Mid-Infrared Spectra of Classical AGNs Observed with the Spitzer Space Telescope

By D. Weedman, L. Hao, S. Higdon, D. Devost, Yanling Wu, Vassilis Charmandaris, B. Brandl, E. Bass, J. Houck. 2005

188 citations recorded by the source corpus.

Full low-resolution (65 < R < 130) and high-resolution (R ~ 600) spectra between 5 and 37 μm obtained with the Infrared Spectrograph (IRS) on the Spitzer Space Telescope are presented for eight classical active galactic nuclei (AGNs) that have been extensively studied previously. Spectra of these AGNs are presented as comparison standards for the many objects, including sources at high redshift, that are being observed spectroscopically in the mid-infrared for the first time using the IRS. The AGNs are NGC 4151, Mrk 3, I Zw 1, NGC 1275, Centaurus A, NGC 7469, Mrk 231, and NGC 3079. These sources are used to demonstrate the range of infrared spectra encountered in objects that have widely different classification criteria at other wavelengths but that unquestionably contain AGNs. Overall spectral characteristics, including continuum shape, nebular emission lines, silicate absorption and emission features, and PAH emission features, are considered to understand how spectral classifications based on mid-infrared spectra relate to those previously derived from optical spectra. The AGNs are also compared to the same parameters for starburst galaxies such as NGC 7714 and the compact, low-metallicity starburst SBS 0335-052 previously observed with the IRS. Results confirm the much lower strengths of PAH emission features in AGNs, but there are no spectral parameters in this sample that unambiguously distinguish AGNs and starbursts based only on the slopes of the continuous spectra.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/bc9833b88554e8aec16b792bfef556e7d2ed62db

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In Astronomy and Astrophysics

