We have used the ACS camera on HST to obtain (V,I) photometry for 57,000 red-giant stars in the halo of the Leo elliptical NGC 3377. We use this sample of stars to derive the metallicity distribution function (MDF) for its halo field stars, and comment on its chemical evolution history compared with both larger and smaller E galaxies. Our ACS/WFC field spans a radial range extending from 4 to 18 kpc projected distance from the center of NGC 3377 and thus covers a significant portion of this galaxy's halo. We find that the MDF is broad, reaching a peak at [m/H] ~ -0.6$, but containing virtually no stars more metal-poor than log [m/H] = -1.5$. It may, in addition, have relatively few stars more metal-rich than [m/H] = -0.3$, although interpretation of the high-metallicity end of the MDF is limited by photometric completeness that affects the detection of the reddest, most metal-rich stars. NGC 3377 appears to have an enrichment history intermediate between those of normal dwarf ellipticals and the much larger giants. As yet, we find no clear evidence that the halo of NGC 3377 contains a significant population of ``young'' (< 3 Gy) stars.
We have used archive HST WFPC2 data for three elliptical galaxies (NGC 3379 in the Leo I group, and NGC 4472 and NGC 4406 in the Virgo cluster) to determine their distances using the Surface Brightness Fluctuation (SBF) method as described by Tonry and Schneider (1988). A comparison of the HST results with the SBF distance moduli of Ciardullo et al (1993) shows significant disagreement and suggests that the r.m.s. error on these ground-based distance moduli is actually as large as +-0.25 mag. The agreement is only slightly improved when we compare our results with the HST and ground-based SBF …
We present deep HST F555W (V) and F814W (I) observations of a central field in the Local Group dwarf spheroidal (dSph) galaxy Leo I. The resulting color-magnitude diagram (CMD) reaches I \simeq 26 and reveals the oldest ~10-15 Gyr old turnoffs. Nevertheless, a horizontal branch is not obvious in the CMD. Given the low metallicity of the galaxy, this likely indicates that the first substantial star formation in the galaxy may have been somehow delayed in Leo I in comparison with the other dSph satellites of the Milky Way. The subgiant region is well and uniformly populated from the oldest turno…
New observations of galaxies in the direction of the Leo group, which were classified as being candidates for M32-like dwarf galaxies by Ferguson & Sandage (1990), show that these galaxies are normal elliptical galaxies at redshifts between z=0.02 and z=0.06. This result adds further evidence that the faint end of the luminosity function of elliptical galaxies falls off very steep and that objects like M32 are extremely rare.
We have used the ACS camera on HST to obtain (V,I) photometry for 5300 red-giant stars in the halo of the dominant Leo-group member NGC 3379, a galaxy usually regarded as a classic normal giant elliptical. We use this sample of stars to derive the metallicity distribution function (MDF) for its outer-halo field stars 33 kpc from the galaxy center. The MDF is distinctly unlike all the other E galaxies for which we have similar data (including the Local Group dwarf ellipticals, the intermediate-luminosity NGC 3377, and the giant NGC 5128). First, the MDF for the NGC 3379 outer halo is broad and …
New ground-based and HST observations of distant clusters make it possible to trace the history of E/S0 galaxies to lookback times of ~10 $h_{50}^{-1}$ Gyr. The data strongly favor a scenario in which cluster ellipticals formed very early with a narrow spread in ages. By z = 1.2 there are changes in color and luminosity consistent with simple passive evolution, but even at that redshift the galaxies appear mature, with red colors suggesting ages of several Gyr. Apparently we are still falling well short of seeing the true epoch of formation.
The combined use of the ESO Very Large Telescope (VLT) UT1 Science Verification (SV) images and of the Hubble Space Telescope (HST) Hubble Deep Field South observations allows us to strengthen the identification as a candidate elliptical galaxy of the Extremely Red Object HDFS 223251-603910 previously identified by us on the basis of NICMOS and Cerro Tololo Interamerican Observatory imaging. The photometry presented here includes VLT data in U, B, V, R, I, a STIS unfiltered image, NICMOS J, H, and K band data, thus combining the 16.5 hours of VLT SV exposures with 101 hours of HST observing. T…
We have obtained HST_NICMOS images for 72 nearby spiral galaxy bulges in the H-band. These data show that galaxies with regular bulges have steeper nuclear cusps than galaxies with irregular bulges. We also show that galaxies with regular bulges fall on the same part of the (<γ>, magnitude)-diagram as elliptical galaxies. This implies that early-type spiral galaxy bulges have a formation process in common with ellipticals.
