Comparison of star-formation rates for the deep field extended groth strip and its dusty star forming galaxies population

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Comparison of star-formation

rates for the deep field Extended

Groth Strip and its Dusty Star

Forming Galaxies population

by

Luisa Fernanda Cardona Torres

Thesis submitted in partial fullfillment of the

requirements for the degree of

MASTER OF SCIENCE IN ASTROPHYSICS

at the

Instituto Nacional de Astrof´ısica, ´Optica y

Electr´onica

September 2019

Tonantzintla, Puebla

Advised by:

PhD. Itziar Aretxaga

Tenured Researcher - INAOE

PhD. Alfredo Monta˜na

Conacyt Fellow - INAOE

c

INAOE 2019

The author hereby grants to INAOE permission to

reproduce and to distribute publicly paper and

electronic copies of this thesis document in whole or

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Abstract

This masters thesis presents the study of the star formation rates (SFR) of submil-limeter galaxies (SMGs) in the deep field Extended Groth Strip (EGS). We used the

SFRs reported in the CANDELS and SCUBA-2 Cosmology Legacy Survey (SCLS2)

catalogues, derived from UV/optical, NIR and submillimeter measurements. We

per-formed the selection of the star-forming galaxies in EGS from the CANDELS

cata-logue. With this sample we adjusted the star formation main sequence to the

star-forming population of EGS for redshift bins (0.5 < z < 6). Our fit best agrees with

the fit by Speagle, et al. (2014) and the high-mass end of the fit by Whitaker, et

al. (2014). However, the exact location of the star formation main sequence is still

uncertain. Then we compared the estimations of the SFRs from both catalogues for the population of SMGs with counterparts identified in the optical and near infrared

bands. The total SFRUV+IR reported in the CANDELS catalogue is derived from

measurements in the UV/optical bands and is corrected for dust extinction with

ob-servations at 24µm and the SFRIR is derived from the submillimeter observations of

SCLS2 at 450 and 850µm. When comparing both estimations we found that in most

cases SFRUV+IR underestimates the total SFR of the SMGs. Nonetheless, 86% of the

SMGs lie within the 3σ region of our star formation main sequence fit, where 4% of

the sample can be classified as starbursts as they are located above the 3σ region

of the fit. We performed follow-up spectroscopic observations of some SMGs at the GTC-MOS Osiris instrument. We were able to identify emission lines in the spectra

and propose candidate spectroscopic redshift when possible. However, we were unable

to measure the flux of emission lines that trace the star formation activity. Finally,

we propose the future work to be developed in a doctorate program.

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Resumen

Esta tesis de maestr´ıa presenta el estudio de las tasas de formaci´on estelar (SFR)

de la población de galaxias submilimétricas en el campo profundo Extended Groth Strip. Se emplearon las SFR reportadas en los catálogos CANDELS y SCUBA-2 Cos-mology Legacy Survey (SCLS2), las cuales han sido estimadas a partir de medidas

realizadas en el UV/´optico, cercano y mediano infrarojo y sub-milim´etrico. Se

re-alizó la selección de las galaxias con formación estelar en el campo EGS del catálogo CANDELS, observadas en el UV/óptico. Con esta muestra se realizó el ajuste de la

secuencia principal de formaci´on estelar a esta poblaci´on de EGS, para corrimientos

al rojo entre 0.5 y 6. Nuestro ajuste concuerda mejor con el ajuste presentado por

Speagle, et al. (2014) y con el ajuste a altas masas de Whitaker, et al. (2014). Sin

embargo, la ubicación exacta de la secuencia principal de formación estelar aún es

incierta. Entonces comparamos las estimaciones de SFRs de ambos cat´alogos para la

poblaci´on de galaxias submilim´etricas con contrapartes identificadas en las bandas

´

opticas y del cercano infrarojo. La tasa de formaci´on total SFRUV+IR, reportada en el

catálogo CANDELS, está derivada de mediciones en el UV/óptico y corregida por la extinción de polvo con observaciones a 24µm y la SFRIR proveniente de las

observa-ciones submilim´etricas de SCLS2 a 450 y 850 µm. Al comparar las dos estimaciones

encontramos que en la mayor´ıa de los casos la SFRUV+IR subestima la SFR total de

las galaxias submlim´etricas. A pesar de esto, 86% de las SMGs yacen dentro de la

region de 3σ de nuestro ajuste de la secuencia principal de formaci´on estelar, donde

4% de la muestra de SMGs pueden ser clasificadas como galaxias starbursts ya que

se encuentran ubicadas sobre la regi´on de 3σ del ajuste. Finalmente, realizamos un

seguimiento espectrosc´opico de algunas SMGs con el GTC/MOS Osiris, en los cuales

identificamos l´ıneas de emisi´on, proponiendo un corrimiento al rojo para los que fue

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posible. Sin embargo, no logramos medir el flujo de l´ıneas de emisi´on que trazaran

la actividad de formaci´on estelar. Finalmente, se plantea una propuesta de trabajo

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Introduction

One of the most important goals of modern astrophysics is to understand the

forma-tion and evoluforma-tion of the universe and the structures it contains. In 1996 the

tenta-tive detection of the Cosmic Infrared Background (CIB) by the Cosmic Background Explorer (COBE) was presented (Puget et al., 1996), which had been predicted be-forehand as the contribution of early galaxies (Partridge & Peebles, 1967). Later on, the confirmation of the CIB measurement was presented, whose integrated energy (in

the 140 to 240 µm range) is _∼ 2.5 times the integrated optical/NIR light from the

galaxies in the Hubble Deep Field (Hauser et al., 1998). This implies that there is a

dust enshrouded population of galaxies at high redshift and that an important

frac-tion of our understanding of the star formafrac-tion history of the universe is obscured by

dust (Dwek et al., 1998). Since then, the technological developments have permitted

the growth of a new kind of astronomical observations at submillimeter wavelengths,

where the dust enshrouded population of the universe and its contribution to the

CIB has been under study (Smail et al., 1997; Hughes et al., 1998; Perera et al., 2008; Hatsukade et al., 2011; Scott et al., 2012; Geach et al., 2013; Zavala et al., 2017).

For instance, Fujimoto et al. (2015) presented a statistical study of sources detected

in the 1.2 mm band at the Atacama Large Millimeter Array/submillimeter (ALMA)

where the integrated flux of these sources accounted for 104+31₋₂₅% of the CIB found byCOBE.

In this work we focus on the physical properties of star-forming galaxies that are

dust enshrouded (DSFGs) within the deep field Extended Groth Strip (EGS).

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1.1 Dusty Star Forming Galaxies

Submillimeter galaxies (SMGs) are a high-z population of star-forming galaxies which

contain large amounts of dust. This implies that a great extent of their UV radiation,

emitted by young stars, is obscured by the dust and thermally re-emitted at longer

wavelengths in the Infrared (IR). They have large IR Luminosities (LIR = 1012L),

which are related to high Star Formation Rates of the order SFR_≈ 300₋3000Myr−1

(Smail et al., 1997; Hughes et al., 1998). The heated dust grains within the DSFGs

emit radiation as a modified black body, and there is not a straight forward way to

discern between the two main possible mechanisms that heat the dust: Active Galactic Nuclei (AGN) or young stars (Blain et al., 2002).

SMGs were discovered in the late 90’s thanks to the technological developments

that allowed observations in the submillimiter range, specifically at 850 µm with the

Submillimeter Common-Use Bolometer Array (SCUBA) at the 15 m James Clerk

Maxwell Telescope (JCMT, i.e. Smail et al., 1997; Hughes et al., 1998; Barger et al., 1998). This marked the beginning of a new research area in astrophysics, which has

been reviewed by Blain et al. (2002) and Casey et al. (2014). As a recently discovered

population, there have been efforts to understand them in terms of local known

ob-jects. For instance, low-zobjects considered analogues to SMGs, similar in luminosity

(Lbol ∼ 1012L), are the Ultra Luminous Infra-Red Galaxies (ULIRGs Blain et al.,

2002), whose dust emission dominates the SED from 8 µm to 1 mm (and therefore

Lbol ≈ LIR). However, whether the SMGs are scaled up versions of ULIRGs at high

redshift or not is still under debate (Casey et al., 2014).

