141 research outputs found
An environmental analysis of the fast transient AT2018cow and implications for its progenitor and late-time brightness
The nature of the newly discovered fast blue optical transients (FBOTs) is
still puzzling astronomers. In this paper we carry out a comprehensive analysis
of the molecular gas, ionized gas and stellar populations in the environment of
the nearby FBOT AT2018cow based on ALMA, VLT/MUSE and HST/WFC3 observations. A
prominent molecular concentration of 6 ( 1) 10 is
found in the vicinity of AT2018cow, which has given rise to two active
star-forming complexes with ages of 4 1 Myr and 2.5 Myr,
respectively. Each star-forming complex has a stellar mass of 3 10
and has photoionized a giant H II region with H luminosity
even comparable to that of the 30 Dor mini-starburst region. AT2018cow is
spatially coincident with one of the star-forming complexes; however, it is
most likely to reside in its foreground since it has a much smaller extinction
than the complex. Its progenitor could have been formed at an earlier epoch in
this area; if it were from a major star-forming event, the non-detection of the
associated stellar population constrains the progenitor's age to be 10
Myr and initial mass to be 20 . We further find the
late-time brightness of AT2018cow is unlikely to be a stellar object. Its
brightness has slightly declined from 2 yr to 4 yr after explosion and is most
likely to originate from AT2018cow itself due to some powering mechanism still
working at such late times.Comment: 13 pages, 10 figures, submitted to MNRA
Cooperative Open-ended Learning Framework for Zero-shot Coordination
Zero-shot coordination in cooperative artificial intelligence (AI) remains a
significant challenge, which means effectively coordinating with a wide range
of unseen partners. Previous algorithms have attempted to address this
challenge by optimizing fixed objectives within a population to improve
strategy or behaviour diversity. However, these approaches can result in a loss
of learning and an inability to cooperate with certain strategies within the
population, known as cooperative incompatibility. To address this issue, we
propose the Cooperative Open-ended LEarning (COLE) framework, which constructs
open-ended objectives in cooperative games with two players from the
perspective of graph theory to assess and identify the cooperative ability of
each strategy. We further specify the framework and propose a practical
algorithm that leverages knowledge from game theory and graph theory.
Furthermore, an analysis of the learning process of the algorithm shows that it
can efficiently overcome cooperative incompatibility. The experimental results
in the Overcooked game environment demonstrate that our method outperforms
current state-of-the-art methods when coordinating with different-level
partners. Our demo is available at https://sites.google.com/view/cole-2023.Comment: 15 pages with 9 pages main bod
Gas dynamics of a luminous = 6.13 quasar ULAS J13190950 revealed by ALMA high resolution observations
We present new Atacama Large Millimeter/submillimeter Array (ALMA)
observations of the dust continuum and [C II] 158 m fine structure line
emission towards a far-infrared-luminous quasar, ULAS J131911.29095051.4 at
, and combine the new Cycle 1 data with ALMA Cycle 0 data. The combined
data have an angular resolution , and resolve both the dust
continuum and the [C II] line emission on few kpc scales. The [C II] line
emission is more irregular than the dust continuum emission which suggests
different distributions between the dust and [C II]-emitting gas. The combined
data confirm the [C II] velocity gradient that we previously detected in lower
resolution ALMA image from Cycle 0 data alone. We apply a tilted ring model to
the [C II] velocity map to obtain a rotation curve, and constrain the circular
velocity to be 427 55 km s at a radius of 3.2 kpc with an
inclination angle of 34. We measure the dynamical mass within the 3.2
kpc region to be 13.4 . This yields
a black hole and host galaxy mass ratio of 0.020, which is
about 4 times higher than the present-day / ratio. This suggests that the supermassive black hole grows the bulk of
its mass before the formation of the most of stellar mass in this quasar host
galaxy in the early universe.Comment: 24 pages, 5 figures, accepted for publication in Ap
Observations by GMRT at 323 MHz of radio-loud quasars at
We present Giant Metrewave Radio Telescope (GMRT) 323 MHz radio continuum
observations toward 13 radio-loud quasars at , sampling the low-frequency
synchrotron emission from these objects. Among the 12 targets successfully
observed, we detected 10 above significance, while 2 remain
undetected. All of the detected sources appear as point sources. Combined with
previous radio continuum detections from the literature, 9 quasars have
power-law spectral energy distributions throughout the radio range; for some
the flux density drops with increasing frequency while it increases for others.
