Galaxies at Cosmic Noon ( z ∼ 2–3) are characterized by rapid star formation that will lead to significant metal enrichment in the interstellar medium (ISM). While much observational evidence suggests that these galaxies are chemically distinct from those in the local Universe, directly measuring the ISM chemistry in large samples of high- z galaxies is only now possible with the observational capabilities of JWST. In this first key paper of the CECILIA program, we present the direct-method physical conditions and multielement abundances in 20 galaxies at Cosmic Noon. Using a combination of archival Keck/MOSFIRE and new ∼30 hr NIRSpec spectroscopy, we measure multiple electron gas densities and the temperature structure from the O ^+ and S ^2+ ions. We find that n _e [O ii ] and n _e [S ii ] are comparable but elevated with respect to n _e in local star-forming galaxies, and the simultaneous T _e [O ii ] and T _e [S iii ] generally agree with photoionization model T _e scaling relations. The O abundances in the CECILIA galaxies range from 12 + log(O/H) = 7.76 to 8.81 (12%–131% solar O/H), representing some of the highest direct-method metallicities and lowest T _e ( T _e [O ii ] ≈ 6500 K) measured with JWST to date. The CECILIA galaxies exhibit significantly subsolar S/O and Ar/O, a signature of predominant enrichment from core-collapse supernovae. The N/O–O/H trends in the CECILIA galaxies generally agree with the abundance trends in local nebulae, but the large scatter in N/O could be sensitive to the star formation history. The CECILIA observations demonstrate that exceptionally deep JWST spectroscopy can unveil the multielement ISM abundance patterns in typical high- z galaxies.

We present the nebular attenuation curves and dust covering fractions for 24 redshift z=1.5-4.4 star-forming galaxies using multiple Balmer and Paschen lines from the JWST/AURORA survey. Nebular reddening derived from Paschen lines exceeds that from Balmer lines for at least half the galaxies in the sample when assuming the commonly-adopted Galactic extinction curve, implying the presence of optically-thick star formation. The nebular attenuation curves exhibit a broad range of normalizations (Rv ~ 3.2-16.4). Motivated by the offsets in reddening deduced from the Balmer and Paschen lines, and the high Rv values for the individual nebular attenuation curves, both of which suggest variations in the dust-stars geometry, we propose a model with a subunity dust covering fraction (fcov). Fitting such a model to the HI recombination line ratios indicates fcov ~ 0.6-1.0. The normalizations of the nebular attenuation curves, Rv, are driven primarily by fcov and the mix of optically-thick and thin OB associations. Thus, the diversity of nebular attenuation curves can be accommodated by assuming dust grain properties similar to that of Milky Way sightlines but with a subunity covering fraction of dust. Integrated measurements of multiple Balmer and Paschen lines can be used to place novel constraints on the dust covering fraction towards OB associations. These, in turn, provide new avenues for exploring the role of dust and gas covering fraction in a number of relevant aspects of high-redshift galaxies, including the impact of stellar feedback on ISM porosity and the escape of Ly-alpha and Lyman continuum radiation.

We present detections of auroral emission lines of [O iii], [O ii], [S iii], and [S ii] in deep JWST/NIRSpec spectroscopy for 41 star-forming galaxies at z = 1.4-7.2 from the AURORA survey. We combine these new observations with 98 star-forming galaxies at z = 1.3-10.6 with detected auroral lines drawn from the literature to form a sample of 139 high-redshift galaxies with robust electron temperature and direct-method oxygen abundance determinations. This sample notably covers a wider dynamic range in metallicity than previous work, spanning 0.02-0.9 Z circle dot. We calibrate empirical relations between 19 emission-line ratios and oxygen abundance, providing a robust tool set to infer accurate gas-phase metallicities of high-redshift galaxies when auroral lines are not detected. While calibrations based on lines of alpha elements (O, Ne, S, Ar) appear reliable, we find significant scatter in calibrations involving lines of N driven by a high dispersion in N/O at fixed O/H, suggesting that N-based line ratios are less reliable tracers of the oxygen abundance at high redshift. These new high-redshift calibrations are notably offset from those based on typical z similar to 0 galaxy and H ii region samples, and are better matched by samples of extreme local galaxies that are analogs of high-redshift sources. The new metallicity calibrations presented in this work pave the way for robust studies of galaxy chemical evolution in the early Universe, leading to a better understanding of baryon cycling and galaxy formation from Cosmic Noon through the Epoch of Reionization.

