Physics welcomes the idea that space contains energy whose gravitational effect approximates that of Einstein's cosmological constant, \ensuremath{\Lambda}; today the concept is termed dark energy or quintessence. Physics also suggests that dark energy could be dynamical, allowing for the arguably appealing picture of an evolving dark-energy density approaching its natural value, zero, and small now because the expanding universe is old. This would alleviate the classical problem of the curious energy scale of a millielectron volt associated with a constant \ensuremath{\Lambda}. Dark energy may have been detected by recent cosmological tests. These tests make a good scientific case for the context, in the relativistic Friedmann-Lema\^{\i}tre model, in which the gravitational inverse-square law is applied to the scales of cosmology. We have well-checked evidence that the mean mass density is not much more than one-quarter of the critical Einstein--de Sitter value. The case for detection of dark energy is not yet as convincing but still serious; we await more data, which may be derived from work in progress. Planned observations may detect the evolution of the dark-energy density; a positive result would be a considerable stimulus for attempts at understanding the microphysics of dark energy. This review presents the basic physics and astronomy of the subject, reviews the history of ideas, assesses the state of the observational evidence, and comments on recent developments in the search for a fundamental theory.

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The Cosmological Constant and Dark Energy

We utilize Sloan Digital Sky Survey imaging and spectroscopy of ~53,000 star-forming galaxies at z ~ 0.1 to study the relation between stellar mass and gas-phase metallicity. We derive gas-phase oxygen abundances and stellar masses using new techniques that make use of the latest stellar evolutionary synthesis and photoionization models. We find a tight (?0.1 dex) correlation between stellar mass and metallicity spanning over 3 orders of magnitude in stellar mass and a factor of 10 in metallicity. The relation is relatively steep from 108.5 to 1010.5 M? h, in good accord with known trends between luminosity and metallicity, but flattens above 1010.5 M?. We use indirect estimates of the gas mass based on the H? luminosity to compare our data to predictions from simple closed box chemical evolution models. We show that metal loss is strongly anticorrelated with baryonic mass, with low-mass dwarf galaxies being 5 times more metal depleted than L* galaxies at z ~ 0.1. Evidence for metal depletion is not confined to dwarf galaxies but is found in galaxies with masses as high as 1010 M?. We interpret this as strong evidence of both the ubiquity of galactic winds and their effectiveness in removing metals from galaxy potential wells.

https://iopscience.iop.org/article/10.1086/423264/pdf

The Origin of the Mass-Metallicity Relation: Insights from 53,000 Star-forming Galaxies in the Sloan Digital Sky Survey

Scene categorization is a fundamental problem in computer vision However, scene understanding research has been constrained by the limited scope of currently-used databases which do not capture the full variety of scene categories Whereas standard databases for object categorization contain hundreds of different classes of objects, the largest available dataset of scene categories contains only 15 classes In this paper we propose the extensive Scene UNderstanding (SUN) database that contains 899 categories and 130,519 images We use 397 well-sampled categories to evaluate numerous state-of-the-art algorithms for scene recognition and establish new bounds of performance We measure human scene classification performance on the SUN database and compare this with computational methods Additionally, we study a finer-grained scene representation to detect scenes embedded inside of larger scenes

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SUN database: Large-scale scene recognition from abbey to zoo

We develop a new method to constrain the star formation histories, dust attenuation and stellar masses of galaxies. It is based on two stellar absorption-line indices, the 4000-A break strength and the Balmer absorption-line index Hδ A . Together, these indices allow us to constrain the mean stellar ages of galaxies and the fractional stellar mass formed in bursts over the past few Gyr. A comparison with broad-band photometry then yields estimates of dust attenuation and of stellar mass. We generate a large library of Monte Carlo realizations of different star formation histories, including starbursts of varying strength and a range of metallicities. We use this library to generate median likelihood estimates of burst mass fractions, dust attenuation strengths, stellar masses and stellar mass-to-light ratios for a sample of 122 808 galaxies drawn from the Sloan Digital Sky Survey. The typical 95 per cent confidence range in our estimated stellar masses is ′40 per cent. We study how the stellar mass-to-light ratios of galaxies vary as a function of absolute magnitude, concentration index and photometric passband and how dust attenuation varies as a function of absolute magnitude and 4000-A break strength. We also calculate how the total stellar mass of the present Universe is distributed over galaxies as a function of their mass, size, concentration, colour, burst mass fraction and surface mass density. We find that most of the stellar mass in the local Universe resides in galaxies that have, to within a factor of approximately 2, stellar masses ∼5 x 10 1 0 M O ., half-light radii ∼3 kpc and half-light surface mass densities ∼10 9 M O .kpc - 2 . The distribution of D n (4000) is strongly bimodal, showing a clear division between galaxies dominated by old stellar populations and galaxies with more recent star formation.

