703 research outputs found
The Nature of the Optical Light in Seyfert 2 Galaxies with Polarized Continuum
We investigate the nature of the optical continuum and stellar population in
the central kpc of the Seyfert 2s Mrk 348, Mrk 573, NGC 1358 and Mrk 1210 using
long-slit spectra obtained along the radio or extended emission axis. These
galaxies are known to have polarized continuum-including polarized broad lines
in Mrk 348 and Mrk 1210--and previous studies indicate featureless continuum
(FC) contributions in the 20-50% range at 5500 A. Nevertheless, our
measurements of the equivalent widths of absorption lines and continuum ratios
as a function of distance from the nuclei show no dilution of the lines nor
bluening of the spectrum, as expected if a blue FC was present at the nucleus
in the above proportions. We investigate one possibility to account for this
effect: that the stellar population at the nucleus is the same as that from the
surrounding bulge and dominates the nuclear light. A spectral analysis confirms
that this hypothesis works for Mrk 348, NGC 1358 and Mrk 1210, for which we
find stellar contributions at the nucleus larger than 90% at all wavelengths.
We find that a larger stellar population contribution to the nuclear spectra
can play the role of the ``second FC'' source inferred from previous studies.
Stellar population synthesis shows that the nuclear regions of Mrk 348 and Mrk
1210 have important contributions of young to intermediate age stars (0--100
Myr), not present in templates of elliptical galaxies. In the case of Mrk 1210,
this is further confirmed by the detection of a ``Wolf-Rayet feature'' in the
nuclear emission-line spectrum.Comment: ApJ, accepted. Uses aaspp4.sty. [22 pages
Hubble Space Telescope Photometry of the Dwarf Spheroidal Galaxy ESO 410-G005
We present HST WFPC2 imaging of the nearby low-surface-brightness dwarf
spheroidal galaxy ESO 410-G005, which has been resolved into stars for the
first time. The resulting color-magnitude diagram for about 2500 stars shows a
red giant branch branch with a tip at I=(22.4+-0.15), which yields a distance
of D=(1.9+-0.2) Mpc. ESO 410-G005 is found to be metal-poor with a mean
metallicity of (-1.8+-0.4) dex estimated from its red giant branch. Upper
asymptotic giant branch stars appear to be present near the center of the
galaxy, indicative of a substantial, centrally concentrated intermediate-age
population, unless these objects are artifacts of crowding. Previous studies
did not detect ESO 410-G005 in H alpha or in HI. ESO 410-G005 is a probable
member of the Sculptor group. Its linear separation from the nearest spiral,
NGC 55, is 230 kpc on the sky. The deprojected separation ranges from 340 to
615 kpc depending on the assumed distance of NGC 55. ESO 410 G005 appears to be
a relatively isolated dSph within the Sculptor group. Its absolute magnitude,
Mv = (-12.1+-0.2) mag, its central surface brightness, mu_V = (22.7+-0.1)
mag/arcsec^2, and its mean metallicity, [Fe/H] = (-1.8+-0.4) dex, follow the
trend observed for dwarf galaxies in the Local Group. (abridged)Comment: Accepted for publication in the Astrophysical Journal, Vol. 542 (Oct
20). 23 pages in AASTEX style, 9 figures, partially in gif format to save
spac
Regional, Geographic, and Racial/Ethnic Variation in Glycemic Control in a National Sample of Veterans With Diabetes
Regional, Geographic, and Racial/Ethnic Variation in Glycemic Control in a National Sample of Veterans With Diabetes
Alignment between PIN1 Polarity and Microtubule Orientation in the Shoot Apical Meristem Reveals a Tight Coupling between Morphogenesis and Auxin Transport
Morphogenesis during multicellular development is regulated by intercellular signaling molecules as well as by the mechanical properties of individual cells. In particular, normal patterns of organogenesis in plants require coordination between growth direction and growth magnitude. How this is achieved remains unclear. Here we show that in Arabidopsis thaliana, auxin patterning and cellular growth are linked through a correlated pattern of auxin efflux carrier localization and cortical microtubule orientation. Our experiments reveal that both PIN1 localization and microtubule array orientation are likely to respond to a shared upstream regulator that appears to be biomechanical in nature. Lastly, through mathematical modeling we show that such a biophysical coupling could mediate the feedback loop between auxin and its transport that underlies plant phyllotaxis
Theoretical Modeling of Starburst Galaxies
We have modeled a large sample of infrared starburst galaxies using both the
PEGASE v2.0 and STARBURST99 codes to generate the spectral energy distribution
of the young star clusters. PEGASE utilizes the Padova group tracks while
STARBURST99 uses the Geneva group tracks, allowing comparison between the two.
