Calibrating the relation of low-frequency radio continuum to star formation rate at 1 kpc scale with LOFAR

V. Heesen, E. Buie, C. J. Huff, L. A. Perez, J. G. Woolsey, D. A. Rafferty, A. Basu, R. Beck, E. Brinks, C. Horellou, Evan Scannapieco, M. Brüggen, R. J. Dettmar, K. Sendlinger, B. Nikiel-Wroczyński, K. T. Chy, P. N. Best, G. H. Heald, R. Paladino

Research output: Contribution to journalArticle

Abstract

Context. Radio continuum (RC) emission in galaxies allows us to measure star formation rates (SFRs) unaffected by extinction due to dust, of which the low-frequency part is uncontaminated from thermal (free-free) emission. Aims. We calibrate the conversion from the spatially resolved 140 MHz RC emission to the SFR surface density (ΣSFR) at 1 kpc scale. Radio spectral indices give us, by means of spectral ageing, a handle on the transport of cosmic rays using the electrons as a proxy for GeV nuclei. Methods. We used recent observations of three galaxies (NGC 3184, 4736, and 5055) from the LOFAR Two-metre Sky Survey (LoTSS), and archival LOw-Frequency ARray (LOFAR) data of NGC 5194. Maps were created with the facet calibration technique and converted to radio ΣSFR maps using the Condon relation. We compared these maps with hybrid ΣSFR maps from a combination of GALEX far-ultraviolet and Spitzer 24 μm data using plots tracing the relation at the highest angular resolution allowed by our data at 1.2 × 1.2 kpc 2 resolution. Results. The RC emission is smoothed with respect to the hybrid ΣSFR owing to the transport of cosmic-ray electrons (CREs) away from star formation sites. This results in a sublinear relation (ΣSFR)RC [(ΣSFR)hyb] a , where a = 0.59 ± 0.13 (140 MHz) and a = 0.75 ± 0.10 (1365 MHz). Both relations have a scatter of σ = 0.3 dex. If we restrict ourselves to areas of young CREs (α > -0.65; Iν ν α ), the relation becomes almost linear at both frequencies with a 0.9 and a reduced scatter of σ = 0.2 dex. We then simulate the effect of CRE transport by convolving the hybrid ΣSFR maps with a Gaussian kernel until the RC-SFR relation is linearised; CRE transport lengths are l = 1-5 kpc. Solving the CRE diffusion equation, assuming dominance of the synchrotron and inverse-Compton losses, we find diffusion coefficients of D = (0.13-1.5) × 10 28 cm 2 s -1 at 1 GeV. Conclusions. A RC-SFR relation at 1.4 GHz can be exploited to measure SFRs at redshift z 10 using 140 MHz observations.

Original languageEnglish (US)
Article numberA8
JournalAstronomy and Astrophysics
Volume622
DOIs
StatePublished - Feb 1 2019

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calibrating
star formation rate
radio
continuums
low frequencies
cosmic ray
cosmic rays
electron
electrons
rate
radio stars
galaxies
electron diffusion
tracing
angular resolution
star formation
flat surfaces
synchrotrons
extinction
diffusion coefficient

Keywords

  • Cosmic rays
  • Galaxies: magnetic fields
  • Galaxies: star formation
  • Radiation mechanisms: non-thermal
  • Radio continuum: galaxies

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Heesen, V., Buie, E., Huff, C. J., Perez, L. A., Woolsey, J. G., Rafferty, D. A., ... Paladino, R. (2019). Calibrating the relation of low-frequency radio continuum to star formation rate at 1 kpc scale with LOFAR. Astronomy and Astrophysics, 622, [A8]. https://doi.org/10.1051/0004-6361/201833905

Calibrating the relation of low-frequency radio continuum to star formation rate at 1 kpc scale with LOFAR. / Heesen, V.; Buie, E.; Huff, C. J.; Perez, L. A.; Woolsey, J. G.; Rafferty, D. A.; Basu, A.; Beck, R.; Brinks, E.; Horellou, C.; Scannapieco, Evan; Brüggen, M.; Dettmar, R. J.; Sendlinger, K.; Nikiel-Wroczyński, B.; Chy, K. T.; Best, P. N.; Heald, G. H.; Paladino, R.

In: Astronomy and Astrophysics, Vol. 622, A8, 01.02.2019.

