31 research outputs found
Massive young stellar objects in the N66/NGC346 region of the SMC
We present HK spectra of three sources located in the N66 region of the Small
Magellanic Cloud. The sources display prominent stellar Br Gamma and extended
H2 emission, and exhibit infrared excesses at lambda > 2 micron. Based on their
spectral features, and photometric spectral energy distributions, we suggest
that these sources are massive young stellar objects (mYSOs). The findings are
interpreted as evidence of on-going high mass star formation in N66.Comment: Accepted for publication on Astronomy and Astrophysics Journal,
acceptance date 21/03/2018 (includes 12 pages, 5 figures
Pillars of creation amongst destruction: Star formation in molecular clouds near R136 in 30 Doradus
New sensitive CO(2-1) observations of the 30 Doradus region in the Large
Magellanic Cloud are presented. We identify a chain of three newly discovered
molecular clouds we name KN1, KN2 and KN3 lying within 2--14 pc in projection
from the young massive cluster R136 in 30 Doradus. Excited H 2.12m
emission is spatially coincident with the molecular clouds, but ionized
Br emission is not. We interpret these observations as the tails of
pillar-like structures whose ionized heads are pointing towards R136. Based on
infrared photometry, we identify a new generation of stars forming within this
structure.Comment: Accepted for publication in ApJ (includes 13 pages, 8 figures). For
higher resolution figures please see
http://www.das.uchile.cl/~vkalari/staplervk.pd
Understanding the chemical evolution of blue Edge-on Low Surface Brightness Galaxies
We present a sample of 330 blue edge-on low surface brightness galaxies
(ELSBGs). To understand the chemical evolution of LSBGs, we derived the
gas-phase abundance and the [/Fe] ratio. Compared with star-forming
galaxies, ELSBGs show a flatter trend in the mass-metallicity ()
relation, suggesting that the oxygen abundance enhancement is inefficient. We
focus on 77 ELSBGs with HI data and found the closed-box model can not explain
their gas fraction and metallicity relation, implying that infall and/or
outflow is needed. We derived the [/Fe] ratio of normal ELSBG (
10M) and massive ELSBG ( 10M) using single
stellar population grids from MILES stellar library. The mean [/Fe]
ratios are 0.18 and 0.4 for normal ELSBG and massive ELSBG, respectively. We
discussed that the long time-scale of star-formation, and/or metal-rich gas
outflow event caused by SNe Ia winds are likely responsible for the
-enhancement of massive ELSBGs.Comment: 9 pages, 9 figures, Accepted for publication in Ap
ALMA Observation of NGC5135: The Circumnuclear CO(6-5) and Dust Continuum Emission at 45 Parsec Resolution[]
We present high-resolution (0.17\arcsec 0.14\arcsec) Atacama Large
Millimeter/submillimeter Array (ALMA) observations of the CO\,(6-5) line, and
435\um\ dust continuum emission within a 9\arcsec 9\arcsec\ 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 between
45-180\,pc and CO\,(6-5) line widths of 60-88\,\kms. The CO\,(6-5)
to dust continuum flux ratios vary among the clumps and show an increasing
trend with the \FeII/Br- ratios, which we interpret as evidence for
supernova-driven shocked gas providing a significant contribution to the \co65\
emission. The central AGN is undetected in continuum, nor in CO\,(6-5) if its
line velocity width is no less than \,40\,\kms. We estimate that the AGN
contributes at most 1\% of the integrated CO\,(6-5) flux of 512
24Jy\kms\ within the ALMA field of view, which in turn accounts for
32\% of the CO\,(6-5) flux of the whole galaxy.Comment: 21 pages, 12 figures, Accepted for publication in Ap
GHOST Commissioning Science Results II: a very metal-poor star witnessing the early Galactic assembly
This study focuses on Pristine (hereafter P180956,
[Fe/H] ), a star selected from the Pristine Inner Galaxy Survey
(PIGS), and followed-up with the recently commissioned Gemini High-resolution
Optical SpecTrograph (GHOST) at the Gemini South telescope. The GHOST
spectrograph's high efficiency in the blue spectral region (~\AA)
enables the detection of elemental tracers of early supernovae (e.g. Al, Mn,
Sr, Eu), which were not accessible in the previous analysis of P180956. The
star exhibits chemical signatures resembling those found in ultra-faint dwarf
systems, characterised by very low abundances of neutron-capture elements (Sr,
Ba, Eu), which are uncommon among stars of comparable metallicity in the Milky
Way. Our analysis suggests that P180956 bears the chemical imprints of a small
number (2 or 4) of low-mass hypernovae (\sim10-15\msun), which are needed to
reproduce the abundance pattern of the light-elements (e.g. [Si, Ti/Mg, Ca]
), and one fast-rotating intermediate-mass supernova (\sim300\kms,
\sim80-120\msun). Both types of supernovae explain the high [Sr/Ba] of
P180956 (). The small pericentric (\sim0.7\kpc) and apocentric
(\sim13\kpc) distances and its orbit confined to the plane (\lesssim
2\kpc), indicate that this star was likely accreted during the early Galactic
assembly phase. Its chemo-dynamical properties suggest that P180956 formed in a
system similar to an ultra-faint dwarf galaxy accreted either alone, as one of
the low-mass building blocks of the proto-Galaxy, or as a satellite of
