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Steven M George - One of the best experts on this subject based on the ideXlab platform.
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thermal atomic layer etching of sio2 by a conversion etch mechanism using sequential reactions of trimethylaluminum and Hydrogen Fluoride
ACS Applied Materials & Interfaces, 2017Co-Authors: Jaime W Dumont, Amy Elizabeth Marquardt, Austin M Cano, Steven M GeorgeAbstract:The thermal atomic layer etching (ALE) of SiO2 was performed using sequential reactions of trimethylaluminum (TMA) and Hydrogen Fluoride (HF) at 300 °C. Ex situ X-ray reflectivity (XRR) measurements revealed that the etch rate during SiO2 ALE was dependent on reactant pressure. SiO2 etch rates of 0.027, 0.15, 0.20, and 0.31 A/cycle were observed at static reactant pressures of 0.1, 0.5, 1.0, and 4.0 Torr, respectively. Ex situ spectroscopic ellipsometry (SE) measurements were in agreement with these etch rates versus reactant pressure. In situ Fourier transform infrared (FTIR) spectroscopy investigations also observed SiO2 etching that was dependent on the static reactant pressures. The FTIR studies showed that the TMA and HF reactions displayed self-limiting behavior at the various reactant pressures. In addition, the FTIR spectra revealed that an Al2O3/aluminosilicate intermediate was present after the TMA exposures. The Al2O3/aluminosilicate intermediate is consistent with a “conversion-etch” mechanism...
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thermal atomic layer etching of zno by a conversion etch mechanism using sequential exposures of Hydrogen Fluoride and trimethylaluminum
Chemistry of Materials, 2017Co-Authors: David R Zywotko, Steven M GeorgeAbstract:The atomic layer etching (ALE) of ZnO thin films was demonstrated using sequential, self-limiting thermal reactions with Hydrogen Fluoride (HF) and trimethylaluminum (TMA) as the reactants. The initial polycrystalline ZnO films were grown by atomic layer deposition (ALD) using diethylzinc (DEZ) and H2O at 150 °C. The thermal ZnO ALE process was then studied between 205 and 295 °C using various techniques. In situ quartz crystal microbalance (QCM) measurements monitored ZnO ALE at 265 °C. The ZnO etching was linear versus number of ALE cycles. The HF exposure caused a mass gain of ΔMHF = +53 ng/cm2 from fluorination. The subsequent TMA exposure caused a large mass loss of ΔMTMA = −172 ng/cm2. This mass loss was much larger than expected from metal Fluoride removal resulting from ligand-exchange transmetalation. The large mass loss suggested that there is a “conversion-etch” mechanism where TMA also converts the ZnO surface to an Al2O3 surface layer. This conversion reaction is believed to occur according t...
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competition between al2o3 atomic layer etching and alf3 atomic layer deposition using sequential exposures of trimethylaluminum and Hydrogen Fluoride
Journal of Chemical Physics, 2017Co-Authors: Jaime W Dumont, Steven M GeorgeAbstract:The thermal atomic layer etching (ALE) of Al2O3 can be performed using sequential and self-limiting reactions with trimethylaluminum (TMA) and Hydrogen Fluoride (HF) as the reactants. The atomic layer deposition (ALD) of AlF3 can also be accomplished using the same reactants. This paper examined the competition between Al2O3 ALE and AlF3 ALD using in situ Fourier transform infrared (FTIR) vibrational spectroscopy measurements on Al2O3 ALD-coated SiO2 nanoparticles. The FTIR spectra could observe an absorbance loss of the Al-O stretching vibrations during Al2O3 ALE or an absorbance gain of the Al-F stretching vibrations during AlF3 ALD. The transition from AlF3 ALD to Al2O3 ALE occurred versus reaction temperature and was also influenced by the N2 or He background gas pressure. Higher temperatures and lower background gas pressures led to Al2O3 ALE. Lower temperatures and higher background gas pressures led to AlF3 ALD. The FTIR measurements also monitored AlCH3* and HF* species on the surface after the TM...
