The Hidden Universe revealed at submm wavelengths - IV
David Hughes
INAOE, Tonantzintla, Puebla, Mexico Evolution of morphology, number-density, physical scale & luminosity of structure
distance, redshift (z) or scale-factor of universe
optical HST observer GTM dΩ
submm JCMT provide N(>flux, mass|distance)/unit area • surveying the universe (i.e. counting the number of galaxies as a function of distance and brightness, and spatial distribution) is the most fundamental observation to understand the evolution of galaxies and clusters
•the observed (submillimetre-wavelength luminosity provides a measure of the star formation rate (since dust absorbs UV-optical radiation from young stars and themally re-radiates at longer FIR-mm wavelengths) Arp 220 (z=0.018) Detecting dust (& galaxy formation) L = 2x1012 L FIR ~ at high-redshift
redshift
850µm . z=0.1
... Flux density z=1 Current SCUBA detection limit . z=3
z=6
z=11 radio 850µm IR observed wavelength Difference between SCUBA & Bolocam surveys of Lockman Hole
Bolocam 1.1mm CSO survey 17 sources in 324 sq. arcmin (Laurent etal 2005 astro-ph/0503249) only 8 overlap with SCUBA
UK 8mJy SCUBA 850um survey Sub-mm & mm extragalactic survey source-counts (from Laurent et al. 2005) IRAS FIR (60um) luminosity function
z=2 z=1
L(z)= L (1+z)3 at z=1, L(z) = 8 L at z=2, L(z) = 27 L L 10L 100L
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Soifer etal. 1986, ApJ Lett. 303, L41 Summary of results from confusion-limited (sub)mm surveys Access to the highest-redshift Universe, potentially un-limited at mm-λ Basic catalogue: • Less than 200 (sub)mm sources detected (S/N > 3)
• Positions with uncertainty ~ 2-3 arcsecs (given 11-15” FWHM) • Sub-mm (SCUBA) and mm (MAMBO) surveys are sensitive 12 to the detection of galaxies with FIR luminosities > 3. 10 L~ and star-formation rates SFRs > 300 M~ /yr (cf. ULIRGS) .... if galaxies lie at z>1
Need identifications, redshifts, SEDs, morphology of hosts, environment (galaxy interaction rate), fraction of (buried?)
AGN, stellar masses, gas (HI, HII, H2) masses ……… Most questions on the nature of the (sub)mm galaxy population require additional X-ray to radio follow-up larger telescopes higher resolution lower confusion limit increased sensitivity
170µm SPITZER
850µm JCMT
SPITZER 3mm LMT
larger-format cameras increased field-of-view faster mapping speed improved source statistics Plan of lectures
I. The Cold Universe. Basic observational properties of the ISM and galaxies at FIR-mm wavelengths. Overview of reasons why submm observations are a necessary contribution to the understanding of the evolutionary history of galaxies and clusters. The early history of FIR-mm astronomy.
II. Dust grains and thermal radiation. IR-mm wavelength spectral energy distributions of starburst galaxies. Calculation of dust masses & SFRs. K-corrections. Arguments to support expectation for luminous submm galaxies in the high-redshift universe.
III. Dust-production by supernovae at high-z? Submm telescopes & instruments. Confusion limits, biases & survey design. Submm galaxy surveys. Evolutionary history of submm population.
IV. Multi-wavelength follow-up of high-redshift submm population. Breaking the redshift deadlock: spectroscopic vs. photometric redshift techniques. Physical nature of submm galaxies. Identifying clusters at submm wavelengths via the Sunyaev-Zeldovich effect. Prospects for the future (including the LMT). UK 8 mJy SCUBA survey of the Lockman Hole & ELAIS N2 fields (Scott et al. 2002, Fox etal. 2002)
Lockman Hole Hubble Deep Field (850um SCUBA survey Hughes et al. 1998)
UK 8mJy survey 260 sq. arcmin 850um survey
2.5mJy r.m.s. at 850um
19 sources (S/N > 4), 38 sources (S/N > 3.5) SCUBA survey of the Hubble Deep Field Hughes etal. 1998, Nature, 394, 241
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160 arcsecs 15-m James Clerk Maxwell Telescope (JCMT) Mauna Kea, Hawaii ~ 4100 m
15 arcsecond beam-size at 850um
σposition ≈Θbeam / (2 S/N) e.g. S/N ~ 4 ~2 “ Problems associated with identifying counterparts to FIR, sub-mm & mm sources with low-resolution experiments
• Positional uncertainty of submm sources due to S/N of source-extraction
σposition ≈Θbeam / (2 S/N),
+ random pointing uncertainty of telescope (~ 1 – 2”)
• Invisible or extremely faint optical, IR or radio counterparts and hence ambiguity in identifying counterparts.
