Browsing by Subject "galaxies: structure"
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Item Angular Momenta, Dynamical Masses, And Mergers Of Brightest Cluster Galaxies(2013-12) Tran, Kim-Vy; Brough, Sarah; Gebhardt, Karl; von der Linden, Anja; Couch, Warrick J.; Sharp, Rob; Gebhardt, KarlUsing the VIMOS integral field unit (IFU) spectrograph on the Very Large Telescope, we have spatially mapped the kinematic properties of 10 nearby brightest cluster galaxies (BCGs) and 4 BCG companion galaxies located within a redshift of z = 0.1. In the hierarchical formation model, these massive galaxies (10(10.5) M-circle dot < M-dyn < 10(11.9) M-circle dot) are expected to undergo more mergers than lower mass galaxies, and simulations show that dry minor mergers can remove angular momentum. We test whether BCGs have low angular momenta by using the lambda(Re) parameter developed by the SAURON and ATLAS(3D) teams and combine our kinematics with Sloan Digital Sky Survey photometry to analyze the BCGs' merger status. We find that 30% (3/10) of the BCGs and 100% of the companion galaxies (4/4) are fast rotators as defined by the ATLAS(3D) criteria. Our fastest rotating BCG has a lambda(Re) = 0.35 +/- 0.05. We increase the number of BCGs analyzed from 1 in the combined SAURON and ATLAS(3D) surveys to 11 BCGs total and find that above M-dyn similar to 11.5 M-circle dot, virtually all galaxies, regardless of environment, are slow rotators. To search for signs of recent merging, we analyze the photometry of each system and use the G - M-20 selection criteria to identify mergers. We find that 40% +/- 20% of our BCGs are currently undergoing or have recently undergone a merger (within 0.2 Gyr). Surprisingly, we find no correlation between galaxies with high angular momentum and morphological signatures of merging.Item Barred Galaxies In The Abell 901/2 Supercluster With Stages(2009-06) Marinova, Irina; Jogee, Shardha; Heiderman, Amanda; Barazza, Fabio D.; Gray, M. E.; Barden, Marco; Wolf, Christian; Peng, Chen Y.; Bacon, David; Balogh, Michael; Bell, Eric F.; Bohm, Asmus; Caldwell, John A. R.; Haussler, Boris; Heymans, Catherine; Jahnke, Knud; van Kampen, Eelco; Lane, Kyle; McIntosh, Daniel H.; Meisenheimer, Klaus; Sanchez, Sebastian F.; Somerville, Rachel; Taylor, Andy; Wisotzki, Lutz; Zheng, Xianzhong; Marinova, Irina; Jogee, Shardha; Heiderman, AmandaWe present a study of bar and host disk evolution in a dense cluster environment, based on a sample of similar to 800 bright (M-V <= -18) galaxies in the Abell 901/2 supercluster at z similar to 0.165. We use Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) F606W imaging from the STAGES survey, and data from Spitzer, XMM-Newton, and COMBO-17. We identify and characterize bars through ellipse-fitting, and other morphological features through visual classification. We find the following results. (1) To define the optical fraction of barred disk galaxies, we explore three commonly used methods for selecting disk galaxies. We find 625, 485, and 353 disk galaxies, respectively, via visual classification, a single component Sersic cut (n <= 2.5), and a blue-cloud cut. In cluster environments, the latter two methods suffer from serious limitations, and miss 31% and 51%, respectively, of visually identified disks, particularly the many red, bulge-dominated disk galaxies in clusters. (2) For moderately inclined disks, the three methods of disk selection, however, yield a similar global optical bar fraction (f(bar-opt)) of 34%(+10%)(-3%) (115/340), 31%(+10%)(-3%) (58/189), and 30%(+10%)(-3%) (72/241), respectively. (3) We explore f(bar-opt) as a function of host galaxy properties and find that it rises in brighter galaxies and those which appear to have no significant bulge component. Within a given absolute magnitude bin, f(bar-opt) is higher in visually selected disk galaxies that have no bulge as opposed to those with bulges. Conversely, for a given visual morphological class, f(bar-opt) rises at higher luminosities. Both results are similar to trends found in the field. (4) For bright early-types, as well as faint late-type systems with no evident bulge, the optical bar fraction in the Abell 901/2 clusters is comparable within a factor of 1.1-1.4 to that of field galaxies at lower redshifts (z < 0.04). (5) Between the core and the virial radius of the cluster (R similar to 0.25-1.2 Mpc) at intermediate environmental densities (log(Sigma(10)) similar to 1.7-2.3), the optical bar fraction does not appear to depend strongly on the local environment density tracers (kappa, Sigma(10), and intracluster medium (ICM) density), and varies at most by a factor of similar to 1.3. Inside the cluster core, we are limited by number statistics, projection effects, and different trends from different indicators, but overall f(bar-opt) does not show evidence for a variation larger than a factor