16 research outputs found
Stellar population analysis on local infrared-selected galaxies
To study the stellar population of local infrared galaxies, which contain
star-forming galaxies, composite galaxies, LINERs, and Seyfert 2s. We also want
to find whether infrared luminosity and spectral class have any effects on
their stellar populations. The sample galaxies are selected from the main
galaxy sample of SDSS-DR4 and then cross-correlated with the IRAS-PSCz catalog.
We fit our spectra (stellar absorption lines and continua) using the spectral
synthesis code STARLIGHT on the base of the templates of Simple Stellar
Population and the spectra of star clusters.Among the 4 spectral classes,
LINERs present the oldest stellar populations, and the other 3 sub-samples all
present substantial young and intermediate age populations and very few old
populations. The importance of young populations decreases from star-forming,
composite, Seyfert 2 to LINER. As to different infrared luminosity bins, ULIGs
& LIGs (log(11) present younger populations than
starbursts and normal galaxies. However, the dominant contributors to mass are
old populations in all sample galaxies. The fittings by using the spectra of
star clusters with different ages and metallicities as templates also give
consistent results. The dominated populations in star-forming and composite
galaxies are those with metallicity , while LINERs and Seyfert 2s
are more metal-rich. The normal galaxies are more metal-rich than the ULIGs &
LIGs and starbursts for the star-forming galaxies within different infrared
luminosity bins. Additionally, we also compare some synthesis results with
other parameters obtained from the MPA/JHU catalog.Comment: 13 pages, 11 figures, accepted for publication by A&
Probing the near infrared stellar population of Seyfert galaxies
We employ IRTF SpeX NIR (0.8-2.4 microns) spectra to investigate the stellar
population (SP), active galactic nuclei (AGN) featureless continuum (FC) and
hot dust properties in 9 Sy 1 and 15 Sy 2 galaxies. Both the starlight code and
the hot dust as an additional base element were used for the first time in this
spectral range. We found evidence of correlation among the equivalent widths
(W) Si I 1.59 microns x Mg I 1.58 microns, equally for both kinds of activity.
Part of the W{Na I 2.21 microns} and W {CO 2.3 microns} strengths may be
related to galaxy inclination. Our synthesis shows significant differences
between Sy 1 and Sy 2 galaxies: the hot dust component is required to fit the
K-band spectra of ~90% of the Sy 1 galaxies, and only of ~25% of the Sy 2;
about 50 % of the Sy 2 galaxies require a component contribution >20%,
while this fraction increases to 60% in the Sy 1; also, in about 50 % of the
Sy2, the combined FC and young components contribute with more than 20%, while
this occurs in 90% of the Sy1, suggesting recent star formation in the central
region. The central few hundred parsecs of our galaxy sample contain a
substantial fraction of intermediate-age SPs with a mean metallicity near
solar. Our SP synthesis confirms that the 1.1 micron CN band can be used as a
tracer of intermediate-age SPs. The simultaneous fitting of SP, FC and hot dust
components increased in ~150% the number of AGNs with hot dust detected and the
mass estimated. The NIR emerges as an excellent window to study the stellar
population of Sy 1 galaxies, as opposed to the usually heavily attenuated
optical range. Our approach opens a new way to investigate and quantify the
individual contribution of the three most important NIR continuum components
observed in AGNs.Comment: The paper contains 14 figures and 5 tables. Accepted for publication
in MNRA
Stellar population properties for a sample of hard X-ray AGNs
The aim of this paper is to study the stellar population of galaxies hosting
an active galactic nucleus (AGN). We studied a sub-sample of hard X-ray
emitting AGNs from the INTEGRAL and Swift catalogs which were previously
identified and characterized through optical spectroscopy. Our analysis
provides complementary information, namely age and metallicity, which is
necessary to complete the panoramic view of such interesting objects.
We selected hard X-ray emitting objects identified as AGNs by checking their
optical spectra in search for absorption lines suitable for the stellar
population analysis. We obtained a final sample consisting of 20 objects with
redshift lower than 0.3. We used the full-spectrum fitting method and, in
particular, the penalized pixel one applying the PPXF code. After masking all
the regions affected by emission lines, we fitted the spectra with the MILES
single stellar population templates and we derived mass-weighted ages and
metallicities.
Most of the objects in our sample show an old stellar population, but three
of them are characterized by a bimodal distribution with a non negligible
contribution from young stars. The values of the mass-weighted metallicity span
a large range of metallicity with most of them slightly above the solar value.
No relations between the stellar population properties and the morphological
ones have been found.Comment: 10 pages, 8 postscript figures and 3 tables. A&A in pres
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