795 research outputs found
Chandra Observations of X-ray Weak Narrow-Line Seyfert 1 Galaxies
We present Chandra observations of 17 optically-selected, X-ray weak
narrow-line Seyfert 1 (NLS1) galaxies. These objects were optically identified
by Williams et al. (2002) in the Sloan Digital Sky Survey Early Data Release,
but were not found in the ROSAT All-Sky Survey (RASS) despite having optical
properties similar to RASS-detected NLS1s. All objects in this sample were
detected by Chandra and exhibit a range of 0.5-2 keV photon indices
Gamma=1.1-3.4. One object was not detected in the soft band, but has a best-fit
Gamma=0.25 over the full 0.5-8 keV range. These photon indices extend to values
far below what are normally observed in NLS1s. A composite X-ray spectrum of
the hardest objects in this sample does not show any signs of absorption,
although the data do not prohibit one or two of the objects from being highly
absorbed. We also find a strong correlation between Gamma and L_1keV; this may
be due to differences in L_bol/L_Edd among the NLS1s in this sample. Such
variations are seemingly in conflict with the current paradigm that NLS1s
accrete near the Eddington limit. Most importantly, this sample shows that
strong, ultrasoft X-ray emission is not a universal characteristic of NLS1s; in
fact, a substantial number may exhibit weak and/or low-Gamma X-ray emission.Comment: Minor changes, added section on X-ray weakness. 25 pages incl. 6
figures, 3 tables, accepted to Ap
Why Global Inequality Matters: Derivative Global Egalitarianism
This article integrates empirical and normative discussions about why global economic inequalities matter in critically examining an approach known as derivative global egalitarianism (DGE). DGE is a burgeoning perspective that opposes excessive global economic inequality not based on the intrinsic value of equality but inequality\u27s negative repercussions on other values. The article aims to advance the research agenda by identifying and critically evaluating four primary varieties of DGE arguments from related but distinct literatures, which span a number of disciplines, including economics, international relations, and political philosophy. Overall, DGE offers a number of persuasive arguments as to why current levels of global inequality are of concern, but aspects of DGE beg further philosophical and empirical examination. By situating DGE within the wider theoretical and empirical contexts, this article provides resources for its critical assessment and theoretical development
Reverberation Mapping Results from MDM Observatory
We present results from a multi-month reverberation mapping campaign
undertaken primarily at MDM Observatory with supporting observations from
around the world. We measure broad line region (BLR) radii and black hole
masses for six objects. A velocity-resolved analysis of the H_beta response
shows the presence of diverse kinematic signatures in the BLR.Comment: To appear in the Proceedings of the IAU Symposium No. 267:
Co-Evolution of Central Black Holes and Galaxies, Rio de Janeiro, 200
The Narrow-Line Regions of LINERs as Resolved with the Hubble Space Telescope
LINERs exist in the nuclei of a large fraction of luminous galaxies, but
their connection with the AGN phenomenon has remained elusive. We present
Hubble Space Telescope narrowband [O III]5007 and H-alpha+[N II] emission-line
images of the central regions of 14 galaxies with LINER nuclei. The compact, ~1
arcsec-scale, unresolved emission that dominates the line flux in ground-based
observations is mostly resolved by HST. The bulk of this emission comes from
regions with sizes of tens to hundreds of parsecs that are resolved into knots,
filaments, and diffuse gas whose morphology differs from galaxy to galaxy. Most
of the galaxies do not show clear linear structures or ionization cones
analogous to those often seen in Seyfert galaxies. An exception is NGC 1052,
the prototypical LINER, in which we find a 3 arcsec-long (~ 250 pc) biconical
structure that is oriented on the sky along the galaxy's radio jet axis. Seven
of the galaxies have been shown in previously published HST images to have a
bright compact ultraviolet nuclear source, while the other seven do not have a
central UV source. Our images find evidence of dust in the nuclear regions of
all 14 galaxies, with clear indications of nuclear obscuration in most of the
"UV-dark" cases. The data suggest that the line-emitting gas in most LINERs is
photoionized by a central source (which may be stellar, nonstellar, or a
combination thereof) but that this source is often hidden from direct view. We
find no obvious morphological differences between LINERs with detected weak
broad H-alpha wings in their spectra and those with only narrow lines.
Likewise, there is no clear morphological distinction between objects whose UV
spectra are dominated by hot stars (e.g., NGC 4569) and those that are AGN-like
(e.g., NGC 4579).Comment: Accepted for publication in the ApJ. 25 pages, 3 tables, 9 JPEG
Figure
Narrow-line Seyfert 1 Galaxies from the Sloan Digital Sky Survey Early Data Release
We present a sample of 150 narrow-line Seyfert 1s (NLS1s) found within the
Sloan Digital Sky Survey Early Data Release (EDR), only two of which were
previously identified as such. This substantially increases the known number of
NLS1s, and provides a basic method by which to identify many more with
subsequent releases of SDSS data. With its large size and homogeneous,
well-defined selection criteria, this sample will help alleviate two major
problems which have plauged NLS1 research in the past; namely, their relative
rarity and significant differences in selection algorithms between the known
samples. 45 of these SDSS-selected NLS1s are detected at energies of 0.1-2 keV
in the ROSAT All-Sky Survey (RASS), and are found to have ultrasoft X-ray
spectra with photon indices of Gamma >~ 2, in agreement with previous results
for NLS1s. However, about 10-20 of those NLS1s that were not detected by ROSAT
have optical properties very similar to the detected objects, and so should
also have been detected by the RASS. This may be due to either significant
intrinsic absorption in many NLS1s, or a significant sub-class of NLS1s that
have uncharacteristic, intrinsically flatter (hence harder) X-ray spectral
energy distributions.Comment: Minor changes, accepted to AJ; 21 pages, 7 figures, AASTEX v5.
