92 research outputs found
Synthetic observations of simulated Pillars of Creation
Barbara Ercolano, James E. Dale, Matthias Gritschneder, and Mark Westmoquette, 'Synthetic observations of simulated Pillars of Creation', Monthly Notices of the Royal Astronomical Society, Vol. 420(1): 1410146, first published online 23 January 2012. The version of record is available online at doi: https://doi.org/10.1111/j.1365-2966.2011.2001.x. Published by Oxford University Press on behalf of the Royal Astronomical Society. © 2011 The Authors. Monthly Notices of the Royal Astronomical Society © 2011 RAS.We present synthetic observations of star-forming interstellar medium structures obtained by hydrodynamic calculations of a turbulent box under the influence of an ionizing radiation field. The morphological appearance of the pillar-like structures in optical emission lines is found to be very similar to observations of nearby star-forming regions. We calculate line profiles as a function of position along the pillars for collisionally excited [O III] λ5007, [N II] λ6584 and [S II] λ6717, which show typical full width at half-maximum of 2–4 km s−1. Spatially resolved emission-line diagnostic diagrams are also presented which show values in general agreement with observations of similar regions. The diagrams, however, also highlight significant spatial variations in the line ratios, including values that would be classically interpreted as shocked regions based on 1D photoionization calculations. These values tend to be instead the result of lines of sight intersecting which intersect for large portions of their lengths the ionized-toneutral transition regions in the gas. We caution therefore against a straightforward application of classical diagnostic diagrams and 1D photoionization calculations to spatially resolved observations of complex 3D star-forming regions.Peer reviewe
The Supernova Triggered Formation and Enrichment of Our Solar System
We investigate the enrichment of the pre-solar cloud core with short lived
radionuclides (SLRs), especially 26Al. The homogeneity and the surprisingly
small spread in the ratio 26Al/27Al observed in the overwhelming majority of
calcium-aluminium-rich inclusions (CAIs) in a vast variety of primitive
chondritic meteorites places strong constraints on the formation of the the
solar system. Freshly synthesized radioactive 26Al has to be included and well
mixed within 20kyr. After discussing various scenarios including X-winds, AGB
stars and Wolf-Rayet stars, we come to the conclusion that triggering the
collapse of a cold cloud core by a nearby supernova is the most promising
scenario. We then narrow down the vast parameter space by considering the
pre-explosion survivability of such a clump as well as the cross-section
necessary for sufficient enrichment. We employ numerical simulations to address
the mixing of the radioactively enriched SN gas with the pre-existing gas and
the forced collapse within 20kyr. We show that a cold clump of 10Msun at a
distance of 5pc can be sufficiently enriched in 26Al and triggered into
collapse fast enough - within 18kyr after encountering the supernova shock -
for a range of different metallicities and progenitor masses, even if the
enriched material is assumed to be distributed homogeneously in the entire
supernova bubble. In summary, we envision an environment for the birth place of
the Solar System 4.567Gyr ago similar to the situation of the pillars in M16
nowadays, where molecular cloud cores adjacent to an HII region will be hit by
a supernova explosion in the future. We show that the triggered collapse and
formation of the Solar System as well as the required enrichment with
radioactive 26Al are possible in this scenario.Comment: 12 pages, 8 figures, accepted for publication in ApJ. Resolution of
most figures degraded to fit within arXiv size limits. A full resolution
version is available at
http://www.usm.uni-muenchen.de/~gritschm/Gritschneder_2011_sun.pd
Protostellar discs formed from turbulent cores
We investigate the collapse and fragmentation of low-mass, trans-sonically
turbulent prestellar cores, using SPH simulations. The initial conditions are
slightly supercritical Bonnor-Ebert spheres, all with the same density profile,
the same mass (M_O=6.1 Msun) and the same radius (R_O=17,000 AU), but having
different initial turbulent velocity fields. Four hundred turbulent velocity
fields have been generated, all scaled so that the mean Mach number is M=1.
