Day 798

Wednesday.

1412.0655
Confirmation of a steep luminosity function for Lyman-alpha Emitters at z=5.7: a major component of reionization
Dressler, et al

Direct and robust measurement of the faint-end slope of LAE LF at z=5.7.  High-res spectroscopy to distinguish high-z LAEs from FG galaxies.  All but 2 of the 42 single-emission-line systems are fainter than F=2e-17 erg/s/cm^2, the faintest emission-lines observed for a z=5.7 sample with known completeness.  Find 13 LAEs for 29 FG galaxies.  Constrain the faint-end slope of LF to 1.95<-alpha<2.35 (1 sigma).  Show how this steep LF should provide, to the limit of the observations, more than 20% of the flux necessary to maintain ionization at z=5.7, with a factor -of-ten extrapolation in flux reaching more than 55%.  Suggest that this bodes well for a comparable contribution by similar, low-mass SF galaxies at higher-z - within the reionization epoch at z>7, only 250 Myr earlier - and that such systems provide a substantial, if not dominant, contribution to the late-stage reionization of the IGM.

1412.0657
Maximum speed of hypervelocity stars ejected from binaries
Tauris

The recent detection of HVSs as late-type B-stars and HVS candidate G/K dwarfs raises the important question of their origin.  In this Letter, investigate the maximum possible velocities of such HVSs if they are produced from binaries which are disrupted via an asymmetric SN explosion.  Find that HVSs up to ~770 km/s and ~1280 km/s are possible in the Galactic rest frame from this scenario for these two subclasses of HVSs, respectively.  Conclude that whereas a binary origin cannot easily explain all of the observed velocities of B-type HVSs (in agreement with their proposed central massive BH origin) it can indeed account for the far majority (if not all) of the recently detected G/K-dwaf HVS candidates.

1412.0661
Cosmological simulations of galaxy formation with cosmic rays
Salem, Bryan, Hummels

Investigate the dynamical impact of CRs in cosmo sims of galaxy formation using AMR of 1e12 Msun halo.  In agreement with previous work, a run with only the standard thermal energy feedback model results in a massive spheroid and unrealistically peaked rotation curves.  However, the addition of a simple two-fluid model for CRs drastically cages the morphology of the forming disk.  Include an isotropic diffuse term and a source term tied to SF dues to (unresolved) SN-driven shocks  Over a wide range of diffusion coefficients, the CRs generate thin, extended disks with a significantly more realistic (though still not flat) rotation curve.  Find that the diffusion of CRs is key to this process, as they escape dense SF clumps and drive outflows within the more diffuse ISM.

1412.0662
The physical nature of cosmic accretion of baryons and dark matter into haloes and their galaxies
Wetzel, Nagai

Cosmic accretion of both DM and baryons drives the formation and evolution of haloes and the galaxies within them.  Cosmic accretion for haloes typically is measured using some evolving viral relation, but a recent work suggests that most inferred halo growth at late cosmic time (z<2) is not physical but rather is the byproduct of a viral radius that evolves according to the BG cosmic density ("pseudo-evolution").  This raises the question: how much physical accretion of baryons do haloes experience to fuel SF and growth of the galaxy inside?  Using Omega25, a suite of cosmo sims that incorporate both DM and gas dynamics with differing treatments of gas cooling, SF and thermal feedback, explore systematically the physics that governs cosmic accretion into haloes and their galaxies.  Physically meaningful cosmic accretion of both DM and baryons occurs at z>1 across the halo mass range: M_200m=1e11-14 Msun.  However, DM, being dissipationless, is deposited (in a time-average sense) at >~R_200m in a shell-like matter, such that DM mass and density experience little-to-no physical growth at any radius within a halo at z<1.  By contrast, gas, being able to cool radiatively, experiences significant accretion at all radii, at a rate that roughly tracks the accretion rate at R_200m, at all redshifts.  Infalling gas starts to decouple from DM at ~1 R_200m and continues to accrete to smaller radii until the onset of strong angular-momentum support at ~0.1 R_200m.  Thus, while the growth of DM is subject to pseudo-evolution, the growth of baryons is not.  This difference provides insight into the tight relations between galaxies and their host haloes across cosmic time.

1412.0757
Cosmology constraints from the weak lensing peak counts and the power spectrum in CFHTLenS
Liu, Petri, Haiman, Hui, Kratochvil, May

Lensing peaks have been proposed as a useful statistic, containing cosmological info from non-Gaussianities that is inaccessible from traditional 2pt statistics such as the PS or 2PCF.  Examine constraints on cosmo parameters from WL peak counts, using publicly available data from CFHTLenS survey.  Utilize a new suite of ray-tracing N-body sims on a grid of 91 cosmo models, covering broad ranges of 3 parameters Omega_m, sigma_8, and w, and replicating the galaxy sky positions, z, and shape noise in the CHFTLenS observations.  Then build an emulator that interpolates the PS and the peak counts to an accuracy of <=5%, and compute the likelihood in the 3-d parameter space (Omega_m, sigma_8, w) from both observables.  Find that constraints from peak counts are comparable to those from the PS, and somewhat tighter when different smoothing scales are combined.  Neither observable can constrain w without external data.  When the PS and peak counts are combined, the area of the error "banana" in the (Omega_m, sigma_8) plane reduces by a factor of ~2, compared to using the PS alone.  For a flat Lambda CDM, combining both statistics, obtain the constraint sigma_8(Omega_m/0.27)^0.63 = 0.78(+0.07,-0.03).