1. The ISM in z~2.5 starbursting galaxies: dust, synchrotron emission and cold molecular gas
Alasdair Thomson
Ian Smail, Mark Swinbank, Rob Ivison, Jacqueline Hodge, Alex Karim
James Simpson, Alice Danielson, Fabian Walter, Frazer Owen
++ ALESS consortium

2. Outline Submillimetre galaxies The ALMA LESS survey Survey overview
Far-IR properties of ALESS SMGs
The radio properties of ALESS SMGs
Trends in α and qIR in starbursting galaxies
The Cosmic Eyelash – a “Rosetta Stone” for the high-z ISM
Identification of ~100pc gas clumps in lensed, z~2.3 ISM
Spatially-resolved gas excitation and star-formation law

3. Submillimetre-selected galaxies
Rest-frame SEDs peak in the far-IR due to dust-reprocessing of optical/UV starlight
<z> ~ can be detected out to z~7 due to negative K-correction
(Ultra-) luminous: LIR ≥ 1012 Lʘ
Massive: M* ≥ 1011 Mʘ
SFR ~ 200 – 1000 Mʘyr-1

4. The LABOCA Extended Chandra Deep Field South Survey (LESS: Weiss et al
ECDFS is the prime extra-galactic survey field, with a wealth of pan-chromatic data from X-ray (Chandra), through UV/optical/mid-IR (Subaru, VLT, Spitzer IRAC), far-IR (Herschel SPIRE) and radio (VLA)
LESS is a contiguous and uniform 870-μm survey reaching S870=1.2mJy over ~30x30'
126 SMGs with S850 > 4.4mJy
APEX LABOCA 870-μm map
However λ/D~18”, so counterpart identifcation potentially tricky...

5. The ALMA LABOCA Extended Chandra Deep Field South Survey (ALESS: Hodge et al. 2013/Karim et al. 2013)
LABOCA ~ 18”
ALMA ~ 1.4”
122 ALMA pointings to observe 122 LABOCA SMGs
ALMA maps ~3x deeper, with ~200x smaller beam than LABOCA
88 best (“MAIN”) maps have σ < 0.6mJy/beam and beam axis ratio < 2
In 69 maps, we detect 99 ALMA sources at >3.5σ (multiplicity) with 18 blank maps (20%) -
Spurious LABOCA detections?
Diffuse emission spread across multiple ALMA beams?
Extreme multiplicity? ?

6. An ALMA survey of submillimetre galaxies in the Extended Chandra Deep Field South: the far-IR properties of SMGs (Swinbank et al. 2013)
To properly characterise far-IR SED, need measurements over the dust peak ( μm)...
...but Herschel SPIRE resolution ~15” at 250μm (35” at 500μm) → need to deblend SPIRE photometry
Swinbank et al. (2013)

7. An ALMA survey of submillimetre galaxies in the Extended Chandra Deep Field South: the far-IR properties of SMGs (Swinbank et al. 2013)

8. An ALMA survey of submillimetre galaxies in the Extended Chandra Deep Field South: redshift distribution (Simpson et al. 2013)
ECDFS deep archival imaging: UBVRIzJHK+IRAC
Of 99 “MAIN” ALMA SMGs, 77 have good photometry in enough bands to determine reliable phot-z's
Calibrated against 5,900 field galaxies in ECDFS
~25 SMGs with spec-z's
<zphot> = 2.3 ± 0.1
Tail out to z~6
Simpson et al. (2013)

9. An ALMA survey of submillimetre galaxies in the Extended Chandra Deep Field South: radio properties and FIRRC (Thomson et al. 2014)
Detect 52 SMGs at > 3σ in VLA 1.4 GHz map (Miller et al. 2013)
Of which 35 detected at > 3σ in GMRT 610 MHz map (Rob Ivison)
SMGs with counterparts in both radio maps:
<α> = ± 0.06
Sυ ~ υα
SMGs with counterparts in VLA map only (stacked):
<α> = ± 0.06
cf. Lockman Hole SMGs (Ibar et al. 2010):
<α> = ± 0.06
Condon, 1992

10. An ALMA survey of submillimetre galaxies in the Extended Chandra Deep Field South: radio properties and FIRRC (Thomson et al. 2014)
Background – Spitzer IRAC 4.5μm
Red – ALMA 870μm (ALESS: σ = 0.3 mJy/beam)
Blue – GMRT 610 MHz: σ = 45 μJy/beam (Rob Ivison)
Green – VLA 1.4 GHz: σ = 7 μJy/beam (Miller et al. 2013)

11. An ALMA survey of submillimetre galaxies in the Extended Chandra Deep Field South: radio properties and FIRRC (Thomson et al. 2014)
Tight empirical correlation between rest-frame far-IR/radio luminosities in star-forming regions over orders of magnitude in size/luminosity/gas surface density/magnetic energy density
Thought to arise due to a balance between thermal dust and synchrotron emission of massive stars
<qIR> = 2.56 ± 0.05
cf. <qIR> = 2.40 ± 0.12 for 0<z<2 Herschel 250μm selected galaxies (Ivison 10a,10b)
De Jong (1985)

