DOCSLIB.ORG

Sections 23-25 Powerpoint

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Sections 23-25 Powerpoint Chapter 23, 24 Galaxies, Quasars and Active Galaxies Chapters 23 and 24 look into the nature of individual galaxies and their environs. 1. The main galaxy types are described, pointing out how they differ in terms of the relative frequency of old and young stars, and interstellar gas, within them. 2. Imaging of galaxies and galaxy clusters reveals that it is a “violent” universe. Evidence for collisions between galaxies is everywhere, although keep in mind that by “collisions” we are talking about events that take place over billions of years, not mere seconds or minutes. The Hubble Sequence: The familiar “tuning fork” diagram developed by Edwin Hubble is an attempt to link the main galaxy types of elliptical (E), spiral (S), barred spiral (SB), and irregular (Ir) classes. The lenticular galaxies (S0, SB0), added later, were a supposed link between spheroidal E galaxies and flattened S and SB galaxies, but unfortunately the diagram was also pictured as an evolutionary sequence. Thus, elliptical galaxies are often referred to as “early- type” galaxies, much like “early-type” OB stars. Elliptical galaxies contain old low-mass stars/no gas or dust and are denoted E0, = circular to E6 = elongated. Sample: IC 4296, E0, NGC 777, E1, NGC 1549, E2, NGC 4365, E3, NGC 4564, E6, NGC 4623, E7. Some are actually lenticulars, S0. Ellipticals are not all the same shape galaxy seen at various angles of projection. Many seem to be oblate (top) or prolate (bottom) spheroids viewed at various angles. Early examples of lenticular = lens-like galaxies. List: NGC 3245, S0, NGC 4251, S0, NGC 4179, S0:, NGC 5422, S0:, NGC 3203, S0:, NGC 4429, S0/Sa. Lenticular galaxies get their name because they are “lens- like,” but are more like spiral and barred spiral galaxies in possessing a flattened disk, rather than like elliptical galaxies which mostly possess ellipsoidal symmetry. The distinguishing feature of lenticulars is that they do not have spiral arms or dust like spiral galaxies. For example, lenticular galaxies seen edge-on do not have dust lanes. van den Bergh suggested a possible origin for lenticular galaxies (S0s) via collisions between spirals. That results in the dust and gas being swept out of the galaxies by ram pressure. Because they have been swept clean of material for making new stars, lenticular galaxies contain only old stars, like elliptical galaxies, and lack the distinguishing features of spirals. The fact that most lenticulars are found in rich clusters of galaxies supports the idea. Hubble Atlas examples of “early-type” spiral galaxies. NGC 3269, Sa, NGC 7096, Sa, NGC 1350, Sa, NGC 1371, Sa, NGC 488, Sab, NGC 2460, Sab. Hubble Atlas examples of “late-type” spiral galaxies. NGC 1566, Sbc, NGC 5247, Sc, NGC 2997, Sc, NGC 3184, Sc, NGC 3938, Sc, NGC 5055, Sbc. The effect of inclination to the line of sight on the appearance of spiral galaxies. Note how dust lanes show up for edge-on spirals. How to get trailing spiral arms from any elongated structure in a disk-dominated galaxy: differential rotation in the disk naturally stretches such features into spiral arms. Note that 2-armed spirals appear to be most common..
Load more

Recommended publications
  • Nuclear Stellar Discs in Low-Luminosity Elliptical Galaxies: NGC 4458 and 4478 L
    Mon. Not. R. Astron. Soc. 354, 753–762 (2004) doi:10.1111/j.1365-2966.2004.08236.x Nuclear stellar discs in low-luminosity elliptical galaxies: NGC 4458 and 4478 L. Morelli,1,2 C. Halliday,3 E. M. Corsini,1 A. Pizzella,1 D. Thomas,4 R. P. Saglia,4 R. L. Davies,5 R. Bender,4,6 M. Birkinshaw7 and F. Bertola1 1Dipartimento di Astronomia, Universitad` iPadova, vicolo dell’Osservatorio 2, I-35122 Padova, Italy 2European Southern Observatory, 3107 Alonso de Cordova, Santiago, Chile 3INAF-Osservatorio Astronomico di Padova, vicolo dell’Osservatorio 5, I-35122 Padova, Italy 4Max-Planck Institut fur¨ extraterrestrische Physik, Giessenbachstrasse, D-85748 Garching, Germany 5Department of Astrophysics, University of Oxford, Keble Road, Oxford OX1 3RH 6Universitas-Sternwarte,¨ Scheinerstrasse 1, D-81679 Muenchen, Germany 7H. H. Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Bristol BS8 1TL Accepted 2004 July 19. Received 2004 July 12; in original form 2004 May 12 ABSTRACT We present the detection of nuclear stellar discs in the low-luminosity elliptical galaxies, NGC 4458 and 4478, which are known to host a kinematically decoupled core. Using archival Hubble Space Telescope imaging, and available absorption line-strength index data based on ground-based spectroscopy, we investigate the photometric parameters and the properties of the stellar populations of these central structures. Their scalelength, h, and face-on central surface µc µc brightness, 0,fitonthe 0 –h relation for galaxy discs. For NGC 4458, these parameters are typical for nuclear discs, while the same quantities for NGC 4478 lie between those of nuclear discs and the discs of discy ellipticals.
