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All sourcesNASA NTRSDOE OSTI
NASA NTRS1999

Direct Measurement of the Supernova Rate in Starburst Galaxies

Supernovae play a key role in the dynamics, structure, and chemical evolution of galaxies. The massive stars that end their lives as supernovae live for short times. Many are still associated with dusty star formation regions when they explode, making them difficult to observe at visible wavelengths. In active star forming regions (galactic nuclei and starburst regions), dust extintion is especially severe. Thus, determining the supernova rate in the active star forming regions of galaxies, where the supernova rate can be one or two orders of magnitude higher than the average, has proven to be difficult. From observations of SN1987A, we know that the [NiII] 6.63 micron emission line was the strongest line in the infrared spectrum for a period of a year and a half after the explosion. Since dust extintion is much less at 6.63 pm than at visible wavelengths (A(sub 6.63)/A(sub V) = 0.025), the NiII line can be used as a sensitive probe for the detection of recent supernovae. We have observed a sample of starburst galaxies at 6.63 micron using ISOCAM to search for the NiII emission line characteristic of recent supernovae. We did not detect any NiII line emission brighter than a 5sigma limit of 5 mJy. We can set upper limits to the supernova rate in our sample, scaled to the rate in M82, of less than 0.3 per year at the 90% confidence level using Bayesian methods. Assuming that a supernova would have a NiII with the same luminosity as observed in SN1987A, we find less than 0.09 and 0.15 per year at the 50% and 67% confidence levels. These rates are somewhat less if a more normal type II supernovae has a NiII line luminosity greater than the line in SN1987A.

Bregman, Jesse D.↗
NASA NTRS2000

Direct Measurement of the Supernova Rate in Starburst Galaxies

Supernovae play a key role in the dynamics, structure, and chemical evolution of galaxies. The massive stars that end their lives as supernovae live for short enough times that many are still associated with dusty star formation regions when they explode, making them difficult to observe at visible wavelengths. In active star forming regions (galactic nuclei and starburst regions), dust extinction is especially severe. Thus, determining the supernova rate in active star forming regions of galaxies, where the supernova rate can be one or two orders of magnitude higher than the average, has proven to be difficult. From observations of SN1987A, we know that the [NiII] 6.63 micrometer emission line was the strongest line in the infrared spectrum for a period of a year and half after th explosion. Since dust extinction is much less at 6.63 micrometers than at visible wavelengths (A(sub 6.63)/A(sub V) = 0.025), the [NiII] line can be used as a sensitive probe for the detection of recent supernovae. We have observed a sample of starburst galaxies at 6.63 micrometers using ISOCAM to search for the [NiII] emission line characteristic of recent supernovae. We did not detect any [NiII] line emission brighter than a 5-sigma limit of 5 mJy. We can set upper limits to the supernova rate in our sample, scaled ot the rate in M82, of less than 0.3 per year at the 90% confidence level using Bayesian methods. Assuming that a supernova would have a [NiII] line with the same luminosity as observed in SN1987A, we find less than 0.09 and 0.15 per year at the 50% and 67% confidence levels. These rates are somewhat less if a more normal type II supernovae has a [NiII] line luminosity greater than the line in SN1987A.

