QSO Evolution Research Articles

Exploring the radio loudness of SDSS quasars with spectral stacking

ABSTRACT We use new 144 MHz observations over 5634 deg2 from the LOFAR (Low Frequency Array) Two-metre Sky Survey (LoTSS) to compile the largest sample of uniformly selected, spectroscopically confirmed quasars from the 14th data release of the Sloan Digital Sky Survey (SDSS-DR14). Using the classical definition of radio loudness, R = log (L1.4GHz/Li), we identify 3697 radio-loud (RL) and 111 132 radio-quiet (RQ) sources at 0.6 < z < 3.4. To study their properties, we develop a new rest-frame spectral stacking algorithm, designed with forthcoming massively multiplexed spectroscopic surveys in mind, and use it to create high signal-to-noise composite spectra of each class, matched in redshift and absolute i-band magnitude. We show that RL quasars have redder continuum and enhanced [O ii] emission than their RQ counterparts. These results persist when additionally matching in black hole mass, suggesting that this parameter is not the defining factor in making a quasi-stellar object (QSO) RL. We find that these features are not gradually varying as a function of radio loudness, but are maintained even when probing deeper into the RQ population, indicating that a clear-cut division in radio loudness is not apparent. Upon examining the star formation rates (SFRs) inferred from the [O ii] emission line, with the contribution from active galactic nucleus removed using the [Ne v] line, we find that RL quasars have a significant excess of star formation relative to RQ quasars out to z = 1.9 at least. Given our findings, we suggest that RL sources either preferably reside in gas-rich systems with rapidly spinning black holes, or represent an earlier obscured phase of QSO evolution.

A striking relationship between dust extinction and radio detection in DESI QSOs: evidence for a dusty blow-out phase in red QSOs

ABSTRACT We present the first eight months of data from our secondary target programme within the ongoing Dark Energy Spectroscopic Instrument (DESI) survey. Our programme uses a mid-infrared and optical colour selection to preferentially target dust-reddened quasi-stellar objects (QSOs) that would have otherwise been missed by the nominal DESI QSO selection. So far, we have obtained optical spectra for 3038 candidates, of which ∼70 per cent of the high-quality objects (those with robust redshifts) are visually confirmed to be Type 1 QSOs, consistent with the expected fraction from the main DESI QSO survey. By fitting a dust-reddened blue QSO composite to the QSO spectra, we find they are well-fitted by a normal QSO with up to AV ∼ 4 mag of line-of-sight dust extinction. Utilizing radio data from the LOFAR Two-metre Sky Survey (LoTSS) DR2, we identify a striking positive relationship between the amount of line-of-sight dust extinction towards a QSO and the radio detection fraction, that is not driven by radio-loud systems, redshift and/or luminosity effects. This demonstrates an intrinsic connection between dust reddening and the production of radio emission in QSOs, whereby the radio emission is most likely due to low-powered jets or winds/outflows causing shocks in a dusty environment. On the basis of this evidence, we suggest that red QSOs may represent a transitional ‘blow-out’ phase in the evolution of QSOs, where winds and outflows evacuate the dust and gas to reveal an unobscured blue QSO.

Trends among Flux, Luminosity, and Color Indices in High Redshift QSOs

The following study discusses the relationship of high redshift(z) Quasi Stellar Objects’(QSOs) flux, luminosity, and color indices. The paper analyzes observable trends among these 3 variables and uses them to understand the distribution of QSOs across space-time. While many such studies have been conducted in redshift ranges of 1<z<4, the following research or study has been done in the relatively unexplored date range of 2 <z<7. To answer this question, we used the Sloan Digital Sky Survey to obtain samples, curate the data, and analyze it using Python Data Science tools including Pandas and Matplotlib. The results suggest a general trend of increasing data density with the progression of distance and convergence of QSO Magnitude distributions about the median. This research provides insight into the evolution of QSOs over space-time and why they occurred.

