I'm an astrophysicist
working at the Instituto de Radioastronomía y Astrofísica of the
National Autonomous University of Mexico (UNAM). I was born in Mexico
City where I spent my student years. I got my bachelor's degree in
Physics Engineering at Universidad Iberoamericana and then my Masters
and PhD in Astrophysics at UNAM. I then moved to Korea to work as a
postdoc at KASI, then to Shanghai to work with prof. Cheng Li at the
Shanghai Astronomical Observatory and finally to Seoul to work with
prof. Changbom Park at the Korea Institute for Advance Study.
My research field is
Extragalactic Astrophysics. I am interested in how galaxies acquire
their present day structural parameters, specially how angular momentum
is acquired, the influence of the environment on the evolution of
galaxies and more recently I'm trying to understand why some galaxies
develop stellar bars and why some others don't, although they share
similar overall physical parameters.
About 30% of galaxies in the local Unvierse present elongated
features in their centers, such as the one shown in the next figure
showing the famous galaxy NGC 1300. These elongated features are
commonly know as bars and are conformed by stars, gas and dust. If you
take a careful look of the image you will also notice many background
galaxies, farther away than NGC 1300, many of them also barred galaxies.
Numerical simulations have shown that rotating disks are highly unstable and form spontaneously bars. From the earliest simulations,
it was noted that the inclusion of a gravitationally dominating dark
matter halo helps to stabilize the disk and prevent and/or delay the
formation of the bar. Later on, several theoretical studies have
addressed this issue but until recently, no observational effort was
directed to prove or disprove such claim. In a couple of papers we
studied if the fraction of barred galaxies depends on the
stellar-to-halo mass ratio, in order to see if the amount of dark
matter has any relevance on the presence of bars in spiral galaxies.
Using a large sample of galaxies (about ~10,000 galaxies) form the
Sloan Digital Sky Survey (SDSS), we first looked at the dependence of
the bar fraction (fbar) on the stellar-to-halo mass ratio.
The next figure on the left clearly shows that as the stellar-to-halo
mass ratio increases, fbar
increases, specially for the case of strong bars. It can be argued that
this effect is due entirely by the dependence the bar fraction shows
with the stellar mass. To see if fbar
presents a variation with varing halo mass at fixed stellar mass, we
looked at in a 2D plane shown in the next figure, right panels.
The color contours denote the bar fraction for the full sample,
including strong and weak bars, but also differentiating between the
two types. It is clear, at least for the case of strong bars, that at
fixed stellar mass, there is a systematic increase of fbar
with decreasing halo mass. This results suggest that dark matter halos
have a stabilizing effect against bar formation. For more details on
this work check our paper.
The dark matter halo masses for the previous results were based on an
indirect method by looking at the spatial distribution of galaxies in
the SDSS and assigning masses by ranking galaxies according to their
luminosities. To double-check that our results were insensitive to this
method of assigning masses, I studied the same problem but estimating
halo masses by looking at the kinematic information of the HI gas of
those galaxies. In the next figure I present the bar fraction as a
function of stellar mass splitting the sample in two, a high halo mass
sub-sample and a low halo-mass subsample. The two columns correspond to
two different halo mass estimators. Again, for the case of strong bars,
the bar fraction of galaxies having heavy dark matter halos is
statistically lower than that of the sub-sample with low halo masses,
supporting our previous results.
Having HI mass information already at hand, we also explored
if the gas content of galaxies has any influence on the presence of
bars. We found, as previous studies had already reported, that the bar
fraction decreases with increasing gas-to-stellar mass ratio. This
result can be consequence of two different mechanisms: (i) strong
bars promote the consumption of atomic gas and, (ii) gas prevents the
formation/growth of bars. Our results show that barred galaxies in our
sample are not consuming their gas in a more efficient way than their
unbarred counterparts (look at the gas consumption timescale in the
figure), hence favoring the second explanation; increasing the gas
content in disk galaxies prevents the formation of bars, they grow more
slowly or they are destroyed directly or in- directly by the presence
of gas.
More recently, in collaboration with my student Osbaldo Sánchez, we
have been studying Low Surface Brightness galaxies (LSBs). These
galaxies are interesting because they are very extended systems with
low density stellar disks and by consequence, strongly dark matter
dominated. Here some examples, taken again form the SDSS:
Given that LSBs are gravitationally dominated by dark matter at all
radii, is logical to expect that the fraction of LSBs hosting stellar
bars would be low. This is exactly the case as we show in the next
figure, where we contrast the bar fraction of LSBs in comparison with
the same fraction for High Surface Brigthness galaxies (HSBs).
Institute of Astronomy
Universidad Nacional Autónoma de México
Mexico City, Mexico
• Ph. D., Astronomy
Thesis title: Dimensionless
angular momentum parameter λ: galaxy characterization
and
large scale structure of the Universe
Advisor: Professor Xavier N. Hernández Doring
Magna cum Laude
2007-2009
• M. S., Astronomy
Advisor: Professor Xavier N. Hernández Doring Average grade: 9.67/10.0
2005–2007
Universidad Iberoamericana
Mexico City, Mexico
• B. S., Physics Engineering
Average grade: 9.61/10.0
Magna cum Laude
1999–2004
Osbaldo Sánchez García.
Got his bachelor's degree in Physics at Universidad Autónoma de
Zacatecas, under the supervision of José Luis Saucedo and Bernardo
Cervantes Sodi. He is now pursuing his Master's degree at IRyA studying
the likelihood of low surface brightness galaxies hosting stellar bars.
Luis Enrique Pérez Montaño.
Got his bachelor's degree in Physics at Universidad Autónoma de Puebla.
He started working with me during a summer program for undergraduate
research at IRyA in 2016 and after joining our Master's program he
continued his research focused on determining the galactic spin of low
surface brightness galaxies to see if their spin is the physical
parameter responsible for their characteristic features.
