arXiv subjects

Yingjie Peng

Publications and source records attributed to Yingjie Peng.

At least 73 records · Page 4Linked to original sources

arXiv2021

From haloes to galaxies. III. The gas cycle of local galaxy populations

In Dou et al. (2021), we introduced the Fundamental Formation Relation (FFR), a tight relation between specific SFR (sSFR), H$_2$ star formation efficiency (SFE$_{\rm H_2}$), and the ratio of H$_2$ to stellar mass. Here we show that atomic gas HI does not follow a similar FFR as H$_2$. The relation between SFE$_{\rm HI}$ and sSFR shows significant scatter and strong systematic dependence on all of the key galaxy properties that we have explored. The dramatic difference between HI and H$_2$ indicates that different processes (e.g., quenching by different mechanisms) may have very different effects on the HI in different galaxies and hence produce different SFE$_{\rm HI}$-sSFR relations, while the SFE$_{\rm H_2}$-sSFR relation remains unaffected. The facts that SFE$_{\rm H_2}$-sSFR relation is independent of other key galaxy properties, and that sSFR is directly related to the cosmic time and acts as the cosmic clock, make it natural and very simple to study how different galaxy populations (with different properties and undergoing different processes) evolve on the same SFE$_{\rm H_2}$-sSFR $\sim t$ relation. In the gas regulator model (GRM), the evolution of a galaxy on the SFE$_{\rm H_2}$-sSFR($t$) relation is uniquely set by a single mass-loading parameter $λ_{\rm net,H_2}$. This simplicity allows us to accurately derive the H$_2$ supply and removal rates of the local galaxy populations with different stellar masses, from star-forming galaxies to the galaxies in the process of being quenched. This combination of FFR and GRM, together with the stellar metallicity requirement, provide a new powerful tool to study galaxy formation and evolution.

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arXiv2021

Mass and Environment as Drivers of Galaxy Evolution. IV. On the Quenching of Massive Central Disk Galaxies in The Local Universe

The phenomenological study of evolving galaxy populations has shown that star forming galaxies can be quenched by two distinct processes: mass quenching and environment quenching (Peng et al. 2010). To explore the mass quenching process in local galaxies, we study the massive central disk galaxies with stellar mass above the Schechter characteristic mass. In Zhang et al. (2019), we showed that during the quenching of the massive central disk galaxies as their star formation rate (SFR) decreases, their molecular gas mass and star formation efficiency drop rapidly, but their HI gas mass remains surprisingly constant. To identify the underlying physical mechanisms, in this work we analyze the change during quenching of various structure parameters, bar frequency, and active galactic nucleus (AGN) activity. We find three closely related facts. On average, as SFR decreases in these galaxies: (1) they become progressively more compact, indicated by their significantly increasing concentration index, bulge-to-total mass ratio, and central velocity dispersion, which are mainly driven by the growth and compaction of their bulge component; (2) the frequency of barred galaxies increases dramatically, and at a given concentration index the barred galaxies have a significantly higher quiescent fraction than unbarred galaxies, implying that the galactic bar may play an important role in mass quenching; and (3) the "AGN" frequency increases dramatically from 10% on the main sequence to almost 100% for the most quiescent galaxies, which is mainly driven by the sharp increase of LINERs. These observational results lead to a self-consistent picture of how mass quenching operates.

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arXiv2020

From haloes to galaxies -- II. The fundamental relations in star formation and quenching

Star formation and quenching are two of the most important processes in galaxy formation and evolution. We explore in the local Universe the interrelationships among key integrated galaxy properties, including stellar mass $M_*$, star formation rate (SFR), specific SFR (sSFR), molecular gas mass $M_{\rm H_2}$, star formation efficiency (SFE) of the molecular gas and molecular gas to stellar mass ratio $μ$. We aim to identify the most fundamental scaling relations among these key galaxy properties and their interrelationships. We show the integrated $M_{\rm H_2}$-SFR, SFR-$M_*$ and $M_{\rm H_2}$-$M_*$ relation can be simply transformed from the $μ$-sSFR, SFE-$μ$ and SFE-sSFR relation, respectively. The transformation, in principle, can increase or decrease the scatter of each relation. Interestingly, we find the latter three relations all have significantly smaller scatter than the former three corresponding relations. We show the probability to achieve the observed small scatter by accident is extremely close to zero. This suggests that the smaller scatters of the latter three relations are driven by a more fundamental physical connection among these quantities. We then show the large scatters in the former relations are due to their systematic dependence on other galaxy properties, and on star formation and quenching process. We propose the sSFR-$μ$-SFE relation as the Fundamental Formation Relation (FFR), which governs the star formation and quenching process, and provides a simple framework to study galaxy evolution. Other scaling relations, including integrated Kennicutt-Schmidt law, star-forming main sequence and molecular gas main sequence, can all be derived from the FFR.

