1,782 research outputs found
An Integrated Picture of Star Formation, Metallicity Evolution, and Galactic Stellar Mass Assembly
We present an integrated study of star formation and galactic stellar mass
assembly from z=0.05-1.5 and galactic metallicity evolution from z=0.05-0.9
using a very large and highly spectroscopically complete sample selected by
rest-frame NIR bolometric flux in the GOODS-N. We assume a Salpeter IMF and fit
Bruzual & Charlot (2003) models to compute the galactic stellar masses and
extinctions. We determine the expected formed stellar mass density growth rates
produced by star formation and compare them with the growth rates measured from
the formed stellar mass functions by mass interval. We show that the growth
rates match if the IMF is slightly increased from the Salpeter IMF at
intermediate masses (~10 solar masses). We investigate the evolution of galaxy
color, spectral type, and morphology with mass and redshift and the evolution
of mass with environment. We find that applying extinction corrections is
critical when analyzing galaxy colors; e.g., nearly all of the galaxies in the
green valley are 24um sources, but after correcting for extinction, the bulk of
the 24um sources lie in the blue cloud. We find an evolution of the
metallicity-mass relation corresponding to a decrease of 0.21+/-0.03 dex
between the local value and the value at z=0.77 in the 1e10-1e11 solar mass
range. We use the metallicity evolution to estimate the gas mass of the
galaxies, which we compare with the galactic stellar mass assembly and star
formation histories. Overall, our measurements are consistent with a galaxy
evolution process dominated by episodic bursts of star formation and where star
formation in the most massive galaxies (>1e11 solar masses) ceases at z<1.5
because of gas starvation. (Abstract abridged)Comment: 48 pages, Accepted by the Astrophysical Journa
The bar PANDA focussing-lightguide disc DIRC
bar PANDA will be a fixed target experiment internal to the HESR antiproton storage ring at the future FAIR complex. The ANDA detector requires excellent particle-identification capabilities in order to achieve its scientific potential. Cherenkov counters employing the DIRC principle were chosen as PID detectors for the Target Spectrometer. The proposed Focussing-Lightguide Disc DIRC will cover the forward part of the Target Spectrometer acceptance in the angular range between 5° and 22°. Its design includes a novel approach to mitigate dispersion effects in the solid radiator of a DIRC counter using optical elements. The dispersion correction will enable the Focussing-Lightguide Disc DIRC to provide pion-kaon identification for momenta well above 3.5 GeV/c
Optically Faint Microjansky Radio Sources
We report on the identifications of radio sources from our survey of the
Hubble Deep Field and the SSA13 fields, both of which comprise the deepest
radio surveys to date at 1.4 GHz and 8.5 GHz respectively. About 80% of the
microjansky radio sources are associated with moderate redshift starburst
galaxies or AGNs within the I magnitude range of 17 to 24 with a median of I =
22 mag. Thirty-one (20%) of the radio sources are: 1) fainter than 25 mag,
with two objects in the HDF 28.5, 2) often identified with very red
objects 4, and 3) not significantly different in radio properties than
the brighter objects. We suggest that most of these objects are associated with
heavily obscured starburst galaxies with redshifts between 1 and 3. However,
other mechanisms are discussed and cannot be ruled out with the present
observations.Comment: to appear in Astrophysical Journal Letters, 3 figures, 1 tabl
Galaxy Halo Masses from Galaxy-Galaxy Lensing
We present measurements of the extended dark halo profiles of bright early
type galaxies at redshifts 0.1 to 0.9 obtained via galaxy-galaxy lensing
analysis of images taken at the CFHT using the UH8K CCD mosaic camera. Six half
degree fields were observed for a total of 2 hours each in I and V, resulting
in catalogs containing ~20 000 galaxies per field. We used V-I color and I
magnitude to select bright early type galaxies as the lens galaxies, yielding a
sample of massive lenses with fairly well determined redshifts and absolute
magnitudes M ~ M_* \pm 1. We paired these with faint galaxies lying at angular
distances 20" to 60", corresponding to physical radii of 26 to 77 kpc (z = 0.1)
and 105 to 315 kpc (z = 0.9), and computed the mean tangential shear of the
faint galaxies. The shear falls off with radius roughly as expected for flat
rotation curve halos. The shear values were weighted in proportion to the
square root of the luminosity of the lens galaxy. Our results give a value for
the average mean rotation velocity of an L_* galaxy halo at r~50-200 kpc of v_*
= 238^{+27}_{-30} km per sec for a flat lambda (Omega_m0 = 0.3, Omega_l0 = 0.7)
cosmology (v_* = 269^{+34}_{-39} km per sec for Einstein-de Sitter), and with
little evidence for evolution with redshift. We compare to halo masses measured
by other groups/techniques. We find a mass-to-light ratio of ~121\pm28h(r/100
kpc) and these halos constitute Omega ~0.04 \pm 0.01(r/100 kpc) of closure
density. (abridged)Comment: Accepted for publication in ApJ (minor modifications) - 32 pages, 11
figs, 5 table
The Radio/Optical Catalog of the SSA13 Field
We present a 1.4-GHz catalog of 810 radio sources (560 sources in the
complete sample) with 1.8" resolution found within a 17' radius in the SSA13
