Galactic synchrotron emission and the far-infrared-radio correlation at high redshift

Journal Article · Sat Aug 20 04:00:00 EDT 2016 · Astrophysical Journal

DOI:https://doi.org/10.3847/0004-637X/827/2/109· OSTI ID:22868772

Schober, J. ^[1]; Schleicher, D. R. G. ^[2]

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1. Nordita, KTH Royal Institute of Technology and Stockholm University, Roslagstullsbacken 23, SE-10691 Stockholm (Sweden)
2. Departamento de Astronomía, Facultad Ciencias Físicas y Matemáticas, Universidad de Concepción, Av. Esteban Iturra s/n Barrio Universitario, Casilla 160-C, Concepción (Chile)

Theoretical scenarios, including the turbulent small-scale dynamo, predict that strong magnetic fields already exist in young galaxies. Based on the assumption of energy equipartition between magnetic fields and turbulence, we determine the galactic synchrotron flux as a function of redshift z. Galaxies in the early universe are different from local galaxies, in particular, the former have more intense star formation. To cover a large range of conditions, we consider two different systems: one model galaxy comparable to the Milky Way and one typical high-z starburst galaxy. We include a model of the steady-state cosmic ray spectrum and find that synchrotron emission can be detected up to cosmological redshifts with current and future radio telescopes. The turbulent dynamo theory is in agreement with the origin of the observed correlation between the far-infrared (FIR) luminosity L {sub FIR} and the radio luminosity L {sub radio}. Our model reproduces this correlation well at z = 0. We extrapolate the FIR–radio correlation to higher redshifts and predict a time evolution with a significant deviation from its present-day appearance already at z≈2 for a gas density that increases strongly with z. In particular, we predict a decrease of the radio luminosity with redshift which is caused by the increase of cosmic ray energy losses at high z. The result is an increase of the ratio between L {sub FIR} and L {sub radio}. Simultaneously, we predict that the slope of the FIR–radio correlation becomes shallower with redshift. This behavior of the correlation could be observed in the near future with ultra-deep radio surveys.

• OSTI ID: 22868772
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 827; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
COMPARATIVE EVALUATIONS
CORRELATIONS
COSMIC RADIATION
DENSITY
EMISSION
ENERGY LOSSES
GALACTIC EVOLUTION
LUMINOSITY
MAGNETIC FIELDS
MAGNETOHYDRODYNAMICS
MILKY WAY
RADIO TELESCOPES
RED SHIFT
SPECTRA
STARS
STEADY-STATE CONDITIONS
SYNCHROTRON RADIATION
TURBULENCE
UNIVERSE