arXiv subjects

Paul Goudfrooij

Publications and source records attributed to Paul Goudfrooij.

At least 19 recordsLinked to original sources

arXiv2026

A Colour-colour Fingerprint Links the UV Upturn in Early-type Galaxies to Second-generation Stars from Dissolved Globular Clusters

We address two mass-dependent properties among early-type galaxies (ETGs): (1) abundance ratios [N/Fe] and [Na/Fe], and (2) the centrally concentrated "UV upturn" at far-UV (FUV) wavelengths, which is likely produced by extreme horizontal branch stars with supersolar helium abundances. Using new HST/WFC3 observations of one FUV-weak and one FUV-bright ETG, we probe the "MP scenario" by Goudfrooij who posited that the UV upturn and the mass-dependent abundance variations of N and Na within and among ETGs are physically connected and produced by dissolution of metal-rich globular clusters, which represent the only galactic environment where mass-dependent enrichment of He, N, and Na is known to occur (i.e., second-generation stars of the "multiple stellar populations" (MPs) phenomenon). We show that passbands F275W and F390W are uniquely sensitive to correlated changes in $Y$ and [N/Fe] in integrated-light photometry when combined with archival data in F475W and F850LP. While F475W-F850LP is found to decrease with increasing radius in both galaxies, consistent with known metallicity gradients, F275W-F390W increases with increasing radius, as expected if the UV upturn is caused by second-generation stars with supersolar $Y$ and [N/Fe]. Furthermore, the radial gradient in F275W-F390W and the implied fractions of He- and N-enhanced stars are found to be significantly larger in the FUV-bright ETG than in the FUV-weak one, consistent with the predictions of the MP scenario.

astro-ph.GA↗

arXiv2026

Nowhere Left to Hide: Uncovering All of the Massive Young Embedded Star Clusters in the Antennae with JWST

The Antennae galaxies merger produces the brightest infrared emission of any galaxy within ~20 Mpc, mostly from intense star formation taking place in supergiant molecular cloud complexes in the overlap region. Here, we present new, high-resolution NIRCam and MIRI images of the Antennae galaxies taken with the F150W, F187N, F335M, F360M, F410M, and F770W filters on JWST to search for the predicted but as-yet-undiscovered population of deeply embedded, optically obscured star clusters. We identify a population of 45 sources, 40 previously unknown, with high Bralpha/Halpha and Paalpha/Halpha flux ratios which are likely very young clusters still embedded or just emerging from their natal cocoons, and estimate their age, extinction (A_V), and mass. We find that all are extremely young (< 2.5 Myr), have A_V between 2 and 10 mag, and masses between ~ 10^4 and several x 10^6~Msun. We believe we have now uncovered all clusters with M > 3 x 10^4 Msun and A_V > 2 mag in the Antennae. While our sample represents a small fraction(~15%) of clusters younger than 3~Myr by number, it dominates the ionizing photon luminosity across the galaxy pair (~60%). We find elevated H_2/PAH ratios of the ISM surrounding the most massive pair of embedded clusters, supporting the idea that merger-induced shock-heated gas play an important role in the formation of extremely massive clusters.

astro-ph.GA↗

arXiv2025

Strikingly high fraction of fast rotators in Magellanic Cloud star clusters

There has been growing evidence that the rich star clusters in the Magellanic Clouds contain significant fractions of rapidly rotating stars. In this work, we aim to constrain these fractions by studying the colour-magnitude diagrams of four star clusters, selected among those with the most striking signatures of fast rotators. Using isochrones derived from PARSEC v2.0 stellar tracks, we generate distinct stellar populations, each covering a limited interval of initial rotation rates $ω_\mathrm{i}$, referred to as 'Partial Models' (PMs). Using optimization algorithms and Monte Carlo Markov Chains, PMs are combined to create the final best-fitting model. In our analysis, we adopt two key assumptions: a uniform age and an isotropic distribution of stellar spin axes within each cluster. The solutions are allowed to explore the entire range of $ω_\mathrm{i}$, and different values of age, metallicity, distance and foreground extinction. We find that the rotational velocity distributions in all four clusters reveal a high fraction of stars with $ω_\mathrm{i}$ close to the break-up value, in all cases. Specifically, the fraction of stars with $ω_\mathrm{i}>0.7$ exceeds $80\%$ in the clusters NGC 419 of the Small Magellanic Cloud (SMC) and NGC 1831 and NGC 1866 of the Large Magellanic Cloud (LMC). For NGC 2203 of the LMC, this fraction is smaller, although it still exceeds $50\%$, confirming that also this cluster is mainly populated by fast-rotating stars.

