USING TRANSIENTS TO ILLUMINATE THE DARK UNIVERSE R. Chris Smith NOAO/CTIO ESSENCE, SuperMACHO, and the Dark Energy Survey
Todays BIG Questions: Dark Energy & Dark Matter Dark Energy is the dominant constituent of the Universe. Dark Matter is next. 95% of the Universe is in Dark Energy and Dark Matter, for which we have little or no detailed understanding. 1998 and 2003 Science breakthroughs of the year
Transients illuminate the Darkness Dark Matter Microlensing a key probe of local dark matter Previous microlensing surveys provided enigmatic results; more questions to be answered Dark Energy Supernovae are the most precise distance indicators at large distances First clear indications of dark energy came from studies of distant supernova light curves
Microlensing Primer star D2D2 D1D1 detector b mass M Macho collaboration Gravitational amplification of the light of an unresolved light source Depends on mass, velocity, and geometry(b, D 1, D 2 ). Degeneracy!
Assumes uniform priors in f and log(m) Best fit is f = 0.2, M=0.5 Note that f = 0 and 100% are both excluded! Even at f=0.2, this is more mass than all known MW components Assumes uniform priors in f and log(m) Best fit is f = 0.2, M=0.5 Note that f = 0 and 100% are both excluded! Even at f=0.2, this is more mass than all known MW components MACHO Project
Where are the lenses? We need many more LMC microlensing events
SuperMacho Goal: Differentiate between whether lenses are in the LMC or Halo Need ~50 well-characterized events Single band: VR = 5200–7200Å ~60 fields = ~21 deg 2 Half-nights every 2 nights for 3 months (Oct-Dec) Exposure times optimized to maximize # of stars, ranging from 20s to 200s = 0.1 mag at 23rd http://www.ctio.noao.edu/~supermacho
A Repulsive Result! Expansion of Universe is accelerating!!! Implies NEW PHYSICS! Regions of empty space REPEL each other! Cosmological constant? Einsteins greatest blunder… OR NOT?!! Something going on in the vacuum? Characterize equation of state of dark energy Key parameter, w, in generalized EOS P=wρ w = -1 for cosmological constant
Attacking the Questions of Dark Matter & Dark Energy Classical approach wont work Not enough telescope time Difficult to control calibrations & systematics LARGE SURVEYS Goal: Provide large, uniform, well calibrated, controlled, and documented datasets to allow for advanced statistical analyses Control calibrations & systematics to <1% Larger collaborations provide both manpower and diverse expertise Including both traditional astronomers and high-energy physicists
Dark Energy ROADMAP to understanding Today ESSENCE, rolling search 3 months per year CFHT SNLS, more time = more Supernovae! Coming Soon to a telescope nearby PanSTARRs PanSTARRs 1 going into operations in 2006 PanSTARRs 4 moving forward Dark Energy Survey Camera to be built by Fermilab w/ DOE funding (2009?) The next BIG step LSST Scanning the sky repeatedly to around 24th mag Stepping UP Space-based work: JDEM (SNAP and/or others) Going after higher redshift, and higher order effects!
ESSENCE GOAL: Constrain value of w to within about 10% Need ~200 Type Ia SNe: Populate bins of z=0.1 in range of 0.15 < z < 0.75 Multiple bands: RI, R=200s to get out to z~0.8 Cover redshift range and SN colors ~32 fields = ~12 deg 2 16 fields in half nights every 4 nights for 3 months http://www.ctio.noao.edu/wproject or http://www.ctio.noao.edu/essence
Today: ESSENCE + SuperMACHO Use a LARGE (~200 SNe), UNIFORM set of supernova light curves to allow us to study the evolution of the expansion of the universe Constrain w, the equation of state parameter of Dark Energy, to ~10% Use other half of nights to constrain possible DARK MATTER candidates The SuperMACHO project Search the Large Magellanic Cloud for microlensing 30 SN+SM nights/year for 5 years (2002-2006)
Common Requirements Detect and follow faint transients with variability on timescales of days Detection of faint transients on complicated backgrounds Area+Depth: Need wide field + ~4m aperture Sampling: between nightly and weekly Rapid transient detection for alerts and planning of follow- up observations Ability to process >20 GB/night in near real time Detections matched against catalogs: new object? Transient alerts <12 hours after observations for follow-up on large telescopes
The Strategy Repeatable Reliable Wide-field Multi-color Imaging CTIO Blanco 4m + MOSAIC II Every other night, Oct - Dec, 2002-2006
