mem oria joves i ci encia centre de recerca...
TRANSCRIPT
Memoria Joves i Ciencia Centre de Recerca 2016
Programa Joves i Ciencia
Research Science Institute
Center for Excellence in Education
Massachusetts Institute of Technology
Magalı Luna i Perello
2 Oct. 2016
1 Introduccio
Durant la segona fase del Programa Joves i Ciencia, l’estada als Centres de Recerca,
he tingut la meravellosa oportunitat d’assistir al Research Science Institute (RSI).
El programa RSI permet a 82 estudiants d’arreu del mon (Suecia, Israel, Xina,
India...i Estars Units, es clar) dur a terme durant sis setmanes una recerca personal
en un laboratori o departament de prestigioses universitats com el Massachusetts
Institute of Technology (MIT) o Harvard, aixı com en empreses privades o hospitals.
Durant aquestes sis setmanes aprendras mes del que creies poder i coneixeras a gent
que traspassa els nivells de la excel·lencia, tant a nivell academic com en l’aspecte
personal. Conviuras amb professors, tutors i mentors que estaran disposats a ajudar-
te en qualsevol moment (literal, 24h al dia). A mes, si t’estresses massa despres de
haver superat el teu record d’hores sense dormir varies vegades, tindras els teus
companys, TAs i counselors que estaran sempre al teu costat per fer-te veure que,
per la ciencia, tot val la pena. Hauras de treballar com mai abans, i per si encara et
sobrava temps, hauras de redactar un article que defensaras al final de l’estada davant
de tots els que t’han acompanyat en aquesta aventura...i de les seves preguntes.
Sentiras concerts de genis, soparas amb premis Nobel i jugaras partits de Ultimate
Fresbee amb promeses de les matematiques. Cada ”rickoid”, cada estudiant del RSI,
recorda el seu estiu d’una manera diferent. Pero us asseguro que ningu l’oblida.
2 Campus
El RSI es duu a terme des de fa bastants anys al campus del MIT, a Cambridge,
Boston. Tot i aixı, depenent de la materia de la teva investigacio pot ser que acabis
treballant al campus de Hardvar o en algun edifici extern als campus a les ciutats
de Cambridge o Boston. El desplacament (principalment autobusos) estan totes
cobertes, aixı que l’unic problema de treballar off-campus es el fet d’haver-te de
llevar abans per arribar puntual al ”mentorship” (que sembla no tenir importancia,
pero feu-me cas, cap a la tercera setmana comencareu a enyorar desesperadament
aquella mitja hora de mes que gaudeixen els estudiants residents).
1
3 Perıode de Realitzacio de l’Estada
En el meu cas, el RSI es va dur a terme del 25 de juny al 6 d’agost de 2016. Tot
i que sempre dura sis setmanes practicament exactes, les dates varien de l’ordre de
pocs dies d’una edicio a una altra.
4 Adreca
El programe es va dur a terme al campus del Massachussets Istitute of Technology:
77 Massachusetts Ave,
Cambridge, MA 02139
Estats Units
Vam viure a la residencia estudiantil del West Campus del MIT ”Maseeh Hall”:
305 Memorial Dr,
Cambridge, MA 02139,
Estats Units
I jo personalment vaig treballar al MIT Kavli Istitute for Astrophysics and Space
Research:
77 Massachusetts Ave 37-241,
Cambridge, MA 02139,
Estats Units
5 Descripcio del Campus
El campus principal, el del MIT, es una immensa extensio de prats verds, edificis
grisos. Es tan enorme que pots viure perfectament sense sortir-ne...sempre i quan
no t’importi degradar l’accio menjar a un tramit merament de supervivencia. A mes
dels ”restaurants”, hi trobaras sales d’ordinadors (en les quals passaras encantadores
nits abans de les ”deadlines”), biblioteques (massa silencioses per el teu nivell de
2
somnolencia) i obviament la residencia on viuras (que si tens sort com jo, podras
tenir unes magnıfiques vistes del Riu Charles des de la finestra).
