Merger History Research Articles

Rise and fall of post-starburst galaxies in Magneticum Pathfinder

ABSTRACT Post-starburst (PSB) galaxies belong to a short-lived transition population between star-forming (SF) and quiescent galaxies. Deciphering their heavily discussed evolutionary pathways is paramount to understanding galaxy evolution. We aim to determine the dominant mechanisms governing PSB evolution in both the field and in galaxy clusters. Using the cosmological hydrodynamical simulation suite Magneticum Pathfinder, we identify 647 PSBs with z ∼ 0 stellar mass $M_* \ge 5 \times 10^{10} \, \mathrm{M_{\odot }}$ . We track their galactic evolution, merger history, and black hole activity over a time-span of $3.6\,$ Gyr. Additionally, we study cluster PSBs identified at different redshifts and cluster masses. Independent of environment and redshift, we find that PSBs, like SF galaxies, have frequent mergers. At z = 0, $89{{\ \rm per\ cent}}$ of PSBs have experienced mergers and $65{{\ \rm per\ cent}}$ had at least one major merger within the last $2.5\,$ Gyr, leading to strong star formation episodes. In fact, $23{{\ \rm per\ cent}}$ of z = 0 PSBs were rejuvenated during their starburst. Following the mergers, field PSBs are generally shutdown via a strong increase in active galactic nucleus (AGN) feedback (power output $P_{\rm AGN,PSB} \ge 10^{56}\,$ erg Myr−1). We find agreement with observations for both stellar mass functions and z = 0.9 line-of-sight phase space distributions of PSBs in galaxy clusters. Finally, we find that z ≲ 0.5 cluster PSBs are predominantly infalling, especially in high-mass clusters and show no signs of enhanced AGN activity. Thus, we conclude that the majority of cluster PSBs are shutdown via an environmental quenching mechanism such as ram-pressure stripping, while field PSBs are mainly quenched by AGN feedback.

On the Evolution of Supermassive Primordial Stars in Cosmological Flows

Abstract Primordial supermassive stars (SMSs) formed in atomic-cooling halos at z ∼ 15–20 are leading candidates for the seeds of the first quasars. Past numerical studies of the evolution of SMSs have typically assumed constant accretion rates rather than the highly variable flows in which they form. We model the evolution of SMSs in the cosmological flows that create them using the Kepler stellar evolution and implicit hydrodynamics code. We find that they reach masses of 1 − 2 × 105 M⊙ before undergoing direct collapse to black holes (DCBHs) during or at the end of their main-sequence hydrogen burning, at 1–1.5 Myr, regardless of halo mass, spin, or merger history. We also find that realistic, highly variable accretion histories allow for a much greater diversity of supermassive stellar structures, including in some cases largely thermally relaxed objects, which may provide a significant source of radiative feedback. Our models indicate that the accretion histories predicted for purely atomic-cooling halos may impose a narrow spectrum of masses on the seeds of the first massive quasars; however, further studies incorporating realistic feedback will be essential in order to confirm whether or not this holds true in all cases. Our results also indicate that multiple SMSs at disparate stages of evolution can form in these halos, raising the possibility of SMS binaries and supermassive X-ray binaries, as well as DCBH mergers that could be detected by LISA.

GW190521 from the Merger of Ultradwarf Galaxies.

We present an alternative formation scenario for the gravitational wave event GW190521 that can be explained as the merger of central black holes (BHs) from two ultradwarf galaxies of stellar mass ∼10^{5}-10^{6} M_{⊙}, which had themselves previously undergone a merger. The GW190521 components' masses of 85_{-14}^{+21} M_{⊙} and 66_{-18}^{+17} M_{⊙} challenge standard stellar evolution models, as they fall in the so-called mass gap. We demonstrate that the merger history of ultradwarf galaxies at high redshifts (1≲z≲2) matches well the LIGO-Virgo inferred merger rate for BHs within the mass range of the GW190521 components, resulting in a likely time delay of ≲4 Gyr considering the redshift of this event. We further demonstrate that the predicted timescales are consistent with expectations for central BH mergers, although with large uncertainties due to the lack of high-resolution simulations in low-mass dwarf galaxies. Our findings show that this BH production and merging channel is viable and extremely interesting as a new way to explore galaxies' BH seeds and galaxy formation. We recommend this scenario be investigated in detail with simulations and observations.