The parsec-scale structure of radio-loud broad absorption line quasars

Broad absorption line quasars (BAL QSOs) belong to a class of objects not well-understood as yet. Their UV spectra show BALs in the blue wings of the UV resonance lines, owing to ionized gas with outflow velocities up to 0.2 c. They can have radio emission that is difficult to characterize and that needs to be studied at various wavelengths and resolutions. We aim to study the pc-scale properties of their synchrotron emission and, in particular, to determine their core properties. We performed observations in the Very Long Baseline Interferometry (VLBI) technique, using both the European VLBI Network (EVN) at 5 GHz, and the Very Long Baseline Array (VLBA) at 5 and 8.4 GHz to map the pc-scale structure of the brightest radio-loud objects of our sample, allowing a proper morphological interpretation. A variety of morphologies have been found: 9 BAL QSOs on a total of 11 observed sources have a resolved structure. Core-jet, double, and symmetric objects are present, suggesting different orientations. In some cases the sources can be young GPS or CSS. The projected linear size of the sources, also considering observations from our previous work for the same objects, can vary from tens of pc to hundreds of kpc. In some cases, a diffuse emission can be supposed from the missing flux-density with respect to previous lower resolution observations. Finally, the magnetic field strength does not significantly differ from the values found in the literature for radio sources with similar sizes. These results are not easily interpreted with the youth scenario for BAL QSOs, in which they are generally compact objects still expelling a dust cocoon. The variety of orientations, morphologies, and extensions found are presumably related to different possible angles for the BAL producing outflows, with respect to the jet axis. Moreover, the phenomenon could be present in various phases of the QSO evolution.

The central structure of Broad Absorption Line QSOs: observational characteristics in the cm-mm wavelength domain

Accounting for ∼20% of the total QSO population, Broad Absorption Line QSOs are still an unsolved problem in the AGN context. They present wide troughs in the UV spectrum, due to material with velocities up to 0.2 c toward the observer. The two models proposed in literature try to explain them as a particular phase of the evolution of QSOs or as normal QSOs, but seen from a particular line of sight.We built a statistically complete sample of Radio-Loud BAL QSOs, and carried out an observing campaign to piece together the whole spectrum in the cm wavelength domain, and highlight all the possible differences with respect to a comparison sample of Radio-Loud non-BAL QSOs. VLBI observations at high angular resolution have been performed, to study the pc-scale morphology of these objects. Finally, we tried to detect a possible dust component with observations at mm-wavelengths.Results do not seem to indicate a young age for all BAL QSOs. Instead a variety of orientations and morphologies have been found, constraining the outflows foreseen by the orientation model to have different possible angles with respect to the jet axis.

Detecting the highest redshift (z > 8) quasi-stellar objects in a wide, near-infrared slitless spectroscopic survey

We investigate the prospects of extending observations of high redshift QSOs to z>8 by means of a very wide-area near-infrared slitless spectroscopic survey, e.g. the planned survey with the European Space Agency's Euclid telescope. For any QSOs at z>8.06 the strong Lyman-alpha line will enter the wavelength range of the Euclid near-infrared spectrometer and imaging photometer (NISP). We perform a detailed simulation of Euclid NISP slitless spectroscopy (with the parameters of the wide survey) in an artificial field containing QSO spectra at all redshifts up to z=12. The simulation spectra are analysed with an automated redshift finder, and a detection rate estimated as a function of H magnitude and redshift. Spectroscopic identification of QSOs would reach deeper limits for the redshift ranges where either H-alpha (0.67<z<2.05) or Lyman-alpha (z>8.06) is visible. Furthermore, if photometrically-selected z>8 spectra can be re-examined and re-fitted to minimize the effects of spectral contamination, the QSO detection rate in the Lyman-alpha window will be increased by an estimated 60% and will then be better here than at any other redshift, with an effective limit H=21.5. With an extrapolated rate of QSO evolution, we predict the Euclid wide (15000 sq. deg.) spectroscopic survey will identify 20-35 (19-33 with a small correction for lineless objects) very luminous QSOs at z>8.06.

