Efstathiou, Andreas

We investigate the relation between star formation rates (M˙s) and AGN properties in optically selected type 1 quasars at 2 < z < 3 using data from Herschel and the SDSS. We find that M˙s remains approximately constant with redshift, at 300 ± 100M⊙ yr-1. Conversely, M˙s increases with AGN luminosity, up to a maximum of ~600M⊙ yr-1, and with CIV FWHM. In context with previous results, this is consistent with a relation between M˙s and black hole accretion rate (M˙bh) existing in only parts of the z - M˙s - M˙bh plane, dependent on the free gas fraction, the trigger for activity, and the processes that may quench star formation. The relations between M˙s and both AGN luminosity and C IV FWHM are consistent with star formation rates in quasars scaling with black hole mass, though we cannot rule out a separate relation with black hole accretion rate. Star formation rates are observed to decline with increasing CIV equivalent width. This decline can be partially explained via the Baldwin effect, but may have an additional contribution from one or more of three factors; Mi is not a linear tracer of L2500, the Baldwin effect changes form at high AGN luminosities, and high C IV EW values signpost a change in the relation between M˙s and M˙bh. Finally, there is no strong relation between M˙s and Eddington ratio, or the asymmetry of the C IV line. The former suggests that star formation rates do not scale with how efficiently the black hole is accreting, while the latter is consistent with C IV asymmetries arising from orientation effects.

We present Herschel observations of 6 fine-structure lines in 25 ultraluminous infrared galaxies at z < 0.27. The lines, [O III]52 μm, [N III]57 μm, [O I]63 μm, [N II]122 μm, [O I]145 μm, and [C II]158 μm, are mostly single Gaussians with widths <600 km s-1 and luminosities of 107-109 LO. There are deficits in the [O I]63/L IR, [N II]/L IR, [O I]145/L IR, and [C II]/L IR ratios compared to lower luminosity systems. The majority of the line deficits are consistent with dustier H II regions, but part of the [C II] deficit may arise from an additional mechanism, plausibly charged dust grains. This is consistent with some of the [C II] originating from photodissociation regions or the interstellar medium (ISM). We derive relations between far-IR line luminosities and both the IR luminosity and star formation rate. We find that [N II] and both [O I] lines are good tracers of the IR luminosity and star formation rate. In contrast, [C II] is a poor tracer of the IR luminosity and star formation rate, and does not improve as a tracer of either quantity if the [C II] deficit is accounted for. The continuum luminosity densities also correlate with the IR luminosity and star formation rate. We derive ranges for the gas density and ultraviolet radiation intensity of 101 < n < 102.5 and 102.2 < G 0 < 103.6, respectively. These ranges depend on optical type, the importance of star formation, and merger stage. We do not find relationships between far-IR line properties and several other parameters: active galactic nucleus (AGN) activity, merger stage, mid-IR excitation, and SMBH mass. We conclude that these far-IR lines arise from gas heated by starlight, and that they are not strongly influenced by AGN activity.

We present Herschel photometry and spectroscopy, carried out as part of the Herschel ultraluminous infrared galaxy (ULIRG) survey, and a model for the infrared to submillimetre emission of the ULIRG IRAS 08572+3915. This source shows one of the deepest known silicate absorption features and no polycyclic aromatic hydrocarbon emission. The model suggests that this object is powered by an active galactic nucleus (AGN) with a fairly smooth torus viewed almost edge-on and a very young starburst. According to our model, the AGN contributes about 90 per cent of the total luminosity of 1.1 × 1013 L⊙, which is about a factor of 5 higher than previous estimates. The large correction of the luminosity is due to theanisotropy of the emission of the best-fitting torus. Similar corrections may be necessary for other local and high-z analogues. This correction implies that IRAS 08572+3915 at a redshift of 0.058 35 may be the nearest hyperluminous infrared galaxy and probably the most luminous infrared galaxy in the local (z < 0.2) Universe. IRAS 08572+3915 shows a low ratio of [C II] to IR luminosity (log L[C II]/LIR < -3.8) and a [OI]63 μm to [CII]158 μm line ratio of about 1 that supports the model presented in this Letter.

