Tomoki Hayashino

Detections of Lyman Continuum from Star-Forming Galaxies at z ~ 3 through Subaru/Suprime-Cam Narrow-Band Imaging

Knowing the amount of ionizing photons from young star-forming galaxies is of particular importance to understanding the reionization process. Here we report initial results of Subaru/Suprime-Cam deep imaging observation of the SSA22 proto-cluster region at z=3.09, using a special narrow-band filter to optimally trace Lyman continuum (LyC) from galaxies at z~3. The unique wide field-of-view of Suprime-Cam enabled us to search for ionizing photons from 198 galaxies (73 Lyman break galaxies (LBGs) and 125 Ly-alpha emitters (LAEs)) with spectroscopically measured redshifts z~3.1. We detected LyC from 7 LBGs, as well as from 10 LAE candidates. Some of the detected galaxies show significant spatial offsets of LyC from non-ionizing UV emission. For some LBGs the observed non-ionizing UV to LyC flux density ratios are smaller than values expected from population synthesis models with a standard Salpeter initial mass function (IMF) with moderate dust attenuation (which is suggested from the observed UV slopes), even if we assume very transparent IGM along the sightlines of these objects. This implies an intrinsically bluer spectral energy distribution, e.g, that produced by a top-heavy IMF, for these LBGs. The observed flux desity ratios of non-ionizing UV to LyC of 7 detected LBGs range from 2.4 to 23.8 and the median is 6.6. The observed flux density ratios of the detected LAEs are even smaller than LBGs, if they are truly at z~3.1. We find that the median value of the flux density ratio for the deteced LBGs suggest that their escape fractions is likely to be higher than 4%, if the LyC escape is isotropic. The results imply that some of the LBGs in the proto-cluster at z~3 have the escape fraction significantly higher than that of galaxies (in a general field) at z~1 studied previously.

Lyα Emitters at z = 5.7 in the Subaru Deep Field

PASJ: Publ. Astron. Soc. Japan , 1–??, c 2008. Astronomical Society of Japan. Lyα Emitters at z = 5.7 in the Subaru Deep Field Kazuhiro Shimasaku, 1,2 Nobunari Kashikawa, 3,4 Mamoru Doi, 5,2 Chun Ly, 6 Matthew A.Malkan, 6 Yuichi Matsuda, 7 Masami Ouchi, 8,‡ Tomoki Hayashino, 9 Masanori Iye, 3,4 Kentaro Motohara, 5 Takashi Murayama, Tohru Nagao, 3,11 Kouji Ohta, 12 Sadanori Okamura, 1,2 Toshiyuki Sasaki, 13 Yasuhiro Shioya, 10 Yoshiaki Taniguchi 10 arXiv:astro-ph/0602614v1 28 Feb 2006 Department of Astronomy, School of Science, The University of Tokyo, Tokyo 113-0033 Email (KS): shimasaku@astron.s.u-tokyo.ac.jp Research Center for the Early Universe, School of Science, The University of Tokyo, Tokyo 113-0033 Optical and Infrared Astronomy Division, National Astronomical Observatory, Mitaka, Tokyo 181-8588 Department of Astronomy, School of Science, Graduate University for Advanced Studies, Mitaka, Tokyo 181-8588 Institute of Astronomy, School of Science, The University of Tokyo, Mitaka 181-0015 Department of Astronomy, University of California at Los Angeles, Los Angeles, CA 90095-1547, USA Department of Astronomy, Graduate School of Science, Kyoto University, Kyoto 606-8502 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA Research Center for Neutrino Science, Graduate School of Science, Tohoku University, Aramaki, Aoba, Sendai 980-8578 Astronomical Institute, Graduate School of Science, Tohoku University, Aramaki, Aoba, Sendai 980-8578, Japan INAF / Osservatorio Astrofisico di Arcetri Largo E. Fermi 5, 50125 Firenze, Italy Kouji Ohta Department of Astronomy, Kyoto University, Kyoto 606-8502 Subaru Telescope, National Astronomical Observatory of Japan, 650 N. A’ohoku Place, Hilo, HI 96720, USA (Received 2005 October 26; accepted 2006 February 27) Abstract We present the properties of Lyα emitters (LAEs) at z = 5.7 in the Subaru Deep Field. A photometric sample of 89 LAE candidates is constructed from narrow-band (NB816) data down to N B816 = 26.0 (AB) in a continuous 725 arcmin 2 area. Spectra of 39 objects satisfying the photometric selection criteria for LAEs were obtained with Subaru and Keck II Telescopes, among which 28 were confirmed LAEs, one was a nearby galaxy, and eight were unclassified. We also obtained spectra of another 24 NB816-excess objects in the field, identifying six additional LAEs. We find that the Lyα luminosity function derived from the photometric sample is reproduced well by a Schechter function with L ⋆ = 7.9 +3.0 erg s −1 and φ ⋆ = 6.3 −2.0 × 10 −4 Mpc −3 for α = −1.5 (fixed) over the whole luminosity range of L ≃ 3 × 10 42 – 3 × 10 43 erg s −1 . We then measure rest-frame Lyα equivalent widths (EWs) for the confirmed LAEs, to find that the median among the 28 objects satisfying the photometric selection criteria is W i0 = 233 ˚ A. We infer that 30% – 40% of LAEs at z = 5.7 exceed W i0 = 240 ˚ A. These large-EW objects probably cannot be accounted for by ordinary star-forming populations with a Salpeter IMF. We also find that LAEs with fainter far-UV luminosities have larger EWs. Finally, we derive the far-UV luminosity function of LAEs down to M UV ≃ −19.6 using the photometric sample, and compare it with that of Lyman-break galaxies (LBGs). We find that as high as about 80% of LBGs at z ∼ 6 have W i0 ≥ 100 ˚ A, in sharp contrast to lower-z counterparts. Key words: galaxies: evolution — galaxies: high-redshift — galaxies: luminosity function, mass function — galaxies: photometry

