arXiv subjects
Publications and source records attributed to Terry Bridges.
We present a preliminary analysis of HST-WFPC2 observations of globular cluster systems in the two brightest galaxies, UGC 9799 (cD) and NGC 1129 (non-cD), located in the center of rich clusters.
We perform a joint likelihood analysis of the power spectra of the 2dF Galaxy Redshift Survey (2dFGRS) and the cosmic microwave background (CMB) anisotropies under the assumptions that the initial fluctuations were adiabatic, Gaussian and well described by power laws with scalar and tensor indices of n_s and n_t. On its own, the 2dFGRS sets tight limits on the parameter combination Omega_m h, but relatively weak limits on the fraction of the cosmic matter density in baryons Omega_b/Omega_m. The CMB anisotropy data alone set poor constraints on the cosmological constant and Hubble constant because of a `geometrical degeneracy' among parameters. Furthermore, if tensor modes are allowed, the CMB data allow a wide range of values for the physical densities in baryons and cold dark matter. Combining the CMB and 2dFGRS data sets helps to break both the geometrical and tensor mode degeneracies. The values of the parameters derived here are consistent with the predictions of the simplest models of inflation, with the baryon density derived from primordial nucleosynthesis and with direct measurements of the Hubble parameter. In particular, we find strong evidence for a positive cosmological constant with a pm 2sigma range of 0.65 < Omega_Lambda < 0.85, completely independently of constraints on Omega_Λderived from Type Ia supernovae.
We present recent multi-object spectroscopy of globular clusters in the Virgo gEs M49 and M87. In M49, we have a total of 144 confirmed clusters out to 8 arcmin radius (~6 R_eff or 35 kpc). We find that the blue (metal-poor) clusters have both a higher velocity dispersion and rotation than the red (metal-poor) clusters. For the metal-rich population we place an upper limit of (v/sigma)_proj < 0.34 at 99% confidence. We calculate the velocity dispersion as a function of radius, and show that this is consistent with isotropic cluster orbits and the M49 mass distribution determined from X-ray data. For M87, we combine new CFHT data with previous data to obtain a total sample of 278 clusters out to 10 arcmin radius (~45 kpc). We find a similar global rotation for the metal-poor and metal-rich clusters of 160-170 km/sec. Beyond ~ 2 R_eff (15 kpc), both the metal-poor and metal-rich clusters appear to rotate about the photometric minor axis. The combined cluster sample is consistent with isotropic orbits, but when considered separately, the metal-poor clusters show significant tangential bias of beta_cl ~ -0.4, while the metal-rich clusters show a radial bias with beta_cl ~ +0.4. In both galaxies, the metal-rich and metal-poor clusters share different kinematics, but there is no clear preference for any one formation scenario.
The 2dF Galaxy Redshift Survey has now measured in excess of 160000 galaxy redshifts. This paper presents the power spectrum of the galaxy distribution, calculated using a direct FFT-based technique. We argue that, within the k-space region 0.02<k<0.15 h Mpc^-1, the shape of this spectrum should be close to that of the linear density perturbations convolved with the window function of the survey. This window function and its convolving effect on the power spectrum estimate are analyzed in detail. By convolving model spectra, we are able to fit the power-spectrum data and provide a measure of the matter content of the universe. Our results show that models containing baryon oscillations are mildly preferred over featureless power spectra. Analysis of the data yields 68% confidence limits on the total matter density times the Hubble parameter Ω_m h = 0.20 +/- 0.03, and the baryon fraction Ω_b/Ω_m = 0.15 +/- 0.07, assuming scale-invariant primordial fluctuations.
We present the catalogue of a wide-field CFHT/WHT spectroscopic survey of the lensing cluster Cl0024+1654 at z=0.395. This catalogue contains 618 new spectra, of which 581 have identified redshifts. Adding redshifts available from the literature, the final catalogue contains data for 687 objects with redshifts identified for 650 of them. 295 galaxies have redshifts in the range 0.37<z<0.41, i. e. are cluster members or lie in the immediate neighbourhood of the cluster. The area covered by the survey is 21x25 arcmin2 in size, corresponding to 4x4.8 h^-2 Mpc2 at the cluster redshift. The survey is 45% complete down to V=22 over the whole field covered; within 3 arcmin of the cluster centre the completeness exceeds 80% at the same magnitude. A detailed completeness analysis is presented. The catalogue gives astrometric position, redshift, V magnitude and V-I colour, as well as the equivalent widths for a number of lines. Apart from the cluster Cl0024+1654 itself, three other structures are identified in redshift space: a group of galaxies at z=0.38, just in front of Cl0024+1654 and probably interacting with it, a close pair of groups of galaxies at z~0.495 and an overdensity of galaxies at z~0.18 with no obvious centre. The spectroscopic catalogue will be used to trace the three-dimensional structure of the cluster Cl0024+1654 as well as study the physical properties of the galaxies in the cluster and in its environment.