The mid-infrared spectra of ultraluminous infrared galaxies (ULIRGs) contain a variety of spectral features that can be used as diagnostics to characterize the spectra. However, such diagnostics are biased by our prior prejudices on the origin of the features. Moreover, by using only part of the spectrum they do not utilize the full information content of the spectra. Blind statistical techniques such as principal component analysis (PCA) consider the whole spectrum, find correlated features and separate them out into distinct components. We further investigate the principal components (PCs) of ULIRGs derived in Wang et al. We quantitatively show that five PCs are optimal for describing the Infrared Spectrograph spectra. These five components (PC1-PC5) and the mean spectrum provide a template basis set that reproduces spectra of all z < 0.35 ULIRGs within the noise. For comparison, the spectra are also modelled with a combination of radiative transfer models of both starbursts and the dusty torus surrounding active galactic nuclei (AGN). The five PCs typically provide better fits than the models. We argue that the radiative transfer models require a colder dust component and have difficulty in modelling strong polycyclic aromatic hydrocarbon features. Aided by the models we also interpret the physical processes that the PCs represent. The third PC is shown to indicate the nature of the dominant power source, while PC1 is related to the inclination of the AGN torus. Finally, we use the five PCs to define a new classification scheme using 5D Gaussian mixture modelling and trained on widely used optical classifications. The five PCs, average spectra for the four classifications and the code to classify objects are made available at: http://www.phys.susx.ac.uk/pdh21/PCA/.

We examine the power source of 41 local ultraluminous infrared galaxies (ULIRGs) using archival infrared (IR) and optical photometry. We fit the observed spectral energy distributions with starburst and active galactic nucleus (AGN) components, each component being drawn from a family of templates. We find that all of the sample require a starburst, whereas only half require an AGN. In 90 per cent of the sample the starburst provides over half the IR emission, with a mean fractional luminosity of 82 per cent. When combined with other galaxy samples we find that starburst and AGN luminosities correlate over six decades in IR luminosity, suggesting that a common factor governs both luminosities, plausibly the gas masses in the nuclear regions. We find no trend for increasing fractional AGN luminosity with increasing total luminosity, contrary to previous claims. We find that the mid-IR F7.7/C 7.7 line-continuum ratio is no indication of the starburst luminosity, or the fractional AGN luminosity, and therefore that F 7.7/C7.7 is not a reliable diagnostic of the power source in ULIRGs. The radio flux correlates with the starburst luminosity, but shows no correlation with the AGN luminosity, in line with previous results. We propose that the scatter in this correlation is due to a skewed starburst initial mass function and/or relic relativistic electrons from a previous starburst, rather than contamination from an obscured AGN. We show that most ULIRGs undergo multiple starbursts during their lifetime, and by inference that mergers between more than two galaxies may be common amongst ULIRGs. Our results support the evolutionary model for ULIRGs proposed by Farrah et al., where they can follow many different evolutionary paths of starburst and AGN activity in transforming merging spiral galaxies into elliptical galaxies, but that most do not go through an optical quasi-stellar object phase. The lower level of AGN activity in our local sample compared with z ∼ 1 hyperluminous infrared galaxies implies that the two samples are distinct populations. We postulate that different galaxy formation processes at high z are responsible for this difference.

