Metallicity Structure in the Milky Way Disk Revealed by Galactic H ii Regions

The present-day chemical structure of the Milky Way disk is an important constraint on models of Galactic chemodynamical evolution (e.g., Chiappini et al. 2003; Minchev et al. 2014, 2018; Snaith et al. 2015). Radial metallicity gradients, for example, are found in both the Milky Way and other spiral galaxies in studies using collisionally excited lines in ionized star-forming regions (e.g., Searle 1971; Shaver et al. 1983) and stellar abundances (e.g., Bovy et al. 2014; Hayden et al. 2014). These gradients reveal the history of star formation, stellar migration, and chemical enrichment by stars across galactic disks (Minchev et al. 2018). Stellar and gaseous tracers provide complementary information about the chemodynamical history of the Galaxy. The chemical abundances of stars represent the enrichment of the interstellar medium (ISM) when the stars were born, whereas the abundances of gaseous tracers represent the end product of billions of years of stellar evolution and ISM enrichment.

Evidence for azimuthal variations in galactic radial metallicity gradients is observed in both the Milky Way (e.g., Balser et al. 2015, hereafter B15) and other galaxies (e.g., Sánchez-Menguiano et al. 2016, 2017; Ho et al. 2017, 2018). Azimuthal abundance variations in the Milky Way are identified in multiple elements and tracers, such as the oxygen abundances of H ii regions (e.g., B15) and the iron abundances of Cepheids (e.g., Luck et al. 2006; Pedicelli et al. 2009). Such variations are not expected in an old and well-mixed galaxy (Balser et al. 2011), and chemodynamical models of galaxies typically assume axisymmetric metallicity gradients (e.g., Chiappini et al. 2003). Azimuthal variations may be caused by streaming motions and radial migration induced by galactic bars (Di Matteo et al. 2013), spiral arms (Grand et al. 2016; Ho et al. 2017; Mollá et al. 2019b; Spitoni et al. 2019), and/or perturbations from minor galaxy interactions (Bird et al. 2012).

Here we expand the Galactic H ii region metallicity surveys of Quireza et al. (2006b), Balser et al. (2011), and B15 to create a more complete map of metallicity structure in the Milky Way disk and to search for evidence of azimuthal variations in the Galactic radial metallicity gradient. H ii regions are the sites of recent high-mass star formation. These nebulae are an ideal tracer of Galactic metallicity structure because (1) they live for ≲10 Myr, and they therefore reveal the current enrichment of the ISM; (2) their distances can be derived accurately using maser parallax measurements (e.g., Reid et al. 2014) or kinematic techniques (e.g., Wenger et al. 2018); and (3) their metallicities are easily derived using optical and infrared collisionally excited lines or inferred from the nebular electron temperatures. The radio recombination line (RRL) and radio-continuum emission from H ii regions are an extinction-free diagnostic of the nebular electron temperature (Mezger & Henderson 1967), which is empirically related to the H ii region metallicity (Shaver et al. 1983). Radio wavelength observations of H ii regions can reveal metallicity structure across the Milky Way disk due to the lack of dust extinction.

The local thermodynamic equilibrium (LTE) electron temperature of an ionized gas can be derived from the RRL-to-continuum brightness ratio when the nebula is optically thin (B15). The electron temperature surveys of Galactic H ii regions by B15, Balser et al. (2011), and Quireza et al. (2006b) used single-dish telescopes. Although these instruments are extremely sensitive to faint RRL emission, they are not ideal for measuring accurate RRL-to-continuum brightness ratios because of the uncertainties in the continuum brightnesses. The single-dish continuum brightness of an H ii region is measured by scanning the telescope across the source in multiple directions. Then, a baseline fit to the diffuse background continuum emission is removed. The accuracy of the radio-continuum brightness is limited by the ability to accurately remove this diffuse component.

An interferometer is the ideal tool for measuring the RRL-to-continuum brightness ratio of Galactic H ii regions. By their nature, interferometers are not sensitive to large scale, diffuse emission, such as the nonthermal radio-continuum emission that permeates the Galactic plane. We measure the total continuum flux density of nebulae more accurately with an interferometer than with a single-dish telescope if the angular size of the source is smaller than the largest angular scale of the telescope. Too, interferometer data can be constructed as a high angular resolution image or data cube. These images and cubes reduce source confusion and can provide maps of electron temperature variations across a resolved nebula. Finally, interferometers like the National Radio Astronomy Observatory (NRAO) Karl G. Jansky Very Large Array (VLA) simultaneously measure both radio-continuum and RRL emission. Any systematic calibration or weather issues affecting the data will be removed in the RRL-to-continuum flux ratio.

We use the VLA to derive the nebular electron temperatures and metallicities of Galactic H ii regions across the Milky Way disk. A subset of these nebulae overlap with previous single-dish surveys, which allows us to compare the interferometer-derived electron temperatures with those derived from single-dish observations.

Recent RRL surveys have more than doubled the number of known Galactic H ii regions (Bania et al. 2010, 2012; Anderson et al. 2014, 2015a, 2015b, 2018; Wenger et al. 2019). The Widefield Infrared Survey Explorer (WISE) Catalog of Galactic H ii Regions (hereafter, WISE Catalog) contains the infrared and radio properties of more than 2000 known nebulae (Anderson et al. 2014). To derive accurate electron temperatures, we require the subset of WISE Catalog nebulae observable by the VLA. Our selection criteria are nebulae with (1) a single RRL velocity component, (2) a maser parallax measurement or an accurate kinematic distance, and (3) a predicted RRL flux density >1.7 mJy beam⁻¹.

When this survey began, the WISE Catalog contained RRL measurements of ∼1200 unique Galactic H ii regions. Many of these nebulae are clustered in H ii region groups or complexes, and a single-dish observation will see the combined emission from multiple discrete sources. These star-forming complexes are the source of ionizing photons, which may leak out into and ionize the diffuse ISM. In these cases, the RRL spectrum of the H ii region will show multiple velocity components from either multiple discrete H ii regions or a mix of H ii regions and diffuse ionized gas. The presence of spectrally confused, or blended, RRL components will limit our ability to derive the nebular RRL flux density accurately. Therefore, we remove ∼100 nebulae with multiple velocity component RRLs in the WISE Catalog.

In order to study Galactic metallicity structure, accurate distances to tracers are needed. Therefore, we further limit the WISE Catalog sample to those nebulae with published maser parallax measurements and/or accurate kinematic distances. We adopt the kinematic distance uncertainty model of Anderson et al. (2012) to estimate the accuracy of kinematic distances in the WISE Catalog. Because we aim to generate a Galactocentric map of the Milky Way metallicity structure, we require kinematic distance accuracies such that the uncertainty in the Galactocentric radius is σ_R < 2 kpc and the uncertainty in Galactocentric azimuth is σ_θ < 20°. Out of our sample of ∼1100 single-velocity RRL component nebulae, 107 have an associated maser parallax measurement and 364 have a kinematic distance meeting these accuracy thresholds. This brings our total sample of H ii regions to 471 nebulae.

Finally, we identify the subset of this sample with previously measured RRL flux densities bright enough to be detected by the VLA in a 10 minute observation. The point-source sensitivity of the VLA with this integration time is ∼2 mJy beam⁻¹ per 31.25 kHz channel at ∼9 GHz. By smoothing the spectra to 5 km s⁻¹ resolution and averaging seven RRL transitions, we estimate a spectral rms noise of ∼0.3 mJy beam⁻¹ per channel. We thus require our sample of H ii regions to have a predicted 9 GHz RRL flux density greater than five times this sensitivity limit, ∼1.7 mJy beam⁻¹.

All previously measured RRL flux densities of northern sky H ii regions in the WISE catalog were made with single-dish telescopes around ∼9 GHz. We first scale the observed RRL brightness temperatures to exactly 9 GHz assuming the RRL brightness temperature is proportional to the RRL frequency (B15). We convert these scaled RRL brightness temperatures to point-source flux densities assuming telescope gains of ∼2 K Jy⁻¹ for the Green Bank Observatory (GBO) Green Bank Telescope (GBT; Balser et al. 2011), ∼0.27 K Jy⁻¹ for the NRAO 140 Foot Telescope (hereafter, 140 Foot; Balser et al. 2016), and ∼5 K Jy⁻¹ for the Arecibo Observatory (Bania et al. 2012). Any source with a predicted 9 GHz RRL flux density S_{L,9 GHz} > 1.7 mJy beam⁻¹ fulfills our sensitivity criterion. This threshold removes only 10 nebulae from our sample, bringing the total number of observable H ii regions to 461.

The VLA is not sensitive to emission on scales larger than ∼145'' in the D (most compact) configuration at ∼9 GHz. If we assume that the radio size of an H ii region is approximately one-half of the infrared size (e.g., Bihr et al. 2016), then 30% of the H ii regions in our sample have radio diameters greater than this largest angular scale. Our observations will not be sensitive to these angularly large nebulae if their emission is uniform on such large spatial scales. We expect to detect clumpy emission within these large H ii regions, however, so we do not use any size restriction when defining our sample.

Finally, we select our observing targets from this sample of 461 nebulae to maximize our coverage of the Galactic disk. We divide the Galaxy into 120 bins of size 12° in Galactocentric azimuth, over the azimuth range −30° to 150°, and 2 kpc in Galactocentric radius, up to 18 kpc. Using the maser parallax distance, when available, or the WISE Catalog kinematic distance to compute the Galactocentric radii and azimuths of the nebulae, we identify the two brightest and most compact H ii regions in each bin. Some bins only have one (or zero) nebulae that meet our distance accuracy and predicted RRL flux density requirements. Figure 1 shows the Galactocentric positions of the 128 H ii regions we select using these criteria as well as the 20 nebulae observed in the pilot survey. One H ii region, G032.272-0.226, is observed in both the pilot survey and main survey. Of the 120 position bins, 78 (65%) contain at least one H ii region that meets our selection criteria.

Zoom In Zoom Out Reset image size

Our final H ii region target catalog contains 147 unique nebulae. Table 1 lists information about these H ii regions: the WISE Catalog name; the VLA project in which it was observed (13A-030 is the pilot survey and 15B-178 is the main survey); the WISE infrared position; the WISE infrared radius, R_IR; the estimated 9 GHz RRL flux density, S_{9 GHz,L}; the telescope and reference for the previous RRL detection; the previously measured RRL-to-continuum brightness ratio, S_L/S_C, and derived electron temperature, T_e; and the reference for the RRL-to-continuum brightness ratio and electron temperature.

We used the VLA to simultaneously observe radio-continuum and RRL emission toward our sample of 147 Galactic H ii regions. The data were acquired in the most compact (D) antenna configuration as part of two projects: the pilot survey (13A-030; 5 hr) in Feb and Apr 2013, and the main survey (15B-178; 30 hr) in Oct and Nov 2015. A summary of the observations is in Table 2.

The VLA X-band receiver covers the frequency range ∼8–12 GHz. We used the Wideband Interferometric Digital ARchitecture (WIDAR) correlator in the 8-bit sampler mode to simultaneously measure ∼8–10 GHz radio-continuum emission and eight hydrogen RRL transitions in both linear polarizations. The continuum data were measured by 16 low spectral resolution spectral windows (hereafter, continuum windows) covering 7.8–8.9 GHz and 9–10 GHz continuously. The RRL spectra were measured by eight high-spectral resolution (31.25 kHz) spectral windows (hereafter, spectral line windows), each with 16 MHz of frequency coverage. There are only seven Hα RRL transitions in this frequency range (H87α to H93α), so we tuned one of the spectral line windows to H109β. The native velocity resolution ranges from 0.9 km s⁻¹ at H87α to 1.2 km s⁻¹ at H93α, with a velocity coverage ranging from 488 km s⁻¹ to 600 km s⁻¹ for these transitions, respectively. In one observing session of the pilot survey, the spectral line window for H88α was mistuned, so we exclude that spectral window from these analyses. Table 3 lists the following properties for each spectral window: the center frequency, ν_center; the bandwidth; the number of channels; the channel width, Δν; the targeted RRL transition; and the RRL rest frequency, ν_RRL.

Our targets are clustered into 12 observing sessions based on position, with ∼10 H ii regions per group. Every observing session begins with a ∼15 minute integration on a primary calibrator, which is used for the absolute flux, delay, and bandpass calibration, followed by a ∼10 minute integration on a secondary calibrator located near the H ii region science targets, which is used for the complex gain calibration. These calibrators are listed in Table 2. We observe each science target for 10–15 minutes to reach the necessary spectral sensitivity, then we return to the secondary calibrator for ∼5 more minutes. During each observing session, we repeat this process for each science target.

We use the Wenger Interferometry Software Package (WISP) to calibrate, reduce, and analyze these data (Wenger 2018). WISP is a Python wrapper for the Common Astronomy Software Applications package (CASA; McMullin et al. 2007). Although WISP was developed to reduce Australia Telescope Compact Array data for the Southern H ii Region Discovery Survey (Wenger et al. 2019), its modular framework can be applied to any radio interferometric data set. We follow the Wenger et al. (2019) data reduction process, which we briefly describe here.

3.1. Calibration

3.2. Imaging

The data analysis process for this survey closely follows the Wenger et al. (2019) strategy. Because multiple nebulae may be observed in a single VLA pointing, we first identify unique WISE Catalog sources in each 8–10 GHz MS-MFS continuum image. Emission is associated with the WISE Catalog nebulae as long as the peak continuum brightness pixel is within a circle centered on the WISE Catalog position with a radius equal to the WISE Catalog infrared radius. We manually locate these peak continuum brightness pixels for each nebula with detected radio-continuum emission.

