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Sloan Digital Sky Survey
Review of Observing Systems and Survey Operations 

SDSS Science Accomplishments
January - March 2000 
Jim Gunn
April 11, 2000


The big news this quarter is the resumption of data taking after the re-installation and testing of the repaired secondary mirror. Data taking was resumed in February, and several exciting science results were obtained from analysis of the imaging data from the February and March dark runs. This is a tribute both to the performance of the repaired telescope and the fast data processing turnaround. In the first quarter of 2000, the SDSS acquired imaging of 500 square degrees and 10,000 spectra. Many of the results below were presented and discussed at the SDSS projectís biannual Collaboration meeting, held in Seattle in March 2000.


Large Scale Structure

Graduate students Ryan Scranton, Dave Woods (Chicago), Rita Kim and Hiranya Peiris (Princeton) have analyzed the angular cross-correlation function between galaxies and (color-selected) quasars. They find a signal indicative of weak lensing of the quasar population by the large-scale structure of the foreground galaxies. Attempts to normalize the signal using the correlation function of galactic stars revealed the presence of wide binaries in the Galactic stellar distribution, an interesting result in its own right.

Scranton, Woods, Dave Johnston, Andy Connolly (Pittsburgh) and Istvan Szapudi (Durham) have been measuring the angular correlation function of galaxies as a function of magnitude, as well as higher-order statistics. They have shown that systematic effects in these statistics are at an impressively small level for galaxies brighter than r'=21.5, and are preparing a series of papers describing their results.


New high redshift quasars have been found, including a quasar at z = 5.82, the highest redshift object known. This quasar was found by its colors in the March 2000 imaging data by Xiaohui Fan and Michael Strauss (Princeton) and the spectrum measured at the Keck 10 m telescope. The absorption from the Ly-alpha forest is very strong, but residual flux remains blueward of Ly-alpha emission, implying that this redshift is still below the epoch of reionization. Wei Zheng and Zlatan Tsvetanov (JHU) have found three quasars with redshifts in excess of z = 4.7, including an object at z = 5.3. SDSS has now discovered two dozen quasars with redshifts greater than 4.5 and more than 120 with redshifts greater than 3.6.

Fan is completing analysis of the evolution of the quasar luminosity function from z = 3.5 to z = 5. He finds results consistent with conventional wisdom (although with substantially smaller error bars); the number density of quasars drops dramatically over this redshift range. Several papers on this subject are in preparation.

There are roughly 1000 quasars confirmed spectroscopically thus far from the SDSS spectroscopic survey, making it one of the largest such samples yet. Dan vanden Berk (FNAL) has used these data to make a composite average quasar spectrum, with a signal-to-noise ratio of 100 per resolution element. Many faint lines of extremely high ionization elements (up to Fe X) are visible, which will be very useful for constraining models of the central engine.

Clusters of Galaxies

Rita Kim (Princeton), Marc Postman (STScI), Jim Annis (FNAL), Bob Nichol (Carnegie Mellon) and others are carrying out detailed comparisons between cluster catalogs found from the SDSS data using a variety of different methods. A promising new technique, developed by Annis, defines a cluster as a Brightest Cluster Galaxy plus a population of red elliptical galaxies. Finding the ridgeline of ellipticals in a color-magnitude diagram allows an accurate determination of what is essentially a photometric redshift.


David Hogg (IAS), Vijay Narayan and Iskra Strateva (Princeton), in collaboration with Masataka Fukugita and Naoki Yasuda (JPG) have completed an analysis of the bright galaxy counts, from r'=12 to r' = 21 on a common, CCD-based system. The results are consistent with a power law, which calls into doubt recent suggestions that the local galaxy distribution exhibits a hole.

Mariangela Bernardi (UC) and Scott Burles (FNAL) have developed code to measure the velocity dispersion of galaxies from their spectra. They used these results to determine the fundamental plane of elliptical galaxies, based on over 1000 objects. The scatter in the resulting distance indicator is comparable to or better than the best results in the literature; moreover, they are able to determine the fundamental plane in four bands simultaneously.

Michael Blanton (Fermilab) shows that the galaxy luminosity function found by SDSS gives a luminosity density for the Universe about a factor of two higher than previous estimates - this is due to the more complete galaxy fluxes (Petrosian rather than isophotal magnitudes) measured by SDSS. He is studying the dependence of the luminosity function on galaxy type, size, and color.

Tim McKay, Phil Fischer (U. Michigan), and collaborators are continuing their analysis of weak lensing of background galaxies by foreground galaxies, and thus constraining the mass profiles of these galaxies. They are finding that elliptical galaxies show substantially stronger shear; they are more massive by roughly a factor of three. They are measuring the shear around clusters, and are finding a strong effect. Finally, they are beginning to measure the ellipticity of the mass profiles of galaxies; initial results are that these are consistent with the light profiles.


Carbon Stars

The SDSS has spectroscopically identified four faint high latitude carbon stars, two of which at least are high proper motion dwarfs. Matching of SDSS and 2MASS data (from the new 2MASS data release) has produced a further 10 candidates.

RR Lyrae and A Stars

 Two papers on the structure of the Galactic halo have been accepted by the journals. They show complex structure on the halo, including the presence of recognizable tidal remnants, which manifest themselves as clumps in the distribution of stars. One of these studies is based on A stars (Heidi Newberg, RPI, and Brian Yanny, FNAL). The other is based on identifying RR Lyrae stars using their variability on overlap scans (Zeljko Ivezic, undergraduate students Josh Goldston and Kristian Finlator, and Jill Knapp Princeton). Light curves for ten of these stars have been obtained by Bing Chen (JHU) and Kevin Krisciunas and Beth Willman (University of Washington); they have confirmed that they are indeed RR Lyraes.

Brown Dwarfs

The last gap in the spectral sequence from O stars to planets is well on the way to being filled in. Three very red objects discovered in the imaging data from February were observed at UKIRT in March and proved to be the so-called transition objects between spectral types L and T, with methane bands of increasing strength. These objects are brown dwarfs with masses somewhere in the 20 - 50 Jupiter mass range, and the spectra of these and other methane dwarfs tell us what the planets recently discovered around nearby stars are likely to look like. SDSS has by far the best potential of any current or planned project for delineating the details of the brown dwarf spectra sequence and other properties. This work was done by Jill Knapp, Xiaohui Fan, undergraduate Alex McDaniel (Princeton), Dave Golimowski and Todd Henry (JHU), in collaboration with Sandy Leggett (UKIRT) and Tom Geballe (Gemini).


 SDSS has obtained imaging data of the SIRTF quick look fields. These data will be reduced by SDSS and made available to the US community through the SIRTF science center.

 Review of Observing Systems and Survey Operations
Apache Point Observatory
April 25-27, 2000

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