arXiv subjects

Zhixiong Liang

Publications and source records attributed to Zhixiong Liang.

12 recordsLinked to original sources

arXiv2023

The Hubble Deep Hydrogen Alpha (HDH$α$) Project: I. Catalog of Emission-line Galaxies

We present the first results of the Hubble Deep Hydrogen Alpha (HDH$α$) project, which analyzes the space-borne deep H$α$ narrowband imaging data in the GOODS-S region. The HDH$α$ data comprises 72 orbits' images taken with the HST ACS/WFC F658N filter. The exposure time varies across a total area of $\sim$76.1 $\rm{arcmin}^2$, adding up to a total exposure time of 195.7 ks, among which 68.8 ks are spent in the deepest region. These images are aligned, reprojected, and combined to have the same pixel grid as the Hubble Legacy Fields (HLF). The scientific goals of the HDH$α$ include establishing a sample of emission-line galaxies (ELGs) including [O III] emitters at $z\sim$ 0.3, [O II] emitters at $z\sim$ 0.8, and Lyman-$α$ emitters (LAEs) at $z \sim 4.4$, studying the line morphology of ELGs with high resolution imaging data, and statistically analyzing the line luminosity functions and line equivalent-width distributions of ELGs selected with HST. Furthermore, the HDH$α$ project enhances the legacy value of the GOODS-S field by contributing the first HST-based narrowband image to the existing data sets, which includes the HST broadband data and other ancillary data from X-ray to radio taken by other facilities. In this paper, we describe the data reduction process of the HDH$α$, select ELGs based on HST's F658N and broadband data, validate the redshifts of the selected candidates by cross matching with the public spectroscopic catalogs in the GOODS-S, and present a final catalog of the confirmed [O III] emitters at $z\sim$ 0.3, [O II] emitters at $z\sim$ 0.8, and LAEs at $z \sim 4.4$.

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arXiv2023

Dwarf galaxies with the highest concentration are not thicker than ordinary dwarf galaxies

The formation mechanism of high-concentration dwarf galaxies is still a mystery. We perform a comparative study of the intrinsic shape of nearby low-mass galaxies with different stellar concentration. The intrinsic shape is parameterized by the intermediate-to-major axis ratios B/A and the minor-to-major axis ratios C/A of triaxial ellipsoidal models. Our galaxies ($10^{7.5} M_\odot$ < $M_\star$ < $10^{10.0} M_\odot$) are selected to have spectroscopic redshift from SDSS or GAMA, and have broadband optical images from the HSC-SSP Wide layer survey. The deep HSC-SSP images allow to measure the apparent axis ratios $q$ at galactic radii beyond the central star-forming area of our galaxies. We infer the intrinsic axis ratios based on the $q$ distributions. We find that 1) our galaxies have typical intrinsic shape similarly close to be oblate ($μ_{B/A}$ $\sim$ 0.9--1), regardless of the concentration, stellar mass, star formation activity, and local environment (being central or satellite); 2) galaxies with the highest concentration tend to have intrinsic thickness similar to or (in virtually all cases) slightly thinner (i.e. smaller mean $μ_{C/A}$ or equivalently lower triaxiality) than ordinary galaxies, regardless of other properties explored here. This appears to be in contrast with the expectation of the classic merger scenario for high-concentration galaxies. Given the lack of a complete understanding of dwarf-dwarf merger, we cannot draw a definite conclusion about the relevance of mergers in the formation of high-concentration dwarfs. Other mechanisms such as halo spin may also play important roles in the formation of high-concentration dwarf galaxies.

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arXiv2022

Discovery of a Bimodal Environmental Distribution of Compact Ellipticals in the Local Universe

Low-mass compact stellar systems (CSSs; $M_{\star}$ $<$ 10$^{10}$ M$_{\odot}$) are thought to be a mixed bag of objects with various formation mechanisms. Previous surveys of CSSs were biased to relatively high-density environments and cannot provide a complete view of the environmental dependence of the formation of CSSs. We conduct the first-ever unbiased flux-limited census of nearby quiescent CSSs over a total sky area of $\sim$ 200 deg$^{2}$ observed by the GAMA spectroscopic survey. The complete sample includes 82 quiescent CSSs, of which 85\% fall within the stellar mass range of classical compact ellipticals (cEs).\ By quantifying the local environment with the normalized projected distance $D/R_{\rm vir}$ to the nearest luminous neighboring galaxy, we find that these CSSs have a bimodal $D/R_{\rm vir}$ distribution, with one group peaking near $\sim$ 0.1$\times$$R_{\rm vir}$ (satellite) and the other peaking near $\sim$ 10$\times$$R_{\rm vir}$ (field). In contrast to the CSSs, ordinary quiescent galaxies of similar masses have unimodal $D/R_{\rm vir}$ distribution.\ Satellite CSSs are older and more metal-rich than field CSSs on average. The bimodal $D/R_{\rm vir}$ distribution of quiescent CSSs reinforces the existence of two distinct formation channels (tidal stripping and born-to-be) for cEs and may be understood in two mutually inclusive perspectives, i.e., substantial tidal stripping happens only when satellite galaxies travel sufficiently close to their massive hosts, and there exists an excess of high-density cE-bearing subhalos close to massive halos.

