K. M. Menten

VLBI observations of the 6.7 GHz methanol masers toward W3(OH)

We have conducted very long baseline interferometric (VLBI) observations of the 6.668 GHz maser transition of interstellar methanol toward the ultracompact H II region W3(OH). We have determined absolute maser positions with an accuracy of 0″.05 and produced maps that show that the methanol masers have a distribution similar to the hydroxyl masers in this source. The intrinsic sizes of individual maser spots are ≃0″.0014 (FWHM), or ≃3 AU, and are not significantly affected by interstellar scattering

Methanol as a diagnostic tool of interstellar clouds - II. Modelling high-mass protostellar objects

Context. Fundamental properties of interstellar clouds must be known to investigate the initial conditions of star formation within them and the interaction of newly formed stars with their environment. Methanol has proven to be useful to probe densities and temperatures of various environments within interstellar clouds. Aims. We aim to explore the potential of methanol as a tracer molecule for regions in which high-mass stars are forming or have recently formed, in particular so-called high-mass protostellar objects (HMPOs) and infrared dark clouds (IRDCs). Methods. We present and analyse multi-frequency centimetre and (sub)millimetre single-dish observations of methanol toward a sample of 13 sources that are in the poorly understood earliest phases of evolution of high-mass stars (HMPOs and IRDCs). For each source in our sample, we derive physical parameters such as the kinetic temperature, the spatial density. and the methanol column density. We apply our large velocity gradient modelling and fitting technique that involves fitting a synthetic spectrum to all the measured lines simultaneously. Results. In several sources, we find that more than one physical component is necessary to fit the spectra; moreover, broad non-Gaussian linewidths suggest outflows in many sources from both the IRDC and the HMPO subsamples. Kinetic temperatures are found to be between 10 and 60 K and spatial densities in the range 10 5 -10 6 cm -3 . Hotter, denser cores are found in a few HMPOs, indicating that these sources already harbour hot cores heated by protostars.

Microarcsecond proper motions of extragalactic water vapor masers in M33

We present a second-epoch spectral line VLBI synthesis map of the H 2 O maser associated with the H II region IC 133 in the galaxy M33. This map is about 2.5 times more sensitive than the earlier one. Thirty-two spatially distinct maser features have been identified, and we have discovered a second center of maser activity within the IC 133 complex, IC 133 West, which is displaced ≃0″.3 (1 pc at a nominal distance of 720 kpc) from IC 133 Main. The most blueshifted maser features are located in IC 133 West, which may mark the location of a separate star forming region. Comparing the two available maps of IC 133, we have estimated the right ascension components of proper motion over a period of 479 days for five maser features to accuracies of between 7 and 16 μas

THE VLA VIEW OF THE HL TAU DISK: DISK MASS, GRAIN EVOLUTION, AND EARLY PLANET FORMATION

The first long-baseline ALMA campaign resolved the disk around the young star HL Tau into a number of axisymmetric bright and dark rings. Despite the very young age of HL Tau these structures have been interpreted as signatures for the presence of (proto)planets. The ALMA images triggered numerous theoretical studies based on disk-planet interactions, magnetically driven disk structures, and grain evolution. Of special interest are the inner parts of disks, where terrestrial planets are expected to form. However, the emission from these regions in HL Tau turned out to be optically thick at all ALMA wavelengths, preventing the derivation of surface density profiles and grain size distributions. Here, we present the most sensitive images of HL Tau obtained to date with the Karl G. Jansky Very Large Array at 7.0 mm wavelength with a spatial resolution comparable to the ALMA images. At this long wavelength the dust emission from HL Tau is optically thin, allowing a comprehensive study of the inner disk. We obtain a total disk dust mass of 0.001 - 0.003 Msun, depending on the assumed opacity and disk temperature. Our optically thin data also indicate fast grain growth, fragmentation, and formation of dense clumps in the inner densest parts of the disk. Our results suggest that the HL Tau disk may be actually in a very early stage of planetary formation, with planets not already formed in the gaps but in the process of future formation in the bright rings.

The CO line SED and atomic carbon in IRAS F10214+4724

Using the IRAM 30 m telescope and the Plateau de Bure interferometer we have detected the C I((3)P(2) -> (3)P(1)) and the CO 3-2, 4-3, 6-5, 7-6 transitions as well as the dust continuum at 3 and 1.2 mm towards the distant luminous infrared galaxy IRAS F10214+4724 at z = 2.286. The C I((3)P(2) -> (3)P(1)) line is detected for the first time towards this source and IRAS F10214+4724 now belongs to a sample of only 3 extragalactic sources at any redshift where both of the carbon fine structure lines have been detected. The source is spatially resolved by our C I((3)P(2) -> (3)P(1)) observation and we detect a velocity gradient along the east-west direction. The CI line ratio allows us to derive a carbon excitation temperature of 42(-9)(+12) K. The carbon excitation in conjunction with the CO ladder and the dust continuum constrain the gas density to n(H(2)) = 10(3.6-4.0) cm(-3) and the kinetic temperature to T(kin) = 45-80 K, similar to the excitation conditions found in nearby starburst galaxies. The rest-frame 360 mu m dust continuum morphology is more compact than the line emitting region, which supports previous findings that the far infrared luminosity arises from regions closer to the active galactic nucleus at the center of this system.