FORMATION OF HIGH-REDSHIFT (z&gt;6) QUASARS DRIVEN BY NUCLEAR STARBURSTS

Based on the physical model of a supermassive black hole (SMBH) growth via gas accretion in a circumnuclear disk (CND) proposed by Kawakatu & Wada (2008), we describe the formation of high-$z$ ($z > 6$) quasars (QSOs) whose BH masses are M_{BH}> 10^{9} M_{\odot}. We derive the necessary conditions to form QSOs at z > 6 by only gas accretion: (i) A large mass supply with M_{sup} > 10^{10}M_{\odot} from host galaxies to CNDs, because the final BH mass is only 1-10% of the total supplied mass from QSO hosts. (ii) High star formation efficiency for a rapid BH growth. We also find that if the BH growth is limited by the Eddington accretion, the final BH mass is greatly suppressed. Thus, the super-Eddington growth is required for the QSO formation. The evolution of the QSO luminosity depends on the redshift z_{i} at which accretion onto a seed BH is initiated. In other words, the brighter QSOs at z >6 favor the late growth of SMBHs (i.e., z_{i}=10) rather than early growth (i.e., z_{i}=30). Moreover, we predict the observable properties and the evolution of QSOs at z >6. In a QSO phase, there should exist a stellar rich massive CND, whose gas mass is about 10% of the dynamical mass inside 0.1-1 kpc}. On the other hand, in a phase where the BH grows (i.e., a proto-QSO phase), the proto-QSO has a gas rich massive CNDs whose gas mass is comparable to the dynamical mass (abridged).

Toward Precise Constraints on the Growth of Massive Black Holes

Growth of massive black holes (MBHs) in galactic centers comes mainly from gas accretion during their QSO/AGN phases. In this paper we apply an extended Soltan argument, connecting the local MBH mass function with the time-integral of the QSO luminosity function, to the demography of MBHs and QSOs from recent optical and X-ray surveys, and obtain robust constraints on the luminosity evolution (or mass growth history) of individual QSOs (or MBHs). We find that the luminosity evolution probably involves two phases: an initial exponentially increasing phase set by the Eddington limit and a following phase in which the luminosity declines with time as a power law (with a slope of -1.2--1.3) set by a self-similar long-term evolution of disk accretion. Neither an evolution involving only the increasing phase with a single Eddington ratio nor an exponentially declining pattern in the second phase is likely. The period of a QSO radiating at a luminosity higher than 10% of its peak value is about (2-3)x10^8 yr, during which the MBH obtains ~80% of its mass. The mass-to-energy conversion efficiency is $0.16\pm0.04 ^{+0.05}_{-0}$, with the latter error accounting for the maximum uncertainty due to Compton-thick AGNs. The expected Eddington ratios in QSOs from the constrained luminosity evolution cluster around a single value close to 0.5-1 for high-luminosity QSOs and extend to a wide range of lower values for low-luminosity ones. The Eddington ratios for high luminosity QSOs appear to conflict with those estimated from observations (~0.25) by using some virial mass estimators for MBHs in QSOs unless the estimators systematically over-estimate MBH masses by a factor of 2-4. We also infer the fraction of optically obscured QSOs ~60-80%. Further applications of the luminosity evolution of individual QSOs are also discussed.

The luminosity function of high-redshift quasi-stellar objects. A combined analysis of GOODS and SDSS

Aims. In this work the luminosity function of QSOs is measured in the redshift range for the absolute magnitude interval . Determining the faint-end of the luminosity function at these redshifts provides important constraints on models of the joint evolution of galaxies and AGNs.Methods. We have defined suitable criteria to select faint QSOs in the GOODS fields, checking their effectiveness and completeness in detail. A spectroscopic follow-up of the resulting QSO candidates was carried out. The confirmed sample of faint QSOs is compared with a brighter one derived from the SDSS. We used a Monte-Carlo technique to estimate the properties of the luminosity function, checking various parameterizations for its shape and evolution.Results. Models based on pure density evolution show better agreement with observation than do models based on pure luminosity evolution. However, a different break magnitude with respect to is required at . Models with a steeper faint-end score a higher probability. We do not find any evidence for a bright-end flattening at redshift .Conclusions. The estimated space density evolution of QSOs indicates a suppression of the formation and/or feeding of supermassive black holes at these redshifts. The QSO contribution to the UV background is insufficient for ionizing the IGM at .

