We present new limits on the ejection of metal-rich old-population hypervelocity stars (HVSs) from the Galactic center (GC) as probed by the SEGUE-2 survey. Our limits are a factor of 3-10 more stringent than previously reported, depending on stellar type. Compared to the known population of B-star ejectees, there can be no more than 30 times more metal-rich old-population F/G stars ejected from the GC. Because B stars comprise a tiny fraction of a normal stellar population, this places significant limits on the combination of the GC mass function and the ejection mechanism for HVSs. In the presence of a normal GC mass function, our results require an ejection mechanism that is about 5.5 times more efficient at ejecting B stars compared to low-mass F/G stars.

The intergalactic medium (IGM) is the dominant reservoir of baryons at all cosmic epochs. In this paper, we investigate the evolution of the IGM from z = 2 -> 0 in (48h(-1) Mpc)(3), 110-million particle cosmological hydrodynamic simulations using three prescriptions for galactic outflows. We focus on the evolution of IGM physical properties, and how such properties are traced by Ly alpha absorption as detectable using Hubble's Cosmic Origins Spectrograph (COS). Our results broadly confirm the canonical picture that most Ly alpha absorbers arise from highly ionized gas tracing filamentary large-scale structure. Growth of structure causes gas to move from the diffuse photoionized IGM into other cosmic phases, namely stars, cold and hot gas within galaxy haloes, and the unbound and shock-heated warm-hot intergalactic medium (WHIM). By today, baryons are comparably divided between bound phases (35 per cent in our favoured outflow model), the diffuse IGM (41 per cent) and the WHIM (24 per cent). Here we (re) define the WHIM as gas with overdensities lower than that in haloes (rho/(rho) over bar less than or similar to 100 today) and temperatures T > 10(5) K, to more closely align it with the 'missing baryons' that are not easily detectable in emission or Ly alpha absorption. Strong galactic outflows can have a noticeable impact on the temperature of the IGM, though with our favoured momentum-driven wind scalings they do not. When we (mildly) tune our assumed photoionizing background to match the observed evolution of the Ly alpha mean flux decrement, we obtain line count evolution statistics that broadly agree with available (pre-COS) observations. We predict a column density distribution slope of f(N(HI)) alpha N(HI)(-1.70) for our favoured wind model, in agreement with recent observational estimates, and it becomes shallower with redshift. Winds have a mostly minimal impact, but they do result in a shallower column density slope and more strong lines. With improved statistics, the frequency of strong lines can be a valuable diagnostic of outflows, and the momentum-driven wind model matches existing data significantly better than the two alternatives we consider. The relationship between column density and physical density broadens mildly from z = 2 -> 0, and evolves as rho alpha N(HI)(0.74)10(-0.37z) for diffuse absorbers, consistent with previous studies. Linewidth distributions are quite sensitive to spectral resolution; COS should yield significantly broader lines than higher resolution data. Thermal contributions to linewidths are typically subdominant, so linewidths only loosely reflect the temperature of the absorbing gas. This will hamper attempts to quantify the WHIM using broad Ly alpha absorbers, though it may still be possible to do so statistically. Together, COS data and simulations such as these will provide key insights into the physical conditions of the dominant reservoir of baryons over the majority of cosmic time.

The Sloan Digital Sky Survey (SDSS) started a new phase in 2008 August, with new instrumentation and new surveys focused on Galactic structure and chemical evolution, measurements of the baryon oscillation feature in the clustering of galaxies and the quasar Ly alpha forest, and a radial velocity search for planets around similar to 8000 stars. This paper describes the first data release of SDSS-III (and the eighth counting from the beginning of the SDSS). The release includes five-band imaging of roughly 5200 deg(2) in the southern Galactic cap, bringing the total footprint of the SDSS imaging to 14,555 deg(2), or over a third of the Celestial Sphere. All the imaging data have been reprocessed with an improved sky-subtraction algorithm and a final, self-consistent photometric recalibration and flat-field determination. This release also includes all data from the second phase of the Sloan Extension for Galactic Understanding and Exploration (SEGUE-2), consisting of spectroscopy of approximately 118,000 stars at both high and low Galactic latitudes. All the more than half a million stellar spectra obtained with the SDSS spectrograph have been reprocessed through an improved stellar parameter pipeline, which has better determination of metallicity for high-metallicity stars.

