arXiv subjects

Duilia F. de Mello

Publications and source records attributed to Duilia F. de Mello.

34 records · Page 2Linked to original sources

arXiv2010

A Deep HST Search for Escaping Lyman Continuum Flux at z~1.3: Evidence for an Evolving Ionizing Emissivity

We have obtained deep Hubble Space Telescope far-UV images of 15 starburst galaxies at z~1.3 in the GOODS fields to search for escaping Lyman continuum photons. These are the deepest far-UV images m_{AB}=28.7, 3σ, 1" diameter) over this large an area (4.83 arcmin^2) and provide the best escape fraction constraints for any galaxy at any redshift. We do not detect any individual galaxies, with 3σlimits to the Lyman Continuum (~700 Å) flux 50--149 times fainter (in f_nu) than the rest-frame UV (1500 Å) continuum fluxes. Correcting for the mean IGM attenuation (factor ~2), as well as an intrinsic stellar Lyman Break (~3), these limits translate to relative escape fraction limits of f_{esc,rel}<[0.03,0.21]. The stacked limit is f_{esc,rel}(3σ)<0.02. We use a Monte Carlo simulation to properly account for the expected distribution of IGM opacities. When including constraints from previous surveys at z~1.3 we find that, at the 95% confidence level, no more than 8% of star--forming galaxies at z~1.3 can have relative escape fractions greater than 0.50. Alternatively, if the majority of galaxies have low, but non-zero, escaping Lyman Continuum, the escape fraction can not be more than 0.04. Both the stacked limits, and the limits from the Monte Carlo simulation suggest that the average ionizing emissivity (relative to non-ionizing UV emissivity) at z~1.3 is significantly lower than has been observed in Lyman Break Galaxies (LBGs) at z~3. If the ionizing emissivity of star-forming galaxies is in fact increasing with redshift, it would help to explain the high photoionization rates seen in the IGM at z>4 and reionization of the intergalactic medium at z>6. [Abridged]

astro-ph.CO↗

arXiv2009

Near-UV Sources in the Hubble Ultra Deep Field: The Catalog

The catalog from the first high resolution U-band image of the Hubble Ultra Deep Field, taken with Hubble's Wide Field Planetary Camera 2 through the F300W filter, is presented. We detect 96 U-band objects and compare and combine this catalog with a Great Observatories Origins Deep Survey (GOODS) B-selected catalog that provides B, V, i, and z photometry, spectral types, and photometric redshifts. We have also obtained Far-Ultraviolet (FUV, 1614 Å) data with Hubble's Advanced Camera for Surveys Solar Blind Channel (ACS/SBC) and with Galaxy Evolution Explorer (GALEX). We detected 31 sources with ACS/SBC, 28 with GALEX/FUV, and 45 with GALEX/NUV. The methods of observations, image processing, object identification, catalog preparation, and catalog matching are presented.

astro-ph.GA↗

arXiv2009

Structures of Local Galaxies Compared to High Redshift Star-forming Galaxies

The rest-frame far-ultraviolet (FUV) morphologies of 8 nearby interacting and starburst galaxies (Arp 269, M 82, Mrk 8, NGC 520, NGC 1068, NGC 3079, NGC 3310, NGC 7673) are compared with 54 galaxies at z ~ 1.5 and 46 galaxies at z ~ 4 observed in the GOODS-ACS field. The nearby sample is artificially redshifted to z ~ 1.5 and 4. We compare the simulated galaxy morphologies to real z ~ 1.5 and 4 UV-bright galaxy morphologies. We calculate the Gini coefficient (G), the second-order moment of the brightest 20% of the galaxy's flux (M_20), and the Sersic index (n). We explore the use of nonparametric methods with 2D profile fitting and find the combination of M_20 with n an efficient method to classify galaxies as having merger, exponential disk, or bulge-like morphologies. When classified according to G and M_20, 20/30% of real/simulated galaxies at z ~ 1.5 and 37/12% at z ~ 4 have bulge-like morphologies. The rest have merger-like or intermediate distributions. Alternatively, when classified according to the Sersic index, 70% of the z ~ 1.5 and z ~ 4 real galaxies are exponential disks or bulge-like with n > 0.8, and ~30% of the real galaxies are classified as mergers. The artificially redshifted galaxies have n values with ~35% bulge or exponential at z ~ 1.5 and 4. Therefore, ~20-30% of Lyman-break galaxies (LBGs) have structures similar to local starburst mergers, and may be driven by similar processes. We assume merger-like or clumpy star-forming galaxies in the GOODS field have morphological structure with values n < 0.8 and M_20 > -1.7. We conclude that Mrk 8, NGC 3079, and NGC 7673 have structures similar to those of merger-like and clumpy star-forming galaxies observed at z ~ 1.5 and 4.

