984 research outputs found
ESO 3060170 -- a massive fossil galaxy group with a heated gas core?
We present a detailed study of the ESO 3060170 galaxy group combining
Chandra, XMM and optical observations. The system is found to be a fossil
galaxy group. The group X-ray emission is composed of a central dense cool core
(10 kpc in radius) and an isothermal medium beyond the central 10 kpc. The
region between 10 and 50 kpc (the cooling radius) has the same temperature as
the gas from 50 kpc to 400 kpc although the gas cooling time between 10 and 50
kpc (2 - 6 Gyr) is shorter than the Hubble time. Thus, the ESO 3060170 group
does not have a group-sized cooling core. We suggest that the group cooling
core may have been heated by a central AGN outburst in the past and the small
dense cool core is the truncated relic of a previous cooling core. The Chandra
observations also reveal a variety of X-ray features in the central region,
including a ``finger'', an edge-like feature and a small ``tail'', all aligned
along a north-south axis, as are the galaxy light and group galaxy
distribution. The proposed AGN outburst may cause gas ``sloshing'' around the
center and produce these asymmetric features. The observed flat temperature
profile to 1/3 R_vir is not consistent with the predicted temperature profile
in recent numerical simulations. We compare the entropy profile of the ESO
3060170 group with those of three other groups and find a flatter relation than
that predicted by simulations involving only shock heating, S r. This is direct evidence for the importance of non-gravitational
processes in group centers. We derive the mass profiles within 1/3 R_vir and
find the ESO 3060170 group is the most massive fossil group known (1 - 2 X
10 M). The M/L ratio of the system, ~ 150 at 0.3 R_vir, is
normal.Comment: 17 pages, 12 figures, to appear in ApJ. A high-resolution version can
be downloaded from http://cxc.harvard.edu/~msun/esoa.p
CHANDRA observations of the NGC 1550 galaxy group -- implication for the temperature and entropy profiles of 1 keV galaxy groups
We present a detailed \chandra study of the galaxy group NGC 1550. For its
temperature (1.370.01 keV) and velocity dispersion ( 300 km
s), the NGC 1550 group is one of the most luminous known galaxy groups
(L = 1.65 erg s within 200 kpc, or 0.2 \rv).
We find that within kpc, where the gas cooling time is less than a
Hubble time, the gas temperature decreases continuously toward the center,
implying the existence of a cooling core. The temperature also declines beyond
100 kpc (or 0.1 \rv). There is a remarkable similarity of the
temperature profile of NGC 1550 with those of two other 1 keV groups with
accurate temperature determination. The temperature begins to decline at 0.07 -
0.1 \rv, while in hot clusters the decline begins at or beyond 0.2 \rv. Thus,
there are at least some 1 keV groups that have significantly different
temperature profiles from those of hot clusters, which may reflect the role of
non-gravitational processes in ICM/IGM evolution. NGC 1550 has no isentropic
core in its entropy profile, in contrast to the predictions of `entropy-floor'
simulations. We compare the scaled entropy profiles of three 1 keV groups
(including NGC 1550) and three 2 - 3 keV groups. The scaled entropy profiles of
1 keV groups show much larger scatter than those of hotter systems, which
implies varied pre-heating levels. We also discuss the mass content of the NGC
1550 group and the abundance profile of heavy elements.Comment: emulateapj5.sty, 18 pages, 11 figures (including 4 color), to appear
in ApJ, v598, n1, 20 Nov 200
A Multi-wavelength Study of the Host Environment of SMBHB 4C+37.11
4C+37.11, at z=0.055 shows two compact radio nuclei, imaged by VLBI at 7mas
separation, making it the closest known resolved super-massive black hole
binary (SMBHB). An important question is whether this unique object is young,
caught on the way to a gravitational in-spiral and merger, or has `stalled' at
7pc. We describe new radio/optical/X-ray observations of the massive host and
its surrounding X-ray halo. These data reveal X-ray/optical channels following
the radio outflow and large scale edges in the X-ray halo. These structures are
promising targets for further study which should elucidate their relationship
to the unique SMBHB core.Comment: To appear in the Astrophysical Journa