    [Show full text]
  • SAC's 110 Best of the NGC
    SAC's 110 Best of the NGC by Paul Dickson Version: 1.4 | March 26, 1997 Copyright °c 1996, by Paul Dickson. All rights reserved If you purchased this book from Paul Dickson directly, please ignore this form. I already have most of this information. Why Should You Register This Book? Please register your copy of this book. I have done two book, SAC's 110 Best of the NGC and the Messier Logbook. In the works for late 1997 is a four volume set for the Herschel 400. q I am a beginner and I bought this book to get start with deep-sky observing. q I am an intermediate observer. I bought this book to observe these objects again. q I am an advance observer. I bought this book to add to my collect and/or re-observe these objects again. The book I'm registering is: q SAC's 110 Best of the NGC q Messier Logbook q I would like to purchase a copy of Herschel 400 book when it becomes available. Club Name: __________________________________________ Your Name: __________________________________________ Address: ____________________________________________ City: __________________ State: ____ Zip Code: _________ Mail this to: or E-mail it to: Paul Dickson 7714 N 36th Ave [email protected] Phoenix, AZ 85051-6401 After Observing the Messier Catalog, Try this Observing List: SAC's 110 Best of the NGC [email protected] http://www.seds.org/pub/info/newsletters/sacnews/html/sac.110.best.ngc.html SAC's 110 Best of the NGC is an observing list of some of the best objects after those in the Messier Catalog.
    [Show full text]
  • L41 the Ages of Globular Clusters in Ngc 4365
    The Astrophysical Journal, 634:L41–L44, 2005 November 20 ൴ ᭧ 2005. The American Astronomical Society. All rights reserved. Printed in U.S.A. THE AGES OF GLOBULAR CLUSTERS IN NGC 4365 REVISITED WITH DEEP HST OBSERVATIONS1 Arunav Kundu,2 Stephen E. Zepf,2 Maren Hempel,2 David Morton,2,3 Keith M. Ashman,3 Thomas J. Maccarone,4 Markus Kissler-Patig,5 Thomas H. Puzia,6 and Enrico Vesperini7 Received 2005 August 4; accepted 2005 October 12; published 2005 November 8 ABSTRACT We present new Hubble Space Telescope (HST) NIC3, near-infrared H-band photometry of globular clusters (GCs) around NGC 4365 and NGC 1399 in combination with archival HST WFPC2 and ACS optical data. We find that NGC 4365 has a number of globular clusters with bluer optical colors than expected for their red optical– to–near-infrared colors and an old age. The only known way to explain these colors is with a significant population of intermediate-age (2–8 Gyr) clusters in this elliptical galaxy. On the other hand, our result for NGC 1399 is in agreement with previous spectroscopic work that suggests that its clusters have a large metallicity spread and are nearly all old. In the literature, there are various results from spectroscopic studies of modest samples of NGC 4365 globular clusters. The spectroscopic data allow for either the presence or absence of a significant population of intermediate-age clusters, given the index uncertainties indicated by comparing objects in common between these studies and the few spectroscopic candidates with optical–to–near-IR colors indicative of inter- mediate ages.