Bregman, J. D.↗
DOE OSTI2012

MIXING OF CLUMPY SUPERNOVA EJECTA INTO MOLECULAR CLOUDS

Several lines of evidence, from isotopic analyses of meteorites to studies of the Sun's elemental and isotopic composition, indicate that the solar system was contaminated early in its evolution by ejecta from a nearby supernova. Previous models have invoked supernova material being injected into an extant protoplanetary disk, or isotropically expanding ejecta sweeping over a distant (>10 pc) cloud core, simultaneously enriching it and triggering its collapse. Here, we consider a new astrophysical setting: the injection of clumpy supernova ejecta, as observed in the Cassiopeia A supernova remnant, into the molecular gas at the periphery of an H II region created by the supernova's progenitor star. To track these interactions, we have conducted a suite of high-resolution (1500{sup 3} effective) three-dimensional numerical hydrodynamic simulations that follow the evolution of individual clumps as they move into molecular gas. Even at these high resolutions, our simulations do not quite achieve numerical convergence, due to the challenge of properly resolving the small-scale mixing of ejecta and molecular gas, although they do allow some robust conclusions to be drawn. Isotropically exploding ejecta do not penetrate into the molecular cloud or mix with it, but, if cooling is properly accounted for, clumpy ejecta penetrate to distances {approx}10{sup 18} cm and mix effectively with large regions of star-forming molecular gas. In fact, the {approx}2 M{sub Sun} of high-metallicity ejecta from a single core-collapse supernova is likely to mix with {approx}2 Multiplication-Sign 10{sup 4} M{sub Sun} of molecular gas material as it is collapsing. Thus, all stars forming late ( Almost-Equal-To 5 Myr) in the evolution of an H II region may be contaminated by supernova ejecta at the level {approx}10{sup -4}. This level of contamination is consistent with the abundances of short-lived radionuclides and possibly some stable isotopic shifts in the early solar system and is potentially consistent with the observed variability in stellar elemental abundances. Supernova contamination of forming planetary systems may be a common, universal process.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Fluid dynamic mathematical aspects of supernova remnants

Supernovae—explosions of stars—are a central problem in astrophysics since they contain information on the entire process of stellar evolution and nucleosynthesis. Rayleigh–Taylor (RT) and Richtmyer–Meshkov (RM) instabilities, developing during the supernova blast, lead to intense interfacial RT/RM mixing of the star's materials and couple astrophysical to atomic scales. This work analyzes some fluid dynamic mathematical aspects of the titanic task of supernova's blast. We handle mathematical challenges of RT/RM dynamics in supernova relevant conditions by directly linking the conservation laws governing RT/RM dynamics to symmetry-based momentum model, by exactly deriving the model parameters in the scale-dependent and scale-invariant regimes, and by exploring the special self-similar class for RT/RM interfacial mixing with variable accelerations. Here we reveal that RT/RM dynamics is strongly influenced by deterministic (the initial and the flow) conditions in the scale-dependent linear and nonlinear regimes and in the self-similar mixing regime. The theory outcomes are consistent with the observations of supernova remnants, explain the results of the scaled laboratory experiments in high energy density plasmas, and yield the design of future experiments for the accurate quantification of RT/RM dynamics in supernova relevant conditions. We find that from fluid dynamic mathematical perspectives, supernovae can be regarded as an astrophysical initial value problem. Along with the guidance of what explodes at microscopic scales, supernova remnants encapsulate information on the explosion hydrodynamics and the associated deterministic conditions at macroscopic scales. We urge such effects be considered in interpretations of the observational data.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

zBEAMS: a unified solution for supernova cosmology with redshift uncertainties

Supernova cosmology without spectra will be an important component of future surveys such as LSST. This lack of supernova spectra results in uncertainty in the redshifts which, if ignored, leads to significantly biased estimates of cosmological parameters. Here we present a hierarchical Bayesian formalism— zBEAMS—that addresses this problem by marginalising over the unknown or uncertain supernova redshifts to produce unbiased cosmological estimates that are competitive with supernova data with spectroscopically confirmed redshifts. zBEAMS provides a unified treatment of both photometric redshifts and host galaxy misidentification (occurring due to chance galaxy alignments or faint hosts), effectively correcting the inevitable contamination in the Hubble diagram. Like its predecessor BEAMS, our formalism also takes care of non-Ia supernova contamination by marginalising over the unknown supernova type. We illustrate this technique with simulations of supernovae with photometric redshifts and host galaxy misidentification. A novel feature of the photometric redshift case is the important role played by the redshift distribution of the supernovae.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

COMMON ENVELOPE EVOLUTION LEADING TO SUPERNOVAE WITH DENSE INTERACTION

A variety of supernova events, including Type IIn supernovae and ultraluminous supernovae, appear to have lost up to solar masses of their envelopes in tens to hundreds of years leading up to the explosion. In order to explain the close timing of the mass loss and supernova events, we explore the possibility that the mass loss is driven by common envelope evolution of a compact object (neutron star or black hole) in the envelope of a massive star and the supernova is triggered by the inspiral of the compact object to the central core of the companion star. The expected rate of such events is smaller than the observed rate of Type IIn supernovae but the rates may agree within the uncertainties. The mass loss velocity is related to the escape velocity from the common envelope system and is comparable to the observed velocity of hundreds of kilometers per second in Type IIn events. The mass loss is expected to be denser near the equatorial plane of the binary system and there is good evidence that the circumstellar media in Type IIn supernovae are asymmetric. Some of these supernova types show evidence for energies in excess of the canonical 10{sup 51} erg, which might be the result of explosions from rapid accretion onto a compact object through a disk.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

