7d NGC SBNG 2d º º39.56 SBNG 6d a IdentiÐcation for the nucleus. : ÏÏ indicates an uncertain classi- Ðcation. b S/N at 5500 A. c Logarithm of the Ha luminosity in units of ergs s~1. Lower limits for regions with no internal extinction correction are indicated by a º ÏÏ sign. d Region corresponds to nucleus. e ClassiÐcation from Ho et al. 1997c. low-ionization H II regions [log ([O III]j5007/Hb) ¹ 0.4]. No evidence for di use, high-excitation disk gas was found (e.g., Wang, Heckman, & Lehnert 1997). The Ha luminosities of the disk H II regions are in the range of approxi- FIG. 5.ÈReddening-corrected [O III] j5007/hb vs. [O I] j6300/ha line ratios. Symbols and curves as in Fig. 3.

10 LONG-SLIT SPECTROSCOPY OF SPIRAL GALAXIES 1407 mately 1038 ¹ (Ha) ¹ 1041 ergs s~1. This range of Ha luminosities is consistent with those of giant extragalactic H II regions (Kennicutt 1988). No further classiðcation of the disk H II regions is attempted owing to the difficulty in assessing the reliability of the Ha luminosities. Individual disk H II regions will be discussed below Notes on Individual Objects NGC 4237.ÈWe have extracted spectra for six regions in this galaxy, including nuclear spectra along the major and minor axes. We have found no previous spectra of this Virgo Cluster galaxy in the literature. NGC 4237 is included in KennicuttÏs study of extragalactic H II regions (Kennicutt 1988). That study Ðnds an average Ha luminosity of 5.88 ] 1038 ergs s~1 for the three brightest H II regions. Our average Ha luminosity for the four extranuclear H II regions of 2.73 ] 1038 ergs s~1 is in good agreement with that Ðnding. We classify NGC 4237 as a nuclear H II region based on the uncorrected [N II] j6584/ha line ratio (0.40). The Ha luminosity of the nucleus is relatively modest [L (Ha) D 1.5 ] 1038 ergs s~1). Kennicutt & Kent (1983) report an integrated Ha luminosity (3@ aperture) of 7.76 ] 1039 ergs s~1 (all values quoted from Kennicutt & Kent 1983 have be corrected to H \ 75 km s~1 Mpc~1). 0 NGC 4651.ÈHo et al. (1995) obtained a nuclear spectrum of NGC 4651 and presented an extensive analysis in Ho, Filippenko, & Sargent (1997c). We have extracted nine spectra for NGC 4651 including two nuclear spectra obtained at di erent position angles. Kennicutt & Kent (1983) Ðnd an integrated Ha luminosity (3@ aperture) of 7.08 ] 1040 ergs s~1. The disk H II regions span a range of Ha luminosities (Table 4) consistent with the range found for large extragalactic H II regions (Kennicutt 1988). The nuclear spectrum of NGC 4651 is interesting in that there is no apparent Ha emission although [N II] and [S II] are relatively strong (Table 2). The absence of Ha emission indicates that a correction for underlying stellar continuum absorption is important (Ho 1996). Because of the absence of template spectra and the low resolution of our spectra, we do not attempt such a correction. However, even with a correction, it is unlikely that the [N II] j6584/ha line ratio would be less than 1. We do not detect [O III] in our spectra. The inferred high [N II] j6584/ha ratio combined with the low-excitation spectrum suggests a tentative LINER classiðcation based on our spectra. The detailed analysis of Ho et al. (1997c), which does correct for the underlying stellar absorption, Ðnds [N II] j6584/ha \ 1.84 and [O III] j5007/hb \ 1.82 along with [O I] j6300 emission, deðnitively identifying NGC 4651 as a LINER. NGC 5016.