Searching for the largest bound atoms in space

Abstract

(abridged) Radio recombination lines (RRLs) at frequencies $\nu$ < 250 MHz trace the cold, diffuse phase of the ISM. 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. 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 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. 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 Cas A, we uncover three new detections: (1) C$\epsilon$-transitions ($\Delta$n = 5) for the first time at low radio frequencies, (2) H$\alpha$-transitions at 64 MHz with a FWHM of 3.1 km/s, the most narrow and one of the lowest frequency detections of hydrogen to date, and (3) C$\alpha$ at v${}_{LSR}$ = 0 km/s in the frequency range 55-78 MHz for the first time. Additionally we recover C$\alpha$, C$\beta$, C$\gamma$, and C$\delta$ from the -47 km/s and -38 km/s components. In the nearby starburst galaxy, M 82, we do not find a significant feature. Our current searches for RRLs in LOFAR observations are limited to narrow (< 100 km/s) features, owing to the relatively small number of channels available for continuum estimation. Future strategies making use of larger contiguous frequency coverage would aid calibration to deeper sensitivities and broader features.

arXiv comment21 pages, 21 figures, accepted in A&A

References in corpus (27)

• LOFAR: The LOw-Frequency ARray
• Astrophysics Source Code Library
• The Murchison Widefield Array: the Square Kilometre Array Precursor at low radio frequencies
• WSClean: an implementation of a fast, generic wide-field imager for radio astronomy
• The LOFAR Two-metre Sky Survey - II. First data release
• A morphological algorithm for improving radio-frequency interference detection
• Ionospheric Calibration of Low Frequency Radio Interferometric Observations using the Peeling Scheme: I. Method Description and First Results
• LOFAR facet calibration
• The Extragalactic Distance Database: Color-Magnitude Diagrams
• LOFAR 150-MHz observations of the Boötes field: Catalogue and Source Counts
• Systematic effects in LOFAR data: A unified calibration strategy
• The cosmic ray ionization rate in the Galactic disk, as determined from observations of molecular ions
• The LOFAR radio environment
• The Chemical Evolution of Helium
• The effect of the ionosphere on ultra-low frequency radio-interferometric observations
• Radio recombination lines from the largest bound atoms in space
• Carbon and hydrogen radio recombination lines from the cold clouds towards Cassiopeia A
• Low Frequency Carbon Radio Recombination Lines I: Calculations of Departure Coefficients
• Discovery of Carbon Radio Recombination Lines in M82
• LOFAR observations of decameter carbon radio recombination lines towards Cassiopeia A
• Discovery of Carbon Radio Recombination Lines in absorption towards Cygnus~A
• Low Frequency Carbon Radio Recombination Lines II: The Diffuse Interstellar Medium
• Mapping low frequency carbon radio recombination lines towards Cassiopeia A at 340, 148, 54 and 43 MHz
• The first detection of radio recombination lines at cosmological distances
• The Host Galaxy and the Environment of the z = 1.195 Quasar 3C 190
• Pipeline Collector: gathering performance data for distributed astronomical pipelines
• Spectroscopy with the Engineering Development Array: cold H${}^{+}$ at 63 MHz towards the Galactic Centre

Cited by in corpus (6)

• The LOFAR Two-metre Sky Survey -- V. Second data release
• The LOFAR LBA Sky Survey I. survey description and preliminary data release
• The First Large Absorption Survey in HI (FLASH): I. Science Goals and Survey Design
• Discovery of Hydrogen Radio Recombination Lines at z=0.89 towards PKS 1830-211
• Constraints on the properties of warm ionized gas from low-frequency hydrogen radio recombination lines
• Observations of Carbon Radio Recombination Lines with the NenuFAR telescope. I. Cassiopeia A and Cygnus A