Studies of neutral hydrogen gas in distant galaxies using the spectral stacking technique

Plin neutralnog vodika (HI) smatra se građevnom jedinicom galaksija jer služi kao primarno gorivo za stvaranje zvijezda. Izravna opažanja HI emisijske linije na 21 cm ograničena su granicama osjetljivosti radio teleskopa. Kako bi nadišli ovaj problem, koristimo relativno novu metodu slaganja spektara kako bi pomaknuli granice crvenih pomaka u radio opažanjima dalje nego li je moguće ostalim opažačkim metodama. U ovom radu predstavljena je statistička metoda slaganja HI spektara galaksija lociranih u tzv. G09 nebeskom polju, u rasponu crvenih pomaka 0.039<z<0.134. HI opažanja smiljena su Parkes radio teleskopom (New South Wales, Australija). Položaji galaksija i crveni pomaci nalaze se u katalogu dobavljenom iz baze podataka Galaxy and Mass Assembly (GAMA) istraživanja. Slažući spektre 7049 galaksija, ekstrahirane iz Parkes podatkovne kocke, postižemo dobar omjer signala i šuma, S/N=11.9. Šum pokazuje karakteristike Gaussiana, uz malo odstupanje zbog prisutnosti rezidualne radio-frekventne interferencije i emisije od snažnih izvora u podacima. Usrednjene veličine karakteristične HI dobivamo integrirajući složene spektre u granicama ±300 kms^−1 od sustava mirovanja. Taj raspon odgovara iznosu najveće očekivane širine HI profila. Srednja vrijednost gustoće toka, usrednjena masa HI i usrednjeni omjer mase i luminoziteta HI su (tim redoslijedom): (S)=(1.07±0.09)mJy, (M_HI)=(2.97±0.38)×10^9ℎ^−2M_⊙ i M_HI/L_r)=(1.58±0.39) M_⊙L_⊙^−1. Pri izračunu kozmičke gustoće mase HI (Ω_HI) testiramo dvije formule. Kako bi u izračun uključili i efekt konfuzije, koristimo faktor konfuzije.Neutral hydrogen gas (HI) is the building block of galaxies as it is a primary fuel for star formation. Direct observations of the HI 21 cm emission line are restricted by the limited sensitivities of radio telescopes. To overcome this issue, we employ the relatively new technique of spectral stacking to push the redshift limits of radio observations further than otherwise possible. This thesis presents an HI spectral stacking analysis of galaxies within the Galaxy and Mass Assembly (GAMA) 9^h field and over the redshift range 0.039< z <0.134. HI data was collected with the Parkes radio telescope in New South Wales, Australia. Galaxy positions and spectroscopic redshifts are provided by the GAMA survey. By co-adding the spectra of 7049 galaxies extracted from the Parkes data cube, we obtain a strong integrated signal-to-noise ratio of S/N=11.9. The rms noise behaves in a Gaussian manner, with slight deviation caused by the residual radio frequency interference and continuum source emission in the data. We measure average HI properties by integrating stacked spectra over ±300 kms^−1 from rest frame, the range equivalent to the maximum expected width of the HI profile. The resulting average flux density, average HI mass and average HI mass-to-light ratio are, respectively: (S)=(1.07±0.09)mJy, (M_HI)=(2.97±0.38)×10^9h^−2 M_⊙ and (M_HI/L_r)=(1.58±0.39)M_⊙L_⊙^1. We test two different strategies in calculating the cosmic HI mass density (ΩHI). To account for source confusion effect, we apply the confusion facto

The VLA-COSMOS 3 GHz Large Project: Star formation properties and radio luminosity functions of AGN with moderate-to-high radiative luminosities out to z∼6z\sim6