Ly α emission with a dominant blueshifted peak can probe gas flowing through the circumgalactic medium as it accretes onto galaxies and fuels new star formation, although it has seldom actually been observed. Here we present new Keck Cosmic Web Imager observations of the extended Ly α halos surrounding Q1700-BX710 and Q1700-BX711, a pair of UV continuum-selected Keck Baryonic Structure Survey galaxies at z = 2.3 in the HS1700+643 protocluster. We find that BX710's and BX711’s Ly α halos are aligned with a large-scale galaxy filament consisting of 13 spectroscopically identified protocluster galaxies. By measuring the peak separation and blue-to-red peak flux ratio of the Ly α emission profiles throughout these galaxies’ Ly α halos, we have obtained measurements of their spatially varying velocity structure. The prevalence of blue-dominated Ly α emission profiles throughout BX711’s Ly α halo suggests actively accreting gas. We fit a clumpy, multiphase Monte Carlo Radiative Transfer model, which assumes a radially varying clump velocity to the spatially resolved Ly α emission throughout BX710's and BX711’s Ly α halos and simultaneously fit these galaxies’ average down-the-barrel UV absorption profile with a radially varying velocity model. The results of these models are consistent with a combination of H i and higher-metallicity gas accretion for both galaxies, especially BX711, which exhibits inflow-driven kinematics throughout most of its Ly α halo. We consider various accretion scenarios to explain these findings, including accretion of metal-enriched gas from the cosmic web, galaxy interactions, and recycled gas from the circumgalactic medium, all of which are compatible with our current observations.

We use JWST/NIRSpec observations from the Assembly of Ultradeep Rest-optical Observations Revealing Astrophysics survey to constrain the shape of the nebular attenuation curve of a star-forming galaxy at z = 4.41, GOODSN-17940. We utilize 12 H i recombination lines to derive the attenuation curve spanning optical to near-infrared wavelengths (3751–9550 Å). We then leverage a high signal-to-noise ratio spectroscopic detection of the rest-frame ultraviolet continuum in combination with rest-UV photometric measurements to constrain the shape of the curve at ultraviolet wavelengths. While this UV constraint is predominantly based on stellar emission, the large measured equivalent widths of H α and H β indicate that GOODSN-17940 is dominated by an extremely young stellar population <10 Myr in age such that the UV stellar continuum experiences similar attenuation to that of the nebular emission. The resulting combined nebular attenuation curve spans 1400–9550 Å and has a shape that deviates significantly from commonly assumed dust curves in high-redshift studies. Relative to the Milky Way, SMC, and Calzetti curves, the new curve has a steeper slope at long wavelengths ( λ > 5000 Å) while displaying a similar slope across blue-optical wavelengths ( λ = 3750–5000 Å). In the ultraviolet, the new curve is shallower than the SMC and Calzetti curves and displays no significant 2175 Å bump. This work demonstrates that the most commonly assumed dust curves are not appropriate for all high-redshift galaxies. These results highlight the ability to derive nebular attenuation curves for individual high-redshift sources with deep JWST/NIRSpec spectroscopy, thereby improving the accuracy of physical properties inferred from nebular emission lines.