Then a subset of these, having a range of net angular momenta, j, has been
evolved. The evolution of these turbulent cores is not strongly correlated with
j. Instead it is moderated by the formation of filamentary structures due to
converging turbulent flows. A high fraction (~ 82%) of the protostars forming
from turbulent cores are attended by protostellar accretion discs, but only a
very small fraction (~16%) of these discs is sufficiently cool and extended to
develop non-linear gravitational instabilities and fragment.Comment: 10 pages, 8 figures, submitte
The Pillars of Creation revisited with MUSE: gas kinematics and high-mass stellar feedback traced by optical spectroscopy
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society. © 2015 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.Integral field unit (IFU) data of the iconic Pillars of Creation in M16 are presented. The ionization structure of the pillars was studied in great detail over almost the entire visible wavelength range, and maps of the relevant physical parameters, e.g. extinction, electron density, electron temperature, line-of-sight velocity of the ionized and neutral gas are shown. In agreement with previous authors, we find that the pillar tips are being ionized and photoevaporated by the massive members of the nearby cluster NGC 6611. They display a stratified ionization structure where the emission lines peak in a descending order according to their ionization energies. The IFU data allowed us to analyse the kinematics of the photoevaporative flow in terms of the stratified ionization structure, and we find that, in agreement with simulations, the photoevaporative flow is traced by a blueshift in the position-velocity profile. The gas kinematics and ionization structure have allowed us to produce a sketch of the 3D geometry of the Pillars, positioning the pillars with respect to the ionizing cluster stars. We use a novel method to detect a previously unknown bipolar outflow at the tip of the middle pillar and suggest that it has an embedded protostar as its driving source. Furthermore we identify a candidate outflow in the leftmost pillar. With the derived physical parameters and ionic abundances, we estimate a mass-loss rate due to the photoevaporative flow of 70 M⊙ Myr−1 which yields an expected lifetime of approximately 3 Myr.Peer reviewe
Atomic resolution force microscopy imaging on a strongly ionic surface with differently functionalized tips
金沢大学理工研究域数物科学系Three types of tips for noncontact atomic force microscopy imaging, namely, a silicon nanopillar tip, a carbon nanopillar tip, and a fluoride cluster tip, are prepared for atomic resolution imaging on the CaF2 (111) surface. The most enhanced atomic corrugation is obtained with the fluoride cluster tip prepared by gently touching the fluorite surface. Atom resolved images are much harder to obtain with the other tips. This demonstrates the importance of having a polar tip for atomic resolution imaging of an ionic surface and supports the general notion that a surface is best imaged with a tip of the same material. © 2010 American Vacuum Society
Carina's Pillars of Destruction: the view from ALMA
Forming high-mass stars have a significant effect on their natal environment.
Their feedback pathways, including winds, outflows, and ionising radiation,
shape the evolution of their surroundings which impacts the formation of the
next generation of stars. They create or reveal dense pillars of gas and dust
towards the edges of the cavities they clear. They are modelled in feedback
simulations, and the sizes and shapes of the pillars produced are consistent
with those observed. However, these models predict measurably different
kinematics which provides testable discriminants. Here we present the first
ALMA Compact Array (ACA) survey of 13 pillars in Carina, observed in CO,
CO and CO J=2-1, and the 230 GHz continuum. The pillars in this
survey were chosen to cover a wide range in properties relating to the amount
and direction of incident radiation, proximity to nearby irradiating clusters
and cloud rims, and whether they are detached from the cloud. With these data,
we are able to discriminate between models. We generally find pillar velocity
dispersions of 1 km s and that the outer few layers of molecular
emission in these pillars show no significant offsets from each other,
suggesting little bulk internal motions within the pillars. There are instances
where the pillars are offset in velocity from their parental cloud rim, and
some with no offset, hinting at a stochastic development of these motions.Comment: 24 Pages, 19 figures. Accepted to MNRA
The JCMT 12CO(3-2) Survey of the Cygnus X Region: I. A Pathfinder
Cygnus X is one of the most complex areas in the sky. This complicates
interpretation, but also creates the opportunity to investigate accretion into
molecular clouds and many subsequent stages of star formation, all within one
small field of view. Understanding large complexes like Cygnus X is the key to
understanding the dominant role that massive star complexes play in galaxies
across the Universe.
The main goal of this study is to establish feasibility of a high-resolution
CO survey of the entire Cygnus X region by observing part of it as a
Pathfinder, and to evaluate the survey as a tool for investigating the
star-formation process.
A 2x4 degree area of the Cygnus X region has been mapped in the 12CO(3-2)
line at an angular resolution of 15" and a velocity resolution of ~0.4km/s
using HARP-B and ACSIS on the James Clerk Maxwell Telescope. The star formation
process is heavily connected to the life-cycle of the molecular material in the
interstellar medium. The high critical density of the 12CO(3-2) transition
reveals clouds in key stages of molecule formation, and shows processes that
turn a molecular cloud into a star.
