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33 results, page 1 of 4

Aperture corrections for disk galaxy properties derived from the CALIFA survey: Balmer emission lines in spiral galaxies

Fernando Fabián Rosales Ortega (2013)

This work investigates the effect of the aperture size on derived galaxy properties for which we have spatially-resolved optical spectra.We focus on some indicators of star formation activity and dust attenuation for spiral galaxies that have been widely used in previous work on galaxy evolution. We investigated 104 spiral galaxies from the CALIFA survey for which 2D spectroscopy with complete spatial coverage is available. From the 3D cubes we derived growth curves of the most conspicuous Balmer emission lines (Hα, Hβ) for circular apertures of different radii centered at the galaxy’s nucleus after removing the underlying stellar continuum. We find that the Hα flux ( f (Hα)) growth curve follows a well-defined sequence with aperture radius that shows a low dispersion around the median value. From this analysis, we derived aperture corrections for galaxies in different magnitude and redshift intervals. Once stellar absorption is properly accounted for, the f (Hα)/ f (Hβ) ratio growth curve shows a smooth decline, pointing toward the absence of differential dust attenuation as a function of radius. Aperture corrections as a function of the radius are provided in the interval [0.3, 2.5]R₅₀. Finally, the Hα equivalent-width (EW(Hα)) growth curve increases with the size of the aperture and shows a very high dispersion for small apertures. This prevents us from using reliable aperture corrections for this quantity. In addition, this result suggests that separating star-forming and quiescent galaxies based on observed EW(Hα) through small apertures will probably result in low EW(Hα) star-forming galaxies begin classified as quiescent.



A massive bubble of extremely metal-poor gas around a collapsing Lyα blob at z = 2.54

Andrew Humphrey Itziar Aretxaga (2013)

Using long-slit optical spectroscopy obtained at the 10.4 m Gran Telescopio Canarias, we have examined the gaseous environment of the radio-loud quasar TXS 1436+157 (z = 2.54),previously known to be associated with a large Lyαnebula and a spatially extended Lyα-absorbing structure. From the Lyαnebula, we measure kinematic properties consistent withinfall at a rate of ∼10–100 M⊙ yr⁻¹ – more than sufficient to power a quasar at the top of theluminosity function.The absorbing structure lies outside of the Lyαnebula, at a radius of ≳40 kpc from thequasar. Against the bright unresolved continuum and line emission from the quasar, we detectin absorption the NVλλ1239, 1241, CIVλλ1548, 1551 and Si IVλλ1394, 1403 doublets, withno unambiguous detection of absorption lines from any low-ionization species of metal. Themetal column densities, taken together with the HI column density measurement from the literature, indicate that the absorbing gas is predominantly ionized by the quasar, has a massof hydrogen of ≳1.6 × 10¹¹ M⊙, a gas density of ≤18 cm⁻³, a line-of-sight thickness of≥18 pc and a covering factor approaching unity. While this absorbing structure is clearly notcomposed of pristine gas, it has an extremely low metallicity, with ionizationmodels providinga 3σ limit of 12+log(O/H) ≤ 7.3.To explain these results, we discuss a scenario involving starburst-driven superbubbles andthe creation of infalling filaments of cold gas which fuel/trigger the quasar. We also discussthe possibility of detecting large-scale absorbers such as this in emission when illuminated bya powerful quasar.


Galaxies: active Galaxies: evolution Galaxies: ISM Quasars: absorption lines Qasars: emission lines Quasars: individual: TXS 1436+157 CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA ASTRONOMÍA Y ASTROFÍSICA ASTRONOMÍA Y ASTROFÍSICA

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

Fernando Fabián Rosales Ortega (2013)

We studied 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 a resolution high enough to separate individual HII regions and/or aggregations. About 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 ratio to derive the oxygen abundance and star-formation rate associated with each region. In addition, we 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 lower than the one already reported in the literature (σ∆log(o/H) = 0.07 dex). Indeed, this dispersion is only slightly higher than the typical error derived for our oxygen abundances. However, we found no secondary relation with the star-formation rate other than the one induced by the primary relation of this quantity with the stellar mass. The analysis for our sample of ~3000 individual HII regions confirms (i) a local mass-metallicity relation and (ii) the lack of a secondary relation with the star-formation rate. The same analysis was performed with similar results for the specific star-formation rate. Our results agree with the scenario in which gas recycling in galaxies, both locally and globally, is much faster than other typical timescales, such 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.


