Hubble Space Telescope Wide Field Planetary Camera 2 imaging of UGC 12695: A remarkably unevolved galaxy at low redshift

Karen O'Neil, G. D. Bothun, C. D. Impey, S. McGaugh

Research output: Contribution to journalArticle

7 Scopus citations

Abstract

Utilizing the F814W and F300W filters, short-exposure Hubble Space Telescope Wide Field Planetary Camera 2 images were taken of UGC 12695, a nearby (z ∼ 0.021) low surface brightness disk galaxy. UGC 12695 has an unusual morphology, consisting of a Y-shaped nucleus surrounded by a faint spiral arm with a number of bright H II regions interspersed throughout the galaxy. Surface photometry indicates that the majority of recent star formation in this galaxy occurred in these very localized regions, most of which have a radius of ≲2″. This uneven stellar distribution, combined with the galaxy's overall extremely blue color and low metallicity, indicates that UGC 12695 is an unevolved galaxy. Some of the structural peculiarities of this galaxy arise because a number of background galaxies, previously thought to be morphological components of this galaxy, are showing through both the outer nucleus and spiral arms of UGC 12695. Surface photometry of these galaxies shows them to be fairly small (α < 1″.8) disk galaxies with total magnitudes ranging from 19.6 through 24.2 mag and central surface brightnesses in the range 20.2 mag arcsec-2 ≤ μ(0) ≤ 23.1 mag arcsec-2. When possible, the U, B, V, and I colors of these galaxies were measured using ground-based images, which show the galaxies to be fairly red, indicating that they are likely at redshifts z ≥ 0.5. Inclusion of them in the photometry of UGC 12695 makes the galaxy appear significantly redder. When these galaxies are masked out, the resultant U-I color of UGC 12695 is -0.2 ± 0.1, making it perhaps the bluest galaxy ever measured in this color system and confirming its nature as a very unevolved galaxy at low redshift. Spectroscopy of these background galaxies, through the transparent disk of UGC 12695, may help to clarify its chemical evolution and current heavy-element content.

Original languageEnglish (US)
Pages (from-to)657-672
Number of pages16
JournalAstronomical Journal
Volume116
Issue number2
DOIs
StatePublished - Aug 1998

Keywords

  • Evolution - galaxies
  • Fundamental parameters - galaxies
  • Galaxies
  • ISM - galaxies
  • Individual (UGC 1.2695) - Galaxies
  • Photometry - Magellanic Clouds

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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