arXiv subjects

M. J. Griffin

Publications and source records attributed to M. J. Griffin.

At least 19 recordsLinked to original sources

arXiv2021

A PPMAP analysis of the filamentary structures in Ophiuchus L1688 and L1689

We use the PPMAP (Point Process MAPping) algorithm to re-analyse the \textit{Herschel} and SCUBA-2 observations of the L1688 and L1689 sub-regions of the Ophiuchus molecular cloud. PPMAP delivers maps with high resolution (here $14''$, corresponding to $\sim 0.01\,{\rm pc}$ at $\sim 140\,{\rm pc}$), by using the observations at their native resolutions. PPMAP also delivers more accurate dust optical depths, by distinguishing dust of different types and at different temperatures. The filaments and prestellar cores almost all lie in regions with $N_{\rm H_2}\gtrsim 7\times 10^{21}\,{\rm cm}^{-2}$ (corresponding to $A_{_{\rm V}}\gtrsim 7$). The dust temperature, $T$, tends to be correlated with the dust opacity index, $β$, with low $T$ and low $β$ tend concentrated in the interiors of filaments. The one exception to this tendency is a section of filament in L1688 that falls -- in projection -- between the two B stars, S1 and HD147889; here $T$ and $β$ are relatively high, and there is compelling evidence that feedback from these two stars has heated and compressed the filament. Filament {\sc fwhm}s are typically in the range $0.10\,{\rm pc}$ to $0.15\,{\rm pc}$. Most filaments have line densities in the range $25\,{\rm M_{_\odot}\,pc^{-1}}$ to $65\,{\rm M_{_\odot}\,pc^{-1}}$. If their only support is thermal gas pressure, and the gas is at the canonical temperature of $10\,{\rm K}$, the filaments are highly supercritical. However, there is some evidence from ammonia observations that the gas is significantly warmer than this, and we cannot rule out the possibility of additional support from turbulence and/or magnetic fields. On the basis of their spatial distribution, we argue that most of the starless cores are likely to disperse (rather than evolving to become prestellar).

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arXiv2020

The Herschel SPIRE Fourier Transform Spectrometer Spectral Feature Finder I. The Spectral Feature Finder and Catalogue

We provide a detailed description of the Herschel-SPIRE Fourier Transform Spectrometer (FTS) Spectral Feature Finder (FF). The FF is an automated process designed to extract significant spectral features from SPIRE FTS data products. Optimising the number of features found in SPIRE-FTS spectra is challenging. The wide SPIRE-FTS frequency range (447-1568 GHz) leads to many molecular species and atomic fine structure lines falling within the observed bands. As the best spectral resolution of the SPIRE-FTS is ~1.2 GHz, there can be significant line blending, depending on the source type. In order to find, both efficiently and reliably, features in spectra associated with a wide range of sources, the FF iteratively searches for peaks over a number of signal-to-noise ratio (SNR) thresholds. For each threshold, newly identified features are rigorously checked before being added to the fitting model. At the end of each iteration, the FF simultaneously fits the continuum and features found, with the resulting residual spectrum used in the next iteration. The final FF products report the frequency of the features found and the associated SNRs. Line flux determination is not included as part of the FF products, as extracting reliable line flux from SPIRE-FTS data is a complex process that requires careful evaluation and analysis of the spectra on a case-by-case basis. The FF results are 100% complete for features with SNR greater than 10 and 50-70% complete at SNR of 5. The FF code and all FF products are publicly available via the Herschel Science Archive.

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arXiv2019

L1495 Revisited: A PPMAP View of a Star-Forming Filament

We have analysed the Herschel and SCUBA-2 dust continuum observations of the main filament in the Taurus L1495 star forming region, using the Bayesian fitting procedure PPMAP. (i) If we construct an average profile along the whole length of the filament, it has fwhm $\simeq 0.087\pm 0.003\,{\rm pc};\;$, but the closeness to previous estimates is coincidental. (ii) If we analyse small local sections of the filament, the column-density profile approximates well to the form predicted for hydrostatic equilibrium of an isothermal cylinder. (iii) The ability of PPMAP to distinguish dust emitting at different temperatures, and thereby to discriminate between the warm outer layers of the filament and the cold inner layers near the spine, leads to a significant reduction in the surface-density, $\varSigma$, and hence in the line-density, $μ$. If we adopt the canonical value for the critical line-density at a gas-kinetic temperature of $10\,{\rm K}$, $μ_{_{\rm CRIT}}\simeq 16\,{\rm M_{_\odot}\,pc^{-1}}$, the filament is on average trans-critical, with ${\barμ}\sim μ_{_{\rm CRIT}};\;$ local sections where $μ>μ_{_{\rm CRIT}}$ tend to lie close to pre-stellar cores. (iv) The ability of PPMAP to distinguish different types of dust, i.e. dust characterised by different values of the emissivity index, $β$, reveals that the dust in the filament has a lower emissivity index, $β\leq1.5$, than the dust outside the filament, $β\geq 1.7$, implying that the physical conditions in the filament have effected a change in the properties of the dust.

