TY - JOUR
T1 - Cloud-by-cloud, multiphase, Bayesian modelling
T2 - Application to four weak, low-ionization absorbers
AU - Sameer,
AU - Charlton, Jane C.
AU - Norris, Jackson M.
AU - Gebhardt, Matthew
AU - Churchill, Christopher W.
AU - Kacprzak, Glenn G.
AU - Muzahid, Sowgat
AU - Narayanan, Anand
AU - Nielsen, Nikole M.
AU - Richter, Philipp
AU - Wakker, Bart P.
N1 - Publisher Copyright:
© 2021 The Author(s).
PY - 2021/2/1
Y1 - 2021/2/1
N2 - We present a new method aimed at improving the efficiency of component by component ionization modelling of intervening quasar absorption-line systems. We carry out cloud-by-cloud, multiphase modelling making use of cloudy and Bayesian methods to extract physical properties from an ensemble of absorption profiles. Here, as a demonstration of method, we focus on four weak, low-ionization absorbers at low redshift, because they are multiphase but relatively simple to constrain. We place errors on the inferred metallicities and ionization parameters for individual clouds, and show that the values differ from component to component across the absorption profile. Our method requires user input on the number of phases and relies on an optimized transition for each phase, one observed with high resolution and signal-to-noise ratio. The measured Doppler parameter of the optimized transition provides a constraint on the Doppler parameter of H i, thus providing leverage in metallicity measurements even when hydrogen lines are saturated. We present several tests of our methodology, demonstrating that we can recover the input parameters from simulated profiles. We also consider how our model results are affected by which radiative transitions are covered by observations (for example, how many H i transitions) and by uncertainties in the b parameters of optimized transitions. We discuss the successes and limitations of the method, and consider its potential for large statistical studies. This improved methodology will help to establish direct connections between the diverse properties derived from characterizing the absorbers and the multiple physical processes at play in the circumgalactic medium.
AB - We present a new method aimed at improving the efficiency of component by component ionization modelling of intervening quasar absorption-line systems. We carry out cloud-by-cloud, multiphase modelling making use of cloudy and Bayesian methods to extract physical properties from an ensemble of absorption profiles. Here, as a demonstration of method, we focus on four weak, low-ionization absorbers at low redshift, because they are multiphase but relatively simple to constrain. We place errors on the inferred metallicities and ionization parameters for individual clouds, and show that the values differ from component to component across the absorption profile. Our method requires user input on the number of phases and relies on an optimized transition for each phase, one observed with high resolution and signal-to-noise ratio. The measured Doppler parameter of the optimized transition provides a constraint on the Doppler parameter of H i, thus providing leverage in metallicity measurements even when hydrogen lines are saturated. We present several tests of our methodology, demonstrating that we can recover the input parameters from simulated profiles. We also consider how our model results are affected by which radiative transitions are covered by observations (for example, how many H i transitions) and by uncertainties in the b parameters of optimized transitions. We discuss the successes and limitations of the method, and consider its potential for large statistical studies. This improved methodology will help to establish direct connections between the diverse properties derived from characterizing the absorbers and the multiple physical processes at play in the circumgalactic medium.
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U2 - 10.1093/mnras/staa3754
DO - 10.1093/mnras/staa3754
M3 - Article
AN - SCOPUS:85100269910
SN - 0035-8711
VL - 501
SP - 2112
EP - 2139
JO - Monthly Notices of the Royal Astronomical Society
JF - Monthly Notices of the Royal Astronomical Society
IS - 2
ER -