1,456 research outputs found
1.65mic (H-band) surface photometry of galaxies. VI: The history of star formation in normal late-type galaxies
We have collected a large body of NIR (H band), UV (2000 A) and Halpha
measurements of late-type galaxies. These are used, jointly with spectral
evolutionary synthesis models, to study the initial mass function (IMF) in the
mass range m > 2 Mo. For spirals (Sa-Sd), Magellanic irregulars (Im) and blue
compact dwarfs (BCD), our determination is consistent with a Salpeter IMF with
an upper mass cutoff M_up = 80 Mo. The history of star formation and the amount
of total gas (per unit mass) of galaxies are found to depend primarily on their
total masses (as traced by the H band luminosities) and only secondarily on
morphological type. The present star formation activity of massive spirals is
up to 100 times smaller than that average over their lifetime, while in low
mass galaxies it is comparable to or higher than that at earlier epochs. Dwarf
galaxies have presently larger gas reservoirs per unit mass than massive
spirals. The efficiency in transforming gas into stars and the time scale for
gas depletion (10 Gyrs) are independent of the luminosity and/or of the
morphological type. These evidences are consistent with the idea that galaxies
are coeval systems,that they evolved as closed-boxes forming stars following a
simple, universal star formation law whose characteristic time scale is small
(1 Gyr) in massive spirals and large (10 Gyr) in low mass galaxies. A similar
conclusion was drawn by Gavazzi and Scodeggio (1996) to explain the
colour-magnitude relation of late-type galaxies. The consequences of this
interpretation on the evolution of the star formation rate and of the gas
density per comoving volume of the Universe with look-back time are discussed.Comment: LaTex, 24 pages, 12 figures, accepted for publication on Astronomical
Journa
Introducing GOLDMine: A new Galaxy Database on the WEB
The new World Wide Web site "GOLDMine" (Galaxy On Line Database Milano
Network) (http://goldmine.mib.infn.it) contains a multiwavelength data-base of
an optically selected sample of 3267 galaxies in the Virgo cluster and in the
Coma Supercluster. It is designed for professional astronomers who wish to find
data and images for these galaxies.
Data, gathered in 15 years of observational campaigns by the authors or taken
from the literature include general parameters (catalogue names, celestial
coordinates, morphological type, recessional velocity etc.); multiwavelength
continuum photometry (total UV, U, B, V, J, H, K, FIR and radio magnitudes/flux
densities); line photometry (HI, H_2, H_alpha); dynamical parameters
(rotational velocity from the HI and H_alpha lines, velocity dispersion) and
structural parameters (light concentration index, effective radius and
brightness, asymptotic magnitude) in the optical (B and V) and Near Infrared (H
or K) bands. Images include finding charts, optical (B and V), H_alpha, Near
Infrared (H and/or K) and true color RGB frames (when available). Radial light
profiles obtained from the B, V, H or K band images are also available.
Integrated optical spectra along with broad Spectral Energy Distributions (SED)
from the UV to the radio domain are given. All images can be obtained in JPG
format, but the original (reduced) FITS images can be downloaded as well. The
database will be updated regularly and will be extended to other local clusters
and superclusters. Astronomers who wish to have their images included in
GOLDMine are strongly encouraged to send us their material.Comment: 5 pages, 2 figures, accepted for pubblication in Astronomy &
Astrophysic
Radio continuum spectra of galaxies in the Virgo cluster region
New radio continuum observations of galaxies in the Virgo cluster region at
4.85, 8.6, and 10.55 GHz are presented. These observations are combined with
existing measurements at 1.4 and 0.325 GHz. The sample includes 81 galaxies
were spectra with more than two frequencies could be derived. Galaxies that
show a radio-FIR excess exhibit central activity (HII, LINER, AGN). The four
Virgo galaxies with the highest absolute radio excess are found within 2
degrees of the center of the cluster. Galaxies showing flat radio spectra also
host active centers. There is no clear trend between the spectral index and the
galaxy's distance to the cluster center.Comment: 13 pages, 12 figures. Accepted for publication in A&
Mid--IR emission of galaxies in the Virgo cluster: II. Integrated properties
We analyse the integrated properties of the Mid-IR emission of a complete,
optically selected sample of galaxies in the Virgo cluster observed with the
ISOCAM instrument on board the ISO satellite. The analysis shows that the
Mid-IR emission up to 15 mic of optically-selected, normal early-type galaxies
(E, S0 and S0a) is dominated by the Rayleigh-Jeans tail of the cold stellar
component. The Mid-IR emission of late-type galaxies is instead dominated by
the thermal emission from dust. The small dust grains emitting in the Mid-IR
have an excess of emission if compared to big grains emitting in the Far-IR.
