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We present a statistical study of velocities of Lya, interstellar (IS)
absorption, and nebular lines and gas covering fraction for Lya emitters (LAEs)
at z~2. We make a sample of 22 LAEs with a large Lya equivalent width (EW) of >
50A based on our deep Keck/LRIS observations, in conjunction with spectroscopic
data from the Subaru/FMOS program and t...
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Context 1
... parameter a asym After correcting for the heliocentric motion of Earth for the redshifts of Lyα and nebular lines 11 , we cal- culate ∆v Lyα following Equation 1. Table 2 lists the z Lyα , z sys , and ∆v Lyα for the 26 Lyα-detected objects observed with LRIS. Figure 4 present Lyα spectra as a function of velocity for LAEs with detections of nebu- lar emission lines. In Table 3, we also list these quanti- ties of the four LAEs with detections of Lyα and neb- ular lines obtained by previous Magellan/IMACS ob- servations ( Nakajima et al. 2012). Almost all objects observed with LRIS have a ∆v Lyα of ∼ 200 km s −1 which is consistent with values in previous studies (e.g., Hashimoto et al. 2013). ...
Citations
... In the following, we will compare MUSE-selected LAEs to, mostly, Lyman-break-selected samples. It is known that LAEs may be the extreme end of the LBG population (e.g., Dijkstra & Wyithe 2012;Morales et al. 2021), undergoing very recent star formation, and are more likely to be low mass, less dusty, and show lower Lyα velocity offsets than Lyman-break-selected samples (e.g., Hashimoto et al. 2013;Shibuya et al. 2014). ...
... In the following section we present our results and look for evidence of trends that can explain the mechanisms behind the shift of Lyα emission from the systemic redshift. As described above, our sample is not magnitude complete so our comparison to the literature is qualitative and the sample selection is different from literature samples which are LBG selected (and we expect LAEs to be typically lower mass and less dusty than LBGs; e.g., Kornei et al. 2010;Shibuya et al. 2014). Nevertheless, we find our sample is representative of z ∼ 6 UV-faint LBGs, of interest during reionization. ...
... The shift of Lyα photons to wavelengths redward and/or blueward of the central wavelength is due to resonant scattering with neutral hydrogen in the ISM and absorption by dust (e.g., Neufeld 1991;Verhamme et al. 2006). The amplitude of the velocity shift will be linked to the number of scattering events, which is set by the column density of neutral gas, N HI (e.g., Neufeld 1990;Verhamme et al. 2006;Hashimoto et al. 2015;Henry et al. 2015;Kakiichi & Gronke 2021), its covering fraction (e.g., Shibuya et al. 2014;Jaskot et al. 2019), and the velocity of H I gas and any outflows (e.g., Pettini et al. 2001;Shapley et al. 2003). ...
Ly α emission from galaxies can be used to trace neutral hydrogen in the epoch of reionization, however, there is a degeneracy between the attenuation of Ly α in the intergalactic medium (IGM) and the line profile emitted by the galaxy. Large shifts of Ly α redward of systemic due to scattering in the interstellar medium can boost Ly α transmission in the IGM during reionization. The relationship between the Ly α velocity offset from systemic and other galaxy properties is not well established at high redshift or low luminosities, due to the difficulty of observing emission lines which trace the systemic redshift. Rest-frame optical spectroscopy with JWST/NIRSpec has opened a new window into understanding Ly α at z > 3. We present a sample of 12 UV-faint galaxies (−20 ≲ M UV ≲ −16) at 3 ≲ z ≲ 6, with Ly α velocity offsets, Δ v Ly α , measured from the Very Large Telescope/MUSE and JWST/NIRSpec from the GLASS-JWST Early Release Program. We find a median Δ v Ly α of 205 km s ⁻¹ and standard deviation of 75 km s ⁻¹ , compared to 320 and 170 km s ⁻¹ , respectively, for M UV < −20 galaxies in the literature. Our new sample demonstrates the previously observed trend of decreasing Ly α velocity offset with decreasing UV luminosity and optical line velocity dispersion, which extends to M UV ≳ −20, consistent with a picture where the Ly α profile is shaped by gas close to the systemic redshift. Our results imply that during reionization Ly α from UV-faint galaxies will be preferentially attenuated, but that detecting Ly α with low Δ v Ly α can be an indicator of large ionized bubbles.
