1,760 research outputs found
Exploring X-ray Binary Populations in Compact Group Galaxies with
We obtain total galaxy X-ray luminosities, , originating from
individually detected point sources in a sample of 47 galaxies in 15 compact
groups of galaxies (CGs). For the great majority of our galaxies, we find that
the detected point sources most likely are local to their associated galaxy,
and are thus extragalactic X-ray binaries (XRBs) or nuclear active galactic
nuclei (AGNs). For spiral and irregular galaxies, we find that, after
accounting for AGNs and nuclear sources, most CG galaxies are either within the
scatter of the Mineo et al. (2012) - star formation rate
(SFR) correlation or have higher than predicted by this correlation for
their SFR. We discuss how these "excesses" may be due to low metallicities and
high interaction levels. For elliptical and S0 galaxies, after accounting for
AGNs and nuclear sources, most CG galaxies are consistent with the Boroson et
al. (2011) - stellar mass correlation for low-mass XRBs, with larger
scatter, likely due to residual effects such as AGN activity or hot gas.
Assuming non-nuclear sources are low- or high-mass XRBs, we use appropriate XRB
luminosity functions to estimate the probability that stochastic effects can
lead to such extreme values. We find that, although stochastic effects do
not in general appear to be important, for some galaxies there is a significant
probability that high values can be observed due to strong XRB
variability.Comment: Accepted by Ap
Stellar Populations in Compact Galaxy Groups: a Multi-Wavelength Study of HCGs 16, 22, and 42, their Star Clusters and Dwarf Galaxies
We present a multi-wavelength analysis of three compact galaxy groups, HCGs
16, 22, and 42, which describe a sequence in terms of gas richness, from space-
(Swift, HST, Spitzer) and ground-based (LCO, CTIO) imaging and spectroscopy. We
study various signs of past interactions including a faint, dusty tidal feature
about HCG 16A, which we tentatively age-date at <1 Gyr. This represents the
possible detection of a tidal feature at the end of its phase of optical
observability. Our HST images also resolve what were thought to be double
nuclei in HCG 16C and D into multiple, distinct sources, likely to be star
clusters. Beyond our phenomenological treatment, we focus primarily on
contrasting the stellar populations across these three groups. The star
clusters show a remarkable intermediate-age population in HCG 22, and identify
the time at which star formation was quenched in HCG 42. We also search for
dwarf galaxies at accordant redshifts. The inclusion of 33 members and 27
'associates' (possible members) radically changes group dynamical masses, which
in turn may affect previous evolutionary classifications. The extended
membership paints a picture of relative isolation in HCGs 16 and 22, but shows
HCG 42 to be part of a larger structure, following a dichotomy expected from
recent studies. We conclude that (a) star cluster populations provide an
excellent metric of evolutionary state, as they can age-date the past epochs of
star formation; and (b) the extended dwarf galaxy population must be considered
in assessing the dynamical state of a compact group.Comment: 29 pages, 13 figures. Accepted for publication in The Astrophysical
Journa
A View of Point Sources in Hickson Compact Groups: High AGN fraction but a dearth of strong AGNs
We present X-ray point source catalogs for 9 Hickson Compact Groups
(HCGs, 37 galaxies) at distances Mpc. We perform detailed X-ray point
source detection and photometry, and interpret the point source population by
means of simulated hardness ratios. We thus estimate X-ray luminosities ()
for all sources, most of which are too weak for reliable spectral fitting. For
all sources, we provide catalogs with counts, count rates, power-law indices
(), hardness ratios, and , in the full ( keV), soft
( keV) and hard ( keV) bands. We use optical emission-line
ratios from the literature to re-classify 24 galaxies as star-forming,
accreting onto a supermassive black hole (AGNs), transition objects, or
low-ionization nuclear emission regions (LINERs). Two-thirds of our galaxies
have nuclear X-ray sources with /UVOT counterparts. Two nuclei have
~ erg s, are strong
multi-wavelength AGNs and follow the known correlation for strong AGNs. Otherwise, most nuclei are X-ray faint,
consistent with either a low-luminosity AGN or a nuclear X-ray binary
population, and fall in the "non-AGN locus" in space, which also hosts other, normal, galaxies. Our results suggest
that HCG X-ray nuclei in high specific star formation rate spiral galaxies are
likely dominated by star formation, while those with low specific star
formation rates in earlier types likely harbor a weak AGN. The AGN fraction in
HCG galaxies with and erg
s is , somewhat higher than the fraction
in galaxy clusters.Comment: 77 pages (emulateapj), 28 tables, 11 figures. Accepted by ApJS on
March 5, 201
Existence of global strong solutions to a beam-fluid interaction system
We study an unsteady non linear fluid-structure interaction problem which is
a simplified model to describe blood flow through viscoleastic arteries. We
consider a Newtonian incompressible two-dimensional flow described by the
Navier-Stokes equations set in an unknown domain depending on the displacement
of a structure, which itself satisfies a linear viscoelastic beam equation. The
fluid and the structure are fully coupled via interface conditions prescribing
the continuity of the velocities at the fluid-structure interface and the
action-reaction principle. We prove that strong solutions to this problem are
global-in-time. We obtain in particular that contact between the viscoleastic
wall and the bottom of the fluid cavity does not occur in finite time. To our
knowledge, this is the first occurrence of a no-contact result, but also of
existence of strong solutions globally in time, in the frame of interactions
between a viscous fluid and a deformable structure
A Kato type Theorem for the inviscid limit of the Navier-Stokes equations with a moving rigid body
The issue of the inviscid limit for the incompressible Navier-Stokes
equations when a no-slip condition is prescribed on the boundary is a famous
open problem. A result by Tosio Kato says that convergence to the Euler
equations holds true in the energy space if and only if the energy dissipation
rate of the viscous flow in a boundary layer of width proportional to the
viscosity vanishes. Of course, if one considers the motion of a solid body in
an incompressible fluid, with a no-slip condition at the interface, the issue
of the inviscid limit is as least as difficult. However it is not clear if the
additional difficulties linked to the body's dynamic make this issue more
difficult or not. In this paper we consider the motion of a rigid body in an
incompressible fluid occupying the complementary set in the space and we prove
that a Kato type condition implies the convergence of the fluid velocity and of
the body velocity as well, what seems to indicate that an answer in the case of
a fixed boundary could also bring an answer to the case where there is a moving
body in the fluid
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