Showing papers by "Narciso Benítez published in 2006"

Galaxies in the Hubble Ultra Deep Field. I. Detection, Multiband Photometry, Photometric Redshifts, and Morphology

Abstract: We present aperture-matched point-spread function (PSF)-corrected BVi'z'JH photometry and Bayesian photometric redshifts (BPZ) for objects detected in the Hubble Ultra Deep Field (UDF), 8042 of which are detected at the 10 σ level (e.g., i' < 29.01 or z' < 28.43). Most of our objects are defined identically to those in the public STScI catalogs, enabling a straightforward object-by-object comparison. We have combined detections from i', z', J + H, and B + V + i' + z' images into a single comprehensive segmentation map. Using a new program called SExSeg, we are able to force this segmentation map into SExtractor for photometric analysis. The resulting photometry is corrected for the wider NIC3 PSFs using our ColorPro software. We also correct for the ACS z'-band PSF halo. Offsets are applied to our NIC3 magnitudes, which are found to be too faint relative to the ACS fluxes. Based on BPZ spectral energy distribution (SED) fits to objects of known spectroscopic redshift, we derived corrections of -0.30 ± 0.03 mag in J and -0.18 ± 0.04 mag in H. Our offsets appear to be supported by a recent recalibration of the UDF NIC3 images combined with nonlinearity measured in NICMOS itself. The UDF reveals a large population of faint blue galaxies (presumably young starbursts), bluer than those observed in the original Hubble Deep Fields. To accommodate these galaxies, we have added two new starburst templates to the SED library used in previous BPZ papers. The resulting photometric redshifts are accurate to within 0.04(1 + zspec) out to z < 6. Our BPZ results include a full redshift probability distribution for each galaxy. By adding these distributions, we obtain the redshift probability histogram for galaxies in the UDF. Median redshifts are also provided for different magnitude-limited samples. Finally, we measure galaxy morphology, including Sersic index and asymmetry. Simulations allow us to quantify the reliability of our morphological results. Our full catalog, along with our software packages SExSeg and ColorPro, is available from our ACS Web site.

Hubble Space Telescope ACS Multiband Coronagraphic Imaging of the Debris Disk around β Pictoris

Abstract: We present F435W (B), F606W (broad V), and F814W (broad I) coronagraphic images of the debris disk around β Pictoris obtained with the Hubble Space Telescope's Advanced Camera for Surveys. These images provide the most photometrically accurate and morphologically detailed views of the disk between 30 and 300 AU from the star ever recorded in scattered light. We confirm that the previously reported warp in the inner disk is a distinct secondary disk inclined by ~5° from the main disk. The projected spine of the secondary disk coincides with the isophotal inflections, or "butterfly asymmetry," previously seen at large distances from the star. We also confirm that the opposing extensions of the main disk have different position angles, but we find that this "wing-tilt asymmetry" is centered on the star rather than offset from it, as previously reported. The main disk's northeast extension is linear from 80 to 250 AU, but the southwest extension is distinctly bowed with an amplitude of ~1 AU over the same region. Both extensions of the secondary disk appear linear, but not collinear, from 80 to 150 AU. Within ~120 AU of the star, the main disk is ~50% thinner than previously reported. The surface brightness profiles along the spine of the main disk are fitted with four distinct radial power laws between 40 and 250 AU, while those of the secondary disk between 80 and 150 AU are fitted with single power laws. These discrepancies suggest that the two disks have different grain compositions or size distributions. The F606W/F435W and F814W/F435W flux ratios of the composite disk are nonuniform and asymmetric about both projected axes of the disk. The disk's northwest region appears 20%-30% redder than its southeast region, which is inconsistent with the notion that forward scattering from the nearer northwest side of the disk should diminish with increasing wavelength. Within ~120 AU, the m_(F435W) - m_(F606W) and m_(F435W) - m_(F814W) colors along the spine of the main disk are ~10% and ~20% redder, respectively, than those of β Pic. These colors increasingly redden beyond ~120 AU, becoming 25% and 40% redder, respectively, than the star at 250 AU. These measurements overrule previous determinations that the disk is composed of neutrally scattering grains. The change in color gradient at ~120 AU nearly coincides with the prominent inflection in the surface brightness profile at ~115 AU and the expected water-ice sublimation boundary. We compare the observed red colors within ~120 AU with the simulated colors of nonicy grains having a radial number density ∝r^(-3) and different compositions, porosities, and minimum grain sizes. The observed colors are consistent with those of compact or moderately porous grains of astronomical silicate and/or graphite with sizes ≳ 0.15-0.20 μm, but the colors are inconsistent with the blue colors expected from grains with porosities ≳ 90%. The increasingly red colors beyond the ice sublimation zone may indicate the condensation of icy mantles on the refractory grains, or they may reflect an increasing minimum grain size caused by the cessation of cometary activity.

