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Register a new userSub-millimetre observations of hyperluminous infrared galaxies
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D. Farrah
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We present sub-mm photometry for 11 Hyperluminous Infrared Galaxies (HLIRGs) and use radiative transfer models for starbursts and AGN to investigate the IR emission. In all sources both a starburst and AGN are required to explain the IR emission. The mean starburst fraction is 35%, with a range spanning 80% starburst dominated to 80% AGN dominated. In all cases the starburst dominates at rest-frame wavelengths >50 microns, with star formation rates >500 solar masses per year. The trend of increasing AGN fraction with increasing IR luminosity seen in IRAS galaxies peaks in HLIRGs, and is not higher than the fraction seen in bright ULIRGs. The AGN and starburst luminosities correlate, suggesting that a common physical factor, plausibly the dust masses, governs their luminosities. Our results suggest that the HLIRG population is comprised both of ULIRG-like galaxy mergers, and of young galaxies going through their maximal star formation periods whilst harbouring an AGN. The coeval AGN and starburst activity in our sources implies that starburst and AGN activity, and the peak starburst and AGN luminosities, can be coeval in active galaxies generally. When extrapolated to high-z our sources have comparable sub-mm fluxes to sub-mm survey sources. At least some sub-mm survey sources are therefore likely to be comprised of similar galaxy populations to those found in the HLIRG population. It is also plausible from these results that high-z sub-mm sources harbour heavily obscured AGN. The differences in X-ray and sub-mm properties between HLIRGs at z~1 and sub-mm sources at z~3 implies evolution between the two epochs. Either the mean AGN obscuration level is greater at z~3 than at z~1, or the fraction of IR-luminous sources at z~3 that contain AGN is smaller than that at z~1.
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We present a catalogue of 179 hyperluminous infrared galaxies (HLIRGs) from the Imperial IRAS-FSS Redshift (IIFSCz) Catalogue. Of the 92 with detections in at least two far infrared bands, 62 are dominated by an M82-like starburst, 22 by an Arp220-like starburst and 8 by an AGN dust torus. On the basis of previous gravitational lensing studies and an examination of HST archive images for a further 5 objects, we estimate the fraction of HLIRGs that are significantly lensed to be 10-30%. We show simple infrared template fits to the SEDs of 23 HLIRGs with spectroscopic redshifts and at least 5 photometric bands. Most can be fitted with a combination of two simple templates: an AGN dust torus and an M82-like starburst. In the optical, 17 of the objects are fitted with QSO templates, 6 are fitted with galaxy templates. 20 of the 23 objects (87%) show evidence of an AGN either from the optical continuum or from the signature of an AGN dust torus, but the starburst component is the dominant contribution to bolometric luminosity in 14 out of 23 objects (61%). The implied star-formation rates, even after correcting for lensing magnification, are in excess of 1000 Mo /yr. We use infrared template-fitting models to predict fluxes for all HLIRGs at submillimetre wavelengths, and show predictions at 350 and 850 mu. Most would have 850 mu fluxes brighter than 5 mJy so should be easily detectable with current submillimetre telescopes. At least 15% should be detectable in the Planck all-sky survey at 350 mu and all Planck all-sky survey sources with z < 0.9 should be IIFSCz sources. From the luminosity-volume test we find that HLIRGs show strong evolution. A simple exponential luminosity evolution applied to all HLIRGs would be consistent with the luminosity functions found in redshift bins 0.3-0.5, 0.5-1 and 1-2.
We make use of multi-wavelength data of a large hyperluminous infrared (HLIRG) sample to derive their main physical properties, e.g., stellar mass, star-formation rate (SFR), volume density, contribution to the cosmic stellar mass density and to the cosmic SFR density. We also study the black hole (BH) growth rate and its relationship with the SFR of the host galaxy. We select 526 HLIRGs in three deep fields (Bo$o$tes, Lockman-Hole, ELAIS-N1) and adopt two spectral energy distribution (SED) fitting codes, CIGALE, which assumes energy balance, and CYGNUS, which is based on radiative transfer models and does not adopt energy balance principle. We use two different active galactic nucleus (AGN) models in CIGALE and three AGN models in CYGNUS to compare the results estimated using different SED fitting codes and different AGN models. The stellar mass, total IR luminosity and AGN luminosity agree well between different models with a typical median offset of 0.1 dex. The SFR estimates show the largest dispersions (up to 0.5 dex). This dispersion has an impact on the subsequent analysis, which may suggest that previous contradictory results could partly be due to different choices of methods. HLIRGs are ultra-massive galaxies with 99% of them having stellar masses larger than $10^{11} M_{odot}$. Our results reveal a higher space density of ultra-massive galaxies than found in previous surveys or predicted by simulations. We find that HLIRGs contribute more to the cosmic SFR density as redshift increases. In terms of BH growth, the two SED fitting methods provide different results. We can see a clear trend in which SFR decreases as AGN luminosity increases when using CYGNUS estimates, possibly implying quenching by AGN, while this trend is much weaker when using CIGALE estimates. This difference is also influenced by the dispersion between SlFR estimates obtained by the two codes.
