The Elliptical-Spheroidal and Elliptical-Elliptical Galaxy Dichotomies
John Kormendy
备注：
8 pages, 4 figures, requires asp2006.sty, to be published in Galaxy Evolution: Emerging Insights and Future Challenges, ed. S. Jogee et al., Astron. Soc. Pacific, 2009
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 new feature of this "E-E dichotomy": Coreless ellipticals have extra light at the center with respect to an inward extrapolation of the outer Sersic profile. We suggest that extra light is made in starbursts that swamp core scouring in wet mergers. In general, only giant, core ellipticals contain X-ray gas halos. We suggest that they formed in mergers that were kept dry by X-ray gas heated by active galactic nuclei.
We present new measurements of central line-strength indices (namely Mg2, <Fe>, and Hbeta and gradients for a sample of 6 bright spheroidal galaxies (Sph's) in the Virgo cluster. Comparison with similar measurements for elliptical galaxies (E's), galactic globular clusters (GGC's), and stellar population models yield the following results: (1) In contrast with bright E's, bright Sph's are consistent with solar abundance [Mg/Fe] ratios; (2) Bright Sph's exhibit metallicities ranging from values typical for metal-rich GGC's to those for E's; (3) Although absolute mean ages are quite model depend…
New surface photometry of all known elliptical galaxies in the Virgo cluster is added to published data to derive composite profiles over large dynamic ranges. Sersic functions fit them remarkably well. Effective brightnesses and radii are derived via Sersic fits and by integrating the profiles nonparametrically. We strongly confirm two dichotomies: (1) Elliptical galaxies from cDs to M32 form a tight sequence in Fundamental Plane parameter space that is almost perpendicular to the sequence of spheroidal galaxies from NGC 205 to Draco. This is consistent with our understanding of their differe…
We summarize current models of the formation of spheroidal stellar systems. Whereas globular clusters form in an efficient mode of star formation inside turbulent molecular clouds, the origin of galactic spheroids, that is bulges, dwarf ellipticals, and giant ellipticals, is directly coupled with structure formation and merging of structures in the Universe. Disks are the fundamental building blocks of galaxies and the progenitors of galactic spheroids. The origin of the various types of spheroids and their global properties can be understood as a result of disk heating by external perturbatio…
Updating Kormendy & Kennicutt (2004, ARAA, 42, 603), we review internal secular evolution of galaxy disks. One consequence is the growth of pseudobulges that often are mistaken for true (merger-built) bulges. Many pseudobulges are recognizable as cold, rapidly rotating, disky structures. Bulges have Sersic function brightness profiles with index n > 2; most pseudobulges have n <= 2. Recognition of pseudobulges makes the biggest problem with cold dark matter galaxy formation more acute: How can hierarchical clustering make so many pure disk galaxies with no evidence for merger-built bulges? E. …
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…
In hierarchical models, where spheroidals are primarily produced via the merger of disk galaxies, the number of intrinsically red systems at faint limits will be substantially lower than that expected in "traditional" models where the bulk of star formation was completed at high redshifts. We analyse the optical--near-infrared colour distribution of a large flux-limited sample of field spheroidal galaxies identified morphologically from archival Hubble Space Telescope data. The $I_{814}-HK'$ colour distribution for a sample jointly limited at $I_{814}<$23 mag and $HK'<$19.5 mag is used to cons…
We study the formation of hot spheroidal systems within the frame of a scenario where galaxy formation and evolution is related to the gentle mass aggregation history and primordial angular momentum of protogalaxies, both defined by the cosmological initial conditions. We explore two cases: (1) the hot spheroidal system forms from the dynamical instabilities of the stellar disks, and (2) the spheroidal systems are formed during the dissipative collapse of the gas before falling to the disk in centrifugal equilibrium. In the former case a good agreement with observations for late type galaxies …
The aim of this paper is to cast light on the formation and evolution of elliptical galaxies by means of N-body/hydro-dynamical simulations that include star formation, feed-back and chemical evolution. Particular attention is paid to the case of dwarf spheroidals of the Local Group which, thanks to their proximity and modern ground-based and space instrumentation, can be resolved into single stars so that independent determinations of their age and star formation history can be derived. Dwarf galaxies are known to exhibit complicated histories of star formation ranging from a single very old …
