arXiv subjects

R. P. Saglia

Publications and source records attributed to R. P. Saglia.

At least 91 records · Page 5Linked to original sources

arXiv2001

The evolution of the Tully-Fisher relation of spiral galaxies

We present the B-band Tully-Fisher relation (TFR) of 60 late-type galaxies with redshifts 0.1-1. The galaxies were selected from the FORS Deep Field with a limiting magnitude of R=23. Spatially resolved rotation curves were derived from spectra obtained with FORS2 at the VLT. High-mass galaxies with v_max>=150 km/s show little evolution, whereas the least massive systems in our sample are brighter by about 1-2 mag compared to their local counterparts. For the entire distant sample, the TFR slope is flatter than for local field galaxies (-5.77+-0.45 versus -7.92+-0.18). Thus, we find evidence for evolution of the slope of the TFR with redshift on the 3-sigma level. This is still true when we subdivide the sample into three redshift bins. We speculate that the flatter tilt of our sample is caused by the evolution of luminosities and an additional population of blue galaxies at z>=0.2. The mass dependence of the TFR evolution also leads to variations for different galaxy types in magnitude-limited samples, suggesting that selection effects can account for the discrepant results of previous TFR studies on the luminosity evolution of late-type galaxies.

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arXiv2001

Gravitationally lensed high redshift galaxies in the field of 1E0657-56

We present images and long-slit spectra obtained with FORS1 at UT1 of the VLT centered on the gravitational arc of the galaxy cluster 1E0657-56 (z = 0.296). The cluster is one of the hottest, most massive clusters known so far and acts as a powerful gravitational telescope, amplifying the flux of background sources by up to a factor of 17. We present photometric results together with the spectra of the gravitational arc (z = 3.24) and four additional amplified high redshift objects (z = 2.34 to 3.08) that were also included in the slit by chance coincidence. A magnification map has been obtained from a lens model derived from the multiple image systems. We compare our observed spectra with models and briefly discuss the stellar contents of these galaxies. Furthermore we measured the equivalent widths of the CIV 1550 and SiIV 1400 absorption lines for the objects behind 1E0657-56 studied here, as well as for some additional starburst galaxies (nearby and at high z). For CIV we find an increasing absorption equivalent width with decreasing redshift. We discuss whether this correlation could be related to the increase of metallicity with the age of the universe.

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arXiv2001

Line-of-sight velocity distributions of low-luminosity elliptical galaxies

The shape of the line-of-sight velocity distribution (LOSVD) is measured for a sample of 14 elliptical galaxies, predominantly low-luminosity ellipticals. The sample is dominated by galaxies in the Virgo cluster but also contains ellipticals in nearby groups and low density environments. The parameterization of the LOSVD due to Gerhard and van der Marel and Franx is adopted, which measures the asymmetrical and symmetrical deviations of the LOSVD from a Gaussian by the amplitudes h3 and h4 of the Gauss-Hermite series. Rotation, velocity dispersion, h3 and h4 are determined as a function of radius for both major and minor axes. Non-Gaussian LOSVDs are found for all galaxies along the major axes. Deviations from a Gaussian LOSVD along the minor axis are of much lower amplitude if present at all. Central decreases in velocity dispersion are found for three galaxies. Two galaxies have kinematically-decoupled cores: NGC 4458 and the well-known case of NGC 3608.

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arXiv2000

The Peculiar Motions of Early-Type Galaxies in Two Distant Regions VI: The Maximum Likelihood Gaussian Algorithm

