This appendix contains a brief discussion of some of the ongoing and planned sky surveys in various wavelength bands, in order to place the SDSS in the context of major parallel efforts in observational cosmology. Much of this work has been mentioned already in the body of the proposal as it relates to the planning for the SDSS. First we discuss imaging surveys at optical and other wavelengths; these now cover essentially the entire electromagnetic spectrum with few gaps (cf., McLean 1997 for an excellent overview of the whole field). Our preparation for the SDSS includes an effort to get these surveys on line, for several purposes. First, the image processing software needs to be alerted if an object that will cause the data processing difficulty (say, a globular cluster) is in the field. Second, the efficient discovery of unusual objects will be greatly aided if the software can immediately access information at other wavelengths. Third, comparison of the diffuse emission found in other bands with results from the SDSS can tell us much about the physical mechanism of that emission (this is relevant in particular in comparing the extended emission at far-infrared wavelengths with the reddening map to be produced by the SDSS). Finally, and perhaps most important, we will extract atlas images not only at the positions where objects are found in the SDSS, but also at the positions of sources found at other wavelengths. Thus we will have a complete set of postage stamp images in five colors for every one of (for example) the ROSAT sources, whether or not the data reduction software finds an optical object there. This will allow us to put upper limits on optical emission corresponding to a source in another waveband, or pull a weak source out of the noise, given that we know where to look for it.
The second part of this brief summary contains a discussion of current and planned redshift surveys. Of particular importance here are comparisons with very deep redshift surveys where we can hope to see evolutionary effects in the comparison of the two samples.
The venerable Palomar Observatory Sky Survey (POSS) has been available to the astronomical community for over 35 years, and its counterpart, the SERC survey carried out at ESO in the South, for fifteen years. Only recently, however, with the advent of fast photoelectric scanners and high-speed computers, has it been possible to digitize the plates and process the resulting object list electronically. In addition, a second generation POSS survey is currently in progress with superior plate material (e.g. Reid and Djorgovski 1993), and the Southern survey is being repeated as well. The two POSS surveys give V-R colors to V = 19.5 and proper motions for stars over the 30-year baseline between the two surveys.
A number of groups are digitizing the POSS and related surveys:
The Hipparcos satellite (Perryman et al. 1992) is doing astrometry over the entire sky for 118,000 stars, with accuracy of 2-4 milliarcseconds. This survey will be important for the final calibration of the SDSS astrometry (see Chapter 10).
There are a number of surveys of the radio sky, dating back to the first Cambridge surveys of such great importance to the study of distant radio galaxies and quasars. More recently, J.J. Condon (NRAO) and collaborators have carried out a number of surveys at 6 and 20 cm using the Green Bank and Parkes radio telescopes (Gregory and Condon 1991; Griffith and Wright 1993); these surveys have a typical limit of 40 mJy, and a positional accuracy of ~ 20" at the survey limit.
The National Radio Astronomy Observatory has begun two major continuum sky surveys at lambda = 20 cm using the VLA. Condon is leading a team to carry out a survey of the entire sky north of delta = -42° using the `D' (most compact) configuration, which will have an angular resolution of about 54" and a 5 sigma limit of 2 mJy (Condon 1993). The positional accuracy at the survey limit is expected to be about 5" r.m.s. In parallel with this effort, a group led by D. Helfand (Columbia), R. White (STScI) and R. Becker (UC Davis) (Becker et al. 1995) is using the `B' array to survey the North Galactic Pole, in a region explicitly chosen to coincide with the footprint of the SDSS, with positional accuracy better than 1" at the survey limit of 1 mJy. As of this writing, this FIRST survey (Faint Images of the Radio Sky at Twenty centimeters) has been granted time to finish half of the SDSS Northern survey area, 5000 square degrees, plus time to survey the Southern stripe as well. The sensitivity of these surveys is such that they detect the radio emission from Seyfert nuclei, starburst galaxies and spiral galaxy disks as well as the much more luminous radio quasars and radio galaxies. The positional accuracy of the FIRST survey is such as to make optical identification from the SDSS straightforward. The science expected from comparisons of these surveys and the SDSS include the tying together of the radio and optical astrometric reference frames, the identification of a wide range of radio sources, the study of large-scale structure of radio sources, the relation between radio emission and galaxy morphological and photometric properties in the optical, and the radio luminosity functions of quasars, radio galaxies, Seyferts and normal galaxies. As we discuss in Sections 3.8 and Sections 3.3, we will spectroscopically target stellar objects with radio identifications from the FIRST survey to augment our quasar selection criteria (cf. Gregg et al. 1996), and to search serendipitously for other classes of rare radio sources.
