We study cosmic metal enrichment via adaptive mesh refinement hydrodynamical simulations in a (10 Mpc h...)3 volume following the Population III (PopIII)-PopII transition and for different PopIII ...initial mass function (IMFs). We have analysed the joint evolution of metal enrichment on galactic and intergalactic scales at z = 6 and z = 4. Galaxies account for ...9 per cent of the baryonic mass; the remaining gas resides in the diffuse phases: (a) voids, i.e. regions with extremely low density (... ≤ 1), (b) the true intergalactic medium (IGM, 1 < ... ≤ 10) and (c) the circumgalactic medium (CGM, 10 < ... ≤ 10...), the interface between the IGM and galaxies. At z = 6, a galactic mass-metallicity relation is established. At z = 4, galaxies with a stellar mass M* ... 10... M... show log(O/H)+12=8.19, consistent with observations. The total amount of heavy elements rises from ...=1.52x10... at z = 6 to 8.05 x 10... at z = 4. Metals in galaxies make up to ...0.89 of such budget at z = 6; this fraction increases to ...0.95 at z = 4. At z = 6 (z = 4), the remaining metals are distributed in CGM/IGM/voids with the following mass fractions: 0.06/0.04/0.01 (0.03/0.02/0.01). Analogously to galaxies, at z = 4 a density-metallicity (...-Z) relation is in place for the diffuse phases: the IGM/voids have a spatially uniform metallicity, Z ... 10... Z...; in the CGM, Z steeply rises with density up to ...10... Z... In all diffuse phases, a considerable fraction of metals is in a warm/hot (T...>10...K) state. Due to these physical conditions, Civ absorption line experiments can probe only ...2 per cent of the total carbon present in the IGM/CGM; however, metal absorption line spectra are very effective tools to study reionization. Finally, the PopIII star formation history is almost insensitive to the chosen PopIII IMF. PopIII stars are preferentially formed in truly pristine (Z = 0) gas pockets, well outside polluted regions created by previous star formation episodes. (ProQuest: ... denotes formulae/symbols omitted.)
Bright quasars, powered by accretion onto billion-solar-mass black holes, already existed at the epoch of reionization, when the Universe was 0.5-1 billion years old
. How these black holes formed in ...such a short time is the subject of debate, particularly as they lie above the correlation between black-hole mass and galaxy dynamical mass
in the local Universe. What slowed down black-hole growth, leading towards the symbiotic growth observed in the local Universe, and when this process started, has hitherto not been known, although black-hole feedback is a likely driver
. Here we report optical and near-infrared observations of a sample of quasars at redshifts 5.8 ≲ z ≲ 6.6. About half of the quasar spectra reveal broad, blueshifted absorption line troughs, tracing black-hole-driven winds with extreme outflow velocities, up to 17% of the speed of light. The fraction of quasars with such outflow winds at z ≳ 5.8 is ≈2.4 times higher than at z ≈ 2-4. We infer that outflows at z ≳ 5.8 inject large amounts of energy into the interstellar medium and suppress nuclear gas accretion, slowing down black-hole growth. The outflow phase may then mark the beginning of substantial black-hole feedback. The red optical colours of outflow quasars at z ≳ 5.8 indeed suggest that these systems are dusty and may be caught during an initial quenching phase of obscured accretion
.
We present the results of observations taken with the X-shooter spectrograph devoted to the study of quasars at z ∼ 6. This paper focuses on the properties of metals at high redshift traced, in ...particular, by the C iv doublet absorption systems. Six objects were observed with resolutions 27 and 34 km s−1 in the visual, and 37.5 and 53.5 km s−1 in the near-infrared. We detected 102 C iv lines in the range: 4.35 < z < 6.2 of which 27 are above z ∼ 5. Thanks to the characteristics of resolution and spectral coverage of X-shooter, we could also detect 25 Si iv doublets associated with the C iv at z 5. The column density distribution function of the C iv line sample is observed to evolve in redshift for z 5.3, with respect to the normalization defined by low-redshift (1.5 < z < 4) C iv lines. This behaviour is reflected in the redshift evolution of the C iv cosmic mass density,
, of lines with column density in the range
, which is consistent with a drop of a factor of ∼2 for z 5.3. Considering only the stronger C iv lines (
),
gently rises by a factor of ∼10 between z 6.2 and z 1.5 with a possible flattening towards z ∼ 0. The increase is well fitted by a power law:
. An insight into the properties of the C iv absorbers and their evolution with redshift is obtained by comparing the observed column densities of associated C iv, Si iv and C ii absorptions with the output of a set of cloudy photoionization models. As already claimed by cosmological simulations, we find that C iv is a good tracer of the metallicity in the low-density intergalactic medium (IGM) gas at z ∼ 5-6 while at z ∼ 3 it arises in gas with overdensity δ ∼ 100.
