DOCSLIB.ORG

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

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
(1968) 139, 425-459. Photometry, Kinematics And 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.
Load more

Recommended publications
  • Messier Objects
    Messier Objects From the Stocker Astroscience Center at Florida International University Miami Florida The Messier Project Main contributors: • Daniel Puentes • Steven Revesz • Bobby Martinez Charles Messier • Gabriel Salazar • Riya Gandhi • Dr. James Webb – Director, Stocker Astroscience center • All images reduced and combined using MIRA image processing software. (Mirametrics) What are Messier Objects? • Messier objects are a list of astronomical sources compiled by Charles Messier, an 18th and early 19th century astronomer. He created a list of distracting objects to avoid while comet hunting. This list now contains over 110 objects, many of which are the most famous astronomical bodies known. The list contains planetary nebula, star clusters, and other galaxies. - Bobby Martinez The Telescope The telescope used to take these images is an Astronomical Consultants and Equipment (ACE) 24- inch (0.61-meter) Ritchey-Chretien reflecting telescope. It has a focal ratio of F6.2 and is supported on a structure independent of the building that houses it. It is equipped with a Finger Lakes 1kx1k CCD camera cooled to -30o C at the Cassegrain focus. It is equipped with dual filter wheels, the first containing UBVRI scientific filters and the second RGBL color filters. Messier 1 Found 6,500 light years away in the constellation of Taurus, the Crab Nebula (known as M1) is a supernova remnant. The original supernova that formed the crab nebula was observed by Chinese, Japanese and Arab astronomers in 1054 AD as an incredibly bright “Guest star” which was visible for over twenty-two months. The supernova that produced the Crab Nebula is thought to have been an evolved star roughly ten times more massive than the Sun.
    [Show full text]
  • THE 1000 BRIGHTEST HIPASS GALAXIES: H I PROPERTIES B
    The Astronomical Journal, 128:16–46, 2004 July A # 2004. The American Astronomical Society. All rights reserved. Printed in U.S.A. THE 1000 BRIGHTEST HIPASS GALAXIES: H i PROPERTIES B. S. Koribalski,1 L. Staveley-Smith,1 V. A. Kilborn,1, 2 S. D. Ryder,3 R. C. Kraan-Korteweg,4 E. V. Ryan-Weber,1, 5 R. D. Ekers,1 H. Jerjen,6 P. A. Henning,7 M. E. Putman,8 M. A. Zwaan,5, 9 W. J. G. de Blok,1,10 M. R. Calabretta,1 M. J. Disney,10 R. F. Minchin,10 R. Bhathal,11 P. J. Boyce,10 M. J. Drinkwater,12 K. C. Freeman,6 B. K. Gibson,2 A. J. Green,13 R. F. Haynes,1 S. Juraszek,13 M. J. Kesteven,1 P. M. Knezek,14 S. Mader,1 M. Marquarding,1 M. Meyer,5 J. R. Mould,15 T. Oosterloo,16 J. O’Brien,1,6 R. M. Price,7 E. M. Sadler,13 A. Schro¨der,17 I. M. Stewart,17 F. Stootman,11 M. Waugh,1, 5 B. E. Warren,1, 6 R. L. Webster,5 and A. E. Wright1 Received 2002 October 30; accepted 2004 April 7 ABSTRACT We present the HIPASS Bright Galaxy Catalog (BGC), which contains the 1000 H i brightest galaxies in the southern sky as obtained from the H i Parkes All-Sky Survey (HIPASS). The selection of the brightest sources is basedontheirHi peak flux density (Speak k116 mJy) as measured from the spatially integrated HIPASS spectrum. 7 ; 10 The derived H i masses range from 10 to 4 10 M .
