Semester: 2004B		Partner reference: Not Available		PI time requested: 20.0 hours
Gemini reference: Not Available		Partner ranking: Not Available		PI minimum time requested: 10.0 hours
Instruments(s): GMOS North		NTAC recommended time: 0.0 nights		PI future time requested: 120.0 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)

This proposal falls under the QR (quick response) category, for which the triggers are supernova discoveries from the CFHT Legacy Survey.

Science Justification

Despite the emergence of this "cosmic concordance" model, the physical origin of the non-zero Omega_Lambda is not yet understood. The primary goal of the SNLS is to determine the equation of state parameter w (relating the pressure and density of the Universe through w=P/rho), and to distinguish among different physical models for the dark energy. (For instance, a classical fixed cosmological constant gives w=-1, whereas quintessence yields w>-1.)

Whereas non-zero Omega_Lambda values can now be deduced by other means (e.g. Efstathiou et al 2002, Bennett et al 2003), geometric distance measurements of SNe Ia are unique in directly tracing the cosmic expansion and are the most straightforward route to the determination of w. To make this determination, a concerted program to find ~1000 SNe Ia at 0.2<z<0.9 (a tenfold increase over the sample size available prior to SNLS) and obtain multi-colour (g'r'i'z') light curves with excellent (~2-3 day rest-frame) sampling is required. These multi-colour/multi-epoch observations improve both SN reddening corrections and our ability to determine the epoch of maximum light and light-curve "stretch factor", both of which are required for an accurate determination of the SN peak brightness.

SNLS and CFHTLS

The CFHT Legacy Survey (CFHTLS) has allocated 202 nights of queue-scheduled telescope time over 5 years to SNLS, providing more than 500 epochs on four 1 square degree fields sampled every ~2 days rest-frame in g'r'i'z' filters, with almost real-time SN triggers (see http://www.cfht.hawaii.edu/Science/CFHTLS for more information). This unsurpassed "rolling search" strategy is possible thanks to both 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 near maximum light; (2) the flux of the target is known since it is measured one or two days before spectroscopic observation, allowing an accurate estimate of exposure time; and (3) pre-maximum colours and fluxes allow excellent discrimination of SNe Ia from other events (e.g. SNe II, AGN, and variable stars).

The SNLS team is now routinely delivering SN detections and photometry within 12-24 hr of data being taken. The reader is referred to the Technical Justification for more information, and to http://legacy.astro.utoronto.ca/ for "up-to-the-minute" information on SN discoveries.

THIS PROPOSAL

This application is to obtain vital spectroscopic classifications and redshifts for candidate SNLS SNe. The confirmed sample of SNe Ia 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. 3b. The goal for this semester is to obtain spectroscopy for 30 SNe Ia candidates (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 with time being applied for at Keck (PI Perlmutter) and Magellan (PI Carlberg). Gemini plays a key role by allowing queue scheduled observations in the North. More details of the spectroscopic followup strategy appear below.

DISCUSSION

Supernova observations can be subjected to many straightforward tests to check for systematic effects. The CFHTLS g'r'i'z' data can be used to measure SN colours and hence test for reddening by comparison with colours of nearby SNe. (note-other collaborative plans to use IR data to extend colour measurements to the highest redshift objects in our sample at z~0.9 are in place). In addition we will have a large enough sample to study subsets divided by host galaxy type (derived from the host galaxy spectra, CFHTLS colours, 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 340, 1057). The SN spectra themselves can be stacked to obtain a high S/N mean spectrum for different host galaxy types or redshift ranges; these can be compared against local SN spectra to check for subtle evolutionary effects. Statistical studies of individual spectral features are possible and have been started with the semester 2003B data.

Although the primary goal is to study SNe Ia, some objects will turn out to be core collapse SNe. These are of interest in their own right, as measurements of star formation rate as a function of redshift and studies of the relation between max brightness and envelope expansion velocity (Hamuy etal, astro-ph/0309122) can be made from the data obtained from these SNe.

This project is the first step in measuring w: it will assume constant w, and test the possibility that the dark energy is the cosmological constant alone, i.e. the zero-point energy of the vacuum. This is perhaps the simplest and best known dark energy model.

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 large GMOS overheads, it is most efficient to use GMOS on these fainter, higher redshift objects ( hence the numbers of SNe observed at Gemini do not represent the survey as a whole). Based on results from the recently-completed first semester of Gemini follow-up (2003B), these SNe will have i'=23-24.5, requiring GMOS exposures of around 1.5hrs. With future changes to setup procedures (see below for examples) it should be possible to reduce current overheads - assuming 1800s per object, we request 60hr (total - all partners) in order to observe approximately 30 SN candidates in 2004A.

