arXiv subjects

Danielle A. Berg

Publications and source records attributed to Danielle A. Berg.

At least 73 records · Page 4Linked to original sources

arXiv2024

TEMPLATES: Direct Abundance Constraints for Two Lensed Lyman-Break Galaxies

Using integrated spectra for two gravitationally lensed galaxies from the JWST TEMPLATES Early Release Science program, we analyze faint auroral lines, which provide direct measurements of the gas-phase chemical abundance. For the brighter galaxy, SGAS1723$+$34 ($z = 1.3293$), we detect the [OIII]$\lambda4363$, [SIII]$\lambda6312$, and [OII]$λλ$7320,7330 auroral emission lines, and set an upper limit for the [NII]$\lambda5755$ line. For the second galaxy, SGAS1226$+$21 ($z = 2.925$), we do not detect any auroral lines, and report upper limits. With these measurements and upper limits, we constrain the electron temperatures in different ionization zones within both of these galaxies. For SGAS1723$+$34, where auroral lines are detected, we calculate direct oxygen and nitrogen abundances, finding an N/O ratio consistent with observations of nearby ($z\sim 0$) galaxies. These observations highlight the potent combination of JWST and gravitational lensing to measure faint emission lines in individual distant galaxies and to directly study the chemical abundance patterns in those galaxies.

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arXiv2024

Synergistic Radiative Transfer Modeling of MgII and Lyα Emission in Multiphase, Clumpy Galactic Environments: Application to Low-Redshift Lyman Continuum Leakers

We conducted systematic radiative transfer (RT) modeling of the Mg II doublet line profiles for 33 low-redshift Lyman continuum (LyC) leakers, and Ly$α$ modeling for a subset of six objects, using a multiphase, clumpy circumgalactic medium (CGM) model. Our RT models successfully reproduced the Mg II line profiles for all 33 galaxies, revealing a necessary condition for strong LyC leakage: high maximum clump outflow velocity ($v_{\rm MgII,\,max} \gtrsim 390\,\rm km\,s^{-1}$) and low total Mg II column density ($N_{\rm MgII,\,tot} \lesssim 10^{14.3}\,\rm cm^{-2}$). We found that the clump outflow velocity and total Mg II column density have the most significant impact on Mg II spectra and emphasized the need for full RT modeling to accurately extract the CGM gas properties. In addition, using archival HST COS/G160M data, we modeled Ly$α$ profiles for six objects and found that their spectral properties do not fully align with the conventional LyC leakage criteria, yet no clear correlation was identified between the modeled parameters and observed LyC escape fractions. We inferred LyC escape fractions based on HI properties from Ly$α$ RT modeling and found that LyC leakage is primarily governed by the number of optically thick HI clumps per sightline ($f_{\rm cl}$). Intriguingly, two galaxies with relatively low observed LyC leakage exhibited the highest RT-inferred LyC escape fractions due to their lowest $f_{\rm cl}$ values, driven by the strong blue peaks of their Ly$α$ emission. Future high-resolution, spatially resolved observations are crucial for resolving this puzzle. Overall, our results support a "picket fence" geometry over a "density-bounded" scenario for the CGM, where a combination of high Mg II outflow velocities and low Mg II column densities may be correlated with the presence of more low-density HI channels that facilitate LyC escape.

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arXiv2024

Strong rest-UV emission lines in a "little red dot" AGN at $z=7$: Early SMBH growth alongside compact massive star formation?