We study a sample of 1,604 moderate-to-high radiative luminosity active galactic nuclei (HLAGN) selected at 3 GHz within the VLA-COSMOS 3 GHz Large Project. These were classified by combining multiple AGN diagnostics: X-ray data, mid-infrared data and broad-band spectral energy distribution fitting. We decompose the total radio 1.4 GHz luminosity ($\mathrm{L_{1.4\ GHz,TOT}}$) into the emission originating from star formation and AGN activity by measuring the excess in $\mathrm{L_{1.4\ GHz,TOT}}$ relative to the infrared-radio correlation of star-forming galaxies. To quantify the excess, for each source we calculate the AGN fraction ($\mathrm{f_{AGN}}$), the fractional contribution of AGN activity to $\mathrm{L_{1.4\ GHz,TOT}}$. The majority of the HLAGN, $(68.0\pm1.5)\%$, are dominated by star-forming processes ($f_{AGN}\leq0.5$), while $(32.0\pm1.5)\%$ are dominated by AGN-related radio emission ($0.5<f_{AGN}\leq1$). We use the AGN-related 1.4 GHz emission to derive the 1.4 GHz AGN luminosity functions of HLAGN. By assuming pure density and pure luminosity evolution models we constrain their cosmic evolution out to $z\sim6$, finding $\mathrm{\Phi^* (z) \propto (1+z)^{(2.64\pm0.10)+(-0.61\pm0.04) z}}$ and $\mathrm{L^* (z) \propto (1+z)^{(3.97\pm0.15) + (-0.92\pm0.06)z}}$. These evolutionary laws show that the number and luminosity density of HLAGN increased from higher redshifts ($z\sim6$) up to a maximum in the redshift range $1<z<2.5$, followed by a decline towards local values. By scaling the 1.4 GHz AGN luminosity to kinetic luminosity using the standard conversion, we estimate the kinetic luminosity density as a function of redshift. We compare our result to the semi-analytic models of radio mode feedback finding that this feedback could have played an important role in the context of AGN-host coevolution in HLAGN which show evidence of AGN-related radio emission ($f_{AGN}>0$).Comment: 20 pages, 14 figure

Faraday tomography of LoTSS-DR2 data: I. Faraday moments in the high-latitude outer Galaxy and revealing Loop III in polarisation

Observations of synchrotron emission at low radio frequencies reveal a labyrinth of polarised Galactic structures. However, the explanation for the wealth of structures remains uncertain due to the complex interactions between the interstellar medium and the magnetic field. A multi-tracer approach to the analysis of large sky areas is needed. This paper aims to use polarimetric images from the LOFAR Two metre Sky Survey (LoTSS) to produce the biggest mosaic of polarised emission in the northern sky at low radio frequencies (150 MHz) to date. The large area this mosaic covers allows for detailed morphological and statistical studies of polarised structures in the high-latitude outer Galaxy, including the well-known Loop III region. We produced a 3100 square degree Faraday tomographic cube using a rotation measure synthesis tool. We calculated the statistical moments of Faraday spectra and compared them with data sets at higher frequencies (1.4 GHz) and with a map of a rotation measure derived from extragalactic sources. The mosaic is dominated by polarised emission connected to Loop III. Additionally, the mosaic reveals an abundance of other morphological structures, mainly {narrow and extended} depolarisation canals, which are found to be ubiquitous. We find a correlation between the map of an extragalactic rotation measure and the LoTSS first Faraday moment image. The ratio of the two deviates from a simple model of a Burn slab (Burn 1966) along the line of sight, which highlights the high level of complexity in the magnetoionic medium that can be studied at these frequencies.Comment: 20 pages, 25 figures, accepted for publication in A&

LOFAR Deep Fields: Probing faint Galactic polarised emission in ELAIS-N1

We present the first deep polarimetric study of Galactic synchrotron emission at low radio frequencies. Our study is based on 21 observations of the European Large Area Infrared Space Observatory Survey-North 1 (ELAIS-N1) field using the Low-Frequency Array (LOFAR) at frequencies from 114.9 to 177.4 MHz. These data are a part of the LOFAR Two-metre Sky Survey Deep Fields Data Release 1. We used very low-resolution ($4.3'$) Stokes QU data cubes of this release. We applied rotation measure (RM) synthesis to decompose the distribution of polarised structures in Faraday depth, and cross-correlation RM synthesis to align different observations in Faraday depth. We stacked images of about 150 hours of the ELAIS-N1 observations to produce the deepest Faraday cube at low radio frequencies to date, tailored to studies of Galactic synchrotron emission and the intervening magneto-ionic interstellar medium. This Faraday cube covers $\sim36~{\rm deg^{2}}$ of the sky and has a noise of $27~{\rm \mu Jy~PSF^{-1}~RMSF^{-1}}$ in polarised intensity. This is an improvement in noise by a factor of approximately the square root of the number of stacked data cubes ($\sim\sqrt{20}$), as expected, compared to the one in a single data cube based on five-to-eight-hour observations. We detect a faint component of diffuse polarised emission in the stacked cube, which was not detected previously. Additionally, we verify the reliability of the ionospheric Faraday rotation corrections estimated from the satellite-based total electron content measurements to be of $~\sim0.05~{\rm rad~m^{-2}}$. We also demonstrate that diffuse polarised emission itself can be used to account for the relative ionospheric Faraday rotation corrections with respect to a reference observation.Comment: 15 pages, 15 figures, accepted for publication in A&

