arXiv subjects

Shengdong Lu

Publications and source records attributed to Shengdong Lu.

34 records · Page 2Linked to original sources

arXiv2023

Kinematical coherence between satellite galaxies and host stellar discs for MaNGA & SAMI galaxies

The effect of angular momentum on galaxy formation and evolution has been studied for several decades. Our recent two papers using IllustrisTNG-100 simulation have revealed the acquisition path of the angular momentum from large-scale environment (satellites within hundreds of kpc) through the circum-galactic medium (CGM) to the stellar discs, putting forward the co-rotation scenario across the three distance scales. In real observations, although the rotation signature for the CGM and environmental three-dimensional (3d) angular momentum are difficult to obtain, line-of-sight kinematics of group member galaxies and stellar disc kinematics of central galaxies are available utilizing existing group catalogue data and integral field unit (IFU) data. In this paper, we use (1) the group catalogue of SDSS DR7 and MaNGA IFU stellar kinematic maps and (2) the group catalogue of GAMA DR4 data and SAMI IFU stellar kinematic maps, to test if the prediction above can be seen in real data. We found the co-rotation pattern between stellar discs and satellites can be concluded with 99.7 percent confidence level ($\sim 3σ$) when combining the two datasets. And the random tests show that the signal can be scarcely drawn from random distribution.

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arXiv2023

MaNGA DynPop -- III. Stellar dynamics versus stellar population relations in 6000 early-type and spiral galaxies: Fundamental Plane, mass-to-light ratios, total density slopes, and dark matter fractions

We present dynamical scaling relations, combined with the stellar population properties, for a subsample of about 6000 nearby galaxies with the most reliable dynamical models extracted from the full MaNGA sample of 10K galaxies. We show that the inclination-corrected mass plane (MP) for both early-type galaxies (ETGs) and late-type galaxies (LTGs), which links dynamical mass, projected half-light radius $R_{\rm e}$, and the second stellar velocity moment $σ_{\rm e}$ within $R_{\rm e}$, satisfies the virial theorem and is even tighter than the uncorrected one. We find a clear parabolic relation between $\lg(M/L)_{\rm e}$, the total mass-to-light ratio within a sphere of radius $R_{\rm e}$, and $\lgσ_{\rm e}$, with the $M/L$ increasing with $σ_{\rm e}$ and for older stellar populations. However, the relation for ETGs is linear and the one for the youngest galaxies is constant. We confirm and improve the relation between average logarithmic total density slopes $\overline{γ_{\rm T}}$ and $σ_{\rm e}$: $\overline{γ_{\rm T}}$ become steeper with increasing $σ_{\rm e}$ until $\lg(σ_{\rm e}/{\rm km\,s^{-1}})\approx 2.2$ and then remain constant around $\overline{γ_{\rm T}}\approx -2.2$. The $\overline{γ_{\rm T}}-σ_{\rm e}$ variation is larger for LTGs than ETGs. At fixed $σ_{\rm e}$ the total density profiles steepen with galaxy age and for ETGs. We find generally low dark matter fractions, median $f_{\rm DM}(<R_{\rm e})=8$ per cent, within a sphere of radius $R_{\rm e}$. However, we find that $f_{\rm DM}(<R_{\rm e})$ depends on $σ_{\rm e}$ better than stellar mass: dark matter increases to a median $f_{\rm DM}(<R_{\rm e})=33$ percent for galaxies with $σ_{\rm e}\lesssim100{\rm km\,s^{-1}}$. The increased $f_{\rm DM}(<R_{\rm e})$ at low $σ_{\rm e}$ explains the parabolic $\lg(M/L)_{\rm e}-\lgσ_{\rm e}$ relation.