On the Formation and Evolution of QSOs

I had the privilege, many years ago, to be supervised by Alfonso Cavaliere in my Master thesis work. I remember the great patience and enthusiasm with which, in a warm summer day, he presented to me a score of exciting astrophysical problems. We finally determined to study the relationship of QSOs and BL Lacs—then considered rather exotic object—with normal galaxies. In the years I have continued on this line of research, reacting far too slowly to the wealth of new ideas that Alfonso has been continuously injecting in our conversations. As examples I will report two recent results on the chemical abundances of QSO host galaxies and on the space density of high-z QSOs, which are closely related to our shared interest on AGN.

Feii/MgiiEmission‐Line Ratios of QSOs. II.z&gt; 6 Objects

Near-infrared spectra of four QSOs located at z > 6 are obtained with the OH-airglow suppressor mounted on the Subaru telescope. The Fe II/Mg II emission-line ratios of these QSOs are examined by the same fitting algorithm as in our previous study of z < 5.3 QSOs. The fitting results show that two out of the four z > 6 QSOs have significant Fe II emission in their rest-UV spectra, while the other two have almost no Fe II features. We also applied our fitting algorithm to more than 10,000 SDSS QSOs and found two trends in the distribution of Fe II/Mg II against redshift: (1) the upper envelope of the Fe II/Mg II distribution at z > 3 shows a probable declination toward high redshift, and (2) the median distribution settles into lower ratios at z ~ 1.5 with small scatter compared to the other redshift. We discuss an Fe/Mg abundance evolution of QSOs with a substantial contribution from the diverse nature of the broad-line regions in high-redshift QSOs.

Constraints on QSO Models from a Relation between the QSO Luminosity Function and the Local Black Hole Mass Function

QSOs are believed to be powered by accretion onto massive black holes (BHs). In this paper, assuming that each central BH in nearby galaxies has experienced the QSO phase and ignoring BH mergers, we establish a relation between the QSO luminosity function (LF) and the local BH mass function (MF). The QSOLF is jointly controlled by the luminosity evolution of individual QSOs and the triggering history of the accretion onto seed BHs. By comparing the time integral of the QSOLF with that inferred from local BHs, we separate the effect of the luminosity evolution of individual QSOs from the effect of the triggering history. Assuming that the nuclear luminosity evolution includes two phases (first increasing at the Eddington luminosity with growth of BHs and then declining), we find that observations are generally consistent with the expected relation between the QSOLF and the local BHMF and obtain the following constraints on QSO models and BH growth: (i) The QSO mass-to-energy efficiency should be ≳0.1. (ii) The lifetime (defined directly through the luminosity evolution of individual QSOs here) should be ≳4 × 107 yr. The characteristic declining timescale in the second phase should be significantly shorter than the Salpeter timescale τSp, and BH growth should not be dominated by the second phase. (iii) The ratio of obscured QSOs/AGNs to optically bright QSOs should be not larger than 7 at MB ~ -23 and 3 at MB ~ -26 if = 0.31, and not larger than 1 at MB ~ -23 and negligible at MB ~ -26 if = 0.1. (iv) It is unlikely that most QSOs are accreting at super-Eddington luminosities. We point out that it is hard to accurately estimate the value of the QSO lifetime from the QSOLF and/or the local BHMF, if it is longer than a certain value (e.g., ~4τSp in this study). We discuss the importance of accurate measurements of the intrinsic scatter in the BH mass and velocity dispersion relation of local galaxies and the scatter in the bolometric correction of QSOs. We also discuss some possible applications of the work in this paper, such as to the study of the demography of QSOs and the demography of normal galaxies at intermediate redshift.

The environments of hyperluminous infrared galaxies at 0.44 &lt;z&lt; 1.55

We present deep wide-field Ks-band observations of six Hyperluminous Infrared Galaxies (HLIRGs) spanning a redshift range 0.44 = 190 +/- 45 Mpc1.77. The range in environments, and the mean clustering level, are both greater than those seen in local IR-luminous galaxies, from which we infer that the range of galaxy evolution processes driving IR-luminous galaxy evolution at z > 0.5 is greater than locally, and includes mergers between gas-rich spiral galaxies in the field, but also includes encounters in clusters and hierarchical build-up. The similarity in the range of environments and mean clustering amplitude between our sample and QSOs over a similar redshift range is consistent with the interpretation where evolutionary connections between IR-luminous galaxies and QSOs are stronger at z > 0.5 than locally, and that, at these redshifts, the processes that drive QSO evolution are similar to those that drive IR-luminous galaxy evolution. From comparison of the HLIRG and QSO host galaxies we further postulate that a larger fraction of IR-luminous galaxies pass through an optical QSO stage at z > 0.5 than locally.

