Gemini Deep Deep Survey VI: Massive Hdelta-strong galaxies at z=1

We show that there has been a dramatic decline in the abundance of massive galaxies with strong Hdelta stellar absorption lines from z=1.2 to the present. These ``Hdelta-strong'', or HDS, galaxies have undergone a recent and rapid break in their star-formation activity. Combining data from the Gemini Deep Deep and the Sloan Digital Sky Surveys to make mass-matched samples (M*>=10^10.2 Msun), with 25 and 50,255 galaxies, respectively), we find that the fraction of galaxies in an HDS phase has decreased from about 50% at z=1.2 to a few percent today. This decrease in fraction is due to an actual decrease in the number density of massive HDS systems by a factor of 2-4, coupled with an increase in the number density of massive galaxies by about 30 percent. We show that this result depends only weakly on the threshold chosen for the Hdelta equivalent width to define HDS systems (if greater than 4 A) and corresponds to a (1+z)^{2.5\pm 0.7} evolution. Spectral synthesis studies of the high-redshift population using the PEGASE code, treating Hdelta_A, EW[OII], Dn4000, and rest-frame colors, favor models in which the Balmer absorption features in massive Hdelta-strong systems are the echoes of intense episodes of star-formation that faded about 1 Gyr prior to the epoch of observation. The z=1.4-2 epoch appears to correspond to a time at which massive galaxies are in transition from a mode of sustained star formation to a relatively quiescent mode with weak and rare star-formation episodes. We argue that the most likely local descendants of the distant massive HDS galaxies are passively evolving massive galaxies in the field and small groups.Comment: 16 pages, 12 figures, 3 tables, uses emulateapj.sty; updated to match the version accepted by ApJ. One figure added, conclusions unchange

Triggered Star Formation in Galaxy Pairs at z=0.08-0.38

We measure the strength, frequency, and timescale of tidally triggered star formation at redshift z=0.08-0.38 in a spectroscopically complete sample of galaxy pairs drawn from the magnitude-limited redshift survey of 9,825 Smithsonian Hectospec Lensing Survey (SHELS) galaxies with R<20.3. To examine the evidence for tidal triggering, we identify a volume-limited sample of major (|\Delta M_R|1/5) pair galaxies with $M_R < -20.8 in the redshift range z=0.08-0.31. The size and completeness of the spectroscopic survey allows us to focus on regions of low local density. The spectrophotometric calibration enables the use of the 4000 Ang break (D_n4000), the H\alpha specific star formation rate (SSFR_{H\alpha}), and population models to characterize the galaxies. We show that D_n4000 is a useful population classification tool; it closely tracks the identification of emission line galaxies. The sample of major pair galaxies in regions of low local density with low D_n4000 demonstrates the expected anti-correlation between pair-wise projected separation and a set of star formation indicators explored in previous studies. We measure the frequency of triggered star formation by comparing the SSFR_{H\alpha} in the volume-limited sample in regions of low local density: 32 +/-7% of the major pair galaxies have SSFR_{H\alpha} at least double the median rate of the unpaired field galaxies. Comparison of stellar population models for pair and for unpaired field galaxies implies a timescale for triggered star formation of ~300-400 Myr.Comment: 25 pages, 15 figures. Accepted to A

Nebular Attenuation in H\alpha-selected Star-forming Galaxies at z=0.8 from the NewH\alpha\ Survey

