arXiv subjects

J. M. Vilchez

Publications and source records attributed to J. M. Vilchez.

At least 55 records · Page 3Linked to original sources

arXiv2014

CALIFA, the Calar Alto Legacy Integral Field Area survey. III. Second public data release

This paper describes the Second Public Data Release (DR2) of the Calar Alto Legacy Integral Field Area (CALIFA) survey. The data for 200 objects are made public, including the 100 galaxies of the First Public Data Release (DR1). Data were obtained with the integral-field spectrograph PMAS/PPak mounted on the 3.5 m telescope at the Calar Alto observatory. Two different spectral setups are available for each galaxy, (i) a low-resolution V500 setup covering the wavelength range 3745-7500 Å with a spectral resolution of 6.0 Å (FWHM), and (ii) a medium-resolution V1200 setup covering the wavelength range 3650-4840 Å with a spectral resolution of 2.3 Å (FWHM). The sample covers a redshift range between 0.005 and 0.03, with a wide range of properties in the Color-Magnitude diagram, stellar mass, ionization conditions, and morphological types. All released cubes were reduced with the latest pipeline, including improved spectrophotometric calibration, spatial registration and spatial resolution. The spectrophotometric calibration is better than 6% and the median spatial resolution is 2.5". Altogether the second data release contains over 1.5 million spectra. It is available at http://califa.caha.es/DR2.

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arXiv2014

Fossil Groups Origins III. Characterization of the sample and observational properties of fossil systems

(Abridged) Fossil systems are group- or cluster-sized objects whose luminosity is dominated by a very massive central galaxy. In the current cold dark matter scenario, these objects formed hierarchically at an early epoch of the Universe and then slowly evolved until present day. That is the reason why they are called {\it fossils}. We started an extensive observational program to characterize a sample of 34 fossil group candidates spanning a broad range of physical properties. Deep $r-$band images were taken for each candidate and optical spectroscopic observations were obtained for $\sim$ 1200 galaxies. This new dataset was completed with SDSS DR7 archival data to obtain robust cluster membership and global properties of each fossil group candidate. For each system, we recomputed the magnitude gaps between the two brightest galaxies ($Δm_{12}$) and the first and fourth ranked galaxies ($Δm_{14}$) within 0.5 $R_{\rm 200}$. We consider fossil systems those with $Δm_{12} \ge 2$ mag or $Δm_{14} \ge 2.5$ mag within the errors. We find that 15 candidates turned out to be fossil systems. Their observational properties agree with those of non-fossil systems. Both follow the same correlations, but fossils are always extreme cases. In particular, they host the brightest central galaxies and the fraction of total galaxy light enclosed in the central galaxy is larger in fossil than in non-fossil systems. Finally, we confirm the existence of genuine fossil clusters. Combining our results with others in the literature, we favor the merging scenario in which fossil systems formed due to mergers of $L^\ast$ galaxies. The large magnitude gap is a consequence of the extreme merger ratio within fossil systems and therefore it is an evolutionary effect. Moreover, we suggest that at least one candidate in our sample could represent a transitional fossil stage.

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arXiv2013

Star formation activity and gas stripping in the Cluster Projected Phase-Space (CPPS)

This work is focused on the study of the distribution in the CPPS of passive and star-forming galaxy populations and also, the intense and quiescent star-forming populations for a set of 9 nearby z<0.05 galaxy clusters. Furthermore, we compare the CPPS distribution of the passive galaxy population with the accreted halo population of a set of 28 simulated clusters and the star-forming population with the non-accreted population. We consider various cluster accretion epochs and accretion radii where it is assumed that star formation in galaxies becomes quenched, in order to segregate the accreted population from the non-accreted population. Just applying this segregation in simulations, we get a qualitative agreement between the CPPS distributions of the passive and the accreted populations and also between the star-forming and the non-accreted populations. The uncertainty in cluster centering strongly affects the pronounced cuspy profiles of the projected density and also, it can explain the main difference (i.e. inner slope) between the CPPS distribution of passive and accreted populations. The CPPS density of star-forming galaxies and the intensity of ram-pressure stripping present an opposite trend throughout the CPPS. This implies that ram-pressure stripping significantly contributes to modulate the observed CPPS distribution of star-forming galaxies inside and around cluster virial regions. The significant fraction of star-forming galaxies at the projected center of clusters are mainly those galaxies with low l-o-s velocities and they can be mainly identified as those galaxies with a remaining star formation activity (quiescent star-forming galaxies) inside the physical virial region or, in a lower degree, as galaxy interlopers i.e. outside the physical virial region.(abridged)

