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Sheldon E.S.,Brookhaven National Laboratory | Cunha C.E.,University of Michigan | Cunha C.E.,Kavli Institute for Particle Astrophysics and Cosmology | Mandelbaum R.,Princeton University | And 3 more authors.
Astrophysical Journal, Supplement Series | Year: 2012

We present redshift probability distributions for galaxies in the Sloan Digital Sky Survey (SDSS) Data Release 8 imaging data. We used the nearest-neighbor weighting algorithm to derive the ensemble redshift distribution N(z), and individual redshift probability distributions P(z) for galaxies with r < 21.8 and u < 29.0. As part of this technique, we calculated weights for a set of training galaxies with known redshifts such that their density distribution in five-dimensional color-magnitude space was proportional to that of the photometry-only sample, producing a nearly fair sample in that space. We estimated the ensemble N(z) of the photometric sample by constructing a weighted histogram of the training-set redshifts. We derived P(z)'s for individual objects by using training-set objects from the local color-magnitude space around each photometric object. Using the P(z) for each galaxy can reduce the statistical error in measurements that depend on the redshifts of individual galaxies. The spectroscopic training sample is substantially larger than that used for the DR7 release. The newly added PRIMUS catalog is now the most important training set used in this analysis by a wide margin. We expect the primary sources of error in the N(z) reconstruction to be sample variance and spectroscopic failures: The training sets are drawn from relatively small volumes of space, and some samples have large incompleteness. Using simulations we estimated the uncertainty in N(z) due to sample variance at a given redshift to be 10%-15%. The uncertainty on calculations incorporating N(z) or P(z) depends on how they are used; we discuss the case of weak lensing measurements. The P(z) catalog is publicly available from the SDSS Web site. © © 2012. The American Astronomical Society. All rights reserved. Source


Tal T.,Yale University | Wake D.A.,Yale University | Van Dokkum P.G.,Yale University | Van Den Bosch F.C.,Yale University | And 3 more authors.
Astrophysical Journal | Year: 2012

We present a statistical study of the luminosity functions of galaxies surrounding luminous red galaxies (LRGs) at average redshifts 〈z〉 = 0.34 and 〈z〉 = 0.65. The luminosity functions are derived by extracting source photometry around more than 40,000 LRGs and subtracting foreground and background contamination using randomly selected control fields. We show that at both studied redshifts the average luminosity functions of the LRGs and their satellite galaxies are poorly fitted by a Schechter function due to a luminosity gap between the centrals and their most luminous satellites. We utilize a two-component fit of a Schechter function plus a log-normal distribution to demonstrate that LRGs are typically brighter than their most luminous satellite by roughly 1.3mag. This luminosity gap implies that interactions within LRG environments are typically restricted to minor mergers with mass ratios of 1:4 or lower. The luminosity functions further imply that roughly 35% of the mass in the environment is locked in the LRG itself, supporting the idea that mass growth through major mergers within the environment is unlikely. Lastly, we show that the luminosity gap may be at least partially explained by the selection of LRGs as the gap can be reproduced by sparsely sampling a Schechter function. In that case LRGs may represent only a small fraction of central galaxies in similar mass halos. © 2012. The American Astronomical Society. All rights reserved. Source


Murphy T.W.,University of California at San Diego | McMillan R.J.,Apache Point Observatory | Johnson N.H.,University of California at San Diego | Goodrow S.D.,University of California at San Diego
Icarus | Year: 2014

Laser ranging measurements during the total lunar eclipse on 2010 December 21 verify previously suspected thermal lensing in the retroreflectors left on the lunar surface by the Apollo astronauts. Signal levels during the eclipse far exceeded those historically seen at full moon, and varied over an order of magnitude as the eclipse progressed. These variations can be understood via a straightforward thermal scenario involving solar absorption by a ~50% covering of dust that has accumulated on the front surfaces of the reflectors. The same mechanism can explain the long-term degradation of signal from the reflectors as well as the acute signal deficit observed near full moon. © 2013 Elsevier Inc. Source


Murphy T.W.,University of California at San Diego | Adelberger E.G.,University of Washington | Battat J.B.R.,Bryn Mawr College | Hoyle C.D.,Humboldt State University | And 4 more authors.
Classical and Quantum Gravity | Year: 2012

Lunar laser ranging (LLR) has for decades stood at the forefront of tests of gravitational physics, including tests of the equivalence principle (EP). Current LLR results on the EP achieve a sensitivity of Δa/a 10 13 based on few-centimeter data/model fidelity. A recent push in LLR, called APOLLO (the Apache Point Observatory Lunar Laser-ranging Operation) produces millimeter-quality data. This paper demonstrates the few-millimeter range precision achieved by APOLLO, leading to an expectation that LLR will be able to extend EP sensitivity by an order-of-magnitude to Δa/a 10 14, once modeling efforts improve to this level. © 2012 IOP Publishing Ltd. Source


News Article
Site: http://www.rdmag.com/rss-feeds/all/rss.xml/all

How did the Milky Way Galaxy grow? Astronomers from the Sloan Digital Sky Survey (SDSS) have answered that question with the first map charting the growth of our home galaxy. The results were presented last week at the 227th Meeting of the American Astronomical Society. The map, which utilizes the ages of more than 70,000 red giant stars, spans to halfway across the galaxy, around 50,000 light-years away. “Close to the center of our galaxy, we see old stars that were formed when it was young and small. Farther out, we see young stars. We conclude that our galaxy grew up by growing out,” said Melissa Ness, of the Max Planck Institute for Astronomy. “To see this, we needed an age map spanning large distances, and that’s what this new discovery gives us.” First, Ness and colleagues used spectra taken from SDSS’s Apache Point Observatory Galaxy Evolution Experiment (APOGEE), which took high-quality spectra for 300 stars simultaneously over a large swath of sky. “Seeing so many stars at once means getting spectra of 70,000 red giants is actually possible with a single telescope in a few years’ time,” said Univ. of Virginia’s Steve Majewski, the principal investigator of the APOGEE survey. In a separate study, Marie Martig, also of the Max Planck Institute for Astronomy, used mass and age data of 2,000 stars observed by NASA’s Kepler, and compared the values to the respective stars’ carbon and nitrogen levels obtained by APOGEE, according to Space.com. The relationship gleaned was then applied to determine the mass of the 70,000 red giants APOGEE studied. “After combining information from the APOGEE spectra and Kepler light curves, the researchers could then apply their methods to measure ages for all 70,000 red giant stars,” according to SDSS. “Finding masses of red giants has historically been very difficult, but surveys of the galaxy have made new, revolutionary techniques possible,” said Martig.

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