Spectra Of High Redshift QSOs Research Articles

Mg II ABSORPTION AT 2 <z< 6 WITH MAGELLAN/FIRE. II. A LONGITUDINAL STUDY OF H I, METALS, AND IONIZATION IN GALACTIC HALOS

We present a detailed study of HI and metals for 110 MgII absorption systems discovered at 1.98 <= z <= 5.33 in the infrared spectra of high redshift QSOs. Using new measurements of rest-frame UV lines from optical spectra of the same targets, we compare the high redshift sample with carefully constructed low redshift control samples from the literature to study evolutionary trends from z=0 --> 5.33 (>12 Gyr). We observe a significant strengthening in the characteristic N(HI) for fixed MgII equivalent width as one moves toward higher redshift. Indeed at our sample's mean zbar=3.402, all MgII systems are either damped Ly-alpha absorbers or sub-DLAs, with 40.7% of systems exceeding the DLA threshold (compared to 16.7% at zbar=0.927). We set lower limits on the metallicity of the MgII systems where we can measure HI; these results are consistent with the full DLA population. The classical MgII systems (W(2796)=0.3-1.0 Ang), which preferentially associate with sub-DLAs, are quite metal rich at ~0.1 Solar. We applied quantitative classification metrics to our absorbers to compare with low redshift populations, finding that weak systems are similar to classic MgII absorbers at low redshift. The strong systems either have very large MgII and FeII velocity spreads implying non-virialized dynamics, or are more quiescent DLAs. There is tentative evidence that the kinetically complex systems evolve in similar fashion to the global star formation rate. We speculate that if weaker MgII systems represent accreting gas as suggested by recent studies of galaxy-absorber inclinations, then their high metal abundance suggests re-accretion of recently ejected material rather than first-time infall from the metal-poor IGM, even at early times.

QSONG: Supermassive Black Holes in Quasars at World's End

AbstractWe present the initial results of the AKARI mission program QSONG (Quasar Spectroscopic Observation with NIR Grism). QSONG utilizes the unique AKARI capability of performing spectroscopic observations at 2.5–5 μm, with the aim of understanding the mass evolution of ~200 quasars at 3.4 &lt; z &lt; 6.5 from their rest-frame optical spectra. The program also studies the rest-frame NIR spectra of 99 well-studied quasars at low redshift (z &lt; 0.5) and 10 red quasars. With the high-redshift QSONG observations, we detect and resolve redshifted optical lines such as Hα for the first time at this redshift, allowing us to measure the supermassive black hole (SMBH) masses at high redshift using the well-calibrated optical mass estimators and provide an independent assessment of UV line-based mass measurements whose reliability has been controversial. Until the launch of JWST, AKARI will be the only facility in the world capable of studying the rest-frame optical spectra of high-redshift objects out to z ~ 6. Our initial QSONG result indicates a lack of very massive SMBHs at z &gt; 5.5, suggesting that we are possibly witnessing the cosmic growth history of the most massive SMBHs (~ 1010M⊙) in the early universe. Ultimately, an extensive study of the rest-frame optical spectra of high-redshift QSOs will help us understand the evolution and the growth of SMBHs in the early universe.

C, N, O abundances in the most metal-poor damped Lyman alpha systems

This study focuses on some of the most metal-poor damped Lyα (DLA) absorbers known in the spectra of high-redshift QSOs, using new and archival observations obtained with ultraviolet-sensitive echelle spectrographs on the Keck and VLT telescopes. The weakness and simple velocity structure of the absorption lines in these systems allow us to measure the abundances of several elements, and in particular those of C, N and O, a group that is difficult to study in DLAs of more typical metallicities. We find that when the oxygen abundance is less than ∼1/100 of solar, the C/O ratio in high-redshift DLAs and sub-DLAs matches that of halo stars of similar metallicity and shows higher values than expected from galactic chemical evolution models based on conventional stellar yields. Furthermore, there are indications that at these low metallicities the N/O ratio may also be above simple expectations and may exhibit a minimum value, as proposed by Centurion and her collaborators in 2003. Both results can be interpreted as evidence for enhanced production of C and N by massive stars in the first few episodes of star formation, in our Galaxy and in the distant protogalaxies seen as QSO absorbers. The higher stellar yields implied may have an origin in stellar rotation which promotes mixing in the stars' interiors, as considered in some recent model calculations. We briefly discuss the relevance of these results to current ideas on the origin of metals in the intergalactic medium and the universality of the stellar initial mass function.

