Starburst or Seyfert? Adding a Radio and Far-Infrared Perspective to the Investigation of Activity in Composite Galaxies

It was once common to regard Seyfert and starburst galaxies as completely different types of object, but there is growing recognition that these classifications refer to the extremes of a continuous spectrum of galaxy types. In a previous study we investigated a sample of galaxies with ambiguous optical emission-line ratios and concluded from near-infrared spectroscopic observations that the sample consisted of composite galaxies, containing both a starburst and an active galactic nucleus (AGN). We now extend our study using radio synthesis and long-baseline interferometer observations made with the Australia Telescope, together with far-infrared IRAS observations, to discuss the relative contribution of starburst and AGN components to the overall luminosity of the composite galaxies. We find that only a small fraction of the radio emission (<10%) can be attributed to an AGN and that the majority of the far-infrared emission (>90%) is probably due to the starburst component. We also show that an AGN contribution to the optical emission of as little as 10% is sufficient to account for the ambiguous line-ratio diagnostics.

[1]  L. Kewley,et al.  Compact Radio Emission from Warm Infrared Galaxies , 2000 .

[2]  E. Deutsch.  Empirical Uncertainty Estimators for Astrometry from Digital Databases , 1999, astro-ph/9906177.

[3]  L. Kewley,et al.  Near-Infrared Spectral Mapping of NGC 1614 , 1999 .

[4]  R. Sutherland,et al.  Starburst or Seyfert? Using Near-Infrared Spectroscopy to Measure the Activity in Composite Galaxies , 1998, astro-ph/9810384.

[5]  R. Norris,et al.  Seyfert galaxies and the radio—far-infrared correlation , 1998 .

[6]  M. Dopita,et al.  Probing the Dusty Accretion Torus of Seyfert Galaxies , 1998 .

[7]  R. Norris,et al.  Star formation in southern Seyfert galaxies , 1998, astro-ph/9804298.

[8]  M. Haynes,et al.  Starburst Galaxies. III. Properties of a Radio-selected Sample , 1998 .

[9]  C. Lonsdale,et al.  A Starburst Revealed—Luminous Radio Supernovae in the Nuclei of Arp 220 , 1998 .

[10]  C. Lonsdale,et al.  The Starburst-AGN Connection. II. The Nature of Luminous Infrared Galaxies as Revealed by VLBI, VLA, Infrared, and Optical Observations , 1998 .

[11]  D. Kunze,et al.  What Powers Ultraluminous IRAS Galaxies? , 1997, astro-ph/9711255.

[12]  Andreas Quirrenbach,et al.  The Nuclear Stellar Core, the Hot Dust Source, and the Location of the Nucleus of NGC 1068 , 1997 .

[13]  S. Baum,et al.  A direct image of the obscuring disk surrounding an active galactic nucleus , 1997, Nature.

[14]  C. Leitherer,et al.  A Powerful Nuclear Starburst in the Seyfert Galaxy Markarian 477: Implications for the Starburst-Active Galactic Nucleus Connection , 1997 .

[15]  J. Reynolds,et al.  A study of cores in a complete sample of radio sources , 1997 .

[16]  N. Odegard,et al.  Detection and Characterization of Cold Interstellar Dust and Polycyclic Aromatic Hydrocarbon Emission, from COBE Observations , 1996, astro-ph/9610198.

[17]  C. Simpson,et al.  Forbidden Fe+ emission from active galaxies , 1996 .

[18]  B. Rocca-Volmerange,et al.  Near-IR spectral evolution of dusty starburst galaxies , 1996 .

[19]  D. Sanders,et al.  LUMINOUS INFRARED GALAXIES , 1996 .

[20]  B. Partridge,et al.  VLA Observations of Ultraluminous IRAS Galaxies: Active Nuclei or Starbursts? , 1995, astro-ph/9511069.

[21]  R. Hunstead,et al.  Snapshot Imaging with the Australia Telescope Compact Array , 1995 .

[22]  K. Matthews,et al.  The Nuclear Energy Sources Powering Bright Infrared-selected Galaxies , 1995 .