    [Show full text]
  • Making a Sky Atlas
    Appendix A Making a Sky Atlas Although a number of very advanced sky atlases are now available in print, none is likely to be ideal for any given task. Published atlases will probably have too few or too many guide stars, too few or too many deep-sky objects plotted in them, wrong- size charts, etc. I found that with MegaStar I could design and make, specifically for my survey, a “just right” personalized atlas. My atlas consists of 108 charts, each about twenty square degrees in size, with guide stars down to magnitude 8.9. I used only the northernmost 78 charts, since I observed the sky only down to –35°. On the charts I plotted only the objects I wanted to observe. In addition I made enlargements of small, overcrowded areas (“quad charts”) as well as separate large-scale charts for the Virgo Galaxy Cluster, the latter with guide stars down to magnitude 11.4. I put the charts in plastic sheet protectors in a three-ring binder, taking them out and plac- ing them on my telescope mount’s clipboard as needed. To find an object I would use the 35 mm finder (except in the Virgo Cluster, where I used the 60 mm as the finder) to point the ensemble of telescopes at the indicated spot among the guide stars. If the object was not seen in the 35 mm, as it usually was not, I would then look in the larger telescopes. If the object was not immediately visible even in the primary telescope – a not uncommon occur- rence due to inexact initial pointing – I would then scan around for it.
    [Show full text]
  • Ngc Catalogue Ngc Catalogue
    NGC CATALOGUE NGC CATALOGUE 1 NGC CATALOGUE Object # Common Name Type Constellation Magnitude RA Dec NGC 1 - Galaxy Pegasus 12.9 00:07:16 27:42:32 NGC 2 - Galaxy Pegasus 14.2 00:07:17 27:40:43 NGC 3 - Galaxy Pisces 13.3 00:07:17 08:18:05 NGC 4 - Galaxy Pisces 15.8 00:07:24 08:22:26 NGC 5 - Galaxy Andromeda 13.3 00:07:49 35:21:46 NGC 6 NGC 20 Galaxy Andromeda 13.1 00:09:33 33:18:32 NGC 7 - Galaxy Sculptor 13.9 00:08:21 -29:54:59 NGC 8 - Double Star Pegasus - 00:08:45 23:50:19 NGC 9 - Galaxy Pegasus 13.5 00:08:54 23:49:04 NGC 10 - Galaxy Sculptor 12.5 00:08:34 -33:51:28 NGC 11 - Galaxy Andromeda 13.7 00:08:42 37:26:53 NGC 12 - Galaxy Pisces 13.1 00:08:45 04:36:44 NGC 13 - Galaxy Andromeda 13.2 00:08:48 33:25:59 NGC 14 - Galaxy Pegasus 12.1 00:08:46 15:48:57 NGC 15 - Galaxy Pegasus 13.8 00:09:02 21:37:30 NGC 16 - Galaxy Pegasus 12.0 00:09:04 27:43:48 NGC 17 NGC 34 Galaxy Cetus 14.4 00:11:07 -12:06:28 NGC 18 - Double Star Pegasus - 00:09:23 27:43:56 NGC 19 - Galaxy Andromeda 13.3 00:10:41 32:58:58 NGC 20 See NGC 6 Galaxy Andromeda 13.1 00:09:33 33:18:32 NGC 21 NGC 29 Galaxy Andromeda 12.7 00:10:47 33:21:07 NGC 22 - Galaxy Pegasus 13.6 00:09:48 27:49:58 NGC 23 - Galaxy Pegasus 12.0 00:09:53 25:55:26 NGC 24 - Galaxy Sculptor 11.6 00:09:56 -24:57:52 NGC 25 - Galaxy Phoenix 13.0 00:09:59 -57:01:13 NGC 26 - Galaxy Pegasus 12.9 00:10:26 25:49:56 NGC 27 - Galaxy Andromeda 13.5 00:10:33 28:59:49 NGC 28 - Galaxy Phoenix 13.8 00:10:25 -56:59:20 NGC 29 See NGC 21 Galaxy Andromeda 12.7 00:10:47 33:21:07 NGC 30 - Double Star Pegasus - 00:10:51 21:58:39
    [Show full text]
  • Globular Cluster Luminosity Functions and the Hubble Constant From
    Globular Cluster Luminosity Functions and the Hubble Constant from WFPC2 Imaging: The Giant Elliptical NGC 43651 Duncan A. Forbes Lick Observatory, University of California, Santa Cruz, CA 95064 Electronic mail: [email protected] ABSTRACT The turnover, or peak, magnitude in a galaxy’s globular cluster luminosity function (GCLF) may provide a standard candle for an independent distance estimator. Here we examine the GCLF of the giant elliptical NGC 4365 using photometry of 350 globular clusters from the Hubble Space Telescope’s Wide Field and Planetary Camera∼ 2 (WFPC2). The WFPC2 data have several advantages over equivalent ground–based imaging. The membership of NGC 4365 in the Virgo cluster has been the subject of recent debate. We have fit a Gaussian and t5 profile to the luminosity function and 0 find that it can be well represented by a turnover magnitude of mV = 24.2 0.3 and a dispersion σ = 1.28 0.15. After applying a small metallicity correction± to the ‘universal’ globular cluster± turnover magnitude, we derive a distance modulus of (m – M) = 31.6 0.3 which is in reasonable agreement with that from surface brightness fluctuation measurements.± This result places NGC 4365 about 6 Mpc beyond the Virgo −1 +10 cluster core. For a VCMB = 1592 24 km s the Hubble constant is H◦ = 72−12 km s−1 Mpc−1. We also describe our± method for estimating a local specific frequency for the GC system within the central 5 h−1 kpc which has fewer uncertain corrections than a total estimate. The resulting value of 6.4 1.5 indicates that NGC 4365 has a GC richness similar to other early type galaxies.