astro-ph.GA↗

arXiv2024

Clusters, Clumps, Dust, & Gas (CCDG) in NGC1614: Bench-marking Cluster Demographics in Extreme Systems

Observations of young star clusters in a variety of galaxies have been used to constrain basic properties related to star-formation, such as the fraction of stars found in clusters (Gam) and the shape of the cluster mass function. However, the results can depend heavily on the reliability of the cluster age-dating process and other assumptions. One of the biggest challenges for successful age-dating lies in breaking the age-reddening degeneracy, where older, dust-free clusters and young, reddened clusters can have similar broad-band colors. While this degeneracy affects cluster populations in all galaxies, it is particularly challenging in dusty, extreme star-forming environments systems. We study the cluster demographics in the luminous infrared galaxy NGC1614 using Hubble imaging taken in 8 optical-NIR passbands. For age-dating, we adopt a spectral energy distribution fitting process that limits the maximum allowed reddening by region, and includes Ha photometry directly. We find that without these assumptions, essentially all clusters in the dust-free UV-bright arm which should have ages 50-250Myr are incorrectly assigned ages younger than 10Myr. We find this method greatly reduces the number of clusters in the youngest (tau<10Myrs) age bin and shows a fairly uniform distribution of massive clusters, the most massive being few10^7M. A maximum likelihood fit shows that the cluster mass function is well fitted by a power-law with an index -1.8, with no statistically significant high-mass cutoff. We calculate the fraction of stars born in clusters to be Gam1-10=22.4+_5.7%. The fraction of stars in clusters decreases quickly over time, with Gam10-100= 4.5+_1.1% and Gam100-400=1.7+_0.4%, suggesting that clusters dissolve rapidly over the first ~0.5Gyr. The decreasing fraction of stars in clusters is consistent with the declining shape observed for the cluster age distribution.

astro-ph.GA↗

arXiv2024

An Algorithm to Mitigate Charge Migration Effects in Data from the Near Infrared Imager and Slitless Spectrograph on the James Webb Space Telescope

We present an algorithm that mitigates the effects of charge migration due to the "brighter-fatter effect'' (BFE) that occurs for highly illuminated stars in the Teledyne HAWAII-2RG detectors used in the NIRCam, NIRISS, and NIRSpec science instruments aboard the James Webb Space Telescope (JWST). The impact of this effect is most significant for photometry and spectrophotometry of bright stars in data for which the point spread function (PSF) is undersampled, which is the case for several observing modes of the NIRISS instrument. The main impact of the BFE to NIRISS data is incorrect count rate determinations for pixels in the central regions of PSFs of bright stars due to jump detections that are caused by charge migration from peak pixels to surrounding pixels. The effect is especially significant for bright compact sources in resampled, distortion-free images produced by the drizzle algorithm: quantitatively, apparent flux losses of $>$ 50% can occur in such images due to the BFE. We describe the algorithm of the "charge_migration'' mitigation step that has been implemented in version 10.0 of the operational JWST calibration pipeline as of Dec 5, 2023. We illustrate the impact of this step in terms of the resulting improvements of the precision of imaging photometry of point sources. The algorithm renders the effects of the BFE on photometry and surface brightness measurements to stay within 1%.

astro-ph.IM↗

arXiv2023

The Near Infrared Imager and Slitless Spectrograph for the James Webb Space Telescope -- III. Single Object Slitless Spectroscopy

The Near Infrared Imager and Slitless Spectrograph instrument (NIRISS) is the Canadian Space Agency (CSA) contribution to the suite of four science instruments of JWST. As one of the three NIRISS observing modes, the Single Object Slitless Spectroscopy (SOSS) mode is tailor-made to undertake time-series observations of exoplanets to perform transit spectroscopy. The SOSS permits observing point sources between 0.6 and 2.8 um at a resolving power of 650 at 1.25 um using a slit-less cross-dispersing grism while its defocussing cylindrical lens enables observing targets as bright as J=6.7 by spreading light across 23 pixels along the cross-dispersion axis. This paper officially presents the design of the SOSS mode, its operation, characterization, and its performance, from ground-based testing and flight-based Commissioning. On-sky measurements demonstrate a peak photon conversion efficiency of 55% at 1.2 um. The first time-series on the A-type star BD+60o1753 achieves a flux stability close to the photon-noise limit, so far tested to a level of 20 parts per million on 40-minute time-scales after simply subtracting a long-term trend. Uncorrected 1/f noise residuals underneath the spectral traces add an extra source of noise equivalent to doubling the readout noise. Preliminary analysis of a HAT-P-14b transit time-series indicates that it is difficult to remove all the noise in pixels with partially saturated ramps. Overall, the SOSS delivers performance at the level required to tackle key exoplanet science programs such as detecting secondary atmospheres on terrestrial planets and measuring abundances of several chemical species in gas giants.

