arXiv subjects

Luis C. Ho

Publications and source records attributed to Luis C. Ho.

At least 127 records · Page 7Linked to original sources

arXiv2025

Supermassive Black Holes with High Accretion Rates in Active Galactic Nuclei. XII. Reverberation Mapping Results for 15 PG Quasars from a Long-Duration High-Cadence Campaign

We present the first results from long-term high-cadence spectroscopic monitoring of 15 PG quasars with relatively strong Fe II emission as a part of a broader reverberation mapping campaign performed with the Calar Alto Observatory 2.2m telescope. The $V$-band, 5100 Å continuum, and H$β$ broad emission line light curves were measured for a set of quasars for between dozens to more than a hundred epochs from May 2017 to July 2020. Accurate time lags between the variations of the H$β$ broad line fluxes and the optical continuum strength are obtained for all 15 quasars, ranging from $17.0_{-3.2}^{+2.5}$ to $95.9_{-23.9}^{+7.1}$ days in the rest frame. The virial masses of the central supermassive black holes are derived for all 15 quasars, ranging between $0.50_{-0.19}^{+0.18}$ and $19.17_{-2.73}^{+2.98}$ in units of $10^7 M_\odot$. For 11 of the objects in our sample, this is the first reverberation analysis published. Of the rest, two objects have been the subject of previous reverberation studies, but we determine time lags for these that are only half as long as found in the earlier investigations, which had only been able to sample much more sparsely. The remaining two objects have previously been monitored with high sampling rates. Our results here are consistent with the earlier findings in the sense that the time lag and the line width vary inversely consistent with virialization.

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arXiv2025

Supermassive Black Holes with High Accretion Rates in Active Galactic Nuclei. XIV. Long-Duration High-Cadence Reverberation Mapping Results for 11 PG Quasars

We report the results of a long-duration high-cadence reverberation mapping campaign of a second batch of 11 PG quasars using the 2.2m telescope at the Calar Alto Observatory. This follows a similar earlier study of another sample of 15 objects reported by Hu et al. (2021). Among the 11 PG quasars, 8 objects have the H$β$ time lags measured for the first time, while the other 3 objects were observed in previous campaigns, but only had highly uncertain H$β$-lag measurements. Long-term light curves are presented of photometric $V$-band, spectroscopic 5100 Å continuum, and the H$β$ emission line, lasting for $\sim$3--6 years with a cadence of $\sim$6--14 days. Accurate H$β$ time lags ranging from $\sim$20 to 150 days in the rest frame are obtained. The estimated virial masses of the central supermassive black holes range from $\sim$(3--300)$\times10^7 M_\odot$. Combining these results with those reported in Hu et al. (2021), we now have 26 PG quasars, with representative properties, having reliable H$β$ time-lag measurements from our long-duration high-cadence campaign. A tentative fit to the relation between the H$β$ time lag and the continuum luminosity for these 26 objects gives a slope of 0.53.

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arXiv2025

Tracking the jet-like corona of black hole Swift J1727.8-1613 during a flare state through Type-C quasi-periodic oscillations

Type-C quasi-periodic oscillations (QPOs) in black hole X-ray transients typically manifest in the low-hard and hard-intermediate states. This study presents a detailed spectral and temporal analysis of the black hole candidate Swift J1727.8-1613 using NICER observations from August and September 2023, with a focus on the first flare period. We detected Type-C QPOs whose centroid frequency increased from 0.33 Hz to 2.63 Hz. An additional increase in frequency was observed when the outburst entered a flare period. The time-averaged spectra, along with the rms and phase-lag spectra of the QPOs, were jointly fitted using the time-dependent Comptonization model vkompthdk to examine the geometry of the corona during this flare. Correlations between spectral and temporal properties suggest that the detected type-C QPOs are primarily modulated by Lense-Thirring precession. Leveraging simultaneous radio observations that indicate discrete jet ejections, we proposed a scenario to describe the co-evolution of the disk-corona-jet during a flare (~3 days). This scenario is partially supported for the first time by polarization data in the soft gamma-ray band from INTEGRAL/IBIS. A phenomenological analysis of the corona scenario was also conducted.