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arXiv2013

A characteristic oxygen abundance gradient in galaxy disks unveiled with CALIFA

We present the largest and most homogeneous catalog of HII regions and associations compiled so far. The catalog comprises more than 7000 ionized regions, extracted from 306 galaxies observed by the CALIFA survey. We describe the procedures used to detect, select, and analyse the spectroscopic properties of these ionized regions. In the current study we focus on the characterization of the radial gradient of the oxygen abundance in the ionized gas, based on the study of the deprojected distribution of HII regions. We found that all galaxies without clear evidence of an interaction present a common gradient in the oxygen abundance, with a characteristic slope of alpha = -0.1 dex/re between 0.3 and 2 disk effective radii, and a scatter compatible with random fluctuations around this value, when the gradient is normalized to the disk effective radius. The slope is independent of morphology, incidence of bars, absolute magnitude or mass. Only those galaxies with evidence of interactions and/or clear merging systems present a significant shallower gradient, consistent with previous results. The majority of the 94 galaxies with H ii regions detected beyond 2 disk effective radii present a flattening in the oxygen abundance. The flattening is statistically significant. We cannot provide with a conclusive answer regarding the origin of this flattening. However, our results indicate that its origin is most probably related to the secular evolution of galaxies. Finally, we find a drop/truncation of the oxygen abundance in the inner regions for 26 of the galaxies. All of them are non-interacting, mostly unbarred, Sb/Sbc galaxies. This feature is associated with a central star-forming ring, which suggests that both features are produced by radial gas flows induced by resonance processes.

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arXiv2013

Nebular emission and the Lyman continuum photon escape fraction in CALIFA early-type galaxies

We use deep integral field spectroscopy data from the CALIFA survey to study the warm interstellar medium (WIM) of 32 nearby early-type galaxies (ETGs). We propose a tentative subdivision of our sample ETGs into two groups, according to their Ha equivalent width (EW) and Lyman continuum (LyC) photon escape fraction (PLF). Type i ETGs show nearly constant EWs and a PLF~0, suggesting that photoionization by post-AGB stars is the main driver of their faint extranuclear nebular emission. Type ii ETGs are characterized by very low, outwardly increasing EWs, and a PLF as large as ~0.9 in their centers. Such properties point to a low, and inwardly decreasing WIM density and/or volume filling factor. We argue that, because of extensive LyC photon leakage, emission-line luminosities and EWs are reduced in type ii ETG nuclei by at least one order of magnitude. Consequently, the line weakness of these ETGs is by itself no compelling evidence for their containing merely "weak" (sub-Eddington accreting) active galactic nuclei (AGN). In fact, LyC photon escape, which has heretofore not been considered, may constitute a key element in understanding why many ETGs with prominent signatures of AGN activity in radio continuum and/or X-ray wavelengths show only faint emission lines and weak signatures of AGN activity in their optical spectra. The LyC photon escape, in conjunction with dilution of nuclear EWs by line-of-sight integration through a triaxial stellar host, can systematically impede detection of AGN in gas-poor galaxy spheroids through optical emission-line spectroscopy. We further find that type i and ii ETGs differ little (~0.4 dex) in their mean BPT line ratios, which in both cases are characteristic of LINERs. This potentially hints at a degeneracy of the projected, luminosity-weighted BPT ratios for the specific 3D properties of the WIM in ETGs. (abridged)

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arXiv2013

Uncovering multiple Wolf-Rayet star-clusters and the ionized ISM in Mrk178: the closest metal-poor Wolf-Rayet HII galaxy