CONSTRAINING PHYSICAL PROPERTIES OF TYPE IIn SUPERNOVAE THROUGH RISE TIMES AND PEAK LUMINOSITIES

We investigate the diversity in the wind density, supernova ejecta energy, and ejecta mass in Type IIn supernovae based on their rise times and peak luminosities. We show that the wind density and supernova ejecta properties can be estimated independently if both the rise time and peak luminosity are observed. The peak luminosity is mostly determined by the supernova properties and the rise time can be used to estimate the wind density. We find that the ejecta energies of Type IIn supernovae need to vary by factors of 0.2-5 from the average if their ejecta masses are similar. The diversity in the observed rise times indicates that their wind densities vary by factors of 0.2-2 from the average. We show that Type IIn superluminous supernovae should have not only large wind density but also large ejecta energy and/or small ejecta mass to explain their large luminosities and the rise times at the same time. We also note that shock breakout does not necessarily occur in the wind even if it is optically thick, except for the case of superluminous supernovae, and we analyze the observational data both with and without assuming that the shock breakout occurs in the dense wind of Type IIn supernovae.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Development of a Data Overflow Protection System for Super-Kamiokande to Maximize Data from Nearby Supernovae

Neutrinos from very nearby supernovae, such as Betelgeuse, are expected to generate more than ten million events over 10 s in Super-Kamokande (SK). At such large event rates, the buffers of the SK analog-to-digital conversion board (QBEE) will overflow, causing random loss of data that are critical for understanding the dynamics of the supernova explosion mechanism. In order to solve this problem, two new data-acquisition (DAQ) modules were developed to aid in the observation of very nearby supernovae. The first of these, the SN module, is designed to save only the number of hit photomultiplier tubes during a supernova burst and the second, the Veto module, prescales the high-rate neutrino events to prevent the QBEE from overflowing based on information from the SN module. In the event of a very nearby supernova, these modules allow SK to reconstruct the time evolution of the neutrino event rate from beginning to end using both QBEE and SN module data. This paper presents the development and testing of these modules together with an analysis of supernova-like data generated with a flashing laser diode. We demonstrate that the Veto module successfully prevents DAQ overflows for Betelgeuse-like supernovae as well as the long-term stability of the new modules. During normal running the Veto module is found to issue DAQ vetos a few times per month resulting in a total dead-time less than 1 ms, and does not influence ordinary operations. Additionally, using simulation data we find that supernovae closer than 800 pc will trigger the Veto module, resulting in a prescaling of the observed neutrino data.

F20 Instrumentation and technique↗
DOE OSTI2022

Rocks, water, and noble liquids: Unfolding the flavor contents of supernova neutrinos

Measuring core-collapse supernova neutrinos, both from individual supernovae within the Milky Way and from past core collapses throughout the Universe (the diffuse supernova neutrino background, or DSNB), is one of the main goals of current and next generation neutrino experiments. Detecting the heavy-lepton flavor (muon and tau types, collectively v x ) component of the flux is particularly challenging due to small statistics and large backgrounds. Further, while the next galactic neutrino burst will be observed in a plethora of neutrino channels, allowing us to measure a small number of v x events, only upper limits are anticipated for the diffuse v x flux even after decades of data taking with conventional detectors. However, paleo detectors could measure the time-integrated flux of neutrinos from galactic core-collapse supernovae via flavor-blind neutral current interactions. In this work, we show how combining a measurement of the average galactic core-collapse supernova flux with paleo detectors and measurements of the DSNB electron-type neutrino fluxes with the next-generation water Cherenkov detector Hyper-Kamiokande and the liquid noble gas detector DUNE will allow to determine the mean supernova vx flux parameters with precision of order ten percent. Realizing this potential requires both the cosmic supernova rate out to z~1 and the integrated Galactic supernova rate over the last ~1 Gyr to be established at the ~10% level.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1999

