Progenitors Of Globular Clusters Research Articles

Star clusters forming in a low metallicity starburst – rapid self-enrichment by (very) massive stars

Abstract Stellar winds of massive (≳ 9 M⊙) and very massive (≳ 100 M⊙) stars may play an important role in the metal-enrichment during the formation of star clusters. With novel high-resolution hydrodynamical griffin-project simulations, we investigate the rapid recycling of stellar wind-material during the formation of massive star clusters up to Mcluster ∼ 2 × 105 M⊙ in a low-metallicity dwarf galaxy starburst. The simulation realises new stars from a stellar initial mass function (IMF) between 0.08 M⊙ and ∼400 M⊙ and follows stellar winds, radiation and supernova-feedback of single massive stars with evolution tracks. Star clusters form on timescales less than ∼5 Myr, and their supernova-material is very inefficiently recycled. Stellar wind-material, however, is trapped in massive clusters resulting in the formation of stars self-enriched in Na, Al, and N within only a few Myr. Wind-enriched (second population) stars can be centrally concentrated in the most massive clusters (≳ 104 M⊙) and the locked wind-material increases approximately as $M_\mathrm{cluster}^{2}$. These trends resemble the characteristics of observed second population stars in globular clusters. We fit scaling relations to the log-normal distributed wind-mass fractions and extrapolate to possible globular cluster progenitors of Mcluster = 107 M⊙ to investigate whether a dominant second population could form. This can only happen if the IMF is well sampled, single massive stars produce at least a factor of a few more enriched winds e.g. through a top-heavy IMF, and a significant fraction of the first population (unenriched) stars is lost during cluster evolution.

Star cluster formation and feedback in different environments of a Milky Way-like galaxy

ABSTRACT It remains unclear how galactic environment affects star formation and stellar cluster properties. This is difficult to address in Milky Way-mass galaxy simulations because of limited resolution and less accurate feedback compared to cloud-scale models. We carry out zoom-in simulations to re-simulate 100–$300 \,\rm {pc}$ regions of a Milky Way-like galaxy using smoothed particle hydrodynamics, including finer resolution ($0.4 \,\rm {M_{\odot }{}}$ per particle), cluster-sink particles, ray-traced photoionization from O stars, H2/CO chemistry, and interstellar medium heating/cooling. We select ∼$10^{6} \,\rm {M_{\odot }{}}$ cloud complexes from a galactic bar, inner spiral arm, outer arm, and inter-arm region (in order of galactocentric radius), retaining the original galactic potentials. The surface densities of star formation rate and neutral gas follow $\Sigma _\mathrm{SFR}\propto \Sigma _\mathrm{gas}^{1.3}$, with the bar lying higher up the relation than the other regions. However, the inter-arm region forms stars two to three times less efficiently than the arm models at the same Σgas. The bar produces the most massive cluster, the inner arm the second, and the inter-arm the third. Almost all clusters in the bar and inner arm are small (radii <5 pc), while 30–50 per cent of clusters in the outer arm and inter-arm have larger radii more like associations. Bar and inner arm clusters rotate at least twice as fast, on average, than clusters in the outer arm and inter-arm regions. The degree of spatial clustering also decreases from bar to inter-arm. Our results indicate that young massive clusters, potentially progenitors of globular clusters, may preferentially form near the bar/inner arm compared to outer arm/inter-arm regions.

