A Photometric Analysis of the Inner Ring of LEDA
1000714.
A THESIS
SUBMITTED TO THE FACULTY OF THE GRADUATE SCHOOL
OF THE UNIVERSITY OF MINNESOTA
BY
Victoria Kuhn
IN PARTIAL FULFILLMENT OF THE REQUIREMENTS
FOR THE DEGREE OF
MASTER OF SCIENCE
Marc Seigar
August, 2021
© Victoria Kuhn 2021
ALL RIGHTS RESERVED
Acknowledgements
First and foremost I would like to thank my advisor Dr. Marc Seigar for his time,
patience, guidance, and knowledge these past two years. I have learned a tremendous
amount and am grateful that I got to work on and learn more about this unique galaxy.
I would like to express my gratitude to my committee members for their help and com-
ments. I would like to thank Dr. Burc¸in Mutlu-Pakdil for her guidance and knowledge
throughout the majority of my time here. Her insight on many of the programs and
software helped me whenever I got stuck. Last but not least, I would like to thank my
friends and family for their continuous support. You guys were always positive and it
was much appreciated.
i
Do. Or do not. There is no try.
Yoda
ii
Abstract
Ring galaxies are a peculiar type of galaxy and the recent discovery of a double ringed
elliptical, called LEDA 1000714, that resembles Hoag’s Object has given astronomers the
chance to study this rare galaxy. Hoag-type galaxies feature completely detached rings
and in order to understand these galaxies, we need to uncover as much information as
possible to determine their nature, formation, and evolution. Previous study of LEDA
1000714 revealed much about the core and outer ring, including structure and radial
profile of the core, structure of the outer ring, and ages for both parts, but due to poor
resolution in the infrared, not much could be determined about the inner ring. With new
near infrared images, we attempt to reveal a more in-depth analysis of the inner ring.
Due to the outer ring only showing up in shorter wavelengths, we only report on the core
and inner ring. We conducted isophotal analysis on the core to confirm previous findings
on the structure and radial profile. Using the 2D image analysis program GALFIT, we
were unable to obtain an image of the inner ring, but we were still able to recover a
lower limit on magnitude of the ring. Also from GAFLIT, we were able to obtain new
magnitudes of the core, and with previously found magnitudes, were able to produce
the observed Spectral Energy Distribution and the age of the core.
iii
Contents
Acknowledgements i
ii
Abstract iii
List of Tables vi
List of Figures vii
1 Introduction 1
1.1 Galaxy Classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1.1 Elliptical Galaxies . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1.2 Lenticular Galaxies . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1.3 Spiral Galaxies . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1.4 Irregular Galaxies . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2 Ring Galaxies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2.1 Polar Ring Galaxies . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.2.2 Spiral Ring Galaxies . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.2.3 Collisional Ring Galaxies . . . . . . . . . . . . . . . . . . . . . . 7
1.2.4 Hoag’s Object and Hoag-type Galaxies . . . . . . . . . . . . . . . 7
1.3 Previous Study of LEDA 1000714 . . . . . . . . . . . . . . . . . . . . . . 8
1.4 Overview of thesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
iv
2 Data 11
2.1 Obtaining the Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.2 Data Reduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.3 Mask Creation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.4 Isophotal Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
3 Analysis 17
3.1 Introduction to GALFIT . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
3.1.1 Least-Squares Minimization . . . . . . . . . . . . . . . . . . . . . 18
3.1.2 Se´rsic Profile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
3.1.3 Point Spread Function . . . . . . . . . . . . . . . . . . . . . . . . 20
3.2 Initial Parameters and Results . . . . . . . . . . . . . . . . . . . . . . . 21
3.3 Isophotal Modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
4 Results 24
4.1 Final GALFIT Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
4.2 Introduction to HyperZ . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
4.3 HyperZ Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
5 Conclusion and Discussion 35
References 37
v
List of Tables
3.1 Initial GALFIT parameters for the I band taken from [Mutlu Pakdil et al., 2017]. 22
3.2 First set of GALFIT results letting all parameters vary. . . . . . . . . . . 22
4.1 Final Galfit results using single Se´rsic function. . . . . . . . . . . . . . . 25
4.2 SEDs of the galaxy in units of magnitudes. J and H band magni-
tudes are from our own analysis, the rest is from Mutlu-Pakdil et al.
[Mutlu Pakdil et al., 2017]. . . . . . . . . . . . . . . . . . . . . . . . . . 30
vi
List of Figures
1.1 Modified Hubble de Vaucouleurs tuning fork diagram. Elliptical galaxies
are on the left and shown in order of increasing ellipticity. In the middle
are the lenticular galaxies and immediately to the right the model sepa-
rates into three different branches to indicate the ordinary, intermediate,
and barred spirals. On the far right lie the irregular galaxies. Image
credits: Antonio Ciccolella/M. De Leo. . . . . . . . . . . . . . . . . . . . 2
1.2 Left image: Messier 105, an E0-1 galaxy. Right image: Messier 59, an
E5 galaxy. Images courtesy of NASA/ESA Hubble Space Telescope. . . 3
1.3 Spiral galaxy vs. barred spiral galaxy. Left image: NGC 1309, SA(s)bc.
Right image: NGC 1672, Sb(s)b. Images courtesy of NASA, ESA, the
Hubble Heritage Team (STScI/AURA), and A. Riess (STScI). . . . . . 4
1.4 Left image: Phoenix Dwarf, IAm. Right image: NGC 4449, Ibm. Images
courtesy of ESO, NASA, ESA, A. Aloisi (STScI/ESA), and The Hubble
Heritage Team (STScI/AURA)-ESA/Hubble Collaboration. . . . . . . . 5
vii
1.5 Top left: NGC 7098, double barred spiral galaxy. Top middle: NGC
1291, barred spiral galaxy. Top right: NGC 7742 (Fried Egg Galaxy),
non-barred Type II Seyfert galaxy. Middle left: NGC 660, polar ring
galaxy. Middle center: Arp 148 (Mayall’s Object), colliding galaxies
resulting in a collisional ring galaxy. Middle right: Cartwheel Galaxy,
collisional ring galaxy that is turning back into a spiral galaxy. Bot-
tom left: NGC 1350, non-barred spiral galaxy. Bottom center: NGC
6028, barred lenticular galaxy as well as Hoag-type galaxy. Bottom right:
NGC 3081, barred lenticular Type II Seyfert galaxy with nuclear ring.