The Progenitor of the New COMPTEL/ROSAT Supernova Remnant in Vela

We show that (1) the newly discovered supernova remnant (SNR) GROJ0852-4642/RXJ0852.0-4622 was created by a core-collapse supernova of a massive star and (2) the same supernova event that produced the Ti-44 detected by COMPTEL from this source is probably also responsible for a large fraction of the observed Al-26 emission in the Vela region detected by the same instrument. The first conclusion is based on the fact that the remnant is currently expanding too slowly given its young age for it to be caused by a Type la supernova. If the current SNR shell expansion speed is greater than 3000 km/s, a 15 solar mass. Type II supernova with a moderate kinetic energy exploding at about 150 pc away is favored. If the SNR expansion speed is lower than 2000 km/s, as derived naively from X-ray data, a much more energetic supernova is required to have occurred at approximately 250 pc away in a dense environment at the edge of the Gum Nebula. This progenitor has a preferred ejecta mass of less than or equal to 10(Solar Mass), and therefore it is probably a Type Ib or Type Ic supernova. However, the required high ambient density of n(sub H) greater than or equal to 100 cu cm in this scenario is difficult to reconcile with the regional CO data. A combination of our estimates of the age/energetics of the new SNR and the almost perfect positional coincidence of the new SNR with the centroid of the COMPTEL Al-26 emission feature of the Vela region strongly favors a causal connection. If confirmed, this will be the first case in which both Ti-44 and Al-26 are detected from the same young SNR, and together they can be used to select preferred theoretical core-collapse supernova models.

Chen, Wan↗
DOE OSTI2018

Neutrino Oscillations in Supernovae

A (core-collapse) supernova is the final death call of a massive star during which a gigantic amount of a special kind of elementary particles known as neutrinos are released for a brief period of time. An earlier work by the PI and his collaborators has shown that the dense neutrino gas deep inside the supernova can experience "flavor transformation" or "oscillations" in a collective fashion, a macroscopic quantum phenomenon spanning over distances of 100-1000 kilometers. During this process neutrinos of different energies and propagation directions change their identities simultaneously. This phenomenon may be a key to understanding the mechanism of supernova explosion and the origin of many of the chemical elements found on the earth which were produced in the supernovae exploded in the past. The previous understanding of neutrino oscillations in supernovae was based on a stationary 3-dimensional model with 1 spatial dimension and 2 momentum dimensions. In this "neutrino bulb model" neutrinos are emitted from a spherically symmetric surface and they are decoupled from the motion of matter and the production of chemical elements. In order to accurately model the neutrino oscillations in supernovae and determine its physical consequences, sophisticated 7-dimensional (1 temporal dimension + 3 spatial dimensions + 3 momentum dimensions) modelling of neutrino transport must be performed self-consistently together with the hydrodynamic simulation of the flow of energy and matter inside the supernova and with the calculation of the production and destruction of chemical elements through a large nucleosynthesis network. Although it will be long journey to achieve the lofty goal, our project has made important progress in three different fronts towards this goal. In the first front we explored new computing hardware on which the next generation simulation codes may be run. We ported the neutrino bulb code to the platform of Graphics Processing Unit (GPU) and then later developed a new bulb code that can be run on supercomputers equipped with the Intel Xeon CPUs and/or the Xeon Phi coprocessors. In the second front we developed new algorithms that can be used towards computing neutrino oscillations in multi-dimensional models. We have developed a moment expansion method which is approximately 10 times more efficient than the old algorithm. We have also developed numerical codes to solve neutrino oscillations in toy models with two spatial dimensions. In the last front we used analytic methods to study neutrino oscillations in more sophisticated models, e.g. of multiple spatial dimensions and/or with time dependence. By analyzing the neutrino oscillations in toy models with two spacial dimensions we found that the approximate spacial translation symmetry, which is similar to the spherical symmetry in the neutrino bulb model, can be broken spontaneously as neutrino oscillations begin. By analyzing a time-dependent neutrino bulb model we found that certain modes of neutrino oscillations that are suppressed in the stationary model can become active in the time-dependent model. We have also developed theories which give insights to how ordinary matter may affect neutrino oscillations in supernovae and other astrophysical environments.