The HST NICMOS Camera 2 was used for H-band imaging of 12 BL Lacertae objects taken from the larger sample observed with the WFPC2 in the R band (Urry et al. 2000; Scarpa et al. 2000). Ten of the 12 BL Lacs are clearly resolved, and the detected host galaxies are large, bright ellipticals with average H-band absolute magnitude M=-26.2+-0.45 mag and effective radius 10+-5 kpc. The rest-frame integrated color of the host galaxies is on average R-H=2.3+-0.3, consistent with the value for both radio galaxies and normal, non-active elliptical galaxies, and indicating the dominant stellar population…
Due to their star formation history (SFH), the stellar population in Dwarf Galaxies (DG) is likely to have a metallicity spread which is best traced by the morphology of the Red Giant Branch (RGB). We probe here a purely empirical approach aimed at estimating average metallicity (Z) and Z spread by comparing the Color-Magnitude Diagrams (CMD) of galactic Globular Clusters (GCs) with those of two DGs: Leo A (HST data) and Phoe (VLT Fors2 data).
We have obtained Gemini/GMOS spectra for 22 GCs associated with NGC 3379. We derive ages, metallicities and alpha-element abundance ratios from simple stellar population models using the multi-index chi^2 minimisation method of Proctor & Sansom (2002). All of these GCs are found to be consistent with old ages, i.e. >10 Gyr, with a wide range of metallicities. A trend of decreasing alpha-element abundance ratio with increasing metallicity is indicated. The projected velocity dispersion of the GC system is consistent with being constant with radius. Non-parametric, isotropic models require a sig…
We have analyzed archival HST F606W images of 18 dwarf elliptical (dE) galaxy candidates in the Coma Cluster. We model the full radial extent of their light-profiles by simultaneously fitting a PSF-convolved Sersic R^(1/n) model and, when necessary, either a central point-source or a central PSF-convolved Gaussian. The luminosities of the central component L_nuc scale with the host galaxy luminosity L_gal such that L_nuc = 10^(4.76 +/- 0.10)*(L_gal/10^7)^(0.87 +/- 0.26). The underlying host galaxies display systematic departures from an exponential model that are correlated with the model-inde…
Using data from the HST Medium Deep Survey, a long-term Key Project, together with generically similar archived data, we have discovered evidence for weak gravitational `shear' of background field galaxies (I = 22 -- 26) in the vicinity of isolated, foreground galaxies ( I = 15 -- 22), especially those of early type. The statistical lensing is demonstrated by the slight preferential orientation of the major axes of the background galaxies in directions at right angles to the lines joining them to the foreground ones. The detected shear is at the level of $δϕ= 2.5^{o}\pm 1.2^{o}$ averaged over …
We have used the Keck I Telescope to measure K-band surface brightness fluctuations (SBFs) of NGC 4874, the dominant elliptical galaxy in the Coma cluster. We use deep HST WFPC2 optical imaging to account for the contamination due to faint globular clusters and improved analysis techniques to derive measurements of the SBF apparent magnitude. Using a new SBF calibration which accounts for the dependence of K-band SBFs on the integrated color of the stellar population, we measure a distance modulus of 34.99+/-0.21 mag (100+/-10 Mpc) for the Coma cluster. The resulting value of the Hubble consta…
The luminosity functions of E/S0 galaxies are constructed in 3 different redshift bins (0.2 < z < 0.55, 0.55 < z < 0.8, 0.8 < z < 1.2), using the data from the Hubble Space Telescope Medium Deep Survey (HST MDS) and other HST surveys. These independent luminosity functions show the brightening in the luminosity of E/S0s by about 0.5~1.0 magnitude at z~1, and no sign of significant number evolution. This is the first direct measurement of the luminosity evolution of E/S0 galaxies, and our results support the hypothesis of a high redshift of formation (z > 1) for elliptical galaxies, together wi…
The complex phenomenology shown by the UV-bright, variable spike first detected with the Hubble Space Telescope (HST) at the center of the otherwise normal galaxy NGC 4552 is further investigated with both HST imaging (FOC) and spectroscopy (FOS). HST/FOC images taken in 1991, 1993, and 1996 in the near UV have been analyzed in a homogeneous fashion, showing that the central spike has brightened by a factor ~4.5 between 1991 and 1993, and has decreased its luminosity by a factor ~2.0 between 1993 and 1996. FOS spectroscopy extending from the near UV to the red side of the optical spectrum reve…
