Dark Matter Halos of Spiral Galaxies

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1 Dark Matter Halos of Spiral Galaxies Arunima Banerjee National Centre for Radio Astrophysics Tata Institute of Fundamental Research Pune, India Web:

2 PLAN OF THE TALK Spiral Galaxies: An Overview Dark Matter: A Brief History LCDM model: Success & Failure Tracking DM halos using HI Rotation Curve & Scale height data Application & Results Summary

3 Spiral Galaxies: An Overview

4 OUR MILKY WAY

5 OTHER SPIRAL GALAXIES NGC 891 NGC 68

6 THE GALAXY CLASSIFICATION SCHEME NGC 68 FACE-ON SPIRAL GALAXY NGC 891 M87 ELLIPTICAL GALAXY EDGE-ON SPIRAL GALAXY

7 BASIC BUILDING BLOCKS OF A SPIRAL GALAXY Differential Rotation DM MASS (M sun ) 10 1 R Z (KPC) (KPC) σ (km/s) STARS Caveat: Not to Scale! 18 GAS(HI) R

8 A MULTI-WAVELENGTH VIEW OF THE MILKY WAY

9 GALAXY ENVIRONMENT: CLUSTER, GROUP, FIELD Cluster Group Abell 1689 Field Robert s Quartet NGC 891

10 Dark Matter: A Brief History

Matter! T V = 0 i.e. V = -T But V >> Vobs!

11 DARK MATTER: CLUSTER KINEMATICS (1933) Frit Zwicky From Virial Theorem, Coma Cluster (Abell 1669) Hints at the existence of Dark Matter! T V = 0 i.e. V = -T But V >> Vobs!! Estimable from the Doppler Shifts of the galaxy spectra Estimable from the lumininosities of the galaxies

12 DARK MATTER: GALAXY ROTATION CURVE (1980) Vera Rubin Observed M(R) ~ R!! VROT=(GM/R)½ R Vrot (km/s) R(kpc)

13 DARK MATTER: LARGE SCALE STRUCTURE AND COSMOLOGY Observed Large Scale Structure (SDSS) Ansotropiesin the Cosmic Microwave Background (WMAP) Abundance of H, He, Li

14 ΛCDM: STANDARD MODEL OF COSMOLOGY ORDINARY MATTER! Matter-energy budget in the LCDM universe which consists of dark energy and cold, dissipationless and collisionless dark matter

15 LCDM Model: Success & Failure

16 DARK MATTER DISTRIBUTION IN THE UNIVERSE AT PRESENT TIME Millenium Simulation

17 LCDM HALOS: A ONE-SLIDE PRIMER Bettet al. (007) 1. DM halos are triaxial(a > b > c) in general a:long axis b: intermediate axis c: short axis q=c/a: vertical-to-planar axis ratio. There is a preference of prolate (1:1:) over oblate (::1) 3. Spin parameter Λ = JE^½/GM^5/ = Angular momentum J is oriented along the short axis in general c b Triaxial Halo Oblate Prolate(Preferred) a

18 ΛCDM MODEL : PROBLEMS ON GALACTIC SCALE Core/Cusp Issue Missing Satellite Problem Angular Momentum Catastrophe DM BULGE DISK DM DISK Predicted SATELLITES DISK Observed r (kpc)

19 POSSIBLE REMEDY Inclusion of Feedback: Gas accretion, cooling, Star Formation and Feedback (supernovae/agn) Gas Accretion into DM halo Gas Cooling Disk Formation Star Formation Supernovae Feedback

20 POSSIBLE ALTERNATIVES Warm Dark Matter (WDM) Modified Newtonian Dynamics (MOND) NO CONSENSUS REACHED!

21 DM Halos from HI rotation curve & scale height data

22 DM HALO SHAPES: WHY BOTHER? 1. Galaxy Formation & Evolution Halo merger with no angular momentum Prolate Halo Halo merger with angular momentum Oblate Halo Moore et al. 001 Hierarchical build-up of Dark Matter Halos in a LCDM universe: Mergers

23 DM HALO SHAPES: WHY BOTHER? Galaxy Formation & Evolution (continued) Vera Ciroet al. 011 Hierarchical build-up of Dark Matter Halos in a LCDM universe: Accretion

24 DM HALO SHAPES: WHY BOTHER?. AstroparticlePhysics Strong self-scattering produces flatter central density profile

25 DM HALO SHAPES: WHY BOTHER? 3. Disk Structure & Dynamics DISK Galactic Warp A prolate halo sustains a galactic warp Idetaet al. 000

26 WHY HI? Stars HI Spin Flip transition from Ortho to Para state produces 1 cm line HI extends beyond 3-4 times the stellar disk

27 ROTATION CURVE CONSTRAINT ψ total ψ DM = ψ Disk = ψ total ψ DM ψ Disk From modeling disk luminosity profiles etc ψ total R = v rot R Traditional Method V ( R ) Expected curve for visible disk But ψ total =? R Observed Rotation Curve Cannot determine the DM halo uniquely!