We present the Herschel SPIRE Fourier Transform Spectroscopy (FTS) atlas for a complete flux-limited sample of local ultraluminous infrared galaxies (ULIRGs) as part of the HERschel Ultra Luminous InfraRed Galaxy Survey (HERUS). The data reduction is described in detail and was optimized for faint FTS sources ,with particular care being taken for the subtraction of the background, which dominates the continuum shape of the spectra. To improve the final spectra, special treatment in the data reduction has been given to any observation suffering from artifacts in the data caused by anomalous instrumental effects. Complete spectra are shown covering 200-671 μm, with photometry in the SPIRE bands at 250, 350, and 500 μm. The spectra include near complete CO ladders for over half of our sample, as well as fine structure lines from [C i] 370 μm, [C i] 609 μm, and [N ii] 205 μm. We also detect H2O lines in several objects. We construct CO spectral line energy distributions (SLEDs) for the sample, and compare their slopes with the far-infrared (FIR) colors and luminosities. We show that the CO SLEDs of ULIRGs can be broadly grouped into three classes based on their excitation. We find that the mid-J (5 < J < 8) lines are better correlated with the total FIR luminosity, suggesting that the warm gas component is closely linked to recent star formation. The higher J transitions do not linearly correlate with the FIR luminosity, consistent with them originating in hotter, denser gas that is unconnected to the current star formation. We conclude that in most cases more than one temperature component is required to model the CO SLEDs.

We discuss optical associations, spectral energy distributions (SEDs), and photometric redshifts for Spitzer Wide-Area Infrared Extragalactic (SWIRE) Survey sources in the European Large-Area ISO Survey (ELAIS) N1 area and the Lockman Validation Field (VF). The band-merged Infrared Array Camera (IRAC) (3.6,4.5,5.8, and 8.0 μm) and Multiband Imaging Photometer for Spitzer (24, 70, and 160 μm) data have been associated with optical UgriZ data from the Isaac Newton Telescope Wide Field Survey in ELAIS N1 and with our own optical Ugri data in Lockman-VF. Criteria for eliminating spurious infrared sources and for carrying out star-quasar-galaxy separation are discussed, and statistics of the identification rate are given. Thirty-two percent of sources in the ELAIS N1 field are found to be optically blank (to r = 23.5) and 16% in Lockman-VF (to r = 25). The SEDs of selected ELAIS sources in N1 detected by SWIRE, most with spectroscopic redshifts, are modeled in terms of a simple set of galaxy and quasar templates in the optical and near-infrared (NIR), and with a set of dust emission templates (cirrus, M82 starburst, Arp 220 starburst, and active galactic nucleus [AGN] dust torus) in the mid-infrared. The optical data, together with the IRAC 3.6 and 4.5 μm data, have been used to determine photometric redshifts. For galaxies with known spectroscopic redshifts, there is a notable improvement in the photometric redshift when the IRAC data are used, with a reduction in the rms scatter from 10% in (1 + z) to 7%. Although further spectroscopic data are needed to confirm this result, the prospect of determining good photometric redshifts for much of the SWIRE survey, expected to yield over 2 million extragalactic objects, is excellent. Some modifications to the optical templates were required in the previously uninvestigated wavelength region 2-5 μm. The photometric redshifts are used to derive the 3.6 and 24 μm redshift distribution and to compare this with the predictions of models. For those sources with a clear mid-infrared excess, relative to the galaxy starlight model used for the optical and NIR, the mid- and far-infrared data are modeled in terms of the same dust emission templates (cirrus, M82, Arp 220, and AGN dust torus). The proportions found of each template type are cirrus, 31%; M82, 29%; Arp 220,10%; and AGN dust tori, 29%. The distribution of the different infrared SED types in the L IR/L opt versus L IR plane, where L IR and L opt are the infrared and optical bolometric luminosities, respectively, is discussed. There is an interesting population of luminous cool cirrus galaxies with L IR > L opt, implying a substantial dust optical depth. Galaxies with Arp 220-like SEDs, of which there are a surprising preponderance compared with preexisting source count models, tend to have high ratios of infrared to optical bolometric luminosity, consistent with having very high extinction. There is also a high proportion of galaxies whose mid-infrared SEDs are fitted by an AGN dust torus template (29%). Of these only 8% of these are type 1 AGNs according to the optical-NIR template fitting, whereas 25% are fitted with galaxy templates in the optical-NIR and have L IR > L opt and so have to be type 2 AGN. The remainder have L IR < L opt and so can be Seyfert galaxies, in which the optical AGN fails to be detected against the light of the host galaxy. The implied dust covering factor, ≥75%, is much higher than that inferred for bright optically selected quasars.

