Abstract
We present a catalog of 10,718 objects in the COSMOS field, observed through multi-slit spectroscopy with the Deep Imaging Multi-Object Spectrograph (DEIMOS) on the Keck II telescope in the ...wavelength range ∼5500–9800 Å. The catalog contains 6617 objects with high-quality spectra (two or more spectral features), and 1798 objects with a single spectroscopic feature confirmed by the photometric redshift. For 2024 typically faint objects, we could not obtain reliable redshifts. The objects have been selected from a variety of input catalogs based on multi-wavelength observations in the field, and thus have a diverse selection function, which enables the study of the diversity in the galaxy population. The magnitude distribution of our objects is peaked at
I
AB
∼ 23 and
K
AB
∼ 21, with a secondary peak at
K
AB
∼ 24. We sample a broad redshift distribution in the range 0 <
z
< 6, with one peak at
z
∼ 1, and another one around
z
∼ 4. We have identified 13 redshift spikes at
z
> 0.65 with chance probabilities < 4 × 10
−4
, some of which are clearly related to protocluster structures of sizes >10 Mpc. An object-to-object comparison with a multitude of other spectroscopic samples in the same field shows that our DEIMOS sample is among the best in terms of fraction of spectroscopic failures and relative redshift accuracy. We have determined the fraction of spectroscopic blends to about 0.8% in our sample. This is likely a lower limit and at any rate well below the most pessimistic expectations. Interestingly, we find evidence for strong lensing of Ly
α
background emitters within the slits of 12 of our target galaxies, increasing their apparent density by about a factor of 4.
ABSTRACT We measure a relation between the depth of four prominent rest-UV absorption complexes and metallicity for local galaxies and verify it up to . We then apply this relation to a sample of 224 ...galaxies at ( ) in the Cosmic Evolution Survey (COSMOS), for which unique UV spectra from the Deep Imaging Multi-object Spectrograph (DEIMOS) and accurate stellar masses from the Spitzer Large Area Survey with Hyper-Suprime-Cam (SPLASH) are available. The average galaxy population at and is characterized by 0.3-0.4 dex (in units of ) lower metallicities than at z ∼ 2, but comparable to . We find galaxies with weak or no Ly emission to have metallicities comparable to z ∼ 2 galaxies and therefore may represent an evolved subpopulation of galaxies. We find a correlation between metallicity and dust in good agreement with local galaxies and an inverse trend between metallicity and star-formation rate consistent with observations at z ∼ 2. The relation between stellar mass and metallicity (MZ relation) is similar to , but there are indications of it being slightly shallower, in particular for the young, Ly -emitting galaxies. We show that, within a "bathtub" approach, a shallower MZ relation is expected in the case of a fast (exponential) build-up of stellar mass with an e-folding time of 100-200 Myr. Because of this fast evolution, the process of dust production and metal enrichment as a function of mass could be more stochastic in the first billion years of galaxy formation compared to later times.
We report the discovery of three low-mass black hole (BH) candidates residing in the centers of low-mass galaxies at z < 0.3 in the Chandra Deep Field-South Survey. These BHs are initially identified ...as candidate active galactic nuclei based on their X-ray emission in deep Chandra observations. Multi-wavelength observations are used to strengthen our claim that such emission is powered by an accreting supermassive BH. While the X-ray luminosities are low at L sub(X) ~ 10 super(40) erg s super(-1) (and variable in one case), we argue that they are unlikely to be attributed to star formation based on H alpha or UV fluxes. Optical spectroscopy from Keck and the VLT allows us to (1) measure accurate redshifts, (2) confirm their low stellar host mass, (3) investigate the source(s) of photo-ionization, and (4) estimate extinction. With stellar masses of Mlow * < 3 x 10 super(9) M sub(middot in circle) determined from Hubble Space Telescope/Advanced Camera for Surveys imaging, the host galaxies are among the lowest mass systems known to host actively accreting BHs. We estimate BH masses M sub(BH) ~ 2 x 10 super(5) M sub(middot in circle) based on scaling relations between BH mass and host properties for more luminous systems. In one case, a broad component of the H alpha emission-line profile is detected, thus providing a virial mass estimate. BHs in such low-mass galaxies are of considerable interest as the low-redshift analogs to the seeds of the most massive BHs at high redshift which have remained largely elusive to date. Our study highlights the power of deep X-ray surveys to uncover such low-mass systems.
