Probing Dark Energy with Supernovae

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Probing Dark Energy with Supernovae

• Josh Frieman

Benasque Cosmology Workshop, August 17, 2006
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Probing Dark Energy the Present

• Probe dark energy through the history of the
  expansion rate
• H2(z) H20?M (1z)3 (1 ?M)(1z)3(1w)
  flat Universe
• matter dark
  energy constant w
• 2-parameter model
• Geometric tests
• Comoving distance
  r(z) F? dz/H(z)
• Standard Candles Supernovae
  DL(z) (1z) r(z)
• Standard Rulers Baryon Oscillations
  DA(z) (1z)?1 r(z)
• Standard Population Clusters
  dV/dzd? r2(z)/H(z)

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Supernova Data
a(t)
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Is the game over?
Constraints on Dark Energy Equation of State
CFHT SNLS SDSS BAO Astier etal 2005
Complementarity is Critical
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Probing Dark Energy the Future

• Probe dark energy through the history of the
  expansion rate
• H2(z)/H20 ?M(1z)3
  matter
• ?DE exp 3 ?(1w(z)) d
  ln(1z) DE
• (1 ?M
  ?DE)(1z)2 curvature
• Parametrize w(z) w0 waz/(1z)
• And through the growth rate of large-scale
  structure g?/a

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Constraints on Time-varying Dark
Energy 3-parameter model Jarvis etal 2005
Were not there yet!
Assumes flat Universe
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The Cosmic Problems
Cosmological constant problem why is the vacuum
energy density at least 60-120 orders of
magnitude smaller than expected? This problem
predates DE. ?vac ?/8?G ?(1/V) ? h?/2 ?M
h(k2m2)1/2 d3k M4 gtgt (.003 eV)4 Coincidence
problem why do we live at the special epoch
when the dark energy density is comparable to the
matter energy density?
?matter a-3
?DE a-3(1w)
a
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Scalar Field Models Coincidence
Dynamics models (Freezing models)
Mass scale models (Thawing models)
V
V
e.g., e? or ?n
?
?
MPl
Runaway potentials DE/matter ratio
constant (Tracker Solution)
Pseudo-Nambu Goldstone Boson Low mass protected
by symmetry (Cf. axion) JF, Hill, Stebbins,
Waga V(?) M41cos(?/f) f MPlanck M
0.001 eV m?
Ratra Peebles Caldwell, Steinhardt,etal
Albrecht etal,
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Caldwell Linder
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Goal for 2011 SPTDES
Goal for 2015 JDEM, LSST
Caldwell Linder
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Second DE Coincidence Problem is w??1 natural?
If w??1, why is the scalar field dynamics
changing just around the time it begins to
dominate the Universe?
?matter a-3
?DE Tracker
? DE PNGB
a(t)
Today
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Axion (PNGB) Dark Energy
The only symmetries in String Theory which might
yield light scalars are axions. (Banks
Dine) In these models, coincidence problems
indicate a new (effective) mass scale
e.g., 10?3 eV exp(2?2/g2) MSUSY
ma2 exp(8?2/g2) MSUSY4/MPl2
(10-33eV)2
V(?) M41cos(?/f)
JF, Hill, Stebbins, Waga 95 Kim Choi Namura,
etal, Hall, etal 05 There is little reason to
assume that w 1 is particularly likely.
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Ia
Early SN Spectra Filippenko 1997
II
Ic
Ib
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SN1998bu Light curve Suntzeff, etal Jha,
etal Hernandez, etal
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Nearby SN 1994D (Ia)
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Evolution of Spectral Features Patat etal
1996 Filippenko 1997
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Evolution of Spectral Shape Nugent
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Layered Chemical Structure provides clues to
Explosion physics
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Spectral Homogeneity at fixed epoch
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SN2004ar z 0.06 from SDSS galaxy spectrum
Galaxy-subtracted Spectrum SN Ia template
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Type Ia SN Peak Brightness as calibrated Standard
Candle Peak brightness correlates with decline
rate
?m15
Luminosity
15 days
Time
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SN Ia Peak Luminosity Empirically correlated with
Light-Curve Decline Rate Brighter
?? Slower Use to reduce Peak Luminosity
Dispersion Phillips 1993
Peak Luminosity
Rate of decline
Garnavich, etal
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Type Ia SN Peak Brightness as calibrated Standard
Candle Peak brightness correlates with decline
rate After correction, ? 0.15 mag (7
distance error)
?m15
15 days
Luminosity
Time
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Correction for Brightness-Decline relation reduces
scatter in nearby SN Ia Hubble Diagram Riess
etal 1996
??? m(z) MB 5log(H0)255logH0DL(z,?m,?DE,w)
KBx A
Luminosity Distance
Distance modulus
K-correction Extinction
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Type Ia Supernovae

