1,390 research outputs found
Low redshift star-forming galaxies: What can they teach us about primeval galaxies?
The analysis of the UV plus optical spectra of three star-forming galaxies, Mrk 496, Mrk 357, TOL1924-416, obtained by matching the size of the optical aperture with that of IUE, has given unexpected results. These can be summarized as follows: (1) the dereddened Ly(alpha)/H(beta) ratios are consistent with the prediction of case B recombination for nebular emission, within the uncertainties; (2) the decrease of the Ly(alpha)/H(beta) ratio with increasing metallicities is not confirmed in our three objects, although the sample is too small to consider this result definitive. The first result is surprising, mainly because at least the two Markarian galaxies have a large enough H1 content to markedly increase the optical depth for the Ly(alpha) photons and to trigger their absorption by dust. This finding can probably be explained as an effect of the inhomogeneous distribution of gas and dust within the galaxies. On the basis of these results, we conclude that the detection of the Ly(alpha) emission line in searching for primeval galaxies (PG's) can be still considered a valid technique
Characterizing Dust Attenuation in Local Star-Forming Galaxies: Near-Infrared Reddening and Normalization
We characterize the near-infrared (NIR) dust attenuation for a sample of
~5500 local (z<0.1) star-forming galaxies and obtain an estimate of their
average total-to-selective attenuation . We utilize data from the
United Kingdom Infrared Telescope (UKIRT) and the Two Micron All-Sky Survey
(2MASS), which is combined with previously measured UV-optical data for these
galaxies. The average attenuation curve is slightly lower in the far-UV than
local starburst galaxies, by roughly 15%, but appears similar at longer
wavelengths with a total-to-selective normalization at V-band of
. Under the assumption of energy balance,
the total attenuated energy inferred from this curve is found to be broadly
consistent with the observed infrared dust emission () in a small
sample of local galaxies for which far-IR measurements are available. However,
the significant scatter in this quantity among the sample may reflect large
variations in the attenuation properties of individual galaxies. We also derive
the attenuation curve for sub-populations of the main sample, separated
according to mean stellar population age (via ), specific star
formation rate, stellar mass, and metallicity, and find that they show only
tentative trends with low significance, at least over the range which is probed
by our sample. These results indicate that a single curve is reasonable for
applications seeking to broadly characterize large samples of galaxies in the
local Universe, while applications to individual galaxies would yield large
uncertainties and is not recommended.Comment: 14 pages, 10 figures, 1 table. Accepted for publication in Ap
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Nearby Galaxies with Spitzer
We review the main advances brought by the Spitzer Space Telescope in the field of nearby galaxies studies, concentrating on a few subject areas, including: (1) the physics of the Polycyclic Aromatic Hydrocarbons that generate the mid–infrared features between 3.5 ìm and 20 ìm; (2) the use of the mid– and far–infrared emission from galaxies as star formation rate indicators; and (3) the improvement of mid–infrared diagnostics to discriminate between thermal (star–formation)and non–thermal (AGN) emission in galaxies and galaxy centers
The Spectral Energy Distribution of Normal, Starburst and Active Galaxies
We present the results of an extensive literature search of multiwavelength
data for a sample of 59 galaxies, consisting of 26 Starbursts, 15 Seyfert 2's,
5 LINER's, 6 normal spirals and 7 normal elliptical galaxies. The data include
soft X-ray fluxes, ultraviolet and optical spectra, near, mid/far infrared
photometry and radio measurements, selected to match as closely as possible the
IUE aperture (10" X 20"). The galaxies are separated into 6 groups with similar
characteristics, namely, Ellipticals, Spirals, LINER's, Seyfert 2's, Starbursts
of Low and High reddening, for which we create average spectral energy
distributions (SED). The individual groups SED's are normalized to the
7000\AA flux and compared, looking for similarities and differences
among them.The bolometric fluxes of different types of galaxies were calculated
integrating their SED's. These values are compared with individual waveband
flux densities, in order to determine the wavebands which contribute most to
the bolometric flux. Linear regressions were performed between the bolometric
and individual band fluxes for each kind of galaxy. These fits can be used in
the calculation of the bolometric flux for other objects of similar activity
type, but with reduced waveband information. We have also collected
multiwavelength data for 4 HII regions, a thermal supernova remnant, and a
non-thermal supernova remnant (SNR), which are compared with the Starburst
SED's.Comment: 29 pages, 13 postscript figures and 10 tables. To appear in The
Astronomical Journa
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