Abstract
Long-period comet C/2018 F4 (PANSTARRS) was observed to show duplicity of its inner region in 2020 September, suggestive of a splitting event. We here present analyses of our observations of ...the comet taken from the LCO Outbursting Objects Key project and the University of Hawaii 2.2 m telescope after the discovery of the splitting. The two fragments Components A and B, estimated to be ∼60 m to 4 km in radius, remained highly similar to each other in terms of brightness, color, and dust morphology throughout our observing campaign from 2020 September to 2021 December. Our fragmentation model yielded that the two components split at a relative speed of 3.00 ± 0.18 m s
−1
in 2020 late April, implying a specific energy change of
5.3
±
2.8
×
10
3
J kg
−1
, and that Component B was subjected to a stronger nongravitational acceleration than Component A in both the radial and normal directions of the orbit. The obtained splitting time is broadly consistent with the result from the dust morphology analysis, which further suggested that the dominant dust grains were millimeter-sized and ejected at a speed of ∼2 m s
−1
. We postulate that the pre-split nucleus of the comet consisted of two lobes resembling that of 67P, or that the comet used to be a binary system like main-belt comet 288P. Regardless, we highlight the possibility of using observations of split comets as a feasible manner to study the bilobate shape or binarity fraction of cometary nuclei.
ABSTRACT
In this study, we investigate 179 radio-infrared (IR) galaxies drawn from a sample of spectroscopically confirmed galaxies, which are detected in radio and mid-IR (MIR) in the redshift range ...of 0.55 ≤ z ≤ 1.30 in the Observations of Redshift Evolution in Large Scale Environments (ORELSE) survey. We constrain the active galactic nuclei (AGN) contribution to the total IR luminosity (fAGN), and estimate the AGN luminosity (LAGN) and the star formation rate (SFR). Based on the fAGN and radio luminosity, radio–IR galaxies are split into galaxies that host either high- or low-fAGN AGN (high-/low-fAGN), and star-forming galaxies (SFGs) with little to no AGN activity. We study the properties of the three radio–IR sub-samples comparing to an underlying parent sample. In the comparison of radio luminosity of three sub-samples, no significant difference was found, which could be due to the combined contribution of radio emission from AGN and star formation. We find a positive relationship between LAGN and specific SFR (sSFR) for both AGN sub-samples, strongly suggesting a co-evolution scenario of AGN and SF in these galaxies. A toy model is designed to demonstrate this co-evolution scenario, where we find that, in almost all cases, a rapid quenching time-scale is required, which we argue is a signature of AGN quenching. The environmental preference for intermediate/infall regions of clusters/groups remains across the co-evolution scenario, which suggests that galaxies might be in an orbital motion around the cluster/group during the scenario.
Abstract
Radio active galactic nuclei (RAGNs) are mainly found in dense structures (i.e., clusters/groups) at redshifts of
z
< 2 and are commonly used to detect protoclusters at higher redshift. ...Here, we attempt to study the host and environmental properties of two relatively faint (
L
1.4 GHz
∼ 10
25
W Hz
−1
) RAGNs in a known protocluster at
z
= 3.3 in the PCl J0227-0421 field, detected using the latest radio observation obtained as part of the Observations of Redshift Evolution in Large-Scale Environments (ORELSE) survey. Using new spectroscopic observations obtained from the Keck/Multi-Object Spectrometer for Infra-Red Exploration as part of the Charting Cluster Construction with the VIMOS Ultra-Deep Survey (VUDS) and ORELSE (C3VO) survey and previous spectroscopic data obtained as part of the VIMOS-Very Large Telescope Deep Survey and VUDS, we revise the three-dimensional overdensity field around this protocluster. The protocluster is embedded in a large-scale overdensity protostructure. This protostructure has an estimated total mass of ∼2.6 × 10
15
M
⊙
and contains several overdensity peaks. Both RAGNs are hosted by very bright and massive galaxies, while their hosts show extreme differences in color, indicating that they are of different ages and are in different evolutionary stages. Furthermore, we find that they are not in the most locally dense parts of the protostructure, but are fairly close to the centers of their parent overdensity peaks. We propose a scenario where merging might have already happened in both cases, which lowered the local density of their surrounding area and boosted their stellar mass. This work is the first time that two RAGNs at low luminosity have been found and studied within a high-redshift protostructure.
