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What Powers the Lyman α Blob?

What Powers the Lyman α Blob?. James W. Colbert, Spitzer Science Center Harry I. Teplitz, SSC Claudia Scarlata, SSC Paul Francis, Australian National University Povilas Palunas, Las Campanas Observatory Gerard Williger, University of Louisville

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What Powers the Lyman α Blob?

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  1. What Powers the Lyman α Blob? James W. Colbert, Spitzer Science Center Harry I. Teplitz, SSC Claudia Scarlata, SSC Paul Francis, Australian National University Povilas Palunas, Las Campanas Observatory Gerard Williger, University of Louisville Bruce E. Woodgate, Goddard Space Flight Center

  2. What Power… The Lyman α Blob James W. Colbert, Spitzer Science Center Harry I. Teplitz, SSC Claudia Scarlata, SSC Paul Francis, Australian National University Povilas Palunas, Las Campanas Observatory Gerard Williger, University of Louisville Bruce E. Woodgate, Goddard Space Flight Center

  3. Lyman Alpha Blobs • Extended, radio-quiet Lyα emission • First identified by Steidel et al. 2000 • Lyα Blobs seem to only be found in high redshift regions of significant galaxy over-density. • Immense in both size and luminosity. • 50-150 kpc • ~1044 ergs s-1

  4. The z=2.38 Lyman Alpha Filament • The 80 × 80 × 60 co-moving Mpc volume mapped by Lyman alpha emitters shows a tentative filament and void configuration. Also commonly referred to as the Francis Cluster. • Comparable to some of the largest structures seen in the local Universe (i.e. the Great Wall, Geller & Huchra 1989). • Three emitters are Lyman alpha “blobs” • In Spitzer cycle 1 we took IRAC and MIPS 24μm imaging of the central region.

  5. Lyα Blobs are High Redshift ULIRGs • We strongly detect the 3 Lyα blobs in the MIPS 24 μm image: 0.25-0.6 mJy. • Even conservative conversions from the mid-infrared to total infrared flux (using Chary & Elbaz 2001), puts all of these in the class of ULIRGs (> 1012 L○). • Other Lyα blob IR detections: • One 24 μm Lyα blob in the NOAO Deep Wide-Field Survey (0.86 mJy; Dey et al. 2005). • 8 detected in sub-mm • One of filament blobs (B7; Beleen et al. 2008) • 6 in SSA22 field (Geach et al. 2005), 1 in 53w002 field (Smail et al. 2003)

  6. Lyα/IR Relation? • ~10 identified Lyα Blobs with 24um or submm detections • Weak evidence for connection • L Lyα /LBol: 0.05-0.2%

  7. Lyα Blob SEDs • Power source remains ambiguous • No clear 1.6 μm bump • No clearly rising spectrum • Likely composite sources • B5: Not a blob but a lower redshift interloper

  8. HST Blob Images SSA22 blob 1 J2143-4423 B1 Francis et al. 2001, ApJ, 554, 1001 Chapman et al. 2004, ApJ, 606, 85

  9. Powered by Mergers? • Blob B6 is associated with 2 MIPS 24μm sources (~1 mJy total). • A pair of Hyper Luminous Galaxies in the process of merger? • Mergers may play a critical role in production of giant Lyα clouds.

  10. B6 Blob

  11. B7 Blob

  12. SSA22 Blob 1: MIPS 24 μm Despite strong detection at 850μm [17mJy], not visible in original shallow MIPS 24μm. < 0.3 mJy So we followed up with deep, multi-hour MIPS observation: Still no Detection: < 0.04 mJy (3 σ) Submm Contours from Chapman et al. 2004

  13. Ratio of 850 to 24 μm for the Blobs • Potentially powerful diagnostic for distinguishing cold (star-forming) from warm (AGN) ULIRGS. • Works much better the higher one goes in redshift. • Generally, 850/24um line ratio looks cool. • SSA22 Blob 1 is off the chart: • Likely due to large spatial extent as already suggested for high-resolution submm non-detection. Must be quite spread out, as MIPS FWHM is ~6”.

  14. Spitzer Mid-IR Spectroscopy We targeted 5 of the blob ULIRGs with IRS LL1(20-35m) with int. times of 1.3-9 hours in order to detect redshifted 7.7m PAH (GO 30600). One additional IRS spectrum (SST24) was obtained from the archive. B1 B7 B6 The presence of PAHs is a clear star formation indicator that can not be masked by the presence of dust.

  15. PAH % 64% 41% 33% 24% <9% <7% NGC 7714 shown for comparison. The scaling is arbitrary, although the spectra have been presented roughly in order of strength of the PAH feature. The SST24 J1434110+331733 (Dey et al. 2005) spectrum has been shifted from z=2.7 to z=2.4. The yellow percentages are lower limits to PAH contribution to 7-9um mid-infrared flux.

  16. Ly Blobs Contain Significant PAHs 4 of the 6 ULIRGs contain measurable PAH features. Without detection of the rest 5m continuum (observed 16m), estimates of exact line flux are highly uncertain. Removing a simple continuum across rest 7-9m produces a line-to-continuum lower limit. Applying a similar wavelength-limited fit to the starburst NGC 7714 indicates >60% PAH contribution to mid-IR. One further complication is the possible presence of 9.7m (~33m) silicateabsorption, which would push PAH fluxes lower. The LABs appear to cover a spread from SF to AGN-dominated.

  17. Conclusions A large percentage of Blobs, particularly the brighter ones, detected in mid-IR/submm. SEDs including IRAC seem to indicate at least some AGN component likely, BUT: Submm-to-mid IR ratios indicate cool, star forming galaxies, although only significant at higher (z>3) redshifts. A majority of the mid-IR detected Blobs show significant PAH features.

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