We investigate the nebular emission produced by young stellar populations using the new GALSEVN model based on the combination of the SEVN population-synthesis code including binary-star processes ...and the GALAXEV code for the spectral evolution of stellar populations. Photoionization calculations performed with the CLOUDY code confirm that accounting for binary-star processes strongly influences the predicted emission-line properties of young galaxies. In particular, we find that our model naturally reproduces the strong HeII/Hb ratios commonly observed at high Hb equivalent widths in metal-poor, actively star-forming galaxies, which have proven challenging to reproduce using previous models. Including bursty star formation histories broadens the agreement with observations, while the most extreme HeII equivalent widths can be reproduced by models dominated by massive stars. GALSEVN also enables us to compute, for the first time in a way physically consistent with stellar emission, the emission from accretion discs of X-ray binaries (XRBs) and radiative shocks driven by stellar winds and supernova explosions. We find that these contributions are unlikely to prominently affect the predicted HeII/Hb ratio, and that previous claims of a significant contribution by XRBs to the luminosities of high-ionization lines are based on models predicting improbably high ratios of X-ray luminosity to star formation rate, inconsistent with the observed average luminosity function of XRBs in nearby galaxies. The results presented here provide a solid basis for a more comprehensive investigation of the physical properties of observed galaxies with GALSEVN using Bayesian inference.
We follow up emission line galaxies identified through the near-infrared
slitless HST/WFC3 WISP survey with VLT/FORS2 optical spectroscopy. Over 4 WISP
fields, we targetted 85 of 138 line emission ...objects at $0.4<z<2$ identified in
WFC3 spectroscopy. Half the galaxies are fainter than $H_{AB}=24$mag, and would
not have been included in many well-known surveys based on broad-band magnitude
selection. We confirm 95% of the initial WFC3 grism redshifts in the 38 cases
where we detect lines in FORS2 spectroscopy. However, for targets which
exhibited a single emission line in WFC3, up to 65% at $z<1.28$ did not have
expected emission lines detected in FORS2 and hence may be spurious (although
this false-detection rate improves to 33% using the latest public WISP emission
line catalogue). From the Balmer decrement the extinction of the WISP galaxies
is consistent with $A($H$\alpha)=1$mag. From SED fits to multi-band photometry
including Spitzer $3.6\mu$m, we find a median stellar mass of
$\log_{10}(M/M_{\odot})=8.94$. Our emission-line-selected galaxies tend to lie
above the star-forming main sequence (i.e. higher specific star formation
rates). Using OIII, OII and H$\beta$ lines to derive gas-phase
metallicities, we find typically sub-solar metallicities, decreasing with
redshift. Our WISP galaxies lie below the $z=0$ mass-metallicity relation, and
galaxies with higher star formation rates tend to have lower metallicity.
Finally, we find a strong evolution with redshift of the H$\alpha$ rest-frame
equivalent width, $EW_0($H$\alpha)\propto (1+z)^{1.85\pm0.24}$ with higher
$EW_0$ galaxies having larger OIII/H$\beta$ and O32 ratios on average,
suggesting lower metallicity or higher ionisation parameter in these extreme
emission line galaxies.
We present NIRSpec IFS observations of a galaxy group around the massive GS_4891 galaxy at z=3.7 in GOODS-South that includes two other two systems, GS_4891_n to the north and GS_28356 to the east. ...These observations, obtained as part of the GTO GA-NIFS program, allow for the first time to study the spatially resolved properties of the interstellar medium (ISM) and ionized gas kinematics of a galaxy at this redshift. Leveraging the wide wavelength range spanned with the high-dispersion grating (with resolving power R=2700) observations, covering from OII$\lambda$$\lambda\(3726,29 to SII\)\lambda$$\lambda\(6716,31, we explore the spatial distribution of star-formation rate, nebular attenuation and gas metallicity, together with the mechanisms responsible for the excitation of the ionized gas. GS_4891 presents a clear gradient of gas metallicity (as traced by 12 + log(O/H)) by more than 0.2dex from the south-east (where a star-forming clump is identified) to the north-west. The gas metallicity in the less-massive northern system, GS_4891_n, is also higher by 0.2 dex than at the center of GS_4891, suggesting that inflows of lower-metallicity gas might be favoured in higher-mass systems. The kinematic analysis shows that GS_4891 presents velocity gradients in the ionized gas consistent with rotation. The region between GS_4891 and GS_4891_n does not present high gas turbulence which, together with the difference in gas metallicities, suggests that these two systems might be in a pre-merger stage. Finally, GS_4891 hosts an ionized outflow that extends out to r_out=1.2 kpc from the nucleus and reaches maximum velocities v_out of approximately 400 km/s. Despite entraining an outflowing mass rate of M_out\)\sim\(2Msun/yr, the low associated mass-loading factor, \)\eta$=0.05, implies that the outflow does not have a significant impact on the star-formation activity of the galaxy.
