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Register a new userSignatures of long-lived spiral patterns
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Added by
Eric E. Mart\\'inez-Garc\\'ia
Publication date
2013
fields
Physics
and research's language is
English
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Azimuthal age/color gradients across spiral arms are a signature of long-lived spirals. From a sample of 19 normal (or weakly barred) spirals where we have previously found azimuthal age/color gradient candidates, 13 objects were further selected if a two-armed grand-design pattern survived in a surface density stellar mass map. Mass maps were obtained from optical and near-infrared imaging, by comparing with a Monte Carlo library of stellar population synthesis models that allowed us to obtain the mass-to-light ratio in the J band, (M/L)_J, as a function of (g-i) versus (i-J) color. The selected spirals were analyzed with Fourier methods in search for other signatures of long-lived modes related to the gradients, such as the gradient divergence toward corotation, and the behavior of the phase angle of the two-armed spiral in different wavebands, as expected from theory. The results show additional signatures of long-lived spirals in at least 50% of the objects.
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Many barred galaxies harbor small-scale secondary bars in the center. The evolution of such double-barred galaxies is still not well understood, partly because of a lack of realistic N-body models with which to study them. Here we report the generation of such systems in the presence of rotating pseudobulges. We demonstrate with high mass and force resolution collisionless N-body simulations that long-lived secondary bars can form spontaneously without requiring gas, contrary to previous claims. We find that secondary bars rotate faster than primary ones. The rotation is not rigid: the secondary bars pulsate, with their amplitude and pattern speed oscillating as they rotate through the primary bars. This self-consistent study supports previous work based on orbital analysis in the potential of two rigidly rotating bars. We also characterize the density and kinematics of the N-body simulations of the double-barred galaxies, compare with observations to achieve a better understanding of such galaxies. The pulsating nature of secondary bars may have important implications for understanding the central region of double-barred galaxies.
The Type IIn supernova (SN) 2005ip is one of the most well-studied and long-lasting examples of a SN interacting with its circumstellar environment. The optical light curve plateaued at a nearly constant level for more than five years, suggesting ongoing shock interaction with an extended and clumpy circumstellar medium (CSM). Here we present continued observations of the SN from $sim 1000-5000$ days post-explosion at all wavelengths, including X-ray, ultraviolet, near-infrared, and mid-infrared. The UV spectra probe the pre-explosion mass loss and show evidence for CNO processing. From the bolometric light curve, we find that the total radiated energy is in excess of $10^{50}$ erg, the progenitor stars pre-explosion mass-loss rate was $gtrsim 1 times 10^{-2},{rm M_{odot}~ yr}^{-1}$, and the total mass lost shortly before explosion was $gtrsim 1,{rm M_odot}$, though the mass lost could have been considerably larger depending on the efficiency for the conversion of kinetic energy to radiation. The ultraviolet through near-infrared spectrum is characterised by two high density components, one with narrow high-ionisation lines, and one with broader low-ionisation H I, He I, [O I], Mg II, and Fe II lines. The rich Fe II spectrum is strongly affected by Ly$alpha$ fluorescence, consistent with spectral modeling. Both the Balmer and He I lines indicate a decreasing CSM density during the late interaction period. We find similarities to SN 1988Z, which shows a comparable change in spectrum at around the same time during its very slow decline. These results suggest that, at long last, the shock interaction in SN 2005ip may finally be on the decline.
Accretion disks can be eccentric: they support $m=1$ modes that are global and slowly precessing. But whether the modes remain trapped in the disk---and hence are long-lived---depends on conditions at the outer edge of the disk. Here we show that in disks with realistic boundaries, in which the surface density drops rapidly beyond a given radius, eccentric modes are trapped and hence long-lived. We focus on pressure-only disks around a central mass, and show how this result can be understood with the help of a simple second-order WKB theory. We show that the longest lived mode is the zero-node mode in which all of the disks elliptical streamlines are aligned, and that this mode decays coherently on the viscous timescale of the disk. Hence such a mode, once excited, will live for the lifetime of the disk. It may be responsible for asymmetries seen in recent images of protoplanetary disks.
Lifetimes of complexes formed during ultracold collisions are of current experimental interest as a possible cause of trap loss in ultracold gases of alkali-dimers. Microsecond lifetimes for complexes formed during ultracold elastic collisions of K2 with Rb are reported, from numerically-exact quantum-scattering calculations. The reported lifetimes are compared with those calculated using a simple density-of-states approach, which are shown to be reasonable. Long-lived complexes correspond to narrow scattering resonances which we examine for the statistical signatures of quantum chaos, finding that the positions and widths of the resonances follow the Wigner-Dyson and Porter-Thomas distributions respectively.
SDSS J134244.4+053056 is a tidal disruption event candidate with strong temporal coronal line emitters and a long fading, mid-infrared dust echo. We present detailed analyses of X-ray emission from a Swift/XRT observation in 2009 and the most recent XMM-Newton/pn observation in 2020. The two spectra can be modeled with hard and soft components. While no significant variability is detected in the hard component above 2 keV between these two observations, the soft X-ray emission in 0.3-2 keV varies by a factor of $sim5$. The luminosity of this soft component fades from $sim1.8times10^{41}$ to $sim3.7times10^{40}$ erg s$^{-1}$ from the observation in Swift to that of XMM-Newton, which are 8 and 19 years after the outburst occurred, respectively. The evolution of luminosity matches with the $t^{-5/3}$ decline law well; there is a soft X-ray peak luminosity of 10$^{44}$ erg s$^{-1}$ at the time of the optical flare. Furthermore, the spectra of the soft component harden slightly in the decay phase, in which the photon index $Gamma$ varies from $4.8^{+1.2}_{-0.9}$ to $3.7pm0.5$, although they are consistent with each other if we consider the uncertainties. Additionally, by comparing the BH mass estimate between the $M-sigma$ correlation, the broad H$alpha$ emission, and the fundamental plane relation of BH accretion, we find that a value of $sim10^{5}$Msun is favored. If so, taking its X-ray spectral variation, luminosity evolution, and further support from theory into account, we suggest that SDSS J134244.4+053056 is a long-lived tidal disruption event candidate lasting more than 18 years with an intermediate-mass black hole.
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