VLA-COSMOS veliki projekt na 3 GHz : Porijeklo zračenja u radio-području kod radijativno efikasnih aktivnih galaktičkih jezgara i njihov razvoj kroz povijest svemira

To study the origin of radio emission and the cosmic evolution of radio detected radiatively efficient active galactic nuclei, I used the radio data of sources detected within the COSMOS and XXL-S sky fields, which were previously cross-correlated with available multiwavelength data. A sample of 1,604 moderate-to-high radiative luminosity AGN (HLAGN) detected within the COSMOS field was selected using criteria sensitive to the X-ray, MIR and optical emissions expected to arise from the efficient accretion onto a supermassive black hole. I developed a statistical method of radio luminosity decomposition, which I used to separate the observed HLAGN radio emission into AGN and star formation-related contributions to the radio luminosity. This was done via the so-called AGN fraction, defined as the fractional contribution of the AGN-related radio emission to the total observed radio emission. I found that the majority of HLAGN (~ 68%) is dominated by star formation-related radio emission (0_AGN < 0.5). However, there are ~ 32% of HLAGN whose radio emission is dominated by the AGN-related radio emission (0.5 ≤ f_AGN ≤ 1). The AGN fractions obtained for each source via the decomposition method were used to scale the total radio luminosity down to the radio AGN luminosity. Using the obtained AGN luminosities, the radio AGN luminosity functions were constructed and constrained out to z ~ 6. The number and luminosity densities of HLAGN were further constrained, with the peak of the evolution found in the cosmic epoch when the universe was 4 billion years old (z ~ 1 - 2.5). Next, by combining the COSMOS HLAGN data-set with the radio-to-X-ray data for a sample of high-excitation radio galaxies within the XXL-S field, I studied a sample of 274 radio and X-ray selected quasars (XQSOs) at 0.25 < z < 6.1. These were selected by a criterion of L_X[2 - 10 keV] ≥ 10^44 ergs^-1 which broadly selects quasars. By calculating the radio loudness of these sources using four different definitions and applying criteria as commonly used in the literature to separate them into radio-quiet and radio-loud AGN, I found that 18 - 73% of XQSOs are selected as radio-loud. This significant disagreement arises both from the different flux density thresholds of the COSMOS and XXL-S radio surveys, as well as because of different criteria that capture different processes related both to star formation and AGN activity. To study further the origin of radio emission in XQSOs, I constructed radio luminosity functions of XQSOs and constrained their shape in six redshift bins at 0.5 < z < 3.75. The lower-1.4 GHz luminosity end shows a higher normalization than expected only from AGN contribution in all studied redshift bins. I found that the so-called ‘bump’ is mostly dominated by emission due to star-forming processes within the host galaxies of XQSOs. As expected, AGN-related radio emission is the dominant contribution at the higher-luminosity end of the RLF. To test if the environment plays a significant role in the presence of AGN-dominated radio emission in some radiatively efficient AGN, I cross-correlated the HLAGN sample with the X-ray group catalog available within COSMOS finding that 43 HLAGN at 0.2 < z < 1.3 are located within the X-ray groups. For these sources, I found a trend of decreasing AGN fractions with increasing distance from the X-ray group center.Glavna tema ovog rada je proučavanje porijekla zračenja opaženog u radio području koje dolazi od radijativno efikasnih aktivnih galaktičkih jezgri ili AGN-ova (skraćeno od engl. active galactic nuclei) te kako se to zračenje mijenja kroz povijest svemira. Radijativno efikasni AGN-ovi nalaze se u galaksijama domaćinima u kojima se aktivno odvijaju procesi stvaranja zvijezda. Poznato je da i aktivnost galaktičke jezgre, kao i procesi stvaranja zvijezda, mogu proizvesti sinkrotronsko zračenje koje se može opaziti u radio području. Dok je kod galaksija u bliskom svemiru moguće razlučiti pojedine komponente, te na temelju opažanja odrediti odakle dolazi radio zračenje, kod opažanja dalekog svemira većina izvora je nerazlučena i razdioba zračenja na temelju morfologije nije moguća. S tom sam svrhom osmislila statističku metodu razdiobe luminoziteta, detaljno opisanu u daljnjem tekstu. Također, za razumijevanje razvoja galaksija kroz povijest svemira, potrebno je znati kako se pojedine komponente galaksija mijenjaju kroz vrijeme. S tom svrhom, određujem funkcije luminoziteta i pomoću njih računam krivulje razvoja broja i luminoziteta u ovisnosti o crvenom pomaku (engl. redshift). Potom razmatram porijeklo radio zračenja u najekstremnijim aktivnim galaktičkim jezgrama - kvazarima - koji su opaženi u području radio i rendgenskog zračenja. U zadnjem dijelu teze, proučavam ima li lokalno galaktičko okruženje utjecaj na prisutnost radio zračenja kod radijativno efikasnih AGN-ova. U duljenjem tekstu radim kratak uvod u područje astrofizike znano kao razvoj galaksija, u sklopu kojeg je napravljen rad predstavljen u ovoj disertaciji

