FINDING DISTANT GALACTIC H ii REGIONS

Of the 302 detections, 57 have spectra with multiple hydrogen RRL components at different velocities. In total, we detect the emission from 369 RRL components (245 with one line, 47 sources with two lines, and 10 sources with three lines). As in Anderson et al. (2015, hereafter A15) we hypothesize that one of these component is from the discrete H ii region that we targeted and the other(s) are from diffuse ionized gas along the line of sight. To compute kinematic distances, we must determine the correct RRL velocity for these multiple-velocity H ii region spectra.

In A15 we derived a set of criteria that can be used to determine which of the RRL components is from the discrete H ii region. From the data given here, we can use four of their criteria: (1) the presence of a negative RRL velocity component, the association between RRL velocities and those of either (2) molecular gas or (3) carbon RRLs, and (4) an analysis of the electron temperature for each RRL velocity component. As in A15, we require that the results from all four criteria agree with each other. Below we discuss the four criteria, and how we apply them to our data set.

For the first of the four criteria, A15 argue that diffuse ionized gas is unlikely to be found in the outer Galaxy, at negative velocities in the first Galactic quadrant, since the density of free electrons in the outer Galaxy is low (e.g., Taylor & Cordes 1993). As in A15 we therefore assume that for all first-quadrant multiple-velocity H ii regions the negative velocity components are from the discrete H ii regions.

Two of the four criteria rely on the detection of other spectral lines within 10 $\mathrm{km}\;{{\rm{s}}}^{-1}$ of one of the $\langle {\rm{H}}\;{\rm{n}}\;\alpha \rangle$ velocity components. A15 argue that molecular gas and carbon RRLs are more likely to be associated with discrete H ii regions than diffuse ionized gas. For each multiple-velocity H ii region, we correlate the molecular velocities compiled by A14 with the $\langle {\rm{H}}\;{\rm{n}}\;\alpha \rangle$ velocities measured here. We search for carbon lines by examining each spectrum for emission offset $\sim -150\;\mathrm{km}\;{{\rm{s}}}^{-1}$ from the hydrogen RRL velocity that is at least three times the rms, and correlate any such sources with the $\langle {\rm{H}}\;{\rm{n}}\;\alpha \rangle$ velocities. These correlations produce lists of velocity components with associated molecualar gas or carbon RRLs, which we assume are the discrete H ii region velocities.

Finally, A15 use the derived electron temperature values, ${T}_{e}$, for each RRL component to determine the discrete H ii region RRL components. In local thermodynamic equilibrium (LTE), the electron temperature can be computed from observable quantities:

$$\begin{eqnarray}{T}_{e} & = & 7103.3{\left(\displaystyle \frac{\nu }{{\rm{GHz}}}\right)}^{1.1}\left[\displaystyle \frac{{T}_{C}}{{T}_{L}({{\rm{H}}}^{+})}\right]\\ & & \times {\left[\displaystyle \frac{{\rm{\Delta }}v({{\rm{H}}}^{+})}{\mathrm{km}\;{{\rm{s}}}^{-1}}\right]}^{-1}{\left[1+\displaystyle \frac{n{(}^{4}{{\rm{He}}}^{+})}{n({{\rm{H}}}^{+})}\right]}^{-1},\end{eqnarray} \tag{ 2 }$$

