arXiv subjects

Niu Li

Publications and source records attributed to Niu Li.

At least 19 recordsLinked to original sources

arXiv2026

Physical Properties of 6.7 Million Galaxies from the DESI Bright Galaxy Survey: Spectral Fitting and Systematic Tests with Mock Spectra

We present a comprehensive analysis of the physical properties of galaxies in the Dark Energy Spectroscopic Instrument (DESI) Data Release 1 (DR1) Bright Galaxy Survey (BGS), based on full spectral fitting of $\sim 6.7$ million galaxy spectra. Using a customized spectral fitting pipeline, we derive key physical parameters including stellar mass, stellar velocity dispersion, stellar population age, dust attenuation, and emission-line properties. To quantify the reliability and systematic uncertainties of our measurements, we construct a large set of mock spectra that closely reproduce the observed properties of DESI data, including realistic noise and spectral features. By comparing the recovered parameters with the known inputs, we assess the performance of the spectral fitting as a function of stellar continuum signal-to-noise ratio (S/N, defined as the ratio of the median continuum flux to its associated error) and redshift. We find that stellar masses can be robustly recovered with negligible bias for spectra with $\mathrm{S/N} \gtrsim 5$, while low-S/N spectra ($\mathrm{S/N} \lesssim 5$) show a mild systematic overestimation of $\sim 0.1$ dex and increased scatter. Similar trends are observed for stellar population parameters, while emission-line fluxes are recovered with high accuracy and minimal bias. We further validate our stellar mass estimates by comparison with independent measurements from photometric spectral energy distribution fitting, finding good overall consistency within the expected systematic uncertainties. The value-added catalog presented in this work enables a wide range of statistical studies of galaxy evolution with DESI, and provides a foundation for future analyses.

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arXiv2026

Early Near-Infrared Excess and Rapid Disk-Corona Evolution in the Tidal Disruption Event 2024aepd

We present multi-wavelength observations of the tidal disruption event (TDE) 2024aepd, spanning primarily the first $\sim$300 days after discovery. The X-ray spectrum is initially dominated by a thermal disk component accompanied by a hard excess. From $\sim$178 days onward, the spectrum becomes power-law dominated and subsequently hardens, indicating the rapid emergence and strengthening of a hot corona. A prominent near-infrared (NIR) excess is detected as early as $\sim40$ days. Its nearly flat power-law spectrum strongly deviates from the Rayleigh-Jeans tail of the UV-optical blackbody. Although a conventional dust-echo origin cannot be completely ruled out, free-free emission from a reprocessing photospheric envelope provides a more plausible explanation. Moreover, the UV-optical-to-NIR break shifts to higher frequencies as the density-profile index remains nearly constant, implying evolving reprocessing conditions within a broadly unchanged density structure. Together with AT2019azh and TDE 2025abcr, TDE 2024aepd is the third TDE reported to exhibit an early-time NIR excess. A larger sample with early-time NIR coverage is needed to determine whether such excesses are common among TDEs.

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arXiv2026

Mapping Dust Attenuation at Kiloparsec Scales. IV. A Dust-model Interpretation of Attenuation Curves in Nearby Galaxies

In this fourth paper on kiloparsec-scale dust attenuation, we ask whether the empirical trends found in Papers I--III can be translated into effective dust properties. Using attenuation curves for 2487 high-continuum-S/N spaxels in 91 SwiM v4.2 galaxies, we construct a grid of uniform-screen dust models composed of astronomical silicate and graphite grains with MRN-like size distributions. We fit the normalized attenuation-curve shape to constrain model parameters and then use the attenuation amplitude to estimate the model-dependent dust mass surface density. The inferred dust masses, compositions, and small-grain fractions are therefore effective quantities defined within the adopted attenuation model. The fitted models reproduce the main attenuation-curve variations and provide a direct bridge to Papers I--III: within this model, the relative 2175\AA\ bump sequence maps mainly onto the effective fraction of small graphitic/carbonaceous grains, while the NUV-slope sequence maps onto the effective small-silicate grain fraction and total silicate mass fraction. Non-SF regions have higher dust mass surface densities but lower dust-to-stellar mass ratios than SF regions, separating absolute dust content from dust content per unit stellar mass. Regions with larger specific H$\alpha$ surface brightness have larger dust-to-stellar mass ratios but lower inferred small-grain fractions, especially lower small-silicate fractions. In non-SF regions this quantity is interpreted as ionized-gas emission per unit stellar mass rather than as a direct sSFR. These model-dependent trends support a picture in which local dust processing changes the relative abundance of small grains and thereby shapes the attenuation-curve variations found across the series.

