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Major Axis Kinematics of 15 Early-Type Galaxies in the Fornax Cluster

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Major Axis Kinematics of 15 Early-Type Galaxies in the Fornax Cluster A&A manuscript no. (will be inserted by hand later) ASTRONOMY AND Your thesaurus codes are: ASTROPHYSICS 03(11.03.5; 11.05.1; 11.11.1) 3.10.1994 Major axis kinematics of 15 early-type galaxies in the Fornax cluster. ? Mauro D'Onofrio1, Simone R. Zaggia1, Giuseppe Longo2, Nicola Caon1, and Massimo Capaccioli12 1 Dipartimento di Astronomia, Universita di Padova, Vicolo dell'Osservatorio 5, I-35122 -- Padova -- Italy 2 Osservatorio Astronomico di Capodimonte, Via Moiariello 16, I-80131 -- Napoli -- Italy Received ...... ; Accepted ...... Abstract. Major axis rotation curves and velocity dispersions profiles, extending out to about one effective radius, are presented for 15 ellipticals and S0's out of the photometric sample of Fornax cluster galaxies studied by Caon et al. (1994). A brief description of the spectroscopic and photometric characteristics of each galaxy is provided, together with a comparison with previous studies. Six of the nine E's are possibly misclassified S0's or ellipticals harboring a disk-like component. Two galaxies (NGC 1399 and 1404) show a hint of counter-rotation. Evidence is given that the bright and the ordinary families of early-type galaxies, first introduced by Capaccioli et al. (1992), look distinct also in term of the anisotropy parameter (Vm ) . Key words: Galaxies: clusters: Fornax -- galaxies: elliptical and lenticular -- galaxies: kinematics and dynamics 1. Introduction Prompted by the need of adopting standard methodologies, procedures, and strategies for the study of the global properties of early-type galaxies (cf. Capaccioli et al. 1993a), Caon et al. (1990, 1994; hereafter C2D) have recently carried on a program of accurate surface photometry of two luminosity- and volume-limited samples of E and S0 galaxies belonging to the Virgo and Fornax clusters. The C2D data-set has been already utilized for a study of the photometricproperties of faint and bright E and S0 astro-ph/9410006 3 Oct 1994 galaxies in a series of papers. Capaccioli et al. (1992, 1993b), for instance, have analyzed the distributionof C2D galaxies in the plane defined by the global parameters re (effective radius) and e (corresponding surface brightness). The main finding is that, at variance with previous belief (e.g. Kormendy 1977, Djorgovski and Davis 1987), this morphological class is heterogeneous as for the global parameters, and it encompasses two photometric families, named bright and ordinary, which appear distinct also in relation to the environmental characteristics and to the internal kinematics, color gradient, radio and X-ray emission, dust and hydrogen content. Moreover, by lookingat theC2D data-set,Caon et al. (1993)and D'Onofrioet al. (1994)have found that the lightdistribution 1m of early-type galaxies is shaped according to the total luminosity, i.e. the light profiles are better represented by a r formula 14 m than by the universally adopted r law (deVaucouleurs 1948), with increasing monotonically from dwarfs to giants. Along the same vein Jrgensen et al. (1992) and Jrgensen & Franx (1994) have started a systematic analysis of the photometric and geometric properties of the early-type galaxies which are members of the Coma cluster, findingthat faint E and S0 galaxies form a continuous class of objects, different from the giants, but also from the dwarfs. The observed similarities in the photometric properties of normal ellipticals and S0's raises the question if they share also similar dynamical properties (see Capaccioli & Longo 1994 for a review). It is known that, while most normal E galaxies are rotationally flattened, the brightest ellipticals are supported by the anisotropic velocity dispersion (Bertola & Capaccioli 1975, V Illingworth 1977, Binney 1978). The anisotropy parameter (Vm ) --- where m is the maximum rotational velocity, is some Send offprint requests to: Mauro D'Onofrio ? Based on observations made at the European Southern Observatory, La Silla, Chile. Tables A1-A15 are available in electronic form at the CDS: see the Editorial in A&AS 1992, Vol.96, No. 3 2 M. D'Onofrio et al. : Major axis kinematics of 15 early-type galaxies in the Fornax cluster average velocity dispersion, and their ratio is normalized to the values pertinent to an oblate rotator (Davies et al. 1983) --- a correlates with the effective radius re (Capaccioli et al. 1993b) and with the isophotal shape parameter 4 (Bender et al. 1989). The low surface brightness dwarf ellipsoidal systems are mostly supported by the anisotropic velocity dispersion (Bender & Nieto 1990), indicating that the kinematical properties do not vary smoothly from the dwarf