Space Telescope Science Institute

About: Space Telescope Science Institute is a facility organization based out in Baltimore, Maryland, United States. It is known for research contribution in the topics: Galaxy & Stars. The organization has 2448 authors who have published 14154 publications receiving 947296 citations. The organization is also known as: STScI.

Nested and Single Bars in Seyfert and Non-Seyfert Galaxies

Abstract: We analyze the observed properties of nested and single stellar bar systems in disk galaxies. The 112 galaxies in our sample comprise the largest matched Seyfert versus non-Seyfert galaxy sample of nearby galaxies with complete near-infrared or optical imaging sensitive to length scales ranging from tens of parsecs to tens of kiloparsecs. The presence of bars is deduced by —tting ellipses to isophotes in Hubble Space Telescope (HST ) H-band images up to 10A radius and in ground-based near-infrared and optical images outside the H-band images. This is a conservative approach that is likely to result in an underestimate of the true bar fraction. We —nd that a signi—cant fraction of the sample galaxies, 17% ^ 4%, have more than one bar, and that 28% ^ 5% of barred galaxies have nested bars. The bar fractions appear to be stable according to reasonable changes in our adopted bar criteria. For the nested bars, we detect a clear division in length between the large-scale (primary) bars and small-scale (secondary) bars, in both absolute and normalized (to the size of the galaxy) length. We argue that this bimodal distribution can be understood within the framework of disk resonances, speci—cally the inner Lindblad resonances (ILRs), which are located where the gravitational potential of the innermost galaxy switches eUectively from three-dimensional to two-dimensional. This conclusion is further strengthened by the observed distribution of the sizes of nuclear rings which are dynamically associated with the ILRs. While primary bar sizes are found to correlate with the host galaxy sizes, no such correlation is observed for the secondary bars. Moreover, we —nd that secondary bars diUer morphologically from single bars. Our matched Seyfert and non-Seyfert samples show a statistically signi—cant excess of bars among the Seyfert galaxies at practically all length scales. We con—rm our previous results that bars are more abundant in Seyfert hosts than in non-Seyfert galaxies and that Seyfert galaxies always show a preponderance of ii thick ˇˇ bars compared to the bars in non-Seyfert galaxies. Finally, no correlation is observed between the presence of a bar and that of companion galaxies, even relatively bright ones. Overall, since star formation and dust extinction can be signi—cant even in the H band, the stellar dynamics of the central kiloparsec cannot always be revealed reliably by the use of near-infrared surface photometry alone. (%) (%)

Directly Observing the Galaxies Likely Responsible for Reionization

Abstract: We report a new analysis of the Hubble Frontier Fields clusters Abell 2744 and MACS 0416 using wavelet decomposition to remove the cluster light, enabling the detection of highly magnified (>50x) galaxies a factor of 10x fainter in luminosity than previous studies. We find 167 galaxies at z > 6, and with this sample we are able to characterize the UV luminosity function to M_UV = -12.5 at z ~ 6, -14 at z ~ 7 and -15 at z ~ 8. We find a steep faint-end slope (alpha 6, consistent with the number of faint galaxies needed to reionize the Universe under standard assumptions.

New algorithms for reducing cross-dispersed echelle spectra

Abstract: We describe advanced image processing algorithms, implemented in a data analysis package for conven- tional and cross-dispersed echelle spectra. Comparisons with results from other packages illustrate the outstanding quality of the new REDUCE package, particularly in terms of resulting noise level and treatment of CCD defects and cosmic ray spikes. REDUCE can be adapted relatively easily to handle a variety of instrument types, including spec- trographs with prism or grating cross-dispersers, possibly fed by a ber or image slicer, etc. In addition to reduced spectra, an accurate spatial prole is recovered, providing valuable information about the spectrograph PSF and simplifying scattered light corrections.

UV star-formation rates of GRB host galaxies

Abstract: We study a magnitude-limited sample of 10 gamma-ray burst (GRB) host galaxies with known spectroscopic red- shifts (0.43 < z < 2.04). From an analysis of the spectral energy distributions (SEDs), based on published broad-band optical and near-infrared photometry, we derive photometric redshifts, galaxy types, ages of the dominant stellar populations, internal extinctions, and ultraviolet (UV) star-formation rates (SFRs) of the host galaxies. The photometric redshifts are quite accurate despite the heterogeneous nature of the sample: the rms errors are σ(z) = 0.21 and σ(∆z/(1 + zspec)) = 0.16 with no significant systematic offsets. All the host galaxies have SEDs similar to young starburst galaxies with moderate to low extinction. A comparison of specific SFRs with those of high-redshift galaxies in the Hubble Deep Fields shows that GRB hosts are most likely similar to the field galaxies with the largest specific SFRs. On the other hand, GRB hosts are not significantly younger than starburst field galaxies at similar redshifts, but are found to be younger than a sample of all types of field galaxies.

Spectral Properties Of Cool Stars : Extended Abundance Analysis Of 1,617 Planet-Search Stars

Abstract: We present a catalog of uniformly determined stellar properties and abundances for 1,617 F, G, and K stars using an automated spectral synthesis modeling procedure. All stars were observed using th ...