We analyse the spectral energy distributions (SEDs) of 23 submm galaxies and 3 ISO-detected EROs, all of which have the spectroscopic redshifts, by using an evolutionary SED model of starbursts. This SED model allows us to investigate intrinsic properties of starbursts, such as the starburst age and the mean stellar metallicity, as it takes into account the chemical evolution. Also, the intrinsic size of the starburst region is estimated from observed SEDs. Using this SED model, we predict colour, magnitude, and size of present-day descendants of submm galaxies, and derive scaling relations, s…
The small scatter observed for the U-V colors of spheroidal galaxies in nearby clusters of galaxies provides a powerful constraint on the history of star formation in dense environments. However, with local data alone, it is not possible to separate models where galaxies assembled synchronously over redshifts 0<z<1 from ones where galaxies formed stochastically at much earlier times. Here we attempt to resolve this ambiguity via high precision rest-frame UV-optical photometry of a large sample of morphologically-selected spheroidal galaxies in three z~0.54 clusters which have been observed wit…
We present an analysis of the density profile in the central region of the Sagittarius dwarf spheroidal galaxy. A strong density enhancement of Sgr stars is observed. The position of the peak of the detected cusp is indistinguishable from the center of M54. The photometric properties of the cusp are fully compatible with those observed in the nuclei of dwarf elliptical galaxies, indicating that the Sgr dSph would appear as a nucleated galaxy independently of the presence of M54 at its center.
The central surface brightness ($μ_V(0)$) of the dwarf spheroidal satellites of our own Galaxy is found to correlate with their distance from the Galactic Center ($R_{GC}$). This observational evidence suggests that environmental effects could strongly influence their structure. This suggestion is further supported by a clear-cut bivariate correlation linking $μ_V(0)$ to a linear combination of $M_V$, the absolute integrated magnitude, and $R_{GC}$, which seems to be shared also by the M31 spheroidals. Possible implications for the Fundamental Plane of elliptical galaxies and Dark Matter conte…
The Sloan Digital Sky Survey (SDSS) has scanned the entire region containing the Draco dwarf spheroidal galaxy to 23rd magnitude in g*. We present a catalog of stars found in a 453 square arcminute, elliptical region centered on the Draco dwarf spheroidal galaxy. Objects in the catalog are matched with five previously published catalogs. The catalog contains SDSS photometry for 5634 individual objects, and also the photometry from matches to any of the other catalogs. A comparison of the photometry between catalogs allows us to identify 142 candidate variable objects. One hundred and twelve of…
We present a study of the central parts of the Sagittarius dwarf spheroidal galaxy (Sgr). We found a clear overdensity of Sgr's stars around M~54 (hereafter NS). NS is well represented by a King model and it has the characteristics of a typical dwarf elliptical nucleus. Whether this means that M~54 has spiraled into the potential well of NS or that M~54 is the real nucleus and NS has formed into its potential wells, remains an open question to be addressed.
We report preliminary results of a project to homogeneously measure star formation histories for the majority of Local Group dwarf galaxies, based on archival WFPC2 observations. For the dwarf spheroidal and elliptical galaxies, we find that the more luminous systems all show extended star formation episodes, while the less luminous systems typically formed most of their stars over ten Gyr ago. Irregular galaxies show no comparable trend. We find that a galaxy's classification as an irregular or spheroidal is entirely explained by its star formation within the past Gyr or less. Several ellipti…
Extremely Red Objects (EROs) provide the important possibility to shed light on the formation and evolution of the present-day massive ellipticals. On one hand, they allow to select z>1 old passively evolving spheroidals and to compare their abundance with the predictions of galaxy formation scenarios. On the other hand, they provide the possibility to find dust obscured starbursts, a fraction of which may trace the formation of proto-ellipticals at z>2. In this paper, the most recent results on EROs are reviewed and the main implications discussed.