Unlike Wenger et al. (2019), we wish to derive the total fluxes of extended sources in addition to their peak fluxes. We use a watershed segmentation algorithm to identify the pixels associated with the manually identified continuum peaks in our images and data cubes. This algorithm considers an image as a three-dimensional topological surface, where the image brightness corresponds to the "depth" of the surface. The algorithm identifies the basins that would be filled by flooding the surface from a given starting point (see Bertrand 2005). In cases where multiple starting points will flood the same basin (i.e., in confused fields), the algorithm divides the basin into separate regions for each flooding source. Hereafter, we will use "watershed region" to describe the regions identified by the watershed segmentation algorithm.

We set the manually identified continuum brightness peak locations as the flooding sources for the watershed segmentation algorithm. Using the MS-MFS images clipped at five times the spatial rms noise, we run the algorithm to identify the watershed regions associated with each continuum source. Figure 2 shows an example region identified by this algorithm. We use the clipped continuum images to avoid low-brightness noise spikes in the watershed regions, but, as a result, we also miss faint emission associated with the nebulae. Therefore, our total continuum fluxes are systematically underestimated, especially for faint sources.

Zoom In Zoom Out Reset image size

For each continuum source we measure the brightness and total flux at the location of the peak brightness and within the watershed region, respectively. The uncertainty of the peak continuum brightness is derived as the spatial rms of the CLEAN residual image divided by the VLA primary beam response at the peak continuum brightness position. To compute the uncertainty on the total continuum flux, we must consider that the spatial noise in an interferometric image is correlated on the scale of the synthesized beam. The variance in the sum of the brightnesses of N pixels within a region is

$$\begin{eqnarray}&&{\sigma }_{T}^{2}=\displaystyle \sum _{i}^{N}\displaystyle \sum _{j}^{N}{\rho }_{{ij}}{\sigma }_{i}{\sigma }_{j},\end{eqnarray} \tag{ 1 }$$

where σ_i is the spatial rms of the CLEAN residual image divided by the VLA primary beam response at the position of the ith pixel, ρ_ij is the correlation coefficient between the ith and jth pixels, and the sums are taken over all N pixels within the region. We use the two-dimensional Gaussian synthesized beam to define the correlation coefficient:

$$\begin{eqnarray}&&{\rho }_{{ij}}=\exp \left[-A{\rm{\Delta }}{x}^{2}-2B{\rm{\Delta }}x{\rm{\Delta }}y-C{\rm{\Delta }}{y}^{2}\right],\end{eqnarray} \tag{ 2 }$$

where

$$\begin{eqnarray*}\begin{array}{rcl}A & = & \displaystyle \frac{{\cos }^{2}\phi }{2{\theta }_{\mathrm{maj}}^{2}}+\displaystyle \frac{{\sin }^{2}\phi }{2{\theta }_{\min }^{2}},\\ B & = & -\displaystyle \frac{\sin (2\phi )}{4{\theta }_{\mathrm{maj}}^{2}}+\displaystyle \frac{\sin (2\phi )}{4{\theta }_{\min }^{2}},\\ C & = & \displaystyle \frac{{\sin }^{2}\phi }{2{\theta }_{\mathrm{maj}}^{2}}+\displaystyle \frac{{\cos }^{2}\phi }{2{\theta }_{\min }^{2}},\end{array}\end{eqnarray*}$$

Δx and Δy are the angular separations between the ith and jth pixels in the east–west and north–south directions, respectively, and θ_maj, θ_min, and ϕ are the synthesized beam major axis, minor axis, and north-through-east position angle, respectively. In the simple case where σ_i ≃ σ_j ≃ σ (i.e., the noise is constant across the source), Equation (1) reduces to

$$\begin{eqnarray}&&{\sigma }_{T}^{2}\simeq {\sigma }^{2}\displaystyle \sum _{i}^{N}\displaystyle \sum _{j}^{N}{\rho }_{{ij}}\simeq {\sigma }^{2}{N}_{\mathrm{beam}},\end{eqnarray} \tag{ 3 }$$

where N_beam is the number of synthesized beams contained within the region. Many of our sources are extended or located near the edge of the primary beam, such that the primary beam response and noise varies across the source. Therefore, we use Equation (1) to derive the total continuum flux uncertainties.

We maximize our sensitivity to the faint RRL emission by averaging each observed Hnα RRL transition and both polarizations. This average spectrum is denoted by $\langle \mathrm{Hn}\alpha \rangle$. For non-tapered images, we extract spectra from each line spectral window data cube at the location of the peak continuum brightness. The $\langle \mathrm{Hn}\alpha \rangle$ spectrum is computed as the weighted average of the individual RRL transitions. The weights are given by ${w}_{i}={S}_{C,i}/{\mathrm{rms}}_{i}^{2}$ where S_C,i is the continuum brightness and rms_i is the spectral rms noise of the ith spectral window, both measured in the line-free region of the spectrum. For uv-tapered images, we spatially smooth the data cubes to a common beam size, then extract the spectra and compute the $\langle \mathrm{Hn}\alpha \rangle$ spectrum in the same fashion.

The total RRL emission within the watershed regions is extracted from the data cubes differently than for the peak position. For each pixel in the region, we measure the median continuum brightness in the line-free region of the spectrum, S_C,i. Then we sum each pixel's spectrum, S_L,i, weighted by the median continuum brightness in that pixel. The final extracted spectrum for this spectral window is normalized by the ratio of the median non-weighted sum and median weighted sum:

$$\begin{eqnarray}\begin{array}{rcl}{S}_{L}(\nu ) & = & \left(\displaystyle \sum _{i}{S}_{L,i}(\nu ){S}_{C,i}\right)\\ & & \times \,\displaystyle \frac{\mathrm{median}\left({\displaystyle \sum }_{i}{S}_{L,i}\right)}{\mathrm{median}\left({\displaystyle \sum }_{i}{S}_{L,i}(\nu ){S}_{C,i}\right)}.\end{array}\end{eqnarray} \tag{ 4 }$$

This complicated procedure correctly weights the final spectrum by the continuum level in each pixels' spectra, thereby maximizing the signal-to-noise ratio of the RRL and ensuring that the final spectrum has the correct flux density. The watershed region $\langle \mathrm{Hn}\alpha \rangle$ spectrum is then computed using the same weighted average of the individual RRL transitions as for the peak positions.

Finally, we measure the $\langle \mathrm{Hn}\alpha \rangle$ RRL properties. We first identify the line-free regions of the spectrum to estimate the spectral rms noise and to fit and remove a third-order polynomial baseline. Then we fit a Gaussian to the baseline-subtracted spectrum and measure the RRL brightness, the FWHM line width, and the LSR velocity.

5.1. VLA Data Products

Our goal is to derive an accurate nebular electron temperature for as many of the observed Galactic H ii regions as possible. Given that some of these nebulae will be extremely faint, spatially resolved, and/or in confusing fields, no single data analysis method will work for each nebula. For each source, we therefore employ a suite of different analysis methods and then we pick the combination of non-tapered or uv-tapered images and peak position $\langle \mathrm{Hn}\alpha \rangle$ or watershed region $\langle \mathrm{Hn}\alpha \rangle$ spectra that maximizes our RRL sensitivity and minimizes our electron temperature uncertainty.

We detect radio-continuum emission in 88 (59%) of the 148 observed fields. This low detection rate is a result of the relatively poor surface brightness sensitivity of the VLA. Many of the fields, however, contain multiple WISE Catalog H ii regions and/or H ii region candidates. We detect radio-continuum emission toward 114 known or candidate H ii regions. Table 4 lists the measured radio-continuum properties of these nebulae: the WISE Catalog source name; the MS-MFS synthesized frequency of the combined continuum spectral windows, ν_C; the peak continuum flux density, ${S}_{C}^{{\rm{P}}};$ a quality factor (QF) for the peak flux density, ${\mathrm{QF}}_{C}^{{\rm{P}}};$ a column indicating whether the peak flux density was measured using the non-tapered (N) or uv-tapered (Y) image; the total flux density within the watershed region, ${S}_{C}^{{\rm{T}}};$ a QF for the total flux density, ${\mathrm{QF}}_{C}^{{\rm{T}}};$ and a column indicating whether the peak flux density was measured using the non-tapered or uv-tapered image. The MS-MFS synthesized frequency varies slightly for each field due to differences in data flagging. We select either non-tapered or uv-tapered based on which gives the smallest fractional uncertainty in the final electron temperature derivation (if the source also has a RRL detection), or which has the smallest fractional uncertainty in the continuum flux density. For resolved nebulae, the uv-tapered images typically have a smaller fractional electron temperature or continuum flux density uncertainty.