New integral field spectroscopy (IFS) has been obtained for the nearby metal-poor WR galaxy Mrk178 to examine the spatial correlation between its WR stars and the neighbouring ionized ISM. The strength of the broad WR features and its low metallicity make Mrk178 an intriguing object. We have detected the blue and red WR bumps in different locations across the FOV (~ 300 pc x 230 pc) in Mrk178. The study of the WR content has been extended, for the first time, beyond its brightest star-forming knot uncovering new WR star-clusters. Using SMC/LMC-template WR stars we empirically estimate a minimum of ~ 20 WR stars within the region sampled. Maps of the spatial distribution of the emission-lines and of the physical-chemical properties of the ionized ISM have been created and analyzed. Here we refine the statistical methodology by Perez-Montero et al.(2011) to probe the presence of variations in the ISM properties. An error-weighted mean of 12+log(O/H)=7.72 +/- 0.01 is taken as the representative oxygen abundance for Mrk178. A localized N and He enrichment, spatially correlated with WR stars, is suggested by this analysis. Nebular HeII4686 emission is shown to be spatially extended reaching well beyond the location of the WR stars. This spatial offset between WRs and HeII emission can be explained based on the mechanical energy input into the ISM by the WR star winds, and does not rule out WR stars as the HeII ionization source. We study systematic aperture effects on the detection and measurement of the WR features, using SDSS spectra combined with the power of IFS. In this regard, the importance of targeting low metallicity nearby systems is discussed.

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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

The metallicity - redshift relations for emission-line SDSS galaxies: examination of the dependence on the star formation rate

We analyse the oxygen abundance and specific star formation rates (sSFR) variations with redshift in star-forming SDSS galaxies of different masses. We find that the maximum value of the sSFR, sSFRmax, decreases when the stellar mass, Ms, of a galaxy increases, and decreases with decreasing of redshift. The sSFRmax can exceed the time-averaged sSFR by about an order of magnitude for massive galaxies. The metallicity - redshift relations for subsamples of galaxies with sSFR = sSFRmax and with sSFR = 0.1sSFRmax coincide for massive (log(Ms/Mo) > 10.5, with stellar mass Ms in solar units) galaxies and differ for low-mass galaxies. This suggests that there is no correlation between oxygen abundance and sSFR in massive galaxies and that the oxygen abundance correlates with the sSFR in low-mass galaxies. We find evidence in favour of that the irregular galaxies show, on average, higher sSFR and lower oxygen abundances than the spiral galaxies of similar masses and that the mass - metallicity relation for spiral galaxies differs slightly from that for irregular galaxies. The fact that our sample of low-mass galaxies is the mixture of spiral and irregular galaxies can be responsible for the dependence of the metallicity - redshift relation on the sSFR observed for the low-mass SDSS galaxies. The mass - metallicity and luminosity - metallicity relations obtained for irregular SDSS galaxies agree with corresponding relations for nearby irregular galaxies with direct abundance determinations. We find that the aperture effect does not make a significant contribution to the redshift variation of oxygen abundances in SDSS galaxies.

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arXiv2013

HeI in the central Giant HII Region of NGC 5253. A 2D observational approach to collisional and radiative transfer effects

ABRIDGED: NGC5253 is an ideal laboratory for detailed studies of starburst galaxies. We present for the first time in a starburst galaxy a 2D study of the spatial behavior of collisional and radiative transfer effects in He^+. The HeI lines are analysed based on data obtained with FLAMES and GMOS. Collisional effects are negligible for transitions in the singlet cascade while relatively important for those in the triplet cascade. In particular, they can contribute up to 20% of the flux in the HeIl7065 line. Radiative transfer effects are important over an extended and circular area of 30pc in diameter centered at the Super Star Clusters. HeI abundance, y^+, has been mapped using extinction corrected fluxes of six HeI lines, realistic assumptions for T_e, n_e, and the stellar absorption equivalent width as well as the most recent emissivities. We found a mean of 10^3 y^+ ~80.3 over the mapped area. The relation between the excitation and the total helium abundance, y_tot, is consistent with no abundance gradient. Uncertainties in the derivation of He abundances are dominated by the adopted assumptions. We illustrated the difficulty of detecting a putative He enrichment due to the presence of Wolf-Rayet stars in the main GHIIR. Data are marginally consistent with an excess in the N/He ratio in the N enriched area of the order of both, the atmospheric N/He ratios in WR stars and the uncertainties estimated for the N/He ratios.