Images courtesy of ESO, NASA/JPL-Caltech, Hubble Heritage Team
(AURA/STScI/NASA/ESA), CHART32 Team, ESA, A. Evans, and SDSS. 6
1.6 Hoag’s Object. In between the core and ring, there is another Hoag-
type object. Image courtesy of NASA and the Hubble Heritage Team
(STScI/AURA). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.7 The 2D B-I color index map showing the outer ring (light blue) as well as
the existence of the inner ring (medium green). Image size is 79”x110”.
[Mutlu Pakdil et al., 2017] . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.1 The image on the left is the H band and the image on the right is the
J band. These images are a combination of several images put together
to help bring out more detail. The left image is 225.8” x 222.6” and the
right image is 255” x 252.3”. . . . . . . . . . . . . . . . . . . . . . . . . 12
2.2 An image of objects masked out using SExtractor. . . . . . . . . . . . . 13
2.3 Top row shows H band. Bottom row shows J band. In both bands, the
isophotes show a slightly elliptical nature of the light from the core. The
residuals for both bands do not show the same structure. It should be
noted that neither residual show any sign of a ring. Images are 31.8” x
31.8”. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.4 The first column shows the variation in ellipticity. The second column
shows the c4 variation. The third column shows the s4 variation. De-
viations start occurring around 6-7” for all the plots, indicating there is
another component besides the core. . . . . . . . . . . . . . . . . . . . . 16
3.1 Example input file that includes two fitting functions. . . . . . . . . . . 19
viii
3.2 PSF, created from GALFIT using eight stars, used for the H band. Image
size is 5.88” x 5.88”. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
3.3 These are the results after removing the first 25 points from the MPFIT
fitting. The Se´rsic value for H is what we were expecting, but the value
for J is much lower than expected and there might have been a problem
during fitting. The bottom panel shows the residuals from the fitting.
Deviations start occurring at around 7”, which is about where we believe
the inner ring to lie. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
4.1 The 2D images are shown in I, J, and H from left to right. Image size for
I is 68”x68” and image size for J and H is 64”x64”. The top row depicts
the original image, the middle row are the models that GALFIT generated,
and the bottom row are the residuals. The outer ring is only visible in
the I band. The inner ring also appears in the I band, but does not seem
to appear in either the J or H band. . . . . . . . . . . . . . . . . . . . . 26
4.2 Left image is the J band and right image is the H band. Two ellipse
regions are shown to indicate about where the inner ring lies. . . . . . . 27
4.3 First part of the hyperz.param. . . . . . . . . . . . . . . . . . . . . . . . 28
4.4 Second part of the hyperz.param. . . . . . . . . . . . . . . . . . . . . . 29
4.5 The left image shows the best fit model while using a fixed metallicity
and only evolving synthetic models. The right image shows the best fit
model from [Mutlu Pakdil et al., 2017]. The observed SEDs are in red
and the best fitting model is shown in black. . . . . . . . . . . . . . . . 33
4.6 Flowchart explaining how HyperZ works. . . . . . . . . . . . . . . . . . 34
ix
Chapter 1
Introduction
1.1 Galaxy Classification
Even though astronomers have been looking at the skies for hundreds of years, galax-
ies were not categorized until the 1920’s. Edwin Hubble had been studying galax-
ies, or nebulae, as they had been called back then and created a classification scheme
[Hubble, 1926, Hubble, 1927] called the Hubble tuning fork diagram, a visual represen-
tation of galaxies [Hubble, 1936]. This diagram classified galaxies into four different
types: ellipticals, spirals (normal and barred), and irregulars [Hubble, 1926]. Elliptical
galaxies were on the left and spiral galaxies were on the right where they branched off
into different directions. It was later modified in 1959 [de Vaucouleurs, 1959] and again
in 1963 [de Vaucouleurs, 1963] by Gerard de Vaucouleurs. Figure 1.1 shows this modi-
fied diagram which continues to be used to this day. This modified classification scheme
has since come to include lenticular and intermediate galaxies, as well as reclassify-
ing normal spirals as ordinary and classifying galaxies as either ringed or spiral-shaped
[de Vaucouleurs, 1963].
1.1.1 Elliptical Galaxies
Elliptical galaxies are the oldest type of galaxies in the universe and they appear either
elliptical or circular in nature. They are commonly given a classification of E0 to E7,
based on the equation 10 × (1 − ba) with b being the semi-minor axis and a the semi-
major axis. E0 galaxies are the circular galaxies and E7 galaxies are extremely elliptical
1
2Figure 1.1: Modified Hubble de Vaucouleurs tuning fork diagram. Elliptical galaxies
are on the left and shown in order of increasing ellipticity. In the middle are the
lenticular galaxies and immediately to the right the model separates into three different
branches to indicate the ordinary, intermediate, and barred spirals. On the far right lie
the irregular galaxies. Image credits: Antonio Ciccolella/M. De Leo.
and appear almost flat when seen edge on. Figure 1.2 shows some examples of elliptical
galaxies. These galaxies can vary wildly in luminosity, size, and mass. They tend to form
and live in clusters of galaxies since it is believed that they mostly form from collisions
between other galaxies. These collisions happened billions of years ago which is why
these galaxies have settled into their current state and they appear redder than other
galaxies due to inactive star formation. Ellipticals are among the largest and smallest
galaxies, with sizes ranging from < 1 kpc up to 600 kpc. Studies have shown that a
supermassive black hole resides at the center of every elliptical galaxy and that the mass
of the black hole is is correlated with the mass of the galaxy [Ferrarese and Merritt, 2000,
Tremaine et al., 2002].
1.1.2 Lenticular Galaxies
Lenticular galaxies are a transition galaxy between late type (spiral) and early type
(elliptical) and have the classification S0. These galaxies have a bright central bulge or
spheroidal core (similar to elliptical galaxies) surrounded by a flat, structureless region
3Figure 1.2: Left image: Messier 105, an E0-1 galaxy. Right image: Messier 59, an E5
galaxy. Images courtesy of NASA/ESA Hubble Space Telescope.
(similar to spirals, but without the arms) [Binney and Merrifield, 1998]. Lenticular
galaxies can host a bar.
1.1.3 Spiral Galaxies
Spiral galaxies are galaxies that contain a bulge, that may or may not have a bar,
surrounded by a rotating flat disk of stars, gas, and dust. They can have as few as
one arm and as many as five arms. These arms are a breeding ground for new star
formation, which is why the arms appear blue in color. In barred spirals, the arms
originate from the bar. Some studies have shown that bars appear in over 60% of spiral
galaxies and are more common in present day [Sheth et al., 2008].