We present new results on the spatial structure and kinematics of the circumgalactic medium (CGM) of z 2 star-forming galaxies drawn from the Keck Baryonic Structure Survey, using Lya and metallic ion absorption recorded in spectra of background galaxies whose sightlines are projected within 30" (physical distances D_tran < 250 kpc) of the foreground galaxy. The sample of 1033 foreground galaxies ( = 2.03; 8 < log(M_star/M_sun) < 11) is probed by the spectra of 736 background galaxies obtained using Keck/KCWI (R 1800) and Keck/LRIS (R 1200). Using the galaxy pair ensemble, we present measurements of absorption strength (W_lambda) and line-of-sight velocity dispersion (sigma) as a function of D_tran, which together with "down-the-barrel" spectra of the foreground galaxies provide unprecedented maps of neutral hydrogen and ionized metals throughout the CGM of star-forming galaxies at "cosmic noon". A 2D map of Lya absorption depth (vs. line-of-sight velocity and D_tran) for the full ensemble shows a distinct transition near D_tran 80 kpc (close to the virial radius of the average foreground galaxy) where the line-of-sight velocity dispersion reaches a minimum and beyond which the Lya absorption depth flattens. Splitting the sample into subsets based on foreground galaxy properties, we find a strong and monotonic correlation of both W_lambda(C IV) and sigma(C IV) with stellar mass (M_star) at all D_tran including DTB (i.e., D_tran 0 - 250 kpc). Taken together, our results suggest that the kinematics, covering fraction, and spatial extent of CGM gas traced by Lya and (especially) CIV are modulated primarily by halo mass, and that a significant fraction of the CGM gas may be unbound.

We investigate galaxy populations in the HS 1700 + 64 protocluster at z = 2 . 30, characterized by two prominent linear filaments traced by spatially extended Ly alpha blobs. We conducted a wide area mapping of emission line galaxies across the protocluster using the unique combination of three matched narrow-band filters, corresponding to Ly alpha, H alpha, and [O III ] emission lines at z = 2 . 30. We find that H alpha emitters are strongly clustered at the intersection of the filaments, suggesting a protocluster core. In contrast, Ly alpha emitters tend to avoid the dense region and the filaments, likely due to the resonant scattering of Ly alpha photons by HI gas and/or enhanced dust attenuation in galaxies associated with these structures. These findings support a scenario in which cold gas flows via filaments and to the core, fed by the cold-stream mode accretion in the early phase of protocluster assembly, and promoting active star formation there. Further evidence of the scenario comes from the alignment of massive, evolved galaxies in those filaments traced by distant red galaxies, suggesting accelerated galaxy growth in the filaments in the early Universe. This study clearly shows observationally that accelerated galaxy formation takes place not only in the protocluster core but also in the associated surrounding filamentary structure. This underscores the critical role of large-scale filaments in efficiently accumulating the cold gas and channelling it to galaxies therein and to the protocluster core. Such vigorous gas assembly facilitates star formation activity and drives galaxy growth in the early stage of cluster formation.

We present results on the emission-line properties of z = 1.4–7.5 star-forming galaxies in the Assembly of Ultradeep Rest-optical Observations Revealing Astrophysics (AURORA) Cycle 1 JWST/NIRSpec program. Based on its depth, continuous wavelength coverage from 1 to 5 μ m, and medium spectral resolution ( R ∼ 1000), AURORA includes detections of a large suite of nebular emission lines spanning a broad range in rest-frame wavelength. We investigate the locations of AURORA galaxies in multiple different emission-line diagrams, including traditional BPT diagrams of [O iii ] λ 5007/H β versus [N ii ] λ 6583/H α , [S ii ] λλ 6717, 6731/H α , and [O i ] λ 6300/H α , and the ionization–metallicity diagram of [O iii ] λ 5007/[O ii ] λ 3727 (O _32 ) versus ([O iii ] λ 5007+[O ii ] λ 3727)/H β ( R _23 ). We also consider a bluer rest-frame ionization–metallicity diagram introduced recently to characterize z > 10 galaxies, [Ne iii ] λ 3869/[O ii ] λ 3727 versus ([Ne iii ] λ 3869+[O ii ] λ 3727)/H δ , as well as longer-wavelength diagnostic diagrams extending into the rest-frame near-IR: [O iii ] λ 5007/H β versus [S iii ] λλ 9069, 9532/[S ii ] λλ 6717, 6731 (S _32 ), and He i λ 1.083 μ m/Pa γ and [S iii ] λ 9532/Pa γ versus [Fe ii ] λ 1.257 μ m/Pa β . With a significant boost in signal-to-noise ratio and large, representative samples of individual galaxy detections, the AURORA emission-line diagrams presented here definitively confirm a physical picture in which chemically young, α -enhanced, massive stars photoionize the interstellar medium (ISM) in distant galaxies with a harder ionizing spectrum at fixed nebular metallicity than in their z ∼ 0 counterparts. We also uncover previously unseen evolution prior to z ∼ 2 in the [O iii ] λ 5007/H β versus [N ii ] λ 6583/H α diagram, which motivates deep NIRSpec observations at even higher redshift. Finally, we present the first statistical sample of rest-frame near-IR emission-line diagnostics in star-forming galaxies at high redshift. In order to truly interpret rest-frame near-IR line ratios including [Fe ii ] λ 1.257 μ m, we must obtain better constraints on dust depletion in the high-redshift ISM.

