Models for Low-Mass X-Ray Binaries in the Elliptical Galaxies NGC3379 and NGC4278: Comparison with Observations
T. Fragos, V. Kalogera, K. Belczynski, G. Fabbiano, D. -W. Kim, N. J. Brassington, L. Angelini, R. L. Davies, J. S. Gallagher, A. R. King, S. Pellegrini, G. Tri… 展开作者
T. Fragos, V. Kalogera, K. Belczynski, G. Fabbiano, D. -W. Kim, N. J. Brassington, L. Angelini, R. L. Davies, J. S. Gallagher, A. R. King, S. Pellegrini, G. Trinchieri, S. E. Zepf, A. Zezas
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54 pages, 22 figure, submitted to The Astrophysical Journal
We present theoretical models for the formation and evolution of populations of low-mass X-ray binaries (LMXB) in the two elliptical galaxies NGC 3379 and NGC 4278. The models are calculated with the recently updated StarTrack code (Belczynski et al., 2006), assuming only a primordial galactic field LMXB population. StarTrack is an advanced population synthesis code that has been tested and calibrated using detailed binary star calculations and incorporates all the important physical processes of binary evolution. The simulations are targeted to modeling and understanding the origin of the X-ray luminosity functions (XLF) of point sources in these galaxies. For the first time we explore the population XLF down to luminosities of 3X10^36 erg/s, as probed by the most recent observational results (Kim et al., 2006). We consider models for the formation and evolution of LMXBs in galactic fields with different CE efficiencies, stellar wind prescriptions, magnetic braking laws and initial mass functions. We identify models that produce an XLF in excellent agreement with the observations both in shape and absolute normalization. We also find that the treatment of the outburst luminosity of transient systems remains a crucial factor for the determination of the XLF since the modeled populations are dominated by transient X-ray systems.
The radial velocity curves of many spectroscopic binaries (SBs) are perturbed by gas streams or proximity effects. For SBs with circular orbits, these perturbations can give rise to spurious orbital eccentricities of high statistical significance. But tests to identify such anomalous orbits can be constructed since perturbed velocity curves are in general no longer Keplerian. The derived tests are applied both to synthetic and to observed velocity curves.
Chandra observations of elliptical galaxies have revealed large numbers of Low Mass X-ray Binaries (LMXBs) accreting at rates above 10^-9 solar masses per year. One scenario which generates this transfer rate from an old stellar population is nuclear driven mass transfer onto a neutron star or black hole from a Roche lobe filling red giant. However, in our Galaxy, most of these systems accrete sporadically as transients due to a thermal instability in the accretion disk. Using the common criterion for disk instability (including irradiation), we find that this mode of mass transfer leads to tr…
The X-ray emission from normal elliptical galaxies has two major components: soft emission from diffuse gas and harder emission from populations of accreting (low-mass) stellar X-ray binaries (LMXB). If LMXB populations are tied to the field stellar populations in galaxies, their total X-ray luminosities should be proportional to the optical luminosities of galaxies. However, recent ASCA and Chandra X-ray observations show that the global luminosities of LMXB components in ellipticals exhibit significant scatter at a given optical luminosity. This scatter may reflect a range of evolutionary st…
Chandra observations of distant elliptical galaxies have revealed large numbers of Low Mass X-ray Binaries (LMXBs) accreting at rates in excess of 10^{-8} solar masses per year. The majority of these LMXBs reside in globular clusters (GCs) and it has been suggested that many of the field LMXBs also originated in GCs. We show here that ultracompact binaries with orbital periods of 8-10 minutes and He or C/O donors of 0.06-0.08 solar masses naturally provide the observed accretion rates from gravitational radiation losses alone. Such systems are predicted to be formed in the dense GC environment…
This article reviews the popular reasons for the belief that dwarf elliptical galaxies and (ordinary) elliptical galaxies are distinct and separate species. They include: light-profile shape (or similarly image concentration); the magnitude-central surface brightness diagram; the magnitude-effective surface brightness diagram (or similarly the magnitude-effective radius diagram); and the Fundamental Plane. It is shown how a continuous trend between luminosity and a) light-profile shape, and b) central surface brightness (until the onest of core formation at M_B ~ -20.5 mag, results in a unific…
Chandra's high angular resolution can resolve emission from stellar X-ray binaries out of the diffuse X-ray emission from gaseous atmospheres within elliptical galaxies. Variations in the X-ray binary populations (per unit galaxian optical luminosity) are correlated with variations in the specific frequency of globular clusters in ellipticals. This indicates that X-ray binaries are largely formed in globular clusters, rather than being a primordial field population.
