arXiv subjects

P. Petitjean

Publications and source records attributed to P. Petitjean.

At least 163 records · Page 9Linked to original sources

arXiv2004

Probing the cosmological variation of the fine-structure constant: Results based on VLT-UVES sample

Development of fundamental physics relies on the constancy of various fundamental quantities such as the fine structure constant. Detecting or constraining the possible time variations of these fundamental physical quantities is an important step toward a complete understanding of basic physics. Here we present the results from a detailed many-multiplet analysis performed using high signal-to-noise ratio, high spectral resolution observations of 23 Mg II systems detected toward 18 QSOs in the redshift range 0.4<z<2.3 obtained using UVES at the VLT. We validate our procedure and define the selection criteria that will avoid possible systematics using detail analysis of simulated data set. We show our Voigt profile fitting code recovers the variation in αvery accurately when we use single component systems and multiple component systems that are not heavily blended. Spurious detections are frequently seen when we use heavily blended systems or the systems with very weak lines. Thus we avoided heavily blended systems and the systems with Fe II column density < 2x10^12 cm^-2 in the analysis. All steps involved in the analysis are presented in detail. The weighted mean value of the variation in αobtained from our analysis over the redshift range 0.4<z<2.3 is {Δα/α} = (-0.06+/-0.06)x10^-5. The median redshift of our sample is 1.55 the 3σupper limit on the time variation of $α$ is -2.5x10^-16 yr^-1< (Δα/αΔt) <+1.2x10^-16 yr^-1. To our knowledge this is the strongest constraint from quasar absorption line studies till date.

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arXiv2003

The VLT-UVES survey for molecular hydrogen in high-redshift damped Lyman-alpha systems

We have searched for molecular hydrogen in damped Lyman-alpha (DLA) and sub-DLA systems at z>1.8 using UVES at the VLT. Out of the 33 systems in our sample, 8 have firm and 2 have tentative detections of associated H2 absorption lines. Considering that 3 detections were already known from past searches, H2 is detected in 13 to 20 percent of the newly-surveyed systems. We report new detections of molecular hydrogen at z=2.087 and 2.595 toward, respectively, Q 1444+014 and Q 0405-443, and also reanalyse the system at z=3.025 toward Q 0347-383. We find that there is a correlation between metallicity and depletion factor in both our sample and also the global population of DLA systems (60 systems in total). The DLA and sub-DLA systems where H2 is detected are usually amongst those having the highest metallicities and the largest depletion factors. Moreover, the individual components where H2 is detected have depletion factors systematically larger than other components in the profiles. In two different systems, one of the H2-detected components even has [Zn/Fe]>=1.4. These are the largest depletion factors ever seen in DLA systems. All this clearly demonstrates the presence of dust in a large fraction of the DLA systems. The mean H2 molecular fraction is generally small in DLA systems and similar to what is observed in the Magellanic Clouds. From 58 to 75 percent of the DLA systems have log f<-6. This can be explained if the formation rate of H2 onto dust grains is reduced in those systems, probably because the gas is warm (T>1000 K) and/or the ionizing flux is enhanced relative to what is observed in our Galaxy.

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arXiv2003

The correlation of the Lyman-alpha forest in close pairs and groups of high-redshift quasars: clustering of matter on scales 1-5 Mpc

We study the clustering of matter in the intergalactic medium from the Lyman-alpha forests seen in the spectra of pairs or groups of z ~ 2 quasars observed with FORS2 and UVES at the VLT-UT2 Kueyen ESO telescope. The sample consists of five pairs with separations 0.6, 1, 2.1, 2.6 and 4.4 arcmin and a group of four quasars with separations from 2 up to 10 arcmin. This unprecedented data set allows us to measure the transverse flux correlation function for a range of angular scales. Correlations are clearly detectable at separations smaller than 3 arcmin. The shape and correlation length of the transverse correlation function on these scales is in good agreement with those expected from absorption by the photoionized warm intergalactic medium associated with the filamentary and sheet-like structures predicted in CDM-like models for structure formation. At larger separation no significant correlation is detected. Assuming that the absorbing structures are randomly orientated with respect to the line of sight, the comparison of transverse and longitudinal correlation lengths constrains the cosmological parameters (as a modified version of the Alcock & Paczyński test). The present sample is too small to get significant constraints. Using N-body simulations, we investigate the possibility to constrain Ol from future larger samples of QSO pairs with similar separations. The observation of a sample of 30 pairs at 2, 4.5 and 7.5 arcmin should constrain the value of Ol at +- 15 % (2 sigma level). We further use the observed spectra of the group of four quasars, to search for underdense regions in the intergalactic medium. We find a quasi-spherical structure of reduced absorption with radius 12.5 h^{-1} Mpc which we identify as an underdense region.