    [Show full text]
  • X-Ray Binary Luminosity Function Scaling Relations in Elliptical
    Draft version April 29, 2020 Typeset using LATEX twocolumn style in AASTeX62 X-ray Binary Luminosity Function Scaling Relations in Elliptical Galaxies: Evidence for Globular Cluster Seeding of Low-Mass X-ray Binaries in Galactic Fields Bret D. Lehmer,1 Andrew P. Ferrell,1 Keith Doore,1 Rafael T. Eufrasio,1 Erik B. Monson,1 David M. Alexander,2 Antara Basu-Zych,3,4 William N. Brandt,5,6,7 Greg Sivakoff,8 Panayiotis Tzanavaris,3,4 Mihoko Yukita,9 Tassos Fragos,10 and Andrew Ptak3,9 1Department of Physics, University of Arkansas, 226 Physics Building, 825 West Dickson Street, Fayetteville, AR 72701, USA 2Department of Physics, University of Durham, South Road, Durham DH1 3LE, UK 3NASA Goddard Space Flight Center, Code 662, Greenbelt, MD 20771, USA 4Center for Space Science and Technology, University of Maryland Baltimore County, 1000 Hilltop Circle, Baltimore, MD 21250, USA 5Department of Astronomy & Astrophysics, Pennsylvania State University, University Park, PA 16802, USA 6Institute for Gravitation and the Cosmos, The Pennsylvania State University, 525 Davey Lab, University Park, PA 16802, USA 7Department of Physics, The Pennsylvania State University, University Park, PA 16802, USA 8Department of Physics, University of Alberta, CCIS 4-183 Edmonton, AB T6G 2E1, Canada 9The Johns Hopkins University, Homewood Campus, Baltimore, MD 21218, USA 10Geneva Observatory, Geneva University, Chemin des Maillettes 51, 1290 Sauverny, Switzerland ABSTRACT We investigate X-ray binary (XRB) luminosity function (XLF) scaling relations for Chandra detected populations of low-mass XRBs (LMXBs) within the footprints of 24 early-type galaxies. Our sample includes Chandra and HST observed galaxies at D ∼< 25 Mpc that have estimates of the globular cluster (GC) specific frequency (SN ) reported in the literature.
    [Show full text]
  • Stellar Populations in Seyfert 2 Galaxies
    A&A 380, 19–30 (2001) Astronomy DOI: 10.1051/0004-6361:20011252 & c ESO 2001 Astrophysics Stellar populations in Seyfert 2 galaxies I. Atlas of near-UV spectra?,?? B. Joguet1,D.Kunth1,J.Melnick2,R.Terlevich3,???, and E. Terlevich4,† 1 Institut d’Astrophysique de Paris, 98bis boulevard Arago, 75014 Paris, France e-mail: [email protected] 2 European Southern Observatory, Casilla 19001, Santiago 19, Chile e-mail: [email protected] 3 Institute of Astronomy, Madingley Road, Cambridge CB3 0HA, UK e-mail: [email protected] 4 Instituto Nacional de Astrof´ısica, Optica´ y Electr´onica, Apdo. postal 25 y 216, 72000 Puebla, Pue., Mexico e-mail: [email protected] Received 4 April 2001 / Accepted 6 August 2001 Abstract. We have carried out a uniform spectroscopic survey of Seyfert 2 galaxies to study the stellar populations of the host galaxies. New spectra have been obtained for 79 Southern galaxies classified as Seyfert 2 galaxies, 7 normal galaxies, and 73 stars at a resolution of 2.2 A˚ over the wavelength region 3500–5300 A.˚ Cross-correlation between the stellar spectra is performed to group the individual observations into 44 synthesis standard spectra. The standard groups include a solar abundance sequence of spectral types from O5 to M3 for dwarfs, giants, and supergiants. Metal-rich and metal-weak F-K giants and dwarfs are also included. A comparison of the stellar data with previously published spectra is performed both with the individual spectra and the standard groups. For each galaxy, two distinct spatial regions are considered: the nucleus and the external bulge.
