Engineering topics

Goss, W. M.

Publications and source records attributed to Goss, W. M..

At least 19 records

DOE OSTI2020

Time-variable Radio Recombination Line Emission in W49A

We present new Jansky Very Large Array (VLA) images of the central region of the W49A star-forming region at 3.6 cm and at 7 mm at resolutions of 0.″15 (1650 au) and 0.″04 (440 au), respectively. The 3.6 cm data reveal new morphological detail in the ultracompact H ii region population, as well as several previously unknown and unresolved sources. In particular, source A shows elongated, edge-brightened bipolar lobes, indicative of a collimated outflow, and source E is resolved into three spherical components. We also present VLA observations of radio recombination lines at 3.6 cm and 7 mm, and IRAM Northern Extended Millimeter Array (NOEMA) observations at 1.2 mm. Three of the smallest ultracompact H ii regions (sources A, B2, and G2) all show broad kinematic linewidths, with ΔV {sub FWHM} ≳ 40 km s{sup −1}. A multi-line analysis indicates that broad linewidths remain after correcting for pressure broadening effects, suggesting the presence of supersonic flows. Substantial changes in linewidth over the 21 yr time baseline at both 3.6 cm and 7 mm are found for source G2. At 3.6 cm, the linewidth of G2 changed from 31.7 ± 1.8 km s{sup −1} to 55.6 ± 2.7 km s{sup −1}, an increase of +23.9 ± 3.4 km s{sup −1}. The G2 source was previously reported to have shown a 3.6 cm continuum flux density decrease of 40% between 1994 and 2015. This source sits near the center of a very young bipolar outflow whose variability may have produced these changes.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2017

ALMA Detects CO(3–2) within a Super Star Cluster in NGC 5253

We present observations of CO(3–2) and {sup 13}CO(3–2) emission near the supernebula in the dwarf galaxy NGC 5253, which contains one of the best examples of a potential globular cluster in formation. The 0.″3 resolution images reveal an unusual molecular cloud, “Cloud D1,” that is coincident with the radio-infrared supernebula. The ∼6 pc diameter cloud has a linewidth, Δ v = 21.7 km s{sup −1}, that reflects only the gravitational potential of the star cluster residing within it. The corresponding virial mass is 2.5 × 10{sup 5} M{sub ⊙}. The cluster appears to have a top-heavy initial mass function, with M {sub *} ≳ 1–2 M{sub ⊙}. Cloud D1 is optically thin in CO(3–2), probably because the gas is hot. Molecular gas mass is very uncertain but constitutes <35% of the dynamical mass within the cloud boundaries. In spite of the presence of an estimated ∼1500–2000 O stars within the small cloud, the CO appears relatively undisturbed. We propose that Cloud D1 consists of molecular clumps or cores, possibly star-forming, orbiting with more evolved stars in the core of the giant cluster.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2017

JVLA Observations of IC 342: Probing Star Formation in the Nucleus

IC 342 is a nearby, late-type spiral galaxy with a young nuclear star cluster surrounded by several giant molecular clouds. The IC 342 nuclear region is similar to the Milky Way and therefore provides an interesting comparison. We explore star formation in the nucleus using radio recombination line (RRL) and continuum emission at 5, 6.7, 33, and 35 GHz with the JVLA. These radio tracers are largely unaffected by dust and therefore sensitive to all of the thermal emission from the ionized gas produced by early-type stars. We resolve two components in the RRL and continuum emission within the nuclear region that lie east and west of the central star cluster. These components are associated both spatially and kinematically with two giant molecular clouds. We model these regions in two ways: a simple model consisting of uniform gas radiating in spontaneous emission, or as a collection of many compact H ii regions in non-local thermodynamic equilibrium. The multiple H ii region model provides a better fit to the data and predicts many dense (n{sub e}∼10{sup 4}--10{sup 5} cm{sup −3}), compact (≲0.1 pc) H ii regions. For the whole nuclear region as defined by RRL emission, we estimate a hydrogen-ionizing rate of N{sub L} ∼ 2×10{sup 52} s{sup −1}, corresponding to the equivalent of ∼2000 O6 stars and a star formation rate of ∼0.15 M {sub ⊙} yr{sup −1}. We detect radio continuum emission west of the southern mini molecular spiral arm, consistent with trailing spiral arms.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2016

