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تسجيل مستخدم جديدConstraining dark matter halo profiles and galaxy formation models using spiral arm morphology. I. Method outline
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Marc S. Seigar
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We investigate the use of spiral arm pitch angles as a probe of disk galaxy mass profiles. We confirm our previous result that spiral arm pitch angles (P) are well-correlated with the rate of shear (S) in disk galaxy rotation curves, by using a much larger sample (51 galaxies) than used previously (17 galaxies). We use this correlation to argue that imaging data alone can provide a powerful probe of galactic mass distributions out to large lookback times. In contrast to previous work, we show that observed spiral arm pitch angles are similar when measured in the optical (at 0.4 um) and the near-infrared (at 2.1 um) with a mean difference of 2.3+/-2.7 degrees. This is then used to strengthen the known correlation between P and S using B-band images. We then use two example galaxies to demonstrate how an inferred shear rate coupled with a bulge-disk decomposition model and a Tully-Fisher derived velocity normalization can be used to place constraints on a galaxys baryon fraction and dark matter halo profile. We show that ESO 582-G12, a galaxy with a high shear rate (slightly declining rotation curve) at ~10 kpc, favors an adiabatically contracted halo, with high initial NFW concentration (c_vir > 16) and a high fraction of halo baryons in the form of stars (~15-40%). In contrast, IC 2522 has a low shear rate (rising rotation curve) at ~10 kpc and favors non-adiabatically contracted models with low NFW concentrations (c_vir ~ 2-8) and a low stellar baryon fraction <10%.
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We investigate the use of spiral arm pitch angles as a probe of disk galaxy mass profiles. We confirm our previous result that spiral arm pitch angles (P) are well correlated with the rate of shear (S) in disk galaxy rotation curves. We use this corr
elation to argue that imaging data alone can provide a powerful probe of galactic mass distributions out to large look-back times. We then use a sample of 13 galaxies, with Spitzer 3.6-$mu$m imaging data and observed H$alpha$ rotation curves, to demonstrate how an inferred shear rate coupled with a bulge-disk decomposition model and a Tully-Fisher-derived velocity normalization can be used to place constraints on a galaxys baryon fraction and dark matter halo profile. Finally we show that there appears to be a trend (albeit a weak correlation) between spiral arm pitch angle and halo concentration. We discuss implications for the suggested link between supermassive black hole (SMBH) mass and dark halo concentration, using pitch angle as a proxy for SMBH mass.
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