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arXiv2002

Does the proton-to-electron mass ratio vary in the course of cosmological evolution?

The possible cosmological variation of the proton-to-electron mass ratio was estimated by measuring the H_2 wavelengths in the high-resolution spectrum of the quasar Q~0347-382. Our analysis yielded an estimate for the possible deviation of μvalue in the past, 10 Gyr ago: for the unweighted value $Δμ/ μ= (3.0\pm2.4)\times10^{-5}$; for the weighted value \[ Δμ/ μ= (5.02\pm1.82)\times10^{-5}\] Since the significance of the both results does not exceed 3$σ$, further observations are needed to increase the statistical significance. In any case, this result may be considered as the most stringent estimate on an upper limit of a possible variation of μ(95% C.L.): \[ |Δμ/ μ| < 8\times 10^{-5} \] This value serves as an effective tool for selection of models determining a relation between possible cosmological deviations of the fine-structure constant αand the elementary particle masses (m$_p$, m$_e$, etc.).

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arXiv2002

A VLT/FORS2 spectroscopic survey in the HDF-S

We report on low-resolution multi-object spectroscopy of 65 objects from I(AB) ~= 20 to I(AB) ~= 25 in the HDF-S obtained with the VLT Focal Reducer/low dispersion Spectrograph (FORS2). 18 objects belong to the HDF-S proper, i.e. the WFPC2 deep area. 15 high-redshift galaxies with 2.0 < z < 3.5 (10 in the HDF-S proper) have been identified. The spectroscopic redshifts are in good agreement with the photometric ones derived from a chi^{2} minimization technique comparing the observed spectral energy distribution with synthetic libraries and with a new neural network (NN) approach. The dispersion with the former method is sigma_z=0.16 whereas the latter provides sigma_z=0.13. No "catastrophic" difference is encountered. The inferred star formation rates of the individual objects range from tens to a few hundreds of M_{\odot} yr^{-1} and the global star formation rate of the Universe at =~2.4 is estimated to be 0.15 M_{\odot} yr^{-1} Mpc^{-3} with a statistical error of 0.04. Evidence for large scale structure is found with two groups' redshifts observed at z ~= 2.1 and z ~= 2.7 and a pronounced low redshift peak around z ~= 0.58. An elliptical galaxy lensing a background object turns out to be at a redshift z=0.577.

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arXiv2002

Detection of molecular hydrogen in a near Solar-metallicity damped Lyman-alpha system at z_abs~2 toward Q 0551-366

We report the detection of H_2, CI, CI*, CI** and Cl I lines in a near Solar-metallicity ([Zn/H]=-0.13) damped Lyman-alpha (DLA) system at z_abs=1.962 observed on the line of sight to the quasar Q 0551-366. The iron-peak elements, X=Fe, Cr and Mn are depleted compared to zinc, [X/Zn] -0.8, probably because they are tied up onto dust grains. Among the three detected H_2-bearing clouds, spanning 55 km s^-1 in velocity space, we derive a total molecular hydrogen column density N(H_2)=2.6x10^17 cm^-2 and a mean molecular fraction f=2N(H_2)/(2N(H_2)+N(HI))=1.7x10^-3. The depletion of heavy elements (S, Si, Mg, Mn, Cr, Fe, Ni and Ti) in the central component is similar to that observed in the diffuse neutral gas of the Galactic halo. This depletion is approximately the same in the six CI-detected components independently of the presence or absence of H_2. The gas clouds in which H_2 is detected always have large densities, n_H>30 cm^-3, and low temperatures, T_01<~100 K. This shows that presence of dust, high particle density and/or low temperature are required for molecules to be present. The photo-dissociation rate derived in the components where H_2 is detected suggests the existence of a local UV radiation field similar in strength to the one in the Galaxy. Star formation therefore probably occurs near these H_2-bearing clouds.

