arXiv subjects

A. Saxena

Publications and source records attributed to A. Saxena.

At least 37 records · Page 2Linked to original sources

arXiv2023

Identification and properties of intense star-forming galaxies at redshifts z>10

Surveys with James Webb Space Telescope (JWST) have discovered candidate galaxies in the first 400 Myr of cosmic time. Preliminary indications have suggested these candidate galaxies may be more massive and abundant than previously thought. However, without confirmed distances, their inferred properties remain uncertain. Here we identify four galaxies located in the JWST Advanced Deep Extragalactic Survey (JADES) Near-Infrared Camera (NIRCam) imaging with photometric redshifts z~10-13. These galaxies include the first redshift z>12 systems discovered with distances spectroscopically confirmed by JWST in a companion paper. Using stellar population modelling, we find the galaxies typically contain a hundred million solar masses in stars, in stellar populations that are less than one hundred million years old. The moderate star formation rates and compact sizes suggest elevated star formation rate surface densities, a key indicator of their formation pathways. Taken together, these measurements show that the first galaxies contributing to cosmic reionisation formed rapidly and with intense internal radiation fields.

astro-ph.GA↗

arXiv2023

Insights into the reionization epoch from cosmic-noon-CIV emitters in the VANDELS survey

Recently, intense emission from nebular C III] and C IV emission lines have been observed in galaxies in the epoch of reionization ($z>6$) and have been proposed as the prime way of measuring their redshift and studying their stellar populations. These galaxies might represent the best examples of cosmic reionizers, as suggested by recent low-z observations of Lyman Continuum emitting galaxies, but it is hard to directly study the production and escape of ionizing photons at such high redshifts. The ESO spectroscopic public survey VANDELS offers the unique opportunity to find rare examples of such galaxies at cosmic noon ($z\sim 3$), thanks to the ultra deep observations available. We have selected a sample of 39 galaxies showing C IV emission, whose origin (after a careful comparison to photoionization models) can be ascribed to star formation and not to AGN. By using a multi-wavelength approach, we determine their physical properties including metallicity and ionization parameter and compare them to the properties of the parent population to understand what are the ingredients that could characterize the analogs of the cosmic reionizers. We find that C IV emitters are galaxies with high photons production efficiency and there are strong indications that they might have also large escape fraction: given the visibility of C IV in the epoch of reionization this could become the best tool to pinpoint the cosmic reioinzers.

astro-ph.GA↗

arXiv2023

Radio antenna design for sky-averaged 21 cm cosmology experiments: the REACH case

Following the reported detection of an absorption profile associated with the 21~cm sky-averaged signal from the Cosmic Dawn by the EDGES experiment in 2018, a number of experiments have been set up to verify this result. This paper discusses the design process used for global 21~cm experiments, focusing specifically on the Radio Experiment for the Analysis of Cosmic Hydrogen (REACH). This experiment will seek to understand and compensate for systematic errors present using detailed modelling and characterization of the instrumentation. There is detailed the quantitative figures of merit and numerical modelling used to assist the design process of the REACH dipole antenna (one of the 2 antenna designs for REACH Phase I). This design process produced a 2.5:1 frequency bandwidth dipole. The aim of this design was to balance spectral smoothness and low impedance reflections with the ability to describe and understand the antenna response to the sky signal to inform the critically important calibration during observation and data analysis.

astro-ph.IM↗

arXiv2022

Discovery of 24 radio-bright quasars at $4.9 \leq z \leq6.6$ using low-frequency radio observations