... In an early phase of the galactic evolution, the strongest emission in the pan-galactic light is Lyman-a (Lya) line, an emission peaked at 10.2 eV due to a relaxation from the first excited state to the ground state of a hydrogen atom. This early phase is categorized as Lya emitters (LAEs) (Shibuya et al., 2014). ...
... To complete our analysis, we calculated the convolutions of the derived %ee CD spectra with an LAE spectrum to verify the generation of %ee by CP-Lya (Fig. 3). To this aim, ee employed a spectrum composed of eight LAEs at a redshift near the value z = 2.2 of the luminosity z, as a typical average spectrum of LAEs (Shibuya et al., 2014). The background continuum component (hm < 10.17 eV and hm > 10.23 eV) far from the intense LAE peak at 10.19 eV (121.66 nm) were not integrated since the diffuse background continuum is ex-pected to be nonpolarized. ...
The enantiomeric excess (ee) of l-form amino acids found in the Murchison meteorite poses some issues about the cosmic origin of their chirality. Circular dichroism (CD) spectra of amino acids in the far-ultraviolet (FUV) at around 6.8 eV (182 nm) indicate that the circularly polarized light can induce ee through photochemical reactions. Here, we resort to ab initio calculations to extract the CD spectra up to the vacuum-ultraviolet (VUV) region (∼11 eV), and we propose a novel equation to compute the ee applicable to a wider range of light frequency than what is available to date. This allows us to show that the strength of the induced ee (|ee|) in the 10 eV VUV region is comparable to the one in the 6.8 eV FUV region. This feature is common for some key amino acids (alanine, 2-aminobutyric acid, and valine). In space, intense Lyman-α (Lyα) light of 10.2 eV is emitted from star forming regions. This study provides a theoretical basis that Lyα emitter from an early starburst in the Milky Way plays a crucial role in initiating the ee of amino acids.
... The asymmetric line width σ is further defined as σ = a(v − v 0 ) + d, where a and d describe the asymmetry and width of the profile respectively. A single asymmetric Gaussian has been previously used to fit Lyα profiles at high redshift by Shibuya et al. (2014), Leclercq et al. (2020); here, we introduce separate components for the blue and red parts of the lines, given the strong double-peaked nature of our sources. Double asymmetric Gaussian fits to the spatially integrated Lyα spectra are shown in Figure 1, demonstrating that they generally provide an excellent representation of the line profile. ...
The resonantly scattered Ly α line illuminates the extended halos of neutral hydrogen in the circumgalactic medium of galaxies. We present integral field Keck Cosmic Web Imager observations of double-peaked, spatially extended Ly α emission in 12 relatively low-mass ( M ⋆ ∼ 10 ⁹ M ⊙ ) z ∼ 2 galaxies characterized by extreme nebular emission lines. Using individual spaxels and small bins as well as radially binned profiles of larger regions, we find that for most objects in the sample the Ly α blue-to-red peak ratio increases, the peak separation decreases, and the fraction of flux emerging at line center increases with radius. We use new radiative transfer simulations to model each galaxy with a clumpy, multiphase outflow with radially varying outflow velocity, and self-consistently apply the same velocity model to the low-ionization interstellar absorption lines. These models reproduce the trends of peak ratio, peak separation, and trough depth with radius, and broadly reconcile outflow velocities inferred from Ly α and absorption lines. The galaxies in our sample are well-described by a model in which neutral, outflowing clumps are embedded in a hotter, more highly ionized inter-clump medium (ICM), whose residual neutral content produces absorption at the systemic redshift. The peak ratio, peak separation, and trough flux fraction are primarily governed by the line-of-sight component of the outflow velocity, the H i column density, and the residual neutral density in the ICM respectively. The azimuthal asymmetries in the line profile further suggest nonradial gas motions at large radii and variations in the H i column density in the outer halos.
