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Probing He II reionization with GALEX-selected quasar sightlines in the HST/COS era Gbor Worseck (UCO/Lick) & J. X. Prochaska (UCO/Lick), L. Wisotzki (AIP), M. McQuinn (UCB), A. DallAglio (AIP), J. F. Hennawi (MPIA), C. Fechner (UP),

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SLIDE 1

Probing He II reionization with GALEX-selected quasar sightlines in the HST/COS era

Gábor Worseck (UCO/Lick) &

  • J. X. Prochaska (UCO/Lick), L. Wisotzki (AIP), M. McQuinn (UCB),
  • A. Dall’Aglio (AIP), J. F. Hennawi (MPIA), C. Fechner (UP),

P . Richter (UP), P . Madau (UCSC), S. Gallerani (INAF),

  • J. M. O’Meara (St. Michaels), R. A. Simcoe (MIT), D. Reimers (Hamburg)

Cosmological Reionization Harish-Chandra Research Institute, February 16–20 2010

  • G. Worseck (UCO/Lick)

Probing He II reionization with GALEX-selected quasar sightlines in the HST/COS era 1 / 13

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Outline

1

Introduction: The quest for intergalactic He II absorption

2

GALEX UV color selection of likely transparent He II sightlines

3

Our survey for new He II sightlines

4

Conclusions and Outlook

  • G. Worseck (UCO/Lick)

Probing He II reionization with GALEX-selected quasar sightlines in the HST/COS era 2 / 13

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SLIDE 3

Why do we care about intergalactic helium?

2nd most abundant element created in the Big Bang IGM of hydrogen and helium photoionized by UV background He II− →He III requires hν > 54.4 eV photons

◮ He II/H I traces SED of UV radiation field ◮ late helium reionization epoch at z ∼ 3 (QSOs required)

IGM at z ∼ 3 much better probed than at z ∼ 6 but: He II difficult to observe

◮ He II Lyα at λrest = 303.78 Å only observable from space at z > 2 ◮ far-UV emission of most quasars extinguished by H I

Lyman limit systems

  • G. Worseck (UCO/Lick)

Probing He II reionization with GALEX-selected quasar sightlines in the HST/COS era 3 / 13

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SLIDE 4

Status prior to HST SM4

extensive “blind” surveys for UV emission of high-z quasars

  • nly 5 sightlines studied at R > 800 (HST/STIS, FUSE)

main features: GP trough at z > 3, patchy He II absorption at 2.7 < z < 3, forest at z < 2.7

Worseck & Wisotzki (2006)

  • G. Worseck (UCO/Lick)

Probing He II reionization with GALEX-selected quasar sightlines in the HST/COS era 4 / 13

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SLIDE 5

GALEX− →We are not lacking photons, but resolution!

GALEX: first UV extragalactic all-sky survey at mAB < ∼ 21 Syphers et al. (2009): GALEX UV pre-selection − → 22/53 z > 3.1 targets detected in He II (R ∼ 200) SM4 restored UV spectroscopic capabilities of HST BUT: several faint QSOs (mFUV > ∼ 22.5), expensive follow-up

Syphers et al. (2009)

  • G. Worseck (UCO/Lick)

Probing He II reionization with GALEX-selected quasar sightlines in the HST/COS era 5 / 13

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SLIDE 6

Our GALEX UV color selection technique

two GALEX bands: NUV (1750–2200Å) and FUV (1350–1750Å) NUV flux alone is not sufficient (low-z Lyman limits) significant FUV flux required (at least for z < ∼ 3.5 targets)

  • G. Worseck (UCO/Lick)

Probing He II reionization with GALEX-selected quasar sightlines in the HST/COS era 6 / 13

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SLIDE 7

GALEX finds all known needles in the haystack

  • G. Worseck (UCO/Lick)

Probing He II reionization with GALEX-selected quasar sightlines in the HST/COS era 7 / 13

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SLIDE 8

Blue GALEX colors − → high He II detection rate

  • G. Worseck (UCO/Lick)

Probing He II reionization with GALEX-selected quasar sightlines in the HST/COS era 8 / 13

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Our successful Cycle 17 He II survey

HST/COS FUV spectroscopy of 8 FUV-bright QSOs (21 orbits) UV-bright QSOs: simultaneous efficient confirmation and follow-up 2 QSOs observed so far: both sightlines transparent first clear detection of cosmic variance in He II absorption: GP trough vs. voids at z ≃ 2.9