Massive, starbursting galaxies in the early Universe represent some of the most extreme objects in the study of galaxy evolution. One such source is HFLS3 (z~6.34), which was originally identified as ...an extreme starburst galaxy with mild gravitational magnification (\(\mu\)~2.2). Here, we present new observations of HFLS3 with the JWST/NIRSpec IFU in both low (PRISM/CLEAR; R~100) and high spectral resolution (G395H/290LP; R~2700), with high spatial resolution (~0.1") and sensitivity. Thanks to the combination of the NIRSpec data and a new lensing model with accurate spectroscopic redshifts, we find that the 3"x3" field is crowded, with a lensed arc (C, \(z=6.3425\pm0.0002\)), two galaxies to the south (S1 and S2, \(z=6.3592\pm0.0001\)), two galaxies to the west (W1, \(z=6.3550\pm0.0001\); W2, \(z=6.3628\pm0.0001\)), and two low-redshift interlopers (G1, \(z=3.4806\pm0.0001\); G2, \(z=2.00\pm0.01\)). We present spectral fits and morpho-kinematic maps for each bright emission line from the R2700 data for all sources except G2. From a line ratio analysis, the galaxies in component C are likely powered by star formation, while we cannot rule out or confirm the presence of AGN in the other high-redshift sources. We perform gravitational lens modelling, finding evidence for a two-source composition of the lensed central object and a comparable magnification factor (\(\mu\)=2.1-2.4) to previous work. The projected distances and velocity offsets of each galaxy suggest that they will merge within the next ~1Gyr. Finally, we examine the dust extinction-corrected SFR(Ha) of each z>6 source, finding that the total star formation (\(510\pm140\)Msol/yr, magnification-corrected) is distributed across the six z~6.34-6.36 objects over a region of diameter ~11kpc. Altogether, this suggests that HFLS3 is not a single starburst galaxy, but instead is a merging system of star-forming galaxies in the Epoch of Reionisation.
We investigate the production efficiency of ionizing photons ($\xi_{ion}^*$)
of 1174 galaxies with secure redshift at z=2-5 from the VANDELS survey to
determine the relation between ionizing emission ...and physical properties of
bright and massive sources. We constrain $\xi_{ion}^*$ and galaxy physical
parameters by means of spectro-photometric fits performed with the BEAGLE code.
The analysis exploits the multi-band photometry in the VANDELS fields, and the
measurement of UV rest-frame emission lines (CIII$\lambda 1909$, HeII$\lambda
1640$, OIII$\lambda 1666$) from deep VIMOS spectra. We find no clear evolution
of $\xi_{ion}^*$ with redshift within the probed range. The ionizing efficiency
slightly increases at fainter $M_{UV}$, and bluer UV slopes, but these trends
are less evident when restricting the analysis to a complete subsample at
log(M$_{star}$/M$_{\odot}$)$>$9.5. We find a significant trend of increasing
$\xi_{ion}^*$ with increasing EW(Ly$\alpha$), with an average
log($\xi_{ion}^*$/Hz erg$^{-1}$)$>$25 at EW$>$50\AA, and a higher ionizing
efficiency for high-EW CIII$\lambda 1909$ and OIII$\lambda 1666$ emitters.
The most significant correlations are found with respect to stellar mass,
specific star-formation rate (sSFR) and SFR surface density ($\Sigma_{SFR}$).
