arXiv subjects

D. Scholte

Publications and source records attributed to D. Scholte.

15 recordsLinked to original sources

arXiv2026

Linking neutral gas inflows and outflows to offsets in the star-forming main sequence and mass-metallicity relation

Gas inflows and outflows regulate galaxy growth, but direct observational links between measured gas flows and galaxy scaling relations remain limited. Using ~6,000 star-forming galaxies with down-the-barrel Na I D absorption from DESI DR2, we examine how systems with detected neutral-gas inflows and outflows populate the star-forming main sequence (SFMS) and mass-metallicity relation (MZR). Inflow and outflow hosts are compared with stellar-mass- and redshift-matched controls, and with SFMS and MZR fits derived from galaxies without detected gas flows. Outflow hosts (v_flow $\leq$ -50 km s$^{-1}$) show enhanced sSFRs by 0.25-0.40 dex and elevated central metallicities by 0.04-0.06 dex in the lower-redshift sample. Slow inflow hosts (0 $<$ v_flow $<$ 100 km s$^{-1}$) show similarly enhanced sSFRs of 0.20-0.30 dex, but no significant metallicity offset, while fast inflow hosts (v_flow $\geq$ 100 km s$^{-1}$) show weaker SFR enhancement and modestly lower metallicities. Together, these trends support a regulator picture in which neutral gas flows trace different phases of the baryon cycle. Slow inflow hosts lie above the SFMS, consistent with accretion sustaining enhanced star formation without strong central metallicity dilution. This may indicate that inflowing gas is already metal-enriched or has mixed or enriched over extended timescales. By contrast, outflow hosts lie near the upper 1{$\sigma$} SFMS envelope, consistent with feedback regulating subsequent growth. Gas-flow hosts also show small but systematic offsets in the narrow 4000 {\AA} break strength ($D_n$4000) relative to controls matched in redshift, stellar mass and SFR. Our results show that neutral gas flows are associated with population-level offsets from the SFMS and MZR, consistent with a baryon-cycle contribution to scaling-relation scatter.

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arXiv2026

Beyond the Fundamental Metallicity Relation: galaxy sizes encode the link between inflow and metallicity

Gas-phase chemical abundances are key observable consequences of galaxy evolution, being intrinsically tied to galaxy formation histories. Gas metallicity rises with increasing stellar mass ($\mathrm{M_*}$), forming the well-known mass-metallicity relation (MZR). MZR residuals have separately been shown to anti-correlate with star-formation rate (the ``fundamental'' metallicity relation), with gas mass and with optical size, but no single analysis has considered all trends together. We thus perform a combined analysis of all three trends, utilizing optical MaNGA integral field spectroscopy, HI-MaNGA gas masses, and MaNGA DynPop dynamical masses. We estimate inner gas masses for $\sim$1500 star-forming galaxies, finding this to be the most important parameter after $\mathrm{M_*}$ in predicting gas metallicities. We obtain equivalent results for stellar metallicities and gaseous N/O, suggesting that current inner gas masses are intrinsically linked to long-term chemical evolution histories. We show that more compact galaxies have lower dynamical masses, challenging suggestions that deeper gravitational potentials confer higher metallicities. We find a strong correlation between inner gas mass and galaxy size, meaning that short term inflow fluctuations cannot be responsible for the MZR residuals. With chemical evolution models, we show that our results can instead be explained by differences in long-term inflow histories. The earlier inflow histories of compact galaxies lead to lower gas masses and more rapidly declining gas reservoirs at late times, leading to higher metallicities. At fixed stellar mass, galaxy size therefore encodes the link between halo assembly histories, long-term gas inflow histories, current gas reservoirs and metallicity.

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arXiv2026

Electron temperature relations and the direct N, O, Ne, S and Ar abundances of 49959 star-forming galaxies in DESI Data Release 2

