S0 Galaxies Research Articles

Dominant dark matter and a counter-rotating disc: MUSE view of the low-luminosity S0 galaxy NGC 5102

The kinematics and stellar populations of the low-mass nearby S0 galaxy NGC 5102 are studied from integral field spectra taken with the Multi-Unit Spectroscopic Explorer (MUSE). The kinematic maps reveal for the first time that NGC 5102 has the characteristic 2 sigma peaks indicative of galaxies with counter-rotating discs. This interpretation is quantitatively confirmed by fitting two kinematic components to the observed spectra. Through stellar population analysis we confirm the known young stellar population in the centre and find steep age and metallicity gradients. We construct axisymmetric Jeans anisotropic models of the stellar dynamics to investigate the initial mass function (IMF) and the dark matter halo of the galaxy. The models show that this galaxy is quite different from all galaxies previously studied with a similar approach: even within the half-light radius, it cannot be approximated with the self-consistent mass-follows-light assumption. Including an NFW dark matter halo, we need a heavy IMF and a dark matter fraction of 0.37+-0.04 within a sphere of one effective radius to describe the stellar kinematics. The more general model with a free slope of the dark matter halo shows that slope and IMF are degenerate, but indicates that a light weight IMF (Chabrier-like) and a higher dark matter fraction, with a steeper (contracted) halo, fit the data better. Regardless of the assumptions about the halo profile, we measure the slope of the total mass density to be -1.75+-0.04. This is shallower than the slope of -2 of an isothermal halo and shallower than published slopes for more massive early type galaxies.

THE LOCAL BLACK HOLE MASS FUNCTION DERIVED FROM THE MBH–P AND THE MBH–n RELATIONS

ABSTRACT We present a determination of the supermassive black hole (SMBH) mass function for early- and late-type galaxies in the nearby universe (z < 0.0057), established from a volume-limited sample consisting of a statistically complete collection of the brightest spiral galaxies in the southern hemisphere. The sample is defined by limiting luminosity (redshift-independent) distance, D L = 25.4 Mpc, and a limiting absolute B-band magnitude, . These limits define a sample of 140 spiral, 30 elliptical (E), and 38 lenticular (S0) galaxies. We established the Sérsic index distribution for early-type (E/S0) galaxies in our sample. Davis et al. established the pitch angle distribution for their sample, which is identical to our late-type (spiral) galaxy sample. We then used the pitch angle and the Sérsic index distributions in order to estimate the SMBH mass function for our volume-limited sample. The observational simplicity of our approach relies on the empirical relation between the mass of the central SMBH and the Sérsic index for an early-type galaxy or the logarithmic spiral-arm pitch angle for a spiral galaxy. Our SMBH mass function agrees well at the high-mass end with previous values in the literature. At the low-mass end, although inconsistencies exist in previous works that still need to be resolved, our work is more in line with expectations based on modeling of black hole evolution.

IFU spectroscopy of 10 early-type galactic nuclei– IV. Properties of the circumnuclear stellar kinematics

The study of stellar kinematic properties may provide hints on the formation and evolution of elliptical and lenticular galaxies. Although most previous studies have focused on the large scale of these galaxies, their central regions (scales of $\sim$ 100 pc) may contain important clues about their structure, such as kinematically decoupled cores. This is the fourth paper on a sample of 10 massive ($\sigma$ $>$ 200 km s$^{-1}$) and nearby ($d$ $<$ 31 Mpc) early-type galaxies, observed with the integral field unit of the Gemini South Multi Object Spectrograph. Here, we analyse the properties of the stellar kinematics in the circumnuclear region. We fitted the line-of-sight velocity distribution with a Gauss-Hermite function. In seven galaxies of the sample, we detected a rotation pattern in their radial velocity maps that are anti-correlated with $h_3$. We interpret this as stellar structures in rotation embedded in the bulges of the objects. Comparing the stellar kinematic results with the PCA Tomography results and also with the gas kinematic results of IC 5181, it seems that this object may have a non-axisymmetric potential at its centre. The velocity dispersion maps of four objects have a nuclear peak, which must correspond, in part, to unresolved stellar rotation. In NGC 1404, we detected a kinematic decoupled core with an extension of $\sim$ 200 pc. This galaxy also has a $\sigma$-drop in the centre, which may be related to both stellar components in counterrotation or with a kinematically cold star-forming region.

