Astronomy-Related Research Activities

AGN Evolution:

    Super-massive black holes (SMBHs; >1e6 Msun) are now believed to reside at the centers of nearly all massive galaxies. As such, the cosmological evolution of AGNs and the growth of the SMBHs that power them are extremely important constraints on models of galaxy formation and evolution. Obtaining a true census of these AGN, however, has proven difficult due to various observational biases. Invariably, one must look to several different tracers such as >2keV X-ray continuum, mid-IR continuum, radio continuum/morphology, and high-ionization emission lines to understand the true AGN population.

    Since 2001, I have worked with a team of scientists to study the evolution of AGN in the Chandra Deep Fields (CDFs). The CDFs (North and South) are the two most data-rich regions in the entire sky, with some of the deepest Chandra, HST, Spitzer, and ground based observations ever performed. In addition to helping assemble various source catalogs for these fields (e.g., Alexander et al. 2003; Brandt et al. 2001a; Lehmer et al. 2005; Luo et al. 2008), I have led several exciting follow-up programs to quantify the faint X-ray source population, which are predominantly distant AGN. Dr. Niel Brandt has assembled a compilation of our work ( CDF-N, CDF-S, E-CDF-S).

    Current works in progress:

    • X-ray Spectroscopy of Distant AGN in the CDFs
    • NIR spectroscopic follow-up of Distant AGN/ULIRGs (ECDFs, COSMOS, field)
    • Constraints on the Nature of the Faint Radio Galaxy Population
    • Improving the Positional Uncertainties of Chandra Sources
    • Uniform ACIS EXTRACT reduction of several key survey fields
    • NuSTAR X-ray Observatory Survey of ECDFS and COSMOS fields
    • NuSTAR X-ray Observatory Constraints on Nearby Heavily-Obscured AGN
    • Optical/NIR Follow-up of WISE-detected Heavily-Obscured AGN
    • Deep ALMA Observations of Lensed Clusters

    There is still much to be done, however, as extrapolation of the above work only accounts for ~50% of the X-ray background near the 30 keV peak, implying a substantial population of missing AGN. Many of the wider-field surveys have yet to be systematically explored and, in the near term, we hope to produce uniform X-ray catalogs for ~20 survey fields in order to build substantially larger samples of detected and undetected objects.


    I began studying supernovae (SNe) through the serendipitous detection of SN1996cr wth Chandra in 2000 June (Sambruna et al. 2001, Bauer et al. 2001), which I eventually confirmed as a type IIn SN in 2006 using VLT spectroscopy (Bauer et al. 2007; 2008). SN1996cr showed several parallels with the peculiar SN 1987A (albeit >1000 times more luminous!), as well as nearby SN 1978K and SN 1979C. The archival X-ray and radio lightcurves and spectra for SN 1996cr indicated that a compact, dense shell was formed by the progenitor due to a dramatic stellar wind changes as little as 100 yrs prior to the SN, which created a wind-blown bubble; this rapid evolution is intriguing and must be reconciled against theoretical stellar evolution models. I have initiated wide-ranging follow-up observations of SN1996cr (see below). SN1996cr piqued my interest in massive core-collapse SNe in general, and I am currently developing follow-up programs to place constraints on these intriguing objects in conjunction with both the Millenium Chilean Supernova Search group and several international collaborations. I list below my ongoing/proposed projects.

      Follow-up programs of SN 1996 to study its evolution:
    • HETGS X-ray observation (500ks Chandra)
    • IR detection and dust characterization (Spitzer IRAC/MIPS + DDT IRS)
      Other things:
    • Expanding strong multi-wavelength constraints to other nearby SNe
    • Polarimetry of SN2010jl
Galactic Center:

    I am involved in a Legacy project of the Galactic Center to study both high- and low-mass X-ray binaries (HMXBs, LMXBs) using 1.2~Ms of Chandra observations covering the inner 300 pc of our Galaxy. The goals of this study are to test various models for the Galactic Center star formation history, constrain the origin and fate of hot, X-ray emitting plasma that suffuses the region, and assemble a large sample of quiescent HMXBs for spectroscopic follow-up. My role have been to provide a catalog of X-ray sources with accurate astrometry (~0.2") in order to facilitate meaningful multi-wavelength follow-up studies for the various underlying source populations, including the HMXBs. Early notable results are the identification of 16 high-mass interacting-wind binaries (Mauerhan et al. 2008) and the lack of any new transients, which strengthens the argument that the the inner few parsecs of the Galactic Center act as an LMXB factory (Muno et al. 2005). Forthcoming UKIDSS data to K>17 may allow us to substantially expand our HMXB candidate list, although confusion will be a MAJOR problem in certain areas of the field.

    • NuSTAR X-ray Observatory Survey of Galactic "Nursery" Fields
    • Spectroscopic follow-up of HMXB candidates
    • Near-IR variability searches
Other Focused Projects:

    CG X-2 : I occasionally study ultraluminous X-ray sources (>1e39 erg/s) in nearby galaxies. I am currently working on new constraints for CG X-2, a periodic binary in the Circinus Galaxy.

    • Improving astrometry and studying the Halpha nebula around CG X-2
    • Investigating multi-epoch temporal/spectral properties of CG X-2

    AGN Tracer correlations : I have an ongoing project to compare several AGN tracers for a large sample of type 1 and 2 AGN spanning 5-6 orders of magnitude in luminosity.

RBSC-NVSS Cross-Correlation:

    For my PhD thesis (along with Jim Condon, Trinh Thuan, and John Broderick), I cross-identified the ROSAT All Sky Survey Bright Source Catalogue (RBSC; Voges et al. 1998) with the NRAO VLA Sky Survey (NVSS; Condon et al. 1998) and the USNO optical catalogue (USNO; Monet et al. 1999) to produce a well-defined sample of 1556 IDs for multi-wavelength studies. Here is a link to the full thesis in all its beastly glory (and ADS reference in case you wish to cite something from it). Here are the relevant chapters:

    • RBSC-NVSS I: Sample definition and ID methodology (ps)

      Table 1 (ps, txt) - RBSC-NVSS stellar objects (44)
      Table 2 (ps, txt) - RBSC-NVSS extragalactic objects (1512)

    • RBSC-NVSS II: Optical Spectroscopic properties - unpublished (sigh)

      Spectra Data (tgz) - ascii spectra, fit parameters, and plots of resulting fits

    • RBSC-NVSS III: Multiwavelength properties, Analysis, Luminosity
      Functions, etc. - unpublished and largely outdated now (sigh)