[annotated] HST WFPC2 images were taken of three LSB dwarf elliptical galaxies in the Virgo cluster. The intent of the observations was to determine the small scale structure in these enigmatic galaxies, and to attempt to learn something about the nature of their giant branch through the detection of luminosity fluctuations. In two of the three studied galaxies, V7L3 and V1L4, the luminosity fluctuations were unambiguously detected, yielding a density of 2 - 10 red giants/pixel. Using the observed B-V and V-I colors as a constraint, we could find no model that would reproduce the observed fluc…
A sample of field early-type galaxies (E/S0) at intermediate redshift ($z\sim0.1-0.6$) is selected, based on morphology and colours from HST-WFPC2 parallel images. Photometric structural parameters (effective radius $R_{\tx{e}}$ and effective surface brightness $SB_{\tx{e}}$) are derived through the F606W and F814W filters, using luminosity profile fitting and two-dimensional fitting techniques. The combined parameter that enters the Fundamental Plane ($\log R_{\tx{e}}-βSB_{\tx{e}}$, with $β\approx0.32$) is shown to suffer from significantly smaller uncertainties (r.m.s. 0.03) than the individ…
We report the serendipitous discovery of ``Einstein cross'' gravitational lens candidates using the Hubble Space Telescope. We have so far discovered two good examples of such lenses, each in the form of four faint blue images located in a symmetric configuration around a red elliptical galaxy. The high resolution of HST has facilitated the discovery of this optically selected sample of faint lenses with small (~1 arcsec) separations between the (I ~ 25-27) lensed components and the much brighter (I ~ 19-22) lensing galaxies. The sample has been discovered in the routine processing of HST fiel…
The ``MORPHS'' group has completed the cataloging, parameterization, and morphological classification of ~2000 galaxies in 10 rich clusters from 0.36 < z < 0.56. From a weak lensing analysis using these data, which compares the X-ray properties (L_X) of the clusters with virial temperature estimates (T_v) from the lensing shear strength, we find little evidence for evolution in the L_X-T_v relation from that observed for local clusters. We discuss how this observation constrains models for the X-ray evolution of clusters. The data have also been used to study the color dispersion of bona-fide …
We have witnessed a dramatic increase over the last five years in results on distant galaxies, in large part because of the high resolution imaging capability of HST, and the multiobject spectroscopic capability of the Keck telescopes. Our program to obtain wide-field, multi-color WFPC2 mosaics with HST of intermediate redshift clusters, and spectroscopic membership and high S/N spectroscopy with LRIS on Keck, has provided new insights into the nature of elliptical and S0 galaxies in the cluster environment over a wide range of densities. In particular, most ellipticals, and a significant frac…
Keck/ESI spectroscopy is presented for six Virgo Cluster dwarf elliptical (dE) galaxies. The mean line-of-sight velocity and velocity dispersion are resolved as a function of radius along the major axis of each galaxy, nearly doubling the total number of dEs with spatially-resolved stellar kinematics. None of the observed objects shows evidence of strong rotation: upper limits on v_rot/sigma are well below those expected for rotationally-flattened objects. Such limits place strong constraints on dE galaxy formation models. Although these galaxies continue the trend of low rotation velocities o…
We present an analysis of the globular cluster systems of 28 elliptical galaxies using archival WFPC2 images in the V and I-bands. The V-I color distributions of at least 50% of the galaxies appear to be bimodal {\it at the present level of photometric accuracy}. We argue that this is indicative of multiple epochs of cluster formation early in the history of these galaxies, possibly due to mergers. We also present the first evidence of bimodality in low luminosity galaxies and discuss its implication on formation scenarios. The mean color of the 28 cluster systems studied by us is V-I = 1.04$\…
