arXiv subjects

Laura C. Parker

Publications and source records attributed to Laura C. Parker.

At least 37 records · Page 2Linked to original sources

arXiv2019

Smaller stellar disc scale lengths in rich environments

We investigate the dependence of stellar disc scale lengths on environment for a sample of Sloan Digital Sky Survey Data Release 7 galaxies with published photometric bulge-disc decompositions. We compare disc scale lengths at fixed bulge mass for galaxies in an isolated field environment to galaxies in X-ray rich and X-ray poor groups. At low bulge mass, stellar disc scale lengths in X-ray rich groups are smaller compared to discs in both X-ray poor groups and in isolated field environments. This decrease in disc scale length is largely independent of halo mass, though shows some dependence on group-centric distance. We also find that stellar disc scale lengths are smaller in X-ray rich environments for a subset of star-forming galaxies and for galaxies of different morphological types. We note that disc scale lengths of low mass galaxies are known to have large systematic uncertainties, however we focus on differences between samples with the same measurement biases. Our results show that stellar disc scale lengths depend on X-ray brightness, a tracer of IGM density, suggesting a role for hydrodynamic processes such as ram-pressure stripping and/or starvation.

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arXiv2019

Linking bar- and interaction-driven molecular gas concentration with centrally-enhanced star formation in EDGE-CALIFA galaxies

We study the spatially resolved star formation history and molecular gas distribution of 58 nearby galaxies, using integral field spectroscopy from the CALIFA survey and CO $J=1\rightarrow 0$ intensity mapping from the CARMA EDGE survey. We use the 4000 Å break (D$_n$4000), the equivalent width of the H$δ$ absorption line (EW H$δ_A$), and the equivalent width of the H$α$ emission line (EW H$α$) to measure the recent star formation history (SFH) of these galaxies. We measure radial profiles of the three SFH indicators and molecular gas mass surface density, from which we measure the level of centrally enhanced star formation and the molecular gas concentration. When we separate our galaxies into categories of barred (17 galaxies), unbarred (24 galaxies), and merging/paired (17 galaxies) we find that the galaxies which have centrally-enhanced star formation (19/58) are either barred (13/19) or in mergers/pairs (6/19) with relatively high molecular gas concentrations. A comparison between our barred galaxies and a snapshot of a hydrodynamic $N$-body simulation of a barred galaxy shows that the current theory of bar formation and evolution can qualitatively reproduce the main features of the observed galaxies in our sample, including both the sharp decrease of stellar age in the galactic center and the gradual decrease of age with increasing distance from center. These findings provide substantial evidence for a picture in which cold gas is transported inward by a bar or tidal interaction, which leads to the growth and rejuvenation of star formation in the central region.

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arXiv2018

The trajectories of galaxies in groups: mass loss and preprocessing

We present a study of environmental effects and preprocessing in a large galaxy group using a high-resolution, zoom-in simulation run with the GASOLINE2 hydrodynamics code. We categorize galaxies that were always in distinct haloes as unaccreted, galaxies that were distinct before accretion onto the main group as single, and galaxies that were in external sub-groups before accretion onto the main group as grouped. The unaccreted galaxy population experiences steady growth in dark matter, gas and stellar mass. Both single- and group-accreted galaxies begin to lose dark matter and gas after first accretion onto any host but continue to grow in stellar mass. Individual trajectories show that galaxies cease mass growth within roughly three virial radii of the main group. Single galaxies continue to form stars until the group virial radius is crossed, when they begin to lose both dark matter and gas. Grouped galaxies peak in mass when joining their external sub-group, indicating that they experience preprocessing. Most accreted galaxies retain their accumulated stellar mass. The total mass loss is dominated by tidal stripping, with evidence for additional gas stripping via ram pressure. Most accreted galaxies are quenched $\sim$(0.5-2.5) Gyr after accretion onto any group. These differing histories place unaccreted, single and grouped galaxies in distinct regions of the stellar mass-to-halo mass (SMHM) relation. This suggests that preprocessed galaxies are a key source of scatter in the SMHM relation for mixed galaxy populations.