Stellar populations in the bulges of isolated galaxies

We present photometry and long-slit spectroscopy for 12 S0 and spiral galaxies selected from the Catalogue of Isolated Galaxies. The structural parameters of the sample galaxies are derived from the Sloan Digital Sky Survey i-band images by performing a two-dimensional photometric decomposition of the surface brightness distribution. This is assumed to be the sum of the contribution of a S\`ersic bulge, an exponential disc, and a Ferrers bar characterized by elliptical and concentric isophotes with constant ellipticity and position angles. The rotation curves and velocity dispersion profiles of the stellar component are measured from the spectra obtained along the major axis of galaxies. The radial profiles of the H{\beta}, Mg and Fe line-strength indices are derived too. Correlations between the central values of the Mg 2 and Fe line-strength indices and the velocity dispersion are found. The mean age, total metallicity and total {\alpha}/Fe enhancement of the stellar population in the centre and at the radius where the bulge gives the same contribution to the total surface brightness as the remaining components are obtained using stellar population models with variable element abundance ratios. We identify intermediate-age bulges with solar metallicity and old bulges with a large spread in metallicity. Most of the sample bulges display super-solar {\alpha}/Fe enhancement, no gradient in age and negative gradients of metallicity and {\alpha}/Fe enhancement. These findings support a formation scenario via dissipative collapse where environmental effects are remarkably less important than in the assembly of bulges of galaxies in groups and clusters.

Molecular gas kinematics and line diagnostics in early-type galaxies: NGC 4710 and NGC 5866

We present interferometric observations of CO lines (12CO(1-0, 2-1) and 13CO(1-0, 2-1)) and dense gas tracers (HCN(1-0), HCO+(1-0), HNC(1-0) and HNCO(4-3)) in two nearby edge-on barred lenticular galaxies, NGC 4710 and NGC 5866, with most of the gas concentrated in a nuclear disc and an inner ring in each galaxy. We probe the physical conditions of a two-component molecular interstellar medium in each galaxy and each kinematic component by using molecular line ratio diagnostics in three complementary ways. First, we measure the ratios of the position-velocity diagrams of different lines, second we measure the ratios of each kinematic component's integrated line intensities as a function of projected position, and third we model these line ratios using a non-local thermodynamic equilibrium radiative transfer code. Overall, the nuclear discs appear to have a tenuous molecular gas component that is hotter, optically thinner and with a larger dense gas fraction than that in the inner rings, suggesting more dense clumps immersed in a hotter more diffuse molecular medium. This is consistent with evidence that the physical conditions in the nuclear discs are similar to those in photo-dissociation regions. A similar picture emerges when comparing the observed molecular line ratios with those of other galaxy types. The physical conditions of the molecular gas in the nuclear discs of NGC4710 and NGC5866 thus appear intermediate between those of spiral galaxies and starbursts, while the star formation in their inner rings is even milder.

A monolithic collapse origin for the thin and thick disc structure of the S0 galaxy ESO 243-49

ESO 243-49 is a high-mass (circular velocity $v_{\rm c}\approx200\,{\rm km\,s^{-1}}$) edge-on S0 galaxy in the Abell 2877 cluster at a distance of $\sim95\,{\rm Mpc}$. To elucidate the origin of its thick disc, we use MUSE science verification data to study its kinematics and stellar populations. The thick disc emits $\sim80\%$ of the light at heights in excess of $3.5^{\prime\prime}$ ($1.6\,{\rm kpc}$). The rotation velocities of its stars lag by $30-40\,{\rm km\,s^{-1}}$ compared to those in the thin disc, which is compatible with the asymmetric drift. The thick disc is found to be more metal-poor than the thin disc, but both discs have old ages. We suggest an internal origin for the thick disc stars in high-mass galaxies. We propose that the thick disc formed either ${\rm a)}$ first in a turbulent phase with a high star formation rate and that a thin disc formed shortly afterwards, or ${\rm b)}$ because of the dynamical heating of a thin pre-existing component. Either way, the star formation in ESO 243-49 was quenched just a few Gyrs after the galaxy was born and the formation of a thin and a thick disc must have occurred before the galaxy stopped forming stars. The formation of the discs was so fast that it could be described as a monolithic collapse where several generations of stars formed in a rapid succession.

