The first detection of radio recombination lines at cosmological distances

Emig, K. L.; Salas, P.; Gasperin, F. de; Oonk, J. B. R.; Toribio, M. C.; Röttgering, H. J. A.; Tielens, A. G. G. M.

doi:10.1051/0004-6361/201834052

Cited by 15 publications

(23 citation statements)

References 58 publications

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“…We ultimately find αtransition RRLs at z = 1.12355 assuming carbon, as reported in Emig et al (2019). In Figure 15, we also show the spectrum when extending the line-blanking region to ±25 km s −1 as in Emig et al (2019). We do not find a significant signal at the systemic redshift of 3C 190 or at the redshifts of the reported absorption features and place a 3σ upper limit of 4.6 Hz for a line width of ±7.5 km s −1 .…”

Section: C 190supporting

confidence: 71%

“…The results of the method when line-blanking ±7.5 km s −1 are shown in Figure 15. We ultimately find αtransition RRLs at z = 1.12355 assuming carbon, as reported in Emig et al (2019). In Figure 15, we also show the spectrum when extending the line-blanking region to ±25 km s −1 as in Emig et al (2019).…”

Section: C 190supporting

confidence: 69%

“…Our method was developed to search blindly in redshift for RRLs in the LOFAR HBA spectrum of 3C 190, in which we have identified an RRL in emission at z = 1.12355 ± 0.00005 (assuming a carbon origin). This was the first detection of RRLs outside of the local universe (Emig et al 2019). To demonstrate and test the limitations of the method, we also apply it to existing LOFAR observations of the sources Cas A and M 82.…”

Section: Resultsmentioning

confidence: 99%

“…The fit to the solutions of each station, which is transferred to the target, is shown in black. (Emig et al 2019). We explain processing of LOFAR 110-165 MHz observations for spectroscopic analysis (Section 2).…”

Section: Introductionmentioning

confidence: 99%

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Searching for the largest bound atoms in space

Emig

Salas

Gasperin

et al. 2020

A&A

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Context. Radio recombination lines (RRLs) at frequencies ν < 250 MHz trace the cold, diffuse phase of the interstellar medium. Yet, RRLs have been largely unexplored outside of our Galaxy. Next generation low frequency interferometers, such as LOFAR, MWA and the future SKA, with unprecedented sensitivity, resolution, and large fractional bandwidths, are enabling the exploration of the extragalactic RRL universe. Aims. We describe methods used to (1) process LOFAR high band antenna (HBA) observations for RRL analysis, and (2) search spectra for the presence of RRLs blindly in redshift space. Methods. We observed the radio quasar 3C 190 (z ≈ 1.2) with the LOFAR HBA. In reducing this data for spectroscopic analysis, we have placed special emphasis on bandpass calibration. We devised cross-correlation techniques that utilize the unique frequency spacing between RRLs to significantly identify the presence of RRLs in a low frequency spectrum. We demonstrate the utility of this method by applying it to existing low-frequency spectra of Cassiopeia A and M 82, and to the new observations of 3C 190. Results. RRLs have been detected in the foreground of 3C 190 at z = 1.12355 (assuming a carbon origin), owing to the first detection of RRLs outside of the local universe (first reported in Emig et al. 2019). Towards the Galactic supernova remnant Cassiopeia A, we uncover three new detections: (1) stimulated C -transitions (∆n = 5) for the first time at low radio frequencies, (2) Hα transitions at 64 MHz with a FWHM of 3.1 km s −1 the most narrow and one of the lowest frequency detections of hydrogen to date, and (3) Cα at v LSR ≈ 0 km s −1 in the frequency range 55-78 MHz for the first time. Additionally we recover Cα, Cβ, Cγ, and Cδ from the -47 km s −1 and -38 km s −1 components. In the nearby starburst galaxy, M 82, we do not find a significant feature. With previously used techniques, we reproduce the previously reported line properties. Conclusions. RRLs have been blindly searched and successfully identified in Galactic (to high order transitions) and extragalactic (to high redshift) observations with our spectral searching method. Our current searches for RRLs in LOFAR observations are limited to narrow (< 100 km s −1 ) features, owing to the relatively small number of channels available for continuum estimation. Future strategies making use of a wider band (covering multiple LOFAR subbands) or designs with larger contiguous frequency chunks would aid calibration to deeper sensitivities and broader features.