Microarcsecond VLBI pulsar astrometry with PSRπ. I. Two binary millisecond pulsars with white dwarf companions

Model-independent distance constraints to binary millisecond pulsars (MSPs) are of great value to both the timing observations of the radio pulsars and multiwavelength observations of their companion stars. Astrometry using very long baseline interferometry (VLBI) can be employed to provide these model-independent distances with very high precision via the detection of annual geometric parallax. Using the Very Long Baseline Array, we have observed two binary MSPs, PSR J1022+1001 and J2145–0750, over a two-year period and measured their distances to be 700{sub −10}{sup +14} pc and 613{sub −14}{sup +16} pc respectively. We use the well-calibrated distance in conjunction with revised analysis of optical photometry to tightly constrain the nature of their massive (M∼0.85 M{sub ⊙}) white dwarf companions. Finally, we show that several measurements of the parallax and proper motion of PSR J1022+1001 and PSR J2145–0750 obtained by pulsar timing array projects are incorrect, differing from the more precise VLBI values by up to 5σ. We investigate possible causes for the discrepancy, and find that imperfect modeling of the solar wind is a likely candidate for the errors in the timing model given the low ecliptic latitude of these two pulsars.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2016

ORION’S VEIL: MAGNETIC FIELD STRENGTHS AND OTHER PROPERTIES OF A PDR IN FRONT OF THE TRAPEZIUM CLUSTER

We present an analysis of physical conditions in the Orion Veil, an atomic photon-dominated region (PDR) that lies just in front (≈2 pc) of the Trapezium stars of Orion. This region offers an unusual opportunity to study the properties of PDRs, including the magnetic field. We have obtained 21 cm H i and 18 cm (1665 and 1667 MHz) OH Zeeman effect data that yield images of the line-of-sight magnetic field strength B {sub los} in atomic and molecular regions of the Veil. We find B {sub los} ≈ −50 to −75 μ G in the atomic gas across much of the Veil (25″ resolution) and B {sub los} ≈ −350 μ G at one position in the molecular gas (40″ resolution). The Veil has two principal H i velocity components. Magnetic and kinematical data suggest a close connection between these components. They may represent gas on either side of a shock wave preceding a weak-D ionization front. Magnetic fields in the Veil H i components are 3–5 times stronger than they are elsewhere in the interstellar medium where N (H) and n (H) are comparable. The H i components are magnetically subcritical (magnetically dominated), like the cold neutral medium, although they are about 1 dex denser. Comparatively strong fields in the Veil H i components may have resulted from low-turbulence conditions in the diffuse gas that gave rise to OMC-1. Strong fields may also be related to magnetostatic equilibrium that has developed in the Veil since star formation. We also consider the location of the Orion-S molecular core, proposing a location behind the main Orion H{sup +} region.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2015

Extremely bright submillimeter galaxies beyond the Lupus-I star-forming region

We report detections of two candidate distant submillimeter galaxies (SMGs), MM J154506.4−344318 and MM J154132.7−350320, which are discovered in the AzTEC/ASTE 1.1 mm survey toward the Lupus-I star-forming region. The two objects have 1.1 mm flux densities of 43.9 and 27.1 mJy, and have Herschel/SPIRE counterparts as well. The Submillimeter Array counterpart to the former SMG is identified at 890 μm and 1.3 mm. Photometric redshift estimates using all available data from the mid-infrared to the radio suggest that the redshifts of the two SMGs are z{sub photo}≃4–5 and 3, respectively. Near-infrared objects are found very close to the SMGs and they are consistent with low-z ellipticals, suggesting that the high apparent luminosities can be attributed to gravitational magnification. The cumulative number counts at S{sub 1.1mm}⩾25 mJy, combined with the other two 1.1 mm brightest sources, are 0.70{sub −0.34}{sup +0.56} deg{sup −2}, which is consistent with a model prediction that accounts for flux magnification due to strong gravitational lensing. Unexpectedly, a z>3 SMG and a Galactic dense starless core (e.g., a first hydrostatic core) could be similar in the mid-infrared to millimeter spectral energy distributions and spatial structures at least at ≳1′′. This indicates that it is necessary to distinguish the two possibilities by means of broadband photometry from the optical to centimeter and spectroscopy to determine the redshift, when a compact object is identified toward Galactic star-forming regions.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2015

