The Physics of the Far-Infrared-Radio Correlation. I. Calorimetry, Conspiracy, and Implications

Lacki, Brian C.; Thompson, Todd A.; Quataert, Eliot

doi:10.1088/0004-637x/717/1/1

Cited by 226 publications

(331 citation statements)

References 110 publications

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“…Therefore the difference in the properties between this sample and such extreme galaxies as SMGs is expected. Such explanation was offered by Lacki et al (2009) and Lacki & Thompson (2009). Their numerical modelling showed that cosmic-ray electrons in "puffy starbursts" (vertically and radially extended galaxies with vertical scale heights ∼1 kpc) experience weaker bremsstrahlung and ionization losses resulting in stronger radio emission.…”

Section: Ir-radio Correlationmentioning

confidence: 96%

Cosmic evolution of submillimeter galaxies and their contribution to stellar mass assembly

Michalowski

Hjorth

Watson

2010

A&A

234

278

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The nature of galaxies selected at submillimeter wavelengths (SMGs, S 850 3 mJy), some of the bolometrically most luminous objects at high redshifts, is still elusive. In particular their star formation histories and source of emission are not accurately constrained. In this paper we introduce a new approach to analyse the SMG data. Namely, we present the first self-consistent UV-to-radio spectral energy distribution fits of 76 SMGs with spectroscopic redshifts using all photometric datapoints from ultraviolet to radio simultaneously. We find that they are highly star-forming (median star formation rate 713 M yr −1 for SMGs at z > 0.5), moderately dust-obscured (median A V ∼ 2 mag), hosting significant stellar populations (median stellar mass 3.7 × 10 11 M ) of which only a minor part has been formed in the ongoing starburst episode. This implies that in the past, SMGs experienced either another starburst episode or merger with several galaxies. The properties of SMGs suggest that they are progenitors of present-day elliptical galaxies. We find that these bright SMGs contribute significantly to the cosmic star formation rate density (∼20%) and stellar mass density (∼30-50%) at redshifts 2-4. Using number counts at low fluxes we find that as much as 80% of the cosmic star formation at these redshifts took place in SMGs brighter than 0.1 mJy. We find evidence that a linear infrared-radio correlation holds for SMGs in an unchanged form up to redshift of 3.6, though its normalization is offset from the local relation by a factor of ∼2.1 towards higher radio luminosities. We present a compilation of photometry data of SMGs and determinations of cosmic SFR and stellar mass densities.

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Section: Ir-radio Correlationmentioning

confidence: 96%

Cosmic evolution of submillimeter galaxies and their contribution to stellar mass assembly

Michalowski

Hjorth

Watson

2010

A&A

234

278

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“…Thus the time scale for vertical losses is much shorter than that for radial losses, by the factor r 2 /h 2 ≈ 15 2 /5 2 = 9, if the diffusion is isotropic with D r = D z . Models by Segalovitz (1977) and Lacki et al (2010) include a simple escape term controlled by an escape time τ esc .…”

Section: Vertical Escape Of Cres From M 51mentioning

confidence: 99%

“…is used in models by Lacki et al (2010). The 3 GeV condition they use allows them to model the radio-far-infrared correlation from normal spirals to dense starbursts; they were able to reproduce a linear correlation consistent with both local and integrated Galactic constraints on the energy in CR protons.…”

Section: Energy Dependent Diffusivitymentioning

confidence: 99%

“…Recently, Buffie et al (2013) theoretically reproduced the perpendicular diffusion coefficient found from radio observations of NGC 253 (Heesen et al 2009). Lacki et al (2010) used a steady-state model for the cosmic ray distribution in a homogeneous disk to predict the far-infrared (FIR) radio correlation (van der Kruit 1971(van der Kruit , 1973. However, the authors note that in weaker starbursts, where the cooling and escape times are several megayears, the evolution of the CREs via diffusion and convection become important and the steady-state approximation will fail.…”

Section: Introductionmentioning

confidence: 99%

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Modelling the cosmic ray electron propagation in M 51