Indicators of black-hole mass and Eddington accretion ratio from QSO X-ray and UV spectra

The evolution of luminous QSOs is linked to the evolution of massive galaxies. We know this because the relic black-holes found locally have masses dependent on the properties of the host galaxy’s bulge. An important way to explore this evolution would be to measure dependences of black-hole masses and Eddington accretion ratios over a range of redshifts, i.e., with cosmological age. For low redshift QSOs (and their lower luminosity Seyfert galaxy counterparts) it has been possible to infer black-hole masses from the luminosities and velocity dispersions of their host-galaxy bulges. These masses agree with those virial black-hole masses calculated from the Doppler widths of the broad Hβ emission lines. The latter method can then be extended to more distant and luminous QSOs, up to redshifts of 0.6 with ground-based optical observations. We discuss ways to extend these explorations to higher redshifts – up to ∼3 using the widths of QSOs’ broad UV emission lines, and in principle, and to redshifts near 4 from ground-based infrared observations of rest-frame Hβ at 2.5 μm. We discuss the possibility of investigating the accretion history of the higher redshift QSOs using measures of Eddington accretion ratio – the soft X-ray spectral index and the eigenvectors of Principal Components Analyses of QSOs’ UV emission-line spectra.

The Second Byurakan Survey - The Final Results. The Multiwavelength AGN Survey in the SBS Area

AbstractOn the basis of the Second Byurakan Survey (SBS) we have produced the largest and most homogeneous new complete samples of faint Markarian galaxies, Sy galaxies and bright QSOs. The General Catalogue of the SBS Survey, which is completed and prepared for publication, contains the data for more than 3600 objects, half of which are star-like objects while the other half are galaxies. Nearly 2500 slit spectra were obtained for about 2100 SBS objects. 561 new QSOs and AGNs in the magnitude range 15.5 &lt; B &lt; 19.5 with redshifts 0.0 &lt; z &lt;3.2 were spectroscopically confirmed. A sample of 17 BLL has been isolated as well.The volume for reliable investigation of faint Markarian UVX galaxies has been extended out to a distance of about ~ 500 Mpc, more than 50 times deeper than in the FBS. Faint Markarian UVX galaxies from the SBS survey comprise ~ 12% of field galaxies, slightly greater than in the First Markarian survey; ~ 10% of them (~ 120) turned out to be Sy galaxies.A complete sample of faint (B ≤ 17.0, z ≤ 0.1) Sy galaxies has been constructed. In the spatial volume with radius of about 500 Mpc, the relative number of AGNs is 1.2% of field galaxies. One of the most complete and representative samples of bright QSOs (~ 130) in the magnitude range 15.7 &lt; B ≤ 17.5 with redshifts 0.3 ≤ z ≤ 2.2 has been constructed as well.The objects in the combined complete sample of SBS Sy galaxies and QSOs might be roughly divided into two groups: classical Sy galaxies and QSOs in agreement with the previous classification scheme and nonclassical SyG and QSOs for which the existing classification scheme is not sufficient for their classification. The presence of narrow line QSOs (NLQSOs) or so-called QSO II type objects is established. There is a continuous transition of all properties between all types of Sy galaxies and QSOs, from Liners through Sy2, NLSyls, BLSyl to NLQSOs and BLQSOs.Preliminary results from the Multiwavelength AGN Survey (MWAGN) in X-ray, Radio and IR wavebands in the SBS area are presented. The MWAGN survey in the SBS area shows that the ROSAT or FIRST surveys by themselves cannot represent the whole AGN/QSO sample. The ROSAT Bright sources along with the FIRST sources comprise only 25% of the whole SBS QSO sample. The IRAS survey is effective for a redshift less than z &lt; 0.05. All classical Sy2s but only ~ 50% of classical Syls are IRAS sources. Luminous and Ultraluminous IRAS SBS AGNs comprise ~ 25% of the whole AGN sample. The greater part of SBS AGN/QSOs are neither ROSAT nor FIRST nor IRAS LIG or ULIG sources. They are optically emitting AGN/QSOs.The multiwavelength “complete” sample of bright QSOs in the SBS area allows us to conclude that the fast evolution of bright QSOs is more likely the result of a selection effect than the result of fast cosmological evolution. The LogN-B relation for these QSOs reduces to the value LogN − B = 0.67 ± 0.005.A direct empirical estimate of the effect of overlapping images is obtained from the MWAGN survey. The effect of overlap comprises ~ 5% for QSOs brighter than B ≤ 17.0 and ~ 10% for QSOs brighter than B ≤ 17.5.

