Based on the wealth of multiwavelength imaging data from the SDSS, we investigate whether dwarf and giant early-type galaxies in the Virgo cluster follow a continuum in their structural parameters and their stellar population characteristics. More specifically we study the relation between size and brightness for the galaxies and their color magnitude relation. In both cases, we find noticeable deviations from a simple joint behavior of dwarfs and giants. We discuss these findings in the light of the different formation mechanisms commonly assumed for dwarf and giant early types, thereby taking into account the existence of several distinct early-type dwarf subclasses. By comparing our results to a semianalytic model of galaxy formation, we argue that the analyzed relations might be reproduced by processes that form dwarfs and giants altogether. The work presented here is based on Janz & Lisker 2008, 2009.
The ALFALFA (Arecibo Legacy Fast ALFA) blind survey is providing a census of HI in galaxies of all types in a range of environments. Here we report on ALFALFA results for Virgo Cluster early-type dwarfs between declinations of 4 and 16 degrees. Less than 2% of the Virgo early-type dwarf population is detected, compared to 70-80% of the Im/BCD dwarf population. Most of the dwarfs detected in HI show evidence for ongoing or recent star formation. Early-type galaxies with HI tend to be located in the outer regions of the cluster and to be brighter. Early-type dwarfs with HI may be undergoing morp…
The Next Generation Virgo Cluster Survey (NGVS) is a CFHT Large Program that is using the wide field of view capabilities of the MegaCam camera to map the entire Virgo Cluster from its core to virial radius. The observing strategy has been optimized to detect very low surface brightness structures in the cluster, including intracluster stellar streams and faint dwarf spheroidal galaxies. We present here the current status of this ongoing survey, with an emphasis on the detection and analysis of the very low-mass galaxies in the cluster that have been revealed by the NGVS.
We investigate the dwarf (M_B> -16) galaxies in the Virgo cluster in the radio, optical, and ultraviolet regimes. Of the 365 galaxies in this sample, 80 have been detected in HI by the Arecibo Legacy Fast ALFA survey. These detections include 12 early-type dwarfs which have HI and stellar masses similar to the cluster dwarf irregulars and BCDs. In this sample of 12, half have star-formation properties similar to late type dwarfs, while the other half are quiescent like typical early-type dwarfs. We also discuss three possible mechanisms for their evolution: that they are infalling field galaxi…
Dwarf elliptical galaxies are the most common galaxy type in nearby galaxy clusters, yet they remain relatively poorly studied objects and many of their basic properties have yet to be quantified. In this contribution we present the preliminary results of a study of 4 Virgo and 1 field galaxy obtained with the SAURON integral field unit on the William Herschel Telescope (La Palma). While traditional long-slit observations are likely to miss more complicated kinematic features, with SAURON we are able to study both kinematics and stellar populations in two dimensions, obtaining a much more deta…
We use dust scaling relations to investigate the hypothesis that Virgo cluster transition-type dwarfs are infalling star-forming field galaxies, which is argued based on their optical features (e.g. disks, spiral arms, bars) and kinematic properties similar to late-type galaxies. After their infall, environmental effects gradually transform them into early-type galaxies through the removal of their interstellar medium and quenching of all star formation activity. In this paper, we aim to verify whether this hypothesis holds using far-infrared diagnostics based on Herschel observations of the V…
We show the effects of environmental evolution on Virgo cluster and field dwarf elliptical galaxies (dEs), presenting the first large-scale integral-field spectroscopic data for this galaxy class. The great variety of morphological, kinematic, and stellar population parameters seen in our data supports the claim that dEs are defunct dwarf spiral/irregular galaxies and points to a formation scenario that allows for a stochastic shaping of galaxy properties. We further investigate the properties of our sample by analyzing its kinematic and dynamical properties. We compare the level of rotational…
