On the Formation of Boxy and Disky Elliptical Galaxies

The origin of boxy and disky elliptical galaxies is investigated. The results of two collisionless N-body simulations of spiral-spiral mergers with mass ratios of 1:1 and 3:1 are discussed and the projected properties of the merger remnants are investigated. It is shown that the equal-mass merger leads to an anisotropic, slowly rotating system with preferentially boxy isophotes and significant minor axis rotation. The unequal-mass merger results in the formation of a rotationally supported elliptical with disky isophotes and small minor axis rotation. The observed scatter in the kinematical and isophotal properties of both classes of elliptical galaxies can be explained by projection effects.Comment: 12 pages, incl. 5 figures, accepted by ApJ Letter

Applications of PTTI to new techniques for determining crustal movements, polar motion, and the rotation of the earth

New extra-terrestrial techniques are discussed for geodesy and geodynamics include laser range measurements to the moon or to artificial satellites, Doppler measurements with the Transit satellite system, and both independent-clock and linked-antenna microwave interferometry. The ways in which PTTI measurements are used in these techniques will be reviewed, and the accuracies expected during the latter half of the 1970's will be discussed. At least 3 of the techniques appear capable of giving accuracies of 5 cm or better in each coordinate for many points on the earth's surface, and comparable accuracies for the earth's rotation and polar motion. For fixed stations or for sites a few hundred km apart, baseline lengths accurate to 1 cm may be achieved. Ways in which the complementary aspects of the different techniques can be exploited will be discussed, as well as how they tie in with improved ground techniques for determining crustal movements. Some recent results from the extra-terrestrial methods will be mentioned

The Mgb-sigma Relation of Elliptical Galaxies at z=0.37

We derive absorption indices of ellipticals in clusters at z=0.37 from medium-resolution spectroscopy together with kinematical parameters. These galaxies exhibit a relationship between the Mgb linestrength and their internal velocity dispersion similar to local dynamically hot galaxies. But for any given sigma, Mgb of the distant ellipticals is significantly lower than the mean value of the nearby sample. The difference of Mgb between the two samples is small and can be fully attributed to the younger age of the distant stellar populations in accordance with the passive evolution model. The low reduction of Mgb at a look-back time of about 5 Gyrs requires that the bulk of the stars in cluster ellipticals have formed at very high redshifts of z_f>2. For the most massive galaxies, where the reduction is even lower, z_f probably exceeds 4. Unlike most methods to measure the evolution of ellipticals using luminosities, surface brightnesses or colours, the Mgb linestrength does not depend on corrections for extinction and cosmic expansion (K-correction) and only very little on the slope of the initial mass function. The combination of a kinematical parameter with a stellar population indicator allows us to study the evolution of very similar objects. In addition, the good mass estimate provided by sigma means that the selection criteria for the galaxy sample as a whole are well controlled. (abriged)Comment: 25 pages, Latex, uses mn.sty and mncite.sty, accepted by MNRAS, also available at http://www.usm.uni-muenchen.de:8001/people/ziegler/pubs.htm

Interfirm Job Mobility of Two Cohorts of Young German Men 1979 - 1990: An analysis of the (West-)German Employment Statistic Register Sample concerning multivariate failure times and unobserved heterogeneity

The OECD (1993) has documented that the majority of workers in industrialised countries can look forward to finding a stable employment relationship. However new entrants into the labor force experience high turnover. Promoting institutions which support longer tenures and worker participation (or ''voice`` in the firm) utilize strategies to encourage enterprise and employee efforts in skill formation and training. The results of the OECD (1993) study show that attachments between employee and employer are more likely to endure for Japanese, French and German workers. Furthermore Germany has the highest share of young new recruits who received any formal training from their employer. In Germany, 71.5 % of young new recruits were trained at any job within 7 years after leaving school, whereas in the U.S. only 10.2 % of young new recruits were similarly trained (cf. OECD 1993, 137). It is sometimes assumed that employment protection policies have been exogenously imposed and thus probably impair efficiency. However, research on the micro-economics of labor markets has shown that employers may be interested in long-term employment relationships (cf. Levine 1991). Here, the job training model focusing on the importance of human capital investment, specifically the job shopping and matching model stressing the process of information gathering through employment experience should be mentioned. In such models employment protection legislation has not only desirable distributional effects but also help to ensure efficient outcomes. Therefore, it is important to assess the relevance of micro- economic theories empirically. This paper provides an empirical analysis of job durations in Western Germany using information from two cohorts of new entrants to the labor force documented in the (West-)German employment statistic register sample (cf. Bender and Hilzendegen 1996). The appropriate empirical technique to study job length is event history or survival analysis. In labor market research, survival analysis has primarily focused on explaining the length of unemployment spells. Application of this technique to employment is less common 1 , because huge longitudinal data sets are needed. Apart from testing hypotheses about the effect of personal characteristics and labor demand variables (e.g. firm size and industry affiliation), we will assess the influence of heterogeneity of the members of the two cohorts on their duration profile. The applied model and estimation method allow for unobserved heterogeneity and correlation between the clustered failure times of one employee as well as for right-censored spells. Our analysis is not restricted to the beginning of the working life of the employees. The individual retirement decision is affected by employment protection and early retirement regulations which differ widely between the firms. The respective data are missing in the employment statistic register, so that the retirement decision cannot be modelled explicitly

Constraints on galaxy formation from alpha-enhancement in luminous elliptical galaxies

We explore the formation of alpha-enhanced and metal-rich stellar populations in the nuclei of luminous ellipticals under the assumption of two extreme galaxy formation scenarios based on hierarchical clustering, namely a fast clumpy collapse and the merger of two spirals. We investigate the parameter space of star formation time-scale, IMF slope, and stellar yields. In particular, the latter add a huge uncertainty in constraining time-scales and IMF slopes. We find that -- for Thielemann, Nomoto & Hashimoto nucleosynthesis -- in a fast clumpy collapse scenario an [alpha/Fe] overabundance of approx. 0.2 dex in the high metallicity stars can be achieved with a Salpeter IMF and star formation time-scales of the order 10^9 yr. The scenario of two merging spirals which are similar to our Galaxy, instead, fails to reproduce alpha-enhanced abundance ratios in the metal-rich stars, unless the IMF is flattened during the burst ignited by the merger. This result is independent of the burst time-scale. We suggest that abundance gradients give hints to distinguish between the two extreme formation scenarios considered in this paper.Comment: Accepted for publication in MNRAS, LaTex 2.09 with mn.sty, 13 pages, 5 figure

Multiple-Scale Analysis of the Quantum Anharmonic Oscillator

Conventional weak-coupling perturbation theory suffers from problems that arise from resonant coupling of successive orders in the perturbation series. Multiple-scale perturbation theory avoids such problems by implicitly performing an infinite reordering and resummation of the conventional perturbation series. Multiple-scale analysis provides a good description of the classical anharmonic oscillator. Here, it is extended to study the Heisenberg operator equations of motion for the quantum anharmonic oscillator. The analysis yields a system of nonlinear operator differential equations, which is solved exactly. The solution provides an operator mass renormalization of the theory.Comment: 12 pages, Revtex, no figures, available through anonymous ftp from ftp://euclid.tp.ph.ic.ac.uk/papers/ or on WWW at http://euclid.tp.ph.ic.ac.uk/Papers/papers_95-6_.htm