ABSTRACT Using moderate-resolution optical spectra from 58 background Lyman-break galaxies and quasars at within a 11 5 × 13 5 area of the COSMOS field ( projected area density or mean transverse ...separation), we reconstruct a 3D tomographic map of the foreground Ly forest absorption at 2.2 < z < 2.5 with an effective smoothing scale of comoving. Comparing with 61 coeval galaxies with spectroscopic redshifts in the same volume, we find that the galaxy positions are clearly biased toward regions with enhanced intergalactic medium (IGM) absorption in the tomographic map. We find an extended IGM overdensity with deep absorption troughs at z = 2.45 associated with a recently discovered galaxy protocluster at the same redshift. Based on simulations matched to our data, we estimate the enclosed dark matter mass within this IGM overdensity to be , and argue based on this mass and absorption strength that it will form at least one z ∼ 0 galaxy cluster with , although its elongated nature suggests that it will likely collapse into two separate clusters. We also point out a compact overdensity of six MOSDEF galaxies at z = 2.30 within a radius and Δz ∼ 0.006, which does not appear to have a large associated IGM overdensity. These results demonstrate the potential of Ly forest tomography on larger volumes to study galaxy properties as a function of environment, as well as revealing the large-scale IGM overdensities associated with protoclusters or other features of large-scale structure.
We present the first observations of foreground Ly alpha forest absorption fromhigh-redshift galaxies, targeting 24 star-forming galaxies (SFGs) with z similar to 2.3-2.8 within a 5' x 14' region of ...the COSMOS field. The transverse sightline separation is similar to 2h(-1) Mpc comoving, allowing us to create a tomographic reconstruction of the three-dimensional (3D) Lya forest absorption field over the redshift range 2.20 \textless= z \textless= 2.45. The resulting map covers 6h(-1) Mpc x 14h(-1) Mpc in the transverse plane and 230h(-1) Mpc along the line of sight with a spatial resolution of approximate to 3.5h(-1) Mpc, and is the firsthigh-fidelity map of a large-scale structure on similar to Mpc scales at z \textgreater 2. Our map reveals significant structures with greater than or similar to 10h(-1) Mpc extent, including several spanning the entire transverse breadth, providing qualitative evidence for the filamentary structures predicted to exist in thehigh-redshift cosmic web. Simulated reconstructions with the same sightline sampling, spectral resolution, and signal-to-noise ratio recover the salient structures present in the underlying 3D absorption fields. Using data from other surveys, we identified 18 galaxies with known redshifts coeval with our map volume, enabling a direct comparison with our tomographic map. This shows that galaxies preferentially occupyhigh-density regions, in qualitative agreement with the same comparison applied to simulations. Our results establish the feasibility of the CLAMATO survey, which aims to obtain Ly alpha forest spectra for similar to 1000 SFGs over similar to 1deg(2) of the COSMOS field, in order to map out the intergalactic medium large-scale structure at \textless z \textgreater similar to 2.3 over a large volume (100h(-1) Mpc)(3).
We analyze the spectra, spatial distributions, and kinematics of H{alpha}, N II, and S II emission in a sample of 38, z {approx} 2.2 UV/optically selected star-forming galaxies (SFGs) from the SINS ...and zC-SINF surveys, 34 of which were observed in the adaptive optics mode of SINFONI and 30 of those contain data presented for the first time here. This is supplemented by kinematic data from 43 z {approx} 1-2.5 galaxies from the literature. None of these 81 galaxies is an obvious major merger. We find that the kinematic classification of high-z SFGs as ''dispersion dominated'' or ''rotation dominated'' correlates most strongly with their intrinsic sizes. Smaller galaxies are more likely ''dispersion-dominated'' for two main reasons: (1) the rotation velocity scales linearly with galaxy size but intrinsic velocity dispersion does not depend on size or may even increase in smaller galaxies, and as such, their ratio is systematically lower for smaller galaxies, and (2) beam smearing strongly decreases large-scale velocity gradients and increases observed dispersion much more for galaxies with sizes at or below the resolution. Dispersion-dominated SFGs may thus have intrinsic properties similar to ''rotation-dominated'' SFGs, but are primarily more compact, lower mass, less metal enriched, and may have higher gas fractions, plausibly because they represent an earlier evolutionary state.
