分类： 天文学 >> 天文学 提交时间： 2023-02-19
Yuming Fu
Xue-Bing Wu
Linhua Jiang
Yanxia Zhang
Zhi-Ying Huo
Y. L. Ai
Qian Yang
Qinchun Ma
Xiaotong Feng
Ravi Joshi
Wei Jeat Hon
Christian Wolf
Jiang-Tao Li
Junjie Jin
Su Yao
Yuxuan Pang
Jian-Guo Wang
Kai-Xing Lu
Chuan-Jun Wang
Jie Zheng
摘要： Quasars behind the Galactic plane (GPQs) are important astrometric references and valuable probes of Galactic gas, yet the search for GPQs is difficult due to severe extinction and source crowding in the Galactic plane. In this paper, we present a sample of 204 spectroscopically confirmed GPQs at |b|<20{\deg}, 191 of which are new discoveries. This GPQ sample covers a wide redshift range from 0.069 to 4.487. For the subset of 230 observed GPQ candidates, the lower limit of the purity of quasars is 85.2%, and the lower limit of the fraction of stellar contaminants is 6.1%. Using a multicomponent spectral fitting, we measure the emission line and continuum flux of the GPQs, and estimate their single-epoch virial black hole masses. Due to selection effects raised from Galactic extinction and target magnitude, these GPQs have higher black hole masses and continuum luminosities in comparison to the SDSS DR7 quasar sample. The spectral-fitting results and black hole mass estimates are compiled into a main spectral catalog, and an extended spectral catalog of GPQs. The successful identifications prove the reliability of both our GPQ selection methods and the GPQ candidate catalog, shedding light on the astrometric and astrophysical programs that make use of a large sample of GPQs in the future.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We present a catalog of 1.4 million photometrically-selected quasar
candidates in the southern hemisphere over the $\sim 5000\,{\rm deg^2}$ Dark
Energy Survey (DES) wide survey area. We combine optical photometry from the
DES second data release (DR2) with available near-infrared (NIR) and the
all-sky unWISE mid-infrared photometry in the selection. We build models of
quasars, galaxies, and stars with multivariate Skew-t distributions in the
multi-dimensional space of relative fluxes as functions of redshift (or color
for stars) and magnitude. Our selection algorithm assigns probabilities for
quasars, galaxies, and stars, and simultaneously calculates photometric
redshifts (photo-$z$) for quasar and galaxy candidates. Benchmarking on
spectroscopically confirmed objects, we successfully classify (with photometry)
94.7% of quasars, 99.3% of galaxies, and 96.3% of stars when all IR bands (NIR
$YJHK$ and WISE $W1W2$) are available. The classification and photo-$z$
regression success rates decrease when fewer bands are available. Our quasar
(galaxy) photo-$z$ quality, defined as the fraction of objects with the
difference between the photo-$z$ $z_p$ and the spectroscopic redshift $z_s$,
$|\Delta z| = |z_s - z_p|/(1 + z_s)\le 0.1$, is 92.2% (98.1%) when all IR bands
are available, decreasing to 72.2% (90.0%) using optical DES data only. Our
photometric quasar catalog achieves estimated completeness of 89% and purity of
79% at $r<21.5$ (0.68 million quasar candidates), with reduced completeness and
purity at $21.5
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Grisha Zeltyn
Benny Trakhtenbrot
Michael Eracleous
Jessie Runnoe
Jonathan R. Trump
Jonathan Stern
Yue Shen
Lorena Hernandez-Garcia
Franz E. Bauer
Qian Yang
Tom Dwelly
Claudio Ricci
Paul Green
Scott F. Anderson
Roberto J. Assef
Muryel Guolo
Chelsea MacLeod
Megan C. Davis
Logan Fries
Suvi Gezari
摘要： We report the discovery of a new ``changing-look'' active galactic nucleus (CLAGN) event, in the quasar SDSS J162829.17+432948.5 at z=0.2603, identified through repeat spectroscopy from the fifth Sloan Digital Sky Survey (SDSS-V). Optical photometry taken during 2020--2021 shows a dramatic dimming of ${\Delta}$g${\approx}$1 mag, followed by a rapid recovery on a timescale of several months, with the ${\lesssim}$2 month period of rebrightening captured in new SDSS-V and Las Cumbres Observatory spectroscopy. This is one of the fastest CLAGN transitions observed to date. Archival observations suggest that the object experienced a much more gradual dimming over the period of 2011--2013. Our spectroscopy shows that the photometric changes were accompanied by dramatic variations in the quasar-like continuum and broad-line emission. The excellent agreement between the pre- and postdip photometric and spectroscopic appearances of the source, as well as the fact that the dimmest spectra can be reproduced by applying a single extinction law to the brighter spectral states, favor a variable line-of-sight obscuration as the driver of the observed transitions. Such an interpretation faces several theoretical challenges, and thus an alternative accretion-driven scenario cannot be excluded. The recent events observed in this quasar highlight the importance of spectroscopic monitoring of large active galactic nucleus samples on weeks-to-months timescales, which the SDSS-V is designed to achieve.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Logan B. Fries
Jonathan R. Trump
Megan C. Davis
C. J. Grier
Yue Shen
Scott F. Anderson
Tom Dwelly
Michael Eracleous
Y. Homayouni
Keith Horne
Mirko Krumpe
Sean Morrison
Jessie C. Runnoe
Benny Trakhtenbrot
Roberto J. Assef
W. N. Brandt
Joel Brownstein
Collin Dabbieri
Alexander Fix
Gloria Fonseca Alvarez
摘要： We present a high-cadence multi-epoch analysis of dramatic variability of three broad emission lines (MgII, H$\beta$, and H$\alpha$) in the spectra of the luminous quasar ($\lambda L_{\lambda}$(5100\r{A}) = $4.7 \times 10^{44}$ erg s$^{-1}$) SDSS J141041.25+531849.0 at $z = 0.359$ with 127 spectroscopic epochs over 9 years of monitoring (2013-2022). We observe anti-correlations between the broad emission-line widths and flux in all three emission lines, indicating that all three broad emission lines "breathe" in response to stochastic continuum variations. We also observe dramatic radial velocity shifts in all three broad emission lines, ranging from $\Delta{v}$ $\sim$400 km s$^{-1}$ to $\sim$800 km s$^{-1}$, that vary over the course of the monitoring period. Our preferred explanation for the broad-line variability is complex kinematics in the broad-line region gas. We suggest a model for the broad-line variability that includes a combination of gas inflow with a radial gradient, an azimuthal asymmetry (e.g., a hot spot), superimposed on the stochastic flux-driven changes to the optimal emission region ("line breathing"). Similar instances of line-profile variability due to complex gas kinematics around quasars are likely to represent an important source of false positives in radial velocity searches for binary black holes, which typically lack the kind of high-cadence data we analyze here. The long-duration, wide-field, and many-epoch spectroscopic monitoring of SDSS-V BHM-RM provides an excellent opportunity for identifying and characterizing broad emission-line variability, and the inferred nature of the inner gas environment, of luminous quasars.
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