astro-ph.IM↗

arXiv2023

The Near Infrared Imager and Slitless Spectrograph for the James Webb Space Telescope -- I. Instrument Overview and in-Flight Performance

The Near-Infrared Imager and Slitless Spectrograph (NIRISS) is the science module of the Canadian-built Fine Guidance Sensor (FGS) onboard the James Webb Space Telescope (JWST). NIRISS has four observing modes: 1) broadband imaging featuring seven of the eight NIRCam broadband filters, 2) wide-field slitless spectroscopy (WFSS) at a resolving power of $\sim$150 between 0.8 and 2.2 $μ$m, 3) single-object cross-dispersed slitless spectroscopy (SOSS) enabling simultaneous wavelength coverage between 0.6 and 2.8 $μ$m at R$\sim$700, a mode optimized for exoplanet spectroscopy of relatively bright ($J<6.3$) stars and 4) aperture masking interferometry (AMI) between 2.8 and 4.8 $μ$m enabling high-contrast ($\sim10^{-3}-10^{-4}$) imaging at angular separations between 70 and 400 milliarcsec for relatively bright ($M<8$) sources. This paper presents an overview of the NIRISS instrument, its design, its scientific capabilities, and a summary of in-flight performance. NIRISS shows significantly better response shortward of $\sim2.5\,μ$m resulting in 10-40% sensitivity improvement for broadband and low-resolution spectroscopy compared to pre-flight predictions. Two time-series observations performed during instrument commissioning in the SOSS mode yield very stable spectro-photometry performance within $\sim$10% of the expected noise. The first space-based companion detection of the tight binary star AB Dor AC through AMI was demonstrated.

astro-ph.IM↗

arXiv2022

The Near Infrared Imager and Slitless Spectrograph for the James Webb Space Telescope -- IV. Aperture Masking Interferometry

The James Webb Space Telescope's Near Infrared Imager and Slitless Spectrograph (JWST-NIRISS) flies a 7-hole non-redundant mask (NRM), the first such interferometer in space, operating at 3-5 \micron~wavelengths, and a bright limit of $\simeq 4$ magnitudes in W2. We describe the NIRISS Aperture Masking Interferometry (AMI) mode to help potential observers understand its underlying principles, present some sample science cases, explain its operational observing strategies, indicate how AMI proposals can be developed with data simulations, and how AMI data can be analyzed. We also present key results from commissioning AMI. Since the allied Kernel Phase Imaging (KPI) technique benefits from AMI operational strategies, we also cover NIRISS KPI methods and analysis techniques, including a new user-friendly KPI pipeline. The NIRISS KPI bright limit is $\simeq 8$ W2 magnitudes. AMI (and KPI) achieve an inner working angle of $\sim 70$ mas that is well inside the $\sim 400$ mas NIRCam inner working angle for its circular occulter coronagraphs at comparable wavelengths.

astro-ph.IM↗

arXiv2022

The Near Infrared Imager and Slitless Spectrograph for JWST -- V. Kernel Phase Imaging and Data Analysis

