Molecular Cloud Structure in the Magellanic Clouds: Effect of Metallicity

The chemical structure of neutral clouds in low metallicity environments is examined with particular emphasis on the H to H_2 and C+ to CO transitions. We observed near-IR H_2 lines and the CO J=1-0 line from 30 Doradus and N159/N160 in the Large Magellanic Cloud and from DEM S 16, DEM S 37, and LI-SMC 36 in the Small Magellanic Cloud. We find that the H_2 emission is UV-excited and that (weak) CO emission always exists (in our surveyed regions) toward positions where H_2 and [CII] emission have been detected. Using a PDR code and a radiative transfer code, we simulate the emission of line radiation from spherical clouds and from large planar clouds. Because the [CII] emission and H_2 emission arise on the surface of the cloud and the lines are optically thin, these lines are not affected by changes in the relative sizes of the neutral cloud and the CO bearing core, while the optically thick CO emission can be strongly affected. The sizes of clouds are estimated by measuring the deviation of CO emission strength from that predicted by a planar cloud model of a given size. The average cloud column density and therefore size increases as the metallicity decreases. Our result agrees with the photoionization regulated star formation theory by Mc Kee (1989).Comment: 45 Pages including 15 figures. To be published in the ApJ May 10, 1998 issue, Vol. 49

Two-Phased Intra-Cluster Medium in the Centaurus Cluster of Galaxies

ASCA and ROSAT data of the Centaurus cluster were analyzed. A central excess in the radial brightness profile is found in the hard energy band up to 10keV. This requires a deeper central potential than a King-type one. A double-beta brightness distribution gives a good account of the data. A deprojected energy spectrum within a spherical region of radius 30 kpc at the cluster center indicates that the ICM cannot be isothermal there. Simultaneous fitting of the three (PSPC, GIS, and SIS) energy spectra extracted from the central 3' region showed that a two-temperature model that has temperatures of 1.4keV and 4.4keV and a common metallicity of 1.0 solar with the Galactic absorption gives the best description to the spectra. A cooling-flow spectral model did not give satisfactory fit. A 3-dimensional cluster model incorporating the two-phase picture, the double-beta brightness distribution, and the central metallicity increase reproduced the overall ASCA and ROSAT data successfully. The derived spatial distribution of the dark matter deviates from a King-type profile exhibiting a central excess, which is consistent with the Navvaro-Frenk-White model. The iron is revealed to be more widely spread than stars, which may have been caused by energetic supernovae and the motion of the cD galaxy. Since the derived characteristics of the cool phase including the temperature, angular extent, gas mass, and metallicity, are on a smooth extension of those of inter-stellar medium (ISM) of elliptical galaxies, the cool phase can be regarded as the ISM associated with the cD galaxy. The cool-phase X-ray emission is presumably sustained by energies dissipated by infalling mass to the cD galaxy in the course of cluster evolution.Comment: accepted for publication in Ap

A spectral study of gamma-ray emitting AGN

In this paper we present a statistical analysis of the gamma-ray spectra of flat-spectrum radio quasars (FSRQ) compared to those of BL Lacs. The average spectra and possible systematic deviations from power-law behaviour are investigated by summing up the intensity and the power-law fit statistic for both classes of objects. We also compare the time-averaged spectrum to that at the time of gamma-ray outbursts. The spectrum of the average AGN is softer than that of the extragalactic gamma-ray background. It may be that BL Lacs, which on average have a harder spectrum than FSRQs, make up the bulk of the extragalactic background. We also find apparent cut-offs at both low and high energies in the spectra of FSRQs at the time of gamma-ray outbursts. While the cut-off at high energies may have something to do with opacity, the cut-off at low energies may be taken as indication that the gamma-ray emission of FSRQs is not a one component spectrum.Comment: 8 pages, accepted for publication in A&

X-ray analysis of Abell 2634 and its central galaxy 3C465

An analysis of a ROSAT/PSPC observation of the galaxy cluster A2634 is presented. It has a luminosity of 7.9#+-#0.1 x 10"4"3 erg/s in the ROSAT band (0.1-2.4 keV). The temperature profile decreases from about 3 keV in the outer parts to 1.2 keV in the centre. Within a radius of 1.5 MPc the gas mass of the cluster is 0.51 x 10"1"4 M_sun and the total mass amounts to 4.1_-_1_._8"+"2"."6 x 10"1"4M_sun. The X-ray morphology shows two peculiar features - a strongly peaked emission in the centre and an excess emission in the south-west. The central emission probably originates from a weak cooling flow, the SW emission is possibly associated with higher density regions in pressure equilibrium with the intra-cluster medium. This region of excess emission is somewhat embraced by the wide-angle radio tails associated with 3C465 suggesting that the overpressure of the relativistic particles has displaced the thermal gas. (orig.)Available from FIZ Karlsruhe / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Interaction in the bimodal galaxy cluster A3528

