我们发现，在21个BAL类星体中，电离连续谱的分数变化与C IV和/或Si IV BALs的分数变化之间存在显著（显著性水平>99%）的相关性，这些BAL类星体至少有5个历元来自斯隆数字巡天I/II/III的观测。这一结果表明，电离连续的波动是大多数这些BAL变化的驱动程序。其中，17条谱线呈现负相关，4条谱线呈现正相关，这与光电离模型预测的吸收谱线变化对电离变化的响应不是单调的一致。在21个类星体中，有8个在几天的静止帧时间尺度上被观测了至少30次，这表明即使在如此短的时间内，入射电离连续统的变化也会导致BAL变异。此外，我们发现，大多数的类星体显示更大的变化幅度在Si IV比C IV，这揭示了饱和的普遍存在，在这些BALs（至少对C IV BALs）。
英文摘要：
We discover the significant (significance level of >99%) correlations between the fractional variation of the ionizing continuum and that of the C IV and/or Si IV BALs in each of 21 BAL quasars that have at least five-epoch observations from the Sloan Digital Sky Survey-I/II/III. This result reveals that the fluctuation of the ionizing continuum is the driver of most of these BAL variations. Among them, 17 show negative correlations and the other 4 positive correlations, which agrees with the prediction of photoionization models that absorption line variability response to ionization changes is not monotonic. 8 quasars out of 21 examples have been observed at least 30 times on rest-frame timescales as short as a few days, which reveals that changes in the incident ionizing continuum can cause BAL variability even in such a short period of time. In addition, we find that most of the 21 quasars show larger variation amplitude in Si IV than C IV, which reveals the ubiquity of saturation in these BALs (at least for C IV BALs).
Correlation between the variation of the ionizing continuum and broad absorption lines
在这封信中，我们提出了一个宽吸收线（BALs）和连续的可变性之间的关系的分析。我们的样本是斯隆数字巡天I/II/III（SDSS-I/II/III）对483个类星体的多历元观测。我们推导出的分数通量变化的连续和分数等效宽度（EW）的变化为C IV和Si IV BALs，并探讨三者之间的相关性。我们的研究结果揭示了中等的CIV和Si IV BALs的连续分数通量变化和分数EW变化之间的高显着性水平的EFT关系。我们还证明了C IV和Si IV BALs的分数EW变化之间的显着正相关性，这与以前的几项研究一致。我们的发现可以作为证据的想法：电离连续体的变化是BAL变异性的主要驱动力。
Measurements of quasar proximity zones with the Ly$α$ forest of DESI Y1 quasars
The Ohio State University（俄亥俄州立大学）；Academia Sinica（中央研究院）；The University of Utah（犹他大学）；Lawrence Berkeley National Laboratory（劳伦斯伯克利国家实验室）；Boston University（波士顿大学）
Quasars and active galactic nuclei (AGN) are significant contributors to the metagalactic ionizing background at redshifts z < 3. Recent HST/COS composite spectra of AGN find a harder flux distribution in the Lyman continuum, F_nu ~ nu^{-alpha_s} (alpha_s = 1.41+/-0.15) compared to previous studies. This index appears to be inconsistent with observed He II / H I absorption ratios (eta) in the Lya forest. We explore effects of internal AGN absorption in the He II (4 ryd) continuum using an analytic source-function model of the ionizing background in which the emissivity (j_nu) arises from quasa…
We present a study of quasars with very redward asymmetric (RA) ultraviolet (UV) broad emission lines (BELs). An excess of redshifted emission has been previously shown to occur in the BELs of radio loud quasars and is most extreme in certain blazars. Paradoxically, blazars are objects that are characterized by a highly relativistic blue-shifted outflow towards Earth. We show that the red emitting gas resides in a very broad component (VBC) that is typical of Population B quasars that are defined by a wide H$β$ BEL profile. Empirically, we find that RA BEL blazars have both low Eddington rates…
Variation of ionizing continuum: the main driver of Broad Absorption Line Variability
我们提出了一个统计分析的变化宽吸收线（BALs）的类星体使用大型多历元光谱数据集的斯隆数字巡天数据发布12（SDSS DR 12）。我们将样品分为两组，根据的变化模式的C iv BAL相对于连续体：的等效宽度（EW）的BAL减少（增加）时，连续体变亮（变暗）的T1组和EW和连续体的变化在相反的关系作为T2组。我们发现，T2组的Si iv与C iv BAL的EW比值（R）显著高于T1组（P_T<10-6，Students T检验）。我们的结果与光电离模型的预测一致，即如果有（或没有）C +3电离前沿，C +3柱密度增加（减少），而R随入射连续谱而减少。我们发现，在至少80%的类星体中，BAL变异是由电离连续体的变化驱动的，而其他预测不相关的BAL和连续体变异的模型贡献不到20%。考虑到连续通量校准中的大不确定性，后一部分可能小得多。当样本被分到两个观测之间的不同时间间隔时，我们发现在所有时间段内T1和T2之间的R分布差异显著，Δ T < 6天，这表明在一部分类星体中的BAL流出只有几天的重组时间尺度。
The connection between the escape fraction of ionizing radiation ($f_{esc}$) and the properties of galaxies, such as stellar mass (M*), age, star-formation rate (SFR), and dust content, are key inputs for reionization models, but many of these relationships remain untested at high redshift. We present an analysis of a sample of 96 z~3 galaxies from the Keck Lyman Continuum Spectroscopic Survey (KLCS). These galaxies have both sensitive Keck/LRIS spectroscopic measurements of the Lyman continuum (LyC) region, and multi-band photometry that places constraints on stellar population parameters. We…
