60 research outputs found
Trends for Outer Disk Profiles
The surface-brightness profiles of galaxy disks fall into three main classes,
based on whether they are simple exponentials (Type I), bend down at large
radii (Type II, "truncations") or bend up at large radii (Type III,
"antitruncations"). Here, we discuss how the frequency of these different
profiles depends on Hubble type, environment, and the presence or absence of
bars; these trends may herald important new tests for disk formation models.Comment: LaTeX, 2 pages, 1 EPS figure, uses modified newpasp.sty (included).
To appear in Formation and Evlution of Galaxy Disks, eds. J.G. Funes and E.M.
Corsin
Phenomenological Study of Engaging Mindset Development in Authentic, Applied Learning Environments in a Secondary School
This qualitative, phenomenological study investigated the perceptions of 16 adults regarding their learning experiences while enrolled as high school students in journalism or engineering classes. The study focused on students\u27 participation in these applied learning experiences, and the effects on the initial and subsequent development of engaging mindsets , also known as noncognitive mindsets (self-efficacy, belief in effort-based achievement, sense of belonging, and appreciating the value and meaning of work), in their post-secondary educational and career experiences.
Participants described seven factors of the learning environment positively affecting their learning and future growth: complex, open-ended problem solving; choice and creativity; student independence; real world relevance; products or performances for authentic audiences; relationship and collaboration skill development; and the shifted role of the teacher. Participants conveyed four key enduring effects of applied learning experiences carrying forward into their adulthood: increased autonomy, cognitive freedom, and willingness to take risks; appreciation for collaborative, empowering relationships; meaningful self-discovery; and a greater sense of purpose.
I analyzed the participants\u27 reflections through the lens of three theoretical frameworks: educational theories related to applied learning environment design, self-determination theory regarding universal psychological needs, and theories looking at the importance of authentic, real world experiences.
I discovered applied learning might hold promise for developing engaging mindsets. Applied learning creates an educational structure teachers can follow, contains elements that fulfill universal psychological needs, and includes important, authentic, real world connections for students
The Outer Structure of Galactic Disks: Connections Between Bars, Disks, and Environments
Surface-brightness profiles for early-type (S0-Sb) disks exhibit three main
classes (Type I, II, and III). Type II profiles are more common in barred
galaxies, and most of the time appear to be related to the bar's Outer Lindblad
Resonance. Roughly half of barred galaxies in the field have Type II profiles,
but almost none in the Virgo Cluster do; this might be related to ram-pressure
stripping in clusters. A strong \textit{anti}correlation is found between Type
III profiles ("antitruncations") and bars: Type III profiles are most common
when there is no bar, and least common when there is a strong bar.Comment: LaTeX, 4 pages, 2 EPS figures, uses modified newpasp.sty (included).
To appear in Pathways through an Eclectic Universe, eds. J. H. Knapen, T. J.
Mahoney, & A. Vazdeki
On the 3 dimensional structure of edge-on disk galaxies
A simple algorithm is employed to deproject the two dimensional images of a
pilot sample of 12 high-quality images of edge-on disk galaxies and to study
their intrinsic 3 dimensional stellar distribution. We examine the radial
profiles of the stars as a function of height above the plane and report a
general trend within our sample of an increasing radial scalelength with height
outside of the dustlane. This could be explained by the widespread presence of
a thick disk component in these galaxies. In addition, the 3 dimensional view
allows the study of the vertical distribution of the outer disk, beyond the
break region, where we detect a significant increase in scalelength with
vertical distance from the major axis for the truncated disks. This could be
regarded as a weakening of the "truncation" with increasing distance from the
plane. Furthermore, we conclude that the recently revised classification of the
radial surface brightness profiles found for face-on galaxies is indeed
independent of geometry. In particular, we find at least one example of each of
the three main profile classes as defined in complete samples of intermediate
to face-on galaxies: not-truncated, truncated and antitruncated. The position
and surface brightness that mark the break location in the radial light
distribution are found to be consistent with those of face-on galaxies.Comment: LaTeX, 25 pages, 10 figures (some low resolution), MNRAS accepted.
Version with all figures in full resolution (~6MB) available at
http://www.astro.rug.nl/~pohlen/pohlen_3Dedgeon.p
Stellar disk truncations at high-z: probing inside-out galaxy formation
We have conducted a systematic search for stellar disk truncations in
disk-like galaxies at intermediate redshift (z<1.1) using the Hubble Ultra Deep
Field (UDF) data. We use the position of the truncation as a direct estimator
of the size of the stellar disk. After accounting for the surface brightness
evolution of the galaxies, our results suggest that the radial position of the
truncations has increased with cosmic time by ~1-3 kpc in the last ~8 Gyr. This
result indicates a small to moderate (~25%) inside-out growth of the disk
galaxies since z~1.Comment: 2 figures, ApJL in pres
Discovery of a Giant Stellar Tidal Stream Around the Disk Galaxy NGC 4013
We report the discovery of a giant, loop-like stellar structure around the
edge-on spiral galaxy NGC 4013. This arcing feature extends 6 arcmin (~26 kpc
in projected distance) northeast from the center and 3 arcmin (~=12 kpc) from
the disk plane; likely related features are also apparent on the southwest side
of the disk, extending to 4 arcmin (~17 kpc). The detection of this low
surface-brightness muR= 27.0+0.3-0.2 mag/sqarcsec) structure is independently
confirmed in three separate datasets from three different telescopes.
