arXiv subjects

W. Ubachs

Publications and source records attributed to W. Ubachs.

76 records · Page 5Linked to original sources

arXiv2010

A High-Velocity Narrow Absorption Line Outflow in the Quasar J212329.46-005052.9

We report on a variable high-velocity narrow absorption line outflow in the redshift 2.3 quasar J2123-0050. Five distinct outflow systems are detected with velocity shifts from -9710 to -14,050 km/s and CIV 1548,1551 line widths of FWHM = 62-164 km/s. These data require five distinct outflow structures with similar kinematics, physical conditions and characteristic sizes of order 0.01-0.02 pc. The most likely location is ~5 pc from the quasar. The coordinated line variations in <0.63 yr (rest) are best explained by global changes in the outflow ionization caused by changes in the quasar's ionizing flux. The absence of strong X-ray absorption shows that radiative shielding is not needed to maintain the moderate ionizations and therefore, apparently, it is not needed to facilitate the radiative acceleration to high speeds. The kinetic energy yield of this flow is at least two orders of magnitude too low to be important for feedback to the host galaxy's evolution.

astro-ph.CO↗

arXiv2010

Cosmological concordance or chemical coincidence? Deuterated molecular hydrogen abundances at high redshift

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.

astro-ph.CO↗

arXiv2008

Direct frequency comb spectroscopy of trapped ions

Direct frequency comb spectroscopy of trapped ions is demonstated for the first time. It is shown that the 4s^2S_(1/2)-4p^2P_(3/2) transition in calcium ions can be excited directly with a frequency comb laser that is upconverted to 393 nm. Detection of the transition is performed using a shelving scheme to suppress background signal from non-resonant comb modes. The measured transition frequency of f=761 905 012.7(0.5) MHz presents an improvement in accuracy of more than two orders of magnitude.

physics.atom-ph↗

arXiv2008

Frequency metrology on the 4s 2S1/2 - 4p 2P1/2 transition in the calcium ion for a comparison with quasar data

High accuracy frequency metrology on the 4s 2S1/2 - 4p 2P1/2 transition in calcium ions is performed using laser cooled and crystallized ions in a linear Paul trap. Calibration is performed with a frequency comb laser, resulting in a transition frequency of f=755222766.2(1.7) MHz. The accuracy presents an improvement of more than one order of magnitude, and will facilitate a comparison with quasar data in a search for a possible change of the fine structure constant on a cosmological time scale.

physics.atom-ph↗