Spirals are considered late-type galaxies and have two main classifications: ordinary
(SA, formerly S) and barred (SB) with barred being the more common type. A third
type, intermediate (SAB) [de Vaucouleurs, 1959], was added later on by de Vaucouleurs
to classify those galaxies with weak bars, but spiral arms. Spiral galaxies are further
classified (a, ab, b, bc, c, cd, d) by how tightly their arms are wound. A classification
of ”a” means that the arms are tightly wound, a ”d” indicates the arms are very loosely
bound, and ”b” and ”c” fall in-between the two. The double classifications are for those
4galaxies whose arms fall between two categories. Figure 1.3 shows some examples of
spiral galaxies.
Figure 1.3: Spiral galaxy vs. barred spiral galaxy. Left image: NGC 1309, SA(s)bc.
Right image: NGC 1672, Sb(s)b. Images courtesy of NASA, ESA, the Hubble Heritage
Team (STScI/AURA), and A. Riess (STScI).
1.1.4 Irregular Galaxies
Irregular galaxies are galaxies that often appear chaotic in nature, tend to be on the
smaller side (< 10 kpc), and unlike spirals and ellipticals, generally don’t have any sort
of well defined structure. There are several classifications of irregulars, but the two main
categories are Irr I and Irr II. Irr I galaxies have some features of a structure, like a
bar or a bulge, but not enough to classify them as such. They are also lacking in heavy
elements. Irr II galaxies do not have any structure to them (see Fig. 1.4). They tend
to have active star regions and have high levels of interstellar matter, making most of
them starburst galaxies [Longair, 2008].
1.2 Ring Galaxies
Ring galaxies are considered to be a peculiar type of galaxy. These galaxies feature a
bright circle of young blue stars. There are several types including: polar ring, nuclear,
collisional, barred spiral, non-barred spiral, and Hoag-type (see Fig. 1.5).
5Figure 1.4: Left image: Phoenix Dwarf, IAm. Right image: NGC 4449, Ibm. Images
courtesy of ESO, NASA, ESA, A. Aloisi (STScI/ESA), and The Hubble Heritage Team
(STScI/AURA)-ESA/Hubble Collaboration.
1.2.1 Polar Ring Galaxies
Polar ring galaxies are mainly edge-on lenticular galaxies whose rotation axis is perpen-
dicular or almost perpendicular to the plane on which a gas ring rotates [Schweizer et al., 1983,
Whitmore et al., 1990]. There are two main theories for the formation of these types
of galaxies. The first is that the polar ring is the result of a merger. This scenario
states that an intruder galaxy collides head-on with a second galaxy and the gas from
this second galaxy forms the polar ring [Bekki, 1998]. The second scenario is that the
galaxy accreted gas from a nearby or passing galaxy [Schweizer et al., 1983]. Whitmore
et al. [Whitmore et al., 1990] found that about 0.5% of all lenticular galaxies host a
polar ring and up to 5% have or have had a polar ring at some point.
1.2.2 Spiral Ring Galaxies
Rings can occur in both barred and non-barred spiral galaxies. However, they are not
as common in non-barred galaxies as opposed to barred galaxies [Grouchy et al., 2010].
Spiral galaxies can have three types of rings: nuclear (r/a < 1), inner (r/a ' 1),
and outer (r/a > 1) [Binney and Merrifield, 1998]. Nuclear rings mainly appear in
barred galaxies and are believed to form from the bars [Athanassoula, 1992]. In barred
ring galaxies, gases accumulate at the resonances and they speed up creating a ring
6Figure 1.5: Top left: NGC 7098, double barred spiral galaxy. Top middle: NGC
1291, barred spiral galaxy. Top right: NGC 7742 (Fried Egg Galaxy), non-barred Type
II Seyfert galaxy. Middle left: NGC 660, polar ring galaxy. Middle center: Arp 148
(Mayall’s Object), colliding galaxies resulting in a collisional ring galaxy. Middle right:
Cartwheel Galaxy, collisional ring galaxy that is turning back into a spiral galaxy. Bot-
tom left: NGC 1350, non-barred spiral galaxy. Bottom center: NGC 6028, barred lentic-
ular galaxy as well as Hoag-type galaxy. Bottom right: NGC 3081, barred lenticular
Type II Seyfert galaxy with nuclear ring. Images courtesy of ESO, NASA/JPL-Caltech,
Hubble Heritage Team (AURA/STScI/NASA/ESA), CHART32 Team, ESA, A. Evans,
and SDSS.
7[Buta and Combes, 1996, Shlosman, 2001, Schwarz, 1984]. Rings in non-barred galax-
ies are believed to form from secular evolution [Buta and Combes, 1996]. There is an-
other theory that the bar could have dissolved and simulations have shown that the ring
remains well after the dissolution of the bar [Athanassoula, 1996].
1.2.3 Collisional Ring Galaxies
Collisional ring galaxies are the most common true ring galaxy type. These galaxies are
formed when an intruder galaxy crashes through the center of another galaxy, which trig-
gers star formation from the resulting density waves [Appleton and Struck-Marcell, 1996].
These waves then push out and evolve into the shape of a ring. Figure 1.5 shows the
famous Cartwheel Galaxy, whose spokes are connecting the outer ring to the inner ring,
as well as Arp 148, which is in the middle of the collision process.
1.2.4 Hoag’s Object and Hoag-type Galaxies
Hoag-type galaxies are the last type of ring galaxy. The prototype for this galaxy was
discovered in 1950 in the constellation Serpens Caput by Arthur Hoag [Hoag, 1950].
These galaxies feature a bright elliptical core with a circular detached outer ring and are
very rare [Schweizer et al., 1987]. The core of Hoag’s Object is a spheroid [Schweizer et al., 1987]
and the brightest part of the ring is circular (see Fig. 1.6), but the isophotes on the
outside of the ring are slightly extended [Brosch, 1985].
The origin of these galaxies has been debated on for several years. Hoag origi-
nally thought that the ring could be due to a diffraction effect or gravitational lensing
[Hoag, 1950], but this has been ruled out by both Hoag and Schweizer [Schweizer et al., 1987].
They both agree that this was not formed from a collision. The parameters for this to
happen had to be very specific and if even one of them was off by a little, it would result
in a non-uniform or elliptical ring or it would have an off-center core [Brosch, 1985].
