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Appleton P.N.,NASA | Guillard P.,CNRS Paris Institute of Astrophysics | Togi A.,University of Toledo | Alatalo K.,Carnegie Institution for Science | And 7 more authors.
Astrophysical Journal | Year: 2017

We map for the first time the two-dimensional H2 excitation of warm intergalactic gas in Stephan's Quintet on group-wide (50 × 35 kpc2) scales to quantify the temperature, mass, and warm H2 mass fraction as a function of position using Spitzer. Molecular gas temperatures are seen to rise (to T > 700 K) and the slope of the power-law density-temperature relation flattens along the main ridge of the filament, defining the region of maximum heating. We also performed MHD modeling of the excitation properties of the warm gas, to map the velocity structure and energy deposition rate of slow and fast molecular shocks. Slow magnetic shocks were required to explain the power radiated from the lowest-lying rotational states of H2, and strongly support the idea that energy cascades down to small scales and low velocities from the fast collision of NGC 7318b with group-wide gas. The highest levels of heating of the warm H2 are strongly correlated with the large-scale stirring of the medium as measured by [C ii] spectroscopy with Herschel. H2 is also seen associated with a separate bridge that extends toward the Seyfert nucleus in NGC 7319, from both Spitzer and CARMA CO observations. This opens up the possibility that both galaxy collisions and outflows from active galactic nuclei can turbulently heat gas on large scales in compact groups. The observations provide a laboratory for studying the effects of turbulent energy dissipation on group-wide scales, which may provide clues about the heating and cooling of gas at high z in early galaxy and protogalaxy formation. © 2017. The American Astronomical Society. All rights reserved.

Lisenfeld U.,University of Granada | Lisenfeld U.,Instituto Carlos I Of Fisica Teorica Y Computacional | Braine J.,French National Center for Scientific Research | Duc P.A.,University Paris Diderot | And 7 more authors.
Astronomy and Astrophysics | Year: 2016

The physical mechanisms driving star formation (SF) in galaxies are still not fully understood. Tidal dwarf galaxies (TDGs), made of gas ejected during galaxy interactions, seem to be devoid of dark matter and have a near-solar metallicity. The latter makes it possible to study molecular gas and its link to SF using standard tracers (CO, dust) in a peculiar environment. We present a detailed study of a nearby TDG in the Virgo Cluster, VCC 2062, using new high-resolution CO(1-0) data from the Plateau de Bure, deep optical imaging from the Next Generation Virgo Cluster Survey (NGVS), and complementary multiwavelength data. Until now, there was some doubt whether VCC 2062 was a true TDG, but the new deep optical images from the NGVS reveal a stellar bridge between VCC 2062 and its parent galaxy, NGC 4694, which is clear proof of its tidal origin. Several high-resolution tracers (Hα, UV, 8 μm, and 24 μm) of the star formation rate (SFR) are compared to the molecular gas distribution as traced by the CO(1-0). Coupled with the SFR tracers, the NGVS data are used with the CIGALE code to model the stellar populations throughout VCC 2062, yielding a declining SFR in the recent past, consistent with the low Hα/UV ratio, and a high burst strength. HI emission covers VCC 2062, whereas the CO is concentrated near the HI maxima. The CO peaks correspond to two very distinct regions: one with moderate SF to the NE and one with only slightly weaker CO emission but with nearly no SF. Even where SF is clearly present, the SFR is below the value expected from the surface density of the molecular and the total gas as compared to spiral galaxies and other TDGs. After discussing different possible explanations, we conclude that the low surface brightness is a crucial parameter to understand the low SFR. © 2016 ESO.

Zurita A.,University of Granada | Zurita A.,Instituto Carlos I Of Fisica Teorica Y Computacional | Bresolin F.,Institute for Astronomy
Monthly Notices of the Royal Astronomical Society | Year: 2012

We have obtained multislit spectroscopic observations from 3700 to 9200Å with Low Resolution Imaging Spectrometer at the Keck I telescope for 31 Hii regions in the disc of the Andromeda galaxy (M31), spanning a range in galactocentric distance from 3.9 to 16.1kpc. In nine Hii regions we measure one or several auroral lines ([Oiii] λ4363, [Nii] λ5755, [Siii] λ6312, [Oii] λ7325) from which we determine the electron temperature (T e) of the gas and derive chemical abundances using the direct T e-based method. We analyse, for the first time in M31, abundance trends with galactocentric radius from the direct method, and find that the Ne/O, Ar/O, N/O and S/O abundance ratios are consistent with a constant value across the M31 disc, while the O/H abundance ratio shows a weak gradient. We have combined our data with all spectroscopic observations of Hii regions in M31 available in the literature, yielding a sample of 85 Hii regions spanning distances from 3.9 to 24.7kpc (0.19-1.2R 25) from the galaxy centre. We have tested a number of empirical calibrations of strong emission line ratios. We find that the slope of the oxygen abundance gradient in M31 is -0.023 ± 0.002dexkpc -1, and that the central oxygen abundance is in the range 12+log(O/H) 8.71-8.91dex (i.e. between 1.05 and 1.66 times the solar value, for 12+log(O/H) ⊙ = 8.69), depending on the calibration adopted. The Hii region oxygen abundances are compared with the results from other metallicity indicators (supergiant stars and planetary nebulae). The comparison shows that Hii region O/H abundances are systematically ∼0.3dex below the stellar ones. This discrepancy is discussed in terms of oxygen depletion on to dust grains and possible biases affecting T e-based oxygen abundances at high metallicity. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.

