Spectroscopy with the Engineering Development Array: cold H+ at 63 MHz towards the Galactic Centre

Oonk, J. B. R.; Alexander, Emma L; Broderick, J. W.; Sokołowski, M.; Wayth, R. B.

doi:10.1093/mnras/stz950

Cited by 5 publications

(18 citation statements)

References 59 publications

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“…Both are generally in good agreement with previous measurements. The undiluted τdν estimates for Cα, Cβ, and Hα match the observations of Oonk et al (2019) within about 20%. We investigate the frequency dependence for each of Cα, Cβ, and Hα line strengths further in Section 3.6.…”

Section: Inner Galactic Planesupporting

confidence: 65%

“…where ν 0 is the center frequency of the line, k is the Boltzmann constant, T is the temperature of the gas, and V T is the turbulent velocity (see Gordon & Sorochenko 2009, for a detailed explanation). For the most extreme case of hot hydrogen gas at T = 7000 K (Oonk et al 2019), the characteristic thermal velocity is about 11 km s −1 . An example H463α line, near the mean effective frequency of 66.1 MHz for α lines in the EDGES band (see Section 2.4), would have Δν G ≈ 4 kHz in the absence of any turbulent motion.…”

Section: Line Widthsmentioning

confidence: 99%

“…The 1σ uncertainty for each line is estimated from the residual spectrum rms, scaled to each line frequency by a power law matching the sky spectrum. For LST 18 hr, we plot the undiluted estimates and compare them with the Oonk et al (2019) and Erickson et al (1995) observations of the Galactic center region. The Oonk et al (2019) data were reported as τdν integrals, where τ = T RRL /T cont is the observed line-tocontinuum ratio.…”

Section: Frequency Dependence Of Rrlsmentioning

confidence: 99%

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Low-frequency Radio Recombination Lines Away from the Inner Galactic Plane

Vydula,

Bowman,

Lewis

et al. 2023

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Diffuse radio recombination lines (RRLs) in the Galaxy are possible foregrounds for redshifted 21 cm experiments. We use EDGES drift scans centered at −26.°7 decl. to characterize diffuse RRLs across the southern sky. We find that RRLs averaged over the large antenna beam (72° × 110°) reach minimum amplitudes of R.A. = 2–6 hr. In this region, the Cα absorption amplitude is 33 ± 11 mK (1σ) averaged over 50–87 MHz (27 ≳ z ≳ 15 for the 21 cm line) and increases strongly as frequency decreases. Cβ and Hα lines are consistent with no detection with amplitudes of 13 ± 14 and 12 ± 10 mK (1σ), respectively. At 108–124.5 MHz (z ≈ 11) in the same region, we find no evidence for carbon or hydrogen lines at the noise level of 3.4 mK (1σ). Conservatively assuming that observed lines come broadly from the diffuse interstellar medium, as opposed to a few compact regions, these amplitudes provide upper limits on the intrinsic diffuse lines. The observations support expectations that Galactic RRLs can be neglected as significant foregrounds for a large region of sky until redshifted 21 cm experiments, particularly those targeting cosmic dawn, move beyond the detection phase. We fit models of the spectral dependence of the lines averaged over the large beam of EDGES, which may contain multiple line sources with possible line blending, and find that including degrees of freedom for expected smooth, frequency-dependent deviations from local thermodynamic equilibrium (LTE) is preferred over simple LTE assumptions for Cα and Hα lines. For Cα we estimate departure coefficients 0.79 < b n β n < 4.5 along the inner Galactic plane and 0 < b n β n < 2.3 away from the inner Galactic plane.

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Section: Inner Galactic Planesupporting

confidence: 65%

Section: Line Widthsmentioning

confidence: 99%

Section: Frequency Dependence Of Rrlsmentioning

confidence: 99%

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Low-frequency Radio Recombination Lines Away from the Inner Galactic Plane

Vydula,

Bowman,

Lewis

et al. 2023

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“…We also report the detection of an Hα emission line as a result of stacking 43 lines at an average frequency of 64.08 MHz, one of the lowest frequency detections to date (see also Oonk et al 2019, towards the Galactic Center at 63 MHz) and a valuable probe of the cold partially ionized phase of the ISM. This feature (see Table 2 for line properties) has been significantly identified in each step of our method (see Figure 11), most prominently in the stack cross-correlation with a 5.4σ confidence.…”

Section: Hydrogen Rrl Resultsmentioning

confidence: 81%

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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“…The detection of low-frequency CRRLs from a well known HISA region -the Heeschen-Riegel-Crutcher region (HRC, Heeschen 1955;Riegel & Crutcher 1972) was reported by Roshi & Kantharia (2011); Oonk et al (2019). By combining multi-frequency CRRL and H i data, Roshi & Kantharia (2011) were able to constrain the physical properties and processes in the HRC cloud.…”

Section: Introductionmentioning

confidence: 99%

Arecibo-Green Bank-LOFAR Carbon Radio Recombination Line observations toward cold HI Clouds

Roshi

Peters

Emig

et al. 2021

Preprint

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We present results from a search for radio recombination lines in three H i self-absorbing (HISA) clouds at 750 MHz and 321 MHz with the Robert C. Byrd Green Bank Telescope (GBT), and in three Galactic Plane positions at 327 MHz with the Arecibo Telescope. We detect Carbon Recombination Lines (CRRLs) in the direction of DR4 and DR21, as well as in the galactic plane position G34.94+0.0. We additionally detect Hydrogen Recombination Lines (HRRLs) in emission in five of the six sightlines, and a Helium line at 750 MHz towards DR21. Combining our new data with 150 MHz LOFAR detections of CRRL absorption towards DR4 and DR21, we estimate the electron densities of the line forming regions by modeling the line width as a function of frequency. The estimated densities are in the range 1.4 → 6.5 cm −3 towards DR4, for electron temperatures 200 → 20 K. A dual line forming region with densities between 3.5 → 24 cm −3 and 0.008 → 0.3 cm −3 could plausibly explain the observed line width as a function of frequency on the DR21 sightline. The central velocities of the CRRLs compare well with CO emission and HISA lines in these directions. The cloud densities estimated from the CO lines are smaller (at least a factor of 5) than those of the CRRL forming regions. It is likely that the CRRL forming and H i self-absorbing gas is located in a denser, shocked region either at the boundary of or within the CO emitting cloud.

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Spectroscopy with the Engineering Development Array: cold H+ at 63 MHz towards the Galactic Centre

Cited by 5 publications

References 59 publications

Low-frequency Radio Recombination Lines Away from the Inner Galactic Plane

Low-frequency Radio Recombination Lines Away from the Inner Galactic Plane

Searching for the largest bound atoms in space

Arecibo-Green Bank-LOFAR Carbon Radio Recombination Line observations toward cold HI Clouds

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