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arXiv2022

The Size-Mass Relation of Post-Starburst Galaxies in the Local Universe

We present a study of the size--mass relation for local post-starburst (PSB) galaxies at $z\lesssim0.33$ selected from the Sloan Digital Sky Survey Data Release 8. We find that PSB galaxies with stellar mass ($M_*$) at $10^9~M_{\odot}<M_*<10^{12}~M_{\odot}$ have their galaxy size smaller than or comparable with those of quiescent galaxies (QGs). After controlling redshift and stellar mass, the sizes of PSBs are $\sim 13\%$ smaller on average than those of QGs, such differences become larger and significant towards the low-$M_*$ end, especially at $10^{9.5}~M_{\odot} \lesssim M_*\lesssim 10^{10.5}~M_{\odot}$ where PSBs can be on average $\sim 19\%$ smaller than QGs. In comparison with predictions of possible PSB evolutionary pathways from cosmological simulations, we suggest that a fast quenching of star formation following a short-lived starburst event (might be induced by major merger) should be the dominated pathway of our PSB sample. Furthermore, by cross-matching with group catalogs, we confirm that local PSBs at $M_*\lesssim10^{10}~M_{\odot}$ are more clustered than more massive ones. PSBs resided in groups are found to be slightly larger in galaxy size and more disk-like compared to field PSBs, which is qualitatively consistent with and thus hints the environment-driven fast quenching pathway for group PSBs. Taken together, our results support multiple evolutionary pathways for local PSB galaxies: while massive PSBs are thought of as products of fast quenching following a major merger-induced starburst, environment-induced fast quenching should play a role in the evolution of less massive PSBs, especially at $M_*\lesssim 10^{10}~M_{\odot}$.

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arXiv2021

Sub-galactic scaling relations with T$_{\rm e}$-based metallicity of low metallicity regions in galaxies: metal-poor gas inflow may have important effects?

The scaling relationship is a fundamental probe of the evolution of galaxies. Using the integral field spectroscopic data from the Mapping Nearby Galaxies at Apache Point Observatory survey, we select 1698 spaxels with significant detection of the auroral emission line \oiii$λ$4363 from 52 galaxies to investigate the scaling relationships at the low-metallicity end. We find that our sample's star formation rate is higher and its metallicity is lower in the scaling relationship than the star-forming sequence after removing the contribution of the Fundamental Metallicity Relation.We also find that the stellar ages of our sample are younger ($<$ 1 Gyr) and the stellar metallicities are also lower. Morphological parameters from Deep Learning catalog indicate that our galaxies are more likely to be merger. These results suggest that their low metallicity regions may be related to interaction, the inflow of metal-poor gas may dilute the interstellar medium and form new metal-poor stars in these galaxies during interaction.

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arXiv2021

Hosts and triggers of AGNs in the Local Universe

Based on the spectroscopic and shear catalogs for SDSS galaxies in the local Universe, we compare optically-selected active galactic nuclei (AGNs) with control star-forming and quiescent galaxies on galactic, inter-halo and larger scales. We find that AGNs are preferentially found in two specific stages of galaxy evolution: star-burst and `green valley' phases, and that the stellar population of their host galaxies is quite independent of stellar mass, different from normal galaxies. Combining galaxy-galaxy lensing and galaxy clustering on large scales, we measure the mass of AGN host halos. The typical halo mass is about $10^{12}h^{-1}\rm M_{\odot}$, similar to the characteristic mass in the stellar mass-halo mass relation (SHMR). For given stellar mass, AGN host galaxies and star-forming galaxies share the same SHMR, while quiescent galaxies have more massive halos. Clustering analysis on halo scales reveals that AGNs are surrounded by a larger number of satellites (with stellar mass down to 1/1000 of the mass of the central galaxy) than star-forming galaxies, and that galaxies with larger stellar velocity dispersion have more satellites. The number of satellites also increase with halo mass, reaching unity around $10^{12}h^{-1}\rm M_{\odot}$. Our results suggest a scenario, in which the interaction of the central galaxy with the satellites triggers an early episode of star burst and AGN activities, followed by multiple AGN cycles driven by the non-axisymmetric structure produced by the interaction. The feedback from the starburst and AGN reduces the amount of cold gas for fueling the central black hole, producing a characteristic halo mass scale, $\sim 10^{12}h^{-1}\rm M_{\odot}$, where the AGN fraction peaks.

