Unresolved z~8 point sources and their impact on the bright end of the galaxy luminosity function

Abstract

The distribution and properties of the first galaxies and quasars are critical pieces of the puzzle in understanding galaxy evolution and cosmic reionization. Previous studies have often excluded unresolved sources as potential low redshift interlopers. We combine broadband color and photometric redshift analysis with morphological selections to identify a robust sample of candidates consistent with unresolved point sources at redshift $z\sim 8$ using deep Hubble Space Telescope images. We also examine G141 grism spectroscopic data to identify and eliminate dwarf star contaminants. From these analyses, we identify three, bright ($M_{UV}\lesssim -22$ ABmag) dropout point sources at $7.5<z<8.1$. Spectral energy distribution analyses suggest that these sources are either quasars or compact star-forming galaxies. The flux captured by the IRAC 4.5 $\mu$m channel suggests that they have moderate $H\beta$+$[OIII]$ equivalent widths. We calculate the number density of point sources at $z\sim 7$-8, and find that a double powerlaw model well describes the point source distribution. We then extend our analysis to estimate the combined point source + galaxy luminosity function and find that the point sources have a non-negligible contribution to the bright-end excess. The fact that the point sources dominate only at $M_{UV}\lesssim -22$ suggests that their contribution to cosmic reionization is likely limited. While spectroscopic follow-up is needed to confirm the nature of these point sources, this work demonstrates that the inclusion of Lyman dropout point sources is necessary for a complete census of the early galaxies at the epoch of cosmic reionization.

arXiv comment21 pages. 10 figures

References in corpus (103)