We study a possible formation mechanism for elliptical/S0 galaxies using N-body simulations with GRAPE. A close galaxy encounter which does not lead to a merger can induce a strong bar in an initially axisymmetric disk. This bar is unstable against bending oscillations and loses angular momentum to the dark halo. After 6 Gyrs the remnant is spheroidal with a de Vaucouleurs-type surface profile and has ellipticities and rotation properties comparable to observed elliptical/S0 galaxies: the system rotates fast (v/sigma \approx 1) and has disky isophotes.
The fundamental manifold (FM), an extension of the fundamental plane formalism, incorporates all spheroid-dominated stellar systems from dwarf ellipticals up to the intracluster stellar populations of galaxy clusters by accounting for the continuous variation of the mass-to-light ratio within the effective radius r_e with scale. Here, we find that Local Group dwarf spheroidal and dwarf elliptical galaxies, which probe the FM relationship roughly one decade lower in r_e than previous work, lie on the extrapolation of the FM. When combined with the earlier data, these Local Group dwarfs demonstr…
Gravity is nearly a universal constant in the cusp of an NFW galaxy halo. Inside this external field an isothermal gas sphere will collapse and trigger a starburst if above a critical central pressure. Thus formed spheroidal stellar systems have Sersic-profile and satisfy the Faber-Jackson relation. The process is consistent with observed starbursts. We also recover the M_BH vs. velocity dispersion relation, if the gas collapse is regulated or resisted by the feedback from radiation from the central BH.
The dwarf galaxies of the Local Group can be separated in three morphological groups: irregular, elliptical and spheroidal. As in the large galaxy clusters, there seems to be a morphology-position relationship: irregular galaxies are preferentially found in the outskirts (low density regions) of the Local Group, whereas dwarf ellipticals and spheroidals are more frequent in the central, high density regions. To cast light on the nature and origin of dwarf galaxies in the Local Group, Mayer et al.(2001) have suggested that a dwarf irregular galaxy tidally interacting with a galaxy of much large…
The optical-IR images of the Northern and Southern Hubble Deep Fields are used to measure the spectral and density evolution of early-type galaxies. The mean optical SED is found to evolve passively towards a mid F-star dominated spectrum by z ~ 2. We demonstrate with realistic simulations that hotter ellipticals would be readily visible if evolution progressed blueward and brightward at z > 2, following a standard IMF. The colour distributions are best fitted by a `red' IMF, deficient above ~2 M_solar and with a spread of formation in the range 1.5 < z_f < 2.5. Traditional age dating is spuri…
N-body simulations of major spiral-spiral mergers with different mass ratios q <= 4:1 are presented. All mergers lead to spheroidal stellar systems with de Vaucouleurs-like surface density profiles, resembling elliptical galaxies. The internal dynamical structure of the remnants does however depend critically on the adopted mass ratio. Equal-mass mergers with q <= 2:1 form radially anisotropic, slowly rotating systems with preferentially boxy isophotes. Unequal-mass mergers with q > 2:1 result in the formation of rotationally supported ellipticals with disky isophotes and small minor axis rota…
Recent claims in the literature (Bressan, Chiosi & Fagotto 1994) that the epoch describing the onset of galactic winds in spheroidal star systems has been severely overestimated in the past, due to the neglect of energy deposited in the interstellar medium from stellar winds, is evaluated in the light of a more conservative approach to modeling the input of thermal energy to the system from massive stars undergoing mass loss. Applying the most recent models of stellar kinetic energy deposition, coupled with reasonable assumptions regarding the efficiency of thermalisation, it is shown that con…
We present preliminary results of numerical simulations of dissipationless merging of stellar systems, aimed at exploring the consequences of merging between gas free, spheroidal systems. In particular, we study the dynamical and structural characteristics of hierarchical merging between equal mass stellar systems, and we compare the properties of the end-products with the most important structural and dynamical scaling relations obeyed by spheroids. In the explored hierarchy of four successive mergings we find that the FP tilt is marginally conserved, but both the Faber-Jackson and Kormendy r…