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arXiv2002

A collimated flow driven by radiative pressure from the nucleus of quasar Q~1511+091

High velocity outflows from quasars are revealed by the absorption signatures they produce in the spectrum of the quasar. Clues on the nature and origin of these flows are important for our understanding of the dynamics of gas in the central regions of the Active Galactic Nucleus (AGNs) but also of the metal enrichment of the intergalactic space. Line radiation pressure has often been suggested to be an important process in driving these outflows, however no convincing evidence has been given so far. Here we report observation of a highly structured flow, toward Q~1511+091, where the velocity separations between distinct components are similar to O VI, N V and C IV doublet splittings with some of the profiles matching perfectly. This strongly favors the idea that the absorbing clumps originate at similar physical location and are driven by radiative acceleration due to resonance lines. The complex absorption can be understood if the flow is highly collimated so that the different optically thick clouds are aligned and cover the same region of the background source. One component shows saturated H I Lyman series lines together with absorptions from excited levels from C II and Si II but covers only 40% of the source of continuum. The fact that clouds cover only part of the small continuum source implies that the flow is located very close to it.

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arXiv2002

HST STIS observations of four QSO pairs

We present HST STIS observations of four quasar pairs with redshifts 0.84 200 km/s. This probably reflects the fact that the scale probed by our observations is not related to the real size of individual absorbers but rather to large scale correlation. Statistics are too small to conclude about any difference between pairs separated by either 2 or 3 arcmin. A damped Lyman_alpha system is detected at z_abs = 1.2412 toward LBQS0019-0145A with log[N(HI)] ~ 20.5. From the absence of ZnII absorption, we derive a metallicity relative to solar [Zn/H]<-1.75.

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arXiv2002

Adaptive Optics imaging of Quasar Hosts

We present the results of adaptive-optics imaging of 12 (z < 0.6) quasars in the H and K bands using the PUEO system mounted on the Canada-France-Hawaii telescope. The QSOs (m_V > 15.0) themselves are used as reference for the correction. The images, obtained under poor seeing conditions, have typical spatial resolution of FWHM ~ 0.3arcsec before deconvolution. The deconvolved H-band image of PG 1700+514 has a spatial resolution of 0.16arcsec and reveals a wealth of details on the companion and the host-galaxy. The comparison between the HST and CFHT images of PG 1700+514 shows how powerful and competitive ground-based AO can be. Close companions and obvious signs of interactions are found in 4 out of the 12 objects. The 2D images of 3 of the host-galaxies unambiguously reveal bars and spiral arms. The morphology of the other host-galaxies are difficult to determine from 1D surface brightness profiles and deeper images are needed that could be obtained with AO systems on 10m class telescopes. Analysis of mocked data shows that elliptical galaxies are always recognized as such, whereas disk hosts can be missed for small disk scale lengths and large QSO contributions.

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arXiv2002

Dust depletion and abundance pattern in damped Lyman-alpha systems: a sample of Mn and Ti abundances at z<2.2

We analyse a sample of 24 damped Lyman-alpha (DLA)/moderate DLA systems at 0.3 ~-0.5, the intrinsic (dust-corrected) abundance pattern of Si, Ti, Cr and Mn in DLA absorbers closely follows the trends observed in Galactic stars and these absorbers should thus have a chemical evolution similar to that of our Galaxy. At lower metallicity, some absorbers do follow the trends present in Galactic stars but a substantial fraction of them have elemental ratios (in particular [Si/Fe]dc and [Mn/Fe]dc) closer to the solar values than Galactic stars. This could be explained by a larger contribution of type Ia supernovae to the chemical enrichment of these DLA absorbers than in Galactic stars of similar metallicity. This metal-poor DLA absorber population could trace HI-rich dwarf galaxies. (Abridged)

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arXiv2002

Do the Fundamental Constants Vary in the Course of the Cosmological Evolution?

