3,862 research outputs found
Arp 65 interaction debris: massive HI displacement and star formation
Context: Pre-merger interactions between galaxies can induce significant
changes in the morphologies and kinematics of the stellar and ISM components.
Large amounts of gas and stars are often found to be disturbed or displaced as
tidal debris. This debris then evolves, sometimes forming stars and
occasionally tidal dwarf galaxies. Here we present results from our HI study of
Arp 65, an interacting pair hosting extended HI tidal debris. Aims: In an
effort to understand the evolution of tidal debris produced by interacting
pairs of galaxies, including in situ star and tidal dwarf galaxy formation, we
are mapping HI in a sample of interacting galaxy pairs. The Arp 65 pair is one
of them. Methods: Our resolved HI 21 cm line survey is being carried out using
the Giant Metrewave Radio Telescope (GMRT). We used our HI survey data as well
as available SDSS optical, Spitzer infra-red and GALEX UV data to study the
evolution of the tidal debris and the correlation of HI with the star-forming
regions within it. Results: In Arp 65 we see a high impact pre-merger
interaction involving a pair of massive galaxies (NGC 90 and NGC 93) that have
a stellar mass ratio of ~ 1:3. The interaction, which probably occurred ~ 1.0
-- 2.5 10 yr ago, appears to have displaced a large fraction of
the HI in NGC 90 (including the highest column density HI) beyond its optical
disk. We also find extended ongoing star formation in the outer disk of NGC 90.
In the major star-forming regions, we find the HI column densities to be ~ 4.7
10 cm or lower. But no signature of star formation was
found in the highest column density HI debris, SE of NGC 90. This indicates
conditions within the highest column density HI debris remain hostile to star
formation and it reaffirms that high HI column densities may be a necessary but
not sufficient criterion for star formation.Comment: Accepted in A&
Scalable Mining of Common Routes in Mobile Communication Network Traffic Data
A probabilistic method for inferring common routes from mobile communication network traffic data is presented. Besides providing mobility information, valuable in a multitude of application areas, the method has the dual purpose of enabling efficient coarse-graining as well as anonymisation by mapping individual sequences onto common routes. The approach is to represent spatial trajectories by Cell ID sequences that are grouped into routes using locality-sensitive hashing and graph clustering. The method is demonstrated to be scalable, and to accurately group sequences using an evaluation set of GPS tagged data
Compatibility of The Dimensions of Polymer Molecular Aggregates to The Pore Throat of a Reservoir
The compatibility of the dimensions of the polymer molecular aggregates and the pore throat of the reservoir were studied. The W section of Tuha oilfield was the study area and polymers produced by Daqing Refining and Chemical Company were used. The permeability limit of the polymer molecules with different molecular masses and concentrations, matching relationship between the dimension of polymer molecular aggregates and pore throat were obtained by experiments. The results of the research are important for the development and implementation of a polymer flooding technical scheme in the middle and late stages of the operation of the Tuha oilfield
Hot Populations in M87 Globular Clusters
We have obtained HST/STIS far- and near-UV photometry of globular clusters in
four fields in the gE galaxy M87. To a limit of m(FUV) = 25 we detect a total
of 66 globular clusters (GCs) in common with the deep HST optical-band study of
Kundu et al. (1999). Despite strong overlap in V- and I-band properties, the
M87 GCs have UV/optical properties that are distinct from clusters in the Milky
Way and in M31. M87 clusters, especially metal-poor ones, produce larger hot HB
populations than do Milky Way analogues. Cluster mass is probably not a factor
in these distinctions. The most metal-rich M87 GCs in our sample are near Z_sun
and overlap the local E galaxy sample in estimated Mg_2 line indices.
Nonetheless, the clusters produce much more UV light at a given Mg_2, being up
to 1 mag bluer than any gE galaxy in (FUV-V) color. The M87 GCs do not appear
to represent a transition between Milky Way-type clusters and E galaxies. The
differences are in the correct sense if the clusters are significantly older
than the E galaxies. Comparisons with Galactic open clusters indicate that the
hot stars lie on the extreme horizontal branch, rather than being blue
stragglers, and that the EHB becomes well populated for ages > 5 Gyr. We find
that 43 of our UV detections have no optical-band counterparts. Most appear to
be UV-bright background galaxies, seen through M87. Eleven NUV variable sources
detected at only one epoch in the central field are probably classical novae.
[Abridged]Comment: 70 pages, 25 figures (including 4 jpgs), 7 tables. To appear in AJ.
