ABSTRACT
We use TNG and EAGLE hydrodynamic simulations to investigate the central galaxy–dark matter halo relations that are needed for a halo-based empirical model of star formation in galaxies. ...Using a linear dimension reduction algorithm and a model ensemble method, we find that for both star-forming and quenched galaxies, the star formation history (SFH) is tightly related to the halo mass assembly history (MAH). The quenching of a low-mass galaxy is mainly due to the infall-ejection process related to a nearby massive halo, while the quenching of a high-mass galaxy is closely related to the formation of a massive progenitor in its host halo. The classification of star-forming and quenched populations based solely on halo properties contains contamination produced by sample imbalance and overlapping distributions of the two populations. Guided by the results from hydrodynamic simulations, we build an empirical model to predict the SFH of central galaxies based on the MAH of their host haloes, and we model the star-forming and quenched populations separately. Our model is based on the idea of adopting star formation templates from hydrodynamic simulations to reduce model complexity. We use various tests to demonstrate that the model can recover SFHs of individual galaxies, and can statistically reproduce the galaxy bimodal distribution, stellar mass–halo mass and star formation rate–halo mass relations from low to high redshift, and assembly bias. Our study provides a framework of using hydrodynamic simulations to discover, and to motivate the use of, key ingredients to model galaxy formation using halo properties.
Cosmic velocity and tidal fields are important for the understanding of the cosmic web and the environments of galaxies, and can also be used to constrain cosmology. In this paper, we reconstruct ...these two fields in the Sloan Digital Sky Survey (SDSS) volume from dark matter haloes represented by galaxy groups. Detailed mock catalogues are used to test the reliability of our method against uncertainties arising from redshift distortions, survey boundaries and false identifications of groups by our group finder. We find that both the velocity and tidal fields, smoothed on a scale of ∼2 h
−1 Mpc, can be reliably reconstructed in the inner region (∼66 per cent) of the survey volume. The reconstructed tidal field is used to split the cosmic web into four categories: clusters, filaments, sheets and voids, depending on the sign of the eigenvalues of local tidal tensor. The reconstructed velocity field nicely shows how the flows are diverging from the centres of voids, and converging on to clusters, while sheets and filaments have flows that are convergent along one and two directions, respectively. We use the reconstructed velocity field and the Zel'dovich approximation to predict the mass density field in the SDSS volume as function of redshift, and find that the mass distribution closely follows the galaxy distribution even on small scales. We find a large-scale bulk flow of about 117 km s−1 in a very large volume, equivalent to a sphere with a radius of ∼170 h
−1 Mpc, which seems to be produced by the massive structures associated with the SDSS Great Wall. Finally, we discuss potential applications of our reconstruction to study the environmental effects of galaxy formation, to generate initial conditions for simulations of the local Universe, and to constrain cosmological models. The velocity, tidal and density fields in the SDSS volume, specified on a Cartesian grid with a spatial resolution of ∼700 h
−1 kpc, are available from the authors upon request.
Using a sample of spiral galaxies selected from the Sloan Digital Sky Survey Data Release 7 and Galaxy Zoo 2, we investigate the alignment of spin axes of spiral galaxies with their surrounding ...large-scale structure, which is characterized by the large-scale tidal field reconstructed from the data using galaxy groups above a certain mass threshold. We find that the spin axes only have weak tendencies to be aligned with (or perpendicular to) the intermediate (or minor) axis of the local tidal tensor. The signal is the strongest in a cluster environment where all three eigenvalues of the local tidal tensor are positive. Compared to the alignments between halo spins and the local tidal field obtained in N-body simulations, the above observational results are in best agreement with those for the spins of inner regions of halos, suggesting that the disk material traces the angular momentum of dark matter halos in the inner regions.
