Semester: 2003B		Partner reference: Not Available		PI time requested: 20.0 hours
Gemini reference: Not Available		Partner ranking: Not Available		PI minimum time requested: 1.0 nights
Instruments(s): GMOS North		NTAC recommended time: 0.0 nights		PI future time requested: 180.0 hours
Observing mode: queue		NTAC minimum recommended: 0.0 nights		PI total from all partners: 60.0 hours (joint proposals)
Time awarded: Not Available		Proposal submitted to: United Kingdom
		...also submitted to...United States, Canada (joint proposals)

The goal for Gemini this semester is to obtain types and redshifts for ~60 SNeIa out to z~=0.9. This will provide a high quality SNeIa sample comparable in size to existing SNeIa samples, but with superior photometry, light-curve sampling, and colour information. Gemini observations represent a vital component of our overall spectroscopic followup strategy, which lso involves the ESO VLT, Keck, and Magellan telescopes.

Science Justification

Our goal is to distinguish between these models (which arise from fundamental physics) using direct geometric distance measurements of supernovae. To do this requires a concerted program to find ~1000 SNeIa at 0.2<z<1 (more than 10x the current sample), and obtain multi-colour (g'r'i'z') light curves with excellent (2-3d) sampling. (The multicolour observations improve reddening determinations; the time sampling is essential for measuring maximum light and determining the light curve "scale factor", which correlates with maximum light brightness.)

THE CFHT LEGACY SURVEY

The CFHT Legacy Survey (CFHTLS) is tailor-made for this purpose (202 nights of telescope time over 5 years, more than 500 epochs on four 1 sq deg fields, typical photometric sampling every ~2 days rest-frame, g'r'i'z' filters plus some u*, and almost real-time SN triggers - see http://www.cfht.hawaii.edu/Science/CFHTLS for more information). This unsurpassed "rolling search" strategy is possible thanks both to queue scheduling of CFHT, and to an enormous commitment of telescope time; it leads to improved efficiency for spectroscopic followup because: (1) it allows us to monitor the rise of the object and trigger spectroscopy at maximum light; (2) the flux of the target is well known since it is measured one or two days before max; this allows us an improved estimate of exposure time; (3) the detection of objects uses a lightcurve rather than a single flux difference.

THIS PROPOSAL

This application is to enable the vital spectroscopic classification of the candidate SNeIa from the CFHTLS imaging survey. Spectroscopy also provides an accurate estimate of the redshift to the SNeIa. The confirmed sample of SNeIa will be used to obtain a precise measurement of the cosmological parameters (Omega_mass,Omega_Lambda) and a measurement of the equation of state of the dark energy w with a precision of better than +-0.10 (1000 SNe) when combined with weak lensing constraints - see Fig. 2. The goal for this semester is to confirm ~60 SNeIa (z<~0.9) at Gemini.

This proposal is part of a well-organized international collaboration aimed at a precise measurement of cosmological parameters using the CFHTLS. The collaboration involves astronomers in Canada and France, as the lead agencies of the the CFHTLS; it also comprises groups in the USA and Europe. Spectroscopic followup time has been committed at the VLT; time is being applied for at Keck (PI Perlmutter) and Magellan (PI Carlberg, with additional observations by Magellan staff). More details of the spectroscopic followup strategy appear below.

DISCUSSION

Supernova obserations can be subjected to many straightforward tests to check for systematic effects. The CFHTLS u*g'r'i'z' data can be used to measure SN colours and hence test for reddening by comparison with colours for nearby SNe. (We have other collaborative plans to use IR data to extend colour measurements to the highest redshift objects in our sample at z~0.9.). In addition we will have a large enough sample to be able to study subsets divided by host galaxy type (derived from the host galaxy spectra or high resolution imaging), or galactocentric radius - this allows us to check for effects associated with changes in the underlying host galaxy population (metallicity, extinction, age), similar to the study of Sullivan et al (2003 MNRAS, in press, and astro-ph/0211444). The SN spectra themselves can be stacked to obtain a high S/N mean spectrum for different host galaxy types or z ranges; these can be compared against local SN spectra to check for small evolutionary effects.

This project is the first step in measuring w: it will assume constant w, and test the possibility that the dark energy is just the cosmological constant, i.e. the zero-point energy of the vacuum -- perhaps the simplest, best known dark energy model. Although the primary goal is to study SNeIa, some objects will turn out to be core collapse SNe. These are of interest in their own right (for measuring star formation rate as a function of z, and for studying the recently-discovered [Hamuy etal] relation between max brightness and envelope expansion velocity).

