Physical Sciences and Mathematics Commons^™

The Subaru Hsc Weak Lensing Mass-Observable Scaling Relations Of Spectroscopic Galaxy Groups From The Gama Survey, Divya Rana, Surhud More, Hironao Miyatake, Takahiro Nishimichi, Masahiro Takada, Aaron S G Robotham, Andrew M. Hopkins, Benne Holwerda

Faculty Scholarship

We utilize the galaxy shape catalogue from the first-year data release of the Subaru Hyper Suprime-Cam (HSC) survey to study the dark matter content of galaxy groups in the Universe using weak lensing. We use galaxy groups from the Galaxy Mass and Assembly galaxy survey in approximately 100 sq. degrees of the sky that overlap with the HSC survey as lenses. We restrict our analysis to the 1587 groups with at least five members. We divide these groups into six bins each of group luminosity and group member velocity dispersion and measure the lensing signal with a signal-to-noise ratio of …

Deep Extragalactic Visible Legacy Survey: Data Release 1 Blended Spectra Search For Candidate Strong Gravitational Lenses, Benne Holwerda, S Knabel, J E. Thorne, S Bellstedt, M Siudek, L J M Davies

Faculty Scholarship

Here, we present a catalogue of blended spectra in Data Release 1 of the Deep Extragalactic VIsible Legacy Survey (DEVILS) on the Anglo-Australian Telescope. Of the 23 197 spectra, 181 showed signs of a blend of redshifts and spectral templates. We examine these blends in detail for signs of either a candidate strong lensing galaxy or a useful overlapping galaxy pair. One of the three DEVILS target fields, COSMOS (D10), is close to complete and it is fully imaged with Hubble Space Telescope Advanced Camera for Surveys, and we visually examine the 57 blended spectra in this field in the …

Beyond The Local Volume. I. Surface Densities Of Ultracool Dwarfs In Deep Hst/Wfc3 Parallel Fields, Christian Aganze, Adam J. Burgasser, Mathew Malkan, Christopher A. Theissen, Roberto A. Tejada Arevalo, Chih-Chun Hsu, Daniella C. Bardalez Gagliuffi, Russell E. Ryan Jr., Benne Holwerda

Faculty Scholarship

Ultracool dwarf stars and brown dwarfs provide a unique probe of large-scale Galactic structure and evolution; however, until recently spectroscopic samples of sufficient size, depth, and fidelity have been unavailable. Here, we present the identification of 164 M7-T9 ultracool dwarfs in 0.6 deg2 of deep, low-resolution, near-infrared spectroscopic data obtained with the Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) instrument as part of the WFC3 Infrared Spectroscopic Parallel Survey and the 3D-HST survey. We describe the methodology by which we isolate ultracool dwarf candidates from over 200,000 spectra, and show that selection by machine-learning classification is superior to …

Galaxy And Mass Assembly (Gama): The Merging Potential Of Brightest Group Galaxies, K. Banks, S. Brough, Benne Holwerda, A. M. Hopkins, Á. R. López-Sánchez, S. Phillipps, K. A. Pimbblet, A. S. G. Robotham

Faculty Scholarship

Using a volume-limited sample of 550 groups from the Galaxy And Mass Assembly Galaxy Group Catalogue spanning the halo mass range , we investigate the merging potential of central Brightest Group Galaxies (BGGs). We use spectroscopically confirmed close-companion galaxies as an indication of the potential stellar mass buildup of low-redshift BGGs, z ≤ 0.2. We identify 17 close-companion galaxies with projected separations rp < 30 kpc, relative velocities Δv ≤ 300 km s−1, and stellar mass ratios MBGG/MCC ≤ 4 relative to the BGG. These close-companion galaxies yield a total pair fraction of 0.03 ± 0.01. Overall, we find that BGGs …

Measuring Cosmic Density Of Neutral Hydrogen Via Stacking The Dingo-Vla Data, Qingxiang Chen, Martin Meyer, Attila Popping, Lister Staveley-Smith, Julia Bryant, Jacinta Delhaize, Benne Holwerda, M E. Cluver, J Loveday, Angel R. Lopez-Sanchez, Martin Zwaan, E N. Taylor, A M. Hopkins, Angus Wright, Simon Driver, S Brough

