Showing papers by "Duilia F. de Mello published in 2004"

The Great Observatories Origins Deep Survey: Initial results from optical and near-infrared imaging

Abstract: This special issue of the Astrophysical Journal Letters is dedicated to presenting initial results from the Great Observatories Origins Deep Survey (GOODS) that are primarily, but not exclusively, based on multiband imaging data obtained with the Hubble Space Telescope and the Advanced Camera for Surveys (ACS). The survey covers roughly 320 arcmin2 in the ACS F435W, F606W, F814W, and F850LP bands, divided into two well-studied fields. Existing deep observations from the Chandra X-Ray Observatory and ground-based facilities are supplemented with new, deep imaging in the optical and near-infrared from the European Southern Observatory and from the Kitt Peak National Observatory. Deep observations with the Space Infrared Telescope Facility are scheduled. Reduced data from all facilities are being released worldwide within 3-6 months of acquisition. Together, this data set provides two deep reference fields for studies of distant normal and active galaxies, supernovae, and faint stars in our own Galaxy. This Letter serves to outline the survey strategy and describe the specific data that have been used in the accompanying letters, summarizing the reduction procedures and sensitivity limits.

The Hubble Higher z Supernova Search: Supernovae to z 1.6 and Constraints on Type Ia Progenitor Models

Abstract: We present results from the Hubble Higher z Supernova Search, the first space-based open field survey for supernovae (SNe). In cooperation with the Great Observatories Origins Deep Survey, we have used the Hubble Space Telescope with the Advanced Camera for Surveys to cover ~300 arcmin2 in the area of the Chandra Deep Field South and the Hubble Deep Field North on five separate search epochs (separated by ~45 day intervals) to a limiting magnitude of F850LP ≈ 26. These deep observations have allowed us to discover 42 SNe in the redshift range 0.2 < z < 1.6. As these data span a large range in redshift, they are ideal for testing the validity of Type Ia supernova progenitor models with the distribution of expected "delay times," from progenitor star formation to Type Ia SN explosion, and the SN rates these models predict. Through a Bayesian maximum likelihood test, we determine which delay-time models best reproduce the redshift distribution of SNe Ia discovered in this survey. We find that models that require a large fraction of "prompt" (less than 2 Gyr) SNe Ia poorly reproduce the observed redshift distribution and are rejected at greater than 95% confidence. We find that Gaussian models best fit the observed data for mean delay times in the range of 2-4 Gyr.

The Hubble Higher-Z Supernova Search: Supernovae to z=1.6 and Constraints on Type Ia Progenitor Models

Abstract: We present results from the Hubble Higher-z Supernova Search, the first space-based open field survey for supernovae (SNe). In cooperation with the Great Observatories Origins Deep Survey, we have used the Hubble Space Telescope with the Advanced Camera for Surveys to cover 300 square arcmin in the area of the Chandra Deep Field South and the Hubble Deep Field North on five separate search epochs (separated by 45 day intervals) to a limiting magnitude of z'=26. These deep observations have allowed us to discover 42 SNe in the redshift range 0.2 < z < 1.6. As these data span a large range in redshift, they are ideal for testing the validity of Type Ia supernova progenitor models with the distribution of expected ``delay times,'' from progenitor star formation to SN Ia explosion, and the SN rates these models predict. Through a Bayesian maximum likelihood test, we determine which delay-time models best reproduce the redshift distribution of SNe Ia discovered in this survey. We find that models that require a large fraction of ``prompt'' (less than 2 Gyr) SNe Ia poorly reproduce the observed redshift distribution and are rejected at 95% confidence. We find that Gaussian models best fit the observed data for mean delay times in the range of 3 to 4 Gyr.

The Evolution of Disk Galaxies in the GOODS-South Field: Number Densities and Size Distribution*

Abstract: We examine the evolution of the sizes and number densities of disk galaxies using the high-resolution images obtained by the Great Observatories Origins Deep Survey (GOODS) with the Advanced Camera for Surveys on the Hubble Space Telescope. The multiwavelength images are used to classify galaxies based on their rest-frame B-band morphologies out to redshift . In order to minimize the effect of selection biases, we confine our z ∼ 1.25 analysis to galaxies that occupy the region of the magnitude-size plane where the survey is ∼90% complete at all redshifts. The observed size distribution is consistent with a lognormal distribution as seen for the disk galaxies in the local universe and does not show any significant evolution over the redshift range . We 0.25 ≤ z ≤ 1.25 find that the number densities of disk galaxies remains fairly constant over this redshift range, although a modest evolution by a factor of 4 may be possible within the 2 j uncertainties. Subject headings: galaxies: evolution — galaxies: formation — galaxies: fundamental parameters — galaxies: structure

