Stellar populations in central cluster galaxies: the influence of cooling flows

We present detailed, high spatial and spectral resolution, long-slit observations of four central cluster galaxies (Abell 0085, 0133, 0644 and Ophiuchus) recently obtained on the Southern African Large Telescope (SALT). Our sample consists of central cluster galaxies (CCGs) with previously-observed H\alpha-filaments, and have existing data from the X-ray to radio wavelength regimes available. Here, we present the detailed optical data over a broad wavelength range to probe the spatially-resolved kinematics and stellar populations of the stars. We use the Pegase.HR model with the ELODIE v3.1 stellar library to determine the star formation histories of the galaxies using full spectrum fitting. We perform single stellar population (SSP) as well as composite stellar population (CSP) fits to account for more complex star formation histories. Monte-Carlo simulations and \chi 2-maps are used to check the reliability of the solutions. This, combined with the other multiwavelength data, will form a complete view of the different phases (hot and cold gas and stars) and how they interact in the processes of star formation and feedback detected in central galaxies in cooling flow clusters, as well as the influence of the host cluster. We find small, young stellar components in at least three of the four galaxies, even though two of the three host clusters have zero spectrally-derived mass deposition rates from X-ray observations.Comment: Based on observations made with the Southern African Large Telescope (SALT). Accepted for publication in MNRA

The UV-upturn in brightest cluster galaxies

This paper is part of a series devoted to the investigation of a large sample of brightest cluster galaxies (BCGs), their properties and the relationships between these and the properties of the host clusters. In this paper, we compare the stellar population properties derived from high signal-to-noise, optical long-slit spectra with the GALEX ultraviolet (UV) colour measurements for 36 nearby BCGs to understand the diversity in the most rapidly evolving feature in old stellar systems, the UV-upturn. We investigate: (1) the possible differences between the UV-upturn of BCGs and those of a control sample of ordinary ellipticals in the same mass range, as well as possible correlations between the UV-upturn and other general properties of the galaxies; (2) possible correlations between the UV-upturn and the properties of the host clusters; (3) recently proposed scenarios where helium-sedimentation in the cluster centre can produce an enhanced UV-upturn. We find systematic differences between the UV-colours of BCGs and ordinary ellipticals, but we do not find correlations between these colours and the properties of the host clusters. Furthermore, the observations do not support the predictions made by the helium-sedimentation model as an enhancer of the UV-upturn.Comment: 12 pages, accepted for publication in MNRA

Polarization-selective excitation of N-V centers in diamond

The nitrogen-vacancy (N-V) center in diamond is promising as an electron spin qubit due to its long-lived coherence and optical addressability. The ground state is a spin triplet with two levels ($m_s = \pm 1$) degenerate at zero magnetic field. Polarization-selective microwave excitation is an attractive method to address the spin transitions independently, since this allows operation down to zero magnetic field. Using a resonator designed to produce circularly polarized microwaves, we have investigated the polarization selection rules of the N-V center. We first apply this technique to N-V ensembles in [100] and [111]-oriented samples. Next, we demonstrate an imaging technique, based on optical polarization dependence, that allows rapid identification of the orientations of many single N-V centers. Finally, we test the microwave polarization selection rules of individual N-V centers of known orientation

High resolution spectroscopy of single NV defects coupled with nearby 13^{13}C nuclear spins in diamond

We report a systematic study of the hyperfine interaction between the electron spin of a single nitrogen-vacancy (NV) defect in diamond and nearby $^{13}$C nuclear spins, by using pulsed electron spin resonance spectroscopy. We isolate a set of discrete values of the hyperfine coupling strength ranging from 14 MHz to 400 kHz and corresponding to $^{13}$C nuclear spins placed at different lattice sites of the diamond matrix. For each lattice site, the hyperfine interaction is further investigated through nuclear spin polarization measurements and by studying the magnetic field dependence of the hyperfine splitting. This work provides informations that are relevant for the development of nuclear-spin based quantum register in diamond.Comment: 8 pages, 5 figure

The dynamically hot stellar halo around NGC 3311: a small cluster-dominated central galaxy

An important open question is the relation between intracluster light and the halos of central galaxies in galaxy clusters. Here we report results from an on going project with the aim to characterize the dynamical state in the core of the Hydra I (Abell 1060) cluster around NGC 3311. Methods: We analyze deep long-slit absorption line spectra reaching out to ~25 kpc in the halo of NGC 3311. Results: We find a very steep increase in the velocity dispersion profile from a central sigma_0=150 km/s to sigma_out ~450 km/s at R ~ 12 kpc. Farther out, to ~25 kpc, sigma appears to be constant at this value, which is ~60% of the velocity dispersion of the Hydra I galaxies. With its dynamically hot halo kinematics, NGC 3311 is unlike other normal early-type galaxies. Conclusions: These results and the large amount of dark matter inferred from X-rays around NGC 3311 suggest that the stellar halo of this galaxy is dominated by the central intracluster stars of the cluster, and that the transition from predominantly galaxy-bound stars to cluster stars occurs in the radial range 4 to 12 kpc from the center of NGC 3311. We comment on the wide range of halo kinematics observed in cluster central galaxies, depending on the evolutionary state of their host clusters.Comment: 5 pages, 4 figures, 1 table, accepted for publication in A&

