Rsic Index Research Articles

Photometric properties of classical bulge and pseudo-bulge galaxies at 0.5 z<1.0

We compare the photometric properties and specific star formation rate (sSFR) of classical- and pseudo-bulge galaxies with $M_* odot $ at $0.5 z<1.0$, selected from all five CANDELS fields. We also compare these properties of bulge galaxies at lower redshift selected from MaNGA survey in previous work. This paper aims to study the properties of galaxies with classical and pseudo-bulges at intermediate redshift, to compare the differences between different bulge types, and to understand the evolution of bulges with redshift. Galaxies are classified into classical bulge and pseudo-bulge samples according to the S$ e $rsic index n of the bulge component based on results of two-component decomposition of galaxies, as well as the position of bulges on the Kormendy diagram. For the 105 classical bulge and 86 pseudo-bulge galaxies selected, we compare their size, luminosity, and sSFR of various components. At a given stellar mass, most classical bulge galaxies have smaller effective radii, larger $B/T$, brighter and relatively larger bulges, and less active star formation than pseudo-bulge galaxies. In addition, the two types of galaxies have larger differences in sSFR at large radii than at the central region at both low- and mid-redshifts. The differences between the properties of the two types of bulge galaxies are generally smaller at mid-redshift than at low-redshift, indicating that they are evolving to more distinct populations towards the local universe. Bulge type is correlated with the properties of their outer disks, and the correlation is already present at redshifts as high as $0.5<z<1$.

z ∼ 2 dual AGN host galaxies are disky: stellar kinematics in the ASTRID Simulation

We study dual AGN host galaxy morphologies at z=2 using the ASTRID simulation, selecting black hole (BH) pairs with small separation (), high mass ( MBH,12>107M⊙), and luminosity (). We kinematically decompose (using MORDOR) ∼1000 dual AGN hosts into standard components - a ‘disk’ (thin and thick disk, pseudo-bulge) and ‘bulge’ (bulge and halo) and define disk-dominated galaxies by the disk-to-total D/T≥0.5. In ASTRID, 60.9±2.1% of dual AGN hosts (independent of separation) are disk-dominated, with the D/T distribution peaking at ∼0.7. In dual-AGN hosts, the D/T increases from $17% $ at to $ 64% $ for , and the pseudo-bulge is the dominant component of the disk fraction at the high mass end. Moreover, dual AGN hosts exhibit a higher fraction of disk/large pseudo-bulge than single-AGN hosts. The Disk-to-Total ratio is approximately constant with BH mass or AGN luminosity. We also create mock images of dual AGN host galaxies, employing morphological fitting software Statmorph to calculate morphological parameters and compare them with our kinematic decomposition results. Around 83.3±2.4% of galaxies display disk-like profiles, of which ∼60.7±2.2% are kinematically confirmed as disks. Se'rsic indices and half-mass radii of dual AGN host galaxies align with observational measurements from HST at z∼2. Around 34% are identified as mergers from the Gini−M20 relation. We find two dual AGN hosted by galaxies that exhibit disk-like se'rsic index n12<1 and (D/T)12>0.5, which are in remarkable agreement with properties of recently discovered dual quasars in disk galaxies at z∼2.