The EFAR project is designed to measure the properties and peculiar motions of early-type galaxies in two distant regions. Here we describe the maximum likelihood algorithm we developed to investigate the correlations between the parameters of the EFAR database. One-, two-, and three-dimensional gaussian models are constructed to determine the mean value and intrinsic spread of the parameters, and the slopes and intrinsic parallel and orthogonal spread of the Mgb'-Mg2, Mg2-sigma, Mgb'-sigma relations, and the Fundamental Plane. In the latter case, the cluster peculiar velocities are also determined. We show that this method is superior to ``canonical'' approaches of least-squares type, which give biased slopes and biased peculiar velocities. We test the algorithm with Monte Carlo simulations of mock EFAR catalogues and derive the systematic and random errors on the estimated parameters. We find that random errors are always dominant. We estimate the influence of systematic errors due to the way clusters were selected and the hard limits and uncertainties in the selection function parameters for the galaxies. We explore the influence of uniform distributions in the Fundamental Plane parameters and the errors. We conclude that the mean peculiar motions of the EFAR clusters can be determined reliably. In particular, the placement of the two EFAR sample regions relative to the Lauer and Postman dipole allows us to strongly constrain the amplitude of the bulk motion in this direction.

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arXiv2000

Dynamical family properties and dark halo scaling relations of giant elliptical galaxies

Based on a uniform dynamical analysis of line-profile shapes for 21 luminous round elliptical galaxies, we have investigated the dynamical family relations of ellipticals: (i) The circular velocity curves (CVCs) of elliptical galaxies are flat to within ~10% for R>~0.2R_e. (ii) Most ellipticals are moderately radially anisotropic; their dynamical structure is surprisingly uniform. (iii) Elliptical galaxies follow a Tully-Fisher (TF) relation, with v_c^max=300 km/s for an L_B^* galaxy. At given v_c^max, they are ~1 mag fainter in B and appear to have slightly lower baryonic mass than spirals even for maximum M/L_B. (iv) The luminosity dependence of M/L_B is confirmed. The tilt of the Fundamental Plane is not caused by dynamical non-homology, nor only by an increasing dark matter fraction with L. It is, however, consistent with stellar population models based on published metallicities and ages. The main driver is therefore probably metallicity, and a secondary population effect is needed to explain the K-band tilt. (v) These results make it likely that elliptical galaxies have nearly maximal M/L_B (minimal halos). (vi) Despite the uniformly flat CVCs, there is a spread in cumulative M/L_B(r). Some galaxies have no indication for dark matter within 2R_e, whereas others have local M/L_Bs of 20-30 at 2R_e. (vii) In models with maximum stellar mass, the dark matter contributes ~10-40% of the mass within R_e. (viii) The corresponding halo core densities and phase-space densities are at least ~25 times larger and the halo core radii ~4 times smaller than in spiral galaxies of the same v_c^max. The increase in M/L sets in at ~10 times larger acceleration than in spirals. This could imply that elliptical galaxy halos collapsed at high redshift or that some of the dark matter in ellipticals might be baryonic. (abridged)

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arXiv2000

The peculiar motions of early-type galaxies in two distant regions - VII. Peculiar velocities and bulk motions

We present peculiar velocities for 84 clusters of galaxies in two large volumes at distances between 6000 and 15000 km/s in the directions of Hercules-Corona Borealis and Perseus-Pisces-Cetus. These velocities are based on Fundamental Plane (FP) distance estimates for early-type galaxies in each cluster. We fit the FP using a maximum likelihood algorithm which accounts for both selection effects and measurement errors, and yields FP parameters with smaller bias and variance than other fitting procedures. We find a best-fit FP with coefficients consistent with the best existing determinations. We measure the bulk motions of the sample volumes using the 50 clusters with the best-determined peculiar velocities. We find the bulk motions in both regions are small, and consistent with zero at about the 5% level. The EFAR results are in agreement with the small bulk motions found by Dale et al. (1999) on similar scales, but are inconsistent with pure dipole motions having the large amplitudes found by Lauer & Postman (1994) and Hudson et al. (1999). The alignment of the EFAR sample with the Lauer & Postman dipole produces a strong rejection of a large-amplitude bulk motion in that direction, but the rejection of the Hudson et al. result is less certain because their dipole lies at a large angle to the main axis of the EFAR sample. We find the bulk motion of our sample is consistent with most cosmological models that approximately reproduce the shape and normalisation of the observed galaxy power spectrum. We conclude that existing measurements of large-scale bulk motions provide no significant evidence against standard models for the formation of structure.