causes difficulty in determining the nature and star formation history of the submm population z = 0.7 (opt) z =2.35 (IR) 30 arcsec 30 arcsec 10 arcsec
z = 0.7 (opt) z > 2 (IR) 10 arcsec
Before - which optical/IR counterpart ? Now (with HST) - which component of which counterpart? ~4 arcsec ~150 arcsec
IRAM PdB 1.3mm (Downes et al. 1999) JCMT 850µm SCUBA MERLIN+VLA 1.4GHz (Dunlop et al. 2002) (Hughes et al. 1998) Follow up of HDF SCUBA survey: HDF850.1
K = 23.5±0.2 Subaru 9 hours VLA follow-up at 1.4GHz HST/NICMOS From our Monte-Carlo simulations, I > 28.7, I-K > 5.2 we determine that in order to detect 80% of the 8mJy sub-mm galaxies with a significance >3σ, the 1.4GHz follow-up observations have to be carried out to a 3σ depth of ~5µJy. Typical depths are a few × 10 µJy over limited-areas
The optical data (with the 3σ error-bars) constrain 3.0 ≤ zphot ≤ 5.2
Dunlop et al. 2004 Hughes et al. 2002, MNRAS, 335, 871 Ambiguity in optical/IR identifications redshift? luminosity? SFR ?
z = 0.7 (opt) z > 2 (IR) The Achilles heel of all photometric redshift techniques Only a few dozens of well measured SEDs known, including starbursts, ULIRGs and AGN. Are they representative enough of the high-z Universe?
Is there any luminosity or redshift evolution of the SEDs? None is included in order to play conservatively
Library of 20 SEDs of nearby starbursts galaxies, ULIRGs and AGN, normalized at 60µm. They cover the luminosity range 9 12 10 ≤ LFIR/L ≤ 3 × 10 and the temperature range 25 ≤ T/K ≤ 65 (model dependent!) which offers a wide range of shape dispersion Radio to sub-mm photometric-z estimation normalised at 60um
L(1.4 GHz)
L(FIR)
SEDs of local 20 AGN and starburst galaxies normalised at 60um synchrotron/ rel. electrons
SN
OB stars
dust thermal/dust SEDs of local 20 AGN and starburst galaxies Radio to sub-mm photometric-z estimation using 850µm & 1.4GHz - assumes FIR/radio correlation holds at high-z (Hughes et al. 1998, Carilli & Yun 1999, Yun & Carilli 2000, Dunne et al. 2000, Eales et al. 2000)
(Carilli & Yun 2000) Lacking a rigorous analysis of photometric, calibration errors, and uncertainties in SED population Radio identifications of UK 8 mJy survey
(Ivison et al. 2002)
Optical K-band + submm radio
Star formation history Ivison et al. 2002
based on radio-FIR photometric redshifts Spectroscopic observations of SCUBA galaxies
targeted 34 radio-detected submm galaxies with ESI and LRIS on Keck
ESI couterparts I=22.2 – 26.4, i.e. assumes all have radio IDs and optical counterparts yet, already seen evidence to the contrary quotes from Chapman et al.
“taught ourselves to recognise the counterpart”
“go for the most disturbed-looking object”
“even if it’s the wrong object, it’s probably a galaxy associated with the correct ID” Chapman et al. 2003, Nature, 422, 695
Redshift distribution of blank-field sub-mm sources
14 “well-constrained” sources in the UK 8mJy survey (Scott et al. 2002)
Keck z’s
“missing” due to radio-selection bias
70-80% of submm galaxies at 2 < z < 4 50% of galaxies at 1.9 < z < 2.8 (Aretxaga et al. 2003) (Chapman et al. 2003) Chapman et al 2003 Chapman et al 2005 astroph/0412573
median z = 2.2, 1.7(25%) – 2.8 (75%) median L(FIR) ~ 9e12 Lsun sub-mm surveys undertaken have detected 200 sources, however, in general, their identifications and redshifts are uncertain, hence their evolutionary history is uncertain. radio-submm redshifts discriminate z<2 from z> 2,andIR seems the most successful method to identify counterparts, provided K=21-23.
