Monthly Notices of the Royal Astronomical Society

doi: 10.1111/j.1365-2966.2006.11212.xpmid: N/A

Riffel, Rogemar A.; Storchi-Bergmann, Thaisa; Winge, Cláudia; Barbosa, Fausto K. B.

doi: 10.1111/j.1365-2966.2006.11050.xpmid: N/A

We present two-dimensional (2D) gas kinematics and excitation of the inner 300 pc of the Seyfert galaxy ESO 428−G14 at a sampling of 14 pc2, from near-infrared spectroscopic observations at R≈ 6000 obtained with the Integral Field Unit (IFU) of the Gemini Near-Infrared Spectrograph. From measurements of fluxes and profiles of the emission lines [Fe ii]λ1.257 μm, Paβ, H2λ 2.121 μm and Brγ, we construct 2D maps of line intensities and ratios, radial velocities and velocity dispersions. Emission line ‘tomography’ is provided by velocity slices obtained across the line profiles, a unique capability of IFUs, which allows the mapping of not only the peak velocities but including also the wings. We compare these maps with a previously published high spatial resolution radio map and find a tight relation between the radio structure and the emission-line flux distributions and kinematics, revealing that the radio jet plays a fundamental role not only in shaping the narrow-line region but also in the imprint of its kinematics. Blueshifts of up to 400 km s−1 and velocity dispersions of up to 150 km s−1 are observed in association with the radio jet at a position angle (PA) = 129°, which is also the PA of the photometric major axis of the galaxy. We conclude that the radio jet is launched at a small angle relative to the galactic plane, with the north-western side slightly oriented towards us. This angle is small enough for the radio jet to shock and compress the gas in the plane of the galaxy, and for the nuclear continuum to ionize and heat it. The distinct kinematics and flux distributions observed for the different emission lines suggest different origins for their emission. The [Fe ii] shows the largest blueshifts and velocity dispersions and its flux distribution is concentrated along the jet, while the H2 shows the lowest velocity dispersions and has additional flux contribution from regions beyond the jet. Both X-rays emitted by the active galactic nucleus and shocks produced by the radio jet can excite the H2 and [Fe ii] emission lines. We use the 2D velocity dispersion maps to estimate upper limits to the contribution of the radio jet to the excitation of [Fe ii] and H2 which may reach 90 per cent for [Fe ii] and 80 per cent for H2 in the jet region. The [Fe ii]/Paβ emission-line ratios and the association of the [Fe ii] flux distribution and kinematics with the radio structure support a stronger contribution of the radio jet to the [Fe ii] excitation than that of H2. In the regions beyond the jet, the observations favour X-ray excitation.

Casagrande, Luca; Portinari, Laura; Flynn, Chris

doi: 10.1111/j.1365-2966.2006.10999.xpmid: N/A

We derive an empirical effective temperature and bolometric luminosity calibration for G and K dwarfs, by applying our own implementation of the Infrared Flux Method to multiband photometry. Our study is based on 104 stars for which we have excellent BV(RI)CJHKS photometry, excellent parallaxes and good metallicities.Colours computed from the most recent synthetic libraries (ATLAS9 and MARCS) are found to be in good agreement with the empirical colours in the optical bands, but some discrepancies still remain in the infrared. Synthetic and empirical bolometric corrections also show fair agreement.A careful comparison to temperatures, luminosities and angular diameters obtained with other methods in the literature shows that systematic effects still exist in the calibrations at the level of a few per cent. Our Infrared Flux Method temperature scale is 100-K hotter than recent analogous determinations in the literature, but is in agreement with spectroscopically calibrated temperature scales and fits well the colours of the Sun. Our angular diameters are typically 3 per cent smaller when compared to other (indirect) determinations of angular diameter for such stars, but are consistent with the limb-darkening corrected predictions of the latest 3D model atmospheres and also with the results of asteroseismology.Very tight empirical relations are derived for bolometric luminosity, effective temperature and angular diameter from photometric indices.We find that much of the discrepancy with other temperature scales and the uncertainties in the infrared synthetic colours arise from the uncertainties in the use of Vega as the flux calibrator. Angular diameter measurements for a well-chosen set of G and K dwarfs would go a long way to addressing this problem.