STELLAR NUCLEI AND INNER POLAR DISKS IN LENTICULAR GALAXIES

ABSTRACT I analyze statistics of the stellar population properties for stellar nuclei and bulges of nearby lenticular galaxies in different environments by using panoramic spectral data of the integral-field spectrograph SAURON retrieved from the open archive of the Isaac Newton Group. I also estimate the fraction of nearby lenticular galaxies having inner polar gaseous disks by exploring the volume-limited sample of early-type galaxies of the ATLAS-3D survey. By inspecting the two-dimensional velocity fields of the stellar and gaseous components with the running tilted-ring technique, I have found seven new cases of inner polar disks. Together with those, the frequency of inner polar disks in nearby S0 galaxies reaches 10%, which is much higher than the frequency of large-scale polar rings. Interestingly, the properties of the nuclear stellar populations in the inner polar ring hosts are statistically the same as those in the whole S0 sample, implying similar histories of multiple gas-accretion events from various directions.

The influence of host galaxy morphology on the properties of Type Ia supernovae from the JLA compilation

The observational cosmology with distant Type Ia supernovae (SNe) as standard candles claims that the Universe is in accelerated expansion, caused by a large fraction of dark energy. In this paper we investigate the SN Ia environment, studying the impact of the nature of their host galaxies on the Hubble diagram fitting. The supernovae (192 SNe) used in the analysis were extracted from Joint-Light-curves-Analysis (JLA) compilation of high-redshift and nearby supernovae which is the best one to date. The analysis is based on the empirical fact that SN Ia luminosities depend on their light curve shapes and colors. We confirm that the stretch parameter of Type Ia supernovae is correlated with the host galaxy type. The supernovae with lower stretch are hosted mainly in elliptical and lenticular galaxies. No significant correlation between SN Ia colour and host morphology was found. We also examine how the luminosities of SNe Ia change depending on host galaxy morphology after stretch and colour corrections. Our results show that in old stellar populations and low dust environments, the supernovae are slightly fainter. SNe Ia in elliptical and lenticular galaxies have a higher α (slope in luminosity-stretch) and β (slope in luminosity-colour) parameter than in spirals. However, the observed shift is at the 1-σ uncertainty level and, therefore, can not be considered as significant. We confirm that the supernova properties depend on their environment and that the incorporation of a host galaxy term into the Hubble diagram fit is expected to be crucial for future cosmological analyses.

A rare example of low surface-brightness radio lobes in a gas-rich early-type galaxy: the story of NGC 3998

We study the nearby lenticular galaxy NGC 3998. This galaxy is known to host a low-power radio AGN with a kpc-size one-sided jet and a large, nearly polar HI disc. It is therefore a good system to study to understand the relation between the availability of cold-gas and the triggering of AGNs in galaxies. Our new WSRT data reveal two faint, S-shaped radio lobes extending out to $\sim$10 kpc from the galaxy centre. Remarkably, we find that the inner HI disc warps back towards the stellar mid-plane in a way that mirrors the warping of the radio lobes. We suggest that the polar HI disc was accreted through a minor merger, and that the torques causing it to warp in the inner regions are also responsible for feeding the AGN. The "S" shape of the radio lobes would then be due to the radio jets adapting to the changing angular momentum of the accreted gas. The extended radio jets are likely poorly collimated, which would explain their quick fading and, therefore, their rarity in galaxies similar to NGC 3998. The fuelling of the central super-massive black hole is likely occurring via "discrete events", suggested by the observed variability of the radio core and the extremely high core dominance, which we attribute to the formation and ejection of a new jet resulting from a recent fuelling event.