We present measurements of the dust attenuation of H\alpha-selected emission-line galaxies at z=0.8 from the NewH\alpha\ narrowband survey. The analysis is based on deep follow-up spectroscopy with Magellan/IMACS, which captures the strong rest-frame optical emission lines from [OII] \lambda 3727 to [OIII] \lambda 5007. The spectroscopic sample used in this analysis consists of 341 confirmed H\alpha\ emitters. We place constraints on the AGN fraction using diagnostics which can be applied at intermediate redshift. We find that at least 5% of the objects in our spectroscopic sample can be classified as AGN and 2% are composite, i.e. powered by a combination of star-formation and AGN activity. We measure the dust attenuation for individual objects from the ratios of the higher order Balmer lines. The H\beta\ and H\gamma\ pair of lines is detected with S/N>5 in 55 individual objects and the H\beta\ and H\delta\ pair is detected in 50 individual objects. We also create stacked spectra to probe the attenuation in objects without individual detections. The median attenuation at H\alpha\ based on the objects with individually detected lines is A(H\alpha)=0.9+-1.0 magnitudes, in good agreement with the attenuation found in local samples of star-forming galaxies. We find that the z=0.8 galaxies occupy a similar locus of attenuation as a function of magnitude, mass and SFR as a comparison sample drawn from the SDSS DR4. Both the results from the individual z=0.8 galaxies and from the stacked spectra show consistency with the mass -- attenuation and SFR -- attenuation relations found in the local Universe, indicating that these relations are also applicable at intermediate redshift.Comment: Submitted to AJ. Revised per referee's comment

The Star Formation and Nuclear Accretion Histories of Normal Galaxies in the AGES Survey

We combine IR, optical and X-ray data from the overlapping, 9.3 square degree NOAO Deep Wide-Field Survey (NDWFS), AGN and Galaxy Evolution Survey (AGES), and XBootes Survey to measure the X-ray evolution of 6146 normal galaxies as a function of absolute optical luminosity, redshift, and spectral type over the largely unexplored redshift range 0.1 < z < 0.5. Because only the closest or brightest of the galaxies are individually detected in X-rays, we use a stacking analysis to determine the mean properties of the sample. Our results suggest that X-ray emission from spectroscopically late-type galaxies is dominated by star formation, while that from early-type galaxies is dominated by a combination of hot gas and AGN emission. We find that the mean star formation and supermassive black hole accretion rate densities evolve like (1+z)^3, in agreement with the trends found for samples of bright, individually detectable starburst galaxies and AGN. Our work also corroborates the results of many previous stacking analyses of faint source populations, with improved statistics.Comment: 19 pages, 15 figures, 3 tables, accepted for publication in Ap

CANDELS: The Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey

The Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) is designed to document the first third of galactic evolution, over the approximate redshift (z) range 8--1.5. It will image >250,000 distant galaxies using three separate cameras on the Hubble Space Telescope, from the mid-ultraviolet to the near-infrared, and will find and measure Type Ia supernovae at z>1.5 to test their accuracy as standardizable candles for cosmology. Five premier multi-wavelength sky regions are selected, each with extensive ancillary data. The use of five widely separated fields mitigates cosmic variance and yields statistically robust and complete samples of galaxies down to a stellar mass of 10^9 M_\odot to z \approx 2, reaching the knee of the ultraviolet luminosity function (UVLF) of galaxies to z \approx 8. The survey covers approximately 800 arcmin^2 and is divided into two parts. The CANDELS/Deep survey (5\sigma\ point-source limit H=27.7 mag) covers \sim 125 arcmin^2 within GOODS-N and GOODS-S. The CANDELS/Wide survey includes GOODS and three additional fields (EGS, COSMOS, and UDS) and covers the full area to a 5\sigma\ point-source limit of H \gtrsim 27.0 mag. Together with the Hubble Ultra Deep Fields, the strategy creates a three-tiered "wedding cake" approach that has proven efficient for extragalactic surveys. Data from the survey are nonproprietary and are useful for a wide variety of science investigations. In this paper, we describe the basic motivations for the survey, the CANDELS team science goals and the resulting observational requirements, the field selection and geometry, and the observing design. The Hubble data processing and products are described in a companion paper.Comment: Submitted to Astrophysical Journal Supplement Series; Revised version, subsequent to referee repor

Cell Surface Free Thiols Are Elevated On Antigen-Specific Cells Undergoing Recent TCR Stimulation.

