29 research outputs found
Possible depletion of metals into dust grains in the core of the Centaurus cluster of galaxies
We present azimuthally averaged metal abundance profiles from a full,
comprehensive, and conservative re-analysis of the deep (800 ks total net
exposure) \textit{Chandra}/ACIS-S observation of the Centaurus cluster core
(NGC\,4696). After carefully checking various sources of systematic
uncertainties, including the choice of the spectral deprojection method,
assumptions about the temperature structure of the gas, and uncertainties in
the continuum modeling, we confirm the existence of a central drop in the
abundances of the `reactive' elements Fe, Si, S, Mg, and Ca, within
10 kpc. The same drops are also found when analyzing the
\textit{XMM-Newton}/EPIC data (150 ks). Adopting our most conservative
approach, we find that, unlike the central drops seen for Fe, Si, S, Mg and Ca,
the abundance of the `nonreactive' element Ar is fully consistent with showing
no central drop. This is further confirmed by the significant ()
central radial increase of the Ar/Fe ratio. Our results corroborate the
previously proposed `dust depletion scenario' , in which central metal
abundance drops are explained by the deposition of a significant fraction of
centrally cooled reactive metals into dust grains present in the central
regions of the Centaurus cluster. This is also supported by the previous
findings that the extent of the metal abundance drops in NGC\,4696 broadly
coincides with the infrared dust emission.Comment: Accepted for publication in A&A; 12 pages, 5 figures, 2 table
A cluster pair : A3532 and A3530
We present a detailed study of a close pair of clusters of galaxies, A3532
and A3530, and their environments. The \textit{Chandra} X-ray image of A3532
reveals presence of substructures on scales of 20 in its
core. XMM-Newton maps of the clusters show excess X-ray emission from an
overlapping region between them. Spectrally determined projected temperature
and entropy maps do not show any signs of cluster scale mergers either in the
overlapping region or in any of the clusters. In A3532, however, some signs of
the presence of galaxy scale mergers are visible e.g., anisotropic temperature
variations in the projected thermodynamic maps, a wide angled tailed (WAT)
radio source in the brighter nucleus of its dumbbell Brightest Cluster Galaxy
(BCG), and a candidate X-ray cavity coincident with the northwestern extension
of the WAT source in the low-frequency radio observations. The northwestern
extension in A3532 seems either a part of the WAT or an unrelated diffuse
source in A3532 or in the background. There is an indication that the cool core
in A3532 has been disrupted by the central AGN activity. A reanalysis of the
redshift data reinforces the close proximity of the clusters. The excess
emission in the overlapping region appears to be a result of tidal interactions
as the two clusters approach each other for the first time. However, we can not
rule out the possibility of the excess being due to the chance superposition of
their X-ray halos.Comment: Accepted for publication in the Astrophysical Journa
Dynamics of 10 clusters of galaxies with substructures
We present a detailed Chandra study of a sample of 10 clusters of galaxies selected based on the presence of substructures in their optical images. The X-ray surface brightness maps of most of these clusters show anisotropic morphologies, especially in the central regions. A total of 22 well resolved significantly bright X-ray peaks (corresponding with high-density regions) are seen in the central parts (within rc/2) of the clusters. Multiple peaks are seen in central parts of six clusters. We found 11 peaks to have optical counterparts (10 coinciding with the brightest cluster galaxies of the 10 clusters and 1 coinciding with the second brightest galaxy in A539). For most of the clusters, the optical substructures detected in the previous studies are found to be outside the field of view of Chandra. In the spectroscopically produced two-dimensional temperature maps, significantly lower temperatures are seen at the locations of three peaks (two in A539 and one in A376). The centers of five clusters in our sample also host regions of higher temperature compared to the ambient medium, indicating the presence of galaxy scale mergers. The X-ray luminosity, gas mass, and central cooling time estimates for all the clusters are presented. The radial X-ray surface-brightness profiles of all but one of the clusters are found to be best-fitted with a double-β model, pointing toward the presence of double-phased central gas due to cool cores. The cooling time estimates of all the clusters, however, indicate that none of them hosts a strong cool core, although the possibility of weak cool cores cannot be ruled out
Digging for red nuggets: Discovery of hot haloes surrounding massive, compact, relic galaxies
