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- The Astrophysical Journal Letters
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- National Science Foundation
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Abstract Luminous quasars are powerful targets to investigate the role of feedback from supermassive black holes (BHs) in regulating the growth phases of BHs themselves and of their host galaxies, up to the highest redshifts. Here we investigate the cosmic evolution of the occurrence and kinematics of BH-driven outflows, as traced by broad absorption line (BAL) features, due to the C iv ionic transition. We exploit a sample of 1935 quasars at z = 2.1–6.6 with bolometric luminosity log( L bol /erg s −1 ) ≳ 46.5, drawn from the Sloan Digital Sky Survey and from the X-Shooter legacy survey of Quasars at the Reionization Epoch (XQR-30). We consider rest-frame optical bright quasars to minimize observational biases due to quasar selection criteria. We apply a homogeneous BAL-identification analysis, based on employing composite template spectra to estimate the quasar intrinsic emission. We find a BAL quasar fraction close to 20% at z ∼ 2–4, while it increases to almost 50% at z ∼ 6. The velocity and width of the BAL features also increase at z ≳ 4.5. We exclude the possibility that the redshift evolution of the BAL properties is due to differences in terms of quasar luminosity and accretion rate. These results suggest significant BH feedback occurring in the 1 Gyr old universe, likely affecting the growth of BHs and, possibly, of their host galaxies, as supported by models of early BH and galaxy evolution.more » « less
We analyze a sample of 25 [Ne
v] ( λ3426) emission-line galaxies at 1.4 < z< 2.3 using Hubble Space Telescope/Wide Field Camera 3 G102 and G141 grism observations from the CANDELS Ly αEmission at Reionization (CLEAR) survey. [Ne v] emission probes extremely energetic photoionization (creation potential of 97.11 eV) and is often attributed to energetic radiation from active galactic nuclei (AGNs), shocks from supernovae, or an otherwise very hard ionizing spectrum from the stellar continuum. In this work, we use [Ne v] in conjunction with other rest-frame UV/optical emission lines ([O ii] λ λ3726, 3729, [Ne iii] λ3869, H β, [O iii] λ λ4959, 5007, H α+[N ii] λ λ6548, 6583, [S ii] λ λ6716, 6731), deep (2–7 Ms) X-ray observations (from Chandra), and mid-infrared imaging (from Spitzer) to study the origin of this emission and to place constraints on the nature of the ionizing engine. The majority of the [Ne v]-detected galaxies have properties consistent with ionization from AGNs. However, for our [Ne v]-selected sample, the X-ray luminosities are consistent with local ( z≲ 0.1) X-ray-selected Seyferts, but the [Ne v] luminosities are more consistent with those from z∼ 1 X-ray-selected QSOs. The excess [Ne v] emission requires either reduced hard X-rays or a ∼0.1 keV excess. We discuss possible origins of the apparent [Ne v] excess, which could be related to the “soft (X-ray) excess” observed in some QSOs and Seyferts and/or be a consequence of a complex/anisotropic geometry for the narrow-line region, combined with absorption from a warm, relativistic wind ejected from the accretion disk. We also consider implications for future studies of extreme high-ionization systems in the epoch of reionization ( z≳ 6) with the James Webb Space Telescope.
The most reliable single-epoch supermassive black hole mass (
MBH) estimates in quasars are obtained by using the velocity widths of low-ionization emission lines, typically the H β λ4861 line. Unfortunately, this line is redshifted out of the optical band at z≈ 1, leaving MBHestimates to rely on proxy rest-frame ultraviolet (UV) emission lines, such as C iv λ1549 or Mg ii λ2800, which contain intrinsic challenges when measuring, resulting in uncertain MBHestimates. In this work, we aim at correcting MBHestimates derived from the C ivand Mg iiemission lines based on estimates derived from the H βemission line. We find that employing the equivalent width of C ivin deriving MBHestimates based on Mg iiand C ivprovides values that are closest to those obtained from H β. We also provide prescriptions to estimate MBHvalues when only C iv, only Mg ii, and both C ivand Mg iiare measurable. We find that utilizing both emission lines, where available, reduces the scatter of UV-based MBHestimates by ∼15% when compared to previous studies. Lastly, we discuss the potential of our prescriptions to provide more accurate and precise estimates of MBHgiven a much larger sample of quasars at 3.20 ≲ z≲ 3.50, where both Mg iiand H βcan be measured in the same near-infrared spectrum.