We estimate the cosmological variation of the proton-to-electron mass ratio μ=m_p/m_e by measuring the wavelengths of molecular hydrogen transitions in the early universe. The analysis is performed using high spectral resolution observations (FWHM ~ 7 km/s) of two damped Lyman-αsystems at z_{abs}=2.3377 and 3.0249 observed along the lines of sight to the quasars Q 1232+082 and Q 0347-382 respectively. The most conservative result of the analysis is a possible variation of μover the last ~ 10 Gyrs, with an amplitude Δμ/μ= (5.7+-3.8)x10^{-5}. The result is significant at the 1.5σlevel only and should be confirmed by further observations. This is the most stringent estimate of a possible cosmological variation of μobtained up to now.

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arXiv2001

H_2 molecules in damped systems

Damped Lyman alpha systems seen in the spectra of high-z QSOs arise in high-density neutral gas in which molecular hydrogen (H_2) should be conspicuous. Systematic searches to detect the H_2 lines redshifted into the Lyman alpha forest at <3400Åare now possible thanks to the unique capabilities of UVES on the VLT. Here we summarise the present status of our on going programme to search for H_2 in DLAs, discuss the physical conditions in the systems where H_2 is detected and the implications of non-detections.

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arXiv2001

HD Molecular Lines in an Absorption System at Redshift z = 2.3377

We have analyzed the spectrum of the quasar PKS 1232+082 obtained by Petitjean et al. (2000). HD molecular lines are identified in an absorption system at the redshift z=2.3377. The column density of HD molecules in the system is estimated, N(HD)=(1-4)x10^{14} cm^{-2}. The temperature of excitation of the first rotational level J=1 relative to the ground state J=0 is T_ex=70+-7 K. This is, to our knowledge, the first detection of HD molecules at high redshift.

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arXiv2001

Physical properties and small-scale structure of the Lyman-alpha forest: Inversion of the HE 1122-1628 UVES spectrum

We study the physical properties of the Lyman-alpha forest by applying the inversion method described by Pichon et al. (2001) to the high resolution and high S/N ratio spectrum of the z_em=2.40 quasar HE 1122-1628 obtained during Science Verification of UVES at the VLT. We compare the column densities obtained with the new fitting procedure with those derived using standard Voigt profile methods. The agreement is good and gives confidence in the new description of the Lyman-alpha forest as a continuous field as derived from our method. We show that the observed number density of lines with logN>13 and 14 is, respectively, 50 and 250 per unit redshift at z~2. We study the physical state of the gas, neglecting peculiar velocities, assuming a relation between the overdensity and the temperature. T=Tbar * rho^(2beta). There is an intrinsic degeneracy between the parameters beta and Tbar. We demonstrate that, at a fixed beta, the temperature at mean density, Tbar, can be uniquely extracted however. While applying the method to HE 1122-1628, we conclude that for 0.2<beta<0.3, 6000<Tbar<15000 K at z~2. We investigate the small scale structure of strong absorption lines using the information derived from the Lyman-beta, Lyman-gamma and Civ profiles. Introducing the Lyman-beta line in the fit allows us to reconstruct the density field up to rho~10 instead of 5 for the Lyman-alpha line only. There may be small velocity shifts ~10km.s^{-1} between the peaks in the Civ and Hi density profiles. Although the statistics is small, it seems that Civ/Hi and n_HI are anti-correlated. This could be a consequence of the high sensitivity of the Civ/Hi ratio to temperature. The presence of associated Ovi absorption, with similar profile, confirms that the gas is photo-ionized and at a temperature of T~10^5 K.

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arXiv2001

Inversion of the Lyman-$α$ forest: 3D investigation of the intergalactic medium

We discuss the implementation of Bayesian inversion methods in order to recover the properties of the intergalactic medium from observations of the neutral hydrogen Lyman-$α$ absorptions observed in the spectra of high redshift quasars (the so-called Lyman-$α$ forest). We use two complementary schemes (i) a constrained Gaussian random field linear approach and (ii) a more general non-linear explicit Bayesian deconvolution method which offers in particular the possibility to constrain the parameters of the equation of state for the gas. While relying on prior assumption for the two-point correlation functions, we show how to recover, at least qualitatively, the 3D topology of the large scale structures in redshift space by inverting a suitable network of adjacent, low resolution lines of sight. We also discuss the inversion of single lines of sight observed at high spectral resolution. Our preliminary investigations suggest that the explicit Bayesian method can be used to derive quantitative information on the physical state of the gas. Redshift distortion is considered by simultaneous constrained reconstruction of the velocity and the density field in real space while assuming statistical correlation between the two fields. The method seems to work well in the strong prior regime where peculiar velocities are assumed to be the most likely realization in the density field. Finally, we investigate the effect of line of sight separation and number of lines of sight. Our analyses suggest that multiple low resolution lines of sight could be used to improve most likely velocity reconstruction on a high resolution line of sight.

