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Galaxies and cosmology: the promise of ALMA

Galaxies and cosmology: the promise of ALMA. Andrew Blain Caltech 14 th May 2004. ALMA North American Workshop. Contents. CMB and SZ – cosmology aspect Examples of what we know ALMA can see Sub-arcsec resolution microJy sensitivities No confusion noise Continuum and line surveys

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Galaxies and cosmology: the promise of ALMA

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  1. Galaxies and cosmology: the promise of ALMA Andrew Blain Caltech 14th May 2004 ALMA North American Workshop

  2. Contents • CMB and SZ – cosmology aspect • Examples of what we know ALMA can see • Sub-arcsec resolution • microJy sensitivities • No confusion noise • Continuum and line surveys • Advances over all existing/proposed capabilities • Sensitivity is not infinite! • Relatively small field of view

  3. Fine angular scale CMB and SZ • ALMA (with compact array) will be extremely sensitive to arcmin-scale CMB power, from clusters, filaments and primordial fluctuations SZ effect X-ray ALMA Carlstrom et al. Arcmin resolution Chandra – low-z Hydra cluster with substructure Fine resolution will reveal features in the intracluster medium to resolve physical conditions in cluster gas

  4. Example target: the Antennae ISOCAM • Excellent example of distinct opt/UV and IR luminosity • Interaction long known, but great luminosity unexpected • ~90% energy escapes at far-IR wavelengths • Resolved images important • Relevant scales ~1” at high redshift HST WFPC2 CSO/SHARC-2 Dowell et al.

  5. Observed far-IR/submm SEDs • Non-thermal radio • Thermal dust • Dominates luminosity • Hotter in AGN? • See Spitzer • Molecular and atomic lines • Mm CO / HCN • IR: C/N/O/H2 • IR: C=C PAH

  6. Submm population: backgrounds • Many sources of data • Total far-IR and optical background intensity comparable • Most of submm background detected by SCUBA • Backgrounds yield weaker constraints on evolution than counts ISO SCUBA SCUBA Model: BJSLKI ‘ Models: BJSLKI 99

  7. ALMA will resolve the most distant galaxies down to L* • Example objects known from existing ground based observations • High-redshift continuum emission • Marginally resolved CO spectra reveal internal structure, and dynamical masses • Spitzer will reveal a huge sample to follow up • Redshifts are ‘moderate’ z~2-3 • ALMA will see CO structure in detail • ALMA will probe fainter, still unconfused

  8. Example Deep Submm Image • Abell 1835 • Hale 3-color optical • 850-micron SCUBA • Contrast: • Image resolution • Visible populations • Orthogonal submm and optical views • One of 7 images from Smail et al. SCUBA lens survey (97-02) • About 25 SCUBA cluster images Ivison et al. (2000) 2.5’ square

  9. Example IDed submm galaxy Ivison et al (2000, 2001) • Unusually bright example • May not see most important region in the optical • J2 is a Lyman-break galaxy (Adelberger & Steidel 2000) • J1 is a cluster member post-starburst (Tecza et al. 2004) • J1n is an Extremely Red Object (ERO; Ivison 2001) • Remains red in deeper Keck-NIRC data • Both J1n & J2 are at z = 2.55 – radio and mm from J1n

  10. Abell 2218 ISO 15µm and optical image (2.5’ across); Metcalf et al. Orange – left image Red – bottom image High-redshift CO | | | | • SAFIR field exceeds extent of the ISO image, yet has spatial resolution as good as the inteferometer, plus spectral information 40” square Note: submm, optical and mid-IR show different populations  K band image (8” square), with IRAM CO contours of an ultraluminous galaxy at z=3.35 Upper: submm continuum; lower optical HST Abell 851 Genzel et al. (2004)

  11. Submm galaxies in CO(3-2),(4-3) Chapman et al. Smail et al. N2.4 Frayer et al. N4 Neri et al. ApJ (2003); IRAM interferometer; source of detections given on individual frames 8 more now have CO measurements

  12. Population of submm galaxies • Most data is at 850 µm • New bright limit from Barnard et al • Very few are Galactic contaminating clouds • First limit was at 2.8 mm (BIMA) • Also bright 95/175 µm counts (ISO), that will be dramatically improved by Spitzer • Also data at 1.2mm (MAMBO); 1.1mm (BOLOCAM) and 450µm * * * Orange stars – Barnard et al (2004) 850-µm upper limit Blain et al (2002) updated

  13. Unique submm access to highest z • Redshift the steep submm SED • Counteracts inverse square law dimming • Detect high-z galaxies as easily as those at z=0 • Low-z galaxies do not dominate submm images • Unique high-z access in mm and submm • Ultimate limit is CMB heating

  14. Existing limits to information • Limited few arcsec positional accuracy from 10-m class submm telescopes • challenges accurate identification and makes it difficult to target for spectroscopy • So far VLA radio positions required for spectroscopy • Optical spectroscopy has provided redshifts for more of this population that might have been expected (Chapman et al 2003; 2004) • ALMA will not be limited in this way • To only cooler, more luminous, lower redshift systems

  15. 850-µm redshift distribution • Histogram: sample expanded from Nature list • Expected submm & radio redshift distributions from Scott Chapman’s model • Consistent with studeis of star-formation history that show far-IR domiates optical at z~2, but result now MUCH more robust • z~1.5 gap is the ‘spectroscopic desert’ • Bias against highest z is likely modest, but still uncertain Chapman et al. (2003; Nature; 2004; ApJ subm.)