<p>Naïve mice were infected with either LCMV-Armstrong (Acute) or LCMV-Clone 13 (Chronic) and harvested 8 days postinfection. To determine if cell surface free thiol levels correlated with expression of granzyme B (A), splenocytes were stained with anti-CD8α, D^bGP33-41, isotype control or anti-Granzyme B and maleimide-Alexa Fluor 488. The histogram is gated on CD8⁺D^bGP33-41⁺ T cells and the shaded area indicates isotype staining. For each population the Granzyme B expression was divided into negative (neg), intermediate (int) , and high (high) levels of staining. (B) The cell surface free thiol levels compared to those on CD8⁺CD44^loGranzyme B^- T cells from uninfected mice were determined for each antigen-specific population and the average and standard deviation are plotted. To determine whether cell surface free thiols were elevated on antigen specific CD8⁺ T cells that were actively proliferating (C) splenocytes were stained with anti-CD8α, D^bGP33-41, isotype control or anti-Ki-67, and maleimide-Alexa Fluor 488 . Dot plots are gated on total CD8⁺ T cells and the values in each corner indicate the percent of cells that are in that quadrant. (D) The cell surface free thiol levels compared to those on CD8⁺CD44^loKi-67^- T cells from uninfected mice were determined for each antigen-specific population and the average and standard deviation are plotted. (E) To determine recent TCR stimulation splenocytes were stained with anti-CD8α, anti-CD69, anti-PD-1, D^bGP33-41 and maleimide-Pacific Blue. The dot plots are gated on either CD8⁺CD44^lo (naïve) or CD8⁺D^bGP33-41⁺ (infected) T cells. The value in each corner indicates the percent of cells in that quadrant. (F) The cell surface free thiol levels compared to those on CD8⁺PD-1^-CD69^- T cells from uninfected mice were determined for each antigen-specific population and the average and standard deviation are plotted. Six mice were analyzed in two independent experiments. *, significant difference between acute and chronic infection, P<u><</u>0.05.</p

Cell Surface Free Thiols Increase On Activated CD8⁺ T Cells Prior To Division.

<p>Splenocytes were isolated from naïve mice and CD8⁺ T cells were purified and labeled with CFSE. Cells were then stimulated with either 10μg/mL isotype or anti-CD3 and anti-CD28. At the indicated timepoint, cells were harvested and incubated with maleimide-Alexa Fluor 647. Proliferation (A) was assessed by loss of CFSE fluorescence after activation. (B) The fold increase in cell surface free thiols relative to those found on isotype stimulated cells was determined and the average and standard deviation are plotted. Six mice were analyzed in two independent experiments. *, significant difference, P<u><</u>0.05.</p

Cell Surface Free Thiols Are Higher On Effector Compared To Memory CD8⁺T Cells During Acute Infection.

<p>(A) Mice were infected with LCMV-Armstrong and on day 8 postinfection splenocytes were harvested and stained with anti-CD8α, anti-CD44, the indicated MHC Class I tetramer and maleimide-Alexa Fluor 488. The maleimide-Alexa Fluor 488 levels of the gated populations are plotted in the histogram format with the shaded area indicating the staining of CD8⁺CD44^lo T cells from naïve mice. (B) Mice were examined at multiple times following LCMV- Armstrong (1°) infection or Clone 13 rechallenge (2°) and the fold increase in cell surface free thiols relative to naïve phenotype cells from uninfected mice was determined and the average and standard deviation are plotted. Six mice were analyzed in two independent experiments. *, significant difference, P<u><</u>0.05.</p

Cell Surface Free Thiols Remain Elevated On Antigen-Specific CD8⁺ T Cells For Extended Periods During Chronic Viral Infection.

<p>(A) Mice were infected with LCMV-Clone 13 and on day 8 postinfection, splenocytes were harvested and stained with anti-CD8α, anti-CD44, the indicated MHC Class I tetramer and maleimide-Alexa 488. The maleimide-Alexa Fluor 488 level of the gated populations is plotted in the histogram format with the shaded area indicating the staining of CD8⁺CD44^lo T cells from naïve mice. (B) Mice were examined at multiple times following LCMV-Clone 13 infection and the fold increase in cell surface free thiols relative to naïve phenotype cells from uninfected mice was determined and the average and standard deviation are plotted. Six mice were analyzed in two independent experiments. *, significant difference, P<u><</u>0.05.</p