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thermal atomic layer etching of crystalline aluminum nitride using sequential self limiting Hydrogen Fluoride and sn acac 2 reactions and enhancement by h2 and ar plasmas
Journal of Vacuum Science and Technology, 2016Co-Authors: Nicholas R Johnson, Huaxing Sun, K Sharma, Steven M GeorgeAbstract:Thermal atomic layer etching (ALE) of crystalline aluminum nitride (AlN) films was demonstrated using sequential, self-limiting reactions with Hydrogen Fluoride (HF) and tin(II) acetylacetonate [Sn(acac)2] as the reactants. Film thicknesses were monitored versus number of ALE reaction cycles at 275 °C using in situ spectroscopic ellipsometry (SE). A low etch rate of ∼0.07 A/cycle was measured during etching of the first 40 A of the film. This small etch rate corresponded with the AlOxNy layer on the AlN film. The etch rate then increased to ∼0.36 A/cycle for the pure AlN films. In situ SE experiments established the HF and Sn(acac)2 exposures that were necessary for self-limiting surface reactions. In the proposed reaction mechanism for thermal AlN ALE, HF fluorinates the AlN film and produces an AlF3 layer on the surface. The metal precursor, Sn(acac)2, then accepts fluorine from the AlF3 layer and transfers an acac ligand to the AlF3 layer in a ligand-exchange reaction. The possible volatile etch produc...
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atomic layer deposition of alf3 using trimethylaluminum and Hydrogen Fluoride
Journal of Physical Chemistry C, 2015Co-Authors: Younghee Lee, Jaime W Dumont, Andrew S Cavanagh, Steven M GeorgeAbstract:The atomic layer deposition (ALD) of AlF3 was demonstrated using trimethylaluminum (TMA) and Hydrogen Fluoride (HF). The HF source was HF-pyridine. In situ quartz crystal microbalance (QCM), quadrupole mass spectrometer (QMS), and Fourier transform infrared (FTIR) spectroscopy measurements were used to study AlF3 ALD. The AlF3 ALD film growth was examined at temperatures from 75 to 300 °C. Both the TMA and HF reactions displayed self-limiting behavior. The maximum mass gain per cycle (MGPC) of 44 ng/(cm2 cycle) for AlF3 ALD occurred at 100 °C. The MGPC values decreased at higher temperatures. The MGPC values were negative at T > 250 °C when TMA and HF were able to etch the AlF3 films. Film thicknesses were also determined using ex situ X-ray reflectivity (XRR) and spectroscopic ellipsometry (SE) measurements. The AlF3 ALD growth rate determined by the ex situ analysis was 1.43 A/cycle at 100 °C. These ex situ measurements were in excellent agreement with the in situ QCM measurements. FTIR analysis monitor...
T G Phillips - One of the best experts on this subject based on the ideXlab platform.
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Hydrogen Fluoride toward luminous nearby galaxies ngc 253 and ngc 4945
The Astrophysical Journal, 2014Co-Authors: Raquel Monje, David A Neufeld, T G Phillips, D C Lis, S Lord, E Falgarone, R GustenAbstract:We present the detection of Hydrogen Fluoride, HF, in two luminous nearby galaxies NGC 253 and NGC 4945 using the Heterodyne Instrument for the Far-Infrared (HIFI) on board the Herschel Space Observatory. The HF line toward NGC 253 has a P-Cygni profile, while an asymmetric absorption profile is seen toward NGC 4945. The P-Cygni profile in NGC 253 suggests an outflow of molecular gas with a mass of M(H_2)_(out) ~ 1 × 10^7 M_⊙ and an outflow rate as large as Ṁ ~ 6.4 M_⊙ yr^(−1). In the case of NGC 4945, the axisymmetric velocity components in the HF line profile is compatible with the interpretation of a fast rotating nuclear ring surrounding the nucleus and the presence of inflowing gas. The gas falls into the nucleus with an inflow rate of ≤ 1.2 M_⊙ yr^(−1), inside a inner radius of ≤ 200 pc. The gas accretion rate to the central AGN is much smaller, suggesting that the inflow can be triggering a nuclear starburst. From these results, the HF J = 1 − 0 line is seen to provide an important probe of the kinematics of absorbing material along the sight-line to nearby galaxies with bright dust continuum and a promising new tracer of molecular gas in high redshift galaxies.
