Observations of Ultraluminous Infrared Galaxies with the Infrared Spectrograph on the Spitzer Space Telescope. II. The IRAS Bright Galaxy Sample

By Lee Armus, Vassilis Charmandaris, Jeronimo Bernard-Salas, H. Spoon, J. Marshall, S. Higdon, Vandana Desai, H. Teplitz, L. Hao, D. Devost and 6 more. 2006

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We present spectra taken with the Infrared Spectrograph on Spitzer covering the 5-38 μm region of the 10 ultraluminous infrared galaxies (ULIRGs) found in the IRAS Bright Galaxy Sample (BGS). There is a factor of 50 spread in the rest-frame 5.5-60 μm spectral slopes, and the 9.7 μm silicate optical depths range from at least τ9.7 ≤ 0.4 (AV ~ 8) to τ9.7 ≥ 4.2 (AV ≥ 78). There is evidence for water ice and hydrocarbon absorption and C2H2 and HCN absorption features in 4 and possibly 6 of the 10 BGS ULIRGs, indicating shielded molecular clouds and a warm, dense ISM. We have detected [Ne V] emission in 3 of the 10 BGS ULIRGs, at flux levels of 5-18 × 10-14 ergs cm-2 s-1 and [Ne V] 14.3/[Ne II] 12.8 line flux ratios of 0.12-0.85. The remaining BGS ULIRGs have limits on their [Ne V]/[Ne II]line flux ratios, which range from ≤0.15 to ≤0.01. Among the BGS ULIRGs, the AGN fractions implied by either the [Ne V]/[Ne II] or [O IV]/[Ne II] line flux ratios (or their upper limits) are significantly lower than implied by the MIR slope or strength of the 6.2 μm PAH EQW feature. There is evidence for hot (T > 300 K) dust in five of the BGS ULIRGs, with the fraction of hot dust to total dust luminosity ranging from ~1% to 23%, before correcting for extinction. When integrated over the IRAC-8, IRS blue peak-up, and MIPS-24 filter bandpasses, the IRS spectra imply very blue colors for some ULIRGs at z ~ 1.3. The large range in diagnostic parameters among the nearest ULIRGs suggests that matching survey results to a small number of templates may lead to biased results about the fraction of luminous dusty starbursts and AGNs at high z.