We present the high-redshift (3 phot < 3 but with a broad photometric redshift probability distribution, such that z phot + 1 Delta *s > 3. Eighty-one sources are selected in the 0.5-2 keV band, ...fourteen are selected in the 2-10 keV and six in the 0.5-10 keV bands. We sample the high-luminosity (log L (2-10 keV) > 44.15 erg s--1) space density up to z ~ 5 and a fainter luminosity range (43.5 erg s--1 < log L (2-10 keV) < 44.15 erg s--1) than previous studies, up to z = 3.5. We weighted the contribution to the number counts and the space density of the sources with photometric redshift by using their probability of being at z > 3. We find that the space density of high-luminosity AGNs declines exponentially at all the redshifts, confirming the trend observed for optically selected quasars. At lower luminosity, the measured space density is not conclusive, and a larger sample of faint sources is needed. Comparisons with optical luminosity functions and black hole formation models are presented together with prospects for future surveys.
Hayabusa‐returned samples offer a unique perspective for understanding the link between asteroids and cosmomaterials available in the laboratory, and provide insights on the early stages of surface ...space weathering. This study characterizes the mineralogy and the extent of space weathering of the three Itokawa particles RA‐QD02‐0163, RA‐QD02‐0174, and RA‐QD02‐0213 provided by JAXA to our consortium. We report here a series of results based on nondestructive analyses through visible‐near‐infrared reflectance and Raman spectroscopy. Results were obtained on the raw particles, both in their original containers and deposited on diamond windows. Identification of the minerals, characterization of their elemental compositions, and measurements of their relative abundances were led through Raman spectroscopy in punctual and automatic mode. Reflectance spectra in the visible and near‐IR wavelengths constrain the mineralogy of the grains and allow direct comparison with the surface of Itokawa. The spectra reflect the extent of space weathering experienced by the three particles. Particle RA‐QD02‐0163 consists of a heterogeneous mixture of minerals: olivine (Fo76) dominates an assemblage with both Ca‐rich (En50, Wo50) and Ca‐poor (En85) pyroxenes. The elemental compositions of the silicates are consistent with those previously reported for distinct Hayabusa particles. Particles RA‐QD‐0174 and RA‐QD02‐0213 are solely composed of olivine, whose chemical composition is similar to that observed in RA‐QD02‐0163. It has been previously shown that the S‐type asteroid 25143 Itokawa is a breccia of poorly equilibrated LL4 and highly equilibrated LL5 and LL6 materials. The three particles studied here can be related to the least metamorphosed lithology (LL4) based on the high forsterite content of the olivine. Neither carbonaceous matter nor hydrated minerals were detected through Raman on the three allocated particles. The NIR‐VIS reflectance (incidence = 45°, light collection at e = 0°) spectra of the three particles, in particular the 1 μm band, are consistent with the presence of both olivine and pyroxene detected via Raman. The spectra of particles RA‐QD02‐0163 and RA‐QD02‐0213 are also fully compatible with the ground‐based observations of asteroid (25143) Itokawa in terms of both spectral features and slope. By contrast, particle RA‐QD02‐0174 has a similar 1 μm band depth but higher (redder) spectral slope than the surface of Itokawa. This probably reveals a variable extent of space weathering among the regolith particles. RA‐QD02‐0174 may contain a higher amount of nanophase metallic iron and nanophase FeS. Such phases are products by space weathering induced by solar wind, previously detected on other Itokawa particles.