Table 4.  Continuum Data Products

Name	νC	${S}_{C}^{{\rm{P}}}$	${\mathrm{QF}}_{C}^{{\rm{P}}}$	TaperPa	${S}_{C}^{{\rm{T}}}$	${\mathrm{QF}}_{C}^{{\rm{T}}}$	TaperPa
	(MHz)	(mJy beam−1)			(mJy)
G005.885−00.393	8962.2	4516.01 ± 13.31	A	N	5254.49 ± 35.45	A	N
G010.596−00.381	8962.2	395.02 ± 6.66	A	Y	907.08 ± 18.66	A	Y
G013.880+00.285	8962.2	1696.64 ± 3.26	A	Y	3368.06 ± 10.64	B	N
G017.336−00.146	8962.1	10.91 ± 0.29	B	Y	51.38 ± 0.84	B	N
G017.928−00.677	8962.1	14.48 ± 0.37	B	Y	57.76 ± 1.07	B	N
G018.584+00.344	8962.1	22.53 ± 0.82	A	Y	46.79 ± 1.20	A	N
G018.630+00.309	8962.1	13.01 ± 4.37	C	Y	0.04 ± 0.18	C	N
G019.677−00.134	8962.1	163.19 ± 3.36	C	Y	469.63 ± 7.10	C	N
G019.728−00.113	8962.1	24.23 ± 0.40	A	N	27.24 ± 0.68	A	N
G019.754−00.129	8962.1	46.45 ± 0.59	B	N	45.73 ± 1.01	B	N
G020.227+00.110	8962.1	8.61 ± 0.13	B	Y	41.72 ± 0.36	B	N
G020.363−00.014	8962.1	50.30 ± 0.09	A	N	58.28 ± 0.23	A	N
G020.387−00.018	8962.1	8.58 ± 0.16	B	Y	26.85 ± 0.46	B	Y
G021.386−00.255	8962.1	122.94 ± 0.12	A	N	136.88 ± 0.45	A	N
G021.596−00.161	8962.2	5.70 ± 0.16	A	N	6.77 ± 0.26	A	N
G021.603−00.169	8962.2	19.32 ± 0.15	A	N	27.62 ± 0.34	A	N
G023.661−00.252	8962.2	30.11 ± 0.46	B	Y	152.51 ± 1.16	B	N
G024.153+00.163	8962.2	10.94 ± 1.62	C	N	4.60 ± 1.14	C	N
G024.166+00.250	8962.2	16.56 ± 0.79	B	N	17.44 ± 1.11	B	N
G024.195+00.242	8962.2	9.77 ± 0.57	B	N	47.78 ± 1.69	B	N
G024.713−00.125	8962.2	32.51 ± 2.11	C	N	138.58 ± 5.73	C	N
G025.397+00.033	8962.2	229.49 ± 0.56	B	N	494.08 ± 2.57	B	N
G025.398+00.562	8962.1	203.74 ± 0.36	A	Y	221.10 ± 1.21	A	N
G025.401+00.021	8962.2	54.54 ± 0.60	B	N	150.97 ± 1.87	B	N
G027.562+00.084	8898.2	47.71 ± 0.23	A	N	111.74 ± 0.71	A	N
G028.320+01.243	8962.1	21.17 ± 0.04	A	N	30.22 ± 0.11	A	N
G028.438+00.014	8962.2	4.01 ± 0.35	A	N	11.73 ± 0.74	A	N
G028.451+00.001	8962.2	36.09 ± 0.30	A	N	84.81 ± 1.30	A	N
G028.581+00.145	8962.2	25.87 ± 0.18	A	N	39.68 ± 0.41	A	N
G029.770+00.219	8962.2	35.40 ± 0.16	A	N	72.53 ± 0.45	A	N
G029.956−00.020	8962.2	1770.38 ± 4.48	A	N	4299.65 ± 22.54	A	N
G030.211+00.428	8962.2	15.61 ± 0.04	A	N	25.81 ± 0.12	A	N
G031.269+00.064	8962.2	2.70 ± 0.34	A	N	1.00 ± 0.22	A	N
G031.279+00.061	8962.2	125.29 ± 0.35	A	N	306.72 ± 1.15	A	N
G031.580+00.074	8962.2	13.41 ± 0.21	B	N	15.17 ± 0.38	B	N
G032.030+00.048	8962.2	17.10 ± 0.19	A	N	25.83 ± 0.40	A	N
G032.057+00.077	8962.2	13.36 ± 1.03	C	Y	94.17 ± 2.13	C	N
G032.272−00.226	8962.2	147.87 ± 0.18	A	N	330.84 ± 0.75	A	N
G032.928+00.606	8898.2	173.86 ± 0.27	A	N	336.64 ± 1.38	A	N
G033.643−00.229	8962.2	6.37 ± 0.09	A	Y	10.85 ± 0.15	A	N
G034.041+00.052	8962.2	25.97 ± 0.48	A	Y	83.27 ± 1.08	A	N
G034.089+00.438	8962.2	34.42 ± 2.87	C	N	83.68 ± 7.38	C	Y
G034.133+00.471	8962.2	378.58 ± 1.10	A	Y	517.00 ± 2.35	A	N
G034.686+00.068	8962.2	55.42 ± 0.60	A	Y	107.24 ± 0.95	A	N
G035.126−00.755	8962.2	123.85 ± 0.43	A	Y	241.91 ± 0.71	A	N
G035.948−00.149	8962.2	12.05 ± 0.03	A	N	26.66 ± 0.08	A	N
G036.870+00.462	8962.2	3.03 ± 0.31	C	N	9.77 ± 0.67	C	N
G036.877+00.498	8962.2	1.22 ± 0.17	C	N	1.90 ± 0.22	C	N
G036.918+00.482	8962.2	6.21 ± 0.08	A	N	7.56 ± 0.15	A	N
G038.550+00.163	8962.2	54.11 ± 0.25	A	N	122.86 ± 0.77	A	N
G038.643−00.227	8962.3	18.70 ± 0.05	A	N	24.79 ± 0.18	A	N
G038.652+00.087	8962.2	19.77 ± 0.24	A	N	49.91 ± 0.96	A	N
G038.840+00.495	8962.2	4.49 ± 0.09	B	N	84.27 ± 0.66	B	N
G038.875+00.308	8962.2	279.04 ± 0.43	A	N	320.84 ± 1.04	A	N
G039.183−01.422	8962.3	20.75 ± 0.15	A	Y	57.82 ± 0.30	A	N
G039.196+00.224	8962.3	62.54 ± 0.06	A	N	67.11 ± 0.19	A	N
G039.213+00.202	8962.3	5.13 ± 0.09	B	N	5.85 ± 0.16	B	N
G039.864+00.645	8962.3	67.52 ± 0.51	A	Y	103.48 ± 0.79	A	N
G043.146+00.013	8962.3	1434.45 ± 126.49	B	Y	1427.47 ± 158.00	B	Y
G043.165−00.031	8962.3	2330.17 ± 78.58	C	N	3341.55 ± 144.37	C	N
G043.168+00.019	8962.3	332.86 ± 17.06	B	N	600.24 ± 31.78	B	N
G043.170−00.004	8962.3	4331.44 ± 149.88	B	Y	11158.53 ± 398.42	B	Y
G043.432+00.516	8962.3	11.08 ± 0.35	B	Y	82.31 ± 0.83	B	N
G043.523−00.648	8962.3	5.84 ± 0.04	A	Y	13.22 ± 0.09	A	N
G043.818+00.395	8962.3	21.54 ± 0.97	B	Y	94.69 ± 1.89	B	N
G043.968+00.993	8962.2	47.26 ± 0.07	A	N	49.81 ± 0.20	A	N
G043.999+00.978	8962.2	22.23 ± 0.22	C	N	25.05 ± 0.42	C	N
G044.501+00.332	8962.3	21.92 ± 1.24	B	Y	135.68 ± 2.23	B	N
G044.503+00.349	8962.3	7.16 ± 0.36	A	N	8.58 ± 0.54	A	N
G045.197+00.740	8962.3	7.76 ± 0.18	B	N	140.36 ± 1.42	B	N
G048.719+01.147	8962.4	37.12 ± 0.10	A	Y	69.80 ± 0.29	A	N
G049.399−00.490	8962.4	166.98 ± 7.12	A	Y	232.47 ± 8.75	A	N
G052.098+01.042	8962.3	287.77 ± 0.50	A	Y	432.07 ± 0.89	A	N
G052.232+00.735	8962.4	68.65 ± 4.32	C	Y	162.56 ± 5.42	C	N
G054.093+01.748	8962.3	18.84 ± 0.03	A	Y	34.60 ± 0.08	A	Y
G054.490+01.579	8962.3	24.30 ± 0.06	A	Y	44.24 ± 0.13	A	N
G054.543+01.560	8962.3	3.73 ± 0.26	C	Y	3.52 ± 0.21	C	N
G055.114+02.422	8962.3	138.55 ± 1.25	A	Y	618.76 ± 2.79	B	N
G060.592+01.572	8962.3	55.66 ± 0.22	A	Y	166.35 ± 0.51	A	N
G061.720+00.863	8962.7	90.28 ± 0.16	A	N	97.51 ± 0.38	A	N
G062.577+02.389	8962.7	51.31 ± 0.28	B	N	359.10 ± 1.71	B	N
G068.144+00.915	8962.7	42.25 ± 1.61	B	Y	302.02 ± 4.24	B	N
G070.280+01.583	8962.6	542.61 ± 15.70	A	Y	1930.78 ± 37.24	A	N
G070.293+01.599	8962.6	3550.27 ± 9.03	A	N	5690.67 ± 39.20	A	N
G070.304+01.595	8962.6	245.05 ± 9.37	A	N	1829.40 ± 41.28	A	N
G070.329+01.589	8962.6	1067.39 ± 23.78	B	N	2670.68 ± 65.51	B	N
G070.673+01.190	8962.6	260.40 ± 0.72	A	Y	407.26 ± 1.43	A	N
G070.765+01.820	8962.6	28.79 ± 0.52	A	Y	173.85 ± 1.36	B	N
G071.150+00.397	8962.7	208.43 ± 0.25	A	N	392.62 ± 0.92	A	N
G073.878+01.023	8962.6	75.77 ± 0.09	A	N	120.61 ± 0.26	A	N
G074.155+01.646	8962.6	10.25 ± 0.04	A	N	37.97 ± 0.21	A	N
G074.753+00.912	8962.6	55.70 ± 0.07	A	N	74.69 ± 0.20	A	N
G075.768+00.344	8962.6	1059.58 ± 10.20	A	Y	4104.53 ± 20.67	B	N
G078.114−00.550	8962.6	14.17 ± 3.03	C	Y	0.04 ± 0.10	C	N
G078.174−00.550	8962.6	4.21 ± 0.19	B	N	23.01 ± 0.72	B	N
G078.886+00.709	8962.6	83.02 ± 0.08	A	N	110.14 ± 0.25	A	N
G080.191+00.534	8962.6	5.14 ± 0.09	A	N	40.72 ± 0.45	A	N
G094.263−00.414	8963.1	4.40 ± 0.04	B	Y	18.73 ± 0.14	B	N
G096.289+02.593	8963.1	27.93 ± 0.32	B	N	442.24 ± 2.68	B	N
G096.434+01.324	8963.1	23.34 ± 0.10	A	N	36.94 ± 0.25	A	N
G097.515+03.173	8963.1	131.05 ± 0.65	A	Y	508.47 ± 1.73	B	N
G097.528+03.184	8963.1	41.23 ± 0.29	A	N	49.32 ± 0.55	A	N
G101.016+02.590	8963.0	17.71 ± 0.06	A	Y	21.24 ± 0.14	A	N
G104.700+02.784	8963.0	9.00 ± 0.17	A	Y	39.99 ± 0.36	A	N
G109.104−00.347	8963.0	7.10 ± 0.07	A	N	19.36 ± 0.20	A	N
G124.637+02.535	8963.4	252.56 ± 0.20	A	N	293.16 ± 0.62	A	N
G125.092+00.778	8963.5	6.70 ± 0.02	A	Y	20.65 ± 0.07	B	N
G135.188+02.701	8963.4	19.82 ± 0.09	A	Y	65.47 ± 0.18	B	N
G141.084−01.063	8963.8	12.17 ± 0.19	A	Y	62.35 ± 0.37	B	N
G150.859−01.115	8963.8	11.73 ± 0.10	A	Y	18.02 ± 0.15	A	N
G196.448−01.673	8964.0	10.93 ± 0.47	B	N	350.13 ± 4.13	B	N
G218.737+01.850	8964.1	202.41 ± 0.69	A	Y	554.43 ± 1.73	A	N
G351.246+00.673	8962.2	7191.06 ± 24.43	A	Y	11722.85 ± 66.92	A	N
G351.311+00.663	8962.2	2809.89 ± 29.27	A	Y	5561.39 ± 64.30	A	N

Note.

^a"N" if non-tapered image measurement; "Y" if uv-tapered image measurement.

Download table as:  ASCIITypeset images: 1 2

The QF is a qualitative assessment of the accuracy of the continuum flux measurement. QF A detections are isolated, unresolved, and near the center of the primary beam, QF B detections are slightly resolved, in crowded fields, and/or are located off center from the primary beam, QF C detections are well-resolved, in very crowded fields, and/or are located near the edge of the primary beam. Any continuum sources that are confused/blended are assigned QF D. These nebulae are excluded from the tables and all subsequent analysis since we are unable to measure their continuum fluxes accurately. The three nebulae in Figure 2 are examples of each continuum QF: G019.728−00.113 is a QF A detection, G019.754−00.129 is a QF B detection because it is off center, and G019.677−00.134 is a QF C detection because it is resolved and near the edge of the primary beam.

We detect $\langle \mathrm{Hn}\alpha \rangle$ RRL emission toward 82 (72%) of our 114 continuum sources. All RRL detections are toward previously known H ii regions. Figure 3 shows representative $\langle \mathrm{Hn}\alpha \rangle$ RRL detections with different signal-to-noise ratios. Our typical spectral rms noise is ∼1 mJy beam⁻¹, about three times greater than what we estimated using the VLA sensitivity calculator. This decease in sensitivity is likely due to RFI that compromised entire spectral line spectral windows. We may be able to further increase our spectral line sensitivity by self-calibration.

Zoom In Zoom Out Reset image size

Table 5 lists the measured $\langle \mathrm{Hn}\alpha \rangle$ RRL properties of our detections: the WISE Catalog source name; the weighted average frequency of the $\langle \mathrm{Hn}\alpha \rangle$ spectrum, ν_L, where the weights are the same as those used to average the individual RRL transitions (see Section 4); the amplitude of the Gaussian fit to the spectrum extracted from the location of peak continuum brightness, ${S}_{L}^{{\rm{P}}};$ the spectral rms at this position, rms^P; the center LSR velocity of the fitted Gaussian, ${v}_{\mathrm{LSR}}^{{\rm{P}}};$ the FWHM line width of the fitted Gaussian, ΔV^P; a column indicating whether the spectrum was extracted from the non-tapered (N) or uv-tapered (Y) image; the amplitude of the Gaussian fit to the spectrum summed within the watershed region, ${S}_{L}^{{\rm{T}}};$ the spectral rms in this region, rms^T; the center LSR velocity of the fitted Gaussian, ${v}_{\mathrm{LSR}}^{{\rm{T}}};$ the FWHM line width of the fitted Gaussian, ΔV^T; and a column indicating whether the spectrum was extracted from the non-tapered or uv-tapered image. As before, we use either the non-tapered or uv-tapered image, depending on which gives the smallest fractional uncertainty in the derived electron temperature. Unlike B15, we do not assign QFs to our RRL detections. Our spectral baselines are always flat and well modeled by a third-order polynomial, therefore, no qualitative assessment is necessary. Two nebulae, G005.885−00.393 and G070.293+01.599, are excluded from Table 5 because they have blended, non-Gaussian line profiles.