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Hydrogen Fluoride toward luminous nearby galaxies ngc 253 and ngc 4945
arXiv: Astrophysics of Galaxies, 2014Co-Authors: Raquel Monje, David A Neufeld, T G Phillips, D C Lis, S Lord, E Falgarone, R GustenAbstract:We present the detection of Hydrogen Fluoride, HF, in two luminous nearby galaxies NGC 253 and NGC 4945 using the Heterodyne Instrument for the Far-Infrared (HIFI) on board the Herschel Space Observatory. The HF line toward NGC 253 has a P-Cygni profile, while an asymmetric absorption profile is seen toward NGC 4945. The P-Cygni profile in NGC 253 suggests an outflow of molecular gas with a mass of M(H$_2$)$_{out}$ $\sim$ 1 $\times$ 10$^7$ M$_\odot$ and an outflow rate as large as \.{M} $\sim$ 6.4 M$_\odot$ yr$^{-1}$. In the case of NGC 4945, the axisymmetric velocity components in the HF line profile is compatible with the interpretation of a fast-rotating nuclear ring surrounding the nucleus and the presence of inflowing gas. The gas falls into the nucleus with an inflow rate of $\le$ 1.2 M$_\odot$ yr$^{-1}$, inside a inner radius of $\le$ 200 pc. The gas accretion rate to the central AGN is much smaller, suggesting that the inflow can be triggering a nuclear starburst. From these results, the HF $J = 1-0$ line is seen to provide an important probe of the kinematics of absorbing material along the sight-line to nearby galaxies with bright dust continuum and a promising new tracer of molecular gas in high-redshift galaxies.
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discovery of Hydrogen Fluoride in the cloverleaf quasar at z 2 56
arXiv: Cosmology and Nongalactic Astrophysics, 2012Co-Authors: Raquel Monje, David A Neufeld, T G Phillips, D C Lis, Ruisheng Peng, M EmprechtingerAbstract:We report the first detection of Hydrogen Fluoride (HF) toward a high redshift quasar. Using the Caltech Submillimeter Observatory (CSO) we detect the HF J = 1 - 0 transition in absorption toward the Cloverleaf, a broad absorption line (BAL) quasi-stellar object (QSO) at z=2.56. The detection is statistically significant at the ~ 6 sigma level. We estimate a lower limit of 4 \times 1014 cm-2 for the HF column density and using a previous estimate of the Hydrogen column density, we obtain a lower limit of 1.7 \times 10-9 for the HF abundance. This value suggests that, assuming a Galactic N(HF)/NH ratio, HF accounts for at least ~10% of the fluorine in the gas phase along the line of sight to the Cloverleaf quasar. This observation corroborates the prediction that HF should be a good probe of the molecular gas at high redshift. Measurements of the HF abundance as a function of redshift are urgently needed to better constrain the fluorine nucleosynthesis mechanism(s).
