arXiv subjects

Nimisha Kumari

Publications and source records attributed to Nimisha Kumari.

At least 37 records · Page 2Linked to original sources

arXiv2025

Net-zero gas inflow: Measurement of the gas consumption history of a massive quiescent galaxy

JWST is discovering increasing numbers of quiescent galaxies 1--2 billion years after the Big Bang, whose redshift, high mass, and old stellar ages indicate that their formation and quenching were surprisingly rapid. This fast-paced evolution seems to require that feedback from AGN (active galactic nuclei) be faster and/or more efficient than previously expected \citep{Xie24}. We present deep ALMA observations of cold molecular gas (the fuel for star formation) in a massive, fast-rotating, post-starburst galaxy at $z=3.064$. This galaxy hosts an AGN, driving neutral-gas outflows with a mass-outflow rate of $60\pm20$ M$_{\odot}$ yr$^{-1}$, and has a star-formation rate of $<5.6$ M$_{\odot}$ yr$^{-1}$. Our data reveal this system to be the most distant gas-poor galaxy confirmed with direct CO observations (molecular-gas mass $< 10^{9.1}$ M$_{\odot}$; <0.8 % of its stellar mass). Combining ALMA and JWST observations, we estimate the gas-consumption history of this galaxy, showing that it evolved with net zero gas inflow, i.e., gas consumption by star formation matches the amount of gas this galaxy is missing relative to star-forming galaxies. This could arise both from preventive feedback stopping further gas inflow, which would otherwise refuel star formation or, alternatively, from fine-tuned ejective feedback matching precisely gas inflows. Our methods, applied to a larger sample, promise to disentangle ejective vs preventive feedback.

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arXiv2025

The JADES Origins Field: A New JWST Deep Field in the JADES Second NIRCam Data Release

We summarize the properties and initial data release of the JADES Origins Field (JOF), the longest single pointing yet imaged with the James Webb Space Telescope (JWST). This field falls within the GOODS-S region about 8' south-west of the Hubble Ultra Deep Field (HUDF), where it was formed initially in Cycle 1 as a parallel field of HUDF spectroscopic observations within the JWST Advanced Deep Extragalactic Survey (JADES). This imaging was greatly extended in Cycle 2 program 3215, which observed the JOF for 5 days in six medium-band filters, seeking robust candidates for z>15 galaxies. This program also includes ultra-deep parallel NIRSpec spectroscopy (up to 91 hours on-source, summing over the dispersion modes) on the HUDF. Cycle 3 observations from program 4540 added 20 hours of NIRCam slitless spectroscopy and F070W imaging to the JOF. With these three campaigns, the JOF was observed for 380 open-shutter hours with NIRCam using 15 imaging filters and 2 grism bandpasses. Further, parts of the JOF have deep 43 hr MIRI observations in F770W. Taken together, the JOF is one of the most compelling deep fields available with JWST and a powerful window into the early Universe. This paper presents the second data release from JADES, featuring the imaging and catalogs from the year 1 JOF observations.

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arXiv2025

CLASSY XII: Nitrogen Enrichment Shaped by Gas Density and Feedback

We investigate the chemical evolution of N/O using a sample of 45 local star-forming galaxies (SFGs) from the CLASSY survey. This sample spans a wide range of galaxy properties, with robust determinations of nitrogen and oxygen abundances via the direct-$T_{\rm e}$ method. We explore how N/O relates to density structure, stellar mass, star formation rate (SFR), stellar age, compactness, and gas kinematics. In addition, we compare our results with those of galaxies at $z =2-10$ where N/O ratios were derived from optical or UV nitrogen lines, aiming to identify chemical enrichment pathways across cosmic time. Our analysis shows that the N/O-O/H relation in CLASSY galaxies aligns with the trends seen in local galaxies and extragalactic HII regions, and that galaxies at $z = 2-6$ exhibit similar N/O values, indicating no significant redshift evolution in N/O for a fixed metallicity. We identify a significant correlation between electron density $n_{\rm e}$([S II]) and N/O, suggesting that density structure contributes to the scatter in the N/O-O/H relation. The CLASSY galaxies with high SFRs or compact star formation show elevated N/O, though no strong correlation with stellar mass is found. We also find that high-velocity outflows (v$_{out}$ > 350 km/s) and low mass-loading factors are linked to elevated N/O, indicating that feedback plays a significant role. These results highlight the importance of density, star formation, and feedback from young stellar populations in shaping N/O enrichment and provide key insights for interpreting high-$z$ galaxies observed with JWST.