    [Show full text]
  • ASTRONOMY and ASTROPHYSICS the Elliptical Galaxy Formerly Known As the Local Group: Merging the Globular Cluster Systems
    Astron. Astrophys. 358, 471–480 (2000) ASTRONOMY AND ASTROPHYSICS The elliptical galaxy formerly known as the Local Group: merging the globular cluster systems Duncan A. Forbes1,2, Karen L. Masters1, Dante Minniti3, and Pauline Barmby4 1 University of Birmingham, School of Physics and Astronomy, Edgbaston, Birmingham B15 2TT, UK 2 Swinburne University of Technology, Astrophysics and Supercomputing, Hawthorn, Victoria 3122, Australia 3 P. Universidad Catolica,´ Departamento de Astronom´ıa y Astrof´ısica, Casilla 104, Santiago 22, Chile 4 Harvard–Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA Received 5 November 1999 / Accepted 27 January 2000 Abstract. Prompted by a new catalogue of M31 globular clus- al. 1995; Minniti et al. 1996). Furthermore Hubble Space Tele- ters, we have collected together individual metallicity values for scope studies of merging disk galaxies reveal evidence for the globular clusters in the Local Group. Although we briefly de- GC systems of the progenitor galaxies (e.g. Forbes & Hau 1999; scribe the globular cluster systems of the individual Local Group Whitmore et al. 1999). Thus GCs should survive the merger of galaxies, the main thrust of our paper is to examine the collec- their parent galaxies, and will form a new GC system around tive properties. In this way we are simulating the dissipationless the newly formed elliptical galaxy. merger of the Local Group, into presumably an elliptical galaxy. The globular clusters of the Local Group are the best studied Such a merger is dominated by the Milky Way and M31, which and offer a unique opportunity to examine their collective prop- appear to be fairly typical examples of globular cluster systems erties (reviews of LG star clusters can be found in Brodie 1993 of spiral galaxies.
    [Show full text]
  • Spiral Galaxies, Elliptical Galaxies, Irregular Galaxies, Dwarf Galaxies, Peculiar/Interacting Galalxies Spiral Galaxies
    Lecture 33: Announcements 1) Pick up graded hwk 5. Good job: Jessica, Jessica, and Elizabeth for a 100% score on hwk 5 and the other 25% of the class with an A. 2) Article and homework 7 were posted on class website on Monday (Apr 18) . Due on Mon Apr 25. 3) Reading Assignment for Quiz Wed Apr 27 Ch 23, Cosmic Perspectives: The Beginning of Time 4) Exam moved to Wed May 4 Lecture 33: Galaxy Formation and Evolution Several topics for galaxy evolution have already been covered in Lectures 2, 3, 4,14,15,16. you should refer to your in-class notes for these topics which include: - Types of galaxies (barred spiral, unbarred spirals, ellipticals, irregulars) - The Local Group of Galaxies, The Virgo and Coma Cluster of galaxies - How images of distant galaxies allow us to look back in time - The Hubble Ultra Deep Field (HUDF) - The Doppler blueshift (Lectures 15-16) - Tracing stars, dust, gas via observations at different wavelengths (Lecture15-16). In next lectures, we will cover - Galaxy Classification. The Hubble Sequence - Mapping the Distance of Galaxies - Mapping the Visible Constituents of Galaxies: Stars, Gas, Dust - Understanding Galaxy Formation and Evolution - Galaxy Interactions: Nearby Galaxies, the Milky Way, Distant Galaxies - Mapping the Dark Matter in Galaxies and in the Universe - The Big Bang - Fates of our Universe and Dark Energy Galaxy Classification Galaxy: Collection of few times (108 to 1012) stars orbiting a common center and bound by gravity. Made of gas, stars, dust, dark matter. There are many types of galaxies and they can be classfiied according to different criteria.
