Lyα Luminosity Function Research Articles

The end of the re-ionization epoch probed by Lyα emitters at z = 6.5

AbstractWe report an extensive search for Lyα emitters (LAEs) at z = 6.5 in the Subaru Deep Field (SDF). We carried out spectroscopic observations with Subaru/Keck to identify LAEs at z = 6.5 that were selected by narrow-band excess at 920nm. We have identified eight new LAEs based on their significantly asymmetric Lyα emission profiles. This increases the sample of spectroscopically confirmed z = 6.5 LAEs in the SDF to 17. Based on this spectroscopic sample of 17, complemented by a photometric sample of 58 LAEs, we have derived a more accurate Lyα luminosity function (LF) of LAEs at z = 6.5, which reveals an apparent deficit at the bright end, of ∼0.75 mag fainter L*, compared with that observed at z = 5.7. The difference has 3σ significance, which is reduced to 2σ when cosmic variance is taken into account. Several LAEs with high Lyα luminosity have been actually identified by spectroscopy at z<5.7, while our LAE sample at z = 6.5 has no confirmed object having such a high Lyα luminosity. The LF of the rest UV continuum, which is not sensitive to neutral IGM, of our LAE sample has almost the same as those of LAEs at z = 5.7 and i-dropouts at z≃6, even at their bright ends. This result may imply that the reionization of the universe has not been completed at z = 6.5. The decline of the Lyα LF implies the cosmic neutral fraction xHI=0.45 based on a theoretical IGM model, although this predicted value is strongly model dependent. The spatial distribution of our LAE sample was found to be homogeneous over the field, based on three independent methods to quantify the clustering strength. The composite spectrum of our LAE sample clearly reveals an asymmetric Lyα profile with an extended red wing, which can be explained by either a galactic wind model composed of double Gaussian profiles, or by a reionization model expected from the damping wing profile. Although our result has uncertainties in LAE evolution and large cosmic variance, it can be interpreted that LAEs at z = 6.5 are at the end of the reionization epoch.

Intracluster Stars in the Virgo Cluster Core

We have investigated the properties of the diffuse light in the Virgo Cluster core region, based on the detection of intracluster planetary nebulae (PNs) in four fields. We eliminate the bias from misclassified faint continuum objects, using improved Monte Carlo simulations, and the contaminations by high-redshift Lyα galaxies, using the Lyα luminosity function in blank fields. Recent spectroscopic observations confirm that our photometric PN samples are well understood. We find that the diffuse stellar population in the Virgo core region is inhomogeneous on scales of 30'–90': there exist significant field-to-field variations in the number density of PNs and the inferred amount of intracluster light, with some fields empty, some fields dominated by extended Virgo galaxy halos, and some fields dominated by the true intracluster component. There is no clear trend with distance from M87. The mean surface luminosity density, its rms variation, and the mean surface brightness of diffuse light in our four fields are ΣB = 2.7 × 106 LB⊙ arcmin-2, rms = 2.1 × 106 LB⊙ arcmin-2, and B = 29.0 mag arcsec-2, respectively. Our results indicate that the Virgo Cluster is a dynamically young environment and that the intracluster component is associated partially with local physical processes like galaxy interactions or harassment. We also argue, based on kinematic evidence, that the so-called over-luminous PNs in the halo of M84 are dynamically associated with this galaxy and must thus be brighter than, and part of a different stellar population from, the normal PN population in elliptical galaxies.

Constraining Reionization with the Evolution of the Luminosity Function of Lyα Emitting Galaxies

At redshifts beyond z 6, as the mean fraction of neutral hydrogen xH i in the intergalactic medium (IGM) increases, the line flux of Lyα emitters can be significantly attenuated, which can result in a decrease in the observed number of emitters at a given Lyα flux. However, cosmological H II regions surrounding the Lyα emitting galaxies alleviate these effects. We use simple models of the Lyα line attenuation that incorporate the presence of H II regions to predict the overall effect of the Lyα absorption on the Lyα luminosity function (LF). We find, in agreement with other recent studies, that a fully neutral IGM is inconsistent with the Lyα LF remaining unchanged from z = 5.7 to z = 6.5, as suggested by recent observations. However, the presence of local H II regions prohibits placing a tight constraint on the mean neutral fraction. We find x 0.25; the presence of strong winds and/or the clustering of ionizing sources would further weaken this constraint. We conclude that the evolution of the Lyα LF is consistent with reionization occurring near this redshift, as suggested by other observations. Finally, we suggest that a measurement of observed Lyα line width as a function of the Lyα luminosity, in a future, larger sample of Lyα emitters, may serve as a robust diagnostic of the neutral fraction in the IGM.