of 1.5. We discuss the implications of our results for the evolution of bars and disks in dense environments.Item Bulge n And B/T In High-Mass Galaxies: Constraints On The Origin Of Bulges In Hierarchical Models(2009-05) Weinzirl, Tim; Jogee, Shardha; Khochfar, S.; Burkert, Andreas; Kormendy, John; Weinzirl, Tim; Jogee, Shardha; Kormendy, JohnWe use the bulge Sersic index n and bulge-to-total mass ratio (B/T) to explore the fundamental question of how bulges form. We perform two-dimensional bulge-disk-bar decomposition on H-band images of 143 bright, high-mass (M(*) >= 1.0 x 10(10) M(circle dot)) low-to-moderately inclined (i < 70 degrees) spirals. Our results are as follows. (1) Our H-band bar fraction (similar to 58%) is consistent with that from ellipse fits. (2) 70% of the stellar mass is in disks, 10% in bars, and 20% in bulges. (3) A large fraction (similar to 69%) of bright spirals have B/T <= 0.2, and similar to 76% have low n <= 2 bulges. These bulges exist in barred and unbarred galaxies across a wide range of Hubble types. (4) About 65% (68%) of bright spirals with n <= 2 (B/T <= 0.2) bulges host bars, suggesting a possible link between bars and bulges. (5) We compare the results with predictions from a set of ACDM models. In the models, a high-mass spiral can have a bulge with a present-day low B/T <= 0.2 only if it did not undergo a major merger since z <= 2. The predicted fraction (similar to 1.6%) of high-mass spirals, which have undergone a major merger since z <= 4 and host a bulge with a present-day low B/T <= 0.2, is a factor of over 30 smaller than the observed fraction (similar to 66%) of high-mass spirals with B/T <= 0.2. Thus, contrary to common perception, bulges built via major mergers since z <= 4 seriously fail to account for the bulges present in similar to 66% of high mass spirals. Most of these present-day low B/T <= 0.2 bulges are likely to have been built by a combination of minor mergers and/or secular processes since z <= 4.Item Bulgeless Giant Galaxies Challenge Our Picture Of Galaxy Formation By Hierarchical Clustering(2010-11) Kormendy, John; Drory, Niv; Bender, Ralf; Cornell, Mike E.; Kormendy, John; Cornell, Mike E.To better understand the prevalence of bulgeless galaxies in the nearby field, we dissect giant Sc-Scd galaxies with Hubble Space Telescope (HST) photometry and Hobby-Eberly Telescope (HET) spectroscopy. We use the HET High Resolution Spectrograph (resolution R equivalent to lambda/FWHM similar or equal to 15,000) to measure stellar velocity dispersions in the nuclear star clusters and (pseudo) bulges of the pure-disk galaxies M 33, M 101, NGC 3338, NGC 3810, NGC 6503, and NGC 6946. The dispersions range from 20 +/- 1 km s(-1) in the nucleus of M 33 to 78 +/- 2 km s(-1) in the pseudobulge of NGC 3338. We use HST archive images to measure the brightness profiles of the nuclei and (pseudo) bulges in M 101, NGC 6503, and NGC 6946 and hence to estimate their masses. The results imply small mass-to-light ratios consistent with young stellar populations. These observations lead to two conclusions. (1) Upper limits on the masses of any supermassive black holes are M(center dot) less than or similar to (2.6 +/- 0.5) x 10(6) M(circle dot) in M 101 and M(center dot) less than or similar to (2.0 +/- 0.6) x 10(6) M(circle dot) in NGC 6503. (2) We show that the above galaxies contain only tiny pseudobulges that make up less than or similar to 3% of the stellar mass. This provides the strongest constraints to date on the lack of classical bulges in the biggest pure-disk galaxies. We inventory the galaxies in a sphere of radius 8 Mpc centered on our Galaxy to see whether giant, pure-disk galaxies are common or rare. We find that at least 11 of 19 galaxies with V(circ) > 150 km s(-1), including M 101, NGC 6946, IC 342, and our Galaxy, show no evidence for a classical bulge. Four may contain small classical bulges that contribute 5%-12% of the light of the galaxy. Only four of the 19 giant galaxies are ellipticals or have classical bulges that contribute similar to 1/3 of the galaxy light. We conclude that pure-disk galaxies are far from rare. It is hard to understand how bulgeless galaxies could form as the quiescent tail of a distribution of merger histories. Recognition of pseudobulges makes the biggest problem with cold dark matter galaxy formation more acute: How can hierarchical clustering make so many giant, pure-disk galaxies with no evidence for merger-built bulges? Finally, we emphasize that this problem is a strong function of environment: the Virgo cluster is not a puzzle, because more than 2/3 of its stellar mass is in merger remnants.Item Bulges Of Nearby Galaxies With Spitzer: Scaling Relations In Pseudobulges And Classical Bulges(2010-06) Fisher, David B.; Drory, Niv; Fisher, David B.We investigate scaling relations of bulges using bulge-disk decompositions