Galaxy: abundances Galaxies: ISM Galaxies: fundamental parameters Galaxies: spiral Galaxies: structure Galaxies: evolution CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA ASTRONOMÍA Y ASTROFÍSICA ASTRONOMÍA Y ASTROFÍSICA

Discovery of x-ray emission from young suns in the small magellanic cloud


We report the discovery of extended X-ray emission within the young star cluster NGC602a in the Wing of the Small Magellanic Cloud (SMC) based on observations obtained with the Chandra X-ray Observatory. X-ray emission is detected from the cluster core area with the highest stellar density and from a dusty ridge surrounding the HII region. We use a census of massive stars in the cluster to demonstrate that a cluster wind or wind-blown bubble is unlikely to provide a significant contribution to the X-ray emission detected from the central area of the cluster. We therefore suggest that X-ray emission at the cluster core originates from an ensemble of low- and solar-mass pre-main-sequence (PMS) stars, each of which would be too weak in X-rays to be detected individually. We attribute the X-ray emission from the dusty ridge to the embedded tight cluster of the new-born stars known in this area from infrared studies. Assuming that the levels of X-ray activity in young stars in the low-metallicity environment of NGC 602a are comparable to their Galactic counterparts, then the detected spatial distribution, spectral properties, and level of X-ray emission are largely consistent with those expected from low- and solar-mass PMS stars and young stellar objects (YSOs). This is the first discovery of X-ray emission attributable to PMS stars and YSOs in the SMC, which suggests that the accretion and dynamo processes in young, low-mass objects in the SMC resemble those in the Galaxy.


Magellanic Clouds ISM: bubbles HII regions Stars: winds, outflows Stars: pre-main sequence X-rays: stars CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA ASTRONOMÍA Y ASTROFÍSICA ASTRONOMÍA Y ASTROFÍSICA

The O3N2 and N2 abundance indicators revisited: improved calibrations based on CALIFA and Te-based literature data*,**

Fernando Fabián Rosales Ortega (2013)

The use of integral field spectroscopy is since recently allowing to measure the emission line fluxes of an increasingly large number of star-forming galaxies, both locally and at high redshift. Many studies have used these fluxes to derive the gas-phase metallicity of the galaxies by applying the so-called strong-line methods. However, the metallicity indicators that these datasets use were empirically calibrated using few direct abundance data points (Te-based measurements). Furthermore, a precise determination of the prediction intervals of these indicators is commonly lacking in these calibrations. Such limitations might lead to systematic errors in determining the gas-phase metallicity, especially at high redshift, which might have a strong impact on our understanding of the chemical evolution of the Universe. The main goal of this study is to review the most widely used empirical oxygen calibrations, O3N2 and N2, by using new direct abundance measurements. We pay special attention to (1) the expected uncertainty of these calibrations as a function of the index value or abundance derived and (2) the presence of possible systematic offsets. This is possible thanks to the analysis of the most ambitious compilation of Te-based HII regions to date. This new dataset compiles the Te-based abundances of 603 HII regions extracted from the literature but also includes new measurements from the CALIFA survey. Besides providing new and improved empirical calibrations for the gas abundance, we also present a comparison between our revisited calibrations with a total of 3423 additional CALIFA HII complexes with abundances derived using the ONS calibration from the literature. The combined analysis of Te-based and ONS abundances allows us to derive their most accurate calibration to date for both the O3N2 and N2 singleratio indicators, in terms of all statistical significance, quality, and coverage of the parameters space. In particular, we infer that these indicators show shallower abundance dependencies and statistically significant offsets compared to others’. The O3N2 and N2 indicators can be empirically applied to derive oxygen abundances calibrations from either direct abundance determinations with random errors of 0.18 and 0.16, respectively, or from indirect ones (but based on a large amount of data), reaching an average precision of 0.08 and 0.09 dex (random) and 0.02 and 0.08 dex (systematic; compared to the direct estimations), respectively.