Environmental effects as a key factor in shaping star-forming S0 galaxies

The origins of lenticular galaxies (S0s) can be classified into two main categories: ``minor mergers" in low-density environments (LDEs) and ``faded spirals" in high-density environments (HDEs). The transitional phase in the evolution of S0s, namely, star-forming lenticular galaxies (SFS0s), can serve as an important probe for analyzing the complex processes involved in the transformation between different galaxy types and the quenching of star formation (SF). We attempt to find the impact of different environments on the global properties and spatially resolved quantities of SFS0s. We selected 71 SFS0s from the SDSS-IV MaNGA Survey, comprising 23 SFS0s in HDEs (SFS0s$\_$HE) and 48 SFS0s in LDEs (SFS0s$\_$LE). We examined the effects of the environment, by studying the global properties, concentration index, and radial profiles of the derived quantities. The varied environments of SFS0s do not lead to any significant difference in global properties (e.g., S$ e $rsic index). By calculating $CI_ alpha /cont $, we observe that different environments may cause varying concentrations of SF. Specifically, SFS0s$\_$LE, affected by external gas mergers or inflow, exhibit a more centrally concentrated SF (i.e., larger alpha /cont $). This trend is further supported by $CI_ SFR alpha $, which only considers the gas disk of the galaxy. This observation is aligned with the observed shrinking of gas disks in galaxies affected by ram-pressure stripping in HDEs. Furthermore, their $ SFR $ or resolved sSFR are comparable. On average, SFS0s$\_$LE display significantly higher values for both quantities. Finally, the observed n 4000$ and gas-phase metallicity gradient correspond well to their assumed origins. However, we did not find a significantly lower gas-phase metallicity in SFS0s$\_$LE. We suggest that different environments (i.e., origins) do not have a significant impact on the global properties of SFS0s, but they do indeed affect the distribution of SF. Considering the size of our sample and the unique nature of the galaxy, additional atomic and molecular gas data may provide further details to improve our understanding of these systems.

The PSF smoothing effect on concentration-related parameters of high-redshift galaxies in HST and JWST

Aims. We performed a comprehensive investigation of the PSF smoothing effect on the measurement of concentration-related parameters (C, Gini, and M20) of high-redshift galaxies in the HST and JWST surveys. Methods. Our sample contains massive galaxies (109.5 M⊙ ≤ M* ≤ 1011.5 M⊙) from the CANDELS/EGS survey (at redshift 0 < z < 2), and the CEERS survey (at redshift 1 < z < 3). The non-parametric concentration-related parameters (R20, R80, C, Gini, and M20) and the model-dependent parameters (n and Re) of these galaxies were derived from Statmorph and GALFIT, respectively. The best-fit Sérsic index (n) derived from image modelling is generally robust against the PSF smoothing effect and can be used to describe the intrinsic light distribution of galaxies. On the other hand, the concentration-related parameters are significantly affected by the PSF smoothing effect since they are directly calculated from the pixels of galaxy images. We tried to evaluate the PSF smoothing effect by comparing the concentration-related parameters to the Sérsic index in both observations and mock images. Results. We find that the concentration index is generally underestimated, especially for smaller galaxies with a higher Sérsic index (eventually converging to the concentration index of the PSF). However, galaxies with a lower Sérsic index (n ≤ 1) or larger relative size (Re/FWHM > 3) are less affected by the PSF smoothing effect. Tests with idealised mock images reveal that overestimating the measured R20/Re ratio leads to underestimating the concentration index C. Another commonly used concentration index C59, derived from R50 and R90 values, is less affected by the PSF. The Gini coefficient and the absolute M20 statistic also show a similar behaviour as the concentration index. Caution should be taken for the possible correction of the concentration-related parameters, where both the relative size and the Sérsic index of the galaxy are important. We also generated high-redshift artificial images from the low-redshift HST observations and confirm that the traditional correction method that simply adds a single term to the non-parametric indicators of galaxies at higher redshifts is unable to reliably recover the true distribution of the structural parameters. Compared to the HST images, the PSF smoothing is much less severe for images in the CEERS survey (for the short-wavelength filters) due to the much higher spatial resolution. In fact, it is better to use the Sérsic index rather than the non-parametric morphology indicators to trace the light concentration for galaxies at high redshifts. From the single Sérsic modelling of the HST and JWST images, we also confirm that galaxies at higher redshifts are more compact with smaller Re. The low-mass galaxies are more disc-like (n ∼ 1) compared to the high-mass galaxies that are more spheroid dominated (n ∼ 3).

