333 research outputs found
Aboriginal Education in Winnipeg Inner City High Schools
This study investigates "the educational circumstances of Aboriginal students in Winnipeg inner city high schools... Responses by Aboriginal people to our questions about their experiences in school reveal the existence of what we have identified as a cultural/class/experiential divide between Aboriginal students and their families on the one hand, and the school system on the other. The life experiences and cultural values of many Aboriginal students and their families differ significantly from what they experience in the schools, which are run largely by non-Aboriginal, middle class people for the purpose of advancing the values of the dominant culture. The educational system marginalizes Aboriginal students, does not adequately reflect their cultural values and their daily realities, and feels alien to many Aboriginal people... The face that schools present to Aboriginal students is decidedly non-Aboriginal: for example, there are few Aboriginal teachers, and little Aboriginal content in the curriculum.
The evidence that we have gathered suggests to us that Aboriginal people want the education that is needed to enable them to participate fully in Canadian society and in their own self-governance, but they do not want to abandon what it is to be Aboriginal in order to do so. What Aboriginal people have said to us about the educational system is not that Aboriginal people should be forced to change in order to fit into and ‘succeed’ in school—this is what the residential schools attempted, unsuccessfully, to do—but rather that schools and the educational system generally need to change in order to better reflect the rapidly changing demographic and cultural realities of our community
The ultraviolet visibility and quantitative morphology of galactic disks at low and high redshift
We used ultraviolet (200 nm) images of the local spiral galaxies M33, M51,
M81, M100, M101 to compute morphological parameters of galactic disks at this
wavelength : half-light radius , surface brightness distributions,
asymmetries () and concentrations (). The visibility and the evolution
of the morphological parameters are studied as a function of the redshift. The
main results are : local spiral galaxies would be hardly observed and
classified if projected at high redshifts (z 1) unless a strong
luminosity evolution is assumed. Consequently, the non-detection of large
galactic disks cannot be used without caution as a constraint on the evolution
of galatic disks. Spiral galaxies observed in ultraviolet appear more irregular
since the contribution from the young stellar population becomes predominent.
When these galaxies are put in a (log vs. log ) diagram, they move to
the irregul ar sector defined at visible wavelengths. Moreover, the log
parameter is degenerate and cannot be used for an efficient classification of
morphological ultraviolet types. The analysis of high redshift galaxies cannot
be carried out in a reliable way so far and a multi-wavelength approach is
required if one does not want to misinterpret the data.Comment: 12 pages, accepted for publication in A&A on 15 January 200
Astrophysically Motivated Bulge-Disk Decompositions of SDSS Galaxies
We present a set of bulge-disk decompositions for a sample of 71,825 SDSS
main-sample galaxies in the redshift range 0.003<z<0.05. We have fit each
galaxy with either a de Vaucouleurs ('classical') or an exponential ('pseudo-')
bulge and an exponential disk. Two dimensional Sersic fits are performed when
the 2-component fits are not statistically significant or when the fits are
poor, even in the presence of high signal-to-noise. We study the robustness of
our 2-component fits by studying a bright subsample of galaxies and we study
the systematics of these fits with decreasing resolution and S/N. Only 30% of
our sample have been fit with two-component fits in which both components are
non-zero. The g-r and g-i colours of each component for the two-component
models are determined using linear templates derived from the r-band model. We
attempt a physical classification of types of fits into disk galaxies,
pseudo-bulges, classical bulges, and ellipticals. Our classification of
galaxies agrees well with previous large B+D decomposed samples. Using our
galaxy classifications, we find that Petrosian concentration is a good
indicator of B/T, while overall Sersic index is not. Additionally, we find that
the majority of green valley galaxies are bulge+disk galaxies. Furthermore, in
the transition from green to red B+D galaxies, the total galaxy colour is most
strongly correlated with the disk colour.Comment: 28 pages, 34 figures, MNRAS accepte
Structural properties of discs and bulges of early-type galaxies
We have used the EFAR sample of galaxies to study the light distributions of
early-type galaxies. We decompose the 2D light distribution of the galaxies in
a flattened spheroidal component with a Sersic radial light profile and an
inclined disc component with an exponential light profile. We show that the
brightest, bulge dominated elliptical galaxies have a fairly broad distribution
in the Sersic profile shape parameter n_B, with a median of about 3.7 and a
sigma of ~0.9. Other galaxies have smaller n_B values, meaning that spheroids
are in general less concentrated than the n_B=4 de Vaucouleurs-law profile.
