The cosmological origin of the Tully-Fisher relation

We use high-resolution cosmological simulations that include the effects of gasdynamics and star formation to investigate the origin of the Tully-Fisher relation in the standard Cold Dark Matter cosmogony. Luminosities are computed for each model galaxy using their full star formation histories and the latest spectrophotometric models. We find that at z=0 the stellar mass of model galaxies is proportional to the total baryonic mass within the virial radius of their surrounding halos. Circular velocity then correlates tightly with the total luminosity of the galaxy, reflecting the equivalence between mass and circular velocity of systems identified in a cosmological context. The slope of the relation steepens slightly from the red to the blue bandpasses, and is in fairly good agreement with observations. Its scatter is small, decreasing from \~0.45 mag in the U-band to ~0.34 mag in the K-band. The particular cosmological model we explore here seems unable to account for the zero-point of the correlation. Model galaxies are too faint at z=0 (by about two magnitudes) if the circular velocity at the edge of the luminous galaxy is used as an estimator of the rotation speed. The Tully-Fisher relation is brighter in the past, by about ~0.7 magnitudes in the B-band at z=1, at odds with recent observations of z~1 galaxies. We conclude that the slope and tightness of the Tully-Fisher relation can be naturally explained in hierarchical models but that its normalization and evolution depend strongly on the star formation algorithm chosen and on the cosmological parameters that determine the universal baryon fraction and the time of assembly of galaxies of different mass.Comment: 5 pages, 4 figures included, submitted to ApJ (Letters

The relationship between corpus callosum size and forebrain volume

Using high-resolution in vivo magnetic resonance morphometry we measured forebrain volume (FBV), midsagittal size of the corpus callosum (CC) and four CC subareas in 120 young and healthy adults (49 women, 71 men). We found moderate linear and quadratic correlations, indicating that the CC and all CC subareas increase with FBV both in men and women (multiple r2 ranging from 0.10 to 0.28). Allometric equations revealed that these increases were less than proportional to FBV (r2 ranging from 0.02 to 0.30). Absolute CC measurements, as well as CC subareas relative to total CC or FBV (the latter measures termed the CC ratios), were further analyzed with regard to possible effects of handedness, gender, or handedness by gender interaction. Contrary to previous reports, left-handers did not show larger CC measurements compared to right-handers. The only apparent influence of gender was on the CC ratios, which were larger in women. However, smaller brains had larger CC ratios which were mainly independent of gender, a result of the less than proportional increase of callosal size with FBV. We suggest that the previously described gender differences in CC anatomy may be better explained by an underlying effect of brain size, with larger brains having relatively smaller callosa. This lends empirical support to the hypothesis that brain size may be an important factor influencing interhemispheric connectivity and lateralizatio

CIV Absorption From Galaxies in the Process of Formation

We investigate the heavy element QSO absorption systems caused by gas condensations at high redshift which evolve into galaxies with circular velocity of 100 to 200 km/s at the present epoch. Artificial QSO spectra were generated for a variety of lines-of-sight through regions of the universe simulated with a hydrodynamics code. The CIV and HI absorption features in these spectra closely resemble observed CIV and HI absorption systems over a wide range in column density. CIV absorption complexes with multiple-component structure and velocity spreads up to about 600 km/s are found. The broadest systems are caused by lines-of-sight passing through groups of protogalactic clumps with individual velocity dispersions of less than 150 km/s aligned along filamentary structures. The temperature of most of the gas does not take the photoionization equilibrium value. This invalidates density and size estimates derived from thermal equilibrium models. Consequences for metal abundance determinations are briefly discussed. We predict occasional exceptionally large ratios of CIV to HI column density (up to a third) for lines-of-sight passing through compact halos of hot gas with temperature close to 3 10^5 K. Our model may be able to explain both high-ionization multi-component heavy-element absorbers and damped Lyman alpha systems as groups of small protogalactic clumps.Comment: 13 pages, uuencoded postscript file, 4 figures included submitted to ApJ (Letters); complete version also available at http://www.mpa-garching.mpg.de/Galaxien/prep.htm

Star Formation, Supernovae Feedback and the Angular Momentum Problem in Numerical CDM Cosmogony: Half Way There?

We present a smoothed particle hydrodynamic (SPH) simulation that reproduces a galaxy that is a moderate facsimile of those observed. The primary failing point of previous simulations of disk formation, namely excessive transport of angular momentum from gas to dark matter, is ameliorated by the inclusion of a supernova feedback algorithm that allows energy to persist in the model ISM for a period corresponding to the lifetime of stellar associations. The inclusion of feedback leads to a disk at a redshift $z=0.52$, with a specific angular momentum content within 10% of the value required to fit observations. An exponential fit to the disk baryon surface density gives a scale length within 17% of the theoretical value. Runs without feedback, with or without star formation, exhibit the drastic angular momentum transport observed elsewhere.Comment: 4 pages, 3 figures, accepted for publication in ApJ Letter

A real-time digital computer program for the simulation of a single rotor helicopter

A computer program was developed for the study of a single-rotor helicopter on the Langley Research Center real-time digital simulation system. Descriptions of helicopter equations and data, program subroutines (including flow charts and listings), real-time simulation system routines, and program operation are included. Program usage is illustrated by standard check cases and a representative flight case