The redshifts of all cosmologically distant sources are expected to experience a small, systematic drift as a function of time due to the evolution of the Universe's expansion rate. A measurement of ...this effect would represent a direct and entirely model-independent determination of the expansion history of the Universe over a redshift range that is inaccessible to other methods. Here we investigate the impact of the next generation of Extremely Large Telescopes on the feasibility of detecting and characterizing the cosmological redshift drift. We consider the Lyα forest in the redshift range 2 < z < 5 and other absorption lines in the spectra of high-redshift QSOs as the most suitable targets for a redshift drift experiment. Assuming photon-noise-limited observations and using extensive Monte Carlo simulations we determine the accuracy to which the redshift drift can be measured from the Lyα forest as a function of signal-to-noise ratio and redshift. Based on this relation and using the brightness and redshift distributions of known QSOs we find that a 42-m telescope is capable of unambiguously detecting the redshift drift over a period of ∼20 yr using 4000 h of observing time. Such an experiment would provide independent evidence for the existence of dark energy without assuming spatial flatness, using any other cosmological constraints or making any other astrophysical assumption.
We performed a kinematical analysis of the CII line emission of the BR 1202-0725 system at z ~ 4.7 using ALMA science verification observations. The most prominent sources of this system are a quasar ...(QSO) and a submillimeter galaxy (SMG), separated by a projected distance of about ~24 kpc and characterized by very high star formation rates, higher than ~1000 M⊙ yr-1. However, the ALMA observations reveal that these galaxies apparently have undisturbed rotating disks, which is at variance with the commonly accepted scenario in which strong star formation activity is induced by a major merger. We also detected faint components which, after spectral deblending, were spatially resolved from the main QSO and SMG emissions. The relative velocities and positions of these components are compatible with orbital motions within the gravitational potentials generated by the QSO host galaxy and the SMG, suggesting that they are smaller galaxies in interaction or gas clouds in accretion flows of tidal streams. Moreover, we did not find any clear spectral evidence for outflows caused by active galactic nuclei or stellar feedback. This suggests that the high star formation rates might be induced by interactions or minor mergers with these companions, which do not affect the large-scale kinematics of the disks, however. Alternatively, the strong star formation may be fueled by the accretion of pristine gas from the host halo. Our kinematical analysis also indicates that the QSO and the SMG have similar dynamical masses, mostly in the form of molecular gas, and that the QSO host galaxy and the SMG are seen close to face-on with slightly different disk inclinations: the QSO host galaxy is seen almost face-on (i ~ 15°), while the SMG is seen at higher inclinations (i ~ 25°). Finally, the ratio between the black hole mass of the QSO, obtained from new X-shooter spectroscopy, and the dynamical mass of the host galaxy is similar to value found in very massive local galaxies, suggesting that the evolution of black hole galaxy relations is probably better studied with dynamical than with stellar host galaxy masses.
We present a sample of 38 intervening damped Lyman ... (DLA) systems identified towards 100 z > 3.5 quasars, observed during the XQ-100 survey. The XQ-100 DLA sample is combined with major DLA ...surveys in the literature. The final combined sample consists of 742 DLAs over a redshift range approximately 1.6 < z sub( abs) < 5.0. We develop a novel technique for computing ... as a continuous function of redshift, and we thoroughly assess and quantify the sources of error therein, including fitting errors and incomplete sampling of the high column density end of the column density distribution function. There is a statistically significant redshift evolution in ... ( greater than or equal to 3...) from z ~ 2 to z ~ 5. In order to make a complete assessment of the redshift evolution of ...HI, we combine our high-redshift DLA sample with absorption surveys at intermediate redshift and 21-cm emission line surveys of the local universe. Although ...DLAHI, and hence its redshift evolution, remains uncertain in the intermediate-redshift regime (0.1 < z sub( abs) < 1.6), we find that the combination of high-redshift data with 21-cm surveys of the local universe all yield a statistically significant evolution in ... from z ~ 0 to z ~ 5 ( greater than or equal to 3...). Despite its statistical significance, the magnitude of the evolution is small: a linear regression fit between ... and z yields a typical slope of ~0.17 x 10 super( -3), corresponding to a factor of ~4 decrease in ... between z = 5 and z = 0. (ProQuest: ... denotes formulae/symbols omitted.)