The results of our light decompositions are robust, even though without
kinematic information we cannot prove that the spheroids and discs are really
pressure- and rotation-supported stellar systems. If we assume that the
detected spheroids and discs are indeed separate components, we can draw the
following conclusions: 1) the spheroid and disc scale sizes are correlated; 2)
bulge-to-total luminosity ratios, bulge effective radii, and bulge n_B values
are all positively correlated; 3) the bivariate space density distribution of
elliptical galaxies in the (luminosity, scale size)-plane is well described by
a Schechter luminosity function in and a log-normal scale-size distribution at
a given luminosity; 4) at the brightest luminosities, the scale size
distribution of elliptical galaxies is similar to those of bright spiral
galaxies; at fainter luminosities the elliptical scale size distribution peaks
at distinctly smaller sizes than the spiral galaxy distribution; and 5) bulge
components of early-type galaxies are typically a factor 1.5 to 2.5 smaller
than the disks of spiral galaxies, while disc components of early-type galaxies
are typically twice as large as the discs of spiral galaxies. [abridged]Comment: 16 pages, 18 figures. Accepted for publication in the MNRA
The Role of Metalanguage in Supporting Academic Language Development
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/96715/1/j.1467-9922.2012.00742.x.pd
The Tully-Fisher Relation in Cluster Cl0024+1654 at z=0.4
Using moderate-resolution Keck spectra, we have examined the velocity
profiles of 15 members of cluster Cl0024+1654 at z=0.4. WFPC2 images of the
cluster members have been used to determine structural parameters, including
disk sizes, orientations, and inclinations. We compare two methods of optical
rotation curve analysis for kinematic measurements. Both methods take seeing,
slit size and orientation, and instrumental effects into account and yield
similar rotation velocity measurements. Four of the galaxies in our sample
exhibit unusual kinematic signatures, such as non-circular motions. Our key
result is that the Cl0024 galaxies are marginally underluminous (0.50 +/- 0.23
mag), given their rotation velocities, as compared to the local Tully-Fisher
relation. In this analysis, we assume no slope evolution, and take into account
systematic differences between local and distant velocity and luminosity
measurements. Our result is particularly striking considering the Cl0024
members have very strong emission lines, and local galaxies with similar Halpha
equivalent widths tend to be overluminous on the Tully-Fisher relation. Cl0024
Tully-Fisher residuals appear to be correlated most strongly with galaxy
rotation velocities, indicating a possible change in the slope of the
Tully-Fisher relation. However, we caution that this result may be strongly
affected by magnitude selection and by the original slope assumed for the
analysis. Cl0024 residuals also depend weakly on color, emission line strength
and extent, and photometric asymmetry. In a comparison of stellar and gas
motions in two Cl0024 members, we find no evidence for counter-rotating stars
and gas, an expected signature of mergers.Comment: 38 pages, 10 figures, accepted for publication in ApJ; version with
full-resolution figures can be downloaded from
http://www.ucolick.org/~anne/recent_pubs.htm
The Millennium Galaxy Catalogue: the space density and surface brightness distribution(s) of galaxies
We recover the joint and individual space density and surface brightness
distribution(s) of galaxies from the Millennium Galaxy Catalogue. The MGC is a
local survey spanning 30.9 sq deg and probing approximately one--two mag/sq
arcsec deeper than either the Two-Degree Field Galaxy Redshift Survey (2dFGRS)
or the Sloan Digital Sky Survey (SDSS). The MGC contains 10,095 galaxies to
B_mgc < 20 mag with 96 per cent spectroscopic completeness. We implement a
joint luminosity-surface brightness step-wise maximum likelihood method to
recover the bivariate brightness distribution (BBD) inclusive of most selection
effects. Integrating the BBD over surface brightness we recover the following
Schechter function parameters: phi* = (0.0177 +/- 0.0015) h^3 Mpc^{-3}, M_{B}*
- 5 log h = (-19.60 +/- 0.04) mag and alpha =-1.13 +/- 0.02. Compared to the
2dFGRS (Norberg et al 2002) we find a consistent M* value but a slightly
flatter faint-end slope and a higher normalisation, resulting in a final
luminosity density j_{b_J} = (1.99 +/- 0.17) x 10^8 h L_{odot} Mpc^{-3}. The
MGC surface brightness distribution is a well bounded Gaussian at the M* point
with phi* = (3.5 +/- 0.1) x 10^{-2} h^3 Mpc^{-3}, mu^{e*} = (21.90 +/- 0.01)
mag/sq arcsec and sigma_{ln R_e} = 0.35 +/- 0.01. The characteristic surface
brightness for luminous systems is invariant to M_{B} - 5 log h ~ -19 mag
faintwards of which it moves to lower surface brightness. Higher resolution
(FWHM 26 mag/sq arcsec in the B-band)
observations of the local universe are now essential to probe to lower
luminosity and lower surface brightness levels. [abridged]Comment: Accepted for publication in MNRAS, 26 pages with 21 figures (some
degraded). A full pdf version, along with MGC data release, is available from
the MGC website at, http://www.eso.org/~jliske/mg
Evolution along the sequence of S0 Hubble types induced by dry minor mergers. I - Global bulge-to-disk structural relations
Recent studies have argued that galaxy mergers are not important drivers for
the evolution of S0's, on the basis that mergers cannot preserve the coupling
between the bulge and disk scale-lengths observed in these galaxies and the
lack of correlation of their ratio with the S0 Hubble type. We investigate
whether the remnants resulting from collision-less N-body simulations of
intermediate and minor mergers onto S0 galaxies evolve fulfilling global
structural relations observed between the bulges and disks of these galaxies.
