Low-redshift Quasars Research Articles

Simulations of thermally broadened H I Ly α absorption arising in the warm-hot intergalactic medium

Recent far-ultraviolet (FUV) absorption line measurements of low-redshift quasars have unveiled a population of intervening broad Hi Ly α absorbers (BLAs) with large Doppler parameters (b ≥ 40 km s -1 ). If the large width of these lines is dominated by thermal line broadening, the BLAs may trace highly-ionized gas in the warm-hot intergalactic medium (WHIM) in the temperature range T ≈ 10 5 -10 6 K, a gas phase that is expected to contain a large fraction of the baryons at low redshift. In this paper we use a hydrodynamical simulation to study frequency, distribution, physical conditions, and baryon content of the BLAs at z ≈ 0. From our simulated spectra we derive a number of BLAs per unit redshift of (dN/dz) BLA ≈ 38 for HI absorbers with log (N(cm -2 )/b(km s -1 )) > 10.7, b > 40 km s -1 , and total hydrogen column densities N(H II) < 10 20.5 cm -2 . The baryon content of these systems is Ω b (BLA) = 0.0121 h 65 -1 , which represents ∼25 percent of the total baryon budget in our simulation. Our results thus support the idea that BLAs represent a significant baryon reservoir at low redshift. BLAs predominantly trace shock-heated collisionally ionized WHIM gas at temperatures log T ≈ 4.4-6.2. About 27 percent of the BLAs in our simulation originate in the photoionized Ly a forest (log T < 4.3) and their large line widths are determined by non-thermal broadening effects such as unresolved velocity structure and macroscopic turbulence. Our simulation implies that for a large-enough sample of BLAs in FUV spectra it is possible to obtain a reasonable approximation of the baryon content of these systems solely from the measured H I column densities and b values.

AChandraSnapshot Survey of Representative High-Redshift Radio-Loud Quasars from the Parkes-MIT-NRAO Sample

We present the results of Chandra ACIS-S snapshot observations of six radio-loud quasars (RLQs) at z ≈ 3.5-4.7. These observations sample luminous RLQs with moderate to high radio loudness (R ≈ 200-9600) and aim to connect the X-ray properties of radio-quiet quasars (R 1000) at high redshift. This work extends a study by Bassett and coworkers that used similar methods to examine z > 4 RLQs with moderate radio loudness (R ≈ 40-400). All of our targets are clearly detected. A search for extended X-ray emission associated with kiloparsec-scale radio jets revealed only limited evidence for X-ray extension in our sample: three sources showed no evidence of X-ray extension, and the other three had 3%-30% of their total X-ray fluxes extended >1'' away from their X-ray cores. In addition, we do not observe any systematic flattening of the optical-to-X-ray spectral index (αox) compared to low-redshift quasars. These results suggest that kiloparsec-scale X-ray jet emission is not dominated by inverse Compton scattering of cosmic microwave background seed photons off jet electrons. We measured X-ray continuum shapes and performed individual and joint spectral fits of our data combined with eight archival RLQs. A single power-law model acceptably fitted the data, with best-fit photon indices of 1.72 for moderate-R sources and 1.47 for high-R sources. We added an intrinsic absorption component to our model, and neither the moderate-R nor the high-R fits set a lower bound on NH. The upper limits were NH < 3.0 × 1022 cm-2 and NH < 2.8 × 1022 cm-2, respectively. Our spectral results suggest that intrinsic absorption does not strongly depend on radio loudness, and high-R sources have flatter power laws than moderate-R sources. Overall, our high-redshift RLQs have basic X-ray properties consistent with similar RLQs in the local universe.