While the Far-IR emission increases with the intensity of the interstellar
radiation field, their Mid-IR emission is non--linearly related to the UV
radiation field. The spectral energy distributions of the target galaxies
indicate that there is a linear relationship between the UV radiation field and
the Mid-IR emission of galaxies for low or intermediate activities of star
formation, while the emission from the hot dust seems to drop for strong UV
fields. The Mid-IR colour of late-type galaxies is not related to their
activity of star formation. The properties of the dust emission in the Mid-IR
seem more related to the mass than to the morphological type of the target
galaxy. Since the activity of star formation is anticorrelated to the mass of
galaxies, this reflects a relationship between the emission of dust in the
Mid-IR and the UV radiation field: galaxies with the lowest Mid-IR emission for
a given UV field are low mass, dwarf galaxies. These observational evidences
are easily explained if the carriers of the Unidentified Infrared Bands that
dominate the 6.75 mic emission are destroyed by the intense UV radiation field
of dwarf galaxies, although abundance effects can also play a role.Comment: 17 pages, Latex, 7 figures; to be published in Astronomy &
Astrophysics, Main Journal; Figure legend should be corrected in: 1 - 1a; 2 -
1b; 3 - 2; 4 - 3a; 5 - 3b; 6 - 3c; 7 - 3d; 8 - 3e; 9 - 4; 10 - 5; 11 - 6; 12
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The census of nuclear activity of late-type galaxies in the Virgo cluster
The first spectroscopic census of AGNs associated to late-type galaxies in
the Virgo cluster is carried on by observing 213 out of a complete set of 237
galaxies more massive than M_dyn>10^{8.5} solar masses. Among them, 77 are
classified as AGNs (including 21 transition objects, 47 LINERs and 9 Seyferts),
and comprize 32% of the late-type galaxies in Virgo. Due to spectroscopic
incompleteness at most 21 AGNs are missed in the survey, so that the fraction
would increase up to 41%. Using corollary Near-IR observations, that enable us
to estimate galaxies dynamical masses, it is found that AGNs are hosted
exclusively in massive galaxies, i.e. M_dyn\gsim 10^{10} solar masses. Their
frequency increases steeply with the dynamical mass from zero at
M_dyn\approx10^{9.5} solar masses to virtually 1 at M_dyn>10^{11.5} solar
masses. These frequencies are consistent with the ones of low luminosity AGNs
found in the general field by the SDSS. Massive galaxies that harbor AGNs
commonly show conspicuous r-band star-like nuclear enhancements. Conversely
they often, but not necessarily contain massive bulges. Few well known AGNs
(e.g. M61, M100, NGC4535) are found in massive Sc galaxies with little or no
bulge. The AGN fraction seems to be only marginally sensitive to galaxy
environment. We infer the black hole masses using the known scaling relations
of quiescent black holes. No black holes lighter than \msol are
found active in our sample.Comment: The paper contains 13 figures and 5 tables; accepted for publication
in MNRA
Campus and Community Leadership in the Spotlight: How University Presidents and City Managers View Town/Gown Relationships
This paper begins by reviewing literature that underscores the critical role university presidents play in establishing functional campus/community relationships. Using the metaphor of marriage, a conceptual and methodological framework is offered for understanding and assessing the quality of the town/gown interaction. The presentation of a town/gown relationship model based on the twin dimensions of effort and comfort levels sets the stage for the presentation of results from interviews conducted with university presidents and city managers that focused specific attention on their perceptions of town/gown relationship types. More specifically, these leaders were asked to discuss the type of relationship they inherited at the start of their tenure, as well as how the town/gown interactions in which they were immersed had evolved over time. Finally, themes are presented as a set of “Town/Gown Ten Commandments” that highlight the critical role both campus and community leaders play in the development and maintenance of harmonious town/gown relationships
Teaching Excellence: The Core of the Land-Grant Mission
