arXiv subjects

J. S. Lawrence

Publications and source records attributed to J. S. Lawrence.

At least 37 records · Page 2Linked to original sources

arXiv2017

The KMOS Redshift One Spectroscopic Survey (KROSS): the origin of disk turbulence in z~0.9 star-forming galaxies

We analyse the velocity dispersion properties of 472 z~0.9 star-forming galaxies observed as part of the KMOS Redshift One Spectroscopic Survey (KROSS). The majority of this sample is rotationally dominated (83 +/- 5% with v_C/sigma_0 > 1) but also dynamically hot and highly turbulent. After correcting for beam smearing effects, the median intrinsic velocity dispersion for the final sample is sigma_0 = 43.2 +/- 0.8 km/s with a rotational velocity to dispersion ratio of v_C/sigma_0 = 2.6 +/- 0.1. To explore the relationship between velocity dispersion, stellar mass, star formation rate and redshift we combine KROSS with data from the SAMI survey (z~0.05) and an intermediate redshift MUSE sample (z~0.5). While there is, at most, a weak trend between velocity dispersion and stellar mass, at fixed mass there is a strong increase with redshift. At all redshifts, galaxies appear to follow the same weak trend of increasing velocity dispersion with star formation rate. Our results are consistent with an evolution of galaxy dynamics driven by disks that are more gas rich, and increasingly gravitationally unstable, as a function of increasing redshift. Finally, we test two analytic models that predict turbulence is driven by either gravitational instabilities or stellar feedback. Both provide an adequate description of the data, and further observations are required to rule out either model.

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arXiv2017

Self-consistent bulge/disk/halo galaxy dynamical modeling using integral field kinematics

We introduce a method for modeling disk galaxies designed to take full advantage of data from integral field spectroscopy (IFS). The method fits equilibrium models to simultaneously reproduce the surface brightness, rotation and velocity dispersion profiles of a galaxy. The models are fully self-consistent 6D distribution functions for a galaxy with a Sersic-profile stellar bulge, exponential disk and parametric dark matter halo, generated by an updated version of GalactICS. By creating realistic flux-weighted maps of the kinematic moments (flux, mean velocity and dispersion), we simultaneously fit photometric and spectroscopic data using both maximum-likelihood and Bayesian (MCMC) techniques. We apply the method to a GAMA spiral galaxy (G79635) with kinematics from the SAMI Galaxy Survey and deep $g$- and $r$-band photometry from the VST-KiDS survey, comparing parameter constraints with those from traditional 2D bulge-disk decomposition. Our method returns broadly consistent results for shared parameters, while constraining the mass-to-light ratios of stellar components and reproducing the HI-inferred circular velocity well beyond the limits of the SAMI data. While the method is tailored for fitting integral field kinematic data, it can use other dynamical constraints like central fibre dispersions and \HI circular velocities, and is well-suited for modelling galaxies with a combination of deep imaging and HI and/or optical spectra (resolved or otherwise). Our implementation (MagRite) is computationally efficient and can generate well-resolved models and kinematic maps in under a minute on modern processors.

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arXiv2017

The SAMI Galaxy Survey: understanding observations of large-scale outflows at low redshift with EAGLE simulations

This work presents a study of galactic outflows driven by stellar feedback. We extract main sequence disc galaxies with stellar mass $10^9\le$ M$_{\star}/$M$_{\odot} \le 5.7\times10^{10}$ at redshift $z=0$ from the highest resolution cosmological simulation of the Evolution and Assembly of GaLaxies and their Environments (EAGLE) set. Synthetic gas rotation velocity and velocity dispersion ($σ$) maps are created and compared to observations of disc galaxies obtained with the Sydney-AAO Multi-object Integral field spectrograph (SAMI), where $σ$-values greater than $150$ km s$^{-1}$ are most naturally explained by bipolar outflows powered by starburst activity. We find that the extension of the simulated edge-on (pixelated) velocity dispersion probability distribution depends on stellar mass and star formation rate surface density ($Σ_{\rm SFR}$), with low-M$_{\star}/$low-$Σ_{\rm SFR}$ galaxies showing a narrow peak at low $σ$ ($\sim30$ km s$^{-1}$) and more active, high-M$_{\star}/$high-$Σ_{\rm SFR}$ galaxies reaching $σ>150$ km s$^{-1}$. Although supernova-driven galactic winds in the EAGLE simulations may not entrain enough gas with T $<10^5$ K compared to observed galaxies, we find that gas temperature is a good proxy for the presence of outflows. There is a direct correlation between the thermal state of the gas and its state of motion as described by the $σ$-distribution. The following equivalence relations hold in EAGLE: $i)$ low-$σ$ peak $\,\Leftrightarrow\,$ disc of the galaxy $\,\Leftrightarrow\,$ gas with T $<10^5$ K; $ii)$ high-$σ$ tail $\,\Leftrightarrow\,$ galactic winds $\,\Leftrightarrow\,$ gas with T $\ge 10^5$ K.

