1,184 research outputs found
XMM-Newton Witness of M86 X-ray Metamorphosis
The environmental influence of cluster media on its member galaxies, known as
Butcher--Oemler effect, has recently been subject to revision due to numerous
observations of strong morphological transformations occurring outside the
cluster virial radii, caused by some unidentified gas removal processes. In
this context we present new XMM-Newton observations of M86 group. The unique
combination of high spatial and spectral resolution and large field of view of
XMM-Newton allows an in-depth investigation of the processes involved in the
spectacular disruption of this object. We identify a possible shock with Mach
number of ~1.4 in the process of crushing the galaxy in the North-East
direction. The latter is ascribed to the presence of a dense X-ray emitting
filament, previously revealed in the RASS data. The shock is not associated
with other previously identified features of M86 X-ray emission, such as the
plume, the north-eastern arm and the southern extension, which are found to
have low entropy, similar to the inner 2 kpc of M86. Finally, mere existence of
the large scale gas halo around the M86 group, suggests that the disruptions of
M86's X-ray halo may be caused by small-scale types of interactions such as
galaxy-galaxy collisions.Comment: 11 pages, A&A in pres
Metallicity structure in X-ray bright galaxy groups
Using Chandra X-ray data of a sample of 15 X-ray bright galaxy groups, we
present preliminary results of a coherent study of the radial distribution of
metal abundances in the hot gas in groups. The iron content in group outskirts
is found to be lower than in clusters by a factor of ~2, despite showing mean
levels in the central regions comparable to those of clusters. The abundance
profiles are used to constrain the contribution from supernovae type Ia and II
to the chemical enrichment and thermal energy of the intragroup medium at
different group radii. The results suggest a scenario in which a substantial
fraction of the chemical enrichment of groups took place in filaments prior to
group collapse.Comment: 5 pages, 2 figures. To appear in the proceedings of ESO Astrophysics
Symposia: "Groups of Galaxies in the Nearby Universe", eds. I. Saviane, V.
Ivanov, J. Burissova (Springer
Clustering of X-Ray-Selected AGN
The study of the angular and spatial structure of the X-ray sky has been
under investigation since the times of the Einstein X-ray Observatory. This
topic has fascinated more than two generations of scientists and slowly
unveiled an unexpected scenario regarding the consequences of the angular and
spatial distribution of X-ray sources. It was first established from the
clustering of sources making the CXB that the source spatial distribution
resembles that of optical QSO. It then it became evident that the distribution
of X-ray AGN in the Universe was strongly reflecting that of Dark Matter. In
particular one of the key result is that X-ray AGN are hosted by Dark Matter
Halos of mass similar to that of galaxy groups. This result, together with
model predictions, has lead to the hypothesis that galaxy mergers may
constitute the main AGN triggering mechanism. However detailed analysis of
observational data, acquired with modern telescopes, and the use of the new
Halo Occupation formalism has revealed that the triggering of an AGN could also
be attributed to phenomena like tidal disruption or disk instability, and to
galaxy evolution. This paper reviews results from 1988 to 2011 in the field of
X-ray selected AGN clustering.Comment: 19 pages, 4 Figures, review paper published on Advances in Astronomy
Special Issue "Seeking for the Leading Actor on the Cosmic Stage: Galaxies
versus Supermassive Black Holes", v2, final versio
Clustering of gamma-ray selected 2LAC Fermi Blazars
We present the first measurement of the projected correlation function of 485
gamma-ray selected Blazars, divided in 175 BLLacertae (BL Lacs) and 310 Flat
Spectrum Radio Quasars (FSRQs) detected in the 2-year all-sky survey by
Fermi-Large Area Telescope. We find that Fermi BL Lacs and FSRQs reside in
massive dark matter halos (DMHs) with logMh=13.35+0.20/-0.14 and logMh =
13.40+0.15/-0.19 Msun/h, respectively, at low (z=0.4) and high (z =1.2)
redshift. In terms of clustering properties, these results suggest that BL Lacs
and FSRQs are similar objects residing in the same dense environment typical of
galaxy groups, despite their different spectral energy distribution, power and
accretion rate. We find no difference in the typical bias and hosting halo mass
between Fermi Blazars and radio-loud AGN, supporting the unifcation scheme
simply equating radio-loud objects with misaligned Blazar counterparts. This
similarity in terms of typical environment they preferentially live in,
suggests that Blazars preferentially occupy the centre of DMHs, as already
pointed out for radio-loud AGN. This implies, in light of several projects
looking for the gamma-ray emission from DM annihilation in galaxy clusters, a
strong contamination from Blazars to the expected signal from DM annihilation.Comment: Accepted for publication in The Astrophysical Journa
X-ray Evidence for Spectroscopic Diversity of Type Ia Supernovae: XMM observation of the elemental abundance pattern in M87
We present the results of a detailed element abundance study of hot gas in
M87, observed by XMM-Newton. We choose two radial bins, 1'-3' and 8'-16'
(8'-14' for EMOS; hereafter the central and the outer zones), where the
temperature is almost constant, to carry out the detailed abundance
measurements of O, Ne, Mg, Si, S, Ar, Ca, Fe and Ni using EPIC-PN (EPN) and
-MOS (EMOS) data. First, we find that the element abundance pattern in the