Attachments:

Technical Justification

We propose to use the GMOS spectrographs on Gemini N/S to obtain types and redshifts of supernovae with roughly 0.6<z<0.9. (Given the overheads with Gemini, it is most efficient to use GMOS on these fainter objects.) Based on our previous work (Hook, Perlmutter etal) these SNe will have I=23-24; GMOS exposures of up to 3600s will be needed, although in some cases 1800s will be sufficient. The goal in this proposal is to identify ~60 SNeIa in 2003B. Assuming overheads of 1800s per object and an equal split of 1800s and 3600s per target, a total of 60hr is requested. With experience, it may be possible to reduce overheads below 1800s.

All observations will use a 0.75" slit, the R400_G5305 grating, and OG515 order sorting filter. Our experience shows that the dispersion of the R400 grating (~2A/pix) gives excellent sky subtraction, and we can rebin the data ~10x afterwards for redshifts and SN typing. Nod-and-shuffle will be used for the faintest targets. Given the time between SN discovery and spectroscopic observation, it is unfortunately not possible to design masks for multislit observations, though this option may be possible in the future.

Guide stars: The coordinates quoted here are the coordinates for the main search fields. The exact coordinates of targets and associated guide stars will be entered into the Phase II file when known - based on previous experience we do not expect any difficulty in finding guide stars.

Gemini types and redshifts will be made public within a month of the observations being received from the Gemini Project Office.

SCHEDULING AND LOGISTICS

SNeIa will be discovered, and reach maximum light, throughout the semester. Thus observing time should be spread through the entire semester. We will obtain SN ID's in almost real time at CFHT (~24 hr turnaround), and will constantly update our Phase 2 proposal.

Jim Rich will be in charge of managing the distribution of SN ID's to the various telescopes involved in spectroscopy. In preparation for a given night, he will check the results of previous nights of spectroscopy, make a prioritized candidate list, and dispatch objects on this list to various telescopes. Gemini observations coordinator will be Isobel Hook (our contact for Phase 2 purposes).

INTERNATIONAL COLLABORATION

Spectroscopy on 8m class telescopes is essential for this project to succeed; the total amount of 8m time needed is well beyond the reach of any one group or nation. Our strategy for spectroscopic followup has progressed rapidly over the past few months, and at present is as follows:

o Gemini (this proposal) - We are applying for 6 nights per semester (2 UK, 3 Canada, 1 US). We have a preference for GMOS-N because of the lower fringing of the GMOS-N detectors, hence this UK proposal is for GMOS-N only. However we would be able to use time on either telescope if that is easier to scehdule, and indeed overall we are applying for a balance of time roughly in the proportion 2:1 N:S.

o ESO VLT - FORS1 time has been allocated over the next 2 years (60 hrs in 2003A, 60hrs in 2003B). The PI is R. Pain; this group consists of U.K, French and other European collaborators.

o Keck - Perlmutter et al. will apply for 4 nights of Keck time in Semester A. (The need for extra semester A time is discussed below.)

o Magellan - We will apply for 2-3 nights of Canadian time on Magellan. Carnegie scientists have also agreed to an informal arrangement in which they take spectra of z<~0.6 SNe in exchange for use of these SNe ID's for their own program of IR followup.

The following should be noted:

(1) The role of followup spectroscopy is pivotal to the SN survey; hence UK has agreed to the principle that it will be represented on the Collaboration Board (which manages the survey) along with French and Canadian astronomers (who are the principals behind the CFHT Legacy survey) if UK contributes equal resources to the collaboration. The amount of UK Gemini + VLT time requested roughly satisfies this agreement.

(2) The ratio of 1 US to 2 UK to 3 Canadian Gemini nights recognizes the fact that our US collaborators are contributing 4 nights of Keck time, and UK is also contributing ESO time.

(3) Gemini time plays a key role in our observations. The time is essential for observations of the Groth strip (1419+52 - not observable from Chile) in semester A; it is essential for SN coverage in May-July, when the weather is bad in Chile. Finally, Gemini is queue-scheduled, a fact that makes the time enormously useful for observations of transient objects, compared to block-scheduled telescopes such as Keck.

(4) The DEEP survey team (S. Faber PI) has agreed in principle to coordinating our observations with DEEP survey observations; this potentially optimizes or increases our Keck allocation. R. Ellis has agreed to provide a few SN spectra and types in the Groth strip; in exchange we provide him with ID's and photometry to complement his high resolution followup. (Our first attempt at this will be in the Mar 20 - Apr 10 dark period.)

(5) Allowing for overheads, and for time lost to weather and misidentifications (e.g. AGN's, SNeII), the total time to be allocated will allow the followup of roughly 200 SNeIa per year.

