A model-independent reconstruction of the cosmic expansion rate is essential to a robust analysis of cosmological observations. Our goal is to demonstrate that current data are able to provide reasonable constraints on the behavior of the Hubble parameter with redshift, independently of any cosmological model or underlying gravity theory. Using type Ia supernova data, we show that it is possible to analytically calculate the Fisher matrix components in a Hubble parameter analysis without assumptions about the energy content of the Universe. We used a principal component analysis to reconstruct the Hubble parameter as a linear combination of the Fisher matrix eigenvectors (principal components). To suppress the bias introduced by the high redshift behavior of the components, we considered the value of the Hubble parameter at high redshift as a free parameter. We first tested our procedure using a mock sample of type Ia supernova observations, we then applied it to the real data compiled by the Sloan Digital Sky Survey (SDSS) group. In the mock sample analysis, we demonstrate that it is possible to drastically suppress the bias introduced by the high redshift behavior of the principal components. Applying our procedure to the real data, we show that it allows us to determine the behavior of the Hubble parameter with reasonable uncertainty, without introducing any ad-hoc parameterizations. Beyond that, our reconstruction agrees with completely independent measurements of the Hubble parameter obtained from red-envelope galaxies.
An analytical solution for the discrepancy between observed core-like profiles and predicted cusp profiles in dark matter halos is studied. We calculate the distribution function for Navarro-Frenk-White halos and extract energy from the distribution, taking into account the effects of baryonic physics processes. We show with a simple argument that we can reproduce the evolution of a cusp to a flat density profile by a decrease of the initial potential energy.
We study the impact of modifying the vector sector of gravity on the CMB polarization. We employ the Einstein-aether theory as a concrete example. The Einstein-aether theory admits dynamical vector perturbations generated during inflation, leaving imprints on the CMB polarization. We derive the perturbation equations of the aether vector field in covariant formalism and compute the CMB B-mode polarization using the modified CAMB code. It is found that the amplitude of the B-mode signal from the aether field can surpass the one from the inflationary gravitational waves. The shape of the spectrum is clearly understood in an analytic way using the tight coupling approximation.
We are now exploring the inner region of Type 1 AGNs with the Keck interferometer in the near-infrared. Here we report further measurements of K-band (2.2 um) visibilities on four more targets, namely AKN120, IC4329A, Mrk6, and the radio-loud QSO 3C273 at z=0.158. The observed visibilities are quite high for all the targets. We interpret these as an indication of partially resolving the dust sublimation region. The effective ring radii derived from the observed visibilities approximately scale with L^1/2 where L is the AGN luminosity. Comparing the radii with those from independent optical-infrared reverberation measurements, the new data further support our previous claim that the interferometric ring radius is either roughly equal to or slightly larger than the reverberation radius. We interpret the ratio of these two radii for a given L as an approximate probe for the radial distribution of the inner accreting material. We show tentative evidence that this inner radial structure might closely be related to the radio-loudness of the central engine. Finally, we re-observed the brightest Seyfert 1 galaxy NGC4151. The marginally higher visibility at a shorter projected baseline, compared to our previous measurements obtained one year before, supports the partial resolution of the inner structure. We did not detect any significant change in the implied emission size when the K-band flux is brightened up by a factor of 1.5 over a time interval of one year.