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arXiv2025

FEASTS Combined with Interferometry. III. The Low Column Density HI Around M51 and Possibility of Turbulent-mixing Gas Accretion

With a new joint-deconvolution pipeline, we combine the single-dish and interferometric atomic hydrogen (HI) data of M51 observed by the Five-hundred-meter Aperture Spherical radio Telescope (FAST) (FEASTS program) and the Very Large Array (VLA) (THINGS). The product data cube has a typical line width of $13\,\text{km}\,\text{s}^{-1}$ and a $2σ$ line-of-sight (LOS) sensitivity of HI column density $N_\text{HI}\sim3.2\times10^{18}\,\text{cm}^{-2}$ at a spatial resolution of ${\sim}18''$ (${\sim}0.7\,\text{kpc}$). Among the HI-detected LOSs extending to ${\sim}50\,\text{kpc}$, ${\sim}89\%$ consist of diffuse HI only, which is missed by previous VLA observations. The distribution of dense HI is reproduced by previous hydrodynamical simulations of this system, but the diffuse component is not, likely due to unresolved physics related to the interaction between the circumgalactic and interstellar media. With simple models, we find that these low-$N_\text{HI}$ structures could survive the background ultraviolet photoionization, but are susceptible to the thermal evaporation. We find a positive correlation between LOS velocity dispersion ($σ_v$) and $N_\text{HI}$ with a logarithmic index of ${\sim}0.5$. Based on existing turbulent mixing layer (TML) theories and simulations, we propose a scenario of hot gas cooling and accreting onto the disk through a TML, which could reproduce the observed power index of ${\sim}0.5$. We estimate the related cooling and accretion rates to be roughly one-third to two-thirds of the star-formation rate. A typical column density of diffuse HI (${\sim}10^{19}\,\text{cm}^{-2}$) can be accreted within $300\,\text{Myr}$, the interaction time scale previously estimated for the system. Such a gas accretion channel has been overlooked before, and may be important for gas-rich interacting systems and for high redshift galaxy evolution.

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arXiv2025

Detecting Intermediate-mass Black Holes Using Quasar Microlensing

Recent studies suggest that numerous intermediate-mass black holes (IMBHs) may wander undetected across the Universe, emitting little radiation. These IMBHs largely preserve their birth masses, offering critical insights into the formation of heavy black hole seeds and the dynamical processes driving their evolution. We propose that such IMBHs could produce detectable microlensing effects on quasars. Their Einstein radii, comparable to the scale of quasar broad-line regions, magnify radiation from the accretion disk and broad emission lines, making these quasars outliers in flux scaling relations. Meanwhile, the microlensing causes long-term, quasi-linear variability that is distinguishable from the stochastic variability of quasars through its coherent multi-wavelength behavior. We develop a matched-filtering technique that effectively separates the long-term lensing signal from the intrinsic quasar variability, with sensitivity tripling each time the observational time span doubles. Moreover, as IMBHs are often surrounded by dense star clusters, their combined gravitational field produces substantial extended, concentric caustics. These caustics induce significant variability in optical, ultraviolet, and X-ray bands over decade timescales, alongside hour-to-day-scale flux fluctuations in broad emission lines. We predict a substantial number of detectable events in the upcoming surveys by the Vera C. Rubin Observatory, considering recent IMBH mass density estimates. Even in the absence of positive detections, searches for these microlensing signals will place meaningful constraints on the cosmological mass density of IMBHs, advancing our understanding of their role in cosmic evolution.

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arXiv2025

Analysis of Multi-epoch JWST Images of $\sim 300$ Little Red Dots: Tentative Detection of Variability in a Minority of Sources

James Webb Space Telescope (JWST) has revealed a population of red and compact sources at $z \gtrsim 5$ known as ``Little Red Dots'' (LRDs) that are likely active galactic nuclei (AGNs). Here we present a comprehensive study of the variability of 314 LRDs with multi-epoch JWST observations in five deep fields: UDS, GOODS-S, GOODS-N, Abell 2744, and COSMOS. Our analyses use all publicly available JWST NIRCam imaging data in these fields, together with multi-epoch JWST MIRI images available. We measure the significance (signal-to-noise ratio or ${\rm SNR}_{\rm var}$) of the variabilities for all LRDs and statistically evaluate their variabilities using the ${\rm SNR}_{\rm var}$ distributions. We pay particular attention to the systematic offsets of photometric zero points among different epochs that seem to commonly exist. The derived ${\rm SNR}_{\rm var}$ distributions of the LRDs, including those with broad H$α$/H$β$ emission lines, follow the standard Gaussian distribution, and are generally consistent with those of the comparison samples of objects detected in the same images. This finding suggests that the LRD population on average does not show strong variability, which can be explained by super-Eddington accretion of the black holes in AGNs. Alternatively, many of them may be dominated by galaxies. We also find eight strongly variable LRD candidates with variability amplitudes of 0.24 -- 0.82 mag. The rest-frame optical SEDs of these variable LRDs should have significant AGN contribution. Future JWST observations will provide more variability information of LRDs.