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arXiv2018

Probing the High-Redshift Universe with SPICA: Toward the Epoch of Reionization and Beyond

With the recent discovery of a dozen dusty star-forming galaxies and around 30 quasars at z>5 that are hyper-luminous in the infrared ($μ$$L_{\rm IR}>10^{13}$ L$_{\odot}$, where $μ$ is a lensing magnification factor), the possibility has opened up for SPICA, the proposed ESA M5 mid-/far-infrared mission, to extend its spectroscopic studies toward the epoch of reionization and beyond. In this paper, we examine the feasibility and scientific potential of such observations with SPICA's far-infrared spectrometer SAFARI, which will probe a spectral range (35-230 $μ$m) that will be unexplored by ALMA and JWST. Our simulations show that SAFARI is capable of delivering good-quality spectra for hyper-luminous infrared galaxies (HyLIRGs) at z=5-10, allowing us to sample spectral features in the rest-frame mid-infrared and to investigate a host of key scientific issues, such as the relative importance of star formation versus AGN, the hardness of the radiation field, the level of chemical enrichment, and the properties of the molecular gas. From a broader perspective, SAFARI offers the potential to open up a new frontier in the study of the early Universe, providing access to uniquely powerful spectral features for probing first-generation objects, such as the key cooling lines of low-metallicity or metal-free forming galaxies (fine-structure and H2 lines) and emission features of solid compounds freshly synthesized by Population III supernovae. Ultimately, SAFARI's ability to explore the high-redshift Universe will be determined by the availability of sufficiently bright targets (whether intrinsically luminous or gravitationally lensed). With its launch expected around 2030, SPICA is ideally positioned to take full advantage of upcoming wide-field surveys such as LSST, SKA, Euclid, and WFIRST, which are likely to provide extraordinary targets for SAFARI.

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arXiv2018

Correcting the extended-source calibration for the Herschel-SPIRE Fourier-Transform Spectrometer

We describe an update to the Herschel-SPIRE Fourier-Transform Spectrometer (FTS) calibration for extended sources, which incorporates a correction for the frequency-dependent far-field feedhorn efficiency, $η_\mathrm{FF}$. This significant correction affects all FTS extended-source calibrated spectra in sparse or mapping mode, regardless of the spectral resolution. Line fluxes and continuum levels are underestimated by factors of 1.3-2 in the Spectrometer Long-Wavelength band (SLW, 447-1018 GHz; 671-294 $μ$m) and 1.4-1.5 in the Spectrometer Short-Wavelength band (SSW, 944-1568 GHz; 318-191 $μ$m). The correction was implemented in the FTS pipeline version 14.1 and has also been described in the SPIRE Handbook since Feb 2017. Studies based on extended-source calibrated spectra produced prior to this pipeline version should be critically reconsidered using the current products available in the Herschel Science Archive. Once the extended-source calibrated spectra are corrected for $η_\mathrm{FF}$, the synthetic photometry and the broadband intensities from SPIRE photometer maps agree within 2-4% -- similar levels to the comparison of point-source calibrated spectra and photometry from point-source calibrated maps. The two calibration schemes for the FTS are now self-consistent: the conversion between the corrected extended-source and point-source calibrated spectra can be achieved with the beam solid angle and a gain correction that accounts for the diffraction loss.