We present a photometric study of the globular clusters (GCs) in the Virgo giant elliptical galaxy M86 based on Washington CT1 images. The colors of the GCs in M86 show a bimodal distribution with a blue peak at (C -T1) = 1.30 and a red peak at (C -T1) = 1.72. The spatial distribution of the red GCs is elongated similarly to that of the stellar halo, while that of the blue GCs is roughly circular. The radial number density profile of the blue GCs is more extended than that of the red GCs. The radial number density profile of the red GCs is consistent with the surface brightness profile of the …
We use the Science Demonstration Phase data of the Herschel Virgo Cluster Survey to search for dust emission of early-type dwarf galaxies in the central regions of the Virgo Cluster as an alternative way of identifying the interstellar medium.We present the first possible far-infrared detection of cluster early-type dwarf galaxies: VCC781 and VCC951 are detected at the 10 sigma level in the SPIRE 250 micron image. Both detected galaxies have dust masses of the order of 10^5 Msun and average dust temperatures ~20K. The detection rate (less than 1%) is quite high compared to the 1.7% detection r…
What happens to dwarf galaxies as they enter the cluster potential well is one of the main unknowns in studies of galaxy evolution. Several evidence suggests that late-type galaxies enter the cluster and are transformed to dwarf early-type galaxies (dEs). We study the Virgo cluster to understand which mechanisms are involved in this transformation. We find that the dEs in the outer parts of Virgo have rotation curves with shapes and amplitudes similar to late-type galaxies of the same luminosity. These dEs are rotationally supported, have disky isophotes, and younger ages than those dEs in the…
We present ultraviolet (UV) color-magnitude relations (CMRs) of early-type dwarf galaxies in the Virgo cluster, based on Galaxy Evolution Explorer (GALEX) UV and Sloan Digital Sky Survey (SDSS) optical imaging data. We find that dwarf lenticular galaxies (dS0s), including peculiar dwarf elliptical galaxies (dEs) with disk substructures and blue centers, show a surprisingly distinct and tight locus separated from that of ordinary dEs, which is not clearly seen in previous CMRs. The dS0s in UV CMRs follow a steeper sequence than dEs and show bluer UV-optical color at a given magnitude. We also f…
We present the dust properties of a small sample of Virgo cluster dwarf galaxies drawn from the science demonstration phase data set of the Herschel Virgo Cluster Survey. These galaxies have low metallicities (7.8 < 12 + log(O/H) < 8.3) and star-formation rates < 10^{-1} M_{sun}/yr. We measure the spectral energy distribution (SED) from 100 to 500 um and derive dust temperatures and dust masses. The SEDs are fitted by a cool component of temperature T < 20 K, implying dust masses around 10^{5} M_{sun} and dust-to-gas ratios D within the range 10^{-3}-10^{-2}. The completion of the full survey …
We present spectroscopic observations of ultra compact dwarf (UCD) galaxies in the Fornax and Virgo Clusters made to measure and compare their stellar populations. The spectra were obtained on the Gemini-North (Virgo) and Gemini-South (Fornax) Telescopes using the respective Gemini Multi-Object Spectrographs. We estimated the ages, metallicities and abundances of the objects from mea- surements of Lick line-strength indices in the spectra; we also estimated the ages and metallicities independently using a direct spectral fitting technique. Both methods re- vealed that the UCDs are old (mean ag…
We present the first large-scale stellar kinematic and line-strength maps for dwarf elliptical galaxies (9 in the Virgo Cluster and 3 in the field environment) obtained with the SAURON integral-field unit. No two galaxies in our sample are alike: we see that the level of rotation is not tied to flattening (we have, e.g. round rotators and flattened nonrotators); we observe kinematic twists in 1 Virgo and 1 field object; we discover large-scale kinematically-decoupled components in 2 field galaxies; we see varying gradients in line-strength maps, from nearly flat to strongly peaked in the cente…
We present an investigation into the origins of a series of interlaced narrow filamentary stellar structures, loops and plumes in the vicinity of the Virgo Cluster, edge-on spiral galaxy, NGC 4216 that were previously identified by the Blackbird Telescope. Using the deeper, higher-resolution and precisely calibrated optical CFHT/MegaCam images obtained as part of the Next Generation Virgo Cluster Survey (NGVS), we confirm the previously identified features and identify a few additional structures. The NGVS data allowed us to make a physical study of these low-surface brightness features and in…
