Introductory Astronomy as a Measure of Grade Inflation

We use four years of introductory astronomy scores to analyze the ability of the current population to perform college level work and measure the amount of grade inflation across various majors. Using an objective grading scale, one that is independent of grading curves, we find that 29% of intro astronomy students fail to meet minimal standards for college level work. Of the remaining students, 41% achieve satisfactory work, 30% achieve mastery of the topics. Intro astronomy scores correlate with SAT and college GPA. Sequential mapping of the objective grade scheme onto GPA finds that college grades are inflated by 0.2 for natural sciences majors, 0.3 for social sciences, professional schools and undeclared majors), 0.5 for humanities majors. It is unclear from the data whether grade inflation is due to easier grading curves or depression of course material. Experiments with student motivation tools indicates that poor student performance is due to deficiency in student abilities rather than social factors (such as study time or decreased interest in academics), i.e., more stringent admission standards would resolve grade inflation.Comment: 16 pages, 6 figures, not to be submitted to any journa

AGN Activity in Giant LSB Galaxies

A search of large, HI-rich disk galaxies finds a significantly higher fraction of low luminosity AGN signatures compared to other late-type galaxies. Approximately half of the galaxies selected in this sample have AGN-like behavior in their cores, the rest have HII nuclei resulting from simple star formation. Since AGN behavior is not evident in all the sample galaxies, which where selected by high gas mass, we speculate that it is the fuel flow rate that is the common feature between late-type LSB disks and other active nuclear galaxies.Comment: 12 pages, LaTeX/AAS macros, 1 table, 3 postscript figures, accepted for publication in A

The Structure of Galaxies: II. Fitting Functions and Scaling Relations for Ellipticals

Surface photometry of 311 ellipticals from the 2MASS imaging database is analyzed with respect to the two most common fitting functions; the r^1/4 law and the Sersic r^1/n model. The advantages and disadvantages of each fitting function are examined. In particular, the r^1/4 law performs well in the middle regions, but is inadequate for the core (inner 5 kpcs) and the outer regions (beyond the half-light radius) which do not have r^1/4 shapes. It is found that the Sersic r^1/n model produce good fits to the core regions of ellipticals (r < r_half), but is an inadequate function for the entire profile of an elliptical from core to halo due to competing effects on the Sersic n index and the fact that the interior shape of an elliptical is only weakly correlated with its halo shape. In addition, there are a wide range of Sersic parameters that will equally describe the shape of the outer profile, degrading the Sersic models usefulness as a describer of the entire profile. Empirically determined parameters, such as half-light radius and total luminosity, have less scatter than fitting function variables. The scaling relations for ellipticals are often non-linear, but for ellipticals brighter than M_J < -23 the following structural relations are found: L propto r^0.8 \pm 0.1, L propto Sigma^-0.5 \pm 0.1 and Sigma propto r^-1.5 \pm 0.1.Comment: 26 pages, 15 Figures, accepted by PAS

ARCHANGEL Galaxy Photometry System

Photometry of galaxies has typically focused on small, faint systems due to their interest for cosmological studies. Large angular size galaxies, on the other hand, offer a more detailed view into the properties of galaxies, but bring a series of computational and technical difficulties that inhibit the general astronomer from extracting all the information found in a detailed galaxy image. To this end, a new galaxy photometry system has been developed (mostly building on tools and techniques that have existed in the community for decades) that combines ease of usage with a mixture of pre-built scripts. The audience for this system is a new user (graduate student or non-optical astronomer) with a fast, built-in learning curve to offer any astronomer, with imaging data, a suite of tools to quickly extract meaningful parameters from decent data. The tools are available either by a client/server web site or by tarball for personal installation. The tools also provide simple scripts to interface with various on-line datasets (e.g. 2MASS, Sloan, DSS) for data mining capability of imaged data. As a proof of concept, we preform a re-analysis of the 2MASS Large Galaxy Atlas to demonstrate the differences in an automated pipeline, with its emphasis on speed, versus this package with an emphasis on accuracy. This comparison finds the structural parameters extracted from the 2MASS pipeline is seriously flawed with scale lengths that are too small by 50% and central surface brightness that are, on average, 1 to 0.5 mags too bright. A cautionary tale on how to reduce information-rich data such as surface brightness profiles. This document and software can be found at http://abyss.uoregon.edu/~js/archangel.Comment: 31 pages, 14 figures, software package at http://abyss.uoregon.edu/~js/archange

Systematic Bias in 2MASS Galaxy Photometry

We report the discovery of a serious bias in galaxy photometry reported in the 2MASS Extended Source Catalog (Jarrett et al. 2000). Due to an undetermined flaw in the 2MASS surface photometry routines, isophotal and total magnitudes calculated by their methods underestimate the luminosity of galaxies from 10% to 40%. This is found to be due to incorrectly determined scalelengths and isophotal radii, which are used to define the aperture sizes for Kron and total fluxes. While 2MASS metric aperture luminosities are correct (and, thus, colors based on those apertures), comparison to other filters (e.g. optical) based on total magnitudes will produce erroneous results. We use our own galaxy photometry package (ARCHANGEL) to determine correct total magnitudes and colors using the same 2MASS images, but with a more refined surface brightness reduction scheme. Our resulting colors, and color-magnitude relation, are more in line with model expectations and previous pointed observations.Comment: 13 pages, 8 figures, comment to communit