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arXiv2001

A near-solar metallicity damped Lyman-alpha system toward the BAL quasar Tol 1037-2703

We report the detection of a Broad Absorption Line (BAL) outflow in the spectrum of Tol 1037-2703 with three main BALs at 36000, 25300 and 22300~\kms outflow velocities. Although the overall flow is dominated by high ionization lines like and C IV, the gas of highest velocity shows absorption from Mg I, Mg II and Fe II. Covering factor arguments suggest that the absorbing complexes are physically associated with the QSO and have transverse dimensions smaller than that of the UV continuum emitting region (r<0.1 pc). We show that the C IV absorption at \zabs=2.082 has a covering factor $\sim$ 0.86 and the absorption profile has varied over the last four years. The detection of absorption from excited fine structure levels of C II and Si II in narrow components embedded in the C IV trough reveals large density inhomogeneities. IR pumping is the most likely excitation process. The \zabs=2.139 system is a damped system with log N(H I) ~ 19.7. The weakness of the metal lines together with the high quality of the data make the metallicity measurements particularly reliable. The absolute metallicity is close to solar with [Zn/H]=-0.26. The $α$-chain elements have metallicities consistently solar (respectively +0.05, -0.02, -0.03 and -0.15 for [Mg/H], [Si/H], [P/H] and [S/H]) and iron peak elements are depleted by a factor of about two ([Fe/Zn], [Cr/Zn], [Mn/Zn] and [Ni/Zn] are equal to -0.39, -0.27, -0.49, -0.30). Lines from C I are detected but H$_2$ is absent with a molecular fraction less than 8$\times10^{-6}$. High metallicity and low nitrogen abundance, [N/Zn]=-1.40, favor the idea that metals have been released by massive stars during a starburst of less than 0.5 Gyr of age. (abridged)

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arXiv2001

Adaptive optics imaging of low and intermediate redshift quasars

We present the results of adaptive-optics imaging in the H and K bands of 12 low and intermediate redshift (z<0.6) quasars using the PUEO system mounted on the Canada-France-Hawaii telescope. Five quasars are radio-quiet and seven are radio-loud. The images, obtained under poor seeing conditions, and with the QSOs (mV>15.0) themselves as reference for the correction, have typical spatial resolution of FWHM~0.3 arcsec before deconvolution. The deconvolved H-band image of PG1700+514 has a spatial resolution of 0.16 arcsec and reveals a wealth of details on the companion and the host-galaxy. Four out of the twelve quasars have close companions and obvious signs of interactions. The two-dimensional images of three of the host-galaxies unambiguously reveal bars and spiral arms. The morphology of the other objects are difficult to determine from one dimensional surface brightness profile and deeper images are needed. Analysis of mocked data shows that elliptical galaxies are always recognized as such, whereas disk hosts can be missed for small disk scale lengths and large QSO contributions.

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arXiv2000

Integral field spectroscopy of the radio galaxy 3C 171

We have performed integral field spectroscopy of the radio galaxy 3C 171 (redshift z=0.238) with the TIGER instrument at the Canada France Hawaii telescope in the Hbeta-[OIII]4959-5007 wavelength region. We present the reconstructed Hbeta and [OIII] images and compare them to the HST and radio maps. We discuss the variations of the [OIII]/Hbeta line ratio throughout the nebulosity. We also analyze the velocity field in detail, in particular the presence of several components. We find that the kinematics derived with emission lines in the central region (inside 1 arcsec) are compatible with a disk-like rotation of low amplitude (50 km/s). The continuum surface brightness profile follows an r^{1/4} law, suggesting that the underlying galaxy is an elliptical with an effective radius of 15 kpc. We have fit two components in the region centered 2.7 arcsec to the West and of extension 3 arcsec^2. We find that the blueshifted component is an extension of the central part, whereas the second one is redshifted by 600 km/s. In both components, line ratios and FWHM are compatible with the presence of shocks induced by jet-cloud interactions.

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