Selection of Four Deep Drilling Fields for the LSST

The LSST Science Council has selected four distant extragalactic survey fields that the project guarantees to observe as Deep Drilling Fields with deeper coverage and more frequent temporal sampling than provided by the standard LSST observing pattern. These four fields are only the first chosen for deep-drilling observations; more such fields will be chosen later.

In addition to executing its 18,000 deg² main survey via its “universal cadence”, the LSST will also intensively observe a set of Deep Drilling Fields. Deeper coverage and more frequent temporal sampling (in at least some of the LSST’s ugrizy filters) will be obtained for the Deep Drilling Fields than for typical points on the sky. The full Deep Drilling Field program will address a broad range of science topics, including Solar System, Galactic, and extragalactic studies. Up to about 10% of the LSST time will be devoted to Deep Drilling Fields and other cadence programs outside the universal cadence. Chapter 2 of the LSST Science book provides additional details.

Science possibilities for the LSST Deep Drilling Fields are currently being investigated by the LSST Deep Drilling Interest Group and the LSST Science Council. The LSST Deep Drilling Interest Group includes more than 60 members of the astronomy and physics communities who are members of LSST Science Collaborations and the LSST Project. Additional members are welcome; those interested should first join one of the LSST Science Collaborations via the proposal process operated by NOAO.

Informed by feedback from the LSST Deep Drilling Interest Group, the LSST Science Council has selected for prompt announcement four distant extragalactic survey fields, each covering approximately 9.6 deg², which the LSST Project will commit to observing as Deep Drilling Fields. These are four well-studied survey fields with substantial existing multiwavelength coverage and other positive attributes. In addition to enabling their primary distant extragalactic science, these fields will enable Solar System and Galactic science as well. The four fields, listed below, are just part of the broader LSST Deep Drilling Field program. There will be additional fields chosen in the future for Solar System, Galactic, and extragalactic studies. In total there may plausibly be 20-40 Deep Drilling Fields to cover all the science topics. The aim will be to have these well distributed across the sky to enable efficient LSST observing.

The LSST Science Council’s motivation for prompt selection of these four distant extragalactic Deep Drilling Fields is one of community service. For example, the Science Council recognizes that space-based multiwavelength observatories have limited lifetimes, and thus it is important to declare a few fields promptly so they can be appropriately observed over the needed approximately 9.6 deg². Similarly, extensive ground-based efforts will be needed to acquire requisite supporting data (e.g., in the near-infrared and with narrow-band filters).

While the locations of these fields have been chosen, many observational details, such as for the best choices of cadence, filter balance, and total time investment, remain to be determined and may vary from field to field. These issues will be considered by the LSST Deep Drilling Interest Group, the LSST Project, and the broader scientific community over the coming years. Constructive feedback on observational details may be sent to lsst-deepdrill@lsstcorp.org.

The table below lists the four selected fields with approximate field center positions. Each field is approximately circular with diameter 3.5 degrees. Some observational dithering will likely be used (both in position angle and boresight location) to fill in CCD gaps, aid with artifact removal, etc. The details of the dithering are yet to be determined.

	ELAIS S1	XMM-LSS	Extended Chandra Deep Field-South	COSMOS
RA 2000	00 37 48	02 22 50	03 32 30	10 00 24
DEC 2000	-44 00 00	-04 45 00	-28 06 00	+02 10 55
Galactic l	311.30	171.20	224.07	236.83
Galactic b	-72.90	-58.77	-54.47	42.09
Ecliptic l	345.97	31.04	40.29	150.70
Ecliptic b	-43.18	-17.90	-45.47	-9.39

Article written by Niel Brandt