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discovery of Hydrogen Fluoride in the cloverleaf quasar at z 2 56
The Astrophysical Journal, 2011Co-Authors: Raquel Monje, David A Neufeld, T G Phillips, D C Lis, Ruisheng Peng, M EmprechtingerAbstract:We report the first detection of Hydrogen Fluoride (HF) toward a high-redshift quasar. Using the Caltech Submillimeter Observatory, we detect the HF J = 1-0 transition in absorption toward the Cloverleaf, a broad absorption line quasi-stellar object at z = 2.56. The detection is statistically significant at the ~6σ level. We estimate a lower limit of 4 × 10^(14) cm^(–2) for the HF column density and using a previous estimate of the Hydrogen column density, we obtain a lower limit of 1.7 × 10^(–9) for the HF abundance. This value suggests that, assuming a Galactic N(HF)/N H ratio, HF accounts for at least ~10% of the fluorine in the gas phase along the line of sight to the Cloverleaf quasar. This observation corroborates the prediction that HF should be a good probe of the molecular gas at high redshift. Measurements of the HF abundance as a function of redshift are urgently needed to better constrain the fluorine nucleosynthesis mechanism(s).
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herschel hifi observations of Hydrogen Fluoride toward sagittarius b2 m
arXiv: Astrophysics of Galaxies, 2011Co-Authors: Raquel Monje, David A Neufeld, T G Phillips, M Emprechtinger, D C Lis, Paul F Goldsmith, E A Bergin, T A Bell, Paule SonnentruckerAbstract:Herschel/HIFI observations have revealed the presence of widespread absorption by Hydrogen Fluoride (HF) J = 1-0 rotational transition, toward a number of Galactic sources. We present observations of HF J = 1-0 toward the high-mass star-forming region Sagittarius B2(M). The spectrum obtained shows a complex pattern of absorption, with numerous features covering a wide range of local standard of rest velocities (-130 to 100 km -1). An analysis of this absorption yields HF abundances relative to H2 of ~1.3 {\times}10-8, in most velocity intervals. This result is in good agreement with estimates from chemical models, which predict that HF should be the main reservoir of gas-phase fluorine under a wide variety of interstellar conditions. Interestingly, we also find velocity intervals in which the HF spectrum shows strong absorption features that are not present, or are very weak, in spectra of other molecules, such as 13CO (1-0) and CS (2-1). HF absorption reveals components of diffuse clouds with small extinction that can be studied for the first time. Another interesting observation is that water is significantly more abundant than Hydrogen Fluoride over a wide range of velocities toward Sagittarius B2(M), in contrast to the remarkably constant H2O/HF abundance ratio with average value close to unity measured toward other Galactic sources.
David A Neufeld - One of the best experts on this subject based on the ideXlab platform.
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Hydrogen Fluoride toward luminous nearby galaxies ngc 253 and ngc 4945
The Astrophysical Journal, 2014Co-Authors: Raquel Monje, David A Neufeld, T G Phillips, D C Lis, S Lord, E Falgarone, R GustenAbstract:We present the detection of Hydrogen Fluoride, HF, in two luminous nearby galaxies NGC 253 and NGC 4945 using the Heterodyne Instrument for the Far-Infrared (HIFI) on board the Herschel Space Observatory. The HF line toward NGC 253 has a P-Cygni profile, while an asymmetric absorption profile is seen toward NGC 4945. The P-Cygni profile in NGC 253 suggests an outflow of molecular gas with a mass of M(H_2)_(out) ~ 1 × 10^7 M_⊙ and an outflow rate as large as Ṁ ~ 6.4 M_⊙ yr^(−1). In the case of NGC 4945, the axisymmetric velocity components in the HF line profile is compatible with the interpretation of a fast rotating nuclear ring surrounding the nucleus and the presence of inflowing gas. The gas falls into the nucleus with an inflow rate of ≤ 1.2 M_⊙ yr^(−1), inside a inner radius of ≤ 200 pc. The gas accretion rate to the central AGN is much smaller, suggesting that the inflow can be triggering a nuclear starburst. From these results, the HF J = 1 − 0 line is seen to provide an important probe of the kinematics of absorbing material along the sight-line to nearby galaxies with bright dust continuum and a promising new tracer of molecular gas in high redshift galaxies.