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arXiv2020

The weak imprint of environment on the stellar populations of galaxies

We investigate the environmental dependence of the stellar populations of galaxies in SDSS DR7. Echoing earlier works, we find that satellites are both more metal-rich (<0.1 dex) and older (<2 Gyr) than centrals of the same stellar mass. However, after separating star-forming, green valley and passive galaxies, we find that the true environmental dependence of both stellar metallicity (<0.03 dex) and age (<0.5 Gyr) is in fact much weaker. We show that the strong environmental effects found when galaxies are not differentiated result from a combination of selection effects brought about by the environmental dependence of the quenched fraction of galaxies, and thus we strongly advocate for the separation of star-forming, green valley and passive galaxies when the environmental dependence of galaxy properties are investigated. We also study further environmental trends separately for both central and satellite galaxies. We find that star-forming galaxies show no environmental effects, neither for centrals nor for satellites. In contrast, the stellar metallicities of passive and green valley satellites increase weakly (< 0.05 dex and < 0.08 dex, respectively) with increasing halo mass, increasing local overdensity and decreasing projected distance from their central; this effect is interpreted in terms of moderate environmental starvation (`strangulation') contributing to the quenching of satellite galaxies. Finally, we find a unique feature in the stellar mass--stellar metallicity relation for passive centrals, where galaxies in more massive haloes have larger stellar mass (~0.1 dex) at constant stellar metallicity; this effect is interpreted in terms of dry merging of passive central galaxies and/or progenitor bias.

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arXiv2020

Physical Explanation for the Galaxy Distribution on the $(λ_{\rm R}, \varepsilon)$ and $(V/σ, \varepsilon)$ Diagrams or for the Limit on Orbital Anisotropy

In the $(λ_{\rm R}, \varepsilon)$ and $(V/σ, \varepsilon)$ diagrams for characterizing dynamical states, the fast-rotator galaxies (both early-type and spirals) are distributed within a well-defined leaf-shaped envelope. This was explained as due to an upper limit to the orbital anisotropy increasing with galaxy intrinsic flattening. However, a physical explanation for this empirical trend was missing. Here we construct Jeans Anisotropic Models (JAM), with either cylindrically or spherically aligned velocity ellipsoid (two extreme assumptions), and each with either spatially-constant or -variable anisotropy. We use JAM to build mock samples of axisymmetric galaxies, assuming on average an oblate shape for the velocity ellipsoid (as required to reproduce the rotation of real galaxies), and limiting the radial anisotropy $β$ to the range allowed by physical solutions. We find that all four mock samples naturally predict the observed galaxy distribution on the $(λ_{\rm R}, \varepsilon)$ and $(V/σ, \varepsilon)$ diagrams, without further assumptions. Given the similarity of the results from quite different models, we conclude that the empirical anisotropy upper limit in real galaxies, and the corresponding observed distributions in the $(λ_{\rm R}, \varepsilon)$ and $(V/σ, \varepsilon)$ diagrams, are due to the lack of physical axisymmetric equilibrium solutions at high $β$ anisotropy when the velocity ellipsoid is close to oblate.

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arXiv2020

The VLA-COSMOS 3 GHz Large Project: Evolution of specific star formation rates out to $z\sim5$