Evolution of Disk Galaxies in the GOODS-South Field: Number Densities and Size Distribution

Abstract: We examine the evolution of the sizes and number densities of disk galaxies using the high resolution images obtained by the Great Observatories Origins Deep Survey (GOODS) with the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope (HST). The multiwavelength (B,V,i,z) images allow us to classify galaxies based on their rest-frame B-band morphologies out to redshift z = 1.25. In order to minimize the effect of selection biases, we confine our analysis to galaxies which occupy the region of magnitude-size plane where the survey is almost 90% complete at all redshifts. The observed size distribution is consistent with a log-normal distribution as seen for the disk galaxies in the local Universe and does not show any significant evolution over the redshift range 0.25 < z < 1.25. We find that the number densities of disk galaxies remains fairly constant over this redshift range, although a modest evolution by a factor of four may be possible within the 2-sigma uncertainties.

Observing the Formation of the Hubble Sequence in the Great Observatories Origins Deep Survey

Abstract: Understanding the physical formation of the Hubble sequence remains one of the most important unsolved astrophysical problems. Searches for protodisks and proto-elliptical galaxies can now be effectively done using deep wide-field Hubble Space Telescope images taken with the new Advanced Camera for Surveys. Through an analysis of the concentrations (C), asymmetries (A), and clumpiness values (S) of galaxies found in the Great Observatories Origins Deep Survey Field South, we are able to identify objects possibly forming onto the Hubble sequence. Using this approach, we detect a sizeable population of star-forming luminous diffuse objects and star-forming luminous asymmetric objects between redshifts 0.5 2 and z < 1. The luminous asymmetric objects are found at a similar abundance, with a peak at z ~ 1. We argue that these galaxies are a subset of modern disks and elliptical galaxies in formation. The comoving volume density of the luminous diffuse objects between z = 1 and 2 is similar to the local density of bright disk galaxies, with values ~5 × 105 Gpc-3. The spectral energy distributions of these objects are mostly consistent with starbursts, or star-forming normal galaxies, with average uncorrected for extinction star formation rates of ~4 M☉ yr-1. These galaxies also host 35%-40% of the star formation activity at 1 < z < 2. We briefly discuss the implications of these objects for understanding the origin of the Hubble sequence.

Evolution in the colors of lyman break galaxies from z ∼ 4 to z ∼ 3

Abstract: The integrated colors of distant galaxies provide a means for interpreting the properties of their stellar content. Here we use rest-frame UV-to-optical colors to constrain the spectral energy distributions and stellar populations of color-selected, B-dropout galaxies at z ~ 4 in the Great Observatories Origins Deep Survey (GOODS). We combine the Advanced Camera for Surveys data with ground-based near-infrared images, which extend the coverage of galaxies at z ~ 4 to the rest-frame B band. We observe a color-magnitude trend in the rest-frame m(UV)-B versus B diagram for the z ~ 4 galaxies that has a fairly well-defined "blue envelope," and is strikingly similar to that of color-selected, U-dropout galaxies at z ~ 3. We also find that although the co-moving luminosity density at rest-frame UV wavelengths (1600 A) is roughly comparable at z ~ 3 and ~4, the luminosity density at rest-frame optical wavelengths increases by about one-third from z ~ 4 to ~3. Although the star formation histories of individual galaxies may involve complex and stochastic events, the evolution in the global luminosity density of the UV-bright galaxy population corresponds to an average star formation history with a star formation rate that is constant or increasing over these redshifts. This suggests that the evolution in the luminosity density corresponds to an increase in the stellar mass density of 33%.

