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Register a new userSILVERRUSH. XI. Intensity Mapping for Lya Emission Extending over $100-1000$ comoving kpc around $zsim2-7$ LAEs with Subaru HSC-SSP and CHORUS Data
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Added by
Shotaro Kikuchihara
Publication date
2021
fields
Physics
and research's language is
English
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We conduct intensity mapping to probe for extended diffuse Ly$alpha$ emission around Ly$alpha$ emitters (LAEs) at $zsim2-7$, exploiting very deep ($sim26$ mag at $5sigma$) and large-area ($sim4.5$ deg$^2$) Subaru/Hyper Suprime-Cam narrow-band (NB) images and large LAE catalogs consisting of a total of 1781 LAEs at $z=2.2$, $3.3$, $5.7$, and $6.6$ obtained by the HSC-SSP SILVERRUSH and CHORUS projects. We calculate the spatial correlations of these LAEs with $sim1-2$ billion pixel flux values of the NB images, deriving the average Ly$alpha$ surface brightness (${rm SB_{Lyalpha}}$) radial profiles around the LAEs. By carefully estimating systematics such as fluctuations of sky background and point spread functions, we detect diffuse Ly$alpha$ emission ($sim10^{-20}-10^{-19}$ erg s$^{-1}$ cm$^{-2}$ arcsec$^{-2}$) at $100-1000$ comoving kpc around $z=3.3$ LAEs at the $4.1sigma$ level and tentatively ($sim2sigma$) at the other redshifts, beyond the virial radius of a dark-matter halo with a mass of $10^{11} M_odot$. While the observed ${rm SB_{Lyalpha}}$ profiles have similar amplitudes at $z=2.2-6.6$ within the uncertainties, the intrinsic ${rm SB_{Lyalpha}}$ profiles (corrected for the cosmological dimming effect) increase toward high redshifts. This trend may be explained by increasing hydrogen gas density due to the evolution of the cosmic volume. Comparisons with theoretical models suggest that extended Ly$alpha$ emission around a LAE is powered by resonantly scattered Ly$alpha$ photons in the CGM and IGM that originates from the inner part of the LAE, and/or neighboring galaxies around the LAE.
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We investigate Lya, [OIII]5007, Ha, and [CII]158um emission from 1124 galaxies at z=4.9-7.0. Our sample is composed of 1092 Lya emitters (LAEs) at z=4.9, 5.7, 6.6, and 7.0 identified by Subaru/Hyper Suprime-Cam (HSC) narrowband surveys covered by Spitzer large area survey with Subaru/HSC (SPLASH) and 34 galaxies at z=5.148-7.508 with deep ALMA [CII]158um data in the literature. Fluxes of strong rest-frame optical lines of [OIII] and Ha (Hb) are constrained by significant excesses found in the SPLASH 3.6 and 4.5um photometry. At z=4.9, we find that the rest-frame Ha equivalent width and the Lya escape fraction f_Lya positively correlate with the rest-frame Lya equivalent width EW^0_Lya. The f_Lya-EW^0_Lya correlation is similarly found at z~0-2, suggesting no evolution of the correlation over z~0-5. The typical ionizing photon production efficiency of LAEs is logxi_ion/[Hz erg^-1]~25.5 significantly (60-100%) higher than those of LBGs at a given UV magnitude. At z=5.7-7.0, there exists an interesting turn-over trend that the [OIII]/Ha flux ratio increases in EW^0_Lya~0-30 A, and then decreases out to EW^0_Lya~130 A. We also identify an anti-correlation between a [CII] luminosity to star-formation rate ratio (L_[CII]/SFR) and EW^0_Lya at the >99% confidence level. We carefully investigate physical origins of the correlations with stellar-synthesis and photoionization models, and find that a simple anti-correlation between EW_Lya^0 and metallicity explains self-consistently all of the correlations of Lya, Ha, [OIII]/Ha, and [CII] identified in our study, indicating detections of metal-poor (~0.03 Zo) galaxies with EW^0_Lya~200 A.
We present results of the cross-correlation Ly$alpha$ intensity mapping with Subaru/Hyper Suprime-Cam (HSC) ultra-deep narrowband images and Ly$alpha$ emitters (LAEs) at $z=5.7$ and $6.6$ in a total area of $4$ deg$^2$. Although overwhelming amount of data quality controls have been performed for the narrowband images, we further conduct extensive analysis evaluating systematics of large-scale point-spread-function wings, sky subtractions, and unknown errors based on physically uncorrelated signals and sources found in real HSC images and object catalogs, respectively. Removing the systematics, we carefully calculate cross-correlations between Ly$alpha$ intensity of the narrowband images and the LAEs. We tentatively identify very diffuse Ly$alpha$ emission with the $simeq 3sigma$ ($simeq 2sigma$) significance at $gtrsim$ 100 comoving kpc (ckpc) far from the LAEs at $z=5.7$ ($6.6$), around and probably even beyond a virial radius of star-forming galaxies with $M_mathrm{h}sim10^{11}M_odot$. The diffuse Ly$alpha$ emission possibly extends up to $1$,$000$ ckpc with the surface brightness of $10^{-20}$-$10^{-19}$ erg s$^{-1}$ cm$^{-2}$ arcsec$^{-2}$. We confirm that the small-scale ($<150$ ckpc) Ly$alpha$ radial profiles of LAEs are consistent with those obtained by recent MUSE observations. Comparisons with numerical simulations suggest that the large-scale ($sim150$-$1$,$000$ ckpc) Ly$alpha$ emission are not explained by unresolved faint neighboring galaxies including satellites, but by a combination of Ly$alpha$ photons emitted from the central LAE and other unknown sources, such as cold-gas streams and galactic outflow. We find no evolution in the Ly$alpha$ radial profiles of our LAEs from $z=5.7$ to $6.6$, where theoretical models predict a flattening of the profile slope made by cosmic reionization, albeit with our moderately large observational errors.
