Publications (7)0 Total impact
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Article: Cosmological concordance or chemical coincidence? Deuterated molecular hydrogen abundances at high redshift
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ABSTRACT: We report two detections of deuterated molecular hydrogen (HD) in QSO absorption-line systems at $z > 2$. Toward J2123-0500, we find $N$(HD) $= 13.84 \pm 0.2$ for a sub-DLA with metallicity $\simeq 0.5Z_{\odot}$ and $N$(H$_2$) = $17.64 \pm 0.15$ at $z = 2.0594$. Toward FJ0812+32, we find $N$(HD) $= 15.38 \pm 0.3$ for a solar-metallicity DLA with $N$(H$_2$) = $19.88 \pm 0.2$ at $z = 2.6265$. These systems have ratios of HD to H$_2$ above that observed in dense clouds within the Milky Way disk and apparently consistent with a simple conversion from the cosmological ratio of D/H. These ratios are not readily explained by any available model of HD chemistry and there are no obvious trends with metallicity or molecular content. Taken together, these two systems and the two published $z > 2$ HD-bearing DLAs indicate that HD is either less effectively dissociated or more efficiently produced in high-redshift interstellar gas, even at low molecular fraction and/or solar metallicity. It is puzzling that such diverse systems should show such consistent HD/H$_2$ ratios. Without clear knowledge of all the aspects of HD chemistry that may help determine the ratio HD/H$_2$, we conclude that these systems are potentially more revealing of gas chemistry than of D/H itself and that it is premature to use such systems to constrain D/H at high-redshift. Comment: accepted for publication in ApJ Letters, 5 pages emulate ApJ text06/2010; -
Article: Probing fundamental constant evolution with neutral atomic gas lines
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ABSTRACT: We have detected narrow HI 21cm and CI absorption at $z \sim 1.4 - 1.6$ towards Q0458$-$020 and Q2337$-$011, and use these lines to test for possible changes in the fine structure constant $\alpha$, the proton-electron mass ratio $\mu$, and the proton gyromagnetic ratio $g_p$. A comparison between the HI 21cm and CI line redshifts yields $\Delta X/X = [+6.8 \pm 1.0] \times 10^{-6}$ over $0 < \le 1.46$, where $X = g_p \alpha^2/\mu$, and the errors are purely statistical, from the gaussian fits. The simple line profiles and the high sensitivity of the spectra imply that statistical errors in this comparison are an order of magnitude lower than in previous studies. Further, the CI lines arise in cold neutral gas that also gives rise to HI 21cm absorption, and both background quasars are core-dominated, reducing the likelihood of systematic errors due to local velocity offsets between the hyperfine and resonance lines. The dominant source of systematic error lies in the absolute wavelength calibration of the optical spectra, which appears uncertain to $\sim 2$ km/s, yielding a maximum error in $\Delta X/X$ of $\sim 6.7 \times 10^{-6}$. Including this, we obtain $\Delta X/X = [+6.8 \pm 1.0 (statistical) \pm 6.7 (max. systematic)] \times 10^{-6}$ over $0 < \le 1.46$. Using literature constraints on $\Delta \mu/\mu$, this is inconsistent with claims of a smaller value of $\alpha$ from the many-multiplet method, unless fractional changes in $g_p$ are larger than those in $\alpha$ and $\mu$. Comment: 5 pages, 3 figures, accepted for publication in ApJL03/2010; -
Article: New limit on a varying proton-to-electron mass ratio from high-resolution optical quasar spectra
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ABSTRACT: Molecular transitions recently discovered at redshift zabs=2.059 toward the bright background quasar J2123-0050 are analysed to limit cosmological variation in the proton-to-electron mass ratio, μ ≡ mp/me. Observed with the Keck telescope, the optical spectrum has the highest resolving power and largest number (86) of H2 transitions in such analyses so far. Also, (7) HD transitions are used for the first time to constrain μ-variation. These factors, and an analysis employing the fewest possible free parameters, strongly constrain μ's relative deviation from the current laboratory value: Δμ/μ =(+5.6±5.5stat±2.7sys)×10−6. This is the first Keck result to complement recent constraints from three systems at zabs>2.5 observed with the Very Large Telescope.Proceedings of the International Astronomical Union 10/2009; 5:321 - 321. -
Article: A search for HI 21cm absorption in strong MgII absorbers in the redshift desert