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arXiv2025

REBELS-IFU: on the origin of the elevated [OIII]/[CII] ratios in the early Universe

We present new ALMA [OIII]$_{88}$ observations of eight previously [CII]$_{158}$-detected galaxies at $6.8 \lesssim z \lesssim 7.7$. Six of our targets -- the primary sample -- are massive, UV-luminous galaxies drawn from the REBELS survey, while the remaining two are UV-fainter galaxies that were previously serendipitously detected through their luminous [CII] lines in the REBELS fields. We detect [OIII]$_{88}$ emission in all eight galaxies at $6.2 - 17.7σ$ significance, and find them to be consistent with the local dwarf galaxy relation between $L_\mathrm{[OIII]}$ and star formation rate. Our sample spans [OIII]/[CII] $\approx 1.9 - 9.6$, which is typical for the high-redshift galaxy population. Five of the primary targets benefit from JWST/NIRSpec observations, enabling a direct comparison of the [OIII]/[CII] ratio against rest-optical ISM diagnostics. We supplement our high-redshift sample with eleven $z\approx6-14$ galaxies in the literature for which similar ALMA and JWST observations are available, and furthermore compare to the [OIII]/[CII] ratios measured for local dwarf galaxies. We find that, at fixed metallicity and ionization parameter, $z>6$ galaxies show elevated [OIII]/[CII] ratios compared to local dwarfs. Instead, we find that a large [OIII]$_{4959,5007}$+H$β$ equivalent width -- a proxy for burstiness -- is the main driver of the high [OIII]/[CII] ratios seen in the early Universe, which is primarily due to [CII] being suppressed in bursty galaxies. Given the apparent validity of the [OIII]$_{88}$-SFR relation across most of cosmic time, as well as the abundance of young, bursty galaxies at high redshift, [OIII]$_{88}$ is set to remain a powerful ISM tracer at the cosmic dawn.

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arXiv2025

Detection of the 2175Å UV Bump at z>7: Evidence for Rapid Dust Evolution in a Merging Reionisation-Era Galaxy

Dust is a fundamental component of the interstellar medium within galaxies, as dust grains are highly efficient absorbers of ultraviolet (UV) and optical photons. Accurately quantifying this obscuration is crucial for interpreting galaxy spectral energy distributions (SEDs). The extinction curves in the Milky Way (MW) and Large Magellanic Cloud exhibit a strong feature known as the 2175 Å UV bump, most often attributed to small carbonaceous dust grains. This feature was recently detected in faint galaxies out to z=7.55, suggesting rapid formation channels. Here, we report the detection of a strong UV bump in a luminous Lyman-break galaxy at z_prism=7.11235, GNWY-7379420231, through observations taken as part of the NIRSpec Wide GTO survey. We fit a dust attenuation curve that is consistent with the MW extinction curve within 1σ, in a galaxy just ~700 Myr after the Big Bang. From the integrated spectrum, we infer a young mass-weighted age (t~22-59 Myr) for this galaxy, however spatially resolved SED fitting unveils the presence of an older stellar population (t~252 Myr). Furthermore, morphological analysis provides evidence for a potential merger. The underlying older stellar population suggests the merging system could be pre-enriched, with the dust illuminated by a merger-induced starburst. Moreover, turbulence driven by stellar feedback in this bursty region may be driving polycyclic aromatic hydrocarbon formation through top-down shattering. The presence of a UV bump in GNWY-7379420231 solidifies growing evidence for the rapid evolution of dust properties within the first billion years of cosmic time

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arXiv2025

Exploring the mysterious high-ionization source powering [Ne V] in high-z analog SBS0335-052 E with JWST/MIRI