g', r', and i' images obtained with the Gemini Multi-Object Spectrograph (GMOS) on Gemini North are used to investigate the metallicity and stellar content of the M31 dwarf spheroidal companion galaxy And V. Red giant branch (RGB) stars are traced out to radii in excess of 126 arcsec from the galaxy center, indicating that And V extends over a diameter approaching 1 kpc. The mean g'-i' color of the RGB does not change with radius. Based on the slope of the RGB in the (i', g'-i') color-magnitude diagram we conclude that [Fe/H] = -2.2 +/- 0.1. This metallicity is lower than earlier estimates, an…
We present new size, line ratio, and velocity width measurements for six strong emission-line galaxies in the galaxy cluster, Cl 0024+1654, at redshift z~0.4. The velocity widths from Keck spectra are all narrow (30<sigma<120 km/s), with three profiles showing double peaks. Four galaxies have low masses (M<10^{10} Mo). Whereas three galaxies were previously reported to be possible AGNs, none exhibit AGN-like emission line ratios or velocity widths. Two or three appear as very blue spirals with the remainder more akin to luminous H-II galaxies undergoing a strong burst of star formation. We pro…
We examine resolved spectroscopic data obtained with the Keck II telescope for 44 spheroidal galaxies in the fields of two rich clusters, Cl0024+16 (z=0.40) and MS0451-03 (z=0.54), and contrast this with similar data for 23 galaxies within the redshift interval 0.3<z<0.65 in the GOODS northern field. For each galaxy we examine the case for systemic rotation, derive central stellar velocity dispersions sigma and photometric ellipticities, epsilon. Using morphological classifications obtained via Hubble Space Telescope imaging as the basis, we explore the utility of our kinematic quantities in d…
We derive the luminosity functions of elliptical galaxies, galaxy bulges, galaxy pseudo-bulges and galaxy discs from our structural catalogue of 10,095 galaxies. In addition we compute their associated luminosity and stellar mass densities. We show that spheroidal systems (elliptical galaxies and the bulges of disc galaxies) exhibit a strong color bimodality indicating two distinct types of spheroid which are separated by a core color of (u-r) ~ 2 mag. We argue that the similarity of the red elliptical and the red bulge luminosity functions supports our previous arguments that they share a com…
We investigate the present-day photometric properties of the dwarf spheroidal galaxies in the Local Group. From the analysis of their integrated colours, we consider a possible link between dwarf spheroidals and giant ellipticals. From the analysis of the V vs (B-V) plot, we search for a possible evolutionary link between dwarf spheroidal galaxies (dSphs) and dwarf irregular galaxies (dIrrs). By means of chemical evolution models combined with a spectro-photometric model, we study the evolution of six Local Group dwarf spheroidal galaxies (Carina, Draco, Sagittarius, Sculptor, Sextans and Ursa…
We investigate the chemical properties of M32, the bulges of M31 and the Milky Way, and the dwarf spheroidal galaxies NGC 205, NGC 185, Sagittarius, and Fornax using previously published oxygen abundances for their planetary nebulae. Our principal result is that the mean stellar oxygen abundances for all of these galaxies correlate very well with their mean velocity dispersions. This implies that the balance between energy input from type II supernovae and the gravitational potential energy controls how far chemical evolution proceeds in bulges, ellipticals, and dwarf spheroidals. It appears t…
We investigate the relationship between black hole mass and host galaxy properties for active galaxies with the lowest black hole masses currently known in galaxy nuclei. Hubble Space Telescope imaging confirms that the host galaxies have correspondingly low luminosity; they are ~1 mag below L*. In terms of morphology, ~60% of the members of the sample are disk-dominated, and all of these are consistent with containing a bulge or (more likely) pseudobulge, while the remainder are compact systems with no discernible disk component. In general the compact components of the galaxies do not obey t…
