Research

Supermassive black holes in galaxy centers

Observations show that large galaxies contain black holes at their centers, having masses of millions to billions of solar masses, but we still lack a full understanding of the demographics of black holes and their relationship to their host galaxies.  Our understanding of the black hole population is particularly uncertain at the very top end of the mass range, above around a billion solar masses, and at the bottom end, below a few million solar masses (comparable to the mass of the black hole in the center of the Milky Way Galaxy).  Our group uses the Hubble Space Telescope and the Keck Observatory to carry out direct measurements of black hole masses in the centers of nearby galaxies. We’ve also recently been awarded ALMA observing time for a pilot project to try to measure black hole masses in elliptical galaxies through observations of the rotation of molecular gas disks. Other current projects involve studies of the central compact star clusters in low-mass spiral galaxies, which may be homes of intermediate-mass black holes having masses below 1 million solar masses.

Selected publications:

  • Measurement of the Black Hole Mass in NGC 1332 from ALMA Observations at 0.044 Arcsecond Resolution. A. J. Barth et al, 2016, The Astrophysical Journal Letters, 822, L28 (article link)
  • Toward Precision Black Hole Masses with ALMA: NGC 1332 as a Case Study in Molecular Disk Dynamics. A. J. Barth et al, 2016, accepted for publication in The Astrophysical Journal. (preprint)
  • The M87 Black Hole Mass from Gas-dynamical Models of Space Telescope Imaging Spectrograph Observations. J. L. Walsh et al, 2013, The Astrophysical Journal, 770, 86 (ADS link)
  • A Stellar Dynamical Mass Measurement of the Black Hole in NGC 3998 from Keck Adaptive Optics Observations. J. L. Walsh et al, 2012, The Astrophysical Journal, 753, 79 (ADS link)
  • Dynamical Constraints on the Masses of the Nuclear Star Cluster and Black Hole in the Late-Type Spiral Galaxy NGC 3621. A. J. Barth et al. 2009, The Astrophysical Journal, 690, 1031 (ADS link)

 

Reverberation mapping of active galactic nuclei

Active galactic nuclei (AGNs) and quasars have strong, broad emission lines from ionized gas orbiting very close to the black hole. Understanding the structure and dynamics of this “broad-line region” is an important goal but these regions are so small and so distant that we have no way to image their structure directly.  Instead, we can use time variability of the quasar emission to produce an “echo map” of the ionized gas within just a few light days of black holes that are hundreds of millions of light-years away.  These reverberation mapping observations are a key to understanding the masses and growth rates of supermassive black holes in active galaxies. Our group has led large observing campaigns at Lick Observatory to monitor temporal changes in the brightness of the emission from active galaxies in order to study their inner structure and determine the masses of their black holes.  Our Lick AGN Monitoring Project collaboration involves astronomers from five UC campuses and several other institutions.

Selected publications:

  • Robotic Reverberation Mapping of Arp 151. S Valenti et al, 2015, The Astrophysical Journal Letters, 813:L36 (ADS link)
  • The Lick AGN Monitoring Project 2011: Spectroscopic Campaign and Emission-Line Light Curves.  A. J. Barth et al, 2015, The Astrophysical Journal Supplement Series, 217:26 (ADS link)
  • The Lick AGN Monitoring Project 2011: Fe II Reverberation from the Outer Broad-line Region.  A. J. Barth et al, 2013, The Astrophysical Journal 769, 128 (ADS link)
  • The Lick AGN Monitoring Project: Recalibrating Single-epoch Virial Black Hole Mass Estimates. D. Park et al, 2012, The Astrophysical Journal 747, 30 (ADS link)
  • The Lick AGN Monitoring Project 2011: Reverberation Mapping of Markarian 50.  A. J. Barth et al, 2011, The Astrophysical Journal Letters 743, L4 (ADS link)
  • The Lick AGN Monitoring Project: Broad-line Region Radii and Black Hole Masses from Reverberation Mapping of Hbeta. M. C. Bentz et al, 2009, The Astrophysical Journal, 705, 99 (ADS link)

Other topics

Other research topics include studies of the structure and morphology of nearby galaxies to understand their formation history, through the Carnegie-Irvine Galaxy Survey collaboration and using Hubble Space Telescope imaging data.  In the distant past I’ve also spent a bit of time working on observations of supernovae and gamma-ray bursts.

Selected publications:

  • Fossil Evidence for the Two-phase Formation of Elliptical Galaxies. S. Huang et al, 2013, The Astrophysical Journal Letters, 768, L28 (ADS link)
  • The Carnegie-Irvine Galaxy Survey. III. The Three-component Structure of Nearby Elliptical Galaxies. S. Huang et al, 2013, The Astrophysical Journal, 766, 47 (ADS link)
  • A Normal Stellar Disk in the Galaxy Malin 1.  A. J. Barth, 2007, The Astronomical Journal, 133, 1085 (ADS link)
  • Optical Spectropolarimetry of the GRB 020813 Afterglow. A. J. Barth et al, 2003, The Astrophysical Journal Letters, 584, L47 (ADS link)

Links to my complete publication list are on the publications page.