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High -Redshift Quasars and Galaxies at the Epoch of Cosmic Reionization. Linhua Jiang (Arizona State University). Collaborators: F. Bian , Z. Cai , B. Clement, S.H. Cohen, R . Dave ,

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High -Redshift Quasars and Galaxies at the Epoch of Cosmic Reionization


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    1. High-Redshift Quasars and Galaxies at the Epoch of Cosmic Reionization Linhua Jiang (Arizona State University) Collaborators: F. Bian, Z. Cai, B. Clement, S.H. Cohen, R. Dave, E. Egami, X. Fan, K. Finlator, N. Kashikawa, H.B. Krug, I.D. McGreer, M. Mechtley, M. Ouchi, K. Shimasaku, M.A. Strauss, D.P. Stark, R. Wang, R.A. Windhorst, and others Hubble Fellow Symposium 2014

    2. Cosmic reionization and high-z objects • Cosmic reionization • Neutral IGM ionized by the first astrophysical objects at 6 < z < 15 • Evidence: CMB polarization + GP troughs in quasars + … • High-z (z ≥6) objects • Quasars and galaxies • SNe and gamma-ray bursts • Responsible sources for reionization (Robertson 2011)

    3. Outline • High-z galaxies • A large sample of spectroscopically-confirmed galaxies at z ≥ 6 • UV continuum slopes • Galaxy morphology • Lyα luminosity function (LF) at z > 5.7 and implication for reionization • High-z quasars • Surveys of z ≥ 6 quasars using the SDSS data • Quasar LF and implication for reionization

    4. Part I. High-Redshift Galaxies • Current studies • HST + the largest ground-based telescopes • A few hundred galaxies or candidates at z ≥ 6; many at z ≥ 8(e.g.; Bouwens • 2011; Oesch 2012; Ellis 2013; and many more papers) • One issue • Mostly done with photometrically-selected LBGs with decent IR data • (e.g., several HST ultra/deep fields) • Lack of a large spectroscopically-confirmed sample with deep IR data • (HST + Spitzer) • A simple idea • HST and Spitzer imaging of spectroscopically-confirmed galaxies in the • Subaru Deep Field (SDF) and Subaru-XMM Deep Field (SXDS) • The largest sample of spec-confirmed galaxies at z ≥ 6 (Robertson+2011)

    5. A study of spectroscopically-confirmed galaxies at z ≥ 6 • Our galaxy sample • About 70 galaxies from z = 5.6 to 7.0, including LBGs and LAEs • Three HST programs and two Spitzer programs (PIs: Jiang and Egami) • Our imaging data • Optical data from Subaru • Suprime-Cam (PSF ≈ 0.6−0.7”) • Broad-band data (AB mag at 3σ): • BVRi ≈ 28.5, z ≈ 27.5, y ≈ 26.5 • Narrow-band data (26 mag): • NB816 and NB921, NB973 (25 mag) • HST near-IR data (~2 orbits per band): • WFC3 F125W (or F110W) and F160W • Spitzer mid-IR data (3 ~ 7 hrs): • IRAC 1 and 2 • A new large Spitzer program (PI: Jiang) • just approved last year (total 132 hrs).

    6. Rest-frame UV continuum slope • UV continuum slope β (fλ~ λβ) • –1.5 ≤ β ≤ –3.5; median β ≈ –2.3 • Slightly steeper than LBGs in previous studies (β ≈ –2 ~ –2.1) • The β – M1500 relation is weak at the bright end • LAEs do not have steeper β than LBGs (Jiang et al. 2013a)

    7. Extremely blue galaxies • Statistically significant excess of galaxies with β ~ –3 • Nearly zero dust and metallicity+ extremely young + … • Current simulations cannot produce β ≤ –3 (Finlator 2011) • How to: top-heavy IMF, high escape fraction, etc. (e.g. Bouwens 2010) (Jiang et al. 2013a)

    8. Lyα morphology in LAEs • Diffuse Lyα halos • Based on ground-based NB (Lyα) images • At low redshift: controversial • At high redshift: predicted by simulations 2 < z < 3 (Steidel 2011) z = 3.1 LAEs (Matsuda 2012) z = 3.1 LAEs (Feldmeier 2013) z = 5.7 LAEs (Zheng 2011)

    9. No Lyα halos found at z=5.7 and 6.5 • Stack 43 LAEs at z=5.7 and 40 LAEs at z=6.5 • Stacked images: resolved but not very extended • Possible reasons: dust, halo distribution, or no halos, etc. 20” x 20” (Jiang et al. 2013b)

