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We present a new set of synthesis models for stellar populations obtained
with Starburst99, which are based on new stellar evolutionary tracks with
rotation. We discuss models with zero rotation velocity and with velocities of
40% of the break-up velocity on the zero-age main-sequence. These values are
expected to bracket realistic rotation velocit...
Contexts in source publication
Context 1
... are plotting the evolution of the spectrum between 1200 and 2500 Å for a single stellar population with ages from 1 to 9 Myr in Figure 1 and Figure 2 v00-h, see Figure 3; v40-h, see Figure 5) but not at low metallicity (1994-l, see Figure 2; ...
Context 2
... are plotting the evolution of the spectrum between 1200 and 2500 Å for a single stellar population with ages from 1 to 9 Myr in Figure 1 and Figure 2 v00-h, see Figure 3; v40-h, see Figure 5) but not at low metallicity (1994-l, see Figure 2; ...
Context 3
... examples of the evolution of broadband colors we are including (BV) and Figure 22, which is a direct tracer of RSGs. The CO index was introduced by Doyon, Joseph, & Wright (1994) who define the index as CO = 2.5 log R 2.36 , ...
Context 4
... equivalent width of nebular Hα emission is reproduced in Figure 23. The final Starburst99 predictions addressed in this paper concern non-radiative ...
Context 5
... In Figure 26 we show the mass loss by stellar winds and core-collapse supernovae. The values of ̇ are from the published tables of the evolutionary tracks. ...
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Citations
... How does this compare to expectations? In Figure 5 we plot results for an SSP using the default assumptions from STARBURST99 (SB99 Leitherer et al. 1999Leitherer et al. , 2014. We plot the cumulative distribution functions (CDFs) as a function of time for both the number of SNe explosions and H-ionizing photon production, which should map to Hα emission. ...
We present a statistical analysis of the local, ≈50–100 pc scale, H α emission at the locations of recent (≤125 yr) supernovae (SNe) in nearby star-forming galaxies. Our sample consists of 32 SNe in 10 galaxies that are targets of the PHANGS-MUSE survey. We find that 41% (13/32) of these SNe occur coincident with a previously identified H ii region. For comparison, H ii regions cover 32% of the area within ±1 kpc of any recent SN. Contrasting this local covering fraction with the fraction of SNe coincident with H ii regions, we find a statistical excess of 7.6% ± 8.7% of all SNe to be associated with H ii regions. This increases to an excess of 19.2% ± 10.4% when considering only core-collapse SNe (CCSNe). These estimates appear to be in good agreement with qualitative results from new, higher-resolution Hubble Space Telescope H α imaging, which also suggests many CCSNe detonate near but not in H ii regions. Our results appear consistent with the expectation that only a modest fraction of stars explode during the first ≲5 Myr of the life of a stellar population when H α emission is expected to be bright. Of the H ii region associated SNe, 85% (11/13) also have associated detected CO (2–1) emission, indicating the presence of molecular gas. The SNe associated with H ii regions have typical extinctions of A V ∼ 1 mag, consistent with a significant amount of pre-clearing of gas from the region before the SNe explode.
... In addition to uncertainties in the ISM physics, there are also uncertainties related to the initial mass function and population synthesis model, especially at low metallicities and high redshifts (e.g., Conroy 2013; Eldridge & Stanway 2022). In this paper, we simply keep both stellar models unchanged from the standard choice we made for solar neighborhood conditions, i.e., STARBURST99 (Leitherer et al. 1999(Leitherer et al. , 2014 coupled with a Kroupa IMF (Kroupa 2001) and the Geneva evolutionary tracks for non-rotating stars. More realistically, at low metallicities UV radiation may be stronger for the same population of stars (e.g., Grasha et al. 2021), shifting up the normalization for thermal feedback yield related to the ratio of FUV radiation to SFR, Σ FUV /Σ SFR . ...