The Strategy: Details Rolling Searches Continuous (3 month) search: Half night every other night (dark+grey) for 3 mo. Actually visit SAME field every 4th night; adequate light curve coverage for intermediate z SNe Multi-color search in RI (SNe) and VR (MLs) Multi-color light curves for free No CR splits require coincidence in 2 bands AND/OR across >2 epochs SNe Equatorial fields (+5 to -30), SM in LMC Including fields in NDWFS Cetus, SDSS overlap, etc. Monitor 12 sq. deg. (ESSENCE), 25 sq. deg (SM) Exposure times optimized for distribution of SN z ESSENCE: Expect ~20 SNe / month (all types) SuperMACHO: Expect ~3-4 microlensing events / month
ESSENCE+SuperMACHO The data flows… The telescope CTIOs Blanco 4m The camera MOSAIC 8Kx8K imager (67 megapixels) Exposures of 60s to 400s Collect 20GB of RAW data per night Data must be reduced and analyzed in near REAL TIME (within ~30min) Data Reduction = 5x EXPANSION! Roughly 3TB per year
… and flows much larger data flow than most other astronomical projects With ADDITIONAL complication of real-time reduction & alert requirement Must plan spectroscopic follow up on largest telescopes (Gemini, Keck, VLT, Magellan, …) We THOUGHT we were ready A few CPUs (cluster of 20 x 1GHz) A few disks (4 x 4TB data bricks) But…
Identify variability in near- real time, classify ASAP Remove instrumental artifacts Flatfield, illumination, astrometric & photometric calib Frame subtraction to identify transients Geometrical registration Convolution with varying kernel Subtraction Object identification on difference image Classification (SN, asteroid, etc.) Need a LOT of information to do well Usually requires several visits
Searching for SNe, MLs, and other transients High-z SN Team
Web based management Web-sniff preliminary pass Eliminate most false positives Good candidates moved to Alert list Reviewed again, ranked priority Put on spectroscopic target list Ranked by spec priority Updated as spectroscopy comes in
Public Web Announcements Announcements immediately upon confirmation RA, Dec, magnitudes, offsets Finder charts: PDF, PS, and FITS data! redshift (to one decimal) when known all SNe sent to IAU Circulars SNe used by two projects for I-band cosmology at z=0.5 (CSP and PUC) Final reductions archived in NOAO Science Archive
Data Management: Distribution No proprietary period on survey images Distribute RAW data ASAP after observations Distribute REDUCED (flat-fielded) data soon after (final?) reduction No proprietary period on transient announcements and followup information SN and other transients posted to web in real time, also announced via IAUCs and email Additional spectroscopic info also posted
Future: Dark Energy Camera Proposal by Fermilab, CTIO, Univ. Chicago, Univ. Illinois, NCSA, LBNL, and more each month! Dark Energy CAMERA 2-deg diameter imager, pi square degrees on CTIO4m Dark Energy SURVEY FOUR complementary science projects Cluster work (based on SZ work), Weak Lensing, SNe 5000 sq. deg covered in griz (cluster and lensing) 30% of time on CTIO 4m over 5 years, 2009–2014
The Data: Dark Energy Survey Each image ~ 1GB 350 GB of raw data / night Data must be moved to NCSA before next night begins (<24 hours) >36Mbps internationally Data must be processed within ~24 hours Need to inform next nights observing Total raw data ~0.2 PB TOTAL Dataset 1 to 5 PB Reprocessing planned using Grid resources
Dark Energy Camera SN survey Dark Energy Survey team to dedicate ~10% of time for SN search and science Strawman strategy 1 hour per night for 4 months for 5 years riz in ~40 sq-deg 3 day sampling for each field >2000 SNe in range 0.25 < z < 0.75 statistical accuracy of 0.02 in w NOT including systematics! Floor probably well above
Dark Energy Camera SNe Projected constraints on WM and w from the five-year DES SN survey. A flat cosmology has been assumed. Red: the SN survey alone; blue: joint constraints from SNe + 2dF (WM = 0.278 ± 0.042) (left) and joint constraints from SNe and the SPT +DES cluster survey (right). Contours represent 1, 2, and 3 confidence levels. The curves at right represent the constraints on w after marginalization over WM. BUT CAN WE DO THIS WITH LIMITED SPECTROSCOPY? Simulations by G. Miknaitis, using Tonry-tool
Hi-ho, hi-ho… Back to looking for diamonds in the data mines.
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