567 research outputs found
Diamonds on the Hat: Globular Clusters in The Sombrero Galaxy (M104)
Images from the HST ACS are used to carry out a new photometric study of the
globular clusters (GCs) in M104, the Sombrero galaxy. The primary focus of our
study is the characteristic distribution function of linear sizes (SDF) of the
GCs. We measure the effective radii for 652 clusters with PSF-convolved King
and Wilson dynamical model fits. The SDF is remarkably similar to those
measured for other large galaxies of all types, adding strong support to the
view that it is a "universal" feature of globular cluster systems.
We develop a more general interpretation of the size distribution function
for globular clusters, proposing that the shape of the SDF that we see today
for GCs is strongly influenced by the early rapid mass loss during their star
forming stage, coupled with stochastic differences from cluster to cluster in
the star formation efficiency (SFE) and their initial sizes. We find that the
observed SDF shape can be accurately predicted by a simple model in which the
protocluster clouds had characteristic sizes of pc and SFEs of
. The colors and luminosities of the M104 clusters show the
clearly defined classic bimodal form. The blue sequence exhibits a
mass/metallicity relation (MMR), following a scaling of heavy-element abundance
with luminosity of very similar to what has been found in most
giant elliptical galaxies. A quantitative self-enrichment model provides a good
first-order match to the data for the same initial SFE and protocluster size
that were required to explain the SDF. We also discuss various forms of the
globular cluster Fundamental Plane (FP) of structural parameters, and show that
useful tests of it can be extended to galaxies beyond the Local Group.Comment: In press for MNRA
Are the hosts of VLBI selected radio-AGN different to those of radio-loud AGN?
Recent studies have found that radio-AGN selected by radio-loudness show
little difference in terms of their host galaxy properties when compared to
non-AGN galaxies of similar stellar mass and redshift. Using new 1.4~GHz VLBI
observations of the COSMOS field we find that approximately 49\% of
high-mass (M 10 M), high luminosity (L
10 W~Hz) radio-AGN possess a VLBI detected counterpart. These
objects show no discernible bias towards specific stellar masses, redshifts or
host properties other than what is shown by the radio-AGN population in
general. Radio-AGN that are detected in VLBI observations are not special, but
form a representative sample of the radio-loud AGN population.Comment: 6 pages, 4 figures, lette
In Vitro Demonstration of Delayed Hypersensitivity in Patients with Berylliosis
To clarify immunopathological mechanisms in granulomatous hypersensitivity (GHR) to beryllium (Be), migration inhibitory factor (MIF) was assayed. Blood lymphocytes from three patients with GHR to Be and two normal persons were isolated and cultured with and without BeO or other antigens. Cell-free supernatants removed daily were dialyzed, lyophilized and assayed for MIF by measuring the area of migration of normal guinea pig peritoneal exudate cells out of capillary tubes within 24 hours after exposure to the supernatant. BeO added to sensitized lymphocytes produced supernatant that decreased migration, in contrast to supernatant from non-sensitized lymphocytes, indicating that BeO-sensitized lymphocytes cultured with Be elaborate a soluble factor, MIF, which correlates with delayed hypersensitivity and may play a role in granuloma formation. It may also prove useful in diagnosis of berylliosis
Infrared-faint Radio Sources Remain Undetected at Far-infrared Wavelengths
published_or_final_versio
A Blue Tilt in the Globular Cluster System of the Milky Way-like Galaxy NGC 5170
Here we present HST/ACS imaging, in the B and I bands, of the edge-on Sb/Sc
galaxy NGC 5170. Excluding the central disk region region, we detect a 142
objects with colours and sizes typical of globular clusters (GCs). Our main
result is the discovery of a `blue tilt' (a mass-metallicity relation), at the
3sigma level, in the metal-poor GC subpopulation of this Milky Way like galaxy.
The tilt is consistent with that seen in massive elliptical galaxies and with
the self enrichment model of Bailin & Harris. For a linear mass-metallicity
relation, the tilt has the form Z ~ L^{0.42 +/- 0.13}. We derive a total GC
system population of 600 +/- 100, making it much richer than the Milky Way.