We used our MAPPINGS III code to compute photoionization models which include a
self-consistent treatment of dust physics and chemical depletion. We use the
standard optical diagnostic diagrams as indicators of the hardness of the EUV
radiation field in these galaxies. These diagnostic diagrams are most sensitive
to the spectral index of the ionizing radiation field in the 1-4 Rydberg
region. We find that warm infrared starburst galaxies contain a relatively hard
EUV field in this region. The PEGASE ionizing stellar continuum is harder in
the 1-4 Rydberg range than that of STARBURST99. As the spectrum in this regime
is dominated by emission from Wolf-Rayet (W-R) stars, this difference is most
likely due to the differences in stellar atmosphere models used for the W-R
stars. We believe that the stellar atmospheres in STARBURST99 are more
applicable to the starburst galaxies in our sample, however they do not produce
the hard EUV field in the 1-4 Rydberg region required by our observations. The
inclusion of continuum metal blanketing in the models may be one solution.
Supernova remnant (SNR) shock modeling shows that the contribution by
mechanical energy from SNRs to the photoionization models is << 20%. The models
presented here are used to derive a new theoretical classification scheme for
starbursts and AGN galaxies based on the optical diagnostic diagrams.Comment: 36 pages, 16 figures, to be published in ApJ, July 20, 200
Two-Dimensional Electronic Spectroscopy of Chlorophyll a: Solvent Dependent Spectral Evolution
The interaction of the monomeric chlorophyll Q-band electronic transition with solvents of differing physical-chemical properties is investigated through two-dimensional electronic spectroscopy (2DES). Chlorophyll constitutes the key chromophore molecule in light harvesting complexes. It is well-known that the surrounding protein in the light harvesting complex fine-tunes chlorophyll electronic transitions to optimize energy transfer. Therefore, an understanding of the influence of the environment on the monomeric chlorophyll electronic transitions is important. The Q-band 2DES is inhomogeneous at early times, particularly in hydrogen bonding polar solvents, but also in nonpolar solvents like cyclohexane. Interestingly this inhomogeneity persists for long times, even up to the nanosecond time scale in some solvents. The reshaping of the 2DES occurs over multiple time scales and was assigned mainly to spectral diffusion. At early times the reshaping is Gaussian-like, hinting at a strong solvent reorganization effect. The temporal evolution of the 2DES response was analyzed in terms of a Brownian oscillator model. The spectral densities underpinning the Brownian oscillator fitting were recovered for the different solvents. The absorption spectra and Stokes shift were also properly described by this model. The extent and nature of inhomogeneous broadening was a strong function of solvent, being larger in H-bonding and viscous media and smaller in nonpolar solvents. The fastest spectral reshaping components were assigned to solvent dynamics, modified by interactions with the solute
Water Dynamics at Protein Interfaces: Ultrafast Optical Kerr Effect Study
The behavior of water molecules surrounding a protein can have an important bearing on its structure and function. Consequently, a great deal of attention has been focused on changes in the relaxation dynamics of water when it is located at the protein surface. Here we use the ultrafast optical Kerr effect to study the H-bond structure and dynamics of aqueous solutions of proteins. Measurements are made for three proteins as a function of concentration. We find that the water dynamics in the first solvation layer of the proteins are slowed by up to a factor of 8 in comparison to those in bulk water. The most marked slowdown was observed for the most hydrophilic protein studied, bovine serum albumin, whereas the most hydrophobic protein, trypsin, had a slightly smaller effect. The terahertz Raman spectra of these protein solutions resemble those of pure water up to 5 wt % of protein, above which a new feature appears at 80 cmâ1, which is assigned to a bending of the protein amide chain
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