Massive red spiral galaxies in SDSS-IV MaNGA survey

ABSTRACT Massive red spiral galaxies (MRSGs) are supposed to be the possible progenitors of lenticular galaxies (S0s). We select a large sample of MRSGs ($M_*\gt 10^{10.5}\rm {\rm M}_{\odot }$) from Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) DR17 using the g − r colour versus stellar mass diagram, along with control samples of blue spirals and S0s. Our main results are as follows: (1) After comparing the Sérsic index, concentration parameter, asymmetry parameter distribution, size–mass relation, and Σ1 (stellar mass surface density within the central 1 kpc)−mass relation, we find MRSGs are similar to S0s and have more compact and symmetric structures than blue spirals. MRSGs also resemble S0s in Dn4000, metallicity, Mgb/$\rm \left\langle Fe \right\rangle$, and V/σ radial profile. (2) By using MaNGA 2D spectra data, we separate the spatial regions into inner (R < 0.8Re) and outer (0.8 < R < 1.5Re) regions, and detect residual star formation in the outer regions of MRSGs. (3) When we select a sub-sample of MRSGs with NUV − r > 5, we find that they are completely star formation quenched in both inner and outer regions. Compared to optically selected MRSGs, NUV − r selected MRSGs appear to be more concentrated and have more massive dark matter haloes. The similarities between S0s and MRSGs suggest the possible evolutionary trend between MRSGs and S0s.

The evolution and dependence of the local mass–metallicity relation

We present a sample of 86,111 star-forming galaxies (SFGs) selected from the catalogue of the MPA-JHU emission-line measurements for SDSS DR7 to investigate the evolution of mass-metallicity (MZ) relation. We find that: under the $\rm log(L_{H \alpha})>41.0$ threshold, the $0.04<z\leqslant0.06$ SFGs with $9.2<$ log($M_{\star}/M_{\sun})<9.5$ have always higher metallicities ($\sim 0.1$ dex) than the $0.10<z<0.12$ SFGs by using the closely-matched control sample method; under the $\rm log(L_{\OIII})>39.7$ threshold, the $0.04<z\leqslant0.06$ SFGs with $9.2<$ log($M_{\star}/M_{\sun})<9.5$ do not exhibit the evolution of the MZ relation, in contrast to the $0.10<z<0.12$ SFGs. We find that the metallicity tends to be lower in galaxies with a higher concentration, higher S\'{e}rsic index, or higher SFR. In addition, we can see that the stellar mass and metallicity usually present higher in galaxies with a higher $D_{n}4000$ or higher log(N/O) ratio. Moreover, we present the two galaxy populations with log($M_{\star}/M_{\sun}$) below $10.0$ or greater than $10.5$ in the MZ relation, showing clearly an anticorrelation and a positive correlation between specific star formation rate and 12+log(O/H).

NIHAO XXI: the emergence of low surface brightness galaxies

The existence of galaxies with a surface brightness $\mu$ lower than the night sky has been known since three decades. Yet, their formation mechanism and emergence within a $\rm\Lambda CDM$ universe has remained largely undetermined. For the first time, we investigated the origin of Low Surface Brightness (LSB) galaxies with M$_{\star}$$\sim$10$^{9.5-10}$M$_{\odot}$, which we are able to reproduce within hydrodynamical cosmological simulations from the NIHAO suite. The simulated and observed LSBs share similar properties, having large HI reservoir, extended star formation histories and effective radii, low S\'{e}rsic index and slowly rising rotation curves. The formation mechanism of these objects is explored: simulated LSBs form as a result of co-planar co-rotating mergers and aligned accretion of gas at early times, while perpendicular mergers and mis-aligned gas accretion result in higher $\mu$ galaxies by $z$=0. The larger the merger, the stronger the correlation between merger orbital configuration and final $\mu$. While the halo spin parameter is consistently high in simulated LSB galaxies, the impact of halo concentration, feedback-driven gas outflows and merger time only plays a minor-to-no role in determining $\mu$. Interestingly, the formation scenario of such `classical' LSBs differs from the one of less massive, M$_{\star}$$\sim$10$^{7-9}$M$_{\odot}$, Ultra-Diffuse Galaxies, the latter resulting from the effects of SNae driven gas outflows: a M$_{\star}$ of $\sim$10$^9$M$_{\odot}$ thus represents the transition regime between a feedback-dominated to an angular momentum-dominated formation scenario in the LSB realm. Observational predictions are offered regarding spatially resolved star formation rates through LSB discs: these, together with upcoming surveys, can be used to verify the proposed emergence scenario of LSB galaxies.