A preserved high-z compact progenitor in the heart of NGC 3311 revealed with MUSE 2D stellar population analysis

Context. Massive early-type galaxies are believed to be the end result of an extended mass accretion history. The stars formed in situ very early on in the initial phase of the mass assembly might have originated from an extremely intense and rapid burst of star formation. These stars may still be found within the cores of such galaxies at z = 0, depending on their accretion and merger histories. Aims. We wish to investigate the presence of a surviving high-z compact progenitor component in the brightest galaxy of the Hydra I cluster, NGC 3311, by mapping its 2D kinematics and stellar population out to 2 effective radii. Our goal is to understand the formation of its several structural components and trace their mass assembly back in time. Methods. We combined MUSE observations, a customized and extended version of the state-of-the-art EMILES single stellar population models, and a newly developed parametric fully Bayesian framework to model the observed spectra using full-spectrum fitting. Results. We present 2D maps and radial profiles of the stellar velocity dispersion, age, total metallicity, α-element, sodium abundance ([Na/Fe]), and the initial mass function (IMF) slope. All properties have significant gradients, confirming the existence of multiple structural components, also including a “blue spot” characterized by younger and more metal-rich stars. We find that the component dominating the light budget of NGC 3311 within R ≲ 2.0 kpc is the surviving z = 0 analog of a high-z compact core. This concentrated structure has a relatively small velocity dispersion (σ* ≈ 180 km s−1), is very old (ages ≳ 11 Gyr), metal-rich ([Z/H] ∼ 0.2 and [Na/Fe] ∼ 0.4), and has a bottom-heavy IMF (with slope Γb ∼ 2.4). In the outer region, instead, the line-of-sight velocity distribution becomes increasingly broad, and the stars are younger. They are also more metal and sodium poor but are richer in α-elements. The low-mass end of the IMF slope becomes Chabrier-like with increasing galactocentric distance. Conclusions. The existence of multiple structural components in NGC 3311 from photometry, kinematics, and stellar populations confirms the predictions from the two-phase formation scenario for NGC 3311, according to which a first very short, high-z star-formation episode formed a compact stellar structure in its core, which then grew in size by the extended mass assembly of relatively massive satellites. Interestingly, the outer stellar population has an overabundant [α/Fe], most likely because NGC 3311, located at the center of the galaxy cluster, accreted stars from rapidly quenched satellites.

The SLUGGS survey: combining stars, globular clusters, and planetary nebulae to understand the assembly history of early-type galaxies from their large radii kinematics

ABSTRACT We investigate the kinematic properties of nine nearby early-type galaxies with evidence of a disc-like component. Three of these galaxies are located in the field, five in the group, and only one in the cluster environment. By combining the kinematics of the stars with those of the globular clusters (GCs) and planetary nebulae (PNe), we probe the outer regions of our galaxies out to $\sim 4\!-\!6\, R_{\mathrm{e}}$. Six galaxies have PNe and red GCs that show good kinematic alignment with the stars, whose rotation occurs along the photometric major-axis of the galaxies, suggesting that both the PNe and red GCs are good tracers of the underlying stellar population beyond that traced by the stars. Additionally, the blue GCs also show rotation that is overall consistent with that of the red GCs in these six galaxies. The remaining three galaxies show kinematic twists and misalignment of the PNe and GCs with respect to the underlying stars, suggesting recent galaxy interactions. From the comparison with simulations, we propose that all six aligned galaxies that show similar dispersion-dominated kinematics at large radii ($\gt 2\!-\!3\, R_{\mathrm{e}}$) had similar late (z ≲ 1) assembly histories characterized by mini mergers (mass-ratio < 1:10). The different Vrot/σ profiles are then the result of an early (z > 1) minor merger (1:10 < mass-ratio < 1:4) for the four galaxies with peaked and decreasing Vrot/σ profiles and of a late minor merger for the two galaxies with flat Vrot/σ profiles. The three misaligned galaxies likely formed through multiple late minor mergers that enhanced their velocity dispersion at all radii, or a late major merger that spun-up both the GC subpopulations at large radii. Therefore, lenticular galaxies can have complex merger histories that shape their characteristic kinematic profile shapes.

