PAHs as a tracer of star formation

By E. Peeters, H. Spoon, A. Tielens. 2004

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IR emission bands at 3.3, 6.2, 7.7, 8.6 and 11.3 um are generally attributed to IR fluorescence from (mainly) FUV pumped PAHs. As such, they trace the FUV stellar flux and are a measure of star formation. We examined the IR spectral characteristics of Galactic star forming regions, normal and starburst galaxies, AGNs and ULIRGs. The goal is to analyze if PAH bands are a good qualitative and/or quantitative tracer of star formation and hence the application of PAH bands as a diagnostic in order to identify the dominant processes contributing to the IR emission from Seyfert's and ULIRGs. We develop a MIR/FIR diagnostic and compare it to known diagnostics, with these also applied to the Galactic sample. This diagnostic is based on the FIR normalized 6.2 um PAH flux and the FIR normalized 6.2 um continuum flux. The Galactic sources form a sequence spanning a range of 3 orders of magnitude, from embedded compact HII regions to exposed PDRs and the (D)ISM. The variation in the 6.2 um PAH/continuum ratio is relative small. Normal and starburst galaxies ressemble exposed PDRs. While Seyfert-2's coincide with the starburst trend, Seyfert-1's are displaced by at least a factor 10 in 6.2 um continuum flux. ULIRGs show a diverse spectral appearance (AGN hot dust continuum, starburst-like or strong dust obscuration in the nucleus). ULIRGs also seems to have more prominent FIR emission than either starburst galaxies or AGNs. We discuss the observed variation in the Galactic sample in view of the evolutionary state and the PAH/dust abundance and the use of PAHs as quantitative tracers of star formation activity. We find that PAHs may be better suited as a tracer of B stars, which dominate the Galactic stellar energy budget, than as a tracer of massive star formation (O stars).

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/8b7f54485e1b40f6d6321922c6beaef37bfe36de