Star cluster formation and survival in the first galaxies

ABSTRACT Using radiation-hydrodynamic cosmological simulations, we present a detailed (0.1 pc resolution), physically motivated portrait of a typical-mass dwarf galaxy before the epoch of reionization, resolving the formation, and evolution of star clusters into individual 10 M⊙ star particles. In the rest-frame ultraviolet, the galaxy has an irregular morphology with no bulge or disc, dominated by light emitted from numerous, compact, and gravitationally-bound star clusters. This is especially interesting in light of recent James Webb Space Telescope observations that − aided by the magnifying power of gravitational lenses – have imaged, at parsec-scale resolution, individual young star clusters forming in similar galaxies at z> 6. Because of their low metallicities and high temperatures, star-forming gas clouds in this galaxy have densities ∼100 times higher than typical giant molecular clouds; hence, their expected star formation efficiencies (SFEs) are high enough (around 10 − 70 per cent) to produce a sizeable population of potential globular cluster progenitors, but typically smaller (a few 100 − 2 ×104M⊙, half-mass radii of up to 3 pc) and of lower metallicities (10−3.5– 10−2.5 Z⊙). The initial mass function of the star-forming clouds is log-normal, whereas the bound star cluster mass function is a power-law with a slope that depends mainly on SFE but also on the temporal proximity to a major starburst. We find slopes between −0.5 and −2.5 depending on the assumed sub-grid SFE. Star formation is self-regulated on galactic scales; however, the multimodal metallicity distribution of the star clusters and the fraction of stars locked into surviving bound star clusters depends on SFE.

Uniform modelling of the stellar density of thirteen tidal streams within the Galactic halo

ABSTRACT We present the results of fitting a flexible stellar stream density model to a collection of thirteen streams around the Milky Way, using photometric data from DES, DECaLS, and Pan-STARRS. We construct density maps for each stream and characterize their tracks on the sky, width, and distance modulus curves along the length of each stream. We use these measurements to compute lengths and total luminosities of streams and identify substructures. Several streams show prominent substructures, such as stream broadening, gaps, large deviations of stream tracks, and sharp changes in stream densities. Examining the group of streams as a population, as expected we find that streams with globular cluster progenitors are typically narrower than those with dwarf galaxy progenitors, with streams around 100 pc wide showing overlap between the two populations. We also note the average luminosity of globular cluster streams is significantly lower than the typical luminosity of intact globular clusters. The likely explanation is that observed globular cluster streams preferentially come from lower luminosity and lower density clusters. The stream measurements done in a uniform manner presented here will be helpful for more detailed stream studies such as identifying candidate stream members for spectroscopic follow up and stellar stream dynamical modelling.

The Supersonic Project: SIGOs, A Proposed Progenitor to Globular Clusters, and Their Connections to Gravitational-wave Anisotropies

Abstract Supersonically induced gas objects (SIGOs), are structures with little to no dark-matter component predicted to exist in regions of the universe with large relative velocities between baryons and dark matter at the time of recombination. They have been suggested to be the progenitors of present-day globular clusters. Using simulations, SIGOs have been studied on small scales (around 2 Mpc) where these relative velocities are coherent. However, it is challenging to study SIGOs using simulations on large scales due to the varying relative velocities at scales larger than a few Mpc. Here, we study SIGO abundances semi-analytically: using perturbation theory, we predict the number density of SIGOs analytically, and compare these results to small-box numerical simulations. We use the agreement between the numerical and analytic calculations to extrapolate the large-scale variation of SIGO abundances over different stream velocities. As a result, we predict similar large-scale variations of objects with high gas densities before reionization that could possibly be observed by JWST. If indeed SIGOs are progenitors of globular clusters, then we expect a similar variation of globular cluster abundances over large scales. Significantly, we find that the expected number density of SIGOs is consistent with observed globular cluster number densities. As a proof-of-concept, and because globular clusters were proposed to be natural formation sites for gravitational wave sources from binary black-hole mergers, we show that SIGOs should imprint an anisotropy on the gravitational wave signal on the sky, consistent with their distribution.

