Reinaldo R. de Carvalho

Near-Infrared Imaging of Early-Type Galaxies. III. The Near-Infrared Fundamental Plane

?????Near-infrared imaging data on 251 early-type galaxies in clusters and groups are used to construct the near-infrared fundamental plane (FP) The slope of the FP therefore departs from the virial expectation of reff ? ?? at all optical and near-infrared wavelengths, which could be a result of the variation of M/L along the elliptical galaxy sequence or a systematic breakdown of homology among the family of elliptical galaxies. The slope of the near-infrared FP excludes metallicity variations as the sole cause of the slope of the FP. Age effects, dynamical deviations from a homology, or any combination of these (with or without metallicity), however, are not excluded. The scatter of both the near-infrared and optical FP are nearly identical and substantially larger than the observational uncertainties, demonstrating small but significant intrinsic cosmological scatter for the FP at all wavelengths. The lack of a correlation of the residuals of the near-infrared FP and the residuals from the Mg2-?0 relation indicates that the thickness of these relations cannot be ascribed only to age or metallicity effects. Because of this metallicity independence, the small scatter of the near-infrared FP excludes a model in which age and metallicity effects conspire to keep the optical FP thin. All of these results suggest that the possible physical origins of the FP relations are complicated due to combined effects of variations of stellar populations and structural parameters among elliptical galaxies.

Near-Infrared Imaging of Early-Type Galaxies. IV. The Physical Origins of the Fundamental Plane Scaling Relations

The physical origins of the fundamental plane (FP) scaling relations are investigated using large samples of early-type galaxies observed at optical and near-infrared wavelengths. The slope a in the FP relation reff ∝ σΣ is shown to increase systematically with wavelength from the U band (λ ~ 0.35 μm) through the K band (λ ~ 2.2 μm). A distance-independent construction of the observables is described that provides an accurate measurement of the change in the FP slope between any pair of bandpasses. The variation of the FP slope with wavelength is strong evidence of systematic variations in stellar content along the elliptical galaxy sequence, but is insufficient to discriminate between a number of simple models for possible physical origins of the FP. The intercept of the diagnostic relationship between log DK/DV and log σ0 shows no significant dependence on environment within the uncertainties of the Galactic extinction corrections, demonstrating the universality of the stellar population contributions at the level of Δ(V - K) = 0.03 mag to the zero point of the global scaling relations. Several other constraints on the properties of early-type galaxies—the slope of the Mg2-σ0 relation, the slope of the FP in the K band, the effects of stellar population gradients, and the effects of deviations of early-type galaxies from a dynamically homologous family—are included to construct an empirical, self-consistent model that provides a complete picture of the underlying physical properties that are varying along the early-type galaxy sequence. The fundamental limitations to providing accurate constraints on the individual model parameters (variations in age and metallicity, and the size of the homology breaking) appear to be subtle variations between stellar population synthesis models and poorly constrained velocity dispersion aperture effects. This empirical approach nonetheless demonstrates that there are significant systematic variations in both age and metallicity along the elliptical galaxy sequence, and that a small, but systematic, breaking of dynamical homology (or a similar, wavelength-independent effect) is required. The intrinsic thickness of the FP can then be easily understood as small variations in age and metallicity, as well as deviations from a homology at any particular point along the FP. The model parameters will be better constrained by measurements of the change of the slope of the FP with redshift; predictions for this evolution with redshift are described. This model for the underlying physical properties that produce the FP scaling relations provides a comprehensive framework for future investigations of the global properties of early-type galaxies and their evolution.

Radio Properties of z > 4 Optically Selected Quasars

We report on two programs to address differential evolution between the radio-loud and radio-quiet quasar populations at high (z > 4) redshift. Both programs entail studying the radio properties of optically selected quasars. First, we have observed 32 optically selected, high-redshift (z > 4) quasars with the VLA at 6 cm (5 GHz). These sources represent a statistically complete and well-understood sample. We detect four quasars above our 3 σ limit of ≈0.15 mJy, which is sufficiently sensitive to detect all radio-loud quasars at the probed redshift range. Second, we have correlated 134 z > 4 quasars, comprising all such sources that we are aware of as of mid-1999, with the FIRST survey and the NRAO VLA Sky Survey. These two recent 1.4 GHz VLA sky surveys reach 3 σ limits of approximately 0.6 and 1.4 mJy, respectively. We identify a total of 15 z > 4 quasars, of which six were not previously known to be radio-loud. The depth of these surveys does not reach the radio-loud/radio-quiet demarcation luminosity density (L1.4 GHz = 1032.5 h ergs s-1 Hz-1) at the redshift range considered; this correlation therefore provides only a lower limit to the radio-loud fraction of quasars at high redshift. The two programs together identify eight new radio-loud quasars at z > 4, a significant increase over the seven currently in the published literature. We find no evidence that the radio-loud fraction depends on optical luminosity for -25 > MB > -28 at z 2 or for -26 > MB > -28 at z > 4. Our results also show no evolution in the radio-loud fraction between z 2 and z > 4 (for -26 > MB > -28).

