Showing papers by "Duilia F. de Mello published in 2012"

What turns galaxies off? The different morphologies of star-forming and quiescent galaxies since z ~ 2 from CANDELS

Abstract: We use HST/WFC3 imaging from the CANDELS multicyc1e treasury survey, in conjunction with the Sloan Digital Sky Survey, to explore the evolution of galactic structure for galaxies with stellar masses > 3 x 10(exp 10) Solar Mass from Z= 2.2 to the present epoch, a time span of 10 Gyr. We explore the relationship between rest-frame optical color, stellar mass, star formation activity and the structural parameters of galaxies as determined from parametric fits to the surface brightness profiles of galaxies. We confirm the dramatic evolution from z= 2.2 to the present day in the number density of non-star-forming galaxies above 3 x 10(exp 10) Solar Mass reported by other authors. We find that the vast majority of these quiescent systems have concentrated light profiles, as parameterized by the Sersic index, and the population of concentrated galaxies grows similarly rapidly. We examine the joint distribution of star formation activity, Sersic index, stellar mass, mass divided by radius (a proxy for velocity dispersion), and stellar surface density. Quiescence correlates poorly with stellar mass at all z < 2.2 (given the approx < 0.2 dex scatter between halo mass and stellar mass at z approximates 0 inferred by More et al, this argues against halo mass being the only factor determining quiescence). Quiescence correlates better with Sersic index, 'velocity dispersion' and stellar surface density, where Sersic index correlates the best (increasingly so at lower redshift). Yet, there is significant scatter between quiescence and galaxy structure: while the vast majority of quiescent galaxies have prominent bulges, many of them have significant disks, and a number of bulge-dominated galaxies have significant star formation. Noting the rarity of quiescent galaxies without prominent bulges, we argue that a prominent bulge (and, perhaps by association, a supermassive black hole) is a necessary but not sufficient condition for quenching star formation on galactic scales over the last 10 Gyr; such a result is qualitatively consistent with the expectations of the AGN feedback paradigm.

Star formation in H i tails: HCG 92, HCG 100 and six interacting systems

Abstract: We present new Gemini spectra of 14 new objects found within the HI tails of Hickson Compact Groups 92 and 100. Nine of them are GALEX Far-UV (FUV) and Near-UV (NUV) sources. The spectra confirm that these objects are members of the compact groups and have metallicities close to solar, with an average value of 12+log(O/H)approx.8.5. They have average FUV luminosities 7 x 10(exp 40) erg/s, very young ages (< 100 Myr) and two of them resemble tidal dwarf galaxies (TDGs) candidates. We suggest that they were created within gas clouds that were ejected during galaxy-galaxy interactions into the intergalactic medium, which would explain the high metallicities of the objects, inherited from the parent galaxies from which the gas originated. We conduct a search for similar objects in 6 interacting systems with extended HI tails, NGC 2623, NGC 3079, NGC 3359, NGC 3627, NGC 3718, NGC 4656. We found 35 UV sources with ages < 100 Myr, however most of them are on average less luminous/massive than the UV sources found around HCG 92 and 100. We speculate that this might be an environmental effect and that compact groups of galaxies are more favorable to TDG formation than other interacting systems.

Star formation in HI tails: HCG 92, HCG 100 and 6 interacting systems

Abstract: We present new Gemini spectra of 14 new objects found within the HI tails of Hickson Compact Groups 92 and 100. Nine of them are GALEX Far-UV (FUV) and Near-UV (NUV) sources. The spectra confirm that these objects are members of the compact groups and have metallicities close to solar, with an average value of 12+log(O/H)~8.5. They have average FUV luminosities 7 x 10^40 erg/s, very young ages (< 100 Myr) and two of them resemble tidal dwarf galaxies (TDGs) candidates. We suggest that they were created within gas clouds that were ejected during galaxy-galaxy interactions into the intergalactic medium, which would explain the high metallicities of the objects, inherited from the parent galaxies from which the gas originated. We conduct a search for similar objects in 6 interacting systems with extended HI tails, NGC 2623, NGC 3079, NGC 3359, NGC 3627, NGC 3718, NGC 4656. We found 35 UV sources with ages < 100 Myr, however most of them are on average less luminous/massive than the UV sources found around HCG 92 and 100. We speculate that this might be an environmental effect and that compact groups of galaxies are more favorable to TDG formation than other interacting systems.