A very important new generation survey in the study of DSFGs is the

SCUBA-2 Cosmology Legacy Survey (SCLSSCUBA-2, see section SCUBA-2.1.4), which observed over 3000

submillimeter sources at 850µm approaching the confusion limit (Geach et al., 2017)

of the JCMT. The confusion limit happens when the noise is neither dominated by

atmospheric noise nor by instrumentation noise, but instead by the blurring of faint

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1.2 K-correction 3

There is a selection bias upon the wavelength at which DSFGs are detected in

these surveys. For instance, Casey et al. (2013) report a higher peakz for the 850µm

detected galaxies than the 450µm detected ones. Likewise, galaxies selected at shorter

wavelengths (i.e. 450µm) have higher dust temperatures, implying a warmer

popula-tion (Casey et al., 2013). Zavala et al. (2014) further studied these selecpopula-tion effects and they showed that the variations upon the peakz for different observation wavelengths

are consistent with a common parent distribution.

In order to gain a more complete understanding of a population, it is common to

associate sources detected at a certain wavelength with counterparts found at other

wavelengths. Since single-dish submillimeter observations usually have poor resolution

(θ _≈15₋30arcsec), we resort to sources detected at higher positional certainties at

other wavelengths, like radio wavelenghts, given the known correlation between FIR

and radio for starburst galaxies (Condon, 1992; Carilli & Yun, 2000), or mid-infrared

24 µm, where we look for the emission of dust at shorter wavelengths (Pope et al., 2006). This is, however, a very difficult endeavour for SMGs, where counterparts

cannot be found for complete samples (Casey et al., 2013; Zavala et al., 2018).

1.2 K-correction

The distribution of the flux-density over wavelength (or frequency) emitted by an

object is known as its Spectral Energy Distribution (SED). The shape of the SED depends upon the mechanisms of emission of the object. As it was mentioned in the

previous section, the thermal emission of dust, which dominates the SED of DSFGs,

is commonly modeled with a modified black body distribution. The flux-density at

frequencyν is given by:

Sν = [1−e

−₍ν_/

ν₀) β

]2hν

3

c2

1

ehν/kT ₋₁, (1.2.1)

where ν0 is the frequency at which the emission becomes optically thick, β is the

emissivity index, and T is the temperature of the emitting source, which in the case

of DSFGs is considered to be the dust-temperature.

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Figure 1.1: (Left panel) Modified black body for a source with luminosity LIR =

1_×1012_L

, dust-temperatureTd= 42 K, emissivity indexβ = 1.8 and ν0 =c/100µm

(Casey et al., 2014). The SEDs are redshifted to lower ν as z increases. The vertical lines correspond to observed wavelengths: 2.1 mm (blue dash-dot line),1.1 mm (red line), 850 µm (green dashed line), 450 µm (cyan dotted line) and 70 µm (red dash-dot line). (Right panel) Flux density at the observed λ (following the same colors and symbols as in the left panel) for the same modified black body (LIR,β,ν0,Td). We

can see that for λ = 70 µm there is a strong positive K-correction, while at larger λ

(λ_≥450 µm) the effect is opposite (negative K-correction).

As we observe sources with the same luminosity at higher redshifts, the SED shifts

to higher wavelengths and the peak brightness decreases its intensity. It is necessary

to apply the K-correction in order to estimate the emitted flux-density by the source.

This effect is shown in Figure 1.1, with a modified black body SED redshifted to a

set of values, and the resulting observed flux density as a function of redshift. In the

left panel it can be appreciated how the peak of the SED approaches submillimeter

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1.3 Star Formation Rate 5

which shows how the flux density of a galaxy with fixed L changes as a function of

z, we can see that at λ _∼ 1 mm the flux density remains almost constant (or even

increases) atz _≈1₋10. This aids the observation of this type of galaxies up to high

redshifts at wavelengths higher than λ >250 µm (Blain et al., 2002). The observed

flux density can be estimated through the equation (Casey et al., 2014):

Sν,obs =

LIR(1 +z)

4πD2

L

Sν

R1000µm

8µm Sν(Td)dν

, (1.2.2)

whereDLis the luminosity distance,Sνis the source emitted flux density at rest-frame

frequencyν,LIRthe galaxy infrared luminosity,zis the redshift, and

R1000µm

8µm Sν(Td)dν

is the modified black body emission integrated over the 8µm₋1 mm wavelength range. Given that in the case of DSFGs, detected at submillimeter wavelengths, the effect

of the K-correction is applied to decrease the observed flux-density to estimate the

rest-frame flux density, then it is known as negative K-correction.

1.3 Star Formation Rate

The Star Formation Rate (SFR) is a measurement of the rate at which stars are

born in a galaxy, or a particular region within it, and how they transform gas into

stars. It is typically measured in units of solar masses per year (M yr−1). There are

several calibrated methods to estimate the SFR, according to tracers associated with

young stellar populations at different wavelengths. Some of the most used methods

presented in Kennicutt (1998) are the following:

• SFR derived from the UV luminosity:

SFRUV(M yr−1) = 1.4×10−28LUV(erg s−1 Hz−1) (1.3.1)

• SFR derived from recombination lines like Hα:

SFRHα(M yr−1) = 7.9×10−42L(Hα)(erg s−1) (1.3.2)

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• SFR derived from forbidden lines like [OII]:

SFR[OII](M yr−1) = 1.4×10−41L[OII](erg s−1) (1.3.3)

• SFR derived from the IR luminosity:

SFRIR(M yr−1) = 4.5×10−44LIR(erg s−1) (1.3.4)

These relations may vary according to the initial mass function (IMF) considered

by the author. The most frequently used IMFs are those by Salpeter (1955), Kroupa

(2001) and Chabrier (2003). Kennicutt (1998) used the Salpeter IMF for equations

1.3.1 - 1.3.4. If, instead of the Salpeter IMF, a Chabrier IMF (2003) is employed, then the SFRIR is lower by a 1.8 factor (Casey et al., 2014).

Figure 1.2: SED fitting of the observational flux-densities for an example galaxy (irac131161) at redshift z _∼ 1. The SCLS2 450 µm and 850 µm fluxes would lie in the rightmost region of the SED, where there is an extrapolation in the fit. Image from Barro et al. (2011a).

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1.3 Star Formation Rate 7

UV-based determinations are affected by dust extinction, which is often difficult to

determine. The estimation of IR-based SFRs is also affected by different assumptions.

For example, the SED templates used to fit the fluxes of high-z galaxies are adopted

local low-z analogues (Barro et al., 2011a). There could also be some radiation

con-tribution from obscured AGNs, which can heat the dust, but would not be related to the star-forming mechanisms (Casey et al., 2014). Furthermore, for the IR derived

luminosity, few galaxies have deep data beyond 70µm (e.g. fromSpitzer/MIPS Barro et al., 2011a). This affects the calculations of SFR as there are not enough data points

to correctly constrain the full IR-SED. Hence, theLIR and SFRIR determinations can

be affected by the indetermination of the SED fit and the assumption of a single T

throughout the galaxy. As it was mentioned previously, SMGs are bright in the

sub-millimeter range and, therefore, in principle they can provide more data points to fit

the SED and achieve more accurate IR-based luminosities and star-formation rates.

1.3.1 Star-formation main sequence

The star-formation main sequence is a correlation between the stellar mass (M?) and

the star-formation rate (SFR) shown by the majority of star-forming galaxies. The

concept was first introduced by Noeske et al. (2007) for optically selected galaxies

that had SFRHα and later on expanded by Daddi et al. (2007) for 24 µm selected

galaxies. There have been several works that fitted a star-formation main sequence:

64 of those fits were studied by Speagle et al. (2014) for a comprehensive relation that holds up toz = 6. Before the work by Speagle et al. (2014) there were no quantitative

comparisons and, given that each work uses different calibrations and methods (e.g.

IMFs, Stellar Population Synthesis models, extinction curves), they converted the

necesary parameters and derived a time and stellar mass dependent equation.

There are still contradictory results. For instance, Whitaker et al. (2014) studied

the low-mass slope of the star-formation main sequence for the redshift range 0.5 <

z < 2.5. They considered the deep photometry and grism spectra from CANDELS

and 3D-HST and three methods for estimating the SFR: SFRUV+IR,β-dust corrected

UV SFR and Hα SFR. On the other hand Koprowski et al. (2016) present the main

sequence for galaxies detected in the 850 µm SCLS2, in the high-mass end of the

main sequence. Koprowski et al. (2016) discuss the various main sequence fits and

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how the FIR/sub-millimeter selected samples yield different relations to the optically

selected fits, where some find a decline in the slope for masses above logM?/M ≈10.5

(Whitaker et al., 2014), while others find no differences (Schreiber et al., 2015). They

emphasize on the main sequence relation depending upon the sample selection, and

the need of the SED fitting to encompass optical-IR data in order to estimate the SFR.