  • G. Worseck (UCO/Lick)

Probing He II reionization with GALEX-selected quasar sightlines in the HST/COS era 9 / 13

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SLIDE 10

Comparison H I & He II − → UVB spectral shape

H I: complementary optical program (Keck/HIRES & VLT/UVES) η=He II/H I∝ ΓH I/ΓHe II procedure: fit H I forest & find η matching unresolved He II absorption UVB shape fluctuates, η ≫ 100 indicates low ΓHe II − → large He II fraction, either soft galaxies contribute to UVB or QSO radiation strongly filtered

  • G. Worseck (UCO/Lick)

Probing He II reionization with GALEX-selected quasar sightlines in the HST/COS era 10 / 13

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SLIDE 11

Comparison to simulations: Understanding the physics

3D rad. transfer simulations predict large variance in He II spectra extended He II reionization due to patchy QSO distribution

  • ur COS spectra assess variance in He II absorption

The astronomer’s desire: more data, high-z targets, high S/N

0.5 1 3 3.02 3.04 3.06 3.08 3.1 redshift 0.5 1 transmission / xHeII 0.5 1 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.001 0.01 0.1 probability per unit log mean transmission mean transmission xHeIII = 0.99 xHeIII = 0.94 xHeIII = 0.85

McQuinn et al. 2009

  • G. Worseck (UCO/Lick)

Probing He II reionization with GALEX-selected quasar sightlines in the HST/COS era 11 / 13

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SLIDE 12

Comparison to simulations: Understanding the physics

3D rad. transfer simulations predict large variance in He II spectra extended He II reionization due to patchy QSO distribution

  • ur COS spectra assess variance in He II absorption

The astronomer’s desire: more data, high-z targets, high S/N

0.5 1 3 3.02 3.04 3.06 3.08 3.1 redshift 0.5 1 transmission / xHeII 0.5 1 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.001 0.01 0.1 probability per unit log mean transmission mean transmission xHeIII = 0.99 xHeIII = 0.94 xHeIII = 0.85

McQuinn et al. 2009

  • G. Worseck (UCO/Lick)

Probing He II reionization with GALEX-selected quasar sightlines in the HST/COS era 11 / 13

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SLIDE 13

GALEX: There’s hope at z < 4!

Number density of LLSs H I LyC opacity at He II rest frame Predicted number of UV-bright QSOs

  • G. Worseck (UCO/Lick)

Probing He II reionization with GALEX-selected quasar sightlines in the HST/COS era 12 / 13

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SLIDE 14

Outlook: Understanding He II reionization via He II absorption spectra

Efficient He II target selection via GALEX photometry

◮ Blue GALEX colors indicate transparent sightlines ◮ ∼ 100 z > 2.7 targets in GALEX GR4

Promising results with COS in Cycle 17

◮ 2/8 targets observed so far, 100% success, science-ready data ◮ variance in He II absorption at z ∼ 2.9 ◮ Future: correlate voids and foreground quasars

Joint analysis of He II and H I forests

◮ spectral shape of UV radiation field at z ∼ 3 ◮ evolution of the UV background approaching He II reionization ◮ constrain ionizing source population at z ∼ 3

Goal: A definitive HST/COS He II Legacy Sample

  • G. Worseck (UCO/Lick)

Probing He II reionization with GALEX-selected quasar sightlines in the HST/COS era 13 / 13

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SLIDE 15

Outlook: Understanding He II reionization via He II absorption spectra

Efficient He II target selection via GALEX photometry

◮ Blue GALEX colors indicate transparent sightlines ◮ ∼ 100 z > 2.7 targets in GALEX GR4

Promising results with COS in Cycle 17

◮ 2/8 targets observed so far, 100% success, science-ready data ◮ variance in He II absorption at z ∼ 2.9 ◮ Future: correlate voids and foreground quasars

Joint analysis of He II and H I forests

◮ spectral shape of UV radiation field at z ∼ 3 ◮ evolution of the UV background approaching He II reionization ◮ constrain ionizing source population at z ∼ 3

Goal: A definitive HST/COS He II Legacy Sample

  • G. Worseck (UCO/Lick)

Probing He II reionization with GALEX-selected quasar sightlines in the HST/COS era 13 / 13