1307.4758
Stars were born in significantly denser regions in the early Universe
Shirazi, Brinchmann, Rahmati
The density of the warm ionized gas in high-z galaxies is known to be higher than what is typical in local galaxies on similar scales. At the same time, the mean global properties of the high- and low-redshift galaxies are quite different. Present a detailed differential analysis of the ionization parameters of 14 star forming galaxies at redshift 2.6-3.4, compiled from the literature. For each of those high-z galaxies, construct a comparison sample of low-z galaxies closely matched in specific SFR and stellar mass, thus ensuring that their global physical conditions are similar to the high-z galaxy. Find that the median log [OII] 3727/[OIII] 5007 line ratio of the high-z galaxies is 0.5 dex higher than their local counterparts. Construct a new calibration between the [OII] 3727 / [OIII] 5007 emission line ratio and ionization parameter to estimate the difference between the ionization parameters in the high and low-redshift samples. Using this, show that the typical density of the warm ionized gas in SF regions decreases by a median factor of 8 from z~3.3 to z~0 at fixed mass and sSFR. Show that metallicity differences can not explain the observed density differences. Because the high- and low-z samples are comparable in size, infer that the relationship between SFR density and gas density must have been significantly less efficient at z~2-3 than what is observed in nearby galaxies with similar levels of SF activity.
1307.4759
The LS2S Galaxy-scale Lens sample. IV. The dependence of the total mass density profile of early-type galaxies on redshift, stellar mass, and size
Sonnenfeld, Treu, .. Suyu, Marshall, ... et al
Optical and NIR spectroscopy of 36 secure SL and 17 candidates as part of SL2S survey. The deflectors are massive early-type galaxies in 0.2<z<0.8, while the lensed sources are 1<z<3.5. Combine data with photometric and lensing measurements presented in paper III and with lenses from SLACS and LSD surveys to investigate the cosmic evolution of the internal structure of massive early-type galaxies over half the age of the universe. Study the dependence of the slope of the total mass density profile gamma' (rho(r) ~ r^{-gamma'}) on M*, size, and redshift. Find that two parameters are sufficient to determine gamma' with less than 6% residual scatter. At fixed redshift, gamma' depends solely on the surface stellar mass density: d gamma'/ d Sigma* = 0.38 pm 0.07. At fixed M* and R_eff, gamma' depends on redshift: galaxies at lower z have steeper slopes (d gamma' / d z = -0.31). However, the mean redshift evolution of gamma' for an individual galaxy is consistent with zero d gamma' / dz = -0.10pm0.12. This result is obtained by combining the measured dependencies of gamma' on z, M*, R_eff with the evolution of the R_eff-M* taken from the literature, and is broadly consistent with current models of the formation and evolution of massive early-type galaxies. Detailed quantitative comparisons of our results with theory will provide qualitatively new information on the detailed physical processes at work.
1307.4762
Modelling the nucleosynthetic properties of carbon-enhanced metal-poor RR Lyrae stars
Stancliffe, Kennedy, Lau, Beers
Certain C-enhanced metal-poor stars likely obtained their composition via pollution from some of the earliest generations of AGB stars and as such provide important clues to early Universe nucleosynthesis. Recently, Kinman+ discovered that the highly C- and Ba-enriched metal-poor star SDSS J1707+58 is in fact an RR Lyrae pulsator. This gives an object in a definite evolutionary state where the effects of dilution of material during the MS are minimised owing to the object having passed through first dredge-up. Perform detailed stellar modeling of putative progenitor systems in which .. accreted material from AGB stars in the mass range 1-2 Msun. Investigate how the surface abundances are affected by the inclusion of mechanisms like thermohaline mixing and gravitational settling. Able to find a reasonable fit to the C and Na abundances of the star, suggesting accretion of around 0.1 Msun from a 2 Msun companion, but the Sr and Ba abundances remain problematic and this object may have experienced something other than a standard s process. More success in fitting the abundances of the mildly C-enriched, metal-poor RR Lyrae pulsator TY Gru, which suggest received 0.1 Msun of material from a companion of around 1 Msun.
1307.4764
The SL2S galaxy-scale lens sample. III. Lens models, surface photometry and stellar masses for the final sample
Sonnenfeld, Gavazzi, Suyu, Treu, Marshall
HST imaging data and CHFT NIR images for the final sample of 56 galaxy-scale lenses in the CFHTLS as part of the SL in the Legacy survey (SL2S) project. The new images are used to perform lens modeling, measure surface photometry, and estimate stellar masses of the deflector early-type galaxies. Lens modeling is performed on the HST images (or CFHT when HST not available) by fitting the spatially extended light distribution of the lensed features assuming a singular isothermal ellipsoid mass profile and by reconstructing the intrinsic source light distribution on a pixelized grid. Based on the analysis of systematic uncertainties and comparison with inference based on different methods, estimate that the Einstein Radii are accurate to ~3%. HST imaging provides a much higher success rate in confirming gravitational lenses and measuring their Einstein radii than CFHT imaging does. Lens modeling with ground-based images, however, when successful, yields Einstein radius measurements that are competitive with spaced-based images. Information from the lens models is used together with spectroscopic information from the companion paper IV to classify the systems, resulting in a final sample of 39 confirmed (grade-A) lenses and 17 promising candidates. The redshifts of the main deflector span a range 0.3 < z<0.8, providing and excellent sample for the study of the cosmic evolution of the mass distribution of early-type galaxies over the second half of the history of the Universe.
