Browsing by Author "Kraan-Korteweg, Renee Christine"
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- ItemOpen AccessDeep NIR imaging of galaxy clusters in the Vela supercluster(2022) Hatamkhani, Narges; Kraan-Korteweg, Renee Christine; Blyth, Sarah-LouiseGravitational forces of large galaxy over densities can perturb the smooth motions expected from the expanding universe, causing peculiar motions. The observed Cosmic Microwave Background (CMB) dipole is the result of the Local Group's peculiar motion, the direction and amplitude of which are still not fully resolved. The newly discovered Vela Supercluster (VSCL, ` = 272. ◦5±20◦ , b = 0◦±10◦ ), an extended structure behind the Zone of Avoidance (ZoA) at cz ∼ 18000 km s−1 , may be a not insignificant contributor to the residual bulk flow that arises beyond cz ∼ 16000 km s−1 . Knowledge of the structure and richness of galaxy clusters within the VSCL will enable us to assess the morphology and mass of this partially obscured supercluster. Compared to the shorter optical wavelengths, near infrared (NIR) observations are less affected by dust obscuration in the ZoA and therewith offer a better tool to probe galaxy clusters in the VSCL, and get a better understanding of this extended supercluster. A series of deep NIR observations of prospective clusters identified in the VSCL were conducted in the J, H and Ks bands with the InfraRed Survey Facility (IRSF) telescope. For 6 (VC02, VC04, VC05, VC08, VC10 and VC11) out of 20 potential clusters a complete set of science quality images were obtained (out to ∼ 70% of the Abell radius) and were fully reduced. I identified galaxy candidates in each cluster using the Source Extractor software, validated them through visual inspection of the RGB composite images and created a catalogue of galaxies with their astrometric and photometric parameters using the IRSF pipeline. There are a total number of 1715 identified galaxies distributed over the six clusters, of which only ∼ 15% were previously known. Investigating the effect of foreground extinction in the region of the observed clusters shows that, the VC02 cluster has the highest foreground extinction while VC04 and VC05 have the lowest (hAKsi = 0. m10, hAKsi = 0. m07 and hAKsi = 0. m06 respectively). I show that the effect of extinction on the isophotal magnitudes is small compared to the foreground extinction and additional extinction-correction is not required. The extinction-corrected completeness magnitude limit for this survey is Mo Ks < −21. m5 which is ∼ 2. m0 deeper than 2MASX. The six observed clusters were analysed in detail out to the cluster centric completeness radius of rc < 1.5 Mpc and Mo Ks < −21. m5. Comparison of the iso-density contour maps and radial density profiles of the VSCL clusters with Ks-band data of well-known clusters (Coma, Norma, 3C129 and Virgo), finds VC04 to be a regular and massive cluster comparable to Coma and Norma (although its velocity dispersion seems rather low for a rich cluster); it is the richest of the six. H I analysis (using MeerKAT-16 data) shows that the spiral galaxies in VC04 are severely H I deficient which is consistent with its richness. VC02 and VC05 are found to be relatively rich clusters while VC08 is rather poor. VC10 has a filament-like structure and is not a cluster. VC11 is an intermediate cluster which contains two major subclusters. It appears that many of the VSCL clusters (VC02, VC04, VC05 and VC11) are not relaxed yet and are still evolving. The Ks-band Luminosity Function (LF) was derived for the VSCL clusters up to Mo Ks < −21. m5 (∼ 2. m5 deeper than M∗ ). I demonstrate that the Red-Sequence (RS) method is a reliable method to measure the LFs of the clusters and then compute the Ks-band LFs of the Coma, Norma and Virgo clusters using the RS method to compare to the LFs of the VSCL clusters. The comparisons show that M∗ derived for the LF of VC04 (M∗ = −24. m70 ± 0.42) agrees well with those of other local clusters. The bright end of the VC04 LF is compatible with that of massive clusters that are dominated by early-type galaxies such as Norma, while the slope (α = −0.89±0.13) is shallower compared to those of younger clusters. The analysis of this to date small sample of the VSCL clusters (6 out of at least 20) shows that the VSCL contains potentially many more rich clusters indicative of it being a rich supercluster.