    10. Deep spectroscopy of a z=7.7 LAE candidate • Observations • Target: brightest z=7.7 LAE candidate from Krug et al. (2012) • Instrument: LUCI on the 2×8.4m LBT; tint = 7.5 hrs, with good conditions • Results: non-detection  not a LAE at z=7.7 (confirmed by Faisst 2014)

    11. Observed Lyα LF at z ≥ 5.7 • Rapid evolution from z = 5.7 to 6.5 based on a large sample of LAEs • A z=7 LAE and a z=7.2 LAE suggest such a trend towards higher redshift • The upper limit at z=7.7 is >5 times lower than the z=6.5 LF • Explanations: • Not likely by intrinsic evolution • Likely by neutral IGM • Lyα reduced by a factor of two (Jiang et al. 2013c)

    12. Part II. High-Redshift Quasars • Quasars are boring: z ~ 6 quasars look similar to z ~ 0 quasars z~6 composite z = 7.08 Lya Low-z composite NV SiIV OI Lya forest (Mortlock2011) (Jiang et al.2007)

    13. zAB < 20 AB mag in the SDSS

    14. Surveys of z ≥ 6 quasars • The first z~6 quasars found by the SDSS main survey (Fan 2000−2006) • Followed by the SDSS deep survey (Jiang 2008,2009), the CFHTQS • (Willott 2005−2010), the UKIDSS (Venemans 2007, Mortlock 2009,2011), • the Pan-STARRS1 (Morganson 2012, Banados 2014), and the VISTA VIKING • (Venemans 2014) • More than 60 quasars have been found so far, half of them found by the SDSS • The most distant one at z = 7.08 (Mortlock2011) • Three quasars at z > 6.5 (Venemans 2014)

    15. Surveys of high-z quasars • Quasars (z ~ 6) in the SDSS • High-z quasars in the SDSS main survey • High-z quasars in the SDSS deep survey (Stripe 82) • High-z quasars in the SDSS overlap regions • Quasars in the SDSS main survey • A total of 14555 deg2 of unique sky area (Ahn 2012) • Completed: 8500 deg2 (Fan 2000−2006); zAB < 20 mag • To do: >4000 deg2

    16. Quasars in the SDSS deep survey • Stripe 82: a total of ~300 deg2 • −60° (20h) < RA < 60° (4h) • −1.26° < Dec < 1.26° • Repeatedly scanned 70-90 times by the SDSS • Two mag deeper than single-epoch data • Depth-optimized co-adds by Jiang et al. (2014a) • Current survey status: almost completed; • 12 quasars published; 1 to be published −60° 0° 60° (Jiang et al. 2014a)

    17. zAB < 21 mag zAB < 22 mag

    18. Quasars in the SDSS overlap regions • SDSS: drift scan along great circles • Adjacent runs overlap • A total of >3000 deg2 • Allow selection of quasars ~0.5 mag fainter (Jiang et al. 2014b)

    19. Quasar luminosity function at z ~ 6 SDSS main+deep (Jiang et al. 2009, AJ, 138, 305) SDSS + CFHTQS (Willott et al. 2010, AJ, 139, 906)

    20. Quasar contribution to the UV background: • Double power-law QLF ϕ(M1450) = ϕ* / (100.4(α+1)(M1450-M1450*) + 100.4(β+1)(M1450-M1450*) ) • β = −3 • α = [−2.2, −1.2] • M1450* = [−25, −21] Results: • Not sensitive to α, but strongly depends on M* and clumping factor C • Quasar/AGN population can provide enough photons only if the IGM is very homogeneous and the break luminosity is very low

    21. Search for z>6.5 quasars in Stripe 82 • Stripe 82data +VISTA VHS J and K-band data • Need Y-band imaging data

    22. g r i z J K

    23. Brand new: Close companions to z ~ 6 quasars in HST images

    24. Summary • A systematic study of spectroscopically-confirmed galaxies at z ≥ 6 • Steep UV continuum slopes • No diffuse Lyα halos were found around LAEs • Rapid evolution of Lyα LF from z=5.7 to 7.7 caused by the IGM • Surveys of z~6 quasars using the SDSS data • Quasar luminosity function and its implication • Future search for z>6.5 quasars in the SDSS stripe 82 • Quasar close companions