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(1968) 139, 425-459. Photometry, Kinematics And

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Mon, Not, R, astr. Soc, (1968) 139, 425-459. PHOTOMETRY, KINEMATICS AND DYNAMICS OF THE MAGELLANIC-TYPE BARRED SPIRAL GALAXY NGC 4027* Gerard de Vaucouleurs, Antoinette de Vaucouleurs and Kenneth C, Freeman (Received 1967 December 27)f Summary Photometric and spectroscopic observations with the 36-in. and 82-in. reflectors are analysed to derive a mean rotation curve, total mass and mass- luminosity ratio of the Magellanic-type barred spiral NGC 4027. For an estimated distance A = 12*5 Mpc the adopted values are T = (13 ±3) x I°9»/b = 1*85 ±0*4 with By = ii*7o±o-o5, (B-V)t = +0*54, {U-B)t = —0-03. The mass is close to that of the Large Magellanic Cloud, but the mass- luminosity ratio is lower because of the relatively higher surface brightness of NGC 4027. The rotation curve is asymmetric with respect to the centre of the bar as previously observed in galaxies of the same type (LMC, NGC 55, 4631). A model consisting of a prolate spheroid (bar) offset from the centre of a larger oblate spheroid is described; it accounts qualitatively and quantita- tively for the residual velocity pattern (non-circular motions) observed in NGC 4027 and the Large Cloud. Detailed isophotometry of emission and absorption lines in the bar confirms the previously reported evidence for large scale gas streaming away from the centre and along the major axis of the bar, but it also reveals that, as theoreti- cally predicted, the mean motion of the stars near the minor axis of the bar is in a direction opposite to that of the gas and of the figure of the bar. i. Introduction, Several late-type barred spiral galaxies similar to the Large Magellanic Cloud have been observed in detail with the B-spectrograph at the prime-focus of the 82-in. Struve reflector since i960. The initial objective was to determine whether the peculiar, asymmetric rotation curve first observed in the Large Cloud (Kerr & de Vaucouleurs 1955, 1956; de Vaucouleurs 1960a; Feast, Thackeray & Wesselink 1961 ; McGee & Milton 1966) and later in NGC 55 (de Vaucouleurs 1961; Epstein 1964; Robinson & van Damme 1964, 1966) is a general phenomenon, characteristic of this galaxy type and reflecting its structural asymmetry (de Vaucouleurs 1954, 1955, 1960a). The second objective was to obtain additional information on the large-scale gas streaming motions in the bars first detected in NGC 4631 (de Vaucouleurs & de Vaucouleurs 1963a) and later in NGC 4027 and NGC 7741 (de Vaucouleurs & de Vaucouleurs 1963b; de Vaucouleurs 1964). The final objective is to provide tests for the dynamical models of barred spiral galaxies developed in recent years (Freeman 1966a, b), and in particular to check certain theoretical predictions on the relative peculiar motions of stars and gas (Freeman & de Vaucouleurs 1966). We report here on our analysis of NGC 4027 which, as explained previously (de Vaucouleurs 1964), is one of the very few objects suitably orientated and large * Contributions from the McDonald Observatory, University of Texas, No. 424. f Received in original form 1967 September 16. © Royal Astronomical Society • Provided by the NASA Astrophysics Data System 426 Gerard de Vaucouleurs et ah Vol. 139 .425D enough to be observed in some detail with the 82-in. reflector. The main elements of this galaxy are listed in Table I. It forms a probably physical triplet with the well-known interacting pair NGC 4038-39 (Burbidge et al. 1966) at 41' and has a o 68MNRAS.139. faint dwarf Magellanic irregular companion NGC 4027-A at 4'o in p.a. 190 (see 19 Appendix II). Fig. 1 is a photograph taken (in poor seeing) at the Cassegrain focus of the 