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arXiv2017

Far-infrared observations of a massive cluster forming in the Monoceros R2 filament hub

We present far-infrared observations of Monoceros R2 (a giant molecular cloud at approximately 830 pc distance, containing several sites of active star formation), as observed at 70 μm, 160 μm, 250 μm, 350 μm, and 500 μm by the Photodetector Array Camera and Spectrometer (PACS) and Spectral and Photometric Imaging Receiver (SPIRE) instruments on the Herschel Space Observatory as part of the Herschel imaging survey of OB young stellar objects (HOBYS) Key programme. The Herschel data are complemented by SCUBA-2 data in the submillimetre range, and WISE and Spitzer data in the mid-infrared. In addition, C18O data from the IRAM 30-m Telescope are presented, and used for kinematic information. Sources were extracted from the maps with getsources, and from the fluxes measured, spectral energy distributions were constructed, allowing measurements of source mass and dust temperature. Of 177 Herschel sources robustly detected in the region (a detection with high signal-to-noise and low axis ratio at multiple wavelengths), including protostars and starless cores, 29 are found in a filamentary hub at the centre of the region (a little over 1% of the observed area). These objects are on average smaller, more massive, and more luminous than those in the surrounding regions (which together suggest that they are at a later stage of evolution), a result that cannot be explained entirely by selection effects. These results suggest a picture in which the hub may have begun star formation at a point significantly earlier than the outer regions, possibly forming as a result of feedback from earlier star formation. Furthermore, the hub may be sustaining its star formation by accreting material from the surrounding filaments.

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arXiv2016

Calibration of Herschel SPIRE FTS observations at different spectral resolutions

The SPIRE Fourier Transform Spectrometer on board the Herschel Space Observatory had two standard spectral resolution modes for science observations: high resolution (HR) and low resolution (LR), which could also be performed in sequence (H+LR). A comparison of the HR and LR resolution spectra taken in this sequential mode, revealed a systematic discrepancy in the continuum level. Analysing the data at different stages during standard pipeline processing, demonstrates the telescope and instrument emission affect HR and H+LR observations in a systematically different way. The origin of this difference is found to lie in the variation of both the telescope and instrument response functions, while it is triggered by fast variation of the instrument temperatures. As it is not possible to trace the evolution of the response functions through auxiliary housekeeping parameters, the calibration cannot be corrected analytically. Therefore an empirical correction for LR spectra has been developed, which removes the systematic noise introduced by the variation of the response functions.

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arXiv2016

The data processing pipeline for the Herschel SPIRE Fourier Transform Spectrometer

We present the data processing pipeline to generate calibrated data products from the Spectral and Photometric Imaging Receiver (SPIRE) imaging Fourier Transform Spectrometer on the Herschel Space Observatory. The pipeline processes telemetry from SPIRE observations and produces calibrated spectra for all resolution modes. The spectrometer pipeline shares some elements with the SPIRE photometer pipeline, including the conversion of telemetry packets into data timelines and calculation of bolometer voltages. We present the following fundamental processing steps unique to the spectrometer: temporal and spatial interpolation of the scan mechanism and detector data to create interferograms; Fourier transformation; apodization; and creation of a data cube. We also describe the corrections for various instrumental effects including first- and second-level glitch identification and removal, correction of the effects due to emission from the Herschel telescope and from within the spectrometer instrument, interferogram baseline correction, temporal and spatial phase correction, non-linear response of the bolometers, and variation of instrument performance across the focal plane arrays. Astronomical calibration is based on combinations of observations of standard astronomical sources and regions of space known to contain minimal emission.

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arXiv2016

A census of dense cores in the Taurus L1495 cloud from the Herschel Gould Belt Survey

We present a catalogue of dense cores in a $\sim 4^\circ\times2^\circ$ field of the Taurus star-forming region, inclusive of the L1495 cloud, derived from Herschel SPIRE and PACS observations in the 70 $μ$m, 160 $μ$m, 250 $μ$m, 350 $μ$m, and 500 $μ$m continuum bands. Estimates of mean dust temperature and total mass are derived using modified blackbody fits to the spectral energy distributions. We detect 525 starless cores of which $\sim10$-20% are gravitationally bound and therefore presumably prestellar. Our census of unbound objects is $\sim85$% complete for $M>0.015\,M_\odot$ in low density regions ($A_V\stackrel{<}{_\sim}5$ mag), while the bound (prestellar) subset is $\sim85$% complete for $M>0.1\,M_\odot$ overall. The prestellar core mass function (CMF) is consistent with lognormal form, resembling the stellar system initial mass function, as has been reported previously. All of the inferred prestellar cores lie on filamentary structures whose column densities exceed the expected threshold for filamentary collapse, in agreement with previous reports. Unlike the prestellar CMF, the unbound starless CMF is not lognormal, but instead is consistent with a power-law form below $0.3\,M_\odot$ and shows no evidence for a low-mass turnover. It resembles previously reported mass distributions for CO clumps at low masses ($M\stackrel{<}{_\sim}0.3\,M_\odot$). The volume density PDF, however, is accurately lognormal except at high densities. It is consistent with the effects of self-gravity on magnetized supersonic turbulence. The only significant deviation from lognormality is a high-density tail which can be attributed unambiguously to prestellar cores.

