arXiv subjects

Patrick B. Hall

Publications and source records attributed to Patrick B. Hall.

At least 91 records · Page 5Linked to original sources

arXiv2009

Clustering of Low-Redshift (z <= 2.2) Quasars from the Sloan Digital Sky Survey

We present measurements of the quasar two-point correlation function, ξ_{Q}, over the redshift range z=0.3-2.2 based upon data from the SDSS. Using a homogeneous sample of 30,239 quasars with spectroscopic redshifts from the DR5 Quasar Catalogue, our study represents the largest sample used for this type of investigation to date. With this redshift range and an areal coverage of approx 4,000 deg^2, we sample over 25 h^-3 Gpc^3 (comoving) assuming the current LCDM cosmology. Over this redshift range, we find that the redshift-space correlation function, xi(s), is adequately fit by a single power-law, with s_{0}=5.95+/-0.45 h^-1 Mpc and γ_{s}=1.16+0.11-0.16 when fit over s=1-25 h^-1 Mpc. Using the projected correlation function we calculate the real-space correlation length, r_{0}=5.45+0.35-0.45 h^-1 Mpc and γ=1.90+0.04-0.03, over scales of rp=1-130 h^-1 Mpc. Dividing the sample into redshift slices, we find very little, if any, evidence for the evolution of quasar clustering, with the redshift-space correlation length staying roughly constant at s_{0} ~ 6-7 h^-1 Mpc at z<2.2 (and only increasing at redshifts greater than this). Comparing our clustering measurements to those reported for X-ray selected AGN at z=0.5-1, we find reasonable agreement in some cases but significantly lower correlation lengths in others. We find that the linear bias evolves from b~1.4 at z=0.5 to b~3 at z=2.2, with b(z=1.27)=2.06+/-0.03 for the full sample. We compare our data to analytical models and infer that quasars inhabit dark matter haloes of constant mass M ~2 x 10^12 h^-1 M_Sol from redshifts z~2.5 (the peak of quasar activity) to z~0. [ABRIDGED]

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arXiv2008

Quasar Clustering from SDSS DR5: Dependences on Physical Properties

Using a homogenous sample of 38,208 quasars with a sky coverage of $4000 {\rm deg^2}$ drawn from the SDSS Data Release Five quasar catalog, we study the dependence of quasar clustering on luminosity, virial black hole mass, quasar color, and radio loudness. At $z<2.5$, quasar clustering depends weakly on luminosity and virial black hole mass, with typical uncertainty levels $\sim 10%$ for the measured correlation lengths. These weak dependences are consistent with models in which substantial scatter between quasar luminosity, virial black hole mass and the host dark matter halo mass has diluted any clustering difference, where halo mass is assumed to be the relevant quantity that best correlates with clustering strength. However, the most luminous and most massive quasars are more strongly clustered (at the $\sim 2σ$ level) than the remainder of the sample, which we attribute to the rapid increase of the bias factor at the high-mass end of host halos. We do not observe a strong dependence of clustering strength on quasar colors within our sample. On the other hand, radio-loud quasars are more strongly clustered than are radio-quiet quasars matched in redshift and optical luminosity (or virial black hole mass), consistent with local observations of radio galaxies and radio-loud type 2 AGN. Thus radio-loud quasars reside in more massive and denser environments in the biased halo clustering picture. Using the Sheth et al.(2001) formula for the linear halo bias, the estimated host halo mass for radio-loud quasars is $\sim 10^{13} h^{-1}M_\odot$, compared to $\sim 2\times 10^{12} h^{-1}M_\odot$ for radio-quiet quasar hosts at $z\sim 1.5$.

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arXiv2008

A Catalog of Broad Absorption Line Quasars in Sloan Digital Sky Survey Data Release 5

