arXiv subjects

Shengxiu Sun

Publications and source records attributed to Shengxiu Sun.

10 recordsLinked to original sources

arXiv2026

Luminosity function of quasars at $1.0<z<3.5$ from SDSS and DESI

We present a study of the evolution of type 1 quasars at $1.0<z<3.5$, covering the peak epoch of quasar activity. The quasar evolution has been extensively explored by a variety of previous works and the derived quasar luminosity functions (QLFs) are not well consistent with each other, presumably due to the complexities introduced by different quasar selection techniques and associated completeness corrections. We use a new strategy to construct QLFs based on a library of all known quasars. We focus on a wide region of $\sim$1700 deg$^2$ and a deep field of $\sim$265 deg$^2$ that have rich spectroscopic data primarily from SDSS and DESI. We then apply traditional color cuts in the rest-frame UV/optical to select quasar candidates and use the quasar library to identify them. Our final sample consists of 62,426 quasars at $1.0<z<3.5$, with a high completeness ($\sim$96%) and a high purity ($\sim$93%) in the color selection. Simple color cuts can potentially minimize selection biases for the study of quasar evolution. We derive binned QLFs and characterize them using a double power-law model. Sample incompleteness and contamination are considered as part of the uncertainties in the calculation. Compared to previous results, our QLFs are slightly higher at the faint end, and also higher at the bright end at $2.5<z<3.5$. The QLFs suggest that the quasar evolution at $1.0 < z < 2.5$ can be well described by the pure luminosity evolution model, while at $2.5 < z < 3.5$, it can be described by either the pure luminosity evolution or the pure density evolution model.

astro-ph.GA↗

arXiv2026

Changing-Look AGNs from DESI. VI. Host Galaxies

Changing-look (CL) AGNs trace rapid changes in nuclear activity, but their connection to host galaxy properties remains unclear. We present a study of the host galaxies of 105 CL AGNs previously selected by comparing DESI and SDSS data. We apply a two-epoch spectrophotometric decomposition to the DESI and SDSS spectra of the 105 objects. Meanwhile, HSC images are used to constrain their varying AGN components and non-varying stellar population components. We find that 79 of the 105 (75.2%) CL AGN hosts are quiescent galaxies, and 31/105 (29.5%) also show post-starburst signatures. We focus on 82 CL AGNs with extended host emission in the HSC images and compare them with extended quasars at similar redshift and stellar mass. Their star formation activity, Balmer absorption, and quiescent fractions are broadly consistent with those of the comparison quasars, although post-starburst hosts are more common among the CL AGNs. Our CL AGNs with extended host emission are more often quiescent than those with compact morphology, but this difference is not apparent after matching in redshift and stellar mass. The $\mathrm{O\, \small II}$ and $\mathrm{O\, \small III}$ narrow lines show no population-wide response to the continuum and broad line changes, consistent with the slower response expected from the narrow line region. Together, these results favor changes in the central supermassive black hole accretion rate as the main origin of the CL transitions.

astro-ph.GA↗

arXiv2026

Broad Paschen lines as black hole mass tracers: A reverberation mapping calibration

Single-epoch (SE) black hole mass estimators based on rest-frame ultraviolet or optical broad lines can be limited by dust attenuation or wavelength coverage. We calibrate estimators based on broad Paschen P$\alpha$ and P$\beta$ directly against reverberation mapping (RM) masses. We obtained LBT/LUCI near-infrared spectra of 27 SDSS-RM quasars and combined them with archival Paschen measurements for AGNs with RM masses. After continuum subtraction, we measured line luminosities and full widths at half maximum (FWHMs) using multi-component and single-Gaussian profile models. We fitted $\log(M_{\rm BH}/M_\odot)=a+b\log(L/10^{41}\,{\rm erg\,s^{-1}})+c\log({\rm FWHM}/10^3\,{\rm km\,s^{-1}})$, including intrinsic scatter. The fiducial relations use photometrically corrected line luminosities and FWHMs of the combined broad profiles. For P$\alpha$, we obtain $(a,b,c)=(6.86^{+0.24}_{-0.25},0.47^{+0.11}_{-0.10},1.24^{+0.49}_{-0.48})$ with an intrinsic scatter of $0.28^{+0.08}_{-0.06}$ dex. For P$\beta$, we obtain $(7.00\pm0.24,0.48^{+0.10}_{-0.09},0.91^{+0.46}_{-0.47})$ with a scatter of $0.32^{+0.08}_{-0.06}$ dex. Relations using single-Gaussian widths, 5100 {\AA} continuum luminosities, or fixed virial slopes have scatters consistent within the uncertainties. These relations provide complementary mass estimators when ultraviolet or optical broad lines are attenuated or unavailable. They should be applied within the parameter ranges of the calibration sample and remain subject to the systematic uncertainty associated with the RM virial factor.

astro-ph.GA↗

arXiv2026

Quiescent Host Galaxies of Extended Quasars Revealed by Spectrophotometric Decomposition