Per altra banda, el campus de Harvard es molt diferent. Principalment, es mes
bonic (almenys en la meva opinio). Els edificis son de pedra roja, i estan envoltats
de petites clarianes amb arbres altıssims. Desgraciadament no puc parlar molt mes
d’aquest campus, dons jo vaig treballar al del MIT i no vaig tenis tantes ocasions
per visitar Harvard com hauria volgut.
6 Objectius del Programa
El RSI es un programa que, contrariament a molts altres de naturalesa semblant, no
esta especialitzat en un ambit de la ciencia concret. Tan pot ser que facis recerca
en bioquımica, com en matematica pura com en psicologia del consumidor. Pero
aquesta distincio comenca a la segona setmana. Independentment del teu tema
d’investigacio, durant la primera setmana tots els rickoids assisteixen a tres classes
obligatories i dues d’opcionals. Tothom cursa estadıstica, informatica i humanitats
(si, humanitats. No desespereu que acaba sent terriblement divertit). A mes a mes,
has de triar dues assignatures d’entre cinc ciencies: matematiques, fısica, quımica,
biologia i enginyeria. Jo personalment vaig triar fısica i biologia, i ambdues em van
fascinar. Tot i aixı, les altres tres assignatures tambe van ser (i seran) impartides de
manera excel·lent (vaig assistir a unes poques de matematiques i van ser igualment
interessantıssimes).
Acabada aquesta primera part, comences la que sera la principal ocupacio del RSI:
el ”mentorship”. Durant les cinc setmanes restants, es duu a terme una investigacio
en el teu tema d’interes: en el meu cas vaig treballar en el MIT Kavli Instiute
for Astrophysics and Spece Research, on vaig desenvolupar un projecte que es va
titular Measurement of the Circumgalactic Gas Around 1.8 ≤ z ≤ 3.0 Galaxies Using
Foreground-Background Galaxy Pairs (si us interessa, l’adjunto a l’annex).
El mentorship es una recerca propia, pero no estas sol: tens un exercit de professionals
”al teu servei” per ajuda-te a resoldre qualsevol problema que puguis tenir. Els tutors
i els TAs t’ajudaran en la redaccio i presentacio de l’article. El mentor t’ajudara en el
desenvolupament de la investigacio. I els counselors i els propis companys t’ajudaran
3
en qualsevol tema social o personal.
El RSi no nomes busca donar als estudiants una experiencia unica de recerca, sino
tambe una valuosa llico de vida. El RSI et canvia, i et canvia a millor.
7 Activitats
A part de tot el treball academic, es realitzen moltes activitats ludico-socials durant
l’estada. S’organitzen tornejos de ping-pong i de jocs de taula. Es fa una Casino
Night, una International Night (on gaudiras de menjar de veritat per primera i tris-
tament ultima vegada) i un Talent Show (on descobriras que els teus impressionants
companys encara ho son mes del que pensaves). Potser l’activitat mes...interessant
(antropologicament parlant) es la celebracio el 4th of July. Haureu de viure el patri-
oterisme america en el seu estat mes pur. Morireu de calor (avis de cortesia: porteu
paraigues pel sol), pero els focs d’artifici ho valen. I no penseu que la cosa acaba aixı,
hi ha moltes mes activitats i sortides pero...aixo millor us ho deixare com a sorpresa.
No us puc explicar el RSI, s’ha de viure.
8 Valoracio
Que puc dir: es inoblidable. Es magnıfic en moltes coses i no nomes parlo de
ciencia. Les classes son una autentica passada, i els professors son gent oberta a
qualsevol dubte de la materia o de qualsevol cosa, de fet. El ”mentorship” es igual
d’apassionant o mes: treballes cada dia un nombre insa d’hores amb el constant
suport del mentor. Vaig arribar a estimar moltıssim el temps que passava asseguda
davant de l’ordinador, barallat-me amb les lınies de codi mentre el meu mentor mi-
rava de resoldre’m la vida des de la taula del costat. El fet de ”patir un mateix
mal” t’uneix amb els teus companys d’una manera unica. Coneixeras el que es fer-se
immune a la cafeına per exces de consumicio, perdras tota la dignitat que en un prin-
cipi haguessis pogut tenir i sabras el que se sent al ser ric (et donaran una ”targeta
black” amb la qual hauras de comprar ”nomes menjar”). Vendras la teva racional-
itat a canvi d’uns amics iirreemplacables, i no te’n penediras. L’ultima setmana
l’anomenen ”Hell Week”, pero contrariament al seu nom per a mi va ser la millor de
4
les sis. Es el moment on obtens els resultats de la teva investigacio, on passes nits
senceres treballant i descobreixes que aquell amb qui no havies parlat mai resulta
que es el que et cau millor. Es el moment on caus i, des del fons, t’aixeques mes gran
que mai. Al final de l’estada ja no queden murs entre staff i estudiants: tots som
part de la Rickoid Family. Si esteu preparats, hi sereu benvinguts. Bona sort!
