arXiv subjects

R. Cid Fernandes

Publications and source records attributed to R. Cid Fernandes.

At least 73 records · Page 4Linked to original sources

arXiv2013

Resolving galaxies in time and space: II: Uncertainties in the spectral synthesis of datacubes

In a companion paper we have presented many products derived from the application of the spectral synthesis code STARLIGHT to datacubes from the CALIFA survey, including 2D maps of stellar population properties and 1D averages in the temporal and spatial dimensions. Here we evaluate the uncertainties in these products. Uncertainties due to noise and spectral shape calibration errors and to the synthesis method are investigated by means of a suite of simulations based on 1638 CALIFA spectra for NGC 2916, with perturbations amplitudes gauged in terms of the expected errors. A separate study was conducted to assess uncertainties related to the choice of evolutionary synthesis models. We compare results obtained with the Bruzual & Charlot models, a preliminary update of them, and a combination of spectra derived from the Granada and MILES models. About 100k CALIFA spectra are used in this comparison. Noise and shape-related errors at the level expected for CALIFA propagate to 0.10-0.15 dex uncertainties in stellar masses, mean ages and metallicities. Uncertainties in A_V increase from 0.06 mag in the case of random noise to 0.16 mag for shape errors. Higher order products such as SFHs are more uncertain, but still relatively stable. Due to the large number statistics of datacubes, spatial averaging reduces uncertainties while preserving information on the history and structure of stellar populations. Radial profiles of global properties, as well as SFHs averaged over different regions are much more stable than for individual spaxels. Uncertainties related to the choice of base models are larger than those associated with data and method. Differences in mean age, mass and metallicity are ~ 0.15 to 0.25 dex, and 0.1 mag in A_V. Spectral residuals are ~ 1% on average, but with systematic features of up to 4%. The origin of these features is discussed. (Abridged)

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arXiv2013

Resolving galaxies in time and space: I: Applying STARLIGHT to CALIFA data cubes

Fossil record methods based on spectral synthesis techniques have matured over the past decade, and their application to integrated galaxy spectra fostered substantial advances on the understanding of galaxies and their evolution. Yet, because of the lack of spatial resolution, these studies are limited to a global view, providing no information about the internal physics of galaxies. Motivated by the CALIFA survey, which is gathering Integral Field Spectroscopy over the full optical extent of 600 galaxies, we have developed an end-to-end pipeline which: (i) partitions the observed data cube into Voronoi zones in order to, when necessary and taking due account of correlated errors, increase the S/N, (ii) extracts spectra, including propagated errors and bad-pixel flags, (iii) feeds the spectra into the STARLIGHT spectral synthesis code, (iv) packs the results for all galaxy zones into a single file, (v) performs a series of post-processing operations, including zone-to-pixel image reconstruction and unpacking the spectral and stellar population properties into multi-dimensional time, metallicity, and spatial coordinates. This paper provides an illustrated description of this whole pipeline and its products. Using data for the nearby spiral NGC 2916 as a show case, we go through each of the steps involved, presenting ways of visualizing and analyzing this manifold. These include 2D maps of properties such as the v-field, stellar extinction, mean ages and metallicities, mass surface densities, star formation rates on different time scales and normalized in different ways, 1D averages in the temporal and spatial dimensions, projections of the stellar light and mass growth (x,y,t) cubes onto radius-age diagrams, etc. The results illustrate the richness of the combination of IFS data with spectral synthesis, providing a glimpse of what is to come from CALIFA and future surveys. (Abridged)

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arXiv2013

The Mass-Metallicity relation explored with CALIFA: I. Is there a dependence on the star formation rate?

