Figure-Of-Eight Velocity Curves: UGC 10205? J.C
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AND Your thesaurus codes are: ASTROPHYSICS 03(11.09.1 UGC 10205; 11.11.1; 11.19.2; 11.19.6) 9.5.1997 Figure-of-eight velocity curves: UGC 10205? J.C. Vega1,E.M.Corsini2, A. Pizzella2, and F. Bertola2 1 Telescopio Nazionale Galileo, Osservatorio Astronomico di Padova, vicolo dell’Osservatorio 5, I-35122 Padova, Italy 2 Dipartimento di Astronomia, Universit`a di Padova, vicolo dell’Osservatorio 5, I-35122 Padova, Italy Received..................; accepted................... Abstract. We measured the velocity curve Boulesteix 1996). and the velocity dispersion profile of the ion- In the inner regions of the Sc NGC 5907 Miller ized gas along the major axis of the edge-on & Rubin (1995) observed double-valued ion- galaxy UGC 10205. The observed kinematics ized gas emissions. They attributed the higher extends up to about 4000 from the nucleus. In velocity system to disk gas near the nucleus, the inner ±1300 of this early-type spiral three and the lower velocity system to an outer kinematically distinct gaseous components are gas ring. Although these two gas components present. We disentangle a fast-rotating and are supposed to be spatially distinct, they are a slow-rotating component. They give to the viewed superimposed along the line-of-sight on UGC 10205 velocity curve a “figure-of-eight” account of NGC 5907 high inclination. appearance. A third velocity component is The spirals NGC 5746 (Kuijken & Merrifield also detected on the southeast side of the 1995; Bureau & Freeman 1996), NGC 5965 galaxy. Possibly it is produced by gas in non- (Kuijken & Merrifield 1995), IC 5096 (Bureau circular motions. & Freeman 1996) and NGC 2683 (Merrifield 1996) have boxy/peanut bulges and double- Key words: galaxies: individual: UGC 10205 peaked gas line profiles. Kuijken & Merrifield — galaxies: kinematics and dynamics — (1995) explained these features as the signa- galaxies: spiral — galaxies: structure ture of a disk non-axisymmetric potential due to the presence of a bar. In this paper we show yet an other case of edge-on disk galaxy with a multiple-valued gas velocity curve, namely UGC 10205. For 1. Introduction projected distances lower than 1300 from the Within the last year ionized gas kinematics nucleus UGC 10205 it is characterized by has revealed in a number of edge-on disk the presence of three kinematically distinct galaxies double-peaked emission lines. The gaseous components, two of which give to its analysis of the line profiles allows to derive in- velocity curve a “figure-of-eight ” appearance. dividual rotation curves characteristic of two UGC 10205 is classified as Sa spiral by Nilson kinematically distinct gas components. (1973) and by de Vaucouleurs et al. (1991). The edge-on S0 galaxy NGC 7332 has been Its total B-band magnitude is BT =14.4mag found to have an “x-shaped” velocity curve, (RC3) and the inclination of the galaxy de- ◦ indicating two gas components counterrotat- duced from the disk parameters is i =84 ing one with respect to the other (Plana & (Rubin et al. 1985). The distance is 132 Mpc −1 −1 (H0 =50kms Mpc ). Send offprint requests to:J.C.Vega; [email protected] ? Based on observations carried out at the INT 2. Observations and data reduction operated on the island La Palma by the Royal Greenwich Observatory in the Spanish Observa- The spectroscopic observations of UGC 10205 torio del Roque de Los Muchachos of the Instituto were carried out on March 19-21, 1996 at the de Astrof´ısica de Canarias, Tenerife, Spain. Isaac Newton Telescope (INT) in La Palma us- Fig. 1. UGC 10205 major axis 100 minutes spectrum in the Hα region after removal of sky and stellar continuum. Note the multiple-peaked emissions of the Hα and the [N II](λ6583.4 A)˚ lines in the central regions of the spectrum (|r|≤1300) ing the Intermediate Dispersion Spectrograph lines have a Gaussian profile shape, were de- (IDS). rived by means of the MIDAS package ALICE. The H1800V We measured the Hα and the [N II](λ6583.4 grating with 1800 grooves mm−1 was used in A)˚ lines, where they were clearly detected. The the first order in combination with a 1.900 × position, the FWHM and the uncalibrated flux 4.00 slit, the 500 mm camera and the AgRed of each emission line were individually deter- collimator. It yielded a wavelength coverage mined by interactively fitting one Gaussian of ∼ 240 A˚ between 6650 A˚ and 6890 Awith˚ plus a polynomial to each emission and to a reciprocal dispersion of 9.92 Amm˚ −1.We its surrounding continuum. The wavelength of checked that the measured FWHMs do not the Gaussian center was converted to the ve- depend on wavelength and we found a mean locity v = cz, and then an heliocentric correc- value of FWHM = 0.86 A˚ (i.e. σ =0.37 A)˚ tion of ∆v =+15.5kms−1 was applied. The that, in the range of the observed gas emission Gaussian FWHM was corrected for the in- lines, corresponds to ∼ 17 km s−1.Noon-chip strumental FWHM and then converted to the binning was done on the adopted 1024×1024 velocity dispersion σ. The ionized gas emis- TK1024A CCD. Each 24 µm × 24 µm image sion lines are double-peaked for −1300 ≤ r< pixel corresponds to 0.24 A˚ × 0.3300. 