675 research outputs found
Tracing the Conversion of Gas into Stars in Young Massive Cluster Progenitors
Whilst young massive clusters (YMCs; 10 M, age
100 Myr) have been identified in significant numbers, their
progenitor gas clouds have eluded detection. Recently, four extreme molecular
clouds residing within 200 pc of the Galactic centre have been identified as
having the properties thought necessary to form YMCs. Here we utilise far-IR
continuum data from the Herschel Infrared Galactic Plane Survey (HiGAL) and
millimetre spectral line data from the Millimetre Astronomy Legacy Team 90 GHz
Survey (MALT90) to determine their global physical and kinematic structure. We
derive their masses, dust temperatures and radii and use virial analysis to
conclude that they are all likely gravitationally bound -- confirming that they
are likely YMC progenitors. We then compare the density profiles of these
clouds to those of the gas and stellar components of the Sagittarius B2 Main
and North proto-clusters and the stellar distribution of the Arches YMC. We
find that even in these clouds -- the most massive and dense quiescent clouds
in the Galaxy -- the gas is not compact enough to form an Arches-like ( =
2x10 M, R = 0.4 pc) stellar distribution. Further
dynamical processes would be required to condense the resultant population,
indicating that the mass becomes more centrally concentrated as the
(proto)-cluster evolves. These results suggest that YMC formation may proceed
hierarchically rather than through monolithic collapse.Comment: 12 pages, 8 figures, 1 table. Accepted by MNRA
High Performance Algorithms for Counting Collisions and Pairwise Interactions
The problem of counting collisions or interactions is common in areas as
computer graphics and scientific simulations. Since it is a major bottleneck in
applications of these areas, a lot of research has been carried out on such
subject, mainly focused on techniques that allow calculations to be performed
within pruned sets of objects. This paper focuses on how interaction
calculation (such as collisions) within these sets can be done more efficiently
than existing approaches. Two algorithms are proposed: a sequential algorithm
that has linear complexity at the cost of high memory usage; and a parallel
algorithm, mathematically proved to be correct, that manages to use GPU
resources more efficiently than existing approaches. The proposed and existing
algorithms were implemented, and experiments show a speedup of 21.7 for the
sequential algorithm (on small problem size), and 1.12 for the parallel
proposal (large problem size). By improving interaction calculation, this work
contributes to research areas that promote interconnection in the modern world,
such as computer graphics and robotics.Comment: Accepted in ICCS 2019 and published in Springer's LNCS series.
Supplementary content at https://mjsaldanha.com/articles/1-hpc-ssp
Variations in the Galactic star formation rate and density thresholds for star formation
The conversion of gas into stars is a fundamental process in astrophysics and
cosmology. Stars are known to form from the gravitational collapse of dense
clumps in interstellar molecular clouds, and it has been proposed that the
resulting star formation rate is proportional to either the amount of mass
above a threshold gas surface density, or the gas volume density. These
star-formation prescriptions appear to hold in nearby molecular clouds in our
Milky Way Galaxy's disk as well as in distant galaxies where the star formation
rates are often much larger. The inner 500 pc of our Galaxy, the Central
Molecular Zone (CMZ), contains the largest concentration of dense, high-surface
density molecular gas in the Milky Way, providing an environment where the
validity of star-formation prescriptions can be tested. Here we show that by
several measures, the current star formation rate in the CMZ is an
order-of-magnitude lower than the rates predicted by the currently accepted
prescriptions. In particular, the region 1 deg < l < 3.5 deg, |b| < 0.5 deg
contains ~10^7 Msun of dense molecular gas -- enough to form 1000 Orion-like
clusters -- but the present-day star formation rate within this gas is only
equivalent to that in Orion. In addition to density, another property of
molecular clouds, such as the amplitude of turbulent motions, must be included
in the star-formation prescription to predict the star formation rate in a
given mass of molecular gas.Comment: 17 pages, 6 figures, submitted MNRA
VLASSICK: The VLA Sky Survey in the Central Kiloparsec
At a distance of 8 kpc, the center of our Galaxy is the nearest galactic
nucleus, and has been the subject of numerous key projects undertaken by great
observatories such as Chandra, Spitzer, and Herschel. However, there are still
no surveys of molecular gas properties in the Galactic center with less than
30" (1 pc) resolution. There is also no sensitive polarization survey of this
region, despite numerous nonthermal magnetic features apparently unique to the
central 300 parsecs. In this paper, we outline the potential the VLASS has to
fill this gap. We assess multiple considerations in observing the Galactic
center, and recommend a C-band survey with 10 micro-Jy continuum RMS and
sensitive to molecular gas with densities greater than 10^4 cm^{-3}, covering
17 square degrees in both DnC and CnB configurations ( resolution ~5"),
totaling 750 hours of observing time. Ultimately, we wish to note that the
upgraded VLA is not just optimized for fast continuum surveys, but has a
powerful correlator capable of simultaneously observing continuum emission and
dozens of molecular and recombination lines. This is an enormous strength that
should be fully exploited and highlighted by the VLASS, and which is ideally
suited for surveying the center of our Galaxy.Comment: 13 pages, 3 figures, a White Paper submitted to provide input in
planning the Very Large Array Sky Surve
A Pilot Survey for the HO Southern Galactic Plane Survey (HOPS)
We describe observations with the Mopra radiotelescope designed to assess the
feasibility of the HO maser southern Galactic plane survey (HOPS). We
mapped two one-square-degree regions along the Galactic plane using the new 12
mm receiver and the UNSW Mopra spectrometer (MOPS). We covered the entire
spectrum between 19.5 and 27.5 GHz using this setup with the main aims of
finding out which spectral lines can be detected with a quick mapping survey.