HST/ACS Multiband Coronagraphic Imaging of the Debris Disk around Beta Pictoris

Abstract: (Abridged.) We present F435W (B), F606W (Broad V), and F814W (Broad I) coronagraphic images of the debris disk around Beta Pictoris obtained with HST's Advanced Camera for Surveys. We confirm that the previously reported warp in the inner disk is a distinct secondary disk inclined by ~5 deg from the main disk. The main disk's northeast extension is linear from 80 to 250 AU, but the southwest extension is distinctly bowed with an amplitude of ~1 AU over the same region. Both extensions of the secondary disk appear linear, but not collinear, from 80 to 150 AU. Within ~120 AU of the star, the main disk is ~50% thinner than previously reported. The surface-brightness profiles along the spine of the main disk are fitted with four distinct radial power laws between 40 and 250 AU, while those of the secondary disk between 80 and 150 AU are fitted with single power laws. These discrepancies suggest that the two disks have different grain compositions or size distributions. The F606W/F435W and F814W/F435W flux ratios of the composite disk are nonuniform and asymmetric about both projected axes of the disk. Within ~120 AU, the m_F435W-m_F606W and m_F435W-m_F814W colors along the spine of the main disk are ~10% and ~20% redder, respectively, than those of Beta Pic. These colors increasingly redden beyond ~120 AU, becoming 25% and 40% redder, respectively, than the star at 250 AU. We compare the observed red colors within ~120 AU with the simulated colors of non-icy grains having a radial number density ~r^-3 and different compositions, porosities, and minimum grain sizes. The observed colors are consistent with those of compact or moderately porous grains of astronomical silicate and/or graphite with sizes >0.15-0.20 um, but the colors are inconsistent with the blue colors expected from grains with porosities >90%.

Lyman break galaxies, Lya emitters and a radio galaxy in a protocluster at z=4.1

Abstract: We present deep HST/ACS observations in g,r,i,z towards the z=4.1 radio galaxy TN J1338-1942 and its overdensity of >30 spectroscopically confirmed Lya emitters (LAEs). We select 66 g-band dropouts to z=27, 6 of which are also a LAE. Although our color-color selection results in a relatively broad redshift range centered on z=4.1, the field of TN J1338-1942 is richer than the average field at the >5 sigma significance, based on a comparison with GOODS. The angular distribution is filamentary with about half of the objects clustered near the radio galaxy, and a small, excess signal (2 sigma) in the projected pair counts at separations of = 0.13") galaxies, and we derive a mean stellar mass of ~10^8-9 Msun based on a stacked K-band image. We determine star formation rates, sizes, morphologies, and color-magnitude relations of the g-dropouts and find no evidence for a difference between galaxies near TN J1338-1942 and in the field. We conclude that environmental trends as observed in clusters at much lower redshift are either not yet present, or are washed out by the relatively broad selection in redshift. The large galaxy overdensity, its corresponding mass overdensity and the sub-clustering at the approximate redshift of TN J1338-1942 suggest the assemblage of a >10^14 Msun structure, confirming that it is possible to find and study cluster progenitors in the linear regime at z>4.

Clustering of Star-forming Galaxies Near a Radio Galaxy at z=5.2

Abstract: We present HST ACS observations of the most distant radio galaxy known, TN J0924-2201 at z = 5.2. This radio galaxy has six spectroscopically confirmed Ly?-emitting companion galaxies and appears to lie within an overdense region. The radio galaxy is marginally resolved in i775 and z850, showing continuum emission aligned with the radio axis, similar to what is observed for lower redshift radio galaxies. Both the half-light radius and the UV star formation rate are comparable to the typical values found for Lyman break galaxies at z ~ 4-5. The Ly? emitters are sub-L* galaxies, with deduced star formation rates of 1-10 M? yr-1. One of the Ly? emitters is only detected in Ly?. Based on the star formation rate of ~3 M? yr-1 calculated from Ly?, the lack of continuum emission could be explained if the galaxy is younger than ~2 Myr and is producing its first stars. Observations in V606i775z850 were used to identify additional Lyman break galaxies associated with this structure. In addition to the radio galaxy, there are 22 V606 break (z ~ 5) galaxies with z850 99%), based on a counts-in-cells analysis applied to the control field. The excess suggests that the V606 break objects are associated with a forming cluster around the radio galaxy.

