Radio and Far-IR Emission Associated with a Massive Star-forming Galaxy Candidate at z\${\textbackslash}simeq\$6.8: A Radio-Loud AGN in the Reionization Era?. Endsley, R., Stark, D. P., Fan, X., Smit, R., Wang, F., Yang, J., Hainline, K., Lyu, J., Bouwens, R., & Schouws, S. Technical Report August, 2021. Publication Title: arXiv e-prints ADS Bibcode: 2021arXiv210801084E Type: article
Radio and Far-IR Emission Associated with a Massive Star-forming Galaxy Candidate at z\${\textbackslash}simeq\$6.8: A Radio-Loud AGN in the Reionization Era? [link]Paper  abstract   bibtex   
We report the identification of radio (1.4 and 3 GHz) and mid-infrared, far-infrared, and sub-mm (24-850\${\textbackslash}mu\$m) emission at the position of one of 41 UV-bright (\${\textbackslash}mathrm\{M_\{UV\}{\textasciicircum}\{\}\}{\textbackslash}lesssim-21.25\$) \$z{\textbackslash}simeq6.6-6.9\$ Lyman-break galaxy candidates in the 1.5 deg\${\textasciicircum}2\$ COSMOS field. This source, COS-87259, exhibits a sharp flux discontinuity (factor \${\textgreater}\$3) between two narrow/intermediate bands at 9450 \${\textbackslash}mathring\{A\}\$ and 9700 \${\textbackslash}mathring\{A\}\$ and is undetected in all nine bands blueward of 9600 \${\textbackslash}mathring\{A\}\$, as expected from a Lyman-alpha break at \$z{\textbackslash}simeq6.8\$. The full multi-wavelength (X-ray through radio) data of COS-87529 can be self-consistently explained by a very massive (M\$_\{{\textbackslash}ast\}=10{\textasciicircum}\{10.8\}\$ M\$_\{{\textbackslash}odot\}\$) and extremely red (rest-UV slope \${\textbackslash}beta=-0.59\$) \$z{\textbackslash}simeq6.8\$ galaxy with hyperluminous infrared emission (L\$_\{{\textbackslash}mathrm\{IR\}\}=10{\textasciicircum}\{13.6\}\$ L\$_\{{\textbackslash}odot\}\$) powered by both an intense burst of highly-obscured star formation (SFR\${\textbackslash}approx\$1800 M\$_\{{\textbackslash}odot\}\$ yr\${\textasciicircum}\{-1\}\$) and an obscured (\${\textbackslash}tau_\{{\textbackslash}mathrm\{9.7{\textbackslash}mu m\}\}=7.7{\textbackslash}pm2.5\$) radio-loud (L\$_\{{\textbackslash}mathrm\{1.4{\textbackslash} GHz\}\}{\textbackslash}sim10{\textasciicircum}\{25.5\}\$ W Hz\${\textasciicircum}\{-1\}\$) AGN. The radio emission is compact (1.04\${\textbackslash}pm\$0.12 arcsec) and exhibits an ultra-steep spectrum between 1.4-3 GHz (\${\textbackslash}alpha=-2.06{\textasciicircum}\{+0.27\}_\{-0.25\}\$) with evidence of spectral flattening at lower frequencies, consistent with known \$z{\textgreater}4\$ radio galaxies. We also demonstrate that COS-87259 may reside in a significant (11\${\textbackslash}times\$) galaxy overdensity at \$z{\textbackslash}simeq6.6-6.9\$, as common for systems hosting radio-loud AGN. Nonetheless, a spectroscopic redshift will ultimately be required to establish the true nature of COS-87259 as we cannot yet completely rule out low-redshift solutions. If confirmed to lie at \$z{\textbackslash}simeq6.8\$, the properties of COS-87259 would be consistent with a picture wherein AGN and highly-obscured star formation activity are fairly common among very massive (M\$_\{{\textbackslash}ast\}{\textgreater}10{\textasciicircum}\{10\}\$ M\$_\{{\textbackslash}odot\}\$) reionization-era galaxies.
