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A Comparative Study of the Absolute Magnitude Distributions of Supernovae
The Asiago Supernova Catalog is used to carry out a comparative study ofsupernova absolute magnitude distributions. An overview of the absolutemagnitudes of the supernovae in the current observational sample ispresented, and the evidence for subluminous and overluminous events isexamined. The fraction of supernovae that are subluminous(MB>-15) appears to be higher (perhaps much higher) than1/5 but it remains very uncertain. The fraction that are overluminous(MB>-20) is lower (probably much lower) than 0.01. Theabsolute magnitude distributions for each supernova type, restricted toevents within 1 Gpc, are compared. Although these distributions areaffected by observational bias in favor of the more luminous events,they are useful for comparative studies. We find mean absolute bluemagnitudes (for H0=60) of -19.46 for normal Type Iasupernovae (SNe Ia), -18.04 for SNe Ibc, -17.61 and -20.26 for normaland bright SNe Ibc considered separately, -18.03 for SNe II-L, -17.56and -19.27 for normal and bright SNe II-L considered separately, -17.00for SNe II-P, and -19.15 for SNe IIn.
| On the Ionizing Continuum in Active Galactic Nuclei: Clues from the Infrared Space Observatory
The Infrared Space Observatory (ISO) coronal line spectrum of thebrightest Seyfert galaxies from the CfA sample is presented and modeled.ISO observations of [O IV] 25.9 μm, [Ne V] 14.3 μm, [Mg VIII] 3.02μm, and [Si IX] 2.58 μm lines are presented; their relationshipwith the soft part of the ionizing spectrum from 50 to 300 eV isinvestigated. Pure photoionization models reproduce the line ratios,setting ranges for the ionization parameter and the optical depth of theemitting clouds. On the basis of the available data alone it is notpossible to distinguish between a power-law or a blackbody distributionas the intrinsic shape of the UV-ionizing spectrum. However, for thebrightest Seyfert galaxies analyzed, namely, NGC 1068, Circinus, and NGC4151, a blackbody UV continuum is favored.
| The Southern Sky Redshift Survey
We report redshifts, magnitudes, and morphological classifications for5369 galaxies with m_B <= 15.5 and for 57 galaxies fainter than thislimit, in two regions covering a total of 1.70 sr in the southerncelestial hemisphere. The galaxy catalog is drawn primarily from thelist of nonstellar objects identified in the Hubble Space TelescopeGuide Star Catalog (GSC). The galaxies have positions accurate to ~1"and magnitudes with an rms scatter of ~0.3 mag. We compute magnitudes(m_SSRS2) from the relation between instrumental GSC magnitudes and thephotometry by Lauberts & Valentijn. From a comparison with CCDphotometry, we find that our system is homogeneous across the sky andcorresponds to magnitudes measured at the isophotal level ~26 magarcsec^-2. The precision of the radial velocities is ~40 km s^-1, andthe redshift survey is more than 99% complete to the m_SSRS2 = 15.5 maglimit. This sample is in the direction opposite that of the CfA2; incombination the two surveys provide an important database for studies ofthe properties of galaxies and their large-scale distribution in thenearby universe. Based on observations obtained at Cerro TololoInter-American Observatory, National Optical Astronomy Observatories,operated by the Association of Universities for Research in Astronomy,Inc., under cooperative agreement with the National Science Foundation;Complejo Astronomico El Leoncito, operated under agreement between theConsejo Nacional de Investigaciones Científicas de laRepública Argentina and the National Universities of La Plata,Córdoba, and San Juan; the European Southern Observatory, LaSilla, Chile, partially under the bilateral ESO-ObservatórioNacional agreement; Fred Lawrence Whipple Observatory;Laboratório Nacional de Astrofísica, Brazil; and the SouthAfrican Astronomical Observatory.
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