LoCuSS: The Splashback Radius of Massive Galaxy Clusters and Its Dependence on Cluster Merger History

Abstract We present the direct detection of the splashback feature using the sample of massive galaxy clusters from the Local Cluster Substructure Survey (LoCuSS). This feature is clearly detected (above 5σ) in the stacked luminosity density profile obtained using the K-band magnitudes of spectroscopically confirmed cluster members. We obtained the best-fit model by means of Bayesian inference, which ranked models including the splashback feature as more descriptive of the data with respect to models that do not allow for this transition. In addition, we have assessed the impact of the cluster dynamical state on the occurrence of the splashback feature. We exploited the extensive multiwavelength LoCuSS data set to test a wide range of proxies for the cluster formation history, finding the most significant dependence of the splashback feature location and scale according to the presence or absence of X-ray emitting galaxy groups in the cluster infall regions. In particular, we report for the first time that clusters that do not show massive infalling groups present the splashback feature at a smaller clustercentric radius r sp/r 200,m = 1.158 ± 0.071 than clusters that are actively accreting groups r sp/r 200,m = 1.291 ± 0.062. The difference between these two subsamples is significant at 4.2σ, suggesting a correlation between the properties of the cluster potential and its accretion rate and merger history. Similarly, clusters that are classified as old and dynamically inactive present stronger signatures of the splashback feature, with respect to younger, more active clusters. We are directly observing how fundamental dynamical properties of clusters reverberate across vastly different physical scales.

Multimessenger probes of inflationary fluctuations and primordial black holes

Next generation cosmic microwave background spectral distortion and pulsar timing array experiments have the potential to probe primordial fluctuations at small scales with remarkable sensitivity. We demonstrate the potential of these probes to either detect signatures of primordial black holes (PBHs) sourced from primordial overdensities within the standard thermal history of the universe over a 13-decade mass range ${\cal O}(0.1-10^{12})M_\odot$, or constrain their existence to a negligible abundance. Our conclusions are based only on global cosmological signals, and are robust under changes in i) the statistical properties of the primordial density fluctuations (whether Gaussian or non-Gaussian), ii) the merger and accretion history of the PBHs and assumptions about associated astrophysical processes, and iii) clustering statistics. Any positive detection of enhanced primordial fluctuations at small scales would have far-reaching implications from the content of dark matter to origin of BHs in the centers of galaxies, and to the field content of the inflation. On the other hand, their non-detection would also have important corollaries. For example, non-detection up to forecast sensitivities would tell us that PBHs larger than a fraction of a solar mass can constitute no more than a negligible fraction of dark matter. Moreover, non-detection will also rule out the scenario that PBHs generated by primordial overdensities could be the progenitors of super-massive black holes (SMBHs), of topical interest as there are only a few widely accepted proposals for the formation of SMBHs, an even more pressing question after the detection of active galactic nuclei over a billion solar masses at redshifts $z \geq 7$. Finally, non-detection sets the strongest bounds on the amplitude of small scale inflationary fluctuations for over 6 decades.

The stellar halos of ETGs in the IllustrisTNG simulations

Stellar halos in early-type galaxies (ETGs) are shaped by their accretion and merger histories. We use a sample of 1114 ETGs in the TNG100 simulation of the IllustrisTNG suite with stellar masses 1010.3 ≤ M*/M⊙ ≤ 1012, selected at z = 0 within the range of the g − r colour and λ-ellipticity diagram populated by observed ETGs. We study how the rotational support and intrinsic shapes of the stellar halos depend on the fraction of stars accreted, both overall and separately, by major, minor, and mini mergers. Accretion histories in TNG100 ETGs as well as the final radial distributions of ex-situ stars fexsitu(R) relative to in-situ (“accretion classes”) strongly correlate with stellar mass. Low-mass galaxies have characteristic peaked rotation profiles and near-oblate shapes with rounder halos that are completely driven by the in-situ stars. At high fexsitu, major mergers decrease the in-situ peak in rotation velocity, flatten the V*/σ*(R) profiles, and increase the triaxiality of the stellar halos. Kinematic transition radii do not trace the transition between in-situ- and ex-situ-dominated regions, but for systems with M* > 1010.6 M⊙ the local rotational support of the stellar halos decreases with the local ex-situ fraction fexsitu(R) at fixed M*, and their triaxiality increases with fexsitu(R). These correlations between rotational support, intrinsic shapes, and local fexsitu are followed by fast and slow rotators alike with a continuous and overlapping sequence of properties, but slow rotators are concentrated at the high-fexsitu end dominated by dry major mergers. We find that in ∼20% of high-mass ETGs, the central regions are dominated by stars from a high-redshift compact progenitor. Merger events dynamically couple stars and dark matter: in high-mass galaxies and at large radii where fexsitu ≳ 0.5, both components tend to have similar intrinsic shapes and rotational support, and nearly aligned principal axes and spin directions. Based on these results we suggest that extended photometry and kinematics of massive ETGs (M* > 1010.6 M⊙) can be used to estimate the local fraction of ex-situ stars, and to approximate the intrinsic shapes and rotational support of the co-spatial dark matter component.