High redshift quasars ($z>5$) that also shine brightly at radio wavelengths are unique signposts of supermassive black hole activity in the early universe. However, bright radio sources at $z\ge5$ are extremely rare and therefore we have started a campaign to search for new high-$z$ quasars by combining an optical dropout selection driven by the $g$, $r$, and $z$ bands from the Dark Energy Spectroscopic Instrument (DESI) Legacy Imaging Surveys with low-frequency radio observations from the LOFAR Two-metre Sky Survey (LoTSS). Currently, LoTSS covers a large fraction of the northern sky (5720 deg$^2$) to such a depth (median noise level of 83 $μ$Jy beam$^{-1}$) that about 30% of the general quasar population is detected $-$ which is a factor of 5-10 more than previous large sky radio surveys such as NVSS and FIRST, respectively. In this paper, we present the discovery of 20 new quasars (and the independent confirmation of 4) between $4.9\leq z\leq 6.6$. Out of the 24 quasars, 21 satisfy the traditional radio-loudness criterion of $R=f_{5\text{GHz}}/f_{4400A} > 10$, with the full sample spanning $R\sim$6-1000, thereby more than doubling the sample of known radio-loud quasars at $z \ge 5$. Our radio detection requirement strongly decreases the contamination of stellar sources and allows one to select these quasars in a broad redshift range. Despite selecting our quasar candidates using fewer and less conservative colour restrictions, both the optical and near-infrared colours, Ly$α$ emission line properties, and dust reddening, $E(B-V)$, measurements of our quasar sample do not deviate from the known radio-quiet quasar population, suggesting similar optical quasar properties of the radio-loud and radio-quiet quasar population at high-$z$. Our campaign demonstrates the potential for discovering new high-$z$ quasar populations through next generation radio continuum surveys.

astro-ph.GA↗

arXiv2022

Strong C IV emission from star-forming galaxies: a case for high Lyman continuum photon escape

Finding reliable indicators of Lyman continuum (LyC) photon leakage from galaxies is essential in order to infer their escape fraction in the epoch of reionisation, where direct measurements of LyC flux are impossible. To this end, here we investigate whether strong C IV $λλ1548,1550$ emission in the rest-frame UV spectra of galaxies traces conditions ripe for ample production and escape of LyC photons. We compile a sample of 19 star-forming galaxies in the redshift range $z=3.1-4.6$ from the VANDELS survey that exhibit strong C IV emission, producing a stacked spectrum where all major rest-UV emission lines are clearly detected. Best-fitting spectral energy distribution models containing both stellar and nebular emission suggest the need for low stellar metallicities ($Z=0.1-0.2\,Z_\odot$), young stellar ages ($\log(\rm{age/yr}) = 6.1-6.5$), a high ionisation parameter ($\log U = -2$) and little to no dust attenuation ($E(B-V)=0.00-0.01$). However, these models are unable to fully reproduce the observed C IV and He II line strengths. We find that the Ly$α$ line in the stacked spectrum is strong and peaks close to the systemic velocity, features that are indicative of significant LyC photon leakage along the line-of-sight. The covering fractions of low-ionisation interstellar absorption lines are also low implying LyC escape fraction in the range $\approx 0.05-0.30$, with signatures of outflowing gas. Finally, C IV/C III] ratios of >0.75 for a subset of individual galaxies with reliable detections of both lines are also consistent with physical conditions that enable significant LyC leakage. Overall, we report that multiple spectroscopic indicators of LyC leakage are present in the stacked spectrum of strong C IV emitting galaxies, potentially making C IV an important tracer of LyC photon escape at $z>6$.

astro-ph.GA↗

arXiv2022

The REACH radiometer for detecting the 21-cm hydrogen signal from redshift 7.5 to 28

Observations of the 21-cm line from primordial hydrogen promise to be one of the best tools to study the early epochs of the Universe: the Dark Ages, the Cosmic Dawn, and the subsequent Epoch of Reionization. In 2018, the EDGES experiment caught the attention of the cosmology community with a potential detection of an absorption feature in the sky-averaged radio spectrum centred at 78 MHz. The feature is deeper than expected, and, if confirmed, would call for new physics. However, different groups have re-analyzed the EDGES data and questioned the reliability of the signal. The Radio Experiment for the Analysis of Cosmic Hydrogen (REACH) is a sky-averaged 21-cm experiment aiming at improving the current observations by tackling the issues faced by current instruments related to residual systematic signals in the data. The novel experimental approach focuses on detecting and jointly explaining these systematics together with the foregrounds and the cosmological signal using Bayesian statistics. To achieve this, REACH features simultaneous observations with two different antennas, an ultra wideband system (redshift range 7.5 to 28), and a receiver calibrator based on in-field measurements. Simulated observations forecast percent-level constraints on astrophysical parameters, potentially opening up a new window to the infant Universe.