Faculty Scholarship

We use the 21-cm emission-line data from the Deep Investigation of Neutral Gas Origin-Very Large Array (DINGO-VLA) project to study the atomic hydrogen gas H I of the Universe at redshifts z < 0.1. Results are obtained using a stacking analysis, combining the H I signals from 3622 galaxies extracted from 267 VLA pointings in the G09 field of the Galaxy and Mass Assembly Survey (GAMA). Rather than using a traditional one-dimensional spectral stacking method, a three-dimensional cubelet stacking method is used to enable deconvolution and the accurate recovery of average galaxy fluxes from this high-resolution interferometric data set. By probing down to galactic scales, this experiment also overcomes confusion corrections that have been necessary to include in previous single-dish studies. After stacking and deconvolution, we obtain a 30σ H I mass measurement from the stacked spectrum, indicating an average H I mass of MHI=(1.67±0.18)×109 M⊙" role="presentation" style="box-sizing: border-box; margin: 0px; padding: 0px; border: 0px; font-variant: inherit; font-stretch: inherit; line-height: normal; font-family: inherit; vertical-align: baseline; display: inline; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; position: relative;">MHI=(1.67±0.18)×109 M⊙MHI=(1.67±0.18)×109 M⊙⁠. The corresponding cosmic density of neutral atomic hydrogen is ΩHI=(0.38±0.04)×10−3" role="presentation" style="box-sizing: border-box; margin: 0px; padding: 0px; border: 0px; font-variant: inherit; font-stretch: inherit; line-height: normal; font-family: inherit; vertical-align: baseline; display: inline; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; position: relative;">ΩHI=(0.38±0.04)×10−3ΩHI=(0.38±0.04)×10−3 at redshift of z = 0.051. These values are in good agreement with …

Galaxy And Mass Assembly (Gama): The Environmental Impact On Sfr And Metallicity In Galaxy Groups, D Sotillo-Ramos, M A. Lara-López, A M. Pérez-García, R Pérez-Martínez, A M. Hopkins, Benne Holwerda, J Liske, A R. López-Sánchez, M S. Owers, K A. Pimbblet

Faculty Scholarship

We present a study of the relationships and environmental dependencies between stellar mass, star formation rate, and gas metallicity for more than 700 galaxies in groups up to redshift 0.35 from the Galaxy And Mass Assembly (GAMA) survey. To identify the main drivers, our sample was analysed as a function of group-centric distance, projected galaxy number density, and stellar mass. By using control samples of more than 16 000 star-forming field galaxies and volume-limited samples, we find that the highest enhancement in SFR (0.3 dex) occurs in galaxies with the lowest local density. In contrast to previous work, our data …

Galaxy And Mass Assembly (Gama), U. Sureshkumar, A. Durkalec, A. Pollo, M. Bilicki, J. Loveday, D. J. Farrow, Benne Holwerda, A. M. Hopkins, J. Liske, K. A. Pimbblet, E. N. Taylor, A. H. Wright

Faculty Scholarship

Context. Galaxies are biased tracers of the underlying network of dark matter. The strength of this bias depends on various galaxy properties and on redshift. One of the methods used to study these dependences of the bias is measurement of galaxy clustering. Such studies are made using galaxy samples from various catalogues, which frequently bear their own problems related to sample selection methods. It is therefore crucial to understand how sample choice influences clustering measurements and which galaxy property is the most direct tracer of the galaxy environment.

Aims. We investigate how different galaxy properties, such as luminosities in the …

Galaxy And Mass Assembly (Gama): The Clustering Of Galaxy Groups, S D. Riggs, R W Y M Barbhuiyan, J Loveday, S Brough, Benne Holwerda, A M. Hopkins, S Phillipps

Faculty Scholarship

We explore the clustering of galaxy groups in the Galaxy and Mass Assembly (GAMA) survey to investigate the dependence of group bias and profile on separation scale and group mass. Due to the inherent uncertainty in estimating the group selection function, and hence the group autocorrelation function, we instead measure the projected galaxy–group cross-correlation function. We find that the group profile has a strong dependence on scale and group mass on scales r⊥≲1h−1" role="presentation" style="box-sizing: border-box; margin: 0px; padding: 0px; border: 0px; font-variant: inherit; font-stretch: inherit; line-height: normal; font-family: inherit; vertical-align: baseline; display: inline; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; …

Tess As A Low-Surface-Brightness Observatory: Cutouts From Wide-Area Coadded Images, G. Bruce Berriman, John C. Good, Benne Holwerda

Faculty Scholarship

We present a mosaic of those co-added Full Frame Images acquired by the TESS satellite that had been released in 2020 April. The mosaic shows substantial stray light over the sky. Yet over spatial scales of a few degrees, the background appears uniform. This result indicates that TESS has considerable potential as a Low Surface Brightness Observatory. The co-added images are freely available as a High Level Science Product (HLSP) at MAST and accessible through a Jupyter Notebook.

