Publications (9)0 Total impact
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Article: The ionized gas in the CALIFA early-type galaxies I. Mapping two representative cases: NGC 6762 and NGC 5966
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ABSTRACT: As part of the ongoing CALIFA survey, we have conducted a thorough bidimensional analysis of the ionized gas in two E/S0 galaxies, NGC 6762 and NGC 5966, aiming to shed light on the nature of their warm ionized ISM. Specifically, we present optical (3745-7300 Å) integral field spectroscopy obtained with the PMAS/PPAK integral field spectrophotometer. Its wide field-of-view (1 ′ x 1 ′) covers the entire optical extent of each galaxy down to faint continuum surface brightnesses. To recover the nebular lines, we modeled and subtracted the underlying stellar continuum from the observed spectra using the STARLIGHT spectral synthesis code. The pure emission-line spectra were used to investigate the gas properties and determine the possible sources of ionization. We show the advantages of IFU data in interpreting the complex nature of the ionized gas in NGC 6762 and NGC 5966. In NGC 6762, the ionized gas and stellar emission display similar morphologies, while the emission line morphology is elongated in NGC 5966, spanning ∼ 6 kpc, and is oriented roughly orthogonal to the major axis of the stellar continuum ellipsoid. Whereas gas and stars are kinematically aligned in NGC 6762, the gas is kinematically decoupled from the stars in NGC 5966. A decoupled rotating disk or an "ionization cone" are two possible interpretations of the elongated ionized gas structure in NGC 5966. The latter would be the first "ionization cone" of such a dimension detected within a weak emission-line galaxy. Both galaxies have weak emission-lines relative to the continuum [EW(Hα) 3 Å] and have very low excitation, log([Oiii]λ5007/Hβ) 0.5. Based on optical diagnostic ratios ([Oiii]λ5007/Hβ, [Nii]λ6584/Hα, [Sii]λ6717,6731/Hα, [Oi]λ6300/Hα), both objects contain a LINER nucleus and an extended LINER-like gas emission. The emission line ratios do not vary significantly with radius or aperture, which indicates that the nebular properties are spatially homogeneous. The gas emission in NGC 6762 can be best explained by photoionization by pAGB stars without the need of invoking any other excitation mechanism. In the case of NGC 5966, the presence of a nuclear ionizing source seems to be required to shape the elongated gas emission feature in the "ionization cone" scenario, although ionization by pAGB stars cannot be ruled out. Further study of this object is needed to clarify the nature of its elongated gas structure.03/2012; -
Article: Bar pattern speed evolution over the last 7 Gyr
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ABSTRACT: The tumbling pattern of a bar is the main parameter characterising its dynamics. From numerical simulations, its evolution since bar formation is tightly linked to the dark halo in which the bar is formed through dynamical friction and angular momentum exchange. Observational measurements of the bar pattern speed with redshift can restrict models of galaxy formation and bar evolution. We aim to determine, for the first time, the bar pattern speed evolution with redshift based on morphological measurements. We have selected a sample of 44 low inclination ringed galaxies from the SDSS and COSMOS surveys covering the redshift range 0 <z< 0.8 to investigate the evolution of the bar pattern speed. We have derived morphological ratios between the deprojected outer ring radius (R_{ring}) and the bar size (R_{bar}). This quantity is related to the parameter {\cal R}=R_{CR}/R_{bar} used for classifiying bars in slow and fast rotators, and allow us to investigate possible differences with redshift. We obtain a similar distribution of $R$ at all redshifts. We do not find any systematic effect that could be forcing this result. The results obtained here are compatible with both, the bulk of the bar population (~70%) being fast-rotators and no evolution of the pattern speed with redshift. We argue that if bars are long-lasting structures, the results presented here imply that there has not been a substantial angular momentum exchange between the bar and halo, as predicted by numerical simulations. In consequence, this might imply that the discs of these high surface-brightness galaxies are maximal.02/2012; -
Article: CALIFA, the Calar Alto Legacy Integral Field Area survey: I. Survey presentation
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ABSTRACT: We present here the Calar Alto Legacy Integral Field Area (CALIFA) survey, which has been designed to provide a first step in this direction.We summarize the survey goals and design, including sample selection and observational strategy.We also showcase the data taken during the first observing runs (June/July 2010) and outline the reduction pipeline, quality control schemes and general characteristics of the reduced data. This survey is obtaining spatially resolved spectroscopic information of a diameter selected sample of $\sim600$ galaxies in the Local Universe (0.005< z <0.03). CALIFA has been designed to allow the building of two-dimensional maps of the following quantities: (a) stellar populations: ages and metallicities; (b) ionized gas: distribution, excitation mechanism and chemical abundances; and (c) kinematic properties: both from stellar and ionized gas components. CALIFA uses the PPAK Integral Field Unit (IFU), with a hexagonal field-of-view of $\sim1.3\sq\arcmin'$, with a 100% covering factor by adopting a three-pointing dithering scheme. The optical wavelength range is covered from 3700 to 7000 {\AA}, using two overlapping setups (V500 and V1200), with different resolutions: R\sim850 and R\sim1650, respectively. CALIFA is a legacy survey, intended for the community. The reduced data will be released, once the quality has been guaranteed. The analyzed data fulfill the expectations of the original observing proposal, on the basis of a set of quality checks and exploratory analysis. We conclude from this first look at the data that CALIFA will be an important resource for archaeological studies of galaxies in the Local Universe.11/2011; -