where ν is the observing frequency, T_C/T_L is the continuum-to-line intensity ratio, Δv is the RRL FWHM line width, and $n{(}^{4}{{\rm{He}}}^{+})/n({{\rm{H}}}^{+})$ is the helium ionic abundance ratio by number, ${y}^{+}.$ Each multiple-velocity H ii region has a single value for T_C, but multiple values for T_L and Δv, and therefore has a different ${T}_{e}$ for each RRL component. Assuming that only one of the detected lines is from a discrete H ii region, the line-to-continuum intensity ratio is only physically meaningful for this component. Therefore, whereas the electron temperature can be computed for all detected lines for each multiple-velocity H ii region, the line from the H ii region should have a reasonable value of ${T}_{e}$ while the others may not. Based on their analysis of single-velocity H ii regions from the HRDS, A15 define this "reasonable" range of ${T}_{e}$ values (in Kelvin) as a function of Galactocentric radius, $\;{R}_{G}$ (kpc), for high quality sources to be: $860+544\;{R}_{G}\lt {T}_{e}\lt 2040+544\;{R}_{G}.$ A high quality source is one with a peak continuum intensity of at least 100 mK, a peak within $10^{\prime\prime}$ of the nominal centroid pointing, and radio continuum emission that can be modeled with a single Gaussian component. A range for low-quality sources not meeting at least one of the above criteria is defined by A15 to be: ${T}_{e}\lt 6300+544\;{R}_{G}.$ Here, we compute a value of ${T}_{e}$ for each detected hydrogen component using 8.7 GHz for ν, and assuming ${y}^{+}=0.07$ (Quireza et al. 2006b). We use the "reasonable" range of values above to identify which RRLs originate from discrete H ii regions.

We derive kinematic distances for 131 of the detected H ii regions. Of these, 105 are outer-Galaxy regions ($\;{R}_{G}\gt 8.5\;\mathrm{kpc}$) and 26 are inner-Galaxy regions. The results of our kinematic distance analysis, in addition to the numbers of regions known previously, are summarized in Table 3.

Table 3.  H ii Region Kinematic Distance Summary^a

Category	Previously Known	This Work
Inner Galaxy ($\;{R}_{G}\lt 8.5\;\mathrm{kpc}$)	661	26
Sharpless (Near Distance)	17	4
Tangent Point	166	6
KDAR	478	16
Outer Galaxy ($\;{R}_{G}\gt 8.5\;\mathrm{kpc}$)	160	105
1st Quadrant	54	34
2nd Quadrant	72	66
3rd Quadrant (${\ell }\lt 225^\circ$)	27	1
4th Quadrant (${\ell }\gt 340^\circ$)	7	4
Total	821	131

Note.

^aTable only includes H ii regions with known distances. The "Previously Known" values are from A14.

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Kinematic distances use a model for Galactic rotation to give distances as a function of observed velocity for a given line of sight. We derive all kinematic distance parameters using the Brand & Blitz (1993) rotation curve. Kinematic distances are prone to large uncertainties in certain parts of the Galaxy. As in previous work, we estimate kinematic distance uncertainties by adding in quadrature the uncertainties associated with the rotation curve choice, streaming motions of 7 $\mathrm{km}\;{{\rm{s}}}^{-1}$, and changes to the Solar circular rotation speed. Such uncertainties were first computed by Anderson et al. (2012a), and expanded to the entire Galaxy by A14. We use the latter analysis here.

Kinematic distances are possible for 185 nebulae. We do not compute kinematic distances for sources within 10° of the Galactic center or within 20° of the Galactic anti-center because such distances would be uncertain by ≳50% (A14). We also exclude H ii regions with multiple RRL velocities for which the source velocity is unknown, as they have at least two possible kinematic distances. We exclude sources in the first and fourth Galactic quadrants for which the absolute value of the tangent point velocity is less than 10 $\mathrm{km}\;{{\rm{s}}}^{-1}$. Finally, we do not provide distances of outer Galaxy regions whose distance uncertainties are >50% that of their kinematic distances.

Sources in the inner Galaxy suffer from the well-known kinematic distance ambiguity (KDA): inner Galaxy H ii regions have two possible Heliocentric distances (called "near" and "far") for each measured velocity. The KDA does not exist for the 105 Outer Galaxy H ii regions in our sample (including the 34 first-quadrant sources with negative RRL velocities and the four fourth quadrant sources with positive velocities). For all regions, there is no ambiguity in the calculation of Galactocentric distances.