Observational insights on the origin of giant low surface brightness galaxies

ABSTRACT Giant low surface brightness galaxies (gLSBGs) with dynamically cold stellar discs reaching the radius of 130 kpc challenge currently considered galaxy formation mechanisms. We analyse new deep long-slit optical spectroscopic observations, archival optical images, and published Hi and optical spectroscopic data for a sample of seven gLSBGs, for which we performed mass modelling and estimated the parameters of dark matter haloes assuming the Burkert dark matter density profile. Our sample is not homogeneous by morphology, parameters of stellar populations, and total mass, however, six of seven galaxies sit on the high-mass extension of the baryonic Tully–Fisher relation. In UGC 1382, we detected a global counterrotation of the stellar high surface brightness (HSB) disc with respect to the extended LSB disc. In UGC 1922 with signatures of a possible merger, the gas counterrotation is seen in the inner disc. Six galaxies host active galactic nuclei, three of which have the estimated black hole masses substantially below those expected for their (pseudo-)bulge properties suggesting poor merger histories. Overall, the morphology, internal dynamics, and low star formation efficiency in the outer discs indicate that the three formation scenarios shape gLSBGs: (i) a two-stage formation when an HSB galaxy is formed first and then grows an LSB disc by accreting gas from an external supply; (ii) an unusual shallow and extended dark matter halo; (iii) a major merger with fine-tuned orbital parameters and morphologies of the merging galaxies.

Very Large Array observations of the mini-halo and AGN feedback in the Phoenix cluster

Context. The relaxed cool-core Phoenix cluster (SPT-CL J2344-4243) features an extremely strong cooling flow, as well as a mini halo. Strong star formation in the brightest cluster galaxy indicates that active galactic nucleus (AGN) feedback has been unable to inhibit this cooling flow. Aims. We aim to study the strong cooling flow in the Phoenix cluster by determining the radio properties of the AGN and its lobes. In addition, we used spatially resolved radio observations to investigate the origin of the mini halo. Methods. We present new multifrequency Very Large Array 1–12 GHz observations of the Phoenix cluster, which resolve the AGN and its lobes in all four frequency bands as well as the mini-halo in the L and S bands. Results. Using our L-band observations, we measure the total flux density of the radio lobes at 1.5 GHz to be 7.6 ± 0.8 mJy, and the flux density of the mini halo to be 8.5 ± 0.9 mJy. Using high-resolution images in the L and X bands, we produced the first spectral index maps of the lobes from the AGN and find the spectral indices of the northern and southern lobes to be −1.35 ± 0.07 and −1.30 ± 0.12, respectively. Similarly, using L- and S-band data, we mapped the spectral index of the mini halo, and obtain an integrated spectral index of α = −0.95 ± 0.10. Conclusions. We find that the mini halo is most likely formed by turbulent re-acceleration powered by sloshing in the cool core due to a recent merger. In addition, we find that the feedback in the Phoenix cluster is consistent with the picture that stronger cooling flows are to be expected for massive clusters such as this one, as these may feature an underweight supermassive black hole due to their merging history. Strong time variability of the AGN on Myr timescales may help explain the disconnection between the radio and the X-ray properties of the system. Finally, a small amount of jet precession of the AGN likely contributes to the relatively low intracluster medium re-heating efficiency of the mechanical feedback.