VLA-COSMOS veliki projekt na 3 GHz : Porijeklo zračenja u radio-području kod radijativno efikasnih aktivnih galaktičkih jezgara i njihov razvoj kroz povijest svemira

To study the origin of radio emission and the cosmic evolution of radio detected radiatively efficient active galactic nuclei, I used the radio data of sources detected within the COSMOS and XXL-S sky fields, which were previously cross-correlated with available multiwavelength data. A sample of 1,604 moderate-to-high radiative luminosity AGN (HLAGN) detected within the COSMOS field was selected using criteria sensitive to the X-ray, MIR and optical emissions expected to arise from the efficient accretion onto a supermassive black hole. I developed a statistical method of radio luminosity decomposition, which I used to separate the observed HLAGN radio emission into AGN and star formation-related contributions to the radio luminosity. This was done via the so-called AGN fraction, defined as the fractional contribution of the AGN-related radio emission to the total observed radio emission. I found that the majority of HLAGN (~ 68%) is dominated by star formation-related radio emission (0_AGN < 0.5). However, there are ~ 32% of HLAGN whose radio emission is dominated by the AGN-related radio emission (0.5 ≤ f_AGN ≤ 1). The AGN fractions obtained for each source via the decomposition method were used to scale the total radio luminosity down to the radio AGN luminosity. Using the obtained AGN luminosities, the radio AGN luminosity functions were constructed and constrained out to z ~ 6. The number and luminosity densities of HLAGN were further constrained, with the peak of the evolution found in the cosmic epoch when the universe was 4 billion years old (z ~ 1 - 2.5). Next, by combining the COSMOS HLAGN data-set with the radio-to-X-ray data for a sample of high-excitation radio galaxies within the XXL-S field, I studied a sample of 274 radio and X-ray selected quasars (XQSOs) at 0.25 < z < 6.1. These were selected by a criterion of L_X[2 - 10 keV] ≥ 10^44 ergs^-1 which broadly selects quasars. By calculating the radio loudness of these sources using four different definitions and applying criteria as commonly used in the literature to separate them into radio-quiet and radio-loud AGN, I found that 18 - 73% of XQSOs are selected as radio-loud. This significant disagreement arises both from the different flux density thresholds of the COSMOS and XXL-S radio surveys, as well as because of different criteria that capture different processes related both to star formation and AGN activity. To study further the origin of radio emission in XQSOs, I constructed radio luminosity functions of XQSOs and constrained their shape in six redshift bins at 0.5 < z < 3.75. The lower-1.4 GHz luminosity end shows a higher normalization than expected only from AGN contribution in all studied redshift bins. I found that the so-called ‘bump’ is mostly dominated by emission due to star-forming processes within the host galaxies of XQSOs. As expected, AGN-related radio emission is the dominant contribution at the higher-luminosity end of the RLF. To test if the environment plays a significant role in the presence of AGN-dominated radio emission in some radiatively efficient AGN, I cross-correlated the HLAGN sample with the X-ray group catalog available within COSMOS finding that 43 HLAGN at 0.2 < z < 1.3 are located within the X-ray groups. For these sources, I found a trend of decreasing AGN fractions with increasing distance from the X-ray group center.Glavna tema ovog rada je proučavanje porijekla zračenja opaženog u radio području koje dolazi od radijativno efikasnih aktivnih galaktičkih jezgri ili AGN-ova (skraćeno od engl. active galactic nuclei) te kako se to zračenje mijenja kroz povijest svemira. Radijativno efikasni AGN-ovi nalaze se u galaksijama domaćinima u kojima se aktivno odvijaju procesi stvaranja zvijezda. Poznato je da i aktivnost galaktičke jezgre, kao i procesi stvaranja zvijezda, mogu proizvesti sinkrotronsko zračenje koje se može opaziti u radio području. Dok je kod galaksija u bliskom svemiru moguće razlučiti pojedine komponente, te na temelju opažanja odrediti odakle dolazi radio zračenje, kod opažanja dalekog svemira većina izvora je nerazlučena i razdioba zračenja na temelju morfologije nije moguća. S tom sam svrhom osmislila statističku metodu razdiobe luminoziteta, detaljno opisanu u daljnjem tekstu. Također, za razumijevanje razvoja galaksija kroz povijest svemira, potrebno je znati kako se pojedine komponente galaksija mijenjaju kroz vrijeme. S tom svrhom, određujem funkcije luminoziteta i pomoću njih računam krivulje razvoja broja i luminoziteta u ovisnosti o crvenom pomaku (engl. redshift). Potom razmatram porijeklo radio zračenja u najekstremnijim aktivnim galaktičkim jezgrama - kvazarima - koji su opaženi u području radio i rendgenskog zračenja. U zadnjem dijelu teze, proučavam ima li lokalno galaktičko okruženje utjecaj na prisutnost radio zračenja kod radijativno efikasnih AGN-ova. U duljenjem tekstu radim kratak uvod u područje astrofizike znano kao razvoj galaksija, u sklopu kojeg je napravljen rad predstavljen u ovoj disertaciji