at 3.6 mu m and present bulge classifications for 173 E-Sd galaxies within 20 Mpc. Pseudobulges and classical bulges are identified using Sersic index, Hubble Space Telescope morphology, and star formation activity ( traced by 8 mu m emission). In the near-IR pseudobulges have n(b) < 2 and classical bulges have n(b) > 2, as found in the optical. Sersic index and morphology are essentially equivalent properties for bulge classification purposes. We confirm, using a much more robust sample, that the Sersic index of pseudobulges is uncorrelated with other bulge structural properties, unlike for classical bulges and elliptical galaxies. Also, the half-light radius of pseudobulges is not correlated with any other bulge property. We also find a new correlation between surface brightness and pseudobulge luminosity; pseudobulges become more luminous as they become more dense. Classical bulges follow the well-known scaling relations between surface brightness, luminosity, and half-light radius that are established by elliptical galaxies. We show that those pseudobulges (as indicated by Sersic index and nuclear morphology) that have low specific star formation rates are very similar to models of galaxies in which both a pseudobulge and classical bulge exist. Therefore, pseudobulge identification that relies only on structural indicators is incomplete. Our results, especially those on scaling relations, imply that pseudobulges are very different types of objects than elliptical galaxies.Item Bulges Of Nearby Galaxies With Spitzer: The Growth Of Pseudobulges In Disk Galaxies And Its Connection To Outer Disks(2009-05) Fisher, David B.; Drory, Niv; Fabricius, Maximilian H.; Fisher, David B.We study star formation rates (SFRs) and stellar masses in bulges of nearby disk galaxies. For this we construct a new SFR indicator that linearly combines data from the Spitzer Space Telescope and the Galaxy Evolution Explorer. All bulges are found to be forming stars irrespective of bulge type (pseudobulge or classical bulge). At present-day SFR the median pseudobulge could have grown the present-day stellar mass in 8 Gyr. Classical bulges have the lowest specific SFR implying a growth times that are longer than a Hubble time, and thus the present-day SFR does not likely play a major role in the evolution of classical bulges. In almost all galaxies in our sample the specific SFR (SFR per unit stellar mass) of the bulge is higher than that of the outer disk. This suggests that almost all galaxies are increasing their B/T through internal star formation. The SFR in pseudobulges correlates with their structure. More massive pseudobulges have higher SFR density, this is consistent with that stellar mass being formed by moderate, extended star formation. Bulges in late-type galaxies have similar SFRs as pseudobulges in intermediate-type galaxies, and are similar in radial size. However, they are deficient in mass; thus, they have much shorter growth times, similar to 2 Gyr. We identify a class of bulges that have nuclear morphology similar to pseudobulges, significantly lower specific SFR than pseudobulges, and are closer to classical bulges in structural parameter correlations. These are possibly composite objects, evolved pseudobulges or classical bulges experiencing transient, enhanced nuclear star formation. Our results are consistent with a scenario in which bulge growth via internal star formation is a natural, and near ubiquitous phenomenon in disk galaxies. Those galaxies with large classical bulges are not affected by the in situ bulge growth, likely because the majority of their stellar mass comes from some other phenomenon. Yet, those galaxies without a classical bulge, over long periods of extended star formation are able to growth a pseudobulge. Though cold accretion is not ruled out, for pseudobulge galaxies an addition of stellar mass from mergers or accretion is not required to explain the bulge mass. In this sense, galaxies with pseudobulges may very well be bulgeless (or "quasi-bulgeless") galaxies, and galaxies with classical bulges are galaxies in which both internal evolution and hierarchical merging are responsible for the bulge mass by fractions that vary from galaxy to galaxy.Item CANDELS Observations Of The Environmental Dependence Of The Color-Mass-Morphology Relation At Z=1.6(2013-06) Bassett, Robert; Papovich, Casey; Lotz, Jennifer M.; Bell, Eric F.; Finkelstein, Steven L.; Newman, Jeffrey A.; Tran, Kim-Vy; Almaini, Omar; Lani, Caterina; Cooper, Michael; Croton, Darren; Dekel, Avishai; Ferguson, Henry C.; Kocevski, Dale D.; Koekemoer, Anton M.; Koo, David C.; McGrath, Elizabeth J.; McIntosh, Daniel H.; Wechsler, Risa; Finkelstein, Steven L.We study the environmental dependence of color, stellar mass, and morphology by comparing galaxies in a forming cluster to those in the field at z = 1.6 with Hubble Space Telescope