Kernel phase imaging (KPI) enables the direct detection of substellar companions and circumstellar dust close to and below the classical (Rayleigh) diffraction limit. We present a kernel phase analysis of JWST NIRISS full pupil images taken during the instrument commissioning and compare the performance to closely related NIRISS aperture masking interferometry (AMI) observations. For this purpose, we develop and make publicly available the custom "Kpi3Pipeline" enabling the extraction of kernel phase observables from JWST images. The extracted observables are saved into a new and versatile kernel phase FITS file (KPFITS) data exchange format. Furthermore, we present our new and publicly available "fouriever" toolkit which can be used to search for companions and derive detection limits from KPI, AMI, and long-baseline interferometry observations while accounting for correlated uncertainties in the model fitting process. Among the four KPI targets that were observed during NIRISS instrument commissioning, we discover a low-contrast (~1:5) close-in (~1 $λ/D$) companion candidate around CPD-66~562 and a new high-contrast (~1:170) detection separated by ~1.5 $λ/D$ from 2MASS~J062802.01-663738.0. The 5-$σ$ companion detection limits around the other two targets reach ~6.5 mag at ~200 mas and ~7 mag at ~400 mas. Comparing these limits to those obtained from the NIRISS AMI commissioning observations, we find that KPI and AMI perform similar in the same amount of observing time. Due to its 5.6 times higher throughput if compared to AMI, KPI is beneficial for observing faint targets and superior to AMI at separations >325 mas. At very small separations (<100 mas) and between ~250-325 mas, AMI slightly outperforms KPI which suffers from increased photon noise from the core and the first Airy ring of the point-spread function.

astro-ph.IM↗

arXiv2022

When Do Stars Go BOOM?

The maximum mass of a star that can produce a white dwarf (WD) is an important astrophysical quantity. One of the best approaches to establishing this limit is to search for WDs in young star clusters in which only massive stars have had time to evolve and where the mass of the progenitor can be established from the cooling time of the WD together with the age of the cluster. Searches in young Milky Way clusters have not thus far yielded WD members more massive than about 1.1$~M_{\odot}$, well below the Chandrasekhar mass of $1.38~M_{\odot}$, nor progenitors with masses in excess of about $6~M_{\odot}$. However, the hunt for potentially massive WDs that escaped their cluster environs is yielding interesting candidates. To expand the cluster sample further, we used HST to survey four young and massive star clusters in the Magellanic Clouds for bright WDs that could have evolved from stars as massive as 10$~M_{\odot}$. We located five potential WD candidates in the oldest of the four clusters examined, the first extragalactic single WDs thus far discovered. As these hot WDs are very faint at optical wavelengths, final confirmation will likely have to await spectroscopy with 30-metre class telescopes.

astro-ph.SR↗

arXiv2022

On the Precision of Full-Spectrum Fitting of Simple Stellar Populations. IV. A Systematic Comparison with Results from Colour-Magnitude Diagrams

In this fourth paper of a series on the precision of ages of stellar populations obtained through the full-spectrum fitting technique, we present a first systematic analysis that compare the age, metallicity and reddening of star clusters obtained from resolved and unresolved data (namely colour-magnitude diagrams (CMDs) and integrated-light spectroscopy) using the same sets of isochrones. We investigate the results obtained with both Padova isochrones and MIST isochrones. We find that there generally is a good agreement between the ages derived from CMDs and integrated spectra. However, for metallicity and reddening, the agreement between results from analyses of CMD and integrated spectra is significantly worse. Our results also show that the ages derived with Padova isochrones match those derived using MIST isochrones, both with the full spectrum fitting technique and the CMD fitting method. However, the metallicity derived using Padova isochrones does not match that derived using MIST isochrones using the CMD method. We examine the ability of the full-spectrum fitting technique in detecting age spreads in clusters that feature the extended Main Sequence Turn Off (eMSTO) phenomenon using two-population fits. We find that 3 out of 5 eMSTO clusters in our sample are best fit with one single age, suggesting that eMSTOs do not necessarily translate to detectable age spreads in integrated-light studies.

astro-ph.GA↗

arXiv2022

The Near Infrared Imager and Slitless Spectrograph for the James Webb Space Telescope -- II. Wide Field Slitless Spectroscopy

We present the wide field slitless spectroscopy mode of the NIRISS instrument on the James Webb Space Telescope. This mode employs two orthogonal low-resolution (resolving power $\approx 150$) grisms in combination with a set of six blocking filters in the wavelength range 0.8 to $2.3\,μ$m to provide a spectrum of almost every source across the field-of-view. When combined with the low background, high sensitivity and high spatial resolution afforded by the telescope, this mode will enable unprecedented studies of the structure and evolution of distant galaxies. We describe the performance of the as-built hardware relevant to this mode and expected imaging and spectroscopic sensitivity. We discuss operational and calibration procedures to obtain the highest quality data. As examples of the observing mode usage, we present details of two planned Guaranteed Time Observations programs: The Canadian NIRISS Unbiased Cluster Survey (CANUCS) and The NIRISS Survey for Young Brown Dwarfs and Rogue Planets.

