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Dark Energy Survey Dark Energy Survey 47th Fermilab Users Mee2ng, June 2014 Marisa Cris2na March on behalf of The Dark Energy Survey Collaboraon 25 ins2tu2ons ~300 scien2sts Image credit: FNAL [email protected] University of Pennsylvania 1 Dark energy and cosmic acceleraon Pre 1998: Hubble’s expanding Universe Post 1998: Accelera2ng Universe 2011 Nobel Prize in Physics: Acceleraon! ! “nothing short of a revoluon in our understanding of fundamental physics will be required to achieve a full understanding of the velocity cosmic accelera2on. …. the nature of dark energy ranks among the very most compelling of all outstanding problems in physical science …. demand an ambious observaonal program to distance! determine the dark energy proper2es as well as possible.” (Dark Energy Task Force, June 2006 ) 2 Dark energy parameters and current combined constraints Dark energy equa2on of state: • Ra2o of dark energy p pressure to density. w = ⇢ • Does w evolve with redshiT? 1 w(z)=w + w 0 a (1 + z) Dark energy eq. of state, w et al 2014 MaRer density wa • Dark energy is best constrained by combining different types of observaons. • What is best dark energy model? Betoule • Dark energy or modified gravity? • Cosmological constant? Plots: M. w0 3 A biography of the Dark Energy Survey 1998 Discovery of Universal acceleraon – dark energy? 2003 DECam and the Dark Energy Survey (DES) proposed. 2008 DECam and DES approved. 2008-12 Construc2on of parts. 2010-11 Shipping of parts to the telescope at CTIO in Chile. 2010-12 Assembly at telescope. Sept 2012 First Light – Science Verificaon commences. Sept 2013 Year 1 of survey begins. Aug 2014 Image credit: FNAL Year 2 of survey begins. 4 Dark Energy Camera: DECam Right: Dark Energy Camera focal plane. Below: Single DECam image with moon superimposed to scale. : mounted on the Blanco telescope DECam The 570 megapiXel Dark Energy Camera was built to Image credit: FNAL carry out an imaging survey to probe the nature of dark energy. The aim is to move from dark energy discovery to precision measurements of dark energy. 5 Dark Energy Survey (DES) DES is inves2gang the nature of dark energy using four different types of This plot to be updated measurements: wa 1. Supernovae type Ia 2. Weak gravitaonal lensing of galaxies. 3. Large Scale Structure. 4. Galaxy cluster measurements. w0 Survey: - 5000 square degrees -525 nights over 5 seasons. -10 supernovae fields. 6 Using standard candles to measure dark energy If you have objects of a standard brightness, you can work out how far away they are based on how bright they appear to be. Define the ‘observed’ distance modulus, to be the difference between the apparent (observed) and absolute magnitudes (brightness) of your standard object: observed µ = mB M0 absolute magnitude − Recipe: apparent magnitude dark energy (1) Measure the apparent The theore2cal distance modulus depends on equaon of magnitude. the redshid and the cosmological parameters: state (2) Measure the redshid. µtheory = f z,⌦ , ⌦ , ⌦ ,w(z) (3) Work out what values the { m ⇤ } cosmological parameters must be to get: redshi maer curvature dark energy theory observed density density density µ = µ 7 Using supernovae type Ia as standard candles We use the stretch and color of the SNe light curves to apply small correcons to (i.e. to standardize) their brightness. stretch µobserved = m M + ↵x βc B − 0 1 − color nuisance parameters SNe Ia thermonuclear explosions come from white dwarf binary mass transfer. magnitude days 8 Type Ia supernovae search with DES SNe Survey operaons: 1. Before survey, make ‘templates’. 