There is also no galaxy nearby that could have acted as the intruder and the rela-
tive velocity for these galaxies would have had to be at least 100 km/s, but the ve-
locity difference between the core and the ring is almost zero [Schweizer et al., 1987].
Brosch and Schweizer do agree that the ring is between 1 and 3 Gyr old [Brosch, 1985,
Schweizer et al., 1987].
8Figure 1.6: Hoag’s Object. In between the core and ring, there is another Hoag-type
object. Image courtesy of NASA and the Hubble Heritage Team (STScI/AURA).
Brosch suggested that the galaxy could have formed from an extreme case of bar
instability and the bar has since dissolved [Brosch, 1985]. However, this was ruled out
by the spheroidal, and not disky, nature of the core [Schweizer et al., 1987]. Schweizer
instead suggested that a major accretion event occurred. A newer study by Finkelman
et al. showed that the core formed more than 10 Gyr ago and they think that the ring
formed by accretion of gas from the intergalactic medium onto an already formed ellip-
tical galaxy that currently serves as the core of Hoag’s Object [Finkelman et al., 2011].
1.3 Previous Study of LEDA 1000714
In 2017, a new ring galaxy was discovered by Burc¸in Mutlu-Pakdil [Mutlu Pakdil et al., 2017]
and is listed as LEDA 1000714 (previously PGC 1000714). This galaxy features two
completely detached rings around a bright central core. Formerly classified as an (R)SAa
in the NASA/IPAC Extragalactic Database, it has been reclassified as a double ringed
elliptical (E2). Previous analysis was done on LEDA 1000714 in the near-ultraviolet
(NUV), optical (BVRI), near-infrared (NIR), and mid-infrared (MIR) bands.
The isophotal analysis from the IRAF task ELLIPSE showed that the galaxy is
9slightly elliptical, with  ∼ 0.1, and there appears to be no sign of a bar at the core.
A 1D fitting was used to understand the radial profile of the galaxy. A Se´rsic model
was used and converged to the de Vaucouleurs law (see Chapter 3.1.2) with residuals
showing a reddish substructure. During the 2D fitting of the galaxy, it was discovered
that the galaxy had a second diffuse inner ring (see Fig. 1.7) and explained the residuals
in the 1D fitting.
Figure 1.7: The 2D B-I color index map showing the outer ring (light blue) as
well as the existence of the inner ring (medium green). Image size is 79”x110”.
[Mutlu Pakdil et al., 2017]
The outer ring is clearly visible in the NUV and optical bands, but is undetectable
in the MIR. The outer ring extends from ∼ 20” until it fades away at ∼ 40”. The peak
surface brightness is fainter than that for Hoag’s Object [Finkelman et al., 2011]. The
residuals from the 1D fitting showed the inner ring to lie from ∼ 8” to ∼ 15”. The
inner ring is nearly undetectable in the B band, but becomes more visible in the longer
10
wavelengths. Spectral analysis was done on only the core and the outer ring and they
were found to be 5.5 Gyr and 0.13 Gyr, respectively.
Due to the color difference between the rings, it is believed that this galaxy has
two formation periods. The galaxy lies in a low density environment and therefore a
collision formation is not probable. An accretion event is the most likely scenario for the
creation of the outer ring, but there was not enough data to determine the formation
of the inner ring. Since this galaxy has two detached rings, it is not a Hoag-type, but
an entirely new type of galaxy.
1.4 Overview of thesis
The goals of this thesis are to investigate further the inner ring of LEDA 1000714.
The structure for this thesis is organized as follows. Chapter 2 describes the data and
preliminary findings on the general properties of LEDA 1000714. Chapter 3 gives an
introduction to GALFIT and MPFIT. Here we talk about important aspects of our 2D and
1D fitting and give a brief overview of initial results. Chapter 4 introduces HyperZ, a
SED fitting code and goes through the final results obtained from GALFIT as well as
HyperZ. Chapter 5 will give the final conclusions, a discussion on the results, and talk
about future work.
We used a standard cosmology of H0=73 km/s/Mpc, ΩM=0.3, ΩΛ=0.7, and mag-
nitudes are given in the Vega system.
Chapter 2
Data
2.1 Obtaining the Data
Due to the low resolution of the images in the near-infrared from previous study, LEDA
1000714 had to be re-imaged with better resolution. New images were taken during local
dark time on 16 January 2018 with the FourStar Infrared Camera on the 6.5-m Baade
Telescope at Las Campanas Observatory in Chile. The FourStar camera has a 4096 x
4096 pixel area which covers the J (1.25µm), H (1.64µm), and Ks (2.15µm) bands for
a total field of view of 10.8’x10.8’. The camera has four Teledyne HAWAII-2RG arrays
to achieve this total area. The scale length is 0.159” per pixel.
2.2 Data Reduction
Due to the size of the galaxy, it was able to be imaged on only one array. We used
SAOImage ds9 to display our images. The galaxy did not show up on the Ks band
images and therefore our analysis was done with only the J and H bands. While looking
through the images, we discovered a defect on several of the images. This defect appears
in several of the J and H images that contained the galaxy, however this has not had
any impact on our analysis.
Image reduction was done using the Image Reduction and Analysis Facility (IRAF)
software written by the National Optical Astronomy Observatory. The images were
combined within their respective bands using the IRAF IMCOMBINE command. We
11
12
first used IMSHIFT to shift each of the images so that the galaxy had the same image
coordinates. We then used the IMSTATISTICS task on each corner of the images to find
the sky background, averaged them, then subtracted it off of the images. We were then
able to combine the images into an H band and J band image respectively (Figure 2.1).
The H band had 10 images that contained the galaxy and the J band had 16 images.
The exposure time for the H band was 2 x 64.042 s, 3 x 20.377 s, and 5 x 11.644 s for
a total time of 247.435 seconds and the J band had an exposure time of 5 x 64.042 s,
8 x 20.377 s, and 3 x 78.597 s for a total time of 719.017 seconds. The zeropoints were
found to be 15.3 and 14.3 mag for the J and H band respectively.
Figure 2.1: The image on the left is the H band and the image on the right is the J
band. These images are a combination of several images put together to help bring out
more detail. The left image is 225.8” x 222.6” and the right image is 255” x 252.3”.
2.3 Mask Creation
Before we began the analysis, we had to create masks for our images. There are two
fairly large bright objects near the core of the galaxy that needed to be masked out.
This needs to be done so that the analysis could be as precise as possible without
interference from those other sources. We used the Source Extractor (SExtractor)
[Bertin and Arnouts, 1996] program to create a mask for both the J and H band images.