Nearby blue compact dwarf galaxies (BCDs) share similar properties with objects from the Epoch of Reionization revealed by JWST, in terms of low stellar mass, low metallicity and high specific star-formation rate. Thus, they represent ideal local laboratories for detailed multi-wavelength studies to understand their properties and the mechanisms shaping them. We report the first JWST MIRI/MRS observations of the BCD SBS 0335-052 E, analyzing MIR emission lines tracing different levels of ionization (e.g., [NeII], [SIV], [NeIII], [OIV], [NeV]) of the ionized gas. SBS 0335-052 E MIR emission is characterized by a bright point source, located in one of the youngest and most embedded stellar clusters ($t\sim3$ Myr, $A_V\sim15$), and underlying extended high-ionization emission (i.e., [OIV], [NeV]) from the surroundings of the older and less dusty stellar clusters ($t< 20 $ Myr, $A_V\sim8$). From the comparison with state-of-the-art models, we can exclude shocks, X-ray binaries, and old stellar populations as the main sources of the high ionization. Interestingly, a 4-16% contribution of a $\sim10^5$ M$_\odot$ intermediate massive black hole (IMBH) is needed to justify the strong [NeV]/[NeII] and would be consistent with optical/UV line ratios from previous studies. However, even IMBH models cannot explain the strongest [OIV]/[NeIII]. Also, star-forming models (regardless of including X-ray binaries) struggle to reproduce even the lower ionization line ratios (e.g., [SIV]/[NeII]) typically observed in BCDs. Overall, while current models suggest the need to account for an accreting IMBH in this high-$z$ analog, limitations still exist in predicting high-ionization emission lines (I.P. $>54$ eV) when modeling these low-metallicity environments, thus other sources of ionization cannot be fully ruled out.

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arXiv2025

JADES: Nitrogen Enhancement in High-Redshift Broad-Line Active Galactic Nuclei

The unexpectedly high nitrogen-to-oxygen (N/O) ratios observed in high-redshift (z) galaxies have challenged our understanding of early star formation. Notably, many of these nitrogen-rich galaxies show signatures of active galactic nuclei (AGNs), suggesting a possible connection between black hole formation and nitrogen enrichment. To explore this connection, we analyse stacked spectra of z=4-7 broad-line and narrow-line AGNs using deep NIRSpec data from the JADES survey. We identify a significant Niii] quintuplet and a high electron density ($\sim10^{4}\,\mathrm{cm^{-3}}$) only in the broad-line AGN stack, indicating nitrogen-rich ($\log(\mathrm{N/C})\simeq0.5$, $\log(\mathrm{N/O})>-0.6$) and dense gas similar to the high-z nitrogen-rich galaxies. Our findings suggest that dense nuclear star formation may trap nitrogen-rich gas in proto-globular clusters, in line with the high N/O observed in local globular clusters; associated runaway stellar collisions could produce intermediate-mass black hole seeds, as predicted by some models and simulations, whose accretion results into AGN signatures. These findings support scenarios connecting the early black hole seeding and growth to merging processes within and between proto-globular clusters in primeval galaxies.

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arXiv2025

Deciphering the Nature of Virgil: An Obscured AGN Lurking Within an Apparently Normal Lyman-α Emitter During Cosmic Reionization

We present a comprehensive analysis of the MIRI Extremely Red Object Virgil, a Lyman-$α$ emitter at $z_{spec} = 6.6379 \pm 0.0035$ with the photometric properties of a Little Red Dot. Leveraging new JWST/MIRI imaging from the MIDIS and PAHSPECS programs, we confirm Virgil's extraordinary nature among galaxies in JADES/GOODS-South, exhibiting a strikingly red NIRCam-to-MIRI color (F444W $-$ F1500W = $2.84\pm0.04$ mag). Deep NIRSpec/PRISM spectroscopy from the OASIS program offers key insights into the host galaxy, revealing properties of an average star-forming galaxy during Cosmic Reionization, such as a subsolar metallicity, low-to-moderate dust content, and a relatively high ionization parameter and electron temperature. By estimating the star formation rate of Virgil from UV and H$α$, we find evidence that the galaxy is either entering or fading out of a bursty episode. Although line-ratio diagnostics employed at high-$z$ would classify Virgil as an Active Galactic Nucleus (AGN), this classification becomes ambiguous once redshift evolution is considered. Nonetheless, Virgil occupies the same parameter space as recently confirmed AGNs at similar redshifts. The new deep MIRI data at 15 $μ$m reinforce the AGN nature of Virgil, as inferred from multiple spectral energy distribution (SED) fitting codes. Virgil's rising infrared SED and UV excess resemble those of Dust-Obscured Galaxies (DOGs) studied with Spitzer at Cosmic Noon, particularly blue-excess HotDOGs. Our results highlight the need for a multi-wavelength approach incorporating MIRI to uncover such extreme sources at $z\gtrsim6$ and to shed light on the interplay between galaxy evolution and early black hole growth during Cosmic Reionization.