    [Show full text]
  • Extraplanar HII Regions in the Edge-On Spiral Galaxies NGC 3628 and NGC 4522? Y
    A&A 605, A5 (2017) DOI: 10.1051/0004-6361/201730589 Astronomy & c ESO 2017 Astrophysics Extraplanar HII regions in the edge-on spiral galaxies NGC 3628 and NGC 4522? Y. Stein1, D. J. Bomans1; 2, A. M. N. Ferguson3, and R.-J. Dettmar1; 2 1 Astronomisches Institut (AIRUB), Ruhr-Universität Bochum, Universitätsstrasse 150, 44801 Bochum, Germany e-mail: [email protected] 2 Research Department: Plasmas with Complex Interactions, Ruhr-Universität Bochum, Universitätsstrasse 150, 44801 Bochum, Germany 3 Institute for Astronomy, University of Edinburgh, Blackford Hill, Edinburgh EH9 3HJ, UK Received 9 February 2017 / Accepted 30 May 2017 ABSTRACT Context. Gas infall and outflow are critical for determining the star formation rate and chemical evolution of galaxies but direct measurements of gas flows are difficult to make. Young massive stars and Hii regions in the halos of galaxies are potential tracers for accretion and/or outflows of gas. Aims. Gas phase abundances of three Hii regions in the lower halos of the edge-on galaxies NGC 3628 and NGC 4522 are determined by analyzing optical long-slit spectra. The observed regions have projected distances to the midplane of their host from 1.4 to 3 kpc. Methods. With the measured flux densities of the optical nebular emission lines, we derived the oxygen abundance 12 + log(O/H) for the three extraplanar Hii regions. The analysis was based on one theoretical and two empirical strong-line calibration methods. Results. The resulting oxygen abundances of the extraplanar Hii regions are comparable to the disk Hii regions in one case and are a little lower in the other case.
    [Show full text]
  • The Herschel Sprint PHOTO ILLUSTRATION: PATRICIA GILLIS-COPPOLA, HERSCHEL IMAGE: WIKIMEDIA S&T
    The Herschel Sprint PHOTO ILLUSTRATION: PATRICIA GILLIS-COPPOLA, HERSCHEL IMAGE: WIKIMEDIA S&T 34 April 2015 sky & telescope William Herschel’s Extraordinary Night of DiscoveryMark Bratton Recreating the legendary sweep of April 11, 1785 There’s little doubt that William Herschel was the most clearly with his instruments. As we will see, he did make signifi cant astronomer of the 18th century. His accom- occasional errors in interpretation, despite the superior plishments included the discovery of Uranus, infrared optics; for instance, he thought that the planetary nebula radiation, and four planetary satellites, as well as the M57 was a ring of stars. compilation of two extensive catalogues of double and The other factor contributing to Herschel’s interest multiple stars. His most lasting achievement, however, was the success of his sister, Caroline, in her study of the was his exhaustive search for undiscovered star clusters sky. He had built her a small telescope, encouraging her and nebulae, a key component in his quest to understand to search for double stars and comets. She located Messier what he called “the construction of the heavens.” In Her- objects and more, occasionally fi nding star clusters and schel’s time, astronomers were concerned principally with nebulae that had escaped the French astronomer’s eye. the study of solar system objects. The search for clusters Over the course of a year of observing, she discovered and nebulae was, up to that point, a haphazard aff air, with about a dozen star clusters and galaxies, occasionally not- a total of only 138 recorded by all the observers in history.
    [Show full text]
  • A Search For" Dwarf" Seyfert Nuclei. VII. a Catalog of Central Stellar
    TO APPEAR IN The Astrophysical Journal Supplement Series. Preprint typeset using LATEX style emulateapj v. 26/01/00 A SEARCH FOR “DWARF” SEYFERT NUCLEI. VII. A CATALOG OF CENTRAL STELLAR VELOCITY DISPERSIONS OF NEARBY GALAXIES LUIS C. HO The Observatories of the Carnegie Institution of Washington, 813 Santa Barbara St., Pasadena, CA 91101 JENNY E. GREENE1 Department of Astrophysical Sciences, Princeton University, Princeton, NJ ALEXEI V. FILIPPENKO Department of Astronomy, University of California, Berkeley, CA 94720-3411 AND WALLACE L. W. SARGENT Palomar Observatory, California Institute of Technology, MS 105-24, Pasadena, CA 91125 To appear in The Astrophysical Journal Supplement Series. ABSTRACT We present new central stellar velocity dispersion measurements for 428 galaxies in the Palomar spectroscopic survey of bright, northern galaxies. Of these, 142 have no previously published measurements, most being rela- −1 tively late-type systems with low velocity dispersions (∼<100kms ). We provide updates to a number of literature dispersions with large uncertainties. Our measurements are based on a direct pixel-fitting technique that can ac- commodate composite stellar populations by calculating an optimal linear combination of input stellar templates. The original Palomar survey data were taken under conditions that are not ideally suited for deriving stellar veloc- ity dispersions for galaxies with a wide range of Hubble types. We describe an effective strategy to circumvent this complication and demonstrate that we can still obtain reliable velocity dispersions for this sample of well-studied nearby galaxies. Subject headings: galaxies: active — galaxies: kinematics and dynamics — galaxies: nuclei — galaxies: Seyfert — galaxies: starburst — surveys 1. INTRODUCTION tors, apertures, observing strategies, and analysis techniques.