... It is well known that the Ly α emission peak is generally redshifted by a few hundred of km s −1 with respect to the systemic redshift of a galaxy (see Shibuya et al. 2014 ;Verhamme et al. 2018 ). The Ly α peak redshifts of the 96 LAEs are corrected using the empirical relation V offset = 0.89 × FWHM − 58 km s −1 obtained in Muzahid et al. ( 2020 ) for our sample, where V offset is the velocity offset between the Ly α emission peak and the systemic redshift and FWHM is the full width at half-maximum of the Ly α line. ...
We present a detailed study of the column density and covering fraction profiles of C iv absorption around 86 redshift z ≈ 3.3 Lyα emitters (LAEs) detected in 8 Multi-Unit Spectroscopic Explorer (MUSE) fields of 1′ × 1′ centered on 8 bright background quasars as part of the MUSEQuBES survey. Using Voigt profile fitting of all the C iv absorbers detected along these 8 sightlines, we generated a “blind” absorber catalog consisting of 489 C iv absorption components. We cross-matched this blind C iv catalog with the MUSE-detected LAE catalog and found a significant enhancement of C iv components within ≈±400 $\rm km\, s^{-1}$ of the systemic redshifts of the LAEs. Neither the C iv column density (N) nor the Doppler parameter (b) of individual C iv components shows any significant anti-correlation with impact parameter (ρ) of the LAEs in the 68 percentile range of 90 ≤ ρ ≤ 230 physical kpc (pkpc). We find a covering fraction of ≈60% for a threshold $N({{\rm C\,{\small IV}}})$ of 1012.5 cm−2 , which is roughly twice as high as in random regions. The C iv covering fraction remains constant at $\approx 50~{{\%}}$ for impact parameters in the range 150–250 pkpc (≈3 − 6R200). Using the covering fraction profile, we constrain the LAE–C iv absorber two-point correlation function, and obtain $r_0 = 3.4^{+1.1}_{-1.0}$ comoving Mpc (cMpc) and $\gamma = 1.2^{+0.2}_{-0.3}$ for a threshold $N({{\rm C\,{\small IV}}})$ of 1013.0 cm−2 . The C iv covering fraction is found to be enhanced for the LAEs that are part of a “pair/group” compared to the isolated ones.
... In the following, we will compare MUSE-selected Lyα-emitters (LAEs) to, mostly, Lyman-break selected samples. It is known that LAEs may be the extreme end of the Lyman break galaxy population (e.g., Dijkstra & Wyithe 2012;Morales et al. 2021), undergoing very recent star formation, and are more likely to be low mass, less dusty and show lower Lyα velocity offsets than Lyman-break selected samples (e.g., Hashimoto et al. 2013;Shibuya et al. 2014). ...
... In the following section we present our results and look for evidence of trends that can explain the mechanisms behind the shift of Lyα emission from the systemic redshift. As described above, our sample is not magnitude-complete so our comparison to the literature is qualitative and the sample-selection is different from literature samples which are Lyman-break galaxy selected (and we expect LAEs to be typically lower mass and less dusty than Lyman-break galaxies, e.g., Kornei et al. 2010;Shibuya et al. 2014). Nevertheless, we find our sample is representative of z∼6 UV-faint LBGs, of interest during reionization. ...
... The shift of Lyα photons to wavelengths redward and/or blueward of central wavelength is due to resonant scattering with neutral hydrogen in the ISM and absorption by dust (e.g., Neufeld 1991;Verhamme et al. 2006). The amplitude of the velocity shift will be linked to the number of scattering events: set by the column density of neutral gas, N HI (e.g., Neufeld 1990;Verhamme et al. 2006;Hashimoto et al. 2015;Henry et al. 2015 & Gronke 2021), and its covering fraction (e.g., Shibuya et al. 2014;Jaskot et al. 2019) and the velocity of HI gas and any outflows (e.g., Pettini et al. 2001;Shapley et al. 2003). ...
Lyman-alpha (Ly$\alpha$) emission from galaxies can be used to trace neutral hydrogen in the epoch of reionization, however, there is a degeneracy between the attenuation of Ly$\alpha$ in the intergalactic medium (IGM) and the line profile emitted from the galaxy. Large shifts of Ly$\alpha$ redward of systemic due to scattering in the interstellar medium can boost Ly$\alpha$ transmission in the IGM during reionization. The relationship between Ly$\alpha$ velocity offset from systemic and other galaxy properties is not well-established at high-redshift or low luminosities, due to the difficulty of observing emission lines which trace systemic redshift. Rest-frame optical spectroscopy with JWST/NIRSpec has opened a new window into understanding of Ly$\alpha$ at z>3. We present a sample of 12 UV-faint galaxies ($-20 \lesssim$ MUV $\lesssim -16$) at $3 \lesssim z \lesssim 6$, with Ly$\alpha$ velocity offsets, $\Delta v_{\mathrm{Ly}\alpha}$, measured from VLT/MUSE and JWST/NIRSpec from the GLASS-JWST Early Release Program. We find median $\Delta v_{\mathrm{Ly}\alpha}$ of 205 km s$^{-1}$ and standard deviation 75 km s$^{-1}$, compared to 320 and 170km s$^{-1}$ for MUV < -20 galaxies in the literature. Our new sample demonstrates the previously observed trend of decreasing Ly$\alpha$ velocity offset with decreasing UV luminosity and optical line velocity dispersion, extends to MUV $\gtrsim$ -20, consistent with a picture where the Ly$\alpha$ profile is shaped by gas close to the systemic redshift. Our results imply that during reionization Ly$\alpha$ from UV-faint galaxies will be preferentially attenuated, but that detecting Ly$\alpha$ with low $\Delta v_{\mathrm{Ly}\alpha}$ can be an indicator of large ionized bubbles.
... Such an early phase of galaxies is categorized as Lyα emitters (LAEs). 27,28 Recently, it has been shown that high CPL of Lyα originates from scattering with interstellar dust. 29,30 Another unsolved issue is that the asymmetric photoreactions supposed to determine the final ee values of AAs are not entirely clarified. ...
High enantiomeric excesses (ee's) of l-amino acids, including non-proteinogenic amino acid isovaline (Iva), were discovered in the Murchison meteorite, but the detailed molecular mechanism responsible for the observed ee of amino acids remains elusive and inconsistent, because Iva has an inverted circular dichroism (CD) spectrum with respect to α-H amino acids, e.g., alanine. To address this issue, we resort to accurate ab initio calculations for amino acids and their precursors in the Strecker synthesis. We evaluated their photolysis-induced ee in the range 5-11 eV including the Lyman alpha emission line (Lyα), the typical intensive 10.2 eV radiation ascribed to the early phase of galactic evolution. We show that only the aminonitrile precursors are characterized by positive ee in the Lyα region, explaining why right-handed circularly polarized Lyα (R-CP-Lyα) induces homologous l-amino acids. This study shows that the homochirality of amino acids is produced at the aminonitrile precursors stage.
... For the galaxy surveys, there is the potential for the measured redshift values from Lyα lines to be systematically offset from the true galaxy redshifts (e.g., Shapley et al. 2003;Erb et al. 2014;Shibuya et al. 2014;Mason et al. 2018;Endsley et al. 2022). As we show in the above analysis, accurately determined spectroscopic redshift values are key to yielding a statistically significant detection. ...
The cross-correlation between the 21 cm field and the galaxy distribution is a potential probe of the Epoch of Reionization (EoR). The 21 cm signal traces neutral gas in the intergalactic medium and, on large spatial scales, this should be anticorrelated with the high-redshift galaxy distribution, which partly sources and tracks the ionized gas. In the near future, interferometers such as the Hydrogen Epoch of Reionization Array (HERA) are projected to provide extremely sensitive measurements of the 21 cm power spectrum. At the same time, the Nancy Grace Roman Space Telescope (Roman) will produce the most extensive catalog to date of bright galaxies from the EoR. Using seminumeric simulations of reionization, we explore the prospects for measuring the cross-power spectrum between the 21 cm and galaxy fields during the EoR. We forecast a 12 σ detection between HERA and Roman, assuming an overlapping survey area of 500 deg ² , redshift uncertainties of σ z = 0.01 (as expected for the high-latitude spectroscopic survey of Ly α -emitting galaxies), and an effective Ly α emitter duty cycle of f LAE = 0.1. Thus the HERA–Roman cross-power spectrum may be used to help verify 21 cm detections from HERA. We find that the shot-noise in the galaxy distribution is a limiting factor for detection, and so supplemental observations using Roman should prioritize deeper observations, rather than covering a wider field of view. We have made a public GitHub repository containing key parts of the calculation, which accompanies this paper: https://github.com/plaplant/21cm_gal_cross_correlation.
... This confirms that the large Ly EW is not simply due to efficient ionizing photon production, but the transmission is also enhanced. Such strong Ly emitters tend to have a large fraction of their Ly profile escaping near the systemic redshift (e.g., Hashimoto et al. 2013;Erb et al. 2014;Shibuya et al. 2014;Tang et al. 2021b), but Figure 16. Spatial distribution of spectroscopically confirmed galaxies at > 7 that are in the three groups of Ly emitters in the EGS field (7.38 < < 7.58, left panel; 7.63 < < 7.83, middle panel; 8.60 < < 8.90, right panel). ...
We describe new JWST/NIRSpec observations of galaxies at $z\gtrsim7$ taken as part of the CEERS survey of the EGS field. Previous observations of this area have revealed associations of Ly$\alpha$ emitters at redshifts ($z=7.5$, $7.7$, $8.7$) where the IGM is thought mostly neutral, leading to suggestions that these systems are situated in large ionized bubbles. We identify 21 $z\gtrsim7$ galaxies with robust redshifts in the CEERS dataset, including 10 in the Ly$\alpha$ associations. Their spectra are indicative of very highly ionized and metal poor gas, with line ratios (O32 $=17.84$ and Ne3O2 $=0.89$) and metallicity ($12+\log{[\rm{O/H}]}=7.84$) that are rarely seen at lower redshifts. We find that the most extreme spectral properties are found in the six $z\gtrsim7$ Ly$\alpha$ emitting galaxies in the sample. Each have hard ionizing spectra indicating that their visibility is likely enhanced by efficient ionizing photon production. Ly$\alpha$ velocity offsets are found to be very large ($\gtrsim300$ km s$^{-1}$), likely also contributing to their detectability. We find that Ly$\alpha$ in $z\gtrsim7$ galaxies is $6-12\times$ weaker than in lower redshift samples with matched rest-frame optical spectral properties. If the bubbles around the Ly$\alpha$ emitters are relatively small ($\lesssim0.5-1$ pMpc), we may expect such significant attenuation of Ly$\alpha$ in these ionized regions. We discuss several other effects that may contribute to weaker Ly$\alpha$ emission at $z\gtrsim7$. Deep spectroscopy of fainter galaxies in the vicinity of the Ly$\alpha$ emitters will better characterize the physical scale of the ionized bubbles in this field.
... At least some of these differences can be attributed to different spatial resolutions: the density contrast could be more washed out in the COSTCO field due to its coarser 3D spatial resolution compared to TARDIS. In this study, we used several spectroscopic catalogs targeting 2.0 ≤ z ≤ 2.55 galaxies and constructed a complied catalog (Smolčić et al. 2012;Hashimoto et al. 2013;Nakajima et al. 2013;Shibuya et al. 2014;Le Fèvre et al. 2015;Kriek et al. 2015;Nanayakkara et al. 2016;Lee et al. 2016Lee et al. , 2018Brisbin et al. 2017;Micha lowski et al. 2017;Champagne et al. 2021;Lilly et al. in prep). First, we extracted galaxies at 2.0 ≤ z ≤ 2.55 laying within the COSMOS field. ...
