Time Domain, Cosmology, Physics Working Group


  • External Chair: Geoff Bower (ASIAA)
  • Internal Chair: Paul Demorest (NRAO)
  • Jim Braatz
  • Avery Broderick
  • Sarah Burke-Spolaor
  • Bryan Butler
  • Tzu-Ching Chang
  • Laura Chomiuk
  • Jim Cordes
  • Jeremy Darling
  • Jean Eilek
  • Dale Frail
  • Gregg Hallinan
  • Nissim Kanekar
  • Dan Marrone
  • Walter Max-Moerbeck
  • Brian Metzger
  • Miguel Morales
  • Steve Myers
  • Rachel Osten
  • Frazer Owen
  • Michael Rupen
  • Andrew Siemion
  • Ashley Zauderer

Science Topics

  • Galactic Center Pulsars
  • Cosmology with Megamasers
    • Currently ~ 150 known H2O system among ~3000 AGNs searched. Surveys are sensitivity limited. Surveys focus on nearby galaxies. All but 2 H2O megamasers have z < 0.05. The two high-z systems are not disk masers.
    • ~30 are in AGN accretion disks, ~10 are interesting for measuring geometric distances.
    • Existing telescopes that are good at K-band: GBT and VLA are good, Bonn ok at K-band (limited by surface of the dish, and weather), QTT good but limited visibility overlap, SRT and LMT will give incremental improvements, good for long baselines.
    • To improve significantly on existing instrumentation, we need more collecting area, and we need at least 5 GBT-quality antennas with long (1000's of km) baselines.
    • Science goals:
      • H0 to ~1-2%,
      • measure BH masses to understand galaxy-BH scaling relations, e.g. M-sigma, and how it relates to galactic evolution.
      • High-z masers interesting; largely uncharacterized.
  • Dual AGN
    • At high frequency (>10 GHz) frequencies surveys will be largely dominated by AGN cores rather than lobe/jet structures.
    • A high resolution (180-300km baseline) survey can identify resolved point sources down to several pc in the source rest frame. Dual and triple systems can be readily identifiable via imaging.
    • Could be achieved through either a large-area survey or simply imaging full FOV of archival images.
  • Imaging galactic transients
    • High resolution + high sensitivity ==> image Galactic transients in exquisite detail on timescales of days to months
    • Go from current blobs to images a la Cyg A with current VLA -- but with superb spectral information
      • Also measure polarizations, which currently are massively depolarized by the beam size (synchrotron sources have unresolved pol'n fractions generally of order a per cent, should be MUCH higher with RM synthesis [high spectral res'n] and high spatial res'n)
    • MERLIN "done right" -- we should look at their science case too
    • Watch changes in opacity, on-going interactions
      • opacity measures densities; also "peel the onion" as you see deeper into the remnant as the source expands
      • interactions reveal both the outflow and the surrounding medium, with potential to determine masses, energies
      • also constrain shaping mechanisms, which are a perennial problem in almost all sources
    • Expansion + velocities ==> direct distances -- always a major concern in the galaxy
    • Triggers could be internal or external
    • Examples: microquasars, CV outbursts of all sorts, SGRs
    • Also "slow" explosions -- planetary nebulae, Hii regions, old novae/SNe
      • e.g. make images at very high resolution of old remnants -- comparative astrometry at high SNR and res'n measures expansion rate; careful flux density monitoring gives
    • 10-ish GHz is "just right" for this science -- sources evolve far too fast at ALMA frequencies; SKA1 doesn't have the resolution, nor the frequency coverage you want to track the changing opacity at early times
      • want full time coverage to track change from "pure explosion" to "hitting junk nearby (e.g., stellar wind)" to "hitting the ISM"
    • Wide instantaneous frequency coverage is great to watch evolving spectra, esp. since you don't know a priori what stage your source will be at on a given day
      • Interesting example: we have a nova outburst where early MERLIN images showed thermal emission from surrounding CSM ionized by initial outburst; recomb. time gives density. Then at late times the ejected material slams into the same material and you see the same structure in the shock.
      • Again for novae NGVLA will have the sensitivity to detect (and image, if we have continental baseline) the same gas as gives you the X-ray and early optical emission. [Complex geometry means you can see into the center to see this stuff.]
  • Note the high-resolution SKA science case manifesto in http://arxiv.org/pdf/1111.6398v1.pdf
    This paper focuses on low frequency and ~3000km baselines. However, some of the science goals outlined can be achieved by NGVLA and perhaps not by SKA if its longest baselines are insufficient.
  • Plasma physics on stars, star-planet interactions:
    • By the time of the mid-2020s and later, we will have moved beyond detection of exoplanets and into the era of detailed characterization of exoplanet atmospheres and environments. A next generation VLA, with increased sensitivity at higher frequencies, can characterize the stellar winds of nearby stars and investigate the impact of the stellar wind on planetary environments. There are already hints at evaporating planetary atmospheres due to radiation effects of host stars (Vidal-Madjar et al. 2003), with some evidence for the particle influence of the stellar wind on planetary atmosphere evaporation (Lecavelier des Etangs et al. 2012). Optically thick radio emission from a fully ionized stellar wind has a ν^0.6 dependence, favoring higher frequencies. Mass loss in the cool half of the HR diagram, along/near the main sequence, has been notoriously difficult to detect, due in part to the much lower values of mass loss here compared to other stellar environments (upwards of 10^-5 solar masses per year for massive stars, compared with 10^-14 solar masses per year for the Sun). Most efforts to detect cool stellar mass loss rely on indirect methods; i.e. inferring stellar mass loss by examining absorption signatures of an astrosphere. A direct measurement of stellar mass loss through its radio signature would be a significant leap forward not only for understanding the plasma physics of the stars themselves, but also for understanding what kind of environment those stars create.

Telecon notes

Topic attachments
I Attachment Action Size Date Who Comment
EVLA-IIoutflows.pdfpdf EVLA-IIoutflows.pdf manage 2 MB 2014-11-24 - 13:37 MichaelRupen NSF presentation for EVLA Phase II: simulations of transient observations
VLANext_SpecificationsOverview_v2.pdfpdf VLANext_SpecificationsOverview_v2.pdf manage 71 K 2014-11-04 - 13:57 GeoffreyBower Specifications for NGVLA
Topic revision: r20 - 2015-01-02, PaulDemorest
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