field (RA=13h12m,DEC=42d38'). The radio image from the VLA has an rms noise
level of 4.82 microJy/beam at the field center, and Subaru optical images in
r-band (6300A) and z-band (9200A) have a three-sigma detection magnitude of
26.1 and 24.9, respectively. 88% of the radio sources are identified with an
optical counterpart, and there is significantly more reddening for objects
fainter than 24-mag. The radio and optical parameters are tabulated, and source
morphologies are displayed by radio contours overlaying optical false-color
images. The radio structures show a wealth of complexity and these are
classified into a small number of categories. About one-third of the radio
sources are larger than 1.2" and their orientation is often similar to that of
the associated galaxy or binary-galaxy system. The density of sources in the
SSA13 field above 75 microJy is 0.40 per square arcmin, with a slope of -2.43
in the differential counts. The radio spectral index may steepen for sources
below 75 microJy. We estimate that at most 40% of the microJansky radio sources
are dominated by AGN processes.Comment: 50 pages, 14 figures of which fig 6 contains 33 parts. In press,
Astrophysical Journal, Supp
HST and Spitzer Observations of the Host Galaxy of GRB 050904: A Metal-Enriched, Dusty Starburst at z=6.295
We present deep Hubble Space Telescope and Spitzer Space Telescope
observations of the host galaxy of GRB 050904 at z=6.295. The host is detected
in the H-band and marginally at 3.6 micron. From these detections, and limits
in the z'-band and 4.5 micron, we infer an extinction-corrected absolute
magnitude, M(UV)=-20.7 mag, or ~L*, a substantial star formation rate of 15
solar masses per year, and a stellar mass of a few 10^9 solar masses. A
comparison to the published sample of spectroscopically-confirmed galaxies at
z>5.5 reveals that the host of GRB 050904 would evade detection and/or
confirmation in any of the current surveys due to the lack of detectable
Ly-alpha emission, which is likely the result of dust extinction (A[1200]~1.5
mag). This suggests that not all luminous starburst galaxies at z~6 are
currently being accounted for. Most importantly, using the metallicity of
Z~0.05 solar inferred from the afterglow absorption spectrum, our observations
indicate for the first time that the observed evolution in the mass- and
luminosity-metallicity relations from z=0 to z~2 continues on to z>6. The ease
of measuring redshifts and metallicities from the afterglow emission suggests
that in tandem with the next generation ground- and space-based telescopes, a
GRB mission with dedicated near-IR follow-up can provide unique information on
the evolution of stars and galaxies through the epoch of re-ionization.Comment: Submitted to ApJ; 11 pages, 5 figures; A high-resolution version of
figure 1 can be found at http://www.ociw.edu/~eberger/fig1.050904.berger.ep
Dusty star forming galaxies at high redshift
The global star formation rate in high redshift galaxies, based on optical
surveys, shows a strong peak at a redshift of z=1.5, which implies that we have
already seen most of the formation. High redshift galaxies may, however, emit
most of their energy at submillimeter wavelengths if they contain substantial
amounts of dust. The dust would absorb the starlight and reradiate it as
far-infrared light, which would be redshifted to the submillimeter range. Here
we report a deep survey of two blank regions of sky performed at submillimeter
wavelengths (450 and 850-micron). If the sources we detect in the 850-micron
band are powered by star formation, then each must be converting more than 100
solar masses of gas per year into stars, which is larger than the maximum star
formation rates inferred for most optically-selected galaxies. The total amount
of high redshift star formation is essentially fixed by the level of background
light, but where the peak occurs in redshift for the submillimeter is not yet
established. However, the background light contribution from only the sources
detected at 850-micron is already comparable to that from the
optically-selected sources. Establishing the main epoch of star formation will
therefore require a combination of optical and submillimeter studies.Comment: 10 pages + 2 Postscript figures, under embargo at Natur
Thermal and Photochemical Reduction and Functionalization Chemistry of the Uranyl Dication, [U VI O2] 2+
The uranyl ion, [UVIO2]2+, possesses rigorously trans, strongly covalent, and chemically robust U-oxo groups. However, through the use of anaerobic reaction techniques, both one- and two-electron reductive functionalization of the uranyl oxo groups has been discovered and developed. Prior to 2010, this unusual reactivity centered around the reductive silylation of the uranyl ion which entailed conversion of the oxo ligands into siloxy ligands and reductive metalation of the uranyl oxo with Group 1 and f-block metals. This review surveys the large number of new examples of reductive functionalization of the uranyl ion that have been reported since 2010, including reductive borylation and alumination, metalation with d- or f-block metals, and new examples of reductive silylation. Other examples of oxo-group functionalization of [UVIO2]2+ that do not involve reduction, mainly with Group 1 cations, are also covered, along with new advances in the photochemistry of the uranyl(VI) ion that involve the transient formation of formally uranyl(V) [UVO2]+ ion
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