9 Annex
Article cientıfic: Measurement of the Circumgalactic Gas Around 1.8 ≤ z ≤ 3.0
Galaxies Using Foreground-Background Galaxy Pairs.
5
Measurement of the Circumgalactic Gas Around1.8 ≤ z ≤ 3.0 Galaxies Using Foreground-Background
Galaxy Pairs
Magali Luna
under the direction ofDr. Rongmon Bordoloi
MIT Kavli Institute for Astrophysics and Space ResearchMassachusetts Institute of Technology
Research Science InstituteAugust 2, 2016
Abstract
The majority of baryonic matter does not emit or reflect visible light, and is located inthe intergalactic medium. To detect it, we use pairs of galaxies: one foreground galaxy andone background galaxy. We look for the interaction between the photons emitted for thebackground galaxies and the particles of the gas located around the foreground galaxies. Westudy the elements’ absorption lines in the background galaxies’ light spectra. We confirma significant presence of Si II, O I, and C IV around galaxies with a redshift 1.8 ≤ z ≤ 3.0.If we study higher redshift galaxies (2.2 ≤ z ≤ 3.0) we also detect the presence of Ly α, thefirst transition of Hydrogen. We calculated the relation between the impact parameter ofgalaxies and the equivalent width of the absorption lines of various elements. This relationprovides a map of the elements’ distribution in the intergalactic gas.
Summary
Normal matter is only 4.6% of all the composition of the universe. However, the majorityof the normal matter does not emit or reflect visible light, and is located in the gas betweenthe galaxies. We have performed a study about the composition of this gas. To do this, westudied how light of distant galaxies is absorbed by the gas. The way in which the light isabsorbed gives us information about how the gas is distributed between galaxies, its chemicalcomposition and its distribution.
1 Introduction
1.1 Galaxy Formation and Evolution
The evolution of the universe as we understand it is divided in several epochs.
This research is focused in the Galaxy Formation and Evolution epoch: this period oc-
curred from 1 Gigayears (Gy) to 10 Gy after the formation of the universe, the Big Bang.
Objects from the Galaxy Formation epoch have redshifts between 0.4 and 6. Some of the
more active research fields of astrophysics are interested in studying phenomena that took
place during Galaxy Evolution epoch, such as the formation of a heterogeneous universe
from a homogeneous beginning or the formation of the first galaxies and their evolution over
time.
1.2 Circumgalactic Gas
The circumgalactic gas is an ionized hot gas halo (105 to 107 K) that surrounds the galaxies.
This circumgalactic gas contains a 40% - 50% of all the baryonic matter [1, 2]. Knowledge
about this gas contributes to our understanding of galaxy formation and evolution, but its
composition and distributions is still not clear. This is because the particles of this gas do
not emit or reflect light. Therefore we must use indirect methods to detect this gas.
1.3 Spectral Elements’ Absorption Lines
We use the light spectra absorption lines to study this gas halo. The spectral absorption lines
show the presence of an interaction between photons and particles of the circumgalactic gas.
We use these absorption lines to define the composition and distribution of this circumgalac-
tic gas. Each ionization of each element has a particular rest wavelength. We may use the
identification of the wavelengths of absorption lines to determine the chemical composition
1
of the circumgalactic gas. We also study the relation between these absorption lines and the
impact parameter. This study will provide a map of the elements’ distribution in the sky.