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arXiv2015

A census of dense cores in the Aquila cloud complex: SPIRE/PACS observations from the Herschel Gould Belt survey

We present and discuss the results of the Herschel Gould Belt survey observations in a ~11 deg^2 area of the Aquila molecular cloud complex at d~260 pc, imaged with the SPIRE/PACS cameras from 70 to 500 micron. We identify a complete sample of starless dense cores and embedded protostars in this region, and analyze their global properties and spatial distributions. We find a total of 651 starless cores, ~60% of which are gravitationally bound prestellar cores, and they will likely form stars in the future. We also detect 58 protostellar cores. The core mass function (CMF) derived for the prestellar cores is very similar in shape to the stellar initial mass function (IMF), supporting the earlier view that there is a close physical link between the IMF and the CMF. The global shift in mass scale observed between the CMF and the IMF is consistent with a typical star formation efficiency of ~40%. By comparing the numbers of starless cores to the number of young stellar objects, we estimate that the lifetime of prestellar cores is ~1 Myr. We find a strong correlation between the spatial distribution of prestellar cores and the densest filaments. About 90% of the Herschel-identified prestellar cores are located above a background column density corresponding to A_V~7, and ~75% of them lie within filamentary structures with supercritical masses per unit length >~16 M_sun/pc. These findings support a picture wherein the cores making up the peak of the CMF (and probably responsible for the base of the IMF) result primarily from the gravitational fragmentation of marginally supercritical filaments. Given that filaments appear to dominate the mass budget of dense gas at A_V>7, our findings also suggest that the physics of prestellar core formation within filaments is responsible for a characteristic "efficiency" SFR/M_dense ~5+-2 x 10^-8 yr^-1 for the star formation process in dense gas.

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arXiv2015

The JCMT Gould Belt Survey: First results from the SCUBA-2 observations of the Ophiuchus molecular cloud and a virial analysis of its prestellar core population

In this paper we present the first observations of the Ophiuchus molecular cloud performed as part of the James Clerk Maxwell Telescope (JCMT) Gould Belt Survey (GBS) with the SCUBA-2 instrument. We demonstrate methods for combining these data with previous HARP CO, Herschel, and IRAM N$_{2}$H$^{+}$ observations in order to accurately quantify the properties of the SCUBA-2 sources in Ophiuchus. We produce a catalogue of all of the sources found by SCUBA-2. We separate these into protostars and starless cores. We list all of the starless cores and perform a full virial analysis, including external pressure. This is the first time that external pressure has been included in this level of detail. We find that the majority of our cores are either bound or virialised. Gravitational energy and external pressure are on average of a similar order of magnitude, but with some variation from region to region. We find that cores in the Oph A region are gravitationally bound prestellar cores, while cores in the Oph C and E regions are pressure-confined. We determine that N$_{2}$H$^{+}$ is a good tracer of the bound material of prestellar cores, although we find some evidence for N$_{2}$H$^{+}$ freeze-out at the very highest core densities. We find that non-thermal linewidths decrease substantially between the gas traced by C$^{18}$O and that traced by N$_{2}$H$^{+}$, indicating the dissipation of turbulence at higher densities. We find that the critical Bonnor-Ebert stability criterion is not a good indicator of the boundedness of our cores. We detect the pre-brown dwarf candidate Oph B-11 and find a flux density and mass consistent with previous work. We discuss regional variations in the nature of the cores and find further support for our previous hypothesis of a global evolutionary gradient across the cloud from southwest to northeast, indicating sequential star formation across the region.

