2,033 research outputs found
Irregular conformal blocks, with an application to the fifth and fourth Painlev\'e equations
We develop the theory of irregular conformal blocks of the Virasoro algebra.
In previous studies, expansions of irregular conformal blocks at regular
singular points were obtained as degeneration limits of regular conformal
blocks; however, such expansions at irregular singular points were not clearly
understood. This is because precise definitions of irregular vertex operators
had not been provided previously. In this paper, we present precise definitions
of irregular vertex operators of two types and we prove that one of our vertex
operators exists uniquely. Then, we define irregular conformal blocks with at
most two irregular singular points as expectation values of given irregular
vertex operators. Our definitions provide an understanding of expansions of
irregular conformal blocks and enable us to obtain expansions at irregular
singular points.
As an application, we propose conjectural formulas of series expansions of
the tau functions of the fifth and fourth Painlev\'e equations, using
expansions of irregular conformal blocks at an irregular singular point.Comment: 26 page
Sub-parsec-scale Accleration of the Radio Jet in the Powerful Radio Galaxy NGC 6251
In order to investigate the genesis of powerful radio jet, we have mapped the
central 10 pc region of the nearby radio galaxy NGC 6251 with a 0.2 pc
resolution using Very Long Baseline Interferometer (VLBI) at two radio
frequencies, 5 GHz and 15 GHz, we have found the sub-parsec-scale counterjet
for the first time in this radio galaxy. This discovery allows us to
investigate the jet acceleration based on the relativistic beaming model.Comment: 7 pages with 7 figures. To appear in PASJ, 52, No. 5, Oct. 25, 200
An Origin of the Huge Far-Infrared Luminosity of Starburst Mergers
Recently Taniguchi and Ohyama found that the higher CO to CO
integrated intensity ratios at a transition =1--0, CO)CO) , in a sample of starburst merging
galaxies such as Arp 220 are mainly attributed to the depression of CO
emission with respect to CO. Investigating the same sample of galaxies
analyzed by Taniguchi & Ohyama, we find that there is a tight, almost linear
correlation between the dust mass and CO luminosity. This implies that
dust grains are also depressed in the high- starburst mergers, leading to
the higher dust temperature () in them because of the relative
increase in the radiation density. Nevertheless, the average dust mass () of the high- starburst mergers is higher significantly than that of
non-high galaxies. This is naturally understood because the galaxy mergers
could accumulate a lot of dust grains from their progenitor galaxies together
with supply of dust grains formed newly in the star forming regions. Since
(FIR) given the dust emissivity law, , the increases in both and
explain well why the starburst mergers are so bright in the FIR. We discuss
that the superwind activity plays an important role in destroying dust grains
as well as dense gas clouds in the central region of mergers.Comment: 10 pages (aaspp4.sty), 3 postscript figures (embedded). Accepted for
publication in Astrophysical Journal Letter
Large-scale distributions of mid- and far-infrared emission from the center to the halo of M82 revealed with AKARI
The edge-on starburst galaxy M82 exhibits complicated distributions of
gaseous materials in its halo, which include ionized superwinds driven by
nuclear starbursts, neutral materials entrained by the superwinds, and
large-scale neutral streamers probably caused by a past tidal interaction with
M81. We investigate detailed distributions of dust grains and polycyclic
aromatic hydrocarbons (PAHs) around M82 to understand their interplay with the
gaseous components. We performed mid- (MIR) and far-infrared (FIR) observations
of M82 with the Infrared Camera and Far-Infrared Surveyor on board AKARI. We
obtain new MIR and FIR images of M82, which reveal both faint extended emission
in the halo and very bright emission in the center with signal dynamic ranges
as large as five and three orders of magnitude for the MIR and FIR,
respectively. We detect MIR and FIR emission in the regions far away from the
disk of the galaxy, reflecting the presence of dust and PAHs in the halo of
M82. We find that the dust and PAHs are contained in both ionized and neutral
gas components, implying that they have been expelled into the halo of M82 by
both starbursts and galaxy interaction. In particular, we obtain a tight
correlation between the PAH and H emission, which provides evidence
that the PAHs are well mixed in the ionized superwind gas and outflowing from
the disk.Comment: 12 pages, 8 figures, accepted for publication in A&
AKARI Detections of Hot Dust in Luminous Infrared Galaxies
We present a new sample of active galactic nuclei (AGNs) identified using the