We present a catalog of 5039 broad absorption line (BAL) quasars (QSOs) in the Sloan Digital Sky Survey (SDSS) Data Release 5 (DR5) QSO catalog that have absorption troughs covering a continuous velocity range >= 2000 km/s. We have fit ultraviolet (UV) continua and line emission in each case, enabling us to report common diagnostics of BAL strengths and velocities in the range -25,000 to 0 km/s for SiIV $λ$1400, CIV $λ$1549, AlIII $λ$1857, and MgII $λ$2799. We calculate these diagnostics using the spectrum listed in the DR5 QSO catalog, and also for spectra from additional SDSS observing epochs when available. In cases where BAL QSOs have been observed with Chandra or XMM-Newton, we report the X-ray monochromatic luminosities of these sources. We confirm and extend previous findings that BAL QSOs are more strongly reddened in the rest-frame UV than non-BAL QSOs and that BAL QSOs are relatively X-ray weak compared to non-BAL QSOs. The observed BAL fraction is dependent on the spectral signal-to-noise (S/N); for higher-S/N sources, we find an observed BAL fraction of approximately 15%. BAL QSOs show a similar Baldwin effect as for non-BAL QSOs, in that their CIV emission equivalent widths decrease with increasing continuum luminosity. However, BAL QSOs have weaker CIV emission in general than do non-BAL QSOs. Sources with higher UV luminosities are more likely to have higher-velocity outflows, and the BAL outflow velocity and UV absorption strength are correlated with relative X-ray weakness. These results are in qualitative agreement with models that depend on strong X-ray absorption to shield the outflow from over-ionization and enable radiative acceleration....

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arXiv2008

Rapidly Spinning Black Holes in Quasars: An Open Question

Wang et al. (2006) estimated an average radiative efficiency of 30% -- 35% for quasars at moderate redshift. We find that their method is not independent of quasar lifetimes and thus that quasars do not necessarily have such high efficiencies. Nonetheless, it is possible to derive interrelated constraints on quasar lifetimes, Eddington ratios, and radiative efficiencies of supermassive black holes. We derive such constraints using a statistically complete sample of quasars with black hole mass estimates from broad Mg II, made both with and without the radiation pressure correction of Marconi et al. (2008). We conclude that for quasars with L/LEdd > 0.02, lifetimes can range from 140 to 750 Myr for Schwarzschild black holes. Coupled with observed black hole masses, quasar lifetimes of < 140 Myr would imply that radiatively inefficient accretion or BH mergers must be important in the accretion history of quasars. Given reasonable assumptions about the quasar population, if the average quasar lifetime is < 1 Gyr, and if radiatively inefficient accretion is unimportant, then not many BHs with Eddington ratio < 0.2 can be rapidly spinning.

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arXiv2008

A Nearby Old Halo White Dwarf Candidate from the Sloan Digital Sky Survey

We report the discovery of a nearby, old, halo white dwarf candidate from the Sloan Digital Sky Survey. SDSS J110217.48+411315.4 has a proper motion of 1.75 arcsec/year and redder optical colors than all other known featureless (type DC) white dwarfs. We present SDSS imaging and spectroscopy of this object, along with near-infrared photometry obtained at the United Kingdom Infra-Red Telescope. Fitting its photometry with up-to-date model atmospheres, we find that its overall spectral energy distribution is fit reasonably well with a pure hydrogen composition and T_eff~3800 K (assuming log g=8). That temperature and gravity would place this white dwarf at 35 pc from the Sun with a tangential velocity of 290 km/s and space velocities consistent with halo membership; furthermore, its combined main sequence and white dwarf cooling age would be ~11 Gyr. However, if this object is a massive white dwarf, it could be a younger object with a thick disk origin. Whatever its origin, the optical colors of this object are redder than predicted by any current pure hydrogen, pure helium or mixed hydrogen-helium atmospheric model, indicating that there remain problems in our understanding of the complicated physics of the dense atmospheres of cool white dwarfs.

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arXiv2008

A Large Sample of BL Lacs from SDSS and FIRST

We present a large sample of 501 radio-selected BL Lac candidates from the combination of the Sloan Digital Sky Survey (SDSS) Data Release 5 optical spectroscopy and from the Faint Images of the Radio Sky at Twenty-Centimeters (FIRST) radio survey; this is one of the largest BL Lac samples yet assembled, and each object emerges with homogeneous data coverage. Each candidate is detected in the radio from FIRST and confirmed in SDSS optical spectroscopy to have: (1) no emission feature with measured rest equivalent width larger than 5 Angstroms; and (2) no measured Ca II H/K depression larger than 40%. We subdivide our sample into 426 higher confidence candidates and 75 lower confidence candidates. We argue that contamination from other classes of objects that formally pass our selection criteria is small, and we identify a few very rare radio AGN with unusual spectra that are probably related to broad absorption line quasars. About one-fifth of our sample were known BL Lacs prior to the SDSS. A preliminary analysis of the sample generally supports the standard beaming paradigm. While we recover sizable numbers of low-energy and intermediate-energy cutoff BL Lacs (LBLs and IBLs, respectively), there are indications of a potential bias toward recovering high-energy cutoff BL Lacs (HBLs) from SDSS spectroscopy. Such a large sample may eventually provide new constraints on BL Lac unification models and their potentially peculiar cosmic evolution; in particular, our sample contains a significant number of higher redshift objects, a sub-population for which the standard paradigm has yet to be rigorously constrained.

