Moran S.M.,Johns Hopkins University |
Kauffmann G.,Max Planck Institute for Astrophysics |
Heckman T.M.,Johns Hopkins University |
Gracia-Carpio J.,Max Planck Institute for Extraterrestrial Physics |
And 10 more authors.
Astrophysical Journal | Year: 2010
We report new observations of the galaxy UGC8802 obtained through the GALEX Arecibo SDSS Survey (GASS), which show this galaxy to be in a remarkable evolutionary state. UGC8802 (GASS35981) is a disk galaxy with stellar mass M* = 2 × 1010M⊙, which appears to contain an additional 2.1 × 1010M⊙ of Hi gas. New millimeter observations with the IRAM 30 m telescope indicate a molecular gas mass only a tenth this large. Using deep long-slit spectroscopy, we examine the spatially resolved star formation rate (SFR) and metallicity profiles of GASS35981 for clues to its history. We find that the star formation surface density in this galaxy is low (Σsfr = 0.003 M ⊙ yr-1 kpc-2) and that the star formation is spread remarkably evenly across the galaxy. The low molecular gas masses measured in our three IRAM pointings are largely consistent with the total star formation measured within the same apertures. Our MMT long-slit spectrum reveals a sharp drop in metallicity in the outer disk of GASS35981. The ratio of current SFR to existing stellar mass surface density in the outer disk is extremely high, implying that all the stars must have formed within the past ∼1 Gyr. At current SFRs, however, GASS35981 will not consume its Hi reservoir for another 5-7 Gyr. Despite its exceptionally large gas fraction for a galaxy this massive, GASS35981 has a regular rotation curve and exhibits no sign of a recent interaction or merger. We speculate that GASS35981 may have acquired its gas directly from the intergalactic medium, and that GASS35981 and other similar galaxies identified in the GASS survey may provide rare local glimpses of gas accretion processes that were more common during the prime epoch of disk galaxy formation at z ∼ 1. © 2010. The American Astronomical Society. All rights reserved. Printed in the U.S.A.
Agudo I.,Institute Astrofisica Of Andalucia |
Agudo I.,Boston University |
Thum C.,Institute Of Radio Astronomie Millimetrique |
Wiesemeyer H.,Max Planck Institute for Radio Astronomy |
And 5 more authors.
Astronomy and Astrophysics | Year: 2012
Context. Several millimeter and submillimeter facilities with linear polarization observing capabilities have started operating during the last years. These facilities, as well as other previous millimeter telescopes and interferometers, require bright and stable linear polarization calibrators to calibrate new instruments and to monitor their instrumental polarization. The current limited number of adequate calibrators implies difficulties in the acquisition of these calibration observations. Aims. Looking for additional linear polarization calibrators in the millimeter spectral range, we started monitoring 3C 286 in mid-2006. This source is a standard and highly stable polarization calibrator for radio observations. Methods. Here we present the 3 mm and 1 mm monitoring observations obtained between September 2006 and January 2012 with the XPOL polarimeter on the IRAM 30 m Millimeter Telescope. Results. Our observations show that 3C 286 is a bright source of constant total flux with 3 mm flux density S 3 mm = (0.91 ± 0.02) Jy. The 3 mm linear polarization degree (p 3 mm = [13.5 ± 0.3] %) and polarization angle (χ 3 mm = [37.3 ± 0.8] °, expressed in the equatorial coordinate system) were also constant during the time span of our observations. Although with poorer time sampling and signal-to-noise ratio, our 1 mm observations of 3C 286 are also reproduced by a constant source of 1 mm flux density (S 1 mm = [0.30 ± 0.03] Jy), polarization fraction (p 1 mm = [14.4 ± 1.8] %), and polarization angle (χ 1 mm = [33.1 ± 5.7]°). Conclusions. This, together with the previously known compact structure of 3C 286-extended by ∼3.5′′ in the sky-allow us to propose 3C 286 as a new calibrator for both single-dish and interferometric polarization observations at 3 mm, and possibly at shorter wavelengths. © 2012 ESO.
Angelakis E.,Max Planck Institute for Radio Astronomy |
Fuhrmann L.,Max Planck Institute for Radio Astronomy |
Marchili N.,University of Padua |
Foschini L.,National institute for astrophysics |
And 9 more authors.
