The origin of the mu_e - M_B and Kormendy relations in dwarf elliptical galaxies

The present work is aimed at studying the distribution of galaxies of different types and luminosities along different structural scaling relations to see whether massive and dwarf ellipticals have been shaped by the same formation process. This exercise is here done by comparing the distribution of Virgo cluster massive and dwarf ellipticals and star forming galaxies along the B band effective surface brightness and effective radius vs. absolute magnitude relations and the Kormendy relation to the predictions of models tracing the effects of ram-pressure stripping on disc galaxies entering the cluster environment and galaxy harassment. Dwarf ellipticals might have been formed from low luminosity, late-type spirals that recently entered into the cluster and lost their gas because of a ram-pressure stripping event, stopping their activity of star formation. The perturbations induced by the abrupt decrease of the star formation activity are sufficient to modify the structural properties of disc galaxies into those of dwarf ellipticals. Galaxy harassment induce a truncation of the disc and generally an increase of the effective surface brightness of the perturbed galaxies. The lack of dynamical simulations of perturbed galaxies spanning a wide range in luminosity prevents us to drive any firm conclusion on a possible harassment-induced origin of the low surface brightness dwarf elliptical galaxy population inhabiting the Virgo cluster. Although the observed scaling relations are consistent with the idea that the distribution of elliptical galaxies along the mentioned scaling relation is just due to a gradual variation with luminosity of the Sersic index n, the comparison with models indicates that dwarf ellipticals might have been formed by a totally different process than giant ellipticalsComment: Accepted for publication on A&

Virgo cluster early-type dwarf galaxies with the Sloan Digital Sky Survey. IV. The color-magnitude relation

We present an analysis of the optical colors of 413 Virgo cluster early-type dwarf galaxies (dEs), based on Sloan Digital Sky Survey imaging data. Our study comprises (1) a comparison of the color-magnitude relation (CMR) of the different dE subclasses that we identified in Paper III of this series, (2) a comparison of the shape of the CMR in low and high-density regions, (3) an analysis of the scatter of the CMR, and (4) an interpretation of the observed colors with ages and metallicities from population synthesis models. We find that the CMRs of nucleated (dE(N)) and non-nucleated dEs (dE(nN)) are significantly different from each other, with similar colors at fainter magnitudes (r > 17 mag), but increasingly redder colors of the dE(N)s at brighter magnitudes. We interpret this with older ages and/or higher metallicities of the brighter dE(N)s. The dEs with disk features have similar colors as the dE(N)s and seem to be only slightly younger and/or less metal-rich on average. Furthermore, we find a small but significant dependence of the CMR on local projected galaxy number density, consistently seen in all of u-r, g-r, and g-i, and weakly i-z. We deduce that a significant intrinsic color scatter of the CMR is present, even when allowing for a distance spread of our galaxies. No increase of the CMR scatter at fainter magnitudes is observed down to r = 17 mag (Mr = -14 mag). The color residuals, i.e., the offsets of the data points from the linear fit to the CMR, are clearly correlated with each other in all colors for the dE(N)s and for the full dE sample. We conclude that there must be at least two different formation channels for early-type dwarfs in order to explain the heterogeneity of this class of galaxy. (Abridged)Comment: 17 pages + 12 figures. Accepted for publication in A

The young stellar population at the center of NGC 205

Context. NGC 205 is a peculiar dwarf elliptical galaxy hosting in its center a population of young blue stars. Their origin is still matter of debate, the central fresh star formation activity possibly being related to dynamical interactions between NGC 205 and M31. Aims. The star formation history in the central 30\arcsec ($\sim$120 pc) around the NGC 205 central nucleus is investigated in order to obtain clues to the origin of the young stellar population. Methods. Deep HST/ACS CCD photometry is compared with theoretical isochrones and luminosity functions to characterize the stellar content of the region under study and compute the recent SF rate. Results. Our photometry reveals a previously undetected blue plume of young stars clearly distinguishable down to I$\simeq$26. Our analysis suggests that 1.9$\times10^5$ M$_\odot$ were produced between approximately 62 Myr and 335 Myr ago in the NGC 205 inner regions, with a latest minor episode occurring $\sim$25 Myr ago. This implies a star formation rate of $\sim7\times10^{-4}$ M$_\odot$/yr over this period. Conclusions. The excellent fit of the observed luminosity function of young main sequence stars obtained with a model having a constant star formation rate argues against a tidally triggered star formation activity over the last $\sim$300 Myr. Rather, a constant SF may be consistent with NGC 205 being on its first interaction with M 31.Comment: 5 pages, 2 figures, accepted for publication in A&A letter

Auditory Enhancement and Second Language Experience in Spanish and English Weighting of Secondary Voicing Cues

