Abstract
The Trifid Nebula is a young, nearby star-forming region where star formation is proposed to have been triggered by cloud–cloud collision (CCC), based on observations of molecular clouds. It ...offers a unique opportunity to test whether the CCC hypothesis is supported by the spatial distribution and star formation chronology of young stars. We present the first study of the optically visible pre-main sequence (PMS) population of the region using
ri
H
α
imaging and Gaia astrometry. Combined with an analysis of young stellar objects (YSOs) using infrared imaging, we capture the spatial distribution and star formation chronology of the young stellar population. From the analysis, 15 Flat/Class I YSOs, 46 Class II YSOs, and 41 accreting PMS stars are identified (diskless/non-accreting sources are not included in the analysis). The distance based on Gaia parallaxes is ∼1250 pc, significantly closer than previously reported. The Class II YSOs and PMS stars (∼1.5 Myr old) are spread toward the edge of the molecular clouds. They are slightly younger than the estimated crossing time of ∼2.7 Myr and closer to the estimated dynamical age ∼0.85 Myr. Younger Class I YSOs are more concentrated spatially. There exists a cavity devoid of young stars where the two clouds overlap. This evidence suggests that the current generation of stars formed after the collision of two clouds ∼1 Myr ago, and this result can be corroborated using future spectroscopic studies.
NGC 796 is a massive young cluster located 59 kpc from us in the diffuse intergalactic medium of the 1/5-1/10 Z☉ Magellanic Bridge, allowing us to probe variations in star formation and stellar ...evolution processes as a function of metallicity in a resolved fashion, and providing a link between resolved studies of nearby solar-metallicity and unresolved distant metal-poor clusters located in high-redshift galaxies. In this paper, we present adaptive optics griH imaging of NGC 796 (at 0 5, which is ∼0.14 pc at the cluster distance) along with optical spectroscopy of two bright members to quantify the cluster properties. Our aim is to explore whether star formation and stellar evolution vary as a function of metallicity by comparing the properties of NGC 796 to higher-metallicity clusters. We find an age of 20 − 5 + 12 Myr from isochronal fitting of the cluster main sequence in the color-magnitude diagram. Based on the cluster luminosity function, we derive a top-heavy stellar initial mass function (IMF) with a slope = 1.99 0.2, hinting at a metallicity and/or environmental dependence of the IMF, which may lead to a top-heavy IMF in the early universe. Study of the H emission-line stars reveals that classical Be stars constitute a higher fraction of the total B-type stars when compared with similar clusters at greater metallicity, providing some support to the chemically homogeneous theory of stellar evolution. Overall, NGC 796 has a total estimated mass of 990 200 M , and a core radius of 1.4 0.3 pc, which classifies it as a massive young open cluster, unique in the diffuse interstellar medium of the Magellanic Bridge.
ABSTRACT Using Gaia DR2 data, combined with OmegaCAM ground-based optical photometry from the Accretion Disc with OmegaCAM survey, and detailed radial velocity measurements from ESO-Gaia, we analyse ...in detail a 10 × 5 deg region around the Wolf–Rayet Star γ2 Vel, including the previously known clusters Gamma Vel and NGC2547. Using clustering analysis that considers positions, proper motions, and parallax, we discover six clusters or associations – four of which appear new. Analysis of the colour–magnitude diagram for these clusters shows that four of them formed coevally from the same molecular clouds 10 Myr ago, while NGC 2547 formed together with a newly discovered cluster 30 Myr ago. This study shows the incredible wealth of data provided by Gaia for the study of young stellar clusters.
Resolving the Core of R136 in the Optical Kalari, Venu M.; Horch, Elliott P.; Salinas, Ricardo ...
The Astrophysical journal,
08/2022, Letnik:
935, Številka:
2
Journal Article
Recenzirano
Odprti dostop
Abstract
The sharpest optical images of the R136 cluster in the Large Magellanic Cloud are presented, allowing us for the first time to resolve members of the central core, including R136a1, the ...most-massive star known. These data were taken using the Gemini speckle imager Zorro in medium-band filters with effective wavelengths similar to
BVRI
achieving angular resolutions between 30–40 mas. All stars previously known in the literature, having
V
< 16 mag within the central 2″ × 2″, were recovered. Visual companions (≥40 mas; 2000 au) were detected for the WN5h stars R136 a1 and a3. Photometry of the visual companion of a1 suggests it is of mid-O spectral type. Based on new photometric luminosities using the resolved Zorro imaging, the masses of the individual WN5h stars are estimated to be between 150 and 200
M
⊙
, lowering significantly the present-day masses of some of the most-massive stars known. These mass estimates are critical anchor points for establishing the stellar upper-mass function.