We observed ~15% of Cygnus X, and demonstrated that a full survey would be
feasible and rewarding. We detected three distinct layers of 12CO(3-2)
emission, related to the Cygnus Rift (500-800 pc), to W75N (1-1.8 kpc), and to
DR21 (1.5-2.5 kpc). Within the Cygnus Rift, HI self-absorption features are
tightly correlated with faint diffuse CO emission, while HISA features in the
DR21 layer are mostly unrelated to any CO emission. 47 molecular outflows were
detected in the Pathfinder, 27 of them previously unknown. Sequentially
triggered star formation is a widespread phenomenon.Comment: 18 pages, 13 figures, accepted for publication in Astronomy &
Astrophysic
IVINE - Ionization in the parallel tree/sph code VINE: First results on the observed age-spread around O-stars
We present a three-dimensional, fully parallelized, efficient implementation of ionizing ultraviolet (UV) radiation for smoothed particle hydrodynamics (sph) including self-gravity. Our method is based on the sph/tree code vine. We therefore call it iVINE (for Ionization + VINE). This approach allows detailed high-resolution studies of the effects of ionizing radiation from, for example, young massive stars on their turbulent parental molecular clouds. In this paper, we describe the concept and the numerical implementation of the radiative transfer for a plane-parallel geometry and we discuss several test cases demonstrating the efficiency and accuracy of the new method. As a first application, we study the radiatively driven implosion of marginally stable molecular clouds at various distances of a strong UV source and show that they are driven into gravitational collapse. The resulting cores are very compact and dense exactly as it is observed in clustered environments. Our simulations indicate that the time of triggered collapse depends on the distance of the core from the UV source. Clouds closer to the source collapse several 105 yr earlier than more distant clouds. This effect can explain the observed age spread in OB associations where stars closer to the source are found to be younger. We discuss possible uncertainties in the observational derivation of shock front velocities due to early stripping of protostellar envelopes by ionizing radiation
The Milky Way Project: A statistical study of massive star formation associated with infrared bubbles
The Milky Way Project citizen science initiative recently increased the
number of known infrared bubbles in the inner Galactic plane by an order of
magnitude compared to previous studies. We present a detailed statistical
analysis of this dataset with the Red MSX Source catalog of massive young
stellar sources to investigate the association of these bubbles with massive
star formation. We particularly address the question of massive triggered star
formation near infrared bubbles. We find a strong positional correlation of
massive young stellar objects (MYSOs) and H II regions with Milky Way Project
bubbles at separations of < 2 bubble radii. As bubble sizes increase, a
statistically significant overdensity of massive young sources emerges in the
region of the bubble rims, possibly indicating the occurrence of triggered star
formation. Based on numbers of bubble-associated RMS sources we find that
67+/-3% of MYSOs and (ultra)compact H II regions appear associated with a
bubble. We estimate that approximately 22+/-2% of massive young stars may have
formed as a result of feedback from expanding H II regions. Using MYSO-bubble
correlations, we serendipitously recovered the location of the recently
discovered massive cluster Mercer 81, suggesting the potential of such analyses
for discovery of heavily extincted distant clusters.Comment: 16 pages, 17 figures. Accepted for publication in ApJ, comments
welcome. Milky Way Project public data release available at
http://www.milkywayproject.org/dat
VLT/FLAMES-ARGUS observations of stellar wind--ISM cloud interactions in NGC 6357
We present optical/near-IR IFU observations of a gas pillar in the Galactic
HII region NGC 6357 containing the young open star cluster Pismis 24. These
observations have allowed us to examined in detail the gas conditions of the
strong wind-clump interactions taking place on its surface. We identify the
presence of a narrow (~20 km/s) and broad (50-150 km/s) component to the
H_alpha emission line, where the broadest broad component widths are found in a
region that follows the shape of the eastern pillar edge. These connections
have allowed us to firmly associate the broad component with emission from
ionized gas within turbulent mixing layers on the pillar's surface set up by
the shear flows of the O-star winds from the cluster. We discuss the
implications of our findings in terms of the broad emission line component that
is increasingly found in extragalactic starburst environments. Although the
broad line widths found here are narrower, we conclude that the mechanisms
producing both must be the same. The difference in line widths may result from
the lower total mechanical wind energy produced by the O stars in Pismis 24
compared to that from a typical young massive star cluster found in a starburst
galaxy. The pillar's edge is also clearly defined by dense (<5000 cm^-3), hot
(>20000 K), and excited (via [NII]/H_a and [SII]/H_a ratios) gas conditions,
implying the presence of a D-type ionization front propagating into the pillar
surface. Although there must be both photoevaporation outflows produced by the
ionization front, and mass-loss through mechanical ablation, we see no evidence
for any significant bulk gas motions on or around the pillar. We postulate that
the evaporated/ablated gas must be rapidly heated before being entrained.Comment: 9 pages, 5 figures (3 colour). Accepted for publication in MNRA
- …