CHARACTERIZATION OF A SAMPLE OF INTERMEDIATE-TYPE AGN. I. Spectroscopic properties and serendipitous discovery of new Dual AGN

Vahram Chavushyan (2012)

A sample of 10 nearby intermediate-type active galactic nuclei (AGN) drawn from the Sloan Digital Sky Survey (SDSS-DR7) is presented. The aim of this work is to provide estimations of the black hole mass for the sample galaxies from the dynamics of the broad line region. For this purpose, a detailed spectroscopic analysis of the objects was done. Using BPT diagnostic diagrams we have carefully classified the objects as true intermediate-type AGN and found that 80%⁺⁷˙²%₋₁₇̣ ̣₃% are composite AGN. The black hole mass estimated for the sample is within 6.54±0.16< log MBH <7.81±0.14.Profile analysis show that five objects (J120655.63+501737.1, J121607.08+504930.0, J141238.14+391836.5, J143031.18+524225.8 and J162952.88+242638.3) have narrow double-peaked emission lines in both the red (Hα, [N II]λλ6548,6583 and [S II]λλ6716,6731) and the blue (Hβ and [O III]λλ4959,5007) region of the spectra,with velocity differences (ΔV) between the double peaks within 114 <ΔV <256km s⁻¹. Two of them, J121607.08+504930.0 and J141238.14+391836.5 are candidates for dual AGN since their double-peaked emission lines are dominated by AGN activity. In searches of dual AGN; Type 1, Type 1I and intermediate-type AGN shouldbe carefully separated, due to the high serendipitous number of narrow double-peaked sources (50%±14.4%) found in our sample.




Carlos del Burgo Díaz (2013)

Infrared excesses associated with debris disk host stars detected so far, peak at wavelengths around ~100 μm or shorter. However, six out of 31 excess sources studied in the Herschl ͣ Open Time Key Programme, DUNES, have been seen to show significant – and in some cases extended – excess emission at 160 μm, which is larger than the 100 μm excess. This excess emission has been attributed to circumstellar dust and has been suggested to stem from debris disks colder than those known previously. Since the excess emission of the cold disk candidates is extremely weak, challenging even the unrivaled sensitivity of Herschel, it is prudent to carefully consider whether some or even all of them may represent unrelated galactic or extragalactic emission, or even instrumental noise. We readdress these issues using several distinct methods and conclude that it is highly unlikely that none of the candidates represents a true circumstellar disk. For true disks, both the dust temperatures inferred from the spectral energy distributions and the disk radii estimated from the images suggest that the dust is nearly as cold as a blackbody. This requires the grains to be larger than ~100 μm, even if they are rich in ices or are composed of any other material with a low absorption in the visible. The dearth of small grains is puzzling, since collisional models of debris disks predict that grains of all sizes down to several times the radiation pressure blowout limit should be present. We explore several conceivable scenarios: transport-dominated disks, disks of low dynamical excitation, and disks of unstirred primordial macroscopic grains. Our qualitative analysis and collisional simulations rule out the first two of these scenarios, but show the feasibility of the third one. We show thatsuch disks can indeed survive for gigayears, largely preserving the primordial size distribution. They should be composed of macroscopic solids larger than millimeters, but smaller than a few kilometers in size. If larger planetesimals were present, they would stir the disk, triggering a collisional cascade and thus causing production of small debris, which is not seen. Thus planetesimal formation, at least in the outer regions of the systems, has stopped before “cometary” or “asteroidal” sizes were reached.


Stars: individual: (HIP 29271, HIP 49908, HIP 109378, HIP 92043, HIP 171, HIP 73100) Circumstellar matter Planetary systems: formation Planetary systems: protoplanetary disks Galaxies: statistics CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA ASTRONOMÍA Y ASTROFÍSICA ASTRONOMÍA Y ASTROFÍSICA

How Significant is Radiation Pressure in the Dynamics of the Gas Around Young Stellar Clusters?