The Fundamental Plane of Massive Quiescent Galaxies at z ∼ 2

Abstract We examine the Fundamental Plane (FP) and mass-to-light ratio (M/L) scaling relations using the largest sample of massive quiescent galaxies at 1.5 < z < 2.5 to date. The FP (r e , σ e , I e ) is established using 19 UVJ quiescent galaxies from COSMOS with Hubble Space Telescope H F160W rest-frame optical sizes and X-shooter absorption line-measured stellar velocity dispersions. For a very massive, log ( M * / M ⊙ ) > 11.26 , subset of eight quiescent galaxies at z > 2, from Stockmann et al., we show that they cannot passively evolve to the local Coma cluster relation alone and must undergo significant structural evolution to mimic the sizes of local massive galaxies. The evolution of the FP and M/L scaling relations, from z = 2 to present day, for this subset are consistent with passive aging of the stellar population and minor merger structural evolution into the most massive galaxies in the Coma cluster and other massive elliptical galaxies from the MASSIVE Survey. Modeling the luminosity evolution from minor merger-added stellar populations favors a history of merging with “dry” quiescent galaxies.

Ancient Very Metal-poor Stars Associated with the Galactic Disk in the H3 Survey

Abstract Ancient, very metal-poor (VMP) stars offer a window into the earliest epochs of galaxy formation and assembly. We combine data from the H3 Spectroscopic Survey and Gaia to measure metallicities, abundances of α elements, stellar ages, and orbital properties of a sample of 482 VMP ([Fe/H] < −2) stars in order to constrain their origins. This sample is confined to 1 ≲ ∣Z∣ ≲ 3 kpc from the Galactic plane. We find that >70% of VMP stars near the disk are on prograde orbits and this fraction increases toward lower metallicities. This result is unexpected if metal-poor stars are predominantly accreted from many small systems with no preferred orientation, as such a scenario would imply a mostly isotropic distribution. Furthermore, we find there is some evidence for higher fractions of prograde orbits among stars with lower [α/Fe]. Isochrone-based ages for main-sequence turn-off stars reveal that these VMP stars are uniformly old (≈12 Gyr) irrespective of the α abundance and metallicity, suggesting that the metal-poor population was not born from the same well-mixed gas disk. We speculate that the VMP population has a heterogeneous origin, including both in situ formation in the ancient disk and accretion from a satellite with the same direction of rotation as the ancient disk at early times. Our precisely measured ages for these VMP stars on prograde orbits show that the Galaxy has had a relatively quiescent merging history over most of cosmic time, and implies the angular momentum alignment of the Galaxy has been in place for at least 12 Gyr.

Bimodality of [α Fe]–[Fe/H] distributions is a natural outcome of dissipative collapse and disc growth in Milky Way-type galaxies

ABSTRACT By using chemo-dynamical simulations of the Milky Way-type galaxies formation, we find that the two α-sequences are formed in quite different physical environments. The high-α sequence is formed early from a burst of star formation in a turbulent, compact gaseous disc that forms a thick disc. The low-α stellar population is the result of quiescent star formation supported by the slow accretion of enriched gas on to a radially extended thin disc. Feedback-driven outflows during the formation of the thick disc are responsible for the enrichment of the surrounding gaseous halo, which subsequently feeds the disc on a longer time-scale. During the thin disc phase, chemical evolution reaches an equilibrium metallicity and abundance, where the stars pile-up. This equilibrium metallicity decreases towards the outer disc, generating the ridge line that forms the low-α sequence. We identify a second mechanism capable of creating a low-α sequence in one of our simulations. A rapid shutdown of the star formation due to feedback at the end of the thick disc phase, suppresses the chemical enrichment of the halo gas, which, once accreted on to the star-forming disc, dilutes the interstellar medium at the beginning of the thin disc formation. Therefore, the bimodality is independent of any particular merger history, suggesting that it could be much more widespread than has been claimed. We also find that radial migration has a negligible effect on the $\rm [\alpha / Fe]\!-\![Fe / H]$ distribution over time, suggesting that α-bimodality results purely from the presence of different star formation regimes over the galaxy’s formation.

