CNO emission of an unlensed submillimeter galaxy at z=4.3
  We present the results from ALMA observations of [NII]205 micron, [CII]158
micron, and [OII]88 micron lines in an unlensed submillimeter galaxy at z=4.3,
COSMOS-AzTEC-1, hosting a compact starburst core with an effective radius of 1
kpc. The [CII] and [NII] emission are spatially-resolved in 0.3
arcsec-resolution (1 kpc in radius). The kinematic properties of the [NII]
emission are consistent with those of the CO(4-3) and [CII] emission,
suggesting that the ionized gas feels the same gravitational potential as the
associated molecular gas and photodissociation regions (PDRs). On the other
hand, the spatial extent is different among the lines and dust continuum: the
[CII] emitting gas is the most extended and the dust is the most compact,
leading to a difference of the physical conditions in the interstellar medium.
We derive the incident far-ultraviolet flux and the hydrogen gas density
through PDR modeling by properly subtracting the contribution of ionized gas to
the total [CII] emission. The observed [CII] emission is likely produced by
dense PDRs with nH(PDR)=10^(5.5-5.75) cm^-3 and G0=10^(3.5-3.75) in the central
1 kpc region and nH(PDR)=10^(5.0-5.25) cm^-3 and G0=10^(3.25-3.5) in the
central 3 kpc region. We have also successfully measured the line ratio of
[OIII/[NII] in the central 3 kpc region of COSMOS-AzTEC-1 at z=4.3, which is
the highest redshift where both nitrogen and oxygen lines are detected. Under
the most likely physical conditions, the measured luminosity ratio of
L([OIII])/L([NII])=6.4+-2.2 indicates a near solar metallicity with
Zgas=0.7-1.0 Zsol, suggesting a chemically evolved system at z=4.3.
