The Mass of the Centaurus A Group of Galaxies

The mass M, and the radius R_h, of the Centaurus A group are estimated from the positions and radial velocities of 30 probable cluster members. For an assumed distance of 3.9 Mpc it is found that R_h \sim 640 kpc. The velocity dispersion in the Cen A group is 114 \pm 21 km/s. From this value, and R_h = 640 kpc, the virial theorem yields a total mass of 1.4 \times 10^{13} M_{\sun} for the Cen A group. The projected mass method gives a mass of 1.8 \times 10^{13} M_{\sun}. These values suggest that the Cen A group is about seven times as massive as the Local Group. The Cen A mass-to-light ratio is found to be M/L_B = 155-200 in solar units. The cluster has a zero-velocity radius R_0 = 2.3 Mpc.Comment: 8 pages, 1 figure, in LaTeX format; to appear in the Astronomical Journal in January 200

Are the Luminosities of RR Lyrae Stars Affected by Second Parameter Effects?

There is a serious discrepancy between the distance to the LMC derived from the Cepheid Period-Luminosity relation and that obtained by using the Galactic calibration for the luminosity of RR Lyrae stars. It is suggested that this problem might be due to the fact that second parameter effects make it inappropriate to apply Galactic calibrations to RR Lyrae variables in the Magellanic Clouds, i.e. Mv(RR) could depend on both [Fe/H] and on one or more second parameters.Comment: 10 pages as uuencoded compressed Postscript. Also available at http://www.dao.nrc.ca/DAO/SCIENCE/science.htm

The Luminosity Distribution of Local Group Galaxies

From a rediscussion of Local Group membership, and of distances to individual galaxies, we obtain $M_V$ values for 35 probable and possible Local Group members. The luminosity function of these objects is well fitted by a Schechter function with faint end slope $\alpha = -1.1 \pm 0.1$. The probability that the luminosity distribution of the Local Group is a single Schechter function with $\alpha$ steeper than -1.3 is less than 1 per cent. However, more complicated luminosity functions, such as multi-component Schechter functions with steep faint-end slopes, cannot be ruled out. There is some evidence that the luminosity distribution of dwarf spheroidal galaxies in the Local Group is steeper than that of dwarf irregular galaxies.Comment: 13 pages, 2 figures, accepted for publication in The Astronomical Journal. Figure 2 replaced, conclusion based on this figure change

Killing spinor space-times and constant-eigenvalue Killing tensors

A class of Petrov type D Killing spinor space-times is presented, having the peculiar property that their conformal representants can only admit Killing tensors with constant eigenvalues.Comment: 11 pages, submitted to CQ

Some Global Characteristics of the Galactic Globular Cluster System

The relations between the luminosities $M_{V}$, the metallicities $[Fe/H]$, the Galactocentric radii $R$, and the central concentration indices $c$ of Galactic globular clusters are discussed. It is found that the most luminous clusters rarely have collapsed cores. The reason for this might be that the core collapse time scales for such populous clusters are greater than the age of the Galaxy. Among those clusters, for which the structure has not been modified by core collapse, there is a correlation between central concentration and integrated luminosity, in the sense that the most luminous clusters have the strongest central concentration. The outermost region of the Galaxy with $R>10$ kpc was apparently not able to form metal-rich $([Fe/H]>-1.0)$ globular clusters, whereas such clusters (of which Ter 7 is the prototype) were able to form in some nearby dwarf spheroidal galaxies. It is not yet clear how the popular hypothesis that globular clusters were initially formed with a single power law mass spectrum can be reconciled with the observation that both (1) Galactic globular clusters with $R>80$ kpc, and (2) the globulars associated with the Sagittarius dwarf, appear to have bi-modal luminosity functions.Comment: 15 pages, 1 figur

Embracing uncertainty in multi-step inference

This dissertation focuses on embracing the uncertainty that is associated with multi-step inference. Typically, statistical analyses consist of multiple steps that build on each other and are executed sequentially. Common practice is that each consecutive step ignores the uncertainty of the preceding steps. Throughout this dissertation, it is shown that not embracing uncertainty leads to overconfidence and biased conclusions. Furthermore, I have demonstrated that this uncertainty can be accounted for by averaging across models or by performing the steps that involve uncertainty simultaneously in a single model. For example, instead of averaging the scores from repeated measurements and then analyzing the averages, it is better to directly analyze the unaggregated data. These situations occur with scores given to patients by different raters, as in Chapters 3 and 4, but also with repeated measures ANOVA, as illustrated in Chapters 9 and 10. The discussion suggests several ideas for making the adoption of methods that appropriately account for uncertainty more easily accessible and more standardized. Overall, my hope with this dissertation is that the practice of ignoring uncertainty by tying together several inferential steps becomes a relic of the past and that future studies embrace the uncertainty in the individual steps by adopting multi-model inference

