Far-ultraviolet Color Gradients in Early-Type Galaxies

We discuss far-UV (FUV) (1500 Å) surface photometry and FUV-B color profiles for eight E/S0 galaxies from images taken with the Ultraviolet Imaging Telescope, primarily during the Astro-2 mission. In three cases, the FUV radial profiles are more consistent with an exponential than a de Vaucouleurs function, but there is no other evidence for the presence of a disk or of young, massive stars. In all cases except M32, the FUV-B color becomes redder at larger radii. There is a wide range of internal radial FUV-B color gradients. However, we find no correlation between the FUV-B color gradients and internal metallicity gradients based on Mg absorption features. We conclude that metallicity is not the sole parameter controlling the "UV upturn component" in old populations.

[1]  ApJ, in press , 1999 .

[2]  J. Holtzman,et al.  Far-Ultraviolet and Visible Imaging of the Nucleus of M32 , 1998, astro-ph/9804014.

[3]  S. Faber,et al.  Old Stellar Populations. VI. Absorption-Line Spectra of Galaxy Nuclei and Globular Clusters , 1997, astro-ph/9712258.

[4]  P. Demarque,et al.  On the Origin of the Ultraviolet Upturn in Elliptical Galaxies. II. Test of the Horizontal-Branch Hypothesis , 1997, astro-ph/9708185.

[5]  P. Demarque,et al.  On the Origin of the UV Upturn in Elliptical Galaxies. I. Sensitivity of UV Population Synthesis to Various Input Parameters , 1997, astro-ph/9705173.

[6]  Morton S. Roberts,et al.  THE ULTRAVIOLET IMAGING TELESCOPE: INSTRUMENT AND DATA CHARACTERISTICS , 1997, astro-ph/9704297.

[7]  Jang-Hyun Park,et al.  Evidence for a Sizable Age Spread among Galaxies from the Ultraviolet-Upturn Phenomenon in Early-type Systems , 1997 .

[8]  S. Pedraz,et al.  Stellar Populations in Dwarf Elliptical Galaxies , 1998 .

[9]  William B. Sparks,et al.  The Jet of M87 at Tenth-Arcsecond Resolution: Optical, Ultraviolet, and Radio Observations , 1996 .

[10]  H. Ferguson,et al.  A Far-Ultraviolet Analysis of the Stellar Populations in Six Elliptical and S0 Galaxies , 1996, astro-ph/9701235.

[11]  Jr.,et al.  Hubble Space Telescope Observations of M32: The Color-Magnitude Diagram , 1996, astro-ph/9607094.

[12]  Joy S. Nichols,et al.  The Final Archive and Recalibration of the International Ultraviolet Explorer (IUE) Satellite , 1996 .

[13]  Eric P. Smith,et al.  Ground-based CCD imaging in support of the ASTRO-1/UIT Space Shuttle mission , 1996 .

[14]  P. Dokkum,et al.  DUST IN THE CORES OF EARLY-TYPE GALAXIES , 1995, astro-ph/9507101.

[15]  J. González,et al.  Spectroscopic Gradients in Elliptical Galaxies , 1995, astro-ph/9507042.

[16]  D. Burstein,et al.  Hubble Space Telescope far-ultraviolet imaging of M31, M32, and NGC 205 , 1995 .

[17]  R. Rood,et al.  Ultraviolet radiation from evolved stellar populations. 2: The ultraviolet upturn phenomenon in elliptical galaxies , 1994, astro-ph/9405030.

[18]  G. Worthey.  Comprehensive stellar population models and the disentanglement of age and metallicity effects , 1994 .

[19]  Alessandro Bressan,et al.  Spectrophotometric evolution of elliptical galaxies. 1: Ultraviolet excess and color-magnitude-redshift relations , 1994 .

[20]  J. Rose.  The integrated spectra of M32 and of 47 Tuc: A comparative study at high spectral resolution , 1994 .

[21]  G. Joncas,et al.  A Study of the Stellar Populations of M32 Based on its Spacially Resolved Spectrum , 1994 .

[22]  H. Ferguson,et al.  The hot stellar component in elliptical galaxies and spiral bulges. I - The far-ultraviolet spectrum of the bulge of M31 , 1993 .

[23]  Wendy L. Freedman,et al.  Infrared-luminous giants in M32 - an intermediate-age population? , 1992 .

[24]  Sandra M. Faber,et al.  MG and Fe absorption features in elliptical galaxies , 1992 .

[25]  Gerd Weigelt,et al.  Preliminary analysis of an ultraviolet Hubble Space Telescope faint object camera image of the center of M31 , 1992 .

[26]  R. Hill,et al.  Ultraviolet imaging of old population in nearby galaxies , 1992 .

[27]  R. O’Connell,et al.  Ultraviolet Imaging Telescope Images of the Reflection Nebula NGC 7023: Derivation of Ultraviolet Scattering Properties of Dust Grains , 1992 .

[28]  M. Pinsonneault,et al.  The evolution of high-metallicity horizontal-branch stars and the origin of the ultraviolet light in elliptical galaxies , 1992 .

[29]  T. Davidge.  Absorption line gradients in the spectrum of M32 , 1991 .

[30]  A. Renzini,et al.  Clues on the hot star content and the ultraviolet output of elliptical galaxies , 1990 .

[31]  L. E. Davis,et al.  CCD surface photometry of galaxies with dynamical data. II. UBR photometry of 39 elliptical galaxies , 1990 .

[32]  B. McNamara,et al.  Star formation in cooling flows in clusters of galaxies , 1989 .

[33]  T. Lauer,et al.  The far-ultraviolet spectra of early-type galaxies , 1988 .

[34]  Roger L. Davies,et al.  Line-Strength Gradients in Elliptical Galaxies , 1993 .

[35]  T. X. Thuan,et al.  The strong UV source in the active E Galaxy NGC 4552 , 1986 .

[36]  R. Hill,et al.  Images in the rocket ultraviolet - The stellar population in the central bulge of M31 , 1985 .

[37]  G. Welch.  The ultraviolet spectrum of the center of M 31. , 1982 .

[38]  J. B. Oke,et al.  IUE observations of two elliptical galaxies - NGC 3379 and NGC 4472 , 1981 .

[39]  Allan Sandage,et al.  Revised Shapley-Ames Catalog of Bright Galaxies , 1980 .

[40]  A. Code,et al.  Ultraviolet photometry from the Orbiting Astronomical Observatory. XXVI. Energy distributions of seven early-type galaxies and the central bulge of M31. , 1979 .

[41]  G. de Vaucouleurs,et al.  Second reference catalogue of bright galaxies , 1976 .

[42]  R. Redman.  Stellar Populations , 1960, Nature.