arXiv subjects

Chris P. Haines

Publications and source records attributed to Chris P. Haines.

16 recordsLinked to original sources

arXiv2021

LoCuSS: The splashback radius of massive galaxy clusters and its dependence on cluster merger history

We present the direct detection of the splashback feature using the sample of massive galaxy clusters from the Local Cluster Substructure Survey (LoCuSS). This feature is clearly detected (above $5σ$) in the stacked luminosity density profile obtained using the K-band magnitudes of spectroscopically confirmed cluster members. We obtained the best-fit model by means of Bayesian inference, which ranked models including the splashback feature as more descriptive of the data with respect to models that do not allow for this transition. In addition, we have assessed the impact of the cluster dynamical state on the occurrence of the splashback feature. We exploited the extensive multi-wavelength LoCuSS dataset to test a wide range of proxies for the cluster formation history, finding the most significant dependence of the splashback feature location and scale according to the presence or absence of X-ray emitting galaxy groups in the cluster infall regions. In particular, we report for the first time that clusters that do not show massive infalling groups present the splashback feature at a smaller clustercentric radius $ r_{\rm{sp}}/r_{\rm{200,m}} = 1.158 \pm 0.071$ than clusters that are actively accreting groups $r_{\rm{sp}}/r_{\rm{200,m}} = 1.291 \pm 0.062$. The difference between these two sub-samples is significant at $4.2σ$, suggesting a correlation between the properties of the cluster potential and its accretion rate and merger history. Similarly, clusters that are classified as old and dynamically inactive present stronger signatures of the splashback feature, with respect to younger, more active clusters. We are directly observing how fundamental dynamical properties of clusters reverberate across vastly different physical scales.

astro-ph.GA↗

arXiv2020

LoCuSS: exploring the connection between local environment, star formation and dust mass in Abell 1758

We explore the connection between dust and star formation, in the context of environmental effects on galaxy evolution. In particular, we exploit the susceptibility of dust to external processes to assess the influence of dense environment on star-forming galaxies. We have selected cluster Abell 1758 from the Local Cluster Substructure Survey (LoCuSS). Its complex dynamical state is an ideal test-bench to track dust removal and destruction in galaxies due to merger and accretion shocks. We present a systematic panchromatic study (from 0.15 $\rm μ$m with GALEX to 500 $\rm μ$m with Herschel) of spectroscopically confirmed star-forming cluster galaxies at intermediate redshift. We observe that the main subclusters (A1758N and A1758S) belong to two separate large-scale structures, with no overlapping galaxy members. Star-forming cluster members are distributed preferentially outside cluster central regions, and are not grouped in substructures. Rather, these galaxies are being funneled towards the main subclusters along separate accretion filaments. Additionally, we present the first study of dust-to-stellar (DTS) mass ratio used as indicator for local environmental influence on galaxy evolution. Star-forming cluster members show lower mean values (32% at 2.4$\rm σ$) of DTS mass ratio and lower levels of infrared emission from birth clouds with respect to coeval star-forming field galaxies. This picture is consistent with the majority of star-forming cluster members infalling in isolation. Upon accretion, star-formation is observed to decrease and warm dust is destroyed due to heating from the intracluster medium radiation, ram-pressure stripping and merger shocks.

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arXiv2019

Forming one of the most massive objects in the Universe: The quadruple merger in Abell 1758

Abell1758 is a system of two galaxy clusters, a more massive, northern cluster and a southern cluster. Both parts are undergoing major merger events at different stages. Although the mass of the merger constituents provides enough energy to produce visible shock fronts in the X-ray, none have been found to date. We present detailed temperature and abundance maps based on Chandra ACIS data, and identify several candidates for shocks and cold fronts from a smoothed gradient map of the surface brightness. One candidate can be confirmed as the missing shock front in the northern cluster through X-ray spectroscopy. Non-thermal radio emission observed with the GMRT confirms the presence of radio halos in the northern and southern clusters, and shows evidence for a relic in the periphery of the southern cluster. We do not find evidence for shocked gas between A1758N and A1758S.

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arXiv2019

Detection of anti-correlation of hot and cold baryons in galaxy clusters

The largest clusters of galaxies in the Universe contain vast amounts of dark matter, plus baryonic matter in two principal phases, a majority hot gas component and a minority cold stellar phase comprising stars, compact objects, and low-temperature gas. Hydrodynamic simulations indicate that the highest-mass systems retain the cosmic fraction of baryons, a natural consequence of which is anti-correlation between the masses of hot gas and stars within dark matter halos of fixed total mass. We report observational detection of this anti-correlation based on 4 elements of a $9\times9$ element covariance matrix for nine cluster properties, measured from X-ray, optical, infrared and millimetre wavelength observations of 41 clusters from the Local Cluster Substructure Survey. These clusters were selected using explicit and quantitative selection rules that were then encoded in our hierarchical Bayesian model. Our detection of anti-correlation is consistent with predictions from contemporary hydrodynamic cosmological simulations that were not tuned to reproduce this signal.