• Astropy: A Community Python Package for Astronomy
• emcee: The MCMC Hammer
• Star Formation in Galaxies Along the Hubble Sequence
• CANDELS: The Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey
• CANDELS: The Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey - The Hubble Space Telescope Observations, Imaging Data Products and Mosaics
• Composite Quasar Spectra From the Sloan Digital Sky Survey
• EAZY: A Fast, Public Photometric Redshift Code
• A luminous quasar at a redshift of z = 7.085
• UV Luminosity Functions at redshifts z~4 to z~10: 10000 Galaxies from HST Legacy Fields
• An Observational Determination of the Bolometric Quasar Luminosity Function
• An 800-million-solar-mass black hole in a significantly neutral Universe at redshift 7.5
• 3D-HST WFC3-selected Photometric Catalogs in the Five CANDELS/3D-HST Fields: Photometry, Photometric Redshifts and Stellar Masses
• Cosmic Reionization and Early Star-Forming Galaxies: A Joint Analysis of New Constraints from Planck and Hubble Space Telescope
• Cluster Lensing And Supernova survey with Hubble (CLASH): An Overview
• UltraVISTA: a new ultra-deep near-infrared survey in COSMOS
• Inferring the star-formation histories of massive quiescent galaxies with BAGPIPES: Evidence for multiple quenching mechanisms
• Confirmation of the remarkable compactness of massive quiescent galaxies at z~2.3: early-type galaxies did not form in a simple monolithic collapse
• The 3D-HST Survey: Hubble Space Telescope WFC3/G141 grism spectra, redshifts, and emission line measurements for $\sim 100,000$ galaxies
• The Evolution of the Galaxy Rest-Frame Ultraviolet Luminosity Function Over the First Two Billion Years
• 3D-HST: A wide-field grism spectroscopic survey with the Hubble Space Telescope
• Statistics of 207 Lya Emitters at a Redshift Near 7: Constraints on Reionization and Galaxy Formation Models
• The Assembly of the First Massive Black Holes
• The Frontier Fields: Survey Design
• The Chandra Deep Field-South Survey: 7 Ms Source Catalogs
• A Remarkably Luminous Galaxy at z=11.1 Measured with Hubble Space Telescope Grism Spectroscopy
• CANDELS Multi-wavelength Catalogs: Source Detection and Photometry in the GOODS-South Field
• The Abundance of Star-Forming Galaxies in the Redshift Range 8.5 to 12: New Results from the 2012 Hubble Ultra Deep Field Campaign
• The Sloan Digital Sky Survey Quasar Catalog: Fourteenth Data Release
• A Luminous Quasar at Redshift 7.642
• Spectroscopy of Lyman Break Galaxies in the Hubble Deep Field
• New Determinations of the UV Luminosity Functions from z~9 to z~2 show a remarkable consistency with halo growth and a constant star formation efficiency
• UV-Continuum Slopes of >4000 z~4-8 Galaxies from the HUDF/XDF, HUDF09, ERS, CANDELS-South, and CANDELS-North Fields
• The Cosmic Evolution Survey (COSMOS): Subaru Observations of the HST COSMOS Field
• Lyman-alpha and CIII] Emission in z=7-9 Galaxies: Accelerated Reionization Around Luminous Star Forming Systems?
• Pōniuā'ena: A Luminous $z=7.5$ Quasar Hosting a 1.5 Billion Solar Mass Black Hole
• Eddington-limited accretion and the black hole mass function at redshift 6
• Red Nuggets at z~1.5: Compact passive galaxies and the formation of the Kormendy Relation
• The Reionization of the Universe by the First Stars and Quasars
• The Final SDSS High-Redshift Quasar Sample of 52 Quasars at z>5.7
• CANDELS Multiwavelength catalogs: Source Identification and Photometry in the CANDELS UKIDSS Ultra-Deep Survey Field
• The HST eXtreme Deep Field XDF: Combining all ACS and WFC3/IR Data on the HUDF Region into the Deepest Field Ever
• Rapid Reionization by the Oligarchs: The Case for Massive, UV-Bright, Star-Forming Galaxies with High Escape Fractions
• Evidence for Ubiquitous, High-EW Nebular Emission in z~7 Galaxies: Towards a Clean Measurement of the Specific Star Formation Rate using a Sample of Bright, Magnified Galaxies
• Full-Data Results of Hubble Frontier Fields: UV Luminosity Functions at $z\sim 6-10$ and a Consistent Picture of Cosmic Reionization
• The Spectral Energy Distributions Of z~8 Galaxies From The IRAC Ultra Deep Fields: Emission Lines, Stellar Masses, And Specific Star Formation Rates At 650 Myr
• New observations of z~7 galaxies: evidence for a patchy reionization
• Lyman-alpha Emission from a Luminous z=8.68 Galaxy: Implications for Galaxies as Tracers of Cosmic Reionization
• The z~6 Luminosity Function Fainter than -15 mag from the Hubble Frontier Fields: The Impact of Magnification Uncertainties
• Inferences on the Timeline of Reionization at z~8 From the KMOS Lens-Amplified Spectroscopic Survey
• Structure and Morphologies of z~7-8 Galaxies from ultra-deep WFC3/IR Imaging of the HUDF
• The Extreme Faint End of the UV Luminosity Function at $z\sim 6$ Through Gravitational Telescopes: a comprehensive assessment of strong lensing uncertainties
• Z > 7 galaxies with red Spitzer/IRAC [3.6]-[4.5] colors in the full CANDELS data set: the brightest-known galaxies at Z ~ 7-9 and a probable spectroscopic confirmation at Z=7.48
• Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs). V. Quasar Luminosity Function and Contribution to Cosmic Reionization at z = 6
• A lack of evolution in the very bright-end of the galaxy luminosity function from z = 8-10
• The Great Observatories Origins Deep Survey