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arXiv2023

MaNGA DynPop -- II. Global stellar population, gradients, and star-formation histories from integral-field spectroscopy of 10K galaxies: link with galaxy rotation, shape, and total-density gradients

This is the second paper of the MaNGA DynPop series, which analyzes the global stellar population, radial gradients, and non-parametric star-formation history of $\sim 10$K galaxies from the MaNGA Survey final data release 17 (DR17) and relates them with dynamical properties of galaxies. We confirm the correlation between the stellar population properties and the stellar velocity dispersion $σ_{\rm e}$, but also find that younger galaxies are more metal-poor at fixed $σ_{\rm e}$. Stellar age, metallicity, and mass-to-light ratio $M_{\ast}/L$ all decrease with increasing galaxy rotation, while their radial gradients become more negative (i.e. lower value at the outskirts). The exception is the slow rotators, which also appear to have significantly negative metallicity gradients, confirming the mass-metallicity gradient correlation. Massive disk galaxies in the green valley, on the $(σ_{\rm e},\rm Age)$ plane, show the most negative age and metallicity gradients, consistent with their old central bulges surrounded by young star-forming disks and metal-poor gas accretion. Galaxies with high $σ_{\rm e}$, steep total mass-density slope, low dark matter fraction, high $M_{\ast}/L$, and high metallicity have the highest star-formation rate at earlier times, and are currently quenched. We also discover a population of low-mass star-forming galaxies with low rotation but physically distinct from the massive slow rotators. A catalogue of these stellar population properties is provided publicly.

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arXiv2023

A complete catalogue of broad-line AGNs and double-peaked emission lines from MaNGA integral-field spectroscopy of 10K galaxies: stellar population of AGNs, supermassive black holes, and dual AGNs

We analyse the integral-field spectroscopy data for the $\approx10,000$ galaxies in final data release of the MaNGA survey. We identify 188 galaxies for which the emission lines cannot be described by single Gaussian components. These galaxies can be classified into (1) 38 galaxies with broad $Hα$ and [OIII] $λ$5007 lines, (2) 101 galaxies with broad $Hα$ lines but no broad [OIII] $λ$5007 lines, and (3) 49 galaxies with double-peaked narrow emission lines. Most of the broad line galaxies are classified as Active Galactic Nuclei (AGN) from their line ratios. The catalogue helps us further understand the AGN-galaxy coevolution through the stellar population of broad-line region host galaxies and the relation between broad lines' properties and the host galaxies' dynamical properties. The stellar population properties (including mass, age and metallicity) of broad-line host galaxies suggest there is no significant difference between narrow-line Seyfert-2 galaxies and Type-1 AGN with broad $Hα$ lines. We use the broad-$Hα$ line width and luminosity to estimate masses of black hole in these galaxies, and test the $M_{BH}-σ_{e}$ relation in Type-1 AGN host galaxies. Furthermore we find three dual AGN candidates supported by radio images from the VLA FIRST survey. This sample may be useful for further studies on AGN activities and feedback processes.

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arXiv2023

Velocity Dispersion $σ_{\rm aper}$ Aperture Corrections as a Function of Galaxy Properties from Integral-field Stellar Kinematics of 10,000 MaNGA Galaxies

The second moment of the stellar velocity within the effective radius, denoted by $σ_{\rm e}^2$, is a crucial quantity in galaxy studies as it provides insight into galaxy properties and their mass distributions. However, large spectroscopic surveys typically do not measure $σ_{\rm e}$ directly, instead providing $σ_{\rm aper}$, the second moment of the stellar velocity within a fixed fiber aperture. In this paper, we derive an empirical aperture correction formula, given by $σ_{\rm aper}/σ_{\rm e}=(R_{\rm aper}/R_{\rm e})^α$, using spatially resolved stellar kinematics extracted from approximately 10,000 Sloan Digital Sky Survey-Mapping Nearby Galaxies at Apache Point Observatory (SDSS-MaNGA) integral field unit observations. Our analysis reveals a strong dependence of $α$ on the $r$-band absolute magnitude $M_{\rm r}$, $g-i$ color, and Sersic index $n_{\rm Ser}$, where $α$ values are lower for brighter, redder galaxies with higher Sersic indices. Our results demonstrate that the aperture correction derived from previous literature on early-type galaxies cannot be applied to predict the aperture corrections for galaxies with intermediate Sersic indices. We provide a lookup table of $α$ values for different galaxy types, with parameters in the ranges of $-18>M_{\rm r}>-24$, $0.4<g-i<1.6$, and $0<n_{\rm Ser}<8$. A Python script is provided to obtain the correction factors from the lookup table.