Orbital Clustering Identifies the Origins of Galactic Stellar Streams

Abstract The origins of most stellar streams in the Milky Way are unknown. With improved proper motions provided by Gaia EDR3, we show that the orbits of 23 Galactic stellar streams are highly clustered in orbital phase space. Based on their energies and angular momenta, most streams in our sample can plausibly be associated with a specific (disrupted) dwarf galaxy host that brought them into the Milky Way. For eight streams we also identify likely globular cluster progenitors (four of these associations are reported here for the first time). Some of these stream progenitors are surprisingly far apart, displaced from their tidal debris by a few to tens of degrees. We identify stellar streams that appear spatially distinct, but whose similar orbits indicate they likely originate from the same progenitor. If confirmed as physical discontinuities, they will provide strong constraints on the mass loss from the progenitor. The nearly universal ex situ origin of existing stellar streams makes them valuable tracers of galaxy mergers and dynamical friction within the Galactic halo. Their phase-space clustering can be leveraged to construct a precise global map of dark matter in the Milky Way, while their internal structure may hold clues to the small-scale structure of dark matter in their original host galaxies.

The Supersonic Project: To Cool or Not to Cool Supersonically Induced Gas Objects (SIGOs)?

Abstract Supersonically induced gas objects (SIGOs) primarily form in the early universe, outside of dark matter halos due to the presence of a relative stream velocity between baryons and dark matter. These structures may be the progenitors of globular clusters. Since SIGOs are made out of pristine gas, we investigate the effect of atomic cooling on their properties. We run a suite of simulations by using the moving-mesh code arepo, with and without baryon dark matter relative velocity and with and without the effects of atomic cooling. We show that SIGO’s density, temperature, and prolateness are determined by gravitational interactions rather than cooling. The cold gas fraction in SIGOs is much higher than that of dark matter halos. Specifically, we show that SIGO’s characteristically low temperature and extremely high gas density forges a nurturing ground for the earliest star formation sites.

Constraints on the [C ii] luminosity of a proto-globular cluster at z ∼ 6 obtained with ALMA

ABSTRACT We report on ALMA observations of D1, a system at z ∼ 6.15 with stellar mass $M_{*} \sim 10^7 \, \mathrm{M}_{\odot }$ containing globular cluster (GC) precursors, strongly magnified by the galaxy cluster MACS J0416.1-2403. Since the discovery of GC progenitors at high redshift, ours is the first attempt to probe directly the physical properties of their neutral gas through infrared observations. A careful analysis of our data set, performed with a suitable procedure designed to identify faint narrow lines and which can test various possible values for the unknown linewidth value, allowed us to identify a 4σ tentative detection of [C ii] emission with intrinsic luminosity $L_{\rm [C\, \rm {\small II}]}=(2.9 \pm 1.4)~10^6 \, {\it L}_{\odot }$, one of the lowest values ever detected at high redshift. This study offers a first insight on previously uncharted regions of the $L_{\rm [C\, \rm {\small II}]}{-}{\rm SFR}$ relation. Despite large uncertainties affecting our measure of the star formation rate, if taken at face value our estimate lies more than ∼1 dex below the values observed in local and high redshift systems. Our weak detection indicates a deficiency of [C ii] emission, possibly ascribed to various explanations, such as a low-density gas and/or a strong radiation field caused by intense stellar feedback, and a low metal content. From the non-detection in the continuum, we derive constraints on the dust mass, with 3σ upper limit values as low as ∼ a few 104 M⊙, consistent with the values measured in local metal-poor galaxies.

The predicted properties of helium-enriched globular cluster progenitors at high redshift