astro-ph.CO↗

arXiv2022

Properties of the interstellar medium in star-forming galaxies at redshifts 2 < z < 5 from the VANDELS survey

Gaseous flows inside and outside galaxies are key to understanding galaxy evolution, as they regulate their star formation activity across cosmic time. We study the ISM kinematics of 330 CIII or HeII emitters, using far-UV ISM absorption lines detected in the VANDELS spectra. These galaxies span a broad range of stellar masses M$_\ast$ from $10^8$ to $10^{11}$ M$_\odot$, and SFRs from 1 to 500 M$_\odot$/yr, in the redshift range between 2 and 5. We find that the bulk ISM velocity v$_{ism}$ is globally in outflow, with v$_{ism}$ of -60 $\pm$ 10 km/s for low ionization gas traced by SiII 1260 Angstrom, CII 1334, SiII 1526, and AlII 1670, and v$_{ism}$ of -160 $\pm$ 30 and -170 $\pm$ 30 km/s for higher ionization gas traced respectively by AlIII 1854-1862 and SiIV 1393-1402. Interestingly, BPASS models are able to better reproduce the stellar continuum around the SiIV doublet than other stellar population templates. For individual galaxies, $34\%$ of the sample has a positive ISM velocity shift, almost double the fraction reported at lower redshifts. Comparing v$_{ism}$ to the host galaxies properties, we find no significant correlations with M$_\ast$ or SFR, and only a marginally significant dependence (at $\sim 2σ$) on morphology-related parameters, with slightly higher velocities in galaxies of smaller size (probed by the equivalent radius), higher concentration, and higher SFR surface density. The outflows are consistent with models of accelerating, momentum-driven winds, with densities decreasing towards the outskirts. Our moderately lower ISM velocities compared to those found in similar studies at lower redshifts suggest that inflows and internal turbulence might play an increased role at $z>2$. We estimate mass outflow rates comparable to the SFRs of the galaxies, and an average escape velocity of 625 km/s, suggesting that most of the ISM will remain bound to the galaxy halo.

astro-ph.GA↗

arXiv2022

The LOFAR Two-metre Sky Survey -- V. Second data release

In this data release from the LOFAR Two-metre Sky Survey (LoTSS) we present 120-168MHz images covering 27% of the northern sky. Our coverage is split into two regions centred at approximately 12h45m +44$^\circ$30' and 1h00m +28$^\circ$00' and spanning 4178 and 1457 square degrees respectively. The images were derived from 3,451hrs (7.6PB) of LOFAR High Band Antenna data which were corrected for the direction-independent instrumental properties as well as direction-dependent ionospheric distortions during extensive, but fully automated, data processing. A catalogue of 4,396,228 radio sources is derived from our total intensity (Stokes I) maps, where the majority of these have never been detected at radio wavelengths before. At 6" resolution, our full bandwidth Stokes I continuum maps with a central frequency of 144MHz have: a median rms sensitivity of 83$μ$Jy/beam; a flux density scale accuracy of approximately 10%; an astrometric accuracy of 0.2"; and we estimate the point-source completeness to be 90% at a peak brightness of 0.8mJy/beam. By creating three 16MHz bandwidth images across the band we are able to measure the in-band spectral index of many sources, albeit with an error on the derived spectral index of +/-0.2 which is a consequence of our flux-density scale accuracy and small fractional bandwidth. Our circular polarisation (Stokes V) 20" resolution 120-168MHz continuum images have a median rms sensitivity of 95$μ$Jy/beam, and we estimate a Stokes I to Stokes V leakage of 0.056%. Our linear polarisation (Stokes Q and Stokes U) image cubes consist of 480 x 97.6 kHz wide planes and have a median rms sensitivity per plane of 10.8mJy/beam at 4' and 2.2mJy/beam at 20"; we estimate the Stokes I to Stokes Q/U leakage to be approximately 0.2%. Here we characterise and publicly release our Stokes I, Q, U and V images in addition to the calibrated uv-data.

