arXiv subjects
Publications and source records attributed to A. Renzini.
We report on a large survey for double degenerate (DD) binaries as potential progenitors of type Ia supernovae with the UVES spectrograph at the ESO VLT (ESO SN Ia Progenitor surveY - SPY).
We present the redshift distribution of a complete sample of 480 galaxies with Ks<20 distributed over two independent fields covering a total area of 52 arcmin^2. The redshift completeness is 87% and 98% respectively with spectroscopic and high-quality and tested photometric redshifts. The redshift distribution of field galaxies has a median redshift z_{med}\sim 0.80, with \sim 32% and \sim 9% of galaxies at z>1 and z>1.5 respectively. A ``blind'' comparison is made with the predictions of a set of the most recent LambdaCDM hierarchical merging and pure luminosity evolution (PLE) models. The hierarchical merging models overpredict and underpredict the number of galaxies at low-z and high-z respectively, whereas the PLE models match the median redshift and the low-z distribution, still being able to follow the high-z tail of N(z). We briefly discuss the implications of this comparison and the possible origins of the observed discrepancies. We make the redshift distribution publicly available.
We present the complete photometric database and the color-magnitude diagrams for 74 Galactic globular clusters observed with the HST/WFPC2 camera in the F439W and F555W bands. A detailed discussion of the various reduction steps is also presented, and of the procedures to transform instrumental magnitudes into both the HST F439W and F555W flight system and the standard Johnson B and V systems. We also describe the artificial star experiments which have been performed to derive the star count completeness in all the relevant branches of the color magnitude diagram. The entire photometric database and the completeness function will be made available on the Web immediately after the publication of the present paper.
The K20 survey is an ESO VLT optical and near-infrared spectroscopic survey aimed at obtaining spectral information and redshifts of a complete sample of about 550 objects to K_s\leq20.0 over two independent fields with a total area of 52 arcmin^2. In this paper we discuss the scientific motivation of such a survey, we describe the photometric and spectroscopic properties of the sample, and we release the $K_s$-band photometric catalog. Extensive simulations showed that the sample is photometrically highly complete to K_s=20. The observed galaxy counts and the R-K_s color distribution are consistent with literature results. We observed spectroscopically 94% of the sample, reaching a spectroscopic redshift identification completeness of 92% to K_s\leq20.0 for the observed targets, and of 87% for the whole sample (i.e. counting also the unobserved targets). Deep spectroscopy was complemented with multi-band deep imaging in order to derive tested and reliable photometric redshifts for the galaxies lacking spectroscopic redshifts. The results show a very good agreement between the spectroscopic and the photometric redshifts with =0.01 and with a dispersion of σ_{Δz}=0.09. Using both the spectroscopic and the photometric redshifts, we reached an overall redshift completeness of about 98%. The size of the sample, the redshift completeness, the availability of high quality photometric redshifts and multicolor spectral energy distributions make the K20 survey database one of the most complete samples available to date for constraining the currently competing scenarios of galaxy formation and for a variety of other galaxy evolution studies.
Currently public ESO data sets pertinent to the CDFS/GOODS field are briefly illustrated along with an indication on how to get access to them. Future ESO plans for complementing the GOODS database with optical/IR imaging and optical spectroscopy are also described.
We have started a large survey for double degenerate (DD) binaries as potential progenitors of type Ia supernovae with the UVES spectrograph at the ESO VLT (ESO SN Ia Progenitor surveY - SPY). About 400 white dwarfs were checked for radial velocity variations during the first 15 months of this project, twice the number of white dwarfs investigated during the last 20 years. We give an overview of the SPY project and present first results Fifty four new DDs have been discovered, seven of them double lined (only 18 and 6 objects of these groups were known before, respectively). The final sample is expected to contain 150 to 200 DDs. Eight new pre-cataclysmic binaries were also detected. SPY is the first DD survey which encompasses also non-DA white dwarfs. SPY produces an immense, unique sample of very high resolution white dwarf spectra, which provides a lot of spin-off opportunities. We describe our projects to exploit the SPY sample for the determination of basic parameters, kinematics, and rotational velocities of white dwarfs. A catalogue with a first subset of our white dwarf data has already been published by Koester et al. 2001.