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arXiv2017

The SAMI Galaxy Survey: Data Release One with Emission-line Physics Value-Added Products

We present the first major release of data from the SAMI Galaxy Survey. This data release focuses on the emission-line physics of galaxies. Data Release One includes data for 772 galaxies, about 20% of the full survey. Galaxies included have the redshift range 0.004 < z < 0.092, a large mass range (7.6 < log(Mstellar/M$_\odot$) < 11.6), and star-formation rates of 10^-4 to 10^1\ M$_\odot$/yr. For each galaxy, we include two spectral cubes and a set of spatially resolved 2D maps: single- and multi-component emission-line fits (with dust extinction corrections for strong lines), local dust extinction and star-formation rate. Calibration of the fibre throughputs, fluxes and differential-atmospheric-refraction has been improved over the Early Data Release. The data have average spatial resolution of 2.16 arcsec (FWHM) over the 15~arcsec diameter field of view and spectral (kinematic) resolution R=4263 (sigma=30km/s) around Halpha. The relative flux calibration is better than 5\% and absolute flux calibration better than $\pm0.22$~mag, with the latter estimate limited by galaxy photometry. The data are presented online through the Australian Astronomical Observatory's Data Central.

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arXiv2017

The SAMI Galaxy Survey: Disk-halo interactions in radio-selected star-forming galaxies

In this paper, we compare the radio emission at 1.4 GHz with optical outflow signatures of edge-on galaxies. We report observations of six edge-on star-forming galaxies in the Sydney-AAO Multi-object Integral-field spectrograph (SAMI) Galaxy Survey with 1.4 GHz luminosities $> 1\times10^{21}$ W Hz$^{-1}$. Extended minor axis optical emission is detected with enhanced \nii/H$α$ line ratios and velocity dispersions consistent with galactic winds in three of six galaxies. These galaxies may host outflows driven by a combination of thermal and cosmic ray processes. We find that galaxies with the strongest wind signatures have extended radio morphologies. Our results form a baseline for understanding the driving mechanisms of galactic winds.

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arXiv2017

Modal noise in an integrated photonic lantern fed diffraction-limited spectrograph

In an attempt to develop a streamlined astrophotonic instrument, we demonstrate the realization of an all-photonic device capable of both multimode to single mode conversion and spectral dispersion on an 8-m class telescope with efficient coupling. The device was a monolithic photonic spectrograph which combined an integrated photonic lantern, and an efficient arrayed waveguide grating device. During on-sky testing, we discovered a previously unreported type of noise that made spectral extraction and calibration extremely difficult. The source of the noise was traced to a wavelength-dependent loss mechanism between the feed fiber's multimode near-field pattern, and the modal acceptance profile of the integrated photonic lantern. Extensive modeling of the photonic components replicates the wavelength-dependent loss, and demonstrates an identical effect on the final spectral output. We outline that this could be mitigated by directly injecting into the integrated photonic lantern.