Predicting The Spectrum Of Ugc 2885, Rubin’S Galaxy With Machine Learning, Benne Holwerda, John F. Wu, William C. Keel, Jason Young, Ren Mullins, Joannah Hinz, K. E. Saavik Ford, Pauline Barmby, Rupali Chandar, Jeremy Bailin, Josh Peek, Tim Pickering, Torsten Böker

Faculty Scholarship

Wu & Peek predict SDSS-quality spectra based on Pan-STARRS broadband grizy images using machine learning (ML). In this article, we test their prediction for a unique object, UGC 2885 ("Rubin's galaxy"), the largest and most massive, isolated disk galaxy in the local universe (D < 100 Mpc). After obtaining the ML predicted spectrum, we compare it to all existing spectroscopic information that is comparable to an SDSS spectrum of the central region: two archival spectra, one extracted from the VIRUS-P observations of this galaxy, and a new, targeted MMT/Binospec observation. Agreement is qualitatively good, though the ML prediction prefers line ratios slightly more toward those of an active galactic nucleus (AGN), compared to archival and VIRUS-P observed values. The MMT/Binospec nuclear spectrum unequivocally shows strong emission lines except Hβ, the ratios of which are consistent with AGN activity. The ML approach to galaxy spectra may be a viable way to identify AGN supplementing NIR colors. How such a massive disk galaxy (M* = 1011 M⊙), which uncharacteristically shows no sign of interaction or mergers, manages to fuel its central …

The Observable Supernova Rate In Galaxy–Galaxy Lensing Systems With The Tess Satellite, Benne Holwerda, S Knabel, R C. Steele, L Strolger, J Kielkopf, A Jacques, W Roemer

Faculty Scholarship

The Transiting Exoplanet Survey Satellite (TESS) is the latest observational effort to find exoplanets and map bright transient optical phenomena. Supernovae (SNe) are particularly interesting as cosmological standard candles for cosmological distance measures. The limiting magnitude of TESS strongly constrains SN detection to the very nearby Universe (m ∼ 19, z < 0.05). We explore the possibility that more distant SNe that are gravitationally lensed and magnified by a foreground galaxy can be detected by TESS, an opportunity to measure the time delay between light paths and constrain the Hubble constant independently. We estimate the rate of occurrence of such systems, assuming reasonable distributions of magnification, host dust attenuation, and redshift. There are approximately 16 Type Ia SNe (SNIa) and …

Deep Extragalactic Visible Legacy Survey (Devils): Sed Fitting In The D10-Cosmos Field And The Evolution Of The Stellar Mass Function And Sfr–M⋆ Relation, Jessica E. Thorne, Aaron S G Robotham, Luke J M Davies, Sabine Bellstedt, Simon P. Driver, Matías Bravo, Malcolm N. Bremer, Benne Holwerda, Andrew M. Hopkins, Claudia Del P Lagos, Steven Phillipps, Malgorzata Siudek, Edward N. Taylor, Angus H. Wright

Faculty Scholarship

We present catalogues of stellar masses, star formation rates (SFRs), and ancillary stellar population parameters for galaxies spanning 0 < z < 9 from the Deep Extragalactic VIsible Legacy Survey (DEVILS). DEVILS is a deep spectroscopic redshift survey with very high completeness, covering several premier deep fields including COSMOS (D10). Our stellar mass and SFR estimates are self-consistently derived using the spectral energy distribution (SED) modelling code PROSPECT, using well-motivated parametrizations for dust attenuation, star formation histories, and metallicity evolution. We show how these improvements, and especially our physically motivated assumptions about metallicity evolution, have an appreciable systematic effect on the inferred stellar masses, at the level of ∼0.2 dex. To illustrate the scientific value of these data, we map the evolving galaxy stellar mass function (SMF) and the SFR–M_⋆ relation for 0 < z < 4.25. In agreement with past studies, we find that most of the evolution in the SMF is driven by the characteristic density parameter, with little evolution in the characteristic mass and low-mass slopes. Where the SFR–M_⋆ relation is indistinguishable from a power law at z > 2.6, we see evidence of a bend in the relation at low redshifts (z < 0.45). This suggests evolution in both the normalization and shape of the SFR–M_⋆ relation since cosmic noon. It is significant that we only clearly see this bend when combining our new DEVILS measurements with consistently derived values for lower redshift galaxies from the Galaxy And Mass Assembly (GAMA) survey: this shows the power of …

Galaxy And Mass Assembly (Gama): The Inferred Mass–Metallicity Relation From Z = 0 To 3.5 Via Forensic Sed Fitting, Sabine Bellstedt, Aaron S G Robotham, Simon P. Driver, Jessica E. Thorne, Luke J M Davies, Benne Holwerda, Andrew M. Hopkins, Maritza A. Lara-Lopez, Ángel R. López-Sánchez, Steven Phillipps

