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Max Pettini - One of the best experts on this subject based on the ideXlab platform.
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A search for H i 21 cm absorption towards a radio-selected quasar sample – II. A new low Spin Temperature DLA at high redshift
Monthly Notices of the Royal Astronomical Society, 2012Co-Authors: Nissim Kanekar, Sara L. Ellison, Emmanuel Momjian, Brian A. York, Max PettiniAbstract:We report results from a deep search for redshifted HI 21cm absorption from eight damped Lyman-$\alpha$ absorbers (DLAs) detected in our earlier optical survey for DLAs towards radio-loud quasars. HI 21cm absorption was detected from the $z = 2.192$ DLA towards TXS2039+187, only the sixth case of such a detection at $z > 2$, while upper limits on the HI 21cm optical depth were obtained in six other DLAs at $z > 2$. Our detection of HI 21cm absorption in the eighth system, at $z = 2.289$ towards TXS0311+430, has been reported earlier. We also present high spatial resolution images of the background quasars at frequencies close to the redshifted HI 21cm line frequency, allowing us to estimate the covering factor of each DLA, and then determine its Spin Temperature $T_s$. For three non-detections of HI 21cm absorption, we obtain strong lower limits on the Spin Temperature, $T_s \gtrsim 790$ K, similar to the bulk of the high-$z$ DLA population; three other DLAs yield weak lower limits, $T_s > 140-400$ K. However, for the two DLAs with detections of HI 21cm absorption, the derived Spin Temperatures are both low $T_s = (160 \pm 35) \times (f/0.35)$ K for the $z = 2.192$ DLA towards TXS2039+187 and $T_s = (72 \pm 18) \times (f/0.52)$ K for the $z = 2.289$ DLA towards TXS0311+430. These are the first two DLAs at $z > 1$ with $T_s$ values comparable to those obtained in local spiral galaxies. Based on the observed correlations between Spin Temperature and metallicity and velocity spread and metallicity in DLAs, we suggest that the hosts of the two absorbers are likely to be massive, high-metallicity galaxies.
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Discovery of 21-cm absorption in a zabs= 2.289 damped Lyman α system towards TXS 0311+430: the first low Spin Temperature absorber at z > 1
Monthly Notices of the Royal Astronomical Society: Letters, 2007Co-Authors: Brian A. York, Nissim Kanekar, Sara L. Ellison, Max PettiniAbstract:We report the detection of H i 21-cm absorption from the z= 2.289 damped Lyman α system (DLA) towards TXS 0311+430 with the Green Bank Telescope. The 21-cm absorption has a velocity spread (between nulls) of ∼110 km s−1 and an integrated optical depth of . We also present new Giant Metrewave Radio Telescope 602-MHz imaging of the radio continuum. TXS 0311+430 is unresolved at this frequency, indicating that the covering factor of the DLA is likely to be high. Combining the integrated optical depth with the DLA H i column density of yields a Spin Temperature of Ts= (138 ± 36) K, assuming a covering factor of unity. This is the first case of a low Spin Temperature ( 1 DLA and is among the lowest Temperatures ever measured in any DLA. Indeed, the Ts measured for this DLA is similar to values measured in the Milky Way and local disc galaxies. We also determine a lower limit (Si/H) ≳ 1/3 solar for the DLA metallicity, amongst the highest abundances measured in DLAs at any redshift. Based on low-redshift correlations, the low Ts, large 21-cm absorption width and high metallicity all suggest that the z∼ 2.289 DLA is likely to arise in a massive, luminous disc galaxy.
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discovery of 21 cm absorption in a zabs 2 289 damped lyman α system towards txs 0311 430 the first low Spin Temperature absorber at z 1
Monthly Notices of the Royal Astronomical Society: Letters, 2007Co-Authors: Brian A. York, Nissim Kanekar, Sara L. Ellison, Max PettiniAbstract:We report the detection of H i 21-cm absorption from the z= 2.289 damped Lyman α system (DLA) towards TXS 0311+430 with the Green Bank Telescope. The 21-cm absorption has a velocity spread (between nulls) of ∼110 km s−1 and an integrated optical depth of . We also present new Giant Metrewave Radio Telescope 602-MHz imaging of the radio continuum. TXS 0311+430 is unresolved at this frequency, indicating that the covering factor of the DLA is likely to be high. Combining the integrated optical depth with the DLA H i column density of yields a Spin Temperature of Ts= (138 ± 36) K, assuming a covering factor of unity. This is the first case of a low Spin Temperature ( 1 DLA and is among the lowest Temperatures ever measured in any DLA. Indeed, the Ts measured for this DLA is similar to values measured in the Milky Way and local disc galaxies. We also determine a lower limit (Si/H) ≳ 1/3 solar for the DLA metallicity, amongst the highest abundances measured in DLAs at any redshift. Based on low-redshift correlations, the low Ts, large 21-cm absorption width and high metallicity all suggest that the z∼ 2.289 DLA is likely to arise in a massive, luminous disc galaxy.