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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

HI asymmetry in the isolated galaxy CIG 85 (UGC 1547)

We present the results from the Giant Metrewave Radio Telescope (GMRT) interferometric HI and 20 cm radio continuum observations of CIG 85, an isolated asymmetric galaxy from the AMIGA (Analysis of the Interstellar Medium of Isolated GAlaxies) sample. Despite being an isolated galaxy, CIG 85 showed an appreciable optical and HI spectral asymmetry and therefore was an excellent candidate for resolved HI studies to understand the reasons giving rise to asymmetries in isolated galaxies. The galaxy was imaged in HI and 20 cm radio continuum using the GMRT. For a detailed discussion of the results we also made use of multi-wavelength data from archival SDSS, GALEX and Halpha imaging. We find the HI in CIG 85 to have a clumpy, asymmetric distribution which in the NW part is correlated with optical tail like features, but the HI velocity field displays a relatively regular rotation pattern. Evaluating all the observational evidence, we come to a conclusion that CIG 85 is most likely a case of a disturbed spiral galaxy which now appears to have the morphology of an irregular galaxy. Although it is currently isolated from major companions, the observational evidence is consistent with HI asymmetries, a highly disturbed optical disk and recent increase in star formation having been caused by a minor merger, remnants of which are now projected in front of the optical disk. If this is correct, the companion will be fully accreted by CIG 85 in the near future.

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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

Disentangling the role of environmental processes in galaxy clusters

In this work we present the results of a novel approach devoted to disentangle the role of the environmental processes affecting galaxies in clusters. This is based on the analysis of the NUV-r' distributions of a large sample of star-forming galaxies in clusters spanning more than four absolute magnitudes. The galaxies inhabit three distinct environmental regions: virial regions, cluster infall regions and field environment. We have applied rigorous statistical tests in order to analyze both, the complete NUV-r' distributions and their averages for three different bins of r'-band galaxy luminosity down to M_r' ~ -18, throughout the three environmental regions considered. We have identified the environmental processes that significantly affect the star-forming galaxies in a given luminosity bin by using criteria based on the characteristics of these processes: their typical time-scales, the regions where they operate and the galaxy luminosity range for which their effects are more intense. We have found that the high-luminosity (M_r'<=-20) star-forming galaxies do not show significant signs in their star formation activity neither of being affected by the environment in the last ~10^8 yr nor of a sudden quenching in the last 1.5 Gyr. The intermediate-luminosity (-20<M_r'<=-19) star-forming galaxies appear to be affected by starvation in the virial regions and by the harassment both, in the virial and infall regions. Low-luminosity (-19<M_r'<=-18.2) star-forming galaxies seem to be affected by the same environmental processes as intermediate-luminosity star-forming galaxies in a stronger way, as it would be expected for their lower luminosities.

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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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arXiv2012

UV to FIR catalogue of a galaxy sample in nearby clusters: SEDs and environmental trends

In this paper, we present a sample of cluster galaxies devoted to study the environmental influence on the star-formation activity. This sample of galaxies inhabits in clusters showing a rich variety in their characteristics and have been observed by the SDSS-DR6 down to M_B ~ -18 and by the GALEX AIS throughout sky regions corresponding to several megaparsecs. We assign the broad-band and emission-line fluxes from ultraviolet to far-infrared to each galaxy performing an accurate spectral energy distribution for spectral fitting analysis. The clusters follow the general X-ray luminosity vs. velocity dispersion trend of L_X/sigma_c^4.4. The analysis of the distributions of galaxy density counting up to the 5th nearest neighbor Sigma_5 shows: (1) the virial regions and the cluster outskirts share a common range in the high density part of the distribution. This can be attributed to the presence of massive galaxy structures in the surroundings of virial regions (2) The virial regions of massive clusters (sigma_c>550 km s^-1) present a Sigma_5 distribution statistically distinguishable (~96%) from the corresponding distribution of lowmass clusters (sigma_c<550 km s^-1). Both massive and low-mass clusters follow a similar density-radius trend, but the low-mass clusters avoid the high density extreme. We illustrate, with Abell 1185, the environmental trends of galaxy populations. Maps of sky projected galaxy density show how low-luminosity star-forming galaxies appear distributed along more spread structures than their giant counterparts, whereas low-luminosity passive galaxies avoid the low-density environment. Giant passive and star-forming galaxies share rather similar sky regions with passive galaxies exhibiting more concentrated distributions.