astro-ph.GA↗

arXiv2022

High accuracy, high resolution 235U(n,f) cross section from n_TOF (CERN) in the thermal to 10 keV energy range

The 235U(n,f) cross section was measured in a wide energy range (25 meV - 170 keV) at the n_TOF facility at CERN, relative to 6Li(n,t) and 10B(n,alpha) standard reactions, with high resolution and accuracy, with a setup based on a stack of six samples and six silicon detectors placed in the neutron beam. In this paper we report on the results in the region between thermal and 10 keV neutron energy. A resonance analysis has been performed up to 200 eV, with the code SAMMY. The resulting fission kernels are compared with the ones extracted on the basis of the resonance parameters of the most recent major evaluated data libraries. A comparison of the n_TOF data with the evaluated cross sections is also performed from thermal to 10 keV neutron energy for the energy-averaged cross section in energy groups of suitably chosen width. A good agreement is found in average between the new results and the latest evaluated data files ENDF-B/VIII and JEFF-3.3, as well as with respect to the IAEA reference files. However, some discrepancies are still present in some specific energy regions. The new dataset here presented, characterized by unprecedented resolution and accuracy, can help improving the evaluations in the Resolved Resonance Region and up to 10 keV, and reduce the uncertainties that affect this region.

nucl-ex↗

arXiv2022

Revealing new high redshift quasar populations through Gaussian mixture model selection

We present a novel method to identify candidate high redshift quasars (HzQs; ($z\gtrsim5.5$), which are unique probes of supermassive black hole growth in the early Universe, from large area optical/infrared photometric surveys. Using Gaussian Mixture Models to construct likelihoods and incorporate informed priors based on population statistics, our method uses a Bayesian framework to assign posterior probabilities that differentiate between HzQs and contaminating sources. We additionally include deep radio data to obtain informed priors. Using existing HzQ data in the literature, we set a posterior threshold that accepts ${\sim}90\%$ of known HzQs while rejecting $>99\%$ of contaminants such as dwarf stars or lower redshift galaxies. Running the probability selection on test samples of simulated HzQs and contaminants, we find that the efficacy of the probability method is higher than traditional colour cuts, decreasing the fraction of accepted contaminants by 86% while retaining a similar fraction of HzQs. As a test, we apply our method to the Pan-STARRS Data Release 1 (PS1) source catalogue within the HETDEX Spring field area on the sky, covering 400 sq. deg. and coinciding with deep radio data from the LOFAR Two-metre Sky Survey Data Release 1 (LoTSS DR1). From an initial sample of ${\sim}5\times10^5$ sources in PS1, our selection shortlists 251 candidate HzQs, which are further reduced to 63 after visual inspection. Shallow spectroscopic follow-up of 13 high probability HzQs resulted in the confirmation of a previously undiscovered quasar at $z=5.66$ with photometric colours $i-z = 1.4$, lying outside the typically probed regions when selecting HzQs based on colours. This discovery demonstrates the efficacy of our probabilistic HzQ selection method in selecting more complete HzQ samples, which holds promise when employed on large existing and upcoming photometric data sets.

astro-ph.GA↗

arXiv2022

No strong dependence of Lyman continuum leakage on physical properties of star-forming galaxies at $\mathbf{3.1 \lesssim z \lesssim 3.5}$

