Table of contents

We present a survey of the extinction properties of 10 lensing galaxies, in the redshift range z = 0.04-1.01, using multiply lensed quasars imaged with the ESO VLT in the optical and near-infrared. The multiple images act as "standard light sources" shining through different parts of the lensing galaxy, allowing for extinction studies by comparison of pairs of images. We explore the effects of systematics in the extinction curve analysis, including extinction along both lines of sight and microlensing, using theoretical analysis and simulations. In the sample, we see variation in both the amount and type of extinction. Of the 10 systems, seven are consistent with extinction along at least one line of sight. The mean differential extinction for the most extinguished image pair for each lens is (V) = 0.56 ± 0.04, using Galactic extinction law parameterization. The corresponding mean _V = 2.8 ± 0.4 is consistent with that of the Milky Way at R_V = 3.1, where R_V = A(V)/E(B - V). We do not see any strong evidence for evolution of extinction properties with redshift. Of the 10 systems, B1152+199 shows the strongest extinction signal of A(V) = 2.43 ± 0.09 and is consistent with a Galactic extinction law with R_V = 2.1 ± 0.1. Given the similar redshift distribution of SN Ia hosts and lensing galaxies, a large space-based study of multiply imaged quasars would be a useful complement to future dark energy SN Ia surveys, providing independent constraints on the statistical extinction properties of galaxies up to z ~ 1.

We present an analysis of the mid-infrared (MIR) and optical properties of type 1 (broad-line) quasars detected by the Spitzer Space Telescope. The MIR color-redshift relation is characterized to z ~ 3, with predictions to z = 7. We demonstrate how combining MIR and optical colors can yield even more efficient selection of active galactic nuclei (AGNs) than MIR or optical colors alone. Composite spectral energy distributions (SEDs) are constructed for 259 quasars with both Sloan Digital Sky Survey and Spitzer photometry, supplemented by near-IR, GALEX, VLA, and ROSAT data, where available. We discuss how the spectral diversity of quasars influences the determination of bolometric luminosities and accretion rates; assuming the mean SED can lead to errors as large as 50% for individual quasars when inferring a bolometric luminosity from an optical luminosity. Finally, we show that careful consideration of the shape of the mean quasar SED and its redshift dependence leads to a lower estimate of the fraction of reddened/obscured AGNs missed by optical surveys as compared to estimates derived from a single mean MIR to optical flux ratio.

We present a compilation of spectra of 101 Seyfert galaxies obtained with the Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph (STIS), covering the UV and/or optical spectral range. Information on all the available spectra have been collected in a Mastertable, which is a very useful tool for anyone interested in a quick glance at the existent STIS spectra for Seyfert galaxies in the HST archive, and it can be recovered electronically. Nuclear spectra of the galaxies have been extracted in windows of 02 for an optimized sampling (as this is the slit width in most cases) and combined in order to improve the signal-to-noise ratio and provide the widest possible wavelength coverage. These combined spectra are also available electronically.

We present a survey of the photometric and kinematic properties of 39 nearby, nearly face-on disk galaxies. Our approach exploits echelle-resolution integral-field spectroscopy of the Hα regions, obtained with DensePak on the WIYN 3.5 m telescope Bench Spectrograph. These data are complemented by H I line profiles observed with the Nançay radio telescope for 25 of these sample galaxies. Twelve additional line widths are available for sample galaxies from the literature. In this paper, we introduce the goals of this survey, define the sample selection algorithm, and amass the integral field spectroscopic data and H I line widths. We establish spatially integrated Hα line widths for the sample. We test the veracity of these spatially integrated line profiles by convolving narrowband imaging data with velocity field information for one of the sample galaxies, PGC 38268, and also by comparing to H I line profiles. We find H I and Hα line profiles to be similar in width but different in shape, indicating that we are observing different spatial distributions of ionized and neutral gas in largely axisymmetric systems with flat outer rotation curves. We also find vertical velocity dispersions of the ionized disk gas within several disk scale lengths have a median value of 18 km s^-1 and an 80% range of 12-26 km s^-1. This is only a factor of ~2 larger than what is observed for neutral atomic and molecular gas. With standard assumptions for intrinsic and thermal broadening for Hα, this translates into a factor of 3 range in turbulent velocities, between 8 and 25 km s^-1.