The excess of far-ultraviolet (far-UV) radiation in elliptical galaxies has remained one of their most enduring puzzles. In contrast, the origin of old blue stars in the Milky Way, hot subdwarfs, is now reasonably well understood: they are hot stars that have lost their hydrogen envelopes by various binary interactions. Here, we review the main evolutionary channels that produce hot subdwarfs in the Galaxy and present the results of binary population synthesis simulations that reproduce the main properties of the Galactic hot-subdwarf population. Applying the same model to elliptical galaxies,…
Bright elliptical galaxies have a markedly different distribution of Hubble types than faint ellipticals; the division occurs near M_B=-20 and bright ellipticals are rounder on average. The Hubble types of galaxies in both groups are narrowly clustered, around E1.5 in the case of the bright galaxies and around E3 for the fainter ones. The Hubble-type distribution of the faint ellipticals is consistent with oblate symmetry, but the oblate hypothesis fails for the bright ellipticals. However a distribution of triaxial intrinsic shapes can successfully reproduce the apparent shape data for either…
Recent work on the construction of spherical, Axisymmetric and triaxial dynamical models for elliptical galaxies is reviewed briefly, including their role in providing evidence for dark halos and central black holes. The different orbital structures and shapes of low-mass and giant elliptical galaxies provide essential constraints on scenarios of galaxy formation.
The distribution and kinematics of the molecular gas in elliptical galaxies give information on the origin and history of the gas and the rate of star formation activity in ellipticals. I describe some preliminary results of a survey which will more than double the number of elliptical galaxies with resolved molecular distributions.
Elliptical galaxies outside dense clusters are observed to contain small amounts (relative to spiral galaxies) of cold interstellar gas. This review discusses the atomic gas, the molecular gas, and the dust in elliptical galaxies. Field elliptical galaxies contain about 0.01 to 0.1 of the cold interstellar matter content of spiral galaxies of similar luminosity, and support a low level of star formation. The surface densities of cold gas clouds in the centers of some elliptical galaxies are comparable to those in the densest regions of the Galactic disk. These observations suggest that ellipti…
Ellipticals in very low density environments are extremely rare but hold important clues about galaxy formation and evolution. In this paper we continue our study of isolated elliptical galaxies, presenting results on the radial stellar kinematics for 13 isolated early-type galaxies. We derive radial rotation velocity, velocity dispersion and hermite terms to ~1 effective radius. We observe a dichotomy in kinematic properties similar to that in the elliptical population as a whole, where low luminosity ellipticals tend to be rotationally supported. For all galaxies the V/sigma ratio increases …
The luminosity dependence of kinematical and isophotal properties of elliptical galaxies is investigated using numerical simulations of galaxy merging, combined with semi-analytical models of hierarchical structure formation. Mergers of spiral galaxies as the only formation mechanism for elliptical galaxies can neither reproduce the kinematical and photometric properties of very massive elliptical galaxies nor the change from rotationally flattened disky to anisotropic boxy systems with increasing luminosity. We present numerical simulations showing that binary mergers of early-type galaxies o…
It is shown that the MOdified Newtonian Dynamics (MOND) explains the tilt of the fundamental plane of elliptical galaxies without the need of non-baryonic dark matter. Results found for elliptical galaxies extends to globular clusters and galaxy clusters, showing that MOND agrees with observations over 7 order of magnitude in acceleration.
This paper has been withdrawn by the author due to the discovery of a serious bias resulting from the systematic dimming of galaxies with larger ellipticities away from the North Galactic Pole. Thus the conclusion that there is a special axis along which the elliptical galaxies tend to be aligned is incorrect.