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arXiv2023

MaNGA DynPop -- I. Quality-assessed stellar dynamical modelling from integral-field spectroscopy of 10K nearby galaxies: a catalogue of masses, mass-to-light ratios, density profiles and dark matter

This is the first paper in our series on the combined analysis of the Dynamics and stellar Population (DynPop) for the MaNGA survey in the final SDSS Data Release 17 (DR17). Here we present a catalogue of dynamically-determined quantities for over 10000 nearby galaxies based on integral-field stellar kinematics from the MaNGA survey. The dynamical properties are extracted using the axisymmetric Jeans Anisotropic Modelling (JAM) method, which was previously shown to be the most accurate for this kind of study. We assess systematic uncertainties using eight dynamical models with different assumptions. We use two orientations of the velocity ellipsoid: either cylindrically-aligned JAM$_{\rm cyl}$ or spherically-aligned JAM$_{\rm sph}$. We also make four assumptions for the models' dark vs. luminous matter distributions: (1) mass-follows-light, (2) free NFW dark halo, (3) cosmologically-constrained NFW halo, (4) generalized NFW dark halo, i.e. with free inner slope. In this catalogue, we provide the quantities related to the mass distributions (e.g. the density slopes and enclosed mass within a sphere of a given radius for total mass, stellar mass, and dark matter mass components). We also provide the complete models which can be used to compute the full luminous and mass distribution of each galaxy. Additionally, we visually assess the qualities of the models to help with model selections. We estimate the observed scatter in the measured quantities which decreases as expected with improvements in quality. For the best data quality, we find a remarkable consistency of measured quantities between different models, highlighting the robustness of the results.

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arXiv2021

From large-scale environment to CGM angular momentum to star forming activities -- I: star-forming galaxies

The connection between halo gas acquisition through the circumgalactic medium (CGM) and galaxy star formation has long been studied. In this series of two papers, we put this interplay within the context of the galaxy environment on large scales (several hundreds of kpc), which, to a certain degree, maps out various paths for galaxy interactions. We use the IllustrisTNG-100 simulation to demonstrate that the large-scale environment modulates the circumgalactic gas angular momentum, resulting in either enhanced (Paper I) or suppressed (Paper II) star formation inside a galaxy. In this paper (Paper I), we show that the large-scale environment around a star-forming galaxy is often responsible for triggering new episodes of star formation. Such an episodic star formation pattern is well synced with a pulsating motion of the circumgalactic gas, which, on the one hand receives angular momentum modulations from the large-scale environment, yielding in-spiralling gas to fuel the star-forming reservoir, while, on the other hand, is affected by the feedback activities from the galaxy centre. As a result, a present-day star-forming galaxy may have gone through several cycles of star-forming and quiescent phases during its evolutionary history, with the circumgalactic gas carrying out a synchronized cadence of "breathing in and out" motions out to $\sim 100$ kpc.

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arXiv2021

From large-scale environment to CGM angular momentum to star forming activities -- II: quenched galaxies

