G. Vladilo

The Astronomical Observatory of Brera, Merate, Lombardy, Italy

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Publications (141)305.27 Total impact

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    ABSTRACT: In this work, we study argon abundances in the interstellar medium of high-redshift galaxies (2<z(abs)<4.2) detected as Damped Lya absorbers (DLA) in the spectra of background quasars. We use high-resolution quasar spectra obtained from the ESO-UVES advanced data products (EUADP) database. We present 3 new measurements and 5 upper limits of ArI. We further compiled DLAs/sub-DLA data from the literature with measurements available of argon and alpha-capture elements (S or Si), making up a total of 37 systems, i.e. the largest DLA argon sample investigated so far. We confirm that argon is generally deficient in DLAs, with a mean value [Ar/alpha]= -0.4+/-0.06dex (standard error of the mean). The [Ar/alpha] ratios show a weak, positive trend with increasing NHI and increasing absorption redshift, and a weak, negative trend with dust-free metallicity, [S/H]. Detailed analysis of the abundance ratios indicates that ArI ionisation, rather than dust depletion or nucleosynthetic evolution, is responsible for the argon deficiency. Altogether, the observational evidence is consistent with a scenario of argon ionisation dominated by quasar metagalactic radiation modulated by local HI self-shielding inside the DLA host galaxies. Our measurements and limits of argon abundances suggest that the cosmic reionisation of HeII is completed above z=3, but more measurements at z(abs)>3.5 are required to probe the final stages of this process of cosmic reionisation.
    Monthly Notices of the Royal Astronomical Society 09/2014; 445(2). · 5.23 Impact Factor
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    ABSTRACT: We report here a study of nitrogen and $\alpha$-capture element (O, S, and Si) abundances in 18 Damped Ly$\alpha$ Absorbers (DLAs) and sub-DLAs drawn from the ESO-UVES Advanced Data Products (EUADP) database. We report 9 new measurements, 5 upper and 4 lower limits of nitrogen that when compiled with available nitrogen measurements from the literature makes a sample of 108 systems. The extended sample presented here confirms the [N/$\alpha$] bimodal behaviour suggested in previous studies. Three-quarter of the systems show $\langle$[N/$\alpha$]$\rangle=-0.85$ ($\pm$0.20 dex) and one-quarter ratios are clustered at $\langle$[N/$\alpha$]$\rangle= -1.41$ ($\pm$0.14 dex). The high [N/$\alpha$] plateau is consistent with the HII regions of dwarf irregular and blue compact dwarf galaxies although extended to lower metallicities and could be interpreted as the result of a primary nitrogen production by intermediate mass stars. The low [N/$\alpha$] values are the lowest ever observed in any astrophysical site. In spite of this fact, even lower values could be measured with the present instrumentation, but we do not find them below [N/$\alpha$] $\approx$ $-1.7$. This suggests the presence of a floor in [N/$\alpha$] abundances, which along with the lockstep increase of N and Si may indicate a primary nitrogen production from fast rotating, massive stars in relatively young or unevolved systems.
    Monthly Notices of the Royal Astronomical Society 07/2014; 444(1). · 5.23 Impact Factor
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    ABSTRACT: Absorption lines in the spectra of distant quasars whose sightlines pass through foreground galaxies provide a valuable tool to probe the dust and gas compositions of the interstellar medium (ISM) in galaxies. The first evidence of silicate dust in a quasar absorption system (QAS) was provided through our detection of the 10 micron silicate feature in the z=0.52 absorber toward the quasar AO 0235+164. We present results from 2 follow-up programs using archival Spitzer Space Telescope infrared spectra to study the interstellar silicate dust grain properties in a total of 13 QASs at 0.1<z<1.4. We find clear detections of the 10 micron silicate feature in the QASs studied. We also detect the 18 micron silicate feature in the sources with adequate spectral coverage. We find variations in the breadth, peak wavelength, and substructure of the 10 micron interstellar silicate absorption features among the absorbers. This suggests that the silicate dust grain properties in these distant galaxies may differ relative to one another, and relative to those in the Milky Way. We also find suggestions in several sources, based on comparisons with laboratory-derived profiles from the literature, that the silicate dust grains may be significantly more crystalline than those in the amorphous Milky Way ISM. This is particularly evident in the z=0.89 absorber toward the quasar PKS 1830-211, where substructure near 10 micron is consistent with a crystalline olivine composition. If confirmed, these grain property variations may have implications for both dust and galaxy evolution over the past 9 Gyrs, and for the commonly-made assumption that high-redshift dust is similar to local dust. We also discuss indications of trends between silicate dust absorption strength and both carbonaceous dust properties and gas-phase metal properties, such as the gas velocity spread, determined from UV/optical spectra.