@techreport{2021arXiv210801084E,
	title = {Radio and {Far}-{IR} {Emission} {Associated} with a {Massive} {Star}-forming {Galaxy} {Candidate} at z\${\textbackslash}simeq\$6.8: {A} {Radio}-{Loud} {AGN} in the {Reionization} {Era}?},
	shorttitle = {Radio and {Far}-{IR} {Emission} {Associated} with a {Massive} {Star}-forming {Galaxy} {Candidate} at z\${\textbackslash}simeq\$6.8},
	url = {https://ui.adsabs.harvard.edu/abs/2021arXiv210801084E},
	abstract = {We report the identification of radio (1.4 and 3 GHz) and mid-infrared, far-infrared, and sub-mm (24-850\${\textbackslash}mu\$m) emission at the position of one of 41 UV-bright (\${\textbackslash}mathrm\{M\_\{UV\}{\textasciicircum}\{\}\}{\textbackslash}lesssim-21.25\$) \$z{\textbackslash}simeq6.6-6.9\$ Lyman-break galaxy candidates in the 1.5 deg\${\textasciicircum}2\$ COSMOS field. This source, COS-87259, exhibits a sharp flux discontinuity (factor \${\textgreater}\$3) between two narrow/intermediate bands at 9450 \${\textbackslash}mathring\{A\}\$ and 9700 \${\textbackslash}mathring\{A\}\$ and is undetected in all nine bands blueward of 9600 \${\textbackslash}mathring\{A\}\$, as expected from a Lyman-alpha break at \$z{\textbackslash}simeq6.8\$. The full multi-wavelength (X-ray through radio) data of COS-87529 can be self-consistently explained by a very massive (M\$\_\{{\textbackslash}ast\}=10{\textasciicircum}\{10.8\}\$ M\$\_\{{\textbackslash}odot\}\$) and extremely red (rest-UV slope \${\textbackslash}beta=-0.59\$) \$z{\textbackslash}simeq6.8\$ galaxy with hyperluminous infrared emission (L\$\_\{{\textbackslash}mathrm\{IR\}\}=10{\textasciicircum}\{13.6\}\$ L\$\_\{{\textbackslash}odot\}\$) powered by both an intense burst of highly-obscured star formation (SFR\${\textbackslash}approx\$1800 M\$\_\{{\textbackslash}odot\}\$ yr\${\textasciicircum}\{-1\}\$) and an obscured (\${\textbackslash}tau\_\{{\textbackslash}mathrm\{9.7{\textbackslash}mu m\}\}=7.7{\textbackslash}pm2.5\$) radio-loud (L\$\_\{{\textbackslash}mathrm\{1.4{\textbackslash} GHz\}\}{\textbackslash}sim10{\textasciicircum}\{25.5\}\$ W Hz\${\textasciicircum}\{-1\}\$) AGN. The radio emission is compact (1.04\${\textbackslash}pm\$0.12 arcsec) and exhibits an ultra-steep spectrum between 1.4-3 GHz (\${\textbackslash}alpha=-2.06{\textasciicircum}\{+0.27\}\_\{-0.25\}\$) with evidence of spectral flattening at lower frequencies, consistent with known \$z{\textgreater}4\$ radio galaxies. We also demonstrate that COS-87259 may reside in a significant (11\${\textbackslash}times\$) galaxy overdensity at \$z{\textbackslash}simeq6.6-6.9\$, as common for systems hosting radio-loud AGN. Nonetheless, a spectroscopic redshift will ultimately be required to establish the true nature of COS-87259 as we cannot yet completely rule out low-redshift solutions. If confirmed to lie at \$z{\textbackslash}simeq6.8\$, the properties of COS-87259 would be consistent with a picture wherein AGN and highly-obscured star formation activity are fairly common among very massive (M\$\_\{{\textbackslash}ast\}{\textgreater}10{\textasciicircum}\{10\}\$ M\$\_\{{\textbackslash}odot\}\$) reionization-era galaxies.},
	urldate = {2021-09-07},
	author = {Endsley, Ryan and Stark, Daniel P. and Fan, Xiaohui and Smit, Renske and Wang, Feige and Yang, Jinyi and Hainline, Kevin and Lyu, Jianwei and Bouwens, Rychard and Schouws, Sander},
	month = aug,
	year = {2021},
	note = {Publication Title: arXiv e-prints
ADS Bibcode: 2021arXiv210801084E
Type: article},
	keywords = {Astrophysics - Astrophysics of Galaxies},
}

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