astro-ph.CO↗

arXiv2007

Star-formation in the HI bridge between M81 and M82

We present multi-wavelength observations of stellar features in the HI tidal bridge connecting M81 and M82 in the region called Arp's Loop. We identify eight young star-forming regions from Galaxy Evolution Explorer ultraviolet observations. Four of these objects are also detected at Hα. We determine the basic star formation history of Arp's Loop using F475W and F814W images obtained with the Advanced Camera for Surveys on board the Hubble Space Telescope. We find both a young (< 10 Myr) and an old (>1 Gyr) stellar population with a similar spatial distribution and a metallicity Z~0.004. We suggest that the old stellar population was formed in the stellar disk of M82 and/or M81 and ejected into the intergalactic medium during a tidal passage (~ 200-300 Myr ago), whereas the young UV-bright stars have formed in the tidal debris. The UV luminosities of the eight objects are modest and typical of small clusters or OB associations. The tidal bridge between M81-M82 therefore appears to be intermediate between the very low levels of star formation seen in the Magellanic bridge and actively star-forming tidal tails associated with major galaxy mergers.

astro-ph↗

arXiv2007

Searching for Star Formation Outside Galaxies: Multiwavelength Analysis of the Intragroup Medium of HCG100

We used multiwavelength data (HI, FUV, NUV, R) to search for evidence of star formation in the intragroup medium of the Hickson Compact Group 100. We find that young star-forming regions are located in the intergalactic HI clouds of the compact group which extend to over 130 kpc away from the main galaxies. A tidal dwarf galaxy candidate is located in the densest region of the HI tail, 61 kpc from the brightest group member and its age is estimated to be only 3.3 Myr. Fifteen other intragroup HII regions and TDG candidates are detected in the GALEX FUV image and within a field 10'x10' encompassing the HI tail. They have ages <200 Myr, HI masses of 10^(9.2-10.4) Msun, 0.001< SFR <0.01 Msun yr^-1, and stellar masses 10^4.3--10^6.5 Msun. The HI clouds to which many of them are associated have column densities about one order of magnitude lower than N(HI)~10^21 cm^-2.

astro-ph↗

arXiv2007

New Constraints on the Lyman Continuum Escape Fraction at z~1.3

We examine deep far-ultraviolet (1600 Angstrom) imaging of the Hubble Deep Field-North (HDFN) and the Hubble Ultra Deep Field (HUDF) to search for leaking Lyman continuum radiation from starburst galaxies at z~1.3. There are 21 (primarily sub-L*) galaxies with spectroscopic redshifts between 1.1<z<1.5 and none are detected in the far-UV. We fit stellar population templates to the galaxies' optical/near-infrared SEDs to determine the starburst age and level of dust attenuation, giving an accurate estimate of the intrinsic Lyman continuum ratio, f_1500/f_700, and allowing a conversion from f_700 limits to relative escape fractions. We show that previous high-redshift studies may have underestimated the amplitude of the Lyman Break, and thus the relative escape fraction, by a factor of ~2. Once the starburst age and intergalactic HI absorption are accounted for, 18 galaxies in our sample have limits to the relative escape fraction, f_esc,rel < 1.0 with some limits as low as f_esc,rel < 0.10 and a stacked limit of f_esc,rel < 0.08. This demonstrates, for the first time, that most sub-L* galaxies at high redshift do not have large escape fractions. When combined with a similar study of more luminous galaxies at the same redshift we show that, if all star-forming galaxies at z~1 have similar relative escape fractions, the value must be less than 0.14 (3 sigma). We also show that less than 20% (3 sigma) of star-forming galaxies at z~1 have relative escape fractions near unity. These limits contrast with the large escape fractions found at z~3 and suggest that the average escape fraction has decreased between z~3 and z~1. (Abridged)