Table 5.  RRL Data Products

Name	νL	${S}_{L}^{{\rm{P}}}$	rmsP	${v}_{\mathrm{LSR}}^{{\rm{P}}}$	ΔVP	TaperPa	${S}_{L}^{{\rm{T}}}$	rmsT	${v}_{\mathrm{LSR}}^{{\rm{T}}}$	ΔVT	TaperTa
	(MHz)	(mJy	(mJy	(km s−1)	(km s−1)		(mJy)	(mJy)	(km s−1)	(km s−1)
		beam−1)	beam−1)
G009.612+00.205	8862.2	5.53 ± 0.39	1.19	2.5 ± 0.8	22.2 ± 1.9	N	2.71 ± 0.08	0.24	3.2 ± 0.3	22.1 ± 0.8	N
G009.613+00.200	8786.3	81.07 ± 0.67	1.97	4.0 ± 0.1	20.4 ± 0.2	Y	133.99 ± 1.12	3.29	3.8 ± 0.1	20.5 ± 0.2	N
G010.596−00.381	8816.4	59.07 ± 0.60	1.87	1.1 ± 0.1	23.3 ± 0.3	Y	107.40 ± 0.98	3.06	1.1 ± 0.1	23.1 ± 0.2	Y
G010.621−00.380	8789.6	80.22 ± 0.52	1.67	−0.5 ± 0.1	24.8 ± 0.2	N	3.61 ± 0.03	0.10	−0.7 ± 0.1	24.9 ± 0.2	N
G010.623−00.385	8737.2	175.69 ± 1.08	4.12	1.1 ± 0.1	35.0 ± 0.2	Y	182.71 ± 0.99	4.03	0.9 ± 0.1	39.9 ± 0.2	N
G012.805−00.196	8779.1	1097.15 ± 3.02	11.78	36.3 ± 0.0	36.4 ± 0.1	Y	2079.31 ± 5.80	22.02	36.7 ± 0.0	34.5 ± 0.1	Y
G012.813−00.200	8767.2	199.79 ± 1.44	4.85	30.2 ± 0.1	27.2 ± 0.2	N	74.74 ± 0.65	2.20	30.4 ± 0.1	27.7 ± 0.3	N
G013.880+00.285	8806.2	267.42 ± 0.64	1.90	52.4 ± 0.0	21.5 ± 0.1	Y	530.66 ± 1.35	4.06	52.0 ± 0.0	21.6 ± 0.1	Y
G017.928−00.677	8738.1	⋯	⋯	⋯	⋯	⋯	10.52 ± 1.04	3.06	38.4 ± 1.0	21.1 ± 2.5	Y
G018.584+00.344	8806.1	3.57 ± 0.35	1.09	14.4 ± 1.2	24.1 ± 3.0	Y	7.58 ± 0.60	1.80	14.3 ± 0.9	22.2 ± 2.1	Y
G019.677−00.134	8595.3	18.57 ± 1.27	4.14	54.7 ± 0.9	27.0 ± 2.4	Y	50.04 ± 2.52	8.33	55.6 ± 0.7	26.6 ± 1.6	N
G019.728−00.113	8883.1	4.09 ± 0.34	1.08	53.6 ± 1.0	25.3 ± 2.5	Y	3.29 ± 0.25	0.81	52.9 ± 0.9	25.0 ± 2.3	N
G020.363−00.014	8832.6	7.16 ± 0.32	0.98	55.1 ± 0.5	22.3 ± 1.2	N	7.90 ± 0.34	1.05	55.5 ± 0.5	22.5 ± 1.1	N
G021.603−00.169	8886.8	2.67 ± 0.30	0.87	−4.9 ± 1.3	23.0 ± 3.8	Y	⋯	⋯	⋯	⋯	⋯
G023.661−00.252	8885.9	5.28 ± 0.34	1.03	66.5 ± 0.7	22.2 ± 1.7	Y	26.59 ± 1.08	3.17	67.2 ± 0.4	20.5 ± 1.0	Y
G024.195+00.242	8819.2	3.38 ± 0.50	1.53	33.0 ± 1.8	24.3 ± 4.8	Y	3.52 ± 0.55	1.72	31.9 ± 1.9	25.1 ± 5.0	N
G025.397+00.033	8826.1	20.71 ± 0.28	0.94	−14.0 ± 0.2	28.0 ± 0.4	N	35.95 ± 0.56	1.88	−14.0 ± 0.2	27.3 ± 0.5	N
G025.398+00.562	8775.9	15.47 ± 0.27	0.98	11.7 ± 0.3	32.0 ± 0.6	Y	15.69 ± 0.29	1.07	11.5 ± 0.3	31.3 ± 0.7	N
G025.401+00.021	8867.2	10.30 ± 0.55	1.73	−10.7 ± 0.6	24.3 ± 1.5	Y	12.38 ± 0.51	1.54	−10.2 ± 0.4	22.4 ± 1.1	N
G026.597−00.024	8892.9	7.09 ± 0.21	0.80	17.3 ± 0.5	34.6 ± 1.2	N	15.57 ± 0.51	1.78	18.6 ± 0.5	30.0 ± 1.1	Y
G027.562+00.084	8542.6	15.65 ± 0.53	1.55	88.2 ± 0.3	20.4 ± 0.8	Y	18.08 ± 0.59	1.74	88.2 ± 0.3	20.8 ± 0.8	N
G028.320+01.243	8893.2	1.77 ± 0.26	0.65	−40.5 ± 1.1	15.0 ± 2.7	N	1.76 ± 0.30	0.86	−39.6 ± 4.5	34.1 ± 21.9	N
G028.451+00.001	8840.4	5.07 ± 0.32	1.10	−7.2 ± 0.9	28.7 ± 2.2	Y	5.96 ± 0.36	1.20	−6.9 ± 0.8	27.2 ± 1.9	N
G028.581+00.145	8860.3	2.84 ± 0.24	0.76	−13.1 ± 1.0	24.4 ± 2.5	N	3.58 ± 0.28	0.94	−13.0 ± 1.0	26.9 ± 2.6	N
G029.770+00.219	8778.8	5.85 ± 0.38	1.15	−30.9 ± 0.7	21.6 ± 1.7	Y	7.10 ± 0.47	1.39	−30.9 ± 0.7	21.4 ± 1.6	N
G030.211+00.428	8715.8	2.83 ± 0.37	0.97	−10.8 ± 1.1	16.6 ± 2.6	Y	3.00 ± 0.38	1.02	−11.5 ± 1.1	17.6 ± 2.6	N
G031.580+00.074	8828.1	3.51 ± 0.46	1.04	100.4 ± 0.8	12.0 ± 1.8	N	3.27 ± 0.39	0.93	100.8 ± 0.8	13.5 ± 1.9	N
G032.030+00.048	8848.2	5.13 ± 0.39	0.99	89.8 ± 0.6	15.3 ± 1.3	Y	4.81 ± 0.31	0.80	90.3 ± 0.5	16.1 ± 1.2	N
G032.272−00.226	8819.0	21.61 ± 0.40	1.32	22.9 ± 0.2	26.5 ± 0.6	Y	27.01 ± 0.49	1.63	22.9 ± 0.2	26.9 ± 0.6	N
G032.928+00.606	8590.7	13.70 ± 0.29	1.00	−37.9 ± 0.3	28.9 ± 0.7	N	20.89 ± 0.49	1.63	−38.2 ± 0.3	26.9 ± 0.7	N
G034.041+00.052	8776.4	4.10 ± 0.40	1.26	36.9 ± 1.1	23.6 ± 2.7	Y	12.60 ± 0.91	2.80	37.7 ± 0.8	22.7 ± 1.9	Y
G034.133+00.471	8801.3	42.46 ± 0.44	1.41	36.1 ± 0.1	24.6 ± 0.3	Y	56.32 ± 0.58	1.86	36.1 ± 0.1	24.6 ± 0.3	N
G034.686+00.068	8724.2	7.06 ± 0.37	1.15	50.5 ± 0.6	23.8 ± 1.4	Y	14.29 ± 0.63	1.94	50.4 ± 0.5	22.4 ± 1.1	Y
G035.126−00.755	8814.3	17.99 ± 0.40	1.17	35.0 ± 0.2	20.0 ± 0.5	Y	34.45 ± 0.71	2.05	35.3 ± 0.2	19.9 ± 0.5	N
G035.948−00.149	8872.5	1.87 ± 0.24	0.74	51.4 ± 1.4	22.6 ± 3.6	N	3.15 ± 0.41	1.19	49.3 ± 1.4	21.0 ± 3.6	N
G038.550+00.163	8758.9	11.79 ± 0.37	1.18	27.6 ± 0.4	23.7 ± 0.9	Y	14.88 ± 0.46	1.46	27.7 ± 0.4	23.8 ± 0.9	N
G038.643−00.227	8762.5	2.70 ± 0.41	1.12	69.4 ± 1.4	18.5 ± 3.5	Y	3.81 ± 0.64	1.61	68.4 ± 1.3	15.6 ± 3.3	Y
G038.840+00.495	8764.1	⋯	⋯	⋯	⋯	⋯	7.57 ± 0.98	2.80	−42.8 ± 1.3	20.3 ± 3.2	Y
G038.875+00.308	8808.9	25.36 ± 0.26	0.89	−13.4 ± 0.1	27.8 ± 0.3	N	27.91 ± 0.31	1.07	−13.8 ± 0.2	28.3 ± 0.4	N
G039.196+00.224	8787.5	4.51 ± 0.24	0.84	−21.7 ± 0.8	28.7 ± 1.9	N	4.88 ± 0.27	0.95	−21.1 ± 0.8	29.2 ± 2.0	N
G039.864+00.645	8738.8	5.21 ± 0.34	1.14	−41.3 ± 0.9	27.3 ± 2.1	Y	8.57 ± 0.51	1.72	−42.0 ± 0.8	27.6 ± 2.0	N
G043.146+00.013	8708.1	134.45 ± 0.75	2.67	8.7 ± 0.1	30.2 ± 0.2	Y	101.01 ± 0.52	1.86	8.5 ± 0.1	31.1 ± 0.2	Y
G043.151+00.011	8695.6	62.31 ± 0.51	1.84	5.8 ± 0.1	31.8 ± 0.3	N	48.52 ± 0.35	1.27	6.0 ± 0.1	31.9 ± 0.3	N
G043.162+00.005	8768.7	42.28 ± 0.66	2.22	6.5 ± 0.2	27.0 ± 0.5	N	15.82 ± 0.21	0.70	6.2 ± 0.2	27.1 ± 0.4	N
G043.165−00.031	8665.8	154.87 ± 2.24	8.99	6.8 ± 0.3	38.8 ± 0.7	N	128.59 ± 1.59	6.41	7.5 ± 0.2	39.0 ± 0.6	N
G043.168+00.019	8762.5	46.09 ± 0.53	1.69	9.9 ± 0.1	24.1 ± 0.3	N	20.67 ± 0.22	0.70	9.8 ± 0.1	24.1 ± 0.3	N
G043.170−00.004	8670.2	223.40 ± 0.87	3.38	7.8 ± 0.1	36.0 ± 0.2	Y	851.52 ± 2.80	10.04	4.5 ± 0.0	30.7 ± 0.1	Y
G043.175+00.025	8739.0	40.65 ± 0.58	2.02	14.9 ± 0.2	28.7 ± 0.5	N	22.55 ± 0.27	0.95	14.9 ± 0.2	29.6 ± 0.4	N
G043.432+00.516	8896.0	⋯	⋯	⋯	⋯	⋯	6.81 ± 0.97	2.92	−11.8 ± 1.8	25.1 ± 5.6	Y
G043.818+00.395	8881.8	⋯	⋯	⋯	⋯	⋯	8.70 ± 0.60	2.11	−8.5 ± 1.0	31.0 ± 2.6	Y
G043.968+00.993	8789.7	3.87 ± 0.24	0.87	−25.5 ± 1.0	31.9 ± 2.5	N	3.92 ± 0.26	0.94	−25.4 ± 1.0	31.2 ± 2.6	N
G044.501+00.332	8806.0	2.80 ± 0.29	0.85	−41.6 ± 1.1	22.0 ± 2.8	Y	6.46 ± 0.37	1.05	−43.4 ± 0.5	19.7 ± 1.3	Y
G048.719+01.147	8828.4	3.70 ± 0.32	1.05	−25.6 ± 1.1	26.5 ± 2.8	Y	6.51 ± 0.55	1.79	−25.9 ± 1.1	26.6 ± 2.8	N
G049.399−00.490	8880.6	21.50 ± 0.43	1.34	62.7 ± 0.2	22.7 ± 0.5	Y	24.46 ± 0.40	1.28	61.5 ± 0.2	24.1 ± 0.5	Y
G052.098+01.042	8835.7	24.43 ± 0.33	1.15	37.5 ± 0.2	29.3 ± 0.5	Y	36.72 ± 0.47	1.63	37.3 ± 0.2	28.7 ± 0.4	N
G052.232+00.735	8756.0	5.54 ± 0.90	2.72	−1.1 ± 2.2	26.2 ± 6.9	Y	19.84 ± 1.48	4.37	−2.3 ± 0.8	20.8 ± 1.8	Y
G055.114+02.422	8859.8	6.60 ± 0.30	1.08	−73.6 ± 0.7	32.8 ± 1.8	Y	29.62 ± 0.78	2.87	−74.8 ± 0.4	32.6 ± 1.0	Y
G060.592+01.572	8864.6	3.93 ± 0.32	1.05	−50.2 ± 1.1	27.2 ± 2.7	Y	11.25 ± 0.76	2.50	−48.5 ± 0.9	26.8 ± 2.2	Y
G061.720+00.863	8808.8	7.00 ± 0.67	2.11	−69.6 ± 1.2	25.9 ± 3.3	N	7.39 ± 0.78	2.42	−68.4 ± 1.3	24.5 ± 3.3	N
G062.577+02.389	8747.3	8.53 ± 0.98	2.95	−71.2 ± 1.3	22.3 ± 3.2	Y	24.80 ± 2.49	7.44	−72.0 ± 1.1	22.0 ± 2.7	Y
G070.280+01.583	8782.7	49.01 ± 0.86	2.68	−23.6 ± 0.2	23.4 ± 0.5	Y	186.56 ± 1.83	5.95	−25.1 ± 0.1	25.3 ± 0.3	Y
G070.304+01.595	8763.0	72.95 ± 1.10	3.53	−18.2 ± 0.2	24.5 ± 0.4	Y	51.50 ± 0.84	2.63	−17.6 ± 0.2	23.4 ± 0.4	N
G070.329+01.589	8694.4	157.24 ± 2.52	8.96	−18.4 ± 0.2	30.4 ± 0.6	Y	123.82 ± 1.89	6.77	−17.8 ± 0.2	30.6 ± 0.5	N
G070.765+01.820	8843.3	⋯	⋯	⋯	⋯	⋯	13.56 ± 1.53	4.85	−78.1 ± 1.4	24.9 ± 3.4	N
G071.150+00.397	8783.3	34.14 ± 0.49	1.56	−12.2 ± 0.2	24.2 ± 0.4	Y	38.36 ± 0.62	1.99	−12.2 ± 0.2	24.6 ± 0.5	Y
G073.878+01.023	8815.2	6.24 ± 0.32	1.12	−49.5 ± 0.7	29.6 ± 1.8	N	8.50 ± 0.41	1.47	−50.3 ± 0.7	30.8 ± 1.8	N
G074.155+01.646	8798.0	4.15 ± 0.46	1.18	−32.2 ± 0.9	15.9 ± 2.0	Y	5.86 ± 0.74	1.88	−31.6 ± 1.0	15.7 ± 2.3	Y
G074.753+00.912	8840.0	5.45 ± 0.33	1.04	−48.9 ± 0.7	23.7 ± 1.7	N	6.42 ± 0.37	1.25	−49.6 ± 0.8	27.9 ± 1.9	N
G075.768+00.344	8789.4	100.01 ± 0.64	2.09	−8.6 ± 0.1	25.5 ± 0.2	Y	364.25 ± 1.98	6.65	−8.7 ± 0.1	27.0 ± 0.2	Y
G078.886+00.709	8821.1	12.24 ± 0.37	1.04	−1.9 ± 0.3	19.1 ± 0.7	N	15.90 ± 0.46	1.31	−1.9 ± 0.3	19.5 ± 0.7	N
G096.289+02.593	8873.2	4.36 ± 0.29	0.97	−87.5 ± 0.9	26.8 ± 2.1	Y	27.37 ± 0.93	3.18	−97.7 ± 0.5	28.3 ± 1.1	Y
G096.434+01.324	8856.1	3.89 ± 0.28	0.85	−77.8 ± 0.8	21.8 ± 1.9	Y	4.08 ± 0.29	0.88	−77.9 ± 0.8	21.8 ± 1.8	N
G097.515+03.173	8865.1	9.56 ± 0.29	1.00	−76.8 ± 0.4	28.0 ± 1.0	Y	35.06 ± 0.79	2.72	−74.4 ± 0.3	28.2 ± 0.7	Y
G097.528+03.184	8901.3	4.34 ± 0.26	0.79	−71.6 ± 0.7	23.1 ± 1.6	N	4.55 ± 0.25	0.79	−72.0 ± 0.7	24.1 ± 1.6	N
G101.016+02.590	8896.8	2.57 ± 0.36	0.92	−70.2 ± 1.1	16.3 ± 2.7	Y	2.85 ± 0.38	1.00	−70.2 ± 1.1	16.8 ± 2.7	N
G109.104−00.347	8852.5	2.98 ± 0.29	0.90	−44.1 ± 1.1	22.7 ± 2.6	Y	3.60 ± 0.34	1.09	−44.4 ± 1.2	25.7 ± 2.9	N
G124.637+02.535	8817.1	16.81 ± 0.27	0.96	−77.5 ± 0.2	30.5 ± 0.6	N	18.35 ± 0.33	1.18	−77.6 ± 0.3	30.7 ± 0.6	N
G135.188+02.701	8974.4	2.61 ± 0.37	1.06	−73.2 ± 1.4	19.9 ± 3.3	Y	6.42 ± 0.88	2.59	−72.2 ± 2.8	31.9 ± 12.6	Y
G141.084−01.063	8853.2	⋯	⋯	⋯	⋯	⋯	8.50 ± 1.15	3.15	−25.2 ± 1.3	18.8 ± 3.2	Y
G196.448−01.673	8872.6	4.71 ± 0.37	1.08	10.9 ± 0.8	20.8 ± 1.9	Y	27.00 ± 0.98	3.00	12.5 ± 0.4	22.6 ± 0.9	Y
G351.246+00.673	8789.9	851.65 ± 2.69	8.64	−0.4 ± 0.0	24.7 ± 0.1	Y	1474.38 ± 3.93	12.75	−0.1 ± 0.0	25.1 ± 0.1	Y
G351.311+00.663	8839.3	356.60 ± 1.81	5.76	−6.9 ± 0.1	24.2 ± 0.1	Y	774.71 ± 2.46	7.79	−6.2 ± 0.0	24.1 ± 0.1	Y

Note.