- ItemOpen AccessExploring the evolution and hidden large-scale structures of galaxies with MeerKAT HI surveys(2024) Rajohnson, Sambatriniaina Hagiriche Aycha; Kraan-Korteweg, Renee Christine; Frank BradleyBuilding upon previous high-resolution and high-sensitivity H I surveys conducted over narrow angles of the sky, such as the COSMOS H I Large Extragalactic Survey (CHILES), a new era has begun with the emergence of SKA Pathfinders such as MeerKAT and ASKAP. Deep systematic interferometric H I surveys of unprecedented sensitivity and resolution over very wide angles of the sky are now possible. In this thesis, I use the capabilities of MeerKAT to explore H I galaxy scaling relations and investigate concealed large-scale structures (LSS) linked to dynamically significant structures in the Southern Zone of Avoidance (ZOA). To achieve these objectives, I worked on three blind systematic H I surveys conducted with the 4k L-band data from the complete MeerKAT64 array: the MIGHTEE-H I Early Science data, the Vela SARAO MeerKAT Galactic Plane Survey (Vela– SMGPS), and the MeerKAT Vela Supercluster survey (Vela–H I). As a first step, I validated the MIGHTEE-H I Early Science data covering a total of ⇠5 deg2, distributed across three XMMLSS fields (⇠3.5 deg2) and one COSMOS field (⇠1.5 deg2). The spectral line data achieved 1200⇥1000 and 14.500⇥1100 angular resolutions, with an rms sensitivity of 81 and 44 `Jy beam–1 per 44.1 km s–1 channel, for a total observing time of 13 and 17 hours per XMMLSS and COSMOS field, respectively. Following visual source identification and morphological classification, the sample comprised 276 galaxies – 176 spirals, 72 irregulars, 19 mergers, and 9 early-type galaxies. To independently verify the derived H I properties, I cross-referenced fluxes from COSMOS detections with ALFALFA galaxies, revealing agreement for high-signal-to-noise ratio sources. As an application of the data verification process, I constructed the H I size-mass relation, investigating potential systematic eects present in the early data. This relation was derived for the first time from a uniform interferometric sample, reaching an unprecedented redshift range of z ⇠ 0.084. Based on a subsample of 204 galaxies, the relation was found to be consistent with the literature at z ⇠ 0 and indicated that in the absence of significant environmental influences, gas distribution and mean surface mass density within galaxy discs have remained relatively stable over the past one billion years. A 10% intrinsic variation (0.054 ± 0.003 dex) in the H I size at a given H I mass was observed, but no evidence for evolution over the explored redshift range. I performed a detailed census to blindly map signatures of hidden LSS in the Vela region, aiming to narrow down the ZOA in redshift space. This unexplored area hosts the enigmatic Vela Supercluster (VSCL), with its potential merging walls and an inner core obscured in the innermost ZOA. The location of the VSCL is also essential for addressing persistent bulk flow discrepancies. I pursued a two-phase mapping of the VSCL, with a focus on identifying its gas-rich spirals. Firstly, using data from Vela–SMGPS, which surveyed a narrow strip covering 90 deg2 (260 ✓ 290, –2 b 1). I imaged 157 individual pointings with a total observing time of ⇠211 hours. This produced 10 contiguous mosaics with an average rms of 0.39 mJy beam–1 per 44 km s–1 channel and an angular resolution of 3000⇥2700 (±100). Secondly, the MeerKAT Vela–H I survey was designed to explicitly fill the gaps above and below the Galactic Plane (GP) between Vela–SMGPS and prior Vela spectroscopic survey regions (263 ✓ 284, –6.7 b –2, 1 b 6.2). I processed the 667 Nyquist-sampled fields and generated 32 mosaics. With 67 hours of observations over a 242 deg2 area, the survey reached an average rms of 0.74 mJy beam–1 per 44 km s–1 channel for the beam size of 3800⇥3100 (±300). By focusing on the mostly RFI-free band of 250 < Vhel < 25000 km s–1, I identified 843 and 719 heavily obscured galaxy candidates in Vela–SMGPS and Vela–H I, respectively, most of which were previously unknown. When comparing the distribution to simulations based on the SKA H I-science method which assumes a homogeneous distribution, and examining onsky