Table of contents

We present the results of reconstruction analysis of the galaxy distribution in a spherical region of radius 50 h^-1 Mpc centered on the Local Group, as mapped by the IRAS Point Source Catalog Redshift Survey (PSCz). We reconstruct this galaxy distribution using 15 different models for structure formation in the universe, each model consisting of a set of assumptions regarding the value of the cosmological mass-density parameter Ω_m and the amplitude and nature of the biasing between IRAS galaxies and the underlying mass. For every model, we also reconstruct 10 mock PSCz catalogs derived from the outputs of numerical simulations that have the appropriate values of Ω_m and bias. We quantify the accuracy of a reconstruction using a variety of statistics and compare the accuracy of each reconstruction of the PSCz catalog with the accuracy expected based on the mock-catalog reconstructions of the corresponding model. We find that gravitational instability of Gaussian primordial mass-density fluctuations can account for the galaxy distribution in the PSCz catalog, at least for some plausible assumptions about the value of Ω_m and the biasing between IRAS galaxies and mass. However, unbiased models in which IRAS galaxies trace mass fail to reconstruct the PSCz catalog accurately, both for Ω_m = 0.4 and for Ω_m = 1. Low-Ω_m models in which IRAS galaxies are antibiased with respect to the mass distribution are the most successful in reconstructing the PSCz catalog. In particular, a model with Ω_m = 0.4 and IRAS galaxies related to the mass distribution according to the predictions of a semianalytic galaxy formation model is very successful in reproducing the properties of the PSCz galaxy distribution.

We present a method to determine the star formation history of a mixed stellar population from its photometry. We perform a χ² minimization between the observed photometric distribution and a model photometric distribution, based on theoretical isochrones. The initial mass function, distance modulus, interstellar reddening, binary fraction, and photometric errors are incorporated into the model, making it directly comparable to the data. The model is a linear combination of individual synthetic color-magnitude diagrams (CMDs), each of which represents the predicted photometric distribution of a stellar population of a given age and metallicity. While the method is similar to existing synthetic CMD algorithms, we describe several key improvements in our implementation. In particular, we focus on the derivation of accurate error estimates on the star formation history to enable comparisons between such histories, either from different objects or from different regions of a single object. We present extensive tests of the algorithm, using both simulated and actual photometric data. From a preliminary application of the algorithm to a subregion of the Large Magellanic Cloud (LMC), we find that the that the lull in star formation observed among the LMC's cluster population between 3 and 8 Gyr ago is also present in the field population. The method was designed with flexibility and generality in mind, and we make the code available for use by the astronomical community.

Imaging Fabry-Perot data has been acquired for a sample of seven late-type spiral galaxies from which two-dimensional velocity fields have been constructed on a subkiloparsec resolution scale. The kinematic disk (i.e., tilted ring) modeling procedure is used to fit the velocity field and recover its rotational structure. From this fit, different schemes are used to extract the major-axis rotation curve, as well as velocity profiles along the minor axis. Rotation curves found from deprojection of the velocity field using mean geometric parameters invariably produce small-scale "bumps and wiggles," which are a reflection of the inclusion of noncircular motions. In the best-rotation curve method, the rotation curve is derived from the best fit to the entire velocity field. This method is shown to minimize the effects of noncircular motions. The kinematic center of the velocity field is allowed to vary, and those results are directly compared with cases where the kinematic center is held fixed. In virtually all cases, we find that the variable center model produces the smoothest and most symmetric rotation curves and minor-axis velocity profiles. Our results indicate that the kinematic center of mass is moving around in these disk systems with an amplitude of plus or minus ∼300 pc. Finally, we investigate the effects of small, systematic errors in centering and find that small minor-axis displacements can artificially produce spurious slopes in the rotation curve at large radius, including producing rotation curves that are apparently falling.

We present near-IR integral field spectroscopy of a sample of 31 Seyfert and LINER galaxies which were selected both to span a wide range of nuclear magnitudes and to possess roughly equal numbers of Seyfert type 1 and 2 nuclei. Moderate resolution (R ~ 1000; R ~ 2000 for three cases) integral field K-band spectra were obtained for all 31 galaxies in our sample and for 18 galaxies (R ~ 1000; R ~ 2000 for four cases) H-band integral field spectra were also obtained. In each case, we present nuclear, larger aperture, and difference spectra with corresponding information about emission line wavelengths, fluxes, and widths. Line-free H- and K-band continuum images as well as [Fe II] λ1.644 μm, Brγ, and H₂ 1-0 S(1) emission lines are also presented. In addition, we provide extensive information about each galaxy obtained from the literature that will be useful subsequently for characterizing the sample and for comparison with our near-IR data.