to the giant types, as suggested by the light profiles. However, it is presently unclear how much the amount of pressure-support is correlated with the morphology for galaxies of different luminosities. A more complete understanding of the properties of the early-type galaxies awaits larger and more homogeneous data-sets. At present, the only sample of spectroscopic data fulfillingpart of these requirements is that of the7 Samurai (Davies et al. 1987) which, however, does not provide extended rotation curves and velocity dispersion profiles. Sparse data can be found in quite a few papers, as those dealing with the tridimensional structure of ellipticals and the peculiar motions; for updated compilations see Busarello et al. (1989, 1994). It is for these reasons that we decided to embark in a program of detailed spectroscopic observations for galaxies in the C2D sample. This paper reports on the major axis rotation curves (RC) and velocity dispersion (VD) profiles for 15 early-type galaxies members of the Fornax cluster. The observational material and the most important steps of the data reduction are described in Sections 2 and 3. We comment on the individual galaxies in Sect. 4, compare our results with the literature in Sect. 5, and discuss the correlation of the kinematical and photometrical parameters in Sect. 6. 2. Observations Spectra of 15 early-type galaxies of the Fornax cluster were collected in November 1991 with the B&C spectrograph attached at the Cassegrain focus of the ESO 1.5 m telescope. The objects, selected from Ferguson's (1989; hereafter F89) catalogue of the Fornax cluster, are E's and S0's in common with the C2D sample, with the exception of IC 1963. This first contribution, in a long-range project aimed at providing kinematics data for all the galaxies of the C2D dataset, deals with 62% of the Fornax population of E's and S0's (according to the membership list of F89). The target list is presented in Table 1; columns from 1 to6 give the names of the galaxies, the morphological types according to F89 and deVaucouleurs et al. (1991; hereafter RC3) catalogue, the total luminosities BT and the position angles (P.A.) of the major axes from C2D, and the epochs of the spectra. Table 1. Target list Galaxy Morph. RC3 BT P.A. Date Name Type [mag] [deg] (1991) IC1963 S01(9) .L..../ 13.00 84 12/11 NGC1316 S03 pec PLXS0P. 9.23 50 11/11 NGC1336 E4 .LA.-.. 13.27 20 16/11 NGC1339 E4 .E+..P* 12.70 175 12/11 NGC1351 E5 .LA.-P* 12.30 141 15/11 NGC1374 E0 .E..... 11.94 119 15/11 NGC1375 S0(cross) .LX.0*/ 13.21 88 16/11 NGC 1379 E0 .E..... 12.03 7 11/11 NGC 1380 S0/a .LA.... 10.82 7 14/11 NGC 1380A S02(9) .L..0*/ 13.29 177 12/11 NGC1381 S0(9) .LA..*/ 12.32 139 15/11 NGC1399 E0 .E.1.P. 10.01 112 11/11 NGC1404 E2 .E.1... 10.93 159 14/11 NGC1419 E0 .E...P* 13.56 65 16/11 NGC1427 E4 .E+.... 11.82 79 14/11 The detector was the ESO CCD#27 Ford chip, which has a very good cosmetics and a readout noise of 3.1 e . To limit the readout time, the CCD was windowed to 2048 500 pixels. This subframe is large enough to contain the dark level of the science exposures in the parts not covered by the spectrum. We used grating #26 (1200 mm1) giving a dispersion of 1.0A 0 00 1 pix over a range of 2000A centered at 5900A. The spectrograph slit was chosen to be 220 m wide (2 on the sky) and 2 9 00 1 long (the maximum value allowed). The scale in the direction perpendicular to the dispersion was 0 68 pix . Each galaxy was observed twice, with a typical exposure time of one hour per spectrum. The slit was centered on the galaxy nucleus and aligned with the photometric major axis (Table 1). We had to reject one of the two spectra of NGC 1316 and of M. D'Onofrio et al. : Major axis kinematics of 15 early-type galaxiesintheFornaxcluster 3 Fig. 1. Comparison of the light profiles along the major axis of NGC 1375 from high precision surface photometry (C2D; solid line) and from one spectrum of the galaxy (open circles). NGC 1379 due to bad tracking of the telescope. Template spectra of KIII standard stars were obtained each night, together with spectra of the dawn sky-light (in order to check the flatness of the slit profile), and the usual series of bias, dark, and flat-field exposures. 3. Data reduction The first part of the data reduction was almost standard, except for one problem. We realized that the spectra were misaligned 00 with respect to the CCD columns, with a difference of a maximum of 6 pixels( 4 ) between the two extremes of the spectra. This defect which, if overlooked, would have affected both the RC and the VD measurements, was corrected as follows. For each CCD column (i.e. in the direction perpendicular to the dispersion), a gaussian curve was fitted to the light profile of the object (galaxy or template), and the position of the maximum measured.
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