they correspond to ultraluminous infrared
galaxies (ULIRGs). In the local Universe, the
far-infrared emission from ULIRGs is typically
powered by starbursts and AGN. To obtain
redshift estimates, and to disentangle the
contribution of these two power sources, we
used multiwavelength data from surveys in
the optical and infrared, as well as new ra-
dio continuum data from the Australia Tele-
scope Compact Array and Very Large Array.
The ULIRGs we identify consist of a combi-
nation of pure starburst galaxies and com-
posite AGN/starburst objects. We find that
the ULIRGS with strong AGN tend to reside
in hosts with smaller scale sizes than purely
star-forming galaxies of similar infrared lu-
minosity.
Like their local counterparts, the ULIRGs
in this study seem to show signs of recent
merger activity, such as highly disturbed
morphologies. We also find a candidate tri-
ple AGN system (Figure 3), which consists
of three AGN with photometric redshifts of
z = 1.4 (spectroscopic redshifts are required
to confirm the triple AGN system): one is a
radio-loud AGN, suggesting the presence
of radio jets and lobes; one is a Type-2 AGN,
showing both narrow and broadened op-
tical spectral emission lines; and one is a
Type-1 AGN, showing narrow emission lines
only (though still wider than emission lines
in normal galaxies). Both the Type-1 and
Type-2 AGN have strong mid-infrared emis-
sion that identifies them as probable AGN.
This system was not identified as multiple in
the standard photometry products from the
VIDEO or SERVS surveys, raising the possibil-
ity that many more such systems may exist
unrecognized in current surveys.
In the future, we believe that observations
of extragalactic fields with MCAO will fulfill
a valuable role supplementing deeper, but
more resource intensive, observations with
space-based platforms such as the James
Webb Space Telescope (JWST) (Kalirai, 2018).
6
GeminiFocus
For example, surveys of high-redshift ULIRGs
with ground-based MCAO could be used to
pick interesting individual targets for JWST.
References:
Jarvis, M. J., Bonfield, D. G., Bruce, V. A., et al.,
Monthly Notices of the Royal Astronomical Soci-
ety, 428: 1281, 2013
Kalirai, J., Contemporary Physics, 59: 251, 2018
Lacy, M., Nyland, K., Mao, M., et al., The Astro-
physical Journal, 864: 8, 2018
Lonsdale, C., Smith H. E., Rowan-Robinson,
M., et al., Publications of the Astronomical Society
of the Pacific, 115: 897, 2003
Mauduit, J.-C., Lacy, M., Farrah, D., et al., Publi-
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Rigaut, F., Neichel, B., Boccas, M., et al., Month-
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Mark Lacy is a Staff Scientist at the National Radio
Astronomy Observatory. He can be reached at:
[email protected]
Kristina Nyland is a Research Associate at the Na-
tional Radio Astronomy Observatory. She can be
reached at: [email protected]
Susan Ridgway is an Associate Scientist at the Na-
tional Optical Astronomy Observatory. She can be
reached at: [email protected]
October 2018