- ID:
- ivo://CDS.VizieR/J/MNRAS/382/1552
- Title:
- Multiwavelength study of nearby galaxy nuclei
- Short Name:
- J/MNRAS/382/1552
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present optical and infrared broad-band images, radio maps, and optical spectroscopy for the nuclear region of a sample of nearby galaxies. The galaxies have been drawn from a complete volume-limited sample for which we have already presented X-ray imaging. We modelled the stellar component of the spectroscopic observations to determine the star formation history of our targets. Diagnostic diagrams were used to classify the emission-line spectra and determine the ionizing mechanism driving the nuclear regions. All those sources classified as active galactic nuclei present small Eddington ratios (~10^-3^-10^-6^), implying a very slow growth rate of their black holes. We finally investigate the relative numbers of active and normal nuclei as a function of host galaxy luminosity and find that the fraction of active galaxies slowly rises as a function of host absolute magnitude in the MB~-12 to -22 range.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/789/81
- Title:
- Multiwavelength survey of HII regions in NGC 300
- Short Name:
- J/ApJ/789/81
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a galaxy-wide study of molecular gas and star formation in a sample of 76 H II regions in the nearby spiral galaxy NGC 300. We have measured the molecular gas at 250pc scales using pointed CO(J=2-1) observations with the Atacama Pathfinder Experiment telescope. We detect CO in 42 of our targets, deriving molecular gas masses ranging from our sensitivity limit of ~10^5^M_{sun}_ to 7x10^5^M_{sun}_. We find a clear decline in the CO detection rate with galactocentric distance, which we attribute primarily to the decreasing radial metallicity gradient in NGC 300. We combine Galaxy Evolution Explorer far-ultraviolet, Spitzer 24{mu}m, and H{alpha} narrowband imaging to measure the star formation activity in our sample. We have developed a new direct modeling approach for computing star formation rates (SFRs) that utilizes these data and population synthesis models to derive the masses and ages of the young stellar clusters associated with each of our H II region targets. We find a characteristic gas depletion time of 230Myr at 250pc scales in NGC 300, more similar to the results obtained for Milky Way giant molecular clouds than the longer (>2Gyr) global depletion times derived for entire galaxies and kiloparsec-sized regions within them. This difference is partially due to the fact that our study accounts for only the gas and stars within the youngest star-forming regions. We also note a large scatter in the NGC 300 SFR-molecular gas mass scaling relation that is furthermore consistent with the Milky Way cloud results. This scatter likely represents real differences in giant molecular cloud physical properties such as the dense gas fraction.
- ID:
- ivo://CDS.VizieR/J/A+A/539/A149
- Title:
- Multiwavelength view of blazar PKS 2155-304
- Short Name:
- J/A+A/539/A149
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Multiwavelength (MWL) observations of the blazar PKS 2155-304 during two weeks in July and August 2006, the period when two exceptional flares at very high energies (VHE, E>=100GeV) occurred, provide a detailed picture of the evolution of its emission. The complete data set from this campaign is presented, including observations in VHE gamma-rays (H.E.S.S.), X-rays (RXTE, CHANDRA, SWIFT XRT), optical (SWIFT UVOT, Bronberg, Watcher, ROTSE), and in the radio band (NRT, HartRAO, ATCA). Optical and radio light curves from 2004 to 2008 are compared to the available VHE data from this period, to put the 2006 campaign into the context of the long-term evolution of the source. The data set offers a close view of the evolution of the source on different time scales and yields new insights into the properties of the emission process. The predictions of synchrotron self-Compton (SSC) scenarios are compared to the MWL data, with the aim of describing the dominant features in the data down to the hour time scale. The spectral variability in the X-ray and VHE bands is explored and correlations between the integral fluxes at different wavelengths are evaluated. SSC modelling is used to interpret the general trends of the varying spectral energy distribution.
