18 research outputs found
Streamlined Lensed Quasar Identification in Multiband Images via Ensemble Networks
Quasars experiencing strong lensing offer unique viewpoints on subjects
related to the cosmic expansion rate, the dark matter profile within the
foreground deflectors, and the quasar host galaxies. Unfortunately, identifying
them in astronomical images is challenging since they are overwhelmed by the
abundance of non-lenses. To address this, we have developed a novel approach by
ensembling cutting-edge convolutional networks (CNNs) -- for instance, ResNet,
Inception, NASNet, MobileNet, EfficientNet, and RegNet -- along with vision
transformers (ViTs) trained on realistic galaxy-quasar lens simulations based
on the Hyper Suprime-Cam (HSC) multiband images. While the individual model
exhibits remarkable performance when evaluated against the test dataset,
achieving an area under the receiver operating characteristic curve of 97.3%
and a median false positive rate of 3.6%, it struggles to generalize in real
data, indicated by numerous spurious sources picked by each classifier. A
significant improvement is achieved by averaging these CNNs and ViTs, resulting
in the impurities being downsized by factors up to 50. Subsequently, combining
the HSC images with the UKIRT, VISTA, and unWISE data, we retrieve
approximately 60 million sources as parent samples and reduce this to 892,609
after employing a photometry preselection to discover lensed quasars
with Einstein radii of arcsec. Afterward, the ensemble
classifier indicates 3080 sources with a high probability of being lenses, for
which we visually inspect, yielding 210 prevailing candidates awaiting
spectroscopic confirmation. These outcomes suggest that automated deep learning
pipelines hold great potential in effectively detecting strong lenses in vast
datasets with minimal manual visual inspection involved.Comment: Accepted for publication in the Astronomy & Astrophysics journal. 28
pages, 11 figures, and 3 tables. We welcome comments from the reade
Staring at the Shadows of Archaic Galaxies: Damped Ly and Metal Absorbers toward a Young Weak-line Quasar
We characterize the Ly halo and absorption systems toward PSO
J083+11, a unique weak-line quasar, using Gemini/GNIRS,
Magellan/FIRE, and VLT/MUSE data. Strong absorptions by hydrogen and several
metal lines (e.g., CII, MgII, and OI) are discovered in the spectrum, which
indicates the presence of: (i) a proximate sub-damped Ly (sub-DLA)
system at and (ii) a MgII absorber at . To describe the
observed damping wing signal, we model the Ly absorption with a
combination of a sub-DLA with the neutral hydrogen column density of cm and absorption from the intergalactic
medium with a neutral fraction of around 10 percent. The sub-DLA toward PSO
J083+11 has an abundance ratio of [C/O] and metallicity of
[O/H] , similar to those of low-redshift metal-poor DLAs.
These measurements suggest that the sub-DLA might truncate PSO J083+11's
proximity zone size and complicate the quasar lifetime measurement. However,
this quasar shows no sign of a Ly halo in the MUSE datacube, where the
estimated limit of surface brightness is erg
s cm arcsec at aperture size of 1 arcsecond, or equivalent
to a Ly luminosity of erg s. This non-detection,
while being only weak independent evidence on its own, is at least consistent
with a young quasar scenario, as expected for a quasar with a short accretion
timescale.Comment: 22 pages, 12 figures, and 1 table. Accepted for publication in The
Astronomical Journal. We welcome the comments from the reader. Related paper:
arXiv:2009.0778
No Redshift Evolution in the Broad Line Region Metallicity up to z=7.54: Deep NIR Spectroscopy of ULAS J1342+0928
We present deep (9 hours) Gemini-N/GNIRS near-infrared spectroscopic
observations of ULAS J1342+0928, a luminous quasar at z=7.54. Various broad
emission lines were detected, as well as the underlying continuum and iron
forests over the rest-frame wavelength 970-2930A. There is a clear trend that
higher-ionization emission lines show larger blueshifts with CIV1549 exhibiting
5510^{+240}_{-110} km s-1 blueshift with respect to the systematic redshift
from the far-infrared [CII] 158um emission line. Those high ionization lines
have wide profiles with FWHM more than 10000 km s-1. A modest blueshift of
340^{+110}_{-80} km s-1 is also seen in MgII, the lowest ionization line
identified in the spectrum. The updated MgII-based black hole mass of
M_BH=9.1_{-1.3}^{+1.4} x 10^8 M_sun and the Eddington ratio of
L_bol/L_Edd=1.1_{-0.2}^{+0.2} confirm that ULAS J1342+0928 is powered by a
massive and actively accreting black hole. There is no significant difference
in the emission line ratios such as SiIV/CIV and AlIII/CIV when compared to
lower-redshift quasars in a similar luminosity range, which suggests early
metal pollution of the broad-line-region clouds. This trend also holds for the
FeII/MgII line ratio, known as a cosmic clock that traces the iron enrichment
in the early universe. Different iron templates and continuum fitting ranges
were used to explore how the FeII/MgII measurement changes as a function of
spectral modeling. Quasars at even higher redshift or at fainter luminosity
range (L_bol<10^46 erg s-1) are needed to probe the sites of early metal
enrichment and a corresponding change in the FeII/MgII ratio.Comment: 21 pages, 8 figures, 3 tables, accepted for publication in Ap
Probing the Nature of High Redshift Weak Emission Line Quasars: A Young Quasar with a Starburst Host Galaxy
We present the discovery of PSO J083.8371+11.8482, a weak emission line
quasar with extreme star formation rate at . This quasar was selected
from Pan-STARRS1, UHS, and unWISE photometric data. Gemini/GNIRS spectroscopy
follow-up indicates a MgII-based black hole mass of
and an
Eddington ratio of , in line