ÈA search of the literature yielded no previous spectroscopic data on this galaxy. We have extracted spectra for seven regions in this galaxy, four of which had measurable Hb emission, including nuclear spectra along the major and minor axes. The two extranuclear H II regions (regions 3 and 4; see Fig. 1) are on the upper edge of the distribution of large extragalactic H II regions (e.g., Kennicutt 1988), having Ha luminosities of 3.4 ] 1040 and 6.8 ] 1040 ergs s~1, respectively, implying SFRs of 0.3 and 0.6 M yr~1. Region 3 is separated from the nucleus by _ only 4A (675 pc), whereas region 4 is substantially farther out in the disk (D3.6 kpc). The nuclear spectrum of NGC 5016 is characteristic of an H II region. In Figure 3, the nucleus of NGC 5016 falls on the border separating nuclear H II region galaxies and AGNs, whereas its position in Figure 4 places it well within the H II region of the plot. There is a substantial di erence [9 ] 1039 ergs s~1 ¹ L (Ha) ¹ 4 ] 1040 ergs s~1] in the reddeningcorrected Ha luminosity and hence the SFR of the nucleus derived from our two slit positions. This di erence reñects the fact that the spectrum of the nucleus taken along the major axis (region 2) was extracted with a smaller aperture along the slit to minimize contamination from region 3. Taking the nuclear SFR implied by the Ha luminosity of nucleus, it is apparent that there is substantial star formation occurring in the nucleus of NGC 5016 with an SFR of D0.35 M yr~1. The inferred SFR rate for the nucleus of _ NGC 5016 is at the lower limit of starburst nuclei, and we tentatively classify it as such. NGC 5962.ÈVe ron-cetty & Ve ron (1986) classify NGC 5962 as a nuclear H II region galaxy, Ðnding [N II] j6584/ Ha D Ho et al. (1995) obtained a nuclear spectrum of NGC 5962 and included it in their detailed analysis (Ho et al. 1997c). We have extracted spectra for nine regions from our observations of NGC 5962, including two nuclear spectra. A direct comparison of our spectra with that of Ho et al. (1995) is complicated by di erent slit sizes and extraction apertures; however, the shape of the spectra and the approximate Ñux levels are consistent between the two observations. Màrquez & Moles (1996) report evidence for low-level nuclear activity in NGC 5962 and report [S II] j6717/[s II] j6731 D 0.95 and [N II] j6584/ha[1. We have not derived a correction for internal extinction for our nuclear spectra owing to the weakness of Hb emission and contamination from Balmer absorption. However, the [S II] j6717/[s II] j6731 and [N II] j6584/ha line ratios are minimally a ected by extinction and we derive 0.82 and 0.62 for these ratios, respectively. Although classiðcation of emission-line regions based on single line ratios is problematic, our uncorrected values of [N II] j6584/ha and [S II] jj6716, 6731/Ha (0.62 and 0.32, respectively) are consistent with the H II region classiðcation for the nucleus of NGC Our uncorrected Ha Ñuxes imply an Ha luminosity of the nucleus of L º 1.6 ] 1039 ergs s~1, indicating some Ha moderate level of star formation. We classify NGC 5962 as a nuclear H II region galaxy; the relatively low nuclear Ha luminosity precludes an SBNG classiðcation. Ho et al.

11 1408 MISSELT, CLAYTON, & GORDON (1997c) Ðnd 0.51 and 0.24 for the [N II] j6584/ha and [S II] jj6716, 6731/Ha line ratios, respectively, in good agreement with our determinations and also arrive at a nuclear H II region classiðcation. Ho et al. (1997c) Ðnd an Ha luminosity of 1.62 ] 1039 ergs s~1, in excellent agreement with our estimate. In addition to the nucleus, we extracted spectra from seven outlying H II regions, several of which have Ha luminosities consistent with giant extragalactic H II regions (Kennicutt 1988). Kennicutt & Kent (1983) report an integrated Ha luminosity of 1.5 ] 1041 ergs s~1 through a 3@ aperture. The integrated Ha luminosity of our nine regions (including the lower limits for the regions without reddening corrections) is 8.7 ] 1040 ergs s~1. NGC 5970.ÈHo et al. (1995) obtained a nuclear spectrum of NGC 5970 and presented an extensive analysis in Ho et al. (1997c). We have extracted eight spectra for NGC 5970 including two nuclear spectra obtained at di erent position angles. Kennicutt & Kent (1983) Ðnd an integrated Ha luminosity (3@ aperture) of 2.95 ] 1041 ergs s~1. Our nuclear spectra of NGC 5970 are similar to those of NGC 4651 in that we see no evidence for Ha emission; in addition, the [N II] emission is weak and we see no [S II] emission; apparently correction for underlying absorption is quite important. Based on our spectra, no classiðcation of NGC 5970 is feasible, although the absence of Ha with weak [N II] emission is suggestive of a LINER classi- Ðcation. Ho et al. (1997c) correct for underlying absorption and arrive at a LINER/transition classiðcation, where transition ÏÏ refers to properties intermediate between a nuclear H II region galaxy and a LINER. NGC 6012.