Nagy A.,Debrecen University | Romera E.,Instituto Carlos I Of Fisica Teorica Y Computacional
Chemical Physics Letters | Year: 2010

A relationship between three measures of Fisher information constructed from generalized pair density functions is presented. A connection to the kinetic energy is emphasized and illustrated by the Moshinsky model. © 2010 Elsevier B.V. All rights reserved.

Moglia B.,National University of La Plata | Albano E.V.,National University of La Plata | Villegas P.,Instituto Carlos I Of Fisica Teorica Y Computacional | Munoz M.A.,Instituto Carlos I Of Fisica Teorica Y Computacional
Journal of Statistical Mechanics: Theory and Experiment | Year: 2014

Interfaces advancing through random media represent a number of different problems in physics, biology and other disciplines. Here, we study the pinning/depinning transition of the prototypical non-equilibrium interfacial model, i.e. the Kardar-Parisi-Zhang equation, advancing in a disordered medium. We will separately analyze the cases of positive and negative nonlinearity coefficients, which are believed to exhibit qualitatively different behavior: the positive case shows a continuous transition that can be related to directed-percolation-depinning, while in the negative case there is a discontinuous transition and faceted interfaces appear. Some studies have argued from different perspectives that both cases share the same universal behavior. By using a number of computational and scaling techniques we will shed light on this puzzling situation and conclude that the two cases are intrinsically different. © 2014 IOP Publishing Ltd.

Florido E.,University of Granada | Florido E.,Instituto Carlos I Of Fisica Teorica Y Computacional | Zurita A.,University of Granada | Zurita A.,Instituto Carlos I Of Fisica Teorica Y Computacional | And 5 more authors.
Astronomy and Astrophysics | Year: 2015

Context. Bar-induced gas inflows towards galaxy centres are recognised as a key agent for the secular evolution of galaxies. One immediate consequence of this inflow is the accumulation of gas in the centre of galaxies where it can form stars and alter the chemical and physical properties. Aims. Our aim is to study whether the properties of the ionised gas in the central parts of barred galaxies are altered by the presence of a bar and whether the change in central properties is related to bar and/or parent galaxy properties. Methods. We use a sample of nearby face-on disc galaxies with available SDSS spectra, morphological decomposition, and information on the stellar population of their bulges, to measure the internal Balmer extinction from the Hα to Hβ line ratio, star formation rate, and relevant line ratios to diagnose chemical abundances and gas density. Results. The distributions of all the parameters analysed (internal Balmer extinction at Hβ (c(Hβ)), star formation rate per unit area, electron density, [N ii]λ6583/Hα emission-line ratio, ionisation parameter, and nitrogen-to-oxygen (N/O) abundance ratio) are different for barred and unbarred galaxies, except for the R23 metallicity tracer and the oxygen abundance obtained from photoionisation models. The median values of the distributions of these parameters point towards (marginally) larger dust content, star formation rate per unit area, electron density, and ionisation parameter in the centres of barred galaxies than in their unbarred counterparts. The most remarkable difference between barred and unbarred galaxies appears in the [N ii]λ6583/Hα line ratio that is, on average, 25% higher in barred galaxies, due to an increased N/O abundance ratio in the centres of these galaxies compared to the unbarred ones. We analyse these differences as a function of galaxy morphological type (as traced by bulge-to-disc light ratios and bulge mass), total stellar mass, and bulge Sérsic index. We observe an enhancement of the differences between central gas properties in barred and unbarred galaxies in later-type galaxies or galaxies with less massive bulges. However, the bar seems to have a lower impact on the central gas properties for galaxies with bulges above 1010 M or total mass M1010.8 M. Conclusions. We find observational evidence that the presence of a galactic bar affects the properties of the ionised gas in the central parts of disc galaxies (radii 0.6-2.1 kpc). The most striking effect is an enhancement in the N/O abundance ratio. This can be interpreted qualitatively in terms of our current knowledge of bar formation and evolution, and of chemical evolution models, as being the result of a different star formation history in the centres of barred galaxies caused by the gas inflow induced by the bar. Our results lend support to the scenario in which less massive and more massive bulges have different origins or evolutionary processes, with the gaseous phase of the former currently having a closer relation to the bars. © ESO, 2015.

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