We analyse the properties of the early-type dwarf galaxy population in the Hydra I cluster. We investigate the galaxy luminosity function (LF), the colour-magnitude relation (CMR), and the magnitude-surface brightness relation down to M_V~-10 mag. Another goal of this study is to find candidates for ultra-compact dwarf galaxies (UCDs). Two spectroscopic surveys performed with Magellan I/LDSS2 and VLT/VIMOS, as well as deep VLT/FORS1 images in V and I bands were examined. We identify cluster members by radial velocity measurements and select other cluster galaxy candidates by their morphology. One possible UCD candidate with M_V=-13.26 mag is found. Our sample of 100 morphologically selected dwarf galaxies defines a CMR that extends the CMR of the giant cluster galaxies to the magnitude limit of our survey (M_V~-10 mag). It matches the relations found for the Local Group and the Fornax cluster dwarfs almost perfectly. The Hydra I dwarfs also follow a magnitude-surface brightness relation similar to that of the LG dwarfs. Moreover, we observe a continuous relation for dwarf galaxies and giant early-type galaxies when plotting the central surface brightness μ_0 of a Sérsic model vs. the galaxy magnitude. The effective radius is found to be largely independent of the luminosity for M_V>-18 mag, being R_e~0.8 kpc. We derive a very flat faint-end slope of the LF (α= -1.13 \pm 0.04) from fitting a Schechter function, whereas fitting a power law for M_V>-14 mag gives α= -1.40 \pm 0.18. Our findings suggest that early-type dwarf and giant galaxies are the same class of objects. The similarity of the dwarf galaxy scaling relations to other environments implies that internal processes could be more important for their global photometric properties than external influences. (abridged)
Using SpeX at the NASA Infrared Telescope Facility and the Spitzer Infrared Spectrograph, we have obtained infrared spectra from 0.7 to 30um for three young brown dwarfs in the TW Hydra Association (~10 Myr), 2M J1207-3932, 2M J1139-3159, and SS J1102-3431. The spectral energy distribution for 2M J1139-3159 is consistent with a stellar photosphere for the entire wavelength range of our data while the other two objects exhibit significant excess emission at >5um. We are able to reproduce the excess emission from each brown dwarf using our models of irradiated accretion disks. According to our m…
NGC 3311, the giant cD galaxy in the Hydra cluster (A1060), has one of the largest globular cluster systems known. We describe new Gemini GMOS (g',i') photometry of the NGC 3311 field which reveals that the red, metal-rich side of its globular cluster population extends smoothly upward into the mass range associated with the new class of Ultra-Compact Dwarfs (UCDs). We identify 29 UCD candidates with estimated masses > 6x10^6 solar masses and discuss their characteristics. This UCD-like sequence is the most well defined one yet seen, and reinforces current ideas that the high-mass end of the g…
In this contribution, first results of deep VLT photometry (V,I) in the central region of the Hydra I galaxy cluster are presented. Many star clusters have been identified not only around several early-type galaxies, but also in the intra-cluster field, as far as 250 kpc from the cluster center. Outside the bulges of the central galaxies NGC 3311 and NGC 3309, the intra-cluster globular cluster system is dominated by blue clusters whose spatial distribution is similar to that of the (newly discovered) dwarf galaxies in Hydra I. The color distributions of globular clusters around NGC 3311 and N…
We study the galaxy population in the central region and a region about 0.6 Mpc away from the center of the Hydra I cluster in B- and Rc-bands down to M~-10 using the Subaru Suprime-Cam photometry. We find that the luminosity function of the entire population has a slightly steeper slope (alpha~-1.6) in the range of -20<M<-10 than those reported for other clusters in slightly brighter ranges. The slope appears to be steeper in poorer clusters. The number of faint galaxies (M>-14) increases in the cluster center as well as bright galaxies. The Hydra I cluster is dominated by red dwarfs and the …
We report the discovery of a population of late-M and L field dwarfs with unusual optical and near-infrared spectral features that we attribute to low gravity -- likely uncommonly young, low-mass brown dwarfs. Many of these new-found young objects have southerly declinations and distance estimates within 60 parsecs. Intriguingly, these are the same properties of recently discovered, nearby, intermediate-age (5-50 Myr), loose associations such as Tucana/Horologium, the TW Hydrae association, and the Beta Pictoris moving group. We describe our efforts to confirm cluster membership and to further…
Early-type dwarf galaxies dominate cluster populations, but their formation and evolutionary histories are poorly understood. The ALFALFA (Arecibo Legacy Fast ALFA) survey has completed observations of the Virgo Cluster in the declination range of 6 - 16 degrees. Less than 2% of the early-type dwarf population is detected, a significantly lower fraction than reported in previous papers based on more limited samples. In contrast ~30 of the irregular/BCD dwarf population is detected. The detected early-type galaxies tend to be located in the outer regions of the cluster, with a concentration in …
We have identified 7 new magnetic DA white dwarfs in the Early Data Release of the Sloan Digital Sky Survey. Our selection strategy has also recovered all the previously known magnetic white dwarfs contained in the SDSS EDR, KUV03292+0035 and HE0330-0002. Analysing the SDSS fibre spectroscopy of the magnetic DA white dwarfs with our state-of-the-art model spectra, we find dipole field strengths 1.5<=B_d<=63MG and effective temperatures 8500<=Teff<=39000K. As a conservative estimate, we expect that the complete SDSS will increase the number of known magnetic white dwarfs by a factor 3.
