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Cosmology with Type-Ia Supernovae. Ramon Miquel Lawrence Berkeley National Laboratory and ICREA / IFAE, Barcelona. IRGAC, July 11-15 2006, Barcelona. Type-Ia SNe as cosmological tools Cosmological analysis Systematic uncertainties Current surveys: SNLS Future surveys: SNAP Summary. - PowerPoint PPT Presentation
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Cosmology with Type-Ia Supernovae
Ramon Miquel
Lawrence Berkeley National Laboratoryand
ICREA / IFAE, Barcelona
IRGAC, July 11-15 2006, Barcelona
July 13, 2006 Ramon Miquel IRGAC 2006 2
Outline
• Type-Ia SNe as cosmological tools• Cosmological analysis• Systematic uncertainties• Current surveys: SNLS• Future surveys: SNAP• Summary
July 13, 2006 Ramon Miquel IRGAC 2006 3
Type-Ia SNe probe dark energy through the history of the expansion rate
• Friedmann-Lemaître Equations (GR + homogeneity and isotropy):
a : scale factor : energy density p : pressure k : curvature
• After specifying a equation of state p = p() for each component:
H2(z) = H20 [M (1+z)3 + DE (1+z)3(1+w)] , a = (1+z)-1
matter dark energy flat universe, constant w = p/
• Measuring the history of the expansion rate, H(z), we can learn about the universe constituents, M, DE, w.
Universe Constituents and Dynamics
2
2
3
8
33
4
a
kρ
πG
a
a
pρπG
a
a
aaH /.
July 13, 2006 Ramon Miquel IRGAC 2006 4
• Standard candles provide a measurement of the luminosity distance as a function of redshift:
: flux
L : intrinsic luminosity
dL : luminosity distance
r(z) : co-moving distance
• Astronomers measure the apparent magnitude and redshift:
– M is the (assumed unknown) absolute magnitude of a type-Ia SN.– H0 dL does NOT depend on H0
Probing Dark Energy with Type-Ia SNe
z
L
zH
dzzr
r(z)z)(zd
0 )'(
')(
1)(
]Mpcs km100/[log525
)]([log5)/(log5.2)(11
010
010010
HM
zdHzm L
M
M
24/ LdL
(geometric test of dark energy)
July 13, 2006 Ramon Miquel IRGAC 2006 5
Type-Ia Supernovae (I)
• Defined empirically as supernovae without Hydrogen but with Silicon in spectrum.
• Progenitor understood as a white dwarf accreting material from a binary companion.
• As the white dwarf approaches Chandrasekhar mass, a thermonuclear runaway is triggered.
• A naturally triggered and standard bomb.
July 13, 2006 Ramon Miquel IRGAC 2006 6
Type-Ia Supernovae (II)
• General properties:– Homogeneous class of events: luminosity, color, spectrum at
maximum light. Only small (correlated) variations– Rise time: ~ 15 – 20 days– Decay time: ~ 2 months
– Bright: MB ~ –19.5 at peak
• No hydrogen in the spectra:– Early spectra: Si, Ca, Mg, ...(absorption)– Late spectra: Fe, Ni,…(emission)
• SN Ia found in all types of galaxies, including ellipticals– Progenitor systems must have long lifetimes
July 13, 2006 Ramon Miquel IRGAC 2006 7
Discovering Supernovae
8Ramon Miquel IRGAC 2006July 13, 2006
Are Type-Ia SNe Standard Candles?
apparent magnitude → distance → time
July 13, 2006 Ramon Miquel IRGAC 2006 9
Type-Ia SNe as Standardizable Candles
• Nearby (z < 0.1) supernovae used to study SNe light curves• Brightness not quite standard• Intrinsically brighter SNe last longer• Correction needed
Peak-magnitude dispersion of 0.25 – 0.30 mag
~ 0.10 – 0.15 mag dispersion(5 – 7% precision in distance)
• After correction, standardcandles in optical region (at least).