The 21-SPONGE H i absorption survey. I. Techniques and initial results

We present methods and results from “21 cm Spectral Line Observations of Neutral Gas with the EVLA” (21-SPONGE), a large survey for Galactic neutral hydrogen (H i) absorption with the Karl G. Jansky Very Large Array (VLA). With the upgraded capabilities of the VLA, we reach median rms noise in optical depth of σ{sub τ}=9×10{sup −4} per 0.42 km s{sup −1} channel for the 31 sources presented here. Upon completion, 21-SPONGE will be the largest H i absorption survey with this high sensitivity. We discuss the observations and data reduction strategies, as well as line fitting techniques. We prove that the VLA bandpass (BP) is stable enough to detect broad, shallow lines associated with warm H i, and we show that BP observations can be combined in time to reduce spectral noise. In combination with matching H i emission profiles from the Arecibo Observatory (∼3.′5 angular resolution), we estimate excitation (or spin) temperatures (T{sub s}) and column densities for Gaussian components fitted to sightlines along which we detect H i absorption (30/31). We measure temperatures up to T{sub s}∼1500 K for individual lines, showing that we can probe the thermally unstable interstellar medium (ISM) directly. However, we detect fewer of these thermally unstable components than expected from previous observational studies. We probe a wide range in column density between ∼10{sup 16} and >10{sup 21} cm{sup −2} for individual H i clouds. In addition, we reproduce the trend between cold gas fraction and average T{sub s} found by the Kim et al. synthetic observations of a hydrodynamic ISM simulation. Finally, we compare methods for estimating T{sub s} using H i observations.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2015

AUTONOMOUS GAUSSIAN DECOMPOSITION

We present a new algorithm, named Autonomous Gaussian Decomposition (AGD), for automatically decomposing spectra into Gaussian components. AGD uses derivative spectroscopy and machine learning to provide optimized guesses for the number of Gaussian components in the data, and also their locations, widths, and amplitudes. We test AGD and find that it produces results comparable to human-derived solutions on 21 cm absorption spectra from the 21 cm SPectral line Observations of Neutral Gas with the EVLA (21-SPONGE) survey. We use AGD with Monte Carlo methods to derive the H i line completeness as a function of peak optical depth and velocity width for the 21-SPONGE data, and also show that the results of AGD are stable against varying observational noise intensity. The autonomy and computational efficiency of the method over traditional manual Gaussian fits allow for truly unbiased comparisons between observations and simulations, and for the ability to scale up and interpret the very large data volumes from the upcoming Square Kilometer Array and pathfinder telescopes.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2014

Very large array and green bank telescope observations of Orion B (NGC 2024, W12): photodissociation region properties and magnetic field

We present images of C110α and H110α radio recombination line (RRL) emission at 4.8 GHz and images of H166α, C166α, and X166α RRL emission at 1.4 GHz, observed toward the star-forming region NGC 2024. The 1.4 GHz image with angular resolution ∼70'' is obtained using Very Large Array (VLA) data. The 4.8 GHz image with angular resolution ∼17'' is obtained by combining VLA and Green Bank Telescope data in order to add the short and zero spacing data in the uv plane. These images reveal that the spatial distributions of C110α line emission is confined to the southern rim of the H II region close to the ionization front whereas the C166α line emission is extended in the north-south direction across the H II region. The LSR velocity of the C110α line is 10.3 km s{sup –1} similar to that of lines observed from molecular material located at the far side of the H II region. This similarity suggests that the photodissociation region (PDR) responsible for C110α line emission is at the far side of the H II region. The LSR velocity of C166α is 8.8 km s{sup –1}. This velocity is comparable with the velocity of molecular absorption lines observed from the foreground gas, suggesting that the PDR is at the near side of the H II region. Non-LTE models for carbon line-forming regions are presented. Typical properties of the foreground PDR are T {sub PDR} ∼ 100 K, n{sub e}{sup PDR}∼5 cm{sup –3}, n {sub H} ∼ 1.7 × 10{sup 4} cm{sup –3}, and path length l ∼ 0.06 pc, and those of the far side PDR are T {sub PDR} ∼ 200 K, n{sub e}{sup PDR}∼ 50 cm{sup –3}, n {sub H} ∼ 1.7 × 10{sup 5} cm{sup –3}, and l ∼ 0.03 pc. Our modeling indicates that the far side PDR is located within the H II region. We estimate the magnetic field strength in the foreground PDR to be 60 μG and that in the far side PDR to be 220 μG. Our field estimates compare well with the values obtained from OH Zeeman observations toward NGC 2024. The H166α spectrum shows narrow (1.7 km s{sup –1}) and broad (33 km s{sup –1}) line features. The narrow line has spatial distribution and central velocity (∼9 km s{sup –1}) similar to that of the foreground carbon line emission, suggesting that they are associated. Modeling the narrow H166α emission provides physical properties T {sub PDR} ∼ 50 K, n{sub e}{sup PDR}∼4 cm{sup –3}, and l ∼ 0.01 pc and implies an ionization fraction of ∼10{sup –4}. The broad H166α line originates from the H II region. The X166α line has a different spatial distribution compared to other RRLs observed toward NGC 2024 and is probably associated with cold dust clouds. Based on the expected low depletion of sulfur in such clouds and the –8.1 km s{sup –1} velocity separation between the X166α and C166α lines, we interpret that the X166α transition arises from sulfur.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2014

