The CFHTLS over the year
2001
December 2001
After the CFHT Board meeting in December 2001,
the CFHLS becomes
the CFHTLS
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.
The CFHLS proposal - Version 2.3 (Oct. 19, 2001)
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Appendix on SNe (Oct. 29, 2001)
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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 |