Relation between source and temperature fluctuations in photoionized nebulae

The magnitude of the temperature fluctuations (t^2) required to explain the observed inconsistencies between metallicities inferred from recombination lines and from forbidden lines cannot be attained by steady-state equilibrium photoionization models. If on the other hand the nebular ionizing source was variable, the temperature fluctuations t^2 would be significantly larger. We investigate the time-dependent response of the nebular ionization and temperature structure when photoionized by a periodically varying source. We study how the asymptotic mean value, , behaves as a function of the period or amplitude of the source variability. We find that the temperature fluctuations occur only in the outer section of the nebula, close to the ionization front, within a zone corresponding to 8-20% of the ionized layer's thickness. We conclude that the amplitude of the exciting star variations required to achieve a = 0.025 (as in the Orion nebula) is unacceptably large. Source variability is therefore not a viable mechanism to explain the observed values of t^2. We reach a similar conclusion from studies of the temporal variability resulting from intermittent shadows behind opaque condensations. We find that photoionized nebulae are on average less massive but somewhat hotter in the case of cyclicly variable ionizing sources.Comment: 15 pages, 6 figures, submitted to Revista Mexicana de Astronomia y Astrofisica, revised versio

A two-arm gaseous spiral in the inner 200 pc of the early-type galaxy NGC 2974: signature of an inner bar

TIGER integral-field spectrography and HST/WFPC2 imaging of the E3 galaxy NGC 2974 are used to derive the kinematics of the stellar and ionized gas components in its central 500 pc. We derive a numerical two-integral distribution function from a MGE mass model using the HQ formalism. The TIGER as well as published long-slit stellar kinematics are well fitted with this self-consistent model, requiring neither the addition of a significant mass contribution from a hidden disc structure, nor the presence of a central dark mass. The data reveal the presence of a striking, highly contrasted, two-arm gaseous spiral structure within a radius of ~200 pc, corresponding to a total mass of 6.8x10^4 Msun of ionized gas. We use a deconvolved TIGER datacube to probe its kinematics at a resolution of about 0.35 arcsec. Strong departures from circular motions are observed, as well as high velocity dispersion values on the inner side of the arms. We interpret the observed gas morphology and kinematics as the signature of streaming gas flows driven by a ~540 pc diameter bar with Ome=700+/-100 km/s/kpc. This hypothesis is strongly supported by the predictions of a density wave model. This model predicts that the bar should lie at about 35 degree from the line of nodes, and implies gas inflow towards the central ~50 pc. The quadrupole pertubation due to this bar is estimated to represent less than 2% of the underlying gravitational potential. Despite its weakness, the inner bar of NGC 2974 may be able to drive some gas within a 10 pc radius. We suggest that the presence of such inner bars might be more common among early-type disk galaxies than is generally thought, and that deep high-resolution emission-line imagery may be the best way to detect such structures.Comment: 17 pages, 21 figures. MNRAS in press. Full resolution paper at http://www-obs.univ-lyon1.fr/eric.emsellem/papers/n2974.ps.g

Gas and stellar dynamics in NGC 1068. Probing the galactic gravitational potential