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arXiv2000

The evolution of the color gradients of early-type cluster galaxies

We investigate the origin of color gradients in cluster early-type galaxies to probe whether pure age or pure metallicity gradients can explain the observed data in local and distant (z approx 0.4) samples. We measure the surface brightness profiles of the 20 brightest early-type galaxies of CL0949+44 (hereafter CL0949) at redshift z=0.35-0.38 from HST WF2 frames taken in the filters F555W, F675W, F814W. We determine the color profiles (V-R)(r), (V-I)(r), and (R-I)(r) as a function of the radial distance r in arcsec, and fit logarithmic gradients in the range -0.2 to 0.1 mag per decade. These values are similar to what is found locally for the colors (U-B), (U-V), (B-V) which approximately match the (V-R), (V-I), (R-I) at redshift approx 0.4. We analyse the results with up to date stellar population models. We find that passive evolution of metallicity gradients (approx 0.2 dex per radial decade) provides a consistent explanation of the local and distant galaxies' data. Invoking pure age gradients (with fixed metallicity) to explain local color gradients produces too steep gradients at redshifts z approx 0.4. Pure age gradients are consistent with the data only if large present day ages (>=15 Gyr) are assumed for the galaxy centers.

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arXiv2000

Spectra of High Redshift Galaxies using a Cluster as a Gravitational Telescope

Using the Focal Reducer Spectrograph (FORS) at the Very Large Telescope (VLT) during the FORS commissioning time in December 1998 we took long slit spectra of the gravitational arc visible on images of the galaxy cluster 1E 0657 (z = 0.296). This cluster is one of the hottest (massive) cluster known so far and hence perfectly acts as a gravitational telescope magnifying the flux of background sources up to a factor of 17. Here we present the spectra of the gravitational arc (z = 3.23) and 4 additional high redshift objects (z=2.35 to 3.09), that also fall on the slit by chance coincidence. We briefly discuss the stellar contents of these galaxies and show first models of the observed spectra. Furthermore we point out the effectivity of using FORS in combination with available gravitational telescopes.

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arXiv1999

The orbital structure and potential of NGC 1399

Accurate and radially extended stellar kinematic data reaching R=97'' from the center are presented for the cD galaxy of Fornax, NGC 1399. The stellar rotation is small (<= 30 km/s); the stellar velocity dispersion remains constant at 250-270 km/s. The deviations from Gaussian line of sight velocity distributions are small, at the percent level. We construct dynamical models of the galaxy, deprojecting its nearly round (E0-E1) surface brightness distribution, and determining the spherical distribution function that best fits (at the 4 percent level) the kinematic data on a grid of parametrized potentials. We find that the stellar orbital structure is moderately radial, with beta=0.3 +- 0.1 for R<=60'', similar to results found for some normal giant ellipticals. The gravitational potential is dominated by the luminous component out to the last data point, with a mass-to-light ratio M/L_B=10 solar units, although the presence of a central black hole of M approx 5 x 10^8 solar masses is compatible with the data in the inner 5 arcsec. The influence of the dark component is marginally detected starting from R approx 60''. Using the radial velocities of the globular clusters and planetary nebulae of the galaxy we constrain the potential more strongly, ruling out the self-consistent case and finding that the best fit solution agrees with X-ray determinations. The resulting total mass and mass-to-light ratio are M=1.2-2.5 x 10^12 solar masses and M/L_B=22-48 M solar units inside R=417'' or 35 kpc for D=17.6 Mpc.

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arXiv1999

EFAR peculiar velocities and bulk motions

The EFAR project has measured peculiar motions in two distant volumes of the universe using Fundamental Plane (FP) distances for 85 clusters with cz=6000-15000 km/s. The scatter in distance about the FP is observed to be 20% per galaxy for EFAR sample, resulting in peculiar velocities with a median precision of 1075 km/s for the 50 clusters with 3 or more galaxies. We find that there is no evidence for a large bulk flow within either of the two volumes sampled by the EFAR clusters. The measured bulk motion in both regions is small and consistent with zero. The Lauer and Postman (1994) bulk motion is ruled out at the 4-sigma level. There is no evidence supporting the SMAC (Hudson et al. 1999) or LP10K (Willick 1999) bulk motions, but the directionality of the EFAR sample would only allow a weak (2-sigma) detection at best.