JWST has now revealed a population of broad-line AGN at $z>4$ characterized by a distinctive SED shape, with very red rest-frame optical and very blue rest-frame UV continuum. While the optical continuum is thought to originate from the accretion disk, the origin of the UV continuum has been largely unclear. We report the detection of the strong rest-frame UV emission lines of CIII]$λλ$1907,1909 and CIV$λλ$1549,1551 in a "little red dot" AGN, COS-66964. Spectroscopically confirmed at $z=7.0371$, COS-66964 exhibits broad H$α$ emission (FWHM $\sim 2000$ km s$^{-1}$), and weak broad H$β$, implying significant dust attenuation to the BLR ($A_V = 3.9^{+1.7}_{-0.9}$). The H$α$ line width implies a central SMBH mass of $M_{\rm BH} = \left(1.9^{+1.6}_{-0.7}\right)\times10^{7}$ M$_\odot$, and an Eddington ratio $λ\sim0.3$-$0.5$. While marginal HeII$\lambda4687$ and [FeX]$\lambda6376$ detections further indicate that the AGN dominates in the rest-frame optical, the non-detection of HeII$\lambda1640$ in the UV despite high EW CIII] and CIV ($\sim 35$ Å) is more consistent with photoionization by massive stars. The non-detection of MgII$λλ$2800 is similarly inconsistent with an AGN scattered light interpretation. Assuming the rest-frame UV is dominated by stellar light, we derive a stellar mass of $\log M_\star/M_\odot\sim8.5$, implying an elevated $M_{\rm BH}/M_\star$ ratio $\sim2$ orders of magnitude above the local relation, but consistent with other high-$z$ AGN discovered by JWST. The source is unresolved in all bands, implying a very compact size $\lesssim200$ pc in the UV. This suggests that the simultaneous buildup of compact stellar populations (i.e., galaxy bulges) and the central SMBH is ongoing even at $z>7$.

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arXiv2024

CLASSY XI: Tracing Neutral Gas Properties using UV Absorption Lines and 21-cm Observations

Rest-frame far-ultraviolet (FUV) observations from JWST are revolutionizing our understanding of the high-z galaxies that drove reionization and the mechanisms by which they accomplished it. To fully interpret these observations, we must be able to diagnose how properties of the interstellar medium (ISM; e.g., column density, covering fraction, outflow velocity) directly relate to the absorption features produced. Using the high-S/N and high-resolution FUV spectra of 45 nearby star-forming galaxies from CLASSY, we present the largest uniform, simultaneous characterization of neutral and low-ionization state (LIS) interstellar UV absorption lines (OI, SiII, SII, CII, AlII) across a wide range of galaxy properties. We also present 21-cm HI observations for 35 galaxies, multiple of which are gas-poor or non-detected, possibly indicating the onset of a post-starburst phase. We find that our simultaneous 1-component Voigt profile fits are capable of accurately modeling the LIS absorption for ~75% of galaxies, mitigating challenges associated with saturation, infilling, and degeneracies. While the most massive galaxies require additional components, our 1-component fits return average properties of the absorbing gas and follow the scaling relations described by a single gas cloud. We explore connections between LIS absorption and direct tracers of the neutral ISM (OI, Ly-alpha, HI 21-cm), finding that CII most closely traces the neutral gas trends while other ions exhibit weaker correlations. Given the challenges with directly observing HI at higher-z, we demonstrate that LIS absorption can be a powerful means to study the neutral ISM and present empirical relationships for predicting neutral gas properties.

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arXiv2024

The Ancient Star Formation History of the Extremely Low-Mass Galaxy Leo P: An Emerging Trend of a Post-Reionization Pause in Star Formation

Isolated, low-mass galaxies provide the opportunity to assess the impact of reionization on their star formation histories (SFHs) without the ambiguity of environmental processes associated with massive host galaxies. There are very few isolated, low-mass galaxies that are close enough to determine their SFHs from resolved star photometry reaching below the oldest main sequence turnoff. JWST has increased the volume for which this is possible, and here we report on JWST observations of the low-mass, isolated galaxy Leo P. From NIRCam imaging in F090W, F150W, and F277W, we derive a SFH which shows early star formation followed by a pause subsequent to the epoch of reionization which is then later followed by a re-ignition of star formation. This is very similar to the SFHs from previous studies of other dwarf galaxies in the ``transition zone'' between quenched very low-mass galaxies and the more massive galaxies which show no evidence of the impact of reionization on their SFHs; this pattern is rarely produced in simulations of SFHs. The lifetime SFH reveals that Leo P's stellar mass at the epoch of reionization was in the range that is normally associated with being totally quenched. The extended pause in star formation from z~5-1 has important implications for the contribution of low-mass galaxies to the UV photon budget at intermediate redshifts. We also demonstrate that, due to higher sensitivity and angular resolution, observing in two NIRCam short wavelength filters is superior to observing in a combination of a short and a long wavelength filter.

