Table of contents

We revisit a recently introduced power spectrum estimation technique based on Gibbs sampling, with the goal of applying it to the high-resolution WMAP data. In order to facilitate this analysis, a number of sophistications have to be introduced, each of which is discussed in detail. We have implemented two independent versions of the algorithm to cross-check the computer codes and to verify that a particular solution to any given problem does not affect the scientific results. We then apply these programs to simulated data with known properties at intermediate (N_side = 128) and high (N_side = 512) resolutions, to study effects such as incomplete sky coverage and white versus correlated noise. From these simulations we also establish the Markov chain correlation length as a function of signal-to-noise ratio and give a few comments on the properties of the correlation matrices involved. Parallelization issues are also discussed, with emphasis on real-world limitations imposed by current supercomputer facilities. The scientific results from the analysis of the first-year WMAP data are presented in a companion letter.

We present an empirical algorithm for obtaining photometric redshifts of quasars using five-band Sloan Digital Sky Survey (SDSS) photometry. Our algorithm generates an empirical model of the quasar color-redshift relation, compares the colors of a quasar candidate with this model, and calculates possible photometric redshifts. Using the 3814 quasars of the SDSS Early Data Release (EDR) Quasar Catalog to generate a median color-redshift relation as a function of redshift we find that, for this same sample, 83% of our predicted redshifts are correct to within |Δz| < 0.3. The algorithm also determines the probability that the redshift is correct, allowing for even more robust photometric redshift determination for smaller, more restricted samples. We apply this technique to a set of 8740 quasar candidates selected by the final version of the SDSS quasar-selection algorithm. The photometric redshifts assigned to nonquasars are restricted to a few well-defined values. In addition, 90% of the objects with spectra that have photometric redshifts between 0.8 and 2.2 are quasars with accurate (|Δz| < 0.3) photometric redshifts. Many of these quasars lie in a single region of color space; judicious application of color-cuts can effectively select quasars with accurate photometric redshifts from the SDSS database—without reference to the SDSS quasar selection algorithm. When the SDSS is complete, this technique will allow the determination of photometric redshifts for ~10⁶ faint SDSS quasar candidates, enabling advances in our knowledge of the quasar luminosity function, gravitational lensing of quasars, and correlations among quasars and between galaxies.

We present a catalog of 100,563 unresolved, UV-excess (UVX) quasar candidates to g = 21 from 2099 deg² of the Sloan Digital Sky Survey (SDSS) Data Release One (DR1) imaging data. Existing spectra of 22,737 sources reveals that 22,191 (97.6%) are quasars; accounting for the magnitude dependence of this efficiency, we estimate that 95,502 (95.0%) of the objects in the catalog are quasars. Such a high efficiency is unprecedented in broadband surveys of quasars. This "proof-of-concept" sample is designed to be maximally efficient, but still has 94.7% completeness to unresolved, g ≲ 19.5, UVX quasars from the DR1 quasar catalog. This efficient and complete selection is the result of our application of a probability density type analysis to training sets that describe the four-dimensional color distribution of stars and spectroscopically confirmed quasars in the SDSS. Specifically, we use a nonparametric Bayesian classification, based on kernel density estimation, to parameterize the color distribution of astronomical sources—allowing for fast and robust classification. We further supplement the catalog by providing photometric redshifts and matches to FIRST/VLA, ROSAT, and USNO-B sources. Future work needed to extend this selection algorithm to larger redshifts, fainter magnitudes, and resolved sources is discussed. Finally, we examine some science applications of the catalog, particularly a tentative quasar number counts distribution covering the largest range in magnitude (14.2 < g < 21.0) ever made within the framework of a single quasar survey.