Astronomy and Astrophysics | Year: 2015
Context. With the current study we aim at understanding the properties of radio emission and the assumed jet from four radio-loud and γ-ray-loud narrow-line Seyfert 1 galaxies that have been detected by Fermi. These are Seyfert 1 galaxies with emission lines at the low end of the FWHM distribution. Aims. The ultimate goal is twofold: first we investigate whether a relativistic jet is operating at the source producing the radio output, and second, we quantify the jet characteristics to understand possible similarities with and differences from the jets found in typical blazars. Methods. We relied on the most systematic monitoring of radio-loud and γ-ray-detected narrow-line Seyfert 1 galaxies in the cm and mm radio bands conducted with the Effelsberg 100 m and IRAM 30 m telescopes. It covers the longest time-baselines and the most radio frequencies to date. This dataset of multi-wavelength, long-term radio light-curves was analysed from several perspectives. We developed a novel algorithm to extract sensible variability parameters (mainly amplitudes and time scales) that were then used to compute variability brightness temperatures and the corresponding Doppler factors. The jet powers were computed from the light curves to estimate the energy output and compare it with that of typical blazars. The dynamics of radio spectral energy distributions were examined to understand the mechanism causing the variability. Results. The length of the available light curves for three of the four sources in the sample allowed a firm understanding of the general behaviour of the sources. They all display intensive variability that appears to be occurring at a pace rather faster than what is commonly seen in blazars. The flaring events become progressively more prominent as the frequency increases and show intensive spectral evolution that is indicative of shock evolution. The variability brightness temperatures and the associated Doppler factors are moderate, implying a mildly relativistic jet. The computed jet powers show very energetic flows. The radio polarisation in one case clearly implies a quiescent jet underlying recursive flaring activity. Finally, in one case, the sudden disappearance of a γ-ray flare below some critical frequency in our band needs a more detailed investigation of the possible mechanism causing the evolution of broadband events. Conclusions. Despite the generally lower flux densities, the sources appear to show all typical characteristics seen in blazars that are powered by relativistic jets, such as intensive variability, spectral evolution across the different bands following evolutionary paths explained by travelling shocks, and Doppler factors indicating mildly relativistic speeds. © ESO, 2015.
Agudo I.,Institute Astrofisica Of Andalucia Csic |
Agudo I.,Boston University |
Thum C.,Institute Of Radio Astronomie Millimetrique |
Wiesemeyer H.,Institute Radio Astronomia Milimetrica |
Krichbaum T.P.,Max Planck Institute for Radio Astronomy
Astrophysical Journal, Supplement Series | Year: 2010
We present the results from the first large (>100 sources) 3.5mm polarimetric survey of radio-loud active galactic nuclei (AGNs). This wavelength is favorable within the radio-millimeter range for measuring the intrinsic linearly polarized emission from AGNs, since in general it is only marginally affected by Faraday rotation of the electric vector position angle and depolarization. The I, Q, U, and V Stokes parameter observations were performed with the XPOL polarimeter at the IRAM 30m Telescope on different observing epochs from 2005 July (when most of the measurements were made) to 2009 October. Our sample consists of 145 flat-radio-spectrum AGNs with declination >-30°(J2000.0) and flux density ≳1Jy at ∼ 86GHz, as measured at the IRAM 30m Telescope from 1978 to 1994. This constraint on the radio spectrum causes our sample to be dominated by blazars, which allows us to conduct new statistical studies on this class of high-luminosity, relativistically beamed emitters. We detect linear and circular polarization (above minimum 3σ levels of ∼ 1.5% and ∼ 0.3%) for 76% and 6% of the sample, respectively. We find a clear excess in degree of linear polarization detected at 86GHz with regard to that at 15GHz by a factor of 2. Over our entire source sample, the luminosity of the jets is anticorrelated with the degree of linear polarization. Consistent with previous findings claiming larger Doppler factors for brighter γ-ray blazars, quasars listed in our sample, and in the Fermi Large Area Telescope Bright Source Catalog (LBAS), show larger luminosities than non-LBAS ones, but our data do not allow us to confirm the same for BL Lac objects. We do not find a clear relation between the linear polarization angle and the jet structural position angle for any source class in our sample. We interpret this as the consequence of a markedly non-axisymmetric character of the 3mm emitting region in the jets. We find that intrinsic circular polarization is the most likely mechanism for generation of the circular polarization detected in our observations. Our new data can be used to estimate the 3.5mm AGN contribution to measurements of the linear polarization of the cosmic microwave background, such as those performed by the Planck satellite. © 2010 The American Astronomical Society.