July 13, 2006 Ramon Miquel IRGAC 2006 10
Near-Optical Bands
g r i z
July 13, 2006 Ramon Miquel IRGAC 2006 11
Near-Optical Bands
U B V Rz = 0.5
→ ·(1+z)
I
z = 1.0 U B V R
July 13, 2006 Ramon Miquel IRGAC 2006 12
Type-Ia SN Spectral Features
• Spectra at near maximum light are used to determine type of SN (Si-II feature)
• And to measure the redshift, z, by observing the shift in the spectrum
Si-II
July 13, 2006 Ramon Miquel IRGAC 2006 13
Images
Spectra
Redshift & spectral properties
Light Curves
Data Analysis Science
M and
w and wa
SN Analysis
July 13, 2006 Ramon Miquel IRGAC 2006 14
Hubble Diagram
July 13, 2006 Ramon Miquel IRGAC 2006 15
Discovery of Acceleration
July 13, 2006 Ramon Miquel IRGAC 2006 16
High-z Results
Riess et al. 2004; also Knop et al. 2003
• Expansion went from deceleration to acceleration
• Exclude simple gray dust models
(m
-M)
(mag
)
redshift
July 13, 2006 Ramon Miquel IRGAC 2006 17
Current Surveys
(300)
July 13, 2006 Ramon Miquel IRGAC 2006 18
Systematic Errors
• Statistical error is dominated by intrinsic SN peak magnitude dispersion int = 0.10–0.15
• Many systematic errors will be totally correlated for SNe at similar redshifts
– Current and near-future surveys will have O(100) SNe for z = 0.1 redshift bin.
– Therefore, systematic errors of order int/√NSN = 0.01–0.02 will already become important or even dominant.
July 13, 2006 Ramon Miquel IRGAC 2006 19
Sources of Systematic Errors
Error Source ControlHost-galaxy dust extinction
Wavelength-dependent absorption identified with high S/N multi-band photometry.
Supernova evolution
Supernova sub-classified with high S/N light curves and peak-brightness spectrum.
Flux calibration error
Program to construct a set of 1% error flux standard stars.
Malmquist bias Supernova discovered early with high S/N multi-band photometry.
K-corrections Construction of a library of supernova spectra.
Gravitational lensing
Measure the average flux for a large number of supernovae in each redshift bin.
Non-Type-Ia contamination
Classification of each event with a peak-brightness spectrum.
*
*
*
*
Kim, Linder, Miquel, Mostek, MNRAS 347 (2004) 909
July 13, 2006 Ramon Miquel IRGAC 2006 20
Extinction by Dust (I)
Dust in the path between the SN and the telescope attenuates the amount of light measured
• Milky Way dust is well measured and understood (Schlegel, Finkbeiner & Davis 1998)
• Host galaxy extinction leads to reddening of supernova colors:
AV = RV · E(B-V)
• In another band j, the extinction is (Cardelli, Clayton & Mathis 1989)
AV : increase in magnitude in V bandE(B-V): excess in B-V color over expectedRV ≈ 3.1 in nearby galaxies
)()()()(
)( jjVjV
jjVjj baRVBEm
R
baAmm
known
(≈ 0-0.10)
2600 citations
1400 citations
What is the value of RV in distant galaxies?
July 13, 2006 Ramon Miquel IRGAC 2006 21
Extinction by Dust (II)
Different approaches to RV determination:
• Riess et al. 2004 (HZT) assume RV = 3.1, as it appears to be in the local universe. Include exponential prior on AV. Bias?
• Astier et al. 2006 (SNLS) instead determine one RV value for all their high-z SNe, coming up with a much lower value RV = 0.57 ± 0.15
– Their RV effectively includes any other effect that might correlate SN color and magnitude.
• SNAP will determine RV for each SN independently.
– Needs at least 3 bands for each SN
)()()()(
)( jjVjV
jjVjj baRVBEm
R
baAmm
July 13, 2006 Ramon Miquel IRGAC 2006 22
Dust Biases
Linder & Miquel 2004
Current data quality
No extinction (e.g. only SNe in ellipticals) Extinction corrected With AV bias With AV and RV biases
w(z) = w0 + (1-a) wa
Linder 2003
July 13, 2006 Ramon Miquel IRGAC 2006 23
Gray Dust?