Evolution of the Color-Magnitude Relation in High-Redshift Clusters: Blue Early-Type Galaxies and Red Pairs in RDCS J0910+5422

Abstract: The color-magnitude relation has been determined for the RDCS J0910+5422 cluster of galaxies at redshift z = 1.106. Cluster members were selected from HST Advanced Camera for Surveys (ACS) images, combined with ground–based near–IR imaging and optical spectroscopy. Postman et al. (2005) morphological classifications were used to identify the early-type galaxies. The observed early–type color–magnitude relation (CMR) in (i775 z850) versus z850 shows an intrinsic scatter in color of 0.060±0.009 mag, within 1 ′ from the cluster X–ray emission center. Both the ellipticals and the S0s show small scatter about the CMR of 0.042 ± 0.010 mag and 0.044± 0.020 mag, respectively. From the scatter about the CMR, a mean luminosity–weighted age t > 3.3 Gyr (zf > 3) is derived for the elliptical galaxies, assuming a simple stellar population modeling (single burst solar metallicity). This is consistent with a previous study of the cluster RDCS1252.9-292 at z=1.24 (Blakeslee et al.). Strikingly, the S0 galaxies in RDCS J0910+5422 are systematically bluer in (i775 z850) by 0.07 ± 0.02 mag, with respect to the ellipticals. The blue S0s are predominantly elongated in shape; the distribution of their ellipticities is inconsistent with a population of axisymmetric disk galaxies viewed at random orientations, suggesting either that they are intrinsically prolate or there is some orientation bias in the S0 classification. The ellipticity distribution as a function of color indicates that the face-on S0s in this particular cluster have likely been classified as elliptical. Thus, if anything, the offset in color between the elliptical and S0 populations may be even more significant. The color offset between S0 and E corresponds to an age difference of � 1 Gyr, for a singleburst solar metallicity model. Alternatively, it could be the result of a different star formation history; a solar metallicity model with an exponential decay in star formation will reproduce the offset for an age of 3.5 Gyr, i.e. the S0s have evolved gradually from star forming progenitors. The color offset could also be reproduced by a factor of �2 difference in metallicity, but the two populations would each need to have very small scatter in metallicity to reproduce the small scatter in color. The early–type population in this cluster appears to be still forming. The blue early-type disk galaxies in RDCS J0910+5422 likely represent the direct progenitors of the more evolved S0s that follow the same red sequence as ellipticals in other clusters. Thirteen red galaxy pairs are observed and the galaxies associated in pairs constitute �40% of the CMR galaxies in this cluster. This finding is consistent with the conclusions of van Dokkum and Tran et al. that most of the early–type galaxies grew from passive red mergers.

GRB 060121: implications of a short-/intermediate-duration γ-ray burst at high redshift

Abstract: Since the discovery of the first short-population γ-ray burst (GRB) afterglows in 2005, the handful of observed events have been found to be embedded in nearby (z 102). A photometric redshift for this event places the progenitor at a most probable redshift of z = 4.6, with a less probable scenario of z = 1.7. In either case, GRB 060121 could be the farthermost short-population GRB detected to date and implies an isotropic-equivalent energy release in gamma rays comparable to that seen in long-population bursts. We discuss the implications of the released energy on the nature of the progenitor. These results suggest that GRB 060121 may belong to a family of energetic short-population events, lying at z > 1 and whose optical afterglows would outshine their host galaxies, unlike the first short GRBs observed in 2005. The possibility of GRB 060121 being an intermediate-duration burst is also discussed.

GRB 060121: Implications of a Short/Intermediate Duration Gamma-Ray Burst at High Redshift

Abstract: Since the discovery of the first short-hard gamma-ray burst afterglows in 2005, the handful of observed events have been found to be embedded in nearby (z 10^2). A photometric redshift for this event places the progenitor at a most probable redshift of z = 4.6, with a less probable scenario of z = 1.7. In either case, GRB 060121 could be the farthermost short-duration GRB detected to date and implies an isotropic-equivalent energy release in gamma-rays comparable to that seen in long-duration bursts. We discuss the implications of the released energy on the nature of the progenitor. These results suggest that GRB 060121 may belong to a family of energetic short-duration events, lying at z > 1 and whose optical afterglows would outshine their host galaxies, unlike the first short-duration GRBs observed in 2005. The possibility of GRB 060121 being an intermediate duration burst is also discussed.

