ASTRONOMY & ASTROPHYSICS FEBRUARY I 1999, PAGE 437 SUPPLEMENT SERIES Astron. Astrophys. Suppl. Ser. 134, 437–451 (1999) Structure and kinematics of the peculiar galaxy NGC 128? M. D’Onofrio1, M. Capaccioli2,3, P. Merluzzi2,S.Zaggia2, and J. Boulesteix4 1 Dipartimento di Astronomia, Universit`a di Padova, vicolo dell’Osservatorio 5, I-35122 Padova, Italy 2 Osservatorio Astronomico di Capodimonte, via Moiariello 16, I-80131 Napoli, Italy 3 Dipartimento di Scienze Fisiche, Universit`a di Napoli, Mostra d’Oltremare, Padiglione 19, I-80125 Napoli, Italy 4 Observatoire de Marseille, 2 place Le Verrier, F-13248 Marseille Cedex 04, France Received February 13; accepted August 31, 1998 Abstract. This is a multiband photometric and spectro- 1. Introduction scopic study of the peculiar S0 galaxy NGC 128. We present results from broad (B and R) and narrow (Hα) The connection between the boxy/peanut morphology of band optical CCD photometry, near (NIR) and far (FIR) galactic bulges and the presence of a bar is difficult to infrared observations, long slit spectroscopy, and Fabry- prove observationally. The main difficulty comes from the Perot interferometry (CIGALE). fact that the peculiar morphology can be seen only in The peculiar peanut shape morphology of the galaxy almost edge-on systems. is observed both at optical and near-infrared wavelengths. Photometric evidences of a bar in boxy/peanut galax- The stellar disk is thick and distorted (arc-bended), with a ies have been found only in a few cases, e.g. the barred color asymmetry along the major axis due to the presence galaxy NGC 4442 at intermediate inclination (Bettoni of a large amount of dust, estimated through NIR and FIR & Galletta 1994), the edge-on S0 galaxy NGC 1381 (de 6 data of ∼ 610 M , in the region of interaction with the Carvalho & da Costa 1987), NGC 5170 (Dettmar companion galaxy NGC 127. & Barteldrees 1988), NGC 2654, and NGC 4469 (Jarvis The color maps are nearly uniform over the whole 1986). galaxy, but for the major axis asymmetry, and a small The kinematic observations offer further evidences of gradient toward the center indicating the presence of a this connection. Kuijken & Merrifield (1995) obtained a redder disk-like component. The Hα image indeed reveals characteristic “figure-of-eight” rotation curve, which is the existence of a tilted gaseous “disk” around the cen- likely the strong signature for the presence of a bar, for ter, oriented with the major axis toward the companion two peanut shape objects: NGC 5746 and NGC 5965. galaxy NGC 127. Other known cases of galaxies with these peculiar rotation Long slit and CIGALE data confirm the presence of curves are IC 5096 (Bureau & Freeman 1997), NGC 2683 gas in a disk-like component counter-rotating and inclined (Merrifield 1996), NGC 5907 (Miller & Rubin 1995, and approximately of 50◦ to the line of sight. The mass of the UGC 10205 (Vega et al. 1997). 4 gas disk in the inner region is ∼ 2.710 M . Of course, given the small number of cases, new accu- The stellar velocity field is cylindrical up to the last rate photometric and spectroscopic observations are nec- measured points of the derived rotation curves, while the essary for solving the peanut/bar connection. velocity dispersion profiles are typical for an S0 galaxy, Here we present a large data-set for the most represen- but for an extended constant behaviour along the minor tative object of this class: NGC 128, the standard peanut- axis. shaped galaxy (Sandage 1961). In the following sections we describe the peculiar Key words: galaxies: individual: NGC 128 — galaxies: morphology of NGC 128 and its group, present a 2D ap- elliptical and lenticular, cD — galaxies: photometry — proximated model of the surface brightness of the galaxy galaxies: kinematics and dynamics — galaxies: structure (Sect. 2), give the results of long slit and CIGALE data (Sect. 3), show the surface brightness and color profiles of the galaxy at optical and near infrared wavelengths Send offprint requests to: M. D’Onofrio (Sect. 4), present the results of Hα and NIR observa- ? Based on observations taken at ESO La Silla and at tions (Sect. 5 and Sect. 6), analyze the far infrared IRAS the Special Astrophysical Observatory (SAO) of the Russian Academy of Sciences (RAS). 438 M. D’Onofrio et al.: The peculiar galaxy NGC 128 data (Sect. 7), and briefly summarize the whole datasets (Sect. 8). The technical solutions adopted for the data reduction are given in the Appendix. 