^a"N" if non-tapered image measurement; "Y" if uv-tapered image measurement.

Download table as:  ASCIITypeset images: 1 2

5.2. Electron Temperatures

Thermal bremsstrahlung (free–free) emission is the primary source of H ii region radio-continuum emission. Its intensity depends on the plasma electron temperature, the plasma electron density, and the stellar ionizing photon rate. The free–free opacity of an H ii region in LTE is well-approximated by

$$\begin{eqnarray}&&{\tau }_{C}\simeq 3.28\times {10}^{-7}{\left(\displaystyle \frac{{T}_{e}}{{10}^{4}{\rm{K}}}\right)}^{-1.35}{\left(\displaystyle \frac{\nu }{{\rm{G}}{\rm{H}}{\rm{z}}}\right)}^{-2.1}\left(\displaystyle \frac{{\rm{E}}{\rm{M}}}{{\rm{p}}{\rm{c}}\,{{\rm{c}}{\rm{m}}}^{-6}}\right)\end{eqnarray} \tag{ 5 }$$

where T_e is the plasma electron temperature, EM is the emission measure, and ν is the frequency (Mezger & Henderson 1967). The emission measure is the integral of the squared electron number density, n_e², along the line-of-sight path through the nebula: $\mathrm{EM}=\int {n}_{e}^{2}\,{dl}$. An optically thin H ii region has a continuum brightness temperature T_C ≃ τ_CT_e. Without an independent determination of the emission measure, we are unable to use the continuum emission alone to derive the nebular electron temperature.

The RRL intensity and line width reveal the physical characteristics of an H ii region. The line center opacity of an H ii region in LTE is approximated by

$$\begin{eqnarray}&&{\tau }_{L}\simeq 1.92\times {10}^{3}{\left(\displaystyle \frac{{T}_{e}}{{\rm{K}}}\right)}^{-2.5}\left(\displaystyle \frac{\mathrm{EM}}{\mathrm{pc}\ {\mathrm{cm}}^{-6}}\right){\left(\displaystyle \frac{{\rm{\Delta }}\nu }{\mathrm{kHz}}\right)}^{-1}\end{eqnarray} \tag{ 6 }$$

where Δν is the full-width half-maximum (FWHM) line width in frequency units (Kardashev 1959; Mezger & Hoglund 1967). Similar to the continuum, we need an independent measurement of the emission measure in order to use the RRL properties to derive the electron temperature.

The typical hydrogen RRL line width for Galactic H ii regions is ∼25 km s⁻¹ (Wenger et al. 2019). There are four physical effects that contribute to the RRL FWHM line width: (1) intrinsic broadening, due to the uncertainty principle; (2) collisional broadening, due to the collisions of the emitting atoms; (3) thermal Doppler broadening, due to the Maxwellian velocity distribution of emitting atoms in the plasma; and (4) nonthermal Doppler broadening. Of these, thermal and nonthermal Doppler broadening are the most significant contributors to the width of RRLs. The nonthermal (i.e., turbulent) components can only be constrained with additional information. RRL line width measurements for nebular plasma atoms other than hydrogen are needed, since atoms with different masses have different Maxwellian velocity distributions. Alternatively, the thermal contribution to the RRL line width can be determined by deriving the plasma temperature.

We derive the nebular electron temperature from the RRL-to-continuum brightness ratio. For an H ii region in LTE that is optically thin to both continuum and RRL emission, the ratio of the radio-continuum brightness temperature to the RRL peak brightness temperature is equal to the ratio of the continuum opacity to the line center opacity. This ratio is independent of the emission measure. A complete derivation of the electron temperature equation is in the Appendix. For RRLs near H90α, assuming the continuum and RRL emission originate in the same volume of gas, we find

$$\begin{eqnarray}\begin{array}{rcl}\displaystyle \frac{{T}_{e}}{{\rm{K}}} & \simeq & \left[7.100\times {10}^{3}{\left(\displaystyle \frac{{\nu }_{L}}{\mathrm{GHz}}\right)}^{1.1}\left(\displaystyle \frac{{S}_{C}}{{S}_{L}}\right)\right.\\ & & \times \,{\left.{\left(\displaystyle \frac{{\rm{\Delta }}V}{\mathrm{km}{{\rm{s}}}^{-}1}\right)}^{-1}{\left(1+{y}^{+}\right)}^{-1}\right]}^{0.87}\end{array}\end{eqnarray} \tag{ 7 }$$

where ν_L is the RRL frequency, S_C is the continuum flux density, S_L is the RRL center flux density, ΔV is the RRL FWHM line width in velocity units, and y⁺ is the ratio of the number density of singly ionized helium to hydrogen.

We use Equation (7) to derive the electron temperatures of the 72 nebulae in our sample with a VLA $\langle \mathrm{Hn}\alpha \rangle$ RRL detection and a continuum QF A, B, or C. We only detect helium RRLs in a few, bright sources, so we assume y⁺ = 0.08 for all VLA detections, following Balser et al. (2011) and B15. Equation (7) is only weakly dependent on y⁺. A 10% increase from y⁺ = 0.08 results in a mere 0.6% increase in T_e. We do not consider uncertainties in y⁺ in the subsequent analyses because the electron temperature uncertainties are typically much greater than 0.6%. Furthermore, we assume non-LTE effects and collisional broadening are negligible at these frequencies (see Balser et al. 1999). The RRL flux density, RRL FWHM line width, and continuum flux density are measured in the $\langle \mathrm{Hn}\alpha \rangle$ stacked spectrum, and the RRL frequency is the weighted average frequency of the individual RRL transitions. Again, the frequency weights are the same as those used to average the individual RRL transitions (see Section 4). In the Appendix, we show that this strategy can produce accurate electron temperatures.

Table 6 lists the WISE Catalog source name, the telescope used for the observation, the measured RRL-to-continuum flux ratios, the RRL FWHM line widths, and the derived electron temperatures for the B15 single dish and our VLA H ii region samples. This table only lists the highest quality electron temperature derivations; we remove all QF D sources from the B15 and VLA samples. The electron temperature uncertainties are computed by propagating the RRL-to-continuum flux ratio and FWHM line width uncertainties through Equation (7). For VLA sources, the "Type" column indicates whether the position of peak continuum brightness (P) or watershed region (T) is used to measure the RRL-to-continuum flux ratio. The "Taper" column identifies which data cube is used (N for non-tapered and Y for uv-tapered). We select the combination of "Type" and "Taper" that minimizes the fractional uncertainty in the derived electron temperature. In cases where the same source is detected in multiple surveys, we only list the VLA values, if available. If the source is not observed or detected in the VLA survey, we list the GBT values. If the source is not in the VLA survey nor the GBT survey, we list the 140 Foot values. Table 6 also includes information about the H ii region distances, which is discussed in Section 5.4.

