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Damped Ly (damped + ly)
Selected AbstractsProbing feedback in protogalaxies: multiphase gas in a DLA at z, 2.4MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2008N. Lehner ABSTRACT We investigate the physical processes occurring in the multiphase gas of a damped Ly, absorber (DLA). We base our analysis on a high-quality Keck High-Resolution Echelle Spectrometer (HIRES) spectrum of the QSO J1211+0422 in which a DLA is detected at z, 2.377. There is little contamination of the high-ion (O vi, N v, C iv, Si iv) absorption, allowing us to explore the properties of the highly ionized gas and its connection to other gas phases. The metallicity ([Z/H]=,1.41 ± 0.08), H i column density [], full-width velocity (,vneut, 70 km s,1) and relative abundances ([Si/Fe]=+0.23 ± 0.05 and [N/Si]=,0.88 ± 0.07) of this DLA are not unusual. However, we derive the lowest C ii* cooling rate in a DLA, lc < 10,27.8 erg s,1 per H atom (3,). Using this stringent limit, we show that the neutral gas (confined at |v| < +39 km s,1) must be warm and the star formation rate is <7.1 × 10,3 M, yr,1 kpc,2. Surprisingly, the gas shows strong, complex absorption profiles from highly ionized gas whose kinematics appear connected to each other and the low ions. The total amount of highly and weakly ionized gas is very large with ,1.5. At |v| ,+39 km s,1, the gas is fully and highly ionized []. Based on ionization models, O vi and N v are generally difficult to produce by hard photons, while Si iv and C iv can be photoionized to a large extent. There is, however, no evidence of O vi -bearing gas at T, 106 K associated with this DLA. In contrast, there is some evidence for narrow O vi, N v and C iv components (unexplained by photoionization), implying too low temperatures (T < 105 K) for simple collisional ionization models to produce their observed column densities. Stellar feedback is a possible source for producing the high ions, but we cannot rule out accretion of non-pristine material on to the protogalaxy. [source] Where are the cosmic metals at z, 3?MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2008Jesper Sommer-Larsen ABSTRACT The global temperature distribution of the cosmic gas-phase oxygen at z, 3 is determined by combining high-resolution cosmological simulations of individual protogalactic as well as larger regions with the observed, extinction-corrected, rest-frame V -band galaxy luminosity function. The simulations have been performed with three different stellar initial mass functions (IMFs), a Kroupa (K98), a Salpeter (S) and an Arimoto,Yoshii (AY), spanning a range of a factor of 5 in chemical yield and specific supernova type II energy feedback. Gas-phase oxygen is binned according to T as log(T) , 4.0 (,cold'), log(T) , 4.5 (,warm') and log(T) , 5.0, 5.5, 6.0, 6.5, 7.0 (,hot' phases). Oxygen is found to be distributed over all T phases, in particular for the top-heavy AY IMF. But, at variance with previous works, it is found that for the K98 and S IMFs the cold phase is the most important. For these IMFs it contains 47 and 37 per cent, respectively, of all gas-phase oxygen, mainly at fairly high density, nH, 0.1 cm,3. The implications of this in relation to observational damped Ly, absorber studies are discussed. In relation to ,missing metals' it is found that a significant fraction of the oxygen is located in a warm/hot phase that may be very difficult to detect. Moreover, it is found that less than about 20,25 per cent of the cosmic oxygen is associated with galaxies brighter than MV,,22, i.e. the faintest galaxy luminosities probed by current metallicity determinations for Lyman-break galaxies (LBGs). Hence, 75,80 per cent of the oxygen is also in this sense ,missing'. From the LBG-based, ,, 1500Å ultraviolet luminosity density history at z, 3, we obtain an essentially IMF-independent constraint on the mean oxygen density at z= 3. We compare this to what is obtained from our models, for the three different IMFs. We find that the K98 IMF is strongly excluded, as the chemical yield is simply too small, the Salpeter is marginally excluded, and the AY matches the constraint well. The K98 IMF can only match the data if the ,, 1500Å extinction corrections have been overestimated by factor of ,4, which seems highly unlikely. The yields for K98 are also far too small to match the observational data for C iv. The optimal IMF should have a yield intermediate between the S and AY. [source] Fate of clumps in