We have measured the absolute proper motion of the Fornax dwarf spheroidal galaxy from a combination of photographic plate material and HST WFPC2 data that provide a time baseline of up to 50 years. The extragalactic reference frame consists of 8 QSO images and 48 galaxies. The absolute proper motion is mu_alpha cos(delta) = 0.59 +-0.16 mas/yr and mu_delta = -0.15 +- 0.16 mas/yr. The corresponding orbit of Fornax is polar, with an eccentricity of 0.27, and a radial period of 4.5 Gyr. Fornax's current location is near pericenter. The direction of the motion of Fornax supports the notion that Fo…
Newly obtained HST/WFPC2 images of the disturbed elliptical galaxy NGC 5018 show that the average amount of internal reddening due to the its complex ``dust web'' is as low as E(B-V)~0.02 within the IUE aperture, thus implying that its observed and intrinsic energy distributions do not differ significantly down to UV wavelengths. This, in turn, is quite relevant to the current debate on the age of its dominant stellar population.
(abridged) We present kinematic results for a sample of 387 stars located near Leo I based on spectra obtained with the MMT's Hectochelle spectrograph near the MgI/Mgb lines. We estimate the mean velocity error of our sample to be 2.4 km/s, with a systematic error of < 1 km/s. We produce a final sample of 328 Leo I red giant members, from which we measure a mean heliocentric radial velocity of 282.9 +/- 0.5 km/s, and a mean radial velocity dispersion of 9.2 +/- 0.4 km/s for Leo I. The dispersion profile of Leo I is flat out to beyond its classical `tidal' radius. We fit the profile to a variet…
We report the first results from an imaging program with the ACS camera on HST designed to measure the structural characteristics of a wide range of globular clusters in NGC 5128, the nearest giant elliptical galaxy. From 12 ACS/WFC fields, we have measured a total of 62 previously known globular clusters and have discovered 69 new high-probability cluster candidates not found in any previous work. We present magnitudes and color indices for all of these, along with rough measurements of their effective diameters and ellipticities. The luminosity distribution of this nearly-uncontaminated samp…
Recent observations of globular clusters (GCs) in intermediate-age (2-4 Gyr old), early-type merger remnants have provided the hitherto `missing link' between young merger remnants and `normal' elliptical galaxies in the form of a GC subsystem with colors and luminosities consistent with population synthesis model predictions for those ages and ~solar metallicity. Here we present new, deep observations of the GC system of the intermediate-age merger remnant NGC 1316, using the ACS camera aboard Hubble Space Telescope, which allowed us to create luminosity functions (LFs) as a function of galac…
We report on the optical properties of a sample of 30 BL Lac host galaxies in the redshift range $0.03<z<0.2$, as derived from HST observations. All galaxies are fully resolved in the WFPC2 (F702W filter) images, allowing a quantitative analysis in two dimensions. Most and possibly all these galaxies have characteristics very similar to those of ``normal'' giant ellipticals. The luminosity, ellipticity, isophote twisting and amount of disky or boxy isophotes are consistent with those found in non-active ellipticals and in radio galaxies. In all cases the BL Lac nucleus is well centered in the …
We have non-parametrically determined the luminosity density profiles and their logarithmic slopes for 42 early-type galaxies observed with HST. Assuming that the isodensity contours are spheroidal, then the luminosity density is uniquely determined from the surface brightness data through the Abel equation. For nearly all the galaxies in our sample, the logarithmic slope of the luminosity density measured at 0.1" (the innermost reliable measurement with the uncorrected HST) is significantly different from zero; i.e. most elliptical galaxies have cusps. There are only two galaxies for which an…
We present preliminary results of an HST/NICMOS program to image merger remnants in the J, H and K bands. The nuclear brightness profiles for most sample galaxies are similar to those typical for elliptical galaxies, but some (including the well-studied NGC 3921 and 7252) have an unusually high luminosity density at small radii. This is consistent with the prediction of N-body simulations that gas flows to the center during a merger and forms new stars.