We provide a coherent, uniform measurement of the evolution of the logarithmic star formation rate (SFR) - stellar mass ($M_*$) relation, called the main sequence of star-forming galaxies (MS), for galaxies out to $z\sim5$. We measure the MS using mean stacks of 3 GHz radio continuum images to derive average SFRs for $\sim$200,000 mass-selected galaxies at $z>0.3$ in the COSMOS field. We describe the MS relation adopting a new model that incorporates a linear relation at low stellar mass (log($M_*$/M$_\odot$)$<$10) and a flattening at high stellar mass that becomes more prominent at low redshift ($z<1.5$). We find that the SFR density peaks at $1.5<z<2$ and at each epoch there is a characteristic stellar mass ($M_* = 1 - 4 \times 10^{10}\mathrm{M}_\odot$) that contributes the most to the overall SFR density. This characteristic mass increases with redshift, at least to $z\sim2.5$. We find no significant evidence for variations in the MS relation for galaxies in different environments traced by the galaxy number density at $0.3<z<3$, nor for galaxies in X-ray groups at $z\sim0.75$. We confirm that massive bulge-dominated galaxies have lower SFRs than disk-dominated galaxies at a fixed stellar mass at $z<1.2$. As a consequence, the increase in bulge-dominated galaxies in the local star-forming population leads to a flattening of the MS at high stellar masses. This indicates that "mass-quenching" is linked with changes in the morphological composition of galaxies at a fixed stellar mass.

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arXiv2020

SDSS-IV MaNGA: The kinematic-morphology of galaxies on the mass vs star-formation relation in different environments

We study the link between the kinematic-morphology of galaxies, as inferred from integral-field stellar kinematics, and their relation between mass and star formation rate (SFR). Our sample consists of $\sim 3200$ galaxies with integral-field spectroscopic data from the MaNGA survey with available determinations of their effective stellar angular momentum within the half-light radius $λ_{R_e}$. We find that for star-forming galaxies, namely along the star formation main sequence (SFMS), the $λ_{R_e}$ values remain large and almost unchanged over about two orders of magnitude in stellar mass, with the exception of the lowest masses $\mathcal{M}_{\star}\lesssim2\times10^{9} \mathcal{M}_{\odot}$, where $λ_{R_e}$ slightly decreases. The SFMS is dominated by spiral galaxies with small bulges. Below the SFMS, but above the characteristic stellar mass $\mathcal{M}_{\rm crit}\approx2\times10^{11} \mathcal{M}_{\odot}$, there is a sharp decrease in $λ_{R_e}$ with decreasing star formation rate: massive galaxies well below the SFMS are mainly slow-rotator early-type galaxies, namely genuinely spheroidal galaxies without disks. Below the SFMS and below $\mathcal{M}_{\rm crit}$ the decrease of $λ_{R_e}$ with decreasing SFR becomes modest or nearly absent: low-mass galaxies well below the SFMS, are fast-rotator early-type galaxies, and contain fast-rotating stellar disks like their star-forming counterparts. We also find a small but clear environmental dependence for the massive galaxies: in the mass range $10^{10.9}-10^{11.5} \mathcal{M}_{\odot}$, galaxies in rich groups or denser regions or classified as central galaxies have lower values of $λ_{R_e}$. While no environmental dependence is found for galaxies of lower mass. We discuss how our results can be understood as due to the different star formation and mass assembly histories of galaxies with varying mass.

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arXiv2020

The KLEVER Survey: Spatially resolved metallicity maps and gradients in a sample of 1.2 < z < 2.5 lensed galaxies

We present near-infrared observations of 42 gravitationally lensed galaxies obtained in the framework of the KMOS Lensed Emission Lines and VElocity Review (KLEVER) Survey, a program aimed at investigating the spatially resolved properties of the ionised gas in 1.2 3$σ$) "inverted" gradients are also found, showing an anti-correlation between metallicity and star formation rate density on local scales, possibly suggesting recent episodes of pristine gas accretion or strong radial flows in place. Nevertheless, the individual metallicity maps are characterised by a variety of different morphologies, with flat radial gradients sometimes hiding non-axisymmetric variations on kpc scales which are washed out by azimuthal averages, especially in interacting systems or in those undergoing local episodes of recent star formation.

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arXiv2019

Further evidence for a population of dark-matter-deficient dwarf galaxies

In the standard cosmological model, dark matter drives the structure formation and constructs potential wells within which galaxies may form. The baryon fraction in dark halos can reach the universal value (15.7%) in massive clusters and decreases rapidly as the mass of the system decreases. The formation of dwarf galaxies is sensitive both to baryonic processes and the properties of dark matter owing to the shallow potential wells in which they form. In dwarf galaxies in the Local Group, dark matter dominates the mass content even within their optical-light half-radii (r_e ~ 1 kpc). However, recently it has been argued that not all dwarf galaxies are dominated by dark matter. Here we report 19 dwarf galaxies that could consist mainly of baryons up to radii well beyond r_e, at which point they are expected to be dominated by dark matter. Of these, 14 are isolated dwarf galaxies, free from the influence of nearby bright galaxies and high dense environments. This result provides observational evidence that could challenge the formation theory of low-mass galaxies within the framework of standard cosmology. Further observations, in particular deep imaging and spatially-resolved kinematics, are needed to constrain the baryon fraction better in such galaxies.

