About Professor Joss Bland-Hawthorn

Research is an exhilarating journey of discovery; you learn something new and exciting each week of the year. And there is a strong sense of community with researchers throughout Australia and the international scene.

Joss specializes in extragalactic and galactic astronomy, and in developing astronomical instrumentation.

Joss Bland-Hawthorn is an astrophysicist and the most recent recipient of a Federation Fellowship at the University of Sydney. He specializes in galactic research and instrumentation. In 1986, he obtained his PhD in astrophysics from the Royal Greenwich Observatory prior to taking up appointments in Hawaii and Texas. In 1993, he moved to the Anglo-Australian Observatory where he was Head of a highly successful group that pioneered astronomical concepts with names like Nod & Shuffle, Dazle, Starbugs, Honeycomb, and so on. In 1995, he developed TTF, the first tunable filter in astronomy, a concept that he helped to transport to other telescopes: MMTF on Magellan, Osiris on Grantecan, and F2T2 on Gemini. Joss was also pivotal to the development of the DAZLE concept for the VLT designed to detect the earliest galaxies in the universe. In 2002, he wrote papers on the prospect of optical lasers being used to communicate data from satellites back to Earth. The concept was finally demonstrated by the MESSENGER satellite in 2006 on its way to Mercury. In 2003, he proposed the new field of astrophotonics that sits at the interface of astronomy and photonics. His group at the University of Sydney is now close to solving three longstanding problems: (i) how to suppress the bright infrared sky; (ii) how to build miniature spectrographs; (iii) how to image the sky simultaneously at hundreds of distinct locations over a wide field.

Joss’ main area of interest in astrophysics is galaxy formation and evolution. His approach has been to focus on stellar and gas content of nearby galaxies. For two decades, Joss and colleagues have studied the impact of starbursts and supermassive black holes on the host galaxy. He is an authority on the phenomenon of galactic winds, having identified that this is going on even in our Galaxy. Joss first established the distances to the mysterious “high velocity clouds” around the Galaxy. The Galaxy is encircled by a band of hydrogen gas called the Magellanic Stream that is surrounded by a plasma gas defying explanation for over a decade. With colleague Ralph Sutherland, Joss demonstrated that there is a cascading shock along the Stream causing it to dissolve along its orbit. Joss first showed that the outer gas disks of spirals become ionized and thus invisible to radio telescopes at their outermost limits.

With Ken Freeman, Joss developed the concept of near field cosmology in order to challenge the prevailing cold dark matter (CDM) paradigm with inferences from nearby galaxies. In particular, they developed “chemical tagging” as a technique to determine which stars in the general field were born at a common birth site. This work inspired the creation of the RAVE, SEGUE, HERMES and WFMOS million-star surveys. In 2005, Joss showed that at least some stellar disks do not truncate suddenly but extend out to the limits of the hydrogen gas. Moreover, the declining metallicity gradient flattens off in the outer disk, something that was not expected in existing models.

