CHORUS. III. Photometric and Spectroscopic Properties of Lyα Blobs at z = 4.9–7.0

Haibin Zhang; Masami Ouchi; Ryohei Itoh; Takatoshi Shibuya; Yoshiaki Ono; Yuichi Harikane; Akio K. Inoue; Michael Rauch; Shotaro Kikuchihara; Kimihiko Nakajima; Hidenobu Yajima; Shohei Arata; Makito Abe; Ikuru Iwata; Nobunari Kashikawa; Satoshi Kawanomoto; Satoshi Kikuta; Masakazu A. R. Kobayashi; Haruka Kusakabe; Ken Mawatari; Tohru Nagao; Kazuhiro Shimasaku; Yoshiaki Taniguchi

doi:10.3847/1538-4357/ab7917

1. Introduction

Lyα emitters (LAEs) are important objects to study the formation and evolution of star-forming galaxies (SFGs) at high redshifts where the redshifted Lyα emission becomes observable with ground-based telescopes (e.g., Ouchi et al. 2003, 2008). Previous narrowband imaging surveys have identified LAEs with very luminous Lyα emission (log $({L}_{\mathrm{Ly}\alpha }/[\mathrm{erg}\ {{\rm{s}}}^{-1}])\gtrsim 43.4$ ) and a large isophotal area (≳150 kpc²) at z ∼ 2–7. These luminous and spatially extended LAEs are often referred to as Lyα blobs (LABs; e.g., Keel et al. 1999; Steidel et al. 2000; Francis et al. 2001; Matsuda et al. 2004). One well-known example of LABs is LAB1 (Steidel et al. 2000) at z = 3.1, while the most distant ones are Himiko (Ouchi et al. 2009) and CR7 (Sobral et al. 2015) at z = 6.6. LABs are important objects for studying massive galaxies and their circumgalactic medium (CGM) in the early universe. Although LABs have been analyzed individually by many studies, the relation between LABs at different epochs of z ∼ 3 (e.g., LAB1) and z ≳ 6 (e.g., Himiko and CR7) is still unclear.

Following the identification of LABs, diffuse Lyα nebulae called Lyα halos (LAHs) are found ubiquitously around typical LAEs with $\mathrm{log}({L}_{\mathrm{Ly}\alpha }/[\mathrm{erg}\ {{\rm{s}}}^{-1}])\sim 42\mbox{--}43$ at z ∼ 3−6 and have been identified individually (e.g., Rauch et al. 2008; Wisotzki et al. 2016; Leclercq et al. 2017) or statistically by stacking analysis (e.g., Hayashino et al. 2004; Steidel et al. 2011; Matsuda et al. 2012; Feldmeier et al. 2013; Momose et al. 2014, 2016; Wisotzki et al. 2018). The typical isophotal area of LAHs is smaller than that of LABs at similar redshifts. However, the isophotal area measurement can be largely affected by both the detection limits and the surface brightnesses of LAHs and LABs. At the same detection limit, faint LAHs show smaller isophotal areas than bright LABs if the radial profile shapes are the same, as the Lyα luminosities of LAHs are fainter than those of LABs by an order of magnitude. Nevertheless, it is still unclear whether LAHs and LABs at z ≳ 5 have similar shapes of Lyα radial profiles to understand if LAHs and LABs at high z are distinct populations.

Although it is not clear if LAHs and LABs are distinct populations, there may be one difference between LAHs and LABs related to active galactic nuclei (AGNs). Konno et al. (2016) and Sobral et al. (2018) suggest that AGNs exist in LAEs brighter than a luminosity limit of log $({L}_{\mathrm{Ly}\alpha }/[\mathrm{erg}\ {{\rm{s}}}^{-1}])\gtrsim 43.4$ at z ∼ 2−3. Because most LABs exceed this luminosity limit, it is expected that LABs have AGN activities. Previously, AGNs have been identified in some LABs (e.g., LAB2 in Steidel et al. 2000; Basu-Zych & Scharf 2004), while no evidence of AGNs is found in other LABs (e.g., LAB1; Geach et al. 2007; Matsuda et al. 2007). Statistically, Geach et al. (2009) investigate 29 LABs at z = 3.09 and find that ∼10%–30% of the LABs contain AGNs. To explain these observational results, there are two possibilities. One possibility is that all LABs intrinsically have AGNs, and that some AGNs are obscured or too faint to be identified. Another possibility is that there exist two kinds of LABs, with and without AGNs.

Related to the possible AGN activities in LABs, the extended Lyα emission can be explained by the several scenarios listed below.

1.
Fluorescence. There exists some neutral hydrogen gas in the CGM around a galaxy that is heated by an AGN or star formation. The neutral hydrogen gas is photoionized by the ionizing photons from the galaxy center or UV background. Lyα photons are then emitted during the recombination process (e.g., Cantalupo et al. 2014; Prescott et al. 2015; Mas-Ribas & Dijkstra 2016).
2.
Resonant scattering. Lyα photons escape to the CGM from a galaxy center and are resonantly scattered by the neutral hydrogen in the CGM. This process causes the galaxy to have Lyα emission more extended than the UV continuum (e.g., Hayes et al. 2011; Cen & Zheng 2013; Geach et al. 2014, 2016; Lake et al. 2015; Beck et al. 2016; Mas-Ribas et al. 2017).
3.
Gravitational cooling radiation. Some inflow streams exist around a galaxy and accrete onto the galaxy center. Lyα photons are emitted by the collisional excitation of neutral hydrogen in the streams. In this radiation process, the streams release their gravitational potential energy (e.g., Haiman et al. 2000; Fardal et al. 2001; Dekel et al. 2009; Martin et al. 2015).
4.
Outflows. Multiple supernova explosions in a galaxy produce hot gas outflows. The outflows drive shocked cooling shells that emit Lyα photons (e.g., Taniguchi & Shioya 2000; Bower et al. 2004; Mori et al. 2004; Wilman et al. 2005).
5.
Satellite galaxies. A central galaxy is surrounded by multiple satellite galaxies that emit Lyα photons during star formation. In this scenario, a galaxy may exhibit both extended Lyα emission and extended UV continuum (e.g., Prescott et al. 2012; Francis et al. 2013; Geach et al. 2016; Mas-Ribas et al. 2017).

Because the different possible scenarios are expected to cause different shapes of Lyα radial profiles, various studies have tried to pinpoint the origin of extended Lyα emission by comparing Lyα radial profiles from models with those from observations (e.g., Lake et al. 2015; Mas-Ribas & Dijkstra 2016; Mas-Ribas et al. 2017). However, these studies target LAEs with fainter Lyα luminosities (log $({L}_{\mathrm{Ly}\alpha }/[\mathrm{erg}\ {{\rm{s}}}^{-1}])\lt 43$ ) than those of LABs. These models may not well explain the physical origin of the luminous and extended Lyα emission of LABs.