Multi-tracer analysis of straight depolarisation canals in the surroundings of the 3C 196 field

Context. Faraday tomography of a field centred on the extragalactic point source 3C 196 with the LOw Frequency ARray (LOFAR) revealed an intertwined structure of diffuse polarised emission with straight depolarisation canals and tracers of the magnetised and multi-phase interstellar medium (ISM), such as dust and line emission from atomic hydrogen (HI). Aims. This study aims at extending the multi-tracer analysis of LOFAR data to three additional fields in the surroundings of the 3C 196 field. For the first time, we study the three-dimensional structure of the LOFAR emission by determining the distance to the depolarisation canals. Methods. We used the rolling Hough transform to compare the orientation of the depolarisation canals with that of the filamentary structure seen in HI, and based on starlight and dust polarisation data, with that of the plane-of-the-sky magnetic field. Stellar parallaxes from Gaia complemented the starlight polarisation with the corresponding distances. Results. Faraday tomography of the three fields shows a rich network of diffuse polarised emission at Faraday depths between − 10 and + 15 rad m−2. A complex system of straight depolarisation canals resembles that of the 3C 196 field. The depolarisation canals align both with the HI filaments and with the magnetic field probed by dust. The observed alignment suggests that an ordered magnetic field organises the multiphase ISM over a large area (~20°). In one field, two groups of stars at distances below and above 200 pc, respectively, show distinct magnetic field orientations. These are both comparable with the orientations of the depolarisation canals in the same field. We conclude that the depolarisation canals likely trace the same change in the magnetic field as probed by the stars, which corresponds to the edge of the Local Bubble

c 305 Public Halls Act

Based on a sample of over 1800 radio AGN at redshifts out to z ~ 5, which have typical stellar masses within ~3 × (1010 − 1011)M⊙, and 3 GHz radio data in the COSMOS field, we derived the 1.4 GHz radio luminosity functions for radio AGN (L1.4 GHz~ 1022 − 1027 W Hz-1) out to z ~ 5. We constrained the evolution of this population via continuous models of pure density and pure luminosity evolutions, and we found best-fit parametrizations of Φ∗ ∝ (1 + z)(2.00 ± 0.18) − (0.60 ± 0.14)z, and L∗ ∝ (1 + z)(2.88 ± 0.82) − (0.84 ± 0.34)z, respectively, with a turnover in number and luminosity densities of the population at z ≈ 1.5. We converted 1.4 GHz luminosity to kinetic luminosity taking uncertainties of the scaling relation used into account. We thereby derived the cosmic evolution of the kinetic luminosity density provided by the AGN and compared this luminosity density to the radio-mode AGN feedback assumed in the Semi-Analytic Galaxy Evolution (SAGE) model, i.e., to the redshift evolution of the central supermassive black hole accretion luminosity taken in the model as the source of heating that offsets the energy losses of the cooling, hot halo gas, and thereby limits further stellar mass growth of massive galaxies. We find that the kinetic luminosity exerted by our radio AGN may be high enough to balance the radiative cooling of the hot gas at each cosmic epoch since z ~ 5. However, although our findings support the idea of radio-mode AGN feedback as a cosmologically relevant process in massive galaxy formation, many simplifications in both the observational and semi-analytic approaches still remain and need to be resolved before robust conclusions can be reached