3,111 research outputs found
On constructions preserving the asymptotic topology of metric spaces
We prove that graph products constructed over infinite graphs with bounded
clique number preserve finite asymptotic dimension. We also study the extent to
which Dranishnikov's property C, and Dranishnikov and Zarichnyi's straight
finite decomposition complexity are preserved by constructions such as unions,
free products, and group extensions.Comment: 13 pages, accepted for publication in NC Journal of Mathematics and
Statistic
On Product Stability of Asymptotic Property C
Asymptotic property C is a dimension-like large-scale invariant of metric spaces that is of interest when applied to spaces with infinite asymptotic dimension. It was first described by Dranishnikov, who based it on Haver\u27s topological property C. Topological property C fails to be preserved by products in very striking ways and so a natural question that remained open for some 10+ years is whether asymptotic property C is preserved by products. Using a technique inspired by Rohm we show that asymptotic property C is preserved by direct products of metric spaces
The JCMT Transient Survey: An Extraordinary Submillimetre Flare in the T Tauri Binary System JW 566
The binary T Tauri system JW 566 in the Orion Molecular Cloud underwent an
energetic, short-lived flare observed at submillimetre wavelengths by the
SCUBA-2 instrument on 26 November 2016 (UT). The emission faded by nearly 50%
during the 31 minute integration. The simultaneous source fluxes averaged over
the observation are 500 +/- 107 mJy/beam at 450 microns and 466 +/- 47 mJy/beam
at 850 microns. The 850 micron flux corresponds to a radio luminosity of
erg/s/Hz, approximately one order of magnitude
brighter (in terms of ) than that of a flare of the young star
GMR-A, detected in Orion in 2003 at 3mm. The event may be the most luminous
known flare associated with a young stellar object and is also the first
coronal flare discovered at sub-mm wavelengths. The spectral index between 450
microns and 850 microns of is broadly consistent with
non-thermal emission. The brightness temperature was in excess of
K. We interpret this event to be a magnetic reconnection that
energised charged particles to emit gyrosynchrotron/synchrotron radiation.Comment: Accepted in ApJ. 16 pages (single column), 6 figure
The JCMT Transient Survey: An Extraordinary Submillimeter Flare in the T Tauri Binary System JW 566
© 2019 The American Astronomical Society. All rights reserved.The binary T Tauri system JW 566 in the Orion Molecular Cloud underwent an energetic, short-lived flare observed at submillimetre wavelengths by the SCUBA-2 instrument on 26 November 2016 (UT). The emission faded by nearly 50% during the 31 minute integration. The simultaneous source fluxes averaged over the observation are 500 +/- 107 mJy/beam at 450 microns and 466 +/- 47 mJy/beam at 850 microns. The 850 micron flux corresponds to a radio luminosity of erg/s/Hz, approximately one order of magnitude brighter (in terms of ) than that of a flare of the young star GMR-A, detected in Orion in 2003 at 3mm. The event may be the most luminous known flare associated with a young stellar object and is also the first coronal flare discovered at sub-mm wavelengths. The spectral index between 450 microns and 850 microns of is broadly consistent with non-thermal emission. The brightness temperature was in excess of K. We interpret this event to be a magnetic reconnection that energised charged particles to emit gyrosynchrotron/synchrotron radiation.Peer reviewedFinal Published versio
Similarity Properties and Scaling Laws of Radiation Hydrodynamic Flows in Laboratory Astrophysics
The spectacular recent development of modern high-energy density laboratory
facilities which concentrate more and more energy in millimetric volumes allows
the astrophysical community to reproduce and to explore, in millimeter-scale
targets and during very short times, astrophysical phenomena where radiation
and matter are strongly coupled. The astrophysical relevance of these
experiments can be checked from the similarity properties and especially
scaling laws establishment, which constitutes the keystone of laboratory
astrophysics. From the radiating optically thin regime to the so-called
optically thick radiative pressure regime, we present in this paper, for the
first time, a complete analysis of the main radiating regimes that we
encountered in laboratory astrophysics with the same formalism based on the
Lie-group theory. The use of the Lie group method appears as systematic which
allows to construct easily and orderly the scaling laws of a given problem.
This powerful tool permits to unify the recent major advances on scaling laws
and to identify new similarity concepts that we discuss in this paper and which
opens important applications for the present and the future laboratory
astrophysics experiments. All these results enable to demonstrate theoretically
that astrophysical phenomena in such radiating regimes can be explored
experimentally thanks to powerful facilities. Consequently the results
presented here are a fundamental tool for the high-energy density laboratory
astrophysics community in order to quantify the astrophysics relevance and
justify laser experiments. Moreover, relying on the Lie-group theory, this
paper constitutes the starting point of any analysis of the self-similar
dynamics of radiating fluids.Comment: Astrophys. J. accepte
A trio of new Local Group galaxies with extreme properties
We report on the discovery of three new dwarf galaxies in the Local Group.