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arXiv2015

Systematic characterisation of the Herschel SPIRE Fourier Transform Spectrometer

A systematic programme of calibration observations was carried out to monitor the performance of the SPIRE FTS instrument on board the Herschel Space Observatory. Observations of planets (including the prime point-source calibrator, Uranus), asteroids, line sources, dark sky, and cross-calibration sources were made in order to monitor repeatability and sensitivity, and to improve FTS calibration. We present a complete analysis of the full set of calibration observations and use them to assess the performance of the FTS. Particular care is taken to understand and separate out the effect of pointing uncertainties, including the position of the internal beam steering mirror for sparse observations in the early part of the mission. The repeatability of spectral line centre positions is <5km/s, for lines with signal-to-noise ratios >40, corresponding to <0.5-2.0% of a resolution element. For spectral line flux, the repeatability is better than 6%, which improves to 1-2% for spectra corrected for pointing offsets. The continuum repeatability is 4.4% for the SLW band and 13.6% for the SSW band, which reduces to ~1% once the data have been corrected for pointing offsets. Observations of dark sky were used to assess the sensitivity and the systematic offset in the continuum, both of which were found to be consistent across the FTS detector arrays. The average point-source calibrated sensitivity for the centre detectors is 0.20 and 0.21 Jy [1 sigma; 1 hour], for SLW and SSW. The average continuum offset is 0.40 Jy for the SLW band and 0.28 Jy for the SSW band.

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arXiv2014

A Far-Infrared Spectroscopic Survey of Intermediate Redshift (Ultra) Luminous Infrared Galaxies

We present Herschel far-IR photometry and spectroscopy as well as ground based CO observations of an intermediate redshift (0.21 < z < 0.88) sample of Herschel-selected (ultra)-luminous infrared galaxies (L_IR > 10^11.5L_sun). With these measurements we trace the dust continuum, far-IR atomic line emission, in particular [CII]\,157.7microns, as well as the molecular gas of z~0.3 (U)LIRGs and perform a detailed investigation of the interstellar medium of the population. We find that the majority of Herschel-selected intermediate redshift (U)LIRGs have L_CII/L_FIR ratios that are a factor of about 10 higher than that of local ULIRGs and comparable to that of local normal and high-$z$ star forming galaxies. Using our sample to bridge local and high-z [CII] observations, we find that the majority of galaxies at all redshifts and all luminosities follow a L_CII-L_FIR relation with a slope of unity, from which local ULIRGs and high-z AGN dominated sources are clear outliers. We also confirm that the strong anti-correlation between the L_CII/L_FIR ratio and the far-IR color L_60/L_100 observed in the local Universe holds over a broad range of redshifts and luminosities, in the sense that warmer sources exhibit lower L_CII/L_FIR at any epoch. Intermediate redshift ULIRGs are also characterised by large molecular gas reservoirs and by lower star formation efficiencies compared to that of local ULIRGs. The high L_CII/L_FIR ratios, the moderate star formation efficiencies (L_LIR/L_CO or L_IR/M_gas) and the relatively low dust temperatures of our sample (which are also common characteristics of high-z star forming galaxies with ULIRG-like luminosities) indicate that the evolution of the physical properties of (U)LIRGs between the present day and z > 1 is already significant by z ~ 0.3.

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arXiv2014

Flux Calibration of Broadband Far Infrared and Submillimetre Photometric Instruments: Theory and Application to Herschel-SPIRE

Photometric instruments operating at far infrared to millimetre wavelengths often have broad spectral passbands (central wavelength/bandwidth ~ 3 or less), especially those operating in space. A broad passband can result in significant variation of the beam profile and aperture efficiency across the passband, effects which thus far have not generally been taken into account in the flux calibration of such instruments. With absolute calibration uncertainties associated with the brightness of primary calibration standards now in the region of 5% or less, variation of the beam properties across the passband can be a significant contributor to the overall calibration accuracy for extended emission. We present a calibration framework which takes such variations into account for both antenna-coupled and absorber-coupled focal plane architectures. The scheme covers point source and extended source cases, and also the intermediate case of a semi-extended source profile. We apply the new method to the Herschel-SPIRE space-borne photometer.

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arXiv2014

EChOSim: The Exoplanet Characterisation Observatory software simulator

EChOSim is the end-to-end time-domain simulator of the Exoplanet Characterisation Observatory (EChO) space mission. EChOSim has been developed to assess the capability EChO has to detect and characterize the atmospheres of transiting exoplanets, and through this revolutionize the knowledge we have of the Milky Way and of our place in the Galaxy. Here we discuss the details of the EChOSim implementation and describe the models used to represent the instrument and to simulate the detection. Software simulators have assumed a central role in the design of new instrumentation and in assessing the level of systematics affecting the measurements of existing experiments. Thanks to its high modularity, EChOSim can simulate basic aspects of several existing and proposed spectrometers for exoplanet transits, including instruments on the Hubble Space Telescope and Spitzer, or ground-based and balloon borne experiments. A discussion of different uses of EChOSim is given, including examples of simulations performed to assess the EChO mission.