Faculty Scholarship

We analyse the metallicity histories of ∼4500 galaxies from the GAMA survey at z < 0.06 modelled by the SED-fitting code PROSPECT using an evolving metallicity implementation. These metallicity histories, in combination with the associated star formation histories, allow us to analyse the inferred gas-phase mass–metallicity relation. Furthermore, we extract the mass– metallicity relation at a sequence of epochs in cosmic history, to track the evolving mass–metallicity relation with time. Through comparison with observations of gas-phase metallicity over a large range of redshifts, we show that, remarkably, our forensic SED analysis has produced an evolving mass–metallicity relationship that is consistent with observations at all epochs. We additionally analyse the three-dimensional mass–metallicity–SFR space, showing that galaxies occupy a clearly defined plane. This plane is shown to be subtly evolving, displaying an increased tilt with time caused by general enrichment, and also the slowing down of star formation with cosmic time. This evolution is most apparent at lookback times greater than 7 Gyr. The trends in metallicity recovered in this work highlight that the evolving metallicity implementation used within the SED-fitting code PROSPECT produces reasonable metallicity results over the history of a galaxy. This is expected to provide a significant improvement to the accuracy of the SED-fitting outputs.

Galaxy And Mass Assembly: Group And Field Galaxy Morphologies In The Star-Formation Rate - Stellar Mass Plane, W. J. Pearson, L. Wang, S. Brough, Benne Holwerda, A. M. Hopkins, J. Loveday

Faculty Scholarship

Aims. We study the environment in which a galaxy lies (i.e. field or group) and its connection with the morphology of the galaxy. This is done by examining the distribution of parametric and non-parametric statistics across the star-formation rate (SFR) - stellar mass (M?) plane and studying how these distributions change with the environment in the local universe (z < 0.15). Methods. We determine the concentration (C), Gini, M20, asymmetry, Gini-M20 bulge statistic (GMB), 50% light radius (r50), total Sérsic index, and bulge Sérsic index (nBulge) for galaxies from the Galaxy and Mass Assembly (GAMA) survey using optical images from the Kilo Degree Survey. We determine the galaxy environment using the GAMA group catalogue and split the galaxies into field or group galaxies. The group galaxies are further divided by the group halo mass (Mh) - 11 ≤ log(Mh /M*) < 12, 12 ≤ log(Mh /M*) < 13, and 13 ≤ log(Mh /M*) < 14 - and into central and satellite galaxies. The galaxies in each of these samples are then placed onto the SFR-M? plane, and each parameter is used as a third dimension. We fit the resulting distributions for each parameter in each sample using two two-dimensional Gaussian distributions: one for star-forming galaxies and one for quiescent galaxies. The coefficients of these Gaussian fits are then compared between environments. Results. Using C and r50, we find that galaxies typically become larger as the group mass increases. This change is greater for larger galaxies. There is no indication that galaxies are typically more or less clumpy as the environment changes. Using GMB and nBulge , we see that the star-forming galaxies do not become more bulge or disk dominated as the group mass changes. Asymmetry does not appear to be greatly influenced by environment.

Galaxy And Mass Assembly (Gama): The Interplay Between Galaxy Mass, Sfr, And Heavy Element Abundance In Paired Galaxy Sets, L. E. Garduno, M. A. Lara-Lopez, O. Lopez-Cruz, A. M. Hopkins, M. S. Owers, K. A. Pimbblet, Benne Holwerda

Faculty Scholarship

We study the star formation rate (SFR), stellar mass (M), and the gas metallicity (Z) for 4636 galaxy pairs using the Galaxy And Mass Assembly (GAMA) survey. Our galaxy pairs lie in a redshift range of 0

Galaxy And Mass Assembly (Gama): A Wise Study Of The Activity Of Emission-Line Systems In G23, H. F.M. Yao, T. H. Jarrett, M. E. Cluver, L. Marchetti, Edward N. Taylor, M. G. Santos, Matt S. Owers, Angel R. Lopez-Sanchez, Y. A. Gordon, M. J.I. Brown, S. Brough, S. Phillipps, Benne Holwerda, A. M. Hopkins, L. Wang

Faculty Scholarship

We present a detailed study of emission-line systems in the Galaxy And Mass Assembly (GAMA) G23 region, making use of Wide-field Infrared Survey Explorer (WISE) photometry that includes carefully measured resolved sources. After applying several cuts to the initial catalog of. 41,000 galaxies, we extract a sample of 9809 galaxies. We then compare the spectral diagnostic Baldwin, Philips & Terlevich (BPT) classification of 1154 emission-line galaxies (38% resolved in W1) to their location in the WISE color-color diagram, leading to the creation of a new zone for mid-infrared "warm"galaxies located 2μm above the star-forming sequence, below the standard WISE active …