In the course of our search for double degenerate (DD) binaries as potential progenitors of type Ia supernovae with the UVES spectrograph at the ESO VLT (ESO SN Ia Progenitor surveY - SPY) we discovered that the white dwarf HE 1414-0848 is a double-lined DA+DA binary with an orbital period of P = 12h 25m 39s. Semi-amplitudes of 128km/s and 100km/s are derived for the individual components. The amplitude ratio and the measured difference in gravitational redshift is used to estimate the masses of the individual components: 0.55Msol and 0.71Msol. Hence the total mass of the HE 1414-0848 system is 1.26Msol, only 10% below the Chandrasekhar limit. The results of a model atmosphere analysis are consistent with our mass estimated from the orbit. Temperatures of the individual components are also determined. Possible scenarios for the formation of this system are discussed. The system will merge due to loss of angular momentum via gravitational wave radiation after two Hubble times. HE 1414-0848 does not qualify as a SN Ia progenitor, but it is the most massive close DD known today.
We compare the 3D clustering of old passively-evolving and dusty star-forming z~1 EROs from the K20 survey. With detailed simulations of clustering, the comoving correlation length of dusty star-forming EROs is constrained to be less than r_0~2.5 Mpc/h. In contrast, the old EROs are much more positively correlated, with 5.5<~r_0/(Mpc/h)<~16, consistent with previous claims for z~1 field early-type galaxies based on analyses of ERO angular clustering. The low level of clustering of dusty star-forming EROs does not support these to be major mergers building up an elliptical galaxy, or typical counterparts of SCUBA sources, but it is instead consistent with the weak clustering of high redshift blue galaxies and of luminous local IRAS galaxies. Current hierarchical merging models can explain the large r_0 for z~1 field early-type galaxies, but fail in matching their high number density and overall old ages.
We present the results of VLT optical spectroscopy of a complete sample of 78 EROs with R-Ks\geq5 over a field of 52 arcmin^2. About 70% of the 45 EROs with Ks\leq19.2 have been spectroscopically identified with old passively evolving and dusty star-forming galaxies at 0.7<z<1.5. The two classes are about equally populated and for each of them we present and discuss the average spectrum. From the old ERO average spectrum and for Z=Z_{\odot} we derive a minimum age of \sim 3 Gyr, corresponding to a formation redshift of z_f \gtsima 2.4. PLE models with such formation redshifts well reproduce the density of old EROs (consistent with being passively evolving ellipticals), whereas the predictions of the current hierarchical merging models are lower than the observed densities by large factors (up to an order of magnitude). From the average spectrum of the star-forming EROs we estimate a substantial dust extinction with E(B-V) \gtsima 0.5. The star formation rates, corrected for the average reddening, suggest a significant contribution from EROs to the cosmic star-formation density at z \sim 1.
We present results from NICMOS Hubble Space Telescope observations of the reddened bulge globular clusters NGC 6528, Terzan 5, Liller 1, UKS 1 and Terzan 4, obtained through the filters F110W and F160W (nearly equivalent to J and H). For the first time the turnoff region of Liller 1 and the main sequence of Terzan 5 and Terzan 4 are reached, as well as the horizontal branch of UKS 1. The magnitude difference between the turnoff and the red horizontal branch $Δm_{110}=m_{110}^{HB}- m_{110}^{TO}$ is used as an age indicator. From comparisons with new isochrones in the NICMOS photometric system, we conclude that the two metal-rich clusters NGC 6528 and Terzan 5 are coeval within uncertainties ($\sim 20%$) with 47 Tucanae. Liller 1 and UKS 1 are confirmed as metal-rich globular clusters. Terzan 4 is confirmed as an interesting case of a metal-poor cluster in the bulge with a blue horizontal branch.
