Adam G. Riess

The High-Z Supernova Search: Measuring Cosmic Deceleration and Global Curvature of the Universe Using Type Ia Supernovae*

The High-Z Supernova Search is an international collaboration to discover and monitor Type Ia supernovae (SNe Ia) at z > 0.2 with the aim of measuring cosmic deceleration and global curvature. Our collaboration has pursued a basic understanding of supernovae in the nearby universe, discovering and observing a large sample of objects and developing methods to measure accurate distances with SNe Ia. This paper describes the extension of this program to z ≥ 0.2, outlining our search techniques and follow-up program. We have devised high-throughput filters that provide accurate two-color rest frame B and V light curves of SNe Ia, enabling us to produce precise, extinction-corrected luminosity distances in the range 0.25 M=-0.2 -->−0.8+1.0 if ΩΛ = 0. For a spatially flat universe composed of normal matter and a cosmological constant, we find Ω -->M=0.4 -->−0.4+0.5, Ω

A Precise distance indicator: Type Ia supernova multicolor light curve shapes

{Λ}

A geometric distance to the galaxy NGC4258 from orbital motions in a nuclear gas disk

-->=0.6 -->−0.5+0.4. We demonstrate that with a sample of ~30 objects, we should be able to determine relative luminosity distances over the range 0 < z < 0.5 with sufficient precision to measure ΩM with an uncertainty of ±0.2.

Is the Dust Obscuring Supernovae in Distant Galaxies the Same as Dust in the Milky Way

We present an empirical method that uses multicolor light-curve shapes (MLCSs) to estimate the luminosity, distance, and total line-of-sight extinction of Type Ia supernovae (SNe Ia). The empirical correlation between the MLCSs and the luminosity is derived from a training set of nine SN Ia light curves with independent distance and reddening estimates. We find that intrinsically dim SN Ias are redder and have faster light curves than the bright ones, which are slow and blue. By 35 days after maximum, the intrinsic color variations become negligible. A formal treatment of extinction employing Bayess theorem is used to estimate the best value and its uncertainty. Applying the MLCS method to both light curves and to color curves provides enough information to determine which supernovae are dim because they are distant, which are intrinsically dim, and which are dim because of extinction by dust. The precision of the MLCS distances is examined by constructing a Hubble diagram with an independent set of 20 SN Ias. The dispersion of 0.12 mag indicates a typical distance accuracy of 5% for a single object, and the intercept yields a Hubble constant on the Sandage et al. Cepheid distance scale of H0 = 64 ± 3 (statistical) km s–1 Mpc–1 (±6 total error). The slope of 0.2010 ± 0.0035 mag over the distance interval 32.2 < μ < 38.3 yields the most precise confirmation of the linearity of the Hubble law.

Time Dilation in the Light Curve of the Distant Type Ia Supernova SN 1995K

The accurate measurement of extragalactic distances is a central challenge of modern astronomy, being required for any realistic description of the age, geometry and fate of the Universe. The measurement of relative extragalactic distances has become fairly routine, but estimates of absolute distances are rare. In the vicinity of the Sun, direct geometric techniques for obtaining absolute distances, such as orbital parallax, are feasible, but such techniques have hitherto been difficult to apply to other galaxies. As a result, uncertainties in the expansion rate and age of the Universe are dominated by uncertainties in the absolute calibration of the extragalactic distance ladder. Here we report a geometric distance to the galaxy NGC4258, which we infer from the direct measurement of orbital motions in a disk of gas surrounding the nucleus of this galaxy. The distance so determined—7.2 ± 0.3u2009Mpc—is the most precise absolute extragalactic distance yet measured, and is likely to play an important role in future distance-scale calibrations.

Determining the Motion of the Local Group Using SN Ia Light Curve Shapes

Previous attempts to correct type Ia supernovae (SN Ias) for host galaxy extinction have given strange results: increased dispersion on the Hubble diagram or impossibly low values of the reddening ratio for dust in distant galaxies. The cause is the incorrect assumption that SN Ias have a uniform intrinsic luminosity and color at maximum light. Our multicolor light-curve shape (MLCS) method establishes the relation between intrinsic luminosity and color for SN Ias using information in light-curve shapes. Here we estimate the B - V, V - R, and V - I color excess for 20 SN Ias using MLCS and estimate the reddening ratios of dust in distant galaxies. The ratios of selective to total absorption from dust in distant galaxies hosting SN Ias are consistent with the galactic extinction law. The SN Ias in late-type galaxies are often obscured by dust, while those in early-type galaxies are dust free. This suggests that SN Ia extinction is caused by interstellar (not circumstellar) dust, with similar optical properties as the dust in the Milky Way.

Simulations of the WFIRST Supernova Survey and Forecasts of Cosmological Constraints

The light curve of a distant Type Ia supernova acts like a clock that can be used to test the expansion of the universe. SN 1995K, at a spectroscopic redshift of z = 0.479, provides one of the first meaningful data sets for this test. We find that all aspects of SN 1995K resemble local Type Ia supernova events when the light curve is dilated by (1 + z), as prescribed by cosmological expansion. In a static, nonexpanding universe, SN 1995K would represent a unique object with a spectrum identifying it as a regular Type Ia supernova but with a light-curve shape and luminosity that do not follow the well-established relations for local events. We conclude that SN 1995K provides strong evidence for an interpretation of cosmological redshifts as being due to universal expansion. Theories in which photons dissipate their energy during travel are excluded as are age-redshift dependencies.The light curve of a distant Type Ia supernova acts like a clock that can be used to test the expansion of the universe. SN 1995K, at a spectroscopic redshift of z 5 0.479, provides one of the first meaningful data sets for this test. We find that all aspects of SN 1995K resemble local Type Ia supernova events when the light curve is dilated by (1 1 z), as prescribed by cosmological expansion. In a static, nonexpanding universe, SN 1995K would represent a unique object with a spectrum identifying it as a regular Type Ia supernova but with a light-curve shape and luminosity that do not follow the well-established relations for local events. We conclude that SN 1995K provides strong evidence for an interpretation of cosmological redshifts as being due to universal expansion. Theories in which photons dissipate their energy during travel are excluded as are age-redshift dependencies. Subject headings: cosmology: observations— galaxies: distances and redshifts — supernovae: general — supernovae: individual (SN 1995K)

Pan-STARRS1 DISCOVERY OF TWO ULTRALUMINOUS SUPERNOVAE AT z Almost-Equal-To 0.9

We have measured our Galaxys motion relative to distant galaxies in which type Ia supernovae (SN Ia) have been observed. The effective recession velocity of this sample is 7000 km s

Pan-STARRS1 DISCOVERY OF TWO ULTRALUMINOUS SUPERNOVAE AT(z) approximate to 0.9

^{-1}

Should Type Ia Supernova Distances be Corrected for their Local Environments

, which approaches the depth of the survey of brightest cluster galaxies by Lauer and Postman (1994). We use the Light Curve Shape (LCS) method for deriving distances to SN Ia, providing relative distance estimates to individual supernovae with a precision of