Commissioning the H i Observing Mode of the Beam Former for the Cryogenically Cooled Focal L-band Array for the GBT (FLAG)

Pingel, N. M.; Pisano, D. J.; Ruzindana, M.; Burnett, Maria; Rajwade, Kaustubh; Black, Richard A.; Jeffs, Brian D.; Warnick, Karl F.; Lorimer, D. R.; Roshi, A.; Prestage, Richard; McLaughlin, M. A.; Agarwal, Devansh; Chamberlin, T.; Hawkins, L.; Jensen, Laura; Marganian, P.; Nelson, J. D.; Shillue, Bill; Smith, Edward K.; Simon, B.; Tonder, V. van; White, S.

doi:10.3847/1538-3881/abdec2

Cited by 10 publications

(7 citation statements)

References 38 publications

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“…The Parkes-IMAGINE (Imaging Galaxies Intergalactic and Nearby Environments) survey has mapped the entire CGM of 28 nearby galaxies in H i, reaching sensitivities comparable to our GBT observation (Sardone et al 2020). In the future, coordinated and deeper interferometric surveys and single-dish observations outfitted with phased array feeds or FLAG (The Focal L-band Array for the GBT; Pingel et al 2021) architecture would substantially improve our understanding of the large-scale H i accretion in the CGM, the true radial extent of H i disk, and the relation between H i accretion and star-formation in the disk. Measurements of low ionized metal absorbers would constrain the gas-phase metallicity and the ionization fraction of the H i emitters.…”

Section: Discussionmentioning

confidence: 99%

Detection of the Diffuse H i Emission in the Circumgalactic Medium of NGC 891 and NGC 4565

Das

Sardone

Leroy

et al. 2020

ApJ

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We present detections of 21 cm emission from neutral hydrogen (H I) in the circumgalactic medium (CGM) of the local edge-on galaxies NGC 891 and NGC 4565 using the Robert C. Byrd Green Bank Telescope (GBT). With our 5σ sensitivity of 8.2 10 16 cm −2 calculated over a 20 km s −1 channel, we achieve s >5 detections out to -90 120 kpc along the minor axes. The velocity width of the CGM emission is as large as that of the disk »500 km s −1 , indicating the existence of a diffuse component permeating the halo. We compare our GBT measurements with interferometric data from the Westerbork Synthesis Radio Telescope (WSRT). The WSRT maps the H Iemission from the disk at high signal-to-noise ratio but has limited surface brightness sensitivity at the angular scales probed with the GBT. After convolving the WSRT data to the spatial resolution of the GBT (FWHM=9 1), we find that the emission detected by the WSRT accounts for -+ 48 25 15 % ( -+ 58 18 4 %) of the total flux recovered by the GBT from the CGM of NGC 891 (NGC 4565). The existence of significant GBT-only flux suggests the presence of a large amount of diffuse, low column density H I emission in the CGM. For reasonable assumptions, the extended diffuse H I could account for 5.2±0.9% and 2.0±0.8% of the total H I emission of NGC 891 and NGC 4565. Unified Astronomy Thesaurus concepts: Circumgalactic medium (1879); Extragalactic astronomy (506); H I line emission (690); Radio spectroscopy (1359); Single-dish antennas (1460); Diffuse radiation (383); Extended radiation sources (504)

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Section: Discussionmentioning

confidence: 99%

Detection of the Diffuse H i Emission in the Circumgalactic Medium of NGC 891 and NGC 4565

Das

Sardone

Leroy

et al. 2020

ApJ

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“…Unfortunately, single-beam L-band (centimeter) instruments would potentially require a prohibitive amount of time to survey Local Group galaxies at the 18 cm OH lines. New multibeam phased array feeds (e.g., Roshi et al 2018;Pingel et al 2021;Burnett et al 2023) will drastically improve mapping speeds for large single-dish telescopes by orders of magnitude. In the near future, these instruments will be able to ).…”

Section: Discussionmentioning

confidence: 99%

First Extragalactic Detection of Thermal Hydroxyl (OH) 18 cm Emission in M31 Reveals Abundant CO-faint Molecular Gas