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arXiv2024

The Effect of Radiation and Supernovae Feedback on LyC Escape in Local Star-forming Galaxies

Feedback is widely recognized as an essential condition for Lyman continuum (LyC) escape in star-forming galaxies. However, the mechanisms by which galactic outflows clear neutral gas and dust remain unclear. In this paper, we model the Mg II 2796Å, 2804Å absorption + emission lines in 29 galaxies taken from the Low-z LyC Survey (LzLCS) to investigate the impact of (radiation + mechanical) feedback on LyC escape. Using constraints on Mg$^+$ and photoionization models, we map the outflows' neutral hydrogen content and predict $f_{esc}^{LyC}$ with a multiphase wind model. We measure mass, momentum, and energy loading factors for the neutral winds, which carry up to 10% of the momentum and 1% of the energy in SFR-based deposition rates. We use SED template fitting to determine the relative ages of stellar populations, allowing us to identify radiation feedback dominant systems. We then examine feedback related properties (stellar age, loading factors, etc.) under conditions that optimize feedback efficiency, specifically high star formation rate surface density and compact UV half-light radii. Our findings indicate that the strongest leakers are radiation feedback dominant, lack Mg II outflows, but have extended broad components in higher ionization lines like [O III] 5007Å, as observed by Amorín et al. (2024). In contrast, galaxies experiencing supernovae feedback typically exhibit weaker $f_{esc}^{LyC}$ and show evidence of outflows in both Mg II and higher ionization lines. We attribute these findings to rapid or "catastrophic" cooling in the radiation-dominant systems, which, given the low metallicities in our sample, are likely experiencing delayed supernovae.

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arXiv2024

Observations of Extremely Metal-Poor O Stars: Weak Winds and Constraints for Evolution Models

Metal-poor massive stars drive the evolution of low-mass galaxies, both locally and at high redshift. However, quantifying the feedback they impart to their local surroundings remains uncertain because models of stellar evolution, mass loss, and ionizing spectra are unconstrained by observations below 20% solar metallicity ($Z_\odot$). We present new Keck Cosmic Web Imager optical spectroscopy of three O stars in the nearby dwarf galaxies Leo P, Sextans A, and WLM, which have gas-phase oxygen abundances of 3-14% $Z_\odot$. To characterize their fundamental stellar properties and radiation-driven winds, we fit PoWR atmosphere models to the optical spectra simultaneously with Hubble Space Telescope far-ultraviolet (FUV) spectra and multi-wavelength photometry. We find that all three stars have effective temperatures consistent with their spectral types and surface gravities typical of main-sequence dwarf stars. Yet, the combination of those inferred parameters and luminosity for the two lower-$Z$ stars is not reproduced by stellar evolution models, even those that include rotation or binary interactions. The scenario of multiple-star systems is difficult to reconcile with all available data, suggesting that these observations pose a challenge to current evolution models. We highlight the importance of validating the relationship between stellar mass, temperature, and luminosity at very low $Z$ for accurate estimates of ionizing photon production and spectral hardness. Finally, all three stars' FUV wind profiles reveal low mass-loss rates and terminal wind velocities in tension with expectations from widely adopted radiation-driven wind models. These results provide empirical benchmarks for future development of mass-loss and evolution models for metal-poor stellar populations.

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arXiv2024

The First Billion Years, According to JWST

With stunning clarity, JWST has revealed the Universe's first billion years. The scientific community is analyzing a wealth of JWST imaging and spectroscopic data from that era, and is in the process of rewriting the astronomy textbooks. Here, 1.5 years into the JWST science mission, we provide a snapshot of the great progress made towards understanding the initial chapters of our cosmic history. We highlight discoveries and breakthroughs, topics and issues that are not yet understood, and questions that will be addressed in the coming years, as JWST continues its revolutionary observations of the Early Universe. While this compendium is written by a small number of authors, invited to ISSI Bern in March 2024 as part of the 2024 ISSI Breakthrough Workshop, we acknowledge the work of a large community that is advancing our collective understanding of the evolution of the Early Universe.

