Synthetic properties of starburst galaxies

“Here we use the “standard” calibration for starbursts by Kennicutt (1998), based on the Starburst 99 models of Leitherer & Heckman (1995): SFRHα = 7.9× 10−42 [ LHα/erg.s −1] (1) Using the surface brightness per square arc sec. and the distance we can translate this star formation rate to the…”

“SF-related heating sources are photo-ionisation, shocks and/or turbulent mixing layers, but in principle all energy comes from processes relating to the evolution of high-mass stars (winds and type II supernovae; Leitherer & Heckman 1995; Leitherer et al. 1999).”

“The lines of Civ and Si iv already have been studied extensively in the literature (Storchi-Bergmann et al. 1994; Leitherer & Heckman 1995; Leitherer et al. 1999; Heckman et al. 1998; Rix et al. 2004).”

“This is compa-M _ \M* \ 125 M _rable to the relation derived from the models of Leitherer & Heckman (1995).”

“Assuming no ionizing photons escape the galaxy ( f esc = 0) and case B recombination, we can relate ˙n ion to L H α ,int via the relation of Leitherer & Heckman (1995): This equation assumes a temperature of 10 4 K and an electron density of 100 cm − 3 , but is not sensitive to the choice of…”

“Leitherer & Heckman (1995) presented the evolution of both supernova rate and the injection rate of mechanical energy for longer term evolution, up to ages of 300 Myr.”

“The measured fluxes should thus mainly represent the stellar continuum emission of the objects, with a contribution from nebular continuum emission depending on the strength and age of the starburst (see Leitherer & Heckman 1995; Kruger, Fritze-von Alvensleben, & Loose 1995).”

“…1 2 N ∑ i wiṁi(t)v 2 ∞,i(t), (13) where ṁi(t) is obtained from interpolations of the tracks and v∞,i(t) is derived from the interpolated luminosity, the effective temperature, the mass mi, and the metallicity of the star of initial mass Mi at the given age, following Leitherer and Heckman (1995).”

“…the level of SSPs and again no dust at the level of the galaxy model (see e.g. Arimoto & Yoshii 1987; Arimoto & Tarrab 1990; Bruzual & Charlot 1993; Leitherer & Heckman 1995; Leitherer et al. 1999; Tantalo et al. 1996; Kodama & Arimoto 1997; Kodama et al. 1998; Tantalo et al. 1998; Buzzoni 2002,…”

“To do this, we first calculate hydrogen recombination line strength following the relation from Leitherer & Heckman (1995), scaling from integrated Lyman-continuum flux, and then follow the strengths determined with nebular line ratios by Anders & Fritze-v.”

“The lowest expected value, β = −3, corresponds to the spectrum of individual O-type stars (Leitherer & Heckman 1995).”

“It is not surprising that most of line emission results from photoionization since the ionizing radiation energy from OB stars is about an order of magnitude higher than the total kinetic energy released by supernovae and stellar winds (cf. Leitherer & Heckman 1995).”

“SB99 synthesis models (Leitherer et al. 1999) are based on the original models by Leitherer & Heckman (1995), but have been continuously updated with new evolutionary tracks and stellar atmospheres.”

“A nebular contribution to the SED is also considered, following the recipe of Leitherer & Heckman (1995).”

“…lifetime (t[Fe II]) of a single SNR, one can define the supernova rate, η, as: η = L[Fe II] t[Fe II] L[Fe II] yr−1 (1) This quantity can be used, for instance, to set constraints on the star formation history of starburst galaxies (e.g. Leitherer & Heckman 1995; Kotilainen et al. 1996). c© 2001 RAS”

“The third category is to use some feature of the YMC, such as surface brightness fluctuations, the size of the bubble created by the YMC in the surrounding ISM (e.g, Whitmore et al. 2011), or the equivalent width of recombination lines (e.g. Leitherer & Heckman 1995) as a proxy for the cluster age.”

“According to Leitherer & Heckman (1995) the assumed injected energy corresponds to an instantaneous starburst of ∼ 2× 106 M⊙.”

“As noted by Byler et al. (2017), other combinations of ionizing spectra and photoionization codes, 14 such as those presented in Dopita et al. (2013) using STARBURST99 (Leitherer & Heckman 1995) and MAPPINGS III (Sutherland & Dopita 1993) can produce [O III]/Hβ ratios that more closely resemble our sample.”