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arXiv2017

The SAMI Galaxy Survey: energy sources of the turbulent velocity dispersion in spatially-resolved local star-forming galaxies

We investigate the energy sources of random turbulent motions of ionised gas from H$α$ emission in eight local star-forming galaxies from the Sydney-AAO Multi-object Integral field spectrograph (SAMI) Galaxy Survey. These galaxies satisfy strict pure star-forming selection criteria to avoid contamination from active galactic nuclei (AGN) or strong shocks/outflows. Using the relatively high spatial and spectral resolution of SAMI, we find that -- on sub-kpc scales our galaxies display a flat distribution of ionised gas velocity dispersion as a function of star formation rate (SFR) surface density. A major fraction of our SAMI galaxies shows higher velocity dispersion than predictions by feedback-driven models, especially at the low SFR surface density end. Our results suggest that additional sources beyond star formation feedback contribute to driving random motions of the interstellar medium (ISM) in star-forming galaxies. We speculate that gravity, galactic shear, and/or magnetorotational instability (MRI) may be additional driving sources of turbulence in these galaxies.

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arXiv2017

The SAMI Galaxy Survey: mass as the driver of the kinematic morphology - density relation in clusters

We examine the kinematic morphology of early-type galaxies (ETGs) in eight galaxy clusters in the Sydney-AAO Multi-object Integral field spectrograph (SAMI) Galaxy Survey. The clusters cover a mass range of 14.2<log(M_200/M_odot)<15.2 and we measure spatially-resolved stellar kinematics for 315 member galaxies with stellar masses 10.0<log(M_*/M_odot)<11.7 within 1R_200 of the cluster centers. We calculate the spin parameter, lambda_R and use that to classify the kinematic morphology of the galaxies as fast or slow rotators. The total fraction of slow rotators in the early-type galaxy population, F_SR=0.14+/-0.02 and does not depend on host cluster mass. Across the eight clusters, the fraction of slow rotators increases with increasing local overdensity. We also find that the slow-rotator fraction increases at small clustercentric radii (R_cl<0.3R_200), and note that there is also an increase in slow-rotator fraction at R_cl~0.6R_200. The slow rotators at these larger radii reside in cluster substructure. We find the strongest increase in slow-rotator fraction occurs with increasing stellar mass. After accounting for the strong correlation with stellar mass, we find no significant relationship between spin parameter and local overdensity in the cluster environment. We conclude that the primary driver for the kinematic morphology--density relationship in galaxy clusters is the changing distribution of galaxy stellar mass with local environment. The presence of slow rotators in substructure suggests that the cluster kinematic morphology--density relationship is a result of mass segregation of slow-rotating galaxies forming in groups that later merge with clusters and sink to the cluster center via dynamical friction.

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arXiv2017

The SAMI Galaxy Survey: Kinematics of Dusty Early-Type Galaxies

Recently, large samples of visually classified early-type galaxies (ETGs) containing dust have been identified using space-based infrared observations with the Herschel Space Telescope. The presence of large quantities of dust in massive ETGs is peculiar as X-ray halos of these galaxies are expected to destroy dust in 10 Myr (or less). This has sparked a debate regarding the origin of the dust: is it internally produced by asymptotic giant branch (AGB) stars, or is it accreted externally through mergers? We examine the 2D stellar and ionised gas kinematics of dusty ETGs using IFS observations from the SAMI galaxy survey, and integrated star-formation rates, stellar masses, and dust masses from the GAMA survey. Only 8% (4/49) of visually-classified ETGs are kinematically consistent with being dispersion-supported systems. These "dispersion-dominated galaxies" exhibit discrepancies between stellar and ionised gas kinematics, either offsets in the kinematic position angle or large differences in the rotational velocity, and are outliers in star-formation rate at a fixed dust mass compared to normal star-forming galaxies. These properties are suggestive of recent merger activity. The remaining 90% of dusty ETGs have low velocity dispersions and/or large circular velocities, typical of "rotation-dominated galaxies". These results, along with the general evidence of published works on X-ray emission in ETGs, suggest that they are unlikely to host hot, X-ray gas consistent with their low stellar mass when compared to dispersion-dominated galaxies. This means dust will be long lived and thus these galaxies do not require external scenarios for the origin of their dust content.

