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Register a new userOrphan galaxies in semi-analytic models
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Added by
Facundo Manuel Delfino
Publication date
2021
fields
Physics
and research's language is
English
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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 limited mass resolution, halo finders lose track of their dark matter subhalos and can no longer be distinguished as self-bound overdensities within the larger host system. Since the evolution of orphans depends strongly on the orbit they describe within their host halo, a proper treatment of their evolution is crucial in predicting the distribution of subhalos and satellite galaxies. The model proposed takes into account the dynamical friction drag, mass loss by tidal stripping and a proximity merger criterion, also it is simple enough to be inexpensive from a computational point of view. To calibrate this model, we apply it onto a dark matter only simulation and compare the results with a high resolution simulation, considering the halo mass function and the two-point correlation function as constraints. We show that while the halo mass function fails to put tight constraints on the dynamical friction, the addition of clustering information helps to better define the parameters of the model related to the spatial distribution of subhalos. Using the model with the best fit parameters allows us to reproduce the halo mass function to a precision better than 5 per cent, and the two point correlation function at a precision better than 10 per cent.
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The sterile neutrino is a viable dark matter candidate that can be produced in the early Universe via non-equilibrium processes, and would therefore possess a highly non-thermal spectrum of primordial velocities. In this paper we analyse the process of structure formation with this class of dark matter particles. To this end we construct primordial dark matter power spectra as a function of the lepton asymmetry, $L_6$, that is present in the primordial plasma and leads to resonant sterile neutrino production. We compare these power spectra with those of thermally produced dark matter particles and show that resonantly produced sterile neutrinos are much colder than their thermal relic counterparts. We also demonstrate that the shape of these power spectra is not determined by the free-streaming scale alone. We then use the power spectra as an input for semi-analytic models of galaxy formation in order to predict the number of luminous satellite galaxies in a Milky Way-like halo. By assuming that the mass of the Milky Way halo must be no more than $2times10^{12}M_{odot}$ (the adopted upper bound based on current astronomical observations) we are able to constrain the value of $L_6$ for $M_sle 8$~keV. We also show that the range of $L_6$ that is in best agreement with the 3.5~keV line (if produced by decays of 7~keV sterile neutrino) requires that the Milky Way halo has a mass no smaller than $1.5times10^{12}M_{odot}$. Finally, we compare the power spectra obtained by direct integration of the Boltzmann equations for a non-resonantly produced sterile neutrino with the fitting formula of Viel~et~al. and find that the latter significantly underestimates the power amplitude on scales relevant to satellite galaxies.
We study the correlation between the specific star formation rate of central galaxies and neighbour galaxies, also known as galactic conformity, out to 20 Mpc/h using three semi-analytic models (SAMs, one from L-GALAXIES and other two from GALFORM). The aim is to establish whether SAMs are able to show galactic conformity using different models and selection criteria. In all the models, when the selection of primary galaxies is based on an isolation criterion in real space, the mean fraction of quenched galaxies around quenched primary galaxies is higher than that around star-forming primary galaxies of the same stellar mass. The overall signal of conformity decreases when we remove satellites selected as primary galaxies, but the effect is much stronger in GALFORM models compared with the L-GALAXIES model. We find this difference is partially explained by the fact that in GALFORM once a galaxy becomes a satellite remains as such, whereas satellites can become centrals at a later time in L-GALAXIES. The signal of conformity decreases down to 60% in the L-GALAXIES model after removing central galaxies that were ejected from their host halo in the past. Galactic conformity is also influenced by primary galaxies at fixed stellar mass that reside in dark matter haloes of different masses. Finally, we explore a proxy of conformity between distinct haloes. In this case the conformity is weak beyond ~ 3 Mpc/h (<3% in L-GALAXIES, <1-2% in GALFORM models). Therefore, it seems difficult that conformity is directly related with a long-range effect.
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 a direct comparison between the observed star formation rate functions (SFRF) and the state-of-the-art predictions of semi-analytic models (SAM) of galaxy formation and evolution. We use the PACS Evolutionary Probe Survey (PEP) and Herschel Multi-tiered Extragalactic Survey (HerMES) data-sets in the COSMOS and GOODS-South fields, combined with broad-band photometry from UV to sub-mm, to obtain total (IR+UV) instantaneous star formation rates (SFRs) for individual Herschel galaxies up to z~4, subtracted of possible active galactic nucleus (AGN) contamination. The comparison with model predictions shows that SAMs broadly reproduce the observed SFRFs up to z~2, when the observational errors on the SFR are taken into account. However, all the models seem to under-predict the bright-end of the SFRF at z>2. The cause of this underprediction could lie in an improper modelling of several model ingredients, like too strong (AGN or stellar) feedback in the brighter objects or too low fall-back of gas, caused by weak feedback and outflows at earlier epochs.
We present results for a galaxy formation model that includes a simple treatment for the disruption of dwarf galaxies by gravitational forces and galaxy encounters within galaxy clusters. This is implemented a posteriori in a semi-analytic model by considering the stability of cluster dark matter sub-haloes at z=0. We assume that a galaxy whose dark matter substructure has been disrupted will itself disperse, while its stars become part of the population of intracluster stars responsible for the observed intracluster light. Despite the simplicity of this assumption, our results show a substantial improvement over previous models and indicate that the inclusion of galaxy disruption is indeed a necessary ingredient of galaxy formation models. We find that galaxy disruption suppresses the number density of dwarf galaxies by about a factor of two. This makes the slope of the faint end of the galaxy luminosity function shallower, in agreement with observations. In particular, the abundance of faint, red galaxies is strongly suppressed. As a result, the luminosity function of red galaxies and the distinction between the red and the blue galaxy populations in colour-magnitude relationships are correctly predicted. Finally, we estimate a fraction of intracluster light comparable to that found in clusters of galaxies.
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