413 research outputs found
Near-Infrared H2 and Continuum Survey of Extended Green Objects
The Spitzer GLIMPSE survey has revealed a number of "Extended Green Objects"
(EGOs) which display extended emission at 4.5 micron. These EGOs are potential
candidates for high mass protostellar outflows. We have used high resolution (<
1") H2 1-0 S(1) line, K, and H-band images from the United Kingdom Infrared
Telescope to study 34 EGOs to investigate their nature. We found that 12 EGOs
exhibit H2 outflows (two with chains of H2 knotty structures; five with
extended H2 bipolar structures; three with extended H2 lobes; two with pairs of
H2 knots). In the 12 EGOs with H2 outflows, three of them exhibit similar
morphologies between the 4.5 micron and H2 emission. However, the remaining 9
EGOs show that the H2 features are more extended than the continuum features,
and the H2 emission is seldom associated with continuum emission. Furthermore,
the morphologies of the near-infrared continuum and 4.5 micron emission are
similar to each other for those EGOs with K-band emission, implying that at
least a part of the IRAC-band continuum emission of EGOs comes from scattered
light from the embedded YSOs.Comment: accepted for publication in ApJ
Multiwavelength Observations of Massive Stellar Cluster Candidates in the Galaxy
The Galaxy appears to be richer in young, massive stellar clusters than
previously known, due to advances in infrared surveys which have uncovered
deeply embedded regions of star formation. Young, massive clusters can
significantly impact the surrounding interstellar medium (ISM) and hence radio
observations can also be an important tracer of their activity. Several hundred
cluster candidates are now known by examining survey data. Here we report on
multiwavelength observations of six of these candidates in the Galaxy. We
carried out 4.9 and 8.5 GHz VLA observations of the radio emission associated
with these clusters to obtain the physical characteristics of the surrounding
gas, including the Lyman continuum photon flux and ionized gas mass. Spitzer
Infrared Array Camera observations were also made of these regions, and provide
details on the stellar population as well as the dust continuum and polycyclic
aromatic hydrocarbon emission. When compared to the known young, massive
clusters in the Galaxy, the six cluster candidates have less powerful Lyman
ionizing fluxes and ionize less of the H II mass in the surrounding ISM.
Therefore, these cluster candidates appear to be more consistent with
intermediate-mass clusters (10^3-10^4 Msun).Comment: 39 pages, 20 figures. Accepted in the Astronomical Journal; to be
published Fall 201
The cometary HII regions of DR 21: Bow shocks or champagne flows or both?
We present deep Very Large Array H66 radio recombination line (RRL)
observations of the two cometary HII regions in DR 21. With these sensitive
data, we test the "hybrid" bow shock/champagne flow model previously proposed
for the DR 21 HII regions. The ionized gas down the tail of the southern HII
region is redshifted by up to ~30 km/s with respect to the ambient molecular
gas, as expected in the hybrid scenario. The RRL velocity structure, however,
reveals the presence of two velocity components in both the northern and
southern HII regions. This suggests that the ionized gas is flowing along
cone-like shells, swept-up by stellar winds. The observed velocity structure of
the well-resolved southern HII region is most consistent with a picture that
combines a stellar wind with stellar motion (as in bow shock models) along a
density gradient (as in champagne flow models). The direction of the implied
density gradient is consistent with that suggested by maps of dust continuum
and molecular line emission in the DR 21 region.Comment: 22 pages, 9 figures, 2 tables, accepted for publication in A&
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
Nanocomposite membranes with Au nanoparticles for dialysis-based catalytic reduction-separation of nitroaromatic compounds
Apart from the fact that nitroaromatic compounds (NARs) have toxic and
mutagenic characteristics, they are also essential substrates for the synthesis
of aromatic amines (AAMs). In this context, the present study presents a new
approach that enables NAR-contaminated wastewaters to be treated as a reagent
for the synthesis of AAMs. It involves the fabrication of anion exchange
membranes with Au nanoparticles (AuNPs) that simultaneously reduce
4-nitrophenol (4-NP) and separate the resultant 4-aminophenol (4-AP) via. the
dialysis mechanism. The nanocomposite membranes were prepared by
amino-modification of poly(vinyl chloride) films obtained in the presence of
cyclohexanone (CH) or tetrahydrofuran (THF), followed by Au(III) reduction
coupled-adsorption. The nanomaterials were analysed using scanning transmission
electron microscopy (STEM) and Fourier-transformation infrared spectroscopy
(FT-IR). The catalytic reaction was carried out in a dialysis unit, where the
concentration of 4-NP in the wastewater, and the concentration of separated
4-AP were monitored using UV-Vis spectroscopy. The nanocomposite membranes
formed using THF effectively reduced the 4-NP and separated the resultant 4-AP.
