| Research Interests |
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| Research Interests |
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I received my Ph.D. in Physics from UCLA for the dissertation A Multi-Wavelength Study of the Nearby Starburst Galaxy Maffei 2. Subsequently I have been employed as a postdoctoral researcher at the University of California at Riverside working with Professor Mary Barsony studying the earliest stages of star formation. You may access more information on Astrophysics at UC Riverside as well, including links to preprints. I currently am a National Research Council Fellow at the Infrared Processing and Analysis Center (IPAC) working on a survey of distant luminous infrared galaxies using the Infrared Space Observatory ( ISO).
In this section you can find a summary of my research interests. Don't worry, though: I put in some pretty pictures if you don't want to read the text.
From here you may also peruse my bibliography of publications or check over my curriculum vitae if you are so motivated (though neither are entirely up to date yet...).
Once I have the opportunity to update my science page properly, here's where you will be able to read about the project I'm currently working on...
Though this isn't part of my research, watching comets is always fun. Comet Hyakutake made such a spectacular pass through our neighborhood you could see it from downtown LA if you knew where to look. However, going north of the city it was stunning. This image was captured by Murray Silverstone and myself using a simple setup of 400 ASA film and a 1 minute exposure on a tripod. The three brightest stars to the top of the image are the handle of the Big Dipper. The stunning green glow around the head of the comet is caused by C2 emission lines.
My postdoctoral research has concentrated on the study of "Class 0" protostars. These heavily embedded objects have yet to accrete the bulk of their initial main sequence mass from their infall envelopes and represent the youngest (a few x 104 yr) protostellar sources. Their defining observational characteristics include a high ratio of mm/submm to bolometric luminosity, the presence of molecular outflows, invisibility shortward of 10 um, and spectral energy distributions (SEDs) resembling modified blackbodies with T < 30 K.
The Serpens Cloud Core is a spectacular source of candidate Class 0 protostars, harboring at least five millimeter continuum sources which lack 2 um counterparts. The gas properties in the cores of such young protostellar sources are best studied with carefully-chosen molecular tracers; formaldehyde (H2CO) is an ideal molecule for probing the dense, warm cores of these objects. In a detailed H2CO survey of these sources (Hurt, Barsony, and Wootten 1996) we have found evidence for centrally- heated cores that are dense (n(H2) ~ 106-106.5 cm-3) and substantially warmer (Tex ~ 40-85 K) than their surrounding envelopes. We have even detected evidence for gas infall in the line profiles of many of these sources.
Clear identification of these sources as Class 0 objects hinges on determining their SEDs, showing them to be well fit by cool, single-component blackbodies. We have just completed a study of far infrared emission in the Serpens Core using HIRES- processed IRAS data. By modeling the emission from the known 2 um and millimeter continuum sources we have determined SEDs for all 5 of the Class 0 candidates in the Serpens Core. Their characteristic dust temperatures range from 20-29 K with no evidence for 12 or 25 um excesses that would be associated with more evolved objects. Their dust mass to bolometric luminosity ratios place them squarely in the domain of Class 0 sources, making the Serpens core the densest collection known of such objects (Hurt and Barsony 1996).
This image shows the Serpens Cloud Core at infrared and millimeter wavelengths. Near infrared is shown in blue (2.2 um), far infrared in green (60 um), and millimeter in red (1.1 mm, courtesy of Casali and Eiroa). The red and red-yellow sources, which lack visible 2 um emission, are the candidate Class 0 protostars.
My most recent extragalactic work has been directed towards more fully understanding the nature of the molecular gas in galaxies undergoing vigorous star formation in their nuclei. Using the newly-implemented On-the-Fly (OTF) mapping mode of NRAO's 12m telescope we are mapping the full extent of CO with the full sampling of a single dish; we do not "resolve out" any extended emission that may be missed in an interferometer. With OTF mapping the dish scans rapidly across the map, allowing one to cover the entire area in an hour or less. Thus one can build up an image of uniform sensitivity and pointing, improving greatly on more traditional point-and-integrate methods.
The results in IC 342 have been striking; we find extensive molecular gas in both arm and inter-arm regions. Most interesting is the region of "inhibited" star formation we find coincident with the extended stellar bar; although there are large quantities of molecular gas throughout the bar there is virtually no corresponding star formation outside of the inner nucleus. This result indicates that the presence of molecular clouds is not necessarily sufficient to trigger star formation in this region (Hurt et al. 1996). We have just obtained similar maps for Maffei 2 in both the CO (1-0) and (2-1) transitions. Together with OVRO and BIMA interferometric mosaics along the bar in Maffei 2 we intend to assemble a complete picture of the gas morphology and dynamics of this region.
In this image, the molecular gas is displayed in red while the radio continuum emission (associated with star formation) is displayed in blue. The red bar to the north and south of the nucleus indicates large quantities of molecular gas without significant star formation.
In my dissertation and subsequent research I have observationally tackled the puzzle of nuclear starbursts in spiral galaxies. Starbursts are defined as regions of vigorous star formation confined to spatial extents of several hundreds of parsecs. As star formation rates can equal or exceed those found throughout entire disks of galaxies like the Milky Way, one is driven to ask what processes could trigger and sustain these events. In this I have concentrated on nearly normal spiral galaxies with high rates of nuclear star formation.
I have worked most extensively on the nearby starburst galaxy Maffei 2. Its strong emission in the far infrared, radio continuum, and Brackett gamma are all indicative of a strong burst of nuclear star formation. Because of its close proximity (~ 5 Mpc) and large angular extent (~ 10'), it has been an excellent subject for study of the starburst phenomenon at high angular resolutions. Optical studies of this galaxy have been impaired due to the high foreground extinction (AV ~ 5 mag) caused by its location behind the Galactic plane; as such it has been largely neglected despite its intriguing properties.
Our near infrared (NIR) study of Maffei 2 was the first to unambiguously identify its morphology. Using observations made with NOAO's Simultaneous Quad Infrared Imaging Detector (SQIID) we obtained a 10' x 10' mosaic that clearly revealed it to be strongly barred, of type SBb, with asymmetries that indicate it may have been disrupted recently by a gravitational tidal encounter (Hurt et al. 1993). NIR wavelengths were necessary for estimating the extinction in the nuclear starburst region as well as penetrating the screen of foreground Galactic dust.
The morphological asymmetries in Maffei 2 are found in every other tracer of gas and stars in this galaxy. The dense molecular gas associated with the nuclear starburst, traced by interferometric 13CO (1-0) OVRO and single-dish CO (3-2) CSO observations, is found to lie in a linear structure indicative of a density wave phenomenon reaching to within 50 pc of the nucleus of the galaxy (Hurt and Turner 1991; Hurt et al. 1993b). The asymmetries in the spiral arms are particularly evident in HI observations from the VLA. On the basis of the near infrared morphology and the HI distribution and kinematics we argue for an ongoing merger with a small satellite galaxy as the driving force behind the nuclear starburst (Hurt, Turner, and Ho 1996).
In this image, near infrared emission is shown in red, radio continuum (associated with star formation) in green, and hydrogen gas in blue. The disruption to the galaxy is clearly traced by all of these. The proposed merging companion is the blob near the top of the image.