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Hydrogen Fluoride toward luminous nearby galaxies ngc 253 and ngc 4945
arXiv: Astrophysics of Galaxies, 2014Co-Authors: Raquel Monje, David A Neufeld, T G Phillips, D C Lis, S Lord, E Falgarone, R GustenAbstract:We present the detection of Hydrogen Fluoride, HF, in two luminous nearby galaxies NGC 253 and NGC 4945 using the Heterodyne Instrument for the Far-Infrared (HIFI) on board the Herschel Space Observatory. The HF line toward NGC 253 has a P-Cygni profile, while an asymmetric absorption profile is seen toward NGC 4945. The P-Cygni profile in NGC 253 suggests an outflow of molecular gas with a mass of M(H$_2$)$_{out}$ $\sim$ 1 $\times$ 10$^7$ M$_\odot$ and an outflow rate as large as \.{M} $\sim$ 6.4 M$_\odot$ yr$^{-1}$. In the case of NGC 4945, the axisymmetric velocity components in the HF line profile is compatible with the interpretation of a fast-rotating nuclear ring surrounding the nucleus and the presence of inflowing gas. The gas falls into the nucleus with an inflow rate of $\le$ 1.2 M$_\odot$ yr$^{-1}$, inside a inner radius of $\le$ 200 pc. The gas accretion rate to the central AGN is much smaller, suggesting that the inflow can be triggering a nuclear starburst. From these results, the HF $J = 1-0$ line is seen to provide an important probe of the kinematics of absorbing material along the sight-line to nearby galaxies with bright dust continuum and a promising new tracer of molecular gas in high-redshift galaxies.
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discovery of Hydrogen Fluoride in the cloverleaf quasar at z 2 56
arXiv: Cosmology and Nongalactic Astrophysics, 2012Co-Authors: Raquel Monje, David A Neufeld, T G Phillips, D C Lis, Ruisheng Peng, M EmprechtingerAbstract:We report the first detection of Hydrogen Fluoride (HF) toward a high redshift quasar. Using the Caltech Submillimeter Observatory (CSO) we detect the HF J = 1 - 0 transition in absorption toward the Cloverleaf, a broad absorption line (BAL) quasi-stellar object (QSO) at z=2.56. The detection is statistically significant at the ~ 6 sigma level. We estimate a lower limit of 4 \times 1014 cm-2 for the HF column density and using a previous estimate of the Hydrogen column density, we obtain a lower limit of 1.7 \times 10-9 for the HF abundance. This value suggests that, assuming a Galactic N(HF)/NH ratio, HF accounts for at least ~10% of the fluorine in the gas phase along the line of sight to the Cloverleaf quasar. This observation corroborates the prediction that HF should be a good probe of the molecular gas at high redshift. Measurements of the HF abundance as a function of redshift are urgently needed to better constrain the fluorine nucleosynthesis mechanism(s).
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discovery of Hydrogen Fluoride in the cloverleaf quasar at z 2 56
The Astrophysical Journal, 2011Co-Authors: Raquel Monje, David A Neufeld, T G Phillips, D C Lis, Ruisheng Peng, M EmprechtingerAbstract:We report the first detection of Hydrogen Fluoride (HF) toward a high-redshift quasar. Using the Caltech Submillimeter Observatory, we detect the HF J = 1-0 transition in absorption toward the Cloverleaf, a broad absorption line quasi-stellar object at z = 2.56. The detection is statistically significant at the ~6σ level. We estimate a lower limit of 4 × 10^(14) cm^(–2) for the HF column density and using a previous estimate of the Hydrogen column density, we obtain a lower limit of 1.7 × 10^(–9) for the HF abundance. This value suggests that, assuming a Galactic N(HF)/N H ratio, HF accounts for at least ~10% of the fluorine in the gas phase along the line of sight to the Cloverleaf quasar. This observation corroborates the prediction that HF should be a good probe of the molecular gas at high redshift. Measurements of the HF abundance as a function of redshift are urgently needed to better constrain the fluorine nucleosynthesis mechanism(s).
