A Survey of Faint Galaxy Pairs

A sample of faint, V magnitude selected, galaxy pairs, having physical separations less than approximately 20\hkpc, is used to examine the rise in the merger rate with redshift and the statistical relations between close pairs and the field galaxy population. Redshifts have been obtained for 14 galaxies ($V \le 22.5$) that are in close (\theta < 6\arcs) pairs, along with a comparison sample of 38 field galaxies. Two color photometry is available for about 1000 galaxies in the same fields. The average redshift of the $V\le22.5$ field population is 0.36, statistically equal to the average redshift of 0.42 for the pairs. The similarity of the two redshift distributions, $\Delta z\le 0.1$, limits any differential luminosity enhancement of close pairs to less than half a magnitude. The pairs are somewhat bluer than the field and have nearly twice the average [O~II] detection rate of the field, but the differences are not statistically significant. The field population has an angular correlation at separations of $\theta\le$6\arcs\ higher than the inward extrapolation of $\omega(\theta)\propto \theta^{-0.8}$, which may be a population of ``companions'' not present at the current epoch, or, luminosity enhancement of intrinsically faint galaxies in pairs. Physical pairs comprise about 7\% of the faint galaxies in our survey fields. The same physical separation applied to local galaxies finds only 2.6\% in pairs. If the rise in close low relatively velocity pairs with redshift is parameterized as $(1+z)^m$, then $m=2.9\pm0.8$. If all pairs at low velocities and $r\le 20$\hkpc\ merge, then theComment: 16p plain tex, uuencoded compressesd postscript available via anonymous ftp from moonray.astro.utoronto.ca in pub/pairs.ps.Z.uu Problems and queries to [email protected]

B-R Colors of Globular Clusters in NGC 6166 (A2199)

We have analysed new R-band photometry of globular clusters in NGC 6166, the cD galaxy in the cooling flow cluster A2199. In combination with the earlier B photometry of Pritchet \& Harris (1990), we obtain B$-$R colours for $\sim$ 40 globular clusters in NGC 6166. The mean B$-$R is 1.26 $\pm$ 0.11, corresponding to a mean [Fe/H] = $-$1 $\pm$ 0.4. Given that NGC 6166 is one of the most luminous cD galaxies studied to date, our result implies significant scatter in the relationship between mean cluster [Fe/H] and parent galaxy luminosity. We obtain a globular cluster specific frequency of S$_N$ $\sim$ 9, with a possible range between 5 and 18. This value is inconsistent with the value of S$_N$ $\leq$ 4 determined earlier by Pritchet \& Harris (1990) from B-band photometry, and we discuss possible reasons for the discrepancy. Finally, we reassess whether or not cooling flows are an important mechanism for forming globular clusters in gE/cD galaxies.Comment: 8 pages, uuencoded, gzipped tar file with latex file, 6 figures (Fig 1 omitted because of size), and mn.sty file. Figures will be embedded into the postscript file. Accepted (March 1996) for publication in MNRA

The Clustering Properties of Faint Galaxies

The two-point angular correlation function of galaxies, \wte, has been computed from a new survey of faint galaxies covering a 2 deg$^2$ area near the North Galactic Pole. This survey, which is complete to limiting magnitudes \jmag=24 and \fmag=23, samples angular scales as large as 1\degpoint5. Faint galaxies are found to be more weakly clustered (by a factor of at least two) compared to galaxies observed locally. Clustering amplitudes are closer to model predictions in the red than in the blue. The weak clustering of faint galaxies cannot be explained by any plausible model of clustering evolution with redshift. However, one possible explanation of the clustering properties of intermediate redshift galaxies is that they resemble those of starburst galaxies and H II region galaxies, which are observed locally to possess weak clustering amplitudes. Our clustering amplitudes are also similar to those of nearby late-type galaxies, which are observed to be more weakly clustered than early-type galaxies A simple, self-consistent model is presented that predicts the fraction of galaxies in the ``excess'' population at intermediate redshifts, and correctly matches observed color distributions. The available data on the clustering properties of faint galaxies are consistent with this model if the ``excess'' population of faint blue galaxies is also the weakly clustered population. Evidence is presented that the power-law slope of the angular correlation function becomes shallower at fainter magnitudes. A similar effect is seen locally both for dwarf galaxies and for galaxies with late morphological type;Comment: 23 pages, uuencoded compressed PostScript file, figures anonymous ftp to 146.155.21.10 file pub/p3/p3fig.uu.Z, accepted ApJ, IP/3/9