234 research outputs found
SILCC-ZOOM: The early impact of ionizing radiation on forming molecular clouds
As part of the SILCC-ZOOM project we present our first sub-parsec resolution
radiation-hydrodynamic simulations of two molecular clouds self-consistently
forming from a turbulent, multi-phase ISM. The clouds have similar initial
masses of few 10 M, escape velocities of ~5 km s, and a
similar initial energy budget. We follow the formation of star clusters with a
sink based model and the impact of radiation from individual massive stars with
the tree-based radiation transfer module TreeRay. Photo-ionizing radiation is
coupled to a chemical network to follow gas heating, cooling and molecule
formation and dissociation. For the first 3 Myr of cloud evolution we find that
the overall star formation effciency is considerably reduced by a factor of ~4
to global cloud values of < 10 % as the mass accretion of sinks that host
massive stars is terminated after <1 Myr. Despite the low effciency, star
formation is triggered across the clouds. Therefore, a much larger region of
the cloud is affected by radiation and the clouds begin to disperse. The time
scale on which the clouds are dispersed sensitively depends on the cloud
substructure and in particular on the amount of gas at high visual extinction.
The damage of radiation done to the highly shielded cloud (MC1) is delayed. We
also show that the radiation input can sustain the thermal and kinetic energy
of the clouds at a constant level. Our results strongly support the importance
of ionizing radiation from massive stars for explaining the low observed star
formation effciency of molecular cloud
SILCC VII -- Gas kinematics and multiphase outflows of the simulated ISM at high gas surface densities
We present magnetohydrodynamic (MHD) simulations of the star-forming
multiphase interstellar medium (ISM) in stratified galactic patches with gas
surface densities 10, 30, 50, and 100
. The SILCC project simulation framework accounts
for non-equilibrium thermal and chemical processes in the warm and cold ISM.
The sink-based star formation and feedback model includes stellar winds,
hydrogen-ionising UV radiation, core-collapse supernovae, and cosmic ray (CR)
injection and diffusion. The simulations follow the observed relation between
and the star formation rate surface density
. CRs qualitatively change the outflow phase structure.
Without CRs, the outflows transition from a two-phase (warm and hot at 1 kpc)
to a single-phase (hot at 2 kpc) structure. With CRs, the outflow always has
three phases (cold, warm, and hot), dominated in mass by the warm phase. The
impact of CRs on mass loading decreases for higher and
the mass loading factors of the CR-supported outflows are of order unity
independent of . Similar to observations, vertical
velocity dispersions of the warm ionised medium (WIM) and the cold neutral
medium (CNM) correlate with the star formation rate as , with . In the absence of stellar
feedback, we find no correlation. The velocity dispersion of the WIM is a
factor higher than that of the CNM, in agreement with local
observations. For the WIM motions
become supersonic.Comment: 19 pages, 9 figures, submitted to MNRA
Mergers and Mass Accretion Rates in Galaxy Assembly: The Millennium Simulation Compared to Observations of z~2 Galaxies
Recent observations of UV-/optically selected, massive star forming galaxies
at z~2 indicate that the baryonic mass assembly and star formation history is
dominated by continuous rapid accretion of gas and internal secular evolution,
rather than by major mergers. We use the Millennium Simulation to build new
halo merger trees, and extract halo merger fractions and mass accretion rates.
We find that even for halos not undergoing major mergers the mass accretion
rates are plausibly sufficient to account for the high star formation rates
observed in z~2 disks. On the other hand, the fraction of major mergers in the
Millennium Simulation is sufficient to account for the number counts of
submillimeter galaxies (SMGs), in support of observational evidence that these
are major mergers. When following the fate of these two populations in the
Millennium Simulation to z=0, we find that subsequent mergers are not frequent
enough to convert all z~2 turbulent disks into elliptical galaxies at z=0.