/pdf/stellar-masses-and-star-formation-histories-for-105-galaxies-25rhcec6uj.pdf

Stellar masses and star formation histories for 105 galaxies from the Sloan Digital Sky Survey

We use a large sample of galaxies from the Two Micron All Sky Survey(2MASS) and the Sloan Digital Sky Survey (SDSS) to calculate galaxy luminosity and stellar mass functions in the local Universe. We estimate corrections for passband shifting and galaxy evolution, as well as present-day stellar mass-to-light (M/L) ratios, by fitting the optical‐near-infrared galaxy data with simpl e models. Accounting for the 8% galaxy overdensity in the SDSS early data release region, the optical and near-infrared luminosity functions we construct for this sample agree with most recent literature optical and near-infrare d determinations within the uncertainties. We argue that 2MASS is biased against low surface brightness galaxies, and use SDSS plus our knowledge of stellar populations to estimate the ‘true’ K-band luminosity function. This has a steeper faint end slope and a slightly higher overall luminosity density than the direct estimate. Furthermore, assuming a universally-applicable stellar initial mass function (IMF), we find good agreement between the stellar ma ss function we derive from the 2MASS/SDSS data and that derived by Cole et al. (2001; MNRAS, 326, 255). The faint end slope slope for the stellar mass function is steeper than -1.1, reflecting the low stellar M/L ratios characteristic of lo w-mass galaxies. We estimate an upper limit to the stellar mass density in the local Universe ∗h = 2.0 ± 0.6 × 10 -3 by assuming an IMF as rich in low-mass stars as allowed by observations of galaxy dynamics in the local Universe. The stellar mass density may be lower than this value if a different IMF with fewer low-mass stars is assumed. Finally, we examine typedependence in the optical and near-infrared luminosity functions and the stellar mass function. In agreement with previous work, we find that the characteristic luminosity or mass of early-type galaxies is larger than for later types, and the faint end slope is steeper for later types than for earlier types. Accounting for typing uncertainties, we estimate that at least half, and perhaps as much as 3/4, of the stellar mass in the Universe is in early-type galaxies. As an aid to workers in the field, we present in an appendix the r elationship between model stellar M/L ratios and colors in SDSS/2MASS passbands, an updated discussion of near-infrared stellar M/L ratio estimates, and the volume-corrected distribution of g and K-band stellar M/L ratios as a function of stellar mass. Subject headings: galaxies: luminosity function, mass function ‐ galaxies: g eneral — galaxies: evolution — galaxies: stellar content

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The optical and near-infrared properties of galaxies. I. Luminosity and stellar mass functions

We describe the design and construction of a formatted fiber field unit, SparsePak, and characterize its optical and astrometric performance. This array is optimized for spectroscopy of low surface brightness extended sources in the visible and near‐infrared. SparsePak contains 82, 4 \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $\farcs$\end{document} 7 fibers subtending an area of \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pif...

http://www.astro.wisc.edu/~mab/publications/spkI_re.pdf

SparsePak: A Formatted Fiber Field Unit for the WIYN Telescope Bench Spectrograph. I. Design, Construction, and Calibration

