Studying the formation and evolution of
massive galaxies towards protoclusters
using millimetre observations
by
M.Sc. Milagros Zeballos Rebaza
A thesis submitted to the Instituto Nacional de Astrof´ısica, ´Optica y Electr´onica for the degree of Doctor of Philosophy
in the department of Astrophysics.
Supervisors: Dr. David H. Hughes
Dr. Itziar Aretxaga
Sta. Ma. Tonantzintla, Pue. April, 2013
©INAOE, 2013 Derechos reservados
El autor otorga al INAOE el permiso de reproducir y distribuir copias de esta tesis en su totalidad o en partes
Agradecimientos
Quiero expresar mi enorme gratitud a mis asesores de tesis, los doctores David H. Hughes e Itziar Aretxaga, por abrirme las puertas del campo de la astronom´ıa milim´etrica y por integrarme al grupo de investigaci´on de la c´amara AzTEC. Su apoyo incondicional, tiempo y dedicaci´on han sido piezas clave para mi formaci´on acad´emica.
De igual forma quiero agradecer al Dr. Grant Wilson de la Universidad de Mas-sachusetts (UMASS) Amherst, por darme la oportunidad de aprender todo lo relacionado con AzTEC. Quiero agradecer tambi´en a Kim Scott, Min Yun, Jay Austermann y Thushara Perera, de quienes tuve el privilegio de aprender durante mi estancia en UMASS.
Extiendo adem´as mis agradecimientos a todas las personas que hicieron posible el ´exito de las dos campa˜nas de AzTEC en ASTE. En especial agradezco a Ko-taro Kohno, Hajime Ezawa, Tetsuhiro Minamidani, Takashi Tsukagoshi, Yoshito Shimajiri y Sumiko Harasawa, con quienes tuve la oportunidad de colaborar di-rectamente y de quienes pude aprender mucho durante mi estancia en Chile.
De manera muy especial quiero agradecer a mis amigos y compa˜neros del grupo de astrof´ısica e instrumentaci´on milim´etrica del INAOE por hacer de mi estancia en M´exico una experiencia muy grata. En particular quiero agradecer a Daniel Ferrusca y Miguel Vel´azquez por su apoyo y sus sabios consejos para sobrevivir a un doctorado; a Alfredo Monta˜na por aclarar mis dudas y darme sugerencias para mejorar mi trabajo; a David S´anchez por su apoyo incansable en la reducci´on de datos, a Emmaly Aguilar, Salvador Ventura e Idalia Hern´andez por compartir largas jornadas de observaci´on en el INAOE, ASTE y GTM; y a Mauricio G´omez, V´ıctor G´omez y Eduardo Ibarra, por la amena compa˜n´ıa durante varios fines de semana escribiendo nuestras respectivas tesis.
Aunque f´ısicamente no estuvieron cerca, de igual manera quiero agradecer el apoyo incondicional de mi familia y amigos en el extranjero. De manera muy
especial quiero agradecer a mis queridos hermanos, Patricia y Roberto, por per-mitirme vivir lejos de casa con la tranquilidad de saber que todo queda en buenas manos. Quiero agradecer adem´as el aliento constante y la gran amistad de Alinda Damsma, Gina Luque y Young Cho. Su respaldo, confianza y consejos han sido muy valiosos durante mi trabajo de tesis.
Finalmente quiero agradecer a CONACYT por la beca de doctorado 212181, a la Dra. Itziar Aretxaga por la beca de investigaci´on 18718, y al Dr. Murphy por la ayuda econ´omica brindada. Todos estos apoyos contribuyeron en gran medida a la conclusi´on de este trabajo.
Resumen
Esta tesis describe la distribuci´on espacial de galaxias submilim´etricas (SMGs) en los alrededores de 16 potentes radio galaxias y un quasar, a los que por sim-plicidad llamar´e AGN, ubicados a altos corrimientos al rojo. Seg´un el modelo de formaci´on de estructura actualmente m´as aceptado (ΛCDM), estos potentes AGN se forman en los picos del campo de densidad del Universo y, por lo tanto, sus ubicaciones se˜nalan posibles regiones de formaci´on de c´umulos de galaxias. En esta tesis se utilizan observaciones tomadas a 1.1 mm con la c´amara AzTEC para estudiar la formaci´on estelar oscurecida en estas regiones y as´ı comprender el proceso de formaci´on de las galaxias que predominan en los c´umulos: las el´ıpticas masivas. Estas observaciones forman parte del censo milim´etrico denominado AzTEC Cluster Environment Survey (ACES), el cual fue dise˜nado para estudiar las propiedades de las SMGs, no solo en regiones proto-cumulares, sino tambi´en en c´umulos a bajos corrimientos al rojo.
Al examinar la densidad superficial (o n´umero de cuentas) de las SMGs en los mapas individuales de la muestra proto-cumular de ACES, se encuentra que en la mayor´ıa de los casos la densidad de fuentes con flujos mayores a 4 mJy cae dentro del intervalo de confianza del 95% de la densidad de fuentes de un campo blanco, lo que significa que estas densidades no se pueden diferenciar de la de un campo sin sesgo. Solo en los alrededores de 4C+23.56, PKS1138-262 y MRC0355-037 se detecta una sobre densidad de fuentes de∼2, con una significaci´on estad´ıstica de
∼ 3σ. Cuando se realiza el an´alisis conjunto de todos los campos, se encuentra que la densidad de fuentes efectivamente sobrepasa la densidad t´ıpica en un factor de ∼ 2 con una significaci´on estad´ıstica de 3.5σ. Esta sobre densidad cubre un ´area de 3 minutos de arco de di´ametro centrada en los AGN, lo que corresponde a un di´ametro co-m´ovil de 1.7 - 7.5 Mpc en el rango de corrimientos al rojo de la muestra: 0.5 < z < 6.3. Este resultado coincide plenamente con el an´alisis realizado en estudios previos. Sin embargo, es importante resaltar que el mayor tama˜no de la muestra de ACES permite tener resultados estad´ısticamente m´as significativos. Asimismo, los mapas individuales, al abarcar una mayor ´area com-parada con la de otros censos, permiten establecer que m´as all´a de un radio de
ii
1.5 minutos de arco la densidad superficial de SMGs cae r´apidamente hasta al-canzar el valor de un campo blanco. La extensi´on de esta sobre densidad coincide plenamente con las estimaciones hechas de radios viriales en c´umulos de galaxias locales.
Esta tesis tambi´en examina si las SMGs se alinean en alguna direcci´on preferente con respecto a los radio chorros de las radio galaxias centrales a sus respectivos mapas. Usando el tensor de inercia encontramos que existe una tendencia de las SMGs para alinearse en una orientaci´on que es cercana a la direcci´on perpen-dicular con respecto a los radio chorros: 73−14
+13 grados. Este anti alineamiento
es encontrado a escalas entre los 4-20 Mpc, tiene una significaci´on estad´ıstica de
∼5σ con respecto a la direcci´on de los radio chorros, y aparentemente no tiene dependencia con la luminosidad de las SMGs (es decir con su masa), aunque el rango din´amico de masas de esta muestra limitada en flujo probablemente no es lo suficientemente grande como para llegar a una conclusi´on definitiva. En esta tesis se propone que este anti alineamiento es el producto de una fracci´on de SMGs que estar´ıan habitando los filamentos m´as masivos que alimentar´ıan a los proto-c´umulos centrales. Estos filamentos ser´ıan adem´as las estructuras originales de las radio galaxias. Esta hip´otesis est´a de acuerdo con simulaciones de materia oscura, en las cuales el eje de rotaci´on de una galaxia masiva (y probablemente el eje de rotaci´on del gas que alimenta su agujero negro s´uper masivo central, y por lo tanto el del radio chorro en caso de una radio galaxia) estar´ıa alineado perpendicularmente a la direcci´on del filamento al que pertenece la galaxia.
Estas propiedades sugieren que las regiones proto-cumulares son, en efecto, sitios de intensa formaci´on oscurecida. Debido a que en el Universo local los centros de los c´umulos gal´acticos m´as ricos son habitados preferentemente por galaxias el´ıpticas masivas, y si suponemos que estas galaxias pasan por una fase sub-milim´etrica, podemos especular que una buena parte de su poblaci´on estelar se estar´ıa formando en las SMGs. Asimismo, este trabajo de tesis muestra que las SMGs podr´ıan estar contribuyendo a la formaci´on estelar en las estructuras fila-mentarias alrededor de los proto-c´umulos, ya que parecen trazar por lo menos los filamentos dominantes.