We report differential I-band photometry of four early L-dwarfs obtained to study variability. We detect variability on the timescale of hours in two objects, 2M0746425+200032 (at a level of 0.007 mag -- 6.5 sigma) and 2M1108307+683017 (0.012 mag -- 5 sigma). We also place upper limits of 0.02 mag (1 sigma) on the variability of two others.
We report the discovery of three cool brown dwarfs which fall in the effective temperature gap between the latest L dwarfs currently known, with no methane absorption bands in the 1-2.5um range, and the previously known methane (T) dwarfs, whose spectra are dominated by methane and water. The newly discovered objects were detected as very red objects in the Sloan Digital Sky Survey imaging data and have JHK colors between the red L dwarfs and the blue Gl229B-like T dwarfs. They show both CO and methane absorption in their near-infrared spectra in addition to water, with weaker methane absorpti…
We present I-band Surface Brightness Fluctuations (SBF) measurements for 16 early type galaxies (3 giants, 13 dwarfs) in the central region of the Hydra cluster, based on deep photometric data in 7 fields obtained with VLT FORS1. From the SBF-distances to the galaxies in our sample we estimate the distance of the Hydra cluster to be 41.2 +/- 1.4 Mpc ((m-M)=33.07 +/- 0.07 mag). Based on an improved correction for fluctuations from undetected point sources, we revise the SBF-distance to the Centaurus cluster from Mieske & Hilker (2003) upwards by 10% to 45.3 +/- 2.0 Mpc ((m-M)=33.28 +/- 0.09 mag…
Following the discovery of spiral structure in IC3328 (Jerjen et al.~2000), we present further evidence that a sizable fraction of bright early-type dwarfs in the Virgo cluster are genuine disk galaxies, or are hosting a disk component. Among a sample of 23 nucleated dwarf ellipticals and dS0s observed with the Very Large Telescope in $B$ and $R$, we found another four systems exhibiting non-axisymmetric structures, such as a bar and/or spiral arms, indicative of a disk (IC0783, IC3349, NGC4431, IC3468). Particularly remarkable are the two-armed spiral pattern in IC0783 and the bar and trailin…
We present a systematic search for disks in 476 Virgo cluster early-type dwarf (dE) galaxies. Disk features (spiral arms, edge-on disks, or bars) were identified by applying unsharp masks to a combined image from three bands (g, r, i), as well as by subtracting the axisymmetric light distribution of each galaxy from that image. 14 objects are unambiguous identifications of disks, 10 objects show 'probable disk' features, and 17 objects show 'possible disk' features. The number fraction of these galaxies, for which we introduce the term dEdi, reaches more than 50% at the bright end of the dE po…
Despite the common picture of an early-type dwarf (dE) as a quiescent galaxy with no star formation and little gas, we identify 23 dEs that have blue central colors caused by recent or ongoing star formation in our sample of 476 Virgo cluster dEs. In addition, 14 objects that were mostly classified as (candidate) BCDs have similar properties. Among the certain cluster members, the dEs with blue centers reach a fraction of more than 15% of the dE population at brighter (B<=16) magnitudes. A spectral analysis of the centers of 16 galaxies reveals in all cases an underlying old population that do…
In this contribution, we report on the discovery of dwarf spheroidals (dSphs) in the core of the Fornax cluster. Their photometric properties -- like magnitude, colour, surface brightness -- are very similar to those of Local Group dSphs. However, at a given total magnitude, dSphs in Fornax seem to be more extended than their Local Group counterparts. The membership of several dwarf galaxy candidates in Fornax has been confirmed by surface brightness fluctuation measurements on deep wide-field images taken with the Magellan telescope. The analysis of these images also confirms the flat faint 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…
We report discovery of significant depletion of Li on the surfaces of F dwarf stars in the 150-Myr-old open cluster M35, analagous to a feature in the 700-Myr-old Hyades cluster that has been referred to as the ``Li gap.'' We have caught the gap in the act of forming: using high resolution, high S/N, WIYN/Hydra observations, we detect Li in all but a few M35 F stars; the maximum depletion lies at least 0.6-0.8 dex below minimally depleted (or undepleted) stars. The M35 Li depletion region, a) is quite wide, with clear depletion seen from 6000K to 6700K or hotter; b) shows a significant dispers…