z = 0.7 (opt) z > 2 (IR)
Is there a better way to estimate redshifts? Conclusions from exisiting sub-mm follow-up;
• the consequence of the ambiguity and inherent biases in the identifications of the optical, IR and radio counterparts to blank-field submm sources is that the z-distribution for the whole population is still poorly constrained
•the observing time required to provide ultra-deep radio/mm (e.g. VLA, IRAM PdB), optical and IR imaging, and then optical and/or IR spectroscopic follow-up for each sub-mm source is prohibitive (>> 20 hours/galaxy)
• therefore, there is both an increasing need for larger samples from wider-area and deeper submm surveys to better constrain counts and clustering (i.e. to challenge formation models and history of evolution), and to provide robust and unambiguous means to derive the redshift distribution and to unambiguously identify counterparts P.I. Mark Devlin Constraining the star formation history of obscured galaxies • requires FIR luminosities (SFR) and redshifts
Need photometric colours that bracket the rest-frame FIR peak in the SED at all redshifts – ideally data at 1000 – 50um.
TFIR=70K z=1 Flux density
TFIR=70K z=4
350 IR radio 500µm 250µm observed wavelength
Long-duration balloon-flight mirror Test-flight mirror 2-m (by COI) 1.8 m (by Bosma)
September 2003 http://chile1.physics.upenn.edu/blastpublic/
BLAST overview • 2-m primary aperture • Simultaneous imaging 250, 350 & 500 microns • Resolution 30, 45, 60 arcsecs •Arrays -FOV 85 sq. arcmins (cf. 3 sq. arcmin with SCUBA, MAMBO)
• Conduct 10-15 day long duration balloon (LDB) flights • Example 50-hr survey – map 1 sq deg, 1 sigma = 5 mJy in all 3 bands and detect 800 galaxies
• goal: to combine with existing & future ground-based (mm) and satellite (FIR) surveys provide additional colour information and constrain redshifts, and hence luminosities and SFRs
• Kiruna (Sweden) April-May-June 2005 Long-Duration Balloon (LDB) flight • Antarctica December 2006 LDB 10-15 days 250 µm
350 µm
BLAST observes simultaneously at 3 wavelengths each array has FOV ~ 85 sq. arcmin (~ 25 x SCUBA) 500 µm
Colour-colour diagram, without errors
Recipe to derive photometric redshifts (Hughes et al. 2002, MNRAS) Add photometric and calibration errors to the maps, and extract the galaxies that can be detected in the considered multi-wavelength surveys under analysis (taking into account confusion and survey depth). Calculate the Colour-colour diagram, with errors probability of identifying the colours of mock galaxies with the colours of a real sub-mm Observed colours and 1σ error galaxy through a multi-variate gaussian box distribution. BLAST false-colour image - 50 hour survey simulation [250um+350um+500um] Comparison of the accuracies obtained by photometric redshifts derived for optical and submm surveys z ∆z ∆z ∆z interval optical SHADES submm/radio 0.5 The average 1σ photometric precision for sub-mm galaxies detected simultaneously in the 3 BLAST passbands is ∆z = ±0.5 When these bands are combined with an intermediate-depth (3σ = 8 mJy) 850µm survey, the average 1σ photometric precision is ∆z = ±0.4 (Hughes et al. 2002) Model predictions compared clustering strength redshift distributions Van Kampen et al. 2005 The promise of photometric redshifts : a summary Photometric redshifts based on bracketing the FIR emission peak have the advantage of not relying on ambiguous detections (e.g. optical, radio). The distribution of blank field sub-mm galaxies is such that ~7% are at z<2, ~50−100% are at 2≤z≤4, and potentially, ~40% could be at z>4. We have demonstrated that an accuracy of ∆z =±0.4 for sub-mm/mm photometric redshifts is to be expected for the bright sources detected with balloon-borne (BLAST 2003), or satellite (Herschel 2008) missions combined with ground-based sub-mm/mm observations (JCMT, IRAM, SMA 2003, LMT 2005, ALMA 2010, ...) 