Accurate positions of H2O masers in the Large Magellanic Cloud

Lazendić, J. S.; Whiteoak, J. B.; Klamer, I. J.; Harbison, P. D.; Kuiper, T. B. H.

doi:10.1046/j.1365-8711.2002.05251.x

Cited by 34 publications

(72 citation statements)

References 18 publications

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“…As evidenced by both the spectral features (ice and silicate absorption) and the radiative transfer models, the sources in this catalog are young, embedded massive YSOs. The youth of one source, YSO 053929.21−694719.0, is further supported by its associate H 2 O maser emission (Lazendic et al 2002).…”

Section: Target Selection and Makeupmentioning

confidence: 83%

The Evolution of Massive Young Stellar Objects in the Large Magellanic Cloud. Ii. Thermal Processing of Circumstellar Ices

Seale

Looney

Chen

et al. 2010

ApJ

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We present Spitzer Space Telescope spectroscopy of the CO 2 ice absorption feature at 15.2 μm toward 41 high-mass young stellar objects in the Large Magellanic Cloud (LMC). As the shape of the CO 2 absorption profile is a measure of both the composition and thermal history of the ice, we have performed a decomposition of the spectral profiles to determine the nature of the CO 2 ice. We fit the absorption profiles to laboratory analogues of ice spectra with two different methods: (1) a five-component fit with polar and apolar ices and (2) a two-component fit with a polar and an annealed H 2 O:CH 3 OH:CO 2 ice mixture. Many of the LMC sources have a pronounced double peak in their CO 2 feature profiles analogous to that seen from pure CO 2 or annealed CO 2 laboratory ice mixtures; these represent the first direct detections of the characteristic double peak in an extragalactic environment. Fits to annealed laboratory ices suggest that the ices around massive LMC young stellar objects (YSOs) have been warmed and thermally processed. We find that a majority of the CO 2 is embedded in a polar ice matrix; however, the observations suggest that a lower fraction of CO 2 is locked in polar ices in the LMC compared to the Milky Way, which is in agreement with the proposed lower LMC abundance of water ice. In addition, we find that the ices are best fit with laboratory ice mixtures composed of less than 50% methanol, and most absorption spectra can be fit by ices with no methanol. Finally, we corroborate mounting evidence of an enhanced CO 2 ice abundance in the LMC relative to the Milky Way, and determine a CO 2 /H 2 O ratio of 0.33 ± 0.01 by combining the column densities of these observations with those in the literature.

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Section: Target Selection and Makeupmentioning

confidence: 83%

The Evolution of Massive Young Stellar Objects in the Large Magellanic Cloud. Ii. Thermal Processing of Circumstellar Ices

Seale

Looney

Chen

et al. 2010

ApJ

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“…2. Open blue squares and red triangles in the CO(4-3) map show the position of stars with a spectral type of O7 or earlier and O7 to B1, respectively, from Fariña et al (2009), the filled blue star marks the position of LMC X-1, the blue asterisks are compact H ii regions (Indebetouw et al 2004), and the red diamond marks the position of an H 2 O maser (Lazendic et al 2002).…”

Section: Resultsmentioning

confidence: 99%

Velocity resolved [C ii], [C i], and CO observations of the N159 star-forming region in the Large Magellanic Cloud: a complex velocity structure and variation of the column densities

Okada

Requeña-Torres

Güsten

et al. 2015

A&A

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Context. The [C ii] 158 µm fine structure line is one of the dominant cooling lines in star-forming active regions. Together with models of photon-dominated regions, the data is used to constrain the physical properties of the emitting regions, such as the density and the radiation field strength. According to the modeling, the [C ii] 158 µm line integrated intensity compared to the CO emission is expected to be stronger in lower metallicity environments owing to lower dust shielding of the UV radiation, a trend that is also shown by spectral-unresolved observations. In the commonly assumed clumpy UV-penetrated cloud scenario, the models predict a [C ii] line profile similar to that of CO. However, recent spectral-resolved observations by Herschel/HIFI and SOFIA/GREAT (as well as the observations presented here) show that the velocity resolved line profile of the [C ii] emission is often very different from that of CO lines, indicating a more complex origin of the line emission including the dynamics of the source region. Aims. The Large Magellanic Cloud (LMC) provides an excellent opportunity to study in great detail the physics of the interstellar medium (ISM) in a low-metallicity environment by spatially resolving individual star-forming regions. The aim of our study is to investigate the physical properties of the star-forming ISM in the LMC by separating the origin of the emission lines spatially and spectrally. In this paper, we focus on the spectral characteristics and the origin of the emission lines, and the phases of carbon-bearing species in the N159 star-forming region in the LMC. Methods. We mapped a 4 ′ ×(3 ′ -4 ′ ) region in N159 in [C ii] 158 µm and [N ii] 205 µm with the GREAT instrument on board SOFIA. We also observed CO(3-2), (4-3), (6-5), 13 CO(3-2), and [C i] 3 P 1 -3 P 0 and 3 P 2 -3 P 1 with APEX. All spectra are velocity resolved. Results. The emission of all transitions observed shows a large variation in the line profiles across the map and in particular between the different species. At most positions the [C ii] emission line profile is substantially wider than that of CO and [C i]. We estimated the fraction of the [C ii] integrated line emission that cannot be fitted by the CO line profile to be 20% around the CO cores, and up to 50% at the area between the cores, indicating a gas component that has a much larger velocity dispersion than the ones probed by the CO and [C i] emission. We derived the relative contribution from C + , C, and CO to the column density in each velocity bin. The result clearly shows that the contribution from C + dominates the velocity range far from the the velocities traced by the dense molecular gas. Spatially, the region located between the CO cores of N159 W and E has a higher fraction of C + over the whole velocity range. We estimate the contribution of the ionized gas to the [C ii] emission using the ratio to the [N ii] emission, and find that the ionized gas contributes ≤ 19% to the [C ii] emission at its peak position, and ≤ 15% over the whol...