We present Lyman continuum (LyC) radiation escape fraction $f_{\rm{esc}}$ measurements for 183 spectroscopically confirmed star-forming galaxies in the redshift range $3.11 < z < 3.53$ in the \textit{Chandra} Deep Field South. We use ground-based imaging to measure $f_{\rm{esc}}$, and use ground- and space-based photometry to derive galaxy physical properties using spectral energy distribution (SED) fitting. We additionally derive [O III]+H$β$ equivalent widths (that fall in the observed K band) by including nebular emission in the SED fitting. After removing foreground contaminants, we report the discovery of 11 new candidate LyC leakers, with absolute LyC escape fractions, $f_{\rm{esc}}$ in the range $0.14-0.85$. From non-detections, we place $1σ$ upper limits of $f_{\rm{esc}}<0.12$, where the Lyman-break selected galaxies have $f_{\rm{esc}} < 0.11$ and `blindly' discovered galaxies with no prior photometric selection have $f_{\rm{esc}}<0.13$. We find a slightly higher $1σ$ limit of $f_{\rm{esc}}<0.20$ for extreme emission line galaxies with rest-frame [O III]+H$β$ equivalent widths $>300$A. For candidate LyC leakers, we find a weak negative correlation between $f_{\rm{esc}}$ and galaxy stellar masses, no correlation between $f_{\rm{esc}}$ specific star-formation rates (sSFRs) and a positive correlation between $f_{\rm{esc}}$ and EW$_0$([O III]+H$β$). The weak/no correlations between stellar mass and sSFRs may be explained by misaligned viewing angles and/or non-coincident timescales of starburst activity and periods of high $f_{\rm{esc}}$. Alternatively, escaping radiation may predominantly occur in highly localised star-forming regions, or $f_{\rm{esc}}$ measurements may be impacted by stochasticity of the intervening neutral medium, obscuring any global trends with galaxy properties. These hypotheses have important consequences for models of reionisation.

astro-ph.GA↗

arXiv2022

Nonlinear Anti-(Parity-Time) symmetric dimer

In the present work we propose a nonlinear anti-$\mathcal{PT}$-symmetric dimer, that at the linear level has been experimentally created in the realm of electric circuit resonators. We find four families of solutions, the so-called upper and lower branches, both in a symmetric and in an asymmetric (symmetry-broken) form. We unveil analytically and confirm numerically the critical thresholds for the existence of such branches and explore the bifurcations (such as saddle-node ones) that delimit their existence, as well as transcritical ones that lead to their potential exchange of stability. We find that out of the four relevant branches, only one, the upper symmetric branch, corresponds to a spectrally and dynamically robust solution. We subsequently leverage detailed direct numerical computations in order to explore the dynamics of the different states, corroborating our spectral analysis results.

nlin.PS↗

arXiv2021

The VANDELS survey: global properties of CIII]$λ$1908Å emitting star-forming galaxies at z$\sim$3

We study the mean properties of a large representative sample of 217 galaxies showing CIII] emission at $2<z<4$, selected from a parent sample of $\sim$750 main-sequence star-forming galaxies in the VANDELS survey. These CIII] emitters have a broad range of UV luminosities, thus allowing a detailed stacking analysis to characterize their stellar mass, star formation rate (SFR) and stellar metallicity, as a function of the UV emission line ratios, EWs, and the carbon-to-oxygen (C/O) abundance ratio. Reliable CIII] detections represent $\sim$30% of the parent sample. Extreme CIII] emitters (EW(CIII])$\gtrsim$8Å) are exceedingly rare ($\sim$3%) in VANDELS. The UV line ratios of the sample suggest no ionization source other than massive stars. Stacks with larger EW(CIII]) show larger EW(Ly$α$) and lower metallicity, but not all CIII] emitters are Ly$α$ emitters. The stellar metallicities of CIII] emitters are not significantly different from that of the parent sample, increasing from $\sim$10% to $\sim$40% solar for stellar masses $\log$(M$_{\star}$/M$_{\odot})\sim$9-10.5. The stellar mass-metallicity relation of the CIII] emitters is consistent with previous works showing strong evolution from $z=0$ to $z\sim3$. The C/O abundances of the sample range 35%-150% solar, with a noticeable increase with FUV luminosity and a smooth decrease with the CIII] EW. We discuss the CIII] emitters in the C/O-Fe/H and the C/O-O/H planes and find they follow stellar and nebular abundance trends consistent with those of Milky Way halo and thick disc stars and local HII galaxies, respectively. A qualitative agreement is also found with chemical evolution models, which suggests that CIII] emitters at $z\sim$3 are experiencing an active phase of chemical enrichment.