Stellar population gradients in brightest cluster galaxies

We present the stellar population and velocity dispersion gradients for a sample of 24 brightest cluster galaxies (BCGs) in the nearby Universe for which we have obtained high quality long-slit spectra at the Gemini telescopes. With the aim of studying the possible connection between the formation of the BCGs and their host clusters, we explore the relations between the stellar population gradients and properties of the host clusters as well as the possible connections between the stellar population gradients and other properties of the galaxies. We find mean stellar population gradients (negative {\Delta}[Z/H]/log r gradient of -0.285{\pm}0.064; small positive {\Delta}log (age)/log r gradient of 0.069{\pm}0.049; and null {\Delta}[E/Fe]/log r gradient of -0.008{\pm}0.032) that are consistent with those of normal massive elliptical galaxies. However, we find a trend between metallicity gradients and velocity dispersion (with a negative slope of -1.616{\pm}0.539) that is not found for the most massive ellipticals. Furthermore, we find trends between the metallicity gradients and K-band luminosities (with a slope of 0.173{\pm}0.081) as well as the distance from the BCG to the X-ray peak of the host cluster (with a slope of -7.546{\pm}2.752). The latter indicates a possible relation between the formation of the cluster and that of the central galaxy.Comment: 23 pages, 18 figures, accepted for publication in MNRAS. arXiv admin note: text overlap with arXiv:1104.2376v

The nitrogen-vacancy center in diamond re-visited

Symmetry considerations are used in presenting a model of the electronic structure and the associated dynamics of the nitrogen-vacancy center in diamond. The model accounts for the occurrence of optically induced spin polarization, for the change of emission level with spin polarization and for new measurements of transient emission. The rate constants given are in variance to those reported previously.Comment: 12 pages 10 figure

Energy levels and decoherence properties of single electron and nuclear spins in a defect center in diamond

The coherent behavior of the single electron and single nuclear spins of a defect center in diamond and a 13C nucleus in its vicinity, respectively, are investigated. The energy levels associated with the hyperfine coupling of the electron spin of the defect center to the 13C nuclear spin are analyzed. Methods of magnetic resonance together with optical readout of single defect centers have been applied in order to observe the coherent dynamics of the electron and nuclear spins. Long coherence times, in the order of microseconds for electron spins and tens of microseconds for nuclear spins, recommend the studied system as a good experimental approach for implementing a 2-qubit gate.Comment: 4 pages, 4 figure

Meaning and purpose in the occupations of gang-involved young men in Cape Town

INTRODUCTION: Involvement in gangs negatively influences the lives of many young men living in Cape Town, South Africa. There is a need to better understand young men's motives and reasons for belonging to gangs as efforts to reduce gang involvement have shown little success. METHODOLOGY: A descriptive qualitative study was conducted to explore the meaning and purpose of engaging in occupations related to being a gang member, and the influence on other occupations. In-depth, semi-structured interviews were conducted with four participants who were purposively selected from a Special Youth Care Centre in Cape Town. FINDINGS: Five themes emerged: Why am I where I am?; To strengthen the camp; Attraction to gangs; It's difficult but it's life; and Threshold to manhood. The participants' involvement in gangs meant social support, material resources including drugs and money, independence, thrills and excitement. The purpose of engaging in gang-related occupations was to strengthen the gang, gain belonging, prove manhood and for survival. However, gang-involvement deprived participants from engaging in other occupations and roles including schooling, leisure activities and relationships with mothers and girlfriends. CONCLUSIONS: Understanding gang-related occupations assists occupational therapists to plan relevant programmes to support young men's disengagement from gangs and reintegration into the community in pro-social ways.DHE

Properties of nitrogen-vacancy centers in diamond: group theoretic approach

We present a procedure that makes use of group theory to analyze and predict the main properties of the negatively charged nitrogen-vacancy (NV) center in diamond. We focus on the relatively low temperatures limit where both the spin-spin and spin-orbit effects are important to consider. We demonstrate that group theory may be used to clarify several aspects of the NV structure, such as ordering of the singlets in the ($e^2$) electronic configuration, the spin-spin and the spin-orbit interactions in the ($ae$) electronic configuration. We also discuss how the optical selection rules and the response of the center to electric field can be used for spin-photon entanglement schemes. Our general formalism is applicable to a broad class of local defects in solids. The present results have important implications for applications in quantum information science and nanomagnetometry.Comment: 30 pages, 6 figure