Observing Conditions at Mt.Graham: VATT UBVR Sky Surface Brightness and Seeing Measurements from 1999 through 2003

We present measurements of sky surface brightness and seeing on Mt.Graham obtained at the Vatican Advanced Technology Telescope (VATT) during 16 observing runs between April 1999 and December 2003. We show that the sky surface brightness is significantly darker during photometric conditions, and can be highly variable over the course of a single observing run as well as from one run to the next, regardless of photometricity. In our photometric observations we find an average low-airmass (sec z < 1.2) sky surface brightness of 22.00, 22.53, 21.49, and 20.88 mag arcsec^-2 in U, B, V, and R, respectively. The darkest run (02/00 in U and 02/01 in BVR) had an average sky surface brightness of 22.38, 22.86, 21.72, and 21.19 mag arcsec^-2 in U, B, V, and R, respectively. With these results we show that under the best conditions, Mt. Graham can compete with the darkest sites in Hawaii and Chile, thanks in part to the strict dark-sky ordinances in place in Tucson and Safford. We expect the sky over Mt. Graham to be even darker than our 1999--2003 results during solar minimum (2006--2007). We find a significant improvement of about 0.45 arcsec in our measured stellar FWHM after improvements to the telescope were made in Summer and Fall 2001. Stellar FWHM values are highly variable, with median R-band focus FWHM values in each observing run ranging from 0.97 arcsec to 2.15 arcsec. Significantly sub-arcsecond seeing was occasionally achieved with values as low as 0.65 arcsec FWHM in R. There may possibly still be a significant telescope contribution to the seeing at the VATT, but nearby trees as high as the dome are currently the dominant factor.Comment: 22 pages, 11 figures, to appear in PAS

The Young Stellar Population of the Nearby Late-Type Galaxy NGC 1311

We have extracted PSF-fitted stellar photometry from near-ultraviolet, optical and near-infrared images, obtained with the Hubble Space Telescope, of the nearby (D ~ 5.5 Mpc) SBm galaxy NGC 1311. The ultraviolet and optical data reveal a population of hot main sequence stars with ages of 2-10 Myr. We also find populations of blue supergiants with ages between 10 and 40 Myr and red supergiants with ages between 10 and 100 Myr. Our near-infrared data shows evidence of star formation going back ~1 Gyr, in agreement with previous work. Fits to isochrones indicate a metallicity of Z ~ 0.004. The ratio of blue to red supergiants is consistent with this metallicity. This indicates that NGC 1311 follows the well-known luminosity-metallicity relation for late-type dwarf galaxies. About half of the hot main sequence stars and blue supergiants are found in two regions in the inner part of NGC 1311. These two regions are each about 200 pc across, and thus have crossing times roughly equal to the 10 Myr age we find for the dominant young population. The Luminosity Functions of the supergiants indicate a slowly rising star formation rate (of 0.001 Solar masses per year) from ~100 Myr ago until ~15 Myr ago, followed by a strong enhancement (to 0.01 Solar Masses per year) at ~10 Myr ago. We see no compelling evidence for gaps in the star-forming history of NGC 1311 over the last 100 Myr, and, with lower significance, none over the last Gyr. This argues against a bursting mode, and in favor of a gasping or breathing mode for the recent star-formation history.Comment: AASTex, 34 pages, 13 postscript figures. Accepted for publication by The Astronomical Journa

UV-Optical Pixel Maps of Face-On Spiral Galaxies -- Clues for Dynamics and Star Formation Histories

UV and optical images of the face-on spiral galaxies NGC 6753 and NGC 6782 reveal regions of strong on-going star formation that are associated with structures traced by the old stellar populations. We make NUV--(NUV-I) pixel color-magnitude diagrams (pCMDs) that reveal plumes of pixels with strongly varying NUV surface brightness and nearly constant I surface brightness. The plumes correspond to sharply bounded radial ranges, with (NUV-I) at a given NUV surface brightness being bluer at larger radii. The plumes are parallel to the reddening vector and simple model mixtures of young and old populations, thus neither reddening nor the fraction of the young population can produce the observed separation between the plumes. The images, radial surface-brightness, and color plots indicate that the separate plumes are caused by sharp declines in the surface densities of the old populations at radii corresponding to disk resonances. The maximum surface brightness of the NUV light remains nearly constant with radius, while the maximum I surface brightness declines sharply with radius. An MUV image of NGC 6782 shows emission from the nuclear ring. The distribution of points in an (MUV-NUV) vs. (NUV-I) pixel color-color diagram is broadly consistent with the simple mixture model, but shows a residual trend that the bluest pixels in (MUV-NUV) are the reddest pixels in (NUV-I). This may be due to a combination of red continuum from late-type supergiants and [SIII] emission lines associated with HII regions in active star-forming regions. We have shown that pixel mapping is a powerful tool for studying the distribution and strength of on-going star formation in galaxies. Deep, multi-color imaging can extend this to studies of extinction, and the ages and metallicities of composite stellar populations in nearby galaxies.Comment: LaTeX with AASTeX style file, 29 pages with 12 figures (some color, some multi-part). Accepted for publication in The Astrophysical Journa

