747 research outputs found
Energy Diagnoses of Nine Infrared Luminous Galaxies Based on 3--4 Micron Spectra
The energy sources of nine infrared luminous galaxies (IRLGs) are diagnosed
based on their ground-based 3--4 m spectra. Both the equivalent width of
the 3.3 m polycyclic aromatic hydrocarbon (PAH) emission feature and the
3.3 m PAH to far-infrared luminosity ratio () are
analyzed. Assuming nuclear compact starburst activity in these sources produces
the 3.3 m PAH emission as strongly as that in starburst galaxies with
lower far-infrared luminosities, the followings results are found: For six
IRLGs, both the observed equivalent widths and the ratios
are too small to explain the bulk of their far-infrared luminosities by compact
starburst activity, indicating that active galactic nucleus (AGN) activity is a
dominant energy source. For the other three IRLGs, while the 3.3 m PAH
equivalent widths are within the range of starburst galaxies, the
ratios after correction for screen dust extinction are a
factor of 3 smaller. The uncertainty in the dust extinction correction
factor and in the scatter of the intrinsic ratios for
starburst galaxies do not allow a determination of the ultimate energy sources
for these three IRLGs.Comment: 29 pages, 2 figures, Accepted for publication in Ap
A Study of the Populations of X-ray Sources in the Small Magellanic Cloud with ASCA
The Advanced Satellite for Cosmology and Astrophysics (ASCA) has made
multiple observations of the Small Magellanic Cloud (SMC). X-ray mosaic images
in the soft (0.7--2.0 keV) and hard (2.0--7.0 keV) bands are separately
constructed, and the latter provides the first hard X-ray view of the SMC. We
extract 39 sources from the two-band images with a criterion of S/N>5, and
conduct timing and spectral analyses for all of these sources. Coherent
pulsations are detected from 12 X-ray sources; five of which are new
discoveries. Most of the 12 X-ray pulsars are found to exhibit long-term flux
variabilities, hence they are likely to be X-ray binary pulsars (XBPs). On the
other hand, we classify four supernova remnants (SNRs) as thermal SNRs, because
their spectra exhibit emission lines from highly ionized atoms. We find that
XBPs and thermal SNRs in the SMC can be clearly separated by their hardness
ratio (the ratio of the count rate between the hard and soft bands). Using this
empirical grouping, we find many XBP candidates in the SMC, although no
pulsations have yet been detected from these sources. Possible implications on
the star-formation history and evolution of the SMC are presented by a
comparison of the source populations in the SMC and our Galaxy.Comment: 11 pages, 39 Figures, to be published in ApJ Supplement. Tables (body
and figures also) are available at
http://www-cr.scphys.kyoto-u.ac.jp/member/jun/job
Hard X-ray Luminosities of Multinuclei Infrared Luminous Galaxies Showing a Radio/Far-Infrared Excess
We report the results of hard X-ray observations of four multinuclei merging
infrared luminous galaxies (IRLGs). We selected these four sources for their
excess of radio to far-infrared luminosity ratio compared with starburst
galaxies. This excess suggests that activity associated with a supermassive
black hole (SMBH) contributes strongly to the IRLGs' bolometric luminosities.
Although we expect strong hard X-ray emission from the SMBH-driven activity,
the radio-excess multinuclei merging IRLGs show considerably smaller hard X-ray
luminosities relative to far-infrared (40500 m) and infrared (81000
m) luminosities than active galactic nuclei (AGNs) showing a similar
radio-excess. This result may demonstrate that emission in the hard X-ray
region from SMBH-driven activity in the multinuclei merging IRLGs is severely
suppressed compared to a typical spectral energy distribution of SMBH-driven
activity in AGNs. If this is a common property of merging IRLGs, without its
correction, hard X-ray observations underestimate the contribution of
SMBH-driven activity to the bolometric luminosities of merging IRLGs.Comment: 25 pages of text, 4 figures, aaspp4.sty, Astrophysical Journal, in
press (1999, Volume 527
On the disappearance of a cold molecular torus around the low-luminosity active galactic nucleus of NGC 1097
We used the Atacama Large Millimeter/submillimeter Array (ALMA) to map the
CO(3-2) and the underlying continuum emissions around the type 1 low-luminosity
active galactic nucleus (LLAGN; bolometric luminosity
erg~s) of NGC 1097 at pc resolution. These observations
revealed a detailed cold gas distribution within a pc of this LLAGN.