300 andeventriple-peakedfor300 ≤ r ≤ 1300. We took two separate major axis spectra They have been fitted using the above package (P.A. = 132◦) for a total exposure time of with two or three Gaussians respectively and 100 minutes (Fig. 1). The slit was centered vi- a polynomial continuum. At each radius this sually on the galaxy nucleus. A comparison multiple-Gaussian fit has been done separately copper-argon lamp exposure was obtained be- for each emission line. tween the two object integrations. All the im- The gas velocity curves and the velocity ages were reduced using standard MIDAS rou- dispersion profiles independently derived from tines. Considering a sample of 8 bright OH the Hα (Fig. 2) and the [N II] (Fig. 3) lines are night-sky emission lines, we found a mean in good agreement at all radii. The kinemati- deviation from the theorical predicted wave- cal data from Hα and [N II] lines are given in length (Osterbrock & Martel, 1992) corre- Table 1 and in Table 2 respectively. Each table sponding to ∼ 1kms−1. provides the radial distance from the galaxy The gas velocities and velocity dispersions center r in arcsec (col. 1), the observed helio- for |r| > 1300, where the ionized gas emission centric velocity v (col. 2) and the velocity dis- persion σ (col.3)inkms ,thenumbernof The reciprocal dispersion (25 A mm ) and spectrum rows binned along the spatial direc- the spatial scale (2500 mm−1) of their image- tion to improve the signal-to-noise ratio of the tube spectrum were respectively 3 and 2 times emission lines (col. 4) and the identification i lower than those of our CCD spectrum. So of the kinematically distinct gas components they did not disentangle the component (i) (col. 5). from the (ii), detecting them as a unique one. They observed a second velocity system, corre- sponding to velocity curve of component (iii). 3. Results Finally, for two distinct radii at r ∼−500 The observed gas kinematics extends out to they measured intermediate velocities between 4200 (∼ 27 kpc) in the receding NW side and those of the first and the second system and about up to 3000 (∼ 19 kpc) in the SE ap- considered them as related to a third velocity proaching side respectively. component. For |r|≤1300 (∼ 8 kpc) we are able to disen- tangle (Fig. 1 and Fig. 2) three kinematically distinct gaseous components, named as fast- 4. Discussion rotating (i), slow-rotating (ii) and third (iii). 00 The fast-rotating gas component (i) shows In the inner ±13 UGC 10205 we are facing a velocity curve with a very steep gradient, two main kinematically distinct gaseous com- reaching an observed maximum rotation of ponents, namely (i) and (ii). They have quite 240 km s−1 at |r|∼300 (∼ 2kpc)fromthe similar velocity dispersion profiles but very center and remaining almost constant for |r| > different velocity curves, which produce the 300. Its velocity dispersion has a central peak of “figure-of-eight” appearance of UGC 10205 about 90 km s−1 and it shows a sharp decrease velocity curve. to values lower than 25 km s−1 outwards. The What is the real spatial distribution of these radial velocity of the slow-rotating gas com- two components? Are they really cospatial or ponent (ii) increases linearly with the distance are they spatially distinct and seen superim- from the galaxy center reaching 240 km s−1 at posed on account of a projection effect? |r|∼1400 (∼ 9 kpc). The velocity dispersion The simultaneous presence of the two gas remains between 40 km s−1 and 50 km s−1. components at the same distance of the galaxy This range is larger in the [N II] line, which center raises the problem of the viscous in- however is characterized by a lower signal-to- teraction of distinct gaseous structures with noise ratio. In the radial range between r ∼ 300 different kinematical characteristics. One pos- and r ∼ 1300 along the SE side of the major sibility is the gas to be distributed in colli- axis the Hα and [N II] emissions have triple- sionless cloudlets, as suggested by Cinzano & peaked lines. Indeed in this region the compo- van der Marel (1994) to explain the ionized nent (iii) is observed. It has a radial velocity gas kinematics in the E4 NGC 2974.