central compared to the outer zone in M87 is characterized by SN Ia enrichment
of a high (roughly solar) ratio of Si-group elements (Si, S, Ar, Ca) to Fe,
implying that Si burning in SN Ia is highly incomplete. In nucleosynthesis
modeling this is associated with either a lower density of the
deflagration-detonation transition and/or lower C/O and/or lower central
ignition density and observationally detected as optically subluminous SNe Ia
in early-type galaxies. Second, we find that SN Ia enrichment has a
systematically lower ratio of the Si-group elements to Fe by 0.2 dex in the
outer zone associated with the ICM of the Virgo cluster. We find that such a
ratio and even lower values by another 0.1 dex are a characteristic of the ICM
in many clusters using observed Si:S:Fe ratios as found with ASCA. Third, the
Ni/Fe ratio in the central zone of M87 is 1.5+/-0.3 solar (meteoritic), while
values around 3 times solar are reported for other clusters. In modeling of SN
Ia, this implies a reduced influence of fast deflagration SN Ia models in the
chemical enrichment of M87's ISM. Thus, to describe the SN Ia metal enrichment
in clusters, both deflagration as well as delayed detonation scenarios are
required, supporting a similar conclusion, derived from optical studies on SNe
Ia. Abridged.Comment: 11 pages, A&A, in pres
Details of the mass--temperature relation for clusters of galaxies
We present results on the total mass and temperature determination using two
samples of clusters of galaxies. One sample is constructed with emphasis on the
completeness of the sample, while the advantage of the other is the use of the
temperature profiles, derived with ASCA. We obtain remarkably similar fits to
the M-T relation for both samples, with the normalization and the slope
significantly different from both prediction of self-similar collapse and
hydrodynamical simulations. We discuss the origin of these discrepancies and
also combine the X-ray mass with velocity dispersion measurements to provide a
comparison with high-resolution dark matter simulations. Finally, we discuss
the importance of a cluster formation epoch in the observed M-T relation.Comment: 12 pages, A&A 2001 in pres
XMM-Newton discovery of an X-ray filament in Coma
XMM-Newton observations of the outskirts of the Coma cluster of galaxies
confirm the existence of a soft X-ray excess claimed previously and show it
comes from warm thermal emission. Our data provide a robust estimate of its
temperature (~0.2 keV) and oxygen abundance (~0.1 solar). Using a combination
of XMM-Newton and ROSAT All-Sky Survey data, we rule out a Galactic origin of
the soft X-ray emission. Associating this emission with a 20 Mpc region in
front of Coma, seen in the skewness of its galaxy velocity distribution, yields
an estimate of the density of the warm gas of ~50 f_baryon rho_critical, where
f_baryon is the baryon fraction of the gas and rho_critical is the critical
density needed to halt the expansion of the universe. Our measurement of the
gas mass associated with the warm emission strongly support its nonvirialized
nature, suggesting that we are observing the warm-hot intergalactic medium
(WHIM). Our measurements provide a direct estimate of the O, Ne and Fe
abundance of the WHIM. Differences with the reported Ne/O ratio for some OVI
absorbers hints at a different origin of the OVI absorbers and the Coma
filament. We argue that the Coma filament has likely been preheated, but at a
substantially lower level compared to what is seen in the outskirts of groups.
The thermodynamic state of the gas in the Coma filament reduces the
star-formation rate in the embedded spiral galaxies, providing an explanation
for the presence of passive spirals observed in this and other clusters.Comment: 9 pages, 5 figures, accepted by A&
Temperature and abundance profiles of hot gas in galaxy groups - I. Results and statistical analysis
The distribution of metals in groups of galaxies holds important information
about the chemical enrichment history of the Universe. Here we present radial
profiles of temperature and the abundance of iron and silicon of the hot
intragroup medium for a sample of 15 nearby groups of galaxies observed by
Chandra, selected for their regular X-ray morphology. All but one group display
a cool core, the size of which is found to correlate with the mean temperature
of the group derived outside this core. When scaled to this mean temperature,
the temperature profiles are remarkably similar, being analogous to those of
more massive clusters at large radii but significantly flatter inwards of the
temperature peak. The Fe abundance generally shows a central excess followed by
a radial decline, reaching a typical value of 0.1 solar within r_500, a factor
of two lower than corresponding results for clusters. Si shows less systematic
radial variation, on average displaying a less pronounced decline than Fe and
showing evidence for a flattening at large radii. Off-centre abundance peaks
are seen both for Fe and Si in a number of groups with well-resolved cores.
Derived abundance ratios indicate that supernovae type Ia are responsible for
80 per cent of the Fe in the group core, but the type II contribution increases
with radius and completely dominates at r_500. We present fitting formulae for
the radial dependence of temperature and abundances, to facilitate comparison
to results of numerical simulations of group formation and evolution. In a
companion paper, we discuss the implications of these results for feedback and
enrichment in galaxy groups.Comment: 21 pages, 11 figures, accepted for publication in MNRA
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