S0 Galaxies Research Articles

Imagery and long-slit spectroscopy of the polar ring galaxy AM 2020-504

Interactions between galaxies are very common. There are special kinds of interactions that produce systems called Polar Ring Galaxies (PRGs), composed by a lenticular, elliptical, or spiral host galaxy, surrounded by a ring of stars and gas, orbiting in an approximately polar plane. The present work aims to study AM2020-504, a PRG with an elliptical host galaxy, and a narrow and well defined ring, probably formed by accretion of material from a donor galaxy, collected by the host galaxy. Our observational study was based on BVRI broad band imagery as well as longslit spectroscopy in the wavelenght range 4100--8600\AA, performed at the 1.6m telescope at the Observat\'orio do Pico dos Dias (OPD), Brazil. We estimated a redshift of z= 0.01683, corresponding a heliocentric radial velocity of 5045 +/-23 km/s. The (B-R) color map shows that the ring is bluer than the host galaxy, indicating that the ring is a younger structure. Standard diagnostic diagrams were used to classify the main ionizing source of selected emission-line regions (nucleus, host galaxy and ring). It turns out that the ring regions are mainly ionized by massive stars while the nucleus presents AGN characteristics. Using two empirical methods, we found oxygen abundances for the HII regions located in the ring in the range 12+log(O/H)=8.3-8.8 dex, the presence of an oxygen gradient across the ring, and that AM2020-504 follows the metallicity-luminosity relation of spiral galaxies. These results support the accretion scenario for this object and rules out cold accretion as source for the HI gas in the polar ring.

The evolution of the mass–size relation for early-type galaxies from z ∼ 1 to the present: dependence on environment, mass range and detailed morphology

We study the dependence of the galaxy size evolution on morphology, stellar mass and large-scale environment for a sample of 298 group and 384 field quiescent early-type galaxies from the COSMOS survey, selected from z ∼ 1 to the present, and with masses log(M/M⊙) > 10.5. From a detailed morphological analysis we infer that ∼80 per cent of passive galaxies with mass log(M/M⊙) > 10.5 have an early-type morphology and that this fraction does not evolve over the last 6 Gyr. However, the relative abundance of lenticular and elliptical galaxies depends on stellar mass. Elliptical galaxies dominate only at the very high mass end – log(M/M⊙) > 11 – while S0 galaxies dominate at lower stellar masses – 10.5 < log(M/M⊙) < 11. The galaxy size growth depends on galaxy mass range and early-type galaxy morphology, e.g. elliptical galaxies evolve differently than lenticular galaxies. At the low-mass end – 10.5 < log(M/M⊙) < 11 – ellipticals do not show strong size growth from z ∼ 1 to the present (10 to 30 per cent depending on the morphological classification). On the other end, massive ellipticals – log(M/M⊙) > 11.2 – approximately doubled their size. Interestingly, lenticular galaxies display different behaviour: they appear more compact on average and they do show a size growth of ∼60 per cent since z = 1 independent of stellar mass range. We compare our results with state-of-the art semi-analytic models. While major and minor mergers can account for most of the galaxy size growth, we find that with present data and the theoretical uncertainties in the modelling we cannot state clear evidence favouring either merger or mass-loss via quasar and/or stellar winds as the primary mechanism driving the evolution. The galaxy mass–size relation and size growth do not depend on environment in the halo mass range explored in this work (field to group mass log(Mh/M⊙) < 14), i.e. group and field galaxies follow the same trends. At low redshift, where we examine both Sloan Digital Sky Survey and COSMOS groups, this result is at variance with predictions from some current hierarchical models that show a clear dependence of size growth on halo mass for massive ellipticals (log(M*/M⊙) > 11.2). In future work, we will analyse in detail if this result is specific of the observations and model used in this work. Brightest Cluster Galaxies (BCG) and satellite galaxies lie on the same mass–size relation, at variance with predictions from hierarchical models, which predict that BCGs should have larger sizes than satellites because they experience more mergers in groups over the halo mass range probed.