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arXiv2025

Witnessing the onset of reionisation via Lyman-$α$ emission at redshift 13

$\require{mediawiki-texvc}$Cosmic Reionisation commenced when ultraviolet (UV) radiation produced in the first galaxies began illuminating the cold, neutral gas that filled the primordial Universe. Recent James Webb Space Telescope (JWST) observations have shown that surprisingly UV-bright galaxies were in place beyond redshift $z = 14$, when the Universe was less than $300 \, \mathrm{Myr}$ old. Smooth turnovers of their UV continua have been interpreted as damping-wing absorption of Lyman-$α$ (Ly$α$), the principal hydrogen transition. However, spectral signatures encoding crucial properties of these sources, such as their emergent radiation field, largely remain elusive. Here we report spectroscopy from the JWST Advanced Deep Extragalactic Survey (JADES) of a galaxy at redshift $z = 13.0$ that reveal a singular, bright emission line unambiguously identified as Ly$α$, in addition to a smooth turnover. We observe an equivalent width of $\text{EW}_\mathrm{Lyα} > 40 \, Å$ (rest frame), previously only seen at $z < 9$ where the intervening intergalactic medium (IGM) becomes increasingly ionised. Together with an extremely blue UV continuum, the unexpected Ly$α$ emission indicates the galaxy is a prolific producer and leaker of ionising photons. This suggests massive, hot stars or an active galactic nucleus (AGN) have created an early reionised region to prevent complete extinction of Ly$α$, thus shedding new light on the nature of the earliest galaxies and the onset of Reionisation only $330 \, \mathrm{Myr}$ after the Big Bang.

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arXiv2025

Zapped then Napped? A rapidly quenched remnant leaker candidate with a steep spectroscopic $β_{UV}$ slope at z=8.5

We use NIRSpec MSA spectroscopy and NIRCam Photometry to explore the properties of JADES-GS8-RL-1, a rapidly quenched, $z=8.5$ galaxy with a stellar mass of $10^{8.9}M_\odot$, a steep blue UV slope, a Balmer break, and no sign of strong emission lines. With a $β_{UV}$=-2.8$\pm 0.2$, as measured from the NIRSpec spectrum, JADES-GS8-RL-1 is consistent with negligible dust attenuation and little to no contribution from the nebular continuum alongside a probable high escape fraction. The $β_{UV}$ slope measured from photometry varies from -3.0 in the central regions to -2.2 at the outskirts suggesting possible regional differences in the escape fraction. There are no high-ionisation emission lines, only a tentative 2.9\sig detection of [OII]. Using photometry, this emission appears to be extended, possibly corresponding to weakly ionised gas expelled during or after the quenching process. JADES-GS8-RL-1 is spatially resolved with a half-light radius of 240 pc and has an exponential, disc-like morphology. It appears to have formed all its stars in a short burst within the past 100 Myr with a formation time of $\approx$70 Myr and a quenching time of $\approx$30 Myr. This quenching would have occurred rapidly, making it a more distant example of the kind of low-mass "mini-quenched" galaxies previously observed at high-z. Due to the extremely blue $β_{UV}$ slope, our best-fit model predicts a high value for \fesc of >10\%, consistent with the value derived from the $β_{UV}$ slope, which when combined with our extraordinarily low O32 upper limit suggests JADES-GS8-RL-1 is a fascinating example of a high-z "remnant leaker" in one of its earliest phases, deep in the epoch of reionisation.

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arXiv2025

GA-NIFS: High number of dual active galactic nuclei at z~3

Merger events can trigger gas accretion onto supermassive black holes (SMBHs) located at the centre of galaxies, and form close pairs of AGN. The fraction of AGN in pairs offers critical insights into the dynamics of galaxy interactions, SMBH growth, and their co-evolution with host galaxies. However, the identification of dual AGN is difficult, as it requires high-quality spatial and spectral data; hence, only very few pairs have been found in the distant Universe so far. This study aims to provide a first observational estimate of the fraction of dual AGN at 2<z<6 by analysing a sample of 16 AGN observed with JWST/NIRSpec IFS, as part of the GA-NIFS survey. For two AGN in our sample, we also incorporate archival VLT/MUSE data to expand the search area. We searched for nearby companion galaxies and emission-line sources within the ~20x20 kpc field of view of the NIRSpec data cubes, extending up to ~50 kpc using the MUSE data cubes. We analysed the spectra of such emitters to determine their physical and kinematic properties. We report the serendipitous discovery of a triple AGN and four dual AGN (two of which considered as candidates), with projected separations in the range 3-28 kpc. Their AGN classification is mainly based on standard optical emission line flux ratios, as observed with JWST/NIRSpec, and is complemented with additional multi-wavelength diagnostics. The identification of these 3-5 multiple AGN out of the 16 AGN systems in GA-NIFS (i.e. ~20-30%) suggests they might be more common than previously thought based on other observational campaigns. Moreover, our inferred fraction of dual AGN moderately exceeds predictions from cosmological simulations that mimic our observational criteria (~10%). This work highlights the exceptional capabilities of NIRSpec for detecting distant dual AGN, and prompts new investigations to constrain their fraction across cosmic time.

