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.

The extragalactic background light (EBL) is of fundamental importance both for understanding the entire process of galaxy evolution and for γ‐ray astronomy, but the overall spectrum of the EBL between 0.1 and 1000 μm has never been determined directly from galaxy spectral energy distribution (SED) observations over a wide redshift range. The evolving, overall spectrum of the EBL is derived here utilizing a novel method based on observations only. This is achieved from the observed evolution of the rest‐frame K‐band galaxy luminosity function up to redshift 4, combined with a determination of galaxy‐SED‐type fractions. These are based on fitting Spitzer Wide‐Area Infrared Extragalactic Survey (SWIRE) templates to a multiwavelength sample of about 6000 galaxies in the redshift range from 0.2 to 1 from the All‐wavelength Extended Groth Strip International Survey (AEGIS). The changing fractions of quiescent galaxies, star‐forming galaxies, starburst galaxies and active galactic nucleus (AGN) galaxies in that redshift range are estimated, and two alternative extrapolations of SED types to higher redshifts are considered. This allows calculation of the evolution of the luminosity densities from the ultraviolet (UV) to the infrared (IR), the evolving star formation rate density of the Universe, the evolving contribution to the bolometric EBL from the different galaxy populations including AGN galaxies and the buildup of the EBL. Our EBL calculations are compared with those from a semi‐analytic model, another observationally based model and observational data. The EBL uncertainties in our modelling based directly on the data are quantified, and their consequences for attenuation of very‐high‐energy γ‐rays due to pair production on the EBL are discussed. It is concluded that the EBL is well constrained from the UV to the mid‐IR, but independent efforts from IR and γ‐ray astronomy are needed in order to reduce the uncertainties in the far‐IR.

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We present the broadband UV through mid-infrared spectral energy distributions (SEDs) of a sample of 72 spectroscopically confirmed star-forming galaxies at z ¼ 2:30 AE 0:3. Located in a 72 arcmin 2 field centered on the bright background QSO, HS 1700+643, these galaxies were preselected to lie at z $ 2 solely on the basis of their restframe UV colors and luminosities and should be representative of UV-selected samples at high redshift. In addition to deep ground-based photometry spanning from 0.35 to 2.15 m, we make use of Spitzer IRAC data, which probe the rest-frame near-IR at z $ 2. The range of stellar populations present in the sample is investigated with simple, singlecomponent stellar population synthesis models. The inability to constrain the form of the star formation history limits our ability to determine the parameters of extinction, age, and star formation rate without using external multiwavelength information. Emphasizing stellar mass estimates, which are much less affected by these uncertainties, we find h log M Ã /M i ¼ 10:32 AE 0:51 for the sample. The addition of Spitzer IRAC data as a long-wavelength baseline reduces stellar mass uncertainties by a factor of 1.5-2 relative to estimates based on optical-K s photometry alone. However, the total stellar mass estimated for the sample is remarkably insensitive to the inclusion of IRAC data. We find correlations between stellar mass and rest-frame R band (observed K s ) and rest-frame 1.4 m (observed 4.5 m) luminosities, although with significant scatter. Even at rest-frame 1.4 m, the mass-to-light ratio varies by a factor of 15 indicating that even the rest-frame near-IR, when taken alone, is a poor indicator of stellar mass in star-forming galaxies at z $ 2. Allowing for the possibility of episodic star formation, we find that typical galaxies in our sample could contain up to 3 times more stellar mass in an old underlying burst than what was inferred from singlecomponent modeling. In contrast, mass estimates for the most massive galaxies in the sample (M Ã > 10 11 M ) are fairly insensitive to the method used to model the stellar population. Galaxies in this massive tail, which are also the oldest objects in the sample, could plausibly evolve into the passive galaxies discovered at z $ 1:7 with near-IR selection techniques. In the general framework of hierarchical galaxy formation and mergers, which implies episodic star formation histories, galaxies at high redshift may pass in and out of UV-selected and near-IR color-selected samples as they evolve from phases of active star formation to quiescence and back again.