Previous works of low-redshift quasar host galaxies have focused on compact quasars and found that their host galaxies are mainly star-forming galaxies. Here we present a study of host galaxies for quasars with extended morphologies in ground-based optical images. We select a sample of more than 1000 type 1 quasars at redshift $0.1<z<1$ that are classified as extended objects by DESI. Combining high-resolution spectra from DESI and high-quality images from Subaru HSC, we develop a spectrophotometric decomposition technique to iteratively decompose each quasar into an AGN component and its host galaxy. The technique can effectively break the degeneracy between the AGN and host components and capture the host spectral features. Our results show that the host galaxies of most quasars have low star-formation rates (SFRs) and low specific SFRs, indicating that they are quiescent galaxies. Many of them exhibit prominent post-starburst features with the existence of significant old stellar populations. These properties are quite different from the nature of compact quasars with star-forming host galaxies. In addition, the relation between the black hole mass and stellar mass for our sample is broadly consistent with the canonical local relations. This work is complementary to the previous studies and suggests that the host galaxies of low-redshift quasars are more diverse than what was thought.

astro-ph.GA↗

arXiv2026

A Rare Eddington-Limited, Heavily Obscured Low-Mass Active Galactic Nucleus Likely Triggered by a Galaxy Merger

We report a detailed analysis of GAMA 376183, a powerful, heavily obscured active galactic nucleus (AGN) hosted by a low-mass galaxy ($M_\star \approx 10^{10}~M_{\odot}$) likely experiencing a galaxy merger. The source was initially identified due to its remarkably strong [Ne v] $\lambda3426$ emission, exhibiting a rest-frame equivalent width (EW) of $\approx 48$ A. We present $\sim100$ ks Nuclear Spectroscopic Telescope Array follow-up observations, confirming its heavily obscured nature with a column density (in $\mathrm{cm^{-2}}$) of $\log N_\mathrm{H} = 23.3^{+0.4}_{-1.2}$ and an intrinsic $2$--$10$ keV luminosity (in $\mathrm{erg~s^{-1}}$) of $\log L_\mathrm{X,int} = 42.92^{+0.24}_{-0.20}$. GAMA 376183 thus represents one of the few known heavily obscured AGNs in low-mass galaxies. Its estimated Eddington ratio is $\lambda_\mathrm{Edd}\approx0.8$, indicative of rapid black-hole growth. High-resolution optical images reveal a disturbed, likely merging morphology, while its multiwavelength spectral energy distribution indicates a recent starburst in its host galaxy. These pieces of evidence suggest that the ongoing merger has triggered both the heavily obscured, Eddington-limited accretion and the starburst, making GAMA 376183 a rare observed case in low-mass galaxies. Overall, this unique source demonstrates that (i) [Ne v] can help identify heavily obscured low-mass AGNs, and (ii) the merger-driven coevolution framework established for massive galaxies may also extend to low-mass galaxies.

astro-ph.GA↗

arXiv2026

COSMOS-3D: Black Hole Mass Estimators and Luminosity Functions of Paschen-line AGNs

Near-IR Paschen lines are potentially an excellent tracer of Type 1 AGNs that is hardly affected by dust extinction. JWST allows us, for the first time, to explore Paschen-line objects at redshift z>1. Here we present a study of 62 AGNs with broad Pa$\alpha$ and Pa$\beta$ lines at 1<z<3 using data from the JWST COSMOS-3D program. These AGNs are efficiently selected and identified using NIRCam imaging and grism slitless spectroscopic data. We separate the AGN-host emission with image decomposition and quantify dust attenuation with multi-band data. We construct a calibration sample with optical spectroscopy and use single-epoch, Mg II-based black hole masses ($M_{\mathrm{BH}}$) as an anchor to derive new, Paschen-based $M_{\mathrm{BH}}$ estimators. We obtain three sets of $M_{\mathrm{BH}}$ estimators based on Paschen line luminosities and AGN continuum luminosities at 1 and 2 $\mu$m, respectively. After dust corrections, they are well consistent with each other, and also broadly agree with previous results. With this AGN sample, we further construct the first Pa$\alpha$ and Pa$\beta$ luminosity functions (LFs) of Type 1 AGNs. The derived LFs are 3-5 times higher than those of UV/optical-selected AGNs, indicating that Paschen-selected Type 1 AGNs are more complete. In addition, the intrinsic properties of our AGNs show no dependence on dust reddening, suggesting that the observed reddening is unrelated to the central engine and is thus likely caused by line-of-sight obscuration.

astro-ph.GA↗

arXiv2025

Changing-look Active Galactic Nuclei from the Dark Energy Spectroscopic Instrument. IV. Broad Emission Line Evolution Sequence Among H{\alpha}, Mg II, and H{\beta}