Abstract
We attempt to detect a signal of Yarkovsky-related acceleration in the orbits of 134 main belt asteroids (MBAs) we observed with the University of Hawai’i 88 inch telescope, supplemented ...with observations publicly available from the Minor Planet Center and Gaia Data Release 3. We estimated the expected Yarkovsky acceleration values based on parameters derived through thermophysical modeling, but we were not able to find any reliable detections of Yarkovsky in our sample. Through tests with synthetic observations, however, we estimated the minimum observational arc length needed to detect the Yarkovsky effect for all of our sample MBAs, which in nearly every case exceeded the current arc length of the existing observations. We find that the Yarkovsky effect could be detectable within a couple of decades of discovery for a 100 m MBA assuming 0.″1 astrometric accuracy, which is at the size range detectable by the upcoming Vera Rubin Observatory Legacy Survey of Space and Time.
Abstract
We present a study of the star formation rate (SFR)–density relation at $z$ ∼ 0.9 using data drawn from the Observations of Redshift Evolution in Large Scale Environments (ORELSE) survey. We ...find that SFR does depend on environment, but only for intermediate-stellar mass galaxies (1010.1 < M*/M⊙ < 1010.8) wherein the median SFR at the highest densities is 0.2–0.3 dex less than at lower densities at a significance of 4σ. Galaxies that are more/less massive than this have SFRs that vary at most by ${\approx }20{{\ \rm per\ cent}}$ across all environments, but show no statistically significant trend. We further split galaxies into low-redshift ($z$ ∼ 0.8) and high-redshift ($z$ ∼ 1.05) subsamples and observe nearly identical behaviour. We devise a simple toy model to explore possible star formation histories for galaxies evolving between these redshifts. The key assumption in this model is that star-forming galaxies in a given environment-stellar mass bin can be described as a superposition of two exponential time-scales (SFR ∝ e−t/τ): a long−τ time-scale with τ = 4 Gyr to simulate ‘normal’ star-forming galaxies, and a short-τ time-scale with free τ (between 0.3 ≤ τ/Gyr ≤ 2) to simulate galaxies on a quenching trajectory. In general, we find that galaxies residing in low/high environmental densities are more heavily weighted to the long-τ/short-τ pathways, respectively, which we argue is a signature of environmental quenching. Furthermore, for intermediate-stellar mass galaxies this transition begins at intermediate-density environments suggesting that environmental quenching is relevant in group-like haloes and/or cluster infall regions.
Recent hydrodynamic simulations and observations of radio jets have shown that the surrounding environment has a large effect on their resulting morphology. To investigate this, we use a sample of 50 ...Extended Radio Active Galactic Nuclei (ERAGN) detected in the Observations of Redshift Evolution in Large-Scale Environments survey. These sources are all successfully cross-identified to galaxies within a redshift range of 0.55 ≤ z ≤ 1.35, either through spectroscopic redshifts or accurate photometric redshifts. We find that ERAGN are more compact in high-density environments than those in low-density environments at a significance level of 4.5 . Among a series of internal properties under our scrutiny, only the radio power demonstrates a positive correlation with their spatial extent. After removing the possible radio power effect, the difference of size in low- and high-density environments persists. In the global environment analyses, the majority (86%) of high-density ERAGN reside in the cluster/group environment. In addition, ERAGN in the cluster/group central regions are preferentially compact with a small scatter in size, compared to those in the cluster/group intermediate regions and fields. In conclusion, our data appear to support the interpretation that the dense intracluster gas in the central regions of galaxy clusters plays a major role in confining the spatial extent of radio jets.
Sigma-1 receptor (Sig-1R) functions as a chaperon that interacts with multiple proteins and lipids and is implicated in neurodegenerative and psychiatric diseases. Here, we used Sig-1R KO mice to ...examine brain expression profiles of astrocytes and ubiquitinated proteins, which are both hallmarks of central nervous system (CNS) pathologies. Our results showed that Sig-1R KO induces increased glial fibrillary acidic protein (GFAP) expression in primary neuron-glia cultures and in the whole brain of fetus mice with concomitantly increased accumulations of ubiquitinated proteins. Astrogliosis was also observed in the neuron-glia culture. Upon proteasome or autophagy inhibitor treatments, the pronounced ubiquitinated proteins were further increased in Sig-1R KO neurons, indicating that the Sig-1R regulates both protein degradation and quality control systems. We found that Nrf2 (nuclear factor erythroid 2-related factor 2), which functions to overcome the stress condition, was enhanced in the Sig-1R KO systems especially when cells were under stressful conditions. Mutation or deficiency of Sig-1Rs has been observed in neurodegenerative models. Our study identifies the critical roles of Sig-1R in CNS homeostasis and supports the idea that functional complementation pathways are triggered in the Sig-1R KO pathology.