We report the discovery of a strongly lensed arc system around a field elliptical galaxy in Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) images of a parallel field observed during NICMOS observations of the HST Ultra-Deep Field. The ACS parallel data comprise deep imaging in the F435W, F606W, F775W, and F850LP bandpasses. The main arc is at a radius of 1.6 arcsec from the galaxy center and subtends about 120 deg. Spectroscopic follow-up at Magellan Observatory yields a redshift z=0.6174 for the lensing galaxy, and we photometrically estimate z_phot = 2.4\pm0.3 for the arc. We…
We present a study of the evolved stellar populations in the dwarf spheroidal galaxy LeoII, based on JHKs observations obtained with the near-infrared array WFCAM at the UKIRT telescope. Combining the new data with optical data, we derived photometric estimates of the distribution of global metallicity [M/H] of individual red giant stars from their V-Ks colours. We used the new data to derive the properties of a nearly complete sample of asymptotic giant branch (AGB) stars in LeoII. Using a near-infrared two-colour diagram, we were able to obtain a clean separation from Milky Way foreground st…
We have obtained high resolution UV images with the HST+WFPC2 of the central region of the dwarf elliptical galaxy NGC 205. Our images reveal that many of the hot UV stars previously detected and studied from the ground are actually multiple systems, open clusters and star associations. We have performed photometry of two such clusters and we find our data are consistent with stellar ages of 50 and 100 Myr, respectively. From the number of massive stars in NGC 205 we estimate that the star formation episode in this galaxy has turned ~1,000 Msolar of gas into stars over the last 100 Myr.
Relatively few intensively star-forming galaxies at redshifts z>2.5 have been found in the Hubble Deep Field (HDF). This has been interpreted to imply a low space density of elliptical galaxies at high z, possibly due to a late (z<2.5) epoch of formation, or to dust obscuration of the ellipticals that are forming at z~3. I use HST UV (2300 Ang) images of 25 local early-type galaxies to investigate a third option, that ellipticals formed at z>4.5, and were fading passively by 2<z<4.5. Present-day early-types are faint and centrally concentrated in the UV. If ellipticals formed their stars in a …
We present optical and near-infrared colour maps of the central regions of bulges of S0 and spiral galaxies obtained with WFPC2 and NICMOS on the HST. By combined use of HST and ground-based data the colour information spans from a few tens of pc to a few kpc. In almost all galaxies the colour profiles in the central 100-200 pc become more rapidly redder. We attribute the high central colour indices to a central concentration of dust. We infer an average extinction at the center of A_V = 0.6 - 1.0 mag. Several objects show central dust rings or disks at sub-kpc scales similar to those found by…
SHARC II, 350-micron continuum and archival HST J-H band maps are presented of NGC 3656, the brightest of our sample of six elliptical galaxies for which resolved CO gas disks have recently been detected with 7''-spatial-resolution, interferometry mapping. These gas disks confirm the conclusions of earlier results showing optical dust lanes and unresolved CO that implied the common existence of molecular gas in ellipticals and the disk-like structure of this gas. The presented SHARC II mapping results provide the best to date resolved FIR-submm extent of NGC 3656 and of any elliptical galaxy >…
We report the discovery of (stellar) spiral-like structure in Hubble Space Telescope images of two dwarf galaxies (GMP 3292 and GMP 3629) belonging to the Coma cluster. GMP 3629 is the faintest such galaxy detected in a cluster environment, and it is the first such galaxy observed in the dense Coma cluster. The large bulge and the faintness of the broad spiral-like pattern in GMP 3629 suggests that its disk may have been largely depleted. >We may therefore have found an example of the ``missing link'' in theories of galaxy evolution which have predicted that dwarf spiral galaxies, particularly…
We present a quantitative analysis of the star formation history (SFH) of the Local Group dSph galaxy Leo I, from the information in its HST [(V-I),I] color-magnitude diagram (CMD). The method we use is based in comparing, via synthetic CMDs, the expected distribution of stars in the CMD for different evolutionary scenarios, with the observed distribution. We consider the SFH to be composed by the SFR(t), the Z(t), the IMF, and a function $β(f,q)$, controlling the fraction $f$ and mass ratio distribution $q$ of binary stars. The comparison between the observed CMD and the model CMDs is done th…
We present the surface photometry of star clusters in the nearby dwarf elliptical galaxies NGC 185 and NGC 205, obtained from deep HST WFPC2 F555W (V) and F814W (I) images. We have obtained surface brightness and color profiles of six star clusters in NGC 185, seven star clusters in NGC 205, and one recently discovered non-stellar object in NGC 205. The surface brightness profiles of ten star clusters are fitted well by the King model, and those of four star clusters are fitted well by the power-law. Three out of ten star clusters fitted well with King model show signs of tidal tails.