Galaxy And Mass Assembly: A Comparison Between Galaxy⇓Galaxy Lens Searches In Kids/Gama, Shawn Knabel, Rebecca L. Steele, Benne W. Holwerda, Joanna S. Bridge, Alice Jacques, Andrew M. Hopkins, Stephen P. Bamford, Michael J.I. Brown, Sarah Brough, Lee Kelvin, Maciej Bilicki, John Kielkopf

Faculty Scholarship

Strong gravitational lenses are a rare and instructive type of astronomical object. Identification has long relied on serendipity, but different strategies—such as mixed spectroscopy of multiple galaxies along the line of sight, machine-learning algorithms, and citizen science—have been employed to identify these objects as new imaging surveys become available. We report on the comparison between spectroscopic, machine-learning, and citizen-science identification of galaxy–galaxy lens candidates from independently constructed lens catalogs in the common survey area of the equatorial fields of the Galaxy and Mass Assembly survey. In these, we have the opportunity to compare high completeness spectroscopic identifications against high-fidelity imaging …

Galaxy And Mass Assembly: Luminosity And Stellar Mass Functions In Gama Groups, J. A. Vazquez-Mata, J. Loveday, S. D. Riggs, I. K. Baldry, L. J.M. Davies, A. S.G. Robotham, Benne W. Holwerda, M. J.I. Brown, M. E. Cluver, L. Wang, M. Alpaslan, J. Bland-Hawthorn, S. Brough, S. P. Driver, A. M. Hopkins, E. N. Taylor, A. H. Wright

Faculty Scholarship

How do galaxy properties (such as stellar mass, luminosity, star formation rate, and morphology) and their evolution depend on the mass of their host dark matter halo? Using the Galaxy and Mass Assembly group catalogue, we address this question by exploring the dependence on host halo mass of the luminosity function (LF) and stellar mass function (SMF) for grouped galaxies subdivided by colour, morphology, and central/satellite. We find that spheroidal galaxies in particular dominate the bright and massive ends of the LF and SMF, respectively. More massive haloes host more massive and more luminous central galaxies. The satellites LF and …

The Sizes Of Z ∼ 9-10 Galaxies Identified In The Brightest Of Reionizing Galaxies (Borg) Survey, Benne W. Holwerda, Joanna S. Bridge, Rebecca L. Steele, Samir Kusmic, Larry Bradley, Rachael Livermore, Stephanie Bernard, Alice Jacques

Faculty Scholarship

Redshift z = 9-10 object selection is the effective limit of Hubble Space Telescope (HST) imaging capability, even when confirmed with Spitzer. If only a few photometry data points are available, it becomes attractive to add criteria based on their morphology in these J- and H-band images. One could do so through visual inspection, a size criterion, or alternate morphometrics. We explore a vetted sample of Brightest of Reionizing Galaxies (BoRG) z ∼ 9 and z ∼ 10 candidate galaxies and the object rejected by Morishita+ to explore the utility of a size criterion in z = 9-10 candidate selection. …

Is Ngc 300 A Pure Exponential Disk Galaxy?, In Sung Jang, Roelof S. De Jong, Ivan Minchev, Eric F. Bell, Antonela Monachesi, Benne W. Holwerda, Jeremy Bailin, Adam Smercina, Richard D'Souza

Faculty Scholarship

NGC 300 is a low-mass disk galaxy in the Sculptor group. In the literature, it has been identified as a pure exponential disk galaxy, as its luminosity profile can be well fit with a single exponential law over many disk scale lengths (Type I). We investigate the stellar luminosity distribution of NGC 300 using Hubble Space Telescope archive data, reaching farther and deeper than any other previous studies. Color-magnitude diagrams show a significant population of old red giant branch (RGB) stars in all fields out to R ∼ 19 kpc (32′), as well as younger populations in the inner regions. …

Galaxy And Mass Assembly (Gama): Demonstrating The Power Of Wise In The Study Of Galaxy Groups To Z < 0.1, M. E. Cluver, T. H. Jarrett, E. N. Taylor, A. M. Hopkins, S. Brough, S. Casura, B. W. Holwerda, J. Liske, K. A. Pimbblet, A. H. Wright

