A Catalog of Smaller Planets

Earth, Moon, and Planets - A compilation was made of N?=?89 planets or moons for which the mass and radius are known, between the limits of 0.01 and 10 times the mass of Earth. Although...     

Extended gas in Seyfert 2 galaxies: implications for the nuclear source

We use long-slit spectroscopic optical data to derive the properties of the extended emitting gas and the nuclear luminosity of a sample of 18 Seyfert 2 galaxies. From the emission-line luminosities and ratios we derive the density, reddening and mass of the ionized gas as a function of distance up to 2–4 kpc from the nucleus. Taking into account the geometric dilution of the nuclear radiation, we derive the radial distribution of covering factors and the minimum rate of ionizing photons emitted by the nuclear source. This number is an order of magnitude larger than that obtained from the rate of ionizing photons 'intercepted' by the gas and measured from the Hα luminosity. A calibration is proposed to recover this number from the observed luminosity. The He  ii λ4686/Hβ line ratio was used to calculate the slope of the ionizing spectral energy distribution (SED), which in combination with the number of ionizing photons allows the calculation of the hard X-ray luminosities. These luminosities are consistent with those derived from X-ray spectra in the eight cases for which such data are available and recover the intrinsic X-ray emission in Compton-thick cases. Our method can thus provide reliable estimates of the X-ray fluxes in Seyfert 2 galaxies for the cases where it is not readily available. We also use the ionizing SED and luminosity to predict the infrared luminosity under the assumption that it is dominated by reprocessed radiation from a dusty torus, and find a good agreement with the observed IRAS luminosities.     

The Rest-Frame Optical Spectrum of MS 1512-cB58

Moderate-resolution, near-IR spectroscopy of MS 1512-cB58 is presented, obtained during commissioning of the near-infrared spectrometer (NIRSPEC) on the Keck II telescope. The strong lensing of this z=2.72 galaxy by the foreground cluster MS 1512+36 makes it the best candidate for detailed study of the rest-frame optical properties of Lyman-break galaxies. In 80 minutes of on-source integration, we have detected Halpha, [N ii] lambdalambda6583, 6548, [O i] lambda6300, He i lambda5876, [O iii] lambdalambda5007, 4959, Hbeta, Hgamma, [O ii] lambda3727, and a strong continuum signal in the range of 1.29-2.46 μm. A redshift of z=2.7290+/-0.0007 is inferred from the emission lines, in contrast to the z=2.7233 calculated from UV observations of interstellar absorption lines. Using the Balmer line ratios, we find an extinction of E(B-V) = 0.27. Using the line strengths, we infer a star formation rate (SFR) of 620+/-18 M middle dot in circle yr-1 (H0=75, q0=0.1, and Lambda=0), which is a factor of 2 higher than that measured from narrowband imaging observations of the galaxy but is a factor of almost 4 lower than the SFR inferred from the UV continuum luminosity. The width of the Balmer lines yields a mass of Mvir=1.2x1010 M middle dot in circle. We find that the oxygen abundance is 13 solar, in good agreement with other estimates of the metallicity. However, we infer a high nitrogen abundance, which may argue for the presence of an older stellar population.     

Communicating science: A media dilemma an editorial/review essay

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