There are 80 inner-Galaxy H ii regions in our sample for which kinematic distances are possible. We provide a kinematic distance ambiguity resolution (KDAR) for 26 of these (33%). Four of these are Sharpless regions, which we assume lie at their near distances since they are optically visible (note, however, the extreme distance to S83 discussed later). We analyze the remaining 76 first-quadrant nebulae using the H i E/A method (Anderson & Bania 2009; Anderson et al. 2012a), employing VGPS 21 cm data. The H i E/A method uses the fact that H i between the observer and the H ii region is detected in absorption when the brightness temperature of the H ii region plasma at 21 cm is greater than that of the foreground H i. H i beyond the H ii region will be seen in emission. This method becomes unreliable if the source velocity is near the tangent point, and therefore we give the six nebulae that have LSR velocities within 10 $\mathrm{km}\;{{\rm{s}}}^{-1}$ of the tangent point the tangent point distance. We are only able to provide a KDAR for 16 of the remaining 70 inner-Galaxy nebulae. To determine distances to the other 54 nebulae we would need more sensitive H i observations.

We give the kinematic distance parameters for all 131 H ii regions with kinematic distances in Table 4, which lists the source name, the LSR velocity, the near, far, and tangent point distances, the Galactocentric radius, the tangent point velocity, the KDAR ("N"—near distance, "F"—far distance, "T"—tangent point distance, "O"—outer Galaxy), the Heliocentric distance (with uncertainties), and the vertical distance, z, from the Galactic mid-plane.

Table 4.  Kinematic Distances

Name	VLSR	DN	DF	DT	$\;{R}_{G}$	VT	KDARa	D⊙	σD⊙	z
	($\mathrm{km}\;{{\rm{s}}}^{-1}$)	(kpc)	(kpc)	(kpc)	(kpc)	($\mathrm{km}\;{{\rm{s}}}^{-1}$)		(kpc)	(kpc)	(pc)
G010.621−00.318	−10.0	⋯	19.8	8.4	11.6	168.7	O	19.8	3.1	−110
G010.630−00.338	−9.1	⋯	19.5	8.4	11.2	168.7	O	19.5	3.0	−114
S47	69.2	5.1	11.3	8.2	3.8	154.4	N	5.1	0.4	16
G019.716−00.261	40.1	3.3	12.7	8.0	5.5	139.9	F	12.7	0.4	−57
G021.603−00.169a	−4.7	⋯	16.5	7.9	9.2	133.9	O	16.5	1.1	−48
S57	31.0	2.5	13.1	7.8	6.3	129.8	N	2.5	0.5	29
G023.295−00.280b	61.6	4.2	11.4	7.8	4.9	128.4	F	11.4	0.6	−55
G025.520+00.215a	37.4	2.8	12.6	7.7	6.1	121.4	F	12.6	0.7	47
G025.651−00.031	87.5	5.3	10.0	7.7	4.4	121.0	F	10.0	0.4	−5
S61	37.3	2.7	12.5	7.6	6.2	118.4	N	2.7	0.4	83

Note.

^aKinematic distance ambiguity resolution: "N"—near distance; "F"—far distance; "O"—outer Galaxy source.

Only a portion of this table is shown here to demonstrate its form and content. A machine-readable version of the full table is available.

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In addition to the kinematic distances described above, there are a number of regions that based on their $({\ell },{\text{}}b,v)$ coordinates are physically near to the Galactic center. We observed four single-velocity regions that are associated with Sgr B2, and four that are associated with Sgr E. These two star forming complexes are physically near to the Galactic center (∼100 pc Liszt 1992; Reid et al. 2009). While we do not provide distance parameters for these sources in Table 5, in later plots we do use a Heliocentric distance of 8.5 kpc and a Galactocentric radius of 0.1 kpc for these eight regions.