Duan, Huaiyu↗
DOE OSTI2014

Multi-epoch very long baseline interferometric observations of the nuclear starburst region of NGC 253: Improved modeling of the supernova and star formation rates

The results of multi-epoch observations of the southern starburst galaxy, NGC 253, with the Australian Long Baseline Array at 2.3 GHz are presented. As with previous radio interferometric observations of this galaxy, no new sources were discovered. By combining the results of this survey with Very Large Array observations at higher frequencies from the literature, spectra were derived and a free-free absorption model was fitted of 20 known sources in NGC 253. The results were found to be consistent with previous studies. The supernova remnant, 5.48-43.3, was imaged with the highest sensitivity and resolution to date, revealing a two-lobed morphology. Comparisons with previous observations of similar resolution give an upper limit of 10{sup 4} km s{sup –1} for the expansion speed of this remnant. We derive a supernova rate of <0.2 yr{sup –1} for the inner 300 pc using a model that improves on previous methods by incorporating an improved radio supernova peak luminosity distribution and by making use of multi-wavelength radio data spanning 21 yr. A star formation rate of SFR(M ≥ 5 M {sub ☉}) < 4.9 M {sub ☉} yr{sup –1} was also estimated using the standard relation between supernova and star formation rates. Our improved estimates of supernova and star formation rates are consistent with studies at other wavelengths. The results of our study point to the possible existence of a small population of undetected supernova remnants, suggesting a low rate of radio supernova production in NGC 253.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

A GLOBAL MODEL OF THE LIGHT CURVES AND EXPANSION VELOCITIES OF TYPE II-PLATEAU SUPERNOVAE

We present a new self-consistent and versatile method that derives photospheric radius and temperature variations of Type II-Plateau supernovae based on their expansion velocities and photometric measurements. We apply the method to a sample of 26 well-observed, nearby supernovae with published light curves and velocities. We simultaneously fit ∼230 velocity and ∼6800 mag measurements distributed over 21 photometric passbands spanning wavelengths from 0.19 to 2.2 μm. The light-curve differences among the Type II-Plateau supernovae are well modeled by assuming different rates of photospheric radius expansion, which we explain as different density profiles of the ejecta, and we argue that steeper density profiles result in flatter plateaus, if everything else remains unchanged. The steep luminosity decline of Type II-Linear supernovae is due to fast evolution of the photospheric temperature, which we verify with a successful fit of SN 1980K. Eliminating the need for theoretical supernova atmosphere models, we obtain self-consistent relative distances, reddenings, and nickel masses fully accounting for all internal model uncertainties and covariances. We use our global fit to estimate the time evolution of any missing band tailored specifically for each supernova, and we construct spectral energy distributions and bolometric light curves. We produce bolometric corrections for all filter combinations in our sample. We compare our model to the theoretical dilution factors and find good agreement for the B and V filters. Our results differ from the theory when the I, J, H, or K bands are included. We investigate the reddening law toward our supernovae and find reasonable agreement with standard R{sub V}∼3.1 reddening law in UBVRI bands. Results for other bands are inconclusive. We make our fitting code publicly available.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

ON THE INJECTION OF SHORT-LIVED RADIONUCLIDES FROM A SUPERNOVA INTO THE SOLAR NEBULA: CONSTRAINTS FROM THE OXYGEN ISOTOPES

Injection of short-lived radionuclides from a nearby core-collapse Type II supernova into the already-formed solar protoplanetary disk was proposed to account for the former presence of {sup 26}Al, {sup 41}Ca, and {sup 60}Fe in the early solar system inferred from isotopic analysis of meteoritic samples. One potential corollary of this ''late-injection'' scenario is that the disk's initial (pre-injection) oxygen isotopic composition could be significantly altered, as supernova material that carried the short-lived radionuclides would also deliver oxygen components synthesized in that given star. Therefore, the change in the oxygen isotopic composition of the disk caused by injection could in principle be used to constrain the supernova injection models. Previous studies showed that although supernova oxygen could result in a wide range of shifts in {sup 17}O/{sup 16}O and {sup 18}O/{sup 16}O of the disk, a couple of cases existed where the calculated oxygen changes in the disk would be compatible with the meteoritic and solar wind data. Recently, the initial abundances of {sup 41}Ca and {sup 60}Fe in the solar system were revised to lower values, and the feasibility of supernova injection as a source for the three radionuclides was called into question. In this study, supernova parameters needed for matching {sup 26}Al, {sup 41}Ca, and {sup 60}Fe to their early solar system abundances were reinvestigated and then were used to infer the pre-injection O-isotope composition of the disk. The result suggested that a supernova undergoing mixing fallback might be a viable source for the three radionuclides.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

