Showing papers by "Duilia F. de Mello published in 2006"

Far-ultraviolet imaging of the Hubble Deep Field-North: Star formation in normal galaxies at z < 1

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.

Star-forming Galaxies at Intermediate Redshifts: Morphology, Ages, and Sizes

Abstract: We present an analysis of the deepest near-UV image obtained with the Hubble Space Telescope using the WFPC2 (F300W) as part of the parallel observations of the Hubble Ultra Deep Field campaign. The U-band 10 σ limiting magnitude measured over 0.2 arcsec2 is mAB = 27.5, which is 0.5 mag deeper than that in the Hubble Deep Field–North. We matched the U-band catalogs with those from the ACS (BViz) taken during the Great Observatories Origins Deep Survey observations of the Chandra Deep Field–South and obtained photometric redshifts for 306 matched objects. We find that the UV-selected galaxies span all the major morphological types at 0.2 100 Myr. The average half-light radius (rest-frame 1200–1800 A) of the UV-selected galaxies at 0.66 < zphot < 1.5 is 026 ± 001 (2.07 ± 0.08 kpc). The UV-selected galaxies are on average fainter (MB = -18.43 ± 0.13) than Lyman break galaxies (LBGs; MB = -23 ± 1). Our sample includes early-type galaxies that are presumably massive and forming stars only in their cores, as well as starburst-type systems that are more similar to the LBGs, although much less luminous. This implies that even the starbursts in our sample are either much less massive than LBGs or forming stars at a much lower rate, or both. The low surface brightness galaxies have no overlap with the LBGs and form an interesting new class of their own.

Faint U-Band Dropouts in the WFPC2 Parallels of the Hubble Ultra Deep Field

Abstract: We combine data from the extremely deep Hubble Space Telescope U (F300W) image, obtained using WFPC2 as part of the parallel observations of the Hubble Ultra Deep Field campaign, with BVi images from the Great Observatories Origins Deep Survey to identify a sample of Lyman break galaxies in the redshift range 2.0 z 3.5. We use recent stellar population synthesis models with a wide variety of ages, metallicities, redshifts, and dust content, and a detailed representation of the H I cosmic opacity as a function of redshift to model the colors of galaxies in our combination of WFPC2 and ACS filters. Using these models, we derive improved color selection criteria that provide a clean selection of relatively unobscured star-forming galaxies in this redshift range. Our WFPC2 F300W image is the deepest image ever obtained at that wavelength. The 10 σ limiting magnitude measured over 0.2 arcsec2 is 27.5 mag in the WFPC2 F300W image, about 0.5 mag deeper than the F300W image in the Hubble Deep Field (HDF)-North. This extra depth relative to the HDFs allows us to directly probe the luminosity function about 0.5 mag deeper than the depth accessible with the HDF data along an independent line of sight. Our sample of star-forming galaxies with 2.0 z 3.5 includes 125 objects, the majority of which show clumpy morphologies. We measure a star formation rate density of 0.18 M⊙ yr-1 Mpc-3, marginally higher than the value measured for the HDFs.

Medium-resolution spectroscopy of galaxies with redshifts 2.3 $< z <$ 3.5

Abstract: Using FORS2 at the ESO VLT we obtained medium-resolution ($R \approx 2000$) spectra of 12 galaxies with $2.37 \leq z \leq 3.40$ in the FORS Deep Field. Two individual spectra with good S/N and a composite of all 12 spectra were used to derive properties of the stellar and interstellar absorption lines of galaxies in this redshift range. Systematic differences between the individual spectra were found for the strength and profiles of the intrinsic interstellar lines. For eight spectra with sufficient S/N , we measured the “1370” and “1425” metallicity indices, from which we find for our sample that galaxies at $ z > 3$ have lower mean metallicity than galaxies at $2.3 < z < 3$. However uncertainties remain concerning the absolute calibration of the metallicity tracers in use for high-redshift galaxies. Additional modeling will be needed to resolve these uncertainties.

Near-Ultraviolet Sources in the Great Observatories Origins Deep Survey Fields

Abstract: We present an ultraviolet-selected sample of 268 objects in the two fields of the Great Observatories Origins Deep Survey (GOODS). We used the parallel observations taken with the Wide Field Planetary Camera 2 in the U band (F300W), which covered 88% of the GOODS fields, to identify sources and selected only objects with GOODS Advanced Camera for Surveys counterparts. Spectroscopic redshifts for 95 of these sources are available, and we have used the multiwavelength GOODS data to estimate photometric redshifts for the others. Most of the objects have redshifts 0.2 < z < 0.8. We used the spectral types obtained by photometric redshift fitting to identify starburst galaxies. We have also visually checked all objects and looked for tidal effects and nearby companions. We find that (1) 45% of the UV-selected galaxies are starbursts, (2) nearly 75% of the starbursts have tidal tails or show some peculiarity typical of interactions or mergers, and (3) ~50% have companions within an area of 5'' × 5''. The UV-selected sample has an average rest-frame MB = -19.9 ± 0.1. The bluest objects in the sample (U - B < 0.2 and B - V < 0.1) are at 1.1 < z < 1.9 and have peculiar morphologies that resemble either tadpoles, chains, or double-clump galaxies. Starbursts with tadpole or clump morphologies at z = 0.8-1.3 have sizes comparable to Lyman break galaxies and compact UV-luminous galaxies.

The Nature of Near Ultraviolet Sources in the GOODS Fields

Abstract: Abstract We present the latest results of the survey searching for the nature of UV-selected galaxies in the Great Observatories Origins Deep Survey fields. By searching for UV-bright galaxies at intermediate redshifts (z ~ 1) we aim at understanding the nature of star-forming galaxies and their counterparts at higher-z, the so-called Lyman Break Galaxies.