1,505 research outputs found
A new astrophysical solution to the Too Big To Fail problem - Insights from the MoRIA simulations
We test whether advanced galaxy models and analysis techniques of simulations
can alleviate the Too Big To Fail problem (TBTF) for late-type galaxies, which
states that isolated dwarf galaxy kinematics imply that dwarfs live in
lower-mass halos than is expected in a {\Lambda}CDM universe. Furthermore, we
want to explain this apparent tension between theory and observations. To do
this, we use the MoRIA suite of dwarf galaxy simulations to investigate whether
observational effects are involved in TBTF for late-type field dwarf galaxies.
To this end, we create synthetic radio data cubes of the simulated MoRIA
galaxies and analyse their HI kinematics as if they were real, observed
galaxies. We find that for low-mass galaxies, the circular velocity profile
inferred from the HI kinematics often underestimates the true circular velocity
profile, as derived directly from the enclosed mass. Fitting the HI kinematics
of MoRIA dwarfs with a theoretical halo profile results in a systematic
underestimate of the mass of their host halos. We attribute this effect to the
fact that the interstellar medium of a low-mass late-type dwarf is continuously
stirred by supernova explosions into a vertically puffed-up, turbulent state to
the extent that the rotation velocity of the gas is simply no longer a good
tracer of the underlying gravitational force field. If this holds true for real
dwarf galaxies as well, it implies that they inhabit more massive dark matter
halos than would be inferred from their kinematics, solving TBTF for late-type
field dwarf galaxies.Comment: 21 pages, 21 figures. Accepted for publication in A&A. Corrected
certain values in Table
Recommended from our members
Impact of phonons and spin-orbit coupling on Auger recombination in InAs
Phonon-assisted optical absorption in silicon from first principles
The phonon-assisted interband optical absorption spectrum of silicon is
calculated at the quasiparticle level entirely from first principles. We make
use of the Wannier interpolation formalism to determine the quasiparticle
energies, as well as the optical transition and electron-phonon coupling matrix
elements, on fine grids in the Brillouin zone. The calculated spectrum near the
onset of indirect absorption is in very good agreement with experimental
measurements for a range of temperatures. Moreover, our method can accurately
determine the optical absorption spectrum of silicon in the visible range, an
important process for optoelectronic and photovoltaic applications that cannot
be addressed with simple models. The computational formalism is quite general
and can be used to understand the phonon-assisted absorption processes in
general
Gold-induced nanowires on the Ge(100) surface yield a 2D, and not a 1D electronic structure
Atomic nanowires on semiconductor surfaces induced by the adsorption of
metallic atoms have attracted a lot of attention as possible hosts of the
elusive, Tomonaga-Luttinger liquid. The Au/Ge(100) system in particular is the
subject of controversy as to whether the Au-induced nanowires do indeed host
exotic, 1D metallic states. We report on a thorough study of the electronic
properties of high quality nanowires formed at the Au/Ge(100) surface. High
resolution ARPES data show the low-lying Au-induced electronic states to
possess a dispersion relation that depends on two orthogonal directions in
k-space. Comparison of the E(k,k) surface measured using ARPES to
tight-binding calculations yields hopping parameters in the two different
directions that differ by a factor of two. We find that the larger of the two
hopping parameters corresponds, in fact, to the direction perpendicular to the
nanowires (t). This, the topology of the = contour in
k, and the fact that / proves that the
Au-induced electron pockets possess a 2D, closed Fermi surface, this firmly
places the Au/Ge(100) nanowire system outside being a potential hosts of a
Tomonaga-Luttinger liquid. We combine these ARPES data with STS measurements of
the spatially-resolved electronic structure and find that the spatially
straight conduction channels observed up to energies of order one electron volt
below the Fermi level do not originate from the Au-induced states seen in the
ARPES data. The former are more likely to be associated with bulk Ge states
that are localized to the subsurface region. Despite our proof of the 2D nature
of the Au-induced nanowire and sub-surface Ge-related states, an anomalous
suppression of the density of states at the Fermi level is observed in both the
STS and ARPES data, this phenomenon is discussed in the light of the effects of
disorder.Comment: 17 pages, 8 figure
The irreducible vectors of a lattice:Some theory and applications
The main idea behind lattice sieving algorithms is to reduce a sufficiently large number of lattice vectors with each other so that a set of short enough vectors is obtained. It is therefore natural to study vectors which cannot be reduced. In this work we give a concrete definition of an irreducible vector and study the properties of the set of all such vectors. We show that the set of irreducible vectors is a subset of the set of Voronoi relevant vectors and study its properties. For extremal lattices this set may contain as many as 2^n vectors, which leads us to define the notion of a complete system of irreducible vectors, whose size can be upperbounded by the kissing number. One of our main results shows thatmodified heuristic sieving algorithms heuristically approximate such a set (modulo sign). We provide experiments in low dimensions which support this theory. Finally we give some applications of this set in the study of lattice problems such as SVP, SIVP and CVPP. The introduced notions, as well as various results derived along the way, may provide further insights into lattice algorithms and motivate new research into understanding these algorithms better
ARPES insights on the metallic states of YbB6(001): E(k) dispersion, temporal changes and spatial variation
We report high resolution Angle Resolved PhotoElectron Spectroscopy (ARPES)
results on the (001) cleavage surface of YbB, a rare-earth compound which
has been recently predicted to host surface electronic states with topological
character. We observe two types of well-resolved metallic states, whose Fermi
contours encircle the time-reversal invariant momenta of the YbB(001)
surface Brillouin zone, and whose full (E,)-dispersion relation can be
measured wholly unmasked by states from the rest of the electronic structure.