In contrast to the luminous Seyfert galaxy NGC 1068, where a pc cold
molecular torus was recently revealed, a distinctively dense and compact torus
is missing in our CO(3-2) integrated intensity map of NGC 1097. Based on the
CO(3-2) flux, the gas mass of the torus of NGC 1097 would be a factor of
less than that found for NGC 1068 by using the same CO-to-H
conversion factor, which implies less active nuclear star formation and/or
inflows in NGC 1097. Our dynamical modeling of the CO(3-2) velocity field
implies that the cold molecular gas is concentrated in a thin layer as compared
to the hot gas traced by the 2.12 m H emission in and around the
torus. Furthermore, we suggest that NGC 1097 hosts a geometrically thinner
torus than NGC 1068. Although the physical origin of the torus thickness
remains unclear, our observations support a theoretical prediction that
geometrically thick tori with high opacity will become deficient as AGNs evolve
from luminous Seyferts to LLAGNs.Comment: 9 pages, 5 figures. Accepted for publication in ApJ
Molecular lines as tracers of Compton-thick AGN ?
Recently, Papadopoulos et al., 2010 using sub-mm CO molecular line
observations of nearby ultra-luminous IRAS galaxies, (U)LIRGs, have found that
exceptionally large gas column densities (N_H > 10^25 cm-2) can be present
across some of the very dense gaseous disks that are typically found in these
objects. They also proposed a diagnostic for finding such sources using CO and
HCN molecular lines. Given that such high column densities are expected to
absorb any X-ray luminous AGN, yielding Compton-thick sources, we set out
toexplore whether this can be discerned using X-ray observations. More
specifically we examine X-ray spectral observations of 14 sources in their
sample, using public Chandra observations (0.5-10 keV) for eleven sources as
well as BeppoSAX results (2-100 keV) from the literature for another three
sources. Our goal is to find candidate Compton-thick AGN and to check whether
the molecular line selection criterion is successful in selecting such systems.
X-ray spectroscopy reveals four candidate Compton-thick AGN of which half fall
within the high obscuration region in the molecular line ratio diagnostics. Of
the remaining five sources falling into the `high dust obscuration' box, one
(Mrk273) is highly obscured (N_H ~4x10^23 cm-2) while in the other four the
X-ray emission is most probably associated with star-forming processes rather
than an AGN on the basis of their X-ray and mid-infrared properties. Overall,
we argue that although this method as expected cannot recover all Compton-thick
AGN, there are no examples of X-ray luminous AGN inside that region that have
low obscuration, suggesting that this method is efficient in finding heavily
obscured AGN in dust-enshrouded star-forming galaxies. The above results bear
important implications for future joint ALMA and X-ray observations for the
detection of Compton-thick AGN.Comment: To appear in A&A Letter
Comparison of Nuclear Starburst Luminosities between Seyfert 1 and 2 Galaxies Based on Near-infrared Spectroscopy
We report on infrared K- (2-2.5 micron) and L-band (2.8-4.1 micron) slit
spectroscopy of 23 Seyfert 1 galaxies in the CfA and 12 micron samples. A
polycyclic aromatic hydrocarbon (PAH) emission feature at 3.3 micron in the L
band is primarily used to investigate nuclear star-forming activity in these
galaxies. The 3.3 micron PAH emission is detected in 10 sources (=43%),
demonstrating that detection of nuclear star-formation in a significant
fraction of Seyfert 1 galaxies is now feasible. For the PAH-detected nuclei,
the surface brightness values of the PAH emission are as high as those of
typical starbursts, suggesting that the PAH emission probes the putative
nuclear starbursts in the dusty tori around the central active galactic nuclei
(AGNs). The magnitudes of the nuclear starbursts are quantitatively estimated
from the observed 3.3 micron PAH emission luminosities. The estimated starburst
luminosities relative to some indicators of AGN powers in these Seyfert 1s are
compared with 32 Seyfert 2s in the same samples that we have previously
observed. We find that there is no significant difference in nuclear starburst
to AGN luminosity ratios between Seyfert 1 and 2 galaxies, and that nuclear
starburst luminosity positively correlates with AGN power in both types of
Seyferts. Our results favor a slightly-modified AGN unification model, which
predicts that nuclear starbursts occurring in the dusty tori of Seyferts are
physically connected to the central AGNs, rather than the classical unification
paradigm, in which the dusty tori simply hide the central AGNs of Seyfert 2s
and reprocess AGN radiation as infrared dust emission in Seyferts. No
significant differences in nuclear star formation properties are recognizable
between Seyfert 1s in the CfA and 12 micron samples.Comment: 39 pages, 6 figures, Accepted for publication in ApJ (10 December
