A new era of fine structure constant measurements at high redshift
Date Issued
2021
Author(s)
Abstract
New observations of the quasar HE0515$-$4414 have been made using the HARPS
spectrograph on the ESO 3.6m telescope, aided by the Laser Frequency Comb
(LFC). We present three important advances for $\alpha$ measurements in quasar
absorption spectra from these observations. Firstly, the data have been
wavelength calibrated using LFC and ThAr methods. The LFC wavelength
calibration residuals are six times smaller than when using the standard ThAr
calibration. We give a direct comparison between $\alpha$ measurements made
using the two methods. Secondly, spectral modelling was performed using
Artificial Intelligence (fully automated, all human bias eliminated), including
a temperature parameter for each absorption component. Thirdly, in contrast to
previous work, additional model parameters were assigned to measure $\alpha$
for each individual absorption component. The increase in statistical
uncertainty from the larger number of model parameters is small and the method
allows a substantial advantage; outliers that would otherwise contribute a
significant systematic, possibly corrupting the entire measurement, are
identified and removed, permitting a more robust overall result. The $z_{abs} =
1.15$ absorption system along the HE0515$-$4414 sightline yields 40 new
$\alpha$ measurements. We constrain spatial fluctuations in $\alpha$ to be
$\Delta\alpha/\alpha \leq 9 \times 10^{-5}$ on scales $\approx 20\;{\rm
km\,s}^{-1}$, corresponding to $\approx25\;$kpc if the $z_{abs} = 1.15$ system
arises in a $1\;$Mpc cluster. Collectively, the 40 measurements yield
$\Delta\alpha/\alpha=-0.27\pm2.41\times10^{-6}$, consistent with no variation.
Volume
500
Issue
1
Start page
1
Issn Identifier
0035-8711
Rights
open.access
File(s)![Thumbnail Image]()
Loading...
Name
staa3217.pdf
Size
2.93 MB
Format
Adobe PDF
Checksum (MD5)
c132d45fbb6e668598a871710513609f