Using ∼5000 spectroscopically-confirmed galaxies drawn from the Observations of Redshift Evolution in Large Scale Environments (ORELSE) survey we investigate the relationship between color and galaxy density for galaxy populations of various stellar masses in the redshift range 0.55 ≤ z ≤ 1.4. The fraction of galaxies with colors consistent with no ongoing star formation ( f q ) is broadly observed to increase with increasing stellar mass, increasing galaxy density, and decreasing redshift, with clear differences observed in f q between field and group/cluster galaxies at the highest redshifts studied. We use a semi-empirical model to generate a suite of mock group/cluster galaxies unaffected by environmentally-specific processes and compare these galaxies at fixed stellar mass and redshift to observed populations to constrain the efficiency of environmentally-driven quenching (Ψ convert ). High-density environments from 0.55 ≤ z ≤ 1.4 appear capable of efficiently quenching galaxies with log(M * /M ⊙ ) > 10.45. Lower stellar mass galaxies also appear efficiently quenched at the lowest redshifts studied here, but this quenching efficiency is seen to drop precipitously with increasing redshift. Quenching efficiencies, combined with simulated group/cluster accretion histories and results on the star formation rate-density relation from a companion ORELSE study, are used to constrain the average time from group/cluster accretion to quiescence and the elapsed time between accretion and the inception of the quenching event. These timescales were constrained to be t convert = 2.4 ± 0.3 and t delay = 1.3 ± 0.4 Gyr, respectively, for galaxies with log(M * /M ⊙ ) > 10.45 and t convert = 3.3 ± 0.3 and t delay = 2.2 ± 0.4 Gyr for lower stellar mass galaxies. These quenching efficiencies and associated timescales are used to rule out certain environmental mechanisms as being the primary processes responsible for transforming the star-formation properties of galaxies over this 4 Gyr window in cosmic time.
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 (10 10.1 < M * /M < 10 10.8 ) wherein the median SFR at the highest densities is 0.2 − 0.3 dex less than at lower densities at a significance of 4σ. Interestingly, mass does not drive SFR; galaxies that are more/less massive have SFRs that vary at most by ≈ 20% across all environments showing no statistically significant dependence. We further split galaxies into low-redshift (z ∼ 0.8) and high-redshift (z ∼ 1.05) subsamples and observe nearly identical behavior. We devise a simple toy model to explore possible star-formation histories (SFHs) 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 timescales (SFR ∝ e −t/τ ): a long−τ timescale with τ = 4 Gyr to simulate "normal" star-forming galaxies, and a short−τ timescale 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 halos and/or cluster infall regions. formation in galaxies and how this changes over cosmic history. Efforts over the past several decades have found that there is no simple solution to these questions, but have instead revealed that there are many nuances that govern this aspect of galaxy evolution. This has led many investigators to take a reductionist approach to the subject by studying
The Observations of Redshift Evolution in Large Scale Environments (ORELSE) survey is an ongoing imaging and spectroscopic campaign initially designed to study the effects of environment on galaxy evolution in high-redshift (z ∼ 1) large-scale structures. We use its rich data in combination with a powerful new technique, Voronoi tessellation Monte-Carlo (VMC) mapping, to search for serendipitous galaxy overdensities at 0.55 < z < 1.37 within 15 ORELSE fields, a combined spectroscopic footprint of ∼1.4 square degrees. Through extensive tests with both observational data and our own mock galaxy catalogs, we optimize the method's many free parameters to maximize its efficacy for general overdensity searches. Our overdensity search yielded 402 new overdensity candidates with precisely measured redshifts and an unprecedented sensitivity down to low total overdensity masses (M tot > ∼ 5 × 10 13 M ). Using the mock catalogs, we estimated the purity and completeness of our overdensity catalog as a function of redshift, total mass, and spectroscopic redshift fraction, finding impressive levels of both 0.92/0.83 and 0.60/0.49 for purity/completeness at z = 0.8 and z = 1.2, respectively, for all overdensity masses at spectroscopic fractions of ∼20%. With VMC mapping, we are able to measure precise systemic redshifts, provide an estimate of the total gravitating mass, and maintain high levels of purity and completeness at z ∼ 1 even with only moderate levels of spectroscopy. Other methods (e.g., red-sequence overdensities and hot medium reliant detections) begin to fail at similar redshifts, which attests to VMC mapping's potential to be a powerful tool for current and future wide-field galaxy evolution surveys at z ∼ 1 and beyond. 1 The particular type of i filter curve will differ from field to field, e.g., I + (equivalent to SDSS i ) or Cousins I , and some fields have multiple i-bands available. This is also true for the r-and z-bands used. For the sake of simplicity in this paper, we will refer to all variants of these bands by their the redshift of the targeted large-scale structure was greater than 0.95), a magnitude range that encompasses nearly all high-quality ORELSE objects. Every field's detection limit is fainter than 24.5, so our magnitude cut homogenizes the completeness statistics for all fields. Optical/Near-infrared Imaging and Photometry
We present a study of interstellar comet 2I/2019 Q4 (Borisov) using both preperihelion and postperihelion observations spanning late September 2019 through late January 2020. The intrinsic brightness of the comet was observed to continuously decline throughout the timespan, not due to the phase effect but the decreasing effective scattering cross-section as a result of volatile sublimation with a slope of −0.43 ± 0.02 km 2 d −1 . Given the measurement uncertainties, we witnessed no change in the slightly reddish colour of the comet, with mean values of g − r = 0.68 ± 0.04, r − i = 0.23 ± 0.03, and the normalised reflectivity gradient across the g and i bands S (g, i) = (10.6 ± 1.4) % per 10 3 Å, all unremarkable in the context of solar system comets. Using the available astrometric observations, we have a statistically confident detection of the nongravitational acceleration of the comet, implying that the nucleus is most likely 0.4 km in radius, and that a fraction of 0.4% of the total nucleus in mass has been eroded due to the sublimation activity since the earliest observation of the comet in 2018 December by the time of perihelion. Our morphology simulation suggests that the dust ejection speed increased from ∼4 m s −1 in 2019 September to ∼7 m s −1 around perihelion for the optically dominant dust grains of β ∼ 0.01, and that the observable dust grains are no smaller than micron size.
In this study we investigate 179 radio-IR galaxies drawn from a sample of spectroscopically-confirmed galaxies that are detected in radio and mid-infrared (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 in the total IR luminosity (f AGN ), and estimate the AGN luminosity (L AGN ) and the star formation rate (SFR) using the CIGALE Spectral Energy Distribution (SED) fitting routine. Based on the f AGN and radio luminosity, radio-IR galaxies are split into: galaxies that host either high or low f AGN AGN (high-/lowf AGN ), and star forming galaxies with little to no AGN activity (SFGs). We study the colour, stellar mass, radio luminosity, L AGN and SFR properties of the three radio-IR sub-samples, comparing to a spec-IR sample drawn from spectroscopically-confirmed galaxies that are also detected in MIR. No significant difference between radio luminosity of these sub-samples was found, which could be due to the combined contribution of radio emission from AGN and star formation. We find a positive relationship between L AGN 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 timescale 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.
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