2. Morphology The peculiar edge-on S0 galaxy NGC 128 is the dominant member of a group which includes NGC 126 (E/SB0), NGC 127 (Sa), NGC 130 (E5), a faint anonymous Sa galaxy 5.06 North and 9.05 preceding NGC 128, and possibly NGC 125 (S0 pec) (Zwicky et al. 1965). The membership of NGC 125 is controversial since its recession velocity is higher than average by ∼ 1000 km s−1. Burbidge & Burbidge (1959), Hodge & Merchant (1966), and Bertola & Capaccioli (1977, BC77) provided the first data for NGC 128 and its group. The galaxies of this group are late Ellipticals and early Spirals, and the recession velocities are in the range 4200 − 4600 km s−1. NGC 128 is connected by a bridge to NGC 127, and ac- cording to BC77 a set of filaments protrudes southwards Fig. 1. B-band maps of the O-C residuals for NGC 128: Upper to NGC 126. The galaxy NGC 125 is surrounded by a panel: the result of the unsharp masking technique; Middle large ring (BC77 estimated a diameter of ∼70 kpc) which panel: the X-structure and the disk of NGC 128 after the sub- is asymmetrically placed with respect to the center of the traction of a model of the bulge component, obtained by fitting galaxy. the inner isophotes with ellipses; Bottom panel: the result of the subtraction of a model of the bulge and disk component (see NGC 128 is classified as BS-I in the list of de Souza & 00 dos Anjos (1987). The peculiar peanut shape of the bulge text). North is on the left, West is up. The image is ∼100 in the N-S direction is clearly visible even in the innermost isophotes: the bulge appears squared by four symmetric bumps, forming an distribution along cuts perpendicular to the disk major X-structure with arms at ∼ 45◦ from the major axis of the axis have a maximum shift of 700 (1.9 kpc). 00 1 galaxy and extended, in projection, for ∼20 (5.4 kpc) . We tempted to highlight the peculiar morphology of The peculiar morphology is not due to extinction effects NGC 128 in different ways using the images with the best (see next sections). seeing and higher S/N ratio (the B-band frames). First we As suggested by Pfenniger & Friedli (1991) the subtracted a model of the bulge component of the galaxy X-structure is likely an optical illusion. We clearly see this (Fig. 1, middle panel) obtained by fitting with ellipses effect in the original frame by changing the cuts: a thin the inner isophotal contours of the galaxy. In the residual disk and a small, and approximately round, bulge are seen map we identify the X-structure (in white color) and the in the center at the higher counts, while an increase of the disk component, which appears thicker in the outer region. thickness of the disk is apparent at lower counts. Such The X-structure contributes approximately only to ∼5% “flaring” seems to originate the X-structure. The impres- of the total luminosity of the galaxy. This means that it is sion one has is that of looking to a “papillon”. The stars a projection effect rather than a physical new component. seem pulled out of the disk, the maximum effect taking While the X-structure and the bending of the disk are place at ∼11 arcsec, corresponding to ∼3kpc. clearly visible in the original CCD frames, the increasing The galaxy is seen approximately edge-on. We derived thickness of the disk in the outer region is possibly the alog(a25/b25) ratio of 0.76, a value which is in rela- result of the bulge subtraction (we verified this fact by tive good agreement with that found by Guthrie (1992) simulating an edge-on S0 galaxy and subtracting the bulge in his sample of edge-on galaxies for the S0 class. The component). Using the unsharp masking technique (Fig. 1, observed major axis diameter is ∼ 50 kpc (at µB = upper panel) we were able to confirm the bending of the −2 26.0 mag arcsec ), and the thickness along the minor disk on both sides, but not the flaring of the outer disk. axis ∼ 21 kpc. The X-structure is obviously not visible in such image. The disk appears bended toward West on both sides, Notice that in Fig. 1 (middle and lower panels) the either in the visual and in the NIR images, in particular disk is fainter along the North direction. Here there is a toward the South-West direction, where the bending starts strong absorption in correspondence of the encounter of at r =3700 (10 kpc) from the center. The peaks of the light the disk of NGC 128 with the arm of NGC 127. 1 We assume throughout the paper a distance of 56 Mpc for Since the X-structure is the result of the subtraction −1 −1 the galaxy and H0 =75kms Mpc . of a model built with elliptical isophotes on a galaxy with M. D’Onofrio et al.: The peculiar galaxy NGC 128 439 a pronounced boxy shape, we realized a new 2D model of the galaxy taking into account the boxiness of the bulge.