Empirical evidence suggests that elliptical galaxies hosting a radio source may not be different from normal non-radio ellipticals. To test this possibility, we use Monte Carlo simulations to reproduce the distribution of radio galaxies in the radio-optical luminosity plane. The input parameters of the simulation are the optical luminosity function (LF) of ellipticals and the radio LF of radio galaxies, linked by a function giving the probability for an elliptical to be a radio galaxy. Simulations reproduce the observations well, supporting unification of radio and non-radio ellipticals, provi…
In this paper we present a quantitative analysis of the chemical abundances in "monolithic" N-body-Tree-SPH models of elliptical galaxies to determine whether the ratio [alpha/Fe] increases with the galaxy mass as suggested by observational data.
We determine relative stellar ages and metallicities mainly for about 80 elliptical galaxies in low and high density environments via the latest binary stellar population (BSP) synthesis model and test a latest hierarchical formation model of elliptical galaxies which adopted the new $Λ$CDM cosmology for the first time. The stellar ages and metallicities of galaxies are estimated from two high-quality published spectra line indices, i.e. H$β$ and [MgFe]. The results show that elliptical galaxies have stellar populations older than 3.9 Gyr and more metal rich than 0.02. Most of our results are …
In models of galaxy formation in a hierarchical Universe, elliptical galaxies form through the merging of smaller disk systems. These models yield a number of testable predictions if reliable techniques for determining the relative ages and compositions of the stellar populations of different galaxies can be found: 1) ellipticals in low-density environments form later than ellipticals in clusters, 2) more massive ellipticals form later, 3) more massive ellipticals form in dissipationless mergers from disk galaxies with low gas content. While colours and the Balmer line strengths of galaxies ca…
The traditional view of elliptical galaxies has been that they formed in a single, rapid burst of star formation at high redshift, and have evolved quiescently since that time. In opposition to this traditional view is evidence that at least some elliptical galaxies have formed from the merger of two disk galaxies. What has not been clear is which process is the dominant formation mechanism for the large majority of elliptical galaxies. This question has significant implications for cosmological models, as different models make different predictions for the formation mechanism and epoch of ell…
In this work we discuss on the basis of the instantaneous recycling approximation the possibility of determining a relation between matter distribution (luminous and dark) in elliptical galaxies and the observed metallicity gradients. A particular case is developed in detail yielding an analitycal expression of the above relation.
We present here the results about the determination of the Luminosity Function (LF) for elliptical galaxies in the core of fairly rich clusters as a function of redshift and try to compare with the known LF of close, better studied clusters of galaxies. We then outline the first use of a new method of selecting member elliptical galaxies using an unsupervised Artificial Neural Network (ANN) working on a purely photometric set of data.
We present a study focusing on the nature of compact groups through the study of their elliptical galaxies. We determine velocity dispersions ($σ$) for 18 18 bright elliptical galaxies located in the core of Hickson compact groups and a control sample of 12 bright bona fide ellipticals located in the field or very loose groups. Several tests are carried out to avoid sources of 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 (Bu…
We present UBVRI surface photometry for 16 dwarf elliptical galaxies in the Virgo Cluster with previously measured kinematic properties. The global optical colors are red, with median values for the sample of 0.24 +/- 0.03 in (U-B), 0.77 +/- 0.02 in (B-V), and 1.02 +/- 0.03 in (V-I). We recover the well known color-magnitude relation for cluster galaxies, but find no significant difference in dominant stellar population between rotating and non-rotating dwarf elliptical galaxies; the average age of the dominant stellar population is 5-7 Gyr in all 16 galaxies in this sample. Analysis of optica…
We present narrow band data on dwarf ellipticals in nearby (Virgo, Fornax) and intermediate redshift clusters (A2125, A2218) in order to study their mean age and metallicities. In all four clusters, nucleated dwarf ellipticals display colors that place them on the high metallicity end of the Milky Way globular cluster sequence. Normal dwarf ellipticals display colors, and resulting metallicities and ages, that align them with bright ellipticals. This suggests that dE,N's may be the ancestors to the red GC population found around many elliptical galaxies.