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ABSTRACT: We report results from a deep search for redshifted HI 21cm absorption in 55 strong MgII$\lambda$2796 absorbers (having $W (MgII) > 0.5 \AA$) at intermediate redshifts, $0.58 < z_{\rm abs} < 1.70$, with the Green Bank Telescope (GBT) and the Giant Metrewave Radio Telescope (GMRT). Nine detections of HI 21cm absorption were obtained, all at $1.17 < z_{\rm abs} < 1.68$, including three systems reported earlier by Gupta et al. (2007). Absorption was not detected at $> 3\sigma$ significance in 32 other MgII absorbers, with 26 of these providing strong upper limits to the HI 21cm optical depth, $\tau_{3\sigma} < 0.013$ per $\sim 10$ km/s. For the latter 26 systems, the spin temperature $T_s$ of the absorber must be $> [800 \times f]$ K (where $f$ is the covering factor), if the HI column density is $\ge 2 \times 10^{20}$ cm$^{-2}$, i.e. if the absorber is a damped Lyman-$\alpha$ system (DLA). Data on the remaining 13 systems of the sample were affected by radio frequency interference and were hence not useful. Excluding "associated" systems (within 3000 km/s of the quasar redshift), the detection rate of HI 21cm absorption in strong MgII absorbers is $x_{\rm 21,MgII} ({\bar z} = 1.1) = 25^{+11}_{-8}$%, at a $3\sigma$ optical depth sensitivity of $\sim 0.013$ per 10 km/s. Comparing the detection rates of HI 21cm and damped Lyman-$\alpha$ absorption in strong MgII absorber samples yields a detection rate of HI 21cm absorption in DLAs of $x_{\rm 21,DLA} ({\bar z} = 1.1) = (73 \pm 27)$%, consistent with the detection rate of HI 21cm absorption in low-$z$ DLAs. Since HI 21cm absorption arises in cold neutral gas, this indicates that most gas-rich galaxies contain significant fractions of cold HI by $z \sim 1$. (abridged)04/2009; -
Article: H i 21 cm absorption at z∼ 2.347 towards PKS B0438–436
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ABSTRACT: We report the detection of redshifted H i 21-cm absorption in the z∼ 2.347 damped Lyman α absorber (DLA) towards PKS B0438−436 with the Green Bank Telescope. This is the second-highest redshift at which 21-cm absorption has been detected in a DLA. The absorption extends over ∼60 km s−1 and has two distinct components, at z= 2.347 477(12) and z= 2.347 869(20). A similar velocity structure is seen in optical metal lines, although the peak absorption here is offset by ∼11 km s−1 from the peak in the 21-cm line. We obtain a high spin temperature Ts∼ (886 ± 248) × (f/0.58) K, using a covering factor estimated from 2.3-GHz very long baseline interferometry data. However, the current data cannot rule out a low spin temperature. The non-detection of CO 3–2 absorption places the upper limit NCO < 3.8 × 1015 (Tx/10) cm−2 on the CO column density.Monthly Notices of the Royal Astronomical Society Letters 06/2006; 370(1):L46 - L50. -
Article: HI 21cm Absorption at $z \sim 2.347$ towards PKS B0438-436
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ABSTRACT: We report the detection of redshifted HI~21cm absorption in the $z \sim 2.347$ damped Lyman-$\alpha$ absorber (DLA) towards PKS B0438-436, with the Green Bank Telescope. This is the second-highest redshift at which 21cm absorption has been detected in a DLA. The absorption extends over $\sim 60$ km/s and has two distinct components, at $z = 2.347477 (12)$ and $z = 2.347869 (20)$. A similar velocity structure is seen in optical metal lines, although the peak absorption here is offset by $\sim 11$ km/s from the peak in the 21cm line. We obtain a high spin temperature $T_s \sim (886 \pm 248) \times (f/0.58)$ K, using a covering factor estimated from 2.3 GHz VLBI data. However, the current data cannot rule out a low spin temperature. The non-detection of CO 3-2 absorption places the upper limit $N_{CO} < 3.8 \times 10^{15} \times (T_x/10)$ cm$^{-2}$ on the CO column density. Comment: 5 pages, 5 figures; accepted for publication in MNRAS (Letters)05/2006; -
Article: The first detection of cobalt in a damped Lyman alpha system
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ABSTRACT: The study of elemental abundances in damped Lyman alpha systems (DLAs) at high redshift represents one of our best opportunities to probe galaxy formation and chemical evolution at early times. By coupling measurements made in high-z DLAs with our knowledge of abundances determined locally and with nucleosynthetic models, we can start to piece together the star formation histories of these galaxies. Here, we discuss the clues to galactic chemical evolution that may be gleaned from studying the abundance of Co in DLAs. We present high resolution echelle spectra of two quasi-stellar objects (QSOs), Q22062199 and Q1223117, both already known to exhibit intervening damped systems. These observations have resulted in the first ever detection of Co at high redshift, associated with the z abs 1:92 DLA in the sightline towards Q22062199. We find that the abundance of Co is approximately 1/4 solar and that there is a clear overabundance relative to iron, ^ 0:05. From the abundance of Zn, we determine that this is a relatively metal-rich DLA, with a metallicity of approximately 1=3Z ( . Therefore, this first detection of Co is similar to the marked overabundance relative to Fe seen in Galactic bulge and thick-disc stars.10/2001;
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Institutions
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2006–2009
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University of Victoria
- Department of Physics and Astronomy
Victoria, British Columbia, Canada
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