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The Dark Side of the Universe

The Dark Side of the Universe. Sukanya Chakrabarti (FAU). what’s the universe made of?. The visible part of the universe is a tiny fraction!. how do we know dark matter exists? can we figure out where it is?. Nomenclature. pc: typical distance between stars [3x10 18 cm].

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The Dark Side of the Universe

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  1. The Dark Side of the Universe • Sukanya Chakrabarti (FAU)

  2. what’s the universe made of? The visible part of the universe is a tiny fraction!

  3. how do we know dark matter exists? • can we figure out where it is?

  4. Nomenclature • pc: typical distance between stars [3x1018cm]. • Orion: D ~ 400 pc ~ 1200 Lyrs. • Rd: Scale length of spiral galaxies: ~ 3 kpc • Galaxies are made up of: gas, stars and dark matter. Sound speeds of cold gaseous component in galaxies ~ 7 km/s; effective sound speeds of stellar component: ~ 30 km/s

  5. The History of Dark Matter:Discovery of Neptune • Urbain Le Verrier: Aug 13 1846: predicted azimuth of Neptune

  6. History: Dark Matter 2005 Millennium Simulation. Cold dark matter paradigm: accretion • Flat Rotation Curves: Rubin et al.1978, Bosma 1978. • Σ☆ ∝ exp (-r/Rd). Rd ~ 3 kpc. Unseen dark mass producing flat rotation curves.

  7. Galaxy composition Stars -- 1011 stars Gas -- 1010 Msun Dark Matter Halo -- makes up the rest. Total mass of our galaxy: 1012 Msun

  8. Gravitational lensing

  9. how do we know dark matter exists? ... you can infer its existence from its gravitational effect (tides on the earth’s ocean from the moon) • can we figure out where it is?

  10. Overview • Cold gas as tracer of perturbing dark-matter dominated dwarf galaxies • Galaxies with optical companions : Proof of Principle • Milky Way • Inferring distribution of dark matter in galaxies

  11. The Cold Dark Matter Paradigm & the distribution of galaxies Simulations correctly recover the observed distribution of galaxies on large scales (Davis et al. 1985; Springel et al. 2006) Springel et al. 2006

  12. Dark Matter: Structure on Sub-Galactic Scales

  13. Dark Sub-Halos: Expectations from Simulations • Diemand et al. 2008 - theory predicts: should be ~1000 sub-halos with M> 107 Msun, ~ 1 sub-halo of mass 1010MsunWhere are the rest? Can you find them by looking for their signatures on gas disks?

  14. Large Magellanic Cloud

  15. Sagittarius Dwarf

  16. Infrared (2MASS) Map of Milky Way

  17. Tidal Imprints (footprints) of Dark Subhalos on Outskirts of Galaxies • Coldest Component Responds the Most! (by ratio of inverse sound speed squared). Gas has short-term memory. • Maximize rate of detection of dark subhalos by looking for their tidal footprints on atomic hydrogen gas disks. Atomic hydrogen (HI) Maps! Footprints of Dark Sub-Halos

  18. Disturbances in HI disks in Local Spirals: Proof of Principle

  19. M51 HI Map optical image am(r)=∫Σ(r,ϕ)e-imϕdϕ Local Fourier Amplitudes of HI data: Metric of Comparison to simulations

  20. M51 Simulation Comparison 3-D stereoscopic rendering shown at AAS 2011 Chakrabarti, Bigiel, Chang & Blitz, 2011

  21. Tidal Interaction of Satellite with Galaxy • forced response • inferring satellite mass & location from ripples in galactic disk -- throwing pebbles in a pond

  22. Variance Vs Variance Best-fits -- close to origin on variance vs variance plot (S1-S1-4), shown at best-fit time. “Variants” include varying initial conditions (ICs), interstellar medium (ISM), star formation prescription, orbital inclination, etc. Our estimate of Ms (1:3) close to observational numbers.

  23. Galaxies with known optical companions contd. • ~1:100 satellite, Rperi = 7kpc (close agreement with Koribalski & Sanchez 09) (global fourier amplitudes) • Method works for 1:3 - 1:100 mass ratio satellites

  24. HI Map of Milky Way • HI maps: Levine, Blitz & Heiles 2006. What caused these structures well outside the solar circle? am(r)=∫Σ(r,ϕ)e-imϕdϕ

  25. Simulations • Parameter space survey of simulations to explain observed disturbances in HI map of Milky Way. Chakrabarti & Blitz 2009.

  26. Initial Conditions, Orbits -- what really matters? • Not very sensitive to initial conditions (for parameters comparable to spirals). CB09 -- Ms and Rperi are what really matter

  27. Hunting for the Dark Dwarf Galaxy • Known Milky Way companions have been discovered so far in the optical bands. Huge obscuration in the plane! Prediction for azimuth of satellite (Chakrabarti & Blitz 2011) • Why haven’t we seen it yet?

  28. Infrared (2MASS) Map of Milky Way but 2MASS is not deep enough. GLIMPSE survey of galactic plane will search for putative dwarf galaxy

  29. In Closing ...

  30. Gravitational Lensing • Lensing and Tidal Analysis are complementary methods to probe CDM sub-structure and dark matter and do not rely on the stellar light distribution Vegetti et al. 2010 -- characterizing dwarfs through gravitational imaging

  31. 1800s -- > 2012 Statistics from many galaxies! and our own (GLIMPSE) Gives us a chance to understand statistical viability of Tidal Analysis

  32. Summary & Future • Analysis of perturbations in cold gas on outskirts of galaxies constrains mass,R,and azimuth of dark (or luminous) perturbers. New method to characterize satellites (to see dark galaxies). Method tested for satellites with mass ratio: ~1:100 - 1:3. Extended to infer dark matter density profile of spirals. • Next decade - complex interplay of baryons and dark matter. • Computational study of galaxy evolution & cosmology on galactic and sub-galactic scales. • From the skeletal structure of the universe to understanding the guts of galaxy evolution.

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