The gas needed to sustain star formation in galaxies is supplied by the circumgalactic medium (CGM), which in turn is affected by accretion from large scales. In a series of two papers, we examine the interplay between a galaxy's ambient CGM and central star formation within the context of the large-scale environment. We use the IllustrisTNG-100 simulation to show that the influence exerted by the large-scale galaxy environment on the CGM gas angular momentum results in either enhanced (Paper I) or suppressed (Paper II, this paper) star formation inside a galaxy. We find that for present-day quenched galaxies, both the large-scale environments and the ambient CGM have always had higher angular momenta throughout their evolutionary history since at least $z=2$, in comparison to those around present-day star-forming disk galaxies, resulting in less efficient gas inflow into the central star-forming gas reservoirs. A sufficiently high CGM angular momentum, as inherited from the larger-scale environment, is thus an important factor in keeping a galaxy quenched, once it is quenched. The process above naturally renders two key observational signatures: (1) a coherent rotation pattern existing across multiple distances from the large-scale galaxy environment, to the circumgalactic gas, to the central stellar disk; and (2) an anti-correlation between galaxy star-formation rates and orbital angular momenta of interacting galaxy pairs or groups.

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arXiv2021

Quenched, bulge-dominated, but dynamically cold galaxies in IllustrisTNG and their real-world counterparts

Galaxy morphologies, kinematics, and stellar populations are thought to be linked to each other. However, both simulations and observations have pointed out mismatches therein. In this work, we study the nature and origin of the present-day quenched, bulge-dominated, but dynamically cold galaxies within a stellar mass range of $10.3\,\leqslant\,\log\,M_{\ast}/\mathrm{M_{\odot}}\,\leqslant\,11.2$ in the IllustrisTNG-100 Simulation. We compare these galaxies with a population of normal star-forming dynamically cold disc galaxies and a population of normal quenched dynamically hot elliptical galaxies within the same mass range. The populations of the present-day quenched and bulge-dominated galaxies (both being dynamically cold and hot) used to have significantly higher star-formation rates and flatter morphologies at redshift of $z\sim 2$. They have experienced more frequent larger mass-ratio mergers below $z \sim 0.7$ in comparison to their star-forming disc counterparts, which is responsible for the formation of their bulge-dominated morphologies. The dynamically cold populations (both being star-forming and quenched) have experienced more frequent prograde and tangential mergers especially below $z \sim 1$, in contrast to the dynamically hot ellipticals, which have had more retrograde and radial mergers. Such different merging histories can well explain the differences on the cold and hot dynamical status among these galaxies. We point out that the real-world counterparts of these dynamically cold and hot bulge-dominated quenched populations are the fast- and slow-rotating early-type galaxies, respectively, as seen in observations and hence reveal the different evolution paths of these two distinct populations of early-type galaxies.

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arXiv2021

Hot and counter-rotating star-forming disk galaxies in IllustrisTNG and their real-world counterparts

A key feature of a large population of low-mass, late-type disk galaxies are star-forming disks with exponential light distributions. They are typically also associated with thin and flat morphologies, blue colors, and dynamically cold stars moving along circular orbits within co-planar thin gas disks. However, the latter features do not necessarily always imply the former, in fact, a variety of different kinematic configurations do exist. In this work, we use the cosmological hydrodynamical IllustrisTNG Simulation to study the nature and origin of dynamically hot, sometimes even counter-rotating, star-forming disk galaxies in the lower stellar mass range (between $5\times 10^9\,\mathrm{M_{\odot}}$ and $2\times 10^{10}\,\mathrm{M_{\odot}}$). We find that being dynamically hot arises in most cases as an induced transient state, for example due to galaxy interactions and merger activities, rather than as an age-dependent evolutionary phase of star-forming disk galaxies. The dynamically hot but still actively star-forming disks show a common feature of hosting kinematically misaligned gas and stellar disks, and centrally concentrated on-going star formation. The former is often accompanied by disturbed gas morphologies, while the latter is reflected in low gas and stellar spins in comparison to their dynamically cold, normal disk counterparts. Interestingly, observed galaxies from MaNGA with kinematic misalignment between gas and stars show remarkably similar general properties as the IllustrisTNG galaxies, and therefore are plausible real-world counterparts. In turn, this allows us to make predictions for the stellar orbits and gas properties of these misaligned galaxies.