The Sharpless regions we detected have velocities similar to those observed in Hα by Fich et al. (1990), although the FWHM line widths are discrepant. We show these comparisons for the H ii regions with one velocity component in Figure 2. By comparing with the H109α measurements of Lockman (1989), Fich et al. (1990) also found very good agreement between Hα and RRL velocities, but large discrepancies between the line width measurements. They note a mean Hα and RRL velocity difference of 0.82 ± 3.46 $\mathrm{km}\;{{\rm{s}}}^{-1}$, whereas we find $0.38\pm 2.73\;\mathrm{km}\;{{\rm{s}}}^{-1}$ (quoted uncertainties here are the dispersion). The mean absolute velocity difference ($\langle | {v}_{{\rm{RRL}}}-{v}_{{\rm{H}}\alpha }| \rangle$) is $2.02\pm 1.41\;\mathrm{km}\;{{\rm{s}}}^{-1}.$ The Hα line widths are systematically greater than those we measure for RRLs, in agreement with the results of Fich et al. (1990). The average line width ratio ${\rm{\Delta }}{V}_{{\rm{RRL}}}/{\rm{\Delta }}{V}_{{\rm{H}}\alpha }$ is 0.82 ± 0.17, whereas Fich et al. (1990) found 0.83 ± 0.18. Therefore, the line width discrepancy with Hα is the same, regardless of the observed radio frequency. We hypothesize that the Hα observations are broadened by the relatively low spectral resolution of $\sim 15\;\mathrm{km}\;{{\rm{s}}}^{-1}.$ We can spectrally deconvolve the Hα linewidths using ${\rm{\Delta }}{V}_{{\rm{true}}}^{2}={\rm{\Delta }}{V}_{{\rm{H}}\alpha }^{2}-{\rm{\Delta }}{V}_{{\rm{Res.}}}^{2},$ where the instrumental spectral resolution ${V}_{{\rm{Res.}}}=15\;\mathrm{km}\;{{\rm{s}}}^{-1}.$ Doing so, we find that the average line width ratio ${\rm{\Delta }}{V}_{{\rm{RRL}}}/{\rm{\Delta }}{V}_{{\rm{H}}\alpha }$ is 0.90 ± 0.24. The spectral resolution can therefore only explain part of the linewidth difference.

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There are 24 Sharpless H ii regions that have both spectrophotometric distances and kinematics distances derived here. We give the spectrophotometric and kinematic distances for these regions in Table 5 and compare the distances in Figure 3. We take the spectrophotometric distance values and uncertainties from Russeil et al. (2007) if possible, or otherwise from Russeil (2003). While there are more recent spectrophotometric distances for some regions, using distances from these two papers reduces uncertainties caused by different methodologies. The two distances are correlated but there is considerable scatter, especially for sources with small spectrophotometric distances. The mean difference ($\langle {d}_{{\rm{Kin}}}-{d}_{{\rm{Spec}}}\rangle$) between kinematic and spectrophotometric distances is 1.0 ± 2.0 kpc. As a percentage of the spectrophotometric distances, the differences are on average 47 ± 90% discrepant. The average absolute difference ($\langle | {d}_{{\rm{kin}}}-{d}_{{\rm{spec}}}| \rangle$) in kinematic and spectrophotometric distances is $1.8\pm 1.3\;\mathrm{kpc}.$ The agreement is improved if the Reid et al. (2014) rotation curve is used.

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The largest discrepancies between distances are for H ii regions with small spectrophotometric distances in the zone $136^\circ \gt {\ell }\gt 105^\circ .$ For example, S135, S164, S170, S175, and S193 all have spectrophotometric distances $\lt 2.5\;{\rm{kpc}},$ but kinematic distances from the Brand & Blitz (1993) rotation curve ≥100% discrepant. The $({\ell },{\text{}}b,v)$ locii of these regions is suggests that they lie in the Perseus spiral arm where perhaps non-circular motions are leading to erroneously large kinematic distances (Choi et al. 2014). This explanation assumes that the spectrophotometric distances are more accurate than the kinematic distances, which has not been proven to be the case. We do note that for S170 the maser parallax distance of 3.34 kpc (Choi et al. 2014) is in better agreement with the spectrophotometric distance of 2.6 kpc compared with our kinematic distance of 5.8 kpc. Choi et al. (2014) list kinematic distances for this source of 3.0 and 4.0 kpc for different rotation curve models based on their maser parallax distances, which implies that the Brand & Blitz (1993) curve dramatically overestimates kinematic distances in this direction.

