Engaging Students in the Basic Course By Asking Big Questions

This paper advocates for the inclusion of big questions into the basic course curriculum. It begins by exploring the nature of big questions as those that engage pressing and perennial civic and global issues, and details their effectiveness in encouraging students and faculty to think about interpersonal responsibility and social space as dynamically interfacing and mutually reflexive, thus challenging us to negotiate the civic call of engaging in democratic processes. The basic course, whether public speaking or hybrid, offers a crucial opportunity for big questions to emerge because it brings people together to critically question and produce messages about the social and civic contexts in which we all engage as students, faculty, employees, family, and citizens. Thus, the article includes examples from several basic course instructors and administrators of how big questions can be incorporated into the curriculum to enhance the learning outcomes of students, while at the same time situating the basic course as more deeply embedded into the stated mission and requirements of our departments, colleges, and general education programs

The Specific Globular Cluster Frequencies of Dwarf Elliptical Galaxies from the Hubble Space Telescope

The specific globular cluster frequencies (S_N) for 24 dwarf elliptical (dE) galaxies in the Virgo and Fornax Clusters and the Leo Group imaged with the Hubble Space Telescope are presented. Combining all available data, we find that for nucleated dEs --- which are spatially distributed like giant ellipticals in galaxy clusters --- S_N(dE,N)=6.5 +- 1.2 and S_N increases with M_V, while for non-nucleated dEs --- which are distributed like late-type galaxies --- S_N(dE,noN)=3.1 +- 0.5 and there is little or no trend with M_V. The S_N values for dE galaxies are thus on average significantly higher than those for late-type galaxies, which have S_N < 1. This suggests that dE galaxies are more akin to giant Es than to late-type galaxies. If there are dormant or stripped irregulars hiding among the dE population, they are likely to be among the non-nucleated dEs. Furthermore, the similarities in the properties of the globular clusters and in the spatial distributions of dE,Ns and giant Es suggest that neither galaxy mass or galaxy metallicity is responsible for high values of S_N. Instead, most metal-poor GCs may have formed in dwarf-sized fragments that merged into larger galaxies.Comment: 12 pages (uses aaspp4.sty), 2 figures, 1 table, to appear in the Astrophysical Journa

Evidence for the Direct Detection of the Thermal Spectrum of the Non-Transiting Hot Gas Giant HD 88133 b

We target the thermal emission spectrum of the non-transiting gas giant HD 88133 b with high-resolution near-infrared spectroscopy, by treating the planet and its host star as a spectroscopic binary. For sufficiently deep summed flux observations of the star and planet across multiple epochs, it is possible to resolve the signal of the hot gas giant's atmosphere compared to the brighter stellar spectrum, at a level consistent with the aggregate shot noise of the full data set. To do this, we first perform a principal component analysis to remove the contribution of the Earth's atmosphere to the observed spectra. Then, we use a cross-correlation analysis to tease out the spectra of the host star and HD 88133 b to determine its orbit and identify key sources of atmospheric opacity. In total, six epochs of Keck NIRSPEC L band observations and three epochs of Keck NIRSPEC K band observations of the HD 88133 system were obtained. Based on an analysis of the maximum likelihood curves calculated from the multi-epoch cross correlation of the full data set with two atmospheric models, we report the direct detection of the emission spectrum of the non-transiting exoplanet HD 88133 b and measure a radial projection of the Keplerian orbital velocity of 40 $\pm$ 15 km/s, a true mass of 1.02$^{+0.61}_{-0.28}M_J$, a nearly face-on orbital inclination of 15${^{+6}_{-5}}^{\circ}$, and an atmosphere opacity structure at high dispersion dominated by water vapor. This, combined with eleven years of radial velocity measurements of the system, provides the most up-to-date ephemeris for HD 88133.Comment: 9 pages, 6 figures; accepted for publication in Ap