The Herschel Extragalactic Legacy Project (HELP) brings together a vast range of data frommany astronomical observatories. Its main focus is on the Herschel data, which maps dustobscured star formation over 1300 deg2. With this unprecedented combination of data sets, it is possible to investigate how the star formation versus stellar mass relation (main sequence)of star-forming galaxies depends on environment. In this pilot study, we explore this question within 0.1 2. We also estimate the evolution of the star formation rate density in the COSMOS field, and our results are consistent with previous measurements at z < 1.5 and z > 2 but we find a 1.4+0.3 -0.2 times higher peak value of the star formation rate density at z ~ 1.9.

There is significant scientific value to be gained from combining AKARI fluxes with data at other far-infrared (IR) wavelengths from the Infrared Astronomical Satellite (IRAS) and Herschel missions. To be able to do this we must ensure that there are no systematic differences between the data sets that need to be corrected before the fluxes are compatible with each other. One such systematic effect identified in the Bright Source Catalog version 1 (BSCv1) data is the issue of beam corrections. We determine these for the BSC version 2 (BSCv2) data by correlating ratios of appropriate IRAS and AKARI bands with the difference in 2 Micron All Sky Survey (2MASS) J-band extended and point source magnitudes for sources cross-matched between the IRAS Faint Source Catalog (FSC), AKARI BSCv2 and 2MASS catalogs. We find significant correlations (p < 10 -13) indicating that beam corrections are necessary in the 65 and 90 μm bands. We then use these corrected fluxes to supplement existing data in spectral energy distribution (SED) fits for ultraluminous infrared galaxies (ULIRGs) in the Herschel ULIRG Survey (HERUS). The addition of AKARI fluxes makes little difference to the results of simple (T, β) fits to the SEDs of these sources, though there is a general decrease in reduced Ï ‡ 2 values. The utility of the extra AKARI data, however, is in allowing physically more realistic SED models with more parameters to be fitted to the data. We also extend our analysis of beam correction issues in the AKARI data by examining the Herschel Reference Sample (HRS) galaxies, which have Herschel photometry from 100 to 500 μm and which are more spatially extended than the HERUS ULIRGs. 34 of the HRS sources have good Herschel SEDs and matching data from AKARI. This investigation finds that our simple 2MASS-based beam correction scheme is inadequate for these larger and more complex sources. There are also indications that additional beam corrections at 140 and 160 μm are needed for these sources, extended on scales >1′.

We present a study of the infrared properties for a sample of seven spectroscopically confirmed submillimeter galaxies (SMGs) at z > 4.0. By combining ground-based near-infrared, Spitzer IRAC and MIPS, Herschel SPIRE, and ground-based submillimeter/millimeter photometry, we construct their spectral energy distributions (SEDs) and a composite model to fit the SEDs. The model includes a stellar emission component at λrest < 3.5 μm, a hot dust component peaking at λrest ∼ 5 μm, and cold dust component which becomes significant for λrest > 50 μm. Six objects in the sample are detected at 250 and 350 μm. The dust temperatures for the sources in this sample are in the range of 40-80 K, and their LFIR ∼ 1013 L⊙ qualifies them as hyper-luminous infrared galaxies. The mean FIR-radio index for this sample is around 〈q〉 = 2.2 indicating no radio excess in their radio emission. Most sources in the sample have 24 μm detections corresponding to a rest-frame 4.5 μm luminosity of Log10(L4.5/L ⊙) = 11 ∼ 11.5. Their L4.5/LFIR ratios are very similar to those of starburst-dominated SMGs at z ∼ 2. The L CO-LFIR relation for this sample is consistent with that determined for local ULIRGs and SMGs at z ∼ 2. We conclude that SMGs at z > 4 are hotter and more luminous in the FIR but otherwise very similar to those at z ∼ 2. None of these sources show any sign of the strong QSO phase being triggered.