415 research outputs found
Random Matrices with Correlated Elements: A Model for Disorder with Interactions
The complicated interactions in presence of disorder lead to a correlated
randomization of states. The Hamiltonian as a result behaves like a
multi-parametric random matrix with correlated elements. We show that the
eigenvalue correlations of these matrices can be described by the single
parametric Brownian ensembles. The analogy helps us to reveal many important
features of the level-statistics in interacting systems e.g. a critical point
behavior different from that of non-interacting systems, the possibility of
extended states even in one dimension and a universal formulation of level
correlations.Comment: 19 Pages, No Figures, Major Changes to Explain the Mathematical
Detail
The time resolved measurement of ultrashort THz-band electric fields without an ultrashort probe
The time-resolved detection of ultrashort pulsed THz-band electric field
temporal profiles without an ultrashort laser probe is demonstrated. A
non-linear interaction between a narrow-bandwidth optical probe and the THz
pulse transposes the THz spectral intensity and phase information to the
optical region, thereby generating an optical pulse whose temporal electric
field envelope replicates the temporal profile of the real THz electric field.
This optical envelope is characterised via an autocorrelation based FROG
measurement, hence revealing the THz temporal profile. The combination of a
narrow-bandwidth, long duration, optical probe and self-referenced FROG makes
the technique inherently immune to timing jitter between the optical probe and
THz pulse, and may find particular application where the THz field is not
initially generated via ultrashort laser methods, such as the measurement of
longitudinal electron bunch profiles in particle accelerators.Comment: 7 pages, 3 figures, submitted to AP
The Snedden-Farnsworth Exchanges of 1917 and 1918 on the Value of Music and Art in Education
In 1917 and 1918, Charles Hubert Farnsworth, a leading music educator from Teachers College, Columbia University, and David Snedden, a critic and educational theorist of national repute, privately exchanged views on the role of art and music in society and in education. Snedden mulled over Herbert Spencer's query “What knowledge is of most worth?” and concluded that music must have practical survival value: it must contribute primarily to the maintenance of social and political order and secondarily to other aims. Farnsworth, on the other hand, thought that music performance or appreciation should be for the immediate joy that it gives the individual, not for some deferred social purpose no matter how important it might be. These divergent positions are explained in light of Farnsworth's interests in philosophy and Snedden's schooling in Spencerian and Darwinian thought.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/68979/2/10.2307_3345173.pd
Multi-Channel Transport in Disordered Medium under Generic Scattering Conditions
Our study of the evolution of transmission eigenvalues, due to changes in
various physical parameters in a disordered region of arbitrary dimensions,
results in a generalization of the celebrated DMPK equation. The evolution is
shown to be governed by a single complexity parameter which implies a deep
level of universality of transport phenomena through a wide range of disordered
regions. We also find that the interaction among eigenvalues is of many body
type that has important consequences for the statistical behavior of transport
properties.Comment: 19 Pages, No Figure
Discovery of New Ultracool White Dwarfs in the Sloan Digital Sky Survey
We report the discovery of five very cool white dwarfs in the Sloan Digital
Sky Survey (SDSS). Four are ultracool, exhibiting strong collision induced
absorption (CIA) from molecular hydrogen and are similar in color to the three
previously known coolest white dwarfs, SDSS J1337+00, LHS 3250 and LHS 1402.
The fifth, an ultracool white dwarf candidate, shows milder CIA flux
suppression and has a color and spectral shape similar to WD 0346+246. All five
new white dwarfs are faint (g > 18.9) and have significant proper motions. One
of the new ultracool white dwarfs, SDSS J0947, appears to be in a binary system
with a slightly warmer (T_{eff} ~ 5000K) white dwarf companion.Comment: 15 pages, 3 figures, submitted to ApJL. Higher resolution versions of
finding charts are available at
http://astro.uchicago.edu/~gates/findingchart
Radial Velocity Offsets Due to Mass Outflows and Extinction in Active Galactic Nuclei
We present a study of the radial velocity offsets between narrow emission
lines and host galaxy lines (stellar absorption and H I 21-cm emission) in
Seyfert galaxies with observed redshifts less than 0.043. We find that 35% of
the Seyferts in the sample show [O III] emission lines with blueshifts with
respect to their host galaxies exceeding 50 km/s, whereas only 6% show
redshifts this large, in qualitative agreement with most previous studies. We
also find that a greater percentage of Seyfert 1 galaxies show blueshifts than
Seyfert 2 galaxies. Using HST/STIS spatially-resolved spectra of the Seyfert 2
galaxy NGC 1068 and the Seyfert 1 galaxy NGC 4151, we generate geometric models
of their narrow-line regions (NLRs) and inner galactic disks, and show how
these models can explain the blueshifted [O III] emission lines in collapsed
STIS spectra of these two Seyferts. We conclude that the combination of mass
outflow of ionized gas in the NLR and extinction by dust in the inner disk
(primarily in the form of dust spirals) is primarily responsible for the
velocity offsets in Seyfert galaxies. More exotic explanations are not needed.