[Abridged] We present two-dimensional line-of-sight stellar kinematics of the lens galaxy in the Einstein Cross, obtained with the GEMINI 8m telescope, using the GMOS integral-field spectrograph. The velocity map shows regular rotation up to ~100 km/s around the minor axis of the bulge, consistent with axisymmetry. The velocity dispersion map shows a weak gradient increasing towards a central (R<1") value of sigma_0=170+/-9 km/s. We deproject the observed surface brightness from HST imaging to obtain a realistic luminosity density of the lens galaxy, which in turn is used to build axisymmetric dynamical models that fit the observed kinematic maps. We also construct a gravitational lens model that accurately fits the positions and relative fluxes of the four quasar images. We find that the resulting luminous and total mass distribution are nearly identical around the Einstein radius R_E = 0.89", with a slope that is close to isothermal, but which becomes shallower towards the center if indeed mass follows light. The dynamical model fits to the observed kinematic maps result in a total mass-to-light ratio (M/L)_dyn=3.7+/-0.5 M_sun/L_sun,I (in the I-band). This is consistent with the Einstein mass M_E = 1.54 x 10^10 M_sun divided by the (projected) luminosity within R_E, which yields a total mass-to-light ratio of (M/L)_E=3.4 M_sun/L_sun,I, with an error of at most a few per cent. We estimate from stellar populations model fits to colors of the lens galaxy a stellar mass-to-light ratio (M/L)_* from 2.8 to 4.1 M_sun/L_sun,I. Although a constant dark matter fraction of 20 per cent is not excluded, dark matter may play no significant role in the bulge of this ~L* early-type spiral galaxy.
We present a harmonic expansion of the observed line-of-sight velocity field as a method to recover and investigate spiral structures in the nuclear regions of galaxies. We apply it to the emission-line velocity field within the circumnuclear starforming ring of NGC1097, obtained with the GMOS-IFU spectrograph. The radial variation of the third harmonic terms are well described by a logarithmic spiral, from which we interpret that the gravitational potential is weakly perturbed by a two-arm spiral density wave with inferred pitch angle of of 52+/-4 degrees. This interpretation predicts a two-arm spiral distortion in the surface brightness, as hinted by the dust structures in central images of NGC1097, and predicts a combined one-arm and three-arm spiral structure in the velocity field, as revealed in the non-circular motions of the ionised gas within the circumnuclear region of this galaxy. Next, we use a simple spiral perturbation model to constrain the fraction of the measured non-circular motions that is due to radial inflow. We combine the resulting inflow velocity with the gas density in the spiral arms, inferred from emission line ratios, to estimate the mass inflow rate as a function of radius, which reaches about 0.011 Msun/yr at a distance of 70 pc from the center. This value corresponds to a fraction of about 4.2 x 10^{-3} of the Eddington mass accretion rate onto the central black hole in this LINER/Seyfert1 galaxy. We conclude that the line-of-sight velocity not only can provide a cleaner view of nuclear spirals than the associated dust, but that the presented method also allows the quantitative study of these possibly important links in fueling the centers of galaxies, including providing a handle on the mass inflow rate as a function of radius.
Boltzmann equations and their matrix valued generalisations are commonly used to describe nonquilibrium phenomena in cosmology. On the other hand, it is known that in gauge theories at high temperature processes involving many quanta, which naively are of higher order in the coupling, contribute to the relaxation rate at leading order. How does this accord with the use of single particle distribution functions in the kinetic equations? When can these effects be parametrised in an effective quasiparticle description? And what is the kinematic role of their thermal masses? We address these questions in the framework of nonequilibrium quantum field theory and develop an intuitive picture in which contributions from higher order processes are parametrised by the widths of resonances in the plasma. In the narrow width limit we recover the quasiparticle picture, with the additional processes giving rise to off-shell parts of quasiparticles that appear to violate energy conservation. In this regime we give analytic expressions for the scalar and fermion nonequilibrium propagators in a medium. We compare the efficiency of decays and scatterings involving real quasiparticles, computed from analytic expressions for the relaxation rates via trilinear scalar and Yukawa interactions for all modes, to off-shell contributions and find that the latter can be significant even for moderate widths. Our results apply to various processes including thermal production of particles from a plasma, dissipation of fields in a medium and particle propagation in dense matter. We discuss cosmological implications, in particular for the maximal temperature achieved during reheating by perturbative inflaton decay.
As we shall briefly recall, Nordstr\"om's theory of gravity is observationally ruled out. It is however an interesting example of non-minimal coupling of matter to gravity and of the role of conformal transformations. We show in particular that they could be useful to extend manifolds through curvature singularities.
