Date: Tuesday 19-Aug-2014
Speaker: Joanna Corby (UVA, Charlottesville)
Title: Sagittarius B2 at 7-mm: When Chemical Complexity Meets Broadband Interferometry
Sagittarius B2 is the massive star forming region in the Galactic center and hosts the most complex chemistry observed in the ISM. The North core of Sgr B2 (Sgr B2(N)) has compact and extended HII regions and a well-known hot core, the Large Molecule Heimat (LMH). To date, only a few molecular lines have been mapped with the spatial resolution required to distinguish the distinct chemical environments in Sgr B2(N). With the arrival of broadband radio interferometers however, interferometric line surveys are efficient, providing access to the spatial distributions of hundreds of molecular lines within a reasonable observing time. With the new wealth of information available, however, come new challenges in data analysis that require automated methods.
I describe centimeter wave interferometric observations towards Sgr B2(N) that reveal the distinct chemical environments in Sgr B2(N) and focus on a 30 - 50 GHz survey towards Sgr B2(N) conducted with the Australia Telescope Compact Array (ATCA). More than 1000 spectral features are detected in the survey, requiring automated methods of data handling. I present a methodology for an automated line fitting and identification routine applied to the ATCA survey. Further, I highlight the physical and chemical stories emerging from the data set.
Date: Monday 22-Sept-2014
Speaker: Dr. Mike Dunham (Smithsonian Astrophysical Observatory)
Title: The Evolution of Protostars: Assembling Stars from Dense Cores
Stars form from the gravitational collapse of dense molecular cloud cores. In th e protostellar phase, mass accretes from the core onto a protostar, likely throu gh an accretion disk, and it is during this phase that the initial masses of sta rs and the initial conditions for planet formationare set. Over the past decade , new observational capabilities provided by the Spitzer Space Telescope and Her schel Space Observatory have enabled wide-field surveys of entire star-forming c louds with unprecedented sensitivity, resolution, and infrared wavelength covera ge. In this talk I will review resulting advances in the field of protostellar evolution, focusing on observational constraints on the problem of how protostar s gain their mass.
Date: Monday 20-Oct-2014
Speaker: Dr. Marco Chiaberge (STScI)
Title: The hosts and the environment of radio galaxies: clues on the origin of radio-loud activity
I will focus on results from our studies of radio galaxies from z~0 to z~2 and above. While we still don't know the details of the physics of the jet launch, we learned that the nuclei of lower power objects are fundamentally different from all other AGNs. This allowed us to investigate the relationship between the nuclear properties of these AGNs and their black holes. Our results show that, differently from radio quiet AGNs, radio galaxies are invariably associated with BH masses larger than ~10^8 M_sun. I will also present first results form our most recent HST survey of high-power radio galaxies at z>1, which allows us a detailed comparison of the properties of the environment of these sources over more than four decades in radio power. We find strong evidence that mergers are the ultimate triggering mechanism for radio galaxy activity.
Date: Monday 17-Nov-2014
Speaker: Dr. Chun Ly, NASA GSFC
Title: Cosmic Evolution with Gas Metallicities of Star-Forming Galaxies
The chemical enrichment of galaxies, driven by star formation and regulated by gas flows from supernova "feedback" and cosmic accretion, is a key process in galaxy formation. Efforts to study the dependence of the gas-phase oxygen abundance ("metallicity"; Z) against stellar mass (M) and star formation rate (SFR) of galaxies have produced a tight correlation for local star-forming galaxies. In 2010, it was argued that higher redshift galaxies follow this M-Z-SFR relation; however, more recent z~1-2 studies are finding contradicting results. To better understand the M-Z-SFR relation and its redshift dependence, I have conducted three spectroscopic studies at z~1 using the Subaru Deep Field, the DEEP2, and the NewH Survey.
Together, these studies span massive and dwarf galaxies, and galaxies undergoing intense star formation. I will discuss our findings, which have recently been reported in Ly et al. (2014) and de los Reyes, Ly et al. (2014), and future plans to re-calibrate "strong-line" metallicity diagnostics using a sample with "direct" oxygen abundance measurements from detections of the weak [OIII]4363 excitation line.
