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Cosmology with Type-Ia Supernovae

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.

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Cosmology with Type-Ia Supernovae

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  1. Cosmology with Type-Ia Supernovae Ramon Miquel Lawrence Berkeley National Laboratory and ICREA / IFAE, Barcelona IRGAC, July 11-15 2006, Barcelona

  2. Type-Ia SNe as cosmological tools Cosmological analysis Systematic uncertainties Current surveys: SNLS Future surveys: SNAP Summary Outline Ramon Miquel IRGAC 2006

  3. Universe Constituents and Dynamics Type-Ia SNe probe dark energy through the history of the expansion rate • Friedmann-Lemaître Equations (GR + homogeneity and isotropy): a : scale factor r : energy density p : pressure k : curvature • After specifying a equation of state p = p(r) 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/r • Measuring the history of the expansion rate, H(z), we can learn about the universe constituents, WM, WDE, w. . Ramon Miquel IRGAC 2006

  4. Probing Dark Energy with Type-Ia SNe • Standard candles provide a measurement of the luminosity distance as a function of redshift: f : 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 (geometric test of dark energy) 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. 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 Ramon Miquel IRGAC 2006

  7. DiscoveringSupernovae Ramon Miquel IRGAC 2006

  8. Are Type-Ia SNe Standard Candles? apparent magnitude → distance → time 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 • After correction, standard • candles in optical region (at least). ~ 0.10 – 0.15 mag dispersion (5 – 7% precision in distance) Ramon Miquel IRGAC 2006

  10. Near-Optical Bands g r i z Ramon Miquel IRGAC 2006

  11. Near-Optical Bands l → l·(1+z) z = 0.5 U B V R I z = 1.0 U B V R 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 Ramon Miquel IRGAC 2006

  13. SN Analysis Light Curves Images Redshift & spectral properties M and L w and wa Spectra Data Analysis Science Ramon Miquel IRGAC 2006

  14. Hubble Diagram Ramon Miquel IRGAC 2006

  15. Discovery of Acceleration Ramon Miquel IRGAC 2006

  16. High-z Results D(m-M) (mag) redshift Riess et al. 2004; also Knop et al. 2003 • Expansion went from deceleration to acceleration • Exclude simple gray dust models Ramon Miquel IRGAC 2006

  17. Current Surveys (300) Ramon Miquel IRGAC 2006

  18. Systematic Errors • Statistical error is dominated by intrinsic SN peak magnitude dispersion sint = 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 Dz = 0.1 redshift bin. • Therefore, systematic errors of order sint/√NSN = 0.01–0.02 will already become important or even dominant. Ramon Miquel IRGAC 2006

  19. Sources of Systematic Errors * * * * Kim, Linder, Miquel, Mostek, MNRAS 347 (2004) 909 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) 2600 citations AV : increase in magnitude in V band E(B-V): excess in B-V color over expected RV≈ 3.1 in nearby galaxies 1400 citations known (≈ 0-0.10) What is the value of RV in distant galaxies? 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 oneRV 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 Ramon Miquel IRGAC 2006

  22. Dust Biases No extinction (e.g. only SNe in ellipticals) Extinction corrected With AV bias With AV and RV biases Current data quality Linder & Miquel 2004 w(z) = w0 + (1-a) wa Linder 2003 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 LCDM D(m-M) (mag) Riess et al. 2004; also Knop et al. 2003 Ramon Miquel IRGAC 2006

  24. K-corrections l → l·(1+z) z = 0.5 U B V R 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. ≈ O(0.5 mag) Ramon Miquel IRGAC 2006

  25. Standard scal = 0.005 Standard scal= 0.001 Self scal= 0.005 wa * 68% CL contours w0 Calibration • Calibration ≡ determining the “zero-points” f0,jof each filter j • Overall normalization is irrelevant • Relative filter-to-filter normalization is crucial (K-corrections, dust-extinction corrections) Standard procedure uses well-understood stars to get scal = 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) Kim & Miquel 2006 Ramon Miquel IRGAC 2006

  26. Current SNe Surveys ESSENCE SNLS SuperNova Factory SDSS-II / SNe 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… Ramon Miquel IRGAC 2006

  28. SNLS Data z = 0.36 z = 0.91 day z = 0.285 Ramon Miquel IRGAC 2006

  29. 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. SNLS Analysis x : free parameter q: cosmological params. Ramon Miquel IRGAC 2006

  30. SNLS Hubble Diagram First-Year SNLS Hubble Diagram 73 high-z SNe magnitude (B-band) + constant sint = 0.12 mag redshift Astier et al. 2006 Ramon Miquel IRGAC 2006

  31. SNLS Results SNLS + BAO (Einsestein et al. 2005) SNLS + WMAP-3 (Spergel et al. 2006) Flat universe assumed Ramon Miquel IRGAC 2006

  32. Next Generation SNe Surveys from the Ground (2008-2012) Pan-STARRS DES LSST Ramon Miquel IRGAC 2006

  33. 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: ??? SNe without spectroscopy? Ramon Miquel IRGAC 2006

  34. SNLS Photo-z’s and Photo-zTyping Sullivan et al. 2006 ◊ Fail c2 cut • 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. WM=0.25, WL=0.75 WM = 1, WL = 0 Ramon Miquel IRGAC 2006

  35. Future SNe Surveys from Space (2013-2016) JDEM/Destiny JDEM/SNAP JDEM/JEDI DUNE Ramon Miquel IRGAC 2006

  36. Why Space? SNAP simulation • 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 (l > 1.2 mm) • Atmospheric absorption is large in IR region Need space-based telescope Miquel 2004 Ramon Miquel IRGAC 2006 Precision on wa as a function of zmax Precision on wa as a function of zmax

  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. Ramon Miquel IRGAC 2006

  38. SNAP Focal Plane D=56.6 cm (13.0 mrad) 0.7 square degrees Focus star projectors Guider NIR Visible Integral Field Spectrograph Spectrograph port Calibration projectors Fixed filters atop the sensors Ramon Miquel IRGAC 2006

  39. SNAP (and DES) Optical Detectors • New LBNL technology: thick back-illuminated CCD detector. • Better red response (up to l = 1 mm) than “thinned” CCDs devices in use at most telescopes. • High-purity silicon has better radiation tolerance for space applications. Ramon Miquel IRGAC 2006

  40. 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) (Some) SNAP Systematics Ramon Miquel IRGAC 2006

  41. SNAP Reach • For a fiducial LCDM 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 Linder 2005 Ramon Miquel IRGAC 2006

  42. 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 Summary Ramon Miquel IRGAC 2006

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