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Abstract The ideal spectral averaging method depends on one’s science goals and the available information about one’s data. Including low-quality data in the average can decrease the signal-to-noise ratio (S/N), which may necessitate an optimization method or a consideration of different weighting schemes. Here, we explore a variety of spectral averaging methods. We investigate the use of three weighting schemes during averaging: weighting by the signal divided by the variance (“intensity-noise weighting”), weighting by the inverse of the variance (“noise weighting”), and uniform weighting. Whereas for intensity-noise weighting the S/N is maximized when all spectra are averaged, for noise and uniform weighting we find that averaging the 35%–45% of spectra with the highest S/N results in the highest S/N average spectrum. With this intensity cutoff, the average spectrum with noise or uniform weighting has ∼95% of the intensity of the spectrum created from intensity-noise weighting. We apply our spectral averaging methods to GBT Diffuse Ionized Gas hydrogen radio recombination line data to determine the ionic abundance ratio,y⁺, and discuss future applications of the methodology. 

Abstract The Green Bank Telescope Diffuse Ionized Gas Survey (GDIGS) traces ionized gas in the Galactic midplane by observing radio recombination line (RRL) emission from 4 to 8 GHz. The nominal survey zone is 32.°3 >ℓ> −5°, ∣b∣ < 0.°5. Here, we analyze GDIGS Hnαionized gas emission toward discrete sources. Using GDIGS data, we identify the velocity of 35 Hiiregions that have multiple detected RRL velocity components. We identify and characterize RRL emission from 88 Hiiregions that previously lacked measured ionized gas velocities. We also identify and characterize RRL emission from eight locations that appear to be previously unidentified Hiiregions and 30 locations of RRL emission that do not appear to be Hiiregions based on their lack of mid-infrared emission. This latter group may be a compact component of the Galactic Diffuse Ionized Gas. There are an additional 10 discrete sources that have anomalously high RRL velocities for their locations in the Galactic plane. We compare these objects’ RRL data to¹³CO, Hi,and mid-infrared data, and find that these sources do not have the expected 24μm emission characteristic of Hiiregions. Based on this comparison we do not think these objects are Hiiregions, but we are unable to classify them as a known type of object. 

Abstract The Large Magellanic Cloud (LMC) has an extensive Hαemission halo that traces an extended, warm ionized component of its interstellar medium. Using the Wisconsin HαMapper telescope, we present the first kinematic Hαsurvey of an extensive region around the LMC, from (ℓ,b) = (264.°5, − 45.°5) to (295.°5, − 19.°5), covering +150 ≤v_LSR≤ + 390 km s⁻¹. We find that ionized hydrogen exists throughout the galaxy and extends several degrees beyond detected neutral hydrogen emission $(\log \left(N_{\mathrm{H}\mathrm{I}/{\mathrm{cm}}^{-2}}\right)\approx 18.3)$as traced by 21 cm in current surveys. Using the column density structure of the neutral gas and stellar line-of-sight depths as a guide, we estimate the upper limit mass of the ionized component of the LMC to be roughlyM_ionized≈ (0.6–1.8) × 10⁹M_☉, which is comparable to the total neutral atomic gas mass in the same region (M_neutral≈ 0.76–0.85 × 10⁹M_☉). Considering only the atomic phases, we findM_ionized/M_{ionized+neutral}, to be 46%–68% throughout the LMC and its extended halo. Additionally, we find an ionized gas cloud that extends off of the LMC at (ℓ,b) ≈ (285°, − 28°) into a region previously identified as the Leading Arm complex. This gas is moving at a similar line-of-sight velocity as the LMC and hasM_ionized/M_{ionized+neutral}= 13%–51%. This study, combined with previous studies of the SMC and extended structures of the Magellanic Clouds, continues to suggest that warm, ionized gas is as massive and dynamically important as the neutral gas in the Magellanic System. 

Optical emission lines are used to categorize galaxies into three groups according to their dominant central radiation source: active galactic nuclei, star formation, or low-ionization (nuclear) emission regions [LI(N)ERs] that may trace ionizing radiation from older stellar populations. Using the Wisconsin H-Alpha Mapper, we detect optical line emission in low-extinction windows within eight degrees of Galactic Center. The emission is associated with the 1.5-kiloparsec-radius “Tilted Disk” of neutral gas. We modify a model of this disk and find that the hydrogen gas observed is at least 48% ionized. The ratio [NII] λ6584 angstroms/Hα λ6563 angstroms increases from 0.3 to 2.5 with Galactocentric radius; [OIII] λ5007 angstroms and Hβ λ4861 angstroms are also sometimes detected. The line ratios for most Tilted Disk sightlines are characteristic of LI(N)ER galaxies. 

Despite the fact that Warm Ionized Medium (WIM) is a major component of the Interstellar Medium our knowledge about it and its relationship with H II regions is very limited. Understanding the WIM better will give us insight into the formation of galaxies and evolution of high-mass star formation regions. Previous surveys of the WIM and H II regions had low spectral and spatial resolutions or looked at Hα, which suffers from extinction. In this project we attempt to get additional value from the GBT Diffuse Ionized Gas Survey (GDIGS), by making continuum maps using the existing data. The goal is to assess whether the GDIGS data can be used to measure the radio recombination line to continuum emission ratio for the diffuse ionized gas. 

The Warm Ionized Medium (WIM) is a low density, diffuse ionized component of the Milky Way. The WIM is the last major component of the interstellar medium to be studied at high spatial and spectral resolution, and therefore many of its fundamental properties are not clear. Radiation from massive, OB-type stars, which live in the inner galaxy, is thought to escape discrete HII regions to ionize the WIM. However, the inner Galaxy has not been well studied due to extinction from dust at optical wavelengths. GDIGS is a fully-sampled Radio Recombination Line (RRL) survey of the inner Galactic Plane at C-band (4-8 GHz). RRL emission is not affected by extinction from dust, and GDIGS has sufficient spatial resolution to distinguish between HII regions and the WIM emission. Here we discuss the status of GDIGS and some preliminary results from the spectral analysis of the RRLs.