SPECTROSCOPIC CONFIRMATION OF THREE z-DROPOUT GALAXIES AT z = 6.844–7.213: DEMOGRAPHICS OF Lyα EMISSION IN z ∼ 7 GALAXIES

We present the results of our ultra-deep Keck/DEIMOS spectroscopy of z-dropout galaxies in the Subaru Deep Field and Great Observatories Origins Deep Survey's northern field. For 3 out of 11 objects, we detect an emission line at ~1 ?m with a signal-to-noise ratio of ~10. The lines show asymmetric profiles with high weighted skewness values, consistent with being Ly?, yielding redshifts of z = 7.213, 6.965, and 6.844. Specifically, we confirm the z = 7.213 object in two independent DEIMOS runs with different spectroscopic configurations. The z = 6.965 object is a known Ly? emitter, IOK-1, for which our improved spectrum at a higher resolution yields a robust skewness measurement. The three z-dropouts have Ly? fluxes of 3 ? 10?17?erg?s?1?cm?2 and rest-frame equivalent widths EWLy? 0 = 33-43 ?. Based on the largest spectroscopic sample of 43 z-dropouts, which is the combination of our and previous data, we find that the fraction of Ly?-emitting galaxies (EWLy? 0 > 25 ?) is low at z ~ 7; 17% ? 10% and 24% ? 12% for bright (M UV ?21) and faint (M UV ?19.5) galaxies, respectively. The fractions of Ly?-emitting galaxies drop from z ~ 6 to 7 and the amplitude of the drop is larger for faint galaxies than for bright galaxies. These two pieces of evidence would indicate that the neutral hydrogen fraction of the intergalactic medium increases from z ~ 6 to 7 and that the reionization proceeds from high- to low-density environments, as suggested by an inside-out reionization model.

[1]  Mark Lacy,et al.  The contribution of high-redshift galaxies to cosmic reionization: New results from deep WFC3 imaging of the Hubble Ultra Deep Field , 2009, 0909.2255.

[2]  A. Ferrara,et al.  Signatures of reionization on Lyα emitters , 2008, 0807.2975.

[3]  H. Ferguson,et al.  ON THE STELLAR POPULATIONS AND EVOLUTION OF STAR-FORMING GALAXIES AT 6.3 < z ⩽ 8.6 , 2009, 0912.1338.

[4]  M. Jarvis,et al.  Probing $\sim L_{*}$ Lyman-break Galaxies at $z\approx 7$ in GOODS-South with WFC3 on HST , 2009, 0910.1098.

[5]  S. Furlanetto,et al.  Lyα emitters during the early stages of reionization , 2007, 0708.0006.

[6]  S. M. Fall,et al.  LARGE AREA SURVEY FOR z = 7 GALAXIES IN SDF AND GOODS-N: IMPLICATIONS FOR GALAXY FORMATION AND COSMIC REIONIZATION , 2009, 0908.3191.

[7]  Gas metallicity in the narrow-line regions of high-redshift active galactic nuclei , 2005, astro-ph/0508652.

[8]  J. Dunlop,et al.  A robust sample of galaxies at redshifts 6.0 , 2011, 1102.4881.

[9]  L. Cowie,et al.  Mapping Extremely Low Metallicity Galaxies to Redshift One , 2007 .

[10]  Probing the Reionization History Using the Spectra of High-Redshift Sources , 2004, astro-ph/0401130.

[11]  Mamoru Doi,et al.  The Subaru Deep Field: The Optical Imaging Data , 2004 .

[12]  T. Hayashino,et al.  Lyα emitters at z= 6.5 in the SSA22 field: an area more neutral or void at the end of the re‐ionization epoch★ , 2010, 1011.5313.

[13]  L. Pozzetti,et al.  The Star Formation History of Field Galaxies , 1997, astro-ph/9708220.

[14]  A. Grazian,et al.  The unusual Niv)-emitter galaxy GDS J033218.92-275302.7: star formation or AGN-driven winds from a massive galaxy at z=5.56 , 2009, 0912.3007.