    05/2014;
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    ABSTRACT: We report the detection of interstellar silicate dust in the z_abs=0.685 absorber along the sightline toward the gravitationally lensed blazar TXS 0218+357. Using Spitzer Space Telescope Infrared Spectrograph data we detect the 10 micron silicate absorption feature with a detection significance of 10.7-sigma. We fit laboratory-derived silicate dust profile templates obtained from literature to the observed 10 micron absorption feature, and find that the best single-mineral fit is obtained using an amorphous olivine template with a measured peak optical depth of tau_10=0.49+/-0.02, which rises to tau_10~0.67+/-0.04 if the covering factor is taken into account. We also detected the 18 micron silicate absorption feature in our data with a >3-sigma significance. Due to the proximity of the 18 micron absorption feature to the edge of our covered spectral range, and associated uncertainty about the shape of the quasar continuum normalization near 18 micron, we do not independently fit this feature. We find, however, that the shape and depth of the 18 micron silicate absorption are well-matched to the amorphous olivine template prediction, given the optical depth inferred for the 10 micron feature. The measured 10 micron peak optical depth in this absorber is significantly higher than those found in previously studied quasar absorption systems. The reddening, 21-cm absorption, and velocity spread of Mg II are not outliers relative to other studied absorption systems, however. This high optical depth may be evidence for variations in dust grain properties in the ISM between this and the previously studied high redshift galaxies.
    The Astrophysical Journal 02/2014; 785(1). · 6.28 Impact Factor
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    ABSTRACT: Nitrogen is thought to have both primary and secondary origins depending on whether the seed carbon and oxygen are produced by the star itself (primary) or already present in the interstellar medium (secondary) from which star forms. DLA and sub-DLA systems with typical metallicities of -3.0<Z/Z_sun<-0.5 are excellent tools to study nitrogen production. We made a search for nitrogen in the ESO-UVES advanced data products (EUADP) database. In the EUADP database, we find 10 new measurements and 9 upper limits of nitrogen. We further compiled DLA/sub-DLA data from the literature with estimates available of nitrogen and alpha-elements. This yields a total of 98 systems, i.e. the largest nitrogen abundance sample investigated so far. In agreement with previous studies, we indeed find a bimodal [N/alpha] behaviour: three-quarter systems show a mean value of [N/alpha]=-0.87 with a scatter of 0.21 dex and one-quarter shows ratios clustered at [N/alpha]=-1.43 with a lower dispersion of 0.13 dex. The high [N/alpha] group is consistent with the blue compact dwarves and dwarf irregular galaxies, suggesting primary nitrogen production. The low [N/alpha] group is the lowest ever observed in any astrophysical site and probably provides an evidence of the primary production by fast rotating massive stars in young sites. Moreover, we find a transition between the two [N/alpha] groups around [N/H]=-2.5. The transition is not abrupt and there are a few systems lying in the transition region. Additional observations of DLAs/sub-DLAs below [N/H]<-2.5 would provide more clues.
    01/2014;
  • memsai. 01/2014; 85:63.
  • memsai. 01/2014; 85:70.