The role of secondary cues in voicing categorization was investigated in three listener groups: Monolingual English (n=20) and Spanish speakers (n=20), and Spanish speakers with significant English experience (n=16). Results showed that, in all three groups, participants used onset f0 in making voicing decisions only in the positive voice onset time (VOT) range (short lag and long lag tokens), while there was no effect of onset f0 on voicing categorization within the negative VOT range (voicing lead tokens) for any of the participant groups. These results support an auditory enhancement view of perceptual cue weighting: Onset f0 serves as a secondary cue to voicing only in the positive VOT range where it is not overshadowed by the presence of pre-voicing. Moreover, results showed that Spanish learners of English gave a significantly greater weight to onset f0 in their voicing decisions than did listeners in either of the other two groups. This result supports the view that learners may overweight secondary cues to distinguish between non-native categories that are assimilated to the same native category on the basis of a primary cue

The ESO supernovae type Ia progenitor survey (SPY) : The radial velocities of 644 DA white dwarfs

Accepted for publication in A&A. 59 pages.Close double degenerate binaries are one of the favoured progenitor channels for type Ia supernovae, but it is unclear how many suitable systems there are in the Galaxy. We report results of a large radial velocity survey for double degenerate (DD) binaries using the UVES spectrograph at the ESO VLT (ESO SN Ia Progenitor surveY - SPY). Exposures taken at different epochs are checked for radial velocity shifts indicating close binary systems. We observed 689 targets classified as DA (displaying hydrogen-rich atmospheres), of which 46 turned out to possess a cool companion. We measured radial velocities (RV) of the remaining 643 DA white dwarfs. We managed to secure observations at two or more epochs for 625 targets, supplemented by eleven objects meeting our selection criteria from literature. The data reduction and analysis methods applied to the survey data are described in detail. The sample contains 39 double degenerate binaries, only four of which were previously known. 20 are double-lined systems, in which features from both components are visible, the other 19 are single-lined binaries. We provide absolute RVs transformed to the heliocentric system suitable for kinematic studies. Our sample is large enough to sub-divide by mass: 16 out of 44 low mass targets (0.45 Msun are double. Although the detected fraction amongst the low mass objects (36.4 +/- 7.3%) is significantly higher than for the higher-mass, carbon/oxygen-core dominated part of the sample (3.9 +/- 0.8%), it is lower than the detection efficiency based upon companion star masses >= 0.05 Msun. This suggests either companion stars of mass <0.05 Msun, or that some of the low mass white dwarfs are single.Peer reviewe

The Fornax Deep Survey with VST. I. The extended and diffuse stellar halo of NGC~1399 out to 192 kpc

[Abrigded] We have started a new deep, multi-imaging survey of the Fornax cluster, dubbed Fornax Deep Survey (FDS), at the VLT Survey Telescope. In this paper we present the deep photometry inside two square degrees around the bright galaxy NGC1399 in the core of the cluster. We found a very extended and diffuse envelope surrounding the luminous galaxy NGC1399: we map the surface brightness out to 33 arcmin (~ 192 kpc) from the galaxy center and down to about 31 mag/arcsec^2 in the g band. The deep photometry allows us to detect a faint stellar bridge in the intracluster region between NGC1399 and NGC1387. By analyzing the integrated colors of this feature, we argue that it could be due to the ongoing interaction between the two galaxies, where the outer envelope of NGC1387 on its east side is stripped away. By fitting the light profile, we found that it exists a physical break radius in the total light distribution at R=10 arcmin (~58 kpc) that sets the transition region between the bright central galaxy and the outer exponential stellar halo. We discuss the main implications of this work on the build-up of the stellar halo at the center of the Fornax cluster. By comparing with the numerical simulations of the stellar halo formation for the most massive BCGs, we find that the observed stellar halo mass fraction is consistent with a halo formed through the multiple accretion of progenitors with a stellar mass in the range 10^8 - 10^11 M_sun. This might suggest that the halo of NGC1399 has also gone through a major merging event. The absence of a significant number of luminous stellar streams and tidal tails out to 192 kpc suggests that the epoch of this strong interaction goes back to an early formation epoch. Therefore, differently from the Virgo cluster, the extended stellar halo around NGC1399 is characterised by a more diffuse and well-mixed component, including the ICL.Comment: Accepted for publication in ApJ; 25 pages and 14 figures. An higher resolution file is available at the following link https://www.dropbox.com/s/fvltppduysdn6pb/NGC1399_fin_2c.pdf?dl=

The Sensitivity of Harassment to Orbit: Mass Loss from Early-Type Dwarfs in Galaxy Clusters