Recent results from gravitational lensing are combined with new modeling of the stellar velocity distributions in nearby galaxies to probe the connection between the luminous and the dark matter in elliptical galaxies. From analysing a small number of luminous ellipticals the following picture appears to emerge: (1) the best fitting total mass distribution (luminous and dark) leads to a flat rotation curve (v2=RdPhi/dR) from 0.3 to >= 3 effective radii; (2) half the total mass inside the effective radius (~3kpc) may already be dark, and (3) ellipticals reside in much denser halos than spiral g…
We present a discovery of a giant stellar halo in NGC 6822, a dwarf irregular galaxy in the Local Group. This halo is mostly made of old red giants, showing striking features: 1) it is several times larger than the main body of the galaxy seen in the optical images, and 2) it is elongated in the direction almost perpendicular to the HI disk of NGC 6822. The structure of this stellar halo looks similar to the shape of dwarf elliptical galaxies, indicating that the halos of dwarf irregular galaxies share the same origin with those of the dwarf elliptical galaxies.
We report an ultra-high-resolution simulation that follows evolution from the earliest stages of galaxy formation through the period of dynamical relaxation. The bubble structures of gas revealed in our simulation ($< 3\times 10^8$ years) resemble closely the high-redshift Lyman $α$ emitters (LAEs). After $10^9$ years these bodies are dominated by stellar continuum radiation and look like the Lyman break galaxies (LBGs) known as the high-redshift star-forming galaxies at which point the abundance of elements appears to be solar. After $1.3\times10^{10}$ years, these galaxies resemble present-d…
This paper looks for any correlation between the internal dynamics of elliptical galaxies and the relatively mild nuclear activity found in many such systems. We show that there is such a relation in the sense that the active ellipticals tend to be significantly less rotationally supported than their inactive cousins. The correlation can partly be related to the galaxies' luminosities: the brightest galaxies tend to be more active and less rotationally supported. However, even at lower luminosities the active and inactive galaxies seem to have systematically different dynamics. This variation …
This review is focussed on the outer halos of elliptical galaxies. Its emphasis is on (i) planetary nebulae as test particles to trace the stellar kinematics at large radii, (ii) the observed angular momentum in elliptical galaxy halos and its theoretical relevance, (iii) dynamical modelling of stellar-kinematic data, and (iv) a discussion of the evidence for dark matter halos in ellipticals from a wide range of measurements.
Hubble Space Telescope (HST) observations reveal that the density of stars in most elliptical galaxies rises toward the center in a power-law cusp. Many of these galaxies also contain central dark objects,possibly supermassive black holes. The gravitational force from a steep cusp or black hole will destroy most of the box orbits that constitute the ``backbone'' of a triaxial stellar system. Detailed modelling demonstrates that the resulting chaos can preclude a self-consistent, strongly triaxial equilibrium. Most elliptical galaxies may therefore be nearly axisymmetric, either oblate or prola…
Most elliptical galaxies contain central black holes, whose masses scale proportionally to the observed central velocity dispersions of the host galaxies according to the so-called Mbh-sigma relation. Here we discuss some consequences that can be derived by combining the Mbh-sigma relation with the scaling relation describing the Fundamental Plane of elliptical galaxies. In particular, the possibility of substantial dissipationless merging in the formation and evolution of elliptical galaxies is discussed. Enforcing the merger end-products to satisfy the two scaling relations mentioned above, …
This paper summarizes Kormendy et al. (2009, ApJS, in press, arXiv:0810.1681). We confirm that spheroidal galaxies have fundamental plane correlations that are almost perpendicular to those for bulges and ellipticals. Spheroidals are not dwarf ellipticals. They are structurally similar to late-type galaxies. We suggest that they are defunct ("red and dead") late-type galaxies transformed by a variety of gas removal processes. Minus spheroidals, ellipticals come in two varieties: giant, non-rotating, boxy galaxies with cuspy cores and smaller, rotating, disky galaxies that lack cores. We find a…
We review the origin and structure of hot (cooling flow) gas in elliptical galaxies. X-ray observations can be used to determine the stellar mass to light ratio, the mass profiles of dark matter halos, and the interstellar magnetic field. Interstellar gas cools over a large volume, forming stars with a bottom-heavy IMF. For consistency with the thin fundamental plane, young stars must be optically luminous. Circular X-ray isophotes in rotating elliptical galaxies indicate distributed radiative cooling or strong interstellar turbulence.
