10 research outputs found
Globular cluster population of the HST frontier fields galaxy J07173724+3744224
We present the first measurement of the globular cluster population
surrounding the elliptical galaxy J07173724+3744224 (z=0.1546). This galaxy is
located in the foreground in the field-of-view of the Hubble Space Telescope
(HST) Frontier Fields observations of galaxy cluster MACS J0717.5+3745
(z=0.5458). Based on deep HST ACS F435W, F606W, and F814W images, we find a
total globular cluster population of N_tot = 3441 +/- 1416. Applying the
appropriate extinction correction and filter transformation from ACS F814W to
the Johnson V-band, we determine that the host galaxy has an absolute magnitude
of M_V = -22.2. The specific frequency was found to be S_N = 4.5 +/- 1.8. The
radial profile of the globular cluster system was best fit using a powerlaw of
the form , with the globular cluster population found to
be more extended than the halo light of the host galaxy (). The F435W-F814W colour distribution suggests a bimodal population,
with red globular clusters 1-3x more abundant than blue clusters. These results
are consistent with the host elliptical galaxy J07173724+3744224 having formed
its red metal-rich GCs in situ, with the blue metal-poor globular clusters
accreted from low-mass galaxies.Comment: 21 pages, 14 figures, 2 tables, revised following peer-review,
accepted for publication in MNRA
Star formation in low-redshift cluster dwarf galaxies
Evolution of galaxies in dense environments can be affected by close encounters with neighbouring galaxies and interactions with the intracluster medium. Dwarf galaxies (dGs) are important as their low mass makes them more susceptible to these effects than giant systems. Combined luminosity functions (LFs) in the r and u band of 15 galaxy clusters were constructed using archival data from the CanadaâFranceâHawaii Telescope. LFs were measured as a function of clustercentric radius from stacked cluster data. Marginal evidence was found for an increase in the faint-end slope of the u-band LF relative to the r-band with increasing clustercentric radius. The dwarf-to-giant ratio (DGR) was found to increase toward the cluster outskirts, with the u-band DGR increasing faster with clustercentric radius compared to the r-band. The dG blue fraction was found to be âŒ2 times larger than the giant galaxy blue fraction over all clustercentric distance (âŒ5Ï level). The central concentration (C) was used as a proxy to distinguish nucleated versus non-nucleated dGs. The ratio of high-C to low-C dGs was found to be âŒ2 times greater in the inner cluster region compared to the outskirts (2.8Ï level). The faint-end slope of the r-band LF for the cluster outskirts (0.6 †r/r200 \u3c 1.0) is steeper than the Sloan Digital Sky Survey field LF, while the u-band LF is marginally steeper at the 2.5Ï level. Decrease in the faint-end slope of the r- and u-band cluster LFs towards the cluster centre is consistent with quenching of star formation via ram pressure stripping and galaxyâgalaxy interactions
Characterizing the Complex Two NâWave Ionospheric Signature of the 2016 Kaikoura Earthquake
Characterizing the Complex Two NâWave Ionospheric Signature of the 2016 Kaikoura Earthquake
Computer aided detection of transient inflation events at Alaskan volcanoes using GPS measurements from 2005â2015
© 2016 Elsevier B.V. Analysis of transient deformation events in time series data observed via networks of continuous Global Positioning System (GPS) ground stations provide insight into the magmatic and tectonic processes that drive volcanic activity. Typical analyses of spatial positions originating from each station require careful tuning of algorithmic parameters and selection of time and spatial regions of interest to observe possible transient events. This iterative, manual process is tedious when attempting to make new discoveries and does not easily scale with the number of stations. Addressing this challenge, we introduce a novel approach based on a computer-aided discovery system that facilitates the discovery of such potential transient events. The advantages of this approach are demonstrated by actual detections of transient deformation events at volcanoes selected from the Alaska Volcano Observatory database using data recorded by GPS stations from the Plate Boundary Observatory network. Our technique successfully reproduces the analysis of a transient signal detected in the first half of 2008 at Akutan volcano and is also directly applicable to 3 additional volcanoes in Alaska, with the new detection of 2 previously unnoticed inflation events: in early 2011 at Westdahl and in early 2013 at Shishaldin. This study also discusses the benefits of our computer-aided discovery approach for volcanology in general. Advantages include the rapid analysis on multi-scale resolutions of transient deformation events at a large number of sites of interest and the capability to enhance reusability and reproducibility in volcano studies