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Recent Press:

Research:

Recent Research Highlights:

• The Chemical Structure of Galaxies:

  We have been surveying the chemical structure of nearby star forming galaxies at spatial resolutions that approach individual giant molecular clouds. Different environments and star formation rates are sampled. This work builds upon the initial discovery work on resolved extragalactic astrochemistry presented in Meier & Turner 2005. In Meier & Turner 2012 we study the chemical structure of the very nearby, nuclear barred starburst, Maffei 2, with the OVRO and BIMA millimeter interferometers. We discover, for the first time, extremely dramatic variations in the gas chemistry at 50 - 100 pc scales across this nucleus. A principle-component analysis shows that certain groups of species are very tightly correlated, while others are not correlated at all. Moreover, the differences in chemistry match the changing structural properties of the nucleus. HCN, HCO+, HNC, HC3N and C2H are tightly correlated with star formation. Star formation is intimately related to the abundance of dense gas. C2H shows that this dense gas is beginning to experience radiative feedback from the current starburst episode. We discover, for the first time, a minor-axis molecular outflow in C2H, which allows us to kinematically date the age of this burst. SiO, HNCO, and CH3OH are coupled and trace shocked gas associated with colliding molecular clouds in the barred potential. This study represent some of the clearest evidence to date of the potential of large scale chemistry to diagnose structural properties in galaxies.
  In Meier et al. 2014 we image the nuclear starburst and inner disk of the nearby luminous infrared galaxy (LIRG), IRAS 04296+2923 with the CARMA interferometer. This work builds on the previous chemical surveys by pushing the frontiers of the extragalatic chemical surveys to more intense star forming environments and to regions outside the nucleus. These two environments are key to broadening the range of physical and chemical parameter space covered. Comparisons of the CO isotopologues (13CO and C18O) demonstrate that the nucleus of this LIRG has a different molecular cloud structure and possible nucleo-synthetic history from the inner disk. The isotopic abundances suggest, that away from the starburst, a relatively unprocessed disk dominates, consistent with that found in Meier et al. 2010. We tentatively detect shocked CH3OH emission well outside the nucleus. The emission is found at the end of the large scale bar, indicating that large scale bars have the same chemical structure as their smaller nuclear counterparts. Toward the nuclear starburst dense, low opacity molecular gas dominates, explaining the extreme star formation rate.
  In Meier et al. 2015 we use the new ALMA interferometer to map, at giant molecular cloud scales, the structure of 50 different spectral lines, towards the nearby prototypical starburst galaxy NGC 253. This is one of the most extensive imaging surveys of the molecular properties of an external galaxy. A core of intense star formation, traced by radio recombination lines, is embedded in the center of a rich molecular gas disk. The molecular gas disk is dense, warm and opaque even in HCN and HCO+. A sheath of UV irradiated gas envelops the central starburst. Shocked gas signatures are seen across the disk reack out to the base of the minor axis molecular outflow. Large molecules with seven atoms (and possibly more) are clearly seen and extended across the entirety of the nucleus, demonstrating the rich, complex chemistry supported by the interstellar medium in this object.

  
  

  (Left) The molecular morphology of ten species towards the nuclear bar, Maffei 2. Blue contours are CO, yellow contours are 13CO and the colorscale are the chemical tracers. Peach contours delineate the nuclear starburst (Meier & Turner 2012). (Right) The molecular morphology taken along a slice through the major axis of NGC 253 vs. the frequency. Species are labeled. Those in italics are considered tentative indentifications (Meier et al. 2015).

  
  
  

  We are also actively involved in a major (500 + hour) ATCA survey ofthe center of our own Galaxy, entitled SWAG: Survey of Water and Ammonia in the Galactic center. This survey, for which the observations have just been completed, will be an imaging survey covering spatial scales from about 1pc to nearly 500 pc across the central molecular zone in more than 40 different important spectral lines, including but not limited to transitions of H, He, C, H2O, NH3, CH3OH, OH, HCN, HC5N, HNCO, and SO2. Goals of the survey include invetorying molecular clump structure, obtaining resolved, full CMZ physical conditions maps, obtaining an unbias H2O maser survey, full CMZ chemical structure maps and detailed characterization of ionized gasproperties across the nucleus.
  For updates, keep an eye on the survey webpage: SWAG

• The Structure, Star Formation and Physical Conditions of Starbursts:

  To understand the evolution of molecular gas in galaxies and its impact on future generations of star formation, it is necessary to determine the structure and physical properties of that gas. To do this we map the structure and excitation of molecules and correlate them with locations of star formation, shocks and radiative feedback. In Meier et al. 2011 we present spatially resolved radiative transfer modeling of the J=5-4, 10-9, and 16-15 transitions of cyanoacetylene (HC3N) in IC 342, using the VLA, OVRO, and PdB interferometers. This gives a detailed characterization of gas physical conditions of this Milky Way Galactic center clone, at subarcsecond resolution. Comparisons of HC3N with literature studies of other species reveal a multicomponent interstellar medium in IC 342. Away from the starburst, densities and temperatures are fairly uniform, being relatively high and cool. These dense cool cores are the proto-starbursts that are just beginning their starburst phase. The current starburst, however, is unique. It shows faint, but hot HC3N. Implied thermal pressures argue that the (small amount of) very dense gas here is in pressure equilibrium with the starburst ionized gas HII region. The extreme star formation efficiency and pressure equilibrium indicates that the starburst must be more evolved and have nearly finished consuming / dispersing the natal fuel that drove the burst. This study demonstrates that spatially resolved physio-chemical modeling can be a powerful tool for studying starburst / galaxy evolution.
  In Meier et al. 2010 we execute the first detailed, multiwave-wavelength study of one of the closest luminous infrared galaxies (LIRGs), IRAS 04296+2923. LIRGs are rare in the local Universe, so increasing the number of well-studied LIRGs is vital. This LIRG lies (optically) hidden behind the Taurus Molecular Cloud and hence has remained unstudied. We combine Palomar near infrared, Keck mid infrared, OVRO millimeter and VLA radio continuum observations to investigate the structure and star formation properties of this LIRG. The galaxy appears as a 'normal' barred spiral with little indication of interaction, which is rare for (U)LIRGs. This suggests that slow bar-driven transport drives the (secular) evolution. We determine that it is one of the most molecular gas-rich objects out to its distance. The nucleus has two very compact (<50 pc) super star clusters that have a total star formation rate >10x that of the entirety of the Milky Way. Based on the rate of gas consumption and transport, this LIRG appears to be experiencing one of its first major starburst, bulge-building episodes.

  (Left) Shows the HC3N flux vs. rotational quantum number towards a 'proto-starburst' core (Far Left - Top) and towards the current (mature) starburst (Far Left - Bottom), along with fitted Large-Velocity-Gradient radiative transfer models. (Middle Left) The HC3N(5-4) nuclear morphology compared to existing HCN(1-0) observations (Downes et al. 1992) (Meier et al. 2011). (Right) The optical image of the Taurus Molecular Cloud Region (courtesy of W.-H. Wang) with the (invisible) location of IRAS 04296+2923 indicated. (Upper Far Right) The CO(1-0) emission, tracing the total molecular gas distibution, overlaid on the 6 cm radio continuum which locates the nuclear super star cluster. (Lower Far Right) The Palomar near infrared image of the disk ( Meier et al. 2010).

  
  

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Molecular Spectroscopy Notes:

EXTRAGALACTIC MOLECULAR LINE PRIMER (ALMA bands 3 & 6)

EXTRAGALACTIC MOLECULAR LINE PRIMER (VLA bands L - Q)