We present new medium resolution kinematic data for a sample of 21 dwarf early-type galaxies (dEs) mainly in the Virgo cluster, obtained with the WHT and INT telescopes at the Roque de los Muchachos Observatory (La Palma, Spain). These data are used to study the origin of the dwarf elliptical galaxy population inhabiting clusters. We confirm that dEs are not dark matter dominated galaxies, at least up to the half-light radius. We also find that the observed galaxies in the outer parts of the cluster are mostly rotationally supported systems with disky morphological shapes. Rotationally support…
We present new observational results on the kinematical, morphological, and stellar population properties of a sample of 21 dEs located both in the Virgo cluster and in the field, which show that 52% of the dEs i) are rotationally supported, ii) exhibit structural signs of typical rotating systems such as discs, bars or spiral arms, iii) are younger (~3 Gyr) than non-rotating dEs, and iv) are preferentially located either in the outskirts of Virgo or in the field. This evidence is consistent with the idea that rotationally supported dwarfs are late type spirals or irregulars that recently ente…
In the last decade we witness an advent of new types of dwarf stellar systems in cluding ultra-compact dwarfs, ultra-faint dwarf spheroidals, and exotic globular clusters, breaking the old simple paradigm for dwarf galaxies and globular clusters. These objects become more intriguing, and understanding of these new findings be comes more challenging. Recently we discovered a new type of large scale structure in the Virgo cluster of galaxies: it is composed of globular clusters. Globular clusters in Virgo are found wandering between galaxies (intracluster globular clusters) as well as in galaxie…
Early-type dwarfs (dEs) are by far the most abundant galaxy population in nearby clusters. Whether these objects are primordial, or the recent end-products of the different physical mechanisms that can transform galaxies once they enter these high-density environments, is still a matter of debate. Here we present a novel approach to test these scenarios by comparing the properties of the globular cluster systems (GCSs) of Virgo dEs and their potential progenitors with simple predictions from gravitational and hydrodynamical interaction models. We show that low-mass (Mstar < 2E8 Msun) dEs have …
To address the question of whether the so-called ultra compact dwarf galaxies (UCDs) are the remnant nuclei of destroyed early-type dwarf galaxies (dEs), we analyze the stellar population parameters of the nuclei of 34 Virgo dEs, as well as ten Virgo UCDs, including one that we discovered and which we report on here. Based on absorption line strength (Lick index) measurements, we find that nuclei of Virgo dEs have younger stellar population ages than UCDs, with averages of 5 Gyr and >10 Gyr, respectively. In addition to this, the metallicity also differs: dE nuclei are on average more metal-ri…
We present the first spectroscopic study of the globular clusters (GCs) in the giant elliptical galaxy (gE) M86 in the Virgo cluster. Using spectra obtained in the Multi-Object Spectroscopy (MOS) mode of the Faint Object Camera and Spectrograph (FOCAS) on the Subaru telescope, we measure the radial velocities for 25 GCs in M86. The mean velocity of the GCs is derived to be vp = -354+81 -79 km/s, which is different from the velocity of the M86 nucleus (vgal = -234\pm41 km/s). We estimate the velocity dispersion of the GCs, σp = 292+32-32 km/s, and find a hint of rotation of the M86 GC system. A…
Dwarf elliptical galaxies (dEs) are the most common galaxy type in nearby galaxy clusters; even so, many of their basic properties have yet to be quantified. Here we present the results of our study of 4 Virgo dwarf ellipticals obtained with the SAURON integral field unit on the William Herschel Telescope (La Palma, Spain). While traditional long-slit observations are likely to miss more complicated kinematic features, with SAURON we are able to study both kinematics and stellar populations in two dimensions, obtaining a much more detailed view of the mass distribution and star formation histo…
