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Rotation Axes of Gas and Stars in Elliptical Galaxies D 329. P.A. Shaver: Clustering at High Redshifts. To appear in "Inner 334. E.A. Valentijn and A. F. M. Moorwood: The Stellar Content 01 the Space/Outer Space", proceedings of a conference held at A 496 cO Galaxy. Astronomy and Astrophysics. July 1984. Fermilab, 2-5 May 1984 (University of Chicago Press. June 335. A.C. Danks and J. Materne: The Galaxy Group Klemola 25. 1984). Astronomy and Astrophysics. July 1984. 330. M.-P. Veron-Cetty: Study of a Complete Sampie of Galaxies. I. 336. S. R. Federman, A. C. Danks and D. l. lambert: The CN Radical UBV Aperture Photometry. Astronomy andAstrophysics Suppl. in Diffuse Interstellar Clouds. Astrophysical Journal. July 1984. June 1984. 337. S. D'Odorico, R. G. Gratton and D. Ponz: A High Dispersion 331. B. Reipurth and P. Bouchet: Star Formation in Bok Globules and Analysis of a Giant Star in 47 Tucanae.Astronomy andAstrophy­ low-Mass Clouds. 11. A Collimated Flow in the Horsehead. sics. August 1984. Astronomy and Astrophysics, letters. July 1984. 338. F. Matteucci and A. Tornambe: Carbon Dellagrating Supernovae 332. B. Barbanis: The Stochastic Behaviour 01 a Galactic Model and the Chemical History of the Solar Neighbourhood. Dynamical System. Celestial Mechanics. July 1984. Astronomy and Astrophysics. August 1984. 333. l. Maraschi et al.: Coordinated UV and Optical Observations 01 339. C. Barbieri, S. Cristiani, S. Omizzolo and G. Romano: The the AM-Her Object E 1405-451 in High and low State. Variable Extragalactic Object 3C 446. AstronomyandAstrophy­ Astrophysical Journal. July 1984. sics. August 1984. Rotation Axes of Gas and Stars in Elliptical Galaxies D. Bettoni, Padova Astronomical Observatory, Italy Recent studies (1, 2) of the distribution and kinematics of the line strength y for each position angle (P. A.) observed. The gas in elliptical galaxies have revealed that in most cases there emission lines were measured with the ESO Grant machine is no correlation between the position angle of the major axis of and the data were reduced at the Padova Observatory compu­ the gas and that of the stellar isophotes. In addition, a ter centre. An additional measurement of redshift and FWHM decoupling is present in the kinematical axes of these compo­ of emission lines has been performed by using a non interac­ nents, in that the kinematical major axes of gas and stars do tive batch IHAP programme, the result being in good agree­ not coincide. ment with the Grant measurements. But until now a comparative study of gaseous and stellar In Table 1 we list the galaxies observed, their morphological dynamics has been made for only very few of these systems; in characteristics (3) and the distances, obtained from the red­ 1 the past only the stellar or only the gaseous dynamics have shift, assuming Ho = 50 km sec- Mpc-'. We report also the been studied in detail. In order to extend this study to a wider dynamical behaviour, i. e. the position angle of maximum sampie of objects, it is necessary to have simultaneously the rotation, for stars and gas, estimated by means of cosinusoi­ kinematical properties of both gas and stars. dal interpolation of the eentral veloeity gradients versus P.A., For this purpose we started observations in March and in and the value of Vrr/oo observed for the eentral regions. The May 1983 and in March 1984 with the image tube + B & C error in the P. A. of the line of nodes obtained by this proeedure o 4 spectrograph attached to the 1.52 m and 3.6 mESO tele­ is about ro . All the galaxies follow with little seatter the Lex: 0 scopes with dispersion of 29 and 39 Älmm, in order to obtain a (4) and the log (Vrn/Oo)vs MB (5) relations for elliptieal galaxies. complete velocity field for 6 elliptical galaxies, listed in Table 1. Despite these eommon morphologieal and kinematieal properties, the galaxies eonsidered show many differenees eoneerning the internal dynamies of gas and stars. All but one TABlE 1 case show that gas and stars have different rotation axes, whieh in most eases are nearly perpendieular. NGC Type MBr P.A. kin. maj. axis °0 Vrrl°o 1 Stars Gas (Km sec- ) NGC 2974 is the only galaxy in whieh gas and stars share the same velocity trend along all the position angles observed. In 2325 E4 - 21.01 6° - 181 ± 12 0.31 (maj. ax.) Fig. 1a, bare shown the rotation eurves along the major and minor axis respectively. The gas seems to be in a disk with the 2974 E4 - 21.01 45° 45° 221 _ 30 0.83 (maj. ax.) (maj. ax.) line of nodes eoineident with the major axis of the stellar component, in agreement with previous observations (2). The 3962 E1 240 _ 50 0.27 - 20.91 0° 90° same behaviour is exhibited by the stars. The representative (maj. ax.) (min. ax.) point of NGC 2974 in the Vrn/Oo-E diagram falls exaetly on the 5077 E3 + - 21.05 ]O? 97° 307 ± 50 0.095 line of oblate isotropie rotation, a fact whieh, together with the (maj. ax.) (min. ax.) previously eited gas and stars spin axes alignment, implies 5846 EO+ - 21.22 4°? 