3 research outputs found
A census of baryons in the Universe from localized fast radio bursts
More than three quarters of the baryonic content of the Universe resides in a
highly diffuse state that is difficult to observe, with only a small fraction
directly observed in galaxies and galaxy clusters. Censuses of the nearby
Universe have used absorption line spectroscopy to observe these invisible
baryons, but these measurements rely on large and uncertain corrections and are
insensitive to the majority of the volume, and likely mass. Specifically,
quasar spectroscopy is sensitive either to only the very trace amounts of
Hydrogen that exists in the atomic state, or highly ionized and enriched gas in
denser regions near galaxies. Sunyaev-Zel'dovich analyses provide evidence of
some of the gas in filamentary structures and studies of X-ray emission are
most sensitive to gas near galaxy clusters. Here we report the direct
measurement of the baryon content of the Universe using the dispersion of a
sample of localized fast radio bursts (FRBs), thus utilizing an effect that
measures the electron column density along each sight line and accounts for
every ionised baryon. We augment the sample of published arcsecond-localized
FRBs with a further four new localizations to host galaxies which have measured
redshifts of 0.291, 0.118, 0.378 and 0.522, completing a sample sufficiently
large to account for dispersion variations along the line of sight and in the
host galaxy environment to derive a cosmic baryon density of (95% confidence). This independent
measurement is consistent with Cosmic Microwave Background and Big Bang
Nucleosynthesis values.Comment: Published online in Nature 27 May, 202
Polarized point sources in the LOFAR Two-meter Sky Survey: A preliminary catalog
The polarization properties of radio sources at very low frequencies (<200 MHz) have not been widely measured, but the new generation of low-frequency radio telescopes, including the Low Frequency Array (LOFAR: a Square Kilometre Array Low pathfinder), now gives us the opportunity to investigate these properties. In this paper, we report on the preliminary development of a data reduction pipeline to carry out polarization processing and Faraday tomography for data from the LOFAR Two-meter Sky Survey (LOTSS) and present the results of this pipeline from the LOTSS preliminary data release region (10h45m–15h30m right ascension, 45°–57° declination, 570 square degrees). We have produced a catalog of 92 polarized radio sources at 150 MHz at 4:03 resolution and 1 mJy rms sensitivity, which is the largest catalog of polarized sources at such low frequencies. We estimate a lower limit to the polarized source surface density at 150 MHz, with our resolution and sensitivity, of 1 source per 6.2 square degrees. We find that our Faraday depth measurements are in agreement with previous measurements and have significantly smaller errors. Most of our sources show significant depolarization compared to 1.4 GHz, but there is a small population of sources with low depolarization indicating that their polarized emission is highly localized in Faraday depth. We predict that an extension of this work to the full LOTSS data would detect at least 3400 polarized sources using the same methods, and probably considerably more with improved data processing