65 research outputs found
Investigating the outskirts of Abell 133 with Suzaku and Chandra observations
Past observations and simulations predict an increasingly inhomogeneous gas
distribution towards the outskirts of galaxy clusters, but the exact properties
of such gas clumping are not yet well known. The outskirts of Abell 133 benefit
from deep X-ray observations, with a 2.4 Ms ultra-deep Chandra exposure as well
as eight archival Suzaku pointings, making it a unique laboratory to study the
clumping of the intracluster medium. We searched for significant clump
candidates, in particular aiming to identify those that could represent genuine
ICM inhomogeneity. To further understand how clumping biases the thermodynamic
profiles, we compared the measurements including and excluding the clump
candidates. We jointly analyzed Chandra and Suzaku observations of Abell 133.
We selected clump candidates with at least 2 significance based on the
Chandra image and further discussed their origins using information from the
DESI Legacy Imaging Surveys cluster catalogue, as well as the CFHT r-band
image. We performed multiple rounds of Suzaku spectral analysis with different
corrections for the underlying point sources and clump distribution, and
compared the resulting thermodynamic profiles. We detected 16 clump candidates
using Chandra, most of which are identified as background clusters or galaxies
as opposed to intrinsic inhomogeneity. Even after the correction of the
resolved clumps, the entropy profile approaching the outskirts still flattens,
deviating from the power law model expected from self-similar evolution, which
implies that unresolved clumping and other complex physics should contribute to
the entropy flattening in the outskirts.Comment: 15 pages, 13 figures, submitted to A&
The Metallicity of the Intracluster Medium Over Cosmic Time: Further Evidence for Early Enrichment
We use Chandra X-ray data to measure the metallicity of the intracluster
medium (ICM) in 245 massive galaxy clusters selected from X-ray and
Sunyaev-Zel'dovich (SZ) effect surveys, spanning redshifts .
Metallicities were measured in three different radial ranges, spanning cluster
cores through their outskirts. We explore trends in these measurements as a
function of cluster redshift, temperature, and surface brightness "peakiness"
(a proxy for gas cooling efficiency in cluster centers). The data at large
radii (0.5--1 ) are consistent with a constant metallicity, while at
intermediate radii (0.1-0.5 ) we see a late-time increase in
enrichment, consistent with the expected production and mixing of metals in
cluster cores. In cluster centers, there are strong trends of metallicity with
temperature and peakiness, reflecting enhanced metal production in the
lowest-entropy gas. Within the cool-core/sharply peaked cluster population,
there is a large intrinsic scatter in central metallicity and no overall
evolution, indicating significant astrophysical variations in the efficiency of
enrichment. The central metallicity in clusters with flat surface brightness
profiles is lower, with a smaller intrinsic scatter, but increases towards
lower redshifts. Our results are consistent with other recent measurements of
ICM metallicity as a function of redshift. They reinforce the picture implied
by observations of uniform metal distributions in the outskirts of nearby
clusters, in which most of the enrichment of the ICM takes place before cluster
formation, with significant later enrichment taking place only in cluster
centers, as the stellar populations of the central galaxies evolve.Comment: 13 pages. Accepted version, to appear in MNRA
The Physics of Galaxy Cluster Outskirts
As the largest virialized structures in the universe, galaxy clusters
continue to grow and accrete matter from the cosmic web. Due to the low gas
density in the outskirts of clusters, measurements are very challenging,
requiring extremely sensitive telescopes across the entire electromagnetic
spectrum. Observations using X-rays, the Sunyaev-Zeldovich effect, and weak
lensing and galaxy distributions from the optical band, have over the last
decade helped to unravel this exciting new frontier of cluster astrophysics,
where the infall and virialization of matter takes place. Here, we review the
current state of the art in our observational and theoretical understanding of
cluster outskirts, and discuss future prospects for exploration using newly
planned and proposed observatories.Comment: 56 pages. Review paper. Published in Space Science Review