We present the largest direct-method abundance catalogue of galaxies to date, containing measurements of 49959 star-forming galaxies at z < 0.96 from DESI Data Release 2. By directly measuring electron temperatures across multiple ionisation zones, we provide constraints on a number of electron temperature relations. Using the temperature measurements, we derive reliable abundances for N, O, Ne, S and Ar and measure the evolution of abundances and abundance ratios of as a function of metallicity and other galaxy properties. Our measurements include direct oxygen abundances for 49507 galaxies, leading to the discovery of the two most metal-poor galaxies in the nearby Universe, with oxygen abundances of 12+log(O/H) = $\rm 12+\log(O/H) = 6.77_{-0.03}^{+0.03}~\rm dex $ (1.2\% $\rm Z_{\odot}$) and $\rm 12+\log(O/H) = 6.81_{-0.04}^{+0.04}~\rm dex$ (1.3\% $\rm Z_{\odot}$). We identify a rare outlier population of 24 galaxies with high N/O ratios at low metallicity, reminiscent of galaxy abundances observed in the early Universe. We find the Ne/O ratio is constant at low metallicity but increases gradually at $\rm 12+log(O/H) > 8.105\pm0.004$ dex. We show that the S/O and Ar/O abundance ratios are strongly correlated, consistent with the expected additional Type Ia enrichment channel for S and Ar. In this work we present an initial survey of the key properties of the sample, with this dataset serving as a foundation for extensive future work on galaxy abundances at low redshift.

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arXiv2025

Why the Northern Hemisphere Needs a 30-40 m Telescope and the Science at Stake: Northern Local Star-forming Dwarf Galaxies. Analogues of the First Galaxies and Probes of the Cosmic Metallicity Scale

Star-forming dwarf galaxies in the local Universe, especially extremely metal-poor ones, can be considered analogous to early galaxies of the Epoch of Reionization (z >= 6). Currently available telescopes cannot adequately detect and measure heavy element recombination lines and certain faint collisionally excited lines, which are essential for exploring the effects and biases that potential inhomogeneities in electron temperature and density of the ionized gas may have on determining the chemical composition of these galaxies. On the other hand, the origin of very high-ionization lines (e.g. He II, [Ne V], C IV]) measured in the spectra of an important fraction of these objects remains unknown and a challenge to current stellar models, suggesting the presence of Population III-like stars and/or the existence of non-conventional ionizing sources. Obtaining very deep spectra for a selected sample of local star-forming dwarf galaxies would provide unprecedented constraints on their nature, ionization and true chemical abundances, and could change the metallicity scale we assume to understand the chemical evolution of galaxies over cosmic time.

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arXiv2025

The JWST EXCELS Survey: gas-phase metallicity evolution at 2 < z < 8

We present an analysis of the gas-phase mass-metallicity relationship (MZR) and fundamental metallicity relationship (FMR) for $65$ star-forming galaxies at $2 < z < 8$ from the JWST/EXCELS survey. We calculate gas-phase metallicities (12 + log(O/H)) using strong-line calibrations explicitly tested against the EXCELS sample, and report direct-method metallicities for $19$ galaxies. Our sample spans $8.1<\log(\rm M_\star/M_\odot)<10.3$ and $0<\log(\rm SFR/M_\odot \, yr^{-1})<2$, consistent with main-sequence star-forming galaxies at the same redshifts. We find a clear MZR at both $2 3$ studies. We discuss potential drivers of this offset, noting that high-redshift samples have significantly different physical properties compared to local samples used to define the $z=0$ FMR. Our results confirm that low-mass, high specific star-formation rate galaxies common at high redshift are inconsistent with the equilibrium conditions underlying the local FMR, and highlight the rapid chemical enrichment at early cosmic epochs.

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arXiv2025

The JWST EXCELS Survey: A spectroscopic investigation of the ionizing properties of star-forming galaxies at 1<z<8

Charting the Epoch of Reionization demands robust assessments of what drives the production of ionizing photons in high-redshift star-forming galaxies (SFGs), and requires better predictive capabilities from current observations. Using a sample of $N=159$ SFGs at $1<z<8$, observed with deep medium-resolution spectroscopy from the JWST/NIRSpec EXCELS survey, we perform a statistical analysis of their ionizing photon production efficiencies ($\xi_\rm{ion}$). We consider $\xi_\rm{ion}$, measured with Balmer line measurements, in relation to a number of key galaxy properties including; nebular emission line strengths ($W_\lambda(\rm{H\alpha})$ and $W_\lambda$( [OIII])), UV luminosity ($M_\rm{UV}$) and UV slope ($\beta_\rm{UV}$), as well as dust attenuation ($E(B-V)_\rm{neb}$) and redshift. Implementing a Bayesian linear regression methodology, we fit $\xi_\rm{ion}$ against the principal observables while fully marginalising over all measurement uncertainties, mitigating against the impact of outliers and determining the intrinsic scatter. Significant relations between $\xi_\rm{ion}$ and $ W_\lambda(\rm{H\alpha})$, $W_\lambda$([OIII]) and $\beta_\rm{UV}$ are recovered. Moreover, the weak trends with $M_\rm{UV}$ and redshift can be fully explained by the remaining property dependencies. Expanding our analysis to multivariate regression, we determine that $W_\lambda(\rm{H\alpha})$ or $W_\lambda$([OIII]), along with $\beta_\rm{UV}$ and $E(B-V)_\rm{neb}$, are the most important observables for accurately predicting $\xi_\rm{ion,0}$. The latter identifies the most common outliers as SFGs with relatively high $E(B-V)_\rm{neb}\gtrsim0.5$, possibly indicative of obscured star-formation or strong differential attenuation. Combining these properties enable $\xi_\rm{ion,0}$ to be inferred with an accuracy of $\sim0.15\,$dex, with a population intrinsic scatter of $\sigma_\rm{int}\sim0.035\,$dex.