Faculty Scholarship

Combining high-fidelity group characterization from the Galaxy and Mass Assembly survey and source-tailored z < 0.1 photometry from the Wide-Field Infrared Survey Explorer (WISE) survey, we present a comprehensive study of the properties of ungrouped galaxies, compared to 497 galaxy groups (4 ≤ N FoF ≤ 20) as a function of stellar and halo mass. Ungrouped galaxies are largely unimodal in WISE color, the result of being dominated by star-forming, late-type galaxies. Grouped galaxies, however, show a clear bimodality in WISE color, which correlates strongly with stellar mass and morphology. We find evidence for an increasing early-type fraction, in stellar mass bins between 1010 M o˙ ≲ M stellar ≲ 1011 M o˙, with increasing halo mass. Using ungrouped, late-type galaxies with star-forming colors (W2-W3 > 3), we define a star-forming main sequence (SFMS), which we use to delineate systems that have moved below the sequence ("quenched"for the purposes of this work). We find that with increasing halo mass, the relative number of late-type systems on the SFMS decreases, with a corresponding increase in early-type, quenched systems at high stellar mass (M stellar > 1010.5 M o˙), consistent with mass quenching. Group galaxies with masses M stellar < 1010.5 M o˙ show evidence of quenching consistent with environmentally driven processes. The stellar mass distribution of late-type, quenched galaxies suggests that it may be an intermediate population as systems transition from being star-forming and late-type to the "red sequence."Finally, we use the projected area of groups on the sky to extract groups that are (relatively) compact for their halo mass. Although these show a marginal increase in their proportion of high-mass and early-type galaxies compared to nominal groups, a clear increase in quenched fraction is not evident.

Wallaby – An Ska Pathfinder H I Survey, Bärbel S. Koribalski, L. Staveley-Smith, T. Westmeier, P. Serra, K. Spekkens, O. I. Wong, K. Lee-Waddell, C. D.P. Lagos, D. Obreschkow, E. V. Ryan-Weber, M. Zwaan, V. Kilborn, G. Bekiaris, K. Bekki, F. Bigiel, A. Boselli, A. Bosma, B. Catinella, G. Chauhan, M. E. Cluver, M. Colless, H. M. Courtois, R. A. Crain, W. J.G. De Blok, H. Dénes, A. R. Duffy, A. Elagali, C. J. Fluke, B. Q. For, G. Heald, P. A. Henning, K. M. Hess, Benne W. Holwerda

Faculty Scholarship

The Widefield ASKAP L-band Legacy All-sky Blind surveY (wallaby) is a next-generation survey of neutral hydrogen (H i) in the Local Universe. It uses the widefield, high-resolution capability of the Australian Square Kilometer Array Pathfinder (ASKAP), a radio interferometer consisting of 36 × 12 -m dishes equipped with Phased-Array Feeds (PAFs), located in an extremely radio-quiet zone in Western Australia. wallaby aims to survey three-quarters of the sky (− 90 ∘< δ< + 30 ∘) to a redshift of z≲ 0.26 , and generate spectral line image cubes at ∼30 arcsec resolution and ∼1.6 mJy beam−1 per 4 km s−1 channel sensitivity. ASKAP’s instantaneous field of view at 1.4 GHz, delivered by the PAF’s 36 beams, is about 30 sq deg. At an integrated signal-to-noise ratio of five, wallaby is expected to detect around half a million galaxies with a mean redshift of z∼ 0.05 (∼200 Mpc). The scientific goals of wallaby include: (a) a census of gas-rich galaxies in the vicinity of the Local Group; (b) a study of the H i properties of galaxies, groups and clusters, in particular the influence of the environment on galaxy evolution; and (c) the refinement of cosmological parameters using the spatial and redshift distribution of low-bias gas-rich galaxies. For context we provide an overview of recent and planned large-scale H i surveys. Combined with existing and new multi-wavelength sky surveys, wallaby will enable an exciting new generation of panchromatic studies of the Local Universe. — First results from the wallaby pilot survey are revealed, with initial data products publicly available in the CSIRO ASKAP Science Data Archive (CASDA).

Mergers Trigger Active Galactic Nuclei Out To Z ∼0.6, F. Gao, L. Wang, W. J. Pearson, Y. A. Gordon, Benne W. Holwerda, A. M. Hopkins, M. J.I. Brown, J. Bland-Hawthorn, M. S. Owers