Links to: arXiv, form interface, find, astro-ph, recent, 1012, contact, help (Access key information)
A model-independent reconstruction of the cosmic expansion rate is essential to a robust analysis of cosmological observations. Our goal is to demonstrate that current data are able to provide reasonable constraints on the behavior of the Hubble parameter with redshift, independently of any cosmological model or underlying gravity theory. Using type Ia supernova data, we show that it is possible to analytically calculate the Fisher matrix components in a Hubble parameter analysis without assumptions about the energy content of the Universe. We used a principal component analysis to reconstruct the Hubble parameter as a linear combination of the Fisher matrix eigenvectors (principal components). To suppress the bias introduced by the high redshift behavior of the components, we considered the value of the Hubble parameter at high redshift as a free parameter. We first tested our procedure using a mock sample of type Ia supernova observations, we then applied it to the real data compiled by the Sloan Digital Sky Survey (SDSS) group. In the mock sample analysis, we demonstrate that it is possible to drastically suppress the bias introduced by the high redshift behavior of the principal components. Applying our procedure to the real data, we show that it allows us to determine the behavior of the Hubble parameter with reasonable uncertainty, without introducing any ad-hoc parameterizations. Beyond that, our reconstruction agrees with completely independent measurements of the Hubble parameter obtained from red-envelope galaxies.
An analytical solution for the discrepancy between observed core-like profiles and predicted cusp profiles in dark matter halos is studied. We calculate the distribution function for Navarro-Frenk-White halos and extract energy from the distribution, taking into account the effects of baryonic physics processes. We show with a simple argument that we can reproduce the evolution of a cusp to a flat density profile by a decrease of the initial potential energy.
We study the impact of modifying the vector sector of gravity on the CMB polarization. We employ the Einstein-aether theory as a concrete example. The Einstein-aether theory admits dynamical vector perturbations generated during inflation, leaving imprints on the CMB polarization. We derive the perturbation equations of the aether vector field in covariant formalism and compute the CMB B-mode polarization using the modified CAMB code. It is found that the amplitude of the B-mode signal from the aether field can surpass the one from the inflationary gravitational waves. The shape of the spectrum is clearly understood in an analytic way using the tight coupling approximation.
We are now exploring the inner region of Type 1 AGNs with the Keck interferometer in the near-infrared. Here we report further measurements of K-band (2.2 um) visibilities on four more targets, namely AKN120, IC4329A, Mrk6, and the radio-loud QSO 3C273 at z=0.158. The observed visibilities are quite high for all the targets. We interpret these as an indication of partially resolving the dust sublimation region. The effective ring radii derived from the observed visibilities approximately scale with L^1/2 where L is the AGN luminosity. Comparing the radii with those from independent optical-infrared reverberation measurements, the new data further support our previous claim that the interferometric ring radius is either roughly equal to or slightly larger than the reverberation radius. We interpret the ratio of these two radii for a given L as an approximate probe for the radial distribution of the inner accreting material. We show tentative evidence that this inner radial structure might closely be related to the radio-loudness of the central engine. Finally, we re-observed the brightest Seyfert 1 galaxy NGC4151. The marginally higher visibility at a shorter projected baseline, compared to our previous measurements obtained one year before, supports the partial resolution of the inner structure. We did not detect any significant change in the implied emission size when the K-band flux is brightened up by a factor of 1.5 over a time interval of one year.