In this paper, we present the identification of two new LABs at z = 4.9 and 7.0. Including five LABs at z = 5.7 and 6.6 identified by previous studies, we investigate the photometric and spectroscopic properties of a total of seven LABs. We perform profile fitting to model the extended Lyα emission around LABs, and compare our best-fit models of LABs with those of LAHs in the literature. We investigate AGN activities in LABs with X-ray data and UV-line ratio diagnostics, and discuss the possible physical origins of the extended Lyα emission around LABs.

This paper is organized as follows. In Section 2, we describe the observations, data, and identification of two new LABs. In Section 3, we present the spectroscopic analysis of LABs. Our results are shown in Section 4, and the discussions are presented in Section 5. We summarize our findings in Section 6. Throughout this paper, we use AB magnitudes (Oke & Gunn 1983) and physical distances unless we indicate otherwise. A ΛCGM cosmology with Ω_m = 0.3, Ω_Λ = 0.7, and h = 70 is adopted.

2. Observations, Data, and LAB Identification

In this paper, we study a total of seven LABs that include two new LABs from our observations and five LABs from previous studies. We use photometric and spectroscopic data either from our observations or in the literature.

2.1. New LABs Identified by the CHORUS Survey

2.1.1. Imaging Observations and Data Reduction

We carried out narrowband imaging observations with Subaru/Hyper Suprime-Cam (HSC; Furusawa et al. 2018; Kawanomoto et al. 2018; Komiyama et al. 2018; Miyazaki et al. 2018) in the course of project Cosmic HydrOgen Reionization Unveiled with Subaru (CHORUS; PI: A. K. Inoue). We used two narrow bands of NB718 (λ_c = 7170 Å, FWHM = 110 Å) and NB973 (λ_c = 9715 Å, FWHM = 100 Å). The central wavelengths of the NB718 and NB973 filters were chosen to detect redshifted Lyα emission at z = 4.9 and 7.0, respectively. The NB718 data were taken on 2017 February 25, March 23, and March 25, while the NB973 observations were conducted on 2017 January 26 and 28. The NB718 observations covered the COSMOS field, and the NB973 observations were carried out in the SXDS and COSMOS fields. The effective survey areas were 1.64 and 1.50 deg² in the COSMOS and SXDS fields, respectively. The typical seeing sizes during observations were 0 farcs 6–0 farcs 9.

We reduce the NB718 and NB973 images with the HSC pipeline (Bosch et al. 2018) that uses codes from the Large Synoptic Survey Telescope (LSST) pipeline (Ivezić et al. 2019; Axelrod et al. 2010; Jurić et al. 2017). The astrometry and photometry are calibrated with the imaging data from the Panoramic Survey Telescope and Rapid Response System 1 (Pan-STARRS1; Schlafly et al. 2012; Tonry et al. 2012; Magnier et al. 2013) survey. We do not use exposures with seeing sizes larger than 0 farcs 9 during the reduction because these exposures were taken under bad weather conditions. The total integration times of the reduced NB718 and NB973 images are 6.3 hr and 14.7 hr, respectively. The typical 5σ limiting magnitudes in a 1 farcs 5 diameter aperture are 26.2 in NB718 data and 24.9 in NB973 data.

During the reduction, in addition to the NB718 and NB973 images, we also use the ultra-deep layer data of broad bands (g, r, i, z, and y) from the Subaru Strategic Program (SSP) survey (PI: S. Miyazaki; Aihara et al. 2018) for source detection and forced photometry. Details of the source detection and forced photometry are described in Bosch et al. (2018). We do not use areas contaminated either by halos of bright stars (Coupon et al. 2018) or low signal-to-noise ratio pixels such as field edges. The catalogs produced in this procedure are referred to as source catalogs in the following sections.

2.1.2. Photometric Samples of LAEs at z = 4.9 and 7.0

To select LAEs at z = 4.9, we use source catalogs of the NB718, g, r, and i filters. We apply the following color criteria:

$\begin{eqnarray}&&\begin{array}{l}{ri}-\mathrm{NB}718\gt 0.7\ \mathrm{and}\ r-i\gt 0.8\ \mathrm{and}\\ {ri}-\mathrm{NB}718\gt {({ri}-\mathrm{NB}718)}_{3\sigma }\ \mathrm{and}\\ \mathrm{NB}{718}^{\mathrm{ap}}\lt \mathrm{NB}{718}_{5\sigma }^{\mathrm{ap}}\ \mathrm{and}\ {g}^{\mathrm{ap}}\geqslant {g}_{2\sigma }^{\mathrm{ap}},\end{array}\end{eqnarray} \tag{ 1 }$

where the superscript "ap" indicates the aperture magnitude in a 2 farcs 0 diameter, and no superscript corresponds to the total magnitude. The total magnitude is measured by the CModel photometry described in Bosch et al. (2018). The 2σ, 3σ, and 5σ subscripts stand for 2σ, 3σ, and 5σ detection limits, respectively. In Equation (1), ri is calculated by the linear combination of the fluxes in the r band, f_r, and i band, f_i, following ${f}_{\mathrm{ri}}=0.3{f}_{{\rm{r}}}+0.7{f}_{{\rm{i}}}$ . The 3σ error of the ${ri}-\mathrm{NB}718$ color is given by ${({ri}-\mathrm{NB}718)}_{3\sigma }\,=-2.5\mathrm{log}(1\pm 3\sqrt{{f}_{\mathrm{err},\mathrm{ri}}^{2}+{f}_{\mathrm{err},\mathrm{NB}718}^{2}}/{f}_{\mathrm{NB}718})$ , where ${f}_{\mathrm{err},\mathrm{ri}}$ and ${f}_{\mathrm{err},\mathrm{NB}718}$ are the 1σ errors in ri and NB718, respectively. These criteria allow us to choose LAEs with rest-frame Lyα equivalent widths (EW₀) greater than 10 Å.

In total, 727 objects meet the color criteria. We then visually inspect these objects and exclude 586 spurious sources such as satellite trails. Finally, we obtain 141 LAE candidates at z = 4.9. Figure 1 shows the color–magnitude diagram of our LAE candidates at z = 4.9.