Complex central structures suggest complex evolutionary paths for barred S0 galaxies

We investigate three barred lenticular galaxies (NGC 2681, NGC 3945 and NGC 4371) which were previously reported to have complex central structures but without a detailed structural analysis of these galaxies' high-resolution data. We have therefore performed four- to six-component (pseudo-)bulge/disk/bar/ring/point source) decompositions of the composite (Hubble Space Telescope plus ground-based) surface brightness profiles. We find that NGC 2681 hosts three bars, while NGC 3945 and NGC 4371 are double- and single-barred galaxies, respectively, in agreement with past isophotal analysis. We find that the bulges in these galaxies are compact, and have S\'ersic indices of $n\sim 2.2 - 3.6$ and stellar masses of $M_{*}$ $\sim 0.28\times10^{10} - 1.1\times10^{10} M_{\sun}$. NGC 3945 and NGC 4371 have intermediate-scale `pseudo-bulges' that are well described by a S\'ersic model with low $n \la 0.5$ instead of an exponential ($n=1$) profile as done in the past. We measure emission line fluxes enclosed within 9 different elliptical apertures, finding that NGC 2681 has a LINER-type emission inside $R \sim 3\arcsec$, but the emission line due to star formation is significant when aperture size is increased. In contrast, NGC 3945 and NGC 4371 have composite (AGN plus star forming)- and LINER-type emissions inside and outside $R \sim 2\arcsec$, respectively. Our findings suggest that the three galaxies have experienced a complex evolutionary path. The bulges appear to be consequences of an earlier violent merging event while subsequent disk formation via gas accretion and bar-driven perturbations may account for the build-up of pseudo-bulges, bars, rings and point sources.

Morphological and photometric properties of active and non-active galaxies in the green valley

Context: The differences in properties of active and non-active galaxies in the green valley have been studied in the quest of finding the driving mechanism behind the evolutionary transition from the blue cloud to the red sequence galaxies.Aims: Using COSMOS data, as one of the deepest surveys, and X-ray detected active galaxies, we studied their properties in the green valley, and established the differences in comparison with the non-active ones.Methods: Green valley galaxies were selected using the U-B colour criteria of 0.8 ≤ U- B ≤ 1.2. We then studied different properties between the two samples such as their morphologies, colours, stellar masses, photometric redshift distributions, and sizes, and performed a statistical comparative study.Results: We found that in the green valley, active galaxies are dominated by earlier morphological types (elliptical and lenticular galaxies), are more massive, have higher photometric redshifts and redder colours than non-active galaxies.Conclusions: Our findings suggest that the non-active galaxies in the green valley are different from the active ones, with active galaxies being more evolved.Keywords: galaxies: active, galaxies: fundamental parameters, galaxies: structure, Xrays: galaxies

Morphological and photometric properties of active and non-active galaxies in the green valley

Context: The differences in properties of active and non-active galaxies in the green valley have been studied in the quest of finding the driving mechanism behind the evolutionary transition from the blue cloud to the red sequence galaxies.Aims: Using COSMOS data, as one of the deepest surveys, and X-ray detected active galaxies, we studied their properties in the green valley, and established the differences in comparison with the non-active ones.Methods: Green valley galaxies were selected using the U-B colour criteria of 0.8 ≤ U- B ≤ 1.2. We then studied different properties between the two samples such as their morphologies, colours, stellar masses, photometric redshift distributions, and sizes, and performed a statistical comparative study.Results: We found that in the green valley, active galaxies are dominated by earlier morphological types (elliptical and lenticular galaxies), are more massive, have higher photometric redshifts and redder colours than non-active galaxies.Conclusions: Our findings suggest that the non-active galaxies in the green valley are different from the active ones, with active galaxies being more evolved.Keywords: galaxies: active, galaxies: fundamental parameters, galaxies: structure, Xrays: galaxies

Which bulges are favoured by barred S0 galaxies?

Abstract S0 galaxies are known to host classical bulges with a broad range of size and mass, while some such S0s are barred and some not. The origin of the bars has remained a long-standing problem – what made bar formation possible in certain S0s? By analysing a large sample of S0s with classical bulges observed by the Spitzer Space Telescope, we find that most of our barred S0s host comparatively low-mass classical bulges, typically with bulge-to-total ratio less than 0.5, whereas S0s with more massive classical bulges than these do not host any bar. Furthermore, we find that amongst the barred S0s, there is a trend for the longer and massive bars to be associated with comparatively bigger and massive classical bulges – possibly suggesting bar growth being facilitated by these classical bulges. In addition, we find that the bulge effective radius is always less than the bar effective radius – indicating an interesting synergy between the host classical bulge and bars being maintained while bar growth occurred in these S0s.

