212 research outputs found
IDCS J1426.5+3508: The Most Massive Galaxy Cluster at
We present a deep (100 ks) Chandra observation of IDCS J1426.5+3508, a
spectroscopically confirmed, infrared-selected galaxy cluster at .
This cluster is the most massive galaxy cluster currently known at ,
based on existing Sunyaev-Zel'dovich (SZ) and gravitational lensing detections.
We confirm this high mass via a variety of X-ray scaling relations, including
-M, -M, -M and -M, finding a tight distribution of masses
from these different methods, spanning M = 2.3-3.3
M, with the low-scatter -based mass M. IDCS J1426.5+3508 is currently the
only cluster at for which X-ray, SZ and gravitational lensing mass
estimates exist, and these are in remarkably good agreement. We find a
relatively tight distribution of the gas-to-total mass ratio, employing total
masses from all of the aforementioned indicators, with values ranging from
= 0.087-0.12. We do not detect metals in the intracluster medium
(ICM) of this system, placing a 2 upper limit of . This upper limit on the metallicity suggests that this system may
still be in the process of enriching its ICM. The cluster has a dense,
low-entropy core, offset by 30 kpc from the X-ray centroid, which makes
it one of the few "cool core" clusters discovered at , and the first
known cool core cluster at . The offset of this core from the
large-scale centroid suggests that this cluster has had a relatively recent
(500 Myr) merger/interaction with another massive system.Comment: Minor changes to match accepted version, results unchanged; ApJ in
pres
Spectroscopic survey of faint planetary-nebula nuclei. I. Six new "O VI" central stars
We report initial results from an ongoing spectroscopic survey of central
stars of faint planetary nebulae (PNe), obtained with the Low-Resolution
Spectrograph on the Hobby-Eberly Telescope. The six PN nuclei (PNNi) discussed
here all have strong emission at the O VI 3811-3834 A doublet, indicative of
very high temperatures. Five of them--the nuclei of Ou 2, Kn 61, Kn 15, Abell
72, and Kn 130--belong to the hydrogen-deficient PG 1159 class, showing a
strong absorption feature of He II and C IV at 4650-4690 A. Based on
exploratory comparisons with synthetic model-atmosphere spectra, and the
presence of Ne VIII emission lines, we estimate them to have effective
temperatures of order 170,000 K. The central star of Kn 15 has a
Wolf-Rayet-like spectrum, with strong and broad emission lines of He II, C IV,
N V, and O V-VI. We classify it [WO2], but we note that the N V 4604-4620 A
emission doublet is extremely strong, indicating a relatively high nitrogen
abundance. Several of the emission lines in Kn 15 vary in equivalent width by
factors as large as 1.5 among our four observations from 2019 to 2022, implying
significant variations in the stellar mass-loss rate. We encourage
spectroscopic monitoring. Follow-up high-time-resolution photometry of these
stars would be of interest, given the large fraction of pulsating variables
seen among PG 1159 and [WO] PNNi.Comment: Accepted by MNRA
The Massive Distant Clusters of WISE Survey: The First Distant Galaxy Cluster Discovered by WISE
We present spectroscopic confirmation of a z=0.99 galaxy cluster discovered
using data from the Wide-field Infrared Survey Explorer (WISE). This is the
first z~1 cluster candidate from the Massive Distant Clusters of WISE Survey
(MaDCoWS) to be confirmed. It was selected as an overdensity of probable z>~1
sources using a combination of WISE and SDSS-DR8 photometric catalogs. Deeper
follow-up imaging data from Subaru and WIYN reveal the cluster to be a rich
system of galaxies, and multi-object spectroscopic observations from Keck
confirm five cluster members at z=0.99. The detection and confirmation of this
cluster represents a first step towards constructing a uniformly-selected
sample of distant, high-mass galaxy clusters over the full extragalactic sky
using WISE data.Comment: 6 pages, 5 figures, ApJL Accepte
Star Formation and AGN Activity in Galaxy Clusters from : a Multi-wavelength Analysis Featuring /PACS
We present a detailed, multi-wavelength study of star formation (SF) and AGN
activity in 11 near-infrared (IR) selected, spectroscopically confirmed,
massive () galaxy clusters at . Using
new, deep /PACS imaging, we characterize the optical to far-IR
spectral energy distributions (SEDs) for IR-luminous cluster galaxies, finding
that they can, on average, be well described by field galaxy templates.
Identification and decomposition of AGN through SED fittings allows us to
include the contribution to cluster SF from AGN host galaxies. We quantify the
star-forming fraction, dust-obscured SF rates (SFRs), and specific-SFRs for
cluster galaxies as a function of cluster-centric radius and redshift. In good
agreement with previous studies, we find that SF in cluster galaxies at
is largely consistent with field galaxies at similar epochs,
indicating an era before significant quenching in the cluster cores
(Mpc). This is followed by a transition to lower SF activity as
environmental quenching dominates by . Enhanced SFRs are found in lower
mass () cluster galaxies. We
find significant variation in SF from cluster-to-cluster within our uniformly
selected sample, indicating that caution should be taken when evaluating
individual clusters. We examine AGN in clusters from , finding an
excess AGN fraction at , suggesting environmental triggering of AGN
during this epoch. We argue that our results a transition from field-like
to quenched SF, enhanced SF in lower mass galaxies in the cluster cores, and
excess AGN are consistent with a co-evolution between SF and AGN in
clusters and an increased merger rate in massive haloes at high redshift.Comment: 26 pages, 14 figures, 6 tables with appendix, accepted for
publication in the Astrophysical Journa
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