503 research outputs found
The Stability of the Weak Skyrmions
We consider a set of gauge invariant terms in higher order effective
Lagrangians of the strongly interacting scalar of the electroweak theory. The
terms are introduced in the framework of the hidden gauge symmetry formalism.
The usual gauge term is known to stabilize the skyrmion but only in the large
vector mass limit. We find that adding higher-order gauge terms is insufficient
to insure stability. We then proceed to analyze other gauge invariant
interaction terms. Some of the conclusions also apply to QCD skyrmions.Comment: 3 pages, revtex v3, (optional), LAVAL-PHY-11-9
Dust Abundance and Properties in the Nearby Dwarf Galaxies NGC 147 and NGC 185
We present new mid- to far-infrared images of the two dwarf compact elliptical galaxies that are satellites of M31, NGC 185, and NGC 147, obtained with the Spitzer Space Telescope. Spitzer's high sensitivity and spatial resolution enable us for the first time to look directly into the detailed spatial structure and properties of the dust in these systems. The images of NGC 185 at 8 and 24 ÎŒm display a mixed morphology characterized by a shell-like diffuse emission region surrounding a central concentration of more intense infrared emission. The lower resolution images at longer wavelengths show the same spatial distribution within the central 50" but beyond this radius, the 160 ÎŒm emission is more extended than that at 24 and 70 ÎŒm. On the other hand, the dwarf galaxy NGC 147, located only a small distance away from NGC 185, shows no significant infrared emission beyond 24 ÎŒm and therefore its diffuse infrared emission is mainly stellar in origin. For NGC 185, the derived dust mass based on the best fit to the spectral energy distribution is 1.9 Ă 10^3 M_â, implying a gas mass of 3.0 Ă 10^5 M_â. These values are in agreement with those previously estimated from infrared as well as CO and H I observations and are consistent with the predicted mass return from dying stars based on the last burst of star formation 1 Ă 10^9 yr ago. Based on the 70-160 ÎŒm flux density ratio, we estimate a temperature for the dust of ~17 K. For NGC 147, we obtain an upper limit for the dust mass of 4.5 Ă 10^2 M_â at 160 ÎŒm (assuming a temperature of ~20 K), a value consistent with the previous upper limit derived using Infrared Space Observatory observations of this galaxy. In the case of NGC 185, we also present full 5-38 ÎŒm low-resolution (R ~ 100) spectra of the main emission regions. The Infrared Spectrograph spectra of NGC 185 show strong polycyclic aromatic hydrocarbons emission, deep silicate absorption features and H_2 pure rotational line ratios consistent with having the dust and molecular gas inside the dust cloud being impinged by the far-ultraviolet radiation field of a relatively young stellar population. Therefore, based on its infrared spectral properties, NGC 185 shows signatures of recent star formation (a few Ă10^8 yr ago), although its current star formation rate is quite low
Infrared signature of active massive black holes in nearby dwarf galaxies
We investigate the possible presence of active galactic nuclei (AGN) in dwarf
galaxies and other nearby galaxies to identify candidates for follow-up
confirmation and dynamical mass measurements. We use the Wide-field Infrared
Survey Explorer (WISE) All-Sky Release Source Catalog and examine the infrared
colours of a sample of dwarf galaxies and other nearby galaxies in order to
identify both unobscured and obscured candidate AGN by applying the infrared
colour diagnostic. Stellar masses of galaxies are obtained using a combination
of three independent methods. Black hole masses are estimated using the
bolometric luminosity of the AGN candidates and computed for three cases of the
bolometric-to-Eddington luminosity ratio. We identify 303 candidate AGN, of
which 276 were subsequently found to have been independently identified as AGN
via other methods. The remaining 9% require follow-up observations for
confirmation. The activity is detected in galaxies with stellar masses from ~
10^6 to 10^9 solar masses; assuming the candidates are AGN, the black hole
masses are estimated to be ~ 10^3 - 10^6 solar masses, adopting L_bol = 0.1
L_Edd. The black hole masses probed are several orders of magnitude smaller
than previously reported for centrally located massive black holes. We examine
the stellar mass versus black hole mass relationship in this low galaxy mass
regime. We find that it is consistent with the existing relation extending
linearly (in log-log space) into the lower mass regime. These findings suggest
that CMBH are present in low-mass galaxies and in the Local Universe, and
provide new impetus for follow-up dynamical studies of quiescent black holes in