The Nature of the Activity in Hickson Compact Groups of Galaxies

We present the results of the spectral classification of the 82 brightest galaxies in a sample of 17 compact groups. We verify that the active galactic nuclei (AGNs) are preferentially located in the most early-type and luminous galaxies of the groups, as is usually observed in the field. But these AGNs also appear to be systematically concentrated toward the central parts of the groups. Our observations suggest a correlation between activity types, morphologies, and densities of galaxies in the compact groups. This is consistent with a scenario in which galaxies of compact groups evolve by interacting with their environment and are currently in a quiet phase of their activity.

Redshift Survey of Galaxies around a Selected Sample of Compact Groups

We report the results of a spectroscopic survey of faint galaxies in the regions surrounding Hickson compact groups. Our sample is composed of 17 groups within 9000 km s-1. The spectra were taken at the prime focus of the Tololo 4 m telescope, using the ARGUS fiber-fed spectrograph. From these observations, redshifts were determined for the faint galaxies previously identified by de Carvalho, Ribeiro, & Zepf in the surroundings of the groups. Statistical methods were applied to the resultant catalog in order to determine the kinematical structure of each group. This analysis confirms the idea that the Hickson sample of compact groups contains a wide variety of projection and dynamical configurations. Our results demonstrate the necessity of new spectroscopic surveys around compact groups in order to assess their complete velocity distribution.

The Relation between Activity and Environment in Compact Groups of Galaxies

We present the results of the classification of spectral activity types for 193 galaxies from a new sample of 49 compact groups of galaxies in the southern hemisphere (SCGs). The SCGs represents a new sample of compact groups selected in automated fashion from a digitized galaxy catalog, covering an area of ~5200 deg2 around the south Galactic pole. It is complete up to m ~ 14.5 in bj for the brightest galaxy of the group. This sample is very well suited for statistical studies of compact groups properties as it is unaffected by the biases introduced by visual selection methods. The spectral analysis of the SCG galaxies confirms the results previously obtained from the observation of a smaller sample of 17 CGs in Hicksons sample (HCG). We confirm the luminosity-activity and morphology-activity relations previously observed in HCGs: (1) low-luminosity AGNs and AGNs are preferentially located in the most luminous galaxies in the groups, while non-emission–line galaxies and star-forming galaxies share a common distribution among the less luminous galaxies; (2) the non-emission–line galaxies, the low-luminosity AGNs and AGNs are nearly all in early-type galaxies, while the star-forming galaxies are preferentially located in late-type spirals. We also verified that the number of evolved galaxies (early-type non-emission–line galaxies) significantly increases with the number of members in the group. Finally, we confirm that AGNs (including low-luminosity or dwarf AGNs) are the most frequent (41%) activity type encountered in CGs. The SCGs contain more star-forming galaxies and less non-emission–line galaxies than HCGs. This difference is possibly related to the different selection criteria of SCGs with respect to HCGs. Being selected in an automated way, the SCGs probe a wider range of physical properties than the HCGs, which are biased toward more easily detectable, denser and therefore more evolved groups. The star-forming galaxies in SCGs are composed of few starburst galaxies and a higher number of H II nucleus galaxies, which generally have less intense star formation than starburst galaxies. As a consequence, the star formation activity in SCGs is remarkably low. At the same time, we found clear evidence for nuclear activity in all the star-forming galaxies. Adding up the percentage of AGNs and star-forming galaxies showing evidence of nuclear activity would result in more than 70% of the galaxies in SCGs having an active nucleus. If these results are further confirmed, CGs will be in the local universe the best location where to find AGNs. Curiously, however, this characteristic of CGs generally excludes Seyfert 1 galaxies.