We have used the Very Large Array to search for compact milliarcsecond-size radio sources near methanol masers in high-mass star-forming regions. Such sources are required for very long baseline Interferometry phase-referencing observations. We conducted pointed observations of 234 compact sources found in the NVSS survey and find 92 sources with unresolved components and synchrotron spectral indexes. These sources are likely the cores of AGNs and, thus, are good candidates for astrometric calibrators.

We present a database (LOGPHOT) of stellar photometry of Local Group galaxies obtained with the Hubble Space Telescope using the Wide Field Planetary Camera 2 (WFPC2). The database includes photometry from all WFPC2 observations taken through 2003 with long exposures (>500 s) in F555W and F814W, and many observations in which long exposures were taken in at least two broadband filters. We have attempted to derive and use techniques that produce the best photometry; the database has been fully populated using the HSTphot photometry package. To test the effects of different techniques, independent reductions were made for a few fields, and the comparison of these highlights some important issues and gives an estimate of plausible errors; these tests also led to some minor modifications and improvements to HSTphot. We provide both point-spread function photometry and subtracted-frame aperture photometry and discuss the merits of each. The database is available electronically. In addition to discussing the techniques used to construct the database, we present color-magnitude diagrams from single fields in each of the Local Group galaxies that have been observed; these provide an educational and visual display of the variety of star formation histories observed in Local Group galaxies.

We present a photometric study of the star-forming region NGC 346 and its surrounding field in the Small Magellanic Cloud, using data taken with the Advanced Camera for Surveys (ACS) on board the Hubble Space Telescope (HST). The data set contains both short and long exposures for increased dynamic range, and photometry was performed using the ACS module of the stellar photometry package DOLPHOT. We detected almost 100,000 stars over a magnitude range of V ~ 11 to V ~ 28 mag, including all stellar types from the most massive young stars to faint lower main-sequence and pre-main-sequence stars. We find that this region, which is characterized by a plethora of stellar systems and interesting objects, is an outstanding example of mixed stellar populations. We take into account different features of the color-magnitude diagram of all the detected stars to distinguish the two dominant stellar systems: The stellar association NGC 346 and the old spherical star cluster BS 90. These observations provide a complete stellar sample of a field about 5' × 5' around the most active star-forming region in this galaxy. Considering the importance of these data for various investigations in the area, we provide the full stellar catalog from our photometry. This paper is the first part of an ongoing study to investigate in detail the two dominant stellar systems in the area and their surrounding field.

Carbon soot has been prepared by laser-induced pyrolysis of a mixture of ethylene (C₂H₄) and benzene (C₆H₆) vapor. The soluble part of the carbonaceous powder has been separated from its insoluble counterpart by soxhlet extraction in toluene. Several techniques were applied to obtain information on the composition of the extract. These included UV/visible and IR spectroscopy in solid and liquid phase, gas chromatography combined with mass spectrometry, gas-phase laser spectroscopy in a supersonic jet, and matrix spectroscopy in helium droplets, the latter being also combined with mass spectrometry. The analysis revealed that the carbonaceous powder contained various polycyclic aromatic hydrocarbons (PAHs). The highest concentration was found for the three-membered catacondensed PAHs, phenanthrene and anthracene. The results are discussed in view of the possible role of these molecules as interstellar dust components.

We have identified 41 infrared dark clouds from the 8 μm maps of the Midcourse Space Experiment (MSX), selected to be found within 1 deg² areas centered on known ultracompact H II regions. We have mapped these infrared dark clouds in N₂H⁺1→0, CS 2→1, and C¹⁸O 1→0 emission using the Five College Radio Astronomy Observatory. The maps of the different species often show striking differences in morphologies, indicating differences in evolutionary state and/or the presence of undetected, deeply embedded protostars. We derive an average mass for these clouds using N₂H⁺ column densities of ≈2500 M_☉, a value comparable to that found in previous studies of high-mass star-forming cores using other mass tracers. The line widths of these clouds are typically ~2.0-2.9 km s^-1. Based on the fact that they are dark at 8 μm, compact, and massive, and have large velocity dispersions, we suggest that these clouds may be the precursor sites of intermediate- and high-mass star formation.

