arXiv subjects

G. P. Tiede

Publications and source records attributed to G. P. Tiede.

5 recordsLinked to original sources

arXiv2007

Distances to Populous Clusters in the LMC via the K-Band Luminosity of the Red Clump

We present results from a study of the distances and distribution of a sample of intermediate-age clusters in the Large Magellanic Cloud. Using deep near-infrared photometry obtained with ISPI on the CTIO 4m, we have measured the apparent K-band magnitude of the core helium burning red clump stars in 17 LMC clusters. We combine cluster ages and metallicities with the work of Grocholski & Sarajedini to predict each cluster's absolute K-band red clump magnitude, and thereby calculate absolute cluster distances. An analysis of these data shows that the cluster distribution is in good agreement with the thick, inclined disk geometry of the LMC, as defined by its field stars. We also find that the old globular clusters follow the same distribution, suggesting that the LMC's disk formed at about the same time as the globular clusters, ~ 13 Gyr ago. Finally, we have used our cluster distances in conjunction with the disk geometry to calculate the distance to the LMC center, for which we find (m-M)o = 18.40 +/- 0.04_{ran} +/- 0.08_{sys}, or Do = 47.9 +/- 0.9 +/- 1.8 kpc.

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arXiv2006

Mid-Infrared Selection of Brown Dwarfs and High-Redshift Quasars

We discuss color selection of rare objects in a wide-field, multiband survey spanning from the optical to the mid-infrared. Simple color criteria simultaneously identify and distinguish two of the most sought after astrophysical sources: the coolest brown dwarfs and the most distant quasars. We present spectroscopically-confirmed examples of each class identified in the IRAC Shallow Survey of the Bootes field of the NOAO Deep Wide-Field Survey. ISS J142950.9+333012 is a T4.5 brown dwarf at a distance of approximately 42 pc, and ISS J142738.5+331242 is a radio-loud quasar at redshift z=6.12. Our selection criteria identify a total of four candidates over 8 square degrees of the Bootes field. The other two candidates are both confirmed 5.5<z<6 quasars, previously reported by Cool et al. (2006). We discuss the implications of these discoveries and conclude that there are excellent prospects for extending such searches to cooler brown dwarfs and higher redshift quasars.

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arXiv2005

Near Infrared Survey of Populous Clusters in the LMC: Preliminary Results

We report preliminary results from our near-infrared JHK survey of star clusters in the LMC. The primary goals of the survey are to study the three-dimensional structure and distance of the LMC. In 2003 and 2004 we used the Infrared Side Port Imager (ISPI) on the CTIO 4m to obtain near infrared photometry for a sample of populous LMC clusters. We utilize the K-band luminosity of core helium burning red clump (RC) stars to obtain individual cluster distances and present a preliminary assessment of the structure and geometry of the LMC based on a subset of our data.

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arXiv2004

The IRAC Shallow Survey

The IRAC shallow survey covers 8.5 square degrees in the NOAO Deep Wide-Field Survey in Bootes with 3 or more 30 second exposures per position. An overview of the survey design, reduction, calibration, star-galaxy separation, and initial results is provided. The survey includes approximately 370,000, 280,000, 38,000, and 34,000 sources brighter than the 5 sigma limits of 6.4, 8.8, 51, and 50 microJy at 3.6, 4.5, 5.8, and 8 microns respectively, including some with unusual spectral energy distributions.

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arXiv2003

172 ks Chandra Exposure of the LALA Boötes Field: X-ray Source Catalog

We present an analysis of a deep, 172 ks Chandra observation of the Large Area Lyman Alpha Survey (LALA) Boötes field, obtained with the Advanced CCD Imaging Spectrometer (ACIS-I) on the Chandra X-ray Observatory. This is one of the deepest Chandra images of the extragalactic sky; only the 2 Ms CDF-N and 1 Ms CDF-S are substantially deeper. A total of 168 X-ray sources were detected. The X-ray source counts were derived and compared with those from other Chandra deep surveys; the hard X-ray source density of the LALA Boötes field is 33% higher than that of CDF-S at the flux level of 2.0E-15 ergs/cm^2/s, confirming the field-to-field variances of the hard band source counts reported by previous studies. The deep exposure resolves > 72% of the 2-10 keV X-ray background. Our primary optical data are R-band imaging from NOAO Deep Wide-Field Survey (NDWFS), with limiting magnitude of R = 25.7 (Vega, 3sigma, 4" diameter aperture). We have found optical counterparts for 152 of the 168 Chandra sources (90%). Among the R-band non-detected sources, not more than 11 of them can possibly be at z > 5, based on the hardness ratios of their X-ray emission and nondetections in bluer bands. The majority (~76%) of the X-ray sources are found to have log(f_X/f_R) within 0.0+-1, which are believed to be AGNs.Most of the X-ray faint/optically bright sources (log(f_X/f_R) < -1.0) are optically extended, which are low-z normal galaxies or low luminosity AGNs. There is also a population of sources which are X-ray overluminous for their optical magnitudes (log(f_X/f_R) > 1.0), which are harder in X-ray and are probably obscured AGNs. (abridged)

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