Some comments on certain technical aspects on geographic information systems Technical report no. 2

Two-dimensional machine language and spatial statistics for design and development of geographic information system

Review and synthesis of problems and directions for large scale geographic information system development

Problems and directions for large scale geographic information system development were reviewed and the general problems associated with automated geographic information systems and spatial data handling were addressed

The Flux Auto- and Cross-Correlation of the Lyman-alpha Forest. II. Modelling Anisotropies with Cosmological Hydrodynamic Simulations

The isotropy of the Lyman-alpha forest in real-space uniquely provides a measurement of cosmic geometry at z > 2. The angular diameter distance for which the correlation function along the line of sight and in the transverse direction agree corresponds to the correct cosmological model. However, the Lyman-alpha forest is observed in redshift-space where distortions due to Hubble expansion, bulk flows, and thermal broadening introduce anisotropy. Similarly, a spectrograph's line spread function affects the autocorrelation and cross-correlation differently. In this the second paper of a series on using the Lyman-alpha forest observed in pairs of QSOs for a new application of the Alcock-Paczynski (AP) test, these anisotropies and related sources of potential systematic error are investigated with cosmological hydrodynamic simulations. Three prescriptions for galactic outflow were compared and found to have only a marginal effect on the Lyman-alpha flux correlation (which changed by at most 7% with use of the currently favored variable-momentum wind model vs. no winds at all). An approximate solution for obtaining the zero-lag cross-correlation corresponding to arbitrary spectral resolution directly from the zero-lag cross-correlation computed at full-resolution (good to within 2% at the scales of interest) is presented. Uncertainty in the observationally determined mean flux decrement of the Lyman-alpha forest was found to be the dominant source of systematic error; however, this is reduced significantly when considering correlation ratios. We describe a simple scheme for implementing our results, while mitigating systematic errors, in the context of a future application of the AP test.Comment: 20 page

The Spitzer Local Volume Legacy: Survey Description and Infrared Photometry

The survey description and the near-, mid-, and far-infrared flux properties are presented for the 258 galaxies in the Local Volume Legacy (LVL). LVL is a Spitzer Space Telescope legacy program that surveys the local universe out to 11 Mpc, built upon a foundation of ultraviolet, H-alpha, and HST imaging from 11HUGS (11 Mpc H-alpha and Ultraviolet Galaxy Survey) and ANGST (ACS Nearby Galaxy Survey Treasury). LVL covers an unbiased, representative, and statistically robust sample of nearby star-forming galaxies, exploiting the highest extragalactic spatial resolution achievable with Spitzer. As a result of its approximately volume-limited nature, LVL augments previous Spitzer observations of present-day galaxies with improved sampling of the low-luminosity galaxy population. The collection of LVL galaxies shows a large spread in mid-infrared colors, likely due to the conspicuous deficiency of 8um PAH emission from low-metallicity, low-luminosity galaxies. Conversely, the far-infrared emission tightly tracks the total infrared emission, with a dispersion in their flux ratio of only 0.1 dex. In terms of the relation between infrared-to-ultraviolet ratio and ultraviolet spectral slope, the LVL sample shows redder colors and/or lower infrared-to-ultraviolet ratios than starburst galaxies, suggesting that reprocessing by dust is less important in the lower mass systems that dominate the LVL sample. Comparisons with theoretical models suggest that the amplitude of deviations from the relation found for starburst galaxies correlates with the age of the stellar populations that dominate the ultraviolet/optical luminosities.Comment: Accepted for publication in ApJ; Figures 1,8,9 provided as jpeg

The Flux Auto- and Cross-Correlation of the Lyman-alpha Forest. I. Spectroscopy of QSO Pairs with Arcminute Separations and Similar Redshifts

The Lyman-alpha forest has opened a new redshift regime for cosmological investigation. At z > 2 it provides a unique probe of cosmic geometry and an independent constraint on dark energy that is not subject to standard candle or ruler assumptions. In Paper I of this series on using the Lyman-alpha forest observed in pairs of QSOs for a new application of the Alcock-Paczynski test, we present and discuss the results of a campaign to obtain moderate-resolution spectroscopy (FWHM ~ 2.5 Angstroms) of the Lyman-alpha forest in pairs of QSOs with small redshift differences (Delta z 2.2) and arcminute separations (< 5'). This data set, composed of seven individual QSOs, 35 pairs, and one triplet, is also well-suited for future investigations of the coherence of Lyman-alpha absorbers on ~ 1 Mpc transverse scales and the transverse proximity effect. We note seven revisions for previously published QSO identifications and/or redshifts.Comment: 20 page

The Calibration of Monochromatic Far-Infrared Star Formation Rate Indicators

(Abridged) Spitzer data at 24, 70, and 160 micron and ground-based H-alpha images are analyzed for a sample of 189 nearby star-forming and starburst galaxies to investigate whether reliable star formation rate (SFR) indicators can be defined using the monochromatic infrared dust emission centered at 70 and 160 micron. We compare recently published recipes for SFR measures using combinations of the 24 micron and observed H-alpha luminosities with those using 24 micron luminosity alone. From these comparisons, we derive a reference SFR indicator for use in our analysis. Linear correlations between SFR and the 70 and 160 micron luminosity are found for L(70)>=1.4x10^{42} erg/s and L(160)>=2x10^{42} erg/s, corresponding to SFR>=0.1-0.3 M_sun/yr. Below those two luminosity limits, the relation between SFR and 70 micron (160 micron) luminosity is non-linear and SFR calibrations become problematic. The dispersion of the data around the mean trend increases for increasing wavelength, becoming about 25% (factor ~2) larger at 70 (160) micron than at 24 micron. The increasing dispersion is likely an effect of the increasing contribution to the infrared emission of dust heated by stellar populations not associated with the current star formation. The non-linear relation between SFR and the 70 and 160 micron emission at faint galaxy luminosities suggests that the increasing transparency of the interstellar medium, decreasing effective dust temperature, and decreasing filling factor of star forming regions across the galaxy become important factors for decreasing luminosity. The SFR calibrations are provided for galaxies with oxygen abundance 12+Log(O/H)>8.1. At lower metallicity the infrared luminosity no longer reliably traces the SFR because galaxies are less dusty and more transparent.Comment: 69 pages, 19 figures, 2 tables; accepted for publication on Ap

Early results from the SAGE-SMC Spitzer legacy

Early results from the SAGE-SMC (Surveying the Agents of Galaxy Evolution in the tidally-disrupted, low-metallicity Small Magellanic Cloud) Spitzer legacy program are presented. These early results concentrate on the SAGE-SMC MIPS observations of the SMC Tail region. This region is the high H i column density portion of the Magellanic Bridge adjacent to the SMC Wing. We detect infrared dust emission and measure the gas-to-dust ratio in the SMC Tail and find it similar to that of the SMC Body. In addition, we find two embedded cluster regions that are resolved into multiple sources at all MIPS wavelengths. © 2009 International Astronomical Union