**Figure 1.** Color–magnitude diagram of our LAE candidates at z = 4.9. The red filled circles and triangles are the 141 selected LAE candidates. The triangles denote the LAEs whose ri – NB718 colors are greater than 3. The black filled circles are the other objects (including spurious sources) in our source catalog. The dashed lines present the color criteria in Equation (1).
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The selection of LAEs at z = 7.0 is presented in Itoh et al. (2018). Briefly, Itoh et al. (2018) select LAEs with NB973 and broad bands (g, r, i, z, and y) following the criteria:

$\begin{eqnarray}&&\begin{array}{l}[({y}^{\mathrm{ap}}\lt {y}_{3\sigma }^{\mathrm{ap}}\ \mathrm{and}\ y-\mathrm{NB}973\gt 1)\ \mathrm{or}\ {y}^{\mathrm{ap}}\gt {y}_{3\sigma }^{\mathrm{ap}}]\ \mathrm{and}\\ [({z}^{\mathrm{ap}}\lt {z}_{3\sigma }^{\mathrm{ap}}\ \mathrm{and}\ z-y\gt 2)\ \mathrm{or}\ {z}^{\mathrm{ap}}\gt {z}_{3\sigma }^{\mathrm{ap}}]\ \mathrm{and}\\ \mathrm{NB}{973}^{\mathrm{ap}}\lt \mathrm{NB}{973}_{5\sigma }^{\mathrm{ap}}\ \mathrm{and}\ {g}^{\mathrm{ap}}\geqslant {g}_{2\sigma }^{\mathrm{ap}}\ \mathrm{and}\\ {r}^{\mathrm{ap}}\geqslant {r}_{2\sigma }^{\mathrm{ap}}\ \mathrm{and}\ {i}^{\mathrm{ap}}\geqslant {i}_{2\sigma }^{\mathrm{ap}},\end{array}\end{eqnarray} \tag{ 2 }$

where the meanings of the superscripts and subscripts are the same as in Equation (1).

Finally, there are 34 LAE candidates at z = 7.0 after we conduct the color selection and visual inspection.

2.1.3. Identification of Two LABs

We select LAB candidates based on isophotal areas and narrowband magnitudes in a manner similar to the one in Shibuya et al. (2018). Figure 2 shows isophotal areas as a function of total narrowband magnitude for our LAE candidates at z = 4.9 and 7.0. The isophotal area is defined as the area with a surface brightness above the 2σ detection limit. We estimate the isophotal area–magnitude relations of point sources using the point-spread functions (PSFs) in the NB718 and NB973 images. The isophotal areas of LAB candidates are larger than the 2.5σ confidence levels of the point sources. The narrowband magnitudes of the LAB candidates are brighter than 23.9 mag for NB718 and 24.1 mag for NB973. These two narrowband magnitudes, together with the 24.0 mag at z ∼ 6 that is used in Shibuya et al. (2018), correspond to a Lyα luminosity of ∼1.6 × 10⁴³ erg s⁻¹ if we assume the UV continuum is negligible compared to the Lyα emission. We consider the changes of the luminosity distances and filter response curves in the calculation.

By the criteria of isophotal areas and narrowband magnitudes, nine and one LAB candidates are selected at z = 4.9 and 7.0, respectively, as shown in Figure 2. The number densities of our LAB candidates are ∼6.0 × 10⁻⁶ and 2.8 × 10⁻⁷ Mpc⁻³ at z = 4.9 and 7.0, respectively, which are comparable to the number densities of ∼10⁻⁷–10⁻⁶ Mpc⁻³ at z = 5.7 and 6.6 in Shibuya et al. (2018). For the first step of our statistical study and follow-up spectroscopy, we select the brightest LAB candidates at z = 4.9 and 7.0, which are named z49-1 (R.A. $=\,{10}^{{\rm{h}}}{01}^{{\rm{m}}}45.977$ , decl. = +2°02'44 farcs 28 [J2000]) and z70-1 (R.A. $=\,{10}^{{\rm{h}}}{02}^{{\rm{m}}}15.521$ , decl. = +2°40'33 farcs 23 [J2000]), respectively. The objects of z49-1 and z70-1 show large isophotal areas (157.5 and 42.2 physical kpc²) and bright Lyα luminosities (3.5 × 10⁴³ and 2.6 × 10⁴³ erg s⁻¹) that are distinguished from the other LAE candidates at each redshift. Snapshots of z49-1 and z70-1 are presented in Figure 3. The images of z49-1 and z70-1 from UltraVista (Y, J, H, and K bands) and Spitzer/IRAC (3.6 and 4.5 μm bands) are shown in Figure 4 and will be analyzed in Section 4.

**Figure 3.** Snapshots of the seven LABs. The size of each image is 5'' × 5''. *HST* corresponds to *HST*/WFC3 F814W, F125W, and F110W images for z49-1, z66-1 and z66-2, respectively.
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**Figure 4.** Snapshots of z49-1 and z70-1 in the narrow band and Y, J, H, K, 3.6, and 4.5 μm bands. The size of each image is 5'' × 5''.
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2.1.4. Spectroscopic Observations

We carried out spectroscopic observations for z49-1 with Magellan/LDSS3 on 2017 May 28. The object of z49-1 was observed with an on-source exposure time of 1800 s. The observations were conducted in the long-slit mode with a slit width of 2 farcs 0. We used the OG590 filter with the VPH-Red grism (R ≃ 680) to cover the expected Lyα emission line at z = 4.9.

Spectroscopic observations for z70-1 were performed with Keck/DEIMOS (Faber et al. 2003) on 2019 January 6. The total on-source exposure time was 3.7 hr. However, we only used the data in the last 1.7 hr because the data in the first 2 hr were taken under bad weather conditions. The slit width was 1 farcs 0 during the observations in the multiobject spectroscopy (MOS) mode. The OG550 filter and the 830 G grating (R ≃ 2900 at 9700 Å) were chosen to cover the wavelength where the Lyα emission line at z = 7.0 was expected.

2.2. LABs Identified in Previous Studies

From previous studies, we use five LABs including z57-1 and z57-2 (HSC J161927+551144 and HSC J161403+535701 in Shibuya et al. 2018) at z = 5.7, z66-1 (Himiko in Ouchi et al. 2009), z66-2 (CR7 in Sobral et al. 2015), and z66-3 (HSC J100334+024546 in Shibuya et al. 2018) at z = 6.6. Because these five LABs pass the LAB selection criteria in Shibuya et al. (2018) that are similar to ours, the LABs would also be selected by us if they fall in our survey. The imaging data are available from the SSP survey and shown in Figure 3. The spectra of z66-1, z66-2, and z66-3 are taken from Ouchi et al. (2009), Sobral et al. (2015), and Shibuya et al. (2018), respectively.

We carried out spectroscopic follow-up observations for z57-1 and z57-2 with Subaru/FOCAS on 2018 July 17. We chose a slit width of 0 farcs 8 in the MOS mode. The O58 filter and VPH900 grism (R ≃ 1500) were used to cover the expected Lyα emission line at z = 5.7. Finally, we obtained data with an on-source exposure time of 1200 s for each target.

2.3. Summary of Our LAB Samples

Our final LAB samples include z49-1, z57-1, z57-2, z66-1, z66-2, z66-3, and z70-1, which are referred to as the seven LABs in the following sections. From the snapshots of the seven LABs in Figure 3, we can see that apparently all of the seven LABs are more extended in the narrowband images (NB718, NB816, NB921, and NB973) than the corresponding offband images (i, z, y, and y). Photometric properties of the seven LABs are summarized in Table 1. Details of spectroscopic observations of the seven LABs are presented in Table 2. The spectroscopic data will be shown and discussed in the next section.

