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Patrick Petitjean

Publications and source records attributed to Patrick Petitjean.

At least 145 records · Page 8Linked to original sources
arXiv2005

Molecular hydrogen in the diffuse interstellar medium at high redshift

Physical conditions within DLAs can reveal the star formation history, determine the chemical composition of the associated ISM, and hence document the first steps in the formation of present day galaxies. Here we present calculations that self-consistently determine the gas ionization, level populations (atomic fine-structure levels and rotational levels of H_2), grain physics, and chemistry. We show that for a low-density gas (n< 0.1 cm^-3) the meta-galactic UV background due to quasars is sufficient to maintain H_2 column densities below the detection limit (i.e N(H_2)< 10^14 cm^-2) irrespective of the metallicity and dust content in the gas. Such a gas will have a 21 cm spin temperature in excess of 7000 K and very low C I and C II* column densities for H I column densities typically observed in DLAs. We show that the observed properties of the ~15% per cent of the DLAs that do show detectable H_2 absorption cannot be reproduced with only the quasar dominated meta-galactic UV radiation field. Gas with higher densities (n>10 cm^-3), a moderate radiation field (flux density one to ten times that of the background radiation of the Galactic ISM), the observed range of metallicity and dust-to-gas ratio reproduce all the observed properties of the DLAs that show H_2 absorption lines. This favors the presence of ongoing star formation in DLAs with H_2. The absence of detectable H_2 and C I absorption in a large fraction of DLAs can be explained if they originate either in a low-density gas or in a high-density gas with a large ambient radiation field. The absence of 21 cm absorption and C II* absorption will be consistent with the first possibility. The presence of 21 cm absorption and strong C II* without H_2 and C I absorption will suggest the second alternative. (Abridged)

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arXiv2005

The VLT-UVES survey for molecular hydrogen in high-redshift damped Lyman-alpha systems: Physical conditions in the neutral gas

We study the physical conditions in DLAs, using a sample of 33 systems toward 26 QSOs acquired for a recently completed survey of H_2 by Ledoux et al. (2003). We use the column densities of H_2 in different rotational levels, together with those of C I, C I*, C I**, C II* and singly ionized atomic species to discuss the kinetic temperature, the density of hydrogen and the electronic density in the gas together with the ambient UV radiation field. Detailed comparisons are made between the observed properties in DLAs, the interstellar medium (ISM) of the Galaxy, LMC and SMC. The mean kinetic temperature of the gas corresponding to DLA subcomponents in which H_2 absorption line is detected, derived from the ortho-to-para ratio (153+/-78 K), is higher than that measured in the ISM (77+/-17 K) and the Magellanic clouds (82+/-21 K). Typical pressure in these components (corresponding to T = 100-300 K and n = 10-200 cm^-3), measured using C I fine-structure excitation, are higher than what is measured along ISM sightlines. This is consistent with the corresponding higher values for N(H_2,J=2)/N(H_2,J=0) seen in DLAs. From the column densities of the high-J rotational levels, we derive that the typical radiation field in the H_2 bearing components is of the order of or slightly higher than the mean UV field in the Galactic ISM. Determination of electron density in the gas with H_2 and C I show the ionization rate is similar to that of a cold neutral medium (CNM) in a moderate radiation field. This, together with the fact that we see H_2 in 13-20% of the DLAs, can be used to conclude that DLAs at z>1.9 could contribute as much as 50% star formation rate density seen in Lyman break galaxies (LBGs). (Abridged)

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arXiv2004

Probing the time-variation of the fine-structure constant: Results based on Si IV doublets from a UVES sample

We report a new constraint on the variation of the fine-structure constant based on the analysis of 15 Si IV doublets selected from a ESO-UVES sample. We find Δα/α= (+0.15+/-0.43) x 10^-5 over a redshift range of 1.59< z < 2.92 which is consistent with no variation in α. This result represents a factor of three improvement on the constraint on Δα/αbased on Si IV doublets compared to the published results in the literature. The alkali doublet method used here avoids the implicit assumptions used in the many-multiplet method that chemical and ionization inhomogeneities are negligible and isotopic abundances are close to the terrestrial value.