This paper investigates the statistical properties of the Tully-Fisher (TF) relations for a volume-limited complete sample of spiral galaxies in the nearby Ursa Major Cluster. The merits of B, R, I, and K' surface photometry and the availability of detailed kinematic information from H I synthesis imaging have been exploited. In addition to the corrected H I global profile widths W, the available H I rotation curves allow direct measurements of the observed maximum rotational velocities Vmax and the amplitudes Vflat of the outer flat parts. The dynamical state of the gas disks could also be determined in detail from the radio observations. The four luminosity and three kinematic measures allowed the construction of 12 correlations for various subsamples. For large galaxy samples, the M-log W correlation in conjunction with strict selection criteria is preferred for distance determinations with a 7% accuracy. Galaxies with rotation curves that are still rising at the last measured point lie systematically on the low-velocity side of the TF relation. Galaxies with a partly declining rotation curve (Vmax > Vflat) tend to lie systematically on the high-velocity side of the relation when using W or Vmax. However, systematic offsets are eliminated when Vflat is used. Residuals of the M-log(2Vflat) relation correlate consistently with global galaxy properties along the Hubble sequence like morphological type, color, surface brightness, and gas mass fraction. These correlations are absent for the near-infrared M-log(2Vflat) residuals. The tightest correlation (? = 1.1) is found for the M-log(2Vflat) relation, which has a slope of -11.3 ? 0.5 and a total observed scatter of 0.26 mag with a most likely intrinsic scatter of zero. The tightness of the near-infrared correlation is preserved when converting it into a baryonic TF relation that has a slope of -10.0 in the case (gas/L) = 1.6 while a zero intrinsic scatter remains most likely. Based on the tightness of the near-infrared and baryonic correlations, it is concluded that the TF relation reflects a fundamental correlation between the mass of the dark matter halo, measured through its induced maximum rotational velocity Vflat, and the total baryonic mass bar of a galaxy where bar V. Although the actual distribution of the baryonic matter inside halos of similar mass can vary significantly, it does not affect this relation.

https://iopscience.iop.org/article/10.1086/323887/pdf

The Ursa Major Cluster of Galaxies. V. H I Rotation Curve Shapes and the Tully-Fisher Relations

Proceedings of the SPIE

Magnitude-limited samples of spiral galaxies drawn from the Ursa Major and Pisces Clusters are used to determine their extinction properties as a function of inclination. Imaging photometry is available for 87 spirals in the B, R, I, and K' bands. Extinction causes systematic scatter in color-magnitude plots. A strong luminosity dependence is found. Relative edge-on to face-on extinction of up to 1.7 mag is found at B for the most luminous galaxies but is unmeasurably small for faint galaxies. At R the differential absorption with inclination reaches 1.3 mag, at I it reaches 1.0 mag, and at K' the differential absorption can in the extreme be as great as 0.3 mag. The luminosity dependence of reddening can be translated into a dependence on rotation rate, which is a distance-independent observable. Hence, corrections can be made that are useful for distance measurements. The strong dependence of the corrections on luminosity act to steepen luminosity-line width correlations. The effect is greatest toward the blue, with the consequence that luminosity-line width slope dependencies are now only weakly a function of color.

Global Extinction in Spiral Galaxies

In this data paper we present the results of an extensive 21 cm-line synthesis imaging survey of 43 spiral galaxies in the nearby Ursa Major cluster using the Westerbork Synthesis Radio Telescope. Detailed kinematic information in the form of position-velocity diagrams and rotation curves is presented in an atlas together with HI channel maps, 21 cm continuum maps, global HI profiles, radial HI surface density profiles, integrated HI column density maps, and HI velocity fields. The relation between the corrected global HI linewidth and the rotational velocities V-max and V-flat as derived from the rotation curves is investigated. Inclination angles obtained from the optical axis ratios are compared to those derived from the inclined HI disks and the HI velocity fields. The galaxies were not selected on the basis of their HI content but solely on the basis of their cluster membership and inclination which should be suitable for a kinematic analysis. The observed galaxies provide a well-defined, volume limited and equidistant sample, useful to investigate in detail the statistical properties of the Tully-Fisher relation and the dark matter halos around them.

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Marc Verheijen

Papers

SparsePak: A Formatted Fiber Field Unit for the WIYN Telescope Bench Spectrograph. I. Design, Construction, and Calibration

The Ursa Major Cluster of Galaxies. V. H I Rotation Curve Shapes and the Tully-Fisher Relations

Proceedings of the SPIE

Global Extinction in Spiral Galaxies

The ursa major cluster of galaxies - IV. HI synthesis observations