The Ultraviolet, Optical, and Infrared Properties of Sloan Digital Sky Survey Sources Detected byGALEX

We discuss the UV, optical, and IR properties of the SDSS sources detected by GALEX as part of its All-sky Imaging Survey Early Release Observations. Virtually all of the GALEX sources in the overlap region are detected by SDSS. GALEX sources represent ~2.5% of all SDSS sources within these fields and about half are optically unresolved. Most unresolved GALEX/SDSS sources are bright blue turn-off thick disk stars and are typically detected only in the GALEX near-UV band. The remaining unresolved sources include low-redshift quasars, white dwarfs, and white dwarf/M dwarf pairs, and these dominate the optically unresolved sources detected in both GALEX bands. Almost all the resolved SDSS sources detected by GALEX are fainter than the SDSS 'main' spectroscopic limit. These sources have colors consistent with those of blue (spiral) galaxies (u-r<2.2), and most are detected in both GALEX bands. Measurements of their UV colors allow much more accurate and robust estimates of star-formation history than are possible using only SDSS data. Indeed, galaxies with the most recent (<20 Myr) star formation can be robustly selected from the GALEX data by requiring that they be brighter in the far-UV than in the near-UV band. However, older starburst galaxies have UV colors similar to AGN, and thus cannot be selected unambiguously on the basis of GALEX fluxes alone. With the aid of 2MASS data, we construct and discuss median 10 band UV-optical-IR spectral energy distributions for turn-off stars, hot white dwarfs, low-redshift quasars, and spiral and elliptical galaxies. We point out the high degree of correlation between the UV color and the contribution of the UV flux to the UV-optical-IR flux of galaxies detected by GALEX.

Oii] Emission in Quasar Host Galaxies: Evidence for a Suppressed Star Formation Efficiency

The [O II] 3727 line, a commonly used estimator of star formation rate in extragalactic surveys, should be an equally effective tracer of star formation in the host galaxies of quasars, whose narrow-line regions are expected to produce weak low-ionization emission. Quasar spectra generally show little or no [O II] emission beyond that expected from the active nucleus itself. The inferred star formation rates in optically selected quasars are typically below a few solar masses per yr, and some significantly less. Quasars do not appear to occur coevally with starbursts. Recent observations, on the other hand, reveal abundant molecular gas in low-redshift quasars. These two results suggest that the star formation efficiency in quasar host galaxies is somehow suppressed during the active phase of the nucleus. The low star formation rates also imply that the nonstellar nucleus powers the bulk of the thermal infrared emission in radio-quiet quasars.

Active Galactic Nuclei in the Sloan Digital Sky Survey. II. Emission-Line Luminosity Function

The emission line luminosity function of active galactic nuclei (AGN) is measured from about 3000 AGN included in the main galaxy sample of the Sloan Digital Sky Survey within a redshift range of $0<z<0.15$. The $\Ha$ and [OIII]$\lambda 5007$ luminosity functions for Seyferts cover luminosity range of $10^{5-9}$$L_\odot$ in H$\alpha$ and the shapes are well fit by broken power laws, without a turnover at fainter nuclear luminosities. Assuming a universal conversion from emission line strength to continuum luminosity, the inferred B band magnitude luminosity function is comparable both to the AGN luminosity function of previous studies and to the low redshift quasar luminosity function derived from the 2dF redshift survey. The inferred AGN number density is approximately 1/5 of all galaxies and about $6\times 10^{-3}$ of the total light of galaxies in the $r$-band comes from the nuclear activity. The numbers of Seyfert 1s and Seyfert 2s are comparable at low luminosity, while at high luminosity, Seyfert 1s outnumber Seyfert 2s by a factor of 2-4. In making the luminosity function measurements, we assumed that the nuclear luminosity is independent of the host galaxy luminosity, an assumption we test {\it a posteriori}, and show to be consistent with the data. Given the relationship between black hole mass and host galaxy bulge luminosity, the lack of correlation between nuclear and host luminosity suggests that the main variable that determines the AGN luminosity is the Eddington ratio, not the black hole mass. This appears to be different from luminous quasars, which are most likely to be shining near the Eddington limit.

