Integration and the Achievement Gap: Innovation in Dallas, Texas

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The Local Environment of HII Galaxies

We address the question of whether violent star formation in HII galaxies is induced by low mass companions by describing statistically their local environment as estimated by the correlation function. We argue that even if low mass companions were mainly intergalactic HI clouds, their optical counterparts should be detectable at faint limits of the Automatic Plate Measuring Machine scans. We then cross-correlate a large sample of HII galaxies with the APM faint field galaxy catalogue. The preliminary results are all consistent with HII galaxies being a randomly selected sample of normal faint field galaxy with no extra clustering. This suggests that at least in these dwarf starburst galaxies star formation is not triggered by tidal interactions and may have a different origin.Comment: 4 pages, 2 Postscript figures, uses moriond.sty. To appear in ``Dwarf Galaxies and Cosmology'', Eds. T.X. Thuan, C. Balkowski, V. Cayette, J. Tran Than Van, Editions Frontieres (Gyf-sur-Yvette, France

The Redshift Evolution of Clustering in the HDF

We present a correlation function analysis for the catalogue of photometric redshifts obtained from the Hubble Deep Field image by Fernandez-Soto et al., 1998. By dividing the catalogue into redshift bins of width $\Delta z=0.4$ we measured the angular correlation function $w(\theta)$ as a function of redshift up to $z\sim 4.8$. From these measurements we derive the trend of the correlation length $r_0$. We find that $r_0(z)$ is roughly constant with look-back time up to $z \simeq 2$, and then increases to higher values at z\simgt 2.4. We estimate the values of $r_0$, assuming $\xi(r,z)=(r/r_0(z))^{-\gamma}$, $\gamma=1.8$ and different geometries. For $\Omega_0=1$ we find $r_0(z=3)\simeq 7.00\pm 4.87 h^{-1}$ Mpc, in good agreement with the values obtained from analysis of the Lyman Break Galaxies.Comment: 6 pages, 4 postscript figures, version to appear on MNRA