Why this field?
The Chandra Deep Field South has been extensively studied at many wavelengths. A good discussion of its initial selection over other regions in the sky may be found here. Chandra observed the original field in one single pointing for one million seconds, with the single pointing limiting the total area covered to less than one-tenth of a square degree. To increase the area, and thereby the number of objects included, the Extended Chandra Deep Field South reobserved the region using a grid of four separate pointings each of 250 thousand seconds duration. Hereafter, we will use "CDFS" when referring to the smaller central area and "ECDFS" when the larger area is explored. Recently (late 2007), the initial Chandra pointing of the CDF-S was re-observed for an additional one million seconds to produce a deep field consistent to the northern Chandra deep field. There are numerous programs and surveys spanning the entire electromagnetic spectrum and directed at the CDFS and ECDFS. Many of these are linked in the Where can I find other information on the ECDFS? portion of this FAQ.
There are other deep fields with comparable ancillary datasets, including some in the Northern sky and thus more readily accessible to the VLA. So again, why this field? We believe that the ECDFS is the most important deep field for future study. ALMA, the Atacama Large Millimeter Array, will be the preeminent instrument for the study of star formation and active galactic nuclei in the high redshift universe. From its location in Chile, ALMA will be well positioned to study the ECDFS. Thus, we expect the ECDFS to be the key link between our current understanding of the high-redshift universe as gleaned from deep field observations and future observations with ALMA.
When were the observations?
The observations occurred during Summer 2007, when the VLA was in its largest configuration (A array). Since the ECDFS is located in the Southern sky, it is only observable by the VLA for a small portion of the day. We observed in five-hour blocks when the ECDFS was at its highest point in the sky, which corresponded to mornings for New Mexico. With 240 hours of total time, this meant the observations were spread over 48 days beginning in June 2007 and running through September 2007 (you can see the schedule here). In actuality, more than 48 days were scheduled due to unforeseen complications. Such a large commitment of VLA time was made thanks to the selection of this program through the VLA Large Proposal process.
How good are the data?
The program had 240 hours of time scheduled for observations of the ECDFS, including observation of calibration sources. The observing time was spread evenly across six pointings in a hexagonal grid, which produces a fairly uniform sensitivity map covering the full roughly 0.25 square degree area of the ECDFS. Even with the VLA's lessened sensitivity at 1.4GHz while pointing at low elevations, this will ultimately produce an output map with an rms sensitivity of under 7 microJanskies per beam, where the beam size will be about 2 arcseconds. The first data release image achieves an rms sensitivity of around 8 microJanskies per beam, giving us confidence that the intended sensitivity will be obtained in the second data release.
What sorts of objects will be detected?
The radio data will detect galaxies which either are actively forming stars or have an active supermassive black hole at their centers (or both). The survey limit was carefully selected to complement the data at other wavelengths in detecting and assessing such galaxies. There is a well-known correlation between infrared and radio emission for star-forming galaxies in the local universe, and should this correlation hold at high redshift the VLA data will detect all star-forming galaxies identified in a new Spitzer Legacy program (recently named "FIDEL" in the spirit of cool acronyms). Similarly, based on the results of other radio and X-ray investigations, the ECDFS radio data should detect the majority of X-ray sources identified from the Chandra ECDFS X-ray data. Most of these will have active black holes in their centers, although some will also be star-forming galaxies.
When will we see the data?
There is a lot of painstaking detail that goes into deep L-band data reduction, but we recognize that the data will be of great interest to the astronomy community. We will therefore release the data in stages. The first data release was summarized at the 211th AAS meeting in Austin, Texas in January 2008 and is available through our Data page. It represents a best first pass at the full reductions and a conservative source catalog. Achieving the best sensitivity allowed by the data requires more attention to fine details, which basically amounts to more careful imaging of the data in smaller pieces instead of all at once. These more thorough reductions should improve the sensitivity by about 10%, and will be released in January 2009.
Where can I find other information on the ECDFS?
In addition to the Chandra X-ray data (CDFS and ECDFS), the ECDFS has been observed at a host of wavelengths. In the ultraviolet, it was observed by the GALEX satellite as part of both its ultradeep imaging survey and deep spectroscopic survey. The Hubble Space Telescope and its Advanced Camera for Surveys has observed the entire ECDFS to varying depths. The deepest optical image ever obtained, the Hubble Ultradeep Field is a small portion of the CDFS. A larger area which covers most of the CDFS is part of the optical portion of the GOODS project, and the GEMS (Galaxy Evolution from Morphology and SEDs) project extends the HST ACS coverage to nearly canvas the full ECDFS. There are also numerous ground-based optical and near-infrared imaging campaigns, and the COMBO-17 (Classifying Objects through Medium-Band Observations, a spectrophotometric 17-filter survey) program includes the ECDFS among its fields. Optical spectroscopy of CDFS galaxies, many of which were collected using the VLT, are available and necessary for determining the redshifts (and hence distances) of detected objects (alternate site through VIMOS VLT Deep Survey). Finally, the other main component of the GOODS program is infrared data obtained using Spitzer. The main infrared data collected for GOODS using IRAC (images at wavelengths of 3.6, 4.5, 5.8, and 8.0 microns) and MIPS (images at wavelengths of 24, 70, and 160 microns) may be found here. In addition, new Spitzer Legacy programs provide deeper IRAC (SIMPLE, for Spitzer IRAC/MUSYC Public Legacy in ECDFS) and MIPS (FIDEL, for Far-Infrared Deep Extragalactic Legacy) images over nearly the entire ECDFS area. Finally, the ECDFS will be the target of programs at sub-millimeter wavelengths. It is among the regions to be covered by the SCUBA-2 Cosmology Legacy Survey and will be observed with LABOCA.
A nifty visual representation of the areas covered by most of the various multiwavelength programs may be found here.
Where can I find prior press releases and images?
The Chandra website has a Photo Album for the CDFS, which includes images and the original press release from the X-ray observations. Subsequent press releases and images include one from ESO on ground-based optical follow-up, and several from the Hubblesite on HST and Spitzer observations from the GOODS project.
Why no cool acronym?
Every big-time program you've ever heard of has a cool acronym, like GOODS (for Great Observatories Origins Deep Survey) or COSMOS (for Cosmological Evolution Survey). So what gives? Well, we tried but ran into a lot of problems. You see, we're already using VLA for Very Large Array, and even that's a bit shakey right now since the VLA is in the midst of a facelift and becoming the EVLA ("Expanded" VLA). With just under half the VLA dishes converted to EVLA at the time of our observations, should we use "V", or "E", or the full acronyms themselves? There aren't a lot of neat words using the sequence "EVLA" (other than "KEVLAR" but we couldn't make that work with the rest of the program). Then we've got similar issues with the CDFS being extended to the ECDFS - do we use the "C", the "E", or the whole thing? The best we could do and keep things short was "ELSE", for EVLA L-band Survey of the ECDFS, but we kind of find nested acronyms repulsive. So we've just told it like it is and gone with the dry "VLA 1.4GHz Survey of the Extended Chandra Deep Field South".
Want to know more about radio astronomy?
A great place to start is the NRAO What is Radio Astronomy page. Links from that page can take you to pages discussing the history of radio astronomy, how radio telescopes work, and other useful information. You might also check out the Image Gallery to find pretty pictures of radio sources and telescopes.