Dynamical Friction in dE Globular Cluster Systems

The dynamical friction timescale for globular clusters to sink to the center of a dwarf elliptical galaxy (dE) is significantly less than a Hubble time if the halos have King-model or isothermal profiles and the globular clusters formed with the same radial density profile as the underlying stellar population. We examine the summed radial distribution of the entire globular cluster systems and the bright globular cluster candidates in 51 Virgo and Fornax Cluster dEs for evidence of dynamical friction processes. We find that the summed distribution of the entire globular cluster population closely follows the exponential profile of the underlying stellar population. However, there is a deficit of bright clusters within the central regions of dEs (excluding the nuclei), perhaps due to the orbital decay of these massive clusters into the dE cores. We also predict the magnitude of each dE's nucleus assuming the nuclei form via dynamical friction. The observed trend of decreasing nuclear luminosity with decreasing dE luminosity is much stronger than predicted if the nuclei formed via simple dynamical friction processes. We find that the bright dE nuclei could have been formed from the merger of orbitally decayed massive clusters, but the faint nuclei are several magnitudes fainter than expected. These faint nuclei are found primarily in M_V > -14 dEs which have high globular cluster specific frequencies and extended globular cluster systems. In these galaxies, supernovae-driven winds, high central dark matter densities, extended dark matter halos, the formation of new star clusters, or tidal interactions may act to prevent dynamical friction from collapsing the entire globular cluster population into a single bright nucleus.Comment: 15 pages, 2 tables, 7 figures; to appear in the Astrophysical Journal, April 20, 200

Constraining mean-field models of the nuclear matter equation of state at low densities

An extension of the generalized relativistic mean-field (gRMF) model with density dependent couplings is introduced in order to describe thermodynamical properties and the composition of dense nuclear matter for astrophysical applications. Bound states of light nuclei and two-nucleon scattering correlations are considered as explicit degrees of freedom in the thermodynamical potential. They are represented by quasiparticles with medium-dependent properties. The model describes the correct low-density limit given by the virial equation of state (VEoS) and reproduces RMF results around nuclear saturation density where clusters are dissolved. A comparison between the fugacity expansions of the VEoS and the gRMF model provides consistency relations between the quasiparticles properties, the nucleon-nucleon scattering phase shifts and the meson-nucleon couplings of the gRMF model at zero density. Relativistic effects are found to be important at temperatures that are typical in astrophysical applications. Neutron matter and symmetric matter are studied in detail.Comment: 50 pages, 21 figure

The SAURON project. II. Sample and early results

Early results are reported from the SAURON survey of the kinematics and stellar populations of a representative sample of nearby E, S0 and Sa galaxies. The survey is aimed at determining the intrinsic shape of the galaxies, their orbital structure, the mass-to-light ratio as a function of radius, the age and metallicity of the stellar populations, and the frequency of kinematically decoupled cores and nuclear black holes. The construction of the representative sample is described, and its properties are illustrated. A comparison with long-slit spectroscopic data establishes that the SAURON measurements are comparable to, or better than, the highest-quality determinations. Comparisons are presented for NGC 3384 and NGC 4365 where stellar velocities and velocity dispersions are determined to a precision of 6 km/s, and the h3 and h4 parameters of the line-of-sight velocity distribution to a precision of better than 0.02. Extraction of accurate gas emission-line intensities, velocities and line widths from the datacubes is illustrated for NGC 5813. Comparisons with published line-strengths for NGC 3384 and NGC 5813 reveal uncertainties of < 0.1 A on the measurements of the Hbeta, Mgb and Fe5270 indices. Integral-field mapping uniquely connects measurements of the kinematics and stellar populations to the galaxy morphology. The maps presented here illustrate the rich stellar kinematics, gaseous kinematics, and line-strength distributions of early-type galaxies. The results include the discovery of a thin, edge-on, disk in NGC 3623, confirm the axisymmetric shape of the central region of M32, illustrate the LINER nucleus and surrounding counter-rotating star-forming ring in NGC 7742, and suggest a uniform stellar population in the decoupled core galaxy NGC 5813.Comment: 20 pages, 17 figures. To be published in MNRAS. Version with full resolution images available at http://www.strw.leidenuniv.nl/~dynamics/Instruments/Sauron/pub_list.htm

Galaxy mapping with the SAURON integral-field spectrograph: The star formation history of NGC 4365

We report the first wide-field mapping of the kinematics and stellar populations in the E3 galaxy NGC 4365. The velocity maps extend previous long-slit work. They show two independent kinematic subsystems: the central 300 x 700 pc rotates about the projected minor axis, and the main body of the galaxy, 3 x 4 kpc, rotates almost at right angles to this. The line-strength maps show that the metallicity of the stellar population decreases from a central value greater than solar, to one-half solar at a radius of 2 kpc. The decoupled core and main body of the galaxy have the same luminosity-weighted age, of ~14 Gyr, and the same elevated magnesium-to-iron ratio. The two kinematically distinct components have thus shared a common star formation history. We infer that the galaxy underwent a sequence of mergers associated with dissipative star formation that ended >12 Gyr ago. The misalignment between the photometric and kinematic axes of the main body is unambiguous evidence of triaxiality. The similarity of the stellar populations in the two components suggests that the observed kinematic structure has not changed substantially in 12 Gyr.Comment: 5 pages, accepted for publication in ApJ Letter

Nonperturbative effects and nonperturbative definitions in matrix models and topological strings

