A symmetry-induced model of elliptical galaxy patterns

Sérsic (Atlas de Galaxias Australes, Observatorio Astronómico, 1968) generalized the de Vaucouleurs law which follows the projected (observed) one dimensional radial profile of elliptical galaxies closely and Dehnen (Mon. Not. R. Astron. Soc. 265:250, 1993) proposed an analytical formula of the 3-dimensional light distributions whose projected line profile resembles the de Vaucouleurs law. This paper is involved to recover the Dehnen model and generalize the model to account for galaxy elliptical shapes by means of curvilinear coordinate systems and employing a symmetry principle. The symmetry principle maps an orthogonal coordinate system to a light distribution pattern. The coordinate system for elliptical galaxy patterns turns out to be the one which is formed by the complex-plane reciprocal transformation Z=1/W. The resulting spatial (3-dimensional) light distribution is spherically symmetric and has infinite gradient at its center, which is called spherical-nucleus solution and is used to model galaxy central area. We can make changes of the coordinate system by cutting out some column areas of its definition domain, the areas containing the galaxy center. The resulting spatial (3-dimensional) light distributions are axisymmetric or triaxial and have zero gradient at the center, which are called elliptical-shape solutions and are used to model global elliptical patterns. The two types of logarithmic light distributions are added together to model full elliptical galaxy patterns. The model is a generalization of the Dehnen model. One of the elliptical-shape solutions permits realistic numerical calculation and is fitted to all R-band elliptical images from Frei et al. (Astron. J. 111:174, 1996) galaxy sample. The fitting is satisfactory. This suggests that elliptical galaxy patterns can be represented in terms of a few basic parameters.     

Morphology and Structure of High-redshift Massive Galaxies in the CANDELS Fields

Using the multi-band photometric data of all five CANDELS (Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey) fields and the near-infrared (F125W and F160W) high-resolution images of HST WFC3 (Hubble Space Telescope Wide Field Camera 3), a quantitative study of morphology and structure of mass-selected galaxies is presented. The sample includes 8002 galaxies with a redshift 1 < z < 3 and stellar mass M_*> 10¹⁰M_⊙. Based on the Convolutional Neural Network (ConvNet) criteria, we classify the sample galaxies into SPHeroids (SPH), Early-Type Disks (ETD), Late-Type Disks (LTD), and IRRegulars (IRR) in different redshift bins. The findings indicate that the galaxy morphology and structure evolve with redshift up to z ～ 3, from irregular galaxies in the high-redshift universe to the formation of the Hubble sequence dominated by disks and spheroids. For the same redshift interval, the median values of effective radii (r_e) of different morphological types are in a descending order: IRR, LTD, ETD, and SPH. But for the Sérsic index (n), the order is reversed (SPH, ETD, LTD, and IRR). In the meantime, the evolution of galaxy size (r_e) with the redshift is explored for the galaxies of different morphological types, and it is confirmed that their size will enlarge with time. However, such a phenomenon is not found in the relations between the redshift (1 < z < 3) and the mean axis ratio (b/a), as well as the Sérsic index (n).     

The Fundamental Plane of E Galaxies in Compact Groups

We present a study focusing on the nature of compact groups through the study of their elliptical galaxies. We determine central velocity dispersions (σ_o) for 18 bright elliptical galaxies located in the core of Hickson compact groups and a control sample of 12 brightbona fide ellipticals located in the field or very loose groups. Several tests are carried out to avoid systematic effects in σ measurements. We use these velocity dispersions to compare the position of 11 compact group galaxies in the Fundamental Plane to that of a large and homogeneous sample of elliptical galaxies (Burstein et al., 1987).We find that little or no significant difference exists, as far as the Fundamental Plane is concerned, between ellipticals in compact groups and their counterparts in other environments. This revised version was published online in July 2006 with corrections to the Cover Date.     

