The study of galaxy morphology is fundamental to understand the physical processes driving the structural evolution of galaxies. It has long been known that dense environments host high fractions of early-type galaxies and low fractions of late-type galaxies, indicating that the environment affects the structural evolution of galaxies. In this paper we present an analysis of the morphological composition of red sequence galaxies in a sample of 9 galaxy clusters at $0.8<z<1.5$ drawn from the HAWK-I cluster survey (HCS), with the aim of investigating the evolutionary paths of galaxies with different morphologies. We classify galaxies according to their apparent bulge-to-total light ratio and compare with red sequence galaxies from the lower-redshift WINGS and EDisCS surveys. We find that, while the HCS red sequence is dominated by elliptical galaxies at all luminosities and stellar masses, the WINGS red sequence is dominated by elliptical galaxies only at its bright end ($M_V<-21.0$ mag), while S0s become the most frequent class at fainter luminosities. Disc-dominated galaxies comprise 10-14\% of the red sequence population in the low (WINGS) and high (HCS) redshift samples, although their fraction increases up to 40\% at $0.4 < z < 0.8$ (EDisCS). We find a 20\% increase in the fraction of S0 galaxies from $z \sim 1.5$ to $z \sim 0.05$ on the red sequence. These results suggest that elliptical and S0 galaxies follow different evolutionary histories and, in particular, that S0 galaxies result, at least at intermediate luminosities ($-22.0 < M_V < -20.0$), from the morphological transformation of quiescent spiral galaxies.
We present a study of a sample of 254 clusters from the SDSS-DR7 Yang Catalog and an auxiliary sample of field galaxies to perform a detailed investigation on how galaxy quenching depends on both environment and galaxy stellar mass. Our samples are restricted to 0.03$\leq$z$\leq$0.1 and we only consider clusters with $\rm log(M_{halo}/M_{\odot}) \geq 14$. Comparing properties of field and cluster galaxies in the Blue Cloud, Green Valley and Red Sequence, we find evidence that field galaxies in the red sequence hosted star formation events $\rm 2.1 \pm 0.7$ Gyr ago, on average, more recently th…
We have carried out a joint photometric and structural analysis of red sequence galaxies in four clusters at a mean redshift of z ~ 1.25 using optical and near-IR HST imaging reaching to at least 3 magnitudes fainter than $M^*$. As expected, the photometry and overall galaxy sizes imply purely passive evolution of stellar populations in red sequence cluster galaxies. However, the morphologies of red sequence cluster galaxies at these redshifts show significant differences to those of local counterparts. Apart from the most massive galaxies, the high redshift red sequence galaxies are significa…
We applied the image-based approach with a convolutional neural network model to the sample of low-redshifts galaxies with $-24^{m}<M_{r}<-19.4^{m}$ from the SDSS DR9. We divided it into two subsamples, SDSS DR9 galaxy dataset and Galaxy Zoo 2 (GZ2) dataset, considering them as the inference and training datasets, respectively. As a result, we created the morphological catalog of 315782 galaxies at 0.02<z<0.1, where morphological five classes and 34 detailed features (bar, rings, number of spiral arms, mergers, etc.) were first defined for 216148 galaxies (inference dataset) by the image-based…
Galaxies arrive on the red sequences of clusters at high redshift ($z>1$) once their star formation is quenched and evolve passively thereafter. However, we have previously found that cluster red sequence galaxies (CRSGs) undergo significant morphological evolution subsequent to the cessation of star formation, at some point in the past 9-10~Gyr. Through a detailed study of a large sample of cluster red sequence galaxies spanning $0.2<z<1.4$ we elucidate the details of this evolution. Below $z \sim 0.5-0.6$ (in the last 5-6 Gyr) there is little or no morphological evolution in the population a…
The well-known cluster of galaxies ZwCl0024+1652 at z $\sim$ 0.4, lacks an in-depth morphological classification of its central region. While previous studies provide a visual classification of a patched area, we used the public code called galaxy Support Vector Machine (galSVM) and HST/ACS data as well as WFP2 master catalogue to automatically classify all cluster members up to 1 Mpc. galSVM analyses galaxy morphologies through Support Vector Machine (SVM). From the 231 cluster galaxies, we classified 97 as early-types (ET) and 83 as late-types (LT). The remaining 51 stayed unclassified (or u…