[15]  A. Fontana,et al.  THE LACK OF INTENSE Lyα IN ULTRADEEP SPECTRA OF z = 7 CANDIDATES IN GOODS-S: IMPRINT OF REIONIZATION? , 2010, 1010.2754.

[16]  T. Totani,et al.  Lyman Alpha Emitters in the Hierarchically Clustering Galaxy Formation , 2007, 0705.4349.

[17]  Zurich,et al.  The effect of the intergalactic environment on the observability of Lyα emitters during reionization , 2007, 0711.2944.

[18]  Mamoru Doi,et al.  Lyα Emitters at z = 5.7 in the Subaru Deep Field , 2006, astro-ph/0602614.

[19]  M. Franx,et al.  ULTRADEEP INFRARED ARRAY CAMERA OBSERVATIONS OF SUB-L* z ∼ 7 AND z ∼ 8 GALAXIES IN THE HUBBLE ULTRA DEEP FIELD: THE CONTRIBUTION OF LOW-LUMINOSITY GALAXIES TO THE STELLAR MASS DENSITY AND REIONIZATION , 2009, 0910.0838.

[20]  A. Henry,et al.  THE WFC3 INFRARED SPECTROSCOPIC PARALLEL (WISP) SURVEY , 2010, 1005.4068.

[21]  Robert H. Becker,et al.  Constraining the Evolution of the Ionizing Background and the Epoch of Reionization with z ∼ 6 Quasars. II. A Sample of 19 Quasars , 2005, astro-ph/0512082.

[22]  Oxford,et al.  Constraints on star-forming galaxies at z≥ 6.5 from HAWK-I Y-band imaging of GOODS-South , 2009, 0909.4205.

[23]  R. Bouwens,et al.  Spectroscopy of z ~ 6 i-Dropout Galaxies: Frequency of Lyα Emission and the Sizes of Lyα-emitting Galaxies , 2006, astro-ph/0612454.

[24]  E. Salpeter.  The Luminosity function and stellar evolution , 1955 .

[25]  A. Mesinger,et al.  The detectability of Lyα emission from galaxies during the epoch of reionization , 2011, 1101.5160.

[26]  S. Borgani,et al.  Lyman alpha emitter evolution in the reionization epoch , 2009, 0907.0337.

[27]  M. Zaldarriaga,et al.  The effects of reionization on Lyα galaxy surveys , 2005, astro-ph/0507266.

[28]  J. B. Oke,et al.  Secondary standard stars for absolute spectrophotometry , 1983 .

[29]  Richard S. Ellis,et al.  Keck spectroscopy of faint 3 < z < 7 Lyman break galaxies – I. New constraints on cosmic reionization from the luminosity and redshift-dependent fraction of Lyman α emission , 2010, 1003.5244.

[30]  O. University,et al.  Photometric selection of z∼ 5 Lyman break galaxies in the ESO Remote Galaxy Survey , 2009, 0909.0746.

[31]  Arjun Dey,et al.  First results from the Large-Area Lyman Alpha survey , 1999 .

[32]  A. Fontana,et al.  A critical analysis of the UV Luminosity Function at redshift~7 from deep WFC3 data , 2010, 1011.6569.

[33]  S. Okamura,et al.  Subaru Deep Survey. VI. A Census of Lyman Break Galaxies at z ≃ 4 and 5 in the Subaru Deep Fields: Clustering Properties* , 2003 .

[34]  M. Franx,et al.  VERY BLUE UV-CONTINUUM SLOPE β OF LOW LUMINOSITY z ∼ 7 GALAXIES FROM WFC3/IR: EVIDENCE FOR EXTREMELY LOW METALLICITIES? , 2009, 0910.0001.

[35]  M. Dickinson,et al.  z ∼ 4 Hα EMITTERS IN THE GREAT OBSERVATORIES ORIGINS DEEP SURVEY: TRACING THE DOMINANT MODE FOR GROWTH OF GALAXIES , 2011 .