We present radial velocities for 144 globular clusters around the Virgo gE NGC 4472 (M49), and ages and metallicities from co-added spectra of 131 clusters. We confirm our earlier finding that the metal-poor clusters have a significantly higher velocity dispersion than the metal-rich clusters, and we find little or no rotation in the metal-rich clusters. The velocity dispersion profile is consistent with isotropic orbits for the clusters and the NGC 4472 mass distribution inferred from X-ray data. Our sample of clusters spans a metallicity range of -1.6 < [Fe/H] < 0 dex. The metal-poor and metal-rich cluster populations are coeval within the errors, and all clusters are older than 6 Gyr at 95% confidence. Our findings are consistent with a merger origin for NGC 4472, but other elliptical formation models cannot be ruled out.
We present a detailed velocity histogram from a wide-field spectroscopic survey in the field of the cluster lens Cl0024 showing an unrelaxed foreground structure in addition to the relaxed main cluster. This finding reduces the velocity dispersion of the main cluster compared to previous studies by a factor of about 2 and thus resolves the discrepancy between previous mass estimates for this cluster.
I summarize recent observations of the kinematics of hot tracers in elliptical galaxy halos (globular clusters, planetary nebulae, and integrated stellar light), and what these tell us about the dynamics, dark matter content, and formation of ellipticals. A generic result is the ubiquity of dark matter halos in ellipticals. Studies of globular clusters and planetary nebulae are now finding outer-halo rotation in many ellipticals, with V/sigma ~ 1 beyond a few R_e. In some giant ellipticals (M49, M87), there are possible kinematic differences between metal-poor and metal-rich globular clusters. These results are consistent with a merger origin for ellipticals. High-quality data and new modelling techniques now make it possible to determine simultaneously the orbital anisotropy and gravitational potential in ellipticals from integrated-light measurements; such studies now provide the best evidence for dark matter halos in ellipticals.The new generation of 8-10m telescopes, with multi-object and integral-field spectrographs, will dramatically increase sample sizes of discrete tracers and provide two-dimensional spectroscopy of elliptical halos. New methods of analysis will allow robust determinations of stellar kinematics and dark matter distributions in a much larger number of ellipticals. Comparison with numerical simulations, which are becoming ever more detailed and physically realistic, will become increasingly important.
The central arcminute of the Perseus cooling flow galaxy, NGC 1275, has been mapped with the JCMT in 12CO(2-1) at 21 arcsec resolution, with detections out to at least 36 arcsec (12 kpc). Within the limits of the resolution and coverage, the distribution of gas appears to be roughly E-W, consistent with previous observations of CO, X-ray, H alpha, and dust emission. The total detected molecular hydrogen mass is ~ 1.6 x 10^10 solar masses, using a Galactic conversion factor. The inner central rotating disk is apparent in the data, but the overall distribution is not one of rotation. Rather, the line profiles are bluewards asymmetric, consistent with previous observations in HI and [OIII]. We suggest that the blueshift may be due to an acquired mean velocity of ~ 150 km/sec imparted by the radio jet in the advancing direction. Within the uncertainties of the analysis, the available radio energy appears to be sufficient, and the interpretation is consistent with that of Bohringer et al. (1993) for displaced X-ray emission. We have also made the first observations of 13CO(2-1) and 12CO(3-2) emission from the central 21 arcsec region of NGC 1275 and combined these data with IRAM data supplied by Reuter et al. (1993) to form line ratios over equivalent, well-sampled regions. An LVG radiative transfer analysis indicates that the line ratios are not well reproduced by a single value of kinetic temperature, molecular hydrogen density, and abundance per unit velocity gradient. At least two temperatures are suggested by a simple two-component LVG model, possibly reflecting a temperature gradient in this region.