13
SExtractor is run from the command line using the command sex image.fits -c
config file.sex. There are two main files that the user needs to run SExtractor: the
.sex file and the .param file. The .param file has a list of all the different measurements
that SExtractor could print out, but for our purposes, we just needed a list of the number
of objects in our image within a certain brightness. The .sex file is the configuration
file where the user has to make parameter specifications according to their data. This
file has an array of parameters in it, but the ones that we mainly changed were the
detection and analysis threshold, seeing FWHM (full-width at half maximum), pixel
scale, and image type. The seeing FWHM is based on the FWHM we got from our
point spread function (see Ch. 3.1.3).
Since there are two objects that were so close to the core, we had to be very careful
about masking out only those objects and not the core. We had to keep changing the
detection threshold and analysis threshold parameters in order to get as clean of a mask
as possible with minimal overlap from the core.
Figure 2.2: An image of objects masked out using SExtractor.
14
2.4 Isophotal Analysis
We used the Elliptical Isophote Analysis subpackage [Bradley et al., 2020], as part of the
Astropy Project [Astropy Collaboration et al., 2013, Astropy Collaboration et al., 2018],
to fit elliptical isophotes to the galaxy. This subpackage requires the x and y pixel coor-
dinates of the object that is being fitted as well as the semi-major axis, position angle,
and ellipticity. The isophotes measured are taken from the procedure described by
Jedrzejewski [Jedrzejewski, 1987]. The first column in Figure 2.3 shows the isophotes
for the galaxy. The isophotes are almost evenly spaced out indicating a fairly smooth
profile and are slightly elliptical. The second column shows the model image that the
package created. The third column shows the residual image. One interesting thing to
note is that the residuals are not the same in the H and J bands. We would expect
them to have similar residuals, but the J band appears to show a possible bar at the
center of the galaxy.
The ellipticity plots are in agreement with each other and previous study. The core
of the galaxy is fairly round and has an ellipticity value of  ∼ 0.11 ± 0.01. We can look
further at the structure of the core by looking at the isophotal shape parameters (c4 and
s4) that can be printed out as part of the IsophoteList. The isophotes for an elliptical
galaxy can take on either a boxy shape (c4<0) or a disky shape (c4>0), as described
by Milvang-Jensen and Jørgensen [Milvang-Jensen and Jørgensen, 1999]. The s4 and
c4 values represent the Fourier modes (sin4θ and cos4θ, respectively) and are calculated
from
y(φ, order) = y0 +An ∗ sin(order ∗ φ) +Bn ∗ cos(order ∗ φ) (2.1)
where φ is the angle along the elliptical path, order is the harmonic that is being
fitted, An represents s4, and Bn represents c4.
From Figure 2.4, we can see that around 7” the c4 and s4 values start to deviate
from zero and this is an indication that there is some sort of underlying structure in
this galaxy. These deviations are most likely caused by the inner ring.
15
Figure 2.3: Top row shows H band. Bottom row shows J band. In both bands, the
isophotes show a slightly elliptical nature of the light from the core. The residuals for
both bands do not show the same structure. It should be noted that neither residual
show any sign of a ring. Images are 31.8” x 31.8”.
16
Figure 2.4: The first column shows the variation in ellipticity. The second column
shows the c4 variation. The third column shows the s4 variation. Deviations start
occurring around 6-7” for all the plots, indicating there is another component besides
the core.
Chapter 3
Analysis
3.1 Introduction to GALFIT
To better understand the residuals and to look at the parameters of LEDA 1000714, we
used the GALFIT software. GALFIT, written by Chien Peng [Peng et al., 2002, Peng et al., 2010],
is a data analysis algorithm that fits 2D functions to user supplied imaging data. In the
latest version, GALFIT can model many different objects to all kinds of different galaxies
with intricate structures. All of our analysis was done using version 3.0.5, released in
2013, which can be downloaded in binary form on GALFIT’s website located here1.
GALFIT is run by using the command galfit galfit.feedme, where galfit.feedme
is the input file the user needs to run GALFIT and where they need to state the func-
tions they wish to model their galaxy with. Figure 3.1 shows an example input file
with two functions. The input file has two main sections: IMAGE and GALFIT CONTROL
PARAMETERS and INITIAL FITTING PARAMETERS. There are four columns in the file.
The first column indicates the item number (A-P, 1-10, or Z, among others). The sec-
ond column are the guesses/values/file names that the user identifies and supplies. The
third column (this is only in the second section) is either 0 or 1 and is used to either
hold (0) or vary (1) the parameters. Lastly, the fourth column is a brief description of
the parameter on that line.
The first section has 13 parameters, labeled A-K, O, P that the user needs to
change/specify for their specific data. The important parameters are the input file,
1https://users.obs.carnegiescience.edu/peng/work/galfit/galfit.html
17
18
the output file, the sigma image if the user has one (GALFIT will internally create one
if one is not supplied), point spread function, mask, image region of fitting, zeropoint,
and plate scale.
The second section is where the user determines which functions to use. The most
commonly used functions are nuker, se´rsic, expdisk, devauc, gaussian, moffat, and sky.
Each function has between 3 and 10 parameters that need to be identified. These
parameters can either be guesses or actual values that the user knows. If the user is
fitting only one function, then the guess can be an estimate, but as the number of
functions goes up, the more accurate the initial guesses have to be in order for GALFIT
to converge on a solution.
When GALFIT is run, it continuously outputs the fitting parameters with what it
thinks is the correct solution. It will run through several iterations before it finds the best
solution and converges on it. When it is done running, there are three ouputs: fit.log,
galfit.NN, and imgblock.fits. The fit.log shows the best fitting parameters with
their uncertainties, number of degrees of freedom (Ndof ), chi-square (χ
2), and reduced
chi-square (χ2ν). The best fitting parameters are added on to the end of the file each
time GALFIT is run. The galfit.NN goes more in depth for each run. The .NN starts
at .01 and increases every time GALFIT is run so that the files are not written over each
other. This file has the same format as the input file, except the parameters in the
second half are replaced with the best fit parameters that were found. This file also
includes the Ndof , χ
2, and χ2ν . The last output file is the imgblock.fits. This fits file
has four separate images on it: [0] is a blank image, [1] is the region that the user wants
to fit based on the convolution box size, [2] is the final model that GALFIT generates,
and [3] is the residual image.
