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Gravitational Bar Torques in the Spiral/S0 Divide

Gravitational Bar Torques in the Spiral/S0 Divide. Ron Buta University of Alabama. Why study bar properties in S0s?. Bars are common to spirals and S0s the bars are “clean”, more symmetric, and largely stellar dynamical

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Gravitational Bar Torques in the Spiral/S0 Divide

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  1. Gravitational Bar Torques in the Spiral/S0 Divide Ron Buta University of Alabama

  2. Why study bar properties in S0s? • Bars are common to spirals and S0s • the bars are “clean”, more symmetric, and largely stellar dynamical • distribution of bar strengths in S0s may shed light on S0 origins and also bar origins and evolution (primordial vs. time-dependent distribution)

  3. Why study near-IR properties of S0 bars? • To get a fair comparison with bars in spirals • minimize effects of any extinction, however small • near-IR is best wavelength regime to define stellar potentials (Quillen et al. 1994)

  4. NGC 4340 NGC 4596 NGC 4754 NGC 4608 IC 4290 NGC 1433 NGC 5850 NGC 5921 NGC 1073 NGC 4519 NGC 4027 NGC 4618 The de Vaucouleurs Atlas of Galaxies: B-band images

  5. Barred spiral varieties (B-band) NGC 2523 SB(r) NGC 266 SB(rs) NGC 1300 SB(s) NGC 1433 SB(r) NGC 4548 SB(rs) NGC 7479 SB(s)

  6. NGC 4442 NGC 2983 NGC 4754 NGC 936 NGC 4596 NGC 4608 Varieties among SB0 and SB0/a galaxies (B-band) NGC 4340 NGC 7079

  7. NGC 1452 NGC 4245 NGC 6654 IC 1438 NGC 5701 NGC 7743 Early-type spirals in the “divide” (B-band)

  8. Quantification of Bar Strengths in Disk Galaxies Gravitational Torque Method (GTM) Sanders & Tubbs 1980; Combes & Sanders 1981; Quillen Frogel, & Gonzalez 1994; Buta & Block 2001; Laurikainen et al. 2004 Ratio map: Q(i,j)=FT(i,j)/F0R(i,j) QT( r) = |FT( r )/F0R( r )|max FT=tangential force F0R=mean radial force

  9. NGC 6951 Ks image FT/F0R Force ratio map

  10. Qg=maximum gravitational torque per unit mass per unit square of circular speed NGC 6951

  11. Bars and the Evolution of Galaxies • Distribution of bar strengths (Sellwood 2000) • buildup of central mass concentration & bar destruction (Pfenniger & Norman 1990) • bar destruction & reformation via gas accretion (Bournaud & Combes 2002) • bar regeneration and tidal interactions (Berentzen et al. 2004) • pseudobulge and lens formation (Kormendy & Kennicutt 2004)

  12. Gravitational Torques in Spiral Galaxies • Quantitative dust-penetrated bar classification (Buta & Block 2001) • distribution & type dependence of Qg values for OSUBGS sample (Buta, Laurikainen, & Salo 2004) • active vs nonactive galaxies (Laurikainen, Salo, & Buta 2004) • bar strength and inner ring shape (Buta 2002) • bar/spiral separation and correlations between bar and spiral arm strengths (Buta, Block, & Knapen 2003, Block et al. 2004)

  13. Distribution of Maximum Relative Torques Buta, Laurikainen, & Salo 2004

  14. Bar/Spiral SeparationButa, Block, & Knapen 2003 • Use Fourier techniques to separate bars and spirals • plots of Im/I0 versus radius r • symmetry assumption • construction of bar+disk and spiral+disk images

  15. m=2 and 4 relative intensity amplitudes for NGC 6951 in Ks band crosses show “symmetry assumption”

  16. Separation for NGC 6951

  17. Qb = bar strength Qs = spiral strength Strong bars, weak spirals: Qb ~ Qg Strong spirals, weak bars: Qs ~ Qg NGC 6951

  18. Application of bar/spiral separation to 17 spiralsBlock, Buta, Knapen, D. M. & B. G. Elmegreen,Puerari 2004 • 17 spirals types Sab to Scd • Qb, Qs values from separation • result: correlation between Qs and Qb for Qb > 0.3

  19. Gravitational Torques in SB0 and SB0/a Galaxies • “Near-IR S0 Survey” (NIRS0S, Laurikainen, Buta, Salo, et al.) • Ks band, 2.2 microns • Goal: ~100 S0s in well-defined sample similar to OSUBGS • 2D three-component decompositions • revised classifications

  20. Deprojected Ks-band images NGC 936 NGC 4596 NGC 4608 NGC 4643

  21. Preliminary distribution of maximum relative torques Qg for 24 S0, S0/a galaxies

  22. Strongest known Bars in Early and Intermediate Type Galaxies NGC 1530 SB(rs)b NGC 1452 (R’)SB(r )0/a Qb=0.5 Qb=0.6

  23. Relative Fourier Intensity Amplitudes for SB0 and SB0/a galaxies • 5 of 8 studied show symmetric even Fourier terms to m=20 • verify symmetry assumption for early-type bars • 3 of 8 showed asymmetric profiles of either m=2 or all even m to m=20

  24. Symmetric relative Fourier intensity profiles (m=2 & 4)

  25. Asymmetric relative Fourier intensity profiles (m=2 & 4)

  26. Force ratio maps for two early-type barred galaxies NGC 4596 NGC 4643

  27. Bar/spiral separation for NGC 4596 as compared to NGC 6951

  28. Bar Strengths in the Spiral/S0 Divide Galaxy Type hz(pc) Qb r(Qb)/ro Qs r(Qs)/ro NGC 936 SB(rs)0+ 740 0.22 0.28 0.04: 0.57: NGC 1452 (R’)SB( r )0/a 570 0.48 0.52 0.09: 0.68: NGC 2859 (R)SB( r )0+ 940 0.16 0.31 0.02: 0.46: NGC 4245 SB( r )0/a 360 0.17 0.32 0.05: 0.46: NGC 4596 SB(rs)0/a 890 0.26 0.41 0.03: 0.79: NGC 4608 SB( r )0o 630 0.28 0.42 0.04: 0.55: NGC 4643 SB(rs)0/a 850 0.30 0.46 0.05: 0.91: ro = extinction-corrected radius at 25.0 B mag/arcsec2

  29. Comparison of Bar and Spiral Strengths

  30. Conclusions • The NIRS0S will continue to try and do for S0s what the OSUBGS did for spirals • preliminary results show a wide range of Qg for SB0 and SB0/a galaxies • typical SB0s have Qb~0.15-0.3 • symmetry assumption for early-type bars verified Acknowledgments: Much thanks to Eija Laurikainen, Heikki Salo Alice Quillen, and Dave Block for helping to make this presentation possible. This work was supported by NSF grant AST0205143.

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