Cosmology

Abstract:

In this paper, we extend the Bayesian model fitting shape measurement method presented in Miller et al., and use the method to estimate the shear from the Shear TEsting Programme simulations (STEP). The method uses a fast model fitting algorithm that uses realistic galaxy profiles and analytically marginalizes over the position and amplitude of the model by doing the model fitting in Fourier space. This is used to find the full posterior probability in ellipticity. The shear is then estimated in a Bayesian way from this posterior probability surface. The Bayesian estimation allows measurement bias arising from the presence of random noise to be removed. In this paper, we introduce an iterative algorithm that can be used to estimate the intrinsic ellipticity prior and show that this is accurate and stable. We present results using the STEP parametrization that relates the input shear γT to the estimated shear γM by introducing a bias m and an offset c: γM - γT = mγT + c. The average number density of galaxies used in the STEP1 analysis was 9 per square arcminute, for STEP2 the number density was 30 per square arcminute. By using the method to estimate the shear from the STEP1 simulations we find the method to have a shear bias of m = 0.006 ± 0.005 and a variation in shear offset with point spread function type of σc = 0.0002. Using the method to estimate the shear from the STEP2 simulations we find that the shear bias and offset are m = 0.002 ± 0.016 and c = -0.0007 ± 0.0006, respectively. In addition, we find that the bias and offset are stable to changes in the magnitude and size of the galaxies. Such biases should yield any cosmological constraints from future weak lensing surveys robust to systematic effects in shape measurement. Finally, we present an alternative to the STEP parametrization by using a quality factor that relates the intrinsic shear variance in a simulation to the variance in shear that is measured and show that the method presented has an average of Q ≳ 100 which is at least a factor of 10 times better than other shape measurement methods. © 2008 RAS.

Abstract:

In this work, we test the assertion that the scatter in the mass of black holes which drive quasars should be luminosity dependent with less scatter in more luminous objects. To this end, we measure the width of the Mg ii λ2799 line in quasar spectra from the Sloan Digital Sky Survey (SDSS), 2df QSO Redshift survey (2QZ) and 2dF SDSS LRG And QSO (2SLAQ) surveys and, by invoking an unnormalized virial mass estimator, relate the scatter in linewidth to the scatter of mass in the underlying black hole population. We find conclusive evidence for a trend such that there is less scatter in linewidth, and hence black hole mass, in more luminous objects. However, the most luminous objects in our sample show such a low degree of scatter in linewidth that, when combined with measures for the intrinsic scatter in the radius-luminosity relation for the broad-line region (BLR) in active galaxies, an inconsistency arises in the virial technique for estimating black hole masses. This analysis implies that, at least for the most luminous quasars, either there is little-to-no intrinsic scatter in the radius-luminosity relation or the Mg ii broad emission-line region is not totally dominated by virial velocities. Finally, we exploit the measured scatter in linewidths to constrain models for the velocity field of the BLR. We show that the lack of scatter in broad-line widths for luminous quasars is inconsistent with a pure planar/disc-like geometry for the BLR. In the case of a BLR with purely polar flows, the opening angle to luminous quasars must be less than ∼55°. We then explore the effects of adding a random or spherically symmetric component to the velocities of gas clouds in the BLR. Assuming an opening angle to quasars of 45°, a planar field can be made consistent with our results if ∼ 40-50 per cent of the velocities are randomly distributed. © 2008 The Authors.

Abstract:

We compute Fourier-resolved X-ray spectra of the Seyfert 1 Markarian 766 to study the shape of the variable components contributing to the 0.3-10 keV energy spectrum and their time-scale dependence. The fractional variability spectra peak at 1-3 keV, as in other Seyfert 1 galaxies, consistent with either a constant contribution from a soft excess component below 1 keV and Compton reflection component above 2 keV or variable warm absorption enhancing the variability in the 1-3 keV range. The rms spectra, which show the shape of the variable components only, are well described by a single power law with an absorption feature around 0.7 keV, which gives it an apparent soft excess. This spectral shape can be produced by a power law varying in normalization, affected by an approximately constant (within each orbit) warm absorber, with parameters similar to those found by Turner et al. for the warm-absorber layer covering all spectral components in their scattering scenario [NH ∼ 3 × 1021 cm-2, log(ξ) ∼ 1]. The total soft excess in the average spectrum can therefore be produced by a combination of constant warm absorption on the power-law plus an additional less variable component. On shorter time-scales, the rms spectrum hardens and this evolution is well described by a change in power-law slope, while the absorption parameters remain the same. The frequency dependence of the rms spectra can be interpreted as variability arising from propagating fluctuations through an extended emitting region, whose emitted spectrum is a power law that hardens towards the centre. This scenario reduces the short time-scale variability of lower energy bands making the variable spectrum harder on shorter time-scales and at the same time explains the hard lags found in these data by Markowitz et al. © 2008 RAS.

Abstract:

This paper discusses infrared and millimetre-wavelength observations of a Lyman α blob (LAB) discovered by Smith & Jarvis, a candidate for ionization by the cold accretion scenario discussed in Fardal et al. and Dijkstra et al. We have observed the counterpart galaxy at infrared wavelengths in deep observations with the Spitzer Space Telescope using the IRAC 3.6, 4.5, 5.8 and 8.0 μm and MIPS 24 μm bands, as well as using the Max-Planck Millimeter Bolometer (MAMBO-2) at a wavelength of 1.2 mm with the IRAM 30 m telescope. These observations probe the ≳95 kpc Lyman α halo for the presence of obscured active galactic nucleus (AGN) components or the presence of a violent period of star formation invoked by other models of ionization for these mysterious objects. 24 μm observations suggest that an obscured AGN would be insufficiently luminous to ionize the halo, and that the star formation rate within the halo may be as low as <140 M⊙ yr -1 depending on the model spectral energy distribution (SED) used. This is reinforced by our observations at 1.2 mm using MAMBO-2, which yield an upper limit of star formation rate <550 M⊙ yr-1 from our non-detection to a 3σ flux limit of 0.86 mJy beam-1. Finding no evidence for either AGN or extensive star formation, we conclude that this halo is ionized by a cold accretion process. We derive model SEDs for the host galaxy, and use the Bruzual & Charlot and Maraston libraries to show that the galaxy is well described by composite stellar populations of total mass 3.42 ± 0.13 × 1011 or 4.35 ± 0.16 × 1011 M⊙ depending on the model SEDs used. © 2008 RAS.

Abstract:

We use a multidimensional Monte Carlo code to compute X-ray spectra for a variety of active galactic nucleus (AGN) disc-wind outflow geometries. We focus on the formation of blueshifted absorption features in the Fe K band and show that line features similar to those which have been reported in observations are often produced for lines of sight through disc-wind geometries. We also discuss the formation of other spectral features in highly ionized outflows. In particular, we show that, for sufficiently high wind densities, moderately strong Fe K emission lines can form and that electron scattering in the flow may cause these lines to develop extended red wings. We illustrate the potential relevance of such models to the interpretation of real X-ray data by comparison with observations of a well-known AGN, Mrk 766. Journal compilation © 2008 RAS.