Showing papers by "Duilia F. de Mello published in 2017"
TL;DR: In this article, the spectral energy distribution (SED) was used to measure the color gradient of clumps in distant galaxies, and the authors found that the color gradients of the clumps are steeper than those of intra-clump regions.
Abstract: Studying giant star-forming clumps in distant galaxies is important to understand galaxy formation and evolution. At present, however, observers and theorists have not reached a consensus on whether the observed "clumps" in distant galaxies are the same phenomenon that is seen in simulations. In this paper, as a step to establish a benchmark of direct comparisons between observations and theories, we publish a sample of clumps constructed to represent the commonly observed "clumps" in the literature. This sample contains 3193 clumps detected from 1270 galaxies at $0.5 \leq z < 3.0$. The clumps are detected from rest-frame UV images, as described in our previous paper. Their physical properties, e.g., rest-frame color, stellar mass (M*), star formation rate (SFR), age, and dust extinction, are measured by fitting the spectral energy distribution (SED) to synthetic stellar population models. We carefully test the procedures of measuring clump properties, especially the method of subtracting background fluxes from the diffuse component of galaxies. With our fiducial background subtraction, we find a radial clump U-V color variation, where clumps close to galactic centers are redder than those in outskirts. The slope of the color gradient (clump color as a function of their galactocentric distance scaled by the semi-major axis of galaxies) changes with redshift and M* of the host galaxies: at a fixed M*, the slope becomes steeper toward low redshift, and at a fixed redshift, it becomes slightly steeper with M*. Based on our SED-fitting, this observed color gradient can be explained by a combination of a negative age gradient, a negative E(B-V) gradient, and a positive specific star formation rate gradient of the clumps. We also find that the color gradients of clumps are steeper than those of intra-clump regions. [Abridged]
63 citations
University of Minnesota1, Space Telescope Science Institute2, Goddard Space Flight Center3, University of California, Riverside4, California Institute of Technology5, University of Texas at Austin6, Rutgers University7, Swinburne University of Technology8, The Catholic University of America9, Purdue University10
TL;DR: In this paper, the authors present the rest-1500 A UV luminosity functions (LF) for star-forming galaxies during the cosmic high noon, the peak of cosmic star formation rate at 1.5 < z < 3.
Abstract: We present the rest-1500 A UV luminosity functions (LF) for star-forming galaxies during the cosmic high noon—the peak of cosmic star formation rate at 1.5 < z < 3. We use deep NUV imaging data obtained as part of the Hubble Ultra-Violet Ultra Deep Field (UVUDF) program, along with existing deep optical and NIR coverage on the HUDF. We select F225W, F275W, and F336W dropout samples using the Lyman break technique, along with samples in the corresponding redshift ranges selected using photometric redshifts, and measure the rest-frame UV LF at z ~ 1.7, 2.2, 3.0, respectively, using the modified maximum likelihood estimator. We perform simulations to quantify the survey and sample incompleteness for the UVUDF samples to correct the effective volume calculations for the LF. We select galaxies down to M_(UV) = -15.9, -16.3, -16.8 and fit a faint-end slope of α = -1.20^(+0.10)_(-0.13), -1.32^(+0.10)_(-0.14), -1.39^(+0.08)_(-0.12) at 1.4 < z < 1.9, 1.8 < z < 2.6, and 2.4 < z < 3.6, respectively. We compare the star formation properties of z ~ 2 galaxies from these UV observations with results from Hα and UV+IR observations. We find a lack of high-SFR sources in the UV LF compared to the Hα and UV+IR, likely due to dusty SFGs not being properly accounted for by the generic IRX-β relation used to correct for dust. We compute a volume-averaged UV-to-Hα ratio by abundance matching the rest-frame UV LF and Hα LF. We find an increasing UV-to-Hα ratio toward low-mass galaxies (M_∗ ≾ 5 x 10^9 M_⊙). We conclude that this could be due to a larger contribution from starbursting galaxies compared to the high-mass end.
37 citations
TL;DR: In this paper, the authors measured the photometry of the clumps and determined the mass, age, and star formation rates (SFR) utilizing the SED-fitting code FAST.
Abstract: We present an investigation of clumpy galaxies in the Hubble Ultra Deep Field at 0.5 $\leq z \leq$ 1.5 in the rest-frame far-ultraviolet (FUV) using HST WFC3 broadband imaging in F225W, F275W, and F336W. An analysis of 1,404 galaxies yields 209 galaxies that host 403 kpc-scale clumps. These host galaxies appear to be typical star-forming galaxies, with an average of 2 clumps per galaxy and reaching a maximum of 8 clumps. We measure the photometry of the clumps, and determine the mass, age, and star formation rates (SFR) utilizing the SED-fitting code FAST. We find that clumps make an average contribution of 19% to the total rest-frame FUV flux of their host galaxy. Individually, clumps contribute a median of 5% to the host galaxy SFR and an average of $\sim$4% to the host galaxy mass, with total clump contributions to the host galaxy stellar mass ranging widely from less than 1% up to 93%. Clumps in the outskirts of galaxies are typically younger, with higher star formation rates, than clumps in the inner regions. The results are consistent with clump migration theories in which clumps form through violent gravitational instabilities in gas-rich turbulent disks, eventually migrate toward the center of the galaxies, and coalesce into the bulge.
34 citations
TL;DR: In this paper, the authors measured the photometry of clumps and determined the mass, age, and star formation rates (SFR) using the spectral energy distribution fitting code FAST.