12 With these photometric redshifts, the SFR history of luminous (L ≥ 3×10 L~) starburst galaxies at 1 ≤ z ≤ 5can be reconstructed with an accuracy of ~ 20%. SHADES (SCUBA Half Degree Extragalactic Survey) 180 nights (8 hrs/night) on JCMT time over 3 yr (2002-2005) allocated AzTEC (LMT first light instrument) will replace SCUBA on JCMT Molecular gas in submm galaxies Greve et al. 2005, astroph/0503055 Greve et al. 2005, astroph/0503055 astroph/0502096 Evidence for galactic-scale winds? Large Millimetre Telescope Sierra Negra, 4680m Mexico Resolving 100% of the mm-background in confusion-limited LMT surveys 20-50% of 850um background resolved 3 arcmins LMT 25 sq. arcmin survey (50 hours, 1σ ~ 0.02 mJy) detects > 600 galaxies (> 100 M~/yr) SCUBAi.e. LMT HDF is > 50100 hour times 850 fasterµm survey than theon 15-m largest JCMT submm , 0.0016 telescopes sq. deg. and can go > 10 times3σ ~ deeper 2 mJy, (i.e only. can 1 sourceresolve > 100%8 mJy of millimetre extragalactic background) Wide-area GTM surveys detecting the hyper-luminous (& highest-redshift?) galaxies in the universe •To detect the most luminous (rarest) galaxies at high-redshift, 30 sq. deg GTM survey, forming stars at highest-rates, i.e. building biggest galaxies, we need to 600 hours, 72000 sources survey areas > 30 sq. degrees with 1-30 of the most extreme galaxies in the universe detected by the GTM i.e. 3σ~1mJy at 1.1mm equivalent luminosity sensitivity to the SHADES survey (180x8hr shifts) on JCMT 0.5 deg for 3 years detecting ~300 submm sources GTM/BOLOCAM-II simulation including high-redshift starburst galaxies, Galactic cirrus, Sunyaev-Zel’dovich clusters, Cosmic Microwave Background 22 Clusters of galaxies 1Mpc = 3x10 m diameter of Galaxy = 30 kpc Clusters are the youngest (under a hierarchical scenario), most 13 15 massive (10 -10 Msun), largest (R ~ 1-5 Mpc), self-gravitating structures and hence trace the large-scale structure of the Universe. Since clusters collapsed from large volumes of space (> 10 h-1 Mpc), they are considered representative samples of the Universe. An individual cluster can be treated a closed box (chemically, environmentally, dynamically, …), and appropriate measurements can lead to a measure of ΩDM/ΩB. Clusters also belong to larger structures – superclusters, that have not yet reached equilibrium conditions , and hence probe the dynamics of the Universe on the largest scales. 100 Mpc 2 Mpc 4% baryons 23% dark matter Sunyaev-Zel’dovich effect Sunyaev & Zel’dovich (1970, 1972) • Atmosphere of cluster (hot electrons) scatter CMB photons as they travel through the intracluster medium L Cosmic Cosmic micro-wave background 7 9 hot electons (ne), Tgas~ 10 –10 K electron-scattering off nuclei produces X-ray (or thermal bremstrahlung) emission inverse Compton optical-depth τe ~ ne σT L ~ 0.01 i.e. only 1% of CMB photons will scatter in cluster from S-Z review by E. Reese astro-ph/0306073 Sunyaev-Zeldovich effect amplitude of distortion (~ fractional energy gain x optical depth) 8 frequency dependence of effect Tgas~ 1x10 K ≈ 10 keV 2 kTe/mec ~ 0.02 assumptions neσTL ~ 0.01 1. Tgas is much hotter than Trad ∆T = 2x10-4 T 2. CMB radiation behaves as a blackbody SZE CMB 3. each photon will only scatter once ~ 500µK Sunyaev – Zel’dovich effect leads to distinctive spectral distortion of CMB (due to IC scattering of foreground clusters) S-Z null at ~ 1.36mm IMPORTANT : SZE has a unique spectral feature with a strength (∆T (K), ∆F (mJy) that is independent of redshift ACBAR (at South Pole) interometric observations of low-redshift clusters Simultaneous observations at 150, 220, 280 GHz (ΘFWHM ~ 4.7, 4.2, 3.9 arcmin) 1E0657-67 (z=0.299) Jeff Peterson The high-l, small-scale CMB anisotropy spectrum is dominated by non-linear effects (generally from the re-ionized Universe at z ~ 1000 – 5, & clusters at lower-redshifts ). Re-ionisation changes ionization fraction (e- density) , & influences photon (thermal) spectrum via scattering (Ostriker-Vishniac effect). Clusters (with large masses of hot, ionised gas) provide the largest (secondary) distortion of the CMB spectrum (Sunyaev-Zel’dovich effect). linear-regime non-linear Secondary anisotropies (e.g. thermal regime Sunyaev-Zel’dovich, O-V) in the CMB Acoustic peaks reflect dominate at small-scales l > 3000, conditions prior to de-coupling or Θ < 5 arcmin (e.g WMAP probed l < 760) Θ (degs) ~ 180/l(multipole) Primary signal becomes negligible due to (Silk) damping, and therefore need high fidelity imaging (& spectral information) to separate primary & secondary anisotropy components 1 deg 5 arcmin Seeds of large scale structure formation – but still no S-Z all-sky WMAP now WMAP (l < 800) + CBI & ACBAR Need large-area Boomerang d am S-Z cluster surveys pin g t ail ? ?? S-Z Θ ~ 5’ ACBAR 1 degree Bond, Contaldi, Pogosyan (2003) Interferometers used to measure the SZ effect towards known nearby (z < 1) clusters Ryle Array • This 8 element array is located in Cambridge, UK, and operates at 15 GHz (2 cm.) Berkeley Illinois Maryland Association (BIMA) • This millimeter-wave array is located in Hat Creek, CA. 10 antennae operate at 30 GHz (1cm.). Owens Valley Radio Observatory (OVRO) • This millimeter-wave array is located in Bishop, CA and run by Caltech. 6 x 10.4m antennae at 30 GHz (1 cm.). Interferometers used to measure the SZ effect towards known nearby (z < 1) clusters Cosmic Background Imager (CBI) • Located at the ALMA cite in Chajantor, Chile. These 13 (x 0.9m) antennae operate at 26-36 GHz. Arcminute Cosmology Bolometer Array Receiver (ACBAR) • On VIPER telescope at South Pole 16 receivers @ 150,220,280 GHz Degree Angular Scale Interferometer (DASI) • A sister project to the CBI, located at the South Pole. With baselines of 1-6m, CBI is sensitive to scales of 3-20 arcmin. Beam-sizes (FWHM) of order 1-5 arcmins for these experiments A selection of OVRO/BIMA interferometric observations at 30 GHz of the SZE in Abell clusters at z = 0.17 – 0.88 tlookback ~ 2 – 7 Gyr • small baselines to ensure large-beams (~1 arcmin FWHM) & higher surface-brightness sensitivity S-Z easily detectable to z~1, but generally the mm-observations are follow-up of known optical & X-ray clusters, however, SZ signature has similar size, and similar strength peak (TSZ ~ 500 - 800µK) despite the difference in redshift (~ x 5) Carlstrom et al. 2001 from Reese etal. 2003 Mohr et al. 2001 Optimal filtered ACBAR data at 150 GHz (20S-Z sq. degs)distortion to search for of massive CMB clusters can be used to search for massive structres (clusters of galaxies) “Aat handful all redshifts. of candidate sources Optical/IR follow-up can exceedingidentify 3 sigma substructure in each field” J. Peterson in clusters, i.e.with dynamical CTIO 4-m follow-up state – age of cluster The redshift evolution of number density of clusters is critically dependent on the underlying cosmological parameters1 degree (which control the rate of growth and scale of structure)R-band I-band Deriving H0 from SZ measurements - Measuring the size of a cluster • combined observations of X-ray ∆T /T L.n surface brightness Ix and ∆T SZ CMB α e measure the path length along the line of sight. X-ray intensity 2 Ix α L.n • use the radius of the cluster (R=L/2) e and the angular size to make an 2 estimate at the cluster distance. R = (∆TSZ /TCMB) / 2.Ix • we assumed that the cluster was spherical. R Θ) dA ne T dA ~ R/Θ i.e. distance measurement independent of redshift ! Joe Mohr SZE distance measurements & deriving H0 with a sample of clusters, and after measuring redshifts from optical follow- up, one can fit cluster-redshifts to the angular-diameter vs. redshift relation with the Hubble constant, H0, as the normalisation constant 