We report measurements of the mass density, Omega_M, and
cosmological-constant energy density, Omega_Lambda, of the universe based on
the analysis of 42 Type Ia supernovae discovered by the Supernova Cosmology
Project. The magnitude-redshift data for these SNe, at redshifts between 0.18
and 0.83, are fit jointly with a set of SNe from the Calan/Tololo Supernova
Survey, at redshifts below 0.1, to yield values for the cosmological
parameters. All SN peak magnitudes are standardized using a SN Ia lightcurve
width-luminosity relation. The measurement yields a joint probability
distribution of the cosmological parameters that is approximated by the
relation 0.8 Omega_M - 0.6 Omega_Lambda ~= -0.2 +/- 0.1 in the region of
interest (Omega_M <~ 1.5). For a flat (Omega_M + Omega_Lambda = 1) cosmology we
find Omega_M = 0.28{+0.09,-0.08} (1 sigma statistical) {+0.05,-0.04}
(identified systematics). The data are strongly inconsistent with a Lambda = 0
flat cosmology, the simplest inflationary universe model. An open, Lambda = 0
cosmology also does not fit the data well: the data indicate that the
cosmological constant is non-zero and positive, with a confidence of P(Lambda >
0) = 99%, including the identified systematic uncertainties. The best-fit age
of the universe relative to the Hubble time is t_0 = 14.9{+1.4,-1.1} (0.63/h)
Gyr for a flat cosmology. The size of our sample allows us to perform a variety
of statistical tests to check for possible systematic errors and biases. We
find no significant differences in either the host reddening distribution or
Malmquist bias between the low-redshift Calan/Tololo sample and our
high-redshift sample. The conclusions are robust whether or not a
width-luminosity relation is used to standardize the SN peak magnitudes.

/pdf/measurements-of-omega-and-lambda-from-42-high-redshift-z1htxv5kgf.pdf

Measurements of Omega and Lambda from 42 High-Redshift Supernovae

We present spectral and photometric observations of 10 Type Ia supernovae (SNe Ia) in the redshift range 0.16 " z " 0.62. The luminosity distances of these objects are determined by methods that employ relations between SN Ia luminosity and light curve shape. Combined with previous data from our High-z Supernova Search Team and recent results by Riess et al., this expanded set of 16 high-redshift supernovae and a set of 34 nearby supernovae are used to place constraints on the following cosmo- logical parameters: the Hubble constant the mass density the cosmological constant (i.e., the (H 0 ), () M ), vacuum energy density, the deceleration parameter and the dynamical age of the universe ) " ), (q 0 ), ) M \ 1) methods. We estimate the dynamical age of the universe to be 14.2 ^ 1.7 Gyr including systematic uncer- tainties in the current Cepheid distance scale. We estimate the likely e†ect of several sources of system- atic error, including progenitor and metallicity evolution, extinction, sample selection bias, local perturbations in the expansion rate, gravitational lensing, and sample contamination. Presently, none of these e†ects appear to reconcile the data with and ) " \ 0 q 0 " 0.

/pdf/observational-evidence-from-supernovae-for-an-accelerating-2hxji77uix.pdf

Observational Evidence from Supernovae for an Accelerating Universe and a Cosmological Constant