Kinematics and stellar populations of 17 dwarf early-type galaxies

We present kinematics and stellar population properties of 17 dwarf early-type galaxies in the luminosity range -14 ≥ M _B ≥ -19. Our sample fills the gap between the intensively studied giant elliptical and Local Group dwarf spheroidal galaxies. The dwarf ellipticals of the present sample have constant velocity dispersion profiles within their effective radii and do not show significant rotation, hence are clearly anisotropic. The dwarf lenticulars, instead, rotate faster and are, at least partially, supported by rotation. From optical Lick absorption indices, we derive metallicities and element abundances. Combining our sample with literature data of the Local Group dwarf spheroidals and giant ellipticals, we find a surprisingly tight linear correlation between metallicity and luminosity over a wide range: -8 ≥ M _B ≥ -22. The α/Fe ratios of our dwarf ellipticals are significantly lower than the ones of giant elliptical galaxies, which is in agreement with spectroscopy of individual stars in Local Group dwarf spheroidals. Our results suggest the existence of a clear kinematic and stellar population dichotomy between dwarf and giant elliptical galaxies. This result is important for theories of galaxy formation, because it implies that present-day dwarf ellipticals are not the fossiled building blocks of giant ellipticals. This revised version was published online in August 2006 with corrections to the Cover Date.     

Galaxy Evolution from Deep Field Galaxy Counts

We present deep galaxy number counts and colours of K—band selected galaxy surveys. We argue that primeval galaxies are present within the survey data, but have remained unidentified. There are few objects with the colours of an L ^* elliptical galaxy at a redshift of z ≈ 1, in contradiction to standard luminosity evolution models. We present K—band photometry of the objects in a spectroscopic redshift survey selected at 21 < B < 22.5. The absolute K magnitudes of the galaxies are consistent with the no-evolution or pure luminosity evolution models. The excess faint blue galaxies seen in the B—band number counts at intermediate magnitudes are a result of a low normalization, and do not dominate the population until B ≈ 25. Extreme merging or excess dwarf models are not needed at z < 1. This revised version was published online in July 2006 with corrections to the Cover Date.     

UV-radiation in galaxies

I review the origin of UV-radiation in galaxies of different morphological types. UV-excess in spectra of massive elliptical galaxies which have predominantly old stellar populations is traditionally explained by the contribution of low-mass stars at very late, poorly known stages of evolution—by so called ‘AGB-manqué’ stars or by the population of extended horizontal branch. However recent results from the GALEX survey of a large sample of nearby ellipticals have also demonstrated probable traces of recent star formation in a third of all ellipticals observed. In spiral galaxies extended UV-disks have been discovered by the GALEX; they are certainly illuminated by the current star formation, but what has provoked star formation in the areas of very low gas density, beyond the distribution of older stars, is a puzzle yet. The UV-spectra of starburst galaxies or starforming galactic nuclei are characterized by weak emission lines, if any, quite dissimilar to their optical spectra.     

Mass of Galaxies in Pairs

We have compared the frequency distribution of the dynamical observedquantity log (V _z ² r _p), for a sample of 46 pairs of elliptical galaxies, to the distribution of this quantity obtained from numerical simulations of pairs of galaxies. From such an analysis, where we have considered the structure of the galaxies and its influence in the orbital evolution of the system, we have obtained the characteristic mass and the mass-luminosity ratio for the sample. Our results show that the hypothesis of point-mass in elliptical orbits is, for this sample, an approximation as good as the model that takes into account the structure of the galaxies. The statistical method used here gives an estimate of a more reliable mass, it minimizes the contamination of spurious pairs and it considers adequately the contribution of the physical pairs. We have obtained a characteristic mass to the 46 elliptical pairs of 1.68 × 10¹² ± 7.01 ×10¹¹ M_⊙ with M/L = 17.6 ± 7.3 (H ₀ = 60 km s^-1Mpc^-1). This revised version was published online in July 2006 with corrections to the Cover Date.     