Este trabajo de tesis adem´as analiza las propiedades milim´etricas de las 16 radio galaxias de ACES, 11 de las cuales son detectadas a 1.1 mm. Un an´alisis de api-lamiento de la emisi´on milim´etrica de estas radio galaxias, previamente rotadas de tal manera que sus radio chorros est´en alineados, muestra que la extensi´on espacial de esta emisi´on no es m´as elongada a lo largo del eje del radio chorro que en la direcci´on perpendicular, lo que aparentemente contradice estudios previos.
iii
Sin embargo, hay que tener en cuenta que la resoluci´on de estas observaciones es mayor que la de estos estudios previos (30 segundos de arco), por lo que el resultado no es concluyente. Asimismo, se encuentra una anticorrelaci´on entre el tama˜no de la radio fuente y la intensidad de la emisi´on milim´etrica de su galaxia anfitriona, de lo que se puede concluir que las fuentes de radio m´as peque˜nas est´an asociadas a brotes de formaci´on estelar oscurecidos m´as intensos.
Finalmente, los cat´alogos de ACES muestran un grupo de fuentes puntuales muy brillantes, cuyas densidades de flujo (S1.1mm > 8 mJy) las identifican como una
rara ocurrencia en los mapas de campos blancos menores a <0.5 grados cuadra-dos. Con el fin de escoger a las fuentes con mayores posibilidades de ser SMGs intr´ınsecamente muy brillantes, se descartan aquellas fuentes con posibles contra-partes a corrimientos al rojo bajos, aquellas con posibles contracontra-partes en cat´alogos de radio fuentes, y aquellas con posibilidades de ser fuentes fuertemente ampli-ficadas por lentes gravitacionales. Estimando el n´umero de densidad de las can-didatas a ser fuentes intr´ınsecamente brillantes, se encuentra que este n´umero tiende a divergir hacia valores mayores que el esperado de la extrapolaci´on del n´umero de densidad de fuentes menos brillantes (1 mJy < S1.1mm < 8 mJy).
Para descartar que esta divergencia se deba a una sobre densidad de fuentes en regiones cumulares o proto-cumulares, este an´alisis se realiza removiendo adem´as las fuentes que est´an localizadas dentro de un radio de 2 minutos de arco del centro de nuestros mapas. Si estas candidatas a ser fuentes intr´ınsecamente brillantes se muestran como objetos puntuales en futuras observaciones de mayor resoluci´on, y se descarta toda posibilidad de que sean fuentes amplificadas gravitacional-mente, entonces su n´umero de densidad podr´ıa poner fuertes constre˜nimientos a los modelos actuales de formaci´on de galaxias.
En resumen, esta tesis presenta los resultados obtenidos al analizar las propiedades de las fuentes milim´etricas detectadas en la muestra proto-cumular de ACES. Tanto el tama˜no de la muestra como el tama˜no de los mapas individuales permiten obtener resultados con una significaci´on estad´ıstica mayor a la de estudios previos sobre un rango amplio de corrimientos al rojo y de propiedades ambientales. Ob-servaciones futuras con la siguiente generaci´on de telescopios milim´etricos, ya sean interfer´ometros o telescopios de un solo plato, mejorar´an nuestro entendimiento sobre la formaci´on estelar y de galaxias en los picos de densidad de la distribuci´on de materia en el Universo.
Abstract
In this thesis we study the spatial distribution of extremely luminous high-redshift dust-enshrouded star-forming submillimetre galaxies (SMGs) towards the envi-ronments of 16 powerful high-redshift radio galaxies and a quasar (AGN) using continuum observations at 1.1 mm taken with the AzTEC camera. This AGN sample represents a subset of the ongoing AzTEC Cluster Environment Survey (ACES). We target powerful high-redshift AGN, using them as signposts of pro-toclusters, since under the ΛCDM scenario these early structures are formed in the highest density regions of the Universe.
The number of ACES targets and the increased area covered by each AzTEC map of our protocluster sample allows us to examine the surface density (number counts) of SMGs towards these regions with greater significance than previous studies. We estimate the integrated number counts for the fields of individual ACES targets, but in the majority of cases the density of sources with S1.1mm>4
mJy falls within the 95% confidence interval of the density of sources in a com-parison sample of unbiased blank fields. Only in the surroundings of 4C+23.56, PKS1138-262 and MRC0355-037 do we detect individual overdensity signals of
∼ 2 with a significance of ∼ 3σ. When we perform a stacking analysis on the complete sample of AzTEC maps, we also find an overdensity of∼2, with greater statistical significance, covering an area of 3-arcmin diameter centred on the AGN (corresponding to a co-moving diameter of 1.7-7.5 Mpc over the redshift range 0.5 < z < 6.3 of the sample). This is in good agreement with the analysis of previous studies. In addition, the large size of our maps allows us to establish that beyond a radius of 1.5 arcmin, the radial surface density of SMGs falls very quickly to reach a typical value for a blank field distribution of SMGs. The mea-sured angular extent of this overdensity is in agreement with estimates of the virial radii of local clusters.
We also examine if there is a preferred direction in which the SMGs align around our sample of high-redshift AGN. Using a modified tensor of inertia, we find that there is a trend for SMGs to align along an orientation that is closer to a
per-vi
pendicular direction with respect to the radio jets of our powerful radio galaxies (73−14
+13 degrees) than to the parallel direction. This misalignment is found over
co-moving scales of 4-20 Mpc, has a statistical significance of ∼ 5σ, and appar-ently has no dependence on the source luminosity (i.e. on mass) although the dynamical range of the SMG masses that we can detect in our flux-limited sam-ple is probably not large enough to draw a definite conclusion. We propose that this misalignment is the result of a fraction of SMGs preferentially inhabiting the mass-dominant filaments funneling material towards the protoclusters, which are also the parent structures of our radio galaxies. Since these radio galaxies are massive sources, according to simulations their dark matter halo spin axes (and probably their molecular gas and black hole spin axes) align perpendicularly to the direction of the dominant filaments.
The properties of the SMG distribution described above suggest that protocluster regions are sites of enhanced dust-obscured star formation. In the local Universe the centres of rich clusters are inhabited preferentially by massive elliptical galax-ies. Assuming their progenitors go through a submillimetre phase, we speculate that SMGs in these environments are forming a large fraction of the stellar popu-lation of the massive ellipticals. Moreover, these properties also show that SMGs are probably contributing to the formation of the stellar population in the fila-mentary structure around them, since they appear to be tracing at least the most dominant structures.
As part of this thesis we also explore the millimetre properties of our 16 powerful high-redshift radio galaxies, eleven of which were detected at 1.1 mm. We perform a stacking analysis on the sample of maps, previously rotated to co-align the indi-vidual radio jets. Measurements of the spatial extent of their millimetre emission leads to the conclusion that it is no more elongated along the radio axis than it is along the orthogonal axis, at least at the spatial resolution (30 arcsec) of our ob-servations. Therefore, the apparent alignment between the extended radio source and the submm/mm emission from the host galaxy found in previous studies is contradicted by our ACES selection of targets. We also identified a statistically significant anticorrelation between the size of the radio source and the brightness of the millimetre continuum emission of the host galaxy, from which we conclude that smaller radio sources are associated with more powerful obscured starbursts.
Finally, a group of ultra-bright point-sources were identified and extracted from our catalogues. The measured flux densities of these sources (S1.1mm > 8 mJy)
makes them a rare occurrence in the small (< 0.5 deg2) individual blank-field
vii
was performed in order to discard nearby, synchrotron-dominated and possibly strongly lensed galaxies as the source of such high luminosities. An analysis of the number density of intrinsically bright sources shows a tentative divergence to higher number densities when compared to the extrapolation of the number of less bright (i.e. normal, 1 mJy < S1.1mm < 8 mJy) SMGs. For this analysis we
removed the bright sources that are located inside areas of 2-arcmin radius from the centre our maps in order to exclude sources associated with the (proto)cluster cores. This divergence is therefore unlikely to be due to an overdensity. If the na-ture of these bright sources is identified, and they can be shown to be individual objects in higher resolution observations and their brightness is not the result of amplification due to lensing, then their abundance will put strong constraints on galaxy formation models.
This thesis describes the results of the ACES protocluster sample. The analysis presented here, and the complementary observations towards lower redshift X-ray and optically-selected clusters described elsewhere, allow the studies of the spa-tial distributions and properties of SMGs with increased statistical significance over a wide range of environments and redshifts. Future observations with the next generation of interferometric and larger single-dish millimetre telescopes will continue to improve our understanding of star formation and galaxy formation in the high density peaks of the underlying matter distribution in the early Universe.