distributions, a total of six overdensities were observed. With regard to VSCL, the new detections hint at the presence of two wall-like overdensities at 16000 – 19000 km s–1 (W1) and 19000 – 23000 km s–1(W2). These may well intersect within the longitude range 270 ✓ 279 at the lowest latitudes. Other major overdensities include the confirmation of the presence of the Hydra/Antlia wall traversing the GP at ✓ ⇠ 280 ± 2 at Vhel ⇠ 2500 – 4000 km s–1 and the discovery of a 30 long, narrow filament in the GP at ⇠12000 km s–1. By only considering the complete sample from Vela–SMGPS and Vela–H I, I calculated the H I mass function (HIMF) of the two surveys in an attempt to quantify these VSCL overdensities. The overall pattern of the HIMF closely aligns with the ALFALFA HIMF. Additionally, I estimated upper limit overdensity values of 3.5 ± 1.6 and 1.8 ± 2.4 in the inner ZOA for W1 and W2, respectively. The accomplishments of the MIGHTEE-H I Early Science survey, Vela–SMGPS, and Vela–H I oer a promising glimpse into the immense capabilities that await H I science with the forthcoming SKA
- ItemOpen AccessExploring the evolution and hidden large-scale structures of galaxies with MeerKAT HI surveys(2024) Rajohnson, Sambatriniaina Hagiriche Aycha; Kraan-Korteweg, Renee Christine; Frank BradleyBuilding upon previous high-resolution and high-sensitivity H I surveys conducted over narrow angles of the sky, such as the COSMOS H I Large Extragalactic Survey (CHILES), a new era has begun with the emergence of SKA Pathfinders such as MeerKAT and ASKAP. Deep systematic interferometric H I surveys of unprecedented sensitivity and resolution over very wide angles of the sky are now possible. In this thesis, I use the capabilities of MeerKAT to explore H I galaxy scaling relations and investigate concealed large-scale structures (LSS) linked to dynamically significant structures in the Southern Zone of Avoidance (ZOA). To achieve these objectives, I worked on three blind systematic H I surveys conducted with the 4k L-band data from the complete MeerKAT64 array: the MIGHTEE-H I Early Science data, the Vela SARAO MeerKAT Galactic Plane Survey (Vela– SMGPS), and the MeerKAT Vela Supercluster survey (Vela–H I). As a first step, I validated the MIGHTEE-H I Early Science data covering a total of ⇠5 deg2, distributed across three XMMLSS fields (⇠3.5 deg2) and one COSMOS field (⇠1.5 deg2). The spectral line data achieved 1200⇥1000 and 14.500⇥1100 angular resolutions, with an rms sensitivity of 81 and 44 `Jy beam–1 per 44.1 km s–1 channel, for a total observing time of 13 and 17 hours per XMMLSS and COSMOS field, respectively. Following visual source identification and morphological classification, the sample comprised 276 galaxies – 176 spirals, 72 irregulars, 19 mergers, and 9 early-type galaxies. To independently verify the derived H I properties, I cross-referenced fluxes from COSMOS detections with ALFALFA galaxies, revealing agreement for high-signal-to-noise ratio sources. As an application of the data verification process, I constructed the H I size-mass relation, investigating potential systematic eects present in the early data. This relation was derived for the first time from a uniform interferometric sample, reaching an unprecedented redshift range of z ⇠ 0.084. Based on a subsample of 204 galaxies, the relation was found to be consistent with the literature at z ⇠ 0 and indicated that in the absence of significant environmental influences, gas distribution and mean surface mass density within galaxy discs have remained relatively stable over the past one billion years. A 10% intrinsic variation (0.054 ± 0.003 dex) in the H I size at a given H I mass was observed, but no evidence for evolution over the explored redshift range. I performed a detailed census to blindly map signatures of hidden LSS in the Vela region, aiming to narrow down the ZOA in redshift space. This unexplored area hosts the enigmatic Vela Supercluster (VSCL), with its potential merging walls and an inner core obscured in the innermost ZOA. The location of the VSCL is also essential for addressing persistent bulk flow discrepancies. I pursued a two-phase mapping of the VSCL, with a focus on identifying its gas-rich spirals. Firstly, using data from Vela–SMGPS, which surveyed