The Morphological Demographics of Galaxies in the Advanced Camera for Surveys Hubble Ultra Deep Parallel Fields

Abstract: We present a morphological analysis of distant field galaxies using the deep Advanced Camera for Surveys images from the public parallel Near-Infrared Camera and Multi-Object Spectrometer observations of the Hubble Ultra Deep Field obtained in the F435W (B435), F606W (V606), F775W (i775), and F850LP (z850) filters. We morphologically segregate galaxies using a combination of visual classification and objective machine-based selection. We use the asymmetry (A) and central concentration (C) parameters to characterize galaxies up to z850,AB < 25 mag. We take advantage of the multicolor data set and estimate redshifts for our sample using the Bayesian photometric redshift, which enables us to investigate the evolution of their morphological demographics with redshift. Using a template fitting model and a maximum likelihood approach, we compute the star formation rate (SFR) for galaxies up to z 1.3 and its contributions from different morphological types. We report that spiral galaxies are the main providers to the total SFR. The E/S0 contribution flattens out at z 1, while the irregular/peculiar (Irr/Pec) galaxy populations continuously rise to match the spiral contribution at z 1.0. We use the i775 - z850 and V606 - i775 color-magnitude diagrams to constrain the galaxies' formation histories and find that E/S0s show both a population of luminous red galaxies in place at z ~ 1.2 and a bluer and fainter population resembling that of Irr/Pec at similar redshifts.

Mass Modeling of Abell 1689 Advanced Camera for Surveys Observations with a Perturbed Navarro-Frenk-White Model

Abstract: The combined resolution and sensitivity of the Advanced Camera for Surveys deep imaging provides the capability of high-accuracy lens modeling of Abell 1689. Originally based on the technique of Broadhurst and coworkers, our software is designed to provide a precise and efficient method of modeling cluster lenses without assumptions relating the large-scale cluster dark matter to the light. Abell 1689 is robustly modeled using a freely varying cluster halo component consisting of an NFW profile, shapelets (Refregier), and a mass sheet, as well as a galaxy component based on the light. Another improvement over previous modeling techniques is the application ofmagnification-correctedimagemagnitudeconstraints.Themasswithinthe � 50 00 Einsteinradiuswasfoundtobe 2:04 þ0:03

Galaxies in the Hubble Ultra Deep Field: I. Detection, Multiband Photometry, Photometric Redshifts, and Morphology

Abstract: We present aperture-matched PSF-corrected BVi'z'JH photometry and Bayesian photometric redshifts (BPZ) for objects detected in the Hubble Ultra Deep Field (UDF), 8,042 of which are detected at the 10-sigma level (e.g., i'<29.01 or z'<28.43). Most of our objects are defined identically to those in the public STScI catalogs, enabling straightforward object-by-object comparison. We have combined detections from i', z', J+H, and B+V+i'+z' images into a single comprehensive segmentation map. Using a new program called SExSeg we are able to force this segmentation map into SExtractor for photometric analysis. The resulting photometry is corrected for the wider NIC3 PSFs using our ColorPro software. We also correct for the ACS z'-band PSF halo. The NIC3 magnitudes are found to be too faint relative to the ACS fluxes. Based on BPZ SED fits to objects of know spectroscopic redshift, we derived corrections of -0.30 +/- 0.03 mag in J and -0.18 +/- 0.04 mag in H. The offsets appear to be supported by a recent recalibration of the UDF NIC3 images combined with non-linearity measured in NICMOS itself. The UDF reveals a large population of faint blue galaxies (presumably young starbursts), bluer than those observed in the original Hubble Deep Fields (HDF). To accommodate these galaxies, we have added two new starburst templates to the SED library used in previous BPZ papers. The resulting photometric redshifts are accurate to within 0.04 * 1+z_spec out to z < 6. Finally, we measure galaxy morphology, including Sersic index and asymmetry. Our full catalog, software packages, and more are available at this http URL (abridged)

Using Weak Lensing Dilution to Improve Measurements of the Luminous and Dark Matter in A1689

