This pages lists the Seminars that were given at the EAO offices in Hilo in 2016. The EAO staff would like to thank all guest speakers and encourage new astronomers/instrument specialists to give talks when visiting.
December 29th, 2016, 2pm (HST)
Title: Role of the magnetic field at ≤ 100 AU: New insights on star formation revealed with ALMA
Satoko Takahashi, NAOJ / Joint ALMA Observatory
With the longest baseline currently available with ALMA, we have performed linear polarization observations of 1.1mm continuum emission toward a candidate of the youngest intermediate mass protostellar source. We have achieved a spatial angular resolution of 0″.03 × 0″.02 that corresponds to the linear size scale of ~10 AU at the distance to the source. Our image demonstrated in great detail the distribution of material and changes of measured polarization vectors within a size scale of similar to that of the solar system. Detected polarization vectors are spatially resolved and clearly show organized structures. Assuming that the grain alignment caused by the radiation torque plays a major role for the observed polarized emission, our result suggests: (1) that the magnetic field vectors are parallel to the major axis of the detected disk-like structure which is consistent with the cloud scale magnetic field direction, while (2) the magnetic field associated with surrounding structure is almost perpendicular to the field associated with the disk-like structure. The changes of field directions from the outer area to the central disk-like structure could be explained by toroidal wrapping of the magnetic fields as predicted by recent numerical simulations.
December 28th, 2016, 2pm (HST)
Title: Young, Blue, and Cold – A Blind Survey of Nearby Dusty Galaxies with Herschel-ATLAS
Christopher Clark, Cardiff University, UK
I will present the HAPLESS survey; using the Herschel-ATLAS, we have assembled a blind, FIR-selected sample of nearby galaxies, which reveals a surprising diversity of systems. The galaxies of our blind sample tend to be very dust rich, very HI-rich, and host to very cold dust – despite having particularly high SSFRs. The physical nature of the dust varies greatly between galaxies; bizarrely, we find that the more dust-rich a galaxy is, the smaller the fraction of a galaxy’s UV light gets absorbed by dust. We use our sample to study how the cold dust in galaxies is heated. We consider star formation and the older stellar population, and find that the surface density of these heating sources plays only a minor role. Rather, it is the total quantity of a given heating source – relative to the dust mass – that appears to be the driver.
Prominent in our survey is a subset of extremely blue galaxies, which have been severely under-sampled by previous targeted and less-sensitive surveys of dust in the local universe. Often irregular and/or highly flocculent in morphology, they exhibit the coldest dust, the largest atomic gas fractions, and the highest SSFRs. Although containing only 6% of our sample’s stellar mass, they account for over 35% of its dust mass. Despite being so dust-rich, they also exhibit the least dust attenuation and appear to be immature, and as such they provide valuable insights into the chemical evolution of young galaxies.
Additionally, I will discuss some recent work we have conducted on deriving an empirical value for the notoriously poorly constrained dust mass absorption coefficient.
November 17th, 2016, 2pm (HST)
Title: A Chandrasekhar-Fermi analysis of OMC 1
Kate Pattle, University of Central Lancashire, UK
I will present early results from the BISTRO survey, demonstrating methods for combining BISTRO data with previous SCUBA-2 and HARP observations in order to perform a Chandrasekhar-Fermi analysis. We find a total magnetic field strength in OMC 1 in the range 4 – 14 mG, with our best estimate being |B| = 9.4 mG. The Chandrasekhar-Fermi analysis suggests that magnetic energy density in OMC 1 is comparable both to the energy density in the gravitational field of the Orion BN/KL-AS system and to the energy density in the Orion BN/KL outflow. I will discuss whether the BN/KL outflow could have caused large-scale distortion of the local magnetic field in the lifetime of the outflow, or whether the magnetic field morphology in OMC 1 is caused by the compression of a primordial magnetic field by the gravitational attraction of the BN/KL and AS clumps.
November 3rd, 2016, 2pm (HST)
Suzie Ramsay, ESO
We have been seeking to understand the nature of the formation of massive stars by using observations of shock-excited molecular Hydrogen to detect and characterise outflows around candidate high mass young stellar objects. In this talk, we present new results from observations around the candidate high mass young stellar object (HMYSO) IRAS 18264-1152. The region hosts a spectacular, parsec scale outflow apparently centred on the location of the deeply embedded HMYSO. New 3D spectroscopic observations taken using the ESO VLT K-band Multi Object Spectrograph reveal that life is never that simple!
