Aavso paper Session I sunday Sunday, May 22, 2011, 9: 30 am – 12: 00 pm

408

Galaxies, Galaxy Clusters and Friends

Poster Session

Essex Ballroom

408.01

8:00 AM - 12:00 PM

The 6dF Galaxy Survey (6dFGS) is an all southern sky galaxy survey, including 125,000 redshifts and a Fundamental Plane (FP) subsample of 10,000 peculiar velocities, making it the largest peculiar velocity sample to date. We have developed a robust procedure for fitting the FP, performing a maximum likelihood fit to a tri-variate Gaussian. We have subsequently examined the variation of a variety of properties across and through the FP, including environment, morphology, metallicity, alpha-enhancement, and stellar age. We find little variation in the FP with global environment. Some variation of morphology is found along the plane, though this is likely a consequence of selection effects. Elemental abundances are found to vary both across and through the FP. The parameter that varies most directly through the FP is stellar age. We find that galaxies with stellar populations with average ages older than 3 Gyr occupy a thinner FP than those younger than 3 Gyr. Thus, a modest improvement in distance errors is realized if one divides the sample into subsamples segregated by age, and fits the FP of each subsample independently.

408.02

Do Disk Galaxies Have Different Central Velocity Dispersions At A Given Rotation Velocity?

Taissa Danilovich¹, H. Jones², J. Mould³, E. Taylor⁴, C. Tonini¹, R. Webster^1
1University of Melbourne, Australia, ²Monash University, Australia, ³Swinburne University of Technology, Australia, ⁴University of Sydney, Australia.

8:00 AM - 12:00 PM

Hubble’s classification of spiral galaxies was one dimensional. Actually it was 1.5 dimensional, as he distinguished barred spirals. Van den Bergh’s was two dimensional: spirals had luminosity classes too. Other schemes are summarized at http://www.daviddarling.info/encyclopedia/G/galaxyclassification.html

408.03

8:00 AM - 12:00 PM

The near IR regime offers the opportunity to provide a quantitative means of classifying deprojected spiral galaxies by making use of a constant mass to light ratio and determining their gravitational torques. This gravitational torque parameter provides a single quantitative description of the strength of the luminous features, such as galactic bars and spiral arms. This quantitative approach is applied to Spitzer 3.6μm and 4.5μm images of a selected number of nearby barred spiral galaxies. The preliminary results reveal an almost perfect one to one correlation between stellar emissions at 3.6μm and 4.5μm.

408.04

8:00 AM - 12:00 PM

We have constructed a sample of 51 unobscured Seyferts selected from a cross-correlation between the 2XMMi catalog and SDSS DR7, which included 12 Narrow Line Seyfert 1s (NLS1s). Plus in some cases we have aperture photometry from the XMM Optical Monitor. We use these data to produce Spectral Energy Distributions (SEDs), from 10keV to just shortward of 1 micron.

408.05

8:00 AM - 12:00 PM

Combination of X-ray with sub-mm observations provides the most robust constraints on the star-formation of AGN to test competing models for the interplay between galaxy formation and black hole growth. The Herschel Multi-tiered Extragalactic Survey (HerMES), the largest project that will ever be performed with Herschel, is ideally suited to studying star formation over the z=1-3 epoch. Here we will present the X-ray/sub-mm properties of the HerMES/Lockman sources detected by Chandra. Less than 25% of the X-ray sources have a 250µm counterpart. The majority of the latter (>50%) are AGN dominated in X-rays. A key finding is that the hardness ratio distributions of the 250µm detected and undetected sources imply a strong connection between X-ray absorption and rapid star-formation in AGN. The prevalence of X-ray absorption in star-forming AGN suggests an alternative source of absorbing material, perhaps related to the gas which is fuelling the star- formation or to outowing material from the early stages of AGN feedback.