Abstract: We present an investigation of clumpy galaxies in the Hubble Ultra Deep Field at 05 ≤ z ≤ 1.5 in the rest-frame far-ultraviolet (FUV) using Hubble Space Telescope Wide Field Camera 3 broadband imaging in F225W, F275W, and F336W. An analysis of 1404 galaxies yields 209 galaxies that host 403 kpc scale clumps. These host galaxies appear to be typical star-forming galaxies, with an average of 2 clumps per galaxy and reaching a maximum of 8 clumps. We measure the photometry of the clumps and determine the mass, age, and star formation rates (SFR) using the spectral energy distribution fitting code FAST. We find that clumps make an average contribution of 19% to the total rest-frame FUV flux of their host galaxy. Individually, clumps contribute a median of 5% to the host galaxy SFR and an average of ~4% to the host galaxy mass, with total clump contributions to the host galaxy stellar mass ranging widely from lower than 1% up to 93%. Clumps in the outskirts of galaxies are typically younger, with higher SFRs, than clumps in the inner regions. The results are consistent with clump migration theories in which clumps form through violent gravitational instabilities in gas-rich turbulent disks, eventually migrate toward the center of the galaxies, and coalesce into the bulge.
31 citations
University of Minnesota1, Goddard Space Flight Center2, Space Telescope Science Institute3, University of California, Riverside4, California Institute of Technology5, University of Texas at Austin6, Rutgers University7, Swinburne University of Technology8, The Catholic University of America9, Purdue University10
TL;DR: In this paper, the authors present the rest-1500\AA\ UV luminosity functions (LF) for star-forming galaxies during the cosmic ''high noon'' peak of cosmic star formation rate at $1.5
Abstract: We present the rest-1500\AA\ UV luminosity functions (LF) for star-forming galaxies during the cosmic \textit{high noon} -- the peak of cosmic star formation rate at $1.5
12 citations
TL;DR: In this paper, the authors obtained new multislit spectroscopy of six young star-forming regions around NGC2865, to determine their redshifts and metallicities.
Abstract: Interacting galaxies surrounded by HI tidal debris are ideal sites for the study of young clusters and tidal galaxy formation. The process that triggers star formation in the low-density environments outside galaxies is still an open question. New clusters and galaxies of tidal origin are expected to have high metallicities for their luminosities. Spectroscopy of such objects is, however, at the limit of what can be done with existing 8-10m class telescopes, which has prevented statistical studies of these objects. NGC2865 is an UV-bright merging elliptical galaxy with shells and extended HI tails. The regions observed in this work were previously detected using multi-slit imaging spectroscopy. We obtain new multislit spectroscopy of six young star-forming regions around NGC2865, to determine their redshifts and metallicities. The six emission-line regions are located 16-40 kpc from NGC2865 and they have similar redshifts. They have ages of ~10Myears and an average metallicity of 12+log(O/H) ~ 8.6, suggesting a tidal origin for the regions. It is noted that they coincide with an extended HI tail, which has projected density of N$_{HI}$ < 10$^{19}$ cm$^{-2}$, and displays a low surface brightness counterpart. These regions may represent the youngest of the three populations of star clusters already identified in NGC2865. The high, nearly-solar, oxygen abundances found for the six regions in the vicinity of NGC2865 suggest that they were formed by pre-enriched material from the parent galaxy, from gas removed during the last major merger. Given the mass and the location of the HII regions, we can speculate that these young star-forming regions are potential precursors of globular clusters that will be part of the halo of NGC2865 in the future. Our result supports the use of the multi-slit imaging spectroscopy as a useful tool for finding nearly-formed stellar systems around galaxies.
3 citations
TL;DR: In this article, the authors obtained new multi-slit spectroscopy of six young star-forming regions around NGC 2865, to determine their redshifts and metallicities.
Abstract: Context. Interacting galaxies surrounded by Hi tidal debris are ideal sites for the study of young clusters and tidal galaxy formation. The process that triggers star formation in the low-density environments outside galaxies is still an open question. New clusters and galaxies of tidal origin are expected to have high metallicities for their luminosities. Spectroscopy of such objects is, however, at the limit of what can be done with existing 8−10 m class telescopes, which has prevented statistical studies of these objects.Aims. NGC 2865 is a UV-bright merging elliptical galaxy with shells and extended Hi tails. In this work we aim to observe regions previously detected using multi-slit imaging spectroscopy.Methods. We obtained new multi-slit spectroscopy of six young star-forming regions around NGC 2865, to determine their redshifts and metallicities.Results. The six emission-line regions are located 16−40 kpc from NGC 2865 and they have similar redshifts. They have ages of ~10 Myr and an average metallicity of ~ 12 +log (O/H)~ 8.6, suggesting a tidal origin for the regions. We note that they coincide with an extended Hi tail, which has projected density of N HI cm-2 , and displays a low surface brightness counterpart. These regions may represent the youngest of the three populations of star clusters already identified in NGC 2865.Conclusions. The high, nearly-solar, oxygen abundances found for the six regions in the vicinity of NGC 2865 suggest that they were formed by pre-enriched material from the parent galaxy, from gas removed during the most recent major merger. Given the mass and the location of the Hii regions, we can speculate that these young star-forming regions are potential precursors of globular clusters that will be part of the halo of NGC 2865 in the future. Our result supports the use of the multi-slit imaging spectroscopy as a useful tool for finding nearly-formed stellar systems around galaxies.
2 citations