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    ABSTRACT: Intervening absorption systems towards distant QSOs can be used to compare the value of dimensionless fundamental constants such as the fine-structure constant, α of remote regions of the Universe to their present value on Earth. We here report on the stringent bound for {Delta α/α} obtained for the absorber at mÅthrm zabs = 1.6919 towards HE 2217-2818. The absorption profile is complex and is modeled with 32 velocity components. The relative variation in α in this system is +1.3± 2.4mÅthrm stat ± 1.0mÅthrm sys ppm (parts per million) derived by means of Al II lambda 1670 Å and three Fe II transitions, and +1.1 ± 2.6mÅthrm stat ppm whith only Fe II transitions. This bound reveals no evidence for variation in α at the 3-ppm precision level (1-sigma confidence). At this sky position of the recently-reported dipolar variation of α is (3.2-5.4)±1.7 ppm. At face value this constraint is not supporting the spatial dipole model but not inconsistent with it at the 3sigma level. Beside, asteroid observations revealed the presence of a possible wavelength dependent velocity drift and of inter-order distortions. A systematic error which is a serious obstacle to improve the accuracy of this kind of measurements.Based on observations obtained with UVES at the the 8.2m Kueyen ESO telescope programme L185.A-0745
    11/2013;
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    ABSTRACT: We study the variation of proton-to-electron mass ratio, mu , using the H_2 absorption lines from the z_abs ̃ 2.4018 DLA system towards HE 0027 - 1836 observed with the VLT/UVES as a part of the ESO Large Program for testing fundamental physics. A cross-correlation analysis between individual exposures and the combined spectrum and asteroid observations show the existence of a possible wavelength dependent drift in the UVES observation. We find that a two component Voigt profile model can best fit the H_2 absorption profile and give Delta mu /mu = -2.5 ± 8.1_stat ± 6.2_sys ppm. When we apply the correction to the wavelength dependent velocity drift we find Delta mu /mu = -7.6 ± 8.1_stat± 6.3_sys ppm.
    11/2013;
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    ABSTRACT: Absorption-line systems detected in high resolution quasar spectra can be used to compare the value of dimensionless fundamental constants such as the fine-structure constant, alpha, and the proton-to-electron mass ratio, mu = m_p/m_e, as measured in remote regions of the Universe to their value today on Earth. In recent years, some evidence has emerged of small temporal and also spatial variations in alpha on cosmological scales which may reach a fractional level of 10 ppm . We are conducting a Large Programme of observations with VLT UVES to explore these variations. We here provide a general overview of the Large Programme and report on the first results for these two constants, discussed in detail in Molaro et al. and Rahmani et al. A stringent bound for Delta(alpha)/Alpha is obtained for the absorber at_abs = 1.6919 towards HE 2217-2818. The absorption profile is complex with several very narrow features, and is modeled with 32 velocity components. The relative variation in alpha in this system is +1.3+-2.4_{stat}+-1.0_{sys} ppm if Al II lambda 1670AA and three Fe II transitions are used, and +1.1+-2.6_{stat} ppm in a lightly different analysis with only Fe II transitions used. The expectation at this sky position of the recently-reported dipolar variation of alpha is (3.2--5.4)+-1.7 ppm depending on dipole model. This constraint of Delta(alpha)/alpha at face value is not supporting this expectation but is not inconsistent with it at the 3 sigma level. For the proton-to-electron mass ratio the analysis of the H_2 absorption lines of the z_{abs}~2.4018 damped Ly alpha system towards HE 0027- 1836 provides Delta(mu)/mu = (-7.6 +- 8.1_{stat} +- 6.3_{sys}) ppm which is also consistent with a null variation. (abridged)
    Astronomische Nachrichten 10/2013; 335(1). · 1.12 Impact Factor
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    ABSTRACT: We present an accurate analysis of the H2 absorption lines from the zabs ~ 2.4018 damped Ly{\alpha} system towards HE 0027-1836 observed with the Very Large Telescope Ultraviolet and Visual Echelle Spectrograph (VLT/UVES) as a part of the European Southern Observatory Large Programme "The UVES large programme for testing fundamental physics" to constrain the variation of proton-to-electron mass ratio, {\mu} = mp/me. We perform cross-correlation analysis between 19 individual exposures taken over three years and the combined spectrum to check the wavelength calibration stability. We notice the presence of a possible wavelength dependent velocity drift especially in the data taken in 2012. We use available asteroids spectra taken with UVES close to our observations to confirm and quantify this effect. We consider single and two component Voigt profiles to model the observed H2 absorption profiles. We use both linear regression analysis and Voigt profile fitting where {\Delta}{\mu}/{\mu} is explicitly considered as an additional fitting parameter. The two component model is marginally favored by the statistical indicators and we get {\Delta}{\mu}/{\mu} = (-2.5 +/- 8.1(stat) +/- 6.2(sys)) ppm. When we apply the correction to the wavelength dependent velocity drift we find {\Delta}{\mu}/{\mu} = (-7.6 +/- 8.1(stat) +/- 6.3(sys)) ppm. It will be important to check the extent to which the velocity drift we notice in this study is present in UVES data used for previous {\Delta}{\mu}/{\mu} measurements.
