1,565 research outputs found
Expanding the search for galaxies at z ~7-10 with new NICMOS Parallel Fields
We have carried out a search for galaxies at z ~ 7-10 in ~14.4 sq. arcmin of
new NICMOS parallel imaging taken in the Great Observatories Origins Deep
Survey (GOODS, 5.9 sq. arcmin), the Cosmic Origins Survey (COSMOS, 7.2 sq.
arcmin), and SSA22 (1.3 sq. arcmin). These images reach 5 sigma sensitivities
of J110 = 26.0-27.5 (AB), and combined they increase the amount of deep
near-infrared data by more than 60% in fields where the investment in deep
optical data has already been made. We find no z>7 candidates in our survey
area, consistent with the Bouwens et al. (2008) measurements at z~7 and 9 (over
23 sq. arcmin), which predict 0.7 galaxies at z~7 and <0.03 galaxies at z~9. We
estimate that 10-20% of z>7 galaxies are missed by this survey, due to
incompleteness from foreground contamination by faint sources. For the case of
luminosity evolution, assuming a Schecter parameterization with a typical phi*
= 10^-3 Mpc^-3, we find M* > -20.0 for z~7 and M* > -20.7 for z~9 (68%
confidence). This suggests that the downward luminosity evolution of LBGs
continues to z~7, although our result is marginally consistent with the z~6 LF
of Bouwens et al.(2006, 2007). In addition we present newly-acquired deep
MMT/Megacam imaging of the z~9 candidate JD2325+1433, first presented in Henry
et al. (2008). The resulting weak but significant detection at i' indicates
that this galaxy is most likely an interloper at z~2.7.Comment: Accepted to ApJ. Replacement includes updated discussion of
incompleteness from foreground contaminatio
Spitzer IRAC confirmation of z_850-dropout galaxies in the Hubble Ultra Deep Field: stellar masses and ages at z~7
Using Spitzer IRAC mid-infrared imaging from the Great Observatories Origins
Deep Survey, we study z_850-dropout sources in the Hubble Ultra Deep Field.
After carefully removing contaminating flux from foreground sources, we clearly
detect two z_850-dropouts at 3.6 micron and 4.5 micron, while two others are
marginally detected. The mid-infrared fluxes strongly support their
interpretation as galaxies at z~7, seen when the Universe was only 750 Myr old.
The IRAC observations allow us for the first time to constrain the rest-frame
optical colors, stellar masses, and ages of the highest redshift galaxies.
Fitting stellar population models to the spectral energy distributions, we find
photometric redshifts in the range 6.7-7.4, rest-frame colors U-V=0.2-0.4,
V-band luminosities L_V=0.6-3 x 10^10 L_sun, stellar masses 1-10 x 10^9 M_sun,
stellar ages 50-200 Myr, star formation rates up to ~25 M_sun/yr, and low
reddening A_V<0.4. Overall, the z=7 galaxies appear substantially less massive
and evolved than Lyman break galaxies or Distant Red Galaxies at z=2-3, but
fairly similar to recently identified systems at z=5-6. The stellar mass
density inferred from our z=7 sample is rho* = 1.6^{+1.6}_{-0.8} x 10^6 M_sun
Mpc^-3 (to 0.3 L*(z=3)), in apparent agreement with recent cosmological
hydrodynamic simulations, but we note that incompleteness and sample variance
may introduce larger uncertainties. The ages of the two most massive galaxies
suggest they formed at z>8, during the era of cosmic reionization, but the star
formation rate density derived from their stellar masses and ages is not nearly
sufficient to reionize the universe. The simplest explanation for this
deficiency is that lower-mass galaxies beyond our detection limit reionized the
universe.Comment: 4 pages, 3 figures, emulateapj, Accepted for publication in ApJ
Letter
Evidence for a fast evolution of the UV luminosity function beyond redshift 6 from a deep HAWK-I survey of the GOODS-S field
We perform a deep search for galaxies in the redshift range 6.5<z<7.5, to
measure the evolution of the number density of luminous galaxies in this
redshift range and derive useful constraints on the evolution of their
Luminosity Function. We present here the first results of an ESO Large Program,
that exploits the unique combination of area and sensitivity provided in the
near-IR by the camera Hawk-I at the VLT. We have obtained two Hawk-I pointings
on the GOODS South field for a total of 32 observing hours, covering ~90
arcmin2. The images reach Y=26.7 mags for the two fields. We have used public
ACS images in the z band to select z-dropout galaxies with the colour criteria
Z-Y>1, Y-J<1.5 and Y-K<2. The other public data in the UBVRIJHK bands are used
to reject possible low redshift interlopers. The output has been compared with
extensive Monte Carlo simulations to quantify the observational effects of our
selection criteria as well as the effects of photometric errors. We detect 7
high quality candidates in the magnitude range Y=25.5-26.7. This interval
samples the critical range for M* at z>6 (M_1500 ~- 19.5 to -21.5). After
accounting for the expected incompleteness, we rule out at a 99% confidence
level a Luminosity Function constant from z=6 to z=7, even including the
effects of cosmic variance. For galaxies brighter than M_1500=-19.0 we derive a
luminosity density rho_UV=1.5^{+2.0}_{-0.9} 10^25 erg/s/Hz/Mpc3, implying a
decrease by a factor 3.5 from z=6 to z~6.8. On the basis of our findings, we
make predictions for the surface densities expected in future surveys surveys,
based on ULTRA-VISTA, HST-WFC3 or JWST-NIRCam, evaluating the best
observational strategy to maximise their impact.Comment: Accepted for publication in Astronomy & Astrophysic
Rationale Document: Entity Information And Entity Interaction In A Distributed Interactive Simulation
Report on efforts to define and develop a standard communication protocol at the protocol data unit level