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arXiv2019

LoCuSS: Scaling relations between galaxy cluster mass, gas, and stellar content

We present a simultaneous analysis of galaxy cluster scaling relations between weak-lensing mass and multiple cluster observables, across a wide range of wavelengths, that probe both gas and stellar content. Our new hierarchical Bayesian model simultaneously considers the selection variable alongside all other observables in order to explicitly model intrinsic property covariance and account for selection effects. We apply this method to a sample of 41 clusters at $0.15<z<0.30$, with a well-defined selection criteria based on RASS X-ray luminosity, and observations from Chandra / XMM, SZA, Planck, UKIRT, SDSS and Subaru. These clusters have well-constrained weak-lensing mass measurements based on Subaru / Suprime-Cam observations, which serve as the reference masses in our model. We present 30 scaling relation parameters for 10 properties. All relations probing the intracluster gas are slightly shallower than self-similar predictions, in moderate tension with prior measurements, and the stellar fraction decreases with mass. K-band luminosity has the lowest intrinsic scatter with a 95th percentile of 0.16, while the lowest scatter gas probe is gas mass with a fractional intrinsic scatter of $0.16 \pm 0.03$. We find no distinction between the core-excised X-ray or high-resolution Sunyaev-Zel'dovich relations of clusters of different central entropy, but find with modest significance that higher entropy clusters have higher stellar fractions than their lower entropy counterparts. We also report posterior mass estimates from our likelihood model.

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arXiv2018

An interacting galaxy pair at the origin of a light echo

In a low-density region of the Shapley supercluster we identified an interacting galaxy pair at redshift z=0.04865 in which the Seyfert-2 nucleus of the main galaxy (ShaSS 073) is exciting an extended emission line region (EELR, ~170 kpc^2) in the disk of the less massive companion (ShaSS 622). New integral-field spectroscopy and the multi-band data-set, spanning from far-ultraviolet to far-infrared and radio wavelengths, allowed us to obtain a detailed description of the ShaSS 622-073 system. The gas kinematics shows hints of interaction, although the overall velocity field shows a quite regular rotation in both galaxies, thus suggesting that we are observing their first encounter as confirmed by the estimated distance of 21 kpc between the two galaxy centers. The detected ~2-3 kpc AGN outflow and the geometry of the EELR in ShaSS 622 support the presence of a hollow bicone structure. The status and sources of the ionization across the whole system have been analysed through photoionization models and a Bayesian approach which prove a clear connection between the AGN and the EELR. The luminosity of the AGN (2.4x10^44 erg/s) is a factor 20 lower than the power needed to excite the gas in the EELR (4.6x10^45 erg/s) indicating a dramatic fading of the AGN in the last 3x10^4 yr. ShaSS 073-622 provides all the ingredients listed in the recipe of a light echo where a highly ionised region maintains memory of a preceding more energetic phase of a now faded AGN. This is the first case of a light echo observed between two galaxies.

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arXiv2017

LoCuSS: Pre-processing in galaxy groups falling into massive galaxy clusters at z=0.2

We report direct evidence of pre-processing of the galaxies residing in galaxy groups falling into galaxy clusters drawn from the Local Cluster Substructure Survey (LoCuSS). 34 groups have been identified via their X-ray emission in the infall regions of 23 massive ($\rm \langle M_{200}\rangle = 10^{15}\,M_{\odot}$) clusters at $0.15<z<0.3$. Highly complete spectroscopic coverage combined with 24 $\rmμ$m imaging from Spitzer allows us to make a consistent and robust selection of cluster and group members including star forming galaxies down to a stellar mass limit of $\rm M_{\star} = 2\times10^{10}\,M_{\odot}$. The fraction $\rm f_{SF}$ of star forming galaxies in infalling groups is lower and with a flatter trend with respect to clustercentric radius when compared to the rest of the cluster galaxy population. At $\rm R\approx1.3\,r_{200}$ the fraction of star forming galaxies in infalling groups is half that in the cluster galaxy population. This is direct evidence that star formation quenching is effective in galaxies already prior to them settling in the cluster potential, and that groups are favourable locations for this process.