We present a new suite of numerical simulations of the star-forming interstellar medium (ISM) using the TIGRESS-NCR framework, covering a wide range of galactic conditions including metallicity. The TIGRESS-NCR framework is a model of the ISM in galactic disks that solves ideal MHD equations with self-gravity in a local shearing-box, including explicit treatment of cooling and heating processes coupled with ray-tracing UV radiation transfer and resolved supernova feedback. The TIGRESS-NCR suite presented in this paper covers metallicity variation $Z'\equiv Z/Z_\odot\sim 0.1-3$, gas surface density $\Sigma_{\rm gas}\sim5-150{\,M_{\odot}{\rm pc^{-2}}}$, and stellar surface density $\Sigma_{\rm star}\sim1-50{M_{\odot}{\rm pc^{-2}}}$, leading to emergent SFR surface density $\Sigma_{\rm SFR}\sim 10^{-4}-0.5{M_{\odot}{\rm kpc^{-2}yr^{-1}}}$ and ISM total midplane pressure $P_{\rm tot}/k_B=10^3-10^6 {\rm cm^{-3}K}$, with $P_{\rm tot}$ equal to the ISM weight $W$. In our simulation suite, $\Sigma_{\rm SFR} \propto {Z'}^{0.3}$, which can be understood based on feedback physics. We present a new calibration for the components of feedback yield $\Upsilon$, defined as ratios between pressure (thermal, turbulent, and magnetic) and $\Sigma_{\rm SFR}$. We find that the thermal feedback yield varies sensitively as $\Upsilon_{\rm th}\propto W^{-0.46}Z'^{-0.53}$, while the combined turbulent and magnetic feedback yield shows weaker dependence $\Upsilon_{\rm turb+mag}\propto W^{-0.22}Z'^{-0.18}$. The reduced $\Sigma_{\rm SFR}$ at low metallicity is due mainly to enhanced thermal feedback yield resulting from reduced attenuation of UV radiation. Combining vertical dynamical equilibrium, feedback yield, and effective equation of state, we provide a new metallicity-dependent subgrid star formation prescription that can be used in cosmological simulations where the ISM is unresolved.
... Since the G130M/1055 spectra have different initial extracted spectral sampling from the G130M/1300 and G160M/1600 data (0.6 and 0.4 Å px −1 , respectively), the final combined UV spectrum has sampling of 1.2 and 0.8 Å px −1 , over the respective ranges, while the optical MUSE data sampling is 1.2 Å px −1 . The combined spectra of the three knots are shown We use Starburst99 (Leitherer et al. 1999(Leitherer et al. , 2014) model spectra of varying cluster ages (1-100 Myr), masses (10 5 -10 9 M e ), and extinctions (E(B − V ) = 0-1). We also consider different star formation histories (SFHs), specifically, continuous star formation (CSF) or single stellar populations (SSPs). ...
As the nearest confirmed Lyman continuum (LyC) emitter, Haro 11 is an exceptional laboratory for studying LyC escape processes crucial to cosmic reionization. Our new Hubble Space Telescope/Cosmic Origins Spectrograph G130M/1055 observations of its three star-forming knots now reveal that the observed LyC originates in Knots B and C, with 903–912 Å luminosities of 1.9 ± 1.5 × 10 ⁴⁰ erg s ⁻¹ and 0.9 ± 0.7 × 10 ⁴⁰ erg s ⁻¹ , respectively. We derive local escape fractions f esc,912 = 3.4% ± 2.9% and 5.1% ± 4.3% for Knots B and C, respectively. Our Starburst99 modeling shows dominant populations on the order of ∼1–4 Myr and 1–2 × 10 ⁷ M ⊙ in each knot, with the youngest population in Knot B. Thus, the knot with the strongest LyC detection has the highest LyC production. However, LyC escape is likely less efficient in Knot B than in Knot C due to higher neutral gas covering. Our results therefore stress the importance of the intrinsic ionizing luminosity, and not just the escape fraction, for LyC detection. Similarly, the Ly α escape fraction does not consistently correlate with LyC flux, nor do narrow Ly α red peaks. High observed Ly α luminosity and low Ly α peak velocity separation, however, do correlate with higher LyC escape. Another insight comes from the undetected Knot A, which drives the Green Pea properties of Haro 11. Its density-bounded conditions suggest highly anisotropic LyC escape. Finally, both of the LyC-leaking Knots, B and C, host ultraluminous X-ray sources (ULXs). While stars strongly dominate over the ULXs in LyC emission, this intriguing coincidence underscores the importance of unveiling the role of accretors in LyC escape and reionization.