Busch

2024

ApJ

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The most abundant interstellar molecule, molecular hydrogen (H2), is practically invisible in cold molecular clouds. Astronomers typically use carbon monoxide (CO) to trace the bulk distribution and mass of H2 in our galaxy and many others. CO observations alone fail to trace a significant component of molecular gas known as “CO-dark” molecular gas, which can be probed with molecules such as OH and CH. We present an extremely sensitive pilot search for the 18 cm hydroxyl (OH) lines in the Andromeda galaxy (M31) with the 100 m Robert C. Byrd Green Bank Telescope. We successfully detected the 1665 and 1667 MHz OH lines in faint emission. The 1665/1667 MHz line ratio displays the characteristic 5:9 ratio predicted under conditions of local thermodynamic equilibrium. To our knowledge, this is the first detection of nonmaser 18 cm OH emission in another galaxy. We compare our OH and H i observations with archival CO (1–0) observations. Our OH detection position overlaps with the previously discovered Arp Outer Arm in CO. Our best estimates show that the amount of H2 traced by OH is 100%–140% higher than the amount traced by CO in this sight line. The amount of dark molecular gas implied by dust data supports this conclusion. We conclude that the 18 cm OH lines hold promise as a valuable tool for mapping of the “CO-dark” and “CO-faint” molecular gas phase in nearby galaxies, especially with upcoming multibeam, phased-array feed receivers on radio telescopes, which will allow for drastically improved mapping speeds of faint signals.

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“…We simulated single-dish N 2 H + (1-0) observations for a 8.1 ′′ beam, which corresponds to a 100-m dish such as the Green Bank Telescope (GBT) 12 . The observational noise was set to 0.1 K, which is realistic for GBT data (Pingel et al 2021). The single-dish observations were used as a model in the CASA tclean 13 procedure, resulting in a spectral cube with information also of the largest scales.…”

Section: Combination Of Interferometer and Single-dish Datamentioning

confidence: 99%

Synthetic Next Generation Very Large Array line observations of a massive star-forming cloud

Juvela

Mannfors

Liu

et al. 2022

A&A

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Context. Studies of the interstellar medium and the pre-stellar cloud evolution require spectral line observations that have a high sensitivity and high angular and velocity resolution. Regions of high-mass star formation are particularly challenging because of line-of-sight confusion, inhomogeneous physical conditions, and potentially very high optical depths. Aims. We wish to quantify to what accuracy the physical conditions within a massive star-forming cloud can be determined from observations. We are particularly interested in the possibilities offered by the Next Generation Very Large Array (ngVLA) interferometer. Methods. We used data from a magnetohydrodynamic simulation of star formation in a high-density environment. We concentrated on the study of a filamentary structure that has physical properties similar to a small infrared-dark cloud. We produced synthetic observations for spectral lines observable with the ngVLA and analysed these to measure column density, gas temperature, and kinematics. Results were compared to ideal line observations and the actual 3D model. Results. For a nominal cloud distance of 4 kpc, ngVLA provides a resolution of ∼0.01 pc even in its most compact configuration. For abundant molecules, such as HCO + , NH 3 , N 2 H + , and CO isotopomers, cloud kinematics and structure can be mapped down to subarcsecond scales in just a few hours. For NH 3 , a reliable column density map could be obtained for the entire 15 ′′ × 40 ′′ cloud, even without the help of additional single-dish data, and kinetic temperatures are recovered to a precision of ∼1 K. At higher frequencies, the loss of large-scale emission becomes noticeable. The line observations are seen to accurately trace the cloud kinematics, except for the largest scales, where some artefacts appear due to the filtering of low spatial frequencies. The line-of-sight confusion complicates the interpretation of the kinematics, and the usefulness of collapse indicators based on the expected blue asymmetry of optically thick lines is limited. Conclusions. The ngVLA will be able to provide accurate data on the small-scale structure and the physical and chemical state of star-forming clouds, even in high-mass star-forming regions at kiloparsec distances. Complementary single-dish data are still essential for estimates of the total column density and the large-scale kinematics.

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Commissioning the H i Observing Mode of the Beam Former for the Cryogenically Cooled Focal L-band Array for the GBT (FLAG)

Cited by 10 publications

References 38 publications

Detection of the Diffuse H i Emission in the Circumgalactic Medium of NGC 891 and NGC 4565

Detection of the Diffuse H i Emission in the Circumgalactic Medium of NGC 891 and NGC 4565

First Extragalactic Detection of Thermal Hydroxyl (OH) 18 cm Emission in M31 Reveals Abundant CO-faint Molecular Gas

Synthetic Next Generation Very Large Array line observations of a massive star-forming cloud

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