526 research outputs found
Characterizing simulated galaxy stellar mass histories
Cosmological galaxy formation simulations can now produce rich and diverse ensembles of galaxy histories. These simulated galaxy histories, taken all together, provide an answer to the question ‘How do galaxies form?’ for the models used to construct them. We characterize such galaxy history ensembles both to understand their properties and to identify points of comparison for histories within a given galaxy formation model or between different galaxy formation models and simulations. We focus primarily on stellar mass histories of galaxies with the same final stellar mass, for six final stellar mass values and for three different simulated galaxy formation models (a semi-analytic model built upon the dark matter Millennium simulation and two models from the hydrodynamical OverWhelmingly Large Simulations project). Using principal component analysis (PCA) to classify scatter around the average stellar mass history, we find that one fluctuation dominates for all sets of histories we consider, although its shape and contribution can vary between samples. We correlate the PCA characterization with several z = 0 galaxy properties (to connect with survey observables) and also compare it to some other galaxy history properties. We then explore separating galaxy stellar mass histories into classes, using the largest PCA contribution, k-means clustering, and simple Gaussian mixture models. For three component models, these different methods often gave similar results. These history classification methods provide a succinct and often quick way to characterize changes in the full ensemble of histories of a simulated population as physical assumptions are varied, to compare histories of different simulated populations to each other, and to assess the relation of simulated histories to fixed time observations
Chromospheric counterparts of solar transition region unresolved fine structure loops
Low-lying loops have been discovered at the solar limb in transition region
temperatures by the Interface Region Imaging Spectrograph (IRIS). They do not
appear to reach coronal temperatures, and it has been suggested that they are
the long-predicted unresolved fine structures (UFS). These loops are dynamic
and believed to be visible during both heating and cooling phases. Making use
of coordinated observations between IRIS and the Swedish 1-m Solar Telescope,
we study how these loops impact the solar chromosphere. We show for the first
time that there is indeed a chromospheric signal of these loops, seen mostly in
the form of strong Doppler shifts and a conspicuous lack of chromospheric
heating. In addition, we find that several instances have a inverse Y-shaped
jet just above the loop, suggesting that magnetic reconnection is driving these
events. Our observations add several puzzling details to the current knowledge
of these newly discovered structures; this new information must be considered
in theoretical models.Comment: 5 pages, 3 figures, 2 movies; accepted for publication in A&A Letter
Beter grip op het multifunctioneel landbouwbedrijf, Stappen naar samenwerking op multifunctionele landbouwbedrijven, verantwoordingsdocument
Multifunctionele landbouwondernemers die hun bedrijf willen ontwikkelen kunnen dit doen door binnen hun bedrijf samen te werken met andere ondernemers. Dit vraagt echter wel om een zorgvuldige afweging van de ondernemer. De stappen die genomen moeten worden in een samenwerking zijn in deze rapportage weergegeven. Daarnaast is het proces en de reflectie van een aantal werksessies beschreven. Deze sessies zijn gehouden met multifunctionele landbouwondernemers die nagedacht hebben over de mogelijkheid van samenwerking op hun bedrijf. Deze rapportage is een verantwoordingsdocument
Quantifying Spicules
Understanding the dynamic solar chromosphere is fundamental in solar physics.
Spicules are an important feature of the chromosphere, connecting the
photosphere to the corona, potentially mediating the transfer of energy and
mass. The aim of this work is to study the properties of spicules over
different regions of the sun. Our goal is to investigate if there is more than
one type of spicules, and how spicules behave in the quiet sun, coronal holes,
and active regions. We make use of high-cadence and high-spatial resolution Ca
II H observations taken by Hinode/SOT. Making use of a semi-automated detection
algorithm, we self-consistently track and measure the properties of 519
spicules over different regions. We find clear evidence of two types of
spicules. Type I spicules show a rise and fall and have typical lifetimes of
150-400 s and maximum ascending velocities of 15-40 km/s, while type II
spicules have shorter lifetimes of 50-150 s, faster velocities of 30-110 km/s,
and are not seen to fall down, but rather fade at around their maximum length.