Aims: ``Compact ellipticals'' are so rare that a search for M32 analogs is needed to ensure the very existence of this class. Methods: We report here the discovery of A496cE, a M32 twin in the cluster Abell 496, located in the halo of the central cD. Results: Based on CFHT and HST imaging we show that the light profile of A496cE requires a two component fit: a Sersic bulge and an exponential disc. The spectrum of A496cE obtained with the ESO-VLT FLAMES/Giraffe spectrograph can be fit by a stellar synthesis spectrum dominated by old stars, with high values of [Mg/Fe] and velocity dispersion. Co…
We present results from a morphological study of the distant X-ray cluster MS1054-03 at z=0.83. We have obtained a large, two color HST WFPC2 mosaic of this cluster, and measured redshifts of 186 galaxies in the MS1054-03 field with the 10m Keck telescope. Of 81 spectroscopically confirmed cluster galaxies observerd with HST, 13 are merger systems. Most of these mergers will likely evolve into luminous elliptical galaxies, and some may evolve into S0 galaxies. If the galaxy population in MS1054-03 is typical for its redshift up to 50% of ellipticals may have formed in mergers at z<1. The merge…
The specific globular cluster frequencies (S_N) for 24 dwarf elliptical (dE) galaxies in the Virgo and Fornax Clusters and the Leo Group imaged with the Hubble Space Telescope are presented. Combining all available data, we find that for nucleated dEs --- which are spatially distributed like giant ellipticals in galaxy clusters --- S_N(dE,N)=6.5 +- 1.2 and S_N increases with M_V, while for non-nucleated dEs --- which are distributed like late-type galaxies --- S_N(dE,noN)=3.1 +- 0.5 and there is little or no trend with M_V. The S_N values for dE galaxies are thus on average significantly highe…
We present a thorough investigation of stellar photometry based on HST imaging of crowded fields at 85 and 10 arcsec from the centre of the high-surface brightness elliptical M32. The Principal Investigators of the present archive data have elsewhere presented an impressive colour-magnitude diagram of the field at 85 arcsec. Based on the same data we enlarge on their photometric analysis and supplement with error estimators that more clearly show the implications of severe image crowding on the stellar photometry. We show that the faintest stars (I>25.0, V>26.0) are found too bright by several…
The UV upturn phenomenon observed in elliptical galaxies is attractive for its potential value as an age indicator of old stellar systems. We present our most recent population models for the UV evolution of elliptical galaxies. We confirm that the dominant UV sources are either metal-poor or metal-rich hot horizontal-branch (HB) stars in local giant ellipticals, but we also note that the contribution from post-asymptotic-giant-branch (PAGB) stars overwhelms the UV spectrum at higher redshifts (look-back times). The model UV spectral energy distribution (SED) is therefore strongly affected by …
We have observed a complete sample of 21 nearby (D < 70h^{-1} Mpc) Fanaroff & Riley Type I galaxies with HST/WFPC2 and detected dust disks and lanes in 19 of them. The radio jets are roughly perpendicular to the dust which is used to constrain the Doppler boosting factors of the radio jet and cores. The VLBA core flux correlates with the central Halpha+[NII] flux which might indicate that the VLBA core is dominated by an isotropic component. Twelve galaxies show nuclear optical sources. We discuss various possible origins for this emission.