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arXiv2025

Connection between galaxy morphology and dark-matter halo structure I: a running threshold for thin discs and size predictors from the dark sector

We study the connection between galaxy morphology and host dark matter (DM) halo structure using cosmological simulations. Introducing a new kinematic decomposition scheme, we robustly separate thin and thick discs and measure halo properties, including cosmic web locations, internal structures, and assembly histories. In the TNG50 simulation, we find that the orbital-circularity threshold for disc differentiation varies systematically with galaxy mass and redshift. Similarly, the energy threshold between stellar halos and inner galaxies depends on mass and redshift, minimizing at sub-Galactic halo mass where the circularity threshold approaches its peak. Revisiting galaxy size predictors, we show that disc sizes in TNG50 correlate with three structural parameters beyond virial mass and redshift: 1) a positive correlation with halo spin $λ$ across redshifts -- stronger than previously reported for zoom-in simulations but still weaker than the simple $r_{1/2}/R_{\rm vir} \propto λ$ scaling; 2) an anti-correlation with DM concentration $c$; 3) larger discs in more actively accreting haloes. Disc mass fraction is higher in rounder haloes and in cosmic knots and filaments, implying that disc development needs both stable halo conditions and continuous material supply. Our methodology is public and adaptable to other simulations.

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arXiv2025

Formation and Environmental Context of Giant Bulgeless Disk Galaxies in the Early Universe: Insights from Cosmological Simulations

Giant bulgeless disk galaxies, theoretically expected to be rare in the early Universe, have been confirmed by the James Webb Space Telescope (JWST) to exist as early as 2 billion years after the Big Bang. These morphologically extreme systems offer valuable insights into the physics of disk formation and the interplay between galaxies and their dark-matter halos. Using cosmological simulations, we identify analogs of such galaxies with stellar masses around $10^{11} M_\odot$ and half-light radii up to 6 kpc at $z \sim 3$ and characterize the factors that contribute to their formation. These galaxies form in young cosmic knots, populating host halos of high spin, low concentration, and spherical shapes. They feature dynamically coherent circum-galactic medium, as well as gas-rich, coherent mergers, which preserve their disk morphology and drive their large sizes. Interestingly, all the simulated giant disks harbor a compact, aligned inner disk, marginally resolvable in JWST images with a Sérsic index near unity. These findings highlight the environmental and structural conditions necessary for forming and sustaining giant bulgeless disks and provide a theoretical framework for interpreting JWST observations of extreme disk morphologies in the early Universe.

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arXiv2025

The Origin of the Gas and Its Low Star Formation Efficiency in Quiescent Galaxies

Quiescent galaxies (QGs) typically have little cold gas to form stars. The discovery of gas-rich QGs challenges our conventional understanding of the evolutionary paths of galaxies. We take advantage of a new catalog of nearby, massive galaxies with robust, uniformly derived physical properties to better understand the origin of gas-rich QGs. We perform a comparative analysis of the cold interstellar medium and star formation properties of carefully matched samples of galaxies with varying degrees of star formation activity and gas richness. QGs with different gas content have virtually identical morphological types, light concentration, mass-size relation, stellar age, dark matter halo mass, and black hole activity. The only distinguishing characteristic is the environment. Gas-rich satellite QGs reside in a lower-density environment than their gas-poor counterparts, as a consequence of which they manage to retain their gas and experience a higher probability of cold gas accretion or gas-rich mergers. The environmental densities of central QGs are similar regardless of their gas content. We suggest that the cold gas resides mainly in the outskirts of the gas-rich QGs, where bars, if present, cannot transport it inward efficiently to fuel central star formation. The prominent bulges in gas-rich QGs stabilize the cold gas from fragmentation and leads to low star formation efficiency.