Although the two-dimensional character of these metallic states is confirmed by
their lack of out-of-plane dispersion, two new aspects are revealed in these
experiments. Firstly, these states do not resemble two branches of opposite,
linear velocity that cross at a Dirac point, but rather straightforward
parabolas which terminate to high binding energy with a clear band bottom.
Secondly, these states are sensitive to time-dependent changes of the YbB
surface under ultrahigh vacuum conditions. Adding the fact that these data from
cleaved YbB surfaces also display spatial variations in the electronic
structure, it appears there is little in common between the theoretical
expectations for an idealized YbB(001) crystal truncation on the one
hand, and these ARPES data from real cleavage surfaces on the other.Comment: 8 pages, 4 figures (accepted in Physical Review B
Constraints on the Binary Companion to the SN Ic 1994I Progenitor
Core-collapse supernovae (SNe), which mark the deaths of massive stars, are among the most powerful explosions in the universe and are responsible, e.g., for a predominant synthesis of chemical elements in their host galaxies. The majority of massive stars are thought to be born in close binary systems. To date, putative binary companions to the progenitors of SNe may have been detected in only two cases, SNe 1993J and 2011dh. We report on the search for a companion of the progenitor of the Type Ic SN 1994I, long considered to have been the result of binary interaction. Twenty years after explosion, we used the Hubble Space Telescope to observe the SN site in the ultraviolet (F275W and F336W bands), resulting in deep upper limits on the expected companion: F275W > 26.1 mag and F336W > 24.7 mag. These allow us to exclude the presence of a main sequence companion with a mass ≳ 10 M_⊙. Through comparison with theoretical simulations of possible progenitor populations, we show that the upper limits to a companion detection exclude interacting binaries with semi-conservative (late Case A or early Case B) mass transfer. These limits tend to favor systems with non-conservative, late Case B mass transfer with intermediate initial orbital periods and mass ratios. The most likely mass range for a putative main sequence companion would be ~5–12 M_⊙, the upper end of which corresponds to the inferred upper detection limit
Effect of binary evolution on the inferred initial and final core masses of hydrogen-rich, Type~II supernova progenitors
The majority of massive stars, the progenitors of core-collapse supernovae
(SNe), are found in close binary systems. Zapartas et al. (2019) modeled the
fraction of hydrogen-rich, Type II SN progenitors which have their evolution
affected by mass exchange with their companion, finding this to be between 1/3
and 1/2 for most assumptions. Here we study in more depth the impact of this
binary history of Type II SN progenitors on their final pre-SN core mass
distribution, using population synthesis simulations. We find that binary star
progenitors of Type II SNe typically end their life with a larger core mass
than they would have had if they had lived in isolation, because they gained
mass or merged with a companion before explosion. The combination of the
diverse binary evolutionary paths typically lead to a marginally shallower
final core mass distribution. Discussing our results in the context of the red
supergiant problem, i.e., the reported lack of detected high luminosity
progenitors, we conclude that binary evolution does not seem to significantly
affect the issue. This conclusion is quite robust against our variations in the
assumptions of binary physics. We also predict that inferring the initial
masses of Type II SN progenitors from "age-dating" its surrounding environment
systematically yields lower masses compared to methods that probe the pre-SN
core mass or luminosity. A robust discrepancy between the inferred initial
masses of a SN progenitor from those different techniques could indicate an
evolutionary history of binary mass accretion or merging.Comment: Published in Astronomy & Astrophysics, Volume 64
Ultraviolet Detection of the Binary Companion to the Type IIb SN 2001ig
We present HST/WFC3 ultraviolet imaging in the F275W and F336W bands of the
Type IIb SN 2001ig at an age of more than 14 years. A clear point source is
detected at the site of the explosion having and
mag. Despite weak constraints on both the
distance to the host galaxy NGC 7424 and the line-of-sight reddening to the
supernova, this source matches the characteristics of an early B-type main
sequence star having K and . A BPASS v2.1 binary evolution model, with
primary and secondary masses of 13 M and 9 M respectively,
is found to resemble simultaneously in the Hertzsprung-Russell diagram both the
observed location of this surviving companion, and the primary star
evolutionary endpoints for other Type IIb supernovae. This same model exhibits
highly variable late-stage mass loss, as expected from the behavior of the
radio light curves. A Gemini/GMOS optical spectrum at an age of 6 years reveals
a narrow He II emission line, indicative of continuing interaction with a dense
circumstellar medium at large radii from the progenitor. We review our findings
on SN 2001ig in the context of binary evolution channels for stripped-envelope
supernovae. Owing to the uncrowded nature of its environment in the
ultraviolet, this study of SN 2001ig represents one of the cleanest detections
to date of a surviving binary companion to a Type IIb supernova.Comment: 8 pages, 3 figures. Resubmitted to ApJ after minor changes requested
by refere
- …