Deconvolving the Wedge: Maximum-Likelihood Power Spectra via Spherical-Wave Visibility Modeling

Direct detection of the Epoch of Reionization (EoR) via the red-shifted 21-cm line will have unprecedented implications on the study of structure formation in the infant Universe. To fulfill this promise, current and future 21-cm experiments need to detect this weak EoR signal in the presence of foregrounds that are several orders of magnitude larger. This requires extreme noise control and improved wide-field high dynamic-range imaging techniques. We propose a new imaging method based on a maximum likelihood framework which solves for the interferometric equation directly on the sphere, or equivalently in the $uvw$-domain. The method uses the one-to-one relation between spherical waves and spherical harmonics (SpH). It consistently handles signals from the entire sky, and does not require a $w$-term correction. The spherical-harmonics coefficients represent the sky-brightness distribution and the visibilities in the $uvw$-domain, and provide a direct estimate of the spatial power spectrum. Using these spectrally-smooth SpH coefficients, bright foregrounds can be removed from the signal, including their side-lobe noise, which is one of the limiting factors in high dynamics range wide-field imaging. Chromatic effects causing the so-called "wedge" are effectively eliminated (i.e. deconvolved) in the cylindrical ($k_{\perp}, k_{\parallel}$) power spectrum, compared to a power spectrum computed directly from the images of the foreground visibilities where the wedge is clearly present. We illustrate our method using simulated LOFAR observations, finding an excellent reconstruction of the input EoR signal with minimal bias.Comment: 13 pages, 8 figures. Replaced to match accepted MNRAS version; few typos corrected & textual clarification added (no changes to results

The Sloan Lens ACS Survey. I. A Large Spectroscopically Selected Sample of Massive Early-Type Lens Galaxies

The Sloan Lens ACS (SLACS) Survey is an efficient Hubble Space Telescope Snapshot imaging survey for new galaxy-scale strong gravitational lenses. The targeted lens candidates are selected spectroscopically from within the Sloan Digital Sky Survey (SDSS) database of galaxy spectra for having multiple nebular emission lines at a redshift significantly higher than that of the SDSS target galaxy. In this paper, we present a catalog of 19 newly discovered gravitational lenses, along with 9 other observed candidate systems that are either possible lenses, non-lenses, or non-detections. The survey efficiency is thus >=68%. We also present Gemini and Magellan IFU data for 9 of the SLACS targets, which further support the lensing interpretation. A new method for the effective subtraction of foreground galaxy images to reveal faint background features is presented. We show that the SLACS lens galaxies have colors and ellipticities typical of the spectroscopic parent sample from which they are drawn (SDSS luminous red galaxies and quiescent main-sample galaxies), but are somewhat brighter and more centrally concentrated. Several explanations for the latter bias are suggested. The SLACS survey provides the first statistically significant and homogeneously selected sample of bright early-type lens galaxies, furnishing a powerful probe of the structure of early-type galaxies within the half-light radius. The high confirmation rate of lenses in the SLACS survey suggests consideration of spectroscopic lens discovery as an explicit science goal of future spectroscopic galaxy surveys (abridged).Comment: ApJ, in press. 20 pages, numerous figures, uses emulateapj. Replaced to include full-resolution spectro figures. Version with full-resolution imaging figures available at http://www.cfa.harvard.edu/~abolton/slacs1_hires.pdf (PDF) or at http://www.cfa.harvard.edu/~abolton/slacs1_hires.ps.gz (PS). Additional SLACS survey info at http://www.slacs.or

Bulk Flows and End of the Dark Ages with the SKA

The early Universe is a precious probe of the birth of primordial objects, first star formation events and consequent production of photons and heavy elements. Higher-order corrections to the cosmological linear perturbation theory predicts the formation of coherent supersonic gaseous streaming motions at decoupling time. These bulk flows impact the gas cooling process and determine a cascade effect on the whole baryon evolution. By analytical estimates and N-body hydrodynamical chemistry numerical simulations including atomic and molecular evolution, gas cooling, star formation, feedback effects and metal spreading for individual species from different stellar populations according to the proper yields and lifetimes, we discuss the role of these primordial bulk flows at the end of the dark ages and their detectable impacts during the first Gyr in view of the upcoming SKA mission. Early bulk flows can inhibit molecular gas cooling capabilities, suppressing star formation, metal spreading and the abundance of small primordial galaxies in the infant Universe. This can determine a delay in the re-ionization process and in the heating of neutral hydrogen making the observable HI signal during cosmic evolution patchier and noisier. The planned SKA mission will represent a major advance over existing instruments, since it will be able to probe the effects on HI 21cm at z ~ 6-20 and on molecular line emissions from first collapsing sites at z ~ 20-40. Therefore, it will be optimal to address the effects of primordial streaming motions on early baryon evolution and to give constraints on structure formation in the first Gyr

