2,546 research outputs found
Comparison of dust-to-gas ratios in luminous, ultraluminous, and hyperluminous infrared galaxies
The dust-to-gas ratios in three different samples of luminous, ultraluminous,
and hyperluminous infrared galaxies are calculated by modelling their radio to
soft X-ray spectral energy distributions using composite models which account
for the photoionizing radiation from HII regions, starbursts, or AGNs, and for
shocks. The models are limited to a set which broadly reproduces the mid-IR
fine structure line ratios of local, IR bright, starburst galaxies. The results
show that two types of clouds contribute to the IR emission. Those
characterized by low shock velocities and low preshock densities explain the
far-IR dust emission, while those with higher velocities and densities
contribute to mid-IR dust emission. An AGN is found in nearly all of the
ultraluminous IR galaxies and in half of the luminous IR galaxies of the
sample. High IR luminosities depend on dust-to-gas ratios of about 0.1 by mass,
however, most hyperluminous IR galaxies show dust-to-gas ratios much lower than
those calculated for the luminous and ultraluminous IR galaxies.Comment: 19 pages+ 7 figures. in press in A
Modelling galaxy spectra at redshifts 0.2<z<2.3 by the [OII]/Hb and [OIII]/Hb line ratios
We present the detailed modelling of line spectra emitted from galaxies at
redshifts 0.2<z<2.3. The spectra account only for a few oxygen to Hb line
ratios. The results show that [OII]3727+3729/Hb and [OIII]5007+4959/Hb are not
sufficient to constrain the models. The data at least of an auroral line, e.g.
[OIII]4363, should be known. We have found by modelling the spectra observed
from ultrastrong emission line galaxy and faint galaxy samples, O/H relative
abundances ranging between 1.8 X 10^{-4} and 6.6 X 10^{-4}.Comment: 11 pages, 8 figures. Accepted for publication in Astronomy and
Astrophysic
Activity and quiescence in galaxies at redshifts 1.4<z<3.5. The role of the starburst temperature
We investigate 'activity' and 'quiescence' in galaxies at relatively high
redshifts by modelling the line(and continuum) spectra of each object. The
models account consistently for photoionization and shocks. We claim that the
starburst effective temperature, the flux from an AGN, and the shock velocity
are critical to activity. The results confirm that two sample galaxies show
intense starburst activity with temperatures reaching Ts=2x10^5K and shock
velocities Vs> 250 km/s, while for the remaining galaxies of our sample the
models show quiescent star formation with Ts< 7x10^4K. A Seyfert 2 like AGN is
proposed in one galaxy. The O/H relative abundances derived by the detailed
modelling of the spectra are nearly solar for all the sample galaxies, in
contrast to those obtained by direct methods.Comment: 5 pages, 3 figures, in press in A&
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