408.06

8:00 AM - 12:00 PM

The luminosities of Active Galactic Nuclei are well known to vary over time. However, the driving force behind this variability is not fully understood. Using multi-epoch photometric observations of 5801 spectroscopically confirmed quasars in the Sloan Digital Sky Survey equatorial stripe, we focus on determining whether the environment surrounding the quasar is a contributing factor to the variability in quasar luminosity. Specifically, we examine the relationship between density and variability. The density is calculated by counting the number of neighboring quasars within a fixed volume around each quasar. Maximum variation within the r band is used as a proxy for variability. We find no clear correlation between variability and environment

408.07

An Unusual Pan-STARRS Selected AGN

Martin J. Ward¹, S. Hutton¹, S. Mattila², R. Kotak^3
1Durham University, United Kingdom, ²University of Turku, Finland, ³Queen's University Belfast, United Kingdom.

8:00 AM - 12:00 PM

The Pan-STARRS telescope commenced regular science observations in May 2010. Since then it has performed a transient object search which has discovered numerous new supernovae. In addition the survey has indentified variable AGN. One such, named ID85, has displayed highly unusual properties. It brightened by several magnitudes with respect to data from SDSS (unfortunately no SDSS spectrum was taken). New optical spectra show it to have a redshift of 0.203, and to be very blue. However its optical emission lines are extremely narrow (few hundred km/s), but it is not a Seyfert 2. It appears to be an extreme example of a NLS1. Swift observations failed to detect it X-rays, indicating a very steep index of alpha OX. Over the past year its optical blue continuum has declined by about one magnitude, whereas its K-band (2.2 micron) flux has remained constant.

408.08

8:00 AM - 12:00 PM

We report ongoing spectroscopic observations of 3C 454.3 using the Small and Moderate Aperture Research Telescope System SMARTS 1.5m telescope + RC Spectrograph located at Cerro-Tololo Inter-American Observatory (CTIO). Spectra have been obtained roughly every 14 days from August 2008 through January 2011, during which 3C 454.3 has undergone several prominent optical (and $\gamma$-ray) flares. We find that while the equivalent width (EW) of 3C 454.3 varies, the line flux remains constant. This result suggests that the Broad Line Region is photoionized by the slowly varying accretion disk rather than radiation from the relativistic jet. We find the strength of the MgII line to be consistent with a constant line flux of $\sim$ 2.0$\times$ 10$^{-14}$~erg s$^{-1}$ cm$^2$ A$^{-1}$. This constant line flux argues against the photoionization of the BLR from the relativistic jet, as this source has undergone a number of flares during the course of observation with no corresponding change in line flux. This finding also implies that accretion disk is non-variable on timescales of at least 2.5 years.

408.09

8:00 AM - 12:00 PM

We present analysis of Chandra X-ray imaging and spectroscopy for a sample of 14 quasars in close pairs, targeted as part of a complete sample of binary quasar candidates with small transverse separations drawn from Sloan Digital Sky Survey (SDSS). One pair, SDSS\,J1254+0846 at z=0.44 clearly inhabits an ongoing, pre-coalescence galaxy merger showing obvious tidal tails. We measure the X-ray properties of all 14 QSOs, and study the distribution of X-ray and optical-to-X-ray power-law indices in these binary quasars, and find no significant difference with large control samples of isolated quasars. We present near-IR photometry from UKIDDS, 2MASS or the MMT with SWIRC, and fit simple spectral energy distributions to all 14 QSOs, and find preliminary evidence that substantial contributions from star formation are required, but no more so than for isolated X-ray-detected QSOs. Sensitive searches of the X-ray images for extended emission, and the optical images for optical galaxy excess show that these binary QSOs, while likely occurring in strong peaks of the dark matter distribution, are not preferentially found in rich cluster environments.

408.10

8:00 AM - 12:00 PM

We present new observations of the CO (2-1) line emission toward five z~6 quasars using the Ka-band receiver on the Expand Very Large Array (EVLA) and two of them have been detected. CO (2-1) transition is an ideal indicator of the total molecular gas masses, as it is suggested to be thermalized in the quasar host galaxies. The new Ka band receiver on the EVLA opens a unique and important window for observations of the CO (2-1) line emission toward the earliest quasars with ideal spectral sensitivity. The observations, together with the previous measurements of the CO (6-5) and (5-4) lines, reveals important constraints on the molecular gas properties and CO excitation in the quasar host galaxies. Additionally, we have resolve the CO (2-1) line emission in the z=6.2 quasar J1429+5447 into two distinct peaks. The result suggests a possible gas-rich, major merging system at the earliest epoch.