Two of these sources appear to have spectral turnover. For the power-law-like
sources, the power-law indices have a positive range between 0.18 and 0.67 and
a negative values between and . For the turnover sources, the
radio peaks around and GHz in the rest frame, the optically
thin indices are and , and the optically thick indices are 0.50
and 1.20. A magnetic field and spectral age analysis of SDSS
J114657.59+403708.6 at may indicate that the turnover is not caused by
synchrotron self-absorption, but rather by free-free absorption by the
high-density medium in the nuclear region. Alternatively, the apparent turnover
may be an artifact of source variability. Finally, we calculated the radio
loudness for our sample, which spans a very wide range from
12 to 4982.Comment: 13 pages; Accepted by A&
High-free Fatty Acid Treatment Induced Anti-inflammatory Changes in a Natural Killer (NK) Cell Line
Background: Natural killer (NK) cells play a role in the pathogenesis of various metabolic diseases related to obesity. While our initial findings have indicated a potential involvement of NK cells in the pathogenesis of type 2 diabetes mellitus, the precise mechanism underlying NK cell-mediated development of this form of diabetes remains inadequately comprehended.Objective: To investigate the impact and the underlying mechanism of high glucose and elevated levels of free fatty acids (FFAs) on immune and inflammatory responses and oxidative stress in NK92 cells.Methods: In this experiment, the CCK8 cytotoxicity assay was used to select the 44.4 mM and 1.5 mM concentrations of high glucose and high FFAs, respectively, to treat NK92 cells for 4 days. The concentrations of superoxide dismutase (SOD) and glutathione (GSH) were determined using a biochemical analyzer. Intracellular reactive oxygen species (ROS) levels, cytokines concentrations (TNF-α, IFN-γ, IL-6, and IL-10), and the expression levels of intracellular molecules (perforin and granzyme B) were assessed by flow cytometry.Results: The number of NK92 cell clumps was significantly reduced in the high-FFA (HF) group. In addition, the production of ROS and levels of cytokines (TNF-α, IFN-γ, IL-6, and IL-10) significantly decreased in the HF group but showed no significant change in the high-glucose (HG) group. This observation was consistent with the expression levels of perforin and granzyme B that decreased in the HF group.Conclusion: High FFAs induced morphological changes and serious damage to oxidative stress and inflammatory response in NK92 cells
The First Data Release of the Beijing-Arizona Sky Survey
The Beijing-Arizona Sky Survey (BASS) is a new wide-field legacy imaging
survey in the northern Galactic cap using the 2.3m Bok telescope. The survey
will cover about 5400 deg in the and bands, and the expected
5 depths (corrected for the Galactic extinction) in the two bands are
24.0 and 23.4 mag, respectively. BASS started observations in January 2015, and
has completed about 41% of the whole area as of July 2016. The first data
release contains both calibrated images and photometric catalogs obtained in
2015 and 2016. The depths of single-epoch images in the two bands are 23.4 and
22.9 mag, and the full depths of three epochs are about 24.1 and 23.5 mag,
respectively.Comment: 16 pages, published by A
SCUBA2 High Redshift Bright Quasar Survey: Far-infrared Properties and Weak-line Features
We present a submillimetre continuum survey ('SCUBA2 High rEdshift bRight
quasaR surveY', hereafter SHERRY) of 54 high redshift quasars at
with quasar bolometric luminosities in a range of (0.2, using the Submillimetre Common-User Bolometer
Array-2 (SCUBA2) on the James Clerk Maxwell Telescope. About 30% (16/54) of the
sources are detected with a typical 850m rms sensitivity of 1.2 (-5 mJy, at ). The new
SHERRY detections indicate far-infrared (FIR) luminosities of to , implying extreme star
formation rates of 90 to 1060 yr in the quasar host
galaxies. Compared with 25 samples, the FIR luminous quasars () are more rare at . The
optical/near-infrared (NIR) spectra of these objects show 11% (6/54) of the
sources have weak Ly, emission line features, which may relate to
different sub-phases of the central active galactic nuclei (AGNs). Our SCUBA2
survey confirms the trend reported in the literature that quasars with
submillimeter detections tend to have weaker ultraviolet (UV) emission lines
compared to quasars with nondetections. The connection between weak UV quasar
line emission and bright dust continuum emission powered by massive star
formation may suggest an early phase of AGN-galaxy evolution, in which the
broad line region is starting to develop slowly or is shielded from the central
ionization source, and has unusual properties such as weak line features or
bright FIR emission.Comment: 28 pages, 10 figures, published in Ap
The interstellar medium distribution, gas kinematics, and system dynamics of the far-infrared luminous quasar SDSS J2310+1855 at
We present ALMA sub-kpc- to kpc-scale resolution observations of the [CII],
CO(9-8), and OH\,(--) lines along with their dust continuum
emission toward the FIR luminous quasar SDSS J231038.88+185519.7 at . The [CII] brightness follows a flat distribution with a Sersic index
of 0.59. The CO(9-8) line and the dust continuum can be fit with an unresolved
nuclear component and an extended Sersic component with a Sersic index of ~1.
The dust temperature drops with distance from the center. The effective radius
of the dust continuum is smaller than that of the line emission and the dust
mass surface density, but is consistent with that of the star formation rate
surface density. The OH\,(--) line shows a P-Cygni profile
with an absorption, which may indicate an outflow with a neutral gas mass of
along the line of sight. We employed a 3D
tilted ring model to fit the [CII] and CO(9-8) data cubes. The two lines are
both rotation dominated and trace identical disk geometries and gas motions. We
decompose the circular rotation curve measured from the kinematic model fit to
the [CII] line into four matter components (black hole, stars, gas, and dark
matter). The quasar-starburst system is dominated by baryonic matter inside the
central few kiloparsecs. We constrain the black hole mass to be
; this is the first time that the
dynamical mass of a black hole has been measured at . A massive stellar
component (on the order of ) may have already existed when
the Universe was only ~0.93 Gyr old. The relations between the black hole mass
and the baryonic mass of this quasar indicate that the central supermassive
black hole may have formed before its host galaxy. [Abridged version. Please
see the full abstract in the manuscript.]Comment: Accepted for publication in A&
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