387 research outputs found
NIHAO XX: The impact of the star formation threshold on the cusp-core transformation of cold dark matter haloes
We use cosmological hydrodynamical galaxy formation simulations from the
NIHAO project to investigate the impact of the threshold for star formation on
the response of the dark matter (DM) halo to baryonic processes. The fiducial
NIHAO threshold, , results in strong expansion of the DM
halo in galaxies with stellar masses in the range . We find that lower thresholds such as (as employed
by the EAGLE/APOSTLE and Illustris/AURIGA projects) do not result in
significant halo expansion at any mass scale. Halo expansion driven by
supernova feedback requires significant fluctuations in the local gas fraction
on sub-dynamical times (i.e., < 50 Myr at galaxy half-light radii), which are
themselves caused by variability in the star formation rate. At one per cent of
the virial radius, simulations with have gas fractions of
and variations of , while simulations have order of
magnitude lower gas fractions and hence do not expand the halo. The observed DM
circular velocities of nearby dwarf galaxies are inconsistent with CDM
simulations with and , but in reasonable agreement with .
Star formation rates are more variable for higher , lower galaxy masses, and
when star formation is measured on shorter time scales. For example,
simulations with have up to 0.4 dex higher scatter in specific star
formation rates than simulations with . Thus observationally
constraining the sub-grid model for star formation, and hence the nature of DM,
should be possible in the near future.Comment: 18 pages, 13 figures, accepted to MNRA
The edge of galaxy formation III: The effects of warm dark matter on Milky Way satellites and field dwarfs
In this third paper of the series, we investigate the effects of warm dark
matter with a particle mass of on the smallest
galaxies in our Universe. We present a sample of 21 hydrodynamical cosmological
simulations of dwarf galaxies and 20 simulations of satellite-host galaxy
interaction that we performed both in a Cold Dark Matter (CDM) and Warm Dark
Matter (WDM) scenario. In the WDM simulations, we observe a higher critical
mass for the onset of star formation. Structure growth is delayed in WDM, as a
result WDM haloes have a stellar population on average two Gyrs younger than
their CDM counterparts. Nevertheless, despite this delayed star formation, CDM
and WDM galaxies are both able to reproduce the observed scaling relations for
velocity dispersion, stellar mass, size, and metallicity at . WDM
satellite haloes in a Milky Way mass host are more susceptible to tidal
stripping due to their lower concentrations, but their galaxies can even
survive longer than the CDM counterparts if they live in a dark matter halo
with a steeper central slope. In agreement with our previous CDM satellite
study we observe a steepening of the WDM satellites' central dark matter
density slope due to stripping. The difference in the average stellar age for
satellite galaxies, between CDM and WDM, could be used in the future for
disentangling these two models.Comment: 10 pages, 11 figures, accepted for publication on MNRA
Inspiraling Halo Accretion Mapped in Lyman- Emission around a Quasar
In an effort to search for Ly emission from circum- and intergalactic
gas on scales of hundreds of kpc around quasars, and thus characterise
the physical properties of the gas in emission, we have initiated an extensive
fast-survey with the Multi Unit Spectroscopic Explorer (MUSE): Quasar Snapshot
Observations with MUse: Search for Extended Ultraviolet eMission (QSO MUSEUM).
In this work, we report the discovery of an enormous Ly nebula (ELAN)
around the quasar SDSS~J102009.99+104002.7 at , which we followed-up
with deeper MUSE observations. This ELAN spans projected kpc, has an
average Ly surface brightness erg s cm arcsec (within the
isophote), and is associated with an additional four, previously unknown
embedded sources: two Ly emitters and two faint active galactic nuclei
(one Type-1 and one Type-2 quasar). By mapping at high significance the
line-of-sight velocity in the entirety of the observed structure, we unveiled a
large-scale coherent rotation-like pattern spanning km s with
a velocity dispersion of km s, which we interpret as a signature
of the inspiraling accretion of substructures within the quasar's host halo.
Future multiwavelength data will complement our MUSE observations, and are
definitely needed to fully characterise such a complex system. None the less,
our observations reveal the potential of new sensitive integral-field
spectrographs to characterise the dynamical state of diffuse gas on large
scales in the young Universe, and thereby witness the assembly of galaxies.Comment: 39 pages with 27 figures and 5 appendices. Accepted to MNRA
NIHAO XVIII: Origin of the MOND phenomenology of galactic rotation curves in a LCDM universe
The phenomenological basis for Modified Newtonian Dynamics (MOND) is the
radial-acceleration-relation (RAR) between the observed acceleration,
, and the acceleration accounted for by the observed baryons
(stars and cold gas), . We show that the RAR arises
naturally in the NIHAO sample of 89 high-resolution LCDM cosmological galaxy
formation simulations. The overall scatter from NIHAO is just 0.079 dex,
consistent with observational constraints. However, we show that the scatter
depends on stellar mass. At high masses ( Msun) the
simulated scatter is just dex, increasing to dex at
low masses (Msun). Observations show a similar
dependence for the intrinsic scatter. At high masses the intrinsic scatter is
consistent with the zero scatter assumed by MOND, but at low masses the
intrinsic scatter is non-zero, strongly disfavoring MOND. Applying MOND to our
simulations yields remarkably good fits to most of the circular velocity
profiles. In cases of mild disagreement the stellar mass-to-light ratio and/or
"distance" can be tuned to yield acceptable fits, as is often done in
observational mass models. In dwarf galaxies with Msun MOND
breaks down, predicting lower accelerations than observed and in our LCDM
simulations. The assumptions that MOND is based on (e.g., asymptotically flat
rotation curves, zero intrinsic scatter in the RAR), are approximately, but not
exactly, true in LCDM. Thus if one wishes to go beyond Newtonian dynamics there
is more freedom in the RAR than assumed by MOND.Comment: 15 pages, 15 figures, accepted to MNRA
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