Context: Dwarf galaxies can arise from self-gravitating structures emerging from tidal tails. What fraction of the known dwarf galaxies in the Local Universe can have this origin is still a matter of debate. Aims: In our effort to understand the origin and evolution of tidal dwarf galaxies and their correspondence with local objects, the first step is to understand how these galaxies (which are supposed to have a limited amount of dark matter) react to the feedback of the ongoing star formation. Methods: We make use of 2-D chemodynamical calculations in order to study the early evolution of is…
Our aim is to study the evolution of tidal dwarf galaxies. The first step is to understand whether a model galaxy without Dark Matter can sustain the feedback of the ongoing star formation. We present tests of the evolution of models in which star formation efficiency, temperature threshold, initial distribution of gas and infall are varied. We conclude that it is feasible to keep a fraction of gas bound for several hundreds of Myr and that the development of galactic winds does not necessarily stop continuous star formation.
We present analyses of high resolution and medium resolution spectra of early L dwarfs. We used our latest set of model atmospheres to reproduce and analyze the observed features. We can model the optical flux and the atomic line profiles with the best accuracy to date. The models used to reproduce the observations include dust condensation and dust opacities. Compared to previous studies using older models we find that our dust treatment is much improved. The derived parameters for the objects are well in the expected range for old very low mass objects. This is also supported by the absence …
We have carried out surface photometry and an isophotal analysis for a sample of 25 early-type dwarf (dE and dS0) galaxies in the Virgo cluster based on CCD images taken at the VLT with FORS1 and FORS2. For each galaxy we present $B$ and $R$-band surface brightness profiles, as well as the radial colour ($B-R$) profile. We give total apparent $BR$ magnitudes, effective radii, effective surface brightnesses and total colour indices. The light profiles have been fitted with Sérsic models and the corresponding parameters are compared to the ones for other classes of objects. The observed profiles…
We have obtained new CCD photometry for a sample of $\simeq 800$ early-type galaxies (dwarf and giant ellipticals) in the central 700 arcmin$^2$ of the Coma cluster, complete in color and in magnitude to $R = 22.5$ mag ($M_R \simeq -12$ mag for $H_0 = 86$ km/sec/Mpc). The composite luminosity function for all galaxies in the cluster core (excluding NGC 4874 and NGC 4889) is modeled as the sum of a Gaussian distribution for the giant galaxies and a Schechter function for the dwarf elliptical galaxies. We determine that the early-type dwarf-to-giant ratio (EDGR) for Coma is identical to that mea…
We present the photometric and spectroscopic results of a survey done in a wide-field area of nearby groups and poor clusters. The main goals are identifying and characterizing the properties of low-surface-brightness dwarf galaxies and determining the galaxy luminosity function for Mv>-13. We surveyed areas (typically 0.1--1.0 square degrees) of the groups NGC 6868 (Telescopium), NGC 5846, HCG 42, Hydra I, Dorado and the poor clusters IC 4765 in V and I. In this work we present the results and the analysis of the photometry and spectroscopy done in four groups: HCG 42, NGC 6868, NGC 5846 and …
The pulsar B1620-26 has two companions, one of stellar mass and one of planetary mass. We detected the stellar companion using Hubble Space Telescope observations. The color and magnitude of the stellar companion indicate that it is an undermassive white dwarf ($0.34 \pm 0.04 M_{\odot}$) of age $480\pm 140$ Myr. This places a constraint on the recent history of this triple system and supports a scenario in which the current configuration arose through a dynamical exchange interaction in the cluster core. This implies that planets may be relatively common in low-metallicity globular clusters an…