X-ray mosaics of the Large Magellanic Cloud (LMC) taken with the ROSAT Position Sensitive Proportional Counter (PSPC) have revealed extensive diffuse X-ray emission, indicative of hot ≥10⁶ K gas associated with this irregular galaxy on scales from ∼10 to ≥1000 pc. We have selected regions of large-scale (d ≥ 600 pc) diffuse X-ray emission, such as supergiant shells, the LMC Spur, and the LMC Bar, and examined the physical conditions of the hot gas associated with them. We find that for these objects the plasma temperatures range from kT ~ 0.15 to 0.60 keV and the derived electron densities range from n_e ∼ 0.005 to 0.03 cm^-3. Furthermore, we have examined the fraction of diffuse X-ray emission from the LMC and compared it to the total X-ray emission. We find that discrete sources such as X-ray binaries and supernova remnants account for ~41% and ~21% of the X-ray emission from the LMC, respectively. In contrast, diffuse X-ray emission from the field and from supergiant shells account for ~30% and ~6% of the total X-ray emission, respectively.

We present ROSAT observations and analysis of thirteen superbubbles in the Large Magellanic Cloud. Eleven of these observations have not been previously reported. We have studied the X-ray morphology of the superbubbles and have extracted and analyzed their X-ray spectra. Diffuse X-ray emission is detected from each of these superbubbles, and X-ray emission is brighter than that theoretically expected for a wind-blown bubble, suggesting that the X-ray emission from the superbubbles has been enhanced by interactions between the superbubble shell and interior supernova remnants. We have also found significant positive correlations between the X-ray luminosity of a superbubble and its Hα luminosity, expansion velocity, and OB star count. Further, we have found that a large fraction of the superbubbles in the sample show evidence of breakout regions, where hot X-ray-emitting gas extends beyond the Hα shell.

A survey is presented of the Galactic plane in the J = 1-0 transition of ¹³CO. About 73,000 spectra were obtained with the 7 m telescope at Bell Laboratories over a 10 yr period. The coverage of the survey is (l, b) = (-5° to 117°, -1° to 1°), or 244 deg², with a grid spacing of 3' for |b| < 05 and a grid spacing of 6' for |b| > 05. The data presented here have been resampled onto a 3' grid. For 0.68 km s^-1 channels, the rms noise level of the survey is 0.1 K on the T scale. The raw data have been transformed into FITS format, and all the reduction processes, such as correcting for emission in the reference positions, baseline removal, and interpolation, were conducted within IRAF using the FCRAO task package and additional programs. The reduced data are presented here in the form of longitude-velocity color maps at each latitude. These data allow identification and classification of molecular clouds with masses in excess of ∼10³M_☉ throughout the first quadrant of the Galaxy. Spiral structure is manifested by the locations of the largest and brightest molecular clouds.

As a part of the Tokyo-Onsala-ESO-Calán Galactic CO survey, we have made large-scale mapping observations of the Galactic center in the CO J = 2-1 line using the 60 cm survey telescope in Chile. The data were taken with the same beam size (9') and sampling grid (75) as the CO J = 1-0 Columbia survey, so that the two data sets can be compared directly. Velocity channel maps and longitude-velocity diagrams of the ¹²CO J = 2-1 line, covering -6° ≤ l ≤ 6°, -2° ≤ b ≤ 2°, -300 ≤ v_LSR ≤ 300 km s^-1, are presented, along with the corresponding maps of the ¹²CO J = 2-1/J = 1-0 intensity ratio [R_2-1/1-0(¹²CO)]. A longitude-velocity diagram of the ¹³CO J = 2-1 line intensity and corresponding ¹³CO J = 2-1/¹²CO J = 2-1 intensity ratio [R_13/12(J = 2-1)] is also presented at b = 0°. The overall R_2-1/1-0(¹²CO) in the central 900 pc of the Galaxy is 0.96 ± 0.01, which is higher than the typical value in the Galactic disk, 0.6-0.7. The isotopic intensity ratio R_13/12(J = 2-1) is 0.10 ± 0.01. The two observed intensity ratios [R_2-1/1-0(¹²CO) and R_13/12(J = 2-1)] indicate that the optical depth of the ¹²CO J = 1-0 line is ~1 or smaller in the Galactic center molecular clouds, much smaller than those of the giant molecular clouds (GMCs) in the Galactic disk. Longitude-velocity distributions of physical properties of molecular gas are derived using a large velocity gradient analysis. Molecular gas in the Galactic center generally shows a high pressure. In particular, there is a high-pressure region in the central ∼100 pc where the pressure is an order of magnitude higher than that in GMCs in the Galactic disk. This region is dominated by high-density gas and contains star-forming regions.

Observations of the planetary nebulae NGC 6302, NGC 6543, and NGC 7027 by the Short Wavelength Spectrometer (SWS) on board the Infrared Space Observatory (ISO) have been used to determine rest wavelengths of spectral lines. We report on improved accuracies for wavelengths of seven mid-infrared ionic fine-structure lines.