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arXiv2026

Environmental Imprints on the Assembly of the Cool Gas around Bright Cluster Galaxies

Galaxy clusters represent extreme cosmic laboratories where environmental processes dramatically reshape their constituent galaxies, yet their effect on the gaseous halos of central galaxies remains poorly constrained. Here we present the first statistical mapping of cool gas around massive brightest cluster galaxies (BCGs) at $z\approx0.55$. Using Mg II absorption in stacked sight-line spectra from over a million background quasars observed by the Dark Energy Spectroscopic Instrument, we compare BCGs to a matched sample of field galaxies and trace the radial profile from 40 kpc to 15 Mpc. Our analysis reveals a striking dual environmental signature: within 200 kpc, the circumgalactic medium (CGM) around BCGs is significantly suppressed compared to that of field galaxies, while at larger radii (200 kpc to 10 Mpc) a pronounced excess of cool gas emerges. This clear transition from suppression in the core to enhancement on such large scales delineates a novel observed pattern for gas regulation by the dense environment. It suggests that clusters may not only strip gas in the core but also facilitate its accumulation in the outskirts. Our results provide key observational constraints on theoretical models of environmental processing in and around the most massive dark matter halos.

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arXiv2026

Mapping Dust Attenuation at Kiloparsec Scales. III. The 2175\AA\ Bump

We combine the SwiM_v4.2 Swift/UVOT+MaNGA catalog with 2MASS $K_s$ imaging to map the 2175{\AA} attenuation bump at kiloparsec scales in nearby galaxies. We use two complementary estimators: an ultraviolet-to-near-infrared attenuation-curve method, yielding $A_{bump}^{UOIR}$ and $B$ for 2487 high-continuum-S/N spaxels, and the NUV-only method of Battisti et al. (2025), yielding $A_{bump}^{NUV}$ and $k_{bump}$ for 7934 spaxels. The two absolute bump estimates agree well where they overlap. We compare bump strength with local stellar-population, emission-line, attenuation-curve, and geometric diagnostics after separating star-forming (SF) and non-SF regions. The strongest bumps occur at low specific H$\alpha$ surface brightness, $\Sigma_{\text{H}\alpha}/\Sigma_\ast$, especially in non-SF regions, where this ratio traces ionized-gas emission per unit stellar mass rather than sSFR. The bump also weakens with EW(H$\alpha$) and strengthens with $D_n4000$ and stellar age. In contrast, metallicity, inclination, galactocentric radius, $A_V$, and optical attenuation-curve slope are secondary predictors. The absolute strength $A_{bump}^{NUV}$ increases with $\Sigma_{\text{H}\alpha}$ and $\Sigma_\ast$, while the relative strengths $k_{bump}$ and $B$ do not, indicating that absolute bump amplitude partly follows dust column whereas normalized strengths better trace effective bump prominence. These results support local radiation-field processing of the 2175{\AA} carriers.

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arXiv2026

Discovery of low-redshift analogues to "Little Red Dots" in DESI: A later evolutionary stage of compact LRDs?

The James Webb Space Telescope (JWST) has recently discovered a population of compact, red sources at z > 4 known as "Little Red Dots" (LRDs). They are characterized by their V-shaped continuum spectra and prominent broad Balmer emission lines. As their underlying physical nature remains debated and direct study at high-redshift is challenging; therefore, we seek to identify and characterize LRD analogues in the low-redshift universe to constrain their properties and potential evolutionary pathways. We identified five candidates at z = 0.2-0.4 from the Dark Energy Spectroscopic Instrument (DESI) that exhibit spectral energy distributions (SEDs) and broad Balmer emission lines closely resembling their high-redshift counterparts. However, we find significant differences: our low-redshift sample occupies a different region on the Baldwin, Phillips \& Terlevich (BPT) diagram, and their stellar masses are significantly higher, suggesting a more substantial host galaxy contribution. These sources are not necessarily direct local analogues of high-redshift LRDs, but may represent later evolutionary stages of compact, rapidly accreting systems, or systems with related observational properties arising under different physical conditions. This sample provides a valuable laboratory for detailed follow-up studies to elucidate the nature of LRD-like phenomena.

