Tight Constraints on the Excess Radio Background at $z = 9.1$ from LOFAR. (arXiv:2004.00678v1 [astro-ph.CO])

Tight Constraints on the Excess Radio Background at $z = 9.1$ from LOFAR. (arXiv:2004.00678v1 [astro-ph.CO])
<a href="http://arxiv.org/find/astro-ph/1/au:+Mondal_R/0/1/0/all/0/1">R. Mondal</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Fialkov_A/0/1/0/all/0/1">A. Fialkov</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Fling_C/0/1/0/all/0/1">C. Fling</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Iliev_I/0/1/0/all/0/1">I.T. Iliev</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Barkana_R/0/1/0/all/0/1">R. Barkana</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ciardi_B/0/1/0/all/0/1">B. Ciardi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Mellema_G/0/1/0/all/0/1">G. Mellema</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Zaroubi_S/0/1/0/all/0/1">S. Zaroubi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Koopmans_L/0/1/0/all/0/1">L.V.E Koopmans</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Mertens_F/0/1/0/all/0/1">F. G. Mertens</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Gehlot_B/0/1/0/all/0/1">B. K. Gehlot</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ghara_R/0/1/0/all/0/1">R. Ghara</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ghosh_A/0/1/0/all/0/1">A. Ghosh</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Giri_S/0/1/0/all/0/1">S. K. Giri</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Pandey_V/0/1/0/all/0/1">V.N. Pandey</a>

The ARCADE2 and LWA1 experiments have claimed an excess over the Cosmic
Microwave Background (CMB) at low radio frequencies. If the cosmological
high-redshift contribution to this radio background is between 0.1% and 22% of
the CMB at $1.42,$GHz, it could explain the tentative EDGES Low-Band detection
of the anomalously deep absorption in the 21-cm signal of neutral hydrogen
(Fialkov & Barkana 2019). We use the upper limit on the 21-cm signal from the
Epoch of Reionization ($z=9.1$) based on $141,$hours of observations with
LOFAR (Mertens et al. 2020) to evaluate the contribution of the high redshift
Universe to the detected radio background. Marginalizing over astrophysical
properties of star-forming halos, we find (at 68% C.L.) that the cosmological
radio background can be at most 0.7% of the CMB at $1.42,$GHz. This limit
rules out strong contribution of the high-redshift Universe to the ARCADE2 and
LWA1 measurements. Even though LOFAR places limit on the extra radio
background, excess of $0.1-0.7$% over the CMB (at $1.42,$GHz) is still allowed
and could explain the EDGES Low-Band detection. We also constrain the thermal
and ionization state of the gas at $z = 9.1$, and put limits on the properties
of the first star-forming objects. We find that, in agreement with the limits
from EDGES High-Band data, LOFAR data disfavour scenarios with inefficient
X-ray sources and cases where the Universe was ionized by massive halos only.

The ARCADE2 and LWA1 experiments have claimed an excess over the Cosmic
Microwave Background (CMB) at low radio frequencies. If the cosmological
high-redshift contribution to this radio background is between 0.1% and 22% of
the CMB at $1.42,$GHz, it could explain the tentative EDGES Low-Band detection
of the anomalously deep absorption in the 21-cm signal of neutral hydrogen
(Fialkov & Barkana 2019). We use the upper limit on the 21-cm signal from the
Epoch of Reionization ($z=9.1$) based on $141,$hours of observations with
LOFAR (Mertens et al. 2020) to evaluate the contribution of the high redshift
Universe to the detected radio background. Marginalizing over astrophysical
properties of star-forming halos, we find (at 68% C.L.) that the cosmological
radio background can be at most 0.7% of the CMB at $1.42,$GHz. This limit
rules out strong contribution of the high-redshift Universe to the ARCADE2 and
LWA1 measurements. Even though LOFAR places limit on the extra radio
background, excess of $0.1-0.7$% over the CMB (at $1.42,$GHz) is still allowed
and could explain the EDGES Low-Band detection. We also constrain the thermal
and ionization state of the gas at $z = 9.1$, and put limits on the properties
of the first star-forming objects. We find that, in agreement with the limits
from EDGES High-Band data, LOFAR data disfavour scenarios with inefficient
X-ray sources and cases where the Universe was ionized by massive halos only.

http://arxiv.org/icons/sfx.gif