Space does not allow for a complete list of the collaboration members. The Co-I's on this proposal represent the core group; see www.astro.uvic.ca/~pritchet/SN/03Bco-i.html for a complete list.

FUTURE TIME

Though the CFHTLS is a 5 year program, the first two years of the spectroscopy (~240 hr total) are critical: observations over this period will enable a first estimate of w with reasonable errors. We will also submit proposals with time requests like this one in 04A, 04B, and 05A. A detailed analysis of the photometric properties of SNe may provide an alternative to spectroscopic typing in the future.

Observation Details

Resources

• Gemini North
  • GMOS North
    • Focal Plane Unit
      • Nod and Shuffle 0.75 arcsec
      • Longslit 0.75 arcsec
    • Disperser
      • R400_G5305
    • Filter
      • OG515_G0306
• Gemini South

Observing Conditions

Name	Image Quality	Sky Background	Water Vapor	Cloud Cover
SN spec	70%	50%	Any	50%

Scheduling Information:

Synchronous dates:

Optimal dates:

Impossible dates:

Additional Information

Keywords: Cosmological distance scale, Dark matter, Survey

Publications:

• Aldering G, Knop R., Nugent P., (2000) "The rise times of High- and Low- redshift Type Ia Supernovae are consistent", AJ, 119, 2110
• Perlmutter S. et al (1999) "Measurements of Omega and Lambda from 42 High-z Supernovae", ApJ, 517, 565
• Perlmutter S. et al, (1998) "Discovery of a supernova explosion at half the age of the Universe and its cosmological implications", Nature 391, 51.
• Perlmutter S. et al (1997) "Measurement of the cosmological parameters Omega and Lambda from the first 7 supernovae at z>0.35", ApJ, 483, 565
• Pain R. et al (2001) : "The Distant Type Ia SN rate" 2002, ApJ, 577, 120
• G. Goldhaber, et al, (2001), Timescale Stretch Parameterization of Type Ia Supernova B-Band Light Curves, Astrophysical Journal, 558, 359
• R. Knop, et al, (2000), Latest Cosmological Results from Type Ia Supernovae, Bulletin of the American Astronomical Society, 197, 950
• A. Goobar et al, (2000), The acceleration of the Universe: measurement of cosmological parameters from type Ia supernovae, Physica Scripta, T85, 47.
• R. Pain, I. Hook, S. Perlmutter, et al., (1996) , The Type Ia supernova rate at z~0.4, Astrophysical Journal, 473, 356
• R.Knop, et al, (2001), New Limits on Cosmological Parameters Omega_M and Omega_Lambda from HST Observations of Eleven Supernovae at Redshifts z=0.36-0.86, in preparation
• Supernova 2001ay in IC 4423, Circular 7612, P.Nugent, G.Aldering, I.Hook, S.Perlmutter, L.Wang
• Supernovae 1999bi, 1999bj, 1999bk, 1999bl, 1999bm, 1999bn, 1999bo, 1999bp, 1999bq, Circular 7136, Supernova Cosmology Project.

Allocations:

Reference	Time	% Useful	Comment
GN2001A-Q-10	12.0 hours	50	This was a joint proposal with GN2001A-Q-16 (submitted to the U.S. TAC) to observe distant supernovae with NIRI. Both were ranked highly and the full amount of requested time (35hrs) was awarded by the respective TACs. Because of cancellation of the queue this program was not carried out in queue mode. However it was used as a test program for NIRI SV (broadband imaging mode with the f/6 camera). About 12 hours of useful data were obtained, approximately half of our original request (when overheads are taken into account). We intend to obtain a final reference image for this SN with NIRI in semester 02B.
GN2002A-Q-30	12.0 hours	50	This was a joint proposal with GN2002A-Q18 (submitted to U.S. TAC) for GMOS observations of distant supernovae. Some data was acquired and a paper is in preparation. Poor weather on Mauna Kea during our window of opportunity prevented us using more time.
GN2002A-Q-31	12.0 hours	25	This was a joint proposal with GN2002A-Q37 (submitted to U.S. TAC) for NIRI observations of distant supernovae. Some data obtained. Paper in preparation. Poor weather and competeition with other queue programs in our RA range prevented us getting more time.
GN2002A-Q-75	6.5 hours	100	This was a joint proposal with GN2002A-Q9 (submitted to Candian TAC) for GMOS spectroscopy of z>5 QSO candidates. Program completed and paper in preparation.
GN2002B-Q-30	10.3 hours	100	Joint proposal with U.S. (Knop et al) for NIRI and GMOS follow up of SNeIa. Only GMOS time was awarded by the UK TAC, and all this was used.

Proposal Contents