    [Show full text]
  • The Relationship Between the Sérsic Law Profiles Measured Along The
    Mon. Not. R. Astron. Soc. 347, 824Ð832 (2004) The relationship between the Sersic« law profiles measured along the major and minor axes of elliptical galaxies F. Ferrari,1† H. Dottori,1 N. Caon,2 A. Nobrega1,3 and D. B. Pavani1‡ 1Instituto de F«õsica Ð UFRGS, Av. Bento Gonc¸alves, 9500 Porto Alegre RS, Brazil 2Instituto de Astrof«õsica de Canarias, Via Lactea,« E-38200 La Laguna, Tenerife, Canary Islands, Spain 3CETEC Ð UNOCHAPECO,« Av. Senador Att«õlio Fontana, s/n, Chapeco« SC, Brazil Accepted 2003 September 30. Received 2003 September 30; in original form 2002 May 17 ABSTRACT In this paper we discuss the reason why the parameters of the Sersic« model best-fitting the major axis light profile of elliptical galaxies can differ significantly from those derived for the minor axis profile. We show that this discrepancy is a natural consequence of the fact that the isophote eccentricity varies with the radius of the isophote and present a mathematical transformation that allows the minor axis Sersic« model to be calculated from the major axis model, provided that the elliptical isophotes are aligned and concentric and that their eccentricity can be represented by a well behaved, though quite general, function of the radius. When there is no variation in eccentricity only the effective radius changes in the Sersic« model, while for radial-dependent eccentricity the transformation, which allows the minor axis Sersic« model to be calculated from the major axis model is given by the Lerch transcendental function. The proposed transformation was tested using photometric data for 28 early-type galaxies.
    [Show full text]
  • Accretion and Nuclear Activity in Virgo Early-Type Galaxies⋆
    A&A 522, A89 (2010) Astronomy DOI: 10.1051/0004-6361/201014611 & c ESO 2010 Astrophysics Accretion and nuclear activity in Virgo early-type galaxies S. Vattakunnel1,3, E. Trussoni2, A. Capetti2, and R. D. Baldi2,3 1 Dipartimento di Fisica Università di Trieste, piazzale Europa 1, 34127 Trieste, Italy e-mail: [email protected] 2 INAF – Osservatorio Astronomico di Torino, via Osservatorio 20, 10025 Pino Torinese, Italy e-mail: [trussoni;capetti;[email protected]] 3 Università di Torino, via P. Giuria 1, 10125 Torino, Italy Received 31 March 2010 / Accepted 29 June 2010 ABSTRACT We use Chandra observations to estimate the accretion rate of hot gas onto the central supermassive black hole in four giant (of 11 12 stellar mass M∗ ∼ 10 −10 M) early-type galaxies located in the Virgo cluster. They are characterized by an extremely low radio luminosity, in the range L 3×1025−1027 erg s−1 Hz−1. We find that, accordingly, accretion in these objects occurs at an extremely low −3 −1 rate, 0.2−3.7 × 10 M yr , and that they smoothly extend the relation accretion-jet power found for more powerful radio-galaxies. This confirms the dominant role of hot gas and of the galactic coronae in powering radio-loud active galactic nuclei across ∼4orders of magnitude in luminosity. A suggestive trend between jet power and location within the cluster also emerges. Key words. galaxies: active – galaxies: jets – galaxies: elliptical and lenticular, cD – galaxies: ISM 1. Introduction of 23 objects with X-ray data of sufficient quality (including the sources analyzed in Allen et al.) they showed that the correla- The origin of the energetic processes occurring in active galactic tion between the jet and accretion power holds over ∼3 decades, nuclei (AGN) has been one of the most relevant astrophysical down to a jet power of ∼1042 erg s−1.
