18 research outputs found
Submillimetre line spectrum of the Seyfert galaxy NGC1068 from the Herschel-SPIRE Fourier Transform Spectrometer
The first complete submillimetre spectrum (190-670um) of the Seyfert 2 galaxy
NGC1068 has been observed with the SPIRE Fourier Transform Spectrometer onboard
the {\it Herschel} Space Observatory. The sequence of CO lines (Jup=4-13),
lines from water, the fundamental rotational transition of HF, two o-H_2O+
lines and one line each from CH+ and OH+ have been detected, together with the
two [CI] lines and the [NII]205um line. The observations in both single
pointing mode with sparse image sampling and in mapping mode with full image
sampling allow us to disentangle two molecular emission components, one due to
the compact circum-nuclear disk (CND) and one from the extended region
encompassing the star forming ring (SF-ring). Radiative transfer models show
that the two CO components are characterized by density of n(H_2)=10^4.5 and
10^2.9 cm^-3 and temperature of T=100K and 127K, respectively. The comparison
of the CO line intensities with photodissociation region (PDR) and X-ray
dominated region (XDR) models, together with other observational constraints,
such as the observed CO surface brightness and the radiation field, indicate
that the best explanation for the CO excitation of the CND is an XDR with
density of n(H_2) 10^4 cm^-3 and X-ray flux of 9 erg s^-1 cm^-2, consistent
with illumination by the active galactic nucleus, while the CO lines in the
SF-ring are better modeled by a PDR. The detected water transitions, together
with those observed with the \her \sim PACS Spectrometer, can be modeled by an
LVG model with low temperature (T_kin \sim 40K) and high density (n(H_2) in the
range 10^6.7-10^7.9 cm^-3).Comment: Accepted for publication on the Astrophysical Journal, 30 August 201
Herschel SPIRE-FTS Observations of Excited CO and [CI] in the Antennae (NGC 4038/39): Warm and Cold Molecular Gas
We present Herschel SPIRE-FTS observations of the Antennae (NGC 4038/39), a
well studied, nearby ( Mpc) ongoing merger between two gas rich spiral
galaxies. We detect 5 CO transitions ( to ), both [CI]
transitions and the [NII] transition across the entire system, which
we supplement with ground based observations of the CO , and
transitions, and Herschel PACS observations of [CII] and [OI].
Using the CO and [CI] transitions, we perform both a LTE analysis of [CI], and
a non-LTE radiative transfer analysis of CO and [CI] using the radiative
transfer code RADEX along with a Bayesian likelihood analysis. We find that
there are two components to the molecular gas: a cold ( K)
and a warm ( K) component. By comparing the warm gas mass
to previously observed values, we determine a CO abundance in the warm gas of
. If the CO abundance is the same in the warm and
cold gas phases, this abundance corresponds to a CO luminosity-to-mass
conversion factor of $\alpha_{CO} \sim 7 \ M_{\odot}{pc^{-2} \ (K \ km \
s^{-1})^{-1}}_263\mu m\sim 0.01 L_{\odot}/M_{\odot}G_0\sim 1000$. Finally, we find
that a combination of turbulent heating, due to the ongoing merger, and
supernova and stellar winds are sufficient to heat the molecular gas.Comment: 50 pages, 15 figures, 8 tables, Accepted for publication in The
Astrophysical Journa
Spectral and morphological analysis of the remnant of Supernova 1987A with ALMA & ATCA
We present a comprehensive spectral and morphological analysis of the remnant
of Supernova (SN) 1987A with the Australia Telescope Compact Array (ATCA) and
the Atacama Large Millimeter/submillimeter Array (ALMA). The non-thermal and
thermal components of the radio emission are investigated in images from 94 to
672 GHz ( 3.2 mm to 450 m), with the assistance of a
high-resolution 44 GHz synchrotron template from the ATCA, and a dust template
from ALMA observations at 672 GHz. An analysis of the emission distribution
over the equatorial ring in images from 44 to 345 GHz highlights a gradual
decrease of the east-to-west asymmetry ratio with frequency. We attribute this
to the shorter synchrotron lifetime at high frequencies. Across the transition
from radio to far infrared, both the synchrotron/dust-subtracted images and the
spectral energy distribution (SED) suggest additional emission beside the main
synchrotron component () and the thermal component
originating from dust grains at K. This excess could be due to
free-free flux or emission from grains of colder dust. However, a second
flat-spectrum synchrotron component appears to better fit the SED, implying
that the emission could be attributed to a pulsar wind nebula (PWN). The
residual emission is mainly localised west of the SN site, as the spectral
analysis yields across the western regions,
with around the central region. If there is a PWN in the remnant
interior, these data suggest that the pulsar may be offset westward from the SN
position.Comment: ApJ accepted. 21 pages, emulateapj. References update
Herschel/SPIRE Sub-millimeter Spectra of Local Active Galaxies
We present the sub-millimeter spectra from 450 GHz to 1550 GHz of eleven
nearby active galaxies observed with the SPIRE Fourier Transform Spectrometer
(SPIRE/FTS) onboard Herschel. We detect CO transitions from J_up = 4 to 12, as
well as the two [CI] fine structure lines at 492 and 809 GHz and the [NII] 461
GHz line. We used radiative transfer models to analyze the observed CO spectral
line energy distributions (SLEDs). The FTS CO data were complemented with
ground-based observations of the low-J CO lines. We found that the warm
molecular gas traced by the mid-J CO transitions has similar physical
conditions (n_H2 ~ 10^3.2 - 10^3.9 cm^-3 and T_kin ~ 300 - 800 K) in most of
our galaxies. Furthermore, we found that this warm gas is likely producing the
mid-IR rotational H2 emission. We could not determine the specific heating
mechanism of the warm gas, however it is possibly related to the star-formation
activity in these galaxies. Our modeling of the [CI] emission suggests that it
is produced in cold (T_kin 10^3 cm^-3) molecular gas.