“The 0.25 Z⊙ evolutionary synthesis models of Leitherer & Heckman (1995), for example, predict a spectral hardness Q(He) / Q(H) = 0.23 and Q(He)/Q(H) = 0.07 from stellar populations continuously forming stars with a Salpeter initial mass function (IMF) and upper mass limits of mu = 100 M⊙ and 30 M⊙…”

“A first estimate of the mass deposition rate, Ṁ for a 107M⊙ starburst, with Z = 0.3Z⊙ and c© 0000 RAS, MNRAS 000, 000–000 t = 5.8 Myr can be obtained from the starburst evolutionary synthesis models (Leitherer & Heckman 1995; Leitherer et al. 1999), and gives Ṁ ∼ 0.17M⊙ yr−1.”

“Figure 6 (bottom right panel ) shows the histogram of the H equivalent-width log(EW[H ]) of the 12 central sources in units of log(8) (from Table 2) and the associated ages according to Leitherer & Heckman (1995).”

“As the FIR luminosity is an excellent indicator of the current SFR (e.g., Leitherer & Heckman 1995; Kennicutt 1998), we can use the David et al. (1992) correlation to convert LX to SFR via the predicted LFIR.”

“However, the lack of 12 km emission, corresponding to (using conver-L IR[ 108 L _sion factors discussed in Leitherer & Heckman 1995 and Devereux & Young 1990), limits the current star formation rate even more, to yr~1.”

“…the same time, as might be expected from a large-scale gravitational instability, then their J[K colors would be 0.7 mag for an age of 107 yr, based on a comparison of the J[K colors with models of cluster evolution (e.g., Leitherer & Heckman 1995 ; Mayya 1995 ; Girardi & Bertelli 1998).”

“For a starburst population with a reasonable IMF, the ratio L/Mdyn should be less than 500 L⊙/M⊙ (Leitherer & Heckman 1995, Scoville et al. 1997b), and objects with an LFIR/MH2 ratio > 500 L⊙/M⊙ require a significant luminosity contribution from an active nucleus.”

“(2) The Kennicutt (1998) relation is dependent on the models of Leitherer & Heckman (1995).”

“Star formation produces stars with a range of masses, some of which will be sufficiently massive to explode as supernova very quickly (∼ 106 years; Leitherer & Heckman 1995), injecting heavy metals into the interstellar medium and producing large quantities of dust on short time scales (∼ 100 – 200…”

“…would however reach the critical value after 4 Myr and 5 Myr, depending if one assumes solar or 0.1 solar as the original cluster metallicity (see Leitherer & Heckman, 1995; their Figure 37), and the UV radiation a couple of Myr after this will not suffice to sustain even the star cluster volume…”

“It should be pointed out that, at the burst age of 4-5 Myr for our three WR galaxies, the continuum emission from the gas is negligible (Leitherer & Heckman 1995).”

“63l predict for young, ionizing starburst populations (see, e.g., Leitherer & Heckman 1995).”

“21c and 21g corresponds to the region occupied by a young/intermediate age stellar population component with ages ranging from 106 to 108 years, calculated from the models of Leitherer & Heckman (1995).”

“Assuming Case-B recombination, the intrinsic Hα luminosity is LHα[erg s −1] = 1.36 × 10−12Q(H0) (Leitherer & Heckman 1995), and the SFR [Me yr −1] ≈ 2.09× 10−42 L(Hα) [erg s−1] (Reddy et al. 2022).”

“This has been achieved in the last few years by several independent groups (e.g. Cerviño & Mas-Hesse 1994; Garcı́a-Vargas, Bressan & Dı́az 1995; Leitherer & Heckman 1995).”

“A K-band flux excess was also reported in previous studies that fitted SEDs with Starburst99 (Surace & Sanders (1999) for warm ULIGs; Mazzarella et al. (1992) for the nuclei of Arp 220), which was compensated adding a hot dust (800 K) component contributing to 10-30% of the emission (Surace & Sanders 1999).”

“The UV β slope depends on the age and dust attenuation of the galaxy (and the SFH, Leitherer & Heckman 1995; Meurer et al. 1999).”