[36]  Max Pettini Alice E. Shapley Charles C. Steidel Jean-G Giavalisco.  The Rest-Frame Optical Spectra of Lyman Break Galaxies: Star Formation, Extinction, Abundances, and Kinematics* , 2001 .

[37]  S. Okamura,et al.  The Subaru/XMM-Newton Deep Survey (SXDS). IV. Evolution of Lyα Emitters from z = 3.1 to 5.7 in the 1 deg2 Field: Luminosity Functions and AGN , 2007, 0707.3161.

[38]  M. Dickinson,et al.  Spectroscopic Confirmation of a Population of Normal Star-forming Galaxies at Redshifts z > 3* , 1996 .

[39]  M. Jarvis,et al.  Probing ∼L* Lyman‐break galaxies at z≈ 7 in GOODS‐South with WFC3 on Hubble Space Telescope , 2010 .

[40]  A. Fontana,et al.  SPECTROSCOPIC CONFIRMATION OF z ∼ 7 LYMAN BREAK GALAXIES: PROBING THE EARLIEST GALAXIES AND THE EPOCH OF REIONIZATION , 2011, 1107.1376.

[41]  M. Zaldarriaga,et al.  Studying reionization with Lyα emitters , 2007, 0704.2239.

[42]  Edward J. Wollack,et al.  FIVE-YEAR WILKINSON MICROWAVE ANISOTROPY PROBE OBSERVATIONS: COSMOLOGICAL INTERPRETATION , 2008, 0803.0547.

[43]  J. Rhoads,et al.  The GLARE Survey – II. Faint z≈ 6 Lyα line emitters in the HUDF , 2007, astro-ph/0701211.

[44]  M. Nonino,et al.  SPECTROSCOPIC OBSERVATIONS OF LYMAN BREAK GALAXIES AT REDSHIFTS ∼4, 5, AND 6 IN THE GOODS-SOUTH FIELD , 2009, 0901.4364.

[45]  The End of the Reionization Epoch Probed by Lyα Emitters at z = 6.5 in the Subaru Deep Field* ** , 2006, astro-ph/0604149.

[46]  M. Halpern,et al.  FIVE-YEAR WILKINSON MICROWAVE ANISOTROPY PROBE OBSERVATIONS: LIKELIHOODS AND PARAMETERS FROM THE WMAP DATA , 2008, 0803.0586.

[47]  Marijn Franx,et al.  THE STELLAR MASS DENSITY AND SPECIFIC STAR FORMATION RATE OF THE UNIVERSE AT z ∼ 7 , 2009, 0909.3517.

[48]  C. Steidel,et al.  Accepted for publication in ApJ Preprint typeset using L ATEX style emulateapj v. 12/14/05 Hα OBSERVATIONS OF A LARGE SAMPLE OF GALAXIES AT z ∼ 2: IMPLICATIONS FOR STAR FORMATION IN HIGH REDSHIFT GALAXIES 1 , 2006 .

[49]  R. Davé,et al.  PROBING POPULATION III STARS IN GALAXY IOK-1 AT z = 6.96 THROUGH He ii EMISSION , 2011, 1105.2319.

[50]  M. D. Lehnert,et al.  Spectroscopic confirmation of a galaxy at redshift z = 8.6 , 2010, Nature.

[51]  Simulating Cosmic Reionization at Large Scales I: the Geometry of Reionization , 2005, astro-ph/0512187.

[52]  R. O’Connell,et al.  Galaxy formation in the reionization epoch as hinted by wide field camera 3 observations of the hubble ultra deep field , 2009, 0910.0077.

[53]  T. Abel,et al.  The epoch of helium reionization , 2001, astro-ph/0112297.

[54]  R. Bouwens,et al.  EXPANDED SEARCH FOR z ∼ 10 GALAXIES FROM HUDF09, ERS, AND CANDELS DATA: EVIDENCE FOR ACCELERATED EVOLUTION AT z > 8? , 2011, 1105.2297.

[55]  S. Okamura,et al.  STELLAR POPULATIONS OF Lyα EMITTERS AT z ∼ 6–7: CONSTRAINTS ON THE ESCAPE FRACTION OF IONIZING PHOTONS FROM GALAXY BUILDING BLOCKS , 2010, 1004.0963.