astro-ph.GA↗

arXiv2021

Low frequency radio properties of the $z>5$ quasar population

Optically luminous quasars at $z > 5$ are important probes of super-massive black hole (SMBH) formation. With new and future radio facilities, the discovery of the brightest low-frequency radio sources in this epoch would be an important new probe of cosmic reionization through 21-cm absorption experiments. In this work, we systematically study the low-frequency radio properties of a sample of 115 known spectroscopically confirmed $z>5$ quasars using the second data release of the Low Frequency Array (LOFAR) Two Metre Sky survey (LoTSS-DR2), reaching noise levels of $\sim$80 $μ$Jy beam$^{-1}$ (at 144 MHz) over an area of $\sim5720$ deg$^2$. We find that 41 sources (36%) are detected in LoTSS-DR2 at $>2 σ$ significance and we explore the evolution of their radio properties (power, spectral index, and radio loudness) as a function of redshift and rest-frame ultra-violet properties. We obtain a median spectral index of $-0.29^{+0.10}_{-0.09}$ by stacking 93 quasars using LoTSS-DR2 and Faint Images of the Radio Sky at Twenty Centimetres (FIRST) data at 1.4 GHz, in line with observations of quasars at $z<3$. We compare the radio loudness of the high-$z$ quasar sample to a lower-$z$ quasar sample at $z\sim2$ and find that the two radio loudness distributions are consistent with no evolution, although the low number of high-z quasars means that we cannot rule out weak evolution. Furthermore, we make a first order empirical estimate of the $z=6$ quasar radio luminosity function, which is used to derive the expected number of high-$z$ sources that will be detected in the completed LoTSS survey. This work highlights the fact that new deep radio observations can be a valuable tool in selecting high-$z$ quasar candidates for follow-up spectroscopic observations by decreasing contamination of stellar dwarfs and reducing possible selection biases introduced by strict colour cuts.

astro-ph.GA↗

arXiv2021

Measurement and Memory in the Periodically Driven Complex Ginzburg-Landau equation

In the present work we illustrate that classical but nonlinear systems may possess features reminiscent of quantum ones, such as memory, upon suitable external perturbation. As our prototypical example, we use the two-dimensional complex Ginzburg-Landau equation in its vortex glass regime. We impose an external drive as a perturbation mimicking a quantum measurement protocol, with a given "measurement rate" (the rate of repetition of the drive) and "mixing rate" (characterized by the intensity of the drive). Using a variety of measures, we find that the system may or may not retain its coherence, statistically retrieving its original glass state, depending on the strength and periodicity of the perturbing field. The corresponding parametric regimes and the associated energy cascade mechanisms involving the dynamics of vortex waveforms and domain boundaries are discussed.

nlin.PS↗

arXiv2021

The VANDELS Survey: New constraints on the high-mass X-ray binary populations in normal star-forming galaxies at 3 < z < 5.5