[23]  S. Veilleux,et al.  Optical Spectroscopy of Luminous Infrared Galaxies II. Analysis of the Nuclear and long-Slit Data , 1995 .

[24]  Alfred Krabbe,et al.  Infrared Imaging and Spectroscopy of NGC 7469 , 1995 .

[25]  Fionn Murtagh,et al.  In Astronomical Data Analysis Software and Systems IV , 1995 .

[26]  E. Greisen,et al.  The NRAO VLA Sky Survey , 1996 .

[27]  R. Ekers,et al.  Parsec-scale radio cores in early-type galaxies , 1994 .

[28]  M. Rowan-Robinson,et al.  Optical structure of a large sample of ultraluminous IRAS galaxies , 1994 .

[29]  G. Helou,et al.  A physical model of the infrared-to-radio correlation in galaxies , 1993 .

[30]  M. Dopita,et al.  Cooling functions for low-density astrophysical plasmas , 1993 .

[31]  M. Malkan,et al.  The Extended 12-micron galaxy sample , 1993, astro-ph/9306013.

[32]  C. Lonsdale,et al.  The starburst-AGN connection : a sensitive VLBI survey of luminous IRAS galaxies , 1993 .

[33]  Y. Taniguchi,et al.  The excitation mechanism of forbidden Fe II 1.644 micron emission in Seyfert and starburst galaxies revisited , 1993 .

[34]  C. Lonsdale,et al.  A VLBI search for AGN radio cores in starburst galaxies , 1992 .

[35]  J. Arens,et al.  Subarcsecond mid-infrared imaging of the nuclei of the infrared bright galaxies NGC 1614 and NGC 7469 , 1992 .

[36]  James J. Condon,et al.  Radio Emission from Normal Galaxies , 1992 .

[37]  D. Heeschen,et al.  Two radio supernovae in the unusual galaxy Markarian 297 , 1991, Nature.

[38]  C. Haniff,et al.  The starburst ring around the Seyfert nucleus in NGC 7469 , 1991 .

[39]  P. Alexander,et al.  A composite plot of far-infrared versus radio luminosity, and the origin of far-infrared luminosity in quasars , 1991 .

[40]  N. Panagia,et al.  Radio emission from supernovae. II, SN 1986J : a different kind of type II , 1990 .

[41]  Y. Taniguchi,et al.  Excitation mechanism of forbidden Fe II 1.644 micron emission in Seyfert and starburst galaxies , 1990 .

[42]  P. Wilkinson,et al.  Shell-like structure in 41.9 + 58, a powerful supernova remnant in M82 , 1990 .

[43]  J. Condon,et al.  A new starburst model applied to the clumpy irregular galaxy Markarian 325 , 1990 .

[44]  J. Hutchings,et al.  NGC 1614 - An IR-luminous merger but not (yet?) an active galaxy , 1990 .

[45]  M. Rowan-Robinson,et al.  High-luminosity IRAS galaxies. II - Optical spectroscopy, modelling of starburst regions and comparison with structure , 1989 .

[46]  P. Roche,et al.  The radio emission from far-infrared galaxies: Seyfert or starburst? , 1988 .

[47]  G. Neugebauer,et al.  Ultraluminous infrared galaxies and the origin of quasars , 1988 .

[48]  R. Edelson.  Broad-band properties of the CfA Seyfert galaxies. I: Radio properties , 1987 .

[49]  S. Veilleux,et al.  Spectral Classification of Emission-Line Galaxies , 1986 .

[50]  R. Sramek,et al.  Radio observations of starburst galaxies , 1986 .

[51]  M. Kesteven,et al.  The Parkes-Tidbinbilla Interferometer , 1988, Publications of the Astronomical Society of Australia.

[52]  E. Becklin,et al.  The 3 kiloparsec radio disk and halo of NGC 1068. , 1985 .

[53]  E. Salpeter,et al.  1.4 GHz continuum sources in the Hercules cluster , 1984 .

[54]  A. Wilson,et al.  Radio structures of Seyfert galaxies. IV. Jets (. ) in NGC 1068 and NGC 4151 , 1982 .

[55]  D. G. Hummer,et al.  Model Atmospheres for the Central Stars of Planetary Nebulae , 1970 .