arXiv subjects

R. L. Davies

Publications and source records attributed to R. L. Davies.

At least 37 records · Page 2Linked to original sources

arXiv2019

The KMOS^3D Survey: data release and final survey paper

We present the completed KMOS$^\mathrm{3D}$ survey $-$ an integral field spectroscopic survey of 739, $\log(M_{\star}/M_{\odot})>9$, galaxies at $0.6 10.5$). We confirm our first year results of a high rotation dominated fraction (monotonic velocity gradient and $v_\mathrm{rot}$/$σ_0 > \sqrt{3.36}$) of 77% for the full KMOS$^\mathrm{3D}$ H$α$sample. The rotation-dominated fraction is a function of both stellar mass and redshift with the strongest evolution measured over the redshift range of the survey for galaxies with $\log(M_{\star}/M_{\odot})<10.5$. With this paper we include a final data release of all 739 observed objects.

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arXiv2019

The KMOS^3D Survey: Demographics and Properties of Galactic Outflows at z = 0.6 - 2.7

We present a census of ionized gas outflows in 599 normal galaxies at redshift 0.6 11.2 galaxies. The incidence, strength, and velocity of AGN-driven winds strongly correlates with stellar mass and central concentration. Their outflowing ionized gas appears denser (n_e~1000 cm^-3), and possibly compressed and shock-excited. These winds have comparable mass loading factors as the SF-driven winds but carry ~10 (~50) times more momentum (energy). The results confirm our previous findings of high duty cycle, energy-driven outflows powered by AGN above the Schechter mass, which may contribute to star formation quenching.

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arXiv2018

The KMOS$^\mathrm{3D}$ Survey: rotating compact star forming galaxies and the decomposition of integrated line widths

Using integral field spectroscopy we investigate the kinematic properties of 35 massive centrally-dense and compact star-forming galaxies (${\log{\overline{M}_*}}=11.1$, $\log{(Σ_\mathrm{1kpc})}>9.5$, $\log{(M_\ast/r_e^{1.5})}>10.3$) at $z\sim0.7-3.7$ within the KMOS$^\mathrm{3D}$survey. We spatially resolve 23 compact star-forming galaxies (SFGs) and find that the majority are dominated by rotational motions with velocities ranging from {$95-500$ km s$^{-1}$}. The range of rotation velocities is reflected in a similar range of integrated H$α$ linewidths, $75-400$ km s$^{-1}$, consistent with the kinematic properties of mass-matched extended galaxies from the full KMOS$^\mathrm{3D}$ sample. The fraction of compact SFGs that are classified as `rotation-dominated' or `disk-like' also mirrors the fractions of the full KMOS$^\mathrm{3D}$ sample. We show that integrated line-of-sight gas velocity dispersions from KMOS$^\mathrm{3D}$ are best approximated by a linear combination of their rotation and turbulent velocities with a lesser but still significant contribution from galactic scale winds. The H$α$ exponential disk sizes of compact SFGs are on average $2.5\pm0.2$ kpc, $1-2\times$ the continuum sizes, in agreement with previous work. The compact SFGs have a $1.4\times$ higher AGN incidence than the full KMOS$^\mathrm{3D}$ sample at fixed stellar mass with average AGN fraction of 76\%. Given their high and centrally concentrated stellar masses as well as stellar to dynamical mass ratios close to unity, the compact SFGs are likely to have low molecular gas fractions and to quench on a short time scale unless replenished with inflowing gas. The rotation in these compact systems suggests that their direct descendants are rotating passive galaxies.

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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

A photometric analysis of Abell 1689: two-dimensional multi-structure decomposition, morphological classification, and the Fundamental Plane

We present a photometric analysis of 65 galaxies in the rich cluster Abell 1689 at $z=0.183$, using the Hubble Space Telescope Advanced Camera for Surveys archive images in the rest-frame $V$-band. We perform two-dimensional multi-component photometric decomposition of each galaxy adopting different models of the surface-brightness distribution. We present an accurate morphological classification for each of the sample galaxies. For 50 early-type galaxies, we fit both a de Vaucouleurs and Sérsic law; S0s are modelled by also including a disc component described by an exponential law. Bars of SB0s are described by the profile of a Ferrers ellipsoid. For the 15 spirals, we model a Sérsic bulge, exponential disc, and, when required, a Ferrers bar component. We derive the Fundamental Plane by fitting 40 early-type galaxies in the sample, using different surface-brightness distributions. We find that the tightest plane is that derived by Sérsic bulges. We find that bulges of spirals lie on the same relation. The Fundamental Plane is better defined by the bulges alone rather than the entire galaxies. Comparison with local samples shows both an offset and rotation in the Fundamental Plane of Abell 1689.

