An imminent problem in mapping an astronomical object is that the true image is convolved with the sensitivity pattern of the observing telescope and, in addition, degraded by noise and other various ...sources of error. We approach the problem of deconvolving the observed image by introducing a totally scale-free prior map of intensity distributions which, using Bayes' equation, can be combined with observed data to form the posterior map of intensity distributions. Approximate equations for solving out the mean and the dispersion of the map posterior intensities are then derived.
Apart from being an important coolant, water is known to be a tracer of high-velocity molecular gas. Recent models predict relatively high abundances behind interstellar shockwaves. Using the ...Herschel Space Observatory, it is now possible to observe water emission from supersonic molecular outflows at high spectral and spatial resolution. This paper aims to determine the abundance and distribution of water, its kinematics, and the physical conditions of the gas responsible for the water emission. The observed line profile shapes help them understand the dynamics in molecular outflows. Spectral features and components, tracing gas in different excitation conditions, allow them to constrain the density and temperature of the gas. The water emission originates in a region where temperatures are comparable to that of the warm H sub( 2) gas. Thus, the water emission traces a gas component significantly warmer than the gas responsible for the low-J CO emission. The water column densities at the CO peak positions are low.
We present super(12)CO J = 1-0 and J = 2-1 Swedish-ESO Submillimetre Telescope (SEST) observations of the barred spiral galaxy M 83 (NGC 5236). The size of the CO maps is 10' x 10' and they cover the ...entire optical disk. The grid spacing is 11" for CO(J = 1-0) and 11" or 7" for CO(J = 2-1) depending on the position in the galaxy. In total we have obtained spectra in 1900 and 2574 positions in the CO(J = 1-0) and CO(J = 2-1) lines, respectively. The CO emission is strongly peaked toward the nucleus, which breaks up into two separate components in the CO(J = 2-1) data due to the higher spatial resolution. Emission from the bar is strong, in particular on the leading edges of the bar. The molecular gas arms are clearly resolved and can be traced for more than 360 degree . Emission in the inter-arm regions is detected. The average CO (J = 2-1)/(J = 1-0) line ratio is 0.77. The ratio is lower than this on the spiral arms and higher in the inter-arm regions. The arms show regularly spaced concentrations of molecular gas, Giant Molecular Associations (GMA's), whose masses are of the order 10 super(7) M. The total molecular gas mass is estimated to be 3.9 x 10 super(9) M. This mass is comparable to the total HI mass, but H sub(2) dominates in the optical disk. In the disk, H sub(2) and HI show very similar distributions, including small scale clumping. We compare the molecular gas distribution with those of other star formation tracers, such as B and H alpha images.
Aims. Our aim is to observationally investigate the cosmic Dark Ages in order to constrain star and structure formation models, as well as the chemical evolution in the early Universe. Methods. ...Spectral lines from atoms and molecules in primordial perturbations at high redshifts can give information about the conditions in the early universe before and during the formation of the first stars in addition to the epoch of reionisation. The lines may arise from moving primordial perturbations before the formation of the first stars (resonant scattering lines), or could be thermal absorption or emission lines at lower redshifts. The difficulties in these searches are that the source redshift and evolutionary state, as well as molecular species and transition are unknown, which implies that an observed line can fall within a wide range of frequencies. The lines are also expected to be very weak. Observations from space have the advantages of stability and the lack of atmospheric features which is important in such observations. We have therefore, as a first step in our searches, used the Odin (Odin is a Swedish-led satellite project funded jointly by the Swedish National Space Board (SNSB), the Canadian Space Agency (CSA), the National Technology Agency of Finland (Tekes) and Centre National d'Etudes Spatiales (CNES). The Swedish Space Corporation was the prime contractor and also is responsible for the satellite operation.) satellite to perform two sets of spectral line surveys towards several positions. The first survey covered the band 547–578 GHz towards two positions, and the second one covered the bands 542.0–547.5 GHz and 486.5–492.0 GHz towards six positions selected to test different sizes of the primordial clouds. Two deep searches centred at 543.250 and 543.100 GHz with 1 GHz bandwidth were also performed towards one position. The two lowest rotational transitions of H2 will be redshifted to these frequencies from z ~ 20–30, which is the predicted epoch of the first star formation. Results. No lines are detected at an rms level of 14–90 and 5–35 mK for the two surveys, respectively, and 2–7 mK in the deep searches with a channel spacing of 1–16 MHz. The broad bandwidth covered allows a wide range of redshifts to be explored for a number of atomic and molecular species and transitions. From the theoretical side, our sensitivity analysis show that the largest possible amplitudes of the resonant lines are about 1 mK at frequencies $\la$200 GHz, and a few μK around 500–600 GHz, assuming optically thick lines and no beam-dilution. However, if existing, thermal absorption lines have the potential to be orders of magnitude stronger than the resonant lines. We make a simple estimation of the sizes and masses of the primordial perturbations at their turn-around epochs, which previously has been identified as the most favourable epoch for a detection. This work may be considered as an important pilot study for our forthcoming observations with the Herschel Space Observatory.