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arXiv2017

Galaxy cluster luminosities and colours, and their dependence on cluster mass and merger state

We study a sample of 19 galaxy clusters in the redshift range $0.15<z<0.30$ with highly complete spectroscopic membership catalogues (to $K < K^{\ast}(\rm z)+1.5$) from the Arizona Cluster Redshift Survey (ACReS); individual weak-lensing masses and near-infrared data from the Local Cluster Substructure Survey (LoCuSS); and optical photometry from the Sloan Digital Sky Survey (SDSS). We fit the scaling relations between total cluster luminosity in each of six bandpasses (${\it grizJK}$) and cluster mass, finding cluster luminosity to be a promising mass proxy with low intrinsic scatter $σ_{\ln L|M}$ of only $\sim 10-20$ per cent for all relations. At fixed overdensity radius, the intercept increases with wavelength, consistent with an old stellar population. The scatter and slope are consistent across all wavelengths, suggesting that cluster colour is not a function of mass. Comparing colour with indicators of the level of disturbance in the cluster, we find a narrower variety in the cluster colours of 'disturbed' clusters than of 'undisturbed' clusters. This trend is more pronounced with indicators sensitive to the initial stages of a cluster merger, e.g. the Dressler Schectman statistic. We interpret this as possible evidence that the total cluster star formation rate is 'standardised' in mergers, perhaps through a process such as a system-wide shock in the intracluster medium.

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arXiv2016

BUDHIES III: The fate of HI and the quenching of galaxies in evolving environments

In a hierarchical Universe clusters grow via the accretion of galaxies from the field, groups and even other clusters. As this happens, galaxies can lose their gas reservoirs via different mechanisms, eventually quenching their star-formation. We explore the diverse environmental histories of galaxies through a multi-wavelength study of the combined effect of ram-pressure stripping and group "processing" in Abell 963, a massive growing cluster at $z=0.2$ from the Blind Ultra Deep HI Environmental Survey (BUDHIES). We incorporate hundreds of new optical redshifts (giving a total of 566 cluster members), as well as Subaru and XMM-Newton data from LoCuSS, to identify substructures and evaluate galaxy morphology, star-formation activity, and HI content (via HI deficiencies and stacking) out to $3\times R_{200}$. We find that Abell 963 is being fed by at least 7 groups, that contribute to the large number of passive galaxies outside the cluster core. More massive groups have a higher fraction of passive and HI-poor galaxies, while low-mass groups host younger (often interacting) galaxies. For cluster galaxies not associated with groups we corroborate our previous finding that HI gas (if any) is significantly stripped via ram-pressure during their first passage through the intra-cluster medium, and find mild evidence for a starburst associated with this event. In addition, we find an overabundance of morphologically peculiar and/or star-forming galaxies near the cluster core. We speculate that these arise as groups pass through the cluster (post-processing). Our study highlights the importance of environmental quenching and the complexity added by evolving environments.

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arXiv2015

Early Science with the Large Millimeter Telescope: COOL BUDHIES I - a pilot study of molecular and atomic gas at z~0.2

An understanding of the mass build-up in galaxies over time necessitates tracing the evolution of cold gas (molecular and atomic) in galaxies. To that end, we have conducted a pilot study called CO Observations with the LMT of the Blind Ultra-Deep H I Environment Survey (COOL BUDHIES). We have observed 23 galaxies in and around the two clusters Abell 2192 (z = 0.188) and Abell 963 (z = 0.206), where 12 are cluster members and 11 are slightly in the foreground or background, using about 28 total hours on the Redshift Search Receiver (RSR) on the Large Millimeter Telescope (LMT) to measure the $^{12}$CO J = 1 --> 0 emission line and obtain molecular gas masses. These new observations provide a unique opportunity to probe both the molecular and atomic components of galaxies as a function of environment beyond the local Universe. For our sample of 23 galaxies, nine have reliable detections (S/N$\geq$3.6) of the $^{12}$CO line, and another six have marginal detections (2.0 < S/N < 3.6). For the remaining eight targets we can place upper limits on molecular gas masses roughly between $10^9$ and $10^{10} M_\odot$. Comparing our results to other studies of molecular gas, we find that our sample is significantly more abundant in molecular gas overall, when compared to the stellar and the atomic gas component, and our median molecular gas fraction lies about $1σ$ above the upper limits of proposed redshift evolution in earlier studies. We discuss possible reasons for this discrepancy, with the most likely conclusion being target selection and Eddington bias.