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arXiv2018

Red Misfits in the Sloan Digital Sky Survey: Properties of Star-forming Red Galaxies

We study Red Misfits, a population of red, star-forming galaxies in the local Universe. We classify galaxies based on inclination-corrected optical colours and specific star formation rates derived from the Sloan Digital Sky Survey Data Release 7. Although the majority of blue galaxies are star-forming and most red galaxies exhibit little to no ongoing star formation, a small but significant population of galaxies ($\sim$11 per cent at all stellar masses) are classified as red in colour yet actively star-forming. We explore a number of properties of these galaxies and demonstrate that Red Misfits are not simply dusty or highly-inclined blue cloud galaxies or quiescent red galaxies with poorly-constrained star formation. The proportion of Red Misfits is nearly independent of environment and this population exhibits both intermediate morphologies and an enhanced likelihood of hosting an AGN. We conclude that Red Misfits are a transition population, gradually quenching on their way to the red sequence and this quenching is dominated by internal processes rather than environmentally-driven processes. We discuss the connection between Red Misfits and other transition galaxy populations, namely S0's, red spirals and green valley galaxies.

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arXiv2018

Connecting optical and X-ray tracers of galaxy cluster relaxation

Substantial effort has been devoted in determining the ideal proxy for quantifying the morphology of the hot intracluster medium in clusters of galaxies. These proxies, based on X-ray emission, typically require expensive, high-quality X-ray observations making them difficult to apply to large surveys of groups and clusters. Here, we compare optical relaxation proxies with X-ray asymmetries and centroid shifts for a sample of SDSS clusters with high-quality, archival X-ray data from Chandra and XMM-Newton. The three optical relaxation measures considered are: the shape of the member-galaxy projected velocity distribution -- measured by the Anderson-Darling (AD) statistic, the stellar mass gap between the most-massive and second-most-massive cluster galaxy, and the offset between the most-massive galaxy (MMG) position and the luminosity-weighted cluster centre. The AD statistic and stellar mass gap correlate significantly with X-ray relaxation proxies, with the AD statistic being the stronger correlator. Conversely, we find no evidence for a correlation between X-ray asymmetry or centroid shift and the MMG offset. High-mass clusters ($M_\mathrm{halo} > 10^{14.5}\,\mathrm{M_\odot}$) in this sample have X-ray asymmetries, centroid shifts, and Anderson-Darling statistics which are systematically larger than for low-mass systems. Finally, considering the dichotomy of Gaussian and non-Gaussian clusters (measured by the AD test), we show that the probability of being a non-Gaussian cluster correlates significantly with X-ray asymmetry but only shows a marginal correlation with centroid shift. These results confirm the shape of the radial velocity distribution as a useful proxy for cluster relaxation, which can then be applied to large redshift surveys lacking extensive X-ray coverage.

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arXiv2017

Gemini Observations of Galaxies in Rich Early Environments (GOGREEN) I: Survey Description

We describe a new Large Program in progress on the Gemini North and South telescopes: Gemini Observations of Galaxies in Rich Early Environments (GOGREEN). This is an imaging and deep spectroscopic survey of 21 galaxy systems at $1 10$ in halo mass. The scientific objectives include measuring the role of environment in the evolution of low-mass galaxies, and measuring the dynamics and stellar contents of their host haloes. The targets are selected from the SpARCS, SPT, COSMOS and SXDS surveys, to be the evolutionary counterparts of today's clusters and groups. The new red-sensitive Hamamatsu detectors on GMOS, coupled with the nod-and-shuffle sky subtraction, allow simultaneous wavelength coverage over $λ\sim 0.6$--$1.05μ$m, and this enables a homogeneous and statistically complete redshift survey of galaxies of all types. The spectroscopic sample targets galaxies with AB magnitudes $z^{\prime}<24.25$ and [3.6]$μ$m$<22.5$, and is therefore statistically complete for stellar masses $M_\ast\gtrsim10^{10.3}M_\odot$, for all galaxy types and over the entire redshift range. Deep, multiwavelength imaging has been acquired over larger fields for most systems, spanning $u$ through $K$, in addition to deep IRAC imaging at 3.6$μ$m. The spectroscopy is $\sim 50$ per cent complete as of semester 17A, and we anticipate a final sample of $\sim 500$ new cluster members. Combined with existing spectroscopy on the brighter galaxies from GCLASS, SPT and other sources, GOGREEN will be a large legacy cluster and field galaxy sample at this redshift that spectroscopically covers a wide range in stellar mass, halo mass, and clustercentric radius.