Galaxy And Mass Assembly (GAMA): The sSFR-M* relation part I – σsSFR-M* as a function of sample, SFR indicator and environment

Recently a number of studies have proposed that the dispersion along the star formation rate - stellar mass relation ($\sigma_{\mathrm{sSFR}}$-M$_{*}$) is indicative of variations in star-formation history (SFH) driven by feedback processes. They found a 'U'-shaped dispersion and attribute the increased scatter at low and high stellar masses to stellar and active galactic nuclei feed-back respectively. However, measuring $\sigma_{\mathrm{sSFR}}$ and the shape of the $\sigma_{\mathrm{sSFR}}$-M$_{*}$ relation is problematic and can vary dramatically depending on the sample selected, chosen separation of passive/star-forming systems, and method of deriving star-formation rates ($i.e.$ H$\alpha$ emission vs spectral energy distribution fitting). As such, any astrophysical conclusions drawn from measurements of $\sigma_{\mathrm{sSFR}}$ must consider these dependencies. Here we use the Galaxy And Mass Assembly survey to explore how $\sigma_{\mathrm{sSFR}}$ varies with SFR indicator for a variety of selections for disc-like `main sequence' star-forming galaxies including colour, star-formation rate, visual morphology, bulge-to-total mass ratio, S\'{e}rsic index and mixture modelling. We find that irrespective of sample selection and/or SFR indicator, the dispersion along the sSFR-M$_{*}$ relation does follow a 'U'-shaped distribution. This suggests that the shape is physical and not an artefact of sample selection or method. We then compare the $\sigma_{\mathrm{sSFR}}$-M$_{*}$ relation to state-of-the-art hydrodynamical and semi-analytic models and find good agreement with our observed results. Finally, we find that for group satellites this 'U'-shaped distribution is not observed due to additional high scatter populations at intermediate stellar masses.

Morpho-z: improving photometric redshifts with galaxy morphology

We conduct a comprehensive study of the effects of incorporating galaxy morphology information in photometric redshift estimation. Using machine learning methods, we assess the changes in the scatter and catastrophic outlier fraction of photometric redshifts when galaxy size, ellipticity, S\'{e}rsic index and surface brightness are included in training on galaxy samples from the SDSS and the CFHT Stripe-82 Survey (CS82). We show that by adding galaxy morphological parameters to full $ugriz$ photometry, only mild improvements are obtained, while the gains are substantial in cases where fewer passbands are available. For instance, the combination of $grz$ photometry and morphological parameters almost fully recovers the metrics of $5$-band photometric redshifts. We demonstrate that with morphology it is possible to determine useful redshift distribution $N(z)$ of galaxy samples without any colour information. We also find that the inclusion of quasar redshifts and associated object sizes in training improves the quality of photometric redshift catalogues, compensating for the lack of a good star-galaxy separator. We further show that morphological information can mitigate biases and scatter due to bad photometry. As an application, we derive both point estimates and posterior distributions of redshifts for the official CS82 catalogue, training on morphology and SDSS Stripe-82 $ugriz$ bands when available. Our redshifts yield a 68th percentile error of $0.058(1+z)$, and a catastrophic outlier fraction of $5.2$ per cent. We further include a deep extension trained on morphology and single $i$-band CS82 photometry.

