Time-domain science with DESI - On behalf of the DESI time-domain WG, including: (+DES-GW)

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Time-domain science with DESI - On behalf of the DESI time-domain WG, including: (+DES-GW)
Time-domain science
 with DESI
 Antonella Palmese
 22 August 2019

 On behalf of the DESI time-domain WG, including:
 Segev BenZvi, Divyanshu Gandhi, Ouail Kitouni, Or Graur,
Alex Kim, Satya Gontcho A Gontcho, Tri Nguyen, Maayane Soumagnac & more
 (+DES-GW)
Time-domain science with DESI - On behalf of the DESI time-domain WG, including: (+DES-GW)
Introduction

Discovery & Follow-up Cosmology
Classification SNe
 Standard Sirens
Time-domain science with DESI - On behalf of the DESI time-domain WG, including: (+DES-GW)
~450 members, 70 institutions
Time-domain science with DESI - On behalf of the DESI time-domain WG, including: (+DES-GW)
The Dark Energy Spectroscopic
Instrument (DESI)
• 5000-fiber spectrograph on Kitt
 Peak Mayall 4m Telescope (AZ)
• 8 deg2 FoV
• Medium resolution spectroscopy,
 R up to 5500, λ = 360 - 980 nm
• Stage-IV BAO/RSD DE experiment
 over a broad redshift range: 0.5 < z
 < 1.6, 2.2 < z < 3.5
• Sky area: 14,000 sq. deg.
• >30M galaxy redshifts
Time-domain science with DESI - On behalf of the DESI time-domain WG, including: (+DES-GW)
SDSS+eBOSS
 Overdensities
 Underdensities

160k Ly- QSOs
 500k QSOs:
 z < 3.5
 12

 10

 8 o n
 i l li
 ( b
 e
 6 tim s)
 175k Emission Line ck ar
 Galaxies (ELGs): ba ye
 0.6 < z < 1.1 4 o k
 Lo 1.5M Luminous Red Galaxies (LRGs)
 2 z < 0.7
Time-domain science with DESI - On behalf of the DESI time-domain WG, including: (+DES-GW)
The Dark Energy Spectroscopic
Instrument (DESI)
0.7M Ly- QSOs
 1.7M QSOs:
 1.0 < z < 3.5

 r = 5.0 Gpc/h

 z=4 r = 4.0 Gpc/h
 z=3

 z=2 r = 3.0 Gpc/h
18M Emission Line
 z = 1.5
 Galaxies (ELGs):
 r = 2.0 Gpc/h
 0.6 < z < 1.6 z=1
 z = 0.7 Magnitude limited!
 z = 0.5
4M Luminous Red Galaxies (LRGs) r = 1.0 Gpc/h 10M bright galaxies (BGS)
 0.4 < z < 1.0 z = 0.2 r < 19.5, z < 0.4
 r = 0.5 Gpc/h
 Milky Way Survey: ~10M stars

 Dark time Bright time
Time-domain science with DESI - On behalf of the DESI time-domain WG, including: (+DES-GW)
Dark Energy Spectroscopic Instrument

Commissioning ongoing
Start April 1st
Whirlpool galaxy

 The Dark Energy Spectroscopic Instrument (DESI)
 First light - Commisioning Instrument - April 1st 2019
Time-domain science with DESI - On behalf of the DESI time-domain WG, including: (+DES-GW)
DESI timeline
2013 2015 2017 2019 2021 2023 2025 2027 2029
 BOSS
 DES
 HETDEX

 HSC PFS Spec

 eBOSS Stage III
 CI Science Verification (Feb 2020) Stage IV

 DESI Imaging DESI DESI II?
 Survey (June 2020-2025)
 Commissioning
 LSST

 Euclid
Imaging
Spectroscopy WFIRST
Time-domain science with DESI - On behalf of the DESI time-domain WG, including: (+DES-GW)
Discovery & Follow-up Cosmology
Classification
Time-domain science with DESI - On behalf of the DESI time-domain WG, including: (+DES-GW)
Divyanshu Gandhi, Ouail Kitouni, Segev BenZvi