We present the kinematics of the molecular gas in the barred spiral galaxy M 83 (NGC 5236). The study is based on super(12)CO(J = 1-0 and 2-1) observations with the Swedish-ESO Submillimetre ...Telescope (SEST). Iso-velocity maps of the entire optical disk, 10' x 10' or 13 x 13 kpc, are produced. They show the pattern of an inclined, rotating disk, but also the effects of streaming motions along the spiral arms. A dynamical mass of about 6 x 10 super(10) M is estimated by fitting the rotation curve of an exponential disk model to these data. The gas constitutes about 13% of the disk mass. The pattern speed is determined from the residual velocity pattern. The locations of various resonances are discussed. The molecular gas velocity dispersion is determined, and a trend of decreasing dispersion with increasing galactocentric radius is found. A total gas (H sub(2) + HI + He) mass surface density map is presented, and compared to the critical density for star formation of an isothermal gaseous disk. The critical density is exceeded in the spiral arms, but not in the interarm regions. The locations of Giant Molecular Associations (GMAs) and H II regions are consistent with this scenario of dynamically induced star formation.
Context.
The
Odin
satellite is now into its twentieth year of operation, much surpassing its design life of two years. One of its major astronomical pursuits was the search for and study of water ...vapor in diverse regions of the Solar System and the Milky Way galaxy. The
Herschel
space observatory was needed to detect water vapor in external galaxies.
Aims.
Our goal is to study the distribution and excitation of water vapor and other molecules in the barred spiral galaxy NGC 1365.
Methods.
Herschel
has observed the central region of NGC 1365 in two positions, and both its SPIRE and PACS observations are available in the
Herschel
Science Archive.
Herschel
PACS images have been produced of the 70 and 160
μ
m infrared emission from the whole galaxy, and also of the cold dust distribution as obtained from the ratio of the 160 to 70
μ
m images. The
Herschel
SPIRE observations have been used to produce simultaneously observed maps of the 557 GHz o-H
2
O, 752 GHz p-H
2
O, 691 GHz CO(6−5), 1037 GHz CO(9−8), 537 GHz CH, 835 GHz CH
+
, and the 1461 GHz N
II
lines (efficiently probing the warm ionized medium) in the inner bar and circumnuclear torus region; – however, these observations have no effective velocity resolution. For this reason
Odin
has recently observed the 557 GHz ortho-H
2
O ground state line in the central region with high (5 km s
−1
) spectral resolution.
Results.