- ID:
- ivo://CDS.VizieR/J/ApJ/755/47
- Title:
- Murchison Widefield Array 110-200MHz observations
- Short Name:
- J/ApJ/755/47
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Murchison Widefield Array (MWA) is a new low-frequency, wide field-of-view radio interferometer under development at the Murchison Radio-astronomy Observatory in Western Australia. We have used a 32 element MWA prototype interferometer (MWA-32T) to observe two 50{deg} diameter fields in the southern sky, covering a total of ~2700deg^2^, in order to evaluate the performance of the MWA-32T, to develop techniques for epoch of reionization experiments, and to make measurements of astronomical foregrounds. We developed a calibration and imaging pipeline for the MWA-32T, and used it to produce ~15' angular resolution maps of the two fields in the 110-200MHz band. We perform a blind source extraction using these confusion-limited images, and detect 655 sources at high significance with an additional 871 lower significance source candidates. We compare these sources with existing low-frequency radio surveys in order to assess the MWA-32T system performance, wide-field analysis algorithms, and catalog quality. Our source catalog is found to agree well with existing low-frequency surveys in these regions of the sky and with statistical distributions of point sources derived from Northern Hemisphere surveys; it represents one of the deepest surveys to date of this sky field in the 110-200MHz band.
- ID:
- ivo://CDS.VizieR/J/A+A/641/A17
- Title:
- Musca APEX 12CO(2-1), 12CO(3-2) & 12CO(4-3) data
- Short Name:
- J/A+A/641/A17
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Observations with the Herschel Space Telescope have established that most star forming gas is organised in filaments, a finding that is supported by numerical simulations of the supersonic interstellar medium (ISM) where dense filamentary structures are ubiquitous. We aim to understand the formation of these dense structures by performing observations covering the ^12^CO(4-3), ^12^CO(3-2), and various CO(2-1) isotopologue lines of the Musca filament, using the APEX telescope. The observed CO intensities and line ratios cannot be explained by PDR (photodissociation region) emission because of the low ambient far-UV field that is strongly constrained by the non-detections of the [CII] line at 158um and the [OI] line at 63um, observed with the upGREAT receiver on SOFIA, as well as a weak [CI] 609um line detected with APEX. We propose that the observations are consistent with a scenario in which shock excitation gives rise to warm and dense gas close to the highest column density regions in the Musca filament. Using shock models, we find that the CO observations can be consistent with excitation by J-type low-velocity shocks. A qualitative comparison of the observed CO spectra with synthetic observations of dynamic filament formation simulations shows a good agreement with the signature of a filament accretion shock that forms a cold and dense filament from a converging flow. The Musca filament is thus found to be dense molecular post-shock gas. Filament accretion shocks that dissipate the supersonic kinetic energy of converging flows in the ISM may thus play a prominent role in the evolution of cold and dense filamentary structures.
- ID:
- ivo://CDS.VizieR/J/A+A/489/533
- Title:
- M83 volume densities of giant molecular clouds
- Short Name:
- J/A+A/489/533
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using observed GALEX far-ultraviolet (FUV) fluxes and VLA images of the 21-cm HIcolumn densities, along with estimates of the local dust abundances, we measure the volume densities of a sample of actively star-forming giant molecular clouds (GMCs) in the nearby spiral galaxy M83 on a typical resolution scale of 170 pc. Our approach is based on an equilibrium model for the cycle of molecular hydrogen formation on dust grains and photodissociation under the influence of the FUV radiation on the cloud surfaces of GMCs. We find a range of total volume densities on the surface of GMCs in M83, namely 0.1-400cm^-3^ inside R_25_, 0.5-50cm^-3^ outside R_25_. Our data include a number of GMCs in the HI-ring surrounding this galaxy. Finally, we discuss the effects of observational selection, which may bias our results.
- ID:
- ivo://CDS.VizieR/J/ApJ/771/105
- Title:
- MWA Stokes I 189MHz sources
- Short Name:
- J/ApJ/771/105
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a Stokes I, Q and U survey at 189MHz with the Murchison Widefield Array 32 element prototype covering 2400deg^2^. The survey has a 15.6' angular resolution and achieves a noise level of 15mJy/beam. We demonstrate a novel interferometric data analysis that involves calibration of drift scan data, integration through the co-addition of warped snapshot images, and deconvolution of the point-spread function through forward modeling. We present a point source catalog down to a flux limit of 4Jy. We detect polarization from only one of the sources, PMN J0351-2744, at a level of 1.8%+/-0.4%, whereas the remaining sources have a polarization fraction below 2%. Compared to a reported average value of 7% at 1.4GHz, the polarization fraction of compact sources significantly decreases at low frequencies. We find a wealth of diffuse polarized emission across a large area of the survey with a maximum peak of ~13K, primarily with positive rotation measure values smaller than +10rad/m2. The small values observed indicate that the emission is likely to have a local origin (closer than a few hundred parsecs). There is a large sky area at {alpha}>=2^h^30^m^ where the diffuse polarized emission rms is fainter than 1K. Within this area of low Galactic polarization we characterize the foreground properties in a cold sky patch at ({alpha},{delta})=(4^h^,-27.6{deg}) in terms of three-dimensional power spectra.