Drahus M.,University of California at Los Angeles |
Jewitt D.,University of California at Los Angeles |
Guilbert-Lepoutre A.,University of California at Los Angeles |
Waniak W.,Jagiellonian University |
Sievers A.,Institute Radio Astronomia Milimetrica
Astrophysical Journal | Year: 2012
One of the least understood properties of comets is the compositional structure of their nuclei, which can either be homogeneous or heterogeneous. The nucleus structure can be conveniently studied at millimeter wavelengths, using velocity-resolved spectral time series of the emission lines, obtained simultaneously for multiple molecules as the body rotates. Using this technique, we investigated the sources of CH3OH and HCN in comet 103P/Hartley 2, the target of NASA's EPOXI mission, which had an exceptionally favorable apparition in late 2010. Our monitoring with the IRAM 30m telescope shows short-term variability of the spectral lines caused by nucleus rotation. The varying production rates generate changes in brightness by a factor of four for HCN and by a factor of two for CH3OH, and they are remarkably well correlated in time. With the addition of the velocity information from the line profiles, we identify the main sources of outgassing: two jets, oppositely directed in a radial sense, and icy grains, injected into the coma primarily through one of the jets. The mixing ratio of CH3OH and HCN is dramatically different in the two jets, which evidently shows large-scale chemical heterogeneity of the nucleus. We propose a network of identities linking the two jets with morphological features reported elsewhere and postulate that the chemical heterogeneity may result from thermal evolution. The model-dependent average production rates are 3.5 × 10 26moleculess-1 for CH3OH and 1.25 × 1025moleculess-1 for HCN, and their ratio of 28 is rather high but not abnormal. The rotational temperature from CH3OH varied strongly, presumably due to nucleus rotation, with the average value being 47K. © 2012. The American Astronomical Society. All rights reserved.
Moor A.,Konkoly Observatory |
Muller T.G.,Max Planck Institute for Extraterrestrial Physics |
Kiss C.,Konkoly Observatory |
Balog Z.,Max Planck Institute for Astronomy |
And 2 more authors.
Experimental Astronomy | Year: 2014
The absolute stability of the PACS bolometer response over the entire mission lifetime without applying any corrections is about 0.5 % (standard deviation) or about 8 % peak-to-peak. This fantastic stability allows us to calibrate all scientific measurements by a fixed and time-independent response file, without using any information from the PACS internal calibration sources. However, the analysis of calibration block observations revealed clear correlations of the internal source signals with the evaporator temperature and a signal drift during the first half hour after the cooler recycling. These effects are small, but can be seen in repeated measurements of standard stars. From our analysis we established corrections for both effects which push the stability of the PACS bolometer response to about 0.2 % (stdev) or 2 % in the blue, 3 % in the green and 5 % in the red channel (peak-to-peak). After both corrections we still see a correlation of the signals with PACS FPU temperatures, possibly caused by parasitic heat influences via the Kevlar wires which connect the bolometers with the PACS Focal Plane Unit. No aging effect or degradation of the photometric system during the mission lifetime has been found. © 2013 Springer Science+Business Media Dordrecht.
Billot N.,California Institute of Technology |
Billot N.,Institute Radio Astronomia Milimetrica |
Morales-Calderon M.,Spitzer Science Center |
Stauffer J.R.,Spitzer Science Center |
And 2 more authors.
Astrophysical Journal Letters | Year: 2012
We have obtained time series observations of the Orion Nebula Cluster at 70 μm and 160 μm from the Herschel/PACS Photometer. This represents the first wide-field far-infrared photometric monitoring of a young star-forming region. The acquired 35′ × 35′ maps show complex extended structures, with unprecedented detail, that trace the interaction between the molecular gas and the young hot stars. We detect 43 protostars, most of which are situated along the integral-shaped filament extending from the Orion nebula, through OMC2 and OMC3. We present high-reliability light curves for some of these objects using the first six epochs of our observing program spread over 6 weeks. We find amplitude variations in excess of 20% for a fraction of the detected protostars over periods as short as a few weeks. This is inconsistent with the dynamical timescales of cool far-IR emitting material that orbits at hundreds of AU from the protostar, and it suggests that the mechanism(s) responsible for the observed variability originates from the inner region of the protostars, likely driven by variable mass accretion. © 2012. The American Astronomical Society. All rights reserved..