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arXiv2017

The SAMI Galaxy Survey: The cluster redshift survey, target selection and cluster properties

We describe the selection of galaxies targeted in eight low redshift clusters (APMCC0917, A168, A4038, EDCC442, A3880, A2399, A119 and A85; $0.029 < z < 0.058$) as part of the Sydney-AAO Multi-Object integral field Spectrograph Galaxy Survey (SAMI-GS). We have conducted a redshift survey of these clusters using the AAOmega multi-object spectrograph on the 3.9m Anglo-Australian Telescope. The redshift survey is used to determine cluster membership and to characterise the dynamical properties of the clusters. In combination with existing data, the survey resulted in 21,257 reliable redshift measurements and 2899 confirmed cluster member galaxies. Our redshift catalogue has a high spectroscopic completeness ($\sim 94\%$) for $r_{\rm petro} \leq 19.4$ and clustercentric distances $R< 2\rm{R}_{200}$. We use the confirmed cluster member positions and redshifts to determine cluster velocity dispersion, $\rm{R}_{200}$, virial and caustic masses, as well as cluster structure. The clusters have virial masses $14.25 \leq {\rm log }({\rm M}_{200}/\rm{M}_{\odot}) \leq 15.19$. The cluster sample exhibits a range of dynamical states, from relatively relaxed-appearing systems, to clusters with strong indications of merger-related substructure. Aperture- and PSF-matched photometry are derived from SDSS and VST/ATLAS imaging and used to estimate stellar masses. These estimates, in combination with the redshifts, are used to define the input target catalogue for the cluster portion of the SAMI-GS. The primary SAMI-GS cluster targets have $R< \rm{R}_{200}$, velocities $|v_{\rm pec}| < 3.5σ_{200}$ and stellar masses $9.5 \leq {\rm log(M}^*_{approx}/\rm{M}_{\odot}) \leq 12$. Finally, we give an update on the SAMI-GS progress for the cluster regions.

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arXiv2016

The SAMI Galaxy Survey: Asymmetry in Gas Kinematics and its links to Stellar Mass and Star Formation

We study the properties of kinematically disturbed galaxies in the SAMI Galaxy Survey using a quantitative criterion, based on kinemetry (Krajnovic et al.). The approach, similar to the application of kinemetry by Shapiro et al. uses ionised gas kinematics, probed by Hα emission. By this method 23+/-7% of our 360-galaxy sub-sample of the SAMI Galaxy Survey are kinematically asymmetric. Visual classifications agree with our kinemetric results for 90% of asymmetric and 95% of normal galaxies. We find stellar mass and kinematic asymmetry are inversely correlated and that kinematic asymmetry is both more frequent and stronger in low-mass galaxies. This builds on previous studies that found high fractions of kinematic asymmetry in low mass galaxies using a variety of different methods. Concentration of star forma- tion and kinematic disturbance are found to be correlated, confirming results found in previous work. This effect is stronger for high mass galaxies (log(M*) > 10) and indicates that kinematic disturbance is linked to centrally concentrated star formation. Comparison of the inner (within 0.5Re) and outer Hα equivalent widths of asymmetric and normal galaxies shows a small but significant increase in inner equivalent width for asymmetric galaxies.

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arXiv2016

The SAMI Galaxy Survey: Spatially resolving the environmental quenching of star formation in GAMA galaxies