I review the current status of understanding when, how long, and how giant elliptical galaxies formed, focusing on the globular clusters. Several observational evidences show that massive elliptical galaxies formed at $z>2$ ($>10$ Gyr ago). Giant elliptical galaxies show mostly a bimodal color distribution of globular clusters, indicating a factor of $\approx 20$ metallicity difference between the two peaks. The red globular clusters (RGCs) are closely related with the stellar halo in color and spatial distribution, while the blue globular clusters (BGCs) are not. The ratio of the number of th…
We present a new model for the chemical evolution of elliptical galaxies taking into account SN feedback, detailed nucleosynthesis and galactic winds. We discuss the effect of galactic winds on the chemical enrichment of the ICM and compute the energy per particle injected by the galaxies into the ICM.
Multiple, sequential mergers are unavoidable in the hierarchical build-up picture of galaxies, in particular for the minor mergers that are frequent and highly likely to have occured several times for most present-day galaxies. However, the effect of repeated minor mergers on galactic structure and evolution has not been studied systematically so far. We present a numerical study of multiple, subsequent, minor galaxy mergers, with various mass ratios ranging from 4:1 to 50:1. The N-body simulations include gas dynamics and star formation. We study the morphological and kinematical properties o…
We use semi-analytical modelling of galaxy formation to predict the redshift-size-evolution of elliptical galaxies. Using a simple model in which relative sizes of elliptical galaxies of a given mass correlate with the fraction of stars formed in a star burst during a major merger event, we are able to reproduce the observed size redshif t evolution. The size evolution is a result of the amount of cold gas available during the major merger. Mergers at high redshifts are gas-rich and produce ellipticals with smaller sizes. In particular we find a power-law relation between the sizes at differen…
The detection of resonance absorption lines against known objects such as individual galaxies and clusters of galaxies is a powerful approach for studying the gas content of these systems. We describe an efficient method of identifying background quasars suitable for absorption line studies. In this finding technique, we identify serendipitous X-ray sources, about 1/8 of which are suitably bright quasars at moderate redshift. We identify 16 new quasars and galaxies with active galactic nuclei (AGNs), and confirm 5 known quasars and AGNs, superimposed behind elliptical galaxies and clusters of …
(Abridged) We investigate the number of physical companion galaxies for a sample of relatively isolated elliptical galaxies. NED has been used to reinvestigate the incidence of satellite galaxies for a sample of 34 elliptical galaxies, first investigated by Bothun & Sullivan in a visual search out to a projected search radius of 75 kpc. We have repeated their original investigation using data cataloged in NED. Nine of these elliptical galaxies appear to be members of galaxy clusters; the remaining sample of 25 galaxies reveals an average of +1.0+/-0.5 apparent companions per galaxy within a pr…
The origin of boxy and disky elliptical galaxies is investigated. The results of two collisionless N-body simulations of spiral-spiral mergers with mass ratios of 1:1 and 3:1 are discussed and the projected properties of the merger remnants are investigated. It is shown that the equal-mass merger leads to an anisotropic, slowly rotating system with preferentially boxy isophotes and significant minor axis rotation. The unequal-mass merger results in the formation of a rotationally supported elliptical with disky isophotes and small minor axis rotation. The observed scatter in the kinematical an…
The simple reading of the evidence is that the large elliptical galaxies existed at about the present star mass and comoving number density at redshift z=2. This is subject to the usual uncertainties of measurement and interpretation in astronomy, but should be taken seriously because it is indicated by quite a few lines of evidence. And it might be a guide to a more perfect theory of galaxy formation.