We present the results of a Hubble Space Telescope NICMOS imaging survey of 22 T-type field brown dwarfs. Five are resolved as binary systems with angular separations of 005-035, and companionship is established on the basis of component F110W - F170M colors (indicative of CH₄ absorption) and low probabilities of background contamination. Prior ground-based observations show 2MASS 1553+1532AB to be a common proper-motion binary. The properties of these systems—low multiplicity fraction (12% resolved, as corrected for sample selection biases), close projected separations (ρ = 1.8-5.0 AU) and near-unity mass ratios—are consistent with previous results for field brown dwarf binaries. Three of the binaries have components that span the poorly understood transition between L dwarfs and T dwarfs. Spectral decomposition analysis of one of these, SDSS 1021-0304AB, reveals a peculiar flux reversal between its components, as its cooler T5 secondary is ~30% brighter at 1.05 and 1.27 μm than its T1 primary. This system, 2MASS 0518-2828AB, and SDSS 1534+1615AB all demonstrate that the J-band brightening observed between late-type L to mid-type T dwarfs is an intrinsic feature of this spectral transition, albeit less pronounced than previously surmised. We also find that the resolved binary fraction of L7 to T3.5 dwarfs is twice that of other L and T dwarfs, an anomaly that can be explained by a relatively rapid evolution of brown dwarfs through the L/T transition, perhaps driven by dynamic (nonequilibrium) depletion of photospheric condensates.

A 1.5-dimensional, time-dependent magnetohydrodynamic (MHD) model that includes an energy equation and anisotropic electrical conductivity tensor for a variably ionized, multispecies plasma is presented. The model includes an algorithm that reduces the numerical dissipation rate far below the dissipation rate determined by the conductivity tensor. This is necessary for accurate calculation of resistive heating rates. The model is used to simulate the propagation of Alfvén waves launched near the base of the middle chromosphere. The background state is the FAL CM equilibrium with a vertical magnetic field. The initial magnetic energy of a wave is almost completely damped out in the chromosphere by the time the disturbance propagates a distance of one wavelength. The energy is converted mainly into thermal energy. The remainder is converted into bulk flow kinetic energy and a Poynting flux with nonzero divergence. The thermal energy is generated almost entirely by Pedersen current dissipation. The corresponding heating rates are close to the FAL CM values near the base of the middle chromosphere. Dynamo action is observed. The damping of a continuously driven Alfvén wave train is also simulated, yielding results similar to those of the single wave cases. It is the strong magnetization and weak ionization of the chromosphere that allows for strong heating by Pedersen current dissipation. This distinguishes the chromosphere from the weakly magnetized and weakly ionized photosphere, and the strongly magnetized and strongly ionized corona where Pedersen current dissipation is not significant on the length and timescales simulated.

Electron collision excitation strengths and rates for infrared and ultraviolet lines arising from transitions between the fine-structure levels of the 2s²2p, 2s2p², 2p³, 2s²3s, 2s²3p, 2s²3d, 2s2p3s, 2s2p3p, 2s2p3d, 2s²4s, and 2s²4p configurations of O IV have been calculated using Breit-Pauli R-matrix approach. Configuration-interaction wave functions have been used for an accurate representation of target levels. These wave functions give excitation energies that are in close agreement with experiment. Oscillator strengths and transition probabilities for UV and EUV lines compare very well with previous calculations. The Rydberg series of resonances converging to the excited levels are explicitly included in the scattering calculation and are found to make substantial contribution to collision strengths. The effective collision strengths are obtained by integrating total collision strengths over a Maxwellian distribution of electron energies, and these are presented over a wide temperature range suitable for modeling of astrophysical plasmas. Significant qualitative and quantitative differences with earlier results of effective collision strengths are noted.

Iso-propanol [(CH₃)₂CHOH], an isomer of n-propanol, has been studied in the millimeter- and submillimeter-wave region of the electromagnetic spectrum with our FASSST spectrometer through 360 GHz. Spectra arising from the ground vibrational state of all three hydroxyl torsional substates, given the labels symmetric gauche, antisymmetric gauche, and trans in order of increasing energy, have been observed. We have successfully assigned ~7600 pure rotational transitions within the torsional substates as well as ~4700 torsional-rotational transitions between the symmetric and antisymmetric gauche substates through the lower rotational quantum number J'' = 68. Spectral lines involving one or both of the two gauche forms have been simultaneously analyzed with a 2 × 2 effective torsional-rotational Hamiltonian, which includes terms through fifth order in the torsional-rotational interaction. Excluding perturbed transitions, the assigned transitions were fitted to a root mean square deviation of 76 kHz. The trans substate was analyzed as a semirigid rotor, and its unperturbed transitions fitted to a root mean square deviation of 63 kHz. A perturbation was seen at transitions with J'' > 50 in the trans substate. The torsional excitation energy for the trans substate above ground was estimated from intensity ratios to be about 120 K.