790 research outputs found
Subarcsecond Imaging of the NGC 6334 I(N) Protocluster: Two Dozen Compact Sources and a Massive Disk Candidate
Using the SMA and VLA, we have imaged the massive protocluster NGC6334I(N) at
high angular resolution (0.5"~650AU) from 6cm to 0.87mm, detecting 18 new
compact continuum sources. Three of the new sources are coincident with
previously-identified water masers. Together with the previously-known sources,
these data bring the number of likely protocluster members to 25 for a
protostellar density of ~700 pc^-3. Our preliminary measurement of the
Q-parameter of the minimum spanning tree is 0.82 -- close to the value for a
uniform volume distribution. All of the (nine) sources with detections at
multiple frequencies have SEDs consistent with dust emission, and two (SMA1b
and SMA4) also have long wavelength emission consistent with a central
hypercompact HII region. Thermal spectral line emission, including CH3CN, is
detected in six sources: LTE model fitting of CH3CN(J=12-11) yields
temperatures of 72-373K, confirming the presence of multiple hot cores. The
fitted LSR velocities range from -3.3 to -7.0 km/s, with an unbiased mean
square deviation of 2.05 km/s, implying a dynamical mass of 410+-260 Msun for
the protocluster. From analysis of a wide range of hot core molecules, the
kinematics of SMA1b are consistent with a rotating, infalling Keplerian disk of
diameter 800AU and enclosed mass of 10-30 Msun that is perpendicular (within 1
degree) to the large-scale bipolar outflow axis. A companion to SMA1b at a
projected separation of 0.45" (590AU; SMA1d), which shows no evidence of
spectral line emission, is also confirmed. Finally, we detect one 218.440GHz
and several 229.7588GHz Class-I methanol masers.Comment: 54 pages, 11 figures. Accepted for publication in The Astrophysical
Journal. Version 2: Keywords updated, and three "in press" citations updated
to journal reference. Version 3: corrected the error in the quantum numbers
of the 218 GHz methanol transition in the text and in Table 8. For a PDF
version with full-resolution figures, see
http://www.cv.nrao.edu/~thunter/papers/ngc6334in2014.pd
First Results from a 1.3 cm EVLA Survey of Massive Protostellar Objects: G35.03+0.35
We have performed a 1.3 centimeter survey of 24 massive young stellar objects
(MYSOs) using the Expanded Very Large Array (EVLA). The sources in the sample
exhibit a broad range of massive star formation signposts including Infrared
Dark Clouds (IRDCs), UCHII regions, and extended 4.5 micron emission in the
form of Extended Green Objects (EGOs). In this work, we present results for
G35.03+0.35 which exhibits all of these phenomena. We simultaneously image the
1.3 cm ammonia (1,1) through (6,6) inversion lines, four methanol transitions,
two H recombination lines, plus continuum at 0.05 pc resolution. We find three
areas of thermal ammonia emission, two within the EGO (designated the NE and SW
cores) and one toward an adjacent IRDC. The NE core contains an UCHII region
(CM1) and a candidate HCHII region (CM2). A region of non-thermal, likely
masing ammonia (3,3) and (6,6) emission is coincident with an arc of 44 GHz
methanol masers. We also detect two new 25 GHz Class I methanol masers. A
complementary Submillimeter Array 1.3 mm continuum image shows that the
distribution of dust emission is similar to the lower-lying ammonia lines, all
peaking to the NW of CM2, indicating the likely presence of an additional MYSO
in this protocluster. By modeling the ammonia and 1.3 mm continuum data, we
obtain gas temperatures of 20-220 K and masses of 20-130 solar. The diversity
of continuum emission properties and gas temperatures suggest that objects in a
range of evolutionary states exist concurrently in this protocluster.Comment: To appear in Astrophysical Journal Letters Special Issue on the EVLA.
16 pages, 3 figures. Includes the complete version of Figure 3, which was
unable to fit into the journal article due to the number of panel
The Protocluster G18.67+0.03: A Test Case for Class I Methanol Masers as Evolutionary Indicators for Massive Star Formation
We present high angular resolution Submillimeter Array (SMA) and Karl G.
Jansky Very Large Array (VLA) observations of the massive protocluster
G18.67+0.03. Previously targeted in maser surveys of GLIMPSE Extended Green
Objects (EGOs), this cluster contains three Class I methanol maser sources,
providing a unique opportunity to test the proposed role of Class I masers as
evolutionary indicators for massive star formation. The millimeter observations
reveal bipolar molecular outflows, traced by 13CO(2-1) emission, associated
with all three Class I maser sources. Two of these sources (including the EGO)
are also associated with 6.7 GHz Class II methanol masers; the Class II masers
are coincident with millimeter continuum cores that exhibit hot core line
emission and drive active outflows, as indicated by the detection of SiO(5-4).
