scholarly journals Herschel spectroscopy of massive young stellar objects in the Magellanic Clouds

2019 ◽  
Vol 490 (3) ◽  
pp. 3909-3935
Author(s):  
J M Oliveira ◽  
J Th van Loon ◽  
M Sewiło ◽  
M-Y Lee ◽  
V Lebouteiller ◽  
...  
Keyword(s):  
Line Emission ◽  
Far Infrared ◽  
Magellanic Clouds ◽  
Young Stellar Objects ◽  
Stellar Objects ◽  
Heating Efficiency ◽  
Photodetector Array ◽  
The Galaxy ◽  
Low Metallicity ◽  
Ir Emission

ABSTRACT We present Herschel Space Observatory Photodetector Array Camera and Spectrometer (PACS) and Spectral and Photometric Imaging Receiver Fourier Transform Spectrometer (SPIRE FTS) spectroscopy of a sample of 20 massive Young Stellar Objects (YSOs) in the Large and Small Magellanic Clouds (LMC and SMC). We analyse the brightest far-infrared (far-IR) emission lines, that diagnose the conditions of the heated gas in the YSO envelope and pinpoint their physical origin. We compare the properties of massive Magellanic and Galactic YSOs. We find that [O i] and [C ii] emission, that originates from the photo-dissociation region associated with the YSOs, is enhanced with respect to the dust continuum in the Magellanic sample. Furthermore the photoelectric heating efficiency is systematically higher for Magellanic YSOs, consistent with reduced grain charge in low metallicity environments. The observed CO emission is likely due to multiple shock components. The gas temperatures, derived from the analysis of CO rotational diagrams, are similar to Galactic estimates. This suggests a common origin to the observed CO excitation, from low-luminosity to massive YSOs, both in the Galaxy and the Magellanic Clouds. Bright far-IR line emission provides a mechanism to cool the YSO environment. We find that, even though [O i], CO, and [C ii] are the main line coolants, there is an indication that CO becomes less important at low metallicity, especially for the SMC sources. This is consistent with a reduction in CO abundance in environments where the dust is warmer due to reduced ultraviolet-shielding. Weak H2O and OH emission is detected, consistent with a modest role in the energy balance of wider massive YSO environments.

Resolved star formation in the metal-poor star-forming region Magellanic Bridge C

2020 ◽  
Vol 499 (2) ◽  
pp. 2534-2553
Author(s):  
Venu M Kalari ◽  
Monica Rubio ◽  
Hugo P Saldaño ◽  
Alberto D Bolatto
Keyword(s):  
Star Formation ◽  
Infrared Imaging ◽  
Far Infrared ◽  
Young Stellar Objects ◽  
Molecular Gas ◽  
Stellar Objects ◽  
Filamentary Structure ◽  
Star Forming ◽  
The Galaxy ◽  
Pms Stars

ABSTRACT Magellanic Bridge C (MB-C) is a metal-poor (∼1/5 Z⊙) low-density star-forming region located 59 kpc away in the Magellanic Bridge, offering a resolved view of the star formation process in conditions different to the Galaxy. From Atacama Large Millimetre Array CO (1–0) observations, we detect molecular clumps associated with candidate young stellar objects (YSOs), pre-main sequence (PMS) stars, and filamentary structure identified in far-infrared imaging. YSOs and PMS stars form in molecular gas having densities between 17 and 200 M⊙ pc−2, and have ages between ≲0.1 and 3 Myr. YSO candidates in MB -C have lower extinction than their Galactic counterparts. Otherwise, our results suggest that the properties and morphologies of molecular clumps, YSOs, and PMS stars in MB -C present no patent differences with respect to their Galactic counterparts, tentatively alluding that the bottleneck to forming stars in regions similar to MB-C is the conversion of atomic gas to molecular.

scholarly journals Far-IR Spectrophotometry of HH Flows with the ISO Long-Wavelength Spectrometer

1997 ◽  
Vol 182 ◽  
pp. 111-120
Author(s):  
R. Liseau ◽  
T. Giannini ◽  
B. Nisini ◽  
P. Saraceno ◽  
L. Spinoglio ◽  
...  
Keyword(s):  
Mass Loss ◽  
Line Emission ◽  
Young Stellar Objects ◽  
Stellar Objects ◽  
Star Forming ◽  
Star Forming Regions ◽  
Shock Models ◽  
Ir Spectrophotometry ◽  
Hh Objects ◽  
Loss Rates

