6,954 research outputs found

    The Radio-to-Submillimeter Flux Density Ratio of Galaxies as a Measure of Redshift

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    We re-examine the technique of determining the redshifts of galaxies from the ratio of the submillimeter-to-radio continuum flux densities based on a recently published catalog of 850~μ\mum sources. We derived the expected variation of this ratio as a function of redshift incorporating the expected average luminosity and the spectral energy distribution (SED) of dust emission and the radio continuum. We find that the existing data for most of the high redshift (z \gtsim 1) sources correspond to our new calculation. Amongst the well-identified sources, there is none with an index significantly higher than predicted. Sources which have an index lower than predicted are either within the error zone or much lower, the latter presumably having AGN-dominated radio-continuum emission. We find the median redshift to be 2\sim 2, which is consistent with that deduced by previous work (3\sim 3) within the error. We also discuss the various systematic effects that can affect the accuracy of the redshift estimate. We examine other methods of redshift estimation, like photometric ratio in the submillimeter and locating the peak of the SED in the rest system of the objects. We conclude that while the various methods are helpful in identifying high-redshift objects and making a crude estimate of the redshift, they are not, at present, accurate enough for a detailed study of redshift distribution of the submillimeter galaxies.Comment: 6 pages LaTeX, PASJ in pres

    Structure of Stationary Photodissociation Fronts

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    The structure of stationary photodissociation fronts is revisited. H_2 self- shielding is discussed, including the effects of line overlap. We find that line overlap is important for N(H_2) > 10^{20} cm^{-2}. We compute multiline UV pumping models, and compare these with simple analytic approximations for the effects of self-shielding. The overall fluorescent efficiency of the photodissociation front is obtained for different ratios of chi/n_H (where chi characterizes the intensity of the incident UV) and different dust extinction laws. The dust optical depth tau_{pdr} to the point where 50% of the H is molecular is found to be a simple function of a dimensionless quantity phi_0 depending on chi/n_H, the rate coefficient for H_2 formation on grains, and the UV dust opacity. The fluorescent efficiency of the PDR also depends primarily on phi_0 for chi<3000 and n_H<10^4 cm^{-3}; for stronger radiation fields and higher densities radiative and collisional depopulation of vibrationally-excited levels interferes with the radiative cascade. The emission spectrum from the PDR is essentially independent of the color temperature TcolorT_{color} of the incident UV for T_{color}>10^4K, but shows some sensitivity to the v-J distribution of newly-formed H_2. The 1-0S(1)/2-1S(1) and 2-1S(1)/6-4Q(1) intensity ratios, the ortho/para ratio, and the rotational temperature in the vv=1 and vv=2 levels are computed as functions of the temperature and density, for different values of chi and n_H. We apply our models to the reflection nebula NGC 2023. We are best able to reproduce the observations with models having chi=5000, n_H=10^5 cm^{-3}.Comment: 50 pages, 24 eps figures, uses aaspp4.sty . To appear in Ap.

    Whitham Deformations of Seiberg-Witten Curves for Classical Gauge Groups

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    Gorsky et al. presented an explicit construction of Whitham deformations of the Seiberg-Witten curve for the SU(N+1)SU(N+1) \calN = 2 SUSY Yang-Mills theory. We extend their result to all classical gauge groups and some other cases such as the spectral curve of the A2N(2)A^{(2)}_{2N} affine Toda Toda system. Our construction, too, uses fractional powers of the superpotential W(x)W(x) that characterizes the curve. We also consider the uu-plane integral of topologically twisted theories on four-dimensional manifolds XX with b2+(X)=1b_2^{+}(X) = 1 in the language of these explicitly constructed Whitham deformations and an integrable hierarchy of the KdV type hidden behind.Comment: latex, 39pp, no figure; some more comments and references on integrable systems are added, and many typos are correcte
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