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arXiv1999

Probing early-type galaxy evolution with the Kormendy relation

We investigate the evolution of early-type galaxies in four clusters at z=0.4 (Abell370, Cl0303+17, Cl0939+47 and Cl1447+26) and in one at z=0.55 (Cl0016+16). The galaxies are selected according to their spectrophotometrically determined spectral types and comprise the morphological classes E, S0 and Sa galaxies. Structural parameters are determined by a two-component fitting of the surface brightness profiles derived from HST images. Exploring a realistic range of K-corrections using Bruzual and Charlot models, we construct the rest-frame B-band Kormendy relations (mu_e-log(R_e)) for the different clusters. We do not detect a systematic change of the slope of the relation as a function of redshift. We discuss in detail how the luminosity evolution, derived by comparing the Kormendy relations of the distant clusters with the local one for Coma, depends on various assumptions and give a full description of random and systematic errors by exploring the influences of selection bias, different star formation histories and K-corrections. Early-type galaxies with modest disk components (S0 and Sa) do not differ significantly in their evolution from disk-less ellipticals. The observed luminosity evolution is compatible with pure passive evolution models (with redshift of formation z>2) but also with models that allow ongoing star formation on a low level, like exponentially decaying star formation models with an e-folding time of tau=1 Gyr.

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arXiv1998

Dynamical analysis of elliptical galaxy halos

We describe a non-parametric method for determining both the anisotropy and mass profiles of elliptical galaxies from velocity dispersions and velocity profile shapes along the line of sight. In this way, mass-to-light ratios out to 2-3 effective radii can be derived from stellar absorption line spectroscopy. We discuss two illustrative cases, NGC 1399 and NGC 6703. So far, all ellipticals which have been analysed show evidence for dark matter dominating in the outer parts. The circular velocity curves are nearly flat, as in spiral galaxies.

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arXiv1998

The peculiar motions of early-type galaxies in two distant regions - II. The spectroscopic data

We present the spectroscopic data for the galaxies studied in the EFAR project, which is designed to measure the properties and peculiar motions of early-type galaxies in two distant regions. We have obtained 1319 spectra of 714 early-type galaxies over 33 observing runs on 10 different telescopes. We describe the observations and data reductions used to measure redshifts, velocity dispersions and the Mgb and Mg2 Lick linestrength indices. Detailed simulations and intercomparison of the large number of repeat observations lead to reliable error estimates for all quantities. The measurements from different observing runs are calibrated to a common zeropoint or scale before being combined, yielding a total of 706 redshifts, 676 velocity dispersions, 676 Mgb linestrengths and 582 Mg2 linestrengths. The median estimated errors in the combined measurements are dcz=20 km/s, dsigma/sigma=9.1%, dMgb/Mgb=7.2% and dMg2=0.015 mag. Comparison of our measurements with published datasets shows no systematic errors in the redshifts or velocity dispersions and only small zeropoint corrections to bring our linestrengths onto the standard Lick system. We have assigned galaxies to physical clusters by examining the line-of-sight velocity distributions based on EFAR and ZCAT redshifts, together with the projected distributions on the sky. We derive mean redshifts and velocity dispersions for these clusters, which will be used in estimating distances and peculiar velocities and to test for trends in the galaxy population with cluster mass. The spectroscopic parameters presented here for 706 galaxies combine high quality data, uniform reduction and measurement procedures, and detailed error analysis. They form the largest single set of velocity dispersions and linestrengths for early-type galaxies published to date.

