Galaxy formation and evolution

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A UV flare at the center of the elliptical galaxy NGC 4552

IAU SYMP (1999) 389-393

Authors:

LM Buson, F Bertola, D Burstein, M Cappellari, SD Alighieri, L Greggio, A Renzini

Abstract:

A self-consistent analysis of near-UV, HST/FOC images of the elliptical galaxy NGC 4552 is used to show that its central spike has brightened by a factor similar to 4.5 between 1991 and 1993, and has decreased its luminositv by a factor similar to 2.0 between 1993 and 1996. A strong UV continuum over the energy distribution of the underlying galaxy is concurrently revealed shortward of lambda similar to 3200 Angstrom by our FOS spectra extending from the near-UV to red wavelengths. Nuclear emission-line profiles of both permitted and forbidden lines are best modelled with a combination of broad and narrow components, with FWHM of similar to 3000 km s(-1) and similar to 700 km s(-1), respectively. Current diagnostics based on the emission line intensity ratios definitely places the spike among AGNs, just at the border between Seyferts and LINERs. This evidence argues for the variable central spike being produced by a modest accretion event onto a central massive black hole (BH), with the accreted material having possibly being stripped from a star in a close fly-by with the BH. In this regard, one has to look at NGC 4552 as the faintest known AGN.
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A large mid-infrared spectroscopic and near-infrared imaging survey of ultraluminous infrared galaxies: Their nature and evolution

ASTRONOMICAL JOURNAL 118:6 (1999) 2625-2645

Authors:

D Rigopoulou, HWW Spoon, R Genzel, D Lutz, AFM Moorwood, QD Tran
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A large-scale bulk flow of galaxy clusters

ASTROPHYSICAL JOURNAL 512:2 (1999) L79-L82

Authors:

MJ Hudson, RJ Smith, JR Lucey, DJ Schlegel, RL Davies
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A serendipitous search for hy-redshift Lyα emission:: A case study of two sources at z ≃ 3

HY-REDSHIFT UNIVERSE: GALAXY FORMATION AND EVOLUTION AT HIGH REDSHIFT 193 (1999) 521-524

Authors:

C Manning, D Stern, H Spinrad, AJ Bunker
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An ISO survey of PAH features in Ultraluminous Infrared Galaxies

ASTR SOC P 177 (1999) 171-174

Authors:

D Lutz, R Genzel, D Rigopoulou, HWW Spoon, D Tran, AFM Moorwood

Abstract:

We have obtained ISOPHOT-S low resolution mid-infrared spectra of a sample of 60 Ultraluminous Infrared Galaxies (ULIRGs). We use the strength of the 'PAH' mid-infrared features as a discriminator between starburst and AGN activity, and to probe for evolutionary effects. Observed ratios of PAH features in ULIRGs differ slightly from those in lower luminosity starbursts. We suggest that such PAH ratio changes relate to the conditions in the interstellar medium in these galaxies, and in particular to extinction.
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