Erdoğdu, Pirin; Lahav, Ofer; Huchra, John P.; Colless, Matthew; Cutri, Roc M.; Falco, Emilio; George, Teddy; Jarrett, Thomas; Jones, D. Heath; Macri, Lucas M.; Mader, Jeff; Martimbeau, Nathalie; Pahre, Michael A.; Parker, Quentin A.; Rassat, Anaïs;

Gao, Liang; White, Simon D. M.

doi: 10.1111/j.1365-2966.2006.11048.xpmid: N/A

Many galaxies display warps, lopsided images, asymmetric rotation curves or other features which suggest that their immediate dynamical environment is neither static nor in equilibrium. In cold dark matter (CDM) theories, such non-equilibrium features are expected in the inner regions of many dark haloes as a result of recent hierarchical growth. We used the excellent statistics provided by the very large Millennium Simulation to study (i) how the distribution of position and velocity asymmetries predicted for halo cores by the concordance ΛCDM cosmogony depends on halo mass and (ii) how much of the dark matter in the inner core has been added at relatively recent times. Asymmetries are typically larger in more massive haloes. Thus 20 per cent of cluster haloes have density centre separated from barycentre by more than 20 per cent of the virial radius, while only 7 per cent of Milky Way haloes have such large asymmetries. About 40 per cent of all cluster haloes have a mean core velocity which differs from the barycentre velocity by more than a quarter of the characteristic halo circular velocity, whereas only 10 per cent of Milky Way haloes have such large velocity offsets. About 25 per cent of all cluster haloes have acquired more than a quarter of the mass currently in their inner 10 kpc through mergers since z= 1. The corresponding percentage of Milky Way haloes is 15 per cent. These numbers seem quite compatible with the levels of asymmetry seen in the observable regions of galaxies, but quantitative comparison requires more detailed modelling of the observable components.

Lyutikov, M.

doi: 10.1111/j.1365-2966.2006.10835.xpmid: N/A

Sharp fronts observed by the Chandra satellite between dense cool cluster cores moving with near-sonic velocity through the hotter intergalactic gas, require strong suppression of thermal conductivity across the boundary. This may be due to magnetic fields tangential to the contact surface separating the two plasma components. We point out that a super-Alfvenic motion of a plasma cloud (a core of a merging galaxy) through a weakly magnetized intercluster medium leads to ‘magnetic draping’, formation of a thin, strongly magnetized boundary layer with a tangential magnetic field. For supersonic cloud motion, Ms≥ 1, magnetic field inside the layer reaches near-equipartition values with thermal pressure. Typical thickness of the layer is ∼L/M2A≪L, where L is the size of the obstacle (plasma cloud) moving with Alfvén Mach number MA≫ 1. To a various degree, magnetic draping occurs for both subsonic and supersonic flows, random and ordered magnetic fields and it does not require plasma compressibility. The strongly magnetized layer will thermally isolate the two media and may contribute to the Kelvin–Helmholtz stability of the interface. Similar effects occur for radio bubbles, quasi-spherical expanding cavities blown up by active galactic nucleus jets; in this case, the thickness of the external magnetized layer is smaller, ∼L/M3A≪L.

Parker, Quentin A.; Acker, A.; Frew, D. J.; Hartley, M.; Peyaud, A. E. J.; Ochsenbein, F.; Phillipps, S.; Russeil, D.; Beaulieu, S. F.; Cohen, M.; Köppen, J.; Miszalski, B.; Morgan, D. H.; Morris, R. A. H.; Pierce, M. J.; Vaughan, A. E.