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arXiv2025

The eventful life of a luminous galaxy at z = 14: metal enrichment, feedback, and low gas fraction?

JADES-GS-z14-0 is the most distant spectroscopically confirmed galaxy yet, at $z>14$. With a UV magnitude of -20.81, it is one of the most luminous galaxies at cosmic dawn and its half-light radius of 260 pc means that stars dominate the observed UV emission. We report ALMA detection of [OIII]88$μ$m line emission with a significance of 6.67$σ$ and at a frequency of 223.524~GHz, corresponding to a redshift of $14.1796\pm0.0007$, which is consistent with the candidate CIII] line detected in the NIRSpec spectrum. At this spectroscopic redshift, the Lyman-$α$ break identified with NIRSpec requires a damped Lyman-$α$ absorber with a column density of $\log(N_{\rm HI}/\mathrm{cm}^{-2})=21.96$. The total [O\,{\sc iii}]88$μ$m luminosity (log$(L_{\rm [OIII]}/L_\odot) = 8.3\pm 0.1$) is fully consistent with the local $L_{\rm [OIII]}-SFR$ relation and indicating a gas-phase metallicity $>0.1~{\rm Z_{\rm \odot}}$. Using \texttt{prospector} SED modeling and combining the ALMA data with JWST observations, we find $Z=0.17~{\rm Z_{\rm \odot}}$ and a non-zero escape fraction of ionizing photons ($\sim11\%$), which is necessary by the code to reproduce the UV spectrum. We measure an ${\rm [O III]}5007$Å/[O III]88$μ$m line flux ratio between 1 and 20, resulting in an upper limit to the electron density of roughly 700 cm$^{-3}$ assuming a single-cloud photoionization model. The [OIIII]88$μ$m emission line is spectrally resolved, with a FWHM of 100 km/s, resulting in a dynamical mass of log($M_{\rm dyn}/M_\odot$) = 9.0$\pm0.2$. When compared to the stellar mass, this value represents a conservative upper limit on the gas mass fraction, which ranges from 50\% to 80\%, depending on the assumed star formation history. Past radiation-driven outflows may have cleared the galaxy from the gas, reducing the gas fraction and thus increasing the escape fraction of ionizing photons.

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arXiv2025

JADES: The star-formation and chemical enrichment history of a luminous galaxy at z~9.43 probed by ultra-deep JWST/NIRSpec spectroscopy

We analyse ultra-deep JWST observations of the galaxy JADES-GS-z9-0 at z = 9.4327, and derive detailed stellar and interstellar medium (ISM) properties of this luminous (MUV=-20.43) high-redshift system. Complementary information from NIRCam imaging and NIRSpec (both low- and medium-resolution) spectroscopy reveal a compact system (Re ~110 pc) characterised by a steeply rising star formation history, which is reflected in the inferred young stellar age (t ~ 3 Myr, light-weighted), high star-formation rate surface density (ΣSFR ~ 72 M yr-1 kpc-2), high ionisation parameter (log(U) ~ -1.5), low metallicity (12+log(O/H) ~ 7.5), and low carbon-over-oxygen abundance ([C/O] = -0.64). Leveraging the detection of N iii]1750 we derive nitrogen-over-oxygen abundance ([N/O] ~ 0) higher than the plateau followed by low-redshift galaxies of similar metallicity, possibly revealing the imprint from (very) massive stars on the ISM enrichment and favouring a top-heavy Initial Mass Function (IMF) scenario. Massive stars powering a hard radiation field are also required to explain the rest-frame UV line ratios, though the presence of the high-excitation [Ne v]λ3426 emission line possibly hints at additional ionization from an AGN. We also report the tentative detection of Lyα emission in the G140M spectrum, shifted by ~450 km/s redward of the systemic redshift. Combined with a modelling of the Lyα spectral break, we rule out the presence of very high column densities of neutral gas pertaining to local absorbers, as well as any extended surrounding ionised bubble, suggesting that JADES-GS-z9-0 has not yet significantly contributed to cosmic Reionization.