Full resolution version available at
http://www.astro.virginia.edu/~rwo/m87/m87-hotpops.pd
Optimum Tower Crane Selection and Supporting Design Management
To optimize tower crane selection and supporting design, lifting requirements (as well as stability) should be examined, followed by a review of economic feasibility. However, construction engineers establish plans based on data provided by equipment suppliers since there are no tools with which to thoroughly examine a support design’s suitability for various crane types, and such plans lack the necessary supporting data. In such cases it is impossible to optimize a tower crane selection to satisfy lifting requirements in terms of cost, and to perform lateral support and foundation design. Thus, this study is intended to develop an optimum tower crane selection and supporting design management method based on stability. All cases that are capable of generating an optimization of approximately 3,000 ~ 15,000 times are calculated to identify the candidate cranes with minimized cost, which are examined. The optimization method developed in the study is expected to support engineers in determining the optimum lifting equipment management
The Extended Shapes of Galactic Satellites
We are exploring the extended stellar distributions of Galactic satellite
galaxies and globular clusters. For seven objects studied thus far, the
observed profile departs from a King function at large r, revealing a ``break
population'' of stars. In our sample, the relative density of the ``break''
correlates to the inferred M/L of these objects. We discuss opposing hypotheses
for this trend: (1) Higher M/L objects harbor more extended dark matter halos
that support secondary, bound, stellar ``halos''. (2) The extended populations
around dwarf spheroidals (and some clusters) consist of unbound, extratidal
debris from their parent objects, which are undergoing various degrees of tidal
disruption. In this scenario, higher M/L ratios reflect higher degrees of
virial non-equilibrium in the parent objects, thus invalidating a precept
underlying the use of core radial velocities to obtain masses.Comment: 8 pages, including 2 figures Yale Cosmology Workshop: The Shapes of
Galaxies and Their Halo
Multiple Stellar Populations in the Globular Cluster omega Centauri as Tracers of a Merger Event
The discovery of the Sagittarius dwarf galaxy, which is being tidally
disrupted by and merging with the Milky Way, supports the view that the halo of
the Galaxy has been built up at least partially by the accretion of similar
dwarf systems. The Sagittarius dwarf contains several distinct populations of
stars, and includes M54 as its nucleus, which is the second most massive
globular cluster associated with the Milky Way. The most massive globular
cluster is omega Centauri, and here we report that omega Centauri also has
several distinct stellar populations, as traced by red-giant-branch stars. The
most metal-rich red-giant-branch stars are about 2 Gyr younger than the
dominant metal-poor component, indicating that omega Centauri was enriched over
this timescale. The presence of more than one epoch of star formation in a
globular cluster is quite surprising, and suggests that omega Centauri was once
part of a more massive system that merged with the Milky Way, as the
Sagittarius dwarf galaxy is in the process of doing now. Mergers probably were
much more frequent in the early history of the Galaxy and omega Centauri
appears to be a relict of this era.Comment: 7 pages, 3 figures, Latex+nature.sty (included), To appear in
November 4th issue of Natur
The magnetic field structure in CTA 102 from high-resolution mm-VLBI observations during the flaring state in 2016-2017
CONTEXT: Investigating the magnetic field structure in the innermost regions of relativistic jets is fundamental to understanding the crucial physical processes giving rise to jet formation, as well as to their extraordinary radiation output up to γ-ray energies.
AIMS: We study the magnetic field structure of the quasar CTA 102 with 3 and 7 mm VLBI polarimetric observations, reaching an unprecedented resolution (∼50 μas). We also investigate the variability and physical processes occurring in the source during the observing period, which coincides with a very active state of the source over the entire electromagnetic spectrum.
METHODS: We perform the Faraday rotation analysis using 3 and 7 mm data and we compare the obtained rotation measure (RM) map with the polarization evolution in 7 mm VLBA images. We study the kinematics and variability at 7 mm and infer the physical parameters associated with variability. From the analysis of γ-ray and X-ray data, we compute a minimum Doppler factor value required to explain the observed high-energy emission.
RESULTS: Faraday rotation analysis shows a gradient in RM with a maximum value of ∼6 × 104⁴ rad m⁻² and intrinsic electric vector position angles (EVPAs) oriented around the centroid of the core, suggesting the presence of large-scale helical magnetic fields. Such a magnetic field structure is also visible in 7 mm images when a new superluminal component is crossing the core region. The 7 mm EVPA orientation is different when the component is exiting the core or crossing a stationary feature at ∼0.1 mas. The interaction between the superluminal component and a recollimation shock at ∼0.1 mas could have triggered the multi-wavelength flares. The variability Doppler factor associated with such an interaction is large enough to explain the high-energy emission and the remarkable optical flare occurred very close in time.Accepted manuscrip
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