• RELICS: Reionization Lensing Cluster Survey
• A Near-Infrared Spectral Template for Quasars
• CANDELS Multiwavelength Catalogs: Source Identification and Photometry in the CANDELS Extended Groth Strip
• The UV continua and inferred stellar populations of galaxies at z ~ 7 - 9 revealed by the Hubble Ultra Deep Field 2012 campaign
• The CANDELS/SHARDS multi-wavelength catalog in GOODS-N: Photometry, Photometric Redshifts, Stellar Masses, Emission line fluxes and Star Formation Rates
• The WIRCam Deep Survey I: Counts, colours and mass-functions derived from near-infrared imaging in the CFHTLS deep fields
• Constraining the neutral fraction of hydrogen in the IGM at redshift 7.5
• High-precision Photometric Redshifts from Spitzer/IRAC: Extreme [3.6]-[4.5] Colors Identify Galaxies in the Redshift Range z~6.6-6.9
• High-redshift AGN in the Chandra Deep Fields: the obscured fraction and space density of the sub-$L_{\ast }$ population
• Accelerated Evolution of Ly$\alpha$ Luminosity Function at $\text{z}\gtrsim 7$ Revealed by the Subaru Ultra-Deep Survey for Ly$\alpha$ Emitters at $\text{z}=7.3$
• AEGIS-X: Deep Chandra imaging of the Central Groth Strip
• The Brightest of Reionizing Galaxies Survey: Constraints on the Bright End of the z~8 Luminosity Function
• CANDELS Multiwavelength Catalogs: Source Identification and Photometry in the CANDELS COSMOS Survey Field
• The Brightest Of Reionizing Galaxies Survey: Design and Preliminary Results
• Evolution of the Sizes of Galaxies over 7<z<12 Revealed by the 2012 Hubble Ultra Deep Field Campaign
• SEDfit: Software for Spectral Energy Distribution Fitting of Photometric Data
• Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs). X. Discovery of 35 Quasars and Luminous Galaxies at 5.7 $\le$ z $\le$ 7.0
• A spectroscopic search for AGN activity in the reionization era
• The Brightest $z\gtrsim 8$ Galaxies over the COSMOS UltraVISTA Field
• Expanded Search for z~10 Galaxies from HUDF09, ERS, and CANDELS Data: Evidence for Accelerated Evolution at z>8?
• Beacons into the Cosmic Dark Ages: Boosted transmission of Ly$\alpha$ from UV bright galaxies at $z\gtrsim 7$
• Correcting the z~8 Galaxy Luminosity Function for Gravitational Lensing Magnification Bias
• The Reionization Lensing Cluster Survey (RELICS) and the Brightest High-z Galaxies
• A dusty compact object bridging galaxies and quasars at cosmic dawn
• The bright-end galaxy candidates at z ~ 9 from 79 independent HST fields
• The Sizes of Candidate $z\sim 9-10$ Galaxies: confirmation of the bright CANDELS sample and relation with luminosity and mass
• Simulating galaxies in the reionization era with FIRE-2: morphologies and sizes
• Newly Discovered Bright z~9-10 Galaxies and Improved Constraints on Their Prevalence Using the Full CANDELS Area
• Massive Dead Galaxies at z~2 with HST Grism Spectroscopy I. Star Formation Histories and Metallicity Enrichment
• Contamination of Broad-Band Photometry by Nebular Emission in High Redshift Galaxies: Investigations with Keck's MOSFIRE Near-Infrared Spectrograph
• Revealing the Accretion Physics of Supermassive Black Holes at Redshift z~7 with Chandra and Infrared Observations
• QSO obscuration at high redshift ($z\gtrsim 7$): Predictions from the BlueTides simulation
• Bright galaxies at Hubble's redshift detection frontier: Preliminary results and design from the redshift z~9-10 BoRG pure-parallel HST survey
• The UV-brightest Lyman continuum emitting star-forming galaxy
• HST imaging of the brightest z~8-9 galaxies from UltraVISTA: the extreme bright end of the UV luminosity function
• Chandra X-rays from the redshift 7.54 quasar ULAS J1342+0928
• Discovery of the first heavily obscured QSO candidate at $z>6$ in a close galaxy pair
• SuperBoRG: Exploration of point sources at $z\sim 8$ in HST parallel fields
• Prospects for distinguishing galaxy evolution models with surveys at redshifts $z\gtrsim 4$
• SuperBoRG: Search for The Brightest of Reionizing Galaxies and Quasars in HST Parallel Imaging Data
• Observing the host galaxies of high-redshift quasars with JWST: predictions from the BlueTides simulation
• The discovery of the most UV-Lya luminous star-forming galaxy: a young, dust- and metal-poor starburst with QSO-like luminosities
• Beyond the Local Volume. I. Surface Densities of Ultracool Dwarfs in Deep HST/WFC3 Parallel Fields
• Galaxy Morphologies Revealed with Subaru HSC and Super-Resolution Techniques I: Major Merger Fractions of L_UV~3-15 L_UV* Dropout Galaxies at z~4-7
• GLACiAR, an open-source python tool for simulations of source recovery and completeness in galaxy surveys
• Stochastic Processes as the Origin of the Double-Power Law Shape of the Quasar Luminosity Function
• Substellar and low-mass dwarf identification with near-infrared imaging space observatories
• A Physical Model for the Quasar Luminosity Function Evolution between Cosmic Dawn and High Noon

Cited by in corpus (4)

• A Candidate of a Least-Massive Black Hole at the First 1.1 Billion Years of the Universe
• Physical Characterization of Early Galaxies in the Webb's First Deep Field SMACS J0723.3-7323
• The UV luminosity functions of Bright z>8 Galaxies: Determination from ~0.41 deg2 of HST Observations along ~sim 300 independent sightlines
• ΛCDM is still not broken: empirical constraints on the star formation efficiency at z ~ 12-30