Ages and abundances in large-scale stellar discs of nearby S0 galaxies

By undertaking deep long-slit spectroscopy with the focal reducer SCORPIO of the Russian 6m telescope, we studied stellar population properties and their variation with radius in 15 nearby S0 galaxies sampling a wide range of luminosities and environments. For the large-scale stellar disks of S0s, we have measured SSP-equivalent metallicities ranging from the solar one down to [Z/H]=-0.4 - -0.7, rather high magnesium-to-iron ratios, [Mg/Fe] > +0.2, and mostly old SSP-equivalent ages. Nine of 15 (60%) galaxies have large-scale stellar disks older than 10 Gyr, and among those we find all the galaxies which reside in denser environments. The isolated galaxies may have intermediate-age stellar disks which are 7-9 Gyr old. Only two galaxies of our sample, NGC 4111 and NGC 7332, reveal SSP-equivalent ages of their disks of 2-3 Gyrs. Just these two young disks appear to be thin, while the other, older disks have scale heights typical for thick stellar disks. The stellar populations in the bulges at radii of 0.5r_eff are on the contrary more metal-rich than the solar metallicity, with the ages homogeneously distributed between 2 and 15 Gyr, being almost always younger than the disks. We conclude that S0 galaxies could not form in groups at z=0.4 as is thought now; a new scenario of the general evolution of disk galaxies is proposed instead.

THE GLOBULAR CLUSTER POPULATIONS OF GIANT GALAXIES: MOSAIC IMAGING OF FIVE MODERATE-LUMINOSITY EARLY-TYPE GALAXIES

This paper presents results from wide-field imaging of the globular cluster (GC) systems of five intermediate-luminosity (M_V ~-21 to -22) early-type galaxies. The aim is to accurately quantify the global properties of the GC systems by measuring them out to large radii. We obtained BVR imaging of four lenticular galaxies (NGC 5866, NGC 4762, NGC 4754, NGC 3384) and one elliptical galaxy (NGC 5813) using the KPNO 4m telescope and MOSAIC imager and traced the GC population to projected galactocentric radii ranging from ~20 kpc to 120 kpc. We combine our imaging with Hubble Space Telescope data to measure the GC surface density close to the galaxy center. We calculate the total number of GCs (N_GC) from the integrated radial profile and find N_GC = 340 +/- 80 for NGC 5866, N_GC = 2900 +/- 400 for NGC 5813, N_GC = 270 +/- 30 for NGC 4762, N_GC = 115 +/- 15$ for NGC 4754, and N_GC = 120 +/- 30 for NGC 3384. The measured GC specific frequencies are S_N between 0.6 and 3.6 and T in the range 0.9 to 4.2. These values are consistent with the mean specific frequencies for the galaxies' morphological types found by our survey and other published data. Three galaxies (NGC 5866, NGC 5813, NGC 4762) had sufficient numbers of GC candidates to investigate color bimodality and color gradients in the GC systems. NGC 5813 shows strong evidence (>3 sigma) for bimodality and a B-R color gradient resulting from a more centrally concentrated red (metal-rich) GC subpopulation. We find no evidence for statistically significant color gradients in the other two galaxies.

An over-massive black hole in the compact lenticular galaxy NGC 1277

Most massive galaxies have supermassive black holes at their centres, and the masses of the black holes are believed to correlate with properties of the host-galaxy bulge component. Several explanations have been proposed for the existence of these locally established empirical relationships, including the non-causal, statistical process of galaxy-galaxy merging, direct feedback between the black hole and its host galaxy, and galaxy-galaxy merging and the subsequent violent relaxation and dissipation. The empirical scaling relations are therefore important for distinguishing between various theoretical models of galaxy evolution, and they furthermore form the basis for all black-hole mass measurements at large distances. Observations have shown that the mass of the black hole is typically 0.1 per cent of the mass of the stellar bulge of the galaxy. Until now, the galaxy with the largest known fraction of its mass in its central black hole (11 per cent) was the small galaxy NGC 4486B. Here we report observations of the stellar kinematics of NGC 1277, which is a compact, lenticular galaxy with a mass of 1.2 × 10(11) solar masses. From the data, we determine that the mass of the central black hole is 1.7 × 10(10) solar masses, or 59 per cent of its bulge mass. We also show observations of five other compact galaxies that have properties similar to NGC 1277 and therefore may also contain over-massive black holes. It is not yet known if these galaxies represent a tail of a distribution, or if disk-dominated galaxies fail to follow the usual black-hole mass scaling relations.

