Extremely red objects in the fields of high redshift radio galaxies

We are engaged in a program of infrared imaging photometry of high redshift radio galaxies. The observations are being done using NICMOS2 and NICMOS3 arrays on the DuPont 100-inch telescope at Las Campanas Observatory. In addition, Persson and Matthews are measuring the spectral energy distributions of normal cluster galaxies in the redshift range 0 to 1. These measurements are being done with a 58 x 62 InSb array on the Palomar 5-m telescope. During the course of these observations we have imaged roughly 20 square arcminutes of sky to limiting magnitudes greater than 20 in the J, H, and K passbands (3 sigma in 3 square arcseconds). We have detected several relatively bright, extremely red, extended objects during the course of this work. Because the radio galaxy program requires Thuan-Gunn gri photometry, we are able to construct rough photometric energy distributions for many of the objects. A sample of the galaxy magnitudes within 4 arcseconds diameter is given. All the detections are real; either the objects show up at several wavelengths, or in subsets of the data. The reddest object in the table, 9ab'B' was found in a field of galaxies in a rich cluster at z = 0.4; 9ab'A' lies 8 arcseconds from it

Time-resolved spectroscopy of the excited electronic state of reaction centers of Rhodopseudomonas viridis

The spectral properties of the excited electronic state of the reaction centers of Rhodopseudomonas (Rps.) viridis are studied by dichroic transient absorption spectroscopy with sub-picosecond time resolution. The theoretical analysis of the experimental results allows the assignment of the transient absorption from two dimer bands of the special pair and show its excitonic coupling to other pigments

Evolution since z = 0.5 of the Morphology-Density relation for Clusters of Galaxies

Using traditional morphological classifications of galaxies in 10 intermediate-redshift (z~0.5) clusters observed with WFPC-2 on the Hubble Space Telescope, we derive relations between morphology and local galaxy density similar to that found by Dressler for low-redshift clusters. Taken collectively, the `morphology-density' relationship, M-D, for these more distant, presumably younger clusters is qualitatively similar to that found for the local sample, but a detailed comparison shows two substantial differences: (1) For the clusters in our sample, the M-D relation is strong in centrally concentrated ``regular'' clusters, those with a strong correlation of radius and surface density, but nearly absent for clusters that are less concentrated and irregular, in contrast to the situation for low redshift clusters where a strong relation has been found for both. (2) In every cluster the fraction of elliptical galaxies is as large or larger than in low-redshift clusters, but the S0 fraction is 2-3 times smaller, with a proportional increase of the spiral fraction. Straightforward, though probably not unique, interpretations of these observations are (1) morphological segregation proceeds hierarchically, affecting richer, denser groups of galaxies earlier, and (2) the formation of elliptical galaxies predates the formation of rich clusters, and occurs instead in the loose-group phase or even earlier, but S0's are generated in large numbers only after cluster virialization.Comment: 35 pages, 19 figures, uses psfig. Accepted for publication in Ap

Observations of Stripped Edge-on Virgo Cluster Galaxies

We present observations of highly inclined, HI deficient, Virgo cluster spiral galaxies. Our high-resolution VLA HI observations of edge-on galaxies allow us to distinguish extraplanar gas from disk gas. All of our galaxies have truncated H-alpha disks, with little or no disk gas beyond a truncation radius. While all the gas disks are truncated, the observations show evidence for a continuum of stripping states: symmetric, undisturbed truncated gas disks indicate galaxies that were stripped long ago, while more asymmetric disks suggest ongoing or more recent stripping. We compare these timescale estimates with results obtained from two-dimensional stellar spectroscopy of the outer disks of galaxies in our sample. One of the galaxies in our sample, NGC 4522 is a clear example of active ram-pressure stripping, with 40% of its detected HI being extraplanar. As expected, the outer disk stellar populations of this galaxy show clear signs of recent (and, in fact, ongoing) stripping. Somewhat less expected, however, is the fact that the spectrum of the outer disk of this galaxy, with very strong Balmer absorption and no observable emission, would be classified as ``k+a'' if observed at higher redshift. Our observations of NGC 4522 and other galaxies at a range of cluster radii allow us to better understand the role that clusters play in the structure and evolution of disk galaxies.Comment: 4 pages, 2 figures, to appear in the proceedings of the Island Universes conference held in Terschelling, Netherlands, July 2005, ed. R. de Jong, version with high resolution figures can be downloaded from ftp://ftp.astro.yale.edu/pub/hugh/papers/iu_crowl_h.ps.g

Structure and spatial distribution of Ge nanocrystals subjected to fast neutron irradiation

The influence of fast neutron irradiation on the structure and spatial distribution of Ge nanocrystals (NC) embedded in an amorphous SiO2 matrix has been studied. The investigation was conducted by means of laser Raman Scattering (RS), High Resolution Transmission Electron Microscopy (HR-TEM) and X-ray photoelectron spectroscopy (XPS). The irradiation of NC-Ge samples by a high dose of fast neutrons lead to a partial destruction of the nanocrystals. Full reconstruction of crystallinity was achieved after annealing the radiation damage at 800 deg. C, which resulted in full restoration of the RS spectrum. HR-TEM images show, however, that the spatial distributions of NC-Ge changed as a result of irradiation and annealing. A sharp decrease in NC distribution towards the SiO2 surface has been observed. This was accompanied by XPS detection of Ge oxides and elemental Ge within both the surface and subsurface region