October 26th, 2016, 2pm (HST)
Title: Measuring the Hubble Constant, Black Hole mass and beyond with H2O megamaser disks
Feng Gao, Shanghai Astronomical Observatory, China
22 GHz H2O megamaser disks, which trace a thin sub-pc scale molecular disk in Keplerian rotation movement around central SMBHs, provide us with a unique dynamic tool for measuring the geometric distance and enclosed mass to/within such systems. The Megamaser Cosmology Project (MCP) aims to constrain the Hubble Constant to better than 3% uncertainty with such disk maser systems. In the first part of my talk, I will give an update on the recent progress of MCP, as we have finished geometric distance measurements to 4 megamaser disk systems and they together yield H0 of 67.6 ± 4.0 km/s/Mpc. In addition, we also recently finished BH mass measurement in 5 new disk maser systems. Combined with velocity dispersion measurements, we confirmed that the megamaser disk hosting galaxies do not follow the empirical M-σ relationship defined by elliptical galaxies. Beyond these, of particular interest in the mm/sub-mm domain, strong CO(2-1) emission have been detected in several disk maser systems, which will be utilized to calibrate the CO-based BH mass measurement method. This CO emission could also be used to study the geometry and orientation of the molecular disks beyond the maser disk scale. Finally, I will also mention results from our recent attempts to search for high frequency (321, 325, 658 GHz) H20 maser emission in several disk maser systems.
October 19th, 2016, 2pm (HST)
Title: Environmental Variations in the Atomic and Molecular Gas Radial Profiles of Nearby Spiral Galaxies
Angus Mok, McMaster University, Canada
We present an analysis of the radial profiles of a sample of 43 HI-flux selected spiral galaxies from the Nearby Galaxies Legacy Survey (NGLS) with resolved James Clerk Maxwell Telescope (JCMT) CO (3-2) and/or Very Large Array (VLA) HI maps. Comparing the Virgo and non-Virgo populations, we confirm that the HI disks are truncated in the Virgo sample, even for these relatively HI-rich galaxies. On the other hand, the molecular gas distribution is enhanced for Virgo galaxies near their centres, resulting in higher H2-to-HI ratios and steeper radial profiles. This is likely due to the effects of moderate ram pressure stripping in the cluster environment, which would preferentially remove low density gas in the outskirts while enhancing molecular gas near the centre. Combined with Hα star formation rate maps, we find that the star formation efficiency (SFR / H2) is relatively constant with radius for both samples, but with the Virgo galaxies having a lower star formation efficiency than non-Virgo galaxies. These results suggest that the environment of spiral galaxies can play a role in the formation of molecular gas and the star formation process.
September 28th, 2016, 2pm (HST)
Fabrizio Arrigoni Battaia, ESO, Garching
Recently, giant (>300 kpc) and luminous Lyman-alpha nebulosities have been discovered around radio-quiet z ~ 2 – 3 quasars. Being currently explained as powered by the ionizing radiation of quasars, these bright large-scale nebulosities suggest the possibility of studying the circum/inter-galactic gas in emission around individual systems, and not only in the Lyman-alpha line. Indeed, observations of high-ionization emission lines like He II (1640 Å) and C IV (1549 Å) provide important diagnostics of physical conditions in these nebulae, and clues to the mechanism that powers them.
In the first part of my talk, I will present sensitive observations of these emission lines for a giant Lyman-alpha nebula around a quasar, and I will show how photoionization models can be used to interpret such observations.
In the second part of the talk, I will instead focus on the search for additional targets for this experiment. Indeed, current statistics seems to reflect that only less than 10% of radio-quiet quasars show such bright giant extended Lyman-alpha emission on >100 kpc scales, and this seems to happen in the presence of a clear overdensity. In this framework, I will present the results of the narrow-band FLASHLIGHT-GMOS survey, and of the ongoing IFU QSO MUSUEM survey, both targeting the quasar population at z ~ 2 – 3. Finally, I will explain the role of JCMT in this context.
September 13th, 2016, 2pm (HST)
Jean-François Robitaille, Jodrell Bank Observatory, University of Manchester, UK
Diffuse synchrotron is a powerful tracer of the magnetised turbulent non-thermal medium over a broad range of spatial scales. Recently, several surveys of the Galactic polarised emission over a large portion of the sky have been successfully completed (e.g. CGPS, S-PASS, GALFACTS, GLEAM). These surveys have revealed the complexity of the Galactic magnetic field structures on all scales. Unfortunately, a clear interpretation of the Stokes parameters Q and U, and of the associated polarisation vector P, is difficult. Stokes Q and U are not invariant under rotation. Large-scale Faraday screens can produce a rotation of the Q-U plane and affect the interpretation the polarisation distribution. Also, polarisation data are usually interpreted in terms of the amplitude or the angle of the polarisation separately, which leads to an incomplete analysis of the magnetic field power spectrum in the interstellar medium.