Cosmic dynamics in the era of Extremely Large Telescopes

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 characterising the cosmological redshift drift. We consider the Lyman alpha 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 Ly alpha forest as a function of signal-to-noise 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.

Reconciling the local galaxy population with damped Lyman α cross-sections and metal abundances

A comprehensive analysis of 355 high-quality Westerbork Synthesis Radio Telescope (WSRT) HI 21-cm line maps of nearby galaxies shows that the properties and incident rate of damped Lyman alpha absorption systems (DLAs) observed in the spectra of high-redshift QSOs are in good agreement with DLAs originating in gas discs of galaxies like those in the z approximate to 0 population. Comparison of low-z DLA statistics with the HI incidence rate and column density distribution f(N (HI)) for the local galaxy sample shows no evidence for evolution in the integral 'cross-section density' = l(-1) (l = mean free path between absorbers) below z approximate to 1.5, implying that there is no need for a hidden population of galaxies or H I clouds to contribute significantly to the DLA cross-section. Compared with z approximate to 4, our data indicate evolution of a factor of 2 in the comoving density along a line of sight. We find that dN/dz(z = 0) = 0.045 +/- 0.006. The idea that the local galaxy population can explain the DLAs is further strengthened by comparing the properties of DLAs and DLA galaxies with the expectations based on our analysis of local galaxies. The distribution of luminosities of DLA host galaxies, and of impact parameters between QSOs and the centres of DLA galaxies, is in good agreement with what is expected from local galaxies. Approximately 87 per cent of low-z DLA galaxies are expected to be fainter than L-*, and 37 per cent have impact parameters less than 1 arcsec at z = 0.5. The analysis shows that some host galaxies with very low impact parameters and low luminosities are expected to be missed in optical follow-up surveys. The well-known metallicity-luminosity relation in galaxies, in combination with metallicity gradients in galaxy discs, causes the expected median metallicity of low-z DLAs to be low (similar to 1/7 solar), which is also in good agreement with observations of low-z DLAs. We find that f(N H I) can be fitted satisfactorily with a gamma distribution, a single power law is not a good fit at the highest column densities N H I > 10(21) cm(-2). The vast majority (approximate to 81 per cent) of the H I gas in the local Universe resides in column densities above the classical DLA limit (N (H I) > 2 x 10(20) cm(-2)), with N (H I) similar to 10(21) cm(-2) dominating the cosmic H I mass density.

Intergalactic medium

The absorption lines seen in the spectra of high redshift QSOs are important tools for studying the early evolution of galaxies and intergalactic medium. In this presentation I briefly review various available observations, our understanding of different types of absorption systems, and highlight some of the issues that can be addressed with ELTs.

Hβ spectra of high-redshift QSOs: Eigenvector 1 at high luminosities

We present VLT–ISAAC spectra of unprecedented S/N and resolution for the Hβ region in a sample of n = 17 quasars in the range z=0.8–2.5. The data represent our first attempt to test source occupation and line properties for the Eigenvector 1 parameter space that was defined using a sample of sources with z&lt;0.8. We find no strong luminosity/redshift dependent effects with the possible exception of an increase in the minimum broad line profile width from 1000 to 3000 km s−1 between MB≈−20 and −28.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Statistics of Neutral Regions during Hydrogen Reionization

We present predictions for two statistical measures of the hydrogen reionization process at high redshift. The first statistic is the number of neutral segments identified in spectra of high-redshift QSOs as a function of their length. The second is the cross-correlation of neutral regions with possible sources of ionizing radiation. These independent probes are sensitive to the topology of the ionized regions. If reionization proceeded from high- to low-density regions, then the cross-correlation will be negative, while if voids were ionized first we expect a positive correlation and a relatively small number of long neutral segments. We test the sensitivity of these statistics for reionization by stars in high-redshift galaxies. The flux of ionizing radiation emitted from stars is estimated by identifying galaxies in an N-body simulation using a semianalytic galaxy formation model. The spatial distribution of ionized gas is traced in various models for the propagation of the ionization fronts. A model with ionization proceeding from high- to low-density regions is consistent with the observations of Becker et al., while models in which ionization begins in the lowest density regions appear to be inconsistent with the present data. Further data are required to confirm this result.