We examine the spatial clustering of extremely red objects (EROs) found in a relatively large survey of 700 arcmin^2, containing 400 galaxies with R-Ks>5 to Ks=19.2. A comoving correlation length r_0=12\pm3 /h Mpc is derived, under the assumption that the selection function is described by a passively evolving early-type galaxy population, with an effective redshift of z~1.2. This correlation length is very similar to that of local L* elliptical galaxies implying, at face value, no significant clustering evolution in comoving coordinates of early-type galaxies to the limiting depth of our sample, z~1.5. A rapidly evolving clustering bias can be designed to reproduce a null result; however, our data do not show the corresponding strong reduction in the average population density expected for consistency with underlying growth of the mass-function. We discuss our data in the context of recent ideas regarding bias evolution. The uncertainty we quote on r_0 accounts for the spikey redshift distribution expected along relatively narrow sightlines, which we quantify with detailed simulations. This is an improvement over the standard use of Limber's equation which, because of its implicit assumption of a smooth selection function, underestimates the true noise by a factor of ~ 3 for the parameters of our survey. We propose a general recipe for the analysis of angular clustering, suggesting that any measurement of the angular clustering amplitude, A, has an intrinsic additional uncertainty of σ_A/A=\sqrt{AC}, where AC is the appropriate integral constraint.
We present a new determination of the distance (and age) of the Galactic globular cluster 47 Tucanae (NGC 104) based on the fit of its white dwarf (WD) cooling sequence with the empirical fiducial sequence of local WD with known trigonometric parallax, following the method described in Renzini et al. (1996). Both the cluster and the local WDs were imaged with HST+WFPC2 using the same instrument setup. We obtained an apparent distance modulus of $(m-M)_V=13.27\pm0.14$ consistent with previous ground-based determinations and shorter than that found using HIPPARCOS subdwarfs. Coupling our distance determination with a new measure of the apparent magnitude of the main sequence turnoff, based on our HST data, we derive an age of $13\pm2.5$ Gyr.
WFPC2 images obtained with the Hubble Space telescope 4.16 years apart have allowed us to measure the proper motion of the metal rich globular cluster NGC 6553 with respect to the background bulge stars. With a space velocity of ($Π, Θ, W$) = (-3.5, 230, -3) km s$^{-1}$, NGC 6553 follows the mean rotation of both disk and bulge stars at a Galactocentric distance of 2.7 kpc. While the kinematics of the cluster is consistent with either a bulge or a disk membership, the virtual identity of its stellar population with that of the bulge cluster NGC6528 makes its bulge membership more likely. The astrometric accuracy is high enough for providing a measure of the bulge proper motion dispersion and confirming its rotation. A selection of stars based on the proper motions produced an extremely well defined cluster color-magnitude diagram (CMD), essencially free of bulge stars. The improved turnoff definition in the decontaminated CMD confirms an old age for the cluster (~13 Gyr) indicating that the bulge underwent a rapid chemical enrichment while being built up at in the early Universe. An additional interesting feature of the cluster color-magnitude diagram is a significant number of blue stragglers stars, whose membership in the cluster is firmly established from their proper motions.
We have obtained HST-NICMOS observations of five of M31's most metal rich globular clusters. These data allow photometry of individual stars in the clusters and their surrounding fields. However, to achieve our goals -- obtain accurate luminosity functions to compare with their Galactic counterparts, determine metallicities from the slope of the giant branch, identify long period variables, and estimate ages from the AGB tip luminosity, we must be able to disentangle the true properties of the population from the observational effects associated with measurements made in very crowded fields. In this paper we present a careful analysis of photometry in crowded regions, and show how image blending affects the results and interpretation of such data. Although this analysis is specifically for our NICMOS observations in M31, the techniques we develop can be applied to any imaging data taken in crowded fields; we show how the effects of image blending will even limit NGST. We use three different techniques to analyze the effects of crowding on our data, including the insertion of artificial stars (traditional completeness tests) and the creation of completely artificial clusters. They are used to derive threshold- and critical-blending radii for each cluster, which determine how close to the cluster center reliable photometry can be achieved. The simulations also allow us to quantify and correct for the effects of blending on the slope and width of the RGB at different surface brightness levels.