Galaxies exhibit a sequence of various morphological types, i.e., the Hubble sequence, and they are basically composed of spheroidal components (elliptical galaxies and bulges in spiral galaxies) and disks. It is known that spheroidal components are found only in relatively massive galaxies with M=10^{10-12} M_sun, and all stellar populations in them are very old, but there is no clear explanation for these facts. Here we present a speculative scenario for the origin of the Hubble sequence, in which magnetic fields ubiquitously seen in galaxies have played a crucial role. We first start from a…
We present the results of a series of gas dynamical cosmological simulations of the formation of individual massive field galaxies in the standard concordance \LCDM and in a \LWDM cosmology. The galaxies form in an initial burst of star formation followed by accretion of small satellites. The simulated galaxies are old ($\approx$ 10 $Gyrs$) hot stellar systems with masses of $\approx 1.7 \times 10^{11} M_{\odot}$. Baryonic matter dominates the mass in the luminous part of the galaxies up to $\approx 5$ effective radii. The \LCDM galaxy is a slowly rotating spheroidal stellar system (E2) with p…
I will review the role of massive stars in galactic evolution both from the nucleosynthesis and energetics point of view. In particular, I will highlight some important observational facts explained by means of massive stars in galaxies of different morphological type: the Milky Way, ellipticals and dwarf spheroidals. I will describe first the time-delay model and its interpretation in terms of abundance ratios in galaxies, then I will discuss the importance of mass loss in massive stars to reproduce the data in the Galactic bulge and disk. I will discuss also how massive stars can be importan…
The virial mass ($M_{\rm vir}$)-metallicity relation among the Local Group dwarf spheroidal galaxies (dSphs) is examined. Hirashita, Takeuchi, & Tamura showed that the dSphs can be divided into two distinct classes with respect to the relation between their virial masses and luminosities: low-mass ($M_{\rm vir} \la 10^8 M_\odot$) and high-mass ($M_{\rm vir} \ga 10^8 M_\odot$) groups. We see that both the mass-metallicity and the mass-luminosity relations of the high-mass dSphs are understood as a low-mass extension of giant ellipticals. On the contrary, we find that the classical galactic-wind…
We derive the light profiles for a sample of 25 dwarf elliptical galaxies observed by us with HST/WFPC2 in F555W and F814W. These profiles are fitted with Nuker, R^1/4, exponential, and Sersic laws, and are also used to derive the nuclear cusp slopes gamma. We discuss the correlation of nuclear cusp slope with galactic luminosity, presence of a nucleus, and type of light profile. The results are compared to those found in the literature for elliptical galaxies and the bulges of spiral galaxies. We find that as a class the nuclear regions of dwarf ellipticals are very similar to those of the ex…
We have performed a deep spectroscopic survey of extremely red galaxies on the GOODS-South field, using GMOS on Gemini South. We present here spectra and redshifts for 16 ERGs at 0.87<z<2.02, to a limit K=20.2. The ERHs are a mixture of spheroidals, mergers and spirals, with one AGN. For at least 10 of these galaxies we observe [OII] emission lines. We perform an age-dating analysis by fitting the spectra and 9-band photometry of the ERGs with models of passively evolving stellar populations combined with a younger star-forming component. The best-fitting ages for the old stellar components ra…
(ABRIDGED) We examine the fundamental scaling relations of elliptical galaxies formed through mergers. Using hundreds of simulations to judge the impact of progenitor galaxy properties on merger remnants, we find that gas dissipation provides an important contribution to tilt in the Fundamental Plane relation. Dissipationless mergers of disks produce remnants that occupy the virial plane. As the gas content of disk galaxies is increased, the tilt of the Fundamental Plane relation increases and the slope of the Re-M_* relation steepens. For gas fractions fgas > 30%, the simulated Fundamental Pl…