Subfields: Astronomy and Astrophysics, Instrumentation

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Citations in the corpus

• The Star Formation History of the Universe as Revealed by Deep Radio Observations (2008, methodology): “First, we assembled a local comparison sample of ULIRGs dominated by star formation (according to the studies of Farrah et al. 2003; Armus et al. 2007) and with radio measurements at least at 1.4 and 8.4 GHz (Condon et al. 1991).”
• A physical model for z∼ 2 dust-obscured galaxies (2009, methodology): “We additionally include template SEDs for local galaxies Mrk 231 (Armus et al. 2007; Chary & Elbaz 2001, R. Chary, private communication), and Arp 220 (Rieke et al. 2009), each scaled to match the Bussmann et al. MultiBand Imaging Photometer for SIRTF (MIPS) 24-μm point and redshifted to z = 2.0.”
• The Stellar Mass Assembly of Galaxies from z = 0 to z = 4: Analysis of a Sample Selected in the Rest-Frame Near-Infrared with Spitzer (2007, methodology): “For ULIRGs, we used spectra from Armus et al. (2007) for the star-forming galaxies IRAS 1211, 1434, 1525, 2249, in addition to the data on Arp 220 and IRAS 17208 described by Donley et al. (2007).”
• THE MULTIPHASE STRUCTURE AND POWER SOURCES OF GALACTIC WINDS IN MAJOR MERGERS (2013, background): “Hot dust emission also points to an AGN (Armus et al. 2007).”
• The Herschel census of infrared SEDs through cosmic time (2013, background): “…1984b; Klaas et al. 1997; Clements, Dunne & Eales 2010), strong silicate absorption and polycyclic aromatic hydrocarbon (PAH) emission features in their mid-IR continuum (e.g., Brandl et al. 2006; Armus et al. 2007), as well as compact starburst sizes (e.g. Condon et al. 1991; Soifer et al. 2001).”
• MID-INFRARED SPECTROSCOPY OF SUBMILLIMETER GALAXIES: EXTENDED STAR FORMATION IN MASSIVE HIGH-REDSHIFT GALAXIES (2009, methodology): “We compare the mid-IR properties of the SMGs in our sample with those of starburst-dominated low-redshift galaxies (Brandl et al. 2006), select local ULIRGs from the Bright IRAS sample (Armus et al. 2006, 2007) and the mid-IR selected sources of Sajina et al. (2007) and Farrah et al. (2008).”
• EXPLAINING THE [C ii]157.7 μm DEFICIT IN LUMINOUS INFRARED GALAXIES—FIRST RESULTS FROM A HERSCHEL/PACS STUDY OF THE GOALS SAMPLE (2013, methodology): “This is most noticeable at mid-IR wavelengths (Laurent et al. 2000; Armus et al. 2007; Mullaney et al. 2011) but a non-negligible fraction of the far-IR emission of ULIRGs can also be powered by an AGN.”
• Luminous Infrared Galaxies with the Submillimeter Array. I. Survey Overview and the Central Gas to Dust Ratio (2008, methodology): “Armus et al. (2007) detect continuum emission from dust hotter than 300 K, which also indicates the presence of an AGN.”
• MID-INFRARED PROPERTIES OF NEARBY LUMINOUS INFRARED GALAXIES. I. SPITZER INFRARED SPECTROGRAPH SPECTRA FOR THE GOALS SAMPLE (2013, background): “At the highest luminosities, local ultraluminous infrared galaxies (ULIRGs; LIR ≥ 1012L ) have been heavily studied (Armus et al. 2007; Sanders et al. 1988; Murphy et al. 1996; Spoon et al. 2006; Desai et al. 2007; Rigopoulou et al. 1999; Genzel et al. 1998), and a clear formation picture has been…”
• 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, methodology): “…by a torus-shaped dust distribution, with a well-developed NLR, is thus distinguishable from a starburst galaxy relatively easily, through optical spectroscopy (classified as Seyfert 2; Veilleux&Osterbrock 1987) or high-resolution infrared spectroscopy (Genzel et al. 1998; Armus et al. 2007).”
• Active galactic nuclei: what’s in a name? (2017, background): “…based on certain spectral features, such as high ionisation emission lines like [Nev], [Ne ii] and [O iv], the EW of PAH features and the strength of the silicate feature at 9.7 µm (see, e.g. Spoon et al. 2007; Armus et al. 2007; Veilleux et al. 2009; Hernán-Caballero and Hatziminaoglou 2011).”
• SPITZER QUASAR AND ULIRG EVOLUTION STUDY (QUEST). IV. COMPARISON OF 1 Jy ULTRALUMINOUS INFRARED GALAXIES WITH PALOMAR-GREEN QUASARS (2009, methodology): “The observational setup used for the archival IRS spectra is described in detail in Armus et al. (2007) and references therein.”
• Mid-Infrared Spectral Diagnosis of Submillimeter Galaxies (2007, methodology): “Armus et al. (2007) presented IRS spectroscopy of 10 ULIRGs from the Bright Galaxy Sample (BGS; S60 > 5:4mJy; Soifer et al. 1987), and the IRS spectra for a sample of over 100 ULIRGs were recently presented in Desai et al. (2007) and Farrah et al. (2007).”
• A NEW DIAGNOSTIC OF ACTIVE GALACTIC NUCLEI: REVEALING HIGHLY ABSORBED SYSTEMS AT REDSHIFT >0.3 (2011, background): “9µm or [Nev]λ14µm in the infrared regime (Sturm et al. 2002; Armus et al. 2004, 2007; Diamond-Stanic et al. 2009; Rigby et al. 2009; LaMassa et al. 2010).”
• Multiwavelength Study of Massive Galaxies at z~2. I. Star Formation and Galaxy Growth (2007, background): “Spitzer observations show a substantial scatter in the local correlation of mid-IR luminosity versus the total infrared luminosity LIR (Dale et al. 2005; Smith et al. 2007; Armus et al. 2007).”
• Ionized gas outflows and global kinematics of low-z luminous star-forming galaxies (2014, background): “%) having signatures of an AGN (Armus et al. 2007, Desai et al. 2007, Farrah et al. 2007), with about 20% - 40% dominated by the AGN (at least at mid-IR wavelengths).”
• High-Resolution Mid-Infrared Spectroscopy of Ultraluminous Infrared Galaxies (2007, methodology): “In Figures 19 and 20 we plot [Ne v]/[Ne ii] and [O iv]/[Ne ii] against the equivalent width of the 6.2 mPAH feature, together with the linear mixing ratios from Sturm et al. (2002) and Armus et al. (2007).”