A mid-life crisis? Sudden changes in radio and X-ray emission from supernova 1970G

Supernovae (SNe) provide a backdrop from which we can probe the end state of stellar evolution in the final years before the progenitor star explodes. As the shock from the SN expands, the timespan of mass-loss history we are able to probe also extends, providing insight to rapid timescale processes that govern the end state of massive stars. While SNe transition into remnants on timescales of decades to centuries, observations of this phase are currently limited. Here, we present observations of SN 1970G, serendipitously observed during the monitoring campaign of SN 2011fe, which shares the same host galaxy. Utilizing the new Jansky Very Large Array (VLA) upgrade and a deep X-ray exposure taken by Chandra, we are able to recover this middle-aged SN and distinctly resolve it from the H II cloud with which it is associated. We find that the flux density of SN 1970G has changed significantly since it was last observed—the X-ray luminosity has increased by a factor of ∼3, while we observe a significantly lower radio flux of only 27.5 μJy at 6.75 GHz, a level only detectable through the upgrades now in operation at the Jansky VLA. These changes suggest that SN 1970G has entered a new stage of evolution toward an SN remnant, and we may be detecting the turn-on of the pulsar wind nebula. Deep radio observations of additional middle-aged SNe with the improved radio facilities will provide a statistical census of the delicate transition period between SN and remnant.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2014

Study of interstellar molecular clouds using formaldehyde absorption toward extragalactic radio sources

We present new Very Large Array 6 cm H{sub 2}CO observations toward four extragalactic radio continuum sources (B0212+735, 3C 111, NRAO 150, and BL Lac) to explore the structure of foreground Galactic clouds as revealed by absorption variability. This project adds a new epoch in the monitoring observations of the sources reported by Marscher and collaborators in the mid-1990s. Our new observations confirm the monotonic increase in H{sub 2}CO absorption strength toward NRAO 150. We do not detect significant variability of our 2009 spectra with respect to the 1994 spectra of 3C111, B0212+735, and BL Lac; however, we find significant variability of the 3C111 2009 spectrum with respect to archive observations conducted in 1991 and 1992. Our analysis supports that changes in absorption lines could be caused by chemical and/or geometrical gradients in the foreground clouds and not necessarily by small-scale (∼10 AU) high-density molecular clumps within the clouds.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2014

FLICKERING OF 1.3 cm SOURCES IN SGR B2: TOWARD A SOLUTION TO THE ULTRACOMPACT H II REGION LIFETIME PROBLEM

Accretion flows onto massive stars must transfer mass so quickly that they are themselves gravitationally unstable, forming dense clumps and filaments. These density perturbations interact with young massive stars, emitting ionizing radiation, alternately exposing and confining their H II regions. As a result, the H II regions are predicted to flicker in flux density over periods of decades to centuries rather than increase monotonically in size as predicted by simple Spitzer solutions. We have recently observed the Sgr B2 region at 1.3 cm with the Very Large Array in its three hybrid configurations (DnC, CnB, and BnA) at a resolution of ∼0.''25. These observations were made to compare in detail with matched continuum observations from 1989. At 0.''25 resolution, Sgr B2 contains 41 ultracompact (UC) H II regions, 6 of which are hypercompact. The new observations of Sgr B2 allow comparison of relative peak flux densities for the H II regions in Sgr B2 over a 23 year time baseline (1989-2012) in one of the most source-rich massive star forming regions in the Milky Way. The new 1.3 cm continuum images indicate that four of the 41 UC H II regions exhibit significant changes in their peak flux density, with one source (K3) dropping in peak flux density, and the other three sources (F10.303, F1, and F3) increasing in peak flux density. The results are consistent with statistical predictions from simulations of high mass star formation, suggesting that they offer a solution to the lifetime problem for UC H II regions.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2014

