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Pattern Speed and Galaxy Morphology

Pattern Speed and Galaxy Morphology. Ron Buta University of Alabama. The diversity of galaxy morphology…. De Vaucouleurs sketch circa 1962. To what extent does it depend on pattern speed(s)?. Many factors can influence the morphology of a given galaxy, such as: - gas content

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Pattern Speed and Galaxy Morphology

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  1. Pattern Speed and Galaxy Morphology Ron Buta University of Alabama

  2. The diversity of galaxy morphology…. De Vaucouleurs sketch circa 1962 To what extent does it depend on pattern speed(s)?

  3. Many factors can influence the morphology of a given galaxy, such as: - gas content - frequency of past interactions/mergers - basic state characteristics (star/gas surface densities, velocity dispersion, rotation curve) - strength of internal perturbations and secular evolution - rotation rate of patterns etc Pattern speed is just one factor influencing morphology! However, it is not arbitrary but should come with the mode that spontaneously arises out of the basic state.

  4. Pattern speed is relevant to galaxy morphology because it: - determines the location of all resonances, and resonances can limit the extent of patterns (e.g., Contopoulos 1980) and influence angular momentum transfer to the outer regions (Lynden-Bell & Kalnajs 1972; Athanassoula 2003) - affects the properties of periodic orbits, which can affect the morphology of features such as rings (Contopoulos 1979; Buta & Combes 1996) - determines rate at which bars and spirals influence galaxy evolution (Zhang 1996, 1998, 1999; Zimmer et al. 2004). - can determine the lifetime of a pattern (Merrifield et al. 2006).

  5. Density wave theory led to discussions of the role of pattern speed on spiral structure. Roberts, Roberts, and Shu 1975: the value of Omega_p should affect the radial extent of three tracers: 1. The prominent spiral structure 2. The “easily visible disk” 3. The distribution of HII regions These result because pattern speed and the rotation curve determine the speed at which stars and gas clouds encounter the pattern.

  6. To understand connections between pattern speed and morphology, one can - directly measure pattern speeds or resonance locations and connect observed features to resonances - compare sequences of numerical simulations with actual galaxies, either through generic modeling or modeling of a specific galaxy Garcia-Burillo et al. 1993: modeling of M51: “The gas response is very sensitive to [pattern speed]; we obtain a spiral structure similar to what is observed only for a narrow range of Omega_p.”

  7. Rings are believed to be direct tracers of the pattern speed. Buta & Combes 1996: “Rings are a precious tool to measure the pattern speed, when the rotation curve is known.” Examine models of ringed galaxies to see how pattern speed might affect what we see.

  8. Types of models (or interpretations) • test particles, analytic, rigidly rotating bars (e.g., Schwarz 1981; Byrd et al 1994) • Similar, but bar potential from near-IR image (e.g., Salo et al. 1999) • N-body allowing multiple modes, plus gas test particles (e.g., Rautiainen & Salo 2000) • Hydrodynamical (e.g., Lindblad et al. 1996; L.-H. Lin, C. Yuan*, et al. 2008) • Invariant manifolds around equilibrium points of barred galaxy (Romero-Gomez et al. 2006, rR1 rings) • * Deceased 24 August 2008

  9. R1’ R1R2’ R2’ These simulated patterns were discovered in high pattern speed models by Schwarz 1981. CR and OLR are the main resonances. The outer spirals extend to the OLR. UGC 12646 ESO 577-3 ESO 509-98 The outer spirals of these galaxies show similarities to the above models. R1’, R1R2’, and R2’ are called “OLR subclasses.”

  10. Do some galaxies wear their resonances like “crowns”: Background-disk-subtracted B-band image of NGC 3081: can you “eyeball” corotation in this galaxy? OLR orbits

  11. This low pattern speed model from Simkin, Su, and Schwarz 1980 shows how inner and nuclear rings might develop when the inner resonances (ILR, I/4:1)exist.

  12. IC 5240 NGC 7098 NGC 6782 NGC 1433 The alignment between these inner rings and their bars depends on pattern speed. If the ring/spirals did not share the same pattern speed with the bar, misalignment would likely be the rule.

  13. high medium Sequences of simulations for different pattern speeds of a barred galaxy, from Byrd et al. 1994.

  14. Low pattern speed simulations from Byrd et al. 1994. Use the “Catalogue of Southern Ringed Galaxies” (CSRG, Buta 1995) to evaluate these simulations.

  15. Pattern speed “domains” (Byrd et al. 1994): could these really exist? ILR: Omega_p=Omega-kappa/2 I/4:1: Omega_p=Omega-kappa/4 OLR: Omega_p=Omega+kappa/2

  16. Comparison of Byrd et al. (1994) high pattern speed models with observed (CSRG) deprojected galaxies. Models have CR and OLR only. Omega_b=0.27 NGC 3358 ESO 509-98 These galaxies lack inner and nuclear rings. Could this mean they lack the required resonances? Omega_b=0.22 ESO 365-35

  17. Omega_b=0.10 ESO 575-47 ESO 426-2 ESO 577-3 Medium pattern speed models of Byrd et al. 1994 compared with observed galaxies. The models have an inner 4:1 resonance as well as OLR and CR. The three galaxies all have red nuclei, which could imply the lack of an ILR.

  18. Omega_b=0.06 ESO 437-67 ESO 325-28 Low pattern speed sequence having OLR, inner 4:1, CR, and barely an ILR. The two galaxies have blue nuclei. Does this imply that they have an ILR?