    Monthly Notices of the Royal Astronomical Society 07/2013; 435(1). · 5.23 Impact Factor
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    ABSTRACT: We present the results of observations taken with the X-shooter spectrograph devoted to the study of quasars at z ~ 6. This paper focuses on the properties of metals at high redshift traced, in particular, by the C IV doublet absorption systems. Six objects were observed with resolutions ~27 and 34 km/s in the visual, and 37.5 and 53.5 km/s in the near infrared. We detected 102 C IV lines in the range: 4.35 < z < 6.2 of which 27 are above z ~ 5. Thanks to the characteristics of resolution and spectral coverage of X-shooter, we could also detect 25 Si IV doublets associated with the C IV at z>5. The column density distribution function of the C IV line sample is observed to evolve in redshift for z>~ 5.3, with respect to the normalization defined by low redshift (1.5 < z <4) C IV lines. This behaviour is reflected in the redshift evolution of the C IV cosmic mass density, Omega_CIV, of lines with column density in the range 13.4 < log N(C IV) < 15, which is consistent with a drop of a factor of ~2 for z>~ 5.3. Considering only the stronger C IV lines (13.8 < log N(CIV) < 15), Omega_CIV gently rises by a factor of ~10 between z ~ 6.2 and z~ 1.5 with a possible flattening toward z ~ 0. The increase is well fitted by a power law: Omega_CIV = (2+-1)x10^{-8} [(1+z)/4]^{-3.1+-0.1}. An insight into the properties of the C IV absorbers and their evolution with redshift is obtained by comparing the observed column densities of associated C IV, Si IV and C II absorptions with the output of a set of CLOUDY photo-ionization models. As already claimed by cosmological simulations, we find that C IV is a good tracer of the metallicity in the low-density intergalacitc medium gas at z ~ 5-6 while at z ~ 3 it arises in gas with over density delta ~100.
    Monthly Notices of the Royal Astronomical Society 06/2013; 435(2). · 5.23 Impact Factor
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    ABSTRACT: Absorption line systems detected in quasar spectra can be used to compare the value of the fine-structure constant, {\alpha}, measured today on Earth with its value in distant galaxies. In recent years, some evidence has emerged of small temporal and also spatial variations of {\alpha} on cosmological scales which may reach a fractional level of ~ 10 ppm (parts per million). To test these claims we are conducting a Large Program with the VLT UVES . We are obtaining high-resolution (R ~ 60000 and high signal-to-noise ratio (S/N ~ 100) UVES spectra calibrated specifically for this purpose. Here we analyse the first complete quasar spectrum from this Program, that of HE 2217-2818. We apply the Many Multiplet method to measure {\alpha} in 5 absorption systems towards this quasar: zabs = 0.7866, 0.9424, 1.5558, 1.6279 and 1.6919. The most precise result is obtained for the absorber at zabs = 1.6919 where 3 Fe II transitions and Al II {\lambda}1670 have high S/N and provide a wide range of sensitivities to {\alpha}. The absorption profile is complex, with several very narrow features, and requires 32 velocity components to be fitted to the data. Our final result for the relative variation in {\alpha} in this system is Delta{\alpha}/{\alpha} = +1.3 +/- 2.4stat +/- 1.0sys ppm. This is one of the tightest current bounds on {\alpha} variation from an individual absorber. The absorbers towards quasar HE 2217-2818 reveal no evidence for variation in {\alpha} at the 3 ppm precision level (1{\sigma} confidence). If the recently reported 10 ppm dipolar variation of {\alpha} across the sky were correct, the expectation at this sky position is (3.2-5.4) +/-1.7 ppm depending on dipole model used . Our constraint of Delta{\alpha}/{\alpha}=+1.3+/-2.4stat +/-1.0sys ppm is not inconsistent with this expectation.