z≳ 1 most often have redshifts measured from rest-frame ultraviolet emission lines. One of the most common such lines, C iv λ1549, shows blueshifts up to ≈5000 km s−1and in rare cases even higher. This blueshifting results in highly uncertain redshifts when compared to redshift determinations from rest-frame optical emission lines, e.g., from the narrow [O iii] λ5007 feature. We present spectroscopic measurements for 260 sources at 1.55 ≲ z≲ 3.50 having −28.0 ≲ M i≲ − 30.0 mag from the Gemini Near Infrared Spectrograph–Distant Quasar Survey (GNIRS-DQS) catalog, augmenting the previous iteration, which contained 226 of the 260 sources whose measurements are improved upon in this work. We obtain reliable systemic redshifts based on [O iii] λ5007 for a subset of 121 sources, which we use to calibrate prescriptions for correcting UV-based redshifts. These prescriptions are based on a regression analysis involving C ivfull-width-at-half-maximum intensity and equivalent width, along with the UV continuum luminosity at a rest-frame wavelength of 1350 Å. Applying these corrections can improve the accuracy and the precision in the C iv-based redshift by up to ∼850 km s−1and ∼150 km s−1, respectively, which correspond to ∼8.5 and ∼1.5 Mpc in comoving distance at z= 2.5. Our prescriptions also improve the accuracy of the best available multifeature redshift determination algorithm by ∼100 km s−1, indicating that the spectroscopic properties of the C ivemission line can provide robust redshift estimates for high-redshift quasars. We discuss the prospects of our prescriptions for cosmological and quasar studies utilizing upcoming large spectroscopic surveys.
Spectroscopic studies of extreme-ionization galaxies (EIGs) are critical to our understanding of exotic systems throughout cosmic time. These EIGs exhibit spectral features requiring >54.42 eV photons: the energy needed to ionize helium into He2+fully and emit He
iirecombination lines. Spectroscopic studies of EIGs can probe exotic stellar populations or accretion onto intermediate-mass black holes (∼102–105 M⊙), which are the possibly key contributors to the reionization of the Universe. To facilitate the use of EIGs as probes of high-ionization systems, we focus on ratios constructed from several rest-frame UV/optical emission lines: [O iii] λ5008, H β, [Ne iii] λ3870, [O ii] λ λ3727, 3729, and [Ne v] λ3427. These lines probe the relative intensity at energies of 35.12, 13.62, 40.96, 13.62, and 97.12 eV, respectively, covering a wider range of ionization than traced by other common rest-frame UV/optical techniques. We use the ratios of these lines ([Ne v]/[Ne iii] ≡ Ne53, [O iii]/H β, and [Ne iii]/[O ii]), which are nearby in wavelength, mitigating the effects of dust attenuation and uncertainties in flux calibration. We make predictions from photoionization models constructed from Cloudythat use a broad range of stellar populations and black hole accretion models to explore the sensitivity of these line ratios to changes in the ionizing spectrum. We compare our models to observations from the Hubble Space Telescope and JWST of galaxies with strong high-ionization emission lines at z∼ 0, z∼ 2, and 5 < z< 8.5. We show that the Ne53 ratio can separate galaxies with ionization from “normal” stellar populations from those with active galactic nuclei and even “exotic” Population III models. We introduce new selection methods to identify galaxies with photoionization driven by Population III stars or intermediate-mass black hole accretion disks that could be identified in upcoming high-redshift spectroscopic surveys.