“9), which is almost constant in the inner 3 kpc. Applying the population synthesis models for instantaneous bursts described by Leitherer & Heckman (1995) and assuming (as we explained in ° 3) that the e†ect of the underlying population is not signiÐcant, it is possible to derive the age of each…”

“This latter component may be contaminated by nebular continuum emission from HII regions, but nebular emission amounts to only 30% of the light during the first few Myrs of a starburst, and becomes negligible as soon as the first red supergiants appear, at about 106.9 yr (Leitherer & Heckman 1995).”

“−2.0, as suggested in Calzetti et al. 1994; Leitherer & Heckman 1995; Meurer et al. 1999), and any change in this slope results from wavelength-selective absorption of photons by dust grains.”

“The rate of energy deposition into the ISM from the subsequent supernovae rises at this time and remains fairly constant for∼ 3 × 107 yr (Leitherer & Heckman 1995; Cervino, Mas-Hesse & Kunth 2002).”

“As shown by the models of Leitherer & Heckman (1995), the ratio between the mechanical energy and the ionizing Lyman continuum, both injected in the ISM by the massive star population, rapidly increases during the stellar cluster evolution.”

“They used Leitherer & Heckman (1995) population synthesis models to estimate the ages of the emission zones detected in their images, finding that some of these emission knots are around 5 Myr old.”

“Then we can estimate Hβ luminosity, L(Hβ) using the following formula (Leitherer & Heckman 1995), L(Hβ) = 4.76× 10−13NLyc erg s −1.”

“The estimated age of the most-recent star forming event can be derived from the Hα equivalent width, W(Hα), of the star-forming knots, because this value decreases with time (e.g. Leitherer & Heckman 1995; Johnson & Conti 2000).”

“7 of Leitherer & Heckman (1995); (b) the mass functions φ(logM) ∝ M φ(M) (number per decade in mass), really the distributions of starburst masses, arbitrarily choosing M∗ = 106 M⊙; (c) the bolometric luminosity functions φ(logLbol) ∝ Lbol φ(Lbol) (number per decade in luminosity) produced by the…”

“Nevertheless, models for starbursts (Leitherer & Heckman 1995), which have been found to be generally consistent with observations (Stasińska & Leitherer 1996), indicate that Hα EWs can be as high as 3000 for ages up to 3 × 106 years and can remain above ∼ 300 up to ages of 108 years (these models…”

“Overall, starburst galaxies cover a broad range in morphology from blue compact dwarfs (BCDs, which share common properties with the high-z environments; e.g., Izotov et al. 2021) to spiral galaxies and merging systems (Leitherer & Heckman 1995; Leitherer et al. 1995; Annibali & Tosi 2022).”

“This calibration assumes that the Lbol of a constant SF lasting 100 Myr is totally emitted in the IR (K98; Leitherer & Heckman,1995 LH95 hereafter).”

“First, we calculate the luminosity of Hβ emission line, L(Hβ), using the following relation (Leitherer & Heckman 1995): L(Hβ) (erg s−1) = 4.76×10−13NLyc (s−1), (1) whereNLyc is the ionizing photon production rate estimated in each SED model.”

“The major difference between the two galaxies does not lie in the total energy output, but in the size of the region over which the energy is produced in stellar winds and supernovae (Leitherer & Heckman 1995) and released into the ISM.”

“If all the Lyman continuum photons are used for ionizing the surrounding gas, the luminosity of Hβ is calculated according to the following formula; L(Hβ)(erg s−1) = 4.76 × 10−13NLy(s −1) (5) (Leitherer & Heckman 1995).”

“If one scales the evolutionary synthesis models (e.g. Leitherer & Heckman 1995) for star clusters generated by a constant star formation rate to the values inferred from the SCUBA sources (≥ 100 M⊙ yr −1; e.g. Greve et al. 2005; Swinbank et al. 2006; Tacconi et al. 2006), one sees that as a result…”

“We estimate the mass-loss rate ṀSC using the Starburst99 models (Leitherer & Heckman1995; Leitherer et al.1999)3 with the appropriate cluster masses and a Salpeter initial mass function (IMF) including stars between 1 and 100M .”