The tripartite mission of the land-grant university – teaching, research, and community engagement – has evolved over the course of the past 150 years. The intensified concentration on empirical activities in the last half century, however, is thought to have created a mission-related imbalance that often has relegated teaching and community engagement activities to second-tier status within the academy. In tandem, there have been several unforced errors on the part of universities that have diminished the public’s belief in the return on investment associated with a college degree. The argument is made for an increased emphasis on teaching and learning activities in order to properly align the land-grant mission for the 21st century needs of our nation
The tilt of the Fundamental Plane of Early-type galaxies: wavelength dependence
The photometric parameters R_e and mu_e of 74 early-type (E+S0+S0a) galaxies
in the Coma cluster are derived for the first time in the near IR H band. These
are used, coupled with measurements of the central velocity dispersion found in
the literature, to determine the H band Fundamental Plane (FP) relation of this
cluster. The same procedure is applied to previously available photometric data
in the B, V, r, I, and K bands, to perform a multi-wavelength study of the FP.
Because systematic uncertainties in the value of the FP parameters are
introduced both by the choice of the fitting algorithm, and by the presence of
statistical biases connected with the sample selection procedure, we emphasize
the importance of deriving the FP parameters in the six photometric bands using
an identical fitting algorithm, and appropriate corrections to eliminate the
effects of sample incompleteness. We find that the FP mu_e coefficient is
stable with wavelength, while the sigma coefficient increases significantly
with increasing wavelength, in agreement with an earlier result presented by
Pahre & Djorgovski. The slope of the FP relation, although changing with
wavelength, never approaches the virial theorem expectation. We also find that
the magnitude of the slope change can be entirely explained by the presence of
the well known relation between color and magnitude among early-type galaxies.
We conclude that the tilt of the Fundamental Plane is significant, and must be
due to some form of broken homology among early-type galaxies, while its
wavelength dependence derives from whatever mechanism (currently the preferred
one is the existence of a mass-metal content sequence) produces the
color-magnitude relation in those galaxies.Comment: 8 pages, 7 figures, 6 tables; table 3 should be printed in landscape
mode, and inserted into the text. Accepted for publication in MNRA
1.65 micron (H-band) surface photometry of galaxies. VIII: the near-IR k-space at z=0
We present the distribution of a statistical sample of nearby galaxies in the
k-space (k1 ~ log M, k2 ~ log Ie, k3 ~ log M/L). Our study is based on near-IR
(H-band: lambda = 1.65 micron) observations, for the first time comprising
early- and late-type systems. Our data confirm that the mean effective
dynamical mass-to-light ratio M/L of the E+S0+S0a galaxies increases with
increasing effective dynamical mass M, as expected from the existence of the
Fundamental Plane relation. Conversely, spiral and Im/BCD galaxies show a broad
distribution in M/L with no detected trend of M/L with M, the former galaxies
having M/L values about twice larger than the latter, on average. For all the
late-type galaxies, the M/L increases with decreasing effective surface
intensity Ie, consistent with the existence of the Tully--Fisher relation.
These results are discussed on the basis of the assumptions behind the
construction of the k-space and their limitations. Our study is complementary
to a previous investigation in the optical (B-band: lambda = 0.44 micron) and
allows us to study wavelength-dependences of the galaxy distribution in the
k-space. As a first result, we find that the galaxy distribution in the k1--k2
plane reproduces the transition from bulge-less to bulge-dominated systems in
galaxies of increasing dynamical mass. Conversely, it appears that the M/L of
late-types is higher (lower) than that of early-types with the same M in the
near-IR (optical). The origins of this behaviour are discussed in terms of dust
attenuation and star formation history.Comment: 11 pages, 1 Postscript table, 3 Postscript figures, accepted for
publication in MNRA
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