早型旋涡星系M81 (NGC 3031)的形态学解构研究

利用星系解构软件GALFIT通过面亮度轮廓拟合对近邻早型旋涡星系M81 (NGC 3031)进行形态学解构,旨在探究M81星系的结构组成并对其进行形态学量化.通过6种解构模式,对M81进行了不同复杂程度的结构分解,其中最复杂的解构模式包含核球、盘、外旋臂、内旋臂、星系核5个子结构.研究结果显示, M81有一个Sérsic指数约为5.0的经典核球,其形态和光度在不同解构模式中均保持稳定; M81星系盘的Sérsic指数约为1.2,但它的形态参数和光度与是否分解内旋臂相关.不同子结构的组合对作为混合体的星系整体的形态有不可忽视的影响.星系解构的结果提供了不同解构模式适用性的建议:其中核球+盘+星系核的三成分解构适用于大样本星系的核-盘研究;而考虑旋臂的复杂解构则适合于对星系子结构的精确测量,如小样本(或个源)研究.基于Spitzer-The Infrared Array Camera (IRAC) 4.5μm的单波段图像的形态学解构研究是后续一系列研究的开始,在此基础上未来将会对M81进行多波段解构,同时研究不同子结构的光谱能量分布和星族性质,并推断M81各子结构的形成历史和演化过程.     

The Stellar Populations of Early-Type Galaxies in the Fornax Cluster

We have measured central line strengths for a complete sample of early-type galaxies in the Fornax Cluster comprising 11 elliptical and 11 lenticular galaxies, more luminous than M _B=–17. We find that the centres of Fornax ellipticals follow the locus of galaxies of fixed age in Worthey's models and have metallicities varying roughly from half to 2.5 times solar. The centres of (relatively low luminosity) lenticular galaxies, however, exhibit a substantial spread to younger luminosity-weighted ages indicating amore extended star formation history. Our conclusions are based on two age/metallicity diagnostic diagrams in the Lick/IDS system comprising established indices such as [MgFe]and H_β as well as new and more sensitive indices, such as Fe3and H . The inferred difference in the age distribution between lenticular and elliptical galaxies is a robust conclusion as the models generate consistent relative ages using different age and metallicity indicators even though the absolute ages remain uncertain. The absolute age uncertainty is caused mainly by the effects of non-solar abundance ratios, which are not accounted for in the stellar population models. We find that Es are generally overabundant in magnesium and the most luminous galaxies show stronger overabundances. The luminosity-weighted stellar populations of young S0s are consistent with solar abundance ratios or a weak Mg under abundance. Two of the faintest lenticular galaxies in our sample have blue continua and extremely strong Balmer-line absorptions suggesting starbursts <2 Gyr ago. This revised version was published online in July 2006 with corrections to the Cover Date.     

核盘晕星系相互作用的模拟研究

用一个星系相互作用数值模拟的综合三体模型，研究椭圆星系是否由盘星系合并而成。结果表明，主要取决于星系的盘面和星系运行轨道面的夹角。如果夹角不等于零，盘星系的相互作用是可能形成椭圆星系的，否则还是盘星系。     

Tidal dwarf galaxies at intermediate redshifts

We present the first attempt at measuring the production rate of tidal dwarf galaxies (TDGs) and estimating their contribution to the overall dwarf population. Using HST/ACS deep imaging data from GOODS and GEMS surveys in conjunction with photometric redshifts from COMBO-17 survey, we performed a morphological analysis for a sample of merging/interacting galaxies in the Extended Chandra Deep Field South and identified tidal dwarf candidates in the rest-frame optical bands. We estimated a production rate about 1.4×10⁻⁵ per Gyr per comoving volume for long-lived TDGs with stellar mass 3×10⁸⁻⁹ M_⊙ at 0.5<z<1.1. Together with galaxy merger rates and TDG survival rate from the literature, our results suggest that only a marginal fraction (less than 10%) of dwarf galaxies in the local universe could be tidally-originated. TDGs in our sample are on average bluer than their host galaxies in the optical. Stellar population modelling of optical to near-infrared spectral energy distributions (SEDs) for two TDGs favors a burst component with age 400/200 Myr and stellar mass 40%/26% of the total, indicating that a young stellar population newly formed in TDGs. This is consistent with the episodic star formation histories found for nearby TDGs.     

Application of a newN-body code to the encounters of galaxies and dissipationless formation of elliptical galaxies

A new code has been used to simulate the formation of elliptical galaxies via a dissipationless collapse by a numerical experiment. Preliminary results of numerical simulations are presented for initial 2T/|W| conditions ranging from 10^–2 to 10^–5. The importance of inhomogeneity in the initial density distribution and of merging is outlined.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.     