a narrow strip covering 90 deg2 (260 ✓ 290, –2 b 1). I imaged 157 individual pointings with a total observing time of ⇠211 hours. This produced 10 contiguous mosaics with an average rms of 0.39 mJy beam–1 per 44 km s–1 channel and an angular resolution of 3000⇥2700 (±100). Secondly, the MeerKAT Vela–H I survey was designed to explicitly fill the gaps above and below the Galactic Plane (GP) between Vela–SMGPS and prior Vela spectroscopic survey regions (263 ✓ 284, –6.7 b –2, 1 b 6.2). I processed the 667 Nyquist-sampled fields and generated 32 mosaics. With 67 hours of observations over a 242 deg2 area, the survey reached an average rms of 0.74 mJy beam–1 per 44 km s–1 channel for the beam size of 3800⇥3100 (±300). By focusing on the mostly RFI-free band of 250 < Vhel < 25000 km s–1, I identified 843 and 719 heavily obscured galaxy candidates in Vela–SMGPS and Vela–H I, respectively, most of which were previously unknown. When comparing the distribution to simulations based on the SKA H I-science method which assumes a homogeneous distribution, and examining onsky distributions, a total of six overdensities were observed. With regard to VSCL, the new detections hint at the presence of two wall-like overdensities at 16000 – 19000 km s–1 (W1) and 19000 – 23000 km s–1(W2). These may well intersect within the longitude range 270 ✓ 279 at the lowest latitudes. Other major overdensities include the confirmation of the presence of the Hydra/Antlia wall traversing the GP at ✓ ⇠ 280 ± 2 at Vhel ⇠ 2500 – 4000 km s–1 and the discovery of a 30 long, narrow filament in the GP at ⇠12000 km s–1. By only considering the complete sample from Vela–SMGPS and Vela–H I, I calculated the H I mass function (HIMF) of the two surveys in an attempt to quantify these VSCL overdensities. The overall pattern of the HIMF closely aligns with the ALFALFA HIMF. Additionally, I estimated upper limit overdensity values of 3.5 ± 1.6 and 1.8 ± 2.4 in the inner ZOA for W1 and W2, respectively. The accomplishments of the MIGHTEE-H I Early Science survey, Vela–SMGPS, and Vela–H I oer a promising glimpse into the immense capabilities that await H I science with the forthcoming SKA
- ItemOpen AccessExploring the evolution and hidden large-scale structures of galaxies with MeerKAT HI surveys(2024) Rajohnson, Sambatriniaina Hagiriche Aycha; Kraan-Korteweg, Renee Christine; Frank BradleyBuilding upon previous high-resolution and high-sensitivity H I surveys conducted over narrow angles of the sky, such as the COSMOS H I Large Extragalactic Survey (CHILES), a new era has begun with the emergence of SKA Pathfinders such as MeerKAT and ASKAP. Deep systematic interferometric H I surveys of unprecedented sensitivity and resolution over very wide angles of the sky are now possible. In this thesis, I use the capabilities of MeerKAT to explore H I galaxy scaling relations and investigate concealed large-scale structures (LSS) linked to dynamically significant structures in the Southern Zone of Avoidance (ZOA). To achieve these objectives, I worked on three blind systematic H I surveys conducted with the 4k L-band data from the complete MeerKAT64 array: the MIGHTEE-H I Early Science data, the Vela SARAO MeerKAT Galactic Plane Survey (Vela– SMGPS), and the MeerKAT Vela Supercluster survey (Vela–H I). As a first step, I validated the MIGHTEE-H I Early Science data covering a total of ⇠5 deg2, distributed across three XMMLSS fields (⇠3.5 deg2) and one COSMOS field (⇠1.5 deg2). The spectral line data achieved 1200⇥1000 and 14.500⇥1100 angular resolutions, with an rms sensitivity of 81 and 44 `Jy beam–1 per 44.1 km s–1 channel, for a total observing time of 13 and 17 hours per XMMLSS and COSMOS field, respectively. Following visual source identification and morphological classification, the sample comprised 276 galaxies – 176 spirals, 72 irregulars, 19 mergers, and 9 early-type galaxies. To independently verify the derived H I properties, I cross-referenced fluxes from COSMOS detections with ALFALFA galaxies, revealing agreement for high-signal-to-noise ratio sources. As an application of the data verification process, I constructed the H I size-mass relation, investigating potential systematic eects present in the early data. This relation was derived for the first time from