The Phenomenon of the Galaxy NGC 6286: a Forming Polar Ring Or A
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Astronomy Letters, Vol. 30, No. 1, 2004, pp. 1–13. Translated from Pis’ma v Astronomicheski˘ı Zhurnal, Vol. 30, No. 1, 2004, pp. 3–16. Original Russian Text Copyright c 2004 by Shalyapina, Moiseev, Yakovleva, Hagen-Thorn, Burenkov. The Phenomenon of the Galaxy NGC 6286: AFormingPolarRingoraSuperwind? L. V. Shalyapina1*, A.V.Moiseev2, V.A.Yakovleva1, V. A. Hagen-Thorn 1, and A. N. Burenkov2 1Astronomical Institute, St. Petersburg State University, Bibliotechnaya pl. 2, Petrodvorets, 198904 Russia 2Special Astrophysical Observatory, Russian Academy of Sciences, Nizhnii Arkhyz, 357147 Karachai-Cherkessian Republic, Russia Received March 20, 2003; in final form, May 26, 2003 Abstract—We present our observations of the pair of interacting galaxies NGC 6285/86 carried out with the 6-m Special Astrophysical Observatory (SAO) telescope using 1D and 2D spectroscopy. The observations of NGC 6286 with a long-slit spectrograph (UAGS) near the Hα line revealed the rotation of the gaseous disk around an axis offset by 5–7 from the photometric center and a luminous gas at a distance up to 9 kpc in a direction perpendicular to the galactic plane. Using a multipupil fiber spectrograph (MPFS), we constructed the velocity fields of the stellar and gaseous components in the central region of this galaxy, which proved to be similar. The close radial velocities of the pair and the wide (5 × 5) field of view of the scanning Fabry–Perot interferometer (IFP) allowed us to simultaneously obtain images in the Hα and[NII]λ6583 lines and in the continuum, as well as to construct the radial velocity fields and to map the distribution of the [N II] λ6583/Hα ratio for both galaxies. Based on all these data, we studied the 11 gas kinematics in the galaxies, constructed their rotation curves, and estimated their masses (2 × 10 M 10 for NGC 6286 and 1.2 × 10 M for NGC 6285). We found no evidence of gas rotation around the major axis of NGC 6286, which argues against the assumption that this galaxy has a forming polar ring. The IFP observations revealed an emission nebula around this galaxy with a structure characteristic of superwind galaxies. The large [N II] λ6583/Hα ratio, which suggests the collisional excitation of its emission, and the high infrared luminosity are additional arguments for the hypothesis of a superwind in the galaxy NGC 6286. A close encounter between the two galaxies was probably responsible for the starburst and the bipolar outflow of hot gas from the central region of the disk. c 2004 MAIK “Nauka/Interperiodica”. Key words: polar-ring galaxies, NGC 6285/86, superwind, kinematics. INTRODUCTION runs at an angle to the stellar disk of the galaxy. NGC 6285/86 (Arp 293) is a pair of interacting Since, according to IRAS data, this galaxy has galaxies (Fig. 1) with similar luminosities and ra- a high infrared luminosity, log(LFIR/L)=11.28 dial velocities.1 They are ∼1.5 apart, which corre- (Soifer et al. 1987), it was included in the studies of sponds to ∼40 kpc for a distance D =91Mpc (at bright infrared galaxies (see, e.g., Baan 1989; Young − − sys − et al. 1989). The infrared fluxes from NGC 6286 were H =65 km s 1 Mpc 1 and V = 5925 km s 1; 0 gal measured at various wavelengths (Soifer et al. 1987, see below). A faint bridge can be seen between the 1989). These fluxes were used to determine the dust galaxies in deep CCD images. Whitmore et al. (1990) temperature and mass (Young et al. 1989) and to included one of the galaxies from the pair, NGC 6286, −1 estimate the star-formation rate, SFR ∼ 56M yr in the catalog of polar-ring galaxies as a possible (Smith et al. 1998). Based on radio data, Sanders candidate (C 51), because a diffuse structure (semi- et al. (1986) estimated the H mass for this galaxy, ring) located to the southeast (SE) of the main body 2 log M(H )/M =9.97. of the galaxy is clearly seen in the reproduction in the 2 atlas by Arp (1966). The optical spectra of this galaxy have been de- NGC 6286 is a spiral Sb-type (RC3) galaxy scribed by several authors. Reshetnikov and Сombes seen almost edge-on with a thick dust lane that (1994) classified its nuclear spectrum as H II and pointed out a peculiarity in the radial velocity distri- *E-mail: [email protected] bution of the gas along the minor axis of the galaxy. 