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The Dark Matter Problem: Elliptical and Dwarf Galaxies

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The Dark Matter Problem: Elliptical and Dwarf Galaxies The dark matter problem: Elliptical and dwarf galaxies Françoise Combes Among all galaxy types Elliptical Spirals Dwarfs 2 The early part of the tuning fork Are these systems the most simple? En n=10(1-b/a) 3 Rotation and elliptical galaxies Historically, ellipticals were thought to be flattened by rotation, like spirals are In 1978, it is realized that it is not the case (Illingworth et al 1978) The kinetic support is an anisotropic velocity dispersion This property comes certainly from their formation by merger 4 Measure of velocities in Ellipticals It is very difficult to measure the rotation in elliptical galaxies Stellar spectra (absorption lines) are individually and and intrinsically very broad (> 200km/s) Due to the high pressure of their hot atmosphere A deconvolution must be carried out: correlation with templates Template as a function of type and stellar populations 5 Stellar spectra galaxy • Absorption lines star Calcium Triplet Deconvolution: [Ang] GS*G = S* LOSVD LOSVD LOSVD : “Line Of Sight VlVeloc ity Di strib uti on” Distrib ut ion of vel oci ti es retrieved V [km/s] 6 Rotation of Ellipticals FllFull cilircles: small mass Empty circles: massive Elliptical galaxies Crosses= Bulges Davies et al (1983) Solid curve: relation for objects flattened by rotation and with an isotopic velocity dispersion (Binney 1978) 7 Observation: Densityyp profiles 1/4 1/4 Light profile of deVaucouleurs in r log(I/Ie)= -3.33 (r/re -1) -2 Hubble profile I/Io = [r/a+1] 8 Theoryyg: King Profiles F(E) = 0 E> Eo 2 -151.5 2 F(E) = (2 ) o [exp(E[ exp(Eo-E)/ -1] E < Eo C=log(rt/ro) rt =tidal radius ro= core radius 9 Deformations of light profiles The different profiles correspond to tidal deformations of elliptical galaxies T1: isolated galaxies T3: with nearbyneihbighbors Departure from the de Vaucouleurs profile KdKormendy 1982 10 Possi ble sh ape f or sph er oï ds Oblate Prolate Spheroïds of revolution 2 equal axes If equal axes are major= Oblate, disk, pancake If equal axes are minor= Prolate, cigar, rugby ball Hope to consider in the general case 2 axes as close, even if they are not equal To reduce to quasi spheroids ? 11 Triaxiality of ellipticals Observations show that elliptical galaxies have a triiliaxial shape, rather than sphïdlheroïdal wihith 2 equal axes, like oblate/prolate With triaxiality and a variation of ellipticity with radius, There exists a rotation of isophotes, or twist This is not an intrinsic deformation! 12 Isophote twist and variation of ellipticity with radius •A triaxial body seen from a random direction will reveal an isophote twist, except when seen along symmetry axes (i.e. PA changes with radius) a) b) a) Surfaces of constant density. The outer surface is oblate with x:y:z = 1:1:0.46. The inner surface is triaxial with x:y:z = 1:0.5:0.25. b) Image in projection c) Isophotes in projection c) d) d) Isophotes of central region- notice the isophote twist • Variation of ellipticity of isophotes with radius radius 13 Disky or boxy morphology •80% of Ellipticals: isophotes deviate from pure ellipses •These deviations at ~1% can be parametrized by decomposing the isophotoal profiles in Fourier series in azimuth I() = ao +a+ a2cos2 +a+ a4cos4 ellipse component “a4” Modification of the Hubble tuning fork 14 Isophotes « box » or « disk » a4=0 Pure ellipse “ ” a4<0 box •Formedbd by mergers of spiral galaxies •Massive ellipticals •Have in general •Very little rotation Isophote twists •Triaxial a4>0 “disk” •Indication of a weak disk •Average size •Rotation more •ellipticals pronounced •Oblate 15 Ellipticals & early type Spirals Certain galaxies are difficult to classify, between lenticulars and ellipticals. The majority of ellipticals have a stellar disk 16 300 galaxies: ATLAS-3D = Degree of rotation = apparent e llip tic ity About 85% of spheroidal galaxies have a slow rotation The objects without or with little rotation are giant ellipticals, essentially in dense environments Capellari et al 2011 Emsellem et al 2011 17 Emsellem et al 2007 Velocity fields of ellipticals/S0 Emsellem et al 2007 19 Faber-Jackson relation for ellipticals Virgo cluster Coma cluster RtltRemote clusters Field galaxies Ziegler et al 2005 20 Fundamental plane of ellipticals Re:radius: radius containing half of Discovered by Djorgovski et al 1987 the light 21 Scaling relations Linking dark matter, responsible of the kinematics Vflat for spirals, dispersion for Ellipticals 4 • Tully-Fisher: Mbaryons ~ v • Faber-Jackson: L ~ 4 • Fundamental plane: 22 Simppylified dynamical eq uilibrium Hydrostatic equilibrium –dP/dr = G M(r) (r)/r2 (isothermal sphere) Pressure P = (()r) 2 (()r) ~ 1/r2 2 ~ GM(r)/r, i.e. M(r) ~ 2 r 2 4 Luminosity L = re L ~ /, si M/L = cste A simple law is not expected, but a lot of scatter instead According to the surface density Does this imply M ~ R2 ? 