The CFHTLS over the year 2001
CFHLS Forum MegaCam Survey Working Group MegaPrime

December 2001

After the CFHT Board meeting in December 2001, 
the CFHLS becomes the CFHTLS

Summary of principal actions taken 
at the December 12-15, 2001 meeting 
of the Board of Directors 
Data Access 

October 2001

A proposal to the CFHT Scientific Advisory Council

525 nights on 5 years with MegaPrime/MegaCam for a Legacy Survey in three components:
Very Wide Shallow, Wide Synoptic, Deep Synoptic.

CFHLS at a Glance
The CFHLS proposal - Version 2.3 (Oct. 19, 2001)
ps  (1025kB)
ps.gz  (327kB)
 pdf  (768kB)
Appendix on SNe (Oct. 29, 2001)
ps (619kB)
pdf (493kB)

Three surveys... from the solar system to the remote universe

A very wide shallow survey

Covering 5000 square degrees in two filters on the ecliptic, the survey will be made of sequences of three 2mn r' exposures (r'=24.1 on a single exposure, 24.7 if stacked) and one 2mn exposure in z', reaching z' = 22.0. About half of the fields will be selected so that they coincide with regions of star formation and the Pleiades and Hyades young open clusters. The observations will be sequenced on a night in r' over at least three hours with the z' observation the following day. This survey will provide an unprecedented sampling of our galaxy and a unique exploration of the ecliptic, leading to more than 2000 Kuiper Belt Object discoveries, including a few Neptune-like objects (if any), and to a first sampling to such a depth on such a field of the Main Belt and Near Earth asteroids. In the star-forming regions and young Pleiades and Hyades clusters, hundreds of brown dwarfs with ages between 1 Myr and 600 Myr and dozens of edge-on disks will be discovered. This survey will provide the most numerous sample of objects for studies of brown dwarf formation and evolution, and of the evolution and structure of circumstellar disks around pre-main sequence stars. 

A wide synoptic survey

Covering 208 square degrees in four patches, three of square degrees and one of , through the whole filter set (u*g'r'i'z') down to i'=24.5, this survey will allow the study of the large scale structures and matter distribution in the universe, through weak lensing and galaxy distribution. Thanks to the sequencing of the r' observations in two phases, early in the survey and three years later, proper motions will be available for galactic structure studies. All fields will be used for stellar population investigations and searched for moving objects and transient phenomena. 

A deep synoptic survey

Covering 4 square degrees in four MegaCam fields through the whole filter set (u*g'r'i'z') with integration times ranging from 33 to 132 hours depending on the filter (u*:33 g':33, r':66, i':132, z':66), this survey will be sequenced over 5 years at an average rate of 5.25 nights a dark run for 5 runs in a row each year on each field. Aimed mainly at the detection and monitoring of as many as 2000 type I SNe and at the study of the galaxy distribution on images reaching r' 28, this survey will allow a better understanding of the early universe as well as a determination of the dark energy parameter with an unprecedented accuracy. The galaxies and quasars will allow to build statistical samples bringing strong constraints on galaxy evolution and global star formation history. Thanks to the sequencing, transient phenomena and moving objects will be detected and followed up, providing a unique monitoring over five years of fields at various galactic and ecliptic latitudes. 

The CFHLS at a glance

Survey  area  filters  depth  total  observing  Total
Location  deg x deg  S/N = 5 -1.15" ap.  exp time  strategy  nights 
(tentative)  point source 
Very Wide 
Ecliptic  5000  r'  24.1 (2mn)  3x2mn  spread over 2 hrs 
+/- 7 deg  z' 22.0  2mn  2 day after r' obs. 127 
Wide Synoptic 
02:20 -5 (XMM)  10x10  + 3(6x6) u*  25.5  6000 s 
10:00 0  g'  26.5  2500 s 
14:00 +52  r'  25.7  2000 s  1000 s early 
(Groth Strip)  1000 s 3yrs later 
22:00 0  i'  25.5  4300 s 
z'  24.0  7200 s  196
Deep Synoptic 
A 1x1 subset  4(1x1)  u* 27  33 hr  5.25 nights 
of each of the  g' 28.4  33 hr  per run 
fields of the  r' 28  66 hr  5 runs a year 
Wide Synoptic  i' 27.8 132 hr  for each field 
z' 26  66 hr  202

- Fields for the Wide Synoptic survey have been selected for their interest (XMM LSS field and Groth Strip) and the fact that they allow a spread of the observations all along the year. Other choices can be made, though the 10x10 patch makes really sense on the XMM field.

- The expected performances reached by MegaPrime, expressed in the Vega system, have been computed by various groups using the CFH12K performances measured on the sky and the characteristics of the various components of MegaPrime, from the wide field corrector to the CCDs of MegaCam. They are summarized in the following table: 

  u* g' r' i' z'
limiting magnitudes (Vega)          
30mn - 0.8" seeing - S/N=5 - 1.16" ap. - point source 24.9 26.4 25.5 24.9 23.4
30mn - 0.8" seeing - S/N=5  - 3" ap. - extended source  23.9 25.4 24.5 23.9 22.4
- The CFHLS would mainly need a seeing of 0.9" or better, which is anticipated to happen 85% of the clear observing time. 

Note: One nights in queued service observing mode is equivalent to 6.5 hours of observing time for science programs 

Comments welcome...