The impact of primordial supersonic flows on early structure formation, reionization and the lowest-mass dwarf galaxies

Tseliakhovich and Hirata recently discovered that higher order corrections to the cosmological linear-perturbation theory lead to supersonic coherent baryonic flows just after recombination (i.e. z ≈ 1020), with rms velocities of ˜30 km s-1 relative to the underlying dark matter distribution, on comoving scales of ≲3 Mpc h-1. To study the impact of these coherent flows, we performed high-resolution N-body plus smoothed particle hydrodynamic simulations in boxes of 5.0 and 0.7 Mpc h-1, for bulk-flow velocities of 0 (as reference), 30 and 60 km s-1. The simulations follow the evolution of cosmic structures by taking into account detailed, primordial, non-equilibrium gas chemistry (i.e. H, He, H2, HD, HeH, etc.), cooling, star formation and feedback effects from stellar evolution. We find that these bulk flows suppress star formation in low-mass haloes (i.e. Mvir≲ 108 M⊙ until z ˜ 13), lower the abundance of the first objects by ˜1-20 per cent and as a consequence delay cosmic star formation history by ˜2 × 107 yr. The gas fractions in individual objects can change by up to a factor of 2 at very early times. Coherent bulk flow therefore has implications for (i) the star formation in the lowest-mass haloes (e.g. dSphs); (ii) the start of reionization by suppressing it in some patches of the Universe; and (iii) the heating (i.e. spin temperature) of neutral hydrogen. We speculate that the patchy nature of reionization and heating on several Mpc scales could lead to enhanced differences in the H I spin temperature, giving rise to stronger variations in the H I brightness temperatures during the late dark ages

Finding Black Holes with Microlensing

The MACHO and OGLE collaborations have argued that the three longest duration bulge microlensing events are likely caused by nearby black holes, given the small velocities measured with microlensing parallax and nondetection of the lenses. However, these events may be due to lensing by more numerous lower mass stars at greater distances. We find a posteriori probabilities of 76%, 16%, and 4% that the three longest events are black holes, assuming a Salpeter initial mass function (IMF) and a 40 M cutoff for neutron star progenitors; the numbers depend strongly on the assumed mass function but favor a black hole for the longest event for most standard IMFs. The longest events (>600 days) have an a priori 26% probability of being black holes for a standard mass function. We propose a new technique for measuring the lens mass function using the mass distribution of long events measured with the Advanced Camera for Surveys on the Hubble Space Telescope, the Very Large Telescope Interferometer, the Space Interferometry Mission, or the Global Astrometric Interferometer for Astrophysics.Comment: final version with additional significant correction

Reionization and cosmic dawn astrophysics from the Square Kilometre Array:impact of observing strategies

Interferometry of the cosmic 21-cm signal is set to revolutionize our understanding of the epoch of reionization (EoR) and the cosmic dawn (CD). The culmination of ongoing efforts will be the upcoming Square Kilometre Array (SKA), which will provide tomography of the 21-cm signal from the first billion years of our Universe. Using a galaxy formation model informed by high-z luminosity functions, here we forecast the accuracy with which the first phase of SKA-low (SKA1-low) can constrain the properties of the unseen galaxies driving the astrophysics of the EoR and CD. We consider three observing strategies: (i) deep (1000 h on a single field); (ii) medium-deep (100 h on 10 independent fields); and (iii) shallow (10 h on 100 independent fields). Using the 21-cm power spectrum as a summary statistic, and conservatively only using the 21-cm signal above the foreground wedge, we predict that all three observing strategies should recover astrophysical parameters to a fractional precision of 3c0.1-10 per cent. The reionization history is recovered to an uncertainty of \u394z 7e 0.1 (1\u3c3 ) for the bulk of its duration. The medium-deep strategy, balancing thermal noise against cosmic variance, results in the tightest constraints, slightly outperforming the deep strategy. The shallow observational strategy performs the worst, with up to an 3c10-60 per cent increase in the recovered uncertainty. We note, however, that non-Gaussian summary statistics, tomography, as well as unbiased foreground removal would likely favour the deep strategy