We conduct a comprehensive numerical study of the orbital dependence of harassment on early-type dwarfs consisting of 168 different orbits within a realistic, Virgo-like cluster, varying in eccentricity and pericentre distance. We find harassment is only effective at stripping stars or truncating their stellar disks for orbits that enter deep into the cluster core. Comparing to the orbital distribution in cosmological simulations, we find that the majority of the orbits (more than three quarters) result in no stellar mass loss. We also study the effects on the radial profiles of the globular cluster systems of early-type dwarfs. We find these are significantly altered only if harassment is very strong. This suggests that perhaps most early-type dwarfs in clusters such as Virgo have not suffered any tidal stripping of stars or globular clusters due to harassment, as these components are safely embedded deep within their dark matter halo. We demonstrate that this result is actually consistent with an earlier study of harassment of dwarf galaxies, despite the apparent contradiction. Those few dwarf models that do suffer stellar stripping are found out to the virial radius of the cluster at redshift=0, which mixes them in with less strongly harassed galaxies. However when placed on phase-space diagrams, strongly harassed galaxies are found offset to lower velocities compared to weakly harassed galaxies. This remains true in a cosmological simulation, even when halos have a wide range of masses and concentrations. Thus phase-space diagrams may be a useful tool for determining the relative likelihood that galaxies have been strongly or weakly harassed.Comment: 17 pages, 13 figures, Accepted to MNRAS 8th September 201

Properties of the Dwarf Galaxy Population in Galaxy Clusters

We present the observational properties of the dwarf galaxy population (Mr > M*+1) corresponding to one of the largest samples of spectroscopically confirmed galaxy cluster members reported in the literature. We have observed that red dwarf galaxies (u-r > 2.22) share the same cluster environment as the brightest cluster members (Mr < -21), but are not in dynamical equilibrium. We computed the dwarf-to-giant ratio (DGR) using a spectroscopically selected sample. The DGR was found to vary with clustercentric distance, essentially due to the blue dwarf population (u-r < 2.22). The u-r color of red dwarf galaxies was independent of their environment and similar to the color of red isolated dwarfs. Blue dwarf galaxies located outside r200 show similar u-r colors to those of the field population, while strong reddening was observed toward the cluster center. We also present evidence that the fraction of red to blue dwarf galaxies in clusters is larger in the innermost cluster regions. We conclude that the present red dwarf population observed in the central regions of nearby galaxy clusters could be related to the blue dwarf population observed in clusters at high redshift.Comment: 5 pages, 3 color figures, accepted for publication in the ApJ Letter

The sensitivity of harassment to orbit: Mass loss from early-type dwarfs in galaxy clusters

We conduct a comprehensive numerical study of the orbital dependence of harassment on early-type dwarfs consisting of 168 different orbits within a realistic, Virgo-like cluster, varying in eccentricity and pericentre distance. We find harassment is only effective at stripping stars or truncating their stellar discs for orbits that enter deep into the cluster core. Comparing to the orbital distribution in cosmological simulations, we find that the majority of the orbits (more than three quarters) result in no stellar mass loss. We also study the effects on the radial profiles of the globular cluster systems of early-type dwarfs. We find these are significantly altered only if harassment is very strong. This suggests that perhaps most early-type dwarfs in clusters such as Virgo have not suffered any tidal stripping of stars or globular clusters due to harassment, as these components are safely embedded deep within their dark matter halo. We demonstrate that this result is actually consistent with an earlier study of harassment of dwarf galaxies, despite the apparent contradiction. Those few dwarf models that do suffer stellar stripping are found out to the virial radius of the cluster at redshift = 0, which mixes them in with less strongly harassed galaxies. However when placed on phase-space diagrams, strongly harassed galaxies are found offset to lower velocities compared to weakly harassed galaxies. This remains true in a cosmological simulation, even when haloes have a wide range of masses and concentrations. Thus phase-space diagrams may be a useful tool for determining the relative likelihood that galaxies have been strongly or weakly harassed

The Fornax Deep Survey with VST. II. Fornax A: a two-phase assembly caught on act

As part of the Fornax Deep Survey with the ESO VLT Survey Telescope, we present new $g$ and $r$ bands mosaics of the SW group of the Fornax cluster. It covers an area of $3 \times 2$ square degrees around the central galaxy NGC1316. The deep photometry, the high spatial resolution of OmegaCam and the large covered area allow us to study the galaxy structure, to trace stellar halo formation and look at the galaxy environment. We map the surface brightness profile out to 33arcmin ($\sim 200$kpc $\sim15R_e$) from the galaxy centre, down to $\mu_g \sim 31$ mag arcsec$^{-2}$ and $\mu_r \sim 29$ mag arcsec$^{-2}$. This allow us to estimate the scales of the main components dominating the light distribution, which are the central spheroid, inside 5.5 arcmin ($\sim33$ kpc), and the outer stellar envelope. Data analysis suggests that we are catching in act the second phase of the mass assembly in this galaxy, since the accretion of smaller satellites is going on in both components. The outer envelope of NGC1316 still hosts the remnants of the accreted satellite galaxies that are forming the stellar halo. We discuss the possible formation scenarios for NGC1316, by comparing the observed properties (morphology, colors, gas content, kinematics and dynamics) with predictions from cosmological simulations of galaxy formation. We find that {\it i)} the central spheroid could result from at least one merging event, it could be a pre-existing early-type disk galaxy with a lower mass companion, and {\it ii)} the stellar envelope comes from the gradual accretion of small satellites.Comment: Accepeted for publication in Ap