The yield of the 4-NP conversion reached 80% with a rate constant of 11.30 10-3
min-1. Based on the results, THF contributed to the formation of diffusion
paths in which the 4-NP was simultaneously separated and reduced
Digging into NGC 6334I(N): Multiwavelength Imaging of a Massive Protostellar Cluster
We present a high-resolution, multi-wavelength study of the massive
protostellar cluster NGC 6334I(N) that combines new spectral line data from the
Submillimeter Array (SMA) and VLA with a reanalysis of archival VLA continuum
data, 2MASS and Spitzer images. As shown previously, the brightest 1.3 mm
source SMA1 contains substructure at subarcsecond resolution, and we report the
first detection of SMA1b at 3.6 cm along with a new spatial component at 7 mm
(SMA1d). We find SMA1 (aggregate of sources a, b, c, and d) and SMA4 to be
comprised of free-free and dust components, while SMA6 shows only dust
emission. Our 1.5" resolution 1.3 mm molecular line images reveal substantial
hot-core line emission toward SMA1 and to a lesser degree SMA2. We find CH3OH
rotation temperatures of 165\pm 9 K and 145\pm 12 K for SMA1 and SMA2,
respectively. We estimate a diameter of 1400 AU for the SMA1 hot core emission,
encompassing both SMA1b and SMA1d, and speculate that these sources comprise a
>800 AU separation binary that may explain the previously-suggested precession
of the outflow emanating from the SMA1 region. The LSR velocities of SMA1,
SMA2, and SMA4 all differ by 1-2 km/s. Outflow activity from SMA1, SMA2, SMA4,
and SMA6 is observed in several molecules including SiO(5--4) and IRAC 4.5
micron emission; 24 micron emission from SMA4 is also detected. Eleven water
maser groups are detected, eight of which coincide with SMA1, SMA2, SMA4, and
SMA6. We also detect a total of 83 Class I CH3OH 44GHz maser spots which likely
result from the combined activity of many outflows. Our observations paint the
portrait of multiple young hot cores in a protocluster prior to the stage where
its members become visible in the near-infrared.Comment: Accepted to ApJ, 24 pages, a full high resolution version is
available at http://www.cv.nrao.edu/~cbrogan/ms.long.pd
Near-infrared H2 and continuum survey of extended green objects. II. Complete census for the northern Galactic plane
We discuss 94 Extended Green Objects (EGOs) in the northern Galactic plane cataloged by Cyganowski et al., based on near-infrared narrow H2 (2.122 μm) and continuum observations from the United Kingdom Infrared Telescope. This data set is three times larger than the one in our previous study and is unbiased by preselection. As discussed in the previous paper, the morphologies of the 4.5 μm emission generally resemble those of the near-infrared continuum, but are different from those of the H2 emission. Of our sample, only 28% of EGOs with H2 emission show similar morphologies between 4.5 μm and H2 emission. These results suggest that the 4.5 μm emission mainly comes from scattered continuum from the embedded young stellar objects, and partially from H2 emission. About half of EGOs are associated with H2 outflows, if the H 2 outflow incompleteness is considered. The H2 outflow detection rate for EGOs with K-band detections (61%) is significantly higher than for those without K-band detections (36%). This difference may be due to the fact that both H2 and K-band emissions are associated with outflows, i.e., H2 emission and K-band continuum are associated with shocks and outflow cavities, respectively. We also compared the correlation between the H2 outflows and Class I 44 GHz methanol masers from the literature. The methanol masers can be located upstream or downstream of the H2 outflows and some bright H2 spots or outflows are not associated with methanol masers, suggesting that methanol masers and H 2 emission trace different excitation conditions. © 2013. The American Astronomical Society. All rights reserved.
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
A Mid-Infrared Census of Star Formation Activity in Bolocam Galactic Plane Survey Sources
We present the results of a search for mid-infrared signs of star formation
activity in the 1.1 mm sources in the Bolocam Galactic Plane Survey (BGPS). We
have correlated the BGPS catalog with available mid-IR Galactic plane catalogs
based on the Spitzer Space Telescope GLIMPSE legacy survey and the Midcourse
Space Experiment (MSX) Galactic plane survey. We find that 44% (3,712 of 8,358)
of the BGPS sources contain at least one mid-IR source, including 2,457 of
5,067 (49%) within the area where all surveys overlap (10 deg < l < 65 deg).
Accounting for chance alignments between the BGPS and mid-IR sources, we
conservatively estimate that 20% of the BPGS sources within the area where all
surveys overlap show signs of active star formation. We separate the BGPS
sources into four groups based on their probability of star formation activity.
Extended Green Objects (EGOs) and Red MSX Sources (RMS) make up the highest
probability group, while the lowest probability group is comprised of
"starless" BGPS sources which were not matched to any mid-IR sources. The mean
1.1 mm flux of each group increases with increasing probability of active star
formation. We also find that the "starless" BGPS sources are the most compact,
while the sources with the highest probability of star formation activity are
on average more extended with large skirts of emission. A subsample of 280 BGPS
sources with known distances demonstrates that mass and mean H_2 column density
also increase with probability of star formation activity.Comment: 20 pages, 12 figures, 3 tables. Accepted for publication in ApJ. Full
Table 2 will be available online through Ap
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
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