Synthetic properties of starburst galaxies

“…non-ionizing UV luminosity density L UV estimated at 1,500 Å in units of erg s −1 Hz −1 : where N ( H 0 ) can be estimated from the Hα Balmer line 77 assuming a case B recombination theory 78 : −1 esc where L (Hα) is in units of erg s −1 and f esc is the escape fraction of Lyman continuum…”

“We expect the K-band luminosity to trace the stellar mass to a factor of roughly 2 (e.g., Leitherer & Heckman 1995; Bell & de Jong 2001; Dasyra et al. 2006).”

“If the star formation in a galaxy is instantaneous, then such strong Hα emission (EWHα 100 Å) is short-lived, lasting for only ∼5 Myr after the starburst (Leitherer & Heckman 1995).”

“If stars are formed at a constant rate over 107 − 108 yr with a Salpeter initial mass function (φ(m) ∝ m−2.35; 0.1 ≤ m ≤ 100 M⊙), a luminosity of 10 11 L⊙ corresponds to a star formation rate Ṁ between 14− 24M⊙ yr −1 (Leitherer and Heckman 1995).”

“…this trend is consistent with the canonical picture of galactic-scale outflows arising from the combined effects of stellar and supernovae winds 13 (Leitherer & Heckman 1995; Veilleux et al. 2005), recent studies probing more limited ranges in SFR have often failed to reproduce the Martin (2005)…”

“The amount of mass returned directly by supernovae and stellar winds during the last 10È15 Myr will only be D105 (Leitherer & Heckman 1995).”

“This method was applied by McGaugh (1991) for zero-age clusters, and taking into account the temporal evolution of the clusters by Garćıa-Vargas & D́ıaz (1994), Cerviño & Mas-Hesse (1994), GarćıaVargas et al. (1995), and Leitherer & Heckman (1995).”

“In practice, we adopt spectral templates computed for a Salpeter IMF (Salpeter 1955) from 0.1 to 100 M , and we properly treat the returned ISM mass from stars.”

“Kennicutt (1998) presented the equation (4) to calculate SFR based on IR luminosity: SFR(M yr 1) ¼ 4:5 ; 10 44L FIRð Þ (ergs s 1); ð14Þ The calibration factor was derived by applying the models of Leitherer & Heckman (1995) for continuous bursts of age 10Y 100 Myr and adopting the same Salpeter IMF.”

“Our models are based on the synthetic properties of starbursts, as derived by Mas-Hesse & Kunth (1991) and Leitherer & Heckman (1995); and consider a mechanical energy injection rate (E0 ∼ 10 38 −−1042 erg s−1) which over several 107 yr is equivalent to some tens of thousand of supernova…”

“We use the relation of Leitherer & Heckman (1995) to convert our dust-corrected Hα luminosity (Section 2.2) to N(H0): N(H0) [s−1] = 1 1.36 × 1012L(Hα) [erg s−1].”

“Leitherer & Heckman (1995) for example, model the ratio of Wolf-Rayet stars to O stars in evolving starbursts using the Geneva tracks, and derive an order of magnitude increase in the metallicity range 0.25 to 2 Z⊙; this range approximately corresponds to the metallicity spread in our sample.”

“We use the number of ionizing photons reported by SB99 for a 2 MyrÈold cluster scaled by and the transform-L 1500obs /L 1500modelations of Leitherer & Heckman (1995) to predict an extinction-corrected Ha luminosity of L Ha^ 3.6] 1039ergs s~1.”

“The strength of this redshifted component suggests the presence of a large number of very massive stars (>30M ; Leitherer & Heckman 1995).”

“Starbursts that have little obscuration have UV slopes similar to theoretical predictions for young OB stellar populations (β ≈ −2.5; Leitherer & Heckman 1995).”

“Comparison with STARBURST99 evolutionary tracks indicates that some of the regions are due to very young (∼6 Myr) and massive (∼ 108 M⊙) bursts, while other regions may have been forming stars in a more continuous manner for several tens to several hundreds of Myr as indicated by their relatively red colors and high H…”

“When the spectrum is dominated by a young stellar population the ultraviolet spectral slope β, is found to have a weak dependence on metallicity, IMF, and star formation history (Leitherer & Heckman 1995).”

“…= N(H0) LUV , (7) where N(H0) is the production rate of the ionizing photon which can be estimated from the Hα luminosity using a conversion factor by Leitherer & Heckman (1995), LintHα[erg s −1] = 1.36× 10−12Nobs(H0)[s−1] = 1.36× 10−12(1− f ionesc )N(H0)[s−1], (8) where f ionesc is the ionizing…”

“Rather than reconfigure our starburst program for an instantaneous burst, we use Leitherer & Heckman (1995).”

“The parameter ξion is related to the observed Hα emission and depends on the metallicity and star formation rate of the galaxies (Leitherer & Heckman 1995; Bruzual & Charlot 2003).”