https://biblio.ugent.be/publication/685594/file/1130605.pdf

Review of Particle Physics

The combination of seven-year data from WMAP and improved astrophysical data rigorously tests the standard cosmological model and places new constraints on its basic parameters and extensions. By combining the WMAP data with the latest distance measurements from the baryon acoustic oscillations (BAO) in the distribution of galaxies and the Hubble constant (H0) measurement, we determine the parameters of the simplest six-parameter ΛCDM model. The power-law index of the primordial power spectrum is ns = 0.968 ± 0.012 (68% CL) for this data combination, a measurement that excludes the Harrison–Zel’dovich–Peebles spectrum by 99.5% CL. The other parameters, including those beyond the minimal set, are also consistent with, and improved from, the five-year results. We find no convincing deviations from the minimal model. The seven-year temperature power spectrum gives a better determination of the third acoustic peak, which results in a better determination of the redshift of the matter-radiation equality epoch. Notable examples of improved parameters are the total mass of neutrinos, � mν < 0.58 eV (95% CL), and the effective number of neutrino species, Neff = 4.34 +0.86 −0.88 (68% CL), which benefit from better determinations of the third peak and H0. The limit on a constant dark energy equation of state parameter from WMAP+BAO+H0, without high-redshift Type Ia supernovae, is w =− 1.10 ± 0.14 (68% CL). We detect the effect of primordial helium on the temperature power spectrum and provide a new test of big bang nucleosynthesis by measuring Yp = 0.326 ± 0.075 (68% CL). We detect, and show on the map for the first time, the tangential and radial polarization patterns around hot and cold spots of temperature fluctuations, an important test of physical processes at z = 1090 and the dominance of adiabatic scalar fluctuations. The seven-year polarization data have significantly improved: we now detect the temperature–E-mode polarization cross power spectrum at 21σ , compared with 13σ from the five-year data. With the seven-year temperature–B-mode cross power spectrum, the limit on a rotation of the polarization plane due to potential parity-violating effects has improved by 38% to Δα =− 1. 1 ± 1. 4(statistical) ± 1. 5(systematic) (68% CL). We report significant detections of the Sunyaev–Zel’dovich (SZ) effect at the locations of known clusters of galaxies. The measured SZ signal agrees well with the expected signal from the X-ray data on a cluster-by-cluster basis. However, it is a factor of 0.5–0.7 times the predictions from “universal profile” of Arnaud et al., analytical models, and hydrodynamical simulations. We find, for the first time in the SZ effect, a significant difference between the cooling-flow and non-cooling-flow clusters (or relaxed and non-relaxed clusters), which can explain some of the discrepancy. This lower amplitude is consistent with the lower-than-theoretically expected SZ power spectrum recently measured by the South Pole Telescope Collaboration.

/pdf/seven-year-wilkinson-microwave-anisotropy-probe-wmap-19dgu0rhy7.pdf

Seven-year wilkinson microwave anisotropy probe (wmap *) observations: cosmological interpretation

We present spectral and photometric observations of 10 type Ia supernovae (SNe Ia) in the redshift range 0.16 � z � 0.62. The luminosity distances of these objects are determined by methods that employ relations between SN Ia luminosity and light curve shape. Combined with previous data from our High-Z Supernova Search Team (Garnavich et al. 1998; Schmidt et al. 1998) and Riess et al. (1998a), this expanded set of 16 high-redshift supernovae and a set of 34 nearby supernovae are used to place constraints on the following cosmological parameters: the Hubble constant (H0), the mass density (M), the cosmological constant (i.e., the vacuum energy density, �), the deceleration parameter (q0), and the dynamical age of the Universe (t0). The distances of the high-redshift SNe Ia are, on average, 10% to 15% farther than expected in a low mass density (M = 0.2) Universe without a cosmological constant. Different light curve fitting methods, SN Ia subsamples, and prior constraints unanimously favor eternally expanding models with positive cosmological constant (i.e., � > 0) and a current acceleration of the expansion (i.e., q0 < 0). With no prior constraint on mass density other than M � 0, the spectroscopically confirmed SNe Ia are statistically consistent with q0 < 0 at the 2.8�

Observational Evidence from Supernovae for an Accelerating Universe and a Cosmological Constant To Appear in the Astronomical Journal

Observations of M 100 with the Einstein Observatory shortly after theexplosion of its fourth supernova, SN 1979C.

We present the results of observations of the radio emission from SN 2001gd in NGC5033 from 2002 February 8 through 2006 September 25. The data were obtained using the VLA at wavelengths of 1.3 cm (22.4 GHz), 2 cm (14.9 GHz), 3.6 cm (8.4 GHz), 6 cm (4.9 GHz), and 20 cm (1.5 GHz), with one upper limit at 90 cm (0.3 GHz). In addition, one detection has been provided by the GMRT at 21 cm (1.4 GHz). SN 2001gd was discovered in the optical well past maximum light, so that it was not possible to obtain many of the early radio "turn-on" measurements that are important for estimating the local CSM properties. Only at 20 cm were turn-on data available. However, our analysis and fitting of the radio light curves, along with the assumption that the Type IIb SN 2001gd resembles the much better studied Type IIb SN 1993J, enables us to describe the radio evolution as being very regular through day ~550 and consistent with a nonthermal-emitting model with a thermal absorbing CSM. The presence of SSA at early times is implied by the data, but determination of the exact relationship between the SSA component from the emitting region and the free-free absorption component from the CSM is not possible, as there are insufficient early measurements to distinguish between models. After day ~550, the radio emission exhibits a dramatically steeper decline rate, which, assuming similarity to SN 1993J, can be described as an exponential decrease with an e-folding time of 500 days. We interpret this abrupt change in the radio flux density decline rate as implying a transition of the shock front into a more tenuous region of circumstellar material. A similar change in radio evolution has been seen earlier in other SNe, such as SN 1988Z, SN 1980K, and SN 1993J.