We present wide-field mapping at 850 μ m and 450 μ m of the z = 2.85 protocluster in the HS 1549+19 field using the Submillimetre Common-User Bolometer Array 2. Spectroscopic follow-up of 18 bright sources selected at 850 μ m, using the Northern Extended Millimeter Array and Atacama Large Millimeter/submillimeter Array, confirms that the majority lie near z ≃ 2.85 and are likely members of the structure. Interpreting the spectroscopic redshifts as distance measurements, we find that the submillimeter galaxies (SMGs) span 123 pMpc ^2 in the plane of the sky and demarcate a 3600 pMpc ^3 “pancake”-shaped structure in three dimensions. We find that the high star formation rates of these SMGs result in a total star formation rate of 20,000 M _⊙ yr ^−1 from just the brightest galaxies in the protocluster. These rapidly star-forming SMGs can be interpreted as massive galaxies growing rapidly at large clustercentric distances before collapsing into a virialized structure. We find that the SMGs trace the Ly α surface density profile. Comparison with simulations suggests that HS 1549+19 could be building a structure comparable to the most massive clusters in the present-day Universe.

We present the large-scale spatial Lya profiles of galaxies from the Keck Baryonic Structure Survey (KBSS) at 2 50 kpc, theta > 6”). We find that the scale length of the Lya halo is not strongly dependent on the properties of the central galaxy, including its net continuum luminosity or EW_Lya, although we find a possible weak tendency of continuum-faint, high-EW_Lya galaxies to exhibit larger Lya halos in contrast with previous work.

The metal enrichment of a galaxy is determined by the cycle of baryons in outflows, inflows, and star formation. The relative contribution and timescale of each process sets the relationship between stellar mass, metallicity, and the star formation rate (SFR). In the local Universe, galaxies evolve in an equilibrium state where the timescales on which SFR and metallicity vary are comparable, and they define a surface in mass–metallicity–SFR space known as the fundamental metallicity relation (FMR). However, high-redshift observations suggest that this state of equilibrium may not persist throughout cosmic time. Using galaxies from the Keck Baryonic Structure Survey (KBSS) observed with MOSFIRE, we explore the relationship between stellar mass, gas-phase oxygen abundance, and SFR at z ∼ 2.3. Across multiple strong-line calibrations and SFR calculation methods, KBSS galaxies are inconsistent with the locally defined FMR. We use both parametric and nonparametric methods of exploring a mass–metallicity–SFR relation. When using a parametric approach, we find no significant reduction mass–metallicity relation scatter when folding in SFR as a third parameter, although a nonparametric approach reveals that there could be a weak, redshift-dependent anticorrelation between residual gas-phase oxygen abundance and SFR. Injection-recovery tests show that a significant reduction in scatter requires a stronger anticorrelation between SFR and residual metallicity. Our results suggest that the local FMR may not persist to z ∼ 2.3, implying that z ∼ 2.3 galaxies at this redshift may not be in the equilibrium state described by the FMR and are more similar to higher-redshift galaxies.