• General properties
• Homogeneous class of events, only small
  (correlated) variations
• Rise time 15 20 days
• Decay time many months
• Bright MB 19.5 at peak
• No hydrogen in the spectra
• Early spectra Si, Ca, Mg, ...(absorption)
• Late spectra Fe, Ni,(emission)
• Very high velocities (10,000 km/s)
• SN Ia found in all types of galaxies, including
  ellipticals
• Progenitor systems must have long lifetimes

luminosity, color, spectra at max. light
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Caveat Comparison of 3 Brightness-Decline Methods
1. ?m15 (Phillips etal) 2. Stretch (Perlmutter
etal) 3. MLCS (Riess etal) Substantial
differences on SN-by-SN basis seen in nearby and
distant samples Yet cosmological results agree
Liebundgut 2000
Extinction
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Caveat Peculiar SNe Ia that dont fit the
Brightness- Decline relation Sn2000cx See also
2002cx Li etal 2001
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Spectral Correlates With Peak Luminosity Possible
Ia Subclasses based on velocity gradients
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SN Ia Theory

• Standard model
• SNe Ia are thermonuclear
• explosions of CO white
• dwarf stars.
• Evolution to criticality
• Accretion from a binary companion leads to growth
  of the WD to the critical Chandrasekhar mass
• ( 1.4 solar masses).
• After 1000 years of slow thermonuclear
  cooking, a violent explosion is triggered at or
  near the center complete incineration within
  less than two seconds, no compact remnant

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Chandrasekhar Mass Models
WD accretes H or He from non-degenerate
companion, burns on the surface to CO
(alternate WD binary merger) When M MCh,
compressional heating--gt thermonuclear
instability C, O burn explosively to 56Ni (np)
in the core ? explosion driven by Ekin
released from fusion reactions in a few
seconds. Free expansion of unbound ejecta
thereafter, with velocities 104 km/sec.
Outer regions burn to Si, Ar, Ca, seen in
early spectra. Radioactive decays 56Ni ? 56Co
? 56Fe MeV photons ?s downscatter,
thermalizeand escape as optical/NIR
light light curve 0th order homogeneity MCh
fully burned ? MNi 0.6 Msun ?
fixed Lmax
days
months
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Chandrasekhar Mass Models
1st order diversity spread in progenitor Mass
(17 Msun) or metals ? spread in WD C/O ?
spread in MNi produced Ekin ? spread in
Lmax Other diversity factors varying accretion
rates, rotation speeds, magnetic fields,
metallicity Correlation between Lpeak and
decline rate (?m15, LCS, stretch) Increase
MNi ? increase L Increase MNi ? increase T ?
increase opacity ? increase photon
diffusion time ? longer decline
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Type Ia Supernovae

• Popular Explosion model
• Deflagration Subsonic burning turbulent,
  pre-expands WD, allowing production of
  intermediate-mass elements (in addition to Ni)
• Delayed Detonation Supersonic burning leads to
  layered chemical structure
• Main parameter density at deflagration-detonation
  transition
• Parametrized models reproduce LCs, spectra
  reasonably well

Khoklov, Hoflich, etal
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Delayed-Detonation Model Subluminous SN
1999by Model fit to B, V light curves predicts
near IR spectral evolution Höflich et al.
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Brightness/decline and Color relations for
Chandrasekhar Delayed-detonation models

