Time-domain science with DESI - On behalf of the DESI time-domain WG, including: (+DES-GW)
←
→
Page content transcription
If your browser does not render page correctly, please read the page content below
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)
Introduction Discovery & Follow-up Cosmology Classification SNe Standard Sirens
~450 members, 70 institutions
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
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
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
Dark Energy Spectroscopic Instrument Commissioning ongoing Start April 1st Whirlpool galaxy The Dark Energy Spectroscopic Instrument (DESI) First light - Commisioning Instrument - April 1st 2019
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
Discovery & Follow-up Cosmology Classification
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
You can also read
