1,345 research outputs found
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 sâest fortement dĂ©gradĂ© pour atteindre â 1,6 % du PIB. Les investissements directs ont enregistrĂ© 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 , 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 and log t; and
(2) a relation between [E/Fe] and in which [E/Fe] is larger in
high- galaxies. Cluster and field ellipticals follow the same
hyperplane, but their (,t) distributions within it differ. Nearly all
cluster galaxies are old; the field ellipticals span a large range in SSP age.
The tight Mg-- 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 . The relation between [E/Fe] and is consistent
with a higher effective yield of Type II SNe elements at higher . 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 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
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