catalog of the AKARI Mid-infrared(MIR) All-Sky Survey. Our MIR search has an
advantage in detecting AGNs that are obscured at optical wavelengths due to
extinction. We first selected AKARI 9micron excess sources with
F(9micron)/F(K_S)>2 where K_S magnitudes were taken from the Two Micron All Sky
Survey. We then obtained follow-up near-infrared spectroscopy with the
AKARI/IRC, to confirm that the excess is caused by hot dust. We also obtained
optical spectroscopy with the Kast Double Spectrograph on the Shane 3-m
telescope at Lick Observatory. On the basis of on these observations, we
detected hot dust with a characteristic temperature of ~500K in two luminous
infrared galaxies. The hot dust is suspected to be associated with AGNs that
exhibit their nonstellar activity not in the optical, but in the near- and
mid-infrared bands, i.e., they harbor buried AGNs. The host galaxy stellar
masses of 4-6 x 10^9 M_sun are small compared with the hosts in
optically-selected AGN populations. These objects were missed by previous
surveys, demonstrating the power of the AKARI MIR All-Sky Survey to widen AGN
searches to include more heavily obscured objects. The existence of multiple
dusty star clusters with massive stars cannot be completely ruled out with our
current data.Comment: 15 pages, 4 figures, to be published in Astronomy & Astrophysic
The AKARI 2.5-5 Micron Spectra of Luminous Infrared Galaxies in the Local Universe
We present AKARI 2.5-5um spectra of 145 local luminous infrared galaxies in
the Great Observatories All-sky LIRG Survey. In all of the spectra, we measure
the line fluxes and EQWs of the polycyclic aromatic hydrocarbon (PAH) at 3.3um
and the hydrogen recombination line Br-alpha, with apertures matched to the
slit sizes of the Spitzer spectrograph and with an aperture covering ~95% of
the total flux in the AKARI 2D spectra. The star formation rates (SFRs) derived
from Br-alpha measured in the latter aperture agree well with SFRs(LIR), when
the dust extinction correction is adopted based on the 9.7um absorption
feature. Together with the Spitzer spectra, we are able to compare the 3.3 and
6.2um PAH features, the two most commonly used near/mid-IR indicators of
starburst (SB) or active galactic nucleus (AGN) dominated galaxies. We find
that the 3.3 and 6.2um PAH EQWs do not follow a linear correlation and at least
1/3 of galaxies classified as AGN-dominated using 3.3um PAH are classified as
starbursts based on 6.2um PAH. These galaxies have a bluer continuum slope than
galaxies that are indicated to be SB-dominated by both PAH features. The bluer
continuum emission suggests that their continuum is dominated by stellar
emission rather than hot dust. We also find that the median Spitzer spectra of
these sources are remarkably similar to the pure SB-dominated sources indicated
by high PAH EQWs in both 3.3 and 6.2um. We propose a revised SB/AGN diagnostic
diagram using 2-5um data. We also use the AKARI and Spitzer spectra to examine
the performance of our new diagnostics and to estimate 3.3um PAH fluxes using
the JWST photometric bands in 0<z<5. Of the known PAH features and mid-IR high
ionization emission lines used as SB/AGN indicators, only the 3.3um PAH feature
is observable with JWST at z>3.5, because the rest of the features at longer
wavelengths fall outside the JWST wavelength coverage.Comment: 13 pages (without appendices), 12 figures, Accepted for publication
in A&
AKARI near-infrared spectroscopy of the aromatic and aliphatic hydrocarbon emission features in the galactic superwind of M 82
Aims. We investigate the properties of hydrocarbon grains in the galactic
superwind of M 82. Methods. With AKARI, we performed near-infrared (2.5 - 4.5
um) spectroscopic observations of 34 regions in M 82 including its northern and
southern halos. Results. Many of the spectra show strong emission at 3.3 um due
to polycyclic aromatic hydrocarbons (PAHs) and relatively weak features at 3.4
- 3.6 um due to aliphatic hydrocarbons. In particular, we clearly detect the
PAH 3.3 um emission and the 3.4 - 3.6 um features in halo regions, which are
located at a distance of 2 kpc away from the galactic center. We find that the
ratios of the 3.4 - 3.6 um features to the 3.3 um feature intensity
significantly increase with distance from the galactic center, while the ratios
of the 3.3 um feature to the AKARI 7 um band intensity do not. Conclusions. Our
results clearly confirm the presence of small PAHs even in a harsh environment
of the halo of M 82. The results also reveal that the aliphatic hydrocarbons
emitting the 3.4 - 3.6 um features are unusually abundant in the halo,
suggesting that small carbonaceous grains are produced by shattering of larger
grains in the galactic superwind.Comment: 5 pages, 3 figures, 1 table, accepted for publication in A&
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