Table 1. Photometric Properties of the Seven LABs

ID	Object Name	Redshift	NB_tot	BB_tot	log L_Lyα	EW₀	δ
			(1)	(2)	(3)	(Å)	(4)
z49-1	⋯	4.9	22.66	23.89	43.54	47.5	5.68
z57-1	HSC J161927+551144^a	5.7	22.88	24.86	43.6	71.4	1.57
z57-2	HSC J161403+535701^a	5.7	23.53	25.32	43.2	20.6	4.14
z66-1	Himiko^b	6.6	23.55	25.00	43.40	78	2.09
z66-2	CR7^c	6.6	23.24	24.92	43.93	211	0.62
z66-3	HSC J100334+024546^a	6.6	23.61	24.97	43.50	61.1	4.28
z70-1	⋯	7.0	23.40	25.09	43.41	73	3.65

Notes.

^aColumn 1: total narrowband magnitude in units of mag. Column 2: total broadband magnitude in units of mag. Column 3: photometric Lyα luminosity in units of erg s⁻¹. Column 4: LAE overdensity described in Section 4.2. ^bShibuya et al. (2018). ^cOuchi et al. (2009). ^dSobral et al. (2015).

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Table 2. Summary of Spectroscopy

ID	Instrument	Filter	Grism/Grating	Exp. Time (s)	Slit Width ('')	z_spec
z49-1	Magellan/LDSS3	OG590	VPH-Red	1800	2.0	4.888
z57-1	Subaru/FOCAS	O58	VPH900	1200	0.8	5.709
z57-2	Subaru/FOCAS	O58	VPH900	1200	0.8	5.733
z66-1^a	Keck/DEIMOS	GG495	830 G	10,800	1.0	6.595
z66-2^b	VLT/X-SHOOTER	⋯	⋯	8100	0.9	6.604
z66-3^c	Subaru/FOCAS	O58	VPH900	6000	0.8	6.575
z70-1	Keck/DEIMOS	OG550	830 G	6000	1.0	6.965

Notes.

^aOuchi et al. (2009). ^bSobral et al. (2015). ^cShibuya et al. (2018).

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3. Spectroscopic Analysis

The spectrum of z70-1 is shown in Figure 5. Because the emission line at 9686 Å is partly overlapped by nearby sky lines, the line shape may be affected by the sky residual after sky subtraction. This emission line cannot be explained by an O ii doublet, because the two peaks of an O ii doublet at this wavelength would have a separation of ∼8 Å that is broader than the line observed. We find no other emission lines between ∼6000 and 10000 Å that indicate a foreground source. We conclude that z70-1 is not likely a low-z object but an LAB at z = 6.965.

Figure 6 presents the spectra of z49-1, z57-1, z57-2, z66-1, z66-2, and z66-3. The spectrum of z49-1 shows an emission line whose line center is at 7160 Å. The line center is measured by fitting a Gaussian function to the emission line. Additionally, on the spectrum, we find another emission line whose line center is at 9131 Å, as presented in Figure 7. These two emission lines can only be explained by an object emitting Lyα and C iv lines simultaneously at z = 4.888. The emission line at 7160 Å is asymmetric and has a red wing that is consistent with a high-z Lyα emission line. The object of z49-1 is confirmed as an LAB at z = 4.888. The Lyα and C iv fluxes of z49-1 measured from the spectrum are (1.52 ± 0.048) × 10⁻¹⁶ and (1.61 ± 0.29) × 10⁻¹⁷ erg s⁻¹ cm⁻², respectively.

**Figure 7.** Same as Figure 5, but for the C iv emission of z49-1.
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Figure 8 shows the line-center offset Δλ_c and FWHM of the Lyα emission line as a function of positional offset Δd. Δd is the distance between the position of a measurement and a Lyα source center. By definition, the Lyα-source center is located at Δd = 0. The positive direction of Δd is from the blueshifted side to the redshifted side. Δλ_c is calculated following ${\rm{\Delta }}{\lambda }_{{\rm{c}}}={\lambda }_{{\rm{c}}}({\rm{\Delta }}d)-{\lambda }_{{\rm{c}}}(0)$ . Because the Lyα emission line of z70-1 is affected by nearby sky lines as we discussed earlier, we do not include z70-1 in this analysis. In Figure 8, Δλ_c has a positive correlation with Δd although the correlation for z66-2 is weak. The correlation between Δλ_c and Δd indicates velocity gradients in the Lyα emission lines of our LABs. We notice that the FWHM also positively correlates with Δd. Clearly, z49-1 and z57-2 have larger velocity gradients and FWHMs than the other LABs.

4. Results

4.1. Lyα Surface Brightness Profiles

To make Lyα images of the seven LABs, we first match the PSFs of narrowband and offband images, and then subtract the offband images from the corresponding narrowband images. We use a PSF matching method similar to the one discussed in Aniano et al. (2011). The PSF matching procedure is briefly described below.

First, we extract the PSFs of narrowband and offband images by stacking 200–300 bright and unsaturated ( $19\lt {m}_{\mathrm{AB}}\lt 22$ ) point sources in each filter. These PSFs are referred to as initial PSFs. We choose the PSF with the largest FWHM among initial PSFs as the target PSF. Then, we calculate convolution kernels that are used to convolve the initial PSFs to the target PSF by

$\begin{eqnarray}&&K={\mathrm{FT}}^{-1}\left(\mathrm{FT}({\mathrm{PSF}}_{{\rm{t}}})\times \displaystyle \frac{1}{\mathrm{FT}({\mathrm{PSF}}_{{\rm{i}}})}\right),\end{eqnarray} \tag{ 3 }$

where K, FT, FT⁻¹, PSF_i, and PSF_t stand for the convolution kernel, Fourier transform, inverse Fourier transform, initial PSF, and target PSF, respectively. Finally, we convolve the narrowband and offband images of the seven LABs with the corresponding kernels to obtain PSF-matched images. The PSFs before and after matching are shown in Figure 9.

