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The Distribution of Atomic Hydrogen in the Host Galaxies of FRBs

Hugh Roxburgh, Marcin Glowacki, Clancy W. James, Nathan Deg, Qifeng Huang, Karen Lee-Waddell, Jing Wang, Manisha Caleb, Adam T. Deller, Laura N. Driessen, Alexa C. Gordon, Kelley M. Hess, J. Xavier Prochaska, Ryan M. Shannon, Yuanming Wang, Ziteng Wang, Dong Yang

Abstract

We probe the atomic hydrogen (HI) emission from the host galaxies of fast radio bursts (FRBs) to investigate the emerging trend of disturbance and asymmetry in the population. Quadrupling the sample size, we detect 16 out of 17 new hosts in HI, with the single non-detection arising in a galaxy known to be transitioning towards quiescence. With respect to typical local Universe galaxies, FRB hosts are generally massive in HI ($M_{HI}>10^9 M_\odot$), which aligns with previous studies reporting that FRB hosts also tend to have high stellar masses and are star-forming. However, they span a broad range of other HI derived properties. Using visual inspection alongside various asymmetry metrics, we identify six unambiguously settled host galaxies, demonstrating for the first time that a disturbed HI morphology is not a universal feature of FRB host galaxies. However, we find another six that show clear signs of disturbance, one borderline case, and three which require deeper or more targeted observations to reach a conclusion; this brings the confirmed ratio of disturbed-to-settled FRB hosts to 11:6. Given that roughly a 1:1 ratio is expected for random background galaxies of similar type, our observed ratio yields a p-value of 0.222. Therefore, we conclude that contrary to earlier indications, there is no statistically significant excess of HI disturbance in this sample of FRB host galaxies with respect to the general galaxy population, and hence we find no evidence for a fundamental connection between FRB progenitor formation and merger-induced star formation activity.

The Distribution of Atomic Hydrogen in the Host Galaxies of FRBs

Abstract

We probe the atomic hydrogen (HI) emission from the host galaxies of fast radio bursts (FRBs) to investigate the emerging trend of disturbance and asymmetry in the population. Quadrupling the sample size, we detect 16 out of 17 new hosts in HI, with the single non-detection arising in a galaxy known to be transitioning towards quiescence. With respect to typical local Universe galaxies, FRB hosts are generally massive in HI (), which aligns with previous studies reporting that FRB hosts also tend to have high stellar masses and are star-forming. However, they span a broad range of other HI derived properties. Using visual inspection alongside various asymmetry metrics, we identify six unambiguously settled host galaxies, demonstrating for the first time that a disturbed HI morphology is not a universal feature of FRB host galaxies. However, we find another six that show clear signs of disturbance, one borderline case, and three which require deeper or more targeted observations to reach a conclusion; this brings the confirmed ratio of disturbed-to-settled FRB hosts to 11:6. Given that roughly a 1:1 ratio is expected for random background galaxies of similar type, our observed ratio yields a p-value of 0.222. Therefore, we conclude that contrary to earlier indications, there is no statistically significant excess of HI disturbance in this sample of FRB host galaxies with respect to the general galaxy population, and hence we find no evidence for a fundamental connection between FRB progenitor formation and merger-induced star formation activity.

Paper Structure

This paper contains 36 sections, 8 equations, 18 figures, 5 tables.

Table of Contents

  1. Introduction
  2. Data
  3. FRB Host Galaxy Targets
  4. H i Observations & Processing
  5. GMRT Observations and Data Reduction
  6. MeerKAT Observations and Data Reduction
  7. FAST Observations and Data Reduction
  8. H i Results
  9. Marginal / Non-Detections
  10. Asymmetry Calculations
  11. Asymmetry Metrics
  12. Asymmetry Thresholds
  13. Uncertainties
  14. Target Analysis
  15. FRB 20181220A
  16. ...and 21 more sections

Figures (18)

  • Figure 1: H i spectra of the FRB host galaxies. The red, green, and blue colours represent dedicated observations from FAST, GMRT, and MeerKAT, with the two orange spectra taken from archival data. When necessary, the data are binned by various channel widths; fainter lines in the plots represent the raw data, with bolder lines representing the binned data. The vertical dashed line represents the rest frame of the hosts', determined by their optical redshifts.
  • Figure 2: FRB host galaxy H i spectra (continued)
  • Figure 3: FRB host galaxy moment maps, displaying total intensity (left), velocity (centre) and velocity dispersion (right). The lowest contours are at the 3$\sigma$ level, with the higher contours set at varying multiples of that level. When the FRB's localisation region is significantly smaller than the size of its host, we include its position shown in magenta in the intensity maps and black in the others; a star represents a localisation region too small to be shown, whereas a cross and dashed ellipse shows the estimated position and 1$\sigma$ uncertainty region. The beam sizes are shown in the upper right hand corner. Velocities are displayed in the rest frame, defined with respect to the optical redshift.
  • Figure 4: FRB host galaxy moment maps (continued).
  • Figure 5: FRB host galaxy moment maps (continued).
  • ...and 13 more figures