41 SZ cluster distances vs. redshift Ho = 63 ± 3 km/s/Mpc for ΩM = 0.3 and ΩΛ = 0.7, fitting all SZE distances • SZE distances are direct (rather than relative) • SZE distances possible at very large lookback times • can see the theoretical angular diameter distance relation. • high systematic uncertainties (30%) Ho = 57 km/s/Mpc for an open ΩM = 0.3 Ho = 53 km/s/Mpc for a flat ΩM = 1 from Reese et al. 2003 Previous SZ experiments (single-dish and interferometers) have demonstrated the potential to extract important cosmological information for clusters already identified in X-ray or optical/IR surveys The ATACAMA COSMOLOGY TELESCOPE (ACT) has been designed to exploit this potential, and will conduct sensitive large-area SZ surveys, with the goal of determining (in an unbiased way) the redshift distribution & evolution of the number density of clusters. ACT science goals ● Investigate the growth of structure in the Universe Probe the nature of the “dark energy” driving the accelerating expansion of the Universe. Put limits on the mass of neutrinos. ● Measure the initial density perturbations in the Universe -33 Test models for the Universe at age 10 seconds. ● Detect gravitational lensing of the microwave background Probe directly the distribution of mass in the Universe ● Investigate the epoch of the first stars and their properties ● Probe the evolution and redshift distribution of galaxy clusters Atacama Cosmology Telescope (ACT) P.I. Lyman Page (Princeton), ● Remote Controlled Collaborators at PUC (Chile), INAOE (Mexico) ● Flexible Focal Plane UPenn, Rutgers, UMass, GSFC (USA) ● Near the ALMA Site, on Cardiff (UK), Cerro Toco Toronto (Canada) ● 6 Meter Aperture Conceptual Design Conceptual design ● Low Ground Pickup (< 20µK dc) ● No Moving Optics No existing telescope incorporates the features required for these measurements. Extreme control of systematic errors is required to measure dT/T ~ 10-6 temperature fluctuations. Scenario for the hierarchical formation of structure 100 Mpc (DM) 1 Mpc (DM) 1Mpc 100kpc Elliptical galaxy 50% 85% +/- ?? 85-50% look-back time • What are the first astrophysical objects? single stars / proto-galaxies /what’s the mass ? • When did they form ? z > 7. More likely z > 10. • Where did they form ? in dark matter halos ? in the 1-σ, 3-σ, 5-σ over-density peaks • How abundant were they ? are the numbers of galaxies (on all scales - dwarfs to ellipticals) consistent? Submillimetre cosmology at INAOE • LMT (www.lmtgtm.org) • AzTEC, SPEED, z-machine, CIS •SHADES •SCUBA-2 •BLAST • Atacama Cosmology Telescope • Penn Array (3mm camera for the GBT) • Instrumentation • ALFA network (LENAC – Latin America European Network for Astrophysics & Cosmology) •Contact David Hughes ([email protected]) Itziar Aretxaga ([email protected]) Enrique Gaztanaga ([email protected]) Selected Bibliography • General review Blain et al. 2002, PhR, 369, 111 (high-z submm galaxies) Sanders & Mirabel, 1996, AR&AA, 34, 749 (low-z ULIRGS) • General properties of dust Draine 2001, AR&AA, 41, 241 (review) • Key Survey (discovery) papers Smail et al. 1997, ApJ, 490, L5. Hughes et al. 1998, Nature, 394, 241 Eales et al. 1999, ApJ, 515, 518 Scott S. E. et al., 2002, MNRAS, 331, 817. Borys et al. 2002, MNRAS, 330, 63 Laurent et al. astro-ph/0503249 • Multi-wavelength follow-up Ivison et al. 2002, MNRAS, 337, 1 (radio) Greve et al. 2005, astro-ph/0503055 (molecular gas) Chapman et al. 2005, astro-ph/0412573 (spectroscopic redshifts) Smail et al. 2002, MNRAS, 331, 495 Alexander et al., 2003, AJ, 125, 383 (X-ray) Swinbank et al. 2005 astro-ph/0502096 (IFU) • Photometric redshifts & SED fitting Yun & Carilli 2002, ApJ, 568, 88 (radio 1.4GHz - submm 850um method) Hughes et al. 2002, MNRAS, 335, 871 (FIR - submm method) Aretxaga et al. 2003, MNRAS, 342, 759 (full submm SED fitting) Hughes et al. 1993, MNRAS, 263, 607 ?