CCD Imaging of the Bo\"otes Void to Delineate Void Volume

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Session 119 -- Galaxies and Clusters of Galaxies, X-Ray Observationsd
Oral presentation, Thursday, 12, 1995, 2:00pm - 3:30pm

[119.06] CCD Imaging of the Bo\"otes Void to Delineate Void Volume

S.B.Johnson (Idaho State University), J.W.Moody (BYU), I.K.Horowitz (Idaho State University), K.A.Adams (U. of Maryland), B.Paul (BYU)

The Bo\"otes void has been defined as a sphere with a diameter of 6,300 km s$^{-1}$ centered at $\alpha$ = 14h50m, $\delta$ = +46$\deg$, and cz = 15,500 km s$^{-1}$ (Kirshner, 1987, Ap.J. , 314 , 493). Since then several dozen galaxies have been found within this void. However a 4,000 km s$^{-1}$ diameter volume displaced to the southwest of the original void center remains completely empty raising the possibility that the true void is at a lower declination and is smaller than originally defined.

As a first step in testing this idea, we have taken deep R-filter CCD images with the CWRU Burrell Schmidt telescope during 1994. The observations cover 28 square degrees in a horizontal strip extending from 14h07m $< \alpha <$ 15h13m and +42$\deg$ $< \delta <$ +44$\deg$ and a vertical strip extending from 14h49m $< \alpha <$ 15h01m and +44$\deg$ $< \delta <$ +47$\deg$. The total integration time for each one-square-degree field is on the order of 9000 seconds. Point sources were removed using the photometry package DoPHOT (Schecter, Mateo and Saha, 1993, PASP , 105 , 1353) and the remaining extended sources in each field were morphologially typed using an algorithm which measured the asymptotic magnitude and surface brightness profile (see Hintz, this volume, for a description of the algorithm). The morphological information was used to further guard against stellar contamination.

Plots of galaxy counts versus magnitude for each field show that we clearly detect the back edge of the void. There is a deficit of galaxies over roughly a four magnitude range centered on M* at the distance of the void center. We report on how this absence of galaxies and the overall shape of the plots constrain possible void densities and edge populations.

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