Baryonic Masses from Rotation Curves. Stacy McGaugh University of Maryland

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1 Unveiling the Mass - Extracting and Interpreting Galaxy Masses, Kingston, Ontario, 19 June 2009 Baryonic Masses from Rotation Curves Stacy McGaugh University of Maryland

2 Rotation curves tend to become flat M R ρ R 2 Rubin, Thonnard, & Ford 1978, ApJ, 225, L107

3 Boomsma 2005: HI Vflat baryons dark matter NGC 6946

4 Rotation curve shapes correlate with galaxy properties Rubin, Burstein, & Thonnard 1980, ApJ, 242, L149

5 Rotation curve amplitude and shape correlate with luminosity Rubin Verheijen Begeman Broeils

6 NGC 2403 HSB UGC 128 LSB Same global Mb,V Very different mass distributions

7 V p V p R p R p

8 Σ b = 3 4 M b R 2 p Central baryonic surface density of the equivalent exponential disk for a galaxy of baryonic mass Mb whose rotation curve peaks at Rp M b = M L L + M g Use Bell et al. (2003) M*/L for starters.

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10 Pizagno et al. McGaugh (2005) Stellar Mass TF Baryonic TF

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17 Tully-Fisher Relation M =Υ L McGaugh (2005) Pizagno et al.

18 Baryonic Tully-Fisher Mb = M + Mgas line: log M b = 4 log V f +1.7 (McGaugh 2005)

19 Reduce dependence on stellar M*/L - select gas dominated galaxies with M <M g optical HI

20 Baryonic Tully-Fisher Relation Stark, McGaugh, & Swaters (2009 AJ, 138, 392) Bell03 diet Salpeter IMF M >M g M <M g Trachternach et al. log M b =3.93 log V f +1.80

21 Baryonic Tully-Fisher Relation Stark, McGaugh, & Swaters (2009 AJ, 138, 392) Portinari04 Kroupa IMF M >M g M <M g Trachternach et al. log M b =3.93 log V f +1.78

22 Baryonic Tully-Fisher Relation Stark, McGaugh, & Swaters (2009 AJ, 138, 392) Bell03 Kroupa IMF M >M g M <M g Trachternach et al. log M b =4.01 log V f +1.61

23 What M*/L puts star dominated galaxies on the BTF?

24 BTF (gas dominated calibration) Stark, McGaugh, & Swaters (2009, AJ, 138, 392) Recovers expected slope normalization scatter constrains IMF: ~ Kroupa

25 dsphs Ultra-Faints

26 No residuals from TF with surface density gas dominated star dominated Degree of disk maximality must depend on surface brightness. Halo contribution at Rp anticorrelates with baryon contribution. V 2 = GM R McGaugh 2005, PRL 95,

27 Rotation curve shapes depend on luminosity and surface density

28 The mass discrepancy sets in sooner and is more severe in LSB galaxies

29 Acceleration related to baryonic surface density

30 Renzo s Rule: When you see a feature in the light, you see a corresponding feature in the rotation curve. (Sancisi 1995, private communication; 2004 IAU) The distribution of mass is coupled to the distribution of light.

31 Renzo s rule - bumps & wiggles in light distribution & rotation curve Need baryons. Can t make DM go up & down & up again. NGC 6946 Daigle et al. 2006: FP Boomsma 2005: HI

32 Mass Discrepancy-Acceleration Relation V 2 = ν ( a a ) V 2 b Spiral galaxies generally obey a mass discrepancy-acceleration relation (McGaugh 2004). Can fit the data for this function. Note that the mass discrepancy never appears above a critical acceleration a

33 Renzo s rule holds even in LSB galaxies, where DM dominates NGC 1560

34 Mass Discrepancy-Acceleration Relation maps between observed baryons and total rotation NGC 1560

35 Mass Discrepancy-Acceleration Relation McGaugh (2004, ApJ, 609, 652) Can use this to write an analytical expression for the dark matter distribution: if you know the distribution of baryons, you know the DM distribution.

36 The halo-only rotation curves of all spirals are strikingly similar (McGaugh et al. 2007) log V h = 1 2 log R ρ = R M pc 3 = 1.27 R GeV cm 3

37 Statistical properties of disk galaxies provide additional information that breaks the disk-halo degeneracy. Physics of 21 cm spin-flip transition calibrates BTF relation Implies reasonable M*/L constrains IMF to be close to Kroupa/ Chabrier The mass discrepancy sets in at a particular acceleration scale