a uniform interferometric sample, reaching an unprecedented redshift range of z ⇠ 0.084. Based on a subsample of 204 galaxies, the relation was found to be consistent with the literature at z ⇠ 0 and indicated that in the absence of significant environmental influences, gas distribution and mean surface mass density within galaxy discs have remained relatively stable over the past one billion years. A 10% intrinsic variation (0.054 ± 0.003 dex) in the H I size at a given H I mass was observed, but no evidence for evolution over the explored redshift range. I performed a detailed census to blindly map signatures of hidden LSS in the Vela region, aiming to narrow down the ZOA in redshift space. This unexplored area hosts the enigmatic Vela Supercluster (VSCL), with its potential merging walls and an inner core obscured in the innermost ZOA. The location of the VSCL is also essential for addressing persistent bulk flow discrepancies. I pursued a two-phase mapping of the VSCL, with a focus on identifying its gas-rich spirals. Firstly, using data from Vela–SMGPS, which surveyed a narrow strip covering 90 deg2 (260 ✓ 290, –2 b 1). I imaged 157 individual pointings with a total observing time of ⇠211 hours. This produced 10 contiguous mosaics with an average rms of 0.39 mJy beam–1 per 44 km s–1 channel and an angular resolution of 3000⇥2700 (±100). Secondly, the MeerKAT Vela–H I survey was designed to explicitly fill the gaps above and below the Galactic Plane (GP) between Vela–SMGPS and prior Vela spectroscopic survey regions (263 ✓ 284, –6.7 b –2, 1 b 6.2). I processed the 667 Nyquist-sampled fields and generated 32 mosaics. With 67 hours of observations over a 242 deg2 area, the survey reached an average rms of 0.74 mJy beam–1 per 44 km s–1 channel for the beam size of 3800⇥3100 (±300). By focusing on the mostly RFI-free band of 250 < Vhel < 25000 km s–1, I identified 843 and 719 heavily obscured galaxy candidates in Vela–SMGPS and Vela–H I, respectively, most of which were previously unknown. When comparing the distribution to simulations based on the SKA H I-science method which assumes a homogeneous distribution, and examining onsky distributions, a total of six overdensities were observed. With regard to VSCL, the new detections hint at the presence of two wall-like overdensities at 16000 – 19000 km s–1 (W1) and 19000 – 23000 km s–1(W2). These may well intersect within the longitude range 270 ✓ 279 at the lowest latitudes. Other major overdensities include the confirmation of the presence of the Hydra/Antlia wall traversing the GP at ✓ ⇠ 280 ± 2 at Vhel ⇠ 2500 – 4000 km s–1 and the discovery of a 30 long, narrow filament in the GP at ⇠12000 km s–1. By only considering the complete sample from Vela–SMGPS and Vela–H I, I calculated the H I mass function (HIMF) of the two surveys in an attempt to quantify these VSCL overdensities. The overall pattern of the HIMF closely aligns with the ALFALFA HIMF. Additionally, I estimated upper limit overdensity values of 3.5 ± 1.6 and 1.8 ± 2.4 in the inner ZOA for W1 and W2, respectively. The accomplishments of the MIGHTEE-H I Early Science survey, Vela–SMGPS, and Vela–H I oer a promising glimpse into the immense capabilities that await H I science with the forthcoming SKA
- ItemOpen AccessFirst MeerKAT HI survey results mapping large scale structures hidden behind the Milky Way out to z = 0.08(2023) Steyn, Nadia; Kraan-Korteweg, Renee Christine; Frank BradleySKA pathfinders (e.g., ASKAP and MeerKAT) are performing large HI surveys, surpassing previous-generation radio surveys in angular resolution, volume, and depth — going nearly two orders of magnitude deeper. The vast amount of data being produced by these telescopes creates a need for new tools and techniques, such as automated source-extraction. One particular science goal is to trace the large scale structure of galaxies in the local Universe behind the Zone of Avoidance (ZoA). This is difficult to do in the optical and infrared bands because of the thick dust and stellar crowding along the plane of the Milky Way. HI surveys are ideal because the 21 cm spectral line emission of neutral hydrogen (HI) atoms is unaffected by these features. This dissertation presents two HI surveys in the ZoA: the MeerKAT16 Early Science project, conducted before the completion of the full array, with 16-dish subarrays and the ROACH-32k correlator; and later, the Galactic Plane Legacy Survey (GPS), a larger MeerKAT survey project utilising 60-dish subarrays and the SKARAB-4k correlator. The motivation of the MeerKAT16 survey was two-fold: serving as a pilot project for the envisioned large MeerKAT64 Vela Supercluster (VSCL) survey; and a test-bed for optimising galaxy identification processes using automated pipelines. The survey aimed to map the rich galaxy cluster VC04, embedded in one of the prospective VSCL walls. We searched two mosaic cubes for HI sources by means of a deep visual search, and then using the Source Finding Application (SoFiA; version 1.3.2). The purpose of using both methods was to understand and optimise the SoFiA pipeline on real data, which is important for the development of source finding strategies for future large surveys. We catalogued 119 reliable galaxy detections (and an additional 37 candidates with lower certainty) within the early science data. SoFiA found galaxies all the way at the VSCL distance (V(hel) ≈ 18 000 km/s), where we detected hints of two walls, and HI deficiency in the centre of VC04. GPS surveyed a long narrow strip (|b| ≤ 2°) along the Galactic plane, with the aim of penetrating the most obscured part of the ZoA. A segment of the data spanning 302° ≤ l ≤ 332° was reduced, imaged, and analysed as part of this project. This region is interesting because it encompasses the Great Attractor (GA) — a massive overdensity highly influential to the local flow of galaxies. Aided by the newer version of SoFiA (v2.3.1), we found 477 galaxy candidates, most of which are new discoveries, and performed an in-depth comparison against the largest systematic HI survey covering the southern ZoA up to this point — the Parkes HIZOA survey. Additionally, we compared our results to simulations that follow the method used for the SKA HI science case. The GPS redshift distribution reveals a striking overdensity at the GA distance (V(hel) ≈ 4000 km/s), inconsistent with a uniform galaxy distribution, whereas the high-redshift end is more underdense than predicted by the simulation. These deep interferometric HI surveys provided a new glimpse of highly interesting structures crossing the Galactic plane, demonstrating that large scale structure can be mapped even in the deepest part of the ZoA. The success of MeerKAT16 and GPS is a preview of the HI science potential of the upcoming SKA, which will surpass MeerKAT in depth, sensitivity and resolution.
- ItemOpen AccessGalaxy groups in the updated 2MRS using a graph-theory based friends-of-friends algorithm(2020) Lambert, Trystan; Kraan-Korteweg, Renee Christine; Jarrett, Thomas H.A galaxy group catalogue for the recently-completed 2MASS Redshift Survey (2MRS, Macri et al., 2019) is presented which consists of 44572 redshifts, including 1041 new measurements for galaxies mostly located within the Zone of Avoidance. The galaxy group catalogue is generated using a novel, graph-theory based, modified version of the Friends-of-Friends algorithm. Several graph-theory examples are presented throughout this paper, and include a new method to identify substructures within groups. The results and graph-theory methods have been thoroughly interrogated against previous 2MRS group catalogues and a Theoretical Astrophysical Observatory (TAO) mock by making use of cutting-edge visualization techniques including immersive facilities, a digital planetarium, and virtual reality. This has resulted in a stable and robust catalogue with on-sky positions and line-of-sight distances within 0.5 Mpc and 2 Mpc of the group respectively. It has recovered all major groups and clusters. The final catalogue consists of 3022 groups, resulting in the most complete “whole-sky” galaxy group catalogue to date. The 3D-positions of the groups are presented, as well as their luminosity and comoving distances, observed and corrected number of members, richness metric, velocity dispersion, and estimates of R200 and M200. Three additional catalogues are provided: 2MRS galaxies found in groups, a catalogue of subgroups, and the catalogue of 687 new group candidates which had no counterparts in previous 2MRS-based analyses.