The Radio Evolution of SN 2001gd

The nebula around the luminous blue variable (LBV) η Car is extremely N rich and C and O poor, which is indicative of CNO-cycle products. On the other hand, the recent Hubble Space Telescope-Goddard High-Resolution Spectrograph observation of the nucleus of η Car shows the spectrum of a star with stellar-wind lines of C II, C IV, Si II, Si IV, etc. The spectrum is very similar to those of the LBV star P Cygni and of WN9/Ofpe stars. This line spectrum is indicative of a photosphere that is only mildly enhanced by CN-cycle products. This situation of a nebula that is chemically more advanced than the central star cannot be reached by the evolution of a single star. The dichotomy shows that the star whose spectrum now dominates the nucleus was not the star that ejected the nebula. We discuss this evidence for multiplicity and combine it with the information about the 5.5 yr periodicity in the emission lines.

On the Multiplicity of η Carinae

Supernovae (SNe) and supernova remnants (SNRs) represent an important area of research in astrophysics because they are central to our understanding of such diverse fields as the late stages of stellar evolution, mass loss from late-type stars, nucleosynthesis, and interstellar medium processes and abundances. In addition, they provide a laboratory for investigating the physics of explosion mechanisms, blast waves and dust grain formation and destruction. SNe and young SNRs provide information on the dynamics of the explosion, and the abundances in the ejecta provide direct evidence for nucleosynthesis. In some cases, this information can be used with stellar evolution models to infer the properties of the precursor star. Evolved remnants can be used as probes of normally invisible regions of the interstellar medium (ISM). The passage of a SN blast wave heats and compresses the ISM, and observation of the subsequent cooling flow provides information on abundances and physical conditions in both the pre-shock and post-shock gas. Extensive reviews on SNe and SNRs can be found in the proceedings of several recent conferences, including IAU Symposium 101 (Danziger and Gorenstein, 1983), ‘Supernovae as Distance Indicators’ (Bartel, 1985), the NATO ASI on ‘Supernovae: A Survey of Current Research’ (Rees and Stoneham 1982) and the Cargese conference on ‘High Energy Phenomena Around Collapsed Stars’ (Pacini, 1986). Several recent reviews on SNRs have addressed both the observational (Raymond, 1983, 1984; Lozinskaya, 1984) and theoretical (McKee and Hollenbach, 1980) aspects of these objects.

Supernovae and Their Remnants

We report on the properties of the low-mass stars that recently formed in the central ~ 2.7'x2.7' of 30 Dor including the R136 cluster. Using the photometric catalogue of De Marchi et al. (2011c), based on observations with the Hubble Space Telescope (HST), and the most recent extinction law for this field, we identify 1035 bona-fide pre-main sequence (PMS) stars showing Halpha excess emission at the 4 sigma level with Halpha equivalent width of 20 AA or more. We find a wide spread in age spanning the range ~ 0.1-50 Myr. We also find that the older PMS objects are placed in front of the R136 cluster and are separated from it by a conspicuous amount of absorbing material, indicating that star formation has proceeded from the periphery into the interior of the region. We derive physical parameters for all PMS stars, including masses m, ages t, and mass accretion rates M_acc. To identify reliable correlations between these parameters, which are intertwined, we use a multivariate linear regression fit of the type log M_acc = a log t + b log m + c. The values of a and b for 30 Dor are compatible with those found in NGC 346 and NGC 602. We extend the fit to a uniform sample of 1307 PMS stars with 0.5 < m/Msun < 1.5 and t < 16 Myr in six star forming regions in the Large and Small Magellanic Clouds and Milky Way with metallicities in the range 0.1-1.0 Zsun. We find a=-0.59+/-0.02 and b=0.78+/-0.08. The residuals are systematically different between the six regions and reveal a strong correlation with metallicity Z, of the type c = (-3.69+/-0.02) - (0.30+/-0.04) log Z/Zsun. A possible interpretation of this trend is that when the metallicity is higher so is the radiation pressure and this limits the accretion process, both in its rate and duration.

Nino Panagia

Papers

Observations of M 100 with the Einstein Observatory shortly after theexplosion of its fourth supernova, SN 1979C.

The Radio Evolution of SN 2001gd

On the Multiplicity of η Carinae

Supernovae and Their Remnants

Photometric determination of the mass accretion rates of pre-main sequence stars. V. Recent star formation in the 30 Dor nebula