ABSTRACT Globular cluster progenitors may have been detected by Hubble Space Telescope, and are predicted to be observable with James Webb Space Telescope (JWST) and ground-based extremely large telescopes with adaptive optics. This has the potential to elucidate the issue of globular cluster formation and the origins of significantly helium-enriched subpopulations, a problem in Galactic astronomy with no satisfactory theoretical solution. Given this context, we use model stellar tracks and isochrones to investigate the predicted observational properties of helium-enriched stellar populations in globular cluster progenitors. We find that, relative to helium-normal populations, helium-enriched (ΔY = +0.12) stellar populations similar to those inferred in the most massive globular clusters, are expected, modulo some rapid fluctuations in the first ∼30 Myr, to be brighter and redder in the rest frame. At fixed age, stellar mass, and metallicity, a helium-enriched population is predicted to converge to being ∼0.40 mag brighter at $\lambda \approx 2.0\, {\mu \rm m}$, and to be 0.30-mag redder in the JWST–NIRCam colour (F070W − F200W), and to actually be fainter for $\lambda \lesssim 0.50 \, {\mu \rm m}$. Separately, we find that the time-integrated shift in ionizing radiation is a negligible $\sim \!5{{\ \rm per\ cent}}$, though we show that the Lyman-α escape fraction could end up higher for helium-enriched stars.

Simulating star clusters across cosmic time – II. Escape fraction of ionizing photons from molecular clouds

ABSTRACT We calculate the hydrogen- and helium-ionizing radiation escaping star-forming molecular clouds, as a function of the star cluster mass and compactness, using a set of high-resolution radiation-magnetohydrodynamic simulations of star formation in self-gravitating, turbulent molecular clouds. In these simulations, presented in He et al., the formation of individual massive stars is well resolved, and their UV radiation feedback and lifetime on the main sequence are modelled self-consistently. We find that the escape fraction of ionizing radiation from molecular clouds, $\langle f_{\rm esc}^{\scriptscriptstyle \rm MC}\rangle$ , decreases with increasing mass of the star cluster and with decreasing compactness. Molecular clouds with densities typically found in the local Universe have negligible $\langle f_{\rm esc}^{\scriptscriptstyle \rm MC}\rangle$ , ranging between $0.5{{\ \rm per\ cent}}$ and $5{{\ \rm per\ cent}}$. 10 times denser molecular clouds have $\langle f_{\rm esc}^{\scriptscriptstyle \rm MC}\rangle$ $\approx 10{{\ \rm per\ cent}}{-}20{{\ \rm per\ cent}}$, while 100× denser clouds, which produce globular cluster progenitors, have $\langle f_{\rm esc}^{\scriptscriptstyle \rm MC}\rangle$ $\approx 20{{\ \rm per\ cent}}{-}60{{\ \rm per\ cent}}$. We find that $\langle f_{\rm esc}^{\scriptscriptstyle \rm MC}\rangle$ increases with decreasing gas metallicity, even when ignoring dust extinction, due to stronger radiation feedback. However, the total number of escaping ionizing photons decreases with decreasing metallicity because the star formation efficiency is reduced. We conclude that the sources of reionization at z > 6 must have been very compact star clusters forming in molecular clouds about 100× denser than in today’s Universe, which lead to a significant production of old globular clusters progenitors.

Simulating star clusters across cosmic time – I. Initial mass function, star formation rates, and efficiencies

ABSTRACT We present radiation-magneto-hydrodynamic simulations of star formation in self-gravitating, turbulent molecular clouds, modelling the formation of individual massive stars, including their UV radiation feedback. The set of simulations have cloud masses between mgas = 103 M⊙ and 3 × 105 M⊙ and gas densities typical of clouds in the local Universe ($\overline{n}_{\rm gas} \sim 1.8\times 10^2$ cm−3) and 10× and 100× denser, expected to exist in high-redshift galaxies. The main results are as follows. (i) The observed Salpeter power-law slope and normalization of the stellar initial mass function at the high-mass end can be reproduced if we assume that each star-forming gas clump (sink particle) fragments into stars producing on average a maximum stellar mass about $40{{\ \rm per\ cent}}$ of the mass of the sink particle, while the remaining $60{{\ \rm per\ cent}}$ is distributed into smaller mass stars. Assuming that the sinks fragment according to a power-law mass function flatter than Salpeter, with log-slope 0.8, satisfy this empirical prescription. (ii) The star formation law that best describes our set of simulation is ${\rm d}\rho _*/{\rm d}t \propto \rho _{\rm gas}^{1.5}$ if $\overline{n}_{\rm gas}\lt n_{\rm cri}\approx 10^3$ cm−3, and ${\rm d}\rho _*/{\rm d}t \propto \rho _{\rm gas}^{2.5}$ otherwise. The duration of the star formation episode is roughly six cloud’s sound crossing times (with cs = 10 km s−1). (iii) The total star formation efficiency in the cloud is $f_*=2{{\ \rm per\ cent}} (m_{\rm gas}/10^4~\mathrm{M}_\odot)^{0.4}(1+\overline{n}_{\rm gas}/n_{\rm cri})^{0.91}$, for gas at solar metallicity, while for metallicity Z < 0.1 Z⊙, based on our limited sample, f* is reduced by a factor of ∼5. (iv) The most compact and massive clouds appear to form globular cluster progenitors, in the sense that star clusters remain gravitationally bound after the gas has been expelled.