An HST Survey of the mid-UV Morphology of Nearby Galaxies

(Abbreviated) We present an imaging survey of 37 nearby galaxies observed with HST/WFPC2 in the mid-UV F300W filter and in F814W. 11 galaxies were also imaged in F255W. These galaxies were selected to be detectable with WFPC2 in one orbit, and cover a wide range of Hubble types and inclinations. The mid-UV spans the gap between our groundbased optical/NIR images and far-UV images available from the Astro/UIT missions. Our first qualitative results are: (1) Early-type galaxies show a significant decrease in surface brightness going from the red to the mid-UV, and in some cases the presence of dust lanes. Some galaxies would be classified different when viewed in the mid-UV, some become dominated by a blue nuclear feature or point source. (2) Half of the mid-type spiral and star-forming galaxies appear as a later morphological type in the mid-UV, as Astro/UIT also found in the far-UV. Some- times these differences are dramatic. The mid-UV images show a considerable range in the scale and surface brightness of individual star-forming regions. Almost all mid-type spirals have their small bulges bi-sected by a dust-lane. (3) Most of the heterogeneous subset of late-type, irregular, peculiar, and merging galaxies display F300W morphologies that are similar to those seen in F814W, but with differences due to recognizable dust features absorbing the bluer light, and due to UV-bright hot stars, star-clusters, and star-forming ridges. In the rest-frame mid-UV, early- to mid-type galaxies are more likely to be misclassified as later types than vice versa. This morphological K-correction explains only part of the excess faint blue galaxies seen in deep HST fields.Comment: 30 pages, LateX (AASTeX5.0), 2 figures and 3 tables included, mid-UV atlas and pan-chromatic atlas provided as 63 JPG figures. Full resolution PS version (~100Mb) available upon request. Accepted for publication in ApJ

Multiple novel prostate cancer susceptibility signals identified by fine-mapping of known risk loci among Europeans

Genome-wide association studies (GWAS) have identified numerous common prostate cancer (PrCa) susceptibility loci. We have fine-mapped 64 GWAS regions known at the conclusion of the iCOGS study using large-scale genotyping and imputation in 25 723 PrCa cases and 26 274 controls of European ancestry. We detected evidence for multiple independent signals at 16 regions, 12 of which contained additional newly identified significant associations. A single signal comprising a spectrum of correlated variation was observed at 39 regions; 35 of which are now described by a novel more significantly associated lead SNP, while the originally reported variant remained as the lead SNP only in 4 regions. We also confirmed two association signals in Europeans that had been previously reported only in East-Asian GWAS. Based on statistical evidence and linkage disequilibrium (LD) structure, we have curated and narrowed down the list of the most likely candidate causal variants for each region. Functional annotation using data from ENCODE filtered for PrCa cell lines and eQTL analysis demonstrated significant enrichment for overlap with bio-features within this set. By incorporating the novel risk variants identified here alongside the refined data for existing association signals, we estimate that these loci now explain ∼38.9% of the familial relative risk of PrCa, an 8.9% improvement over the previously reported GWAS tag SNPs. This suggests that a significant fraction of the heritability of PrCa may have been hidden during the discovery phase of GWAS, in particular due to the presence of multiple independent signals within the same regio

HST MID-UV IMAGING OF NEARBY GALAXIES

Abstract We summarize Hubble Space Telescope projects that imaged a significant sample of nearby galaxies of all types and inclinations in the mid-UV with WFPC2 and some in the near-IR with NICMOS. The sample emphasizes high-surface brightness late-type, irregular, peculiar and merging galaxies, since these objects are the most prevalent at high redshifts. The sample is used to establish a local benchmark for quantitative classifications of galaxies seen by HST in their rest-frame UV, and in the next decade also by the James Webb Space Telescope. We review how nearby galaxies change their rest-frame structure and morphology from the rest-frame UV to the optical as a function of galaxy type and inclination, and other studies that are being done with this HST sample. When observed in the rest-frame mid-UV — early- to mid-type galaxies are more likely misclassified as later types than late-type galaxies are misclassified as earlier types. This is because later-type galaxies are dominated by the same young and hot stars in all filters from the mid-UV to the red, and so have a smaller “morphological K-correction ” than true earlier type galaxies. This  ¢¡¤£¦¥¨§� © can explain a small part, but certainly not all of the excess faint blue late-type galaxies seen in deep HST fields. Contrary to early–mid-type galaxies, the majority of late-type galaxies become redder outward. While young UV/blue-bright stellar populations dominate their inner morphology, most late-type galaxies are inferred to have a significant halo or (thick) disk of older stars. We discuss these results in a cosmological context