However, the circumgalactic gas does not emit or reflect light, so we can not use the gas halo
itself as a light source. To solve this problem, we use an alternative light source to detect
this photon-gas particles interactions.
1.4 Foreground-Background Galaxy Pairs
We work with a galaxy catalog called “zCOSMOS deep catalogue.fits”. The Cosmic Evo-
lution Survey (COSMOS) is an astronomical survey designed to probe the formation and
evolution of galaxies as a function of both cosmic time (redshift) and the local galaxy en-
vironment [3]. zCOSMOS is a large redshift survey taken in the COSMOS field using the
VIMOS spectrograph of the Melipal Unit Telescope of the VLT at ESO’s Cerro Paranal Ob-
servatory, Chile [4]. This catalog contains each galaxy’s position on the sky (right ascension
and declination) and redshift. Using this data, we have classified the galaxies in two blocks:
the foreground galaxies have a redshift 1.8 ≤ z ≤ 3.0; and the background galaxies have a
redshift z ≥ 1.8.
We selected galaxy pairs with one foreground galaxy and one background galaxy each.
We must select the particular background galaxies for each foreground galaxy, because if
we use the original redshift cuts the background group includes the foreground group inside
(1.8 ≤ z ≤ 3.0 is included in z ≥ 1.8.). For each foreground galaxy, we find all the background
galaxies that have a bigger redshift than the particular foreground galaxy selected.
When the background galaxies of the particular foreground galaxy have been identified,
their characteristics are stored in a matrix. We repeat this process for all the foreground
galaxies, obtaining a matrix that contains:
• The id of the foreground galaxy.
2
• The id of all its particular background galaxies.
• The characteristics of the foreground galaxy.
• The characteristics of all its background galaxies.
This matrix also contains the impact parameter between the foreground galaxy and each
background galaxy. The impact parameter is the closest distance between the two galaxies’
nuclei.
We calculate the distance and the angle between each foreground galaxy and all back-
ground galaxies. In Figure 1 we observe multiple background galaxies for one foreground
galaxy.
1.5 Circumgalactic Gas Composition and Distribution
These galaxy pairs allow us to study the interaction between photons and the circumgalactic
gas particles. The background galaxy is used as a light source, emitting photons that interact
with the gas halo particles of the foreground galaxy. These interactions create absorption
points in the spectrum of the background galaxy. The analysis of these background galaxies
light spectra allow us to determine the chemical composition of the gas halo, and also to
quantify the number of particles that have participated in the interaction. The main goal of
this research is to analyze the chemical composition of the circumgalactic gas, and to display
a map of the distribution of the gas halo’s elements in the sky.
3
0.020 0.015 0.010 0.005 0.000 0.005 0.010 0.015 0.020
Right Ascension
0.020
0.015
0.010
0.005
0.000
0.005
0.010
0.015
0.020
Decl
inati
on
Figure 1: Representation of one foreground galaxy in the center (id = 404716.0) and therelative position of its background galaxies. The three circles measure impact parameter(kpc): 100 kpc in blue, 300 kpc in green and 500 kpc in red.
4
2 Spectral Elements’ Absorption Lines Analysis
2.1 Absorption Lines Analysis
The light spectra of distant galaxies are usually noisy. It is necessary to combine these spectra
to clarify which are the real troughs, and which are just noise.
We create six bins using an impact parameter from 0 kpc to 300 kpc in steps of 50 kpc
for all the bins, and make three ranges of redshift: total redshift (Table 1): with a redshift
covering all the redshift range we are working with (1.8 ≤ z ≤ 3.0); low redshift (Table 2):
with a redshift 1.8 ≤ z ≤ 2.2; and high redshift (Table 3): with a redshift 2.2 ≤ z ≤ 3.0.
Impact parameter (kpc) number of galaxies
0-50 94 A
50-100 191 A
100-150 344 A
150-200 517 A
200-250 612 A
250-300 806 A
Table 1: All redshift (1.8 ≤ z ≤ 3.0) bins’ data.
Impact parameter (kpc) number of galaxies
0-50 65 A
50-100 122 A
100-150 217 A
150-200 323 A
200-250 389 A
250-300 536 A
Table 2: Low redshift (1.8 ≤ z ≤ 2.2) bins’ data.
