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Date and Time of the Query: 2019-06-25 T13:24:31 PDT
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For refcode 1995A&A...301...55O:
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Copyright by European Southern Observatory (ESO). Reproduced by permission
1995A&A...301...55O Red supergiants as starburst tracers in galactic nuclei E. Oliva, L. Origlia, J.K. Kotilainen, and A.F.M. Moorwood Osservatorio Astrofisico di Arcetri, Largo E.Fermi 5,I-50125 Firenze, Italy Osservatorio Astronomico di Torino, Strada Osservatorio 20,I-10025 Pino Torinese, Italy European Southern Observatory, Karl Schwarzschild str. 2, D-85748 Garching bei Munchen, Germany Tuorla Observatory, University of Turku Vaisalanti, SF-2 1500 Piikkio, Finland Received 28 November 1994/Accepted 13 February 1995 Abstract. We present infrared spectral observations of CO (1.62, 2.29 microns) and Si (1.59 microns) stellar absorption features in 23 galaxies including 14 calibrators (normal ellipticals/spirals and well known HII galaxies) and 9 Seyferts. Our main aim was to define and calibrate an observational method for tracing red supergiants (i.e. starbursts) in active galaxies. Additional spectra were also obtained around the Br{gamma} hydrogen recombination line. The measured equivalent widths of the absorption features in old stellar systems and HII galaxies are found to be remarkably similar and the CO and Si indices do not therefore provide reliable diagnostics for distinguishing red supergiants (i.e. starbursts) from metallic red giants (i.e. old stellar systems). A more sensitive quantity is found to be the light to mass ratio (L_H_/M) as inferred from the observed 1.65 micron stellar luminosities and velocity dispersions. All HII galaxies and several of the seyfert 2's exhibit L_H_/M values a factor ~5 larger than normal ellipticals and spirals. Both the L_H_/M ratios and the Br{gamma} equivalent widths in Sy 2's are consistent with the presence of starbursts which are older than those in HII galaxies. A large fraction of the near infrared (< 2 micron) continuum in Sy 1's also appears to be stellar but associated with even older starburst activity or normal red giants in the galaxy bulge. These results therefore provide additional support for evolutionary models in which Seyfert activity is related to the presence of a black hole which is formed/fueled by the remnants of a pre-cursor starburst. The origin of the non-stellar 2 micron continuum in Seyferts and the metallicity of ellipticals are also discussed. Key words: galaxies: nuclei - galaxies: Seyfert - galaxies: starburst - galaxies: stellar content - infrared: galaxies
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