Nearby Early-type Galaxies Research Articles

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.

Limits on the Accretion Rates onto Massive Black Holes in Nearby Galaxies

The radio emission from supermassive black holes in nearby early-type galaxies can be used to test possible explanations for their low luminosities. We calculate the expected contribution from thermal synchrotron emission from hot accretion flows to the high radio frequency observations of NGC 2300, NGC 1399, NGC 4278 and NGC 4594. We find that, in all cases, and in accordance with our previous findings, hot flows accreting close to their Bondi rates overestimate significantly the observed fluxes. This implies that simply assuming a low radiative efficiency for the accreting gas is not enough to explain their low luminosities. Smaller central densities and accretion rates, as expected in the presence of strong mass loss or convection in the flows, can help reconcile the models with observations. We also show that a significant contribution to the high-frequency radio spectra can be due to non-thermal synchrotron emission from the small scale radio jets observed in these systems, allowing for even lower accretion rates in the inflows. We suggest that these outflows or jets may dump significant energy into the surronding medium close to the accretion radius and so reduce the accretion rates onto these systems. We discuss the relationship between the radio flux and black hole mass for the observed sample and its potential importance for probing accretion models.

ITAL]HUBBLE SPACE TELESCOPE[/ITAL][ITAL]Hubble Space Telescope[/ITAL] Observations of Nearby Radio-Loud Early-Type Galaxies

We present and analyse HST/WFPC2 broad- and narrow-band observations of the central regions of 19 nearby radio-loud early-type galaxies. Together with two more galaxies they form a complete sample of Fanaroff & Riley Type I galaxies. We obtained V- and I-band images and narrow-band images centered on the \HalphaNII emission lines. We use archival data for six galaxies. We describe the data reduction, give isophotal fits and analyse the central emission-line gas and dust distributions. Our main conclusions are the following. Although obscuration by dust inhibits a direct determination of central cusp slopes, the data suggest most but not all galaxies have shallow cores. Dust is detected in all but two galaxies. There is a wide variety of central dust morphologies, ranging from central disks to lanes and irregular distributions. The analysis suggests the difference between disks and lanes is intrinsic and not due to different viewing angles. Central emission-line gas is detected in all galaxies. Extended low-surface-brightness emission is always associated with the dust features. In a subsequent paper we will present a detailed analysis of the relation between these central properties and the nuclear activity.

Near‐infrared Imaging of Early‐Type Galaxies. II. Global Photometric Parameters

An imaging survey of 341 nearby early-type galaxies in the near-infrared K-band atmospheric window (2.2 μm) is described. The galaxies primarily reside in 13 nearby rich clusters (85%), while some additional galaxies are drawn from loose groups (12%) and the general field (3%). Surface photometry was measured for the entire sample. Detailed corrections were derived from an extensive grid of seeing-convolved r1/4 models and then applied to the isophotal surface brightness, aperture magnitude, and ellipticity profiles. Global photometric parameters were derived from this seeing-corrected photometry. More than 25% of the sample has been observed at least twice, and these repeat measurements demonstrate the small internal uncertainties on the derived global photometric parameters. Extensive comparisons with aperture photometry from the literature demonstrate that the photometric system is fully consistent with other photometric systems to ≤0.01 mag and confirm the estimates of internal random uncertainties. Additional global parameters are drawn from the literature in a homogeneous manner in order to construct a large catalog of galaxy properties: 95% of the galaxies have a velocity dispersion, 69% have a Mg2 index, 80% have an optical reff and μeff, 82% have a Dn, and 81% have a derived optical - infrared color measurement. This large data set provides excellent source material for investigations of the physical origins of the global scaling relations of early-type galaxies, velocity fields in the local universe, and comparisons to higher redshift early-type galaxies.

Hα Imaging of Early-Type ([CLC]Sa[/CLC]–[CLC]Sab[/CLC]) Spiral Galaxies. I.

Hα and continuum images are presented for 27 nearby early-type (Sa–Sab) spiral galaxies. Contrary to popular perception, the images reveal copious massive star formation in some of these galaxies. A determination of the Hα morphology and a measure of the Hα luminosity suggest that early-type spirals can be classified into two broad categories based on the luminosity of the largest H II region in the disk. The first category includes galaxies for which the individual H II regions have LHα < 1039 ergs s-1. Most of the category 1 galaxies appear to be morphologically undisturbed but show a wide diversity in nuclear Hα properties. The second category includes galaxies that have at least one H II region in the disk with LHα ≥ 1039 ergs s-1. All category 2 galaxies show either prominent dust lanes or other morphological peculiarities such as tidal tails, which suggests that the anomalously luminous H II regions in category 2 galaxies may have formed as a result of a recent interaction. The observations, which are part of an ongoing Hα survey, reveal early-type spirals to be a heterogeneous class of galaxies that are evolving in the current epoch. We have also identified some systematic differences between the classifications of spiral galaxies in the Second General Catalog and the Revised Shapley-Ames Catalog that may be traced to subtle variations in the application of the criteria used for classifying spiral galaxies. An examination of earlier studies suggests that perceptions concerning the Hubble-type dependence of star formation rates among spiral galaxies depends on the choice of catalog.