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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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arXiv2014

The SAMI Galaxy Survey: Towards a unified dynamical scaling relation for galaxies of all types

We take advantage of the first data from the Sydney-AAO Multi-object Integral field (SAMI) Galaxy Survey to investigate the relation between the kinematics of gas and stars, and stellar mass in a comprehensive sample of nearby galaxies. We find that all 235 objects in our sample, regardless of their morphology, lie on a tight relation linking stellar mass ($M_{*}$) to internal velocity quantified by the $S_{0.5}$ parameter, which combines the contribution of both dispersion ($σ$) and rotational velocity ($V_{rot}$) to the dynamical support of a galaxy ($S_{0.5}=\sqrt{0.5V_{rot}^{2}+σ^{2}}$). Our results are independent of the baryonic component from which $σ$ and $V_{rot}$ are estimated, as the $S_{0.5}$ of stars and gas agree remarkably well. This represents a significant improvement compared to the canonical $M_{*}$ vs. $V_{rot}$ and $M_{*}$ vs. $σ$ relations. Not only is no sample pruning necessary, but also stellar and gas kinematics can be used simultaneously, as the effect of asymmetric drift is taken into account once $V_{rot}$ and $σ$ are combined. Our findings illustrate how the combination of dispersion and rotational velocities for both gas and stars can provide us with a single dynamical scaling relation valid for galaxies of all morphologies across at least the stellar mass range 8.5$<log(M_{*}/M_{\odot})<$11. Such relation appears to be more general and at least as tight as any other dynamical scaling relation, representing a unique tool for investigating the link between galaxy kinematics and baryonic content, and a less biased comparison with theoretical models.

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arXiv2013

The Atlas3D project -- XXVII. Cold Gas and the Colours and Ages of Early-type Galaxies

We present a study of the cold gas contents of the Atlas3D early-type galaxies, in the context of their optical colours, near-UV colours, and Hβ absorption line strengths. Early-type (elliptical and lenticular) galaxies are not as gas-poor as previously thought, and at least 40% of local early-type galaxies are now known to contain molecular and/or atomic gas. This cold gas offers the opportunity to study recent galaxy evolution through the processes of cold gas acquisition, consumption (star formation), and removal. Molecular and atomic gas detection rates range from 10% to 34% in red sequence early-type galaxies, depending on how the red sequence is defined, and from 50% to 70% in blue early-type galaxies. Notably, massive red sequence early-type galaxies (stellar masses > 5e10 Msun, derived from dynamical models) are found to have HI masses up to M(HI)/Mstar ~ 0.06 and H_2 masses up to M(H$_2$)/Mstar ~ 0.01. Some 20% of all massive early-type galaxies may have retained atomic and/or molecular gas through their transition to the red sequence. However, kinematic and metallicity signatures of external gas accretion (either from satellite galaxies or the intergalactic medium) are also common, particularly at stellar masses <= 5e10 Msun, where such signatures are found in ~ 50% of H$_2$-rich early-type galaxies. Our data are thus consistent with a scenario in which fast rotator early-type galaxies are quenched former spiral galaxies which have undergone some bulge growth processes, and in addition, some of them also experience cold gas accretion which can initiate a period of modest star formation activity. We discuss implications for the interpretation of colour-magnitude diagrams.

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arXiv2013

How typical is the Coma cluster?