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arXiv2025

From Non-Detection to Detection: Atacama Compact Array Mosaic Observations of Faint Extended [C I] Emission in NGC 7679

We report the detection of [C I] $^3P_1$--$^3P_0$ emission in the nearby galaxy NGC 7679 using the Atacama Compact Array (ACA) of the Atacama Large Millimeter/submillimeter Array (ALMA). In Michiyama et al. (2021), [C I] $^3P_1$--$^3P_0$ emission in NGC 7679 was reported as undetected based on ACA observations conducted in 2019 (ALMA Cycle 6). These observations had ~1 minute on-source time and used a single pointing with a field of view (FoV) of ~20 arcsec. In 2023 (Cycle 9), we carried out mosaic observations using seven pointings with an FoV of ~27 arcsec and 4-5 minutes on-source per pointing. The additional data have significantly improved the line sensitivity, uv-sampling, and noise uniformity across the galaxy disk. Our Cycle 9 observations confirm the presence of extended [C I] $^3P_1$--$^3P_0$ emission in NGC 7679, which was completely missed in the Cycle 6 observations due to insufficient sensitivity and uv-sampling. This highlights the basic technical challenges of estimating the total flux by interferometric observations with sparse uv-sampling.

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arXiv2025

Multi-frequency Very Long Baseline Interferometry Study of Emission and Absorption in the Two-Sided Jets of NGC 3998

We present the multi-frequency, multi-epoch Very Long Baseline Interferometry (VLBI) study of the two-sided jets in the low-luminosity active galactic nucleus NGC 3998, where physical properties of the jets on parsec scales remain poorly understood. Using Very Long Baseline Array data observed at 1.4, 1.7, 2.3, and 5 GHz, we detect symmetric twin jets aligned along the north-south direction, with a total extent of $\sim 5.3$ pc. Notably, the position angle of the pc-scale jets differs by $26^\circ$-$30^\circ$ from that of the kpc-scale jets, suggesting the possibility of jet precession. Based on the frequency-dependent core shift and north/south jet brightness ratio, we identify the northern jet as the approaching jet and the southern jet as the counter-jet. Measurements of the radial intensity profile on both sides indicate a change in the counter-jet emission from rapid fading to a slower decline at 1.4, 1.7 and 2.3 GHz. Spectral analysis shows that the approaching jet exhibits an optically thin spectrum, while the counter-jet is dominated by an optically thick, inverted spectrum. These findings tentatively suggest free-free absorption in NGC 3998, which should be verified in future studies. Finally, our observations also reveal a flat-spectrum VLBI core, showing significant radio variability that is likely linked to a jet ejection event.

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arXiv2025

WIggle Corrector Kit for NIRSpEc Data: WICKED

The point-spread function of the integral-field unit (IFU) mode of the JWST's NIRSpec is heavily under-sampled, creating resampling noise seen as low-frequency sinusoidal-like artifacts, or "wiggles". These artifacts in the data are not corrected in the JWST data pipeline, and significantly impact the science that can be achieved at a single-pixel level. We present WICKED (WIggle Corrector Kit for NIRSpEc Data), a tool designed to empirically remove wiggles. WICKED uses the Fast Fourier Transform to identify wiggle-affected spaxels across the data cube. Spectra are modeled with a mix of integrated aperture and annular templates, a power-law, and a second-degree polynomial. The method works across all medium- and high-resolution NIRSpec gratings: F070LP, F100LP, F170LP, and F290LP. WICKED can recover the true overall spectral shape up to a factor of 3.5x better compared to uncorrected spectra. It recovers the equivalent width of absorption lines within 5% of the true value-~3x better than uncorrected spectra and ~2x better than other methods. WICKED significantly improves kinematic measurements, recovering the line-of-sight velocity (LOSV) within 1% of the true value -- more than 100x better than uncorrected spectra at S/N ~40. As a case study, we applied WICKED to G235H/F170LP IFU data of the elliptical galaxy NGC5128, finding good agreement with previous studies. In wiggle-affected regions, the uncorrected spectrum showed stellar LOSV and velocity dispersion differences compared to the WICKED-cleaned spectrum, of ~17x and ~36x larger than the estimated uncertainties, respectively. Wiggles in NIRSpec IFU data can introduce severe biases in spectral shape, line measurements, and kinematics to values larger than the typical uncertainties. WICKED provides a robust, user-friendly solution, enabling precise single-pixel studies and maximizing JWST's potential.

