Deep Wide-field Imaging Research Articles

Statistics of dark matter haloes expected from weak lensing surveys

The distortion of the images of faint high-redshift galaxies can be used to probe the intervening mass distribution. This weak gravitational lensing effect has been used recently to study the (projected) mass distribution of several clusters at intermediate and high redshifts. In addition, the weak lensing effect can be employed to detect (dark) matter concentrations in the Universe, based on their mass properties alone. Thus it is feasible to obtain a mass-selected sample of `clusters', and thereby probe the full range of their mass-to-light ratios. We study the expected number density of such haloes which can be detected in ongoing and future deep wide-field imaging surveys, using the number density of haloes as predicted by the Press-Schechter theory, and modeling their mass profile by the `universal' density profile found by Navarro, Frenk & White. We find that in all cosmological models considered, the number density of haloes with a signal-to-noise ratio larger than 5 exceeds 10 per square degree. With the planned MEGACAM imaging survey of $\sim 25 deg^2$, it will be easily possible to distinguish between the most commonly discussed cosmological parameter sets.

Morphological Classification of the LocalI‐ andK‐Band Galaxy Sample

In this paper, we report on the morphologically segregated I- and K-band number counts at bright magnitudes from a wide-field deep survey. This survey has been carried out with the first large mosaic CCD camera (8192 × 8192) on the University of Hawaii 88 inch (2.24 m) telescope and the Canada-France-Hawaii Telescope (CFHT). This instrument allows us to take deep wide-field galaxy images efficiently. We have been able to obtain I-band number counts in a wide range from I = 12.5 to I = 22.5, and to classify the morphologies of galaxies down to I = 18.5. Morphologically segregated number counts for ellipticals, spirals, and irregulars are obtained for the first time with magnitudes brighter than I = 18.5. The morphological classifications correlate well with the galaxy colors. By modeling these number counts, we confirm that a no-evolution model can fit both K- and I-band number counts of ellipticals and spirals reasonably well, but the irregular/peculiar galaxies show a substantial excess at faint magnitudes over the no-evolution model. With the number counts at bright magnitudes, we further demonstrate that the rise in this excess begins by I = 20. This rise is consistent with a rapidly increasing star formation rate in low-luminosity galaxies at about z = 0.35.

Washington Photometry of the Globular Cluster System of NGC 4472. II. The Luminosity Function and Spatial Structure

We present a comprehensive study of the luminosity function and spatial structure of the globular cluster system of NGC 4472, the brightest galaxy in Virgo, based on deep wide-field Washington CT1 CCD images. The globular cluster luminosity function shows a peak at T1 = 23.3 ± 0.1 mag, about 1.5 mag brighter than our 50% completeness limit. Comparing this value with that of the Galactic globular clusters, we estimate the true distance modulus to NGC 4472 to be (m - M)0 = 31.2 ± 0.2 (corresponding to a distance of 17.4 ± 1.6 Mpc). With our large sample (≈2000) of bright globular clusters over a wide field, we make a definitive investigation of the spatial structures of the metal-poor and metal-rich cluster populations and find that they are systematically different: (1) the metal-rich clusters are more centrally concentrated than the metal-poor clusters; and (2) the metal-rich clusters are elongated roughly along the major axis of the parent galaxy, while the metal-poor clusters are essentially spherically distributed. In general, the metal-rich clusters closely follow the underlying halo starlight of NGC 4472 in terms of spatial structure and metallicity, while the metal-poor clusters do not. The global value of the specific frequency of the globular clusters in NGC 4472 is estimated to be SN = 4.7 ± 0.6. The local specific frequency increases linearly outward from the center of NGC 4472 until ~55, beyond which it levels off at SN ~ 8.5 until the limit of our data at 7'. The specific frequency of both the metal-rich and metal-poor populations shows similar behavior. However, SN of the metal-poor clusters is about a factor of 2 greater than that of the metal-rich clusters in the outer regions. Implications of these results for the origin of the globular clusters in NGC 4472 are discussed. These results are consistent with many of the predictions of both the model of episodic in situ formation plus tidal stripping of globular clusters given by Forbes et al. and the Ashman & Zepf merger formation model, but each of the models also has some problems.