We use data from the Sydney-AAO Multi-Object Integral Field Spectrograph (SAMI) Galaxy Survey and the Galaxy And Mass Assembly (GAMA) survey to investigate the spatially-resolved signatures of the environmental quenching of star formation in galaxies. Using dust-corrected measurements of the distribution of H$α$ emission we measure the radial profiles of star formation in a sample of 201 star-forming galaxies covering three orders of magnitude in stellar mass (M$_{*}$; $10^{8.1}$-$10^{10.95}\, $M$_{\odot}$) and in $5^{th}$ nearest neighbour local environment density ($Σ_{5}$; $10^{-1.3}$-$10^{2.1}\,$Mpc$^{-2}$). We show that star formation rate gradients in galaxies are steeper in dense ($\log_{10}(Σ_{5}/$Mpc$^{2})>0.5$) environments by $0.58\pm 0.29\, dex\, $r$_{e}^{-1}$ in galaxies with stellar masses in the range $10^{10}<$M$_{*}/$M$_{\odot}<10^{11}$ and that this steepening is accompanied by a reduction in the integrated star formation rate. However, for any given stellar mass or environment density the star-formation morphology of galaxies shows large scatter. We also measure the degree to which the star formation is centrally concentrated using the unitless scale-radius ratio ($r_{50,Hα}/r_{50,cont}$), which compares the extent of ongoing star formation to previous star formation. With this metric we find that the fraction of galaxies with centrally concentrated star formation increases with environment density, from $\sim 5\pm 4\%$ in low-density environments ($\log_{10}(Σ_{5}/$Mpc$^{2})<0.0$) to $30\pm 15\%$ in the highest density environments ($\log_{10}(Σ_{5}/$Mpc$^{2})>1.0$). These lines of evidence strongly suggest that with increasing local environment density the star formation in galaxies is suppressed, and that this starts in their outskirts such that quenching occurs in an outside-in fashion in dense environments and is not instantaneous.

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arXiv2016

The SAMI Galaxy Survey: the link between angular momentum and optical morphology

We investigate the relationship between stellar and gas specific angular momentum $j$, stellar mass $M_{*}$ and optical morphology for a sample of 488 galaxies extracted from the SAMI Galaxy Survey. We find that $j$, measured within one effective radius, monotonically increases with $M_{*}$ and that, for $M_{*}>$10$^{9.5}$ M$_{\odot}$, the scatter in this relation strongly correlates with optical morphology (i.e., visual classification and Sérsic index). These findings confirm that massive galaxies of all types lie on a plane relating mass, angular momentum and stellar light distribution, and suggest that the large-scale morphology of a galaxy is regulated by its mass and dynamical state. We show that the significant scatter in the $M_{*}-j$ relation is accounted for by the fact that, at fixed stellar mass, the contribution of ordered motions to the dynamical support of galaxies varies by at least a factor of three. Indeed, the stellar spin parameter (quantified via $λ_R$) correlates strongly with Sérsic and concentration indices. This correlation is particularly strong once slow-rotators are removed from the sample, showing that late-type galaxies and early-type fast rotators form a continuous class of objects in terms of their kinematic properties.

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arXiv2015

The SAMI Galaxy Survey: Gas Streaming and Dynamical M/L in Rotationally Supported Systems

Line-of-sight velocities of gas and stars can constrain dark matter (DM) within rotationally supported galaxies if they trace circular orbits extensively. Photometric asymmetries may signify non-circular motions, requiring spectra with dense spatial coverage. Our integral-field spectroscopy of 178 galaxies spanned the mass range of the SAMI Galaxy Survey. We derived circular speed curves (CSCs) of gas and stars from non-parametric Diskfit fits out to $r\sim2r_e$. For 12/14 with measured H I profiles, ionized gas and H I maximum velocities agreed. We fitted mass-follows-light models to 163 galaxies by approximating the radial starlight profile as nested, very flattened mass homeoids viewed as a Sérsic form. Fitting broad-band SEDs to SDSS images gave median stellar mass/light 1.7 assuming a Kroupa IMF vs. 2.6 dynamically. Two-thirds of the dynamical mass/light measures were consistent with star+remnant IMFs. One-fifth required upscaled starlight to fit, hence comparable mass of unobserved baryons and/or DM distributed similarly across the SAMI aperture that came to dominate motions as the starlight CSC declined rapidly. The rest had mass distributed differently from starlight. Subtracting fits of Sérsic profiles to 13 VIKING Z-band images revealed residual weak bars. Near the bar PA, we assessed m = 2 streaming velocities, and found deviations usually <30 km/s from the CSC; three showed no deviation. Thus, asymmetries rarely influenced our CSCs despite co-located shock-indicating, emission-line flux ratios in more than 2/3.

