CONTAMINATION OF BROADBAND PHOTOMETRY BY NEBULAR EMISSION IN HIGH-REDSHIFT GALAXIES: INVESTIGATIONS WITH KECK'S MOSFIRE NEAR-INFRARED SPECTROGRAPH

Earlier work has raised the potential importance of nebular emission in the derivation of the physical characteristics of high-redshift Lyman break galaxies. Within certain redshift ranges, and especially at z ≃ 6-7, such lines may be strong enough to reduce estimates of the stellar masses and ages of galaxies compared with those derived assuming the broadband photometry represents stellar light alone. To test this hypothesis at the highest redshifts where such lines can be probed with ground-based facilities, we examine the near-infrared spectra of a representative sample of 28 3.0 < z < 3.8 Lyman break galaxies using the newly commissioned MOSFIRE near-infrared spectrograph at the Keck I telescope. We use these data to derive the rest-frame equivalent widths (EWs) of [O III] emission and show that these are comparable with estimates derived using the spectral energy distribution (SED) fitting technique introduced for sources of known redshift by Stark et al. Although our current sample is modest, its [O III] EW distribution is consistent with that inferred for Hα based on SED fitting of Stark et al.'s larger sample of 3.8 < z < 5 galaxies. For a subset of survey galaxies, we use the combination of optical and near-infrared spectroscopy to quantify kinematics of outflows in z ≃ 3.5 star-forming galaxies and discuss the implications for reionization measurements. The trends we uncover underline the dangers of relying purely on broadband photometry to estimate the physical properties of high-redshift galaxies and emphasize the important role of diagnostic spectroscopy.

[1]  R. Ellis,et al.  KECK SPECTROSCOPY OF FAINT 3 < z < 7 LYMAN BREAK GALAXIES. III. THE MEAN ULTRAVIOLET SPECTRUM AT z ≃ 4 , 2011, 1111.5102.

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

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

[4]  Robin Ciardullo,et al.  THE HETDEX PILOT SURVEY. III. THE LOW METALLICITIES OF HIGH-REDSHIFT Lyα GALAXIES , 2010, 1011.0431.

[5]  W. Sargent,et al.  ISOLATED EXTRAGALACTIC H II REGIONS. , 1970 .

[6]  R. Bouwens,et al.  EVOLUTION OF GALAXY STELLAR MASS FUNCTIONS, MASS DENSITIES, AND MASS-TO-LIGHT RATIOS FROM z ∼ 7 TO z ∼ 4 , 2010, 1008.3901.

[7]  G. Cresci,et al.  FIRST SPECTROSCOPIC MEASUREMENTS OF [O iii] EMISSION FROM Lyα SELECTED FIELD GALAXIES AT z ∼ 3.1, , 2010, 1006.1895.

[8]  Brian Siana,et al.  A REFINED ESTIMATE OF THE IONIZING EMISSIVITY FROM GALAXIES AT z ≃ 3: SPECTROSCOPIC FOLLOW-UP IN THE SSA22a FIELD , 2012, 1210.2393.

[9]  Peter Anders,et al.  Spectral and photometric evolution of young stellar populations: The impact of gaseous emission at various metallicities , 2003, astro-ph/0302146.

[10]  Shannon G. Patel,et al.  Hα EQUIVALENT WIDTHS FROM THE 3D-HST SURVEY: EVOLUTION WITH REDSHIFT AND DEPENDENCE ON STELLAR MASS , 2012, Proceedings of the International Astronomical Union.

[11]  AMAZE - I. The evolution of the mass–metallicity relation at z $>$ 3 , 2008, 0806.2410.

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

[13]  L. Cowie,et al.  ULTRADEEP KS IMAGING IN THE GOODS-N , 2010, 1002.1892.

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

[15]  S. Okamura,et al.  GAS MOTION STUDY OF Lyα EMITTERS AT z ∼ 2 USING FUV AND OPTICAL SPECTRAL LINES, , 2012, 1206.2316.

[16]  K. Finlator,et al.  An analytic model for the evolution of the stellar, gas and metal content of galaxies , 2011, 1108.0426.

[17]  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.

[18]  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.

[19]  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 .

[20]  Granada,et al.  Galaxies in the Hubble Ultra Deep Field. I. Detection, Multiband Photometry, Photometric Redshifts, and Morphology , 2006, astro-ph/0605262.

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

[22]  Stefano Casertano,et al.  CANDELS: THE COSMIC ASSEMBLY NEAR-INFRARED DEEP EXTRAGALACTIC LEGACY SURVEY—THE HUBBLE SPACE TELESCOPE OBSERVATIONS, IMAGING DATA PRODUCTS, AND MOSAICS , 2011, 1105.3754.

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

[24]  M. Franx,et al.  STAR FORMATION RATES AND STELLAR MASSES OF z = 7–8 GALAXIES FROM IRAC OBSERVATIONS OF THE WFC3/IR EARLY RELEASE SCIENCE AND THE HUDF FIELDS , 2009, 0911.1356.

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

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

[27]  P. McCarthy,et al.  VERY STRONG EMISSION-LINE GALAXIES IN THE WFC3 INFRARED SPECTROSCOPIC PARALLEL SURVEY AND IMPLICATIONS FOR HIGH-REDSHIFT GALAXIES, , 2011, 1109.0639.

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

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

[30]  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.

[31]  M. Kuhlen,et al.  Concordance models of reionization: implications for faint galaxies and escape fraction evolution , 2012, 1201.0757.

[32]  K. Bundy,et al.  THE EVOLUTIONARY HISTORY OF LYMAN BREAK GALAXIES BETWEEN REDSHIFT 4 AND 6: OBSERVING SUCCESSIVE GENERATIONS OF MASSIVE GALAXIES IN FORMATION , 2009, 0902.2907.

[33]  S. Ravindranath,et al.  CANDELS: THE COSMIC ASSEMBLY NEAR-INFRARED DEEP EXTRAGALACTIC LEGACY SURVEY—THE HUBBLE SPACE TELESCOPE OBSERVATIONS, IMAGING DATA PRODUCTS, AND MOSAICS , 2011, 1105.3753.

[34]  Hooshang Nayyeri,et al.  SPECTROSCOPIC CONFIRMATION OF THREE z-DROPOUT GALAXIES AT z = 6.844–7.213: DEMOGRAPHICS OF Lyα EMISSION IN z ∼ 7 GALAXIES , 2011, 1107.3159.

[35]  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.

[36]  D. Schaerer,et al.  On the physical properties of z ≈ 6–8 galaxies , 2010, 1002.1090.

[37]  Timothy M. Heckman,et al.  Dust Absorption and the Ultraviolet Luminosity Density at z ≈ 3 as Calibrated by Local Starburst Galaxies , 1999, astro-ph/9903054.

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

[39]  J. Dunlop,et al.  KECK SPECTROSCOPY OF 3 < z < 7 FAINT LYMAN BREAK GALAXIES: THE IMPORTANCE OF NEBULAR EMISSION IN UNDERSTANDING THE SPECIFIC STAR FORMATION RATE AND STELLAR MASS DENSITY , 2012, 1208.3529.

[40]  J. Dunlop,et al.  NEW CONSTRAINTS ON COSMIC REIONIZATION FROM THE 2012 HUBBLE ULTRA DEEP FIELD CAMPAIGN , 2013, 1301.1228.