1According to NED data. Veilleux et al. (1995) classified the nuclear spectra 1063-7737/04/3001-0001$26.00 c 2004 MAIK “Nauka/Interperiodica” 2SHALYAPINAet al. interferometer (IFP) in 2002. A log of observations is N given in table. In the UAGS, the detectors were Electron 530× × E 580-pixel and Photometrics 1024 1024-pixel CCD arrays in 1997 and 1999, respectively. The UAGS slit size in the observations was 2 × 140. The observed spectral range included the Hα, [N II] λ6548, 6583, PA = 34 PA = 133 and [S II] λ6716, 6731 emission lines. The UAGS spectroscopic data were reduced in PA = 60 the ESO–MIDAS environment using the LONG context. After the primary reductions, we performed a smoothing along the slit with windows of 0.8 for the central region and 2 starting from a distance PA = 85 of 15 from the center. The radial velocities were measured from the positions of the centers of the PA = 116 10″ Gaussians fitted to the emission lines. The accuracy of these measurements was estimated from the night- sky [O I] λ6300 line to be ±10 km s−1. We also mea- sured the relative intensities and full widths at half maximum (FWHMs) of the above emission lines. The Fig. 1. An R-band image of the NGC 6285/86 pair obtained with the 6-m SAO telescope (for the assumed observed FWHMs were corrected for the FWHM of distance to the galaxies of D =91Mpc; 1 corresponds the instrumental profile by using the standard relation to 0.44 kpc). 2 2 − 2 (FWHM) =(FWHM)obs (FWHM)instr. Accord- ing to the measurements of lines from a calibration lamp, the FWHM of the instrumental profile was of NGC 6286 and NGC 6285 as LINER and H II, ˚ respectively. Smith et al. (1996) used the Hα line 3.6 A. The Hα, [N II] λ6583, and [S II] λ6716, λ6731 to construct the rotation curve for NGC 6286 and emission lines are most intense in the spectrum of this 11 estimated its mass (M =1.3 × 10 M). galaxy. These lines were used to construct the radial velocity curves for the ionized gas. Reshetnikov et al. (1996) performed a detailed photometric study of NGC 6286 in the B,V ,andR During our MPFS observations, we simultane- c ously took spectra from 240 spatial elements (in the bands. Based on peculiarities of the radial velocity × curve along its minor axis and on photometric data, form of square lenses) that formed an array of 16 they assumed that the diffuse structure (semi-ring) 15 elements in the plane of the sky. The angular size of a single element was 1. The detector was located at the SE edge of the galaxy is a forming polar × ring. aTechtronix1024 1024-pixel CCD array. The observations were carried out in two spectral ranges. To analyze the kinematics of the gaseous and The green range included emission lines of the stellar components of the galaxy NGC 6286 in more gaseous component (Hβ, [O III] λ 4959, 5007)and detail, we have undertaken its study using long-slit absorption lines of the stellar population of the galaxy (1D) and 2D spectroscopy. (Mg I λ5175,FeIλ5229,FeI+ Ca Iλ5270,andoth- ers). The red range contained the Hα, [N II] λ 6548, 6583, and [S II] λ 6716, 6730 emission lines. 1. OBSERVATIONS AND DATA REDUCTION We reduced the observations by using the software The spectroscopic observations of NGC 6286 that was developed at the SAO by Afanasiev et al. were made at the prime focus of the 6-m SAO (1995) (SAO) and that runs in the IDL environment. telescope. The first observations were carried out We constructed two-dimensional maps of the inten- with a long-slit spectrograph (UAGS) (Afanasiev sity and radial velocity (velocity field) from the emis- et al. 1995) in 1997 and 1999. The observations with sion lines and fitted the line profiles by Gaussians. The a multipupil fiber spectrograph (MPFS) (a descrip- radial velocities were determined with an accuracy tion of the spectrograph can be found on the Internet of 10–15 km s−1. The radial velocity fields of the at the SAO webpage2) were performed in 2001, and stellar component were constructed by means of a the data were obtained with a scanning Fabry–Perot cross-correlation technique modified to work with 2D spectroscopic data and described in detail by Moi- 2http://www.sao.ru/gafan/devices/mpfs/mpfs_main.htm seev (2001). Spectra of the star HD 148293 and the ASTRONOMY LETTERS Vol. 30 No. 1 2004 THE PHENOMENON OF THE GALAXY NGC 6286 3 Log of observations Reciprocal dispersion, Instrument, year Exposure time, s PA, field Spectral range, A˚ Seeing A/pixel˚ UAGS 3 × 1800 34◦ 6200–7000 1.5 3.2 Sep. 1997 3 × 1800 116 6200–7000 1.5 2.5 3 × 1800 133 6200–7000 1.5 2.5 Aug.–Sep. 1999 3 × 1800 60 6200–7000 1.2 1.6 3 × 1800 85 6200–7000 1.2 1.6 3 × 1800 85 6200–7000 1.2 1.5 3 × 1800 133 6200–7000 1.2 1.6 MPFS 3 × 1200 Center 4900–6200 1.35 2 Apr.–Sep.