2004.08397
The origin and evolution of Lyman-alpha Blobs in cosmological galaxy formation simulations
Kimock, et al
High-redshift Lyman-alpha blobs (LABs) are an enigmatic class of objects that have been the subject of numerous observational and theoretical investigations. It is of particular interest to determine the dominant power sources for the copious luminosity, as direct emission from HII regions, cooling gas, and fluorescence due to the presence of active galactic nuclei (AGN) can all contribute significantly. In this paper, we present the first theoretical model to consider all of these physical processes in an attempt to develop an evolutionary model for the origin of high-z LABs. This is achieved by combining a series of high-resolution cosmological zoom-in simulations with ionization and Lyman-alpha (Lya) radiative transfer models. We find that massive galaxies display a range of Lya luminosities and spatial extents (which strongly depend on the limiting surface brightness used) over the course of their lives, though regularly exhibit luminosities and sizes consistent with observed LABs. The model LABs are typically powered from a combination of recombination in star-forming galaxies, as well as cooling emission from gas associated with accretion. When AGN are included in the model, the fluorescence caused by AGN-driven ionization can be a significant contributor to the total Lya luminosity as well. We propose that the presence of an AGN may be predicted from the Gini coefficient of the blob's surface brightness. Within our modeled mass range, there are no obvious threshold physical properties that predict appearance of LABs, and only weak correlations of the luminosity with the physical properties of the host galaxy. This is because the emergent Lya luminosity from a system is a complex function of the gas temperature, ionization state, and Lya escape fraction.
The origin and evolution of Lyman-alpha Blobs in cosmological galaxy formation simulations
Kimock, et al
High-redshift Lyman-alpha blobs (LABs) are an enigmatic class of objects that have been the subject of numerous observational and theoretical investigations. It is of particular interest to determine the dominant power sources for the copious luminosity, as direct emission from HII regions, cooling gas, and fluorescence due to the presence of active galactic nuclei (AGN) can all contribute significantly. In this paper, we present the first theoretical model to consider all of these physical processes in an attempt to develop an evolutionary model for the origin of high-z LABs. This is achieved by combining a series of high-resolution cosmological zoom-in simulations with ionization and Lyman-alpha (Lya) radiative transfer models. We find that massive galaxies display a range of Lya luminosities and spatial extents (which strongly depend on the limiting surface brightness used) over the course of their lives, though regularly exhibit luminosities and sizes consistent with observed LABs. The model LABs are typically powered from a combination of recombination in star-forming galaxies, as well as cooling emission from gas associated with accretion. When AGN are included in the model, the fluorescence caused by AGN-driven ionization can be a significant contributor to the total Lya luminosity as well. We propose that the presence of an AGN may be predicted from the Gini coefficient of the blob's surface brightness. Within our modeled mass range, there are no obvious threshold physical properties that predict appearance of LABs, and only weak correlations of the luminosity with the physical properties of the host galaxy. This is because the emergent Lya luminosity from a system is a complex function of the gas temperature, ionization state, and Lya escape fraction.
2004.08502
On aging star clusters using red supergiants independent of the fraction of interacting binary stars
Elridge, et al
We use the Binary Population and Spectral Synthesis (BPASS) models to test the recent suggestion that red supergiants can provide an accurate age estimate of a co-eval stellar population that is unaffected by interacting binary stars. Ages are estimated by using both the minimum luminosity red supergiant and the mean luminosity of red supergiants in a cluster. We test these methods on a number of observed star clusters and find our results in agreement with previous estimates. Importantly we find the difference between the ages derived from stellar population models with and without a realistic population of interacting binary stars is only a few 100,000 years at most. We find that the mean luminosity of red supergiants in a cluster is the best method to determine the age of a cluster because it is based o the entire red supergiant population rather than using only the least luminous red supergiant.
2004.09077
On the role of reduced wind mass-loss rate in enabling exoplanets to shape planetary nebulae
Hegazi, Bear, Soker
We use the stellar evolution code MESA-binary and follow the evolution of six exoplanets to determine their potential role in the future evolution of their parent star on the red giant branch (RGB) and on the asymptotic giant branch (AGB). We limit this study to planets with orbits that have semi-major axis of 1AU<a<20AU, a high eccentricity, e>0.25, and having a parent star of mass M>1Mo. We find that the star HIP 75458 will engulf its planet HIP75458 b during its RGB phase. The planet will remove the envelope and terminate the RGB evolution, leaving a bare helium core of mass 0.4Mo that will evolve to form a helium white dwarf. Only in one system out of six, the planet beta Pic c will enter the envelope of its parent star during the AGB phase. For that to occur, we have to reduce the wind mass-loss rate by a factor of about four from its commonly used value. This strengthens an early conclusion, which was based on exoplanets with circular orbits, that states that to have a non-negligible fraction of AGB stars that engulf planets we should consider lower wind mass-loss rates of isolated AGB stars (before they are spun-up by a companion). Such an engulfed planet might lead to the shaping of the AGB mass-loss geometry to form an elliptical planetary nebula.
2004.09401
Galaxy cluster contribution to the diffuse extragalactic ultraviolet background
Welch, McCandiss, Coe
The diffuse ultraviolet background radiation has been mapped over most of the sky with 2\arcmin \ resolution using data from the \textit{GALEX} survey. We utilize this map to study the correlation between the UV background and clusters of galaxies discovered via the Sunyaev-Zeldovich effect in the \textit{Planck} survey. We use only high Galactic latitude ($|b| > 60^{\circ} $) galaxy clusters to avoid contamination by Galactic foregrounds, and we only analyze clusters with a measured redshift. This leaves us with a sample of 142 clusters over the redshift range $0.02 \leq z \leq 0.72$, which we further subdivide into four redshift bins. In analysing our stacked samples binned by redshift, we find evidence for a central excess of UV background light compared to local backgrounds for clusters with $z<0.3$. We then stacked these $z<0.3$ clusters to find a statistically significant excess of $12 \pm 2.3$ photon cm$^{-2}$ s${-1}$ sr$^{-1}$ \AA $^{-1}$ \ over the median of $\sim 380$ photon cm$^{-2}$ s${-1}$ sr$^{-1}$ \AA $^{-1}$ \ measured around random blank fields. We measure the stacked radial profile of these clusters, and find that the excess UV radiation decays to the level of the background at a radius of $\sim 1$ Mpc, roughly consistent with the maximum radial extent of the clusters. Analysis of possible physical processes contributing to the excess UV brightness indicates that non-thermal emission from relativistic electrons in the intracluster medium and faint, unresolved UV emission from cluster member galaxies and intracluster light are likely the dominant contributors.
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