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Register a new userLyman-alpha emission galaxies at a redshift of z = 5.7 in the FORS Deep Field
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We present the results of a search for Lyman-alpha emission galaxies at z~ 5.7 in the FORS Deep Field. The objective of this study is to improve the faint end of the luminosity function of high-redshift Lyman-alpha emitting galaxies and to derive properties of intrinsically faint Lyman-alpha emission galaxies in the young universe. Using FORS2 at the ESO VLT and a set of special interference filters, we identified candidates for high-redshift Lyman-alpha galaxies. We then used FORS2 in spectroscopic mode to verify the identifications and to study their spectral properties. The narrow-band photometry resulted in the detection of 15 likely Lyman-alpha emission galaxies. Spectra with an adequate exposure time could be obtained for eight galaxies. In all these cases the presence of Lyman-alpha emission at z = 5.7 was confirmed spectroscopically. The line fluxes of the 15 candidates range between 3 and 16 * 10^-21 Wm^-2, which corresponds to star-formation rates not corrected for dust between 1 and 5 Msun/yr. The luminosity function derived for our photometrically identified objects extends the published luminosity functions of intrinsically brighter Lyman-alpha galaxies. With this technique the study of high-redshift Lyman-alpha emission galaxies can be extended to low intrinsic luminosities.
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We report results of a deep wide-field narrowband survey for redshift z~5.7 Ly alpha emitters carried out with SuprimeCam on Subaru 8.3-m telescope. Deep narrowband imaging of the SSA22 field through a 120 A bandpass filter centered at 8150 A was combined with deep multicolor RIz SuprimeCam broadband imaging, and BVRZ imaging taken with CFHTs CFH12K camera to select high-redshift galaxy candidates. Spectroscopic observations were made using the new wide-field multi-object DEIMOS spectrograph on Keck for 22 of the 26 candidate objects. Eighteen objects were identified as z~5.7 Lyman alpha emitters, and a further nineteenth candidate was identified based on an LRIS spectrum. At the 3.3 A resolution of the DEIMOS spectra the asymmetric profile for Ly alpha emission with its steep blue fall-off can be clearly seen. We use this to describe the distribution of equivalent widths and the continuum color break properties for z~5.7 Ly alpha galaxies compared with foreground objects. The large majority (>75%) of Ly alpha lines have rest frame equivalent widths less than 240 A and can be understood in terms of young star forming galaxies with a Salpeter initial mass function for the stars. With narrowband selection criteria of I-N > 0.7 and N<25.05 (AB mags) we find a surface density of Ly alpha emitters of 0.03 per square arcminute per (deltaz=0.1) to a limiting flux just under 2e-17 erg/cm2/s. The luminosity function of the Ly alpha emitters is similar to that at lower redshifts to the lowest measurable luminosity of 1e43 ergs/s as is the universal star formation rate based on their continuum properties. We note that the objects are highly structured in both spatial and spectral properties on the angular scale of the fields (~60 Mpc), and that multiple fields will have to be averaged to accurately measure their ensemble properties.
Bright quasars, observed when the Universe was less than one billion years old (z>5.5), are known to host massive black holes (~10$^{9}$ M$_{odot}$), and are thought to reside in the center of massive dark matter overdensities. In this picture, overdensities of galaxies are expected around high redshift quasars. However, observations based on the detection of Lyman Break Galaxies (LBGs) around these quasars do not offer a clear picture: this may be due to the uncertain redshift constraints of LBGs, which are selected through broad-band filters only. To circumvent such uncertainties, we here perform a search for Lyman Alpha Emitting galaxies (LAEs) in the field of the quasar PSO J215.1512-16.0417 at z~5.73, through narrow band, deep imaging with FORS2 at the VLT. We study an area of 37 arcmin$^{2}$, i.e. ~206 comoving Mpc$^{2}$ at the redshift of the quasar. We find no evidence for an overdensity of LAEs in the quasar field with respect to blank field studies. Possible explanations for these findings include that our survey volume is too small, or that the strong ionizing radiation from the quasar hinders galaxy formation in its immediate proximity. Another possibility is that these quasars are not situated in the dense environments predicted by some simulations.