EXCITATION TEMPERATURE OF THE WARM NEUTRAL MEDIUM AS A NEW PROBE OF THE Lyα RADIATION FIELD

We use the Karl G. Jansky Very Large Array to conduct a high-sensitivity survey of neutral hydrogen (H I) absorption in the Milky Way. In combination with corresponding H I emission spectra obtained mostly with the Arecibo Observatory, we detect a widespread warm neutral medium component with excitation temperature 〈T{sub s}〉=7200{sub −1200}{sup +1800} K (68% confidence). This temperature lies above theoretical predictions based on collisional excitation alone, implying that Lyα scattering, the most probable additional source of excitation, is more important in the interstellar medium (ISM) than previously assumed. Our results demonstrate that H I absorption can be used to constrain the Lyα radiation field, a critical quantity for studying the energy balance in the ISM and intergalactic medium yet notoriously difficult to model because of its complicated radiative transfer, in and around galaxies nearby and at high redshift.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2013

OH MASER SOURCES IN W49N: PROBING MAGNETIC FIELD AND DIFFERENTIAL ANISOTROPIC SCATTERING WITH ZEEMAN PAIRS USING THE VERY LONG BASELINE ARRAY

Our analysis of a Very Long Baseline Array 12 hr synthesis observation of the OH masers in the well-known star-forming region W49N has yielded valuable data that enable us to probe distributions of magnetic fields in both the maser columns and the intervening interstellar medium (ISM). The data, consisting of detailed high angular resolution images (with beam width ∼20 mas) of several dozen OH maser sources, or spots, at 1612, 1665, and 1667 MHz, reveal anisotropic scatter broadening with typical sizes of a few tens of milliarcseconds and axial ratios between 1.5 and 3. Such anisotropies have been reported previously by Desai et al. and have been interpreted as being induced by the local magnetic field parallel to the Galactic plane. However, we find (1) apparent angular sizes of, on average, a factor of about 2.5 less than those reported by Desai et al., indicating significantly less scattering than inferred previously, and (2) a significant deviation in the average orientation of the scatter-broadened images (by ∼10°) from that implied by the magnetic field in the Galactic plane. More intriguingly, for a few Zeeman pairs in our set, significant differences (up to 6σ) are apparent in the scatter-broadened images for the two hands of circular polarization, even when the apparent velocity separation is less than 0.1 km s{sup –1}. This may possibly be the first example of a Faraday rotation contribution to the diffractive effects in the ISM. Using the Zeeman pairs, we also study the distribution of the magnetic field in the W49N complex, finding no significant trend in the spatial structure function. In this paper, we present the details of our observations and analysis leading to these findings, discuss implications of our results for the intervening anisotropic magneto-ionic medium, and suggest possible implications for the structure of magnetic fields within this star-forming region.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2013

OH (1720 MHz) MASERS: A MULTIWAVELENGTH STUDY OF THE INTERACTION BETWEEN THE W51C SUPERNOVA REMNANT AND THE W51B STAR FORMING REGION

