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The catastrophic effect of mergers on the angular momentum and morphology of galaxies in EAGLE | | Claudia del P. Lagos
; Adam R.H. Stevens
; Richard G. Bower
; Timothy A. Davis
; Sergio Contreras
; Nelson D. Padilla
; Danail Obreschkow
; Darren Croton
; James W. Trayford
; Charlotte Welker
; Tom Theuns
; | | Date: |
16 Jan 2017 | | Abstract: | We use EAGLE to explore the effect galaxy mergers have on the stellar
specific angular momentum of galaxies, $j_{
m stars}$. We characterise mergers
into: dry (gas-poor)/wet (gas-rich), major/minor, and by different spin
alignments and orbital parameters. Our wet (dry) mergers have an average
neutral gas fraction (i.e. the ratio between the neutral gas and the stellar
masses of the merging system) of $1.1$ ($0.02$), while minor (major) mergers
are those with stellar mass ratios between the secondary and primary galaxy in
the range $0.1-0.3$ ($ge 0.3$). We correlate the positions of galaxies in the
$j_{
m stars}$-stellar mass plane at $z=0$ with their merger history, and find
that galaxies of low spins suffered dry mergers, while galaxies of normal/high
spins suffered predominantly wet mergers, if any at all. The radial $j_{
m
stars}$ profiles of galaxies that went through dry mergers are deficient by
$approx 0.3$~dex at $rlesssim 10,r_{50}$ compared to galaxies that went
through wet mergers. By studying galaxies before and after mergers, we find
that dry mergers reduce $j_{
m stars}$ by $approx 30$%, while wet mergers
increase it by $approx 10$%, on average. The latter is connected to the
build-up of the central stellar over-density by newly formed stars of high
rotational speed. Moving from minor to major mergers mostly accentuates the
effects above. When the spin vectors of the galaxies prior to the dry merger
are misaligned, $j_{
m stars}$ decreases to a greater magnitude, while in wet
mergers, co-rotation and high orbital angular momentum lead to the largest
$j_{
m stars}$ increase. We make predictions for what would be the
observational signatures in the mean $j_{
m stars}$ profiles driven by dry
mergers: (i) shallow radial profiles and (ii) profiles that continue to rise
beyond $approx 10,r_{50}$, both of which are significantly different from
spiral galaxies. | | Source: | arXiv, 1701.4407 | | Services: | Forum | Review | PDF | Favorites | |
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