We present the results on the study of the global and local M-Z relation based on the first data available from the CALIFA survey (150 galaxies). This survey provides integral field spectroscopy of the complete optical extent of each galaxy (up to 2-3 effective radii), with enough resolution to separate individual HII regions and/or aggregations. Nearly $\sim$3000 individual HII regions have been detected. The spectra cover the wavelength range between [OII]3727 and [SII]6731, with a sufficient signal-to-noise to derive the oxygen abundance and star-formation rate associated with each region. In addition, we have computed the integrated and spatially resolved stellar masses (and surface densities), based on SDSS photometric data. We explore the relations between the stellar mass, oxygen abundance and star-formation rate using this dataset. We derive a tight relation between the integrated stellar mass and the gas-phase abundance, with a dispersion smaller than the one already reported in the literature ($σ_{Δ{\rm log(O/H)}}=$0.07 dex). Indeed, this dispersion is only slightly larger than the typical error derived for our oxygen abundances. However, we do not find any secondary relation with the star-formation rate, other than the one induced due to the primary relation of this quantity with the stellar mass. We confirm the result using the $\sim$3000 individual HII regions, for the corresponding local relations. Our results agree with the scenario in which gas recycling in galaxies, both locally and globally, is much faster than other typical timescales, like that of gas accretion by inflow and/or metal loss due to outflows. In essence, late-type/disk dominated galaxies seem to be in a quasi-steady situation, with a behavior similar to the one expected from an instantaneous recycling/closed-box model.

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arXiv2013

CALIFA, the Calar Alto Legacy Integral Field Area survey. II. First public data release

We present the first public data release of the CALIFA survey. It consists of science-grade optical datacubes for the first 100 of eventually 600 nearby (0.005<z<0.03) galaxies, obtained with the integral-field spectrograph PMAS/PPak mounted on the 3.5m telescope at the Calar Alto observatory. The galaxies in DR1 already cover a wide range of properties in color-magnitude space, morphological type, stellar mass, and gas ionization conditions. This offers the potential to tackle a variety of open questions in galaxy evolution using spatially resolved spectroscopy. Two different spectral setups are available for each galaxy, (i) a low-resolution V500 setup covering the nominal wavelength range 3745-7500A with a spectral resolution of 6.0A (FWHM), and (ii) a medium-resolution V1200 setup covering the nominal wavelength range 3650-4840A with a spectral resolution of 2.3A (FWHM). We present the characteristics and data structure of the CALIFA datasets that should be taken into account for scientific exploitation of the data, in particular the effects of vignetting, bad pixels and spatially correlated noise. The data quality test for all 100 galaxies showed that we reach a median limiting continuum sensitivity of 1.0x10^-18erg/s/cm^2/A/arcsec^2 at 5635A and 2.2x10^-18erg/s/cm^2/A/arcsec^2 at 4500A for the V500 and V1200 setup respectively, which corresponds to limiting r and g band surface brightnesses of 23.6mag/arcsec^2 and 23.4mag/arcsec^2, or an unresolved emission-line flux detection limit of roughly 1x10^-17erg/s/cm^2/arcsec^2 and 0.6x10^-17erg/s/cm^2/arcsec^2, respectively. The median spatial resolution is 3.7", and the absolute spectrophotometric calibration is better than 15% (1sigma). We also describe the available interfaces and tools that allow easy access to this first public CALIFA data.

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arXiv2012

The central molecular gas structure in LINERs with low luminosity AGN: evidence for gradual disappearance of the torus

We present observations of the molecular gas in the nuclear environment of three prototypical low luminosity AGN (LLAGN), based on VLT/SINFONI AO-assisted integral-field spectroscopy of H2 1-0 S(1) emission at angular resolutions of ~0.17". On scales of 50-150 pc the spatial distribution and kinematics of the molecular gas are consistent with a rotating thin disk, where the ratio of rotation (V) to dispersion (sigma) exceeds unity. However, in the central 50 pc, the observations reveal a geometrically and optically thick structure of molecular gas (V/sigma<1 and N_H>10^{23} cm^{-2}) that is likely to be associated with the outer extent of any smaller scale obscuring structure. In contrast to Seyfert galaxies, the molecular gas in LLAGN has a V/sigma<1 over an area that is ~9 times smaller and column densities that are in average ~3 times smaller. We interpret these results as evidence for a gradual disappearance of the nuclear obscuring structure. While a disk wind may not be able to maintain a thick rotating structure at these luminosities, inflow of material into the nuclear region could provide sufficient energy to sustain it. In this context, LLAGN may represent the final phase of accretion in current theories of torus evolution. While the inflow rate is considerable during the Seyfert phase, it is slowly decreasing, and the collisional disk is gradually transitioning to become geometrically thin. Furthermore, the nuclear region of these LLAGN is dominated by intermediate-age/old stellar populations (with little or no on-going star formation), consistent with a late stage of evolution.