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arXiv2004

Limits on the time variation of the electromagnetic fine-structure constant in the low energy limit from absorption lines in the spectra of distant quasars

Most of the successful physical theories rely on the constancy of few fundamental quantities (such as the speed of light, $c$, the fine-structure constant, α, the proton to electron mass ratio, μ, etc), and constraining the possible time variations of these fundamental quantities is an important step toward a complete physical theory. Time variation of αcan be accurately probed using absorption lines seen in the spectra of distant quasars. Here, we present the results of a detailed many-multiplet analysis performed on a new sample of Mg II systems observed in high quality quasar spectra obtained using the Very Large Telescope. The weighted mean value of the variation in αderived from our analysis over the redshift range 0.4<z<2.3 is Δα/α= (-0.06+/-0.06) x 10^{-5}. The median redshift of our sample (z=1.55) corresponds to a look-back time of 9.7 Gyr in the most favored cosmological model today. This gives a 3σlimit, -2.5 x 10^{-16} yr^-1 <(Δα/αΔt) <+1.2x10^{-16} yr^-1, for the time variation of α, that forms the strongest constraint obtained based on high redshift quasar absorption line systems.

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arXiv2004

Metals in the Intergalactic Medium

We use high spectral resolution (R=45000) and high signal-to-noise ratio (S/N \~ 35-70 per pixel) spectra of 19 high-redshift (2.1 1. Our observations strongly suggest that the CIV/HI ratio decreases with decreasing tau(HI) with log[tau(CIV)]=1.3xlog[tau(HI)]-3.2. We do not detect CIV absorption statistically associated with gas of tau(HI)<1. However, we observe that a small fraction of the low density gas is associated with strong metal lines as a probable consequence of the IGM enrichment being highly inhomogeneous. We detect the presence of OVI down to tau(HI)~0.2 with log[tau(OVI)/tau(HI)] -2.0. We show that OVI absorption in the lowest density gas is located within ~300 km/s from strong HI lines. This suggests that this OVI phase may be part of winds flowing away from overdense regions. This effect is more important at the largest redshifts (z>2.4). Therefore, at the limit of present surveys, the presence of metals in the underdense regions of the IGM is still to be demonstrated.

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arXiv2003

CIV Absorbers in z>4 Quasars: Tracing Early Galactic Halos Evolution

We use 29 z>4 quasar spectra to build a homogeneous sample of high-redshift CIV absorbers. We use these data to calculate the number density, n(z), of W_rest(CIV)>0.30 A CIV doublets. We find that n(z) increases with time from z ~ 4.5. In addition, W_rest(CIV)>0.15 A CIV systems are more numerous than the former at all redshifts. On the contrary, n(z) of W_rest(MgII)>0.30 A MgII doublets decreases with time, in agreement with results from studies of LLS number densities. Below z<3, none of all the classes of absorbers show signs of evolution. We interpret this as the formation of galactic envelopes from smaller halos. Furthermore, the doublet ratio DR=W(CIV 1548)/W(CIV 1550) is found to decrease with time, a signature of the increase of the mean CIV column density. Finally, the W(SiIV 1393)/W(CIV 1548) ratios in strong absorbers (W_rest(CIV 1548) > 0.50 A) is found to be approximately constant from z=3.5 to z=2.5 and then to decrease with time. This result suggests that the highest column density absorbers are not sensitive to changes in the ionization continuum.

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arXiv2003

The Sizes and Kinematic Structure of Absorption Systems Towards the Lensed Quasar APM08279+5255

We have obtained spatially resolved spectra of the z=3.911 triply imaged QSO APM08279+5255 using the Space Telescope Imaging Spectrograph (STIS) on board the Hubble Space Telescope (HST). We study the line of sight equivalent width (EW) differences and velocity shear of high and low ionization absorbers (including a damped Lyman alpha [DLA] system identified in a spatially unresolved ground based spectrum) in the three lines of sight. We find that high ionization systems (primarily CIV absorbers) do not exhibit strong EW variations on scales <0.4 kpc; their fractional EW differences are typically less than 30%. When combined with previous work on other QSO pairs, we find that the fractional variation increases steadily with separation out to at least ~100 kpc. Conversely, low ionization systems (primarily MgII absorbers) show strong variations (often > 80%) over kpc scales. A minimum radius for strong (EW > 0.3 A) MgII systems of > 1.4 kpc is inferred from absorption coincidences in all lines of sight. For weak MgII absorbers (EW < 0.3 A), a maximum likelihood analysis indicates a most probable coherence scale of 2.0 kpc for a uniform spherical geometry, with 95% confidence limits ranging between 1.5 and 4.4 kpc. Finally, for systems with weak absorption that can be confidently converted to column densities, we find constant N(CIV)/N(SiIV) across the three lines of sight. Similarly, the [Al/Fe] ratios in the z = 2.974 DLA are consistent with solar relative abundances over a transverse distance of \~0.35 kpc. (abrdiged)