Even though the star-formation main sequence is still a subject to debate it is

used as a new definition of starburst galaxies. A starburst galaxy is now defined as

those with elevated sSFR= SFR_M

?, when compared to the main sequence (e.g. Casey

et al., 2014). In their 2014 review on DSFGs Casey et al. showed that it was still

uncertain where the Dusty Star-Forming Galaxy population lies in relation to the

main sequence, which depends upon the method and uncertainties related to the

estimation of SFR and M?. Furthermore, it is unkown which would be the impact of

mergers to the mass build-up of SMGs (Casey et al., 2014).

1.4 Main goals and key questions

The main goal of this thesis is to compare the SFR measurements derived from

ob-servations at UV/optical and submillimeter bands. We will work with data from the

CANDELS and SCLS2 catalogues for the Extended Groth Strip field. We aim to

explore the demographic properties of the galaxies reported in the optical catalogue

CANDELS selecting the star-forming and quiescent galaxies using a color-color

dia-gram. Besides, we would like to examine how DSFGs with identified counterparts in the CANDELS and IRAC catalogues relate to the rest of the population in this field

according to the derived SFR and stellar mass (M?).

Throughout this work we adopted a flat ΛCDM cosmology with the following

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Chapter 2

Extended Groth Strip Data

The Extended Groth Strip (EGS) field is a region between the constellations Ursae Major and Bootes, located at α = 14h19m00s and δ = +52o4800000 and it is 70_×10 square arcminutes in size. It was first observed by theHubble Space Telescope (HST) with the Wide Field Planetary Camera 2 (WFPC1) between March and April 1994

and named after the phycisist Edward Groth (Rhodes, 1999). He was associated with

theHST and worked there as data and operations team leader, where he was P.I. for the Wide Field Camera (WFC) instrument. It is one of the most studied fields, along

with: GOODS-N, GOODS-S, UDS and COSMOS (e.g. Koekemoer et al., 2011)

2.1 Data sources

The EGS field has had a large multi-wavelength coverage from several instruments and

surveys. For instance, the 3D-HST, AEGIS, CANDELS and IRAC surveys include

this deep field. Their data is available in the Rainbow Navigator, presented by Barro

et al. (2011b) 1.

2.1.1 AEGIS

The All-wavelength Extended Groth Strip International Survey (AEGIS) is a

multi-wavelength program whose goal is to understand how galaxies and large-scale

struc-tures form and evolve from early times into the universe we see around us (Davis

et al., 2007). The instruments involved in this survey range from those used at radio

1_{Rainbow Navigator (P´}_{erez - Gonzalez and Barro):}

https://rainbowx.fis.ucm.es/Rainbow˙navigator˙public/

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wavelengths (VLA at 6 and 20 cm) to X-Rays (Chandra/ Advanced CCD Imaging Spectrometer (ACIS) at 4 and 1 keV). It also covers the UV, NIR and IR spectral

re-gions with the following telescopes:Galaxy Evolution Explorer (GALEX),HST in the

V (F606W),I(F814W),J (F110W) andH(F160W) bands, Keck Telescope,

Canada-France-Hawaii Legacy Survey, Palomar/ Wide-Field Infrared Camera, Spitzer/ In-frared Array Camera (IRAC) for the Mid-InIn-frared range (at 3.6, 4.5, 5.8 and 8 µm)

and the Spitzer/ Multiband Imaging Photometer (MIPS) for the far-IR observations (at 24, 70 and 160µm). The resulting data is presented as images, spectra and derived

data products in their web page2_{. However, each instrument had a different coverage}

of the EGS field. Therefore, there are some areas where the surveys do not overlap,

as can be seen in Figure 2.1.

Figure 2.1: AEGIS coverage map of the Extended Groth Strip. In both panels the background gray-scale image shows the HST/ACS mosaic composed image. (Left panel) CFH12K (pink), WIRC from Palomar (red), Keck spectroscopic observations with DEIMOS as part of the DEEP2 collaboration (black), CFHTLS MegaCam (blue). (Right panel) VLA at 20 cm(red), VLA at 6 cm(pink),Spitzer/IRAC (green),

Chandra (blue), GALEX (black). In both panels the cyan region corresponds to the Mini Test Region and the yellow line marks 30 arcmin along the length of the field. Image taken from Davis et al. (2007).

2_{Official web-page of the AEGIS catalogue}

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2.1 Data sources 11

2.1.2 CANDELS catalogue

The Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS)

is anHST survey program that covered 800 arcmin2 over five deep fields (Koekemoer et al., 2011; Grogin et al., 2011). The program was designed to observe up to two

depths: the CANDELS/Deep survey (limited atH=27.7 mag) and CANDELS/Wide survey (limited at H=27 mag). The WFC3 and ACS cameras on board the HST

acquired deep images during 902 orbits between 2010 and 2013. The project was led

by Sandra Faber (U. of California, Santa Cruz) and Henry Ferguson (Space Telescope

Science Institute). The five deep fields observed within this project were:

CANDELS/Deep survey:

• GOODS-N (Great Observatories Origins Deep Survey - North)

• GOODS-S (Great Observatories Origins Deep Survey - South)

CANDELS/Wide survey:

• UDS (Ultra Deep Survey)

• COSMOS (Cosmic Evolution Sur-vey)

• EGS (Extended Groth Strip)

The CANDELS survey has an extensive database for these observed deep fields.

Several sub teams within CANDELS estimated redshifts and other physical parame-ters through various methods, presented and evaluated by Mobasher et al. (2015) and

Santini et al. (2015). There have also been demographic studies for the GOODS-S

and the UDS fields by Fang et al. (2018). The CANDELS catalogue for the EGS field

was presented by Stefanon et al. (2017).

2.1.3 Optical spectra

Within the work in this thesis we present new optical spectra obtained with the 10 m

Gran Telescopio de Canarias (GTC) Multi-Object Spectrograph (MOS) for the

obser-vation proposal GTC-AMEX19 (PI: Aretxaga). We observed, among other objects,

3 submilimeter galaxies selected from the SCLS2 sample, with optical counterparts

presented by Zavala et al. (2017) (section 2.2). Additionally, we observed 4 galaxies

selected from the 3D-HST catalogue. In chapter 4 we present the planning, reduction,

extracted spectra and line identification of these observations.

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2.1.4 Submillimeter data

2.1.4.1 SCUBA-2 Cosmology Legacy Survey

Our submillimeter sample of Dusty Star-Forming Galaxies (DSFGs) are selected from

data acquired with the Submillimetre Common-User Bolometer Array 2 (SCUBA-2)

at the James Clerk Maxwell Telescope in 2014, as part of the SCUBA-2 Cosmology Legacy Survey (SCLS2 Geach et al., 2013, 2017). The catalogue presents observations

at 450 µm and 850 µm, with depths of σ450 µm ≈ 1.9 mJy and σ850 µm ≈ 0.46 mJy

(Zavala et al., 2017). The coverage of the map is _∼70 arcmin2 with angular FWHM of θ450 µm ≈ 7.5 arcsec and θ850 µm ≈ 14.5 arcsec. The sources for a robust sample

were selected as the peak values from the S/N map, taking into account S/N> 3.5.

Considering this threshold, the catalogue has 57 sources at 450µm and 90 at 850 µm

and it is displayed in Figure 2.2 over the corresponding S/N maps at each wavelength.

Figure 2.2: The SCLS2 450 µm (left panel) and 850 µm (right panel) S/N maps of the Extended Groth Strip with detected sources marked with white squares. Image taken from Zavala et al. (2017).

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2.1 Data sources 13

2.1.4.2 AzTEC map

There is also an EGS 1.1 mm map acquired with the AzTEC instrument at the Large

Millimeter Telescope Alfonso Serrano (LMT). It is centered at α = 214.9420396o_,

δ = 52.87861111o _{and has a 91}_._{2 arcmin}2 _{area. The data was acquired in May 2013}

and observed over 11 hours, when the LMT was operating in its 32 m

configura-tion (θ1.1mm ∼ 8.5 arcsec). Figure 2.3 shows the catalogue of SCLS2 sources over

the AzTEC S/N map, where the brightest source at 850 µm (S/N=24.2) appears

with S/N=6.6 at 1.1 mm. As it can be seen, the depth of the 1.1 mm map is low

(S1.1 mm ∼ 0.5 mJy). There will be a new instrument, named TOLTEC, to be

in-stalled at the LMT in late 2019. It is designed to observe at 1.1, 1.4 and 2.0 mm

in the 50 m configuration of the LMT. One of the main projects for this instrument

is the observation of deep fields as part of its legacy programs, where the confusion

limit for the 1.1 mm band will be reached (S1.1 mm ∼0.025 mJy).