**Figure 9.** PSFs before (top) and after (bottom) matching. The solid lines with different colors represent different PSFs. Each PSF is extracted from a 500 × 500 arcsec² region around each LAB in each filter. The names of the filters and LABs are indicated in the legend. Because z66-2, z66-3, and z70-1 reside in the same field (COSMOS), we use the same y-band PSF for z66-2, z66-3, and z70-1. The same NB921 PSF is used for z66-2 and z66-3.
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Figure 10 shows the Lyα surface brightness profiles S_Lyα of the seven LABs. To measure the scale lengths of the seven LABs, we perform a two-component (core and halo) fitting that is similar to the one adopted by Leclercq et al. (2017). Specifically, we decompose the surface brightness profiles into core and halo components, following

$\begin{eqnarray}\begin{array}{rcl}{S}_{\mathrm{cont}}(r) & = & \mathrm{PSF}\ast {A}_{1}\exp (-r/{r}_{{\rm{c}}})\,\mathrm{and}\\ {S}_{\mathrm{Ly}\alpha }(r) & = & \mathrm{PSF}\ast [{A}_{2}\exp (-r/{r}_{{\rm{c}}})+{A}_{3}\exp (-r/{r}_{{\rm{h}}})],\end{array}\end{eqnarray} \tag{ 4 }$

where r_c and r_h are the scale lengths of the core and halo components, respectively. The "∗" sign stands for convolution. The A₁, A₂, and A₃ are free parameters. The continuum profile S_cont is extracted from the offband images, while the Lyα profile S_Lyα is measured in the Lyα images. We first fit S_cont with two free parameters A₁ and r_c to measure r_c. Then, we use this r_c value to fit S_Lyα with three free parameters A₂, A₃, and r_h to measure r_h. The errors of S_cont and S_Lyα are considered in the fitting.

Figure 10 shows the best-fit Lyα surface brightness profiles of our LABs. Because there is an offset between the positions of the Lyα and continuum centers of z57-2, we cannot perform the two-component fitting that requires the Lyα and continuum centers to be the same. Instead, we use a one-component exponential function to fit the Lyα profile of z57-2 in the halo region (r ≳ 5 kpc), following

$\begin{eqnarray}&&{S}_{\mathrm{Ly}\alpha }(r)=\mathrm{PSF}\ast [A\exp (-r/{r}_{{\rm{s}}})],\end{eqnarray} \tag{ 5 }$

where the meanings of S_Lyα, PSF, and the "*" sign are the same as in Equation (4). A is a free parameter. The fitting result of z57-2 is shown in Figure 11.

We estimate the uncertainties of the best-fit parameters with the Monte Carlo method. At each radius, we randomly add sky noise to the continuum and Lyα profiles assuming a Gaussian distribution. After adding the sky noise, we fit the exponential function to the new profiles. We repeat this process (adding sky noise and profile fitting) for 100 times. We plot the histograms of the best-fit parameters and calculate the central 68.3% confidence intervals. We use these confidence intervals as the 1σ uncertainties of the best-fit parameters.

We compare the best-fit scale lengths as a function of Lyα luminosities L_Lyα, Lyα rest-frame EW₀, continuum magnitudes M_UV, and redshifts z of the seven LABs with those of LAHs from Leclercq et al. (2017), as shown in Figures 12–14. When calculating the LAB average value, we do not use the best-fit r_h of z57-2 from the one-component exponential function fitting. In Figures 12 and 13, the relations between the scale lengths and galaxy properties including the L_Lyα, EW₀, and M_UV of our LABs are similar to those of MUSE LAHs. This suggests that our LABs and MUSE LAHs have similar connections between the extended Lyα emission and host galaxies, and that our LABs are likely the bright version of MUSE LAHs. We also find that our LABs are consistent with a positive correlation between r_c as a function of M_UV of MUSE LAHs, which is expected from the size evolution discussed in Shibuya et al. (2015, 2019).

**Figure 12.** Halo scale length as a function of Lyα luminosity (top) and Lyα rest-frame EW₀ (bottom) of the seven LABs (stars) and LAHs (filled circles) from Leclercq et al. (2017). The empty star represents z57-2, which does not have a two-component fitting result. The red filled square shows the average value of our LABs, with error bars indicating the rms. The MUSE LAHs at z < 5 and z ≥ 5 are the blue and cyan filled circles, respectively. The average values of the MUSE LAHs are shown as black filled circles. The black horizontal error bar indicates the bin size, while the black vertical error bar is the rms. In the top panel, we slightly shift z49-1 (boxed star) along the horizontal axis by +0.03 to avoid overlaps.
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**Figure 13.** Same as Figure 12, but for the core scale length (top) and halo scale length (bottom) as a function of continuum magnitude.
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**Figure 14.** Halo scale length as a function of redshift. The MUSE LAHs with M_UV ≥ −20 and M_UV < −20 are presented as cyan and blue filled circles, respectively. The meanings of stars and black filled circles are the same as in Figure 12. We use z66-1, z66-2, and z66-3 to calculate the LAB average value at z = 6.6 (red filled square). The objects of z57-2, z66-1, z66-2, and z66-3 are slightly shifted along the horizontal axis by +0.05, −0.1, +0.1, and +0.03 to avoid overlaps, respectively.
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4.2. Large-scale Structure around LABs

To investigate the large-scale structure around our LABs, we calculate the LAE overdensity δ at z = 4.9, 5.7, 6.6, and 7.0 in the same manner as in Harikane et al. (2019). The δ is defined as

$\begin{eqnarray}&&\delta =\displaystyle \frac{n-\bar{n}}{\bar{n}},\end{eqnarray} \tag{ 6 }$

where n and $\bar{n}$ are the number and average number of LAEs in a cylinder, respectively. The radius of the cylinder is ∼10 comoving Mpc (cMpc). This radius is the typical size of protoclusters whose masses grow to ∼10¹⁵ M_⊙ at z = 0 in Chiang et al. (2013). The length of the cylinder is ∼40 cMpc, consistent with the redshift range of LAEs selected by narrow bands. Figure 15 shows the overdensity maps of LAEs at z = 4.9, 5.7, 6.6, and 7.0. The maps are made by smoothing the calculated overdensities with a Gaussian kernel whose standard deviation σ is ∼10 cMpc at z ∼ 6, in the same manner as Harikane et al. (2019). The δ of each LAB is presented in Table 1. Kikuta et al. (2019) show that most of their LABs reside in overdense regions at z ∼ 3. Similarly, we find that all of the seven LABs are located in overdense regions, and six of the seven LABs have large overdensities above the 1σ significance levels.

**Figure 15.** Overdensity maps of LAEs at z = 4.9, 5.7, 6.6, and 7.0. The red diamonds indicate our LABs, while the other LAEs are shown as black dots. The blue shaded regions present the overdensities of LAEs as indicated by the color bars. Dark blue regions have higher overdensities than the light blue regions.
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Figure 16 shows r_h as a function of the δ of our LABs. To test the correlation between r_h and δ, we calculate the Spearman's rank correlation coefficient ρ to be 0.43 with a p-value of 0.34. We do not consider the errors of r_h and δ when calculating the ρ and p-value. Although Matsuda et al. (2012) find a positive correlation between the halo scale length and LAE overdensity of LAEs at z = 3.1, our correlation test suggests that there is no significant correlation between the r_h and δ of our LABs at z = 4.9–7.0.