ÈThere are no spectroscopic data on this little-studied galaxy in the literature. NGC 6012 has a circumnuclear ring with a radius of D2.4 kpc (see Fig. 1). We have obtained spectra of four disk H II regions and two spectra of the nucleus at di erent position angles. Our slit position at D163 just misses what appears to be a large H II region in the circumnuclear ring although we have extracted a spectrum near its position (region 4; Fig. 1). Three of our four disk H II regions lie in or near the circumnuclear ring, and all four have Ha luminosities within the range of KennicuttÏs (1988) sample of extragalactic H II regions. The nuclear spectra of NGC 6012 are characterized by a relatively high value for the [N II] j6584/ha line ratio (D1.2); thus we tentatively classify NGC 6012 as a LINER. NGC 6246A.ÈThere are very few data available on this galaxy in the literature. In particular, no spectroscopic data have previously been published. We have extracted spectra for seven regions in this galaxy, six of which had measurable Hb emission, including two nuclear spectra. The four reddening-corrected extranuclear regions (regions 1, 4, 5, and 7; see Fig. 1) have Ha luminosities (Table 4) consistent with those of giant extragalactic H II regions (Kennicutt 1988). The weakness of the [O III] j5007 line in the nuclear spectra prevented us from placing the nuclear regions in the diagnostic diagrams (see Figs. 3 and 4); however, the single line ratios [N II] j6584/ha and [S II] jj6716, 6731/Ha are consistent with a nuclear H II region galaxy classiðcation. The Ha luminosity of the nucleus is D2.3 ] 1041 ergs s~1, implying an SFR of D2 M yr~1. The high SFR inferred _ for the nucleus of NGC 6246A indicates that it is a nuclear starburst. NGC 7046.ÈThere are very few data available for this galaxy in the literature. In addition to two nuclear spectra, we have extracted Ðve disk H II region spectra from our data. The uncorrected nuclear [N II] j6584/ha and [S II] jj6716, 6731/Ha line ratios are quite high, D1.00 and 0.5, respectively, suggestive of a LINER classiðcation. NGC 7177.ÈNo disk H II regions were extracted from either of our two slit positions for this object. The nuclear spectra show relatively weak emission in the [N II], [S II], and Ha lines. The uncorrected [N II] j6584/ha and [S II] jj6716, 6731/Ha line ratios (0.84 and 1.0) are suggestive of a LINER classiðcation. NGC 7177 is included in the study of Ho et al. (1997c), and they Ðnd 0.68 and 1.11 for the [N II] j6584/ha and [S II] jj6716, 6731/Ha line ratios, respectively, and classify it as a transition ÏÏ object (LINER]H II region). We Ðnd a nuclear Ha luminosity of D6.4 ] 1038 ergs s~1, in good agreement with the Ho et al. (1997c) determination of 8.71 ] 1038 ergs s~1. NGC 7678.ÈOriginally classiðed as a Seyfert 2 galaxy (Kazarian 1993), NGC 7678 was reclassiðed as an H II region galaxy by GoncÓ alves, Ve ron, & Ve ron-cetty (1998). Both classiðcations were based on nuclear spectra. Our nuclear spectrum conðrms the result of GoncÓ alves et al. (1998). We Ðnd [N II] j6584/ha D 0.49 and [O III] j5007/ Hb D 0.21 (see Table 3 and Fig. 3) compared with their results of D0.52 and D0.25, respectively. NGC 7678 is an asymmetric spiral galaxy with the southern arm having several large H II regions. One of our slit positions lies along this large arm, and we have extracted spectra of these regions (12, 13, and 14; see Fig. 1). Region 13 is also crossed by a second slit position (region 5 in Tables 2 and 3 and Fig. 1). The di erence in measured line