The Structure of Galaxies: III. Two Structural Families of Ellipticals

Using isophotal radius correlations for a sample of 2MASS ellipticals, we have constructed a series of template surface brightness profiles to describe the profile shapes of ellipticals as a function of luminosity. The templates are a smooth function of luminosity, yet are not adequately matched to any fitting function supporting the view that ellipticals are weakly non-homologous with respect to structure. Through comparison to the templates, it is discovered that ellipticals are divided into two families; those well matched to the templates and a second class of ellipticals with distinctly shallower profile slopes. We refer to these second type of ellipticals as D class, an old morphological designation acknowledging diffuse appearance on photographic material. D ellipticals cover the same range of luminosity, size and kinematics as normal ellipticals, but maintain a signature of recent equal mass dry mergers. We propose that normal ellipticals grow after an initial dissipation formation era by accretion of low mass companions as outlined in hierarchical formation scenarios, while D ellipticals are the result of later equal mass mergers producing shallow luminosity profiles.Comment: 32 pages, 12 Figures, 1 table, accepted by A

Tests of Chemical Enrichment Scenarios in Ellipticals Using Continuum Colors and Spectroscopy

We combine spectroscopic metallicity values with integrated narrowband continuum colors to explore the internal metallicity distribution in early-type galaxies. The different techniques for determining metallicity (indices versus colors) allows for an estimate of the contribution from metal-poor stars in a predominantly metal-rich population which, in turn, places constraints on the shape and width of a galaxy's metallicity distribution function (MDF). The color-spectroscopic data is compared to the closed box, infall and inhomogeneous chemical evolution models. The G-dwarf problem, a deficiency in metal-poor stars as compared to closed box models, is evident in the dataset and indicates this deficiency is common to all early-type galaxies. However, even simple infall models predict galaxy colors which are too blue compared to the observations. A simple analytic model is proposed which matches the elliptical data and recent HST observations of M31 (Worthey et al 2005) and NGC 5128 (Harris & Harris 2000) by reducing the number of metal-poor stars in a systematic fashion. While without physical justification, the shape of these models are similar to predictions of inhomogeneous enrichment scenarios.Comment: 21 pages, 6 figures, accepted in A

Color--Mass-to-Light Ratio Relations for Disk Galaxies

We combine Spitzer $3.6\mu$ observations of a sample of disk galaxies spanning over 10 magnitudes in luminosity with optical luminosities and colors to test population synthesis prescriptions for computing stellar mass. Many commonly employed models fail to provide self-consistent results: the stellar mass estimated from the luminosity in one band can differ grossly from that of another band for the same galaxy. Independent models agree closely in the optical ($V$-band), but diverge at longer wavelengths. This effect is particularly pronounced in recent models with substantial contributions from TP-AGB stars. We provide revised color--mass-to-light ratio relations that yield self-consistent stellar masses when applied to real galaxies. The $B-V$ color is a good indicator of the mass-to-light ratio. Some additional information is provided by $V-I$, but neither it nor $J-K_s$ are particularly useful for constraining the mass-to-light ratio on their own. In the near-infrared, the mass-to-light ratio depends weakly on color, with typical values of $0.6\; \mathrm{M}_{\odot}/\mathrm{L}_{\odot}$ in the $K_s$-band and $0.47\; \mathrm{M}_{\odot}/\mathrm{L}_{\odot}$ at $3.6\mu$.Comment: Astronomical Journal, in press. 15 pages, 8 figures, 7 table

Weighing Galaxy Disks with the Baryonic Tully-Fisher Relation

We estimate the stellar masses of disk galaxies with two independent methods: a photometrically self-consistent color$-$mass-to-light ratio relation (CMLR) from population synthesis models, and the Baryonic Tully-Fisher relation (BTFR) calibrated by gas rich galaxies. These two methods give consistent results. The CMLR correctly converts distinct Tully-Fisher relations in different bands into the same BTFR. The BTFR is consistent with $M_b \propto V_f^4$ over nearly six decades in mass, with no hint of a change in slope over that range. The intrinsic scatter in the BTFR is negligible, implying that the IMF of disk galaxies is effectively universal. The gas rich BTFR suggests an absolute calibration of the stellar mass scale that yields nearly constant mass-to-light ratios in the near-infrared (NIR): $0.57\;M_{\odot}/L_{\odot}$ in $K_s$ and $0.45\;M_{\odot}/L_{\odot}$ at $3.6\mu$. There is only modest intrinsic scatter ($\sim 0.12$ dex) about these typical values. There is no discernible variation with color or other properties: the NIR luminosity is a good tracer of stellar mass.Comment: Accepted for publication in the Astrophysical Journal. 6 figures, 5 tables, 17 page

Stellar Populations and the Star Formation Histories of LSB Galaxies: IV Spitzer Surface Photometry of LSB Galaxies

Surface photometry at 3.6$\mu$m is presented for 61 low surface brightness (LSB) galaxies ($\mu_o < 19$ 3.6$\mu$m mag arcsecs$^{-2}$). The sample covers a range of luminosity from $-$11 to $-$22 in $M_{3.6}$ and size from 1 to 25 kpc. The morphologies in the mid-IR are comparable to those in the optical with 3.6$\mu$m imaging reaches similar surface brightness depth as ground-based optical imaging. A majority of the resulting surface brightness profiles are single exponential in shape with very few displaying upward or downward breaks. The mean $V-3.6$ color of LSB is 2.3 with a standard deviation of 0.5. Color-magnitude and two color diagrams are well matched to models of constant star formation, where the spread in color is due to small changes in the star formation rate (SFR) over the last 0.5 Gyrs as also suggested by the specific star formation rate measured by H$\alpha$.Comment: 30 pages, 8 figures, 4 tables, in press, PAS