We present a novel intelligent quasar continuum neural network (iQNet), predicting the intrinsic continuum of any quasar in the rest-frame wavelength range 1020 Angstroms $\leq λ\leq$ 1600 Angstroms. We train this network using high-resolution Hubble Space Telescope/Cosmic Origin Spectrograph ultraviolet quasar spectra at low redshift ($z \sim 0.2$) from the Hubble Spectroscopic Legacy Archive, and apply it to predict quasar continua from different astronomical surveys. We utilize the HSLA quasar spectra that are well-defined in the rest-frame wavelength range [1020, 1600] Angstroms with an ov…
The flux ratios of high-ionization lines are commonly assumed to indicate the metallicity of the broad emission line region in luminous quasars. When accounting for the variation in their kinematic profiles, we show that the NV/CIV, (SiIV+OIV])/CIV and NV/Lya line ratios do not vary as a function of the quasar continuum luminosity, black hole mass, or accretion rate. Using photoionization models from CLOUDY , we further show that the observed changes in these line ratios can be explained by emission from gas with solar abundances, if the physical conditions of the emitting gas are allowed to v…
Faint $z\sim5$ quasars with $M_{1450}\sim-23$ mag are known to be the potentially important contributors to the ultraviolet ionizing background in the post-reionization era. However, their number density has not been well determined, making it difficult to assess their role in the early ionization of the intergalactic medium (IGM). In this work, we present the updated results of our $z\sim5$ quasar survey using the Infrared Medium-deep Survey (IMS), a near-infrared imaging survey covering an area of 85 deg$^{2}$. From our spectroscopic observations with the Gemini Multi-Object Spectrograph (GM…
Evidence of a diffuse, extended continuum source in quasars from the relative sizes of the broad line region and the UV-optical continuum source measured with microlensing
Anisotropic Radiation in Super-Eddington Active Galactic Nuclei: The Responsivity of Broad-Line Regions to Continuum Variability
State Key Laboratory of Particle Astrophysics, Institute of High Energy Physics, Chinese Academy of Sciences（高能物理研究所粒子天体物理国家重点实验室）；National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台）；School of Astronomy and Space Science, University of Chinese Academy of Sciences（中国科学院大学天文与空间科学学院）
The ultraviolet (UV) continuum slope ($β~$where$~f_λ\proptoλ^β$) of galaxies is sensitive to a variety of properties, from the metallicity and age of the stellar population to dust attenuation throughout the galaxy. Considerable attention has focused on identifying reionization-era galaxies with very blue UV slopes ($β<-3$). Not only do such systems provide a signpost of low-metallicity stars, but they also identify galaxies likely to leak ionizing photons from their HII regions as such blue UV slopes require the reddening effect of nebular continuum to be diminished. In this paper we present …
Context: Studies of the production and escape of Lyman Continuum from galaxies often rely on array of indirect observational tracers in preselection of candidate leakers. Aims: Here, we investigate how much ionizing radiation might be missed due to these selection criteria by completely removing them and performing a search selected purely from rest-frame LyC emission; and how that affects our estimates of the ionizing background. Methods: We invert the conventional method and perform a bottom-up search for Lyman-continuum leaking galaxies at redshifts $2 < z < 3.5$. Using archival data from H…
Most of the hydrogen in the intergalactic medium (IGM) was rapidly ionized at high-redshifts. While observations have established that reionization occurred, observational constraints on the emissivity of ionizing photons at high-redshift remains elusive. Here, we present a new analysis of the Low-redshift Lyman Continuum Survey (LzLCS) and archival observations, a combined sample of 89 star-forming galaxies at z~0.3 with Hubble Space Telescope observations of their ionizing continua (or Lyman Continuum, LyC). We find a strong (6$σ$ significant) inverse correlation between the continuum slope …
Exploring the hardness of the ionizing radiation with the infrared softness diagram. II. Bimodal distributions in both the ionizing continuum slope and the excitation in active galactic nuclei
