We analyze a sample of galaxies chosen to have F 24 μm > 0.5 mJy and satisfy a certain IRAC color criterion. Infrared Spectrograph (IRS) spectra yield redshifts, spectral types, and polycyclic ...aromatic hydrocarbons (PAH) luminosities, to which we add broadband photometry from optical through IRAC wavelengths, MIPS from 24-160 μm, 1.1 mm, and radio at 1.4 GHz. Stellar population modeling and IRS spectra together demonstrate that the double criteria used to select this sample have efficiently isolated massive star-forming galaxies at z ~ 1.9. This is the first starburst (SB)-dominated ultraluminous infrared galaxies (ULIRG) sample at high redshift with total infrared luminosity measured directly from FIR and millimeter photometry, and as such gives us the first accurate view of broadband spectral energy distributions for SB galaxies at extremely high luminosity and at all wavelengths. Similar broadband data are assembled for three other galaxy samples—local SB galaxies, local active galactic nucleus (AGN)/ULIRGs, and a second 24 μm-luminous z ~ 2 sample dominated by AGN. L PAH/L IR for the new z ~ 2 SB sample is the highest ever seen, some three times higher than in local SBs, whereas in AGNs this ratio is depressed below the SB trend, often severely. Several pieces of evidence imply that AGNs exist in this SB-dominated sample, except two of which even host very strong AGN, while they still have very strong PAH emission. The Advanced Camera for Surveys images show that most objects have very extended morphologies in the rest-frame ultraviolet band, thus extended distribution of PAH molecules. Such an extended distribution prevents further destruction PAH molecules by central AGNs. We conclude that objects in this sample are ULIRGs powered mainly by SB; and the total infrared luminosity density contributed by this type of objects is 0.9-2.6 × 107 L sun Mpc-3.
This study provides a behavioural analysis of the particular demagnetizing effects displayed by disordered heterostructures close to a particular value (
C
p) of their magnetic load
C. The emphasis ...is put on the convergence of evidences, got from several independent ways (experimental, analytical and numerical), of a percolative phenomenon in random distributions of magnetic particles that rules the sharp variations of the inner and outer demagnetizing effects at concentrations close to
C
p. When
C<
C
p, magnetic gaps, which originate from the magnetic dilution, may cause a cut-off of the magnetic flux paths in the composite medium, leading to inner demagnetizing effects only. When
C>
C
p, the delocalization of the magnetic poles leads the outer demagnetizing factor of the sample to switch from zero to its maximum value. The analytical approach of this phenomenon is based on an effective medium theory. It leads to a description of the interactions between magnetic inclusions that show a deep similarity with the main notions the reciprocity principle calls for.
Aims. We quantify the contributions of 24 µm galaxies to the Far-Infrared (FIR) Background at 70 and 160 µm. We provide new estimates of the Cosmic Infrared Background (CIB), and compare it with the ...Cosmic Optical Background (COB). Methods. Using Spitzer data at 24, 70 and 160 µm in three deep fields, we stacked more than 19000 MIPS 24 µm sources with S 24 ≥ 60 µJy at 70 and 160 µm, and measured the resulting FIR flux densities. Results. This method allows a gain up to one order of magnitude in depth in the FIR. We find that the Mid-Infrared (MIR) 24 µm selected sources contribute to more than 70% of the Cosmic Infrared Background (CIB) at 70 and 160 µm. This is the first direct measurement of the contribution of MIR-selected galaxies to the FIR CIB. Galaxies contributing the most to the total CIB are thus z ∼ 1 luminous infrared galaxies, which have intermediate stellar masses. We estimate that the CIB will be resolved at 0.9 mJy at 70 and 3 mJy at 160 µm. By combining the extrapolation of the 24 µm source counts below analysis, we obtain lower limits of 7.1 ± 1.0 and 13.4 ± 1.7 nW m −2 sr −1 for the CIB at 70 and 160 µm, respectively. Conclusions. The MIPS surveys have resolved more than three quarters of the MIR and FIR CIB. By carefully integrating the Extragalactic Background Light (EBL) SED, we also find that the CIB has the same brightness as the COB, around 24 nW m −2 sr −1. The EBL is produced on average by 115 infrared photons for one visible photon. Finally, the galaxy formation and evolution processes emitted a brightness equivalent to 5% of the primordial electromagnetic background (CMB).
The measurement method presented here permits the determination of the complex permeability /spl mu/* and permittivity /spl epsi/* of rectangular samples of various thicknesses (0.1 /spl mu/m-1800 .../spl mu/m) over the (130 MHz-7 GHz) frequency band. This method is based on the S-parameters measurements of an asymmetrical stripline containing the sample under test. It does not require any magnetic reference sample. The originality of this method is to reproduce the same environment for the material under test as encountered in microwave devices. The results given by this "in situ" measurement technique are more useful to design microwave devices than those given by traditional measurement methods.
When mechanical compression is applied parallel to the direction of magnetic induction in materials with negative magnetostriction constant, a simple theoretical analysis shows that, in most cases, ...the magnetization increases in magnitude because spins rotate into the stress direction. Experiment shows that this is true for materials in which the domain-wall configuration is initially dispersed at random. However, it is demonstrated in the present work that the results are quite different when the domain-wall configuration is already oriented along the stress direction. In this case, it is believed that compression directly acts on the pinning strengths binding the 180 degrees domain walls together through the grain boundaries. A measurement of this pinning effect is made on the basis of a well-tested model. Experiments on toroids of polycrystalline soft magnetic materials, YIG and Ni-Zn ferrites, are reported and the results are discussed.< >
Magnetic behavior of heterogeneous magnetic materials Mattei, J.-L.; Konn, A.M.; Le Floc'h, M.
IEEE transactions on instrumentation and measurement,
04/1993, Letnik:
42, Številka:
2
Journal Article, Conference Proceeding
Recenzirano
The magnetic susceptibility change in heterogeneous magnetic materials as a function of the magnetic matter characteristics (grain size, chemical composition, concentration) and also of the sample ...shape is studied. Techniques for measuring weak susceptibilities are described. They are used to show the existence of macroscopic demagnetizing fields in rod specimens beyond a certain volume of magnetic matter.< >
The transverse susceptibility was measured in polycrystalline soft ferrimagnetic ring samples. It is shown that the very peculiar shape of the transverse susceptibility curve comes form the ...combination of two magnetization processes: the 180 degrees domain-wall motions which give rise to the initial susceptibility, and the sudden rotation of domains magnetized perpendicular to the applied field when a certain threshold of the biasing field is reached. The temperature dependence of this threshold has been investigated and has shown a close connection with the effective anisotropy field.< >
The Neel magnetic hardness was studied in polycrystalline soft magnetic materials. Results show different behaviors, varying with the state of the microstructure. When samples are porous to about ...20%, the approach to saturation follows the Neel law with a magnetic hardness proportional to porosity. However, when samples have a regular distribution of defect-free grains with thin grain boundaries, the Neel law is no longer valid, and magnetic hardness has another definition involving a simple dependence on the effective anisotropy field.< >
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