Constraints on accretion in ultraluminous X-ray sources from Spitzer IRS observations of NGC 4485/4490: Infrared diagnostic diagrams

Gerardo A. Vázquez, Ann E. Hornschemeier, Edward Colbert, Timothy P. Roberts, Martin J. Ward, Sangeeta Malhotra

Research output: Contribution to journalArticle

6 Citations (Scopus)

Abstract

Constraining the astrophysical nature of ultraluminous X-ray (ULX) sources, which have X-ray luminosities exceeding 1039 ergs s-1, has been elusive due to the optical faintness of any counterparts. With high spectral resolution observations in the ∼10-30 μm wavelength range we have conducted an experiment to study six ULX sources in the NGC 4485/4490 galaxy pair. We have found that five of the six ULXs, based on mid-infrared spectral diagnostics, show the characteristic higher ionization features that are found in AGNs. The sixth source, ULX-1, is consistent with being a supernova remnant. The chief infrared spectral diagnostics used are the ratios of [S III]/[Si II] versus [Ne III]/[Ne II]. In two instances fits to the continuum and polycyclic aromatic hydrocarbon (PAH) features also indicate higher dust temperatures, which are characteristic of accreting sources. Overall, however, we find that the continuum is dominated by stellar processes, and the best diagnostic features are the emission lines. High spectral resolution studies in the mid-infrared thus appear to show great promise for determining the astrophysical nature of ULXs.

Original languageEnglish (US)
JournalAstrophysical Journal
Volume658
Issue number1 II
DOIs
StatePublished - Mar 20 2007

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Indian spacecraft
diagram
diagrams
accretion
spectral resolution
astrophysics
x rays
continuums
high resolution
polycyclic aromatic hydrocarbons
supernova remnants
erg
PAH
ionization
dust
luminosity
galaxies
wavelength
wavelengths
experiment

Keywords

  • Galaxies: general
  • Galaxies: individual (NGC 4485, NGC 4490)

ASJC Scopus subject areas

  • Space and Planetary Science
  • Astronomy and Astrophysics

Cite this

Constraints on accretion in ultraluminous X-ray sources from Spitzer IRS observations of NGC 4485/4490 : Infrared diagnostic diagrams. / Vázquez, Gerardo A.; Hornschemeier, Ann E.; Colbert, Edward; Roberts, Timothy P.; Ward, Martin J.; Malhotra, Sangeeta.

In: Astrophysical Journal, Vol. 658, No. 1 II, 20.03.2007.

Research output: Contribution to journalArticle

Vázquez, Gerardo A. ; Hornschemeier, Ann E. ; Colbert, Edward ; Roberts, Timothy P. ; Ward, Martin J. ; Malhotra, Sangeeta. / Constraints on accretion in ultraluminous X-ray sources from Spitzer IRS observations of NGC 4485/4490 : Infrared diagnostic diagrams. In: Astrophysical Journal. 2007 ; Vol. 658, No. 1 II.
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