Charge exchange in galaxy clusters

Liyi Gu, Junjie Mao, Jelle de Plaa, A. J. J. Raassen, Chintan Shah, Jelle S. Kaastra

Research output: Contribution to journalArticle

4 Citations (Scopus)

Abstract

Though theoretically expected, the charge exchange emission from galaxy clusters has not yet been confidently detected. Accumulating hints were reported recently, including a rather marginal detection with the Hitomi data of the Perseus cluster. As suggested in Gu et al. (2015), a detection of charge exchange line emission from galaxy clusters would not only impact the interpretation of the newly-discovered 3.5 keV line, but also open up a new research topic on the interaction between hot and cold matter in clusters. We aim to perform the most systematic search for the O VIII charge exchange line in cluster spectra using the RGS on board XMM. We introduce a sample of 21 clusters observed with the RGS. The dominating thermal plasma emission is modeled and subtracted with a two-temperature CIE component, and the residuals are stacked for the line search. The systematic uncertainties in the fits are quantified by refitting the spectra with a varying continuum and line broadening. By the residual stacking, we do find a hint of a line-like feature at 14.82 A, the characteristic wavelength expected for oxygen charge exchange. This feature has a marginal significance of 2.8 sigma, and the average equivalent width is 2.5E-4 keV. We further demonstrate that the putative feature can be hardly affected by the systematic errors from continuum modelling and instrumental effects, or the atomic uncertainties of the neighbouring thermal lines. Assuming a realistic temperature and abundance pattern, the physical model implied by the possible oxygen line agrees well with the theoretical model proposed previously to explain the reported 3.5 keV line. If the charge exchange source indeed exists, we would expect that the oxygen abundance is potentially overestimated by 8-22% in previous X-ray measurements which assumed pure thermal lines.
Original languageEnglish
Article numberA26
Number of pages11
JournalAstronomy and Astrophysics
Volume611
Early online date20 Mar 2018
DOIs
Publication statusE-pub ahead of print - 20 Mar 2018

Fingerprint

charge exchange
galaxies
oxygen
continuum modeling
thermal plasmas
XMM-Newton telescope
systematic errors
continuums
temperature
wavelengths
x rays
interactions

Keywords

  • astro-ph.HE
  • astro-ph.CO
  • astro-ph.GA
  • physics.atom-ph
  • atomic processes
  • line: identification
  • galaxies: clusters: intracluster medium
  • spectroscopy

Cite this

Gu, L., Mao, J., Plaa, J. D., Raassen, A. J. J., Shah, C., & Kaastra, J. S. (2018). Charge exchange in galaxy clusters. Astronomy and Astrophysics, 611, [A26]. https://doi.org/10.1051/0004-6361/201731861
Gu, Liyi ; Mao, Junjie ; Plaa, Jelle de ; Raassen, A. J. J. ; Shah, Chintan ; Kaastra, Jelle S. / Charge exchange in galaxy clusters. In: Astronomy and Astrophysics. 2018 ; Vol. 611.
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abstract = "Though theoretically expected, the charge exchange emission from galaxy clusters has not yet been confidently detected. Accumulating hints were reported recently, including a rather marginal detection with the Hitomi data of the Perseus cluster. As suggested in Gu et al. (2015), a detection of charge exchange line emission from galaxy clusters would not only impact the interpretation of the newly-discovered 3.5 keV line, but also open up a new research topic on the interaction between hot and cold matter in clusters. We aim to perform the most systematic search for the O VIII charge exchange line in cluster spectra using the RGS on board XMM. We introduce a sample of 21 clusters observed with the RGS. The dominating thermal plasma emission is modeled and subtracted with a two-temperature CIE component, and the residuals are stacked for the line search. The systematic uncertainties in the fits are quantified by refitting the spectra with a varying continuum and line broadening. By the residual stacking, we do find a hint of a line-like feature at 14.82 A, the characteristic wavelength expected for oxygen charge exchange. This feature has a marginal significance of 2.8 sigma, and the average equivalent width is 2.5E-4 keV. We further demonstrate that the putative feature can be hardly affected by the systematic errors from continuum modelling and instrumental effects, or the atomic uncertainties of the neighbouring thermal lines. Assuming a realistic temperature and abundance pattern, the physical model implied by the possible oxygen line agrees well with the theoretical model proposed previously to explain the reported 3.5 keV line. If the charge exchange source indeed exists, we would expect that the oxygen abundance is potentially overestimated by 8-22{\%} in previous X-ray measurements which assumed pure thermal lines.",
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Gu, L, Mao, J, Plaa, JD, Raassen, AJJ, Shah, C & Kaastra, JS 2018, 'Charge exchange in galaxy clusters', Astronomy and Astrophysics, vol. 611, A26. https://doi.org/10.1051/0004-6361/201731861

Charge exchange in galaxy clusters. / Gu, Liyi; Mao, Junjie; Plaa, Jelle de; Raassen, A. J. J.; Shah, Chintan; Kaastra, Jelle S.