NGC 2782: a merger remnant with young stars in its gaseous tidal tail

Abstract: We have searched for young star-forming regions around the merger remnant NGC 2782. By using GALEX FUV and NUV imaging and HI data we found seven UV sources, located at distances greater than 26 kpc from the center of NGG 2782, and coinciding with its western HI tidal tail. These regions were resolved in several smaller systems when Gemini/GMOS r-band images were used. We compared the observed colors to stellar population synthesis models and we found that these objects have ages of ~l to ll11yr and masses ranging from 10(exp 3.9) to l0(exp 4.6) Solar Mass. By using Gemini/GMOS spectroscopic data we confirm memberships and derive high metallicities for three of the young regions in the tail (12+log(O/H)=8.74+/-0.20, 8.81+/-0.20 and 8.78+/-0.20). These metallicities are similar to the value presented by the nuclear region of NGG 2782 and also similar to the value presented for an object located close to the main body of NGG 2782. The high metallicities measured for the star-forming regions in the gaseous tidal tail of NGG 2782 could be explained if they were formed out of highly enriched gas which was once expelled from the center of the merging galaxies when the system collided. An additional possibility is that the tail has been a nursery of a few generations of young stellar systems which ultimately polluted this medium with metals, further enriching the already pre-enriched gas ejected to the tail when the galaxies collided.

Morphologies and Substructures of UV Star-Forming Galaxies at Intermediate-z

Abstract: Exploring potential links between the internal physical processes of galaxies with respect to their external morphologies can reveal connections between past and present populations. One primary physical driver of galaxy evolution is star formation, which is directly detected from UV emission. Here, we summarize a study investigating the optical and UV morphologies of rest-frame UV-detected star-forming galaxies at intermediate redshifts (0.1

NGC 2782: a merger remnant with young stars in its gaseous tidal tail

Abstract: We have searched for young star-forming regions around the merger remnant NGC 2782. By using GALEX FUV and NUV imaging and HI data we found seven UV sources, located at distances greater than 26 kpc from the center of NGC 2782, and coinciding with its western HI tidal tail. These regions were resolved in several smaller systems when Gemini/GMOS r-band images were used. We compared the observed colors to stellar population synthesis models and we found that these objects have ages of ~1 to 11 Myr and masses ranging from 10^3.9 to 10^4.6 Msun. By using Gemini/GMOS spectroscopic data we confirm memberships and derive high metallicities for three of the young regions in the tail (12+log(O/H)=8.74\pm0.20, 8.81\pm0.20 and 8.78\pm0.20). These metallicities are similar to the value presented by the nuclear region of NGC 2782 and also similar to the value presented for an object located close to the main body of NGC 2782. The high metallicities measured for the star-forming regions in the gaseous tidal tail of NGC 2782 could be explained if they were formed out of highly enriched gas which was once expelled from the center of the merging galaxies when the system collided. An additional possibility is that the tail has been a nursery of a few generations of young stellar systems which ultimately polluted this medium with metals, further enriching the already pre-enriched gas ejected to the tail when the galaxies collided.

When the Largest Spiral is Formed

Abstract: Abstract We used UV-to-IR archival data to investigate the nature of the giant spiral galaxy, NGC 6872, 65 Mpc away. It belongs to the southern Pavo group and is interacting with a small lenticular galaxy, IC4970. GALEX UV images show a very large part of the galaxy not seen before, making it one of the largest spiral galaxies known, with a physical size greater than 150 kpc. The SED of 17 regions (10 kpc of diameter) across the two arms show a remarkable spatial distribution, as if they were mirror images with respect to their stellar population. However, the last 40 kpc of the northeastern arm are much bluer than any other region of the southwestern one. There is a strong spatial correlation between the NUV luminosity and the distance to the nucleus. The UV data supports the scenario of an interaction at 130 Myr which triggered star formation all over the disk of NGC 6872. The tip of the northeastern arm resembles a tidal dwarf galaxy in the process of formation.