Contents
1 Introduction 3
1.1 Massive elliptical galaxies . . . 5
1.2 Submm galaxies as progenitors of massive elliptical galaxies . . . 6
1.2.1 Discovery and main properties . . . 6
1.2.2 Formation models in a ΛCDM cosmogony . . . 15
1.3 Using high redshift AGN as protocluster signposts . . . 17
1.3.1 Submm emission of powerful high redshift AGN . . . 18
1.3.2 Protocluster surveys around powerful high redshift AGN . 20 1.4 This work: a millimetre survey towards protoclusters . . . 23
2 Survey description and data selection 27 2.1 The AzTEC Camera . . . 28
2.2 AzTEC performance on the JCMT and ASTE . . . 31
2.3 The AzTEC Cluster Environment Survey . . . 35
2.3.1 Sample selection . . . 37
2.3.1.1 Protocluster sample . . . 37
2.3.1.2 Control fields . . . 44
2.4 Multi-wavelength information on the ACES/protocluster fields . . 47
3 Observations and data reduction 51 3.1 Observations . . . 51
3.1.1 Loadcurves . . . 53
3.1.2 Beammaps . . . 56
3.1.3 Pointing observations . . . 56
3.2 Flux calibration . . . 59
3.3 Reduction process . . . 60
3.3.1 Cleaning the timestream . . . 61
3.3.2 Making the maps . . . 63
3.3.3 Noise maps . . . 64
3.3.4 Map filtering . . . 64
x CONTENTS
3.5 False detection rate . . . 70
3.6 Completeness . . . 70
3.7 Astrometry . . . 75
4 Massive star-forming galaxies in ACES/protocluster fields 79 4.1 Deboosting fluxes . . . 80
4.2 1.1-mm counterparts for ACES/AGN . . . 85
4.3 Individual source number densities . . . 86
4.4 Combined source number densities . . . 91
4.4.1 Source densities at different radii from the AGN . . . 93
4.4.2 Feasibility of detecting an overdensity . . . 100
4.4.3 Implied star formation rates . . . 108
4.4.4 Discussion . . . 108
4.5 Alignment of massive galaxies and radio jets . . . 113
4.5.1 Inertia tensor . . . 115
4.5.2 Combined analysis . . . 120
4.5.3 Discussion . . . 121
5 AzTEC 1.1-mm detections of ACES/AGN 127 5.1 ACES/AGN 1.1 mm flux densities . . . 128
5.2 Consistency with previous measurements . . . 129
5.3 Synchrotron emission . . . 133
5.4 Stacking analysis . . . 135
5.5 Implied star formation rates . . . 137
5.6 Anticorrelation between 1.1-mm flux and radio source size . . . . 139
5.7 Discussion . . . 141
6 A population of ultra-bright submillimetre sources 145 6.1 Ultra-bright sources in ACES cluster and protocluster sample . . 146
6.2 Associations with external catalogs . . . 150
6.3 Follow-up observations of intrinsically luminous candidates . . . . 155
6.4 Number counts for the ACES ultra-bright sources . . . 157
6.4.1 Discussion . . . 162
7 Conclusions and future work 167
A Spectral energy distributions for ACES/RGs 173
B AzTEC 1.1-mm maps of ACES/protoclusters 177
CONTENTS xi
D AzTEC 1.1-mm number counts for ACES/protoclusters 225
List of Figures
1.1 Inhomogeneity of the Universe at small scales: slices through the SDSS 3-dimensional map of the distribution of galaxies. . . 4 1.2 Spectral energy density of the extragalactic background radiation
as a function of wavelength. . . 9 1.3 Spectral Energy Distribution model for the prototypical ultra-luminous
infrared galaxy Arp220 at different redshifts. . . 10 1.4 K-correction plot for a SMG with LIR ∼2×1012 L⊙ derived from
the prototypical ultra-luminous infrared galaxy Arp220. . . 11 1.5 K-z diagram of radio and optically selected galaxies. . . 19 1.6 Object map of the protocluster member candidates towards the
radio galaxy TNJ1338-1942 at z= 4.1. . . 22 2.1 AzTEC 1.1 mm bandpass and atmospheric transmission model for
1 mm of pwv at the JCMT. . . 29 2.2 AzTEC footprint as projected on the sky for the JCMT and ASTE. 30 2.3 AzTEC raster and Lissajous scanning patterns. . . 33 2.4 Noise equivalent flux density (NEFD) for a typical AzTEC bolometer. 34 2.5 Empirical point source mapping speeds for the AzTEC/JCMT and
the AzTEC/ASTE systems as a function of atmospheric opacity. . 35 2.6 Comparison between the ACES/protocluster map towards
TXS2322-040 and a dark matter simulation of a protocluster field. . . 38 2.7 Galactic dust emission at 100 µm for the Northern and Southern
Hemispheres showing the location of the ACES targets at low-emission regions. . . 41 2.8 Radio luminosity-redshift plane for ACES radio galaxies. . . 43 2.9 Radio spectra for the ACES/radio galaxies 4C+23.56 and
TXS2322-040 . . . 45 3.1 Distribution of the atmospheric opacity for the ACES/protocluster
xiv LIST OF FIGURES
3.2 Responsivity versus DC-level for a typical detector during the JCMT/ASTE campaigns. . . 55 3.3 The point spread function (PSF) of a typical AzTEC bolometer at
the ASTE. . . 57 3.4 Linearly interpolated boresight pointing offsets measured during
September 2008 at the ASTE. . . 58 3.5 Example of the PCA cleaning technique applied to the first seconds
of a typical bolometer timestream. . . 61 3.6 Cut in elevation of the point-source kernel for the ACES/protocluster
map towards PKS0529-549. . . 65 3.7 AzTEC signal and weight maps for the ACES/protocluster
candi-date towards the radio-quiet quasar PKS1138-262. . . 68 3.8 Histogram of pixel flux-density values from the signal map towards
PKS1138-262 compared to the average histogram of pixel flux-density values from the corresponding noise maps. . . 69 3.9 Expected number of false detections as a function of limiting S/N
for the ACES/protocluster map towards PKS1138-262. . . 73 3.10 Completeness estimation for AzTEC sources in the
ACES/proto-cluster field towards PKS1138-262. . . 74 3.11 Measured pointing offsets in right ascension and declination for the
AzTEC maps at ASTE and JCMT. . . 76 3.12 Positional uncertainty distribution for TNJ2007-1316 source
can-didates inside three different signal-to-noise bins. . . 77 4.1 Posterior flux density distributions for two sources in the
PKS1138-262 field. . . 82 4.2 Deboosted flux dependence on the prior flux distribution p(Si). . . 84
4.3 AzTEC 1.1 mm differential and integrated number counts for PKS1138-262. . . 89 4.4 Poisson probability distributions of the number of sources with
S1.1mm>4 mJy expected for blank-field maps with sizes similar to
the ACES/protocluster maps. . . 92 4.5 AzTEC 1.1 mm integrated number counts for the combined
sev-enteen ACES/protocluster fields. . . 95 4.6 Confidence limits for the best-fitting parameters of a Schechter
function to the ACES/protocluster number counts. . . 96 4.7 AzTEC 1.1 mm integrated number counts for the combined
seven-teen ACES/protocluster fields inside three different areas centred at the ACES/AGN. . . 101
LIST OF FIGURES xv
4.8 Number of sources with S1.1mm>4 mJy extracted from the
seven-teen ACES/protocluster maps inside an area centred at the AGN and of 1.5 arcmin radius, compared to the distribution of the num-ber of sources extracted from 10,000 synthetic maps with a blank-field population of SMGs. . . 103 4.9 AzTEC 1.1 mm integrated number counts for the combined
seven-teen ACES/protocluster fields inside an area of 1.5-arcmin radius centred at the ACES/AGN. Comparison with previous studies. . . 104 4.10 Projected King density profiles used in simulations of overdensities. 107 4.11 Distribution of the number of sources with S1.1mm>4 mJy found in
17 simulated blank fields compared to the distributions of sources for the same fields but with an overdensity of 2 inserted at each of their centres following three different King profiles. . . 109 4.12 MRC2104-242: Principal axis of the AzTEC source distribution
around the radio galaxy compared to its radio jet. . . 118 4.13 Angular differences between the principal axes of the AzTEC source
distributions and the radio jet PAs for the 16 ACES/radio galaxy fields. . . 119 4.14 Principal axis for the source distribution of the stacked 16 ACES/radio
