Astrophys. J., 752, 2 (2012/June-2)
Ionized nitrogen at high redshift.
DECARLI R., WALTER F., NERI R., BERTOLDI F., CARILLI C., COX P., KNEIB J.P., LESTRADE J.F., MAIOLINO R., OMONT A., RICHARD J., RIECHERS D., THANJAVUR K. and WEISS A.
Abstract (from CDS):
We present secure [N II]_205 µm_ detections in two millimeter-bright, strongly lensed objects at high redshift, APM 08279+5255 (z = 3.911) and MM 18423+5938 (z = 3.930), using the IRAM Plateau de Bure Interferometer. Due to its ionization energy [N II]_205 µm_ is a good tracer of the ionized gas phase in the interstellar medium. The measured fluxes are S([N II]_205 µm_) = (4.8±0.8) Jy km/s and (7.4±0.5) Jy km/s, respectively, yielding line luminosities of L([N II]_205 µm_) = (1.8±0.3)x109 µ–1 L☉ for APM 08279+5255 and L([N II]_205 µm_) = (2.8 ±0.2)x109 µ–1 L☉ for MM 18423+5938. Our high-resolution map of the [N II]_205 µm_ and 1 mm continuum emission in MM 18423+5938 clearly resolves an Einstein ring in this source and reveals a velocity gradient in the dynamics of the ionized gas. A comparison of these maps with high-resolution EVLA CO observations enables us to perform the first spatially resolved study of the dust continuum-to-molecular gas surface brightness (ΣFIR∝Σ^ N ^CO, which can be interpreted as the star formation law) in a high-redshift object. We find a steep relation (N = 1.4±0.2), consistent with a starbursting environment. We measure a [N II]_205 µm_/FIR luminosity ratio in APM 08279+5255 and MM 18423+5938 of 9.0x10–6 and 5.8x10–6, respectively. This is in agreement with the decrease of the [N II]_205 µm_/FIR ratio at high FIR luminosities observed in local galaxies.
galaxies: individual: MM 18423+5938 - galaxies: ISM - quasars: individual: APM 08279+5255
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