These galaxies are found in new CFHT/MegaPrime g,i imaging of the south-western
quadrant of M31, extending our extant survey area to include the majority of
the southern hemisphere of M31's halo out to 150 kpc. All these galaxies have
stellar populations which appear typical of dwarf spheroidal (dSph) systems.
The first of these galaxies, Andromeda XVIII, is the most distant Local Group
dwarf discovered in recent years, at ~1.4 Mpc from the Milky Way (~ 600 kpc
from M31). The second galaxy, Andromeda XIX, a satellite of M31, is the most
extended dwarf galaxy known in the Local Group, with a half-light radius of r_h
~ 1.7 kpc. This is approximately an order of magnitude larger than the typical
half-light radius of many Milky Way dSphs, and reinforces the difference in
scale sizes seen between the Milky Way and M31 dSphs (such that the M31 dwarfs
are generally more extended than their Milky Way counterparts). The third
galaxy, Andromeda XX, is one of the faintest galaxies so far discovered in the
vicinity of M31, with an absolute magnitude of order M_V ~ -6.3. Andromeda
XVIII, XIX and XX highlight different aspects of, and raise important questions
regarding, the formation and evolution of galaxies at the extreme faint-end of
the luminosity function. These findings indicate that we have not yet sampled
the full parameter space occupied by dwarf galaxies, although this is an
essential pre-requisite for successfully and consistently linking these systems
to the predicted cosmological dark matter sub-structure.Comment: 32 pages, 7 figures (ApJ preprint format). Accepted for publication
in Ap
The Far-Ultraviolet Spectra of TW Hya. II. Models of H2 Fluorescence in a Disk
We measure the temperature of warm gas at planet-forming radii in the disk
around the classical T Tauri star (CTTS) TW Hya by modelling the H2
fluorescence observed in HST/STIS and FUSE spectra. Strong Ly-alpha emission
irradiates a warm disk surface within 2 AU of the central star and pumps
certain excited levels of H2. We simulate a 1D plane-parallel atmosphere to
estimate fluxes for the 140 observed H2 emission lines and to reconstruct the
Ly-alpha emission profile incident upon the warm H2. The excitation of H2 can
be determined from relative line strengths by measuring self-absorption in
lines with low-energy lower levels, or by reconstructing the Ly-alpha profile
incident upon the warm H2 using the total flux from a single upper level and
the opacity in the pumping transition. Based on those diagnostics, we estimate
that the warm disk surface has a column density of log
N(H2)=18.5^{+1.2}_{-0.8}, a temperature T=2500^{+700}_{-500} K, and a filling
factor of H2, as seen by the source of Ly-alpha emission, of 0.25\pm0.08 (all
2-sigma error bars). TW Hya produces approximately 10^{-3} L_\odot in the FUV,
about 85% of which is in the Ly-alpha emission line. From the H I absorption
observed in the Ly-alpha emission, we infer that dust extinction in our line of
sight to TW Hya is negligible.Comment: Accepted by ApJ. 26 pages, 17 figures, 6 table
The Rise of Massive Red Galaxies: the color-magnitude and color-stellar mass diagrams for z < ~2 from the MUltiwavelength Survey by Yale-Chile (MUSYC)
We present the color-magnitude and color-stellar mass diagrams for galaxies
with z_phot < ~2, based on a K < 22 (AB) catalog of the Extended Chandra Deep
Field South (ECDFS) from the MUltiwavelength Survey by Yale-Chile (MUSYC). Our
main sample of 7840 galaxies contains 1297 M_* > 10^11 M_Sol galaxies in the
range 0.2 < z_phot < 1.8. We show empirically that this catalog is
approximately complete for M_* > 10^11 M_Sol galaxies for z_phot < 1.8. For
this mass-limited sample, we show that the locus of the red sequence
color-stellar mass relation evolves as Del(u-r) ~ (-0.44+/-0.02) z_phot for
z_phot ~1.3, however, we are no longer able to reliably
distinguish red and blue subpopulations from the observed color distribution;
we show that this would require much deeper near infrared data. At 1.5 < z_phot
10^11 M_Sol galaxies is ~50% of the
local value, with a red fraction of ~33%. Making a parametric fit to the
observed evolution, we find n_tot(z) ~ (1+z_phot)^(-0.52+/-0.12(+/-0.20)). We
find stronger evolution in the red fraction: f_red(z) ~
(1+z_phot)^(-1.17+/-0.18(+/-0.21)). Through a series of sensitivity analyses,
we show that the most important sources of systematic error are: 1. systematic
differences in the analysis of the z~0 and z>>0 samples; 2. systematic effects
associated with details of the photometric redshift calculation; and 3.
uncertainties in the photometric calibration. With this in mind, we show that
our results based on photometric redshifts are consistent with a completely
independent analysis which does not require redshift information for individual
galaxies. Our results suggest that, at most, 1/5 of local red sequence galaxies
with M_* >10^11 M_Sol were already in place at z ~ 2.Comment: Accepted for publication in ApJ. 31 pages in emulateapj format; 18
figues (14 in main text). Additional online data available through
http://www.strw.leidenuniv.nl/~ent
- …