Energetic feedback due to active galactic nuclei (AGNs) is likely to play an important role in the observed antihierarchical trend in the evolution of galaxies, and yet the energy injected into the circumgalactic medium by this process is largely unknown. One promising approach to constrain this feedback is through measurements of spectral distortions in the cosmic microwave background due to the thermal Sunyaev-Zeldovich (tSZ) effect, whose magnitude is directly proportional to the energy input by AGNs. With current instruments, making such measurements requires stacking large numbers of objects to increase signal-to-noise. While one possible target for such stacks is AGNs themselves, these are relatively scarce sources that contain contaminating emission that complicates tSZ measurements. Here we adopt an alternative approach and co-add South Pole Telescope SZ (SPT-SZ) survey data around a large set of massive quiescent elliptical galaxies at  z 0.5, which are much more numerous and less contaminated than active AGNs, yet are subject to the same feedback processes from the AGNs they hosted in the past. We use data from the Blanco Cosmology Survey and VISTA Hemisphere Survey to create a large catalog of galaxies split up into two redshift bins: one with 3394 galaxies at   z 0.5 1.0 and one with 924 galaxies at   z 1.0 1.5, with typical stellar masses of´ M 1.5 10 . 11We then co-add the emission around these galaxies, resulting in a measured tSZ signal at s 2.2 significance for the lower redshift bin and a contaminating signal at s 1.1 for the higher redshift bin. To remove contamination due to dust emission, we use SPT-SZ source counts to model a contaminant source population in both the SPT-SZ bands and Planck highfrequency bands for a subset of 937 galaxies in the low-redshift bin and 240 galaxies in the high-redshift bin. This increases our detection to s 3.6 for low redshifts and s 0.9 for high redshifts. We find the mean angularly integrated Compton-y values to be- 60 erg, respectively. These numbers are higher than expected from simple theoretical models that do not include AGN feedback, and serve as constraints that can be applied to current simulations of massive galaxy formation.

As the Earth's climate has changed, Arctic sea ice extent has decreased drastically. It is likely that the late-summer Arctic will be ice-free as soon as the 2030s. This loss of sea ice represents one of the most severe positive feedbacks in the climate system, as sunlight that would otherwise be reflected by sea ice is absorbed by open ocean. It is unlikely that CO 2 levels and mean temperatures can be decreased in time to prevent this loss, so restoring sea ice artificially is an imperative. Here we investigate a means for enhancing Arctic sea ice production by using wind power during the Arctic winter to pump water to the surface, where it will freeze more rapidly. We show that where appropriate devices are employed, it is possible to increase ice thickness above natural levels, by about 1 m over the course of the winter. We examine the effects this has in the Arctic climate, concluding that deployment over 10% of the Arctic, especially where ice survival is marginal, could more than reverse current trends of ice loss in the Arctic, using existing industrial capacity. We propose that winter ice thickening by wind-powered pumps be considered and assessed as part of a multipronged strategy for restoring sea ice and arresting the strongest feedbacks in the climate system.

We present stellar evolution models for 0.5 -1.2 M ⊙ at scaled metallicities of 0.1 -1.5 Z ⊙ and O/Fe values of 0.44 -2.28 O/Fe ⊙ . The time dependent evolution of habitable zone boundaries are calculated for each stellar evolution track based on stellar mass, effective temperature, and luminosity parameterizations. The rate of change of stellar surface quantities and the surrounding habitable zone position are strong functions of all three quantities explored. The range of orbits that remain continuously habitable, or habitable for at least 2 Gyr, are provided. The results show that the detailed chemical characterization of exoplanet host stars and a consideration of their evolutionary history are necessary to assess the likelihood that a planet found in the instantaneous habitable zone has had sufficient time to develop a biosphere capable of producing detectable biosignatures. This model grid is designed for use by the astrobiology and exoplanet communities to efficiently characterize the time evolution of host stars and their habitable zones for planetary candidates of interest.

The catalog of stellar evolution tracks discussed in our previous work is meant to help characterize exoplanet host-stars of interest for follow-up observations with future missions like JWST. However, the utility of the catalog has been predicated on the assumption that we would precisely know the age of the particular host-star in question; in reality, it is unlikely that we will be able to accurately estimate the age of a given system. Stellar age is relatively straightforward to calculate for stellar clusters, but it is difficult to accurately measure the age of an individual star to high precision. Unfortunately, this is the kind of information we should consider as we attempt to constrain the long-term habitability potential of a given planetary system of interest. This is ultimately why we must rely on predictions of accurate stellar evolution models, as well a consideration of what we can observably measure (stellar mass, composition, orbital radius of an exoplanet) in order to create a statistical framework wherein we can identify the best candidate systems for follow-up characterization. In this paper we discuss a statistical approach to constrain long-term planetary habitability by evaluating the likelihood that at a given time of observation, a star would have a planet in the 2 Gy continuously habitable zone (CHZ 2 ). Additionally, we will discuss how we can use existing observational data (i.e. data assembled in the Hypatia catalog and the Kepler exoplanet host star database) for a robust comparison to the catalog of theoretical stellar models.

We directly measure the thermal energy of the gas surrounding galaxies through the thermal Sunyaev-Zel'dovich (tSZ) effect. We perform a stacking analysis of microwave background images from the Atacama Cosmology Telescope, around 1179 massive quiescent elliptical galaxies at 0.5 ≤ z ≤ 1.0 ("low-z") and 3274 galaxies at 1.0 ≤ z ≤ 1.5 ("high-z"), selected using data from the Wide-Field Infrared Survey Explorer All-Sky Survey and the Sloan Digital Sky Survey (SDSS) within the SDSS Stripe-82 field. The gas surrounding these galaxies is expected to contain energy from past episodes of active galactic nucleus (AGN) feedback, and after using modeling to subtract undetected contaminants, we detect a tSZ signal at a significance of 0.9σ for our low-z galaxies and 1.8σ for our high-z galaxies. We then include data from the high-frequency Planck bands for a subset of 227 low-z galaxies and 529 high-z galaxies and find low-z and high-z tSZ detections of 1.0σ and 1.5σ, respectively. These results indicate an average thermal heating around these galaxies of (5.6 +5.9 −5.6 ) × 10 60 erg for our low-z galaxies and (7.0 +4.7 −4.4 ) × 10 60 erg for our high-z galaxies. Based on simple heating models, these results are consistent with gravitational heating without additional heating due to AGN feedback.