BAL QSOs in the eigenvector 1 context: toward a self-consistent model of the line absorbing/emitting regions

We attempt to define the structural properties of Broad Absorption Line (BAL) QSOs and their relationship with the general quasar population using the Eigenvector 1 correlations. We identify 8 low-redshift quasars (z 1549 emission motivates us to model the BAL systems with an additional component that may share the BLR outflow and may be co-axial with the accretion disk, perhaps associated to a significant black hole spin.

XMM-Newton EPIC observations of 21 low-redshift PG quasars

We present an X-ray spectral analysis of 21 low redshift quasars observed with XMM-Newton EPIC. All the sources are Palomar Green quasars with redshifts between 0.05 and 0.4 and have low Galactic absorption along the line-of-sight. A large majority of quasars in the sample (19/21) exhibit a significant soft excess below ~1–1.5 keV, whilst two objects (PG 1114+445 and I Zw1) show a deficit of soft X-ray flux due to the presence of a strong warm absorber. Indeed, contrary to previous studies with ASCA and ROSAT, we find that the presence of absorption features near 0.6–1.0 keV is common in our sample. At least half of the objects appear to harbor a warm absorber, as found previously in Seyfert 1 galaxies. We find significant detections of Fe Kα emission lines in at least twelve objects, whilst there is evidence for some broadening of the line profile, compared to the EPIC-pn resolution, in five of these quasars. The determination of the nature of this broadening (e.g., Keplerian motion, a blend of lines, relativistic effects) is not possible with the present data and requires either higher S/N or higher resolution spectra. In seven objects the line is located between 6.7–7 keV, corresponding to highly ionized iron, whereas in the other five objects the line energy is consistent with 6.4 keV, i.e. corresponding to near neutral iron. The ionized lines tend to be found in the quasars with the steepest X-ray spectra. We also find a correlation between the continuum power law index Γ and the optical Hβ width, in both the soft and hard X-ray bands, whereby the steepest X-ray spectra are found in objects with narrow Hβ widths, which confirms previous ROSAT and ASCA results. The soft and hard band X-ray photon indices are also strongly correlated, i.e. the steepest soft X-ray spectra correspond the steepest hard X-ray spectra. We propose that a high accretion rate and a smaller black hole mass is likely to be the physical driver responsible for these trends, with the steep spectrum objects likely to have smaller black hole masses accreting near the Eddington rate.

Extreme gas properties in the most distant quasars

We present near-IR, low resolution spectra of eight of the most distant quasars known, with redshifts in the range 4.9<z<6.4. Half of these quasars are characterized by deep, broad and blueshifted absorption features associated with both high and low ionization species (CIV, SiIV, AlIII, MgII), i.e. they belong to the class of Broad Absorption Line (BAL) quasars, which are associated with powerful outflows of dense gas. Although the sample is small, the large fraction of BAL quasars, the depth and ionization state of the absorption features suggest that these most distant quasars are surrounded by a much larger amount of dense gas than lower redshift (z<4) quasars. The possible interpretation in terms of extremely high accretion rates and the association with the early formation of quasars and of their host galaxies is discussed. The absorption properties of the dust, associated with the gas along the line of sight, appear different with respect to lower redshift quasars, possibly indicating different dust physics at these highest redshifts.