We present a measurement of the Lyman α flux probability distribution function (PDF) obtained from a set of eight high-resolution quasar spectra with emission redshifts in the range 3.3 ≤z≤ 3.8. We ...carefully study the effect of metal absorption lines on the shape of the PDF. Metals have a larger impact on the PDF measurements at lower redshift, where there are relatively fewer Lyman α absorption lines. This may be explained by an increase in the number of metal lines that are blended with Lyman α absorption lines towards higher redshift, but may also be due to the presence of fewer metals in the intergalactic medium (IGM) at earlier times. We also provide a new measurement of the redshift evolution of the effective optical depth, τeff, at 2.8 ≤z≤ 3.6, and find no evidence for a deviation from a power-law evolution in the log (τeff)-log (1 +z) plane. The flux PDF measurements are furthermore of interest for studies of the thermal state of the IGM at z≃ 3. By comparing the PDF to state-of-the-art cosmological hydrodynamical simulations, we place constraints on the temperature of the IGM and compare our results with previous measurements of the PDF at lower redshift. At redshift z= 3, our new PDF measurements are consistent with an isothermal temperature-density relation, T=T
0Δγ− 1, with a temperature at the mean density of T
0= 19 250 ± 4800 K and a slope γ= 0.90 ± 0.21 (1σ uncertainties). In comparison, joint constraints with existing lower redshift PDF measurements at z < 3 favour an inverted temperature-density relation with T
0= 17 900 ± 3500 K and γ= 0.70 ± 0.12, in broad agreement with previous analyses.
We statistically study the physical properties of a sample of narrow absorption line (NAL) systems looking for empirical evidences to distinguish between intrinsic and intervening NALs without taking ...into account any a priori definition or velocity cut-off. We analyse the spectra of 100 quasars with 3.5 < z sub( em) < 4.5, observed with X-shooter/Very Large Telescope in the context of the XQ-100 Legacy Survey. We detect an ~8 sigma excess in the C IV number density within 10,000 km s super( -1) of the quasar emission redshift with respect to the random occurrence of NALs. This excess does not show a dependence on the quasar bolometric luminosity and it is not due to the redshift evolution of NALs. It extends far beyond the standard 5000 km s super( -1) cut-off traditionally defined for associated absorption lines. We propose to modify this definition, extending the threshold to 10 000 km s super( -1) when weak absorbers (equivalent width < 0.2 Aa) are also considered. We infer N V is the ion that better traces the effects of the quasar ionization field, offering the best statistical tool to identify intrinsic systems. Following this criterion, we estimate that the fraction of quasars in our sample hosting an intrinsic NAL system is 33 per cent. Lastly, we compare the properties of the material along the quasar line of sight, derived from our sample, with results based on close quasar pairs investigating the transverse direction. We find a deficiency of cool gas (traced by C II) along the line of sight connected to the quasar host galaxy, in contrast with what is observed in the transverse direction.
Abstract
At low densities, the standard ionization history of the intergalactic medium (IGM) predicts a decreasing temperature of the IGM with decreasing density once hydrogen (and helium) ...reionization is complete. Heating the high-redshift, low-density IGM above the temperature expected from photoheating is difficult, and previous claims of high/rising temperatures in low-density regions of the Universe based on the probability density function (PDF) of the opacity in Ly α forest data at 2 < z < 4 have been met with considerable scepticism, particularly since they appear to be in tension with other constraints on the temperature–density relation (TDR). We utilize here an ultrahigh signal-to-noise spectrum of the Quasi-stellar object HE0940-1050 and a novel technique to study the low opacity part of the PDF. We show that there is indeed evidence (at 90 per cent confidence level) that a significant volume fraction of the underdense regions at z ∼ 3 has temperatures as high or higher than those at densities comparable to the mean and above. We further demonstrate that this conclusion is nevertheless consistent with measurements of a slope of the TDR in overdense regions that imply a decreasing temperature with decreasing density, as expected if photoheating of ionized hydrogen is the dominant heating process. We briefly discuss implications of our findings for the need to invoke either spatial temperature fluctuations, as expected during helium reionization, or additional processes that heat a significant volume fraction of the low-density IGM.
In this work, we investigate the abundance and distribution of metals in the intergalactic medium (IGM) at ... through the analysis of an ultra-high signal-to-noise ratio UVES spectrum of the quasar ...HE0940-1050. In the C IV forest, our deep spectrum is sensitive at 3s to lines with column density down to log ... and in 60 per cent of the considered redshift range down to ... In our sample, all H I lines with log ... show an associated C IV absorption. In the range ..., 43 per cent of H I lines has an associated C IV absorption. At log ..., the detection rates drop to <10 per cent, possibly due to our sensitivity limits and not to an actual variation of the gas abundance properties. In the range log ..., we observe a fraction of H I lines with detected C IV a factor of 2 larger than the fraction of H I lines lying in the circumgalactic medium (CGM) of relatively bright Lyman-break galaxies hosted by dark matter haloes with ... The comparison of our results with the output of a grid of photoionization models and of two cosmological simulations implies that the volume filling factor of the IGM gas enriched to a metallicity log ... should be of the order of ~10-13 per cent. In conclusion, our results favour a scenario in which metals are found also outside the CGM of bright star-forming galaxies, possibly due to pollution by lower mass objects and/or to an early enrichment by the first sources. (ProQuest: ... denotes formulae/symbols omitted.)
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