What Powers the Compact Radio Emission in Nearby Elliptical and S0 Galaxies?

Many nearby early-type (elliptical and S0) galaxies contain weak (millijansky level) nuclear radio sources on scales of a few hundred parsecs or less. The origin of the radio emission, however, has remained unclear, especially in volume-limited samples that select intrinsically less luminous galaxies. Both active galactic nuclei and nuclear star formation have been suggested as possible mechanisms for producing the radio emission. This paper utilizes optical spectroscopic information to address this issue. A substantial fraction of the early-type galaxies surveyed with the Very Large Array by Wrobel & Heeschen exhibits detectable optical emission lines in their nuclei down to very sensitive limits. Comparison of the observed radio continuum power with that expected from the thermal gas traced by the optical emission lines implies that the bulk of the radio emission is nonthermal. Both the incidence and the strength of optical line emission correlate with the radio power. At a fixed line luminosity, ellipticals have stronger radio cores than S0s. The relation between radio power and line emission observed in this sample is consistent with the low-luminosity extension of similar relations seen in classical radio galaxies and luminous Seyfert nuclei. A plausible interpretation of this result is that the weak nuclear sources in nearby early-type galaxies are the low-luminosity counterparts of more powerful AGNs. The spectroscopic evidence supports this picture. Most of the emission-line objects are optically classified as Seyfert nuclei or low-ionization nuclear emission-line regions (LINERs), the majority of which are likely to be accretion-powered sources.

Dependence of the Fundamental Plane Scatter on Galaxy Age

The fundamental plane (FP) has an intrinsic scatter that cannot be explained purely by observational errors. Using the recently available age estimates for nearby early-type galaxies, we show that a galaxy's position relative to the FP depends on its age. In particular, the mean FP corresponds to elliptical galaxies with an age of ~10 Gyr. Younger galaxies are systematically brighter, with a higher surface brightness relative to the mean relation. Old elliptical galaxies form an upper envelope to the FP. For our sample of mostly noncluster galaxies, age can account for almost half of the scatter in the B-band FP. Distance determinations based on the FP may have a systematic bias, if the mean age of the sample varies with redshift. We also show that fundamental plane residuals, B-V colors, and Mg2 line strength are consistent with an ageing central burst superposed on an old stellar population. This reinforces the view that these age estimates are tracing the last major episode of star formation induced by a gaseous merger event. We briefly discuss the empirical evolutionary tracks of merger remnants and young elliptical galaxies in terms of their key observational parameters.

