arXiv subjects

Patrick Petitjean

Publications and source records attributed to Patrick Petitjean.

162 records · Page 9Linked to original sources

arXiv2001

Inhomogeneous metal enrichment at z \sim 1.9: the Lyman limit systems in the spectrum of the HDF-S quasar

We present a detailed analysis of three metal absorption systems observed in the spectrum of the HDF-South quasar J2233-606 (z_em = 2.238), taking advantage of new VLT-UVES high resolution data (R=45000, S/N = 40-60, λλ3050-10000 Å). Three main components, spanning about 300 km/s, can be individuated in the Lyman limit system at z~1.92. They show a surprisingly large variation in metallicities, respectively ~1/500, 1/8 and 1/100 solar. The large value found for the second component at z=1.9259, suggests that the line of sight crosses a star-forming region. In addition, there is a definite correlation between velocity position and ionisation state in this component, which we interpret as a possible signature of an expanding H II region. The systems at z~1.94 and z~1.87 have also high metallicity, ~1/4 and 1/3 solar. We find that photoionisation and collisional ionisation are equal alternatives to explain the high excitation phase revealed by O VI absorption, seen in these two systems. From the width of the Si IV, C IV, Si III and C III lines in the system at z~1.87, we can estimate the temperature of the gas to be log T ~ 4.7, excluding collisional ionisation. Finally, we compute the Si IV/C IV ratio for all Voigt profile components in a sample of log N(C IV) > 14 systems at z < 2. The values show a dispersion of more than an order of magnitude and most of them are much larger than what is observed for weaker systems. This is probably an indication that high column density systems preferably originate in galactic halos and are mostly influenced by local ionising sources.

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arXiv2000

The microwave background temperature at the redshift of 2.33771

The Cosmic Microwave Background radiation is a fundamental prediction of Hot Big Bang cosmology. The temperature of its black-body spectrum has been measured at the present time, $T_{\rm CMBR,0}$ = 2.726$\pm$ 0.010 K, and is predicted to have been higher in the past. At earlier time, the temperature can be measured, in principle, using the excitation of atomic fine structure levels by the radiation field. All previous measurements however give only upper limits as they assume that no other significant source of excitation is present. Here we report the detection of absorption from the first {\sl and} second fine-structure levels of neutral carbon atoms in an isolated remote cloud at a redshift of 2.33771. In addition, the unusual detection of molecular hydrogen in several rotational levels and the presence of ionized carbon in its excited fine structure level make the absorption system unique to constrain, directly from observation, the different excitation processes at play. It is shown for the first time that the cosmic radiation was warmer in the past. We find 6.0 < T_{\rm CMBR} < 14 K at z = 2.33771 when 9.1 K is expected in the Hot Big Bang cosmology.

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arXiv2000

ATCA search for 21 cm emission from a candidate damped Ly-$α$ absorber at z = 0.101

We report a deep search for 21 cm emission/absorption from the $z \sim 0.101$ candidate damped Lyman-$α$ system towards PKS 0439-433, using the Australia Telescope Compact Array (ATCA). The spectrum shows a weak absorption feature --- at the $3.3 σ$ level --- which yields a lower limit of 730 K on the spin temperature of the system. No HI emission was detected: the $3σ$ upper limit on the HI mass of the absorber is $2.25 \times 10^9 M_{\odot}$, for a velocity spread of $\sim 70$ km s$^{-1}$. The low HI mass and the high spin temperature seem to rule out the possibility that the absorber is a large gas-rich spiral galaxy.

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arXiv2000

Molecular hydrogen and the nature of damped Lyman-alpha systems

We report results from our mini-survey for molecular hydrogen in eight high redshift damped Lyman-alpha (DLA) systems using the ESO Ultra-violet and Visible Spectrograph on the VLT. In addition, we investigate two systems using ESO public data. We include in the sample the only system where H2 was previously detected and studied at high-spectral resolution. Altogether our sample consists of eleven absorbers with 1.85 3000 K) implying a low formation rate of H2 onto dust grains. Therefore, most of the DLA systems arise in warm and diffuse neutral gas. (Abridged)

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arXiv2000

Structure of the MgII and damped Lyman-alpha systems along the line of sight to APM 08279+5255