We present observations and analysis of the broad-band afterglow of Swift GRB 071025. Using optical and infrared (RIYJHK) photometry, we derive a photometric redshift of 4.4 < z < 5.2; at this ...redshift our simultaneous multicolour observations begin at ∼30 s after the gamma-ray burst trigger in the host frame, during the initial rising phase of the afterglow. We associate the light-curve peak at ∼580 s in the observer frame with the formation of the forward shock, giving an estimate of the initial Lorentz factor Γ0∼ 200. The red spectral energy distribution (even in regions not affected by the Lyman α break) provides secure evidence of a large dust column. However, the inferred extinction curve shows a prominent flat component between 2000 and 3000 Å in the rest frame, inconsistent with any locally observed template but well fitted by models of dust formed by supernovae. Time-dependent fits to the extinction profile reveal no evidence of dust destruction and limit the decrease in the extinction column to ΔA3000 < 0.54 mag after t= 50 s in the rest frame. Together with studies of high-z quasars, our observations suggest a transition in dust properties in the early Universe, possibly associated with a transition between supernova-dominated and asymptotic giant branch-dominated modes of dust production.
Good outcomes have been reported regarding the use of cochlear implants for mumps deafness. The mumps virus induces meningitis and/or encephalitis, which can cause central nervous system damage ...resulting in retrolabyrinthine hearing loss, for which a cochlear implant would be less effective.
We installed a cochlear implant in two patients with bilateral mumps deafness; one achieved a good result with the cochlear implant, but the other did not. We discuss two possible reasons for the different outcomes. Case 1 was a three-year-old girl with bilateral parotid swelling, vomiting and walking disorder. One year after cochlear implant insertion, speech perception did not develop despite of good pure tone thresholds. Case 2 was an eight-year-old girl with bilateral parotid swelling. A cochlear implant enabled her to improve hearing perception.
Although cochlear implants have been reported to be helpful for mumps deafness, cases that involve central nervous system damage may not achieve good results.
We searched for quasars that are ~3 mag fainter than the SDSS quasars in the redshift range 3.7 z 4.7 in the COSMOS field to constrain the faint end of the quasar luminosity function (QLF). Using ...optical photometric data, we selected 31 quasar candidates with 22 < i' < 24 at z ~ 4. We obtained optical spectra for most of these candidates using FOCAS on the Subaru telescope and identified eight low-luminosity quasars at z ~ 4. In order to derive the QLF based on our spectroscopic follow-up campaign, we estimated the photometric completeness of our quasar survey through detailed Monte Carlo simulations. Our QLF at z ~ 4 has a much shallower faint-end slope ( Delta *b = --1.67+0.11 --0.17) than that obtained by other recent surveys in the same redshift. Our result is consistent with the scenario of downsizing evolution of active galactic nuclei inferred by recent optical and X-ray quasar surveys at lower redshifts.
We report on the stellar content of the COSMOS two degree field, as derived from a rigorous star-galaxy separation approach developed for using stellar sources to define the point-spread function ...variation map used in a study of weak galaxy lensing. The catalog obtained in one filter from the ACS (Advanced Camera for Surveys on the Hubble Space Telescope) is cross-identified with ground-based multiwavelength catalogs obtained using the Suprime-Cam instrument on the Subaru Telescope, which makes possible detailed spectral energy distribution (SED) fitting in order to separate stars from QSOs and compact galaxies. The classification is reliable to magnitude F814W = 24, and the sample is complete even fainter. We construct a color-magnitude diagram and color histograms and compare them with predictions of a standard model of population synthesis at (l, b) = (236.816 degree . +42.12 degree ). We find features corresponding to the halo subdwarf main-sequence turnoff, the thick disk, and the thin disk. We propose improvements to the standard model that give a better fit: this data set provides constraints on the thick disk and spheroid density laws and on the initial mass function at low mass, although complementary lines of sight would help in lifting the degeneracy between model parameters as well as mitigating any variations in the stellar populations. The depth of this survey makes it possible to explore the spheroid up to distances of similar to 80 kpc; we find no evidence of a sharp spheroid edge out to this distance, which corresponds to a galactocentric radius of 83 kpc. We identify a blue population of white dwarfs with counts that agree with model predictions. We find a hint for a possible slight stellar overdensity at about 22-34 kpc, but the data are not strong enough at present to claim detection of a stream feature in the halo.
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