The morphology of galaxies reflects their assembly history and ongoing dynamical perturbations from the environment. Analyzing i-band images from the Pan-STARRS1 Survey, we study the optical morphological asymmetry of the host galaxies of a large, well-defined sample of nearby active galactic nuclei (AGNs) to investigate the role of mergers and interactions in triggering nuclear activity. The AGNs, comprising 245 type 1 and 4514 type 2 objects, are compared with 4537 star-forming galaxies matched in redshift and stellar mass. We develop a comprehensive masking strategy to isolate the emission …
Using the Hubble Space Telescope (HST)/Wide Field Camera 3 (WFC3) near-infrared high-resolution imaging from the 3D-HST survey, we analyze the morphology and structure of 502 ultraluminous infrared galaxies (ULIRGs; $L_{\rm IR}>10^{12}L_{\odot}$) at $1<z<3$. Their rest-frame optical morphologies show that high-redshift ULIRGs are a mixture of mergers or interacting systems, irregular galaxies, disks, and ellipticals. Most of ULIRGs in our sample can be roughly divided into merging systems and late-type galaxies (Sb$-$Ir), with relatively high $M_{20}$ ($>-1.7$) and small Sérsic index ($n<2.5$)…
The Galaxy Zoo has provided morphological data on many galaxies. Several biases have been identified in the Galaxy Zoo data. Here we report on a newly discovered selection effect: astronomers interested in studying spiral galaxies may select a set of spiral galaxies based upon a threshold in spirality (the fraction of Galaxy Zoo humans who report seeing spiral structure). SpArcFiRe is an automated tool that decomposes a spiral galaxy into its constituent spiral arms, providing objective, quantitative data on their structure. SpArcFiRe measures the pitch angle of spiral arms. We have observed t…
We use galaxy groups at redshifts between 0.4 and 1.0 selected from the Great Observatories Origins Deep Survey (GOODS) to study the color-morphological properties of satellite galaxies, and investigate possible alignment between the distribution of the satellites and the orientation of their central galaxy. We confirm the bimodal color and morphological type distribution for satellite galaxies at this redshift range: the red and blue classes corresponds to the early and late morphological types respectively, and the early-type satellites are on average brighter than the late-type ones. Furthe…
We investigate the time evolution of non-parametric morphological quantities and their relationship to major mergers between $4\geq z \geq 2$ in high-resolution cosmological zoom simulations of disk galaxies that implement kinetic wind feedback, $H_2$-based star formation, and minimal ISM pressurisation. We show that the resulting galaxies broadly match basic observed physical properties of $z\sim 2$ objects. We measure the galaxies' concentrations ($C$), asymmetries ($A$), and $Gini$ ($G$) and $M_{20}$ coefficients, and correlate these with major merger events identified from the mass growth …
We tested how the AGN contribution (5% - 75% of the total flux) may affect different morphological parameters commonly used in galaxy classification. We carried out all analysis at $z$,$sim$,0 and at higher redshifts that correspond to the COSMOS field. Using a local training sample of $>$,2000 visually classified galaxies, we carried out all measurements with and without the central source and quantified how the contribution of a bright nuclear point source could affect different morphological parameters, such as: Abraham and Concelice-Bershady indices, Gini, Asymmetry, $M20$ moment of light,…
We explore constraints on the joint photometric and morphological evolution of typical low redshift galaxies as they move from the blue cloud through the green valley and onto the red sequence. We select GAMA survey galaxies with $10.25<{\rm log}(M_*/M_\odot)<10.75$ and $z<0.2$ classified according to their intrinsic $u^*-r^*$ colour. From single component Sérsic fits, we find that the stellar mass-sensitive $K-$band profiles of red and green galaxy populations are very similar, while $g-$band profiles indicate more disk-like morphologies for the green galaxies: apparent (optical) morphologica…
We present the results of a detailed analysis of galaxy properties along the red sequence in XMMU J1229+0151, an X-ray selected cluster at $z=0.98$ drawn from the HAWK-I Cluster Survey (HCS). Taking advantage of the broad photometric coverage and the availability of 77 spectra in the cluster field, we fit synthetic spectral energy distributions, and estimate stellar masses and photometric redshifts, which we use to determine the cluster membership. We investigate morphological and structural properties of red sequence galaxies and find that elliptical galaxies populate the bright end, while S0…
The quenching "maintenance'" and related "cooling flow" problems are important in galaxies from Milky Way mass through clusters. We investigate this in halos with masses $\sim 10^{12}-10^{14}\,{\rm M}_{\odot}$, using non-cosmological high-resolution hydrodynamic simulations with the FIRE-2 (Feedback In Realistic Environments) stellar feedback model. We specifically focus on physics present without AGN, and show that various proposed "non-AGN" solution mechanisms in the literature, including Type Ia supernovae, shocked AGB winds, other forms of stellar feedback (e.g. cosmic rays), magnetic fiel…