We present Sauron 2D spectrography of the central 1.5 kpc of the nearby Sey2 galaxy NGC1068, encompassing the well-known NIR inner bar. We have successively disentangled the respective contributions of the ionized gas and stars, thus deriving their 2D distribution and kinematics. The [OIII] and Hbeta emission lines exhibit very different spatial distribution and kinematics, the latter following inner spiral arms with clumps associated with star formation. Strong inwards streaming motions are observed in both the Hbeta and [OIII] kinematics. The stellar kinematics also exhibit clear signatures of a non-axisymmetric tumbling potential, with a twist in both the velocity and h3 fields. We re-examined the long-slit data of Shapiro et al (2003) using pPXF: a strong decoupling of h3 is revealed, and the central decrease in h4 hinted in the Sauron data is confirmed. These data also suggest that NGC1068 is a good candidate for a so-called sigma-drop. We confirm the possible presence of two pattern speeds. We also examine the stellar kinematics of bars formed in N-body+SPH simulations built from axisymmetric initial conditions. These successfully reproduce a number of properties observed in the 2D kinematics of NGC1068, and the long-slit data, showing that the kinematic signature of the NIR bar is imprinted in the stellar kinematics. The remaining differences between the models and the observed properties are mostly due to the exclusion of star formation and the lack of the primary large-scale oval/bar in the simulations. These models suggest that the inner bar could drive a significant amount of gas down to a scale of ~300 pc. This is consistent with the interpretation of the sigma-drop in NGC1068 being the result of central gas accretion followed by an episode of star formation.Comment: accepted for publication in MNRAS, 20 pages, 17 figures (high res version available at www-obs.univ-lyon1.fr/eric.emsellem/preprints/NGC1068_Emsellemetal_final.pdf

\u3cem\u3eHubble Space Telescope\u3c/em\u3e/Faint Object Spectrograph Spectroscopy of Spatially Resolved Narrow-Line Regions in the Seyfert 2 Galaxies NGC 2110 and NGC 5929

We present the results of UV and optical Hubble Space Telescope/Faint Object Spectrograph spectroscopy of bright, extranuclear regions of line emission in the Seyfert galaxies NGC 2110 and NGC 5929. We have obtained spectra of the brightest region of the ``nuclear jet\u27\u27 of NGC 2110 (75 pc from the nucleus) and of the southwest emission-line cloud of NGC 5929 (90 pc from the nucleus), in the G130H (1090-1605 Å), G190H (1570-2310 Å), G400H (3235-4780 Å), and G570H (4570-6820 Å) configurations. The observed line ratios are compared with the predictions of the two component (matter- and ionization-bounded, MB-IB), central source photoionization models of Binette, Wilson, {\amp} Storchi-Bergmann and of the fast, photoionizing (``autoionizing\u27\u27) shock models of Dopita {\amp} Sutherland. In both objects, the significant reddening inferred from the Balmer line ratios and/or its uncertainty limit the utility of the ultraviolet carbon lines C IV λ1549 and C III] λ1909 for discrimination between the central source and shock-induced photoionization mechanisms. In NGC 2110, shock+precursor models with a shock velocity of ~=400 km s-1 provide a better match to the data than the MB-IB models. However, given the simplifying assumptions made in the latter models, photoionization by a central source cannot be ruled out. We investigate whether photoionizing shocks in the emission-line region of NGC 2110 can power the extended, soft X-ray emission north of the nucleus and find that shock velocities higher than 500 km s-1 are required. In NGC 5929, the MB-IB models have problems reproducing the strengths of the neon lines, while shock+precursor models with a velocity ~=300 km s-1 provide a good match to the data. For both galaxies, the emission-line powers and volumes of the ionized gas inferred from observations imply that both the preshock density (n0) and magnetic parameter (B0/n1/20) must be relatively high (n0\u3e10 cm-3 B0/n1/20~=4 μG cm3/2) for the photoionizing shock models to be viable. Based on observations with the NASA/ESA Hubble Space Telescope obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555

Solar System Observations with the James Webb Space Telescope

The James Webb Space Telescope will enable a wealth of new scientific investigations in the near- and mid-infrared, with sensitivity and spatial/spectral resolution greatly surpassing its predecessors. In this paper, we focus upon Solar System science facilitated by JWST, discussing the most current information available concerning JWST instrument properties and observing techniques relevant to planetary science. We also present numerous example observing scenarios for a wide variety of Solar System targets to illustrate the potential of JWST science to the Solar System community. This paper updates and supersedes the Solar System white paper published by the JWST Project in 2010 (Lunine et al., 2010). It is based both on that paper and on a workshop held at the annual meeting of the Division for Planetary Sciences in Reno, NV in 2012.Comment: 52 pages (with figures), 32 figures; More information about JWST Solar System observations is available at http://www.stsci.edu/jwst/science/solar-syste