X-ray and radio continuum observations of the bimodal cluster A3528 in the Shapley Supercluster are presented. We find evidence in the X-ray temperatures derived from a ROSAT PSPC point observation that the two components of the cluster are in the process of colliding with each other. The intracluster gas in each subcluster shows a tendency to be hotter in the region between the two subclusters. This effect can be interpreted as the signature of interaction of the subclusters. We infer that the centers of the subclusters in A3528 will meet within a few 10"8 years. In continuum observations at 20 cm and at 90 cm with the Very Large Array we find four galaxies having radio emission. One of these galaxies shows a head-tail structure suggesting a motion of the galaxy through the intracluster medium. The radio tail shows an imbalance between the thermal pressure of the intra-cluster gas and the pressure of the relativistic electrons. (orig.)Available from TIB Hannover: RN 9303(316) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

The accuracy of mass determination in galaxy clusters by X-ray observations

We test the reliability of mass determination in clusters of galaxies by X-ray observations. The true mass in cluster models is compared to the mass derived by the X-ray emission and X-ray temperature of a model assuming hydrostatic equilibrium and spherical symmetry. In general we find good agreement between the X-ray mass and the true mass without any systematic over-or underestimation. The average deviation within the central 2Mpc has a r.m.s. of 15%. (orig.)Available from TIB Hannover: RN 9303(311) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Evolution of protoplanetary disks with condensation and coagulation

We investigate the global evolution of the viscous stage of a turbulent protoplanetary disk. The time-dependent radial development of the nebula is calculated with the help of analytical one-zone models of the vertical structure that relate optical properties of grains to turbulent viscosity. Special attention is given to possible growth of dust particles that cause significant opacity and hence viscosity changes. In the framework of a simple two component model for the dust size population we follow the evolution of the total surface density of the disk. Assuming that grain growth is especially rapid in the main condensation regions (e.g. due to enhanced sticking probabilities) we find significant surface density enhancements in these radially confined regions. Moreover a lower turbulence strength in these regions (e.g. caused by the suppression of thermal convection) leads to a further increase in the density. Possible consequences for planet formation are briefly outlined. (orig.)Available from TIB Hannover: RN 9303(294) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Max-Planck-Institut fuer Extraterrestrische Physik. Jahresbericht 1993

The report emphasizes the scientific and technical activities. Some organisational information is listed in the Appendix. Following this introduction the second chapter contains reports from our major research groups, followed by brief reports about our other research areas. The third chapter features selected research highlights of the past year. The supplementary sections tabulate our publication activities, our personnel, the projects and collaborations. (orig.)SIGLEAvailable from TIB Hannover: RA 234:ET(254) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

ROSAT/HRI and ASCA observations of the most luminous-X-ray cluster RXJ1347.5-1145

We report on the X-ray properties of the exceptional X-ray cluster RXJ1347.5-1145 at z=0.451. We confirm that it is with a luminosity L_X(bol)=2x10"4"6 erg/s the most luminous X-ray cluster discovered to date. The mass of the cluster within 1.7 Mpc is 9.8x10"1"4 M_sun. A comparison of the central X-ray mass and the mass determined from a simple gravitational lens model shows a discrepancy of a factor of 2-3 with the X-ray mass being smaller. The temperature of the cluster is 9.3_-_1_._0"+"1"."1 keV. We detect a strong FeK line corresponding to a metallicity of 0.33#+-#0.10 in solar units, which is an unexpectedly high value for a distant and hot cluster. There are several hints that the cluster contains an extremely strong cooling flow. With the usual assumptions we derive formally a mass accretion rate of more than 3000 M_sun/yr indicating that this may be the largest cooling flow detected so far. To find these extreme properties in this distant cluster which can be taken as an indication of a well relaxed and old system is of high importance for the theory of formation and evolution of clusters. (orig.)Available from TIB Hannover: RN 9303(358) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Contributions to the SPIE's international symposium on astronomical telescopes and instrumentation 2000

SIGLEAvailable from TIB Hannover: RN 9303(491) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman