An official website of the United States government
Abstract We present UV and Ly α radial surface brightness (SB) profiles of Ly α emitters (LAEs) at z = 2.84 detected with the Hyper Suprime-Cam on the Subaru Telescope. The depth of our data, together with the wide-field coverage including a protocluster, enable us to study the dependence of Ly α halos (LAHs) on various galaxy properties, including Mpc scale environments. UV and Ly α images of 3490 LAEs are extracted, and stacking the images yields SB sensitivity of ∼ 1 × 10 − 20 erg s − 1 cm − 2 arcsec − 2 in Ly α , reaching the expected level of optically thick gas illuminated by the UV background at z ∼ 3. Fitting of the two-component exponential function gives the scale-lengths of 1.56 ± 0.01 and 10.4 ± 0.3 pkpc. Dividing the sample according to their photometric properties, we find that, while the dependence of halo scale-length on environment outside of the protocluster core is not clear, LAEs in the central regions of protoclusters appear to have very large LAHs, which could be caused by combined effects of source overlapping and diffuse Ly α emission from cool intergalactic gas permeating the forming protocluster core irradiated by active members. For the first time, we identify UV halos around bright LAEs that are probably due to a few lower-mass satellite galaxies. Through comparison with recent numerical simulations, we conclude that, while scattered Ly α photons from the host galaxies are dominant, star formation in satellites evidently contributes to LAHs, and that fluorescent Ly α emission may be boosted within protocluster cores at cosmic noon and/or near bright QSOs.
more »
« less
Emulating extended Lyman-alpha haloes around star-forming galaxies
ABSTRACT Extended $$\mathrm{Ly\,\,\alpha }$$ emission is commonly observed around star-forming galaxies, opening a window for probing the neutral hydrogen gas in the circumgalactic medium (CGM). In this paper, we develop a prescription of spherically symmetric CGM gas properties and build emulators to model circularly averaged surface brightness (SB) profiles of the extended $$\mathrm{Ly\,\alpha }$$ emission. With CGM gas properties parametrized by the density, velocity and temperature profiles, a self-shielding calculation is carried out to obtain the neutral gas distribution with ionizing photons from the ultraviolet (UV) background and star formation in the galaxy. Our calculation reveals three types of systems with distinct neutral gas distribution: non-shielded systems with the CGM being highly ionized across all radii, shielded systems with a neutral gas shell shielding the UV background, and transitional systems in between. $$\mathrm{Ly\,\alpha }$$ SB profiles are obtained through $$\mathrm{Ly\,\alpha }$$ radiative transfer (RT) simulations, performed for the CGM models with three kinds of $$\mathrm{Ly\,\alpha }$$ sources: the star formation from central and satellite galaxies, and the recombination in the CGM. We build emulators to efficiently predict $$\mathrm{Ly\,\alpha }$$ SB profiles for given model parameters and $$\mathrm{Ly\,\alpha }$$ sources, based on Gaussian process regression. After being trained with only 180 RT simulations for each $$\mathrm{Ly\,\alpha }$$ source, the emulators reach an overall accuracy at the level of $$\sim 20$$ per cent. By applying the emulators to fit mock $$\mathrm{Ly\,\alpha }$$ SB profiles constructed from our model, we find a reasonable recovery of model parameters, indicating the potential of extracting physical information of the CGM and galaxies from the observed extended $$\mathrm{Ly\,\alpha }$$ emission.
more »
« less
- Award ID(s):
- 2007499
- PAR ID:
- 10633190
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Monthly Notices of the Royal Astronomical Society
- Volume:
- 542
- Issue:
- 3
- ISSN:
- 0035-8711
- Format(s):
- Medium: X Size: p. 2151-2166
- Size(s):
- p. 2151-2166
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
null (Ed.)ABSTRACT We study the projected spatial offset between the ultraviolet continuum and Ly α emission for 65 lensed and unlensed galaxies in the Epoch of Reionization (5 ≤ z ≤ 7), the first such study at these redshifts, in order to understand the potential for these offsets to confuse estimates of the Ly α properties of galaxies observed in slit spectroscopy. While we find that ∼40 per cent of galaxies in our sample show significant projected spatial offsets ($$|\Delta _{\rm {Ly}\alpha -\rm {UV}}|$$), we find a relatively modest average projected offset of $$|\widetilde{\Delta }_{\rm {Ly}\alpha -\rm {UV}}|$$ = 0.61 ± 0.08 proper kpc for the entire sample. A small fraction of our sample, ∼10 per cent, exhibit offsets in excess of 2 proper kpc, with offsets seen up to ∼4 proper kpc, sizes that are considerably larger than the effective radii of typical galaxies at these redshifts. An internal comparison and a comparison to studies at lower redshift yielded no significant evidence of evolution of $$|\Delta _{\rm {Ly}\alpha -\rm {UV}}|$$ with redshift. In our sample, ultraviolet (UV)-bright galaxies ($$\widetilde{L_{\mathrm{ UV}}}/L^{\ast }_{\mathrm{ UV}}=0.67$$) showed offsets a factor of three greater than their fainter counterparts ($$\widetilde{L_{\mathrm{ UV}}}/L^{\ast }_{\mathrm{ UV}}=0.10$$), 0.89 ± 0.18 versus 0.27 ± 0.05 proper kpc, respectively. The presence of companion galaxies and early stage merging activity appeared to be unlikely causes of these offsets. Rather, these offsets appear consistent with a scenario in which internal anisotropic processes resulting from stellar feedback, which is stronger in UV-brighter galaxies, facilitate Ly α fluorescence and/or backscattering from nearby or outflowing gas. The reduction in the Ly α flux due to offsets was quantified. It was found that the differential loss of Ly α photons for galaxies with average offsets is not, if corrected for, a limiting factor for all but the narrowest slit widths (<0.4 arcsec). However, for the largest offsets, if they are mostly perpendicular to the slit major axis, slit losses were found to be extremely severe in cases where slit widths of ≤1 arcsec were employed, such as those planned for James Webb Space Telescope/NIRSpec observations.more » « less