Although its true three dimensional geometry is unknown, the sky- projected
morphology of this structure displays a match with the theoretical predictions
for the edge-on, projected view of a stellar tidal streams of a dwarf satellite
moving in a low inclined (~25deg), nearly circular orbit. Using the recent
model of the Monoceros tidal stream in the Milky Way by Penarrubia et al. as
template, we find that the progenitor system may have been a galaxy with an
initial mass 6*10^8 Msun, of which current position and final fate is unknown.
According to this simulation, the tidal stream may be approximately ~2.8 Gyr of
age.
Our results demonstrate that NGC 4013, previously considered a prototypical
isolated disk galaxy in spite of having one of the most prominent HI warps
detected thus far, may have in fact suffered a recent minor merger. This
discovery highlights that undisturbed disks at high surface brightness levels
in the optical but warped in HI maps may in fact reveal complex signatures of
recent accretion events in deep photometric surveys.Comment: Comments: LaTeX, ApJ preprint style, 21 pages, 6 figures (reduced
quality), ApJ accepted. A high resolution version of the paper in addition to
a full version of the colour image of NGC 4013 can be found at
http://www.cosmotography.com/images/iac/ngc4013.html . Replaced to match
accepted version after revisions following referee's repor
Anti-Truncation of Disks in Early-Type Barred Galaxies
The disks of spiral galaxies are commonly thought to be truncated: the radial
surface brightness profile steepens sharply beyond a certain radius (3--5
inner-disk scale lengths). Here we present the radial brightness profiles of a
number of barred S0--Sb galaxies with the opposite behavior: their outer
profiles are distinctly shallower in slope than the main disk profile. We term
these "anti-truncations"; they are found in at least 25% of a larger sample of
barred S0--Sb galaxies. There are two distinct types of anti-truncations. About
one-third show a fairly gradual transition and outer isophotes which are
progressively rounder than the main disk isophotes, suggestive of a disk
embedded within a more spheroidal outer zone -- either the outer extent of the
bulge or a separate stellar halo. But the majority of the profiles have rather
sharp surface-brightness transitions to the shallower, outer exponential
profile and, crucially, outer isophotes which are not significantly rounder
than the main disk; in the Sab--Sb galaxies, the outer isophotes include
visible spiral arms. This suggests that the outer light is still part of the
disk. A subset of these profiles are in galaxies with asymmetric outer
isophotes (lopsided or one-armed spirals), suggesting that interactions may be
responsible for at least some of the disklike anti-truncations.Comment: LaTeX, 5 pages, 4 EPS figures. To appear in Astrophysical Journal
Letters. Minor typos fixed; proper acknowledgments adde
Bulge-Disk Decompositions and Structural Bimodality of Ursa Major Cluster Spiral Galaxies
We present bulge and disk (B/D) decompositions of existing K'-band surface
brightness profiles for 65 Ursa Major cluster spiral galaxies. This improves
upon the disk-only fits of Tully et al. (1996). The 1996 disk fits were used by
Tully & Verheijen (1997) for their discovery of the bimodality of structural
parameters in the UMa cluster galaxies. It is shown that our new 1D B/D
decompositions yield disk structural parameters that differ only slightly from
the basic fits of Tully et al. and evidence for structural bimodality of UMa
galaxies is maintained. Our B/D software for the decomposition of 1D surface
brightness profiles of galaxies uses a non-linear minimization scheme to
recover the best fitting Sersic bulge and exponential disk while accounting for
the possible presence of a compact nucleus and spiral arms and for the effects
of seeing and disk truncations. In agreement with Tully & Verheijen, we find
that the distribution of near-infrared disk central surface brightnesses is
bimodal with an F-test confidence of 80%. There is also strong evidence for a
local minimum in the luminosity function at M_K' ~ -22. A connection between
the brightness bimodality and a dynamical bimodality, based on new HI line
widths, is identified. The B/D parameters are presented in an Appendix.Comment: Accepted for publication in MNRA
The Outer Disks of Early-Type Galaxies. I. Surface-Brightness Profiles of Barred Galaxies
We present a study of 66 barred, early-type (S0-Sb) disk galaxies, focused on
the disk surface brightness profile outside the bar region and the nature of
Freeman Type I and II profiles, their origins, and their possible relation to
disk truncations. This paper discusses the data and their reduction, outlines
our classification system, and presents -band profiles and classifications
for all galaxies in the sample.
The profiles are derived from a variety of different sources, including the
Sloan Digital Sky Survey (Data Release 5). For about half of the galaxies, we
have profiles derived from more than one telescope; this allows us to check the
stability and repeatability of our profile extraction and classification. The
vast majority of the profiles are reliable down to levels of mu_R ~ 27 mag
arcsec^-2; in exceptional cases, we can trace profiles down to mu_R > 28. We
can typically follow disk profiles out to at least 1.5 times the traditional
optical radius R_25; for some galaxies, we find light extending to ~ 3 R_25.
We classify the profiles into three main groups: Type I (single-exponential),
Type II (down-bending), and Type III (up-bending). The frequencies of these
types are approximately 27%, 42%, and 24%, respectively, plus another 6% which
are combinations of Types II and III. We further classify Type II profiles by
where the break falls in relation to the bar length, and in terms of the
postulated mechanisms for breaks at large radii ("classical trunction" of star
formation versus the influence of the Outer Lindblad Resonance of the bar). We
also classify the Type III profiles by the probable morphology of the outer
light (disk or spheroid). Illustrations are given for all cases. (Abridged)Comment: 41 pages, 26 PDF figures. To appear in the Astronomical Journal.
Version with full-resolution figures available at
http://www.mpe.mpg.de/~erwin/research
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