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arXiv2003

The Clustering of Intergalactic Metals

We measure the spatial clustering of metals in the intergalactic medium from z = 1.7 to 3.0, as traced by 643 CIV and 104 SiIV N >= 10^12 cm^-2 absorption systems in 19 high signal-to-noise (40-80) and high resolution (R = 45000) quasar spectra. The number densities and two-point correlation functions of both these species are largely constant with redshift, suggesting the bulk of metal ejection occurred at z >= 3. However, at z <= 1.9 some additional signature appears in the CIV correlation function at 500 km/s, associated with four strong and peculiar systems. At all redshifts, the CIV and SiIV correlation functions exhibit a steep rise at large separations and a flatter profile at small separations, with an elbow occurring at ~150 km/s. We show that these properties are consistent with metals confined within bubbles with a typical radius R_s about sources of mass >= M_s, and use numerical simulations to derive best-fit values of R_s ~ 2 comoving Mpc and M_s ~ 5x10^11 solar masses at z = 3. This does not exclude that metals could have been produced at higher redshifts in smaller, but equally rare, objects. At the level of detection of this survey, IGM enrichment is likely to be incomplete and inhomogeneous, with a filling factor ~ 10%.

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arXiv2003

The Structure of High Redshift Galactic Halos

Observations of multiple or lensed QSOs at high redshift can be used to probe transverse structure in intervening absorption systems. Here we present results obtained from STIS spectroscopy of the unique triply imaged QSO APM08279+5255 at z = 3.9 and study the coherence scales of intervening low and high ionization absorbers.

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arXiv2003

Outflowing material in the zem = 4.92 BAL QSO SDSS~J160501.21-011220.0

We present the analysis of two BALs seen in the spectrum of the QSO SDSS J160501.21-011220.0. Our UVES spectrum shows two well detached BALs at z(abs)= 4.685 and 4.855. The system at z(abs)= 4.855 covers the background source completely suggesting that the gas is located outside the BLR. On the contrary the system at z(abs)= 4.685 has a covering factor of ~0.9. The observed H I absorption line together with the limits on C II and Si II absorptions suggest that 16<log N(H I) (cm^{-2})<~17 in z(abs) = 4.855 absorption system. Comparison with models show that the observed column densities of N V, Si IV and C IV in this system require that N is underabundant by more than a factor 3 compared to Si if the ionizing radiation is similar to a typical QSO spectrum. This is contrary to what is usually derived for the emission line gas in QSOs. We show that the relative suppression in the N V column density can be explained for Solar abundance ratios or abundance ratios typical of Starburst abundances if an ionizing spectrum devoid of X-rays is used instead. Thus, if the composition of BAL is like that of BLR then it is most likely that the cloud sees a spectrum devoid of X-rays similar to what we observe from this QSO. This is consistent with the fact that none of our models have high Compton optical depth to remove X-rays from the QSO. Similar arguments lead to the conclusion that the system at z(abs)= 4.685 as well is not Compton thick. The estimated black hole mass is 8 10^8 solar mass suggesting the accretion onto the seed black hole must have started as early as z = 11.