Revisiting the bulge–halo conspiracy – II. Towards explaining its puzzling dependence on redshift

We carry out a systematic investigation of the total mass density profile of massive (Mstar~3e11 Msun) early-type galaxies and its dependence on redshift, specifically in the range 0<z<1. We start from a large sample of SDSS early-type galaxies with stellar masses and effective radii measured assuming two different profiles, de Vaucouleurs and S\'{e}rsic. We assign dark matter haloes to galaxies via abundance matching relations with standard LCDM profiles and concentrations. We then compute the total, mass-weighted density slope at the effective radius gamma', and study its redshift dependence at fixed stellar mass. We find that a necessary condition to induce an increasingly flatter gamma' at higher redshifts, as suggested by current strong lensing data, is to allow the intrinsic stellar profile of massive galaxies to be S\'{e}rsic and the input S\'{e}rsic index n to vary with redshift approximately as n(z)~(1+z)^(-1). This conclusion holds irrespective of the input Mstar-Mhalo relation, the assumed stellar initial mass function, or even the chosen level of adiabatic contraction in the model. Secondary contributors to the observed redshift evolution of gamma' may come from an increased contribution at higher redshifts of adiabatic contraction and/or bottom-light stellar initial mass functions. The strong lensing selection effects we have simulated seem not to contribute to this effect. A steadily increasing S\'{e}rsic index with cosmic time is supported by independent observations, though it is not yet clear whether cosmological hierarchical models (e.g., mergers) are capable of reproducing such a fast and sharp evolution.

Galaxy And Mass Assembly (GAMA): Galaxy colour gradients versus colour, structure, and luminosity

Using single-component fits to SDSS/UKIDSS images of galaxies in the G09 region of the GAMA survey we study radial colour gradients across the galaxy population. We use the multiwavelength information provided by MegaMorph analysis of galaxy light profiles to calculate intrinsic colour gradients, and divide into six subsamples split by overall S\'{e}rsic index ($n$) and galaxy colour. We find a bimodality in the colour gradients of high- and low-$n$ galaxies in all wavebands, which varies with overall galaxy luminosity. Global trends in colour gradients therefore result from combining the contrasting behaviour of a number of different galaxy populations. The ubiquity of strong negative colour gradients supports the picture of inside-out growth through gas accretion for blue, low-$n$ galaxies, and through dry minor mergers for red, high-$n$ galaxies. An exception is the blue high-n population, with properties indicative of dissipative major mergers.

The transformation of Spirals into S0 galaxies in the cluster environment

We discuss the observational evidences of the morphological transformation of Spirals into S0 galaxies in the cluster environment exploiting two big databases of galaxy clusters: WINGS (0.04<z<0.07)andEDisCS(0.4<z<0.8). The most important results are: 1) the average number of S0 galaxies in clusters is almost a factor of ∼ 3 − 4 larger today than at redshift z ∼ 1; 2) the fraction of S0’s to Spirals increases on average by a factor ∼ 2 every Gyr; 3) the average rate of transformation for Spirals (not considering the infall of new galaxies from the cosmic web) is: ∼ 5 Sp→S0’s per Gyr and ∼ 2 Sp→E’s per Gyr; 4) there are evidences that the interstellar gas of Spirals is stripped by an hot intergalactic medium; 5) there are also indirect hints that major/minor merging events have played a role in the transformation of Spiral galaxies. In particular, we show that: 1) the ratio between the number of S0’s and Spirals (NS0/NSp) in the WINGS clusters is correlated with their X-ray luminosity LX ; 2) that the brightest and massive S0’s are always close to the cluster center; 3) that the mean Se rsic index of S0’s is always larger than that of Spirals (and lower than E’s) for galaxy stellar masses above 10^9.5M⊙; 4) that the number of E’s in clusters cannot be constant; 5) that the largest difference between the mean mass of S0’s and E’s with respect to Spirals is observed in clusters with low velocity dispersion. Finally, by comparing the properties of the various morphological types for galaxies in clusters and in the field, we find that the most significant effect of the environment is the stripping of the outer galaxy regions, resulting in a systematic difference in effective radius and Se rsic index.

