Galaxy Kinematics With Virus-P: The Dark Matter Halo Of M87

We present two-dimensional stellar kinematics of M87 out to R = 238 '' taken with the integral field spectrograph VIRUS-P. We run a large set of axisymmetric, orbit-based dynamical models and find clear evidence for a massive dark matter halo. While a logarithmic parameterization for the dark matter halo is preferred, we do not constrain the dark matter scale radius for a Navarro-Frenk-White (NFW) profile and therefore cannot rule it out. Our best-fit logarithmic models return an enclosed dark matter fraction of 17.2(-5.0)(+5.0)% within one effective radius (R-e congruent to 100 ''), rising to 49.4(-8.8)(+7.2)% within 2 R-e. Existing SAURON data (R <= 13 ''), and globular cluster (GC) kinematic data covering 145 '' <= R <= 554 '' complete the kinematic coverage to R = 47 kpc (similar to 5R(e)). At this radial distance, the logarithmic dark halo comprises 85.3(-2.4)(+2.5)% of the total enclosed mass of 5.7(-0.9)(+1.3) x 10(12) M-circle dot making M87 one of the most massive galaxies in the local universe. Our best-fit logarithmic dynamical models return a stellar mass-to-light ratio (M/L) of 9.1(-0.2)(+0.2) (V band), a dark halo circular velocity of 800(-25)(+75) km s(-1), and a dark halo scale radius of 36(-3)(+7) kpc. The stellar M/L, assuming an NFW dark halo, is well constrained to 8.20(-0.10)(+0.05) (V band). The stars in M87 are found to be radially anisotropic out to R congruent to 0.5 R-e, then isotropic or slightly tangentially anisotropic to our last stellar data point at R = 2.4 R-e where the anisotropy of the stars and GCs are in excellent agreement. The GCs then become radially anisotropic in the last two modeling bins at R = 3.4 R-e and R = 4.8 R-e. As one of the most massive galaxies in the local universe, constraints on both the mass distribution of M87 and anisotropy of its kinematic components strongly inform our theories of early-type galaxy formation and evolution in dense environments.Astronom

Retaining Black Holes with Very Large Recoil Velocities

Recent numerical simulations of binary black hole mergers show the possibility of producing very large recoil velocities (> 3000 km/s). Kicks of this magnitude should be sufficient to eject the final black hole from virtually any galactic potential. This result has been seen as a potential contradiction with observations of supermassive black holes residing in the centers of most galaxies in the local universe. Using an extremely simplified merger tree model, we show that, even in the limit of very large ejection probability, after a small number of merger generations there should still be an appreciable fraction (>50%) of galaxies with supermassive black holes today. We go on to argue that the inclusion of more realistic physics ingredients in the merger model should systematically increase this retention fraction, helping to resolve a potential conflict between theory and observation. Lastly, we develop a more realistic Monte Carlo model to confirm the qualitative arguments and estimate occupation fractions as a function of the central galactic velocity dispersion.Comment: 6 pages, 3 figures; Comments welcom

Myelin basic protein peptide 45–89 induces the release of nitric oxide from microglial cells.

Continuous (24 h) exposure of mixed oligodendrocyte/microglial cells to peptides 45–89 derived from citrullinated C8 isoforms of myelin basic protein (MBP) induces cell death. In contrast, MBP-C8 at the same molecular concentration is not toxic to oligodendrocyte/microglial cells as detected by the MTT test and trypan blue exclusion method. The loss of oligodendrocyte/microglial cells resulted in the release of cytochrome c from mitochondria, suggesting MBP 45–89-induced apoptosis. On the other hand, peptides 45–89 stimulated the secretion of nitric oxide from microglial cells only via induction of iNOS. The addition of peptide 45–89 to the microglial cells led to a decrease of the level of the inhibitory protein IkB, indicating that activation of the transcription factor NF-kB is involved in these processes. We propose that the immunodominant peptide 45–89 induces damage of oligodendrocytes by activation of microglial cells and subsequent generation of nitric oxide, and that this may be the first step in the initiation of autoimmunity