galaxy fields. . . 122 4.15 Probability distribution for the principal axis of the stacked
distri-bution of sources around the 16 ACES radio galaxy fields. . . 123 4.16 Angular differences between the aligned radio jets and the principal
axes for the stacked distribution of sources with various flux density cuts around the 16 ACES/radio galaxy fields. . . 124 5.1 Postage stamps of 1.1 mm AzTEC signal-to-noise maps for 16
ACES radio galaxies. . . 130 5.2 SDSSJ1030+0524: postage stamp of the 1.1 mm AzTEC
signal-to-noise map. . . 131 5.3 Observer-frame radio spectral energy distributions of the ACES
ra-dio galaxies and a power law extrapolation to estimate synchrotron contamination. . . 134 5.4 Postage stamps of the stacked ACES/AGN images. . . 138 5.5 Anticorrelation between 1.1 mm flux density and radio source
di-ameter. . . 142 6.1 Test to discard a non-astronomical origin for ultra bright source
AzTEC/ACES5. . . 149 6.2 Spectral energy distributions (SED) of 76 SMGs. . . 158 6.3 S350µm/S1.1mm ratio as a function of redshift for 79 SMG SEDs. . . 159
xvi LIST OF FIGURES
6.4 1.1mm/20cm spectral index as a function of redshift for 79 SMG SEDs. . . 160 6.5 Multi-wavelength observations of AzTEC/ACES5. . . 161 6.6 AzTEC 1.1-mm differential number counts for the combined
blank-fields. . . 163 A.1 TNJ0924-2201, TNJ1338-1942, TNJ2007-1316, 4C+41.17,
TNJ2009-3040 and MRC0316-257 radio spectra. . . 174 A.2 PKS0529-549, MRC2104-242, 4C+23.56, PKS1138-262,
MRC0355-037 and MRC2048-272 radio spectra. . . 175 A.3 TXS2322-040, MRC2322-052, MRC2008-068 and MRC2201-555
radio spectra. . . 176 B.1 SDSSJ1030+0524: AzTEC 1.1-mm map, weight map, histogram,
false detection rate, completeness and positional uncertainty. . . . 179 B.2 TNJ0924-2201: AzTEC 1.1-mm map, weight map, histogram, false
detection rate, completeness and positional uncertainty. . . 180 B.3 TNJ1338-1942: AzTEC 1.1-mm map, weight map, histogram, false
detection rate, completeness and positional uncertainty. . . 181 B.4 TNJ2007-1316: AzTEC 1.1-mm map, weight map, histogram, false
detection rate, completeness and positional uncertainty. . . 182 B.5 4C+41.17: AzTEC 1.1-mm map, weight map, histogram, false
detection rate, completeness and positional uncertainty. . . 183 B.6 TNJ2009-3040: AzTEC 1.1-mm map, weight map, histogram, false
detection rate, completeness and positional uncertainty. . . 184 B.7 MRC0316-257: AzTEC 1.1-mm map, weight map, histogram, false
detection rate, completeness and positional uncertainty. . . 185 B.8 PKS0529-549: AzTEC 1.1-mm map, weight map, histogram, false
detection rate, completeness and positional uncertainty. . . 186 B.9 MRC2104-242: AzTEC 1.1-mm map, weight map, histogram, false
detection rate, completeness and positional uncertainty. . . 187 B.10 4C+23.56: AzTEC 1.1-mm map, weight map, histogram, false
detection rate, completeness and positional uncertainty. . . 188 B.11 PKS1138-262: AzTEC 1.1-mm map, weight map, histogram, false
detection rate, completeness and positional uncertainty. . . 189 B.12 MRC0355-037: AzTEC 1.1-mm map, weight map, histogram, false
detection rate, completeness and positional uncertainty. . . 190 B.13 MRC2048-272: AzTEC 1.1-mm map, weight map, histogram, false
detection rate, completeness and positional uncertainty. . . 191 B.14 TXS2322-040: AzTEC 1.1-mm map, weight map, histogram, false
LIST OF FIGURES xvii
B.15 MRC2322-052: AzTEC 1.1-mm map, weight map, histogram, false detection rate, completeness and positional uncertainty. . . 193 B.16 MRC2008-068: AzTEC 1.1-mm map, weight map, histogram, false
detection rate, completeness and positional uncertainty. . . 194 B.17 MRC2201-555: AzTEC 1.1-mm map, weight map, histogram, false
detection rate, completeness and positional uncertainty. . . 195 D.1 SDSSJ1030+0524: AzTEC 1.1-mm differential and integrated
num-ber counts. . . 226 D.2 TNJ0924-2201: AzTEC 1.1-mm differential and integrated number
counts. . . 227 D.3 TNJ1338-1942: AzTEC 1.1-mm differential and integrated number
counts. . . 228 D.4 TNJ2007-1316: AzTEC 1.1-mm differential and integrated number
counts. . . 229 D.5 4C +41.17: AzTEC 1.1-mm differential and integrated number
counts. . . 230 D.6 TNJ2009-3040: AzTEC 1.1-mm differential and integrated number
counts. . . 231 D.7 MRC0316-257: AzTEC 1.1-mm differential and integrated number
counts. . . 232 D.8 PKS0529-549: AzTEC 1.1-mm differential and integrated number
counts. . . 233 D.9 MRC2104-242: AzTEC 1.1-mm differential and integrated number
counts. . . 234 D.10 4C +23.56: AzTEC 1.1-mm differential and integrated number
counts. . . 235 D.11 PKS1138-262: AzTEC 1.1-mm differential and integrated number
counts. . . 236 D.12 MRC0355-037: AzTEC 1.1-mm differential and integrated number
counts. . . 237 D.13 MRC2048-272: AzTEC 1.1-mm differential and integrated number
counts. . . 238 D.14 TXS2322-040: AzTEC 1.1-mm differential and integrated number
counts. . . 239 D.15 MRC2322-052: AzTEC 1.1-mm differential and integrated number
counts. . . 240 D.16 MRC2008-068: AzTEC 1.1-mm differential and integrated number
counts. . . 241 D.17 MRC2201-555: AzTEC 1.1-mm differential and integrated number
xviii LIST OF FIGURES
E.1 TNJ0924-2201 and TNJ1338-1942: Principal axis of the AzTEC source distribution around the radio galaxy compared to its radio jet. . . 244 E.2 TNJ2007-1316 and 4C+41.17: Principal axis of the AzTEC source
distribution around the radio galaxy compared to its radio jet. . . 245 E.3 TNJ2009-3040 and MRC0316-257: Principal axis of the AzTEC
source distribution around the radio galaxy compared to its radio jet. . . 246 E.4 PKS0529-549 and MRC2104-242: Principal axis of the AzTEC
source distribution around the radio galaxy compared to its radio jet. . . 247 E.5 4C+23.56 and PKS1138-262: Principal axis of the AzTEC source
distribution around the radio galaxy compared to its radio jet. . . 248 E.6 MRC0355-037 and MRC2048-272: Principal axis of the AzTEC
source distribution around the radio galaxy compared to its radio jet. . . 249 E.7 TXS2322-040 and MRC2322-052: Principal axis of the AzTEC
source distribution around the radio galaxy compared to its radio jet. . . 250 E.8 MRC2008-068 and MRC2201-555: Principal axis of the AzTEC
source distribution around the radio galaxy compared to its radio jet. . . 251
List of Tables
2.1 AzTEC 1.1 mm parameters and performance characteristics for the JCMT and ASTE observations. . . 32 2.2 General properties of the ACES/protocluster sample. . . 39 2.3 General properties of the ACES/cluster sample. . . 40 2.4 Best fitting parameters to the observed radio spectra of ACES/radio
galaxies. . . 46 2.5 Summary of the AzTEC blank-field surveys. . . 48 3.1 Main properties of the AzTEC maps for the ACES/protocluster
sample. . . 54 3.2 SDSSJ1030+0524: AzTEC 1.1-mm source catalogue. . . 71 3.2 SDSSJ1030+0524: AzTEC 1.1-mm source catalogue (continued) . 72 4.1 Parameters for the best-fit model to the differential number counts
derived from the combined AzTEC blank-field surveys. . . 83 4.2 ACES/AGN counterpart candidates at 1.1 mm. . . 87 4.3 PKS1138-262: 1.1-mm differential and integrated number counts. 88 4.4 Estimated overdensity of sources with S1.1mm > 4 mJy for three
individual ACES/protocluster fields: 4C+23.56, PKS1138-262 and MRC0355-037. . . 91 4.5 ACES/protoclusters combined differential and integrated number
counts. . . 94 4.6 Parameters for the best-fit model to the differential number counts
derived from the combined ACES/protocluster survey. . . 94 4.7 ACES/protoclusters combined differential and integrated number
counts for an area of 1.5-arcmin radius centred at the AGN. . . . 100 4.8 ACES/protoclusters combined differential and integrated number