The Voronoi Tessellation cluster finder in 2+1 dimensions

We present a detailed description of the Voronoi Tessellation (VT) cluster finder algorithm in 2+1 dimensions, which improves on past implementations of this technique. The need for cluster finder algorithms able to produce reliable cluster catalogs up to redshift 1 or beyond and down to 10 13.5 solar masses is paramount especially in light of upcoming surveys aiming at cosmological constraints from galaxy cluster number counts. We build the VT in photometric redshift shells and use the two-point correlation function of the galaxies in the field to both determine the density threshold for detection of cluster candidates and to establish their significance. This allows us to detect clusters in a self-consistent way without any assumptions about their astrophysical properties. We apply the VT to mock catalogs which extend to redshift 1.4 reproducing the ΛCDM cosmology and the clustering properties observed in the Sloan Digital Sky Survey data. An objective estimate of the cluster selection function in terms of the completeness and purity as a function of mass and redshift is as important as having a reliable cluster finder. We measure these quantities by matching the VT cluster catalog with the mock truth table. We show that the VT can produce a cluster catalog with completeness and purity > 80% for the redshift range up to ∼1 and mass range down to ∼10 13.5 solar masses.

HCG 16: A High Concentration of Active Galaxies in the Nearby Universe

In the course of an extensive campaign to measure radial velocities of galaxies in a selected sample of compact groups photometrically studied by de Carvalho et al., we report the discovery of a system very rich in starburst galaxies and active galactic nuclei. This is the system HCG 16 of Hicksons catalog of compact groups. The seven brightest galaxies form a kinematical group with biweighted estimate mean velocity of VBI = 3959 ± 66 km s-1, dispersion σBI = 86 ± 55 km s-1, a median radius R = 0.197 Mpc, a mean density of D = 217 galaxies Mpc-3, and a total absolute magnitude of MB = -22.1. From their spectral characteristics, we have identified one Seyfert 2 galaxy, two LINERs, and three starburst galaxies. Thus, HCG 16 appears to be a dense concentration of active galaxies. In our sample of 17 Hickson groups, HCG 16 is unique in this regard, which suggests that it is an uncommon structure in the nearby universe.

The Evolution of Galaxies in Compact Groups

We present an analysis of the spectra of 62 galaxies in 15 compact groups. The galaxies are classified into four activity classes: galaxies without emission, starburst galaxies, luminous AGNs (Seyfert and LINERs), and low-luminosity AGNs (LLAGNs). The star formation in the Hickson compact group (HCG) starbursts is more intense than in normal spirals, but comparable to that observed in starburst-nucleus galaxies (SBNGs) in the field. In general, the HCG starbursts have mean solar gas metallicity and do not follow the metallicity-luminosity relation traced by the early-type SBNGs in the field, suggesting that most of them are late-type SBNGs. This morphology preference, coupled with the observation that the HCG starbursts are predominantly located in the halos of the groups, is consistent with the idea that compact groups are embedded in sparser structures. The stellar metallicities of the nonstarburst galaxies are comparable to those observed in normal galaxies with similar morphologies, but are relatively high for their luminosities. In these galaxies, the metal absorption line equivalent widths are slightly narrower than normal, while the Balmer absorption lines are relatively strong. All these observations suggest the presence of a population of intermediate-age stars. These galaxies could be poststarburst, but at a very advanced stage of evolution, the last bursts having happened more than 2 Gyr in the past. Our observations support a scenario in which the cores of the groups are slowly collapsing evolved systems embedded in more extended structures. In the cores of the groups, the interactions were more frequent and the galaxies evolved at a more rapid rate than in their halos.

Environments of Redshift Survey Compact Groups of Galaxies

Redshift survey compact groups (RSCGs) are tight knots of N ≥ 3 galaxies selected from the CfA2+SSRS2 redshift survey. The selection is based on physical extent and association in redshift space alone. We measured 300 new redshifts of fainter galaxies within 1 h-1 Mpc of 14 RSCGs to explore the relationship between RSCGs and their environments. Thirteen of 14 RSCGs are embedded in overdense regions of redshift space. The systems range from a loose group of five members to an Abell cluster. The remaining group, RSCG 64, appears isolated. RSCGs are isolated and distinct from their surroundings to varying degrees, as are the Hickson compact groups. Among the 13 embedded RSCGs, three are distinct from their general environments (RSCG 9, RSCG 11, and RSCG 85).