Relation of radio-quiet quasars to galaxy clusters at z &lt; 0.3

We investigate whether radio-quiet quasars (RQQs) with z < 0.3 (and predominantly of low luminosity) are located preferentially in specific regions with respect to the centres and boundaries of neighbouring galaxy clusters. This way of characterizing the environment of RQQs differs from previous studies, which relied on the galaxy excess statistics within small radii around the quasars. For the detection of galaxy clusters we use a robust, semiparametric method based on a maximum likelihood estimate applied to Voronoi tessellation and enhanced by a colour-cut approach, allowing boundary determination and redshift estimates. We find that most of the RQQs reside within 3 h−1 Mpc of the centre of a galaxy cluster with comparable redshift and that none of them lies in the core itself. About 20 per cent of the investigated quasars reside between two galaxy clusters, which are possibly at an early stage of merger. Consequently, we suggest that quasars found in rich environments are associated with cluster mergers whereas those found in poorer environments are associated with infall towards a cluster. The information on larger scales provided by our analysis thus allows a clearer interpretation of the diverse environments that have for many years been reported in the literature for smaller scales. We discuss our findings in the context of existing quasar formation models and suggest that at least two formation mechanisms coexist. Additionally, we confirm, using multiple data sets, that low-redshift quasars follow a narrow channel of width ∼10 h−1 Mpc around the large-scale structure (LSS) traced by galaxy clusters, in agreement with the first report of this effect by Söchting, Clowes & Campusano. Such a result, if it applies to quasars at higher redshifts, has the potential to explain the clustering of quasars on scales <10 h−1 Mpc found initially by Shanks et al. The association of the LSS in clusters with the spatial distribution of quasars is not reproduced by samples of narrow emission-line galaxies (NELGs), indicating that the occurrence of NELGs does not require the same environmental conditions as that of quasars.

Host Galaxies of Low‐zRadio‐loud Quasars: A Search ofHubble Space TelescopeArchives

We searched the Hubble Space Telescope (HST) archives for unpublished Wide Field Planetary Camera 2 images of low-redshift (z < 0.5) radio-loud quasars (RLQs). This led to the identification of 11 objects. Here we present the results of the analysis of these images from which we derive the properties of their host galaxies. All objects are clearly resolved, and their surrounding nebulosity is consistent with an elliptical galaxy model. These new data, together with previous published HST observations, form a sample of 34 sources that significantly expand all previous studies of low-redshift RLQs based on HST data. For this full sample we derive the average absolute magnitude of the host galaxies = -24.01 ± 0.48 and the effective radius = 10.5 ± 3.7 kpc. No significant correlation is found between the nucleus and the host galaxy luminosity. Using the relationship between black hole mass (BH) and bulge luminosity we investigate the relation between BH and total radio power for RLQs and compare it with other classes of radio sources. The overall distribution of active galactic nuclei in the BH-Pradio plane exhibits a trend for increasing BH with increasing Pradio but with a substantial spread. RLQs occupy the region of the most powerful sources and the most massive black hole. The quasars appear to emit over a wide range of power with respect to their Eddington luminosity, as deduced by the estimated BH.

Feii/MgiiEmission‐Line Ratio in High‐Redshift Quasars

We present results of the analysis of near-infrared spectroscopic observations of six high-redshift quasars (z 4), emphasizing the measurement of the ultraviolet Fe II/Mg II emission-line strength to estimate the beginning of intense star formation in the early universe. To investigate the evolution of the Fe II/Mg II ratio over a wider range in cosmic time, we measured this ratio for composite quasar spectra that cover a redshift range 0 z 5 with nearly constant luminosity, as well as for those that span ~6 orders of magnitude in luminosity. A detailed comparison of the high-redshift quasar spectra with those of low-redshift quasars with comparable luminosity shows essentially the same Fe II/Mg II emission ratios and very similar continuum and line spectral properties, i.e., a lack of evolution of the relative iron-to-magnesium abundance of the gas in bright quasars since z 5. Current nucleosynthesis and stellar evolution models predict that α-elements such as magnesium are produced in massive stars ending in Type II supernovae, while iron is formed predominantly in Type Ia supernovae with intermediate-mass progenitors. This results in an iron enrichment delay of ~0.2-0.6 Gyr. We conclude that intense star formation activity in the host galaxies of z 4 quasars must have started already at an epoch corresponding to zf 6-9, when the age of the universe was ~0.5 Gyr (H0 = 72 km s-1 Mpc-1, ΩM = 0.3, ΩΛ = 0.7). This epoch corresponds well to the reionization era of the universe.

