406 research outputs found
The Infrared Camera (IRC) for AKARI - Design and Imaging Performance
The Infrared Camera (IRC) is one of two focal-plane instruments on the AKARI
satellite. It is designed for wide-field deep imaging and low-resolution
spectroscopy in the near- to mid-infrared (1.8--26.5um) in the pointed
observation mode of AKARI. IRC is also operated in the survey mode to make an
all-sky survey at 9 and 18um. It comprises three channels. The NIR channel
(1.8--5.5um) employs a 512 x 412 InSb array, whereas both the MIR-S
(4.6--13.4um) and MIR-L (12.6--26.5um) channels use 256 x 256 Si:As impurity
band conduction arrays. Each of the three channels has a field-of-view of about
10' x 10' and are operated simultaneously. The NIR and MIR-S share the same
field-of-view by virtue of a beam splitter. The MIR-L observes the sky about
$25' away from the NIR/MIR-S field-of-view. IRC gives us deep insights into the
formation and evolution of galaxies, the evolution of planetary disks, the
process of star-formation, the properties of interstellar matter under various
physical conditions, and the nature and evolution of solar system objects. The
in-flight performance of IRC has been confirmed to be in agreement with the
pre-flight expectation. This paper summarizes the design and the in-flight
operation and imaging performance of IRC.Comment: Publications of the Astronomical Society of Japan, in pres
Magnetism, Critical Fluctuations and Susceptibility Renormalization in Pd
Some of the most popular ways to treat quantum critical materials, that is,
materials close to a magnetic instability, are based on the Landau functional.
The central quantity of such approaches is the average magnitude of spin
fluctuations, which is very difficult to measure experimentally or compute
directly from the first principles. We calculate the parameters of the Landau
functional for Pd and use these to connect the critical fluctuations beyond the
local-density approximation and the band structure.Comment: Replaced with the revised version accepted for publication.
References updated, errors corrected, other change
A Study of the Distribution of Star-Forming Regions in Luminous Infrared Galaxies by Means of H Imaging Observations
We performed H-alpha imaging observations of 22 luminous infrared galaxies to
investigate how the distribution of star-forming regions in these galaxies is
related to galaxy interactions. Based on correlation diagrams between H-alpha
flux and continuum emission for individual galaxies, a sequence for the
distribution of star-forming regions was found: very compact (~100 pc) nuclear
starbursts with almost no star-forming activity in the outer regions (type 1),
dominant nuclear starbursts < 1 kpc in size and a negligible contribution from
the outer regions (type 2), nuclear starbursts > 1 kpc in size and a
significant contribution from the outer regions (type 3), and extended
starbursts with relatively faint nuclei (type 4). These classes of star-forming
region were found to be strongly related to global star-forming properties such
as star-formation efficiency, far-infrared color, and dust extinction. There
was a clear tendency for the objects with more compact distributions of
star-forming regions to show a higher star-formation efficiency and hotter
far-infrared color. An appreciable fraction of the sample objects were
dominated by extended starbursts (type 4), which is unexpected in the standard
scenario of interaction-induced starburst galaxies. We also found that the
distribution of star-forming regions was weakly but clearly related to galaxy
morphology: severely disturbed objects had a more concentrated distribution of
star-forming regions. This suggests that the properties of galaxy interactions,
such as dynamical phase and orbital parameters, play a more important role than
the internal properties of progenitor galaxies, such as dynamical structure or
gas mass fraction. We also discuss the evolution of the distribution of
star-forming regions in interacting galaxies.Comment: 44 pages, LaTeX, Accepted by AJ, Version with full-resolution figures
available at http://www.oao.nao.ac.jp/support/staff/hattori/lirgs_paper.ps.g
Competing Ground States in Triple-layered Sr4Ru3O10: Verging on Itinerant Ferromagnetism with Critical Fluctuations
Sr4Ru3O10 is characterized by a sharp metamagnetic transition and
ferromagnetic behavior occurring within the basal plane and along the c-axis,
respectively. Resistivity at magnetic field, B, exhibits low-frequency quantum
oscillations when B||c-axis and large magnetoresistivity accompanied by
critical fluctuations driven by the metamagnetism when B^c-axis. The complex