Abstract
We present a sample of 330 blue edge-on low surface brightness galaxies (ELSBGs). To understand the chemical evolution of ELSBGs, we derived the gas-phase abundance and the
α
/Fe ratio. ...Compared with star-forming galaxies, ELSBGs show a flatter trend in the mass–metallicity (
M
*
–
Z
) relation, which suggests that the oxygen abundance enhancement is inefficient. We focused on 77 ELSBGs with H
i
data and found that the closed-box model cannot explain their gas fraction and metallicity relation, which implies that infall and/or outflow is needed. We derived the
α
/Fe ratio of normal ELSBG (<10
9.5
M
⊙
) and massive ELSBG (> = 10
9.5
M
⊙
) using single stellar population grids from the MILES stellar library. The mean
α
/Fe ratios are 0.18 and 0.4 for normal ELSBG and massive ELSBG, respectively. We suggest that the long timescales of star formation and/or metal-rich gas outflow events caused by SNe Ia winds are likely to be responsible for the
α
-enhancement of massive ELSBGs.
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.
We present new sensitive CO(2-1) observations of the 30 Doradus region in the Large Magellanic Cloud. We identify a chain of three newly discovered molecular clouds that we name KN1, KN2, and KN3 ...lying within 2-14 pc in projection from the young massive cluster R136 in 30 Doradus. Excited H2 2.12 m emission is spatially coincident with the molecular clouds, but ionized Brγ emission is not. We interpret these observations as the tails of pillar-like structures whose ionized heads are pointing toward R136. Based on infrared photometry, we identify a new generation of stars forming within this structure.
ABSTRACT
Pristine_183.6849 + 04.8619 (P1836849) is an extremely metal-poor (Fe/H = −3.3 ± 0.1) star on a prograde orbit confined to the Galactic disc. Such stars are rare and may have their origins ...in protogalactic fragments that formed the early Milky Way, in low-mass satellites accreted later, or forming in situ in the Galactic plane. Here, we present a chemo-dynamical analysis of the spectral features between 3700−11 000 Å from a high-resolution spectrum taken during Science Verification of the new Gemini High-resolution Optical SpecTrograph. Spectral features for many chemical elements are analysed (Mg, Al, Si, Ca, Sc, Ti, Cr, Mn, Fe, Ni), and valuable upper limits are determined for others (C, Na, Sr, Ba). This main sequence star exhibits several rare chemical signatures, including (i) extremely low metallicity for a star in the Galactic disc, (ii) very low abundances of the light α-elements (Na, Mg, Si) compared to other metal-poor stars, and (iii) unusually large abundances of Cr and Mn, where Cr, Mn/FeNLTE > +0.5. A comparison to theoretical yields from supernova models suggests that two low-mass Population III objects (one 10 M⊙ supernova and one 17 M⊙ hypernova) can reproduce the abundance pattern well (reduced χ2 < 1). When this star is compared to other extremely metal-poor stars on quasi-circular, prograde planar orbits, differences in both chemistry and kinematics imply there is little evidence for a common origin. The unique chemistry of P1836849 is discussed in terms of the earliest stages in the formation of the Milky Way.
ABSTRACT The Gemini High-resolution Optical SpecTrograph (GHOST) is a new Echelle spectrograph available on the Gemini-South telescope as of Semester 2024A. We present the first high-resolution ...spectrum of the quasar J1449−1227 (redshift zem = 3.27) using data taken during the commissioning of GHOST. The observed quasar hosts an intervening iron-poor {Fe/H = −2.5} damped Lyman α system (DLA) at redshift z = 2.904. Taking advantage of the high spectral resolving power of GHOST (R ≈ 55 000), we are able to accurately model the metal absorption lines of the metal-poor DLA and find a supersolar Si/Fe, suggesting that the DLA gas is in an early stage of chemical enrichment. Using simple ionization models, we find that the large range in the C iv/Si iv column density ratio of individual components within the DLA’s high-ionization absorption profile can be reproduced by several metal-poor Lyman limit systems surrounding the low-ionization gas of the DLA. It is possible that this metal-poor DLA resides within a complex system of metal-poor galaxies or filaments with inflowing gas. The high spectral resolution, wavelength coverage, and sensitivity of GHOST make it an ideal spectrograph for characterizing the chemistry and kinematics of quasar absorption lines.
Abstract
We present high-resolution (0.″17 × 0.″14) Atacama Large Millimeter/submillimeter Array (ALMA) observations of the CO (6–5) line and 435
μ
m dust continuum emission within a ∼9″ × 9″ area ...centered on the nucleus of the galaxy NGC 5135. NGC 5135 is a well-studied luminous infrared galaxy that also harbors a Compton-thick active galactic nucleus (AGN). At the achieved resolution of 48 × 40 pc, the CO (6–5) and dust emissions are resolved into gas “clumps” along the symmetrical dust lanes associated with the inner stellar bar. The clumps have radii in the range of ∼45–180 pc and CO (6–5) line widths of ∼60–88
. The CO (6–5) to dust continuum flux ratios vary among the clumps and show an increasing trend with the Fe
ii
/Br
γ
ratios, which we interpret as evidence for supernova-driven shocked gas providing a significant contribution to the CO (6–5) emission. The central AGN is undetected in continuum, nor is it detected in CO (6–5) if its line velocity width is no less than ∼ 40
. We estimate that the AGN contributes at most 1% of the integrated CO (6–5) flux of 512 ± 24 Jy
within the ALMA field of view, which in turn accounts for ∼32% of the CO (6–5) flux of the whole galaxy.
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