damped Ly, systemsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2006Ilian T. Iliev ABSTRACT Recent observations have revealed that damped Ly, clouds (DLAs) host star formation activity. In order to examine if such star formation activity can be triggered by ionization fronts, we perform high-resolution hydrodynamics and radiative transfer simulations of the effect of radiative feedback from propagating ionization fronts on high-density clumps. We examine two sources of ultraviolet (UV) radiation field to which high-redshift (z, 3) galaxies could be exposed: one corresponding to the UV radiation originating from stars within the DLA, itself, and the other corresponding to the UV background radiation. We find that, for larger clouds, the propagating I-fronts created by local stellar sources can trigger cooling instability and collapse of significant part, up to 85 per cent, of the cloud, creating conditions for star formation in a time-scale of a few Myr. The passage of the I-front also triggers collapse of smaller clumps (with radii below ,4 pc), but in these cases the resulting cold and dense gas does not reach conditions conducive to star formation. Assuming that 85 per cent of the gas initially in the clump is converted into stars, we obtain a star formation rate of ,0.25 M, yr,1 kpc,2. This is somewhat higher than the value derived from recent observations. On the other hand, the background UV radiation which has harder spectrum fails to trigger cooling and collapse. Instead, the hard photons which have long mean free-path heat the dense clumps, which as a result expand and essentially dissolve in the ambient medium. Therefore, the star formation activity in DLAs is strongly regulated by the radiative feedback, both from the external UV background and internal stellar sources and we predict quiescent evolution of DLAs (not starburst-like evolution). [source] A unified model for the evolution of galaxies and quasarsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2000Guinevere Kauffmann We incorporate a simple scheme for the growth of supermassive black holes into semi-analytic models that follow the formation and evolution of galaxies in a cold dark matter-dominated Universe. We assume that supermassive black holes are formed and fuelled during major mergers. If two galaxies of comparable mass merge, their central black holes coalesce and a few per cent of the gas in the merger remnant is accreted by the new black hole over a time-scale of a few times 107 yr. With these simple assumptions, our model not only fits many aspects of the observed evolution of galaxies, but also reproduces quantitatively the observed relation between bulge luminosity and black hole mass in nearby galaxies, the strong evolution of the quasar population with redshift, and the relation between the luminosities of nearby quasars and those of their host galaxies. The strong decline in the number density of quasars from z,2 to z=0 is a result of the combination of three effects: (i) a decrease in the merging rate; (ii) a decrease in the amount of cold gas available to fuel black holes, and (iii) an increase in the time-scale for gas accretion. The predicted decline in the total content of cold gas in galaxies is consistent with that inferred from observations of damped Ly, systems. Our results strongly suggest that the evolution of supermassive black holes, quasars and starburst galaxies is inextricably linked to the hierarchical build-up of galaxies. [source] Probing dark matter, galaxies and the expansion history of the Universe with Ly, in absorption and emissionASTRONOMISCHE NACHRICHTEN, Issue 5 2010M.G. Haehnelt Abstract Ly, radiation is an important diagnostic tool in a wide range of astrophysical environments. I will first describe here how measurements of the matter power spectrum on small scales from Ly, forest data constrain the mass of dark matter particles. I then will report on an ambitious program of searching for very faint spatially extended Ly, emission at z , 3 which has led to the discovery of a new population of faint Ly, emitters which I will argue should be identified with the long searched for host galaxies of damped Ly, absorbers. Finally, I will discuss the possibility of measuring the redshift drift of Ly, absorption features and therefore the change of the expansion rate of the Universe in real time with the ultra-stable high-resolution spectrograph CODEX proposed for the E-ELT (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||