counts for an annulus between radii of 3.0 and 1.5-arcmin centred at the AGN. . . 102
xx LIST OF TABLES
4.9 ACES/protoclusters combined differential and integrated number counts for an annulus between radii of 4.5 and 3.0 arcmin centred at the AGN. . . 102 4.10 Catalogue of AzTEC sources inside the 1.5-arcmin-radius areas
centred at each ACES/AGN. . . 110 4.11 Radio-jet position angles and preferred directions for the
surround-ing mm sources in each ACES/radio-galaxy field. . . 117 5.1 1.1-mm detections of ACES/AGN. . . 132 5.2 Extrapolation of a powerlaw from radio to millimetre wavelengths. 136 6.1 ACES catalogue of sources with flux densities brighter than 8 mJy. 147 6.1 ACES catalogue of sources with flux densities brighter than 8 mJy
(continued) . . . 148 6.2 AzTEC/ACES2 and AzTEC/ACES5 properties obtained from two
different observation campaigns. . . 148 6.3 ACES bright sources multiwavelength information. . . 153 6.3 ACES bright sources multiwavelength information (continued) . . 154 6.4 Summary of the follow-up observations for the ACES bright sources
AzTEC/ACES2, AzTEC/ACES5, and AzTEC/ACES7. . . 157 6.5 ACES bright sources combined differential and integrated number
counts. . . 162 C.1 SDSSJ1030+0524: AzTEC 1.1-mm source catalogue. . . 198 C.1 SDSSJ1030+0524: AzTEC 1.1-mm source catalogue (continued) . 199 C.2 TNJ0924-2201: AzTEC 1.1-mm source catalogue. . . 200 C.3 TNJ1338-1942: AzTEC 1.1-mm source catalogue. . . 201 C.4 TNJ2007-1316: AzTEC 1.1-mm source catalogue. . . 202 C.5 4C+41.17: AzTEC 1.1-mm source catalogue. . . 203 C.5 4C+41.17: AzTEC 1.1-mm source catalogue (continued) . . . 204 C.6 TNJ2009-3040: AzTEC 1.1-mm source catalogue. . . 205 C.7 MRC0316-257: AzTEC 1.1-mm source catalogue. . . 206 C.7 MRC0316-257: AzTEC 1.1-mm source catalogue (continued) . . . 207 C.8 PKS0529-549: AzTEC 1.1-mm source catalogue. . . 208 C.8 PKS0529-549: AzTEC 1.1-mm source catalogue (continued) . . . 209 C.9 MRC2104-242: AzTEC 1.1-mm source catalogue. . . 210 C.10 4C+23.56: AzTEC 1.1-mm source catalogue. . . 211 C.10 4C+23.56: AzTEC 1.1-mm source catalogue (continued) . . . 212 C.11 PKS1138-262: AzTEC 1.1-mm source catalogue. . . 213 C.11 PKS1138-262: AzTEC 1.1-mm source catalogue (continued) . . . 214 C.12 MRC0355-037: AzTEC 1.1-mm source catalogue. . . 215
LIST OF TABLES 1
C.12 MRC0355-037: AzTEC 1.1-mm source catalogue (continued) . . . 216 C.13 MRC2048-272: AzTEC 1.1-mm source catalogue. . . 217 C.14 TXS2322-040: AzTEC 1.1-mm source catalogue. . . 218 C.14 TXS2322-040: AzTEC 1.1-mm source catalogue (continued) . . . 219 C.15 MRC2322-052: AzTEC 1.1-mm source catalogue. . . 220 C.15 MRC2322-052: AzTEC 1.1-mm source catalogue (continued) . . . 221 C.16 MRC2008-068: AzTEC 1.1-mm source catalogue. . . 222 C.16 MRC2008-068: AzTEC 1.1-mm source catalogue (continued) . . . 223 C.17 MRC2201-555: AzTEC 1.1-mm source catalogue. . . 224 D.1 SDSSJ1030+0524: 1.1-mm differential and integrated number counts.226 D.2 TNJ0924-2201: 1.1-mm differential and integrated number counts. 227 D.3 TNJ1338-1942: 1.1-mm differential and integrated number counts. 228 D.4 TNJ2007-1316: 1.1-mm differential and integrated number counts. 229 D.5 4C+41.17: 1.1-mm differential and integrated number counts. . . 230 D.6 TNJ2009-3040: 1.1-mm differential and integrated number counts. 231 D.7 MRC0316-257: 1.1-mm differential and integrated number counts. 232 D.8 PKS0529-549: 1.1-mm differential and integrated number counts. 233 D.9 MRC2104-242: 1.1-mm differential and integrated number counts. 234 D.10 4C+23.56: 1.1-mm differential and integrated number counts. . . 235 D.11 PKS1138-262: 1.1-mm differential and integrated number counts. 236 D.12 MRC0355-037: 1.1-mm differential and integrated number counts. 237 D.13 MRC2048-272: 1.1-mm differential and integrated number counts. 238 D.14 TXS2322-040: 1.1-mm differential and integrated number counts. 239 D.15 MRC2322-052: 1.1-mm differential and integrated number counts. 240 D.16 MRC2008-068: 1.1-mm differential and integrated number counts. 241 D.17 MRC2201-555: 1.1-mm differential and integrated number counts. 242
Chapter 1
Introduction
Understanding how matter aggregation evolves with time is one of the most im-portant issues in observational cosmology. In the current most accepted model for structure formation, the Λ Cold Dark Matter model (ΛCDM; Ostriker and Steinhardt, 1995), cosmic structure is formed solely by gravity, and hence, can be described by Einstein’s theory of gravitation. Under this assumption, if the early Universe had been completely homogenous, following Einstein’s equations, we would have seen today a strictly homogenous matter distribution not only at large but also at small scales. In reality, however, the Universe is visibly inhomo-geneous at small scales, i.e. matter aggregates into galaxies, clusters, filaments and walls (figure 1.1). Therefore, the ΛCDM model proposes that the initial density field of the Universe was not entirely homogeneous but had small per-turbations, which due to the influence of gravity grew to form the large scale structure we see today.
Under this ΛCDM paradigm, gravity acts on the small inhomogeneities of the density field and makes them grow attracting cold (non-relativistic) dark matter particles. Dark matter halos start to form in a wide range of masses, while bary-onic matter follows dark matter particles into the potential wells. Since the largest density fluctuations in the matter distribution occur in the smallest mass scales, cosmic structure starts to form hierarchically, i.e. small objects form quicker and grow in mass and size by merging nearby objects. This bottom-up formation model supports an evolutionary scenario in which massive elliptical galaxies form from mergers of less massive galaxies (Kauffmann et al., 1993).
4 Introduction
Figure 1.1: Slices through the Sloan Digital Sky Survey (SDSS; Raddick, 2003) 3-dimensional map of the distribution of galaxies that show the inhomogeneity of the Universe at small scales. Earth is at the center, and each point represents a galaxy. Galaxies are colored according to the ages of their stars, with the redder, more strongly clustered points showing galaxies that are made of older stars. The outer circle is at a luminosity distance of ∼ 700 Mpc (flat cosmology with ΩM = 0.27, ΩΛ = 0.73 and H0 = 71 km s−1 Mpc−1). The region between the
wedges was not mapped by the SDSS because dust in our own Galaxy obscures the view of the distant Universe in these directions. Both slices contain all galaxies detected by SDSS within -1.25 and 1.25 degrees declination. Credit: M. Blanton and the Sloan Digital Sky Survey website.
1.1 Massive elliptical galaxies 5
1.1
Massive elliptical galaxies
Massive elliptical galaxies are the most massive galactic systems in the local Uni-verse (M > 1011 M
⊙). They belong to a class of objects with old red stellar populations, negligible amounts of cold gas, and little star formation (see Ren-zini, 2006 for a review). They are the dominant population of galaxies in dense environments such as the center of rich galaxy clusters.
The traditional picture for massive elliptical galaxy formation was motivated by their simple appearance. It suggests that massive ellipticals formed in a single and violent burst of star formation at high redshifts, followed by passive evolu-tion of their stellar populaevolu-tion until today (Partridge and Peebles, 1967; Larson, 1975). This scenario, also called monolithic collapse, explains successfully the small scatter in the relations between these galaxies’ physical properties such as the colour-magnitude relation and the fundamental plane (Kodama et al., 1998; van Dokkum and Stanford, 2003).