Intrinsically faint galaxies at z similar to 2-3 offer critical insights into early galaxy formation, tracing low-metallicity, low-mass systems during cosmic noon and serving as analogs to reionization-era galaxies. We present ultradeep JWST/NIRSpec spectroscopy of nine low-luminosity galaxies (-17 less than or similar to M-UV less than or similar to -20, M-star less than or similar to 10(9) M-circle dot) at z similar to 2.5 from the CECILIA program, with similar to 29.5 hr in G235M/F170LP and 1 hr in G395M/F290LP. Our sample includes four Ly alpha emitters, three rest-UV color-selected galaxies, and two serendipitous detections, providing the most sensitive rest-optical spectra of individual faint galaxies at this epoch to date. Balmer-line measurements reveal low star formation rates (SFRs; 0.63 < SFR/(M-circle dot yr(-1)) < 5.43) and a broad range of dust reddening (0 < E(B - V) < 1), with SFRs systematically below those of continuum-selected galaxies. Electron densities are low (n(e) less than or similar to 200 cm(-3)), and emission-line diagnostics indicate low [N II]/H alpha and high [O III]/H beta, suggesting metallicities of . We also present the first O1-BPT constraints in such faint high-redshift galaxies. Notably, two galaxies show low [O III]/H beta despite high Ly alpha EWs and very low [N II]/H alpha, consistent with the predicted turnover in this ratio at very low metallicities, highlighting the need for complementary diagnostics (e.g., N2, O32) to identify metal-poor systems. Direct T-e-based abundances and expanded samples are needed to further trace metallicity and ionization trends in low-mass galaxies.

We present the properties of a massive, large, dusty, metal-rich, star-forming galaxy at z spec = 6.73. GOODSN-100182 was observed with JWST/NIRSpec as part of the Assembly of Ultradeep Rest-optical Observations Revealing Astrophysics (AURORA) survey, and is also covered by public multiwavelength Hubble Space Telescope and JWST imaging. While the large stellar mass of GOODSN-100182 (∼10 10 M ⊙ ) was indicated prior to JWST, NIRCam rest-frame optical imaging now reveals the presence of an extended disk ( r eff ∼ 1.5 kpc). In addition, the NIRSpec R ∼ 1000 spectrum of GOODSN-100182 includes the detection of a large suite of rest-frame optical nebular emission lines ranging in wavelength from [O ii ] λ 3727 up to [N ii ] λ 6583. The ratios of Balmer lines suggest significant dust attenuation ( E ( B − V ) gas = 0.4 0 − 0.09 + 0.10 ), consistent with the red rest-frame UV slope inferred for GOODSN-100182 ( β = −0.50 ± 0.09). The star formation rate based on dust-corrected H α emission is log ( SFR(H α ) / M ⊙ yr − 1 ) = 2.0 2 − 0.14 + 0.13 , well above the z ∼ 7 star-forming main sequence in terms of specific star formation rate. Strikingly, the ratio of [N ii ] λ 6583/H α emission suggests almost solar metallicity, as does the ratio ([O iii ] λ 5007/H β )/([N ii ] λ 6583/H α ) and the detection of the faint [Fe ii ] λ 4360 emission feature. Overall, the excitation and ionization properties of GOODSN-100182 more closely resemble those of typical star-forming galaxies at z ∼ 2–3 rather than z ∼ 7. Based on public spectroscopy of the GOODS-N field, we find that GOODSN-100182 resides within a significant galaxy overdensity, and is accompanied by a spectroscopically confirmed neighbor galaxy. GOODSN-100182 demonstrates the existence of mature, chemically enriched galaxies within the first billion years of cosmic time, whose properties must be explained by galaxy formation models.