New observations show that most of the flattened diffuse elliptical (dE) galaxies are essentially isotropic rotators. This supports the idea that dEs have evolved from fast rotating dIrr systems or late-type spirals after their gas was expelled by SN-driven winds and stripped by ram pressure against the intergalactic medium.
Present knowledge of the distribution of the angle between major optical and radio axes of early-type galaxies is reviewed. While brightest galaxies in Abell clusters show a bimodal distribution of this angle, with both parallel and vertical alignment, ellipticals in general only show a weak preference for vertical alignment. Current plans are outlined to homogenize and largely increase these samples using literature data together with digitized optical Sky Surveys and the ongoing new radio surveys. The results will shed light on both the dynamics of nearby ellipticals, as well as on a possibl…
Using semi-analytical models of galaxy formation, the origin of boxy and disky elliptical galaxies is investigated. We find that the simple scenario, motivated by N-body simulations, in which the isophotal shape is only dependent on the mass ratio of the last major merger, is not able to reproduce the observation that the fraction of boxy and disky ellipticals depends on galaxy luminosity. The observations can however be reproduce with the following reasonable assumptions: (i) equal-mass mergers lead to boxy ellipticals and unequal-mass mergers produce disky ellipticals (as motivated by N-body…
Using well-defined selection criteria applied to the LEDA galaxy catalogue we have derived a sample of elliptical galaxies that can be classified as isolated. From this we have investigated the neighbourhood of these galaxies to determine the frequency and radial distribution of faint galaxies around them and hence derive an estimate of their surrounding satellite population. The results are compared and contrasted to the satellite population around isolated spiral galaxies.
Relying on infrared surface brightness fluctuactions to trace AGB properties in a sample of elliptical galaxies in the Virgo and Fornax clusters, we assess the puzzling origin of the "UV-upturn" phenomenon, recently traced down to the presence of a hot horizontal branch stellar component. We find that the UV-upturn actually signals a profound change in the c-m diagram of stellar populations in elliptical galaxies, involving both the hot stellar component and red-giant evolution.
We present preliminary results from a survey of CO emission from members of a volume-limited sample of non-cluster elliptical galaxies. Our intent is to compare the gas properties of these ellipticals to a sample of lenticulars selected using similar criteria. The data, although still sparse, suggest that the cool gas in ellipticals shows the same puzzling upper mass cutoff found in the lenticular galaxies. We find, however, significantly lower detection rates and possibly much lower H2/HI mass ratios in the ellipticals. The detection rate is higher among the lower-mass galaxies, as has been f…
We present very deep HST/ACS images of five QSO host galaxies, classified as undisturbed ellipticals in earlier studies. For four of the five objects, our images reveal strong signs of interaction such as tidal tails, shells, and other fine structure, suggesting that a large fraction of QSO host galaxies may have experienced a relatively recent merger event. Our preliminary results for a control sample of inactive elliptical galaxies do not reveal comparable fine structure.
We address the problem of deriving, from the observed projected metallicity gradients, the intrinsic metallicity distribution of elliptical galaxies as a function of their integrals of motion. The method is illustrated by an application to anisotropic spherical Hernquist models. We also compare the derived metallicity distribution with those expected from two very simple models of galaxy formation and find that the more dissipative scheme agrees better with the typical metallicity distribution of ellipticals.
Recent work on the equilibrium and stability of ellipsoidal stellar systems is reviewed. The absence of constant-density cores in early-type galaxies implies that chaos and high-order resonances are generic features of the motion in triaxial stellar systems. Bending instabilities are now well understood and may provide the answers to a number of long-standing riddles, including the absence of highly flattened elliptical galaxies and the formation of galactic bulges. Some preliminary results on instabilities in two-integral oblate models are presented.
