Search for: All records

Abstract The cluster environment has been shown to affect the molecular gas content of cluster members, yet a complete understanding of this often subtle effect has been hindered due to a lack of detections over the full parameter space of galaxy star formation rates (SFRs) and stellar masses. Here, we stack CO(2–1) spectra ofz ∼ 1.6 cluster galaxies to explore the average molecular gas fractions of galaxies both at lower mass (log(M_*/M_⊙) ∼ 9.6) and further below the star-forming main sequence (SFMS; ΔMS ∼ −0.9) than other literature studies; this translates to a 3σgas mass limit of  ∼7 × 10⁹M_⊙for stacked galaxies below the SFMS. We divide our sample of 54z ∼ 1.6 cluster galaxies, derived from the Spitzer Adaptation of the Red-Sequence Cluster Survey, into nine groupings, for which we recover detections in 8. The average gas content of the full cluster galaxy population is similar to coeval field galaxies matched in stellar mass and SFR. However, when further split by CO-undetected and CO-detected, we find that galaxies below the SFMS have statistically different gas fractions from the field scaling relations, spanning deficiencies to enhancements from 2σbelow to 3σabove the expected field gas fractions, respectively. These differences betweenz= 1.6 cluster and field galaxies below the SFMS are likely due to environmental processes, though further investigation of spatially resolved properties and more robust field scaling relation calibration in this parameter space are required. 

Abstract We examine the quiescent fractions of massive galaxies in sixz≳ 3 spectroscopically confirmed protoclusters in the COSMOS field, one of which is newly confirmed and presented here. We report the spectroscopic confirmation of MAGAZ3NE J100143+023021 at $z={3.122}_{-0.004}^{+0.007}$by the Massive Ancient Galaxies Atz> 3 NEar-infrared (MAGAZ3NE) survey. MAGAZ3NE J100143+023021 contains a total of 79 protocluster members (28 spectroscopic and 51 photometric). Three spectroscopically confirmed members are star-forming ultramassive galaxies (UMGs; $\log (M_{\star }/M_{\odot })$> 11), the most massive of which has $\log (M_{\star }/M_{\odot })$ $={11.15}_{-0.06}^{+0.05}$. Combining Keck/MOSFIRE spectroscopy and the COSMOS2020 photometric catalog, we use a weighted Gaussian kernel density estimator to map the protocluster and measure its total mass ${2.25}_{-0.65}^{+1.55}\times {10}^{14}{M}_{\odot }$in the dense “core” region. For each of the six COSMOS protoclusters, we compare the quiescent fraction to the status of the central UMG as star-forming or quiescent. We observe that galaxies in these protoclusters appear to obey galactic conformity: Elevated quiescent fractions are found in protoclusters withUVJ-quiescent UMGs and low quiescent fractions are found in protoclusters containingUVJstar-frming UMGs. This correlation of star formation/quiescence in UMGs and the massive galaxies nearby in these protoclusters is the first evidence for the existence of galactic conformity atz> 3. Despite disagreements over mechanisms behind conformity at low redshifts, its presence at these early cosmic times would provide strong constraints on the physics proposed to drive galactic conformity. 

Abstract We  present new high-spectral-resolution observations (R=λ/Δλ= 7000) of the filamentary nebula surrounding NGC 1275, the central galaxy of the Perseus cluster. These observations have been obtained with SITELLE, an imaging Fourier transform spectrometer installed on the Canada–France–Hawai Telescope with a field of view of $11\prime \times 11\prime$, encapsulating the entire filamentary structure of ionized gas despite its large size of 80 kpc × 50 kpc. Here, we present renewed fluxes, velocities, and velocity dispersion maps that show in great detail the kinematics of the optical nebula at [Sii]λ6716, [Sii]λ6731, [Nii]λ6584, Hα(6563 Å), and [Nii]λ6548. These maps reveal the existence of a bright flattened disk-shaped structure in the core extending tor∼10 kpc and dominated by a chaotic velocity field. This structure is located in the wake of X-ray cavities and characterized by a high mean velocity dispersion of 134 km s⁻¹. The disk-shaped structure is surrounded by an extended array of filaments spread out tor∼ 50 kpc that are 10 times fainter in flux, remarkably quiescent, and have a uniform mean velocity dispersion of 44 km s⁻¹. This stability is puzzling given that the cluster core exhibits several energetic phenomena. Based on these results, we argue that there are two mechanisms that form multiphase gas in clusters of galaxies: a first triggered in the wake of X-ray cavities leading to more turbulent multiphase gas and a second, distinct mechanism, that is gentle and leads to large-scale multiphase gas spreading throughout the core.