We present detailed morphological properties of Lyman alpha emitters (LAEs) at z~ 5.7 in the COSMOS field, based on {it Hubble Space Telescope} Advanced Camera for Surveys (ACS) data. The ACS imaging in the F814W filter covered 85 LAEs of the 119 LAEs identified in the full two square degree field, and 47 LAEs of them are detected in the ACS images. Nearly half of them are spatially extended with a size larger than 0.15 arcsec (~0.88 kpc at z=5.7) up to 0.4 arcsec (~2.5 kpc at z=5.7). The others are nearly unresolved compact objects. Two LAEs show double-component structures, indicating interaction or merging of building components to form more massive galaxies. By stacking the ACS images of all the detected sources, we obtain a Sersic parameter of n~0.7 with a half-light radius of 0.13 arcsec (0.76 kpc), suggesting that the majority of ACS detected LAEs have not spheroidal-like but disk-like or irregular light profiles. Comparing ACS F814W magnitudes (I_814) with Subaru/Suprime-Cam magnitudes in the NB816, i, and z bands, we find that the ACS imaging in the F814W band mainly probes UV continuum rather than Lyman alpha line emission. UV continuum sizes tend to be larger for LAEs with larger Lyalpha emission regions as traced by the NB816 imaging. The non-detection of 38 LAEs in the ACS images is likely due to the fact that their surface brightness is even too low both in the UV continuum and Lyalpha emission. Estimating I_814 for the LAEs with ACS non-detection from the z and NB816 magnitudes, we find that 16 of these are probably LAEs with a size larger than 0.15 arcsec in UV continuum. All these results suggest that our LAE sample contains systematically larger LAEs in UV continuum size than those previously studied at z~6.
We study six luminous Lyman-alpha emitters (LAEs) with very blue rest-frame UV continua at $5.7le z le 6.6$. These LAEs have previous HST and Spitzer IRAC observations. Combining our newly acquired HST images, we find that their UV-continuum slopes $beta$ are in a range of $-3.4le beta le -2.6$. Unlike previous, tentative detections of $beta simeq -3$ in photometrically selected, low-luminosity galaxies, our LAEs are spectroscopically confirmed and luminous ($M_{rm UV}<-20$ mag). We model their broadband spectral energy distributions (SEDs), and find that two $betasimeq-2.6pm0.2$ galaxies can be well fitted with young and dust-free stellar populations. However, it becomes increasingly difficult to fit bluer galaxies. We explore further interpretations by including non-zero LyC escape fraction $f_{rm esc}$, very low metallicities, and/or AGN contributions. Assuming $f_{rm esc}simeq0.2$, we achieve the bluest slopes $betasimeq-2.7$ when nebular emission is considered. This can nearly explain the SEDs of two galaxies with $betasimeq-2.8$ and --2.9 ($sigma_{beta}=0.15$). Larger $f_{rm esc}$ values and very low metallicities are not favored by the strong nebular line emission (evidenced by the IRAC flux) or the observed (IRAC 1 - IRAC 2) color. Finally, we find that the $betasimeq-2.9$ galaxy can potentially be well explained by the combination of a very young population with a high $f_{rm esc}$ ($ge0.5$) and an old, dusty population. We are not able to produce two $beta simeq -3.4 pm0.4$ galaxies. Future deep spectroscopic observations are needed to fully understand these galaxies.
We present the first spectroscopic measurements of the [OIII] 5007 A line in two z ~ 3.1 Lyman-alpha emitting galaxies (LAEs) using the new near-infrared instrument LUCIFER1 on the 8.4m Large Binocular Telescope (LBT). We also describe the optical imaging and spectroscopic observations used to identify these Lya emitting galaxies. Using the [OIII] line we have measured accurate systemic redshifts for these two galaxies, and discovered a velocity offset between the [OIII] and Ly-alpha lines in both, with the Lya line peaking 342 and 125 km/s redward of the systemic velocity. These velocity offsets imply that there are powerful outflows in high-redshift LAEs. They also ease the transmission of Lya photons through the interstellar medium and intergalactic medium around the galaxies. By measuring these offsets directly, we can refine both Lya-based tests for reionization, and Lya luminosity function measurements where the Lya forest affects the blue wing of the line. Our work also provides the first direct constraints on the strength of the [OIII] line in high-redshift LAEs. We find [OIII] fluxes of 7 and 36 x 10^-17 erg s^-1 cm^-2 in two z ~ 3.1 LAEs. These lines are strong enough to dominate broad-band flux measurements that include the line (in thiscase, K_s band photometry). Spectral energy distribution fits that do not account for the lines would therefore overestimate the 4000 A (and/or Balmer) break strength in such galaxies, and hence also the ages and stellar masses of such high-z galaxies.
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