astro-ph↗

arXiv2004

K-luminous galaxies at z~2. Metallicity and B stars

We present the results from the analysis of the composite spectrum of five near-IR luminous (K < 20) galaxies at z~2. Several of the strongest absorption lines are present in the merging galaxy NGC 6090 UV spectrum and are not present in the spectra of Lyman Break Galaxies at z~3. They were identified as SiIII 1296, CIII 1428, SiII 1485, and Fe 1380 which are photospheric lines typical of B stars. A metallicity higher than solar is suggested by comparing the pure photospheric lines known as the 1425AA index (SiIII, CIII, FeV) with Starburst99 models. The evidence of high metallicity, together with the high masses, high star-formation rates, and possibly strong clustering, suggest that these galaxies are candidates to become massive spheroids.

astro-ph↗

arXiv2004

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

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.

astro-ph↗

arXiv2003

Evolution in the Colors of Lyman-Break Galaxies from Z~4 to Z~3

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. We combine the ACS 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 Angstroms) is roughly comparable at z ~ 3 and z ~ 4, the luminosity density at rest-frame optical wavelengths increases by about one-third from z ~ 4 to z ~ 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 more than 33%.

astro-ph↗

arXiv2002

A Survey Searching for the Epoch of Assembling of Hubble Types

We have started a survey of galaxies at intermediate redshifts using the HST-STIS parallel fields. Our main goal is to analyse the morphology of faint galaxies in order to estimate the epoch of formation of the Hubble classification sequence. The high resolution of STIS images (0.05'') is ideal for this work and enable us to perform a morphological classification and to analyse the internal structures of galaxies. We find that 40% of the 290 galaxies are early types and that there are more irregulars and ellipticals at the fainter magnitudes.

astro-ph↗

arXiv2001

Environmental effects in galaxies: Molecular Gas, Star Formation, and Activity

In order to study whether there is any correlation between nuclear activities, gas content, and the environment where galaxies reside, we have obtained optical and millimetric spectra for a well-defined sample of intermediate Hubble type spirals in dense environments and in the field. We found that these spirals in dense environments have on average: less molecular gas per blue luminosity, higher atomic gas fraction, lower current star formation rate, and the same star formation efficiency as field galaxies. Although none of these results stand out as a single strong diagnostic, given their statistical significance, taken together they indicate a trend for diminished gas content and star formation activity in galaxies in high density environments. Our results suggest that galaxies in dense environments have either (i) consumed their molecular gas via star formation in the past or (ii) that dense environments leads to an inhibition of molecular gas from atomic phase. The similarities in star formation efficiency of the dense environments and field galaxies suggest that the physical processes controling the formation of stars from the molecular gas are local rather than global. We also found that star formation rate per blue luminosity increases linearly as the total amount of gas increases in LINERs. This result, based on a small sample, suggests that LINERs are powered by star formation rather than an AGN.

astro-ph↗

arXiv2001

Environmental Effects in Galaxies: The Data

We present optical and millimetric data for 47 intermediate Hubble type spiral galaxies located either in dense environments or in the field. We compare correlations between global parameters, such as far-infrared luminosity, blue luminosity, and total molecular gas content, with other samples of galaxies, including normal galaxies, clusters and ultraluminous infrared galaxies. We find that overall our sample is a well defined subset of these other samples of galaxies.

