1209.3741 (Xufen Wu et al.)

The mass and angular momentum distribution of simulated massive galaxies to large radii    [PDF]

Xufen Wu, Ortwin Gerhard, Thorsten Naab, Ludwig Oser, Inma Martinez-Valpuesta, Michael Hilz, Eugene Churazov, Natalya Lyskova

We study the mass distributions, circular velocity curves (CVCs), line-of-sight kinematics and angular momenta out to many Re for a sample of 42 cosmological zoom simulations of massive galaxies. In order to reduce the particle noise at large radii, we temporally smooth the observables of the simulated galaxies in a static potential. The mass of the simulated galaxies is parametrised by vcirc at r=5Re. We find: (i) The projected stellar density distributions at large radii can be well fitted by S'ersic functions. The S'ersic indices range from 3 to 13 and correlate with stellar mass and galaxy size (low n, low mass, small size). (ii) The dark matter halo density profiles are consistent with simple power-law models, corresponding to flat dark matter CVCs for lower-mass systems, and rising CVCs for high-mass halos. (iii) The massive systems have nearly flat total CVCs at large radii, while the less massive systems have mildly decreasing CVCs. The slope of the CVC at large radii correlates with S'ersic index and vcirc itself. (iv) The short axes of simulated galaxies and their host dark matter are well aligned and their short-to-long axis ratios are correlated. (v) Stellar root mean square velocity v_rms(R) profiles are slightly falling, consistent with planetary nebulae observations in the outer halos of most ETGs. There are no analogues in the simulated galaxies of the second group of ETGs with rapidly falling v_rms(R) profiles. (vi) The line-of-sight velocity fields show that rotation properties at small and large radii are correlated. Most radial profiles for the cumulative specific angular momentum parameter lambda(R) are nearly flat or slightly rising from 2Re to 5Re. (vii) Stellar mass, ellipticity at large radii eps(5Re), and lambda(5Re) are correlated:the more massive systems have less angular momentum and are rounder, as for observed ETGs. (Full abstract is in downloadable file)

View original: http://arxiv.org/abs/1209.3741