In the last decade, however, observational evidence (e.g. the Wilkinson Microwave Anisotropy Probe, or WMAP, results; Jarosik et al., 2011) has tipped the balance in favour of the ΛCDM model as the standard cosmological model. Under this sce-nario, massive galaxies form hierarchically by mergers of smaller galaxies drawn together by gravity as their surrounding dark matter haloes coalesced. Spectro-scopic studies from Schweizer and Seitzer (1992) found evidence for bluer colours in elliptical galaxies with increasing morphological disturbance. This supports the idea of relatively recent merging. In addition, Barger et al. (1996) found, using absorption-line indices, that a significant fraction of early-type galaxies in clusters underwent recent star-forming episodes. In the field of numerical simula-tions it has also been shown that the merging of two spiral galaxies of comparable mass could produce a remnant with properties similar to those of elliptical galax-ies (e.g. Negroponte and White, 1983). All these results favour, at least for part of the population, a hierarchical formation scenario. But the debate about ellip-tical galaxy formation is far from closed since the mass fraction involved in these relatively recent merging scenarios and star-forming episodes is small, and the tight correlation in the properties of the massive elliptical galaxies needs to be explained.
Another important piece of the elliptical galaxy formation puzzle is presented by the existence of passively evolving galaxies with stellar masses > 1011 M
⊙ already found at redshifts > 1 (e.g. Daddi et al., 2005; Cimatti et al., 2008), and as high as z ∼ 3 (Gobat et al., 2012). This implies that their old stellar
6 Introduction
population must have formed at z > 3, when the Universe was < 3 Gyr old. Consequently, their formation was probably characterized by very strong (>100 M⊙ yr
−1) and short-lived (0.1-0.3 Gyr) starbursts (Cimatti et al., 2008 and
ref-erences therein). Whether these starbursts are single episodes of star formation, or successive episodes triggered by mergers is part of the debate. There might be a variety of possible scenarios for their formation as shown by recent high spacial resolution observations of massive galaxies at z ∼2 (Bruce et al., 2012).
1.2
Submillimetre galaxies as progenitors of
mas-sive elliptical galaxies
In the last decades, the advent of new technology in submillimetre/millimetre (submm/mm) detectors allowed the discovery of a very luminous high-redshift dust-enshrouded population of galaxies known as submillimetre galaxies (SMGs; e.g. Smail et al., 1997; Hughes et al., 1998). The rest-frame far-infrared (FIR) fluxes for these galaxies suggest that they have luminosities>1012 L
⊙ and star-formation rates (SFRs)>100−1000 M⊙yr
−1 (see Blain et al., 2002 for a review),
which in turn imply that they are massive systems that could very quickly build up the large stellar population found in massive ellipticals. In addition, photomet-ric and spectroscopic studies of SMGs with radio or optical/mid-IR counterparts suggest that their abundance peaks at z ∼ 2.5 (Chapman et al., 2003; Aretx-aga et al., 2003; Chapman et al., 2005; Pope et al., 2005; AretxAretx-aga et al., 2007; Wardlow et al., 2011; Smolcic et al., 2012), although recent discoveries of SMGs atz >4 (e.g. Coppin et al., 2009; Riechers et al., 2010; Cox et al., 2011; Walter et al., 2012) may suggest that their redshift distribution has a tail towards higher values. All these results lead to the idea that SMGs are a young and massive dust-obscured population that could evolve and become the massive ellipticals at z= 0.
1.2.1
Discovery and main properties
Observations of galaxies at high-redshift were made mainly at optical wave-lengths. The reason is that star-forming galaxies contain a large number of hot, short-lived massive stars (OB stars) whose main emission is at ultraviolet (UV) wavelengths but gets redshifted into optical wavelengths. A large number of these young star-forming galaxies were detected in deep optical-near infrared surveys atz >2. Among these galaxies were Lyman-break galaxies (LBGs; Steidel et al.,
1.2 Submm galaxies as progenitors of massive elliptical galaxies 7
1996), BzK-selected galaxies (Daddi et al., 2004), and Lyman-αemitting galaxies (LAEs; Hu et al., 1998).
Estimations of star-formation rates (SFR) for this high-redshift optical/UV-se-lected population showed moderate values between 10−100 M⊙ yr
−1 (Giavalisco,
2002). When extrapolated to the present day, these values fell short to account for the evolved stellar populations found in massive elliptical galaxies (e.g. Jimenez et al., 2007). Massive ellipticals, as mentioned above, contain mainly very old stellar populations, barely form new stars (due to their little content of cold gas and dust), and formed the bulk of their stars at high redshifts. In order to form massive stellar populations in short periods of time since the Big Bang, the pro-genitors of massive ellipticals must have formed with significantly higher SFRs than those measured in LBGs and LAEs.
From local observations it is also known that star-formation occurs within dense molecular clouds which contain large amounts of dust. Dust grains absorb op-tical/UV radiation emitted by nearby star-forming regions and re-radiate this energy at far-infrared (FIR) to millimetre (mm) wavelengths with an emission peak at λ ∼ 60−100 µm (Soifer and Neugebauer, 1991). This suggests that the deepest optical surveys could have been missing a significant fraction of star-formation in galaxies due to heavy dust obscuration.
With all this in mind, in 1983 the Infrared Astronomical Satellite (IRAS) was launched to survey the whole sky at mid-IR to FIR wavelengths (λ = 12−100 µm). This survey discovered a population of extremely luminous galaxies with bolometric luminosities in excess of 1012 L
⊙ and emitting most of their radiation at FIR-mm wavelengths (usually integrated in the 8 µm - 1 mm range). These ultra-luminous infrared galaxies (ULIRGs) were found to be violent mergers of gas-rich disc-galaxies at z < 0.3 (see Sanders and Mirabel, 1996 for a review). IRAS did not have the resolution nor the sensitivity to explore the high-redshift Universe, but allowed the identification and study of starburst galaxies at low redshifts that could be used as templates for the expected high-redshift ones.
In 1989, the Cosmic Background Explorer (COBE) satellite was sent to space to, among other things, measure the integrated infrared (IR) light emitted from all galaxies throughout the history of the Universe. The goal was to determine the contribution of the energy emitted at these wavelengths to the total energy emitted by astronomical sources in the Universe. As shown in figure 1.2, COBE found that optical and infrared light contribute roughly in equal amounts, indi-cating that about half of the light emitted by astronomical objects is obscured
8 Introduction
by dust (e.g. (Hauser and Dwek, 2001; Dole et al., 2006)). In addition, this dis-covery showed that the galaxies detected by IRAS and optical/UV surveys were not accounting for all the brightness in the cosmic IR background radiation from the sky. There had to be a population of high-redshift dusty galaxies, so far undetected, that were contributing to it.
The best wavelength range to observe dust-enshrouded star-formation in the early Universe is the submm and mm range. This is because the peak of the FIR ra-diation emitted by dusty star-forming regions in high-redshift galaxies (z >1) is shifted into submm/mm wavelengths due to the expansion of the Universe. More-over, the steep spectral index of this emission at wavelengths longer that the peak (i.e.λ >100 µm in the rest-frame) results in a large negative K-correction which is enough to compensate for cosmological dimming (figure 1.3). Consequently, the observed flux density at wavelengths between 800 - 2000µm of a dusty galaxy with fixed intrinsic FIR luminosity is expected to be roughly constant at 1 < z <10 (figure 1.4).
This easy access to the young Universe is what drove submm/mm detector tech-nology to improve greatly, and by mid-1990’s, the first submm/mm wavelength astronomical cameras were ready to operate. For the first time they detected dust-obscured star-forming activity in the early Universe. The first submm de-tections were successful pointed observations of known high-redshift sources such as lensed objects (e.g. the Cloverleaf quasar; Barvainis et al., 1995), radio galax-ies (Dunlop et al., 1994; Hughes et al., 1997; Ivison et al., 1998) and quasars (Isaak et al., 1994; Omont et al., 1996). These studies demonstrated that dust-enshrouded star-formation was happening in the high-redshift Universe at rates >100 M⊙ yr
−1, substantially greater than SFRs in LBGs and LAEs.
A key development to submm/mm cosmology was the commissioning of the Sub-millimetre Common-User Bolometer Array (SCUBA; Holland et al., 1999) cam-era at the James Clerk Maxwell Telescope (JCMT) in 1997. This camcam-era, with a 2.5-arcmin-wide field of view (FOV), imaged the sky at both 450 and 850 µm and provided a dramatic leap forward from the pre-existing single-pixel or one-dimensional arrays. SCUBA conducted blank-field (unbiased) submm surveys and detected redshifted thermal dust emission from previously unknown galax-ies, revealing a population of very luminous high-redshift galaxies later named submillimetre galaxies (SMGs), which are responsible for a significant fraction of the energy generated by all galaxies over the history of the Universe (20−30% at 850µm for sources with flux densities >2 mJy; Coppin et al., 2006).