To analyze these light spectra’s absorption lines we use some standard statistical and
mathematical methods:
• Interpolation [5]
5
Impact parameter (kpc) number of galaxies
0-50 28 A
50-100 69 A
100-150 125 A
150-200 193 A
200-250 221 A
250-300 269 A
Table 3: High redshift (2.2 ≤ z ≤ 3.0) bins’ data.
Determination of the value of f(x) for a function of x in which certain values are
known: x0 ≤ · · · ≤ xn, y0 = f(x0), ..., yn = f(xn) and x0 ≤ x ≤ xn.
• Median smoothing [6]
Calculate the median of the points in the spectra and plot a level line. Then use
this level line to normalize the spectrum.
• Sigma clipping [7]
Calculating the mean (α) and standard deviation (σ) of our distribution. Remove
all points that are smaller or larger than α± nσ.
In addition, we plot some graphs looking for the relation between the photon absorption
and the impact parameter. To plot them, we calculate the mean impact parameter and the
median equivalent width for each bin.
The equivalent width Wλ measures the area of the absorption line on a plot of intensity
versus wavelength, in which Wλ =∫
(1 − Fλ/F0)dλ. Fλ is the intensity across the entire
wavelength range studied and F0 represents the continuum intensity level.
At the end of the global analysis, we define an element-absorption-distribution map of
the circumgalactic gas located in the square of the sky in which all our galaxies lie.
6
3 Results and Discussion
3.1 Chemical Composition of the Circumgalactic Gas
Figure 5 shows the distribution of the foreground and background galaxies. We observe a
larger number of background galaxies.
149.6 149.8 150.0 150.2 150.4 150.6 150.8
Right Ascension
1.6
1.8
2.0
2.2
2.4
2.6
2.8
Decl
inati
on
Figure 2: Foreground galaxies (blue) plotted over all the galaxies (red).
We classify the galaxy pairs in three sets of six bins: all redshift, low redshift and high
redshift. We combine the spectra of the galaxies contained in these bins. Figure 3 compares
the absorption line of each combined spectra. These elements’ absorption lines represent
different excited states of these elements, different ionizations.
To perform this analysis, we have used three different statistical methods: median, sigma
7
clip and bootstrap.
3.1.1 Median
We calculate the median of the spectra’s absorption points, from 500 to 5000 A. In these
combined spectra, we look for some specific elements classified in Table 4.
Element’s Ionization Rest Wavelength
Si II 1260 A
O I 1303 A
C II 1334 A
Si IV 1393 A
Si II 1526 A
C IV 1549 A
He II 1640 A
C II 1334 A
Al II 1670 A
Table 4: Elements’ absorption line [8].
Figure 3 and Figure 4 show us different troughs associated a different elements’ absorption
lines. We can observe absorption lines of O I (1303 A), Si II (1260 A) and C IV (1549 A) in
3. In the case of the spectra of low redshift galaxies (Figure 4), we can observe more clearly
the absorption lines of Si IV (1393 A), C IV (1549 A) and Al II (1670 A)).
These strong troughs confirm the real measurement of these elements in the circumgalac-
tic gas of the galaxies studied, because they are too strong to be part of the statistical and
experimental error.
The depth of these troughs is related to the quantity of the element studied in this point.
This provides us a tool to not only define the distribution of this elements in the sky, but
also to to quantify them.
We also observe a significant decrease of the spectra noise from the first co-addition to
the last one. This is because of the larger number of galaxies in the bins with a higher impact
8
1300 1400 1500 1600 1700
Rest Wavelength
0.5
0.0
0.5
1.0
1.5
2.0
Norm
aliz
ed Inte
nsi
ty
SiII
1260
OI 1303
CII 1
334
SiIV
1393
SiII
1526
CIV
1549
FeII 1
608
HeII 1
640
AlII
1670
b < 50 kpc
b=50-100 kpc
b=100-150 kpc
b=150-200 kpc
b=200-250 kpc
b=250-300 kpc
Figure 3: Comparison of the elements’ absorption lines of the six co-added spectra regardinggalaxies within all redshift (1.8 ≤ z ≤ 3.0) using the median method.