The impact of a massive star cluster on its surrounding matter in the Antennae overlap region

Super star clusters (SSCs), likely the progenitors of globular clusters, are one of the most extreme forms of star formation. Understanding how SSCs form is an observational challenge. Theoretical studies establish that, to form such clusters, the dynamical timescale of their parent clouds has to be shorter than the timescale of the disruption of their parent clouds by stellar feedback. However, due to insufficient observational support, it is still unclear how feedback from SSCs acts on their surrounding matter. Studying feedback in SSCs is essential to understand how such clusters form. Based on ALMA and VLT observations, we study this process in a SSC in the overlap region of the Antennae galaxies. We analyze a unique massive (~10^7 Msun) and young (1-3.5 Myr) SSC, still associated with compact molecular and ionized gas emission. The cluster has two CO velocity components, a low velocity one spatially associated with the cluster and a high velocity one distributed in a bubble-like shape around the cluster. Our results on the low velocity component suggest that this gas did not participate in the formation of the SSC. We propose that most of the parent cloud has already been blown away, accelerated at the early stages of the SSC evolution by radiation pressure, in a timescale ~1 Myr. The high velocity component may trace outflowing molecular gas from the parent cloud. Supporting evidence is found in shock heated H2 gas. The low velocity component may be gas that was near the SSC when it formed but not part of its parent cloud or clumps that migrated from the SGMC environment. This gas would be dispersed by stellar winds and supernova explosions. Within ~100 pc from the cluster, we estimate SFE>17%, smaller than the theoretical limit of 30% needed to form a bound cluster. Further higher spatial resolution observations are needed to test and quantify our proposed scenario.

Gas-rich and gas-poor structures through the stream velocity effect

Using adiabatic high-resolution numerical simulations we quantify the effect of the streaming motion of baryons with respect to dark matter at the time of recombination on structure formation and evolution. Formally a second order effect, the baryonic stream velocity has proven to have significant impact on dark matter halo abundance, as well as on the gas content and morphology of small galaxy clusters. In this work, we study the impact of stream velocity on the formation and gas content of haloes with masses up to $10^9 M_{\odot}$, an order of magnitude larger than previous studies. We find that the non-zero stream velocity has a sizable impact on the number density of haloes with masses $\lesssim$ few $\times 10^7 M_{\odot}$ up to $z=10$, the final redshift of our simulations. Furthermore, the gas stream velocity induces a suppression of the gas fraction in haloes, which at z=10 is $\sim 10 \%$ for objects with $M\sim10^7M_{\odot}$, as well as a flattening of the gas density profiles in the inner regions of haloes. We further identify and study the formation, in the context of a non-zero stream velocity, of moderately long lived gas dominated structures at intermediate redshifts $10 < z < 20$, which Naoz and Narayan have recently proposed as potential progenitors of globular clusters.