HOST GALAXY PROPERTIES AND BLACK HOLE MASS OF SWIFT J164449.3+573451 FROM MULTI-WAVELENGTH LONG-TERM MONITORING ANDHSTDATA

We study the host galaxy properties of the tidal disruption object, Swift J164449.3+573451 using long-term optical to near-infrared (NIR) data. First, we decompose the galaxy surface brightness distribution and analyze the morphology of the host galaxy using high resolution \emph{HST} WFC3 images. We conclude that the host galaxy is a bulge-dominant galaxy that is well described by a single S\'{e}rsic model with S\'{e}rsic index $n=3.43\pm0.05$. Adding a disk component, the bulge to total host galaxy flux ratio (B/T) is $0.83\pm0.03$, which still indicates a bulge-dominant galaxy. Second, we estimate multi-band fluxes of the host galaxy through long-term light curves. Our long-term NIR light curves reveal the pure host galaxy fluxes $\sim500$ days after the burst. We fit spectral energy distribution (SED) models to the multi-band fluxes from the optical to NIR of the host galaxy and determine its properties. The stellar mass, the star formation rate, and the age of stellar population are $\log(M_{\star}/M_{\odot}) = 9.14^{+0.13}_{-0.10}$, $0.03^{+0.28}_{-0.03}\, M_{\odot}$/yr, and $0.63^{+0.95}_{-0.43}$ Gyr. Finally, we estimate the mass of the central super massive black hole which is responsible for the tidal disruption event. The black hole mass is estimated to be $10^{6.7\pm0.4}\, M_{\odot}$ from $M_{\mathrm{BH}}$ - $M_{\star,\mathrm{bul}}$ and $M_{\mathrm{BH}}$ - $L_{\mathrm{bul}}$ relations for the $K$ band, although a smaller value of $\sim10^5\, M_{\odot}$ cannot be excluded convincingly if the host galaxy harbors a pseudobulge.

GREAT3 results – I. Systematic errors in shear estimation and the impact of real galaxy morphology

We present first results from the third GRavitational lEnsing Accuracy Testing (GREAT3) challenge, the third in a sequence of challenges for testing methods of inferring weak gravitational lensing shear distortions from simulated galaxy images. GREAT3 was divided into experiments to test three specific questions, and included simulated space- and ground-based data with constant or cosmologically-varying shear fields. The simplest (control) experiment included parametric galaxies with a realistic distribution of signal-to-noise, size, and ellipticity, and a complex point spread function (PSF). The other experiments tested the additional impact of realistic galaxy morphology, multiple exposure imaging, and the uncertainty about a spatially-varying PSF; the last two questions will be explored in Paper II. The 24 participating teams competed to estimate lensing shears to within systematic error tolerances for upcoming Stage-IV dark energy surveys, making 1525 submissions overall. GREAT3 saw considerable variety and innovation in the types of methods applied. Several teams now meet or exceed the targets in many of the tests conducted (to within the statistical errors). We conclude that the presence of realistic galaxy morphology in simulations changes shear calibration biases by $\sim 1$ per cent for a wide range of methods. Other effects such as truncation biases due to finite galaxy postage stamps, and the impact of galaxy type as measured by the S\'{e}rsic index, are quantified for the first time. Our results generalize previous studies regarding sensitivities to galaxy size and signal-to-noise, and to PSF properties such as seeing and defocus. Almost all methods' results support the simple model in which additive shear biases depend linearly on PSF ellipticity.