While the shape of the Ly$\alpha$ profile is viewed as one of the best tracers of ionizing-photon escape fraction ($f_{esc}$) within low redshift (z~0.3) surveys of the Lyman continuum, this connection remains untested at high redshift. Here, we combine deep, rest-UV Keck/LRIS spectra of 80 objects from the Keck Lyman Continuum Spectroscopic Survey with rest-optical Keck/MOSFIRE spectroscopy in order to examine potential correlations between Ly$\alpha$ profile shape and the escape of ionizing radiation within z~3 star-forming galaxies. We measure the velocity separation between double-peaked Ly$\alpha$ emission structure (v$_{\rm sep}$), between red-side Ly$\alpha$ emission peaks and systemic (v$_{\rm Ly\alpha,red}$), and between red-side emission peaks and low-ionization interstellar absorption lines (v$_{\rm Ly\alpha-LIS}$). We find that the IGM-corrected ratio of ionizing to non-ionizing flux density is significantly higher in KLCS objects with lower v$_{\rm Ly\alpha,red}$. We find no significant trend between measures of ionizing-photon escape and v$_{\rm Ly\alpha-LIS}$. We compare our results to measurements of z~0.3 "Green Peas" from the literature and find that KLCS objects have larger v$_{\rm sep}$ at fixed v$_{\rm Ly\alpha,red}$, larger $f_{esc}$ at fixed v$_{\rm Ly\alpha,red}$, and higher v$_{\rm Ly\alpha,red}$ overall than z~0.3 analogs. We conclude that the Ly$\alpha$ profile shapes of our high-redshift sources are fundamentally different, and that measurements of profile shape such as v$_{\rm Ly\alpha,red}$ map on to $f_{esc}$ in different ways. We caution against building reionization-era $f_{esc}$ diagnostics based purely on Ly$\alpha$ profiles of low-redshift dwarf galaxies. Tracing v$_{\rm sep}$, v$_{\rm Ly\alpha,red}$, and $f_{esc}$ in a larger sample of z~3 galaxies will reveal how these variables may be connected for galaxies at the epoch of reionization.

We present the design and first results of the inner circumgalactic medium (CGM) of QSO line-of-sight emitting galaxies at z similar to 2-3, Keck Baryonic Structure Survey (KBSS)-InCLOSE. The survey will connect galaxy properties (e.g., stellar mass M *, interstellar medium, hereafter ISM, metallicity) with the physical conditions of the inner CGM (e.g., kinematics, metallicity) to directly observe the galaxy-scale baryon cycle. We obtain deep Keck/KCWI optical IFU pointings of KBSS QSOs to discover new star-forming galaxies at small projected distances b less than or similar to 12 '' (98 kpc, z=2.3 ), then obtain follow-up Keck/MOSFIRE near-IR spectra to confirm their redshifts. We leverage KBSS images and Keck/High Resolution Echelle Spectrometer QSO spectra to model stellar populations and inner CGM absorption. In this paper, we analyze two QSO fields and discover more than 15 new galaxies with KCWI, then use MOSFIRE for two galaxies Q2343-G1 (z = 2.43; G1) and Q2233-N1 (z = 3.15; N1), which are both associated with damped Ly alpha absorbers. We find that G1 has typical M *, UV/optical emission properties. N1 has lower M * with very strong nebular emission. We jointly analyze neutral phase CGM and ionized ISM in N/O (for the first time at this z), dust extinction, and high-ionization CGM finding that G1's CGM is metal poor and less evolved than its ISM, while N1's CGM and ISM abundances are comparable; their CGM shows similar to 1 dex less dust extinction than the ISM; and G1's CGM has direct evidence of hot, metal-rich galactic outflow ejecta. These findings support that metals and dust are driven into the CGM from outflows, but may also be, e.g., stripped ISM gas or satellite enrichment. The full KBSS-InCLOSE sample will explore these scenarios.

