An HI survey of the Bootes void

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Session 98 -- Galaxies and Cluster Environment
Oral presentation, Friday, January 14, 2:15-3:45, Salon V Room (Crystal Gateway)

[98.05] An HI survey of the Bootes void

A. Szomoru (Kapteyn Astr. Inst.), J.H. van Gorkom (Columbia Univ.), M. Gregg (Lawrence Livermore Nat. Lab.)

We present the results of an HI survey of galaxies in the Bootes void and follow-up optical broadband photometry. We observed 24 fields with the VLA in D-array, centered on galaxies with known optical redshifts, covering a total of 1400 ${\rm Mpc^{3}}$. Of these 24 galaxies, 16 were detected. This method of survey proved very successfull in detecting new void galaxies. A total of 15 uncataloged companions was found, at distances from the target galaxies ranging from $45^{\prime\prime}$ to $14.5^{\prime}$ ($\sim 40-700$ kpc). These new detections have increased the number of galaxies within the void to 56 . In several cases the HI seems associated with more than one optical system. The HI-detected companions are less luminous than the target galaxies. This is probably due to the selection of the target galaxies, most of which were found in the IRAS faint source catalog. HI-masses range from nearly $10^{9}$ to nearly $10^{10} \, M_{\odot}$. Several of the HI-detected galaxies have very extended gaseous disks, with diameters of up to 85 kpc. As a consequence of the low luminosities, ${M_{\rm HI}/L_{\rm B}}$ values of the companions are higher than those of the target galaxies, though not exceptionally high. We show that the HI-mass function of the void is consistent with the mass-function derived by Briggs (1990). The density of the void is constant throughout, with no sign of a smaller void within the original boundaries, as has been suggested earlier.

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