Here, we have added significant numbers of H ii regions to the Galactic census, especially in the sky zones not covered by the original HRDS. In Figure 4 we show the distribution of regions detected here and of all H ii regions known previously. The sample of previously known regions all have ionized gas velocities (RRL or Hα), as compiled in the WISE catalog (A14). The sample here adds considerably to the H ii region census in the portion of the first Galactic quadrant not covered by the original HRDS, $90^\circ \gt {\ell }\gt 65^\circ ,$ with 42 new detections versus 52 regions known previously. We also add 105 outer Galaxy regions (mostly in the second quadrant) versus 160 known previously (Table 4).

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As expected, the regions in the current sample are more distant on average than the population known previously. To illustrate this point, in Figure 5 we show the distributions of Heliocentric and Galactocentric distances for the current census of Galactic H ii regions. The average Heliocentric and Galactocentric distances for the new detections are 9.8 and 11.0 kpc, respectively, while they are 7.4 and 6.8 kpc for the previously known sample compiled by A14. Here we provide kinematic distances for 60 newly found first-quadrant regions. The average Heliocentric distance to these 60 regions is 15.2 kpc, whereas it is 10.1 kpc for the first-quadrant regions in the original HRDS (Anderson et al. 2012a) and 8.4 kpc for the first-quadrant regions known prior to the HRDS (Anderson et al. 2009). The average Galactocentric radius for the 60 first-quadrant sources is 9.4 kpc. Of the 60 regions, 34 have negative RRL velocities and are therefore in the outer Galaxy. In the second quadrant, the average distance is 7.2 kpc, whereas it was 5.7 kpc for regions known previously. We attribute these differences to the fact that we explicitly searched for distant regions following the warp in the first quadrant, and observed fainter sources than were known previously in the second quadrant.

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We detected the RRL emission from 47 H ii regions in the $({\ell },{\text{}}b)$ zone of the OSC searched here: $65^\circ \gt {\ell }\gt 25^\circ ;b\geqslant 1^\circ .$ Of these 47 H ii regions, five have LSR velocities within 15 $\mathrm{km}\;{{\rm{s}}}^{-1}$ of the OSC $({\ell },v)$ locus defined by in Dame & Thaddeus (2011): $v=-1.6\times {\ell }.$ Included in this tally is S83, whose RRL velocity was already known to be consistent with the OSC (e.g., Balser et al. 2011, where it is called "G55.11+2.4"). We also detect the RRL emission from an additional region not in the OSC $({\ell },{\text{}}b)$ zone whose longitude and velocity are nevertheless consistent with membership in the OSC, G039.183−01.422 (see below), bringing the total number of H ii regions identified here that appear to be in the OSC to 6: G033.008+01.151, G039.183−01.422, G041.755+01.451, G041.804+01.503, G054.094+01.749, and S83. The regions G041.755+01.451 and G041.804+01.503 have small angular separations and have RRL velocities within ∼2 $\mathrm{km}\;{{\rm{s}}}^{-1}$ of each other. They are therefore presumably part of the same complex.

We give the parameters of the OSC regions in Table 5, where we list Galactocentric and Heliocentric distances according to the Brand & Blitz (1993; with ${{\rm{\Theta }}}_{0}=220$ $\mathrm{km}\;{{\rm{s}}}^{-1}$ and R₀ = 8.5 kpc) and Reid et al. (2014) rotation curves (with Θ₀ = 240 $\mathrm{km}\;{{\rm{s}}}^{-1}$ and R₀ = 8.34 kpc). The Reid et al. (2014) curve gives distances ∼10% smaller for the OSC sources, on average ∼2 kpc for distances of $\sim 20\;\mathrm{kpc},$ due to the larger rotational speeds of the model.