The impact of radiation pressure on the dynamics of the gas in the vicinity of young stellar clusters is thoroughly discussed. The radiation over the thermal/ram pressure ratio time evolution is calculated explicitely and the crucial role of the cluster mechanical power and of the strong time evolution of the ionizing photon flux and of the bolometric luminosity of the exciting cluster is stressed. It is shown that radiation has only a narrow window of opportunity to dominate the wind-driven shell dynamics. This may occur only at early stages of the bubble evolution and if the shell expands into a dusty and/or a very dense proto-cluster medium. The impact of radiation pressure on the wind-driven shell becomes always negligible after about 3 Myr. Finally, the wind-driven model results allow one to compare the model predictions with the distribution of thermal pressure derived from X-ray observations. The shape of the thermal pressure profile allows then to distinguish between the energy and the momentum dominated regimes of expansion and thus conclude whether radiative losses of energy or the leakage of hot gas from the bubble interior have been significant during the bubble evolution.


Galaxies: star clusters: general HII regions Hydrodynamics ISM: bubbles ISM: kinematics and dynamics CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA ASTRONOMÍA Y ASTROFÍSICA ASTRONOMÍA Y ASTROFÍSICA

Unveiling the nature of INTEGRAL objects through optical spectroscopy*: X. A new multi-year, multi-observatory campaign

Vahram Chavushyan (2013)

Within the framework of our program (running since 2004) of identification of hard X-ray INTEGRAL sources through optical spectroscopy, we present the results concerning the nature of 33 high-energy objects. The data were acquired with the use of six telescopes of different sizes and from one on-line archive. The results indicate that the majority of these objects (23 out of 33) are active galactic nuclei (AGNs), whereas 10 are sources in the local Universe with eight of which in the Galaxy and two in the Small Magellanic Cloud (SMC). Among the identified AGNs, 13 are of Type 1 (i.e., with broad emission lines), eight are of Type 2 (with narrow emissions only), and two are X-ray bright, optically normal galaxies with no apparent nuclear activity in the optical. Six of these AGNs lie at high redshift (z > 0.5). Concerning local objects, we found that five of them are Galactic cataclysmic variables, three are high-mass X-ray binaries (two of which lying in the SMC), one is a low-mass X-ray binary, and one is classified as a flare star that is likely of RS CVn type. The main optical properties and inferred physical characteristics of these sources are presented and discussed.


Galaxies: Seyfert Quasars: emission lines X-rays: binaries Novae, cataclysmic variables Stars: flare CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA ASTRONOMÍA Y ASTROFÍSICA ASTRONOMÍA Y ASTROFÍSICA


Vahram Chavushyan (2013)

We present a study of the host bulge properties and their relations with the blackhole mass on a sample of 10 intermediate-type active galactic nuclei (AGN). Our sample consists mainly of early type spirals, four of them hosting a bar. For 70⁺¹⁰₋₁₇% of thegalaxies we have been able to determine the type of the bulge, and find that these objects probably harbor a pseudobulge or a combination of classical bulge/ pseudobulge, suggesting that pseudobulges mightbe frequent in intermediate-typeAGN. In our sample, 50 ± 14% of the objects show double-peaked emission lines. Therefore, narrowdouble-peaked emission lines seem to be frequent in galaxies harboring a pseudobulgeor a combination of classical bulge/ pseudobulge. Depending on the bulge type, we estimated the black hole mass using the corresponding MBH -σ*relation and found them with a range of: 5.69±0.21 <log Mσ*BH <8.09±0.24. Comparing these Mσ*BH values with masses derived from the FWHM of Hβ and the continuum luminosity at 5100 Å from their SDSS-DR7 spectra (MBH) we find that eight out of ten (80⁺⁷₋₁₇%) galaxies have black hole masses that are compatible within a factor of 3.This result would support that MBH and Mσ*BH are the same for intermediate-typeAGN as has been found for type 1 AGN. However, when the type of the bulge istaken into account only 3 out of the 7 (43⁺¹⁸₋₁₅%) objects of the sample have their Mσ*BH and MBH compatible within 3-σ errors. We also find that estimations basedon the MBH–σ*relation for pseudobulges are not compatible in 50±20% of theobjects.