behavior evidenced in resistivity, magnetization and specific heat presented is
not characteristic of any obvious ground states, and points to an exotic state
that shows a delicate balance between fluctuations and order.Comment: 18 pages, 4 figure
The atmospheric parameters and spectral interpolator for the stars of MILES
Context. Empirical libraries of stellar spectra are used for stellar
classification and synthesis of stellar populations. MILES is a medium
spectral-resolution library in the optical domain covering a wide range of
temperatures, surface gravities and metallicities. Aims. We re-determine the
atmospheric parameters of these stars in order to improve the homogeneity and
accuracy. We build an interpolating function that returns a spectrum as a
function of the three atmospheric parameters, and finally, we characterize the
precision of the wavelength calibration and stability of the spectral
resolution. Methods. We use the ULySS program with the ELODIE library as a
reference and compare the results with literature compilations. Results. We
obtain precisions of 60 K, 0.13 and 0.05 dex respectively for Teff, log g and
[Fe/H] for the FGK stars. For the M stars, the mean errors are 38 K, 0.26 and
0.12 dex, and for the OBA 3.5%, 0.17 and 0.13 dex. We construct an interpolator
that we test against the MILES stars themselves. We test it also by measuring
the atmospheric parameters of the CFLIB stars with MILES as reference and find
it to be more reliable than the ELODIE interpolator for the evolved hot stars,
like in particular those of the blue horizontal branch.Comment: A&A accepted, 29 pages, 6 figure
Clustering of the AKARI NEP deep field 24<i>μ</i>m selected galaxies
Aims. We present a method of selection of 24 μm galaxies from the AKARI north ecliptic pole (NEP) deep field down to 150 μJy and measurements of their two-point correlation function. We aim to associate various 24 μm selected galaxy populations with present day galaxies and to investigate the impact of their environment on the direction of their subsequent evolution.
Methods. We discuss using of Support Vector Machines (SVM) algorithm applied to infrared photometric data to perform star-galaxy separation, in which we achieve an accuracy higher than 80%. The photometric redshift information, obtained through the CIGALE code, is used to explore the redshift dependence of the correlation function parameter (r0) as well as the linear bias evolution. This parameter relates galaxy distribution to the one of the underlying dark matter. We connect the investigated sources to their potential local descendants through a simplified model of the clustering evolution without interactions.
Results. We observe two different populations of star-forming galaxies, at zmed ∼ 0.25, zmed ∼ 0.9. Measurements of total infrared luminosities (LTIR) show that the sample at zmed ∼ 0.25 is composed mostly of local star-forming galaxies, while the sample at zmed ∼ 0.9 is composed of luminous infrared galaxies (LIRGs) with LTIR ∼ 1011.62 L⨀. We find that dark halo mass is not necessarily correlated with the LTIR: for subsamples with LTIR = 1011.15 L⨀ at zmed ∼ 0.7 we observe a higher clustering length (r0 = 6.21 ± 0.78 [h−1Mpc]) than for a subsample with mean LTIR = 1011.84 L⨀ at zmed ∼ 1.1 (r0 = 5.86 ± 0.69 h−1Mpc). We find that galaxies at zmed ∼ 0.9 can be ancestors of present day L∗ early type galaxies, which exhibit a very high r0 ∼ 8h−1 Mpc.</p
A novel class of microRNA-recognition elements that function only within open reading frames.
MicroRNAs (miRNAs) are well known to target 3' untranslated regions (3' UTRs) in mRNAs, thereby silencing gene expression at the post-transcriptional level. Multiple reports have also indicated the ability of miRNAs to target protein-coding sequences (CDS); however, miRNAs have been generally believed to function through similar mechanisms regardless of the locations of their sites of action. Here, we report a class of miRNA-recognition elements (MREs) that function exclusively in CDS regions. Through functional and mechanistic characterization of these 'unusual' MREs, we demonstrate that CDS-targeted miRNAs require extensive base-pairing at the 3' side rather than the 5' seed; cause gene silencing in an Argonaute-dependent but GW182-independent manner; and repress translation by inducing transient ribosome stalling instead of mRNA destabilization. These findings reveal distinct mechanisms and functional consequences of miRNAs that target CDS versus the 3' UTR and suggest that CDS-targeted miRNAs may use a translational quality-control-related mechanism to regulate translation in mammalian cells
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