In this presentation, I will talk about two methods that have been developed to overcome these difficulties. The first is the analysis of the gradient of linear polarisation, commonly called the gradient of P. Introduced by Gaensler et al. (2011), this quantity is invariant under arbitrary translations and rotations of the Q-U plane and allows us to highlight areas of sharp change in the magnetic field and/or the free electron density, which are most likely due to turbulent fluctuations or shocks in the interstellar medium. Recently, Robitaille & Scaife (2015) demonstrated that the gradient of P analysis can be extended to multiple spatial scales, allowing one to calculate the power spectrum of the gradient of P, giving a complete measure of the magnetic field fluctuations. The second method is the spin 2 decomposition of the Stokes Q and U signal in two rotationally invariant quantities, commonly called the E- and B-mode polarisation. Mainly used for cosmic microwave background analysis, this decomposition can also be applied to polarised synchrotron emission to reveal previously hidden patterns in the polarisation signal that are correlated with H-alpha emission and gradient of P features. I will underline the interesting relationships that exist between both methods and demonstrate that analyses of local variations in both decompositions can be used as complementary tools to each other in order to develop a better understanding of the origin of magnetic field structures and their underlying physics.
August 29th, 2016, 2pm (HST)
Title: The star-forming properties of CHIMPS
Andy Rigby, Cardiff University, UK
CHIMPS is a JCMT spectral survey of 13CO and C18O (3–2) which spans approximately l = 28 – 46 degrees in Galactic longitude, and |b| < 0.5 degrees in latitude. Owing to the comparatively rare isotopologues and high-critical density transition, the survey traces more optically thin and denser gas than other publicly available surveys such as the Galactic Ring Survey (GRS) and the CO High-Resolution Survey (COHRS), and as such ought to be more closely linked to star formation. The CHIMPS data go hand-in-hand with the GRS and COHRS, and I will demonstrate how their combination allows the physical parameters of the 13CO clouds to be determined. I explore the accessible parameter space for the dense clump and cloud population and, by finding star-forming content in the form of compact 70-micron Hi-GAL sources associated with the CHIMPS clouds, I calculate the star formation efficiency and examine the distribution across this section of the inner Galactic plane.
August 22nd, 2016, 2pm (HST)
Ching Tao-Chung, National Tsing Hua University, Taiwan
We present Submillimeter Array 345 GHz polarization observations of six massive dense cores in the DR21 filament. In contrast to the ordered parsec-scale magnetic fields of the filament revealed by the JCMT polarization map, the SMA dust polarization shows complex magnetic field structures in the 0.1 pc massive cores. The orientations of the massive cores appear to be either parallel or perpendicular to the magnetic fields of the filament but randomly aligned with the mean magnetic field of the cores, suggesting that the parsec-scale fields play a more significant role than the 0.1 pc scale fields during the formation of massive cores. A statistical analysis of the observed polarization dispersion yields a magnetic field strength of 0.4 – 0.6 mG in the massive cores. Taking the turbulent, magnetic, and gravitational energies into account, we estimate the virial parameters of the sources. The results show that except for the most massive source, DR21(OH), which is a clear supercritical core, other cores have the turbulent energy dominates magnetic and gravitational energies. Since protostars exist in our sources, we speculate that the star formation in massive cores is regulated at scales below 0.1 pc.
Beside the work of the DR21 filament, I will briefly introduce SMA polarization mosaic observations which together with the ongoing JCMT BISTRO project, aim to reveal complete view of magnetic fields in molecular clouds.