Gaia-Sausage-Enceladus. The combination of Gemini's large aperture with GHOST's
high efficiency and broad spectral coverage makes this new spectrograph one of
the leading instruments for near-field cosmology investigations.Comment: Submitted to MNRAS. 8 figures, 15page
SPLUS J142445.34-254247.1: An R-Process Enhanced, Actinide-Boost, Extremely Metal-Poor star observed with GHOST
We report on the chemo-dynamical analysis of SPLUS J142445.34-254247.1, an
extremely metal-poor halo star enhanced in elements formed by the rapid
neutron-capture process. This star was first selected as a metal-poor candidate
from its narrow-band S-PLUS photometry and followed up spectroscopically in
medium-resolution with Gemini South/GMOS, which confirmed its low-metallicity
status. High-resolution spectroscopy was gathered with GHOST at Gemini South,
allowing for the determination of chemical abundances for 36 elements, from
carbon to thorium. At [Fe/H]=-3.39, SPLUS J1424-2542 is one of the lowest
metallicity stars with measured Th and has the highest logeps(Th/Eu) observed
to date, making it part of the "actinide-boost" category of r-process enhanced
stars. The analysis presented here suggests that the gas cloud from which SPLUS
J1424-2542 was formed must have been enriched by at least two progenitor
populations. The light-element (Z<=30) abundance pattern is consistent with the
yields from a supernova explosion of metal-free stars with 11.3-13.4 Msun, and
the heavy-element (Z>=38) abundance pattern can be reproduced by the yields
from a neutron star merger (1.66Msun and 1.27Msun) event. A kinematical
analysis also reveals that SPLUS J1424-2542 is a low-mass, old halo star with a
likely in-situ origin, not associated with any known early merger events in the
Milky Way.Comment: 26 pages, 11 figures, accepted for publication on Ap
Spectroscopic survey of the low mass population in the star-forming region Lagoon nebula
Using data from the GAIA-ESO spectroscopic survey, we describe the determination of spectroscopic and stellar parameters of circa 400 low-mass members of the Lagoon Nebula. Based on this analysis, we discuss the luminosity/age spread in the H-R diagram, lithium evolution and place in our findings in context of recent theoretical and observational works. We also compare our results with time-series and near-mid infrared data
Massive Star Formation in the Tarantula Nebula
In this work, we present 299 candidate young stellar objects (YSOs) in 30 Doradus discovered using Spitzer and Herschel point-source catalogs, 276 of which are new. We study the parental giant molecular clouds in which these YSO candidates form using recently published Atacama Large Millimeter/submillimeter Array (ALMA) Cycle 7 observations of ^12 CO and ^13 CO. The threshold for star formation in 30 Doradus inferred by the LTE-based mass surface density is 178 M _⊙ pc ^−2 , 40% higher than the threshold for star formation in the Milky Way. This increase in star formation threshold in comparison to the Milky Way and increase in line width seen in clumps 11 pc away in comparison to clumps 45 pc away from the R136 super star cluster could be due to injected turbulent energy, increase in interstellar medium pressure, and/or local magnetic field strength. Of the 299 YSO candidates in this work, 62% are not associated with ^12 CO molecular gas. This large fraction can be explained by the fact that 75%–97% of the H _2 gas is not traced by CO. We fit a Kroupa initial mass function to the YSO candidates and find that the total integrated stellar mass is 18,000 M _⊙ and that the region has a star formation rate (SFR) of 0.18 M _⊙ yr ^−1 . The initial mass function determined here applies to the four 150″ × 150″ (37.5 pc × 37.5 pc) subfields and one 150″ × 75″ (37.5 pc × 18.8 pc) subfield observed with ALMA. The SFR in 30 Doradus has increased in the past few million years
The structure and dynamics of the 30 Doradus molecular cloud as revealed by ALMA
International audienceWe present results of a wide-field (approximately 60 × 90 pc) ALMA mosaic of CO(2-1) and 13CO(2-1) emission from the molecular cloud associated with the 30 Doradus star-forming region. Three main emission complexes, including two forming a bowtie-shaped structure extending northeast and southwest from the central R136 cluster, are resolved into complex filamentary networks. Consistent with previous studies, we find that the central region of the cloud has higher line widths at fixed size relative to the rest of the molecular cloud and to other LMC clouds, indicating an enhanced level of turbulent motions. However, there is no clear trend in gravitational boundedness (as measured by the virial parameter) with distance from R136. Structures observed in 13CO are spatially coincident with filaments and are close to a state of virial equilibrium. In contrast, 12CO structures vary greatly in virialization, with low CO surface brightness structures outside of the main filamentary network being predominantly unbound. The low surface brightness structures constitute ~10% of the measured CO luminosity; they may be shredded remnants of previously star-forming gas clumps, or alternatively the CO-emitting parts of more massive, CO-dark structures