1,721,063 research outputs found
BLACK HOLE MASS ESTIMATES AND EMISSION-LINE PROPERTIES OF A SAMPLE OF REDSHIFT z > 6.5 QUASARS
No full textWe present the analysis of optical and near-infrared spectra of the only four z > 6.5 quasars known to date, discovered in the UKIDSS-LAS and VISTA-VIKING surveys. Our data set consists of new Very Large Telescope/X-Shooter and Magellan/FIRE observations. These are the best optical/NIR spectroscopic data that are likely to be obtained for the z > 6.5 sample using current 6-10 m facilities. We estimate the black hole (BH) mass, the Eddington ratio, and the Si IV/C IV, C III]/C IV, and Fe II/Mg II emission-line flux ratios. We perform spectral modeling using a procedure that allows us to derive a probability distribution for the continuum components and to obtain the quasar properties weighted upon the underlying distribution of continuum models. The z > 6.5 quasars show the same emission properties as their counterparts at lower redshifts. The z > 6.5 quasars host BHs with masses of ~10[superscript 9] M [subscript ☉] that are accreting close to the Eddington luminosity ( = –0.4 ± 0.2), in agreement with what has been observed for a sample of 4.0 < z < 6.5 quasars. By comparing the Si IV/C IV and C III]/C IV flux ratios with the results obtained from luminosity-matched samples at z ~ 6 and 2 ≤ z ≤ 4.5, we find no evidence of evolution of the line ratios with cosmic time. We compare the measured Fe II/Mg II flux ratios with those obtained for a sample of 4.0 < z < 6.4 sources. The two samples are analyzed using a consistent procedure. There is no evidence that the Fe II/Mg II flux ratio evolves between z = 7 and z = 4. Under the assumption that the Fe II/Mg II traces the Fe/Mg abundance ratio, this implies the presence of major episodes of chemical enrichment in the quasar hosts in the first ~0.8 Gyr after the Big Bang
The Carbon Content of Intergalactic Gas at Z=4.25 and Its Evolution toward Z=2.4
Full text linkThis paper presents ionization-corrected measurements of the carbon abundance in intergalactic gas at 4.0 over /] 1.6, we derive a median carbon abundance of [C/H]=–3.55, with lognormal scatter of approximately σ ≈ 0.8 dex. This median value is a factor of two to three lower than similar measurements made at z ~ 2.4 using C IV and O VI. The strength of evolution is modestly dependent on the choice of UV background spectrum used to make ionization corrections, although our detection of an abundance evolution is generally robust with respect to this model uncertainty. We present a framework for analyzing the effects of spatial fluctuations in the UV ionizing background at frequencies relevant for C IV production. We also explore the effects of reduced flux between 3 and 4 Rydbergs (as from He II Lyman series absorption) on our abundance estimates. At He II line absorption levels similar to published estimates, the effects are very small, although a larger optical depth could reduce the strength of the abundance evolution. Our results imply that ~50% of the heavy elements seen in the intergalactic medium at z ~ 2.4 were deposited in the 1.3 Gyr between z ~ 4.3 and z ~ 2.4. The total implied mass flux of carbon into the Lyα forest would constitute ~30% of the IMF-weighted carbon yield from known star-forming populations over this period.Alfred P. Sloan FoundationNational Science Foundation (U.S.) (Grant AST-0908920
Are we witnessing the epoch of reionization at z=7.1 from the spectrum of J1120+0641?