The ASAS-SN bright supernova catalogue – I. 2013–2014

We present basic statistics for all supernovae discovered by the All-Sky Automated Survey for SuperNovae (ASAS-SN) during its first year-and-a-half of operations, spanning 2013 and 2014. We also present the same information for all other bright (m V ≤ 17), spectroscopically confirmed supernovae discovered from 2014 May 1 through the end of 2014, providing a comparison to the ASAS-SN sample starting from the point where ASAS-SN became operational in both hemispheres. In addition, we present collected redshifts and near-UV through IR magnitudes, where available, for all host galaxies of the bright supernovae in both samples. This work represents a comprehensive catalogue of bright supernovae and their hosts from multiple professional and amateur sources, allowing for population studies that were not previously possible because the all-sky emphasis of ASAS-SN redresses many previously existing biases. In particular, ASAS-SN systematically finds bright supernovae closer to the centres of host galaxies than either other professional surveys or amateurs, a remarkable result given ASAS-SN's poorer angular resolution. In conclusion, this is the first of a series of yearly papers on bright supernovae and their hosts that will be released by the ASAS-SN team.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

The ASAS-SN Bright Supernova Catalog – II. 2015

Here, this paper presents information for all supernovae discovered by the All-Sky Automated Survey for SuperNovae (ASAS-SN) during 2015, its second full year of operations. The same information is presented for bright (mV ≤ 17), spectroscopically confirmed supernovae discovered by other sources in 2015. As with the first ASAS-SN bright supernova catalogue, we also present redshifts and near-ultraviolet through infrared magnitudes for all supernova host galaxies in both samples. Combined with our previous catalogue, this work comprises a complete catalogue of 455 supernovae from multiple professional and amateur sources, allowing for population studies that were previously impossible. This is the second of a series of yearly papers on bright supernovae and their hosts from the ASAS-SN team.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

The ASAS-SN bright supernova catalogue – III. 2016

In this catalogue we summarize information for all supernovae discovered by the All-Sky Automated Survey for SuperNovae (ASAS-SN) and all other bright (m peak ≤ 17), spectroscopically confirmed supernovae discovered in 2016. We then gather the near-infrared through ultraviolet magnitudes of all host galaxies and the offsets of the supernovae from the centres of their hosts from public data bases. We illustrate the results using a sample that now totals 668 supernovae discovered since 2014 May 1, including the supernovae from our previous catalogues, with type distributions closely matching those of the ideal magnitude limited sample from Li et al. This is then the third of a series of yearly papers on bright supernovae and their hosts from the ASAS-SN team.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

The global star formation law by supernova feedback

ABSTRACT We address a simple model where the Kennicutt–Schmidt (KS) relation between the macroscopic densities of star formation rate (SFR, ρsfr) and gas (n) in galactic discs emerges from self-regulation of the SFR via supernova feedback. It arises from the physics of supernova bubbles, insensitive to the microscopic SFR recipe and not explicitly dependent on gravity. The key is that the filling factor of SFR-suppressed supernova bubbles self-regulates to a constant, f ∼ 0.5. Expressing the bubble fading radius and time in terms of n, the filling factor is $f\propto S\, n^{-s}$ with s ≃ 1.5, where S is the supernova rate density. A constant f thus refers to ρsfr ∝ n1.5, with a density-independent SFR efficiency per free-fall time ∼0.01. The self-regulation to f ∼ 0.5 and the convergence to a KS relation independent of the local SFR recipe are demonstrated in cosmological and isolated-galaxy simulations using different codes and recipes. In parallel, the spherical analysis of bubble evolution is generalized to clustered supernovae, analytically and via simulations, yielding s ≃ 1.5 ± 0.5. An analysis of photoionized bubbles about pre-supernova stars yields a range of KS slopes but the KS relation is dominated by the supernova bubbles. Superbubble blowouts may lead to an alternative self-regulation by outflows and recycling. While the model is oversimplified, its simplicity and validity in the simulations may argue that it captures the origin of the KS relation.

79 ASTRONOMY AND ASTROPHYSICS↗