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arXiv2017

Preprocessing, mass loss and mass segregation of galaxies in DM simulations

We investigate the mass loss of galaxies in groups and clusters with high-resolution DM simulations. We detect weak mass segregation in the inner regions of group/cluster haloes, consistent with observational findings. This applies to samples of galaxy analogues selected using either their present-day mass or past maximum (peak) mass. We find a strong radial trend in the fractional mass lost by the galaxies since peak, independent of their mass. This suggests that segregation is due to massive galaxies having formed closer to the halo centres and not the preferential destruction of smaller galaxies near halo centres. We divide our sample into galaxies that were accreted as a group vs. as a single, distinct halo. We find strong evidence for preprocessing -- the grouped galaxies lose $\sim 35-45\%$ of their peak mass before being accreted onto their final host haloes, compared to single galaxies which lose $\sim12\%$. After accretion, however, the single galaxies lose more mass compared to the grouped ones. These results are consistent with a scenario in which grouped galaxies are preprocessed in smaller haloes while single galaxies `catch up' in terms of total mass loss once they are accreted onto the final host halo. The fractional mass loss is mostly independent of the galaxy mass and host mass, and increases with amount of time spent in a dense environment.

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arXiv2017

Evidence of pre-processing and a dependence on dynamical state for low-mass satellite galaxies

We study the dependence of satellite star formation rate and morphology on group dynamics for a sample of SDSS groups. We classify the group dynamical state and study satellite properties for populations of galaxies at small and large group-centric radii. For galaxies at large radii we find no differences in the star-forming or disc fraction for those in Gaussian groups compared to those in non-Gaussian groups. By comparing the star-forming and disc fractions of infalling galaxies to field galaxies we find evidence for the pre-processing of both star formation rate and morphology. The strength of pre-processing increases with halo mass and is highest for low-mass galaxies infalling onto high-mass haloes. We show that the star formation rate of galaxies at small radii correlates with group dynamical state, with galaxies in non- Gaussian groups showing enhanced star-forming fractions compared to galaxies in Gaussian groups. Similar correlations are not seen for the disc fractions of galaxies at small radii. This seems to suggest that either the mechanisms driving star formation quenching at small halo-centric radii are more efficient in dynamically relaxed groups, or that non-Gaussian groups have assembled more recently and therefore satellites of the groups will have been exposed to these transforming mechanisms for less time.

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arXiv2016

Uncovering Mass Segregation with Galaxy Analogues in Dark Matter Simulations

We investigate mass segregation in group and cluster environments by identifying galaxy analogues in high-resolution dark matter simulations. Subhalos identified by the AHF and ROCKSTAR halo finders have similar mass functions, independent of resolution, but different radial distributions due to significantly different subhalo hierarchies. We propose a simple way to classify subhalos as galaxy analogues. The radial distributions of galaxy analogues agree well at large halo-centric radii for both AHF and ROCKSTAR but disagree near parent halo centres where the phase-space information used by ROCKSTAR is essential. We see clear mass segregation at small radii (within $0.5\,r_{vir}$) with average galaxy analogue mass decreasing with radius. Beyond the virial radius, we find a mild trend where the average galaxy analogue mass increases with radius. These mass segregation trends are strongest in small groups and dominated by the segregation of low mass analogues. The lack of mass segregation in massive galaxy analogues suggests that the observed trends are driven by the complex accretion histories of the parent halos rather than dynamical friction.