Elliptical Galaxies: Structure, Stellar Content, and Evolution

A near-infrared imaging survey of 341 nearby early-type galaxies, combined with optical imaging and spectroscopic data from the literature, are used to construct the global scaling relations for this population of galaxies. These data demonstrate a number of important features of the early-type galaxy sequence: (1) the slope of the fundamental plane (FP) correlations systematically increases with wavelength; (2) the slope of these FP correlations deviates from the virial expectation at all wavelengths, implying a breakdown of either or both of the assumptions of constant mass-to-light ratio and homology; (3) the intrinsic scatter of the FP correlations is small but resolved at all wavelengths, implying a small cosmic scatter of earlytype galaxy properties at any position in the galaxy sequence and contradicting any model in which various stellar populations parameters “conspire” with each other to keep the correlations thin at optical wavelengths; (4) there is no correlation among residuals of the metallicity-independent near-infrared FP and the metallicity-sensitive Mg2-j0 relation, implying that both age and metallicity variations contribute to the cosmic scatter of both correlations; and (5) the effective radii systematically decrease with increasing wavelength, fully consistent with the general presence of stellar population gradients in early-type galaxies. A comprehensive and self-consistent model is described that simultaneously explains these and other global properties of the early-type galaxy sequence. This model demonstrates that age, metallicity, deviations from a dynamically homologous family, and population gradients are all contributing to the form of the global scaling relations; the latter two effects are the least constrained by the observations and model, respectively. Additional constraints on the role of age in the global scaling relations are obtained by observing early-type galaxies at higher redshifts. This has been studied using three approaches: color evolution, evolution of the slope and intercept of the K-band FP correlations, and evolution of the absorption-line strengths. The galaxies in each cluster are identified in a systematic way using two-color (three bandpass) imaging—sampling approximately the U, V, and I bandpasses in the rest frame—to eliminate late-type cluster member and general field interloper galaxies. This method is more than 90% effective in identifying early-type galaxies at the target cluster redshift. Weak color evolution in rest-frame has been de(U V )0 tected in 26 rich clusters of galaxies. The bluing trend in color is mag at , mag at , 0.05 0.03 z 0.2 0.12 0.04 z 0.4 and ∼ mag at . Using stellar population 0.23 0.05 z 0.54 synthesis models from the literature, this color evolution is fully consistent with the galaxy population as a whole having formed at . 1 ! z ! 5 f The FP correlations are studied for 128 galaxies in eight rich clusters at using moderate dispersion spectros0.1 ! z ! 0.6 copy (110 of the measurements are new) and imaging in the near-infrared K band. These data more than quadruple the data in the literature that can be used to study the FP at high redshift. The near-infrared FP is constructed at high redshifts for the first time. The intercept of the FP on the surface brightness axis is observed to dim with redshift, as expected for the Tolman signal in an expanding world model. A small amount of luminosity evolution mag is detected DK ≈ 2.5 log (1 z) on top of the Tolman signal, which is consistent with the passive evolution of a stellar population that formed at high redshift. The slope of the near-infrared FP is observed to flatten with redshift, implying that the least luminous galaxies are evolving faster than the luminous galaxies. This is strong evidence that low-luminosity elliptical galaxies have a stellar content that is up to a factor of 2 times younger than high-luminosity elliptical galaxies, but age spreads much larger than this appear to be excluded, and age spreads somewhat smaller than this are still allowed depending on the choice of nearby galaxy sample used in the comparison. The absorption-line strengths of the galaxies are observed to evolve slowly with redshift: the Mg2 and AFeS indices weaken while the HbG index strengthens. The latter effect in particular is another strong indication that the mean age of the stellar populations in early-type galaxies formed at redshifts 3 ! . All of these properties are moderately consistent with z ! 5 f the models derived above based on the samples of nearby galaxies, implying that age is an important physical parameter underlying the global scaling relations for early-type galaxies.

5.18. Molecular gas in the poststarburst galaxy NGC7331

To understand the origin and evolution of starburst activity, we must study the full evolution of starburst; i.e., pre-, on-going, and post-starburst phases. It seems reasonable to suppose the numerous A-type stars indicate past starburst and they show strong Balmer absorption. NGC7331, nearby early-type spiral galaxy, is one of the poststarburst galaxies which show strong Balmer absorption. The optical spectra of NGC7331 were dominated by component of intermediate-age (5 × 109 years) stellar populations (Ohyama &amp; Taniguchi 1996). We present the result of the high resolution CO observations of NGC7331 using Nobeyama Milimeter Array.

Gas Outflow in the Seyfert Galaxy IC 5063

IC 5063 (PKS 2048–572) is a nearby (z = 0.0110) early-type galaxy hosting a Seyfert 2 nucleus. In broad-band optical images, it shows a complex dust lane, while the ionized gas extends up to ~ 20 kpc and has an unusual X-shaped structure (Danziger et al. 1981, Colina et al. 1990). A faint, very broad emissionline component has been detected (Bergeron et al. 1983, Colina et al. 1991) together with an off-nuclear broad emission-line region (Wagner &amp; Appenzeller 1989). Broad Hα emission was also detected in polarized light (Inglis et al. 1993). Thus, it is likely that this galaxy has a broad-line region which is obscured from our direct view (while the broad-line radiation is scattered into our line of sight by scatterers outside the obscuring regions). The radio luminosity of IC 5063 is nearly two orders of magnitude larger than typical values for nearby Seyferts (Ulvestad &amp; Wilson 1984), making it one of the strongest radio sources found in Seyfert galaxies (1.3 Jy at 1.4 GHz, i.e., 2 × 1023W Hz−1 for H0 = 50 km s−1 Mpc−1). Its H I content is also very high: Danziger et al. (1981) found 1.0 × 1010M⊙, which gives MHI/LB = 0.4, quite anomalous for this type of object.

Ages of Galaxies Bulges and Disks From Optical and Near-Infrared Colors

For a sample of bright nearby early-type galaxies we have obtained surface photometry in bands ranging from U to K. Since the galaxies have inclinations larger than 50 deg. it is easy to separate bulges and disks. By measuring the colours in special regions, we minimize the effects of extinction, and by looking at B-K colour gradients we can show that for these type of spirals the colours mainly give information about stellar populations, and not extinction. We find that the differences between bulges and disks in all colours is very small, and using simple population models we can show that on the average the age difference between the bulge and the disk at 2 scale length is smaller than 30%, and much smaller if part of the difference is caused by a gradient in metallicity.

