Statistics of the structure components in S0s: implications for bar induced secular evolution

The fractions and dimension of bars, rings and lenses are studied in the Near-IR S0 galaxy Survey (NIRS0S). We find evidence that multiple lenses in some barred S0s are related to bar resonances in a similar manner as the inner and outer rings, for which the outer/inner length ratio 2. Inner lenses in the non-barred galaxies normalized to galaxy diameter are clearly smaller than those in the barred systems. Interestingly, these small lenses in the non-barred galaxies have similar sizes as barlenses (lens-like structures embedded in a bar), and therefore might actually be barlenses in former barred galaxies, in which the outer, more elongated bar component, has been destroyed. We also find that fully developed inner lenses are on average a factor 1.3 larger than bars, whereas inner rings have similar sizes as bars. The fraction of inner lenses is found to be constant in all family classes (A, AB, B). Nuclear bars appear most frequently among the weakly barred (AB) galaxies, which is consistent with the theoretical models by Maciejewski & Athanassoula (2008). Similar sized bars as the nuclear bars were detected in seven 'non-barred' S0s. Galaxy luminosity does not uniquely define the sizes of bars or bar-related structures, neither is there any upper limit in galaxy luminosity for bar formation. Although all the family classes cover the same range of galaxy luminosity, the non-barred (A) galaxies are on average 0.6 mag brighter than the strongly barred (B) systems. Overall, our results are consistent with the idea that bars play an important role in the formation of the structure components of galaxies. The fact that multiple lenses are common in S0s, and that at least the inner lenses can have very old stellar populations, implies that the last destructive merger, or major gas accretion event, must have taken place at a fairly high redshift.Comment: 36 pages (include 13 figures, 11 tables). Accepted to MNRAS 2013 Jan 2

Halo Geometry and Dark Matter Annihilation Signal

We study the impact of the halo shape and geometry on the expected weakly interacting massive particle (WIMP) dark matter annihilation signal from the galactic center. As the halo profile in the innermost region is still poorly constrained, we consider different density behaviors like flat cores, cusps and spikes, as well as geometrical distortions. We show that asphericity has a strong impact on the annihilation signal when the halo profile near the galactic center is flat, but becomes gradually less significant for cuspy profiles, and negligible in the presence of a central spike. However, the astrophysical factor is strongly dependent on the WIMP mass and annihilation cross-section in the latter case.Comment: 5 pages, 4 figures, PR

Antimatter cosmic rays from dark matter annihilation: First results from an N-body experiment

[Abridged]. We take advantage of the galaxy-like 3D dark matter map extracted from the HORIZON Project results to calculate the positron and antiproton fluxes from dark matter annihilation, in a model-independent approach as well as for dark matter particle benchmarks relevant at the LHC scale (from supersymmetric and extra-dimensional theories). Such a study is dedicated to a better estimate of the theoretical uncertainties affecting predictions, while the PAMELA and GLAST satellites are currently taking data which will soon provide better observational constraints. We discuss the predictions of the antiproton and positron fluxes, and of the positron fraction as well, as compared to the current data. We finally discuss the limits of the Nbody framework in describing the dark matter halo of our Galaxy.Comment: 19 pages, 9 figures. Backgrounds included and additional comments and figures on the positron fraction. Accepted for publication in PR

A Search for Kinematic Evidence of Radial Gas Flows in Spiral Galaxies

CO and HI velocity fields of seven nearby spiral galaxies, derived from radio-interferometric observations, are decomposed into Fourier components whose radial variation is used to search for evidence of radial gas flows. Additional information provided by optical or near-infrared isophotes is also considered, including the relationship between the morphological and kinematic position angles. To assist in interpreting the data, we present detailed modeling that demonstrates the effects of bar streaming, inflow, and a warp on the observed Fourier components. We find in all of the galaxies evidence for either elliptical streaming or a warped disk over some range in radius, with deviations from pure circular rotation at the level of ~20-60 km/s. Evidence for kinematic warps is observed in several cases well inside R_{25}. No unambiguous evidence for radial inflows is seen in any of the seven galaxies, and we are able to place an upper limit of ~5-10 km/s (3-5% of the circular speed) on the magnitude of any radial inflow in the inner regions of NGC 4414, 5033 and 5055. We conclude that the inherent non-axisymmetry of spiral galaxies is the greatest limitation to the direct detection of radial inflows.Comment: 22 emulateapj pages with bitmapped colour figures, to appear in ApJ (April 2004). For full resolution figures go to http://www.atnf.csiro.au/people/twong/preprints