9
1250 1300 1350 1400 1450 1500 1550 1600 1650 1700
Rest Wavelength
0.5
0.0
0.5
1.0
1.5
2.0
Norm
aliz
ed Inte
nsi
ty
SiII
1260
OI 1303
CII 1
334
SiIV
1393
SiII
1526
CIV
1549
FeII 1
608
HeII 1
640
AlII
1670
b < 50 kpc
b=50-100 kpc
b=100-150 kpc
b=150-200 kpc
b=200-250 kpc
b=250-300 kpc
Figure 4: Comparison of the elements’ absorption lines of the six co-added spectra regardinggalaxies within a low redshift (1.8 ≤ z ≤ 2.2) using the median method.
10
parameter.
1200 1300 1400 1500 1600 1700
Rest Wavelength
0.5
0.0
0.5
1.0
1.5
2.0
Norm
aliz
ed Inte
nsi
ty
SiII
I 1206
Ly a
1215
SiII
1260
OI 1303
CII 1
334
SiIV
1393
SiII
1526
CIV
1549
FeII 1
608
HeII 1
640
AlII
1670
b < 50 kpc
b=50-100 kpc
b=100-150 kpc
b=150-200 kpc
b=200-250 kpc
b=250-300 kpc
Figure 5: Comparison of the elements’ absorption lines of the six co-added spectra regardinggalaxies within a high redshift (2.2. ≤ z ≤ 3.) using the median method.
Figure 5 shows noisier spectra, but provides us information about more distant galaxies.
This allows us to detect two more absorption lines (Table 5):
Element’s Ionization Rest Wavelength
Si III 1206 A
Ly α 1215 A
Table 5: High redshift elements’ absorption line [8].
One of these lines, Ly α, is special. Ly α is the first transition of Hydrogen, the most
common element in the universe. This first transition is the strongest one, and it is especially
11
abundant in the early universe. That is the reason we see this absorption line in high redshift
galaxies and not in the nearby galaxies.
In Figure 5 we observe that the trough of this element’s absorption line is significant, so
we conclude that the measurement of the Ly α is real, and not just a product of the spectra’s
noise.
3.1.2 Sigma Clip
We calculate spectra combinations using the sigma clip method. The mathematic explanation
is in Section 2.1.
1300 1350 1400 1450 1500 1550 1600 1650 1700
Rest Wavelength
0.5
0.0
0.5
1.0
1.5
2.0
Norm
aliz
ed Inte
nsi
ty
CII 1
334
SiIV
1393
SiII
1526
CIV
1549
FeII 1
608
HeII 1
640
AlII
1670
b < 50 kpc
b=50-100 kpc
b=100-150 kpc
b=150-200 kpc
b=200-250 kpc
b=250-300 kpc
Figure 6: Comparison of the elements’ absorption lines of the six co-added spectra regardinggalaxies within all redshift (1.8 ≤ z ≤ 3.0) using the sigma clip method.
12
This method provide a less noisy spectra. In Figure 6 we observe absorptions in Si IV
(1393 A) and in C IV (1549 A). We also observe a less pronounced absorption of Si II (1526
A), but spectral analysis with a higher number of galaxies in each bin are needed to confirm
its presence.
3.1.3 Bootstrap
Bootstrap is used to decrease the importance of the noise peaks and troughs. The procedure
of bootstrapping simply replaces part of the real data with random variables of the existing
data sets and calculates the median of this new data, part original and part random [9]. This
process is called re-sampling. We re-sampled the data 200 times to create a new co-added
spectra. This allows us to compute the uncertainties in the co-add by looking at the standard
deviation of the bootstrapped data.
We repeat the approach used in the median method. We create three selections of six
bins: all redshift, low redshift and high redshift.
In Figure 7 we observe a decrease in the noise relative to the noise of the plots created
using the median or the sigma clip methods. The elements’ absorption lines are less deep,
but more reliable. In Figure 7 we observe a significant presence of O I (1303 A) and C IV
(1549 A). Carbon IV especially can be observed along the different impact parameter bins,
confirming its reliability this way.