- ID:
- ivo://CDS.VizieR/J/other/PASA/33.20
- Title:
- MWA Survey of Galactic HII regions
- Short Name:
- J/other/PASA/33.
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have compiled a catalogue of HII regions detected with the Murchison Widefield Array between 72 and 231MHz. The multiple frequency bands provided by the Murchison Widefield Array allow us identify the characteristic spectrum generated by the thermal Bremsstrahlung process in HII regions. We detect 306 HII regions between 260{deg}<l<340{deg} and report on the positions, sizes, peak, integrated flux density, and spectral indices of these HII regions. By identifying the point at which HII regions transition from the optically thin to thick regime, we derive the physical properties including the electron density, ionised gas mass, and ionising photon flux, towards 61 HII regions. This catalogue of HII regions represents the most extensive and uniform low frequency survey of HII regions in the Galaxy to date.
1089. MWC 480 ALMA image
- ID:
- ivo://CDS.VizieR/J/A+A/622/A75
- Title:
- MWC 480 ALMA image
- Short Name:
- J/A+A/622/A75
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Gap-like structures in protoplanetary disks are likely related to planet formation processes. In this work, we present and analyze high-resolution 1.3mm ALMA continuum observations of the protoplanetary disk around the Herbig Ae star MWC 480. Our observations show for the first time a gap centered at ~74AU with a width of ~23AU, surrounded by a bright ring centered at ~98AU from the central star. Detailed radiative transfer modeling of the ALMA image and the broadband spectral energy distribution is used to constrain the surface density profile and structural parameters of the disk. If the width of the gap corresponds to 4-8 times the Hill radius of a single forming planet, then the putative planet would have a mass of 0.4~3M_J_. We test this prediction by performing global three-dimensional smoothed particle hydrodynamic gas/dust simulations of disks hosting a migrating and accreting planet. We find that the dust emission across the disk is consistent with the presence of an embedded planet with a mass of ~2.3M_J_ at an orbital radius of ~78AU. Given the surface density of the best-fit radiative transfer model, the amount of depleted mass in the gap is higher than the mass of the putative planet, which satisfies the basic condition for the formation of such a planet.
- ID:
- ivo://CDS.VizieR/VIII/61
- Title:
- NAIC 611 MHz Survey Source List
- Short Name:
- VIII/61
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The 1000 foot Arecibo reflector was used with a multiple feed system to map the region 0h < RA < 12h, -2d < DEC < +18d at 611 MHz. The observations were made in meridian transit mode using an array of ten line feeds with the electric polarization vector in the east-west plane. The beam power pattern of each feed was approximately Gaussian and circulary symmetric with a half power beam width of about 12.6 arcmin. A source list was produced containing fluxes and positions of 3118 radio sources stronger than 0.35 Jy. The source list is complete for strong, unresolved sources. However it is not intended to be complete for objects highly resolved by the 12.6 arcmin beamsize. The list's lower limit of 0.35 Jy is about 5 times the average sky confusion. The survey was calibrated to the KPW (Kellermann, Pauliny-Toth, and Williams 1969ApJ...157....1K) flux scale. The secondary calibrators were ten sources measured at Arecibo at 606 MHz based on the KPW scale (Condon, Niell and Jauncey 1971). Marked by an asterisk in Table 2, these sources were too few to be used alone to calibrate all of the declination strips. Since a more complete list of good calibration sources did not exist at 611 MHz, the fluxes of 159 additional sources were independently measured accurate to about 7 percent at Arecibo in the Fall of 1973. Table 2 gives their assigned fluxes. These sources were tied to the KPW scale through the ten secondary calibrators.