astro-ph↗

arXiv2001

A close look into an intermediate redshift galaxy using STIS

We present a detailed view of a galaxy at z=0.4 which is part of a large database of intermediate redshifts using high resolution images. We used the STIS parallel images and spectra to identify the object and obtain the redshift. The high resolution STIS image (0.05'') enabled us to analyse the internal structures of this galaxy. A bar along the major axis and hot-spots of star formation separated by 0.37'' (1.6 kpc) are found along the inner region of the galaxy. The analysis of the morphology of faint galaxies like this one is an important step towards estimating the epoch of formation of the Hubble classification sequence.

astro-ph↗

arXiv1999

B stars as a diagnostic of star-formation at low and high redshift

We have extended the evolutionary synthesis models by Leitherer et al. (1999b) by including a new library of B stars generated from the IUE high-dispersion spectra archive. We present the library and show how the stellar spectral properties vary according to luminosity classes and spectral types. We have generated synthetic UV spectra for prototypical young stellar populations varying the IMF and the star formation law. Clear signs of age effects are seen in all models. The contribution of B stars in the UV line spectrum is clearly detected, in particular for greater ages when O stars have evolved. With the addition of the new library we are able to investigate the fraction of stellar and interstellar contributions and the variation in the spectral shapes of intense lines. We have used our models to date the spectrum of the local super star cluster NGC1705-1. Photospheric lines of CIII1247, SiIII1417, and SV1502 were used as diagnostics to date the burst of NGC 1705-1 at 10 Myr. We have selected the star-forming galaxy 1512-cB58 as a first application of the new models to high-z galaxies. This galaxy is at z=2.723, it is gravitationally lensed, and its high signal-to-noise Keck spectrum show features typical of local starburst galaxies, such as NGC 1705-1. Models with continuous star formation were found to be more adequate for 1512-cB58 since there are spectral features typical of a composite stellar population of O and B stars. A model with Z =0.4Z_solar and an IMF with alpha=2.8 reproduces the stellar features of the 1512-cB58 spectrum.

astro-ph↗

arXiv1999

Starburst99: Synthesis Models for Galaxies with Active Star Formation

Starburst99 is a comprehensive set of model predictions for spectrophotometric and related properties of galaxies with active star formation. The models are an improved and extended version of the data set previously published by Leitherer & Heckman (1995). We have upgraded our code by implementing the latest set of stellar evolution models of the Geneva group and the model atmosphere grid compiled by Lejeune et al. (1997). Several predictions which were not included in the previous publication are shown here for the first time. The models are presented in a homogeneous way for five metallicities between Z = 0.040 and 0.001 and three choices of the initial mass function. The age coverage is 10^6 to 10^9 yr. We also show the spectral energy distributions which are used to compute colors and other quantities. The full data set is available for retrieval at http://www.stsci.edu/science/starburst99/. This website allows users to run specific models with non-standard parameters as well. We also make the source code available to the community.

astro-ph↗

arXiv1997

Morphology Transformation in Pairs of Galaxies - The Local Sample

We present photometric analysis of a local sample of 14 isolated pairs of galaxies. The photometric properties analyzed in the local pairs are: colors, morphology, tidal effects and activity. We verify that close pairs have an excess of early-type galaxies and many elliptical galaxies in this pairs are, in fact, lenticular galaxies. Many late-pairs in our sample show strong tidal damage and blue star formation regions. We conclude that pairs of different morphologies may have passed through different evolution processes which violently transformed their morphology. Pairs with at least one early-type component may be descendents of groups of galaxies. However, late-type pairs are probably long-lived showing clearly signs of interaction. Some of them could be seen as an early stage of mergers. These photometric database will be used for future comparison with more distant pairs in order to study galaxy evolution.

astro-ph↗