The near-IR properties and continuum shapes of high redshift quasars from the Sloan Digital Sky Survey

We present J-H-K' photometry for a sample of 45 high redshift quasars found by the Sloan Digital Sky Survey. The sample was originally selected on the basis of optical colors and spans a redshift range from 3.6 to 5.03. Our photometry reflects the rest-frame SED longward of Ly alpha for all redshifts. The results show that the near-IR colors of high redshift quasars are quite uniform. We have modelled the continuum shape of the quasars (from just beyond Ly alpha to ~4000 A) with a power law of the form f_nu \propto nu^alpha, and find <alpha > =-0.57 with a scatter of 0.33. This value is similar to what is found for lower redshift quasars over the same restframe wavelength range, and we conclude that there is hardly any evolution in the continuum properties of optically selected quasars up to redshift 5. The spectral indices found by combining near-IR with optical photometry are in general consistent but slightly flatter than what is found for the same quasars using the optical spectra and photometry alone, showing that the continuum region used to determine the spectral indices can somewhat influence the results.

Iron Emission in the z = 6.4 Quasar SDSS J114816.64+525150.3

We present near-infrared J- and K-band spectra of the z = 6.4 quasar SDSS J114816.64+525150.3 obtained with the NIRSPEC spectrograph at the Keck II telescope, covering the rest-frame spectral regions surrounding the C IV λ1549 and Mg II λ2800 emission lines. The iron emission blend at rest wavelength 2900-3000 A is clearly detected, and its strength appears nearly indistinguishable from that of typical quasars at lower redshifts. The Fe II/Mg II ratio is also similar to values found for lower redshift quasars, demonstrating that there is no strong evolution in Fe/α broad-line emission ratios even out to z = 6.4. In the context of current models for iron enrichment from Type Ia supernovae (SNe Ia), this implies that the SN Ia progenitor stars formed at z 10. We apply the scaling relations of Vestergaard and of McLure & Jarvis to estimate the black hole mass from the widths of the C IV and Mg II emission lines and the ultraviolet continuum luminosity. The derived mass is in the range (2-6) × 109 M☉, with an additional uncertainty of a factor of 3 due to the intrinsic scatter in the scaling relations. This result is in agreement with the previous mass estimate of 3 × 109 M☉ by Willott, McLure, & Jarvis and supports their conclusion that the quasar is radiating close to its Eddington luminosity.

ChandraandXMM-NewtonObservations of the First Quasars: X-Rays from the Age of Cosmic Enlightenment

We report on Chandra and XMM-Newton observations of a sample of 13 quasars at z ? 4.7?5.4 mostly taken from the Sloan Digital Sky Survey (SDSS). The present sample complements previous X-ray studies of z ? 4 quasars, in which the majority of the objects are optically more luminous and at lower redshifts. All but two of our quasars have been detected in the X-ray band, thus doubling the number of z ? 4.8 X-ray?detected quasars. The two nondetections are likely to be due to a short exposure time (SDSSp J033829.31+002156.3) and to the presence of intrinsic absorption (SDSSp J173744.87+582829.5). We confirm and extend to the highest redshifts the presence of a correlation between AB1450(1+z) magnitude and soft X-ray flux for z ? 4 quasars and the presence of a steeper optical?to?X-ray spectral energy distribution (parameterized by ?ox) for high-luminosity, high-redshift quasars than for lower luminosity, lower redshift quasars. The second effect is likely due to the known anticorrelation between ?ox and rest-frame 2500 ? luminosity, whose significance is confirmed via partial correlation analysis. The joint ?2.5?36 keV rest-frame spectrum of the z > 4.8 SDSS quasars observed thus far by Chandra is well parameterized by a power law with photon index ? = 1.84; this photon index is consistent with those of z ? 0?3 quasars and that obtained from joint spectral fitting of z ? 4.1?4.5 optically luminous Palomar Digital Sky Survey quasars. No evidence for widespread intrinsic X-ray absorption has been found (NH 4.0 ? 1022 cm-2 on average at 90% confidence). We also obtained Hobby-Eberly Telescope (HET) photometric observations for eight of our target quasars. None of these shows significant (greater than 30%) optical variability over the time interval of a few years (in the observed frame) between the SDSS and HET observations.

