arXiv subjects

A. Boehm

Publications and source records attributed to A. Boehm.

22 records · Page 2Linked to original sources

arXiv2002

Evidence for chemical evolution in the spectra of high redshift galaxies

Using a sample of 57 VLT FORS spectra in the redshift range 1.37<z<3.40 (selected mainly from the FORS Deep Field survey) and a comparison sample with 36 IUE spectra of local (z ~ 0) starburst galaxies we derive CIV and SiIV equivalent width values and estimate metallicities of starburst galaxies as a function of redshift. Assuming that a calibration of the CIV equivalent widths in terms of the metallicity based on the local sample of starburst galaxies is applicable to high-z objects, we find a significant increase of the average metallicities from about 0.16 Z_sun at the cosmic epoch corresponding to z ~ 3.2 to about 0.42 Z_sun at z ~ 2.3. A significant further increase in metallicity during later epochs cannot be detected in our data. Compared to the local starburst galaxies our high-redshift objects tend to be overluminous for a fixed metallicity. Our observational results are in good agreement with published observational data by other authors and with theoretical predictions of the cosmic chemical evolution.

astro-ph↗

arXiv2001

The evolution of the Tully-Fisher relation of spiral galaxies

We present the B-band Tully-Fisher relation (TFR) of 60 late-type galaxies with redshifts 0.1-1. The galaxies were selected from the FORS Deep Field with a limiting magnitude of R=23. Spatially resolved rotation curves were derived from spectra obtained with FORS2 at the VLT. High-mass galaxies with v_max>=150 km/s show little evolution, whereas the least massive systems in our sample are brighter by about 1-2 mag compared to their local counterparts. For the entire distant sample, the TFR slope is flatter than for local field galaxies (-5.77+-0.45 versus -7.92+-0.18). Thus, we find evidence for evolution of the slope of the TFR with redshift on the 3-sigma level. This is still true when we subdivide the sample into three redshift bins. We speculate that the flatter tilt of our sample is caused by the evolution of luminosities and an additional population of blue galaxies at z>=0.2. The mass dependence of the TFR evolution also leads to variations for different galaxy types in magnitude-limited samples, suggesting that selection effects can account for the discrepant results of previous TFR studies on the luminosity evolution of late-type galaxies.

astro-ph↗

arXiv2001

Observation of the screening signature in the lateral photovoltage of electrons in the Quantum Hall regime

The lateral photovoltage generated in the plane of a two-dimensional electron system (2DES) by a focused light spot, exhibits a fine-structure in the quantum oscillations in a magnetic field near the Quantum Hall conductivity minima. A double peak structure occurs near the minima of the longitudinal conductivity oscillations. This is the characteristic signature of the interplay between screening and Landau quantization.

cond-mat.mes-hall↗

arXiv2001

The FORS Deep Field

Dedicating a major fraction of its guaranteed time, the FORS consortium established a FORS Deep Field which contains a known QSO at z = 3.36. It was imaged in UBgRIz with FORS at the VLT as well as in J and Ks with the NTT. Covering an area 6-8 times larger as the HDFs but with similar depth in the optical it is one of the largest deep fields up to date to investigate i) galaxy evolution in the field from present up to z $\sim$ 5, ii) the galaxy distribution in the line of sight to the QSO, iii) the high-z QSO environment and iv) the galaxy-galaxy lensing signal in such a large field. In this presentation a status report of the FORS Deep Field project is given. In particular, the field selection, the imaging results (number counts, photometric redshifts etc.) and the first spectroscopic results are presented.

astro-ph↗