In Figure 8 we notice a significant presence of Si II (1260 A), O I (1303 A), C II (1334
A), Si IV (1393 A) and C IV (1549 A).
In the case of the high redshift galaxies’ spectra plot (Figure 9), we detect a significant
presence of Ly α (1215 A), and a lesser but strong presence of Si III (1206 A), Si II (1260
A), O I (1303 A), C II (1334 A), Si IV (1393 A) Si II (1526 A) and C IV (1549 A). More
soft absorption lines in Fe II (1608 A) and Al II (1670 A) can be also observed. We conclude
in this case that the only non clear absorption line is He II (1640 A).
13
1300 1400 1500 1600 1700
Rest Wavelength
0.5
0.0
0.5
1.0
1.5
2.0
Norm
aliz
ed Inte
nsi
ty
SiII
1260
OI 1303
CII 1
334
SiIV
1393
SiII
1526
CIV
1549
FeII 1
608
HeII 1
640
AlII
1670
b < 50 kpc
b=50-100 kpc
b=100-150 kpc
b=150-200 kpc
b=200-250 kpc
b=250-300 kpc
Figure 7: Comparison of the elements’ absorption lines of the six co-added spectra regardinggalaxies within all redshift (1.8 ≤ z ≤ 3.0) using the bootstrap method.
14
1300 1400 1500 1600 1700
Rest Wavelength
0.5
0.0
0.5
1.0
1.5
2.0
Norm
aliz
ed Inte
nsi
ty
SiII
1260
OI 1303
CII 1
334
SiIV
1393
SiII
1526
CIV
1549
FeII 1
608
HeII 1
640
AlII
1670
b < 50 kpc
b=50-100 kpc
b=100-150 kpc
b=150-200 kpc
b=200-250 kpc
b=250-300 kpc
Figure 8: Comparison of the elements’ absorption lines of the six co-added spectra regardinggalaxies within a low redshift (1.8 ≤ z ≤ 2.2) using the bootstrap method.
15
1200 1300 1400 1500 1600 1700
Rest Wavelength
0.5
0.0
0.5
1.0
1.5
2.0
Norm
aliz
ed Inte
nsi
ty
SiII
I 1206
Ly a
1215
SiII
1260
OI 1303
CII 1
334
SiIV
1393
SiII
1526
CIV
1549
FeII 1
608
HeII 1
640
AlII
1670
b < 50 kpc
b=50-100 kpc
b=100-150 kpc
b=150-200 kpc
b=200-250 kpc
b=250-300 kpc
Figure 9: Comparison of the elements’ absorption lines of the six co-added spectra regardinggalaxies within a high redshift (2.2 ≤ z ≤ 3.0) using the bootstrap method.
16
3.2 Distribution of the Circumgalactic Gas
To study the distribution of the elements of the circumgalactic gas in the space we plot the
relation between the equivalent width and the impact parameter mean. This relation shows
us the distribution of a specific element as a function of impact parameter.
101 102
<Impact Parameter> (kpc)
10-1
100
Equiv
ale
nt
Wid
th (
Å)
C IV 1549
Figure 10: Relation between the equivalent width of C IV (1549 A) and the impact parametermean. This data has been obtained regarding the three different types of bins: blue for highredshift (2.2 ≤ z ≤ 3.0), red for all redshift (2.2 ≤ z ≤ 3.0) and green for low redshift(1.8. ≤ z ≤ 2.2).
We have used the C IV (1549 A) to do a general analysis because is the strongest ab-
sorption line observed. In Figure 10, the three last measurements for the 2.2 ≤ z ≤ 3.0 and
2.2 ≤ z ≤ 3.0 redshift ranges and the last four measurements for the 1.8. ≤ z ≤ 2.2 redshift
17
range are only upper limits. We define a measurement to be an upper limit if the mea-
sured equivalent widths are smaller than the measurement uncertainties. The upper limits
are useful measurements as they tell you that there is no absorption for this element when
the galaxies are further from the foreground galaxy than the upper limits. For the reliable
measurements, we observe a significant decrease of the equivalent width when the impact
parameter is increased. This indicates a higher density of C IV near the light source.