The fraction of star-forming to quiescent dwarf galaxies varies from almost infinity in the field to zero in the centers of rich galaxy clusters. What is causing this pronounced morphology-density relation? What do quiescent dwarf galaxies look like when studied in detail, and what conclusions can be drawn about their formation mechanism? Here we study a nearly magnitude-complete sample (-19 < M_r < -16 mag) of 121 Virgo cluster early types with deep near-infrared images from the SMAKCED project. We fit two-dimensional models with optional inner and outer components, as well as bar and lens co…
We present a spectroscopic study of the globular clusters (GCs) in the giant elliptical galaxy NGC 4636 in the Virgo cluster. We selected target GC candidates using the Washington photometry derived from the deep CCD images taken at the KPNO 4m. Then we obtained the spectra of 164 target objects in the field of NGC 4636 using the Multi-Object Spectroscopy (MOS) mode of Faint Object Camera and Spectrograph (FOCAS) on the SUBARU 8.2m Telescope. We have measured the velocities for 122 objects: 105 GCs in NGC 4636, the nucleus of NGC 4636, 11 foreground stars, 2 background galaxies, and 3 probable…
In the light of the question whether most early-type dwarf (dE) galaxies in clusters formed through infall and transformation of late-type progenitors, we search for an imprint of such an infall history in the oldest, most centrally concentrated dE subclass of the Virgo cluster: the nucleated dEs that show no signatures of disks or central residual star formation. We select dEs in a (projected) region around the central elliptical galaxies, and subdivide them by their line-of-sight velocity into fast-moving and slow-moving ones. These subsamples turn out to have significantly different shapes:…
We place our sample of 18 Virgo dwarf early-type galaxies (dEs) on the V-K - velocity dispersion, Faber-Jackson, and Fundamental Plane (FP) scaling relations for massive early-type galaxies (Es). We use a generalized velocity dispersion, which includes rotation, to be able to compare the location of both rotationally and pressure supported dEs with those of early and late-type galaxies. We find that dEs seem to bend the Faber-Jackson relation of Es to lower velocity dispersions, being the link between Es and dwarf spheroidal galaxies (dSphs). Regarding the FP relation, we find that dEs are sig…
We report evidence for dynamically significant rotation in the globular cluster systems of two luminous Virgo dwarf ellipticals, VCC1261 and VCC1528. Including previous results for VCC1087, the globular cluster systems of all three Virgo dwarf ellipticals studied in detail to date exhibit v_rot/sigma > 1. Taking the rotation seen in the globular clusters as maximal disk rotation, we find all three dEs lie on the r-band Tully-Fisher relation. We argue that these data support the hypothesis that luminous dEs are the remnants of transformed disk galaxies. We also obtained deep, longslit data for …
We present optical imaging and spectroscopy and HI imaging of the Virgo Cluster galaxy IC 3418, which is likely a "smoking gun" example of the transformation of a dwarf irregular into a dwarf elliptical galaxy by ram pressure stripping. IC 3418 has a spectacular 17 kpc length UV-bright tail comprised of knots, head-tail, and linear stellar features. The only H-alpha emission arises from a few HII regions in the tail, the brightest of which are at the heads of head-tail UV sources whose tails point toward the galaxy ("fireballs"). Several of the elongated tail sources have H-alpha peaks outward…
We use a combination of deep optical and near-infrared light profiles for a morphologically diverse sample of Virgo cluster galaxies to study the radially-resolved stellar populations of cluster galaxies over a wide range of galaxy structure. We find that, in the median, the age gradients of Virgo galaxies are either flat (lenticulars and Sa-Sb spirals) or positive (ellipticals, Sbc+Sc spirals, gas-rich dwarfs, and irregulars), while all galaxy types have a negative median metallicity gradient. Comparison of the galaxy stellar population diagnostics (age, metallicity, and gradients thereof) ag…
We have searched for dust in an optical sample of 910 Early-Type Galaxies (ETG) in the Virgo cluster (447 of which are optically complete at m_pg <= 18.0), extending also to the dwarf ETG, using Herschel images at 100, 160, 250, 350 and 500 microns. Dust was found in 52 ETG (46 are in the optically complete sample), including M87 and another 3 ETG with strong synchrotron emisssion. Dust is detected in 17% of ellipticals, 41% of lenticulars, and in about 4% of dwarf ETG. The dust-to-stars mass ratio increases with decreasing optical luminosity, and for some dwarf ETG reaches values similar to t…