408.11

Dust-obscured Star Formation And The Contribution Of Galaxies Escaping UV/optical Color Selections At z~2

Laurie Riguccini¹, E. Le Floc'h¹, O. Ilbert², H. Aussel¹, M. Salvato³, P. Capak⁴, H. McCracken⁵, J. Kartaltepe⁶, D. Sanders⁷, N. Scoville^4
1CEA-Saclay, France, ²LAM, France, ³IPP, Germany, ⁴Caltech, ⁵IAP, France, ⁶NOAO, ⁷IfA.

8:00 AM - 12:00 PM

This poster focus on the luminous star-forming galaxies at 1.5 < z < 3 potentially missed by the traditional color selection techniques because of dust extinction. We quantify the fraction of these sources and their contribution to the IR luminosity and cosmic star formation density at high redshift. Our work is based on a sample of 24microns sources brighter than 80microJy taken from the Spitzer survey of the COSMOS field. Almost all of these sources have accurate photometric redshifts. I apply to this mid-IR selected sample the BzK and BM/BX criteria as well as the selections of the "IRAC peakers " and the "optically-faint IR-bright " galaxies, and I analyze the fraction of sources identified with these techniques. I also computed 8microns rest-frame luminosity from the 24microns fuxes of our sources, and considering the relationships between L8microns and LPaalpha and between L8microns and LIR, I derived the IR luminosity density and the SFR density for our MIPS sources. The BzK criterion offers an almost complete ( 90%) identification of the 24microns sources at 1.4 < z < 2.5. On the contrary, the BM/BX criterion miss 50% of the MIPS sources. We attribute this bias to the effect of extinction which redden the typical colors of galaxies. The contribution of these two selections to the IR luminosity density produced by all the sources brighter than 80microJy are from the same order. Moreover the criterion based on the presence of a stellar bump in their spectra ("IRAC peakers") miss up to 40% of the IR luminosity density while only 25% of the IR luminosity density at z~2 is produced by "optically-faint IR-bright" galaxies characterized by extreme mid-IR to optical flux ratios.

408.12

Virtual Universes for the Caltech-Cornell Atacama Telescope

Andrew Benson^1
1California Institute of Technology.

8:00 AM - 12:00 PM

I will present results from an ongoing project which is constructing virtual Universes tuned to CCAT science. These consist of catalogs of galaxies in square degree fields of view out to the highest redshifts that CCAT will be able to probe. Galaxy properties are computed using a combination of high resolution N-body simulations of large scale structure and physical models of galaxy formation and radiative transfer of starlight through dust. This results in a virtual universe within which galaxies have fully specified spatial (comoving positions, angular coordinates, redshift including peculiar velocity), spectral (full SED from UV to radio wavelengths, including PAH features) and physical (star and gas masses and metallicities, star formation rate, merger history etc.) properties. These datasets will be invaluable for assessing the ability of CCAT to measure galaxy properties and make inferences about the underlying physics of galaxy formation. Once complete, the full datasets will be made available to the community.

408.13

UV Properties And Morphology Of Spectroscopically-confirmed Galaxies At 5.6 < z < 7

Linhua Jiang¹, E. Egami^1
1University of Arizona.

8:00 AM - 12:00 PM

We present UV properties and morphology of a large sample of bright galaxies at z = 5.6 ~ 7. The sample includes about 20 Lyman-alpha emitters (LAEs) and 10 Lyman-break galaxies (LBGs) that were spectroscopically confirmed in the Subaru Deep Field. Near-IR (or rest-frame UV) imaging data were obtained with HST WFC3. Here we focus on a few interesting aspects of these galaxies from our preliminary results. For example, many galaxies in this sample are likely merging/interacting systems with extended features or even resolved double cores, which is in contrary to the compact morphology of fainter LBG candidates at z > 6 found in the GOODS fields. These galaxies have steep UV slopes (< -2), consistent with previous studies. We did not find significant differences between LAEs and LBGs in the near-IR. We acknowledge NASA/STScI funding for HST programs 11149 and 12329.

