Many properties of the Milky Way's (MW) dark matter halo, including its mass-assembly history, concentration, and subhalo population, remain poorly constrained. We explore the connection between these properties of the MW and its satellite galaxy population, especially the implication of the presence of the Magellanic Clouds for the properties of the MW halo. Using a suite of high-resolution N-body simulations of MW-mass halos with a fixed final M-vir similar to 10(12.1) M-circle dot, we find that the presence of Magellanic Cloud-like satellites strongly correlates with the assembly history, concentration, and subhalo population of the host halo, such that MW-mass systems with Magellanic Clouds have lower concentration, more rapid recent accretion, and more massive subhalos than typical halos of the same mass. Using a flexible semi-analytic galaxy formation model that is tuned to reproduce the stellar mass function of the classical dwarf galaxies of the MW with Markov-Chain Monte-Carlo, we show that adopting host halos with different mass-assembly histories and concentrations can lead to different best-fit models for galaxy-formation physics, especially for the strength of feedback. These biases arise because the presence of the Magellanic Clouds boosts the overall population of high-mass subhalos, thus requiring a different stellar-mass-tohalo-mass ratio to match the data. These biases also lead to significant differences in the mass-metallicity relation, the kinematics of low-mass satellites, the number counts of small satellites associated with the Magellanic Clouds, and the stellar mass of MW itself. Observations of these galaxy properties can thus provide useful constraints on the properties of the MW halo.

Dwarf galaxies are known to have remarkably low star formation efficiency due to strong feedback. Adopting the dwarf galaxies of the Milky Way (MW) as a laboratory, we explore a flexible semi-analytic galaxy formation model to understand how the feedback processes shape the satellite galaxies of the MW. Using Markov Chain Monte Carlo, we exhaustively search a large parameter space of the model and rigorously show that the general wisdom of strong outflows as the primary feedback mechanism cannot simultaneously explain the stellar mass function and the mass-metallicity relation of the MW satellites. An extended model that assumes that a fraction of baryons is prevented from collapsing into low-mass halos in the first place can be accurately constrained to simultaneously reproduce those observations. The inference suggests that two different physical mechanisms are needed to explain the two different data sets. In particular, moderate outflows with weak halo mass dependence are needed to explain the mass-metallicity relation, and prevention of baryons falling into shallow gravitational potentials of low-mass halos (e.g., "pre-heating") is needed to explain the low stellar mass fraction for a given subhalo mass.

Using a cosmological N-body simulation, we investigate the origin and distribution of stars in the intracluster light (ICL) of a Fornax-like cluster. In a dark-matter-only simulation, we identify a halo that, at z = 0, has M-200 similar or equal to 4.1 x 10(13)M(circle dot) and r(200) = 700 kpc, and replace infalling subhalos with models that include spheroid and disc components. As they fall into the cluster, the stars in some of these galaxies are stripped from their hosts, and form the ICL. We consider the separate contributions to the ICL from stars that originate in the haloes and the discs of the galaxies. We find that disc ICL stars are more centrally concentrated than halo ICL stars. The majority of the disc ICL stars are associated with one initially disc-dominated galaxy that falls to the centre of the cluster and is heavily disrupted, producing part of the cD galaxy. At radial distances greater than 200 kpc, well beyond the stellar envelope of the cD galaxy, stars formerly from the stellar haloes of galaxies dominate the ICL. Therefore at large distances, the ICL population is dominated by older stars.

The Galaxy Evolution Probe (GEP) is a concept for a mid and far-infrared space observatory designed to survey sky for star-forming galaxies from redshifts of z = 0 to beyond z = 4. Furthering our knowledge of galaxy formation requires uniform surveys of star-forming galaxies over a large range of redshifts and environments to accurately describe star formation, supermassive black hole growth, and interactions between these processes in galaxies. The GEP design includes a 2 m diameter SiC telescope actively cooled to 4 K and two instruments: (1) An imager to detect star-forming galaxies and measure their redshifts photometrically using emission features of polycyclic aromatic hydrocarbons. It will cover wavelengths from 10 to 400 mu m, with 23 spectral resolution R = 8 filter-defined bands from 10 to 95 mu m and five R = 3.5 bands from 95 to 400 mu m. (2) A 24 - 193 mu m, R = 200 dispersive spectrometer for redshift confirmation, identification of active galactic nuclei, and interstellar astrophysics using atomic fine-structure lines. The GEP will observe from a Sun-Earth L2 orbit, with a design lifetime of four years, devoted first to galaxy surveys with the imager and second to follow-up spectroscopy. The focal planes of the imager and the spectrometer will utilize KIDs, with the spectrometer comprised of four slit-coupled diffraction gratings feeding the KIDs. Cooling for the telescope, optics, and KID amplifiers will be provided by solar-powered cryocoolers, with a multi-stage adiabatic demagnetization refrigerator providing 100 mK cooling for the KIDs.