Type II spicules are the most common, seen in quiet sun and coronal holes. Type
I spicules are seen mostly in active regions. There are regional differences
between quiet sun and coronal hole spicules, likely attributable to the
different field configurations. The properties of type II spicules are
consistent with published results of Rapid Blueshifted Events (RBEs),
supporting the hypothesis that RBEs are their disk counterparts. For type I
spicules we find the relations between their properties to be consistent with a
magnetoacoustic shock wave driver, and with dynamic fibrils as their disk
counterpart. The driver of type II spicules remains unclear from limb
observations.Comment: Accepted for publication in ApJ. 17 pages, 9 figure
Strongly Time-Variable Ultra-Violet Metal Line Emission from the Circum-Galactic Medium of High-Redshift Galaxies
We use cosmological simulations from the Feedback In Realistic Environments
(FIRE) project, which implement a comprehensive set of stellar feedback
processes, to study ultra-violet (UV) metal line emission from the
circum-galactic medium of high-redshift (z=2-4) galaxies. Our simulations cover
the halo mass range Mh ~ 2x10^11 - 8.5x10^12 Msun at z=2, representative of
Lyman break galaxies. Of the transitions we analyze, the low-ionization C III
(977 A) and Si III (1207 A) emission lines are the most luminous, with C IV
(1548 A) and Si IV (1394 A) also showing interesting spatially-extended
structures. The more massive halos are on average more UV-luminous. The UV
metal line emission from galactic halos in our simulations arises primarily
from collisionally ionized gas and is strongly time variable, with
peak-to-trough variations of up to ~2 dex. The peaks of UV metal line
luminosity correspond closely to massive and energetic mass outflow events,
which follow bursts of star formation and inject sufficient energy into
galactic halos to power the metal line emission. The strong time variability
implies that even some relatively low-mass halos may be detectable. Conversely,
flux-limited samples will be biased toward halos whose central galaxy has
recently experienced a strong burst of star formation. Spatially-extended UV
metal line emission around high-redshift galaxies should be detectable by
current and upcoming integral field spectrographs such as the Multi Unit
Spectroscopic Explorer (MUSE) on the Very Large Telescope and Keck Cosmic Web
Imager (KCWI).Comment: 16 pages, 8 figures, accepted for publication in MNRA
Intermittent reconnection and plasmoids in UV bursts in the low solar atmosphere
Magnetic reconnection is thought to drive a wide variety of dynamic phenomena
in the solar atmosphere. Yet the detailed physical mechanisms driving
reconnection are difficult to discern in the remote sensing observations that
are used to study the solar atmosphere. In this paper we exploit the
high-resolution instruments Interface Region Imaging Spectrograph (IRIS) and
the new CHROMIS Fabry-Perot instrument at the Swedish 1-m Solar Telescope (SST)
to identify the intermittency of magnetic reconnection and its association with
the formation of plasmoids in so-called UV bursts in the low solar atmosphere.
The Si IV 1403A UV burst spectra from the transition region show evidence of
highly broadened line profiles with often non-Gaussian and triangular shapes,
in addition to signatures of bidirectional flows. Such profiles had previously
been linked, in idealized numerical simulations, to magnetic reconnection
driven by the plasmoid instability. Simultaneous CHROMIS images in the
chromospheric Ca II K 3934A line now provide compelling evidence for the
presence of plasmoids, by revealing highly dynamic and rapidly moving
brightenings that are smaller than 0.2 arcsec and that evolve on timescales of
order seconds. Our interpretation of the observations is supported by detailed
comparisons with synthetic observables from advanced numerical simulations of
magnetic reconnection and associated plasmoids in the chromosphere. Our results
highlight how subarcsecond imaging spectroscopy sensitive to a wide range of
temperatures combined with advanced numerical simulations that are realistic
enough to compare with observations can directly reveal the small-scale
physical processes that drive the wide range of phenomena in the solar
atmosphere.Comment: Accepted for publication in Astrophysical Journal Letters. Movies are
available at http://folk.uio.no/rouppe/plasmoids_chromis
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