Title Stope stapanja galaksija Title (english) The merger rate of galaxies Author Filip Huško Mentor Vibor Jelić (mentor)Mentor Krešimir Pavlovski (komentor)Committee member Krešimir Pavlovski (predsjednik povjerenstva)Committee member Vibor Jelić (član povjerenstva)Committee member Maro Cvitan (član povjerenstva)Committee member Ivica Smolić (član povjerenstva)Committee member Matko Milin (član povjerenstva)Granter University of Zagreb Defense date and country 2020-07-20, Croatia Scientific / art field, NATURAL SCIENCES Abstract Predstavljamo rezultate proučavanja stapanja galaksija do crvenih pomaka z = 8, za koje je korišten GALFORM model nastanka galaksija postavljen u simulaciji Planck Millennium. Naša statistika stapanja se dobro slaže s opažanjima. U stopi stapanja i udjelu bliskih parova pronalazimo novu značajku: nagli pad na velikim masama (M_* > 10^11.3 M_⊙ na z = 0) koji se pomiče prema nižim masama na većim crvenim pomacima (M_* > 10^10.5 M_⊙ na z = 4), a rezultat je eksponencijalnog pada brojeva galaksija velikih zvjezdanih masa. Sličan pad se vidi u stopi stapanja i udjelu bliskih parova kao funkcije crvenog pomaka. Uz pomoć stope stapanja i udjela bliskih parova smo izračunali vremensku skalu stapanja te pronašli aproksimativnu funkciju koja dobro opisuje njeno ponašanje. Dobivamo strmiju ovisnost o zvjezdanoj masi nego očekivano (T_mg ∝ M_*^-0.5), no slabu ovisnost o crvenom pomaku, u slaganju s prijašnjim rezultatima. Kao funkcija maksimalne projicirane udaljenosti također pronalazimo strmiju ovisnost nego u prijašnjim studijama (T_mg ∝ r^1.5_max). Pronalazimo da je v_max = 1000 kms^-1 dobar opažački kriterij za maksimalnu brzinu udaljavanja obzirom da vremenska skala stapanja, kao i udio bliskih parova, dostiže maksimum do te vrijednosti. Također smo proučavali rast zvjezdane mase galaksija zbog stapanja (i njegovu relativnu ulogu spram nastanka zvijezda), kao i njihov nestanak stapanjima. Galaksije zvjezdanih masa M_* < 10^10.5 M_⊙ dobivaju maleni udio svoje mase stapanjima (< 10%), dok masivnije galaksije pokazuju strmi rast u ex-situ udjelu na svim crvenim pomacima (do 90% na M_* = 10^11.5 M_⊙). Velika stapanja doprinose minimalno 50% rasta stapanjima za galaksije svih masa i na svim crvenim pomacima, a malena stapanja i akrecija oboje doprinose po 25% ili manje. Proučavajući globalnu populaciju galaksija smo pronašli da u današnjem svemiru 40% zvijezda ima vanjsko podrijetlo (29%, 6.5% i 4.5% od velikih i malenih stapanja te akrecije, redom), dok taj udio pada na 5% do z = 4. Udio galaksija nestalih stapanjima je otprilike konstantan kao funkcija zvjezdane mase, te iznosi 30% na z = 0 i 1 - 5% na z = 4.
Abstract (english) We present a study of mergers up to z = 8 using the GALFORM semi-analytical model set in the Planck Millennium simulation. Our merger statistics agrees well with observations. We find a new feature in the merger rate and close pair fraction of galaxies: a sharp decrease for massive galaxies (M_* > 10^11.3 M_⊙ at z = 0), with the position of this drop moving to lower-mass galaxies at higher redshifts (M_* > 10^10.5 M_⊙ at z = 4). This fall is due to the exponential drop in numbers of massive galaxies. As a result, we also predict merger rates and close pair fractions that turn over as functions of redshift. Using merger rates and close pair fractions we calculate a fitting formula for the major merger timescale. We find a steeper dependence on stellar mass than expected (T_mg ∝ M_*^-0.5), and weak dependence on redshift, in agreement with previous results. As a function of the maximal projected separation, we also find a steeper dependence than before (T_mg ∝ r^1.5_max), although this is not surprising since projected close pair counts are expected to scale as f ∝ r^2_max. We find that v_max = 1000 kms^-1 is a good observational cut-off for separation velocities since close pair fractions (and thus merger timescales) saturate by this value. We also studied the stellar mass growth of galaxies due to mergers (and its role in comparison with star formation), as well as the loss of galaxies through merging. Galaxies with M_* < 10^10.5 M^_⊙ gain a small fraction of their mass through mergers (< 10%), while massive galaxies show a steep growth in their ex-situ fraction (up to 90% for M_* = 10^11.5 M_⊙). Major mergers contribute at least 50% of merger growth for galaxies of all masses and at all redshifts, with minor mergers and accretion each contributing 25% or less. We find that 40% of all stellar mass has an external origin (29%, 6.5% i 4.5% gained through major mergers, minor mergers and accretion, respectively), with this fraction dropping to 5% by z = 4. The fraction of galaxies lost through mergers is approximately constant with stellar mass and is 30% at z = 0 and 1 - 5% at z = 4.
Keywords
galaksije
nastanak
evolucija
interakcije
statistika
Keywords (english)
galaxies
formation
evolution
interactions
statistics
Language croatian URN:NBN urn:nbn:hr:217:257587 Study programme Title: Physics; specializations in: Research Type of resource Text File origin Born digital Access conditions Open access Terms of use Created on 2021-05-03 09:30:03