    Astronomy and Astrophysics 05/2013; · 4.48 Impact Factor
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    ABSTRACT: Interstellar dust plays a significant role in the physical processes driving galaxy evolution, such as star-formation, and the heating, cooling, and ionization of interstellar material. While interstellar dust has been studied extensively in local galaxies, much less is known about the properties of dust grains in distant galaxies. One technique to study extragalactic interstellar dust is to look for absorption features produced by the dust in the spectra of background luminous objects, such as quasars. We will present results from an ongoing study of the interstellar silicate dust in several quasar absorption systems using infrared absorption spectra obtained with the Spitzer Space Telescope, and complementary ground-based data on associated gas-phase metal absorption lines. Based on the shape of the 10 micron silicate absorption feature, we find suggestions that the interstellar silicate dust grains in the distant universe may be significantly more crystalline in structure than those in our own Galaxy. If confirmed, this may have implications for both dust and galaxy evolution, and for assumptions about the similarity of dust properties at all epochs. Support for this work is provided by NASA through an award issued by JPL/Caltech. Additional support comes from National Science Foundation grants AST-0908890 and AST-1108830 to the University of South Carolina.
    01/2013;
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    ABSTRACT: We present evidence of a >10-sigma detection of the 10 micron silicate dust absorption feature in the spectrum of the gravitationally lensed quasar PKS 1830-211, produced by a foreground absorption system at redshift 0.886. We have examined more than 100 optical depth templates, derived from both observations of Galactic and extragalactic sources and laboratory measurements, in order to constrain the chemical structure of the silicate dust. We find that the best fit to the observed absorption profile is produced by laboratory crystalline olivine, with a corresponding peak optical depth of tau_10=0.27+/-0.05. The fit is slightly improved upon by including small contributions from additional materials such as silica, enstatite, or serpentine, which suggests that the dust composition may consist of a blend of crystalline silicates. Combining templates for amorphous and crystalline silicates, we find that the fraction of crystalline silicates needs to be at least 95%. Given the rarity of extragalactic sources with such a high degree of silicate crystallinity, we also explore the possibility that the observed spectral features are produced by amorphous silicates in combination with other molecular or atomic transitions, or by foreground source contamination. While we cannot rule out these latter possibilities, they lead to much poorer profile fits than for the crystalline olivine templates. If the presence of crystalline interstellar silicates in this distant galaxy is real, it would be highly unusual, given that the Milky Way interstellar matter contains essentially only amorphous silicates. It is possible that the z=0.886 absorber towards PKS 1830-211, well known for its high molecular content, has a unique star-forming environment that enables crystalline silicates to form and prevail.
    The Astrophysical Journal 01/2012; 748(1). · 6.28 Impact Factor
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    ABSTRACT: We report three additional SINFONI detections of H-alpha emission line from quasar absorbers, two of which are new identifications. These were targeted among a sample of systems with log N(HI)>19.0 and metallicities measured from high-resolution spectroscopy. The detected galaxies are at impact parameters ranging from 6 to 12 kpc from the quasar's line-of-sight. We derive star formation rates (SFR) of a few solar masses per year for the two absorbers at z_abs~1 and SFR=17 solar masses per year for the DLA at z_abs~2. These three detections are found among a sample of 16 DLAs and sub-DLAs (5 at z_abs~1 and 7 at z_abs~2). For the remaining undetected galaxies, we derive flux limits corresponding to SFR<0.1--11.0 solar masses per year depending on redshift of the absorber and depth of the data. When combined with previous results from our survey for galaxy counterparts to HI-selected absorbers, we find a higher probability of detecting systems with higher metallicity as traced by dust-free [Zn/H] metallicity. We also report a higher detection rate with SINFONI for host galaxies at z_abs~1 than for systems at z_abs~2. Using the NII/H-alpha ratio, we can thus compare absorption and emission metallicities in the same high-redshift objects, more than doubling the number of systems for which such measures are possible.
    Monthly Notices of the Royal Astronomical Society 10/2011; · 5.23 Impact Factor
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    ABSTRACT: Evolutionary tracks of the reference model of galactic chemical evolution used to estimate DLA depletions. This model is that of a dwarf galaxy with parameters Minfall=1x109M&sun;, epsilon=0.4Gyr-1, and normal wind with lambdaw=3.5Gyr-1. More details on the model can be found in Section 4 of the paper. The criteria followed to select this particular model are explained in Section 5.1.3. Abundance ratios are by number and are expressed in a logarithmic scale with log(H)=12. (5 data files).
