65 research outputs found
Symfind: Addressing the Fragility of Subhalo Finders and Revealing the Durability of Subhalos
A major question in CDM is what this theory actually predicts for
the properties of subhalo populations. Subhalos are difficult to simulate and
to find within simulations, and this propagates into uncertainty in theoretical
predictions for satellite galaxies. We present Symfind, a new
particle-tracking-based subhalo finder, and demonstrate that it can track
subhalos to orders-of-magnitude lower masses than commonly used halo-finding
tools, with a focus on Rockstar and consistent-trees. These longer survival
mean that at a fixed peak subhalo mass, we find more
subhalos within the virial radius, , and
more subhalos within in the Symphony dark-matter-only
simulation suite. More subhalos are found as resolution is increased. We
perform extensive numerical testing. In agreement with idealized simulations,
we show that the of subhalos is only resolved at high resolutions
(), but that mass loss itself can be
resolved at much more modest particle counts (). We show that Rockstar converges to false solutions for the mass
function, radial distribution, and disruption masses of subhalos. We argue that
our new method can trace resolved subhalos until the point of typical galaxy
disruption without invoking ``orphan'' modeling. We outline a concrete set of
steps for determining whether other subhalo finders meet the same criteria. We
publicly release Symfind catalogs and particle data for the Symphony simulation
suite at \url{http://web.stanford.edu/group/gfc/symphony}.Comment: 45 pages, 19 figure
Association discovery and outlier detection of air pollution emissions from industrial enterprises driven by big data
ABSTRACTAir pollution is a major issue related to national economy and people's livelihood. At present, the researches on air pollution mostly focus on the pollutant emissions in a specific industry or region as a whole, and is a lack of attention to enterprise pollutant emissions from the micro level. Limited by the amount and time granularity of data from enterprises, enterprise pollutant emissions are still understudied. Driven by big data of air pollution emissions of industrial enterprises monitored in Beijing-Tianjin-Hebei, the data mining of enterprises pollution emissions is carried out in the paper, including the association analysis between different features based on grey association, the association mining between different data based on association rule and the outlier detection based on clustering. The results show that: (1) The industries affecting NOx and SO2 mainly are electric power, heat production and supply industry, metal smelting and processing industries in Beijing-Tianjin-Hebei; (2) These districts nearby Hengshui and Shijiazhuang city in Hebei province form strong association rules; (3) The industrial enterprises in Beijing-Tianjin-Hebei are divided into six clusters, of which three categories belong to outliers with excessive emissions of total VOCs, PM and NH3 respectively
UniverseMachine: Predicting Galaxy Star Formation over Seven Decades of Halo Mass with Zoom-in Simulations
We apply the empirical galaxy--halo connection model UniverseMachine to dark
matter-only zoom-in simulations of isolated Milky Way (MW)--mass halos along
with their parent cosmological simulations. This application extends
\textsc{UniverseMachine} predictions into the ultra-faint dwarf galaxy regime
() and yields a well-resolved stellar mass--halo mass
(SMHM) relation over the peak halo mass range to
. The extensive dynamic range provided by the
zoom-in simulations allows us to assess specific aspects of dwarf galaxy
evolution predicted by \textsc{UniverseMachine}. In particular, although
UniverseMachine is not constrained for dwarf galaxies with , our predicted SMHM relation is consistent with
that inferred for MW satellite galaxies at using abundance matching.
However, UniverseMachine predicts that nearly all galaxies are actively star
forming below and that these systems
typically form more than half of their stars at , which is
discrepant with the star formation histories of Local Group dwarf galaxies that
favor early quenching. This indicates that the current UniverseMachine model
does not fully capture galaxy quenching physics at the low-mass end. We
highlight specific improvements necessary to incorporate environmental and
reionization-driven quenching for dwarf galaxies, and provide a new tool to
connect dark matter accretion to star formation over the full dynamic range
that hosts galaxies.Comment: Accepted for publication in ApJ. 21 pages, 8 figures, 1 table. Minor
edits to v1. Added discussion of reionization contribution of ultra-faint
dwarfs in sections 4.4 and
X-ray scaling relations of early-type galaxies in IllustrisTNG and a new way of identifying backsplash objects
We investigate how feedback and environment shapes the X-ray scaling
relations of early-type galaxies (ETGs), especially at the low-mass end. We
select central-ETGs from the IllustrisTNG-100 box that have stellar masses
. We derive mock X-ray
luminosity () and spectroscopic-like temperature
() of hot gas within of the ETG haloes using
the MOCK-X pipeline. The scaling between and the total
mass within 5 effective radii () agrees well with observed ETGs
from Chandra. IllustrisTNG reproduces the observed increase in scatter of
towards lower masses, and we find that ETGs with
with
above-average experienced systematically lower cumulative
kinetic AGN feedback energy historically (vice versa for below-average ETGs).