The reduced proper motion selected halo: Methods and description of the catalogue

Context. The Gaia mission has provided the largest ever astrometric chart of the Milky Way. Using it to map the Galactic halo is helpful for disentangling its merger history. Aims. The identification of halo stars in Gaia DR2 with reliable distance estimates requires special methods because such stars are typically farther away and scarce. Methods. We applied the reduced proper motion method to identify halo main sequence stars on the basis of Gaia photometry and proper motions. Using the colour-absolute-magnitude relation for this type of star, we calculated photometric distances. Our selection results in a set of ∼107 tentative main sequence halo stars with typical distance uncertainties of 7% and with median velocity errors of 20 km s−1. The median distance of our sample is ∼4.4 kpc, with the faintest stars located at ∼16 kpc. Results. The spatial distribution of the stars in our sample is centrally concentrated. A visual inspection of the mean velocities of stars on the sky reveals large-scale patterns as well as clear imprints of the GD-1 stream and tentative hints of the Jhelum and Leiptr streams. Incompleteness and selection effects limit our ability to interpret the patterns reliably as well as to identify new substructures. We define a pseudo-velocity space by setting the line-of-sight velocities of our sample stars to zero. In this space, we recover several known structures such as the footprint of Gaia-Enceladus (i.e., the Gaia-Sausage) as well as the Helmi Streams and some other retrograde substructures (Sequoia, Thamnos). We show that the two-point velocity correlation function reveals significant clustering on scales smaller than 100 km s−1 of a similar amplitude as found for the 6D Gaia halo sample. This clumping of stars in velocity space might hint at the presence of nearby streams that are predominantly phase-mixed. Conclusions. A spectroscopic follow-up of our halo main sequence sample is bound to yield unprecedented views of Galactic history and dynamics. In future Gaia data releases, the level of systematics will be reduced and the astrometry will be more precise, which will allow for the identification of more substructures at larger distances.

Jejtsov senzibilitet, Leda i ambivalentnost u "Mračnoj kćeri" Elene Ferante

In Leda and the Swan, one of the greatest Anglophone lyric poets of the 20th century W. B. Yeats explores the idea of a single act having tremendous importance for human history. Such a momentous event can bring about the end of civilization and become the dawn of a new age. This is a great cataclysmic moment in history (merging history and myth) for Yeats. The paper suggests that Yeats's sensibilities subtly permeate the narrative and form of Elena Ferrante's The Lost Daughter, thus illustrating the mode of ambiguous past penetrating the present-the tradition that interested Yeats - arguably becoming what in Ferrante has been seen as a form of radical and committed reflection on myriad of contemporary issues. In this context, Yeats and Ferrante communicate the ideas of fragmentation and instability, the sensation of the world crumbling and reforming, and, in doing so, they refer to an instability of boundaries and identities. This is a sensation experienced by both female protagonists - Yeats's mythical Leda and her more contemporary counterpart.

ASTROSAT/UVIT Near and Far Ultraviolet Properties of the M31 Bulge

AstroSat has surveyed M31 with the UVIT telescope from 2017 to 2019. The central bulge of M31 was observed in 2750 - 2850 A, 2000 - 2400 A, 1600 - 1850 A, 1450 - 1750 A, and 1200 - 1800 A filters. A radial profile analysis, averaged along elliptical contours which approximate the bulge shape, was carried out in each filter. The profiles follow a Sersic function with an excess for the inner ~8" in all filters, or can be fitted with two Sersic functions (including the excess). The ultraviolet colours of the bulge are found to change systematically with radius, with the center of the bulge bluer (hotter). We fit the UVIT spectral energy distributions (SEDs) for the whole bulge and for 10 elliptical annuli with single stellar population (SSP) models. A combination of two SSPs fits the UVIT SEDs much better than one SSP, and three SSPs fit the data best. The properties of the three SSPs are age, metallicity (Z) and mass of each SSP. The best fit model is a dominant old, metal-poor (1010 yr, , with the solar metallicity) population plus a 15% contribution from an intermediate (109.5 yr, ) population plus a small contribution (~2%) from a young high-metallicity (108.5 yr, ) population. The results are consistent with previous studies of M31 in optical: both reveal an active merger history for M31.

On the flaring of thick discs of galaxies: insights from simulations

ABSTRACT Using simulated galaxies in their cosmological context, we analyse how the flaring of mono-age populations (MAPs) influences the flaring and the age structure of geometrically defined thick discs. We also explore under which circumstances the geometric thin and thick discs are meaningfully distinct components, or are part of a single continuous structure as in the Milky Way. We find that flat thick discs are created when MAPs barely flare or have low surface density at the radius where they start flaring. When looking at the vertical distribution of MAPs, these galaxies show a continuous thin/thick structure. They also have radial age gradients and tend to have quiescent merger histories. Those characteristics are consistent with what is observed in the Milky Way. Flared thick discs, on the other hand, are created when the MAPs that flare have a high surface density at the radius where they start flaring. The thick discs’ scale heights can either be dominated by multiple MAPs or just a few, depending on the mass and scale height distribution of the MAPs. In a large fraction of these galaxies, thin and thick discs are clearly distinct structures. Finally, flared thick discs have diverse radial age gradients and merger histories, with galaxies that are more massive or that have undergone massive mergers showing flatter age radial gradients in their thick disc.