Abundance and temperature distributions in the hot intra-cluster gas of Abell 4059
Using the EPIC and RGS data from a deep (~200 ks) XMM-Newton observation, we
investigate the temperature structure (kT and sigma_T ) and the abundances of 9
elements (O, Ne, Mg, Si, S, Ar, Ca, Fe and Ni) of the intra-cluster medium
(ICM) in the nearby (z=0.046) cool-core galaxy cluster Abell 4059. Next to a
deep analysis of the cluster core, a careful modelling of the EPIC background
allows us to build radial profiles up to 12' (~650 kpc) from the core. Probably
because of projection effects, the temperature ICM is found not to be in single
phase, even in the outer parts of the cluster. The abundances of Ne, Si, S, Ar,
Ca and Fe, but also O are peaked towards the core. Fe and O are still
significantly detected in the outermost annuli; suggesting that the enrichment
by both type Ia and core-collapse SNe started in the early stages of the
cluster formation. However, the particularly high Ca/Fe ratio that we find in
the core is not well reproduced by the standard SNe yield models. Finally, 2-D
maps of temperature and Fe abundance are presented and confirm the existence of
a denser, colder, and Fe-rich ridge southwest of the core, previously observed
by Chandra. The origin of this asymmetry in the hot gas of the cluster core is
still unclear, but might be explained by a past intense ram-pressure stripping
event near the central cD galaxy.Comment: 17 pages, 13 figures, accepted for publication in A&
The Outskirts of Abell 1795: Probing Gas Clumping in the Intra-Cluster Medium
The outskirts of galaxy clusters host complex interactions between the
intra-cluster and circumcluster media. During cluster evolution, ram-pressure
stripped gas clumps from infalling substructures break the uniformity of the
gas distribution, which may lead to observational biases at large radii.
Assessing the contribution of gas clumping, however, poses observational
challenges, and requires robust X-ray measurements in the background-dominated
regime of cluster outskirts. The aims of this work are isolating faint gas
clumps from field sources and from the diffuse emission in the Abell 1795
galaxy cluster, then probing their impact on the observed surface brightness
and thermodynamic profiles. We performed imaging analysis on deep Chandra
ACIS-I observations of the outskirts of Abell 1795, extending to
with full azimuthal coverage. We built the keV
surface brightness distribution from the adaptively binned image of the diffuse
emission and looked for clumps as outliers. Classification of the
clump candidates was based on Chandra and SDSS data. Benefiting from the
Chandra point source list, we extracted the thermodynamic profiles of the
intra-cluster medium from the associated Suzaku XIS data out to using
multiple point source and clump candidate removal approaches. We identified 24
clump candidates in the Abell 1795 field, most of which are likely associated
with background objects, including AGN, galaxies, and clusters or groups of
galaxies, as opposed to intrinsic gas clumps. These sources had minimal impact
on the surface brightness and thermodynamic profiles of the cluster emission.
After correcting for clump candidates, the measured entropy profile still
deviates from a pure gravitational collapse, suggesting complex physics at play
in the outskirts, including potential electron-ion non-equilibrium and
non-thermal pressure support.Comment: 22 pages, 14 figures, submitted to Astronomy & Astrophysic
An Atlas of Gas Motions in the TNG-Cluster Simulation: from Cluster Cores to the Outskirts
Galaxy clusters are unique laboratories for studying astrophysical processes
and their impact on gas kinematics. Despite their importance, the full
complexity of gas motion within and around clusters remains poorly known. This
paper is part of a series presenting first results from the new TNG-Cluster
simulation, a suite of 352 massive clusters including the full cosmological
context, mergers, accretion, baryonic processes, feedback, and magnetic fields.
Studying the dynamics and coherence of gas flows, we find that gas motions in
cluster cores and intermediate regions are largely balanced between inflows and
outflows, exhibiting a Gaussian distribution centered at zero velocity. In the
outskirts, even the net velocity distribution becomes asymmetric, featuring a
double peak where the second peak reflects cosmic accretion. Across all cluster
regions, the resulting net flow distribution reveals complex gas dynamics.