Solar System Observations with JWST

The James Webb Space Telescope will enable a wealth of new scientific investigations in the near- and mid- infrared, with sensitivity and spatial-spectral resolution greatly surpassing its predecessors. In this paper, we focus upon Solar System science facilitated by JWST, discussing the most current information available concerning JWST instrument properties and observing techniques relevant to planetary science. We also present numerous example observing scenarios for a wide variety of Solar System targets to illustrate the potential of JWST science to the Solar System community. This paper updates and supersedes the Solar System white paper published by the JWST Project in 2010 (Lunine et al., 2010). It is based both on that paper and on a workshop held at the annual meeting of the Division for Planetary Sciences in Reno, NV in 2012

Spatial Resolution of High-Velocity Filaments in the Narrow-Line Region of NGC 1068: Associated Absorbers Caught in Emission?

Using the HST STIS spectrograph we have obtained a grid of [O III] and H-beta emission-line spectra at 0"05x0"19 and 60 km/s (FWHM) resolution that covers much of the NLR of NGC 1068. We find emitting knots that have blueshifted radial velocities up to 3200 km/s relative to galaxy systemic, are 70-150 pc NE of the nucleus and up to 40 pc from the radio jet, emit several percent of the NLR line flux but no significant continuum, span velocity extents of up to 1250 km/s but a small fraction of the sky seen from the nucleus, coincide with a region of enhanced IR coronal-line emission, and have ionized masses $\sim$200 Msun/ne4 (ne4=10^4 cm^{-3}). We argue that the blueshifted knots are ablata from disintegrating molecular clouds that are being photoionized by the AGN, and are being accelerated readiatively by the AGN or mechanically by the radio jet. In their kinematic properties, the knots resemble the associated absorbers seen projected on the UV continua of some AGN. Between 2"5-4"5 from the nucleus, emission is redshifted relative to systemic, a pattern that we interpret as gas in the galaxy disk being pushed away from us by the NE radio lobe.Comment: 13 pages LaTeX w/ convenient embedded EPS figs, scheduled for ApJ April 1/0

JWST/NIRSpec Prospects on Transneptunian Objects

The transneptunian region has proven to be a valuable probe to test models of the formation and evolution of the solar system. To further advance our current knowledge of these early stages requires an increased knowledge of the physical properties of Transneptunian Objects (TNOs). Colors and albedos have been the best way so far to classify and study the surface properties of a large number TNOs. However, they only provide a limited fraction of the compositional information, required for understanding the physical and chemical processes to which these objects have been exposed since their formation. This can be better achieved by near-infrared (NIR) spectroscopy, since water ice, hydrocarbons, and nitrile compounds display diagnostic absorption bands in this wavelength range. Visible and NIR spectra taken from ground-based facilities have been observed for ~80 objects so far, covering the full range of spectral types: from neutral to extremely red with respect to the Sun, featureless to volatile-bearing and volatile-dominated (Barkume et al., 2008; Guilbert et al., 2009; Barucci et al., 2011; Brown, 2012). The largest TNOs are bright and thus allow for detailed and reliable spectroscopy: they exhibit complex surface compositions, including water ice, methane, ammonia, and nitrogen. Smaller objects are more difficult to observe even from the largest telescopes in the world. In order to further constrain the inventory of volatiles and organics in the solar system, and understand the physical and chemical evolution of these bodies, high-quality NIR spectra of a larger sample of TNOs need to be observed. JWST/NIRSpec is expected to provide a substantial improvement in this regard, by increasing both the quality of observed spectra and the number of observed objects. In this paper, we review the current knowledge of TNO properties and provide diagnostics for using NIRSpec to constrain TNO surface compositions