arXiv subjects

C. N. A. Willmer

Publications and source records attributed to C. N. A. Willmer.

70 records · Page 4Linked to original sources

arXiv2002

Redshift-distance Survey of Early-type Galaxies: the ENEARc Cluster Sample

This paper presents data on the ENEARc subsample of the larger ENEAR survey of the nearby early-type galaxies. The ENEARc galaxies belong to clusters and were specifically chosen to be used for the construction of a D_n-sigma template. The ENEARc sample includes new measurements of spectroscopic and photometric parameters (redshift, velocity dispersion, line index Mg_2, and the angular diameter d_n) as well as data from the literature. New spectroscopic data are given for 229 cluster early-type galaxies and new photometry is presented for 348 objects. Repeat and overlap observations with external data sets are used to construct a final merged catalog consisting of 640 early-type galaxies in 28 clusters. Objective criteria, based on catalogs of groups of galaxies derived from complete redshift surveys of the nearby universe, are used to assign galaxies to clusters. In a companion paper these data are used to construct the template D_n-sigma distance relation for early-type galaxies which has been used to estimate galaxy distances and derive peculiar velocities for the ENEAR all-sky sample.

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arXiv2001

Mg_2-sigma in Early-Type Galaxies and Spiral Bulges

We analyze new measurements of the Mg_2 central line strength index and velocity dispersion (sigma) for the galaxies of the ENEAR survey. The observations are now complete (da Costa et al. 2000) and the sample contains 1223 early-type galaxies. We also analyze the line strength indices for a sample of 95 spiral bulges (from Sa to Sbc). For the early-type galaxies we find: i) that the Mg_2-sigma relation for Es and S0s are nearly the same, with both populations showing comparable scatter, and ii) a marginal difference in the slope of the Mg_2-sigma relation for cluster and field early-type galaxies. However, we suggest that before interpreting such a difference in the framework of a mass-metallicity relation, it is important to take into account the effects of rotation in the Mg_2-sigma relation. Our preliminary results indicate that once the rotation effects are minimized by choosing a sample containing only slow rotators, the Mg_2-sigma relation is similar both for isolated and clustered galaxies. More data on rotational velocities of early-type galaxies are needed to confirm this result. For spiral bulges, we find that their locus in the Mg_2-sigma plane lies always below the one occupied by early-type galaxies.

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arXiv2000

The DEEP Groth Strip Survey X: Number Density and Luminosity Function of Field E/S0 Galaxies at z < 1

We present the luminosity function and color-redshift relation of a magnitude-limited sample of 145 mostly red field E/S0 galaxies at z < 1 from the DEEP Groth Strip Survey (GSS). Most of the E/S0s (86%) form a red envelope in the redshift-color diagram, consistent with predictions of spectral synthesis models in which the dominant stellar population is formed at redshifts z > 1.5. Constructing a luminosity function of the full sample of 145 E/S0s, we find that there is about 1.1--1.9 magnitude brightening in rest-frame B band luminosity back to z = 0.8 from z=0, consistent with other studies. Together with the red colors, this brightening favors models in which the bulk of stars in red field E/S0s formed before z_{for} > 1.5 and have been evolving rather quiescently with few large starbursts since then. Evolution in the number density of field E/S0 galaxies is harder to measure, and uncertainties in the raw counts and their ratio to local samples might amount to as much as a factor of two. Within that uncertainty, the number density of red E/S0s to z = 0.8 seems relatively static, being comparable to or perhaps moderately less than that of local E/S0s depending on the assumed cosmology. A doubling of E/S0 number density since z = 1 can be ruled out with high confidence (97%) if Ω_{m}=1. Taken together, our results are consistent with the hypothesis that the majority of luminous field E/S0s were already in place by z = 1, that the bulk of their stars were already fairly old, and that their number density has not changed by large amounts since then.

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arXiv2000

Redshift-Distance Survey of Early-Type Galaxies. IV. Dipoles of the Velocity Field

We use the recently completed redshift-distance survey of nearby early-type galaxies (ENEAR) to measure the dipole component of the peculiar velocity field to a depth of cz ~ 6000 km/s. The sample consists of 1145 galaxies brighter than m_B=14.5 and cz < 7000 km/s, uniformly distributed over the whole sky, and 129 fainter cluster galaxies within the same volume. Most of the Dn-sigma distances were obtained from new spectroscopic and photometric observations conducted by this project, ensuring the homogeneity of the data over the whole sky. These 1274 galaxies are objectively assigned to 696 objects -- 282 groups/clusters and 414 isolated galaxies. We find that within a volume of radius ~ 6000 km/s, the best-fitting bulk flow has an amplitude of |vbulk| =220 +/- 42 km/s in the CMB restframe, pointing towards l=304 +/- 16 degrees, b=25 +/- 11 degrees. The error in the amplitude includes statistical, sampling and possible systematic errors. This solution is in excellent agreement with that obtained by the SFI Tully-Fisher survey. Our results suggest that most of the motion of the Local Group is due to fluctuations within 6000 km/s, in contrast to recent claims of large amplitude bulk motions on larger scales.