We have obtained HST-NICMOS observations of five of M31's most metal rich globular clusters: G1, G170, G174, G177 & G280. For the two clusters farthest from the nucleus we statistically subtract the field population and estimate metallicities using K-(J-K) color-magnitude diagrams (CMDs). Based on the slopes of their infrared giant branches we estimate [Fe/H]=-1.22+/-0.43 for G1 and -0.15+/-0.37 for G280. We combine our infrared observations of G1 with two epochs of optical HST-WFPC2 V-band data and identify at least one LPV based on color and variability. The location of G1's giant branch in the K-(V-K) CMD is very similar to that of M107, indicating a higher metallicity than our purely infrared CMD: [Fe/H]=-0.9+/-0.2. For the field surrounding G280, we estimate the metallicity to be -1.3 with a spread of 0.5 from the slope and width of the giant branch. Based on the numbers and luminosities of the brightest giants, we conclude that only a small fraction of the stars in this field could be as young as 2 Gyr, while the majority have ages closer to 10 Gyr. The K-band luminosity functions (LFs) of the upper few magnitudes of G1 and G280, as well as for the fields surrounding all clusters, are indistinguishable from the LF measured in the bulge of our Galaxy. This indicates that these clusters are very similar to Galactic clusters, and at least in the surrounding fields observed, there are no significant populations of young luminous stars.
A comparison is presented between the observed surface density of extremely red objects (EROs) and the densities of red high-z elliptical galaxies predicted by Pure Luminosity Evolution (PLE) and by some CDM hierarchical models. The analysis is based on the widest field survey for EROs available to date (covering in total $\sim$850 arcmin^2), and it takes into account the effects of ERO clustering. Good agreement is found between the observed surface densities of EROs and those predicted by PLE models for ellipticals selected using the same color and luminosity thresholds. Since there is evidence that the bulk of EROs are passively evolving ellipticals, this result implies that most field ellipticals were fully assembled at least by $z\sim$2.5. Existing hierarchical models predict instead a surface density of red ellipticals that is much smaller than that of the EROs.
We present the results of a wide-field survey for extremely red objects (EROs hereafter), the widest so far, based on Ks and R band imaging. The survey covers 701 arcmin^2 and it is 85% complete to Ks\leq18.8 over the whole area and to Ks\leq19.2 over 447.5 arcmin^2. Thanks to the wide field covered, a complete sample of about 400 EROs with R-Ks\geq5 was selected. The distribution of the EROs on the sky is strongly inhomogeneous, being characterized by overdensities and large voids. We detect at the 8 sigma level a strong clustering signal of the EROs which is about an order of magnitude larger than the clustering of K-selected field galaxies in the same magnitude range. A smooth trend of increasing clustering amplitude with the R-Ks color is observed. These results are strong evidence that the largest fraction of EROs is composed of high-z ellipticals, of which we detect for the first time the z\simgt1 large scale structure clustering signal. We show how the surface density variations of the ERO population found in our survey can explain the highly discrepant results obtained so far on the density of z > 1 ellipticals, and we briefly discuss the main implications of our results for the evolution of elliptical galaxies. The number counts and the colors of the K-selected field galaxies are also presented and briefly discussed.
We report on low-resolution multi-object spectroscopy of 30 faint targets (R \~ 24-25) in the HDF-S and AXAF deep field obtained with the VLT Focal Reducer/low dispersion Spectrograph (FORS1). Eight high-redshift galaxies with 2.75< z < 4 have been identified. The spectroscopic redshifts are in good agreement with the photometric ones with a dispersion $σ_z = 0.07$ at z<2 and $σ_z = 0.16$ at z>2. The inferred star formation rates of the individual objects are moderate, ranging from a few to a few tens solar masses per year. Five out of the eight high-z objects do not show prominent emission lines. One object has a spectrum typical of an AGN. In the AXAF field two relatively close pairs of galaxies have been identified, with separations of 8.7 and 3.1 proper Mpc and mean redshifts of 3.11 and 3.93, respectively.