34 research outputs found
High Velocity Line Emission in the NLR of NGC 4151
Narrow-band imaging of the nuclear region of NGC 4151 with the Hubble Space
Telescope is presented. The filter bandpasses isolate line emission in various
high velocity ranges in several ions. Slitless and long-slit spectra of the
region with the Space Telescope Imaging Spectrograph also indicate the
locations of high velocity gas. These emission regions are faint and are
interspersed among the bright emission clouds seen in direct images. They have
radial velocities up to 1400 km/s relative to the nucleus, and are found in
both approach and recession on both sides of the nucleus. This contrasts
strongly with the bright emission line clouds which have been discussed
previously as showing bidirectional outflow with velocities within 400 km/s of
the nucleus. We discuss the possible connections of the high velocity material
with the radio jet and the nuclear radiation.Comment: 12 pages plus 6 figures, to be published in A
HST STIS spectroscopy of the triple nucleus of M31: two nested disks in Keplerian rotation around a Supermassive Black Hole
We present HST spectroscopy of the nucleus of M31 obtained with STIS. Spectra
taken around the CaT lines at 8500 see only the red giants in the double
bright- ness peaks P1 and P2. In contrast, spectra taken at 3600-5100 A are
sensitive to the tiny blue nucleus embedded in P2, the lower surface brightness
red nucleus. P2 has a K-type spectrum, but the embedded blue nucleus has an
A-type spectrum with strong Balmer absorption lines. Given the small likelihood
for stellar collisions, a 200 Myr old starburst appears to be the most
plausible origin of the blue nucleus. In stellar population, size, and velocity
dispersion, the blue nucleus is so different from P1 and P2 that we call it P3.
The line-of-sight velocity distributions of the red stars in P1+P2 strengthen
the support for Tremaine s eccentric disk model. The kinematics of P3 is
consistent with a circular stellar disk in Keplerian rotation around a
super-massive black hole with M_bh = 1.4 x 10^8 M_sun. The P3 and the P1+P2
disks rotate in the same sense and are almost coplanar. The observed velocity
dispersion of P3 is due to blurred rotation and has a maximum value of sigma =
1183+-201 km/s. The observed peak rotation velocity of P3 is V = 618+-81 km/s
at radius 0.05" = 0.19 pc corresponding to a circular rotation velocity at this
radius of ~1700 km/s. Any dark star cluster alternative to a black hole must
have a half-mass radius <= 0.03" = 0.11 pc. We show that this excludes clusters
of brown dwarfs or dead stars on astrophysical grounds.Comment: Astrophysical Journal, Sep 20, 2005, 21 pages including 20 figure
Evidence of a Supermassive Black Hole in the Galaxy NGC 1023 from the Nuclear Stellar Dynamics
We analyze the nuclear stellar dynamics of the SB0 galaxy NGC 1023, utilizing
observational data both from the Space Telescope Imaging Spectrograph aboard
the Hubble Space Telescope and from the ground. The stellar kinematics measured
from these long-slit spectra show rapid rotation (V = 70 km/s at a distance of
0.1 arcsec = 4.9 pc from the nucleus) and increasing velocity dispersion toward
the nucleus (where sigma = 295 +/- 30 km/s). We model the observed stellar
kinematics assuming an axisymmetric mass distribution with both two and three
integrals of motion. Both modeling techniques point to the presence of a
central dark compact mass (which presumably is a supermassive black hole) with
confidence > 99%. The isotropic two-integral models yield a best-fitting black
hole mass of (6.0 +/- 1.4) x 10^7 M_sun and mass-to-light ratio (M/L_V) of 5.38
+/- 0.08, and the goodness-of-fit (chi^2) is insensitive to reasonable values
for the galaxy's inclination. The three-integral models, which
non-parametrically fit the observed line-of-sight velocity distribution as a
function of position in the galaxy, suggest a black hole mass of (3.9 +/- 0.4)
x 10^7 M_sun and M/L_V of 5.56 +/- 0.02 (internal errors), and the edge-on
models are vastly superior fits over models at other inclinations. The internal
dynamics in NGC 1023 as suggested by our best-fit three-integral model shows
that the velocity distribution function at the nucleus is tangentially
anisotropic, suggesting the presence of a nuclear stellar disk. The nuclear
line of sight velocity distribution has enhanced wings at velocities >= 600
km/s from systemic, suggesting that perhaps we have detected a group of stars
very close to the central dark mass.Comment: 21 pages, 12 figures, accepted in the Astrophysical Journa
The Heavy Element Enrichment of Lyman alpha Clouds in the Virgo Supercluster
Using high S/N STIS echelle spectra (FWHM=7 km/s) of 3C 273, we constrain the
metallicities of two Lya clouds in the vicinity of the Virgo cluster. We detect
C II, Si II, and Si III absorption lines in the Lya absorber at z = 0.00530.