Stars were born in significantly denser regions in the early Universe
Shirazi, Brinchmann, Rahmati
The density of the warm ionized gas in high-z galaxies is known to be higher than what is typical in local galaxies on similar scales. At the same time, the mean global properties of the high- and low-redshift galaxies are quite different. Present a detailed differential analysis of the ionization parameters of 14 star forming galaxies at redshift 2.6-3.4, compiled from the literature. For each of those high-z galaxies, construct a comparison sample of low-z galaxies closely matched in specific SFR and stellar mass, thus ensuring that their global physical conditions are similar to the high-z galaxy. Find that the median log [OII] 3727/[OIII] 5007 line ratio of the high-z galaxies is 0.5 dex higher than their local counterparts. Construct a new calibration between the [OII] 3727 / [OIII] 5007 emission line ratio and ionization parameter to estimate the difference between the ionization parameters in the high and low-redshift samples. Using this, show that the typical density of the warm ionized gas in SF regions decreases by a median factor of 8 from z~3.3 to z~0 at fixed mass and sSFR. Show that metallicity differences can not explain the observed density differences. Because the high- and low-z samples are comparable in size, infer that the relationship between SFR density and gas density must have been significantly less efficient at z~2-3 than what is observed in nearby galaxies with similar levels of SF activity.
1307.4759
The LS2S Galaxy-scale Lens sample. IV. The dependence of the total mass density profile of early-type galaxies on redshift, stellar mass, and size
Sonnenfeld, Treu, .. Suyu, Marshall, ... et al
Optical and NIR spectroscopy of 36 secure SL and 17 candidates as part of SL2S survey. The deflectors are massive early-type galaxies in 0.2<z<0.8, while the lensed sources are 1<z<3.5. Combine data with photometric and lensing measurements presented in paper III and with lenses from SLACS and LSD surveys to investigate the cosmic evolution of the internal structure of massive early-type galaxies over half the age of the universe. Study the dependence of the slope of the total mass density profile gamma' (rho(r) ~ r^{-gamma'}) on M*, size, and redshift. Find that two parameters are sufficient to determine gamma' with less than 6% residual scatter. At fixed redshift, gamma' depends solely on the surface stellar mass density: d gamma'/ d Sigma* = 0.38 pm 0.07. At fixed M* and R_eff, gamma' depends on redshift: galaxies at lower z have steeper slopes (d gamma' / d z = -0.31). However, the mean redshift evolution of gamma' for an individual galaxy is consistent with zero d gamma' / dz = -0.10pm0.12. This result is obtained by combining the measured dependencies of gamma' on z, M*, R_eff with the evolution of the R_eff-M* taken from the literature, and is broadly consistent with current models of the formation and evolution of massive early-type galaxies. Detailed quantitative comparisons of our results with theory will provide qualitatively new information on the detailed physical processes at work.
1307.4762
Modelling the nucleosynthetic properties of carbon-enhanced metal-poor RR Lyrae stars
Stancliffe, Kennedy, Lau, Beers
Certain C-enhanced metal-poor stars likely obtained their composition via pollution from some of the earliest generations of AGB stars and as such provide important clues to early Universe nucleosynthesis. Recently, Kinman+ discovered that the highly C- and Ba-enriched metal-poor star SDSS J1707+58 is in fact an RR Lyrae pulsator. This gives an object in a definite evolutionary state where the effects of dilution of material during the MS are minimised owing to the object having passed through first dredge-up. Perform detailed stellar modeling of putative progenitor systems in which .. accreted material from AGB stars in the mass range 1-2 Msun. Investigate how the surface abundances are affected by the inclusion of mechanisms like thermohaline mixing and gravitational settling. Able to find a reasonable fit to the C and Na abundances of the star, suggesting accretion of around 0.1 Msun from a 2 Msun companion, but the Sr and Ba abundances remain problematic and this object may have experienced something other than a standard s process. More success in fitting the abundances of the mildly C-enriched, metal-poor RR Lyrae pulsator TY Gru, which suggest received 0.1 Msun of material from a companion of around 1 Msun.
1307.4764
The SL2S galaxy-scale lens sample. III. Lens models, surface photometry and stellar masses for the final sample
Sonnenfeld, Gavazzi, Suyu, Treu, Marshall
HST imaging data and CHFT NIR images for the final sample of 56 galaxy-scale lenses in the CFHTLS as part of the SL in the Legacy survey (SL2S) project. The new images are used to perform lens modeling, measure surface photometry, and estimate stellar masses of the deflector early-type galaxies. Lens modeling is performed on the HST images (or CFHT when HST not available) by fitting the spatially extended light distribution of the lensed features assuming a singular isothermal ellipsoid mass profile and by reconstructing the intrinsic source light distribution on a pixelized grid. Based on the analysis of systematic uncertainties and comparison with inference based on different methods, estimate that the Einstein Radii are accurate to ~3%. HST imaging provides a much higher success rate in confirming gravitational lenses and measuring their Einstein radii than CFHT imaging does. Lens modeling with ground-based images, however, when successful, yields Einstein radius measurements that are competitive with spaced-based images. Information from the lens models is used together with spectroscopic information from the companion paper IV to classify the systems, resulting in a final sample of 39 confirmed (grade-A) lenses and 17 promising candidates. The redshifts of the main deflector span a range 0.3 < z<0.8, providing and excellent sample for the study of the cosmic evolution of the mass distribution of early-type galaxies over the second half of the history of the Universe.
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