82-in. reflector and shows the inner regions, in particular the short bright bar. Uncalibrated density contours of the 82-in. plate traced with the Griboval isophotometer (de Vaucouleurs, Griboval & White 1965) are shown in Fig. 2. Table I Elements of NGC 4027 Equatorial coordinates (1950)* a = nh 57m*o 8 — — 180 59' New galactic coordinates* Z11 = 286 o *38 b11 = +410 *94 Supergalactic coordinates* L = i32°-8 B = —17°-9 Group membership Pair with NGC 4038-39 Apparent photographic modulus m — M = 30*85 Corrected modulus mo-M = 30*5 + 0*5 (A = 0*35 mag.) Distance in megaparsecs A = i2*5±2*5 Revised type* SB(s)dm Inclination i = 40 0 ± 2 0 (m.e.) Standard photographic diameter* D = 2'*6 ±o'*2 (m.e.) = 9*4 kpc Photographic axis ratio* d/D = 0*775 ±0*05 (m.e.) Reduced (face on) diameter* D{o) = 2,*35±o/*i5 = 8*5 kpc Standard apparent magnitude* B{6) — 11*90 (trie = 12*09) Average surface brightness* B\o) = 13*44 (wc' = 13-63) Microphotometric diameter Dm - 3 *9 = 14 kpc Microphotometric axis ratio dm!Dm -0*75 Photometric effective axes 2ae = T*3 2be = i'*o Apparent colour indices (B-V)(o) = 0*67 (U-B)(o) = -0*03 * Reference Catalogue of Bright Galaxies (1964). A better photograph (Fig. 3) taken by H. D. Abies with the Kron-Lallemand Electronic camera (Kron & Papiashvili 1966) attached to the 40-in. reflector of the U.S. Naval Observatory Flagstaff Station shows details of the spiral pattern and faint outer whorl. On both photographs the asymmetric spiral structure, dominated by the major trailing arm and characteristic of the magellanic-type spirals (de Vaucouleurs 1960a, 1961, 1964) is clearly in evidence. However, its stage is slightly ‘ earlier ’ than the Large Cloud. From a study of morphology and colours, we assign to NGC 4027 the classification SB{s) d or dm in agreement with the Reference Catalogue (de Vaucouleurs & de Vaucoulers 1964). 2. Integrated magnitude and colours. The luminosity distribution in NGC 4027 was investigated photographically in 1940 by F. S. Patterson (now Mrs Jones) in an unpublished Radcliffe College Dissertation (1941). Through the courtesy of Mrs Jones we were able to use her data consisting of magnitude differences ÙM = m — m§, (mo = central magnitude) to prepare the isophote map shown in Fig. 4. The magnitudes were measured at regular intervals of 9"#7 in a rectangular grid (Patterson 1940); isophotes were derived by linear interpolation between adjacent squares without smoothing and with a 9-point gaussian smoothing. The smoothing and plotting program for the CDC 1604 computer was prepared by © Royal Astronomical Society • Provided by the NASA Astrophysics Data System 19 68MNRAS.139. .425D © Royal Astronomical Society • Provided by the NASA Astrophysics Data [Facing System page 426 Fig. i. iVGC 4027 photographed at Cassegrainian focus of 8z-in. Struve reflector (77-in. diaphragm)y 1963 March 1 exposure 2 h 24 m, 103 a-O, no filter, poor seeing. Fig. 3. NGC 4.027 electronograph by H. D. Abies with the Kron-Lallemand camera attached to the 40-in. Ritchey-Chretien reflector of the U.S. Naval Observatory, Flagstaff Station. U.S. Navy Photograph. © Royal Astronomical Society • Provided by the NASA Astrophysics Data System No. 4, 1968 The barred spiral galaxy NGC 4027 .425D 427 68MNRAS.139. 