We discuss the deep galaxy counts from the Hubble Deep Field (HDF) imaging survey. At faint magnitudes, the slope of the differential number–magnitude relation is flatter than 0.2 in all four HDF ...bandpasses. In the ultraviolet, a fluctuation analysis shows that the flattening observed below U300 ≈ 26 mag is not caused by incompleteness and is more pronounced than in the other bands, consistent with the idea that a redshift limit has been reached in the galaxy distribution. A reddening trend of ≈ 0.5 mag is observed at faint fluxes in the colour–magnitude diagram, (U300 − V606)eff versus V606. We interpret these results as the effect of intergalactic attenuation on distant galaxies. At flux levels (in the AB system) of AB ≈ 27 mag and in agreement with the fluctuation analysis and the colour–magnitude relation, about 7 per cent of the sources in U300, 30 per cent in B450 and 35 per cent in V606 are Lyman‐break ‘dropouts’, i.e. candidate star‐forming galaxies at z > 2. By integrating the number counts to the limits of the HDF survey we find that the mean surface brightness of the extragalactic sky is dominated by galaxies that are relatively bright and are known to have 〈z〉 ∼ 0.6. To AB ≈ 29 mag, the integrated light from resolved galaxies in the l‐band is 2.1+0.4−0.3 × 10−20 erg cm−2 s−1 Hz−1 s−1, and its spectrum is well described by a broken power law (lν ∝ λ2 from 2000 to 8000 Å and lν ∝ λ from 8000 to 22 000 Å). We discuss the predictions for the counts, colours and luminosity densities from standard low‐q0 pure‐luminosity‐evolution models without dust obscuration, and find that they are unable to reproduce all the observed properties of faint field galaxies.
We discuss the deep galaxy counts from the Hubble Deep Field (HDF) imaging survey. At faint magnitudes, the slope of the differential number-magnitude relation is flatter than 0.2 in all four HDF ...bandpasses. In the ultraviolet, a fluctuation analysis shows that the flattening observed below U300 ≈ 26 mag is not caused by incompleteness and is more pronounced than in the other bands, consistent with the idea that a redshift limit has been reached in the galaxy distribution. A reddening trend of ≈ 0.5 mag is observed at faint fluxes in the colour-magnitude diagram, (U300 - V606)eff versus V606. We interpret these results as the effect of intergalactic attenuation on distant galaxies. At flux levels (in the AB system) of AB ≈ 27 mag and in agreement with the fluctuation analysis and the colour-magnitude relation, about 7 per cent of the sources in U300, 30 per cent in B450 and 35 per cent in V606 are Lyman-break ‘dropouts’, i.e. candidate star-forming galaxies at z > 2. By integrating the number counts to the limits of the HDF survey we find that the mean surface brightness of the extragalactic sky is dominated by galaxies that are relatively bright and are known to have ⟨z⟩ ∼ 0.6. To AB ≈ 29 mag, the integrated light from resolved galaxies in the l-band is 2.1+0.4+0.3, and its spectrum is well described by a broken power law (lν ∝ λ2 from 2000 to 8000 Å and lν ∝ λ from 8000 to 22 000 Å). We discuss the predictions for the counts, colours and luminosity densities from standard low-q0 pure-luminosity-evolution models without dust obscuration, and find that they are unable to reproduce all the observed properties of faint field galaxies.
THE zCOSMOS 10k-BRIGHT SPECTROSCOPIC SAMPLE Lilly, Simon J.; Maier, Christian; Carollo, Marcella ...
