392 research outputs found
Stereotypes about Boys of Color: Information about Race/Ethnicity and Socioeconomic Status Biases Ratings of Boys’ Behavior
A kinematic study of planetary nebulae in the dwarf irregular galaxy IC10
We present positions, kinematics, and the planetary nebula luminosity
function (PNLF) for 35 planetary nebulae (PNe) in the nearest starburst galaxy
IC10 extending out to 3kpc from the galaxy's centre. We take advantage of the
deep imaging and spectroscopic capabilities provided by the spectrograph FOCAS
on the 8.2m Subaru telescope. The PN velocities were measured through the
slitless-spectroscopy technique, which allows us to explore the kinematics of
IC10 with high precision. Using these velocities, we conclude that there is a
kinematic connection between the HI envelope located around IC10 and the
galaxy's PN population. By assuming that the PNe in the central regions and in
the outskirts have similar ages, our results put strong observational
constraints on the past tidal interactions in the Local Group. This is so
because by dating the PN central stars, we, therefore, infer the epoch of a
major episode of star formation likely linked to the first encounter of the HI
extended envelope with the galaxy. Our deep [OIII] images also allow us to use
the PNLF to estimate a distance modulus of 24.1+/-0.25, which is in agreement
with recent results in the literature based on other techniques.Comment: 10 pages, 9 figures, 2 tables. Accepted for publication in MNRA
A multi-wavelength study of Supernova Remnants in six nearby galaxies. I: Detection of new X-ray selected Supernova Remnants with Chandra
We present results from a study of the Supernova Remnant (SNR) population in
a sample of six nearby galaxies (NGC 2403, NGC 3077, NGC 4214, NGC 4449, NGC
4395 and NGC 5204) based on Chandra archival data. We have detected 244
discrete X-ray sources down to a limiting flux of 10^{-15} erg/s. We identify
37 X-ray selected thermal SNRs based on their X-ray colors or spectra, 30 of
which are new discoveries. In many cases the X-ray classification is confirmed
based on counterparts with SNRs identified in other wavelengths. Three of the
galaxies in our sample (NGC 4214, NGC 4395 and NGC 5204) are studied for the
first time, resulting in the discovery of 13 thermal SNRs. We discuss the
properties (luminosity, temperature, density) of the X-ray detected SNRs in the
galaxies of our sample in order to address their dependence on their
environment. We find that X-ray selected SNRs in irregular galaxies appear to
be more luminous than those in spirals. We attribute this to the lower
metalicities and therefore more massive progenitor stars of irregular galaxies
or the higher local densities of the ISM. We also discuss the X-ray selected
SNR populations in the context of the Star Formation Rate of their host
galaxies. A comparison of the numbers of observed luminous X-ray selected SNRs
with those expected based on the luminosity functions of X-ray SNRs in the MCs
and M33 suggest different luminosity distributions between the SNRs in spiral
and irregular galaxies with the latter tending to have flatter distributions.Comment: 56 pages, 14 figures, 26 tables. Accepted for publication in Ap
Critical curves in conformally invariant statistical systems
We consider critical curves -- conformally invariant curves that appear at
critical points of two-dimensional statistical mechanical systems. We show how
to describe these curves in terms of the Coulomb gas formalism of conformal
field theory (CFT). We also provide links between this description and the
stochastic (Schramm-) Loewner evolution (SLE). The connection appears in the
long-time limit of stochastic evolution of various SLE observables related to
CFT primary fields. We show how the multifractal spectrum of harmonic measure
and other fractal characteristics of critical curves can be obtained.Comment: Published versio
Tailorable Acceptor C 60 − n B n and Donor C 60 − m N m Pairs for Molecular Electronics
Our first-principles calculations demonstrate that C 60-n B n /C 60-m Nm molecules could be engineered acceptor/donor pair needed for molecular electronics by properly controlling the number n and m of the substitutional dopants in C 60 . As an example, we propose that acceptor C 48 B 12 and donor C48 N12 can be promising components for molecular rectifiers, nanotube-based p-type, n-type and n-p-n transistors and p-n junctions
How cyclin A destruction escapes the spindle assembly checkpoint
Cyclin A outcompetes inhibitory spindle assembly checkpoint proteins for binding to the APC/C ubiquitin ligase coactivator Cdc20 to promote its self-destruction even when the checkpoint is active (see also a paper from van Zon et al., in this issue)
The formation of disc galaxies in a LCDM universe
We study the formation of disc galaxies in a fully cosmological framework
using adaptive mesh refinement simulations. We perform an extensive parameter
study of the main subgrid processes that control how gas is converted into
stars and the coupled effect of supernovae feedback. We argue that previous
attempts to form disc galaxies have been unsuccessful because of the universal
adoption of strong feedback combined with high star formation efficiencies.