We present new observational determinations of the evolution of the 2-10keV X-ray luminosity function (XLF) of AGN. We utilise data from a number of surveys including both the 2Ms Chandra Deep Fields and the AEGIS-X 200ks survey, enabling accurate measurements of the evolution of the faint end of the XLF. We combine direct, hard X-ray selection and spectroscopic follow-up or photometric redshift estimates at z<1.2 with a rest-frame UV colour pre-selection approach at higher redshifts to avoid biases associated with catastrophic failure of the photometric redshifts. Only robust optical counterparts to X-ray sources are considered using a likelihood ratio matching technique. A Bayesian methodology is developed that considers redshift probability distributions, incorporates selection functions for our high redshift samples, and allows robust comparison of different evolutionary models. We find that the XLF retains the same shape at all redshifts, but undergoes strong luminosity evolution out to z~1, and an overall negative density evolution with increasing redshift, which thus dominates the evolution at earlier times. We do not find evidence that a Luminosity-Dependent Density Evolution, and the associated flattening of the faint-end slope, is required to describe the evolution of the XLF. We find significantly higher space densities of low-luminosity, high-redshift AGN than in prior studies, and a smaller shift in the peak of the number density to lower redshifts with decreasing luminosity. The total luminosity density of AGN peaks at z=1.2+/-0.1, but there is a mild decline to higher redshifts. We find >50% of black hole growth takes place at z>1, with around half in Lx<10^44 erg/s AGN.Comment: 24 pages, 13 figures, accepted for publication in MNRA

We present the quantitative rest-frame B morphological evolution and galaxy merger fraction at 0:2 < z < 1:2 as observed by the All-Wavelength Extended Groth Strip International Survey (AEGIS). We use the Gini coefficient and M 20 to identify major mergers and classify galaxy morphology for a volume-limited sample of 3009 galaxies brighter than 0:4L Ã B , assuming pure luminosity evolution. We find that the merger fraction remains roughly constant at 10% AE 2% for 0:2 < z < 1:2. The fraction of E/S0/Sa galaxies increases from 21% AE 3% at z $ 1:1 to 44% AE 9% at z $ 0:3, while the fraction of SbYIr galaxies decreases from 64% AE 6% at z $ 1:1 to 47% AE 9% at z $ 0:3. The majority of z < 1:2 Spitzer MIPS 24 m sources with L( IR) > 10 11 L are disk galaxies, and only $15% are classified as major merger candidates. Edge-on and dusty disk galaxies (SbYIr) are almost a third of the red sequence at z $ 1:1, while E/S0/Sa make up over 90% of the red sequence at z $ 0:3. Approximately 2% of our full sample are red mergers. We conclude (1) the merger rate does not evolve strongly between 0:2 < z < 1:2; (2) the decrease in the volumeaveraged star formation rate density since z $ 1 is a result of declining star formation in disk galaxies rather than a disappearing population of major mergers; (3) the build-up of the red sequence at z < 1 can be explained by a doubling in the number of spheroidal galaxies since z $ 1:2.

We present results from the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CAN-DELS) photometric redshift methods investigation. In this investigation, the results from eleven participants, each using a different combination of photometric redshift code, template spectral energy distributions (SEDs) and priors, are used to examine the properties of photometric redshifts applied to deep fields with broad-band multi-wavelength coverage. The photometry used includes U -band through mid-infrared filters and was derived using the TFIT method. Comparing the results, we find that there is no particular code or set of template SEDs that results in significantly better photometric redshifts compared to others. However, we find codes producing the lowest scatter and outlier fraction utilize a training sample to optimize photometric redshifts by adding zero-point offsets, template adjusting or adding extra smoothing errors. These results therefore stress the importance of the training procedure. We find a strong dependence of the photometric redshift accuracy on the signal-to-noise ratio of the photometry. On the other hand, we find a weak dependence of the photometric redshift scatter with redshift and galaxy color. We find that most photometric redshift codes quote redshift errors (e.g., 68% confidence intervals) that are too small compared to that expected from the spectroscopic control sample. We find that all codes show a statistically significant bias in the photometric redshifts. However, the bias is in all cases smaller than the scatter, the latter therefore dominates the errors. Finally, we find that combining results from multiple codes significantly decreases the photometric redshift scatter and outlier fraction. We discuss different ways of combining data to produce accurate photometric redshifts and error estimates. 1 2 Dahlen et al.

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 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-linewidth correlations. The effect is greatest toward the blue, with the consequence that luminosity-linewidth slope dependencies are now only weakly a function of color.Comment: 23 pages, 5 figure