Different initial bulge-to-disk ratios of the primary S0 have been considered,
as well as different satellite densities, mass ratios, and orbits of the
encounter. We have analysed the final morphology of the remnants in images
simulating the typical observing conditions of S0 surveys. We derive bulge+disk
decompositions of the final remnants to compare their global bulge-to-disk
structure with observations. We show that all remnants present undisturbed S0
morphologies according to the prescriptions of specialized surveys. The dry
intermediate and minor mergers induce noticeable bulge growth (S0c --> S0b and
S0b --> S0a), but affect negligibly to the bulge and disk scale-lengths.
Therefore, if a coupling between these two components exists prior to the
merger, the encounter does not break this coupling. This fact provides a simple
explanation for the lack of correlation between the ratio of bulge and disk
scale-lengths and the S0 Hubble type reported by observations. These models
prove that dry intermediate and minor mergers can induce global structural
evolution within the sequence of S0 Hubble types compatible with observations,
meaning that these processes should not be discarded from the evolutionary
scenarios of S0's just on the basis of the strong coupling observed between the
bulge and disk scale-lengths in these galaxies (abridged).Comment: Accepted for publication in Astronomy & Astrophysics, 12 pages, 11
figures. Definitive version after proofs. Corrected typo in the legend of
Fig. 2. Definitive version of Fig. 7 (pending copyright implications in the
previous version). Added references and corrected typo
Growth of galactic bulges by mergers. II. Low-density satellites
Satellite accretion events have been invoked for mimicking the internal
secular evolutionary processes of bulge growth. However, N-body simulations of
satellite accretions have paid little attention to the evolution of bulge
photometric parameters, to the processes driving this evolution, and to the
consistency of this evolution with observations. We want to investigate whether
satellite accretions indeed drive the growth of bulges, and whether they are
consistent with global scaling relations of bulges and discs. We perform N-body
models of the accretion of satellites onto disc galaxies. A Tully-Fisher (M
\propto V_{rot}^ {alpha_TF}) scaling between primary and satellite ensures that
density ratios, critical to the outcome of the accretion, are realistic. We
carry out a full structural, kinematic and dynamical analysis of the evolution
of the bulge mass, bulge central concentration, and bulge-to-disc scaling
relations. The remnants of the accretion have bulge-disc structure. Both the
bulge-to-disc ratio (B/D) and the Sersic index (n) of the remnant bulge
increase as a result of the accretion, with moderate final bulge Sersic
indices: n = 1.0 to 1.9. Bulge growth occurs no matter the fate of the
secondary, which fully disrupts for alpha_TF=3 and partially survives to the
remnant center for alpha_TF = 3.5 or 4. Global structural parameters evolve
following trends similar to observations. We show that the dominant mechanism
for bulge growth is the inward flow of material from the disc to the bulge
region during the satellite decay. The models confirm that the growth of the
bulge out of disc material, a central ingredient of secular evolution models,
may be triggered externally through satellite accretion.Comment: Accepted for publication in A&A, 20 pages, 11 figures. Figs. 1 and 2
are low resolution ones: high-resolution versions available under request to
the author
On the Origin of Exponential Galaxy Disks
We use a disk galaxy evolution model to investigate whether galaxies with
exponential surface brightness profiles can be produced in a cosmologically
motivated framework for disk galaxy formation. Our model follows the accretion,
cooling, and ejection of baryonic mass, as a function of radius, inside growing
dark matter haloes. The surface density profile of the disk is determined by
detailed angular momentum conservation, starting from the distribution of
specific angular momentum as found in cosmological simulations. Exponential and
quasi-exponential disks can be produced by our model through a combination of
supernova driven galactic outflows (which preferentially remove low angular
momentum material), intrinsic variation in the angular momentum distribution of
the halo gas, and the inefficiency of star formation at large radii. We use
observations from the SDSS NYU-VAGC to show that the median Sersic index of
blue galaxies is a strong function of stellar mass. For blue galaxies, low mass
galaxies have a median n=1.3, while high mass galaxies have a median n=4. Our
model with energy driven outflows correctly reproduces this trend, whereas our
models with momentum driven outflows and no outflows over predict the Sersic
indices in low mass galaxies. We show that the observed fraction of
"bulge-less" exponential galaxies is a strong function of stellar mass. For
Milky-Way mass galaxies less than 0.1% of blue galaxies are bulge-less, whereas
for M33 mass galaxies bulge-less and quasi-bulgeless galaxies are typical.
These results suggest that the difficulty of hierarchical formation models to
produce bulge-less Milky-Way mass galaxies is in fact not a problem. However,
the problem of producing M33 like galaxies remains, and will provide a key test
for hierarchical galaxy formation models. [Abridged]Comment: 23 pages, 13 figures, accepted to MNRAS, two new figure
- …