Untargeted transient search
 Search for active transients in targeted DESI galaxies

 • Deep learning to classify known transient types (~103 SNe Ia in BGS)
 • Search for anomalous/weird spectra
Divyanshu Gandhi, Ouail Kitouni, Segev BenZvi

Classification with CNN
 Simulation uses bright galaxy mocks + BGS exposure & observing conditions

 Train CNN on rebinned spectra, without z, to classify hosts, hosts+SN Ia,
 hosts+SN IIp
Divyanshu Gandhi, Ouail Kitouni, Segev BenZvi

Classification with CNN
 All spectra Brightest SNe
 Accuracy: 0.88 Accuracy: 0.96
 Confusion matrix Confusion matrix, flux ratio>0.5

Accuracy: Correct predictions/total predictions
Divyanshu Gandhi, Ouail Kitouni, Segev BenZvi

Classification with CNN

 • Recall: TP that are correctly identified (TP/TP+FN)
 • Transients get misclassified as host galaxies at low SN/host flux ratios.
 • Physically: SN is brighter, or is closer to the galactic nucleus and fiber
 center.
 Takeaway points
 • Recall depends somewhat strongly on SN/host flux ratio
 • Relatively good precision for simulated transients, worse for hosts
 • Adding classes to CNN (KNe, TDEs…)
 • Other public efforts (DASH: Muthukrishna+ 2019, arXiv:1903.02557), difference
 is focus on hosts and no z.
Discovery Follow-up Cosmology
LSST/ZTF follow-up
DESI will cover 3800-5000 deg2 of LSST footprint, most (~14000 deg2) of ZTF
• ~20 pointings per night in dark time/~40 in bright time
• Spare fibers (~500 per pointing in bright, some for MW)
• Observe transients up to r~20 during BGS with nominal exp time
• Type LSST SNe out to z~0.2 (O. Graur)
• Classification+host galaxies z (no further follow-up)
• Vast majority of z
GW follow-up of “golden” events
• “Golden” events (2D 90%CL < tens deg2 +
Alex Kim

Data sharing
• Installed and testing skyportal visualization and event handling app on NERSC
• We welcome non-DESI scientists to test our development skyportal and to provide
 suggestions for improvement
Alex Kim

Data sharing
• Installed and testing skyportal visualization and event handling app on NERSC
• We welcome non-DESI scientists to test our development skyportal and to provide
 suggestions for improvement

 Work in progress,
 Feedback welcome!
Discovery & Follow-up Cosmology
Classification
Growth of Structure and Alex Kim
 avity: Math and Notation
 SNe & Peculiar velocities
 mass density
 mass overdensity
 Photometrically
 ⇢(x,t) ⇢(x,t)
 ¯ identified SNe+DESI will contribute to cosmology:
 x, t) ⌘
 1. “Classic”
 ⇢(x,t)
 ¯
 standard candles: provide host galaxy redshifts for SNe Ia - in prep. for
 x, t) = D(t) (x) to first order
 ZTF SNe
 Testfactor”
 2. growth
 linear gravity through peculiar velocities (PV)! Howlett+17 - ZTF+DESI EC in place

 • “growth
 d ln D
 d ln a :
 Contentsrate”
 in the Universe move due to gravity
 • PVs (motions on top of cosmological expansion) depend on mass overdensities and gravity
uliar velocities sensitive to the combination f D (literature often uses
n f 8)
 • Mass overdensities well measured at the surface of last scattering
 • Measure PV (needs z+distance: SNe) Constrain gravity theories Kim et al. 1903.07652
wth rate depends on gravity. An excellent empirical parameterization is:
 PV can measure: Growth index
 f = ⌦M Depends on gravity
 ✓Z 1 ◆
 f D = ⌦M exp ⌦M d ln a
 a
 Growth rate Linear growth factor
 Relativity, f (R), and DGP gravity predict values of the growth index
0.55, 0.42, 0.68
 Moderately short, low-z SN Ia surveys can
 distinguish popular gravity models to 3σ
Schutz 1986
 Holz & Hughes 2005
 MacLeod & Hogan 2008