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arXiv2024

CHAOS VIII: Far-Ultraviolet Spectra of M101 and The Impact of Wolf-Rayet Stars

We investigate the stellar and nebular properties of 9 H II regions in the spiral galaxy M101 with far-ultraviolet (FUV; ~900-2000 Å) and optical (~3200-10000 Å) spectra. We detect significant C III] 1907,1909 nebular emission in 7 regions, but O III] 1666 only in the lowest-metallicity region. We produce new analytic functions of the carbon ICF as a function of metallicity in order to perform a preliminary C/O abundance analysis. The FUV spectra also contain numerous stellar emission and P-Cygni features that we fit with luminosity-weighted combinations of single-burst Starburst99 and BPASS models. We find that the best-fit Starburst99 models closely match the observed very-high-ionization P-Cygni features, requiring very-hot, young (~< 3 Myr), metal-enriched massive stars. The youngest stellar populations are strongly correlated with broad He II emission, nitrogen Wolf-Rayet (WR) FUV and optical spectral features, and enhanced N/O gas abundances. Thus, the short-lived WR phase may be driving excess emission in several N P-Cygni wind features (955 Å, 991 Å, 1720 Å) that bias the stellar continuum fits to higher metallicities relative to the gas-phase metallicities. Accurate characterization of these H II regions requires additional inclusion of WR stars in the stellar population synthesis models. Our FUV spectra demonstrate that the ~900-1200 Å FUV can provide a strong test-bed for future WR atmosphere and evolution models.

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arXiv2024

JWST Observations of Starbursts: Cold Clouds and Plumes Launching in the M82 Outflow

In this paper we study the filamentary substructure of 3.3 $μ$m PAH emission from JWST/NIRCam observations in the base of the M82 star-burst driven wind. We identify plume-like substructure within the PAH emission with widths of $\sim$50 pc. Several of the plumes extend to the edge of the field-of-view, and thus are at least 200-300 pc in length. In this region of the outflow, the vast majority ($\sim$70\%) of PAH emission is associated with the plumes. We show that those structures contain smaller scale "clouds" with widths that are $\sim$5-15 pc, and they are morphologically similar to the results of "cloud-crushing" simulations. We estimate the cloud-crushing time-scales of $\sim$0.5-3 Myr, depending on assumptions. We show this time scale is consistent with a picture in which these observed PAH clouds survived break-out from the disk rather than being destroyed by the hot wind. The PAH emission in both the midplane and the outflow is shown to tightly correlate with that of Pa$α$ emission (from HST/NICMOS data), at the scale of both plumes and clouds, though the ratio of PAH-to-Pa$α$ increases at further distances from the midplane. Finally, we show that the outflow PAH emission is suppressed in regions of the M82 wind that are bright in X-ray emission. Overall, our results are broadly consistent with a picture in which cold gas in galactic outflows is launched via hierarchically structured plumes, and those small scale clouds are more likely to survive the wind environment when collected into the larger plume structure.

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arXiv2024

A comprehensive metallicity analysis of J0332-3557: establishing a z ~ 4 anchor for direct gas metallicity and C/O abundance investigations

We provide one of the most comprehensive metallicity studies at z $\sim$ 4 by analyzing the UV/optical HST photometry, and rest-frame VLT-FORS2 ultraviolet and VLT-XSHOOTER optical spectra of J0332-3557, a gravitationally lensed galaxy magnified by a factor of 20. With a 5$σ$ detection of the auroral O III]1666 line, we are able to derive a direct gas metallicity estimate for our target. We find Z_gas = 12 + log(O/H) = 8.26 $\pm$ 0.06, which is compatible with an increasing of both the gas fraction and the outflow metal loading factor from z $\sim$ 0 to z $\sim$ 4. J0332-3557 is the most metal-rich individual galaxy at z $\sim$ 4 for which the C/O ratio has been measured. We derive a low log(C/O) = - 1.02 $\pm$ 0.2, which suggests that J0332-3557 is in the early stages of ISM carbon enrichment driven mostly by massive stars. The low C/O abundance also indicates that J0332-3557 is characterized by a low star formation efficiency, higher yields of oxygen, and longer burst duration. We find that EW(C III])1906,9 is as low as $\sim$ 3 Å. The main drivers of the low EW(C III])1906,9 are the higher gas metallicity and the low C/O abundance. J0332-3557 is characterized by one diffuse and two more compact regions $\sim$ 1 kpc in size. We find that the carbon emission mostly originates in the compact knots. Our study on J0332-3557 serves as an anchor for studies investigating the evolution of metallicity and C/O abundance across different redshifts.