This leads to larger gas mass fractions and younger stellar populations with
stronger stellar feedback heating, concertedly resulting in the above-average
. The --
relation shows a similar slope to the observed ETGs but the simulation
systematically underestimates the gas temperature. Three outliers that lie far
below the -- relation all interacted with larger galaxy
clusters recently and demonstrate clear features of environmental heating. We
propose that the distinct location of these backsplash ETGs in the -- plane could provide a new way of identifying backsplash
galaxies in future X-ray surveys.Comment: 16 pages, 10 figures. Submitted to MNRA
Early-type galaxy density profiles from IllustrisTNG – II. Evolutionary trend of the total density profile
We study the evolutionary trend of the total density profile of early-type galaxies (ETGs) in IllustrisTNG. To this end, we trace ETGs from z = 0 to 4 and measure the power-law slope γ′ of the total density profile for their main progenitors. We find that their slopes γ′ steepen on average during z ∼ 4–2, then becoming shallower until z = 1, after which they remain almost constant, aside from a residual trend of becoming shallower towards z = 0. We also compare to a statistical sample of ETGs at different redshifts, selected based on their luminosity profiles and stellar masses. Due to different selection effects, the average slopes of the statistical samples follow a modified evolutionary trend. They monotonically decrease since z = 3, and after z ≈ 1, they remain nearly invariant with a mild increase towards z = 0. These evolutionary trends are mass dependent for both samples, with low-mass galaxies having in general steeper slopes than their more massive counterparts. Galaxies that transitioned to ETGs more recently have steeper mean slopes as they tend to be smaller and more compact at any given redshift. By analysing the impact of mergers and AGN feedback on the progenitors’ evolution, we conjecture a multiphase path leading to isothermality in ETGs: dissipation associated with rapid wet mergers tends to steepen γ′ from z = 4 to 2, whereas subsequent AGN feedback (especially in the kinetic mode) makes γ′ shallower again from z = 2 to 1. Afterwards, passive evolution from z = 1 to 0, mainly through gas-poor mergers, mildly decreases γ′ and maintains the overall mass distribution close to isothermal
Early-type galaxy density profiles from IllustrisTNG: I. Galaxy correlations and the impact of baryons
We explore the isothermal total density profiles of early-type galaxies
(ETGs) in the IllustrisTNG simulation. For the selected 559 ETGs at
with stellar mass , the total power-law slope has a mean of
and a scatter of
over the radial range 0.4 to 4 times the
stellar half mass radius. Several correlations between and
galactic properties including stellar mass, effective radius, stellar surface
density, central velocity dispersion, central dark matter fraction and
in-situ-formed stellar mass ratio are compared to observations and other
simulations, revealing that IllustrisTNG reproduces many correlation trends,
and in particular, is almost constant with redshift below . Through analyzing IllustrisTNG model variations we show that black hole
kinetic winds are crucial to lowering and matching observed
galaxy correlations. The effects of stellar winds on are
subdominant compared to AGN feedback, and differ due to the presence of AGN
feedback from previous works. The density profiles of the ETG dark matter halos
are well-described by steeper-than-NFW profiles, and they are steeper in the
full physics (FP) run than their counterparts in the dark matter only (DMO)
run. Their inner density slopes anti-correlates (remain constant) with the halo
mass in the FP (DMO) run, and anti-correlates with the halo concentration
parameter in both types of runs. The dark matter halos of low-mass
ETGs are contracted whereas high-mass ETGs are expanded, suggesting that
variations in the total density profile occur through the different halo
responses to baryons.Comment: 31 pages, 20 figures, 9 tables. Accepted for publication in MNRAS.
Major revision, added the effects of feedback on the total density profile in
Section 4. Pay attention to changes in Figures 7, 10, 12, and 1
Poly(lactic acid)/cellulose nanocrystal composites via the Pickering emulsion approach: Rheological, thermal and mechanical properties
The use of nanocellulose is an attractive method to improve the characteristics of biodegradable polymers, but its effects are often affected by uneven dispersion. In this work, cellulose nanocrystals (CNCs) were evenly dispersed into poly(lactic acid) (PLA) via the Pickering emulsion approach. The PLA/CNC composites prepared were studied by rheological, thermal as well as mechanical measurements. Changes in the rheological characteristics of the composites showed that CNC promoted the transition of the composites from fluid to solid-like behavior at high temperatures. The introduction of 5 wt% CNC improved the crystallinity of PLA considerably and increased the onset temperature of crystallization by about 10 °C. The storage modulus of the composites increased throughout the entire temperature range of testing. Flexural modulus was improved considerably. All the results indicated that the Pickering emulsion approach improved the dispersion of CNC in the PLA matrix and CNC improved efficiently most properties of PLA
SDSS-IV MaNGA: the inner density slopes of nearby galaxies
We derive the mass-weighted total density slopes within the effective (half-light) radius, γ′, for more than 2000 nearby galaxies from the SDSS-IV (Sloan Digital Sky Survey IV) MaNGA survey using Jeans-anisotropic-models applied to integral field unit observations. Our galaxies span a wide range of the stellar mass (109 M⊙ 100 km s−1, the density slope has a mean value 〈γ′〉 = 2.24 and a dispersion σγ = 0.22, almost independent of velocity dispersion, consistent with previous lensing and stellar dynamical analysis. We also quantitatively confirm with high accuracy a turnover in the γ′–σv relation is present at σ ∼ 100 km s−1, below which the density slope decreases rapidly with σv, consistent with the results reported by previous analysis of ATLAS3D survey. Our analysis shows that a large fraction of dwarf galaxies (below M* = 1010 M⊙) have total density slopes shallower than 1, which implies that they may reside in cold dark matter haloes with shallow density slopes. We compare our results with that of galaxies in hydrodynamical simulations of EAGLE, Illustris, and IllustrisTNG projects, and find all simulations predict shallower density slopes for massive galaxies with high σv. Finally, we explore the dependence of γ′ on the positions of galaxies in haloes, namely centrals versus satellites, and find that for the same velocity dispersion, the amplitude of γ′ is higher for satellite galaxies by about 0.1
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