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arXiv2002

The warm-hot intergalactic medium at z~2.2: Metal enrichment and ionization source

Results are presented for our search for warm-hot gas towards the quasar Q 0329-385. We identify ten OVI systems of which two are within 5000 km/s of z_em and a third one should be of intrinsic origin. The seven remaining systems have HI column densities 10^13.7<N(HI)<10^15.6 cm^-2. At least ~1/3 of the individual OVI sub-systems have temperatures T<1x10^5 K and cannot originate in collisionally ionized gas. Photoionization by a hard UV background field reproduces well the ionic ratios for metallicities in the range 10^-2.5 - 10^-0.5 solar, with possibly sub-solar N/C relative abundance. For [O/C]=0, the sizes inferred for the OVI clouds are in some cases larger than the maximum extent implied by the Hubble flow. This constraint is fulfilled assuming a moderate overabundance of oxygen relative to carbon. For a soft UV ionizing spectrum, an overabundance of O/C is required, [O/C]~0.0-1.3. For a hard(soft) UV spectrum and [O/C]=0(1), the OVI regions have overdensities in 10-40.

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arXiv2002

A new measurement of zinc metallicity in a DLA at z=3.35

We present chemical abundance measurements in the z_abs=3.35045 Damped Lyman-alpha (DLA) system observed in the UVES spectrum of the BAL quasar BR 1117-1329. We measure a neutral hydrogen column density N(HI)=6.9+/-1.7*10^{20} atoms/cm2 and derive mean abundances relative to solar: [Si/H] = -1.26+/-0.13, [Fe/H]=-1.51+/-0.13, [Ni/H]=-1.57+/-0.13, [Cr/H]=-1.36+/-0.13, [Zn/H]=-1.18+/-0.13, [Al/H]>-1.25, [O/H]>-1.25 and [N/H]<-2.24. This is the third measurement of Zn, an element mildly depleted onto dust grain, at z_abs>3. The iron to zinc and chromium to zinc ratios, [Fe/Zn]=-0.33+/-0.05 and [Cr/Zn]=-0.18+/-0.05 demonstrate that the absorber has a low dust content. The nitrogen ratio [N/Si]<-0.98 suggests that the ``secondary'' N production process is taking place in this DLA. Finally, this absorber does not seem to present a convincing alpha-enhancement as shown by the alpha over Fe-peak element ratios: [Si/Fe]=0.25+/-0.06, [Si/Cr]=0.10+/-0.06 and [Si/Zn]=-0.08+/-0.06.

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arXiv2002

The Abundances of Nitrogen and Oxygen in Damped Lyman Alpha Systems

We take a fresh look at the abundance of nitrogen in DLAs with oxygen abundances between 1/10 and 1/100 of solar. This is a metallicity regime poorly sampled in the local universe and where QSO absorbers may hold clues to both the nucleosynthetic origin of N and the chemical evolution of high redshift galaxies. We combine new VLT UVES observations with others from the literature to form a sample of 10 DLAs in which the abundances of N and of one of the two alpha-capture elements O or S have been measured. We confirm earlier reports that the (N/O) ratio exhibits a larger range of values than other ratios of heavy elements in DLAs; however, all 10 DLAs fall in the region of the (N/O) vs. (O/H) plot delimited by the primary and secondary levels of nitrogen production. Our results provide empirical evidence in support of the proposal that intermediate mass stars (with masses less than 7 solar masses) are the main source of primary nitrogen, so that its release into the ISM lags behind that of oxygen, which is produced by Type II SNae. A high proportion (40%) of the DLAs in our sample have apparently not yet attained the full primary level of N enrichment; this finding may be an indication that the metallicity regime we are studying preferentially picks out galaxies which have only recently condensed out of the IGM and begun forming stars. Alternatively, the delay in the release of N following an episode of star formation may increase with decreasing metallicity, if stars of progressively lower masses than 4 solar masses can synthesize N in their hotter interiors.

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arXiv2002

Spatially resolved STIS spectra of the gravitationally lensed BAL quasar APM08279+5255: the nature of component C and evidence for microlensing

While gravitationally lensed quasars are expected to display an odd number of images, invariably systems are observed with an even number of quasars. For this, lensing galaxies must have very small core radii; this provides strong demagnification of one of the images. High resolution imaging of the gravitationally lensed BAL quasar, APM08279+5255, reveals three point-like images. As these images possess similar colours, it has been suggested that each represents a lensed image. Here, spatially resolved spectra of the individual components, obtained with STIS on the HST, are presented, clearly revealing that each is an image of the quasar. This confirms that APM08279+5255 represents the first example of an odd-image gravitationally lensed system. The implications for the properties of the lensing galaxy are discussed. It is also found that the individual images possess spectral differences indicative of the influence of gravitational microlensing in this system.