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arXiv2024

The Next Generation Deep Extragalactic Exploratory Public Near-Infrared Slitless Survey Epoch 1 (NGDEEP-NISS1): Extra-Galactic Star-formation and Active Galactic Nuclei at 0.5 < z < 3.6

The Next Generation Deep Extragalactic Exploratory Public (NGDEEP) survey program was designed specifically to include Near Infrared Slitless Spectroscopic observations (NGDEEP-NISS) to detect multiple emission lines in as many galaxies as possible and across a wide redshift range using the Near Infrared Imager and Slitless Spectrograph (NIRISS). We present early results obtained from the the first set of observations (Epoch 1, 50$\%$ of the allocated orbits) of this program (NGDEEP-NISS1). Using a set of independently developed calibration files designed to deal with a complex combination of overlapping spectra, multiple position angles, and multiple cross filters and grisms, in conjunction with a robust and proven algorithm for quantifying contamination from overlapping dispersed spectra, NGDEEP-NISS1 has achieved a 3$σ$ sensitivity limit of 2 $\times$ 10$^{-18}$ erg/s/cm$^2$. We demonstrate the power of deep wide field slitless spectroscopy (WFSS) to characterize the star-formation rates, and metallicity ([OIII]/H$β$), and dust content, of galaxies at $1<z<3.5$. The latter showing intriguing initial results on the applicability and assumptions made regarding the use of Case B recombination. Further, we identify the presence of active galactic nuclei (AGN) and infer the mass of their supermassive black holes (SMBHs) using broadened restframe MgII and H$β$ emission lines. The spectroscopic results are then compared with the physical properties of galaxies extrapolated from fitting spectral energy distribution (SED) models to photometry alone. The results clearly demonstrate the unique power and efficiency of WFSS at near-infrared wavelengths over other methods to determine the properties of galaxies across a broad range of redshifts.

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arXiv2024

CLASSY IX: The Chemical Evolution of the Ne, S, Cl, and Ar Elements

To study the chemical evolution across cosmic epochs, we investigate Ne, S, Cl, and Ar abundance patterns in the COS Legacy Archive Spectroscopic SurveY (CLASSY). CLASSY comprises local star-forming galaxies (0.02 < z < 0.18) with enhanced star-formation rates, making them strong analogues to high-z star-forming galaxies. With direct measurements of electron temperature, we derive accurate ionic abundances for all elements and assess ionization correction factors (ICFs) to account for unseen ions and derive total abundances. We find Ne/O, S/O, Cl/O, and Ar/O exhibit constant trends with gas-phase metallicity for 12+log(O/H) < 8.5 but significant correlation for Ne/O and Ar/O with metallicity for 12+log(O/H) > 8.5, likely due to ICFs. Thus, applicability of the ICFs to integrated spectra of galaxies could bias results, underestimating true abundance ratios. Using CLASSY as a local reference, we assess the evolution of Ne/O, S/O, and Ar/O in galaxies at z>3, finding no cosmic evolution of Ne/O, while the lack of direct abundance determinations for S/O and Ar/O can bias the interpretation of the evolution of these elements. We determine the fundamental metallicity relationship (FMR) for CLASSY and compare to the high-redshift FMR, finding no evolution. Finally, we perform the first mass-neon relationship analysis across cosmic epochs, finding a slight evolution to high Ne at later epochs. The robust abundance patterns of CLASSY galaxies and their broad range of physical properties provide essential benchmarks for interpreting the chemical enrichment of the early galaxies observed with the JWST.

