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 iiλ2799 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.
We present peculiar velocities for 85 clusters of galaxies in two large volumes at distances between 6000 and 15 000 km s−1 in the directions of Hercules-Corona Borealis and Perseus-Pisces-Cetus (the ...EFAR sample). These velocities are based on Fundamental Plane (FP) distance estimates for early-type galaxies in each cluster. We fit the FP using a maximum likelihood algorithm which accounts for both selection effects and measurement errors, and yields FP parameters with smaller bias and variance than other fitting procedures. We obtain a best-fitting FP with coefficients consistent with the best existing determinations. We measure the bulk motions of the sample volumes using the 50 clusters with the best-determined peculiar velocities. We find that the bulk motions in both regions are small, and consistent with zero at about the 5 per cent level. The EFAR results are in agreement with the small bulk motions found by Dale et al. on similar scales, but are inconsistent with pure dipole motions having the large amplitudes found by Lauer & Postman and Hudson et al. The alignment of the EFAR sample with the Lauer & Postman dipole produces a strong rejection of a large-amplitude bulk motion in that direction, but the rejection of the Hudson et al. result is less certain because their dipole lies at a large angle to the main axis of the EFAR sample. We employ a window function covariance analysis to make a detailed comparison of the EFAR peculiar velocities with the predictions of standard cosmological models. We find that the bulk motion of our sample is consistent with most cosmological models that approximately reproduce the shape and normalization of the observed galaxy power spectrum. We conclude that existing measurements of large-scale bulk motions provide no significant evidence against standard models for the formation of structure.
We examine the effects on the Fundamental Plane (FP) of structural departures from an R ¼ galaxy light profile. We also explore the use of spatial (i.e., volumetric) as well as projected galaxy ...parameters. We fit the Sersic R1/n law to the V-band light profiles of 26 E/S0 Virgo galaxies, where n is a shape parameter that allows for structural differences amongst the profiles. The galaxy light profiles show a trend of systematic departures from a de Vaucouleurs R¼ law, in the sense that n increases with increasing effective half-light radius Re. This results in Re, and the associated mean surface brightness within this radius, having systematic biases when constructed using an R¼ law. Adjustments to the measured velocity dispersion are also made, based upon the theoretical velocity dispersion profile shapes of the different R1/n light profiles, constructed assuming spherical symmetry and isotropic pressure support. We construct the FP for the case when structural homology is assumed (specifically, an R¼ law is fitted to all galaxies) and central velocity dispersions, σ0, are used. The plane we obtain is Re ∝ σ01.33±0.10Σe−0.79±0.11 where Σe is the mean surface brightness within the projected effective radius Re. This agrees with the FP obtained by others, and departs from the virial theorem expectation R ∝ σ2Σ− We find that allowing for broken structural homology through fitting R 1/n profiles (with n a free parameter), but still using central velocity dispersions, actually increases the departure of the observed FP from the virial plane — the increase in effective radius with galaxy luminosity (and n) is overbalanced by an associated decrease in the mean surface brightness. In examining the use of spatial quantities and allowing for the different velocity dispersion profiles corresponding to the observed light profiles, we find that use of the spatial velocity dispersion at the spatial half-light radius decreases the departure of the observed FP from the virial plane. (Use of the spatial half-light radius and mean surface brightness term has no effect on the FP, as they are constant multiples of their projected values.) Through use of the Jeans hydrodynamical equation, we convert the projected central aperture velocity dispersion, σ0, into the infinite aperture velocity dispersion, σtot,n (which is equal to one-third of the virial velocity dispersion). Using both the R1/n fit and σtot,n we obtain Re,n ∝ σtot,n1.44±0.11Σe,n−0.93±0.08. Making the fullest allowance for broken structural homology thus brings the observed FP closer to the virial plane, with the exponent of the surface brightness term consistent with the virial expectation.
Hubble Space Telescope images of a sample of 285 galaxies with measured redshifts from the Canada-France Redshift Survey (CFRS) and Autofib-Low Dispersion Spectrograph Survey (LDSS) redshift surveys ...are analysed to derive the evolution of the merger fraction out to redshifts z∼1. We have performed visual and machine-based merger identifications, as well as counts of bright pairs of galaxies with magnitude differences δm≤1.5 mag. We find that the pair fraction increases with redshift, with up to ∼20 per cent of the galaxies being in physical pairs at z∼0.75–1. We derive a merger fraction varying with redshift as ∝(1+z)3.2±0.6, after correction for line-of-sight contamination, in excellent agreement with the merger fraction derived from the visual classification of mergers for which m=3.4±0.6. After correcting for seeing effects on the ground-based selection of survey galaxies, we conclude that the pair fraction evolves as ∝(1+z)2.7±0.6. This implies that an average L* galaxy will have undergone 0.8–1.8 merger events from z=1 to z=0, with 0.5 to 1.2 merger events occuring in a 2-Gyr time-span at around z∼0.9. This result is consistent with predictions from semi-analytical models of galaxy formation. From the simple coaddition of the observed luminosities of the galaxies in pairs, physical mergers are computed to lead to a brightening of 0.5 mag for each pair on average, and a boost in star formation rate of a factor of 2, as derived from the average O ii equivalent widths. Mergers of galaxies are therefore contributing significantly to the evolution of both the luminosity function and luminosity density of the Universe out to z∼1.
