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Recent observations have constrained the galaxy UV luminosity function up to z~10. However, these observations alone allow for a wide range of reionization scenarios due to uncertainties in the abundance of faint galaxies and the escape fraction of ionizing photons. We show that requiring continuity with post-reionization (z<6) measurements, where the Lya forest provides a complete probe of the cosmological emissivity of ionizing photons, significantly reduces the permitted parameter space. Models that are simultaneously consistent with the measured UV luminosity function, the Thomson optical depth to the CMB, and the Lya forest data require either: 1) extrapolation of the galaxy luminosity function down to very faint UV magnitudes M_lim ~ -10, corresponding roughly to the UV background suppression scale; 2) an increase of f_esc by a factor > ~10 from z=4 (where the best fit is 4%) to z=9; or 3) more likely, a hybrid solution in which undetected galaxies contribute significantly and f_esc increases more modestly. Models in which star formation is strongly suppressed in low-mass, reionization-epoch haloes of mass up to ~10^10 M_sun (e.g., owing to a metallicity dependence) are only allowed for extreme assumptions for the evolution of f_esc. However, variants of such models in which the suppression mass is reduced (e.g., assuming an earlier or higher metallicity floor) are in better agreement with the data. Concordance scenarios satisfying the available data predict a consistent redshift of 50% ionized fraction z_reion(50%) ~ 10. On the other hand, the duration of reionization is sensitive to the relative contribution of bright versus faint galaxies, with scenarios dominated by faint galaxies predicting a more extended reionization event. Scenarios relying too heavily on high-z dwarfs are disfavored by kinetic Sunyaev-Zeldovich measurements, which prefer a short reionization history., Comment: replaced with version accepted for publication in MNRAS

We describe cosmological galaxy formation simulations with the adaptive mesh refinement code Enzo that incorporate a star formation prescription regulated by the local abundance of molecular hydrogen. We show that this H2-regulated prescription leads to a suppression of star formation in low mass halos (M_h < ~10^10 M_sun) at z>4, alleviating some of the dwarf galaxy problems faced by theoretical galaxy formation models. H2 regulation modifies the efficiency of star formation of cold gas directly, rather than indirectly reducing the cold gas content with "supernova feedback". We determine the local H2 abundance in our most refined grid cells (76 proper parsec in size at z=4) by applying the model of Krumholz, McKee, & Tumlinson, which is based on idealized 1D radiative transfer calculations of H2 formation-dissociation balance in ~100 pc atomic--molecular complexes. Our H2-regulated simulations are able to reproduce the empirical (albeit lower z) Kennicutt-Schmidt relation, including the low Sigma_gas cutoff due to the transition from atomic to molecular phase and the metallicity dependence thereof, without the use of an explicit density threshold in our star formation prescription. We compare the evolution of the luminosity function, stellar mass density, and star formation rate density from our simulations to recent observational determinations of the same at z=4-8 and find reasonable agreement between the two., Comment: replaced with version published in ApJ

The velocity distribution function of dark matter particles is expected to show significant departures from a Maxwell-Boltzmann distribution. This can have profound effects on the predicted dark matter - nucleon scattering rates in direct detection experiments, especially for dark matter models in which the scattering is sensitive to the high velocity tail of the distribution, such as inelastic dark matter (iDM) or light (few GeV) dark matter (LDM), and for experiments that require high energy recoil events, such as many directionally sensitive experiments. Here we determine the velocity distribution functions from two of the highest resolution numerical simulations of Galactic dark matter structure (Via Lactea II and GHALO), and study the effects for these scenarios. For directional detection, we find that the observed departures from Maxwell-Boltzmann increase the contrast of the signal and change the typical direction of incoming DM particles. For iDM, the expected signals at direct detection experiments are changed dramatically: the annual modulation can be enhanced by more than a factor two, and the relative rates of DAMA compared to CDMS can change by an order of magnitude, while those compared to CRESST can change by a factor of two. The spectrum of the signal can also change dramatically, with many features arising due to substructure. For LDM the spectral effects are smaller, but changes do arise that improve the compatibility with existing experiments. We find that the phase of the modulation can depend upon energy, which would help discriminate against background should it be found., Comment: 34 pages, 16 figures, submitted to JCAP. Tables of g(v_min), the integral of f(v)/v from v_min to infinity, derived from our simulations, are available for download at http://astro.berkeley.edu/~mqk/dmdd/