Study of the mixed state of La_{1.83}Sr_{0.17}CuO_{4} by means of muon-spin rotation and magnetization experiments in a low magnetic field

Muon-spin rotation (muSR) experiments are often used to study the magnetic field distribution in type-II superconductors in the vortex state. Based on the determination of the magnetic penetration depth it is frequently speculated---also controversially---about the order-parameter symmetry of the studied superconductors. This article reports on a combined muSR and magnetization study of the mixed state in the cuprate high-temperature superconductor La_{1.83}Sr_{0.17}CuO_{4} in a low magnetic field of 20 mT applied along the c axis of a single crystal. The macroscopic magnetization measurements reveal substantial differences for various cooling procedures. Yet, indicated changes in the vortex dynamics between different temperature regions as well as the results of the microscopic muSR experiments are virtually independent of the employed cooling cycles. Additionally, it is found that the mean magnetic flux density, locally probed by the muons, strongly increases at low temperatures. This can possibly be explained by a non-random sampling of the spatial field distribution of the vortex lattice in this cuprate superconductor caused by intensified vortex pinning.Comment: 10 pages, 8 figures, accepted for publication in Physical Review

K-Band Observations of Boxy Bulges. I. Morphology and Surface Brightness Profiles

Kn-band images, unsharp-masked images, as well as major-axis and vertically- summed surface brightness profiles are presented for 30 edge-on spiral galaxies, most with a boxy or peanut-shaped (B/PS) bulge. Such galaxies have more complex morphologies than galaxies of other bulge types, more often showing (off-)centered X structures, secondary major-axis maxima and spiral-like structures. Those features are also observed in N-body simulations of barred discs and may trace the main bar orbit families. The surface brightness profiles of galaxies with a B/PS bulge are also more complex, with typically 3 or more clearly separated regions, including a flat intermediate region (Freeman Type II profiles). Those radial breaks offer evidence for bar-driven transfer of angular momentum and radial redistribution of material. The profiles also suggest a rapid variation of the scaleheight of the disc material, contrary to conventional wisdom but again as expected from vertical resonances and instabilities in barred discs. The steep inner region of the surface brightness profiles is often shorter than the isophotally thick part of the galaxies, itself always shorter than the flat region of the profiles. Contrary to the standard `bulge + disc' model, we thus propose that galaxies with a B/PS bulge are composed of a thin concentrated disc (a disc-like bulge) contained within a partially thick bar (the B/PS bulge) and a thin outer disc. The inner disc likely formed secularly through bar-driven processes and is responsible for the steep inner region of the surface brightness profiles, while the bar is responsible for the flat region and the thick complex morphological structures observed. Those components are strongly coupled dynamically and are formed mostly of the same (disc) material. [Abridged]Comment: 23 pages, 34 figures. Accepted for publication in MNRAS. A version with full resolution figures is available at http://www-astro.physics.ox.ac.uk/~bureau/pub_list.htm

Modeling the Gas Flow in the Bar of NGC 1365

We present new observations of the strongly-barred galaxy NGC 1365, including new photometric images and Fabry-Perot spectroscopy, as well as a detailed re-analysis of the neutral hydrogen observations from the VLA archive. We find the galaxy to be at once remarkably bi-symmetric in its I-band light distribution and strongly asymmetric in the distribution of dust and in the kinematics of the gas in the bar region. The velocity field mapped in the H-alpha line reveals bright HII regions with velocities that differ by 60 to 80 km/s from that of the surrounding gas, which may be due to remnants of infalling material. We have attempted hydrodynamic simulations of the bar flow to estimate the separate disk and halo masses, using two different dark matter halo models and covering a wide range of mass-to-light ratios (Upsilon) and bar pattern speeds (Omega_p). None of our models provides a compelling fit to the data, but they seem most nearly consistent with a fast bar, corotation at sim 1.2r_B, and Upsilon_I simeq 2.0 +- 1.0, implying a massive, but not fully maximal, disk. The fitted dark halos are unusually concentrated, a requirement driven by the declining outer rotation curve.Comment: 43 pages, 15 figures, accepted to appear in Ap

