High Resolution WFPC2 Imaging of IRAS 09104+4109

With a infrared luminosity of nearly 10^13 Lsuns, IRAS 09104+4109 is the most luminous galaxy with z<0.5 in the IRAS All Sky Survey. A radio-loud Seyfert 2 type optical spectrum, a cD host galaxy in a rich cluster, and a massive cooling flow make IRAS 09104+4109 unique among ultraluminous infrared galaxies. Cannibalized cluster members and the cooling intercluster medium may contribute both the fuel and the dust needed to re-radiate the power of IRAS 09104+4109 into the far-infrared. We have imaged IRAS 09104+4109 in the WFPC2 F622W, F814W, and FR680N filters on the HST to obtain rest frame 4300A, 5700A, and [OIII] emission line images on sub-kpc scales. IRAS 09104+4109 displays a complex morphology on the smallest scales, with radiating filaments, an asymmetric [OIII] nebula, and a number of very faint, irregular blue objects surrounding the cD galaxy. We discuss the nature and possible interplay between the enshrouded QSO nucleus, the cD host galaxy and the irregular cluster.Comment: LaTex, 6 pages with 2 postscript and 1 jpg figure. To appear in the proc. of the Ringberg workshop "Ultraluminous Galaxies: Monsters or Babies" (Ringberg castle, Sept. 1998), Ap&SS, in pres

Near Infrared Observations of a Redshift 5.34 Galaxy: Further Evidence for Dust Absorption in the Early Universe

Imaging at 1.25 and 2.20 microns has been obtained of the field containing the galaxy (RD1) found at redshift 5.34 by Dey et al.(1998). This galaxy has been detected at 1.25 microns, while the lower redshift (z=4.02) galaxy also found in the same field by Dey et al. was detected at both 1.25 and 2.20 microns. Comparison to stellar population synthesis models indicates that if RD1 is a young ( 0.5 mag) is indicated. Combined with observations of other high redshift systems, these data show that dust is likely to be an important component of young galaxies even at redshifts of z > 5. The extinction-corrected monochromatic luminosity of RD1 at 1500 angstroms is then a factor of about three larger than L(1500)* as determined by Dickinson (1998) for z ~ 3 starburst galaxies. The implied star formation rate in RD1, corrected for extinction, is ~ 50-100 solar masses per year.Comment: plain LaTex with 1 postscript figure. ApJ Letters, accepte

Analytical approximation of the exterior gravitational field of rotating neutron stars

It is known that B\"acklund transformations can be used to generate stationary axisymmetric solutions of Einstein's vacuum field equations with any number of constants. We will use this class of exact solutions to describe the exterior vacuum region of numerically calculated neutron stars. Therefore we study how an Ernst potential given on the rotation axis and containing an arbitrary number of constants can be used to determine the metric everywhere. Then we review two methods to determine those constants from a numerically calculated solution. Finally, we compare the metric and physical properties of our analytic solution with the numerical data and find excellent agreement even for a small number of parameters.Comment: 9 pages, 10 figures, 3 table

Optical and infrared spectrophotometry of 18 Markarian galaxies

Slit spectra, spectrophotometric scans and infrared broad band observations are presented. Eight of the program galaxies can be classified as Seyfert galaxies. Arguments are given that thermal, nonthermal and stellar radiation components were present. One group of Seyfert galaxies was characterized both by the presence of a high density region of gas and by a continuum dominated by nonthermal radiation. The continua of the remaining program Seyferts, which did not have a high density region of gas, were dominated by thermal radiation from dust and a stellar continuum. Ten of the galaxies, which are not Seyfert galaxies, are shown to be examples of extragalactic H 2 regions

The contact process in heterogeneous and weakly-disordered systems

The critical behavior of the contact process (CP) in heterogeneous periodic and weakly-disordered environments is investigated using the supercritical series expansion and Monte Carlo (MC) simulations. Phase-separation lines and critical exponents $\beta$ (from series expansion) and $\eta$ (from MC simulations) are calculated. A general analytical expression for the locus of critical points is suggested for the weak-disorder limit and confirmed by the series expansion analysis and the MC simulations. Our results for the critical exponents show that the CP in heterogeneous environments remains in the directed percolation (DP) universality class, while for environments with quenched disorder, the data are compatible with the scenario of continuously changing critical exponents.Comment: 5 pages, 3 figure