19 Fig. 2. Uncalibrated density contours of 82-in. photograph of NGC 4027 traced with the Griboval isophotometer. © Royal Astronomical Society Provided by the NASA Astrophysics Data System 428 Gerard de Vaucouleurs et al. Vol. 139 .425D Mr D. Wells. The mean luminosity profiles 1(a), 1(b), I(r*) are given in Fig. 5. The integrated luminosity distribution (•Am 68MNRAS.139. L(Am) = J io-o-4Am dS(Am) 19 derived in relative units by planimetry of the isophotes is shown in Fig. 6. The effective axes are 2^ = zbe = i'o. Fig. 4. Smoothed isophotes of NGC 4027 from the photographic photometry of F. S. Patter son-Jones. Innermost isophote is for log I = — o-6, outer contour for log I = —2-7, level spacing A log I = o-i; unit of I = 19*12 (B) mag sec~2. Weights of smoothing function shown in inset correspond to about 15" resolution. Table II Magnitudes and colours of NGC 4027 A = zr V B-V U-B o'*20 14*06 0*527 + 0*030 0*50 12*87 0*525 -0*074 0*52 12*78 0*533 + 0*023 i *07 11*92 0*497 — 0*129 i *08 11*87 0*501 + 0*005 2*30* 11*37 0*542 — 0*062 2*50* ii • 10 0*539 — 0*011 2*68* II *21 0*528 — 0*030 00 II-I5 o*54 -0*03 * Magnitudes and colours in three largest apertures are corrected for the effect of star A for which V = 14*22, B-V = +0*63, U-B = —0*03 (in). © Royal Astronomical Society • Provided by the NASA Astrophysics Data System No. 4, 1968 The barred spiral galaxy NGC 429 .425D The zero-point calibration of the photographic isophotes was derived by comparison with photoelectric magnitudes in the £/, fi, V system measured with the McDonald 36-inch reflector and listed in Table II. The zero point K of the 68MNRAS.139. photographic magnitude scale is given by 19 ,4Am Br = K—z-$ log (ztt) J io“° r dr where Br is the B magnitude measured through an aperture A = ar. The three larger apertures give B(A = a'5) = 1179 for which A(r* = T25) = 0*915 and a total (asymptotic) magnitude 11*69. Allowing for the effect of a second field star oí 16 (not measured) we adopt Bt = 1170 ±0*05 (m.e.) with (B-V)t = +0-54 (U-B)t = —0*03. Fig. 5. Mean photographic luminosity profiles of NGC 4027 derived from F. S. Jones9 photometry, a, along major aods\ b> minor axis, (r*) equivalent profile.
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  • ASTRONOMY and ASTROPHYSICS Ultraviolet Spectral Properties of Magellanic and Non-Magellanic Irregulars, H II and Starburst Galaxies?

    ASTRONOMY and ASTROPHYSICS Ultraviolet Spectral Properties of Magellanic and Non-Magellanic Irregulars, H II and Starburst Galaxies?

    Astron. Astrophys. 343, 100–110 (1999) ASTRONOMY AND ASTROPHYSICS Ultraviolet spectral properties of magellanic and non-magellanic irregulars, H II and starburst galaxies? C. Bonatto1, E. Bica1, M.G. Pastoriza1, and D. Alloin2;3 1 Universidade Federal do Rio Grande do Sul, IF, CP 15051, Porto Alegre 91501–970, RS, Brazil 2 SAp CE-Saclay, Orme des Merisiers Batˆ 709, F-91191 Gif-Sur-Yvette Cedex, France Received 5 October 1998 / Accepted 9 December 1998 Abstract. This paper presents the results of a stellar popula- we dedicate the present work to galaxy types with enhanced 1 1 tion analysis performed on nearby (VR 5 000 km s− ) star- star formation in the nearby Universe (VR 5 000 kms− ). We forming galaxies, comprising magellanic≤ and non-magellanic include low and moderate luminosity irregular≤ galaxies (magel- irregulars, H ii and starburst galaxies observed with the IUE lanic and non-magellanic irregulars, and H ii galaxies) and high- satellite. Before any comparison of galaxy spectra, we have luminosity ones (mergers, disrupting, etc.). The same method formed subsets according to absolute magnitude and morpho- used in the analyses of star clusters, early-type and spiral gala- logical classification. Subsequently, we have coadded the spec- xies (Bonatto et al. 1995, 1996 and 1998, hereafter referred to tra within each subset into groups of similar spectral proper- as Papers I, II and III, respectively), i.e. that of grouping objects ties in the UV. As a consequence, high signal-to-noise ratio with similar spectra into templates of high signal-to-noise (S/N) templates have been obtained, and information on spectral fea- ratio, is now applied to the sample of irregular and/or peculiar tures can now be extracted and analysed.