Characterizing the Stellar Population in NGC 1705-1

Abstract: We observed the brightest super-star cluster NGC 1705-1 in the nearby dwarf galaxy NGC 1705 with the Space Telescope Imaging Spectrograph in the echelle mode between 1200 and 3100 ?. The data allow a study of the young stellar population at hitherto unprecedented spectral resolution and signal-to-noise ratios. A comprehensive list of strong and weak stellar and interstellar absorption lines is given, together with the measured line parameters. Four distinct velocity systems are identified: stellar lines at the measured H I velocity, blueshifted interstellar lines from outflowing gas, Milky Way foreground absorption, and a high-velocity cloud. Comparison with stellar template spectra indicates an equivalent spectral type of B0 to B1, with mostly dwarf and giant stars contributing. When placed on a theoretical Hertzsprung-Russell diagram, these stars constrain the age of NGC 1705-1 to 12 ? Myr. Since this age is derived purely from spectroscopy, it is independent of reddening corrections. A comparison of the observed and theoretical mass-to-light ratio for the derived age was performed. We find no significant evidence for an anomalous initial mass function at the low-mass end, contrary to suggestions found in the literature. The stellar population of NGC 1705-1 is similar to that in other massive clusters, such as 30 Doradus or NGC 1569-A, after taking into account age differences and model uncertainties. We discuss the difficulty of relating observed and theoretical mass-to-light ratios because of the unknown gas mass fraction lost by the cluster and the uncertain mass-loss rates of asymptotic giant branch stars in population synthesis models.

Far-ultraviolet imaging of the Hubble Deep Field North

Abstract: We present far-ultraviolet (FUV) imaging of the Hubble Deep Field-North (HDF-N) taken with the Solar Blind Channel of the Advanced Camera for Surveys (ACS SBC) and the FUV MAMA detector of the Space Telescope Imaging Spectrograph onboard the Hubble Space Telescope. The full WFPC2 deep field has been observed at 1600 A. We detect 134 galaxies and one star down to a limit of FUV_(AB) ~ 29. All sources have counterparts in the WFPC2 image. Redshifts (spectroscopic or photometric) for the detected sources are in the range 0 < z < 1. We find that the FUV galaxy number counts are higher than those reported by GALEX, which we attribute at least in part to cosmic variance in the small HDF-N field of view. Six of the 13 Chandra sources at z < 0.85 in the HDF-N are detected in the FUV, and those are consistent with starbursts rather than active galactic nuclei. Cross-correlating with Spitzer sources in the field, we find that the FUV detections show general agreement with the expected L_(IR)/L_(UV) versus β relationship. We infer star formation rates (SFRs), corrected for extinction using the UV slope, and find a median value of 0.3 M_☉ yr^(-1) for FUV-detected galaxies, with 75% of detected sources having SFR < 1 M_☉ yr^(-1). Examining the morphological distribution of sources, we find that about half of all FUV-detected sources are identified as spiral galaxies. Half of morphologically selected spheroid galaxies at z < 0.85 are detected in the FUV, suggesting that such sources have had significant ongoing star formation in the epoch since z ~ 1.

Metal Enrichment in Near-Infrared Luminous Galaxies at z ~ 2: Signatures of Proto-elliptical Galaxies?*

Abstract: We present the analysis of the co-added rest-frame UV spectrum (1200 A < z < 2000 A) of five K-luminous galaxies at z ~2 from the K20 survey. The composite spectrum is characterized by strong absorption lines over the UV continuum from C, N, O, Al, Si, and Fe in various ionization stages. While some of these lines are interstellar, several among the strongest absorptions are identified with stellar photospheric lines. Most of the photospheric and interstellar features are stronger in the K-luminous composite spectrum than in Lyman break galaxies at z ~3. This suggests higher metallicity and possibly also larger interstellar velocity dispersion caused by macroscopic motions. The absorption lines and the slope of the UV continuum are well matched by the spectrum of the nearby luminous infrared galaxy NGC 6090, which is in the process of merging. A metallicity higher than solar is suggested by comparing the pure photospheric lines (Si III, C III, and Fe V) with starburst models. The evidence of high metallicity, together with the high masses, high star formation rates, and possibly strong clustering, well qualify these galaxies as progenitors of local massive elliptical galaxies.

Metal enrichment in near-IR luminous galaxies at z~2: signatures of proto-ellipticals?