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herschel hifi observations of Hydrogen Fluoride toward sagittarius b2 m
arXiv: Astrophysics of Galaxies, 2011Co-Authors: Raquel Monje, David A Neufeld, T G Phillips, M Emprechtinger, D C Lis, Paul F Goldsmith, E A Bergin, T A Bell, Paule SonnentruckerAbstract:Herschel/HIFI observations have revealed the presence of widespread absorption by Hydrogen Fluoride (HF) J = 1-0 rotational transition, toward a number of Galactic sources. We present observations of HF J = 1-0 toward the high-mass star-forming region Sagittarius B2(M). The spectrum obtained shows a complex pattern of absorption, with numerous features covering a wide range of local standard of rest velocities (-130 to 100 km -1). An analysis of this absorption yields HF abundances relative to H2 of ~1.3 {\times}10-8, in most velocity intervals. This result is in good agreement with estimates from chemical models, which predict that HF should be the main reservoir of gas-phase fluorine under a wide variety of interstellar conditions. Interestingly, we also find velocity intervals in which the HF spectrum shows strong absorption features that are not present, or are very weak, in spectra of other molecules, such as 13CO (1-0) and CS (2-1). HF absorption reveals components of diffuse clouds with small extinction that can be studied for the first time. Another interesting observation is that water is significantly more abundant than Hydrogen Fluoride over a wide range of velocities toward Sagittarius B2(M), in contrast to the remarkably constant H2O/HF abundance ratio with average value close to unity measured toward other Galactic sources.
Raquel Monje - One of the best experts on this subject based on the ideXlab platform.
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Hydrogen Fluoride toward luminous nearby galaxies ngc 253 and ngc 4945
The Astrophysical Journal, 2014Co-Authors: Raquel Monje, David A Neufeld, T G Phillips, D C Lis, S Lord, E Falgarone, R GustenAbstract:We present the detection of Hydrogen Fluoride, HF, in two luminous nearby galaxies NGC 253 and NGC 4945 using the Heterodyne Instrument for the Far-Infrared (HIFI) on board the Herschel Space Observatory. The HF line toward NGC 253 has a P-Cygni profile, while an asymmetric absorption profile is seen toward NGC 4945. The P-Cygni profile in NGC 253 suggests an outflow of molecular gas with a mass of M(H_2)_(out) ~ 1 × 10^7 M_⊙ and an outflow rate as large as Ṁ ~ 6.4 M_⊙ yr^(−1). In the case of NGC 4945, the axisymmetric velocity components in the HF line profile is compatible with the interpretation of a fast rotating nuclear ring surrounding the nucleus and the presence of inflowing gas. The gas falls into the nucleus with an inflow rate of ≤ 1.2 M_⊙ yr^(−1), inside a inner radius of ≤ 200 pc. The gas accretion rate to the central AGN is much smaller, suggesting that the inflow can be triggering a nuclear starburst. From these results, the HF J = 1 − 0 line is seen to provide an important probe of the kinematics of absorbing material along the sight-line to nearby galaxies with bright dust continuum and a promising new tracer of molecular gas in high redshift galaxies.
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Hydrogen Fluoride toward luminous nearby galaxies ngc 253 and ngc 4945
arXiv: Astrophysics of Galaxies, 2014Co-Authors: Raquel Monje, David A Neufeld, T G Phillips, D C Lis, S Lord, E Falgarone, R GustenAbstract:We present the detection of Hydrogen Fluoride, HF, in two luminous nearby galaxies NGC 253 and NGC 4945 using the Heterodyne Instrument for the Far-Infrared (HIFI) on board the Herschel Space Observatory. The HF line toward NGC 253 has a P-Cygni profile, while an asymmetric absorption profile is seen toward NGC 4945. The P-Cygni profile in NGC 253 suggests an outflow of molecular gas with a mass of M(H$_2$)$_{out}$ $\sim$ 1 $\times$ 10$^7$ M$_\odot$ and an outflow rate as large as \.{M} $\sim$ 6.4 M$_\odot$ yr$^{-1}$. In the case of NGC 4945, the axisymmetric velocity components in the HF line profile is compatible with the interpretation of a fast-rotating nuclear ring surrounding the nucleus and the presence of inflowing gas. The gas falls into the nucleus with an inflow rate of $\le$ 1.2 M$_\odot$ yr$^{-1}$, inside a inner radius of $\le$ 200 pc. The gas accretion rate to the central AGN is much smaller, suggesting that the inflow can be triggering a nuclear starburst. From these results, the HF $J = 1-0$ line is seen to provide an important probe of the kinematics of absorbing material along the sight-line to nearby galaxies with bright dust continuum and a promising new tracer of molecular gas in high-redshift galaxies.