28 THE HI SCALE HEIGHT CONSTRAINT ψ total d =< v 1 > d Observed HI scale height Curve Sensitive to the vertical-to-planar axis ratio, and hence the shape of the halo!

29 OUR STRATEGY V ( R ) Expected curve for visible disk R Observed Rotation Curve Observed HI scale height Curve ψ total R Global constraint on enclosed mass ψ total Constraint on halo flattening

30 DM HALO SHAPE & HI THICKNESS Observed rotation curve - total DM halo mass a c a c h h h a c Prolate (c/a = q > 1) Spherical (c/a = q = 1) Oblate (c/a = q < 1) DM = M/V = M/4ПqR 3 As q, DM, h Observed HI thickness can act as a diagnostic for halo shape!

31 OUR CHOSEN DM HALO PROFILE p c DM R q R R = 0 1 ), ( Core density Density index Core Radius Axis-ratio De Zeeuw& Pfenniger 1988

32 DUAL CONSTRAINTS: 3D GRID 1. Apply rotation curve constraint q { 0, Rc, q} 50,000 grid points to be scanned! p = 1, 1.5, R c. 0 Apply HI scaleheight constraint q { 0, Rc, q} 100 grid points to scan Fit to the observed rotation curve R c 0 Fit to the observed HI scaleheight data

33 OUR THEORETICAL MODEL Vertical hydrostatic equilibrium (i = stars, HI,H ) (1) Joint Poisson equation for disk DM halo () (3) ( ) = > < v total i i i ψ ) ( 4 1 DM H HI s total total G R R R R π ψ ψ = Eliminating ψ total between (1) & (), ( ) [ ] ( ) ) ( rot i i DM H HI s i i i v R R G v > < = π observations

34 ( ) [ ] 1 4 ) ( > < = G v s s DM H HI s i s s π ( ) [ ] 1 4 ) ( > < = G v HI HI DM H HI s i HI HI π SOLUTION OF THE EQUATIONS ( ) [ ] 1 4 ) ( > < = G v H H DM H HI s i H H π At each R, ) ( )),, ( ; (, 0 l theoretica thickness vertical HI p q R c DM HI

35 Applications & Results

36 RESULTS: ANDROMEDA (M31) ( R, ) = 1 R 0 R c q p Surface density of the disk components and Dark Matter vsr q= 0.4 (oblate) Rc~ 4 R D DM dominates beyond 3 R D Banerjee & Jog 008, ApJ, 685, 54

37 RESULTS: UGC 731* ( R, ) = 1 R 0 R c q p Surface density of the disk components and Dark Matter vs R q = 1 Rc~ R D (compact) DM dominates just beyond R D Banerjee, Matthews & Jog 010, NewA, 15, 89

38 RESULTS: THE GALAXY ( R, ) = 1 R 0 R c q p Best-fit vs observed HI thickness q= 1 (spherical) But total DM halo mass small! p = Narayan et al. 005

39 RESULTS: THE GALAXY DM halo isodensity contours q (R) = 0.0R 0.003R^ A progressively more prolate(i.eq increases with R) DM halo! Banerjee & Jog 011, ApJL, 73, L8

40 SUMMARY 1. WeusethejointconstraintoftheHIrotationcurveandthe HI vertical scale height data to track the DM density profiles of nearby edge-on galaxies.. The DM halo shape can vary from oblate, spherical to prolate and can also vary with radius. 3. The DM halo is compact in case of the LSB superthin galaxy whereas extended in case of the HSB galaxies.

41 et cetera.

42 Effect of the DM halos on Disc Structure & Dynamics

43 WHY ARE SOME GALAXIES SUPERTHIN? Banerjee & Jog 013, MNRAS, 431, 58

44 THE SLOW BAR IN NGC 3741 (Debattista & Sellwood 1998, 000) F d ~ /v 3 rel (Chandrasekhar 1943) Banerjee, Patra, Chengalur& Begum 013, MNRAS, 434, 157

45 BROAD AREAS OF DM RESEARCH 1. Dark Matter in Galaxy Formation and Evolution (Simulations). Tracking the Dark Matter density profiles in clusters, groups and galaxies (Observations) 3. Predicting constituent particles for Dark Matter (Astroparticle Physics) 4. Dark Matter detection experiments

Dark Matter Halos of nearby galaxies: The HI probe*

Dark Matter Halos of nearby galaxies: The HI probe* Arunima Banerjee (IUCAA) Chanda Jog (IISc), Lynn Matthews (MIT Haystack Observatory) *Adams et al. 014 Galactic Dark Matter Halos Dark Matter in Galaxies