Statistical study of warps in a sample of spiral and lenticular galaxies

A sample of edge-on (or nearly edge-on) spiral and lenticular galaxies is selected to study the warp phenomenon in their disks. This sample contains 36 disk galaxies selected from Watanabe’s catalogue (Watanabe, 1983). We investigate the existence of physical relations between photometric and spectroscopic parameters and the warp degree of galaxies.

Exploring the mass assembly of the early-type disc galaxy NGC 3115 with MUSE

We present MUSE integral field spectroscopic data of the S0 galaxy NGC 3115 obtained during the instrument commissioning at the ESO Very Large Telescope (VLT). We analyse the galaxy stellar kinematics and stellar populations and present two dimensional maps of their associated quantities. We thus illustrate the capacity of MUSE to map extra-galactic sources to large radii in an efficient manner, i.e., ~4 Re, and provide relevant constraints on its mass assembly. We probe the well known set of substructures of NGC 3115 (its nuclear disc, stellar rings, outer kpc-scale stellar disc and spheroid) and show their individual associated signatures in the MUSE stellar kinematics and stellar populations maps. In particular, we confirm that NGC 3115 has a thin fast rotating stellar disc embedded in a fast rotating spheroid, and that these two structures show clear differences in their stellar age and metallicity properties. We emphasise an observed correlation between the radial stellar velocity, V, and the Gauss-Hermite moment, h3, creating a "butterfly" shape in the central 15" of the h3 map. We further detect the previously reported weak spiral and ring-like structures, and find evidence that these features can be associated with regions of younger mean stellar ages. We provide tentative evidence for the presence of a bar, despite the fact that the V-h3 correlation can be reproduced by a simple axisymmetric dynamical model. Finally, we present a reconstruction of the two dimensional star formation history of NGC 3115 and find that most of its current stellar mass was formed at early epochs (>12Gyr ago), while star formation continued in the outer (kpc-scale) stellar disc until recently. Since z~2, and within ~4 Re, we suggest that NGC 3115 has been mainly shaped by secular processes.

Stellar counter-rotation in lenticular galaxy NGC 448

The counter-rotation phenomenon in disc galaxies directly indicates a complex galaxy assembly history which is crucial for our understanding of galaxy physics. Here we present the complex data analysis for a lenticular galaxy NGC 448, which has been recently suspected to host a counter-rotating stellar component. We collected deep long-slit spectroscopic observations using the Russian 6-m telescope and performed the photometric decomposition of Sloan Digital Sky Survey (SDSS) archival images. We exploited (i) a non-parametric approach in order to recover stellar line-of-sight velocity distributions and (ii) a parametric spectral decomposition technique in order to disentangle stellar population properties of both main and counter-rotating stellar discs. Our spectral decomposition stays in perfect agreement with the photometric analysis. The counter-rotating component contributes $\approx$30 per cent to the total galaxy light. We estimated its stellar mass to be $9.0^{+2.7}_{-1.8}\cdot10^{9}M_\odot$. The radial scale length of counter-rotating disc is $\approx$3 times smaller than that of the main disc. Both discs harbour old stars but the counter-rotating components reveals a detectable negative age gradient that might suggest an extended inside-out formation during $3\dots4$ Gyrs. The counter-rotating disc hosts more metal-rich stars and possesses a shallower metallicity gradient with respect to the main disc. Our findings rule out cosmological filaments as a source of external accretion which is considered as a potential mechanism of the counter-rotating component formation in NGC 448, and favour the satellite merger event with the consequent slow gas accretion.

X-ray sources in dwarf galaxies in the Virgo cluster and the nearby field

Theextenttowhichdwarfgalaxiesrepresentessentiallyscaleddownversionsofgiantgalaxies is an important question with regards the formation and evolution of the galaxy population as a whole. Here, we address the specific question of whether dwarf galaxies behave like smaller versions of giants in terms of their X-ray properties. We discuss two samples of around 100 objects each, dwarfs in the Virgo cluster and dwarfs in a large Northern hemisphere area. We find nine dwarfs in each sample with Chandra detections. For the Virgo sample, these are in dwarf elliptical (or dwarf lenticular) galaxies and we assume that these are (mostly) low-mass X-ray binaries (LMXB) [some may be nuclear sources]. We find a detection rate entirely consistent with scaling down from massive ellipticals, viz. about one bright (i.e.