Whether statin use can reduce the risk of heart failure (HF) remains controversial. The present study evaluates the association between statin use and HF in patients with atrial fibrillation.
...Patients with newly diagnosed atrial fibrillation from 2010 to 2018 were included. An inverse probability of treatment weighting was used to balance baseline covariates between statin users (n=23 239) and statin nonusers (n=29 251). The primary outcome was incident HF. Cox proportional hazard models with competing risk regression were used to evaluate the risk of HF between statin users and nonusers. The median age of the cohort was 74.7 years, and 47.3% were women. Over a median follow-up of 5.1 years, incident HF occurred in 3673 (15.8%) statin users and 5595 (19.1%) statin nonusers. Statin use was associated with a 19% lower risk of HF (adjusted subdistribution hazard ratio, 0.81 95% CI, 0.78-0.85). Restricted to the statin users, duration of statin use was measured during follow-up; compared with short-term use (3 months to <2 years), there was a stepwise reduction in the risk of incident HF among those with 2 to <4 years of statin use (subdistribution hazard ratio, 0.86 95% CI, 0.84-0.88), 4 to <6 years of statin use (subdistribution hazard ratio, 0.74 95% CI, 0.72-0.76), and ≥6 years of statin use (subdistribution hazard ratio, 0.71 95% CI, 0.69-0.74). Subgroup analysis showed consistent reductions in the risk of HF with statin use.
Statin use was associated with a decreased risk of incident HF in a duration-dependent manner among patients with atrial fibrillation.
The Yarkovsky effect is a phenomenon that arises from an anisotropy in an asteroid's surface temperature distribution and resulting thermal emission that induces a secular change on the asteroid's ...semimajor axis, causing the asteroid to drift outwards or inwards in its orbit. It is the main mechanism by which the near-Earth asteroid population is maintained, where main belt asteroids (MBAs) are continuously moved into powerful resonances that eject them into near-Earth orbits. Despite hundreds of successful detection among near-Earth asteroids (NEAs), the Yarkovsky effect has never been detected in MBAs before. The Yarkovsky effect is difficult to predict as it relies on several physical parameters that are often completely unconstrained, but these parameters can be derived by way of thermophysical modeling. Using thermal flux measurements obtained by the Wide-field Infrared Survey Explorer (WISE) combined with shape models and spin information from the Database of Asteroid Models from Inversion Techniques (DAMIT), we obtained newly derived diameters, albedos, and thermal inertia for nearly 2000, primarily main belt, asteroids. With the parameters in hand, we were able to use a rudimentary Yarkovsky model to estimate the acceleration imparted to each of our asteroids. We attempted to confirm our predictions with the University of Hawai'i 88-inch telescope, where we observed a total of 135 MBAs and two NEAs in order to supplement the astrometric data drawn from the Minor Planet Center. Using the OrbFit software package to compute our asteroids' orbits, we found Yarkovsky signal strengths consistent with previous studies for our two NEAs. However, we were unable to find any reliable detections of Yarkovsky in our sample of MBAs due to the limitations of the historical astrometric data. Through tests with synthetic observations, we were able to identify the minimum observational arc length with modern astrometric accuracy needed to detect Yarkovsky for not only all of our sample MBAs, but also any theoretical MBA of a given size and semimajor axis, estimating that Yarkovsky should be detectable within a couple of decades for a 100-m MBA, a size range which should be detectable by the near-future Vera Rubin Observatory Legacy Survey of Space and Time. While current technology is not yet at a sufficient level to detect Yarkovsky in the main belt, the future is promising, especially with the gamut of upcoming infrared and wide-field surveys that will enable even more thermophysical modeling of higher precision in the future.
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