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arXiv2019

X-shooter Spectroscopy and HST Imaging of 15 Ultra Massive Quiescent Galaxies at $z\gtrsim2$

We present a detailed analysis of a large sample of spectroscopically confirmed ultra-massive quiescent galaxies (${\rm{log}}(M_{\ast}/M_{\odot})\sim11.5$) at $z\gtrsim2$. This sample comprises 15 galaxies selected in the COSMOS and UDS fields by their bright K-band magnitudes and followed up with VLT/X-shooter spectroscopy and HST/WFC3 $H_{F160W}$ imaging. These observations allow us to unambiguously confirm their redshifts ascertain their quiescent nature and stellar ages, and to reliably assess their internal kinematics and effective radii. We find that these galaxies are compact, consistent with the high mass end of the mass-size relation for quiescent galaxies at $z=2$. Moreover, the distribution of the measured stellar velocity dispersions of the sample is consistent with the most massive local early-type galaxies from the MASSIVE Survey showing that evolution in these galaxies, is dominated by changes in size. The HST images reveal, as surprisingly high, that $40\ \%$ of the sample have tidal features suggestive of mergers and companions in close proximity, including three galaxies experiencing ongoing major mergers. The absence of velocity dispersion evolution from $z=2$ to $0$, coupled with a doubling of the stellar mass, with a factor of four size increase and the observed disturbed stellar morphologies support dry minor mergers as the primary drivers of the evolution of the massive quiescent galaxies over the last 10 billion years.

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arXiv2019

Both starvation and outflows drive galaxy quenching

Star-forming galaxies can in principle be transformed into passive systems by a multitude of processes that quench star formation, such as the halting of gas accretion (starvation) or the rapid removal of gas in AGN-driven outflows. However, it remains unclear which processes are the most significant, primary drivers of the SF-passive bimodality. We address this key issue in galaxy evolution by studying the chemical properties of 80,000 local galaxies in SDSS DR7. In order to distinguish between different quenching mechanisms, we analyse the stellar metallicities of star-forming, green valley and passive galaxies. We find that the significant difference in stellar metallicity between passive galaxies and their star-forming progenitors implies that for galaxies at all masses, quenching must have involved an extended phase of starvation. However, some form of gas ejection also has to be introduced into our models to best match the observed properties of local passive galaxies, indicating that, while starvation is likely to be the prerequisite for quenching, it is the combination of starvation and outflows that is responsible for quenching the majority of galaxies. Closed-box models indicate that the duration of the quenching phase is 2-3 Gyr, with an $e$-folding time of 2-4 Gyr, after which further star formation is prevented by an ejective/heating mode. Alternatively, leaky-box models find a longer duration for the quenching phase of 5-7 Gyr and an $e$-folding time of $\sim$1 Gyr, with outflows becoming increasingly important with decreasing stellar mass. Finally, our analysis of local green valley galaxies indicates that quenching is slower in the local Universe than at high-redshift.

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arXiv2019

Towards a deeper understanding of the physics driving galaxy quenching -- inferring trends in the gas content via extinction

In order to investigate the importance of different proposed quenching mechanisms, we use an indirect method to estimate gas masses for ~62,000 SDSS DR7 galaxies. We infer gas surface densities from dust column densities as traced by extinction within the fibre, applying a metallicity correction to account for varying dust-to-gas ratios. We find that both gas fraction and star formation efficiency (SFE) decrease moving away from the star forming main sequence (MS) towards quiescence for all galaxy masses. We further show that both quantities correlate similarly strongly with the departure from the MS, implying the need for any physical model of quenching to invoke a change in $\textit{both}$ gas fraction and SFE. Our results call for a better understanding of the physical processes driving the decrease in star formation efficiency, which has received relatively little attention in the theory of quenching until now.

