Herschel-PACS spectroscopy of IR-bright galaxies at high redshift

TL;DR

This study uses Herschel-PACS spectroscopy to analyze infrared emission lines from two high-redshift, ultra-luminous infrared galaxies, revealing their interstellar medium properties and star formation activity, with implications for galaxy evolution models.

Contribution

First combined [OI], [CII], and FIR measurements for PDR modeling of a high-redshift ULIRG, revealing differences from local ULIRGs and insights into star formation and AGN activity.

Findings

MIPS J1428 shows no [OI] deficit unlike local ULIRGs.

F10214 has low [OIII]/FIR ratio, similar to local ULIRGs.

Derived PDR parameters suggest normal star formation efficiency.

Abstract

We present Herschel-PACS observations of rest-frame mid-infrared and far-infrared spectral line emissions from two lensed, ultra-luminous infrared galaxies at high redshift: MIPS J142824.0+352619 (MIPS J1428), a starburst-dominated system at z = 1.3, and IRAS F10214+4724 (F10214), a source at z = 2.3 hosting both star-formation and a luminous AGN. We have detected [OI]63 micron and [OIII]52 micron in MIPS J1428, and tentatively [OIII]52 micron in F10214. Together with the recent ZEUS-CSO [CII]158 micron detection in MIPS J1428 we can for the first time combine [OI], [CII] and far-IR (FIR) continuum measurements for photo-dissociation (PDR) modeling of an ultra-luminous (L_IR > 10^12 L_sun) star forming galaxy at the peak epoch of cosmic star formation. We find that MIPS J1428, contrary to average local ULIRGs, does not show a deficit in [OI] relative to FIR. The combination of far-UV flux G_0 and gas density n (derived from the PDR models), as well as the star formation efficiency (derived from CO and FIR) is similar to normal or starburst galaxies, despite the high infrared luminosity of this system. In contrast, F10214 has stringent upper limits on [OIV] and [SIII], and an [OIII]/FIR ratio at least an order of magnitude lower than local starbursts or AGN, similar to local ULIRGs.