arXiv subjects

Claude R. Canizares

Publications and source records attributed to Claude R. Canizares.

58 records · Page 4Linked to original sources

arXiv1996

The Nature of the X-Ray Emission and the Mass Distributions in Two Early-Type Galaxies

We present spectral analysis of $ASCA$ observations of the early-type galaxies NGC 720 (E4) and NGC 1332 (E7/S0) with emphasis on constraining the relative contribution to the X-ray emission from hot gas and the integrated emission from X-ray binaries. Single-temperature spectral models yield poor fits to the spectrum ($χ^2_{red}\sim 3$) over the $\sim 0.5 - 5$ keV energy range. Two-temperature models significantly improve the spectral fits ($χ^2_{red}\sim 1.5$) and have soft-component temperatures and sub-solar abundances consistent with previous $ROSAT$ single-temperature models ($T_{soft}\sim 0.6$ keV, abundances $\sim 0.1$) and hard-component temperatures ($T_{hard}\gtrsim 3$ keV) consistent with those expected from a discrete component. The soft component dominates the emission in both galaxies, especially in the 0.4 - 2.4 keV band used in previous $ROSAT$ studies. Combining these spectral results with $ROSAT$ data we updated constraints on the mass distributions for NGC 720 and NGC 1332. For NGC 720, which yields the more precise constraints, the ellipticity of the intrinsic shape of the mass is slightly reduced $(Δε_{mass}\approx 0.05)$ when the discrete component is added, $ε_{mass}\sim 0.4-0.6$ $(90%)$. The estimates for the total mass increase with increasing discrete flux, and we find that models with $F_{hard}/F_{soft}=0.45$, the $2σ$ upper limit, have masses that exceed by $\sim 30% - 50%$ those where $F_{hard}/F_{soft}=0$.

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arXiv1996

The Twisting X-ray Isophotes of the Elliptical Galaxy NGC 720

We present spatial analysis of the deep (57ks) ROSAT HRI X-ray image of the E4 galaxy NGC 720. The orientation of the HRI surface brightness is consistent with the optical position angle $(PA)$ interior to semi-major axis $a\sim 60\arcsec$ (optical $R_e\sim 50\arcsec$). For larger $a$ the isophotes twist and eventually $(a\gtrsim 100\arcsec)$ orient along a direction consistent with the $PA$ measured with the PSPC data (Buote & Canizares 1994) -- the $\sim 30\arcdeg$ twist is significant at an estimated 99% confidence level. We argue that this twist is not the result of projected foreground and background sources, ram pressure effects, or tidal distortions. If spheroidal symmetry and a nearly isothermal hot gas are assumed, then the azimuthally averaged radial profile displays features which, when combined with the observed $PA$ twist, are inconsistent with the simple assumptions that the X-ray emission is due either entirely to hot gas or to the combined emission from hot gas and discrete sources. We discuss possible origins of the $PA$ twist and radial profile features (e.g., triaxiality).

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arXiv1995

X-ray Constraints on the Intrinsic Shapes and Baryon Fractions of Five Abell Clusters

We analyzed ROSAT PSPC images of the bright, nearby $(z<0.1)$ galaxy clusters A401, A1656 (Coma), A2029, A2199, and A2256 to constrain their intrinsic shapes and baryon fractions. Following Buote & Tsai we probed the aggregate structure of the clusters on scales $\sim 1.5h^{-1}_{80}$ Mpc to reduce effects of possible substructure on smaller scales ($\lesssim$ a few hundred kpc). The ellipticities of the X-ray isophotes are typically $ε\approx 0.15 - 0.25$ and display negative radial gradients significant (except Coma). By assuming hydrostatic equilibrium and a variety of mass models we obtain ellipticities $ε_{mass} \approx 0.40-0.55$ for isothermal models of the total gravitating matter of the clusters; the $ε_{mass}$ constraints change by $<10%$ upon consideration of the small temperature gradients shown by ASCA to be typical for rich clusters; the observed X-ray ellipticity gradients require that mass models with constant ellipticity have steep density profiles, $ρ\propto r^{-4}$. Estimates of the gas masses are highly insensitive to the ellipticities of the X-ray isophotes. The clusters in our sample have increasing fractions of gas mass to total mass with radius and have $M_{gas}/M_{tot} = (4% - 11%)h^{-3/2}_{80}$ within a radius $1.5h^{-1}_{80}$ Mpc, in excellent agreement with the results of White & Fabian and the Baryon Catastrophe proposed by White et al. (1993). Finally, the ellipticities of the dark matter distributions are essentially identical to $ε_{mass}$ and are consistent with the shapes of dark halos predicted by N-body simulations and the shapes of the galaxy isopleths in the clusters in contrast to our previous conclusions using {\it Einstein} data.

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arXiv1995

X-ray Constraints on the Intrinsic Shape of the Lenticular Galaxy NGC 1332

We have analyzed ROSAT PSPC X-ray data of the optically elongated S0 galaxy NGC 1332 with the purposes of constraining the intrinsic shape of its underlying mass and presenting a detailed investigation of the uncertainties resulting from the assumptions underlying this type of analysis. The X-ray isophotes are elongated with ellipticity $0.10 - 0.27$ (90% confidence) for semi-major axes $75\arcsec -90\arcsec$ and have orientations consistent with the optical isophotes (ellipticity $\sim 0.43$). The spectrum is poorly constrained by the PSPC data and cannot rule out sizeable radial temperature gradients or an emission component due to discrete sources equal in magnitude to the hot gas. Using (and clarifying) the "geometric test" for dark matter, we determined that the hypothesis that mass-traces-light is not consistent with the X-ray data at 68% confidence and marginally consistent at 90% confidence independent of the gas temperature profile. Detailed modeling gives constraints on the ellipticity of the underlying mass of ε_{mass} = 0.47 - 0.72 (0.31 - 0.83) at 68% (90%) confidence for isothermal and polytropic models. The total mass of the isothermal models within a=43.6$ kpc (D = 20h^{-1}_{80} Mpc) is M_{tot} = (0.38 - 1.7) \times 10^{12}M_{\sun} (90% confidence) corresponding to total blue mass-to-light ratio Υ_B = (31.9 - 143) Υ_{\sun}. Similar results are obtained when the dark matter is fit directly using the known distributions of the stars and gas. When possible rotation of the gas and emission from discrete sources are included flattened mass distributions are still required, although the constraints on $ε_{mass}$, but not the total mass, are substantially weakened.

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