Full Iso-Lws spectral scans between about 45 to 190 μm of 17 individual HH objects in 7 star forming regions have revealed essentially only [O I] 63 μm line emission, implying that the Fircooling of these objects is totally dominated by this line alone. In this case, J-shock models can be used to determine the mass loss rates of the HH exciting sources. These mass loss rates are in reasonably good agreement with those estimated for the accompanying CO flows, providing first observational evidence that HH and molecular flows are driven by the same agent. The Lmech – Lbol relation, based on our results with the Lws, implies that young stellar objects of lower mass are loosing mass at relatively higher rates than their more massive counterparts.

scholarly journals Hidden or missing outflows in highly obscured galaxy nuclei?

2019 ◽  
Vol 623 ◽  
pp. A29 ◽  
Author(s):  
N. Falstad ◽  
F. Hallqvist ◽  
S. Aalto ◽  
S. König ◽  
S. Muller ◽  
...  
Keyword(s):  
Line Emission ◽  
Far Infrared ◽  
Spectral Lines ◽  
Absorption Lines ◽  
Wide Angle ◽  
Vibrationally Excited ◽  
Molecular Outflows ◽  
Luminous Infrared Galaxies ◽  
The Galaxy ◽  
Central Regions

Context. Understanding the nuclear growth and feedback processes in galaxies requires investigating their often obscured central regions. One way to do this is to use (sub)millimeter line emission from vibrationally excited HCN (HCN-vib), which is thought to trace warm and highly enshrouded galaxy nuclei. It has been suggested that the most intense HCN-vib emission from a galaxy is connected to a phase of nuclear growth that occurs before the nuclear feedback processes have been fully developed. Aims. We aim to investigate if there is a connection between the presence of strong HCN-vib emission and the development of feedback in (ultra)luminous infrared galaxies ((U)LIRGs). Methods. We collected literature and archival data to compare the luminosities of rotational lines of HCN-vib, normalized to the total infrared luminosity, to the median velocities of 119 μm OH absorption lines, potentially indicating outflows, in a total of 17 (U)LIRGs. Results. The most HCN-vib luminous systems all lack signatures of significant molecular outflows in the far-infrared OH absorption lines. However, at least some of the systems with bright HCN-vib emission have fast and collimated outflows that can be seen in spectral lines at longer wavelengths, including in millimeter emission lines of CO and HCN (in its vibrational ground state) and in radio absorption lines of OH. Conclusions. We conclude that the galaxy nuclei with the highest LHCN − vib/LIR do not drive wide-angle outflows that are detectable using the median velocities of far-infrared OH absorption lines. This is possibly because of an orientation effect in which sources oriented in such a way that their outflows are not along our line of sight also radiate a smaller proportion of their infrared luminosity in our direction. It could also be that massive wide-angle outflows destroy the deeply embedded regions responsible for bright HCN-vib emission, so that the two phenomena cannot coexist. This would strengthen the idea that vibrationally excited HCN traces a heavily obscured stage of evolution before nuclear feedback mechanisms are fully developed.

scholarly journals Validating post-AGB candidates in the LMC and SMC using SALT spectra

2020 ◽  
Vol 641 ◽  
pp. A142
Author(s):  
R. Szczerba ◽  
M. Hajduk ◽  
Ya. V. Pavlenko ◽  
B. J. Hrivnak ◽  
B. M. Kaminsky ◽  
...  
Keyword(s):  
South African ◽  
Stellar Atmosphere ◽  
Magellanic Clouds ◽  
Emission Lines ◽  
Young Stellar Objects ◽  
Agb Stars ◽  
Large Telescope ◽  
Stellar Objects ◽  
Effective Temperatures ◽  
The Continuum

