3,479 research outputs found
Dark Matter and IMF normalization in Virgo dwarf early-type galaxies
In this work we analyze the dark matter (DM) fraction, , and
mass-to-light ratio mismatch parameter, (computed with respect
to a Milky-Way-like IMF), for a sample of 39 dwarf early-type galaxies (dEs) in
the Virgo cluster. Both and are estimated within the
central (one effective radius) galaxy regions, with a Jeans dynamical analysis
that relies on galaxy velocity dispersions, structural parameters, and stellar
M/L ratios from the SMAKCED survey. In this first attempt to constrain,
simultaneously, the IMF normalization and the DM content, we explore the impact
of different assumptions on the DM model profile. On average, for a NFW
profile, the is consistent with a Chabrier-like normalization
(), with . One of the main results of
the present work is that for at least a few systems the is
heavier than the MW-like value (i.e. either top- or bottom-heavy). When
introducing tangential anisotropy, larger and smaller
are derived. Adopting a steeper concentration-mass relation than that from
simulations, we find lower () and larger . A
constant M/L profile with null gives the heaviest
(). In the MONDian framework, we find consistent results to those for
our reference NFW model. If confirmed, the large scatter of for
dEs would provide (further) evidence for a non-universal IMF in early-type
systems. On average, our reference estimates are consistent with those
found for low- () early-type
galaxies (ETGs). Furthermore, we find consistent with values from the
SMAKCED survey, and find a double-value behavior of with stellar mass,
which mirrors the trend of dynamical M/L and global star formation efficiency
with mass.Comment: 11 pages, 3 figures, 1 table, published on MNRAS. Figure 1 has been
updated with respect to version 1, including the range of values found if the
S\'ersic index, n, is varied from 0.5 to 2 (dark-green curves
Central dark matter content of early-type galaxies: scaling relations and connections with star formation histories
We examine correlations between masses, sizes and star formation histories for a large sample of low-redshift early-type galaxies, using a simple suite of dynamical and stellar population models. We confirm an anticorrelation between the size and stellar age and go on to survey for trends with the central content of dark matter (DM). An average relation between the central DM density and galaxy size of 〈ρDM〉∝R−2eff provides the first clear indication of cuspy DM haloes in these galaxies – akin to standard Λ cold dark matter haloes that have undergone adiabatic contraction. The DM density scales with galaxy mass as expected, deviating from suggestions of a universal halo profile for dwarf and late-type galaxies. We introduce a new fundamental constraint on galaxy formation by finding that the central DM fraction decreases with stellar age. This result is only partially explained by the size–age dependencies, and the residual trend is in the opposite direction to basic DM halo expectations. Therefore, we suggest that there may be a connection between age and halo contraction and that galaxies forming earlier had stronger baryonic feedback, which expanded their haloes, or lumpier baryonic accretion, which avoided halo contraction. An alternative explanation is a lighter initial mass function for older stellar populations
Colour gradients of high-redshift Early-Type Galaxies from hydrodynamical monolithic models
We analyze the evolution of colour gradients predicted by the hydrodynamical
models of early type galaxies (ETGs) in Pipino et al. (2008), which reproduce
fairly well the chemical abundance pattern and the metallicity gradients of
local ETGs. We convert the star formation (SF) and metal content into colours
by means of stellar population synthetic model and investigate the role of
different physical ingredients, as the initial gas distribution and content,
and eps_SF, i.e. the normalization of SF rate. From the comparison with high
redshift data, a full agreement with optical rest-frame observations at z < 1
is found, for models with low eps_SF, whereas some discrepancies emerge at 1 <
z < 2, despite our models reproduce quite well the data scatter at these
redshifts. To reconcile the prediction of these high eps_SF systems with the