Recent observational evidence suggests that the coarse angular resolution ($sim20$ FWHM) of single-dish telescopes at sub-mm wavelengths has biased the observed galaxy number counts by blending together the sub-mm emission from multiple sub-mm galaxies (SMGs). We use lightcones computed from an updated implementation of the galform semi-analytic model to generate $50$ mock sub-mm surveys of $0.5$ deg$^2$ at $850$ $mu$m, taking into account the effects of the finite single-dish beam in a more accurate way than has been done previously. We find that blending of SMGs does lead to an enhancement of source extracted number counts at bright fluxes ($S_{mathrm{850}mumathrm{m}}gtrsim1$ mJy). Typically, $sim3{-}6$ galaxies contribute $90%$ of the flux of an $S_{850mumathrm{m}}=5$ mJy source and these blended galaxies are physically unassociated. We find that field-to-field variations are comparable to Poisson fluctuations for our $S_{850mumathrm{m}}>5$ mJy SMG population, which has a median redshift $z_{50}=2.0$, but are greater than Poisson for the $S_{850mumathrm{m}}>1$ mJy population ($z_{50}=2.8$). In a detailed comparison to a recent interferometric survey targeted at single-dish detected sources, we reproduce the difference between single-dish and interferometer number counts and find a median redshift ($z_{50}=2.5$) in excellent agreement with the observed value ($z_{50}=2.5pm 0.2$). We also present predictions for single-dish survey number counts at $450$ and $1100$ $mu$m, which show good agreement with observational data.
We investigate what powers hyperluminous infrared galaxies (HyLIRGs; LIR(8-1000um)>10^13 Lsun) at z~1-2, by examining the behaviour of the infrared AGN luminosity function in relation to the infrared galaxy luminosity function. The former corresponds to emission from AGN-heated dust only, whereas the latter includes emission from dust heated by stars and AGN. Our results show that the two luminosity functions are substantially different below 10^13 Lsun but converge in the HyLIRG regime. We find that the fraction of AGN dominated sources increases with total infrared luminosity and at LIR >10^13.5 Lsun AGN can account for the entire infrared emission. We conclude that the bright end of the 1<z<2 infrared galaxy luminosity function is shaped by AGN rather than star-forming galaxies.
Debris disks, the tenuous rocky and icy remnants of planet formation, are believed to be evidence for planetary systems around other stars. The JCMT/SCUBA-2 debris disk legacy survey SCUBA-2 Observations of Nearby Stars (SONS) observed 100 nearby stars, amongst them HD~76582, for evidence of such material. Here we present imaging observations by JCMT/SCUBA-2 and textit{Herschel}/PACS at sub-millimetre and far-infrared wavelengths, respectively. We simultaneously model the ensemble of photometric and imaging data, spanning optical to sub-millimetre wavelengths, in a self-consistent manner. At far-infrared wavelengths, we find extended emission from the circumstellar disk providing a strong constraint on the dust spatial location in the outer system, although the angular resolution is too poor to constrain the interior of the system. In the sub-millimetre, photometry at 450 and 850~$mu$m reveal a steep fall-off that we interpret as a disk dominated by moderately-sized dust grains ($a_{rm min}~=~36~mu$m), perhaps indicative of a non-steady-state collisional cascade within the disk. A disk architecture of three distinct annuli, comprising an unresolved component at $sim$ 20 au and outer components at 80 and 270 au, along with a very steep particle size distribution ($gamma~=~5$), is proposed to match the observations.
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