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arXiv1998

The peculiar motions of early-type galaxies in two distant regions - V. The Mg-sigma relation, age and metallicity

We examine the Mg-sigma relation for early-type galaxies in the EFAR sample and its dependence on cluster properties. A maximum likelihood fit gives global Mg-sigma relations of Mgb'=0.131log(sigma)-0.131 and Mg2=0.257log(sigma)-0.305, with intrinsic scatter of 0.016 mag in Mgb' and 0.023 mag in Mg2. The zeropoint for cD galaxies is higher than for E/S0 galaxies, implying cDs are older and/or more metal-rich than E/S0s with the same sigma. Mg-sigma zeropoint variations between clusters are consistent with the number of galaxies observed per cluster and the global intrinsic scatter in Mg-sigma. We find no significant correlation between the Mg-sigma zeropoint and the cluster velocity dispersion, X-ray luminosity or X-ray temperature over a wide range in cluster mass. We compare the intrinsic scatter in the Mg-sigma and Fundamental Plane (FP) relations with stellar population models to constrain the dispersion in ages, metallicities and M/L ratios for early-type galaxies at fixed sigma. Variations in age alone or metallicity alone cannot explain the measured intrinsic scatter in both Mg-sigma and the FP. We derive the joint constraints on the dispersion in age and metallicity implied by the scatter in the Mg-sigma and FP relations for a simple Gaussian model. We find upper limits on the dispersions at fixed sigma of 32% in dt/t and 38% in dZ/Z if variations in age and metallicity are uncorrelated; only strongly anti-correlated variations lead to significantly higher upper limits. The joint distribution of residuals from the Mg-sigma and FP relations is only marginally consistent with a model having no correlation between age and metallicity, and is better-matched by a model in which age and metallicity variations are moderately anti-correlated, with younger galaxies being more metal-rich. (Abridged)

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arXiv1998

A NIR search for high-redshift clusters

We describe our preliminary results on a search for high-redshift ($z >$ 0.5) galaxy clusters using near-infrared photometry obtained with the Omega camera at the 3.5m telescope at Calar Alto.

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arXiv1998

The MUNICs project -- a multicolor survey of distant galaxies

The MUNICS project is an ongoing imaging survey designed to cover 3 sq. degrees in V,R,I,J,K'. We describe here partial results of the project concerning the clustering properties of K' < 19.5 galaxies in scales of 3.6'' to 63.0'' over an area of $\sim 800 arcmin^2$. We present K' data for a sample of 20 fields, five of which contain $z > 0.5$ radio-loud quasars with steep spectra, eight contain $z > 0.5$ radio-loud quasars with flat spectra and seven are high-galactic latitude fields with no quasars in them. The two-point angular correlation function for the total sample shows significant clustering at $\sim 5 σ$ level of K'=19.5 galaxies. The correlation angle of the galaxies is $θ_0 = 1.7'' \pm 0.4''$ for K' < 19 mag and $θ_0 = 1.0'' \pm 0.2''$ for K' < 19.5 mag. When the correlation functions for the subsamples are considered, the mean $ω(θ)$ amplitude of the fields which contain steep-spectra $z > 0.5$ radio-loud quasars is determined to be $\sim 2.0 - 2.5$ that of the high-galactic latitude fields.

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arXiv1998

Dynamical Mass Determination for Elliptical Galaxies

The mass and anisotropy of an elliptical galaxy can be simultaneously determined from velocity dispersion and line profile shape measurements. We describe the principles, techniques, and limitations of this approach, and the results obtained sofar. We briefly discuss how best to combine these stellar-dynamical results with X-ray measurements and gravitational lensing analyses.

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arXiv1997

Luminous Cluster Ellipticals as Cosmological Standard Rods?

We explore the possibility to calibrate massive cluster ellipticals as cosmological standard rods. The method is based on the Fundamental Plane relation combined with a correction for luminosity evolution which is derived from the Mg$-σ$ relation. Principle caveats and sources of major errors are briefly discussed. We apply the described procedure to nine elliptical galaxies in two clusters at $z=0.375$ and derive constraints on the cosmological model. For the best fitting $Λ$-free cosmological model we obtain: $q_o \approx 0.1$, with 90% confidence limits being $0 < q_o < 0.7$ (the lower limit being due to the presence of matter in the Universe). If the inflationary scenario applies (i.e., space has flat geometry), then, for the best fitting model, matter and $Λ$ contribute about equally to the critical cosmic density (i.e. $Ω_m \approx Ω_Λ\approx 0.5$). With 90% confidence $Ω_Λ$ should be smaller than 0.9.

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