shallower colour gradients observed at lower z we suggest intervention of 1-2
dry mergers. We suggest that future studies should explore the impact of wet
galaxy mergings, interactions with environment, dust content and a variation of
the Initial Mass Function from the galactic centers to the peripheries.Comment: 13 pages, 7 figures, 1 table, accepted for publication on MNRA
Colour and stellar population gradients in galaxies
We discuss the colour, age and metallicity gradients in a wide sample of
local SDSS early- and late-type galaxies. From the fitting of stellar
population models we find that metallicity is the main driver of colour
gradients and the age in the central regions is a dominant parameter which
rules the scatter in both metallicity and age gradients. We find a consistency
with independent observations and a set of simulations. From the comparison
with simulations and theoretical considerations we are able to depict a general
picture of a formation scenario.Comment: 4 pages, 4 figures. Proceedings of 54th Congresso Nazionale della
SAIt, Napoli 4-7 May 201
Testing Verlinde's emergent gravity in early-type galaxies
Verlinde derived gravity as an emergent force from the information flow,
through two-dimensional surfaces and recently, by a priori postulating the
entanglement of information in 3D space, he derived the effect of the
gravitational potential from dark matter (DM) as the entropy displacement of
dark energy by baryonic matter. In Emergent Gravity (EG) this apparent DM
depends only on the baryonic mass distribution and the present-day value of the
Hubble parameter. In this paper we test the EG proposition, formalized by
Verlinde for a spherical and isolated mass distribution, using the central
velocity dispersion, and the light distribution in a sample of 4260
massive and local early-type galaxies (ETGs) from the SPIDER sample. Our
results remain unaltered if we consider the sample of 807 roundest field
galaxies. We derive the predictions by EG for the stellar mass-to-light ratio
(M/L) and the Initial Mass Function (IMF), and compare them with the same
inferences derived from a) DM-based models, b) MOND and c) stellar population
models. We demonstrate that, consistently with a classical Newtonian framework
with a DM halo component, or alternative theories of gravity as MOND, the
central dynamics can be fitted if the IMF is assumed non-universal. The results
can be interpreted with a IMF lighter than a standard Chabrier at low-,
and bottom-heavier IMFs at larger . We find lower, but still
acceptable, stellar M/L in EG theory, if compared with the DM-based NFW model
and with MOND. The results from EG are comparable to what is found if the DM
haloes are adiabatically contracted and with expectations from spectral
gravity-sensitive features. If the strain caused by the entropy displacement
would be not maximal, as adopted in the current formulation, then the dynamics
of ETGs could be reproduced with larger M/L. (abridged)Comment: 12 pages, 2 figures, submitted to MNRAS. The updated manuscript
presents significantly altered conclusions, after discovering an internal bug
in an older version of the Mathematica package, leading to incorrect
numerical results when calculating the derivatives of Gamma function
Evolution of central dark matter of early-type galaxies up to z ~ 0.8
We investigate the evolution of dark and luminous matter in the central
regions of early-type galaxies (ETGs) up to z ~ 0.8. We use a spectroscopically
selected sample of 154 cluster and field galaxies from the EDisCS survey,
covering a wide range in redshifts (z ~ 0.4-0.8), stellar masses ( ~ 10.5-11.5 dex) and velocity dispersions
( ~ 100-300 \, km/s). We obtain central dark matter (DM)
fractions by determining the dynamical masses from Jeans modelling of galaxy
aperture velocity dispersions and the from galaxy colours, and
compare the results with local samples. We discuss how the correlations of
central DM with galaxy size (i.e. the effective radius, ),
and evolve as a function of redshift, finding
clear indications that local galaxies are, on average, more DM dominated than
their counterparts at larger redshift. This DM fraction evolution with can
be only partially interpreted as a consequence of the size-redshift evolution.