We present new results on the Ly alpha emission-line kinematics of 18 z similar to 2-3 star-forming galaxies with multiple-peaked Lya profiles. With our large spectroscopic database of UV-selected star-forming galaxies at these redshifts, we have determined that similar to 30% of such objects with detectable Ly alpha emission display multiple-peaked emission profiles. These profiles provide additional constraints on the escape of Ly alpha photons due to the rich velocity structure in the emergent line. Despite recent advances in modeling the escape of Ly alpha from star-forming galaxies at high redshifts, comparisons between models and data are often missing crucial observational information. Using Keck II NIRSPEC spectra of H alpha (z similar to 2) and [O III]lambda 5007 (z similar to 3), we have measured accurate systemic redshifts, rest-frame optical nebular velocity dispersions, and emission-line fluxes for the objects in the sample. In addition, rest-frame UV luminosities and colors provide estimates of star formation rates and the degree of dust extinction. In concert with the profile sub-structure, these measurements provide critical constraints on the geometry and kinematics of interstellar gas in high-redshift galaxies. Accurate systemic redshifts allow us to translate the multiple-peaked Ly alpha profiles into velocity space, revealing that the majority (11/18) display double-peaked emission straddling the velocity-field zero point with stronger red-side emission. Interstellar absorption-line kinematics suggest the presence of large-scale outflows for the majority of objects in our sample, with an average measured interstellar absorption velocity offset of = -230 km s(-1). A comparison of the interstellar absorption kinematics for objects with multiple-and single-peaked Ly alpha profiles indicate that the multiple-peaked objects are characterized by significantly narrower absorption line widths. We compare our data with the predictions of simple models for outflowing and infalling gas distributions around high-redshift galaxies. While popular "shell" models provide a qualitative match with many of the observations of Ly alpha emission, we find that in detail there are important discrepancies between the models and data, as well as problems with applying the framework of an expanding thin shell of gas to explain high-redshift galaxy spectra. Our data highlight these inconsistencies, as well as illuminating critical elements for success in future models of outflow and infall in high-redshift galaxies.

We investigate the metallicity evolution and metal content of the intergalactic medium (IGM) and galactic halo gas from z = 2 to 0 using 110-million-particle cosmological hydrodynamic simulations. We focus on the detectability and physical properties of ultraviolet resonance metal-line absorbers observable with Hubble's Cosmic Origins Spectrograph (COS). We confirm that galactic superwind outflows are required to enrich the IGM to observed levels down to z = 0 using three wind prescriptions contrasted to a no-wind simulation. Our favoured momentum-conserved wind prescription deposits metals closer to galaxies owing to its moderate energy input, while the more energetic constant wind model enriches the warm-hot IGM 6.4 times more. Despite these significant differences, all wind models produce metal-line statistics within a factor of 2 of existing observations. This is because O VI, C IV, Si IV and Ne VIII absorbers primarily arise from T < 10(5) K, photoionized gas that is enriched to similar levels in the three feedback schemes. O VI absorbers trace the diffuse phase with rho/<(rho)over bar> less than or similar to 100, which is enriched to similar to 1/50 Z(circle dot) at z = 0, although the absorbers themselves usually exceed 0.3 Z(circle dot) and arise from inhomogeneously distributed, unmixed winds. Turbulent broadening is required to match the observed equivalent width and column density statistics for O VI. C IV and Si IV absorbers trace primarily T similar to 10(4) K gas inside haloes (rho/(rho) over bar greater than or similar to 100), although there appear to be too many C IV absorbers relative to observations. We predict the COS will observe a population of Ne VIII photoionized absorbers tracing T < 10(5) K, rho/<(rho)over bar> similar to 10 gas with equivalent widths of 10-20 m angstrom. Mg X and Si XII are rarely detected in COS signal-to-noise ratio 30 simulated sight-lines (dn/dz << 1), although simulated Si XII detections trace halo gas at T = 10(6)-10(7) K. In general, the IGM is enriched in an outside-in manner, where wind-blown metals released at higher redshift reach lower overdensities, resulting in higher ionization species tracing lower density, older metals. At z = 0, 90 per cent of baryons outside galaxies are enriched to (Z) over bar = 0.096 Z(circle dot), but 65 per cent of unbound baryons in the IGM have (Z) over bar = 0.018 Z(circle dot) and contain only 4 per cent of all metals, a large decline from 20 per cent at z = 2, because metals from early winds often re-accrete on to galaxies while later winds are less likely to escape their haloes. We emphasize that our results are sensitive to how metal mixing is treated in the simulations, and argue that the lack of mixing in our scheme may be the largest difference from other similar publications.

