We propose for PACS spectroscopy of the [O III] 88 micron and [N II] 122 micron lines, and SPIRE far-IR photometry, to observe a sample of 16 low-redshift IR-luminous galaxies, at log L_IR = 11.6 to 12.2 Lsolar, that are distinguished by large size and non-merger structure. In OT1 we are obtaining PACS spectra of [C II] 158 and [O I] 63 microns for this sample. These galaxies are interesting because they have high SFR activity spread over a large physical area, rather than concentrated into extremely dense nuclear regions, as in most local major merger ULIRGs. They are good analogs for high-redshift IR-luminous galaxies, which have far-IR spectral shapes different from local ULIRGs. At z>1, much of the star formation in massive galaxies is at LIRG and ULIRG levels, and U/LIRGs dominate the IR luminosity density. Understanding star forming regions in high-z IR-luminous galaxies is necessary to understand the conditions in which most of the stars in massive galaxies formed. In a few high-z lensed ULIRGs where [C II] can be observed, [C II]/FIR is high, like local star-forming galaxies and unlike local ULIRGs. [C II] is a major cooling line in PDRs and the far-IR lines probe the physical conditions and UV intensity in IR-emitting regions. In our sample observed so far in OT1, [C II]/FIR is high - they do not suffer the [C II] deficit found in local ULIRGs. This suggests that redshift evolution in IR SEDs and line ratios are related to the larger extent of star formation, and that this low-z disky sample are good analogs. The [O III] and [N II] lines provide more detailed probes of the ionization state, gas density, and ionizing SEDs in the star-forming regions: in published samples the [O III]/FIR ratio shows tension with simple models for the line deficit, and [N II] and [O III] can constrain ionizing SED versus gas density. T...he SPIRE far-IR photometry will constrain the total IR luminosity and cold dust in these galaxies, which have cool IR colors and far-IR fluxes rising past 100 microns.
Publication
Instrument
SPIRE_SpirePhoto_small, PACS_PacsLineSpec_point
Temporal Coverage
2012-04-14T23:43:20Z/2013-01-21T06:50:12Z
Version
SPG v14.2.0
Mission Description
Herschel was launched on 14 May 2009! It is the fourth 'cornerstone' mission in the ESA science programme. With a 3.5 m Cassegrain telescope it is the largest space telescope ever launched. It is performing photometry and spectroscopy in approximately the 55-671 µm range, bridging the gap between earlier infrared space missions and groundbased facilities.
European Space Agency, 2013, Physical Conditions In Disky U/Lirgs From Far-Ir Line Flux Ratios - Low-Z Analogs For High-Z Starforming Galaxies, SPG v14.2.0, European Space Agency, https://doi.org/10.5270/esa-o9rynn7