We develop techniques to compute multi-instanton corrections to the 1/N expansion in matrix models described by orthogonal polynomials. These techniques are based on finding trans-series solutions, i.e. formal solutions with exponentially small corrections, to the recursion relations characterizing the free energy. We illustrate this method in the Hermitian, quartic matrix model, and we provide a detailed description of the instanton corrections in the Gross-Witten-Wadia (GWW) unitary matrix model. Moreover, we use Borel resummation techniques and results from the theory of resurgent functions to relate the formal multi-instanton series to the nonperturbative definition of the matrix model. We study this relation in the case of the GWW model and its double-scaling limit, providing in this way a nice illustration of various mechanisms connecting the resummation of perturbative series to nonperturbative results, like the cancellation of nonperturbative ambiguities. Finally, we argue that trans-series solutions are also relevant in the context of topological string theory. In particular, we point out that in topological string models with both a matrix model and a large N gauge theory description, the nonperturbative, holographic definition involves a sum over the multi-instanton sectors of the matrix modelComment: 50 pages, 12 figures, comments and references added, small correction

On the Origin of the Dichotomy of Early-Type Galaxies: The Role of Dry Mergers and AGN Feedback

Using a semi-analytical model for galaxy formation, combined with a large N-body simulation, we investigate the origin of the dichotomy among early-type galaxies. We find that boxy galaxies originate from mergers with a progenitor mass ratio $n < 2$ and with a combined cold gas mass fraction $F_{\rm cold} < 0.1$. Our model accurately reproduces the observed fraction of boxy systems as a function of luminosity and halo mass, for both central galaxies and satellites. After correcting for the stellar mass dependence, the properties of the last major merger of early-type galaxies are independent of their halo mass. This provides theoretical support for the conjecture of Pasquali et al (2007) that the stellar mass of an early-type galaxy is the main parameter that governs its isophotal shape. We argue that the observed dichotomy of early-type galaxies has a natural explanation within hierarchical structure formation, and does not require AGN feedback. Rather, we argue that it owes to the fact that more massive systems (i) have more massive progenitors, (ii) assemble later, and (iii) have a larger fraction of early-type progenitors. Each of these three trends causes the cold gas mass fraction of the progenitors of more massive early-types to be lower, so that their last major merger was dryer. Finally, our model predicts that (i) less than 10 percent of all early-type galaxies form in major mergers that involve two early-type progenitors, (ii) more than 95 percent of all boxy early-type galaxies with M_* < 2 \times 10^{10} h^{-1} \Msun are satellite galaxies, and (iii) about 70 percent of all low mass early-types do not form a supermassive black hole binary at their last major merger. The latter may help to explain why low mass early-types have central cusps, while their massive counterparts have cores.Comment: 13 pages, 8 figures, submitted for publication in MNRA

Angular momentum and galaxy formation revisited

Motivated by new kinematic data in the outer parts of early-type galaxies (ETGs), we re-examine angular momentum (AM) in all galaxy types. We present methods for estimating the specific AM j, focusing on ETGs, to derive relations between stellar j_* and mass M_* (after Fall 1983). We perform analyses of 8 galaxies out to ~10 R_e, finding that data at 2 R_e are sufficient to estimate total j_*. Our results contravene suggestions that ellipticals (Es) harbor large reservoirs of hidden j_* from AM transport in major mergers. We carry out a j_*-M_* analysis of literature data for ~100 nearby bright galaxies of all types. The Es and spirals form parallel j_*-M_* tracks, which for spirals is like the Tully-Fisher relation, but for Es derives from a mass-size-rotation conspiracy. The Es contain ~3-4 times less AM than equal-mass spirals. We decompose the spirals into disks+bulges and find similar j_*-M_* trends to spirals and Es overall. The S0s are intermediate, and we propose that morphological types reflect disk/bulge subcomponents following separate j_*-M_* scaling relations -- providing a physical motivation for characterizing galaxies by mass and bulge/disk ratio. Next, we construct idealized cosmological models of AM content, using a priori estimates of dark matter halo spin and mass. We find that the scatter in halo spin cannot explain the spiral/E j_* differences, but the data are matched if the galaxies retained different fractions of initial j (~60% and ~10%). We consider physical mechanisms for j_* and M_* evolution (outflows, stripping, collapse bias, merging), emphasizing that the vector sum of such processes must produce the observed j_*-M_* relations. A combination of early collapse and multiple mergers (major/minor) may account for the trend for Es. More generally, the observed AM variations represent fundamental constraints for any galaxy formation model.Comment: ApJS, in press, 61 pages, 34 figures, abstract abridge