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Section: C 190supporting

confidence: 71%

Section: C 190supporting

confidence: 69%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Searching for the largest bound atoms in space

Emig

Salas

Gasperin

et al. 2020

A&A

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“…This high time-and frequency-resolution data is kept to reduce time and bandwidth smearing to a level that is tolerable for future studies that will exploit the international baselines of LOFAR (only antennas within the Netherlands are used for the primary objectives of LoTSS). The high spectral resolution (R ∼ 5000−7000 or 22-31 km s −1 velocity resolution) of the data is also facilitating spectral line (Emig et al 2019) and spectro-polarimetric studies.…”

Section: Observation Statusmentioning

confidence: 99%

The LOFAR Two-metre Sky Survey

Shimwell

Tasse

Hardcastle

et al. 2019

A&A

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The LOFAR Two-metre Sky Survey (LoTSS) is an ongoing sensitive, high-resolution 120–168 MHz survey of the entire northern sky for which observations are now 20% complete. We present our first full-quality public data release. For this data release 424 square degrees, or 2% of the eventual coverage, in the region of the HETDEX Spring Field (right ascension 10h45m00s to 15h30m00s and declination 45°00′00″ to 57°00′00″) were mapped using a fully automated direction-dependent calibration and imaging pipeline that we developed. A total of 325 694 sources are detected with a signal of at least five times the noise, and the source density is a factor of ∼10 higher than the most sensitive existing very wide-area radio-continuum surveys. The median sensitivity is S144 MHz = 71 μJy beam−1 and the point-source completeness is 90% at an integrated flux density of 0.45 mJy. The resolution of the images is 6″ and the positional accuracy is within 0.2″. This data release consists of a catalogue containing location, flux, and shape estimates together with 58 mosaic images that cover the catalogued area. In this paper we provide an overview of the data release with a focus on the processing of the LOFAR data and the characteristics of the resulting images. In two accompanying papers we provide the radio source associations and deblending and, where possible, the optical identifications of the radio sources together with the photometric redshifts and properties of the host galaxies. These data release papers are published together with a further ∼20 articles that highlight the scientific potential of LoTSS.

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A search for annihilating dark matter in 47 Tucanae and Omega Centauri

Bond

Bekki

Westmeier

2022

Publ. Astron. Soc. Aust.

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A plausible formation scenario for the Galactic globular clusters 47 Tucanae (47 Tuc) and Omega Centauri $(\omega$ Cen) is that they are tidally stripped remnants of dwarf galaxies, in which case they are likely to have retained a fraction of their dark matter cores. In this study, we have used the ultra-wide band receiver on the Parkes telescope (Murriyang) to place upper limits on the annihilation rate of exotic Light Dark Matter particles $(\chi)$ via the $\chi\chi\rightarrow e^+e^-$ channel using measurements of the recombination rate of positronium (Ps). This is an extension of a technique previously used to search for Ps in the Galactic Centre. However, by stacking of spectral data at multiple line frequencies, we have been able to improve sensitivity. Our measurements have resulted in $3-\sigma$ flux density (recombination rate) upper limits of 1.7 mJy $\left(1.4\times 10^{43}\, \mathrm{s}^{-1}\right)$ and 0.8 mJy $\left(1.1 \times 10^{43} \mathrm{s}^{-1}\right)$ for 47 Tuc and $\omega$ Cen, respectively. Within the Parkes beam at the cluster distances, which varies from 10–23 pc depending on the frequency of the recombination line, and for an assumed annihilation cross-section $\langle\sigma v\rangle = 3\times 10^{-29} \mathrm{cm}^3\, \mathrm{s}^{-1}$ , we calculate upper limits to the dark matter mass and rms dark matter density of ${\lesssim} 1.2-1.3\times 10^5 f_n^{-0.5}$ $\left(m_\chi/\mathrm{MeV\, c}^{-2}\right)$ $\mathrm{M}_{\odot}$ and ${\lesssim} 48-54 f_n^{-0.5}$ $\left(m_\chi/\mathrm{MeV\, c}^{-2}\right)$ $\mathrm{M}_{\odot} \mathrm{pc}^{-3}$ for the clusters, where $f_n=R_n/R_p$ is the ratio of Ps recombination transitions to annihilations, estimated to be ${\sim}0.01$ . The radio limits for $\omega$ Cen suggest that, for a fiducial dark/luminous mass ratio of ${\sim}0.05$ , any contribution from Light Dark Matter is small unless $\langle\sigma v\rangle < 7.9\times 10^{-28}\ \left(m_\chi/\mathrm{MeV\, c}^{-2}\right)^2 \mathrm{cm}^3 \mathrm{s}^{-1}$ . Owing to the compactness and proximity of the clusters, archival 511-keV measurements suggest even tighter limits than permitted by CMB anisotropies, $\langle\sigma v\rangle < 8.6\times 10^{-31}\ (m_\chi/\mathrm{MeV\, c}^{-2})^2 \mathrm{cm}^3 \mathrm{s}^{-1}$ . Due to the very low synchrotron radiation background, our recombination rate limits substantially improve on previous radio limits for the Milky Way.

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The first detection of radio recombination lines at cosmological distances

Cited by 15 publications

References 58 publications

Searching for the largest bound atoms in space

Searching for the largest bound atoms in space

The LOFAR Two-metre Sky Survey

A search for annihilating dark matter in 47 Tucanae and Omega Centauri

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