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Register a new userA multi-epoch spectroscopic study of the BAL quasar APM 08279+5255: I. C IV absorption variability
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Broad Absorption Lines indicate gas outflows with velocities from thousands km/s to about 0.2 the speed of light, which may be present in all quasars and may play a major role in the evolution of the host galaxy. The variability of absorption patterns can provide informations on changes of the density and velocity distributions of the absorbing gas and its ionization status. We collected 23 photometrical and spectro-photometrical observations at the 1.82m Telescope of the Asiago Observatory since 2003, plus other 5 spectra from the literature. We analysed the evolution in time of the equivalent width of the broad absorption feature and two narrow absorption systems, the correlation among them and with the R band magnitude. We performed a structure function analysis of the equivalent width variations. We present an unprecedented monitoring of a broad absorption line quasar based on 28 epochs in 14 years. The shape of broad absorption feature shows a relative stability, while its equivalent width slowly declines until it sharply increases during 2011. In the same time the R magnitude stays almost constant until it sharply increases during 2011. The equivalent width of the narrow absorption redwards of the systemic redshift only shows a decline. The broad absorption behaviour suggests changes of the ionisation status as the main cause of variability. We show for the first time a correlation of this variability with the R band flux. The different behaviour of the narrow absorption system might be due to recombination time delay. The structure function of the absorption variability has a slope comparable with typical optical variability of quasars. This is consistent with variations of the 200 A ionising flux originating in the inner part of the accretion disk.
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Broad absorption lines (BALs) in quasar spectra indicate high-velocity outflows that may be present in all quasars and could be an important contributor to feedback to their host galaxies. Variability studies of BALs help illuminate the structure, evolution, and basic physical properties of the outflows. Here we present further results from an ongoing BAL monitoring campaign of a sample of 24 luminous quasars at redshifts 1.2 < z < 2.9. We directly compare the variabilities in the CIV 1549 and SiIV 1400 absorption to try to ascertain the cause(s) of the variability. We find that SiIV BALs are more likely to vary than CIV BALs. When looking at flow speeds >-20 000 km/s, 47 per cent of quasars exhibited SiIV variability while 31 per cent exhibited CIV variability. Furthermore, ~50 per cent of the variable SiIV regions did not have corresponding CIV variability at the same velocities. When both CIV and SiIV varied, those changes always occurred in the same sense (either getting weaker or stronger). We also include our full data set so far in this paper, which includes up to 10 epochs of data per quasar. The multi-epoch data show that the BAL changes were not generally monotonic across the full ~5 to ~8 yr time span of our observations, suggesting that the characteristic time-scale for significant line variations, and (perhaps) for structural changes in the outflows, is less than a few years. Coordinated variabilities between absorption regions at different velocities in individual quasars seems to favor changing ionization of the outflowing gas as the cause of the observed BAL variability. However, variability in limited portions of broad troughs fits naturally in a scenario where movements of individual clouds, or substructures in the flow, across our lines-of-sight cause the absorption to vary. The actual situation may be a complex mixture of changing ionization and cloud movements.
The Infrared Spectrograph (IRS) onboard the Spitzer Space Telescope (SST) has been used to obtain low and moderate resolution spectra of the dust and gas-rich quasar APM08279+5255 (z=3.91). Broad Paschen $alpha$ and $beta$ recombination lines of hydrogen were detected at wavelengths of 9.235 and 6.315microns, as well as a strong, red continuum that is a smooth power law over the observed (rest frame) wavelength range 5.3-35microns (1.08 - 7.1microns). The observed P$alpha$/P$beta$ line flux ratio of 1.05$pm$0.2 is far from the case B value of ~2 and simple models of high density, high optical depth ionized gas regions (~1.8). This deviation is opposite in sense to the expected effect of reddening. No evidence is found in the spectrum for either the 3.3micron or 6.2micron emission features usually attributed to aromatic hydrocarbons in gas rich galaxies in the local Universe. This is consistent with the high luminosity AGN nature of APM08279+5255.
We report a detection of the excited 220-211 rotational transition of para-H2O in APM 08279+5255 using the IRAM Plateau de Bure interferometer. At z = 3.91, this is the highest-redshift detection of interstellar water to date. From LVG modeling, we conclude that this transition is predominantly radiatively pumped and on its own does not provide a good estimate of the water abundance. However, additional water transitions are predicted to be detectable in this source, which would lead to an improved excitation model. We also present a sensitive upper limit for the HF J = 1 - 0 absorption toward APM 08279+5255. While the face-on geometry of this source is not favorable for absorption studies, the lack of HF absorption is still puzzling and may be indicative of a lower fluorine abundance at z = 3.91 compared with the Galactic ISM.
The gravitationally lensed quasar APM 08279+5255 has the fastest claimed wind from any AGN, with velocities of 0.6-0.7c, requiring magnetic acceleration as special relativisitic effects limit all radiatively driven winds to v<0.3-0.5c. However, this extreme velocity derives from interpreting both the narrow and broad absorption features in the X-ray spectrum as iron absorption lines. The classic ultrafast outflow source PDS 456 also shows similar absorption systems, but here the higher energy, broader feature is generally interpreted as an absorption edge. We reanalyse all the spectra from APM 08279+5255 using a full 3-dimensional Monte Carlo radiative transfer disc wind model for the ionised wind at 0.1-0.2c, together with complex absorption from lower ionisation material, and find that this is a better description of the data. Thus there is no strong requirement for outflow velocities beyond 0.2c, which can be powered by radiation driving. We show that UV line driving is especially likely given the spectral energy distribution of this source which is intrinsically UV bright and X-ray weak. While the peak of this emission is unobservable, it must be luminous enough to power the observed hot dust, favouring at least moderate black hole spin.
The existence of old high-redshift objects provides an important tool for constraining the expanding age of the Universe and the formation epoch of the first objects. In a recent paper, Hasinger {it et al.} (2002) reported the discovery of the quasar APM 08279+5255 at redshift $z=3.91$ with an extremely high iron abundance, and estimated age of 2 - 3Gyr. By assuming the lower limit for this age estimate and the latest measurements of the Hubble parameter as given by the HST key project, we study some cosmological implications from the existence of this object. In particular, we derive new limits on the dark matter and vacuum energy contribution. Our analysis is also extended to quintessence scenarios in which the dark energy is parameterized by a smooth component with an equation of state $p_x = omega_x rho_x$ ($-1leq omega_x < 0$). For flat models with a relic cosmological constant we show that the vacuum energy density parameter is constrained to be $Omega_Lambda geq 0.78$, a result that is marginally compatible with recent observations from type Ia supernovae (SNe Ia) and cosmic microwave background (CMB). For quintessence scenarios the same analysis restricts the cosmic parameter to $omega_x leq -0.22$. Limits on a possible first epoch of quasar formation are also briefly discussed. The existence of this object pushes the formation era back to extremely high redshifts.
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