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arXiv2025

GA-NIFS: JWST/NIRSpec IFS view of the z~3.5 galaxy GS5001 and its close environment at the core of a large-scale overdensity

We present JWST NIRSpec observations in IFS mode of the galaxy GS5001 at redshift z=3.47, the central member of a candidate protocluster in the GOODS-S field. The data cover a field of view (FoV) of 4''$\times$4'' (~$30\times30$~kpc$^2$) and were obtained as part of the GA-NIFS GTO program. The observations include both high (R~2700) and low (R~100) spectral resolution data, spanning the rest-frame wavelength ranges 3700-6780A and 1300-11850A, respectively. We analyse the spatially resolved ionised gas kinematics and interstellar medium properties, including obscuration, gas metallicity, excitation, ionisation parameter, and electron density. In addition to the main galaxy (GS5001), the NIRSpec FoV covers three components in the south, with velocities blue-shifted by -150 km/s with respect to the main galaxy, and another source in the north redshifted by ~200 km/s. Optical line ratio diagnostics indicate star formation ionisation and electron densities of ~500 cm$^{-3}$ across all sources in the FoV. The gas-phase metallicity in the main galaxy is 12+log(O/H) $= 8.45\pm0.04$, and slightly lower in the companions (12+log(O/H)$ = 8.34-8.42$), consistent with the mass-metallicity relation at $z\sim3$. We find peculiar line ratios (high log [NII]/H$α$, low log [OIII]/H$β$) in the northern part of GS5001. These could be attributed to either higher metallicity, or to shocks resulting from the interaction of the main galaxy with the northern source. We identify a spatially resolved outflow in the main galaxy, with an extension of about 3 kpc. We find maximum outflow velocities of ~400 km/s, an outflow mass of $(1.7\pm0.4)\times 10^8$ M$_{\odot}$, a mass outflow rate of $23\pm5$ M$_{\odot}$ yr$^{-1}$ and a mass loading factor of 0.23. These properties are compatible with star formation being the driver of the outflow.

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arXiv2025

JADES: A large population of obscured, narrow line AGN at high redshift

We present the identification of 42 narrow-line active galactic nuclei (type-2 AGN) candidates in the two deepest observations of the JADES spectroscopic survey with JWST/NIRSpec. The spectral coverage and the depth of our observations allow us to select narrow-line AGNs based on both rest-frame optical and UV emission lines up to z=10. Due to the metallicity decrease of galaxies, at $z>3$ the standard optical diagnostic diagrams (N2-BPT or S2-VO87) become unable to distinguish many AGN from other sources of photoionisation. Therefore, we also use high ionisation lines, such as HeII$λ$4686, HeII$λ$1640, NeIV$λ$2422, NeV$λ$3420, and NV$λ$1240, also in combination with other UV transitions, to trace the presence of AGN. Out of a parent sample of 209 galaxies, we identify 42 type-2 AGN (although 10 of them are tentative), giving a fraction of galaxies in JADES hosting type-2 AGN of about $20\pm3$\%, which does not evolve significantly in the redshift range between 2 and 10. The selected type-2 AGN have estimated bolometric luminosities of $10^{41.3-44.9}$ erg s$^{-1}$ and host-galaxy stellar masses of $10^{7.2-9.3}$ M$_{\odot}$. The star formation rates of the selected AGN host galaxies are consistent with those of the star-forming main sequence. The AGN host galaxies at z=4-6 contribute $\sim$8-30 \% to the UV luminosity function, slightly increasing with UV luminosity.