We use VANDELS spectroscopic data overlapping with the $\simeq$7 Ms Chandra Deep Field South survey to extend studies of high-mass X-ray binary systems (XRBs) in 301 normal star-forming galaxies in the redshift range $3 < z < 5.5$. Our analysis evaluates correlations between X-ray luminosities ($L_X$), star formation rates (SFR) and stellar metallicities ($Z_\star$) to higher redshifts and over a wider range in galaxy properties than hitherto. Using a stacking analysis performed in bins of both redshift and SFR for sources with robust spectroscopic redshifts without AGN signatures, we find convincing evolutionary trends in the ratio $L_X$/SFR to the highest redshifts probed, with a stronger trend for galaxies with lower SFRs. Combining our data with published samples at lower redshift, the evolution of $L_X$/SFR to $z\simeq5$ proceeds as $(1 + z)^{1.03 \pm 0.02}$. Using stellar metallicities derived from photospheric absorption features in our spectroscopic data, we confirm indications at lower redshifts that $L_X$/SFR is stronger for metal-poor galaxies. We use semi-analytic models to show that metallicity dependence of $L_X$/SFR alone may not be sufficient to fully explain the observed redshift evolution of X-ray emission from high-mass XRBs, particularly for galaxies with SFR $<30$ $M_\odot$ yr$^{-1}$. We speculate that the discrepancy may arise due to reduced overall stellar ages in the early Universe leading to higher $L_X$/SFR for the same metallicity. We use our data to define the redshift-dependent contribution of XRBs to the integrated X-ray luminosity density and, in comparison with models, find that the contribution of high-mass XRBs to the cosmic X-ray background at $z>6$ may be $\gtrsim 0.25$ dex higher than previously estimated.

astro-ph.GA↗

arXiv2021

HELP: The Herschel Extragalactic Legacy Project

We present the Herschel Extragalactic Legacy Project (HELP). This project collates, curates, homogenises, and creates derived data products for most of the premium multi-wavelength extragalactic data sets. The sky boundaries for the first data release cover 1270 deg2 defined by the Herschel SPIRE extragalactic survey fields; notably the Herschel Multi-tiered Extragalactic Survey (HerMES) and the Herschel Atlas survey (H-ATLAS). Here, we describe the motivation and principal elements in the design of the project. Guiding principles are transparent or "open" methodologies with care for reproducibility and identification of provenance. A key element of the design focuses around the homogenisation of calibration, meta data and the provision of information required to define the selection of the data for statistical analysis. We apply probabilistic methods that extract information directly from the images at long wavelengths, exploiting the prior information available at shorter wavelengths and providing full posterior distributions rather than maximum likelihood estimates and associated uncertainties as in traditional catalogues. With this project definition paper we provide full access to the first data release of HELP; Data Release 1 (DR1), including a monolithic map of the largest SPIRE extragalactic field at 385 deg2 and 18 million measurements of PACS and SPIRE fluxes. We also provide tools to access and analyse the full HELP database. This new data set includes far-infrared photometry, photometric redshifts, and derived physical properties estimated from modelling the spectral energy distributions.

astro-ph.GA↗

arXiv2021

The NIRVANDELS Survey: a robust detection of $α$-enhancement in star-forming galaxies at $z\simeq3.4$

We present results from the NIRVANDELS survey investigating the gas-phase metallicity ($\mathrm{Z}_{\mathrm{gas}}$, tracing O/H) and stellar metallicity ($Z_{\star}$, tracing Fe/H) of 33 star-forming galaxies at redshifts $2.95 < z < 3.80$. Based on a combined analysis of deep optical and near-IR spectra, tracing the rest-frame far ultraviolet and rest-frame optical respectively, we present the first simultaneous determination of the stellar and gas-phase mass-metallicity relationships (MZRs) at $z\simeq3.4$. In both cases, we find that metallicity increases with increasing stellar mass ($M_{\star}$), and that the power-law slope at $M_{\star} \lesssim 10^{10} \mathrm{M}_{\odot}$ of both MZRs scales as $Z \propto M_{\star}^{0.3}$. Comparing the stellar and gas-phase MZRs, we present direct evidence for super-solar O/Fe ratios (i.e., $α$-enhancement) at $z>3$, finding $\mathrm{(O/Fe)}\simeq (2.54 \pm 0.38) \times \mathrm{(O/Fe)}_{\odot}$, with no clear dependence on $M_{\star}$.

astro-ph.GA↗