What Powers the Lyman a Blob

1
What Powers the Lyman a 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 a 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 Lya emission
• First identified by Steidel et al. 2000

• Lya 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 z2.38 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
Lya Blobs are High Redshift ULIRGs

• We strongly detect the 3 Lya 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 (gt 1012 L?).
• Other Lya blob IR detections
• One 24 µm Lya 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
Lya/IR Relation?

• 10 identified Lya Blobs with 24um or submm
  detections
• Weak evidence for connection
• L Lya /LBol
• 0.05-0.2

7
Lya 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 Lya clouds.

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B6 Blob
11
B7 Blob
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SSA22 Blob 1 MIPS 24 µm
Despite strong detection at 850µm 17mJy, not
visible in original shallow MIPS 24µm. lt 0.3
mJy So we followed up with deep, multi-hour MIPS
observation
Still no Detection lt 0.04 mJy (3 s)
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

• The presence of PAHs is a clear star formation
  indicator that can not be masked by the presence
  of dust.

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
15

• 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 J1434110331733 (Dey et al. 2005)
  spectrum has been shifted from z2.7 to z2.4.
• The yellow percentages are lower limits to PAH
  contribution to 7-9um mid-infrared flux.

PAH
64 41 33 24 lt9 lt7
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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 gt60 PAH
  contribution to mid-IR. One further complication
  is the possible presence of 9.7?m (33?m)
  silicate absorption, which would push PAH fluxes
  lower.
• The LABs appear to cover a spread from SF to
  AGN-dominated.

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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 (zgt3) redshifts.
• A majority of the mid-IR detected Blobs show
  significant PAH features.