THE ROLE OF BULGE FORMATION IN THE HOMOGENIZATION OF STELLAR POPULATIONS ATZ∼ 2 AS REVEALED BY INTERNAL COLOR DISPERSION IN CANDELS

We use data from the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey to study how the spatial variation in the stellar populations of galaxies relate to the formation of galaxies at $1.5 < z < 3.5$. We use the Internal Color Dispersion (ICD), measured between the rest-frame UV and optical bands, which is sensitive to age (and dust attenuation) variations in stellar populations. The ICD shows a relation with the stellar masses and morphologies of the galaxies. Galaxies with the largest variation in their stellar populations as evidenced by high ICD have disk-dominated morphologies (with S\'{e}rsic indexes $< 2$) and stellar masses between $10 < \mathrm{Log~M/ M_\odot}< 11$. There is a marked decrease in the ICD as the stellar mass and/or the S\'ersic index increases. By studying the relations between the ICD and other galaxy properties including sizes, total colors, star-formation rate, and dust attenuation, we conclude that the largest variations in stellar populations occur in galaxies where the light from newly, high star-forming clumps contrasts older stellar disk populations. This phase reaches a peak for galaxies only with a specific stellar mass range, $10 < \mathrm{Log~M/ M_\odot} < 11$, and prior to the formation of a substantial bulge/spheroid. In contrast, galaxies at higher or lower stellar masses, and/or higher S\'{e}rsic index ($n > 2$) show reduced ICD values, implying a greater homogeneity of their stellar populations. This indicates that if a galaxy is to have both a quiescent bulge along with a star forming disk, typical of Hubble Sequence galaxies, this is most common for stellar masses $10 < \mathrm{Log~M/M_\odot} < 11$ and when the bulge component remains relatively small ($n<2$).

STRUCTURE AND MORPHOLOGY OF X-RAY-SELECTED ACTIVE GALACTIC NUCLEUS HOSTS AT 1 &lt; z &lt; 3 IN THE CANDELS-COSMOS FIELD

We analyze morphologies of the host galaxies of 35 X-ray selected active galactic nucleus (AGNs) at $z\sim2$ in the Cosmic Evolution Survey (COSMOS) field using Hubble Space Telescope/WFC3 imaging taken from the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS). We build a control sample of 350 galaxies in total, by selecting ten non-active galaxies drawn from the same field with the similar stellar mass and redshift for each AGN host. By performing two dimensional fitting with GALFIT on the surface brightness profile, we find that the distribution of S$\`e$rsic index (n) of AGN hosts does not show a statistical difference from that of the control sample. We measure the nonparametric morphological parameters (the asymmetry index A, the Gini coefficient G, the concentration index C and the M20 index) based on point source subtracted images. All the distributions of these morphological parameters of AGN hosts are consistent with those of the control sample. We finally investigate the fraction of distorted morphologies in both samples by visual classification. Only $\sim$15% of the AGN hosts have highly distorted morphologies, possibly due to a major merger or interaction. We find there is no significant difference in the distortion fractions between the AGN host sample and control sample. We conclude that the morphologies of X-ray selected AGN hosts are similar to those of nonactive galaxies and most AGN activity is not triggered by major merger.

STRUCTURAL PARAMETERS FOR GLOBULAR CLUSTERS IN M31

In this paper, we present surface brightness profiles for 79 globular clusters in M31, using images observed with {\it Hubble Space Telescope}, some of which are from new observations. The structural and dynamical parameters are derived from fitting the profiles to several different models for the first time. The results show that in the majority of cases, King models fit the M31 clusters as well as Wilson models, and better than S\'{e}rsic models. However, there are 11 clusters best fitted by S\'{e}rsic models with the S\'{e}rsic index $n>2$, meaning that they have cuspy central density profiles. These clusters may be the well-known core-collapsed candidates. There is a bimodality in the size distribution of M31 clusters at large radii, which is different from their Galactic counterparts. In general, the properties of clusters in M31 and the Milky Way fall in the same regions of parameter spaces. The tight correlations of cluster properties indicate a "fundamental plane" for clusters, which reflects some universal physical conditions and processes operating at the epoch of cluster formation.