    VizieR Online Data Catalog. 04/2011;
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    Jun Yin, Francesca Matteucci, Giovanni Vladilo
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    ABSTRACT: Dwarf irregular and blue compact galaxies are very interesting objects since they are relatively simple and unevolved. We present new models for the chemical evolution of these galaxies by assuming different regimes of star formation (bursting and continuous) and different kinds of galactic winds (normal and metal-enhanced). Our results show that in order to reproduce all the properties of these galaxies, including the spread in the chemical abundances, the star formation should have proceeded in bursts and the number of bursts should be not larger than 10 in each galaxy, and that metal-enhanced galactic winds are required. A metal-enhanced wind efficiency increasing with galactic mass can by itself reproduce the observed mass-metallicity relation although also an increasing efficiency of star formation and/or number and/or duration of bursts can equally well reproduce such a relation. Metal enhanced winds together with an increasing amount of star formation with galactic mass are required to explain most of the properties of these galaxies. Normal galactic winds, where all the gas is lost at the same rate, do not reproduce the features of these galaxies. We suggest that these galaxies should have suffered a different number of bursts varying from 2 to 10 and that the efficiency of metal-enhanced winds should have been not too high ($\lambda_{mw}\sim1$). We predict for these galaxies present time Type Ia SN rates from 0.00084 and 0.0023 per century. Finally, by comparing the abundance patterns of Damped Lyman-$\alpha$ objects with our models we conclude that they are very likely the progenitors of the present day dwarf irregulars. (abridged)
    Astronomy and Astrophysics 02/2011; 445. · 4.48 Impact Factor
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    ABSTRACT: X-shooter, with its characteristics of resolution, spectral coverage and efficiency, provides a unique opportunity to obtain spectra of the highest-redshift quasars (z ~ 6) that will allow us to carry out successful investigations on key cosmological issues, from the details of the re-ionization process, to the evolution of the first galaxies and AGNs. In this paper, we present the spectra of three z ~ 6 quasars: one obtained during the commissioning of X-shooter and two in the context of our ongoing GTO programme. Combining this sample with data in the literature, we update the value of the C IV cosmic mass density in the range 4.5 < z < 5, confirming the constant trend with redshift between 2.5 and 5.
    Astronomische Nachrichten 01/2011; 332. · 1.12 Impact Factor
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    ABSTRACT: Details of the processes through which galaxies convert their gas into stars need to be studied in order to obtain a complete picture of galaxy formation. One way to tackle these phenomena is to relate the H I gas and the stars in galaxies. Here, we present dynamical properties of damped and subdamped Lyman alpha (DLA) systems identified in Halpha emission with VLT/SINFONI at near-infrared wavelengths. While the DLA towards Q0302 - 223 is found to be dispersion-dominated, the sub-DLA towards Q1009 - 0026 shows clear signatures of rotation. We use a proxy to circular velocity to estimate the mass of the halo in which the sub-DLA resides and find Mhalo= 1012.6 M&sun;. We also derive dynamical masses of these objects, and find Mdyn= 1010.3 and 1010.9 M&sun;. For one of the two systems (towards Q0302 - 223), we are able to derive a stellar mass of M*= 109.5 M&sun; from a spectral energy distribution fit. The gas fraction in this object is one-third, comparable to similar objects at these redshifts. Our work illustrates that detailed studies of quasar absorbers can offer entirely new insights into our knowledge of the interaction between stars and the interstellar gas in galaxies. Based on observations collected during programmes ESO 80.A-0330 and 80.A-0742 at the European Southern Observatory with SINFONI on the 8.2-m YEPUN telescope operated at the Paranal Observatory, Chile.
    Monthly Notices of the Royal Astronomical Society 01/2011; 410:2251-2256. · 5.23 Impact Factor

Publication Stats

584 Citations
305.27 Total Impact Points

Institutions

  • 1986–2014
    • The Astronomical Observatory of Brera
      Merate, Lombardy, Italy
    • Scuola Internazionale Superiore di Studi Avanzati di Trieste
      Trst, Friuli Venezia Giulia, Italy
    • Spanish National Research Council
      Madrid, Madrid, Spain
  • 2004–2013
    • National Institute of Astrophysics
      Roma, Latium, Italy
  • 1994
    • Università degli Studi di Trieste
      Trst, Friuli Venezia Giulia, Italy
  • 1993
    • University of Bonn
      Bonn, North Rhine-Westphalia, Germany
  • 1989–1991
    • Instituto de Astrofísica de Canarias
      San Cristóbal de La Laguna, Canary Islands, Spain
  • 1987
    • French National Centre for Scientific Research
      • Institut d'astrophysique spatiale (IAS)
      Paris, Ile-de-France, France