Unless extreme amounts of energy are injected into the interstellar medium
during supernovae events, these star formation parameters result in bulge
dominated S0/Sa galaxies as star formation is too efficient at z~3. We show
that a low efficiency of star-formation more closely models the subparsec
physical processes, especially at high redshift. We highlight the successful
formation of extended disc galaxies with scale lengths r_d=4-5 kpc, flat
rotation curves and bulge to disc ratios of B/D~1/4. Not only do we resolve the
formation of a Milky Way-like spiral galaxy, we also observe the secular
evolution of the disc as it forms a pseudo-bulge. The disc properties agree
well with observations and are compatible with the photometric and baryonic
Tully-Fisher relations, the Kennicutt-Schmidt relation and the observed angular
momentum content of spiral galaxies. We conclude that underlying small-scale
star formation physics plays a larger role than previously considered in
simulations of galaxy formation.Comment: Published in MNRA
Images IV: Strong evolution of the oxygen abundance in gaseous phases of intermediate mass galaxies since z=0.8
Intermediate mass galaxies (logM(Msun)>10) at z~0.6 are the likeliest
progenitors of the present-day numerous population of spirals. There is growing
evidence that they have evolved rapidly since the last 6 to 8 Gyr ago, and
likely have formed a significant fraction of their stellar mass, often showing
perturbed morphologies and kinematics. We have gathered a representative sample
of 88 such galaxies and have provided robust estimates of their gas phase
metallicity. For doing so, we have used moderate spectral resolution
spectroscopy at VLT/FORS2 with unprecedented high S/N allowing to remove biases
coming from interstellar absorption lines and extinction to establish robust
values of R23=([OII]3727 + [OIII]4959,5007)/Hbeta. We definitively confirm that
the predominant population of z~0.6 starbursts and luminous IR galaxies (LIRGs)
are on average, two times less metal rich than the local galaxies at a given
stellar mass. We do find that the metal abundance of the gaseous phase of
galaxies is evolving linearly with time, from z=1 to z=0 and after comparing
with other studies, from z=3 to z=0. Combining our results with the reported
evolution of the Tully Fisher relation, we do find that such an evolution
requires that ~30% of the stellar mass of local galaxies have been formed
through an external supply of gas, thus excluding the close box model. Distant
starbursts & LIRGs have properties (metal abundance, star formation efficiency
& morphologies) similar to those of local LIRGs. Their underlying physics is
likely dominated by gas infall probably through merging or interactions. Our
study further supports the rapid evolution of z~0.4-1 galaxies. Gas exchanges
between galaxies is likely the main cause of this evolution.Comment: 21 pages, 12 figures, A&A, In pres
The Herschel Virgo Cluster Survey. IX. Dust-to-gas mass ratio and metallicity gradients in four Virgo spiral galaxies
Using Herschel data from the Open Time Key Project the Herschel Virgo Cluster
Survey (HeViCS), we investigated the relationship between the metallicity
gradients expressed by metal abundances in the gas phase as traced by the
chemical composition of HII regions, and in the solid phase, as traced by the
dust-to-gas mass ratio. We derived the radial gradient of the dust-to-gas mass
ratio for all galaxies observed by HeViCS whose metallicity gradients are
available in the literature. They are all late type Sbc galaxies, namely
NGC4254, NGC4303, NGC4321, and NGC4501. We examined different dependencies on
metallicity of the CO-to-H conversion factor (\xco), used to transform the
CO observations into the amount of molecular hydrogen. We found that in
these galaxies the dust-to-gas mass ratio radial profile is extremely sensitive
to choice of the \xco\ value, since the molecular gas is the dominant component
in the inner parts. We found that for three galaxies of our sample, namely
NGC4254, NGC4321, and NGC4501, the slopes of the oxygen and of the dust-to-gas
radial gradients agree up to 0.6-0.7R using \xco\ values in the
range 1/3-1/2 Galactic \xco. For NGC4303 a lower value of \xco
10 is necessary. We suggest that such low \xco\ values might be due to a
metallicity dependence of \xco (from close to linear for NGC4254, NGC4321, and
NGC4501 to superlinear for NGC4303), especially in the radial regions
R0.6-0.7R where the molecular gas dominates. On the other hand, the
outer regions, where the atomic gas component is dominant, are less affected by
the choice of \xco, and thus we cannot put constraints on its value.Comment: 13 pages, 8 figures, A&A accepte
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