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“…We detect the three transitions of para-H 2 CO for the first time. The kinetic temperature derived from para-H 2 CO (3 21 -2 20 /3 03 -2 02 ) is ∼54 K. N113 is the LMC star forming region with the most luminous 22 GHz H 2 O maser (Whiteoak & Gardner 1986;Lazendic et al 2002;Oliveira et al 2006), not quite as spectacular as 30 Dor, but hosts a few bright HII regions whose stellar energy feedback is likely to have elevated its temperature, thus leading to the second highest T kin value. The spatial density derived from para-H 2 CO 3 03 -2 02 /C 18 O 2-1 (ratio data from Wang et al (2009) and Heikkilä et al (1998), assuming that the para-H 2 CO 3 03 -2 02 /C 18 O 2-1 ratio at the SEST beam size, ∼23 ′′ , is similar to that in the APEX beam size, ∼30…”

Section: N113mentioning

confidence: 99%

Kinetic temperature of massive star-forming molecular clumps measured with formaldehyde

Tang

Henkel

Chen

et al. 2017

A&A

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Context. The kinetic temperature of molecular clouds is a fundamental physical parameter affecting star formation and the initial mass function. The Large Magellanic Cloud (LMC), the closest star forming galaxy with low metallicity, provides an ideal laboratory to study star formation in such an environment. Aims. The classical dense molecular gas thermometer NH 3 is rarely available in a low metallicity environment because of photoionization and a lack of nitrogen atoms. Our goal is to directly measure the gas kinetic temperature with formaldehyde toward six star-forming regions in the LMC. Methods. Three rotational transitions (J K A K C = 3 03 -2 02 , 3 22 -2 21 , and 3 21 -2 20 ) of para-H 2 CO near 218 GHz were observed with the Atacama Pathfinder EXperiment (APEX) 12 m telescope toward six star forming regions in the LMC. Those data are complemented by C 18 O 2-1 spectra. Results. Using non-LTE modeling with RADEX, we derive the gas kinetic temperature and spatial density, using as constraints the measured para-H 2 CO 3 21 -2 20 /3 03 -2 02 and para-H 2 CO 3 03 -2 02 /C 18 O 2-1 ratios. Excluding the quiescent cloud N159S, where only one para-H 2 CO line could be detected, the gas kinetic temperatures derived from the preferred para-H 2 CO 3 21 -2 20 /3 03 -2 02 line ratios range from 35 to 63 K with an average of 47 ± 5 K (errors are unweighted standard deviations of the mean). Spatial densities of the gas derived from the para-H 2 CO 3 03 -2 02 /C 18 O 2-1 line ratios yield 0.4 -2.9 × 10 5 cm −3 with an average of 1.5 ± 0.4 × 10 5 cm −3 . Temperatures derived from the para-H 2 CO line ratio are similar to those obtained with the same method from Galactic star forming regions and agree with results derived from CO in the dense regions (n(H 2 ) > 10 3 cm −3 ) of the LMC. A comparison of kinetic temperatures derived from para-H 2 CO with those from the dust also shows good agreement. This suggests that the dust and para-H 2 CO are well mixed in the studied star forming regions. A comparison of kinetic temperatures derived from para-H 2 CO 3 21 -2 20 /3 03 -2 02 and NH 3 (2,2)/(1,1) shows, however, a drastic difference. In the star forming region N159W, the gas temperature derived from the NH 3 (2,2)/(1,1) line ratio is ∼16 K (Ott et al. 2010), which is only half the temperature derived from para-H 2 CO and the dust. Furthermore, ammonia shows a very low abundance in a 30 ′′ beam. Apparently, ammonia only survives in the most shielded pockets of dense gas not yet irradiated by UV photons, while formaldehyde, less affected by photodissociation, is more widespread and is also sampling regions more exposed to the radiation of young massive stars. A correlation between the gas kinetic temperatures derived from para-H 2 CO and infrared luminosity, represented by the 250 µm flux, suggests that the kinetic temperatures traced by para-H 2 CO are correlated with the ongoing massive star formation in the LMC.

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Accurate positions of H2O masers in the Large Magellanic Cloud

Cited by 34 publications

References 18 publications

The Evolution of Massive Young Stellar Objects in the Large Magellanic Cloud. Ii. Thermal Processing of Circumstellar Ices

The Evolution of Massive Young Stellar Objects in the Large Magellanic Cloud. Ii. Thermal Processing of Circumstellar Ices

Velocity resolved [C ii], [C i], and CO observations of the N159 star-forming region in the Large Magellanic Cloud: a complex velocity structure and variation of the column densities

Kinetic temperature of massive star-forming molecular clumps measured with formaldehyde

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