We present the results of our spectroscopic follow-up program of the X-ray sources detected in the 942 ks exposure of the Chandra Deep Field-South (CDFS). A total of 288 possible counterparts were observed at the VLT with the FORS1/FORS2 spectrographs for 251 of the 349 Chandra sources (including three additional faint X-ray sources). Spectra and R-band images are shown for all the observed sources and R - K colors are given for most of them. Spectroscopic redshifts were obtained for 168 X-ray sources, of which 137 have both reliable optical identification and redshift estimate (including 16 external identifications). The R < 24 observed sample comprises 161 X-ray objects (181 optical counterparts), and 126 of them have unambiguous spectroscopic identification. There are two spikes in the redshift distribution, predominantly populated by type 2 active galactic nuclei (AGNs) but also type 1 AGN and X-ray normal galaxies: the one at z = 0.734 is fairly narrow (in redshift space) and comprises two clusters/groups of galaxies centered on extended X-ray sources, the second one at z = 0.674 is broader and should trace a sheetlike structure. The type 1 and type 2 populations are clearly separated in X-ray/optical diagnostics involving parameters sensitive to absorption/reddening: X-ray hardness ratio (HR), optical/near-IR color, soft X-ray flux, and optical brightness. Nevertheless, these two populations cover similar ranges of hard X-ray luminosity and absolute K magnitude, thus trace similar levels of gravitational accretion. Consequently, we introduce a new classification based solely on X-ray properties, HR, and X-ray luminosity, consistent with the unified AGN model. This X-ray classification uncovers a large fraction of optically obscured, X-ray-luminous AGNs missed by the classical optical classification. We find a similar number of X-ray type 1 and type 2 QSOs [L_X(0.5-10 keV) > 10⁴⁴ ergs s^-1] at z > 2 (13 sources with unambiguous spectroscopic identification); most X-ray type 1 QSOs are bright, R ≲ 24, whereas most X-ray type 2 QSOs have R ≳ 24, which may explain the difference with the CDFN results as few spectroscopic redshifts were obtained for R > 24 CDFN X-ray counterparts. There are X-ray type 1 QSOs down to z ~ 0.5, but a strong decrease at z < 2 in the fraction of luminous X-ray type 2 QSOs may indicate a cosmic evolution of the X-ray luminosity function of the type 2 population. An X-ray spectral analysis is required to confirm this possible evolution. The red color of most X-ray type 2 AGNs could be due to dust associated with the X-ray absorbing material and/or a substantial contribution of the host galaxy light. The latter can also be important for some redder X-ray type 1 AGNs. There is a large population of EROs (R - K > 5) as X-ray counterparts, and their fraction strongly increases with decreasing optical flux, up to 25% for the R ≥ 24 sample. They cover the whole range of X-ray hardness ratios, comprise objects of various classes (in particular a high fraction of z ≳ 1 X-ray absorbed AGNs, but also elliptical and starburst galaxies) and more than half of them should be fairly bright X-ray sources [L_X(0.5-10 keV) > 10⁴² ergs s^-1]. Photometric redshifts will be necessary to derive the properties and evolution of the X-ray selected EROs.