Faculty Scholarship

Aims. The fueling and feedback of active galactic nuclei (AGNs) are important for understanding the co-evolution between black holes and host galaxies. Mergers are thought to have the capability to bring gas inward and ignite nuclear activity, especially for more powerful AGNs. However, there is still significant ongoing debate on whether mergers can trigger AGNs and, if they do, whether mergers are a significant triggering mechanism. Methods. We selected a low-redshift (0.005  <   z  <   0.1) sample from the Sloan Digital Sky Survey and a high-redshift (0  <   z  <   0.6) sample from the Galaxy And Mass Assembly survey. We took advantage of the convolutional neural network technique to identify mergers. We used mid-infrared (MIR) color cut and optical emission line diagnostics to classify AGNs. We also included low excitation radio galaxies (LERGs) to investigate the connection between mergers and low accretion rate AGNs. Results. We find that AGNs are more likely to be found in mergers than non-mergers, with an AGN excess up to 1.81 ± 0.16, suggesting that mergers can trigger AGNs. We also find that the fraction of mergers in AGNs is higher than that in non-AGN controls, for both MIR and optically selected AGNs, as well as LERGs, with values between 16.40 ± 0.5% and 39.23 ± 2.10%, implying a non-negligible to potentially significant role of mergers in triggering AGNs. This merger fraction in AGNs increases as stellar mass increases, which supports the idea that mergers are more important for triggering AGNs in more massive galaxies. In terms of merger fraction as a function of AGN power we find a positive trend for MIR selected AGNs and a complex trend for optically selected AGNs, which we interpret under an evolutionary scenario proposed by previous studies. In addition, obscured MIR selected AGNs are more likely to be hosted in mergers than unobscured MIR selected AGNs.

Tracing The Anemic Stellar Halo Of M 101, In Sung Jang, Roelof S. De Jong, Benne W. Holwerda, Antonela Monachesi, Eric F. Bell, Jeremy Bailin

Faculty Scholarship

Models of galaxy formation in a cosmological context predict that massive disk galaxies should have structured extended stellar halos. Recent studies in integrated light, however, report that a few galaxies, including the nearby disk galaxy M 101, have no measurable stellar halos to the detection limit. We aim to quantify the stellar content and structure of M 101's outskirts by resolving its stars. We present the photometry of its stars based on deep F606W and F814W images taken with Hubble Space Telescope (HST) as part of the GHOSTS survey. The HST fields are placed along the east and west sides …

Galaxy And Mass Assembly (Gama): Defining Passive Galaxy Samples And Searching For The Uv Upturn, S. Phillipps, S. S. Ali, M. N. Bremer, R. De Propris, A. E. Sansom, M. E. Cluver, M. Alpaslan, S. Brough, M. J.I. Brown, L. J.M. Davies, S. P. Driver, M. W. Grootes, Benne W. Holwerda, A. M. Hopkins, P. A. James, K. Pimbblet, A. S.G. Robotham, E. N. Taylor, L. Wang

Faculty Scholarship

We use data from the GAMA and GALEX surveys to demonstrate that the UV upturn, an unexpected excess of ultraviolet flux from a hot stellar component, seen in the spectra of many early-type galaxies, arises from processes internal to individual galaxies with no measurable influence from the galaxies' larger environment. We first define a clean sample of passive galaxies without a significant contribution to their UV flux from low-level star formation. We confirm that galaxies with the optical colours of red sequence galaxies often have signs of residual star formation, which, without other information, would prevent a convincing demonstration of …

Galaxy And Mass Assembly (Gama): Properties And Evolution Of Red Spiral Galaxies, Smriti Mahajan, Kriti Kamal Gupta, Rahul Rana, M. J.I. Brown, S. Phillipps, Joss Bland-Hawthorn, M. N. Bremer, S. Brough, Benne W. Holwerda, A. M. Hopkins, J. Loveday, Kevin Pimbblet, Lingyu Wang

Faculty Scholarship

We use multiwavelength data from the Galaxy And Mass Assembly (GAMA) survey to explore the cause of red optical colours in nearby (0.002 < z < 0.06) spiral galaxies. We show that the colours of red spiral galaxies are a direct consequence of some environment-related mechanism(s) that has removed dust and gas, leading to a lower star formation rate. We conclude that this process acts on long time-scales (several Gyr) due to a lack of morphological transformation associated with the transition in optical colour. The specific star formation rate (sSFR) and dust-to-stellar mass ratio of red spiral galaxies is found to be statistically lower than blue spiral galaxies. On the other hand, red spirals are on average 0.9 dex more massive, and reside in environments 2.6 times denser than their blue counterparts. We find no evidence of excessive nuclear activity, or higher inclination angles to support these as the major causes for the red optical colours seen in ≳47 per cent of all spirals in our sample. Furthermore, for a small subsample of our spiral galaxies that are detected in H I, we find that the SFR of gas-rich red spiral galaxies is lower by ∼1 dex than their blue counterparts.