The emission and absorption of H
2
O at 557 GHz, with a velocity resolution of 5 km s
−1
, has been marginally detected in NGC 1365 with
Odin
. The water vapor is predominantly located in a shocked 15″ (1.3 kpc) region near some central compact radio sources and hot-spot H
II
regions, close to the northeast component of the molecular torus surrounding the nucleus. An analysis of the H
2
O line intensities and velocities indicates that a shock-region is located here. This is corroborated by a statistical image deconvolution of our SEST CO(3−2) observations, yielding 5″ resolution, and a study of our Very Large Array H
I
absorption observations, as well as comparisons with published interferometric CO observations. Additionally, an enticing 20″ H
I
ridge is found to extend south-southeast from the nucleus, coinciding in position with the southern edge of an O
III
outflow cone, emanating from the nucleus. The molecular chemistry of the shocked central region of NGC 1365 is analyzed with special emphasis on the CO, H
2
O and CH, CH
+
results.
Conclusions.
The dominating activity near the northeast (NE) torus component may have been triggered by the rapid bar-driven inflow into the circumnuclear torus causing cloud-cloud collisions and shocks, leading to the formation of stellar superclusters and, hence, also to more efficient PDR chemistry, which, here, may also benefit from cosmic ray focusing caused by the observed aligned magnetic field. The very high activity near the NE torus component may reflect the fact that the eastern bar-driven gas inflow into the NE region is much more massive than the corresponding western gas inflow into the southwest region. The H
2
O and CH
+
emissions peak in the NE torus region, but the CO and CH emissions are more evenly distributed across the whole circumnuclear torus. The higher energy CO spectral line energy distribution (SLED) is nicely modeled by a low velocity (10 km s
−1
) shock, which may as well explain the required CH excitation and its high abundance in denser gas. The higher velocity (40 km s
−1
) shock required to model the H
2
O SLED in the NE torus region, paired with the intense UV radiation from the observed massive young stellar superclusters, may also explain the high abundance of CH
+
in this region. The nuclear H
I
ridge may have been created by the action of outflow-driving X-ray photons colliding with ice-covered dust grains. A precessing nuclear engine, as is suggested by the tilted massive inner gas torus, may be necessary to explain the various nuclear outflows encountered.
Context. The Odin satellite is now into its twentieth year of operation, much surpassing its design life of two years. One of its major astronomical pursuits was the search for and study of water ...vapor in diverse regions of the Solar System and the Milky Way galaxy. The Herschel space observatory was needed to detect water vapor in external galaxies. Aims. Our goal is to study the distribution and excitation of water vapor and other molecules in the barred spiral galaxy NGC 1365. Methods. Herschel has observed the central region of NGC 1365 in two positions, and both its SPIRE and PACS observations are available in the Herschel Science Archive. Herschel PACS images have been produced of the 70 and 160 μm infrared emission from the whole galaxy, and also of the cold dust distribution as obtained from the ratio of the 160 to 70 μm images. The Herschel SPIRE observations have been used to produce simultaneously observed maps of the 557 GHz o-H2O, 752 GHz p-H2O, 691 GHz CO(6−5), 1037 GHz CO(9−8), 537 GHz CH, 835 GHz CH+, and the 1461 GHz N II lines (efficiently probing the warm ionized medium) in the inner bar and circumnuclear torus region; – however, these observations have no effective velocity resolution. For this reason Odin has recently observed the 557 GHz ortho-H2O ground state line in the central region with high (5 km s−1) spectral resolution. Results. The emission and absorption of H2O at 557 GHz, with a velocity resolution of 5 km s−1, has been marginally detected in NGC 1365 with Odin. The water vapor is predominantly located in a shocked 15″ (1.3 kpc) region near some central compact radio sources and hot-spot H II regions, close to the northeast component of the molecular torus surrounding the nucleus. An analysis of the H2O line intensities and velocities indicates that a shock-region is located here. This is corroborated by a statistical image deconvolution of our SEST CO(3−2) observations, yielding 5″ resolution, and a study of our Very Large Array H I absorption observations, as well as comparisons with published interferometric CO observations. Additionally, an enticing 20″ H I ridge is found to extend south-southeast from the nucleus, coinciding in position with the southern edge of an O III outflow cone, emanating from the nucleus. The molecular chemistry of the