Previous observations with FUSE have revealed Ly beta - Ly theta lines at this
redshift, thereby accurately constraining N(H I). We model the ionization of
the gas and derive [C/H] = -1.2^{+0.3}_{-0.2}, [Si/C] = 0.2+/-0.1, and log
n_{H} = -2.8+/-0.3. The model implies a small absorber thickness, ~70 pc, and
thermal pressure p/k ~ 40 cm^{-3} K. It is most likely that the absorber is
pressure confined by an external medium because gravitational confinement would
require a very high ratio of dark matter to baryonic matter. Based on Milky Way
sight lines in which carbon and silicon abundances have been reliably measured
in the same interstellar cloud (including new measurements presented herein),
we argue that the overabundance of Si relative to C is not due to dust
depletion. Instead, this probably indicates that the gas has been predominately
enriched by Type II supernovae. Such enrichment is most plausibly provided by
an unbound galactic wind, given the absence of galaxies within a projected
distance of 100 kpc and the presence of galaxies capable of driving a wind at
larger distances. We also constrain the metallicity and physical conditions of
the Virgo absorber at z = 0.00337 based on detections of O VI and H I and an
upper limit on C IV. If this absorber is collisionally ionized, the O VI/C IV
limit requires T > 10^{5.3} K. For either collisional ionization or
photoionization, we find that [O/H] > -2.0 at z = 0.00337.Comment: Final Ap.J. versio
Complex C: A Low-Metallicity High-Velocity Cloud Plunging into the Milky Way
(Abridged) We present a new high-resolution (7 km/s FWHM) echelle spectrum of
3C 351 obtained with STIS. 3C 351 lies behind the low-latitude edge of
high-velocity cloud Complex C, and the new spectrum provides accurate
measurements of O I, Si II, Al II, Fe II, and Si III absorption lines at the
velocity of the HVC. We use collisional and photoionization models to derive
ionization corrections; in both models we find that the overall metallicity Z =
0.1 - 0.3 Z_{solar} in Complex C, but nitrogen must be underabundant. The iron
abundance indicates that Complex C contains very little dust. The absorbing gas
probably is not gravitationally confined. The gas could be pressure-confined by
an external medium, but alternatively we may be viewing the leading edge of the
HVC, which is ablating and dissipating as it plunges into the Milky Way. O VI
column densities observed with FUSE toward nine QSOs/AGNs behind Complex C
support this conclusion: N(O VI) is highest near 3C 351, and the O VI/H I ratio
increases substantially with decreasing latitude, suggesting that the
lower-latitude portion of the cloud is interacting more vigorously with the
Galaxy. The other sight lines through Complex C show some dispersion in
metallicity, but with the current uncertainties, the measurements are
consistent with a constant metallicity throughout the HVC. However, all of the
Complex C sight lines require significant nitrogen underabundances. Finally, we
compare the 3C 351 sight line to the sight line to the nearby QSO H1821+643 to
search for evidence of outflowing Galactic fountain gas that could be mixing
with Complex C. We find that the intermediate-velocity gas detected toward 3C
351 and H1821+643 has a higher metallicity and may well be a fountain/chimney
outflow from the Perseus spiral arm.Comment: Submitted to AJ. Figures 1-4 compressed for astro-ph; better quality
figures are available at
http://astro.princeton.edu/~tripp/astro/qualitypreps/complexc.ps.g
Development of a Tumor-Selective Approach to Treat Metastatic Cancer
BACKGROUND: Patients diagnosed with metastatic cancer have almost uniformly poor prognoses. The treatments available for patients with disseminated disease are usually not curative and have side effects that limit the therapy that can be given. A treatment that is selectively toxic to tumors would maximize the beneficial effects of therapy and minimize side effects, potentially enabling effective treatment to be administered. METHODS AND FINDINGS: We postulated that the tumor-tropic property of stem cells or progenitor cells could be exploited to selectively deliver a therapeutic gene to metastatic solid tumors, and that expression of an appropriate transgene at tumor loci