(ABRIDGED) The ACS camera on board the Hubble Space Telescope has been used to obtain deep images of the giant elliptical galaxy NGC 3610, a well-established dissipative galaxy merger remnant. These observations supersede previous WFPC2 images which revealed the presence of a population of metal-rich globular clusters (GCs) of intermediate age (~1.5-4 Gyr). We detect a total of 580 GC candidates, 46% more than from the previous WFPC2 images. The new photometry strengthens the significance of the previously found bimodality of the color distribution of GCs. Peak colors in V-I are 0.93 +/-0.01 a…
We present new optical spectroscopy of the lens elliptical galax in the ``Einstein Cross'' lens system HST 14176+5226, using the Faint Object Camera and Spectrograph (FOCAS) of the Subaru t Our spectroscopic observations are aimed at measuring the stella dispersion of the lens galaxy, located at high redshift of z_L= as an important component to lens models. We have measured this 230 +- 14 km s^{-1} (1 sigma) inside 0.35 effective radi based on the comparison between the observed galaxy spectrum and templates of three G-K giants by means of the Fourier cross-corr To extract the significance of…
The radial distribution of globular clusters in galaxies is always less peaked to the centre than the halo stars'. Extending previous work to a sample of HST globular cluster systems in ellipticals, we evaluate the number of clusters lost to the galactic centre as the integrals of the difference between the observed globular cluster system distribution and the underlying halo light profile. It results that the initial populations of globular clusters were from 25% to 50% richer than now. This significant number of missing globular clusters supports the hypothesis that a large quantity of globu…
Narrow-band images of the core of the extraordinary poly-polar planetary nebula KjPn 8 have been obtained with the WFPC2 camera on board the Hubble Space Telescope. Spasmodic bipolar ejections, in changing directions have occurred over thousands of years to create KjPn 8. The central star is finally revealed in these observations and its compact nebular core is resolved into a remarkably young, aprox. 500 years old, elliptical ring. The highest speed bipolar outflows are perpendicular to this central ring which is identified as the latest event in the creation of this nebula. The formation his…
We study the surface photometry for 13 single-nucleus ultraluminous IRAS galaxies (ULIRGs), selected from a parent sample of 58 galaxies obtained in a Hubble Space Telescope snapshot survey. We find that these galaxies can be classified into three classes according to their surface photometry. The surface brightness profiles of the four objects in the first class are well fitted by the r^{1/4} law. The isophotes are all disky at R < 1 h^{-1}kpc, consistent with the molecular disks/rings found in nearby ULIRGs from CO observations. Each of the four galaxies in the second class has an inner r^{1…
We have obtained new near-infrared images of both GG Tau and UY Aur circumbinary disks with the polarimetric modes of NICMOS aboard the Hubble Space Telescope. The 1 micron intensity map of GG Tau reveals a more complete elliptical shape than in previous ground-based images. Its eastern and western sides are definitely asymmetric. Our image strongly supports the ring geometry proposed by Guilloteau, Dutrey & Simon (1999) on the basis of their millimetre interferometry images: a geometrically thick and sharply edged ring surrounding an empty gap around the binary. Around UY Aur, we identify str…
We combine spectroscopic metallicity values with integrated narrowband continuum colors to explore the internal metallicity distribution in early-type galaxies. The different techniques for determining metallicity (indices versus colors) allows for an estimate of the contribution from metal-poor stars in a predominantly metal-rich population which, in turn, places constraints on the shape and width of a galaxy's metallicity distribution function (MDF). The color-spectroscopic data is compared to the closed box, infall and inhomogeneous chemical evolution models. The G-dwarf problem, a deficien…