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an imaging and spectroscopic study of the zabs 3 38639 damped lyα system in q0201 1120 clues to star formation at high redshift
The Astrophysical Journal, 2001Co-Authors: Sara L. Ellison, Max Pettini, Charles C Steidel, Alice E ShapleyAbstract:We present the results of a series of imaging and spectroscopic observations aimed at identifying and studying the galaxy responsible for the zabs = 3.38639 damped Lyα system in the zem = 3.61 quasar Q0201+1120. We find that the damped Lyα systems (DLA) is part of a concentration of matter that includes at least four galaxies (probably many more) over linear comoving dimensions greater than 5 h-1 Mpc. The absorber may be a 0.7L* galaxy at an impact parameter of 15 h-1 kpc, but follow-up spectroscopy is still required for positive identification. The gas is turbulent, with many absorption components distributed over ~270 km s-1 and a large Spin Temperature, Ts 4000 K. The metallicity is relatively high for this redshift, ZDLA 1/20 Z☉. From consideration of the relative ratios of elements that have different nucleosynthetic timescales, it would appear that the last major episode of star formation in this DLA occurred at z 4.3, more than ~500 Myr prior to the time when we observe it.
Sara L. Ellison - One of the best experts on this subject based on the ideXlab platform.
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The Spin Temperature of high-redshift damped Lyman α systems
Monthly Notices of the Royal Astronomical Society, 2014Co-Authors: Nissim Kanekar, Alain Smette, Jayaram N. Chengalur, Sara L. Ellison, Emmanuel Momjian, Jason X. Prochaska, Emma V. Ryan-weber, F. Briggs, W. M. Lane, T. DelafosseAbstract:We report results from a programme aimed at investigating the Temperature of neutral gas in high-redshift damped Lyman α absorbers (DLAs). This involved (1) H I 21 cm absorption studies of a large sample of DLAs towards radio-loud quasars, (2) very long baseline interferometric studies to measure the low-frequency quasar core fractions, and (3) optical/ultraviolet spectroscopy to determine DLA metallicities and the velocity widths of low-ionization metal lines. Including literature data, our sample consists of 37 DLAs with estimates of the harmonic mean Spin Temperature Ts. We find a statistically significant (4σ) difference between the Ts distributions in the high-z (z > 2.4) and low-z (z 1.7 have Ts values indicating CNM fractions >20 per cent, comparable to the median value (≈27 per cent) in the Galaxy. We tested whether the H I column density measured towards the optical quasar might be systematically different from that towards the radio core by comparing the H I column densities inferred from H I 21 cm emission studies at different spatial resolutions (≈15 pc-1 kpc) in the Large Magellanic Cloud. The high-resolution NH I values are, on average, larger than the smoothed ones for NH I > 1021 cm-2, but lower than the smoothed NH I estimates for NH I 1. Since all DLAs at z > 1 have angular diameter distances comparable to or larger than those of their background quasars, they have similar efficiency in covering the quasars. We conclude that low covering factors in high-z DLAs cannot account for the observed redshift evolution in Spin Temperatures.
