Robert Michael Rich

The Type I super-luminous supernova SN 2024jlc (ZTF24aapadbb) exploded on 25 May 2024 at z = 0.039. This was the closest supernova of this class discovered in recent years and one of the closest ever. It therefore represented a rare opportunity to study this type of object in detail. We performed a multiwavelength analysis that spanned ten orders of magnitude in frequency and included optical and UV photometry and spectroscopy, soft and hard X-rays, and high-energy γ -rays. We characterized the event as a slow-evolving and He-rich supernova, with one of the lowest peak luminosities reported for a super-luminous event M _g ∼ −19.37 mag, and a light-curve evolution compatible with either a circumstellar interaction and a magnetar spin-down model, with noticeable contribution from ⁵⁶ Ni decay. No significant excess was found in the soft and hard X-ray bands, for which we provide upper limits on the flux. Additionally, we analyzed two years of Fermi -LAT data, from which we report an intriguing hint of a γ -ray signal at the ∼3.6 σ level, although no firm detection can be claimed. The ratio of gamma to optical efficiency, η = 0.38, suggests a central-engine scenario, similar to SN 2017egm. Our analysis suggests that SN 2024jlc might bridge the gap between super-luminous supernovae and classical stripped-envelope supernovae. While still poorly populated, this bridge might consist of all super-luminous Ib supernovae, with the key difference residing in the powering mechanism.

The Blanco DECam Bulge Survey (BDBS) program has surveyed 200 sq. deg. of the Southern Galactic bulge in ugrizY using the Dark Energy Camera on the Blanco 4m telescope at Cerro Tololo, with photometry for : 500 M stars. This multicolor survey is a Rubin Observatory pathfinder; the availability of blue optical colors has enabled the derivation of metallicity for 2.3M red clump giant stars; matching these to the Gaia catalog gives chemistry and kinematics. Calibrating the ( u–i ) ₀ photometric color vs [Fe/H] measured from high resolution spectroscopy, the structure of the bulge as a function of metallicity has been discerned for –10° < l < + 10° and –2.5° < b < + 10°. Well-known features such as the X-shaped bulge can be seen in the metal rich population, but additionally, a striking concentration of metal rich stars toward the Galactic Plane is clearly visible. There is a steep vertical metallicity gradient, and no radial gradient can be discerned over the inner 2 kpc. Confirming many previous studies, the bulge metallicity distribution is bimodal, but at b < =–6° a sub-solar metallicity peak at –0.4 dex is dominant, strongly pointing to a different formation history for that population. Signatures of the bar (the double red clump, and kinematic signatures) are clearly evident at [Fe/H] > –0.4.

In this paper, we present the chemical screening of the complex stellar population discovered in the Bulge Fossil Fragment Liller 1. This study is part of the Bulge Cluster Origin (BulCO) survey based on a Large Program at the ESO-Very Large Telescope with the high-resolution spectrograph CRIRES+. The survey is aimed at performing an unprecedented chemical screening of 17 stellar systems orbiting the Milky Way bulge, with the ultimate goal of unveiling their origin and true nature. We measured precise chemical abundances of iron, CNO, iron-peak, α-elements, a few other light elements, and neutron-capture elements for a sample of 30 red giant branch stars, kinematic members of Liller 1. The presented analysis provides the high-resolution spectroscopic proof of the complex chemistry of this massive stellar system, with multimetallicity subpopulations of different ages that nicely fit into a self-enrichment scenario. We find no evidence for the Na–O anticorrelation associated with genuine globular clusters; rather, the overall abundance trends are similar to those seen in the bulge field and in Terzan 5, providing definitive evidence of an in situ formation of Liller 1 within the Galactic bulge.

We constrain the formation history of the Milky Way bulge using a two-infall galactic chemical evolution (GCE) algorithm implemented in the N’OMEGA+ code. We recover a best-fit scenario in which the bulge forms through an early, rapid starburst ( t ₁ ∼ 0.1 Gyr, τ ₁ ∼ 0.09 Gyr, and star formation efficiency (SFE) ∼ 3 Gyr ⁻¹ ), followed by a delayed, lower-mass second infall ( t ₂ ∼ 5.1 Gyr, τ ₂ ∼ 1.7 Gyr, and σ ₂ ∼ 0.69). Our model adopts mass- and metallicity-dependent nucleosynthetic yields from modern stellar grids and explores a wide GCE parameter space in infall timing, SFE, mass partitioning, initial mass function upper mass, and type Ia supernova normalization, optimized via a hybrid genetic algorithm with Markov Chain Monte Carlo refinement. The later infall features a reduced SFE (ΔSFE ∼ 0.72), reproducing the metal-rich peak of the bulge metallicity distribution function (MDF) and the decline in [ α /Fe] at high [Fe/H]. Our model naturally favors the M. Joyce et al. age–metallicity relation over the ages in T. Bensby et al. Degeneracy and principal component analyses show that the infall history, SFE, and mass partitioning are strongly covariant—the bulge’s observed MDF, abundance trends, and age distribution constrain only their combinations, not each parameter independently. The results support a composite bulge origin—an early, rapid collapse builds the majority of the mass, while a younger component is required to match the late-stage enrichment.