We discuss the implications of this result for the velocity offsets found in
higher redshift AGN.Comment: 25 pages, 7 figures, accepted for publication in the Astrophysical
Journa
Probing the Ionizing Continuum of Narrow-Line Seyfert 1 Galaxies. I.Observational Results
We present optical spectra and emission-line ratios of 12 Narrow-Line Seyfert
1 (NLS1) galaxies that we observed to study the ionizing EUV continuum. A
common feature in the EUV continuum of active galactic nuclei is the big blue
bump (BBB), generally associated with thermal accretion disk emission. While
Galactic absorption prevents direct access to the EUV range, it can be mapped
by measuring the strength of a variety of forbidden optical emission lines that
respond to different EUV continuum regions. We find that narrow emission-line
ratios involving [OII]3727, Hbeta, [OIII]5007, [OI]6300, Halpha,[NII]6583, and
[SII]6716,6731 indicate no significant difference between NLS1s and Broad-Line
Seyfert 1 (BLS1) galaxies, which suggests that the spectral energy
distributions of their ionizing EUV - soft X-ray continua are similar. The
relative strength of important forbidden high ionization lines like [NeV]3426
compared to HeII4686 and the relative strength of [FeX]6374 appear to show the
same range as in BLS1 galaxies. However, a trend of weaker
F([OI]6300)/F(Halpha) emission-line ratios is indicated for NLS1s compared to
BLS1s. To recover the broad emission-line profiles we used Gaussian components.
This approach indicates that the broad Hbeta profile can be well described with
a broad component (FWHM = 3275 +- 800 km/s) and an intermediate broad component
(FWHM = 1200 +- 300 km/s). The width of the broad component is in the typical
range of normal BLS1s. The emission-line flux that is associated with the broad
component in these NLS1s amounts to at least 60% of the total flux. Thus it
dominates the total line flux, similar to BLS1 galaxies.Comment: 34 pages, 9 figures. accepted for publication in the
Astrophys.Journa
Hdelta-Selected Galaxies in the Sloan Digital Sky Survey I: The Catalog
[Abridged] We present here a new and homogeneous sample of 3340 galaxies
selected from the Sloan Digital Sky Survey (SDSS) based solely on the observed
strength of their Hdelta absorption line. These galaxies are commonly known as
``post-starburst'' or ``E+A'' galaxies, and the study of these galaxies has
been severely hampered by the lack of a large, statistical sample of such
galaxies. In this paper, we rectify this problem by selecting a sample of
galaxies which possess an absorption Hdelta equivalent width of EW(Hdelta_max)
- Delta EW(Hdelta_max) > 4A from 106682 galaxies in the SDSS. We have performed
extensive tests on our catalog including comparing different methodologies of
measuring the Hdelta absorption and studying the effects of stellar absorption,
dust extinction, emission-filling and measurement error. The measured abundance
of our Hdelta-selected (HDS) galaxies is 2.6 +/- 0.1% of all galaxies within a
volume-limited sample of 0.05<z<0.1 and M(r*)<-20.5, which is consistent with
previous studies of such galaxies in the literature. We find that only 25 of
our HDS galaxies in this volume-limited sample (3.5+/-0.7%) show no evidence
for OII and Halpha emission, thus indicating that true E+A (or k+a) galaxies
are extremely rare objects at low redshift, i.e., only 0.09+/-0.02% of all
galaxies in this volume-limited sample are true E+A galaxies. In contrast,
89+/-5% of our HDS galaxies in the volume-limited sample have significant
detections of the OII and Halpha emission lines. We find 27 galaxies in our
volume-limited HDS sample that possess no detectable OII emission, but do
however possess detectable Halpha emission. These galaxies may be dusty
star-forming galaxies. We provide the community with this new catalog of
Hdelta-selected galaxies to aid in the understanding of these galaxies.Comment: Submitted to PASJ. Catalog of galaxies available at
http://astrophysics.phys.cmu.edu/~tomo/ea
A New Giant Stellar Structure in the Outer Halo of M31
The Sloan Digital Sky Survey has revealed an overdensity of luminous red
giant stars ~ 3 degrees (40 projected kpc) to the northeast of M31, which we
have called Andromeda NE. The line-of-sight distance to Andromeda NE is within
approximately 50 kpc of M31; Andromeda NE is not a physically unrelated
projection. Andromeda NE has a g-band absolute magnitude of ~ -11.6 and central
surface brightness of ~ 29 mag/sq.arcsec, making it nearly two orders of
magnitude more diffuse than any known Local Group dwarf galaxy at that
luminosity. Based on its distance and morphology, Andromeda NE is likely
undergoing tidal disruption. Andromeda NE's red giant branch color is unlike
that of M31's present-day outer disk or the stellar stream reported by Ibata et
al. (2001), arguing against a direct link between Andromeda NE and these
structures. However, Andromeda NE has a red giant branch color similar to that
of the G1 clump; it is possible that these structures are both material torn
off of M31's disk in the distant past, or that these are both part of one
ancient stellar stream.Comment: 11 pages, 3 figures; ApJ Letters accepted versio
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