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discovery of Hydrogen Fluoride in the cloverleaf quasar at z 2 56
arXiv: Cosmology and Nongalactic Astrophysics, 2012Co-Authors: Raquel Monje, David A Neufeld, T G Phillips, D C Lis, Ruisheng Peng, M EmprechtingerAbstract:We report the first detection of Hydrogen Fluoride (HF) toward a high redshift quasar. Using the Caltech Submillimeter Observatory (CSO) we detect the HF J = 1 - 0 transition in absorption toward the Cloverleaf, a broad absorption line (BAL) quasi-stellar object (QSO) at z=2.56. The detection is statistically significant at the ~ 6 sigma level. We estimate a lower limit of 4 \times 1014 cm-2 for the HF column density and using a previous estimate of the Hydrogen column density, we obtain a lower limit of 1.7 \times 10-9 for the HF abundance. This value suggests that, assuming a Galactic N(HF)/NH ratio, HF accounts for at least ~10% of the fluorine in the gas phase along the line of sight to the Cloverleaf quasar. This observation corroborates the prediction that HF should be a good probe of the molecular gas at high redshift. Measurements of the HF abundance as a function of redshift are urgently needed to better constrain the fluorine nucleosynthesis mechanism(s).
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discovery of Hydrogen Fluoride in the cloverleaf quasar at z 2 56
The Astrophysical Journal, 2011Co-Authors: Raquel Monje, David A Neufeld, T G Phillips, D C Lis, Ruisheng Peng, M EmprechtingerAbstract:We report the first detection of Hydrogen Fluoride (HF) toward a high-redshift quasar. Using the Caltech Submillimeter Observatory, we detect the HF J = 1-0 transition in absorption toward the Cloverleaf, a broad absorption line quasi-stellar object at z = 2.56. The detection is statistically significant at the ~6σ level. We estimate a lower limit of 4 × 10^(14) cm^(–2) for the HF column density and using a previous estimate of the Hydrogen column density, we obtain a lower limit of 1.7 × 10^(–9) for the HF abundance. This value suggests that, assuming a Galactic N(HF)/N H ratio, HF accounts for at least ~10% of the fluorine in the gas phase along the line of sight to the Cloverleaf quasar. This observation corroborates the prediction that HF should be a good probe of the molecular gas at high redshift. Measurements of the HF abundance as a function of redshift are urgently needed to better constrain the fluorine nucleosynthesis mechanism(s).
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herschel hifi observations of Hydrogen Fluoride toward sagittarius b2 m
arXiv: Astrophysics of Galaxies, 2011Co-Authors: Raquel Monje, David A Neufeld, T G Phillips, M Emprechtinger, D C Lis, Paul F Goldsmith, E A Bergin, T A Bell, Paule SonnentruckerAbstract:Herschel/HIFI observations have revealed the presence of widespread absorption by Hydrogen Fluoride (HF) J = 1-0 rotational transition, toward a number of Galactic sources. We present observations of HF J = 1-0 toward the high-mass star-forming region Sagittarius B2(M). The spectrum obtained shows a complex pattern of absorption, with numerous features covering a wide range of local standard of rest velocities (-130 to 100 km -1). An analysis of this absorption yields HF abundances relative to H2 of ~1.3 {\times}10-8, in most velocity intervals. This result is in good agreement with estimates from chemical models, which predict that HF should be the main reservoir of gas-phase fluorine under a wide variety of interstellar conditions. Interestingly, we also find velocity intervals in which the HF spectrum shows strong absorption features that are not present, or are very weak, in spectra of other molecules, such as 13CO (1-0) and CS (2-1). HF absorption reveals components of diffuse clouds with small extinction that can be studied for the first time. Another interesting observation is that water is significantly more abundant than Hydrogen Fluoride over a wide range of velocities toward Sagittarius B2(M), in contrast to the remarkably constant H2O/HF abundance ratio with average value close to unity measured toward other Galactic sources.