might mediate cures of metastatic disease. To test this hypothesis, we injected HB1.F3.C1 cells transduced to express an enzyme that efficiently activates the anti-cancer prodrug CPT-11 intravenously into mice bearing disseminated neuroblastoma tumors. The HB1.F3.C1 cells migrated selectively to tumor sites regardless of the size or anatomical location of the tumors. Mice were then treated systemically with CPT-11, and the efficacy of treatment was monitored. Mice treated with the combination of HB1.F3.C1 cells expressing the CPT-11-activating enzyme and this prodrug produced tumor-free survival of 100% of the mice for >6 months (P<0.001 compared to control groups). CONCLUSIONS: The novel and significant finding of this study is that it may be possible to exploit the tumor-tropic property of stem or progenitor cells to mediate effective, tumor-selective therapy for metastatic tumors, for which no tolerated curative treatments are currently available
Paper Session II-B - Early Results from the Space Telescope Imaging Spectograph
The STIS instrument was installed into HST in February 1997 during the Servicing Mission 2. It has completed checkout and is beginning its science program, and is working well. Several scientific demonstration observations were taken, illustrating some of the range of scientific uses and modes of observation of STIS.
Keywords: Hubble, spectrograph, echelle, ultraviolet, optical, spectra, MAMA, black hole, galaxies, supernov
Linguistic Information and Processing Components: What is modular?
Discourse and texts contain many different types of information for the comprehender tÎż use in constructing a representation of what the speaker or writer intended -- auditory/visual, phonological/orthographic, lexical, syntactic, semantic, pragmatic, and propositional content. How does the comprehender (listener or reader) use these different types of information tÎż construct a representation of what the discourse or text means? Î common assumption, in particular as represented in the modularity hypothesis, is that for each type of information there is a cognitive processing component dedicated to processing that type of information. An alternative analysis assumes that processing components are specified in functional terms, that is, in terms of the requirements of the processing tasks to be completed by the comprehender. Processing components are needed to perceive speech sounds or print, tÎż access information about words, tÎż determine sentence meanings, and to construct a representation of what the discourse Îżr text means. These components may use more than one type of information from the linguistic signal to complete their respective tasks. Behavioral data from reading comprehension tasks support breaking the one- to-one mapping between types of linguistic information and cognitive processing components. The same linguistic information is encoded differently across languages and aÎters how it is processed, thus supporting the separation of linguistic information types from processing components
Beyond Machines: Humans in Cyber Operations, Espionage, and Conflict
It is the height of banality to observe that people, not bullets, fight kinetic wars. The machinery of kinetic warfare is obviously relevant to the conduct of each particular act of warfare, but the reasons for, and meanings of, those acts depend critically on the fact that they are done by humans. Any attempt to understand warfareâits causes, strategies, legitimacy, dynamics, and resolutionsâmust incorporate humans as an intrinsic part, both descriptively and normatively. Humans from general staff to âboots on the groundâ play key roles in all aspects of kinetic warfare, and the literature about it reflects this focus (e.g., the emphasis on understanding the adversaryâs goals and constraints when developing battle plans). 2 In contrast, many discussions of cyberwarfare and cyber-conflict focus principally on the technical aspects of machines, systems, and data, 3 and human agents are included only as collateral effects (e.g., in discussions about the impact of disabling an adversaryâs electrical grid), or as loci of moral responsibility (e.g., providing the ground for the moral justification of a cyber-attack).</p