UNCOVERING THE SPECTRAL ENERGY DISTRIBUTION IN ACTIVE GALAXIES USING HIGH-IONIZATION MID-INFRARED EMISSION LINES

Journal Article · Thu Sep 01 00:00:00 EDT 2011 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/738/1/6· OSTI ID:21582994

Melendez, M; Weaver, K A ^[1]; Kraemer, S B ^[2]; Mushotzky, R F ^[3]

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1. NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)
2. Institute for Astrophysics and Computational Sciences, Department of Physics, Catholic University of America, Washington, DC 20064 (United States)
3. Astronomy Department, University of Maryland, College Park, MD (United States)

The shape of the spectral energy distribution (SED) of active galaxies in the extreme-ultraviolet (EUV)-soft X-ray band (13.6 eV-1 keV) is uncertain because obscuration by dust and gas can hamper our view of the continuum. To investigate the shape of the SED in this energy band, we have generated a set of photoionization models which reproduce the small dispersion found in correlations between high-ionization mid-infrared emission lines in a sample of hard X-ray-selected active galactic nuclei (AGNs). Our calculations show that a broken power-law continuum model is sufficient to reproduce the [Ne V]{sub 14.32{mu}m}/[Ne III], [Ne V]{sub 24.32{mu}m}/[O IV]{sub 25.89{mu}m}, and [O IV]{sub 25.89{mu}m}/[Ne III] ratios and does not require the addition of a 'big bump' EUV model component. We constrain the EUV-soft X-ray slope, {alpha}{sub i}, to be between 1.5 and 2.0 and derive a best fit of {alpha}{sub i} {approx} 1.9 for Seyfert 1 galaxies, consistent with previous studies of intermediate-redshift quasars. If we assume a blue bump model, most sources in our sample have derived temperatures between T{sub BB} = 10{sup 5.18} K and 10{sup 5.7} K, suggesting that the peak of this component spans a large range of energies extending from {approx}600 A to 1900 A. In this case, the best-fitting peak energy that matches the mid-infrared line ratios of Seyfert 1 galaxies occurs between {approx}700 and 1000 A. Despite the fact that our results do not rule out the presence of an EUV bump, we conclude that our power-law model produces enough photons with energies >4 Ry to generate the observed amount of mid-infrared emission in our sample of Burst Alert Telescope AGNs.

• OSTI ID: 21582994
• Journal Information: Astrophysical Journal, Vol. 738, Issue 1; Other Information: DOI: 10.1088/0004-637X/738/1/6; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
EMISSION
ENERGY SPECTRA
EXTREME ULTRAVIOLET RADIATION
GALAXY NUCLEI
HARD X RADIATION
INFRARED RADIATION
PHOTOIONIZATION
SEYFERT GALAXIES
SOFT X RADIATION
X-RAY GALAXIES
COSMIC RAY SOURCES
COSMIC X-RAY SOURCES
ELECTROMAGNETIC RADIATION
GALAXIES
IONIZATION
IONIZING RADIATIONS
RADIATIONS
SPECTRA
ULTRAVIOLET RADIATION
X RADIATION