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arXiv2021

Stellar Dynamical Modeling - Accuracy of 3D Density Estimation for Edge-on Axisymmetric Galaxies

From Rybicki's analysis using the Fourier slice theorem, mathematically it is possible to reproduce uniquely an edge-on axisymmetric galaxy's 3D light distribution from its 2D surface brightness. Utilizing galaxies from a cosmological simulation, we examine the ability of Syer and Tremaine's made-to-measure method and Schwarzschild's method for stellar dynamical modeling to do so for edge-on oblate axisymmetric galaxies. Overall, we find that the methods do not accurately recover the 3D distributions, with the made-to-measure method producing more accurate estimates than Schwarzschild's method. Our results have implications broader than just luminosity density, and affect other luminosity-weighted distributions within galaxies, for example, age and metallicity.

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arXiv2020

SDSS-IV MaNGA: Stellar population correlates with stellar root-mean-square velocity $V_{\rm rms}$ gradients or total-density-profile slopes at fixed effective velocity dispersion $σ_{\rm e}$

Galaxy properties are known to correlate most tightly with the galaxy effective stellar velocity dispersion $σ_{\rm e}$. Here we look for {\em additional} trends at fixed $σ_{\rm e}$ using 1339 galaxies ($M_\ast \gtrsim 6\times10^9$ M$_\odot$) with different morphologies in the MaNGA (DR14) sample with integral-field spectroscopy data. We focus on the gradients ($γ_{\rm rms} \equiv σ(R_{\rm e}/4)/σ_{\rm e}$) of the stellar root-mean-square velocity ($V_{\rm rms} \equiv \sqrt{V^2 + σ^2}$), which we show traces the total mass density gradient $γ_{\rm tot}$ derived from dynamical models and, more weakly, the bulge fraction. We confirm that $γ_{\rm rms}$ increases with $σ_{\rm e}$, age and metallicity. We additionally find that these correlations still exist at fixed $σ_{\rm e}$, where galaxies with larger $γ_{\rm rms}$ are found to be older and more metal-rich. It means that mass density gradients contain information of the stellar population which is not fully accounted for by $σ_{\rm e}$. This result puts an extra constraint on our understanding of galaxy quenching. We compare our results with galaxies in the IllustrisTNG hydrodynamical simulations and find that, at fixed $σ_{\rm e}$, similar trends exist with age, the bulge fraction, and the total mass density slope but, unlike observations, no correlation with metallicity can be detected in the simulations.

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arXiv2020

Star Formation in Massive Galaxies at Redshift $z \sim 0.5$

It is believed that massive galaxies have quenched their star formation because of active galactic nucleus feedback. However, recent studies have shown that some massive galaxies are still forming stars. We analyze the morphology of star formation regions for galaxies of stellar mass larger than 10$^{11.3}$ M$_{\odot}$ at around redshift $z_r=0.5$ using $u-z$ color images. We find that about $20\%$ of the massive galaxies are star-forming (SF) galaxies, and most of them ($\sim 85\%$) have asymmetric structures induced by recent mergers. Moreover, for these asymmetric galaxies, we find that the asymmetry of the SF regions becomes larger for bluer galaxies. Using the Illustris simulation, we can qualitatively reproduce the observed relation between asymmetry parameter and color. Furthermore, using the merger trees in the simulation, we find a correlation between the color of the main branch galaxies at $z_r=0.5$ and the sum of the Star Formation Rates (SFRs) of the recently accreted galaxies, which implies that star formation of the accreted galaxies has contributed to the observed star formation of the massive (host) galaxies (ex situ star formation). Furthermore, we find two blue and symmetric galaxies, candidates for massive blue disks, in our observed sample, which indicates that about $\sim 10\%$ of massive SF galaxies are forming stars in the normal mode of disk star formation (in situ star formation). With the simulation, we find that the disk galaxies at $z_r \approx 0.5$ should have experienced few major mergers during the last 4.3 Gyrs.