... We now compare the HST/UV photometry of the UVdetected subset of our sample with evolutionary models from the stellar population synthesis code STARBURST99 17 (Leitherer et al. 1999(Leitherer et al. , 2010(Leitherer et al. , 2014Vázquez & Leitherer 2005) to examine star formation models and stellar ages that are consistent with a population of stars that could (i) cause the UV continuum emitting clumpy regions in the jet vicinity, and (ii) produce sufficient ionizing photons to power the nebula. STARBURST99 provides predictive SEDs of a young stellar population from the far-UV (FUV) to the near-IR, with varying parameters-IMF, mass range, metallicity, and whether the starburst continuously formed stars (expressed in terms of SFR), as opposed to the single burst scenario (in which case a given starburst mass evolves through time). ...
We present the first systematic search for UV signatures from radio source-driven active galactic nuclei (AGN) feedback in Compact Steep Spectrum (CSS) radio galaxies. Owing to their characteristic sub-galactic jets (1–20 kpc projected linear sizes), CSS hosts are excellent laboratories for probing galaxy scale feedback via jet-triggered star formation. The sample consists of seven powerful CSS galaxies, and two galaxies host to radio sources >20 kpc as the control, at low to intermediate redshifts ( z < 0.6). Our new Hubble Space Telescope images show extended UV continuum emission in six out of seven CSS galaxies, with five CSS hosts exhibiting UV knots cospatial and aligned along the radio-jet axis. Young (≲ 10 Myr), massive (≳ 5 M ⊙ ) stellar populations are likely to be the dominant source of the blue excess emission in radio galaxies at these redshifts. Hence, the radio-aligned UV regions could be attributed to jet-induced starbursts. Lower near-UV star formation rates compared to other indicators suggest low scattered AGN light contribution to the observed UV. Dust attenuation of UV emission appears unlikely from high internal extinction correction estimates in most sources. Comparison with evolutionary synthesis models shows that our observations are consistent with recent (∼1−8 Myr old) star-forming activity likely triggered by current or an earlier episode of radio emission, or by a confined radio source that has frustrated growth, due to a dense environment. While follow-up spectroscopic and polarized light observations are needed to constrain the activity-related components in the observed UV, the detection of jet-induced star formation is a confirmation of an important prediction of the jet feedback paradigm.
... For the second method, we split our sample into two groups: metal-poor galaxies with 12 + log(O/H) < 8.40 and metal-rich galaxies with 12 + log(O/H) 8.40. We then create a grid of SPS models, adopting a pair of Starburst99 models (Leitherer et al. 2014), one metal rich (Z = 0.014 or Z e ) and one metal poor (Z = 0.002 or 0.14 Z e ), and applying the reddening curve of Calzetti et al. (2000) with a range of E(B − V ) values between 0 and 1. We resample the Starburst99 models to match the dispersion of the IUE and COS spectra. ...
... To examine the Si IV and C IV trends further, we investigate the theoretical stellar Si IV λλ1393, 1402 and C IV λλ1548, 1550 profiles as a function of stellar metallicity using synthetic UV spectra from the Starburst99 code (Leitherer et al. 2014). We adopt the library of theoretical spectra derived from WM-Basic model atmospheres (Leitherer et al. 2010) and use the same integration windows as in the corresponding observed spectra to measure the EWs. ...