We discuss our results within galaxy formation scenarios, and conclude that the
growth in size and DM content which we measure within the last 7 Gyr is
incompatible with passive evolution, while it is well reproduced in the
multiple minor merger scenario. We also discuss the impact of the IMF on our DM
inferences and argue that this can be non-universal with the lookback time. In
particular, we find the Salpeter IMF can be better accommodated by low redshift
systems, while producing stellar masses at high- which are unphysically
larger than the estimated dynamical masses (particularly for
lower- systems).Comment: 14 pages, 6 figures, 3 tables, MNRAS in pres
MOND and IMF variations in early-type galaxies from ATLAS3D
MOdified Newtonian dynamics (MOND) represents a phenomenological alternative
to dark matter (DM) for the missing mass problem in galaxies and clusters of
galaxies. We analyze the central regions of a local sample of
early-type galaxies from the survey, to see if the data can be
reproduced without recourse to DM. We estimate dynamical masses in the MOND
context through Jeans analysis, and compare to stellar masses
from stellar population synthesis. We find that the observed stellar
mass--velocity dispersion relation is steeper than expected assuming MOND with
a fixed stellar initial mass function (IMF) and a standard value for the
acceleration parameter . Turning from the space of observables to
model space, a) fixing the IMF, a universal value for cannot be
fitted, while, b) fixing and leaving the IMF free to vary, we find
that it is "lighter" (Chabrier-like) for low-dispersion galaxies, and "heavier"
(Salpeter-like) for high dispersions. This MOND-based trend matches inferences
from Newtonian dynamics with DM, and from detailed analysis of spectral
absorption lines, adding to the converging lines of evidence for a
systematically-varying IMF.Comment: 6 pages, 3 figures, accepted for publication on MNRAS Letters, typos
corrected and further references adde
Systematic variation of central mass density slope in early-type galaxies
We study the total density distribution in the central regions (
effective radius, ) of early-type galaxies (ETGs), using data from
the SPIDER survey. We model each galaxy with two components (dark matter halo +
stars), exploring different assumptions for the dark matter (DM) halo profile,
and leaving stellar mass-to-light () ratios as free fitting
parameters to the data. For a Navarro et al. (1996) profile, the slope of the
total mass profile is non-universal. For the most massive and largest ETGs, the
profile is isothermal in the central regions (), while for
the low-mass and smallest systems, the profile is steeper than isothermal, with
slopes similar to those for a constant-M/L profile. For a concentration-mass
relation steeper than that expected from simulations, the correlation of
density slope with mass tends to flatten. Our results clearly point to a
"non-homology" in the total mass distribution of ETGs, which simulations of
galaxy formation suggest may be related to a varying role of dissipation with
galaxy mass.Comment: 3 pages, 1 figure, to appear on the refereed Proceeding of the "The
Universe of Digital Sky Surveys" conference held at the INAF--OAC, Naples, on
25th-28th november 2014, to be published on Astrophysics and Space Science
Proceedings, edited by Longo, Napolitano, Marconi, Paolillo, Iodic
Population gradients in the Sloan Digital Sky Survey Galaxy Catalogue: the role of merging
We investigate the role of the environment on the colour and stellar population gradients in a local sample of ∼3500 central and ∼1150 satellite Sloan Digital Sky Survey (SDSS) early-type galaxies. The environment is parametrized in terms of the number of satellite galaxies, Ngal, in each group. For central galaxies, we find that both optical colour and mass-to-light (M/L) ratio gradients are shallower in central galaxies residing in denser environments (higher Ngal). This trend is driven by metallicity gradients, while age gradients appear to be less dependent on the environment and to have a larger scatter. On the other hand, satellites do not show any differences in terms of the environment. The same results are found if galaxies are classified by central age, and both central and satellite galaxies have shallower gradients if they are older and steeper gradients if younger, satellites being independent of ages. In central galaxies, we show that the observed trends can be explained with the occurrence of dry mergings, which are more numerous in denser environments and producing shallower colour gradients because of more uniform metallicity distributions due to the mixing of stellar populations, while no final clues about merging occurrence can be obtained for satellites. Finally, we discuss all systematics on stellar population fitting and their impact on the final result
- …