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arXiv2012

Integral field spectroscopy of a sample of nearby galaxies: II. Properties of the H ii regions

In this work we analyze the spectroscopic properties of a large number of H ii regions, \sim2600, located in 38 galaxies. The sample of galaxies has been assembled from the face-on spirals in the PINGS survey and a sample described in Mármol-Queraltó (2011, henceforth Paper I). All the galaxies were observed using Integral Field Spectroscopy with a similar setup, covering their optical extension up to \sim2.4 effective radii within a wavelength range from \sim3700 to \sim6900Å. We develop a new automatic procedure to detect H ii regions, based on the contrast of the Hα intensity maps. Once detected, the procedure provides us with the integrated spectra of each individual segmented region. A well-tested automatic decoupling procedure has been applied to remove the underlying stellar population, deriving the main proper- ties of the strongest emission lines in the considered wavelength range (covering from [O ii] λ3727 to [S ii] λ6731). A final catalogue of the spectroscopic properties of these regions has been created for each galaxy. In the current study we focused on the understanding of the average properties of the H ii regions and their radial distributions. We find that the gas-phase oxygen abundance and the Hα equivalent width present negative and positive gradient, respectively. The distribution of slopes is statistically compatible with a random Gaussian distribution around the mean value, if the radial distances are measured in units of the respective effective radius. No difference in the slope is found for galaxies of different morphologies: barred/non-barred, grand-design/flocculent. Therefore, the effective radius is a universal scale length for gradients in the evolution of galaxies. Other properties have a larger variance across each object.

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arXiv2012

Qualitative interpretation of galaxy spectra

We describe a simple step-by-step guide to qualitative interpretation of galaxy spectra. Rather than an alternative to existing automated tools, it is put forward as an instrument for quick-look analysis, and for gaining physical insight when interpreting the outputs provided by automated tools. Though the recipe is of general application, it was developed for understanding the nature of the Automatic Spectroscopic K-means based (ASK) template spectra. They resulted from the classification of all the galaxy spectra in the Sloan Digital Sky Survey data release 7 (SDSS-DR7), thus being a comprehensive representation of the galaxy spectra in the local universe. Using the recipe, we give a description of the properties of the gas and the stars that characterize the ASK classes, from those corresponding to passively evolving galaxies, to HII galaxies undergoing a galaxy-wide starburst. The qualitative analysis is found to be in excellent agreement with quantitative analyses of the same spectra. A number of byproducts follow from the analysis. There is a tight correlation between the age of the stellar population and the metallicity of the gas, which is stronger than the correlations between galaxy mass and stellar age, and galaxy mass and gas metallicity. The galaxy spectra are known to follow a 1-dimensional sequence, and we identify the luminosity-weighted mean stellar age as the affine parameter that describes the sequence. All ASK classes happen to have a significant fraction of old stars, although spectrum-wise they are outshined by the youngest populations. Old stars are metal rich or metal poor depending on whether they reside in passive galaxies or in star-forming galaxies.

