J/A+A/702/A3ivo://CDS.VizieR/J/A+A/702/A3doi:10.26093/cds/vizier/bc-ny/ldCDSGonzalez-Diaz R.Vilchez J.M.Kehrig C.del Moral-Castro I.,Iglesias-Paramo J.2026-08-31T14:43:14Z2025-09-26T09:59:10ZCDS support team

CDS, Observatoire de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

cds-question@unistra.frgalaxiesspectroscopyvisible-astronomyline-intensitiesThe study of high-redshift galaxies provides critical insights into the early stages of cosmic evolution, particularly during the so-called 'cosmic noon', when star formation activity reached its peak. Within this context, the origin of the nebular emission remains an open question. In this work, we conduct a systematic, multi-wavelength investigation of a sample of z~2-4 emitters from the MUSE Hubble Ultra Deep Field surveys, utilising both MUSE and JWST/NIRSpec data and extending the sample presented by previous studies. We derive gas-phase metallicities and key physical properties, including electron densities, temperatures and the production rates of hydrogen- and He^+^-ionising photons. Our results suggest that a combination of factors-such as stellar mass, initial mass function, stellar metallicity, and stellar multiplicity -- likely contributes to the origin of the observed nebular emission. Specifically, for our galaxies with higher gas-phase metallicity (12+log(O/H)>7.55), we find that models for binary population with Salpeter IMF (Mup=100M_{sun}_) and stellar metallicity ~0.001 (i.e., similar to that of the gas) can reproduce the observed ionising conditions. However at lower metallicities, models for binary population with 'top-heavy' initial mass function (Mup=300M_{sun}_) and Z* much lower (10^-4^<Z*<10^-5^) than that of the gas are required to fully account for the observed ionising photon production. These results reinforce that the ionisation keeps challenging current stellar populations, and the ionisation problem persists in the very low metallicity regime.2025A&A...702A...3Ghttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/702/A3CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toJ/A+A/670/A4 : MUSE Hubble Ultra Deep Field surveys. DR2 (Bacon+, 2023)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/702/A3https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/702/A3http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/702/A3https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/702/A3https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/702/A3http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/702/A3GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/A+A/702/A3/tableb1 (General characteristics of the HeII emitters sample)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/702/A3/tableb1?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/702/A3/tableb1?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/702/A3/tableb1?GETtext/xml+votable180.050000true53.14490833-27.799846390.0055555555555555566/35935https://cdsarc.cds.unistra.fr/viz-bin/moc/J/A+A/702/A3?format=asciiOpticaldefaultJ/A+A/702/A3/tableb1General characteristics of the HeII emitters samplerecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintAllDisplay UV lines fluxes frpm table b2meta.ref.urlcharIDIdentification number (1)meta.id;meta.mainintSimbadSimbad column added by the CDSmeta.ref.urlcharn_ID[*b] Note (2)meta.notecharRAJ2000Right ascension (J2000) (1)pos.eq.ra;meta.mainDEJ2000Declination (J2000) (1)pos.eq.dec;meta.mainEWLya? Lyman{alpha} equivalent width0.1nmspect.line.eqWidthfloatnullablee_EWLya? Lyman{alpha} equivalent width error0.1nmstat.errorfloatnullableEWHeIIHeII equivalent width0.1nmspect.line.eqWidthfloate_EWHeIIHeII equivalent width error0.1nmstat.errorfloatzRedshiftsrc.redshiftfloatlogM*? Stellar mass (1)log(solMass)phys.massfloatnullableE_logM*? Stellar mass error (upper value) (1)log(solMass)stat.error;stat.maxfloatnullablee_logM*? Stellar mass error (lower value) (1)log(solMass)stat.errorfloatnullablelogSFR? Star formation rate (1)log(solMass.yr**-1)phys.SFRfloatnullableE_logSFR? Star formation rate error (upper value) (1)log(solMass.yr**-1)stat.error;stat.maxfloatnullablee_logSFR? Star formation rate error (lower value) (1)log(solMass.yr**-1)stat.error;phys.SFRfloatnullableAV? Extinction in V band (3)magphys.absorptionfloatnullablee_AV? Absorption in V band errormagstat.errorfloatnullableM1500? Absolute magnitude at the 1500{AA} bandmagphys.magAbsfloatnullablee_M1500? Absolute magnitude at the 1500{AA} band errormagstat.errorfloatnullableJ/A+A/702/A3/tableb2UV lines fluxes measured with MUSErecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintLineMUSE line IDmeta.id;spect.linecharF7898? Line flux of the galaxy ID: 78981e-23W.m**-2meta.id;meta.maindoublenullablee_F7898? Line flux error of the galaxy ID: 78981e-23W.m**-2stat.errordoublenullableFWHM7898? Line FWHM of the galaxy ID: 78980.1nmmeta.iddoublenullableF8249? Line flux of the galaxy ID: 82491e-23W.m**-2meta.iddoublenullablee_F8249? Line flux error of the galaxy ID: 82491e-23W.m**-2stat.errordoublenullableFWHM8249? Line FWHM of the galaxy ID: 82490.1nmmeta.iddoublenullableF1059? Line flux of the galaxy ID: 10591e-23W.m**-2meta.iddoublenullablee_F1059? Line flux error of the galaxy ID: 10591e-23W.m**-2stat.errordoublenullableFWHM1059? Line FWHM of the galaxy ID: 10590.1nmmeta.iddoublenullableF1141? Line flux of the galaxy ID: 11411e-23W.m**-2meta.iddoublenullablee_F1141? Line flux error of the galaxy ID: 11411e-23W.m**-2stat.errordoublenullableFWHM1141? Line FWHM of the galaxy ID: 11410.1nmmeta.iddoublenullableF50? Line flux of the galaxy ID: 501e-23W.m**-2meta.iddoublenullablee_F50? Line flux error of the galaxy ID: 501e-23W.m**-2stat.errordoublenullableFWHM50? Line FWHM of the galaxy ID: 500.1nmmeta.iddoublenullableF6664? Line flux of the galaxy ID: 66641e-23W.m**-2meta.iddoublenullablee_F6664? Line flux error of the galaxy ID: 66641e-23W.m**-2stat.errordoublenullableFWHM6664? Line FWHM of the galaxy ID: 66640.1nmmeta.iddoublenullableF8165? Line flux of the galaxy ID: 81651e-23W.m**-2meta.iddoublenullablee_F8165? Line flux error of the galaxy ID: 81651e-23W.m**-2stat.errordoublenullableFWHM8165? Line FWHM of the galaxy ID: 81650.1nmmeta.iddoublenullableF149? Line flux of the galaxy ID: 1491e-23W.m**-2meta.iddoublenullablee_F149? Line flux error of the galaxy ID: 1491e-23W.m**-2stat.errordoublenullableFWHM149? Line FWHM of the galaxy ID: 1490.1nmmeta.iddoublenullableF8414? Line flux of the galaxy ID: 84141e-23W.m**-2meta.iddoublenullablee_F8414? Line flux error of the galaxy ID: 84141e-23W.m**-2stat.errordoublenullableFWHM8414? Line FWHM of the galaxy ID: 84140.1nmmeta.iddoublenullableF103? Line flux of the galaxy ID: 1031e-23W.m**-2meta.iddoublenullablee_F103? Line flux error of the galaxy ID: 1031e-23W.m**-2stat.errordoublenullableFWHM103? Line FWHM