with actively accreting supermassive black hole (SMBH) at . HST
imaging sets strong constraint on lens-boosting, showing no relevant effect on
the apparent emission. The quasar is also observed as a pure point-source with
no additional emission component. The broad line region (BLR) emission is
intrinsically weak and not likely caused by an intervening absorber. We found
rest-frame equivalent widths of EW(Ly+NV) Angstrom,
EW(CIV) Angstrom (3-sigma upper limit), and EW(MgII)
Angstrom. A small proximity zone size ( pMpc) indicates
a lifetime of only years from the last quasar
phase ignition. ALMA shows extended [CII] emission with a mild velocity
gradient. The inferred far-infrared luminosity
() is one of the highest
among all known quasar hosts at . Dust and [CII] emissions put a
constraint on the star formation rate of SFR
, similar to that of hyper-luminous
infrared galaxy. Considering the observed quasar lifetime and BLR formation
timescale, the weak-line profile in the quasar spectrum is most likely caused
by a BLR which is not yet fully formed rather than continuum boosting by
gravitational lensing or a soft continuum due to super-Eddington accretion.Comment: 28 pages, 16 figures, 3 tables, accepted for publication in Ap
JWST and ALMA discern the assembly of structural and obscured components in a high-redshift starburst galaxy
We present observations and analysis of the starburst, PACS-819, at z=1.45
( M), using high-resolution (;
0.8 kpc) ALMA and multi-wavelength JWST images from the COSMOS-Web program.
Dissimilar to HST/ACS images in the rest-frame UV, the redder NIRCam and MIRI
images reveal a smooth central mass concentration and spiral-like features,
atypical for such an intense starburst. Through dynamical modeling of the CO
J=5--4 emission with ALMA, PACS-819 is rotation-dominated thus has a disk-like
nature. However, kinematic anomalies in CO and asymmetric features in the bluer
JWST bands (e.g., F150W) support a more disturbed nature likely due to
interactions. The JWST imaging further enables us to map the distribution of
stellar mass and dust attenuation, thus clarifying the relationships between
different structural components, not discernable in the previous HST images.
The CO J = 5 -- 4 and FIR dust continuum emission are co-spatial with a
heavily-obscured starbursting core (<1 kpc) which is partially surrounded by
much less obscured star-forming structures including a prominent arc, possibly
a tidally-distorted dwarf galaxy, and a clump, either a sign of an ongoing
violent disk instability or a recently accreted low-mass satellite. With
spatially-resolved maps, we find a high molecular gas fraction in the central
area reaching (/) and short depletion times
( 120 Myrs) across the entire system. These
observations provide insights into the complex nature of starbursts in the
distant universe and underscore the wealth of complementary information from
high-resolution observations with both ALMA and JWST.Comment: 18 pages, 12 figures, Submitted to Ap
Uncovering a Massive z~7.65 Galaxy Hosting a Heavily Obscured Radio-Loud QSO Candidate in COSMOS-Web
In this letter, we report the discovery of the highest redshift, heavily
obscured, radio-loud QSO candidate selected using JWST NIRCam/MIRI, mid-IR,
sub-mm, and radio imaging in the COSMOS-Web field. Using multi-frequency radio
observations and mid-IR photometry, we identify a powerful, radio-loud (RL),
growing supermassive black hole (SMBH) with significant spectral steepening of
the radio SED ( mJy, ,
, ). In conjunction
with ALMA, deep ground-based observations, ancillary space-based data, and the
unprecedented resolution and sensitivity of JWST, we find no evidence of QSO
contribution to the UV/optical/NIR data and thus infer heavy amounts of
obscuration (N cm). Using the wealth of deep UV
to sub-mm photometric data, we report a singular solution photo-z of
= 7.65 and estimate an extremely massive
host-galaxy (). This
source represents the furthest known obscured RL QSO candidate, and its level
of obscuration aligns with the most representative but observationally scarce
population of QSOs at these epochs.Comment: Submitted to ApJL, Comments welcom
Detecting unresolved lensed SNe Ia in LSST using blended light curves
International audienceStrong-gravitationally lensed supernovae (LSNe) are promising probes for providing absolute distance measurements using gravitational lens time delays. Spatially unresolved LSNe offer an opportunity to enhance the sample size for precision cosmology. We predict that there will be approximately times more unresolved than resolved LSNe Ia in the Legacy Survey of Space and Time (LSST) by the Rubin Observatory. In this article, we explore the feasibility of detecting unresolved LSNe Ia from the shape of the observed blended light curves using deep learning techniques, and we find that can be detected with a simple 1D CNN using well-sampled -band light curves (with a false-positive rate of ). Even when the light curve is well-observed in only a single band among , , and , detection is still possible with false-positive rates ranging from , depending on the band. Furthermore, we demonstrate that these unresolved cases can be detected at an early stage using light curves up to days from the first observation, with well-controlled false-positive rates, providing ample opportunities for triggering follow-up observations. Additionally, we demonstrate the feasibility of time-delay estimations using solely LSST-like data of unresolved light curves, particularly for doubles, when excluding systems with low time delay and magnification ratio. However, the abundance of such systems among those unresolved in LSST poses a significant challenge. This approach holds potential utility for upcoming wide-field surveys, and overall results could significantly improve with enhanced cadence and depth in the future surveys