Superconductivity and magnetism in RbxFe2-ySe2: Impact of thermal treatment on mesoscopic phase separation

An extended study of the superconducting and normal-state properties of various as-grown and post-annealed RbxFe2-ySe2 single crystals is presented. Magnetization experiments evidence that annealing of RbxFe2-ySe2 at 413 K, well below the onset of phase separation Tp=489 K, neither changes the magnetic nor the superconducting properties of the crystals. In addition, annealing at 563 K, well above Tp, suppresses the superconducting transition temperature Tc and leads to an increase of the antiferromagnetic susceptibility accompanied by the creation of ferromagnetic impurity phases, which are developing with annealing time. However, annealing at T=488K=Tp increases Tc up to 33.3 K, sharpens the superconducting transition, increases the lower critical field, and strengthens the screening efficiency of the applied magnetic field. Resistivity measurements of the as-grown and optimally annealed samples reveal an increase of the upper critical field along both crystallographic directions as well as its anisotropy. Muon spin rotation and scanning transmission electron microscopy experiments suggest the coexistence of two phases below Tp: a magnetic majority phase of Rb2Fe4Se5 and a non-magnetic minority phase of Rb0.5Fe2Se2. Both microscopic techniques indicate that annealing the specimens just at Tp does not affect the volume fraction of the two phases, although the magnetic field distribution in the samples changes substantially. This suggests that the microstructure of the sample, caused by mesoscopic phase separation, is modified by annealing just at Tp, leading to an improvement of the superconducting properties of RbxFe2-ySe2 and an enhancement of Tc.Comment: 13 pages, 12 figure

Comparing peanut-shaped `bulges' to N-body simulations and orbital calculations

We present a near-infrared K_n-band photometric study of edge-on galaxies with a box/peanut-shaped `bulge'. The morphology of the galaxies is analysed using unsharp masking and fits to the vertical surface brightness profiles, and the results are compared to N-body simulations and orbital calculations of barred galaxies. Both theoretical approaches reproduce the main structures observed.Comment: 4 pages, 5 figures, to appear in the proceedings of "The Evoution of Galaxies. III. From simple approaches to self-consistent models" (Kiel, July 2002), G. Hensler et al. (eds.

STIS Longslit Spectroscopy Of The Narrow Line Region Of NGC 4151. I. Kinematics and Emission Line Ratios

Longslit spectra of the Seyfert galaxy NGC 4151 from the UV to near infrared have been obtained with STIS to study the kinematics and physical conditions in the NLR. The kinematics show evidence for three components, a low velocity system in normal disk rotation, a high velocity system in radial outflow at a few hundred km/s relative to the systemic velocity and an additional high velocity system also in outflow with velocities up to 1400 km/s, in agreement with results from STIS slitless spectroscopy (Hutchings et al., 1998, Kaiser et al., 1999, Hutchings et al., 1999) We have explored two simple kinematic models and suggest that radial outflow in the form of a wind is the most likely explanation. We also present evidence indicating that the wind may be decelerating with distance from the nucleus. We find that the emission line ratios along our slits are all entirely consistent with photoionization from the nuclear continuum source. A decrease in the [OIII]5007/H-beta and [OIII]5007/[OII]3727 ratios suggests that the density decreases with distance from the nucleus. This trend is borne out by the [SII] ratios as well. We find no strong evidence for interaction between the radio jet and the NLR gas in either the kinematics or the emission line ratios in agreement with the results of Kaiser et al. (1999) who find no spatial coincidence of NLR clouds and knots in the radio jet. These results are in contrast to other recent studies of nearby AGN which find evidence for significant interaction between the radio source and the NLR gas.Comment: 32 pages, 13 figures, accepted for publication in The Astrophysical Journa