Infrared Emission of Normal Galaxies from 2.5 to 12 Micron: Infrared Space Observatory Spectra, Near-Infrared Continuum, and Mid-Infrared Emission Features

By N. Lu, G. Helou, M. Werner, H. Dinerstein, D. Dale, N. Silbermann, S. Malhotra, C. Beichman, Thomas H. Jarrett. 2003

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We present ISOPHOT spectra of the regions 2.5-4.9 μm and 5.8-11.6 μm for a sample of 45 disk galaxies from the US Infrared Space Observatory Key Project on Normal Galaxies. The galaxies were selected to span the range in global properties of normal, star-forming disk galaxies in the local universe. The spectra can be decomposed into three spectral components: (1) continuum emission from stellar photospheres, which dominates the near-infrared (NIR; 2.5-4.9 μm) spectral region; (2) a weak NIR excess continuum, which has a color temperature of ~103 K, carries a luminosity of a few percent of the total far-infrared (FIR) dust luminosity LFIR and most likely arises from the interstellar medium (ISM); and (3) the well-known broad emission features at 6.2, 7.7, 8.6, and 11.3 μm, which are generally attributed to aromatic carbon particles. These aromatic features in emission (AFEs) dominate the mid-infrared (MIR; 5.8-11.6 μm) part of the spectrum and resemble the so-called type A spectra observed in many nonstellar sources and the diffuse ISM in our own Galaxy. The few notable exceptions include NGC 4418, where a dust continuum replaces the AFEs in MIR, and NGC 1569, where the AFEs are weak and the strongest emission feature is [S IV] 10.51 μm. The relative strengths of the AFEs vary by 15%-25% among the galaxies. However, little correlation is seen between these variations and either IRAS 60 μm/100 μm flux density ratio R(60/100) or the FIR/blue luminosity ratio LFIR/LB, two widely used indicators of the current star formation activity, suggesting that the observed variations are not a consequence of the radiation field differences among the galaxies. We demonstrate that the NIR excess continuum and AFE emission are correlated, suggesting that they are produced by similar mechanisms and similar (or the same) material. On the other hand, as the current star formation activity increases, the overall strengths of the AFEs and the NIR excess continuum drop significantly with respect to that of the FIR emission from large dust grains. In particular, the summed luminosity of the AFEs falls from ~0.2 LFIR for the most "IR-quiescent" galaxies to ~0.1 LFIR for the most "IR-active" galaxies. This is likely a consequence of the preferential destruction in intense radiation fields of the small carriers responsible for the NIR/AFE emission.