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arXiv2026

An Archival Optical Counterpart Search for Extragalactic Fast X-Ray Transients Discovered by Einstein Probe

Extragalactic fast X-ray transients (eFXTs) represent a rapidly growing class of high-energy phenomena, whose physical origins remain poorly understood. With its wide-field, sensitive all-sky monitoring, the Einstein Probe (EP) has greatly increased the discovery rate of eFXTs. The search and identification of the optical counterparts of eFXT are vital for understanding their classification and constraining their physical origin. Yet, a considerable fraction of eFXTs still lack secure classifications due to the absence of timely follow-up observations. We carry out a systematic search of publicly available optical survey data and transient databases (including the Zwicky Transient Facility, ZTF, and the Transient Name Server, TNS) for optical counterparts to eFXT candidates detected by EP. In this paper, we describe our ongoing program and report the first results. Specifically, we identified the eFXT EP240506a to be associated with a UV/optical counterpart, AT 2024ofs. Spectroscopy of its host galaxy with VLT yields a redshift of $z = 0.120 \pm 0.002$. By combining archival survey data with early-time multiwavelength observations, we find that the luminosity and light-curve evolution of AT~2024ofs are consistent with a core-collapse supernova origin. From detectability simulations, we estimate a local event rate density $\rho_{0}=8.8^{+21.2}_{-3.9}\ \mathrm{yr^{-1}\, Gpc^{-3}}$ for EP240506a-like events, and completeness-corrected rate of about $36$--$78\ \mathrm{yr^{-1}\ Gpc^{-3}}$ for EP-detected X-ray transients associated with supernovae. Our results demonstrate the potential of EP to uncover prompt high-energy emission from core-collapse supernovae and underscore the critical importance of timely follow-up of future eFXT events.

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arXiv2025

Galaxy clusters from the DESI Legacy Imaging Surveys -- III. Star-forming fraction of brightest cluster galaxies

This study investigates the evolution of the star-forming fraction ($F_{\mathrm{sf}}$) of Brightest Cluster Galaxies (BCGs) at $z<0.8$, using the galaxy clusters identified from the Legacy Imaging Surveys from the Dark Energy Spectroscopic Instrument (DESI). Star-forming galaxies are identified using the $g-z$ color, and $F_{\mathrm{sf}}$ is measured as a function of redshift, cluster halo mass, and galaxy stellar mass. Field galaxies are used as a comparison sample to reduce selection effects. For BCGs, $F_{\mathrm{sf}}$ increases with redshift, showing a slow rise below $z \sim 0.4 - 0.5$ and a more rapid increase above this range. In contrast, $F_{\mathrm{sf}}$ decreases with increasing cluster halo mass and BCG stellar mass. At the low stellar mass end, BCGs exhibit higher star-forming fractions than field galaxies, suggesting enhanced star formation likely fueled by cold gas accretion from the intracluster medium. Also, star-forming BCGs tend to show larger projected offsets from the optical cluster density peak than quenching BCGs, indicating ongoing assembly. The analysis of the specific star formation rate (sSFR) further indicates a transition in the dominant mechanism driving star formation in BCGs: cooling flows are likely responsible at low redshift, while gas-rich mergers play a greater role at higher redshift. The shift in dominance occurs around $z \sim 0.5$, aligning with the steep rise in $F_{\mathrm{sf}}$ of BCG.

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arXiv2025

Spectral Hardening Reveals Afterglow Emergence in Long-Duration Fast X-ray Transients: A Case Study of GRB 250404A/EP250404a

The prompt emission and afterglow phases of gamma-ray bursts (GRBs) have been extensively studied, yet the transition between these two phases remains inadequately characterized due to limited multiwavelength observational coverage. Among the recent growing samples of fast X-ray transients observed by Einstein Probe (EP), a subgroup of GRBs are captured with long-duration X-ray emission, potentially containing featured evolution from prompt emission to the afterglow phase. In this Letter, we present a detailed analysis of GRB 250404A/EP250404a, a bright fast X-ray transient detected simultaneously by EP and the Fermi Gamma-ray Burst Monitor in X-rays and gamma rays. Its continuous X-ray emission reveals a long-duration tail, accompanied by distinct spectral evolution manifested by the spectral index $\alpha_{\rm X}$ with an initial softening, followed by an evident hardening, eventually reaching a plateau at the value of $\sim$ -2. Early optical and near-infrared observations enable broadband modeling with forward- and reverse-shock components, confirming that the X-ray hardening signals the emergence of the external-shock afterglow. From this spectral hardening we infer that the prompt phase in soft X-rays lasted $\sim300\;\mathrm{s}$, which is more than 3 times longer than the gamma-ray $T_{90}$. This well-tracked soft-hard-flat spectral pattern provides a clear indication of afterglow emergence from the fading prompt emission and offers a practical criterion for identifying a distinct population of GRBs among fast X-ray transients, even when the detection of the gamma-ray counterpart or obvious temporal break is absent.