3.1.1 Least-Squares Minimization
GALFIT is a non-linear least-squares algorithm that uses the Levenberg-Marquardt al-
gorithm to measure the goodness of fit. It does this by calculating the χ2 and adjusting
the parameters to find the best fit. It continues to do this until the best fit is found
where the algorithm will then calculate the χ2ν to indicate the goodness of fit. The χ
2
ν
is described by
19
Figure 3.1: Example input file that includes two fitting functions.
20
χ2ν =
1
Ndof
nx∑
x=1
ny∑
y=1
(fdata(x, y)− fmodel(x, y))2
σ2x,y
(3.1)
where nx and ny are the image dimensions in pixels, fdata(x, y) is the image flux at
(x,y), fmodel(x, y) is the model that GALFIT generates, and σx,y is the sigma image that
either the user provides or GALFIT creates based on gain and read noise.
The χ2ν has an expectation value of 〈χ2ν〉=1 [Bevington and Robinson, 2003]. A
χ2ν=1 means that the model fits the data exactly. If χ
2
ν > 1 or χ
2
ν < 1, then the model is
not fitted well to the data and there may be problems with measurements, uncertainties,
etc.
3.1.2 Se´rsic Profile
The Se´rsic profile [Se´rsic, 1963] is one of the most used profiles to study the morphology
of bulges and elliptical galaxies. This profile is a generalized version of de Vaucouleur’s
law [de Vaucouleurs, 1948], which states that the intensity of light, I, from a galaxy
varies with distance, R, and goes as R1/n where n is the Se´rsic index and has a value of
4 when dealing with the de Vaucouleur profile.
Se´rsic’s equation is more commonly known today as
I(R) = Ieexp
{
−bn
[(
R
Re
)1/n
− 1
]}
(3.2)
where Ie is the intensity at the effective radius Re where half the light from the
galaxy is emitted. The Se´rsic index, n, has several different special cases besides de
Vaucouleurs including n=1 for an exponential profile and n=0.5 for a gaussian profile.
The Se´rsic index tells you about the shape and luminosity of the galaxy. For n ≈ 4, the
galaxy has an elliptical shape and for n ≈ 1, the galaxy has a spiral, disky shape.
3.1.3 Point Spread Function
We first created a point spread function (PSF) using tasks in IRAF. Several stars were
pre-selected as candidates to be used and we found the full-width at half maximum
(FWHM) for each of them. Then we used PHOT, DATAPARS, CENTERPARS, FITSKYPARS,
and PHOTPARS to set up the parameters needed to create a PSF. Once that was done
21
and after running the PHOT command, we again had to select the stars whose radial
profile had a strong, well defined curve. Next, we continued to set up parameters with
the tasks DAOPARS and PSTSEL. Then we ran PSF and after confirming that our stars
were decent candidates, a PSF was created. Our results were extremely noisy and we
were unable to get a useful PSF.
We then turned to GALFIT for creating a PSF (Fig. 3.2). We again used the same
stars as before and modeled them with a gaussian function. We used the IMCOMBINE
task in IRAF to create a strong PSF. One was created for each band studied. The PSFs
have a FWHM of 0.65” and 0.67” for the H and J bands respectively. The intensity
profile for each PSF was checked in IRAF to further insure that they were usable.
Figure 3.2: PSF, created from GALFIT using eight stars, used for the H band. Image
size is 5.88” x 5.88”.
3.2 Initial Parameters and Results
Since we did not know what the parameters for the J and H bands would be, we used
the parameters from the I (0.80 µm) band that were previously listed in Mutlu Pakdil
et al. [Mutlu Pakdil et al., 2017]. For our first run through of the data, we used a
single Se´rsic component and let all parameters vary. Table 3.1 gives the list of initial
22
Table 3.1: Initial GALFIT parameters for the I band taken from
[Mutlu Pakdil et al., 2017].
Band µe (mag arcsec
−2) Re (arcsec) n b/a P.A. (degrees)
I 21.14 5.46 5.02 0.85 48.91
Table 3.2: First set of GALFIT results letting all parameters vary.
Parameters J H
µe (mag arcsec
−2) 24.46 ± 0.03 26.47 ± 0.02
Re (arcsec) 2.77 ± 0.04 3.02 ± 0.04
n 2.20 ± 0.05 3.27 ± 0.05
b/a 0.90 ± 0.01 0.88 ± 0.01
P.A. (degrees) 46.15 ± 4.10 47.78 ± 2.44
parameters.
Our first sets of results produced values that were considerably lower than what we
were expecting. These values are listed in Table 3.2. Since we were getting low n values,
we added an exponential disk function along with our Se´rsic function. This resulted in
an over subtraction of the model.
3.3 Isophotal Modeling
To look more closely at the core of the galaxy, we used the least-squares minimiza-
tion IDL package MPFIT [Markwardt, 2009]. Like GALFIT, MPFIT uses the Levenberg-
Marquardt technique to solve the least squares problem. To do a 1D fitting, the user
supplies the data that they want fit and the certain model they want the data to fit to.
We used our radius, intensity, and intensity error values from the elliptical isophotal
analysis and for our model we used a single Se´rsic bulge model. We also tested the data
with a Se´rsic + exponential disk model based off of the results from GALFIT after using
a Se´rsic and exponential function there. Each model was run four times, ignoring the
first 10, 15, 20, 25 points due to seeing effects.
23
Results from MPFIT report the best fitting parameters as well as the reduced chi-
square. From the MPFIT fitting, we were able to get the surface brightness and initial
surface brightness in both flux and mags, the effective radius and scale length both in
arcsecsonds, and the Se´rsic index.
Figure 3.3: These are the results after removing the first 25 points from the MPFIT
fitting. The Se´rsic value for H is what we were expecting, but the value for J is much
lower than expected and there might have been a problem during fitting. The bottom
panel shows the residuals from the fitting. Deviations start occurring at around 7”,
which is about where we believe the inner ring to lie.
The data showed that as more points were removed, the better the data fit to the
model. The results also showed that a single Se´rsic model best described the data. The
Se´rsic + exponential disk model did not have a good fit, which was also indicated from
the GALFIT results. The best fit was with 25 points removed and a single Se´rsic model
(Fig. 3.3.
The analytical results matched with what we were expecting from previous analysis.
The best fit for the H band gave a Se´rsic index of 5.65 and a surface brightness of 17.72
mag. The results for the J band were still considerably lower than expected and this is
most likely due to a problem in the fitting.