Lodieu, N.; Hambly, N. C.; Jameson, R. F.

doi: 10.1111/j.1365-2966.2006.10958.xpmid: N/A

We present the results of a 9.3-deg2 infrared (ZYJHK) survey in the Upper Scorpius association extracted from the UKIRT Infrared Deep Sky Survey (UKIDSS) Galactic Cluster Survey Early Data Release. We have selected a total of 112 candidates from the (Z−J, Z) colour–magnitude diagram over the Z= 12.5–20.5 magnitude range, corresponding to M= 0.25–0.01 M⊙ at an age of 5 Myr and a distance of 145 pc. Additional photometry in J and K filters revealed most of them as reddened stars, leaving 32 possible members. Among them, 15 have proper motion consistent with higher-mass members from Hipparcos and optical spectra with strong Hα in emission and weak gravity features. We have also extracted two lower-mass candidate members for which no optical spectra are in hand. Three members exhibit strong Hα equivalent widths (>20 Å), suggesting that they could still undergo accretion, whereas two other dwarfs show signs of chromospheric activity. The likelihood of the binarity of a couple of new stellar and substellar members is discussed as well.

Heavens, A. F.; Kitching, T. D.; Taylor, A. N.

doi: 10.1111/j.1365-2966.2006.11006.xpmid: N/A

We present parameter estimation forecasts for present and future 3D cosmic shear surveys. We demonstrate in particular that, in conjunction with results from cosmic microwave background (CMB) experiments, the properties of dark energy can be estimated with very high precision with large-scale, fully 3D weak-lensing surveys. In particular, a five-band, 10 000-deg2 ground-based survey of galaxies to a median redshift of zm= 0.7 could achieve 1σ marginal statistical errors, in combination with the constraints expected from the CMB Planck Surveyor, of Δw0= 0.108 and Δwa= 0.099. We parametrize the redshift evolution of w by w(a) =w0+wa(1 −a) where a is the scalefactor. Such a survey is achievable with a wide-field camera on a 4-m class telescope. The error on the value of w at an intermediate pivot redshift of z= 0.368 is constrained to Δw(z= 0.368) = 0.0175. We compare and combine the 3D weak-lensing constraints with the cosmological and dark energy parameters measured from planned baryon acoustic oscillation (BAO) and supernova Type Ia experiments, and find that 3D weak lensing significantly improves the marginalized errors on w0 and wa in combination, and provides constraints on w(z) at a unique redshift through the lensing effect. A combination of 3D weak-lensing, CMB and BAO experiments could achieve Δw0= 0.037 and Δwa= 0.099. We also show how our results can be scaled to other telescopes and survey designs. Fully 3D weak shear analysis avoids the loss of information inherent in tomographic binning, and we also show that the sensitivity to systematic errors in photometric redshift is much less. In conjunction with the fact that the physics of lensing is very soundly based, the analysis here demonstrates that deep, wide-angle 3D weak-lensing surveys are extremely promising for measuring dark energy properties.

Volonteri, Marta; Salvaterra, Ruben; Haardt, Francesco

doi: 10.1111/j.1365-2966.2006.10976.xpmid: N/A

We investigate how hierarchical models for the co-evolution of the massive black hole (MBH) and active galactic nucleus (AGN) population can reproduce the observed faint X-ray counts. We find that the main variable influencing the theoretical predictions is the Eddington ratio of accreting sources. We compare three different models proposed for the evolution of an AGN Eddington ratio, fEdd: constant fEdd= 1,  fEdd decreasing with redshift and fEdd depending on the AGN luminosity, as suggested by simulations of galactic mergers including MBHs and AGN feedback. We follow the full assembly of MBHs and host haloes from early times to the present in a Λ cold dark matter (ΛCDM) cosmology. An AGN activity is triggered by halo major mergers and MBH accrete mass until they satisfy the observed correlation with velocity dispersion. We find that all the three models can reproduce fairly well the total faint X-ray counts. The redshift distribution is, however, poorly matched in the first two models. The Eddington ratios suggested by merger simulations predict no turn-off of the faint end of the AGN optical luminosity function at redshifts z≳ 1, down to very low luminosity.