Photometric Redshifts from Reconstructed Quasar Templates

From Sloan Digital Sky Survey (SDSS) commissioning photometric and spectroscopic data, we investigate the utility of photometric redshift techniques in the task of estimating QSO redshifts. We consider empirical methods (e.g., nearest neighbor searches and polynomial fitting), standard spectral template fitting, and hybrid approaches (i.e., training spectral templates from spectroscopic and photometric observations of QSOs). We find that in all cases, because of the presence of strong emission lines within the QSO spectra, the nearest neighbor and template-fitting methods are superior to the polynomial-fitting approach. Applying a novel reconstruction technique, we can, from the SDSS multicolor photometry, reconstruct a statistical representation of the underlying SEDs of the SDSS QSOs. Although the reconstructed templates are based on only broadband photometry, the common emission lines present within the QSO spectra can be recovered in the resulting spectral energy distributions. The technique should be useful in searching for spectral differences among QSOs at a given redshift, in searching for spectral evolution of QSOs, in comparing photometric redshifts for objects beyond the SDSS spectroscopic sample with those in the well-calibrated photometric redshifts for objects brighter than 20th magnitude, and in searching for systematic and time-variable effects in the SDSS broadband photometric and spectral photometric calibrations.

The 2dF QSO Redshift Survey -- II. Structure and evolution at high redshift

use a sample of 10 558 QSOs taken from the preliminary data release catalogue of the 2dF QSO Redshift Survey (2QZ). The two-point redshift-space correlation function of QSOs, jQðsÞ; is shown to follow a power law on scales s . 1–35 h Mpc: Fitting a power law of the form jQðsÞ 1⁄4 ðs/ s0Þ to the QSO clustering averaged over the redshift interval 0:3 , z # 2:9; we find s0 1⁄4 3:99 20:34 h Mpc and g 1⁄4 1:58 20:09 for an Einstein–de Sitter cosmology. The effect of a significant cosmological constant, l0, is to increase the separation of QSOs, so that with V0 1⁄4 0:3; l0 1⁄4 0:7 the power law extends to .60 h 21 Mpc and the best fit is s0 1⁄4 5:69 20:50 h Mpc and g 1⁄4 1:56 20:09: These values, measured at a mean redshift of z 1⁄4 1:49; are comparable to the clustering of local optically selected galaxies. We compare the clustering of 2QZ QSOs with generic cold dark matter (CDM) models with shape parameter Geff. Standard CDM with Geff 1⁄4 0:5 is ruled out in both Einstein–de Sitter and cosmological constant dominated cosmologies, where Geff . 0:2–0:4 and Geff . 0:1–0:2 respectively are the allowable ranges. We measure the evolution of QSO clustering as a function of redshift. For V0 1⁄4 1 and l0 1⁄4 0 there is no significant evolution in comoving coordinates over the redshift range of the 2QZ. QSOs thus have similar clustering properties to local galaxies at all redshifts that we sample. In the case of V0 1⁄4 0:3 and l0 1⁄4 0:7, QSO clustering shows a marginal increase at high redshift, s0 being a factor of ,1.4 higher at z . 2:4 than at z . 0:7. Although the clustering of QSOs is measured on large scales where linear theory should apply, the evolution of QSO clustering does not follow the linear theory predictions for growth via gravitational instability (rejected at the .99 per cent confidence level). A redshift-dependent bias is required to reconcile QSO clustering observations with theory. A simple biasing model, in which QSOs have cosmologically long lifetimes (or alternatively form in peaks above a constant threshold in the density field), is acceptable in an V0 1⁄4 1 cosmology, but is only marginally acceptable if V0 1⁄4 0:3 and l0 1⁄4 0:7. Biasing models in which QSOs are assumed to form over a range in redshift, based on the Press–Schechter formalism, are consistent with QSO clustering evolution for a minimum halo mass of ,10 and ,10 M( in an Einstein–de Sitter and cosmological constant dominated universe, respectively. However, until an accurate, physically motivated model of QSO formation and evolution is developed, we should be cautious in interpreting the fits to these biasing models.