Predicting Big Bang Deuterium

We present new upper and lower bounds to the primordial abundances of deuterium and helium-3 based on observational data from the solar system and the interstellar medium. Independent of any model for the primordial production of the elements we find (at the 95\% C.L.): $1.5 \times 10^{-5} \le (D/H)_P \le 10.0 \times 10^{-5}$ and $(^3He/H)_P \le 2.6\times 10^{-5}$. When combined with the predictions of standard big bang nucleosynthesis, these constraints lead to a 95\% C.L. bound on the primordial abundance of deuterium: $(D/H)_{best} = (3.5^{+2.7}_{-1.8})\times 10^{-5}$. Measurements of deuterium absorption in the spectra of high redshift QSOs will directly test this prediction. The implications of this prediction for the primordial abundances of helium-4 and lithium-7 are discussed, as well as those for the universal density of baryons.

Element Abundances at High Redshifts: The N/O Ratio in a Primeval Galaxy

The damped Lyman alpha systems seen in the spectra of high redshift QSOs offer the means to determine element abundances in galaxies observed while still at an early stage of evolution. Such measurements, which have only recently come within reach, complement and extend the data provided by studies of different stellar populations in our Galaxy and of extragalactic H~II regions which have up to now formed the basis of galactic chemical evolution models. In this paper we demonstrate the potential of this new approach with high-resolution echelle observations of several elements in the z(abs) = 2.27936 absorption system in the bright z(em) = 2.940 QSO 2348-147. The absorbing galaxy appears to be chemically unevolved, with heavy element abundances only 1/100 of solar; if it is the progenitor of a spiral galaxy like our own, it is unlikely to have collapsed to form a thin disk by z = 2.3 (corresponding to a look-back time of approximately 13 Gyr for H_0 = 50 km/s/Mpc and q_0 = 0.01). Our data allow us to measure the nitrogen-to-oxygen ratio at a metallicity lower than those of the most metal-poor dwarf galaxies known. We find that, relative to the solar scale, N is more underabundant than O by at least a factor of 15. This result is broadly in line with current ideas on the relative importance of primary and secondary production of N; future measurements in several damped Lyman alpha systems will permit more stringent tests of models for the evolution of the N/O ratio with time. Oxygen and other alpha-elements are overabundant relative to Fe by no more than the factor of about 3 typical of metal-poor stars in the disk and halo of the Milky Way.

Formation and evolution of the disc in spiral galaxies: viscous models without infall

We study models for the evolution of the disc of spiral galaxies that include the effects of viscosity but assume no continuous infall of gas on to the disc. The time-scale for star formation is assumed to be of the same order as the time-scale for viscous redistribution of the mass and angular momentum in the disc. We confirmed that these models are able to reproduce the observed radial distribution of gas and stars for present-day spirals for a variety of model parameters and initial conditions. Furthermore, we generally found that the evolution of both the stellar and gas surface density profiles is approximately self-similar over at least 90 per cent of the history of the disc, and that the size of the initial gas disc is approximately equal to the present Holmberg radius for the galaxy. Implications of these results for the evolution of spiral structure and for the interpretation of damped Ly α lines in the spectra of high-redshift QSOs are considered. A discussion of the possible physical mechanisms for the viscosity and the associated time-scales is also presented.

A new spectroscopic survey for damped Ly-alpha absorption lines from high-redshift galaxies

The results of a new survey for distant galaxies identified on the basis of the damped Lyα absorption lines they produce in the spectra of high-redshift background QSOs are presented. These results are based on new, low-resolution spectroscopy of a sample of 57 QSOs, which are combined with similar low-resolution spectroscopy of 53 QSOs, to yield a total of 101 spectra of high-redshift QSOs which are suitable for identifying damped Lyα absorption lines. The spectra are analyzed to generate a complete sample of absorption features which, if the features are assumed to be Lyα lines, have rest-frame equivalent widths satisfying W ≥ 5 A. A total of 84 such damped Lyα absorption-line candidates are detected.

A high-redshift extension of the survey for C IV absorption in the spectra of QSOs - The redshift evolution of the heavy element absorbers