Similarly, mergers cannot transform the compact SMGs/red sequence galaxies at
z~2 into observed massive cluster ellipticals at z=0. We argue therefore, that
secular and internal evolution must play an important role in the evolution of
a significant fraction of z~2 UV-/optically and submillimeter selected galaxy
populations.Comment: 5 pages, 4 figures, Accepted for publication in Ap
The HI Tully-Fisher Relation of Early-Type Galaxies
We study the HI K-band Tully-Fisher relation and the baryonic Tully-Fisher
relation for a sample of 16 early-type galaxies, taken from the ATLAS3D sample,
which all have very regular HI disks extending well beyond the optical body (>
5 R_eff). We use the kinematics of these disks to estimate the circular
velocity at large radii for these galaxies. We find that the Tully-Fisher
relation for our early-type galaxies is offset by about 0.5-0.7 magnitudes from
the relation for spiral galaxies. The residuals with respect to the spiral
Tully-Fisher relation correlate with estimates of the stellar mass-to-light
ratio, suggesting that the offset between the relations is mainly driven by
differences in stellar populations. We also observe a small offset between our
Tully-Fisher relation with the relation derived for the ATLAS3D sample based on
CO data representing the galaxies' inner regions (< 1 R_eff). This indicates
that the circular velocities at large radii are systematically 10% lower than
those near 0.5-1 R_eff, in line with recent determinations of the shape of the
mass profile of early-type galaxies. The baryonic Tully-Fisher relation of our
sample is distinctly tighter than the standard one, in particular when using
mass-to-light ratios based on dynamical models of the stellar kinematics. We
find that the early-type galaxies fall on the spiral baryonic Tully-Fisher
relation if one assumes M/L_K = 0.54 M_sun/L_sun for the stellar populations of
the spirals, a value similar to that found by recent studies of the dynamics of
spiral galaxies. Such a mass-to-light ratio for spiral galaxies would imply
that their disks are 60-70% of maximal. Our analysis increases the range of
galaxy morphologies for which the baryonic Tully-Fisher relations holds,
strengthening previous claims that it is a more fundamental scaling relation
than the classical Tully-Fisher relation.Comment: Accepted for publication in Astronomy & Astrophysic
Cosmological Simulations of Massive Compact High-z Galaxies
In order to investigate the structure and dynamics of the recently discovered
massive (M_* > 10^11 M_sun) compact z~2 galaxies, cosmological
hydrodynamical/N-body simulations of a proto-cluster region have been
undertaken. At z=2, the highest resolution simulation contains ~5800 resolved
galaxies, of which 509, 27 and 5 have M_* > 10^10 M_sun, > 10^11 M_sun and >
4x10^11 M_sun, respectively. Effective radii and characteristic stellar
densities have been determined for all galaxies. At z=2, for the definitely
well resolved mass range of M_* > 10^11 Msun, the mass-size relation is
consistent with observational findings for the most compact z~2 galaxies. The
very high velocity dispersion recently measured for a compact z~2 galaxy (~510
km/s; van Dokkum et al 2009) can be matched at about the 1-sigma level,
although a somewhat larger mass than the estimated M_* ~ 2 x 10^11 M_sun is
indicated. For the above mass range, the galaxies have an average axial ratio
= 0.64 +/- 0.02 with a dispersion of 0.1, an average rotation to 1D
velocity dispersion ratio = 0.46 +/- 0.06 with a dispersion of 0.3,
and a maximum value of v/sigma ~ 1.1. Rotation and velocity anisotropy both
contribute in flattening the compact galaxies. Some of the observed compact
galaxies appear flatter than any of the simulated galaxies. Finally, it is
found that the massive compact galaxies are strongly baryon dominated in their
inner parts, with typical dark matter mass fractions of order only 20% inside
of r=2R_eff.Comment: 10 pages, 8 figures, submitted to Ap
The ATLAS3D project - XXIV. The intrinsic shape distribution of early-type galaxies
We use the ATLAS3D sample to perform a study of the intrinsic shapes of early-type galaxies, taking advantage of the available combined photometric and kinematic data. Based on our ellipticity measurements from the Sloan Digital Sky Survey Data Release 7, and additional imaging from the Isaac Newton Telescope, we first invert the shape distribution of fast and slow rotators under the assumption of axisymmetry. Theso-obtained intrinsic shape distribution for the fast rotators can be described with a Gaussian with a mean flattening of q=0.25 and standard deviation σq = 0.14, and an additional tail towards rounder shapes.The slow rotators are much rounder, and are well described with a Gaussian with mean q = 0.63 and σq =0.09. We then checked that our results were consistent when applying a different and independent method to obtain intrinsic shape distributions, by fitting the observed ellipticity distributions directly using Gaussian parametrizations for the intrinsic axis ratios. Although both fast and slow rotators are identified as early-type galaxies in morphological studies, and in many previous shape studies are therefore grouped together, their shape distributions are significantly different, hinting at different formation scenarios. The intrinsic shape distribution of the fast rotators shows similarities with the spiral galaxy population. Including the observed kinematic misalignment in our intrinsic shape study shows that the fast rotators are predominantly axisymmetric, with only very little room for triaxiality. For the slow rotators though there are very strong indications that they are (mildly) triaxial.PostprintPeer reviewe