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arXiv2015

Evidence for a change in the dominant satellite galaxy quenching mechanism at z=1

We present an analysis of galaxies in groups and clusters at $0.8 10^{10.3}M_\odot$, we find $f_{\rm convert}\sim 0.4$ in the groups and $\sim 0.6$ in the clusters, similar to comparable measurements at $z=0$. This means the time between first accretion into a more massive halo and final star formation quenching is $t_p\sim 2$ Gyr. This is substantially longer than the estimated time required for a galaxy's star formation rate to become zero once it starts to decline, suggesting there is a long delay time during which little differential evolution occurs. In contrast with local observations we find evidence that this delay timescale may depend on stellar mass, with $t_p$ approaching $t_{\rm Hubble}$ for $M_{\rm star}\sim 10^{9.5}M_\odot$. The result suggests that the delay time must not only be much shorter than it is today, but may also depend on stellar mass in a way that is not consistent with a simple evolution in proportion to the dynamical time. Instead, we find the data are well-matched by a model in which the decline in star formation is due to "overconsumption", the exhaustion of a gas reservoir through star formation and expulsion via modest outflows in the absence of cosmological accretion. Dynamical gas removal processes, which are likely dominant in quenching newly accreted satellites today, may play only a secondary role at $z=1$.

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arXiv2015

Comparing galaxy disk and star-formation properties in X-ray bright and faint groups and clusters

Galaxy morphologies and star-formation rates depend on environment. Galaxies in under-dense regions are generally star-forming and disky whereas galaxies in overdense regions tend to be early-type and not actively forming stars. The mechanism(s) responsible for star-formation quenching and morphological transformation remain unclear, although many processes have been proposed. We study the dependence of star-formation and morphology on X-ray luminosity for galaxies in Sloan Digital Sky Survey Data Release 7 (SDSS-DR7) groups and clusters. While controlling for stellar and halo mass dependencies, we find that galaxies in X-ray strong groups and clusters have preferentially low star-forming and disk fractions -- with the differences being strongest at low stellar masses. The trends that we observe do not change when considering only galaxies found within or outside of the X-ray radius of the host group. When considering central and satellite galaxies separately we find that this dependence on X-ray luminosity is only present for satellites, and we show that our results are consistent with "galaxy stangulation" as a mechanism for quenching these satellites. We investigate the dynamics of the groups and clusters in the sample, and find that the velocity distributions of galaxies beyond the virial radius in low X-ray luminosity halos tend to be less Gaussian in nature than the rest of the data set. This may be indicative of low X-ray luminosity groups and clusters having enhanced populations of star-forming and disk galaxies as a result of recent accretion.

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arXiv2014

Mass segregation trends in SDSS galaxy groups

It has been shown that galaxy properties depend strongly on their host environment. In order to understand the relevant physical processes driving galaxy evolution it is important to study the observed properties of galaxies in different environments. Mass segregation in bound galaxy structures is an important indicator of evolutionary history and dynamical friction timescales. Using group catalogues derived from the Sloan Digital Sky Survey Data Release 7 (SDSS DR7) we investigate mass segregation trends in galaxy groups at low redshift. We investigate average galaxy stellar mass as a function of group-centric radius and find evidence for weak mass segregation in SDSS groups. The magnitude of the mass segregation depends on both galaxy stellar mass limits and group halo mass. We show that the inclusion of low mass galaxies tends to strengthen mass segregation trends, and that the strength of mass segregation tends to decrease with increasing group halo mass. We find the same trends if we use the fraction of massive galaxies as a function of group-centric radius as an alternative probe of mass segregation. The magnitude of mass segregation that we measure, particularly in high-mass haloes, indicates that dynamical friction is not acting efficiently.