Near-Infrared Observations of Extended Emission around PG 1545+210

Infrared images at H and Ks of the quasar PG 1545+210 clearly show both extended emission centered on the quasar and a companion galaxy. The magnitudes of the extended emission deduced from these observations depend strongly on the model adopted for the emission. Both an exponential disk model and a de Vaucouleurs model provide adequate fits to the extended emission. If it is assumed to follow an exponential disk galaxy, these measurements imply that the host galaxy has absolute magnitudes comparable with those of a Schechter L^* galaxy. With this assumption for the intrinsic light distribution, the H magnitude and the Hubble Space Telescope limit on the V magnitude are inconsistent with color predictions for unreddened spiral galaxies at the redshift of the quasar. If the data are fitted to a de Vaucouleurs model, the extended emission dominates the total energy of the system and significantly exceeds that of an L^* galaxy. The companion galaxy has colors consistent with its being at the redshift of the quasar, but its luminosity is at most a small part of that of the entire system. If the companion is at the redshift of PG 1545+210, its absolute magnitude is M_H ∼ -22 mag, significantly fainter than that of an L^* galaxy

Adsorption and desorption of hydrogen at nonpolar GaN(1-100) surfaces: Kinetics and impact on surface vibrational and electronic properties

The adsorption of hydrogen at nonpolar GaN(1-100) surfaces and its impact on the electronic and vibrational properties is investigated using surface electron spectroscopy in combination with density functional theory (DFT) calculations. For the surface mediated dissociation of H2 and the subsequent adsorption of H, an energy barrier of 0.55 eV has to be overcome. The calculated kinetic surface phase diagram indicates that the reaction is kinetically hindered at low pressures and low temperatures. At higher temperatures ab-initio thermodynamics show, that the H-free surface is energetically favored. To validate these theoretical predictions experiments at room temperature and under ultrahigh vacuum conditions were performed. They reveal that molecular hydrogen does not dissociatively adsorb at the GaN(1-100) surface. Only activated atomic hydrogen atoms attach to the surface. At temperatures above 820 K, the attached hydrogen gets desorbed. The adsorbed hydrogen atoms saturate the dangling bonds of the gallium and nitrogen surface atoms and result in an inversion of the Ga-N surface dimer buckling. The signatures of the Ga-H and N-H vibrational modes on the H-covered surface have experimentally been identified and are in good agreement with the DFT calculations of the surface phonon modes. Both theory and experiment show that H adsorption results in a removal of occupied and unoccupied intragap electron states of the clean GaN(1-100) surface and a reduction of the surface upward band bending by 0.4 eV. The latter mechanism largely reduces surface electron depletion

The Nature of the Compact/Symmetric Near-IR Continuum Source in 4C 40.36

Using NICMOS on HST, we have imaged the emission-line nebulae and the line-free continuum in 4C 40.36, a ultra-steep spectrum FR II radio galaxy at z=2.269. The line-free continuum was found to be extremely compact and symmetric while the emission-line nebulae seen in H-alpha+[N II] show very clumpy structures spreading almost linearly over 16 kpc. However, this linear structure is clearly misaligned from the radio axis. The SED of the line-free continuum is very flat, suggesting that if the continuum emission is produced by a single source, it is likely to be a young bursting stellar population or scattered AGN light. However, because of the lack of a line-free optical image with a comparable spatial resolution, we cannot exclude the possibility that the observed SED is a composite of a young blue population and an old red population.Comment: 4 pages, 2 figures; to appear in the proceedings of "The Hy-Redshift Universe: Galaxy Formation and Evolution at High Redshift", eds. A.J.Bunker and W. J. M. van Breuge

Photoproduction of negative and positive pions from deuterium for photon energies 500 to 1000 Mev

The ratio of the yields of negative and positive pions photoproduced in deuterium has been measured at six photon energies between 500 and 1000 Mev and at seven angles between 20° and 160° in the center-of-momentum system of the photon and target nucleon. Pions were selected with a magnetic spectrometer and identified using momentum and specific ionization in a scintillation counter telescope. The spectator model of the deuteron was used to identify the photon energy. Statistical errors assigned to the π- / π+ ratio range between five and fifteen percent. The results of the present experiment join smoothly with the low-energy π- / π+ ratios obtained by Sands et al. At high energies the π- / π+ ratio varies from 0.5 at forward angles and energies near 900 Mev to 2.5 at 160° c.m. and energies 600 to 800 Mev. The cross sections for π- photo-production from neutrons have been derived from the π- / π+ ratio and the CalTech π+ photoproduction data. The angular distributions for π- production are considerably different from those for π+; there is, for example, a systematic increase at the most backward angles. The energy dependence of the total cross section for π- is similar to that for π+, although the second resonance peak occurs at a slightly lower energy, and at 900 and 1000 Mev the π- cross section is smaller by a factor 1.6. A comparison is made of the cross sections for π+ photoproduction from hydrogen and deuterium, although the accuracy of this comparison is not high