171 research outputs found
Infrared 2-4 Micron Spectroscopy and Millimeter Interferometric HCN and HCO+ Observations of the Individual Merging Components of Arp299
We present ground-based infrared K- (2-2.5 micron) and L-band (2.8-4.1
micron) spectroscopy, as well as interferometric observations at 3mm, for the
individual merging components (A, B, and C) of the luminous infrared galaxy Arp
299. We investigate the presence and location of the putative buried active
galactic nucleus (AGN) inferred from previous X-ray observations at E > 10 keV.
Our sub-arcsec-resolution infrared spectra clearly reveal that the putative
buried AGN resides in the nucleus B1 (a subcomponent of B), based on a very low
equivalent width of 3.3 micron polycyclic aromatic hydrocarbon emission, a weak
2.3 micron CO absorption feature, and a large time variation of the K- and
L-band continuum fluxes. In component C, we find strong 3.1 micron ice
absorption at L and weak 2.3 micron CO absorption at K, as expected in a buried
AGN; however, a centrally concentrated young super star cluster is an
alternative possibility because of the modest infrared luminosity and
non-galaxy-nucleus nature of this component. The infrared K- and L-band spectra
of the infrared brightest nucleus, A, are typical of a normal starburst with no
explicit AGN signatures. Our interferometric observations simultaneously obtain
HCN (J=1-0) and HCO+ (J=1-0) emission lines with 4 arcsec resolution, and we
find the HCN to HCO+ brightness-temperature ratios to be as low as those found
in starburst nuclei in all the major merging components of Arp 299. The low
ratio even in the AGN-hosting nucleus B may be due to the presence of a large
amount of high-density molecular gas whose chemistry is dominated by coexisting
starbursts and/or shocks, rather than by the central strong X-ray-emitting AGN.Comment: 20 pages, 8 figures, Accepted for publication in PASJ (Vol. 58, No.
5, 2006 Oct 25 issue
Central Spiral Structure of Molecular Gas in Maffei 2
Distribution and kinematics of molecular gas in the central region of the
barred spiral galaxy Maffei 2 were investigated using a data set of 12CO(1-0),
12CO(2-1), CS(2-1) lines and 103 GHz continuum. We found that the offset ridges
along the kpc-scale bar continue to the central spiral structure embedded in
the weak oval structure which is regarded as x2 orbit in the bar potential. The
spiral structure continues toward the center diverging from the oval structure.
The size of these structures is less than R ~ 100 pc. The mass concentration
within R = 35 pc is estimated to be 2 X 10^8 Mo. The high mass concentration is
consistent with theoretical predictions concerning the creation of such a
nuclear spiral structure. A comparison with the tracers of dense gas and
star-forming region suggests that the dense molecular gas traced by CS(2-1)
line is formed at the crossing points of x1 and x2 orbits and the star-forming
region appears after 2 X 10^5 yr which is comparable with the free-fall time of
the dense gas traced by the CS line (~ 10^5 cm^-3).Comment: 7 pages, 10 figures, Publication of Astronomical Society of Japan, in
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