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Session 110 -- Blazars and BL Lacs

Display presentation, Thursday, 12, 1995, 9:20am - 6:30pm

[110.10] Probing BL Lac and Cluster Evolution via a Wide-angle, Deep X-ray Selected Sample

The WARPS survey (Wide-Angle ROSAT Pointed Survey) has been constructed from the archive of all public ROSAT PSPC observations, and is a subset of the WGACAT catalog. WARPS will include a complete sample of $\ge 100$ BL Lacs at $F_x \ge 10^{-13} {\rm ~erg ~s^{-1} ~cm^{-2}}$. A second selection technique will identify $\approx 100$ clusters at $0.15 Only 171 BL Lacs are known and the largest complete samples are also small, with 20-50 objects each. Current data shows a discrepancy between XBL (X-ray selected BL Lac) and RBL (Radio-selected BL Lac) evolution, with $ = 0.304 \pm 0.062$ for XBLs but $ = 0.60 \pm 0.05$ for RBLs. Models of the X-ray luminosity function (XLF) are also poorly constrained. WARPS will allow us to compute an accurate XLF, decreasing the error bars above by over a factor of two. We will also test for low-luminosity BL Lacs, whose non-thermal nuclear sources are dim compared to the host galaxy. Browne and Marcha (1993) claim the EMSS missed most of these objects and is incomplete. If their predictions are correct, 20-40$\%$ of the BL Lacs we find will fall in this category, enabling us to probe the evolution and internal workings of BL Lacs at lower luminosities than ever before.

By removing likely QSOs before optical spectroscopy, WARPS requires only modest amounts of telescope time. It will extend measurement of the cluster XLF both to higher redshifts (z$>$0.5) and lower luminosities (L$_{X}<$1x10$^{44}$ erg s$^{-1}$) than previous measurements, confirming or rejecting the 3$\sigma$ detection of negative evolution found in the EMSS, and constraining Cold Dark Matter cosmologies. Faint NELGs are a recently discovered major contributor to the X-ray background. They are a mixture of Sy2s, starbursts and galaxies of unknown type. Detailed classification and evolution of their XLF will be determined for the first time.

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