408.14

HI Deficiency Estimates in Galaxy Group WBL 368

Isaac Hughes¹, C. Weigel¹, M. Brault¹, P. Troischt¹, ALFALFA Team
¹Hartwick College.

8:00 AM - 12:00 PM

The Undergraduate ALFALFA (Arecibo Legacy Fast ALFA) Team Groups Project is a collaborative undertaking of faculty and undergraduates at 18 institutions, aimed at investigating properties of galaxy groups surveyed by the ALFALFA blind HI survey. The Hartwick College team is analyzing a 6X6 degree region centered on the galaxy group WBL 368. Using a new determination of group membership, we find the most probable optical counterparts for HI source detections of member galaxies. These detections are used to calculate the HI deficiencies in the group by comparing to a sample of HI field galaxies. This work has been supported by NSF grants AST-0724918, AST-0725267 and AST-0725380.

408.15

Crossing the Streams: A Joint Sunyaev-Zeldovich/Optical Finder for Galaxy Cluster Surveys

Brian Nord¹, M. Jeff^1
1University of Michigan.

8:00 AM - 12:00 PM

We present a new galaxy cluster-finding algorithm that uses information from both galaxy and Sunyaev-Zel'dovich surveys. This new joint-finder uses the full information from optical galaxy catalogues and mm-wave sky maps to probabilistically and robustly detect clusters down to lower masses than possible cluster finders in a single waveband.

408.16

8:00 AM - 12:00 PM

Determining cluster mass through dynamical techniques can be difficult and very uncertain for small groups without large galaxy populations or even modest clusters with limited sampling. A workaround can be achieved by stacking clusters of similar richness, which is known to strongly correlate with cluster mass, to achieve larger samples to perform our analysis. This increases our signal-to-noise ratio and allows us to use the caustic technique to estimate total masses out to the turnaround radius of clusters. We present the caustic mass-optical richness relation for over 1700 clusters in the C4 sample using a kernal density estimator to identify the caustic surfaces in radius-redshift space. This differs from the method described in (Diaferio 99) which uses an adaptive kernal estimator; however, we calibrate to previous caustic mass results and find strong agreement in all final masses. In the future, our results will help provide cosmological constraints and assist in mass estimation of non-virialized high-z clusters where other techniques like weak lensing may struggle. This work is funded in part by the National Science Foundation Graduate Research Fellowship.

408.17

Detection of Dark Matter Filament Signals Through Stacking GMBCG Galaxy Cluster Pairs

Alex Nguyen¹, J. P. Dietrich¹, T. A. McKay^1
1University of Michigan.

8:00 AM - 12:00 PM

One of the prominent features of the large-scale structure is the formation of galaxy clusters at the intersections of dark matter filaments. Given more than 55,000 galaxy clusters in the GMBCG catalog, we devise an algorithm that select cluster pairs with high probability of possessing filaments based on constraints of redshift and the number of closest neighbors. The pair-finder algorithm yields more than 16,000 cluster pairs with intercluster separations up to 50 Mpc. To enhance the filament signals, we stack the cluster pairs and their filament galaxies based on various criteria such as separation, redshift, and cluster richness. Significance maps of these stacks are constructed by using bootstrapping techniques and comparing the stacked signals with respect to the background galaxy density. Preliminary results of the stacking method show that intercluster filaments have overdensity at ∼2σs above the mean background density. The presence of filament signals is also verified by the cross-stacking method. Correlations between intercluster separation, or cluster richness, and the strength of filament signals are not obvious based on the constructed significance maps. Future analyses are suggested which might enhance the filament contrast with the background.