We present a comprehensive view of the W51B H II region complex and the W51C supernova remnant (SNR) using new radio observations from the VLA, VLBA, MERLIN, JCMT, and CSO along with archival data from Spitzer, ROSAT, ASCA, and Chandra. Our VLA data include the first {lambda} = 400 cm (74 MHz) continuum image of W51 at high resolution (88''). The 400 cm image shows non-thermal emission surrounding the G49.2-0.3 H II region, and a compact source of non-thermal emission (W51B{sub N}T) coincident with the previously-identified OH (1720 MHz) maser spots, non-thermal 21 and 90 cm emission, and a hard X-ray source. W51B{sub N}T falls within the region of high likelihood for the position of TeV {gamma}-ray emission. Using the VLBA, three OH (1720 MHz) maser spots are detected in the vicinity of W51B{sub N}T with sizes of 60-300 AU and Zeeman effect magnetic field strengths of 1.5-2.2 mG. The multiwavelength data demonstrate that the northern end of the W51B H II region complex has been partly enveloped by the advancing W51C SNR and this interaction explains the presence of W51B{sub N}T and the OH masers. This interaction also appears in the thermal molecular gas which partially encircles W51B{sub N}T and exhibits narrow pre-shock ({Delta}v {approx} 5 km s{sup -1}) and broad post-shock ({Delta}v {approx} 20 km s{sup -1}) velocity components. RADEX radiative transfer modeling of these two components yield physical conditions consistent with the passage of a non-dissociative C-type shock. Confirmation of the W51B/W51C interaction provides additional evidence in favor of this region being one of the best candidates for hadronic particle acceleration known thus far.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2013

TEARING THE VEIL: INTERACTION OF THE ORION NEBULA WITH ITS NEUTRAL ENVIRONMENT

We present H I 21 cm observations of the Orion Nebula, obtained with the Karl G. Jansky Very Large Array, at an angular resolution of 7.''2 Multiplication-Sign 5.''7 and a velocity resolution of 0.77 km s{sup -1}. Our data reveal H I absorption in the Veil toward the radio continuum of the H II region, and H I emission arising from the Orion Bar photon-dominated region (PDR) and from the Orion-KL outflow. In the Orion Bar PDR, the H I signal peaks in the same layer as the H{sub 2} near-infrared vibrational line emission, in agreement with models of the photodissociation of H{sub 2}. The gas temperature in this region is approximately 540 K, and the H I abundance in the interclump gas in the PDR is 5%-10% of the available hydrogen nuclei. Most of the gas in this region therefore remains molecular. Mechanical feedback on the Veil manifests itself through the interaction of ionized flow systems in the Orion Nebula, in particular the Herbig-Haro object HH 202, with the Veil. These interactions give rise to prominent blueward velocity shifts of the gas in the Veil. The unambiguous evidence for interaction of this flow system with the Veil shows that the distance between the Veil and the Trapezium stars needs to be revised downward to about 0.4 pc. The depth of the ionized cavity is about 0.7 pc, which is much smaller than the depth and the lateral extent of the Veil. Our results reaffirm the blister model for the M42 H II region, while also revealing its relation to the neutral environment on a larger scale.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1995

H110 alpha observations of Sagittarius A West: Ionized gas at peculiar velocities at the galactic center

We present Very Large Array measurements of H110 alpha radio recombination line emission from Sgr A West with a resolution of 11 x 20 arcsec. These observations detected a number of new kinematic components showing a dramatically different velocity field than expected from circular motion of ionized gas in Sgr A West about the dynamical center of the Galaxy. Recent high-resolution molecular observations show a cloud of absorbing gas at -180 km/s within 30 arcsec of the Galactic center. We find evidence of an ionized counterpart to this highly blueshifted molecular gas. This result places this highly blueshifted neutral gas in a hot UV dominated environment of the Galactic center. We suggest that the blueshifted clouds are photoionized externally by the intense UV radiation field at the Galactic center. We also detect H110 alpha emission from large-scale linear features known as the 'streamers', which run primarily perpendicular to the Galactic plane and lie exterior to the 'three-arm' spiral structure of Sgr A West and the circumstellar disk. These observations support an earlier suggestion that the streamers are thermal features whose kniematics deviate from circular motion.

Yusef-Zadeh, Farhad↗

NASA NTRS1994

A bipolar outflow of ionized gas in K3-50A: H76 alpha radio recombination line and continuum observations of K3-50

The H II regions near K3-50 (G70.3 + 1.6) have been imaged at high angular resolution (approximately 1 sec .3) in the continuum and the recombination lines H76(sub alpha and He76(sub alpha) using the Very Large Array (VLA). The helium line is detected in only the brightest component K3-50A while the hydrogen line is detected in three components (K3-50A, B and C1). K3-50A shows a pronounced velocity gradient of approximately 150 km/sec/pc along its major axis (P.A. = 160 deg); in addition a wide range of line widths are observed, from 20 to 65 km/sec. Kinematics from the line data and the morphology of the continuum emission suggest that the ionized material associated with K3-50A is undergoing a high-velocity bipolar outflow.

Depree, C. G.↗