4.3. AGN Activity

Because the bright Lyα luminosities (>10^43.4 erg s⁻¹) of the seven LABs make them possible hosts of AGNs, we investigate the AGN activities in LABs with X-ray and spectroscopic data. None of the seven LABs have X-ray counterparts in images and catalogs of XMM/Newton and Chandra in the literature (Hasinger et al. 2007; Scoville et al. 2007; Civano et al. 2016; Marchesi et al. 2016). The spectra of the seven LABs do not show N v emission indicative of AGNs.

Shibuya et al. (2018) investigate 21 bright LAEs that are not broad-line AGNs at z = 6–7 and find that the LAEs have Lyα line widths of ∼200–400 km s⁻¹. Consistently, z57-1, z66-1, z66-2, z66-3, and z70-1 also show Lyα line widths of ∼200–400 km s⁻¹ in Figure 8, suggesting that z57-1, z66-1, z66-2, z66-3, and z70-1 are not broad-line AGNs. On the other hand, the Lyα line widths of z49-1 and z57-2 are systematically larger than 400 km s⁻¹. Because z49-1 has a very clear continuum center that z57-2 does not show in Figure 3, it is possible that a hidden AGN is the origin of the relatively large Lyα line width of z49-1. The large Lyα line width of z57-2 is not likely caused by an AGN, but by mergers or dense neutral hydrogen gas in the H i region.

In Section 3, we show that z49-1 has a C iv emission line with a line width of 317 ± 132 km s⁻¹. The rest-frame EW₀ of the C iv emission is 8.3 ± 1.5 Å. The spectrum shows no He ii emission above the 2σ detection limit. We use the 2σ detection limit as an upper limit of the He ii flux and find that the lower limit of the C iv to He ii ratio is ∼1.2. We compare the C iv rest-frame EW₀ and C iv to He ii ratio with the AGN and SFG models in Nakajima et al. (2018), and find that z49-1 is consistent with both the AGN and low-metallicity SFG models (Figure 17). This result indicates that z49-1 is a candidate of a high-z AGN, although the possibility of a low-metallicity SFG cannot be ruled out.

**Figure 17.** C iv EW₀ as a function of C iv/He ii ratio. The object z49-1 is represented as a red filled circle. We show two AGN models with power-law indices of α = −2.0 (dotted line) and −1.2 (dashed line), and two SFG models of POPSTAR (solid line) and BPASS (dashed–dotted line) from Nakajima et al. (2018). The ionization parameters log U of the AGN and SFG models are −2.5 (yellow), −2.0 (green), −1.5 (cyan), −1.0 (sky blue), and −0.5 (blue). The black dashed line represents the threshold that distinguishes between AGNs and SFGs.
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As we discussed in Section 1, AGNs have been identified in all of the LAEs with bright Lyα luminosities (log $({L}_{\mathrm{Ly}\alpha }/[\mathrm{erg}\ {{\rm{s}}}^{-1}])\gtrsim 43.4$ ) at z ∼ 2−3 in Konno et al. (2016) and Sobral et al. (2018). Similarly, Overzier et al. (2013) show that at least 63% of LABs at z ∼ 2−3 are associated with luminous AGNs. On the other hand, no AGN has been confirmed to exist in LABs at z ≳ 5, including our LABs. This may suggest that typical LABs at z ≳ 5 are less likely to be powered by luminous AGNs than LABs at z ∼ 2−3.

4.4. Stellar Population

We perform spectral energy distribution (SED) fitting on z49-1 and z70-1 using total magnitudes measured in Subaru HSC (g, r, i, z, y, NB816, and NB921), UltraVista (Y, J, H, and K), and Spitzer/IRAC (3.6 and 4.5 μm bands) images. In our SED fitting, we consider the contributions from both nebular and stellar populations. The nebular spectra (emission lines and continua) are calculated basically following Schaerer & de Barros (2009). We use the stellar population synthesis model GALAXEV (Bruzual & Charlot 2003) with Salpeter's initial mass function (Salpeter 1955) to obtain stellar SEDs. A constant star formation history is assumed. Details of our SED fitting method are described in Ono et al. (2010). Because the 3.6 μm band is contaminated by Hα emission at z = 4.9, we do not use the photometry of the 3.6 μm band in our SED fitting of z49-1. The best-fit SEDs of z49-1 and z70-1 are shown in Figure 18. The properties of the best-fit SEDs are summarized in Table 3.

**Figure 18.** SEDs of the best-fit models of z49-1 (top) and z70-1 (bottom). The SED models are presented by the red solid curves. The black filled circles are total magnitudes measured in the g, r, i, z, y, NB816, NB921, Y, J, H, K, 3.6, and 4.5 μm bands. The black open circle indicates the 3.6 μm band photometry that we do not use in the SED fitting of z49-1. The horizontal error bars represent the filter bandwidths. The vertical error bars show the 1σ errors in magnitude. The arrows indicate 3σ upper limits.
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Table 3. Properties of the Best-fit SEDs

ID	Z	$\mathrm{log}{M}_{* }$	$E{(B-V)}_{* }$	$\mathrm{log}(\mathrm{Age})$	$\mathrm{log}(\mathrm{SFR})$
	(Z_⊙)	(M_⊙)	(mag)	(yr)	(M_⊙ yr⁻¹)
z49-1	0.004	${9.0}_{-0.1}^{+0.2}$	0.05	${6.6}_{-1.5}^{+0.5}$	${2.4}_{-0.3}^{+1.4}$
z66-1^a	0.2	${10.18}_{-0.07}^{+0.05}$	0.15	${8.26}_{-0.05}^{+0.05}$	${2.00}_{-0.01}^{+0.01}$
z66-2^b	0.005–0.2	∼10.3	0.0-0.5	∼8.8	∼1.4
z70-1	0.02	$\lt 9.1$	0.10	$\lt 7.7$	${2.0}_{-0.8}^{+1.8}$

Notes.

^aBest-fit SED from Ouchi et al. (2013). ^bBest-fit SED from Sobral et al. (2015).

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4.5. Hα Emission of z49-1

The 3.6 μm image of z49-1 in Figure 4 shows a clear color excess that is caused by the redshifted Hα. Comparing with the best-fit SED obtained in Section 4.4, we measure the observed 3.6 μm excess that corresponds to a Hα luminosity of $(3.6\pm 1.2)\times {10}^{43}$ erg s⁻¹. Assuming case-B recombination and no dust extinction suggested by the best-fit SED, we estimate the expected Lyα luminosity to be $(3.2\pm 1.1)\,\times {10}^{44}$ erg s⁻¹. The Lyα escape fraction is the observed Lyα luminosity divided by the expected Lyα luminosity, (3.5 × 10⁴³)/(3.2 × 10⁴⁴) = 0.11 ± 0.04.