The unambiguous detection of Galactic dark matter annihilation would unravel one of the most outstanding puzzles in particle physics and cosmology. Recent observations have motivated models in which the annihilation rate is boosted by the Sommerfeld effect, a non-perturbative enhancement arising from a long range attractive force. Here we apply the Sommerfeld correction to Via Lactea II, a high resolution N-body simulation of a Milky-Way-size galaxy, to investigate the phase-space structure of the Galactic halo. We show that the annihilation luminosity from kinematically cold substructure can be enhanced by orders of magnitude relative to previous calculations, leading to the prediction of gamma-ray fluxes from up to hundreds of dark clumps that should be detectable by the Fermi satellite., Comment: 23 pages, 9 figures (includes Supporting Online Material), accepted for publication in Science, v2: added reference, fixed typos

In order to attract and retain excellent researchers and diverse individuals in astrophysics, we recommend action be taken in several key areas impacting young scientists: (1) Maintain balance between large collaborations and individual projects through distribution of funding; encourage public releases of observational and simulation data for use by a broader community. (2) Improve the involvement of women, particularly at leading institutions. (3) Address the critical shortage of child care options and design reasonable profession-wide parental leave policies. (4) Streamline the job application and hiring process. We summarize our reasons for bringing these areas to the attention of the committee, and we suggest several practical steps that can be taken to address them., Comment: 10 pages, no figures, State of Profession paper for the Decadal Survey

Our recently completed one billion particle Via Lactea II simulation of a Milky Way-sized dark matter halo resolves over 50,000 gravitationally bound clumps orbiting today within the virialized region of the main host. About 2,300 of these subhalos have one or more "progenitors" above 1e6 Msun at redshift 11, i.e. massive enough for their gas to have cooled via excitation of H2 and fragmented prior to the epoch of cosmic reionization. We count 4,500 such progenitors: if these were able to convert a fraction of their gas content into very metal-poor stars with a Salpeter initial mass function (IMF), they would be shining today with a visual magnitude M_V=6.7 per solar mass in stars. Assuming a universal baryon fraction, we show that mean star formation efficiencies as low as 0.1% in progenitors below 1e8 Msun would overproduce the abundance of the faint Galatic dwarf spheroidals observed by the Sloan Digital Sky Survey. Star formation at first light must have occurred either with an IMF lacking stars below 0.9 Msun, or was intrinsically very inefficient in small dark matter halos. If the latter, our results may be viewed as another hint of a minimum scale in galaxy formation., Comment: 5 pages, 4 figures, ApJL, in press

It is a clear unique prediction of the cold dark matter paradigm of cosmological structure formation that galaxies form hierarchically and are embedded in massive, extended dark halos teeming with self-bound substructure or "subhalos". The amount and spatial distribution of subhalos around their host provide unique information and clues on the galaxy assembly process and the nature of the dark matter. Here we present results from the Via Lactea INCITE simulation, a one billion particle, one million cpu-hour simulation of the formation and evolution of a Galactic dark matter halo and its substructure population., Comment: 10 pages, Proceedings of the SciDAC 2008 conference, (Seattle, July 13-17, 2008)

In cold dark matter cosmological models, structures form and grow by merging of smaller units. Numerical simulations have shown that such merging is incomplete; the inner cores of halos survive and orbit as "subhalos" within their hosts. Here we report a simulation that resolves such substructure even in the very inner regions of the Galactic halo. We find hundreds of very concentrated dark matter clumps surviving near the solar circle, as well as numerous cold streams. The simulation reveals the fractal nature of dark matter clustering: Isolated halos and subhalos contain the same relative amount of substructure and both have cuspy inner density profiles. The inner mass and phase-space densities of subhalos match those of recently discovered faint, dark matter-dominated dwarf satellite galaxies and the overall amount of substructure can explain the anomalous flux ratios seen in strong gravitational lenses. Subhalos boost gamma-ray production from dark matter annihilation, by factors of 4-15, relative to smooth galactic models. Local cosmic ray production is also enhanced, typically by a factor 1.4, but by more than a factor of ten in one percent of locations lying sufficiently close to a large subhalo. These estimates assume that gravitational effects of baryons on dark matter substructure are small., Comment: 14 pages, 5 figures, to appear in Nature, includes supplementary information. Full version of Figure 1 available at http://www.ucolick.org/~diemand/vl2/fig1.png