We use deep V-band surface photometry of five of the brightest elliptical galaxies in the Virgo cluster to search for diffuse tidal streams, shells, and plumes in their outer halos (r > 50 kpc). We fit and subtract elliptical isophotal models from the galaxy images to reveal a variety of substructure, with surface brightnesses in the range mu_V= 26-29 mag/arcsec^2. M49 possesses an extended, interleaved shell system reminiscent of the radial accretion of a satellite companion, while M89's complex system of shells and plumes suggests a more complicated accretion history involving either multipl…
We compare the galaxy population in the Virgo, Fornax, Coma and Perseus cluster to a state-of-the-art semi-analytic model, focusing on the regime of dwarf galaxies with luminosities from approximately 10^8 L_sun to 10^9 L_sun. We find that the number density profiles of dwarfs in observed clusters are reproduced reasonably well, and that the red fractions of model clusters provide a good match to Coma and Perseus. On the other hand, the red fraction among dwarf galaxies in Virgo is clearly lower than in model clusters. We argue that this is mainly caused by the treatment of environmental effec…
We use a combination of deep optical (gri) and near-infrared (H) photometry to study the radially-resolved colours of a broad sample of 300 Virgo cluster galaxies. For most galaxy types, we find that the median g-H colour gradient is either flat (gas-poor giants and gas-rich dwarfs) or negative (i.e., colours become bluer with increasing radius; gas-poor dwarfs, spirals, and gas-poor peculiars). Later-type galaxies typically exhibit more negative gradients than early-types. Given the lack of a correlation between the central colours and axis ratios of Virgo spiral galaxies, we argue that dust …
We present a kinematic analysis of the globular cluster(GC) system in the giant elliptical galaxy (gE) NGC 4636 in the Virgo cluster. Using the photometric and spectroscopic database of 238 GCs, we have investigated the kinematics of the GC system. The NGC 4636 GC system shows weak overall rotation, which is dominated by the red GCs. However, both the blue GCs and red GCs show some rotation in the inner region at R<4.3'. The velocity dispersion for all the GCs is derived to be sigma_p = 225{+12-9} km/s. The velocity dispersion for the blue GCs (sig=251 km/s) is slightly larger than that for th…
Globular clusters are found usually in galaxies and they are an excellent tracer of dark matter. Long ago it was suggested that there may exist intracluster globular clusters (IGCs) bound to a galaxy cluster rather than to any single galaxy. Here we present a map showing the large scale distribution of globular clusters over the entire Virgo cluster. It shows that IGCs are found out to 5 million light years from the Virgo center, and that they are concentrated in several substructures much larger than galaxies. These objects might have been mostly stripped off from low-mass dwarf galaxies.
The Giant GAlaxies, Dwarfs, and Debris Survey concentrates on the nearby universe to study how galaxies have interacted in groups of different morphology, density, and richness. In these groups we select the dominant spiral galaxy and search its surroundings for dwarf galaxies and tidal interactions. This paper presents the first results from deep wide-field imaging of NGC 7331, where we detect only four low luminosity candidate dwarf companions and a stellar stream that may be evidence of a past tidal interaction. The dwarf galaxy candidates have surface brightnesses of mu_{r} ~ 23-25 mag/arc…
We present IRAM 30m sensitive upper limits on CO emission in the ram pressure stripped dwarf Virgo galaxy IC3418 and in a few positions covering HII regions in its prominent 17 kpc UV/Ha gas-stripped tail. In the central few arcseconds of the galaxy, we report a possible marginal detection of about 1x10^6 M_sun of molecular gas (assuming a Galactic CO-to-H_2 conversion factor) that could correspond to a surviving nuclear gas reservoir. We estimate that there is less molecular gas in the main body of IC3418, by at least a factor of 20, than would be expected from the pre-quenching UV-based star…