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arXiv2012

The ionized gas in the CALIFA early-type galaxies I. Mapping two representative cases: NGC 6762 and NGC 5966

As part of the CALIFA survey, we conducted a thorough 2D analysis of the ionized gas in two E/S0 galaxies, NGC6762 and NGC5966, aiming to shed light on the nature of their warm ionized ISM. We present optical IFS obtained with the PMAS/PPAK spectrophotometer. To recover the nebular lines, we subtracted the underlying stellar continuum from the observed spectra using the STARLIGHT code. In NGC6762, the ionized gas and stellar emission display similar morphologies, while the emission line morphology is elongated in NGC5966, 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 NGC6762, the gas is kinematically decoupled from the stars in NGC5966. A decoupled rotating disk or an ionization cone are two possible interpretations of the elongated ionized gas structure in NGC5966. 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(Ha)< 3 A] and have low excitation, log([OIII]5007/Hb) < 0.5. Based on optical diagnostic ratios ([OIII]5007/Hb,[NII]6584/Ha,[SII]6717,6731/Ha,[OI]6300/Ha), 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 NGC6762 can be best explained by photoionization by pAGB stars without the need of invoking any other excitation mechanism. In the case of NGC5966, 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.(abridged)

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arXiv2010

A comprehensive classification of galaxies in the SDSS: How to tell true from fake AGN?

We use the W_Ha versus [NII]/Ha (WHAN) diagram to provide a comprehensive emission-line classification of SDSS galaxies. This classification is able to cope with the large population of weak line galaxies that do not appear in traditional diagrams due to a lack of some of the diagnostic lines. A further advantage of the WHAN diagram is to allow the differentiation between two very distinct classes that overlap in the LINER region of traditional diagnostic diagrams. These are galaxies hosting a weakly active nucleus (wAGN) and "retired galaxies" (RGs), i.e. galaxies that have stopped forming stars and are ionized by their hot evolved low-mass stars. A useful criterion to distinguish true from fake AGN (i.e. the RGs) is the ratio (ξ) of the extinction-corrected L_Ha with respect to the Ha luminosity expected from photoionization by stellar populations older than 100 Myr. This ratio follows a markedly bimodal distribution, with a ξ>> 1 population composed by systems undergoing star-formation and/or nuclear activity, and a peak at ξ~ 1 corresponding to the prediction of the RG model. We base our classification scheme on the equivalent width of Ha, an excellent observational proxy for ξ. Based on the bimodal distribution of W_Ha, we set the division between wAGN and RGs at W_Ha = 3 A. Five classes of galaxies are identified within the WHAN diagram: (a) Pure star forming galaxies: log [NII]/Ha < -0.4 and W_Ha > 3 A. (b) Strong AGN (i.e., Seyferts): log [NII]/Ha > -0.4 and W_Ha > 6 A. (c) Weak AGN: log [NII]/Ha > -0.4 and W_Ha between 3 and 6 A. (d) RGs: W_Ha < 3 A. (e) Passive galaxies (actually, line-less galaxies): W_Ha and W_[NII] < 0.5 A. A comparative analysis of star formation histories and of other properties in these different classes of galaxies corroborates our proposed differentiation between RGs and weak AGN in the LINER-like family. (Abridged)

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arXiv2010

Extreme Starbursts in the Local Universe

The "Extreme starbursts in the local universe" workshop was held at the Insituto de Astrofisica de Andalucia in Granada, Spain on 21-25 June 2010. Bearing in mind the advent of a new generation of facilities such as JWST, Herschel, ALMA, eVLA and eMerlin, the aim of the workshop was to bring together observers and theorists to review the latest results. The purpose of the workshop was to address the following issues: what are the main modes of triggering extreme starbursts in the local Universe? How efficiently are stars formed in extreme starbursts? What are the star formation histories of local starburst galaxies? How well do the theoretical simulations model the observations? What can we learn about starbursts in the distant Universe through studies of their local counterparts? How important is the role of extreme starbursts in the hierarchical assembly of galaxies? How are extreme starbursts related to the triggering of AGN in the nuclei of galaxies? Overall, 41 talks and 4 posters with their corresponding 10 minutes short talks were presented during the workshop. In addition, the workshop was designed with emphasis on discussions, and therefore, there were 6 discussion sessions of up to one hour during the workshop. Here is presented a summary of the purposes of the workshop as well as a compilation of the abstracts corresponding to each of the presentations. The summary and conclusions of the workshop along with a description of the future prospects by Sylvain Veilleux can be found in the last section of this document. A photo of the assistants is included.