We show that most particle and subhalo orbits in simulated cosmological cold dark matter halos are surprisingly regular and periodic: The phase space structure of the outer halo regions shares some of the properties of the classical self-similar secondary infall model. Some of the outer branches are clearly visible in the radial velocity - radius plane at certain epochs. However, they are severely broadened in realistic, triaxial halos with non-radial, clumpy, mass accretion. This prevents the formation of high density caustics: Even in the best cases there are only broad, very small (<10 percent) enhancements in the spherical density profile. Larger fluctuations in rho(r) caused by massive satellites are common. Infall caustics are therefore too weak to affect lensing or dark matter annihilation experiments. Their detection is extremely challenging, as it requires a large number of accurate tracer positions and radial velocities in the outer halo. The stellar halo of the Milky Way is probably the only target where this could become feasible in the future., Comment: 5 pages, 3 figures, ApJL accepted. MPEG animations of Figures 1 and 2 are available at http://www.ucolick.org/~diemand/vl/movies.html#infall

We present a study of the shapes, orientations, and alignments of Galactic dark matter subhalos in the ``Via Lactea'' simulation of a Milky Way-size LCDM host halo. Whereas isolated dark matter halos tend to be prolate, subhalos are predominantly triaxial. Overall subhalos are more spherical than the host halo, with minor to major and intermediate to major axis ratios of 0.68 and 0.83, respectively. Like isolated halos, subhalos tend to be less spherical in their central regions. The principal axis ratios are independent of subhalo mass, when the shapes are measured within a physical scale like r_Vmax, the radius of the peak of the circular velocity curve. Subhalos tend to be slightly more spherical closer to the host halo center. The spatial distribution of the subhalos traces the prolate shape of the host halo when they are selected by the largest V_max they ever had, i.e. before they experienced strong tidal mass loss. The subhalos' orientation is not random: the major axis tends to align with the direction towards the host halo center. This alignment disappears for halos beyond 3 r_200 and is more pronounced when the shapes are measured in the outer regions of the subhalos. The radial alignment is preserved during a subhalo's orbit and they become elongated during pericenter passage, indicating that the alignment is likely caused by the host halo's tidal forces. These tidal interactions with the host halo act to make subhalos rounder over time., Comment: 12 pages, 11 figures, submitted to ApJ, v2: corrected typo in abstract ("[...] subhalos tend be less spherical in their central regions."), added a few references

We describe a new concept for a MEMS-based active spatial filter for astronomical spectroscopy. The goal of this device is to allow the use of a diffraction-limited spectrometer on a seeing limited observation at improved throughput over a comparable seeing-limited spectrometer, thus reducing the size and cost of the spectrometer by a factor proportional to r0/D (For the case of a 10 meter telescope this size reduction will be approximately a factor of 25 to 50). We use a fiber-based integral field unit (IFU) that incorporates an active MEMS mirror array to feed an astronomical spectrograph. A fast camera is used in parallel to sense speckle images at a spatial resolution of lambda/D and at a temporal frequency greater than that of atmospheric fluctuations. The MEMS mirror-array is used as an active shutter to feed speckle images above a preset intensity threshold to the spectrometer, thereby increasing the signal-to-noise ratio (SNR) of the spectrogram. Preliminary calculations suggests an SNR improvement of a factor of about 1.4. Computer simulations have shown an SNR improvement of 1.1, but have not yet fully explored the parameter space., Comment: 11 pages, 5 figures, presented at SPIE Astronomical Telescopes and Instrumentation, 24 - 31 May 2006, Orlando, Florida USA