We present new, deep narrowband imagery and discuss the nature of SDSO 1, the large [O iii ]-emitting nebula centered 1 . ° 5 SE of M 31. We find strong evidence to support the hypothesis that SDSO 1 is unrelated to M 31 and is instead a faded, giant ( D = 20 pc), ghost planetary nebula (GPN) expelled by the symbiotic white dwarf binary star EG Andromedae. The associated 45 pc long turbulent tail, seen in projection in front of M 31, yields an estimated age of 400 kyr. The initial hypersonic velocity of 91 km s ⁻¹ drives a strong bow shock into the local interstellar medium and a reverse shock into the GPN. SDSO 1 has reached the terminal phase in its evolution where its outward expansion and forward motion have been decelerated greatly by ram pressure and the [O iii ] emission arises primarily from the reverse shock. We establish the shock-powered GPN phase as a new phase of planetary nebula (PN) evolution and identify 24 candidate GPNe by their large size and shock-tail morphology. This includes several giant halos of younger PNe, possibly expelled by now degenerate binary companions. The interaction of an old, fast-moving GPN with the ISM generates shocks that remain visible long after the photoionized PN shell has faded below the limit of detectability.

The James Webb Space Telescope (JWST) provides an exciting opportunity to investigate stellar systems located in heavily obscured regions such as the Galactic bulge. Possibly the most enigmatic among them is Terzan 5; long classified as a globular cluster, it is now known to host distinct stellar populations with different iron abundances (ranging from approximately [Fe/H]=-0.8 to [Fe/H]=+0.3 dex). Indeed, the chemical and structural properties collected so far suggest that it is the remnant of one of the primordial clumps that contributed to the early assembly of the bulge, a so-called “Bulge Fossil Fragment.” Here we present a new photometric analysis of Terzan 5 based on JWST/NIRCam observations in the F115W and F200W filters, as well as archival HST/ACS optical (F606W and F814W) data. The dataset overcomes the severe and spatially variable extinction along the line of sight and yields the deepest color-magnitude diagram ever obtained for Terzan 5. Proper motion selections and high-resolution differential reddening corrections allowed us to isolate bona fide cluster members and to provide an unprecedented view of the main-sequence turn-off region. We clearly identify two main components and determine their respective ages: the old, sub-solar component has an age of 12.5 ± 0.5 Gyr, while the super-solar component is significantly younger with an age of 4.7 ± 0.5 Gyr. Interestingly, we also find hints of an even younger main sequence turn-off and sub-giant branch, consistent with the presence of a further stellar component with an age of 3.8 ± 0.5 Gyr. There is also evidence of a blue plume populated by stars as bright as m _F115W ~ 17.4, suggesting a prolonged period of star formation extending up to 2.5 Gyr ago.

We study the stellar mass function (SMF) of quiescent and star-forming galaxies and its dependence on morphology in ten redshift bins at 0.2 < z < 5.5. We used the COSMOS2025 catalog, built from the 0.54 deg ² JWST imaging from the COSMOS-Web survey, to select galaxies by type using the NUVrJ rest-frame color diagram and to classify them morphologically based on their bulge-to-total light ratio ( B / T ). The SMF of quiescent galaxies shows a rapid early build-up, with the most massive, log( M _★ /M _⊙ )≳11, being assembled by z ∼ 1 and evolving little since. The star-forming SMF evolves more slowly with redshift, following a mass-evolution scenario where galaxies grow in mass via star formation and quench once they reach the characteristic log( M ^∗ /M _⊙ ) ∼ 10.6. Bulge systems ( B / T > 0.6) dominate the quiescent SMF at log( M _★ /M _⊙ ) > 10 at all redshifts, while disk systems ( B / T < 0.2) dominate at log( M _★ /M _⊙ ) < 9. However, most bulge-dominated galaxies in the Universe are star forming, with their fraction increasing with redshift and decreasing mass, consistent with them being progenitors of quiescent bulges. We find evidence for the onset of environmental quenching as early as z ∼ 3 from the upturn in the quiescent SMF at log( M _★ /M _⊙ ) < 9.5. This upturn is contributed by disk-dominated galaxies, consistent with environmental quenching scenarios in which satellites are quenched, but retain their disk morphologies. The number densities of log( M _★ /M _⊙ ) > 10 quiescent galaxies are lower than in the recent literature by 0.1 − 0.7 dex, but agree well with cosmological galaxy formation simulations at 2 < z < 3. However, at z > 3, simulations increasingly underpredict the observations. Finally, we built a simple empirical model to describe the redshift evolution of galaxy number densities by parameterizing the quenching rate of all and bulge-dominated galaxies, stellar fraction, and bulge formation function. Our model is consistent with an evolutionary scenario where star-forming galaxies grow a central bulge before permanently quenching in massive halos.