Coma is frequently used as the archetype z~0 galaxy cluster to compare higher redshift work against. It is not clear, however, how representative the Coma cluster is for galaxy clusters of its mass or X-ray luminosity, and significantly: recent works have suggested that the galaxy population of Coma may be in some ways anomolous. In this work, we present a comparison of Coma to an X-ray selected control sample of clusters. We show that although Coma is typical against the control sample in terms of its internal kinematics (substructure and velocity dispersion profile), it has a significantly high (~3sigma) X-ray temperature set against clusters of comparable mass. By de-redshifting our control sample cluster galaxies star-formation rates using a fit to the galaxy main sequence evolution at z < 0.1, we determine that the typical star-formation rate of Coma galaxies as a function of mass is higher than for galaxies in our control sample at a confidence level of > 99 per cent. One way to alleviate this discrepency and bring Coma in-line with the control sample would be to have the distance to Coma to be slightly lower, perhaps through a non-negligible peculiar velocity with respect to the Hubble expansion, but we do not regard this as likely given precision measurements using a variety of approaches. Therefore in summary, we urge caution in using Coma as a z~0 baseline cluster in galaxy evolution studies.

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arXiv2013

The ATLAS$^{\rm{3D}}$ project - XXV: Two-dimensional kinematic analysis of simulated galaxies and the cosmological origin of fast and slow rotators

We present a detailed two-dimensional stellar dynamical analysis of a sample of 44 cosmological hydrodynamical simulations of individual central galaxies and their satellites. Kinematic maps of the stellar line-of-sight velocity, velocity dispersion, and higher-order Gauss-Hermite moments $h_3$ and $h_4$ are constructed for each central galaxy and for the most massive satellites. The amount of rotation is quantified using the $λ_{\mathrm{R}}$-parameter. The velocity, velocity dispersion, $h_3$, and $h_4$ fields of the simulated galaxies show a diversity similar to observed kinematic maps of early-type galaxies in the ATLAS$^{\rm{3D}}$ survey. This includes fast (regular), slow, and misaligned rotation, hot spheroids with embedded cold disk components as well as galaxies with counter-rotating cores or central depressions in the velocity dispersion. We link the present day kinematic properties to the individual cosmological formation histories of the galaxies. In general, major galaxy mergers have a significant influence on the rotation properties resulting in both a spin-down as well as a spin-up of the merger remnant. Lower mass galaxies with significant in-situ formation of stars, or with additional gas-rich major mergers - resulting in a spin-up - in their formation history, form elongated fast rotators with a clear anti-correlation of $h_3$ and $v/σ$. An additional formation path for fast rotators includes gas poor major mergers leading to a spin-up of the remnants. This formation path does not result in anti-correlated $h_3$ and $v/σ$. The galaxies most consistent with the rare class of non-rotating round early-type galaxies grow by gas-poor minor mergers alone. In general, more massive galaxies have less in-situ star formation since $z \sim 2$, rotate slower and have older stellar populations. (shortened)

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arXiv2012

Fast and slow rotators in the densest environments: a FLAMES/GIRAFFE IFS study of galaxies in Abell 1689 at z=0.183

We present FLAMES/GIRAFFE integral field spectroscopy of 30 galaxies in the massive cluster Abell 1689 at z = 0.183. Conducting an analysis similar to that of ATLAS3D, we extend the baseline of the kinematic morphology-density relation by an order of magnitude in projected density and show that it is possible to use existing instruments to identify slow and fast rotators beyond the local Universe. We find 4.5 +- 1.0 slow rotators with a distribution in magnitude similar to those in the Virgo cluster. The overall slow rotator fraction of our Abell 1689 sample is 0.15 +- 0.03, the same as in Virgo using our selection criteria. This suggests that the fraction of slow rotators in a cluster is not strongly dependent on its density. However, within Abell 1689, we find that the fraction of slow rotators increases towards the centre, as was also found in the Virgo cluster.

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arXiv2012

AGN Feedback Driven Molecular Outflow in NGC 1266

NGC 1266 is a nearby field galaxy observed as part of the ATLAS3D survey (Cappellari et al. 2011). NGC 1266 has been shown to host a compact (< 200 pc) molecular disk and a mass-loaded molecular outflow driven by the AGN (Alatalo et al. 2011). Very Long Basline Array (VLBA) observations at 1.65 GHz revealed a compact (diameter < 1.2 pc), high bright- ness temperature continuum source most consistent with a low-level AGN origin. The VLBA continuum source is positioned at the center of the molecular disk and may be responsible for the expulsion of molecular gas in NGC 1266. Thus, the candidate AGN-driven molecular outflow in NGC 1266 supports the picture in which AGNs do play a significant role in the quenching of star formation and ultimately the evolution of the red sequence of galaxies.