The thermonuclear runaway that culminates in the explosion of a Chandrasekhar mass white dwarf as a Type Ia supernova begins centuries before the star actually explodes. Here, using a 3D anelastic code, we examine numerically the convective flow during the last minute of that runaway, a time that is crucial in determining just where and how often the supernova ignites. We find that the overall convective flow is dipolar, with the higher temperature fluctuations in an outbound flow preferentially on one side of the star. Taken at face value, this suggests an asymmetric ignition that may well persist in the geometry of the final explosion. However, we also find that even a moderate amount of rotation tends to fracture this dipole flow, making ignition over a broader region more likely. Though our calculations lack the resolution to study the flow at astrophysically relevant Rayleigh numbers, we also speculate that the observed dipolar flow will become less organized as the viscosity becomes very small. Motion within the dipole flow shows evidence of turbulence, suggesting that only geometrically large fluctuations (~1 km) will persist to ignite the runaway. We also examine the probability density function for the temperature fluctuations, finding evidence for a Gaussian, rather than exponential distribution, which suggests that ignition sparks may be strongly spatially clustered., Comment: 16 pages, 9 figures, submitted to ApJ. A high resolution version of this paper, as well as movies, can be found at http://www.ucolick.org/~mqk/Carbon

We investigate the environmental impact of the first active galactic nuclei that may have formed ~150 Myr after the big bang in low-mass ~10^6 Msun minihaloes. Using Enzo, an adaptive-mesh refinement cosmological hydrodynamics code, we carry out three-dimensional simulations of the radiative feedback from `miniquasars' powered by intermediate-mass black holes. We follow the non-equilibrium multispecies chemistry of primordial gas in the presence of a point source of X-ray radiation, which starts shining in a rare high-sigma peak at z=21 and emits a power-law spectrum in the 0.2-10 keV range. We find that, after one Salpeter time-scale, the miniquasar has heated up the simulation box to a volume-averaged temperature of 2800 K. The mean electron and H2 fractions are now 0.03 and 4e-5: the latter is 20 times larger than the primordial value, and will delay the buildup of a uniform UV photodissociating background. The net effect of the X-rays is to reduce gas clumping in the IGM by as much as a factor of 3. While the suppression of baryonic infall lowers the gas mass fraction at overdensities delta in the range 20-2000, enhanced molecular cooling increases the amount of dense material at delta>2000. In many haloes within the proximity of our miniquasar the H2-boosting effect of X-rays is too weak to overcome heating, and the cold and dense gas mass actually decreases. We find little evidence for an entropy floor in gas at intermediate densities preventing gas contraction and H2 formation. Overall, the radiative feedback from X-rays enhances gas cooling in lower-sigma peaks that are far away from the initial site of star formation, thus decreasing the clustering bias of the early pregalactic population, but does not appear to dramatically reverse or promote the collapse of pregalactic clouds as a whole. (abridged), Comment: 15 pages, 13 figures, accepted for publication in MNRAS. Minor modifications in response to the referee's comments. A high resolution version of this paper, as well as movies, can be found at http://www.ucolick.org/~mqk/miniqso

We investigate the effect of dark energy on the density profiles of dark matter haloes with a suite of cosmological N-body simulations and use our results to test analytic models. We consider constant equation of state models, and allow both w>-1 and w<-1. Using five simulations with w ranging from -1.5 to -0.5, and with more than ~1600 well-resolved haloes each, we show that the halo concentration model of Bullock et al. (2001) accurately predicts the median concentrations of haloes over the range of w, halo masses, and redshifts that we are capable of probing. We find that the Bullock et al. (2001) model works best when halo masses and concentrations are defined relative to an outer radius set by a cosmology-dependent virial overdensity. For a fixed power spectrum normalization and fixed-mass haloes, larger values of w lead to higher concentrations and higher halo central densities, both because collapse occurs earlier and because haloes have higher virial densities. While precise predictions of halo densities are quite sensitive to various uncertainties, we make broad comparisons to galaxy rotation curve data. At fixed power spectrum normalization (fixed sigma_8), w>-1 quintessence models seem to exacerbate the central density problem relative to the standard w=-1 model. Meanwhile w<-1 models help to reduce the apparent discrepancy. We confirm that the Jenkins et al. (2001) halo mass function provides an excellent approximation to the abundance of haloes in our simulations and extend its region of validity to include models with w<-1., Comment: 16 p., 11 fig.; replaced with revised version, accepted for publication in MNRAS; corrected error (w=-1.5 halo mass function now agrees with Jenkins et al. fitting formula), rewrote several sections, added references

