Quasar BR Research Articles

Probing the He ii re-Ionization ERa via Absorbing C iv Historical Yield (HIERACHY) I: A strong outflow from a z ∼ 4.7 quasar

ABSTRACT Outflows from supermassive black holes (SMBHs) play an important role in the co-evolution of themselves, their host galaxies, and the larger scale environments. Such outflows are often characterized by emission and absorption lines in various bands and in a wide velocity range blueshifted from the systematic redshift of the host quasar. In this paper, we report a strong broad line region (BLR) outflow from the z ≈ 4.7 quasar BR 1202-0725 based on the high-resolution optical spectrum taken with the Magellan Inamori Kyocera Echelle (MIKE) spectrograph installed on the 6.5 m Magellan/Clay telescope, obtained from the ‘Probing the He ii re-Ionization ERa via Absorbing C iv Historical Yield’ (HIERACHY) project. This rest-frame ultraviolet (UV) spectrum is characterized by a few significantly blueshifted broad emission lines from high ions; the most significant one is the C iv line at a velocity of $\sim -6500$ km s−1 relative to the H α emission line, which is among the highest velocity BLR outflows in observed quasars at z > 4. The measured properties of UV emission lines from different ions, except for O i and Ly α, also follow a clear trend that higher ions tend to be broader and outflow at higher average velocities. There are multiple C iv and Si iv absorbing components identified on the blue wings of the corresponding emission lines, which may be produced by either the outflow or the intervening absorbers.

Subaru Deep Spectroscopy of a Star-forming Companion Galaxy of BR 1202-0725 atz = 4.7

We present deep spatially resolved optical spectroscopy of the northwest companion galaxy of the quasar BR 1202-0725 at z = 4.7. Its rest-frame UV spectrum shows star-forming activity in the nuclear region. The Lyα emission profile is symmetric with wavelength, while its line width is unusually wide (FWHM ≃ 1100 km s-1) for such a high-z star-forming galaxy. The spectrum taken along the Lyα nebula elongation, which is almost along the minor axis of the companion host galaxy, reveals that off-nuclear Lyα nebulae have either flat-topped or multipeaked profiles along the extension. All these properties can be understood in terms of superwind activity in the companion galaxy. We also find a diffuse continuum component around the companion, which shows a morphology similar to that of Lyα nebula, and is most likely due to scattering of the quasar light at a dusty halo around the companion. We argue that the superwind could expel dusty material out to the halo region, making a dusty halo for scattering.

XMM-NewtonObservations of Two High-Redshift Quasars: RX J1028-0844 and BR 0351-1034

We report the results of XMM-Newton observations of two high-redshift quasars, one radio-loud, RX J1028.6-0844 (z = 4.276) and one radio-quiet, BR 0351-1034 (z = 4.351). We find that the evidence for strong excess absorption toward RX J1028-0844 is marginal at best, contrary to previous claims. The superior sensitivity and broader, softer energy range of XMM-Newton (0.2–10 keV) allows better determination of spectral parameters than much deeper ASCA observations (0.8–7 keV). Our XMM-Newton observations call into question several other ASCA results of strong absorption toward high-redshift radio-loud quasars. RX J1028.6-0844 occupies the same parameter space in broadband spectral properties as the low-redshift BL Lac objects, showing no obvious evolution with redshift. The radio-quiet quasar BR 0351-1024 became fainter between ROSAT and XMM observations by a factor of at least 5, but with the present data we cannot determine whether there is an associated spectral change. These observations do not support previous claims of weaker X-ray emission from high-redshift, radio-quiet quasars. The soft X-ray spectral slope required to reconstruct the ROSAT PSPC hardness ratio of BR 0351-1034 is about αX = 3.5, the steepest X-ray slope ever observed in a high-redshift quasar and similar to that of low-redshift narrow-line Seyfert 1 galaxies.

A new measurement of zinc metallicity in a DLA at z∼3.35

We present chemical abundance measurements in the z abs=3.35045 Damped Lyman- α (DLA) system observed in the UVES spectrum of the BAL quasar BR 1117-1329. We measure a neutral hydrogen column density N(HI)=6.9±1.7×10 20 atoms cm −2 and derive mean abundances relative to solar: [Si/H]=−1.26±0.13, [Fe/H]=−1.51±0.13, [Ni/H]=−1.57±0.13, [Cr/H]=−1.36±0.13, [Zn/H]=−1.18±0.13, [Al/H]>−1.25, [O/H]>−1.25 and [N/H]<−2.24. This is the third measurement of Zn, an element mildly depleted onto dust grain, at z abs>3. The iron to zinc and chromium to zinc ratios, [Fe/Zn]=−0.33±0.05 and [Cr/Zn]=−0.18±0.05 demonstrate that the absorber has a low dust content. The nitrogen ratio [N/Si]<−0.98 suggests that the ‘secondary’ N production process is taking place in this DLA. Finally, this absorber does not seem to present a convincing α-enhancement as shown by the α over Fe-peak element ratios: [Si/Fe]=0.25±0.06, [Si/Cr]=0.10±0.06 and [Si/Zn]=−0.08±0.06.