Two HI surveys of the entire sky visible from the northern hemisphere have recently been made by Stark et al. (1992) with a spatial resolution of 2° and by D. Hartmann and W. B. Burton (see Hartmann 1994) with a resolution of 30' . Both of these surveys are free from side-lobe contamination from the Galactic plane. The comparison of these surveys with the galaxy count and extinction data from the SDSS will yield information on the gas to dust ratio and the structure of the high latitude interstellar medium.
The COBE all-sky maps of the diffuse emission at wavelengths from 2 µm to 2 mm have now been released. The comparison of the cosmological fluctuations seen by COBE to those seen by the SDSS on large scales (cf. section 3.1.3) is one of the major scientific goals of the SDSS. Comparison of the diffuse Galactic dust emission in the far infrared with the extinction maps from the SDSS will tell us much about the physical properties of interstellar dust.
The IRAS Point Source Catalog, and the more recent IRAS Faint Source Catalogue, have revolutionized many areas of astronomy. The comparison of these data with optical photometry from the SDSS should be invaluable for studies of the ISM content and current star formation of galaxies as a function of environment and morphology; of the emission mechanisms of quasars; and of the cool star luminosity function.
A consortium organized by S. G. Kleinmann and M. Skrutskie (University of Massachusetts) plans to image the sky in the near-infrared bands JHK' using two dedicated 1.3-m telescopes, one in each hemisphere, and an array of 256 x 256 detectors, in a program called the Two Micron All Sky Survey (2MASS); see Section 2.3. The images will have a pixel size of 2.0 arcsecond, and will go to K' = 14.5 for point sources. The survey is scheduled to start operations in the Northern hemisphere in mid-1997 and in the Southern hemisphere in mid-1998. The main scientific drivers for this program are to study Galactic structure, and to provide a uniform galaxy catalog over the entire sky essentially free from selection effects, even at low Galactic latitudes. The DENIS project, described briefly by Harmon and Mamon (1993) is a competing survey in IJK' in the Southern hemisphere, which will go to a comparable depth. The I band will be used to give morphological information and to allow accurate star-galaxy separation to the survey limit. A deeper survey (to 16.5 in K' ) is planned at I,K,L' for a smaller region of the sky by a group at the University of Kyoto and at the University of Hawai`i, led by T. Maihara (see Maihara et al. 1993; for related work, see also Gardner et al. 1996). The addition of the z' band to the SDSS filter complement means that the combination of the SDSS and 2MASS and Kyoto-Hawai`i surveys gives continuous coverage from the UV through 2 µm . The scientific returns can be expected to include the measurement of the bolometric luminosities of large numbers of galaxies and stars, deep galaxy counts, identification of candidate high-redshift quasars and brown dwarf stars, and extension of the study of dust into the near infrared.
At X-ray wavelengths, the current ROSAT All Sky Survey will result in the detection of about 105 X-ray sources to a limiting flux of 5 x 10-13 erg s-1 cm-2 in the band from 0.5 to 2.5 keV. The optical identification of ROSAT sources will be one of the great scientific legacies of the SDSS; we discuss this in detail in Section 2.1.
A number of groups are carrying out redshift surveys that cover large solid angles. These fall into two categories: those attempting to cover the entire sky, and those covering a smaller solid angle. Recent reviews of large-angle redshift surveys include those by Strauss and Willick (1995), Strauss (1996), Guzzo (1996), and Colless (1996).
Two major redshift surveys have been performed of galaxies selected from the IRAS Point Source Catalog. This provides a uniform photometric data base over most of the sky, which is immune to effects of Galactic absorption. Strauss et al. (1990, 1992) and Fisher et al. (1995) have completed a redshift survey of 5313 galaxies complete to 1.2 Jy at 60 µm over 88% of the sky; some of the scientific results of the survey are summarized by Strauss and Willick (1995). Rowan-Robinson et al. (1990) have finished a redshift survey of one in six IRAS galaxies over 82% of the sky to a flux limit of 0.6 Jy, ~ 2387 galaxies in all, and have recently finished measuring redshifts for all ~ 15,000 IRAS galaxies to that flux limit. Details may be found at the following web site: http:/www-astro.physics.ox.ac.uk/ ~ wjs/pscz.html.
da Costa et al. (1989) are completing a diameter-limited redshift survey of optically selected galaxies in the North and South Galactic cap, with a depth similar to that of the CfA survey by Huchra et al. (1983) in the North alone. Santiago et al. (1995, 1996) have a parallel effort to obtain redshifts for all galaxies with B <= 14.5 and |b| > 20° over the sky, a sample consisting of roughly 7000 galaxies.
