2,824 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&
The Non-Destructive and Nano-Microstructural Characterization of Thermal-Barrier Coatings
The durability of thermal barrier coatings (TBCs) plays an important role in the service reliability and maintainability of hot-section components in advanced turbine engines for aerospace and utility applications. Photostimulated luminescence spectroscopy (PSLS) and electrochemical impedance spectroscopy (EIS) are being concurrently developed as complimentary nondestructive evaluation (NDE) techniques for quality control and liferemain assessment of TBCs. This paper discusses recent achievements in understanding the residual stress, phase constituents, and electrochemical resistance (or capacitance) of TBC constituents—with an emphasis on the thermally grown oxide. Results from NDE by PSLS and EIS are correlated to the nano- and microstructural development of TBCs
Fermi Edge Singularities in the Mesoscopic Regime: I. Anderson Orthogonality Catastrophe
For generic mesoscopic systems like quantum dots or nanoparticles, we study
the Anderson orthogonality catastrophe (AOC) and Fermi edge singularities in
photoabsorption spectra in a series of two papers. In the present paper we
focus on AOC for a finite number of particles in discrete energy levels where,
in contrast to the bulk situation, AOC is not complete. Moreover, fluctuations
characteristic for mesoscopic systems lead to a broad distribution of AOC
ground state overlaps. The fluctuations originate dominantly in the levels
around the Fermi energy, and we derive an analytic expression for the
probability distribution of AOC overlaps in the limit of strong perturbations.
We address the formation of a bound state and its importance for symmetries
between the overlap distributions for attractive and repulsive potentials. Our
results are based on a random matrix model for the chaotic conduction electrons
that are subject to a rank one perturbation corresponding, e.g., to the
localized core hole generated in the photoabsorption process.Comment: 10 pages, 8 figures, submitted to Phys. Rev.
The spectral-curvature parameter: an alternative tool for the analysis of synchrotron spectra
The so-called Spectral Curvature Parameter(SCP), when plotted versus the
high-frequency spectral index () of synchrotron sources, provides
crucial parameters on the continuum spectrum of synchrotron radiation without
the more complex modeling of spectral ageing scenarios. An important merit of
the SCP- diagram is the enhanced reliability of extracting multiple
injection spectra, . Different from the colour-colour diagram,
tracks of different s, especially when the synchrotron particles
are young, exhibit less overlap and less smearing in the SCP- diagram.
Three giant radio galaxies(GRGs) and a sample of Compact steep spectrum(CSS)
souces are presented. GRGs exhibit asymmetries of their injection spectral
indices in the SCP- diagram. The obtained
s and the trends in the sources are cross-checked with the
literature and show remarkable confidence. Besides the spectral steepening,
spectral flattening is prominent in the radio lobes. The spectral flattening is
a clue to efficient re-acceleration processes in the lobes. It implies
interaction with the surrounding intergalactic or intra-cluster medium is an
important characteristic of GRGs. In the SW lobe of DA240, there is a clear
sign of CI and KP/JP bifurcation at the source extremity. This indicates a
highly relativistic energy transportation from the core or in situ acceleration
in this typical FR I lobe. Our analysis proves, if exists, KP spectra imply the
existence of strong field with . In the CSS
sources, our result confirms the CI model and . The
synchrotron self-absorption is significant in the CSS sample.Comment: to be published in A&
86 GHz polarimetry of OVV1633+382 after a major mm flare
The 18 mag QSO 1633+382 (4C38.41, z=1.807) showed a very pronounced outburst
in 2001/2002. With a peak amplitude of more than 9 Jy at 90GHz, this flare was
brighter than any known previous flare in this source (data available since
1980).During onset, the mm-flare was particulary fast, with an increase of more
than 2 Jy at 230 GHz in less than 8 days. Since January 2002, the mm-flux of
1633+382 is decaying. During this decline, however, local flux variations with
amplitudes of 1-3 Jy were seen, indicative of underlying and more rapid source
activity on time scales of 1-2 months. After the main peak occurring in
2001.99, the 90 GHz flux showed secondary maxima at approximately half year
intervals in 2002.3, 2002.7 and 2003.13. This kind of periodicity might be
explained via the lighthouse model (Camenzind and Krockenberger 1992), which is
based on the magnetic accelerator of Blanford and Payne (1982). At present the
millimeter flux is nearly back to its quiescent level of 2-2.5 Jy, which the
source had before the flare began. Our VLBA Polarimetry monitoring started June
2002 during the onset of the flare. At cm wavelength, the flare is only
marginally detected which implies very high opacity of the source.Comment: 4 pages. 5 figures. Proceedings of the 7th European VLBI Network
Symposium held in Toledo, Spain on October 12-15, 2004. Editors: R.
Bachiller, F. Colomer, J.-F. Desmurs, P. de Vicente (Observatorio Astronomico
Nacional), p. 85-88. Needs evn2004.cl
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