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arXiv2021

An Extraordinary Response of Iron Emission to the Central Outburst in a Tidal Disruption Event Candidate

Understanding the origin of \feii\ emission is important because it is crucial to construct the main sequence of Active Galactic Nuclei (AGNs). Despite several decades of observational and theoretical effort, the location of the optical iron emitting region and the mechanism responsible for the positive correlation between the \feii\ strength and the black hole accretion rate remain open questions as yet. In this letter, we report the optical \feii\ response to the central outburst in PS1-10adi, a candidate tidal disruption event (TDE) taking place in an AGN at $z = 0.203$ that has aroused extensive attention. For the first time, we observe that the \feii\ response in the rising phase of its central luminosity is significantly more prominent than that in the decline phase, showing a hysteresis effect. We interpret this hysteresis effect as a consequence of the gradual sublimation of the dust grains situating at the inner surface of the torus into gas when the luminosity of the central engine increases. It is the iron element released from the sublimated dust that contributes evidently to the observed \feii\ emission. This interpretation, together with the weak response of the \hb\ emission as we observe, naturally explains the applicability of relative \feii\ strength as a tracer of the Eddington ratio. In addition, optical iron emission of this origin renders the \feii\ time lag a potential "standard candle" with cosmological implications.

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arXiv2020

The Local Star Formation Rate Surface Density And Metallicity Relation For Star-forming Galaxies

We study the relations between gas-phase metallicity ($Z$), local stellar mass surface density ($Σ_*$), and the local star formation surface density ($Σ_{\rm SFR}$) in a sample of 1120 star-forming galaxies from the MaNGA survey. At fixed $Σ_{*}$ the local metallicity increases as decreasing of $Σ_{\rm SFR}$ or vice versa for metallicity calibrators of N2 and O3N2. Alternatively, at fixed $Σ_{\rm SFR}$ metallicity increases as increasing of $Σ_{*}$, but at high mass region, the trend is flatter. However, the dependence of metallicity on $Σ_{\rm SFR}$ is nearly disappeared for N2O2 and N2S2 calibrators. We investigate the local metallicity against $Σ_{\rm SFR}$ with different metallicity calibrators, and find negative/positive correlations depending on the choice of the calibrator. We demonstrate that the O32 ratio (or ionization parameter) is probably dependent on star formation rate at fixed local stellar mass surface density. Additional, the shape of $Σ_*$ -- $Z$ -- $Σ_{\rm SFR}$ (FMR) depends on metallicity calibrator and stellar mass range. Since the large discrepancy between the empirical fitting-based (N2, O3N2) to electronic temperature metallicity and the photoionization model-dependent (N2O2, N2S2) metallicity calibrations, we conclude that the selection of metallicity calibration affects the existence of FMR on $Σ_{\rm SFR}$.

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arXiv2020

New Constraints on the Origin of Surface Brightness Profile Breaks of Disk Galaxies from MaNGA

In an effort to probe the origin of surface brightness profile (SBP) breaks widely observed in nearby disk galaxies, we carry out a comparative study of stellar population profiles of 635 disk galaxies selected from the MaNGA spectroscopic survey. We classify our galaxies into single exponential (TI), down-bending (TII) and up-bending (TIII) SBP types, and derive their spin parameters and radial profiles of age/metallicity-sensitive spectral features. Most TII (TIII) galaxies have down-bending (up-bending) star formation rate (SFR) radial profiles, implying that abrupt radial changes of SFR intensities contribute to the formation of both TII and TIII breaks. Nevertheless, a comparison between our galaxies and simulations suggests that stellar migration plays a significant role in weakening down-bending $Σ_{\star}$ profile breaks. While there is a correlation between the break strengths of SBPs and age/metallicity-sensitive spectral features for TII galaxies, no such correlation is found for TIII galaxies, indicating that stellar migration may not play a major role in shaping TIII breaks, as is evidenced by a good correspondence between break strengths of $Σ_{\star}$ and surface brightness profiles of TIII galaxies. We do not find evidence for galaxy spin being a relevant parameter for forming different SBP types, nor do we find significant differences between the asymmetries of galaxies with different SBP types, suggesting that environmental disturbances or satellite accretion in the recent past do not significantly influence the break formation. By dividing our sample into early and late morphological types, we find that galaxies with different SBP types follow nearly the same tight stellar mass-$R_{25}$ relation, which makes the hypothesis that stellar migration alone can transform SBP types from TII to TI and then to TIII highly unlikely.