  19. At Omega_b=0.05 in the Byrd et al. 1994 models, x1 orbits in the vicinity of ILR produce a highly elongated ring inside the bar. Is this the nature of the feature, seen in NGC 6012? NGC 6012

  20. NGC 1566 This frame in the lowest pattern speed (Omega_b=0.03) Byrd et al 1994 sequence shows some features that might explain galaxies like NGC 1566 where a bright spiral dominates an extended oval zone, from which the faint arms of an R1’ outer pseudoring emerge.

  21. The Rautiainen and Salo (2000) models focused on the impact of Toomre Q-parameter and the background stellar components. Frames showed the response of gas test particles to an n-body bar. Evolution of a misaligned bar-ring model. The reason for the misalignment is that the spiral is a slower mode than the bar. Evidence for multiple pattern speeds in a single galaxy? ESO 565-11 - a misaligned bar/inner ring galaxy

  22. ESO 566-24 Comparison between a four-armed barred galaxy model (Rautiainen et al. 2004) and a very rare but real symmetric m=4 barred spiral. The pattern is confined between the inner and outer 4:1 resonances. Bar potential from near-IR image.

  23. Sticky-particle models of NGC 1433, type (R1’)SB(r )ab, for different pattern speeds (Treuthardt et al. 2008). The appearance of the secondary arcs is sensitive to pattern speed. Bar potential from near-IR image.

  24. CR is far from the ends of the bar in a hydrodynamical model of NGC 6782 by L.H. Lin et al. (2008). This galaxy is also an rR1 example, but the R1 does not reach OLR in this model.

  25. Strong, two-armed logarithmic spiral modes extend to the inner 4:1 resonance N-body model from Patsis & Kaufmann 1999

  26. The Potential-Density Phase-Shift Method for Locating Corotation Radii Xiaolei Zhang and Ron Buta A method that uses the expected phase difference between the density and the potential implied by that density to locate corotation radii in galaxies. The method was conceived by Zhang (1996, 1998, 1999) and first applied to real galaxies by Zhang and Buta (2007). Zhang 1996, ApJ, 457, 125 Zhang 1998, ApJ, 499, 93 Zhang 1999, ApJ, 518, 613 Zhang & Buta, 2007, AJ, 133, 2584

  27. The density spiral is ahead of the potential spiral inside CR and behind outside CR. This leads to a positive to negative phase difference crossing at CR which can be inferred using near-IR images. The torque applied by the spiral potential on the disk density in an annulus at r is: density spiral potential Spiral where: is the disk surface density, V is the disk potential, m is the number of arms, 1 is spiral density perturbation amplitude, V1 is spiral potential perturbation amplitude, L is the angular momentum in the annulus, 0 is the potential/density phase-shift. rco

  28. Physical basis of method: • -global self-consistency requirement of wave modes • -working assumption: spontaneously-formed density wave patterns that have reached a quasi-steady state • corotations are positive-to- negative crossings in phase-shift versus radius • negative-to-positive crossings show extent of modes

  29. Phase-shift analysis of NGC 1530 - Ks-band image A case of a “bar-driven” spiral? This means the bar and spiral are corotating and are likely to have emerged from the same global mode. Another pattern may be decoupling from the bar at r~4kpc.

  30. Ks-band Image of NGC 613 The phase-shift plot suggests decoupling of the bar from the spiral is in progress.

  31. Ks-band image of NGC 175 In this case, the bar and the spiral are likely fully decoupled and may have different pattern speeds.

  32. Ks-band Image of NGC 1300 Not a case of a bar-driven spiral? Inner part of bar has CR halfway out in bar radius. Bar mode ends at the green circle which is the strong negative-to-positive crossing near r/ro(25)~0.5, where ro(25)=Do/2 = half the extinction-corrected isophotal diameter from RC3.

  33. Do phase-shift distributions for ringed galaxies provide any support to the implications from test-particle and other numerical models? NGC 1350, type (R1’)SAB(r )ab - CR of main oval could support OLR interpretation of R1’.

  34. NGC 1433, type (R1’)SB(r )ab Treuthardt et al. 2008 sticky particle model resonances: I/4:1, CR, O/4:1, R1’ not OLR! Rautiainen & Salo 1999 CR-I/4:1 coupling

  35. UGC 12646, type (R1’)SB(r )ab with “dimpled” R1’.

  36. In this grand-design spiral, the phase-shift method places the main CR in the middle of the pattern.

  37. What does the phase-shift method have to say about “fast” and “slow” bars? Debattista & Sellwood 2000: r(CR)/r(bar)<1.4 = fast bars, >1.4=slow bars <---1.4 Phase-shift corotation radius to bar radius for 100 OSUBGS galaxies versus RC3 stage index. Over all types, <r(CR)/r(bar)>=1.17 +/-0.36. Bar radii are from Laurikainen et al. 2004. Sbc and earlier (T<=4) have fast bars on average, Sc and later (T>4) have slow bars on average.

  38. How well do phase-shift CR radii agree with values from other methods? Comparison of bar CR radii from phase-shift method with CR radii determined from the numerical simulation method (Rautiainen et al. 2005).

  39. Conclusions: • - numerical simulations can shed a lot of light on the way pattern speed affects morphology. • - different pattern speed domains may exist • the phase-shift method suggests that multiple pattern speeds are common in spiral and barred galaxies. • Both bar-driven and non-bar-driven spirals are detected, I thank Drs. X. Zhang, E.Laurikainen, and H. Salo for their input in this work. This work was also supported by NSF grant AST050-7140.

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