VISTA HEMISPHERE SURVEY

Planning Meeting; Monday, 23rd Jan, 2006

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Meeting Location:

Institute of Astronomy, Cambridge

AM: Hoyle Building Commitee Room

PM: Earth Sciences Meeting Room

DRAFT AGENDA

10:00  Coffee
10:30  Introduction, general goals (Lawrence)
10:45  ESO proposal process (Emerson)
11:00  VISTA performance (Sutherland)
11:15  Possible filter/depth combinations (McMahon)
11:30  Update from GPS planning meeting (Lucas)
11:45  Other group updates (various)
12:00  General discussion

13:00  Lunch

14:00  Science goals - various 10 min contbns (TBD)
15:00  Discussion
16:00  Next steps (Lawrence)
16:30  End

TALKS and OTHER MATERIAL

• Lawrence ppt talk
• Presentation on Magnitude limits and Overheads(McMahon)(ppt)(pdf)
• davies-vista_prop.doc:
• smith-email.pdf:
• Shanks-email.pdf:

NOTES FROM MEETING

KEY ACTIONS and AGREEMENTS

ACTION :   JPE to find out about VLT time deal
ACTION :   Will to finalise overheads. 
ACTION :   Richard to upload model results
DECISION : Use standard 60sec 2 jitter block unless science case argues otherwise.
ACTION :   Richard to update with new ETC values when available.
DECISION : GP Survey to stay independent but keep strong cross-links and joint planning as far as possible.
ACTION :   Simon Hodgkin to develop brown dwarf science case.
ACTION :   Andy to contact Alan Fitzsimmons to ask for solar system science input.
ACTION :   Naylor/Emerson and others to quantify the need for quasi-simultaneous multi-band photometry.
ACTION :   Richard McM to develop the quasar science case.
ACTION :   Richard and Steve Warren and others to conclude debate on Y/Z depth and make recommendation
ACTION :   Mark W. to determine PM precision for baseline line survey parameters. 
ACTION :   All to send AL or RM suggestions for Euro names
ACTION :   All to consider developing science themes
ACTION :   Andy to email UKIDSS consortium to attract attention to VHS pages.
ACTION :   Andy, Richard and others to construct short "position paper" 
           (to avoid repeating all the same arguments !)

NOTES FROM TALKS

Andy Lawrence : Introduction

Talk attached to wiki page. Main goals of meeting today to be looking at elements of science case; design and strategy; relation to Galactic Plane Survey; and discussion on how to form a Europe-wide consortium and start writing the science case. We should decide a basic standard "shallow survey design" aimed at 50% efficiency, and then make scientific arguments to vary from this. Science case elements divided into a few broad kinds - Legacy; Galactic Structure; Cosmic Structure; very rare objects; sample limited science; and efficient use of observing conditions.

Jim Emerson : Process

PSP has same chair as VST, and 8 members - 4 nom by ESO, 4 by VEB. Deadline is March 15th; there is a standard TeX template, and an Exposure Time Calculator (ETC). There are 236 nts/yr available for public surveys unless Chile chips in. Politically, must be seen to be feeding VLTs - eg don't stray too far to North - and counterparts of KIDS, ATLAS, and VPHAS must have a head start. (Questions about whether teams get VLT time). We should assume 10 hr nts in winter and 8hrs in summer.

ACTION : JPE to find out about VLT time deal

Will Sutherland : Performance issues

Sky limited time (10 x sky) 1 sec HK, 5 sec J, and 20 sec Y so these set minimum sensible individual exposures. Efficiency set by overheads, eg 3 sec between jitters, 6 sec between pawprints. With 48 sec per star, get net speed 90 nts/hemisphere/band. Filter changes take 30-60 sec therefore do a few tiles before change - evey 15-20 mins say - then repeat tiles to make an OB. (Will seemed to have more optimistic overheads than the ETC).

ACTION : Will to finalise overheads

Richard McMahon : Depth/Area tradeoffs

Ran the ETC many times with various parameters. (Result will be uploaded on the wiki). Speeds were broadly comparable to WFCAM but slower at K as expected. Efficiency is never better than 80%. The knee in efficiency is somewhere around 40-60 sec total exposure, depending somewhat on the pattern of observation. We decide on 60sec sky-exposures as our basic standard (each exposure 30s; 2 jitters at each posn; 6 paw prints per tile, overlapping to double the exposure). This has 49% efficiency. Note YZ needs darker lunar sky than JHK; this argues to break these apart. To decide survey speed assume we use 60-80% seeing deciles. This gives us expected 50 nts/year. We can use thin cloud but not thick.

Note: as noted in the meeting the H limit presented looked erroneous. RGM subsequently identified that an error had been made in the H Vega column due to a wrong seeing input into the ETC.

Note: Another issue that arose was that OBs were nominally a maximum of 1hr in length and this may need to be considered when planning.

ACTION Richard to upload model results (completed) DECISION Use standard 60sec 2 jitter block unless science case argues otherwise ACTION Richard to update with new ETC values when available

Ofer Lahav : 5K survey

DES consortium includes UCL. Building new camera for CTIO 4m; plan is 525 nts griz over 2009-2014 for lensing survey. IR coverage would greatly improve photo-z. Depth is z(ab)=23.9 vs our standard depth z(ab)=22. They would need 900s exposures. So, probably not relevant to VHS; this team should talk to the various deep survey proto-consortia.

