We analyze star formation (SF) as a function of stellar mass (M ⋆ ) and redshift z in the All Wavelength Extended Groth Strip International Survey (AEGIS). For 2905 field galaxies, complete to 10 10 (10 10.8 )M ⊙ at z < 0.7(1), with Keck spectroscopic redshifts out to z = 1.1, we compile SF rates (SFR) from emission lines, GALEX, and Spitzer MIPS 24µm photometry, optical-NIR M ⋆ measurements, and HST morphologies. Galaxies with reliable signs of SF form a distinct "main sequence (MS)", with a limited range of SFR at a given M ⋆ and z (1σ ±0.3 dex), and log(SFR) approximately proportional to log(M ⋆ ). The range of log(SFR) remains constant to z > 1, while the MS as a whole moves to higher SFR as z increases. The range of SFR along the MS constrains the amplitude of episodic variations of SF, and the effect of mergers on SFR. Typical galaxies spend ∼ 67(95)% of their lifetime since z = 1 within a factor of 2(4) of their average SFR at a given M ⋆ and z. The dominant mode of the evolution of SF since z ∼ 1 is apparently a gradual decline of the average SFR in most individual galaxies, not a decreasing frequency of starburst episodes, or a decreasing factor by which SFR are enhanced in starbursts. LIRGs at z ∼ 1 seem to mostly reflect the high SFR typical for massive galaxies at that epoch. The smooth MS may reflect that the same set of few physical processes governs star formation prior to additional quenching processes. A gradual process like gas exhaustion may play a dominant role.

Dwarf satellite galaxies are thought to be the remnants of the population of primordial structures that coalesced to form giant galaxies like the Milky Way. It has previously been suspected that dwarf galaxies may not be isotropically distributed around our Galaxy, because several are correlated with streams of H I emission, and may form coplanar groups. These suspicions are supported by recent analyses. It has been claimed that the apparently planar distribution of satellites is not predicted within standard cosmology, and cannot simply represent a memory of past coherent accretion. However, other studies dispute this conclusion. Here we report the existence of a planar subgroup of satellites in the Andromeda galaxy (M 31), comprising about half of the population. The structure is at least 400 kiloparsecs in diameter, but also extremely thin, with a perpendicular scatter of less than 14.1 kiloparsecs. Radial velocity measurements reveal that the satellites in this structure have the same sense of rotation about their host. This shows conclusively that substantial numbers of dwarf satellite galaxies share the same dynamical orbital properties and direction of angular momentum. Intriguingly, the plane we identify is approximately aligned with the pole of the Milky Way's disk and with the vector between the Milky Way and Andromeda.

We report detailed chemical abundance analysis of 27 RGB stars towards the Galactic bulge in Baade's Window for elements produced by massive stars: O, Na, Mg, Al, Si, Ca and Ti. All of these elements are overabundant in the bulge relative to the disk, indicating that the bulge is enhanced in Type II supernova ejecta and most likely formed more rapidly than the disk.Our [Mg/Fe] ratios, confirmed by [Al/Mg], declines much more slowly with [Fe/H] than O, Si, Ca and Ti. The [Mg/Fe] ratio stays above +0.25 dex up to well above solar metallicity. We attribute the rapid decline of [O/Fe] to a metallicity-dependent modulation of the oxygen yield from massive stars, perhaps connected to the Wolf-Reyet phenomenon.The explosive nucleosynthesis alphas, Si, Ca and Ti, relative to Fe, possess identical trends with [Fe/H], consistent with their putative common origin. We note that different behaviors of hydrostatic and explosive alpha elements can be seen in the stellar abundances of stars in Local Group dwarf galaxies. We also attribute the decline of Si,Ca and Ti, relative to Mg, to metallicity-dependent yields for these explosive alpha elements from Type II supernovae. The production of explosive alphas in Type Ia supernovae likely explains the absence of obvious difference between Mg and Si, Ca, Ti trends in the Galactic thin disk.An alternative explanation for the [Mg/] increase with metallicity is an excess population of 30-35M ⊙ stars in the bulge that grew in importance with [Fe/H]. In this model the bulge formation timescale would have been significantly longer than our favored scenario of declining metallicitydependent yields from Type II supernovae.The starkly smaller scatter of [/Fe] with [Fe/H] in the bulge, as compared to the halo, is consistent with expected efficient mixing for the bulge. Since the metal-poor bulge [/Fe] ratios are higher than ∼80% of the halo, the early bulge could not have formed from gas with the present-day halo composition. If the bulge formed from halo gas, it occurred before ∼80% of today's stellar halo; and the halo subsequently reduced its alpha/Fe ratios significantly.The lack of overlap between the thick and thin disk composition with the bulge does not support the idea that the bulge was built by a thickening of the disk driven by the bar.The trend of [Al/Fe] is very sensitive to the chemical evolution environment: a comparison of the bulge, disk and Sagittarius dwarf spheroidal galaxy shows a range of ∼0.7 dex in [Al/Fe] at a given [Fe/H]; presumably due to a range of Type II/Type Ia supernova ratios in these systems.