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A search for H i 21 cm absorption towards a radio-selected quasar sample – II. A new low Spin Temperature DLA at high redshift
Monthly Notices of the Royal Astronomical Society, 2012Co-Authors: Nissim Kanekar, Sara L. Ellison, Emmanuel Momjian, Brian A. York, Max PettiniAbstract:We report results from a deep search for redshifted HI 21cm absorption from eight damped Lyman-$\alpha$ absorbers (DLAs) detected in our earlier optical survey for DLAs towards radio-loud quasars. HI 21cm absorption was detected from the $z = 2.192$ DLA towards TXS2039+187, only the sixth case of such a detection at $z > 2$, while upper limits on the HI 21cm optical depth were obtained in six other DLAs at $z > 2$. Our detection of HI 21cm absorption in the eighth system, at $z = 2.289$ towards TXS0311+430, has been reported earlier. We also present high spatial resolution images of the background quasars at frequencies close to the redshifted HI 21cm line frequency, allowing us to estimate the covering factor of each DLA, and then determine its Spin Temperature $T_s$. For three non-detections of HI 21cm absorption, we obtain strong lower limits on the Spin Temperature, $T_s \gtrsim 790$ K, similar to the bulk of the high-$z$ DLA population; three other DLAs yield weak lower limits, $T_s > 140-400$ K. However, for the two DLAs with detections of HI 21cm absorption, the derived Spin Temperatures are both low $T_s = (160 \pm 35) \times (f/0.35)$ K for the $z = 2.192$ DLA towards TXS2039+187 and $T_s = (72 \pm 18) \times (f/0.52)$ K for the $z = 2.289$ DLA towards TXS0311+430. These are the first two DLAs at $z > 1$ with $T_s$ values comparable to those obtained in local spiral galaxies. Based on the observed correlations between Spin Temperature and metallicity and velocity spread and metallicity in DLAs, we suggest that the hosts of the two absorbers are likely to be massive, high-metallicity galaxies.
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H i content, metallicities and Spin Temperatures of damped and sub-damped Lyα systems in the redshift desert (0.6 < zabs < 1.7)★
Monthly Notices of the Royal Astronomical Society, 2012Co-Authors: Sara L. Ellison, Nissim Kanekar, Emmanuel Momjian, J. Xavier Prochaska, Gabor WorseckAbstract:The H I 21-cm absorption optical depth and the N(H I) column density derived from Lyα absorption can be combined to yield the Spin Temperature (T s) of intervening damped Lyα systems (DLAs). Although Spin Temperatures have been determined for samples of DLAs with zabs 1.7, the intermediate regime currently contains only twoT s measurements, leading to a ‘redshift desert’ that spans 4 Gyr of cosmic time. To connect the low- and highredshift regimes, we present observations of the Lyα line of six 0.6 < zabs < 1.7 H I 21-cm absorbers. The data set is complemented by both low-frequency Very Long Baseline Array observations (to derive the absorber covering factor, f ) and optical echelle spectra from which metal abundances are determined. Our data set therefore not only offers the largest statistical study of H I 21-cm absorbers to date, and bridges the redshift desert, but is also the first to use a fully f -corrected data set to look for metallicity-based trends. The metallicities of H I 21-cm absorbers are consistent with those of optically selected DLAs at the same redshift. In agreement with trends found in Galactic sightlines, we find that the lowest column density absorbers tend to be dominated by warm gas. In the DLA regime, Spin Temperatures show a wider range of values than Galactic data, as may be expected in a heterogeneous galactic population. However, we find that low-metallicity DLAs are dominated by small cold gas fractions and only absorbers with relatively high metallicities exhibit significant fractions of cold gas. Using a compilation of H I 21-cm absorbers which are selected to have covering-factor-corrected Spin Temperatures, we confirm an anticorrelation between metallicity and T s at 3.4σ significance. Finally, one of the DLAs in our sample is a newly discovered H I 21-cm absorber (at zabs = 0.602 towards J1431+3952), which we find to have the lowestf -corrected Spin Temperature yet reported in the literature: Ts = 90±23 K. The observed distribution of T s and metallicities in DLAs and the implications for understanding the characteristics of the interstellar medium in high-redshift galaxies are discussed.