From a parent catalog of 561 changing-look active galactic nuclei (CL-AGNs) identified by Guo et al. (2025), we investigate the evolutionary sequence of broad emission lines using a redshift-selected subset (0.35 < z < 0.45) of 54 CL-AGNs whose Dark Energy Spectroscopic Instrument (DESI) spectra simultaneously cover the H{\alpha}, H\b{eta}, and Mg II emission lines. To provide a baseline for comparison, we construct a control sample of 19,897 normal Type 1 AGNs within the same redshift range from the DESI Year 1 data. Through stacked spectral analysis and line-continuum luminosity correlations, we identify a clear evolutionary sequence in all AGN where broad H\b{eta} fades first, followed by Mg II, and then H{\alpha}, as the AGN luminosity declines - consistent with expectations from reverberation mapping. This trend reflects a radially stratified broad line region (BLR), where each line's responsivity depends on its ionization potential and radial distance from the central engine. In addition, we find that more massive supermassive black holes (SMBHs) require lower Eddington ratios to fully suppress broad emission lines, suggesting that the critical accretion threshold for the CL phenomenon is mass-dependent. Our results present the first statistical confirmation of a stratified broad line fading sequence in AGNs, reinforcing the central role of accretion state in shaping BLR structure and visibility.

astro-ph.GA↗

arXiv2025

Estimating Bolometric Luminosities of Type 1 Quasars with Self-Organizing Maps

We present a new method to calculate bolometric luminosities for unobscured, type 1 quasars with multi-band photometric data. Bolometric luminosity is a fundamental property to understand quasars and it is commonly estimated from monochromatic luminosities using bolometric corrections that often neglect quasar SED diversity. We take advantage of the fact that most quasars now have multi-band observations from UV to mid-IR, and construct SEDs for a well-defined sample of SDSS quasars at $0.5\leq z\leq 2$. Based on this fiducial sample, we explore quasar SEDs, their diversity, and their relations with bolometric luminosities. We then use unsupervised neural network self-organizing maps (SOM) to describe the SED diversity and compute the bolometric luminosities with a fully-trained SOM model. This method reduces systematical uncertainties compared to the traditional method. In addition, we update the multi-linear regression relations between bolometric luminosity and monochromatic luminosities at restframe 1450\r{A}, 3000\r{A}, and 5100\r{A}. Our method is applicable to large quasar samples with a wide range of luminosity and redshift. We have applied it to the SDSS DR16 quasars. We have also made our code publicly available.

astro-ph.CO↗

arXiv2025

Iron-corrected Single-epoch Black Hole Masses of DESI Quasars at low redshift

We present a study on the possible overestimation of single-epoch supermassive black hole (SMBH) masses in previous works, based on more than 55,000 type 1 quasars at $0.25 < z < 0.8$ from the Dark Energy Spectroscopic Instrument (DESI). We confirm that iron emission strength serves as a good tracer of the Eddington ratio, and estimate SMBH masses using an iron-corrected $R$-$L$ relation for H$\beta$, where $R$ is the broad line region size and $L$ is the continuum luminosity. Compared to our measurements, previous canonical measurements without the iron correction are overestimated by a factor of 1.5 on average. The overestimation can be up to a factor of 5 for super-Eddington quasars. The fraction of super-Eddington quasars in our sample is about 5%, significantly higher than 0.4% derived from the canonical measurements. Using a sample featuring both H$\beta$ and MgII emission lines, we calibrate MgII-based SMBH masses using iron-corrected, H$\beta$-based SMBH masses and establish an iron-corrected $R$-$L$ relation for MgII. The new relation adds an extra term of $-0.34R_{\mathrm{Fe}}$ to the $R$-$L$ relation, where $R_{\mathrm{Fe}}$ denotes the relative iron strength. We use this formula to build a catalog of about 0.5 million DESI quasars at $0.6<z<1.6$. If these iron-corrected $R$-$L$ relations for H$\beta$ and MgII are valid at high redshift, current mass measurements of luminous quasars at $z\ge6$ would have been overestimated by a factor of 2.3 on average, alleviating the tension between SMBH mass and growth history in the early universe.

astro-ph.GA↗

arXiv2025

AGN ruled out as the dominant source of cosmic reionization

Cosmic reionization represents the latest phase transition in the Universe, when the Lyman continuum (LyC) photons turned the intergalactic medium (IGM) from neutral to highly ionized. It has long been debated whether galaxies or active galactic nuclei (AGNs) are the major source of LyC photons responsible for reionization. Previous observations slightly favored galaxies as the major ionizing source. However, the James Webb Space Telescope (JWST) recently discovered an unexpectedly high density of AGN candidates at high redshift, which has largely enhanced the influence of AGNs. Here we derive a definitive upper bound on the AGN contribution to reionization using the latest JWST data, and conclusively rule out AGNs as the dominant ionizing source during the peak epoch of reionization (EoR). We build a sample of galaxies and AGNs in a specific redshift range $7.15 \leq z \leq 7.75$ with a high completeness. Each object is then decomposed into a point-source component and an extended component in their rest-frame far-UV JWST images. We assume all point-source components are AGNs. Our fiducial AGN sample reaches an unprecedentedly low luminosity of $M_{\rm UV} \approx -15$ mag. Based on this sample, AGNs can contribute at most one third of the LyC photons budget required at $z\sim7.5$. Our result implies that galaxies dominate the ionizing source during the EoR.

astro-ph.GA↗