Abstract: We present the analysis of the coadded rest-frame UV spectrum (1200

METAL ENRICHMENT IN NEAR-INFRARED LUMINOUS GALAXIES AT z ∼ 2: SIGNATURES OF PROTO-ELLIPTICAL GALAXIES? 1

Abstract: We present the analysis of the co-added rest-frame UV spectrum ( ) of five K-luminous uu 1200 A ! z ! 2000 A galaxies at 2 from the K20 survey. The composite spectrum is characterized by strong absorption lines over z ∼ the UV continuum from C, N, O, Al, Si, and Fe in various ionization stages. While some of these lines are interstellar, several among the strongest absorptions are identified with stellar photospheric lines. Most of the photospheric and interstellar features are stronger in the K-luminous composite spectrum than in Lyman break galaxies at 3. This suggests higher metallicity and possibly also larger interstellar velocity dispersion caused z ∼ by macroscopic motions. The absorption lines and the slope of the UV continuum are well matched by the spectrum of the nearby luminous infrared galaxy NGC 6090, which is in the process of merging. A metallicity higher than solar is suggested by comparing the pure photospheric lines (Si iii ,C iii, and Fe v) with starburst models. The evidence of high metallicity, together with the high masses, high star formation rates, and possibly strong clustering, well qualify these galaxies as progenitors of local massive elliptical galaxies.

Structure and Evolution of Starburst and Normal Galaxies

Abstract: A comparative study of the rest-frame morphology and structural properties of optically selected starburst galaxies at redshift z 1 is carried out using multi-wave-band (BViz) high-resolution images taken by the Advanced Camera for Surveys as part of the Great Observatories Origins Deep Survey. We classify galaxies into starburst, early, and late types by comparing their observed spectral energy distributions with local templates. We find that early-type systems have significantly higher rest-frame B-band concentration indices and active galacic nucleus (AGN) fraction (>25 %) than late-type spirals and optically selected starbursts. These results are consistent with the scenario that early-epoch (z 1) gas-rich dissipative processes (e.g., major mergers) have played an important role in developing large central concentrations in early-type E/Sa galaxies and that a concurrent growth of central black holes and bulges occurs in some of these early merger events. The lower AGN fraction and concentration indices in the majority of the optically selected starbursts at z 1 suggest that either the starbursts and early types are different in nature (being, respectively, disk and bulge dominated) and/or they are in different evolutionary phases, such that some of the starbursts in major mergers evolve into early types as the dynamical phase of the merger evolves and the spectral signature of the starburst fades out. The starbursts have, on average, larger asymmetries than our control sample of normal galaxies in both rest-frame B and R bands, suggesting that a significant fraction of the starburst activity is tidally triggered.

The Nature of Near-Ultraviolet-selected Objects in the Chandra Deep Field-South*

Abstract: We present the first results of the pure parallel near-UV observations with the Wide Field Planetary Camera 2 (WFPC2) in the Chandra Deep Field-South. The main goal is to search for the population of objects that contributes to the rise in the volume-averaged star formation rate at intermediate redshifts (z < 1). A total of 34 objects were identified in the WFPC2 images and their counterparts found in images from the Advanced Camera for Surveys. We use template fitting of the spectral energy distributions to classify the objects and found that 17 are starbursts, nine are late-type galaxies, two are early-type galaxies, and six are stars; two of the late types and one of the starbursts are X-ray sources. The colors of the starbursts were reproduced by the stellar evolutionary synthesis code Starburst99, which shows a mixed population of bursts with ages less than 1 Gyr. Analysis of the light concentration, asymmetry, and clumpiness shows that this sample is a mixed bag, containing dwarf ellipticals, early and late spirals, and peculiar objects that resemble mergers in progress.

Assessing the galaxy population out to z ~ 2 using the Hubble Deep Field South

Abstract: In this work we use the Hubble Deep Field South (HDF-S) version 2 images to assess the galaxy population out to z ∼ 2. We have used two methods of templates fitting of the spectral energy distributions to obtain photometric redshifts and classify the objects. The Bayesian photometric redshifts gave better results when compared with 54 spectroscopic redshifts available in the literature. Analysis of the rest-frame colour distribution shows a bimodality out to z ∼ 1.4. We separated our sample in a blue and a red population at B - V = 0.29. At low redshifts (0.2 0.29 whereas at higher redshifts ∼60% of the galaxies are bluer than B - V < 0.29. Although in low numbers, a population of early-type galaxies (or heavily obscured low redshift galaxies) is seen out to z ∼ 2.

Starbursts at intermediate redshifts

Abstract: In this work I present the survey which is searching for the rise in the volume-averaged star formation rate at intermediate redshifts (z To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html