The morphological study is crucial to investigate the connections between active galactic nuclei (AGN) activities and the evolution of galaxies. Substantial studies have found that radiative-mode AGNs primarily reside in disk galaxies, questioning the merger-driven mechanism of AGN activities. In this study, through S{é}rsic profile fitting and non-parametric morphological parameter measurements, we investigated the morphology of host galaxies of 485 optical variability-selected low luminosity AGNs at $z\lesssim4.26$ in the COSMOS field. We analyzed high-resolution images of the Hubble Space T…
Deep Extragalactic VIsible Legacy Survey (DEVILS): Morphologically-selected galaxy merger fractions and their direct comparison to close-pair samples
The University of Western Australia（西澳大利亚大学）；Monash University（莫纳什大学）；Instituto Astrofisica de Canarias（加那利天体物理研究所）；Institute of Space Sciences (ICE, CSIC)（空间科学研究所）
To explore the evolutionary connection among red, green, and blue galaxy populations, based on a sample of massive ($M_* > 10^{10} M_{\odot} $) galaxies at 0.5<z<2.5 in five 3D-HST/CANDELS fields, we investigate the dust content, morphologies, structures, AGN fractions, and environments of these three galaxy populations. Green valley galaxies are found to have intermediate dust attenuation, and reside in the middle of the regions occupied by quiescent and star-forming galaxies in the UVJ diagram. Compared with blue and red galaxy populations at z<2, green galaxies have intermediate compactness…
The galaxy population is strongly bimodal in both colour and morphology, and the two measures correlate strongly, with most blue galaxies being late-types (spirals) and most early-types, typically ellipticals, being red. This observation has led to the use of colour as a convenient selection criteria to make samples which are then labelled by morphology. Such use of colour as a proxy for morphology results in necessarily impure and incomplete samples. In this paper, we make use of the morphological labels produced by Galaxy Zoo to measure how incomplete and impure such samples are, considering…
We consistently analyse for the first time the impact of survey depth and spatial resolution on the most used morphological parameters for classifying galaxies through non-parametric methods: Abraham and Conselice-Bershady concentration indices, Gini, M20 moment of light, asymmetry, and smoothness. Three different non-local datasets are used, ALHAMBRA and SXDS (examples of deep ground-based surveys), and COSMOS (deep space-based survey). We used a sample of 3000 local, visually classified galaxies, measuring their morphological parameters at their real redshifts (z ~ 0). Then we simulated them…
To figure out the effect of stellar mass and local environment on morphological transformation and star formation quenching in galaxies, we use the massive ($M_* \geq 10^{10} M_{\odot}$) galaxies at $0.5 \leq z \leq 2.5$ in five fields of 3D-HST/CANDELS. Based on the {\it UVJ} diagnosis and the possibility of possessing spheroid, our sample of massive galaxies are classified into four populations: quiescent early-type galaxies (qEs), quiescent late-type galaxies (qLs), star-forming early-type galaxies (sEs), and star-forming late-type galaxies (sLs). It is found that the quiescent fraction is …
In order to obtain morphological information of unlabeled galaxies, we present an unsupervised machine-learning (UML) method for morphological classification of galaxies, which can be summarized as two aspects: (1) the methodology of convolutional autoencoder (CAE) is used to reduce the dimensions and extract features from the imaging data; (2) the bagging-based multiclustering model is proposed to obtain the classifications with high confidence at the cost of rejecting the disputed sources that are inconsistently voted. We apply this method on the sample of galaxies with $H<24.5$ in CANDELS. …
We investigate the fraction of close pairs and morphologically identified mergers on and above the star-forming main sequence (MS) at 0.2$\leq z\leq$2.0. The novelty of our work lies in the use of a non-parametric morphological classification performed on resolved stellar mass maps, reducing the contamination by non-interacting, high-redshift clumpy galaxies. We find that the merger fraction rapidly rises to $\geq$70% above the MS, implying that -- already at $z{\gtrsim}1$ -- starburst (SB) events ($Δ_{\rm MS}\geq$0.6) are almost always associated with a major merger (1:1 to 1:6 mass ratio). T…