Nielbock M.,Max Planck Institute for Astronomy |
Muller T.,Max Planck Institute for Extraterrestrial Physics |
Klaas U.,Max Planck Institute for Astronomy |
Altieri B.,European Space Agency |
And 6 more authors.
Experimental Astronomy | Year: 2013
We present a flux calibration scheme for the PACS chopped point-source photometry observing mode based on the photometry of five stellar standard sources. This mode was used for science observations only early in the mission. Later, it was only used for pointing and flux calibration measurements. Its calibration turns this type of observation into fully validated data products in the Herschel Science Archive. Systematic differences in calibration with regard to the principal photometer observation mode, the scan map, are derived and amount to 5 - 6 %. An empirical method to calibrate out an apparent response drift during the first 300 Operational Days is presented. The relative photometric calibration accuracy (repeatability) is as good as 1 % in the blue and green band and up to 5 % in the red band. Like for the scan map mode, inconsistencies among the stellar calibration models become visible and amount to 2 % for the five standard stars used. The absolute calibration accuracy is therefore mainly limited by the model uncertainty, which is 5 % for all three bands. © 2013 Springer Science+Business Media Dordrecht.
Thum C.,Institute Radio Astronomia Milimetrica |
Neri R.,Institut Universitaire de France |
Baez-Rubio A.,CSIC - National Institute of Aerospace Technology |
Krips M.,Institut Universitaire de France
Astronomy and Astrophysics | Year: 2013
We present new millimeter observations made with the IRAM interferometer and 30 m telescope of the ionized wind from the massive young stellar object LkHα 101. Several recombination lines, including higher order transitions, were detected for the first time at radio wavelengths in this source. From three α-transitions, we derive an accurate value for the stellar velocity and for the first time, an unambiguous expansion velocity of the wind that is 55 km s-1. This velocity is much slower than reported previously, and the resulting mass loss rate is 1.8 × 10-6 M âŠ™ yr-1. The wideband continuum spectra and the interferometer visibilities show that the density of the wind falls off more steeply than what is compatible with constant-velocity expansion. We argue that these properties indicate that the wind is launched from a radially narrow region of the circumstellar disk, and we propose that slow speed and a steep density gradient are characteristic properties of the evolutionary phase, where young stars of intermediate and high mass clear away the gaseous component of their accretion disks. The recombination lines are emitted close to local thermal equilibrium, but the higher order transitions appear systematically broader and weaker than expected, probably because of impact broadening. Finally, we show that LkHα 101 shares many properties with MWC 349, the only other stellar wind source where radio recombination lines have been detected, with some of them masing. We argue that LkHα 101 evades masing at millimeter wavelengths because of the disk's smaller size and unfavorable orientation. Some amplification may however be detectable at shorter wavelengths. © ESO, 2013.
Churchwell E.,University of Wisconsin - Madison |
Sievers A.,Institute Radio Astronomia Milimetrica |
Thum C.,Institut Universitaire de France
Astronomy and Astrophysics | Year: 2010
We report observations, using the IRAM 30 m telescope, of 30 ultracompact and hypercompact HII regions in the lines of HCO +(3-2) and/or HCO +(1-0) and H30α and/or H39α. Images are presented in both HCO +(3-2) and H30α toward a subset of regions (16 in HCO +(3-2), 14 in H30α) with a resolution of 12". In addition, H 13CO +(3-2) observations are reported toward 13 HII regions where HCO +(3-2) displays complex profiles. It is shown that the absorption dips in the HCO + profiles are due to HCO + self-absorption, not absorption of the HII free-free emission or warm dust emission surrounding the HII region or two velocity components along the line of sight. It was found that among the sources with self-absorbed profiles, 8 are contracting and 5 are expanding. Mass fluxes are found to be typically a few times 10 -3 M⊙ yr -1, implying time scales for massive star formation <10 5 yrs. HCO + and H 2 column densities are estimated for a subset of the sources from which masses of the dense central cloud cores were estimated. Implications of the derived column densities, masses, flow velocities, and mass fluxes are discussed. © ESO, 2010.