2. During survey, visit each SNe field a minimum of once every seven days. 3. Subtract the ‘template image’ from the First SN new ‘search image’ and look for SNe confirmed candidates using human scanning and by DES, machine learning. Template z =0.2 (AAT) 4. Classify candidates using a light curve photometric typer. Expected yield: 5. Monitor pipeline by injec2ng fake ~4000 SNe to events. be discovered 6. Follow up ~10% of SNe Ia candidates over 5-years. spectroscopically. Follow up all host galaxies at a later date to get a Challenge: spectroscopic redshid. (Non DES Photometrically instruments) classifying SNe Search Ia without SN spectra. 9 A shallow field DES light curve z=0.32 g-band r-band Data points: search photometry from subtracted DES images. Solid lines: Flux i-band z-band Fit to SALT2 light curve model. Days Graphics: C. D’Andrea, ICG Portsmouth 10 A deep field DES light curve z=0.35 g-band r-band Data points: search photometry from subtracted DES images. Solid lines: Flux i-band z-band Fit to SALT2 light curve model. Days Graphics: C. D’Andrea, ICG Portsmouth 11 A high redshid DES light curve: z=0.9 [Deep field] DES13X3jce g-band r-band 1500 Host specz = 0.9099 1000 g-band r-band Data points: search Flux (nJy) 500 photometry 0 from subtracted Flux i-band z-band DES images. 1500 Solid lines: 1000 i-band z-band Fit to SALT2 light curve Flux (nJy) 500 model. 0 -40 -20 0 20 40 60 80 -40 -20 0 20 40 60 80 Observer Phase (days) Observer Phase (days) Days Graphics: C. D’Andrea, ICG Portsmouth 12 Pre-DES 1st year DES Conley et al 2011 (adapted) RedshiT, z RedshiT, z • Above Hubble plot is from a compilaon • 1st Year DES SNe survey yielded of 475 SNe Ia from four different ~800 Sne type Ia light curves that surveys. (Current largest compilaon pass selec2on and quality cuts. uses ~800 SNe Ia) • EXpected 5 year yield: ~3500 SNe type Ia. 13 Galaxy clusters & tests of analysis methods Opcal DECam image Weak lensing mass contours Cluster members Melchior et al 2014, arXive: 1405.4285 • Background galaxies iden2fied using photometric redshiTs (photo-z). • Cluster member galaxies idenfied using photometry & redMaPPer algorithm. • Test of weak lensing algorithm Im3shape with DECam images. • Good agreement between both mass mapping methods & also previous studies. 14 First wide field weak lensing analysis et al, in prep prep in al, et Vikram V. Weak lensing mass map Foreground galaxies – tracers of maRer. (Uses background galaxies) Weak lensing and foreground are correlated at a stascally significant level ! Good check of weak lensing technique 15 Large scale structure: galaxies & CMB lensing South Pole Telescope (CMB Lensing) et al Bias ~1.05 T.Giannantonio , • Galaxy-galaxy correlaon funcon P.Fosalba probes cosmology. Bias ~1.42 • CMB Lensing is a poten2al future dark energy probe. • Galaxy-galaxy is consistent with Planck. • Galaxy-CMB Lensing is consistent with galaxy-galaxy correlaon funcon 16 Year 1 wide survey progress g-band r-band i-band z-band Y-band • Wide survey area is visited 4 mes in each of the bands: g,r,i,z,Y. • Use the mul band images to get photometric redshiT measurement. • Geng accurate images of the galaxy shape is cri2cal for weak lensing measurement. 17 DES at the end of year 1. Feb 2014 saw the conclusion of a successful • Mass and Cluster Galaxy Distribu2ons of year 1 observing season. Y2 begin August Massive Clusters in DES SV Data 2014! • DES: Redshids, X-ray Temperatures, and Luminosi2es for Clusters in SV Data Look out for these upcoming papers based • Galaxy-galaxy Lensing with DES SV Data on SV & Y1 data: • Wide-Field Mass Mapping with DES SV • Discovery and proper2es of a Data Superluminous SN at high redshid • Galaxy Populaons and Stellar Mass • Orientaon Bias of Op2cally Selected Frac2ons in SZE-selected Clusters Imaged Galaxy Clusters and its Impact on Stacked by the DES Weak Lensing Analyses • Crowded Cluster Cores: Algorithms for Deblending in DES Images • Photometric Redshids in the DES SV Data Set • Joint Op2cal and Near Infrared Photometry from the DES and VHS 18 .
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