• Gray dust would be dust that does not lead to any measurable reddening (equivalently, RV → ∞)
• Therefore, it’s not correctable with the usual methods.• “Natural” models would lead to a dimming of SNe at all redshifts.
Simple gray dust models excluded
Some contrived models are just
indistinguishable from CDM
Riess et al. 2004; also Knop et al. 2003
(m
-M)
(mag
)
July 13, 2006 Ramon Miquel IRGAC 2006 24
U B V Rz = 0.5
→ ·(1+z)
I
• At high z, one needs to relate measured fluxes in, say, R, I, z filters with fluxes in SN rest frame B, V, R bands.
• Good empirical model for SN spectrum from B to z is needed.
K-corrections
))1('()'('
)()(log5.2
)()(
)()(log5.2 10
0
0
10zTd
Td
Td
TdK
RSN
BSN
R
B
BR
≈ O(0.5 mag)
July 13, 2006 Ramon Miquel IRGAC 2006 25
Calibration• Calibration ≡ determining the “zero-points” 0,j of each filter j
• Overall normalization is irrelevant• Relative filter-to-filter normalization is crucial (K-corrections, dust-
extinction corrections) Standard cal = 0.005 Standard cal = 0.001 Self cal = 0.005
w0
wa
68% CL contours
*
Kim & Miquel 2006
Standard procedure uses well-understood stars to get cal = 0.01 at best
Alternative procedure using also SN data themselves achieves a large degree of self-calibration (Kim & Miquel 2006)
Example for SNF + SNAP (300 + 2000 SNe up to z = 1.7)
July 13, 2006 Ramon Miquel IRGAC 2006 26
Current SNe Surveys
SNLS ESSENCE
SDSS-II / SNe SuperNova Factory
July 13, 2006 Ramon Miquel IRGAC 2006 27
The SuperNova Legacy Survey (SNLS)
• Ongoing (2003-2008) SN survey using CFHT (Mauna Kea):
– 3.6 m aperture
– 1 deg2 field of view
– 328 Megapixel camera (MegaCam)
• Photometry for 40 nights/yr during 5 years.
– 4-night cadence rolling search in four 1-deg2 fields in g, r, i, z bands.
• Expect to discover 500-700 type-Ia SNe up to z = 1.
• Spectroscopic follow-up of most good SN candidates in VLT, Gemini, Keck…
July 13, 2006 Ramon Miquel IRGAC 2006 28
SNLS Dataz = 0.36 z = 0.91
day
z = 0.285
July 13, 2006 Ramon Miquel IRGAC 2006 29
SNLS Analysis
• Light-curve fit performs K-corrections and returns miB at peak (SN
rest frame), stretch si and color excess Ei(B-V).
• Every available filter is used in fit, provided it corresponds to U, B, V, R in SN rest frame.
• At least two filters are required.
• The cosmology fit then proceeds as:
• 44 published nearby (z < 0.1) SNe and 73 new high-z SNe are used in the fit.
• Statistical errors dominate now, but systematic errors will dominate with final sample.
– Main systematic error: calibration.
)()1()],([log5 010 VBEszdHm iiiLB
iB M x : free parameter
cosmological params.
July 13, 2006 Ramon Miquel IRGAC 2006 30
SNLS Hubble Diagram
First-Year SNLS Hubble Diagram 73 high-z SNe
Astier et al. 2006
int = 0.12 mag
mag
nitu
de (
B-b
and)
+ c
onst
ant
redshift
July 13, 2006 Ramon Miquel IRGAC 2006 31
SNLS Results
SNLS + BAO (Einsestein et al. 2005) SNLS + WMAP-3 (Spergel et al. 2006)
021.0029.0
066.0085.0
281.0
984.0
M
w
022.0271.0
105.0023.1
M
wFlat universe assumed
1 XM
July 13, 2006 Ramon Miquel IRGAC 2006 32
Next Generation SNe Surveys from the Ground
DES Pan-STARRS
LSST
(2008-2012)
July 13, 2006 Ramon Miquel IRGAC 2006 33
SNe without spectroscopy?
• Next generation SN surveys from the ground will gather about 2000 type-Ia SNe with redshifts up to z = 1.2.– Practically impossible to get spectroscopy for all those SNe.