The relation between $\xi_{ion}^*$ and sSFR shows a monotonic increase from
log($\xi_{ion}^*$/Hz erg$^{-1}$) $\sim$24.5 at log(sSFR)$\sim$-9.5$yr^{-1}$ to
$\sim$25.5 at log(sSFR)$\sim$-7.5$yr^{-1}$, a low scatter and little dependence
on mass. The objects above the main-sequence of star-formation consistently
have higher-than-average $\xi_{ion}^*$. A clear increase of $\xi_{ion}^*$ with
$\Sigma_{SFR}$ is also found, with log($\xi_{ion}^*$/Hz erg$^{-1}$)$>$25 for
objects at $\Sigma_{SFR}>$10 M$_{\odot}/yr/kpc^2$.(Abridged)
Line ratio diagnostics provide valuable clues on the source of ionizing radiation in galaxies with intense black hole accretion and starbursting events, such as local Seyfert or galaxies at the peak ...of the star formation history. We aim to provide a reference joint optical and mid-IR analysis for studying AGN identification via line ratios and testing predictions from photoionization models. We obtained homogenous optical spectra with the Southern Africa Large Telescope for 42 Seyfert galaxies with Spitzer/IRS spectroscopy and X-ray to mid-IR multiband data available. After confirming the power of the main optical (OIII) and mid-IR (NeV, OIV, NeIII) emission lines in tracing AGN activity, we explore diagrams based on ratios of optical and mid-IR lines by exploiting photoionization models of different ionizing sources (AGN, star formation and shocks). We find that pure AGN photoionization models are good at reproducing observations of Seyfert galaxies with an AGN fractional contribution to the mid-IR (5-40 micron) emission larger than 50 per cent. For targets with a lower AGN contribution these same models do not fully reproduce the observed mid-IR line ratios. Mid-IR ratios like NeV/NeII, OIV/NeII and NeIII/NeII show a dependence on the AGN fractional contribution to the mid-IR unlike optical line ratios. An additional source of ionization, either from star formation or radiative shocks, can help explain the observations in the mid-IR. Among combinations of optical and mid-IR diagnostics in line ratio diagrams, only those involving the OI/Halpha ratio are promising diagnostics for simultaneously unraveling the relative role of AGN, star formation and, shocks. A proper identification of the dominant ionizing source would require the exploitation of analysis tools based on advanced statistical techniques as well as spatially resolved data.
A&A 662, A115 (2022) We investigate the ionizing properties of the pair of bright Ly$\alpha$
emitting galaxies BDF521 and BDF2195 at z=7.012 in order to constrain their
contribution to the formation ...of the BDF "reionized bubble". We obtain
constraints on UV emission lines (CIV$\lambda 1548$ doublet, HeII$\lambda
1640$, OIII$\lambda 1660$ doublet, and CIII$\lambda 1909$ doublet) from deep
VLT-XSHOOTER observations and compare them to those available for other
high-redshift objects, and to models with mixed stellar and AGN emission. We
use this spectroscopic information together with the photometry available in
the field to constrain the physical properties of the two objects using the
spectro-photometric fitting code BEAGLE. We do not detect any significant
emission at the expected position of UV lines, with 3$\sigma$ upper limits of
EW$\lesssim$2-7 AA rest-frame. We find that the two objects have lower CIII
emission than expected on the basis of the correlation between the Ly$\alpha$
and CIII EWs. The EW limits on CIV and HeII emission exclude pure AGN
templates at $\sim2-3\sigma$ significance, and only models with a $\lesssim$40%
AGN contribution are compatible with the observations. The two objects are
found to be relatively young ($\sim$20-30 Myrs) and metal-poor ($\lesssim 0.3
Z_{\odot}$) with stellar masses of a few $10^9M_{\odot}$. Their production rate
of hydrogen ionizing photons per intrinsic UV luminosity is
log($\xi_{ion}^*$/Hz erg$^{-1}$)=25.02-25.26, consistent with values typically
found in high-redshift galaxies, but more than twice lower than values measured
in $z>$7 galaxies with strong CIII and/or optical line emission
($\simeq$25.6-25.7). The two BDF emitters have no evidence of higher than
average ionizing capabilities and are not capable of reionizing their
surroundings by their own means under realistic assumptions on the escape
fraction of ionizing photons. (abridged)
Among the nearest most metal-poor starburst-dwarf galaxies known, SBS 0335-052E is the most luminous in integrated nebular He II {\lambda}4686 emission. This makes it a unique target to test spectral ...synthesis models and spectral interpretation tools of the kind that will be used to interpret future rest-frame UV observations of primeval galaxies. Previous attempts to reproduce its He II {\lambda}4686 emission luminosity found that X-ray sources, shocks, and single Wolf-Rayet stars are not main contributors to the He II-ionizing budget; and that only metal-free single rotating stars or binary stars with a top-heavy IMF and an unphysically-low metallicity can reproduce it. We present new UV (COS) and optical (MUSE) spectra which integrate the light of four super star clusters in SBS 0335-052E. Nebular He II, C III, C III, C IV, and O III UV emission lines with equivalent widths between 1.7 and 5 Å, and a C IV {\lambda}{\lambda}1548, 1551 P-Cygni like profile are detected. Recent extremely-metal poor shock + precursor models and binary models fail to reproduce the observed optical emission-line ratios. We use different sets of UV and optical observables to test models of constant star formation with single non-rotating stars which account for very massive stars, as blueshifted O V {\lambda}1371 absorption is present. Simultaneously fitting the fluxes of all high-ionization UV lines requires an unphysically-low metallicity. Fitting the P-Cygni like + nebular components of C IV {\lambda}{\lambda}1548, 1551 does not constrain the stellar metallicity and time since the beginning of star formation. We obtain 12+log(O/H)=7.45\pm0.04 and log(C/O)=-0.45(+0.03)(-0.04) for the galaxy. Model-testing would benefit from higher spatial resolution UV and optical spectroscopy of the galaxy.