Table 6.  H ii Region Distances and Properties

Name	Telescope	SL/SC	ΔV	Te	Typea	Taperb	d	R	Distancec	Distance
			(km s−1)	(K)			(kpc)	(kpc)	Method	Reference
G000.666−00.036	140 Foot	0.0569 ± 0.0033	40.5 ± 0.4	8170 ± 180	⋯	⋯	${7.59}_{-0.65}^{+0.84}$	${0.21}_{-0.11}^{+0.91}$	P	R09c
G001.125−00.106	140 Foot	0.1070 ± 0.0018	24.5 ± 0.2	7130 ± 70	⋯	⋯	⋯d	⋯d	K	⋯
G003.266−00.061	140 Foot	0.0978 ± 0.0100	25.3 ± 0.4	7440 ± 280	⋯	⋯	⋯d	⋯d	K	⋯
G005.900−00.431	140 Foot	0.0691 ± 0.0006	22.5 ± 0.2	11130 ± 170	⋯	⋯	${2.99}_{-0.20}^{+0.17}$	${5.38}_{-0.16}^{+0.19}$	P	S14
G005.987−01.191	140 Foot	0.0840 ± 0.0008	26.5 ± 0.2	8180 ± 70	⋯	⋯	⋯d	⋯d	K	⋯
G008.137+00.232	140 Foot	0.1019 ± 0.0007	25.4 ± 0.1	7090 ± 60	⋯	⋯	⋯d	⋯d	K	⋯
G010.160−00.350	140 Foot	0.0911 ± 0.0005	31.2 ± 0.2	6830 ± 30	⋯	⋯	⋯d	⋯d	K	⋯
G010.308−00.150	140 Foot	0.0874 ± 0.0005	31.6 ± 0.2	6800 ± 40	⋯	⋯	⋯d	⋯d	K	⋯
G010.596−00.381	VLA	0.1506 ± 0.0015	23.1 ± 0.2	5704 ± 72	T	Y	${4.87}_{-0.44}^{+0.55}$	${3.64}_{-0.48}^{+0.42}$	P	Sa14
G012.804−00.207	140 Foot	0.0808 ± 0.0007	30.7 ± 0.3	7620 ± 100	⋯	⋯	${2.83}_{-0.28}^{+0.38}$	${5.61}_{-0.35}^{+0.26}$	P	I13
G013.880+00.285	VLA	0.1568 ± 0.0004	21.5 ± 0.1	5848 ± 19	P	Y	${3.79}_{-0.26}^{+0.49}$	${4.61}_{-0.31}^{+0.39}$	P	S14
G015.097−00.729	140 Foot	0.0938 ± 0.0008	35.3 ± 0.3	5720 ± 60	⋯	⋯	${1.94}_{-0.10}^{+0.16}$	${6.49}_{-0.15}^{+0.09}$	P	X11
G016.993+00.873	140 Foot	0.0928 ± 0.0006	23.6 ± 0.1	6890 ± 60	⋯	⋯	${2.38}_{-0.24}^{+0.27}$	${6.10}_{-0.30}^{+0.22}$	K	⋯
G017.928−00.677	VLA	0.1461 ± 0.0158	21.1 ± 2.5	6269 ± 877	T	Y	${12.65}_{-0.37}^{+0.37}$	${5.41}_{-0.31}^{+0.23}$	K	⋯
G018.144−00.281	140 Foot	0.1052 ± 0.0008	25.2 ± 0.2	7180 ± 70	⋯	⋯	${4.00}_{-0.30}^{+0.36}$	${4.68}_{-0.26}^{+0.28}$	K	⋯
G018.584+00.344	VLA	0.1547 ± 0.0135	22.2 ± 2.1	5712 ± 645	T	Y	${14.36}_{-0.39}^{+0.42}$	${7.02}_{-0.31}^{+0.25}$	K	⋯
G018.669+01.965	140 Foot	0.0907 ± 0.0006	28.4 ± 0.2	7210 ± 60	⋯	⋯	${2.42}_{-0.25}^{+0.25}$	${6.08}_{-0.25}^{+0.27}$	K	⋯
G019.064−00.282	140 Foot	0.2916 ± 0.0052	25.2 ± 0.3	5440 ± 70	⋯	⋯	${4.44}_{-0.29}^{+0.39}$	${4.37}_{-0.27}^{+0.25}$	K	⋯
G019.677−00.134	VLA	0.1166 ± 0.0063	26.6 ± 1.6	6141 ± 429	T	N	${11.66}_{-0.36}^{+0.43}$	${4.75}_{-0.27}^{+0.29}$	K	⋯
G019.728−00.113	VLA	0.1363 ± 0.0115	25.0 ± 2.3	5813 ± 629	T	N	${11.89}_{-0.43}^{+0.36}$	${4.89}_{-0.25}^{+0.28}$	K	⋯
G020.363−00.014	VLA	0.1416 ± 0.0067	22.5 ± 1.1	6150 ± 367	T	N	${11.68}_{-0.40}^{+0.40}$	${4.86}_{-0.29}^{+0.24}$	K	⋯
G020.728−00.105	140 Foot	0.1249 ± 0.0035	26.5 ± 0.1	5590 ± 90	⋯	⋯	${11.74}_{-0.48}^{+0.32}$	${4.91}_{-0.31}^{+0.23}$	K	⋯
G021.603−00.169	VLA	0.1039 ± 0.0121	23.0 ± 3.8	7959 ± 1399	P	Y	${16.03}_{-0.49}^{+0.53}$	${8.81}_{-0.42}^{+0.42}$	K	⋯
G023.423−00.216	140 Foot	0.1162 ± 0.0008	24.3 ± 0.1	6500 ± 55	⋯	⋯	${5.55}_{-0.87}^{+1.37}$	${3.42}_{-0.11}^{+0.71}$	P	B09
G023.661−00.252	VLA	0.1737 ± 0.0079	20.5 ± 1.0	5583 ± 318	T	Y	${10.98}_{-0.44}^{+0.41}$	${4.76}_{-0.31}^{+0.23}$	K	⋯
G023.713+00.175	140 Foot	0.1027 ± 0.0015	26.8 ± 0.4	6840 ± 110	⋯	⋯	${7.63}_{-0.15}^{+0.16}$	${3.62}_{-0.19}^{+0.27}$	K	⋯
G024.195+00.242	VLA	0.1190 ± 0.0187	24.3 ± 4.8	6692 ± 1465	P	Y	⋯d	${6.17}_{-0.23}^{+0.29}$	K	⋯
G024.456+00.489	140 Foot	0.1020 ± 0.0008	29.2 ± 0.5	6370 ± 80	⋯	⋯	${7.56}_{-0.23}^{+0.23}$	${3.80}_{-0.21}^{+0.28}$	K	⋯
G024.844+00.093	140 Foot	0.1326 ± 0.0012	24.9 ± 0.2	5860 ± 90	⋯	⋯	${7.48}_{-0.23}^{+0.23}$	${3.72}_{-0.18}^{+0.19}$	K	⋯
G025.382−00.151	140 Foot	0.0974 ± 0.0027	25.6 ± 0.1	7460 ± 70	⋯	⋯	${3.71}_{-0.25}^{+0.40}$	${5.20}_{-0.29}^{+0.22}$	K	⋯
G025.397+00.033	VLA	0.0853 ± 0.0012	28.0 ± 0.4	7893 ± 142	P	N	${16.40}_{-0.47}^{+0.66}$	${9.53}_{-0.38}^{+0.55}$	K	⋯
G025.398+00.562	VLA	0.0774 ± 0.0014	32.0 ± 0.6	7610 ± 177	P	Y	${14.11}_{-0.36}^{+0.41}$	${7.49}_{-0.28}^{+0.28}$	K	⋯
G025.401+00.021	VLA	0.1074 ± 0.0046	22.4 ± 1.1	7871 ± 438	T	N	${16.00}_{-0.44}^{+0.59}$	${9.25}_{-0.44}^{+0.38}$	K	⋯
G025.867+00.118	140 Foot	0.1189 ± 0.0016	27.3 ± 0.4	6120 ± 100	⋯	⋯	${7.53}_{-0.18}^{+0.13}$	${3.80}_{-0.16}^{+0.17}$	K	⋯
G027.562+00.084	VLA	0.1594 ± 0.0057	20.8 ± 0.8	5765 ± 261	T	N	${9.65}_{-0.58}^{+0.50}$	${4.43}_{-0.25}^{+0.26}$	K	⋯
G028.320+01.243	VLA	0.0819 ± 0.0125	15.0 ± 2.7	14189 ± 2932	P	N	${19.42}_{-0.98}^{+1.15}$	${12.63}_{-0.83}^{+1.05}$	K	⋯
G028.451+00.001	VLA	0.0923 ± 0.0058	27.2 ± 1.9	7576 ± 629	T	N	${15.25}_{-0.46}^{+0.50}$	${8.87}_{-0.38}^{+0.38}$	K	⋯
G028.581+00.145	VLA	0.0946 ± 0.0079	26.9 ± 2.6	7490 ± 837	T	N	${15.83}_{-0.59}^{+0.55}$	${9.38}_{-0.45}^{+0.45}$	K	⋯
G028.746+03.458	GBT	0.1106 ± 0.0007	21.0 ± 0.1	8399 ± 73	⋯	⋯	${14.79}_{-0.54}^{+0.36}$	${8.45}_{-0.38}^{+0.30}$	K	⋯
G029.770+00.219	VLA	0.1029 ± 0.0071	21.4 ± 1.6	8465 ± 755	T	N	${17.46}_{-0.60}^{+0.93}$	${11.00}_{-0.47}^{+0.87}$	K	⋯
G029.956−00.020	140 Foot	0.0992 ± 0.0064	29.8 ± 0.1	6510 ± 90	⋯	⋯	${5.14}_{-0.45}^{+0.65}$	${4.61}_{-0.24}^{+0.21}$	P	Z14
G030.211+00.428	VLA	0.1263 ± 0.0168	17.6 ± 2.6	8355 ± 1446	T	N	${15.46}_{-0.59}^{+0.47}$	${9.28}_{-0.49}^{+0.34}$	K	⋯
G030.758−00.047	GBT	0.0908 ± 0.0003	33.5 ± 0.1	6567 ± 30	⋯	⋯	${7.20}_{-0.17}^{+0.11}$	${4.63}_{-0.22}^{+0.22}$	K	⋯
G031.268+00.478	GBT	0.0944 ± 0.0042	23.2 ± 1.0	8690 ± 462	⋯	⋯	${14.75}_{-0.45}^{+0.49}$	${8.77}_{-0.34}^{+0.39}$	K	⋯
G031.580+00.074	VLA	0.2544 ± 0.0357	13.5 ± 1.9	5769 ± 992	T	N	${4.67}_{-0.59}^{+0.88}$	${4.97}_{-0.41}^{+0.23}$	P	Z14
G032.030+00.048	VLA	0.2159 ± 0.0159	16.1 ± 1.2	5720 ± 519	T	N	${5.16}_{-0.21}^{+0.24}$	${4.81}_{-0.09}^{+0.08}$	P	S14
G032.272−00.226	VLA	0.0850 ± 0.0016	26.9 ± 0.6	8207 ± 200	T	N	${12.52}_{-0.34}^{+0.40}$	${7.04}_{-0.22}^{+0.28}$	K	⋯
G032.733+00.209	GBT	0.1638 ± 0.0037	21.0 ± 0.4	5856 ± 156	⋯	⋯	${12.88}_{-0.35}^{+0.40}$	${7.39}_{-0.25}^{+0.30}$	K	⋯
G032.800+00.190	GBT	0.0750 ± 0.0004	29.5 ± 0.1	8625 ± 49	⋯	⋯	${13.01}_{-0.44}^{+0.33}$	${7.50}_{-0.29}^{+0.27}$	K	⋯
G032.870−00.427	GBT	0.1817 ± 0.0043	18.2 ± 0.4	6074 ± 176	⋯	⋯	${10.99}_{-0.45}^{+0.34}$	${6.03}_{-0.28}^{+0.20}$	K	⋯
G032.928+00.606	VLA	0.0723 ± 0.0016	28.9 ± 0.7	8641 ± 244	P	N	${17.66}_{-0.79}^{+0.91}$	${11.51}_{-0.59}^{+0.91}$	K	⋯
G032.982−00.338	GBT	0.1485 ± 0.0040	20.9 ± 0.5	6411 ± 207	⋯	⋯	${10.91}_{-0.39}^{+0.39}$	${5.99}_{-0.24}^{+0.26}$	K	⋯
G034.041+00.052	VLA	0.1489 ± 0.0119	22.7 ± 1.9	5809 ± 591	T	Y	${11.48}_{-0.43}^{+0.32}$	${6.52}_{-0.26}^{+0.22}$	K	⋯
G034.133+00.471	VLA	0.1140 ± 0.0013	24.6 ± 0.3	6858 ± 96	T	N	${11.55}_{-0.40}^{+0.32}$	${6.59}_{-0.27}^{+0.21}$	K	⋯
G034.256+00.136	GBT	0.0999 ± 0.0006	24.4 ± 0.1	8084 ± 55	⋯	⋯	${3.29}_{-0.38}^{+0.30}$	${5.96}_{-0.26}^{+0.21}$	K	⋯
G034.686+00.068	VLA	0.1232 ± 0.0058	22.4 ± 1.1	6876 ± 418	T	Y	${10.59}_{-0.37}^{+0.43}$	${6.03}_{-0.22}^{+0.25}$	K	⋯
G035.126−00.755	VLA	0.1428 ± 0.0032	19.9 ± 0.5	6793 ± 193	T	N	${2.24}_{-0.31}^{+0.27}$	${6.62}_{-0.23}^{+0.26}$	K	⋯
G035.197−01.756	GBT	0.0947 ± 0.0005	23.6 ± 0.0	8603 ± 40	⋯	⋯	${3.20}_{-0.49}^{+0.49}$	${6.00}_{-0.30}^{+0.28}$	P	Z09
G035.948−00.149	VLA	0.1419 ± 0.0202	22.6 ± 3.6	6148 ± 1143	P	N	${3.15}_{-0.36}^{+0.36}$	${6.10}_{-0.28}^{+0.21}$	K	⋯
G037.754+00.560	GBT	0.1170 ± 0.0028	23.4 ± 0.8	7163 ± 246	⋯	⋯	${11.99}_{-0.34}^{+0.40}$	${7.43}_{-0.24}^{+0.28}$	K	⋯
G038.550+00.163	VLA	0.1149 ± 0.0038	23.8 ± 0.9	7019 ± 299	T	N	${11.29}_{-0.42}^{+0.34}$	${7.05}_{-0.26}^{+0.24}$	K	⋯
G038.643−00.227	VLA	0.1262 ± 0.0204	18.5 ± 3.5	7992 ± 1725	P	Y	${6.51}_{-0.13}^{+0.14}$	${5.62}_{-0.23}^{+0.22}$	K	⋯
G038.652+00.087	GBT	0.0738 ± 0.0015	27.0 ± 0.6	9428 ± 245	⋯	⋯	${16.66}_{-0.85}^{+0.79}$	${11.35}_{-0.63}^{+0.74}$	K	⋯
G038.840+00.495	VLA	0.0900 ± 0.0120	20.3 ± 3.2	9919 ± 1792	T	Y	${16.74}_{-0.76}^{+0.95}$	${11.48}_{-0.66}^{+0.83}$	K	⋯
G038.875+00.308	VLA	0.0882 ± 0.0009	27.8 ± 0.3	7719 ± 107	P	N	${14.06}_{-0.57}^{+0.46}$	${9.16}_{-0.38}^{+0.38}$	K	⋯
G039.196+00.224	VLA	0.0726 ± 0.0041	28.7 ± 1.9	8853 ± 658	P	N	${14.56}_{-0.56}^{+0.60}$	${9.67}_{-0.42}^{+0.49}$	K	⋯
G039.728−00.396	GBT	0.0874 ± 0.0020	25.7 ± 0.7	8503 ± 255	⋯	⋯	${9.18}_{-0.46}^{+0.50}$	${6.00}_{-0.22}^{+0.24}$	K	⋯
G039.864+00.645	VLA	0.0780 ± 0.0048	27.6 ± 2.0	8606 ± 707	T	N	${16.52}_{-0.89}^{+0.72}$	${11.37}_{-0.69}^{+0.69}$	K	⋯
G040.503+02.537	GBT	0.1074 ± 0.0006	22.4 ± 0.1	8223 ± 55	⋯	⋯	${1.41}_{-0.32}^{+0.30}$	${7.35}_{-0.28}^{+0.24}$	K	⋯
G043.146+00.013	VLA	0.0868 ± 0.0005	31.1 ± 0.2	6942 ± 48	T	Y	${11.59}_{-0.42}^{+0.45}$	${7.91}_{-0.27}^{+0.31}$	K	⋯
G043.165−00.031	VLA	0.0542 ± 0.0007	39.0 ± 0.6	8648 ± 144	T	N	${11.05}_{-0.90}^{+0.90}$	${7.47}_{-0.48}^{+0.68}$	P	Z13
G043.168+00.019	VLA	0.1280 ± 0.0015	24.1 ± 0.3	6282 ± 92	T	N	${10.94}_{-0.77}^{+0.98}$	${7.45}_{-0.48}^{+0.67}$	P	Z13
G043.170−00.004	VLA	0.0768 ± 0.0003	30.7 ± 0.1	7876 ± 35	T	Y	${11.11}_{-0.98}^{+0.83}$	${7.60}_{-0.64}^{+0.54}$	P	Z13
G043.432+00.516	VLA	0.0930 ± 0.0138	25.1 ± 5.6	8119 ± 1883	T	Y	${12.93}_{-0.46}^{+0.58}$	${8.95}_{-0.38}^{+0.41}$	K	⋯
G043.818+00.395	VLA	0.0788 ± 0.0056	31.0 ± 2.6	7806 ± 750	T	Y	${12.59}_{-0.42}^{+0.57}$	${8.74}_{-0.29}^{+0.44}$	K	⋯
G043.968+00.993	VLA	0.0822 ± 0.0054	31.9 ± 2.5	7255 ± 647	P	N	${13.88}_{-0.53}^{+0.66}$	${9.79}_{-0.46}^{+0.53}$	K	⋯
G044.418+00.535	GBT	0.0926 ± 0.0026	24.3 ± 0.7	8492 ± 299	⋯	⋯	${16.93}_{-1.06}^{+0.92}$	${12.41}_{-0.92}^{+0.86}$	K	⋯
G044.501+00.332	VLA	0.1064 ± 0.0063	19.7 ± 1.3	9044 ± 694	T	Y	${15.38}_{-0.70}^{+0.88}$	${11.11}_{-0.60}^{+0.70}$	K	⋯
G045.197+00.740	GBT	0.0556 ± 0.0010	30.5 ± 0.6	10841 ± 245	⋯	⋯	${14.50}_{-0.54}^{+0.83}$	${10.45}_{-0.44}^{+0.64}$	K	⋯
G045.453+00.044	GBT	0.0871 ± 0.0007	27.6 ± 0.1	8026 ± 63	⋯	⋯	${8.11}_{-1.10}^{+1.43}$	${6.26}_{-0.31}^{+0.57}$	P	W14
G046.495−00.241	140 Foot	0.1989 ± 0.0071	20.1 ± 0.2	4860 ± 80	⋯	⋯	${5.71}_{-0.08}^{+0.16}$	${6.27}_{-0.19}^{+0.21}$	K	⋯
G048.719+01.147	VLA	0.0943 ± 0.0083	26.6 ± 2.8	7606 ± 900	T	N	${12.90}_{-0.59}^{+0.63}$	${9.70}_{-0.45}^{+0.45}$	K	⋯
G048.922−00.285	140 Foot	0.0805 ± 0.0005	26.7 ± 0.2	8440 ± 60	⋯	⋯	${5.27}_{-0.19}^{+0.22}$	${6.29}_{-0.00}^{+0.01}$	P	W14
G049.002−00.303	140 Foot	0.1859 ± 0.0017	24.4 ± 0.2	8170 ± 50	⋯	⋯	${5.30}_{-0.21}^{+0.20}$	${6.30}_{-0.00}^{+0.01}$	P	W14
G049.201−00.365	140 Foot	0.0650 ± 0.0003	30.3 ± 0.1	9070 ± 70	⋯	⋯	${5.31}_{-0.22}^{+0.18}$	${6.31}_{-0.00}^{+0.01}$	P	W14
G049.384−00.298	140 Foot	0.0786 ± 0.0006	31.6 ± 0.3	8585 ± 65	⋯	⋯	${5.43}_{-0.10}^{+0.11}$	${6.37}_{-0.11}^{+0.19}$	K	⋯
G049.399−00.490	VLA	0.1167 ± 0.0021	24.1 ± 0.5	6675 ± 151	T	Y	${5.34}_{-0.26}^{+0.36}$	${6.33}_{-0.00}^{+0.01}$	P	W14
G049.489−00.378	GBT	0.0903 ± 0.0003	30.2 ± 0.0	7166 ± 25	⋯	⋯	${5.42}_{-0.10}^{+0.11}$	${6.46}_{-0.15}^{+0.19}$	K	⋯
G052.098+01.042	VLA	0.0854 ± 0.0011	28.7 ± 0.4	7725 ± 134	T	N	${3.53}_{-0.82}^{+1.36}$	${6.77}_{-0.19}^{+0.19}$	P	O10
G052.232+00.735	VLA	0.1083 ± 0.0085	20.8 ± 1.8	8258 ± 841	T	Y	${10.47}_{-0.59}^{+0.42}$	${8.44}_{-0.32}^{+0.32}$	K	⋯
G052.766+00.333	GBT	0.0841 ± 0.0011	25.4 ± 0.4	8970 ± 186	⋯	⋯	${9.24}_{-0.37}^{+0.55}$	${7.84}_{-0.23}^{+0.33}$	K	⋯
G055.114+02.422	VLA	0.0484 ± 0.0013	32.6 ± 1.0	11357 ± 409	T	Y	${16.12}_{-1.07}^{+1.23}$	${13.24}_{-0.92}^{+1.13}$	K	⋯