We present Hubble Space Telescope and Far Ultraviolet Spectroscopic Explorer observations of the intergalactic absorption toward QSO PG 1116+215 in the 900-3000 Å spectral region. We detect 25 Lyα absorbers along the sight line at rest-frame equivalent widths W_r > 30 mÅ, yielding (dN/dz)_Lyα = 166 ± 20 over an unblocked redshift path Δz_Lyα = 0.150. Two additional weak Lyα absorbers with W_r ≈ 15-20 mÅ are also present. Eight of the Lyα absorbers have large line widths (b ≳ 40 km s^-1). The detection of narrow O VI absorption in the broad Lyα absorber at z = 0.06244 supports the idea that the Lyα profile is thermally broadened in gas with T > 10⁵ K. We find dN/dz ≈ 53 for broad Lyα absorbers with W_r ≳ 30 mÅ and b ≥ 40 km s^-1. This number drops to dN/dz ≈ 40 if the line widths are restricted to 40 ≤ b ≤ 100 km s^-1. If the broad Lyα lines are dominated by thermal broadening in hot gas, the amount of baryonic material in these absorbers is enormous, perhaps as much as half the baryonic mass in the low-redshift universe. We detect O VI absorption in several of the Lyα clouds along the sight line. Two detections at z = 0.13847 and z = 0.16548 are confirmed by the presence of other ions at these redshifts (e.g., C II-III, N II-III, N V, O I, O VI, and Si II-IV), while the detections at z = 0.04125, 0.05895, 0.05928, and 0.06244 are based upon the Lyα and O VI detections alone. We find (dN/dz) ≈ 18 for O VI absorbers with W_r > 50 mÅ toward PG 1116+215. The information available for 13 low-redshift O VI absorbers with W_r ≥ 50 mÅ along six sight lines yields (dN/dz) ≈ 13 and Ω_b(O ) ≳ 0.0022 h, assuming a metallicity of 0.1 solar and an O VI ionization fraction f ≤ 0.2. The properties and prevalence of low-redshift O VI absorbers suggest that they too may be a substantial baryon repository, perhaps containing as much mass as stars and gas inside galaxies. The redshifts of the O VI absorbers are highly correlated with the redshifts of galaxies along the PG 1116+215 sight line, though few of the absorbers lie closer than ~600 h to any single galaxy. We analyze the kinematics and ionization of the metal-line systems along this sight line and discuss the implications of these observations for understanding the physical conditions and baryonic content of intergalactic matter in the low-redshift universe.

In this second paper dedicated to the study of satellite galaxies we present broadband photometry in the B, V, R, and I filters of 49 satellite galaxies orbiting giant isolated spiral galaxies. First analysis of the properties of these objects are presented by means of color-color and color-magnitude diagrams for early- and late-type satellites. Although we find differences in the slope of the V - I versus M_v color magnitude diagram, as a whole, the relations are in agreement with the trends known to date for galaxies of similar magnitudes in nearby clusters of galaxies. Comparison with the relations found for satellites in the Local Group allows us to sample better the bright end of the luminosity function of satellite galaxies and extends for brighter objects the validity of the color-magnitude relation found for dwarf galaxies in the Local Group. Most of the E/S0 galaxies in our sample show a negative color gradient with values similar to those known for early-type galaxies in other environments.

Seventeen globular clusters in the Large and Small Magellanic Clouds were observed in the mid-infrared wavelength region with the ISOCAM instrument on board the Infrared Space Observatory (ISO). Observations were made using the broadband filters LW1, LW2, and LW10, corresponding to the effective wavelengths of 4.5, 6.7, and 12 μm, respectively. We present the photometry of point sources in each cluster, as well as their precise positions and finding charts.

This is the first in a series of papers presenting a sensitive 20 cm VLA continuum survey of the Galactic center region using new and archival data based on multiconfiguration observations taken with relatively uniform uv coverage. The high dynamic range images cover the regions within -2^° < l < 5^° and -40' < b < 40' with a spatial resolution of ≈30'' and 10''. The wide field imaging technique is used to construct a low-resolution mosaic of 40 overlapping pointings. The mosaic image includes the Effelsburg observations filling the low spatial frequency uv data. We also present high-resolution images of 23 overlapping fields using DnC and CnB array configurations. These high-resolution images are sensitive to both compact and extended continuum features with a wide range of angular scales with rms noise of 0.2 mJy beam^-1 in the outer parts of the Galactic center region. The survey has resulted in a catalog of 345 discrete sources as well as 140 images revealing structural details of H II regions, supernova remnants, pulsar wind nebulae, and more than 80 linear filaments distributed toward the complex region of the Galactic center.