-2.9 -2.2 -1.6 -0.88 -0.21 0.47 1.1 1.8 2.5 3.1 3.8 57 56 55 54 53 52 51 50 49 48 47 46 45 44 43 42 40 39 38 37 36 35 34 33 32 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 94 93 92 91 90 89 88 85 83 82 81 80 79 78 77 75 74 73 72 71 70 69 68 67 66 65 64 63 62 61 60 59 58 57 56 55 54 53 52 51 50 49 48 47 46 45 44 43 42 41 40 39 38 37 36 35 34 33 32 31 30 29 28 27 26 25 24 23 22 21 20 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1

Figure 2.3: The 1.1 mm S/N map of the EGS field observed by AzTEC at the 32 m LMT. This region closely matches the SCLS2 coverage area described in 2.1.4. The 850 µm detected sources are marked in red and the 450 µm detected sources are marked in blue.

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2.2 Optical counterparts to submillimeter galaxies

Once the SCLS2 sources were detected, they were associated with optical

counter-parts using the panchromatic data available for this field (Zavala et al., 2018). The

counterparts were found using: radio VLA at 20 cm, which traces recent star

forma-tion via synchrotron emission (Carilli & Yun, 2000); observaforma-tions at 24 µm, as they

are sensitive to warm dust emission; and 8µm data as a tracer of the older and

mass-dominant stellar population. Counterparts were found within a search radius 2.5 times

the positional uncertainty of each galaxy. They found 71 counterparts. Out of the 71

identified counterparts, 58 lie within the footprint of CANDELS. The remaining 13 galaxies that fall outside the HST/CANDELS coverage, were associated to sources from the IRAC catalogue presented by Barro et al. (2011b). In Table 2.1 we present

the ID and coordinates for the optical counterparts. From now on, we will work with

this sample of DSFGs with identified counterparts. They have reported Stellar-Mass

and SFR values estimated by various teams in the CANDELS catalogue.

Table 2.1: Optical counterparts for the SCLS2 sources. The optical counterpart coor-dinates are those of CANDELS (Stefanon et al., 2017) or IRAC (Barro et al., 2011b) catalogues. Column 1: name in the SCLS2 catalogue at 850 µm. Column 2: identifi-cation in the SCLS2 catalogue at 450µm. Column 3: identification in the CANDELS catalogue with HST observation. Column 4: identification in the IRAC catalogue. Column 5: right-ascension of the optical/IR counterparts. Column 6: Declination of the optical/IR counterparts.

ID850 µm ID450 µm IDHST IDIRAC RAopt DECopt

850.001 450.02 21335 - 214.910882 52.900925

850.002 450.03 16498 - 214.914447 52.875959

850.003 450.05 18656 - 214.916415 52.891337

850.004 450.25 17920 - 214.946689 52.910020

850.005 450.08 - 122794 214.978122 52.811542

850.006 450.13 13658 - 214.974134 52.905954

850.007 450.20 8156 - 214.962443 52.870324

850.008 450.15 8265 - 215.014456 52.901214

850.009 450.12 - 123412 214.843676 52.910939

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2.2 Optical counterparts to submillimeter galaxies 15

Table 2.1 – continued from previous page

850.010 450.14 8340 - 214.919736 52.839658

850.011 450.39 4919 - 214.922389 52.821939

850.012 450.06 12475 - 214.946125 52.876173

850.014 450.46 - 121876 1 214.8562017 52.9287205

850.015 450.09 12874 - 214.938204 52.874313

850.016 450.56 - 120588 215.007724 52.827103

850.017 450.11 13776 - 214.898846 52.852513

850.018 450.84 4996 - 214.974861 52.860563

850.019 450.41 24050 - 214.970982 52.957352

850.020 450.23 7994 - 215.031040 52.916459

850.021 450.17 6891 - 215.054219 52.925918

850.022 450.01 9333 - 214.927684 52.847964

850.024 450.04 16318 - 214.923237 52.882156

850.025 450.29 23205 - 214.850601 52.866404

850.028 450.69 16544 - 214.876329 52.852377

850.029 450.21 21206 - 214.835440 52.843781

850.030 450.10 21235 - 214.877974 52.876880

850.032 450.63 5729 - 214.932895 52.832951

850.037 450.64 - 117087 215.050227 52.853897

850.038 450.27 27358 - 214.864723 52.899081

850.039 450.40 - 117578 215.038863 52.854429

850.041 450.16 1368 - 214.992838 52.850766

850.042 450.26 12502 - 214.979990 52.902444

850.043 450.73 23152 - 214.950132 52.938209

850.052 450.76 - 124474 1 214.827757 52.904873

850.059 450.24 18694 - 214.855508 52.848827

850.060 450.75 - 121668 214.84949 52.938104

850.065 450.18 21212 - 214.875544 52.866459

850.069 450.44 11896 - 214.954780 52.876572

Continued on next page

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850.070 450.34 18143 - 214.968421 52.925046

850.073 450.52 5375 - 214.948005 52.840633

850.078 450.82 - - 215.0377 52.8708..

850.079 450.54 12448 - 215.029611 52.936340

850.085 450.33 - 118504 1 215.015842 52.856805

850.092 450.60 8277 - 214.885212 52.815749

850.095 450.37 - 121835 1 214.996545 52.814086

850.097 450.71 14062 - 214.920611 52.865887

850.104 450.45 - 122942 214.986563 52.80205

850.044 - 2998 - 215.034896 52.891364

850.047 - 20341 - 214.859833 52.860656

850.048 - 2838 - 215.045433 52.894592

850.050 - 17067 - 214.996769 52.94075

850.051 - 10774 - 214.995061 52.906108

850.053 - 3345 - 214.993497 52.864329

850.054 - 15371 - 214.874737 52.843773

850.056 - 4619 - 215.027303 52.894668

850.057 - 7340 - 214.996947 52.889169

850.062 - 1507 - 215.061805 52.900938

850.067 - 28663 - 214.829331 52.893962

850.072 - 14167 - 215.015852 52.939408

850.075 - 26086 - 214.834060 52.870092

850.077 - - 117273 215.029710 52.867911

850.080 - 26097 - 214.923151 52.934686

850.081 - 14924 - 214.954660 52.899053

850.082 - - 115315 215.055684 52.881997

- 450.19 6840 - 214.916970 52.827376

- 450.28 15610 - 214.945929 52.894158

- 450.35 15566 - 214.902474 52.863695

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- 450.36 9195 - 214.936159 52.855855

- 450.42 13677 - 214.905312 52.850914

- 450.43 11923 - 215.020341 52.929760

- 450.48 27020 - 214.908677 52.927897

2.2.1 Derived properties of the SCLS2 galaxies

Zavala et al. (2017) identified the sources in the SCLS2 catalogue, detecting them at

first in the S/N map and then measuring the coordinates, flux density and noise. In

order to measure these quantities, they fitted to each detected source the Point Spread Function (PSF), which was estimated in the reduction procedure. This measured flux

density is called raw flux density, as it does not have any boosting correction. We

measured the raw flux density at the reported coordinates for each wavelength map

and compared it with the raw flux density reported by Zavala et al. (2017). In Figure

2.4, we present a comparison between both reported flux densities for the 450 µm

map, where we can appreciate that there is good agreement between both measured

flux densities. Therefore, we will adopt the derived physical parameters estimated by

Zavala et al. (2017) for our sample from the SCLS2.

2.2.1.1 Deboosted flux

When sources are detected at a low S/N, there occurs contamination from the crowd-ing of sources fainter than the detection threshold, which increases (boosts) the

mea-sured flux density of the detected sources (Coppin et al., 2006). Therefore, the raw flux

densities have to bedeboosted before estimating physical parameters. The deboosting factor is estimated through an statistical process using Monte Carlo simulations, as

described by Zavala et al. (2017). Fainter sources are more boosted than brighter

ones. Considering that we have compared the raw flux densities measured directly

and that they comply with a 1:1 relation (Figure 2.4), we will adopt from now on

the fDeboost from Zavala et al. (2017) and use these values to estimate the infrared

luminosities and star formation rates.

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Figure 2.4: Comparison between the SCLS2 450 µm raw flux densities and fRAW

measured in this work (y-axis) and those reported by Zavala et al. (2017) at map (x-axis).