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arXiv2025

Characterizing the Palomar 5 Stream: HDBSCAN Analysis and Galactic Halo Constraints

We utilize the DESI Legacy Imaging Surveys DR10 to investigate the previously undetected faint extension of the Palomar 5 stellar stream. By applying the HDBSCAN clustering algorithm, we identify stream members and successfully extend the leading arm of the stream to approximately $\mathrm{DEC} \sim -15^\circ$. Combining the fully detected stream with a suite of mock stream simulations, we conduct a detailed comparison to constrain both the intrinsic properties of the stream and the dynamical parameters of the Milky Way (MW) halo. Our analysis yields a best-fit model characterized by eight parameters: $M_{\mathrm{halo}} = 5.67\times10^{11}\ M_{\odot}$, $r_{s,\mathrm{halo}} = 28.94\ \mathrm{kpc}$, $q_z = 0.93$, $M_{\mathrm{gc}} = 4.31\times10^{3}\ M_{\odot}$, $dM_{\mathrm{gc}}/dt = 1.81\ M_{\odot}\ \mathrm{Myr}^{-1}$, $\mu_{\alpha}\cos\delta = -2.28\ \mathrm{mas\ yr}^{-1}$, $\mu_{\delta} = -2.26\ \mathrm{mas\ yr}^{-1}$, and $D = 23.25\ \mathrm{kpc}$. Notably, our constraints on the halo shape indicate that the MW's dark matter halo exhibits a flattened potential, with a minor-to-major axis ratio of $q_z = 0.93$. This finding aligns well with theoretical expectations and previous observational estimates. Additionally, the best-fit model accurately reproduces the observed stream morphology and dynamics, providing a more precise understanding of both the evolution of the stream and the overall structure of the Galactic halo.

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arXiv2025

Mapping Dust Attenuation at Kiloparsec Scales. II. Attenuation Curves from Near-Ultraviolet to Near-Infrared

This is the second paper in a series that utilize IFS from MaNGA, NUV imaging from Swift/UVOT and NIR imaging from 2MASS to study dust attenuation properties on kpc scales in nearby galaxies. We apply the method developed in Paper I (Zhou et al. 2023) to the updated SWiM_v4.2 catalog, and measure the optical attenuation curve and the attenuation in three NUV bands for 2487 spaxels selected from 91 galaxies with S/N>20 and $A_V$>0.25. We classify all spaxels into two subsets: star-forming (SF) regions and non-SF regions. We explore the correlations of optical opacity ($A_V$) and the optical and NUV slopes of attenuation curves ($A_B/A_V$ and $A_{w2}/A_{w1}$) with a broad range of stellar and emission-line properties, including specific surface brightness of H$\alpha$ emission, stellar age, stellar and gas-phase metallicity, and diagnostics of recent star formation history. When comparing SF and non-SF regions, we find that $A_V$ and $A_B/A_V$ exhibit similar correlations with all the stellar population and emission-line properties considered, while the NUV slopes in SF regions tend to be flatter than those in non-SF regions. The NUV slope $A_{w2}/A_{w1}$ exhibits an anti-correlation with specific surface brightness of H$\alpha$ emission, a trend that is primarily driven by the positive correlation between $A_{w2}/A_{w1}$ and $\Sigma_\ast$. The NUV slope flattens in SF regions that contain young stellar populations and have experienced recent star formation, but it shows no obvious dependence on stellar or gas-phase metallicity. The spatially resolved dust attenuation properties exhibit no clear correlations with the inclination of host galaxies or the galactocentric distance of the regions. This finding reinforces the conclusion from Paper I that dust attenuation is primarily regulated by local processes on kpc scales or smaller, rather than by global processes at galactic scales.