R Gusten - One of the best experts on this subject based on the ideXlab platform.
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Hydrogen Fluoride toward luminous nearby galaxies ngc 253 and ngc 4945
The Astrophysical Journal, 2014Co-Authors: Raquel Monje, David A Neufeld, T G Phillips, D C Lis, S Lord, E Falgarone, R GustenAbstract:We present the detection of Hydrogen Fluoride, HF, in two luminous nearby galaxies NGC 253 and NGC 4945 using the Heterodyne Instrument for the Far-Infrared (HIFI) on board the Herschel Space Observatory. The HF line toward NGC 253 has a P-Cygni profile, while an asymmetric absorption profile is seen toward NGC 4945. The P-Cygni profile in NGC 253 suggests an outflow of molecular gas with a mass of M(H_2)_(out) ~ 1 × 10^7 M_⊙ and an outflow rate as large as Ṁ ~ 6.4 M_⊙ yr^(−1). In the case of NGC 4945, the axisymmetric velocity components in the HF line profile is compatible with the interpretation of a fast rotating nuclear ring surrounding the nucleus and the presence of inflowing gas. The gas falls into the nucleus with an inflow rate of ≤ 1.2 M_⊙ yr^(−1), inside a inner radius of ≤ 200 pc. The gas accretion rate to the central AGN is much smaller, suggesting that the inflow can be triggering a nuclear starburst. From these results, the HF J = 1 − 0 line is seen to provide an important probe of the kinematics of absorbing material along the sight-line to nearby galaxies with bright dust continuum and a promising new tracer of molecular gas in high redshift galaxies.
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Hydrogen Fluoride toward luminous nearby galaxies ngc 253 and ngc 4945
arXiv: Astrophysics of Galaxies, 2014Co-Authors: Raquel Monje, David A Neufeld, T G Phillips, D C Lis, S Lord, E Falgarone, R GustenAbstract:We present the detection of Hydrogen Fluoride, HF, in two luminous nearby galaxies NGC 253 and NGC 4945 using the Heterodyne Instrument for the Far-Infrared (HIFI) on board the Herschel Space Observatory. The HF line toward NGC 253 has a P-Cygni profile, while an asymmetric absorption profile is seen toward NGC 4945. The P-Cygni profile in NGC 253 suggests an outflow of molecular gas with a mass of M(H$_2$)$_{out}$ $\sim$ 1 $\times$ 10$^7$ M$_\odot$ and an outflow rate as large as \.{M} $\sim$ 6.4 M$_\odot$ yr$^{-1}$. In the case of NGC 4945, the axisymmetric velocity components in the HF line profile is compatible with the interpretation of a fast-rotating nuclear ring surrounding the nucleus and the presence of inflowing gas. The gas falls into the nucleus with an inflow rate of $\le$ 1.2 M$_\odot$ yr$^{-1}$, inside a inner radius of $\le$ 200 pc. The gas accretion rate to the central AGN is much smaller, suggesting that the inflow can be triggering a nuclear starburst. From these results, the HF $J = 1-0$ line is seen to provide an important probe of the kinematics of absorbing material along the sight-line to nearby galaxies with bright dust continuum and a promising new tracer of molecular gas in high-redshift galaxies.
