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High-Precision Rotation Curves of Disk Galaxies: Cores or Cusps?

This study explores the rotation curves of disk galaxies to determine whether they exhibit cores or cusps in their central regions. Observational limitations and comparisons to numerical models are discussed. Additionally, the presence of warps in galaxies is examined as a possible cause for the observed rotation curve variations.

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High-Precision Rotation Curves of Disk Galaxies: Cores or Cusps?

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  1. High-precision rotation curves of disk galaxies G. Gentile SISSA/UNM G. Józsa RAIUB F. Kenn RAIUB U. Klein RAIUB P. Kalberla RAIUB T. Meisner RAIUB T. Oosterloo ASTRON A. Pizzella Padova P. Sallucci SISSA D. Vergani Meudon DM and rotation curves centres: cores or cusps? peripheries: warps Wien, 09 October 2005

  2. History • J. Oort (1933) vz of stars • F. Zwicky (1933) σv in the Coma cluster of galaxies • V. Rubin (1980) galaxies: H rotation curves • A. Bosma (1981) galaxies: HI rotation curves • COBE (1992) CMB: DM on cosmic scales Wien, 09 October 2005

  3. disk galaxies: circular velocities expected: Kepler rotation observed: Dark Halo Wien, 09 October 2005

  4. DM potetntial: measure circular rotation speed VDM(R) and infer DM(R) using for circular orbits in a spherical dark halo. So: measure Vtot(R), V*(R), Vgas(R), and deduce VDM(R) Wien, 09 October 2005

  5. 90’s: numerical models of cold dark matter (CDM) Navarro et al. (1996), Moore et al. (1998) very successful on large scales  possibility to test (verify / falsify) something!  larger number of observational efforts / more focussed • problems: ‘CDM crises’ 1. predicted cusps in galaxy centres not favoured by observations (> 30 papers over last years) 2. angular momentum (simulated baryonic disks too small) 3. missing satellites “cemented”: H0, Ω0, ΩΛ, Ωm, Ωb , … Burkert (1995): empirical law, complying with observations of dwarf galaxies Wien, 09 October 2005

  6. NFW Burkert Wien, 09 October 2005

  7. shortcomings on the observational side: limitations of observed rotation curves (van den Bosch et al. 2000; Swaters et al. 2003) - optical (H) : extinction, limited radial extents, poor spectral resolution (V  20 km s-1), mostly slit spectroscopy - radio (HI) : poor spatial resolution in the central regions - sensitivity : HI still the best ... one can do better: optimum combination of CO and H (inner parts) and HI (outer parts), V  6 km s-1 DM(r) DM MDM/Mlum progress: Wien, 09 October 2005

  8. Observations (HI, H, CO) : more than 20 papers ... dwarf galaxies DM dominated; some recent results: • Weldrake et al. (2003) : NGC 6822, no cusp (down to 20 pc) • Salucci et al. (2003) : DDO 47, constant density (down to 300 pc) • Swaters et al. (2003) : 15 dwarf & LSBGs cusps not completely ruled out but none requires halo with steep cusp • Gentile et al. (2004) : 7 low-luminosity spiral galaxies Wien, 09 October 2005

  9. Rotation curves Three main tracers: • HI  = 21 cm • H  = 6563 Å data cube: • CO  = 2.6, 1.3, ... mm e.g. HI line: velocity (peak, Gauss fit, 1st moment) column density Wien, 09 October 2005

  10. Rotation curves υ(r) analysis in elliptical rings PV diagramme = cut along major axis Wien, 09 October 2005

  11. Wien, 09 October 2005

  12. Rotation curves: • tilted-ring analysis yields - Vsys - position angle - inclination required: envelope tracing method - asymmetric HI line profiles: tails towards systemic velocity - projected emission from thick disk also accounts for - instrum. V broadening - beam smearing - interst. turbulence Wien, 09 October 2005

  13. Tracer angular spectral resolution resolution H 0.5" … 1.5" 10 … 30 km s-1 HI 7" … 30" 4 … 10 km s-1 CO 1.5" … 8" 5 … 20 km s-1 Wien, 09 October 2005

  14. Cusps or cores? G. Gentile, P. Salucci, U. Klein, D. Vergani, P. Kalberla (MNRAS 351, 903, 2004) sample of spiral galaxies with - precise optical RCs - moderate (L  L*) luminosities - late type (small bulges) - well known distances optical RCs and photometry from Persic & Salucci (1995) culled from high-quality selection of rotation curves by Persic & Salucci (1995) Wien, 09 October 2005

  15. HI distributions (column densities) Wien, 09 October 2005

  16. PV diagrams & rotation curves rotation curves out to  3 · Ropt Wien, 09 October 2005

  17. Comparison with models Fits to numerical models • CDM - NFW - Moore • empirical - Burkert - Salucci URC • others - scaled gaseous disk (HI) - MOND cusps or cores ? Wien, 09 October 2005

  18. Burkert NFW Wien, 09 October 2005

  19. Results: • Burkert profiles: - better fits (2) - consistent M/L and a = Rc/Ropt • NFW profiles: - clearly worse (2), in some cases dramatically - M/L flagrantly low in some cases - Mvir too high - observed V(R) in conflict with central cusps Wien, 09 October 2005

  20. Wien, 09 October 2005

  21. NGC 6822 Weldrake et al. (2003) DDO 47 Salucci et al. (2003) Wien, 09 October 2005

  22. Warps in galaxies possible causes: • tidal forces • IGM (gas infall) • DM halos (non-spherical) Wien, 09 October 2005