It is well known that the clustering of galaxies depends on galaxy type. Such relative bias complicates the inference of cosmological parameters from galaxy redshift surveys, and is a challenge to ...theories of galaxy formation and evolution. In this paper we perform a joint counts-in-cells analysis on galaxies in the 2dF Galaxy Redshift Survey, classified by both colour and spectral type, η, as early- or late-type galaxies. We fit three different models of relative bias to the joint probability distribution of the cell counts, assuming Poisson sampling of the galaxy density field. We investigate the non-linearity and stochasticity of the relative bias, with cubic cells of side 10 =L = 45 Mpc (h = 0.7). Exact linear bias is ruled out with high significance on all scales. Power-law bias gives a better fit, but likelihood ratios prefer a bivariate lognormal distribution, with a non-zero ‘stochasticity’, i.e. scatter that may result from physical effects on galaxy formation other than those from the local density field. Using this model, we measure a correlation coefficient in log-density space (rLN) of 0.958 for cells of length L = 10 Mpc, increasing to 0.970 by L = 45 Mpc. This corresponds to a stochasticity of 0.44 ± 0.02 and 0.27 ± 0.05, respectively. For smaller cells, the Poisson-sampled lognormal distribution presents an increasingly poor fit to the data, especially with regard to the fraction of completely empty cells. We compare these trends with the predictions of semi-analytic galaxy formation models: these match the data well in terms of the overall level of stochasticity, variation with scale and the fraction of empty cells.
We use the Galaxy And Mass Assembly survey (GAMA) I data set combined with GALEX, Sloan Digital Sky Survey (SDSS) and UKIRT Infrared Deep Sky Survey (UKIDSS) imaging to construct the low-redshift (z ...< 0.1) galaxy luminosity functions in FUV, NUV, ugriz and YJHK bands from within a single well-constrained volume of 3.4 × 105 (Mpch-1)3. The derived luminosity distributions are normalized to the SDSS data release 7 (DR7) main survey to reduce the estimated cosmic variance to the 5per cent level. The data are used to construct the cosmic spectral energy distribution (CSED) from 0.1 to 2.1 μm free from any wavelength-dependent cosmic variance for both the elliptical and non-elliptical populations. The two populations exhibit dramatically different CSEDs as expected for a predominantly old and young population, respectively. Using the Driver et al. prescription for the azimuthally averaged photon escape fraction, the non-ellipticals are corrected for the impact of dust attenuation and the combined CSED constructed. The final results show that the Universe is currently generating (1.8 ± 0.3) × 1035h W Mpc-3 of which (1.2 ± 0.1) × 1035h W Mpc-3 is directly released into the inter-galactic medium and (0.6 ± 0.1) × 1035h W Mpc-3 is reprocessed and reradiated by dust in the far-IR. Using the GAMA data and our dust model we predict the mid- and far-IR emission which agrees remarkably well with available data. We therefore provide a robust description of the pre- and post-dust attenuated energy output of the nearby Universe from 0.1 μm to 0.6mm. The largest uncertainty in this measurement lies in the mid- and far-IR bands stemming from the dust attenuation correction and its currently poorly constrained dependence on environment, stellar mass and morphology. PUBLICATION ABSTRACT
We describe the 2dF Galaxy Redshift Survey (2dFGRS) and the current status of the observations. In this exploratory paper, we apply a principal component analysis to a preliminary sample of 5869 ...galaxy spectra and use the two most significant components to split the sample into five spectral classes. These classes are defined by considering visual classifications of a subset of the 2dF spectra, and also by comparison with high-quality spectra of local galaxies. We calculate a luminosity function for each of the different classes and find that later-type galaxies have a fainter characteristic magnitude, and a steeper faint-end slope. For the whole sample we find M*=−19.7 (for Ω=1, H0=100 km s−1 Mpc−1), α=−1.3, φ*=0.017. For class 1 (‘early-type’) we find M*=−19.6, α=−0.7, while for class 5 (‘late-type’) we find M*=−19.0, α=−1.7. The derived 2dF luminosity functions agree well with other recent luminosity function estimates.
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