Central dark matter distribution in dwarf galaxies

Transcription

1 Central dark matter distribution in dwarf galaxies Se-Heon Oh (ICRAR/UWA)

2 Content cusp/core controversy in ΛCDM simulations Dark matter distribution of THINGS dwarf galaxies High-resolution N-body+SPH simulations of dwarf galaxies Comparison of the THINGS dwarfs with the simulations Summary & future directions

3 Cusp/Core problem in ΛCDM simulations ΛCDM simulations Observations Moore (1994) Flores & Primack (1994) Navarro, Frenk & White (1995) Navarro, Frenk & White (1996) Moore et al. (1998) Ghigna et al. (2000) Klypin et al. (2001) Power et al. (2002) Navarro et al. (2004) Diemand et al. (2008) Stadel et al. (2009) Navarro et al. (2010) etc. Velocity log(ρ) R log(r) -1 log(ρ) Velocity R log(r) 0 Flores & Primack (1994) Moore (1994) de Blok et al. (2001) de Blok & Bosma (2002) Bolatto et al. (2002) Weldrake et al. (2003) Simon et al. (2003) Swaters et al. (2003) Kuzio de Naray et al. (2006) Gentile et al. (2007) Oh et al. (2008) Trachternach et al. (2008) de Blok et al. (2008) Oh et al. (2011a, b) etc.

4 Simulation problems? ΛCDM simulations : very successful on large scales but not on small non-linear regimes... Not enough resolution sub-kpc resolution is required (de Blok & Bosma etc.) Cold Dark Matter? warm or self-interacting dark matter particles (Spergel & Steinhardt 2000 etc.) No Baryon physics gas winds caused by vigorous star formation or SNe explosions in the early universe (Mashchenko 2006 etc.)

5 Observation problems? Beam smearing effect? (van den Bosch et al etc.) Kinematic centre offset? (de Blok et al etc.) Non-circular motions? (Swaters et al. 2003)

6 Recent progress on observations THINGS: The HI Nearby Galaxy Survey (Walter et al. 2008) - high angular (~6 ; 100~300 pc) & spectral (2.5~5 km s-1) resolution observations for 34 nearby (< 15 Mpc) galaxies - complemented with multi-λ data (B,V, R, Spitzer SINGS 3.6 and 4.5 μm, CO, GALEX uv etc.) 7 THINGS dwarf galaxies - dark matter dominated - simple dynamical structure (no bulge and spirals) - clear rotation pattern in the velocity field

7 Comparison with ΛCDM simulations I. The rotation curve shape The rotation curves are scaled with respect to the V0.3 at R0.3 where dlogv/dlogr = 0.3. The scaled rotation curves rise too slowly to match the cuspy CDM halos. Instead, they are more consistent with cored pseudoisothermal halo models. Oh et al. 2011a

8 Comparison with ΛCDM simulations II. The inner slopes of mass density profiles The mean value of the slopes is α= 0.29 ± 0.07, consistent with the value of α = 0.2 ± 0.2 found in de Blok et al. (2001, 2002) for LSB galaxies. This is in contrast with the steep slope of α 1.0 predicted from ΛCDM simulations. Oh et al. 2011a

9 The results from the THINGS dwarfs High-quality multi-λ data (THINGS HI, Spitzer 3.6μm and optical data) significantly reduce the observational uncertainties and allow us to derive a more accurate dark matter distribution. The mean of the inner density slopes of the 7 THINGS dwarfs is α= 0.29±0.07, which significantly deviates from 1 predicted from ΛCDM simulations. Despite using high-quality data, no clear evidence was found for the central cusps in the 7 THINGS dwarfs.

10 New dwarf galaxy simulations (Governato et al. 2010) N-body+SPH tree-code GASOLINE Flat Λ-dominated cosmology Baryonic processes are included such as, - gas cooling - cosmic UV field heating - star formation - SNe-driven gas heating There are ~3.3 million particles within the virial radius at z = 0. DM particle mass is M, and gas particle mass is M. The force resolution (gravitational softening) is 86 pc.

11 Gas and stars of DG1 Gas (HI + H2) B R Spitzer 3.6μm i = 90 i = 60 i = 45 i = 0 20 kpc

12 Comparison with the THINGS dwarfs Rotation curve shape Dark matter density profiles Oh et al. 2011b

13 Summary The central dark matter distribution of the 7 THINGS dwarf galaxies from high-quality multi-λ observations appears to be cored. The mean of their inner density slopes is α= 0.29±0.07, which significantly deviates from 1 predicted from dark-matter-only ΛCDM simulations. New high-resolution N-body+SPH simulations including baryonic feedback processes is able to make bulgeless dwarf galaxies with shallow inner mass density profiles. The rotation curve shape and inner mass density slopes of observed and simulated dwarf galaxies are consistent with each other. The baryonic feedback process (e.g., SN-driven gas outflows etc.) in the early Universe is able to not only remove low-angular momentum

14 Future directions (simulations) If baryonic feedback process is a solution for the smallscale ΛCDM problems, then - How the galaxy star formation and chemical histories of the simulations are consistent with observations? - How the spatial distribution of gas/stellar metallicities is consistent with observations? More simulations have been underway (Governato et al.) High-resolution Milky Way type SPH simulations (Mayer et al.)

15 Eris simultaions

16 Future directions (observations) LITTLE THINGS : THINGS-like high-quality multi-λ data (VLA HI, Spitzer, optical, Galex uv, CO etc.) for 41 nearby (< 10 Mpc) dwarf galaxies. Oh et al. in prep.

17 Future directions (observations) LITTLE THINGS : THINGS-like high-quality multi-λ data (VLA HI, Spitzer, optical, Galex uv, CO etc.) for 41 nearby (< 10 Mpc) dwarf galaxies. Oh et al. in prep.

18 Future directions (observations) WALLABY Widefield ASKAP L-band Legacy All-sky Blind survey

19 Disk-halo decomposition Total DM Gas Stars

20 Mass density profiles The inner density slope α= ~ -0.4 is consistent with those of the THINGS dwarfs (α= 0.29 ± 0.07).