We present the dynamical analysis of a sample of 12 dwarf elliptical (dE) galaxies for which we have obtained SAURON large-scale two-dimensional spectroscopic data. We construct Jeans axisymmetric models and obtain total dynamical masses enclosed within one effective radius. We use the obtained values to show that the validity of the dynamical scaling relations of massive early-type galaxies can be extended to these low-mass systems, except that dEs seem to contain relatively larger fraction of dark matter in their inner parts. We then demonstrate that dE galaxies have lower angular momenta th…
[Abridged] Using VLT/FORS2 spectroscopy, we have studied the properties of the central stellar populations of a sample of 38 nucleated early-type dwarf (dE) galaxies in the Virgo Cluster. We find that these galaxies do not exhibit the same average stellar population characteristics for different morphological subclasses. The nucleated galaxies without discs are older and more metal poor than the dEs with discs . The alpha-element abundance ratio appears consistent with the solar value for both morphological types. Besides a well-defined relation of metallicity and luminosity, we also find a cl…
The origin of ultra-compact dwarfs (UCDs)--objects larger and more massive than typical globular clusters (GCs), but more compact than typical dwarf galaxies--has been hotly debated in the 15 years since their discovery. Even whether UCDs should be considered galactic in origin, or simply the most extreme GCs, is not yet settled. We present the dynamical properties of 97 spectroscopically confirmed UCDs (rh >~10 pc) and 911 GCs associated with central cD galaxy of the Virgo cluster, M87. Our UCDs, of which 89% have M_star > ~2X10^6 M_sun and 92% are as blue as the classic blue GCs, nearly trip…
We present evidence for kinematically decoupled cores (KDCs) in two dwarf early-type (dE) galaxies in the Virgo cluster, VCC 1183 and VCC 1453, studied as part of the SMAKCED stellar absorption-line spectroscopy and imaging survey. These KDCs have radii of 1.8'' (0.14 kpc) and 4.2'' (0.33 kpc), respectively. Each of these KDCs is distinct from the main body of its host galaxy in two ways: (1) inverted sense of rotation; and (2) younger (and possibly more metal-rich) stellar population. The observed stellar population differences are probably associated with the KDC, although we cannot rule out…
We present a spectroscopic study of 287 Planetary Nebulas (PNs) in a total area of ~0.4 deg^2 around the BCG M87 in Virgo A. With these data we can distinguish the stellar halo from the co-spatial intracluster light (ICL). PNs were identified from their narrow and symmetric redshifted lambda 5007\4959 Angstrom [OIII] emission lines, and the absence of significant continuum. We implement a robust technique to measure the halo velocity dispersion from the projected phase-space to identify PNs associated with the M87 halo and ICL. The velocity distribution of the spectroscopically confirmed PNs i…
An observational evidence is presented for the alignment between the cosmic sheet and the principal axis of the velocity shear field at the position of the Virgo cluster. The galaxies in and around the Virgo cluster from the Extended Virgo Cluster Catalog recently constructed by Kim et al. are used to determine the direction of the local sheet. The peculiar velocity field reconstructed from the Sloan Digital Sky Survey Data Release 7 is analyzed to estimate the local velocity shear tensor at the Virgo center. Showing first that the minor principal axis of the local velocity shear tensor is alm…
We report the discovery of a new ultra-faint dwarf satellite companion of the Milky Way based on the early survey data from the Hyper Suprime-Cam Subaru Strategic Program. This new satellite, Virgo I, which is located in the constellation of Virgo, has been identified as a statistically significant (5.5 sigma) spatial overdensity of star-like objects with a well-defined main sequence and red giant branch in their color-magnitude diagram. The significance of this overdensity increases to 10.8 sigma when the relevant isochrone filter is adopted for the search. Based on the distribution of the st…
We report the discovery of 11 very faint (r< 23), low surface brightness (μ_r< 27 mag/arcsec^2) dwarf galaxies in one deep field in the Virgo cluster, obtained by the prime focus cameras (LBC) at the Large Binocular Telescope (LBT). These extend our previous sample to reach a total number of 27 galaxies in a field of just of 0.17 deg^2 located at a median distance of 390 kpc from the cluster center. Their association with the Virgo cluster is supported by their separate position in the central surface brightness - total magnitude plane with respect to the background galaxies of similar total m…
