615 research outputs found
Broad P V Absorption in the BALQSO, PG 1254+047: Column Densities, Ionizations and Metal Abundances in BAL Winds
This paper discusses the detection of P V 1118,1128 and other broad
absorption lines (BALs) in archival HST spectra of the low-redshift BALQSO, PG
1254+047. The P V identification is secured by excellent redshift and profile
coincidences with the other BALs, such as C IV 1548,1550 and Si IV 1393,1403,
and by photoionization calculations showing that other lines near this
wavelength, e.g. Fe III 1123, should be much weaker than P V. The observed BAL
strengths imply that either 1) there are extreme abundance ratios such as [C/H]
>~ +1.0, [Si/H] >~ +1.8 and [P/C] >~ +2.2, or 2) at least some of the lines are
much more optically thick than they appear. I argue that the significant
presence of P V absorption indicates severe line saturation, which is disguised
in the observed (moderate-strength) BALs because the absorber does not fully
cover the continuum source(s) along our line(s) of sight. Computed optical
depths for all UV resonance lines show that the observed BALs are consistent
with solar abundances if 1) the ionization parameter is at least moderately
high, log U >~ -0.6, 2) the total hydrogen column density is log N_H(cm-2) >~
22.0, and 3) the optical depths in strong lines like C IV and O VI 1032,1038
are >~25 and >~80, respectively. These optical depths and column densities are
at least an order of magnitude larger than expected from the residual
intensities in the BAL troughs, but they are consistent with the large
absorbing columns derived from X-ray observations of BALQSOs. The outflowing
BALR, at velocities from -15,000 to -27,000 km/s in PG 1254+047, is therefore a
strong candidate for the X-ray absorber in BALQSOs.Comment: 16 pages (LaTeX) plus 8 pages of figures in one file
(pg1254_figs.ps.gz), in press with Ap
Effective sampling for large-scale automated writing evaluation systems
Automated writing evaluation (AWE) has been shown to be an effective
mechanism for quickly providing feedback to students. It has already seen wide
adoption in enterprise-scale applications and is starting to be adopted in
large-scale contexts. Training an AWE model has historically required a single
batch of several hundred writing examples and human scores for each of them.
This requirement limits large-scale adoption of AWE since human-scoring essays
is costly. Here we evaluate algorithms for ensuring that AWE models are
consistently trained using the most informative essays. Our results show how to
minimize training set sizes while maximizing predictive performance, thereby
reducing cost without unduly sacrificing accuracy. We conclude with a
discussion of how to integrate this approach into large-scale AWE systems
Red and Blue Shifted Broad Lines in Luminous Quasars
We have observed a sample of 22 luminous quasars, in the range 2.0<z<2.5, at
1.6 microns with the near-infrared (NIR) spectrograph FSPEC on the Multiple
Mirror Telescope. Our sample contains 13 radio-loud and 9 radio-quiet objects.
We have measured the systemic redshifts z_(sys) directly from the strong [O
III]5007 line emitted from the narrow-line-region. From the same spectra, we
have found that the non-resonance broad H lines have a systematic mean
redward shift of 520+/-80 km/s with respect to systemic. Such a shift was not
found in our identical analysis of the low-redshift sample of Boroson & Green.
The amplitude of this redshift is comparable to half the expected gravitational
redshift and transverse Doppler effects, and is consistent with a correlation
between redshift differences and quasar luminosity. From data in the
literature, we confirm that the high-ionization rest-frame ultraviolet broad
lines are blueshifted ~550-1050 km/s from systemic, and that these velocity
shifts systematically increase with ionization potential. Our results allow us
to quantify the known bias in estimating the ionizing flux from the
inter-galactic-medium J_(IGM) via the Proximity Effect. Using redshift
measurements commonly determined from strong broad line species, like Ly\alpha
or CIV1549, results in an over-estimation of J_(IGM) by factors of ~1.9-2.3.