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arXiv2020

The Most Predictive Physical Properties for the Stellar Population Radial Profiles of Nearby Galaxies

We present a study on the radial profiles of D4000,luminosity-weighted stellar ages $τ_L$,and luminosity-weighted stellar metallicities $[Z/H]_L$ of 3654 nearby galaxies($0.01<z<0.15$)using the IFU spectroscopic data from the MaNGA survey available in the SDSS DR15,in an effort to explore the connection between median stellar population radial gradients($\nabla$D4000,$\nablaτ_L,\nabla[Z/H]_L$)out to~$1.5R_e$ and various galaxy properties,including stellar mass($M_\star$),specific star formation rate(sSFR),morphologies,and local environment. We find that $M_\star$ is the single most predictive physical property for$\nabla$D4000 and$\nabla[Z/H]_L$. The most predictive properties for $\nablaτ_L$ are sSFR,and to a lesser degree,$M_\star$. The environmental parameters,including local galaxy overdensities and central-satellite division,have virtually no correlation with stellar population radial profiles for the whole sample,but the $\nabla$D4000 of star-forming satellite galaxies with$M_\star\lesssim 10^{10}M_\odot$exhibit a significant positive correlation with galaxy overdensities. Galaxies with lower sSFR have on average steeper negative stellar population gradients,and this sSFR dependence is stronger for more massive star-forming galaxies. The negative correlation between the median stellar population gradients and$M_\star$ are best described largely as segmented relationships, whereby median gradients of galaxies with$\log M_\star\lesssim 10$(with the exact value depending on sSFR)have much weaker mass dependence than galaxies with higher$M_\star$. While the dependence of the radial gradients of ages and metallicities on T-Types and central stellar mass surface densities are generally not significant,galaxies with later T-Types or lower central mass densities tend to have significantly lower D4000,younger$τ_L$ and lower$[Z/H]_L$ across the radial ranges probed in this study.

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arXiv2019

The Mass-Metallicity Relation at $z\sim0.8$: Redshift Evolution and Parameter Dependency

The spectra of emission-line galaxies (ELGs) from the extended Baryon Oscillation Spectroscopic Survey (eBOSS) of the Sloan Digit Sky Survey (SDSS) are used to study the mass-metallicity relation (MZR) at $z\sim0.8$. The selected sample contains about 180,000 massive star-forming galaxies with $0.6 < z < 1.05$ and $9 < {\rm log}(M_{\star}/M_{\odot}) < 12$. The spectra are stacked in bins of different parameters including redshift, stellar mass, star formation rate (SFR), specific star formation rate (sSFR), half-light radius, mass density, and optical color. The average MZR at $z\sim0.83$ has a downward evolution in the MZR from local to high-redshift universe, which is consistent with previous works. At a specified stellar mass, galaxies with higher SFR/sSFR and larger half-light radius have systematically lower metallicity. This behavior is reversed for galaxies with larger mass density and optical color. Among the above physical parameters, the MZR has the most significant dependency on SFR. Our galaxy sample at $0.6<z<1.05$ approximately follows the fundamental metallicity relation (FMR) in the local universe, although the sample inhomogeneity and incompleteness might have effect on our MZR and FMR.

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arXiv2018

Mass - metallicity relation and fundamental metallicity relation of metal-poor star-forming galaxies at $0.6<z<0.9$ from the eBOSS survey

The stellar mass-metallicity relation ($M_* - Z$, MZR) indicates that the metallicities of galaxies increase with increasing stellar masses. The fundamental metallicity relation (FMR) suggests that the galaxies with higher star formation rates (SFRs) tend to have lower metallicities for a given stellar mass. To examine whether the MZR and FMR still hold at poorer metallicities and higher redshifts, we compile a sample of 35 star-forming galaxies (SFGs) at $0.6<z<0.9$ using the public spectral database ($\rm v5\_10\_0$) of emission-line galaxies from the extended Baryon Oscillation Spectroscopic Survey (eBOSS). These galaxies are identified for their significant auroral $\rm [OIII]\lambda4363$ emission line ($\rm S/N \geq 3$). With the electronic temperature metallicity calibration, we find nine SFGs are extremely metal-poor galaxies with $\rm 12 + log(O/H) \leq 7.69 \ (1/10 \ Z_\odot)$. The metallicity of the most metal-deficient galaxy is $7.35\pm 0.09$ (about 1/20 $Z_{\odot}$). Compared with the SFGs with normal metallicities in local and high redshift universe, our metal-poor SFGs have more than ten times higher SFRs at a fixed stellar mass. We create a new mass -- SFR relation for these metal-poor galaxies at $0.6<z<0.9$. Due to the higher SFRs and younger stellar ages, our metal-poor SFGs deviate from the MZR and FMR in the local universe toward lower metallicities, confirming the existence of FMR, as well as the cosmic evolution of MZR and FMR with redshift.

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