Semi-empirical catalog of early-type galaxy-halo systems: dark matter density profiles, halo contraction and dark matter annihilation strength

With Sloan Digital Sky Survey galaxy data and halo data from up-to-date N-body simulations within the ΛCDM framework we construct a semi-empirical catalog (SEC) of early-type galaxy-halo systems by making a self-consistent bivariate statistical match of stellar mass (M⋆) and velocity dispersion (σ) with halo virial mass (Mvir) as demonstrated here for the first time. We then assign stellar mass profile and velocity dispersion profile parameters to each system in the SEC using their observed correlations with M⋆ and σ. Simultaneously, we solve for dark matter density profile of each halo using the spherical Jeans equation. The resulting dark matter density profiles deviate in general from the dissipationless profile of Navarro-Frenk-White or Einasto and their mean inner density slope and concentration vary systematically with Mvir. Statistical tests of the distribution of profiles at fixed Mvir rule out the null hypothesis that it follows the distribution predicted by dissipationless N-body simulations for Mvir≲1013.5 – 14.5 M⊙. These dark matter profiles imply that dark matter density is, on average, enhanced significantly in the inner region of halos with Mvir≲1013.5 – 14.5 M⊙ supporting halo contraction. The main characteristics of halo contraction are: (1) the mean dark matter density within the effective radius has increased by a factor varying systematically up to ≈ 3–4 at Mvir = 1012 M⊙, and (2) the inner density slope has a mean of ⟨α⟩ ≈ 1.3 with ρdm(r)∝r−α and a halo-to-halo rms scatter of rms(α) ∼ 0.4–0.5 for 1012 M⊙≲Mvir≲1013 – 14 M⊙ steeper than the NFW profile (α = 1). Based on our results we predict that halos of nearby elliptical and lenticular galaxies can, in principle, be promising targets for γ-ray emission from dark matter annihilation.

Disentangling the stellar populations in the counter-rotating disc galaxy NGC 4550

In order to try and understand its origins, we present high-quality long-slit spectral observations of the counter-rotating stellar discs in the strange S0 galaxy NGC 4550. We kinematically decompose the spectra into two counter-rotating stellar components (plus a gaseous component), in order to study both their kinematics and their populations. The derived kinematics largely confirm what was known previously about the stellar discs, but trace them to larger radii with smaller errors; the fitted gaseous component allows us to trace the hydrogen emission lines for the first time, which are found to follow the same rather strange kinematics previously seen in the [OIII] line. Analysis of the populations of the two separate stellar components shows that the secondary disc has a significantly younger mean age than the primary disc, consistent with later star formation from the associated gaseous material. In addition, the secondary disc is somewhat brighter, also consistent with such additional star formation. However, these measurements cannot be self-consistently modelled by a scenario in which extra stars have been added to initially-identical counter-rotating stellar discs, which rules out Evans & Collett's (1994) elegant "separatrix-crossing" model for the formation of such massive counter-rotating discs from a single galaxy, leaving some form of unusual gas accretion history as the most likely formation mechanism.

Evolution along the sequence of S0 Hubble types induced by dry minor mergers

Recent studies have argued that galaxy mergers are not important drivers for the evolution of S0's, on the basis that mergers cannot preserve the coupling between the bulge and disk scale-lengths observed in these galaxies and the lack of correlation of their ratio with the S0 Hubble type. We investigate whether the remnants resulting from collision-less N-body simulations of intermediate and minor mergers onto S0 galaxies evolve fulfilling global structural relations observed between the bulges and disks of these galaxies. Different initial bulge-to-disk ratios of the primary S0 have been considered, as well as different satellite densities, mass ratios, and orbits of the encounter. We have analysed the final morphology of the remnants in images simulating the typical observing conditions of S0 surveys. We derive bulge+disk decompositions of the final remnants to compare their global bulge-to-disk structure with observations. We show that all remnants present undisturbed S0 morphologies according to the prescriptions of specialized surveys. The dry intermediate and minor mergers induce noticeable bulge growth (S0c --> S0b and S0b --> S0a), but affect negligibly to the bulge and disk scale-lengths. Therefore, if a coupling between these two components exists prior to the merger, the encounter does not break this coupling. This fact provides a simple explanation for the lack of correlation between the ratio of bulge and disk scale-lengths and the S0 Hubble type reported by observations. These models prove that dry intermediate and minor mergers can induce global structural evolution within the sequence of S0 Hubble types compatible with observations, meaning that these processes should not be discarded from the evolutionary scenarios of S0's just on the basis of the strong coupling observed between the bulge and disk scale-lengths in these galaxies (abridged).