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arXiv2014

The GEEC2 spectroscopic survey of Galaxy Groups at $0.8<z<1$

We present the data release of the Gemini-South GMOS spectroscopy in the fields of 11 galaxy groups at $0.8 50$ per cent complete for galaxies within the virial radius, and with stellar mass $M_{\rm star}>10^{10.3}M_\odot$. Including galaxies with photometric redshifts we have an effective sample size of $\sim 400$ galaxies within the virial radii of these groups. We present group velocity dispersions, dynamical and stellar masses. Combining with the GCLASS sample of more massive clusters at the same redshift we find the total stellar mass is strongly correlated with the dynamical mass, with $\log{M_{200}}=1.20\left(\log{M_{\rm star}}-12\right)+14.07$. This stellar fraction of $~\sim 1$ per cent is lower than predicted by some halo occupation distribution models, though the weak dependence on halo mass is in good agreement. Most groups have an easily identifiable most massive galaxy (MMG) near the centre of the galaxy distribution, and we present the spectroscopic properties and surface brightness fits to these galaxies. The total stellar mass distribution in the groups, excluding the MMG, compares well with an NFW profile with concentration $4$, for galaxies beyond $\sim 0.2R_{200}$. This is more concentrated than the number density distribution, demonstrating that there is some mass segregation.

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arXiv2014

The pre-processing of subhaloes in SDSS groups and clusters

We investigate pre-processing using the observed quenched fraction of group and cluster galaxies in the Yang et al. (2007) SDSS-DR7 group catalogue in the redshift range of 0.01 < z < 0.045. We categorize group galaxies as virialized, infall or backsplash and we apply a combination of the Dressler-Shectman statistic and group member velocities to identify subhaloes. On average the fraction of galaxies that reside in subhaloes is a function of host halo mass, where more massive systems have a higher fraction of subhalo galaxies both in the overall galaxy and infall populations. Additionally, we find that between 2 < r_200 < 3 the quiescent fraction is higher in the subhalo population with respect to both the field and non-subhalo populations. At these large radii (2 < r_200 < 3), the majority of galaxies (~ 80 %) belong to the infall population and therefore, we attribute the enhanced quenching to infalling subhalo galaxies, indicating that pre-processing has occurred in the subhalo population. We conclude that pre-processing plays a significant role in the observed quiescent fraction, but only for the most massive (M_halo > 10^14.5 M_sun) systems in our sample.

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arXiv2013

Star Formation and Environmental Quenching of GEEC2 Group Galaxies at z~1

We present new analysis from the GEEC2 spectroscopic survey of galaxy groups at $0.8<z<1$. Our previous work revealed an intermediate population between the star-forming and quiescent sequences and a strong environmental dependence in the fraction of quiescent galaxies. Only $\sim5$ per cent of star-forming galaxies in both the group and field sample show a significant enhancement in star formation, which suggests that quenching is the primary process in the transition from the star-forming to the quiescent state. To model the environmental quenching scenario, we have tested the use of different exponential quenching timescales and delays between satellite accretion and the onset of quenching. We find that with no delay, the quenching timescale needs to be long in order to match the observed quiescent fraction, but then this model produces too many intermediate galaxies. Fixing a delay time of 3 Gyr, as suggested from the local universe, produces too few quiescent galaxies. The observed fractions are best matched with a model that includes a delay that is proportional to the dynamical time and a rapid quenching timescale ($\sim0.25$ Gyr), but this model also predicts intermediate galaxies Hδ strength higher than that observed. Using stellar synthesis models, we have tested other scenarios, such as the rejuvenation of star formation in early-type galaxies and a portion of quenched galaxies possessing residual star formation. If environment quenching plays a role in the GEEC2 sample, then our work suggests that only a fraction of intermediate galaxies may be undergoing this transition and that quenching occurs quite rapidly in satellite galaxies ($\lesssim0.25$ Gyr).

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arXiv2013

Do group dynamics play a role in the evolution of member galaxies?