Effect of binary evolution on the inferred initial and final core masses of hydrogen-rich, Type II supernova progenitors

The majority of massive stars, which are the progenitors of core-collapse supernovae (SNe), are found in close binary systems. In a previous work, we modeled the fraction of hydrogen-rich, Type II SN progenitors whose evolution is affected by mass exchange with their companion, finding this to be between ≈1/3 and 1/2 for most assumptions. Here we study in more depth the impact of this binary history of Type II SN progenitors on their final pre-SN core mass distribution, using population synthesis simulations. We find that binary star progenitors of Type II SNe typically end their life with a larger core mass than they would have had if they had lived in isolation because they gained mass or merged with a companion before their explosion. The combination of the diverse binary evolutionary paths typically leads to a marginally shallower final core mass distribution. In discussing our results in the context of the red supergiant problem, that is, the reported lack of detected high luminosity progenitors, we conclude that binary evolution does not seem to significantly affect the issue. This conclusion is quite robust against our variations in the assumptions of binary physics. We also predict that inferring the initial masses of Type II SN progenitors by “age-dating” their surrounding environment systematically yields lower masses compared to methods that probe the pre-SN core mass or luminosity. A robust discrepancy between the inferred initial masses of a SN progenitor from those different techniques could indicate an evolutionary history of binary mass accretion or merging.

Scaling relations of fuzzy dark matter haloes – I. Individual systems in their cosmological environment

ABSTRACT Dark matter models involving a very light bosonic particle, generally known as fuzzy dark matter (FDM), have been recently attracting great interest in the cosmology community, as their wave-like phenomenology would simultaneously explain the long-standing misdetection of a dark matter particle and help easing the small-scale issues related to the standard cold dark matter (CDM) scenario. With this work, we initiate a series of papers aiming at investigating the evolution of FDM structures in a cosmological framework performed with our N-body code ax-gadget, detailing for the first time in the literature how the actual scaling relations between solitonic cores and host haloes properties are significantly affected by the dynamical state, morphology, and merger history of the individual systems. In particular, in this first paper we confirm the ability of ax-gadget to correctly reproduce the typical FDM solitonic core and we employ it to study the non-linear evolution of eight FDM haloes in their cosmological context through the zoom-in simulation approach. We find that the scaling relations identified in previous works for isolated systems are generally modified for haloes evolving in a realistic cosmological environment, and appear to be valid only as a limit for the most relaxed and spherically symmetric systems.

Self-interacting dark matter and the delay of supermassive black hole growth

ABSTRACT Using cosmological hydrodynamic simulations with physically motivated models of supermassive black hole (SMBH) formation and growth, we compare the assembly of Milky Way-mass (Mvir ≈ 7 × 1011 M⊙ at z = 0) galaxies in cold dark matter (CDM) and self-interacting dark matter (SIDM) models. Our SIDM model adopts a constant cross-section of 1 cm2 g−1. We find that SMBH formation is suppressed in the early Universe due to SIDM interactions. SMBH–SMBH mergers are also suppressed in SIDM as a consequence of the lower number of SMBHs formed. Lack of initial merger-driven SMBH growth in turn delays SMBH growth by billions of years in SIDM compared to CDM. Further, we find that this delayed growth suppresses SMBH accretion in the largest progenitors of the main SIDM galaxies during the first 5 Gyr of their evolution. Nonetheless, by z = 0.8 the CDM and SIDM SMBH masses differ only by around 0.2 dex, so that both remain compatible with the MBH–M* relation. We show that the reduced accretion causes the SIDM SMBHs to less aggressively regulate star formation in their host galaxies than their CDM counterparts, resulting in a factor of 3 or more stars being produced over the lifetime of the SIDM galaxies compared to the CDM galaxies. Our results highlight a new way in which SIDM can affect the growth and merger history of SMBHs and ultimately give rise to very different galaxy evolution compared to the classic CDM model.