AstroGrid-D: Enhancing Astronomic Science with Grid Technology

We present AstroGrid-D, a project bringing together astronomers and experts in Grid technology to enhance astronomic science in many aspects. First, by sharing currently dispersed resources, scientists can calculate their models in more detail. Second, by developing new mechanisms to efficiently access and process existing datasets, scientific problems can be investigated that were until now impossible to solve. Third, by adopting Grid technology large instruments such as robotic telescopes and complex scientific workflows from data aquisition to analysis can be managed in an integrated manner. In this paper, we present prominent astronomic use cases, discuss requirements on a Grid middleware and present our approach to extend/augment existing middleware to facilitate the improvements mentioned above

Accuracy of Mesh Based Cosmological Hydrocodes: Tests and Corrections

We perform a variety of tests to determine the numerical resolution of the cosmological TVD eulerian code developed by Ryu et al (1993). Tests include 512^3 and 256^3 simulations of a Pk=k^{-1} spectrum to check for self-similarity and comparison of results with those from higher resolution SPH and grid-based calculations (Frenk et al 1998). We conclude that in regions where density gradients are not produced by shocks the code degrades resolution with a Gaussian smoothing (radius) length of 1.7 cells. At shock caused gradients (for which the code was designed) the smoothing length is 1.1 cells. Finally, for \beta model fit clusters, we can approximately correct numerical resolution by the transformation R^2_{core}\to R^2_{core}-(C\Delta l)^2, where \Delta l is the cell size and C=1.1-1.7. When we use these corrections on our previously published computations for the SCDM and \Lambda CDM models we find luminosity weighted, zero redshift, X-ray cluster core radii of (210\pm 86, 280\pm 67)h^{-1}kpc, respectively, which are marginally consistent with observed (Jones & Forman 1992) values of 50-200h^{-1}kpc. Using the corrected core radii, the COBE normalized SCDM model predicts the number of bright L_x>10^{43}erg/s clusters too high by a factor of \sim 20 and the \Lambda CDM model is consistent with observations.Comment: ApJ in press (1999

The Effects of a Photoionizing UV Background on the Formation of Disk Galaxies

We use high resolution N-body/gasdynamical simulations to investigate the effects of a photoionizing UV background on the assembly of disk galaxies in hierarchically clustering universes. We focus on the mass and rotational properties of gas that can cool to form centrifugally supported disks in dark matter halos of different mass. Photoheating can significantly reduce the amount of gas that can cool in galactic halos. Depending on the strength of the UV background field, the amount of cooled gas can be reduced by up to $50\%$ in systems with circular speeds in the range $80$-$200$ \kms. The magnitude of the effect, however, is not enough to solve the ``overcooling'' problem that plagues hierarchical models of galaxy formation if the UV background is chosen to be consistent with estimates based on recent observations of QSO absorption systems. Photoionization has little effect on the collapse of gas at high redshift and affects preferentially gas that is accreted at late times. Since disks form inside-out, accreting higher angular momentum gas at later times, disks formed in the presence of a UV background have spins that are even smaller than those formed in simulations that do not include the effects of photoionization. This exacerbates the angular momentum problem that afflicts hierarchical models of disk formation. We conclude that photoionization cannot provide the heating mechanism required to reconcile hierarchically clustering models with observations. Energy feedback and enrichment processes from the formation and evolution of stars must therefore be indispensable ingredients for any successful model of the formation of disk galaxies.Comment: 36 pages, w/ embedded figures, submitted to ApJ. Also available at http://penedes.as.arizona.edu/~jfn/preprints/dskform.ps.g

Differential expression of skeletal muscle genes following administration of clenbuterol to exercised horses.

BackgroundClenbuterol, a beta2-adrenergic receptor agonist, is used therapeutically to treat respiratory conditions in the horse. However, by virtue of its mechanism of action it has been suggested that clenbuterol may also have repartitioning affects in horses and as such the potential to affect performance. Clenbuterol decreases the percent fat and increases fat-free mass following high dose administration in combination with intense exercise in horses. In the current study, microarray analysis and real-time PCR were used to study the temporal effects of low and high dose chronic clenbuterol administration on differential gene expression of several skeletal muscle myosin heavy chains, genes involved in lipid metabolism and the β2-adrenergic receptor. The effect of clenbuterol administration on differential gene expression has not been previously reported in the horse, therefore the primary objective of the current study was to describe clenbuterol-induced temporal changes in gene expression following chronic oral administration of clenbuterol at both high and low doses.ResultsSteady state clenbuterol concentrations were achieved at approximately 50 h post administration of the first dose for the low dose regimen and at approximately 18-19 days (10 days post administration of 3.2 μg/kg) for the escalating dosing regimen. Following chronic administration of the low dose (0.8 μg/kg BID) of clenbuterol, a total of 114 genes were differentially expressed, however, none of these changes were found to be significant following FDR adjustment of the p-values. A total of 7,093 genes were differentially expressed with 3,623 genes up regulated and 3,470 genes down regulated following chronic high dose administration. Of the genes selected for further study by real-time PCR, down-regulation of genes encoding myosin heavy chains 2 and 7, steroyl CoA desaturase and the β2-adrenergic receptor were noted. For most genes, expression levels returned towards baseline levels following cessation of drug administration.ConclusionThis study showed no evidence of modified gene expression following chronic low dose administration of clenbuterol to horses. However, following chronic administration of high doses of clenbuterol alterations were noted in transcripts encoding various myosin heavy chains, lipid metabolizing enzymes and the β2-adrenergic receptor