We present the results of Chandra X-ray observations of the isolated, massive, compact, relic galaxies MRK 1216 and PGC 032873. Compact massive galaxies observed at z > 2, also called red nuggets, formed in quick dissipative events and later grew by dry mergers into the local giant ellipticals. Due to the stochastic nature of mergers, a few of the primordial massive galaxies avoided the mergers and remained untouched over cosmic time.We find that the hot atmosphere surrounding MRK 1216 extends far beyond the stellar population and has a 0.5-7 keV X-ray luminosity of LX = (7.0 ± 0.2) × 1041 erg s-1, which is similar to the nearby X-ray bright giant ellipticals. The hot gas has a short central cooling time of ~50 Myr and the galaxy has an ~13-Gyr-old stellar population. The presence of an X-ray atmosphere with a short nominal cooling time and the lack of young stars indicate the presence of a sustained heating source, which prevented star formation since the dissipative origin of the galaxy 13 Gyr ago. The central temperature peak and the presence of radio emission in the core of the galaxy indicate that the heating source is radio-mechanical active galactic nucleus (AGN) feedback. Given that both MRK 1216 and PGC 032873 appear to have evolved in isolation, the order of magnitude difference in their current X-ray luminosity could be traced back to a difference in the ferocity of the AGN outbursts in these systems. Finally, we discuss the potential connection between the presence of hot haloes around such massive galaxies and the growth of super-/overmassive black holes via chaotic cold accretion. © 2018 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society
Cooling in the X-ray halo of the rotating, massive early-type galaxy NGC 7049
The relative importance of the physical processes shaping the thermodynamics
of the hot gas permeating rotating, massive early-type galaxies is expected to
be different from that in non-rotating systems. Here, we report the results of
the analysis of XMM-Newton data for the massive, lenticular galaxy NGC 7049.
The galaxy harbours a dusty disc of cool gas and is surrounded by an extended
hot X-ray emitting gaseous atmosphere with unusually high central entropy. The
hot gas in the plane of rotation of the cool dusty disc has a multi-temperature
structure, consistent with ongoing cooling. We conclude that the rotational
support of the hot gas is likely capable of altering the multiphase
condensation regardless of the ratio, which is here
relatively high, . However, the measured ratio of cooling time and
eddy turnover time around unity (-ratio ) implies significant
condensation, and at the same time, the constrained ratio of rotational
velocity and the velocity dispersion (turbulent Taylor number)
indicates that the condensing gas should follow non-radial orbits forming a
disc instead of filaments. This is in agreement with hydrodynamical simulations
of massive rotating galaxies predicting a similarly extended multiphase disc.Comment: 11 pages, 12 figures, accepted for publication in MNRA
Thermodynamic properties, multiphase gas, and AGN feedback in a large sample of giant ellipticals
We present a study of the thermal structure of the hot X-ray emitting
atmospheres for a sample of 49 nearby X-ray and optically bright elliptical
galaxies using {\it Chandra} X-ray data. We focus on the connection between the
properties of the hot X-ray emitting gas and the cooler H+[NII]
emitting phase, and the possible role of the latter in the AGN (Active Galactic
Nuclei) feedback cycle. We do not find evident correlations between the
H+[NII] emission and global properties such as X-ray luminosity, mass
of hot gas, and gas mass fraction. We find that the presence of H+[NII]
emission is more likely in systems with higher densities, lower entropies,
shorter cooling times, shallower entropy profiles, lower values of min(), and disturbed X-ray morphologies (linked to turbulent
motions). However, we see no clear separations in the observables obtained for
galaxies with and without optical emission line nebulae. The AGN jet powers of
the galaxies with X-ray cavities show hint of a possible weak positive
correlation with their H+[NII] luminosities. This correlation and the
observed trends in the thermodynamic properties may result from chaotic cold
accretion (CCA) powering AGN jets, as seen in some high-resolution hydrodynamic
simulations.Comment: Published in MNRA
Hot gaseous atmospheres of rotating galaxies observed with XMM-Newton
X-ray emitting atmospheres of non-rotating early-type galaxies and their
connection to central active galactic nuclei have been thoroughly studied over
the years. However, in systems with significant angular momentum, processes of
heating and cooling are likely to proceed differently. We present an analysis
of the hot atmospheres of six lenticulars and a spiral galaxy to study the
effects of angular momentum on the hot gas properties. We find an alignment
between the hot gas and the stellar distribution, with the ellipticity of the
X-ray emission generally lower than that of the optical stellar emission,
consistent with theoretical predictions for rotationally-supported hot
atmospheres. The entropy profiles of NGC 4382 and the massive spiral galaxy NGC
1961 are significantly shallower than the entropy distribution in other
galaxies, suggesting the presence of strong heating (via outflows or
compressional) in the central regions of these systems. Finally, we investigate
the thermal (in)stability of the hot atmospheres via criteria such as the TI-
and C-ratio, and discuss the possibility that the discs of cold gas present in
these objects have condensed out of the hot atmospheres.Comment: 12 pages, 11 figures, submitted to MNRA