G059.796+00.241	GBT	0.0975 ± 0.0008	21.8 ± 0.2	9068 ± 120	⋯	⋯	${8.79}_{-0.65}^{+0.48}$	${8.51}_{-0.34}^{+0.32}$	K	⋯
G060.592+01.572	VLA	0.0692 ± 0.0048	26.8 ± 2.2	9883 ± 922	T	Y	${12.14}_{-0.86}^{+0.75}$	${10.86}_{-0.66}^{+0.53}$	K	⋯
G060.881−00.135	GBT	0.1229 ± 0.0010	21.2 ± 0.2	7463 ± 77	⋯	⋯	${4.06}_{-0.09}^{+0.08}$	${7.66}_{-0.22}^{+0.31}$	K	⋯
G061.473+00.094	GBT	0.0846 ± 0.0004	26.0 ± 0.1	8857 ± 43	⋯	⋯	${3.99}_{-0.09}^{+0.07}$	${7.52}_{-0.22}^{+0.19}$	K	⋯
G061.720+00.863	VLA	0.0777 ± 0.0076	25.9 ± 3.3	9170 ± 1282	P	N	${13.96}_{-1.11}^{+0.96}$	${12.38}_{-0.91}^{+0.85}$	K	⋯
G062.577+02.389	VLA	0.0766 ± 0.0079	22.0 ± 2.7	10626 ± 1470	T	Y	${13.97}_{-1.12}^{+0.96}$	${12.57}_{-0.92}^{+0.79}$	K	⋯
G063.164+00.449	GBT	0.0994 ± 0.0011	25.1 ± 0.1	7760 ± 90	⋯	⋯	${3.76}_{-0.07}^{+0.08}$	${7.78}_{-0.25}^{+0.25}$	K	⋯
G064.130−00.475	GBT	0.0973 ± 0.0005	23.9 ± 0.1	8452 ± 58	⋯	⋯	${3.64}_{-0.07}^{+0.08}$	${7.66}_{-0.21}^{+0.19}$	K	⋯
G068.144+00.915	GBT	0.0697 ± 0.0009	24.7 ± 0.3	10834 ± 207	⋯	⋯	${11.92}_{-0.98}^{+0.90}$	${11.53}_{-0.53}^{+0.88}$	K	⋯
G069.922+01.511	GBT	0.0712 ± 0.0003	27.0 ± 0.1	9703 ± 50	⋯	⋯	${11.56}_{-1.04}^{+0.88}$	${11.69}_{-0.79}^{+0.61}$	K	⋯
G070.280+01.583	VLA	0.0901 ± 0.0009	25.3 ± 0.3	8214 ± 109	T	Y	${7.92}_{-0.63}^{+0.78}$	${9.37}_{-0.41}^{+0.41}$	K	⋯
G070.293+01.599	GBT	0.0505 ± 0.0005	37.0 ± 0.2	10297 ± 121	⋯	⋯	${7.96}_{-0.69}^{+0.69}$	${9.36}_{-0.37}^{+0.43}$	K	⋯
G070.304+01.595	VLA	0.0992 ± 0.0017	23.4 ± 0.4	8211 ± 182	T	N	${7.36}_{-0.71}^{+0.65}$	${8.95}_{-0.26}^{+0.48}$	K	⋯
G070.329+01.589	VLA	0.0745 ± 0.0012	30.6 ± 0.5	8244 ± 170	T	N	${7.35}_{-0.69}^{+0.69}$	${9.03}_{-0.35}^{+0.40}$	K	⋯
G070.765+01.820	VLA	0.0896 ± 0.0105	24.9 ± 3.4	8412 ± 1317	T	N	${12.68}_{-1.19}^{+1.02}$	${12.65}_{-0.90}^{+0.83}$	K	⋯
G071.150+00.397	VLA	0.1035 ± 0.0016	24.2 ± 0.4	7551 ± 147	P	Y	${6.56}_{-0.58}^{+0.81}$	${8.85}_{-0.39}^{+0.30}$	K	⋯
G073.878+01.023	VLA	0.0744 ± 0.0037	30.8 ± 1.8	8177 ± 545	T	N	${9.10}_{-0.63}^{+1.03}$	${10.52}_{-0.46}^{+0.66}$	K	⋯
G074.155+01.646	VLA	0.1929 ± 0.0238	15.9 ± 2.0	6327 ± 980	P	Y	${7.68}_{-0.75}^{+0.75}$	${9.68}_{-0.46}^{+0.46}$	K	⋯
G074.753+00.912	VLA	0.0923 ± 0.0056	27.9 ± 1.9	7386 ± 592	T	N	${9.03}_{-0.80}^{+0.86}$	${10.52}_{-0.53}^{+0.61}$	K	⋯
G075.768+00.344	VLA	0.0900 ± 0.0005	27.0 ± 0.2	7743 ± 57	T	Y	${3.49}_{-0.28}^{+0.28}$	${8.20}_{-0.05}^{+0.05}$	P	A11
G075.842+00.404	GBT	0.0751 ± 0.0003	30.5 ± 0.1	8363 ± 32	⋯	⋯	${3.73}_{-0.39}^{+0.52}$	${8.26}_{-0.08}^{+0.11}$	P	R12
G076.155−00.286	GBT	0.0651 ± 0.0005	30.9 ± 0.2	9498 ± 119	⋯	⋯	${7.13}_{-0.72}^{+0.72}$	${9.66}_{-0.51}^{+0.36}$	K	⋯
G076.384−00.621	GBT	0.0407 ± 0.0002	42.0 ± 0.2	11245 ± 92	⋯	⋯	${1.28}_{-0.08}^{+0.11}$	${8.13}_{-0.01}^{+0.01}$	P	X13
G078.032+00.606	GBT	0.0832 ± 0.0005	27.2 ± 0.2	8567 ± 86	⋯	⋯	${1.51}_{-0.09}^{+0.07}$	${8.16}_{-0.00}^{+0.00}$	P	R12
G078.147+01.820	GBT	0.0910 ± 0.0008	24.6 ± 0.2	8596 ± 107	⋯	⋯	${1.51}_{-0.10}^{+0.07}$	${8.16}_{-0.00}^{+0.00}$	P	R12
G078.886+00.709	VLA	0.1525 ± 0.0048	19.5 ± 0.7	6530 ± 260	T	N	${3.31}_{-0.27}^{+0.29}$	${8.35}_{-0.05}^{+0.06}$	P	R12
G079.270+02.488	GBT	0.1161 ± 0.0021	20.8 ± 0.6	7977 ± 222	⋯	⋯	${1.50}_{-0.09}^{+0.08}$	${8.20}_{-0.00}^{+0.00}$	P	R12
G079.293+01.296	GBT	0.0729 ± 0.0007	30.0 ± 0.1	8693 ± 86	⋯	⋯	${7.22}_{-0.80}^{+0.85}$	${9.90}_{-0.42}^{+0.55}$	K	⋯
G080.350+00.718	GBT	0.0699 ± 0.0007	26.5 ± 0.3	10250 ± 155	⋯	⋯	${9.31}_{-0.89}^{+1.03}$	${11.46}_{-0.68}^{+0.68}$	K	⋯
G080.362+01.212	GBT	0.1058 ± 0.0030	23.0 ± 0.7	7921 ± 294	⋯	⋯	${1.62}_{-0.08}^{+0.06}$	${8.21}_{-0.00}^{+0.00}$	P	R12
G080.938−00.129	GBT	0.0774 ± 0.0004	28.7 ± 0.1	8853 ± 62	⋯	⋯	${1.49}_{-0.07}^{+0.09}$	${8.24}_{-0.00}^{+0.00}$	P	R12
G081.681+00.540	GBT	0.0608 ± 0.0002	35.9 ± 0.1	8829 ± 36	⋯	⋯	${1.49}_{-0.08}^{+0.09}$	${8.26}_{-0.00}^{+0.00}$	P	R12
G082.566+00.362	GBT	0.1038 ± 0.0011	23.4 ± 0.2	8030 ± 128	⋯	⋯	${1.49}_{-0.06}^{+0.10}$	${8.28}_{-0.00}^{+0.00}$	P	R12
G083.792+03.269	GBT	0.0943 ± 0.0012	23.1 ± 0.3	8643 ± 184	⋯	⋯	${1.49}_{-0.08}^{+0.09}$	${8.31}_{-0.01}^{+0.01}$	P	R12
G085.241+00.021	GBT	0.0799 ± 0.0011	26.9 ± 0.3	8824 ± 177	⋯	⋯	${5.93}_{-0.86}^{+0.70}$	${9.76}_{-0.44}^{+0.44}$	K	⋯
G092.920+02.823	140 Foot	0.1308 ± 0.0028	24.8 ± 0.5	10840 ± 270	⋯	⋯	${7.08}_{-0.89}^{+1.03}$	${11.31}_{-0.69}^{+0.65}$	K	⋯
G096.289+02.593	VLA	0.0634 ± 0.0022	28.3 ± 1.1	10169 ± 464	T	Y	${10.13}_{-1.22}^{+1.53}$	${13.76}_{-0.87}^{+1.31}$	K	⋯
G096.434+01.324	VLA	0.1125 ± 0.0085	21.8 ± 1.8	7745 ± 762	T	N	${8.50}_{-1.40}^{+0.70}$	${12.44}_{-0.95}^{+0.65}$	K	⋯
G097.515+03.173	VLA	0.0711 ± 0.0017	28.2 ± 0.7	9226 ± 281	T	Y	${7.27}_{-0.82}^{+1.10}$	${11.78}_{-0.64}^{+0.78}$	P	H15
G097.528+03.184	VLA	0.1029 ± 0.0060	24.1 ± 1.6	7726 ± 584	T	N	${7.26}_{-0.89}^{+1.12}$	${11.76}_{-0.63}^{+0.81}$	P	H15
G101.016+02.590	VLA	0.1510 ± 0.0218	16.8 ± 2.7	7600 ± 1434	T	N	${6.87}_{-0.89}^{+1.09}$	${11.80}_{-0.69}^{+0.79}$	K	⋯
G108.191+00.586	GBT	0.0759 ± 0.0004	25.8 ± 0.1	9590 ± 59	⋯	⋯	${4.25}_{-0.46}^{+0.62}$	${10.48}_{-0.33}^{+0.40}$	P	C14
G108.375−01.056	GBT	0.0806 ± 0.0009	26.1 ± 0.3	8992 ± 131	⋯	⋯	${5.01}_{-0.88}^{+0.77}$	${10.98}_{-0.59}^{+0.64}$	K	⋯
G108.764−00.952	GBT	0.0706 ± 0.0004	29.6 ± 0.2	9404 ± 81	⋯	⋯	${4.54}_{-0.74}^{+0.86}$	${10.61}_{-0.43}^{+0.71}$	K	⋯
G109.104−00.347	VLA	0.1998 ± 0.0222	25.7 ± 2.9	4061 ± 554	T	N	${4.05}_{-0.85}^{+0.69}$	${10.31}_{-0.49}^{+0.57}$	K	⋯
G110.099+00.042	GBT	0.0543 ± 0.0003	38.0 ± 0.2	9240 ± 75	⋯	⋯	${4.56}_{-0.82}^{+0.76}$	${10.75}_{-0.58}^{+0.58}$	K	⋯
G111.558+00.804	GBT	0.0829 ± 0.0005	27.1 ± 0.1	8483 ± 51	⋯	⋯	${2.62}_{-0.10}^{+0.15}$	${9.62}_{-0.06}^{+0.09}$	P	M09
G111.612+00.371	GBT	0.0885 ± 0.0005	26.8 ± 0.1	8428 ± 68	⋯	⋯	${5.99}_{-1.04}^{+0.85}$	${11.92}_{-0.79}^{+0.68}$	K	⋯
G112.212+00.229	GBT	0.0777 ± 0.0008	28.8 ± 0.2	8641 ± 118	⋯	⋯	${3.62}_{-0.60}^{+0.93}$	${10.28}_{-0.44}^{+0.66}$	K	⋯
G115.785−01.561	GBT	0.0806 ± 0.0017	26.8 ± 0.6	8794 ± 242	⋯	⋯	${3.56}_{-0.68}^{+0.79}$	${10.40}_{-0.50}^{+0.59}$	K	⋯
G118.345+04.856	140 Foot	0.0911 ± 0.0193	20.7 ± 0.3	9540 ± 1050	⋯	⋯	${0.56}_{-0.42}^{+0.53}$	${8.66}_{-0.28}^{+0.32}$	K	⋯
G124.637+02.535	VLA	0.0659 ± 0.0011	30.5 ± 0.6	9181 ± 198	P	N	${7.31}_{-1.47}^{+0.90}$	${13.44}_{-0.86}^{+1.22}$	K	⋯
G124.894+00.323	GBT	0.0781 ± 0.0031	27.0 ± 1.2	8975 ± 460	⋯	⋯	${3.22}_{-0.65}^{+0.71}$	${10.50}_{-0.47}^{+0.65}$	K	⋯
G128.772+02.009	GBT	0.0854 ± 0.0028	20.9 ± 0.7	10361 ± 427	⋯	⋯	${8.51}_{-1.14}^{+1.82}$	${15.14}_{-1.09}^{+1.64}$	K	⋯
G132.156−00.729	GBT	0.0769 ± 0.0006	24.9 ± 0.2	9785 ± 123	⋯	⋯	${4.83}_{-0.90}^{+0.96}$	${12.09}_{-0.74}^{+0.86}$	K	⋯
G133.712+01.221	GBT	0.0760 ± 0.0003	27.7 ± 0.0	8977 ± 38	⋯	⋯	${1.95}_{-0.04}^{+0.04}$	${9.79}_{-0.03}^{+0.03}$	P	X06;H06
G133.781+01.428	GBT	0.0785 ± 0.0005	27.5 ± 0.1	8752 ± 74	⋯	⋯	${1.94}_{-0.03}^{+0.05}$	${9.79}_{-0.02}^{+0.04}$	P	X06;H06
G135.188+02.701	VLA	0.1347 ± 0.0204	19.9 ± 3.3	7259 ± 1414	P	Y	${7.37}_{-1.26}^{+1.36}$	${14.52}_{-1.18}^{+1.27}$	K	⋯
G136.884+00.911	GBT	0.0995 ± 0.0025	23.5 ± 0.6	8204 ± 257	⋯	⋯	${1.95}_{-0.04}^{+0.04}$	${9.86}_{-0.03}^{+0.03}$	P	X06;H06
G138.494+01.634	GBT	0.0969 ± 0.0014	23.8 ± 0.3	8302 ± 131	⋯	⋯	${2.87}_{-0.58}^{+0.72}$	${10.75}_{-0.61}^{+0.56}$	K	⋯
G141.084−01.063	VLA	0.1400 ± 0.0203	18.8 ± 3.2	7300 ± 1431	T	Y	${1.99}_{-0.49}^{+0.61}$	${10.04}_{-0.57}^{+0.46}$	K	⋯
G150.596−00.955	GBT	0.0671 ± 0.0005	27.8 ± 0.1	10016 ± 83	⋯	⋯	${2.74}_{-0.65}^{+0.56}$	${10.77}_{-0.63}^{+0.59}$	K	⋯
G151.609−00.233	GBT	0.0543 ± 0.0004	31.7 ± 0.2	10795 ± 98	⋯	⋯	${7.00}_{-1.25}^{+1.44}$	${14.75}_{-1.10}^{+1.56}$	K	⋯
G154.646+02.438	GBT	0.0673 ± 0.0009	28.6 ± 0.4	9734 ± 175	⋯	⋯	${4.39}_{-0.79}^{+1.05}$	${12.33}_{-0.67}^{+1.17}$	K	⋯
G155.372+02.613	GBT	0.0703 ± 0.0013	25.6 ± 0.5	10253 ± 309	⋯	⋯	${6.65}_{-1.26}^{+1.36}$	${14.76}_{-1.30}^{+1.30}$	K	⋯
G169.180−00.905	GBT	0.0872 ± 0.0013	23.1 ± 0.4	9345 ± 179	⋯	⋯	⋯d	⋯d	K	⋯
G173.599+02.803	GBT	0.1060 ± 0.0013	20.9 ± 0.3	8612 ± 137	⋯	⋯	⋯d	⋯d	K	⋯
G173.937+00.298	GBT	0.0935 ± 0.0014	23.0 ± 0.3	8829 ± 158	⋯	⋯	⋯d	⋯d	K	⋯
G192.638−00.008	GBT	0.0971 ± 0.0010	22.1 ± 0.2	8833 ± 107	⋯	⋯	${1.58}_{-0.06}^{+0.08}$	${9.89}_{-0.06}^{+0.08}$	P	R10
G196.448−01.673	VLA	0.0928 ± 0.0035	22.6 ± 0.9	8884 ± 435	T	Y	${5.23}_{-0.33}^{+0.41}$	${13.44}_{-0.32}^{+0.40}$	P	H07
G209.037−19.377	GBT	0.0878 ± 0.0007	26.1 ± 0.0	8322 ± 55	⋯	⋯	${0.41}_{-0.00}^{+0.01}$	${8.70}_{-0.00}^{+0.01}$	P	S07;M07;K08
G213.076−02.213	GBT	0.0564 ± 0.0006	28.6 ± 0.3	11343 ± 162	⋯	⋯	${6.58}_{-1.27}^{+1.27}$	${14.27}_{-1.15}^{+1.23}$	K	⋯
G213.703−12.601	GBT	0.0750 ± 0.0004	29.8 ± 0.1	8986 ± 65	⋯	⋯	${0.80}_{-0.34}^{+0.42}$	${9.01}_{-0.33}^{+0.42}$	K	⋯
G218.737+01.850	GBT	0.0702 ± 0.0007	24.6 ± 0.3	10671 ± 143	⋯	⋯	${5.39}_{-1.11}^{+0.89}$	${12.99}_{-1.00}^{+0.86}$	K	⋯
G220.524−02.759	GBT	0.0473 ± 0.0021	31.8 ± 1.7	12037 ± 725	⋯	⋯	${7.62}_{-1.35}^{+1.47}$	${14.92}_{-1.31}^{+1.42}$	K	⋯
G225.470−02.587	GBT	0.1141 ± 0.0020	22.6 ± 0.4	7537 ± 158	⋯	⋯	${0.09}_{-0.08}^{+0.43}$	${8.56}_{-0.24}^{+0.28}$	K	⋯
G227.760−00.127	GBT	0.0485 ± 0.0007	28.9 ± 0.4	12495 ± 249	⋯	⋯	${4.33}_{-0.84}^{+0.84}$	${11.73}_{-0.72}^{+0.72}$	K	⋯
G231.481−04.401	GBT	0.1011 ± 0.0024	20.5 ± 0.6	9098 ± 286	⋯	⋯	${4.49}_{-0.85}^{+0.79}$	${11.60}_{-0.68}^{+0.73}$	K	⋯
G233.753−00.193	GBT	0.0822 ± 0.0015	24.1 ± 0.4	9482 ± 209	⋯	⋯	${2.68}_{-0.63}^{+0.67}$	${10.13}_{-0.46}^{+0.54}$	K	⋯
G243.244+00.406	GBT	0.0793 ± 0.0014	22.3 ± 0.2	10477 ± 214	⋯	⋯	${4.09}_{-0.60}^{+0.98}$	${10.84}_{-0.52}^{+0.73}$	K	⋯
G345.284+01.463	140 Foot	0.0891 ± 0.0006	24.1 ± 0.2	8530 ± 640	⋯	⋯	⋯d	⋯d	K	⋯
G345.410−00.953	140 Foot	0.1036 ± 0.0004	26.3 ± 0.1	6960 ± 50	⋯	⋯	⋯d	⋯d	K	⋯
G348.249−00.971	140 Foot	0.0918 ± 0.0005	28.2 ± 0.2	6610 ± 100	⋯	⋯	⋯d	⋯d	K	⋯
G348.710−01.044	140 Foot	0.1067 ± 0.0008	24.6 ± 0.2	7150 ± 90	⋯	⋯	${3.32}_{-0.27}^{+0.34}$	${5.12}_{-0.32}^{+0.25}$	P	W12
G351.130+00.449	140 Foot	0.1272 ± 0.0015	22.1 ± 0.2	6650 ± 70	⋯	⋯	⋯d	⋯d	K	⋯
G351.170+00.704	140 Foot	0.1283 ± 0.0009	25.9 ± 0.1	5610 ± 20	⋯	⋯	⋯d	⋯d	K	⋯
G351.246+00.673	VLA	0.1131 ± 0.0003	25.1 ± 0.1	6772 ± 24	T	Y	${1.31}_{-0.12}^{+0.15}$	${7.05}_{-0.15}^{+0.12}$	P	W14
G351.311+00.663	VLA	0.1301 ± 0.0004	24.1 ± 0.1	6230 ± 27	T	Y	${1.32}_{-0.12}^{+0.16}$	${7.04}_{-0.15}^{+0.12}$	P	W14
G351.367+00.640	140 Foot	0.1151 ± 0.0012	23.9 ± 0.1	6840 ± 40	⋯	⋯	${1.31}_{-0.12}^{+0.16}$	${7.05}_{-0.17}^{+0.11}$	P	W14
G351.472−00.458	140 Foot	0.1067 ± 0.0012	23.3 ± 0.5	7460 ± 120	⋯	⋯	⋯d	⋯d	K	⋯
G351.646−01.252	140 Foot	0.0848 ± 0.0005	28.1 ± 0.1	7620 ± 30	⋯	⋯	⋯d	⋯d	K	⋯
G351.688−01.169	140 Foot	0.1029 ± 0.0006	23.6 ± 0.1	7560 ± 90	⋯	⋯	⋯d	⋯d	K	⋯
G352.597−00.188	140 Foot	0.1172 ± 0.0025	20.9 ± 0.9	7560 ± 240	⋯	⋯	⋯d	⋯d	K	⋯
G353.038+00.581	140 Foot	0.1040 ± 0.0012	28.6 ± 0.1	6250 ± 30	⋯	⋯	⋯d	⋯d	K	⋯
G353.092+00.857	140 Foot	0.2296 ± 0.0024	28.7 ± 0.1	5630 ± 40	⋯	⋯	⋯d	⋯d	K	⋯
G353.195+00.910	140 Foot	0.0826 ± 0.0006	30.8 ± 0.2	7100 ± 40	⋯	⋯	⋯d	⋯d	K	⋯
G353.408−00.381	140 Foot	0.0912 ± 0.0008	24.0 ± 0.2	8480 ± 60	⋯	⋯	⋯d	⋯d	K	⋯

