Hubble Space Telescope observations of QSO absorption lines associated with starburst galaxy outflows

Colin A. Norman, David V. Bowen, Tim Heckan, Chris Blades, Laura Danly

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In order to study the physical state of outflows from starburst galaxies, we have been obtaining spectra of QSOs located behind possible starburst outflows and searching for UV absorption by lowionization gas. We have detected strong and probably complex Mg II, Mg I, and Fe II absorption arising from gas in the outer envelope of the starburst galaxy NGC 520 at a distance from the galactic nucleus of 24 h-1 kpc and possible weak Mg II absorption at a distance of 52 h-1 kpc. The detection of absorption at these distances is consistent with the idea that the size of gaseous envelopes around starburst galaxies is greatly enhanced from outflows of gas from the galaxies' nuclei, but it is also possible that the absorption arises from tidally disrupted gas associated with the interactions between NGC 520 and a dwarf galaxy companion. In the former case, the data would be consistent with starburst outflows generating the QSO absorption lines observed in extended halos at high redshift. In the latter case, the data is consistent with the low-redshift Mg II absorbers being associated with tidal debris. We have also searched for Mg II absorption along two sight lines toward NGC 253, both at a distance of 44 kpc from the galaxy. Complex structure is seen, which may arise-in gas associated with NGC 253. However, any absorption at the systemic velocity of NGC 253 is expected to be close to local Galactic absorption, and indeed the Mg II lines seen toward Q0042-2450 from the Milky Way are resolved and asymmetric. However, the sight lines to this QSO pass close to the Magellanic Stream, and we suggest that, with the current data, an equally likely possibility is that the additional absorption may arise in low column density gas associated with the Stream. Further searches for high-ionization absorption lines (such as C iv and N v) from starburst outflows in NGC 253 and other galaxies may well be successful.

Original languageEnglish (US)
Pages (from-to)73-82
Number of pages10
JournalAstrophysical Journal
Issue number1 PART I
StatePublished - 1996
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • Galaxies: halos
  • Galaxies: starburst
  • Quasars: absorption lines
  • Ultraviolet: galaxies


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