We present an analysis of the effects of spectral resolution and aperture scale on derived galaxy properties using far-ultraviolet (FUV) spectra of local star-forming galaxies from the International Ultraviolet Explorer ( R ∼ 250, field of view (FOV) ∼ 10″ × 20″) and Cosmic Origins Spectrograph on the Hubble Space Telescope ( R ∼ 15,000, FOV ∼ 2.″5). Using these spectra, we measured FUV luminosities, spectral slopes, dust attenuation, and equivalent widths. We find that galaxies with one dominant stellar cluster have FUV properties that are independent of aperture size, while galaxies with multiple bright clusters are sensitive to the total light fraction captured by the aperture. Additionally, we find significant correlations between the strength of stellar and interstellar absorption lines and metallicity, indicating metallicity-dependent line-driven stellar winds and interstellar macroscopic gas flows shape stellar and interstellar spectral lines, respectively. The observed line strength versus metallicity relation of stellar-wind lines agrees with the prediction of population synthesis models for young starbursts. In particular, measurements of the strong stellar C iv λλ 1548, 1550 line provide an opportunity to determine stellar abundances as a complement to gas-phase abundances. We provide a relation between the equivalent width of the C iv line and the oxygen abundance of the galaxy. We discuss this relation in terms of the stellar-wind properties of massive stars. As the driving lines in stellar winds are mostly ionized iron species, the C iv line may eventually offer a method to probe α -element-to-iron ratios in star-forming galaxies once consistent models with nonsolar abundance ratios are available. These results have important implications for the galaxy-scale, low-resolution observations of high-redshift galaxies from JWST ( R ∼ 100–3500).
... To calculate the yields from a simple stellar population (SSP) for each stellar particle, we use the Starburst99 model (Leitherer et al. 1999), assuming a Chabrier initial mass function (Chabrier 2005). The Geneva stellar wind model (Schaller et al. 1992;Maeder & Meynet 2000) is used to calculate the tabulated chemical yields from the stellar wind as a function of the age and metallicity of the SSP (see Leitherer et al. 2014 for more details). Therefore, each stellar particle is involved in chemical enrichment based on its evolving age and metallicity. ...
Thick disks are a prevalent feature observed in numerous disk galaxies, including our own Milky Way. Their significance has been reported to vary widely, ranging from a few percent to 100% of the disk mass, depending on the galaxy and the measurement method. We use the NewHorizon simulation, which has high spatial and stellar mass resolutions, to investigate the issue of the thick-disk mass fraction. We also use the NewHorizon2 simulation, which was run on the same initial conditions, but additionally traced nine chemical elements. Based on a sample of 27 massive disk galaxies with M * > 10 ¹⁰ M ⊙ in NewHorizon, the contribution of the thick disk was found to be 20% ± 11% in r -band luminosity or 35% ± 15% in mass to the overall galactic disk, which seems in agreement with observational data. The vertical profiles of 0, 22, and 5 galaxies are best fitted by 1, 2, or 3 sech 2 components, respectively. The NewHorizon2 data show that the selection of thick-disk stars based on a single [ α /Fe] cut is contaminated by stars of different kinematic properties, while missing the bulk of kinematically thick disk stars. Vertical luminosity profile fits recover the key properties of thick disks reasonably well. The majority of stars are born near the galactic midplane with high circularity and get heated with time via fluctuations in the force field. Depending on the star formation and merger histories, galaxies may naturally develop thick disks with significantly different properties.
... They can be the result of a single O-type star evolving into a W-R star (Meynet et al. 2017) or through mass transfer in a binary star system . In metalrich environments (approximately solar metallicity), W-R stars can be produced at later times ∼10 Myr, whereas in metal-poor environments (subsolar metallicity) no W-R stars are expected after 5 Myr (see Figure 14 in Leitherer et al. 2014). In this work we can assume the latter case as the galaxy sample has subsolar metallicity (see Table 1 in Chandar et al. 2004). ...
The ability to determine galaxy properties such as masses, ages, and star formation rates robustly is critically limited by the ability to measure dust attenuation accurately. Dust reddening is often characterized by comparing observations to models of either nebular recombination lines or the UV continuum. Here, we use a new technique to measure dust reddening by exploiting the He ii λ 1640 and λ 4686 emission lines originating from the stellar winds of Wolf–Rayet stars. The intrinsic line ratio is determined by atomic physics, enabling an estimate of the stellar reddening similar to how the Balmer lines probe gas-emission reddening. The He ii line ratio is measured from UV and optical spectroscopy using the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope for eight nearby galaxies hosting young massive star clusters. We compare our results to dust reddening values estimated from UV spectral slopes and from Balmer line ratios and find tentative evidence for systematic differences. The reddening derived from the He ii lines tends to be higher, whereas that from the UV continuum tends to be lower. A larger sample size is needed to confirm this trend. If confirmed, this may indicate an age sequence probing different stages of dust clearing. Broad He ii lines have also been detected in galaxies more distant than in our sample, providing the opportunity to estimate the dust reddening of the youngest stellar populations out to distances of ∼100 Mpc.