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arXiv2025

Strength in Numbers: Red Galaxies Bolster the Cosmic Star Formation Rate Density at z > 3

A comprehensive account of the cosmic star-formation history demands an accurate census of dust-enshrouded star formation over cosmic time. We provide strong new constraints from a large sample of 777 red galaxies, selected based on their dust-reddened, rest-frame UV-optical emission. This sample of 777 galaxies spans $1 < z < 8$ and is selected from PRIMER JWST NIRCam and HST COSMOS optical data, ensuring robust colour criteria. The SEDs indicate that these dust-reddened galaxies are star-forming, with median $\mathrm{SFR \sim 40M_{\odot}yr^{-1}}$ and stellar mass $\log(M_{*}/M_{\odot}) = 10.3^{+0.6}_{-0.8}$; each exceeds the corresponding medians of the full JWST-detected population by over two dex. Our sample thus clearly shows that red galaxies dominate the high-mass end: they comprise 72 \% of galaxies with $\log(M/M_{\odot}) > 10$ at $z = 3.3$, rising to 91\% by $z \sim 7$ (albeit with large uncertainties at the highest redshifts). Crucially, we find that the number density of massive red star-forming galaxies at $z \sim 6$ is sufficient to explain the abundance of quiescent galaxies at $z > 3$, consistent with typical quenching timescales allowed in the $\mathrm{\sim 1Gyr}$ interval from $z \sim 6$ to $z \sim 3$. This large abundance yields a substantial contribution to the cosmic star-formation rate density: at $z \sim 4$, red galaxies provide $\mathrm {\rho_{SFR} = 3.9^{+0.6}_{-0.5} \times 10^{-2} M_{\odot} yr^{-1}Mpc^{-3}}$, and at $z \sim 5$ they supply nearly 40 \% of the total $\rho_{SFR}$. This exceeds the contribution of bright sub(mm)-selected dusty star-forming galaxies by more than an order of magnitude. Future deeper and wider ALMA surveys will provide further opportunities to strengthen and extend our results in our quest to fully quantify the contribution of dust-obscured activity to $\rho_{\mathrm{SFR}}$ at high redshifts.

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arXiv2025

The JWST EXCELS survey: Probing strong-line diagnostics and the chemical evolution of galaxies over cosmic time using Te-metallicities

We present an analysis of the rest-frame optical spectra of 22 [OIII]$\lambda$4363 detected galaxies in the redshift range $1.65 < z < 7.92$ (with $\langle z \rangle$ = 4.05) from JWST/NIRSpec medium-resolution observations taken as part of the EXCELS survey. To supplement these high-redshift sources, we also consider a sample of 782 local [OIII]$\lambda$4363 detected galaxies from the DESI Early Data Release. Our analysis demonstrates that many strong-line calibrations are biased in the early Universe due to the systematic evolution in ionization conditions with redshift. However, the recently introduced $\widehat{R}$ calibration mostly removes the dependence on ionization state and can be considered a largely redshift-independent calibration. In a similar spirit, we introduce a new strong-line diagnostic, $\widehat{RNe}$, which can be used to robustly estimate metallicities when the [OIII]$\lambda$5007 is redshifted out of the wavelength range of JWST/NIRSpec at $z > 9.5$. We also show that strong-line diagnostics using the [NII]$\lambda$6584 emission line are likely to be biased at high-redshift due to a moderate enhancement in the average N/O abundance ratios (at fixed O/H) in these sources. Finally, we discuss the location of our new [OIII]$\lambda$4363 detected galaxies at $z \simeq 4$ on the mass-metallicity plane and investigate the redshift evolution of the fundamental metallicity relation (FMR). We find tentative evidence for an increasing deviation from the FMR at $z > 4$ which might indicate fundamental differences in the baryon cycle at these redshifts. However, more data are required as our high-redshift constraints are still based on a relatively small sample of galaxies and the significance of the deviation is strongly dependent on the assumed form of the fundamental metallicity relation.

