5 research outputs found
Comparison of AGN and Nuclear Starburst Activity in Seyfert 1 and 2 Galaxies over a Wide Luminosity Range Based on Near-infrared 2-4 micrometer Spectroscopy
We present near-infrared K- (1.9-2.5 micrometer) and L- (2.8-4.2 micrometer)
band spectroscopy of 22 Seyfert nuclei. We use two methods to investigate the
presence of nuclear starbursts: (1) the Polycyclic Aromatic Hydrocarbon (PAH)
emission feature at lambda_rest = 3.3 micrometer in the rest frame of L-band
spectrum (a starburst indicator) and (2) the CO absorption feature at
lambda_rest = 2.3-2.4 micrometer in the rest frame of the K-band spectrum,
originating in the CO molecule. We clearly detected the 3.3 micrometer PAH
emission features in five objects and the CO absorption features in 17 objects.
Seyfert 2 galaxies tend to show bluer K-L colors compared with Seyfert 1
galaxies. We interpret the discrepancy as resulting from relative strength of
stellar emission because AGN emission is affected by dust extinction. The 3.3
micrometer PAH emission luminosity (L_3.3PAH) distributions for the Seyfert 1s
and Seyfert 2s are very similar when normalized to the AGN power.
Star-formation rates estimated from L_3.3PAH could be large enough to inflate
the dusty torus by supernova explosion. We find that L_3.3PAH positively
correlates with N-band luminosity with small aperture over a wide AGN
luminosity range, and is independent of physical area we probed. The results
suggest that nuclear region has a concentration of star formation and the star
formation would control AGN activity.Comment: 21 pages, 9 figures, 3 tables, accepted for publication in PAS
Comparison of AGN and Nuclear Starburst Activity in Seyfert 1 and 2 Galaxies over a Wide Luminosity Range Based on Near-infrared 2-4 micrometer Spectroscopy
We present near-infrared K- (1.9-2.5 micrometer) and L- (2.8-4.2 micrometer)
band spectroscopy of 22 Seyfert nuclei. We use two methods to investigate the
presence of nuclear starbursts: (1) the Polycyclic Aromatic Hydrocarbon (PAH)
emission feature at lambda_rest = 3.3 micrometer in the rest frame of L-band
spectrum (a starburst indicator) and (2) the CO absorption feature at
lambda_rest = 2.3-2.4 micrometer in the rest frame of the K-band spectrum,
originating in the CO molecule. We clearly detected the 3.3 micrometer PAH
emission features in five objects and the CO absorption features in 17 objects.
Seyfert 2 galaxies tend to show bluer K-L colors compared with Seyfert 1
galaxies. We interpret the discrepancy as resulting from relative strength of
stellar emission because AGN emission is affected by dust extinction. The 3.3
micrometer PAH emission luminosity (L_3.3PAH) distributions for the Seyfert 1s
and Seyfert 2s are very similar when normalized to the AGN power.
Star-formation rates estimated from L_3.3PAH could be large enough to inflate
the dusty torus by supernova explosion. We find that L_3.3PAH positively
correlates with N-band luminosity with small aperture over a wide AGN
luminosity range, and is independent of physical area we probed. The results
suggest that nuclear region has a concentration of star formation and the star
formation would control AGN activity.Comment: 21 pages, 9 figures, 3 tables, accepted for publication in PAS
Infrared 3-4 Micron Spectroscopy of Nearby PG QSOs and AGN-Nuclear Starburst Connections in High-luminosity AGN Populations
We present the results of infrared L-band (3-4 micron) slit spectroscopy of
30 PG QSOs at z < 0.17, the representative sample of local high-luminosity,
optically selected AGNs. The 3.3 micron polycyclic aromatic hydrocarbon (PAH)
emission feature is used to probe nuclear (< a few kpc) starburst activity and
to investigate the connections between AGNs and nuclear starbursts in PG QSOs.
The 3.3 micron PAH emission is detected in the individual spectra of 5/30 of
the observed PG QSOs. We construct a composite spectrum of PAH-undetected PG
QSOs and discern the presence of the 3.3 micron PAH emission therein. We
estimate the nuclear-starburst and AGN luminosities from the observed 3.3
micron PAH emission and 3.35 micron continuum luminosities, respectively, and
find that the nuclear-starburst-to-AGN luminosity ratios in PG QSOs are similar
to those of previously studied AGN populations with lower luminosities,
suggesting that AGN-nuclear starburst connections are valid over the wide
luminosity range of AGNs in the local universe. The observed
nuclear-starburst-to-AGN luminosity ratios in PG QSOs with available
supermassive black hole masses are comparable to a theoretical prediction based
on the assumption that the growth of a supermassive black hole is controlled by
starburst-induced turbulence.Comment: 10 pages, 5 figures, accepted for publication in PASJ (No. 63, 2011
March, Subaru special issue
Subaru and Gemini High Spatial Resolution Infrared 18 Micron Imaging Observations of Nearby Luminous Infrared Galaxies
We present the results of a ground-based, high spatial resolution infrared 18
micron imaging study of nearby luminous infrared galaxies (LIRGs), using the
Subaru 8.2-m and Gemini South 8.1-m telescopes. The diffraction-limited images
routinely achieved with these telescopes in the Q-band (17-23 micron) allow us
to investigate the detailed spatial distribution of infrared emission in these
LIRGs. We then investigate whether the emission surface brightnesses are
modest, as observed in starbursts, or are so high that luminous active galactic
nuclei (AGNs; high emission surface brightness energy sources) are indicated.
The sample consists of 18 luminous buried AGN candidates and
starburst-classified LIRGs identified in earlier infrared spectroscopy. We find
that the infrared 18 micron emission from the buried AGN candidates is
generally compact, and the estimated emission surface brightnesses are high,
sometimes exceeding the maximum value observed in and theoretically predicted
for a starburst phenomenon. The starburst-classified LIRGs usually display
spatially extended 18 micron emission and the estimated emission surface
brightnesses are modest, within the range sustained by a starburst phenomenon.
The general agreement between infrared spectroscopic and imaging energy
diagnostic methods suggests that both are useful tools for understanding the
hidden energy sources of the dusty LIRG population.Comment: 17 pages, 3 figures, accepted for publication in AJ (No. 141, 2011
May issue). Higher resolution version is available at
http://optik2.mtk.nao.ac.jp/~imanishi/Paper/20um/20um.pd