Similarly, corresponding lower limits on the density of baryon Omega_b will be
over-estimated by factors of ~1.4-1.5. However, the low-ionization MgII2798
broad line is within ~50 km/s of systemic, and thus would be the line of choice
for determining the true redshift of 1.0<z<2.2 quasars without NIR
spectroscopy, and z>3.1 objects using NIR spectroscopy.Comment: 12 pages, Latex, 2 figures, 2 tables, Accepted for publication in ApJ
Letter
Continuum and Emission Line Strength Relations for a large Active Galactic Nuclei Sample
We report on the analysis of a large sample of 744 type 1 Active Galactic Nuclei, including quasars and Seyfert 1 galaxies across the redshift range from 0 < z < 5 and spanning nearly 6 orders of magnitude in continuum luminosity. We discuss correlations of continuum and emission line properties in the rest-frame ultraviolet and optical spectral ranges. The well established Baldwin Effect is detected for almost all emission lines from OVI1034 to [OIII]5007. Their equivalent widths are significantly anti-correlated with the continuum strength, while they are nearly independent of redshift. This is the well known Baldwin Effect. Its slope beta, measured as log W_lambda ~ beta * log lambda * L_lambda (1450A), shows a tendency to become steeper towards higher luminosity. The slope of the Baldwin Effect also increases with the ionization energy needed to create the individual lines. In contrast to this general trend, the NV1240 equivalent width is nearly independent of continuum luminosity and remains nearly constant. The overall line behaviors are consistent with softer UV continuum shapes and perhaps increasing gas metallicity in more luminous Active Galactic Nuclei
Measuring transverse velocities in gravitationally lensed extragalactic systems using an annual parallax effect
A parallax method to determine transverse velocity in a gravitationally
lensed system is described. Using the annual motion of the Earth around the Sun
allows us to probe the local structure of the magnification map that, under
certain assumptions, can be used to infer the effective transverse velocity.
The method is applied to OGLE data for QSO2237+0305 and the velocity value is
estimated to be about (15 +/- 10) km/s if attributed to the lensing galaxy or
about (420 +/- 300) km/s if attributed to the quasar. We find this estimate
unreasonably small and conclude that we have not measured a parallax effect. We
give a short list of properties that a system should possess to allow a
successful implementation of this method.Comment: v2: journal reference update
The CORALS Survey I: New Estimates of the Number Density and Gas Content of Damped Lyman Alpha Systems Free from Dust Bias
(Abridged) We present the first results from the Complete Optical and Radio
Absorption Line System (CORALS) survey. We have compiled a homogeneous sample
of radio-selected QSOs from the Parkes Catalogue and searched for damped Lyman
alpha systems (DLAs) towards every target, irrespective of its optical
magnitude. This approach circumvents selection effects -- particularly from
intervening dust -- which have long been suspected to affect DLA surveys in
optically-selected, magnitude-limited QSO samples. The CORALS data set consists
of 66 z_em > 2.2 QSOs in which 22 DLAs with absorption redshifts 1.8 < z_abs <
z_em have been identified over a total redshift interval Delta z = 55.46. In
this first paper of the CORALS series we describe the sample, present
intermediate resolution spectroscopy and determine the population statistics of
DLAs. We deduce a value of the neutral gas mass density traced by DLAs
(expressed as a fraction of the closure density) log Omega_DLA h =
-2.59^{+0.17}_{-0.24}, and a number density of DLAs per unit redshift n(z) =
0.31^{+0.09}_{-0.08}, both at a mean redshift = 2.37. Taking into account
the errors, we conclude that dust-induced bias in previous surveys may have led
to an underestimate of these quantities by at most a factor of two and we have
not uncovered a previously unrecognised population of high column density DLAs
in front of faint QSOs.Comment: 25 pages, accepted for publication in A&
Assessment of the Albumin-Bilirubin (ALBI) Grade as a Prognostic Indicator for Hepatocellular Carcinoma Patients Treated With Radioembolization.
OBJECTIVE: As the utility of Child-Pugh (C-P) class is limited by the subjectivity of ascites and encephalopathy, we evaluated a previously established objective method, the albumin-bilirubin (ALBI) grade, as a prognosticator for yttrium-90 radioembolization (RE) treatment for patients with hepatocellular carcinoma (HCC).
MATERIALS AND METHODS: A total of 117 patients who received RE for HCC from 2 academic centers were reviewed and stratified by ALBI grade, C-P class, and Barcelona Clinic Liver Cancer stage. The overall survival (OS) according to these 3 criteria was evaluated by Kaplan-Meier survival analysis. The utilities of C-P class and ALBI grade as prognostic indicators were compared using the log-rank test. Multivariate Cox regression analysis was performed to identify additional predictive factors.
RESULTS: Patients with ALBI grade 1 (n=49) had superior OS than those with ALBI grade 2 (n=65) (P=0.01). Meanwhile, no significant difference was observed in OS between C-P class A (n=100) and C-P class B (n=14) (P=0.11). For C-P class A patients, the ALBI grade (1 vs. 2) was able to stratify 2 clear and nonoverlapping subgroups with differing OS curves (P=0.03). Multivariate Cox regression test identified alanine transaminase, Barcelona Clinic Liver Cancer stage, and ALBI grade as the strongest prognostic factors for OS (P\u3c0.10).
CONCLUSIONS: ALBI grade as a prognosticator has demonstrated clear survival discrimination that is superior to C-P class among HCC patients treated with RE, particularly within the subgroup of C-P class A patients. ALBI grade is useful for clinicians to make decisions as to whether RE should be recommended to patients with HCC
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