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arXiv2010

The stellar populations of the AGN/Starburst galaxy NGC7582

NGC 7582 is defined as a Starburst/AGN galaxy, since its optical and X-Ray spectra reveal both characteristics. In this work, we show the results of a stellar population modeling in a datacube taken with the Gemini South telescope. We found that $\sim$ 90% of the light in the field of view is emitted by stars that are less than 1 billion years old. A strong burst occurred about $\sim$ 6 million years ago and has nearly solar metallicity. We also found a Wolf-Rayet cluster.

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arXiv2010

The AGN properties of the starburst galaxy NGC 7582

NGC 7582 was identified as a Starburst galaxy in the optical \cite[(Veron et al. 1981)]{Veron et al.(1981)} but its X-Ray emission is typical of a Seyfert 1 galaxy \cite[(Ward et al. 1978)]{Ward et al.(1978)}. We analyzed a datacube of this object obtained with the GMOS-IFU on the Gemini-South telescope. After a subtraction of the stellar component using the {\sc starlight} code \cite[(Cid Fernandes et al. 2005)]{Cid Fernandes et al. (2005)}, we looked for optical signatures of the AGN. We detected a broad $Hα$ component (figure \ref{fig1}) in the source where \cite[Bianchi et al.(2007)]{Bianchi et al.(2007)} identified the AGN in an HST optical image. We also found a broad $Hβ$ feature (figure \ref{fig2}), but its emission reveals a extended source. We suggest that it is the light of the AGN scattered in the ionization cone. We propose that NGC 7582 is a Seyfert 1 galaxy. A number of other "hot-spots" and Wolf-Rayet features were also identified.

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arXiv2010

Beware of fake AGNs

In the BPT diagram, the distribution of the emission-line galaxies from the Sloan Digital Sky Survey (SDSS) evokes the wings of a seagull. Traditionally, galaxies in the right wing are considered to host AGNs. Our study of the stellar populations of SDSS galaxies showed that about1/4 of galaxies thought to host LINERS are in fact "retired galaxies", i.e. galaxies that stopped forming stars and are ionized by hot post-AGB stars and white dwarfs (Stasinska et al. 2008). When including the galaxies that lack some of the lines needed to place them in the BPT diagram the fraction of retired galaxies is even larger (Cid Fernandes et al., 2009, arXiv:0912.1376)

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arXiv2009

Alternative diagnostic diagrams and the "forgotten" population of weak line galaxies in the SDSS

A numerous population of weak line galaxies (WLGs) is often left out of statistical studies on emission line galaxies (ELGs) due to the absence of an adequate classification scheme, since classical diagnostic diagrams, like [OIII]/Hb vs [NII]/Ha (the BPT diagram), require the measurement of at least 4 emission lines. This paper aims to remedy this situation by transposing the usual divisory lines between Star Forming (SF) and AGN hosts, and between Seyferts and LINERs to diagrams that are more economical in terms of line quality requirements. By doing this, we rescue from the classification limbo a substantial number of sources and modify the global census of ELGs. More specifically: (1) We use the SDSS DR7 to constitute a suitable sample of 280k ELGs, 1/3 of which are WLGs. (2) Galaxies with strong emission lines are classified using the widely applied criteria of Kewley et al (2001), Kauffmann et al (2003), Stasinska et al (2006) and Kewley et al (2006). (3) We transpose these classification schemes to alternative diagrams keeping [NII]/Ha as a horizontal axis, but replacing Hb by a stronger line (Ha or [OII]), or substituting [OIII]/Hb ratio with the equivalent width of Ha. Optimized equations for the transposed divisory lines are provided. (4) We show that nothing significant is lost in the translation, but that the new diagrams allow one to classify up to 50% more ELGs. (5) Introducing WLGs in the census of galaxies in the local Universe increases the proportion of metal-rich SF galaxies and especially LINERs. (abridged)