We study lens statistics in flat, low-density universes with different equations of state $w=p_Q/\rho_Q$ for the dark energy component. Dark energy modifies the distance-redshift relation and the mass function of dark matter halos leading to changes in the lensing optical depth as a function of image separation. Those effects must, however, be distinguished from effects associated with the structure of dark matter halos. Baryonic cooling causes galaxy-mass halos to have different central density profiles than group- and cluster-mass halos, which causes the distribution of normal arcsecond-scale lenses to differ from the distribution of ``wide-separation'' ($\Delta\theta \gtrsim 4\arcsec$) lenses. Fortunately, the various parameters related to cosmology and halo structure have very different effects on the overall image separation distribution: (1) the abundance of wide-separation lenses is exremely sensitive (by orders of magnitude) to the distribution of ``concentration'' parameters for massive halos modeled with the Navarro-Frenk-White profile; (2) the transition between normal and wide-separation lenses depends mainly on the mass scale where baryonic cooling ceases to be efficient; and (3) dark energy has effects at all image separation scales. While current lens samples cannot usefully constrain all of the parameters, ongoing and future imaging surveys should discover hundreds or thousands of lenses and make it possible to disentangle the various effects and constrain all of the parameters simultaneously. (abridged), Comment: 15 pages, 11 figures, accepted for publication in ApJ

The observable properties of a Type Ia supernova are sensitive to how the nuclear runaway ignites in a Chandrasekhar mass white dwarf - at a single point at its center, off-center, or at multiple points and times. We present a simple analytic model for the runaway based upon a combination of stellar mixing-length theory and recent advances in understanding Rayleigh-Benard convection. The convective flow just prior to runaway is likely to have a strong dipolar component, though higher multipoles may contribute appreciably at the very high Rayleigh number (10$^{25}$) appropriate to the white dwarf core. A likely outcome is multi-point ignition with an exponentially increasing number of ignition points during the few tenths of a second that it takes the runaway to develop. The first sparks ignite approximately 150 - 200 km off center, followed by ignition at smaller radii. Rotation may be important to break the dipole asymmetry of the ignition and give a healthy explosion., Comment: 14 pages, 0 figures, submitted to ApJ, corrected typo in first author's name

Signals for processes induced by QCD instantons are searched for in HERA data on the hadronic final state in deep-inelastic scattering. The maximally allowed fraction of instanton induced events is found at 95% confidence level to be on the percent level in the kinematic domain 0.0001

The sensitivity of existing HERA data on the hadronic final state in deep-inelastic scattering (DIS) to processes induced by QCD instantons is systematically investigated. The maximally allowed fraction of such processes in DIS is found to be on the percent level in the kinematic domain 0.0001 < x-Bjorken < 0.01 and 5 < Q squared < 100 GeV squared. The best limits are obtained from the multiplicity distribution., Comment: 5 pages, latex, entire paper w. tex, style and figures

Measurements of structure functions and of the hadronic final state in deep inelastic scattering at HERA are presented. The results comprise the extraction of parton densities, measurements of the strong coupling, and the search for novel QCD effects in the new kinematic regime at HERA., Comment: 19 pages, latex, master file is protvino.tex, 21 figs. as ps/eps

In order to probe the dynamics of parton evolution in deep inelastic scattering at small x, high-p_T particles produced centrally in pseudorapidity are studied. In the BFKL mechanism gluon radiation is expected to be more abundant than for DGLAP evolution with strong ordering of the gluon transverse momenta, leading to harder p_T spectra. The proposed measurements require charged particle tracking capability as much forward as possible in the HERA laboratory frame, for example with a Very Forward Silicon Tracker, and high luminosity for detailed studies., Comment: 5 pages, latex (2 .tex file), 3 figures (5 .eps files)

Hadron transverse momentum spectra are proposed as a means to probe the underlying partonic dynamics in deep inelastic scattering. The BFKL evolution equation, postulated for small Bjorken-$x$, leads to an enhanced parton emission over the conventional DGLAP ansatz, and can thus be tested., Comment: 7 pages, latex, 13 figures as eps files, latex+eps uuencoded

Results on hadronic final states in deeply inelastic scattering are reviewed. They comprise jet production and its interpretation in perturbative QCD, signatures to distinguish conventional QCD dynamics from possible new features of QCD at small $x$, and measurements of inclusive charged particle production. Theoretical developments such as color dipole emission and instanton induced final states are reported on., Comment: 8 pages,latex,epsfig,qcdparis.sty, 12 figues+kuhlen.sty uuencoded