[Abridged] We present two-dimensional line-of-sight stellar kinematics of the lens galaxy in the Einstein Cross, obtained with the GEMINI 8m telescope, using the GMOS integral-field spectrograph. The velocity map shows regular rotation up to ~100 km/s around the minor axis of the bulge, consistent with axisymmetry. The velocity dispersion map shows a weak gradient increasing towards a central (R<1") value of sigma_0=170+/-9 km/s. We deproject the observed surface brightness from HST imaging to obtain a realistic luminosity density of the lens galaxy, which in turn is used to build axisymmetric dynamical models that fit the observed kinematic maps. We also construct a gravitational lens model that accurately fits the positions and relative fluxes of the four quasar images. We find that the resulting luminous and total mass distribution are nearly identical around the Einstein radius R_E = 0.89", with a slope that is close to isothermal, but which becomes shallower towards the center if indeed mass follows light. The dynamical model fits to the observed kinematic maps result in a total mass-to-light ratio (M/L)_dyn=3.7+/-0.5 M_sun/L_sun,I (in the I-band). This is consistent with the Einstein mass M_E = 1.54 x 10^10 M_sun divided by the (projected) luminosity within R_E, which yields a total mass-to-light ratio of (M/L)_E=3.4 M_sun/L_sun,I, with an error of at most a few per cent. We estimate from stellar populations model fits to colors of the lens galaxy a stellar mass-to-light ratio (M/L)_* from 2.8 to 4.1 M_sun/L_sun,I. Although a constant dark matter fraction of 20 per cent is not excluded, dark matter may play no significant role in the bulge of this ~L* early-type spiral galaxy.
We present a harmonic expansion of the observed line-of-sight velocity field as a method to recover and investigate spiral structures in the nuclear regions of galaxies. We apply it to the emission-line velocity field within the circumnuclear starforming ring of NGC1097, obtained with the GMOS-IFU spectrograph. The radial variation of the third harmonic terms are well described by a logarithmic spiral, from which we interpret that the gravitational potential is weakly perturbed by a two-arm spiral density wave with inferred pitch angle of of 52+/-4 degrees. This interpretation predicts a two-arm spiral distortion in the surface brightness, as hinted by the dust structures in central images of NGC1097, and predicts a combined one-arm and three-arm spiral structure in the velocity field, as revealed in the non-circular motions of the ionised gas within the circumnuclear region of this galaxy. Next, we use a simple spiral perturbation model to constrain the fraction of the measured non-circular motions that is due to radial inflow. We combine the resulting inflow velocity with the gas density in the spiral arms, inferred from emission line ratios, to estimate the mass inflow rate as a function of radius, which reaches about 0.011 Msun/yr at a distance of 70 pc from the center. This value corresponds to a fraction of about 4.2 x 10^{-3} of the Eddington mass accretion rate onto the central black hole in this LINER/Seyfert1 galaxy. We conclude that the line-of-sight velocity not only can provide a cleaner view of nuclear spirals than the associated dust, but that the presented method also allows the quantitative study of these possibly important links in fueling the centers of galaxies, including providing a handle on the mass inflow rate as a function of radius.
Boltzmann equations and their matrix valued generalisations are commonly used to describe nonquilibrium phenomena in cosmology. On the other hand, it is known that in gauge theories at high temperature processes involving many quanta, which naively are of higher order in the coupling, contribute to the relaxation rate at leading order. How does this accord with the use of single particle distribution functions in the kinetic equations? When can these effects be parametrised in an effective quasiparticle description? And what is the kinematic role of their thermal masses? We address these questions in the framework of nonequilibrium quantum field theory and develop an intuitive picture in which contributions from higher order processes are parametrised by the widths of resonances in the plasma. In the narrow width limit we recover the quasiparticle picture, with the additional processes giving rise to off-shell parts of quasiparticles that appear to violate energy conservation. In this regime we give analytic expressions for the scalar and fermion nonequilibrium propagators in a medium. We compare the efficiency of decays and scatterings involving real quasiparticles, computed from analytic expressions for the relaxation rates via trilinear scalar and Yukawa interactions for all modes, to off-shell contributions and find that the latter can be significant even for moderate widths. Our results apply to various processes including thermal production of particles from a plasma, dissipation of fields in a medium and particle propagation in dense matter. We discuss cosmological implications, in particular for the maximal temperature achieved during reheating by perturbative inflaton decay.
As we shall briefly recall, Nordstr\"om's theory of gravity is observationally ruled out. It is however an interesting example of non-minimal coupling of matter to gravity and of the role of conformal transformations. We show in particular that they could be useful to extend manifolds through curvature singularities.
Links to: arXiv, form interface, find, astro-ph, recent, 1012, contact, help (Access key information)