1. D. M. Alexander
2. H. Netzer
3. L. Hernquist
4. P. Hopkins
5. R. Maiolino
6. R. Genzel
7. D. Lutz
8. Sylvain Veilleux

Citations in the corpus

• Dust covering factor, silicate emission, and star formation in luminous QSOs (2007, background): “…to: R. Maiolino allowed the detection of MIR emission lines in several AGNs (e.g. Armus et al., 2004; Haas et al., 2005; Sturm et al., 2006a; Weedman et al., 2005), the detection of PAHs in local PG QSOs (Schweitzer et al., 2006), the first detection of the Silicate feature in emission…”
• AGN Dusty Tori. II. Observational Implications of Clumpiness (2008, background): “Unfortunately, NGC 7469 is a clear case where the IR signature is dominated by the starburst component even though the AGN dominates the optical classification (Weedman et al. 2005); therefore, the resolved compact structure cannot be identified with the torus (see alsoDavies et al. 2004).”
• Spitzer Quasar and ULIRG Evolution Study (QUEST). I. The Origin of the Far-Infrared Continuum of QSOs (2006, methodology): “We add two Palomar-Green objects from the Guyon et al. sample previously observed by Spitzer (PG 0050þ 124 ¼ IZw 1 [Weedman et al. 2005] and PG 0157þ 001 ¼ Mrk 1014 [Armus et al. 2004]) and two PGQSOs from another project (PID 20241; PI Lutz).”
• The Mid-Infrared Properties of Starburst Galaxies from Spitzer-IRS Spectroscopy (2006, background): “PAH Strength and Radiation Field It is well known that the equivalent width of PAHs is much reduced in AGN-dominated environments (e.g., Sturm et al. 2000; Genzel & Cesarsky 2000; Weedman et al. 2005).”
• OPTICAL SPECTROSCOPY AND NEBULAR OXYGEN ABUNDANCES OF THE SPITZER/SINGS GALAXIES (2010, background): “Galaxies hosting powerful AGNs were intentionally excluded from the sample as a more complete sample of AGNs have been observed as part of complementary Spitzer Guaranteed Time Observer (GTO) programs (e.g., Weedman et al. 2005; Wu et al. 2009).”
• Towards a complete census of AGN in nearby Galaxies: a large population of optically unidentified AGN (2009, background): “32, 24.32 µm (97.1 eV), mid-IR spectroscopy provides an unambiguous indicator of AGN activity in nearby galaxies (e.g., Weedman et al. 2005; Armus et al. 2006).1 The relative optical depth at midIR wavelengths is also considerably lower than at optical wavelengths (Aλ14.”
• A diversity of dusty AGN tori - Data release for the VLTI/MIDI AGN Large Program and first results for 23 galaxies (2013, background): “In the narrow atmospheric N band the feature is sometimes hard to discern; for a clearer example of the silicate feature in absorption and emission, see the space-based spectra from Spitzer IRS (e.g. Weedman et al., 2005).”
• The Distribution of Silicate Strength in Spitzer Spectra of AGNs and ULIRGs (2006, methodology): “The deepest silicate absorption for sources with unambiguously identified broad Balmer lines is 0.65, from Mrk 231 (Weedman et al. 2005).”
• The active nuclei of z < 1.0 3CRR radio sources (2009, background): “Weedman et al. (2005) argue on the basis of the silicate feature at 10 μm that the Spitzer emission comes from dust rather than non-thermal (i.e. jetrelated) AGN emission, but it is not clear whether the dust emission is truly nuclear or is related to the gas and star formation known to be present…”
• Observations of Ultraluminous Infrared Galaxies with the Infrared Spectrograph on the Spitzer Space Telescope. II. The IRAS Bright Galaxy Sample (2006, methodology): “In both cases the fine structure line ratio is plotted against the 6.2µm PAH equivalent width (EQW) in microns, and a sample of AGN and starburst galaxies observed with the IRS are shown for comparison (Devost et al. 20006, Brandl et al. 2005, Weedman et al. 2005, Hao et al. 2005).”
• THE NEXT GENERATION ATLAS OF QUASAR SPECTRAL ENERGY DISTRIBUTIONS FROM RADIO TO X-RAYS (2011, methodology): “These features have been investigated in detail in previous studies (e.g., Hao et al. 2005; Weedman et al. 2005; Dale et al. 2009; Goulding & Alexander 2009; Diamond-Stanic et al. 2009; Pereira-Santaella et al. 2010; Tommasin et al. 2010), and have been kept in our analyses.”
• Mid-Infrared Galaxy Classification Based on Silicate Obscuration and PAH Equivalent Width (2006, methodology): “This sample is compared to samples of AGN and starburst templates from the IRS GTO programs 14 (Brandl et al. 2006; Weedman et al. 2005) and 96 and to selected AGNs from the GTO programs 82 and 86 (Shi et al. 2006).”
• MID-INFRARED SPECTROSCOPY OF SUBMILLIMETER GALAXIES: EXTENDED STAR FORMATION IN MASSIVE HIGH-REDSHIFT GALAXIES (2009, background): “…investigation of the mid-IR properties of local galaxies with IRS provides for a sample of detailed templates against which high-redshift sources can be compared (e.g., Spoon et al. 2004; Armus et al. 2004, 2006, 2007; Weedman et al. 2005; Brandl et al. 2006; Sturm et al. 2006; Desai et al. 2007).”
• A Spitzer IRS Low-Resolution Spectroscopic Search for Buried AGNs in Nearby Ultraluminous Infrared Galaxies: A Constraint on Geometry between Energy Sources and Dust (2007, background): “A power-law continuum is assumed here, because the intrinsic unabsorbed 5–35 m spectrum of AGN-heated hot dust emission is roughly approximated by a power-law form (Weedman et al. 2005).”
• High-Resolution Mid-Infrared Spectroscopy of Ultraluminous Infrared Galaxies (2007, methodology): “Observationally, however, PAH features are usually prominent in starburst galaxies, with previous authors noting a good correlation between the strength of PAH features and IR luminosity in starbursts (Brandl et al. 2006), but appear to be weak or absent in AGNs (Weedman et al. 2005).”
• Star Formation in the Hosts of High-z QSOs: Evidence from Spitzer PAH Detections (2008, background): “…to the continuum but has similarity with the 8µm feature in the mid-infrared spectrum of the well known Type 1 AGN and ULIRG Mrk 231 (Rigopoulou et al. 1999; Spoon et al. 2002; Weedman et al. 2005; Armus et al. 2007) which may originate from a combination of silicate emission and absorption.”
• Defining the intrinsic AGN infrared spectral energy distribution and measuring its contribution to the infrared output of composite galaxies (2011, methodology): “In previous studies this has been attributed to a dominating warm (i.e.,∼ 170 K) dust component that is heated by the AGN (e.g., Weedman et al. 2005; Buchanan et al. 2 AKARI data were retrieved from the NASA/IPAC Infrared Scienc Archive at http://irsa.ipac.caltech.edu/.”
• Chandra and Spitzer Unveil Heavily Obscured Quasars in the Chandra/SWIRE Survey (2006, background): “In the mid-IR, AGNs are characterized by red and almost featureless spectra (Houck et al. 2005; Hao et al. 2005; Weedman et al. 2005).”