Mulcahy

Fletcher

Beck

et al. 2016

A&A

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Context. Cosmic ray electrons (CREs) are a crucial part of the interstellar medium and are observed via synchrotron emission. While much modelling has been carried out on the CRE distribution and propagation of the Milky Way, little has been done on normal external star-forming galaxies. Recent spectral data from a new generation of radio telescopes enable us to find more robust estimations of the CRE propagation. Aims. To model the synchrotron spectral index of M 51 using the diffusion energy-loss equation and to compare the model results with the observed spectral index determined from recent low-frequency observations with LOFAR. Methods. We solve the time-dependent diffusion energy-loss equation for CREs in M 51. This is the first time that this model for CRE propagation has been solved for a realistic distribution of CRE sources, which we derive from the observed star formation rate, in an external galaxy. The radial variation of the synchrotron spectral index and scale-length produced by the model are compared to recent LOFAR and older VLA observational data and also to new observations of M 51 at 325 MHz obtained with the GMRT. Results. We find that propagation of CREs by diffusion alone is sufficient to reproduce the observed spectral index distribution in M 51. An isotropic diffusion coefficient with a value of 6.6 ± 0.2 × 10 28 cm 2 s −1 is found to fit best and is similar to what is seen in the Milky Way. We estimate an escape time of 11 Myr from the central galaxy to 88 Myr in the extended disk. It is found that an energy dependence of the diffusion coefficient is not important for CRE energies in the range 0.01 GeV-3 GeV. We are able to reproduce the dependence of the observed synchrotron scale-lengths on frequency, with l ∝ ν −1/4 in the outer disk and l ∝ ν −1/8 in the inner disk.

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“…However, an important omission in this simple picture is the role of magnetic fields that determine the intensity of the synchrotron emission with about the square of the field strength. Lacki et al (2010) modeled all relevant processes and found that the linearity of the global radio-IR correlation is due to a conspiracy of several factors (see also Bell 2003). For instance, in galaxies of low surface brightness and low star formation rate (SFR), the weak IR emission is balanced by weak radio emission caused by escape of CREs.…”

Section: Introductionmentioning

confidence: 99%

Multi-scale radio-infrared correlations in M 31 and M 33: The role of magnetic fields and star formation

Tabatabaei

Berkhuijsen

Frick

et al. 2013

A&A

101

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Interstellar magnetic fields and the propagation of cosmic ray electrons have an important impact on the radio-infrared (IR) correlation in galaxies. This becomes evident when studying different spatial scales within galaxies. We investigate the correlation between the IR and free-free/synchrotron radio continuum emission at 20 cm from the two local group galaxies M 31 and M 33 on spatial scales between 0.4 and 10 kpc. The multi-scale radio-IR correlations have been carried out using a wavelet analysis. The free-free and IR emission are correlated on all scales, but on some scales the synchrotron emission is only marginally correlated with the IR emission. The synchrotron-IR correlation is stronger in M 33 than in M 31 on small scales (<1 kpc), but it is weaker than in M 31 on larger scales. Taking the smallest scale on which the synchrotron-IR correlation exists as the propagation length of cosmic ray electrons, we show that the difference on small scales can be explained by the smaller propagation length in M 33 than in M 31. On large scales, the difference is due to the thick disk/halo in M 33, which is absent in M 31. A comparison of our data with data on NGC 6946, the LMC and M 51 suggests that the propagation length is determined by the ratio of ordered-to-turbulent magnetic field strength, which is consistent with diffusion of CR electrons in the ISM. As the diffusion length of CR electrons influences the radio-IR correlation, this dependence is a direct observational evidence of the importance of magnetic fields for the radio-IR correlation within galaxies. The star-formation rate per surface area only indirectly influences the diffusion length as it increases the strength of the turbulent magnetic field.

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The Physics of the Far-Infrared-Radio Correlation. I. Calorimetry, Conspiracy, and Implications

Cited by 226 publications

References 110 publications

Cosmic evolution of submillimeter galaxies and their contribution to stellar mass assembly

Cosmic evolution of submillimeter galaxies and their contribution to stellar mass assembly

Modelling the cosmic ray electron propagation in M 51

Multi-scale radio-infrared correlations in M 31 and M 33: The role of magnetic fields and star formation

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