  16. Signs of large-scale structure • HDF-N/GOODS field submm/radio spectroscopic survey (Chapman et al 2004) • Geometry is extreme pencil beam • 5 x 3000 Mpc • Same for ALMA • Circles: all galaxies with redshifts • Empty: z known • Colored: z in ‘associations’ within 1200 km/s • Note more ‘associations’ than expected unless powerful galaxy-galaxy correlation • r0 ~ 7h-1Mpc • ALMA will resolve less luminous associated structure and map the regions in detail Blain et al. (astro-ph/0405035)

  17. ALMA’s resolution puts it ahead • Resolution is very fine, both to avoid confusion from overlapping sources, and resolve their internal structure • The second absolutely demands ALMA • The first can also be achieved by large aperture single-antenna telescopes on the ground and in space • These can provide wide-field finder images • 25-m submm ‘Atacama Telescope’ Cornell-Caltech study

  18. Confusion noise • Model based on SCUBA/ISO populations • Flux for 1 source per beam ~ RMS noise • Extragalactic sources dominate for small apertures • When < 500µm ~25-m aperture very important • <0.1mJy sure to find submm counterparts to high-z optical galaxies

  19. Time to reach confusion limit • Galactic & extragalactic confusion limits • Sensitivity α D-1 • Practical limit ~10-100hr in any field • At shortest wavelengths need large aperture to allow deep surveys • Note speed at 850µm • 9” resolution

  20. Confusion is avoided with ALMA • Current missions in black • Spitzer is +\ • Green bar is just a 500m baseline ALMA • Red bar is 10-m SAFIR • Confusion from galaxies not met for many minutes or hours • At shortest wavelengths very deep observations are possible • Factor of 10 in resolution over existing facilities is very powerful ▬ ▬

  21. Submm observations of galaxies mature in ALMA era • Resolution to match HST/JWST and resolve internal structure of high-z galaxies • 3-D spectral information of even the most obscured regions • Reveals astrophysics at work • Provides direct redshifts • ALMA astrophysical probes are self contained • New populations of objects, and pre-reionization galaxies • H2 lines / first metals – dust and fine-structure lines

  22. ‘Photometric redshifts’ • Combine different bands to estimate T & z together • No strong far-IR spectral breaks or features • Strongest lever from 200-600µm • Based on knowledge of galaxies/site, can probably design 2 optimal bands • Once z known, get accurate luminosity • ALMA can do this, but combined with real redshift information from spectra

  23. SMGs’ SEDs: FIR-radio assumed Squares: low-z, Dunne et al. Empty circles: moderate z, mainly Stanford et al. Crosses: variety of known redshifts (vertical = lensed) Solid circles: Chapman SMGs Lines: low-z trends Scatter in T by >~40% Radio loud caveat above ~60K ALMA can explore new region here ALMA can explore new region here Solid circles: new Submm sources Blain, Barnard & Chapman 2003; Blain et al (2004; astro-ph/0404438)

  24. Line emission • Optical spectroscopy will probably never be able to keep up with mid-IR discoveries • Especially the ‘hard cases’, deeply enshrouded in dust at z>5 • Far-IR emission lines and CO rotational emission reveal astrophysics of gas involved in star formation • Heterodyne R>106 and 8-GHz bandwidth: ALMA can see details • ALMA can make spatially & spectrally resolved images of the most interesting galaxies found in <1hr • Little information on far-IR lines available so far • SOFIA will test this science • Spitzer covers restframe spectra of low-redshift galaxies • CII and OI pair can give redshifts for z~4.5; CO may be exhausted / not excited / not present at these redshifts • High redshift AGN & LBGs show metallicities are high early on

  25. Lines available for detection • Left: 870µm window; 5x10-21 Wm-2 (10-σ 18 min) • Right: 350µm window; 4-10x10-20 Wm-2 (10-σ 8.7 hr) • Long wavelength – in blind searches detect ~ 1 hour -1 • ALMA is fastest planned instrument working at longer wavelengths • Gives resolved spectroscopy – redshift and dynamical information

  26. Summary • ALMA will detect huge numbers of galaxies, deeper than any other facility • Probe astrophysics • during most active phase at z~2-3 • Prior to re-ionization • Resolved spectral images will reveal masses and mass assembly of galaxies • DRSM shows demand will be high • All areas of extragalactic astrophysics will benefit from ALMA

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