First Investigation of the Clustering Environment of Damped Lyα Absorbers atz ≃ 4

We report the first observations of the clustering environment of damped Lyman α absorption systems at z 4. Color selection and photometric redshifts were used to select 44 candidate Lyman-break galaxies brighter than IAB = 25.5 from deep BRI images of the 35 arcmin2 field containing the quasar BR 0951-04. Multislit spectroscopy of 35 candidate galaxies was performed and eight of these candidates have been confirmed as z > 3.5 Lyman-break galaxies. With only BRI photometry, the photometric redshifts are quite accurate for the spectroscopically confirmed galaxies but have a high rate of misclassification due to color degeneracies between Lyman-break galaxies and low-redshift ellipticals. Both of the z > 3.5 galaxies found within 15'' of the quasar line-of-sight appear to be causing absorption systems in the quasar spectrum. We use a battery of statistical tests to look for clustering in the redshift histogram of the z > 3.5 galaxies but do not find measurable clustering of these Lyman-break galaxies with the damped Lyα absorbers. With a larger sample of galaxies, our method should determine the cross-correlation between these objects, which probes the bias and hence the mass of the damped Lyα absorbers.

ISOobservations of the dusty quasar BR 1202−0725

We present mid- and far-infrared photometry of the high-redshift (z = 4.69) dusty quasar BR 1202−0725. The quasar was detected in the near-infrared, at a flux level (0.7 ± 0.2 mJy) consistent with an average radio-quiet quasar at its redshift. Only upper limits for the emission were obtained in the far-infrared. These upper limits, when combined with data from ground-based telescopes, are the first direct evidence for a turnover in the far-infrared emission, and hence confirm that a blackbody dominates the spectral energy distribution at far-infrared wavelengths. This blackbody is most probably cool dust, constrained to have a temperature below 80 K, for a β of 1.5.

Photometric Redshifts and Selection of High-Redshift Galaxies in the NTT and Hubble Deep Fields

We present and compare in this paper new photometric redshift catalogs of the galaxies in three public fields: the NTT Deep Field, the HDF-N, and the HDF-S. In the case of the NTT Deep Field, we present here a new photometric catalog, obtained by combining the existing BVrI and JKs with new deep U observations acquired with NTT-SUSI2, and which includes also the contiguous field centered on the zem = 4.7 quasar BR 1202-07. Photometric redshifts have been obtained for the whole sample (NTTDF + HDF-N + HDF-S), by adopting a χ2 minimization technique on a spectral library drawn from the Bruzual and Charlot synthesis models, with the addition of dust and intergalactic absorption. The accuracy, determined from 125 galaxies with known spectroscopic redshifts, is σz ~ 0.08 (0.3) in the redshift intervals z = 0–1.5 (1.5–3.5). The global redshift distribution of I-selected galaxies shows a distinct peak at intermediate redshifts, z 0.6 at IAB ≤ 26 and z 0.8 at IAB ≤ 27.5 followed by a tail extending to z 6. Systematic differences exist among the fields, most notably the HDF-S which contains a much smaller number of galaxies at z 0.9 and at z ≥ 4.5 than the HDF-N. We also present for the first time the redshift distribution of the total IR-selected sample to faint limits (Ks ≤ 21 and J ≤ 22). It is found that the number density of galaxies at 1.25 5 candidates in the HDF filter set and that the four brightest candidates at z > 5 in the HDF-S are indeed most likely M stars.

OII] λ 3727 Emission from the Companion to the Quasar BR 1202–0725 at z = 4.7

Results of a narrow-band imaging for the redshifted [OII] λ3727 emission around a quasar at z = 4.7 obtained with the Subaru telescope and CISCO (a Cassegrain near infrared camera) are presented. A significant emission line is detected in the narrow-band H2 [v = 1–0 S(1)] filter at a location ∼ 2″.4 northwest from the quasar, where the presence of a companion has been reported in Lyman α emission and the rest-frame UV continuum. We identify this line as [OII] λ 3727 emission and confirm that the source really is a companion at z = 4.7. The [OII] λ3727 flux from the companion is estimated to be 2.5 × 10−17 erg s−1 cm−2. If the companion is a star-forming object, the inferred star-formation rate is as high as 45–230 M⊙ yr−1, even without assuming an extinction correction. This value is higher than those derived from the Lyman α emission or from the UV continuum. Thus, provided that the difference is caused by dust extinction, the extinction-corrected star-formation rate is calculated to be 45 to 2300 M⊙ yr−1, depending on the assumed extinction curves.

