1,681 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
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
Some Like It Hot: Linking Diffuse X-ray Luminosity, Baryonic Mass, and Star Formation Rate in Compact Groups of Galaxies
We present an analysis of the diffuse X-ray emission in 19 compact groups of
galaxies (CGs) observed with Chandra. The hottest, most X-ray luminous CGs
agree well with the galaxy cluster X-ray scaling relations in and
, even in CGs where the hot gas is associated with only the
brightest galaxy. Using Spitzer photometry, we compute stellar masses and
classify HCGs 19, 22, 40, and 42 and RSCGs 32, 44, and 86 as fossil groups
using a new definition for fossil systems that includes a broader range of
masses. We find that CGs with total stellar and HI masses
M are often X-ray luminous, while lower-mass CGs only sometimes exhibit
faint, localized X-ray emission. Additionally, we compare the diffuse X-ray
luminosity against both the total UV and 24 m star formation rates of each
CG and optical colors of the most massive galaxy in each of the CGs. The most
X-ray luminous CGs have the lowest star formation rates, likely because there
is no cold gas available for star formation, either because the majority of the
baryons in these CGs are in stars or the X-ray halo, or due to gas stripping
from the galaxies in CGs with hot halos. Finally, the optical colors that trace
recent star formation histories of the most massive group galaxies do not
correlate with the X-ray luminosities of the CGs, indicating that perhaps the
current state of the X-ray halos is independent of the recent history of
stellar mass assembly in the most massive galaxies.Comment: 20 pages, 7 figures, accepted for publication in Ap
NASA follow-on to the Bangladesh Agro-Climatic Environmental Monitoring Project
The NASA responsibility and activities for the follow-on to the original Agro-Climatic Environmental Monitoring Project (ACEMP) which was completed during 1987 is described. Five training sessions which comprise the NASA ACEMP follow-on are: Agrometeorology, Meteorology of Severe Storms Using GEMPAK, Satellite Oceanography, Hydrology, and Meteorology with TOVS. The objective of the follow-on is to train Bangladesh Government staff in the use of satellite data for remote sensing applications. This activity also encourages the scientific connection between NASA/Goddard Space Flight Center and The Bangladesh Space and Remote Sensing Organization (SPARRSO)
Global Properties of Neutral Hydrogen in Compact Groups
Compact groups of galaxies provide a unique environment to study the
evolution of galaxies amid frequent gravitational encounters. These nearby
groups have conditions similar to those in the earlier universe when galaxies
were assembled and give us the opportunity to witness hierarchical formation in
progress. To understand how the compact group environment affects galaxy
evolution, we examine the gas and dust in these groups. We present new
single-dish GBT neutral hydrogen (HI) observations of 30 compact groups and
define a new way to quantify the group HI content as the HI-to-stellar mass
ratio of the group as a whole. We compare the HI content with mid-IR indicators
of star formation and optical [g-r] color to search for correlations between
group gas content and star formation activity of individual group members.
Quiescent galaxies tend to live in HI-poor groups, and galaxies with active
star formation are more commonly found in HI-rich groups. Intriguingly, we also
find "rogue" galaxies whose star formation does not correlate with group HI
content. In particular, we identify three galaxies (NGC 2968 in RSCG 34, KUG
1131+202A in RSCG 42, and NGC 4613 in RSCG 64) whose mid-IR activity is
discrepant with the HI. We speculate that this mismatch between mid-IR activity
and HI content is a consequence of strong interactions in this environment that
can strip HI from galaxies and abruptly affect star-formation. Ultimately,
characterizing how and on what timescales the gas is processed in compact
groups will help us understand the interstellar medium in complex, dense
environments similar to the earlier Universe.Comment: Accepted to A
High-resolution sub-millimetre diameter side-viewing all-optical ultrasound transducer based on a single dual-clad optical fibre
All-optical ultrasound (OpUS), where ultrasound is both generated and received using light, has emerged as a modality well-suited to highly miniaturised applications. In this work we present a proof-of-concept OpUS transducer built onto a single optical fibre with a highly miniaturised lateral dimension (0.4 MPa and a corresponding bandwidth >27 MHz. Concurrent ultrasound generation and reception from the transducer enabled imaging via motorised pull-back allowing image acquisition times of 4 s for an aperture of 20 mm. Image resolution was as low as ~50 µm and 190 µm in the axial and lateral extents, respectively, without the need for image reconstruction. Porcine aorta was imaged ex vivo demonstrating detailed ultrasound images. The unprecedented level of miniaturisation along with the high image quality produced by this device represents a radical new paradigm for minimally invasive imaging
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
Dual-modality fibre optic probe for simultaneous ablation and ultrasound imaging
All-optical ultrasound (OpUS) is an emerging high resolution imaging paradigm utilising optical fibres. This allows both therapeutic and imaging modalities to be integrated into devices with dimensions small enough for minimally invasive surgical applications. Here we report a dual-modality fibre optic probe that synchronously performs laser ablation and real-time all-optical ultrasound imaging for ablation monitoring. The device comprises three optical fibres: one each for transmission and reception of ultrasound, and one for the delivery of laser light for ablation. The total device diameter is < 1 mm. Ablation monitoring was carried out on porcine liver and heart tissue ex vivo with ablation depth tracked using all-optical M-mode ultrasound imaging and lesion boundary identification using a segmentation algorithm. Ablation depths up to 2.1 mm were visualised with a good correspondence between the ultrasound depth measurements and visual inspection of the lesions using stereomicroscopy. This work demonstrates the potential for OpUS probes to guide minimally invasive ablation procedures in real time
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