Ages of Galaxy Bulges and Disks from Optical and Near-Infrared Colours

For a sample of bright nearby early-type galaxies we have obtained surface photometry in bands ranging from U to K. Since the galaxies have inclinations larger than 50° it is easy to separate bulges and disks. By measuring the colours in special regions, we minimize the effects of extinction, and by looking at B – K colour gradients we can show that for these type of spirals the colours mainly give information about stellar populations, and not extinction. We find that the differences between bulges and disks in all colours is very small, and using simple population models we can show that on the average the age difference between the bulge and the disk at 2 scale length is smaller than 30%, and much smaller if part of the difference is caused by a gradient in metallicity.

Deep Hubble Space Telescope imaging of a compact radio galaxy at Z = 2.390

We present deep 4 hr HST/WFC images in V and I of the LBDS radio galaxy 53W002, a weak and compact narrow-line galaxy recently discovered at z = 2.390. After deconvolution, the resolution is 0.2" FWHM. Its I- band structure is quite compact with 30% +/- 10% of its flux in the central &lt;~ 1 kpc, presumably from its AGN. This is surrounded by a clearly extended and rather symmetric envelope with effective radius ~1.1" (4-15 kpc for H_0_ = 50-100,q_0_ = 0-0.5). In V, 53W002 is somewhat elongated at the same sky PA as its Lyα cloud and its VLA radio axis. We compare 52W002's rest-frame UV profile to a properly rescaled image of a nearby early-type galaxy. The much younger starburst in 53W002 has 10-20 times higher central UV surface brightness, but otherwise an r^1/4^-like light profile consistent with that of nearby luminous early- type galaxies. The available data are consistent with 53W002 being a genuinely young galaxy that only started forming stars &lt;~0.5 Gyr before z = 2.390, but has nonetheless (just) managed to develop a rather regular light profile at z = 2.390, and suggest that the dynamical collapse of this galaxy started at about the same time as its first major burst of star formation. For this galaxy, both ~0.5 Gyr time scales are consistent with z_form_ = 2.7-4.2 (for H_0_ = 50-100, q_0_ = 0-0.5).

The extended giant branch of M32

Near infrared color-magnitude diagrams have been constructed for the nearby early type galaxy M32. This diagram reveals the presence of an extended giant branch in M32 which reaches M(bol) = −5.5. The extended giant branch of M32 reaches several magnitudes above the tips of the Galactic globular cluster giant branches and has a much larger color dispersion. While the general color distribution of M32 and Baade's Window giant stars are roughly similar, M32 giant stars reach bolometric luminosities ∼1 magnitude greater than Baade's window giant stars. Furthermore, many M32 giant stars are redder (J-K > 1.4) than the reddest Baade's Window stars

Low Activity Nuclei with Strong [NII] Lines

We present results from the study of six low activity galactic nuclei spectra with strong [NII] λλ6548 + 6584 emission lines in order to investigate if this characteristic is due to a peculiar chemical abundance. The selected galaxies NGC1358, NGC1386, NGC4941 and NGC6300 present Seyfert 2 (Sy2) activity, NGC3312 is a LINER and NGC7743 can be classified as intermediate between the two categories. All of them are nearby early type galaxies, whose nucleus present a prominent absorption spectrum with no direct evidence of a non-stellar continuum. Observations were made with the Tololo 1m telescope and 2DFRUTTI detector in the spectral region λλ3700 - 7000 A, with 5A (FWHM) resolution.

Advances in UV Astronomy by the IUE Satellite

AbstractOn 26 January 1978 the International Ultraviolet Explorer (IUE) satellite has been launched into a geosynchronous orbit. Operated jointly by NASA, ESA, and the SERC, it has since collected roughly 50.000 UV spectra of objects of widely different nature such as comets and planets orbiting the Sun, nearby cool late-type stars, interstellar matter in our own and nearby galaxies, local and distant hot early-type stars, entire galaxies, and distant quasars. Even the recent supernova SN 1987a in the Large Magellanic Cloud has been and continues to be a target for this satellite just as many other sources in the sky. A few examples have been selected to highlight some of the unique results that have been achieved through observations with the IUE.

Low-Luminosity Active Nuclei in Elliptical Galaxies

The results of a sensitive radio and optical survey of nearby early-type galaxies show that most (perhaps all) bright ellipticals have ‘active’ nuclei. These are characterized by a central non-thermal radio source and a weak LINER-like optical emission spectrum. There appears to be a smooth continuity in optical and radio properties from the weakest nearby sources to strong radio galaxies. Galaxies with radio sources usually show optical emission lines, but there is no simple relationship between gas content and radio power.