All observations will use a 0.75" slit, the R400_G5305 grating, and OG515 order sorting filter. The slit PA is chosen to pass through both SN and host galaxy. Our experience shows that the dispersion of the R400 grating (~2A/pix) gives excellent nod and shuffle sky subtraction, and we can rebin the data ~10x afterwards for redshifts and SN typing. We routinely use nod and shuffle for the fainter targets, allowing us to confirm and classify many i'=24 candidates (Fig. 2).

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. We have had no difficulty in finding guide stars.

We will continue to make SN types and redshifts from Gemini public within a month of the observations being received from the Gemini Project Office.

PROGRESS AND SCIENCE PLANS

The SNLS team achieved huge gains during Semester 2003B. Several new pipelines were developed, including one to do near-final reductions of spectroscopy and spectroscopic type determination (with SNe template fits) within minutes of the receipt of the data via ftp from Gemini. This allows us to give the queue next-day feedback on integration time. Our photometry pipeline was also refined, and real-time light curve fitting was implemented, enabling photo-z and type estimations of candidates before they are sent for spectroscopy. A preliminary Hubble diagram was also produced from a subset of our real-time data (Fig 3a). The only setbacks during the semester were beyond our control: the weather at Mauna Kea was significanty below average, and MegaCam was still improving in efficiency in 2003B (see http://www.cfht.hawaii.edu/Instruments/Queue/2003b_report.html for the official CFHT MegaCam report).

These efforts have resulted in 130 reliable SN detections with excellent light curves out to z >0.9, of which about 45 have been spectroscopically identified as Ia's. (See http://legacy.astro.utoronto.ca/ for the latest SN discoveries). For comparison, all previous high-z searches over the past 10 years have combined to produce ~100 SNe Ia. A typical CFHTLS queue run produces ~20 high-z SNe candidates per month. We fully expect to achieve our goal of 4-5 epochs (4 filters, 2 fields) in each lunation for future semesters.

To date we have Gemini spectra of 24 targets from 55 hours of observations (including overheads). Three example spectra are shown in Fig. 2; see http://www-astro.physics.ox.ac.uk/~imh/SNLS/ for statistics of observations.

OVERHEADS

Nod and shuffle is working very well (7 minute overhead per 30 minute observations), and we will use electronic offsetting to further reduce this overhead. Our largest overhead is target acquisition. During 2003B we tested blind offseting to acquire our targets, but found that offsets over 25" are not accurate enough for reliable acquisition. We are cooperating with the Observatory to improve the GMOS offsetting accuracy (which probably involves better calibration of the GMOS OIWFS pointing model) so that blind offsetting can be used routinely by this program and the general community.

SCHEDULING AND LOGISTICS

As SNe Ia will be discovered, and reach maximum light, throughout the semester, Observing time should be spread throughout 2004B. We will obtain SN detections in almost real time at CFHT (<24 hr turnaround), and will constantly update our Phase 2 proposal.

Isobel Hook, Stephane Basa, Andy Howell, and Mark Sullivan are in charge of managing the distribution of SN ID's to the various 8m telescopes. In preparation for a given night, they check the results of previous nights of spectroscopy, make a prioritized candidate list, and dispatch objects on this list to various telescopes. The Gemini observations coordinator will be Isobel Hook (project Phase 2 contact).

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, thus spectroscopic follow up will be shared as follows:

o Gemini (this proposal) - 60 hrs per semester (30 hrs Canada, 20hrs UK, 10 hrs US). This ratio recognzes the US contribution of Keck time and UK contributions of ESO time (see below).

o ESO VLT - FORS1 60 hrs each semester (for 2003A, 2003B, 2004A and 2004B). The PI is R. Pain; this group consists of UK, French and other European collaborators.

o Keck - 4 nights of Keck time every 'A' Semester (compensates for the field not visible from VLT/Gemini-S). The PI is S. Perlmutter.

o Magellan - 2-3 nights per semester on Magellan. Carnegie scientists (in an informal arrangement) will take spectra of z<~0.6 SNe.

FUTURE TIME

Observations over the first two years of the survey are critical, and will provide a first estimate of w with reasonable errors (see Fig. 3b). A detailed analysis of the photometric properties of SNe may provide an alternative to spectroscopic typing in the future.

Rollover: We request that this program be approved for rollover into 2005A. We aim to use our time evenly throughout the semester (since candidates are discovered throughout), and this means we must "hold back" a number of hours for the last lunation of the semester. This held-back time is wasted if the weather is bad in the last month. Rollover would provide insurance against losing this time altogether and allow us to obtain the required number of confirmed supernovae.