We selected a sample of post-AGB candidates in the Magellanic Clouds on the basis of their near- and mid-infrared colour characteristics. Fifteen of the most optically bright post-AGB candidates were observed with the South African Large Telescope in order to determine their stellar parameters and thus to validate or discriminate their nature as post-AGB objects in the Magellanic Clouds. The spectral types of absorption-line objects were estimated according to the MK classification, and effective temperatures were obtained by means of stellar atmosphere modelling. Emission-line objects were classified on the basis of the fluxes of the emission lines and the presence of the continuum. Out of 15 observed objects, only 4 appear to be genuine post-AGB stars (27%). In the SMC, 1 out of 4 is post-AGB, and in the LMC, 3 out 11 are post-AGB objects. Thus, we can conclude that the selected region in the colour-colour diagram, while selecting the genuine post-AGB objects, overlaps severely with other types of objects, in particular young stellar objects and planetary nebulae. Additional classification criteria are required to distinguish between post-AGB stars and other types of objects. In particular, photometry at far-IR wavelengths would greatly assist in distinguishing young stellar objects from evolved ones. On the other hand, we showed that the low-resolution optical spectra appear to be sufficient to determine whether the candidates are post-AGB objects.

scholarly journals Characterising the Protostellar Population of the Magellanic Clouds with VLT/SINFONI

2015 ◽  
Vol 11 (S315) ◽  
Author(s):  
Jacob Ward ◽  
Joana Oliveira ◽  
Jacco van Loon ◽  
Marta Sewilo
Keyword(s):  
Star Formation ◽  
Milky Way ◽  
Large Magellanic Cloud ◽  
Magellanic Cloud ◽  
Magellanic Clouds ◽  
Emission Lines ◽  
Young Stellar Objects ◽  
Small Magellanic Cloud ◽  
Stellar Objects ◽  
Accretion Rates

AbstractAt distances of ~50 kpc and ~60 kpc for the Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC) respectively the Magellanic Clouds present us with a unique opportunity to study star formation in environments outside our own galaxy. Through Spitzer and Herschel photometry and spectroscopy, samples of Young Stellar Objects (YSOs) have been selected and spectroscpically confirmed in the Magellanic Clouds. Here we present some of the key results of our SINFONI K-band observations towards massive YSOs in the Magellanic Clouds. We resolve a number of Spitzer sources into multiple, previously unresolved, components and our analysis of emission lines suggest higher accretion rates and different disc properties compared with massive YSOs in the Milky Way.

scholarly journals Formation of high-mass stars in an isolated environment in the Large Magellanic Cloud

2019 ◽  
Vol 71 (2) ◽  
Author(s):  
Ryohei Harada ◽  
Toshikazu Onishi ◽  
Kazuki Tokuda ◽  
Sarolta Zahorecz ◽  
Annie Hughes ◽  
...  
Keyword(s):  
Star Formation ◽  
Large Magellanic Cloud ◽  
Magellanic Cloud ◽  
Young Stellar Objects ◽  
High Mass ◽  
Mass Star ◽  
Giant Molecular Clouds ◽  
Stellar Objects ◽  
Stellar Cluster ◽  
The Galaxy

Abstract The aim of this study is to characterize the distribution and basic properties of the natal gas associated with high-mass young stellar objects (YSOs) in isolated environments in the Large Magellanic Cloud. High-mass stars usually form in giant molecular clouds (GMCs) as part of a young stellar cluster, but some OB stars are observed far from GMCs. By examining the spatial coincidence between the high-mass YSOs and 12CO (J = 1–0) emission detected by NANTEN and Mopra observations, we selected ten high-mass YSOs that are located away from any of the NANTEN clouds but are detected by the Mopra pointed observations. The ALMA observations revealed that a compact molecular cloud whose mass is a few thousand solar masses or smaller is associated with the high-mass YSOs, which indicates that these compact clouds are the sites of high-mass star formation. The high density and high temperature throughout the clouds are explained by the severe photodissociation of CO due to the lower metallicity than in the Galaxy. The star formation efficiency ranges from several to as high as ∼40%, indicating efficient star formation in these environments. The enhanced turbulence may be a cause of the efficient star formation therein, as judged from the gas velocity information and the association with the lower density gas.

scholarly journals Modeling CO, CO2and H2O Ice Abundances in the Envelopes of Young Stellar Objects in the Magellanic Clouds

2017 ◽  
Vol 13 (S332) ◽  
pp. 47-53
Author(s):  
Tyler Pauly ◽  
Robin T. Garrod
Keyword(s):  
Radiation Field ◽  
Magellanic Clouds ◽  
Young Stellar Objects ◽  
Stellar Objects ◽  
Elemental Abundances ◽  
Grain Sizes ◽  
Chemical Models ◽  
Carbon Abundance ◽  
Absorption Features ◽  
Chemical Code