[56]  Mauro Giavalisco,et al.  Lyman-Break Galaxies , 2002 .

[57]  M. Bremer,et al.  On contamination and completeness in z ≥ 5 Lyman-break galaxy surveys , 2007, 0712.2457.

[58]  Z. Haiman,et al.  Models for Dusty Lyα Emitters at High Redshift , 1998, astro-ph/9809223.

[59]  F. Mannucci,et al.  Evidence of a fast evolution of the UV luminosity function beyond redshift 6 from a deep HAWK-I survey of the GOODS-S field , 2009, 0909.2853.

[60]  B. Ciardi,et al.  Probing beyond the epoch of hydrogen reionization with 21 centimeter radiation , 2003 .

[61]  Mark Dickinson,et al.  Clustering Segregation with Ultraviolet Luminosity in Lyman Break Galaxies at z~3 and Its Implications , 2000, astro-ph/0012249.

[62]  Constraining reionization with the evolution of the luminosity function of Lyα emitting galaxies , 2004, astro-ph/0411038.

[63]  Martin J. Rees,et al.  Reionization of the Inhomogeneous Universe , 1998, astro-ph/9812306.

[64]  STAR FORMATION IN GALAXIES ALONG THE HUBBLE SEQUENCE , 1998, astro-ph/9807187.

[65]  A. Fontana,et al.  SPECTROSCOPIC CONFIRMATION OF TWO LYMAN BREAK GALAXIES AT REDSHIFT BEYOND 7 , 2010, 1011.5500.

[66]  High redshift radio galaxies , 1993 .

[67]  Richard S. Ellis,et al.  The Abundance of Low-Luminosity Lyα Emitters at High Redshift* , 2004 .

[68]  A. Kinney,et al.  The Dust Content and Opacity of Actively Star-forming Galaxies , 1999, astro-ph/9911459.

[69]  Edward J. Wollack,et al.  SEVEN-YEAR WILKINSON MICROWAVE ANISOTROPY PROBE (WMAP) OBSERVATIONS: POWER SPECTRA AND WMAP-DERIVED PARAMETERS , 2010, 1001.4635.

[70]  M. Pettini,et al.  Rest-Frame Ultraviolet Spectra of z ∼ 3 Lyman Break Galaxies , 2003, astro-ph/0301230.

[71]  T. Totani,et al.  Lyα Emitters in Hierarchical Galaxy Formation , 2007 .

[72]  Copenhagen,et al.  Spectroscopy of z∼ 5 Lyman break galaxies in the ESO Remote Galaxy Survey , 2010, 1007.2847.

[73]  M. Giavalisco,et al.  The Great Observatories Origins Deep Survey: Initial results from optical and near-infrared imaging , 2003, astro-ph/0309105.

[74]  R. Bouwens,et al.  THROUGH THE LOOKING GLASS: BRIGHT, HIGHLY MAGNIFIED GALAXY CANDIDATES AT z ∼ 7 BEHIND A1703 , 2011, 1104.2035.

[75]  M. Dickinson,et al.  z~4 Halpha Emitters in GOODS : Tracing the Dominant Mode for Growth of Galaxies , 2011, 1103.4124.

[76]  Takashi Hattori,et al.  A galaxy at a redshift z = 6.96 , 2006, Nature.

[77]  Marc Davis,et al.  Science Objectives and Early Results of the DEEP2 Redshift Survey , 2002, SPIE Astronomical Telescopes + Instrumentation.

[78]  S. Okamura,et al.  STATISTICS OF 207 Lyα EMITTERS AT A REDSHIFT NEAR 7: CONSTRAINTS ON REIONIZATION AND GALAXY FORMATION MODELS , 2010, 1007.2961.

[79]  M. Ouchi,et al.  KECK SPECTROSCOPY OF FAINT 3>z>7 LYMAN BREAK GALAXIES: A HIGH FRACTION OF LINE EMITTERS AT REDSHIFT SIX , 2010, 1009.5471.