FLUORINE ABUNDANCES OF GALACTIC LOW-METALLICITY GIANTS

With abundances and 2{\sigma} upper limits of fluorine (F) in seven metal-poor field giants, nucleosynthesis of stellar F at low metallicity is discussed. The measurements are derived from the HF(1-0) R9 line at 23358{\AA} using nearinfrared K-band high-resolution spectra obtained with CRIRES at the Very Large Telescope. The sample reaches lower metallicities than previous studies on F of field giants, ranging from [Fe/H] = -1.56 down to -2.13. Effects of three-dimensional model atmospheres on the derived F and O abundances are quantitatively estimated and shown to be insignificant for the program stars. The observed F yield in the form of [F/O] is compared with two sets of Galactic chemical evolution models, which quantitatively demonstrate the contribution of Type II supernova (SN II) {\nu}-process and asymptotic giant branch/Wolf-Rayet stars. It is found that at this low-metallicity region, models cannot well predict the observed distribution of [F/O], while the observations are better fit by models considering an SN II {\nu}-process with a neutrino energy of E_{\nu} = 3 x 10^53 erg. Our sample contains HD 110281, a retrograde orbiting low-{\alpha} halo star, showing a similar F evolution as globular clusters. This supports the theory that such halo stars are possibly accreted from dwarf galaxy progenitors of globular clusters in the halo.

THE VELA CLOUD: A GIANT H I ANOMALY IN THE NGC 3256 GROUP

We present Australia Telescope Compact Array (ATCA) observations of a galaxy-sized intergalactic HI cloud (the Vela Cloud) in the NGC 3256 galaxy group. The group contains the prominent merging galaxy NGC 3256, which is surrounded by a number of HI fragments, the tidally disturbed galaxy NGC 3263, and several other peculiar galaxies. The Vela Cloud, with an HI mass of 3-5 * 10**9 solar masses, resides southeast of NGC 3256 and west of NGC 3263, within an area of 9' x 16' (100 kpc x 175 kpc for an adopted distance of 38 Mpc). In our ATCA data the Vela Cloud appears as 3 diffuse components and contains 4 density enhancements. The Vela Cloud's properties, together with its group environment, suggest that it has a tidal origin. Each density enhancement contains ~10**8 solar masses of HI gas which is sufficient material for the formation of globular cluster progenitors. However, if we represent the enhancements as Bonnor-Ebert spheres, then the pressure of the surrounding HI would need to increase by at least a factor of 6 in order to cause the collapse of an enhancement. Thus we do not expect them to form massive bound stellar systems like super star clusters or tidal dwarf galaxies. Since the HI density enhancements have some properties in common with High Velocity Clouds, we explore whether they may evolve to be identified with these starless clouds instead.

High-resolution simulations of galaxy mergers: resolving globular cluster formation

Abstract Massive star clusters observed in galaxy mergers are often suggested to be progenitors of globular clusters. To study this hypothesis, we performed the highest resolution simulation of a gas-rich galaxy merger so far. The formation of massive star clusters of 105 to 107 M⊙, triggered by the galaxy interaction, is directly resolved in this model. We show that these clusters are tightly bound structures with little net rotation, due to evolve into compact long-lived stellar systems. Massive clusters formed in galaxy mergers are thus robust candidates for progenitors of long-lived globular clusters. The simulated cluster mass spectrum is consistent with theory and observations. Tidal dwarf galaxies of 108–9 M⊙ can form at the same time, and appear to be part of a different class of objects, being more extended and rotating.