Standard Sirens Nissanke+2010
 Del Pozzo 2012
 Unique host galaxy No EM counterpart: potential host galaxies

 DES galaxies

Soares-Santos+DES 2017

 Bright standard sirens • Dark standard sirens / statistical method
Bright Standard Sirens
 • DESI can help with quick classification, host galaxy redshifts and peculiar
 velocities
 • ~2% measurement in ~2023: enough to solve H0 tension - Chen, Fishbach & Holz 2017
 • DESI+CMB+StS: up to factor 3 improvement on dynamical DE EoS constraints - Di
 Valentino et al. 2018

 AP et al. 2019, arxiv: 1903.04730
Dark standard sirens
 −1
 H0 = 75.2+39.5
 −32.4 km s Mpc−1

 GW170814

 First measurement of
 the Hubble constant
 using a BBH
 DES & LVC 2019
 arxiv:1901.01540

 LVC 2019,1908.06060, combines all O1+O2 events
 Only 170814 significantly improves 170817
 Need for complete/deep galaxy catalogs
O3 Dark standard sirens with
DES+DESI Imaging
 DESI Imaging (+WISE):
 – Dark Energy Camera Legacy Survey (DECaLS)
 – Beijing-Arizona Sky Survey (BASS)
 – Mayall z-band Legacy Survey (MzLS)
 Photo-zs perform well down to r~21 (R. Zhou & J. Newman)
 DECam programs (e.g. 2019B-0371, PI Soares-Santos) to improve i and u coverage
Dark standard sirens with DESI BGS
 Science that will come for free with DESI nominal targets
• 4-5% statistical precision with DES-like data and ~100 GW170814-like events
 100 event sample
 DESI-like
 8
 0.01
 LSST-like 7

 (%)
 + z)

 6

 H0 /H0
 DES-like 0.02
 z /(1

 5

 4
 0.03
 3

 0.10 0.15 0.20
 d /d
 170814,
 190701,
 190814,
 …

 DES & LVC 2019 arxiv:1901.01540
Dark standard sirens with DESI BGS
 Science that will come for free with DESI nominal targets
 • 4-5% statistical precision with DES-like data and ~100 GW170814-like events
 100 event sample
 DESI-like
 8
 0.01
 LSST-like 7

 (%)
 + z)

 6

 H0 /H0
 DES-like 0.02
 z /(1

 5

 4
 0.03
 3

Other science cases
 0.10 0.15 0.20
include host galaxy studies
to understand origin of d /d
 170814,
 190701,
 190814,

GW sources (e.g. Scelfo et
al. 2019,1809.03528)
 …

 DES & LVC 2019 arxiv:1901.01540
Conclusions
 Discovery & Classification:
 • Adding classes to CNN (KNe & TDEs, other SNe)
 • Inputs on public data sharing welcome
 Follow-up:
 • GW, ZTF, LSST
 • Can enable cosmology complementary to BAO/RSD
 Taipan, SDSS-V, 4MOST could work similarly
 Future: make an impact for DESI-II - transients and host
 galaxies

 If you are a collaborator at other facilities and are
 willing to facilitate connections relevant to DESI time
 domain science, we want to hear from you!
 palmese@fnal.gov
Conclusions
 Thank you!
Blah
Divyanshu Gandhi, Ouail Kitouni, Segev BenZvi

Untargeted transient search

 • Precision: positive identifications that are true positives TP/TP+FP
 • Some dependence on object r magnitude, not as much as SN/host ratio
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