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arXiv2025

Temperature Profiles of Accretion Disks in Luminous Active Galactic Nuclei derived from Ultraviolet Spectroscopic Variability

The characteristic timescale ($τ$) of continuum variability of the accretion disk in active galactic nuclei (AGNs) is known to be related to the thermal timescale, which is predicted to scale with AGN luminosity ($L$) and restframe wavelength ($λ_{\rm RF}$) as $t_{\rm th} \propto L^{0.5} λ_{\rm RF}^2$ in the standard disk model. Using multi-epoch spectroscopic data from the Sloan Digital Sky Survey Reverberation Mapping project, we construct ultraviolet ensemble structure functions of luminous AGNs as a function of their luminosity and wavelength. Assuming that AGNs exhibit a single universal structure function when $Δt$ is normalized by $τ$, wherein $τ\propto L^{a} λ_{\rm RF}^{b}$, we find $a=0.50\pm0.03$ and $b=1.42\pm0.09$. While the value of $a$ aligns with the prediction from the standard disk model, $b$ is significantly smaller than expected, suggesting that the radial temperature (color) profile of the accretion disk is significantly steeper (shallower) than the standard disk model. Notably, this discrepancy with theory has been observed in previous studies based on spectroscopic reverberation mapping and gravitational microlensing. Although no current model of accretion disks fully matches our results, our findings provide valuable constraints for testing future physical models.

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arXiv2025

Quasi-periodic oscillations of GHz-band polarization in a black hole

Relativistic jets from accreting black holes (BHs) radiate non-thermal emission which is highly variable in different time scales. Magnetic fields anchored to a rotating BH or accretion disc accelerate and collimate jets of the BH systems. Previous studies on black holes of different mass scales, including supermassive and stellar-mass black holes, only report flux quasi-periodic oscillations in radio, optical, X-ray and gamma-ray bands. No quasi-periodic variations in polarization have yet been detected in any black hole systems. Here, we report the first detection of GHz radio polarization oscillations in GRS 1915+105, which harbors a spinning stellar-mass BH with a relativistic jet. Our observations show that during the increasing phase of radio emission, linear polarization and flux exhibit similar oscillation periods of $\sim 17$ and $33$ seconds, and their variation patterns anti-correlate with each other. These rare, short-period oscillations in both polarization and flux would be important to understand instabilities and special dynamics in magnetized jets.

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arXiv2025

The critical role of dark matter halos in driving star formation

Understanding the physical mechanisms that drive star formation is crucial for advancing our knowledge of galaxy evolution. We explore the interrelationships between key galaxy properties associated with star formation, with a particular focus on the impact of dark matter halos. Given the sensitivity of atomic hydrogen (HI) to external processes, we concentrate exclusively on central spiral galaxies. We find that the molecular-to-atomic gas mass ratio ($M_{\rm H_2}/M_{\rm HI}$) strongly depends on stellar mass and specific star formation rate (sSFR). In the star formation efficiency (SFE)-sSFR plane, most galaxies fall below the H$_2$ fundamental formation relation (FFR), with SFE$_{\rm HI}$ being consistently lower than SFE$_{\rm H_2}$. Using the improved halo masses derived by Zhao et al. (2025), for star-forming galaxies, both SFE$_{\rm HI}$ and $M_{\rm H_2}/M_{\rm HI}$ increase rapidly and monotonically with halo mass, indicating a higher efficiency in converting HI to H$_2$ in more massive halos. This trend ultimately leads to the unsustainable state where SFE$_{\rm HI}$ exceeds SFE$_{\rm H_2}$ at halo mass around $10^{12} \hbox{$M_{\odot}$}$. For halos with masses exceeding $10^{12} \hbox{$M_{\odot}$}$, galaxies predominantly experience quenching. We propose a plausible evolutionary scenario in which the growth of halo mass regulates the conversion of HI to H$_2$, star formation, and the eventual quenching of galaxies. The disk size, primarily regulated by the mass, spin and concentration of the dark matter halo, also significantly influences HI to H$_2$ conversion and star formation. These findings underscore the critical role of dark matter halos as a global regulator of galaxy-wide star formation, a key factor that has been largely underappreciated in previous studies.