Caltech Faint Galaxy Redshift Survey XV: Classification of Galaxies with 0.2 < z < 1.1 in the Hubble Deep Field (North) and its Flanking Fields

To circumvent the spatial effects of resolution on galaxy classification, the images of 233 objects of known redshift in the Hubble Deep Field (HDF) and its Flanking Fields (FF) that have redshifts in the range 0.20 < z < 1.10 were degraded to the resolution that they would have had if they were all located at a redshift z= 1.00. As in paper XIV of the present series, the effects of shifts in rest wavelength were mitigated by using R-band images for the classification of galaxies with 0.2 < z < 0.6 and I-band images for objects with redshifts 0.6 < z < 1.1. A special effort was made to search for bars in distant galaxies. The present data strongly confirm the previous conclusion that the Hubble tuning fork diagram only provides a satisfactory framework for the classification of galaxies with z ~< 0.3. More distant disk galaxies are often difficult to shoehorn into the Hubble classification scheme. The paucity of barred spirals and of grand-design spirals at large redshifts is confirmed. It is concluded that the morphology of disk galaxies observed at look-back times smaller than 3--4 Gyr differs systematically from that of more distant galaxies viewed at look-back times of 4--8 Gyr. The disks of late-type spirals at z >0.5 are seen to be more chaotic than those of their nearer counterparts. Furthermore the spiral structure in distant early-type spirals appears to be less well-developed than it is in nearby early-galaxies.Comment: Accepted for publication in the A

Rotating solenoidal perfect fluids of Petrov type D

We prove that aligned Petrov type D perfect fluids for which the vorticity vector is not orthogonal to the plane of repeated principal null directions and for which the magnetic part of the Weyl tensor with respect to the fluid velocity has vanishing divergence, are necessarily purely electric or locally rotationally symmetric. The LRS metrics are presented explicitly.Comment: 6 pages, no figure

Are prosocials unique in their egalitarianism? The pursuit of equality in outcomes among individualists.

The present research aims to elucidate to what extent the motive to ensure equality in outcomes is general and to what extent it interacts with other important motives such as maximizing own or collective gains. Because individuals may have different considerations and motivations in decision-making situations, it is likely that people with a different social value orientation will respond differently to an unequal distribution of outcomes. Contrary to our expectations, not only prosocials care about equality in outcomes. In study 1, we found that individualists choose to forego personal gains, despite obvious selfish reasons to cooperate, when outcomes were distributed unequally. In a second experiment we replicate this finding and show that individualists, just as do prosocials, demand equality in outcomes in interdependent situations. Our studies suggest that typifying individualists as solely being concerned about enhancing personal outcomes is too limited.Cooperation; Decision making; Demand; Distribution; Equality; Personal; Research; Social Value Orientation; Social values; Studies; Tit-For-Tat; Value;

Twitter: A tool to improve healthcare professionals’ awareness of antimicrobial resistance and antimicrobial stewardship

The World Health Organization urges international collaboration for the containment of antimicrobial resistance (AMR) or ‘superbugs’. If left unchecked, AMR could result in 4.1 million deaths in Africa by 2050. Furthermore,  without effective antibiotics, surgical procedures would become much riskier and in many cases impossible.  Antimicrobial stewardship requires a multidisciplinary approach; however, many programmes still struggle to achieve the ‘reach’ required to educate and engage all healthcare providers (HCPs). Twitter use among South Africans has grown by 129% in 12 months, from 2.4 million to 5.5 million. HCPs can use Twitter to network  and connect with worldwide experts, obtain real-time news from medical conferences, participate in live  Twitter chats conducted by experts or medical organisations, or participate in international journal clubs. Used responsibly and professionally, Twitter can spread the call to action and connect frontline healthcare  professionals to help win the battle against AMR