We present the rotation velocities V and velocity dispersions sigma along the principal axes of seven elliptical galaxies less luminous than M_B= -19.5. These kinematics extend beyond the half-light radii for all systems in this photometrically selected sample. At large radii the kinematics not only confirm that rotation and "diskiness" are important in faint ellipticals, as was previously known, but also demonstrate that in most sample galaxies the stars at large galactocentric distances have (V/sigma)_max of about 2, similar to the disks in bona-fide S0 galaxies. Comparing this high degree o…
It has long been known that the radial density profiles of globular cluster systems (GCSs) in elliptical galaxies vary with the total luminosities of their host galaxies. In order to elucidate the origin of this structural non-homology in GCSs, we numerically investigate the structural properties of GCSs in elliptical galaxies formed from a sequence of major dissipationless galaxy merging. We find that the radial density profiles of GCSs in elliptical galaxies become progressively flatter as the galaxies experience more major merger events. The density profiles of GCSs in ellipticals are well …
We review the origin, evolution and physical nature of hot gas in elliptical galaxies and associated galaxy groups. Unanticipated recent X-ray observations with Chandra and XMM indicate much less cooling than previously expected. Consequently, many long-held assumptions need to be reexamined or discarded and new approaches must be explored. Chief among these are the role of heating by active galactic nuclei, the influence of radio lobes on the hot gas, details of the cooling process, possible relation between the hot and colder gas in elliptical galaxies, and the complexities of stellar enrich…
The present work is aimed at studying the distribution of galaxies of different types and luminosities along different structural scaling relations to see whether massive and dwarf ellipticals have been shaped by the same formation process. This exercise is here done by comparing the distribution of Virgo cluster massive and dwarf ellipticals and star forming galaxies along the B band effective surface brightness and effective radius vs. absolute magnitude relations and the Kormendy relation to the predictions of models tracing the effects of ram-pressure stripping on disc galaxies entering th…
In hierarchical models of galaxy formation, ellipticals form from the merging of disk galaxies drawn together by gravity as their surrounding dark halos coalesce. Using semi-analytic techniques, we are able to follow the merging, star formation and chemical enrichment histories of galaxies for a given choice of cosmological parameters. We calculate the ages and metallicities of elliptical galaxies in a standard CDM cosmology and show that we can reproduce the observed correlation between magnitude and colour, and the scatter about this relation. We also study the evolution of ellipticals to hi…
We present the first results from our population synthesis models of elliptical galaxies. In this paper, we concentrate upon the optical region of the spectrum (3000-7000 A). We model elliptical galaxies as coeval, single-metallicity stellar populations. Integrated spectra are constructed from synthetic spectra of the stars which lie along 6, 10 and 16 Gyr isochrones having [Fe/H]=+0.39, 0.00 and -0.47. Our oldest, solar-metallicity spectrum is found to be an excellent match to a spectrum of the E1/S0 galaxy NGC 4472. The broad-band colors measured from our models infer that the reddest E/S0 g…
Neutral hydrogen is an important component of the interstellar medium in elliptical galaxies as well as a potentially valuable mass tracer. Until recently, HI surveys of early-type galaxies have been sparse and inhomogeneous but this has changed with the advent of the HI Parkes All-Sky Survey (HIPASS; Barnes et al. 2001). We discuss HIPASS observations of a sample of ~2500 nearby E/S0 galaxies, as well as detailed HI imaging of a range of individual objects.
Studies of the Fundamental Plane of early-type galaxies, from small to intermediate redshifts, are often carried out under the guiding principle that the Fundamental Plane reflects the existence of an underlying mass-luminosity relation for such galaxies, in a scenario where elliptical galaxies are homologous systems in dynamical equilibrium. Here I will re-examine the issue of whether empirical evidence supports the view that significant systematic deviations from strict homology occur in the structure and dynamics of bright elliptical galaxies. In addition, I will discuss possible mechanisms…
We study the effect of active galactic nuclei (AGN) heating on the chemodynamical evolution of elliptical galaxies and their X-ray and optical properties using high-resolution Lambda-dominated cold dark matter cosmological simulations. Our model considers an AGN as being ``active'' when a convergent gas inflow condition exists within a galaxy's nucleus; otherwise, the AGN is assumed to remain dormant. This induces a self-regulated activity for the AGN, the result of which leads to a stable hot corona and the suppression of significant late-time star formation - characteristics not encountered …