A key obstacle to developing a satisfying theory of galaxy evolution is the difficulty in extending analytic descriptions of early structure formation into full non-linearity, the regime in which galaxy growth occurs. Extant techniques, though powerful, are based on approximate numerical methods whose Monte Carlo-like nature hinders intuition building. Here, we develop a new solution to this problem and its empirical validation. We first derive closed-form analytic expectations for the evolution of fixed percentiles in the real-space cosmic density distribution, averaged over representative volumes observers can track cross sectionally. Using the Lagrangian forms of the fluid equations, we show that percentiles in delta - the density relative to the median - should grow as delta(t) proportional to delta(alpha)(0) t(beta), where alpha 2 and beta 2 for Newtonian gravity at epochs after the overdensities transitioned to non-linear growth. We then use 9.5 square degress of Carnegie-Spitzer-IMACS Redshift Survey data to map galaxy environmental densities over 0.2 < z < 1.5 (similar to 7 Gyr) and infer alpha = 1.98 +/- 0.04 and beta = 2.01 +/- 0.11 - consistent with our analytic prediction. These findings - enabled by swapping the Eulerian domain of most work on density growth for a Lagrangian approach to real-space volumetric averages - provide some of the strongest evidence that a lognormal distribution of early density fluctuations indeed decoupled from cosmic expansion to grow through gravitational accretion. They also comprise the first exact, analytic description of the non-linear growth of structure extensible to (arbitrarily) low redshift. We hope these results open the door to new modelling of, and insight-building into, galaxy growth and its diversity in cosmological contexts.

We present the first detections of the mean flux of the optical extragalactic background Light (EBL) at 3000, 5500, and 8000 Angstrom, derived from coordinated data sets taken at Las Campanas Observatory and with HST. In addition to detections in all three bands, we identify the minimum surface brightness contributed by resolved galaxies (23 < V < 28 AB mag) using a novel method of aperture photometry to which these data are uniquely suited. By comparing these results to the surface brightness from resolved galaxies measured using standard methods of galaxy photometry, we identify systematic errors in the results of faint galaxy photometry and place Limits on the EBL flux originating from undetected sources.

We present the first detection of the mean Aux of the optical extragalactic background light (EBL) at 3000, 5500, and 8000 Angstrom, derived from coordinated data sets from HST and Las Campanas Observatory. To isolate the extragalactic component, we have measured and subtracted the flux from foreground sources explicitly. In addition to detections in all three bands, we identify the minimum surface brightness contributed by resolved galaxies (23 < V < 28 AB mag) using a non-standard method of aperture photometry to which these data are uniquely suited. Individually resolved galaxies account for similar to 30% of the mean EEL coming from galaxies fainter than V = 23 AB mag. Taking into account the effective surface brightness detection limits of the deepest galaxy counts, and the results of LSB surveys at low redshift, the EEL we detect can be explained by galaxy populations already cataloged.

We present optical (B and R) and infrared (K-s) images and photometry for a sample of 49 extremely late-type, edge-on disk galaxies selected from the Flat Galaxy Catalog of Karenchentsev et al. Our sample was selected to include galaxies with particularly large axial ratios, increasing the likelihood that the galaxies in the sample are truly edge-on. We have also concentrated the sample on galaxies with low apparent surface brightness in order to increase the representation of intrinsically low surface brightness galaxies. Finally, the sample was chosen to have no apparent bulges or optical warps so that the galaxies represent undisturbed, "pure disk" systems. The resulting sample forms the basis for a much larger spectroscopic study designed to place constraints on the physical quantities and processes that shape disk galaxies. The imaging data presented in this paper have been painstakingly reduced and calibrated to allow accurate surface photometry of features as faint as 30 mag arcsec(-2) in B and 29 mag arcsec(-2) in R on scales larger than 10". Because of limitations in sky subtraction and flat-fielding, the infrared data can reach only to 22.5 mag arcsec(-2) in K-s, on comparable scales. As part of this work, we have developed a new method for quantifying the reliability of surface photometry, which provides useful diagnostics for the presence of scattered light, optical emission from infrared cirrus, and other sources of nonuniform sky backgrounds.

We are developing a method for measuring the detailed chemical composition and evolutionary history of extragalactic star clusters from high resolution spectra of their integrated light as one would from spectra of individual stars. In this paper, we show high signal-to-noise ratio echelle spectra of the integrated light of two Galactic globular clusters and equivalent-quality spectra of individual stars in those clusters in order to briefly illustrate some subtleties of the analysis method.

We present optical echelle spectra of four gamma-ray burst (GRB) afterglows ( GRB 050730, GRB 050820, GRB 051111, and GRB 060418) discovered during the first 1.5 yr of operation of the Swift satellite and localized by either the Swift telescope or follow-up ground-based imaging. We analyze the spectra to derive accurate column density measurements for the transitions arising in the interstellar medium( ISM) of the GRB host galaxies. These measurements can be used to constrain the physical properties of the ISM, including the metallicity, dust-to-gas ratio, ionization state, and chemical abundances of the gas. We also present measurements of the strong Mg II systems in the GRB afterglow spectra. With the publication of this paper, we provide the first data release of echelle afterglow spectra by the GRAASP collaboration to the general community.