August 11th, 2016, 2pm (HST)
Hau-Yu Baobab Liu, ESO
We have developed an iterative procedure to systematically combine the millimeter and submillimeter images of OB cluster-forming molecular clouds, which were taken by ground based (JCMT, CSO, APEX, IRAM-30m) and space telescopes (Herschel, Planck), to yield images which have high angular resolution but with little or no loss of extended structures. Based on the combined images, we have derived the ~10″ resolution dust column density and temperature maps for the seven extremely luminous (L > 106 Lsun) Galactic OB cluster-forming molecular clouds, namely W49A, W43-Main, W43-South, W33, G10.6-0.4, G10.2-0.3, G10.3-0.1. These images reveal dramatically different cloud morphologies. For example, molecular clouds W49A and G10.6-0.4 show the highly centrally concentrated geometry, where the central parsec scale dense molecular clumps occupy 10% – 20% of the overall cloud mass. They are connected with radially aligned gas filaments. The W43 molecular clouds, which are known to be relatively turbulent, show larger numbers of widely distributed localized gas cores/clumps. G10.3-0.1 and G10.2-0.3 are interacting with HII regions, and show large-scale clumpy ring-like morphology, or clumpy shells that are closely following the outer rim of the HII regions. Their different cloud morphology may indicate the very different modes of OB cluster-formation, or may indicate parent molecular cloud structures at very different evolutionary stages. We hypothesize that the massive molecular gas clumps located at the centre of G10.6-0.4 and W49A may be direct consequence of the global collapse of the parent molecular clouds. Such kind of massive clumps may be rare, which may eventually form gravitationally bound massive stellar clusters. The can be analogous to the young massive clusters or globular clouds found in the extragalactic surveys. Finally, we found that with the high angular resolution we achieved, our visual classification of cloud morphology can be linked to the systematically derived statistical quantities (i.e. the enclosed mass profile, the column density probability distribution function, the two-point correlation function of column density, and the probability distribution function of clump/core separations). These results may represent a very fundamental step forward in the studies of starbursts and star-formation laws in a systematic and statistical sense.
July 29th 2016, 2pm (HST)
David Clements, Imperial College, London, UK
The role of dusty galaxies in galaxy formation and evolution at very high redshifts (z>4) remains unclear, largely because we have lacked the observation tools to search for them over large areas of the sky. That all changed with the advent of the Herschel Space observatory and specifically the SPIRE instrument. I will describe results from a number of large area SPIRE searches for such objects, the colour selection of candidates, and the results of followup observations that have now found dusty galaxies with very high star formation rates out to z=6.34 and candidate objects at z>4 in surprisingly larger numbers. I will also look at how these searches can be extended to still higher redshifts using instruments such as SCUBA2 and NIKA.
July 19th, 2016, 2pm (HST)
Bumhyun Lee, Yonsei University, Korea
Ram pressure stripping (RPS) due to the intracluster medium (ICM) is a mechanism that can effectively strip the interstellar medium (ISM) from galaxies within a relatively short timescale, making galaxies become red and passive. Much evidence for RPS has been found to date in many HI studies, but it is still arguable whether molecular gas can be also affected by the ram pressure. In this talk, I will present SMA 12CO (2-1) data of three spiral galaxies (NGC 4330, NGC 4402, and NGC 4522) that are undergoing active HI stripping in the Virgo cluster. We aim to study whether the molecular gas properties such as distribution and kinematics are changed due to the ram pressure. We find that both CO distribution and kinematics are asymmetric and disturbed as HI gas. Comparing with multi-wavelength data (optical, HI, UV, Hα), I will discuss how star formation activity changes together with ISM while a galaxy undergoes RPS. In addition, I will present the preliminary results on the physical and chemical status of molecular gas of NGC 4402 that we are currently probing using multiple CO transitions.
June 24th, 2016, 11am (HST)
Claire Moutou, CFHT/CNRS
With more than 3000 exoplanets discovered today, there are still open questions about planetary systems -maybe more than when the solar system was the only known one! For instance, many mysteries remains about the physics of hot Jupiters, 20 years after their first discovery. It does not help that they are extremely rare in the population, after having been the norm for exoplanets. Hot Jupiters have been searched for around young stars for long times, and only recently do we have good evidence that they are here, too. I will present hot Jupiters in general, and focus on the recent discoveries around young stars and their implications for formation and migration theories.
June 16th, 2016, 4pm (HST)
Michal Michalowski, IfA, University of Edinburgh
I will discuss the process of gas inflow on galaxies and subsequent fuelling of star-formation. Using recent ATCA HI observations I will show that galaxies with anomalous local metallicity decrements (gamma-ray burst host galaxies) have substantial atomic gas reservoirs, and are deficient in molecular gas. This suggests that star formation in these galaxies may be fuelled by recent inflow of metal-poor atomic gas. This is controversial, but can happen in low-metallicity gas near the onset of star formation because cooling of gas (necessary for star formation) is faster than the HI-to-H2 conversion.