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arXiv2025

Deep Constraints on [CII]158$μ$m in JADES-GS-z14-0: Further Evidence for a Galaxy with Low Gas Content at z=14.2

We present deep ALMA observations targeting the [CII]$_{158μm}\,$ line in JADES-GS-z14-0, the most distant known galaxy at z=14.1793. We do not detect the [CII]$_{158μm}\,$ line in our deep observations, implying a luminosity of $<$6$\times10^7$ L$_{\odot}$ (3$σ$) for the target. Comparing this with the detected [OIII]$_{88μm}\,$ line, we constrain the [OIII]/[CII] ratio to be $>$3.5, significantly improving our probe of the ionization parameter $U$. The observed ratio is higher than analogues in the local universe, but consistent with galaxies at $z\approx6$-9. Through ISM modeling, we infer extreme ionizing conditions with log(U)$>-$2.0, likely requiring a young stellar population. Our modeling also indicates a relatively low gas density ($51_{-32}^{+116}$ cm$^{-3}$), significantly lower than expected from lower redshift trends. We infer a relatively high gas-phase metallicity (16$\pm$6\% solar) consistent with previous results and implying a rapid build-up of metals. Finally, using [CII]$_{158μm}\,$ as a molecular/cold gas mass tracer, we infer a low gas fraction ($f_\mathrm{gas} < 0.77$), consistent with previous estimates of the dynamical mass from [OIII]$_{88μm}\,$. Combined with the low observed gas density, lack of dust and high ionization parameter, this suggests strong feedback processes are playing an important role in the evolution of this galaxy. Our observations show that JADES-GS-z14-0 is a rapidly evolving galaxy with extreme ISM conditions, shedding light on the earliest phases of galaxy formation.

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arXiv2024

Hitting the slopes: A spectroscopic view of UV continuum slopes of galaxies reveals a reddening at z > 9.5

The UV continuum slope of galaxies, $β$, is a powerful diagnostic. Understanding the redshift evolution of $β$ and its dependence on key galaxy properties can shed light on the evolution of galaxy physical properties over cosmic time. In this study, we present $β$ measurements for 295 spectroscopically confirmed galaxies at $5.5 9.5$ to begin to redden, deviating from the trend observed at $z < 9.5$. By producing stacked spectra in bins of redshift and $β$, we derive trends between $β$ and dust attenuation, metallicity, ionization parameter, and stellar age indicators directly from spectra, finding a lack of dust attenuation to be the dominant driver of bluer $β$ values. We further report six galaxies with $β<-3.0$, which show a range of spectroscopic properties and signs of significant LyC photon leakage. Finally, we show that the redder $β$ values at $z > 9.5$ may require rapid build-up of dust reservoirs in the very early Universe or a significant contribution from the nebular continuum emission to the observed UV spectra, with the nebular continuum fraction depending on the gas temperatures and densities. Our modeling shows that in the absence of dust, nebular emission at $T > 15,000$ K can reproduce the range of $β$ that we see in our sample. Higher gas temperatures driven by hot, massive stars can boost the fraction of nebular continuum emission, potentially explaining the observed $β$ values as well as bright UV magnitudes seen across galaxies at $z > 10$.

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arXiv2024

JADES: Measuring reionization properties using Lyman-alpha emission

Ly$α$ is the transition to the ground state from the first excited state of hydrogen (the most common element). Resonant scattering of this line by neutral hydrogen greatly impedes its emergence from galaxies, so the fraction of galaxies emitting Ly$α$ is a tracer of the neutral fraction of the intergalactic medium (IGM), and thus the history of reionisation. In previous works, we used early JWST/NIRSpec data from the JWST Advanced Deep Extragalactic Survey (JADES) to classify and characterise Ly$α$ emitting galaxies (LAEs). This survey is approaching completion, and the current sample is nearly an order of magnitude larger. From a sample of 795 galaxies in JADES at $4.0<z<14.3$, we find evidence for Ly$α$ emission in 150sources. We reproduce the previously found correlation between Ly$α$ escape fraction ($f_{esc}^{Lyα}$) - Ly$α$ rest-frame equivalent width ($REW_{Lyα}$) and the negative correlation between Ly$α$ velocity offset - $f_{esc}^{Lyα}$. Both $f_{esc}^{Lyα}$ and $REW_{Lyα}$ decrease with redshift ($z\gtrsim5.5$), indicating the progression of reionisation on a population scale. Our data are used to demonstrate an increasing IGM transmission of Ly$α$ from $z\sim14-6$. We measure the completeness-corrected fraction of LAEs (\xlya) from $z=4-9.5$. An application of these \xlya values to the results of previously utilised semi-analytical models suggests a high neutral fraction at $z=7$ ($X_{HI}\sim0.8-0.9$). Using an updated fit to the intrinsic distribution of $REW_{Lyα}$ results in a lower value in agreement with current works ($X_{HI}=0.64_{-0.21}^{+0.13}$). This sample of LAEs will be paramount for unbiased population studies of galaxies in the EoR.

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