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arXiv2019

The evolution of baryonic mass function of galaxies to z=3

We combine the published stellar mass function (SMF) and gas scaling relations to explore the baryonic (stellar plus cold gas) mass function (BMF) of galaxies to redshift $z=3$. We find evidence that at log$(M_{\rm baryon}/M_{\bigodot})>11.3$, the BMF evolves little since $z\sim 2.2$. With the evolution of BMF and SMF, we investigate the baryon net accretion rate ($\dotρ_{\rm baryon}$) and stellar mass growth rate ($\dotρ_{\rm star}$) for the galaxy population of log($M_{\rm star}/M_{\bigodot}$)>10. The ratio between these two quanties, $\dotρ_{\rm baryon}$/$\dotρ_{\rm star}$, decreases from $\dotρ_{\rm baryon}$/$\dotρ_{\rm star}\sim$2 at $z\sim 2.5$ to $\dotρ_{\rm baryon}$/$\dotρ_{\rm star}<$0.5 at $z\sim 0.5$, suggesting that massive galaxies are transforming from the "accretion dominated" phase to the "depletion dominated" phase from high$-z$ to low$-z$. The transition of these two phases occurs at $z\sim1.5$, which is consistent with the onset redshift of the decline of cosmic star formation rate density. This provides evidence to support the idea that the decline of cosmic star formation rate density since $z\sim1.5$ is mainly resulted from the decline of baryon net accretion rate and star formation quenching in galaxies.

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arXiv2019

Nearly all Massive Quiescent Disk Galaxies have a Surprisingly Large Atomic Gas Reservoir

The massive galaxy population above the characteristic Schechter mass M*~10^10.6 Msun contributes to about half of the total stellar mass in the local Universe. These massive galaxies usually reside in hot dark matter haloes above the critical shock-heating mass ~10^12 Msun, where the external cold gas supply to these galaxies is expected to be suppressed. When galaxies run out of their cold gas reservoir, they become dead and quiescent. Therefore, massive quiescent galaxies living in hot haloes are commonly believed to be gas-poor. Based on the data from SDSS, ALFALFA, GASS and COLD GASS surveys, here we show that the vast majority of the massive, quiescent, central disk galaxies in the nearby Universe have a remarkably large amount of cold atomic hydrogen gas, surprisingly similar to star-forming galaxies. Both star-forming and quiescent disk galaxies show identical symmetric double-horn HI spectra, indicating similar regularly rotating HI disks. Relative to their star-forming counterparts, massive quiescent central disk galaxies are quenched because of their significantly reduced molecular gas content, lower dust content, and lower star formation efficiency. Our findings reveal a new picture, which clearly demonstrates the detailed star-formation quenching process in massive galaxies and provides a stringent constraint on the physical mechanism of quenching.

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arXiv2019

The inflow and outflow rate evolution of local Milky Way-mass star-forming galaxies since z=1.3

We study the gas inflow rate ($ζ_{\rm inflow}$) and outflow rate ($ζ_{\rm outflow}$) evolution of local Milky Way-mass star-forming galaxies (SFGs) since $z=1.3$. The stellar mass growth history of Milky Way-mass progenitor SFGs is inferred from the evolution of the star formation rate (SFR)$-$stellar mass ($M_{\ast}$) relation, and the gas mass ($M_{\rm gas}$) is derived using the recently established gas scaling relations. With the $M_{\ast}+M_{\rm gas}$ growth curve, the net inflow rate $κ$ is quantified at each cosmic epoch. At $z\sim 1.3$, $κ$ is comparable with the SFR, whereas it rapidly decreases to $\sim 0.15\times$SFR at $z=0$. We then constrain the average outflow rate $ζ_{\rm outflow}$ of progenitor galaxies by modeling the evolution of their gas-phase metallicity. The best-fit $ζ_{\rm outflow}$ is found to be $(0.5-0.8)\times$SFR. Combining $κ$ and $ζ_{\rm outflow}$, we finally investigate the evolution of $ζ_{\rm inflow}$ since $z=1.3$. We find that $ζ_{\rm inflow}$ rapidly decreases by $\sim$80\% from $z=1.3$ to $z=0.5$. At $z<0.5$, $ζ_{\rm inflow}$ continuously decreases but with a much lower decreasing rate. Implications of these findings on galaxy evolution are discussed.