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arXiv2024

Estimating Dust Attenuation From Galactic Spectra. III. Radial variations of dust attenuation scaling relations in MaNGA galaxies

We investigate the radial dependence of the scaling relations of dust attenuation in nearby galaxies using integral field spectroscopy (IFS) data from MaNGA. We identify ionized gas regions of kpc sizes from MaNGA galaxies, and for each region we estimate both the stellar attenuation $E(B-V)_{\rm star}$ and gas attenuation $E(B-V)_{\rm gas}$. We then quantify the correlations of 15 regional/global properties with $E(B-V)_{\rm gas}$ and $E(B-V)_{\rm star}$, using both the feature importance obtained with the Random Forest regression technique and the Spearman correlation coefficients. The importance of stellar mass, metallicity and nebular velocity dispersion found previously from SDSS-based studies can be reproduced if our analysis is limited to the central region of galaxies. The scaling relations of both $E(B-V)_{\rm gas}$ and $E(B-V)_{\rm star}$ are found to strongly vary as one goes from the galactic center to outer regions, and from H$\alpha$-bright regions to H$\alpha$-faint regions. For $E(B-V)_{\rm gas}$, [NII]/[SII] is top ranked with a much higher correlation coefficient than any other property at $0<R\lesssim R_e$, while [OIII]/[OII] outperforms [NII]/[SII] as the leading property in the outermost region. For $E(B-V)_{\rm star}$, stellar age shows the strongest correlation with no/weak dependence on radial distance, although $\rm \Sigma_{H\alpha}$ and sSFR present similarly strong correlations with $E(B-V)_{\rm star}$ in the galactic center. We find H$\alpha$-bright regions to generally show stronger correlations with $E(B-V)_{\rm gas}$, while H$\alpha$-faint regions are more strongly correlated with $E(B-V)_{\rm star}$, although depending on individual properties and radial distance. The implications of our results on studies of high-$z$ galaxies are discussed.

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arXiv2023

Criss Cross Nebula: Case study of shock regions with resolved microstructures at scales of $\sim$1000 AU

Using integral field spectroscopy from MaNGA, we study the resolved microstructures in a shocked region in Criss Cross Nebula (CCN), with an unprecedentedly high resolution of $\lesssim$1000 AU. We measure surface brightness maps for 34 emission lines, which can be broadly divided into three categories: (1) the [OIII] $\lambda$5007-like group including seven high-ionization lines and two [OII] auroral lines which uniformly present a remarkable lane structure, (2) the H$\alpha$ $\lambda$6563-like group including 23 low-ionization or recombination lines which present a clump-like structure, and (3) [OII] $\lambda$3726 and [OII] $\lambda$3729 showing high densities at both the [OIII] $\lambda$5007 lane and the H$\alpha$ clump. We use these measurements to constrain resolved shock models implemented in MAPPINGS V. We find our data can be reasonably well-fitted by a model which includes a plane-parallel shock with a velocity of $133\pm5$ km/s, plus an isotropic two-dimensional Gaussian component which is likely another clump of gas ionized by photons from the shocked region, and a constant background. We compare the electron density and temperature profiles as predicted by our model with those calculated using observed emission line ratios. We find different line ratios to provide inconsistent temperature maps, and the discrepancies can be attributed to observational effects caused by limited spatial resolution and projection of the shock geometry, as well as contamination of the additional Gaussian component. Implications on shock properties and perspectives on future IFS-based studies of CCN are discussed.

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arXiv2023

Post-starburst galaxies in SDSS-IV MaNGA: Two broad categories of evolutionary pathways

We study the size-mass relation (SMR) and recent star formation history (SFH) of post-starburst (PSB) galaxies in the local Universe, using spatially resolved spectroscopy from the final data release of MaNGA. Our sample includes 489 PSB galaxies: 94 cPSB galaxies with central PSB regions, 85 rPSB galaxies with ring-like PSB regions and 310 iPSB galaxies with irregular PSB regions. When compared to control galaxies of similar SFR, redshift and mass, a similar SMR is found for all types of PSB samples except the cPSB galaxies which have smaller sizes at intermediate masses ($9.5\lesssim \log_{10}(\rm M_\ast/M_\odot)\lesssim 10.5$). The iPSB galaxies in the star-forming sequence (iPSB-SF) show no/weak gradients in $\textrm{D}_{n}(4000)$, $\textrm{EW}(\textrm{H}\delta_{A})$ and $\textrm{EW}(\textrm{H}\alpha)$, consistent with the global star-forming status of this type of galaxies, while the quiescent iPSB (iPSB-Q) sample shows negative gradients in $\textrm{D}_{n}(4000)$ and positive gradients in $\textrm{EW}(\textrm{H}\delta_{A})$, indicating older stellar populations in the inner regions. Both cPSB and rPSB samples show positive gradients in $\textrm{D}_{n}(4000)$ and negative gradients in $\textrm{EW}(\textrm{H}\delta_{A})$, indicating younger stellar populations in the inner regions. These results imply that the four types of PSB galaxies can be broadly divided into two distinct categories in terms of evolutionary pathway: (1) iPSB-SF and iPSB-Q which have SMRs and SFHs similar to control galaxies, preferring an inside-out quenching process, (2) rPSB and cPSB which appear to be different stages of the same event, likely to follow the outside-in quenching process driven by disruption events such as mergers that result in a more compact structure as quenching proceeds.