5. Discussion

5.1. Identification of the Most Distant LAB at z = 7.0

In this study, we have identified the most distant LAB found to date, z70-1 at z = 7.0. The composite pseudocolor image of z70-1 is presented in Figure 19, left. Figure 20 shows the Lyα and continuum profiles of z70-1. To test whether the Lyα profile of z70-1 is more extended than the continuum profile, we fit the exponential function shown in Equation (5) to the Lyα and continuum profiles. In the fitting, the errors of the profiles are considered. The best-fit scale lengths of the Lyα and continuum profiles are 1.43 ± 0.18 and 0.56 ± 0.41 kpc, respectively. We estimate the statistical significance of the difference between the scale lengths of the Lyα and continuum profiles assuming a normal distribution. We find that the Lyα and continuum profiles are different at the 87% confidence level. This suggests that the Lyα emission of z70-1 is more extended than the continuum. Taken together with the identification of the Lyα emission line on the spectrum and the bright Lyα luminosity of z70-1, our result suggests that z70-1 is a real LAB at z = 7.0.

farcs — **Figure 19.** Composite pseudocolor images of z70-1 (left) and z57-2 (right). The upper object in the left panel is a foreground source. The RGB colors of z70-1 are presented by the 3.6 μm, y, and NB973 images, respectively. For z57-2, the RGB colors correspond to the y, z, and NB816 images, respectively. Because z57-2 does not show a clear center in the NB816 image, we smooth the y, z, and NB816 images of z57-2 with a Gaussian kernel whose sigma value is 017 before we make the pseudocolor image. The size of the images is 5'' × 5''. The length of 1'' is indicated as a white bar.
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**Figure 20.** Lyα (black) and continuum (green) surface brightness profiles of z70-1. The filled circles are the profiles measured from images. The solid lines present the best-fit exponential functions. The shaded regions indicate the errors of the best-fit functions. We normalize all the profiles at the radius of ∼0.5 kpc for comparison. To avoid overlaps, the continuum profile is slightly shifted along the horizontal axis by +0.15.
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5.2. An Extremely Extended LAB at z = 5.7

The NB816 image of z57-2 in Figure 3 suggests that z57-2 has very extended Lyα emission presenting no clear center, which is apparently different from the other six LABs. The composite pseudocolor image of z57-2 is shown in Figure 19, right. Figure 21 displays the Lyα surface brightness profile of z57-2, together with the other six LABs and two model galaxies of Halo-11 and Halo-12 (Yajima et al. 2017; Arata et al. 2019) at z ∼ 6. Cosmological hydrodynamic and radiative transfer simulations produce Halo-11 and Halo-12, which have halo masses of 1.6 × 10¹¹ and 7.5 × 10¹¹M_⊙, respectively. As suggested by Behroozi et al. (2013), the halo masses of Halo-11 and Halo-12 correspond to stellar masses of ∼2.0 × 10⁹ and 1.4 × 10¹⁰M_⊙ at z = 6.0, respectively, which are consistent with the stellar masses of our LABs estimated by the SED fitting (Section 4.4). In Figure 21, it is clear that z57-2 has a more extended Lyα profile than the other six LABs. Moreover, model galaxies of Halo-11 and Halo-12 cannot explain the extremely extended Lyα profile of z57-2.

**Figure 21.** Lyα surface brightness profiles of z57-2 (red filled circles), the other six LABs (black filled circles), and two model galaxies of Halo-11 (green dashed–dotted line) and Halo-12 (blue dashed line). The black solid lines are the best-fit total models of the six other LABs in Figure 10. The cyan dotted line represents the PSF. The profiles of Halo-11 and Halo-12 are convolved with the PSF. All of the profiles are normalized at the radius of ∼0 kpc for comparison.
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The spectrum in Figure 6 shows that z57-2 has a Lyα emission line with an FWHM of ∼600 km s⁻¹ that is broader than those of the other six LABs. It should be also noted that the Lyα line of z57-2 shows multiple peaks. These features may be caused by dynamical systems, such as multiple components or mergers. Another possibility is that z57-2 has a nearly static cloud of thick H i gas that resonantly scatters Lyα photons produced at the center of this system. The static cloud should have varying H i column densities that cause the positional dependence of the Lyα line center and line width found in Figure 8.

5.3. Physical Origin of the Extended Lyα Emission of LABs

Previous studies have suggested several physical origins of the extended Lyα emission around a galaxy, including scenarios of photoionization, Lyα resonant scattering, cooling radiation, outflows, and satellite galaxies. We discuss these scenarios separately below.

Mas-Ribas & Dijkstra (2016) suggest that fluorescence can generate Lyα photons that account for extended Lyα emission around LAEs at z = 3.1. As for LABs, fluorescence is very likely to happen because of the large abundance of ionizing photons expected from the bright M_UV, especially for LABs hosting AGNs. Indeed, Prescott et al. (2015) suggest that the extended Lyα emission of an LAB at z ∼ 3 is likely powered by an AGN. Similarly, Geach et al. (2009) and Overzier et al. (2013) argue that fluorescence alone can explain the luminous and extended Lyα emission of LABs hosting AGNs at z ∼ 2−3. Because our LABs have bright M_UV and possible AGN activities, fluorescence may be the origin of the extended Lyα emission.

In the scenario of Lyα resonant scattering, the Lyα photons are emitted by the galaxy center. With the detection of polarized Lyα emission around an LAB at z = 3.1, Hayes et al. (2011) suggest that the surrounding Lyα emission is caused by resonant scattering of Lyα photons from the galaxy center. As for our LABs, although our LABs have very high Lyα luminosities, the Lyα EW₀ are ∼50–200 Å, comparable to the Lyα EW₀ from dust-free star formation estimated in Charlot & Fall (1993). This suggests that the extended Lyα emission may be explained by resonantly scattered Lyα photons generated in the SFG center.

Gravitational cooling radiation may also play an important role in generating an extended Lyα emission. Using Lyα radiative transfer models of LAEs with a mean stellar mass of 2.9 × 10¹⁰ M_⊙ at z = 3.1, Lake et al. (2015) show that cooling radiation can contribute 40%–55% of the total Lyα luminosity within a virial radius of 56 kpc. Observationally, Martin et al. (2015) show that the extended filamentary Lyα emission around a quasi-stellar object at z = 2.3 is likely explained by cooling radiation. On the other hand, if cooling radiation is the major origin of the extended Lyα emission, the Lyα EW₀ would likely be greater than 240 Å, which is the maximum EW₀ predicted by stellar models (Charlot & Fall 1993). Although the Lyα EW₀ of our LABs are smaller than 240 Å, it should be noted that the Lyα escape fractions of our LABs might be low. For example, z49-1 has a Lyα escape fraction of 0.11 as we discussed in Section 4.4. Because the low Lyα EW₀ of our LABs may be caused by low Lyα escape fractions, we cannot rule out the possibility that cooling radiation is the origin of the extended Lyα emission.