These observations show the evidence for an order-of-magnitude increase in the number of faint linear filaments with typical lengths of a few arcminutes. Many of the filaments show morphological characteristics similar to the Galactic center nonthermal radio filaments (NRFs). The linear filaments are not isolated but are generally clustered in star-forming regions where prominent NRFs had been detected previously. The extensions of many of these linear filaments appear to terminate at either a compact source or a resolved shell-like thermal source. A relationship between the filaments, the compact and extended thermal sources, as well as a lack of preferred orientation for many RFs should constrain models that are proposed to explain the origin of nonthermal radio filaments in the Galactic center.

We investigate in detail the white dwarf cooling sequence of the globular cluster Messier 4. In particular, we study the influence of various systematic uncertainties, both observational and theoretical, on the determination of the cluster age from the white dwarf cooling sequence. These include uncertainties in the distance to the cluster and the extinction along the line of sight, as well as the white dwarf mass, envelope, and core compositions and the white dwarf-main-sequence mass relation. We find that fitting to the full two-dimensional color-magnitude diagram offers a more robust method for age determination than the traditional method of fitting the one-dimensional white dwarf luminosity function. After taking into account the various uncertainties, we find a best-fit age of 12.1 Gyr, with a 95% lower limit of 10.3 Gyr. We also perform fits using two other sets of cooling models from the literature. The models of Chabrier et al. yield an encouragingly similar result, although the models of Salaris et al. do not provide as good a fit. Our results support our previous determination of a delay between the formation of the Galactic halo and the onset of star formation in the Galactic disk.

Using the Very Large Array (VLA) of the National Radio Astronomy Observatory in the A and B configurations, we have obtained simultaneous high-resolution observations of both the 22 GHz H₂O maser lines as well as the 22 GHz continuum for the H II regions W49N and Sagittarius B2. The angular resolution of both observations is ~ 01, which at the distance of W49N (11.4 kpc) and Sgr B2 (8.5 kpc) corresponds to a physical size of less than 1000 AU in both sources. The velocity coverage for W49N is ±435 km s^-1; positions for 316 H₂O maser components were obtained. The velocity coverage for Sgr B2 is -40 to +120 km s^-1; positions for 68 maser components were determined in Sgr B2 Main, 79 in Sgr B2 North, 14 in Sgr B2 Mid-North, and 17 in Sgr B2 South, for a total of 178 H₂O maser positions in Sgr B2.

The cross calibration scheme of Reid & Menten was used. Using this procedure, high dynamic range continuum images were obtained with accurate registration (σ ~ 001) of the continuum and maser positions. A detailed comparison between H II components and maser positions for both Sgr B2 and W49N is presented. In Sgr B2 Main, the H₂O masers are predominantly located at the outside edge of the high-frequency continuum, lending support to the proposal that entrainment by stellar winds may play an important role in H₂O maser emission.

We present OH maser observations at 1612, 1665, 1667, and 1720 MHz for 86 likely post-asymptotic giant branch (post-AGB) stars selected from a survey of 1612 MHz maser sources in the Galactic plane. The observations were taken with the Parkes Telescope and the Australia Telescope Compact Array between 2002 September and 2003 August. Post-AGB stars are the precursors to planetary nebulae, the diverse morphological range of which is unexplained. The maser observations were taken to investigate the onset and incidence of stellar wind asymmetries during the post-AGB phase. We redetected all 86 sources at 1612 MHz, while 27 sources were detected at 1665 MHz and 45 at 1667 MHz. One source was redetected at 1720 MHz. We present a classification scheme for the maser profiles and show that 25% of sources in our sample are likely to have asymmetric or bipolar outflows. From a comparison of the maser and far-infrared properties we find that there is a likely evolutionary trend in the shape of the maser profiles with some sources evolving from double-peaked to irregular to fully bipolar profiles. A subset of higher mass sources stand out as having almost no mainline emission and generally double-peaked profiles. At least 30% of sources in the sample have variable peak flux intensities at one or more of the frequencies observed. We also confirm a previously noted 1667 MHz overshoot phenomenon.