    [Show full text]
  • Revealing Hidden Substructures in the $ M {BH} $-$\Sigma $ Diagram
    Draft version November 14, 2019 A Typeset using L TEX twocolumn style in AASTeX63 Revealing Hidden Substructures in the MBH –σ Diagram, and Refining the Bend in the L–σ Relation Nandini Sahu,1,2 Alister W. Graham2 And Benjamin L. Davis2 — 1OzGrav-Swinburne, Centre for Astrophysics and Supercomputing, Swinburne University of Technology, Hawthorn, VIC 3122, Australia 2Centre for Astrophysics and Supercomputing, Swinburne University of Technology, Hawthorn, VIC 3122, Australia (Accepted 2019 October 22, by The Astrophysical Journal) ABSTRACT Using 145 early- and late-type galaxies (ETGs and LTGs) with directly-measured super-massive black hole masses, MBH , we build upon our previous discoveries that: (i) LTGs, most of which have been 2.16±0.32 alleged to contain a pseudobulge, follow the relation MBH ∝ M∗,sph ; and (ii) the ETG relation 1.27±0.07 1.9±0.2 MBH ∝ M∗,sph is an artifact of ETGs with/without disks following parallel MBH ∝ M∗,sph relations which are offset by an order of magnitude in the MBH -direction. Here, we searched for substructure in the MBH –(central velocity dispersion, σ) diagram using our recently published, multi- component, galaxy decompositions; investigating divisions based on the presence of a depleted stellar core (major dry-merger), a disk (minor wet/dry-merger, gas accretion), or a bar (evolved unstable 5.75±0.34 disk). The S´ersic and core-S´ersic galaxies define two distinct relations: MBH ∝ σ and MBH ∝ 8.64±1.10 σ , with ∆rms|BH = 0.55 and 0.46 dex, respectively. We also report on the consistency with the slopes and bends in the galaxy luminosity (L)–σ relation due to S´ersic and core-S´ersic ETGs, and LTGs which all have S´ersic light-profiles.
    [Show full text]
  • Lopsided Spiral Galaxies: Evidence for Gas Accretion
    A&A 438, 507–520 (2005) Astronomy DOI: 10.1051/0004-6361:20052631 & c ESO 2005 Astrophysics Lopsided spiral galaxies: evidence for gas accretion F. Bournaud1, F. Combes1,C.J.Jog2, and I. Puerari3 1 Observatoire de Paris, LERMA, 61 Av. de l’Observatoire, 75014 Paris, France e-mail: [email protected] 2 Department of Physics, Indian Institute of Science, Bangalore 560012, India 3 Instituto Nacional de Astrofísica, Optica y Electrónica, Calle Luis Enrique Erro 1, 72840 Tonantzintla, Puebla, Mexico Received 3 January 2005 / Accepted 15 March 2005 Abstract. We quantify the degree of lopsidedness for a sample of 149 galaxies observed in the near-infrared from the OSUBGS sample, and try to explain the physical origin of the observed disk lopsidedness. We confirm previous studies, but for a larger sample, that a large fraction of galaxies have significant lopsidedness in their stellar disks, measured as the Fourier amplitude of the m = 1 component normalised to the average or m = 0 component in the surface density. Late-type galaxies are found to be more lopsided, while the presence of m = 2 spiral arms and bars is correlated with disk lopsidedness. We also show that the m = 1 amplitude is uncorrelated with the presence of companions. Numerical simulations were carried out to study the generation of m = 1viadifferent processes: galaxy tidal encounters, galaxy mergers, and external gas accretion with subsequent star formation. These simulations show that galaxy interactions and mergers can trigger strong lopsidedness, but do not explain several independent statistical properties of observed galaxies. To explain all the observational results, it is required that a large fraction of lopsidedness results from cosmological accretion of gas on galactic disks, which can create strongly lopsided disks when this accretion is asymmetrical enough.