The source G039.183−01.422 has an LSR velocity consistent with being in the OSC, and yet according to its kinematic distance it lies nearly 500 pc below the Galactic plane. At ${\ell }=39^\circ ,$ the H i in the OSC is centered near b = 3° (c.f. Dame & Thaddeus 2011) or ∼600 pc above the Galactic mid-plane at a Heliocentric distance of ∼20 kpc. There is only a small amount of OSC H i emission seen at the $({\ell },{\text{}}b)$ position of G039.183−01.422 (see Dame & Thaddeus 2011). The implied separation of G039.183−01.422 from the OSC arm centroid therefore corresponds to a vertical offset of >1 kpc. It is unlikely that the high-mass stars capable of producing H ii regions would have strayed this far from their birthplaces. At the nominal lower velocity for a star to be called a "runaway," 30 $\mathrm{km}\;{{\rm{s}}}^{-1}$, it would take over 30 Myr to travel 1 kpc. This neglects motion in the plane of the sky. Of course, if it is indeed a runaway star, its velocity cannot be used for kinematic distances. It is possible that G039.183−01.422 is a planetary nebula, but we regard this as unlikely due to the detection of an H₂O maser at −53 $\mathrm{km}\;{{\rm{s}}}^{-1}$ (Sunada et al. 2007) as well as NH₃ (W. Armentrout, 2015, in preparation).

Three second-quadrant sources have Galactocentric radii from the Brand & Blitz (1993) rotation curve that are greater than 19 kpc: G149.746−00.199, G151.561−00.425, and G151.626−00.456. Based on their WISE emission, the latter two sources appear to be in the same complex as S209, which has a RRL velocity of −51.2 $\mathrm{km}\;{{\rm{s}}}^{-1}$ (Balser et al. 2011). Properties of these nebulae are included in Table 6. The Reid et al. (2014) curve gives Galactocentric distances lower by 3–5 kpc(∼20%; Table 6). Regardless of their exact distances, these sources have the largest Galactocentric radii of any H ii regions discovered and are likely located in the extreme outer Galaxy (EOG Kobayashi et al. 2008; Yasui et al. 2008). With low metallicity and low densities, the EOG is a laboratory for how stars may have formed in the early evolutionary stages of our Milky Way.

The three distant sources may be part of the OSC extension into the second Galactic quadrant that was identified by Sun et al. (2015), whose analysis shows H i emission at $({\ell },v)$ = (∼150°, ∼–70 $\mathrm{km}\;{{\rm{s}}}^{-1}$). While the H ii region velocities are in rough agreement with this $({\ell },v)$ locus, the brightest H i emission near ${\ell }\simeq 150^\circ$ is at $b\simeq -3^\circ$ whereas our sources are much closer to b = 0°. It is therefore not clear at present if these three H ii regions (and S209) lie in the OSC. These distant H ii regions are not spatially coincident with any of the molecular clouds detected by Digel et al. (1994), which have Galactic longitudes of 130°–150° and Galactocentric radii $\gtrsim 17\;\mathrm{kpc}.$

Table 6.  OSC H ii Regions?

