arXiv subjects

P. Noterdaeme

Publications and source records attributed to P. Noterdaeme.

113 records · Page 7Linked to original sources

arXiv2008

First detection of CO in a high-redshift DLA

We present the first detection of carbon monoxide (CO) in a damped Lyman-alpha system (DLA) at z_abs =2.41837 toward SDSS J143912.04+111740.5. We also detected H_2 and HD molecules. The measured total column densities (in log units) of H I, H_2, and CO are 20.10\pm0.10, 19.38\pm0.10, and 13.89\pm0.02, respectively. The molecular fraction, f = 2N(H_2)/(N(HI)+2N(H_2)) = 0.27^{+0.10}_{-0.08}, is the highest among all known DLAs. The abundances relative to solar of S, Zn, Si, and Fe are -0.03\pm0.12, +0.16\pm0.11, -0.86\pm0.11, and -1.32\pm0.11, respectively, indicating a high metal enrichment and a depletion pattern onto dust-grains similar to the cold ISM of our Galaxy. The measured {N(CO)/N(H_2) = 3x10^{-6}} is much less than the conventional CO/H_2 ratio used to convert the CO emission into gaseous mass but is consistent with what is measured along translucent sightlines in the Galaxy. The CO rotational excitation temperatures are higher than those measured in our Galactic ISM for similar kinetic temperature and density. Using the C I fine structure absorption lines, we show that this is a consequence of the excitation being dominated by radiative pumping by the cosmic microwave background radiation (CMBR). From the CO excitation temperatures, we derive T_CMBR = 9.15 \pm 0.72 K, while 9.315 \pm 0.007 K is expected from the hot big-bang theory. This is the most precise high-redshift measurement of T_CMBR and the first confirmation of the theory using molecular transitions at high redshift.

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arXiv2008

Molecular hydrogen in high-redshift Damped Lyman-alpha systems: The VLT/UVES database

We present the current status of ongoing searches for molecular hydrogen in high-redshift (1.8 < zabs <= 4.2) Damped Lyman-alpha systems (DLAs) capitalising on observations performed with the ESO Very Large Telescope (VLT) Ultraviolet and Visual Echelle Spectrograph (UVES). We identify 77 DLAs/strong sub-DLAs, with log N(HI) >= 20 and z_abs > 1.8, which have data that include redshifted H2 Lyman and/or Werner-band absorption lines. This sample of HI, H2 and metal line measurements, performed in an homogeneous manner, is more than twice as large as our previous sample (Ledoux et al. 2003) and considers every system in which searches for H2 could be completed so far, including all non-detections. H2 is detected in thirteen of the systems with molecular fractions of values between f=5x10^-7 and f=0.1, where f=2N(H2)/(2N(H2)+N(HI)). Upper limits are measured for the remaining 64 systems with detection limits of typically log N(H2)=14.3, corresponding to log f<-5. We find that about 35% of the DLAs with metallicities relative to solar [X/H]>=-1.3 (i.e., 1/20th solar), with X = Zn, S or Si, have molecular fractions log f>-4.5, while H2 is detected -- regardless of the molecular fraction -- in 50% of them. In contrast, only about 4% of the [X/H]<-1.3 DLAs have log f>-4.5. We show that the presence of H2 does not strongly depend on the total neutral hydrogen column density, although the probability of finding log f>-4.5 is higher for log N(HI)>=20.8 than below this limit (19% and 7% respectively). The overall H2 detection rate in log N(HI)>=20 DLAs is found to be about 16% (10% considering only log f>-4.5 detections) after correction for a slight bias towards large N(HI). [truncated]

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arXiv2007

Excitation mechanisms in newly discovered H2-bearing Damped Lyman-alpha clouds: systems with low molecular fractions