astro-ph.IM↗

arXiv2021

Role of host galaxy in the formation of multiple stellar populations: Analysis of NGC 1786 and NGC 1898

Even after decades of research, the origin of multiple stellar populations in globular clusters remains enigmatic. The question as to whether the galaxy environment plays a role in their formation remains unanswered. To that extent, we analysed two classical (> 10 Gyr old) Large Magellanic Cloud globular clusters namely, NGC 1786 and NGC 1898, using imaging data from Hubble Space Telescope to compare and contrast them with ancient Galactic globular clusters to assess systematic differences that might exist between their abundance variations. We calculated their Red Giant Branch width, subtracted the effect of metallicity and compared it with the available data on Galactic globular clusters by plotting them against initial and current cluster mass. We see that the two clusters follow the same general trend as that of the Galactic globular clusters and Galactic globular clusters from different progenitors follow the same general trend as one another, indicating that the galaxy environment may only play a minor role in the formation of multiple stellar populations within globular clusters.

astro-ph.GA↗

arXiv2021

On the Precision of Full-spectrum Fitting of Stellar Populations. III. Identifying Age Spreads

In this third paper of a series on the precision of obtaining ages of stellar populations using the full spectrum fitting technique, we examine the precision of this technique in deriving possible age spreads within a star cluster. We test how well an internal age spread can be resolved as a function of cluster age, population mass fraction, and signal-to-noise (S/N) ratio. For this test, the two ages (Age (SSP1) and Age (SSP2)) are free parameters along with the mass fraction of SSP1. We perform the analysis on 118,800 mock star clusters covering all ages in the range 6.8 < log (age/yr) < 10.2, with mass fractions from 10% to 90% for two age gaps (0.2 dex and 0.5 dex). Random noise is added to the model spectra to achieve S/N ratios between 50 to 100 per wavelength pixel. We find that the mean of the derived Age (SSP1) generally matches the real Age (SSP1) to within 0.1 dex up to ages around log (age/yr) = 9.5. The precision decreases for log (age/yr) > 9.6 for any mass fraction or S/N, due to the similarity of SED shapes for those ages. In terms of the recovery of age spreads, we find that the derived age spreads are often larger than the real ones, especially for log(age/yr) < 8.0 and high mass fractions of SSP1. Increasing the age gap in the mock clusters improves the derived parameters, but Age (SSP2) is still overestimated for the younger ages.

astro-ph.GA↗

arXiv2021

The wide upper main sequence and main sequence turnoff of the ~ 800 Myr old star cluster NGC1831

We present the analysis of the colour-magnitude diagram (CMD) morphology of the ~ 800 Myr old star cluster NGC1831 in the Large Magellanic Cloud, exploiting deep, high-resolution photometry obtained using the Wide Field Camera 3 onboard the Hubble Space Telescope. We perform a simultaneous analysis of the wide upper main sequence and main sequence turn-off observed in the cluster, to verify whether these features are due to an extended star formation or a range of stellar rotation rates, or a combination of these two effects. Comparing the observed CMD with Monte Carlo simulations of synthetic stellar populations, we derive that the morphology of NGC1831 can be fully explained in the context of the rotation velocity scenario, under the assumption of a bimodal distribution for the rotating stars, with ~40% of stars being slow-rotators ($Ω$ / $Ω_{crit}$ < 0.5) and the remaining ~ 60% being fast rotators ($Ω$ / $Ω_{crit}$ > 0.9). We derive the dynamical properties of the cluster, calculating the present cluster mass and escape velocity, and predicting their past evolution starting at an age of 10 Myr. We find that NGC1831 has an escape velocity $v_{esc}$ = 18.4 km/s, at an age of 10 Myr, above the previously suggested threshold of 15 km/s, below which the cluster cannot retain the material needed to create second-generation stars. These results, combined with those obtained from the CMD morphology analysis, indicate that for the clusters whose morphology cannot be easily explained only in the context of the rotation velocity scenario, the threshold limit should be at least ~ 20 km/s.

astro-ph.GA↗

arXiv2021

On the precision of full-spectrum fitting of simple stellar populations. II. The dependence on star cluster mass in the wavelength range 0.3-5.0 $μ$m

