98 research outputs found
A Multi-Wavelength Study of Sgr A*: The Role of Near-IR Flares in Production of X-ray, Soft -ray and Sub-millimeter Emission
(abridged) We describe highlights of the results of two observing campaigns
in 2004 to investigate the correlation of flare activity in Sgr A* in different
wavelength regimes, using a total of nine ground and space-based telescopes. We
report the detection of several new near-IR flares during the campaign based on
{\it HST} observations. The level of near-IR flare activity can be as low as
mJy at 1.6 m and continuous up to about 40% of the total
observing time. Using the NICMOS instrument on the {\it HST}, the {\it
XMM-Newton} and CSO observatories, we also detect simultaneous bright X-ray and
near-IR flare in which we observe for the first time correlated substructures
as well as simultaneous submillimeter and near-IR flaring. X-ray emission is
arising from the population of near-IR-synchrotron-emitting relativistic
particles which scatter submillimeter seed photons within the inner 10
Schwarzschild radii of Sgr A* up to X-ray energies. In addition, using the
inverse Compton scattering picture, we explain the high energy 20-120 keV
emission from the direction toward Sgr A*, and the lack of one-to-one X-ray
counterparts to near-IR flares, by the variation of the magnetic field and the
spectral index distributions of this population of nonthermal particles. In
this picture, the evidence for the variability of submillimeter emission during
a near-IR flare is produced by the low-energy component of the population of
particles emitting synchrotron near-IR emission. Based on the measurements of
the duration of flares in near-IR and submillimeter wavelengths, we argue that
the cooling could be due to adiabatic expansion with the implication that flare
activity may drive an outflow.Comment: 48 pages, 12 figures, ApJ (in press
The Resolved Narrow Line Region in NGC4151
We present slitless spectra of the Narrow Line Region (NLR) in NGC4151 from
the Space Telescope Imaging Spectrograph (STIS) on HST, and investigate the
kinematics and physical conditions of the emission line clouds in this region.
Using medium resolution (~0.5 Angstrom) slitless spectra at two roll angles and
narrow band undispersed images, we have mapped the NLR velocity field from 1.2
kpc to within 13 pc (H_o=75 km/s/Mpc) of the nucleus. The inner biconical cloud
distribution exhibits recessional velocities relative to the nucleus to the NE
and approaching velocities to the SW of the nucleus. We find evidence for at
least two kinematic components in the NLR. One kinematic component is
characterized by Low Velocities and Low Velocity Dispersions (LVLVD clouds: |v|
< 400 km/s, and Delta_v < 130 km/s). This population extends through the NLR
and their observed kinematics may be gravitationally associated with the host
galaxy. Another component is characterized by High Velocities and High Velocity
Dispersions (HVHVD clouds: 400 130 km/s). This
set of clouds is located within 1.1 arcsec (~70pc) of the nucleus and has
radial velocities which are too high to be gravitational in origin, but show no
strong correlation between velocity or velocity dispersion and the position of
the radio knots. Outflow scenarios will be discussed as the driving mechanism
for these HVHVD clouds.Comment: 38 pages, 14 figures, accepted by ApJ. For higher resolution images
see http://www.pha.jhu.edu/~kaiser
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A 15 ”m selected sample of hHigh-z starbursts and AGNs
We report results from our Spitzer GO-1 program on IRS spectroscopy of a large sample of Luminous Infrared Galaxies and quasars selected from the European Large Area ISO Survey (ELAIS). The selected ELAIS sources have a wide multi-wavelength coverage, including ISOCAM, ISOPHOT, IRAC
and MIPS (from SWIRE), and optical photometry. Here we present the sample selection and results from the IRS spectroscopy
Dense Molecular Gas Associated with the Circumnuclear Star Forming Ring in the Barred Spiral Galaxy NGC 6951
We present high resolution (3" - 5") observations of CO(1-0) and HCN(1-0)
emission from the circumnuclear star forming ring in the barred spiral galaxy
NGC 6951, a host of a type-2 Seyfert, using the Nobeyama Millimeter Array and
45 m telescope. We find that most of the HCN emission is associated with the
circumnuclear ring, where vigorous star formation occurs. The HCN to CO
integrated intensity ratio is also enhanced in the star forming ring; the peak
value of HCN/CO ratio is 0.18, which is comparable to the ratio in the
starbursts NGC 253 and M82. The formation mechanism of dense molecular gas has
been investigated. We find that the shocks along the orbit crowding do not
promote the formation of the dense molecular gas effectively but enhance the
presence of low density GMCs. Instead, gravitational instabilities of the gas
can account for the dense molecular gas formation. The HCN/CO ratio toward the
Seyfert nucleus of NGC 6951 is a rather normal value (0.086), in contrast with
other Seyferts NGC 1068 and M51 where extremely high HCN/CO value of ~ 0.5 have
been reported.Comment: 33 pages, 17 figures, to appear in the Astrophysical Journa
HST FOC spectroscopy of the NLR of NGC 4151. I. Gas kinematics
We present the results from a detailed kinematic analysis of both
ground-based, and Hubble Space Telescope/Faint Object Camera long-slit
spectroscopy at sub-arcsec spatial resolution, of the narrow-line region of NGC
4151. In agreement with previous work, the extended emission gas (R > 4") is
found to be in normal rotation in the galactic plane, a behaviour that we were
able to trace even across the nuclear region, where the gas is strongly
disturbed by the interaction with the radio jet, and connects smoothly with the
large scale rotation defined by the neutral gas emission. The HST data, at
0.029" spatial resolution, allow us for the first time to truly isolate the
kinematic behaviour of the individual clouds in the inner narrow-line region.