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arXiv2025

The JWST EXCELS survey: an extremely metal-poor galaxy at $z=8.271$ hosting an unusual population of massive stars

We present an analysis of the rest-frame optical ($\lambda \simeq 3100-5600 \,$\r{A}) spectrum of a $\mathrm{log}_{10}(M_*/\mathrm{M_\odot}) = 8.6$ star-forming galaxy at $z=8.271$ from JWST/NIRSpec medium-resolution observations taken as part of the EXCELS survey. The galaxy (EXCELS-63107) is compact, with a size consistent with the size of local star-forming cluster complexes ($r_e < 200 \, \rm{pc}$) and has an extremely steep UV continuum measured from JWST/NIRCam photometry ($\beta=-3.3\pm0.3$). The JWST/NIRSpec G395M spectrum of EXCELS-63107 is notable for its strong [OIII]$\lambda4363$ auroral-line emission relative to the [OIII]$\lambda5007$ forbidden line. Via a detailed emission-line and photoionization-modelling analysis, we find that the the observed properties of EXCELS-63107 are consistent with the presence of an ionizing source with an effective temperature of $T_{\rm eff} \gtrsim 80 \, 000\,\rm{K}$ heating ionized gas with a density of $n_e < 10^4 \, \rm{cm}^{-3}$ to a volume-averaged electron temperature of $T_e \simeq 34 \, 000\,\rm{K}$. Crucially, we find that stellar population models assuming a standard IMF are not capable of producing the required heating. We determine an oxygen abundance of ${12+\mathrm{log(O/H)}= 6.89^{+0.26}_{-0.21}}$ which is one of the lowest directly constrained oxygen abundances measured in any galaxy to date, and $\simeq 10 \times$ lower than is typical for $z\simeq8$ galaxies with the same stellar mass. The extremely low metallicity of EXCELS-63107 places it in a regime in which theoretical models expect a transition to a top-heavy IMF, and we speculate that a $\simeq 10-30 \, \times$ excess of $M > 50 \, \rm{M}_{\odot}$ stars is one plausible explanation for its observed properties. However, more exotic scenarios, such as Pop III star formation within a mildly enriched halo, are also consistent with the observations.

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arXiv2024

The JWST EXCELS survey: direct estimates of C, N, and O abundances in two relatively metal-rich galaxies at $\mathbf{z\simeq5}$

We present a spectroscopic analysis of two star-forming galaxies at $z\simeq5$ observed with JWST/NIRSpec as part of the EXCELS survey. The detection of the CIII]~$\lambda\lambda$1906,09, [OII] $\lambda\lambda$3726,29, [OIII] $\lambda\lambda$4363,5007, and [NII] $\lambda$6584 emission lines enables an investigation of the $\mathrm{C/O}$, $\mathrm{N/O}$, and $\mathrm{C/N}$ abundance ratios using the temperature-sensitive method. The galaxies have stellar masses of ${\mathrm{log}(M_{\star}/\mathrm{M}_{\odot}) = 8.09^{+\, 0.24}_{-0.15}}$ and ${\mathrm{log}(M_{\star}/\mathrm{M}_{\odot}) = 8.02^{+\, 0.06}_{-0.08}}$ with metallicities of $Z \simeq 0.2 \, \rm{Z_{\odot}}$ and $Z \simeq 0.3 \, \rm{Z_{\odot}}$. These metallicities are somewhat higher than is typical for other $z\gtrsim 5$ galaxies with similar stellar mass and are comparable to $z \simeq 0$ analogues. Both galaxies display evidence for elevated N/O ratios with respect to the typical star-forming galaxies at $z\simeq0$, with ${\mathrm{log(N/O)} = -1.07^{+\,0.17}_{-0.13}}$ and ${\mathrm{log(N/O)} = -0.86^{+\,0.15}_{-0.11}}$ respectively. In contrast, we find low C abundances, with ${\mathrm{log(C/O)}=-0.82\pm0.22}$ and ${\mathrm{log(C/O)}=-1.02\pm0.22}$, consistent with the predicted yields of core-collapse supernovae. Following the trend observed in other high-redshift sources, we find that the $\mathrm{C/N}$ ratios are lower at fixed $\mathrm{O/H}$ compared to the majority of local galaxies. Via a comparison to detailed chemical evolution models, we find that a standard or bottom-heavy IMF can explain the observed abundance ratios where the N-enrichment comes from intermediate mass ($\simeq 4-7 \, \mathrm{M}_{\odot}$) stars. Our results demonstrate that robust measurements of CNO abundances with \emph{JWST} can reveal unique enrichment pathways in galaxies as a function of both metallicity and redshift.