Density–potential pairs for spherical stellar systems with Sérsic light profiles and (optional) power-law cores

Popular models for describing the luminosity-density profiles of dynamically hot stellar systems (e.g. Jaffe, Hernquist, Dehnen) were constructed with the desire to match the deprojected form of an   R ^1/4  light profile. Real galaxies, however, are now known to have a range of different light-profile shapes that scale with mass. Consequently, although highly useful, the above models have implicit limitations, and this is illustrated here through their application to a number of real galaxy density profiles. On the other hand, the analytical density profile given by Prugniel & Simien closely matches the deprojected form of Sérsic   R ^{1/ n}   light profiles – including deprojected exponential light profiles. It is thus applicable for describing bulges in spiral galaxies, dwarf elliptical galaxies, and both ordinary and giant elliptical galaxies. Moreover, the observed Sérsic quantities define the parameters of the density model. Here we provide simple equations, in terms of elementary and special functions, for the gravitational potential and force associated with this density profile. Furthermore, to match galaxies with partially depleted cores, and better explore the supermassive black hole/galaxy connection, we have added a power-law core to this density profile and derived similar expressions for the potential and force of this hybrid profile. Expressions for the mass and velocity dispersion, assuming isotropy, are also given. These spherical models may also prove appropriate for describing the dark matter distribution in haloes formed from ΛCDM cosmological simulations.     

Infrared Imaging of Perpendicular Nested Bars in Spiral Galaxies with the Infrared Camera at the Carlos Sánchez Telescope

Images are presented of some of the galaxies in the sample of the BARS `International Time Project' in the near-infrared JHK _s bands, obtained with the Infra-Red Camera at the 1.5 m Carlos Sánchez Telescope, Teide Observatory, between 1996 and 1998. We discuss the scientific importance of imaging galaxies in the near-infrared bands and recent and future developments concerning the Infra-Red Camera. This revised version was published online in July 2006 with corrections to the Cover Date.     

CDM, Feedback and the Hubble Sequence

We have performed TreeSPH simulations of galaxy formation in a standard ΛCDM cosmology, including effects of star formation, energetic stellar feedback processes and a meta-galactic UV field, and obtain a mix of disk, lenticular and elliptical galaxies. The disk galaxies are deficient in angular momentum by only about a factor of two compared to observed disk galaxies. The stellar disks have approximately exponential surface density profiles, and those of the bulges range from exponential to r ^1/4, as observed. The bulge-to-disk ratios of the disk galaxies are consistent with observations and likewise are their integrated B-V colours, which have been calculated using stellar population synthesis techniques. Furthermore, we can match the observed I-band Tully-Fisher (TF) relation, provided that the mass-to-light ratio of disk galaxies is (M/L _I) ≃ 0.6–0.7. The ellipticals and lenticulars have approximately r ^1/4 stellar surface density profiles, are dominated by non-disklike kinematics and flattened due to non-isotropic stellar velocity distributions, again consistent with observations. This revised version was published online in September 2006 with corrections to the Cover Date.     

HST imaging of radio galaxies at z=0.2: a comparison with quasar hosts and normal ellipticals

We summarise the results of our recently completed HST R-band study of low-redshift (0.1<z<0.25) FRII radio galaxies along with the host galaxies of quasars of similar redshifts. We find that, like radio galaxies, the hosts of radio-loud quasars and all but the least luminous radio-quiet quasars are massive elliptical galaxies with relatively large scalelengths (≃10 kpc) and luminosities (>2L*). Indeed the quasar hosts are essentially indistinguishable from the radio galaxies in our sample. Apart from the nuclear activity there is little to distinguish the AGN hosts from inactive massive elliptical galaxies.     