2004, vol 617 issue
The Patterns of High-Level Magnetic Activity Occurring on the Surface of V1285 Aql: The OPEA Model of Flares and DFT Models of Stellar Spots
Statistically analyzing Johnson UBVR observations of V1285 Aql during the
three observing seasons, both activity level and behavior of the star are
discussed in respect to obtained results. We also discuss the out-of-flare
variation due to rotational modulation. Eighty-three flares were detected in
the U-band observations of season 2006 . First, depending on statistical
analyses using the independent samples t-test, the flares were divided into two
classes as the fast and the slow flares. According to the results of the test,
there is a difference of about 73 s between the flare-equivalent durations of
slow and fast flares. The difference should be the difference mentioned in the
theoretical models. Second, using the one-phase exponential association
function, the distribution of the flare-equivalent durations versus the flare
total durations was modeled. Analyzing the model, some parameters such as
plateau, half-life values, mean average of the flare-equivalent durations,
maximum flare rise, and total duration times are derived. The plateau value,
which is an indicator of the saturation level of white-light flares, was
derived as 2.421{\pm}0.058 s in this model, while half-life is computed as 201
s. Analyses showed that observed maximum value of flare total duration is 4641
s, while observed maximum flare rise time is 1817 s. According to these
results, although computed energies of the flares occurring on the surface of
V1285 Aql are generally lower than those of other stars, the length of its
flaring loop can be higher than those of more active stars.Comment: 44 pages, 10 figures, 5 tables, 2011PASP..123..659
Further studies of 1E 1740.7-2942 with ASCA
We report the ASCA results of the Great Annihilator 1E 1740.7-2942 obtained
with five pointing observations in a time span of 3.5 years. The X-ray spectrum
for each period is well fitted with a single power-law absorbed by a high
column of gas. The X-ray flux changes by a factor of 2 from period to period,
but the other spectral parameters show no significant change. The photon index
is flat with \Gamma = 0.9--1.3. The column densities of hydrogen N_H is
1.0 x 10^{23} H cm^{-2} and that of iron N_{Fe} is 10^{19} Fe cm^{-2}.
These large column densities indicate that 1E 1740.7-2942 is near at the
Galactic Center. The column density ratio leads the iron abundance to be 2
times larger than the other elements in a unit of the solar ratio. The
equivalent width of the K\alpha-line from a neutral iron is less than 15 eV in
90% confidence. This indicates that the iron column density within several
parsecs from 1E 1740.7-2942 is less than 5 x 10^{17} Fe cm^{-2}. In addition,
the derived hydrogen column density is about 1/6 of that of giant molecular
clouds in the line of sight. All these facts support that 1E 1740.7-2942 is not
in a molecular cloud, but possibly in front of it; the X-rays are not powered
by accretion from a molecular cloud, but from a companion star like ordinary
X-ray binaries.Comment: To appear in ApJ July 20, 1999 issue, Vol. 520 #1, 23 pages LaTeX
files, uses aasms4.sty and psfig.sty, also available at
http://www-cr.scphys.kyoto-u.ac.jp/member/sakano/work/paper/index-e.htm
Molecules as tracers of galaxy evolution: an EMIR survey. I. Presentation of the data and first results
We investigate the molecular gas properties of a sample of 23 galaxies in
order to find and test chemical signatures of galaxy evolution and to compare
them to IR evolutionary tracers. Observation at 3 mm wavelengths were obtained
with the EMIR broadband receiver, mounted on the IRAM 30 m telescope on Pico
Veleta, Spain. We compare the emission of the main molecular species with
existing models of chemical evolution by means of line intensity ratios
diagrams and principal component analysis. We detect molecular emission in 19
galaxies in two 8 GHz-wide bands centred at 88 and 112 GHz. The main detected
transitions are the J=1-0 lines of CO, 13CO, HCN, HNC, HCO+, CN, and C2H. We
also detect HC3N J=10-9 in the galaxies IRAS 17208, IC 860, NGC 4418, NGC 7771,
and NGC 1068. The only HC3N detections are in objects with HCO+/HCN<1 and warm
IRAS colours. Galaxies with the highest HC3N/HCN ratios have warm IRAS colours
(60/100 {\mu}m>0.8). The brightest HC3N emission is found in IC 860, where we
also detect the molecule in its vibrationally excited state.We find low HNC/HCN
line ratios (<0.5), that cannot be explained by existing PDR or XDR chemical
models. Bright HC3N emission in HCO+-faint objects may imply that these are not
dominated by X-ray chemistry. Thus the HCN/HCO+ line ratio is not, by itself, a
reliable tracer of XDRs. Bright HC3N and faint HCO+ could be signatures of
embedded starformation, instead of AGN activity
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