The Photometric Redshift Distribution and Evolutionary Properties of Galaxies up to [CLC][ITAL]z[/ITAL][/CLC] ∼ 4.5 in the Field of the Quasar BR 1202−0725

?????We present a deep BVrIK multicolor catalog of galaxies in the field of the high-redshift (z = 4.7) quasar BR 1202-0725. Reliable colors have been measured for galaxies selected down to R = 25. Taking advantage of the wide spectral coverage of the galaxies in the field, we compare the observed colors with those predicted by spectral synthesis models including UV absorption by the intergalactic medium and dust reddening. The choice of the optical filters has been optimized to define a robust multicolor selection of galaxies at 3.8 ? z ? 4.5. Within this interval the surface density of galaxy candidates with z ~ 4 in this field is 1 arcmin-2. Photometric redshifts have been derived for the galaxies in the field with the maximum likelihood analysis using the GISSEL library of ~106 synthetic spectra. The accuracy of the method used has been discussed and tested using galaxies in the Hubble Deep Field with known spectroscopic redshifts and accurate photometry. A peak in the redshift distribution is present at z 0.6 with relatively few galaxies at z > 1.5. At variance with brighter surveys (I -19. This increase is reminiscent of that found in the most recent estimates of the local luminosity function, where a similar volume density is reached about 2 mag fainter. The observed cosmological UV luminosity density is computed in the overall redshift interval z = 0.3?4.5, reaching a value ~2 ? 1019 W Hz-1 Mpc-3 at z ~ 0.8. Including recent local estimates, it appears that the UV luminosity density changes by a factor of ~2.5 in the overall redshift interval z = 0.1?4, not including correction for fainter undetected galaxies. Thus we find that the evidence of a marked maximum in the luminosity density at z ~ 1?1.5 for galaxies with R ? 25 is weak. Using the GISSEL libraries we have derived in a homogeneous way the physical parameters connected with the fitted spectral energy distributions. Thanks to this new approach, the problem of the star formation history of the universe is dealt with in a consistent way, taking into account the dust and metallicity distributions derived from the spectrophotometric properties of each galaxy in the sample. The bulk of the blue intermediate-redshift population with z = 0.4?1 mostly consists of very young star-forming galaxies with a median starburst age of the order of a few times 108 yr and typical mass in luminous stars ~2 ? 108 M?. The presence of this young population is in contrast with the pure luminosity evolutionary model based on a single high-formation redshift. The cosmological mass in formed stars per unit comoving volume at z ~ 3 is already ~20% of that formed at z = 0.5 in our magnitude-limited sample. Predictions based on the standard hierarchical clustering models are smaller, although not far from that derived from the observations.

CO (J = 2–1) Observations of the Quasar BR 1202–0725 at Z = 4.7

A 12CO (J=2–1) observation of the quasar BR 1202–0725 at z=4.7, in which a huge amount of molecular gas had been detected in the 12CO (J=5–4) emission line, was made with the Nobeyama 45-m radio telescope. An upper limit of 1.2 mK in TMB ( ∼ 2.8 mJy) was obtained at a velocity resolution of 25 km s−1 . The physical conditions of the molecular gas were examined using the CO emission-line ratios with the LVG model; the line ratios imply that the molecular gas is dense $[n(\textrm H_2)\sim 10^{3.5-5.5}\textrm {cm}^{-3}]$ with a high kinetic temperature (50–100 K). The value of the CO-to-H2 conversion factor in this system is discussed and the molecular-gas mass is estimated to be less than $5.4 \times 10^{11}M \odot$. Using these values, we tried to sketch the distribution of molecular gas in this system and find the possibility that the system consists of many small dense clouds.

Star Formation at [CLC][ITAL]z[/ITAL][/CLC] = 4.7 in the Environment of the Quasar BR 1202−07

We present the spectrum of the galaxy companion to the z = 4.7 quasar BR 1202-0725 in the optical range 6000–9000 A, corresponding to 1050–1580 A in the rest frame. We detect a strong Lyα emission line at z = 4.702, with an integrated flux of 2 × 10-16 ergs cm-2 s-1, and a UV continuum longward of the Lyα emission at a flux level of 3 × 10-19 ergs cm-2 s-1 A-1. We fail to detect any C IV λ1550 emission with a 3 σ upper limit of 3 × 10-17 ergs cm-2 s-1. We show that the ratio between Lyα and continuum intensity and the absence of strong C IV emission imply that the UV continuum radiation is the result of intense star formation activity rather than of reprocessing of the QSO flux. The total estimated star formation rate of this z = 4.7 star-forming region is ~15–54 M⊙ yr-1, depending on the initial mass function and the metallicity. The present data suggest that the Lyα emission has a velocity and spatial structure, with possible velocity differences of 500 km s-1 on scales of a few kiloparsecs. These velocity patterns may be a signature of collapsing or merging phenomena in the QSO and its environment, as expected from current models of galaxy formation at high z.