We examine in detail the dynamical structure of an elliptical galaxy simulated in the Lambda CDM scenario. The morphology of the galaxy evolves dramatically over time in response to the mode and timing of mass accretion; smooth deposition of cooled gas leads to the formation of centrifugally supported disks, whilst major mergers disperse stellar disks into spheroids. These two modes of accretion alternate successively until z~0.6, when the galaxy undergoes one last major (1:2) merger that consumes much of the remaining gas into stars. Little gas cools and accretes subsequently and, as a result…
There is now strong evidence that the metal-rich globular clusters (GC) near the center of our Galaxy are associated with the Galactic bulge rather than the disk as previously thought. Here we extend the concept of bulge GCs to the GC systems of nearby spiral galaxies. In particular, the kinematic and metallicity properties of the GC systems favor a bulge rather than a disk origin. The number of metal-rich GCs normalized by the bulge luminosity is roughly constant (i.e. bulge S_N ~ 1) in nearby spirals, and this value is similar to that for field ellipticals when only the red (metal--rich) GCs…
Recent observational evidence for steep dwarf galaxy luminosity functions in several rich clusters has led to speculation that their precursors may be the source of the majority of gas and metals inferred from intracluster medium (ICM) x-ray observations. Their deposition into the ICM is presumed to occur through early supernovae-driven winds, the resultant systems reflecting the photometric and chemical properties of the low luminosity dwarf spheroidals and ellipticals we observe locally. We consider this scenario, utilising a self-consistent model for spheroidal photo-chemical evolution and …
We present spatial analysis of the deep (57ks) ROSAT HRI X-ray image of the E4 galaxy NGC 720. The orientation of the HRI surface brightness is consistent with the optical position angle $(PA)$ interior to semi-major axis $a\sim 60\arcsec$ (optical $R_e\sim 50\arcsec$). For larger $a$ the isophotes twist and eventually $(a\gtrsim 100\arcsec)$ orient along a direction consistent with the $PA$ measured with the PSPC data (Buote & Canizares 1994) -- the $\sim 30\arcdeg$ twist is significant at an estimated 99% confidence level. We argue that this twist is not the result of projected foreground an…
We study the number and interaction rates of supermassive black holes in galactic bulges as predicted by hierarchical models of galaxy formation in which the spheroidal components of galaxies are formed by mergers. In bright ellipticals, the number of events that can eject a central supermassive binary black hole is large. Central binaries must therefore merge in less than a Hubble time -- otherwise there will be too much scatter in the M-sigma relation and too many off-center galactic nuclei. We propose that binary black holes are able to merge during the major gas accretion events that trigg…
Dwarf galaxies, as the most numerous type of galaxy, offer the potential to study galaxy formation and evolution in detail in the nearby Universe. Although they seem to be simple systems at first view, they remain poorly understood. In an attempt to alleviate this situation, the MAGPOP EU Research and Training Network embarked on a study of dwarf galaxies named MAGPOP-ITP (Peletier et al., 2007). In this paper, we present the analysis of a sample of 24 dwarf elliptical galaxies (dEs) in the Virgo Cluster and in the field, using optical long-slit spectroscopy. We examine their stellar populatio…
We explore observed dynamical trends in a wide range of dark matter dominated systems (about seven orders of magnitude in mass) to constrain hypothetical dark matter candidates and scenarios of structure formation. First, we argue that neither generic warm dark matter (collisionless or collisional) nor self-interacting dark matter can be responsible for the observed cores on all scales. Both scenarios predict smaller cores for higher mass systems, in conflict with observations; some cores must instead have a dynamical origin. Second, we show that the core phase space densities of dwarf spheroi…
