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Peter Eisenhardt

Publications and source records attributed to Peter Eisenhardt.

59 records · Page 4Linked to original sources
arXiv2000

Evidence Against a Redshift z>6 for the Galaxy STIS 123627+621755

The identification of galaxies at extreme distances provides our most direct information on the earliest phases of galaxy formation. The distance implied by redshifts z > 5 makes this a challenging endeavor for even the most luminous sources; interpretation of low signal-to-noise ratio observations of faint galaxies is difficult and occasional misidentifications will occur. Here we report on STIS 123627+621755, a galaxy with a suggested spectroscopic redshift of z = 6.68 and the most distant spectroscopically-identified object claimed. For the suggested redshift and reported spectral energy distribution, the galaxy should be essentially invisible shortward of 9300 Angstroms because the intervening intergalactic medium absorbs essentially all light energetic enough to ionize neutral hydrogen (lambda < (1 + z) x 912 Angstroms; the redshifted Lyman limit). The galaxy should be relatively bright in the near-infrared with f(nu) ~ 1 microJy. Here we report a detection of the galaxy at 6700 Angstroms, below the Lyman limit for z = 6.68. We also report a non-detection at 1.2 microns, implying the flux has dropped by a factor of three or more between rest 1216 Angstroms and rest 1560 Angstroms for z = 6.68. Our observations are inconsistent with the suggested extreme distance of STIS 123627+621755 and conservatively require z < 6.

astro-ph↗
arXiv2000

Discovery of a Color-Selected Quasar at z=5.50

We present observations of RD J030117+002025, a quasar at z=5.50 discovered from deep, multi-color, ground-based observations covering 74 square arcmin. This is the most distant quasar or AGN currently known. The object was targeted as an R-band dropout, with R(AB)>26.3 (3-sigma limit in a 3 arcsec diameter region), I(AB)=23.8, and z(AB)=23.4. The Keck/LRIS spectrum shows broad Lyman-alpha/NV emission and sharp absorption decrements from the highly-redshifted hydrogen forests. The fractional continuum depression due to the Lyman-alpha forest is D(A)=0.90. RD J030117+002025 is the least luminous, high-redshift quasar known (M(B)~-22.7).

astro-ph↗
arXiv1999

Young stars and non-stellar emission in the aligned radio galaxy 3C 256

We present ground-based images of the z=1.824 radio galaxy 3C 256 in the standard BVRIJHK filters and an interference filter centered at 8800A, a Hubble Space Telescope image in a filter dominated by Ly-alpha emission (F336W), and spectra covering rest-frame wavelengths from Ly-alpha to [O III] 5007. Together with published polarimetry observations, we use these to decompose the overall spectral energy distribution into nebular continuum emission, scattered quasar light, and stellar emission. The nebular continuum and scattered light together comprise half (one third) of the V-band (K-band) light within a 4-arcsec aperture, and are responsible for the strong alignment between the optical/near-infrared light and the radio emission. The stellar emission is dominated by a population estimated to be 100-200 Myr old (assuming a Salpeter IMF), and formed in a short burst with a peak star formation rate of 1-4x10^3 Msun/yr. The total stellar mass is estimated to be no more than 2x10^{11} Msun, which is far less than other luminous radio galaxies at similar redshifts, and suggests that 3C 256 will undergo further star formation or mergers.

astro-ph↗
arXiv1997

An IR-Selected Galaxy Cluster at z=1.27

We report the discovery of a galaxy cluster at z=1.27. ClG J0848+4453 was found in a near-IR field survey as a high density region of objects with very red J-K colors. Optical spectroscopy of a limited number of 24 < R < 25 objects in the area shows that 6 galaxies within a 90 arcsec (0.49/h Mpc, q_O = 0.1) diameter region lie at z=1.273 +/- 0.002. Most of these 6 member galaxies have broad-band colors consistent with the expected spectral energy distribution of a passively-evolving elliptical galaxy formed at high redshift. An additional 2 galaxies located ~2 arcmin from the cluster center are also at z=1.27. Using all 8 of these spectroscopic members, we estimate the velocity dispersion is 700 +/- 180 km/s, similar to that of Abell R=1 clusters in the present epoch. A deep Rosat PSPC observation detects X-ray emission at the 5 sigma level coincident with the nominal cluster center. Assuming that the X-ray flux is emitted by hot gas trapped in the potential well of a collapsed system (no AGN is known to exist in the area), the resulting X-ray luminosity in the rest frame 0.1-2.4 keV band of L_x = 1.5 x 10^44 ergs/s suggests the presence of a moderately large mass. ClG J0848+4453 is the highest redshift cluster found without targetting a central active galaxy.

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