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arXiv2000

Comparison of the ENEAR Peculiar Velocities with the PSCz Gravity Field

We present a comparison between the peculiar velocity field measured from the ENEAR all-sky $D_n-σ$ catalog and that derived from the galaxy distribution of the IRAS PSCz redshift survey. The analysis is based on a modal expansion of these data in redshift space by means of spherical harmonics and Bessel functions. The effective smoothing scale of the expansion is almost linear with redshift reaching 1500km/s at 3000km/s. The general flow patterns in the filtered ENEAR and PSCz velocity fields agree well within 6000km/s, assuming a linear biasing relation between the mass and the PSCz galaxies. The comparison allows us to determine the parameter $β=Ω^{0.6}/b$, where $Ω$ is the cosmological density parameter and $b$ is the linear biasing factor. A likelihood analysis of the ENEAR and PSCz modes yields $β=0.5 +- 0.1$, in good agreement with values obtained from Tully-Fisher surveys.

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arXiv2000

Large-Scale Power Spectrum and Structures From the ENEAR galaxy Peculiar Velocity Catalog

We estimate the mass density fluctuations power spectrum (PS) on large scales by applying a maximum likelihood technique to the peculiarvelocity data of the recently completed redshift-distance survey of early-type galaxies (ENEAR). The general results are in agreement with the high amplitude power spectra found from similar analysis of other independent all-sky catalogs of peculiar velocity data such as MARK III and SFI. For Lambda & Open CDM COBE normalized PS models, the best-fit parameters are confined by a contour approximately defined by Omega h^{1.3}=0.377+-0.08 and Omega h^{0.88}=0.517+-0.083, respectively. Gamma-shape models, free of COBE normalization, resultsin the weak constraint of $Γ\geq 0.17$ and in the rather stringent constraint of sigma_8 Omega^{0.6}=1.0+-0.25. All quoted uncertainties refer to 3-sigma confidence-level. The calculated PS is used as a prior for Wiener reconstruction of the density field at different resolutions and the three-dimensional velocity field within a volume of radius ~80 Mpc/h. All major structures in the nearby universe are recovered and are well matched to those predicted from all-sky redshift surveys.

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arXiv2000

ENEAR Redshift-Distance Survey: Cosmological Constraints

We present an analysis of the ENEAR sample of peculiar velocities of elliptical galaxies, obtained with D_n-σdistances. We use the velocity correlation function to analyze the statistics of the field-object's velocities, while the analysis of the cluster data is based on the estimate of their rms peculiar velocity, Vrms. The statistics of the model velocity field is parameterized by the amplitude, η_8=σ_8 Ω_m^{0.6}, and by the shape parameter, Γ. From the velocity correlation statistics we obtain η_8=0.51{-0.09}{+0.24} for Γ=0.25 at the 2σlevel. Even though less constraining, a consistent result is obtained by comparing the measured Vrms of clusters to linear theory predictions. For Γ=0.25 we find η_8=0.63{-0.19}{+0.22}$ at 1σ. Overall, our results point toward a statistical concordance of the cosmic flows traced by spirals and early-type galaxies, with galaxy distances estimated using TF and D_n-σdistance indicators, respectively.

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arXiv1999

Redshift-Distance Survey of Early-type Galaxies. I. Sample Selection, Properties and Completeness

This is the first in a series of papers describing the recently completed all-sky redshift-distance survey of nearby early-type galaxies (ENEAR) carried out for peculiar velocity analysis. The sample is divided into two parts and consists of 1607 elliptical and lenticular galaxies with cz < 7000 km/s and with blue magnitudes brighter than m_B=14.5 (ENEARm), and of galaxies in clusters (ENEARc). Galaxy distances based on the Dn-sigma and Fundamental Plane (FP) relations are now available for 1359 and 1107 ENEARm galaxies, respectively, with roughly 80% based on new data gathered by our group. The Dn-sigma and FP template distance relations are derived by combining 569 and 431 galaxies in 28 clusters, respectively, of which about 60% are based on our new measurements. The ENEARm redshift-distance survey extends the earlier work of the 7S and the recent Tully-Fisher surveys sampling a comparable volume. In subsequent papers of this series we intend to use the ENEAR sample by itself or in combination with the SFI Tully-Fisher survey to analyze the properties of the local peculiar velocity field and to test how sensitive the results are to different sampling and to the distance indicators. We also anticipate that the homogeneous database assembled will be used for a variety of other applications and serve as a benchmark for similar studies at high-redshift.

