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We forecast the abilities of the Atacama Large Millimeter/submillimeter Array (ALMA) and the Square Kilometer Array (SKA) to detect CO and HI emission lines in galaxies at redshift z=3. A particular focus is set on Milky Way (MW) progenitors at z=3 for their detection within 24 h constitutes a key science goal of ALMA. The analysis relies on a semi-analytic model, which permits the construction of a MW progenitor sample by backtracking the cosmic history of all simulated present-day galaxies similar to the real MW. Results: (i) ALMA can best observe a MW at z=3 by looking at CO(3-2) emission. The probability of detecting a random model MW at 3-sigma in 24 h using 75 km/s channels is roughly 50%, and these odds can be increased by co-adding the CO(3-2) and CO(4-3) lines. These lines fall into ALMA band 3, which therefore represents the optimal choice towards MW detections at z=3. (ii) Higher CO transitions contained in the ALMA bands geq6 will be invisible, unless the considered MW progenitor coincidentally hosts a major starburst or an active black hole. (iii) The high-frequency array of SKA, fitted with 28.8 GHz receivers, would be a powerful instrument for observing CO(1-0) at z=3, able to detect nearly all simulated MWs in 24 h. (iv) HI detections in MWs at z=3 using the low-frequency array of SKA will be impossible in any reasonable observing time. (v) SKA will nonetheless be a supreme ha survey instrument through its enormous instantaneous field-of-view (FoV). A one year pointed HI survey with an assumed FoV of 410 sqdeg would reveal at least 10^5 galaxies at z=2.95-3.05. (vi) If the positions and redshifts of those galaxies are known from an optical/infrared spectroscopic survey, stacking allows the detection of HI at z=3 in less than 24 h.
We present an updated model for the evolution of the orbits of orphan galaxies to be used in the SAG semi-analytical model of galaxy formation and evolution. In cosmological simulations, orphan galaxies are those satellite galaxies for which, due to
We follow the structural evolution of star forming galaxies (SFGs) like the Milky Way by selecting progenitors to z~1.3 based on the stellar mass growth inferred from the evolution of the star forming sequence. We select our sample from the 3D-HST su
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