Abstract Using data from ALFALFA, xGASS, H i -MaNGA, and the Sloan Digital Sky Survey (SDSS), we identify a sample of 47 “red but H i -rich” (RR) galaxies with near-UV (NUV) − r > 5 and unusually ...high H i -to-stellar mass ratios. We compare the optical properties and local environments between the RR galaxies and a control sample of “red and H i -normal” (RN) galaxies that are matched in stellar mass and color. The two samples are similar in the optical properties typical of massive red (quenched) galaxies in the local Universe. The RR sample tends to be associated with slightly lower-density environments and has lower clustering amplitudes and smaller neighbor counts at scales from several hundred kiloparsecs to a few megaparsecs. The results are consistent with the RR galaxies being preferentially located at the center of low-mass halos, with a median halo mass ∼10 12 h −1 M ⊙ compared to ∼10 12.5 h −1 M ⊙ for the RN sample. This result is confirmed by the SDSS group catalog, which reveals a central fraction of 89% for the RR sample, compared to ∼60% for the RN sample. If assumed to follow the H i size–mass relation of normal galaxies, the RR galaxies have an average H i -to-optical radius ratio of R HI / R 90 ∼ 4, four times the average ratio for the RN sample. We compare our RR sample with similar samples in previous studies, and quantify the population of RR galaxies using the SDSS complete sample. We conclude that the RR galaxies form a unique but rare population, accounting for only a small fraction of the massive quiescent galaxy population. We discuss the formation scenarios of the RR galaxies.
An intriguing aspect of unconventional superconductivity is that it always appears in the vicinity of other competing phases, whose suppression brings the full emergence of superconductivity. In the ...iron pnictides, these competing phases are marked by a tetragonal-to-orthorhombic structural transition and a collinear spin-density wave (SDW) transition. There has been macroscopic evidence for competition between these phases and superconductivity as the magnitude of both the orthorhombicity and magnetic moment are suppressed in the superconducting state. Here, using angle-resolved photoemission spectroscopy on detwinned underdoped Ba1-x Kx Fe2 As2 , we observe a coexistence of both the SDW gap and superconducting gap in the same electronic structure. Furthermore, our data reveal that following the onset of superconductivity, the SDW gap decreases in magnitude and shifts in a direction consistent with a reduction of the orbital anisotropy. This observation provides direct spectroscopic evidence for the dynamic competition between superconductivity and both SDW and electronic nematic orders in these materials.
ABSTRACT
We present an algorithm to extend subhalo merger trees in a low-resolution dark-matter-only simulation by conditionally matching them to those in a high-resolution simulation. The algorithm ...is general and can be applied to simulation data with different resolutions using different target variables. We instantiate the algorithm by a case in which trees from ELUCID, a constrained simulation of $(500\, h^{-1}\, {\rm Mpc})^3$ volume of the local universe, are extended by matching trees from TNGDark, a simulation with much higher resolution. Our tests show that the extended trees are statistically equivalent to the high-resolution trees in the joint distribution of subhalo quantities and in important summary statistics relevant to modelling galaxy formation and evolution in halos. The extended trees preserve certain information of individual systems in the target simulation, including properties of resolved satellite subhalos, and shapes and orientations of their host halos. With the extension, subhalo merger trees in a cosmological scale simulation are extrapolated to a mass resolution comparable to that in a higher resolution simulation carried out in a smaller volume, which can be used as the input for (sub)halo-based models of galaxy formation. The source code of the algorithm, and halo merger trees extended to a mass resolution of $\sim 2 \times 10^8 \, h^{-1}\, {\rm M_\odot}$ in the entire ELUCID simulation, are available.
We conduct Bayesian model inferences from the observed K-band luminosity function of galaxies in the local Universe, using the semi-analytic model (SAM) of galaxy formation introduced in Lu et al. ...The prior distributions for the 14 free parameters include a large range of possible models. We find that some of the free parameters, e.g. the characteristic scales for quenching star formation in both high-mass and low-mass haloes, are already tightly constrained by the single data set. The posterior distribution includes the model parameters adopted in other SAMs. By marginalizing over the posterior distribution, we make predictions that include the full inferential uncertainties for the colour-magnitude relation, the Tully-Fisher relation, the conditional stellar mass function of galaxies in haloes of different masses, the H i mass function, the redshift evolution of the stellar mass function of galaxies and the global star formation history. Using posterior predictive checking with the available observational results, we find that the model family (i) predicts a Tully-Fisher relation that is curved; (ii) significantly overpredicts the satellite fraction; (iii) vastly overpredicts the H i mass function; (iv) predicts high-z stellar mass functions that have too many low-mass galaxies and too few high-mass ones and (v) predicts a redshift evolution of the stellar mass density and the star formation history that are in moderate disagreement. These results suggest that some important processes are still missing in the current model family, and we discuss a number of possible solutions to solve the discrepancies, such as interactions between galaxies and dark matter haloes, tidal stripping, the bimodal accretion of gas, preheating and a redshift-dependent initial mass function.