view Abstract Citations (141) References (37) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A High-Redshift Extension of the Survey for C IV Absorption in the Spectra of QSOs: The Redshift Evolution of the Heavy-Element Absorbers Steidel, Charles C. Abstract We have obtained spectra with a resolution of 60 km s^-1^ of 11 QSOs with 3.045 <= z_em_ <= 4.104. In general, the spectra cover the wavelength range between the C IV λ1549 and Lyα emission lines. The QSOs were chosen to supplement the large survey for C IV absorption in the spectra of high-redshift QSOs recently published by Sargent, Boksenberg, and Steidel. The combined sample of C IV λλ1548, 1550 doublets now contains 275 redshifts, spanning the redshift range 1.3 <= z_abs_ <= 4.0. The new data considerably improve the statistics of the C IV absorbers for z_abs_ > 2.5. Unbiased subsamples of C IV redshifts have been isolated in order to investigate the evolution of the properties and distribution of the absorbers with redshift, with the following principal results. The number of C IV absorption systems per unit redshift range N(z) decreases with increasing redshift in the range 1.3 <= z_abs_ <= 3.7 in a manner which is inconsistent with a constant comoving density of absorbers. This inconsistency is at the 3.1 σ level for q_0_ = 1/2 and at the 4.0 σ level for q_0_ = 0. Thus, the properties of the absorbers are almost certainly evolving with time. The N(z) curve exhibits a gradual decline for z > 2, as opposed to the rapid fall-off suggested by earlier results. The peak in the C IV two-point correlation function on velocity scales 200 <= {DELTA}v <= 600 km s^-1^ appears to have the same power in high- redshift (z_abs_ > 2.2) and low-redshift (z_abs_ < 2.2) subsamples. There is marginal evidence that the width of the correlation peak on these small velocity scales is smaller in the high-redshift subsample. A 2 σ excess of power on velocity scales 1000 <= {DELTA}v <= 10,000 km s^-1^ exists in the low-redshift subsample, but not in the high-redshift subsample. Arguments are presented which appear to rule out a significant evolution of the gas velocity dispersion parameter b with redshift in the clouds giving rise to the C IV absorption, and therefore the evolution of the number of observed C IV systems is interpreted as a systematic change in the mean C IV column density of the clouds. A changing abundance of C, and not a systematically changing ionization state in the gas, is probably dominating the observed evolution. The evolution of the mean C IV doublet ratio and a changing distribution of equivalent width with redshift indicate that the typical C IV column density, and by extension the typical abundance of C, is increasing by a factor of ~ 3 over the redshift range 3 >= z >= 1.5, corresponding to lookback times of 12.4h^-1^_50_ to 9.8h^-1^_50_ Gyr (q_0_ =1/2) and an e-folding time for chemical enrichment of between 1 and 2 Gyr. An attempt is made to relate the chemical evolution of the absorbers to early enrichment in galactic halos. Publication: The Astrophysical Journal Supplement Series Pub Date: January 1990 DOI: 10.1086/191407 Bibcode: 1990ApJS...72....1S Keywords: Absorption Spectra; Carbon; Galactic Evolution; Quasars; Red Shift; Sky Surveys (Astronomy); Astronomical Spectroscopy; Chemical Evolution; Heavy Elements; Lyman Alpha Radiation; Spectral Resolution; Ultraviolet Astronomy; Astrophysics; GALAXIES: ABUNDANCES; GALAXIES: EVOLUTION; QUASARS full text sources ADS | data products NED (65) SIMBAD (11)

Lyman α Emission from Disk Absorption Systems in QSOs: Star Formation in Young Galaxy Disks

The strong self-damped Lyman α absorption systems present in the spectra of high redshift QSOs represent a unique population of absorber which has recently been associated with the precursors of current disk galaxies. In a low resolution survey for what we have come to call “Lyman α disk systems” performed at Lick Observatory (Wolfe, et al. 1986, Ap. J. Suppl. 61, 249) approximately 18 systems with confirmed damped Lyman α profiles and rest frame equivalent widths greater than 5 Å were detected in a sample of 68 high redshift QSOs (Smith, Cohen and Bradley 1986, Ap. J. 310, 583). Subsequent higher resolution study has shown these systems to have the following properties (Turnshek, et al. 1988, Ap. J., in press): 1.Neutral hydrogen column densities, 2 × 1020 ≤ NHI ≤ 8 × 1021 cm−2.2.Low-mixed ionization state. Typically the low ionization states dominate the high ionization states (e.g. CII ≫ CIV). Some enrichment has occurred, −2≲[X/H]⊙ ≲0.3.Gas density, n ≲ 1 cm−3.4.The gas shows two components, a quiescent (disk) component, σν ≲ 10 km s−1, and a turbulent (halo) component, σν ≲ 20 km s−1. Some systems show only the low velocity dispersion component.5.At least one system intervening toward a radio QSO (Pks 0458-020) shows 21-cm absorption. The system shows multiple cloud structure with σν ≈ 6 km s−1, Ts ≈ 100 K, and structure extended over several kpc on the sky.6.There is evidence that these systems may be self gravitating with scale height of the order of 300 pc.7.These systems represent a unique population of absorber (distinct from the ‘Lyman a forest’ and heavy element systems) covering approximately 20% of the sky to z ≈ 3 and accounting for all of the baryonic matter at that redshift.