Research output: Contribution to journalArticle

Heesen, V, Buie, E, Huff, CJ, Perez, LA, Woolsey, JG, Rafferty, DA, Basu, A, Beck, R, Brinks, E, Horellou, C, Scannapieco, E, Brüggen, M, Dettmar, RJ, Sendlinger, K, Nikiel-Wroczyński, B, Chy, KT, Best, PN, Heald, GH & Paladino, R 2019, 'Calibrating the relation of low-frequency radio continuum to star formation rate at 1 kpc scale with LOFAR' Astronomy and Astrophysics, vol. 622, A8. https://doi.org/10.1051/0004-6361/201833905
Heesen, V. ; Buie, E. ; Huff, C. J. ; Perez, L. A. ; Woolsey, J. G. ; Rafferty, D. A. ; Basu, A. ; Beck, R. ; Brinks, E. ; Horellou, C. ; Scannapieco, Evan ; Brüggen, M. ; Dettmar, R. J. ; Sendlinger, K. ; Nikiel-Wroczyński, B. ; Chy, K. T. ; Best, P. N. ; Heald, G. H. ; Paladino, R. / Calibrating the relation of low-frequency radio continuum to star formation rate at 1 kpc scale with LOFAR. In: Astronomy and Astrophysics. 2019 ; Vol. 622.
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title = "Calibrating the relation of low-frequency radio continuum to star formation rate at 1 kpc scale with LOFAR",
abstract = "Context. Radio continuum (RC) emission in galaxies allows us to measure star formation rates (SFRs) unaffected by extinction due to dust, of which the low-frequency part is uncontaminated from thermal (free-free) emission. Aims. We calibrate the conversion from the spatially resolved 140 MHz RC emission to the SFR surface density (ΣSFR) at 1 kpc scale. Radio spectral indices give us, by means of spectral ageing, a handle on the transport of cosmic rays using the electrons as a proxy for GeV nuclei. Methods. We used recent observations of three galaxies (NGC 3184, 4736, and 5055) from the LOFAR Two-metre Sky Survey (LoTSS), and archival LOw-Frequency ARray (LOFAR) data of NGC 5194. Maps were created with the facet calibration technique and converted to radio ΣSFR maps using the Condon relation. We compared these maps with hybrid ΣSFR maps from a combination of GALEX far-ultraviolet and Spitzer 24 μm data using plots tracing the relation at the highest angular resolution allowed by our data at 1.2 × 1.2 kpc 2 resolution. Results. The RC emission is smoothed with respect to the hybrid ΣSFR owing to the transport of cosmic-ray electrons (CREs) away from star formation sites. This results in a sublinear relation (ΣSFR)RC [(ΣSFR)hyb] a , where a = 0.59 ± 0.13 (140 MHz) and a = 0.75 ± 0.10 (1365 MHz). Both relations have a scatter of σ = 0.3 dex. If we restrict ourselves to areas of young CREs (α > -0.65; Iν ν α ), the relation becomes almost linear at both frequencies with a 0.9 and a reduced scatter of σ = 0.2 dex. We then simulate the effect of CRE transport by convolving the hybrid ΣSFR maps with a Gaussian kernel until the RC-SFR relation is linearised; CRE transport lengths are l = 1-5 kpc. Solving the CRE diffusion equation, assuming dominance of the synchrotron and inverse-Compton losses, we find diffusion coefficients of D = (0.13-1.5) × 10 28 cm 2 s -1 at 1 GeV. Conclusions. A RC-SFR relation at 1.4 GHz can be exploited to measure SFRs at redshift z 10 using 140 MHz observations.",
keywords = "Cosmic rays, Galaxies: magnetic fields, Galaxies: star formation, Radiation mechanisms: non-thermal, Radio continuum: galaxies",
author = "V. Heesen and E. Buie and Huff, {C. J.} and Perez, {L. A.} and Woolsey, {J. G.} and Rafferty, {D. A.} and A. Basu and R. Beck and E. Brinks and C. Horellou and Evan Scannapieco and M. Br{\"u}ggen and Dettmar, {R. J.} and K. Sendlinger and B. Nikiel-Wroczyński and Chy, {K. T.} and Best, {P. N.} and Heald, {G. H.} and R. Paladino",
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TY - JOUR

T1 - Calibrating the relation of low-frequency radio continuum to star formation rate at 1 kpc scale with LOFAR

AU - Heesen, V.

AU - Buie, E.

AU - Huff, C. J.

AU - Perez, L. A.

AU - Woolsey, J. G.

AU - Rafferty, D. A.

AU - Basu, A.

AU - Beck, R.

AU - Brinks, E.

AU - Horellou, C.

AU - Scannapieco, Evan

AU - Brüggen, M.

AU - Dettmar, R. J.

AU - Sendlinger, K.

AU - Nikiel-Wroczyński, B.

AU - Chy, K. T.

AU - Best, P. N.

AU - Heald, G. H.

