Or Graur (NSF Fellow / Harvard CfA)on behalf of the DESI Time Domain Working Group

Northwestern University, 2 June 2016

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DESI will be a 5000-fiber, 8 deg2 spectrograph on the Kitt Peak Mayall 4m Telescope

• Scale up BOSS to a massively parallel fiber-fed spectrometer with 5x more fibers, larger telescope aperture, robotic fiber positioners

• Stage-IV BAO over a broad redshift range: 0.5 < z < 1.6, 2.2 < z < 3.5

• Sky area: 14,000 square degrees

• Number of galaxy redshifts: 30 million

• Medium resolution spectroscopy,

R ~ up to 5500, λ = 360 - 980 nm

• DESI will run for 5 years, starting in 2019.

==> partial overlap with LSST run.

DESI will be composed of several surveys, targeting millions of galaxies.

r < 19.5

z < 20.5 (AB)

r < 23.4 (AB)

Shared equatorial footprint of 3800 deg2 (5000 deg2 if LSST goes to Dec = +4 deg)

LSST r-band footprint DESI tile footprint

[LSST science book 2.0] [DESI+ 16, arXiv:1611.00036]

Some DESI fibers per tile could be allocated to follow LSST candidates.

● How many LSST candidates per night per deg2 in the joint LSST--DESI footprint? As a function of magnitude?

● Should DESI follow transients? Host galaxies? Combination?

● Which LSST candidates should DESI follow?

● DESI is first and foremost a cosmology project

==> some fraction of candidates must be SNe Ia.

● But there is room to follow other types of transients as well.

● Think classification / spec-z, not spectral time series.

Early simulations show DESI could classify SNe Ia out to redshift ~0.2 in bright time.

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~300 of 10,000 LSST candidate SNe Ia classified (Benjamin L’Huillier).

Nominal 15-minute DESI bright-time spectra: SNe Ia classified down to r ~ 19.5 mag (Or Graur)

DES+OzDES: a similar collaboration

● Spectroscopic follow-up of DES deep fields with the 4m Anglo-Australian Telescope, AAOmega-2df.

● 5-year survey started in 2013.

● OzDES has obtained:

– 80,000 spectra + 33,000 unique objects

– 23,000 redshifts

– 4200 SN host redshifts

– 200 SN Ia classifications

● Similar program for DESI + LSST deep drilling fields?

We need your input!

● How can DESI work best with LSST?

– Classification of transient candidates?

– Redshifts of host galaxies?

● SNe Ia must be involved in some form,

but other transient types are welcome.

● It’s early enough that we may be able to influence the DESI observational strategy, e.g., affecting the tiling order to chase LSST fields.

● We’re also in contact (Bob Nichol) with 4MOST, a southern instrument similar to DESI. 4MOST+DESI could work well to cover the LSST field of view. Re Elizabeth Swann’s talk.

We need your input!

● Hypothetical example: 10 LSST targets per tile per night:

– 5 targets: improve Antares classification accuracy by targeting Ia/Ic candidates.

– 5 targets: candidates typed by Antares as weird outliers.

● Every night, DESI will target ~20 tiles in dark time / ~40 tiles in bright time.

==> >200 SNe Ia + >200 unknown transients per night.

Let’s start brainstorming: or.graur@cfa.harvard.edu