1.2 Submm galaxies as progenitors of massive elliptical galaxies 9
Figure 1.2: Spectral energy density of the extragalactic background radiation from 0.1 µm to 1 mm. This image shows observational constraints for the cosmic optical background (COB, with λ ≤ 8 µm) and the cosmic infrared background (CIB, with λ > 8 µm) from different experiments such as the Hubble Space Telescope (HST), the Very High Energy Blazars (VHE Blz; gray region), the Diffuse Infrared Background Experiment (DIRBE) on the Cosmic Background Explorer (COBE), the Infrared Array Camera (IRAC) and the Multi-band Imag-ing Photometer (MIPS) on the Spitzer Space Telescope, and the Submillimetre Common-User Bolometer Array (SCUBA). Black arrows represent lower limits. Purple arrows and lines represent upper limits. This image was taken from (Dole et al., 2006), where details and references on the observational data can be found. Their best COB (blue-shaded, left) and CIB (red-shaded, right) estimates are also shown, which clearly indicate that optical and infrared radiation contain roughly equal amounts of energy. This suggests that around half of the light emitted by astronomical objects in the Universe is obscured by dust.
10 Introduction
Figure 1.3: Spectral Energy Distribution (SED) model for the prototypical ultra-luminous infrared galaxy (ULIRG) Arp220 (z = 0.018) as if it were at four different redshifts: z = 1,2,5,9. A vertical dashed line marks the centre of the 1.1 mm observation window. As can be seen from the image, the observed flux density at 1.1 mm does not decrease with Arp220 being at higher redshifts because the observer detects emission closer to the far-infrared (FIR) peak which compensates for cosmological dimming (negative K-correction). The SED model was obtained from Siebenmorgen and Kr¨ugel (2007) and it is consistent with new spectroscopic and photometric data of Arp220, which show that this ULIRG is a good template for dust-obscured high-redshift galaxies (Rangwala et al., 2011).
1.2 Submm galaxies as progenitors of massive elliptical galaxies 11
Figure 1.4: Multicolour K-correction plot (observed flux density vs redshift) derived from the Siebenmorgen and Kr¨ugel (2007) spectral energy distribu-tion (SED) model for the prototypical ultra-luminous infrared galaxy (ULIRG) Arp220, assuming an infrared luminosity (LIR) of ∼ 2×1012 L⊙, which illus-trates the feasibility of detecting galaxies at extreme redshifts in the submm/mm passbands. The horizontal-line shows the typical 3σ confusion-limited detection threshold of the 1.1 mm camera AzTEC mounted in 10-15 m class telescopes (Scott et al., 2010), and implies that it is sensitive to submillimetre galaxies with a LIR >2×1012 L⊙ (i.e. with a SFR >200 M⊙ yr
−1). As can be seen from the
image, the observed flux density at wavelengths between 800 - 2000µm of a dusty galaxy with fixed intrinsic LIR is expected to be roughly constant at 1 < z <10.
12 Introduction
The Max-Planck Millimetre Bolometer Array (MAMBO; Kreysa et al., 1998) came later with similar capabilities as SCUBA but operating at 1.25 mm from the Institut de Radio Astronomie Millim´etrique (IRAM) 30-m telescope in Spain. This camera helped estimate for the first time the number density of galaxies as a function of observed flux at 1.25 mm. Since then, more sophisticated instruments, i.e. with better sensitivities and larger number of detectors, were developed to carry out surveys on larger sky areas. Some examples I would like to highlight here are: a) SHARC II (Dowell et al., 2003), the first CCD-style bolometer array that employspop-up detector technology to form an 12×32 pixel array which op-erates at 350, 450 and 850µm at the Caltech Submillimeter Observatory (CSO); b) the Balloon-borne Large Aperture Submillimeter Telescope (BLAST; Pascale et al., 2008), a stratospheric balloon-borne 2-m telescope with 270 bolometric de-tectors distributed between three arrays observing simultaneously in three bands at 250, 350, and 500µm; c) AzTEC (Wilson et al., 2008), a 144-bolometer array built up for observations of the continuum at a wavelength of 1.1 mm and a facil-ity instrument for the Large Millimeter Telescope (LMT; Schloerb et al., 2003); d) the Large APEX Bolometer Camera (LABOCA; Siringo et al., 2009), a bolo-metric continuum receiver made of 295 semiconducting bolometers operating in the 870µm atmospheric window at the Atacama Pathfinder Experiment (APEX) 12-m submillimeter telescope; e) SCUBA-2 (Holland et al., 2006), the upgraded version of the SCUBA camera with a total of 10,000 transition-edge sensor (TES) detectors divided in two bands (850 and 450 µm) operating at the JCMT; and f) the Photodetector Array Camera and Spectrometer (PACS; Poglitsch et al., 2010) and the Spectral and Photometric Imaging REceiver (SPIRE; Griffin et al., 2010), two direct detection cameras/medium resolution spectrometers on board Herschel (Pilbratt et al., 2010), a 3.5-m Cassegrain space telescope launched in 2009 to perform photometry and spectroscopy in the 55 - 671 µm range, filling the gap between earlier infrared space missions and ground-based telescopes.
The development of more sophisticated instruments allowed astronomers to con-duct deeper and wider submm/mm surveys. As mentioned in the introcon-duction of this section, these surveys found that SMGs are a gas-rich dusty galaxy population characterised by very large IR luminosities (> 1012 L
⊙). Spectroscopic studies in the near infrared (near-IR; Swinbank et al., 2004), optical/X-ray (Chapman et al., 2003; Alexander et al., 2005), and mid-IR (Valiante et al., 2007; Pope et al., 2008b; Men´endez-Delmestre et al., 2009) showed that star formation is the main contributor to the bulk of the SMG emission. Active Galactic Nuclei (AGN), although present in a significant fraction of SMGs, have only a negligible contri-bution (Alexander et al., 2005). Consequently, IR luminosities can be translated directly into SFR>100−1000 M⊙ yr
1.2 Submm galaxies as progenitors of massive elliptical galaxies 13
Many authors have suggested that the merging of comparable mass systems is what produces the large luminosities found in the SMG population (e.g. Narayanan et al., 2010). One of the reasons is the irregular complex morphologies found in rest-frame UV Hubble Space Telescope (HST) images of some SMGs (Chapman et al., 2004; Smail et al., 2004; Swinbank et al., 2006). It is important to note, however, that UV emission is strongly affected by dust extinction, and therefore morphologies based on UV emission must be treated with caution. In addition, Chapman et al. (2004) and Biggs and Ivison (2008) obtained radio observations of SMGs which showed morphological differences between radio and UV emission. Consequently, a better way to study the morphology and kinematics of SMGs is using high spatial resolution images of a tracer that is not affected by extinction. Interferometric CO line observations offer this possibility. Tacconi et al. (2006, 2008) explored this method and found SMGs to display either double/multiple morphologies with complex gas motions, or dense compact rotating-disc mor-phologies. The first result was interpreted as an indication of merging, and the latter, due to the high gas and matter densities of the discs, as an end-stage of a major merger. Engel et al. (2010) extended the sample of Tacconi et al. to 12 SMGs with subarcsec CO-line observations and reported similar results. In addition, they measured SMG sizes and found that radio and CO data are both consistent with diameters < 5 kpc. These sizes are in agreement with previous work by Chapman et al. (2004); Biggs and Ivison (2008); Men´endez-Delmestre et al. (2009); Younger et al. (2010), although a recent study by Ivison et al. (2011) suggests that the extension of gas reservoirs in SMGs depends on the observed CO transition, with higher-frequency emission lines preferentially tracing denser and more centrally concentrated star-forming gas (i.e. smaller radii) than the more extended reservoirs traced by lower-frequency emission lines.
These results appear to favour merging as the most common mechanism for trig-gering the SMGs large luminosities. However, the small number statistics and the spatial resolution of these experiments is not enough to unambiguously dis-tinguish between a merging or an isolated formation scenario. Recently, the most important advance in this context comes from studies using deep, high-quality, near-infrared imaging provided by the Wide Field Camera 3 (WFC3) on the HST. This imaging targets the rest-frame optical regime at z = 1−3, and therefore, offers the possibility to study sizes, morphologies and masses of the existing stellar population of SMGs at those redshifts. The first results are showing that SMGs are indeed massive galaxies (stellar masses of ∼ 2× 1011
M⊙), but a large fraction of them are well-described by either a single exponen-tial disc or a multiple-component system in which the dominant constituent is
14 Introduction
disc-like (Targett et al., 2012). Bruce et al. (2012) have already noted that a sig-nificant fraction of massive galaxies atz = 1−3 appear to be star-forming discs, but WFC3-IR observations of SMGs are showing that submm/mm selection is a good way of targeting a substantial fraction of the extended disc-dominated sources (half light radii of∼4 kpc). In addition, Targett et al. (2012) show that only a small fraction of SMGs (<25%) are possibly involved in a major galaxy-galaxy interaction. This is an interesting result, since the stellar masses of these SMGs imply that virtually all of them are destined to evolve into massive giant elliptical galaxies in the low-redshift Universe, which display, at most, very low level disc components. The mechanisms involved in the morphological evolution are still a topic of debate.