    [Show full text]
  • The ACS Virgo Cluster Survey. VI. Isophotal Analysis and Surface Brightness Profiles 3 at Odds with Previous Claims in Lauer Et Al
    Rochester Institute of Technology RIT Scholar Works Articles 2006 The CA S Virgo Cluster Survey. VI. Isophotal Analysis and the Structure of Early-Type Galaxies Laura Ferrarese National Research Council of Canada Patrick Côté National Research Council of Canada Andrés Jordán European Southern Observatory Eric W. Peng National Research Council of Canada John P. Blakeslee The Johns Hopkins University See next page for additional authors Follow this and additional works at: http://scholarworks.rit.edu/article Recommended Citation Laura Ferrarese et al 2006 ApJS 164 334 https://doi.org/10.1086/501350 This Article is brought to you for free and open access by RIT Scholar Works. It has been accepted for inclusion in Articles by an authorized administrator of RIT Scholar Works. For more information, please contact [email protected]. Authors Laura Ferrarese, Patrick Côté, Andrés Jordán, Eric W. Peng, John P. Blakeslee, Slawomir Piatek, Simona Mei, David Merritt, Miloš Milosavljević, John L. Tonry, and Michael J. West This article is available at RIT Scholar Works: http://scholarworks.rit.edu/article/1182 Accepted by The Astrophysical Journal Supplements Preprint typeset using LATEX style emulateapj v. 10/10/03 THE ACS VIRGO CLUSTER SURVEY. VI. ISOPHOTAL ANALYSIS AND THE STRUCTURE OF EARLY-TYPE GALAXIES1 Laura Ferrarese2, Patrick Cotˆ e´2, Andres´ Jordan´ 3,4, Eric W. Peng2, John P. Blakeslee5,6, Slawomir Piatek7, Simona Mei5, David Merritt8, Miloˇs Milosavljevic´9,10, John L. Tonry11, & Michael J. West12 Accepted by The Astrophysical Journal Supplements ABSTRACT We present a detailed analysis of the morphology, isophotal parameters and surface brightness profiles for 100 early-type members of the Virgo Cluster, from dwarfs (MB = −15.1 mag) to giants (MB = −21.8 mag).
    [Show full text]
  • THE ULTRALUMINOUS X-RAY SOURCE POPULATION from the CHANDRA ARCHIVE of GALAXIES Douglas A
    The Astrophysical Journal Supplement Series, 154:519–539, 2004 October A # 2004. The American Astronomical Society. All rights reserved. Printed in U.S.A. THE ULTRALUMINOUS X-RAY SOURCE POPULATION FROM THE CHANDRA ARCHIVE OF GALAXIES Douglas A. Swartz,1 Kajal K. Ghosh,1 Allyn F. Tennant,2 and Kinwah Wu3 Receivved 2003 Novvember 19; accepted 2004 May 24 ABSTRACT One hundred fifty-four discrete non-nuclear ultraluminous X-ray (ULX) sources, with spectroscopically de- termined intrinsic X-ray luminosities greater than 1039 ergs sÀ1, are identified in 82 galaxies observed with Chandra’s Advanced CCD Imaging Spectrometer. Source positions, X-ray luminosities, and spectral and timing characteristics are tabulated. Statistical comparisons between these X-ray properties and those of the weaker discrete sources in the same fields (mainly neutron star and stellar-mass black hole binaries) are made. Sources above 1038 ergs sÀ1 display similar spatial, spectral, color, and variability distributions. In particular, there is no compelling evidence in the sample for a new and distinct class of X-ray object such as the intermediate-mass black holes. Eighty-three percent of ULX candidates have spectra that can be described as absorbed power laws 21 À2 with index hÀi¼1:74 and column density hNHi¼2:24 ; 10 cm ,or5 times the average Galactic column. About 20% of the ULXs have much steeper indices indicative of a soft, and likely thermal, spectrum. The locations of ULXs in their host galaxies are strongly peaked toward their galaxy centers. The deprojected radial distribution of the ULX candidates is somewhat steeper than an exponential disk, indistinguishable from that of the weaker sources.
    [Show full text]