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arXiv2012

Abundance determination from global emission-line SDSS spectra: exploring objects with high N/O ratios

We have compared the oxygen and nitrogen abundances derived from global emission-line SDSS spectra of galaxies using (1) the Te method and (2) two recent strong line calibrations: the ON and NS calibrations. Using the Te method, anomously high N/O abundances ratios have been found in some SDSS galaxies. To investigate this, we have Monte Carlo simulated the global spectra of composite nebulae by a mix of spectra of individual components, based on spectra of well-studied HII regions in nearby galaxies. We found that the Te method results in an underestimated oxygen abundance (and hence in an overestimated nitrogen-to-oxygen ratio) if HII regions with different physical properties contribute to the global spectrum of composite nebulae. This effect is somewhat similar to the small-scale temperature fluctuations in HII regions discussed by Peimbert. Our work thus suggests that the high Te-based N/O abundances ratios found in SDSS galaxies may not be real. However, such an effect is not expected to be present in dwarf galaxies since they have generally an uniform chemical composition. The ON and NS calibrations give O and N abundances in composite nebulae which agree with the mean luminosity-weighted abundances of their components to within 0.2 dex.

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arXiv2011

Fossil groups origins II. Unveiling the formation of the brightest group galaxies through their scaling relations

(Abridged) Fossil systems are galaxy associations dominated by a relatively isolated, bright elliptical galaxy, surrounded by a group of smaller galaxies lacking L* objects. We analyzed the near-infrared photometric and structural properties of a sample of 20 BGGs present in FGs in order to better understand their formation mechanisms. Their surface-brightness distribution was fitted to a Sersic profile using the GASP2D algorithm. Then, the standard scaling relations were derived for the first time for these galaxies and compared with those of normal ellipticals and brightest cluster galaxies in non-fossil systems. The BGGs presented in this study represent a subset of the most massive galaxies in the Universe. We found that their ellipticity profiles are continuously increasing with the galactocentric radius. Our fossil BCGs follow closely the fundamental plane described by normal ellipticals. However, they depart from both the log σ_0 vs. log L_{K_{s}} and log r_{\rm e} vs. log L_{K_{s}} relations described by intermediate mass ellipticals. This occurs in the sense that our BGGs have larger effective radii and smaller velocity dispersions than those predicted by these relations. We also found that more elliptical galaxies systematically deviate from the previous relations while more rounder object do not. No similar correlation was found with the Sersic index. The derived scaling relations can be interpreted in terms of the formation scenario of the BGGs. Because our BGGs follow the fundamental plane tilt but they have larger effective radii than expected for intermediate mass ellipticals, we suggest that they only went through dissipational mergers in a early stage of their evolution and then assembled the bulk of their mass through subsequent dry mergers, contrary to previous claims that BGGs in FGs were formed mainly by the merging of gas-rich galaxies.

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arXiv2011

SDSS galaxies with double-peaked emission lines: double starbursts or AGNs?

With the aim of investigating galaxies with two strong simultaneous starbursts, we have extracted a sample of galaxies with double-peaked emission lines in their global spectra from the SDSS spectral database. We then fitted the emission lines Halpha, Hbeta, [OIII]5007, [NII]6584, [SII]6717 and [SII]6731 of 129 spectra by two Gaussians to separate the radiation of the two (blue and red) components. A more or less reliable decomposition of the all those emission lines have been found for 55 spectra. Using a standard BPT classification diagram, we have been able to divide the galaxies from our sample into two subsamples: Sample A consisting of 18 galaxies where both components belong to the photoionised class of objects, and Sample B containing 37 galaxies which show non-thermal ionisation (AGNs). We have examined the properties of the blue and red components, and found that the differences between radial velocities of components lie within 200 - 400 km/s for galaxies of both subsamples. The equivalent number of ionising stars is in the range 10^4 - 10^5 O7V stars for each component in the galaxies of Sample A. We have estimated the oxygen and nitrogen abundances as well as the electron temperatures for each component using the recent NS-calibration and from global spectra for galaxies from Sample A using both the NS and ON-calibration. We have found that the global oxygen abundance is typically in between the measured abundances of individual components for our sample of galaxies, and that both calibrations provide consistent global abundances. Finally, we suggest the classical O/H -- N/O diagram is used to test the reliability of the dividing lines between starburst-like objects and AGNs in the so-called BPT diagram.

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