We report on detected emission from HO masers, NH inversion transitions
(1,1), (2,2) and (3,3), HCN (3-2), as well as several radio recombination
lines.Comment: accepted by PAS
Addressing environmental and atmospheric challenges for capturing high-precision thermal infrared data in the field of astro-ecology
Using thermal infrared detectors mounted on drones, and applying techniques from astrophysics, we hope to support the field of conservation ecology by creating an automated pipeline for the detection and identification of certain endangered species and poachers from thermal infrared data. We test part of our system by attempting to detect simulated poachers in the field. Whilst we find that we can detect humans hiding in the field in some types of terrain, we also find several environmental factors that prevent accurate detection, such as ambient heat from the ground, absorption of infrared emission by the atmosphere, obscuring vegetation and spurious sources from the terrain. We discuss the effect of these issues, and potential solutions which will be required for our future vision for a fully automated drone-based global conservation monitoring system
A Far-UV Spectroscopic Analysis of the Central Star of the Planetary Nebula Longmore 1
We have performed a non-LTE spectroscopic analysis using far-UV and UV data
of the central star of the planetary nebula K1-26 (Longmore 1), and found Teff
= 120+/-10 kK, logg = 6.7 +0.3/-0.7, and y = 0.10. The temperature is
significantly hotter than previous results based on optical line analyses,
highlighting the importance of analyzing the spectra of such hot objects at
shorter wavelengths. The spectra show metal lines (from, e.g, carbon, oxygen,
sulfur, and iron). The signatures of most elements can be fit adequately using
solar abundances, confirming the classification of Longmore 1 as a high gravity
O(H) object. Adopting a distance of 800 pc, we derive R = 0.04 Rsun, L = 250
Lsun, and M = 0.6 Msun. This places the object on the white dwarf cooling
sequence of the evolutionary tracks with an age of ~= 65 kyr.Comment: 14 pages, 4 color figures. Accepted for publication in PAS
Star formation in the warped outer pseudoring of the spiral galaxy NGC 3642
NGC 3642 was classified as a spiral galaxy with three rings and no bar. We
have performed an HI and optical study of this nearly face-on galaxy. We find
that the nuclear ring might in fact be part of an inner one-armed spiral, that
could be driving nuclear accretion and feeding the central activity in the
inner kpc. The inner ring is faint, and the outer ring is a rather ill-defined
pseudoring. Furthermore, the size ratio of the rings is such that they cannot
be due to a single pattern speed linking them together.
The outer pseudoring is peculiar, since it lies in the faint outer parts of
the disk, where star formation is still going on at 1.4 times the optical
radius. Higher HI column densities are associated with these regions and the
atomic gas layer is warped. These perturbations affect only the outer disk,
since the kinematics within the main body conforms well to an ordinary
differentially rotating disk.
We propose here that both nuclear activity and star formation in the warped
outer parts might be linked to the fact that NGC 3642 is located in a rich
environment, where its close neighbors show clear signs of merging. Our
suggestion is that NGC 3642 has captured recently a low-mass, gas-rich dwarf,
and star formation was triggered in this infalling external gas that produced
also a pronounced warp in the gaseous disk.Comment: Accepted for publication in A&A. Full resolution version available at
http://www.iaa.es/~lourdes/3642/H3551.tar.g
- …