Article: Multiwavelength study of the star formation in the bar of NGC 2903
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ABSTRACT: NGC 2903 is a nearby barred spiral with an active starburst in the center and Hii regions distributed along its bar. We aim to analyse the star formation properties in the bar region of NGC 2903 and study the links with the typical bar morphological features. A combination of space and ground-based data from the far-ultraviolet to the sub-millimeter spectral ranges is used to create a panchromatic view of the NGC 2903 bar. We produce two catalogues: one for the current star formation regions, as traced by the halpha compact emission, and a second one for the ultraviolet (UV) emitting knots, containing positions and luminosities. From them we have obtained ultraviolet colours, star formation rates, dust attenuation and halpha EWs, and their spatial distribution have been analysed. Stellar cluster ages have been estimated using stellar population synthesis models (Starburst99). NGC 2903 is a complex galaxy, with a very different morphology on each spectral band. The CO(J=1-0) and the 3.6 micron emission trace each other in a clear barred structure, while the halpha leads both components and it has an s-shape distribution. The UV emission is patchy and does not resemble a bar. The UV emission is also characterised by a number of regions located symmetrically with respect to the galaxy center, almost perpendicular to the bar, in a spiral shape covering the inner ~2.5 kpc. These regions do not show a significant halpha nor 24 micron emission. We have estimated ages for these regions ranging from 150 to 320 Myr, being older than the rest of the UV knots, which have ages lower than 10 Myr. The SFR calculated from the UV emission is ~0.4 M$_{\odot}$/yr, compatible with the SFR as derived from halpha calibrations (M$_{\odot}$/yr). Comment: Accepted for publication in A&A04/2010; -
Article: Deriving the pattern speed using dynamical modelling of gas flows in barred galaxies
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ABSTRACT: In this paper we analyse the methodology to derive the bar pattern speed from dynamical simulations. The results are robust to the changes in the vertical-scale height and in the mass-to-light (M/L) ratios. There is a small range of parameters for which the kinematics can be fitted. We have also taken into account the use of different type of dynamical modelling and the effect of using 2-D vs 1-D models in deriving the pattern speeds. We conclude that the derivation of the bar streaming motions and strength and position of shocks is not greatly affected by the fluid dynamical model used. We show new results on the derivation of the pattern speed for NGC 1530. The best fit pattern speed is around 10 km/s/kpc, which corresponds to a R_cor/R_bar = 1.4, implying a slower bar than previously derived from more indirect assumptions. With this pattern speed, the global and most local kinematic features are beautifully reproduced. However, the simulations fail to reproduce the velocity gradients close to some bright HII regions in the bar. We have shown from the study of the Halpha equivalent widths that the HII regions that are located further away from the bar dust-lane in its leading side, downstream from the main bar dust-lane, are older than the rest by 1.5-2.5 Myr. In addition, a clear spatial correlation was found between the location of HII regions, dust spurs on the trailing side of the bar dust-lane, and the loci of maximum velocity gradients parallel to the bar major axis. Comment: 6 pages, 2 figures. To appear in "Tumbling, twisting, and winding galaxies: Pattern speeds along the Hubble sequence", E. M. Corsini and V. P. Debattista (eds.), Memorie della Societa` Astronomica Italiana02/2010; -
Article: Study of the stellar line-strength indices and kinematics along bars
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ABSTRACT: This is the first paper of a series aimed to understand the formation and evolution of bars in early-type spirals and their influence in the evolution of the galaxy. Optical long-slit spectra along the major axis of the bar of a sample of 20 galaxies are analyzed. Line-strength indices in the bar region are measured to derive stellar mean-age and metallicity distributions along the bars using stellar population models. We find three different types of bars according to their metallicity and age distribution along the radius: 1) Bars with negative metallicity gradients. They show mean young/intermediate population (< 2 Gyr), and have amongst the lowest stellar maximum central velocity dispersion of the sample. 2) Bars with null metallicity gradients. These galaxies tend to have negative age gradients. 3) Bars with positive metallicity gradients. These galaxies are predominantly those with higher velocity dispersion and older mean population. We found no significant correlation between the age and metallicity distribution, and bar/galaxy parameters such as the AGN presence, size or the bar strength. From the kinematics, we find that all the galaxies show a disk-like central component. The results from the metallicity and age gradients indicate that most galaxies with high central stellar velocity dispersion host bars that could have been formed more than 3 Gyrs ago, while galaxies with lower central velocity dispersions show a wider distribution in their population and age gradients. A few bars show characteristics compatible with having been formed less than <2 Gy ago. These results place strong constrains to models of bar formation and evolution. The disk-like central components also show the important role played by bars in the secular evolution of the central structure.01/2009; -
Article: Where are the massive stars of the bar of NGC 1530 forming?
