440 research outputs found
A Variable PV Broad Absorption Line and Quasar Outflow Energetics
Broad absorption lines (BALs) in quasar spectra identify high velocity
outflows that might exist in all quasars and could play a major role in
feedback to galaxy evolution. The viability of BAL outflows as a feedback
mechanism depends on their kinetic energies, as derived from the outflow
velocities, column densities, and distances from the central quasar. We
estimate these quantities for the quasar, Q1413+1143 (redshift ),
aided by the first detection of PV 1118,1128 BAL variability in
a quasar. In particular, PV absorption at velocities where the CIV trough does
not reach zero intensity implies that the CIV BAL is saturated and the absorber
only partially covers the background continuum source (with characteristic size
<0.01 pc). With the assumption of solar abundances, we estimate that the total
column density in the BAL outflow is log N_H > 22.3 (cm^-2). Variability in the
PV and saturated CIV BALs strongly disfavors changes in the ionization as the
cause of the BAL variability, but supports models with high-column density BAL
clouds moving across our lines of sight. The observed variability time of 1.6
yr in the quasar rest frame indicates crossing speeds >750 km/s and a radial
distance from the central black hole of <3.5 pc, if the crossing speeds are
Keplerian. The total outflow mass is ~4100 M_solar, the kinetic energy ~4x10^54
erg, and the ratio of the outflow kinetic energy luminosity to the quasar
bolometric luminosity is ~0.02 (at the minimum column density and maximum
distance), which might be sufficient for important feedback to the quasar's
host galaxy.Comment: 9 pages, 4 figures, accepted for publication in MNRA
Variability in Quasar Broad Absorption Line Outflows I. Trends in the Short-Term versus Long-Term Data
Broad absorption lines (BALs) in quasar spectra identify high velocity
outflows that likely exist in all quasars and could play a major role in
feedback to galaxy evolution. The variability of BALs can help us understand
the structure, evolution, and basic physical properties of the outflows. Here
we report on our first results from an ongoing BAL monitoring campaign of a
sample of 24 luminous quasars at redshifts 1.2<z<2.9, focusing on C IV 1549 BAL
variability in two different time intervals: 4 to 9 months (short-term) and 3.8
to 7.7 years (long-term) in the quasar rest-frame. We find that 39% (7/18) of
the quasars varied in the short-term, whereas 65% (15/23) varied in the
long-term, with a larger typical change in strength in the long-term data. The
variability occurs typically in only portions of the BAL troughs. The
components at higher outflow velocities are more likely to vary than those at
lower velocities, and weaker BALs are more likely to vary than stronger BALs.
The fractional change in BAL strength correlates inversely with the strength of
the BAL feature, but does not correlate with the outflow velocity. Both the
short-term and long-term data indicate the same trends. The observed behavior
is most readily understood as a result of the movement of clouds across the
continuum source. If the crossing speeds do not exceed the local Keplerian
velocity, then the observed short-term variations imply that the absorbers are
<6 pc from the central quasar.Comment: 14 pages, 7 figures, accepted for publication in MNRA
Variability Tests for Intrinsic Absorption Lines in Quasar Spectra
Quasar spectra have a variety of absorption lines whose origins range from
energetic winds expelled from the central engines to unrelated, intergalactic
clouds. We present multi-epoch, medium resolution spectra of eight quasars at
z~2 that have narrow ``associated'' absorption lines (AALs, within 5000 km
s^{-1} of the emission redshift). Two of these quasars were also known
previously to have high-velocity mini-broad absorption lines (mini-BALs). We
use these data, spanning ~17 years in the observed frame with two to four
observations per object, to search for line strength variations as an
identifier of absorption that occurs physically near (``intrinsic'' to) the
central AGN.