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arXiv2008

The Multiwavelength Survey by Yale-Chile (MUSYC): Wide K-band Imaging, Photometric Catalogs, Clustering and Physical Properties of Galaxies at z~2

We present K-band imaging of two ~30'x30' fields covered by the MUSYC Wide NIR Survey. The 1030 and 1255 fields were imaged with ISPI on the 4m Blanco telescope at CTIO to a 5 sigma point-source limiting depth of K~20 (Vega). Combining this data with the MUSYC Optical UBVRIz imaging, we created multi-band K-selected source catalogs for both fields. These catalogs, together with the MUSYC K-band catalog of the ECDF-S field, were used to select K<20 BzK galaxies over an area of 0.71 deg^2. This is the largest area ever surveyed for BzK galaxies. We present number counts, redshift distributions and stellar masses for our sample of 3261 BzK galaxies (2502 star-forming (sBzK) and 759 passively evolving (pBzK)), as well as reddening and star formation rate estimates for the star-forming BzK systems. We also present 2-point angular correlation functions and spatial correlation lengths for both sBzK and pBzK galaxies and show that previous estimates of the correlation function of these galaxies were affected by cosmic variance due to the small areas surveyed. We have measured correlation lengths r_0 of 8.89+/-2.03 Mpc and 10.82+/-1.72 Mpc for sBzK and pBzK galaxies respectively. This is the first reported measurement of the spatial correlation function of passive BzK galaxies. In the LambdaCDM scenario of galaxy formation, these correlation lengths at z~2 translate into minimum masses of ~4x10^{12} M_sun and ~9x10^{12} M_sun for the dark matter (DM) halos hosting sBzK and pBzK galaxies respectively. The clustering properties of the galaxies in our sample are consistent with them being the descendants of bright LBG at z~3, and the progenitors of present-day >1L* galaxies.

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arXiv2008

Narrow associated QSO absorbers: clustering, outflows and the line-of-sight proximity effect

Using data from the Sloan Digital Sky Survey data release 3 (SDSS DR3) we investigate how narrow (<700km/s) CIV and MgII quasar absorption line systems are distributed around quasars. The CIV absorbers lie in the redshift range 1.6 < z < 4 and the MgII absorbers in the range 0.4 40% of CIV absorbers within 3,000km/s of the QSO are not a result of large-scale clustering but rather are directly associated with the quasar itself; (iii) that this intrinsic absorber population extends to outflow velocities of order 12,000km/s; (iv) that this outflow component is present in both radio-loud and radio-quiet quasars; and (v) that a small high-velocity outflow component is observed in the MgII population, but any further intrinsic absorber component is undetectable in our clustering analysis. We also find an indication that absorption systems within 3,000km/s are more abundant for radio-loud than for radio-quiet quasars. This suggests either that radio-loud objects live in more massive halos, or that their radio activity generates an additional low-velocity outflow, or both.

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arXiv2008

C_2 in Peculiar DQ White Dwarfs

White dwarfs (WDs) with carbon absorption features in their optical spectra are known as DQ WDs. The subclass of peculiar DQ WDs are cool objects (T_eff<6000 K) which show molecular absorption bands that have centroid wavelengths ~100-300 Angstroms shortward of the bandheads of the C_2 Swan bands. These "peculiar DQ bands" have been attributed to a hydrocarbon such as C_2H. We point out that C_2H does not show strong absorption bands with wavelengths matching those of the peculiar DQ bands and neither does any other simple molecule or ion likely to be present in a cool WD atmosphere. The most straightforward explanation for the peculiar DQ bands is that they are pressure-shifted Swan bands of C_2. While current models of WD atmospheres suggest that, in general, peculiar DQ WDs do not have higher photospheric pressures than normal DQ WDs do, that finding requires confirmation by improved models of WD atmospheres and of the behavior of C_2 at high pressures and temperatures. If it is eventually shown that the peculiar DQ bands cannot be explained as pressure-shifted Swan bands, the only explanation remaining would seem to be that they arise from highly rotationally excited C_2 (J_peak>45). In either case, the absorption band profiles can in principle be used to constrain the pressure and the rotational temperature of C_2 in the line-forming regions of normal and peculiar DQ WD atmospheres, which will be useful for comparison with models. Finally, we note that progress in understanding magnetic DQ WDs may require models which simultaneously consider magnetic fields, high pressures and rotational excitation of C_2.