2.2.1.2 Infrared Luminosity

The IR luminosity (8₋1000 µm) reported by Zavala et al. (2018) was estimated by

fitting a modified black body, fixed at the redshift provided by the optical catalogues.

The modified black body that was used had an emissivity index β = 1.6 and ν0 =

c/100µm, from equation 1.2.1. OurLIRestimation uses the same modified black body

parameters (β, ν0), the redshift reported in the catalogues for the optical counterparts,

the deboosted flux and the dust temperature (Td) as in Zavala et al. (2017, 2018). We

must point out that in Zavala et al. (2018) they fitted both theLIRandTd. Instead, we

are calculating the IR-luminosity from either the 450µm or 850µm, assuming that the

Td is correct. The resultingLIR comparison is presented in Figure 2.5, where we can

appreciate that the LIR calculated from the 850 µm flux densities are systematically

located above the 1:1 relation. As thef850 µmis placed further away from the modified

black body peak emission the fit is less accurate, in this case overestimating the LIR.

We could safely assume this is the reason for the overestimation, given that this effect

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Figure 2.5: Comparison ofLIR calculated in this work and Zavala et al. (2018), using

the 450 µm (upper panel) and 850 µm (lower panel) deboosted flux densities and

LIR by Zavala et al. (2017). We considered a modified black body with β = 1.6 and

ν0 =c/100 µm,z of the optical counterparts and Td fitted by Zavala et al. (2018).

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2.2.1.3 Infrared star-formation rate for dusty star forming galaxies

Considering theLIR, Zavala et al. (2018) estimate the SFRIR with a Kennicutt (1998)

relation and Chabrier (2003) initial mass function (IMF), whereLIR ∼1012Limplies

a SFR_∼ 100Myr−1. Equation 1.3.4 considers a different IMF, so it must be scaled

to account for this difference with a factor _∼ 1.8. Zavala et al. (2018) use the

star-forming main sequence derived by Speagle et al. (2014), and our sample of DSFG

population lies mostly within the 3σ of this main sequence fit (Figure 2.6).

Figure 2.6: Distribution of the DSFGs from the SCLS2 catalogue with optical coun-terparts in the sSFR-redshift relation by Zavala et al. (2018). The continuous black line and its 3σ uncertainty region (gray-scale) are the star forming main sequence derived by Speagle et al. (2014). The black dots are the galaxies detected at both 450 µm and 850 µm, the blue rectangles are those only detected at 450 µm and the red triangles are the galaxies detected only in the 850 µm data. Image taken from Zavala et al. (2018).

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Chapter 3

Demographics of the EGS

population

The EGS CANDELS catalogue includes physical properties calculated by various

teams, as presented in Mobasher et al. (2015) and Santini et al. (2015), who

com-pare the results from the teams. They concluded that the results are in overall good

agreement, despite the different methods and assumptions (i.e. initial mass functions (IMFs), Stellar Population Synthesis templates, SED fitting code) that each team

considered. We adopt from the CANDELS catalogue the Star Formation Rate (SFR)

presented by Barro et al. (2011a), which is the total SFR_∼SFRIR+UV, according to

equation 3.0.1. In order to obtain the SFRIR+UV they estimated the IR luminosities

(LIR =L[8−1000 µm]) and luminosity at 2800 ˚A. The LIR was calculated by fitting

the MIPS 24 µm fluxes to SED templates, and L2800 was obtained from the best fit

of optical SED templates (Barro et al., 2017, see Figure 1.2).

SFRUV+IR= 1.09×10−10(LIR+ 3.3L2800) (3.0.1)

There have been galaxy demographic studies for the other CANDELS fields, like

those in UDS and GOODS-S conducted by Fang et al. (2018). Following their

proce-dure, we select a sample of galaxies from the EGS catalogue, considering the criteria

below:

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1.- Observed magnitude at the HST F160W band H < 24.5, following the rec-ommendation by van der Wel et al. (2014). The galaxy sizes can be estimated

accurately if this limit is considered when fitted in GALFIT.

2.- SExtractor parameter CLASS STAR<0.9, in order to avoid contamination of

the sample by stars.

3.- As suggested by Santini et al. (2015) we excluded the sources with photometric

defects, like star spikes and hot pixels, which are tagged as PhotFlag=0.

4.- Stellar masses within the range 9.0<log (M?/M) <11.0.

5.- Well-constrained GALFIT measurements, where we accepted the objects with

quality flag value of 0.

The only criterium we will not comply with from Fang et al. (2018) is the redshift

selection (z <2.5), as we wish to explore the redshift evolution of the demographics

up to higher redshifts. In Table 3.1 we present the number of galaxies remaining in

our sample after the selection criteria have been applied, and the percentage they

represent from the entire catalogue. For comparison, we show as well the Fang et al.

(2018) sample in UDS, GOODS-S and for both fields combined. Another difference

between our study and that of Fang et al. (2018) is the adopted SFR estimation. They did not use the SED fitting results by Santini et al. (2015), instead they used

the rest-frame UV (NUV: λ _≈ 2800˚A) luminosity corrected by dust (AV from the

SED fits, where ANUV = 1.8AV) following equation 3.0.2 for a Kroupa IMF (2001).

We will identify this SFR as SFRU V,corr. They justified this selection by comparing

their estimates with the ones presented by other teams in Santini et al. (2015), and

concluded they had good agreement.

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3.1 UVJ diagram 23

Table 3.1: Number of galaxies in each field using: F160W <24.5 mag, PhotFlag=0, Class star< 0.9, 9.0< logM?/M < 11.0. Both the number of galaxies and

percent-ages relate to the whole catalogue for the GOODS-S and UDS fields (taken from Fang et al., 2018), and for the EGS field (this work). Column 1: the selection criteria. Column 2: number of galaxies for the GOODS-S field. Column 3: number of galaxies for the UDS field. Column 4: number of galaxies for the GOODS-S and UDS fields, combined. Column 5: number of galaxies for the EGS field.

Characteristic GOODS-S UDS Combined EGS

Full catalogue 34930 35932 70862 41457

(100%) (100%) (100%) (100%)

z spec 2658

(6.41%)

Selection criteria 4683 5810 10493 7663

(13.4%) (16.2%) (14.2%) (18.5%)

Star-forming galaxies 3581 4479 8060 7137

(10.3%) (12.5%) (11.4%) (17.22%)

Quiescent galaxies 447 628 1075 526

(1.3%) (1.7%) (1.5%) (1.3%)

3.1 UVJ diagram

We used a color-color rest-frame diagram for our star-forming galaxies selection, with

colorsU-V andV-J, which differentiates between quiescent and star-forming galaxies, even those reddened by dust (Patel et al., 2012). From now on we will refer to this

diagram as UVJ diagram, where star-forming galaxies are red in V-J and quiescent galaxies are blue (Williams et al., 2009). In Figure 3.1 and 3.2 we present the UVJ

diagram for the selected sample of galaxies from the CANDELS/EGS catalogue. The

color of the dots represents their specific star-formation rate (log sSFR, considering

the total SFR estimated by Barro et al., 2011a). The optical counterparts identified

by Zavala et al. (2018) in the CANDELS catalogue are marked as downwards red

triangles. Dusty star-forming galaxies (DSFGs) with only IR counterparts in the IRAC

catalogue are not included, as these do not have reported U, V and J magnitudes. The black dashed line is the selection criteria used to discern between quiescent and

star-forming galaxies for up toz= 2, since this is the redshift limit in Williams et al.

(2009).

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0.0 0.5 1.0 1.5 2.0

2.5 logM*< 9.5 9.5 < logM*< 10 10 < logM*< 10.5 10.5 < logM*< 11

z <

0

.5

11 < logM*

0.0 0.5 1.0 1.5 2.0 2.5 0.5 < z < 1 0.0 0.5 1.0 1.5 2.0 2.5 1.0 < z < 1 .5

0 1 2

0.0 0.5 1.0 1.5 2.0 2.5

0 1 2 0 1 2 0 1 2 0 1 2

1.5 < z < 2 .0 −10.5 −10.0 −9.5 −9.0 −8.5 −8.0 Lo g sS FR [ yr − 1 ]

V - J

U

V

Figure 3.1: UVJ rest-frame color diagram for the EGS field selected galaxies at 0< z <2. The color values in this Figure are uncorrected for dust extinction. We present the properties of the galaxies in the EGS field in redshift slides of ∆z = 0.5 (rows) and in stellar mass slides of ∆log M?/M = 0.5 (columns). The color gradient for

the points indicates the log(sSFR) value for each galaxy. The optical counterparts of the SCLS2 sources, identified by Zavala et al. (2018) in the CANDELS catalogue, are marked as downwards red triangles. The dashed black lines define the quiescent region according to Williams et al. (2009).