Parkes neutral hydrogen 21 cm line (HI) observations of the surroundings of 9 early-type Local Group dwarfs are presented. We detected numerous HI clouds in the general direction of those dwarfs and these clouds are often offset from the optical center of the galaxies. Although all the observed dwarfs, except Antlia, occupy phase-space regions where the High-Velocity Cloud (HVC) density is well above average, the measured offsets are smaller than one would expect from a fully random cloud distribution. Possible association is detected for 11 of the 16 investigated clouds, while, for two galaxi…
Using a large sample of optical spectra of late-type dwarfs, we identify a subset of late-M through L field dwarfs that, because of the presence of low-gravity features in their spectra, are believed to be unusually young. From a combined sample of 303 field L dwarfs, we find observationally that 7.6+/-1.6% are younger than 100 Myr. This percentage is in agreement with theoretical predictions once observing biases are taken into account. We find that these young L dwarfs tend to fall in the southern hemisphere (Dec < 0 deg) and may be previously unrecognized, low-mass members of nearby, young …
We study the locus of dwarf and giant early and late-type galaxies on the Tully-Fisher relation (TFR), the stellar mass Tully-Fisher relation (sTFR) and the so-called baryonic or HI gas+stellar mass Tully-Fisher relation (gsTFR). We show that early-type and late-type galaxies, from dwarfs to giants, trace different yet approximately parallel TFRs. Surprisingly, early-type and late-type galaxies trace a single yet curved sTFR over a range of 3.5 orders of magnitude in stellar mass. Moreover, all galaxies trace a single, linear gsTFR, over 3.5 orders of magnitude in HI gas+stellar mass. Dwarf el…
In this contribution, first results of deep VLT photometry (V,I) in the central region of the Hydra I and Centaurus galaxy clusters are presented. In both galaxy clusters, many star clusters have been identified down to the turnover magnitude of the globular cluster luminosity function at V=26.0 mag. They are distributed not only around the several early-type galaxies, but also in the intra-cluster field, as far as 250 kpc from the cluster centers. Outside the bulges of the central galaxies in Hydra I and Centaurus, the intra-cluster globular cluster system is dominated by blue clusters whose …
We present here additional results of a spectropolarimetric survey of a small sample of stars ranging from spectral type M0 to M8 aimed at investigating observationally how dynamo processes operate in stars on both sides of the full convection threshold (spectral type M4). The present paper focuses on early M stars (M0--M3), i.e. above the full convection threshold. Applying tomographic imaging techniques to time series of rotationally modulated circularly polarised profiles collected with the NARVAL spectropolarimeter, we determine the rotation period and reconstruct the large-scale magnetic …
We present our results of deep 21 cm line (HI) observations of five early and mixed-type dwarf galaxies in the nearby Sculptor group using the ATNF 64m Parkes Radio Telescope. Four of these objects, ESO294-G010, ESO410-G005, ESO540-G030, and ESO540-G032, were detected in HI with neutral hydrogen masses in the range of 2-9x10^5 M_{\odot} ($M_{HI}/L_{B}$ = 0.08, 0.13, 0.16, and 0.18, respectively). These HI masses are consistent with the gas mass expected from stellar outflows over a large period of time. Higher resolution radio data from the Australia Telescope Compact Array were further analys…
In this Paper we investigate the kinematical properties of early-type dwarfs by significantly enlarging the scarce observational sample so far available. We present rotation curves and mean velocity dispersions for four bright dwarf ellipticals and two dwarf lenticular galaxies in the Virgo cluster. Most of these galaxies exhibit conspicuous rotation curves. In particular, five out of the six new galaxies are found to be close to the predictions for oblate spheroids flattened by rotation. Therefore, and contrary to the previous observational hints, the present data suggest that an important fr…