A study of the absorption systems toward the gravitationally lensed quasar APM 08279+5255 is presented. Most of the MgII systems in the redshift range 1.2-2.07, although saturated, show large residuals at the bottom of the lines. The most likely interpretation is that individual clouds within MgII halos do cover only one of the two brightest QSO images. This reveals that MgII halos are made of a collection of clouds of radius smaller than about 1 kpc. Two strong MgII absorbers at z = 1.062 and 1.181 are studied in detail. This is the first time that the NaI3303 doublet is detected in such high redshift systems. Together with the detection of the MgI2852 transition, this strongly constrains the physical characteristics of the gas. The N(NaI)/N(MgI) ratio is found to be larger than unity, implying that the gas is cool and neutral. The column densities of NaI, CaII, MgI, TiII, MnII and FeII observed at z = 1.1801 are very close to that observed along the line of sight towards 23 Ori in our Galaxy. The shape of the QSO continuum and the relative depletion of Fe, Ti, Mn and Ca are consistent with the presence of dust at z = 1 (AV = 0.5 mag). Altogether it is found that the HI column density at z = 1 is of the order of 1 to 5 10**21 cm-2, the corresponding metallicity is in the range 1--0.3 Zsol. The objects associated with these two systems could both contribute to the lens together with another possible strong system at z = 1.1727 and the strong Lyman-alpha system at z = 2.974. The probable damped Ly-alpha system at z = 2.974 has 19.8 < log N(HI) < 20.3. The transverse dimension of the absorber is larger than 200 pc. Abundances relative to solar are -2.31, -2.26, -2.10, -2.35 and -2.37 for, respectively, Fe, Al, Si, C and O (for log N(HI) = 20.3). (Abridged)

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arXiv1999

The zabs=zem Absorption Line Systems Toward QSO J2233-606 in the Hubble Deep Field South: NeVIII770,780 absorption and partial coverage

Results of a careful analysis of the highly ionized absorption systems, observed over the redshift range 2.198--2.2215 in the zem=2.24 HDFS-QSO J2233-606, are presented. Strong OVI and NeVIII absorptions are detected. Most of the lines show signature of partial coverage which varies from species to species. This can be understood if the clouds cover the continuum emission region completely and only a fraction of the broad emission line region. Using photo-ionization models we analyze in more detail the component at zabs = 2.198. Absolute abundances are close to solar but the [N/C] abundance ratio is larger than solar. This result, which is consistent with the analysis of high-z QSO broad emission-lines, confirms the physical association of the absorbing gas with the AGN. The observed column densities of NIV, NV and NeVIII favor a two-zone model for the absorbing region where NeVIII is predominantly produced in the highly ionized zone. It is most likely that in QSO J2233-606, the region producing the NeVIII absorption can not be a warm absorber. One of the Lyalpha absorption lines at zabs = 2.2215 has a flat bottom typical of saturated lines and non-zero residual intensity in the core, consistent with partial coverage. There is no metal-line from this Lyalpha cloud detectable in the spectrum which suggests either large chemical inhomogeneities in the gas or that the gas is very highly ionized. If the latter is true the cloud could have a total hydrogen column density consistent with that of X-ray absorbers. It is therefore of first importance to check whether or not there is an X-ray warm-absorber in front of this QSO.

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arXiv1998

QSO Absorption Line Systems

It is difficult to describe in a few pages the numerous specific techniques used to study absorption lines seen in QSO spectra and to review even rapidly the field of research based on their observation and analysis. What follows is therefore a pale introduction to the invaluable contribution of these studies to our knowledge of the gaseous component of the Universe and its cosmological evolution. A rich bibliography is given which, although not complete, will be hopefully useful for further investigations. Emphasis will be laid on the impact of this field on the question of the formation and evolution of galaxies.

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arXiv1998

Molecules in QSOs and QSO Absorption Line Systems at High Redshift

Molecules dominate the cooling function of neutral metal-poor gas at high density. Observation of molecules at high redshift is thus an important tool toward understanding the physical conditions prevailing in collapsing gas. Up to now, detections are sparse because of small filling factor and/or sensitivity limitations. However, we are at an exciting time where new capabilities offer the propect of a systematic search either in absorption using the UV Lyman-Werner H2 bands or in emission using the CO emission lines redshifted in the sub-millimeter.