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arXiv2025

The Convergence of Heavy and Light Seeds to Overmassive Black Holes at Cosmic Dawn

The James Webb Space Telescope (JWST) has revealed low-luminosity active galactic nuclei (AGNs) at redshifts of $z\gtrsim 4-7$, many of which host accreting massive black holes (BHs) with BH-to-galaxy mass ($M_{\rm BH}/M_{\star}$) ratios exceeding the local values by more than an order of magnitude. The origin of these overmassive BHs remains unclear but requires potential contributions from heavy seeds and/or episodes of super-Eddington accretion. We present a growth model coupled with dark matter halo assembly to explore the evolution of the $M_{\rm BH}/M_{\star}$ ratio under different seeding and feedback scenarios. Given the gas inflow rates in protogalaxies, BHs grow episodically at moderate super-Eddington rates and the mass ratio increases early on, despite significant mass loss through feedback. Regardless of seeding mechanisms, the mass ratio converges to a universal value $\sim 0.1-0.3$, set by the balance between gas feeding and star formation efficiency in the nucleus. This behavior defines an attractor in the $M_{\rm BH}-M_{\star}$ diagram, where overmassive BHs grow more slowly than their hosts, while undermassive seeds experience rapid growth before aligning with the attractor. We derive an analytical expression for the universal mass ratio, linking it to feedback strength and halo growth. The convergence of evolutionary tracks erases seeding information from the mass ratio by $z\sim 4-6$. Detecting BHs with $\sim 10^{5-6}~M_\odot$ at higher redshifts that deviate from convergence trend would provide key diagnostics of their birth conditions.

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arXiv2025

Monitoring AGNs with H$β$ Asymmetry. V. Long-term Variation and Evolution of the Broad H$β$ Emission-Line Profiles

The physical origins of the diverse emission-line asymmetries observed in the spectra of active galactic nuclei (AGNs) remain incompletely understood. Monitoring the temporal variations of line profiles offers a promising approach to investigating the underlying physics. In this study, we present an analysis of the broad H$β$ emission line profiles of eight AGNs observed from the end of 2016 to May 2023 as part of the reverberation mapping campaign titled "Monitoring AGNs with H$β$ Asymmetry" (MAHA), utilizing data obtained from the Wyoming Infrared Observatory (WIRO) 2.3-meter telescope. We measure the temporal variations of line asymmetry, width, and central velocity shift for the eight objects. Our findings reveal that the variation in asymmetry is positively correlated with H$β$ flux in five of the eight objects, while the remaining objects exhibit negative or complex correlations. Furthermore, we observe anti-correlations between line width and H$β$ flux for most objects, indicating the presence of the "breathing" phenomenon in their H$β$ emission lines. In contrast, two objects demonstrate an "anti-breathing" phenomenon or complex behavior. We discuss the physical origins of the temporal variations in line profiles and propose the possibility of decomposing the variations in H$β$ asymmetry and width into components: one that corresponds to short-term variations in H$β$ flux and another that reflects long-term variations in continuum light curves, perhaps driven by radiation pressure.

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arXiv2025

The Detection Rate of Associated \mgii\ Absorption Lines in Quasars Depends on Their Radio Emission

In active galactic nuclei, jet-driven feedback plays a significant role in influencing the properties of gas within their host galaxy and the circumgalactic medium. By combining observations from the Very Large Array Sky Survey, the Faint Images of the Radio Sky at Twenty-cm, the LOFAR Two Metre Sky Survey, and the Sloan Digital Sky Survey, we assembled a sample of 3,141 radio-loud quasars, among which 418 exhibit \mgii\ associated absorption lines in their Sloan spectra. We classify these quasars into evolutionary stages based on their radio spectral shapes. Our analysis reveals that evolved quasars exhibit a significantly higher incidence of \mgii\ associated absorption lines compared to younger sources, particularly among quasars with ``non-peaked'' radio spectra, which show an incidence of \mgii\ associated absorbers approximately 1.7 times greater than that of gigahertz-peaked spectrum sources. This observation can be explained effectively by jet-driven feedback. As quasars age, their jets expand and expel substantial amounts of gas from small scales to larger scales, ultimately reaching the circumgalactic medium. The gas expelled from the inner regions and distributed over larger scales results in a greater coverage fraction of absorbing gas. Consequently, evolved quasars exhibit a higher incidence of \mgii\ absorption lines.

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