However when this number is normalised by the host galaxy luminosity or stellar
mass it is similar to that of M31. Finally, we report the presence of a
potential Ultra Compact Dwarf of size ~ 6 pc and luminosity M_I ~ -12.5,
assuming it is physically associated with NGC 5170.Comment: Accepted for publication in MNRAS, 11 pages, 10 figure
Long-term GSHP system performance measurement in the USA and Europe
This paper presents an overview of the International Energy Agency (IEA) technology collaboration program Heat Pumping Technologies (HPT) Annex 52, "Long term performance measurement of ground source heat pump (GSHP) systems serving commercial, institutional and multi-family buildings." This project, which ran from 2018 through 2021, focused on measuring the performance of larger GSHP systems, going beyond energy use intensities which commingle the performance of the building envelope, occupancy effects and the system performance. Instead, performance factors were calculated, similar to coefficients of performance, but measured over various time intervals and system boundaries. The primary objectives of the Annex were refining and extending methodologies to better characterize system performance in larger buildings, creating a library of quality long-term measurements in the form of case studies, and providing guidelines for instrumentation, uncertainty analysis, key performance indicators, data management and quality assurance.This paper summarizes the Annex outcome and illustrates use of the Annex boundary levels with a comparison between typical European and US GSHP systems. It is anticipated that this experience and the guidelines produced as a result of this experience will lower the cost and improve consistency and quality for future performance measurements
Ground-based follow-up observations of TRAPPIST-1 transits in the near-infrared
The TRAPPIST-1 planetary system is a favorable target for the atmospheric
characterization of temperate earth-sized exoplanets by means of transmission
spectroscopy with the forthcoming James Webb Space Telescope (JWST). A possible
obstacle to this technique could come from the photospheric heterogeneity of
the host star that could affect planetary signatures in the transit
transmission spectra. To constrain further this possibility, we gathered an
extensive photometric data set of 25 TRAPPIST-1 transits observed in the
near-IR J band (1.2 m) with the UKIRT and the AAT, and in the NB2090 band
(2.1 m) with the VLT during the period 2015-2018. In our analysis of these
data, we used a special strategy aiming to ensure uniformity in our
measurements and robustness in our conclusions. We reach a photometric
precision of (RMS of the residuals), and we detect no significant
temporal variations of transit depths of TRAPPIST-1 b, c, e, and g over the
period of three years. The few transit depths measured for planets d and f hint
towards some level of variability, but more measurements will be required for
confirmation. Our depth measurements for planets b and c disagree with the
stellar contamination spectra originating from the possible existence of bright
spots of temperature 4500 K. We report updated transmission spectra for the six
inner planets of the system which are globally flat for planets b and g and
some structures are seen for planets c, d, e, and f.Comment: accepted for publication in MNRA
The Observational and Theoretical Tidal Radii of Globular Clusters in M87
Globular clusters have linear sizes (tidal radii) which theory tells us are
determined by their masses and by the gravitational potential of their host
galaxy. To explore the relationship between observed and expected radii, we
utilize the globular cluster population of the Virgo giant M87. Unusually deep,
high signal-to-noise images of M87 are used to measure the effective and
limiting radii of approximately 2000 globular clusters. To compare with these
observations, we simulate a globular cluster population that has the same
characteristics as the observed M87 cluster population. Placing these simulated
clusters in the well-studied tidal field of M87, the orbit of each cluster is
solved and the theoretical tidal radius of each cluster is determined. We
compare the predicted relationship between cluster size and projected
galactocentric distance to observations. We find that for an isotropic
distribution of cluster velocities, theoretical tidal radii are approximately
equal to observed limiting radii for Rgc < 10 kpc. However, the isotropic
simulation predicts a steep increase in cluster size at larger radii, which is
not observed in large galaxies beyond the Milky Way. To minimize the
discrepancy between theory and observations, we explore the effects of orbital
anisotropy on cluster sizes, and suggest a possible orbital anisotropy profile
for M87 which yields a better match between theory and observations. Finally,
we suggest future studies which will establish a stronger link between
theoretical tidal radii and observed radii.Comment: 8 pages, 8 figures, Accepted for publication in Ap
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