Notes.

^a"P" if measured at the location of peak continuum brightness; "T" if measured within the watershed segmentation region ^b"N" if non-tapered image measurement; "Y" if uv-tapered image measurement ^c"K" for Monte Carlo kinematic distance; "P" for parallax distance ^dKinematic distances are unreliable in the direction of the Galactic center and anti-center

References. A11, Ando et al. (2011); B09, Brunthaler et al. (2009); C14, Choi et al. (2014); H06, Hachisuka et al. (2006); H07, Honma et al. (2007); H15, Hachisuka et al. (2015); I13, Immer et al. (2013); K08, Kim et al. (2008); M07, Menten et al. (2007); M09, Moscadelli et al. (2009); O10, Oh et al. (2010); RD09, Roman-Duval et al. (2009); R09a, Reid et al. (2009a); R09c, Reid et al. (2009b); R10, Rygl et al. (2010); R12, Rygl et al. (2012); S07, Sandstrom et al. (2007); S10, Sato et al. (2010); S14, Sato et al. (2014); Sa14, Sanna et al. (2014); U12, Urquhart et al. (2012); W12, Wu et al. (2012); W14, Wu et al. (2014); X06, Xu et al. (2006); X11, Xu et al. (2011); X13, Xu et al. (2013); Z09, Zhang et al. (2009); Z13, Zhang et al. (2013); Z14, Zhang et al. (2014).

Download table as:  ASCIITypeset images: 1 2 3 4 5

In total, there are now 189 Galactic H ii regions with accurate electron temperature determinations. This is an increase of 99 nebulae (110%) over the B15 sample. A fraction of these nebulae have inaccurate distances, however, and cannot be used to investigate Galactic metallicity structure.