Phil Lucas : GPS update

They aim at b==/-5 (mostly at RA 12-20), 0.8" seeing, and a JHK survey with exposures of 80, 80, and 3x40 or possibly 120, 120 and 3x60. They want to stay independent of VHS. This is partly for design reasons - they want good seeing, multi-epochs, and contemporary colours - but also because it is a distinct community, and they want to call their own shots. It can also be done much more quickly than VHS (maybe 2 years) and is well matched to VPHAS; so is a clean strong and simple case to sell to PSP. However, much Galactic science is in VHS - brown dwarf searches, large star formation associations, Galactic populations, thick disc structure and tidal streams etc. Several people present thought separation was a mistake as it weakened both, but the strength of feeling of the people developing the VGPS proposal seemed clear

DECISION Stay independent but keep strong cross-links and joint planning as far as possible

Note : The proto-GCS proposal was not discussed, but here there seems a pretty clear case for staying inside VHS.

Tim Naylor Stellar populations

Described optimal data mining techniques for finding clusters in xy and colour space. Made two key pleas - for simultaneous colours, within an hour - and for using the same colour combination throughout. (Simultaneity based on PMS and TT Tauris varying by 10% within an hour). There was no clear argument for any particular depth other than the standard set. Repeat observations to detect variability (> 1 week) would be good.

Jonathan Davies Dwarf galaxies

With opt-IR colours can measure star formation histories much further away than can get with resolved stellar popns with HST. In Virgo, 2MASS reaches only 1/5 of dwarfs. Hemisphere survey should get 0.1 dwarfs/sq deg. No clear argument for any particular depth other than the standard set. No clear arguments on band choice yet, but more modelling might change this.

Maria-Rosa Cioni : Magellanic Clouds

Euro-wide proposal already quite well developed, linked to an AAOmega project. Aim to YJK to K=21.5 over 300 sq deg. Takes 3 years at 90 nights/year. VHS coverage gets only part of giant branch. However will still be important to measure populations over much larger area, especially the bridge.

Rich Savage : Astro-F

Launching next month. Will make all-sky FIR survey with resolution 30". Expect 1e6 galaxies to z=1-ish. Excellent match to VHS depth, giving photo-zs and lots of good projects. No clear argument for any particular depth other than the standard set. No clear arguments on band choice yet.

Richard McMahon High-z quasars

Point is to get very high-z Qs as beacons. To study the baryonic content of the Universe during the epoch of reionization. A small number will do but the higher-z the better. Goal is 10 quasars at z>6.5, a few at z>7. In zJK Qs at z=6.5-7.2 are outnumbered by BDs by 100 to 1000 in same part of colour-colour plot. Can separate at z>7.2 but needs very deep z at z-J>3. In ZJK diag Qs get clear at z>6.6 but still need v.deep Z. Best diag seems to be ZYJ, but needs fairly good photometry, as Y-J sepn from BDs is only 0.5 mag. zYJ is also good. Need J=19.5 Y=20.5 Z=21.5. ZYJK even better.

Richard suggested Z or Y for 180sec over 5000deg^2 as a baseline since 180secs over 15,000deg could be hard to justify at this stage due to speculative nature of expectations of numbers of quasars and the contamination rates. Decision on Y and/or Z may be clearer when UKIDSS LAS EDR data that would be released on 31st Jan had been studied.

Note : Steve Warren argued for Y=180s to get deep enough. Didn't arrive at a clear answer on this question. Possibly could do deep Y over a sub-area.

ACTION Richard and Steve Warren and others to conclude this debate and make recommendation

BROWN DWARFS. Science case similar to UKIDSS LAS. Not enough of an improvement to go to whole new class, but may probe say 50K cooler.

ACTION : Simon Hodgkin to develop science case in this area

SOLAR SYSTEM. No representative

ACTION : Andy to contact Alan Fitzsimmons to ask for science input

QUASARS. Some of the new quasar science will come in the deeper surveys. However an impressive sample will result, and we should highlight some science from it.

ACTION : Richard, Andy, Steve W and other to discuss this ?

NEXT STEPS. Andy L suggested we contact likely European partners and maybe set up a meeting outside the UK. Jim E said there wasn't enough time for this. The wiki pages were very helpful to enable people to contribute across Europe.

ACTION : all to send AL or RM suggestions for Euro names

ACTION : Andy to email UKIDSS consortium to attract attention to VHS pages

ACTION : Andy, Richard and others to construct short "position paper" to avoid repeating all the same arguments

ATTENDEES

Richard McMahon    Cambridge
Pete Bunclark      Cambridge
Jim Emerson        QMUL
Andy Lawrence      Edinburgh
Simon Hodgkin      Cambridge
Jonathan Davies    Cardiff
Rich Savage        Sussex
Ofer Lahav         UCL
Will Sutherland    Cambridge
Steve Rawlings     Oxford
Maria-Rosa Cioni   Edinburgh
Matt Jarvis        Oxford
Nic Walton         Cambridge
Mike Irwin         Cambridge
Paul O'Brien       Leicester
Phil Lucas         Herts
Mark Wilkinson    Cambridge
Tim Naylor         Exeter
Paul Hewett        Cambridge
Dave Alexander     Cambridge