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arXiv2024

The JWST EXCELS survey: tracing the chemical enrichment pathways of high-redshift star-forming galaxies with O, Ar and Ne abundances

We present an analysis of eight star-forming galaxies with $\langle z \rangle = 4.0$ from the JWST EXCELS survey for which we obtain robust chemical abundance estimates for the $\alpha$-elements O, Ne and Ar. The $\alpha$-elements are primarily produced via core-collapse supernovae (CCSNe) which should result in $\alpha$-element abundance ratios that do not vary significantly across cosmic time. However, Type Ia supernovae (SNe Ia) models predict an excess production of Ar relative to O and Ne. The Ar/O abundance ratio can therefore be used as a tracer of the relative enrichment of CCSNe and SNe Ia in galaxies. Our sample significantly increases the number of sources with measurements of ${\rm Ar/O}$ at $z > 2$, and we find that our sample exhibits sub-solar Ar/O ratios on average, with $\rm{Ar/O} = 0.65 \pm 0.10 \, (\rm{Ar/O})_{\odot}$. In contrast, the average Ne/O abundance is fully consistent with the solar ratio, with $\rm{Ne/O} = 1.07 \pm 0.12 \, (\rm{Ne/O})_{\odot}$. Our results support a scenario in which Ar has not had time to build up in the interstellar medium of young high-redshift galaxies, which are dominated by CCSNe enrichment. We show that these abundance estimates are in good agreement with recent Milky Way chemical evolution models, and with Ar/O trends observed for planetary nebulae in the Andromeda galaxy. These results highlight the potential for using multiple element abundance ratios to constrain the chemical enrichment pathways of early galaxies with JWST.

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arXiv2024

Value Added Catalog of physical properties of more than 1.3 million galaxies from the DESI Survey

Aims. We present an extensive catalog of the physical properties of more than a million galaxies within the Dark Energy Spectroscopic Instrument (DESI), one of the largest spectroscopic surveys to date. Spanning over a full variety of target types, including emission line galaxies and luminous red galaxies as well as quasars, our survey encompasses an unprecedented range of spectroscopic redshifts, stretching from 0 to 6. Methods. The physical properties, such as stellar masses and star formation rates, are derived via the CIGALE spectral energy distribution (SED) fitting code accounting for the contribution coming from active galactic nuclei (AGN). Based on the modeling of the optical-mid-infrared (grz complemented by WISE photometry) SEDs, we study galaxy properties with respect to their location on the main sequence. Results. We revise the dependence of stellar mass estimates on model choices and availability of the WISE photometry. The WISE information is mandatory to minimize the misclassification of star-forming galaxies as AGN. The lack of WISE bands in SED fits leads to elevated AGN fractions for 68% of star-forming galaxies identified using emission line diagnostic diagram but does not significantly affect their stellar mass nor star formation estimates.

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arXiv2024

The atomic gas sequence and mass-metallicity relation from dwarfs to massive galaxies

Galaxy scaling relations provide insights into the processes that drive galaxy evolution. The extension of these scaling relations into the dwarf galaxy regime is of particular interest. This is because dwarf galaxies represent a crucial stage in galaxy evolution, and understanding them could also shed light on their role in reionising the early Universe. There is currently no consensus on the processes that dominate the evolution of dwarfs. In this work we constrain the atomic gas sequence (stellar mass vs. atomic gas fraction) and mass-metallicity relation (stellar mass vs. gas phase metallicity) from dwarf ($10^{6.5}$ $\textrm{M}_{\odot}$) to massive ($10^{11.5}$ $\textrm{M}_{\odot}$) galaxies in the local Universe. The combined optical and 21-cm spectroscopic observations of the DESI and ALFALFA surveys allow us to simultaneously constrain both scaling relations. We find a slope change of the atomic gas sequence at a stellar mass of $\sim 10^{9} ~\textrm{M}_{\odot}$. We also find that the shape and scatter of the atomic gas sequence and mass-metallicity relation are strongly linked for both dwarfs and more massive galaxies. Consequently, the low mass slope change of the atomic gas sequence is imprinted onto the mass-metallicity relation of dwarf galaxies. The mass scale of the measured slope change is consistent with a predicted escape velocity threshold below which low mass galaxies experience significant supernova-driven gas loss, as well as with a reduction in cold gas accretion onto more massive galaxies.

