Star Formation in NGC 5194 (M51a): The Panchromatic View from GALEX to Spitzer

By D. Calzetti, Robert C. Kennicutt Jr., L. Bianchi, D. Thilker, D. Dale, C. Engelbracht, C. Leitherer, Martin M. Meyer, M. Sosey, M. Mutchler and 25 more. 2005

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Far-ultraviolet to far-infrared images of the nearby galaxy NGC 5194 (M51a), from a combination of space-based (Spitzer, GALEX, and Hubble Space Telescope) and ground-based data, are used to investigate local and global star formation and the impact of dust extinction. The Spitzer data provide unprecedented spatial detail in the infrared, down to sizes ~500 pc at the distance of NGC 5194. The multiwavelength set is used to trace the relatively young stellar populations, the ionized gas, and the dust absorption and emission in H II-emitting knots, over 3 orders of magnitude in wavelength range. As is common in spiral galaxies, dust extinction is high in the center of the galaxy (AV ~ 3.5 mag), but its mean value decreases steadily as a function of galactocentric distance, as derived from both gas emission and stellar continuum properties. In the IR/UV-UV color plane, the NGC 5194 H II knots show the same trend observed for normal star-forming galaxies, having a much larger dispersion (~1 dex peak to peak) than starburst galaxies. We identify the dispersion as due to the UV emission predominantly tracing the evolved, nonionizing stellar population, up to ages ~50-100 Myr. While in starbursts the UV light traces the current star formation rate (SFR), in NGC 5194 it traces a combination of current and recent past SFRs. Possibly, mechanical feedback from supernovae is less effective at removing dust and gas from the star formation volume in normal star-forming galaxies than in starbursts because of the typically lower SFR densities in the former. The application of the starburst opacity curve for recovering the intrinsic UV emission (and deriving SFRs) in local and distant galaxies appears therefore appropriate only for SFR densities ≳1 M☉ yr-1 kpc-2. Unlike the UV emission, the monochromatic 24 μm luminosity is an accurate local SFR tracer for the H II knots in NGC 5194, with a peak-to-peak dispersion of less than a factor of 3 relative to hydrogen emission line tracers; this suggests that the 24 μm emission carriers are mainly heated by the young, ionizing stars. However, preliminary results show that the ratio of the 24 μm emission to the SFR varies by a factor of a few from galaxy to galaxy; this variation needs to be understood and carefully quantified before the 24 μm luminosity can be used as an SFR tracer for galaxy populations. While also correlated with star formation, the 8 μm emission is not directly proportional to the number of ionizing photons; it is overluminous, by up to a factor of ~2, relative to the galaxy's average in weakly ionized regions and is underluminous, by up to a factor of ~3, in strongly ionized regions. This confirms earlier suggestions that the carriers of the 8 μm emission are heated by more than one mechanism.

Subfields: Astronomy and Astrophysics

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Modeling the Pan-Spectral Energy Distribution of Starburst Galaxies. IV. The Controlling Parameters of the Starburst SED (2007, background): “The constancy of flux in the ∼ 20µm waveband is somewhat more interesting and is directly related to the strong correlation between the 24µm Spitzer flux and the SFR (Calzetti et al. 2005).”
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Absolute Calibration and Characterization of the Multiband Imaging Photometer for Spitzer. II. 70 μm Imaging (2007, background): “…including the detection and study of cold disks around stars (e.g., Kim et al. 2005; Bryden et al. 2006), imaging of warm dust in galaxies (e.g., Calzetti et al. 2005; Dale et al. 2005; Gordon et al. 2006), and investigation of faint, redshifted galaxies (e.g., Dole et al. 2004a; Frayer et al.…”
Star Formation in NGC 5194 (M51a). II. The Spatially Resolved Star Formation Law (2007, methodology): “In particular, the MIPS 24 µm PSF gives contamination levels of ∼5% for an aperture centered 13′′ away (Calzetti et al. 2005).”
DISCOVERY OF AN ACTIVE GALACTIC NUCLEUS DRIVEN MOLECULAR OUTFLOW IN THE LOCAL EARLY-TYPE GALAXY NGC 1266 (2011, background): “While this outflow rate is equivalent to the total SFR, the star formation in M51 is known to be distributed throughout the disk (Calzetti et al. 2005), and thus is likely unable to effectively drive much of the nuclear molecular gas out.”
TESTING THE UNIFICATION MODEL FOR ACTIVE GALACTIC NUCLEI IN THE INFRARED: ARE THE OBSCURING TORI OF TYPE 1 AND 2 SEYFERTS DIFFERENT? (2011, background): “As found by Spitzer, the ∼8 µm PAH emission of nearby galaxies appears to be more extended than at ∼24 µm (e.g., Helou et al. 2004; Calzetti et al. 2005).”
The Calibration of Mid-Infrared Star Formation Rate Indicators (2007, methodology): “Under most circumstances, each of our apertures will include multiple stellar populations covering a range of ages (Calzetti et al. 2005).”
Investigations of dust heating in M81, M83 and NGC 2403 with the Herschel Space Observatory (2011, background): “…(Werner et al. 2004) demonstrated that optical and ultraviolet star formation tracers were very strongly correlated with 24µm dust emission (Calzetti et al. 2005, 2007; Prescott et al. 2007; Kennicutt et al. 2007, 2009; Zhu et al. 2008) or with total infrared emission (Kennicutt et al.…”
RADIAL DISTRIBUTION OF STARS, GAS, AND DUST IN SINGS GALAXIES. II. DERIVED DUST PROPERTIES (2009, background): “A similar behavior has also been observed for star-forming regions within galaxies (Calzetti et al. 2005).”
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DUST-CORRECTED STAR FORMATION RATES OF GALAXIES. II. COMBINATIONS OF ULTRAVIOLET AND INFRARED TRACERS (2011, background): “…equivalently FUV-NUV color) or the IR/UV versus β relation (e.g. Meurer et al. 1999; Buat et al. 1999; Gordon et al. 2000; Bell 2002; Kong et al. 2004; Calzetti et al. 2005; Seibert et al. 2005; Cortese et al. 2006; Boissier et al. 2007; Gil de Paz et al. 2007; Johnson et al. 2007a,2007b; Panuzzo…”
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ESTIMATING THE STAR FORMATION RATE AT 1 kpc SCALES IN NEARBY GALAXIES (2012, background): “Many studies of nearby galaxies have revealed a strong empirical correlation between 24µm emission and sites of active star formation (e.g., Calzetti et al. 2005; Alonso-Herrero et al. 2006; Pérez-González et al. 2006; Prescott et al. 2007) and it has been used extensively to investigate the…”
OPTICAL SPECTROSCOPY AND NEBULAR OXYGEN ABUNDANCES OF THE SPITZER/SINGS GALAXIES (2010, background): “…al. 2006; Bendo et al. 2007); and the development of robust global and spatially resolved optical and infrared (IR) star formation rate (SFR) diagnostics (Calzetti et al. 2005, 2007, 2010; Kennicutt et al. 2007, 2009; Boquien et al. 2009, 2010), among others.”
A CANDELS–3D-HST SYNERGY: RESOLVED STAR FORMATION PATTERNS AT 0.7 < z < 1.5 (2013, background): “…invoke a rapidly declining star formation rate (see Figure 3), and consequently a prior (possibly very short-lived) phase of even 17 See also Calzetti et al. (2005) for a discussion on the increased efficiency of dust and gas clearing from high star formation density regions, such as…”
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