We analyse the chemical properties of three z~8 galaxies behind the galaxy cluster SMACS J0723.3-7327, observed as part of the Early Release Observations programme of the James Webb Space Telescope ...(JWST). Exploiting O III4363 auroral line detections in NIRSpec spectra, we robustly apply the direct Te method for the very first time at such high redshift, measuring metallicities ranging from extremely metal poor (12+log(O/H)~7) to about one-third solar. We also discuss the excitation properties of these sources, and compare them with local strong-line metallicity calibrations. We find that none of the considered diagnostics match simultaneously the observed relations between metallicity and strong-line ratios for the three sources, implying that a proper re-assessment of the calibrations may be needed at these redshifts. On the mass-metallicity plane, the two galaxies at z~7.6 (log(M*/M_sun) = 8.1, 8.7) have metallicities that are consistent with the extrapolation of the mass-metallicity relation at z~2-3, while the least massive galaxy at z~8.5 (log(M*/M_sun) = 7.8) shows instead a significantly lower metallicity . The three galaxies show different level of offset relative to the Fundamental Metallicity Relation, with two of them (at z~7.6) being marginally consistent, while the z~8.5 source deviating significantly, being probably far from the smooth equilibrium between gas flows, star formation and metal enrichment in place at later epochs.
The Hubble Frontier Fields represent the opportunity to probe the high-redshift evolution of the main sequence of star-forming galaxies to lower masses than possible in blank fields thanks to ...foreground lensing of massive galaxy clusters. We use the BEAGLE SED-fitting code to derive stellar masses, \(\mathrm{M_{\star}}=\log(M/\mathrm{M_{\odot}})\), SFRs, \(\Psi=\log(\psi/\mathrm{M_{\odot}}\,\mathrm{yr}^{-1})\) and redshifts from galaxies within the ASTRODEEP catalogue. We fit a fully Bayesian hierarchical model of the main sequence over \(1.25<z<6\) of the form \(\Psi = \alpha_\mathrm{9.7}(z) + \beta(\mathrm{M_{\star}}-9.7) + \mathcal{N}(0,\sigma^2)\) while explicitly modelling the outlier distribution. The redshift-dependent intercept at \(\mathrm{M_{\star}}=9.7\) is parametrized as \(\alpha_\mathrm{9.7}(z) = \logN (1+z)^{\gamma} + 0.7\). Our results agree with an increase in normalization of the main sequence to high redshifts that follows the redshift-dependent rate of accretion of gas onto dark matter halos with \(\gamma=2.40^{+0.18}_{-0.18}\). We measure a slope and intrinsic scatter of \(\beta=0.79^{+0.03}_{-0.04}\) and \(\sigma=0.26^{+0.02}_{-0.02}\). We find that the sampling of the SED provided by the combination of filters (Hubble + ground-based Ks-band + Spitzer 3.6 and 4.5 \(\mathrm{\mu m}\)) is insufficient to constrain \(\mathrm{M_{\star}}\) and \(\Psi\) over the full dynamic range of the observed main sequence, even at the lowest redshifts studied. While this filter set represents the best current sampling of high-redshift galaxy SEDs out to \(z>3\), measurements of the main sequence to low masses and high redshifts still strongly depend on priors employed in SED fitting (as well as other fitting assumptions). Future data-sets with JWST should improve this.