“Stellar populations <10 Myr old yield SFRs more than 50% higher than given by the Madau, Pozzetti & Dickinson (1998) calibration when modelled using stellar synthesis techniques (Leitherer & Heckman 1995; Kennicutt 1998; Leitherer et al. 1999).”

“%) contribution to the total mechanical power starbursts in general, stellar winds may supply up to half of the mass returned to the ISM (Leitherer et al. 1992; Leitherer & Heckman 1995; Strickland & Heckman 2009).”

“…to determine the X-ray luminosity of a star-forming galaxy as a function of its star formation rate, we use the result from the starburst models of Leitherer & Heckman (1995) that L IR ∼ 1.5 × 1010 ( SFR 1 M yr−1 ) L , (16) together with equation (15) to write the X-ray luminosity as (Helfand &…”

“For an instantaneous burst in the age range between about ten and fifty Myr, the primary heating/ionizing source for the associated gas would be the mechanical energy supplied by supernovae rather than O star ionizing radiation (Leitherer & Heckman 1995).”

“A detailed study of the evolution of these observables has been discussed elsewhere (see Cerviño and Mas-Hesse (1994) for a more detailed description of the evolution, and Leitherer & Heckman (1995), for a comparison with other synthesis models, showing that both codes give quite similar results)3.”

“The kinetic luminosity per unit mass of a starburst remains approximately constant for the first few 107 yr and equal to ∼1035.5 erg s−1M−1⊙ for a Salpeter IMF and Mlow=1M⊙ and Mup=100M⊙ (Leitherer & Heckman 1995).”

“K∼ 1.7 for a 108 yrs old stellar population, Leitherer & Heckman 1995) the observed V–”

“…I systems, winds deliver a mechanical luminosity over the first few Myr that is comparable with the subsequent rate of energy input from supernovae (Shull and Saken 1995; Leitherer and Heckman 1995), in low metallicity systems the input power from winds is negligible compared with supernovae.”

“This is roughly consistent with the relation derived from the Leitherer & Heckman (1995) models for a different IMF and much younger ages of 10 Myr.”

“The Leitherer & Heckman (1995) SEDs are significantly harder than the SED Spinoglio & Malkan (1992) used.”

“̇ We adopt Bouwens et al. (2015) representation of the Leitherer & Heckman (1995) relation between QH0 and the Hβ luminosity L(Hβ), as L(Hβ) [erg s−1] = 1.36× 10−12QH0/2.86 [s −1].”

“While computing the synthetic properties of starburst galaxies, Leitherer and Heckman (1995) computed a Hα EW of ∼ 3200 Å for a population with 0.1Z⊙ and a constant star formation rate.”

“The rate at which a starburst generates mechanical energy is about 1% of its bolometric luminosity (e.g., Leitherer & Heckman 1995).”

“It is useful to compare the parameters we use with the detailed starburst models of Leitherer & Heckman (1995) (LH).”

“…fluxes from the newer photoionization models are in good agreement with the BKG models, which, as mentioned above, were calculated based on the Leitherer & Heckman (1995) SEDs, and were therefore dependent on different stellar tracks and stellar atmospheres than those in the SSL work, except…”

“r radiative flows (see Section2.3). The wind solution is a function of radius r. We take r = r/R as the dimensionless radius, and dimensionless velocity u, density r and pressure P as u = uM˙ 1/2E˙1/2,(18) r = rM˙ 3/2E˙ 1/2R 2,(19) P = PM˙ 1/2E˙1/2R 2,(20) the solutions of these dimensionless variables are shown in Fig…”

“The latter can be calculated using the conversation factor derived in Leitherer & Heckman (1995) as LintHα = 1.36× 10−12 (1− f ionesc )N(H0), (2) where f ionesc is the internal ionizing photon escape fraction.”

“Similar models have been presented by others (e.g. Bruzual & Charlot 1993 (BC93); Leitherer & Heckman 1995; Charlot 1996), and for the same input parameters the various models are in excellent agreement for ages between 1 and 100 Myr.”

“The number of ionizing photons, QH0, can be determined via hydrogen recombination lines such as Hα and Hβ (e.g Leitherer & Heckman 1995), and the UV luminosity, Note. a Limiting magnitude at the 3σ level.”

“…temperature of the injected energy can be expressed as kTq SN ∼ 1.6ZSieSN keV, (32) where ZSi is the ICM Si abundance, relative to solar, and eSN is the average injected energy per supernova (perhaps boosted by stellar winds from SNII progenitors; Leitherer & Heckman 1995) in units of 1051 erg.”

“The total number of ionizing photons for a given region has been derived from the Hα luminosity (Leitherer & Heckman 1995): Q(H0) = 2.1 × 1012 L(Hβ), and the mass of the ionizing cluster Mcl is Mcl = 7.3 × 10−34 ( EW (Hβ) 50 Å )−0.86 .”