Chapter 4
Results
4.1 Final GALFIT Results
After getting results from MPFIT, we went back to GALFIT and used these initial param-
eters. We used the the best fitting H results for both the H and J bands since our J
results were erroneous. After running through these results, we decided to add a sky
component to our fitting.
GALFIT assumes the background is a flat plane, but the user can tilt it in both the
x and y directions. The user tells GALFIT where the center of the galaxy is (x,y) and
GALFIT determines the sky value by
sky(x, y) = sky(xc, yc) + (x− xc)dsky
dx
+ (y − yc)dsky
dy
(4.1)
where (xc,yc) is the fixed geometric center of the image.
Table 4.1 gives the final best fitting parameters. The Se´rsic index for H (5.08) proved
to be good while the index for J (3.34) was still lower than expected. The axis ratio
for each band was 0.90 indicating that this is a slightly elliptical galaxy and it confirms
with the results from the isophotal analysis. The total magnitudes came out to be 13.15
mag for the J band and 12.72 mag for the H band. Previous analysis showed that the
magnitudes were 13.24 mag and 12.80 mag for the J and H band respectively. This
agrees with what we got.
Figure 4.1 shows the final image results. The top row shows the input image from
24
25
Table 4.1: Final Galfit results using single Se´rsic function.
Parameters J H
mtotal (mag) 13.15 ± 0.01 12.72 ± 0.01
µe (mag arcsec
−2) 18.97 ± 0.03 19.35 ± 0.06
Re (arcsec) 3.39 ± 0.06 4.54 ± 0.14
n 3.34 ± 0.08 5.08 ± 0.11
b/a 0.90 ± 0.01 0.90 ± 0.01
P.A. (degrees) 45.37 ± 3.98 49.90 ± 2.62
GALFIT. The middle row shows the models that were generated. The third row shows
the residual images. The I band images are reproduced from the original data from the
Direct CCD Camera on the 2.5-m du Pont Telescope at Las Campanas Observatory.
The inner ring does not show up in the J and H band images, which was not expected.
These residuals also do not show evidence of a bar-like feature in the core.
Though we cannot see the inner ring, we still found the lower limit for the total
magnitude. We used the edit and shape parameters in ds9 to create ellipses of roughly
where the inner ring starts and stops (Fig. 4.2). To determine the magnitude of the
ring, we used the IRAF command IMSTATISTICS on six different 20x20 pixel areas. We
took the means of the areas and averaged them. Next, we found the area of the ring
and used Equation 4.2 to find the magnitude of the inner ring.
mtotal = −2.5log10(mean(area) ∗ area) + zpt (4.2)
The magnitude in the J band is 14.63 mag and the magnitude in the H band is
11.79 mag. These are lower limit magnitudes for the inner ring and the brightest it
could possibly be.
4.2 Introduction to HyperZ
Spectral energy distribution (SED) is the distribution of energy over wavelength. SED
fitting is useful in determining the properties of galaxies and it works by fitting observed
SEDs to model SEDs to find the best fit.
26
Figure 4.1: The 2D images are shown in I, J, and H from left to right. Image size for
I is 68”x68” and image size for J and H is 64”x64”. The top row depicts the original
image, the middle row are the models that GALFIT generated, and the bottom row are
the residuals. The outer ring is only visible in the I band. The inner ring also appears
in the I band, but does not seem to appear in either the J or H band.
27
Figure 4.2: Left image is the J band and right image is the H band. Two ellipse
regions are shown to indicate about where the inner ring lies.
To look at the stellar populations of LEDA 1000714, we used the HyperZ photo-
metric redshift code, version 1.3 [Bolzonella et al., 2000]. We make use of data from
[Mutlu Pakdil et al., 2017], in addition to our own to get an age of the core of the
galaxy. These values are listed in Table 4.2.
In HyperZ, the SED fitting procedure is based on the fit of the overall shape and
detection of spectral properties [Bolzonella et al., 2000]. Under the same photometric
system, the observed SEDs are compared to template SEDs, created from a set of
reference spectra. The best fit is determined by the minimization of χ2.
The code can be run on the command line with the command hyperz. The program
will print out the version of the code that is being used and will ask for the name of
the parameter file. By default, the parameter file is hyperz.param (see Figures 4.3 and
4.4), which controls the input and output data.
Input Files
There are several input files HyperZ needs in order to run. Some the user needs to
define/change and others are provided.
• AOVSED: file for Vega spectrum (provided)
28
Figure 4.3: First part of the hyperz.param.
29
Figure 4.4: Second part of the hyperz.param.
30
Table 4.2: SEDs of the galaxy in units of magnitudes. J and H band magnitudes are
from our own analysis, the rest is from Mutlu-Pakdil et al. [Mutlu Pakdil et al., 2017].
Filters Bulge Inner Ring
Near-UV NUV 17.74 ± 0.24 ...
B 16.36 ± 0.06 ...
Optical V 15.39 ± 0.11 ...
R 15.21 ± 0.10 ...
I 14.06 ± 0.13 ...
J 13.15 ± 0.01 14.63 ± 2.24
Near-IR H 12.72 ± 0.01 11.79 ± 2.24
Ks 12.51 ± 0.34 ...
W1 12.56 ± 0.35 ...
Mid-IR W2 12.61 ± 0.30 ...
W3 11.64 ± 0.44 ...
• FILTERS RES: filter transmission functions (provided, but the user can add their
own transmissions if they are not already included in the list)
• FILTERS FILE: information on the different filters used
• TEMPLATES FILE: SED templates to use and their type
• CATALOG FILE: file containing the input photometric data
Parameters
These are some of the important parameters included in the input file.
• MAG TYPE: the type of magnitude that is used in the CATALOG FILE
• Z MIN and Z MAX: upper and lower limits on redshift range
• REDDENING LAW: law for internal reddening
• AV MIN and AV MAX: upper and lower limits on absorption in the V band
• AGE CHECK: checks to see if the age of the template is less than the age of the
universe
31
• OUTPUT TYPE: flux units for output files
• SPECTRUM: contains spectrum for the best fit model
Output Files
There are up to five files the user can print out. Three of them are described below.
• .obs sed: the observed SEDs as the mean integrated fluxes with their correspond-
ing errors
• .temp sed: the best fit integrated SEDs
• .z phot: the best fit parameters and redshift. This includes the redshift, age, and
reduced chi-square.
• .out phot: summarizes the best fitting parameters. This includes the SEDs used,
redshift range, reddening law, range of magnitudes, and cosmological parameters.