The SLUGGS Survey: kinematics for over 2500 globular clusters in 12 early-type galaxies

We present a spectrophotometric survey of 2522 extragalactic globular clusters (GCs) around 12 early-type galaxies, nine of which have not been published previously. Combining space-based and multicolour wide-field ground-based imaging, with spectra from the Keck/DEep Imaging Multi-Object Spectrograph (DEIMOS) instrument, we obtain an average of 160 GC radial velocities per galaxy, with a high-velocity precision of ∼15 km s−1 per GC. After studying the photometric properties of the GC systems, such as their spatial and colour distributions, we focus on the kinematics of metal-poor (blue) and metal-rich (red) GC subpopulations to an average distance of ∼8 effective radii from the galaxy centre. Our results show that for some systems the bimodality in GC colour is also present in GC kinematics. The kinematics of the red GC subpopulations are strongly coupled with the host galaxy stellar kinematics. The blue GC subpopulations are more dominated by random motions, especially in the outer regions, and decoupled from the red GCs. Peculiar GC kinematic profiles are seen in some galaxies: the blue GCs in NGC 821 rotate along the galaxy minor axis, whereas the GC system of the lenticular galaxy NGC 7457 appears to be strongly rotation supported in the outer region. We supplement our galaxy sample with data from the literature and carry out a number of tests to study the kinematic differences between the two GC subpopulations. We confirm that the GC kinematics are coupled with the host galaxy properties and find that the velocity kurtosis and the slope of their velocity dispersion profiles are different between the two GC subpopulations in more massive galaxies.

EXPLORING THE CORRELATIONS BETWEEN GLOBULAR CLUSTER POPULATIONS AND SUPERMASSIVE BLACK HOLES IN GIANT GALAXIES

This paper presents an analysis of the correlation between the number of globular clusters (N_GC) in giant galaxies and the mass of the galaxies' central supermassive black hole (M_SMBH). I construct a sample of 20 elliptical, spiral, and S0 galaxies with known SMBH masses and with accurately-measured globular cluster system properties derived from wide-field imaging studies. The coefficients of the best-fitting N_GC-M_SMBH relation for the early-type galaxies are consistent with those from previous work but in some cases have smaller relative errors. I examine the correlation between N_GC and M_SMBH for various subsamples and find that elliptical galaxies show the strongest correlation while S0 and pseudobulge galaxies exhibit increased scatter. I also compare the quality of the fit of the numbers of metal-poor globular clusters versus SMBH mass and the corresponding fit for metal-rich globular clusters. I supplement the 20-galaxy sample with ten additional galaxies with reliable N_GC determinations but without measured M_SMBH. I use this larger sample to investigate correlations between N_GC and host galaxy properties like total galaxy luminosity and stellar mass and bulge luminosity and mass. I find that the tightest correlation is between N_GC and total galaxy stellar mass. This lends support to the notion that N_GC and M_SMBH are not directly linked but are correlated because both quantities depend on the host galaxy potential. Finally, I use the N_GC-M_SMBH relation derived from the 20-galaxy sample to calculate predicted M_SMBH values for the ten galaxies with accurate N_GC measurements but without measured SMBH masses.

