Dark Matter Halos of nearby galaxies: The HI probe*

Transcription

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

2 Galactic Dark Matter Halos

3 Dark Matter in Galaxies ubin et al. 1977, 1978, 1979 Observed VOT=(GM/)½ Vrot(km/s) M() ~!! Boundary of the Visible Disk Predicting the rotation curve of the observed light distribution (kpc)

4 DM Halo shapes from Cosmological Simulations Observed Large Scale Structure (SDSS) Bailin& Steinmet 005

5 DM Halo Shapes from otation Curve and Scaleheight Data DAK MATTE HALO OBSEVED SCALEHEIGHT CUVE V OT ψ ψ Z total 0 ~ ~ total OBSEVED OTATION CUVE Duffy et al. 008

6 Dark Matter Halo Shapes: Motivation

7 Cosmological Merger History from DM Halo shapes Moore et al. 001, Vera-Ciro& Helmi001

8 ΛCDM Universe: Galactic Scale Anomalies Core/Cusp Issue Missing Satellite Problem Angular Momentum Catastrophe DM BULGE DISK DM DISK Predicted SATELLITES DISK Observed r (kpc) Stringent constraints on galaxy formation and evolution models Governato et al. 007, 009, 010, 01

9 Dark Matter Halo Shapes: Tracers

10 Kinematics of Stars/Streams* *Galaxy and its immediate neighbours Loebmanet al. 01,Law & Majewski 005

11 DM Halos from HI* *Galaxies in the nearby universe (<0.3) STAS HI HI disk is in general 3-4 times larger than the stellar disk Sofue& ubin 001; Combes00; Gentile et al. 004

12 Disk galaxies: A Crash Course

13 Galaxies: Morphological Classification Disk Galaxies NGC 68 M87 WHILPOOL GALAXY: AN UNBAED SPIAL GALAXY ELLIPTICAL GALAXY Hubble s Tuning Fork Diagram

14 Disk galaxies: Orientations NGC 891 NGC 68 Disk Thickness otational Velocity Edge-on View Face-on View

15 Disk galaxies: A Schematic Differential otation MASS (M sun ) (KPC)

16 Our Galaxy Model: The Work Horse

17 DM Halo Shapes from otation Curve and Scaleheight Data DAK MATTE HALO OBSEVED SCALEHEIGHT CUVE V OT ψ ψ Z total 0 ~ ~ total OBSEVED OTATION CUVE Olling1996 (NGC 444), Becquaert& Combes1997 (NGC 891), Olling& Merrifield 000 (MW), Narayan et al. 005(MW)

18 Verticalhydrostatic equilibrium (i = Stars, HI, H ) (1) JointPoissonequationfordiskDMhalo () (3) ( ) = > < v total i i i ψ ) ( 4 1 DM H HI s total total G π ψ ψ = Eliminating ψ total between (1) & () ( ) [ ] ( ) ) ( rot i i DM H HI s i i i v G v > < = π Our Galaxy Model: The Work Horse 3-coupled, second-order ordinary differential equations Inclusion of Gas-gravity! [Isothermal Disk] [Axisymmetric Galaxy] (Observations) ~ 0 (Flat otation Curve) Modelled/Observations

19 DM (, ) = Our Galaxy Model: The Work Horse Dark Matter Density Profile 1 0 q c p De Zeeuw & Pfenniger 1988 Vertical-to-Planar Axis atio: q Spherical (q=1) Oblate(q<1) Prolate(q>1) 3 D Grid q { 0, c, q} Core Density 0 & Core adius c q=1 p =1, 1.5, 0 c 0 Small c(compact) Large c(non-compact)

20 ( ) [ ] 1 4 ) ( > < = G v s s DM H HI s s s s π ( ) [ ] 1 4 ) ( > < = G v HI HI DM H HI s HI HI HI π ( ) [ ] 1 4 ) ( > < = G v H H DM H HI s H H H π For each grid-pont (0, c, q, p), at each, Stars HI H Our Theoretical Model: The Work Horse ) ( )),, ( ; (, 0 theoretical Scaleheight HI p q c DM HI

21 Application & esults

22 esults: 1. Andromeda (M31) p c q = 0 1 ), ( q= 0.4 Banerjee & Jog 008, ApJ, 685, 54 An oblate dark matter halo! Best-fit vs observed HI thickness

23 esults: 1. Andromeda (M31).. Surface densities vs (, ) = 1 0 q c p c = 4 D A non-compact dark matter halo! Banerjee & Jog 008, ApJ, 685, 54 D is the exponential stellar disk scale length as in Σ= Σ 0 exp(-/ D )

24 esults:. UGC 731 Best-fit vs observed HI thickness (, ) = 1 0 c q p q= 1 An spherical dark matter halo! More Coming! FGC1540, FGC441 (Banerjee, Chengalur al. in prep ) Banerjee, Matthews & Jog 010, NewA, 15, 89

25 esults:. UGC p c q = 0 1 ), ( c ~ D Banerjee, Matthews & Jog 010, NewA, 15, 89 Surface densities vs A compact dark matter halo!

26 Earlier Work: 3.The Galaxy Best-fit vs observed HI thickness (, ) = 1 0 c q p q = 1 p = Underestimates the DM halo mass by an order of magnitude! Narayan et al. 005

27 esults:. The Galaxy.. Best-fit vs observed HI thickness DM halo isodensity contours Banerjee & Jog 011, ApJL, 73, L8 A progressivelymore-prolate DM halo!

28 Summary: DM Halos from HI 1 cm Observations Andromeda 1 Milky Way STAS Stellar Disk DM Core = exp( / 0 D ) Oblate (q = 0.4), Non-compact ( c / D = 4) UGC 731 has a compact dark matter halo! DM 0 (, ) = q 1 c UGC Progressively-more-Prolate(q () > 1), Non-compact ( c / D = 3) 1 Banerjee & Jog 008, Banerjee & Jog 011, 3 Banerjee, Matthews & Jog 010 Spherical (q = 1), Compact( c / D = 1)

29 Limitation/Possible emedy

30 Limitation: Dependence on σ HI Banerjee et al. 010 emedy: Modeling σ HI

31 Other Methods

32 Estimates of Gas Scaleheight for Face-on Galaxies

33 In a Nutshell Motivation LCDM Catastrophe on Galactic Scales Science Goals Density Profiles Of Galactic Dark Matter Halos & Effect Of Dark Matter Halo On Disk Structure & Dynamics Observational Tracer HI 1 cm adio Observations of nearby, edge-on disk galaxies Workhorse: Our theoretical model Our -component of Galactic disk model of gravitationally-coupled stars and gas In a dark matter halo Applications & esults Dark matter halo of the Galaxy, the Andromeda and the superthingalaxy UGC 731 Banerjee& Jog 008, ApJ, 685, 54; Banerjeeet al. 010, NewA, 15, 89, Banerjee& Jog 011, ApJLetters, 73, L8 Future Work Modeling Dark Matter Halos in the Superthin Galaxies FGC 1540, FGC 446