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arXiv2015

The SAMI Pilot Survey: Stellar Kinematics of Galaxies in Abell 85, 168 and 2399

We present the SAMI Pilot Survey, consisting of integral field spectroscopy of 106 galaxies across three galaxy clusters, Abell 85, Abell 168 and Abell 2399. The galaxies were selected by absolute magnitude to have $M_r<-20.25$ mag. The survey, using the Sydney-AAO Multi-object Integral field spectrograph (SAMI), comprises observations of galaxies of all morphological types with 75\% of the sample being early-type galaxies (ETGs) and 25\% being late-type galaxies (LTGs). Stellar velocity and velocity dispersion maps are derived for all 106 galaxies in the sample. The $λ_{R}$ parameter, a proxy for the specific stellar angular momentum, is calculated for each galaxy in the sample. We find a trend between $λ_{R}$ and galaxy concentration such that LTGs are less concentrated higher angular momentum systems, with the fast-rotating ETGs (FRs) more concentrated and lower in angular momentum. This suggests that some dynamical processes are involved in transforming LTGs to FRs, though a significant overlap between the $λ_{R}$ distributions of these classes of galaxies implies that this is just one piece of a more complicated picture. We measure the kinematic misalignment angle, $Ψ$, for the ETGs in the sample, to probe the intrinsic shapes of the galaxies. We find the majority of FRs (83\%) to be aligned, consistent with them being oblate spheroids (i.e. disks). The slow rotating ETGs (SRs), on the other hand, are significantly more likely to show kinematic misalignment (only 38\% are aligned). This confirms previous results that SRs are likely to be mildly triaxial systems.

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arXiv2015

The SAMI Pilot Survey: The Fundamental and Mass Planes in Three Low-Redshift Clusters

Using new integral field observations of 106 galaxies in three nearby clusters we investigate how the intrinsic scatter of the Fundamental Plane depends on the way in which the velocity dispersion and effective radius are measured. Our spatially resolved spectroscopy, combined with a cluster sample with negligible relative distance errors allows us to derive a Fundamental Plane with minimal systematic uncertainties. From the apertures we tested, we find that velocity dispersions measured within a circular aperture with radius equal to one effective radius minimises the intrinsic scatter of the Fundamental Plane. Using simple yet powerful Jeans dynamical models we determine dynamical masses for our galaxies. Replacing luminosity in the Fundamental Plane with dynamical mass, we demonstrate that the resulting Mass Plane has further reduced scatter, consistent with zero intrinsic scatter. Using these dynamical models we also find evidence for a possibly non-linear relationship between dynamical mass-to-light ratio and velocity dispersion.

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arXiv2015

The SAMI Galaxy Survey: Unveiling the nature of kinematically offset active galactic nuclei

We have observed two kinematically offset active galactic nuclei (AGN), whose ionised gas is at a different line-of-sight velocity to their host galaxies, with the SAMI integral field spectrograph (IFS). One of the galaxies shows gas kinematics very different to the stellar kinematics, indicating a recent merger or accretion event. We demonstrate that the star formation associated with this event was triggered within the last 100 Myr. The other galaxy shows simple disc rotation in both gas and stellar kinematics, aligned with each other, but in the central region has signatures of an outflow driven by the AGN. Other than the outflow, neither galaxy shows any discontinuity in the ionised gas kinematics at the galaxy's centre. We conclude that in these two cases there is no direct evidence of the AGN being in a supermassive black hole binary system. Our study demonstrates that selecting kinematically offset AGN from single-fibre spectroscopy provides, by definition, samples of kinematically peculiar objects, but IFS or other data are required to determine their true nature.

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arXiv2015

Photometric Variability in the CSTAR Field: Results From the 2008 Data Set

The Chinese Small Telescope ARray (CSTAR) is the first telescope facility built at Dome A, Antarctica. During the 2008 observing season, the installation provided long-baseline and high-cadence photometric observations in the i-band for 18,145 targets within 20 deg2 CSTAR field around the South Celestial Pole for the purpose of monitoring the astronomical observing quality of Dome A and detecting various types of photometric variability. Using sensitive and robust detection methods, we discover 274 potential variables from this data set, 83 of which are new discoveries. We characterize most of them, providing the periods, amplitudes and classes of variability. The catalog of all these variables is presented along with the discussion of their statistical properties.

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