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Discovery of 21-cm absorption in a zabs= 2.289 damped Lyman α system towards TXS 0311+430: the first low Spin Temperature absorber at z > 1
Monthly Notices of the Royal Astronomical Society: Letters, 2007Co-Authors: Brian A. York, Nissim Kanekar, Sara L. Ellison, Max PettiniAbstract:We report the detection of H i 21-cm absorption from the z= 2.289 damped Lyman α system (DLA) towards TXS 0311+430 with the Green Bank Telescope. The 21-cm absorption has a velocity spread (between nulls) of ∼110 km s−1 and an integrated optical depth of . We also present new Giant Metrewave Radio Telescope 602-MHz imaging of the radio continuum. TXS 0311+430 is unresolved at this frequency, indicating that the covering factor of the DLA is likely to be high. Combining the integrated optical depth with the DLA H i column density of yields a Spin Temperature of Ts= (138 ± 36) K, assuming a covering factor of unity. This is the first case of a low Spin Temperature ( 1 DLA and is among the lowest Temperatures ever measured in any DLA. Indeed, the Ts measured for this DLA is similar to values measured in the Milky Way and local disc galaxies. We also determine a lower limit (Si/H) ≳ 1/3 solar for the DLA metallicity, amongst the highest abundances measured in DLAs at any redshift. Based on low-redshift correlations, the low Ts, large 21-cm absorption width and high metallicity all suggest that the z∼ 2.289 DLA is likely to arise in a massive, luminous disc galaxy.
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discovery of 21 cm absorption in a zabs 2 289 damped lyman α system towards txs 0311 430 the first low Spin Temperature absorber at z 1
Monthly Notices of the Royal Astronomical Society: Letters, 2007Co-Authors: Brian A. York, Nissim Kanekar, Sara L. Ellison, Max PettiniAbstract:We report the detection of H i 21-cm absorption from the z= 2.289 damped Lyman α system (DLA) towards TXS 0311+430 with the Green Bank Telescope. The 21-cm absorption has a velocity spread (between nulls) of ∼110 km s−1 and an integrated optical depth of . We also present new Giant Metrewave Radio Telescope 602-MHz imaging of the radio continuum. TXS 0311+430 is unresolved at this frequency, indicating that the covering factor of the DLA is likely to be high. Combining the integrated optical depth with the DLA H i column density of yields a Spin Temperature of Ts= (138 ± 36) K, assuming a covering factor of unity. This is the first case of a low Spin Temperature ( 1 DLA and is among the lowest Temperatures ever measured in any DLA. Indeed, the Ts measured for this DLA is similar to values measured in the Milky Way and local disc galaxies. We also determine a lower limit (Si/H) ≳ 1/3 solar for the DLA metallicity, amongst the highest abundances measured in DLAs at any redshift. Based on low-redshift correlations, the low Ts, large 21-cm absorption width and high metallicity all suggest that the z∼ 2.289 DLA is likely to arise in a massive, luminous disc galaxy.
Nissim Kanekar - One of the best experts on this subject based on the ideXlab platform.
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The Spin Temperature of high-redshift damped Lyman α systems
Monthly Notices of the Royal Astronomical Society, 2014Co-Authors: Nissim Kanekar, Alain Smette, Jayaram N. Chengalur, Sara L. Ellison, Emmanuel Momjian, Jason X. Prochaska, Emma V. Ryan-weber, F. Briggs, W. M. Lane, T. DelafosseAbstract:We report results from a programme aimed at investigating the Temperature of neutral gas in high-redshift damped Lyman α absorbers (DLAs). This involved (1) H I 21 cm absorption studies of a large sample of DLAs towards radio-loud quasars, (2) very long baseline interferometric studies to measure the low-frequency quasar core fractions, and (3) optical/ultraviolet spectroscopy to determine DLA metallicities and the velocity widths of low-ionization metal lines. Including literature data, our sample consists of 37 DLAs with estimates of the harmonic mean Spin Temperature Ts. We find a statistically significant (4σ) difference between the Ts distributions in the high-z (z > 2.4) and low-z (z 1.7 have Ts values indicating CNM fractions >20 per cent, comparable to the median value (≈27 per cent) in the Galaxy. We tested whether the H I column density measured towards the optical quasar might be systematically different from that towards the radio core by comparing the H I column densities inferred from H I 21 cm emission studies at different spatial resolutions (≈15 pc-1 kpc) in the Large Magellanic Cloud. The high-resolution NH I values are, on average, larger than the smoothed ones for NH I > 1021 cm-2, but lower than the smoothed NH I estimates for NH I 1. Since all DLAs at z > 1 have angular diameter distances comparable to or larger than those of their background quasars, they have similar efficiency in covering the quasars. We conclude that low covering factors in high-z DLAs cannot account for the observed redshift evolution in Spin Temperatures.