Attachments:

Observation Details

Resources

• Gemini North
  • GMOS-N (GMOS North)
    • Focal Plane Unit
      • Nod and Shuffle 0.75 arcsec
      • Longslit 0.75 arcsec
    • Disperser
      • R400_G5305
    • Filter
      • OG515_G0306

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:

• Hook, I. et al. (2004), "The Gemini North Multi-Object Spectrograph: Integration, Tests, and Commissioning", PASP, in press.
• CFHTLS SN Collaboration (2003), "SUPERNOVAE 2003gy, 2003gz, 2003ha, 2003hb", IAUC 8178
• CFHTLS SN Collaboration (2003), "SUPERNOVAE 2003fr-2003gb", IAUC 8149
• CFHTLS SN Collaboration (2003), "SUPERNOVAE IAUC 81482003fl, 2003fm, 2003fn, 2003fo, 2003fp, 2003fq", IAUC 8148
• CFHTLS SN Collaboration (2003),"SUPERNOVAE 2003fe, 2003ff, 2003fg, 2003fh, 2003fi, 2003fj, 2003fk", IAUC 8147
• R.Knop, et al, (2003), New Limits on Cosmological Parameters Omega_M and Omega_Lambda from HST Observations of Eleven Supernovae at Redshifts z=0.36-0.86, ApJ, in press (astro-ph/0309368)
• Sullivan, M. et al. (2003), "The Hubble Diagram of Type Ia Supernovae as a Function of Host Galaxy Morphology", MNRAS, 340, 1057
• Kasen, D. et al. (includes Howell) (2003), "... Flux and Polarization Spectra of the Type Ia Supernova SN 2001el ...", ApJ, 593, 788
• Garnavich et al (includes R. Carlberg) (2003), "Afterglow of GRB 011121 and Its Progenitor SN2001ke", ApJ, 582, 924
• Perlmutter, S., and Schmidt, B. (2003), "Measuring Cosmology with Supernovae". In Supernovae & Gamma Ray Bursts, astro-ph/0303428
• Wang, L., Goldhaber, G., Aldering, G., and Perlmutter, S. (2003), "Multi-Color Light Curves of Type Ia Supernovae on the Color-Magnitude Diagram: a Novel Step Torward More Precise Distance and Extinction Estimates", ApJ, in press. astro-ph/0302341
• Howell, D.A. (2001), "Progenitors of Subluminous Type Ia SNe", ApJL, 554, 193
• McCarthy, Carlberg, et al (2001), "Las Campanas IR Survey: Early Type Galaxies ...", ApJ, 560, L131
• Howell, D. A., Hoeflich, P. Wang, L., and Wheeler, J. C. (2001), "Evidence for Asphericity in a Subluminous Type Ia Supernova: Spectropolarimetry of SN 1999by", ApJ, 556, 302
• 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
• Howell, D. A., Wang, L., Wheeler, J. C. (2000) "The Distribution of High- and Low-Redshift Type Ia Supernovae", ApJ, 530, 166
• 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
• R. Pain, I. Hook, S. Perlmutter, et al., (1996) , The Type Ia supernova rate at z~0.4, Astrophysical Journal, 473, 356

Allocations:

Reference	Time	% Useful	Comment
ESO VLT 2004A	60.0 hours		French + other European collaborators time on FORS1 (VLT) for CFHTLS SN followup; 60 hr allocated in 2003B, 60 hr 2004A, plus more time guaranteed in 2004B. The PI is R. Pain.
GS-2004A-Q-11	15.0 hours		Followup spectroscopy for CFHTLS supernovae - Observations currently underway.
GN-2004A-Q-19	45.0 hours		Followup spectroscopy for CFHTLS supernovae - Observations currently underway.
GN-2003B-Q-9	45.0 hours	100	Followup spectroscopy for CFHTLS supernovae - Observations complete, see report in Technical Case.
GS-2003B-Q-8	15.0 hours	63	Followup spectroscopy for CFHTLS supernovae - Observations complete, see report in Technical Case.
GN-2003A-Q-1	60.0 hours	100	"Gemini Deep Deep Survey" (Abraham, McCarthy, Carlberg et al)
GN-2002B-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.
GN2002B-Q-36	23.0 hours	0	Simard PI - HDF N disk kinematics. No data taken due to heavy schedule of telescope shutdowns and instrument commissioning.
Gemini 02A/B	10.0 nights	95	"Gemini Deep Deep Survey" (Abraham, McCarthy, Carlberg et al) [includes ~5 nights science verification]
Gemini 02A	14.0 hours	75	"Star formation around High z QSO's" (Pritchet, Hartwick, Carlberg et al). Paper in preparation.
GN2002A-Q-30	12.0 hours		Hook PI. 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.
GN2002A-Q-31	12.0 hours		Hook PI. 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
GN2002A-Q-75	6.5 hours		Hook PI. 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.
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.

Proposal Contents