12. An ALMA survey of submillimetre galaxies in the Extended Chandra Deep Field South: radio properties and FIRRC (Thomson et al. 2014)
Evolution of α and qIR?
Bressan et al. (2002)
Condon (1992)

13. An ALMA survey of submillimetre galaxies in the Extended Chandra Deep Field South: radio properties and FIRRC (Thomson et al. 2014)
Evolution of α and qIR?
Young:
M⋆ = (0.84± 0.27) × 1011M⊙
Middle-aged:
M⋆= (1.02 ± 0.28) × 1011M⊙
Old:
M⋆ = (2.12 ± 0.64) × 1011M⊙

14. An ALMA survey of submillimetre galaxies in the Extended Chandra Deep Field South - papers
1. Catalogue paper + Multiplicity (Hodge et al. 2013, ApJ )
2. High resolution sub-mm counts. Influence of blending on counts (Karim et al. 2013, MNRAS 432 2).
3. Serendipitous z=4.4 [CII] identification & the evolution of the [CII] LF (Swinbank et al. 2012, MNRAS )
4. OI 63-um detections in ALMA SMGs (Coppin et al. 2012, MNRAS )
5. N(z), stellar masses and evolution to z=0 (Simpson et al ApJ )
6. FIR colours, luminosities, SFRs (Swinbank et al MNRAS )
7. AGN fraction of ALESS SMGs (Wang et al ApJ )
8. Sub-mm properties of star forming BzKs and BX/BMs from ALMA (Decarli et al ApJ )
9. FIR--radio correlation of ALESS SMGs (Thomson et al MNRAS )
10. Energy balance in ALESS SMGs (E da Cunha et al ApJ, Submitted)
11. The rest-frame optical morphologies of ALESS SMGs from HST (Chen et al. 2015, ApJ )
12. zLESS: The redshift distribution and star formation histories of ALESS SMGs (Danielson et al in prep)

15. The Cosmic Eyelash – a “Rosetta Stone” for the high-z ISM
Typical high-resolution ALMA Cycle 2 870μm images ~ 0.3” (e.g. Simpson et al 2015, in prep)
→ corresponds to a spatial scale of ~2.5kpc at z=2.3, 30x coarser than needed to study Giant Molecular Cloud complexes in which star formation likely to be concentrated
“Eyelash” SMG discovered by LABOCA behind critical curve of MACSJ2135 cluster
~32x gravitational lensing boosts spatial resolution in the image plane to ~100pc
Swinbank et al (2011)

16. The Cosmic Eyelash – a “Rosetta Stone” for the high-z ISM
Danielson et al (2011, 13)

17. The Cosmic Eyelash – a “Rosetta Stone” for the high-z ISM
Gas clump positions identified via two independent methods, using 3D data cube (position, position, velocity): (I) “ClumpFind” algorithm (Williams, 1994); (ii) AIPS task SERCH (e.g. Uson et al)
Only clumps identified via both methods are considered → 4 bright clumps (plus 4 mirror images across critical curve) found
Thomson et al (2015)
CHECK: positions/velocities of clumps consistent with source-integrated line profile
High-res VLA CO(1-0) and C-band continuum observations, plus re-imaging of existing SMA 870μm visibilities reveal dense, gas-rich, clumpy ISM .

18. The Cosmic Eyelash – clump excitation properties
Measure CO SLEDs for the clumps using high-resolution CO(1-0) image, and “deblended” low-resolution mid-J images from PdBI (Danielson et al, 2011)
Model predictions from ΣSFR (Narayanan & Krumholz, 2014; grey band) agree with best-fit radiative transfer model (solid line) in ¾ clumps.

19. The Cosmic Eyelash – clump properties

20. Conclusions
Submillimetre galaxies are a population of intensely star-forming galaxies at high-redshift
Single-dish only studies lack the angular resolution to precisely locate the starburst, requiring probabilistic counterpart identification techniques that assume the underlying SED
ALMA follow-up observations of single-dish detected sub-mm sources circumvents identification problem by precisely locating the SMG in the same band as was used to select the source.
Allows us to study radio properties of a complete, unbiased SMG sample:
<α> = 0.79 ± 0.06 and <q> = 2.56 ± 0.05
Measured α, q and M* consistent with starburst galaxy evolutionary models which suggest radio observations can be useful probes of the phase of galaxy evolution
Gravitational lensing still has a role to play, boosting spatial resolution and allowing us to peer inside the ISM of distant, starbursting galaxies
The Eyelash SMG (z=2.3) is a “standard” but 32.5x lensed SMG, where 0.3” JVLA CO imaging isolates ~100pc clumps
Observations provide an excellent laboratory for the study of dense, high ΣSFR starburst environments
...but still can't definitively rule on nature of high-z, high-ΣSFR SF law!