shocked central region of NGC 1365 is analyzed with special emphasis on the CO, H2O and CH, CH+ results. Conclusions. The dominating activity near the northeast (NE) torus component may have been triggered by the rapid bar-driven inflow into the circumnuclear torus causing cloud-cloud collisions and shocks, leading to the formation of stellar superclusters and, hence, also to more efficient PDR chemistry, which, here, may also benefit from cosmic ray focusing caused by the observed aligned magnetic field. The very high activity near the NE torus component may reflect the fact that the eastern bar-driven gas inflow into the NE region is much more massive than the corresponding western gas inflow into the southwest region. The H2O and CH+ emissions peak in the NE torus region, but the CO and CH emissions are more evenly distributed across the whole circumnuclear torus. The higher energy CO spectral line energy distribution (SLED) is nicely modeled by a low velocity (10 km s−1) shock, which may as well explain the required CH excitation and its high abundance in denser gas. The higher velocity (40 km s−1) shock required to model the H2O SLED in the NE torus region, paired with the intense UV radiation from the observed massive young stellar superclusters, may also explain the high abundance of CH+ in this region. The nuclear H I ridge may have been created by the action of outflow-driving X-ray photons colliding with ice-covered dust grains. A precessing nuclear engine, as is suggested by the tilted massive inner gas torus, may be necessary to explain the various nuclear outflows encountered.
Aims. We aim at determining the spatial distribution of the gas and dust in star-forming regions and address their relative abundances in quantitative terms. We also examine the dust opacity exponent ...beta for spatial and/or temporal variations. Methods. Using mapping observations of the very dense rho Oph A core, we examined standard 1D and non-standard 3D methods to analyse data of far-infrared and submillimetre (submm) continuum radiation. The resulting dust surface density distribution can be compared to that of the gas. The latter was derived from the analysis of accompanying molecular line emission, observed with Herschel from space and with APEX from the ground. As a gas tracer we used N2H+, which is believed to be much less sensitive to freeze-out than CO and its isotopologues. Radiative transfer modelling of the N2H+ (J = 3-2) and (J = 6-5) lines with their hyperfine structure explicitly taken into account provides solutions for the spatial distribution of the column density N(H-2), hence the surface density distribution of the gas. Results. The gas-to-dust mass ratio is varying across the map, with very low values in the central regions around the core SM 1. The global average, = 88, is not far from the canonical value of 100, however. In rho Oph A, the exponent beta of the power-law description for the dust opacity exhibits a clear dependence on time, with high values of 2 for the envelope-dominated emission in starless Class -1 sources to low values close to 0 for the disk-dominated emission in Class III objects. beta assumes intermediate values for evolutionary classes in between. Conclusions. Since beta is primarily controlled by grain size, grain growth mostly occurs in circumstellar disks. The spatial segregation of gas and dust, seen in projection toward the core centre, probably implies that, like (CO)-O-18, also N2H+ is frozen onto the grains.
Context . The Odin satellite is now into its twentieth year of operation, much surpassing its design life of two years. One of its major astronomical pursuits was the search for and study of water ...vapor in diverse regions of the Solar System and the Milky Way galaxy. The Herschel space observatory was needed to detect water vapor in external galaxies.
Aims . Our goal is to study the distribution and excitation of water vapor and other molecules in the barred spiral galaxy NGC 1365.
Methods . Herschel has observed the central region of NGC 1365 in two positions, and both its SPIRE and PACS observations are available in the Herschel Science Archive. Herschel PACS images have been produced of the 70 and 160 mu m infrared emission from the whole galaxy, and also of the cold dust distribution as obtained from the ratio of the 160 to 70 mu m images. The Herschel SPIRE observations have been used to produce simultaneously observed maps of the 557 GHz o-H2O, 752 GHz p-H2O, 691 GHz CO(6-5), 1037 GHz CO(9-8), 537 GHz CH, 835 GHz CH', and the 1461 GHz N IT lines (efficiently probing the warm ionized medium) in the inner bar and circumnuclear torus region; - however, these observations have no effective velocity resolution. For this reason Odin has recently observed the 557 GHz ortho-H2O ground state line in the central region with high (5 km s(-1)) spectral resolution.