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arXiv2007

Do broad absorption line quasars live in different environments from ordinary quasars?

We select a sample of $\sim 4200$ traditionally defined broad absorption line quasars (BALQs) from the Fifth Data Release quasar catalog of the Sloan Digital Sky Survey. For a statistically homogeneous quasar sample with $1.7\le z\le 4.2$, the BAL quasar fraction is $\sim 14%$ and is almost constant with redshift. We measure the auto-correlation of non-BAL quasars (nonBALQs) and the cross-correlation of BALQs with nonBALQs using this statistically homogeneous sample, both in redshift space and using the projected correlation function. We find no significant difference between the clustering strengths of BALQs and nonBALQs. Assuming a power-law model for the real space correlation function $ξ(r)=(r/r_0)^{-1.8}$, the correlation length for nonBALQs is $r_0=7.6\pm 0.8 h^{-1}{\rm Mpc}$; for BALQs, the cross-correlation length is $r_0=7.4\pm 1.1 h^{-1}{\rm Mpc}$. Our clustering results suggest that BALQs live in similar large-scale environments as do nonBALQs.

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arXiv2007

The Sloan Digital Sky Survey Quasar Lens Search. II. Statistical Lens Sample from the Third Data Release

We report the first results of our systematic search for strongly lensed quasars using the spectroscopically confirmed quasars in the Sloan Digital Sky Survey (SDSS). Among 46,420 quasars from the SDSS Data Release 3 (~4188 deg^2), we select a subsample of 22,683 quasars that are located at redshifts between 0.6 and 2.2 and are brighter than the Galactic extinction corrected i-band magnitude of 19.1. We identify 220 lens candidates from the quasar subsample, for which we conduct extensive and systematic follow-up observations in optical and near-infrared wavebands, in order to construct a complete lensed quasar sample at image separations between 1'' and 20'' and flux ratios of faint to bright lensed images larger than 10^{-0.5}. We construct a statistical sample of 11 lensed quasars. Ten of these are galaxy-scale lenses with small image separations (~1''-2'') and one is a large separation (15'') system which is produced by a massive cluster of galaxies, representing the first statistical sample of lensed quasars including both galaxy- and cluster-scale lenses. The Data Release 3 spectroscopic quasars contain an additional 11 lensed quasars outside the statistical sample.

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arXiv2007

The Sloan Digital Sky Survey Quasar Lens Search. III. Constraints on Dark Energy from the Third Data Release Quasar Lens Catalog

We present cosmological results from the statistics of lensed quasars in the Sloan Digital Sky Survey (SDSS) Quasar Lens Search. By taking proper account of the selection function, we compute the expected number of quasars lensed by early-type galaxies and their image separation distribution assuming a flat universe, which is then compared with 7 lenses found in the SDSS Data Release 3 to derive constraints on dark energy under strictly controlled criteria. For a cosmological constant model (w=-1) we obtain Ω_Λ=0.74^{+0.11}_{-0.15}(stat.)^{+0.13}_{-0.06}(syst.). Allowing w to be a free parameter we find Ω_M=0.26^{+0.07}_{-0.06}(stat.)^{+0.03}_{-0.05}(syst.) and w=-1.1\pm0.6(stat.)^{+0.3}_{-0.5}(syst.) when combined with the constraint from the measurement of baryon acoustic oscillations in the SDSS luminous red galaxy sample. Our results are in good agreement with earlier lensing constraints obtained using radio lenses, and provide additional confirmation of the presence of dark energy consistent with a cosmological constant, derived independently of type Ia supernovae.

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arXiv2007

Quasar Clustering at $25\kpch$ from a Complete Sample of Binaries

We present spectroscopy of binary quasar candidates selected from Data Release 4 of the Sloan Digital Sky Survey (SDSS DR4) using Kernel Density Estimation (KDE). We present 27 new sets of observations, 10 of which are binary quasars, roughly doubling the number of known $g < 21$ binaries with component separations of 3 to 6". Only 3 of 49 spectroscopically identified objects are non-quasars, confirming that the quasar selection efficiency of the KDE technique is $\sim95$%. Several of our observed binaries are wide-separation lens candidates that merit additional higher-resolution observations. One interesting pair may be an M star binary, or an M star-binary quasar superposition. Our candidates are initially selected by UV-excess ($u-g < 1$), but are otherwise selected irrespective of the relative colors of the quasar pair, and we thus use them to suggest optimal color similarity and photometric redshift approaches for targeting binary quasars, or projected quasar pairs. From a sample that is complete on proper scales of $23.7 < R_{prop} < 29.7\kpch$, we determine the projected quasar correlation function to be $W_p=24.0 \pm^{16.9}_{10.8}$, which is $2σ$ lower than recent estimates. We argue that our low $W_p$ estimates may indicate redshift evolution in the quasar correlation function from $z\sim1.9$ to $z\sim1.4$ on scales of $R_{prop} \sim25\kpch$. The size of this evolution broadly tracks quasar clustering on larger scales, consistent with merger-driven models of quasar origin. Although our sample alone is insufficient to detect evolution in quasar clustering on small scales, an $i$-selected DR6 KDE quasar catalog, which will contain several hundred $z \leqsim 5$ binary quasars, could easily constrain any clustering evolution at $R_{prop} \sim25\kpch$.

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arXiv2007

A New Quadruply Lensed Quasar: SDSSJ125107.57+293540.5

We report the discovery of a quadruply imaged quasar, SDSSJ125107.57+293540.5, selected from the Sloan Digital Sky Survey. Follow-up imaging reveals that the system consists of four blue point-like components in a typical cusp lens geometry surrounding a central red galaxy. The source redshift is 0.802 and the lens redshift is 0.410. The maximum image separation between the lensed components is 1"79. While the image configuration is well reproduced by standard mass models with reasonable parameter values, the flux ratios predicted by these models differ from the observed ratios in all bands. This is suggestive of small-scale structures in this lens, although the definitive identification of the anomaly requires more accurate photometry and astrometry.

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arXiv2007

Acceleration and Substructure Constraints in a Quasar Outflow

We present observations of probable line-of-sight acceleration of a broad absorption trough of C IV in the quasar SDSS J024221.87+004912.6. We also discuss how the velocity overlap of two other outflowing systems in the same object constrains the properties of the outflows. The Si IV doublet in each system has one unblended transition and one transition which overlaps with absorption from the other system. The residual flux in the overlapping trough is well fit by the product of the residual fluxes in the unblended troughs. For these optically thick systems to yield such a result, at least one of them must consist of individual subunits rather than being a single structure with velocity-dependent coverage of the source. If these subunits are identical, opaque, spherical clouds, we estimate the cloud radius to be r = 3.9 10^15 cm. If they are identical, opaque, linear filaments, we estimate their width to be w = 6.5 10^14 cm. These subunits are observed to cover the Mg II broad emission line region of the quasar, at which distance from the black hole the above filament width is equal to the predicted scale height of the outer atmosphere of a thin accretion disk. Insofar as that scale height is a natural size scale for structures originating in an accretion disk, these observations are evidence that the accretion disk can be a source of quasar absorption systems. Based on data from ESO program 075.B-0190(A).

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arXiv2007

The Sloan Digital Sky Survey Quasar Catalog IV. Fifth Data Release

We present the fourth edition of the Sloan Digital Sky Survey (SDSS) Quasar Catalog. The catalog contains 77,429 objects; this is an increase of over 30,000 entries since the previous edition. The catalog consists of the objects in the SDSS Fifth Data Release that have luminosities larger than M_i = -22.0 (in a cosmology with H_0 = 70 km/s/Mpc, Omega_M = 0.3, and Omega_Lambda = 0.7) have at least one emission line with FWHM larger than 1000 km/s, or have interesting/complex absorption features, are fainter than i=15.0, and have highly reliable redshifts. The area covered by the catalog is 5740 sq. deg. The quasar redshifts range from 0.08 to 5.41, with a median value of 1.48; the catalog includes 891 quasars at redshifts greater than four, of which 36 are at redshifts greater than five. Approximately half of the catalog quasars have i < 19; nearly all have i < 21. For each object the catalog presents positions accurate to better than 0.2 arcsec. rms per coordinate, five-band (ugriz) CCD-based photometry with typical accuracy of 0.03 mag, and information on the morphology and selection method. The catalog also contains basic radio, near-infrared, and X-ray emission properties of the quasars, when available, from other large-area surveys. The calibrated digital spectra cover the wavelength region 3800--9200A at a spectral resolution of ~2000. The spectra can be retrieved from the public database using the information provided in the catalog. The average SDSS colors of quasars as a function of redshift, derived from the catalog entries, are presented in tabular form. Approximately 96% of the objects in the catalog were discovered by the SDSS.

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arXiv2007

On the Spectral Evolution of Cool, Helium-Atmosphere White Dwarfs: Detailed Spectroscopic and Photometric Analysis of DZ Stars

We present a detailed analysis of a large spectroscopic and photometric sample of DZ white dwarfs based on our latest model atmosphere calculations. We revise the atmospheric parameters of the trigonometric parallax sample of Bergeron, Leggett, & Ruiz (12 stars) and analyze 147 new DZ white dwarfs discovered in the Sloan Digital Sky Survey. The inclusion of metals and hydrogen in our model atmosphere calculations leads to different atmospheric parameters than those derived from pure helium models. Calcium abundances are found in the range from log (Ca/He) = -12 to -8. We also find that fits of the coolest objects show peculiarities, suggesting that our physical models may not correctly describe the conditions of high atmospheric pressure encountered in the coolest DZ stars. We find that the mean mass of the 11 DZ stars with trigonometric parallaxes, = 0.63 Mo, is significantly lower than that obtained from pure helium models, = 0.78 Mo, and in much better agreement with the mean mass of other types of white dwarfs. We determine hydrogen abundances for 27% of the DZ stars in our sample, while only upper limits are obtained for objects with low signal-to-noise ratio spectroscopic data. We confirm with a high level of confidence that the accretion rate of hydrogen is at least two orders of magnitude smaller than that of metals (and up to five in some cases) to be compatible with the observations. We find a correlation between the hydrogen abundance and the effective temperature, suggesting for the first time empirical evidence of a lower temperature boundary for the hydrogen screening mechanism. Finally, we speculate on the possibility that the DZA white dwarfs could be the result of the convective mixing of thin hydrogen-rich atmospheres with the underlying helium convection zone.

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arXiv2007

Near-Infrared Properties of Moderate-Redshift Galaxy Clusters: Halo Occupation Number, Mass-to-Light Ratios and Omega_m

Using K-band imaging for 15 of the Canadian Network for Observational Cosmology (CNOC1) clusters we examine the near-infrared properties of moderate-redshift (0.19 < z < 0.55) galaxy clusters. We find that the number of K-band selected cluster galaxies within R_{500} (the Halo Occupation Number, HON) is well-correlated with the the cluster dynamical mass (M_{500}) and X-ray Temperature (T_{x}); however, the intrinsic scatter in these scaling relations is 37% and 46% respectively. Comparison with clusters in the local universe shows that the HON-M_{500} relation does not evolve significantly between z = 0 and z ~ 0.3. This suggests that if dark matter halos are disrupted or undergo significant tidal-stripping in high-density regions as seen in numerical simulations, the stellar mass within the halos is tightly bound, and not removed during the process. The total K-band cluster light (L_{200,K}) and K-band selected richness (parameterized by B_{gc,K}) are also correlated with both the cluster T_{x} and M_{200}. The total (intrinsic) scatter in the L_{200,K}-M_{200} and B_{gc,K}-M_{200} relations are 43%(31%) and 35%(18%) respectively and indicates that for massive clusters both L_{200,K} and B_{gc,K} can predict M_{200} with similar accuracy as T_{x}, L_{x} or optical richness (B_{gc}). Examination of the mass-to-light ratios of the clusters shows that similar to local clusters, the K-band mass-to-light ratio is an increasing function of halo mass. Using the K-band mass-to-light ratios of the clusters, we apply the Oort technique and find Omega_{m,0} = 0.22 pm 0.02, which agrees well with recent combined concordance cosmology parameters, but, similar to previous cluster studies, is on the low-density end of preferred values.

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