Simulations of single- and two-component galaxy decompositions for spectroscopically selected galaxies from the Sloan Digital Sky Survey

We present the results of fitting simulations of an unbiased sample of SDSS galaxies utilizing the fitting routine GALFIT and analysis pipeline PyMorph. These simulations are used to test the two-dimensional decompositions of SDSS galaxies. The simulations show that single S{\'e}rsic models of SDSS data are recovered with $\sigma_{\mathrm{mag}} \approx 0.025$ mag and $\sigma_{\mathrm{radius}} \approx 5\%$. The global values (half-light radius and magnitude) are equally well constrained when a two-component model is used. Sub-components of two-component models present more scatter. SDSS resolution is the primary source of error in the recovery of models. We use a simple statistical correction of the biases in fitted parameters, providing an example using the S{\'e}rsic index. Fitting a two-component S{\'e}rsic + Exponential model to a single S{\'e}rsic galaxy results in a noisier, but unbiased, recovery of the input parameters ($\sigma_{\mathrm{total mag}} \approx 0.075$ mag and $\sigma_{\mathrm{radius}} \approx 10\%$); fitting a single S{\'e}rsic profile to a two-component system results in biases of total magnitude and halflight radius of $\approx 0.05-0.10$ mag and 5\%-10\% in radius. Using an F-test to select the best fit model from among the single- and two-component models is sufficient to remove this bias. We recommend fitting a two-component model to all galaxies when attempting to measure global parameters such as total magnitude and halflight radius.

A SPITZER STUDY OF PSEUDOBULGES IN S0 GALAXIES: SECULAR EVOLUTION OF DISKS

In this Letter, we present a systematic study of lenticular (S0) galaxies based on mid-infrared imaging data on 185 objects taken using the Spitzer Infra Red Array Camera. We identify the S0s hosting pseudobulges based on the position of the bulge on the Kormendy diagram and the S\'{e}rsic index of the bulge. We find that pseudobulges preferentially occur in the fainter luminosity class (defined as having total K-band absolute magnitude M_K fainter than -22.66 in the AB system). We present relations between bulge and disk parameters obtained as a function of the bulge type. The disks in the pseudobulge hosting galaxies are found to have distinct trends on the r_e-r_d and \mu_d (0) - r_d correlations compared to those in galaxies with classical bulges. We show that the disks of pseudobulge hosts possess on average a smaller scale length and have a fainter central surface brightness than their counterparts occurring in classical bulge hosting galaxies. The differences found for discs in pseudobulge and classical bulge hosting galaxies may be a consequence of the different processes creating the central mass concentrations.

STELLAR POPULATION PROPERTIES AND EVOLUTION ANALYSIS OF NGC 628 WITH PANCHROMATIC PHOTOMETRY

Panchromatic spectral energy distribution (SED) from the ultraviolet (UV), optical to infrared (IR) photometry of NGC 628, combined with the evolutionary stellar population synthesis, is used to derive the spatially resolved age, metallicity and reddening maps. These parameter distributions show that the bulge of this galaxy is a disk-like pseudobulge, which has the S{\'e}rsic index close to the exponential law, rich gas, and a young circumnuclear ring structure. We also discover the disk has two distinct regions with different radial age and metallicity gradients. The inner region is older and has a much steeper age gradient than the outer region of the disk. Both these two regions and the central young structure can be seen in the radial profile of the optical color. Based on the age and reddening distributions, we consider that the pseudobulge and disk are likely to have grown via the secular evolution, which is the redistribution of mass and energy through the angular momentum transport caused by the non-axisymmetric potential of the spirals. However, possible gas accretion events could affect the outer region of the disk, due to abundant H{\sc i} gas accumulating in the outer disk.