Carlos G. Bornancini

The VLT LBG Redshift Survey– II. Interactions between galaxies and the IGM at z∼ 3★

We have measured redshifts for 243 z 3 quasars in nine VLT VIMOS LBG redshift survey areas, each of which is centred on a known bright quasar. Using spectra of these quasars, we measure the cross-correlation between neutral hydrogen gas causing the Ly forest and 1020 Lyman-break galaxies at z 3. We nd an increase in neutral hydrogen absorption within 5 h 1 Mpc of a galaxy in agreement with the results of Adelberger et al. (2003, 2005). The Ly -LBG cross-correlation can be described by a power-law on scales larger than 3h 1 Mpc. When galaxy velocity dispersions are taken into account our results at smaller scales (< 2 h 1 Mpc) are also in good agreement with the results of Adelberger et al. (2005). There is little immediate indication of a region with a transmission spike above the mean IGM value which might indicate the presence of star-formation feedback. To measure the galaxy velocity dispersions, which include both intrinsic LBG velocity dispersion and redshift errors, we have used the LBG-LBG redshift space distortion measurements of Bielby et al. (2010). We nd that the redshift-space transmission spike implied in the results of Adelberger et al. (2003) is too narrow to be physical in the presence of the likely LBG velocity dispersion and is likely to be a statistical uke. Nevertheless, neither our nor previous data can rule out the presence of a narrow, real-space transmission spike, given the evidence of the increased Ly absorption surrounding LBGs which can mask the spike’s presence when convolved with a realistic LBG velocity dispersion. Finally, we identify 176 Civ systems in the quasar spectra and nd an LBG-C iv correlation strength on scales of 10 h 1 Mpc consistent with the relation measured at Mpc scales.

Imaging and spectroscopy of ultrasteep spectrum radio sources

We present a sample of 40 Ultra Steep Spectrum (USS, � � 1.3, S� / � � ) radio sources selected from the Westerbork in the Southern Hemisphere (WISH) catalog. The USS sources have been imaged in K–band at the Cerro Tololo Inter-American Observatory (CTIO) and with the Very Large Telescope at Cerro Paranal. We also present VLT, Keck and Willian Herschel Telescope(WHT) optical spectroscopy of 14 targets selection from 4 different USS samples. For 12 sources, we have been able to determine the redshifts, including 4 new radio galaxies at z > 3. We find that most of our USS sources have predominantly small (<6 ′′ ) radio sizes and faint magnitudes (K �18). The mean K band counterpart magnitude is K=18.6. The expected redshift distribution estimated using the Hubble K z diagram has a mean of zexp�2.13, which is higher than the predicted redshift obtained for the SUMSS–NVSS sample and the expected redshift obtained in the 6C ∗∗ survey. The compact USS sample analyzed here may contain a higher fraction of galaxies which are high redshift and/or are heavily obscured by dust. Using the 74, 352 and 1400MHz flux densities of a sub-sample, we construct a radio colour-colour diagram. We find that all but one of our USS sources have a strong tendency to flatten below 352MHz. We also find that the highest redshift source from this paper (at z=3.84) does not show evidence for spectral flattening down to 151MHz. This suggests that very low frequency selected USS samples will likely be more efficient to find high redshift galaxies.

The galaxy density environment of gamma-ray burst host galaxies

We analyze cross-correlation functions between Gamma-Ray Burst (GRB) hosts and surrounding galaxies. We have used data obtained with the Very Large Telescope at Cerro Paranal (Chile), as well as public Hubble Space Telescope data. Our results indicate that Gamma-Ray Burst host galaxies do not reside in high galaxy density environments. Moreover, the host-galaxy cross-correlations show a relatively low amplitude. Our results are in agreement with the cross-correlation function between star-forming galaxies and surrounding objects in the HDF-N.

Clustering and properties of K-band companion galaxies around ultrasteep spectrum radio sources★

We have analysed galaxy properties in the environment of a sample of 70 ultrasteep spectrum (USS) radio sources selected from the Sydney University Molonglo Sky Survey and the National Radio Astronomy Observatories (NRAO) Very Large Array Sky Survey catalogues, using near-infrared data complete down to K s = 20. We have quantified galaxy excess around USS targets using an Abell-type measurement N 0.5 . We find that most of the USS fields studied are compatible with being Abell class 0 richness clusters. A statistical analysis of the distribution of companion galaxies around USS radio sources shows a pronounced tendency for such objects to be found in the direction defined by the radio axis, suggesting that they may be related to the presence of the radio sources. We have also measured the central concentration of light of the USS sample and compared these to the values obtained for field galaxies and galaxies selected using other methods. By using Spearman statistics to disentangle richnesses and concentration indices dependences, we detect a weak, but significant, positive correlation. We find that at z > 2 USS radio sources are more concentrated than field galaxies at similar redshifts, indicating that these objects trace the most massive systems at high redshift.

The VLT LBG redshift survey – VI. Mapping H i in the proximity of z ∼ 3 LBGs with X-Shooter

We present an analysis of the spatial distribution and dynamics of neutral hydrogen gas around galaxies using new X-Shooter observations of z ∼ 2.5–4 quasars. Adding the X-Shooter data to our existing data set of high-resolution quasar spectroscopy, we use a total sample of 29 quasars alongside ∼1700 Lyman Break Galaxies (LBGs) in the redshift range 2 ≲ z ≲ 3.5. We measure the Lyα forest auto-correlation function, finding a clustering length of s0 = 0.081 ± 0.006 h−1 Mpc, and the cross-correlation function with LBGs, finding a cross-clustering length of s0 = 0.27 ± 0.14 h−1 Mpc and power-law slope γ = 1.1 ± 0.2. Our results highlight the weakly clustered nature of neutral hydrogren systems in the Lyα forest. Building on this, we make a first analysis of the dependence of the clustering on absorber strength, finding a clear preference for stronger Lyα forest absorption features to be more strongly clustered around the galaxy population, suggesting that they trace on average higher mass haloes. Using the projected and 2-D cross-correlation functions, we constrain the dynamics of Lyα forest clouds around z ∼ 3 galaxies. We find a significant detection of large-scale infall of neutral hydrogen, with a constraint on the Lyα forest infall parameter of βF = 1.02 ± 0.22.