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ABSTRACT: Aims: NGC 1530 has one of the strongest bars ever observed and recent star formation sites are distributed across its bar. Our aim is to study the photometric properties of the bar and its HII regions, to elucidate the conditions under which HII regions form and their spatial relation to the principal dynamical features of the bar. Methods: We obtained BVRKs and Halpha photometry of the HII regions of the bar in NGC 1530. Broad-band integrated colours and Halpha equivalent widths were carefully measured and analysed as a function of position with respect to the main dust-lanes of the bar. Results: We measured differences in the Halpha equivalent widths of the HII regions that are located in the trailing and leading sides of the bar dust-lane. The possible factors that could produce this difference, such as [NII] contamination, Lyman-continuum-photon dust-extinction, escape of ionizing radiation, metallicity, IMF and age, were carefully analysed. Age differences were confirmed to be the most plausible explanation. This implies that HII regions that are located further away from the bar dust-lane in its leading side, downstream from the main bar dust-lane, are older than the rest by ~1.5-2.5 Myr. In addition, a clear spatial correlation has been found between: location of HII regions, dust spurs on the trailing side of the bar dust-lane, and the loci of maximum velocity gradients parallel to the bar major axis (possibly tracing gas flow towards the main bar dust-lane). These results support the hypothesis that massive stars are forming on the trailing side of the bar dust-lane, and age as they cross the bar, on a timescale that is compatible with the bar dynamics timescale. Comment: Accepted for publication in A&A. 17 pages. 11 figures. Full resolution version available here: http://www.ugr.es/~azurita/investigacion/papers/zurita_perez_08.ps.gz04/2008; -
Article: New light on the formation and evolution of bars: Trends in the stellar line-strength indices distribution inside the bar region
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ABSTRACT: Aim: The aim is to study the stellar content of the bar region to constrain its formation and evolution. Methods: Line-strength indices in the bar region of a sample of 6 barred galaxies were employed to derive age and metallicity gradients along the bars using stellar population models. Results: We find clear radial gradients in the line-strength indices for all the galaxies. We find positive gradients within the bar region in the metal indices in four of the six galaxies, and opposite trends in the other two. These latter two galaxies are classified as SAB and they present exponential bar light profiles. For all the galaxies we find a positive gradient in the Balmer indices. There is a clear correlation between the position of morphological features inside the bar region with changes in the slope and value of the indices, which indicate, using stellar population analysis, changes in the stellar populations. Therefore, it seems that the bar regions show a gradient in both age and metallicity, changing radially to younger and more metal rich populations for all the galaxies except for those two with exponential profiles. Comment: 4 pages, accepted for publication in Astronomy & Astrophysics Letters12/2006; -
Article: The origin of the hot metal-poor gas in NGC1291: Testing the hypothesis of gas dynamics as the cause of the gas heating
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ABSTRACT: In this paper we test the idea that the low-metallicity hot gas in the centre of NGC 1291 is heated via a dynamical process. In this scenario, the gas from the outer gas-rich ring loses energy through bar-driven shocks and falls to the centre. Heating of the gas to X-ray temperatures comes from the high velocity that it reaches ($\approx$ 700 \kms) as it falls to the bottom of the potential well. This would explain why the stellar metallicity in the bulge region is around solar while the hot gas metallicity is around 0.1 solar. We carried out an observational test to check this hypothesis by measuring the metallicity of HII regions in the outer ring to check whether they matched the hot gas metallicity. For this purpose we obtained medium resolution long slit spectroscopy with FORS1 on the ESO VLT at Paranal and obtained the metallicities using emission line ratio diagnostics. The obtained metallicities are compatible with the bulge stellar metallicities but very different from the hot-gas metallicity. However, when comparing the different time-scales, the gas in the ring had time enough to get enriched through stellar processes, therefore we cannot rule out the dynamical mechanism as the heating process of the gas. However, the blue colours of the outer ring and the dust structures in the bar region could suggest that the origin of the X-ray hot gas is due to the infall of material from further out. Comment: 6 pages, 6 figures. A&A accepted04/2006;
Top co-authors
Institutions
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2012
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University of Granada
- Instituto Carlos I de Física Teórica y Computacional
Granada, Andalusia, Spain
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2009
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University of Groningen
Groningen, Province of Groningen, Netherlands
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