of the galaxy ID: 1030.1nmmeta.iddoublenullableF3621? Line flux of the galaxy ID: 36211e-23W.m**-2meta.iddoublenullablee_F3621? Line flux error of the galaxy ID: 36211e-23W.m**-2stat.errordoublenullableFWHM3621? Line FWHM of the galaxy ID: 36210.1nmmeta.iddoublenullableF8369? Line flux of the galaxy ID: 83691e-23W.m**-2meta.iddoublenullablee_F8369? Line flux error of the galaxy ID: 83691e-23W.m**-2stat.errordoublenullableFWHM8369? Line FWHM of the galaxy ID: 83690.1nmmeta.iddoublenullableF6700? Line flux of the galaxy ID: 67001e-23W.m**-2meta.iddoublenullablee_F6700? Line flux error of the galaxy ID: 67001e-23W.m**-2stat.errordoublenullableFWHM6700? Line FWHM of the galaxy ID: 67000.1nmmeta.iddoublenullableF1045? Line flux of the galaxy ID: 10451e-23W.m**-2meta.iddoublenullablee_F1045? Line flux error of the galaxy ID: 10451e-23W.m**-2stat.errordoublenullableFWHM1045? Line FWHM of the galaxy ID: 10450.1nmmeta.iddoublenullableF6999? Line flux of the galaxy ID:69991e-23W.m**-2phot.flux;spect.linedoublenullablee_F6999? Line flux error of the galaxy ID:69991e-23W.m**-2stat.errordoublenullableFWHM6999? Line FWHM of the galaxy ID:69990.1nmspect.line.width;spect.linedoublenullableF164? Line flux of the galaxy ID: 1641e-23W.m**-2meta.iddoublenullablee_F164? Line flux error of the galaxy ID: 1641e-23W.m**-2stat.errordoublenullableFWHM164? Line FWHM of the galaxy ID: 1640.1nmmeta.iddoublenullableF6666? Line flux of the galaxy ID: 66661e-23W.m**-2meta.iddoublenullablee_F6666? Line flux error of the galaxy ID: 66661e-23W.m**-2stat.errordoublenullableFWHM6666? Line FWHM of the galaxy ID: 66660.1nmmeta.iddoublenullableF1024? Line flux of the galaxy ID: 10241e-23W.m**-2meta.iddoublenullablee_F1024? Line flux error of the galaxy ID: 10241e-23W.m**-2stat.errordoublenullableFWHM1024? Line FWHM of the galaxy ID: 10240.1nmmeta.iddoublenullableF1273? Line flux of the galaxy ID: 12731e-23W.m**-2meta.iddoublenullablee_F1273? Line flux error of the galaxy ID: 12731e-23W.m**-2stat.errordoublenullableFWHM1273? Line FWHM of the galaxy ID: 12730.1nmmeta.iddoublenullableF22? Line flux of the galaxy ID: 221e-23W.m**-2meta.iddoublenullablee_F22? Line flux error of the galaxy ID: 221e-23W.m**-2stat.errordoublenullableFWHM22? Line FWHM of the galaxy ID: 220.1nmmeta.iddoublenullableF1036? Line flux of the galaxy ID: 10361e-23W.m**-2meta.iddoublenullablee_F1036? Line flux error of the galaxy ID: 10361e-23W.m**-2stat.errordoublenullableFWHM1036? Line FWHM of the galaxy ID: 10360.1nmmeta.iddoublenullableF1056? Line flux of the galaxy ID: 10561e-23W.m**-2meta.iddoublenullablee_F1056? Line flux error of the galaxy ID: 10561e-23W.m**-2stat.errordoublenullableFWHM1056? Line FWHM of the galaxy ID: 10560.1nmmeta.iddoublenullableF1051? Line flux of the galaxy ID:10511e-23W.m**-2phot.flux;spect.linedoublenullablee_F1051? Line flux error of the galaxy ID:10511e-23W.m**-2stat.errordoublenullableFWHM1051? Line FWHM of the galaxy ID:10510.1nmspect.line.width;spect.linedoublenullableF106? Line flux of the galaxy ID 1061e-23W.m**-2meta.iddoublenullablee_F106? Line flux error of the galaxy ID 1061e-23W.m**-2stat.errordoublenullableFWHM106? Line FWHM of the galaxy ID 1060.1nmmeta.iddoublenullableF51? Line flux of the galaxy ID: 511e-23W.m**-2meta.iddoublenullablee_F51? Line flux error of the galaxy ID: 511e-23W.m**-2stat.errordoublenullableFWHM51? Line flux error of the galaxy ID: 510.1nmmeta.iddoublenullable