We present a new catalog of $9318$ Ly$alpha$ emitter (LAE) candidates at $z = 2.2$, $3.3$, $4.9$, $5.7$, $6.6$, and $7.0$ that are photometrically selected by the SILVERRUSH program with a machine learning technique from large area (up to $25.0$ deg$^2$) imaging data with six narrowband filters taken by the Subaru Strategic Program with Hyper Suprime-Cam (HSC SSP) and a Subaru intensive program, Cosmic HydrOgen Reionization Unveiled with Subaru (CHORUS). We construct a convolutional neural network that distinguishes between real LAEs and contaminants with a completeness of $94$% and a contamination rate of $1$%, enabling us to efficiently remove contaminants from the photometrically selected LAE candidates. We confirm that our LAE catalogs include $177$ LAEs that have been spectroscopically identified in our SILVERRUSH programs and previous studies, ensuring the validity of our machine learning selection. In addition, we find that the object-matching rates between our LAE catalogs and our previous results are $simeq 80$-$100$% at bright NB magnitudes of $lesssim 24$ mag. We also confirm that the surface number densities of our LAE candidates are consistent with previous results. Our LAE catalogs will be made public on our project webpage.
We present the SILVERRUSH program strategy and clustering properties investigated with $sim 2,000$ Ly$alpha$ emitters at $z=5.7$ and $6.6$ found in the early data of the Hyper Suprime-Cam (HSC) Subaru Strategic Program survey exploiting the carefully designed narrowband filters. We derive angular correlation functions with the unprecedentedly large samples of LAEs at $z=6-7$ over the large total area of $14-21$ deg$^2$ corresponding to $0.3-0.5$ comoving Gpc$^2$. We obtain the average large-scale bias values of $b_{rm avg}=4.1pm 0.2$ ($4.5pm 0.6$) at $z=5.7$ ($z=6.6$) for $gtrsim L^*$ LAEs, indicating the weak evolution of LAE clustering from $z=5.7$ to $6.6$. We compare the LAE clustering results with two independent theoretical models that suggest an increase of an LAE clustering signal by the patchy ionized bubbles at the epoch of reionization (EoR), and estimate the neutral hydrogen fraction to be $x_{rm HI}=0.15^{+0.15}_{-0.15}$ at $z=6.6$. Based on the halo occupation distribution models, we find that the $gtrsim L^*$ LAEs are hosted by the dark-matter halos with the average mass of $log (left < M_{rm h} right >/M_odot) =11.1^{+0.2}_{-0.4}$ ($10.8^{+0.3}_{-0.5}$) at $z=5.7$ ($6.6$) with a Ly$alpha$ duty cycle of 1 % or less, where the results of $z=6.6$ LAEs may be slightly biased, due to the increase of the clustering signal at the EoR. Our clustering analysis reveals the low-mass nature of $gtrsim L^*$ LAEs at $z=6-7$, and that these LAEs probably evolve into massive super-$L^*$ galaxies in the present-day universe.
We present proper motion measurements for more than $0.55$ million main-sequence stars, by comparing astrometric positions of matched stars between the multi-band imaging datasets from the Hyper Suprime-Cam (HSC) Survey and the SDSS Stripe 82. In doing this we use $3$ million galaxies to recalibrate the astrometry and set up a common reference frame between the two catalogues. The exquisite depth and the nearly $12$ years of time baseline between HSC and SDSS enable high-precision measurements of statistical proper motions for stars down to $isimeq 24$. A validation of our method is demonstrated by the agreement with the $Gaia$ proper motions, to the precision better than $0.1$ mas yr$^{-1}$. To retain the precision, we make a correction of the subtle effects due to the differential chromatic refraction in the SDSS images based on the comparison with the $Gaia$ proper motions against colour of stars, which is validated using the SDSS spectroscopic quasars. Combining with the photometric distance estimates for individual stars based on the precise HSC photometry, we show a significant detection of the net proper motions for stars in each bin of distance out to $100$ kpc. The two-component tangential velocities after subtracting the apparent motions due to our own motion display rich phase-space structures including a clear signature of the Sagittarius stream in the halo region of distance range $[10, 35]$ kpc. We also measure the tangential velocity dispersion in the distance range $5-20$ kpc and find that the data are consistent with a constant isotropic dispersion of $80pm 10 {rm km/s}$. More distant stars appear to have random motions with respect to the Galactic centre on average.
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