PGC 60020: a polar-ring galaxy

We present an analysis of new observations of a peculiar galaxy PGC 60020, obtained with the 6-m BTA telescope of the SAO RAS with a multimode SCORPIO instrument. The observational data includes direct images in the B, V, Rc photometric bands and long-slit spectra in the red range (the Hα line spectral region). Based on the analysis of these data it was found that PGC 60020 belongs to the type of classical polar-ring galaxies. Its main body is an S0 galaxy, around the major axis of which a disk of gas, dust and stars is rotating in the plane inclined at an angle of about 60 ◦ to the galactic plane. A loop-shaped structure stretches from the southern part of this disk (possibly, a tidal tail) towards the SDSS J 171745.58+404137.1 galaxy. DOI: 10.1134/S1990341312040037

Radially extended kinematics in the S0 galaxy NGC 2768 from planetary nebulae, globular clusters and starlight

There are only a few tracers available to probe the kinematics of individual early-type galaxies beyond one effective radius. Here we directly compare a sample of planetary nebulae (PNe), globular clusters (GCs) and galaxy starlight velocities out to ~4 effective radii, in the S0 galaxy NGC 2768. Using a bulge-to-disk decomposition of a K-band image we assign PNe and starlight to either the disk or the bulge. We show that the bulge PNe and bulge starlight follow the same radial density distribution as the red subpopulation of GCs, whereas the disk PNe and disk starlight are distinct components. We find good kinematic agreement between the three tracers to several effective radii (and with stellar data in the inner regions). Further support for the distinct nature of the two galaxy components come from our kinematic analysis. After separating the tracers into bulge and disk components we find the bulge to be a slowly rotating pressure-supported system, whereas the disk reveals a rapidly rising rotation curve with a declining velocity dispersion profile. The resulting V/sigma ratio for the disk resembles that of a spiral galaxy and hints at an origin for NGC 2768 as a transformed late-type galaxy. A two-component kinematic analysis for a sample of S0s will help to elucidate the nature of this class of galaxy.

GLOBULAR CLUSTER SYSTEMS OF SPIRAL AND S0 GALAXIES: RESULTS FROM WIYN IMAGING OF NGC 1023, NGC 1055, NGC 7332, AND NGC 7339

We present results from a study of the globular cluster (GC) systems of four spiral and S0 galaxies imaged as part of an ongoing wide-field survey of the GC systems of giant galaxies. The target galaxies -- the SB0 galaxy NGC1023, the SBb galaxy NGC1055, and an isolated pair comprised of the Sbc galaxy NGC7339 and the S0 galaxy NGC7332 -- were observed in BVR filters with the WIYN 3.5-m telescope and Minimosaic camera. For two of the galaxies, we combined the WIYN imaging with previously-published data from the Hubble Space Telescope and the Keck Observatory to help characterize the GC distribution in the central few kiloparsecs. We determine the radial distribution (surface density of GCs versus projected radius) of each galaxy's GC system and use it to calculate the total number of GCs (N_GC). We find N_GC = 490+/-30, 210+/-40, 175+/-15, and 75+/-10 for NGC1023, NGC1055, NGC7332, and NGC7339, respectively. We also calculate the GC specific frequency (N_GC normalized by host galaxy luminosity or mass) and find values typical of those of the other spiral and E/S0 galaxies in the survey. The two lenticular galaxies have sufficient numbers of GC candidates for us to perform statistical tests for bimodality in the GC color distributions. We find evidence at a high confidence level (>95%) for two populations in the B-R distribution of the GC system of NGC1023. We find weaker evidence for bimodality (>81% confidence) in the GC color distribution of NGC7332. Finally, we identify eight GC candidates that may be associated with the Magellanic dwarf galaxy NGC1023A, a satellite of NGC1023.

