Abstract
We present a study of the low-frequency radio properties of star-forming
(SF) galaxies and active galactic nuclei (AGNs) up to redshift z = 2.5.
The new spectral window probed by the Low Frequency Array (LOFAR) allows
us to reconstruct the radio continuum emission from 150 MHz to 1.4 GHz
to an unprecedented depth for a radio-selected sample of 1542 galaxies
in ˜ 7 deg2 of the LOFAR Boötes field. Using the
extensive multiwavelength data set available in Boötes and detailed
modelling of the far-infrared to ultraviolet spectral energy
distribution (SED), we are able to separate the star formation (N = 758)
and the AGN (N = 784) dominated populations. We study the shape of the
radio SEDs and their evolution across cosmic time and find significant
differences in the spectral curvature between the SF galaxy and AGN
populations. While the radio spectra of SF galaxies exhibit a weak but
statistically significant flattening, AGN SEDs show a clear trend to
become steeper towards lower frequencies. No evolution of the spectral
curvature as a function of redshift is found for SF galaxies or AGNs. We
investigate the redshift evolution of the infrared-radio correlation for
SF galaxies and find that the ratio of total infrared to 1.4-GHz radio
luminosities decreases with increasing redshift: q1.4 GHz =
(2.45 ± 0.04) (1 + z)-0.15 ± 0.03. Similarly,
q150 MHz shows a redshift evolution following q150
GHz = (1.72 ± 0.04) (1 + z)-0.22 ± 0.05.
Calibration of the 150 MHz radio luminosity as a star formation rate
tracer suggests that a single power-law extrapolation from q1.4
GHz is not an accurate approximation at all redshifts.
Original language | English |
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Pages (from-to) | 3468-3488 |
Journal | Monthly Notices of the Royal Astronomical Society |
Volume | 469 |
Issue number | 3 |
DOIs | |
Publication status | Published - 1 May 2017 |
Keywords
- galaxies: evolution
- galaxies: nuclei
- galaxies: photometry
- galaxies: starburst
- infrared: galaxies
- radio continuum: galaxies