The low dark matter content of the lenticular galaxy NGC 3998

We observed the lenticular galaxy NGC 3998 with the Mitchell Integral-Field Spectrograph and extracted line-of-sight velocity distributions out to 3 half-light radii. We constructed collisionless orbit models in order to constrain NGC 3998's dark and visible structure, using kinematics from both the Mitchell and SAURON instruments. We find NGC 3998 to be almost axisymmetric, seen nearly face on with a flattened intrinsic shape - i.e., a face-on fast-rotator. We find an I-band mass-to-light ratio of $4.7_{-0.45}^{+0.32}$ in good agreement with previous spectral fitting results for this galaxy. Our best-fit orbit model shows a both a bulge and a disc component, with a non-negligible counter-rotating component also evident. We find that relatively little dark matter is needed to model this galaxy, with an inferred dark mass fraction of just $(7.1^{+8.1}_{-7.1})\%$ within one half-light radius.

MCG+08-22-082: A DOUBLE CORE AND BOXY APPEARANCE DWARF LENTICULAR GALAXY SUSPECTED TO BE A MERGER REMNANT

ABSTRACT We present a study on the dwarf lenticular galaxy MCG+08-22-082 (U141), located in the Ursa Major cluster, blue-centered, double-cored, and having a boxy appearance. Using publicly available data from the Sloan Digital Sky Survey (SDSS), we perform an analysis of the structural and stellar population properties of the galaxy and the cores. We find that the light profile of U141 follows an exponential law. U141 has a brightness of M r = − 16.01 mag, and an effective radius of R e = 1.7 kpc . The boxiness parameter a 4 / a is mostly between 0 and −0.05 in the inner parts, reaching an extreme of about −0.1. Double cores are seen at the center of U141; each of these cores has a stellar mass of ∼106 M ☉ and the separation between them is ∼300 pc. Optical spectroscopy of these cores shows prominent emission in Hα, suggesting ongoing star-forming activities. We interpret these morphological properties and speculate that U141 is a merger remnant of two disk galaxies. Thus, we might have discovered an intermediate stage of merging, providing possible evidence of double cores in the center of the galaxy.

DISCOVERY OF THE CANDIDATE OFF-NUCLEAR ULTRASOFT HYPER-LUMINOUS X-RAY SOURCE 3XMM J141711.1+522541

ABSTRACT We report the discovery of an off-nuclear ultrasoft hyper-luminous X-ray source candidate 3XMM J141711.1+522541 in the inactive S0 galaxy SDSS J141711.07+522540.8 (z = 0.41827, d L = 2.3 Gpc) in the Extended Groth Strip. It is located at a projected offset of ∼1.″0 (5.2 kpc) from the nucleus of the galaxy and was serendipitously detected in five XMM-Newton observations in 2000 July. Two observations have enough counts and can be fitted with a standard thermal disk with an apparent inner disk temperature kT MCD ∼ 0.13 keV and a 0.28–14.2 keV unabsorbed luminosity L X ∼ 4 × 1043 erg s−1 in the source rest frame. The source was still detected in three Chandra observations in 2002 August, with similarly ultrasoft but fainter spectra (kT MCD ∼ 0.17 keV, L X ∼ 0.5 × 1043 erg s−1). It was not detected in later observations, including two by Chandra in 2005 October, one by XMM-Newton in 2014 January, and two by Chandra in 2014 September–October, implying a long-term flux variation factor of &gt;14. Therefore the source could be a transient with an outburst in 2000–2002. It has a faint optical counterpart candidate, with apparent magnitudes of m F606W = 26.3 AB mag and m F814W = 25.5 AB mag in 2004 December (implying an absolute V-band magnitude of ∼−15.9 AB mag). We discuss various explanations for the source and find that it is best explained as a massive black hole (BH) embedded in the nucleus of a possibly stripped satellite galaxy, with the X-ray outburst due to tidal disruption of a surrounding star by the BH. The BH mass is ∼105 M ⊙, assuming the peak X-ray luminosity at around the Eddington limit.