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arXiv2024

Aperture and Resolution Effects on Ultraviolet Star-Forming Properties: Insights from Local Galaxies and Implications for High-Redshift Observations

We present an analysis of the effects of spectral resolution and aperture scales on derived galaxy properties using far-ultraviolet (FUV) spectra of local star-forming galaxies from the International Ultraviolet Explorer (R~250, FOV~10"x20") and Cosmic Origins Spectrograph on the Hubble Space Telescope (R~15,000, FOV~2.5"). Using these spectra, we measured FUV luminosities, spectral slopes, dust attenuation, and equivalent widths. We find that galaxies with one dominant stellar cluster have FUV properties that are independent of aperture size, while galaxies with multiple bright clusters are sensitive to the total light fraction captured by the aperture. Additionally, we find significant correlations between the strength of stellar and interstellar absorption-lines and metallicity, indicating metallicity-dependent line-driven stellar winds and interstellar macroscopic gas flows shape the stellar and interstellar spectral lines, respectively. The observed line-strength versus metallicity relation of stellar-wind lines agrees with the prediction of population synthesis models for young starbursts. In particular, measurements of the strong stellar CIV 1548,1550 line provide an opportunity to determine stellar abundances as a complement to gas-phase abundances. We provide a relation between the equivalent width of the CIV line and the oxygen abundance of the galaxy. We discuss this relation in terms of the stellar-wind properties of massive stars. As the driving lines in stellar winds are mostly ionized iron species, the CIV line may eventually offer a method to probe alpha-element-to-iron ratios in star-forming galaxies once consistent models with non-solar abundance ratios are available. These results have important implications for the galaxy-scale, low-resolution observations of high-redshift galaxies from JWST (R~100-3,500).

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arXiv2023

CLASSY VIII: Exploring the Source of Ionization with UV ISM diagnostics in local High-$z$ Analogs

In the current JWST era, rest-frame UV spectra play a crucial role in enhancing our understanding of the interstellar medium (ISM) and stellar properties of the first galaxies in the epoch of reionization (EoR, $z>6$). Here, we compare well-known and reliable optical diagrams sensitive to the main ionization source (i.e., star formation, SF; active galactic nuclei, AGN; shocks) to UV counterparts proposed in the literature - the so-called ``UV-BPT diagrams'' - using the HST COS Legacy Archive Spectroscopic SurveY (CLASSY), the largest high-quality, high-resolution and broad-wavelength range atlas of far-UV spectra for 45 local star-forming galaxies. In particular, we explore where CLASSY UV line ratios are located in the different UV diagnostic plots, taking into account state-of-the-art photoionization and shock models and, for the first time, the measured ISM and stellar properties (e.g., gas-phase metallicity, ionization parameter, carbon abundance, stellar age). We find that the combination of C III] $λλ$1907,9 He II $\lambda1640$ and O III] $λ$1666 can be a powerful tool to separate between SF, shocks and AGN at sub-solar metallicities. We also confirm that alternative diagrams without O III] $λ$1666 still allow us to define a SF-locus with some caveats. Diagrams including C IV $λλ$1548,51 should be taken with caution given the complexity of this doublet profile. Finally, we present a discussion detailing the ISM conditions required to detect UV emission lines, visible only in low gas-phase metallicity (12+log(O/H) $\lesssim8.3$) and high ionization parameter (log($U$) $\gtrsim-2.5$) environments. Overall, CLASSY and our UV toolkit will be crucial in interpreting the spectra of the earliest galaxies that JWST is currently revealing.

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arXiv2023

CLASSY VII Lyα Profiles: The Structure and Kinematics of Neutral Gas and Implications for LyC Escape in Reionization-Era Analogs

Lyman-alpha line profiles are a powerful probe of ISM structure, outflow speed, and Lyman continuum escape fraction. In this paper, we present the Ly$α$ line profiles of the COS Legacy Archive Spectroscopic SurveY, a sample rich in spectroscopic analogs of reionization-era galaxies. A large fraction of the spectra show a complex profile, consisting of a double-peaked Ly$α$ emission profile in the bottom of a damped, Ly$α$ absorption trough. Such profiles reveal an inhomogeneous interstellar medium (ISM). We successfully fit the damped Ly$α$ absorption (DLA) and the Ly$α$ emission profiles separately, but with complementary covering factors, a surprising result because this approach requires no Ly$α$ exchange between high-$N_\mathrm{HI}$ and low-$N_\mathrm{HI}$ paths. The combined distribution of column densities is qualitatively similar to the bimodal distributions observed in numerical simulations. We find an inverse relation between Ly$α$ peak separation and the [O III]/[O II] flux ratio, confirming that the covering fraction of Lyman-continuum-thin sightlines increases as the Ly$α$ peak separation decreases. We combine measurements of Ly$α$ peak separation and Ly$α$ red peak asymmetry in a diagnostic diagram which identifies six Lyman continuum leakers in the CLASSY sample. We find a strong correlation between the Ly$α$ trough velocity and the outflow velocity measured from interstellar absorption lines. We argue that greater vignetting of the blueshifted Ly$α$ peak, relative to the redshifted peak, is the source of the well-known discrepancy between shell-model parameters and directly measured outflow properties. The CLASSY sample illustrates how scattering of Ly$α$ photons outside the spectroscopic aperture reshapes Ly$α$ profiles as the distances to these compact starbursts span a large range.