408.18

8:00 AM - 12:00 PM

We report the analysis results from XMM-Newton data of two clusters of galaxies, which was also known to as strong radio emitters; A194 and A2634. A194 is a nearby (z=0.018) linear cluster in NE-SW direction. The cluster is very faint in X-rays with an average ICM temperature of 2.7 keV. A194 has strong radio lobes hosted by N541 and N547. Temperature map indicates an interesting result of ICM & radio-lobe interactions; the hot X-ray plasma coincides with the rim of radio-lobes, as it was heated. A2634 (z=0.0314) is also has a strong radio emission from its cD galaxy. ICM plasma has an average temperature of 3 keV. The temperature variations of A2634 associate with the radio-jets. The northern part of the cluster is significantly hot (4.5 keV) around the boundaries of radio-jets and very low in metal abundance (<0.1 solar). The analysis results of two-clusters are studied to understand radio and X-ray interactions within ICM. We report that (1) the radio-jets may push ICM and create X-ray cavities (2) radio-rims increases the temperature of ICM by shock-heating.

408.19

Modeling Agn Feedback In Cosmological Simulations

Camille Avestruz^1
1Yale University.

8:00 AM - 12:00 PM

We present results for the effects of thermal energy feedback from active galactic nuclei (AGN) in a Virgo size cluster using a series of cosmological hydrodynamic simulations. We examine the AGN's effect on early rapid black hole growth and its sensitivity to feedback model parameters. With AGN feedback, black hole accretion can reach a so-called 'self-regulating' phase. We find that this self-regulated behavior has important consequences in the role that ensuing mergers have on cooling flows towards the cluster center (r<20kpc).

408.20

8:00 AM - 12:00 PM

The Undergraduate ALFALFA (Arecibo Legacy Fast ALFA) Team Groups Project is a collaborative undertaking of faculty and undergraduates at 18 institutions, aimed at investigating properties of galaxy groups surveyed by the ALFALFA blind HI survey. The Hartwick College team is analyzing a 6X6 degree region around galaxy group WBL 368. Group membership is determined with IDL routines based on RASSCALS x-ray data, optical positions and redshift measurements. Dyanmical mass estimations are then made using Heisler projector methods. This work is done in an effort to develop IDL routines, which could be applied to a broad sample of galaxy groups in the future and has been supported by NSF grants AST-0724918, AST-0725267 and AST-0725380.

408.21

The Galaxy Cluster Environment of Wide Angle Tail Radio Sources

Edmund Douglass¹, E. L. Blanton¹, T. E. Clarke², S. W. Randall^3
1Boston University, ²Naval Research Laboratory, ³Harvard-Smithsonian Center for Astrophysics.

8:00 AM - 12:00 PM

Due to their frequent association with galaxy clusters and their connection to intracluster medium ram pressure, wide angle tail (WAT) radio sources have proven to be reliable tracers of high-density environments at a range of redshifts as well as possible indicators of dynamical activity within their host systems . In an effort to perform a coherent characterization of the global X-ray properties of WAT clusters, we have assembled a sample of 12 WAT systems observed with the Chandra X-ray Observatory, which are publicly available in the archive. We find that many of these clusters display both merger signatures and evidence of cool/high metallicity gas within 100 kpc of the WAT host galaxy, suggesting a possible relation between the formation of WATs and the presence of perturbed cool cores. To understand where WAT-hosting systems fall with respect to general cluster properties, we compare the results with those of an identical analysis of an archival sample of cool core and non-cool core clusters within a similar redshift range in which WAT radio sources are not present.

408.22

8:00 AM - 12:00 PM

We present deep HI observations of two regions in the Virgo Cluster, obtained as part of the Arecibo Galaxy Environment Survey. Our typical rms is 0.6 mJy, equivalent to a sensitivity of 8x10 6Msolar at 17 Mpc distance. Thus far we have 73 cluster detections in 15 square degrees, of which 21 are not members of the Virgo Cluster Catalogue, including 3 that have no clear optical counterparts. 8 detections correspond to early-type galaxies.