Spatial clustering of Ultra Steep Spectrum sources and galaxies

We present measurements of the clustering properties of galaxies in the field of redshift range 0.5 ≤ z ≤ 1.5 Ultra Steep Spectrum radio sources selected from the Sydney University Molonglo Sky Survey and the National Radio Astronomy Observatories Very Large Array Sky Survey. Galaxies in these USS fields were identified in deep near-infrared observations, complete down to K s = 20, using the IRIS2 instrument at the Anglo-Australian Telescope. We used the redshift distribution of K s < 20 galaxies taken from Cimatti et al. (2002) to constrain the correlation length r 0 . We find a strong correlation signal of galaxies with K s < 20 around our USS sample. A comoving correlation length r 0 = 14.0 ± 2.8 h -1 Mpc and y = 1.98 ± 0.15 are derived in a flat cosmological model universe. We compare our findings with those obtained in a cosmological N-body simulation populated with GALFORM semi-analytic galaxies. We find that clusters of galaxies with masses in the range M = 10 13.4-14.2 2 h -1 M ⊙ have a cluster-galaxy cross-correlation amplitude comparable to those found between the USS hosts and galaxies. These results suggest that distant radio galaxies are excellent tracers of galaxy overdensities and pinpoint the progenitors of present day rich clusters of galaxies.

The distant red galaxy neighbour population of 1 ≲z≲ 2 QSOs and optically obscured sources*

We study the distant red galaxy (DRG; J - K s > 2.3) neighbour population of quasi-stellar objects (QSOs) selected from the Sloan Digital Sky Survey (SDSS) in the redshift range 1 ≤ z ≤ 2. We perform a similar analysis for optically obscured active galactic nuclei (AGNs; i.e. with a limiting magnitude I > 24) detected in the mid-infrared (24 μm) with the Spitzer Space Telescope and a mean redshift z ∼2.2 in the Flamingos Extragalactic Survey (FLAMEX). Both QSOs and obscured AGN target samples cover 4.7 deg 2 in the same region of the sky. We find a significant difference in the environment of these two target samples. Neighbouring galaxies close to QSOs tend to be bluer than galaxies in optically obscured source environments. We also present results on the cross-correlation function of DRGs around QSOs and optically faint mid-infrared sources. The corresponding correlation length obtained for the QSO sample targets is r 0 = 5.4 ± 1.6 Mpc h -1 and a slope of y = 1.94 ±0.10. For the optically obscured galaxy sample, we find r 0 = 8.9 ±1.4 Mpc h -1 and a slope of y = 2.27 ± 0.20. These results indicate that optically faint obscured sources are located in denser environment of evolved red galaxies compared to OSOs.

Active galactic nuclei at high redshifts: properties and environment of Type 1 and 2 AGNs

Fil: Bornancini, Carlos Guillermo. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Cordoba. Instituto de Astronomia Teorica y Experimental. Universidad Nacional de Cordoba. Observatorio Astronomico de Cordoba. Instituto de Astronomia Teorica y Experimental; Argentina

Environment of 1 ≤ z ≤ 2 MIR selected obscured and unobscured AGNs in the Extended Chandra Deep Field South

Context. In unified models, different types of active galaxy nuclei (AGN) correspond to a single class of objects, where their observed differences are solely due to the different orientations of the obscuring material around the central inner regions. Recent studies also show that this obscuring material can even extend at galactic scales due to debris from galaxy interactions and/or mergers. In standard unified models the different AGN types are expected to show similar galaxy environments. Aims. We aim to investigate properties and environment of obscured and unobscured AGNs selected from mid-infrared (MIR) bands from the Multiwavelength Survey by Yale-Chile (MUSYC), in order to test the unified model and evolutionary scenarios. Methods. The sample of AGNs was selected from images obtained with the Infrared Array Camera (IRAC) mounted on the Spitzer Space Telescope, based on their MIR colors centered at wavelengths [3.6], [4.5], [5.8] and [8.0] microns. We selected two samples of AGNs with redshifts in the range 1 ≤ z ≤ 2 and rest-frame absolute magnitudes M v ≤ −21: obscured and unobscured AGNs by means of a simple optical-MIR color cut criterion ( R − [4.5] = 3.05.) Results. We find that obscured AGNs are intrinsically optically faint in the R band, suggesting that luminous IR-selected AGNs have a significant dust extinction. From a cross-correlation with several X-ray surveys, we find that the majority of the AGNs in our sample have X-ray luminosities similar to those found in Seyfert-like galaxies. We study the properties of galaxies surrounding these two samples. Neighbouring galaxies located close to (~200 kpc) obscured AGNs tend to have redder colors, compared to the local environment of unobscured AGNs. Results obtained from a KS test show that the two color distributions are different at ~95% confidence level. We find that obscured AGNs are located in denser local galaxy environments compared to the unobscured AGN sample. Conclusions. Our results suggest that AGN obscuration can occur at galactic scales, possibly due to galaxy interactions or mergers, and that the simple unified model based solely on the local torus orientation may not be sufficient to explain all the observations.