Results . The emission and absorption of H2O at 557 GHz, with a velocity resolution of 5 km s(-1), has been marginally detected in NGC 1365 with Odin . The water vapor is predominantly located in a shocked 15 '' (1.3 kpc) region near some central compact radio sources and hot-spot HIT regions, close to the northeast component of the molecular torus surrounding the nucleus. An analysis of the H2O line intensities and velocities indicates that a shock-region is located here. This is corroborated by a statistical image deconvolution of our SEST CO(3-2) observations, yielding 5 '' resolution, and a study of our Very Large Array HI absorption observations, as well as comparisons with published interferometric CO observations. Additionally, an enticing 20 '' HI ridge is found to extend south-southeast from the nucleus, coinciding in position with the southern edge of an O III outflow cone, emanating from the nucleus. The molecular chemistry of the shocked central region of NGC 1365 is analyzed with special emphasis on the CO, H2O and CH, CH+ results.
Conclusions . The dominating activity near the northeast (NE) torus component may have been triggered by the rapid bar-driven inflow into the circumnuclear torus causing cloud-cloud collisions and shocks, leading to the formation of stellar superclusters and, hence, also to more efficient PDR chemistry, which, here, may also benefit from cosmic ray focusing caused by the observed aligned magnetic field. The very high activity near the NE torus component may reflect the fact that the eastern bar-driven gas inflow into the NE region is much more massive than the corresponding western gas inflow into the southwest region. The H2O and CH+ emissions peak in the NE torus region, but the CO and CH emissions are more evenly distributed across the whole circumnuclear torus. The higher energy CO spectral line energy distribution (SLED) is nicely modeled by a low velocity (10 km s(-1)) shock, which may as well explain the required CH excitation and its high abundance in denser gas. The higher velocity (40 km s(-1)) shock required to model the H2O SLED in the NE torus region, paired with the intense UV radiation from the observed massive young stellar superclusters, may also explain the high abundance of CH+ in this region. The nuclear H I ridge may have been created by the action of outflow-driving X-ray photons colliding with ice-covered dust grains. A precessing nuclear engine, as is suggested by the tilted massive inner gas torus, may be necessary to explain the various nuclear outflows encountered.
Physical properties of outflows Bjerkeli, P.; Liseau, R.; Nisini, B. ...
Astronomy & astrophysics,
04/2013, Letnik:
552
Journal Article
Recenzirano
Odprti dostop
Context. The observed physical properties of outflows from low-mass sources put constraints on possible ejection mechanisms. Historically, these quantities have been derived from CO using ...ground-based observations. It is, therefore, important to investigate whether parameters such as momentum rate (thrust) and mechanical luminosity (power) are the same when different molecular tracers are used. Aims. Our objective is to determine the outflow momentum, dynamical time-scale, thrust, energy, and power using CO and H2O as tracers of outflow activity. Methods. Within the framework of the Water In Star-forming regions with Herschel (WISH) key program, three molecular outflows from Class 0 sources have been mapped using the Heterodyne Instrument for the Far Infrared (HIFI) instrument aboard Herschel. We used these observations together with previously published H2 data to infer the physical properties of the outflows. We compared the physical properties derived here with previous estimates based on CO observations. Results. Inspection of the spatial distribution of H2O and H2 confirms that these molecules are co-spatial. The most prominent emission peaks in H2 coincide with strong H2O emission peaks and the estimated widths of the flows when using the two tracers are comparable. Conclusions. For the momentum rate and the mechanical luminosity, inferred values are not dependent on which tracer is used, i.e. the values agree to within a factor of 4 and 3, respectively.
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