Red - vary M, Z

Blue - constant M, Z, vary DDT transition density
Hoflich, etal
- Small spread in brightness-decline requires
similar explosion energies - Progenitor
metallicity (Z0 ... solar) can produce
systematics of about 0.3 mag. - Color change of
about 0.2 mag -gt conflated with reddening
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Turbulent 3-d Hydro w/ Radiation Transport
Detonation restructures the ejecta
Deflagration is the engine of asymmetry
Niemeyer, Hillebrandt, etal
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Deflagration-Detonation Transition not Understood
Deflagration Bubble rises, propagates around
surface, then detonates
Do we need to understand the explosion mechanism
in detail to have confidence in SN systematics?
Plewa etal 2004
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Dark Energy Discovery from High-redshift SNe
Ia Apply same Brightness-Decline relation at
High-z SNe at z0.5 are 0.25 mag fainter than
in an empty Universe
?? 0.7 ?? 0. ?m 1.
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High-z SN Team 1998 Discovery Data Riess
etal 1998
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Supernova Hubble Diagram CFHT Supernova
Legacy Survey Astier etal 2005
70 high-z SNe
44 low-z SNe from literature
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Constraints CFHT SNLSSDSS BAO
Assuming flatness, constant w
Assuming w ?1
Astier etal 2005
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Light Curves for Nearby Supernovae
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Supernova Hubble Diagram CFHT Supernova Legacy
Survey Astier etal 2005 Needed morebetter
data at low and Intermediate redshift
70 high-z SNe
44 low-z SNe from literature
KAIT, SNF, CSP
SDSS
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SDSS 2.5 meter Telescope
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SDSS Imaging Camera Top to bottom g
z u i r Drift Scan Mode
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SDSS II Supernova SurveySept-Nov. 2005-7

• Obtain 200 high-quality SNe Ia light curves in
  the redshift desert z0.05-0.35 for continuous
  Hubble diagram
• Detailed spectroscopic follow-up, including
  multiple epochs, to study evolution and variety
  of SN features
• Probe Dark Energy in z regime complementary to
  other surveys
• Study SN Ia systematics with high photometric
  accuracy
• Search for additional parameters to reduce Ia
  dispersion
• Determine SN/SF rates/properties vs. z,
  environment
• Rest-frame u-band templates for z gt1 surveys
• Database of Type II and rare SN light-curves
  (large survey volume with multi-band coverage)

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SDSS II 130 spectroscopically confirmed Type
Ia Supernovae from the Fall 2005 Season First
results expected by Jan. 07 AAS
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SN 2005 gb
Composite gri images
Before
After
z 0.086, confirmed at ARC 3.5m
Preliminary gri light curve and fit from low-z
templates
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Finding Supernovae Before Peak Light Important
for good light-curve fit, Peak
Magnitude estimate, and early spectrum
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SDSS II SN Follow-up 2005

• Spectroscopy mainly SN typing, redshift
• NIR imaging extinction/reddening and low-z light
  curves
• Optical imaging follow high-z light curves
  beyond SDSS limit
• Spectroscopy ARC 3.5m (31 half-nights), HET (90
  hrs),
• MDM 2.4m (37
  nights), Subaru (share 6 nights),
• WHT (6 nights), Keck
  (opportunity, 1 night)
• 290 spectra taken
• NIR imaging Carnegie Supernova Project (selected
  targets)
• Optical imaging NMSU 1m, MDM, UH 88in (6.5
  nights),
• VATT (7 nights),
  WIYN (3 nights shared),
• INT (1 night),
  Liverpool Telescope (4 hours),
• CSP low-z

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High-quality Spectra for SN studies
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SDSS III proposal ARC Supernova Survey (ARCSS)

• ARC (which owns SDSS 2.5m) considering proposals
  for new operations from mid-2008
• ARCSS proposed 10-month survey (Sept. 08-June
  09) targetting lower-redshift supernovae
• SDSS IIARCSS 250 well-measured SNe Ia at
  zlt0.15, factor 10 larger than currently
  available low-z sample of comparable data quality
• Improved anchor of Hubble diagram for high-z
  surveys
• Improved understanding of SN systematics for
  precision SN cosmology

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Supernovae Where were headed
Cf. Y.B.
On-going SN surveys
(200)
Future Surveys PanSTARRS, DES, JDEM, LSST

(2000) (3000) (105) high-z
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Supernovae the Future

• Goal Determine w0 to 5 and wa to 20 (in
  comb.with CMB)
• Statistical Requirement 1 relative distance
  measurements
• (2 flux) in ?z0.1 redshift bins
• Assume systematic error can be reduced to this
  level
• Kim, etal 04, Kim Miquel 05
  
• Requires 3000 SNe spread over z 0.3-1.7 and a
  larger,
• well-observed sample at low z to
  anchor the Hubble
• diagram. Consequent requirements
  for NIR and
• photometric stability lead to a
  space-based mission.