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3.1 UVJ diagram 25 0.0 0.5 1.0 1.5 2.0

2.0

<

z <

2

.5

11.0 < logM*

0.0 0.5 1.0 1.5 2.0 2.5 2.5 < z < 3 .0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 < z < 3 .5

0 1 2

0.0 0.5 1.0 1.5 2.0 2.5

0 1 2 0 1 2 0 1 2 0 1 2

3.5 < z 4 .0 −10.5 −10.0 −9.5 −9.0 −8.5 −8.0 Lo g sS FR [ yr − 1 ]

V - J

U

V

Figure 3.2: UVJ rest-frame color diagram uncorrected for dust extinction for the selected galaxies in the EGS field that lie beyond z > 2. Same symbols as in Figure 3.1.

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The CANDELS catalogue presents estimated extinction valuesAV (Santini et al.,

2015), therefore, we corrected for dust attenuation the colors presented in the UVJ

diagram, considering a Calzetti et al. (2000) attenuation law with AU = 1.5AV and

AJ = 0.35AV. The effect of this correction can be seen in Figure 3.3 for 0.5< z < 1.0

and 10 < log (M?/M) < 10.5. The UVJ diagrams corrected for dust attenuation

are presented in Figures 3.4 and 3.5. Those galaxies whose colors locate them in the

upper left corner of theUVJ diagram are catalogued as quiescent galaxies and those outside the region limited by the dashed line are classified as star-forming galaxies

(Figure 3.4). For galaxies atz >2, we will consider them all to be star-forming. The

selected number of quiescent and star-forming galaxies are reported in Table 3.1.

0.0 0.5 1.0 1.5 2.0 2.5

0.0 0.5 1.0 1.5 2.0 2.5 −10.5 −10.0 −9.5 −9.0 −8.5 −8.0 Lo g sS FR [ yr 1 ]

V

- J

U

V

UVJ diagram - dust correction

Figure 3.3: UVJ color diagrams for 0.5 < z < 1.0 and 10 < log(M?/M) < 10.5

that shows the effect before (left) and after (right) applying a dust correction. The symbols are the same as in Figure 3.1.

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3.1 UVJ diagram 27 0.0 0.5 1.0 1.5 2.0

z <

0

.5

10.5 < logM*< 11

0.0 0.5 1.0 1.5 2.0 2.5 0.5 < z < 1 .0 0.0 0.5 1.0 1.5 2.0 2.5 1.0 < z < 1 .5

0 1 2

0.0 0.5 1.0 1.5 2.0 2.5

0 1 2 0 1 2 0 1 2 0 1 2

1.5 < z < 2 .0 −10.5 −10.0 −9.5 −9.0 −8.5 −8.0 Lo g sS FR [ yr − 1 ]

V - J

U

V

Figure 3.4:UVJ rest-frame color diagram corrected for dust attenuation for the CAN-DELS/EGS galaxies at 0< z <2. The symbols are the same as in Figure 3.1.

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0.0 0.5 1.0 1.5 2.0

2.0 < z < 2 .5

11 < logM*

0.0 0.5 1.0 1.5 2.0 2.5 2.5 < z < 3 .0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 < z < 3 .5

0 1 2

0.0 0.5 1.0 1.5 2.0 2.5

0 1 2 0 1 2 0 1 2 0 1 2

3.5 < z < 4 .0 −10.5 −10.0 −9.5 −9.0 −8.5 −8.0 Lo g sS FR [ yr − 1 ]

V - J

U

V

Figure 3.5:UVJ rest-frame color diagram corrected for dust attenuation for galaxies at redshifts 2< z <4. The symbols are the same used in Figure 3.1.

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3.2 Star Formation Main Sequence 29

3.2 Star Formation Main Sequence

-3 -2 -1 0 1 2 3 lo g SF R [ M⊙ y r − 1]

z < 0⊙5 0⊙5 < z < 1⊙0 1⊙0 < z < 1⊙5

-3 -2 -1 0 1 2 3 lo g SF R [ M⊙ y r − 1]

1⊙5 < z < 2⊙0 2⊙0 < z < 2⊙5 2⊙5 < z < 3⊙0

9⊙0 10⊙0 11⊙0 12⊙0 log M⋆ [M⊙]

-3 -2 -1 0 1 2 3 lo g SF R [ M⊙ y r − 1]

3⊙0 < z < 3⊙5

9⊙0 10⊙0 11⊙0 12⊙0 log M⋆ [M⊙]

3⊙5 < z < ⋆⊙0

9⊙0 10⊙0 11⊙0 12⊙0 log M⋆ [M⊙]

⋆⊙0 < z

Figure 3.6: Star Formation Rate - Stellar Mass relation for the EGS field. The quies-cent and star-forming galaxies are represented as the yellow empty circles and black dots, respectively. The empty cyan circles represent the galaxies that do not com-ply with some of the selection criteria. The DSFGs with optical counterparts in the CANDELS catalogue are represented as downwards filled red triangles, where empty triangles are those which do not pass the selection criteria. Optical counterparts iden-tified in the IRAC catalogue are represented with an upwards purple triangle. The SFRIR estimated in section 2.2.1.3 from the SCLS2 data is identified with red

(CAN-DELS optical counterparts) or purple (IRAC near-infrared counterparts) diamonds. The vertical black dashed line connects the SFRIR and SFRTotal from Barro et al.

(2011a).

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Once the quiescent and star forming galaxies were selected, we locate them in the

SFR-stellar mass relation diagram (Figure 3.6). As it can be appreciated, most DSFGs

have significantly higher SFRIR calculated from the submillimeter flux densities than

from other methods. Furthermore, this difference is not a fixed factor.

log sSFR [yr−1] = logSFR[Myr

−1_]

M?[M]

= log SFR[Myr−1]−log M?[M] (3.2.1)

In order to explore the star formation main sequence, we transform the previous

estimations to specific star formation rate following equation 3.2.1. We will hence use

a variable which is normalized by galaxy mass. Then we proceeded with a 3 step

iterative linear fit with clipping at σ = 1.5. Our final fits for the star formation main

sequence at each redshift panel are presented as solid red lines in Figure 3.7 and the

coefficients are presented in Table 3.2, according to equation 3.2.2. This procedure is

the same presented by Fang et al. (2018) to ensure that the fit crosses the

highest-density galaxy region in the diagram.

log sSFR [yr−1] =α log M? [M] +β (3.2.2)

There is another approach to select star-forming galaxies, which is the direct selection

upon the SFR vs M? diagram, as presented by Barro et al. (2017) and Liu et al.

(2018). They fitted a star formation main sequence to their data and then selected

the quiescent galaxies as those galaxies located below the ∆SFR = ₋0.7 dex and

∆SFR = ₋1.2 dex from the main sequence, respectively. Within their work they

compare this selection with the UVJ diagram, determining that even though the two selection criteria are consistent, the UVJ diagram is more restrictive towards identifying the quiescent and transition populations (Barro et al., 2017). This justifies

our selection of the UVJ diagram criteria. Furthermore, we aim to calculate the star formation main sequence for our sample from the already selected star-forming

galaxies.

Figure 3.7 also presents the 3σ deviation of the main sequence as a gray region,

along with other fits in the literature: Fang et al. (2018, blue dash-dot line), which

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from CANDELS data; Speagle et al. (2014, purple dash-dot line), which presents a

time and stellar mass dependent estimation for redshifts z < 6; Barro et al. (2017,

cyan dash-dot line), who fitted the high-mass (logM?/M= 10.5) section of the star

formation main sequence and used the GOODS-S field from CANDELS data; and

Whitaker et al. (2014, green dash-dot line), who fitted a broken power law with a mass cut at log M?/M = 10.2 for the AEGIS, COSMOS, GOODS-N, GOODS-S,

and the UKIDSS UDS fields, also using CANDELS data. All the coefficients from the

various fits are presented in Table 3.2.