AbstractMassive young stellar objects (MYSOs) in the Magellanic Clouds (MCs) show infrared absorption features corresponding to significant abundances of CO, CO2and H2O ice along the line of sight, with the relative abundances of these ices varying between sources in the Magellanic Clouds and the Milky Way. We use our gas-grain chemical code MAGICKAL, with multiple grain sizes and grain temperatures, and further expand it with a treatment for increased interstellar radiation field intensity to model the elevated dust temperatures observed in the MCs. We also adjust the elemental abundances used in the chemical models, guided by observations of HII regions in these metal-poor satellite galaxies. With a grid of models, we are able to reproduce the relative ice fractions observed in MC MYSOs, indicating that metal depletion and elevated grain temperature are important drivers of the MYSO envelope ice composition. The observed shortfall in CO in the Small Magellanic Cloud can be explained by a combination of reduced carbon abundance and increased grain temperatures. The models indicate that a large variation in radiation field strength is required to match the range of observed LMC abundances.

scholarly journals Why binary interaction does not necessarily dominate the formation of Wolf-Rayet stars at low metallicity

2020 ◽  
Vol 634 ◽  
pp. A79 ◽  
Author(s):  
T. Shenar ◽  
A. Gilkis ◽  
J. S. Vink ◽  
H. Sana ◽  
A. A. C. Sander
Keyword(s):  
Mass Range ◽  
Magellanic Clouds ◽  
Initial Mass ◽  
Binary Interaction ◽  
Additional Contribution ◽  
Apparent Contradiction ◽  
Single Star ◽  
Binary Channel ◽  
The Galaxy ◽  
Low Metallicity

Context. Classical Wolf-Rayet (WR) stars are massive, hydrogen-depleted, post main-sequence stars that exhibit emission-line dominated spectra. For a given metallicity Z, stars exceeding a certain initial mass MsingleWR(Z) can reach the WR phase through intrinsic mass-loss or eruptions (single-star channel). In principle, stars of lower masses can reach the WR phase via stripping through binary interactions (binary channel). Because winds become weaker at low Z, it is commonly assumed that the binary channel dominates the formation of WR stars in environments with low metallicity such as the Small and Large Magellanic Clouds (SMC, LMC). However, the reported WR binary fractions of 30−40% in the SMC (Z = 0.002) and LMC (Z = 0.006) are comparable to that of the Galaxy (Z = 0.014), and no evidence for the dominance of the binary channel at low Z could be identified observationally. Here, we explain this apparent contradiction by considering the minimum initial mass MspecWR(Z) needed for the stripped product to appear as a WR star. Aims. By constraining MspecWR(Z) and MsingleWR(Z), we estimate the importance of binaries in forming WR stars as a function of Z. Methods. We calibrated MspecWR using the lowest-luminosity WR stars in the Magellanic Clouds and the Galaxy. A range of MsingleWR values were explored using various evolution codes. We estimated the additional contribution of the binary channel by considering the interval [MspecWR(Z), MsingleWR(Z)], which characterizes the initial-mass range in which the binary channel can form additional WR stars. Results. The WR-phenomenon ceases below luminosities of log L ≈ 4.9, 5.25, and 5.6 [L⊙] in the Galaxy, the LMC, and the SMC, respectively, which translates to minimum He-star masses of 7.5, 11, 17 M⊙ and minimum initial masses of MspecWR = 18, 23, 37 M⊙. Stripped stars with lower initial masses in the respective galaxies would tend not to appear as WR stars. The minimum mass necessary for self-stripping, MsingleWR(Z), is strongly model-dependent, but it lies in the range 20−30, 30−60, and ≳40 M⊙ for the Galaxy, LMC, and SMC, respectively. We find that that the additional contribution of the binary channel is a non-trivial and model-dependent function of Z that cannot be conclusively claimed to be monotonically increasing with decreasing Z. Conclusions. The WR spectral appearance arises from the presence of strong winds. Therefore, both MspecWR and MsingleWR increase with decreasing metallicity. Considering this, we show that one should not a-priori expect that binary interactions become increasingly important in forming WR stars at low Z, or that the WR binary fraction grows with decreasing Z.

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