We probe the physical conditions in high-redshift damped Ly-alpha systems using the observed molecular fraction and the rotational excitation of molecular hydrogen. We report two new detections of H2 at z = 2.402 and 1.989 toward, respectively, HE 0027-1836 and HE 2318-1107. We also present a detailed analysis of our recent H2 detection toward Q2343+125. All three systems have low molecular fractions, log f < -4, with f = 2N(H2)/(2N(H2) + N(HI)). Only one such H2 system was known previously. The depletion patterns for Si, S, Ti, Cr, Mn, Fe and Ni in the three systems are found to be very similar to what is observed in diffuse gas of the Galactic halo. H2 absorption from rotational levels up to J = 5 is observed in a single component toward HE 0027-1836. We show that the width (Doppler parameter) of the H2 lines increases with increasing J and that the kinetic energy derived from the Doppler parameter is linearly dependent on the relative energy of the rotational levels. The excitation temperature is found to be 90 K for J = 0 to J = 2 and ~500 K for higher J levels. Single isothermal PDR models fail to reproduce the observed rotational excitations. A two-component model is needed: one component of low density (~50 cm-3) with weak illumination (chi = 1) to explain the J <= 2 rotational levels and another of high density (~500 cm-3) with strong illumination (chi = 30) for J >= 3 levels. However, the juxtaposition of these two PDR components may be ad-hoc and the multicomponent structure could result either from turbulent dissipation or C-shocks.

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arXiv2007

Physical conditions in the neutral interstellar medium at z=2.43 toward Q2348-011

We obtained a high-resolution VLT-UVES spectrum of the quasar Q2348-011 over a wavelength range that covers most of the prominent metal and molecular absorption lines from the log N(HI)=20.50+-0.10 damped Lyman-alpha system at zabs=2.43. From the column density ratios and the relative populations of H2 rotational and CI fine-structure levels, we derive the physical conditions (relative abundances, dust-depletion, particle density, kinetic temperature and ionizing flux) and discuss physical conditions in the neutral phase. Molecular hydrogen is detected in seven components in the first four rotational levels (J = 0-3) of the vibrational ground state. Absorption lines of H2 J = 4 (resp. J = 5) are also detected in six (resp. two) of these components. This leads to a total molecular fraction of log f = -1.69+0.37-0.58. We confirm the earlier findings that there is a correlation between N(FeII)/N(SII) and N(SiII)/N(SII) indicative of a dust-depletion pattern. Surprisingly, however, the depletion of metals onto dust in the H2 components is not large in this system: [Fe/S] = -0.8 to -0.1. The gas in H2-bearing components is found to be cold but still hotter than similar gas in our Galaxy (T > 130 K, instead of typically 80 K). and dense (n=100-200 cm^-3). There is an anti-correlation between the logarithm of the photo-absorption rate, and log N(H2)/N(CI) derived for each H2 component. We show that this is mostly due to shielding effects and implies that the photo- absorption rate is a good indicator of the physical conditions in the gas. We find that the gas is immersed in a intense UV field, about one order of magnitude higher than in the solar vicinity. The results suggest that the gas in H2-bearing DLAs is clumpy, and star-formation occurs in the associated object.

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arXiv2006

Metallicity as a criterion to select H2 bearing Damped Lyman-alpha systems

We characterize the importance of metallicity on the presence of molecular hydrogen in damped Lyman-alpha (DLA) systems. We construct a representative sample of 18 DLA/sub-DLA systems with log N(HI)>19.5 at high redshift (zabs>1.8) with metallicities relative to solar [X/H]>-1.3(with[X/H]= logN(X)/N(H)-log(X/H)solar and X either Zn, S or Si). We gather data covering the expected wavelength range of redshifted H2 absorption lines on all systems in the sample from either the literature (10 DLAs), the UVES-archive or new VLT-UVES observations for four of them. The sample is large enough to discuss for the first time the importance of metallicity as a criterion for the presence of molecular hydrogen in the neutral phase at high-z. From the new observations, we report two new detections of molecular hydrogen in the systems at zabs=2.431 toward Q2343+125 and zabs=2.426 toward Q2348-011. We compare the H2 detection fraction in the high-metallicity sample with the detection fraction in the overall sample from Ledoux et al. (2003). We show that the fraction of DLA systems with logf=log 2N(H2)/(2N(H2)+N(HI))>-4 is as large as 50% for [X/H]>-0.7 when it is only about 5% for [X/H]<-1.3 and about 15% in the overall sample (with -2.5<[X/H]<-0.3). This demonstrates that the presence of molecular hydrogen at high redshift is strongly correlated with metallicity.

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