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arXiv2009

What stellar populations can tell us about the evolution of the mass-metallicity relation in SDSS galaxies

During the last three decades, many papers have reported the existence of a luminosity-metallicity or mass-metallicity (M-Z) relation for all kinds of galaxies: The more massive galaxies are also the ones with more metal-rich interstellar medium. We have obtained the mass-metallicity relation at different lookback times for the same set of galaxies from the Sloan Digital Sky Survey (SDSS), using the stellar metallicities estimated with our spectral synthesis code STARLIGHT. Using stellar metallicities has several advantages: We are free of the biases that affect the calibration of nebular metallicities; we can include in our study objects for which the nebular metallicity cannot be measured, such as AGN hosts and passive galaxies; we can probe metallicities at different epochs of a galaxy evolution. We have found that the M-Z relation steepens and spans a wider range in both mass and metallicity at higher redshifts for SDSS galaxies. We also have modeled the time evolution of stellar metallicity with a closed-box chemical evolution model, for galaxies of different types and masses. Our results suggest that the M-Z relation for galaxies with present-day stellar masses down to 10^10 solar masses is mainly driven by the star formation history and not by inflows or outflows.

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arXiv2009

The star formation histories of fossil group galaxies

A comparison is carried out among the star formation histories of early-type galaxies (ETG) in fossil groups, clusters and low density environments. Although they show similar evolutionary histories, a significant fraction of the fossils are younger than their counterparts, suggesting that fossils can be precursors of the isolated ETGs.

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arXiv2009

On the nature of the near-UV extended light in Seyfert galaxies

We study the nature of the extended near-UV emission in the inner kiloparsec of a sample of 15 Seyfert galaxies which have both near-UV (F330W) and narrow band [OIII] high resolution Hubble images. For the majority of the objects we find a very similar morphology in both bands. From the [OIII] images we construct synthetic images of the nebular continuum plus the emission line contribution expected through the F330W filter, which can be subtracted from the F330W images. We find that the emission of the ionised gas dominates the near-UV extended emission in half of the objects. A further broad band photometric study, in the bands F330W (U), F547M (V) and F160W (H), shows that the remaining emission is dominated by the underlying galactic bulge contribution. We also find a blue component whose nature is not clear in 4 out of 15 objects. This component may be attributed to scattered light from the AGN, to a young stellar population in unresolved star clusters, or to early-disrupted clusters. Star forming regions and/or bright off-nuclear star clusters are observed in 4/15 galaxies of the sample.

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arXiv2009

An analysis of the composite stellar population in M32

We obtained long-slit spectra of high signal-to-noise ratio of the galaxy M32 with the GMOS spectrograph at the GEMINI North telescope. We analysed the integrated spectra by means of full spectral fitting in order to extract the mixture of stellar populations that best represents its composite nature. Three different galactic radii were analysed, from the nuclear region out to 2 arcmin from the centre. This allows us to compare, for the first time, the results of integrated light spectroscopy with those of resolved colour-magnitude diagrams from the literature. As our main result, we propose that an ancient and an intermediate-age population coexist in M32, and that the balance between these two populations change between the nucleus and outside 1 effective radius in the sense that the contribution from the intermediate population is larger at the nuclear region. We retrieve a smaller signal of a young population at all radii whose origin is unclear and may be a contamination from horizontal-branch stars, such as the ones identified by Brown et al. in the nuclear region. We compare our metallicity distribution function for a region 1 to 2 arcmin from the centre to the one obtained with photometric data by Grillmair et al. Both distributions are broad, but our spectroscopically derived distribution has a significant component with $[Z/Z_{\sun}] \leq -1$, which is not found by Grillmair et al.

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