Reddening, Emission-Line, and Intrinsic Absorption Properties in the Narrow-Line Seyfert 1 Galaxy Akn 564
We use Hubble Space Telescope UV and optical spectra of the narrow-line
Seyfert 1 (NLS1) galaxy Akn 564 to investigate its internal reddening and
properties of its emission-line and intrinsic UV absorption gas. We find that
the extinction curve of Akn 564, derived from a comparison of its UV/optical
continuum to that of an unreddened NLS1, lacks a 2200 A bump and turns up
towards the UV at a longer wavelength (4000 A) than the standard Galactic, LMC,
and SMC curves. However, it does not show the extremely steep rise to 1200 A
that characterizes the extinction curve of the Seyfert 1 galaxy NGC 3227. The
emission-lines and continuum experience the same amount of reddening,
indicating the presence of a dust screen that is external to the narrow-line
region (NLR). Echelle spectra from the Space Telescope Imaging Spectrograph
show intrinsic UV absorption lines due to Ly-alpha, N V, C IV, Si IV, and Si
III, centered at a radial velocity of -190 km/s (relative to the host galaxy).
Photoionization models of the UV absorber indicate that it has a sufficient
columnand is at a sufficient distance from the nucleus (D > 95 pc) to be the
source of the dust screen. Thus, Akn 564 contains a dusty ``lukewarm absorber''
similar to that seen in NGC 3227.Comment: 25 pages, 4 figures. LaTeX with encapsulated postscript figures.
Accepted for publication in the Astrophysical Journa
Formation of Ionization-Cone Structures in Active Galactic Nuclei: I. Stationary Model and Linear Stability Analysis
We discuss causes of the formation of the observed kinematics and morphology
of cones of ionized matter in the neighborhood of the nuclei of Seyfert
galaxies. The results of linear stability analysis of an optically thin conic
jet where radiation cooling and gravity play an important part are reported.
The allowance for radiation cooling is shown to result in strong damping of all
acoustic modes and to have insignificant effect on unstable surface
Kelvin--Helmholtz modes. In the case of waveguide--resonance internal gravity
modes radiative cooling suppresses completely the instability of waves
propagating away from the ejection source and, vice versa, reduces
substantially the growth time scale of unstable sourceward propagating modes.
The results obtained can be used to study ionization cones in Seyfert galaxies
with radio jets. In particular, our analysis shows that surface
Kelvin--Helmholtz modes and volume harmonics are capable of producing regular
features observed in optical emission-line images of such galaxies.Comment: 13 pages, published in Astrophysical Bulleti
Humanity or justice?
This paper reflects on a critique of cosmopolitanism mounted by Tom Campbell, who argues that cosmopolitans place undue stress on the issue of global justice. Campbell argues that aid for the impoverished needy in the third world, for example, should be given on the Principle of Humanity rather than on the Principle of Justice. This line of thought is also pursued by ‘Liberal Nationalists’ like Yael Tamir and David Miller. Thomas Nagel makes a similar distinction and questions whether the ideal of justice can even be meaningfully applied on a global scale. The paper explores whether the distinction between the Principle of Humanity and the Principle of Justice might be a false dichotomy in that both principles could be involved in humanitarian assistance. It will suggest that both principles might be grounded in an ethics of caring and that the ethics of caring cannot be so sharply distinguished from the discourse of justice and of rights. As a result, the Principle of Humanity and the Principle of Justice cannot be so sharply distinguished either. It is because we care about others as human beings (Principle of Humanity) that we pursue justice for them (Principle of Justice) and the alleviation of their avoidable suffering
First Space-Based Microlens Parallax Measurement: Spitzer Observations of OGLE-2005-SMC-001
We combine Spitzer and ground-based observations to measure the microlens
parallax of OGLE-2005-SMC-001, the first such space-based determination since
S. Refsdal proposed the idea in 1966. The parallax measurement yields a
projected velocity \tilde v ~ 230 km/s, the typical value expected for halo
lenses, but an order of magnitude smaller than would be expected for lenses
lying in the Small Magellanic Cloud (SMC) itself. The lens is a weak (i.e.,
non-caustic-crossing) binary, which complicates the analysis considerably but
ultimately contributes additional constraints. Using a test proposed by Assef
et al. (2006), which makes use only of kinematic information about different
populations but does not make any assumptions about their respective mass
functions, we find that the likelihood ratio is L_halo/L_SMC = 20. Hence, halo
lenses are strongly favored but SMC lenses are not definitively ruled out.
Similar Spitzer observations of additional lenses toward the Magellanic Clouds
would clarify the nature of the lens population. The Space Interferometry
Mission could make even more constraining measurements.Comment: ApJ, in press. Text and figures are updated to match the journal
versio
Multiwavelength Monitoring of the Narrow-Line Seyfert 1 Galaxy Akn 564. II. Ultraviolet Continuum and Emission-line Variability
We present results of an intensive two-month campaign of approximately daily
spectrophotometric monitoring of the narrow-line Seyfert 1 galaxy Akn 564 with
HST. The fractional variability amplitude of the continuum variations between
1365-3000 A is ~6%, about a factor 3 less than that found in typical Seyfert 1
galaxies over a similar period of time. However, large amplitude, short
time-scale flaring behavior is evident, with trough-to-peak flux changes of
about 18% in approximately 3 days. We present evidence for wavelength-dependent
continuum time delays, with the variations at 3000 A lagging behind those at
1365 A by about 1 day. These delays may be interpreted as evidence for a
stratified continuum reprocessing region, possibly an accretion-disk structure.
The Lyman-alpha 1216 emission-line exhibits flux variations of about 1%
amplitude.Comment: 27 pages, 14 figures. Accepted by Astrophysical Journa
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