9424089
Constraints on the nuclear emission of the Circinus galaxy: the torus
In the context of the unified model of Seyfert galaxies, we use observations from the literature and a radiative transfer model to investigate the near–IR to mm emission produced by the presumed torus in the Circinus galaxy, from 2µm to 1.3mm. From the infrared SED modelling, we find that the total luminosity (LIR) in this wavelength range, consists of similar contributions from the torus and starburst with a ratio of nuclear luminosity to starburst luminosity (LNUC/LSB) � 0.8. By using a similar torus model to that of NGC1068, but without the conical dust, we find an upper limit to the outer torus radius of �12pc with a best fit of �2pc. The upper limit torus size estimated from the radiative transfer modelling is consistent with the 16pc torus radius estimated from near–IR imaging polarimetry of Circinus.
14396422
Nuclear Properties of Nearby Spiral Galaxies from Hubble Space Telescope NICMOS Imaging and STIS Spectroscopy
We investigate the central regions of 23 spiral galaxies using Space Telescope Imaging Spectrograph (STIS) spectroscopy and archival Near-Infrared Camera and Multi-Object Spectrometer (NICMOS) imaging. The sample is taken from our program to determine the masses of central massive black holes (MBHs) in 54 nearby spiral galaxies. Stars are likely to contribute significantly to any dynamical central mass concentration that we find in our MBH program, and this paper is part of a series to investigate the nuclear properties of these galaxies. We use the Nuker law to fit surface brightness profiles, derived from the NICMOS images, to look for nuclear star clusters and find possible extended sources in three of the 23 galaxies studied (13%). The fact that this fraction is lower than that inferred from optical Hubble Space Telescope studies is probably due to the greater spatial resolution of those studies. Using R - H and J - H colors and equivalent widths of Hα emission (from the STIS spectra), we investigate the nature of the stellar population with evolutionary models. Under the assumption of hot stars ionizing the gas, as opposed to a weak active galactic nucleus (AGN), we find that there are young stellar populations (~10–20 Myr); however, these data do not allow us to determine what percentage of the total nuclear stellar population they form. In addition, in an attempt to find any unknown AGN, we use [N II] and [S II] line flux ratios (relative to Hα) and find tentative evidence for weak AGNs in NGC 1300 and NGC 4536.
10731094
The sub-stellar birth rate from UKIDSS
We present a new sample of mid L to mid T dwarfs with effective temperatures of 1100 to 1700 K selected from the UKIDSS Large Area Survey and confirmed with infrared spectra from X-Shooter/VLT. This effective temperature range is especially sensitive to the formation history of Galactic brown dwarfs and allows us to constrain the form of the sub-stellar birth rate, with sensitivity to differentiate between a flat (stellar like) birth rate, and an exponentially declining form. We present the discovery of 63 new L and T dwarfs from the UKIDSS LAS DR7, including the identification of 12 likely unresolved binaries, which form the first complete sub-set from our program, covering 495 sq degrees of sky, complete to J=18.1. We compare our results for this sub-sample with simulations of differing birth rates for objects of mass 0.10-0.03M⊙ and ages 1-10Gyrs. We find that the more extreme birth rates (e.g. a halo type form) can likely be excluded as the true form of the birth rate. In addition we find that although there is substantial scatter we find a preference for a mass function, with a power-law index, α in the range 1 < α < 0 that is consistent (within the errors) with the studies of late T dwarfs.
119416594
PMN J1838−3427: A New Gravitationally Lensed Quasar*
We report the discovery of a new double-image quasar that was found during a search for gravitational lenses in the southern sky. Radio source PMN J1838-3427 is composed of two flat-spectrum components with separation I″.0, flux density ratio 14:1, and matching spectral indices in VLA and VLBA images. Ground-based BRI images show the optical counterpart (total I = 18.6) is also double, with the same separation and position angle as the radio components. An HST/WFPC2 image reveals the lens galaxy. The optical flux ratio (27:1) is higher than the radio value, probably because of differential extinction of the components by the lens galaxy. An optical spectrum of the bright component contains quasar emission lines at z = 2.78 and several absorption features, including prominent Lyα absorption. The lens galaxy redshift could not be measured, but it is estimated to be z = 0.36 ± 0.08. The image configuration is consistent with the simplest plausible models for the lens potential. The flat radio spectrum and observed variability of PMN J1838 - 3427 suggest that the time delay between flux variations of the components is measurable and could thus provide an independent measurement of H 0 .
117103440
FAINT EMISSION LINES IN PLANETARY NEBULAE WITH A [WC] NUCLEUS
Resumen en: We present first results from the analysis of a sample of 14 planetary nebulae with [WC] nucleus with detected faint carbon and oxygen recombination line...
53683483
Global and local expansion of magnetic clouds in the inner heliosphere
Context. Observations of magnetic clouds (MCs) are consistent with the presence of flux ropes detected in the solar wind (SW) a few days after their expulsion from the Sun as coronal mass ejections (CMEs). Aims. Both the in situ observations of plasma velocity profiles and the increase of their size with solar distance show that MCs are typically expanding structures. The aim of this work is to derive the expansion properties of MCs in the inner heliosphere from 0.3 to 1A U. Methods. We analyze MCs observed by the two Helios spacecraft using in situ magnetic field and velocity measurements. We split the sample in two subsets: those MCs with a velocity profile that is significantly perturbed from the expected linear profile and those that are not. From the slope of the in situ measured bulk velocity along the Sun-Earth direction, we compute an expansion speed with respect to the cloud center for each of the analyzed MCs. Results. We analyze how the expansion speed depends on the MC size, the translation velocity, and the heliocentric distance, finding that all MCs in the subset of non-perturbed MCs expand with almost the same non-dimensional expansion rate (ζ). We find departures from this general rule for ζ only for perturbed MCs, and we interpret the departures as the consequence of a local and strong SW perturbation by SW fast streams, affecting the MC even inside its interior, in addition to the direct interaction region between the SW and the MC. We also compute the dependence of the mean total SW pressure on the solar distance and we confirm that the decrease of the total SW pressure with distance is the main origin of the observed MC expansion rate. We found that ζ was 0.91 ± 0.23 for non-perturbed MCs while ζ was 0.48 ± 0.79 for perturbed MCs, the larger spread in the last ones being due to the influence of the solar wind local environment conditions on the expansion.
16730805
Chemical abundances of the Galactic H II region NGC 3576 derived from VLT echelle spectrophotometry
We present echelle spectrophotometry of the Galactic H II region NGC 3576. The data have been taken with the VLT UVES echelle spectrograph in the 3100 to 10400 angstroms range. We have measured the intensities of 458 emission lines, 344 are permitted lines of H0, He0, C+, N0, N+, N++, O0, O+, Ne+, S++, Si0, Si+, Ar0 and Ar+; some of them are produced by recombination and others mainly by fluorescence. Electron temperatures and densities have been determined using different continuum and line intensity ratios. We have derived He+, C++, O+, O++ and Ne++ ionic abundances from pure recombination lines. We have also derived abundances from collisionally excited lines for a large number of ions of different elements. Remarkably consistent estimations of t2 have been obtained by comparing Balmer and Paschen to [O III] temperatures, and O++ and Ne++ ionic abundances obtained from collisionally excited and recombination lines. The chemical composition of NGC 3576 is compared with those of other Galactic H II regions and with the one from the Sun. A first approach to the gas-phase Galactic radial abundance gradient of C as well as of the C/O ratio has been made.