The survival and destruction of X-ray coronae of early-type galaxies in the rich cluster environments: a case study of Abell 1367
A new Chandra observation of the northwest region of the galaxy cluster A1367
reveals four cool galaxy coronae (0.4 - 1.0 keV) embedded in the hot
intracluster medium (ICM) (5 - 6 keV). While the large coronae of NGC 3842 and
NGC 3837 appear symmetric and relaxed, the galaxy coronae of the \lsim L*
galaxies (NGC 3841 and CGCG 97090) are disturbed and being stripped. Massive
galaxies, with dense cooling cores, are better able to resist ram pressure
stripping and survive in rich environments than \lsim L* galaxies whose
galactic coronae are much less dense. The survival of these cool coronae
implies that thermal conduction from the hot surrounding ICM has to be
suppressed by a factor of at least 60, at the corona boundary. Within the
galaxy coronae of NGC 3842 and NGC 3837, stellar mass loss or heat conduction
with the Spitzer value may be sufficient to balance radiative cooling. Energy
deposition at the ends of collimated jets may heat the outer coronae, but allow
the survival of a small, dense gas core (e.g., NGC 3842 in A1367 and NGC 4874
in Coma). The survived X-ray coronae become significantly smaller and fainter
with the increasing ambient pressure.Comment: 11 pages, 7 figures, emulateapj5, accepted by Ap
Direct constraints on the dark matter self-interaction cross-section from the merging galaxy cluster 1E0657-56
We compare new maps of the hot gas, dark matter, and galaxies for 1E0657-56,
a cluster with a rare, high-velocity merger occurring nearly in the plane of
the sky. The X-ray observations reveal a bullet-like gas subcluster just
exiting the collision site. A prominent bow shock gives an estimate of the
subcluster velocity, 4500 km/s, which lies mostly in the plane of the sky. The
optical image shows that the gas lags behind the subcluster galaxies. The
weak-lensing mass map reveals a dark matter clump lying ahead of the
collisional gas bullet, but coincident with the effectively collisionless
galaxies. From these observations, one can directly estimate the cross-section
of the dark matter self-interaction. That the dark matter is not fluid-like is
seen directly in the X-ray -- lensing mass overlay; more quantitative limits
can be derived from three simple independent arguments. The most sensitive
constraint, sigma/m<1 cm^2/g, comes from the consistency of the subcluster
mass-to-light ratio with the main cluster (and universal) value, which rules
out a significant mass loss due to dark matter particle collisions. This limit
excludes most of the 0.5-5 cm^2/g interval proposed to explain the flat mass
profiles in galaxies. Our result is only an order-of-magnitude estimate which
involves a number of simplifying, but always conservative, assumptions;
stronger constraints may be derived using hydrodynamic simulations of this
cluster.Comment: Text clarified; some numbers changed slightly for consistency with
final version of the accompanying lensing paper. 6 pages, uses emulateapj.
ApJ in pres
Memory CD8(+) T Cells Provide Innate Immune Protection against Listeria monocytogenes in the Absence of Cognate Antigen
Interferon (IFN)-γ plays an important role in the innate immune response against intracellular bacterial pathogens. It is commonly thought that natural killer cells are the primary source of this cytokine that is involved in activating antibacterial effects in infected cells and polarizing CD4(+) T cells toward the Th1 subset. However, here we show that both effector and memory CD8(+) T cells have the potential to secrete IFN-γ in response to interleukin (IL)-12 and IL-18 in the absence of cognate antigen. We demonstrate that memory CD8(+) T cells specific for the ovalbumin protein secrete IFN-γ rapidly after infection with wild-type Listeria monocytogenes (LM). Furthermore, small numbers of ovalbumin-specific, memory CD8(+) T cells can reduce spleen and liver bacterial counts in IFN-γ–deficient mice 3 d after LM infection. Up-regulation of the receptors for IL-12 and IL-18 provides a mechanism for the ability of memory CD8(+) T cells to respond in this antigen nonspecific manner. Thus, CD8(+) T cells play an important role in the innate immune response against intracellular pathogens by rapidly secreting IFN-γ in response to IL-12 and IL-18
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