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NOAO Newsletter - NOAO Highlights! - June 1999 - Number 58


The NOAO Deep Wide-Field Survey

The NOAO Deep Wide-Field Survey (NDWFS) is a deep optical and near IR (Bw,R,I,J,H,K) imaging survey of 18 square degrees of the sky with the primary goal of studying the evolution of large-scale structure from z ~ 1 to z ~ 4. The survey should also enable investigation of the formation and evolution of the red-envelope galaxy population and the detection of luminous distant star-forming galaxies and quasars.

image
Figure 1: An approximately 40" 40" sub-region of the NDWFS survey (approximately 0.5h50 Mpc on a side for z ~ 3), comprising less than 0.0001% of the survey area, in which several candidate "Bw-drop-outs" can be seen. As seen by comparison to Figure 2, such drop-outs are possibly high redshift (z > 3) galaxies.

Deep large area surveys are now feasible due to the recent development of wide-field optical and IR imagers. The optical imaging for the NDWFS is being done with the new MOSAIC cameras on NOAO's two 4-m telescopes. Each MOSAIC image covers a a 36' 36' field. The IR imaging is being done with the Ohio State/NOAO Imaging Spectrograph (ONIS; DePoy et al. 1999) at the KPNO 2.1-m. Using a two-quadrant InSb Aladdin I array (developed through a joint NOAO/USNO program), this imager provides a 2.9' 5.8' field of view when used at the KPNO 2.1-m telescope. The filters being used are all standard with the exception of the Bw filter (see Figure 2 and the survey web page http://www.noao.edu/noao/noaodeep).

image


Figure 2: The optical filters used in the NOAO Deep Wide-Field Survey, shown superimposed on the spectra of z = 3 and z = 4 star-forming galaxies. The filter transmission includes the quantum efficiency of the MOSAIC CCDs and the throughput of the CTIO prime focus corrector. The KPNO 4-m PF corrector has higher throughput.


        NOAO Deep Wide-Field Survey Planned Detection Limits

                5  Limit                1  Surf. Brightness
                in 2" Aperture           per square arcsec

Bands AB mag. Vega mag. AB mag. Vega mag. Bw 26.6 26.6 29.0 29.0 R 26.0 25.8 28.4 28.2 I 26.0 25.5 28.4 27.9 J 21.0 20.2 23.4 22.6 H 21.0 19.6 23.4 22.0 K 21.4 19.5 23.8 21.9

The optical survey depths (see Table) were selected to allow detection of an L* star-forming galaxy at z > 3.5. The IR imaging depths were selected to detect an "unevolved" L* elliptical galaxy at z = 1.5, and passively evolving luminous systems to z = 2. The planned depth will also permit the study of the Galactic halo stellar populations, the coolest high-latitude white dwarfs to ~ 1.5 kpc, young (bright) field brown dwarfs (like GL229B) to ~ 75 pc (although the survey area is limited for this topic), distant supernovae, and distant radio sources (FIRST Survey data are available for the entire survey area; Becker et al. 1995). The combination of optical and IR imaging will allow the use of photometric redshifts (e.g. Connolly et al. 1995) to identify samples of objects for efficient spectroscopic follow-up.

The optical observations began in 1997 using the commissioning version of the MOSAIC I prime focus imager with engineering grade CCDs at the Mayall 4-m on Kitt Peak and the Big Throughput Camera (Bernstein et al. 1997) at the Blanco 4-m at CTIO. Both cameras provided a large field of view, but due to the lower sensitivity of the engineering grade CCDs in the MOSAIC and the large gaps between the BTC CCDs, observations were limited to only two of the three optical survey bands (Bw and R) and proceeded at a slower rate than is now possible. With the integration of the science grade detectors into MOSAIC I at Kitt Peak and the completion of MOSAIC II for CTIO, the optical portion of the survey has now begun in all three bands. Having recently completed the first year of observations using the MOSAIC I camera with its science grade CCDs, we have started the process of producing combined data sets using the Bw, R, and I band data. As expected from the survey design and the results of similarly deep multi-band observations designed to find high redshift galaxies (e.g. Steidel et al. 1996), the NDWFS is already producing numerous "Bw-drop outs," objects with candidate redshifts between 3-4 (see Figure 1).

The IR observations are also progressing well, although at a much slower rate of sky coverage due to the much smaller field of view of ONIS (or any IR imager) when compared to the MOSAIC cameras. When the upgraded SQIID camera is available (it is currently being upgraded and is expected to be available in 2000), we will be able to simultaneously image in J,H, and K over a 6.5' 6.5' field.

This survey will be valuable in addressing many other problems; we have designed its execution to try and facilitate its use by other researchers with science goals beyond the main focus of the project. We are working toward our first release of an example data set, currently scheduled for as close to the June 1999 AAS meeting as possible. Further details on the survey design (e.g. field locations), updates on the survey progress, and information on how to obtain data when it is released is available or will be posted at http://www.noao.edu/noao/noaodeep/.

plots
Figure 3: The identification of candidate high-z galaxies can be made using in the BwRI and BwRK color-color planes for different (unevolving) galaxy types (solid: Im; short dashed: Sc; dotted: Sb; long dashed: E). The solid triangles are spaced at unit redshift intervals ( z= 0,1,2,3,4). Intergalactic HI absorption was modeled using the Madau et al. (1996) approximation. The R-K color selection clearly separates out the z > 1 elliptical galaxy population, and the 1 < z < 2 red and blue galaxies are unambiguously identified in the lower part of the BwRK color-color diagram. Candidate objects at z > 4 will be identifiable. The final six-band data set should yield accurate photometric redshifts. The panel at right is a color-color plot constructed from a portion (< 0.2) of the survey data for all objects detected in all three of the optical bands (i.e., candidate "drop-outs" are not yet included in this plot).

Buell T. Jannuzi, Arjun Dey (NDWFS PIs)


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