(Abridged version) Mayall II = G1 is one of the brightest globular clusters belonging to M31, the Andromeda galaxy. Our observations with HST/WFPC2 provide data for the (I vs. V-I) and (V vs. V-I) color-magnitude diagrams. From model fitting, we determine a rather high mean metallicity of [Fe/H] = --0.95 +- 0.09, somewhat similar to 47 Tucanae. We find a larger spread in V-I than can be explained by the measurement errors, and we attribute this to an intrinsic metallicity dispersion amongst the stars of G1. So far, only omega Centauri, the giant Galactic globular cluster, has been known to exh…
We present a model for the broad morphological distinction between the disk and spheroidal components of galaxies. Elaborating on the hierarchical clustering scheme of galaxy formation proposed by Cole et al., we assume that galaxies form stars quiescently in a disk until they are disrupted into a spheroidal configuration by mergers. We calculate formation and merging histories, and the evolution in colour, luminosity and morphology of the galaxy populations in different environments. Roughly $ 50\ %$ of ellipticals in our model have undergone a major merger since $z = 0.5$, yet in spite of th…
The UV upturn is the rising flux with decreasing wavelength between the Lyman limit and 2500Åfound virtually in all bright spheroidal galaxies. It has been a mystery ever since it was first detected by the OAO-2 space telescope (Code & Welch 1979) because such old metal-rich populations were not expected to contain any substantial number of hot stars. It was confirmed by following space missions, ANS (de Boer 1982), IUE (Bertola et al. 1982) and HUT (Brown et al. 1997). The positive correlation between the UV-to-optical colour (i.e., the strength of the UV upturn) and the Mg2 line strength fou…
We have extended our previous analysis of morphologically selected elliptical and S0 galaxies in the Hubble Deep Field (HDF) North to include HST data in the HDF South and the HDFS-NICMOS areas. Our final sample amounts to 69 E/S0 galaxies with $K<20.15$ over an area of 11 square arcmins. Although a moderately small number over a modest sky area, this sample benefits of the best imaging and photometric data available on high-redshift galaxies. Multi-waveband photometry allows us to estimate with good accuracy the redshifts for the majority of these galaxies which lack a spectroscopic measure. …
(Abridged) We develop a model for the cosmological role of mergers in the evolution of starbursts, quasars, and spheroidal galaxies. Combining halo mass functions (MFs) with empirical halo occupation models, we calculate where major galaxy-galaxy mergers occur and what kinds of galaxies merge, at all redshifts. We compare with observed merger MFs, clustering, fractions, and small-scale environments, and show that this yields robust estimates in good agreement with observations. Making the simple ansatz that major, gas-rich mergers cause quasar activity, we demonstrate that this naturally repro…
We collected photometrical and dynamical data for 73 low red-shift (z<0.2) Radio Galaxies (LzRG) in order to study their Fundamental Plane (FP). For 22 sources we also present new velocity dispersion data, that complement the photometric data given in our previous study of LzRG (Govoni et al. 2000a). It is found that the FP of LzRG is similar to the one defined by non-active elliptical galaxies, with LzRG representing the brightest end of the population of early type galaxies. Since the FP mainly reflects the virial equilibrium condition, our result implies that the global properties of early-…
Early-type dwarf galaxies are the most common type of galaxies observed in the Universe. The origin of this kind of systems is still not well understood. The aim of this paper is to investigate whether the different locations of dwarf galaxies with respect to ellipticals in the face-on view of the fundamental plane could be due to the transformation of bright disc galaxies in low-mass systems by harassment. We have run high-resolution N-body numerical simulations to test the tidal stripping scenario of the dE galaxies. The present simulations modelled several individual tidal stripping events …
In this letter we address the problem of the origin of blue cores and inverse color gradients in early-type galaxies reported in the Hubble Deep Field North and South (HDFs) by Menanteau, Abraham & Ellis 2001. We use a multi-zone single collapse model. This model accounts for the observed blue cores by adopting a broad spread in formation redshifts for ellipticals, allowing some of these galaxies begin forming no more than ~1 Gyr before the redshift of observation. The single-zone collapse model then produces cores that are bluer than the outer regions because of the increase of the local pote…