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arXiv1999

Two Galaxy Clusters: A3565 and A3560

We report 102 new redshifts and magnitudes for a sample of galaxies to RF ~ 15.5 mag in a 2.17 deg x 2.17 deg region centered on the galaxy IC 4296, the most luminous member of the A3565 cluster. Up to the limiting magnitude we find 29 cluster members, and measure a velocity dispersion of 228 km/s. The estimated total mass for this system is ~ 3.0 x h**-1 10**13 Msun (where h = H0/100 km/s/Mpc), and its dynamical properties are quite typical of poor clusters presenting X-ray emission. We also find that galaxies with absorption lines are more concentrated towards the center of the cluster, while systems with emission lines are mainly located in the outer parts. The small velocity dispersion of the cluster, coupled to the known presence of an interacting pair of galaxies, and the large extent of the brightest cluster galaxy, could indicate that galaxy formation through mergers may still be underway in this system. The surveyed region also contains galaxies belonging to the Shapley Concentration cluster A3560. Within 30 arc min of the cluster center, we detect 32 galaxies, for which we measure a velocity dispersion of 588 km/s and a mass of ~2 x h**-1 10**14 Msun. However, because our sample is restricted to galaxies brighter than M*, these values should be considered only as rough estimates.

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arXiv1998

The Galaxy Luminosity Function at z < 0.05: Dependence on Morphology

We investigate the dependence of the local galaxy luminosity function on morphology using 5,404 galaxies from the recently enlarged Second Southern Sky Redshift Survey (SSRS2). Over the range -22 \le M_B \le -14 ($H_0 = 100 km/s/Mpc), the luminosity function of early-type galaxies is well fitted by a Schechter function with parameters M_*=-19.37^{+0.10}_{-0.11}, alpha=-1.00^{+0.09}_{-0.09} and phi_*=0.0044 +/- 0.0008 Mpc^{-3}. The spiral luminosity function is very similar and is well fitted by the parameters M_*=-19.43^{+0.08}_{-0.08}, alpha=-1.11^{+0.07}_{-0.06} and phi_*=0.0080 +/- 0.0014 Mpc^{-3} over the same range in absolute magnitude. The flat faint end of the early-type luminosity function is consistent with earlier measurements from the CfA Redshift Survey (Marzke et al. 1994) but is significantly steeper than the slope measured in the Stromlo-APM survey (Loveday et al. 1992). Combined with the increased normalization of the overall LF measured from intermediate redshift surveys, the flat faint-end slope of the E/S0 LF produces no-evolution models which reproduce the deep HST counts of early-type galaxies remarkably well. However, the observed normalization of the SSRS2 LF is consistent with the low value measured in other local redshift surveys. The cause of this low-redshift anomaly remains unknown. The luminosity function of irregular and peculiar galaxies in the SSRS2 is very steep: M_*=-19.78^{+0.40}_{-0.50}, alpha=-1.81^{+0.24}_{-0.24} and phi_*=0.0002 +/- 0.00008 Mpc^{-3}. The steep slope is consistent with the LFs measured for Sm-Im galaxies in the CfA survey, UV-selected galaxies (Treyer et al. 1997), star-forming field galaxies (Bromley et al. 1997) and the bluest galaxies in the SSRS2 (Marzke & da Costa 1997).

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arXiv1998

The Southern Sky Redshift Survey

We report redshifts, magnitudes and morphological classifications for 5369 galaxies with $m_B \leq 15.5$ and 57 galaxies fainter than this limit, in two regions covering a total of 1.70 steradians in the southern celestial hemisphere. The galaxy catalog is drawn primarily from the list of non-stellar objects identified in the Guide Star Catalog (Lasker et al. 1990, AJ 99, 2019; hereafter GSC). The galaxies have positions accurate to about 1 arc sec and magnitudes with an rms scatter of about 0.3 mag. We compute magnitudes ($m_{SSRS2}$) from the relation between instrumental GSC magnitudes and the photometry by Lauberts & Valentijn (1989). From a comparison with CCD photometry, we find that our system is homogeneous across the sky and corresponds to magnitudes measured at the isophotal level $\sim$ 26 mag arcsec$^{-2}$. The precision of the radial velocities is of \sim 40 km/s and the redshift survey is more than 99% complete to the $m_{SSRS2}$ = 15.5 magnitude limit. This sample is in the direction opposite to the CfA2; in combination the two surveys provide an important database for studies of the properties of galaxies and their large-scale distribution in the nearby Universe.

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arXiv1998

Southern Sky Redshift Survey: Clustering of Local Galaxies

We use the two-point correlation function to calculate the clustering properties of the recently completed SSRS2 survey. The redshift space correlation function for the magnitude-limited SSRS2 is given by xi(s)=(s/5.85 h-1 Mpc)^{-1.60} for separations between 2 < s < 11 h-1 Mpc, while our best estimate for the real space correlation function is xi(r) = (r/5.36 h-1 Mpc)^{-1.86}. Both are comparable to previous measurements using surveys of optical galaxies over much larger and independent volumes. By comparing the correlation function calculated in redshift and real space we find that the redshift distortion on intermediate scales is small. This result implies that the observed redshift-space distribution of galaxies is close to that in real space, and that beta = Omega^{0.6}/b < 1, where Omega is the cosmological density parameter and b is the linear biasing factor for optical galaxies. We also use the SSRS2 to study the dependence of xi on the internal properties of galaxies. We confirm earlier results that luminous galaxies (L>L*) are more clustered than sub-L* galaxies and that the luminosity segregation is scale-independent. We find that early types are more clustered than late types, but that in the absence of rich clusters, the relative bias between early and late types in real space, is not as strong as previously estimated. Furthermore, both morphologies present a luminosity-dependent bias, with the early types showing a slightly stronger dependence on luminosity. We also find that red galaxies are significantly more clustered than blue ones, with a mean relative bias stronger than that seen for morphology. Finally, we find that the relative bias between optical and iras galaxies in real space is b_o/b_I $\sim$ 1.4.

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arXiv1997

Study od a Slice at +9 to +15 degrees of Declination: I. The Neutral Hydrogen Content of Galaxies in Loose Groups

We examine the H1 content of spiral galaxies in groups by using a catalog of loose groups of galaxies identified in a magnitude limited sample m < 15.7 spanning the range 8 h to 18 h in right ascension and +9 to +15 in declination. The redshift completeness of the galaxy sample is ~95%. No significant effect of H1 depletion is found, although there may be a hint that the earliest type spirals are slightly deficient.

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arXiv1997

Estimating Galaxy Luminosity Functions

In this work a comparison between different galaxy luminosity function estimators by means of Monte-Carlo simulations is presented. The simulations show that the C- method of Lynden-Bell (1971) and the STY method derived by Sandage, Tammann & Yahil (1979) are the best estimators to measure the shape of the luminosity function. The simulations also show that the STY estimator has a bias such that the faint-end slope is underestimated for steeper inclinations of the Schechter Function, and that this bias becomes quite severe when the sample contains only a few hundred objects. Overall, the C- is the most robust estimator, being less affected by different values of the faint end slope of the Schechter parameterization and sample size. The simulations are also used to compare different estimators of the luminosity function normalization. They demonstrate that most methods bias the recovered mean density towards values which are about 20% lower than the input value.

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arXiv1996

A Medium-Deep Survey of a Mini-Slice at the North Galactic Pole. II. The Data

We report 328 redshifts, b$_J$ magnitudes and b$_J$--r$_F$ colors of galaxies measured in a redshift survey of a 4$^\circ$ $\times$ 0.67$^\circ$ slice close to the north Galactic pole. The faintest galaxies in this survey have a magnitude of b$_J$ $\sim$ 20.5. The redshifts present external errors of the order of 70 \kms, and we estimate that the mean photometry errors are $\sim$ 0.2 for magnitudes and $\sim$ 0.3 for colors. The redshift completeness level of the sample is of the order of $\sim$ 35\% at b$_J$=20, and part of this rather low completeness is the result of the combination of limitations imposed by the multifiber system with the clustering of galaxies, and an insufficient number of configurations. At the nominal magnitude limit of the survey, we were able to measure redshifts for $\sim$ 70 \% of the galaxies we observed. From the correlation between observed properties of the galaxies in this sample, we demonstrate that the mean surface brightness is a major limiting factor in our ability to measure redshifts of faint objects.

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arXiv1996

New Southern Galaxies With Active Nuclei. Part II

This paper contains a list of new AGN candidates identified from the examination of 3500 optical spectra contained in the database of the Southern Sky Redshift Survey Extension (SSRS2). The classification of galaxies was done using standard diagnostics and a total of (5) Seyfert 1, (12) Seyfert 2 and (10) LINERs were found. We also present a list of 60 galaxies for which we could not secure a definite classification, but which might present some level of nuclear activity.

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