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arXiv2002

High matter density peaks from UVES observations of QSO pairs: correlation properties and chemical abundances

We study the transverse clustering properties of high matter density peaks as traced by high column density absorption systems (either Lyman limit systems characterized by N(HI)> 2 x 10^{17} cm^{-2} or CIV systems with W_{r}> 0.5 A) at redshifts between 2 and 3 with UVES spectra of two QSO pairs (UM680/UM681 at 56 arcsec angular separation and Q2344+1228/Q2343+1232 at 5 arcmin angular separation) and a QSO triplet (Q2139-4433/Q2139-4434/Q2138-4427 at 1, 7 and 8 arcmin angular separation). We find 3 damped Ly-alpha systems (N(HI)> 2 x 10^{20} cm^{-2}): 2 coinciding with strong metal systems in the nearby line of sight and 1 matching the emission redshift of the paired QSO; plus 7 Lyman limit systems: 4 forming two matching couples and 3 without a corresponding metal system within ~3000 km/s in the coupled line of sight. In summary, we detect five out of ten matching systems within 1000 km/s, indicating a highly significant overdensity of strong absorption systems over separation lengths from ~1 to 8 h^{-1} Mpc. The observed coincidences could arise in gas due to starburst-driven superwinds associated with a quasar or a galaxy, or gas belonging to large scale structures like filaments or sheets. We also determine chemical abundance ratios for three damped Ly-alpha systems. In particular, for the damped system at z ~ 2.53788 in the spectrum of Q2344+1228, new estimates of the ratios O/Fe, C/Fe are obtained: [C/Fe]<0.06, [O/Fe]<0.2. They indicate that O and C are not over-solar in this system.

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arXiv2002

Molecular hydrogen at z=1.973 toward Q0013-004: Dust depletion pattern in damped Lyman-alpha systems

We study the dust depletion pattern in eight well separated components of the z=1.973, logN(HI)=20.83, damped Lyman-alpha system toward Q0013-004, four of which have detectable H2 absorption. The apparent correlation between the abundance ratios [Fe/S] and [Si/S] in the components indicates that the abundance pattern is indeed due to dust-depletion. In particular, we find evidence for depletion similar to what is observed in cold gas of the Galactic disk ([Fe/Zn]=-1.59, Fe/S=-1.74, Zn/S=-0.15, [Si/S]=-0.85) in one of the weakest components in which molecular hydrogen is detected with logN(H2)=16.5. This is the first time such a large depletion is seen in a DLA system. This observation supports the possibility that current samples of DLA systems might be biased against the presence of cold and dusty gas along the line of sight. The overall metallicities of this peculiar DLA system in which OI and CII are spread over 1050 km/s are [P/H]=-0.64, [Zn/H]=-0.74 and [S/H]=-0.82 relative to solar. The sub-DLA system at z=1.96753 has [P/H]>0.06, [Zn/H]>-0.02 and [S/H]>-0.18. The overall molecular fraction is in the range -2.7<logf<-0.6. CO is not detected (logN(CO)/N(HI)<-8) and HD could be present at z=1.97380. We show that the presence of H2 is closely related to the physical conditions of the gas: high particle density together with low temperature. The observed excitation of high J H2 levels and the molecular fraction show large variations from one component to the other suggesting that the UV radiation field is highly inhomogeneous throughout the system. Gas pressure, estimated from CI absorptions, is larger than what is observed in the ISM of our Galaxy. All this is probably a consequence of intense star-formation activity in the vicinity of the absorbing gas. (Abridged)

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arXiv2001

3D Spatial Distribution of the Intergalactic Medium

Very recently a new inversion method has been developped to analyze the intergalactic medium seen in absorption in quasar spectra (the so-called Lyman-alpha forest). This method is applied to recover the temperature of the gas and the underlying density field. Using constraints from the Lyman-beta forest, it is possible to recover this field up to over-densities delta=10. By inverting the HI and CIV absorptions together it has been shown that the CIV/HI ratio varies through the profile of strong lines, beeing larger in the wings. The method can be applied to reconstruct the 3D density field from multiple lines of sight and is shown to give good results up to mean separations of 3 arcmin. Results from a survey of QSO pairs performed with HST/STIS and VLT/UVES-FORS are summarized.

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