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Probing Dark Energy Evolution 2 Mag Systematic
Error Floors
3000 SNe
JF, Huterer, Linder, Turner
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Proposed Joint Dark Energy Mission (JDEM) to
observe 3000 SNe Ia out to z 1.7. See also
DESTINY, JEDI Why Space? To probe z gt 1, need
NIR Control systematics Wide-field opticalNIR
imager O/IR spectrograph
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Type Ia Supernovae Cosmology

• Advantages
• small dispersion in peak brightness (standardized
  candles)
• single objects (simpler than galaxies)
• can be observed over wide redshift range (bright)

• Challenges/Systematic concerns
• dust extinction (in or beyond host galaxy)
  variations, grey
• chemical composition variations/evolution
• evolution of progenitor population
• photometric calibration, stability, host
  galaxy subtraction
• Malmquist bias
• host galaxy environmental differences
• K correction uncertainties
• Biases in Light Curve Fits

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Can we get there? Systematics Concerns
Luminosity Evolution We believe SNe Ia
at z0.5 are not intrinsically 25 fainter than
nearby SNe (the basis for Dark Energy).
Could SNe at z1.5 be 2
fainter/brighter than those nearby, in a way that
leaves all other observables fixed?
Expectation drift in progenitor population mix
(progenitor mass, age, metallicity, C/O,
accretion rates, etc). Control the variety of
host environments at low redshift spans a
larger range of metallicity, age, etc, than the
median differences between low- and
high-z environments, so we can compare
high-z apples with low-z apples, using host
info., LC shape, colors, spectral
features spectral evolution, and
assuming these exhaust the parameters that
control Lmax.
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Can we get there? Systematics Concerns
Evolution Example SNe in spirals 0.3 mag
brighter on avg. than in ellipticals. Due to
galaxy evolution, morphological mix at z1.7 will
be rather different than today, so mean SN
Lmax will differ as well. Control Out to
z0.8, LC-decline-corrected SNe show no E/S
difference in corrected Lmax, within the
errors cosmology results robust to host
morphology. Also High-z Ia spectra appear
very similar to those at low-z. Note
Require large variety of low-z SNe for control
samples.
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Can we get there? Systematics Concerns
Extinction Is high-z host galaxy dust
similar to Milky Way dust?
Evidence for variations in dust properties
Or could there by grey intergalactic dust that
neither reddens nor increases the
dispersion in peak magnitudes? Controls
Observations over broad range of
wavelengths/passbands. Compare
rest-frame NIR data at high-z and low-z.
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Can we get there? Systematics Concerns

• Other Issues
• Peculiar SNe Ia that dont fit the
  brightness-decline relation
• can they be recognized removed at
  high-z? e.g., 2000cx, 2002cx.
• Malmquist bias
• K-correction errors
• Photometric calibration stability, color
  terms
• Could host-galaxy subtraction be harder at
  high z?

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DES, PanSTARRS, LSST
Can we do SN Cosmology with few/no spectra but
very large numbers?
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Supernovae and photo-z errors
Huterer
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SNe Ia as Dark Energy Probes

• Purely geometrical independent of structure
  formation paradigm (unlike clusters, weak
  lensing)
• Nearly orthogonal parameter degeneracy to
  structure-based probes complementary to WL, BAO,
  clusters, CMB
• Best standardizable candles/relative distance
  indicators
• Lots of information in principle available per
  event to provide systematics cross-checks
  multi-epoch spectrophotometry from near UV to
  near IR. How much of this information do we need
  for each SN at high z?
• Few constraints on w will require exquisite
  control of observational systematics (from
  space), improved local SN templates, improved LC
  analysis algorithms, and preferably better
  theoretical SN modeling