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arXiv1998

HST Observations of the QSO pair Q1026-0045A,B

The spatial distribution of the Ly$α$ forest is studied using new HST data for the quasar pair Q~1026--0045 A and B at $z_{em}$ = 1.438 and 1.520 respectively. The angular separation is 36 arcsec and corresponds to transverse linear separations between lines of sight of $\sim300h^{-1}_{50}$ kpc ($q_{o}$ = 0.5) over the redshift range 0.833 < z < 1.438. From the observed numbers of coincident and anti-coincident Ly$α$ absorption lines, we conclude that, at this redshift, the Ly$α$ structures have typical dimensions of $\sim500h^{-1}_{50}$ kpc, larger than the mean separation of the two lines of sight. The velocity difference, $ΔV$, between coincident lines is surprisingly small (4 and 8 pairs with $ΔV < 50 and 200 km/s respectively). Metal line systems are present at $z_{abs}$ = 1.2651 and 1.2969 in A, $z_{abs}$ = 0.6320, 0.7090, 1.2651 and 1.4844 in B. In addition we tentatively identify a weak Mg II system at $z_{abs}$ = 0.11 in B. It is remarkable that the $z_{abs}$ = 1.2651 system is common to both lines of sight. The system at $z_{abs}$ = 1.4844 %is probably associated and has strong O~VI absorption. There is a metal-poor associated system at $z_{abs}$ = 1.4420 along the line of sight to A with complex velocity profile. We detect a strong Ly$α$ absorption along the line of sight to B redshifted by only 300 km/s relatively to the associated system. It is tempting to interpret this as the presence of a disk of radius larger than 300$h^{-1}_{50}$ kpc surrounding quasar A.

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arXiv1998

Are Damped Lyman alpha Systems Rotating Disks ?

We report on high spectral resolution observations of five damped Lyman alpha systems whose line velocity profiles and abundances are analyzed. By combining these data with information from the literature, we study the kinematics of the low and high ionization phases of damped systems and discuss the possibility that part of the motions is due to rotation.

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arXiv1997

The second detection of CO at redshift larger than 4

We report the detection with the IRAM interferometer at 3mm of J=5-4 CO line in the radio quiet quasar BRI1335-0415 at redshift of z=4.41. After BR1202-0725 at z=4.69 (Ohta etal 1996, Omont etal 1996a), this is the second detection of CO at z>3. The integrated line intensity is 2.8+-0.3 Jy km s^{-1} with a linewidth of 420+-60 km s^{-1}. The dust continuum emission has also been mapped at 1.35mm. The 1.35mm flux is found to be 5.6+-1.1mJy. The ratio of the CO to 1.35mm continuum flux is slightly larger than for BR1202-0725. Contrary to the case of BR1202-0725, there is only marginal evidence of extension of the 1.35mm continuum and 3mm CO emission. In the absence of gravitational lensing, for which there is no a priori evidence, and within the uncertainties of the CO to M(H_2) conversion factors, the mass of molecular gas M(H_2) could be 10^{11} solar masses.

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arXiv1996

Clustering of absorption line systems

Absorption line systems are luminosity unbiased tracers of the spatial distribution of baryons over most of the history of the Universe. I review the importance of studying the clustering properties of the absorbers and the impact of VLT in this subject. The primary aim of the project is to track the evolution of the structures of the Universe back in time.

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arXiv1996

Molecular gas and dust around a radio-quiet quasar at redshift 4.7

We report the detection of emission from dust and carbon monoxide in the radio-quiet quasar BR1202--0725 at redshift z=4.7. Maps of these emissions reveal two objects separated by a few arc seconds, which could indicate either the presence of a companion to the quasar or gravitational lensing of the quasar itself. Regardless of the precise interpretation of the maps, the detection of carbon monoxide confirms the presence of a large mass of molecular gas in one of the most distant galaxies known, and shows that conditions conducive to huge bursts of star formation existed in the early Universe.

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arXiv1996

A damped Ly-alpha candidate at z~0.1 toward Q 0439-433

We report on the detection of a z_gal=0.101 galaxy projected on the sky at 4.2 arcsec (or 5.2 h^{-1} kpc for q_o=0.5) from the quasar Q 0439-433 (z_em=0.594). The HST spectrum of the quasar shows strong MgII, FeII, SiII, AlII and CIV absorption lines at the same redshift as the galaxy. The equivalent width ratios of the low ionization lines indicate that this system is probably damped with a neutral hydrogen column density of N_HI~10^{20}cm^{-2}. The CIV doublet presents a complex structure, and in particular a satellite with a velocity v=1100km/s relative to the galaxy. Additional HST and redshifted 21cm observations of this QSO-galaxy pair would offer an ideal opportunity to study the morphology of a damped absorber and the kinematics of the halo of a low-redshift galaxy.