Abstract: The E/SO sequence of a cluster defines a boundary redward of which a reliable weak lensing signal can be obtained from background galaxies, uncontaminated by cluster members. For bluer colors, both background and cluster members are present, reducing the distortion signal by the proportion of unlensed cluster members. In deep Subaru and HST/ACS images of A1689 the tangential distortion of galaxies with bluer colors falls rapidly toward the cluster center relative to the lensing signal of the red background. We use this dilution effect to derive the cluster light profile and luminosity function to large radius, with the advantage that no subtraction of far-field background counts is required. The light profile declines smoothly to the limit of the data, r<2Mpc/h, with a constant slope, dlog(L)/dlog(r)=-1.12+-0.06, unlike the lensing mass profile which steepens continuously with radius, so that M/L peaks at an intermediate radius, ~100kpc/h. A flatter behavior is found for the more physically meaningful ratio of dark-matter to stellar-matter, when accounting for the color-mass relation of cluster members. The cluster luminosity function has a flat slope, alpha=-1.05+-0.07, independent of radius and with no faint upturn to M_i'<-12. We establish that the very bluest objects are negligibly contaminated by the cluster V-i'<0.2, because their distortion profile rises towards the center following the red background, but offset higher by ~20%. This larger amplitude is consistent with the greater estimated depth of the faint blue galaxies, z~=2.0 compared to z~=0.85 for the red background, a purely geometric effect related to cosmological parameters. Finally, we improve upon our earlier mass profile by combining both the red and blue background populations, clearly excluding low concentration CDM profiles.

Star formation, morphologies and clustering of galaxies in a radio galaxy protocluster at z=4.1

Abstract: We present deep g475r625i775z850KS observations towards the radio galaxy TN J1338–1942 at z = 4.1. The radio galaxy is a ∼ 6L∗z=4 galaxy. The data allow us to study in detail 12 spectroscopically confirmed companions previously found through their excess Lyα emission by Venemans et al. (2002). We conclude that the Lyα emitters (LAEs) are young (a few ×10 yr), dust-free galaxies based on small sizes, steep UV slopes (β ≈ −2) and blue UV-optical colors with star formation rates (SFRs) of < 14 M⊙ yr . When stacking the KS-band fluxes, the LAEs seem to be less massive (masses of a few ×10 M⊙) than UV-selected Lyman break galaxies (LBGs) while having comparable UV SFRs. We estimate the LAE AGN fraction to be minimal. The field further contains 66 g475-dropouts to z850= 27 (5σ), 6 of which are in the LAE sample. Their SFRs, sizes, morphological parameters, UV slope-magnitude and (i775–KS) vs. KS color-magnitude relations are all similar to those found for LBGs in the ‘field’. We quantify the number density and cosmic variance of z ∼ 4 g475-dropouts extracted from a pixel-by-pixel transformation of the B435V606i775z850 GOODS survey to g475r625i775z850, and show that the field of TN J1338–1942 is richer than the average field at the > 5σ significance. The angular distribution is highly filamentary, with about half of the objects clustered in a 4.4 arcmin region that includes the radio galaxy and the brightest LBGs. A second, but much less pronounced concentration of objects is seen around another ∼ 6L LBG located within the same field, for which we obtained a spectroscopic redshift of z = 3.8. The generally fainter LAEs appear to favour regions that are devoid of LBGs, while LBGs detected in the rest-frame optical (KS) tend to lie in the richest region, suggesting a forming ageor mass-density relation. We compare the angular two-point correlation function, w(θ), to the signal measured in similarly sized mock samples with a built-in two-point clustering as measured for field LBGs at z ∼ 4. We find an excess signal (2σ) at separations of θ < 10, corresponding to the typical halo size of dark matter Based on observations made with the NASA/ESA Hubble Space Telescope, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with program # 9291. Based on observations carried out at the European Southern Observatory, Paranal, Chile, programs 071.A-0495(A) and 073.A-0286(A). Leiden Observatory, Postbus 9513, 2300 RA Leiden, Netherlands UCO/Lick Observatory, University of California, Santa Cruz, CA 95064 Royal Observatory Edinburgh, Blackford Hill, Edinburgh, EH9 3HJ, UK Institute of Astronomy, Madingley Road, Cambridge CB3 0HA, UK Department of Physics and Astronomy, The Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218 Inst. Astrof́ısica de Andalućıa (CSIC), Camino Bajo de Huétor, 24, Granada 18008, Spain Max-Planck-Institut fr Astronomie, Knigstuhl 17, D-69117, Heidelberg, Germany National Aeronautics and Space Administration, Washington, DC