A tale of two tails and an off-centered envelope: diffuse light around the cD galaxy NGC 3311 in the Hydra I cluster

The formation of intracluster light and of the extended halos around brightest cluster galaxies is closely related to morphological transformation, tidal stripping, and disruption of galaxies in clusters. We analyze Ks- and V-band surface photometry as well as deep long-slit spectra, and establish a link between the structures in the light distribution, the absorption line kinematics, and the LOS velocity distributions of nearby galaxies and planetary nebulae (PNs). The central galaxy NGC 3311 is surrounded by an extended symmetric outer halo with n=10 and an additional, off-centered envelope ~ 50" to the North-East. Its luminosity L_V= 1.2x10^{10} +/- 6.0 x 10^8 L_sun corresponds to ~50 % of the luminosity of the symmetric halo in the same region. Based on measured PN velocities, at least part of the off-centered envelope consists of high-velocity accreted stars. We have also discovered two tidal streams in the cluster center, emerging from the dwarf galaxy HCC 026 and from the S0 galaxy HCC 007. The HCC 026 stream is redshifted by ~1200 km/s with respect to NGC 3311, similarly as HCC 026 itself, a fraction of PNs in the off-centered envelope, and several other dwarf galaxies nearby. The stars in one of the HCC 026 tails are known to be consistent with the low-metallicity population of HCC 026, and our photometry shows that this galaxy is already mostly dissolved in the tidal field. The tidal stream around HCC 007 extends over at least 110 kpc. It is fairly thick and is brighter on the side of the asymmetric outer halo of NGC 3311, which it may join. Its luminosity is several 10^9 L_sun, similar to the luminosity of the stripped-down galaxy HCC 007. The redshift of the stream is determined from a few PN velocities and is similar to that for HCC 007 and HCC 026.

Clues from star-formation histories - does the formation scenario of S0 galaxies depend on their luminosities?

AbstractLenticular (S0) galaxies are a morphological transition class between ellipticals and early-type spirals. Recent studies indicate that the formation scenario for lenticular galaxies depends on their near-IR luminosity (Barway et al. 2007;2009;2011). Low-luminosity lenticular galaxies likely formed by the stripping of gas from the disc of late-type spiral galaxies, which in turn formed their pseudo bulges through secular evolution processes, possibly involving multiple episodes of star formation. On the other hand, more luminous lenticulars likely formed at early epochs through a rapid collapse followed by rapid star formation, similar to the formation process of elliptical galaxies, and are characterized by a old coeval stellar population in the bulge. To investigate the imprint of these distinct formation scenarios on stellar populations, we combine GALEX/SDSS/2MASS photometry to construct color-color diagrams for a carefully defined sample of ~400 lenticular galaxies. We divide the sample into bright and faint groups as suggested by Barway et al. (2007). We find the (FUV-NUV) versus (NUV-K) color-color diagram shows larger scatter for faint lenticular galaxies while bright lenticular galaxies show a much tighter relation similar to that of ellipticals. Simple Stellar Population (SSP) analysis shows that ellipticals and bright lenticulars are dominated by a stellar population of age &gt;109 years while faint lenticular galaxies are as young as 108 years, providing evidence for relatively recent star formation activity. Further, if we use the (NUV-r) &lt; 5.4 color criterion to identify galaxies with recent (within 500 Myr) star formation, most faint lenticular galaxies fall into this category; bright lenticulars are mostly quiescent. Most faint lenticular galaxies generally have lower velocity dispersions. If we consider velocity as a virial mass indicator, majority of faint, recently star forming, lenticular galaxies have low virial masses compared to brighter lenticular galaxies. Such systematic differences in star formation history between bright and faint lenticular galaxies are consistent with the expectations from the luminosity dependent formation scenario described above.

Internal and environmental secular evolution of disk galaxies

Internal and environmental secular evolution of disk galaxies

Photometric analysis of Abell 1689

AbstractWe carried out a photometric analysis of a sample of early-type galaxies in Abell~1689 at z = 0.183, using HST/ACS archive images in the rest-frame V band. We performed a two-dimensional photometric decomposition of each galaxy surface-brightness distribution using the GASP2D fitting algorithm (Méndez-Abreu et al. 2008). We adopted both a Sérsic and de Vaucouleurs law. S0 galaxies were analysed also taking into account a disc component described by an exponential law. The derived photometric parameters, together with the ones previously obtained with the curve of growth method (Houghton et al. 2012), will be used to analyse the Fundamental Plane of Abell 1689 and quantify how it is affected by the use of different decomposition techniques (Dalla Bontà et al. 2013, in preparation). The stellar velocity dispersions of the sample galaxies were derived by using GEMINI-N/GMOS and VLT/FLAMES (D'Eugenio et al. 2013) spectroscopic data.