Why Can We Detect the High-Redshift Quasar BR 1202–0725 in CO?

We present CO luminosity evolutions of both elliptical and spiral galaxies based on a galactic-wind model and a bulge-disk model, respectively. We have found that the CO luminosity peaks at around the epoch of the galactic wind caused by collective supernovae ∼ 0.85 Gyr after the birth of the elliptical with M = 2 · 1012M⊙, while ∼ 0.36 Gyr after the birth of the bulge with M = 2 · 1011M⊙. After these epochs, the CO luminosity decreased abruptly because the majority of the molecular gas was expelled from the galaxy system as wind. Taking account of typical masses of elliptical galaxies and the bulges of spiral galaxies, we suggest that CO emission can be hardly detected from galaxies with a redshift of z ∼ 1–4 unless some amplification either by galaxy mergers and/or by gravitational lensing is working. Therefore, our study explains reasonably well why CO emission was detected from the high-redshift quasar BR 1202 – 0725 at z = 4.7, while it was not detected from powerful radio galaxies with 1 &amp;lt; z &amp;lt; 4.

Detection of a Lyα Emission-Line Companion to the [ITAL]z[/ITAL] = 4.69 Quasar BR 1202−0725

We report the detection of a nearby emission-line companion to the z = 4.695 quasar BR 1202-0725. Deep narrowband exposures on this field from the University of Hawaii 2.2 m telescope show a Lyα flux of 1.5 × 10-16 ergs cm-2 s-1. High-resolution imaging in the F814W filter band with the Hubble Space Telescope Wide Field Planetary Camera (WFPC2) shows continuum structure near the emission position, at 26 northwest of the quasar, corresponding to a projected separation of ~7.5 h-1 kpc for q0 = 0.5, where h ≡ H0/100 km s-1 Mpc-1. We discuss possible explanations for the combined line and color properties. The ionization is most likely produced by the quasar, but, if due to underlying star formation, would require a star formation rate of ~7 h-2 M☉ yr-1.

A Redshift 4.38 Mg [CSC]ii[/CSC] Absorber Toward BR 1202−0725

We have detected a strong (EWobs = 20 A) redshift 4.38 Mg II absorber toward the redshift 4.68 quasar BR 1202-0725. The identification of this feature as Mg II λλ2796, 2803 is supported by the identification of a damped Lyα absorber and ultraviolet Si II λ1526 absorption at the same redshift. The strengths of Mg II λλ2796, 2803 and Si II λ1526 are consistent with those of strong low-redshift Mg II systems, damped Lyα absorbers, and diffuse clouds within the Milky Way. C IV λλ1548, 1550 is not detected, indicating a lower ionization state than is seen in lower redshift Mg II absorbers and within the interstellar medium of our Galaxy. The detection of a single strong Mg II absorber at z > 4.2, among the three quasars observed with sufficient signal-to-noise ratio to detect an absorber, is consistent with the statistics and evolution of lower redshift Mg II absorbers. Thus, despite being at nearly twice the redshift of any previously identified Mg II absorber, this system appears quite similar to lower redshift Mg II systems that are identified with normal field galaxies. Because of the saturated nature of the Si II and Mg II lines, the metallicity of the gas is uncertain, but it is clear that some enrichment of Si and Mg, probably amounting to more than 1% of solar, has occurred by a redshift of 4.38.

The Gunn-Peterson effect in the spectrum of the Z = 4.7 QSO 1202-0725: The intergalactic medium at very high redshifts

A measure of the average depression between Lyman absorption lines in the spectrum of the faint quasar BR 1202-0725 (Z_em_ = 4.695) is presented. The relatively high resolution of the spectrum (~40 km s^-1^) allows the selection of regions free of strong absorption lines in the Lyα forest. A reliable evaluation of the continuum shape is based on the careful flux calibration and on the large wavelength interval covered (5000-9300 A).HERE A best estimate of τ_GP_ &lt;= 0.02 +/- 0.03 has been found for the Gunn-Peterson optical depth at the highest absorption redshift observed at this resolution, z~4.3. The derived baryon density of the intergalactic medium is {OMEGA}_IGM_ &lt;~ 0.01 if the observed quasars are the major contributor to the ionizing UV background flux. This limit, when compared with the total baryon density deduced from the nucleosynthesis, could imply that most of the baryons are already in bound systems at z ~ 5.