We investigate the structural, kinematical, and spectrophotometric properties of ``E+A'' galaxies -- those with strong Balmer absorption lines but no significant [OII] emission -- using numerical simulations combined with stellar population synthesis codes. We particularly focus on the two-dimensional (2D) distributions of line-of-sight velocity, velocity dispersion, colors, line index in E+A galaxies formed via the interaction and merging of two gas-rich spirals. Our numerical simulations demonstrate that E+A elliptical galaxies formed by major galaxy merging have positive radial color gradie…
Kinematical decoupling between two components of a galaxy suggests the occurrence of a second event. In disk galaxies it is usually observed as a counterrotation of the stellar disk with respect to the gaseous component and/or with respect to a second stellar disk. We discuss here three cases of kinematical orthogonal decoupling of the innermost region of the spheroidal component with respect to the disk (or ring) component in the two Sa spirals NGC 4698 and NGC 4672, and in the elliptical galaxy with a polar ring AM 2020-504. Moreover the major axis of the disk (or ring) component forms an an…
(abridged) We present kinematic results for a sample of 387 stars located near Leo I based on spectra obtained with the MMT's Hectochelle spectrograph near the MgI/Mgb lines. We estimate the mean velocity error of our sample to be 2.4 km/s, with a systematic error of < 1 km/s. We produce a final sample of 328 Leo I red giant members, from which we measure a mean heliocentric radial velocity of 282.9 +/- 0.5 km/s, and a mean radial velocity dispersion of 9.2 +/- 0.4 km/s for Leo I. The dispersion profile of Leo I is flat out to beyond its classical `tidal' radius. We fit the profile to a variet…
Context: The spatial distribution of the stellar populations inside a spheroidal system and their kinematical properties supply important informations about the formation process. Aims: We have performed a detailed stellar population analysis using long slit spectroscopic observations up to almost one effective radius of two different early-type galaxies of low density regions of the local Universe: NGC 1052, a E4 Liner prototype of a loose group that has a stellar rotating disc, and NGC 7796, a E1 of the field which shows a kinematically distinct core. The mean luminosity-weighted stellar age…
We discuss the importance of feedback via photoionization and Compton heating on the co-evolution of massive black holes (MBHs) at the center of spheroidal galaxies and their stellar and gaseous components. We first assess the energetics of the radiative feedback from a typical quasar on the ambient interstellar medium. We then demonstrate that the observed Mbh-sigma relation could be established following the conversion of most of the gas of an elliptical progenitor into stars, specifically when the gas-to-stars mass ratio in the central regions has dropped to a low level ~0.01 or less, so th…
We select a sample of low-redshift (z ~ 0.1) E+A galaxies from the 2dF Galaxy Redshift Survey (2dFGRS). The spectra of these objects are defined by strong hydrogen Balmer absorption lines (H-delta, H-gamma, H-beta) combined with a lack of [OII] 3727A emission, together implying a recently-truncated burst of star formation. The E+A spectrum is thus a signpost to galaxies in the process of evolution. We quantify the local environments, clustering properties and luminosity function of the E+A galaxies. We find that the environments are consistent with the ensemble of 2dFGRS galaxies: low-redshift…
We have identified a sample of 41 low-mass high--oxygen abundance outliers from the mass--metallicity relation of star-forming galaxies measured by Tremonti et al (2004). These galaxies, which have 8.6 < [12 + log(O/H)] < 9.3 over a range of -14.4 > M_B > -19.1 and 7.4 < log M_*/M_solar < 10, are surprisingly non-pathological. They have typical specific star formation rates, are fairly isolated and, with few exceptions, have no obvious companions. Morphologically, they are similar to dwarf spheroidal or dwarf elliptical galaxies. We predict that their observed high oxygen abundances are due to…