We use a complete sample of about 140 000 galaxies from the Sloan Digital Sky Survey (SDSS) to study the size distribution of galaxies and its dependence on their luminosity, stellar mass and ...morphological type. The large SDSS data base provides statistics of unprecedented accuracy. For each type of galaxy, the size distribution at given luminosity (or stellar mass) is well described by a log-normal function, characterized by its median and dispersion σln R. For late-type galaxies, there is a characteristic luminosity at Mr,0∼−20.5 (assuming h= 0.7) corresponding to a stellar mass M0∼ 1010.6 M⊙. Galaxies more massive than M0 have and σln R∼ 0.3, while less massive galaxies have and σln R∼ 0.5. For early-type galaxies, the relation is significantly steeper, , but the σln R–M relation is similar to that of bright late-type galaxies. Faint red galaxies have sizes quite independent of their luminosities. We use simple theoretical models to interpret these results. The observed relation for late-type galaxies can be explained if the fraction of baryons that form stars is as predicted by the standard feedback model. Fitting the observed σln R–M relation requires in addition that the bulge/disc mass ratio be larger in haloes of lower angular momentum and that the bulge material transfers part of its angular momentum to the disc. This can be achieved if bulge formation occurs so as to maintain a marginally stable disc. For early-type galaxies, the observed σln R–M relation is inconsistent with formation through single major mergers of present-day discs. It is consistent with formation through repeated mergers, if the progenitors have properties similar to those of faint ellipticals or Lyman break galaxies and merge from relatively strongly bound orbits.
We develop an empirical approach to infer the star formation rate in dark matter haloes from the galaxy stellar mass function (SMF) at different redshifts and the local cluster galaxy luminosity ...function (CGLF), which has a steeper faint end relative to the SMF of local galaxies. As satellites are typically old galaxies which have been accreted earlier, this feature can cast important constraint on the formation of low-mass galaxies at high redshift. The evolution of the SMFs suggests the star formation in high-mass haloes (>1012 h
−1 M) has to be boosted at high redshift beyond what is expected from a simple scaling of the dynamical time. The faint end of the CGLF implies a characteristic redshift z
c
2 above which the star formation rate in low-mass haloes with masses <1011 h
−1 M must be enhanced relative to that at lower z. This is not directly expected from the standard stellar feedback models. Also, this enhancement leads to some interesting predictions, for instance, a significant old stellar population in present-day dwarf galaxies with M
≤ 108 h
−2 M and steep slopes of high-redshift stellar mass and star formation rate functions.
We use the DR9 of the DESI legacy imaging survey and SDSS galaxy groups to measure the conditional luminosity function (CLF) for groups with halo mass Mh ≥ 1012 M⊙ and redshift 0.01 ≤ z ≤ 0.08, down ...to a limiting r-band magnitude of Mr = −10 to −12. For given halo masses we measure the CLF for the total populations and for the red and blue populations classified using the (g − z) color. We find a clear faint-end upturn in the CLF of red satellites, with a slope α ≈ −1.8, which is almost independent of halo mass. This faint-end upturn is not seen for the blue and total populations. Our stellar population synthesis modeling shows that (g − z) provides a clean red/blue division and that red group galaxies defined by (g − z) are all dominated by old stellar populations. The fraction of old galaxies as a function of galaxy luminosity shows a minimum at Mr ∼ −18, corresponding to M* ∼ 109.5 M⊙. This scale is independent of halo mass and is comparable to the characteristic luminosity at which galaxies show a dichotomy in surface brightness and size, suggesting that the dichotomy in the old fraction and in galaxy structure may have a common origin. The rising of the old fraction at the faint end for Milky Way (MW)−sized halos is in good agreement with the quenched fraction measured for the MW/M31 system and from the ELVES survey. We discuss the implications of our results for the formation and evolution of low-mass galaxies and for the stellar mass functions of low-mass galaxies to be observed at high redshift.
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