Only file that is printed every time hyperz is run.
HyperZ provides both observed and synthetic SEDs, however, the user can add or
take away the templates. Templates can be downloaded here. There are four observed
SEDs from the mean spectra of local galaxies from Coleman, Wu, & Weedman (CWW)
[Coleman et al., 1980]. The synthetic templates comes from the spectral evolution li-
brary of Bruzual & Charlot (BC) [Bruzual A. and Charlot, 1993].
We used a lower and upper initial mass function (IMF) cutoffs of 0.1M and 100M
and used the Salpeter [Salpeter, 1955] and Miller & Scalo [Miller and Scalo, 1979] IMF
laws. We mainly used an exponential decay for our star formation rate (SFR) which is
defined as
ψ(t) =
1
ψ0
exp
−t
τ (4.3)
where τ = 1, 2, 3, 5, 15, and 30 Gyr. We also made use of a single burst and constant
SFR. We used a fixed metallicity equal to the solar metallicity, Z ' 0.02. To account
for dust extinction, we use the reddening law from Calzetti et al. [Calzetti et al., 2000].
32
The first step that HyperZ takes is to read the observed magnitudes, errors, and
limiting magnitudes. Next, a dereddening is applied, if requested, and the magnitudes
and errors are transformed into fluxes. While this is happening, a hypercube is created
which contains the fluxes from the spectra. If the spectra are from the synthetic models,
hyperz rebins it from 221 ages down to 51 ages. These 51 ages range from 0.32 Myr to
19.5 Gyr (age of the universe is ≈ 13.8 Gyr). It is then reddened by the law the user
specified in the hyperz.param file, then depressed with a Lyman forest according to the
redshift step specified. Next, the spectra is convolved with the filter response functions
to get the expected fluxes. Once the hypercube has been built, the χ2 is calculated with
the redshifts, spectral types, ages, and absorption values considered. A flowchart of this
process is shown in Figure 4.6. When running, the program will write out the number
of SEDs being used, the number of filters, and the number of objects in the catalogue.
4.3 HyperZ Results
We got a wide range of ages depending on what templates we used. Using the fixed
metallicity Miller-Scalo IMF SEDs, we got an age range between 0.36 and 11.5 Gyr
starting with just an elliptical model and then using all evolving models. With the
E, S0, Sa, Sb, and Sc templates, we got an age of 5.5 Gyr, which Mutlu-Pakdil et
al. [Mutlu Pakdil et al., 2017] previously reported (see Figure 4.5). However, when we
used the Salpeter and Miller & Scalo IMFs, with constant and evolving metallicities,
we got an age range from 0.255 Gyr to 13.5 Gyr. None of these templates were able to
reproduce the age of 5.5 Gyr. HyperZ appears to be highly dependent on the amount
and types of template SEDs used when determining ages.
33
Figure 4.5: The left image shows the best fit model while using a fixed metallicity
and only evolving synthetic models. The right image shows the best fit model from
[Mutlu Pakdil et al., 2017]. The observed SEDs are in red and the best fitting model is
shown in black.
34
Figure 4.6: Flowchart explaining how HyperZ works.
Chapter 5
Conclusion and Discussion
In this thesis, we presented a photometric study of LEDA 1000714, a recently dis-
covered double ringed elliptical galaxy and an entirely new type of galaxy. We ob-
tained new near-infrared images in the J, H, and Ks bands, but due to issues with
the Ks images, we were left with just the J and H bands. Using the python Elliptical
Isophote Analysis package, we showed that the core is fairly round, with an ellipticity
of ∼ 0.11. The isophotal shape parameters stay fairly close to 0 up until about 6-7”
when they start to deviate, which indicates that there is another structure there. This
structure may be either rings or spiral arms [Gadotti et al., 2007], but other analysis
showed no signs of arms. This is all consistent with what has been previously found
[Mutlu Pakdil et al., 2017].
With the 1D modeling, we found that the data did not have a good fit with a Se´rsic
+ Exponential disk model. The residuals showed that the model started to deviate
from the data starting before 1” from the center. The data had the best fit with just
a single Se´rsic function and those residuals showed no deviation until around 7”, which
is about where the edge of the inner ring begins. Those results yielded a Se´rsic index
of 5.65 and a surface brightness at the half light radius of 17.72 mag arcsec−2 in the H
band while the J band had a Se´rsic index of 2.32 and surface brightness of 16.64 mag
arcsec−2. The Se´rsic index for J was lower than expected. Elliptical galaxies usually
have an n value greater than 4.
We were unable to see the ring during our 2D fitting from GALFIT as well as during
the isophotal analysis. The images we had may not have been deep enough to see it.
35
36
We were able to do a calculation for the lower limit of the magnitude of the inner ring
using the residual images, IRAF, and ds9. Those magnitudes were 14.63 and 11.79 mag
for the J and H band respectively. This is the brightest the ring can be.
During the isophotal analysis, we noticed that the J band had a sort of bar structure.
However, this feature did not show up in the H band nor did it show up in either band
in the GALFIT results. Therefore we conclude that the core is featureless.
Though we did not get images of the inner ring from GALFIT, we were able to obtain
total magnitudes of the core. These are 13.15 mag for J and 12.72 mag for H. These
agree very well with what Mutlu-Pakdil [Mutlu Pakdil et al., 2017] obtained: 13.34 mag
for J and 12.80 mag for H. With these new magnitudes, and previous ones from Mutlu-
Pakdil [Mutlu Pakdil et al., 2017], we used a SED fitting code to study the age of the
galactic core. We found that when we used only one SED template to model, we got
ages that were less than 1 Gyr. The more templates we added, the higher the age
became. This included using a fixed metallicity as well as evolving metallicities. We
were able to reproduce the age Mutlu-Pakdil [Mutlu Pakdil et al., 2017] got for the core,
5.5 Gyr, but our AB magnitudes were much higher. With this, we can say that HyperZ,
in regards to ages, appears to be sensitive to the types and amounts of templates that
are used.
In the future, we want to re-image LEDA 1000714 in the NIR, and perhaps MIR,
to continue our analysis on the inner ring. We also want to do more SED fitting with
HyperZ to get a more accurate age of the core. With more data, we will have a better
chance of studying and getting an image of the ring as well as determining its age. Once
we know the age of the inner ring, we can delve into its formation. This history could
be the key into understanding how this particularly unique galaxy formed and will be
beneficial in our understanding of not just Hoag-type galaxies, but ring galaxies as a
whole.
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