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Chemical Enrichment in
Spheroidal Galaxies
Gustavo A. Lanfranchi
Núcleo de Astrofísica Teórica
Universidade Cruzeiro do Sul
Chemical Enrichment in Spheroidal Galaxies
Dwarf
Spheroidal
Galaxies
M31 bulge
NGC 4325
Discussion
Dwarf Spheroidal Galaxies - dSph
The dSph galaxies are considered to be key objects in galactic evolution and galactic
formation studies and in the analysis of the nucleossynthesis of chemical species.
They could be related to the remains of the building blocks of large systems in the
framework of hierarchical formation of galaxies.
Mechanisms acting in their formation and evolution remain unknown.
Poorly evolved systems with stars that could trace the first stages of star formation in the
universe.
Their proximity allows detailed studies of their stellar population and chemical
abundances.
Dwarf Spheroidal Galaxies
106 – 109M
Rc= 0,09-0,9 kpc
normally, low metal content
(from ~ 0.1 to 0.001 solar).
low luminosity (-18 < MB < -9)
dSph – main properties
dSph are amongst the less luminous known galaxies (MB ~ -9) and with the lowest
superficial brightness (B = 23 mag arcsec-2).
There is almost no detectable neutral gas in the central regions: HI/Mtot ~ 0.001 or less.
They do not exhibit a nucleus or a central stellar concentration.
Brooks & Zolotov, 2014, ApJ 786 87
Dark matter dominated and made of mostly
primordial material.
dSph – evolution
How do they evolve? What physical processes control their evolution? Internal
mechanism or environment?
How much gas can be removed by winds? Is there also external mechanism (ram
pressure, tidal stripping, etc.)?
What defines the observed patterns of the abundance ratios and the shape of the SMDs?
FORNAX
One of the most distant
(135 kpc - Rizzi et al. 2007)
total mass around 108 M
(Walker et al. 2007).
Chemical Evolution Model – Fornax
Model of Lanfranchi & Matteucci (2003, 2004) developed to reproduce local dSph
galaxies. Main properties:
 one zone, with no instantaneous recycling approximation: stellar lifetimes are
taken into account;
 Salpeter IMF (0.1 – 100 M)‫;‏‬
 SFR is proportional to the gas mass and determined by its efficiency;‫‏‬
 yields: Woosley & Weaver (95) for massive stars, Nomoto et al. (97) for SNeIa,
van den Hoek & Groenewegen (97) for IMS, Lanfranchi et al. (06a) for s and r
process elements;
 a galactic wind with high efficiency develops when the thermal energy of the
gas is equal or higher than the binding energy of the galaxy (Eth  Eb);
Chemical Evolution Model
[alpha/Fe] - Fornax
fast injection in the
ISM of  elements
by SNe II (globular
clusters)
injection in the ISM
of Fe by SNe Ia.
galactic wind
Data from Letarte et al. 2010 and 2006
SMD - Fornax
peak at [Fe/H] ~ -0.8, defined
by the low SFR and the
galactic wind
dashed line - data
red and blue lines - models
onset of the galactic
wind – sharp decrease
a slightly lower number
of stars predicted by
the model.
Observations from Kirby et al. 2010 and Letarte et al. 2006
Mass - Fornax
0.2 - 0.8 x108 M and 104 M (Walker et al. 2007).
Stellar mass – slow initial increase due to
the slow SFR. After the onset of the wind,
the SFR decreases to almost zero,
maintaining the stellar mass constant.
Gas mass – initial increase due to infall and
subsequent
decrease
due
to
the
consumption of gas by the SF and to the
removal of gas by the galactic wind.
M31 Bulge
The evolution of the bulge of M31 is investigated by means of a detailed chemical evolution
model and a robust statistical method (cross-entropy).
a sample with the initial
values is randomly
generated
the second and third
steps are repeated until
some stopping criteria
is satisfied.
A new sample is
randomly generated,
updated from the best
previous attemptsolutions
a series of models with
the initial values are run
and their results
compared to the data
A percentage of the
attempt-solutions are
selected - the best
attempt solutions;
M31 Bulge
Model adopts: Salpeter IMF, a Schmidt-Kennicutt law for star formation with an exponent k =1.5,
n = 15 ± 0.27 Gyr−1, and an infall timescale of 0.10 ± 0.03Gyr.
Blue – model; cian – data (Marcon-Uchida et al. 2015).
Blue – M31; red – MW (Marcon-Uchida et al. 2015).
NGC 4235
Investigate the metal enrichment history of the group NGC4325, by means of
a chemical evolution model constrained by stellar population analysis.
The stellar population analysis provides a SFH, which is used as an input to the
models.
Optical spectrum of the central galaxy obtained
from DR10 Sloan Digital Sky Survey
STARLIGHT: three different sets of models
Bruzual & Charlot (2003), González Delgado et al.
(2005), Vazdekis et al. (2010)
Laganá et al. (2015).
NGC 4235
The chemical evolution model predicts the SNe II and Ia rates.
And the total amount of O and Fe released in the IGM by galactic winds until the
present epoch.
NGC 4235
The predicted amount of mass released by the NGC4325 galaxy to the ones derived
through X-ray analysis were compared :
- the winds from the central galaxy alone play a minor role in the IGM metal
enrichment of this group inside r2500;
- SNe winds are responsible for no more than 3% of the iron mass and 21% of the
oxygen mass enclosed within r2500;
- oxygen has been produced in the early stages of the group formation;
- Fe is still being added to the IGM specifically in the core by the SNIa.