www.physics.usyd.edu.au/~jbh

Selected publications

  • K. Freeman & JBH, 2002, ARAA, 40, 487 “The New Galaxy: Signatures of its Formation”
    Breakthrough paper that introduced a number of important concepts: (i) maybe half of all clues to cosmology are to be found in the nearby universe, i.e. near-field cosmology; (ii) galaxy formation is largely about disk formation; (iii) galaxy formation and evolution can be unravelled with chemical tagging, cf. DNA fingerprinting; (iv) astronomers should embark on million-star stellar abundance surveys in order to pursue near-field cosmology seriously. This work motivated the RAVE, SEGUE and WFMOS stellar surveys.
  • JBH, M. Vlajic, K. Freeman & B. Draine, 2005, ApJ, 629, 239 “NGC 300: An Extremely Faint Outer Stellar Disk Observed to 10 Scale Lengths”
    The first demonstration that galaxy disks are much larger than were previously thought. Initially, astronomers were skeptical that this could be true, but this is now known to be true for about 30% of spirals.
  • S. Veilleux, G. Cecil & JBH, 2005, ARAA, 43, 769 “Galactic Winds”
    The first comprehensive review of galactic winds in galaxies.
  • JBH & R. Tully 1988, Nature, 334, 43 “The Large-scale Bipolar Wind in M82”
    The first comprehensive demonstration of a galactic wind in a galaxy, confirmed in more detail in Shopbell & Bland-Hawthorn (1998), ApJ.
  • JBH & M. Cohen, 2003, ApJ, 582, 246 “The Large-scale Bipolar Wind in the Galactic Centre”
    The discovery of a large-scale wind from the Galaxy; this could never have been detected in distant galaxies suggesting that galactic winds may be far more common than we realize.
  • JBH, K. Freeman & P. Quinn, 1997, ApJ, 490, 143 “Where do the Disks of Spiral Galaxies End?”
    The first demonstration that there is ionized gas beyond the HI edge of spirals. Before this time, it was thought that the edges of disks were defined by the HI gas which stretches beyond the stellar disk.
  • JBH & P. Maloney, 1999, ApJ, 510, L33 “The Escape of Ionizing Photons from the Galaxy”
    The first attempt at measuring the escaping UV field from the Galaxy. This was shown to be strong enough to produce Hα emission on the surfaces of cold gas clouds, and therefore to provide a distance to those clouds (see also JBH et al 1998, MNRAS). This ultimately demonstrated that high-velocity clouds are not far away, as Blitz & Spergel had thought, but mostly well within the Magellanic Stream.
  •  JBH, R. Sutherland, O. Agertz & B. Moore, 2007, ApJ, 670, L109  “The Source of Ionization along the Magellanic Stream”
    The solution to a decade-old mystery, i.e. the cause of the Hα emission along the Stream. The answer demonstrates that the Stream is disrupting violently today rather than slowly stretching out. This has important implications for gas falling onto the Galaxy.
  • Key Instrumentation papers
  • JBH, M. Englund & G. Edvell, 2004, Optics Express, 12, 5902 “New Approach to Atmospheric OH Suppression using an Aperiodic Fibre Bragg Grating”
    The first demonstration of an FBG that can knock out many narrow spectral lines that are irregularly spaced; currently under development for suppression night-sky lines in the infrared.
  •  S. Leon-Saval, T. Birks, JBH & M. Englund, 2005, Optics Letters, 30, 2545 “Multimode Fibre Devices with Single-mode Performance”
    The first demonstration of single-mode action in a multimode fibre; crucial extension of the above paper.
  • JBH, S. Buryak & K. Kolossovski, 2008, J. Opt. Soc. Amer. A (Jan 1st) “Optimisation Algorithm for Ultrabroadband Multi-channel Aperiodic FBG Filters”
    The first existence proof of a filter that can simultaneously remove 150 irregularly spaced night-sky lines.
  • JBH & R. Tully, 1989, AJ, 98, 723 “Hawaii Imaging Fabry-Perot Interferometer (HIFI)”
    Years ahead of its time, HIFI has provided the most detailed observations of powerful outflows in active galaxies, i.e. those powered by supermassive black holes and central starbursts.
  • JBH & D. Jones, 1998, PASA, 15, 44 “Taurus Tunable Filter (TTF): a Flexible Approach to Narrowband Imaging”
    The first tunable imaging device where the user can dial up a spectral band of a given bandwidth at any optical wavelength. It was used on the AAT 3.9m and WHT 4.2m during 1995-2003. The concept has been copied on several large telescopes including JWST, Grantecan 10m, Magellan 6.5m, NTT 3.5m.
  • K. Glazebrook & JBH, 2001, PASP, 113, 197 “Microslit Nod & Shuffle: a Technique for Achieving Very High Densities of Spectra”
    Breakthrough paper that showed how the systematics due to sky subtraction can be greatly decreased with a  differential technique where the telescope is nodded backwards and forwards in synchrony with the charge on the detector. It is now used by a number of large telescopes world-wide.
  • JBH & A. Horton, 2006, SPIE, 6269, 21 “Instruments without Optics: an Integrated Photonic Spectrograph”
    A revolutionary approach to the construction of future astronomical instruments. This breakthrough paper is to be explored in a multi-million dollar development funded by the European Union.
  • Offer & JBH, 1998, MNRAS, 299, 176 “Rugate Filters for OH-suppressed Imaging at Near-Infrared Wavelengths”
    The first attempt to knock out irregularly spaced night sky lines with an imaging filter. This idea has been copied by groups in the USA, in particular, at Caltech.