Separation of the first- and second-order contributions in magneto-optic Kerr effect magnetometry of epitaxial FeMn/NiFe bilayers

The influence of second-order magneto-optic effects on Kerr effect magnetometry of epitaxial exchange coupled FeMn/NiFe-bilayers is investigated. A procedure for separation of the first- and second-order contributions is presented. The full angular dependence of both contributions during the magnetization reversal is extracted from the experimental data and presented using gray scaled magnetization reversal diagrams. The theoretical description of the investigated system is based on an extended Stoner-Wohlfarth model, which includes an induced unidirectional and fourfold anisotropy in the ferromagnet, caused by the coupling to the antiferromagnet. The agreement between the experimental data and the theoretical model for both the first- and second-order contributions are good, although a coherent reversal of the magnetization is assumed in the model.Comment: 6 pages, 7 figures, submitted to J. Appl. Phy

The Taurus Tunable Filter Field Galaxy Survey: Sample Selection and Narrowband Number-Counts

Recent evidence suggests a falling volume-averaged star-formation rate (SFR) over z ~ 1. It is not clear, however, the extent to which the selection of such samples influences the measurement of this quantity. Using the Taurus Tunable Filter (TTF) we have obtained an emission-line sample of faint star-forming galaxies over comparable lookback times: the TTF Field Galaxy Survey. By selecting through emission-lines, we are screening galaxies through a quantity that scales directly with star-formation activity for a given choice of initial mass function. The scanning narrowband technique furnishes a galaxy sample that differs from traditional broadband-selected surveys in both its volume-limited nature and selection of galaxies through emission-line flux. Three discrete wavelength intervals are covered, centered at H-alpha redshifts z = 0.08, 0.24 and 0.39. Galaxy characteristics are presented and comparisons made with existing surveys of both broadband and emission-line selection. When the number-counts of emission-line objects are compared with those expected on the basis of existing H-alpha surveys, we find an excess of ~ 3 times at the faintest limits. While these detections are yet to be independently confirmed, inspection of the stronger subsample of galaxies detected in both the line and continuum (line-on-continuum subsample; 13 %) is sufficient to support an excess population. This increase in the emission-line field population implies higher star-formation densities over z ~ 0.4. However, further study in the form of multi-object spectroscopic follow-up is necessary to quantify this and confirm the faintest detections in the sample.Comment: 48 pages, 12 figures. To appear in the Astrophysical Journal. An abridged version of the Abstract is shown her

A Tunable Lyot Filter at Prime Focus: a Method for Tracing Supercluster Scales at z ~ 1

Tunable narrow-band, emission-line surveys have begun to show the ease with which star forming galaxies can be identified in restricted redshift intervals to z ~ 5 with a 4m class telescope. These surveys have been carried out with imaging systems at the Cassegrain or Nasmyth focus and are therefore restricted to fields smaller than 10 arcmin. We now show that tunable narrowband imaging is possible over a 30 arcmin field with a high-performance Lyot filter placed directly in front of a CCD mosaic at the prime focus. Our design is intended for the f/3.3 prime focus of the AAT 3.9m, although similar devices can be envisaged for the Subaru 8m (f/2), Palomar 5m (f/3.4), VISTA 4m (f/6), Mayall 4m (f/2.6) or CFHT 3.6m (f/4). A modified Wynne doublet ensures sub-arcsecond performance over the field. In combination with the new Wide-Field Imaging 8K x 8K mosaic (WFI) at the AAT, the overall throughput (35%) of the system to unpolarised light is expected to be comparable to the TAURUS Tunable Filter (TTF). Unlike the TTF, the field is fully monochromatic and the instrumental profile has much better wing suppression. For targetted surveys of emission-line sources at z ~ 1, a low-resolution (R ~ 150 at 550nm) Lyot filter on a 4m telescope is expected to be comparable or superior to current instruments on 8-10m class telescopes. We demonstrate that the 30 arcmin field is well matched to superclusters at these redshifts such that large-scale structure should be directly observable.Comment: Astrophysical Journal, accepted. 53 pages, 16 figures, aaste