-
ABSTRACT We present the first statistical analysis of kinematically resolved, spatially extended $$\rm Ly\alpha$$ emission around z = 2–3 galaxies in the Keck Baryonic Structure Survey (KBSS) using the Keck Cosmic Web Imager (KCWI). Our sample of 59 star-forming galaxies (zmed = 2.29) comprises the subset with typical KCWI integration times of ∼5 h and with existing imaging data from the Hubble Space Telescope and/or adaptive optics-assisted integral field spectroscopy. The high-resolution images were used to evaluate the azimuthal dependence of the diffuse $$\rm Ly\alpha$$ emission with respect to the stellar continuum within projected galactocentric distances of ≲30 proper kpc. We introduce cylindrically projected 2D spectra (CP2D) that map the averaged $$\rm Ly\alpha$$ spectral profile over a specified range of azimuthal angle, as a function of impact parameter around galaxies. The averaged CP2D spectrum of all galaxies shows clear signatures of $$\rm Ly\alpha$$ resonant scattering by outflowing gas. We stacked the CP2D spectra of individual galaxies over ranges of azimuthal angle with respect to their major axes. The extended $$\rm Ly\alpha$$ emission along the galaxy principal axes is statistically indistinguishable, with residual asymmetry of ≤2 per cent (∼2σ) of the integrated $$\rm Ly\alpha$$ emission. The symmetry implies that the $$\rm Ly\alpha$$ scattering medium is dominated by outflows in all directions within 30 kpc. Meanwhile, we find that the blueshifted component of $$\rm Ly\alpha$$ emission is marginally stronger along galaxy minor axes for galaxies with relatively weak $$\rm Ly\alpha$$ emission. We speculate that this weak directional dependence of $$\rm Ly\alpha$$ emission becomes discernible only when the $$\rm Ly\alpha$$ escape fraction is low. These discoveries highlight the need for similar analyses in simulations with $$\rm Ly\alpha$$ radiative transfer modelling.more » « less
-
ABSTRACT We present new spectroscopic observations of Ly α (Ly α) Blob 2 (z ∼ 3.1). We observed extended Ly α emission in three distinct regions, where the highest Ly α surface brightness (SB) centre is far away from the known continuum sources. We searched through the MOSFIRE slits that cover the high Ly α SB regions, but were unable to detect any significant nebular emission near the highest SB centre. We further mapped the flux ratio of the blue peak to the red peak and found it is anticorrelated with Ly α SB with a power-law index of ∼ –0.4. We used radiative transfer models with both multiphase, clumpy, and shell geometries and successfully reproduced the diverse Ly α morphologies. We found that most spectra suggest outflow-dominated kinematics, while 4/15 spectra imply inflows. A significant correlation exists between parameter pairs, and the multiphase, clumpy model may alleviate previously reported discrepancies. We also modelled Ly α spectra at different positions simultaneously and found that the variation of the inferred clump outflow velocities can be approximately explained by line-of-sight projection effects. Our results support the ‘central powering + scattering’ scenario, i.e. the Ly α photons are generated by a central powering source and then scatter with outflowing, multiphase H i gas while propagating outwards. The infalling of cool gas near the blob outskirts shapes the observed blue-dominated Ly α profiles, but its energy contribution to the total Ly α luminosity is less than 10 per cent, i.e. minor compared to the photoionization by star-forming galaxies and/or AGNs.more » « less
-
ABSTRACT Our understanding of reionization has advanced considerably over the past decade, with several results now demonstrating that the intergalactic medium transitioned from substantially neutral at z = 7 to largely reionized at z = 6. However, little remains known about the sizes of ionized bubbles at z ≳ 7 as well as the galaxy overdensities which drive their growth. Fortunately, rest-ultraviolet (UV) spectroscopic observations offer a pathway towards characterizing these ionized bubbles thanks to the resonant nature of Lyman-alpha photons. In a previous work, we presented Ly α detections from three closely separated Lyman-break galaxies at z ≃ 6.8, suggesting the presence of a large (R > 1 physical Mpc) ionized bubble in the 1.5 deg2 COSMOS field. Here, we present new deep Ly α spectra of 10 UV-bright ($$\mathrm{\mathit{ M}}_{\mathrm{UV}}^{} \le -20.4$$) z ≃ 6.6–6.9 galaxies in the surrounding area, enabling us to better characterize this potential ionized bubble. We confidently detect (S/N > 7) Ly α emission at z = 6.701–6.882 in nine of ten observed galaxies, revealing that the large-scale volume spanned by these sources (characteristic radius R = 3.2 physical Mpc) traces a strong galaxy overdensity (N/〈N〉 ≳ 3). Our data additionally confirm that the Ly α emission of UV-bright galaxies in this volume is significantly enhanced, with 40 per cent (4/10) showing strong Ly α emission (equivalent width >25 Å) compared to the 8–9 per cent found on average at z ∼ 7. The median Ly α equivalent width of our observed galaxies is also ≈2 times that typical at z ∼ 7, consistent with expectations if a very large (R ∼ 3 physical Mpc) ionized bubble is allowing the Ly α photons to cosmologically redshift far into the damping wing before encountering H i.more » « less