[80]  A. Maselli,et al.  The visibility of Lyman α emitters during reionization , 2010, 1002.0839.

[81]  S. Okamura,et al.  COMPLETING THE CENSUS OF Lyα EMITTERS AT THE REIONIZATION EPOCH , 2011, 1104.2330.

[82]  R. Ellis,et al.  KECK SPECTROSCOPY OF FAINT 3 < z < 8 LYMAN BREAK GALAXIES: EVIDENCE FOR A DECLINING FRACTION OF EMISSION LINE SOURCES IN THE REDSHIFT RANGE 6 < z < 8 , 2011, 1107.1261.

[83]  G. Bruzual,et al.  Stellar population synthesis at the resolution of 2003 , 2003, astro-ph/0309134.

[84]  H. Ferguson,et al.  The Large-Scale and Small-Scale Clustering of Lyman Break Galaxies at 3.5 ⩽ z ⩽ 5.5 from the GOODS Survey , 2005, astro-ph/0508090.

[85]  Alison L. Coil,et al.  The DEIMOS spectrograph for the Keck II Telescope: integration and testing , 2003, SPIE Astronomical Telescopes + Instrumentation.

[86]  S. Miyazaki,et al.  A Gunn-Peterson test with a QSO at z=6.4 , 2011, 1104.1636.

[87]  N. Gnedin.  Cosmological Reionization by Stellar Sources , 1999, astro-ph/9909383.

[88]  C. Steidel,et al.  THE STRUCTURE AND KINEMATICS OF THE CIRCUMGALACTIC MEDIUM FROM FAR-ULTRAVIOLET SPECTRA OF z ≃ 2–3 GALAXIES , 2010, 1003.0679.

[89]  Z. Cai,et al.  PROBING VERY BRIGHT END OF GALAXY LUMINOSITY FUNCTION AT z ≳ 7 USING HUBBLE SPACE TELESCOPE PURE PARALLEL OBSERVATIONS , 2010, 1010.2261.

[90]  Arjun Dey,et al.  Spectroscopic Confirmation of Three Redshift z ≈ 5.7 Lyα Emitters from the Large-Area Lyman Alpha Survey , 2002, astro-ph/0209544.

[91]  F. Ozel,et al.  The late reionization of filaments , 2009, 0908.1576.

[92]  M. Dijkstra,et al.  The impact of The IGM on high-redshift Lyα emission lines , 2007, astro-ph/0701667.

[93]  R. Bouwens,et al.  z ∼ 7 GALAXIES IN THE HUDF: FIRST EPOCH WFC3/IR RESULTS , 2009, 0909.1806.

[94]  Piero Madau,et al.  Radiative transfer in a clumpy universe: The colors of high-redshift galaxies , 1995 .

[95]  M. Franx,et al.  ULTRAVIOLET LUMINOSITY FUNCTIONS FROM 132 z ∼ 7 AND z ∼ 8 LYMAN-BREAK GALAXIES IN THE ULTRA-DEEP HUDF09 AND WIDE-AREA EARLY RELEASE SCIENCE WFC3/IR OBSERVATIONS , 2010, 1006.4360.

[96]  D. Schaerer,et al.  The impact of nebular emission on the ages of z~6 galaxies , 2009, 0905.0866.

[97]  A Galaxy at z = 6.545 and Constraints on the Epoch of Reionization , 2004, astro-ph/0407409.

[98]  J. Dunlop,et al.  A critical analysis of the ultraviolet continuum slopes (β) of high-redshift galaxies: no evidence (yet) for extreme stellar populations at z > 6 , 2011, 1102.5005.

[99]  Toru Yamada,et al.  MOIRCS Deep Survey. IX. Deep Near-Infrared Imaging Data and Source Catalog , 2010, 1012.2115.

[100]  M. Pettini,et al.  The Spatial Clustering of Star-forming Galaxies at Redshifts 1.4 ≲ z ≲ 3.5 , 2004, astro-ph/0410165.