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arXiv2023

Zero-sound modes for the nuclear equation of state at supra-normal densities

The meaningful correlations between the zero-sound modes and the stiffness of the nuclear equation of state (EOS) are uncovered in nuclear matter with the relativistic mean-field theory. It is demonstrated that the high-density zero-sound modes merely exist in models with the stiff EOS. While the stiff EOS can be softened by including {\omega}-meson self-interactions (the {\omega}4 term), the weakened coupling of the {\omega}-meson self-interactions reignites the zero sound at high density. These results suggest that the high-density zero-sound modes can be used to probe the stiffness of the EOS at supra-normal densities. The implications and effects of zero sounds are also discussed in heavy ion collisions and neutron stars.

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arXiv2023

Strong correlation of the neutron star core-crust transition density with the $\sigma$-meson mass via vacuum polarization

We study the neutron star core-crust transition density $\rho_t$ with the inclusion of the vacuum polarization in the dielectric function in the nonlinear relativistic Hartree approach (RHAn). It is found that the strong correlation between the $\rho_{t}$ and the scalar meson mass $m_{\sigma}$ strikingly overwhelms the uncertainty of the nuclear equation of state in the RHAn models, in contrast to the usual awareness that $\rho_{t}$ is predominantly sensitive to the isovector nuclear potential and symmetry energy. The accurate extraction of $\rho_{t}$ through the future gravitational wave measurements can thus provide a strong constraint on the longstanding uncertainty of $m_{\sigma}$, which is of significance to better infer the vacuum property. As an astrophysical implication, it suggests that the correlation between $\rho_t$ and $m_\sigma$ is very favorable to reconcile the difficulty in reproducing the large crustal moment of inertia for the pulsar glitches with the well constrained symmetry energy.

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arXiv2022

Mapping dust attenuation and the 2175 {\AA} bump at kpc scales in nearby galaxies

We develop a novel approach to measure dust attenuation properties of galaxies, including the dust opacity, shape of the attenuation curve and the strength of the 2175{\AA} absorption feature. From an observed spectrum, the method uses a model-independent approach to derive a relative attenuation curve, with absolute amplitude calibrated using NIR photometry. The dust-corrected spectrum is fitted with stellar population models to derive the dust-free model spectrum, which is compared with the observed SED/spectrum from NUV to NIR to determine dust attenuation properties. We apply this method to investigate dust attenuation on kpc scales, using a sample of 134 galaxies with integral field spectroscopy from MaNGA, NIR imaging from 2MASS, and NUV imaging from Swift/UVOT. We find the attenuation curve slope and the 2175{\AA} bump in both optical and NUV span a wide range at kpc scales. The slope is shallower at higher optical opacity, regardless of the specific star formation rate (sSFR), minor-to-major axis ratio (b/a) of galaxies and the location of spaxels within individual galaxies. The 2175{\AA} bump presents a strong negative correlation with the sSFR, while the correlations with the optical opacity, b/a and the location within individual galaxies are all weak. All these trends appear to be independent of the stellar mass of galaxies. Our results support the scenario that the variation of the 2175{\AA} bump is driven predominantly by processes related to star formation, such as the destruction of small dust grains by UV radiation in star-forming regions.

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arXiv2021

Nuclear potentials relevant to the symmetry energy in chiral models

We employ the extended Nambu-Jona-Lasinio, linear-$\sigma$ models, and the density-dependent model with chiral limits to work out the mean fields and relevant properties of nuclear matter. To have the constraint from the data, we reexamine the Dirac optical potentials and symmetry potential based on the relativistic impulse approximation (RIA). Unlike the extended NJL and the density-dependent models with the chiral limit in terms of the vanishing scalar density, the extended linear-$\sigma$ model with a sluggish changing scalar field loses the chiral limit at the high density end. The various scalar fields can characterize the different Schr\"odinger-equivalent potentials and kinetic symmetry energy in the whole density region and the symmetry potential in the intermediate density region. The drop of the scalar field due to the chiral restoration results in a clear rise of the kinetic symmetry energy. The chiral limit in the models gives rise to the softening of the symmetry potential and thereof the symmetry energy at high densities.

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