23 Tracers at large distance • Planetary nebulae PN (bright, 30km/s intrinsical dispersion) • Globular clusters GC ((y)but kinematically different?) • X-rays, hydrostatic equilibrium (groups, clusters) Globular clusters are more abundant in Es than in spirals GC form in mergers of galaxies GC are not abundant enough, far from the centre Planetary nebulae, line 5007Å [OIII] They are observed at the end of life of stars like the Sun, red giant, then white dwarf; Asyypmptotic branch of giants AGB Multi-object rapid observation BtBut requ ires Imagery /Spect roscopy Imagery contra-dispersed 24 Gal ax y-gala xy le ns ing (GG L ) Measure the correlation between galaxies and the density field « SSctackin g»: supe rpos itio n o f N objects Future large surveys LSST The dark halos have an isothermal distribution from Re to 150kpc Brimioulle et al 2013 25 Galaxy-Galaxy results z(blue) ~0.35, z(red) ~0.28, M/L ~L0.12, M/L =30-300 L~4 L~4 Brimioulle et al 2013 26 Contra-dispersed imagery (CDI) Field stars have a continuous trace The PN are a point shifted according to V Douglas & Taylor 1999 Planetary nebulae=PN 27 NGC 4494, PNS Perturbing star Velocity field of PNe Napolitano et al 2009 28 Kinematics of N4494 V Dispersion Stars * PN : o Modelisation Major axis A lot of V Dispersion unknown Anisotropies In the ppjrojected velocities Minor ax is Napolitano et al 2009 29 Models with or without DM Fraction of DM from 0 to 40%, at 5 Re Velocity anisotropy Concentration Mass Stars * PN : o Triangle: fast Box slow 30 Dark matter in Ellipticals Planetary nebulae: Romanowsky et al 2003 No dark matter?? N821, N3379, N4494 ….. Visible matter (isotropy) - - - isothermal (isotropy) 31 Velocity anisotropy = 1 – 0, 1 circular, isotropic and radial orbits When galaxies form by mergers, orbits in the outer parts are Radius very radial, which explains the weak velocity dispersion in projection (Dekel et al 2005) The observation of the velocity profile is rather degenerate and cannot yield the dark matter content without ambiguity 32 Young stars = yelow contours DM stars Comparison with observations N821 (green), N3379 (violet) N4494 (brown), N4697 (blue) 33 Dwarfs Irr : DDO154 the prototype Carignan & Beaulieu 1989 Galaxies at low surface core, not cusp brightness are dominated by dark matter There exist halos of mass 10 10 M Swaters et al 2009 34 Ratio between HI and DM Factor 8.2 (10 Hoekstra et al 2001) Lenticulars Early Type dwarfs Irr Strong coupling between baryons and dark matter Swaters et al35 2009 DM/HI M/L ratio of M/L stars , and DM/HI Depends on morphological type but not on total luminosity M/L Swaters et al 2009 36 Spiral structure: dwarf galaxies NGC 2915 (Masset & Bureau 2003) The gas disk is unstable against spiral formation It must beself-graviiitating, not didominated by dkdark matter? Or the dark matter is in the plane 37 Discov er y of dw arf gal axi es At the end of spiral classification, Irr, Im, small masses dwarf irregular (dIrr) have gas, and a disk in rotation dwarf Spheroidal (dSph) ensemble of stars very low Lum, without gas dwarf elliptical (dE) spheroïds of stars, without gas, compact 3 9 Lumi nositi es 10 -10 L Aroud the Milky Way: Large and Small Magellanic Clouds The Catalog DDO (David Dunlap Observatory) is a catalogue of 243 dwarf galaxies (1959-1966) by Sidney van den Bergh. 0.1 galaxy/Mpc3. Dwarfs are more numerous than giants Dwarfs are in general orbiting around giants Mateo, 1998, ARAA Dwarf galaxies (~40) of the Local Group 38 Classification of dwarf galaxies Grebel 2013 L < L*/100 39 Sandage & Binggeli (1984, AJ, 89, 919) Dwarf ellipticals: very little DM High surface density in the center, Sometimes bright nucleus, exponential profile NGC205 Some contain a stellar disk (Lisker et al 2006, 2007) Stu dyof 476 dE in Virgo (Sloan) Satellite of Andromeda Several formation ways Ram pressure in groups Harrassment in clusters Life-time of these spirals? Total image After unsharp masking 40 Influence of the environment dE galaxies with nucleus Relaxed in the cluster The others, with some remaining star formation have just come in come from galaxies of spiral type Projected density of galaxies in the cluster 41 The dwarf galaxies are associdiated to giants Central halo + Satellites Grebel & Guhathakurta 42 Ultra-compact dwarfs UCD Could come from dE with nucleus? But excess of Fe/H Are more similar to globular clusters No DM.. L Francis et al 2012 43 Dwarfs dSpp(ph (spheroïdals) Fornax Galaxies of low surface brightness The smallest known, and the most dominated by the DM Exponential light profile Thei r masses ~glbllobular cltlusters 5 M*~ a few 10 M Velocity dispersion ~10km/s 44 Exampp,ple of Draco, at 71kpc Contours of stellar density, SDSS
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