local dwarf galaxies.Comment: 14 pages, 9 figures, 4 tables, accepted for publication in Astronomy
& Astrophysics. The first version of this paper appeared on astro-ph in 2014
(arXiv:1411.3844). The new version includes 3 new tables, 1 new figure and
updated discussio
Using agronomic practices to increase the per hectare yield of flax fibre
Non-Peer ReviewedThis paper summarizes the results of recent work that has been done in Saskatchewan and Manitoba to find agronomic practices that can be used to increase the per ha production of flax fibre. Such practices include changes in varieties grown, rates of seeding, dates of seeding and methods of harvest. Finding cost-effective ways to increase per ha fibre yields will increase the profits going to farmers and processors and hence make flax straw and fibre production, collection, and processing more financially viable
Galaxy Evolution in the Cluster Abell 85: New Insights from the Dwarf Population
We present the first results of a new spectroscopic survey of the cluster
Abell 85 targeting 1466 candidate cluster members within the central 1
deg of the cluster and having magnitudes using VIMOS/VLT and
HYDRA/WIYN. A total of 520 galaxies are confirmed as either relaxed cluster
members or part of an infalling population. A significant fraction are low
mass; the median stellar mass of the sample is , and 25%
have stellar masses below (i.e. 133 dwarf galaxies). We also
identify seven active galactic nuclei (AGN), four of which reside in dwarf host
galaxies. We probe the evolution of star formation rates, based on H
emission and continuum modeling, as a function of both mass and environment. We
find that more star forming galaxies are observed at larger clustercentric
distances, while infalling galaxies show evidence for recently enhanced star
forming activity. Main sequence galaxies, defined by their continuum star
formation rates, show different evolutionary behavior based on their mass. At
the low mass end, the galaxies have had their star formation recently quenched,
while more massive galaxies show no significant change. The timescales probed
here favor fast quenching mechanisms, such as ram-pressure stripping. Galaxies
within the green valley, defined similarly, do not show evidence of quenching.
Instead, the low mass galaxies maintain their levels of star forming activity,
while the more massive galaxies have experienced a recent burst.Comment: 15 pages, 10 figures, accepted for publication in MNRA
Generating a profit from oilseed flax straw
Non-Peer ReviewedMost Prairie farmers who grow oilseed flax straw have problems dealing with the straw that is produced as a byproduct of producing flaxseed. The straw is either burnt, chopped with difficulty or sold for a very low price to the existing flax straw processors who are targeting the specialty paper and low end plastic reinforcement markets. This paper briefly examines some of the higher value and/or expanding markets for flax fiber based products. It will also outline new straw management techniques that are required to turn flax straw into a significant source of farmer profits
On the electromagnetic form factors of the proton from generalized Skyrme models
We compare the prediction of Skyrme-like effective Lagrangians with data for
electromagnetic form factors of proton and consider the possibility of fixing
the parameters of these higher-order Lagrangians. Our results indicate that one
or two-parameter models can lead to better agreement with the data but more
accurate determination of the effective Lagragian faces theoretical
uncertainties.Comment: 8 pages, 2 figures, revte
Starburst Galaxies in Cluster-feeding Filaments Unveiled by Spitzer
We report the first direct detection with Spitzer of galaxy filaments. Using Spitzer and ancillary optical data, we have discovered two filamentary structures in the outskirts of the cluster Abell 1763. Both filaments point toward Abell 1770, which lies at the same redshift as Abell 1763 (z = 0.23), at a projected distance of ~13 Mpc. The X-ray cluster emission is elongated along the same direction. Most of the far-infrared emission is powered by star formation. According to the optical spectra, only one of the cluster members is classified as an active galactic nucleus. Star formation is clearly enhanced in galaxies along the filaments: the fraction of starburst galaxies in the filaments is more than twice than that in other cluster regions. We speculate that these filaments are feeding the cluster Abell 1763 by the infall of galaxies and galaxy groups. Evidence for one of these groups is provided by the analysis of galaxy kinematics in the central cluster region
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