Dissecting early-type dwarf galaxies into their multiple components

AbstractEarly-type dwarf galaxies are often thought to be either more diffuse versions of giant ellipticals or to be low-mass disk galaxies that were quenched and heated by the environment. In both cases, the picture that most astronomers have in mind probably is that of a dynamically hot, regular shaped galaxy, in which any previous substructure has either been smeared out, or has never been there. However, the early-type dwarfs are not that simple.We analyzed ~100 such objects in the Virgo cluster using deep near-infrared images and found that the majority has a multi-component structure, sometimes even with bars or lenses. The study was done by applying GALFIT to images from the SMAKCED collaboration (Stellar content, MAss and K inematics of Cluster Early-type Dwarfs, http://www.smakced.net). The sample comprises early-type galaxies in the Virgo cluster in a brightness range of −19 ≤ Mr ≤ −16 mag, and the data is complete down to Mr=−16.73 mag. The images typically reach a signal-to-noise ratio of 1 per pixel of ~0.25” at a surface brightness of ~22.5 mag/arcsec2 in the H-band. The galaxies were fitted with two-dimensional models, either with a simple Sérsic model or inner and outer components, as well as bars and lenses. Only a fraction of 31% of the galaxies can be fitted with a single Sérsic function. This fraction of “simple“ galaxies turns out to be a strong function of luminosity, with a smaller fraction for brighter objects. The bar fraction is 14% and also in 14% of the galaxies lenses were fitted.When comparing the flattening distribution, the early-type dwarfs are more similar to spiral galaxies than to elliptical or lenticular galaxies. It is disputable whether or not the dwarfs follow a common relation with the bright elliptical galaxies, e.g. in the brightness versus size diagram. At the same time, they appear as smooth continuation of bright late-type galaxies in this diagram. The inner and outer components, as well as the simple galaxies have similar flattening distributions. The inner components are mostly fitted with Sérsic-n values close to~1, i.e. with nearly exponential profiles. We argue that the inner components in the early-type dwarfs are not be bulges but may form parts of the disks, in which the matter was re-distributed during the transformation process from a late-type progenitor.

Correlation of morphological fraction with redshift in galaxy clusters

AbstractBased on 187 galaxy clusters identified from the photometric redshifts of galaxies in the Cosmic Evolution Survey (COSMOS) field(Wen &amp; Han 2011), cluster galaxies brighter than MV = -20.5 are classified into four categories according to their best-fitting templates of the spectral energy distributions (SEDs) provided by Ilbert et al. (2009): early-type (including elliptical and lenticular) galaxies (E+S0), spiral galaxies (S), irregular galaxies (Irr), and starbursts (SB). The fractions of these four SED types are presented as the functions of redshift in Figure 1. Fraction of each category varies remarkably with cluster redshift: fractions of normal galaxies (E+S0+S+Irr) tend to decrease with redshift, whilst the starburst proportion tends to increase with redshift. For the normal galaxies, there exists a sequence for the decreasing slopes of morphological fractions. Majority of the galaxies in high-redshift clusters (z &gt; 1.0) are experiencing strong star-formation activities, which leads to a very high proportion of starburst.

NIRS0S: Observations of early-type galaxy secular evolution spanning the Sa/S0/disky-E boundaries

AbstractNIRS0S (Near-IR S0 galaxy Survey), is a K-band survey of ~ 200 early-type disk galaxies, mainly S0s, 2-3 mag deeper than the 2Micron All Sky Survey. In depth morphological analysis was done, in which multi-component structural decompositions played an important role. Possible implications to internal dynamical galaxy evolution were discussed. S0s were suggested to be former spirals in which star formation has ceased, forming a parallel sequence with spirals (see Fig. 1). If that evolution is faster among the brighter galaxies, the observed magnitude difference between the barred and non-barred S0s could be understood. Bars are suggested to play a critical role in such evolution. For example, the inner lenses in the bright non-barred S0s can be explained as former barlenses (inner parts of bars), in which the elongated bar component has dissolved. We suggest that the last destructive merger event happened at a fairly large redshift.