ChandraSurvey of Radio‐quiet, High‐Redshift Quasars

We observed 17 optically-selected, radio-quiet high-redshift quasars with the Chandra Observatory ACIS, and detected 16 of them. The quasars have redshift between 3.70 and 6.28 and include the highest redshift quasars known. When compared to low-redshift quasars observed with ROSAT, these high redshift quasars are significantly more X-ray quiet. We also find that the X-ray spectral index of the high redshift objects is flatter than the average at lower redshift. These trends confirm the predictions of models where the accretion flow is described by a cold, optically-thick accretion disk surrounded by a hot, optically thin corona, provided the viscosity parameter alpha >= 0.02. The high redshift quasars have supermassive black holes with masses ~10^{10} M_{sun}, and are accreting material at ~0.1 the Eddington limit. We detect 10 X-ray photons from the z=6.28 quasar SDS 1030+0524, which may have a Gunn-Peterson trough and be near the redshift of reionization of the intergalactic medium. The X-ray data place an upper limit on the optical depth of the intergalactic medium tau(IGM) 20.

A Survey of [CLC][ITAL]z[/ITAL][/CLC] ] 5.7 Quasars in the Sloan Digital Sky Survey. II. Discovery of Three Additional Quasars at [CLC][ITAL]z[/ITAL][/CLC] ] 6

We present the discovery of three new quasars at z > 6 in ∼ 1300 deg2 of Sloan Digital Sky Survey imaging data, J114816.64+525150.3 (z = 6.43), J104845.05+463718.3 (z = 6.23), and J163033.90+401209.6 (z = 6.05). The first two objects have weak Lyα emission lines; their redshifts are determined from the positions of the Lyman break. They are only accurate to ∼0.05 and could be affected by the presence of broad absorption line systems. The last object has a Lyα strength more typical of lower redshift quasars. Based on a sample of six quasars at z > 5.7 that cover 2870 deg2 presented in this paper and in Paper I, we estimate the comoving density of luminous quasars at z ∼ 6 and M1450 < -26.8 to be (8 ± 3) × 10-10 Mpc-3 (for H0 = 50 km s-1 Mpc-1, Ω = 1). Hubble Space Telescope imaging of two z > 5.7 quasars and high-resolution, ground-based images (seeing ∼04) of three additional z > 5.7 quasars show that none of them is gravitationally lensed. The luminosity distribution of the high-redshift quasar sample suggests the bright-end slope of the quasar luminosity function at z ∼ 6 is shallower than Ψ ∝ L-3.5 (2 σ), consistent with the absence of strongly lensed objects.

The CYDER survey: first results

AbstractWe present the Calán‐Yale Deep Extragalactic Research (CYDER) Survey. The broad goals of the survey are the study of stellar populations, the star formation history of the universe and the formation and evolution of galaxies. The fields studied include Chandra deep pointings in order to characterize the X‐ray faint populations. Here we present the results on the first fields studied. We find that the redshift distribution is consistent with that found in the Chandra Deep Field North. The distribution of hardness ratios is, however, softer in our sample. We find a high redshift quasar, CXOCY J125304.0‐090737 at z = 4.179, which suggests that the abundance of low luminosity high redshift quasars may be larger than what would be expected from reasonable extrapolations from the quasar optical luminosity function.