The Astrophysical journal. Supplement series,
10/2009, Letnik:
184, Številka:
2
Journal Article
Recenzirano
We present spectroscopic redshifts of a large sample of galaxies with I {sub AB} < 22.5 in the COSMOS field, measured from spectra of 10,644 objects that have been obtained in the first two years of ...observations in the zCOSMOS-bright redshift survey. These include a statistically complete subset of 10,109 objects. The average accuracy of individual redshifts is 110 km s{sup -1}, independent of redshift. The reliability of individual redshifts is described by a Confidence Class that has been empirically calibrated through repeat spectroscopic observations of over 600 galaxies. There is very good agreement between spectroscopic and photometric redshifts for the most secure Confidence Classes. For the less secure Confidence Classes, there is a good correspondence between the fraction of objects with a consistent photometric redshift and the spectroscopic repeatability, suggesting that the photometric redshifts can be used to indicate which of the less secure spectroscopic redshifts are likely right and which are probably wrong, and to give an indication of the nature of objects for which we failed to determine a redshift. Using this approach, we can construct a spectroscopic sample that is 99% reliable and which is 88% complete in the sample as a whole, and 95% complete in the redshift range 0.5 < z < 0.8. The luminosity and mass completeness levels of the zCOSMOS-bright sample of galaxies is also discussed.
We present a photometric and spectroscopic study of galaxies at 0.5
$\lt$
${z}$
$\lt$
1 as a function of the environment based on data from the zCOSMOS survey. There is a fair amount of evidence that ...galaxy properties depend on the mass of groups and clusters, in the sense that quiescent galaxies prefer more massive systems. We base our analysis on a mass-selected environment using X-ray groups of galaxies, and define the group membership using a large number of spectroscopic redshifts from zCOSMOS. We show that the fraction of red galaxies is higher in groups than in the field at all redshifts probed in our study. Interestingly, the fraction of O II emitters on the red sequence increases at higher redshifts in groups, while the fraction does not strongly evolve in the field. This is due to increased dusty star-formation activities and/or increased activities of active galactic nuclei (AGNs) in high-redshift groups. We investigate these possibilities using the 30-band photometry and X-ray data. We find that the stellar population of the red O II emitters in groups is old, and there is no clear hint of dusty star-formation activities in those galaxies. The observed increase of red O II emitters in groups is likely due to increased AGN activities. However, since our overall statistics are poor, any firm conclusions need to be drawn from a larger statistical sample of
${z}$
$\sim$
1 groups.
In the last decades, an increasing scientific interest has been growing in the elusive population of "dark" (i.e. lacking an optical/NIR counterpart) Dusty Star-Forming Galaxies (DSFGs). Although ...extremely promising for their likely contribution to the cosmic Star Formation Rate Density and for their possible role in the evolution of the first massive and passive galaxies around \(z\sim3\), the difficulty in selecting statistically significant samples of dark DSFGs is limiting their scientific potentialities. This work presents the first panchromatic study of a sample of 263 Radio-Selected NIRdark galaxies discovered in the COSMOS field following the procedure by Talia+21. These sources are selected as radio-bright galaxies (S(3GHz)>12.65 uJy) with no counterpart in the NIR-selected COSMOS2020 catalog (Ks > 25.5 mag). For these sources, we build a new photometric catalog including accurate photometry from the optical to the radio obtained with a new deblending pipeline (PhoEBO: Photometry Extractor for Blended Objects). We employ this catalog to estimate the photo-zs and the physical properties of the galaxies through an SED-fitting procedure performed with two different codes (Magphys and Cigale). Finally, we estimate the AGN contamination in our sample by performing a series of complementary tests. The high values of the median extinction (Av ~ 4) and star formation rate (SFR ~ 500 Msun/yr) confirm the likely DSFG nature of the RS-NIRdark galaxies. The median photo-z (z~3) and the presence of a significant tail of high-z candidates (z>4.5) suggest that these sources are important contributors to the cosmic SFRD and the evolutionary path of galaxies at high redshifts.
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