We present BVRI CCD surface photometry for the central (6'.35 X 6'.35) regions of the dwarf elliptical galaxies NGC 185 and NGC 205 in the Local Group. Surface brightness profiles of NGC 185 (R < 225") and NGC 205 (R < 186") show excess components in the central regions. The colors of NGC 185 get bluer inward at R < 25", while they remain constant at R >= 25". The colors of NGC 205 get bluer inward at 1" < R < 50", and remain flat outside. Our photometry, supplemented by the photometry based on the far-ultraviolet and visual images of the HST archive data, shows that there is an inversion of c…
We present HST WFPC2 I band imaging for a sample of 9 Hyperluminous Infrared Galaxies spanning a redshift range 0.45 < z < 1.34. Three of the sample have morphologies showing evidence for interactions, six are QSOs. Host galaxies in the QSOs are reliably detected out to z ~ 0.8. The detected QSO host galaxies have an elliptical morphology with scalelengths spanning 6.5 < r_{e}(Kpc) < 88 and absolute k corrected magnitudes spanning -24.5 < M_{I} < -25.2. There is no clear correlation between the IR power source and the optical morphology. None of the sources in the sample, including F15307+3252…
We have used deep HST/WFPC2 images in V (F606W) and I (F814W) to measure the luminosity distribution of the globular clusters in NGC 4874, the central cD galaxy of the Coma cluster. We find the ``turnover'' point of the globular cluster luminosity function (GCLF) to lie at V = 27.88 +/- 0.12, while the overall GCLF shape matches the standard Gaussian-like form with dispersion SIGMA_V = 1.49 +/- 0.12. We use the GCLF as a standard candle by matching the turnover points in NGC 4874 and another Coma elliptical, IC 4051, with those of the giant ellipticals in the Virgo cluster (M87 and five others…
Using the HST WFPC2 we perform deep I-band imaging of 9 radio-selected (limit 14 microJanskys at 8.5 GHz) faint galaxies from Roche, Lowenthal and Koo (2002). Two are also observed in V. Six of the galaxies have known redshifs of 0.4<z<1.0. Radial intensity profiles indicate that 7 are disk galaxies and 2 are bulge-dominated. Four of the six with redshifts have a high optical surface brightness compared to typical disk galaxies. Two of the 9 galaxies are in close interacting pairs, another two are very asymmetric and three have large, luminous rings resembling the collisional starburst rings i…
We present the results of a Hubble Space Telescope WFPC2 F555W and F814W survey of 69 dwarf elliptical galaxies (dEs) in the Virgo and Fornax Clusters and Leo Group. The $V-I$ colors of the dE globular clusters, nuclei, and underlying field star populations are used to trace the dE star-formation histories. We find that the dE globular cluster candidates are as blue as the metal-poor globular clusters of the Milky Way. The observed correlation of the dE globular cluster systems' $V-I$ color with the luminosity of the host dE is strong evidence that the globular clusters were formed within the …
We present wide-field spectroscopy of globular clusters around the Leo I group galaxies NGC 3379 and NGC 3384 using the FLAMES multi-fibre instrument at the VLT. We obtain accurate radial velocities for 42 globular clusters (GCs) in total, 30 for GCs around the elliptical NGC 3379, eight around the lenticular NGC 3384, and four which may be associated with either galaxy. These data are notable for their large radial range extending from 0'7 to 14'5 (2 to 42 kpc) from the centre of NGC 3379, and small velocity uncertainties of about 10 km/s. We combine our sample of 30 radial velocities for glo…
Using the surface brightness fluctuations in HST WFPC-2 images, we determine that M87, NGC 4486B, and NGC 4478 are all at a distance of ~16 Mpc, while NGC 4476 lies in the background at ~21 Mpc. We also examine the globular clusters of M87 using archived HST fields. We detect the bimodal color distribution, and find that the amplitude of the red peak relative to the blue peak is greatest near the center. This feature is in good agreement with the merger model of elliptical galaxy formation, where some of the clusters originated in progenitor galaxies while other formed during mergers.
We study surface brightness fluctuations (SBF) in a sample of 8 elliptical galaxies using Advanced Camera for Surveys (ACS) Wide Field Channel (WFC) data drawn from the Hubble Space Telescope (HST) archive. SBF magnitudes in the F814W bandpass, and galaxy colors from F814W, F435W, and F606W images -- when available -- are presented. Galaxy surface brightness profiles are determined as well. We present the first SBF--broadband color calibration for the ACS/WFC F814W bandpass, and (relative) distance moduli estimates for 7 of our galaxies. We detect and study in detail the SBF variations within …
