Detection of Lyman-alpha Emitting Galaxies at Redshift z=4.55

Studies of the formation and early history of galaxies have been hampered by the difficulties inherent in detecting faint galaxy populations at high redshift. As a consequence, observations at the highest redshifts (3.5 < z < 5) have been restricted to objects that are intrinsically bright. These include quasars, radio galaxies, and some Ly alpha-emitting objects that are very close to (within ~10 kpc) -- and appear to be physically associated with -- quasars. But the extremely energetic processes which make these objects easy to detect also make them unrepresentative of normal (field) galaxies. Here we report the discovery using Keck spectroscopic observations of two Ly alpha-emitting galaxies at redshift z = 4.55, which are sufficiently far from the nearest quasar (~700 kpc) that radiation from the quasar is unlikely to provide the excitation source of the Ly alpha emission. Instead, these galaxies appear to be undergoing their first burst of star formation, at a time when the Universe was less than one billion years old.Comment: 8 pages, 1 landscape table, and 3 PostScript figures. Uses aaspp4.sty, flushrt.sty, aj_pt4.sty, overcite.sty (style macros available from xxx.lanl.gov) Figure 1 is bitmapped to 100 dpi. The original PostScript version of Fig. 1 is available via anonymous ftp to ftp://hubble.ifa.hawaii.edu/pub/preprints To appear in Natur

Variability of disk emission in pre-main sequence and related stars. II. Variability in the gas and dust emission of the Herbig Fe star SAO 206462

This is the author accepted manuscript. The final version is available from the publisher via the DOI in this record.We present 13 epochs of near-infrared (0.8-5 μm) spectroscopic observations of the pre-transitional, "gapped" disk system in SAO 206462 (=HD 135344B). In all, six gas emission lines (Brα, Brγ, Paβ, Paγ, Paδ, Paepsilon, and the 0.8446 μm line of O I) along with continuum measurements made near the standard J, H, K, and L photometric bands were measured. A mass accretion rate of approximately 2 × 10–8 M ☉ yr–1 was derived from the Brγ and Paβ lines. However, the fluxes of these lines varied by a factor of over two during the course of a few months. The continuum also varied, but by only ~30%, and even decreased at a time when the gas emission was increasing. The H I line at 1.083 μm was also found to vary in a manner inconsistent with that of either the hydrogen lines or the dust. Both the gas and dust variabilities indicate significant changes in the region of the inner gas and the inner dust belt that may be common to many young disk systems. If planets are responsible for defining the inner edge of the gap, they could interact with the material on timescales commensurate with what is observed for the variations in the dust, while other disk instabilities (thermal, magnetorotational) would operate there on longer timescales than we observe for the inner dust belt. For SAO 206462, the orbital period would likely be 1-3 years. If the changes are being induced in the disk material closer to the star than the gap, a variety of mechanisms (disk instabilities, interactions via planets) might be responsible for the changes seen. The He I feature is most likely due to a wind whose orientation changes with respect to the observer on timescales of a day or less. To further constrain the origin of the gas and dust emission will require multiple spectroscopic and interferometric observations on both shorter and longer timescales that have been sampled so far.This work was supported by NASA ADP grants NNH06CC28C and NNX09AC73G, Hubble Space Telescope grants HST-GO-10764 and HST-GO-10864, Chilean National TAC grants CNTAC-010A-064

Evidence for large-scale structure in the Ly alpha forest at z > 2.6

We present a search for spatial and redshift correlations in a 2 Angstrom, resolution spectroscopic survey of the Ly alpha forest at 2.15 <z <3.37 toward 10 QSOs concentrated within a 1 degrees diameter field. We find a signal at 2.7 sigma significance for correlations of the Ly alpha absorption-line wavelengths between different lines of sight over the whole redshift range. The significance rises to 3.2 sigma if we restrict the redshift range to 2.60 <z <3.37, and to 4.0 sigma if we further restrict the sample to lines with rest equivalent widths 0.1 less than or equal to W-0 <0.9 Angstrom. We conclude that a significant fraction of the Ly alpha forest arises in structures whose correlation length extends at least over 30' (similar to 26 h(-1) comoving Mpc at z = 2.6 for H-0 = 100 h km s(-1) Mpc(-1), Omega = 1.0, Lambda = 0). We have also calculated the three-dimensional two-point correlation function for Ly alpha absorbers; we do not detect any significant signal in the data. However, we note that line blending prevents us from detecting the signal produced by a 100% overdensity of Ly alpha absorbers in simulated data. We find that the Ly alpha forest redshift distribution provides a more sensitive test for such clustering than the three-dimensional two-point correlation function

Limits on the star formation rates of z &gt; 2 damped Ly alpha systems from H alpha spectroscopy

We present the results of a long-slit K-band spectroscopic search for Hα emission from eight damped Lyα absorbers (DLAs) at z &gt; 2 with the goal of measuring the star formation rates in these systems. For each system we searched for compact sources of Hα emission within a solid angle 11 × 2.5 arcsec2 (44 × 10 h-2 kpc2, for q0 = 0.5, H0 = 100 h km s-1 Mpc-1). No Ha emission was detected above 3σ limits in the range (6.5-16) × 10-20 W m-2, equivalent to star formation rates of 5.6-18 h-2 M⊙ yr-1, for a standard initial mass function, assuming the lines are spectrally unresolved (&lt;650km s-1 FWHM). We compare these results against the predictions of the models of Pei and Fall of the global history of star formation, under two different simplifying hypotheses: (i) the space density of DLAs at z = 2.3 is equal to the space density of spiral galaxies today (implying DLA discs were larger in the past, the 'large-disc' hypothesis); (ii) the sizes of DLAs at z = 2.3 were the same as the gas sizes of spiral galaxies today (implying DLA discs were more common in the past, the 'hierarchical' hypothesis). Compared with the previous most sensitive spectroscopic search, our sample is twice as large, our limits are a factor greater than two deeper, and the solid angle surveyed is over three times as great. Despite this, our results are not in conflict with either the large-disc hypothesis, because of the limited solid angle covered by the slit, or the hierarchical hypothesis, because of the limited sensitivity

Evidence for large-scale structure in the Ly alpha forest at z &gt; 2.6

We present a search for spatial and redshift correlations in a 2 Angstrom, resolution spectroscopic survey of the Ly alpha forest at 2.15 &lt;z &lt;3.37 toward 10 QSOs concentrated within a 1 degrees diameter field. We find a signal at 2.7 sigma significance for correlations of the Ly alpha absorption-line wavelengths between different lines of sight over the whole redshift range. The significance rises to 3.2 sigma if we restrict the redshift range to 2.60 &lt;z &lt;3.37, and to 4.0 sigma if we further restrict the sample to lines with rest equivalent widths 0.1 less than or equal to W-0 &lt;0.9 Angstrom. We conclude that a significant fraction of the Ly alpha forest arises in structures whose correlation length extends at least over 30' (similar to 26 h(-1) comoving Mpc at z = 2.6 for H-0 = 100 h km s(-1) Mpc(-1), Omega = 1.0, Lambda = 0). We have also calculated the three-dimensional two-point correlation function for Ly alpha absorbers; we do not detect any significant signal in the data. However, we note that line blending prevents us from detecting the signal produced by a 100% overdensity of Ly alpha absorbers in simulated data. We find that the Ly alpha forest redshift distribution provides a more sensitive test for such clustering than the three-dimensional two-point correlation function.</p