... Here we undertake an analysis of the nebular spectrum with a focus on the inferred metallicity and age/mass of the ionizing stellar population using commonly used spectral synthesis tools Starburst99 (version 7.0.1; Leitherer et al. 1999Leitherer et al. , 2014, Charlot & Bruzual (Bruzual & Charlot 2003 ;Plat et al. 2019 , hereafter CB19) and BPASS (v.2.2.1, Eldridge et al. 2017 ;Stanway & Eldridge 2018 ). A detailed study of the integrated 30 Doradus nebula has been undertaken by Pellegrini, Baldwin & Ferland ( 2011) while Peimbert ( 2003 utilize VLT/UVES spectroscopy for a detailed chemical analysis. ...
... Age estimates from H α are relatively metallicity insensitive, b ut WR b umps and UV diagnostics are strongly metallicity-dependent. Starburst99 (v7.0.1, Leitherer et al. 1999Leitherer et al. , 2014 involves a 1 × 10 5 M burst of star formation, an initial mass function (IMF) from Kroupa ( 2008 ) with an upper mass limit of 120 M . Modern non-rotating and rotating Gene v a e volutionary models at Solar (Z = 0.014 Ekstr öm et al. 2012 ) and SMC (Z = 0.002 Georgy et al. 2013 ) metallicities are available, 5 with the full range of metallicities for historical models available with either standard (Schaller et al. 1992 ) or enhanced mass-loss (Meynet et al. 1994 ( 2002 ) and Leitherer et al. ( 2010 ) and empirical UV spectral templates drawn from either the Milky Way or Magellanic Clouds (Robert, Leitherer & Heckman 1993 ). ...
... In common with previous studies of young extragalactic stellar populations in the UV, we again utilize predictions of the emergent far-UV spectrum from the population synthesis tool Starburst99 (version 7.0.1; Leitherer et al. 1999Leitherer et al. , 2014 (Table C1 ). However, application to theoretical predictions leads to a suppressed continuum extending to ∼1300 Å, contrary to observations. ...
We present the integrated VLT-MUSE spectrum of the central 2 × 2 arcmin2 (30 × 30 pc2) of NGC 2070, the dominant giant H ii region of the Tarantula Nebula in the Large Magellanic Cloud, together with an empirical far-ultraviolet spectrum constructed via LMC template stars from the ULLYSES survey and Hubble Tarantula Treasury Project UV photometry. NGC 2070 provides a unique opportunity to compare results from individual stellar populations (e.g. VLT FLAMES Tarantula Survey) in a metal-poor starburst region to the integrated results from the population synthesis tools Starburst99, Charlot & Bruzual, and BPASS. The metallicity of NGC 2070 inferred from standard nebular strong line calibrations is ∼0.4 ± 0.1 dex lower than obtained from direct methods. The Hα inferred age of 4.2 Myr from Starburst99 is close to the median age of OB stars within the region, although individual stars span a broad range of 1–7 Myr. The inferred stellar mass is close to that obtained for the rich star cluster R136 within NGC 2070, although this contributes only 21 per cent to the integrated far-UV continuum. He ii λ1640 emission is dominated by classical WR stars and main sequence WNh + Of/WN stars. Around 18 per cent of the NGC 2070 far UV continuum flux arises from very massive stars with ≥100 M⊙, including several very luminous Of supergiants. None of the predicted population synthesis models at low metallicities are able to successfully reproduce the far-UV spectrum of NGC 2070. We attribute issues to the treatment of mass-loss in very massive stars, the lack of contemporary empirical metal-poor templates, plus WR stars produced via binary evolution.
... This classical model for mechanical feedback was formulated for effects at solar metallicity and is approximately constant over the cluster lifetime. However, this is not the case at low metallicity, as the initial mechanical feedback of a lowmetallicity cluster is at least an order of magnitude lower than its maximum value well into the cluster lifetime (Leitherer et al. 2014). In this work, we show that this effect is likely to be important and could fundamentally impact galaxy evolution in multiple ways. ...