The stellar masses derived from HST/WFC3-IR imaging for the SMG population at z = 1−3 (Targett et al., 2012), together with estimations of molecular gas masses of ∼ 5×1010 M
⊙ (e.g. Greve et al., 2005; Bothwell et al., 2012), and dust masses of ∼108 M
⊙ (e.g. Chapman et al., 2005; Magnelli et al., 2012) sug-gest that the SMG population reside in some of the most massive dark matter haloes in the high-redshift Universe. This is roughly in line with what might be expected from total halo masses found from the clustering analysis of Hickox et al. (2012), which propose that SMGs typically lie within dark matter haloes of masses Mhalo = 9×1012M⊙. It is important to mention that the uncertainties on these mass estimations are still large (possibly on the order of 2-5; see individual studies for references) because several assumptions such as the kinematics of the gas, the star-formation history and the contribution of an AGN to the shape of the rest-frame near-IR continuum excess had to be made. In addition, these samples are usually biased towards SMGs for which optical/mid-IR/radio counterparts could be identified and spectroscopic or photometric redshifts determined.
Originally, redshift distributions of SMGs show a median of z ∼ 2.5 (Chapman et al., 2003; Aretxaga et al., 2003; Chapman et al., 2005; Pope et al., 2005; Aretx-aga et al., 2007; Wardlow et al., 2011; Smolcic et al., 2012), with few galaxies at z > 3. These studies relied on radio and optical/mid-IR detections to identify SMG counterparts and probably suffered from a selection bias against the very high-redshift (z > 3) population. The reason is that radio and optical/mid-IR observations have a positive K-correction and, consequently, their flux densities have a strong decline with redshift. In addition, the large beam sizes of cur-rent single-dish submm/mm experiments (>10 arcsec) makes the determination of precise positions, and therefore optical/mid-IR counterpart associations, very difficult. Nevertheless, the first examples of SMGs at z > 4 have finally been detected due to submm/mm interferometric observations that provided precise
1.2 Submm galaxies as progenitors of massive elliptical galaxies 15
positions and therefore secure counterparts (e.g. Knudsen et al., 2010), and more importantly, due to CO-line observations at submm/mm/radio wavelengths that allowed a direct and accurate redshift determination (Daddi et al., 2009; Riechers et al., 2010; Carilli et al., 2011; Cox et al., 2011; Walter et al., 2012). To date
∼10z >4 SMGs have been confirmed, and this strongly suggests that the SMG redshift distribution has a tail towards higher values. The presence of a popu-lation of z > 4 SMGs has profound implications for models of galaxy formation and evolution since they should account for such objects given the limited time since the Big Bang. Furthermore, these high-redshift dusty starbursts should provide constraints on models of dust production in the early Universe. The next generation of spectroscopic experiments, designed to detect the rotational lines of CO with wider bandwidths and improved sensitivities, should greatly improve the determination of the redshift distribution of SMGs (e.g. the Redshift Search Receiver installed at the LMT and the Atacama Large Millimeter Array).
1.2.2
Formation models in a
Λ
CDM cosmogony
Several N-body simulations (e.g. the Millennium Simulation; Springel et al., 2005) have been developed to follow the evolution of matter under the principles of the ΛCDM model. The final purpose of these simulations is to track galaxy and quasar evolution and validate the model comparing the results to observables such as clustering, luminosity function, number density, ages, and colour distributions of these sources. One of the main steps in these simulations is the implementa-tion of semi-analytic models to describe the physics of baryonic matter. They are implemented to follow gas, star and supermassive black hole processes.
In the last two decades, several semi-analytic models have been able to repro-duce the luminosity function of high-redshift optical/ultraviolet-selected galaxies (e.g. Lyman Break Galaxies; Steidel et al., 1996), as well as optical and near-infrared (near-IR) properties of local galaxies (e.g. Kauffmann et al., 1993; Cole et al., 1994; Kauffmann et al., 1994). But the discovery of the SMGs presented a problem for these models, since none of them could predict correctly the number density of these massive dusty galaxies (Cole et al., 2000; Somerville et al., 2001; Menci et al., 2002).
New parametric models had to be proposed using different recipes to attack the problem. One way of accounting for the higher fraction of massive stars that are formed in SMGs is to assume a top-heavy initial mass function (IMF) in these regions (Baugh et al., 2005; Swinbank et al., 2008; Lacey et al., 2008). The
16 Introduction
justification for such an IMF is that at high redshifts mergers between galaxies are much more common and violent due to a higher number density of sources and a larger gas content in the galaxies. These models succeed at predicting the luminosity function of LBGs, the evolution of the luminosity function at mid-IR wavelengths, and the number density and redshift distribution of SMGs.
Nevertheless, models involving AGN feedback have also been able to produce adequate numbers of high-mass galaxies without invoking a top-heavy IMF. For example, within the ΛCDM scheme, Granato et al. (2004) and Silva et al. (2005) proposed that massive galaxies form earlier than smaller galaxies due to complex baryonic processes reversing the order of structure formation for luminous mat-ter. An example of these processes is the gas cooling suppression in small dark matter haloes due to feedback from supernovae or active galactic nuclei (AGN). If this gas cooling process is stopped, then massive galaxies will form earlier than smaller ones. These models have been able to describe very well the number counts for mid-IR, submm and mm observations.
Some authors have also argued that the SMG population is compatible with the high mass end of the main sequence of galaxy formation atz = 2−3, with specific star formation rates expected for massivez ∼2 galaxies, and fed by smooth infall rather than major mergers (e.g. Dav´e et al., 2010). The justification is that ma-jor mergers are not sufficiently common around the median redshift range of the SMG population (z ∼2.5), and that the ability of galaxy mergers to significantly enhance the already high specific star-formation rates of galaxies at z ∼2−3 is relatively modest.
Of course the true situation may be complex, and there are recent arguments that present the SMG population as an heterogenous group of sources composed of extreme objects boosted by major mergers, nearby pairs of sources, single discs, or even multiple unrelated sources in the same line of sight (e.g. Wang et al., 2011; Hayward et al., 2012). The question of which one is the dominant group, or in what percentage each of these components contributes to the SMG population is what needs to be addressed with high angular resolution imaging of large samples of SMGs.
1.3 Using high redshift AGN as protocluster signposts 17
1.3
Using high redshift AGN as protocluster
sign-posts
A powerful radio source requires a super massive black hole (SMBH), and due to the correlation between the SMBH mass and the bulge luminosity of the host galaxy, powerful radio galaxies are expected to be massive galaxies (e.g. McLure and Dunlop, 2002). In addition, near-IR studies of radio galaxies found that they are the galaxies with the largest K-band luminosities in the early Universe (figure 1.5). Because the rest-frame emission of an old stellar population at high redshift peaks in the near-IR, the brightness of the K-band emission has long been used to estimate stellar masses. Using this method, radio galaxies at high redshifts (HzRGs) have been determined to have stellar masses of up to 1012 M
⊙ (e.g. Rocca-Volmerange et al., 2004; Seymour et al., 2007. Fits to individual K-band images of z ∼2 radio galaxies also revealed that they are moderately large de Vaucouleurs spheroids displaying a well-defined Kormendy relation, which is offset in surface brightness from the local relation by ∼1.7 mag. This luminosity offset is consistent with that expected due to purely passive evolution between z = 2 and 0 for a stellar population formed at z > 3 (Targett et al., 2011). All this evidence favours the theory of HzRGs being among the most massive galaxies in the Universe, forming the bulk of their stellar population at high redshifts, and possibly evolving into the most massive ellipticals at z = 0.
In addition, luminous radio galaxies show bright emission lines, which allow their redshift to be easily determined. These emission lines are produced by warm (104.5 K) gas and provide a powerful tool for studying physical conditions within
these galaxies. During the early nineties, it was found that the nuclear emission lines of HzRGs are generally accompanied by an additional component that is highly extended in space. This component was identified as giant nebulae (also called halos) of ionized gas with sizes of up to ∼200 kpc. This finding also sug-gests that these radio sources contain enough gas to produce massive galaxies, even as enormous as cD-like galaxies (e.g. Reuland et al., 2003b).
In a ΛCDM scenario, such massive galaxies must reside where the density is much higher than the average. Therefore, HzRGs are likely to inhabit regions that will probably conduct to the formation of rich galaxy clusters. This implies that it is possible to directly search for galaxy-cluster progenitors in the vicinity of HzRGs. At high redshift, any overdense structure must still be forming and cannot be virialized and bound. Consequently, these regions are normally called protoclusters.