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A search for H i 21 cm absorption towards a radio-selected quasar sample – II. A new low Spin Temperature DLA at high redshift
Monthly Notices of the Royal Astronomical Society, 2012Co-Authors: Nissim Kanekar, Sara L. Ellison, Emmanuel Momjian, Brian A. York, Max PettiniAbstract:We report results from a deep search for redshifted HI 21cm absorption from eight damped Lyman-$\alpha$ absorbers (DLAs) detected in our earlier optical survey for DLAs towards radio-loud quasars. HI 21cm absorption was detected from the $z = 2.192$ DLA towards TXS2039+187, only the sixth case of such a detection at $z > 2$, while upper limits on the HI 21cm optical depth were obtained in six other DLAs at $z > 2$. Our detection of HI 21cm absorption in the eighth system, at $z = 2.289$ towards TXS0311+430, has been reported earlier. We also present high spatial resolution images of the background quasars at frequencies close to the redshifted HI 21cm line frequency, allowing us to estimate the covering factor of each DLA, and then determine its Spin Temperature $T_s$. For three non-detections of HI 21cm absorption, we obtain strong lower limits on the Spin Temperature, $T_s \gtrsim 790$ K, similar to the bulk of the high-$z$ DLA population; three other DLAs yield weak lower limits, $T_s > 140-400$ K. However, for the two DLAs with detections of HI 21cm absorption, the derived Spin Temperatures are both low $T_s = (160 \pm 35) \times (f/0.35)$ K for the $z = 2.192$ DLA towards TXS2039+187 and $T_s = (72 \pm 18) \times (f/0.52)$ K for the $z = 2.289$ DLA towards TXS0311+430. These are the first two DLAs at $z > 1$ with $T_s$ values comparable to those obtained in local spiral galaxies. Based on the observed correlations between Spin Temperature and metallicity and velocity spread and metallicity in DLAs, we suggest that the hosts of the two absorbers are likely to be massive, high-metallicity galaxies.
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H i content, metallicities and Spin Temperatures of damped and sub-damped Lyα systems in the redshift desert (0.6 < zabs < 1.7)★
Monthly Notices of the Royal Astronomical Society, 2012Co-Authors: Sara L. Ellison, Nissim Kanekar, Emmanuel Momjian, J. Xavier Prochaska, Gabor WorseckAbstract:The H I 21-cm absorption optical depth and the N(H I) column density derived from Lyα absorption can be combined to yield the Spin Temperature (T s) of intervening damped Lyα systems (DLAs). Although Spin Temperatures have been determined for samples of DLAs with zabs 1.7, the intermediate regime currently contains only twoT s measurements, leading to a ‘redshift desert’ that spans 4 Gyr of cosmic time. To connect the low- and highredshift regimes, we present observations of the Lyα line of six 0.6 < zabs < 1.7 H I 21-cm absorbers. The data set is complemented by both low-frequency Very Long Baseline Array observations (to derive the absorber covering factor, f ) and optical echelle spectra from which metal abundances are determined. Our data set therefore not only offers the largest statistical study of H I 21-cm absorbers to date, and bridges the redshift desert, but is also the first to use a fully f -corrected data set to look for metallicity-based trends. The metallicities of H I 21-cm absorbers are consistent with those of optically selected DLAs at the same redshift. In agreement with trends found in Galactic sightlines, we find that the lowest column density absorbers tend to be dominated by warm gas. In the DLA regime, Spin Temperatures show a wider range of values than Galactic data, as may be expected in a heterogeneous galactic population. However, we find that low-metallicity DLAs are dominated by small cold gas fractions and only absorbers with relatively high metallicities exhibit significant fractions of cold gas. Using a compilation of H I 21-cm absorbers which are selected to have covering-factor-corrected Spin Temperatures, we confirm an anticorrelation between metallicity and T s at 3.4σ significance. Finally, one of the DLAs in our sample is a newly discovered H I 21-cm absorber (at zabs = 0.602 towards J1431+3952), which we find to have the lowestf -corrected Spin Temperature yet reported in the literature: Ts = 90±23 K. The observed distribution of T s and metallicities in DLAs and the implications for understanding the characteristics of the interstellar medium in high-redshift galaxies are discussed.