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arXiv2015

LoCuSS: Exploring the selection of faint blue background galaxies for cluster weak-lensing

Cosmological constraints from galaxy clusters rely on accurate measurements of the mass and internal structure of clusters. An important source of systematic uncertainty in cluster mass and structure measurements is the secure selection of background galaxies that are gravitationally lensed by clusters. This issue has been shown to be particular severe for faint blue galaxies. We therefore explore the selection of faint blue background galaxies, by reference to photometric redshift catalogs derived from the COSMOS survey and our own observations of massive galaxy clusters at z~0.2. We show that methods relying on photometric redshifts of galaxies in/behind clusters based on observations through five filters, and on deep 30-band COSMOS photometric redshifts are both inadequate to identify safely faint blue background galaxies. This is due to the small number of filters used by the former, and absence of massive galaxy clusters at redshifts of interest in the latter. We therefore develop a pragmatic method to combine both sets of photometric redshifts to select a population of blue galaxies based purely on photometric analysis. This sample yields stacked weak-lensing results consistent with our previously published results based on red galaxies. We also show that the stacked clustercentric number density profile of these faint blue galaxies is consistent with expectations from consideration of the lens magnification signal of the clusters. Indeed, the observed number density of blue background galaxies changes by ~10-30 per cent across the radial range over which other surveys assume it to be flat.

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arXiv2014

LoCuSS: The Near-Infrared Luminosity and Weak-Lensing Mass Scaling Relation of Galaxy Clusters

We present the first scaling relation between weak-lensing galaxy cluster mass, $M_{WL}$, and near-infrared luminosity, $L_K$. Our results are based on 17 clusters observed with wide-field instruments on Subaru, the United Kingdom Infrared Telescope, the Mayall Telescope, and the MMT. We concentrate on the relation between projected 2D weak-lensing mass and spectroscopically confirmed luminosity within 1Mpc, modelled as $M_{WL} \propto L_{K}^b$, obtaining a power law slope of $b=0.83^{+0.27}_{-0.24}$ and an intrinsic scatter of $σ_{lnM_{WL}|L_{K}}=10^{+8}_{-5}\%$. Intrinsic scatter of ~10% is a consistent feature of our results regardless of how we modify our approach to measuring the relationship between mass and light. For example, deprojecting the mass and measuring both quantities within $r_{500}$, that is itself obtained from the lensing analysis, yields $σ_{lnM_{WL}|L_{K}}=10^{+7}_{-5}\%$ and $b=0.97^{+0.17}_{-0.17}$. We also find that selecting members based on their (J-K) colours instead of spectroscopic redshifts neither increases the scatter nor modifies the slope. Overall our results indicate that near-infrared luminosity measured on scales comparable with $r_{500}$ (typically 1Mpc for our sample) is a low scatter and relatively inexpensive proxy for weak-lensing mass. Near-infrared luminosity may therefore be a useful mass proxy for cluster cosmology experiments.

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arXiv2010

The evolution of dwarf galaxies in the Coma supercluster

We employ spectroscopic and photometric data from SDSS DR7, in a 500 sq degree region, to understand the evolution of dwarf (~M*+2<M_z<M*+4) galaxies in the Coma supercluster (z=0.023). We show that in the Coma supercluster, the red dwarfs are mostly concentrated in the dense cores of the Coma and Abell 1367 clusters, and in the galaxy groups embedded in the filament connecting them. The post-starburst (k+A) dwarfs however are found in the infall regions of the Coma and Abell 1367 clusters, and occasionally in galaxy groups embedded along the filament, suggesting that strong velocity fields prevalent in the vicinity of deep potential wells may be closely related to the mechanism(s) leading to the post-starburst phase in dwarf galaxies. Moreover, the blue colour of some k+A dwarfs in the Coma cluster, found within its virial radius, suggests that the star formation in these galaxies was quenched very rapidly in the last 500 Myr. More than 60% of all red dwarf galaxies in the supercluster have 0-3 ang of H_δin absorption, which suggests that a major episode of star formation occurred in a non-negligible fraction of these galaxies, ending within the last Gyr, allowing them to move to the red sequence. The distribution of the blue dwarf galaxies in the Coma supercluster is bimodal in the EW(H_α)-EW(H_δ) plane, with one population having very high emission in H_α, and some emission in H_δ. A sub-population of blue dwarfs is coincident with the red dwarfs in the EW(H_α)-EW(H_δ) plane, showing absorption in H_δand relatively lower emission in H_α. We suggest that a large fraction of the latter population are the progenitors of the passive dwarf galaxies that are abundantly found in the cores of low-redshift rich clusters such as Coma.