“While the Hα flux scales directly with the number of ionizing photons emerging from the H II regions in the galaxy (Kennicutt, 1998; Leitherer & Heckman, 1995), the shape of the ionizing spectrum in low metallicity galaxies is poorly constrained.”

“As mentioned in Kennicutt (1998), the calibration of SFRIR is based on the starburst synthesis models of Leitherer & Heckman (1995) assuming a constant SFH with a young age of 10–100Myr (in which time the bolometric luminosityto-SFR ratio is relatively constant), and assuming that dust re-radiates…”

“The presence of WR features in star forming galaxies can only be explained with short bursts of star formation with durations of the order of a few million years (Leitherer & Heckman 1995), as used in our fit to the observed properties of the galaxy.”

“This has been scaled from the synthesis models of Leitherer & Heckman (1995) for a 106 M⊙ starburst under the assumption of a Salpeter IMF with a lower mass limit of 1 M⊙, an upper stellar mass equal to 100 M⊙, and a metalicity Z = 0.1.”

“The implied UV slope for the dust-free case is β0 = −2.12±0.18; this is in agreement with what is expected from stellar population models (Leitherer & Heckman 1995), and favours a continuous star-formation mode.”

“For solar metallicity and an age of 5 Myr, the total mass loss for the two CNSFRs is in the range ≈103–105 M (Leitherer & Heckman 1995).”

“The difference in the number of ionizing photons for metallicities between 0.1 and twice Z⊙ is about 13%, and the difference in the normalized UV flux is about 11% (Leitherer & Heckman 1995).”

“Arguably, stronger outflows are predicted in galaxies with more intense star formation (Leitherer & Heckman 1995; Veilleux et al. 2005; Murray et al. 2011), as it is assumed that the primary energy source behind the outflows is supernovae-driven winds.”

“10 % of the bolometric luminosity of starbursts is emitted below 912 Å (Leitherer & Heckman 1995), and the fraction of ionizing photons that is directly absorbed by dust grains is estimated to be ∼ 25 % (Smith et al. 1978).”

“Solar metallicity is a reasonable assumption for circumnuclear regions of barred spirals, where radial mixing occurs (e.g., Roy & Belley 1993 ; Martin & Belley 1997), and in any event the broadband properties are weakly dependent on metallicity (e.g., Leitherer & Heckman 1995).”

“1ion,0 H UV 0 The number of ionizing photons, QH0, can be determined via hydrogen recombination lines Hβ (e.g., Leitherer & Heckman 1995), and the UV luminosity, LUV, is derived from the Subaru photometry Paper I.”

“Kennicutt (1998) derived from the star-burst synthesis models of Leitherer & Heckman (1995), for solar abundances, Salpeter IMF, and assuming that the dust re-radiates all the bolometric luminosity, a relation between star-forming rate nd LFIR of 1.7 10−10 LFIR M⊙ yr−1 L−1⊙ .”

“A number of authors have discussed the impact of nebular emission on broad-band photometry of young stellar populations based on synthesis modeling (e.g. Krueger et al. 1995; Leitherer & Heckman 1995; Zackrisson et al. 2001; Anders & Fritze-v.”

“According to the models by Leitherer & Heckman (1995), the inferred Star Formation Rate (SFR) depends mostly on the assumed IMF (Initial Mass Function) slope and upper mass cutoff and just slightly on metallicity.”

“This population can account for the observed Balmer-line absorptions and for the low Hb equivalent width of 80 Å. Model predictions for W(Hb) are quite robust (see Leitherer & Heckman 1995) but fail to agree with the observations by a factor of about 3 in the case of NGC 1741B (data from VC).”

“1 SEDs are in units of fλ per M⊙ yr −1 of star formation, so the expected LHα per M⊙ yr −1 of star formation can then be calculated using the equation from Leitherer & Heckman (1995): LHα[erg s −1] = 1.36N(H0) 1012 [s−1].”

“…luminosity and the extinction are instant observables, the infrared-derived star formation luminosity is the result of the integration of bursts of star formation occured over billions of years, assuming that the SF remains constant over the lifetime of the burst (Leitherer & Heckman 1995).”

“Depending upon the exact conversion recipe chosen this yields SFRs of 140–240M⊙ yr −1 (Leitherer & Heckman 1995) or 200–600M⊙ yr −1 (Thronson & Telesco 1986).”

“This equation implies that the UV slope of the dust-free objects is βdust−free = −2.2±0.3 being in agreement, within the errors, what is expected from stellar population models and a constant SFH mode (Leitherer & Heckman 1995).”

“As the cluster ages, mass and energy input from supernova (SN) explosions will begin to dominate (cf. Leitherer & Heckman 1995).”