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arXiv2012

Quenching of Star Formation in Molecular Outflow Host NGC 1266

We detail the rich molecular story of NGC 1266, its serendipitous discovery within the ATLAS3D survey (Cappellari et al. 2011) and how it plays host to an AGN-driven molecular outflow, potentially quenching all of its star formation (SF) within the next 100 Myr. While major mergers appear to play a role in instigating outflows in other systems, deep imaging of NGC 1266 as well as stellar kinematic observations from SAURON, have failed to provide evidence that NGC 1266 has recently been involved in a major interaction. The molecular gas and the instantaneous SF tracers indicate that the current sites of star formation are located in a hypercompact disk within 200 pc of the nucleus (Fig. 1; SF rate ~ 2 Msuns/yr). On the other hand, tracers of recent star formation, such as the Hβ absorption map from SAURON and stellar population analysis show that the young stars are distributed throughout a larger area of the galaxy than current star formation. As the AGN at the center of NGC 1266 continues to drive cold gas out of the galaxy, we expect star formation rates to decline as the star formation is ultimately quenched. Thus, NGC 1266 is in the midst of a key portion of its evolution and continued studies of this unique galaxy may help improve our understanding of how galaxies transition from the blue to the red sequence (Alatalo et al. 2011).

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arXiv2011

The SAURON Project - XIX. Optical and near-infrared scaling relations of nearby elliptical, lenticular and Sa galaxies

[Abridged] We present ground-based MDM V-band and Spitzer/IRAC 3.6um-band photometric observations of the 72 representative galaxies of the SAURON Survey. In combination with the SAURON stellar velocity dispersion measured within an effective radius (se), this allows us to explore the location of our galaxies in the main scaling relations. We investigate the dependence of these relations on our recent kinematical classification of early-type galaxies (i.e. Slow/Fast Rotators) and the stellar populations. Slow Rotator and Fast Rotator E/S0 galaxies do not populate distinct locations in the scaling relations, although Slow Rotators display a smaller intrinsic scatter. Surprisingly, extremely young objects do not display the bluest (V-[3.6]) colours in our sample, as is usually the case in optical colours. This can be understood in the context of the large contribution of TP-AGB stars to the infrared, even for young populations, resulting in a very tight (V-[3.6]) - se relation that in turn allows us to define a strong correlation between metallicity and velocity dispersion. Many Sa galaxies appear to follow the Fundamental Plane defined by E/S0 galaxies. Galaxies that appear offset from the relations correspond mostly to objects with extremely young populations, with signs of on-going, extended star formation. We correct for this effect in the Fundamental Plane, by replacing luminosity with stellar mass using an estimate of the stellar mass-to-light ratio, so that all galaxies are part of a tight, single relation. The new estimated coefficients are consistent in both photometric bands and suggest that differences in stellar populations account for about half of the observed tilt with respect to the virial prediction. After these corrections, the Slow Rotator family shows almost no intrinsic scatter around the best-fit Fundamental Plane.

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arXiv2011

Molecular Gas and Star Formation in Local Early-Type Galaxies

The molecular gas content of local early-type galaxies is constrained and discussed in relation to their evolution. First, as part of the Atlas3D survey, we present the first complete, large (260 objects), volume-limited single-dish survey of CO in normal local early-type galaxies. We find a surprisingly high detection rate of 22%, independent of luminosity and at best weakly dependent on environment. Second, the extent of the molecular gas is constrained with CO synthesis imaging, and a variety of morphologies is revealed. The kinematics of the molecular gas and stars are often misaligned, implying an external gas origin in over a third of the systems, although this behaviour is drastically diffferent between field and cluster environments. Third, many objects appear to be in the process of forming regular kpc-size decoupled disks, and a star formation sequence can be sketched by piecing together multi-wavelength information on the molecular gas, current star formation, and young stars. Last, early-type galaxies do not seem to systematically obey all our usual prejudices regarding star formation, following the standard Schmidt-Kennicutt law but not the far infrared-radio correlation. This may suggest a greater diversity in star formation processes than observed in disk galaxies. Using multiple molecular tracers, we are thus starting to probe the physical conditions of the cold gas in early-types.