In this second paper of a series on the accuracy and precision of the determination of age and metallicity of simple stellar populations (SSPs) by means of the full spectrum fitting technique, we study the influence of star cluster mass through stochastic fluctuations of the number of stars near the top of the stellar mass function, which dominate the flux in certain wavelength regimes depending on the age. We consider SSP models based on the Padova isochrones, spanning the age range 7.0 $\leq$ log (age/yr) $\leq$ 10.1. Simulated spectra of star clusters in the mass range $10^4 \leq M/M_{\odot} < 10^6$ are compared with SSP model spectra to determine best-fit ages and metallicities using a full-spectrum fitting routine in four wavelength regimes: the blue optical (0.35-0.70 $μ$m), the red optical (0.6-1.0 $μ$m), the near-IR (1.0-2.5 $μ$m), and the mid-IR (2.5-5.0 $μ$m). We compare the power of each wavelength regime in terms of both the overall precision of age and metallicity determination, and of its dependence on cluster mass. We also study the relevance of spectral resolution in this context by utilizing two different spectral libraries (BaSeL and BT-Settl). We highlight the power of the mid-IR regime in terms of identifying young massive clusters in dusty star forming regions in external galaxies. The spectra of the simulated star clusters and SSPs are made available online to enable follow-up studies by the community.

astro-ph.GA↗

arXiv2020

On the Precision of Full-spectrum Fitting of Simple Stellar Populations. I. Well-sampled Populations

We investigate the precision of the ages and metallicities of 21,000 mock simple stellar populations (SSPs) determined through full-spectrum fitting. The mock SSPs cover an age range of 6.8 $<$ log (age/yr) $<$ 10.2, for three wavelength ranges in the optical regime, using both Padova and MIST isochrone models. Random noise is added to the model spectra to achieve S/N ratios between 10 to 100 per wavelength pixel. We find that for S/N $\geq$ 50, this technique can yield ages of SSPs to an overall precision of $Δ\,\mbox{log(age/yr)} \sim 0.1$ for ages in the ranges 7.0 $\leq$ log (age/yr) $\leq$ 8.3 and 8.9 $\leq$ log (age/yr) $\leq$ 9.4. For the age ranges of 8.3 $\leq$ log (age/yr) $\leq$ 8.9 and log (age/yr) $\geq$ 9.5, which have significant flux contributions from asymptotic giant branch (AGB) and red giant branch (RGB) stars, respectively, the age uncertainty rises to about $\pm 0.3$ dex. The precision of age and metallicity estimation using this method depends significantly on the S/N and the wavelength range used in the fitting. We quantify the systematic differences in age predicted by the MIST and Padova isochrone models, due to their different assumptions about stellar physics in various important (i.e., luminous) phases of stellar evolution, which needs to be taken in consideration when comparing ages of star clusters obtained using these popular models. Knowing the strengths and limitations of this technique is crucial in interpreting the results obtained for real star clusters and for deciding the optimal instrument setup before performing the observations.

astro-ph.GA↗

arXiv2020

Formation channels of slowly rotating early-type galaxies

We study the evidence for a diversity of formation processes in early-type galaxies by presenting the first complete volume-limited sample of slow rotators with both integral-field kinematics from the ATLAS3D Project and high spatial resolution photometry from the Hubble Space Telescope. Analysing the nuclear surface brightness profiles of 12 newly imaged slow rotators, we classify their light profiles as core-less, and place an upper limit to the core size of ~10 pc. Considering the full magnitude and volume-limited ATLAS3D sample, we correlate the presence or lack of cores with stellar kinematics, including the proxy for the stellar angular momentum and the velocity dispersion within one half-light radius, stellar mass, stellar age, $α$-element abundance, and age and metallicity gradients. More than half of the slow rotators have core-less light profiles, and they are all less massive than $10^{11}$ Msun. Core-less slow rotators show evidence for counter-rotating flattened structures, have steeper metallicity gradients, and a larger dispersion of gradient values than core slow rotators. Our results suggest that core and core-less slow rotators have different assembly processes, where the former are the relics of massive dissipation-less merging in the presence of central supermassive black holes. Formation processes of core-less slow rotators are consistent with accretion of counter-rotating gas or gas-rich mergers of special orbital configurations, which lower the final net angular momentum of stars, but support star formation. We also highlight core fast rotators as galaxies that share properties of core slow rotators and core-less slow rotators. Formation processes similar to those for core-less slow rotators can be invoked to explain the assembly of core fast rotators, with the distinction that these processes form or preserve cores.[Abridged]

astro-ph.GA↗