Table 3.2: Coefficients for the star formation main sequence fits by various authors, as expressed in the corresponding equations a,b,c,d_{. Column 1: redshift range for the}

fit, which corresponds to each panel in Figure 3.7. Column 2: parameters for our fit, considering equation 3.2.2. Column 3: fit coefficients presented by Fang et al. (2018). Column 4: coefficients for the fit by Barro et al. (2017). Column 5: time at mid-bin used in the Speagle et al. (2014) equation c_{. Column 6: coefficients for the broken}

power-law fit by Whitaker et al. (2014), where the fit is split for masses higher and lower than log (M?/M)∼10.2.

z range Our fit Fanga Barrob Speaglec Whitakerd

α β a b µ log C t(z) µlow µhigh log C

0.2-0.5 -0.094 -8.91 -0.009 -9.296 z=0.35

0.5-1.0 -0.325 -6.474 -0.063 -8.987 0.19 1.21 z=0.75 0.94 0.14 1.11 1.0-1.5 -0.576 -3.792 -0.184 -8.860 0.53 1.44 z=1.25 0.99 0.51 1.31 1.5-2.0 0.716 -2.122 -0.255 -8.748 0.64 1.75 z=1.75 1.04 0.62 1.49 2.0-2.5 -0.835 -0.733 -0.311 -8.714 0.68 1.92 z=2.25 0.91 0.67 1.62 2.5-3.0 -0.615 -2.478 z=2.75

3.0-3.5 -0.733 -1.147 z=3.25 3.5-4.0 -0.906 0.918 z=3.75

z >4.0 -0.596 -2.097 z=5.25

a.Fang et al. (2018) log sSFR =a(log M?−10) +b.

b.Barro et al. (2017) log SFR =µhlog M?

M

−10.5i+ log C.

c.Speagle et al. (2014) log SFR(M?, t) = (0.840.026×t)log M?(6.51−0.11×t).

M? corresponds to the stellar mass of each galaxy.

d.Whitaker et al. (2014) log SFR =µhlog M?

M

−10.2i+ log C.

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Figure 3.7: Specific Star Formation Rate - Stellar Mass relation for the EGS field, with the CANDELS catalogue SFR estimated by Barro et al. (2011a). Solid red line: our fit with the 3σ uncertainty (gray shaded region) we estimated, considering

σ2 ₌P

(x₋µ)2_/N₋_{1. Blue dash-dot line: Fang et al. (2018) for the UDS and}

GOODS-S fields. Purple dash-dot line: GOODS-Speagle et al. (2014) time and mass dependent relation. Cyan dash-dot line: Barro et al. (2017) for high-mass galaxies in GOODS-S field. Green dash-dot line: Whitaker et al. (2014) power law fit for the AEGIS, COSMOS, GOODS-N, GOODS-S, and the UKIDSS UDS fields. The red downwards triangles are the CANDELS optical counterparts of the SCLS2 galaxies and the upwards purple triangles are the IRAC identified counterparts (Zavala et al., 2017). The diamonds connected by dashed lines are the corresponding SFRIR estimated by Zavala et al.

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From these results we can conclude that the star formation main sequence is

still a subject open for discussion, where the results can vary depending upon the

population, selection criteria and fitting technique. Our own fit best agrees with the

slope fit by Speagle et al. (2014) at low redshifts (z <1.5), and the high-mass slope

of the fit by Whitaker et al. (2014) up toz _≈2.5.

3.2.1 Location of Dusty Star-Forming Galaxies within the

star formation main sequence

Dusty Star Forming Galaxies typically lie in the high-mass end of the star

forma-tion main sequence. Within our sample, however, there are some low-mass galaxies

log M?/M ∼9.06 at low redshift (z ≤0.5). Considering the UV based SFR corrected

by dust in the CANDELS catalogue, the optical counterparts of the DSFGs lie within

the 3σ range of our main sequence fit, except for three galaxies in the 2.5< z <3.0

redshift bin. When we consider the SFRIR calculated from submillimeter data 62 out

of 68 galaxies are located within the 3σ region and 3 galaxies lie above the 3σ region.

Therefore, 4% of our DSFGs sample can be classified as starburst galaxies. However, as it can be appreciated in Figure 3.8 most of the DSFGs lie above the star-formation

main sequence even if they are located within the 3σ region of the fit.

Here we must emphasize that there is not yet a consensus of where the star

formation main sequence exactly lies. For instance, Zavala et al. (2018) used the

Speagle et al. (2014) SFR-M? relation and found 82% of the same galaxies in the

sample within 3σ of the main sequence (Figure 2.6). However, it seems to be a better

approach to calculate the star formation main sequence from the same field as the

studied DSFG population and with the same methods.

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Figure 3.8: Location of DSFGs to the star-formation main sequence for the same redshift bins as in Figure 3.7. The gaussian is centered on the star-formation main sequence with the corresponding σ of the fit. The blue, purple and pink regions correspond to the 1σ, 2σ and 3σ regions of the fit. The orange rectangles are the histogram of DSFGs. Most of the DSFGs lie in the upper section of the star-formation main sequence fit.

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Chapter 4

GTC-MOS spectra

A proposal for Multi-Object Spectroscopy (MOS) with OSIRIS (Optical System for

Imaging and low-Intermediate-Resolution Integrated Spectroscopy) was presented

and accepted at the Gran Telescopio de Canarias (GTC). I participated in the

plan-ning stage of the proposal GTC-AMEX19 (PI: Aretxaga), selected the target objects

and designed the multi-object mask. Once the spectra were observed and delivered,

we proceeded with the reduction of the data. We present the detected lines and the identification of the candidate rest-frame emission lines.

4.1 Phase II - planning

The field to observe in GTC-AMEX19 was centered at α = 214.8519671o and

δ = +52.8857350o. We selected the Dusty Star-Forming Galaxies (DSFGs) which already had an identified optical counterpart to observe. Whenever there were two

galaxies along the same spatial axis position, we chose the one that did not have

a measured spectroscopic redshift. Once the DSFGs slits were located, the fiducial

stars and sky slits were selected. Finally, suplementary slits were added, if possible,

with 3D-HST galaxies within the observing field. In this thesis we present the results

for 3 submillimeter galaxies, 7 fiducial stars, 4 sky slits and 4 3D-HST galaxies. These

SCLS2 sources and 3D-HST galaxies are listed in Table 4.1. The corresponding slits

for these objects are shown in Figure 4.1.

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Figure 4.1: HST F814W background image with the slits corresponding to GTC-AMEX19. The yellow and black boxes are the 850 µm and 450µm SCLS2 sources, respectively. The blue rectangle is the observed field in the GTC-AMEX19 proposal. The cyan rectangles are the observed slits.

The observations were performed with the R1000R grism of the OSIRIS

Multi-Object Spectrograph, using a 2x2 binning. The observations were acquired in 5

batches, where each batch had 3 exposures of 1168 seconds each, which adds up to

∼5 hours. The observations were initially made on April 7 and 8 of 2019 on service mode. However, upon quality check we discovered one of the batches had to be

repeated due to clouds. The new batch was observed on April 29. Three observation

batches were obtained with a seeing of 0.9 arcsec and the other two with 0.8 arcsec.

We reduced the data in IRAF, with the packages: onedspec,gtcmos1 and inaoe, all developped by D. Mayya for OSIRIS reduction. We calibrated both for

wave-length and flux, using calibration lamps (HgAr, Ne, Xe) and standard stars (HILT600,

Ross640, Feige66), respectively. The final calibrated images were average combined

with the gtcmos/omcombinetask, and the 1D spectrum of each galaxy, with the sky

already substracted, was extracted with the onedspec/apall task.

1

gtcmosIRAF package cookbook:

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4.1 Phase II - planning 37

Table 4.1: Galaxies selected for GTC-MOS optical spectral observations in proposal GTC-AMEX19. Column 1: slit number in the planning stage. Column 2: galaxy ID in the 850 µm SCLS2 catalogue. Column 3: galaxy ID in the 450 µm SCLS2 cata-logue. Column 4: galaxy ID in theHST/CANDELS (c_),_Spitzer_{/IRAC (}d_{) or 3D-HST}

catalogues. Column 5: right ascension coordinate for optical counterparts. Column 6: declination coordinate for optical counterparts. Column 7: reported redshift for the optical counterpart. In parenthesis: method for the redshift reported, where 1 denotes optical photometry, and 2 denotesHST grism.

Slit ID850µm ID450µm ID α δ z (method)

(deg.) (deg.)