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arXiv2014

Calibration of the Herschel SPIRE Fourier Transform Spectrometer

The Herschel SPIRE instrument consists of an imaging photometric camera and an imaging Fourier Transform Spectrometer (FTS), both operating over a frequency range of 450-1550 GHz. In this paper, we briefly review the FTS design, operation, and data reduction, and describe in detail the approach taken to relative calibration (removal of instrument signatures) and absolute calibration against standard astronomical sources. The calibration scheme assumes a spatially extended source and uses the Herschel telescope as primary calibrator. Conversion from extended to point-source calibration is carried out using observations of the planet Uranus. The model of the telescope emission is shown to be accurate to within 6% and repeatable to better than 0.06% and, by comparison with models of Mars and Neptune, the Uranus model is shown to be accurate to within 3%. Multiple observations of a number of point-like sources show that the repeatability of the calibration is better than 1%, if the effects of the satellite absolute pointing error (APE) are corrected. The satellite APE leads to a decrement in the derived flux, which can be up to ~10% (1 sigma) at the high-frequency end of the SPIRE range in the first part of the mission, and ~4% after Herschel operational day 1011. The lower frequency range of the SPIRE band is unaffected by this pointing error due to the larger beam size. Overall, for well-pointed, point-like sources, the absolute flux calibration is better than 6%, and for extended sources where mapping is required it is better than 7%.

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arXiv2014

Properties of Starless and Prestellar Cores in Taurus Revealed by Herschel SPIRE/PACS Imaging

The density and temperature structures of dense cores in the L1495 cloud of the Taurus star-forming region are investigated using Herschel SPIRE and PACS images in the 70 $μ$m, 160 $μ$m, 250 $μ$m, 350 $μ$m and 500 $μ$m continuum bands. A sample consisting of 20 cores, selected using spectral and spatial criteria, is analysed using a new maximum likelihood technique, COREFIT, which takes full account of the instrumental point spread functions. We obtain central dust temperatures, $T_0$, in the range 6-12 K and find that, in the majority of cases, the radial density falloff at large radial distances is consistent with the $r^{-2}$ variation expected for Bonnor-Ebert spheres. Two of our cores exhibit a significantly steeper falloff, however, and since both appear to be gravitationally unstable, such behaviour may have implications for collapse models. We find a strong negative correlation between $T_0$ and peak column density, as expected if the dust is heated predominantly by the interstellar radiation field. At the temperatures we estimate for the core centres, carbon-bearing molecules freeze out as ice mantles on dust grains, and this behaviour is supported here by the lack of correspondence between our estimated core locations and the previously-published positions of H$^{13}$CO$^+$ peaks. On this basis, our observations suggest a sublimation-zone radius typically $\sim 10^4$ AU. Comparison with previously-published N$_2$H$^+$ data at 8400 AU resolution, however, shows no evidence for N$_2$H$^+$ depletion at that resolution.

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arXiv2014

Herschel Observations of Far-Infrared Cooling Lines in intermediate Redshift (Ultra)-luminous Infrared Galaxies

We report the first results from a spectroscopic survey of the [CII] 158um line from a sample of intermediate redshift (0.2 10^11.5 Lsun), using the SPIRE-Fourier Transform Spectrometer (FTS) on board the Herschel Space Observatory. This is the first survey of [CII] emission, an important tracer of star-formation, at a redshift range where the star-formation rate density of the Universe increases rapidly. We detect strong [CII] 158um line emission from over 80% of the sample. We find that the [CII] line is luminous, in the range (0.8-4)x10^(-3) of the far-infrared continuum luminosity of our sources, and appears to arise from photodissociation regions on the surface of molecular clouds. The L[CII]/LIR ratio in our intermediate redshift (U)LIRGs is on average ~10 times larger than that of local ULIRGs. Furthermore, we find that the L[CII]/LIR and L[CII]/LCO(1-0) ratios in our sample are similar to those of local normal galaxies and high-z star-forming galaxies. ULIRGs at z~0.5 show many similarities to the properties of local normal and high-z star forming galaxies. Our findings strongly suggest that rapid evolution in the properties of the star forming regions of luminous infrared galaxies is likely to have occurred in the last 5 billion years.

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