In these cases, the Class I masers are coincident with outflow lobes, and
appear as clear cases of excitation by active outflows. In contrast, the third
Class I source is associated with an ultracompact HII region, and not with
Class II masers. The lack of SiO emission suggests the 13CO outflow is a relic,
consistent with its longer dynamical timescale. Our data show that massive
young stellar objects associated only with Class I masers are not necessarily
young, and provide the first unambiguous evidence that Class I masers may be
excited by both young (hot core) and older (UC HII) MYSOs within the same
protocluster.Comment: Astrophysical Journal Letters, accepted. emulateapj, 7 pages
including 4 figures and 1 table. Figures compressed. v2: coauthor affiliation
updated, emulateapj versio
VLA Observations of the "Eye of the Tornado"- the High Velocity \HII Region G357.63-0.06
The unusual supernova remnant candidate G357.7-0.1 and the compact source
G357.63-0.06 have been observed with the Very Large Array at 1.4 and 8.3 GHz.
The H92 line (8.3 GHz) was detected from the compact source with a
surprising velocity of about -210 km/s indicating that this source is an \HII
region, is most likely located at the Galactic center, and is unrelated to the
SNR. The \HI absorption line (1.4 GHz) data toward these sources supports this
picture and suggests that G357.7-0.1 lies farther away than the Galactic
center.Comment: Latex, 14 pages including 4 figures. Accepted to A
Spatial Variations in Galactic H I Structure on AU-Scales Toward 3C 147 Observed with the Very Long Baseline Array
This paper reports dual-epoch, Very Long Baseline Array observations of H I
absorption toward 3C 147. One of these epochs (2005) represents new
observations while one (1998) represents the reprocessing of previous
observations to obtain higher signal-to-noise results. Significant H I opacity
and column density variations, both spatially and temporally, are observed with
typical variations at the level of \Delta\tau ~ 0.20 and in some cases as large
as \Delta\tau ~ 0.70, corresponding to column density fluctuations of order 5 x
10^{19} cm^{-2} for an assumed 50 K spin temperature. The typical angular scale
is 15 mas; while the distance to the absorbing gas is highly uncertain, the
equivalent linear scale is likely to be about 10 AU. Approximately 10% of the
face of the source is covered by these opacity variations, probably implying a
volume filling factor for the small-scale absorbing gas of no more than about
1%. Comparing our results with earlier results toward 3C 138 (Brogan et al.),
we find numerous similarities, and we conclude that small-scale absorbing gas
is a ubiquitous phenomenon, albeit with a low probability of intercept on any
given line of sight. Further, we compare the volumes sampled by the line of
sight through the Galaxy between our two epochs and conclude that, on the basis
of the motion of the Sun alone, these two volumes are likely to be
substantially different. In order to place more significant constraints on the
various models for the origin of these small-scale structures, more frequent
sampling is required in any future observations.Comment: 16 pages with 10 figures in 24 files; AASTeX format; accepted by A
A Class I and Class II Methanol Maser Survey of Extended Green Objects (EGOs) from the GLIMPSE Survey
We present the results of a high angular resolution Very Large Array (VLA)
Class I 44 GHz and Class II 6.7 GHz methanol maser survey of a sample of ~20
massive young stellar object (MYSO) outflow candidates selected on the basis of
extended 4.5 micron emission in Spitzer Galactic Legacy Infrared Mid-Plane
Survey Extraordinaire (GLIMPSE) images. These 4.5 micron-selected candidates
are referred to as extended green objects (EGOs), for the common coding of this
band as green in three-color IRAC images. The detection rate of 6.7 GHz Class
II methanol masers, which are associated exclusively with massive YSOs, towards
EGOs is greater than ~64%--nearly double the detection rate of surveys using
other MYSO selection criteria. The detection rate of Class I 44 GHz methanol
masers, which trace molecular outflows, is ~89% towards EGOs associated with
6.7 GHz methanol masers. The two types of methanol masers exhibit different
spatial distributions: 6.7 GHz masers are centrally concentrated and usually
coincide with 24 micron emission, while 44 GHz masers are widely distributed
and generally trace diffuse 4.5 micron features. We also present results of a
complementary James Clerk Maxwell Telescope (JCMT) single-pointing molecular
line survey of EGOs in the outflow tracers HCO+(3-2) and SiO(5-4). The HCO+
line profiles and high SiO detection rate (90%) are indicative of the presence
of active outflows. No 44 GHz continuum emission is detected at the 5 mJy/beam
(5 sigma) level towards 95% of EGOs surveyed, excluding bright ultracompact HII
regions as powering sources for the 4.5 micron outflows. The results of our
surveys constitute strong evidence that EGOs are young, massive YSOs, with
active outflows, presumably powered by ongoing accretion.Comment: Accepted, ApJ. 73 pages, 5 figures, plus full content of two online
figure sets and two online-only data tables. Version with full resolution
figures is available at
http://www.astro.wisc.edu/glimpse/EGO_methanol_maser_surve
- …