    [Show full text]
  • ISOCAM Observations of Normal Star-Forming Galaxies: the Key Project Sample’
    ISOCAM Observations of Normal Star-Forming Galaxies: The Key Project Sample’ D.A. Dale,2 N.A. Silbermann,2 G. Heloq2 E. Valjaveq2 S. Malhotra,2 C.A. Beichman,2 J. Brauher,2 A. Contursi,2H. Diner~tein,~D. H~llenbach,~D. Hunter,s S. Kolhatkar,2 K.Y. LO,^ S. Lord,2 N.Y. Lu,~R. Rubiq4 G. Stacey,? H. Thronson, Jr.,’ M. Werner,g H. Corwin2 ABSTRACT We present mid-infrared maps and preliminary analysis for 61 galaxies observed with the Infrared Space Observatory. Many of the general features of galaxies observed at optical wavelengths-spiral arms, disks, rings, and bright knots of emission-are also seen in the mid-infrared, except the prominent optical bulges are absent at 6.75 and 15 pm. In addition, the maps are quite similar at 6.75 and 15 pm, except for a few cases where a central starburst leads to lower !dS3~4ratios in the inner region. kVe also present infrared flux densities and mid-infrared sizes for these galasies. The mid-infrared color Iu(6.Zpm) Iu(l.5pm) shows a distincttrend with the far-infrared color m.The quiescent galasies in our sample 1, (60~)g 0.6) show unity,near ( I,( 1OOpm) whereas this ratio drops significantly for galaxies with higher global heating intensity levels. Azimuthally-averaged surface brightness profiles indicate the extent to which the mid-infrared flux is centrally concerltratecl, a,rltl provide information on the radial dependence of mid-infrared colors. The galaxies are mostly well resolved in these maps: almost half of them have < 10% of their flux in the central resolution element.
    [Show full text]
  • Thick Disks and Halos of Spiral Galaxies M 81, NGC 55 and NGC 300
    A&A 431, 127–142 (2005) Astronomy DOI: 10.1051/0004-6361:20047042 & c ESO 2005 Astrophysics Thick disks and halos of spiral galaxies M 81, NGC 55 and NGC 300 N. A. Tikhonov1,2, O. A. Galazutdinova1,2, and I. O. Drozdovsky3,4 1 Special Astrophysical Observatory, Russian Academy of Sciences, N. Arkhyz, KChR 369167, Russia e-mail: [email protected] 2 Isaac Newton Institute of Chile, SAO Branch, Russia 3 Spitzer Science Center, Caltech, MC 220-6, Pasadena, CA 91125, USA 4 Astronomical Institute, St. Petersburg University, 198504, Russia Received 9 January 2004 / Accepted 28 September 2004 Abstract. By using images from the HST/WFPC2/ACS archive, we have analyzed the spatial distribution of the AGB and RGB stars along the galactocentric radius of nearby spiral galaxies M 81, NGC 300 and NGC 55. Examining color–magnitude diagrams and stellar luminosity functions, we gauge the stellar contents of the surroundings of the three galaxies. The red giant population (RGB) identified at large galactocentric radii yields a distance of 3.85 ± 0.08 Mpc for M 81, 2.12 ± 0.10 Mpc for NGC 55, and 2.00±0.13 Mpc for NGC 300, and a mean stellar metallicity of −0.65, −1.25, and −0.87 respectively. We find that there are two number density gradients of RGB stars along the radius, which correspond to the thick disk and halo components of the galaxies. We confirm the presence of a metallicity gradient of evolved stars in these galaxies, based on the systematic changes of the color distribution of red giant stars.
    [Show full text]
  • 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.
    [Show full text]