arXiv subjects

C. J. Pritchet

Publications and source records attributed to C. J. Pritchet.

58 records · Page 4Linked to original sources

arXiv1996

Close Pairs of Field Galaxies in the CNOC1 Redshift Survey

A redshift sample of 545 field galaxies is used to examine how the galaxy merger rate changes with redshift, and how mergers affect the observed properties of galaxies in close pairs. Close pairs are defined as those with projected separations less than 20 h^{-1} kpc. At a mean redshift of 0.33, it is found that 7.1 +/- 1.4 % of galaxies are in close physical pairs, compared to 4.3 +/- 0.4 % locally. The merger rate is estimated to change with redshift as (1+z)^{2.8 +/- 0.9}. These results are shown to be consistent with previous close pair studies, and provide one of the strongest constraints to date on the redshift dependence of the merger rate. As with earlier studies, no significant differences between the mean properties of paired and isolated galaxies are detected. However, using the subset of confirmed close physical pairs, those which appear to be undergoing interactions or mergers (based on their images) are found to have galaxies with strong emission lines and very blue rest-frame colors. In addition, these pairs have low relative velocities, increasing the likelihood that the galaxies will merge. We interpret this as the first clear evidence of merger-induced star formation occurring in field galaxies at this redshift.

astro-ph↗

arXiv1996

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.

astro-ph↗

arXiv1995

Evidence for Steep Luminosity Functions in Clusters of Galaxies

Luminosity Functions have been obtained for very faint dwarf galaxies in the cores of four rich clusters of galaxies (Abell 2052, 2107, 2199 and 2666). It is found that the luminosity function of dwarf galaxies rises very steeply in these clusters, with a power-law slope of α-2.2 (down to absolute limiting magnitudes M_I = -13 and M_B = -11 for H_0 = 75 km/s/Mpc). A steepening of the luminosity function at faint magnitudes may in fact be a common feature of both cluster and field populations. Such a result may explain the observed excess counts of faint, intermediate redshift galaxies in the Universe, without resorting to more exotic phenomena. An alternate explanation is that star formation in dwarf galaxies is less affected by gas loss in the richest clusters, because of the dense, hot intracluster medium found in such environments.

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arXiv1994

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;

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