A new classification of neutron star cooling scenarios, involving either "minimal" cooling or "enhanced" cooling, is proposed. The minimal cooling scenario replaces and extends the so-called standard cooling scenario to include neutrino emission from the Cooper pair breaking and formation process. This emission dominates that due to the modified Urca process for temperatures close to the critical temperature for superfluid pairing. Minimal cooling is distinguished from enhanced cooling by the absence of neutrino emission from any direct Urca process, due either to nucleons or to exotica such as hyperons, Bose condensates, or deconfined quarks. Within the minimal cooling scenario, theoretical cooling models can be considered to be a four parameter family involving the equation of state (including various compositional possibilities) of dense matter, superfluid properties of dense matter, the composition of the neutron star envelope, and the mass of the neutron star. The consequences of minimal cooling are explored through extensive variations of these parameters. The results are compared with the inferred properties of thermally emitting neutron stars in order to ascertain if enhanced cooling occurs in any of them.

All stars for which thermal emissions have been clearly detected are at least marginally consistent with the lack of enhanced cooling, given the combined uncertainties in ages and temperatures or luminosities. The two pulsars PSR 0833-45 (Vela) and PSR 1706-44 would require enhanced cooling in case their ages and/or temperatures are on the lower side of their estimated values, whereas the four stars PSR 0656+14, PSR 1055-52, Geminga, and RX J0720.4-3125 may require some source of internal heating in case their age and/or luminosity are on the upper side of their estimated values. The new upper limits on the thermal luminosity of PSR J0205+6449 (in the supernova remnant 3C 58) and RX J0007.0+7302 (in CTA 1) are indicative of the occurrence of some enhanced neutrino emission beyond the minimal scenario.

Intermediate-mass stellar evolution tracks from the main sequence to the tip of the AGB for five initial masses (2-6 M_☉) and metallicity Z = 0.0001 have been computed. The detailed one-dimensional structure and evolution models include exponential overshooting, mass loss, and a detailed nucleosynthesis network with updated nuclear reaction rates. The network includes a two-particle heavy neutron sink for approximating neutron density in the He-shell flash. It is shown how the neutron-capture nucleosynthesis is important in models of very low metallicity for the formation of light neutron-heavy species, like sodium or the heavy neon and magnesium isotopes. The models have high resolution, as required for modeling the third dredge-up. All sequences have been followed from the pre-main sequence to the end of the AGB when all envelope mass is lost. Detailed structural and chemical model properties as well as yields are presented. This set of stellar models is based on standard assumptions and updated input physics. It can be confronted with observations of extremely metal-poor stars and may be used to assess the role of AGB stars in the origin of abundance anomalies of some globular cluster members of correspondingly low metallicity.

Convective core overshoot affects stellar evolution rates and the dating of stellar populations. In this paper, we provide a patch to the Y² isochrones with an improved treatment of convective core overshoot. The new tracks cover the transition mass range from no convective core to a fully developed convective core. We compare the improved isochrones to CMDs of a few well-observed open star clusters in the Galaxy and the Large Magellanic Cloud. Finally, we discuss future prospects for improving the treatment of core overshoot with the help of asteroseismology.

We calculate the efficiency of iron K line emission and iron K absorption in photoionized models using a new set of atomic data. These data are more comprehensive than those previously applied to the modeling of iron K lines from photoionized gases and allow us to systematically examine the behavior of the properties of line emission and absorption as a function of the ionization parameter, density, and column density of model constant density clouds. We show that, for example, the net fluorescence yield for the highly charged ions is sensitive to the level population distribution produced by photoionization, and these yields are generally smaller than those predicted assuming the population is according to statistical weight. We demonstrate that the effects of the many strongly damped resonances below the K ionization thresholds conspire to smear the edge, thereby potentially affecting the astrophysical interpretation of absorption features in the 7-9 keV energy band. We show that the centroid of the ensemble of Kα lines, the Kβ energy, and the ratio of the Kα₁ to Kα₂ components are all diagnostics of the ionization parameter of our model slabs.