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arXiv2019

SDSS-IV MaNGA: The Roles of AGNs and Dynamical Processes in Star Formation Quenching in Nearby Disk Galaxies

We study how star formation (SF) is quenched in low-redshift disk galaxies with integral-field spectroscopy. We select 131 face-on spiral galaxies with stellar mass greater than $\rm 3\times10^{10}M_\odot$, and with spatially resolved spectrum from MaNGA DR13. We subdivide the sample into four groups based on the offset of their global specific star formation rate (SFR) from the star-forming main sequence and stack the radial profiles of stellar mass and SFR. By comparing the stacked profiles of quiescent and star-forming disk galaxies, we find that the decrease of the global SFR is caused by the suppression of SF at all radii, but with a more significant drop from the center to the outer regions following an inside-out pattern. As the global specific SFR decreases, the central stellar mass, the fraction of disk galaxies hosting stellar bars, and active galactic nuclei (AGNs; including both LINERs and Seyferts) all increase, indicating dynamical processes and AGN feedback are possible contributors to the inside-out quenching of SF in the local universe. However, if we include only Seyferts, or AGNs with ${\rm EW(Hα)>3Å}$, the increasing trend of AGN fraction with decreasing global sSFR disappears. Therefore, if AGN feedback is contributing to quenching, we suspect that it operates in the low-luminosity AGN mode, as indicated by the increasing large bulge mass of the more passive disk galaxies.

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arXiv2015

Strangulation as the primary mechanism for shutting down star formation in galaxies

Local galaxies are broadly divided into two main classes, star-forming (gas-rich) and quiescent (passive and gas-poor). The primary mechanism responsible for quenching star formation in galaxies and transforming them into quiescent and passive systems is still unclear. Sudden removal of gas through outflows or stripping is one of the mechanisms often proposed. An alternative mechanism is so-called "strangulation", in which the supply of cold gas to the galaxy is halted. Here we report that the difference between quiescent and star forming galaxies in terms of stellar metallicity (i.e. the fraction of metals heavier than helium in stellar atmospheres) can be used to discriminate efficiently between the two mechanisms. The analysis of the stellar metallicity in local galaxies, from 26,000 spectra, clearly reveals that strangulation is the primary mechanism responsible for quenching star formation, with a typical timescale of 4 billion years, at least for local galaxies with a stellar mass less than 10^11 solar masses. This result is further supported independently by the stellar age difference between quiescent and star-forming galaxies, which indicates that quiescent galaxies of less than 10^11 solar masses are on average observed four billion years after quenching due to strangulation.

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arXiv2015

From haloes to Galaxies - I. The dynamics of the gas regulator model and the implied cosmic sSFR history

We explore the basic parameters that drive the evolution of the fundamental properties of star forming galaxies within the gas regulator model, or bathtub-model. We derive the general analytic form of the evolution of the key galaxy properties, i.e. gas mass, star formation rate (SFR), stellar mass, specific SFR, gas fraction, gas phase metallicity and stellar metallicity, without assuming that galaxies live in the equilibrium state. We find that the timescale required to reach equilibrium, tau_eq, which is determined by the product of star-formation efficiency and mass-loading factor, is the central parameter that is essentially in control of the evolution of all key galaxy properties. The scatters in most of the key scaling relations, such as the mass-SFR relation and mass-metallicity relation, are primarily governed by tau_eq. Most strikingly, the predicted sSFR evolution is controlled solely by tau_eq (apart from the cosmic time). Although the precise evolution of the sSFR depends on tau_eq, the sSFR history is largely insensitive to different values of tau_eq. The difference between the minimum and maximum sSFR at any epoch is less than a factor of four. The shape of the predicted sSFR history simply mimics that of the specific mass increase rate of the dark matter halos (sMIR_DM) with the typical value of the sSFR around 2*sMIR_DM, in good agreement with the predictions from typical Semi-Analytic Models (SAMs), but both are fundamentally different from the observed sSFR history. This clearly implies that some key process is missing in both typical SAMs and gas regulator model, and we hint at some possible culprit. We emphasize the critical role of tau_eq in controlling the evolution of the galaxy population, especially for gas rich low mass galaxies that are very unlikely to live around the equilibrium state at any epoch and this has been largely ignored in many similar studies.

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