Using an analytical model and a high-resolution hydrodynamic simulation, respectively, Taniguchi & Shioya (2000) and Mori et al. (2004) argue that outflows driven by multiple supernova explosions are able to produce extended Lyα emission with a Lyα luminosity of ∼10⁴³ erg s⁻¹. The outflows have also been suggested by an observed Lyα absorber that can be explained by a foreground hydrogen shell ejected by an LAB at z = 3.1 (Wilman et al. 2005). It should be noted that our LABs show similar Lyα luminosities of ∼10⁴³ erg s⁻¹ and that our LABs may have starbursts driven by possible mergers, as suggested by the multiple UV components in Figure 3. Multiple supernova explosions are likely to happen in starbursts and drive outflows that produce the luminous and extended Lyα emission of our LABs.

In Figure 3, the HST images of z49-1, z66-1, and z66-2 clearly show multiple UV continuum components. It is likely that having multiple UV continuum components is a common feature of high-z LABs (see also Prescott et al. 2012; Francis et al. 2013). The multiple components may correspond to multiple star-forming clumps in one galaxy, mergers, or satellite galaxies. It is possible that satellite galaxies are responsible for the large continuum size of LABs. On the other hand, if the satellite galaxies are the major contributors to the extended Lyα emission, one would expect that the Lyα and continuum profiles have similar shapes even if the satellite galaxies are not resolved. In Figure 10, it should be noted that the core component has the same shape as the continuum profile, and that the Lyα profile cannot be explained by the single core component. However, the difference between the Lyα and continuum profiles may be caused by satellite galaxies with high Lyα EW₀, such as the faint LAEs at z = 2.9–6.7 found in Maseda et al. (2018). It is possible that satellite galaxies with high Lyα EW₀ are the origin of the extended Lyα emission around LABs.

In conclusion, all of the five scenarios of fluorescence, resonant scattering, gravitational cooling radiation, outflows, and satellite galaxies may contribute to the extended Lyα emission around LABs.

6. Summary

In this study, we investigate the photometric and spectroscopic properties of seven LABs: two LABs at z = 4.888 (z49-1) and z = 6.965 (z70-1) identified by us, and five previously known LABs at z = 5.7–6.6 (z57-1, z57-2, z66-1, z66-2, and z66-3). Our results are summarized below.

1.
We find that z70-1 has extended Lyα emission with a scale length of 1.4 ± 0.2 kpc that is about three times larger than the UV continuum. The object of z70-1 is the most distant LAB identified to date.
2.
We show that z57-2 has Lyα emission that is much more extended than the other six LABs. The origin of the extremely extended Lyα emission of z57-2 is unclear and cannot be explained by cosmological hydrodynamic and radiative transfer simulations.
3.
We measure the core and halo scale lengths of the Lyα profiles of our LABs and show that the relations between the scale lengths and galaxy properties including the L_Lyα, EW₀, and M_UV of our LABs are similar to those of MUSE LAHs. This suggests that our LABs and MUSE LAHs have similar connections between the extended Lyα emission and host galaxies, and that our LABs are likely the bright version of high-z LAHs.
4.
We investigate the large-scale structure around our LABs by measuring the LAE overdensity. We find that all of the seven LABs are located in overdense regions, and six of the seven LABs have large overdensities above the 1σ significance levels. Our LABs show no significant correlation between the halo scale length and LAE overdensity.
5.
The seven LABs except z49-1 exhibit no AGN signatures such as X-ray emission, N v λ1240, or Lyα line broadening. The object of z49-1 has a strong C iv λ1548 emission line that suggests an AGN. We compare the C iv EW₀ and C iv/He ii ratio of z49-1 with the AGN and SFG models in Nakajima et al. (2018) and find that z49-1 is an AGN candidate, although the possibility of a young and low-metallicity SFG cannot be eliminated.
6.
We find that all the Lyα emission lines of the seven LABs show velocity gradients on the spectra. The Lyα velocity gradients and line widths of z49-1 and z57-2 are larger than those of the other five LABs, which may be caused by an AGN (not likely for z57-2), mergers, or dense neutral hydrogen gas in the H i region.
7.
We discuss the physical origin of the extended Lyα emission around our LABs. Fluorescence, resonant scattering, gravitational cooling radiation, outflows, and satellite galaxies can contribute to the extended Lyα emission.

The Hyper Suprime-Cam (HSC) collaboration includes the astronomical communities of Japan and Taiwan, and Princeton University. The HSC instrumentation and software were developed by the National Astronomical Observatory of Japan (NAOJ), the Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU), the University of Tokyo, the High Energy Accelerator Research Organization (KEK), the Academia Sinica Institute for Astronomy and Astrophysics in Taiwan (ASIAA), and Princeton University. Funding was contributed by the FIRST program from the Japanese Cabinet Office, the Ministry of Education, Culture, Sports, Science and Technology (MEXT), the Japan Society for the Promotion of Science (JSPS), Japan Science and Technology Agency (JST), the Toray Science Foundation, NAOJ, Kavli IPMU, KEK, ASIAA, and Princeton University.

This paper makes use of software developed for the Large Synoptic Survey Telescope. We thank the LSST Project for making their code available as free software at http://dm.lsst.org

The Pan-STARRS1 Surveys (PS1) have been made possible through contributions of the Institute for Astronomy, the University of Hawaii, the Pan-STARRS Project Office, the Max-Planck Society and its participating institutes, the Max Planck Institute for Astronomy, Heidelberg, and the Max Planck Institute for Extraterrestrial Physics, Garching, The Johns Hopkins University, Durham University, the University of Edinburgh, Queens University Belfast, the Harvard-Smithsonian Center for Astrophysics, the Las Cumbres Observatory Global Telescope Network Incorporated, the National Central University of Taiwan, the Space Telescope Science Institute, the National Aeronautics and Space Administration under grant No. NNX08AR22G issued through the Planetary Science Division of the NASA Science Mission Directorate, the National Science Foundation under grant No. AST-1238877, the University of Maryland, and Eötvös Lorand University (ELTE), and the Los Alamos National Laboratory.

Based in part on data collected at the Subaru Telescope and retrieved from the HSC data archive system, which is operated by the Subaru Telescope and Astronomy Data Center at the National Astronomical Observatory of Japan.

The NB718 and NB816 filters were supported by Ehime University (PI: Y. Taniguchi). The NB921 and NB973 filters were supported by KAKENHI (23244025) Grant-in-Aid for Scientific Research (A) through the Japan Society for the Promotion of Science (PI: M. Ouchi).

Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.

This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

This work is supported by World Premier International Research Center Initiative (WPI Initiative), MEXT, Japan, and KAKENHI (15H02064, 17H01110, 17H01114, 17H04827, and 18H04570) Grant-in-Aid for Scientific Research (A) through Japan Society for the Promotion of Science.

CHORUS. III. Photometric and Spectroscopic Properties of Lyα Blobs at z = 4.9–7.0

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Abstract

1. Introduction

2. Observations, Data, and LAB Identification