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Register a new userA sparse regression approach to modeling the relation between galaxy stellar masses and their host halos
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Added by
Miguel Icaza-Lizaola Mr.
Publication date
2021
fields
Physics
and research's language is
English
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Sparse regression algorithms have been proposed as the appropriate framework to model the governing equations of a system from data, without needing prior knowledge of the underlying physics. In this work, we use sparse regression to build an accurate and explainable model of the stellar mass of central galaxies given properties of their host dark matter (DM) halo. Our data set comprises 9,521 central galaxies from the EAGLE hydrodynamic simulation. By matching the host halos to a DM-only simulation, we collect the halo mass and specific angular momentum at present time and for their main progenitors in 10 redshift bins from $z=0$ to $z=4$. The principal component of our governing equation is a third-order polynomial of the host halo mass, which models the stellar-mass halo-mass relation. The scatter about this relation is driven by the halo mass evolution and is captured by second and third-order correlations of the halo mass evolution with the present halo mass. An advantage of sparse regression approaches is that unnecessary terms are removed. Although we include information on halo specific angular momentum, these parameters are discarded by our methodology. This suggests that halo angular momentum has little connection to galaxy formation efficiency. Our model has a root mean square error (RMSE) of $0.167 log_{10}(M^*/M_odot)$, and accurately reproduces both the stellar mass function and central galaxy correlation function of EAGLE. The methodology appears to be an encouraging approach for populating the halos of DM-only simulations with galaxies, and we discuss the next steps that are required.
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Existing models of galaxy formation have not yet explained striking correlations between structure and star-formation activity in galaxies, notably the sloped and moving boundaries that divide star-forming from quenched galaxies in key structural diagrams. This paper uses these and other relations to ``reverse-engineer the quenching process for central galaxies. The basic idea is that star-forming galaxies with larger radii (at a given stellar mass) have lower black-hole masses due to lower central densities. Galaxies cross into the green valley when the cumulative effective energy radiated by their black hole equals $sim4times$ their halo-gas binding energy. Since larger-radii galaxies have smaller black holes, one finds they must evolve to higher stellar masses in order to meet this halo-energy criterion, which explains the sloping boundaries. A possible cause of radii differences among star-forming galaxies is halo concentration. The evolutionary tracks of star-forming galaxies are nearly parallel to the green-valley boundaries, and it is mainly the sideways motions of these boundaries with cosmic time that cause galaxies to quench. BH-scaling laws for star-forming, quenched, and green-valley galaxies are different, and most BH mass growth takes place in the green valley. Implications include: the radii of star-forming galaxies are an important second parameter in shaping their black holes; black holes are connected to their halos but in different ways for star-forming, quenched, and green-valley galaxies; and the same BH-halo quenching mechanism has been in place since $z sim 3$. We conclude with a discussion of black hole-galaxy co-evolution, the origin and interpretation of BH scaling laws.
The age distributions of stellar cluster populations have long been proposed to probe the recent formation history of the host galaxy. However, progress is hampered by the limited understanding of cluster disruption by evaporation and tidal shocks. We study the age distributions of clusters in smoothed particle hydrodynamics simulations of isolated disc galaxies, which include a self-consistent, physical model for the formation and dynamical evolution of the cluster population and account for the variation of cluster disruption in time and space. We show that the downward slope of the cluster age distribution due to disruption cannot be reproduced with a single functional form, because the disruption rate exhibits systematic trends with cluster age (the `cruel cradle effect). This problem is resolved by using the median cluster age to trace cluster disruption. Across 120 independent galaxy snapshots and simulated cluster populations, we perform two-dimensional power law fits of the median cluster age to various macroscopic physical quantities and find that it scales as $t_{rm med}propto Sigma^{-0.51pm0.03}sigma_{rm 1D}^{-0.85pm0.10}M_{rm min}^gamma$, for the gas surface density $Sigma$, gas velocity dispersion $sigma_{rm 1D}$, and minimum cluster mass $M_{rm min}$. This scaling accurately describes observed cluster populations and indicates disruption by impulsive tidal shocks from the interstellar medium. The term $M_{rm min}^gamma$ provides a model-independent way to measure the mass dependence of the cluster disruption time $gamma$. Finally, the ensemble-average cluster lifetime depends on the gas density less strongly than the instantaneous disruption time of single clusters. These results reflect the variation of cluster disruption in time and space. We provide quantitative ways of accounting for these physics in cluster population studies.
Supermassive black holes and/or very dense stellar clusters are found in the central regions of galaxies. Nuclear star clusters are present mainly in faint galaxies while upermassive black holes are common in galaxies with masses $geq 10^{10}$ M$_odot $. In the intermediate galactic mass range both types of central massive objects (CMOs) are found. Here we present our collection of a huge set of nuclear star cluster and massive black hole data that enlarges significantly already existing data bases useful to investigate for correlations of their absolute magnitudes, velocity dispersions and masses with structural parameters of their host galaxies. In particular, we directed our attention to some differences between the correlations of nuclear star clusters and massive black holes as subsets of CMOs with hosting galaxies. In this context, the mass-velocity dispersion relation plays a relevant role because it seems the one that shows a clearer difference between the supermassive black holes and nuclear star clusters. The $M_{MBH}-{sigma}$ has a slope of $5.19pm 0.28$ while $M_{NSC}-{sigma}$ has the much smaller slope of $1.84pm 0.64$. The slopes of the CMO mass- host galaxy B magnitude of the two types of CMOs are indistinguishable within the errors while that of the NSC mass-host galaxy mass relation is significantly smaller than for supermassive black holes. Another important result is the clear depauperation of the NSC population in bright galaxy hosts, which reflects also in a clear flattening of the NSC mass vs host galaxy mass at high host masses.
We derive the stellar-to-halo mass relation (SHMR), namely $f_starpropto M_star/M_{rm h}$ versus $M_star$ and $M_{rm h}$, for early-type galaxies from their near-IR luminosities (for $M_star$) and the position-velocity distributions of their globular cluster systems (for $M_{rm h}$). Our individual estimates of $M_{rm h}$ are based on fitting a dynamical model with a distribution function expressed in terms of action-angle variables and imposing a prior on $M_{rm h}$ from the concentration-mass relation in the standard $Lambda$CDM cosmology. We find that the SHMR for early-type galaxies declines with mass beyond a peak at $M_starsim 5times 10^{10}M_odot$ and $M_{rm h}sim 10^{12}M_odot$ (near the mass of the Milky Way). This result is consistent with the standard SHMR derived by abundance matching for the general population of galaxies, and with previous, less robust derivations of the SHMR for early types. However, it contrasts sharply with the monotonically rising SHMR for late types derived from extended HI rotation curves and the same $Lambda$CDM prior on $M_{rm h}$ as we adopt for early types. The SHMR for massive galaxies varies more or less continuously, from rising to falling, with decreasing disc fraction and decreasing Hubble type. We also show that the different SHMRs for late and early types are consistent with the similar scaling relations between their stellar velocities and masses (Tully-Fisher and Faber-Jackson relations). Differences in the relations between the stellar and halo virial velocities account for the similarity of the scaling relations. We argue that all these empirical findings are natural consequences of a picture in which galactic discs are built mainly by smooth and gradual inflow, regulated by feedback from young stars, while galactic spheroids are built by a cooperation between merging, black-hole fuelling, and feedback from AGNs.
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