... We use Starburst99, a well-established evolutionary synthesis code, to model the mechanical feedback of star-forming galaxies with varying SN progenitor masses (Leitherer et al. 2014). It was previously thought that all stars between 8 and 120 M e end their lives as SNe. ...
... Furthermore, we expect the mechanical feedback from stellar winds to be even lower than estimated here, since the adopted mass-loss rates are now thought to be too high (e.g., Ramachandran et al. 2019; Figure 1. Starburst99 models of mechanical luminosity (left) and momentum injection rate (right) from winds and SNe for a 10 6 M e cluster (see Leitherer et al. 2014). The classical (blue) and subsolar unrestricted SNe (red) models have SN progenitor masses of 8-120 M e . ...
The classical model of massive-star mechanical feedback is based on effects at solar metallicity ( Z ⊙ ), yet feedback parameters are very different at low metallicity. Metal-poor stellar winds are much weaker, and more massive supernova progenitors likely collapse directly to black holes without exploding. Thus, for ∼0.4 Z ⊙ we find reductions in the total integrated mechanical energy and momentum of ∼40% and 75%, respectively, compared to values classically expected at solar metallicity. But in particular, these changes effectively delay the onset of mechanical feedback until ages of ∼10 Myr. Feedback from high-mass X-ray binaries could slightly increase mechanical luminosity between ages 5 and 10 Myr, but it is stochastic and unlikely to be significant on this timescale. Stellar dynamical mechanisms remove most massive stars from clusters well before 10 Myr, which would further promote this effect; this process is exacerbated by gas retention implied by weak feedback. Delayed mechanical feedback implies that radiation feedback therefore dominates at early ages, which is consistent with the observed absence of superwinds in some extreme starbursts. This scenario may lead to higher star formation efficiencies, multiple stellar populations in clusters, and higher Lyman continuum escape. This could explain the giant star-forming complexes in metal-poor galaxies and the small sizes of OB superbubble shells relative to their inferred ages. It could also drive modest effects on galactic chemical evolution, including on oxygen abundances. Thus, delayed low-metallicity mechanical feedback may have broad implications, including for early cosmic epochs.
... These are modelled using the mechanical feedback formulation (Hopkins et al. 2014 ;Kimm & Cen 2014 ): numerically the energy, mass and metals injected by each SN are distributed to the 32 nearest neighbours using a smooth particle hydrodynamics kernel. We assume one SN per 100 M of stellar mass formed (Chabrier 2003 ;Leitherer et al. 2014 ), where each SN injects 10 51 ergs s −1 of energy and ejects 10.5 M of mass and 2 M of metals into the surrounding medium. The SNe are detonated with a delay time of 4 Myr, towards the upper end of the range derived from recent observations of feedback disruption (Kruijssen et al. 2019 ;Che v ance et al. 2020Che v ance et al. , 2022. ...
Observations indicate that the central gas discs are smoother in early-type galaxies than their late-type counterparts, while recent simulations predict that the dynamical suppression of star formation in spheroid-dominated galaxies is preceded by the suppression of fragmentation of their interstellar media. The mass surface density power spectrum is a powerful tool to constrain the degree of structure within a gas reservoir. Specifically here, we focus on the power spectrum slope and aim to constrain whether the shear induced by a dominant spheroidal potential can induce sufficient turbulence to suppress fragmentation, resulting in the smooth central gas discs observed. We compute surface density power spectra for the nuclear gas reservoirs of fourteen simulated isolated galaxies and twelve galaxies observed as part of the mm-Wave Interferometric Survey of Dark Object Masses (WISDOM) project. Both simulated and observed galaxies range from disc-dominated galaxies to spheroids, with central stellar mass surface densities, a measure of bulge dominance, varying by more than an order of magnitude. For the simulations, the power spectra steepen with increasing central stellar mass surface density, thereby clearly linking the suppression of fragmentation to the shear-driven turbulence induced by the spheroid. The WISDOM observations show a different (but potentially consistent) picture: while there is no correlation between the power spectrum slopes and the central stellar mass surface densities, the slopes scatter around a value of 2.6. This is similar to the behaviour of the slopes of the simulated galaxies with high central stellar mass surface densities, and could indicate that high shear eventually drives incompressible turbulence.
