1507.02679
Lyman-alpha emission from a luminous z=8.68 galaxy: implications for galaxies as tracers of cosmic reionization
Zitrin, ... Ellis, Oesch, Smit, et al
Report the discovery of Lya in the bright galaxy EGSY8p7 using MOSFIRE spectrograph at Keck. First reported by Roberts-Borsani+2015, it was selected for spectroscopic observations because of z_phot=8.57+0.22-0.43, apparent brightness H_160=25.26, and red Spitzer/IRAC [3.6]-[4.5] color indicative of contamination by strong O emission in the 4.5 band. With a total integration of ~4.3 hours, the data reveal an emission line at ~11776A which is argued to be likely Lya at z_spec=8.68, in good agreement with the photo-z. The line was detected independently on 2 nights using different slit orientations and its detection significance is ~7.5sigma. An overlapping sky line contributes significantly to the uncertainty on the total line flux but not the overall significance. By direct addition and a Gaussian fit, estimate a 95% confidence range of 1.0-2.5e-17 ergs/cm2/sec, corresponding to a rest-frame equivalent width of 17-42A. EGSY8p7 is the most distant galaxy confirmed spectroscopically to date, and the 3rd luminous source in the EGS field beyond z_phot>7.5 with detectable Lya emission viewed at a time when the IGM is expected to be fairly neutral. Although the reionization process was probably patchy, discuss whether luminous sources with prominent IRAC color excesses may harbor harder ionizing spectra than the dominant fainter population thereby creating earlier ionized bubbles. Further spectroscopic follow-up of such bright sources promises important insight into the early formation of galaxies.
1507.02683
Mapping charge transport effects in thick CCDs with a dithered array of 40,000 stars
Bradshaw, Lage, Resseguie, Tyson
Characterize the astrometric distortion at the edges of thick, fully-depleted CCDs in the lab using a bench-top simulation of LSST observing. By illuminating an array of 40k pinholes (30um diameter) at the object plane of a f/1.2 optical reimager, thousands of PSFs can be imaged over a 4kx4k pixel CCD. Each high purity Si pixel, 10um square by 100um deep, can then be individually characterized through a series of sub-pixel dithers in the X/Y plane. The unique character [response, position, shape] of each pixel as a function of flux, wavelength, back side bias, etc. can be investigated. We measure the magnitude and onset of astrometric error at the edges of the detector as a test of the experimental setup, using a LSST prototype CCD. Show that this astrometric error at the edge is sourced from non-uniformities in the E-field lines that define pixel boundaries. This edge distortion must be corrected in order to optimize the science output of WL and LSS measurements for the LSST.
1507.02685
SCORCH I: the galaxy-halo connection in the first billion years
Trac, Cen, Mansfield
Simulations and Constructions of the Reionization of Cosmic Hydrogen (SCORCH) is a new project to study the EoR. In this first paper, probe the connection between observed high-z galaxies and simulated DM haloes in order to better understand the abundance and evolution of the primary source of ionizing radiation. A series of high-resolution N-body simulations is run to quantify the abundance of DM haloes as a function of mass M, acccretion rate Mdot, and redshift z. A new fit for the halo mass function dn/dM is ~20% more accurate at the high-mass end where bright galaxies are expected to reside. A novel approach is used to fit the halo accretion rate function dn/dMdot in terms of the halo mass function. Abundance matching against the observed galaxy luminosity function is used to estimate the luminosity-mass relation and the luminosity-accretion-rate relation. The inferred SF efficiency is not monotonic with M nor Mdot, but reaches a maximum value at a characteristic mass ~2e11 Msun and a characteristic accretion rate ~6e2 Msun/yr at z~6. Find a universal EoR luminosity-accretion-rate relation, which is used to construct a fiducial model for the galaxy luminosity function. The Schechter parameters evolve such that phi* decreases, M* is more positive (fainter), and alpha is more negative (steeper) at higher redshifts. Forecast for the upcoming JWST and show tthat with apparent magnitude limit m_AB~31(32), it can observe >~11(24) unlined galaxies per square degree per unit redshift at least down to M* at z<~13(14).
1507.02687
A large narrow band H$\alpha$ survey at $z\sim0.2$: the bright end of the luminosity function, cosmic variance and clustering across cosmic time
Stroe, Sobral
The largest (>3.5e5 Mpc3, 26 deg2) Ha narrow band survey to date at z~0.2 in SA22, W2 and XMMLSS extragalactic fields. Survey covers a large enough volume to overcome cosmic variance and to sample bright and rare Ha emitters up to an observed luminosity of ~1e42.4 erg/s, equivalent to 11Msun/yr. Using the sample of 220 sources brighter than 1e41.4 erg/s (>1 Msun/yr), derive Ha LFs, which are well described by a Schechter function with phi*=1e-2.85±0.03 Mpc-3 and L*_Ha=1e41.7±0.02 ergs/s (with a fixed faint end slope alpha=-1.35). Find that surveys probing smaller volumes (~3e4 Mpc3) are heavily affected by cosmic variance, which can lead to errors of over 100% in the characteristic density and luminosity of the Ha luminosity function. Derive a SFR density of rho_SFRD=0.0094±0.0008 Msun/yr, in agreement with z-dependent Ha parameterization from Sobral+2013. The 2PCF is described by a single power law omega(theta)=0.159±0.012) theta^(-0.75±0.05), corresponding to a clustering length of r_0=3.3±0.8 Mpc/h. Find that the most luminous Ha emitters at z~0.2 are more strongly clustered than the relatively fainter ones. The L*_Ha Ha emitters at z~0.2 in the sample reside in ~1e12.5-13.5 Msun DM haloes. This implies that the most SF galaxies always reside in relatively massive haloes or group-like environments and that the typical host halo mass of SF galaxies is independent of z if scaled by L_Ha/L*_Ha(z), as proposed by Sobral_2010.
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