Errata : The SUBARU Deep Field Project: Lyman α Emitters at a Redshift of 6.6

We present new results of a deep optical imaging survey using a narrow band filter (NB921) centered at λ = 9196 u A together with B, V, R, i � ,a ndzbroadband filters in the sky area of the Subaru Deep Field, which has been promoted as one of legacy programs of the 8.2m Subaru Telescope. We obtained a photometric sample of 58 Ly α emitter candidates at z ≈ 6.5-6.6 among ∼ 180 strong NB921-excess (z � −NB921 > 1.0) objects together with a color criterion of i � −z � > 1.3. We then obtained optical spectra of 20 objects in our NB921-excess sample, and identified at least nine Ly α emitters at z ∼ 6.5-6.6, including the two emitters reported by Kodaira et al. (2003, PASJ, 55, L17). Since our Ly α-emitter candidates are free from strong amplification of gravitational lensing, we are able to discuss their observational properties from a statistical point of view. Based on these new results, we obtained a lower limit of the star-formation rate density of ρSFR � 5.7 ×10 −4 h0.7 Myr −1 Mpc −3 at z ≈ 6.6, being

Clustering of Lyman Break Galaxies at z = 4 and 5 in the Subaru Deep Field: Luminosity Dependence of the Correlation Function Slope

We explored the clustering properties of Lyman break galaxies at z = 4 and 5 with an angular two-point correlation function on the basis of the very deep and wide Subaru Deep Field data. We confirmed the previous result that the clustering strength of LBGs depends on the UV luminosity in the sense that brighter LBGs are more strongly clustered. In addition, we found an apparent dependence of the correlation function slope on UV luminosity for LBGs at both z = 4 and 5. More luminous LBGs have a steeper correlation function. The bias parameter was found to be a scale-dependent function for bright LBGs, whereas it appears to be almost scale-independent for faint LBGs. Luminous LBGs have a higher bias at smaller angular scales, which decreases as the scale increases. To compare these observational results, we constructed numerical mock LBG catalogs based on a semianalytic model of hierarchical clustering combined with high-resolution N-body simulation, carefully mimicking the observational selection effects. The luminosity functions and the overall correlation functions for LBGs at z = 4 and 5 predicted by this mock catalog were found to be almost consistent with the observation. The observed dependence of the clustering on UV luminosity was not reproduced by the model, unless subsamples of distinct halo mass were considered. That is, LBGs belonging to more massive dark halos had steeper and larger amplitude correlation functions. With this model, we found that LBG multiplicity in massive dark halos amplifies the clustering strength at small scales, which steepens the correlation function. The hierarchical clustering model could therefore be reconciled with the observed luminosity dependence of the correlation function if there is a tight correlation between UV luminosity and halo mass. Our finding that the slope of the correlation function depends on luminosity could be an indication that massive dark halos hosted multiple bright LBGs.

Diffuse Lyα haloes around Lyα emitters at z = 3: do dark matter distributions determine the Lyα spatial extents?

Using stacks of Ly-a images of 2128 Ly-a emitters (LAEs) and 24 protocluster UV-selected galaxies (LBGs) at z=3.1, we examine the surface brightness profiles of Ly-a haloes around high-z galaxies as a function of environment and UV luminosity. We find that the slopes of the Ly-a radial profiles become flatter as the Mpc-scale LAE surface densities increase, but they are almost independent of the central UV luminosities. The characteristic exponential scale lengths of the Ly-a haloes appear to be proportional to the square of the LAE surface densities (r(Lya) \propto Sigma(LAE)^2). Including the diffuse, extended Ly-a haloes, the rest-frame Ly-a equivalent width of the LAEs in the densest regions approaches EW_0(Lya) ~ 200 A, the maximum value expected for young (< 10^7 yr) galaxies. This suggests that Ly-a photons formed via shock compression by gas outflows or cooling radiation by gravitational gas inflows may partly contribute to illuminate the Ly-a haloes; however, most of their Ly-a luminosity can be explained by photo-ionisation by ionising photons or scattering of Ly-a photons produced in HII regions in and around the central galaxies. Regardless of the source of Ly-a photons, if the Ly-a haloes trace the overall gaseous structure following the dark matter distributions, it is not surprising that the Ly-a spatial extents depend more strongly on the surrounding Mpc-scale environment than on the activities of the central galaxies.