408.23

Network Methods Of Centering For The Maxbcg Clusters

Blythe Moreland¹, T. McKay¹, B. Nord^1
1University of Michigan.

8:00 AM - 12:00 PM

To probe the structure of MaxBCG galaxy clusters from the Sloan Digital Sky Survey, we take inspiration from the fields of network and graph theory where objects called nodes are connected by links that contain information about their interaction. Thus we can create a network of member galaxy nodes for each galaxy cluster. Within this network we are able to link each node to every other, weighting the links with a metric that relates to the gravitational potential of the interaction. We can characterize the degree distributions of the galaxy networks and use high node degree as an indicator of centrality. In this project we look at the effectiveness of these methods and comparisons to other centering methods applied to the MaxBCG sample. The research is funded in part by the Michigan Space Grant Consortium.

408.24

Intrinsic Alignment of Cluster Galaxies: the Redshift Evolution

Jiangang Hao¹, J. M. Kubo¹, R. Feldmann¹, J. Annis¹, D. E. Johnston¹, H. Lin¹, T. A. McKay^2
1Fermi National Accelerator Laboratory, ²Department of Physics, University of Michigan.

8:00 AM - 12:00 PM

We present measurements of two types of cluster galaxy alignments based on a volume limited and highly pure ($\ge$ 90\%) sample of clusters from the GMBCG catalog derived from SDSS DR7. We detect a clear BCG alignment (the alignment of major axis of the BCG toward the distribution of cluster satellite galaxies), but do not detect a satellite alignment (the alignment of the major axes of the cluster satellite galaxies toward the BCG). We find that the BCG alignment signal become stronger as the redshift and BCG absolute magnitude decrease, and becomes weaker as BCG stellar mass decreases. No dependence of the BCG alignment on cluster richness is detected. We find that the satellite alignment depends on the apparent magnitudes rather than the absolute magnitudes of the BCGs and the methods used to measure the position angles (PAs, hereafter). This suggests that the reported detections of satellite alignment in the literature are more likely due to the use of isophotal PAs, whose measurements are more susceptible to the contamination from the diffuse light of nearby BCGs.

408.25

The Connection Between Radio Mini-Halos and Core Gas Sloshing

John A. ZuHone¹, M. Markevitch¹, G. Brunetti^2
1NASA/Goddard Space Flight Center, ²INAF, Italy.

8:00 AM - 12:00 PM

Radio mini-halos are diffuse, steep-spectrum synchrotron sources associated with a fraction of relaxed clusters of galaxies. Observations of some mini-halo sources indicate a correlation between the radio emission and the X-ray signature of gas sloshing, ``cold fronts.'' Some authors have suggested turbulence associated with the sloshing motions may reaccelerate relativistic electrons, resulting in emission associated with the fronts. We present MHD simulations of core gas sloshing in a galaxy cluster, where we measure the turbulence created by these motions and employ passive tracer particles to act as relativistic electrons that may be reaccelerated by such turbulence. Our results support such a link between sloshing motions and particle reacceleration.

408.26

8:00 AM - 12:00 PM

We have performed a stacking experiment to detect faint, diffuse non-thermal radio emission in X-ray luminous (> 10⁴⁴ erg s^-1) galaxy clusters in the southern sky with z<0.2. The increased sensitivity of this experiment over existing pointed observations allows us to test models of cluster radio halo bimodality and models of relativistic particle acceleration. We stacked 111 cluster radio images and 111 control fields from the Sydney University Molonglo Sky Survey (SUMSS) at 843 MHz, after filtering out the contribution from compact sources. We tentatively detect diffuse emission from the stacked clusters, but this result may be contaminated by large-scale radio galaxies in the clusters. We therefore use the stacked emission to calculate an upper limit to the effective luminosity from the average halo of 3.2 x 10²³ W/Hz at 1.4 GHz. We will present detections/upper limits separately for the subsets of relaxed and merging clusters and show how these can be used to constrain relativistic particle acceleration models. This work is supported in part by NSF grant AST 0908688 to the University of Minnesota.