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arXiv2024

The NIRVANDELS Survey: the stellar and gas-phase mass-metallicity relations of star-forming galaxies at z = 3.5

We present determinations of the gas-phase and stellar metallicities of a sample of 65 star-forming galaxies at $z \simeq 3.5$ using rest-frame far-ultraviolet (FUV) spectroscopy from the VANDELS survey in combination with follow-up rest-frame optical spectroscopy from VLT/KMOS and Keck/MOSFIRE. We infer gas-phase oxygen abundances ($Z_{\mathrm{g}}$; tracing O/H) via strong optical nebular lines and stellar iron abundances ($Z_{\star}$; tracing Fe/H) from full spectral fitting to the FUV continuum. Our sample spans the stellar mass range $8.5 < \mathrm{log}(M_{\star}/\mathrm{M}_{\odot}) < 10.5$ and shows clear evidence for both a stellar and gas-phase mass-metallicity relation (MZR). We find that our O and Fe abundance estimates both exhibit a similar mass-dependence, such that $\mathrm{Fe/H}\propto M_{\star}^{0.30\pm0.11}$ and $\mathrm{O/H}\propto M_{\star}^{0.32\pm0.09}$. At fixed $M_{\star}$ we find that, relative to their solar values, O abundances are systematically larger than Fe abundances (i.e., $\alpha$-enhancement).We estimate an average enhancement of $\mathrm{(O/Fe)} = 2.65 \pm 0.16 \times \mathrm{(O/Fe)_\odot}$ which appears to be independent of $M_{\star}$. We employ analytic chemical evolution models to place a constraint on the strength of galactic-level outflows via the mass-outflow factor ($\eta$). We show that outflow efficiencies that scale as $\eta \propto M_{\star}^{-0.32}$ can simultaneously explain the functional form of of the stellar and gas-phase MZR, as well as the degree of $\alpha$-enhancement at fixed Fe/H. Our results add further evidence to support a picture in which $\alpha$-enhanced abundance ratios are ubiquitous in high-redshift star-forming galaxies, as expected for young systems whose interstellar medium is primarily enriched by core-collapse supernovae.

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arXiv2020

Study of spider pulsar binary eclipses and discovery of an eclipse mechanism transition

We present a comparative study of the low-frequency eclipses of spider (compact, irradiating binary) PSRs B1957+20 and J1816+4510. Combining these data with those of three other eclipsing systems we study the frequency dependence of the eclipse duration. PSRs B1957+20 and J1816+4510 have similar orbital properties, but the companions to the pulsars have masses that differ by an order of magnitude. A dedicated campaign to simultaneously observe the pulsed and imaged continuum flux densities throughout the eclipses reveals many similarities between the excess material within the two binaries, irrespective of the companion star properties. The observations show that the pulsar fluxes are removed from the line of sight throughout the main body of the eclipses. For PSR J1816+4510 we present the first direct evidence of an eclipse mechanism that transitions from one that removes the pulsar flux from the line of sight to one that merely smears out pulsations, and claim that this is a consequence of scattering in a tail of material flowing behind the companion. Inferred mass loss rates from the companion stars are found to be $\dot{M}_{\text{C}} \sim 10^{-12}~M_\odot$~yr$^{-1}$ and $\dot{M}_{\text{C}} \sim 2 \times 10^{-13}~M_\odot$~yr$^{-1}$ for PSR B1957+20 and PSR J1816+4510, respectively; seemingly too low to evaporate the stars within Hubble time. Measurements of eclipse durations over a wide range of radio-frequencies show a significant dependence of eclipse duration on frequency for all pulsars, with wider eclipses at lower-frequencies. These results provide a marked improvement in the observational constraints available for theoretical studies of the eclipse mechanisms.

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