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Register a new userSpitzer/IRS Observations of the Redshift 3.91 quasar APM 08279+5255
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Added by
Vassilis Charmandaris
Publication date
2004
fields
Physics
and research's language is
English
Authors
B.T. Soifer
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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.
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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 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.
We present a detection of [CI] line emission in the lensed quasar APM 08279+5255 at z=3.91 using the IRAM Plateau de Bure interferometer. The [CI] line velocity and width are similar to the values of previously detected high-J CO and HCN lines in this source, suggesting that the emission from all of these species arises from the same region. The apparent luminosity of the [CI] line is L(CI) = (3.1 +/- 0.4)x10^10 K km/s pc^2, which implies a neutral carbon mass, M(CI) = (4.4+/-0.6)/m x10^7 M_sun, where m is the lensing magnification factor. The [CI] line luminosity is consistent with the large molecular gas mass inferred from the nuclear CO line luminosity ~10^11 /m M_sun. We also present an upper limit on the H2O line luminosity in APM 08279+5255 of, L(H2O) < 1.8x10^10 K km/s pc^2 (3-sigma).
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.
A very low primordial deuterium abundance of D/H = 1.5 10^{-5} has recently been proposed by Molaro et al. in the Lyman limit system with log(N_HI) = 18.1 cm^{-2} at z_a = 3.514 towards the quasar APM08279+5255. The D/H value was estimated through the standard Voigt fitting procedure utilizing a simple one-component model of the absorbing region. The authors assumed, however, that `a more complex structure for the hydrogen cloud with somewhat ad hoc components would allow a higher D/H. We have investigated this system using our new Monte Carlo inversion procedure which allows us to recover not only the physical parameters but also the velocity and density distributions along the line of sight. The absorption lines of HI, CII, CIV, SiIII, and SiIV were analyzed simultaneously. The result obtained shows a considerably lower neutral hydrogen column density log(N_HI) = 15.7 cm^{-2}. Hence, the measurement of the deuterium abundance in this system is rather uncertain. We find that the asymmetric blue wing of the hydrogen Ly-alpha absorption is readily explained by HI alone. Thus, up to now, deuterium was detected in only four QSO spectra (Q1937-1009, Q1009+2956, Q0130-4021, and Q1718+4807) and all of them are in concordance with D/H = 4 10^{-5}.
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