Strong magnetic fields in normal galaxies at high redshift

Abstract

The origin and growth of magnetic fields in galaxies is still something of an enigma1. It is generally assumed that seed fields are amplified over time through the dynamo effect2,3,4,5, but there are few constraints on the timescale. It was recently demonstrated that field strengths as traced by rotation measures of distant (and hence ancient) quasars are comparable to those seen today6, but it was unclear whether the high fields were in the unusual environments of the quasars themselves or distributed along the lines of sight. Here we report high-resolution spectra that demonstrate that the quasars with strong Mg ii absorption lines are unambiguously associated with larger rotation measures. Because Mg ii absorption occurs in the haloes of normal galaxies7,8,9,10,11 along the sightlines to the quasars, this association requires that organized fields of surprisingly high strengths are associated with normal galaxies when the Universe was only about one-third of its present age.

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Figure 1: FRM distributions for different numbers of strong Mg ii absorption lines.
Figure 2: Cumulative FRM distributions for sightlines with and without strong Mg ii absorption line systems.

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Acknowledgements

Our observations were made on the European Southern Observatory’s telescopes at the Paranal Observatory under programme IDs 075.A-0841 and 076.A-0860. M.L.B. acknowledges financial support from the Swiss National Science Foundation, and P.P.K. acknowledges support from the Natural Sciences and Engineering Council of Canada and the US Department of Energy.

Author Contributions M.L.B. reduced the UVES spectra, identified the Mg ii absorbers in them and carried out the statistical analyses that are presented in the paper. F.M. was the principal investigator on the UVES observational project on the Very Large Telescope and made the observations in Chile. F.M. and S.J.L. oversaw the overall design and execution of the research. P.P.K. derived the FRMs from multifrequency polarization measurements obtained at the NRAO Very Large Array and the Max Planck Institute for Radio Astronomy’s Effelsberg 100-m radio telescope, and other radio telescopes. M.D.–Z. advised on the observation and reduction of the UVES data and the identification of Mg ii absorbers.

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Correspondence to Francesco Miniati.

Supplementary information

Supplementary information

The file contains Supplementary Notes and Supplementary Methods. This file contains the following additional information: (a) model used to describe the observed RM data, (b) brief description of the methods used for the statistical analysis. (PDF 180 kb)

Supplementary information

The file contains Supplementary Figure 1. This figure shows the spectra of the 71 QSOs used in the analysis, with wavelength ranging from 3760Å to 8560Å. The strong MgII absorption systems are marked with red filled circles above the λr=2796.35,2803.53 lines. (Spectrum of sources, 4C_m05_64, 4C_p05_64, 4C_m04_04, 4C_p11_69, OX_m173, OX_m192, PKS_0112_017, PKS_2227m08, PKS_1615p029) (PDF 7501 kb)

Supplementary information

The file contains Supplementary Figure 2. This figure shows the spectra of the 71 QSOs used in the analysis, with wavelength ranging from 3760Å to 8560Å. The strong MgII absorption systems are marked with red filled circles above the λr=2796.35,2803.53 lines. ( Spectrum of sources: PKS_2353m18,PKS_2340m036, MRC_0122m003, 3C_057, 3C_454_3, OB_m094, OC_m065, OC_m192, OX_p057) (PDF 6995 kb)

Supplementary information

The file contains Supplementary Figure 3. This figure shows the spectra of the 71 QSOs used in the analysis, with wavelength ranging from 3760Å to 8560Å. The strong MgII absorption systems are marked with red filled circles above the λr=2796.35,2803.53 lines. (Spectrum of sources: PKS_0038m020, PKS_1424m11, PKS_2223m05, PKS_2243m123, PKS_2255m282, 4C_m05_62, OQ_p135, OW_m174, 3C_037) (PDF 7419 kb)

Supplementary information

The file contains Supplementary Figure 4. This figure shows the spectra of the 71 QSOs used in the analysis, with wavelength ranging from 3760Å to 8560Å. The strong MgII absorption systems are marked with red filled circles above the λr=2796.35,2803.53 lines. (Spectrum of sources 3C_039, 3C_298, 4C_p06_69, 4C_m03_79, OC_m259, OX_m325, PKS_2204_54, PKS_2326m477, PKS_2353m68.) (PDF 7323 kb)

Supplementary information

The file contains Supplementary Figure 5. This figure shows the spectra of the 71 QSOs used in the analysis, with wavelength ranging from 3760Å to 8560Å. The strong MgII absorption systems are marked with red filled circles above the λr=2796.35,2803.53 lines. (Spectrum of sources: 3C_094, 3C_095, 3C_208, 3C_245, 3C_281, 4C_20_24, 4C_m00_50, 4C_m02_55, 4C_m06_35.) (PDF 7564 kb)

Supplementary information

The file contains Supplementary Figure 6. This figure shows the spectra of the 71 QSOs used in the analysis, with wavelength ranging from 3760Å to 8560Å. The strong MgII absorption systems are marked with red filled circles above the λr=2796.35,2803.53 lines. (Spectrum of sources: 4C_p01_24, 4C_p02_27, 4C_p06_41, 4C_p13_46, 4C_p19_34, 4C_p19_44, OD_m055, OD_p094_7, OK_186.) (PDF 7566 kb)

Supplementary information

The file contains Supplementary Figure 7. This figure shows the spectra of the 71 QSOs used in the analysis, with wavelength ranging from 3760Å to 8560Å. The strong MgII absorption systems are marked with red filled circles above the λr=2796.35,2803.53 lines. (Spectrum of sources: PKS_0130_m17, PKS_0202_m17, PKS_0332_m403, PKS_0402_m362, PKS_0414_m06, PKS_0420_m01, PKS_0422_m380, PKS_0506_m61, PKS_0839_p18,) (PDF 7472 kb)

Supplementary information

The file contains Supplementary Figure 8. This figure shows the spectra of the 71 QSOs used in the analysis, with wavelength ranging from 3760Å to 8560Å. The strong MgII absorption systems are marked with red filled circles above the λr=2796.35,2803.53 lines. (Spectrum of sources: PKS_1111_p149, PKS_1127_m14, PKS_1143_m245, PKS_1157_p014, PKS_1244_m255, PKS_B1419_m272, TXS_0223_p113,) (PDF 6662 kb)

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Bernet, M., Miniati, F., Lilly, S. et al. Strong magnetic fields in normal galaxies at high redshift. Nature 454, 302–304 (2008). https://doi.org/10.1038/nature07105

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