These are strongly correlated with halo properties: at a given total cluster
mass, unrelaxed, late-forming halos with less massive black holes and lower
accretion rates exhibit a more dynamic behavior. Our analysis shows no clear
relationship between line-of-sight and radial gas velocities, suggesting that
line-of-sight velocity alone is insufficient to distinguish between inflowing
and outflowing gas. Additional properties, such as temperature, can help break
this degeneracy. A velocity structure function (VSF) analysis indicates more
coherent gas motion in the outskirts and more disturbed kinematics towards halo
centers. In all cluster regions, the VSF shows a slope close to the theoretical
models of Kolmogorov (1/3), except within 50 kpc of the cluster cores, where
the slope is significantly steeper. The outcome of TNG-Cluster broadly aligns
with observations of the VSF of multiphase gas across different scales in
galaxy clusters, ranging from 1 kpc to Megaparsec scales.Comment: Submitted to A&A. See the TNG-Cluster website at
https://www.tng-project.org/cluster
Origin of metals in old Milky Way halo stars based on GALAH and Gaia
© 2021 The Royal Astronomical Society. This is the accepted manuscript version of an article which has been published in final form at https://doi.org/10.1093/mnras/stab1982Stellar and supernova nucleosynthesis in the first few billion years of the cosmic history have set the scene for early structure formation in the Universe, while little is known about their nature. Making use of stellar physical parameters measured by GALAH Data Release 3 with accurate astrometry from the Gaia EDR3, we have selected old main-sequence turn-off stars (ages Gyrs) with kinematics compatible with the Milky Way stellar halo population in the Solar neighborhood. Detailed homogeneous elemental abundance estimates by GALAH DR3 are compared with supernova yield models of Pop~III (zero-metal) core-collapse supernovae (CCSNe), normal (non-zero-metal) CCSNe, and Type Ia supernovae (SN Ia) to examine which of the individual yields or their combinations best reproduce the observed elemental abundance patterns for each of the old halo stars ("OHS"). We find that the observed abundances in the OHS with [Fe/H] are best explained by contributions from both CCSNe and SN~Ia, where the fraction of SN~Ia among all the metal-enriching SNe is up to 10-20 % for stars with high [Mg/Fe] ratios and up to 20-27 % for stars with low [Mg/Fe] ratios, depending on the assumption about the relative fraction of near-Chandrasekhar-mass SNe Ia progenitors. The results suggest that, in the progenitor systems of the OHS with [Fe/H], 50-60% of Fe mass originated from normal CCSNe at the earliest phases of the Milky Way formation. These results provide an insight into the birth environments of the oldest stars in the Galactic halo.Peer reviewedFinal Published versio
How do atomic code uncertainties affect abundance measurements in the intracluster medium?
Accurate chemical abundance measurements of X-ray-emitting atmospheres pervading massive galaxies, galaxy groups, and clusters provide essential information on the star formation and chemical enrichment histories of these large-scale structures. Although the collisionally ionized nature of the intracluster medium (ICM) makes these abundance measurements relatively easy, the underlying spectral models can rely on different atomic codes, which brings additional uncertainties on the inferred abundances. Here we provide a simple, yet comprehensive comparison between the codes SPEXACT v3.0.5 (cie model) and AtomDB v3.0.9 (vapec model) in the case of moderate, charged-coupled device-like resolution spectroscopy. We show that in cool plasmas (kT ≲ 2 keV), systematic differences up to ∼20% for the Fe abundance and ∼45% for the O/Fe, Mg/Fe, Si/Fe, and S/Fe ratios may still occur. Importantly, these discrepancies are also found to be instrument-dependent, at least for the absolute Fe abundance. Future improvements in these two codes will be necessary to better address questions on ICM enrichment
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