The Center for Astrophysics team of Geller and Huchra (1990) have almost completed measuring redshifts of the ~ 15,000 Zwicky (1961--1968) galaxies with Blim ~ 15.5 at high Galactic latitudes. da Costa et al. (1994) are doing a parallel survey in the Southern hemisphere to a similar depth.
The APM photometric survey described above has been supplemented by a sparse (one galaxy in 20) redshift survey to bJ = 17.15 with the Anglo-Australian Telescope, consisting of 1787 galaxies, and have used it to measure the amplitude of galaxy fluctuations on scales of 50 h-1 Mpc (Loveday et al. 1992; Loveday 1996).
Sky coverage of various redshift surveys (Strauss 1996)
Geometry of current and planned redshift surveys On smaller angular scales, but going deeper, Shectman et al. (1996) have measured redshifts in the magnitude interval 15.0 <= r <= 17.5 over a series of six ~ 90° x 1.5° stripes on the sky, using a multi-object fiber spectrograph on the 2.5m Du Pont telescope at Las Campanas, Chile. Galaxies are selected from photometry derived from CCD drift scans using the 1-m Swope telescope. The sampling is not uniform; the sampling rate is simply the ratio of number of fibers available in any given field to the number of galaxies to their magnitude limit. This survey covers a total of ~ 700 square degrees, and contains 26,418 redshifts. First scientific results on galaxy clustering from this survey include the power spectrum analyses of Landy et al. (1996) and Lin et al. (1996). A 400-fiber multi-object spectrograph with a two-degree field of view (thus the name 2dF) has been built for the AAT by Taylor (1995) and collaborators. It is undergoing final commissioning at this writing, and a collaboration of British and Australian astronomers are planning to use it for a redshift survey of galaxies selected from the APM galaxy catalog (Maddox et al. 1990a); thus, unlike the SDSS, the 2dF survey does not attempt to create a galaxy catalog from scratch. The survey will cover 1700 square degrees, and will obtain redshifts of galaxies to B = 19.7 (This is slightly deeper than the SDSS, given typical galaxy colors of r' - B ~ -1 ), as measured by the APM. It will consist of three parts, contiguous strips of 75°x12.5° and 65°x7.5° in the Southern and Northern Galactic Caps, respectively, and 100 random circular fields of radius 2° over the Southern Galactic Cap. The survey will contain roughly 250,000 galaxies, and will take roughly 90 nights of AAT dark time. The survey geometry is chosen to maximize sensitivity to large-scale structure; indeed, the 100 random fields give a variety of baselines to probe the power spectrum on the largest scales. The science goals of the 2dF survey are similar to those of the large-scale structure goals of the SDSS, although the two surveys differ on the approach to galaxy catalogs and target selection, the sky coverage, the depth of the survey, and other details. Figure A.1 shows the sky distributions of several of the deep surveys discussed here: the SDSS, 2dF, the Las Campanas Redshift Survey (LCRS), and the ESP (Vettolani et al. 1995). Figure A.2 shows the geometry and depth of these surveys.
A number of redshift surveys of faint galaxies are being planned on large telescopes. These will probe appreciably deeper than the SDSS redshift survey, albeit over a much smaller area of sky, and thus will provide an important complement to the SDSS, in measuring evolution at moderate redshifts ( z ~ 0.5 ) and allowing the calibration of the color-redshift relations to the limits of the SDSS photometric sample.
There will be an extension to the 2dF survey done to measure redshifts for ~ 6000 galaxies to R = 21 to extend large-scale structure studies to redshifts of 0.3. The SDSS will be able to do such studies using the luminous red elliptical sample mentioned in Section 3.2, as well as from the photometric sample (which of course extends quite a bit fainter than the spectroscopic sample).
The Deep Extragalactic Evolutionary Probe (DEEP) consortium headed by G. Illingworth (UC Santa Cruz) plans to use the Keck telescopes for pencil-beam surveys to B = 25.4 (Mould 1993). The project plans to build a new multislit spectrograph, and to perform high signal-to-noise spectroscopy for a total of 15,000 faint galaxies over a period of ~ 5 years. Two members of the SDSS scientific group (R. Kron and A. Szalay) are also part of the DEEP project. A taste of the type of science that can be done with this survey is given in Koo et al. (1996) and Cowie et al. (1996). Comparison of the distant large scale structure revealed by DEEP with the nearby structure revealed by the SDSS will allow us to begin to study the evolution of cosmological structure over a fair fraction of a Hubble time. This survey complements the SDSS beautifully: the SDSS will allow a complete characterization of the properties and large-scale distribution of galaxies at the present, while DEEP will measure evolutionary effects in the properties of individual galaxies, and of large-scale structure.
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