A CANDELS - 3D-HST Synergy: Resolved Star Formation Patterns at 0.7 < z < 1.5

Abstract: We analyze the resolved stellar populations of 473 massive star-forming galaxies at 0.7 < z < 1.5, with multi-wavelength broad-band imaging from CANDELS and Halpha 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 Halpha 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 Halpha dust corrections, which accounts for extra extinction towards HII regions. The prescription leads to consistent SFR estimates and reproduces the observed relation between the Halpha/UV luminosity ratio and visual extinction, both on a pixel-by-pixel and on 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 towards lower equivalent widths are found in the inner regions of galaxies. Clumps and spiral features, on the other hand, are associated with enhanced Halpha equivalent widths, bluer colors, and higher specific star formation rates compared to the underlying disk. Their Halpha/UV luminosity ratio is lower than that of the underlying disk, suggesting 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.

A CANDELS - 3D-HST Synergy: Resolved Star Formation Patterns at 0.7 < z < 1.5

The paper titled "A CANDELS - 3D-HST synergy: resolved star formation patterns at $0.7 < z < 1.5$" presents an in-depth analysis of resolved stellar populations in approximately 473 massive star-forming galaxies, utilizing a combination of multi-band imaging from the CANDELS survey and H$\alpha$ surface brightness profiles obtained via the 3D-HST program. The primary goal is to elucidate the distribution of star formation activity within galaxies during the epoch $0.7 < z < 1.5$, a period critical for understanding the transition from the peak of cosmic star formation to its subsequent decline. This investigation leverages the high spatial resolution provided by HST imaging coupled with emission line mapping via grism spectroscopy, affording unique insights into the assembly of stellar mass and the environments in which new stars are born within these distant galaxies.

Key Findings

• Morphological Correlation: The H$\alpha$ morphologies of the examined galaxies exhibit closer resemblance to those observed in ACS $I$-band imaging compared to WFC3 $H$-band imaging, especially in larger systems. This suggests that rest-UV light and H$\alpha$ emission are predominantly governed by young stellar populations, whereas rest-optical light is more representative of the overall stellar mass distribution.

• Dust Correction Model: A significant contribution of the study is the derivation of a novel method for dust correction of H$\alpha$ emission. The authors argue for additional extinction towards HII regions compared to the diffuse interstellar medium, proposing a formula that results in internally consistent SFR estimates across different tracers.

• Resolved Main Sequence: The paper identifies a correlation between star formation surface density and the assembled stellar mass density within galaxies, akin to the 'main sequence of star formation' seen on a global scale. Deviations from this trend are primarily observed in inner galactic regions showing lower equivalent widths, while clumps and spiral arms demonstrate elevated specific star formation rates.

• Implications of Substructure: Analysis of clumps and spiral features reveals that these regions, although exhibiting enhanced star formation activity, contribute a modest percentage (10-15%) to the total star formation rate when integrated across the galaxy. Most star formation in this redshift range occurs in the disk component rather than concentrated in these high luminosity regions.

Implications and Future Directions

The study underscores the importance of spatially-resolved analyses for advancing our understanding of galaxy evolution. The techniques and insights provided by the CANDELS and 3D-HST synergy offer crucial empirical constraints on models of star formation, dust attenuation, and structural evolution in galaxies. Practically, this enriched understanding aids in refining theoretical models related to galaxy formation and growth, particularly regarding the mechanisms that drive star formation efficiency and structural morphologies over cosmic time.

Future developments, particularly the integration of longer wavelength observations from facilities like ALMA and NOEMA, are positioned to expand upon these findings. Such advancements will facilitate probing the distribution and dynamics of cold gas within galaxies and further disentangle the effects of dust extinction. As the field progresses towards these capabilities, more intricate studies will elucidate the role of molecular gas and its interplay with stellar components, yielding a more cohesive picture of galaxy evolution in the high-redshift universe.