AU - Paladino, R.

PY - 2019/2/1

Y1 - 2019/2/1

N2 - Context. Radio continuum (RC) emission in galaxies allows us to measure star formation rates (SFRs) unaffected by extinction due to dust, of which the low-frequency part is uncontaminated from thermal (free-free) emission. Aims. We calibrate the conversion from the spatially resolved 140 MHz RC emission to the SFR surface density (ΣSFR) at 1 kpc scale. Radio spectral indices give us, by means of spectral ageing, a handle on the transport of cosmic rays using the electrons as a proxy for GeV nuclei. Methods. We used recent observations of three galaxies (NGC 3184, 4736, and 5055) from the LOFAR Two-metre Sky Survey (LoTSS), and archival LOw-Frequency ARray (LOFAR) data of NGC 5194. Maps were created with the facet calibration technique and converted to radio ΣSFR maps using the Condon relation. We compared these maps with hybrid ΣSFR maps from a combination of GALEX far-ultraviolet and Spitzer 24 μm data using plots tracing the relation at the highest angular resolution allowed by our data at 1.2 × 1.2 kpc 2 resolution. Results. The RC emission is smoothed with respect to the hybrid ΣSFR owing to the transport of cosmic-ray electrons (CREs) away from star formation sites. This results in a sublinear relation (ΣSFR)RC [(ΣSFR)hyb] a , where a = 0.59 ± 0.13 (140 MHz) and a = 0.75 ± 0.10 (1365 MHz). Both relations have a scatter of σ = 0.3 dex. If we restrict ourselves to areas of young CREs (α > -0.65; Iν ν α ), the relation becomes almost linear at both frequencies with a 0.9 and a reduced scatter of σ = 0.2 dex. We then simulate the effect of CRE transport by convolving the hybrid ΣSFR maps with a Gaussian kernel until the RC-SFR relation is linearised; CRE transport lengths are l = 1-5 kpc. Solving the CRE diffusion equation, assuming dominance of the synchrotron and inverse-Compton losses, we find diffusion coefficients of D = (0.13-1.5) × 10 28 cm 2 s -1 at 1 GeV. Conclusions. A RC-SFR relation at 1.4 GHz can be exploited to measure SFRs at redshift z 10 using 140 MHz observations.

AB - Context. Radio continuum (RC) emission in galaxies allows us to measure star formation rates (SFRs) unaffected by extinction due to dust, of which the low-frequency part is uncontaminated from thermal (free-free) emission. Aims. We calibrate the conversion from the spatially resolved 140 MHz RC emission to the SFR surface density (ΣSFR) at 1 kpc scale. Radio spectral indices give us, by means of spectral ageing, a handle on the transport of cosmic rays using the electrons as a proxy for GeV nuclei. Methods. We used recent observations of three galaxies (NGC 3184, 4736, and 5055) from the LOFAR Two-metre Sky Survey (LoTSS), and archival LOw-Frequency ARray (LOFAR) data of NGC 5194. Maps were created with the facet calibration technique and converted to radio ΣSFR maps using the Condon relation. We compared these maps with hybrid ΣSFR maps from a combination of GALEX far-ultraviolet and Spitzer 24 μm data using plots tracing the relation at the highest angular resolution allowed by our data at 1.2 × 1.2 kpc 2 resolution. Results. The RC emission is smoothed with respect to the hybrid ΣSFR owing to the transport of cosmic-ray electrons (CREs) away from star formation sites. This results in a sublinear relation (ΣSFR)RC [(ΣSFR)hyb] a , where a = 0.59 ± 0.13 (140 MHz) and a = 0.75 ± 0.10 (1365 MHz). Both relations have a scatter of σ = 0.3 dex. If we restrict ourselves to areas of young CREs (α > -0.65; Iν ν α ), the relation becomes almost linear at both frequencies with a 0.9 and a reduced scatter of σ = 0.2 dex. We then simulate the effect of CRE transport by convolving the hybrid ΣSFR maps with a Gaussian kernel until the RC-SFR relation is linearised; CRE transport lengths are l = 1-5 kpc. Solving the CRE diffusion equation, assuming dominance of the synchrotron and inverse-Compton losses, we find diffusion coefficients of D = (0.13-1.5) × 10 28 cm 2 s -1 at 1 GeV. Conclusions. A RC-SFR relation at 1.4 GHz can be exploited to measure SFRs at redshift z 10 using 140 MHz observations.

KW - Cosmic rays

KW - Galaxies: magnetic fields

KW - Galaxies: star formation

KW - Radiation mechanisms: non-thermal

KW - Radio continuum: galaxies

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