Band-9 ALMA observations of the [NII] 122 micron line and FIR continuum in two high-z galaxies

TL;DR

This study uses Band-9 ALMA observations to analyze the [NII] 122 micron line and FIR continuum in two high-redshift galaxies, revealing extended emission, star formation rates, and detailed structures, advancing understanding of early galaxy properties.

Contribution

First high-resolution Band-9 ALMA observations of [NII] 122 micron line in high-z galaxies, revealing extended emission and detailed star formation characteristics.

Findings

Over 75% of [NII] flux is from star formation

Detected significant unobscured star formation (~1000 solar masses/year)

Resolved structures include a partial Einstein ring and separate components

Abstract

We present Atacama Large Millimeter Array (ALMA) observations of two high-redshift systems (SMMJ02399-0136 and the Cloverleaf QSO) in their rest-frame 122 micron continuum (~650 GHz or ~450 micron on-sky) and [NII] 122 micron line emission. The continuum observations with a synthesized beam of ~0.25" resolve both sources and recover the expected flux. The Cloverleaf is resolved into a partial Einstein ring, while the SMMJ02399-0136 is unambiguously separated into two components; an AGN associated point source and an extend region at the location of a previously identified dusty starburst. We detect the [NII] line in both systems, though significantly weaker than our previous detections made with the 1st generation z(Redshift) and Early Universe Spectrometer. We show that this discrepancy is mostly explained if the line flux is resolved out due to significantly more extended emission and longer ALMA baselines than expected. Based on the ALMA observations we determine that greater than 75% of the total [NII] line flux in each source is produced via star formation. We use the [NII] line flux that is recovered by ALMA to constrain the N/H abundance, ionized gas mass, hydrogen ionizing photon rate, and star formation rate. In SMMJ02399-0136 we discover it contains a significant amount (~1000 solar masses per year) of unobscured star formation in addition to its dusty starburst and argue that SMMJ02399-0136 may be similar to the Antennae Galaxies (Arp 244) locally. In total these observations provide a new look at two well-studied systems while demonstrating the power and challenges of Band-9 ALMA observations of high-z systems.