May 10th, 2016, 2pm (HST)
Guido Roberts-Borsani, University College London
Since the installation of the Wide Field Camera 3 (WFC3) instrument on the Hubble Space Telescope (HST), an increasing number of high redshift galaxy candidates have been identified by means of their photometric properties, with >700 probable galaxies identified at z ∼ 7 – 8 and another 10 – 15 candidates identified even further out at z ∼ 9 – 11. However, the entire enterprise of finding especially bright galaxies at z ≥ 7 has been limited by the availability of sufficiently deep, multi-wavelength near-infrared data over wide areas of the sky. As Y-band observations are not available over the full CANDELS program to perform a standard Lyman-break selection of z>7 galaxies, we employ an alternate strategy using deep Spitzer/IRAC data. We identify z ∼ 7.1 – 9.1 galaxies by selecting z>~6 galaxies from the HST CANDELS data that show quite red IRAC [3.6] − [4.5] colors, indicating strong [OIII]+Hβ lines in the 4.5μm band. Applying this selection criterium over the full ~900 arcmin2 of the CANDELS survey, we identify 4 unusually bright (H160, AB ~7.5). All 4 candidates have been spectroscopically confirmed – with 2 of them breaking the redshift record in the process – with the derived photometric redshifts in excellent agreement with the spectroscopic redshifts, thereby validating our selection criteria.
May 4th, 2016, 2pm (HST)
Zhi-Yu Zhang, IfA, University of Edinburgh/ESO
Recent studies on star formation indicate that stars, especially the massive stars, are predominantly formed in dense molecular cores. I will present a survey of multiple transitions of CS (from J = 1 – 0 to 7 – 6), and HCN/HCO+ J = 4 – 3 in nearby star-forming galaxies, including normal spirals, starburst, and ULIRGs. We find linear correlations between LIR and Lgas for all dense gas tracers across eight magnitudes of IR luminosity (LIR from 104 Lsun to 1012 Lsun), on scales from entire galaxies to Galactic dense cores. Irrespective of the critical density of a specific transition, dense molecular gas is universally related in a linear way to star forming activities for self-gravitationally bound gas systems.
May 3rd, 2016, 2pm (HST)
Title: The state of H2 gas and the initial conditions of star formation in galaxies: A new view in the age of Herschel and ALMA
Padelis Papadopoulos, Cardiff University
I will review and revisit the basic premise that H2 gas in galaxies is always heated by the FUV component of starlight via the photolectric effect on dust grains. Other H2 gas heating mechanisms will be presented, and their effects on the H2 thermal state will be discussed. Their impact on the initial conditions of star formation across the Universe is expected to be profound, and it can no longer hide behind large columns of gas and dust, no matter if it is in the Milky Way or in other galaxies I will end by outlining ways to lift the veil and and we may expect.
March 23rd, 2016, 2pm (HST)
Julie Wardlow, Durham University
Over the past ~20 years the high-redshift Universe has been increasingly opened to scrutiny at far-infrared wavelengths, where cool dust emission from star-formation dominates. The dusty star-forming galaxies (DSFGs) and submillimeter galaxies (SMGs), selected at these wavelengths likely represent an important, but short-lived phase in the growth of massive galaxies. These DSFGs often have star-formation rates in excess of ~1000 solar masses per year and are confirmed out to beyond z~6, although their redshifts and high dust contents make them faint and difficult to study at other wavelengths. Using data from the Herschel Space Observatory I have identified a population of DSFGs that are strongly gravitationally lensed and therefore magnified and available for unprecedented scrutiny. I will describe how this important gravitationally lensed population is identified, and present results from our extensive multi-wavelength, multi-facility follow-up studies, including luminosities, masses, morphologies, and stellar, dust and gas contents.
February 16th, 2016, 2pm (HST)
Alex Tetarenko, University of Alberta
Black hole X-ray binaries (BHXBs) — the stellar-mass counterparts of Active Galactic Nuclei (AGN) — provide ideal laboratories to probe the ubiquitous phenomena of accretion and jet ejection, especially as their rapid evolutionary timescales (typically days to months) allow us to study these processes in real time. In particular, data in the mm/sub-mm regime uniquely probe emission originating close to the black hole, at the base of the relativistic jet in the BHXB. Although several transient BHXBs undergo an outburst period every year, only rare (once per decade), extremely bright outbursts allow us to probe the process of accretion and the physics of accretion-fed outflows near (or above) the Eddington limit, which is essential in understanding jet launching and acceleration mechanisms. After 26 years of quiescence, the BHXB V404 Cygni entered into one of these rare outburst states on June 15, 2015, and swiftly became the most luminous BHXB outburst seen in the past decade. Immediately following its detection, V404 Cygni began displaying extraordinary multi-wavelength flaring activity, seemingly linked to powerful jet ejecta launched from the black hole. In this talk, I will discuss striking first results from our simultaneous multi-wavelength observing campaign (VLA, VLBA, SMA, and JCMT) during the most active phase of this outburst; where interpretations of the synchrotron jet based on radio observations alone (the traditional approach) imply a dramatically different view than what the complete data set (including mm/sub-mm) suggests.