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arXiv2011

Investigating the merger origin of Early-Type Galaxies using ultra-deep optical images

The mass assembly of galaxies leaves various imprints on their surroundings, such as shells, streams and tidal tails. The frequency and properties of these fine structures depend on the mechanism driving the mass assembly: e.g. a monolithic collapse, rapid cold-gas accretion followed by violent disk instabilities, minor mergers or major dry / wet mergers. Therefore, by studying the outskirts of galaxies, one can learn about their main formation mechanism. I present here our on-going work to characterize the outskirts of Early-Type Galaxies (ETGs), which are powerful probes at low redshift of the hierarchical mass assembly of galaxies. This work relies on ultra-deep optical images obtained at CFHT with the wide-field of view MegaCam camera of field and cluster ETGs obtained as part of the Atlas-3D and NGVS projects. State of the art numerical simulations are used to interpret the data. The images reveal a wealth of unknown faint structures at levels as faint as 29 mag arcsec-2 in the g-band. Initial results for two galaxies are presented here.

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arXiv2010

Field and Globular Cluster LMXBs in NGC 4278

We report a detailed spectral analysis of the population of low-mass X-ray binaries (LMXBs) detected in the elliptical galaxy NGC~4278 with Chandra. Seven luminous sources were studied individually, four in globular clusters (GCs), and three in the stellar field. The range of (0.3-8 keV) $L_X$ for these sources suggests that they may be black hole binaries (BHBs). Comparison of our results with simulations allows us to discriminate between disk and power-law dominated emission, pointing to spectral/luminosity variability, reminiscent of Galactic BHBs. The BH masses derived from a comparison of our spectral results with the $L_X \sim T^4_{in}$ relation of Galactic BHBs are in the 5-15 $M_{\odot}$ range, as observed in the Milky Way. The analysis of joint spectra of sources selected in three luminosity ranges suggests that while the high luminosity sources have prominent thermal disk emission components, power-law components are likely to be important in the mid and low-luminosity spectra. Comparing low-luminosity average spectra, we find a relatively larger $N_H$ in the GC spectrum; we speculate that this may point to either a metallicity effect, or to intrinsic physical differences between field and GC accreting binaries. Analysis of average sample properties uncover a previously unreported $L_X - R_G$ correlation (where $R_G$ is the galactocentric radius) in the GC-LMXB sample, implying richer LMXB populations in more central GCs. No such trend is seen in the field LMXB sample. We can exclude that the GC $L_X - R_G$ correlation is the by-product of a luminosity effect, and suggest that it may be related to the presence of more compact GCs at smaller galactocentric radii, fostering more efficient binary formation.

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arXiv2010

The X-ray Spectra of the Luminous LMXBs in NGC 3379: Field and Globular Cluster Sources

From a deep multi-epoch Chandra observation of the elliptical galaxy NGC 3379 we report the spectral properties of eight luminous LMXBs (LX>1.2E38 erg/s). We also present a set of spectral simulations, produced to aid the interpretation of low-count single-component spectral modeling. These simulations demonstrate that it is possible to infer the spectral states of X-ray binaries from these simple models and thereby constrain the properties of the source. Of the eight LMXBs studied, three reside within globular clusters, and one is a confirmed field source. Due to the nature of the luminosity cut all sources are either neutron star binaries emitting at or above the Eddington luminosity or black hole binaries. The spectra from these sources are well described by single-component models, with parameters consistent with Galactic LMXB observations, where hard-state sources have a range in photon index of 1.5-1.9 and thermally dominated sources have inner disc temperatures between ~0.7-1.55 keV. The large variability observed in the brightest globular cluster source (LX>4E38 erg/s) suggests the presence of a black hole binary. At its most luminous this source is observed in a thermally dominated state with kT=1.5 keV, consistent with a black hole mass of ~4 Msol. This observation provides further evidence that globular clusters are able to retain such massive binaries. We also observed a source transitioning from a bright state (LX~1E39 erg/s), with prominent thermal and non-thermal components, to a less luminous hard state (LX=3.8E38 erg/s, Gamma=1.85). In its high flux emission this source exhibits a cool-disc component of ~0.14 keV, similar to spectra observed in some ultraluminous X-ray sources. Such a similarity indicates a possible link between `normal' stellar mass black holes in a high accretion state and ULXs.

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