- ItemOpen AccessOptimisation of galaxy identification methods on large interferometric surveys(2018) Gqaza, Themba; Kraan-Korteweg, Renee Christine; Jarrett, ThomasThe astronomical size of spectral data cubes that will result from the SKA pathfinders planned large HI surveys such as LADUMA; Fornax HI survey; DINGO; WALLABY; etc. necessitate fully automated three-dimensional (3D) source finding and parametrization tools. A fraction of the percentage difference in the performance of these automated tools corresponds to a significant number of galaxies being detected or undetected. Failure or success to resolve satellites around big spirals will affect both the low and the high mass end of the HI mass function. As a result, the performance and efficiency of these automated tools are of great importance, especially in the epoch of big data. Here I present the comprehensive comparison of performance between the fully automated source identification and parametrization software: SOFIA, the visual galaxy identification method and the semi-automated galaxy identification method. Each galaxy identification method has been applied to the same ∼ 35 gigabytes 3D HI data cube. The data cube results from the blind HI imaging survey conducted using the Westerbork Synthesis Radio Telescope (WSRT). The survey mapped the overdensity corresponding to the Perseus-Pisces Supercluster filament crossing the Zone-of-Avoidance (ZoA), at (`, b) ≈ (160◦ , 0.5◦ ). A total of 211 galaxies detected using the semi-automated method by Ramatsoku et al. [2016]. In this work, I detected 194 galaxies (using the visual identification method) of which 89.7% (174) have cross-matches/counterparts on the galaxy catalogue produced through semi-automated identification method. A total of 130 detections were made using SOFIA of which 89 were also identified by the two other methods. I used the sample of 174 visual detections with semi-automated counterparts as a Testbed to calculate the reliability and completeness achieved by SOFIA. The achieved reliability is ∼ 0.68 whereas completeness is ∼ 0.51. Further parameter fine-tuning is necessary to have a better handle on all SOFIA parameters and achieve higher reliability and completeness values.
- ItemOpen AccessThe Galaxy Velocity Function from MIGHTEE-HI Early Science Data(2021) Mulaudzi, Wanga; Frank, Bradley; Kraan-Korteweg, Renee ChristineThe velocity function of MIGHTEE-H I Early Science data is presented. This is the first velocity function that is based on a blind radio interferometric survey. As a precursor, understanding the systematics that affect the Early Science velocity function will optimise the full survey's analysis. PYMULTINEST and the Busy Function are employed to estimate the linewidths of the low spectral resolution data. The performance of PYMULTINEST in estimating known linewidths of simulated H I profiles with varying spectral resolution is assessed. The simulation study shows that the estimated linewidths of the Early Science data, using this novel method, are robust and are recovered within the uncertainty. The effects of cosmic variance, instrumental linewidth broadening and Doppler linewidth broadening on the velocity function are quantified within the context of the limitations of the Early Science data. The MIGHTEE-H I Early Science velocity function is compared with the velocity functions from previous large-scale H I surveys, namely the Arecibo Legacy Fast ALFA (ALFALFA) survey and the H I Parkes All-Sky Survey (HIPASS). There is general agreement with the ALFALFA and HIPASS results, when taking linewidth broadening into account, given that the MIGHTEE-H I Early Science data is strongly affected by cosmic variance. In particular, cosmic variance introduces an average uncertainty of ∼ 24% in the measured Early Science volume densities. The larger effective area of the full survey will reduce the impact of cosmic variance. The full survey velocity function can be further optimised by estimating the rotational velocities using kinematic modelling, and correcting the measured linewidths for instrumental broadening, Doppler broadening, turbulent motion and inclination effects.