Subfields: Astronomy and Astrophysics

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Citations in the corpus

Number Counts at 3 μm < λ < 10 μm from the Spitzer Space Telescope (2004, background): “We attribute the drop to substantial contribution to the fluxes from the strong aromatic feature emission at 6.2 and 7.7 µm (e.g., Lu et al. 2003).”
A simple model to interpret the ultraviolet, optical and infrared emission from galaxies (2008, background): “The above ISO/ISOPHOT observations of a sample of 45 normal star-forming galaxies also reveal a component of near-infrared continuum emission characterised by a very high colour temperature (∼ 1000 K) at wavelengths between 3 and 5 µm (Lu et al. 2003).”
The Anatomy of Star Formation in NGC 300 (2004, methodology): “From the ISO data in Figure 6 of Lu et al. (2003), this underestimate may reach a factor of up to 2.6, 10–20% and 3–4%, respectively at 4.5, 5.8 and 8µm.”
Infrared Power-Law Galaxies in the Chandra Deep Field-South: Active Galactic Nuclei and Ultraluminous Infrared Galaxies (2006, methodology): “In addition to the data from NED, we have made use of ISO data for non-AGN LIRGs from Lu et al. (2003) and for cool ULIRGs from Farrah et al. (2003), as well as optical and near-IR data from Surace et al. (2000).”
A TWO-PARAMETER MODEL FOR THE INFRARED/SUBMILLIMETER/RADIO SPECTRAL ENERGY DISTRIBUTIONS OF GALAXIES AND ACTIVE GALACTIC NUCLEI (2014, methodology): “The average 2.5–11.5 µm mid-infrared spectrum of Lu et al. (2003) was used to replace the PAH spectrum of Désert, Boulanger, & Puget (1990).”
The Behavior of the Aromatic Features in M101 H II Regions: Evidence for Dust Processing (2008, background): “The observed strengths of the aromatic features do not vary much in most normal luminosity galaxies with approximately solar metallicities (Roche et al. 1991; Lu et al. 2003; Smith et al. 2007b) or massive starbursts (Brandl et al. 2006).”
The Mid-Infrared Properties of Starburst Galaxies from Spitzer-IRS Spectroscopy (2006, background): “Lu et al. (2003) have found a 25% spread in the ratio of the 11.3 m/7.7 m PAH fluxes, which they attribute to intrinsic galaxy-to-galaxy variations.”
Metallicity Effects on Mid-Infrared Colors and the 8 μm PAH Emission in Galaxies (2005, background): “…1994; (25) J. Moustakas 2004, private communication; (26) Houck et al. 2004b; (27) C. W. Engelbracht et al. 2005, in preparation; (28) Madden 2002; (29) Roche et al. 1991; (30) Lu et al. 2003; (31) Rigopoulou et al. 1999; (32) Devost et al. 2004; (33) Smith et al. 2004; (34) Cesarsky et al. 1998.”
THE STELLAR MASS CONTENT OF SUBMILLIMETER-SELECTED GALAXIES (2010, background): “…detected from Galactic cirrus (Flagey et al. 2006) and reflection nebulae (e.g., Sellgren et al. 1983) as well as local star-forming galaxies (e.g., Lu et al. 2003), which can be described by graybody emission at temperatures∼ 1000 K. 56% of our sample also meet the criterion of Alonso-Herrero et…”
Spitzer Quasar and ULIRG Evolution Study (QUEST). I. The Origin of the Far-Infrared Continuum of QSOs (2006, methodology): “…group of comparison objects (3) 12 ‘‘FIR-quiescent’’ galaxies (with particularly low LFIR/LB and low S60 /S100) from the sample of normal galaxies of Lu et al. (2003), for which we convert their PAH fluxes measured in ISOPHOT-S spectra to our measurement procedure and apply aperture…”
SPITZER QUASAR AND ULIRG EVOLUTION STUDY (QUEST). IV. COMPARISON OF 1 Jy ULTRALUMINOUS INFRARED GALAXIES WITH PALOMAR-GREEN QUASARS (2009, background): “…from the atmospheres of the young stars in ULIRGs, and the very hot (103 K) small grain NIR dust emission component inferred in ISOPHOT spectra of normal galaxies (Lu et al. 2003) and presumed to also exist in these objects, do not contribute significantly to the observed continuum above ∼ 5 µm.”
The GOODS-MUSIC sample: a multicolour catalog of near-IR selected galaxies in the GOODS-South field , (2006, background): “The galaxy emission is not dominated by the integrated stellar population at λ ≥ 5.5 µm (Dale et al. 2005; Lu et al. 2003) but by the different flavours of dust emission, at least in the case of star-forming galaxies that are not included in the spectral libraries considered here.”
Polycyclic Aromatic Hydrocarbons as a Tracer of Star Formation? (2004, background): “In addition, the ISO PHT-S spectrum is unusual, as it does not show 6.2 m PAH emission (see also, e.g., Lu et al. 2003).”
On Extending the Mass-Metallicity Relation of Galaxies by 2.5 Decades in Stellar Mass (2006, background): “We have also assumed zero extinction at 4.5 m (e.g., Lutz 1999; Indebetouw et al. 2005), and negligible contribution by diffuse H i Br emission to the overall galaxy flux (e.g., Lu et al. 2003; Lu 2004).”
DETERMINING STAR FORMATION RATES FOR INFRARED GALAXIES (2008, background): “Between 3 and 5µm, there is additional emission from warm dust and aromatic features, (e.g., Lu et al. (2003)).”
The relation between AGN hard X-ray emission and mid-infrared continuum from ISO spectra: Scatter and unification aspects , (2004, background): “From four ellipticals without PAH emission (NGC 3379, NGC 4374, NGC 2300, NGC 4649; Lu et al. 2003, Xilouris et al. 2004, S. Madden priv. comm.) we estimate a scaling S 6 µm ∼ 0.19 × S 2.2 µm.”
The Mid-Infrared Spectrum of Star-forming Galaxies: Global Properties of Polycyclic Aromatic Hydrocarbon Emission (2006, methodology): “Lu et al. (2003) found band to band variations of at most 15% out to 11µm.”