Dynamical interactions and the black-hole merger rate of the Universe

Binary black holes can form efficiently in dense young stellar clusters, such as the progenitors of globular clusters, via a combination of gravitational segregation and cluster evaporation. We use simple analytic arguments supported by detailed $N$-body simulations to determine how frequently black holes born in a single stellar cluster should form binaries, be ejected from the cluster, and merge through the emission of gravitational radiation. We then convolve this ``transfer function'' relating cluster formation to black-hole mergers with (i) the distribution of observed cluster masses and (ii) the star formation history of the Universe, assuming that a significant fraction ${g}_{\mathrm{cl}}$ of star formation occurs in clusters and that a significant fraction ${g}_{\mathrm{evap}}$ of clusters undergo this segregation and evaporation process. We predict future ground-based gravitational wave detectors could observe $\ensuremath{\sim}500({g}_{\mathrm{cl}}/0.5)({g}_{\mathrm{evap}}/0.1)$ double black-hole mergers per year, and the presently operating LIGO interferometer would have a chance (50%) at detecting a merger during its first full year of science data. More realistically, advanced LIGO and similar next-generation gravitational wave observatories provide unique opportunities to constrain otherwise inaccessible properties of clusters formed in the early Universe.

Young Star Clusters: Progenitors of Globular Clusters!?

AbstractStar cluster formation is a major mode of star formation in the extreme conditions of interacting galaxies and violent starbursts. Young clusters are observed to form in a variety of such galaxies, a substantial number resembling the progenitors of globular clusters in mass and size, but with significantly enhanced metallicity. From studies of the metal-poor and metal-rich star cluster populations of galaxies, we can therefore learn about the violent star formation history of these galaxies, and eventually about galaxy formation and evolution. We present a new set of evolutionary synthesis models of our GALEV code, with special emphasis on the gaseous emission of presently forming star clusters, and a new tool to compare extensive model grids with multi-color broad-band observations to determine individual cluster masses, metallicities, ages and extinction values independently. First results for young star clusters in the dwarf starburst galaxy NGC 1569 are presented. The mass distributions determined for the young clusters give valuable input to dynamical star cluster system evolution models, regarding survival and destruction of clusters. We plan to investigate an age sequence of galaxy mergers to see dynamical destruction effects in process.

UCH II regions in extragalactic clusters and associations

In recent years, a number of extragalactic massive stars clusters have been detected which are still deeply embedded in their birth material In many cases, these clusters are only visible in the mid-IR to radio regimes, and have typically been detected as ‘inverted’ spectrum radio sources. These clusters appear to have properties which are analogous to those of ultracompact H ii (UCH ii) regions in the Galaxy, albeit vastly scaled up in total mass and luminosity. The ultra-young clusters appear to form with a continuum of masses, and the most massive are consistent with being the progenitors of globular clusters. Here I will overview the properties of the currently known sample of ultradense H ii (UDH ii) regions and examine their relation to Galactic UCH ii regions.

The Fossil Starburst in M82

(Abridged) We present high-resolution HST imaging in the optical (WFPC2) and near-infrared (NICMOS) of a disk region 1 kpc NE of the starburst core in the nearby galaxy M82. This region, M82 ``B,'' has been suspected to be a fossil starburst site in which an intense episode of star formation occurred over 100 Myr ago, and our new observations confirm this intepretation. We find a large, evolved system of super star clusters in M82 B; we identify a total of 113 super star cluster candidates. The clusters range in absolute magnitude from M_V^0 = -6 to -10, with a peak at -7.5. The derived age distribution suggests steady, continuing cluster formation at a modest rate at early times (> 2 Gyr ago), followed by a concentrated formation episode ~600 Myr ago and more recent suppression of cluster formation. The peak episode coincides with independent dynamical estimates for the last tidal encounter with M81. Our J and H band observations resolve the bright giant population in M82's disk for the first time. Star formation evidently continued in M82 B until about 20-30 Myr ago, but none is found associated with the youngest generations in the nuclear starburst (age <= 15 Myr). After correcting the cluster luminosity function to a fiducial age of 50 Myr, we find that the bright end is characterized by a power-law slope with alpha = -1.2 +/- 0.3. Cluster sizes (2.34 <= Reff <= 10 pc, or 2.4 <= Rcore <= 7.9 pc) and estimated masses (a median of 10^5 Msun) are consistent with values found for young super star cluster populations in M82's core and other galaxies and with the progenitors of globular clusters.