Spitzer Observations of Transient, Extended Dust in Two Elliptical Galaxies: New Evidence of Recent Feedback Energy Release in Galactic Cores

Spitzer observations of extended dust in two optically normal elliptical galaxies provide a new confirmation of buoyant feedback outflow in the hot gas atmospheres around these galaxies. AGN feedback energy is required to prevent wholesale cooling and star formation in these group-centered galaxies. In NGC 5044 we observe interstellar (presumably PAH) emission at 8 microns out to about 5 kpc. Both NGC 5044 and 4636 have extended 70 microns emission from cold dust exceeding that expected from stellar mass loss. The sputtering lifetime of this extended dust in the ~1keV interstellar gas, ~10^7 yrs, establishes the time when the dust first entered the hot gas. Evidently the extended dust originated in dusty disks or clouds, commonly observed in elliptical galaxy cores, that were disrupted, heated and buoyantly transported outward. The surviving central dust in NGC 5044 and 4636 has been disrupted into many small filaments. It is remarkable that the asymmetrically extended 8 micron emission in NGC 5044 is spatially coincident with Halpha+[NII] emission from warm gas. A calculation shows that dust-assisted cooling in buoyant hot gas moving out from the galactic core can cool within a few kpc in about ~10^7 yrs, explaining the optical line emission observed. The X-ray images of both galaxies are disturbed. All timescales for transient activity - restoration of equilibrium and buoyant transport in the hot gas, dynamics of surviving dust fragments, and dust sputtering - are consistent with a central release of feedback energy in both galaxies about 10^7 yrs ago.Comment: 13 pages. Accepted by ApJ; minor typos correcte

Extensive near-infrared (H-band) photometry in Coma

We present extensive and accurate photometry in the near-infrared H band of a complete sample of objects in an area of about 400 arcmin2 toward the Coma cluster of galaxies. The sample, including about 300 objects, is complete down to H~17 mag, the exact value depending on the type of magnitude (isophotal, aperture, Kron) and the particular region studied. This is six magnitudes below the characteristic magnitude of galaxies, well into the dwarfs' regime at the distance of the Coma cluster. For each object (star or galaxy) we provide aperture magnitudes computed within five different apertures, the magnitude within the 22 mag arcsec2 isophote, the Kron magnitude and radius, magnitude errors, as well as the coordinates, the isophotal area, and a stellarity index. Photometric errors are 0.2 mag at the completness limit. This sample is meant to be the zero-redshift reference for evolutionary studies of galaxies.Comment: A&AS in press, paper, with high resolution images & tables are available at http://oacosf.na.astro.it/~andreon/listapub.htm

Morphological classification and structural parameter of galaxies in the Coma and Perseus clusters

We present the results of an isophotal shape analysis of galaxies in the Coma and Perseus clusters. These data, together with those of two previous papers, provide two complete samples of galaxies with reliable Hubble types in rich clusters: 1) all galaxies brighter than m_b = 16.5 falling within one degree (=2.3 Mpc) from the center of the Coma cluster (187 galaxies), 2) all galaxies brighter than m_{Zwicky}=15.7 in a region of 5 deg 3' times 5 deg 27' around the center of the Perseus cluster (139 galaxies). These two complete samples cover 5 orders of magnitude in galaxy density and span areas of 91 and 17 Mpc^2, clustercentric radii up to 2.3 and 6.4 Mpc, for Perseus and Coma respectively. They will be used in subsequent papers to study the dependence of galaxy types on cluster environment and as reference samples in comparisons with distant clusters.Comment: A&AS, in press. 14 pages including 2 figures and 5 tables, A&A macro

La balance des paiements en 2005.

Le solde des transactions courantes s’est fortement dégradé pour atteindre – 1,6 % du PIB. Les investissements directs ont enregistré un rebond significatif.Balance des paiements, transactions courantes, solde commercial, investissements directs, investissements de portefeuille, fusions et acquisitions.

The Stellar Population Histories of Early-Type Galaxies. II. Controlling Parameters of the Stellar Populations

We analyze single-stellar-population (SSP) equivalent parameters for 50 local elliptical galaxies as a function of their structural parameters. These galaxies fill a two-dimensional plane in the four-dimensional space of [Z/H], log t, log $\sigma$, and [E/Fe]. SSP age and velocity dispersion can be taken as the two independent parameters that specify a galaxy's location in this ``hyperplane.'' The hyperplane can be decomposed into two sub-relations: (1) a ``Z-plane,'' in which [Z/H] is a linear function of log $\sigma$ and log t; and (2) a relation between [E/Fe] and $\sigma$ in which [E/Fe] is larger in high-$\sigma$ galaxies. Cluster and field ellipticals follow the same hyperplane, but their ($\sigma$,t) distributions within it differ. Nearly all cluster galaxies are old; the field ellipticals span a large range in SSP age. The tight Mg--$\sigma$ relations of these ellipticals can be understood as two-dimensional projections of the metallicity hyperplane showing it edge-on; the tightness of these relations does not necessarily imply a narrow range of ages at fixed $\sigma$. The relation between [E/Fe] and $\sigma$ is consistent with a higher effective yield of Type II SNe elements at higher $\sigma$. The Z-plane is harder to explain and may be a powerful clue to star formation in elliptical galaxies if it proves to be general. Present data favor a ``frosting'' model in which low apparent SSP ages are produced by adding a small frosting of younger stars to an older base population. If the frosting abundances are close to or slightly greater than the base population, simple two-component models run along lines of constant $\sigma$ in the Z-plane, as required. This favors star formation from well-mixed pre-enriched gas rather than unmixed low-metallicity gas from an accreted object. (Abridged)Comment: To be published in the June 2000 issue of the Astronomical Journal. 28 pages, 13 figures, uses emulateap

The SBF Survey of Galaxy Distances. I. Sample Selection, Photometric Calibration, and the Hubble Constant

We describe a program of surface brightness fluctuation (SBF) measurements for determining galaxy distances. This paper presents the photometric calibration of our sample and of SBF in general. Basing our zero point on observations of Cepheid variable stars, we find that the absolute SBF magnitude in the Kron-Cousins I band correlates well with the mean (V-I)o color of a galaxy according to M_Ibar = (-1.74 +/- 0.07) + (4.5 +/- 0.25) [ (V-I)o - 1.15 ] for 1.0 < (V-I) < 1.3. This agrees well with theoretical estimates from stellar population models. Comparisons between SBF distances and a variety of other estimators, including Cepheid variable stars, the Planetary Nebula Luminosity Function (PNLF), Tully-Fisher (TF), Dn-sigma, SNII, and SNIa, demonstrate that the calibration of SBF is universally valid and that SBF error estimates are accurate. The zero point given by Cepheids, PNLF, TF (both calibrated using Cepheids), and SNII is in units of Mpc; the zero point given by TF (referenced to a distant frame), Dn-sigma and SNIa is in terms of a Hubble expansion velocity expressed in km/s. Tying together these two zero points yields a Hubble constant of H_0 = 81 +/- 6 km/s/Mpc. As part of this analysis, we present SBF distances to 12 nearby groups of galaxies where Cepheids, SNII, and SNIa have been observed.Comment: 29 pages plus 8 figures; LaTeX (AASTeX) uses aaspp4.sty (included); To appear in The Astrophysical Journal, 1997 February 1 issue; Compressed PostScript available from ftp://mars.tuc.noao.edu/sbf