  23. Warps in galaxies: a frequent phenomenon! • Reshetnikov & Combes (1998; 1999): - about 40% of late-type galaxies exhibit -shaped warps - tidal interaction a likely cause - no large-scale alignment • García-Ruiz (2001): - all galaxies with an HI disk that is more extended than the optical are warped (corollary: all disk galaxies are warped) - stronger and more asymmetric warps in more rich environ- ments - but also warps in isolated galaxies  other mechanisms Wien, 09 October 2005

  24. most pronounced in the HI line! NGC 4013 NGC 2403 ESO 123-G23 Wien, 09 October 2005

  25. Data and models Data Warp Flare 2 - C Wien, 09 October 2005

  26. G. Gentile, Fraternali, P., Klein, U., P. Salucci, P. (A&A 405, 969, 2003) parameters:  ~ 35º (strong warp!)   0º (close to l.o.s) view of warp Wien, 09 October 2005

  27. Extracting parameters from HI data cubes of warped galaxies Measured (HI) data cube    moment 1 (or peak velocities) tilted-ring analysis initial model - systemic velocity - inclination - position angle model cube  convolution  subtract data cube  check 2 better / worse? new parameters, each ring (Vsys , Vrot , centre, i, p.a., w.a.) TIRIFIC (G. Józsa) Wien, 09 October 2005

  28. Kinematics and morphology of warped disk galaxies G. Józsa, F. Kenn, T. Meisner, T. Oosterloo, U. Klein, ... - galaxies with strong symmetric HI warps - HI observations with WSRT - optical photometry with INT Study galaxies in 3 dimensions, i.e. determine - inclination i (R) - position angle p.a. (R) - systemic velocity Vsys (R) - warp angle w.a. (R) - centreξ0 (R), η0 (R) HI disks of galaxies were previously deemed to have cut-off radii at NHI 1019 cm-2 … but they are (fortunately) larger! Wien, 09 October 2005

  29. Large warps: e.g. NGC 5204 Wien, 09 October 2005

  30. NGC 5204 Wien, 09 October 2005

  31. NGC 755 Wien, 09 October 2005

  32. NGC 755 Wien, 09 October 2005

  33. NGC 2541 UGC 3580 NGC 5204 Wien, 09 October 2005

  34. edge-on galaxies exhibit this: Sharma & Steinmetz (2005): misalignment between angular momentum of disk and dark halo so … Wien, 09 October 2005

  35. … fully in line with Dekel & Shlosman (1983) Toomre (1983) Wien, 09 October 2005

  36. First conclusions: 1. flat inner part • warp starts where - optical disk has faded away - HI surface brightness reaches a constant, low level 3. rotation velocity changes with orientation of the disk  non-spherical DM halo? 4. two coherent kinematic regimes, each with constant LON Wien, 09 October 2005

  37. nature is not necessarily symmetric a lot to be done yet … Wien, 09 October 2005

  38. Large HI disks DDO 54 - D = 3.2 Mpc - Rho = 1.4 kpc - MB = -13.33 - Mtot  3 · 109 M - MHI / M*  5.1 - MDM / Mlum  12 Carignan & Freeman (1988) Carignan & Purton (1998) Wien, 09 October 2005

  39. - 4  12 hrs. WSRT - fast data reduction - warped, asymmetric! Wien, 09 October 2005

  40. UGC 2885: super-massive spiral (Lewis 1985) - D = 120 Mpc - RHI = 108 kpc - Mtot = 2.2 · 1012 M 100 kpc 100 kpc Wien, 09 October 2005

  41. NGC6946 HI mosaic (Oosterloo et al.) • 16 × 12 hrs. • prominent holes • anomalous velocities • outer spiral structure with • large streaming motions Wien, 09 October 2005

  42. M31 deep HI mosaic (Braun et al.) • 27 tracks à 12 hrs. • 163 pointings • 2 Gbyte memory for each channel • 50 pc spatial resol. • V = 2 km s-1 • NHI 1 × 1018 cm-2 • RHI  40 kpc (UV truncation) Wien, 09 October 2005

  43. Outlook past decade has seen enormous progress in theory; models much more realistic (baryonic component) observations are (and will be) improving considerably HI out to many RoptCO towards inner 100 ···200 pc (2  1 line, D  20 Mpc) instrumental artefacts can be overcome giant future telescopes (ALMA, NGST, SKA, ...) - RCs out to z = 0.5 (CO, CI) - TF relation out to z = 3 ··· 5 Wien, 09 October 2005

  44. NGC2541 NGC2685 UGC3580 NGC3718 NGC5204 Wien, 09 October 2005

  45. Sample Galaxy Type MB D ØHI [m] [Mpc] [kpc] NGC 2541 SA(s)cd -18.5 7.4 28 NGC 2685 S0+pec -18.6 13.3 39 UGC 3580 SA(s)a pec -18.2 16.0 40 NGC 3718 SB(s)+pec -20.0 15.6 74 NGC 5204 SA(s)m -17.7 2.7 12 Wien, 09 October 2005

  46. Bosma's law (1991): galaxies with small DM core radii are less likely to be warped → connection between dark halo and warps • Brigg's Laws (1990): 1. The warp starts at the edge of the optical disk (R25) 3. The line-of-nodes (LON) is straight out to Rtr =R25 → self-gravity of the disk plays a role 4. Beyond Rtrthe warp characteristics changes and the LON form a leading spiral → differential precession at large radii? 5. In a certain reference frame two straight LONs exist, one inside Rtr , one outside Wien, 09 October 2005

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