7 850.059 450.24 18694c _214.85551 _52.84883 ₂_.₇₅+0.24

−0.21 (1)

19 39103e _214.83087 _52.89241 ₀_.₇₂₈₁+0.0041

−0.0048 (2)

20a 34861e 214.86507 52.89737 0.7126+0−0..05560302 (2)

20 850.038 450.27 27358c _214.86472 _52.89908 ₁_.₉₃+0.09

−0.01 (2)

28 38223e _214.88542 _52.92622 ₀_.₆₈₆₂+0.1232

−0.1112 (2)

30 40111e 214.88124 52.93277 0.7577+0−0..00190071 (2)

32 850.060 450.75 121668d _214.84949 _52.93810 ₀_.₉₄_±₀_._{06 (1)}

-1.31e-19 4.46e-19 2.76e-18 1.20e-17 4.88e-17 1.94e-16

21 HST-39103.0 HST-34861.0 HST-38223.0 HST-40111.0 18 23 26 24 22 20 19 15 13 12 11 8 5 6 1 850.14 850.60 850.38 850.59 34 33 32 31 30 29 28 27 25 17 16 14 10 9 7 4 3 2

Figure 4.2: 2D spectra reduced with IRAF, calibrated in wavelength and flux. The sky has already been substracted to better observe features. The red labels correspond to the DSFGs from the SCLS2 catalogue and the cyan labels indicate galaxies from the 3D-HST catalogue.

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4.2 Line identification and redshift report

In order to identify the lines in our spectra we explored both the 2D and 1D spectra.

In the following paragraphs we will present the identified lines and derived redshifts,

when possible. We used template spectra of starbursts galaxies and quasars, like the

composite spectrum presented is Figure 4.3 (Francis et al., 1991) and Figure 4.4

(Conti et al., 1996). The reported wavelengths for the lines correspond to the center

value of a gaussian curve fitted to the line in the 1D spectrum.

Figure 4.3: Composite spectrum template for a QSO plotted as λF(λ) vs rest-frame

λ, and the identified lines with their corresponding wavelength. Image taken from Francis et al. (1991)

Figure 4.4: Spectrum for the starburst galaxy NGC 1741B. Image taken from Conti et al. (1996)

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4.2 Line identification and redshift report 39

4.2.1 HST-galaxies

HST 39103has a reported HST grism redshift of z = 0.7281+0₋₀._.0041₀₀₄₈ in the 3D-HST catalogue. There are three lines in our observed spectrum, located at 5074.57, 6461.84

and 7915.96 ˚A. We considered the following cases. If the observed 6461.84 ˚A line

corresponds to [OII]λ3727, then the redshift would bez = 0.7338, but the other lines

observed in the spectrum would be located at the rest-frame wavelength of 2926 ˚A and

4565.67 ˚A, which do not correspond to any known emission lines. If we identify the

observed lines (at 5074.57, 6461.84 and 7915.96 ˚A) as Lyαλ1216, CIVλ1549 and the

blend AlIII + CIII]λλ1892,1909 (Figure 4.5), then we obtain a redshift ofz = 3.1698, with which the SiIV+OIV]λ1400 line would lie (at 5837.7 ˚A) in a region contaminated

by sky lines and, since SiIV + OIV]λ1400 is fainter than Lyα and CIV, we would not

be able to detect it. The observer-frame width of the 7915.96 ˚A line is 13.78 ˚A, and

the candidate blend of AlIII + CIII]λλ1892,1909 is hence unresolved. The apparent

angular size of the galaxy is_∼1.76 arcsec, which at the corresponding redshift would

be an apparent radius of _∼ 6.8 kpc. We will need to check how many lines were

detected in the 3D-HST grism to reconcile these solutions.

HST 34861 has an HST grism redshift of z = 0.7126+0₋₀._.0556₀₃₀₂, reported in the 3D-HST catalogue. We present the slit, spectra and lines in Figure 4.7. Two emission

lines were identified in the extracted spectrum: 6382.85 ˚A and 8572.37 ˚A. These lines

were identified as [OII]λ3727 and [OIII]λ5007 for a redshift ofz = 0.712, respectively.

The line Hβ4861 would lie on top of a sky lines region (at 8324 ˚A) in the observed

spectrum. We also considered the following cases. If the line detected at 6382.85 ˚A

were MgIIλ2798, then the redshift would be z = 1.2812 and the lines CIII]λ1909 and [OII]λ3727 would lie at 4354.8 ˚A and 8502 ˚A, respectively, but these lines were not

detected at those positions, and the observed line 8572.37 ˚A would correspond to the

rest frame wavelength 3757.8 ˚A, where the closest line is 30 ˚A away ([OII]λ3727). If the

line detected at 6382.85 ˚A were Hδ4102, then the redshift would bez= 0.556 and the

lines [OII]λ3727 and Hγ would lie at 5799 ˚A and 6753 ˚A, where no lines are detected,

and the observed line at 8572.37 ˚A, would correspond to a rest-frame wavelength of

5508.9 ˚A, where there are no emission lines in the templates. If the line observed at

8572.37 ˚A corresponded to Hβ, then the lines Hγ4340 and [OIII]λλ4959,5007 would

lie at 7653.59 ˚A, 8745.19 ˚A and 8829.84 ˚A in the observed spectrum, but these lines

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are not detected, and the other observed line at 6382.85 ˚A would correspond to a

rest-frame wavelength of 3618.9 ˚A, where there is no emission line associated. Therefore,

we estimate a z = 0.7123 for this source, in agreement with the 3D-HST reported

redshift.

Figure 4.5: (Top) Observed slit on HST F814w band image. (Middle) Extracted 1D spectra of galaxy HST 39103 with the possible lines: Lyαλ1216, CIVλ1549 and the blend OIII] + CIIIλλ1892,1909. (Bottom) 2D spectra for slit 19 with galaxy HST 39103.

-0.017 -0.013 -0.0083 -0.0038 0.00064 0.0052 0.0096 0.014 0.019 0.023 0.028

15.5377" 19 39103.0

5000 5500 6000 6500 7000 7500 8000 8500 9000

Wavelength [A]

−1 0 1 2 3 4 5

F u

x [

erg

/cm

2/s/

A]

1e−18

Ly

12

16

CIV

15

49

OI

II]+

CII

I]

18

92

,19

09

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Figure 4.6: (Left) 2D spectral lines. (Right) 1D spectral lines. Identified lines at 5074.57 ˚A(Top), 6461.84 ˚A(Middle) and 7915.96 ˚A(Bottom).

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Figure 4.7: (Top) Observed slit onHST F814w band image with HST 34861. (Middle) Extracted 1D spectra of galaxy HST 34861 with the identified lines: [OII]λ3727 and [OIII]λ5007. (Bottom) 2D spectra for slit 20 with galaxy HST 34861.

-0.017 -0.013 -0.0083 -0.0038 0.00064 0.0052 0.0096 0.014 0.019 0.023 0.028

HST-34861

12.6952"

K-38

20

27358

5000 5500 6000 6500 7000 7500 8000 8500 9000

Wavelength [A]

−1 0 1 2 3 4 5

Flu

x [

erg

/cm

2/s/

A]

1e−18

[O

II]

37

27 [O

III]

50

07

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Figure 4.8: Identified lines for HST 34861 at (Top) 6382.85 ˚A and (Bottom) 8572.37˚A. (Left) 2D spectral lines. (Right) 1D spectral lines.

HST 38223 has an HST grism redshift of z = 0.6862+0₋₀._.1232₁₁₁₂. We identified one emission line at 6175.78 ˚A, shown in Figure 4.9. We considered this line to be [OII]λ3727 resulting in z = 0.7586. Therefore, we tried to find the rest-frame

lines MgIIλ2798, Hδ4102, Hγ4340, Hβ4861, but the first line lies outside of the

ob-servational wavelength range and the other three lines lie a region of the spectrum

dominated by sky lines. If we considered the detected line to be MgIIλ2798, then

the redshift would bez = 1.34, and the lines [OII] and CIII] would lie at 8730.12 ˚A

(on sky lines region) and 4471.64 ˚A (outside of the observational wavelength range),

respectively. If we considered the detected line to be Hδ, then the redshift would be

z= 0.5978 and the lines [OII]λ3727, Hγ4340 and Hβ4861 would lie at 5955 ˚A, 6934.45 ˚

A and 7766.9 ˚A in the observed spectrum, but these lines are not detected.

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Figure 4.9: (Top) Observed slit on HST F814w band image with HST 38223. (Middle) Extracted 1D spectra of galaxy HST 38223 with the identified line at 6175.78˚A. Below, 2D spectra for slit 28 with galaxy HST 38223. (Bottom) Identified line [OII]λ3727 at 6175.78˚A in the spectrum of HST 38223. (Left) 2D spectrum. (Right) 1D spectrum.

5000 5500 6000 6500 7000 7500 8000 8500 9000

Wavelength [A]

−1 0 1 2 3 4 5

Flu

x [

erg

/cm

2/s/

A]

1e−18

[O

II]

37

27

Comparison of star-formation rates for the deep field extended groth strip and its dusty star forming galaxies population