Spin and orbital Hall effects for diffracting optical beams in gradient-index media

We examine the evolution of paraxial beams carrying intrinsic spin and orbital angular momenta (AM) in gradient-index media. A parabolic-type equation is derived which describes the beam diffraction in curvilinear coordinates accompanying the central ray. The center of gravity of the beam experiences transverse AM-dependent deflections -- the spin and orbital Hall effects. The spin Hall effect generates a transverse translation of the beam as a whole, in precise agreement with recent geometrical optics predictions. At the same time, the orbital Hall effect is significantly affected by the diffraction in the inhomogeneous medium and is accompanied by changes in the intrinsic orbital AM and deformations of the beam.Comment: 4 pages, 2 figures, to appear in Phys. Rev.

Escape of Ionizing Radiation from High Redshift Galaxies

We model the escape of ionizing radiation from high-redshift galaxies using high-resolution Adaptive Mesh Refinement N-body + hydrodynamics simulations. Our simulations include time-dependent and spatially-resolved transfer of ionizing radiation in three dimensions, including effects of dust absorption. For galaxies of total mass M > 10^11 Msun and star formation rates SFR ~ 1-5 Msun/yr, we find angular averaged escape fractions of 0.01-0.03 over the entire redshift interval studied (3<z<9). In addition, we find that the escape fraction varies by more than an order of magnitude along different lines-of-sight within individual galaxies, from the largest values near galactic poles to the smallest along the galactic disk. The escape fraction declines steeply at lower masses and SFR. We show that the low values of escape fractions are due to a small fraction of young stars located just outside the edge of HI disk. We compare our predicted escape fraction of ionizing photons with previous results, and find a general agreement with both other simulation results and available direct detection measurements at z ~ 3. We also compare our simulations with a novel method to estimate the escape fraction in galaxies from the observed distribution of neutral hydrogen column densities along the lines of sights to long duration gamma-ray bursts. Using this method we find escape fractions of the GRB host galaxies of 2-3%, consistent with our theoretical predictions. [abridged]Comment: submitted to Ap

Towards a complete accounting of energy and momentum from stellar feedback in galaxy formation simulations

Stellar feedback plays a key role in galaxy formation by regulating star formation, driving interstellar turbulence and generating galactic scale outflows. Although modern simulations of galaxy formation can resolve scales of 10-100 pc, star formation and feedback operate on smaller, "subgrid" scales. Great care should therefore be taken in order to properly account for the effect of feedback on global galaxy evolution. We investigate the momentum and energy budget of feedback during different stages of stellar evolution, and study its impact on the interstellar medium using simulations of local star forming regions and galactic disks at the resolution affordable in modern cosmological zoom-in simulations. In particular, we present a novel subgrid model for the momentum injection due to radiation pressure and stellar winds from massive stars during early, pre-supernova evolutionary stages of young star clusters. Early injection of momentum acts to clear out dense gas in star forming regions, hence limiting star formation. The reduced gas density mitigates radiative losses of thermal feedback energy from subsequent supernova explosions, leading to an increased overall efficiency of stellar feedback. The detailed impact of stellar feedback depends sensitively on the implementation and choice of parameters. Somewhat encouragingly, we find that implementations in which feedback is efficient lead to approximate self-regulation of global star formation efficiency. We compare simulation results using our feedback implementation to other phenomenological feedback methods, where thermal feedback energy is allowed to dissipate over time scales longer than the formal gas cooling time. We find that simulations with maximal momentum injection suppress star formation to a similar degree as is found in simulations adopting adiabatic thermal feedback.Comment: ApJ submitted. For a high-resolution version of the paper, see http://kicp.uchicago.edu/~agertz

Simulations of disk galaxies with cosmic ray driven galactic winds

We present results from high-resolution hydrodynamic simulations of isolated SMC- and Milky Way-sized galaxies that include a model for feedback from galactic cosmic rays (CRs). We find that CRs are naturally able to drive winds with mass loading factors of up to ~10 in dwarf systems. The scaling of the mass loading factor with circular velocity between the two simulated systems is consistent with \propto v_c^{1-2} required to reproduce the faint end of the galaxy luminosity function. In addition, simulations with CR feedback reproduce both the normalization and the slope of the observed trend of wind velocity with galaxy circular velocity. We find that winds in simulations with CR feedback exhibit qualitatively different properties compared to SN driven winds, where most of the acceleration happens violently in situ near star forming sites. In contrast, the CR-driven winds are accelerated gently by the large-scale pressure gradient established by CRs diffusing from the star-forming galaxy disk out into the halo. The CR-driven winds also exhibit much cooler temperatures and, in the SMC-sized system, warm (T~10^4 K) gas dominates the outflow. The prevalence of warm gas in such outflows may provide a clue as to the origin of ubiquitous warm gas in the gaseous halos of galaxies detected via absorption lines in quasar spectra.Comment: ApJL accepted. Replaced with accepted version. Minor revision in response to referee comment