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arXiv2023

Using [Ne V]/[Ne III] to Understand the Nature of Extreme-Ionization Galaxies

Spectroscopic studies of extreme-ionization galaxies (EIGs) are critical to our understanding of exotic systems throughout cosmic time. These EIGs exhibit spectral features requiring >54.42 eV photons: the energy needed to fully ionize helium into He2+ and emit He II recombination lines. They are likely key contributors to reionization, and they can also probe exotic stellar populations or accretion onto massive black holes. To facilitate the use of EIGs as probes of high ionization, we focus on ratios constructed from strong rest-frame UV/optical emission lines, specifically [O III] 5008, H-beta, [Ne III] 3870, [O II] 3727,3729, and [Ne V] 3427. These lines probe the relative intensity at energies of 35.12, 13.62, 40.96, 13.62 eV, and 97.12, respectively, covering a wider range of ionization than traced by other common rest-frame UV/optical techniques. We use ratios of these lines ([Ne V]/[Ne III] = Ne53 and [Ne III]/[O II]), which are closely separated in wavelength, and mitigates effects of dust attenuation and uncertainties in flux calibration. We make predictions from photoionization models constructed from Cloudy that use a broad range of stellar populations and black hole accretion models to explore the sensitivity of these line ratios to changes in the ionizing spectrum. We compare our models to observations from the Hubble Space Telescope and James Webb Space Telescope of galaxies with strong high-ionization emission lines at z ~ 0, z ~ 2, and z ~ 7. We show that the Ne53 ratio can separate galaxies with ionization from 'normal' stellar populations from those with AGN and even 'exotic' Population III models. We introduce new selection methods to identify galaxies with photoionization driven by Population III stars or intermediate-mass black hole accretion disks that could be identified in upcoming high-redshift spectroscopic surveys.

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arXiv2023

NGDEEP Epoch 1: The Faint-End of the Luminosity Function at $z \sim$ 9-12 from Ultra-Deep JWST Imaging

We present a robust sample of very high-redshift galaxy candidates from the first epoch of {\it JWST}/NIRCam imaging from the Next Generation Extragalactic Exploratory Deep (NGDEEP) Survey. The NGDEEP NIRCam imaging in the Hubble Ultra Deep Field Parallel Field 2 (HUDF-Par2) reaches $m=30.4$ (5$σ$, point-source) in F277W, making it the deepest public {\it JWST} GO imaging dataset to date. We describe our detailed data reduction process of the six-filter broad-band {\it JWST}/NIRCam imaging, incorporating custom corrections for systematic effects to produce high-quality calibrated images. Using robust photometric redshift selection criteria, we identify a sample of 38 $z \gtrsim 9$ galaxy candidates. These objects span a redshift range of $z=8.5-15.8$, and apparent magnitudes of $m_\mathrm{F277W} = 27-30.5$ AB mag, reaching $\sim 1.5$ mag deeper than previous public {\it JWST} imaging surveys. We calculate the rest-frame ultraviolet (UV) luminosity function at $z \sim$ 9 and 11, and present a new measurement of the luminosity function faint-end slope at $z \sim 11$. There is no significant evolution in the faint-end slope and number density from $z=9$ to 11. Comparing our results with theoretical predictions, we find that some models produce better agreement at the faint end than the bright end. These results will help to constrain how stellar feedback impacts star formation at these early epochs.

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