• Is it possible to do cosmology with type-Ia SNe without spectroscopy?– Redshift determination
• Photometric redshifts
• Host galaxy redshift?
– Typing
• Typing from goodness of light-curve fit.
– Systematic tests: ???
July 13, 2006 Ramon Miquel IRGAC 2006 34
SNLS Photo-z’s and Photo-z Typing
– Photo-z’s:• <|zphot - zspec|> = 0.03*(1+z)
assuming cosmology known. • But small dependency on the
assumed cosmological values.
– Photo-typing: • 90% purity using a real-time
analysis of pre-maximum light curves.
• Presumably, it can be improved using all light-curve information.
M=0.25, =0.75
M = 1, = 0
Sullivan et al. 2006
◊ Fail 2 cut
July 13, 2006 Ramon Miquel IRGAC 2006 35
Future SNe Surveys from Space
JDEM/SNAP JDEM/Destiny
JDEM/JEDIDUNE
(2013-2016)
July 13, 2006 Ramon Miquel IRGAC 2006 36
Why Space?
• Precision on wa increases by going to z > 1
• Window into deceleration (z > 1) era can help with syst. errors.
• For z > 1-1.2, rest-frame B band redshifts into observer IR region ( > 1.2 m)
• Atmospheric absorption is large in IR region
Need space-based telescope
SNAP simulation
Miquel 2004
July 13, 2006 Ramon Miquel IRGAC 2006 37
The SNAP Satellite
• 2m-class wide-field telescope with state of the art optical and NIR camera and spectrograph
– Collect about 2000 type-Ia SNe with z < 1.7
– Study weak lensing from space
• Could fly in ~2013. Part of JDEM (DOE/NASA) competition.
July 13, 2006 Ramon Miquel IRGAC 2006 38
Fixed filters atop the sensors
SNAP Focal Plane
Guider
Spectrograph port
VisibleNIRFocus starprojectors
Calibration projectors
D=56.6 cm (13.0 mrad)
0.7 square degrees
Field beforeslicing
Pseudo-slit
Slicing mirror (S1)
Spectrogram
Pupil mirrors(S2)
To spectrograph
Field optics (slit mirrors S3)
From telescopeand fore-optics
Integral Field Spectrograph
July 13, 2006 Ramon Miquel IRGAC 2006 39
SNAP (and DES) Optical Detectors
• New LBNL technology: thick back-illuminated CCD detector.
• Better red response (up to = 1 m) than “thinned” CCDs devices in use at most telescopes.
• High-purity silicon has better radiation tolerance for space applications.
July 13, 2006 Ramon Miquel IRGAC 2006 40
(Some) SNAP Systematics
• Dust extinction:
– Measure each SN in 9 → 3 (low to high z) filters
– Can determine AV and RV for each SN independently.
• Evolution:– Properties of SNe that correlate with luminosity can change with z
– Get precise spectrum at maximum light for all SNe
– Classify SNe according to sub-type. This needs a large database of nearby SNe with good photometry and spectra (SNF)
– Perform cosmology fits within sub-types including low- and high-z SNe (“like-to-like” comparison).
– In practice, allow for several Mi in cosmology fit (one for each sub-type).
– Statistical degradation because of extra parameters is only few % (Kim, Linder, Miquel, Mostek 2004)
July 13, 2006 Ramon Miquel IRGAC 2006 41
• For a fiducial CDM model
– w0 measured to 10%
– w’ ( ≈ wa / 2) to 10%
• Better for most other models (more sensitive to late-time dark-energy)
• Big improvement after adding weak lensing
w’ ≈
wa /
2
w0
SNAP Reach
Linder 2005
July 13, 2006 Ramon Miquel IRGAC 2006 42
Summary
• Type-Ia SNe provided the “smoking gun” for acceleration.
• Mature technique still being perfected.
• Control of systematic errors key to future improvements.
• Vigorous current and future program:• Low-z from ground: SNF, SDSS-II/SNe, CfA, Carnegie…
• Medium- to high-z from ground: Essence, SNLS, DES, Pan-STARRS, LSST
• High-z from space: HST, JDEM, DUNE
Expect more insight on the nature of Dark Energy from type-Ia SNe studies