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Do LIRGs follow the Tully-Fisher relation?
Verónica Torres Martínez and Adriana J. Colón Rosa, Colegio San Felipe Arecibo
Mentors: Dr. Tapasi Ghosh, Arecibo Observatory
National Astronomy and Ionosphere Center, Arecibo Observatory of Puerto Rico
Abstract
Objectives
The purpose of this research was to study the
LIRGs (Luminous Infrared Galaxies) and see if
they follow the Tully-Fisher relation. The LIRGs
are different to normal galaxies in the fact that
they emit 90% of their light
i in infrared. The TullyFisher relation states that the bigger the galaxy is,
the faster it rotates. The faster the galaxy rotates,
the wider is the emission line in velocity. Also, the
bigger the galaxy, the more is its luminosity. TullyFisher relation shows that for normal galaxies, the
velocity width (W) of the lines is proportional to its
luminosity (L) following an equation, L ∝
In a
sample of 33 LIRGs the neutral hydrogen emission
line width was measured. The luminosities of
these galaxies from literature were found and a
study was made of whether the Tully-Fisher law is
maintained by the LIRGs. This indicates whether
the LIRGs are peculiar either in their motion or in
the amount of light they emit.
W α.
Introduction
Galaxy: is a large system of stars, star clusters,
gas, dust, and nebulae orbiting a common center
of mass.
IR (Infrared) : The portion of the electromagnetic
spectrum with wavelengths longer than red light,
ranging from 700 nm to about 1 mm, between
visible light and radio waves.
The objective of the research is to examine if the
Tully-Fisher relation can be applied to LIRGs.
Methods and Materials
To perform this investigation we spoke
with Professor Neftalí S. Rivera-Castillo of the
University of Puerto Rico at Arecibo, and
with Dr. T. Ghosh of the Arecibo Observatory,
our mentor. They gave us papers, books, web
references and some insights about the subject.
we
reviewed
them
and
developed
an
understanding of the topic.
We then took the following steps.
(1) The Radio spectra for neutral hydrogen, and
OH radicals were taken using the 305-m Arecibo
telescope for a sample of 33 LIRGs during
December 2011
(2) We reduced the data
which involved calibration
and production of averaged
spectra using a standard
IDL software developed at
the Observatory.
(3) Then fitted a baseline
and
subtracted
that
out
to
LIRGs (Luminous Infrared Galaxies): Among the
remove
any
instrumental
various type of galaxies there are the Luminous
effect.
Infrared Galaxies (LIRGs). These are galaxies very
bright in IR (Infrared) region of the spectrum. About
90% of the light LIRGs emit is IR. LIRGs are not (4) The HI spectral line is redshifted due to
common
galactic
bodies,
they
generate expansion of the universe. So, using Doppler
approximately 100 new stars per year. LIRGs are effect, the frequency scale of the spectrum was
converted into velocity scale. The velocity width of
the result of mix or collisions of galaxies.
the line is related to the rotational speed of the
HI Line : Neutral hydrogen in galaxies emit a line galaxy. We measured that out of the plots using the
at 21cm wavelength due to spin-flip transition of IDL software.
the electron and proton in a Hydrogen atom. The
line gets broadened due to the internal rotation of (5) Next, from the NASA Extragalactic
the galaxies, and also due to interaction with other Database(nedwww.ipac.caltech.edu), we gathered
the inclination angle and the H-band (1.65 micron)
closeby galaxies.
absolute luminosity (L_abs) for each object.
(6) We then plotted log(L_abs) against log of
inclination-corrected velocity width, log[(W_c)] for
the LIRGs for which these information were
available and the inclination angle was more than
Results
30 deg.
Tully-Fisher Relation: Astronomers R. Brent Tully
and J. Richard Fisher established that if we know
the rotation velocity of a galaxy we can determine
how bright it is. This correlation is known as TullyFisher (TF) relation. The TF-relation allow us to
find the distance by comparing the magnitude and
the brightness. Astronomers use the TF-relation to
determine when and how LIRGs collision or mix
occurs, also to know the stage of evolution,
distribution and age of the galaxy. The Tully-Fisher
relation allows us to study the galaxies when they
were young. Tully-Fisher relation applies to spiral
galaxies with a normal rotation and a good mass
distribution.
Conclusion
For a small number of galaxies in our sample,
we can say that the T-F relation holds. For the
majority of our objects, we have no data to
investigate if the TF relation is satisfied or not.
Future Work
Due to small number of galaxies, we were
unable to check if some of the LIRGs don’t
follow the TF relation. It is expected that as long
as
the
LIRGs
have
the
rotation
and mass distribution of a normal galaxy, they
will follow the TF-relation. Due to interaction
with closeby galaxies, some of the LIRGs may
not follow this law.
We need to gather data (L_abs, and HI-line
width) for many more LIRGs, and also see if
they are interacting with any nearby galaxy.
Then study TF plots for isolated LIRGs and
interacting LIRGs.
A new step would be to study LIRGs at further
distances to investigate if TF relation is followed
by LIRGs in early stages of development.
References
1) GUZMAN, R., Class Notes, web site,
Ch15.html ,
http://www.astro.ufl.edu/~guzman/ast1002/cl
ass_notes/Ch15/Ch15.html, 05-Jan-2009
2) FREEMAN, K., Structure and Dynamics in the
Local Universe, web site, Dark Matter and
Tully-Fisher Law,
http://www.publish.csiro.au/?act=view_file&file_
id=AS04049.pdf, 2004
3) NEHONSKY, F., Distance measurement in
space, web site, Tully-Fisher Relation,
http://pluslucis.univie.ac.at/FBA/FBA99/Neho/3
_1_3_.html, 1998/99
4) Seeds, M. and Backman, D. (2010/11)
Galaxies, Astro, ( pp. 194-216),(Instructor’s
Edition), Boston, MA, USA : Laura Rush, Bbooks, Ltd.
5) Robert, M. S. & Haynes .M.P. ,1994 Annu. Rev.
Astron. Astrophys., 32: 115
6) Haynes, M.P. & Giovanelli , R. Astron.J. 1984,
89, 758
Acknowledgements
From this plot, and the “trend curve” we see that
L_abs is proportional to W-c for the LIRGs for
which we have been able to collect the relevant
data. L_abs at H-band is dominited by emission
from the stars, and the Hydrogen line width is
describing the motion of gas in those galaxies.
Special thank to:
Dra. Tapasi Ghosh
Prof. Neftalí Sotero Rivera Castillo
Arecibo Observatory
Dr. Juan Arratia
Luis Font
Aida Albó
NSF
Jenipher D. González
Carlos E. Caro