ASTRONOMY AND ASTROPHYSICS Do the central engines of quasars evolve by accretion?

Abstract. According to a currently popular paradigm, nuclear activity in quasars is sustained via accretion of material onto super-massive black holes located at the quasar nuclei. A useful tracer of the gravitational field in the vicinity of such central black holes is available in the form of extremely dense gas clouds within the broad emission-line region (BLR) on the scale of ∼ 1 parsec. Likewise, the radio sizes of the lobe-dominated radio sources are believed to provide a useful statistical indicator of their ages. Using two homogeneously observed (and processed) sets of lobe-dominated radio-loud quasars, taken from literature, we show that a positive correlation exists between the radio sizes of the quasars and the widths of their broad Hβ emission lines, and this correlation is found to be significantly stronger than the other well known correlations involving radio size. This statistical correlation is shown to be consistent with the largest (and, hence, very possibly the oldest) radio sources harboring typically an order-of-magnitude more massive central engines, as compared to the physically smaller and, hence, probably much younger radio sources. This inference is basically in accord with the ”accreting central engine ” picture for the radio-loud quasars

ASTRONOMY AND ASTROPHYSICS

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Molecules in the zabs =2.8112 damped system toward PKS0528–250 ⋆

A&A manuscript no. (will be inserted by hand later) Your thesaurus codes are

ASTRONOMY AND ASTROPHYSICS Physical conditions in broad and associated narrow absorption-line systems toward APM 08279+5255 ⋆

A&A manuscript no. (will be inserted by hand later) Your thesaurus codes are

ASTRONOMY AND ASTROPHYSICS The zabs ∼ zem absorption line systems toward QSO J 2233-606 in the Hubble Deep Field South: Ne VIIIλλ770,780 absorption

Abstract. Results of a careful analysis of the highly ionized absorption systems, observed over the redshift range 2.198–2.2215 in the zem = 2.24 HDFS-QSO J 2233-606, are presented. The strength and covering factor of the O vi and Ne viii absorption lines suggest that the gas is closely associated with the AGN. In addition, most of the lines show signature of partial coverage and the covering factor varies from species to species. This can be understood if the clouds cover the continuum emission region completely and only a fraction of the broad emission line region. Using photo-ionization models we analyze in more detail the component at zabs = 2.198, for which we can derive reliable estimates of column densities for H i and other species. Absolute abundances are close to solar but the [N/C] abundance ratio is larger than solar. This result, which is consistent with the analysi

606 in the Hubble Deep Field South: Neviiiλλ770,780

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ASTRONOMY AND ASTROPHYSICS Physical conditions in broad and associated narrow absorption-line systems toward APM 08279+5255 ⋆

Abstract. Results of a careful analysis of the absorption systems with zabs≃zem seen toward the bright, zem ∼3.91, gravitationally lensed quasar APM 08279+5255 are presented. Two of the narrow-line systems, at zabs = 3.8931 and zabs = 3.9135, show absorptions from singly ionized species with weak or no N v and O vi absorptions at the same redshift. Absorption due to fine structure transitions of C ii and Si ii (excitation energies corresponding to, respectively, 156µm and 34µm) are detected at zabs = 3.8931. Excitation by IR radiation is favored as the column density ratios are consistent with the shape of APM 08279+5255 IR spectrum. The lowionization state of the system favors a picture where the cloud is closer to the IR source than to the UV source, supporting the idea that the extension of the IR source is larger than ∼200 pc. The absence of fine structure lines at zabs = 3.9135 suggest

Probing the dark ages with redshift distribution of GRBs

The usefulness of gamma ray bursts (GRBs) to probe the evolution of the universe is realized ever since the redshift measurements of GRBs became possible (Kulkarni et al. 1998). A direct connection between the GRBs and star formation rate (SFR) in the host galax

Accepted by ApJL Molecular Hydrogen in a Damped Lyman-α System at zabs = 4.224

We present the direct detection of molecular hydrogen at the highest redshift known today (zabs = 4.224) in a Damped Lyman-α (DLA) system toward the quasar PSS J1443+2724. This absorber is remarkable for having one of the highest metallicities amongst DLA systems at zabs> 3, with a measured iron abundance relative to Solar of −1.12 ± 0.10. We provide for the first time in this system accurate measurements of Ni, Mgii, Sii and Ari column densities. The sulfur and nitrogen abundances relative to Solar, −0.63 ± 0.10 and −1.38 ± 0.10 respectively, correspond exactly to the primary nitrogen production plateau. H2 absorption lines are detected in four different rotational levels (J = 0, 1, 2 and 3) of the vibrational ground-state in three velocity components with total column densities of log N(H2) = 17.67, 17.97, 17.48 and 17.26 respectively. The J = 4 level is tentatively detected in the strongest component with log N(H2) ∼ 14. The mean molecular fraction is log f = −2.38 ± 0.13, with f = 2N(H2)/(2N(H2) + N(Hi)). We also measure log N(HD)/N(H2) < −4.2. The excitation temperatures T01 for the two main components of the system are 96 and 136 K respectively. We argue that the absorbing galaxy, whose starformation activity must have started at least 2 − 5 × 10 8 yrs before z = 4.224, is in a quiescent state at the time of observation. The density of the gas is small, nH ≤ 50 cm −3, and the temperature is of the order of T ∼ 90 − 180 K. The high excitation of neutral carbon in one of the components can be explained if the temperature of the Cosmic Microwave Background Radiation has the valu