Regarding only the high redshift bins, we also observe the Ly α (1215 A) absorption line.
101 102 103
<Impact Parameter> (kpc)
10-1
100
101
Equiv
ale
nt
Wid
th (
Å)
Ly α
Figure 11: Relation between the equivalent width of Ly α (1215 A) and the impact parametermean. This data has been obtained regarding the high redshift bin (2.2 ≤ z ≤ 3.0).
In Figure 11 we similarly observe a decrease of the equivalent width when the impact
parameter increases. This seems to indicate that there is a higher density of elements near
18
the light sources in general, not only for these elements. In this case all the measurements
are reliable data. That indicates a strong presence of Ly α (1215 A), more extended than C
IV (1549 A) or any other element we observed.
The non-reliability of part of this data is because the number of galaxies in these bins
is small. More large bins with higher redshift ranges should be used in future studies to
improve the reliability of this data.
4 Conclusion
Study of diffuse gas detected as absorption lines in the spectra of background galaxies reveals
the presence of O I (1303 A), Si II (1260 A) and C IV (1549 A) in circumgalactic gas around
galaxies with a redshift 1.8 ≤ z ≤ 3.0, and the presence of Si IV (1393 A), C IV (1549 A)
and Al II ( C IV (1549 A)) in galaxies with a low redshift (1.8. ≤ z ≤ 2.2).
In addition, a significant presence of Ly α (1215 A) in galaxies with a redshift 2.2 ≤ z ≤
3.0 was found.
Increasing the number of galaxies studied decreases the noise in the light spectra by a
factor of√N , where N is the number of galaxies. Increasing N in future research will increase
the data reliability.
Also, we have displayed a map of the elements’ distribution of the gas in the sky studying
the equivalent width as a function of the impact parameter. We find that the strongest
absorptions occurs at the closest impact parameter of the foreground galaxies. This allows
us to construct a radial profile of absorption of different atoms around a well defined set of
distant galaxies.
The next step of this research could be to study this elements’ absorption lines using
different impact parameter and redshift bins. We expect to verify the Ly α absorption line
looking for the light spectra of galaxies with redshifts as large as 4 or 5.
19
Another improvement of this study could be to study other wavelengths for different
elements’ absorption lines.
Other mathematical and computational methods to combine the light spectra can be
explored to increase the data accuracy and decrease the noise.
5 Acknowledgments
I want to thank the MIT Kavli Institute for Astrophysics and Space Research and especially
my mentor Rongmon Bordoloi for all the time, support and information that he has given
to me during this research. This project could not have been accomplished without him. I
also want to thank my third week mentor, Thomas J. Cooper for his support and guidance
with my project.
I want to thank my tutor Dr. John Rickert for orientating and encouraging me during
this research. I want to thank also my counselor Sanjana Rane for be always there for me.
I want to thank our RSI 2016 Systems Manager, Tina Li, and all the fist week TA’s for
their support with LATEX and the Athena system.
I want to thank Abi Krishnan and all the last week TA’s for their orientation and advices
with the papers and presentations during the last week. I also want to thank Molly Peeples
for her useful comments and suggestions about my paper.
I want to thank my dear department mate Omer Prives for helping me with my program-
ming issues and for all the laughs and the lab-exploration trips. I will never forget these days
when we encourage each other to go further and improve ourselves. I also want to thank my
brother Raimon Luna for his help and orientation with python programming language and
the paper writing process.
I want to thank my sponsors Eva Calves Parcerisas and Carla Conejo-Gonzalez, the
Fundacio Catalunya-La Pedrera and the Joves i Ciencia program for providing me the op-
20
portunity to attend a such exceptional program as RSI is. I will be always grateful.
And finally I really want to thank the Research Science Program, the Center for Excel-
lence in Education and the Massachusetts Institute of Technology for giving me this unique
opportunity to work, learn and understand so much more science than I could ever imagined.
21
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Appendix A Title of Appendix
Appendices may appear after the paper proper. Appendices may hold extra information
that would interrupt the flow of the paper and that is not absolutely necessary for the reader
to appreciate the work. For example, a large number of related figures or a mathematical
derivation could go nicely in an appendix.
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