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Citations in the corpus

C2D Spitzer-IRS spectra of disks around T Tauri stars. II. PAH emission features (2006, background): “Within the Milky Way PAHs are observed in the diffuse medium, dense molecular clouds, circumstellar envelopes, and (proto-)planetary nebulae (see Peeters et al. 2004 for a summary).”
The Mid-Infrared Properties of Starburst Galaxies from Spitzer-IRS Spectroscopy (2006, background): “If the observed PAH flux is integrated over the whole galaxy, it may predominantly trace B stars, which dominate the Galactic stellar energy budget, rather than very recent massive star formation (Peeters et al. 2004).”
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, unknown): “The ratios in normal starburst galaxieswith modest dust obscuration (AV < 20 30 mag) are estimated to be L6:2PAH/LIR 3:4 ; 10 3 (Peeters et al. 2004) and L11:3PAH /LIR 1:4 ; 10 3 (Soifer et al. 2002).”
WHAT DRIVES THE EXPANSION OF GIANT H ii REGIONS?: A STUDY OF STELLAR FEEDBACK IN 30 DORADUS (2010, result): “This result is consistent with the analyses of Peeters et al. (2004), who showed that the ratio of PAH to far-IR (dust continuum) emission in Galactic HII regions is inversely correlated with the intensity of the UV field absorbed by the dust.”
Towards a complete census of AGN in nearby Galaxies: a large population of optically unidentified AGN (2009, background): “Previous studies have shown that the equivalent width of the IR-detected PAH features at 6.2 and 7.7 µm are well correlated with the AGN-starburst activity occurring within a galaxy (e.g., Genzel et al. 1998; Laurent et al. 2000; Peeters et al. 2004; Dale et al. 2006).”
Star Formation in the Milky Way and Nearby Galaxies (2012, background): “…have shown that the PAH luminosity scales relatively well with the SFR in metalrich luminous star-forming galaxies (e.g., Roussel et al. 2001; Peeters et al. 2004; Förster Schreiber et al. 2004; Wu et al. 2005a; Farrah et al. 2007; Calzetti et al. 2007), but the PAH bands weaken…”
Chandra and Spitzer Unveil Heavily Obscured Quasars in the Chandra/SWIRE Survey (2006, background): “…regions is more luminous than that produced by theAGN, e.g., as in the Seyfert 2 galaxiesNGC4945 andNGC6240 (Maiolino et al. 2003; Rigopoulou et al. 1999), the AGN IR emission is fainter or negligible compared to that produced by star formation processes in the host galaxy (Peeters et al. 2004).”
DUST-CORRECTED STAR FORMATION RATES OF GALAXIES. I. COMBINATIONS OF Hα AND INFRARED TRACERS (2009, background): “…longer wavelength tracers such as the 24 μm emission, with systematic dependences of the emissivity on metal abundance, and local radiation field strength and hardness (e.g., Madden 2000; Peeters et al. 2004; Engelbracht et al. 2005, 2008; Dale et al. 2005; Wu et al. 2006; Smith et al. 2007; C07).”
PAH and Mid-Infrared Luminosities as Measures of Star Formation Rate in Spitzer First Look Survey Galaxies (2005, background): “Peeters et al. (2004) have pointed out that PAHs may be better tracers of B stars than tracers of massive star formation (O stars).”
SPITZER QUASAR AND ULIRG EVOLUTION STUDY (QUEST). IV. COMPARISON OF 1 Jy ULTRALUMINOUS INFRARED GALAXIES WITH PALOMAR-GREEN QUASARS (2009, methodology): “Both PAH (e.g., Förster-Schreiber et al. 2004; Peeters et al. 2004; Calzetti et al. 2007) and FIR emission (e.g., Kennicutt 1998) are tracers of star formation in quiescent and actively star forming galaxies.”
The Infrared Luminosity Function of Galaxies at Redshifts z = 1 and z ~ 2 in the GOODS Fields (2007, background): “In general, PAH line equivalent widths appear to be quite independent of the bolometric IR luminosities of star-forming galaxies (Peeters et al. 2004; Brandl et al. 2006).”
A TWO-PARAMETER MODEL FOR THE INFRARED/SUBMILLIMETER/RADIO SPECTRAL ENERGY DISTRIBUTIONS OF GALAXIES AND ACTIVE GALACTIC NUCLEI (2014, background): “…2000; Murphy et al. 1Available at physics.uwyo.edu/∼ddale/research/seds/seds.html 7 2009; Mullaney et al. 2011; Wu et al. 2011) or a combination of the mid-infrared continnum plus mid-infrared fine-structure lines (e.g., Genzel et al. 1998; Peeters et al. 2004; Armus et al. 2007; Dale et al. 2009).”
MID-INFRARED SPECTROSCOPY OF SUBMILLIMETER GALAXIES: EXTENDED STAR FORMATION IN MASSIVE HIGH-REDSHIFT GALAXIES (2009, background): “Such diversity in PAH ratios is also present in local ULIRGs (e.g., Rigopoulou et al. 1999; Peeters et al. 2004), indicating that diverse radiation fields are found amongst both low- and high-redshift IR-luminous sources.”
Mid-Infrared Spectra of Classical AGNs Observed with the Spitzer Space Telescope (2005, background): “An alternative interpretation is that applied to the deeply obscured sources NGC 4418 (Peeters et al. 2004b) and IRAS F00183-7111 (Spoon et al. 2004) for which the apparent hump of emission is actually the underlying continuum which has been absorbed by ice and hydrocarbon features shortward of…”
Analysis of galaxy spectral energy distributions from far-UV to far-IR with CIGALE: studying a SINGS test sample (2009, methodology): “This emission is superimposed by prominent broad emission features of polycyclic aromatic hydrocarbon (PAH) molecules6 ( ee Puget & Léger 1989; Sturm et al. 2000; Draine 2003; Peeters et al. 2004).”
Dust covering factor, silicate emission, and star formation in luminous QSOs (2007, background): “…is at∼ 7.7µm) are emitted by very small carbon grains excited in the Photo Dissociation Regions, that are tracers of star forming activity (although PAHs may not be reliable SF tracers for compact HII regions or heavily embedded starbursts, Peeters et al.,2004; Förster Schreiber et al., 2004).”
DUSTY INFRARED GALAXIES: Sources of the Cosmic Infrared Background (2005, background): “These features result from C-C and C-H stretching/bending vibrational bands excited by the absorption of a single UV or optical photon and are a good tracer of normal and moderately active star formation activity in spiral and irregular galaxies (e.g., Helou et al. 2000; Peeters et al. 2004).”