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arXiv2010

ACCESS III: The Nature of Star Formation in the Shapley Supercluster

We present a joint analysis of panoramic Spitzer/MIPS mid-infrared and GALEX ultraviolet imaging of the Shapley supercluster at z=0.048. Combining this with spectra of 814 supercluster members and 1.4GHz radio continuum maps, this represents the largest complete census of star-formation (both obscured and unobscured) in local cluster galaxies to date, reaching SFRs~0.02Msun/yr. We take advantage of this comprehensive panchromatic dataset to perform a detailed analysis of the nature of star formation in cluster galaxies, using several quite independent diagnostics of the quantity and intensity of star formation to develop a coherent view of the types of star formation within cluster galaxies. We observe a robust bimodality in the infrared (f_24/f_K) galaxy colours, which we are able to identify as another manifestation of the broad split into star-forming spiral and passive elliptical galaxy populations seen in UV-optical surveys. This diagnostic also allows the identification of galaxies in the process of having their star formation quenched as the infrared analogue to the UV "green valley" population. The bulk of supercluster galaxies on the star-forming sequence have specific-SFRs consistent with local field specific-SFR-M* relations, and form a tight FIR-radio correlation confirming that their FIR emission is due to star formation. We show that 85% of the global SFR is quiescent star formation within spiral disks, as manifest by the observed sequence in the IRX-beta relation being significantly offset from the starburst relation of Kong et al. (2004), while their FIR-radio colours indicate dust heated by low-intensity star formation. Just 15% of the global SFR is due to nuclear starbursts. The vast majority of star formation seen in cluster galaxies comes from normal infalling spirals who have yet to be affected by the cluster environment.

astro-ph.CO↗

arXiv2010

ACCESS II: A Complete Census of Star Formation in the Shapley Supercluster - UV and IR Luminosity Functions

We present panoramic Spitzer/MIPS mid- and far-infrared and GALEX ultraviolet imaging of the the most massive and dynamically active system in the local Universe, the Shapley supercluster at z=0.048, covering the 5 clusters which make up the supercluster core. We combine these data with existing spectroscopic data from 814 confirmed supercluster members to produce the first study of a local rich cluster including both ultraviolet and infrared luminosity functions (LFs). This joint analysis allows us to produce a complete census of star-formation (both obscured and unobscured), extending down to SFRs~0.02-0.05Msun/yr, and quantify the level of obscuration of star formation among cluster galaxies, providing a local benchmark for comparison to ongoing and future studies of cluster galaxies at higher redshifts with Spitzer and Herschel. The GALEX NUV and FUV LFs obtained have steeper faint-end slopes than the local field population, due largely to the contribution of massive, quiescent galaxies at M_FUV>-16. The 24um and 70um galaxy LFs for the Shapley supercluster instead have shapes fully consistent with those obtained for the Coma cluster and for the local field galaxy population. This apparent lack of environmental dependence for the shape of the FIR luminosity function suggests that the bulk of the star-forming galaxies that make up the observed cluster infrared LF have been recently accreted from the field and have yet to have their star formation activity significantly affected by the cluster environment. We estimate a global SFR of 327 Msun/yr over the whole supercluster core, of which just ~20% is visible directly in the UV continuum and ~80% is reprocessed by dust and emitted in the infrared. The level of obscuration (L_IR/L_FUV) in star-forming galaxies is seen to increase linearly with L_K over two orders of magnitude in stellar mass.

astro-ph.CO↗

arXiv2010

Star formation, starbursts and quenching across the Coma supercluster

We analyse Spitzer MIPS 24micron observations, and SDSS (DR7) optical broadband photometry and spectra, to investigate the star formation (SF) properties of galaxies residing in the Coma supercluster region. We find that SF in dwarf galaxies is quenched only in the high density environment at the centre of clusters and groups, but passively-evolving massive galaxies are found in all environments, indicating that massive galaxies can become passive via internal processes. We find AGN activity is suppressed in the cluster cores. We present evidence for a strong dependence of the mechanism(s) responsible for quenching SF in dwarf galaxies on the cluster potential. We find a significant increase in the mean EW of Halpha among star-forming dwarf galaxies in the infall regions of the Coma cluster and the core of Abell 1367 with respect to the overall supercluster population, indicative of the infalling dwarf galaxies undergoing a starburst phase. We identify these starburst galaxies as the precursors of the post-starburst k+A galaxies. We find that 11.4% of all dwarf (z mag > 15) galaxies in the Coma cluster and 4.8% in the Abell 1367 have k+A like spectra, while this fraction is just 2.1% when averaged over the entire supercluster region. We show that in the centre of the Coma cluster, the (24-z) colour of galaxies is correlated with their optical (g-r) colour and Halpha emission. By analysing the projected phase space distribution of galaxies detected at 24micron in Coma, we find that the (optically) red 24 micron detected galaxies follow the general distribution of `all' the spectroscopic members, but their (optically) blue counterparts show interesting features, indicative of recent infall.

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