Transitions of other molecules are often detected in our SPIRE/FTS spectra. The
HF J=1-0 transition at 1232 GHz is detected in absorption in UGC05101 and in
emission in NGC7130. In the latter, near-infrared pumping, chemical pumping, or
collisional excitation with electrons are plausible excitation mechanisms
likely related to the AGN of this galaxy. In some galaxies few H2O emission
lines are present. Additionally, three OH+ lines at 909, 971, and 1033 GHz are
identified in NGC7130.Comment: Accepted for publication in ApJ; 20 pages, 9 figure
Observations of Arp 220 using Herschel-SPIRE: An Unprecedented View of the Molecular Gas in an Extreme Star Formation Environment
We present Herschel SPIRE-FTS observations of Arp~220, a nearby ULIRG. The
FTS continuously covers 190 -- 670 microns, providing a good measurement of the
continuum and detection of several molecular and atomic species. We detect
luminous CO (J = 4-3 to 13-12) and water ladders with comparable total
luminosity; very high-J HCN absorption; OH+, H2O+, and HF in absorption; and CI
and NII. Modeling of the continuum yields warm dust, with T = 66 K, and an
unusually large optical depth of ~5 at 100 microns. Non-LTE modeling of the CO
shows two temperature components: cold molecular gas at T ~ 50 K and warm
molecular gas at T ~1350 K. The mass of the warm gas is 10% of the cold gas,
but dominates the luminosity of the CO ladder. The temperature of the warm gas
is in excellent agreement with H2 rotational lines. At 1350 K, H2 dominates the
cooling (~20 L_sun/M_sun) in the ISM compared to CO (~0.4 L_sun/M_sun). We
found that only a non-ionizing source such as the mechanical energy from
supernovae and stellar winds can excite the warm gas and satisfy the energy
budget of ~20 L_sun/M_sun. We detect a massive molecular outflow in Arp 220
from the analysis of strong P-Cygni line profiles observed in OH+, H2O+, and
H2O. The outflow has a mass > 10^{7} M_sun and is bound to the nuclei with
velocity < 250 km/s. The large column densities observed for these molecular
ions strongly favor the existence of an X-ray luminous AGN (10^{44} ergs/s) in
Arp 220.Comment: Accepted in ApJ on September 1, 201
Herschel-ATLAS and ALMA: HATLAS J142935.3-002836, a lensed major merger at redshift 1.027
Context. The submillimetre-bright galaxy population is believed to comprise, aside from local galaxies and radio-loud sources, intrinsically active star-forming galaxies, the brightest of which are lensed gravitationally. The latter enable studies at a level of detail beyond what is usually possible by the observation facility.
Aims. This work focuses on one of these lensed systems, HATLAS J142935.3−002836 (H1429−0028), selected in the Herschel-ATLAS field. Gathering a rich, multi-wavelength dataset, we aim to confirm the lensing hypothesis and model the background source’s morphology and dynamics, as well as to provide a full physical characterisation.
Methods. Multi-wavelength high-resolution data is utilised to assess the nature of the system. A lensing-analysis algorithm that simultaneously fits different wavebands is adopted to characterise the lens. The background galaxy dynamical information is studied by reconstructing the 3D source plane of the ALMA CO (J:4 → 3) transition. Near-IR imaging from HST and Keck-AO allows to constrain rest-frame optical photometry independently for the foreground and background systems. Physical parameters (such as stellar and dust masses) are estimated via modelling of the spectral energy distribution taking source blending, foreground obscuration, and differential magnification into account.
Results. The system comprises a foreground edge-on disk galaxy (at zsp = 0.218) with an almost complete Einstein ring around it. The background source (at zsp = 1.027) is magnified by a factor of μ ~ 8−10 depending on wavelength. It is comprised of two components and a tens-of-kpc-long tidal tail resembling the Antennæ merger. As a whole, the background source is a massive stellar system (1.32-0.41+ 0.63 × 1011 M⊙) forming stars at a rate of 394 ± 90 M⊙ yr-1, and it has a significant gas reservoir MISM = 4.6 ± 1.7 × 1010 M⊙. Its depletion time due to star formation alone is thus expected to be τSF = MISM/ SFR = 117 ± 51 Myr. The dynamical mass of one of the components is estimated to be 5.8 ± 1.7 × 1010 M⊙, and, together with the photometric total mass estimate, it implies that H1429−0028 is a major merger system (1:2.8-1.5+1.8)
Review: Far-infrared instrumentation and technological development for the next decade
This work is licensed under a Creative Commons Attribution 4.0 Unported License.Far-infrared astronomy has advanced rapidly since its inception in the late 1950s, driven by a maturing technology base and an expanding community of researchers. This advancement has shown that observations at far-infrared wavelengths are important in nearly all areas of astrophysics, from the search for habitable planets and the origin of life to the earliest stages of galaxy assembly in the first few hundred million years of cosmic history. The combination of a still-developing portfolio of technologies, particularly in the field of detectors, and a widening ensemble of platforms within which these technologies can be deployed, means that far-infrared astronomy holds the potential for paradigm-shifting advances over the next decade. We examine the current and future far-infrared observing platforms, including ground-based, suborbital, and space-based facilities, and discuss the technology development pathways that will enable and enhance these platforms to best address the challenges facing far-infrared astronomy in the 21st century