Scaling relations of field spirals at intermediate redshift

In the last few years, galaxies at redshifts up to z ∼ 1 have become accessible for medium-resolved spectroscopy thanks to the new generation of 10 m-class telescopes. With kinematic and photometric information on spiral galaxies in this regime, well-known scaling relations like the Tully-Fisher relation (TFR) can be studied over half a Hubble time. By comparison to local samples, these studies facilitate simultaneous tests of the hierarchical merging scenario and stellar population models. Using the Very Large Telescope, we obtained spatially resolved rotation curves of 78 spiral galaxies in the FORS Deep Field (FDF), covering all Hubble types from Sa to Sm/Irr at redshifts 0.1 < z < 1.0. We find evidence for a B-band luminosity increase of up to 2 mag for low-mass spirals, whereas the most massive galaxies are of the same luminosity as their local counterparts. In effect, the TFR slope decreases significantly. This would explain the discrepant results of previous observational studies. We also present the velocity-size relation and compare it to the predictions of numerical simulations based on the hierarchical merging scenario. This revised version was published online in August 2006 with corrections to the Cover Date.     

The Evolutionary Status of Early-type Galaxies in Abell 2390

We explore the evolution of the early-type galaxy population in the rich cluster Abell 2390 at z=0.23. For this purpose, we have obtained spectroscopic data of 51 elliptical and lenticular galaxies with MOSCA at the 3.5 m telescope on Calar Alto Observatory. As our investigation spans both a broad range in luminosity (–22.3≤M_B≤–:19.3)and a wide field of view (10′×10′), the environmental dependence of different formation scenarios can be analysed in detail as a function of radius from the cluster center. In this paper, we present first results on the Faber-Jackson relation and, for a subsample of 14 galaxies with morphological and structural parameters from HST, we also investigate the evolution of the Kormendy relation and the Fundamental Plane. We find a mild luminosity evolution of the early-type galaxies in Abell 2390: our objects are on average brighter by m _B∼0.4 mag. This revised version was published online in July 2006 with corrections to the Cover Date.     

New insights into the photometric structure of Blue Compact Dwarf Galaxies from a deep Near-Infrared study

We present deep Near-Infrared (NIR) imaging of Blue Compact Dwarf Galaxies (BCDs), allowing for the first time to derive and systematize the NIR structural properties of their stellar low-surface brightness (LSB) host galaxies. Compared to optical data, NIR images, being less contamined by the extended stellar and ionized gas emission from the starburst, permit to study the LSB host galaxy closer to its center. We find that radial surface brightness profiles (SBPs) of the LSB hosts show at large radii a mostly exponential intensity distribution, in agreement with previous optical studies. At small to intermediate radii, however, the NIR data reveal an inwards flattening with respect to the outer exponential slope (`type V SBPs', Binggeli and Cameron, 1991) in the LSB component of more than one half of the sample BCDs. This result may constitute an important observational constraint to the dynamics and evolution of BCDs. We apply a modified exponential fitting function (Papaderos et al., 1996a) to parametrize and systematically study type V profiles in BCDs. A Sérsic law is found to be less suitable for studying the LSB component of BCDs, since it yields very uncertain solutions. This revised version was published online in August 2006 with corrections to the Cover Date.     

On the βSPEC Values of Galaxy Clusters During the Merger

Time-dependent, X-ray emission properties of merging subclusters of galaxies are studied by N-body + Hydrodynamic simulations. We consider rather idealized cases, in which two virialized subclusters with the same or different masses collide with each other, eventually merging into one bigger cluster. We find that the various observable quantities, such as the cluster temperature, T_g, the line-of-sight velocity dispersion of galaxies, σ₁, and the specific energy ratio, β_spec ≡ μ m_p σ /k_B T_g (where μ is the mean molecular weight in amu, m_p is the proton mass and k_B is the Boltzmann constant) are distinct in merging clusters from those in isolated clusters. When merging, especially, in addition to having large velocity dispersions, σ_l ≳ 2000 km s^-1, clusters will have large deviations of β_spec from unity; that is, β_spec ≳ 2.0 (or β_spec ≲ 0.5) when seen from the direction parallel (perpendicular) to the collision axis. Temperature profiles are the best indicator of merging process. The calculated temperature maps of merging clusters are compared with those of the observed clusters, such as the Coma cluster, A754, and A401/399 supercluster. These simulated features are in good agreement with what ASCA revealed. Further, we present rather unique features in the temperature profiles that can be caused by a merger (or an encounter) with a subgroup of galaxies. This revised version was published online in July 2006 with corrections to the Cover Date.