intensities between regions 5 and 13 reñects the fact that region 13 was extracted with a smaller aperture than region 5 in order to avoid contamination from region 14, which is separated from region 13 by only D5A (D1 kpc). The spectra and Ha luminosities of regions 5]13 and 14 are characteristic of giant extragalactic H II regions. The star formation rate as estimated from the Ha luminosity is 0.47 M yr~1 for _ region 5]13 (average Ha luminosity from spectra along di erent slit positions) and 0.34 M yr~1 for 14. The line _ ratios derived from the nuclear spectrum of NGC 7678 are consistent with an H II region classiðcation in all three diagnostic diagrams (Figs. 3È5). The Ha luminosity of the nucleus indicates an SFR of 2.28 M yr~1. The low- _ excitation H II spectrum along with the large inferred SFR for the nucleus of NGC 7678 classify it as a starburst

12 LONG-SLIT SPECTROSCOPY OF SPIRAL GALAXIES 1409 nucleus. In addition, the presence of several extranuclear regions with substantial star formation suggest that NGC 7678 may be undergoing a global starburst. NGC 7769.ÈWe have found no previous spectroscopic classiðcations of this galaxy in the literature. We have extracted spectra for six regions in NGC 7769, including two nuclear spectra. Two of the outlying regions (4 and 5; see Fig. 1 and Table 2) had no measurable Hb emission and were not corrected for internal extinction. The two reddening-corrected disk H II regions (1 and 3) have lowexcitation spectra and have Ha luminosities typical of large H II regions. The nuclear spectra of NGC 7769 are higher excitation ([O III] j5007/hb D 0.9) and have measurable [O I] j6300 emission. The diagnostic line ratios for the nucleus of NGC 7769 are consistent with an H II region classiðcation. The Ha luminosity of the nucleus of NGC 7769 is D6 ] 1041 ergs s~1, implying an SFR of D5.5 M _ yr~1. The nuclear H II region spectra combined with the large inferred SFR for the nucleus of NGC 7769 identify it as an SBNG. This research has made use of the NASA/IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. Baldwin, J. A., Phillips, M. M., & Terlevich, R. 1981, PASP, 93, 5 Balzano, V. A. 1983, ApJ, 268, 602 Cardelli, J. A., Clayton, G. C., & Mathis, J. S. 1989, ApJ, 345, 245 Coziol, R. 1996, A&A, 309, 345 Coziol, R., Demers, S., Pen8 a, M., & Barne oud, R. 1994, AJ, 108, 405 de Jong, R. S., & van der Kruit, P. C. 1994, A&AS, 106, 451 Evans, I. N., & Dopita, M. A. 1985, ApJS, 58, 125 Ferland, G. J., & Osterbrock, D. E. 1986, ApJ, 300, 658 Filippenko, A. V. 1996, in ASP Conf. Ser. 103, The Physics of LINERs in View of Recent Observations, ed. M. Eracleous et al. (San Fransisco: ASP), 17 GoncÓ alves, A. C., Ve ron, P., & Ve ron-cetty, M.-P. 1998, A&AS, 127, 107 Heckman, T. M. 1980, A&A, 87, 152 Ho, L. C. 1996, in ASP Conf. Ser. 103, The Physics of LINERs in View of Recent Observations, ed. M. Eracleous et al. (San Fransisco: ASP), 103 Ho, L. C., Filippenko, A. V., & Sargent, W. L. W. 1995, ApJS, 98, 477 ÈÈÈ. 1997a, ApJ, 487, 568 REFERENCES Ho, L. C., Filippenko, A. V., & Sargent, W. L. W. 1997b, ApJ, 487, 579 ÈÈÈ. 1997c, ApJS, 112, 315 Kazarian, M. A. 1993, AstroÐzika, 36, 353 Keel, W. C. 1983, ApJS, 52, 229 Kennicutt, R. C., Jr. 1983, ApJ, 272, 54 ÈÈÈ. 1984, ApJ, 287, 116 ÈÈÈ. 1988, ApJ, 334, 144 Kennicutt, R. C., Jr., Keel, W. C., & Blaha, C. A. 1989, AJ, 97, 1022 Kennicutt, R. C., Jr., & Kent, S. M. 1983, AJ, 88, 1094 Koski, A. T. 1978, ApJ, 223, 56 Màrquez, J., & Moles, M. 1996, A&AS, 120, 1 McCall, M. L., Rybski, P. M., & Shields, G. A. 1985, ApJS, 57, 1 Osterbrock, D. E. 1989, Astrophysics of Gaseous Nebulae and Active Galactic Nuclei (Mill Valley: Univ. Science Books) Schlegel, D. J., Finkbeiner, D. P., & Davis, M. 1998, ApJ, 500, 525 Veilleux, S., & Osterbrock, D. E. 1987, ApJS, 63, 295 Ve ron, P., Ve ron-cetty, M.-P., & GoncÓ alves, A. C. 1997, A&A, 319, 52 Ve ron-cetty, M.-P., & Ve ron, P. 1986, A&AS, 66, 335 Wang, J., Heckman, T. M., & Lehnert, M. D. 1997, ApJ, 491, 114