MID-INFRARED PROPERTIES OF NEARBY LUMINOUS INFRARED GALAXIES. I. SPITZER INFRARED SPECTROGRAPH SPECTRA FOR THE GOALS SAMPLE

By S. Stierwalt, Lee Armus, J. Surace, H. Inami, A. Petric, T. Díaz-Santos, S. Haan, Vassilis Charmandaris, J. Howell, D. Kim and 22 more. 2013

153 citations recorded by the source corpus.

The Great Observatories All-Sky LIRG Survey (GOALS) is a comprehensive, multiwavelength study of luminous infrared galaxies (LIRGs) in the local universe. Here we present low resolution Spitzer Infrared Spectrograph spectra covering 5–38 μm and provide a basic analysis of the mid-IR spectral properties observed for nearby LIRGs. In a companion paper, we discuss detailed fits to the spectra and compare the LIRGs to other classes of galaxies. The GOALS sample of 244 nuclei in 180 luminous (1011 ⩽ LIR/L☉ < 1012) and 22 ultraluminous (LIR/L☉ ⩾ 1012) IR galaxies represents a complete subset of the IRAS Revised Bright Galaxy Sample and covers a range of merger stages, morphologies, and spectral types. The majority (>60%) of the GOALS LIRGs have high 6.2 μm polycyclic aromatic hydrocarbon (PAH) equivalent widths (EQW6.2 μm > 0.4 μm) and low levels of silicate absorption (s9.7 μm > −1.0). There is a general trend among the U/LIRGs for both silicate depth and mid-infrared (MIR) slope to increase with increasing LIR. U/LIRGs in the late to final stages of a merger also have, on average, steeper MIR slopes and higher levels of dust obscuration. Together, these trends suggest that as gas and dust is funneled toward the center of a coalescing merger, the nuclei become more compact and more obscured. As a result, the dust temperature increases also leading to a steeper MIR slope. The sources that depart from these correlations have very low PAH equivalent width (EQW6.2 μm < 0.1 μm) consistent with their emission being dominated by an active galactic nucleus (AGN) in the MIR. These extremely low PAH EQW sources separate into two distinct types: relatively unobscured sources with a very hot dust component (and thus very shallow MIR slopes) and heavily dust obscured nuclei with a steep temperature gradient. The most heavily dust obscured sources are also the most compact in their MIR emission, suggesting that the obscuring (cool) dust is associated with the outer regions of the starburst and not simply a measure of the dust along the line of sight through a large, dusty disk. A marked decline is seen for the fraction of high EQW (star formation dominated) sources as the merger progresses. The decline is accompanied by an increase in the fraction of composite sources while the fraction of sources where an AGN dominates the MIR emission remains low. When compared to the MIR spectra of submillimeter galaxies (SMGs) at z ∼ 2, both the average GOALS LIRG and ULIRG spectra are more absorbed at 9.7 μm and the average GOALS LIRG has more PAH emission. However, when the AGN contributions to both the local GOALS LIRGs and the high-z SMGs are removed, the average local starbursting LIRG closely resembles the starburst-dominated SMGs.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/dd0da5cbb14942a299d23ce85eef2af27e579dac

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In Astronomy and Astrophysics

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

In Instrumentation

1. Sylvain Veilleux
2. D. Rupke
3. R. Maiolino
4. D. Lutz
5. L. Tacconi
6. R. Genzel
7. H. Netzer
8. Roger Davies

Citations in the corpus

• 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): “Furthermore, the existence of an additional hot and obscured dust component in these LIRGs is also consistent with the results presented in Stierwalt et al. (2013a), where it is shown that there is a trend for LIRGs with moderate silicate strengths (S9.”
• AN ATLAS OF GALAXY SPECTRAL ENERGY DISTRIBUTIONS FROM THE ULTRAVIOLET TO THE MID-INFRARED (2013, background): “…measurements of star formation rates (e.g., Moustakas et al. 2006; Kennicutt et al. 2009), fitting or modeling the mid-infrared spectra (e.g., Smith et al. 2007b; Inami et al. 2013; Stierwalt et al. 2013) and estimates of the contribution of AGNs to mid-infrared emission (Petric et al. 2011).”
• A TWO-PARAMETER MODEL FOR THE INFRARED/SUBMILLIMETER/RADIO SPECTRAL ENERGY DISTRIBUTIONS OF GALAXIES AND ACTIVE GALACTIC NUCLEI (2014, background): “…simplification will fail to appropriately characterize all the nuances in mid-infrared spectra for samples specifically selected to be infrared-luminous (e.g., GOALS; Stierwalt et al. 2013), there are very few deeply obscured systems in infrared flux-limited surveys like 5MUSES (Wu et al. 2010).”
• The applicability of far-infrared fine-structure lines as star formation rate tracers over wide ranges of metallicities and galaxy types (2014, methodology): “By relying on the equivalent width of the 6.2 µm PAH feature (EW (PAH 6.2 µm) = 0.29, Stierwalt et al. 2013), we classify the source as an AGN.”
• A Herschel/PACS Far-infrared Line Emission Survey of Local Luminous Infrared Galaxies (2017, background): “…2011; Kim et al. 2013), along with Chandra X-ray (Iwasawa et al. 2011), as well as Spitzer/IRS (Dı́az-Santos et al. 2010b, 2011; Petric et al. 2011; Stierwalt et al. 2013, 2014; Inami et al. 2013) and Herschel/PACS and SPIRE spec- troscopy (Dı́az-Santos et al. 2013, 2014; Zhao et al. 2013; Lu et…”
• FAST MOLECULAR OUTFLOWS IN LUMINOUS GALAXY MERGERS: EVIDENCE FOR QUASAR FEEDBACK FROM HERSCHEL (2013, background): “7um < –2 in Stierwalt et al. 2013) more often show OH purely in absorption than the less obscured systems.”