Nearby, young moving groups are ideal testbeds for studying stellar and planetary evolution. By definition, stars in a given moving group should not have significantly different ages or compositions, therefore one can see how the cluster evolves as a function of mass. Additionally, planetary systems around these young stars are still contracting, and thus are bright in the H and K photometric bands. For this reason, moving groups have become attractive targets for planet searches since the masses of photometrically discovered planets are well constrained from the ages of the host moving group (see Biller et al. 2013). Currently, moving groups are largely characterized based on youth indicators (e.g. lithium absorption, X-ray emission) and space velocities. In this talk, I will discuss recent results which more fully characterize moving groups based on (1) Chemical homogeneity, (2) Origin, and (3) Isochronal Age. These traits have been tested on the well established AB Doradus moving group and the newly discovered Octans-Near moving group. I will show that these methods provide a detailed picture of the AB Doradus group, however, Octans-Near remains difficult to characterize. I will also discuss the future of this technique on low mass members using high resolution H and K spectroscopy.
Lyman break galaxies (LBGs) are often used as prototypes to construct strongly star-forming galaxies, since the Lyman break signature is straightforward to identify at z>3 from the ground. However, at z~2, the Lyman break is located in the UV wavelength range and can only be observed from space. Until the launch of GALEX, large (wide-field) ground-based proxy selection methods for LBGs had to be used, which produce measurable differences from true LBG samples. We will use deep GALEX and ground based U-images to select a true Lyman break sample of z~2 LBGs, and investigate the nature of galaxies which produce the IR background. The GALEUS (GALaxy Evolution UV Survey) will use public wide-deep data to study the physical properties of UV-selected star-forming galaxies at z~2. We propose to investigate the contribution of UV and IR luminous galaxies to the population of LBGs, using UV to FIR data (0.16 to 500~microns) observed by GALEX, Spitzer, and Herschel, with supporting optical/IR data from HST+ACS and ground-based surveys. I will show preliminary results based on spectral energy distributions.
The disk of the Milky Way beyond the solar circle is not open to simple
interpretations. In short, it is a mess. From observations of interstellar
gas it is clear that the disk has both a warp and a flare.
The stellar component is riddled with stellar over-densities and/or streams,
the largest of which is the Monoceros stream. It is unclear whether gas
is in-falling and still building the outer disk, whether the distribution
of dark matter inflates the outer disk, if interactions with satellite
galaxies are perturbing the disk or if disrupted satellites are adding
to the disk. It is possible that all of these effects are contributing.
What is clear is that the outer disk of the Galaxy holds many clues as to
how galaxies form and evolve.
Studying stellar populations in the outer disk is useful but currently has
limitations because spatial and kinematic distributions are not uniquely
described by the various Galactic models. I will discuss our current
attempts at helping to constrain properties of the outer disk using
spectroscopic analysis of A-star samples. Most of the talk will be dedicated
to our analysis of chemically peculiar A-stars in the SDSS DR8 sample and
whether the distribution of these stars indicate that the Monoceros stream
contains ancient blue stragglers or younger A-stars. The latter conclusion
might suggest that the stream is a component of disk of the Galaxy, while the
former might indicate dwarf disruption. I will conclude the talk by showing
our current work on the Canis Major Over-density and our future goal to explore
dust distribution in the disk using A-stars
There is evidence at low redshift of an increase in the AGN fraction of galaxies in close pairs. This naturally suggests a possible relation between galaxy mergers or interactions and AGN activity, but there seems to be no excess of disturbed morphologies in AGN when compared with quiescent galaxies, even to z~2. To investigate this apparent discrepancy, I utilize HST/WFC3 Infrared Grism observations in the CANDELS GOODS-S and Ultra Deep Survey fields to create a NIR redshift catalog with the intent of calculating the fraction of X-Ray and IR selected AGN in close pairs out to z~2.
Super-massive black holes reside at the center of galaxies. And the masses of these black holes correlate to various properties of their host galaxies. These correlations are the foundation for theories of the (co-)evolution of super-massive black holes and their host galaxies. However, very few galaxies are nearby enough for direct black hole mass measurements. To find suitable galaxies, we surveyed a thousand galaxies with the Hobby-Eberly Telescope. The first results of this survey was the discovery of a dozen extremely compact, high-dispersion, galaxies, which are candidates to host extraordinary massive black holes. The prototype is NGC1277, which is a small, Re=1kpc, compact, lenticular galaxy which hosts a 10 billion solar mass black hole. Which is a significant fraction of this galaxies mass. These highly compact galaxies appear to be the passively evolved descendants of the red nuggets, sub-mm galaxies, and quasars found at high redshifts.
Astro Seminar: Time-Dependent Calculations with Cloudy: Application to Coronal Line Emission in NGC 4696
The nature of cooling in galaxy cluster has been puzzling since cool core clusters were first discovered. Even though early X-ray observations suggested copious amount of cooling, optical observations failed to detect star formation at the levels suggested by X-rays. More recently, dispersed spectroscopy with Chandra and XMM-Newton has revealed a dearth of gas below 1/3 of the mean cluster temperature. Heating mechanisms have been invoked to account for the temperature floor and residual star formation, but the details remain unclear. Probes for the hot X-ray (~10 MK), cool optical (~10,000 K), and intermediate temperature (~100,000 -- 1 million K) phases are necessary to unravel the balance between heating and cooling in clusters. Recently, coronal line emission from gas of ~1 million K has been reported near NGC 4696, the Brightest Cluster Galaxy in the Centaurus galaxy cluster. By contast, gas at 2 million K was not detected. In this talk I build upon a new facility in Cloudy that allows for time-dependent, non-advective simulations. I use this capability to follow a parcel of gas as it cools from ~80 MK to ~10,000 K. I show that the lack of 2 million K gas is not due to extinction. I use the observed upper limit to place an upper limit to the temperature of the coronal gas, and find that, if the gas is cooling, it is cooling isochorically. I discuss scenarios for the origin of the coronal gas, and propose observational probes for gas at temperatures between a million and 10,000 K, that could shed some light into cooling processes in galaxy clusters.
We will have Robert Stokes talking about the early history of cosmic microwave background measurements. In the late 60s, Robert was a graduate student at Princeton working with David Wilkinson (the W in WMAP) on measuring the spectrum of CMB. He will have interesting stories to tell about the early days of CMB discovery.