Diffuse Lyman Alpha Haloes around Lyman Alpha Emitters at z=3: Do Dark Matter Distributions Determine the Lyman Alpha Spatial Extents?

Using stacks of Ly-a images of 2128 Ly-a emitters (LAEs) and 24 protocluster UV-selected galaxies (LBGs) at z=3.1, we examine the surface brightness profiles of Ly-a haloes around high-z galaxies as a function of environment and UV luminosity. We find that the slopes of the Ly-a radial profiles become flatter as the Mpc-scale LAE surface densities increase, but they are almost independent of the central UV luminosities. The characteristic exponential scale lengths of the Ly-a haloes appear to be proportional to the square of the LAE surface densities (r(Lya) \propto Sigma(LAE)^2). Including the diffuse, extended Ly-a haloes, the rest-frame Ly-a equivalent width of the LAEs in the densest regions approaches EW_0(Lya) ~ 200 A, the maximum value expected for young (< 10^7 yr) galaxies. This suggests that Ly-a photons formed via shock compression by gas outflows or cooling radiation by gravitational gas inflows may partly contribute to illuminate the Ly-a haloes; however, most of their Ly-a luminosity can be explained by photo-ionisation by ionising photons or scattering of Ly-a photons produced in HII regions in and around the central galaxies. Regardless of the source of Ly-a photons, if the Ly-a haloes trace the overall gaseous structure following the dark matter distributions, it is not surprising that the Ly-a spatial extents depend more strongly on the surrounding Mpc-scale environment than on the activities of the central galaxies.

A Keck/DEIMOS Spectroscopy of Lyα Blobs at Redshift z = 3.1* **

We present the results of intermediate-resolution (~2 ?) spectroscopy of a sample of 37 candidate Ly? blobs and emitters at redshift z = 3.1 using the DEIMOS spectrograph on the 10 m Keck telescope. The emission lines are detected for all 37 objects and show variety in their line profiles. The Ly? velocity widths (FWHM) of the 28 objects with higher quality spectra, measured by fitting a single Gaussian profile, are in the range of 150-1700 km s-1 and correlate with the Ly? spatial extents. All 12 Ly? blobs (?16 arcsec2) have large velocity widths of 500 km s-1. While there are several possible physical interpretations of the Ly? velocity widths (the motion of gravitationally bound gas clouds, inflows, the merging of clumps, or outflows from superwinds), the large velocity widths of the Ly? blobs suggest that they are the sites of massive galaxy formation. If we assume gravitationally bound gas clouds, the dynamical masses of the Ly? blobs are estimated to be ~1012-1013 M?. Even for the case of outflows, the outflow velocities are likely to be comparable to the rotation velocities as inferred from the observational evidence for local starburst galaxies.

The Discovery of Two Lyman α Emitters beyond Redshift 6 in the Subaru Deep Field

We performed a deep optical imaging survey using a narrow-band filter (NB921) centered at λ=9196 u A together

PROFILES OF Lyα EMISSION LINES OF THE EMITTERS AT z = 3.1

We present the results of the observations of the Ly{alpha} line profiles of 91 emission-line galaxies at z = 3.1 with a spectral resolution of {lambda}/{delta}{lambda}(FWHM) Almost-Equal-To 1700 or 180 km s{sup -1}. A significant fraction of {approx}50% of the observed objects show the characteristic double peaks in their Ly{alpha} profile. The red peak is much stronger than the blue one for most of the cases. The red peaks themselves also show weak but significant asymmetry and their widths are correlated with the velocity separation of the red and the blue peaks. This implies that the peaks are not isolated multiple components with different velocities but parts of a single line that are modified by the absorption and/or scattering by the associated neutral hydrogen gas. The characteristic profile can be naturally explained by scattering in the expanding shell of the neutral hydrogen surrounding the Ly{alpha} emitting region while the attenuation by the intergalactic medium should also be considered. Our results suggest that the star formation in these Ly{alpha} emitters are dominated by young burst-like events that produce the intrinsic Ly{alpha} emission as well as the gas outflow.

A Search for Lyα Emitters at Redshift 3.7

We present the results of a survey for emission-line objects based on optical intermediate-band (