Observations of reionization-era analogs at $z\sim3$ are a powerful tool for constraining reionization. Rest-ultraviolet observations are particularly useful, in which both direct and indirect tracers of ionizing-photon production and escape can be observed. We analyse a sample of 124 $z\sim3$ galaxies from the Keck Lyman Continuum Spectroscopic Survey, with sensitive spectroscopic measurements of the Lyman continuum (LyC) region. We present a method of removing foreground contamination from our sample using high-resolution, multiband Hubble Space Telescope imaging. We re-measure the global pr…
We report results for a complete sample of ten luminous radio-quiet quasars with large C IV equivalent widths (EW > 150 A). For 8/10 we performed Chandra snapshot observations. We find that, in addition to the enhanced C IV line EW, their He II and Mg II lines are enhanced, but the C III] line is not. Their X-ray emission is substantially stronger than expected from their ultraviolet luminosity. Additionally, these large C IV EW quasars show small C IV blueshifts and possibly low Eddington ratios, suggesting they are "extreme low Eigenvector 1 (EV1)" quasars. The mean excess He II EW is well-m…
A Galaxy with an Extremely Blue UV Slope $β=-3$ at $z=9.25$ Identified by JWST Spectroscopy: Evidence for a Weak Nebular Continuum and Efficient Ionizing Photon Escape?
We present the composite optical spectrum for the largest sample of giant radio quasars (GRQs). They represent a rare subclass of radio quasars due to their large projected linear sizes of radio structures, which exceed 0.7 Mpc. To construct the composite spectrum, we combined 216 GRQ's optical spectra from Sloan Digital Sky Survey (SDSS). As a result, we obtained the composite spectrum covering the wavelength range from 1400 Å to 7000 Å. We calculated the power-law spectral slope for GRQ's composite, obtaining $α_λ=-1.25$ and compared it with that of the smaller-sized radio quasars, as well a…
The Sloan Digital Sky Survey Reverberation Mapping Project: Investigation of Continuum Lag Dependence on Broad-Line Contamination and Quasar Properties
We present a new set of 84 Broad absorption line (BAL) quasars ( 1.7 $<$ \zem $<$ 4.4) exhibiting an appearance of \civ BAL troughs over 0.3$-$4.8 rest-frame years by comparing the Sloan Digital Sky Survey Data Release (SDSSDR)-7, SDSSDR-12, and SDSSDR-14 quasar catalogs. We contrast the nature of BAL variability in this appearing BAL quasar sample with a disappearing BAL quasar sample studied in literature by comparing the quasar's intrinsic, BAL trough, and continuum parameters between the two samples. We find that appearing BAL quasars have relatively higher redshift and smaller probed time…
The relationship between galaxy characteristics and the reionization of the universe remains elusive, mainly due to the observational difficulty in accessing the Lyman continuum (LyC) at these redshifts. It is thus important to identify low-redshift LyC-leaking galaxies that can be used as laboratories to investigate the physical processes that allow LyC photons to escape. The weakness of the [S II] nebular emission lines relative to typical star-forming galaxies has been proposed as a LyC predictor. In this paper, we show that the [S II]-deficiency is an effective method to select LyC-leaking…
Understanding the escape of ionizing (Lyman continuum) photons from galaxies is vital for determining how galaxies contributed to reionization in the early universe. While directly detecting Lyman continuum from high redshift galaxies is impossible due to the intergalactic medium, low redshift galaxies in principle offer this possibility, but requirie observations from space. The first local galaxy for which Lyman continuum escape was found is Haro11 , a luminous blue compact galaxy at z=0.02, where observations with the FUSE satellite revealed an escape fraction of 3.3 %. However the FUSE ape…
We report the fourth installment in the series of the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) Quasar Survey, which includes quasars observed between September, 2017 and June, 2021. There are in total 13,066 quasars reliably identified, of which 6,685 are newly discovered that are not reported in the SDSS DR14 quasar catalog or Million Quasars catalog. Because LAMOST does not provide accurate absolute flux calibration, we re-calibrate the spectra with the SDSS/Pan-STARRS1 multi-band photometric data. The emission line properties of H$α$, H$β$, Mg\,{\sc ii} and C\,{\sc…