A method of identifiying absorption systems in quasar spectra. I. principles and procedure

We have developed a systematic method on the basis of statistical testing of hypotheses to deal with the problem of identification of absorption redshift systems in the spectra of highredshift QSOs. We have taken account of Bahcall's signal-to-noise ratio /1/. Our procedure consists of the following steps: 1) Set up the identification criteria. 2) Divide the whole redshift ranges into intervals, within each of which the composition of the “visible” set of reference lines is the same. Search on the computer the spectrum at a steplength Δz and count the number of systems supported by 1,2,3… identified lines. 3) For each visible set, calculate the probabilities of random identifications. 4) For each visible set, apply the statistical test to isolate the systems which are in the rejection region of the null-hypothesis. 5) Pick out those systems with high values of the signal-to-noise ratio from amongst the resulting systems in the last step. 6) Apply astrophysical considerations to the surviving systems. This last step will be discussed in a separate paper /10/.

The Statistic Study of Lα Absorption Lines

The statistic studies of the absorbing forest in the spectra of high redshift QSOs will provide an important approach to the understanding of the physical properties of the absorbing materials. For this purpose a collection of uniform samples would be very important and urgent. It is very time consuming of the large telescopes to take the high resolution, high ratio-to-noise and wide coverage of wavelength of the QSO's spectra, therefore, an international collaboration in a uniform way would be very desirable.

The absorption lines in the spectra of high redshift qsos

Based on the spectra of 4 high-redshift quasars (resolution 2A) obtained by us [1–5] using IPCS on the RGO Cassegrain spectrograph of the AAT, we point out the following. 1. Auto-correlation peaks at L α L β and L α L γ in PKS 0805+046 and PKS 1442+101 suggest that the large number of absorption lines shortward of L α in high redshift quasars are due to absorption by hydrogen clouds. 2. The distribution of absorption lines and the correlation function of L α L β indicate that PKS 0528-250 may be an exception, requiring further observation. 3. Absorption redshift systems containing metallic lines may be produced by either matter ejected from the quasar, or an associated galaxy cluster or an intervening galaxy. 4. The randomness in the column density and the dispersion velocity deduced from the curve of growth of the L α L β pair supports the hypothesis that the pure L α absorption comes from primitive hydrogen clouds in the early, exploding universe. 5. The number of hydrogen clouds per unit redshift interval is determined by the data of absorption lines of quasars with Z > 3.

On the possible identification of MG II 2934-A emission in QSOs

view Abstract Citations (21) References (30) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS On the possible identification of Mg II lambda 2934 emission in QSOs. Grandi, S. A. ; Phillips, M. M. Abstract A broad weak emission feature at a rest wavelength of approximately 2950 A is found to be nearly always present in QSO spectra. The identifications with forbidden Mg V, Ne V, or O I transitions which have been suggested in the past do not appear likely. An identification with several lines of Fe II does not seem probable either. A correlation of the strength of 2950-A emission with the Mg II 2798-A resonance doublet suggests that the emission may be Mg II at 2934 A. Two excitation mechanisms for Mg II 2934 A are suggested and discussed: fluorescence by H I L-beta and fluorescence by N V 1240 A. Both mechanisms are shown to lead to appreciable excitation of Mg II 2934 A with respect to Mg II 2798 A. A problem with this identification is that the centroid of the broad 2950-A feature is not aligned exactly with Mg II 2934 A when the redshift determined from the other emission peaks is used. However, it is suggested that Mg II 2934 A may be consistent with a redshift determined from the centroid of the broad components of the Balmer lines. Evidence in support of the proposed emission mechanisms is outlined. Problems such as the apparent weakness of Mg II 1737-, 1750-A emission in the spectra of high-redshift QSOs are also discussed. Publication: The Astrophysical Journal Pub Date: March 1978 DOI: 10.1086/155921 Bibcode: 1978ApJ...220..426G Keywords: Magnesium; Metal Ions; Near Ultraviolet Radiation; Quasars; Ultraviolet Spectra; Astronomical Spectroscopy; Balmer Series; Emission Spectra; Extraterrestrial Radiation; Fluorescence; Forbidden Transitions; Optical Resonance; Red Shift; Astronomy; Quasars:Line Identifications full text sources ADS |