Understanding the processes that trigger morphological transformation is central to understanding how and why the Universe transitions from being disc-dominated at early epochs to having the morphological mix that is observed today. We use Horizon-AGN, a cosmological hydrodynamical simulation, to perform a comprehensive study of the processes that drive morphological change in massive (M > 10^10 MSun) galaxies over cosmic time. We show that (1) essentially all the morphological evolution in galaxies that are spheroids at z=0 is driven by mergers with mass ratios greater than 1:10, (2) major me…
In this investigation, we determined the Concentration (C) and Asymmetry (A) parameters in a sample of Tidal Dwarf Galaxies (TDG) or candidate galaxies. Most of the galaxies in the sample were found to be in a very precise region of the C-A plane, which clearly separates them from other galaxies. In addition, the stellar mass ($M_{star}$) and the star formation rate ($SFR$) in the sample were determined using optical images and GALEX observations. The main results are: the $M_{star}$ and the $SFR$ in the TDG sample do not follow a linear correlation with the $C$ and $A$ respectively, as observ…
Several mechanisms for the transformation of blue star-forming to red quiescent galaxies have been proposed, and the green valley (GV) galaxies amid them are widely accepted in a transitional phase. Thus, comparing the morphological and environmental differences of the GV galaxies with early-type disks (ETDs; bulge dominated and having a disk) and late-type disks (LTDs; disk dominated) is suitable for distinguishing the corresponding quenching mechanisms. A large population of massive ($M_* \geqslant 10^{10}M_\odot$) GV galaxies at $0.5 \leqslant z \leqslant 1.5$ in 3D-HST/CANDELS is selected …
We investigate the contribution of major mergers (mass ratios $>1:5$) to stellar mass growth and morphological transformations around the epoch of peak cosmic star formation ($z\sim2$). We visually classify a complete sample of massive (M $>$ 10$^{10}$M$_{\odot}$) galaxies at this epoch, drawn from the CANDELS survey, into late-type galaxies, major mergers, spheroids and disturbed spheroids which show morphological disturbances. Given recent simulation work, which indicates that recent ($<$0.3-0.4 Gyr) major-merger remnants exhibit clear tidal features in such images, we use the fraction of di…
The Evolution of the SFR-M_* relation at 0.1<z<4: Environmental and Morphological Dependencies
School of Physical Science and Technology, Southwest University（西南大学物理科学与技术学院）；Astronomical Institute, Tohoku University（东北大学天体物理研究所）；Tsung-Dao Lee Institute and Key Laboratory for Particle Physics, Astrophysics and Cosmology, Ministry of Education, Shanghai Jiao Tong University（上海交通大学教育部粒子物理、天体物理与宇宙学重点实验室暨汤川理论物理研究所）
We present a new morphological indicator designed for automated recognition of galaxies with faint asymmetric tidal features suggestive of an ongoing or past merger. We use this new indicator, together with preexisting diagnostics of galaxy structure to study the role of galaxy mergers in inducing (post-)starburst spectral signatures in local galaxies, and investigate whether (post-)starburst galaxies play a role in the build up of the `red sequence'. Our morphological and structural analysis of an evolutionary sample of 335 (post-)starburst galaxies in the SDSS DR7 with starburst ages 0<tSB<0…
We present the data release paper for the Galaxy Zoo: Hubble (GZH) project. This is the third phase in a large effort to measure reliable, detailed morphologies of galaxies by using crowdsourced visual classifications of colour composite images. Images in GZH were selected from various publicly-released Hubble Space Telescope Legacy programs conducted with the Advanced Camera for Surveys, with filters that probe the rest-frame optical emission from galaxies out to $z \sim 1$. The bulk of the sample is selected to have $m_{I814W} < 23.5$,but goes as faint as $m_{I814W} < 26.8$ for deep images c…
Context. Computational techniques are essential for mining large databases produced in modern surveys with value-added products. Aims. This paper presents a machine learning procedure to carry out simultaneously galaxy morphological classification and photometric redshift estimates. Currently, only spectral energy distribution (SED) fitting has been used to obtain these results all at once. Methods. We used the ancillary data gathered in the OTELO catalog and designed a non-sequential neural network that accepts optical and near-infrared photometry as input. The network transfers the results o…
Morphological Bias: How Ellipticals and Spirals Trace the Cosmic Web Differently
Institute of Astronomy, School of Physics, Zhejiang University（浙江大学物理学院天体物理研究所）；Center for Cosmology and Computational Astrophysics, Institute for Advanced Study in Physics, Zhejiang University（浙江大学物理高等研究院宇宙学与计算天体物理中心）；Observatório Nacional（国家天文台）