On-axis spatially resolved spectroscopy of low redshift quasar host galaxies: HE 1503+0228, at $z=0.135$

We present the first result of a comprehensive spectroscopic study of quasar host galaxies. On-axis, spatially resolved spectra of low redshift quasars have been obtained with FORS1, mounted on the 8.2m ESO Very Large Telescope, Antu. The spectra are spatially deconvolved using a spectroscopic version of the ``MCS deconvolution algorithm''. The algorithm decomposes two dimensional spectra into the individual spectra of the central point-like nucleus and of its host galaxy. Applied to HE1503+0228, at z=0.135 (M_B=-23.0), it provides us with the spectrum of the host galaxy between 3600A, and 8500A, (rest-frame), at a mean resolving power of 700. The data allow us to measure several of the important Lick indices. The stellar populations and gas ionization state of the host galaxy of HE1503+0228, are very similar to the ones measured for normal non-AGN galaxies. Dynamical information is also available for the gas and stellar components of the galaxy. Using deconvolution and a deprojection algorithm, velocity curves are derived for emission lines, from the center up to 4arcsec, away from the nucleus of the galaxy. Fitting a simple three-components mass model (point mass, spherical halo of dark matter, disk) to the position-velocity diagram, we infer a mass of M(r<1kpc) = (2.0 +- 0.3) 10^{10} solar mass within the central kiloparsec of the galaxy, and a mass integrated over 10 kpc of M(r<10kpc) = (1.9 +- 0.3) 10^{11} solar mass, with an additional 10% error due to the uncertainty on the inclination of the galaxy. This, in combination with the analysis of the stellar populations indicates that the host galaxy of HE1503+0228, is a normal spiral galaxy.

Determining Central Black Hole Masses in Distant Active Galaxies

An empirical relationship, of particular interest for studies of high-redshift active galactic nuclei (AGNs) and quasars, between the masses of their central black holes and rest-frame ultraviolet (UV) parameters measured in single-epoch AGN spectra is presented. This relationship is calibrated to recently measured reverberation masses of low-redshift AGNs and quasars. An empirical relationship between single-epoch rest-frame optical spectrophotometric measurements and the central masses is also presented. The UV relationship allows reasonable estimates of the central masses to be made for high-redshift AGNs and quasars for which these masses cannot be directly or easily measured by the techniques applicable to the lower luminosity, nearby AGNs. The central mass obtained by this method can be estimated to within a factor of ~3 for most objects. This is reasonable given the intrinsic uncertainty of a factor of less than 2 in the primary methods used to measure the central masses of nearby inactive and active galaxies, namely, resolved gas and stellar kinematics in the underlying host galaxy and reverberation-mapping techniques. The UV relationship holds good potential for being a powerful tool for studying black hole demographics at high redshift as well as statistically studying the fundamental properties of AGNs. The broad-line region size-luminosity relationship is key to the calibrations presented here. The fact that its intrinsic scatter is also the main source of uncertainty in the calibrations stresses the need for better observational constraints to be placed on this relationship. The empirically calibrated relationships presented here will be applied to quasar samples in forthcoming work.

Searching for the Physical Drivers of Eigenvector 1: From Quasars to Nanoquasars

We point out an analogy between two accreting white dwarfs (CH Cyg and MWC 560) with jets and powerful quasars. In spite of the enormous difference in the mass of the central object (a factor ~107), the emission lines are strikingly similar to those of I Zw 1 (the prototype "narrow-line Seyfert 1" nucleus whose spectrum is widely used as an Fe II template for almost all quasars). The spectral similarities give us the unique possibility to consider the optical Eigenvector 1 diagram using objects less massive by a factor of millions. Our results reinforce the interpretation of the "Eigenvector 1 correlations" found for low-redshift quasars as driven mainly by the source luminosity-to-central compact object mass ratio. The accreting white dwarfs CH Cyg and MWC 560, their jets and emission lines, may well represent the low-energy, nonrelativistic end of the accretion phenomena, which encompass the most powerful quasars and microquasars. The remarkable similarities suggest that they may be legitimately considered "nanoquasars."