The 2dF QSO Redshift Survey -- I. The optical luminosity function of quasi-stellar objects

We present a determination of the optical QSO luminosity function and its cosmological evolution with redshift for a sample of over 6000 QSOs identified primarily from the first observations of the 2dF QSO Redshift Survey (2QZ). For QSOs with -26 < M_B < -23 and 0.35 < z < 2.3, we find that pure luminosity evolution (PLE) models provide an acceptable fit to the observed redshift dependence of the luminosity function. The luminosity function is best fit by a two-power-law function of the form. Exponential luminosity evolution models, both as a function of look-back time, and as a general second-order polynomial with redshift, were found to provide acceptable fits to the dataset comprising the 2QZ and the Large Bright Quasar Survey. Exponential evolution with look-back time is prefered for q_0=0.05, while the polynomial evolution model is prefered for q_0=0.5. The shape and evolution of the LF at low redshifts (z<0.5) and/or high luminosities, not currently well sampled by the 2dF QSO survey, may show departures from pure luminosity evolution, but the results presented here show that over a significant range of redshift, PLE is a good description of QSO evolution.

Joint cosmological formation of QSOs and bulge-dominated galaxies

Older and more recent pieces of observational evidence suggest a strong connection between QSOs and galaxies; in particular, the recently discovered correlation between black hole and galactic bulge masses suggests that QSO activity is directly connected to the formation of galactic bulges. The cosmological problem of QSO formation is analysed in the framework of an analytical model for galaxy formation; for the first time a joint comparison with galaxy and QSO observables is performed. In this model it is assumed that the same physical variable that determines galaxy morphology is able to modulate the mass of the black hole responsible for QSO activity. Both halo spin and the occurrence of a major merger are considered as candidates for this role. The predictions of the model are compared with available data for the type-dependent galaxy mass functions, the star formation history of elliptical galaxies, the QSO luminosity function and its evolution (including the obscured objects contributing to the hard-X-ray background), the mass function of dormant black holes and the distribution of black hole-to-bulge mass ratios. A good agreement with observations is obtained if the halo spin modulates the efficiency of black hole formation, and if the galactic haloes at z = 0 have shone in an inverted order with respect to the hierarchical one (i.e., stars and black holes in bigger galactic haloes have formed before those in smaller ones). This inversion of hierarchical order for galaxy formation, which reconciles galaxy formation with QSO evolution, is consistent with many pieces of observational evidence.

University of British Columbia–NASA Multi‐Narrowband Survey. I. Description and Photometric Properties of the Survey

Observations, analysis techniques, and photometric properties of a multi-narrowband survey of a 20 deg2 area of sky at +33° declination are described. The survey is conducted with the 3 m liquid-mirror telescope of the NASA Orbital Debris Observatory using intermediate-bandwidth filters. These filters have central wavelengths ranging from 455 to 948 nm, at intervals of 0.01 in log λ, and give a spectral resolving power of Δλ/λ ~ 44. In two spring observing seasons, we have completed observations in 16 bands. Our preliminary object catalog contains over 105 detections to a typical 50% completeness limit of mAB ~ 20.4. The survey is expected to provide object classifications, spectral energy distributions, and multi-narrowband redshifts for ~104 galaxies and QSOs for use in studies of galaxy and QSO distributions, evolution, and large-scale structure. It will also provide photometry and spectral classifications for over 104 stars.