90° 244 ± 26 0.25 that this galaxy is very similar to a fast spinning disk of stars. 5898 EO - 20.54 150° 150° 174 ± 40 0.3 NGC 5077, on the other hand, is a system where the stars do not show appreciable rotation, while the gas, more extended along the apparent minor axis of the galaxy, shows along this The spectra were digitized with the ESO PDS microden­ axis a weil defined rotation curve (Fig. 2a, b). This behaviour sitometer with an aperture of 12.5 ~l x 50 ~l. All the spectra resembles the visible eonfiguration observed in NGC 5128, were calibrated in intensity and wavelength using the IHAP where the dust lane represents a disk rapidly rotating with the system of Garching. All the calibrated spectra were finally spin axis aligned with the major axis of the stellar body (6). analysed with the Fourier Quotient Method of the Padova This interpretation is eonfirmed by the low value of Vrn/oo for Observatory computer centre in the spectral range the stars wh ich plaees this bright galaxy (M = -21.1) among AA 3900-4500 A. This method allowed us to obtain simul­ the low rotators and weil down the predicted line of prolate taneously the radial velocity V" the velocity dispersion 0 and figures. These two properties suggest that this galaxy repre- 17 NGC 2974 (a) P.A 45' (a) NGC 5077 2050 H?$ ~ g 300e PA ~ 7" =- 1950 280C ~[>~ "Il> -- ~ '"E 1850 Il> :< " ~ '" 2600 >~ E 1750 ~ ~ -'!. NE 2 ? SW :>2400 NE SW -40 30 -20 -10 0 10 20 30 40 40 -30 -20 -10 0 10 20 30 40 r (arcsec) r larcsecj NGC 2974 [> NGC 5077 (b) PA 135- (b) [> [> 2050 PA -97· 3000 [> t>: [>M[> [> [> [> =- 1950 [> 2800 <?OQQ~~~? "Il> ~ R =- [> [> '"E 1850 J'* j :< pt Il> " ~ E2600 [>/ t!'"!:>{,.[>[>[>.6.[> >~ 1750 .:E- I SE NW >.... 2400 SE NW 40 :Jo -20 10 0 10 40 40 30 20 10 0 10 20 30 40 r (ares el r {areseel Fig. 1: Rotation curves ot NGC 2974 along the major (a) and minor (b) Fig. 2: Same as Fig. 1but tor NGC 5077 along the major(a) and minor axes tor gas (,1) and stars (0). The error bars tor the rotation curve ot (b) axis. (The data are trom two 90'" exposure spectra trom the ESO the stars are trom the Fourier Quotient Method. The mean error tor the 3.6 m telescope.) Grant measurements otemission fines (30 km sec-~, is indicated bya bar at the lower lett ot the diagrams. (The data are trom two 60'" exposure spectra trom the ESO 1.5 m telescope.) The other galaxy, NGC 5898, was selected from the list 0\ objects in which Caldwell (8) recently indicated the presence sents a case in which the gas disk, even though not obscuring of emission lines in the central regions. Stars and gas show the the stellar body, lies in the equatorial plane of a prolate or maximum velocity gradient along nearly the same position almost prolate galaxy. angle but they are rotating in opposite senses. Again these NGC 3962 is rounder than NGC 5077 but shows the same properties could be explained if the gas had been acquired kinematical characteristics. The stars have the maximum from the external regions and has not yet settled to a stable velocity gradient along the apparent major axis while the gas, configuration. also in agreement with previous observations (2), reaches the In this small sampie of elliptical galaxies with nuclear maximum rotation along an axis which is nearer to the optical emission lines, we are surprised to detect so great adifference minor axis. This fact, together with the low value of Vm/oo, in the dynamics of gas and stars. The fact that in most ca ses suggests, again like NGC 5077, that the gravitational potential there is no correlation between stellar and gaseous kinemati­ in NGC 3962 is nearly prolate. cal axes strongly suggests that the gas has been acquired In the flattened galaxy NGC 2325 (E 4) the stars do not seem from outside. In this hypothesis, if the mass of gas is negligible to rotate appreciably, although a slight tendency to rotation with respect to the total galaxy mass, its motion will be appears along the apparent major axis. On the contrary, no determined by the gravitational potential of the stellar body rotation is detected for the gas in the two P.
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