We examine galaxy groups from the present epoch to z = 1 to explore the impact of group dynamics on galaxy evolution. We use group catalagues from the Sloan Digital Sky Survey (SDSS), the Group Environment and Evolution Collaboration (GEEC) and the high redshift GEEC2 sample to study how the observed member properties depend on galaxy stellar mass, group dynamical mass and dynamical state of the host group. We find a strong correlation between the fraction of non-star-forming (quiescent) galaxies and galaxy stellar mass, but do not detect a significant difference in the quiescent fraction with group dynamical mass, within our sample halo mass range of 10^13-10^14.5 M_sun, or with dynamical sate. However, at a redshift of approximately 0.4 we do see some evidence that the quiescent fraction in low mass galaxies (log(M_star/M_sun) < 10.5) is lower in groups with substructure. Additionally, our results show that the fraction of groups with non-Gaussian velocity distributions increases with redshift to roughly z = 0.4, while the amount of detected substructure remains constant to z = 1. Based on these results, we conclude that for massive galaxies (log(M_star/M_sun_ > 10.5), evolution is most strongly correlated to the stellar mass of a galaxy with little or no additional effect related to either the group dynamical mass or dynamical state. For low mass galaxies, we do see some evidence of a correlation between the quiescent fraction and the amount of detected substructure, highlighting the need to probe further down the stellar mass function to elucidate the role of the environment in galaxy evolution.

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arXiv2013

Efficient satellite quenching at z~1 from the GEEC2 spectroscopic survey of galaxy groups

We present deep GMOS-S spectroscopy for 11 galaxy groups at 0.8 66%) for eight of the eleven groups. Using an optical-NIR colour-colour diagram, the galaxies in the sample were separated with a dust insensitive method into three categories: passive (red), star-forming (blue), and intermediate (green). The strongest environmental dependence is observed in the fraction of passive galaxies, which make up only ~20 per cent of the field in the mass range 10^{10.3}<M_{star}/M_\odot<10^{11.0} but are the dominant component of groups. If we assume that the properties of the field are similar to those of the `pre-accreted' population, the environment quenching efficiency (ε_ρ) is defined as the fraction of field galaxies required to be quenched in order to match the observed red fraction inside groups. The efficiency obtained is ~0.4, similar to its value in intermediate-density environments locally. While green (intermediate) galaxies represent ~20 per cent of the star-forming population in both the group and field, at all stellar masses, the average sSFR of the group population is lower by a factor of ~3. The green population does not show strong H-delta absorption that is characteristic of starburst galaxies. Finally, the high fraction of passive galaxies in groups, when combined with satellite accretion models, require that most accreted galaxies have been affected by their environment. Thus, any delay between accretion and the onset of truncation of star formation (τ) must be <2 Gyr, shorter than the 3-7 Gyr required to fit data at z=0. The relatively small fraction of intermediate galaxies requires that the actual quenching process occurs quickly, with an exponential decay timescale of τ_q<1 Gyr.

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arXiv2012

Exploring the Diversity of Groups at 0.1<z<0.8 with X-ray and Optically Selected Samples

We present the global group properties of two samples of galaxy groups containing 39 high quality X-ray selected systems and 38 optically (spectroscopically) selected systems in coincident spatial regions at 0.12<z<0.79. Only nine optical systems are associable with X-ray systems. We discuss the confusion inherent in the matching of both galaxies to extended X-ray emission and of X-ray emission to already identified optical systems. Extensive spectroscopy has been obtained and the resultant redshift catalog and group membership are provided here. X-ray, dynamical, and total stellar masses of the groups are also derived and presented. We explore the effects of applying three different kinds of radial cut to our systems: a constant cut of 1 Mpc and two r200 cuts, one based on the velocity dispersion of the system and the other on the X-ray emission. We find that an X-ray based r200 results in less scatter in scaling relations and less dynamical complexity as evidenced by results of the Anderson-Darling and Dressler-Schectman tests, indicating that this radius tends to isolate the virialized part of the system. The constant and velocity dispersion based cuts can overestimate membership and can work to inflate velocity dispersion and dynamical and stellar mass. We find Lx-sigma and Mstellar-Lx scaling relations for X-ray and optically selected systems are not dissimilar. The mean fraction of mass found in stars for our systems is approximately 0.014 with a logarithmic standard deviation of 0.398 dex. We also define and investigate a sample of groups which are X-ray underluminous given the total group stellar mass. For these systems the fraction of stellar mass contributed by the most massive galaxy is typically lower than that found for the total population of groups implying that there may be less IGM contributed from the most massive member in these systems. (Abridged)

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