Engineering topics
Publications and source records attributed to Penarrubia, Jorge.
This white paper summarizes the astronomical observations for next decade to probe the particle properties of dark matter, and concludes that a 10m class wide-field, high-multiplex spectroscopic survey facility is required for the next decade to definitively search for deviations from the cold collisionless dark matter model.
We present a homogeneous kinematic analysis of red giant branch stars within 18 of the 28 Andromeda dwarf spheroidal (dSph) galaxies, obtained using the Keck I/LRIS and Keck II/DEIMOS spectrographs. Based on their g - i colors (taken with the CFHT/MegaCam imager), physical positions on the sky, and radial velocities, we assign probabilities of dSph membership to each observed star. Using this information, the velocity dispersions, central masses, and central densities of the dark matter halos are calculated for these objects, and compared with the properties of the Milky Way dSph population. We also measure the average metallicity ([Fe/H]) from the co-added spectra of member stars for each M31 dSph and find that they are consistent with the trend of decreasing [Fe/H] with luminosity observed in the Milky Way population. We find that three of our studied M31 dSphs appear as significant outliers in terms of their central velocity dispersion, And XIX, XXI, and XXV, all of which have large half-light radii ({approx}> 700 pc) and low velocity dispersions ({sigma}{sub v} < 5 km s{sup -1}). In addition, And XXV has a mass-to-light ratio within its half-light radius of just [M/L]{sub half}=10.3{sup +7.0}{sub -6.7}, making it consistent with a simple stellar system with no appreciable dark matter component within its 1{sigma} uncertainties. We suggest that the structure of the dark matter halos of these outliers have been significantly altered by tides.
We introduce the Minimum Entropy Method, a simple statistical technique for constraining the Milky Way gravitational potential and simultaneously testing different gravity theories directly from 6D phase-space surveys and without adopting dynamical models. We demonstrate that orbital energy distributions that are separable (i.e., independent of position) have an associated entropy that increases under wrong assumptions about the gravitational potential and/or gravity theory. Of known objects, 'cold' tidal streams from low-mass progenitors follow orbital distributions that most nearly satisfy the condition of separability. Although the orbits of tidally stripped stars are perturbed by the progenitor's self-gravity, systematic variations of the energy distribution can be quantified in terms of the cross-entropy of individual tails, giving further sensitivity to theoretical biases in the host potential. The feasibility of using the Minimum Entropy Method to test a wide range of gravity theories is illustrated by evolving restricted N-body models in a Newtonian potential and examining the changes in entropy introduced by Dirac, MONDian, and f(R) gravity modifications.
We calculate the energy that baryons must inject into cold dark matter (CDM) halos in order to remove centrally divergent DM cusps on scales relevant to observations of dwarf spheroidal galaxies (dSphs). We estimate that the CDM halos often associated with the Milky Way's dSphs (M{sub vir}/M{sub Sun} {approx} 10{sup 9-10}) require {Delta}E {approx} 10{sup 53-55} erg in order to form cores on scales comparable to the luminous size of these galaxies. While supernova Type II (SNeII) explosions can in principle generate this energy, the actual contribution is limited by the low star formation efficiency implied by the abundance of luminous satellites. Considering that CDM's well-known 'core/cusp' and 'missing satellite' problems place opposing demands on star formation efficiencies, existing observational evidences for large cores in the most luminous dSphs require that CDM models invoke some combination of the following: (1) efficient (of the order of unity) coupling of SNeII energy into dark matter particles, (2) star formation histories peaking at unexpectedly high redshifts (z {approx}> 6), (3) a top-heavy stellar initial mass function, and/or (4) substantial satellite disruption or other stochastic effects to ease the substructure abundance constraints. Our models show that the tension between CDM problems on small scales would increase if cored DM profiles were to be found in fainter dwarfs.