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A metallicity-Spin Temperature relation in damped Lyα systems
The Astrophysical Journal, 2009Co-Authors: Nissim Kanekar, Alain Smette, Frank H. Briggs, Jayaram N. ChengalurAbstract:We report evidence for an anti-correlation between Spin Temperature Ts and metallicity [Z/H], detected at 3.6� significance in a sample of 26 damped Lyman-� absorbers (DLAs) at redshifts 0.09 1.7 have low metallicities, [Z/H] < -1, implying that the HI in high-z DLAs is predominantly warm. The anti-correlation between Ts and [Z/H] is consistent with the presence of a mass-metallicity relation in DLAs, suggested by the tight correlation between DLA metallicity and the kinematic widths of metal lines. Most high-z DLAs are likely to arise in galaxies with low masses (Mvir < 10 10.5 M⊙), low metallicities ([Z/H]< -1, and low cold gas fractions. Subject headings:galaxies: evolution — galaxies: ISM — radio lines: galaxies
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Discovery of 21-cm absorption in a zabs= 2.289 damped Lyman α system towards TXS 0311+430: the first low Spin Temperature absorber at z > 1
Monthly Notices of the Royal Astronomical Society: Letters, 2007Co-Authors: Brian A. York, Nissim Kanekar, Sara L. Ellison, Max PettiniAbstract:We report the detection of H i 21-cm absorption from the z= 2.289 damped Lyman α system (DLA) towards TXS 0311+430 with the Green Bank Telescope. The 21-cm absorption has a velocity spread (between nulls) of ∼110 km s−1 and an integrated optical depth of . We also present new Giant Metrewave Radio Telescope 602-MHz imaging of the radio continuum. TXS 0311+430 is unresolved at this frequency, indicating that the covering factor of the DLA is likely to be high. Combining the integrated optical depth with the DLA H i column density of yields a Spin Temperature of Ts= (138 ± 36) K, assuming a covering factor of unity. This is the first case of a low Spin Temperature ( 1 DLA and is among the lowest Temperatures ever measured in any DLA. Indeed, the Ts measured for this DLA is similar to values measured in the Milky Way and local disc galaxies. We also determine a lower limit (Si/H) ≳ 1/3 solar for the DLA metallicity, amongst the highest abundances measured in DLAs at any redshift. Based on low-redshift correlations, the low Ts, large 21-cm absorption width and high metallicity all suggest that the z∼ 2.289 DLA is likely to arise in a massive, luminous disc galaxy.
Brian A. York - One of the best experts on this subject based on the ideXlab platform.
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A search for H i 21 cm absorption towards a radio-selected quasar sample – II. A new low Spin Temperature DLA at high redshift
Monthly Notices of the Royal Astronomical Society, 2012Co-Authors: Nissim Kanekar, Sara L. Ellison, Emmanuel Momjian, Brian A. York, Max PettiniAbstract:We report results from a deep search for redshifted HI 21cm absorption from eight damped Lyman-$\alpha$ absorbers (DLAs) detected in our earlier optical survey for DLAs towards radio-loud quasars. HI 21cm absorption was detected from the $z = 2.192$ DLA towards TXS2039+187, only the sixth case of such a detection at $z > 2$, while upper limits on the HI 21cm optical depth were obtained in six other DLAs at $z > 2$. Our detection of HI 21cm absorption in the eighth system, at $z = 2.289$ towards TXS0311+430, has been reported earlier. We also present high spatial resolution images of the background quasars at frequencies close to the redshifted HI 21cm line frequency, allowing us to estimate the covering factor of each DLA, and then determine its Spin Temperature $T_s$. For three non-detections of HI 21cm absorption, we obtain strong lower limits on the Spin Temperature, $T_s \gtrsim 790$ K, similar to the bulk of the high-$z$ DLA population; three other DLAs yield weak lower limits, $T_s > 140-400$ K. However, for the two DLAs with detections of HI 21cm absorption, the derived Spin Temperatures are both low $T_s = (160 \pm 35) \times (f/0.35)$ K for the $z = 2.192$ DLA towards TXS2039+187 and $T_s = (72 \pm 18) \times (f/0.52)$ K for the $z = 2.289$ DLA towards TXS0311+430. These are the first two DLAs at $z > 1$ with $T_s$ values comparable to those obtained in local spiral galaxies. Based on the observed correlations between Spin Temperature and metallicity and velocity spread and metallicity in DLAs, we suggest that the hosts of the two absorbers are likely to be massive, high-metallicity galaxies.