Our main results are the following: Two out of the eight quasars with narrow
AALs exhibit variable AAL strengths. Two out of two quasars with high-velocity
mini-BALs exhibit variable mini-BAL strengths. We also marginally detect
variability in a high-velocity narrow absorption line (NAL) system, blueshifted
\~32,900 km s^{-1}$ with respect to the emission lines. No other absorption
lines in these quasars appeared to vary. The outflow velocities of the variable
AALs are 3140 km s^{-1} and 1490 km s^{-1}. The two mini-BALs identify much
higher velocity outflows of ~28,400 km s^{-1} and ~52,000 km s^{-1}. Our
temporal sampling yields upper limits on the variation time scales from 0.28 to
6.1 years in the quasar rest frames. The corresponding minimum electron
densities in the variable absorbers, based on the recombination time scale, are
\~40,000 cm^{-3} to ~1900 cm^{-3}. The maximum distances of the absorbers from
the continuum source, assuming photoionization with no spectral shielding,
range from ~1.8 kpc to ~7 kpc.Comment: 16 pages, 4 figures, ApJ, accepte
Keck high-resolution spectroscopy of Mrk 335: constraints on the number of emitting clouds in the broad-line region
We present high-resolution (∼6 km s⁻¹), high signal-to-noise ratio (−400 at Hα line centre) spectroscopy of Mrk 335. Cross-correlation (CC) analysis of the data yields a lower limit of ∼ 3 × 10⁶ for the number of emitting clouds in the broad-line region (BLR) of this object. This limit is applicable for clouds with T=2 × 10⁴ K and an optical depth of ∼ 10⁴ in their Hα line. The result is obtained from the absence of a CC signal in the data and from extensive Monte Carlo simulations that show the minimum number of clouds necessary in order to prevent the creation of a detectable CC signal. The simulations can be used to test any BLR model which is based on a contribution from discrete sources provided that the individual emission profile of the sources and their distribution are given. Current BLR models based on stellar atmospheres of bloated stars can be ruled out, unless the linewidth of an individual star exceeds 100 km s⁻¹. The lower limit on the number of emitting clouds also provides constraints on traditional photoionization models for a system of clouds
Keck high-resolution spectroscopy of Mrk 335: constraints on the number of emitting clouds in the broad-line region
We present high-resolution (∼6 km s⁻¹), high signal-to-noise ratio (−400 at Hα line centre) spectroscopy of Mrk 335. Cross-correlation (CC) analysis of the data yields a lower limit of ∼ 3 × 10⁶ for the number of emitting clouds in the broad-line region (BLR) of this object. This limit is applicable for clouds with T=2 × 10⁴ K and an optical depth of ∼ 10⁴ in their Hα line. The result is obtained from the absence of a CC signal in the data and from extensive Monte Carlo simulations that show the minimum number of clouds necessary in order to prevent the creation of a detectable CC signal. The simulations can be used to test any BLR model which is based on a contribution from discrete sources provided that the individual emission profile of the sources and their distribution are given. Current BLR models based on stellar atmospheres of bloated stars can be ruled out, unless the linewidth of an individual star exceeds 100 km s⁻¹. The lower limit on the number of emitting clouds also provides constraints on traditional photoionization models for a system of clouds
The Extreme Hosts of Extreme Supernovae
We use GALEX ultraviolet (UV) and optical integrated photometry of the hosts of 17 luminous supernovae (LSNe, having peak M_V 100 M_☉), by appearing in low-SFR hosts, are potential tests for theories of the initial mass function that limit the maximum mass of a star based on the SFR
A Measurement of the Temperature-Density Relation in the Intergalactic Medium Using a New Lyman-alpha Absorption Line Fitting Method
The evolution of the temperature in the intergalactic medium is related to
the reionization of hydrogen and helium, and has important consequences for our
understanding of the Lya forest and of galaxy formation in gravitational models
of large-scale structure. We measure the temperature-density relation of
intergalactic gas from Lya forest observations of eight quasar spectra with
high resolution and signal-to-noise ratio, using a new line fitting technique
to obtain a lower cutoff of the distribution of line widths from which the
temperature is derived. We carefully test the accuracy of this technique to
recover the gas temperature with a hydrodynamic simulation. The temperature at
redshift z=(3.9, 3.0, 2.4) is best determined at densities slightly above the
mean: T_star=(20200\pm2700, 20200\pm1300, 22600\pm1900)K (statistical error
bars) for gas density (in units of the mean density) Delta_star=(1.42\pm0.08,
1.37\pm0.11, 1.66\pm0.11). The power-law index of the temperature-density
relation, defined by T=T_star(Delta/Delta_star)^{gamma-1}, is gamma-1=
(0.43\pm0.45, 0.29\pm0.30, 0.52\pm0.14) for the same three redshifts. The
temperature at the fixed over-density Delta=1.4 is T_1.4=(20100\pm2800,
20300\pm1400, 20700\pm1900)K. These temperatures are higher than expected for
photoionized gas in ionization equilibrium with a cosmic background, and can be
explained by a gradual additional heating due to on-going HeII reionization.
The measurement of the temperature reduces one source of uncertainty in the
lower limit to the baryon density implied by the observed mean flux decrement.
We find that the temperature cannot be reliably measured for under-dense gas,
because the velocities due to expansion always dominate the widths of the
corresponding weak lines.Comment: submitted to Ap
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The importance of forecasting regional wind power ramping: a case study for the UK
In recent years there has been a significant change in the distribution of wind farms in Great Britain, with a trend towards very large offshore farms clustered together in zones. However, there are concerns these clusters could produce large ramping events on time scales of less than 6 hours as local meteorological phenomena simultaneously impact the production of several farms. This paper presents generation data from the wind farms in the Thames Estuary (the largest cluster in the world) for 2014 and quantifies the high frequency power ramps. Based on a case study of a ramping event which occurred on 3rd November 2014, we show that due to the large capacity of the cluster, a localised ramp can have a significant impact on the cost of balancing the power system on a national level if it is not captured by the forecast of the system operator. The planned construction of larger offshore wind zones will exacerbate this problem. Consequently, there is a need for accurate regional wind power forecasts to minimise the costs of managing the system. This study shows that state-of-the-art high resolution forecast models have capacity to provide valuable information to mitigate this impact
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