We find that, underlying the perturbations introduced by the radio ejecta, the
general velocity field can still be well represented by planar rotation down to
a radius of ~ 0.5" (30 pc), distance at which the rotation curve has its
turnover.
The most striking result that emerges from our analysis is that the galaxy
potential derived fitting the rotation curve changes from a "dark halo" at the
ENLR distances to dominated by the central mass concentration in the NLR, with
an almost Keplerian fall-off in the 1"< R < 4" interval. The observed velocity
of the gas at 0.5" implies a mass of M ~ 10E9 M(sol) within the inner 60 pc.
The presence of a turnover in the rotation curve indicates that this central
mass concentration is extended. The first measured velocity point (outside the
region saturated by the nucleus) would imply an enclosed mass of ~ 5E7 M(sol)
within R ~ 0.15" (10 pc) which represents an upper limit to any nuclear point
mass.Comment: 30 pages (aaspp4.sty), 14 figures. Fig. 1, 2 and 4 available by
anonymous FTP at 143.54.2.51 (cd /pub/winge) as GIF files; or upon request to
[email protected]. Accepted for publication in the Astrophysical Journal
(part 1
Star Formation Efficiencies at Giant Molecular Cloud Scales in the Molecular Disk of the Elliptical Galaxy NGC 5128 (Centaurus A)
We present ALMA CO (1-0) observations toward the dust lane of the nearest elliptical and radio galaxy, NGC 5128 (Centaurus A), with high angular resolution (similar to 1 \u27\u27, or 18 pc), including information from large to small spatial scales and total flux. We find a total molecular gas mass of 1.6 x 10(9) M-circle dot and reveal the presence of filamentary components more extended than previously seen, up to a radius of 4 kpc. We find that the global star formation rate is similar to 1 M-circle dot yr(-1), which yields a star formation efficiency (SFE) of 0.6 Gyr(-1) (depletion time tau = 1.5 Gyr), similar to those in disk galaxies. We show the most detailed view to date (40 pc resolution) of the relation between molecular gas and star formation within the stellar component of an elliptical galaxy, from a scale of several kiloparsecs to the circumnuclear region close to the powerful radio jet. Although on average the SFEs are similar to those of spiral galaxies, the circumnuclear disk (CND) presents SFEs of 0.3 Gyr(-1), lower by a factor of 4 than the outer disk. The low SFE in the CND is in contrast to the high SFEs found in the literature for the circumnuclear regions of some nearby disk galaxies with nuclear activity, probably as a result of larger shear motions and longer active galactic nucleus feedback. The higher SFEs in the outer disk suggest that only central molecular gas or filaments with sufficient density and strong shear motions will remain in similar to 1 Gyr, which will later result in the compact molecular distributions and low SFEs usually seen in other giant ellipticals with cold gas
A giant molecular cloud catalogue in the molecular disc of the elliptical galaxy NGC5128 (Centaurus A)
We sincerely thank the referee (Erik Rosolowsky) for the careful reading and useful comments to improve our manuscript. We would also like to show our gratitude to him for the kind assistance with the usage of CPROPS in the early stages of this work. REM was supported by the ALMA Japan Research Grant of NAOJ ALMA Project, NAOJ-ALMA-222. DE was supported by JSPS KAKENHI grant number JP 17K14254. DE was supported by the ALMA Japan Research Grant of NAOJ ALMA Project, NAOJ-ALMA-0093. MINK was supported by JSPS KAKENHI grant number JP 15J04974. KK was supported by JSPS KAKENHI grant number JP17H06130 and the NAOJ ALMA Scientific Research grant number 2017-06B. SV acknowledges support by the research projects AYA2014-53506-P and AYA2017-84897-P from the Spanish Ministerio de Economia y Competitividad, and by the Consejer ' ia de Conocimiento, Investigaci ' on y Universidad, Junta de Andaluc ' ia (FQM108) and European Regional Development Fund (ERDF)". This study has been partially financed by the Consejer ' ia de Conocimiento, Investigaci ' on y Universidad, Junta de Andaluc ' ia and European Regional Development Fund (ERDF), ref. SOMM17/6105/UGR. Part of this work was achieved using the grant of Visiting Scholars Program supported by the Research Coordination Committee, National Astronomical Observatory of Japan (NAOJ), National Institutes ofNatural Sciences (NINS). SM would like to thank the Ministry of Science and Technology (MOST) of Taiwan, MOST 107-2119-M-001-020. This research has made use of NASA's Astrophysics Data System. This research has made use of Astropy, a community-developed core PYTHON (http://www.python.org) package for Astronomy (Astropy Collaboration 2013, 2018); IPYTHON (Perez & Granger 2007); MATPLOTLIB (Hunter 2007); APLPY, an open-source plotting package for PYTHON (Robitaille & Bressert 2012), and NUMPY (van derWalt, Colbert & Varoquaux 2011). Data analysis was in part carried out on the open use data analysis computer system at the Astronomy Data Center, ADC, of the National Astronomical Observatory of Japan. This research has made use of the NASA/IPAC Infrared Science Archive, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. This paper makes use of the following ALMA data: ADS/JAO.ALMA#2013.1.00803.S. ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada), MOST and ASIAA (Taiwan), and KASI (Republic ofKorea), in cooperationwith theRepublic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ. The NationalRadio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.We present the first census of giant molecular clouds (GMCs) complete down to 106M and within the inner 4 kpc of the nearest
giant elliptical and powerful radio galaxy, Centaurus A. We identified 689 GMCs using CO(1â0) data with 1 arcsec spatial
resolution (âŒ20 pc) and 2 kmsâ1 velocity resolution obtained with the Atacama Large Millimeter/submillimeter Array. The
I(CO)-N(H2) conversion factor based on the virial method is XCO = (2 ± 1) Ă 1020 cmâ2(K km sâ1)â1 for the entire molecular
disc, consistent with that of the discs of spiral galaxies including the Milky Way, and XCO = (5 ± 2) Ă 1020 cmâ2(K km sâ1)â1
for the circumnuclear disc (CND; within a galactocentric radius of 200 pc). We obtained the GMC mass spectrum distribution
and find that the best truncated power-law fit for the whole molecular disc, with index Îł â2.41 ± 0.02 and upper cut-off
mass âŒ1.3 Ă 107M , is also in agreement with that of nearby disc galaxies. A trend is found in the mass spectrum index from
steep to shallow as we move to inner radii. Although the GMCs are in an elliptical galaxy, the general GMC properties in the
molecular disc are as in spiral galaxies. However, in the CND, large offsets in the line-width-size scaling relations (âŒ0.3 dex
higher than those in the GMCs in the molecular disc), a different XCO factor, and the shallowest GMC mass distribution shape (Îł
= â1.1 ± 0.2) all suggest that there the GMCs are most strongly affected by the presence of the active galactic nucleus and/or
shear motions.ALMA Japan Research Grant of NAOJ ALMA Project NAOJ-ALMA-222
NAOJ-ALMA-0093Ministry of Education, Culture, Sports, Science and Technology, Japan (MEXT)
Japan Society for the Promotion of ScienceGrants-in-Aid for Scientific Research (KAKENHI) JP 17K14254
JP 15J04974
JP17H06130NAOJ ALMA Scientific Research grant 2017-06BSpanish Government AYA2014-53506-P
AYA2017-84897-PJunta de Andalucia FQM108European Commission SOMM17/6105/UGRResearch Coordination Committee, National Astronomical Observatory of Japan (NAOJ), National Institutes ofNatural Sciences (NINS)Ministry of Science and Technology, Taiwan MOST 107-2119-M-001-020
2013.1.00803.
ALMA Observations of Asteroid 3 Juno at 60 Kilometer Resolution
We present Atacama Large Millimeter/submillimeter Array (ALMA) 1.3 mm
continuum images of the asteroid 3 Juno obtained with an angular resolution of
0.042 arcseconds (60 km at 1.97 AU). The data were obtained over a single 4.4
hr interval, which covers 60% of the 7.2 hr rotation period, approximately
centered on local transit. A sequence of ten consecutive images reveals
continuous changes in the asteroid's profile and apparent shape, in good
agreement with the sky projection of the three-dimensional model of the
Database of Asteroid Models from Inversion Techniques. We measure a geometric
mean diameter of 259pm4 km, in good agreement with past estimates from a
variety of techniques and wavelengths. Due to the viewing angle and inclination
of the rotational pole, the southern hemisphere dominates all of the images.
The median peak brightness temperature is 215pm13 K, while the median over the
whole surface is 197pm15 K. With the unprecedented resolution of ALMA, we find
that the brightness temperature varies across the surface with higher values
correlated to the subsolar point and afternoon areas, and lower values beyond
the evening terminator. The dominance of the subsolar point is accentuated in
the final four images, suggesting a reduction in the thermal inertia of the
regolith at the corresponding longitudes, which are possibly correlated to the
location of the putative large impact crater. These results demonstrate ALMA's
potential to resolve thermal emission from the surface of main belt asteroids,
and to measure accurately their position, geometric shape, rotational period,
and soil characteristics.Comment: 8 pages, 3 figures, 2 tables, accepted for publication in the
Astrophysical Journal Letter
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