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

/pdf/the-optical-and-near-infrared-properties-of-galaxies-i-ourshxtpmh.pdf

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

We present the optical spectroscopy for the Blind Ultra Deep H I Environmental Survey (BUD-HIES). With the Westerbork Synthesis Radio Telescope, BUDHIES has detected H I in over 150 galaxies in and around two Abell clusters at z similar or equal to 0.2. With the aim of characterizing the environments of the H I-detected galaxies, we obtained multifibre spectroscopy with the William Herschel Telescope. In this paper, we describe the spectroscopic observations, report redshifts and EW[O II] measurements for similar to 600 galaxies, and perform an environmental analysis. In particular, we present cluster velocity dispersion measurements for five clusters and groups in the BUDHIES volume, as well as a detailed substructure analysis.

/pdf/budhies-i-characterizing-the-environments-in-and-around-two-199pwk13qw.pdf

BUDHIES I: characterizing the environments in and around two clusters at z⋍0.2

We present results from 21 cm radio synthesis imaging of 28 spiral galaxies from the DiskMass Survey obtained with the VLA, WSRT, and GMRT facilities. We detail the observations and data reduction procedures and present a brief analysis of the radio data. We construct 21 cm continuum images, global Hi emission-line profiles, column-density maps, velocity fields, and position-velocity diagrams. From these we determine star formation rates (SFRs), Hi line widths, total Hi masses, rotation curves, and azimuthally-averaged radial Hi column-density profiles. All galaxies have an Hi disk that extends beyond the readily observable stellar disk, with an average ratio and scatter of RHI/R25 = 1.35 ± 0.22, and a majority of the galaxies appear to have a warped Hi disk. A tight correlation exists between total Hi mass and Hi diameter, with the largest disks having a slightly lower average column density. Galaxies with relatively large Hi disks tend to exhibit an enhanced stellar velocity dispersion at larger radii, suggesting the influence of the gas disk on the stellar dynamics in the outer regions of disk galaxies. We find a striking similarity among the radial Hi surface density profiles, where the average, normalized radial profile of the late-type spirals is described surprisingly well with a Gaussian profile. These results can be used to estimate Hi surface density profiles in galaxies that only have a total Hi flux measurement. We compare our 21 cm radio continuum luminosities with 60 μm luminosities from IRAS observations for a subsample of 15 galaxies and find that these follow a tight radio-infrared relation, with a hint of a deviation from this relation at low luminosities. We also find a strong correlation between the average SFR surface density and the K-band surface brightness of the stellar disk.

/pdf/the-diskmass-survey-x-radio-synthesis-imaging-of-spiral-q1xjmf86y6.pdf

The DiskMass Survey - X. Radio synthesis imaging of spiral galaxies

We describe a Phased Array Feed (PAF) system, called Apertif, which will be installed in the Westerbork Synthesis Radio Telescope (WSRT). The aim of Apertif is, at frequencies from 1.0 to 1.7 GHz, to increase the instantaneous field of view of the WSRT to 8 deg2 and its observing bandwidth to 300 MHz with high spectral resolution. This system will turn the WSRT into an effective survey telescope with scientific applications ranging from deep surveys of the northern sky of HI and OH emission and polarised continuum to efficient searches for pulsars and transients. We present results obtained with a prototype PAF installed in one of the WSRT dishes. These results demonstrate that at decimetre wavelengths PAFs have excellent performance and that even for a single beam on the sky, they can outperform single feed radio dishes. PAFs turn radio telescopes into very effective survey instruments. Apertif is now fully funded and the community invited to express their interest in using Apertif (see http://www.astron.nl/radio-observatory/call-expressions-interest-apertif-surveys)

The latest on Apertif

Aims:We present a low-resolution spectroscopic survey of the Orion nebula. The data are released for public use. We show the possible applications of this dataset analyzing some of the main properties of the nebula. Methods: We perform an integral field spectroscopy mosaic of an area of ~5 arcmin× 6 arcmin centered on the Trapezium region of the nebula, including the ionization front to the south-east. Analysis of the line fluxes and line ratios of both the individual and integrated spectra allowed us to determine the main characteristics of the ionization throughtout the nebula. Results: The final dataset comprises 8182 individual spectra, sampled in a circular area of ~2.7 arcsec diameter. The data can be downloaded as a single row-stacked spectra fit file plus a position table or as an interpolated datacube with a final sampling of 1.5 arcsec/pixel. The integrated spectrum across the field-of-view was used to obtain the main integrated properties of the nebula, including the electron density and temperature, the dust extinction, the Hα integrated flux (after correcting for dust reddening), and the main diagnostic line ratios. The individual spectra were used to obtain line intensity maps of the different detected lines. These maps were used to study the distribution of the ionized hydrogen, the dust extinction, the electron density and temperature, and the helium and oxygen abundance. All of them show a considerable degree of structure as already shown in previous studies. In particular, there is a tight relation between the helium and oxygen abundances and the ionization structure that cannot be explained by case B recombination theory. Simple arguments like partial ionization and dust mixed with the emitting gas may explain these relations. However a more detailed modeling is required, for which we provide the dataset. Based on observations collected at the Centro Astronḿico Hispano Aleman (CAHA) at Calar Alto, operated jointly by the Max-Planck Institut fur Astronomie and the Instituto de Astrofisica de Andalucia (CSIC).

/pdf/ppak-integral-field-spectroscopy-survey-of-the-orion-nebula-n7jukm2idm.pdf

PPAK integral field spectroscopy survey of the Orion nebula : Data release

We present spatially resolved H I kinematics of 32 spiral galaxies which have Cepheid or/and tip of the red giant branch distances, and define a calibrator sample for the Tully-Fisher relation. The interferometric H I data for this sample were collected from available archives and supplemented with new Giant Metrewave Radio Telescope observations. This paper describes a uniform analysis of the H I kinematics of this inhomogeneous data set. Our main result is an atlas for our calibrator sample that presents global H I profiles, integrated H I column-density maps, H I surface-density profiles and, most importantly, detailed kinematic information in the form of high-quality rotation curves derived from highly resolved, two-dimensional velocity fields and position-velocity diagrams.

/pdf/detailed-h-i-kinematics-of-tully-fisher-calibrator-galaxies-kv9rvelgyn.pdf

Marc Verheijen

Papers

BUDHIES I: characterizing the environments in and around two clusters at z⋍0.2

The DiskMass Survey - X. Radio synthesis imaging of spiral galaxies

The latest on Apertif

PPAK integral field spectroscopy survey of the Orion nebula : Data release

Detailed H i kinematics of Tully–Fisher calibrator galaxies