New H2O masers in Seyfert and FIR bright galaxies II. The intermediate luminosity range

Context. Recently, a relationship between the water maser detection rate and far infrared (FIR) flux density has been found as a result of a 22 GHz maser survey in a sample comprised of northern galaxies with 100 µm flux density >50 Jy and a declination >−30 ◦ . Aims. The survey has been extended toward galaxies with lower FIR flux densities in order to confirm this correlation and to discover additional maser sources for relevant follow-up interferometric studies. Methods. A sample of 41 galaxies with 30 Jy −30 ◦ was observed with the 100-m telescope at Effelsberg in a search for the 22 GHz water vapor line. The average 3σ noise level of the survey is 40 mJy for a 1 km s −1 channel, corresponding to

Detection of "parent" molecules from the inner wind of AGB stars as tracers of non-equilibrium chemistry

Context. Asymptotic Giant Branch (AGB) stars are typified by strong dust-driven, molecular outflows. For long, it was believed that the molecular content of the circumstellar envelope of AGB stars is primarily determined by the atmospheric C/O ratio. However, recent observations of molecules such as HCN, SiO, and SO reveal gas-phase abundances higher than predicted by thermodynamic equilibrium (TE) models. UV-photon initiated dissociation in the outer envelope or non-equilibrium formation by the effect of shocks in the inner envelope may be the origin of the anomolous abundances. Aims. We aim to detect (i) a group of “parent” molecules (CO, SiO, HCN, CS), predicted by non-equilibrium studies to form with almost constant abundances independent of the C/O ratio and the stellar evolutionary stage on the Asymptotic Giant Branch (AGB), and (ii) the few molecules, such as SiS and SO, that are sensitive to the O- or C-rich nature of the star. Methods. Several low and high excitation rotational transitions of key molecules are observed at mm and sub-mm wavelengths with JCMT and APEX in four AGB stars: the oxygen-rich Mira WX Psc, the S star W Aql, and the two carbon stars V Cyg and II Lup. A critical density analysis is performed to determine the formation region of the high-excitation molecular lines. Results. We detect the four “parent” molecules in all four objects, implying that, indeed, these chemical species form whatever the stage of evolution on the AGB. High-excitation lines of SiS are also detected in three stars with APEX, whereas SO is only detected in the oxygen-rich star WX Psc. Conclusions. This is the firstmulti-molecular observational proof that periodically shocked layers above the photosphere of AGB stars show some chemical homogeneity, whatever the photospheric C/O ratio and stage of evolution of the star.

New H2O masers in Seyfert and FIR bright galaxies - IV. Interferometric follow-ups

Context. Very luminous extragalactic water masers, the megamasers, are associated with active galactic nuclei (AGN) in galaxies characterized by accretion disks, radio jets, and nuclear outflows. Weaker masers, the kilomasers, seem to be related mostly to star formation activity, although the possibility exists that some of these sources may belong to the weak tail of the AGN maser distribution. Aims. It is particularly important to accurately locate the water maser emission to reveal its origin and shed light on extragalactic starforming activity or to elucidate the highly obscured central regions of galaxies. Methods. We performed interferometric observations of three galaxies, NGC 3556, Arp 299, and NGC 4151, where water emission was found. Statistical tools were used to study the relation between OH and H2O maser emission in galaxies. Results. The maser in NGC 3556 is associated with a compact radio continuum source that is most likely a supernova remnant or radio supernova. In Arp 299, the luminous water maser has been decomposed in three main emitting regions associated with the nuclear regions of the two main galaxies of the system, NGC 3690 and IC 694, and the region of overlap. In NGC 4151, only one of the two previously observed maser components has been tentatively detected. This feature, if real, is associated with the galaxy’s central region. The only galaxy, so far, where luminous maser emission from two maser species, OH and H2O, has been confidently detected is Arp 299. Weaker masers from these two species instead coexist in a number of objects. A search for emission from both maser species in a larger number of galaxies is, however, needed to assess these last two results better.

Ammonia (J,K) = (1,1) to (4,4) and (6,6) inversion lines detected in the Seyfert 2 galaxy NGC 1068

We present the detection of the ammonia (NH3) (J,K)= (1,1) to (4,4) and (6,6) inversion lines toward the prototypical Seyfert 2 galaxy NGC 1068, made with the Green Bank Telescope (GBT). This is the first detection of ammonia in a Seyfert galaxy. The ortho-to-para-NH3 abundance ratio suggests that the molecule was formed in a warm medium of at least 20 K. For the NH3 column density and fractional abundance, we find (1.09 +/- 0.23) x 10(14) cm(-2) and (2.9 +/- 0.6) x 10(-8), respectively, from the inner similar to 1.2 kpc of NGC 1068. The kinetic temperature can be constrained to 80 +/- 20 K for the bulk of the molecular gas, while some fraction has an even higher temperature of 140 +/- 30 K.

Dust Emission from High-Redshift QSO[CLC]s[/CLC]

We present detections of emission at 250 GHz (1.2 mm) from two high-redshift QSOs from the Sloan Digital Sky Survey sample using the bolometer array at the IRAM 30 m telescope. The sources are SDSSp 015048.83+004126.2 at z=3.7 and SDSSp J033829.31+002156.3 at z=5.0; the latter is the third highest redshift QSO known and the highest redshift millimeter-emitting source yet identified. We also present deep radio continuum imaging of these two sources at 1.4 GHz using the Very Large Array. The combination of centimeter and millimeter observations indicate that the 250 GHz emission is most likely thermal dust emission, with implied dust masses approximately 108 M middle dot in circle. We consider possible dust heating mechanisms, including UV emission from the active galactic nucleus (AGN) and a massive starburst concurrent with the AGN, with implied star formation rates greater than 103 M middle dot in circle yr-1.