text: 315,50,1194335282734227456,23000769,Christopher Conselice,"On the @arxiv on Monday, Amy Whitney (Notts PhD student) et al. released a new paper on the evolution of differential galaxy sizes, accepted to ApJ. A number of things are worth noting in this paper. A thread. (1/n) <LINK> We develop a new method of distinguishing high-z galaxies from foreground galaxies. Because of the Lyman-break, we are able to remove contamination. We call this ""2D Lyman-break imaging""  Example here, 2nd from left is original image, far right, cleaned of foreground. (2/n) <LINK> Using the Petrosian radius, which is independent of distances and surface brightness dimming we can measure how 'inner' and 'outer' parts of galaxies grow with time.  The 'eta' values are the ratio of the surface brightness at a radius to the surface brightness within a radius. <LINK> Taking the difference in the outer and inner radii it is clear that the outer radii are growing at a fast rate than the inner radii at z &lt; 7.  We confirm that this is an actual effect and not a bias by carrying out extensive simulations. (4/n) <LINK> There is more detail in the paper (have a look) but in general this demonstrates that inside-out growth of galaxies is the dominate process for forming galaxies at z=7 down to z=1.  How this happens is another question which we discuss, but minor mergers is one good way. (5/n)",https://arxiv.org/abs/1911.02589,"We present a size analysis of a sample of $\sim$ 49,000 galaxies from the CANDELS GOODS North and South fields using redshift-independent relative surface brightness metrics to determine an unbiased measure of the differential size evolution of galaxies at $1 \leq z \leq 7$. We introduce a novel method of removing foreground objects from distant galaxy ($z > 3$) images that makes use of the Lyman-break at 912{\AA}, in what we call `2-D Lyman-Break Imaging'. The images used are in the rest-frame optical at $z < 3$ and progressively bluer bands at $z > 3$. They are therefore subject to K-correction and cosmological dimming effects which are tested and corrected for. We separately consider a mass-selected sample (with masses in the range 10$^9$M$_{\odot}$$\leq$M$_*$$\leq$10$^{10.5}$M$_{\odot}$) and a number density selected sample (using a constant number density of $n = 1\times10^{-4}$Mpc$^{-3}$). Instead of utilising the commonly used, but potentially biased, effective radii for size measurements, we measure the redshift-independent Petrosian radius, defined by the parameter $\eta$, for each galaxy for three values of $\eta$ and use this as a proxy for size. The evolution of the measured radii can be described by a power-law of the form $R_{Petr} = \alpha(1+z)^\beta$kpc where $\beta < 0$. We find that the outer radius increases more rapidly, suggesting that as a galaxy grows mass is added to its outer regions via an inside-out growth. This growth is stronger for the number density selected sample, with a growth rate of nearly three in the outer radii compared to the inner. We test and confirm these results using a series of image simulations. ","Unbiased Differential Size Evolution and the Inside-Out Growth of