				Brand			Reid
Name	${\ell }$	${\text{}}b$	VLSR	$\;{R}_{G}$	d⊙	z	$\;{R}_{G}$	d⊙	z
	$(^\circ )$	$(^\circ )$	($\mathrm{km}\;{{\rm{s}}}^{-1}$)	(kpc)	(kpc)	(pc)	(kpc)	(kpc)	(pc)
G033.008+01.151	33.008	1.151	−57.6	17.0	23.5	472	14.8	21.1	424
G039.183−01.422	39.183	−1.422	−54.9	14.5	20.1	−499	13.0	18.4	−456
G041.755+01.451	41.755	1.451	−54.8	14.0	19.2	485	12.6	17.6	445
G041.804+01.503	41.804	1.503	−52.6	13.7	18.8	493	12.4	17.3	453
G054.094+01.749	54.094	1.749	−85.3	17.0	20.5	626	14.8	18.0	550
S83	55.114	2.422	−76.1	15.3	18.4	778	13.5	16.5	695
G149.746−00.199	149.746	−0.199	−71.4	25.3	17.5	−60	20.2	12.5	−43
G151.561−00.425	151.561	−0.425	−56.4	19.3	11.4	−84	16.4	8.5	−63
G151.626−00.456	151.626	−0.456	−58.2	20.1	12.2	−97	16.9	9.1	−72

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We detected RRL emission from five H ii regions near ${\ell }=359^\circ$ that have negative velocity components ≲−200 $\mathrm{km}\;{{\rm{s}}}^{-1}$: G358.600−00.057, G358.643−00.034, G358.684−00.116, G358.802−00.011, and G358.946+00.004. These nebulae are part of Sgr E, a well-known complex of H ii regions near the Galactic center (Liszt 1992) that contains at least 30 separate sources identified from their spectral indices (Gray et al. 1993). Few of these 30 regions have ionized gas spectroscopic measurements. Sgr E is thought to be at the outer boundary of the nuclear disk, which implies a distance from the Galactic center of ∼200 pc. It has no counterpart at positive longitudes. Sgr E was previously observed in RRL emission by Cram et al. (1996), and they detected six H ii regions, including four of the regions detected here. The region G358.946+00.004, which was not detected by Cram et al. (1996), has multiple RRL velocities and therefore its membership in Sgr E is less secure.

On the basis of their Galactic location and LSR velocities near $-200\;\mathrm{km}\;{{\rm{s}}}^{-1},$ Sgr E now has 16 H ii regions with measured RRL emission, including nine regions from the original HRDS (one of which, G358.720+0.011, was also observed by Cram et al. 1996). There are two additional H ii regions near $({\ell },{\text{}}b)=(359^\circ ,0^\circ )$ with velocities near 0 $\mathrm{km}\;{{\rm{s}}}^{-1}$ whose membership in Sgr E is unlikely: G358.881+00.057; −7.0 $\mathrm{km}\;{{\rm{s}}}^{-1}$ (detected here) and G358.633+00.062; 14.0 $\mathrm{km}\;{{\rm{s}}}^{-1}$ (detected by A11). We show the infrared emission from the Sgr E region in Figure 6, which has 24 $\mu {\rm{m}}$ Spitzer MIPSGAL data in red, 8.0 $\mu {\rm{m}}$ Spitzer GLIMPSE data in green, and 3.6 $\mu {\rm{m}}$ Spitzer GLIMPSE data in blue.

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The morphology of the Sgr E H ii nebulae is unusual in that their 8.0 $\mu {\rm{m}}$ emission is weak compared to their 24 $\mu {\rm{m}}$ emission. While there is faint 8.0 $\mu {\rm{m}}$ emission surrounding each source, the strongest 8.0 $\mu {\rm{m}}$ emission is found toward the center of the H ii regions. This unusual infrared morphology is not seen outside of the Galactic center. Furthermore, for the two regions whose velocities are not consistent with Sgr E, the 8.0 $\mu {\rm{m}}$ emission is strong, and found surrounding the regions.

The integrated 8.0 to 24 $\mu {\rm{m}}$ ratios are on average ∼3 times less than the Galactic average for H ii regions from Anderson et al. (2012b). Why the 8.0 $\mu {\rm{m}}$ emission in the Sgr E H ii regions is so weak is unknown. The 8.0 $\mu {\rm{m}}$ emission may be attenuated by intervening material, the emission process that produces the 8.0 $\mu {\rm{m}}$ emission may be absent for Sgr E, or the photodissociation regions surrounding the Sgr E regions may not be present.