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arXiv2020

Redshift Evolution of the Fundamental Plane Relation in the IllustrisTNG Simulation

We investigate the fundamental plane (FP) evolution of early-type galaxies in the IllustrisTNG-100 simulation (TNG100) from redshift $z=0$ to $z=2$. We find that a tight plane relation already exists as early as $z=2$. Its scatter stays as low as $\sim 0.08$ dex across this redshift range. Both slope parameters $b$ and $c$ (where $R \propto σ^b I^c$ with $R$, $σ$, and $I$ being the typical size, velocity dispersion, and surface brightness) of the plane evolve mildly since $z=2$, roughly consistent with observations. The FP residual $\rm Res$ ($\equiv\,a\,+\,b\log σ\,+\,c\log I\,-\,\log R$, where $a$ is the zero point of the FP) is found to strongly correlate with stellar age, indicating that stellar age can be used as a crucial fourth parameter of the FP. However, we find that $4c+b+2=δ$, where $δ\sim 0.8$ for FPs in TNG, rather than zero as is typically inferred from observations. This implies that a tight power-law relation between the dynamical mass-to-light ratio $M_{\rm dyn}/L$ and the dynamical mass $M_{\rm dyn}$ (where $M_{\rm dyn}\equiv 5σ^2R/G$, with $G$ being the gravitational constant) is not present in the TNG100 simulation. Recovering such a relation requires proper mixing between dark matter and baryons, as well as star formation occurring with correct efficiencies at the right mass scales. This represents a powerful constraint on the numerical models, which has to be satisfied in future hydrodynamical simulations.

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arXiv2019

A study of stellar orbit fractions: simulated IllustrisTNG galaxies compared to CALIFA observations

Motivated by the recently discovered kinematic "Hubble sequence" shown by the stellar orbit-circularity distribution of 260 CALIFA galaxies, we make use of a comparable galaxy sample at z = 0 with a stellar mass range from 5E9 to 5E11 solar masses, selected from the IllustrisTNG simulation and study their stellar orbit compositions in relation to a number of other fundamental galaxy properties.We find that the TNG100 simulation broadly reproduces the observed fractions of different orbital components and their stellar mass dependencies. In particular, the mean mass dependencies of the luminosity fractions for the kinematically warm and hot orbits are well reproduced within model uncertainties of the observed galaxies. The simulation also largely reproduces the observed peak and trough features at a stellar mass of 1-2E10 solar masses, in the mean distributions of the cold- and hot-orbit fractions, respectively, indicating fewer cooler orbits and more hotter orbits in both more- and less-massive galaxies beyond such a mass range. Several marginal disagreements are seen between the simulation and observations: the average cold-orbit (counter-rotating) fractions of the simulated galaxies below (above) a stellar mass of 6E10 solar masses, are systematically higher than the observational data by < 10% (absolute orbital fraction); the simulation also seems to produce more scatter for the cold-orbit fraction and less so for the non-cold orbits at any given galaxy mass. Possible causes that stem from the adopted heating mechanisms are discussed.

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arXiv2019

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 MaNGA survey using Jeans-anisotropic-models applied to IFU observations. Our galaxies span a wide range of the stellar mass ($10^9$ $M_{\rm \odot}< M_* < 10^{12}$ M$_{\odot}$) and the velocity dispersion (30 km/s $< σ_v <$ 300 km/s). We find that for galaxies with velocity dispersion $σ_v>100$ km/s, the density slope has a mean value $\langle γ^{\prime} \rangle = 2.24$ and a dispersion $σ_γ=0.22$, almost independent of velocity dispersion. A clear turn over in the $γ'-σ_v$ relation is present at $σ\sim 100$ km/s, below which the density slope decreases rapidly with $σ_v$. Our analysis shows that a large fraction of dwarf galaxies (below $M_* = 10^{10}$ M$_{\odot}$) have total density slopes shallower than 1, which implies that they may reside in cold dark matter halos 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 $σ_v$. Finally, we explore the dependence of $γ'$ on the positions of galaxies in halos, namely centrals vs. 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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