We analyze the resolved stellar populations of 473 massive star-forming galaxies at 0.7 {lt} z {lt} 1.5, with multi-wavelength broadband imaging from CANDELS and H{$α$} surface brightness profiles... Show moreWe analyze the resolved stellar populations of 473 massive star-forming galaxies at 0.7 {lt} z {lt} 1.5, with multi-wavelength broadband imaging from CANDELS and H{$α$} surface brightness profiles at the same kiloparsec resolution from 3D-HST. Together, this unique data set sheds light on how the assembled stellar mass is distributed within galaxies, and where new stars are being formed. We find the H{$α$} morphologies to resemble more closely those observed in the ACS I band than in the WFC3 H band, especially for the larger systems. We next derive a novel prescription for H{$α$} dust corrections, which accounts for extra extinction toward H II regions. The prescription leads to consistent star formation rate (SFR) estimates and reproduces the observed relation between the H{$α$}/UV luminosity ratio and visual extinction, on both a pixel-by-pixel and a galaxy-integrated level. We find the surface density of star formation to correlate with the surface density of assembled stellar mass for spatially resolved regions within galaxies, akin to the so-called ''main sequence of star formation'' established on a galaxy-integrated level. Deviations from this relation toward lower equivalent widths are found in the inner regions of galaxies. Clumps and spiral features, on the other hand, are associated with enhanced H{$α$} equivalent widths, bluer colors, and higher specific SFRs compared to the underlying disk. Their H{$α$}/UV luminosity ratio is lower than that of the underlying disk, suggesting that the ACS clump selection preferentially picks up those regions of elevated star formation activity that are the least obscured by dust. Our analysis emphasizes that monochromatic studies of galaxy structure can be severely limited by mass-to-light ratio variations due to dust and spatially inhomogeneous star formation histories. Show less
The central parsec around the supermassive black hole in the Galactic center (GC) hosts more than 100 young and massive stars. Outside the central cusp (R ~ 1'') the majority of these O and Wolf... Show moreThe central parsec around the supermassive black hole in the Galactic center (GC) hosts more than 100 young and massive stars. Outside the central cusp (R ~ 1'') the majority of these O and Wolf-Rayet (W-R) stars reside in a main clockwise system, plus a second, less prominent disk or streamer system at large angles with respect to the main system. Here we present the results from new observations of the GC with the AO-assisted near-infrared imager NACO and the integral field spectrograph SINFONI on the ESO/VLT. These include the detection of 27 new reliably measured W-R/O stars in the central 12'' and improved measurements of 63 previously detected stars, with proper motion uncertainties reduced by a factor of 4 compared to our earlier work. Based on the sample of 90 well measured W-R/O stars, we develop a detailed statistical analysis of their orbital properties and orientations. We show that half of the W-R/O stars are compatible with being members of a clockwise rotating system. The rotation axis of this system shows a strong transition from the inner to the outer regions as a function of the projected distance from Sgr A*. The main clockwise system either is either a strongly warped single disk with a thickness of about 10°, or consists of a series of streamers with significant radial variation in their orbital planes. Eleven out of 61 clockwise moving stars have an angular separation of more than 30° from the local angular momentum direction of the clockwise system. The mean eccentricity of the clockwise system is 0.36 ± 0.06. The distribution of the counterclockwise W-R/O star is not isotropic at the 98% confidence level. It is compatible with a coherent structure such as stellar filaments, streams, small clusters or possibly a disk in a dissolving state: 10 out of 29 counterclockwise moving W-R/O stars have an angular separation of more than 30° from the local angular momentum direction of the counterclockwise system. The observed disk warp and the steep surface density distribution favor in situ star formation in gaseous accretion disks as the origin of the young massive stars. Show less
Franceschini, A.; Berta, S.; Rigopoulou, D.; Aussel, H.; Cesarsky, C.J.; Elbaz, D.; ... ; Werf, P.P. van der 2003