Connection between dynamically derived initial mass function normalization and stellar population parameters
Date of Acceptance: 10/08/2014We report on empirical trends between the dynamically determined stellar initial mass function (IMF) and stellar population properties for a complete, volume-limited sample of 260 early-type galaxies from the ATLAS3D project. We study trends between our dynamically derived IMF normalization αdyn ≡ (M/L)stars/(M/L)Salp and absorption line strengths, and interpret these via single stellar population-equivalent ages, abundance ratios (measured as [α/Fe]), and total metallicity, [Z/H]. We find that old and alpha-enhanced galaxies tend to have on average heavier (Salpeter-like) mass normalization of the IMF, but stellar population does not appear to be a good predictor of the IMF, with a large range of αdyn at a given population parameter. As a result, we find weak αdyn-[α/Fe] and αdyn -Age correlations and no significant αdyn -[Z/H] correlation. The observed trends appear significantly weaker than those reported in studies that measure the IMF normalization via the low-mass star demographics inferred through stellar spectral analysis.Peer reviewe
The ATLAS3D project - XXVI : H I discs in real and simulated fast and slow rotators
One quarter of all nearby early-type galaxies (ETGs) outside Virgo host a disc/ring of H I with size from a few to tens of kpc and mass up to ∼109 M⊙. Here we investigate whether this H I is related to the presence of a stellar disc within the host making use of the classification of ETGs in fast and slow rotators (FR/SR). We find a large diversity of H I masses and morphologies within both families. Surprisingly, SRs are detected as often, host as much H I and have a similar rate of H I discs/rings as FRs. Accretion of H I is therefore not always linked to the growth of an inner stellar disc. The weak relation between H I and stellar disc is confirmed by their frequent kinematical misalignment in FRs, including cases of polar and counterrotating gas. In SRs the H I is usually polar. This complex picture highlights a diversity of ETG formation histories which may be lost in the relative simplicity of their inner structure and emerges when studying their outer regions. We find that Λ CDM hydrodynamical simulations have difficulties reproducing the H I properties of ETGs. The gas discs formed in simulations are either too massive or too small depending on the star formation feedback implementation. Kinematical misalignments match the observations only qualitatively. The main point of conflict is that nearly all simulated FRs and a large fraction of all simulated SRs host corotating H I. This establishes the H I properties of ETGs as a novel challenge to simulationsPeer reviewedFinal Accepted Versio
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The Density Profiles of Massive, Relaxed Galaxy Clusters. II. Separating Luminous and Dark Matter in Cluster Cores
We present stellar and dark matter (DM) density profiles for a sample of
seven massive, relaxed galaxy clusters derived from strong and weak
gravitational lensing and resolved stellar kinematic observations within the
centrally-located brightest cluster galaxies (BCGs). In Paper I of the series,
we demonstrated that the total density profile derived from these data, which
span 3 decades in radius, is consistent with numerical DM-only simulations at
radii >~ 5-10 kpc, despite the significant contribution of stellar material in
the core. Here we decompose the inner mass profiles of these clusters into
stellar and dark components. Parametrizing the DM density profile as a power
law rho_DM ~ r^{-\beta} on small scales, we find a mean slope = 0.50 +-
0.10 (random) +0.14-0.13 (systematic). Alternatively, cored Navarro-Frenk-White
(NFW) profiles with = 1.14 +- 0.13 (random) +0.14-0.22
(systematic) provide an equally good description. These density profiles are
significantly shallower than canonical NFW models at radii <~ 30 kpc,
comparable to the effective radii of the BCGs. The inner DM profile is
correlated with the distribution of stars in the BCG, suggesting a connection
between the inner halo and the assembly of stars in the central galaxy. The
stellar mass-to-light ratio inferred from lensing and stellar dynamics is
consistent with that inferred using stellar population synthesis models if a
Salpeter initial mass function is adopted. We compare these results to theories
describing the interaction between baryons and DM in cluster cores, including
adiabatic contraction models and the possible effects of galaxy mergers and
active galactic nucleus feedback, and evaluate possible signatures of
alternative DM candidates.Comment: Updated to matched the published version in Ap
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