Rationale Document: Entity Information And Entity Interaction In A Distributed Interactive Simulation
Report on the development of a standard communications protocol, networking different operator trainers and developmental simulators together and developing this standard at the protocol data unit level
A candidate redshift z ~ 10 galaxy and rapid changes in that population at an age of 500 Myr
Searches for very-high-redshift galaxies over the past decade have yielded a
large sample of more than 6,000 galaxies existing just 900-2,000 million years
(Myr) after the Big Bang (redshifts 6 > z > 3; ref. 1). The Hubble Ultra Deep
Field (HUDF09) data have yielded the first reliable detections of z ~ 8
galaxies that, together with reports of a gamma-ray burst at z ~ 8.2 (refs 10,
11), constitute the earliest objects reliably reported to date. Observations of
z ~ 7-8 galaxies suggest substantial star formation at z > 9-10. Here we use
the full two-year HUDF09 data to conduct an ultra-deep search for z ~ 10
galaxies in the heart of the reionization epoch, only 500 Myr after the Big
Bang. Not only do we find one possible z ~ 10 galaxy candidate, but we show
that, regardless of source detections, the star formation rate density is much
smaller (~10%) at this time than it is just ~200 Myr later at z ~ 8. This
demonstrates how rapid galaxy build-up was at z ~ 10, as galaxies increased in
both luminosity density and volume density from z ~ 8 to z ~ 10. The 100-200
Myr before z ~ 10 is clearly a crucial phase in the assembly of the earliest
galaxies.Comment: 41 pages, 14 figures, 2 tables, Nature, in pres
A critical analysis of the UV Luminosity Function at redshift~7 from deep WFC3 data
The study of the Luminosity Function (LF) of Lyman Break Galaxies (LBGs) at
z=7 is important for ascertaining their role in the reionization of the
Universe. We perform a detailed and critical analysis of the statistical and
systematic errors in the z~7 LF determination: we have assembled a large sample
of candidate LBGs at z~7 from different surveys, spanning a large variety of
areas and depths. In particular, we have combined data from the deep (J<27.4)
and ultradeep (J<29.2) surveys recently acquired with the new WFC3 NIR camera
on HST, over the GOODS-ERS and the HUDF fields, with ground based surveys in
wide and shallow areas from VLT and Subaru. We have used public ACS images in
the z-band to select z-dropout galaxies, and other public data both in the blue
(BVI) and in the red bands to reject possible low-redshift interlopers. We have
compared our results with extensive simulations to quantify the observational
effects of our selection criteria as well as the effects of photometric
scatter, color selections or the morphology of the candidates. We have found
that the number density of faint LBGs at z~7 is only marginally sensitive to
the color selection adopted, but it is strongly dependent from the assumption
made on the half light distributions of the simulated galaxies, used to correct
the observed sample for incompleteness. The slope of the faint end of the LBGs
LF has thus a rather large uncertainty, due to the unknown distribution of
physical sizes of the z~7 LBGs. We conclude that galaxies at z~7 are unable to
reionize the Universe unless there is a significant evolution in the clumpiness
of the IGM or in the escape fraction of ionising photons or, alternatively,
there is a large population of z~7 LBGs with large physical dimensions but
still not detected by the present observations.Comment: 15 pages, 11 figures, accepted for publication in A&
On the Stellar Populations and Evolution of Star-Forming Galaxies at 6.3 < z < 8.6
We study the physical characteristics of galaxies at 6.3 < z < 8.6, selected
from deep near-infrared imaging with the Wide Field Camera 3 (WFC3) on board
the Hubble Space Telescope. Accounting for the photometric scatter using
simulations, galaxies at z ~ 7 have bluer UV colors compared to typical local
starburst galaxies at > 4 sigma confidence. Although these colors necessitate
young ages (<100 Myr), low or zero dust attenuation, and low metallicities,
these are explicable by normal (albeit unreddened) stellar populations, with no
evidence for near-zero metallicities and/or top-heavy initial mass functions.
The age of the Universe at these redshifts limits the amount of stellar mass in
late-type populations, and the WFC3 photometry implies galaxy stellar masses ~
10^8 - 10^9 Msol for Salpeter initial mass functions to a limiting magnitude of
M_1500 ~ -18. The masses of ``characteristic'' (L*) z > 7 galaxies are smaller
than those of L* Lyman break galaxies (LBGs) at lower redshifts, and are
comparable to less evolved galaxies selected on the basis of their Lyman alpha
emission at 3 < z < 6, implying that the 6.3 < z < 8.6 galaxies are the
progenitors of more evolved galaxies at lower redshifts. We estimate that Lyman
alpha emission is able to contribute to the observed WFC3 colors of galaxies at
these redshifts, with an estimated typical line flux of ~ 10^-18 erg s^-1
cm^-2, roughly a factor of four below currently planned surveys. The integrated
UV specific luminosity for the detected galaxies at z ~ 7 and z ~ 8 is within
factors of a few of that required to reionize the IGM assuming low clumping
factors, implying that in order to reionize the Universe galaxies at these
redshifts have a high ( ~ 50%) escape fraction of Lyman continuum photons,
possibly substantiated by the very blue colors of this population.Comment: Accepted to the Astrophysical Journal; replaced with accepted
version. Minor modifications to sample, conclusions are unchange
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