We examine the global H i properties of galaxies in quarter billion particle cosmological simulations using gadget-2, focusing on how galactic outflows impact H i content. We consider four outflow models, including a new one (ezw) motivated by recent interstellar medium simulations in which the wind speed and mass loading factor scale as expected for momentum-driven outflows for larger galaxies and energy-driven outflows for dwarfs (Sigma < 75 km s(-1)). To obtain predicted H i masses, we employ a simple but effective local correction for particle self-shielding and an observationally constrained transition from neutral to molecular hydrogen. Our ezw simulation produces an H i mass function whose faint-end slope of -1.3 agrees well with observations from the Arecibo Fast Legacy ALFA survey; other models agree less well. Satellite galaxies have a bimodal distribution in H i fraction versus halo mass, with smaller satellites and/or those in larger haloes more often being H i deficient. At a given stellar mass, H i content correlates with the star formation rate and inversely correlates with metallicity, as expected if driven by stochasticity in the accretion rate. To higher redshifts, massive H i galaxies disappear and the mass function steepens. The global cosmic H i density conspires to remain fairly constant from z similar to 5 -> 0, but the relative contribution from smaller galaxies increases with redshift.

We study the physical conditions of the circumgalactic medium (CGM) around z = 0.25 galaxies as traced by H I and metal line absorption, using cosmological hydrodynamic simulations that include galactic outflows. Using lines of sight targeted at impact parameters from 10 kpc to 1 Mpc around galaxies with halo masses from 10(11)-10(13) M-circle dot, we study the physical conditions and their variation with impact parameter b and line-of-sight velocity Delta v in the CGM as traced by H I, Mg II, Si IV, C IV, O VI and Ne VIII absorbers. All ions show a strong excess of absorption near galaxies compared to random lines of sight. The excess continues beyond 1 Mpc, reflecting the correlation of metal absorption with large-scale structure. Absorption is particularly enhanced within about Delta v < 300 km s(-1) and roughly 300 kpc of galaxies (with distances somewhat larger for the highest ion), approximately delineating the CGM; this range contains the majority of global metal absorption. Low ions like Mg II and Si IV predominantly arise in denser gas closer to galaxies and drop more rapidly with b, while high ions O VI and Ne VIII trace more diffusely distributed gas with a comparatively flat radial profile; C IV is intermediate. All ions predominantly trace T similar to 10(4-4.5) K photoionized gas at all b, but when hot CGM gas is present (mostly in larger haloes), we see strong collisionally ionized O VI and Ne VIII at b <= 100 kpc. Larger halo masses generally produce more absorption, though overall the trends are not as strong as that with impact parameter. These findings arise using our favoured outflow scalings as expected for momentum-driven winds; with no winds, the CGM gas remains mostly unenriched, while our outflow model with a constant velocity and mass loading factor produce hotter, more widely dispersed metals.

We present the first definitive measurement of the absolute magnitude of RR Lyrae c-type variable stars (RRc) determined purely from statistical parallax. We use a sample of 242 RRc variables selected from the All Sky Automated Survey for which high-quality light curves, photometry, and proper motions are available. We obtain high-resolution echelle spectra for these objects to determine radial velocities and abundances as part of the Carnegie RR Lyrae Survey. We find that M-V,M-RRc = 0.59 +/- 0.10 at a mean metallicity of [Fe/H] = -1.59. This is to be compared with previous estimates for RRab stars (M-V,M-RRab = 0.76 +/- 0.12) and the only direct measurement of an RRc absolutemagnitude (RZ Cephei, M-V,M-RRc = 0.27 +/- 0.17). We find the bulk velocity of the halo relative to the Sun to be (W-pi, W-theta, W-z) = (12.0,-209.9, 3.0) km s(-1) in the radial, rotational, and vertical directions with dispersions (sigma(W pi), sigma(W theta), sigma(Wz)) = (150.4, 106.1, 96.0) km s(-1). For the disk, we find (W-pi, W-theta, W-z) = (13.0,-42.0,-27.3) km s(-1) relative to the Sun with dispersions (sigma(W pi), sigma(W theta), sigma(Wz)) = (67.7, 59.2, 54.9) km s(-1). Finally, as a byproduct of our statistical framework, we are able to demonstrate that UCAC2 proper-motion errors are significantly overestimated as verified by UCAC4.

Using time-resolved, mid-infrared data from the Wide-field Infrared Survey Explorer (WISE) and geometric parallaxes from the Hubble Space Telescope for four Galactic RR Lyrae variables, we derive the following Population II period-luminosity (PL) relations for the WISE [W1], [W2], and [W3] bands at 3.4, 4.6, and 12 mu m, respectively: