Caleb A. Scharf

Observational tests of the mass-temperature relation for galaxy clusters

We examine the relationship between the mass and X-ray gas temperature of galaxy clusters using data drawn from the literature. Simple theoretical arguments suggest that the mass of a cluster is related to the X-ray temperature as Virial theorem mass estimates based on cluster galaxy velocity M P T X. dispersions seem to be accurately described by this scaling with a normalization consistent with that predicted by the simulations of Evrard, Metzler, and Navarro. X-ray mass estimates that employ spa- tially resolved temperature pro—les also follow a scaling although with a normalization about 40% T X lower than that of the —t to the virial masses. However, the isothermal b-model and X-ray surface brightness deprojection masses follow a steeper scaling. The steepness of the isothermal esti- PT Xh2.0 mates is due to their implicitly assumed dark matter density pro—le of o(r) P r~2 at large radii, whereas observations and simulations suggest that clusters follow steeper pro—les (e.g., o(r) P r~2.4). Subject headings: galaxies: clusters: generalX-rays: galaxies

A spherical harmonic approach to redshift distortion and a measurement of

We examine the nature of galaxy clustering in redshift space, using a method based on an expansion of the galactic density field in spherical harmonics and linear theory. Our approach provides a compact and self-consistent expression for the distortion when applied to flux-limited redshift surveys. The amplitude of the distortion is controlled by the combination of the density and bias parameters, beta = OMEGA0(0.6)/b; we exploit this fact to derive a maximum-likelihood estimator for beta. We check our formalism using N-body simulations, and demonstrate that it provides an unbiased estimate of beta when the amplitude and shape of the galaxy power spectrum are known. Application of the technique to the 1.2-Jy IRAS Redshift Survey yields beta almost-equal-to 1.0; both random errors (from counting statistics and the uncertainties in the power-spectrum normalization) and systematic errors (from the uncertainty in the shape of the power spectrum) individually contribute 20 per cent uncertainties in this estimate. This estimate of beta is comparable (both in amplitude and uncertainty) with previous measurements based on comparisons of the IRAS density field with direct measurements of peculiar velocities and analyses of the acceleration of the Local Group, but the spherical harmonic analysis has the advantage of being easy to implement and largely free of systematic errors.

\Omega_0

The X-ray properties of a sample of 11 high-redshift (0.6 < z < 1 .O) clusters observed with Chardm and/or XMM-Newton are used to investigate the evolution of the cluster scaling relations. The observed evolution in the normalization of the L-T, M-T, M(sub 2)-T and M-L relations is consistent with simple self-similar predictions, in which the properties of clusters reflect the properties of the Universe at their redshift of observation. Under the assumption that the model of self-similar evolution is correct and that the local systems formed via a single spherical collapse, the high-redshift L-T relation is consistent with the high-z clusters having virialized at a significantly higher redshift than the local systems. The data are also consistent with the more realistic scenario of clusters forming via the continuous accretion of material. The slope of the L-T relation at high redshift (B = 3.32 +/- 0.37) is consistent with the local relation, and significantly steeper than the self-similar prediction of B = 2. This suggests that the same non-gravitational processes are responsible for steepening the local and high-z relations, possibly occurring universally at z is approximately greater than 1 or in the early stages of the cluster formation, prior to their observation. The properties of the intracluster medium at high redshift are found to be similar to those in the local Universe. The mean surface-brightness profile slope for the sample is Beta = 0.66 +/- 0.05, the mean gas mass fractions within R(sub 2500(z)) and R(200(z)) are 0.069 +/- 0.012 and 0.11 +/- 0.02, respectively, and the mean metallicity of the sample is 0.28 +/- 0.11 Z(sub solar).

from the 1.2-Jy IRAS Redshift Survey

Extrasolar terrestrial planets with the potential to host life might have large obliquities or be subject to strong obliquity variations. We revisit the habitability of oblique planets with an energy balance climate model (EBM) allowing for dynamical transitions to ice-covered snowball states as a result of ice-albedo feedback. Despite the great simplicity of our EBM, it captures reasonably well the seasonal cycle of global energetic fluxes at Earths surface. It also performs satisfactorily against a full-physics climate model of a highly oblique Earth-like planet, in an unusual regime of circulation dominated by heat transport from the poles to the equator. Climates on oblique terrestrial planets can violate global radiative balance through much of their seasonal cycle, which limits the usefulness of simple radiative equilibrium arguments. High obliquity planets have severe climates, with large amplitude seasonal variations, but they are not necessarily more prone to global snowball transitions than low obliquity planets. We find that terrestrial planets with massive CO2 atmospheres, typically expected in the outer regions of habitable zones, can also be subject to such dynamical snowball transitions. Some of the snowball climates investigated for CO2-rich atmospheres experience partial atmospheric collapse. Since long-term CO2 atmospheric build-up acts as a climatic thermostat for habitable planets, partial CO2 collapse could limit the habitability of such planets. A terrestrial planets habitability may thus sensitively depend on its short-term climatic stability.

The evolution of the cluster X-ray scaling relations in the Wide Angle ROSAT Pointed Survey sample at 0.6 < z < 1.0

We report on our ASCA, Keck, and ROSAT observations of MS 1137.5+6625, the second most distant cluster of galaxies in the Einstein Extended Medium Sensitivity Survey (EMSS), at redshift 0.78. We now have a full set of X-ray temperatures, optical velocity dispersions, and X-ray images for a complete, high-redshift sample of clusters of galaxies drawn from the EMSS. Our ASCA observations of MS 1137.5+6625 yield a temperature of 5.7 keV and a metallicity of 0.43 solar, with 90% confidence limits. Keck II spectroscopy of 22 cluster members reveals a velocity dispersion of 884 km s-1. This cluster is the most distant in the sample with a detected iron line. We also derive a mean abundance at z = 0.8 by simultaneously fitting X-ray data for the two z = 0.8 clusters, and obtain an abundance of ZFe = 0.33 ±. Our ROSAT observations show that MS 1137.5+6625 is regular and highly centrally concentrated. Fitting of a β model to the X-ray surface brightness yields a core radius of only 71 h-1 kpc (q0 = 0.1) with β = 0.70 ±. The gas mass interior to 0.5 h-1 Mpc is thus 1.2 ± ×1013 h-5/2 M☉ (q0 = 0.1). If the clusters gas is nearly isothermal and in hydrostatic equilibrium with the cluster potential, the total mass of the cluster within this same region is 2.1 ± ×1014 h-1 M☉, giving a gas fraction of 0.06 ± 0.04 h-3/2. This cluster is the highest redshift EMSS cluster showing evidence for a possible cooling flow (~20-400 M☉ yr-1). The velocity dispersion, temperature, gas fraction, and iron abundance of MS 1137.5+6625 are all statistically the same as those properties in lower redshift clusters of similar luminosity. With this clusters temperature now in hand, we derive a high-redshift temperature function for EMSS clusters at 0.5 < z < 0.9 and compare it with temperature functions at lower redshifts, showing that the evolution of the temperature function is relatively modest. Supplementing our high-redshift sample with other data from the literature, we demonstrate that neither the cluster luminosity-temperature relation, nor cluster metallicities, nor the cluster gas fraction has detectably evolved with redshift. The very modest degree of evolution in the luminosity-temperature relation inferred from these data is inconsistent with the absence of evolution in the X-ray luminosity functions derived from ROSAT cluster surveys if a critical density structure formation model is assumed.

HABITABLE CLIMATES: THE INFLUENCE OF OBLIQUITY

We present in catalog form the optical identifications for objects from the first phase of the Wide Angle ROSAT Pointed Survey (WARPS). WARPS is a serendipitous survey of relatively deep, pointed ROSAT observations for clusters of galaxies. The X-ray source detection algorithm used by WARPS is Voronoi Tessellation and Percolation (VTP), a technique which is equally sensitive to point sources and extended sources of low surface brightness. WARPS-I is based on the central regions of 86 ROSAT PSPC fields, covering an area of 16.2 square degrees. We describe here the X-ray source screening and optical identification process for WARPS-I, which yielded 34 clusters at 0.06 < z < 0.75. Twenty-two of these clusters form a complete, statistically well-defined sample drawn from 75 of these 86 fields, covering an area of 14.1 square degrees, with a flux limit of F(0.5 × 2.0 keV) = 6.5 × 10-14 erg cm-2 s-1. This sample can be used to study the properties and evolution of the gas, galaxy and dark matter content of clusters and to constrain cosmological parameters. We compare in detail the identification process and findings of WARPS to those from other recently published X-ray surveys for clusters, including RDCS, SHARC-Bright, SHARC-south, and the CfA 160 deg2 survey.

The Second Most Distant Cluster of Galaxies in the Extended Medium Sensitivity Survey

Although Earths orbit is never far from circular, terrestrial planets around other stars might experience substantial changes in eccentricity. Eccentricity variations could lead to climate changes, including possible phase transitions such as the snowball transition (or its opposite). There is evidence that Earth has gone through at least one globally frozen, snowball state in the last billion years, which it is thought to have exited after several million years because global ice-cover shut off the carbonate-silicate cycle, thereby allowing greenhouse gases to build up to sufficient concentration to melt the ice. Due to the positive feedback caused by the high albedo of snow and ice, susceptibility to falling into snowball states might be a generic feature of water-rich planets with the capacity to host life. This paper has two main thrusts. First, we revisit one-dimensional energy balance climate models as tools for probing possible climates of exoplanets, investigate the dimensional scaling of such models, and introduce a simple algorithm to treat the melting of the ice layer on a globally frozen planet. We show that if a terrestrial planet undergoes Milankovitch-like oscillations of eccentricity that are of great enough magnitude, it could melt out of a snowball state. Second, we examine the kinds of variations of eccentricity that a terrestrial planet might experience due to the gravitational influence of a giant companion. We show that a giant planet on a sufficiently eccentric orbit can excite extreme eccentricity oscillations in the orbit of a habitable terrestrial planet. More generally, these two results demonstrate that the long-term habitability (and astronomical observables) of a terrestrial planet can depend on the detailed architecture of the planetary system in which it resides.

The WARPS Survey. VI. Galaxy Cluster and Source Identifications from Phase I

Cosmological simulations predict that a large fraction of the baryonic mass of the universe exists as 105-107 K diffuse, X-ray-emitting gas, tracing low-density filament and sheetlike structures exterior to massive clusters of galaxies. If present, this gas helps reconcile the current shortfall in observed baryon counts relative to the predictions of the standard big bang model. We present here the discovery and analysis of a 5 sigma significance half-degree filamentary structure, which is present in both the I-band galaxy surface density and the unresolved X-ray emission in a deep ROSAT PSPC field. The estimated diffuse X-ray emission component of this structure has a surface brightness of approximately 1.6x10-16 ergs s-1 cm-2 arcmin-2 (0.5-2 keV), comparable to the predictions for intercluster gas, and may represent a direct detection of this currently unconfirmed baryonic component.

GENERALIZED MILANKOVITCH CYCLES AND LONG-TERM CLIMATIC HABITABILITY

We present and analyze the optical and X-ray catalogs of moderate-redshift cluster candidates from the ROSAT Optical X-Ray Survey, or ROXS. The survey covers the sky area contained in the fields of view of 23 deep archival ROSAT PSPC pointings, 4.8 square degrees. The cross-correlated cluster catalogs were constructed by comparing two independent catalogs extracted from the optical and X-ray bandpasses, using a matched-filter technique for the optical data and a wavelet technique for the X-ray data. We cross-identified cluster candidates in each catalog. As reported in Paper I, the matched-filter technique found optical counterparts for at least 60% (26 out of 43) of the X-ray cluster candidates; the estimated redshifts from the matched filter algorithm agree with at least 7 of 11 spectroscopic confirmations (Δz 0.10). The matched filter technique, with an imaging sensitivity of mI ~ 23, identified approximately 3 times the number of candidates (155 candidates, 142 with a detection confidence >3 σ) found in the X-ray survey of nearly the same area. There are 57 X-ray candidates, 43 of which are unobscured by scattered light or bright stars in the optical images. Twenty-six of these have fairly secure optical counterparts. We find that the matched filter algorithm, when applied to images with galaxy flux sensitivities of mI ~ 23, is fairly well-matched to discovering z ≤ 1 clusters detected by wavelets in ROSAT PSPC exposures of 8000-60,000 s. The difference in the spurious fractions between the optical and X-ray (30% and 10%, respectively) cannot account for the difference in source number. In Paper I, we compared the optical and X-ray cluster luminosity functions and we found that the luminosity functions are consistent if the relationship between X-ray and optical luminosities is steep (LX ∝ L). Here, in Paper II, we present the cluster catalogs and a numerical simulation of the ROXS. We also present color-magnitude plots for several of the cluster candidates, and examine the prominence of the red sequence in each. We find that the X-ray clusters in our survey do not all have a prominent red sequence. We conclude that while the red sequence may be a distinct feature in the color-magnitude plots for virialized massive clusters, it may be less distinct in lower mass clusters of galaxies at even moderate redshifts. Multiple, complementary methods of selecting and defining clusters may be essential, particularly at high redshift where all methods start to run into completeness limits, incomplete understanding of physical evolution, and projection effects.

Evidence for X-Ray Emission from a Large-Scale Filament of Galaxies?

The analysis of whole-sky galaxy surveys commonly suffers from the problems of shot-noise and incomplete sky coverage (e.g. at the Zone of Avoidance). The orthogonal set of spherical harmonics is utilized here to expand the observed galaxy distribution. We show that in the framework of Bayesian statistics and Gaussian random fields the