We compare the dust attenuation properties of two samples of galaxies purely selected in the near-ultraviolet (NUV) band (1750-2750Å, λ mean = 2310Å) and in the far-infrared (FIR) at 60 µm . These samples are built using the GALEX

We have analyzed the redshift-dependent fraction of galactic bars over 0:2 < z < 0:84 in 2157 luminous face-on spiral galaxies from the COSMOS 2 deg 2 field. Our sample is an order of magnitude larger than that used in any previous investigation, and is based on substantially deeper imaging data than that available from earlier wide-area studies of high-redshift galaxy morphology. We find that the fraction of barred spirals declines rapidly with redshift. Whereas in the local universe about 65% of luminous spiral galaxies contain bars (SB+SAB), at z $ 0:84 this fraction drops to about 20%. Over this redshift range the fraction of strong bars (SBs) drops from about 30% to under 10%. It is clear that when the universe was half its present age, the census of galaxies on the Hubble sequence was fundamentally different from that of the present day. A major clue to understanding this phenomenon has also emerged from our analysis, which shows that the bar fraction in spiral galaxies is a strong function of stellar mass, integrated color and bulge prominence. The bar fraction in very massive, luminous spirals is about constant out to z $ 0:84, whereas for the low-mass, blue spirals it declines significantly with redshift beyond z ¼ 0:3. There is also a slight preference for bars in bulge-dominated systems at high redshifts that may be an important clue toward the coevolution of bars, bulges, and black holes. Our results thus have important ramifications for the processes responsible for galactic downsizing, suggesting that massive galaxies matured early in a dynamical sense, and not just as a result of the regulation of their star formation rate.

We present an analysis of the large-scale structure of the halo of the Andromeda galaxy, based on the Pan-Andromeda Archeological Survey (PAndAS), currently the most complete map of resolved stellar populations in any galactic halo. Despite the presence of copious substructures, the global halo populations follow closely powerlaw profiles that become steeper with increasing metallicity. We divide the sample into stream-like populations and a smooth halo component (defined as the population that cannot be resolved into spatially distinct substructures with PAndAS). Fitting a three-dimensional halo model reveals that the most metal-poor populations ([Fe/H] < −1.7) are distributed approximately spherically (slightly prolate with ellipticity c/a = 1.09 ± 0.03), with only a relatively small fraction residing in discernible stream-like structures (f stream = 42%). The sphericity of the ancient smooth component strongly hints that the dark matter halo is also approximately spherical. More metal-rich populations contain higher fractions of stars in streams, with f stream becoming as high as 86% for [Fe/H] > −0.6. The space density of the smooth metal-poor component has a global power-law slope of γ = −3.08 ± 0.07, and a nonparametric fit shows that the slope remains nearly constant from 30 kpc to ∼300 kpc. The total stellar mass in the halo at distances beyond 2• is ∼1.1 × 10 10 M , while that of the smooth component is ∼3 × 10 9 M . Extrapolating into the inner galaxy, the total stellar mass of the smooth halo is plausibly ∼8 × 10 9 M . We detect a substantial metallicity gradient, which declines from [Fe/H] = −0.7 at R = 30 kpc to [Fe/H] = −1.5 at R = 150 kpc for the full sample, with the smooth halo being ∼0.2 dex more metal poor than the full sample at each radius. While qualitatively in line with expectations from cosmological simulations, these observations are of great importance as they provide a prototype template that such simulations must now be able to reproduce in quantitative detail.

We introduce the GALEX Arecibo SDSS Survey (GASS), an on‐going large programme that is gathering high quality H i‐line spectra using the Arecibo radio telescope for an unbiased sample of ∼1000 galaxies with stellar masses greater than 1010 M⊙ and redshifts 0.025 < z < 0.05, selected from the Sloan Digital Sky Survey (SDSS) spectroscopic and Galaxy Evolution Explorer (GALEX) imaging surveys. The galaxies are observed until detected or until a low gas mass fraction limit (1.5–5 per cent) is reached. This paper presents the first Data Release, consisting of ∼20 per cent of the final GASS sample. We use this data set to explore the main scaling relations of the H i gas fraction with galaxy structure and NUV−r colour. A large fraction (∼60 per cent) of the galaxies in our sample are detected in H i. Even at stellar masses above 1011 M⊙, the detected fraction does not fall below ∼40 per cent. We find that the atomic gas fraction MH i/M★ decreases strongly with stellar mass, stellar surface mass density and NUV−r colour, but is only weakly correlated with the galaxy bulge‐to‐disc ratio (as measured by the concentration index of the r‐band light). We also find that the fraction of galaxies with significant (more than a few per cent) H i decreases sharply above a characteristic stellar surface mass density of 108.5 M⊙ kpc−2. The fraction of gas‐rich galaxies decreases much more smoothly with stellar mass. One of the key goals of GASS is to identify and quantify the incidence of galaxies that are transitioning between the blue, star‐forming cloud and the red sequence of passively evolving galaxies. Likely transition candidates can be identified as outliers from the mean scaling relations between MH i/M★ and other galaxy properties. We have fitted a plane to the two‐dimensional relation between the H i mass fraction, stellar surface mass density and NUV−r colour. Interesting outliers from this plane include gas‐rich red sequence galaxies that may be in the process of regrowing their discs, as well as blue, but gas‐poor spirals.

We present imaging data and photometry for the COSMOS survey in 15 photometric bands between 0.3µm and 2.4µm. These include data taken on the Subaru 8.3m telescope, the KPNO and CTIO 4m telescopes, and the CFHT 3.6m telescope. Special techniques are used to ensure that the relative photometric calibration is better than 1% across the field of view. The absolute photometric accuracy from standard star measurements is found to be 6%. The absolute calibration is corrected using galaxy spectra, providing colors accurate to 2% or better. Stellar and galaxy colors and counts agree well with the expected values. Finally, as the first step in the scientific analysis of these data we construct panchromatic number counts which confirm that both the geometry of the universe and the galaxy population are evolving.