Understanding the chemical enrichment of different elements is crucial to gaining a complete picture of galaxy chemical evolution. In this study, we present a new sample of 46 low-redshift, low-mass star-forming galaxies at $M_*\sim 10^{8-10}M_{\odot}$ along with two quiescent galaxies at $M_*\sim 10^{8.8}M_{\odot}$ observed with the Keck Cosmic Web Imager (KCWI), aiming to investigate the chemical evolution of galaxies in the transition zone between Local Group satellites and massive field galaxies. We develop a novel method to simultaneously determine stellar abundances of iron and magnesium in star-forming galaxies. With the gas-phase oxygen abundance (O/H)$_{\rm g}$ measured using the strong line method, we are able to make the first-ever apples-to-apples comparison of $\alpha$ elements in the stars and the ISM. We find that the [Mg/H]$_*$-[O/H]$_{\rm g}$ relation is much tighter than the [Fe/H]$_*$-[O/H]$_{\rm g}$ relation, which can be explained by the similar production processes of $\alpha$ elements. Most galaxies in our sample exhibit higher [O/H]$_{\rm g}$ than [Fe/H]$_*$ and [Mg/H]$_*$. In addition, we construct mass-metallicity relations (MZRs) measured as three different elements (Fe$_*$, Mg$_*$, O$_{\rm g}$). Compared to the gas O-MZR, the stellar Fe- and Mg-MZRs show larger scatter driven by variations in specific star formation rates (sSFR), with star-forming galaxies exhibiting higher sSFR and lower stellar abundances at fixed mass. The excess of [O/H]$_{\rm g}$ compared to stellar abundances as well as the anti-correlation between sSFR and stellar abundance suggests that galaxy quenching of intermediate-mass galaxies at $M_*\sim 10^{8-10}M_{\odot}$ is primarily driven by starvation.

We present a new semi-analytic formalism for modeling metal absorption lines that emerge from a clumpy galactic environment, ALPACA. We predict the ''down-the-barrel'' (DTB) metal absorption line profiles and the EW of absorption at different impact parameters as a function of the properties of the clumps, including the clump kinematics, the clump volume filling factor, the clump number density profile and the clump ion column densities. With ALPACA, we jointly model the stacked DTB CII$\lambda$1334 spectrum of a sample of $z \sim$ 3 Lyman break galaxies and the EW v.s. $b$ profile of a sample of $z \sim$ 2 star-forming galaxy-galaxy pairs. ALPACA successfully reproduced two datasets simultaneously, and the best-fit prefers a low clump volume filling factor ($\sim 3 \times 10^{-3}$). The radial velocities of the clumps are a superposition of a rapidly accelerated outflow with a maximum velocity of $\sim 400\,\rm km\,s^{-1}$ and a velocity dispersion of $\sigma_{\rm cl} \sim\,120 \rm km\,s^{-1}$. The joint modeling reveals a physical scenario where the absorption observed at a particular velocity is contributed by the clumps distributed over a fairly broad range of radii. We also find that the commonly adopted Sobolev approximation is at best only applicable within a narrow range of radii where the clumps are undergoing rapid acceleration in a non-volume-filling clumpy medium. Lastly, we find that the clump radial velocity profile may not be fully constrained by the joint modeling and spatially-resolved Ly$\alpha$ emission modeling may help break the degeneracy.

We present Keck Cosmic Web Imager integral-field unit observations around extended Ly alpha halos of 27 typical star-forming galaxies with redshifts 2.0 < z < 3.2 drawn from the MOSFIRE Deep Evolution Field survey. We examine the average Ly alpha surface brightness profiles in bins of star formation rate (SFR), stellar mass (M-*), age, stellar continuum reddening, SFR surface density (Sigma(SFR)), and Sigma(SFR) normalized by stellar mass (Sigma(sSFR)). The scale lengths of the halos correlate with stellar mass, age, and stellar continuum reddening and anticorrelate with SFR, Sigma(SFR), and Sigma(sSFR). These results are consistent with a scenario in which the down-the-barrel fraction of Ly alpha emission is modulated by the low-column-density channels in the interstellar medium, and in which the neutral gas covering fraction is related to the physical properties of the galaxies. Specifically, we find that this covering fraction increases with stellar mass, age, and E(B - V) and decreases with SFR, Sigma(SFR), and Sigma(sSFR). We also find that the resonantly scattered Ly alpha emission suffers greater attenuation than the (nonresonant) stellar continuum emission, and that the difference in attenuation increases with stellar mass, age, and stellar continuum reddening, and decreases with Sigma(sSFR). These results imply that more reddened galaxies have more dust in their circumgalactic medium.