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Discovery of 21-cm absorption in a zabs= 2.289 damped Lyman α system towards TXS 0311+430: the first low Spin Temperature absorber at z > 1
Monthly Notices of the Royal Astronomical Society: Letters, 2007Co-Authors: Brian A. York, Nissim Kanekar, Sara L. Ellison, Max PettiniAbstract:We report the detection of H i 21-cm absorption from the z= 2.289 damped Lyman α system (DLA) towards TXS 0311+430 with the Green Bank Telescope. The 21-cm absorption has a velocity spread (between nulls) of ∼110 km s−1 and an integrated optical depth of . We also present new Giant Metrewave Radio Telescope 602-MHz imaging of the radio continuum. TXS 0311+430 is unresolved at this frequency, indicating that the covering factor of the DLA is likely to be high. Combining the integrated optical depth with the DLA H i column density of yields a Spin Temperature of Ts= (138 ± 36) K, assuming a covering factor of unity. This is the first case of a low Spin Temperature ( 1 DLA and is among the lowest Temperatures ever measured in any DLA. Indeed, the Ts measured for this DLA is similar to values measured in the Milky Way and local disc galaxies. We also determine a lower limit (Si/H) ≳ 1/3 solar for the DLA metallicity, amongst the highest abundances measured in DLAs at any redshift. Based on low-redshift correlations, the low Ts, large 21-cm absorption width and high metallicity all suggest that the z∼ 2.289 DLA is likely to arise in a massive, luminous disc galaxy.
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discovery of 21 cm absorption in a zabs 2 289 damped lyman α system towards txs 0311 430 the first low Spin Temperature absorber at z 1
Monthly Notices of the Royal Astronomical Society: Letters, 2007Co-Authors: Brian A. York, Nissim Kanekar, Sara L. Ellison, Max PettiniAbstract:We report the detection of H i 21-cm absorption from the z= 2.289 damped Lyman α system (DLA) towards TXS 0311+430 with the Green Bank Telescope. The 21-cm absorption has a velocity spread (between nulls) of ∼110 km s−1 and an integrated optical depth of . We also present new Giant Metrewave Radio Telescope 602-MHz imaging of the radio continuum. TXS 0311+430 is unresolved at this frequency, indicating that the covering factor of the DLA is likely to be high. Combining the integrated optical depth with the DLA H i column density of yields a Spin Temperature of Ts= (138 ± 36) K, assuming a covering factor of unity. This is the first case of a low Spin Temperature ( 1 DLA and is among the lowest Temperatures ever measured in any DLA. Indeed, the Ts measured for this DLA is similar to values measured in the Milky Way and local disc galaxies. We also determine a lower limit (Si/H) ≳ 1/3 solar for the DLA metallicity, amongst the highest abundances measured in DLAs at any redshift. Based on low-redshift correlations, the low Ts, large 21-cm absorption width and high metallicity all suggest that the z∼ 2.289 DLA is likely to arise in a massive, luminous disc galaxy.
Robert Tycko - One of the best experts on this subject based on the ideXlab platform.
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optical pumping in indium phosphide 31p nmr measurements and potential for signal enhancement in biological solid state nmr
Solid State Nuclear Magnetic Resonance, 1998Co-Authors: Robert TyckoAbstract:Abstract The initial results of optically-pumped, directly-detected NMR experiments on InP are reported. At low Temperatures (4.2 K and above) and in a 9.39 T magnetic field, irradiation of a sample of an undoped InP wafer with 835-nm-wavelength light from a diode laser enhances the Spin polarization of 31 P nuclei near the sample surface in a manner that depends on the polarization of the light. The nuclear Spin polarization is monitored by direct radio-frequency detection of nuclear free induction-decay signals. The maximum nuclear Spin polarization 〈 S zn 〉 generated by optical pumping is approximately −0.004, corresponding to a Spin Temperature of −0.5 K. The nuclear Spin polarization may be limited in these experiments by the use of a high photon energy (1.484 eV) relative to the InP band gap (1.423 eV at low Temperatures). It is proposed that optically-pumped InP may be useful as a source of enhanced nuclear Spin polarizations for solid state NMR measurements on organic and biological overlayers deposited on InP substrates. Estimates are given for the magnitude of the Spin polarization and the efficiency of the polarization transfer from the semiconductor substrate to the overlayer that would be required to permit solid state NMR measurements on sub-nanomole quantities of molecules in the overlayer. These estimates appear well within the range of possibility.