We study the environmental effect of galaxy evolution as a function of the underlying 3D dark matter density for the first time at $z=2-2.5$, in which the underlying matter density is reconstructed from galaxy and Ly$\alpha$ forest spectroscopy through dynamical forward modeling techniques. Utilizing these maps, we investigate the dependence of the star formation activities and galaxy types (mergers, submillimeter galaxies, active galactic nuclei, and quiescent galaxies) on the matter overdensity $\Delta$ and stellar mass. For the first time, we are able to probe underdense regions ($\Delta <1$) in addition to overdensities. We find that star formation activity generally depend on the stellar mass, not the matter density, except for high-mass galaxies ($M_*\geq10^{10.5}$ M$_\odot$) which show a drop in star formation activities by a factor of more than $30$ if they reside in high density regions with $\Delta\geq4-6$. We also find: (1) an absence of mergers and submillimeter galaxies in higher-density regions but otherwise no trend across lower-density bins, (2) the increase of active galactic nuclei and quiescent galaxy prevalence as a function of matter density, and (3) the increase of all aforementioned categories with the stellar mass. These results indicate that mass is the main driver of galaxy evolution. Nonetheless, we also find evidence for environmental quenching, particularly for high-mass galaxies in high-density environments. Our novel approach directly using reconstructed dark matter density maps demonstrates the new capability of the environmental effect studies in galaxy evolution at higher redshift.
... The spectral shape of the Ly α emission of our target is double peaked. We model each peak through the asymmetric Gaussian profile introduced by Shibuya et al. ( 2014b ). From the best-fitting model, we obtain a Ly α observed total flux of (1.66 ± 0.03) × 10 −17 erg s −1 cm −2 , corresponding to a total luminosity of (2.14 ± 0.02) × 10 42 erg s −1 . ...
... Besides, the lo w δ Ly α v alue is in trend with the observed Ly α EW 0δ Ly α anticorrelation (e.g. Shibuya et al. 2014b ;Hoag et al. 2019 ). Hence, following Claeyssens et al. ( 2022 ), the observed offset in our target could be the consequence of an off-centre star-forming clump harboured in our target. ...
The origin of the Lyman-α (Lyα) emission in galaxies is a long-standing issue: despite several processes known to originate this line (e.g. AGN, star formation, cold accretion, shock heating), it is difficult to discriminate among these phenomena based on observations. Recent studies have suggested that the comparison of the ultraviolet (UV) and optical properties of these sources could solve the riddle. For this reason, we investigate the rest-frame UV and optical properties of A2895b, a strongly lensed Lyα-emitter at redshift z ∼ 3.7. From this study, we find that our target is a compact (rn ∼ 1.2 pkpc) star-forming (star formation rate ≃ 11 M⊙ yr−1) galaxy having a young stellar population. Interestingly, we measure a high ratio of the Hβ and the UV continuum monochromatic luminosities (L(Hβ)/L(UV) ≃ 100). Based on tracks of theoretical stellar models (Starburst99, bpass), we can only partially explain this result by assuming a recent (≲ 10 Myr), bursty episode of star-formation and considering models characterised by binary stars, a top-heavy initial-mass function (IMF) and sub-solar metallicities (Z ≲ 0.01 Z⊙). These assumptions also explain the observed low (C/O) abundance of our target (≃ 0.23(C/O)⊙). By comparing the UV and optical datasets, we find that the Lyα and UV continuum are more extended (× 2) than the Balmer lines, and that the peak of the Lyα is offset (≃ 0.6 pkpc). The multi-wavelength results of our analysis suggest that the observed Lyα emission originates from a recent star-formation burst, likely taking place in an off-centre clump.