Full text linkWe quantify the presence of Lyα damping wing absorption from a partially neutral intergalactic medium (IGM) in the spectrum of the z = 7.08 QSO, ULASJ1120+0641. Using a Bayesian framework, we simultaneously account for uncertainties in: (i) the intrinsic QSO emission spectrum; and (ii) the distribution of cosmic H I patches during the epoch of reionization (EoR). For (i), we use a new intrinsic Lyα emission line reconstruction method, sampling a covariance matrix of emission line properties built from a large data base of moderate-z QSOs. For (ii), we use the Evolution of 21-cm Structure (EOS; Mesinger et al.) simulations, which span a range of physically motivated EoR models. We find strong evidence for the presence of damping wing absorption redward of Lyα (where there is no contamination from the Lyα forest). Our analysis implies that the EoR is not yet complete by z = 7.1, with the volume-weighted IGM neutral fraction constrained to x ̄HI=0.40+0.21−0.19 at 1σ (x ̄HI=0.40+0.41−0.32 at 2σ). This result is insensitive to the EoR morphology. Our detection of significant neutral H I in the IGM at z = 7.1 is consistent with the latest Planck 2016 measurements of the CMB Thompson scattering optical depth
A SURVEY OF Mg II ABSORPTION AT 2 < z < 6 WITH MAGELLAN/FIRE. I. SAMPLE AND EVOLUTION OF THE Mg II FREQUENCY
Full text linkWe present initial results from the first systematic survey for Mg II quasar absorption lines at z > 2.5. Using infrared spectra of 46 high-redshift quasars, we discovered 111 Mg II systems over a path covering 1.9 5, with a maximum of z = 5.33—the most distant Mg II system now known. The comoving Mg II line density for weaker systems (W[subscript r] < 1.0 Å) is statistically consistent with no evolution from z = 0.4 to 5.5, while that for stronger systems increases three-fold until z ~ 3 before declining again toward higher redshifts. The equivalent width distribution, which fits an exponential, reflects this evolution by flattening as z → 3 before steepening again. The rise and fall of the strong absorbers suggests a connection to the star formation rate density, as though they trace galactic outflows or other byproducts of star formation. The weaker systems' lack of evolution does not fit within this interpretation, but may be reproduced by extrapolating low redshift scaling relations between host galaxy luminosity and absorbing halo radius to earlier epochs. For the weak systems, luminosity-scaled models match the evolution better than similar models based on Mg II occupation of evolving cold dark matter halo masses, which greatly underpredict dN/dz at early times unless the absorption efficiency of small halos is significantly larger at early times. Taken together, these observations suggest that the general structure of Mg II-bearing halos was put into place early in the process of galaxy assembly. Except for a transient appearance of stronger systems near the peak epoch of cosmic star formation, the basic properties of Mg II absorbers have evolved fairly little even as the (presumably) associated galaxy population grew substantially in stellar mass and half-light radius.National Science Foundation (U.S.) (Grant AST-0908920
A Calibrated Measurement of the Near-IR Continuum Sky Brightness Using Magellan/FIRE
Full text linkWe characterize the near-IR sky background from 308 observations with the Folded-port InfraRed Echellette (FIRE) spectrograph at Magellan. A subset of 105 observations selected to minimize lunar and thermal effects gives a continuous, median spectrum from 0.83 to 2.5 μ m, which we present in Table 2 . The data are used to characterize the broadband continuum emission between atmospheric OH features and correlate its properties with observing conditions such as lunar angle and time of night. We find that the Moon contributes significantly to the inter-line continuum in and bands, whereas the observed -band continuum is dominated by the blended Lorentzian wings of multiple OH line profiles, even at = 6000 . Lunar effects may be mitigated in and through careful scheduling of observations, but the most ambitious near-IR programs will benefit from allocation during dark observing time if those observations are not limited by read noise. In and , our measured continuum exceeds space-based average estimates of the zodiacal light, but it is not readily identified with known terrestrial foregrounds. If further measurements confirm such a fundamental background, it would impact requirements for OH-suppressed instruments operating in this regime.National Science Foundation (U.S.) (Grant AST-0908920)National Science Foundation (U.S.) (Grant AST-1109115
A Substantial Mass of Cool, Metal-enriched Gas Surrounding the Progenitors of Modern-day Ellipticals
Full text linkThe hosts of luminous z ~ 2 quasars evolve into today's massive elliptical galaxies. Current theories predict that the circumgalactic medium (CGM) of these massive, dark matter halos (M [subscript DM] ~ 10[superscript 12.5] M [subscript ☉]) should be dominated by a T ~ 10[superscript 7] K virialized plasma. We test this hypothesis with observations of 74 close-projected quasar pairs, using spectra of the background QSO to characterize the CGM of the foreground one. Surprisingly, our measurements reveal a cool (T ≈ 10[superscript 4] K), massive (M [subscript CGM] > 10[superscript 10] M [subscript ☉]), and metal-enriched (Z ≳ 0.1 Z [subscript ☉]) medium extending to at least the expected virial radius (r [subscript vir] = 160 kpc). The average equivalent widths of H I Lyα ([_ over W] [subscript [subscript Lyα] = 2.1 ± 0.15 Å for impact parameters R ⊥ 10[superscript 17.2] cm[superscript –2]) within r [subscript vir]; this covering factor is twice that of the contemporaneous Lyman break galaxy population. This unexpected reservoir of cool gas is rarely detected "down-the-barrel" to quasars, and hence it is likely that our background sight lines intercept gas that is shadowed from the quasar ionizing radiation by the same obscuring medium often invoked in models of active galactic nucleus unification. Because the high-z halos inhabited by quasars predate modern groups and clusters, these observations are also relevant to the formation and enrichment history of the intragroup/intracluster medium