Effect Of Galaxy Mergers On Star-Formation Rates, W. J. Pearson, L. Wang, M. Alpaslan, I. Baldry, M. Bilicki, M. J.I. Brown, M. W. Grootes, Benne W. Holwerda, T. D. Kitching, S. Kruk, F. F.S. Van Der Tak

Faculty Scholarship

Context. Galaxy mergers and interactions are an integral part of our basic understanding of how galaxies grow and evolve over time. However, the effect that galaxy mergers have on star-formation rates (SFRs) is contested, with observations of galaxy mergers showing reduced, enhanced, and highly enhanced star formation. Aims. We aim to determine the effect of galaxy mergers on the SFR of galaxies using statistically large samples of galaxies, totalling over 200 000, which is over a large redshift range from 0.0 to 4.0. Methods. We trained and used convolutional neural networks to create binary merger identifications (merger or non-merger) in …

Default Parallels: The Science Potential Of Jwst Parallel Observations During Tso Primary Observations, Benne W. Holwerda, Jonathan Fraine, Nelly Mouawad, Joanna S. Bridge

Faculty Scholarship

The James Webb Space Telescope (JWST) will observe several stars for long cumulative durations while pursuing exoplanets as primary science targets for both Guaranteed Time Observations (GTO) and very likely General Observer (GO) programs. Here we argue in favor of an automatic default parallel program to observe, e.g., using the F200W/F277W filters or grism of NIRCAM/NIRISS in order to find high redshift (z (Formula Presented) 10) galaxies, cool red/brown dwarf substellar objects, solar system objects, and observations of serendipitous planetary transits. We argue here the need for automated exploratory astrophysical observations with unused JWST instruments during these long-duration exoplanet observations. …

Star-Forming, Rotating Spheroidal Galaxies In The Gama And Sami Surveys, Amanda J. Moffett, Steven Phillipps, Aaron S.G. Robotham, Simon P. Driver, Malcolm N. Bremer, Luca Cortese, O. Ivy Wong, Sarah Brough, Michael J.I. Brown, Julia J. Bryant, Christopher J. Conselice, Scott M. Croom, Koshy George, Greg Goldstein, Michael Goodwin, Benne W. Holwerda, Andrew M. Hopkins, Iraklis S. Konstantopoulos, Jon S. Lawrence, Nuria P.F. Lorente, Anne M. Medling, Matt S. Owers, Kevin A. Pimbblet, Samuel N. Richards, Sarah M. Sweet, Jesse Van De Sande

Faculty Scholarship

The Galaxy And Mass Assembly (GAMA) survey has morphologically identified a class of 'Little Blue Spheroid' (LBS) galaxies whose relationship to other classes of galaxies we now examine in detail. Considering a sample of 868 LBSs, we find that such galaxies display similar but not identical colours, specific star formation rates, stellar population ages, massto- light ratios, and metallicities to Sd-Irr galaxies. We also find that LBSs typically occupy environments of even lower density than those of Sd-Irr galaxies, where ∼65 per cent of LBS galaxies live in isolation. Using deep, high-resolution imaging from VST KiDS and the new Bayesian, …

The Super Eight Galaxies: Properties Of A Sample Of Very Bright Galaxies At 7 < Z < 8, Joanna S. Bridge, Benne W. Holwerda, Mauro Stefanon, Rychard J. Bouwens, Pascal A. Oesch, Michele Trenti, Stephanie R. Bernard, Larry D. Bradley, Garth D. Illingworth, Samir Kusmic, Dan Magee, Takahiro Morishita, Guido W. Roberts-Borsani, Renske Smit, Rebecca L. Steele

Faculty Scholarship

We present the Super Eight galaxies - a set of very luminous, high-redshift (7.1 < z < 8.0) galaxy candidates found in the Brightest of Reionizing Galaxies (BoRG) Survey fields. The original sample includes eight galaxies that are Y-band dropout objects with H-band magnitudes of m H < 25.5. Four of these objects were originally reported in Calvi et al. Combining new Hubble Space Telescope (HST) WFC3/F814W imaging and Spitzer IRAC data with archival imaging from BoRG and other surveys, we explore the properties of these galaxies. Photometric redshift fitting places six of these galaxies in the redshift range of 7.1 < z < 8.0, resulting in three new high-redshift galaxies and confirming three of the four high-redshift galaxy candidates from Calvi et al. We calculate the half-light radii of the Super Eight galaxies using the HST F160W filter and find that the Super Eight sizes are in line with the typical evolution of size with redshift. The Super Eights have a mean mass of log (M ∗/M o) ∼10, which is typical for sources in this luminosity range. Finally, we place our sample on the UV z ∼ 8 luminosity function and find that the Super Eight number density is consistent with other surveys in this magnitude and redshift range.