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arXiv1996

Physical conditions in metal line systems toward Q1037-2704: Evidence for superclustering at z=2

We present a high spectral resolution optical spectrum of the bright quasar Q~1037-2704. The large number of absorption systems suggests the presence of an intervening supercluster, but the issue remains controversial.\par We demonstrate that the strong CIV system at z=2.08 spanning more than 1500 km/s is made up of narrow components with typical Doppler parameter b=8 km/s. The gas is probably photo-ionized in which case the photo-ionizing spectrum should be dominated by stellar radiation. Analysis of HI, SiIV, NV and CIV absorptions shows that the gas has a fairly large metal content, Z>0.1Zsolar. We detect CII*1335 absorption in subcomponents of the z=2.133 system, which have moderate total CII column densities implying an electronic density of ne=3/cm3. In addition, the weakness of the OI1302, SiII1304 and FeII1608 lines allows a detailed analysis of the line profiles. The results are that the system has four narrow (b=10km/s) components; the oxygen abundance is of the order of 0.03 solar; the iron abundance is surprisingly large [Fe/O]=[Fe/O]solar+0.3. If photo-ionized by the UV flux from the quasar, the distance between the absorber and the quasar should be larger than 0.3 Mpc. This demontrates that the gas is not associated with the quasar and, together with the detection of eight multiple metal systems between z=1.91 and 2.13, suggests the presence of a coherent structure extended over 80 Mpc along the line of sight.

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arXiv1995

Evolution of the Ly$α$ forest: a consistent picture

We study the evolution with redshift of the number density of Ly$α$ clouds in a CDM model using numerical simulations including photo-ionization and cooling of the baryonic component. The photo-ionizing flux is consistently taken as proportional to the rate at which material cools below 5000~K in the simulation. The number density of lines with $N$(HI)~$>$~10$^{14}$~cm$^{-2}$ given by the simulation can be approximated as d$n$/d$z$~$\sim$~16.8(1+$z$)$^{0.8}$+0.687(1+z)$^{2.5}$ which fits well the data at any redshift. The number of weaker lines is reproduced within a factor of two and does not decrease with time as fast as the number of strong lines. For $N$(HI)~$>$~10$^{13}$~cm$^{-2}$, we find d$n$/d$z$~$\propto$~(1+$z$)$^{0.7}$. \par At $z$~=~0, the two-point correlation function for Lyman$α$ clouds with $N$(HI)~$>$~10$^{13}$ and $>$~10$^{14}$~cm$^{-2}$ has a slope $\sim$~-1.75 comparable to the slope of the two point correlation function for the galaxy distribution. The signal is higher for stronger lines for separations smaller than 1~Mpc. Part of the Lyman$α$ forest is indeed associated with galaxies however the overall picture is that Ly$α$ absorption lines originate in the warm gas that traces the potential wells of filamentary structures defined by the dark matter.

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arXiv1995

The metal line systems in HS1700+6416: Evidence for inhomogeneities

We present a high S/N ratio optical spectrum of the bright quasar HS1700+6416. These data usefully complement the UV HST data from Vogel and Reimers (1995). We analyse the metal line systems using photo-ionization models allowing for inhomogeneities in the gas. The models are able to reproduce within a factor of two the large N(HeI)/N(HI) ratio together with the mean column densities of the heavy element species observed in the z=2 systems. The density contrast between low and high density regions is of the order of 30. Although the [O/C] abundance ratio seems slighly larger than solar, firm conclusion should await higher spectral resolution data. A break at the HeII ionization limit of a factor of ten is acceptable in the ionizing spectrum. Abundances are found to be about 0.08 solar. This together with other determinations from the literature indicates that there is evolution in the metal content of metal line systems with redshift: [Mg/H] is slighly below solar at z=0.7 and [C/H]=0.1-0.01 at z=2. We detect an associated CIV system at z=2.7126 in which there is some evidence for the presence of NeVIII, probably NeVI, NeVII, and possibly SiXII.

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arXiv1995

THE LYMAN-ALPHA FOREST AT LOW REDSHIFT: TRACING THE DARK MATTER FILAMENTS

We study the distribution of low-redshift Ly$α$ clouds in a CDM model using numerical simulations including photoionization and cooling of the baryonic component. The ionizing background is found to be efficient enough to keep most of the gas warm ($T$~=~1--5~10$^4$~K) and to prevent most of it from collapsing. In this scenario, the numerous low redshift ($z$~$<$~0.5) neutral hydrogen Ly$α$ lines recently revealed by HST observations of QSOs originate in the warm gas that traces the potential wells of filamentary structures defined by the dark matter. The predicted line number density is consistent with observations. About 25\% of the Ly$α$ lines are found to arise in extended envelopes of luminous galaxies or groups of galaxies ($M$~$>$~3~10$^{11}$~M$_{\odot}$) of radius of the order of 1.5~Mpc. The exact number, however, is model dependent. The remainder arises in gas independent of any galaxy and at a distance of 2 to 7~Mpc from the first neighbour galaxy.

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