Observations of Mg II Absorption near Z Similar to 1 Galaxies Selected from the Deep2 Redshift Survey
No full textWe study the frequency of Mg II absorption in the outer halos of galaxies at z = 0.6-1.4 (with median z = 0.87), using new spectra obtained of 10 background quasars with galaxy impact parameters of b 1.0 Å, consistent with other samples of galaxy-selected Mg II systems. We speculate that Mg II systems with 0.3 < Wr < 1.0 trace old relic material from galactic outflows and/or the halo assembly process, and that in contrast, systems with large Wr are more likely to reflect the more recent star-forming history of their associated galaxies.National Science Foundation (U.S.) (Grant AST-0908920
Precision of a Low-Cost InGaAs Detector for Near Infrared Photometry
No full textWe have designed, constructed, and tested an InGaAs near-infrared camera to explore whether low-cost detectors can make small (≤1 m) telescopes capable of precise (<1 mmag) infrared photometry of relatively bright targets. The camera is constructed around the 640 × 512 pixel APS640C sensor built by FLIR Electro-Optical Components. We designed custom analog-to-digital electronics for maximum stability and minimum noise. The InGaAs dark current halves with every 7°C of cooling, and we reduce it to 840 e[superscript -]s[superscript -1]pixel[superscript -1] (with a pixel-to-pixel variation of ±200 e[superscript -]s[superscript -1]pixel[superscript -1]) by cooling the array to 20°C. Beyond this point, glow from the readout dominates. The single-sample read noise of 149 [superscript -]e is reduced to 54 [superscript -]e through up-the-ramp sampling. Laboratory testing with a star field generated by a lenslet array shows that two-star differential photometry is possible to a precision of 631 ± 205 ppm (0.68 mmag) hr[superscript -1/2] at a flux of 2.4 × 10[superscript 4] e[superscript -]s[superscript -1]. Employing three comparison stars and decorrelating reference signals further improves the precision to 483 ± 161 ppm (0.52 mmag) hr[superscript -1/2]. Photometric observations of HD80606 and HD80607 (J - 7.7 and 7.8) in the Y band shows that differential photometry to a precision of 415 ppm (0.45 mmag) hr[superscript -1/2] is achieved with an effective telescope aperture of 0.25 m. Next-generation InGaAs detectors should indeed enable Poisson-limited photometry of brighter dwarfs with particular advantage for late-M and L types. In addition, one might acquire near-infrared photometry simultaneously with optical photometry or radial velocity measurements to maximize the return of exoplanet searches with small telescopes.United States. National Aeronautics and Space Administration (Sagan Fellowship
THE PAN-STARRS1 DISTANT z > 5.6 QUASAR SURVEY: MORE THAN 100 QUASARS WITHIN THE FIRST GYR OF THE UNIVERSE
Full text linkLuminous quasars at z > 5.6 can be studied in detail with the current generation of telescopes and provide us with unique information on the first gigayear of the universe. Thus far, these studies have been statistically limited by the number of quasars known at these redshifts. Such quasars are rare, and therefore, wide-field surveys are required to identify them, and multiwavelength data are required to separate them efficiently from their main contaminants, the far more numerous cool dwarfs. In this paper, we update and extend the selection for the z ~ 6 quasars presented in Bañados et al. (2014) using the Pan-STARRS1 (PS1) survey. We present the PS1 distant quasar sample, which currently consists of 124 quasars in the redshift range $5.6 ≲ z ≲ 6.7 that satisfy our selection criteria. Of these quasars, 77 have been discovered with PS1, and 63 of them are newly identified in this paper. We present the composite spectra of the PS1 distant quasar sample. This sample spans a factor of ~20 in luminosity and shows a variety of emission line properties. The number of quasars at z\ > 5.6 presented in this work almost doubles the previously known quasars at these redshifts, marking a transition phase from studies of individual sources to statistical studies of the high-redshift quasar population, which was impossible with earlier, smaller samples.Hubble Fellowship grant HST-HF2-51367.001-A, awarded by the Space Telescope Science Institute
Precious Metals in SDSS Quasar Spectra. I. Tracking the Evolution of Strong, 1.5 < z < 4.5 C IV Absorbers with Thousands of Systems
Full text linkWe have vastly increased the C IV statistics at intermediate redshift by surveying the thousands of quasars in the Sloan Digital Sky Survey (SDSS) Data-Release 7. We visually verified over 16,000 C IV systems with 1.46 5 (infrared) surveys, we see an approximately 10-fold increase in dNCIV/dX over z ≈ 6 → 0, for W r ≥ 0.6 Å. This suggests a monotonic and significant increase in the enrichment of gas outside galaxies over the 12 Gyr lifetime of the universe.National Science Foundation (U.S.) (Astronomy & Astrophysics Postdoctoral Fellowship (AST-1003139))Alfred P. Sloan Foundation (Research Fellowship)Massachusetts Institute of Technology. Dept. of Physic
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