In: Astronomy and Astrophysics, Vol. 611, A26, 20.03.2018.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Charge exchange in galaxy clusters

AU - Gu, Liyi

AU - Mao, Junjie

AU - Plaa, Jelle de

AU - Raassen, A. J. J.

AU - Shah, Chintan

AU - Kaastra, Jelle S.

PY - 2018/3/20

Y1 - 2018/3/20

N2 - Though theoretically expected, the charge exchange emission from galaxy clusters has not yet been confidently detected. Accumulating hints were reported recently, including a rather marginal detection with the Hitomi data of the Perseus cluster. As suggested in Gu et al. (2015), a detection of charge exchange line emission from galaxy clusters would not only impact the interpretation of the newly-discovered 3.5 keV line, but also open up a new research topic on the interaction between hot and cold matter in clusters. We aim to perform the most systematic search for the O VIII charge exchange line in cluster spectra using the RGS on board XMM. We introduce a sample of 21 clusters observed with the RGS. The dominating thermal plasma emission is modeled and subtracted with a two-temperature CIE component, and the residuals are stacked for the line search. The systematic uncertainties in the fits are quantified by refitting the spectra with a varying continuum and line broadening. By the residual stacking, we do find a hint of a line-like feature at 14.82 A, the characteristic wavelength expected for oxygen charge exchange. This feature has a marginal significance of 2.8 sigma, and the average equivalent width is 2.5E-4 keV. We further demonstrate that the putative feature can be hardly affected by the systematic errors from continuum modelling and instrumental effects, or the atomic uncertainties of the neighbouring thermal lines. Assuming a realistic temperature and abundance pattern, the physical model implied by the possible oxygen line agrees well with the theoretical model proposed previously to explain the reported 3.5 keV line. If the charge exchange source indeed exists, we would expect that the oxygen abundance is potentially overestimated by 8-22% in previous X-ray measurements which assumed pure thermal lines.

AB - Though theoretically expected, the charge exchange emission from galaxy clusters has not yet been confidently detected. Accumulating hints were reported recently, including a rather marginal detection with the Hitomi data of the Perseus cluster. As suggested in Gu et al. (2015), a detection of charge exchange line emission from galaxy clusters would not only impact the interpretation of the newly-discovered 3.5 keV line, but also open up a new research topic on the interaction between hot and cold matter in clusters. We aim to perform the most systematic search for the O VIII charge exchange line in cluster spectra using the RGS on board XMM. We introduce a sample of 21 clusters observed with the RGS. The dominating thermal plasma emission is modeled and subtracted with a two-temperature CIE component, and the residuals are stacked for the line search. The systematic uncertainties in the fits are quantified by refitting the spectra with a varying continuum and line broadening. By the residual stacking, we do find a hint of a line-like feature at 14.82 A, the characteristic wavelength expected for oxygen charge exchange. This feature has a marginal significance of 2.8 sigma, and the average equivalent width is 2.5E-4 keV. We further demonstrate that the putative feature can be hardly affected by the systematic errors from continuum modelling and instrumental effects, or the atomic uncertainties of the neighbouring thermal lines. Assuming a realistic temperature and abundance pattern, the physical model implied by the possible oxygen line agrees well with the theoretical model proposed previously to explain the reported 3.5 keV line. If the charge exchange source indeed exists, we would expect that the oxygen abundance is potentially overestimated by 8-22% in previous X-ray measurements which assumed pure thermal lines.

KW - astro-ph.HE

KW - astro-ph.CO

KW - astro-ph.GA

KW - physics.atom-ph

KW - atomic processes

KW - line: identification

KW - galaxies: clusters: intracluster medium

KW - spectroscopy

UR - https://arxiv.org/abs/1710.04784v1

U2 - 10.1051/0004-6361/201731861

DO - 10.1051/0004-6361/201731861

M3 - Article

VL - 611

JO - Astronomy and Astrophysics

JF - Astronomy and Astrophysics

SN - 0004-6361

M1 - A26

ER -

Gu L, Mao J, Plaa JD, Raassen AJJ, Shah C, Kaastra JS. Charge exchange in galaxy clusters. Astronomy and Astrophysics. 2018 Mar 20;611. A26. https://doi.org/10.1051/0004-6361/201731861