near-infrared imaging in the CANDELS/UDS field. We quantify the morphology of the galaxies using the effective radius, r(eff), and Sersic index, n. In both the cluster and field, approximately half of the bulge-dominated galaxies (n > 2) reside on the red sequence of the color-magnitude diagram, and most disk-dominated galaxies (n < 2) have colors expected for star-forming galaxies. There is weak evidence that cluster galaxies have redder rest-frame U - B colors and higher stellar masses compared to the field. Star-forming galaxies in both the cluster and field show no significant differences in their morphologies. In contrast, there is evidence that quiescent galaxies in the cluster have larger median effective radii and smaller Sersic indices compared to the field with a significance of 2 sigma. These differences are most pronounced for galaxies at clustercentric distances 1 Mpc < R-proj < 1.5 Mpc, which have low Sersic indices and possibly larger effective radii, more consistent with star-forming galaxies at this epoch and in contrast to other quiescent galaxies. We argue that star-forming galaxies are processed under the influence of the cluster environment at distances greater than the cluster-halo virial radius. Our results are consistent with models where gas accretion onto these galaxies is suppressed from processes associated with the cluster environment.Item CANDELS Observations Of The Structural Properties Of Cluster Galaxies At Z=1.62(2012-05) Papovich, Casey; Bassett, Robert; Lotz, Jennifer M.; van der Wel, A.; Tran, K. V.; Finkelstein, Steven L.; Bell, Eric F.; Conselice, Christopher J.; Dekel, Avishai; Dunlop, J. S.; Guo, Y. C.; Faber, S. M.; Farrah, D.; Ferguson, Henry C.; Finkelstein, Keely D.; Haussler, Boris; Kocevski, D. D.; Koekemoer, A. M.; Koo, D. C.; McGrath, E. J.; McLure, R. J.; McIntosh, Daniel H.; Momcheva, I.; Newman, Jeffrey A.; Rudnick, Gregory; Weiner, B.; Willmer, Christopher N. A.; Wuyts, S.; Finkelstein, Steven L.; Finkelstein, Keely DWe discuss the structural and morphological properties of galaxies in a z = 1.62 proto-cluster using near-IR imaging data from Hubble Space Telescope Wide Field Camera 3 data of the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey (CANDELS). The cluster galaxies exhibit a clear color-morphology relation: galaxies with colors of quiescent stellar populations generally have morphologies consistent with spheroids, and galaxies with colors consistent with ongoing star formation have disk-like and irregular morphologies. The size distribution of the quiescent cluster galaxies shows a deficit of compact (less than or similar to 1 kpc), massive galaxies compared to CANDELS field galaxies at z = 1.6. As a result, the cluster quiescent galaxies have larger average effective sizes compared to field galaxies at fixed mass at greater than 90% significance. Combined with data from the literature, the size evolution of quiescent cluster galaxies is relatively slow from z similar or equal to 1.6 to the present, growing as (1 + z)(-0.6 +/- 0.1). If this result is generalizable, then it implies that physical processes associated with the denser cluster region seem to have caused accelerated size growth in quiescent galaxies prior to z = 1.6 and slower subsequent growth at z < 1.6 compared to galaxies in the lower density field. The quiescent cluster galaxies at z = 1.6 have higher ellipticities compared to lower redshift samples at fixed mass, and their surface-brightness profiles suggest that they contain extended stellar disks. We argue that the cluster galaxies require dissipationless (i.e., gas-poor or "dry") mergers to reorganize the disk material and to match the relations for ellipticity, stellar mass, size, and color of early-type galaxies in z < 1 clusters.Item Correlations Between Supermassive Black Holes, Velocity Dispersions, and Mass Deficits in Elliptical Galaxies with Cores(2009-02) Kormendy, John; Bender, Ralf; Kormendy, JohnHigh-dynamic-range surface photometry in a companion paper makes possible accurate measurement of the stellar light deficits L(def) and mass deficits M(def) associated with the cores of elliptical galaxies. We show that L(def) correlates with velocity dispersions sigma of the host galaxy bulge averaged outside the central region that may be affected by a supermassive black hole (BH). We confirm that L(def) correlates with BH mass M(center dot). Also, the fractional light deficit L(def)/L(*) correlates with M(center dot)/M(*), the ratio of BH mass to the galaxy stellar mass. All three correlations have scatter similar to or smaller than the scatter in the well-known correlation between M(center dot) and sigma. The new correlations are remarkable in view of the dichotomy between ellipticals with cores and those with central extra light. Core light deficit correlates closely with M(center dot) and sigma, but extra light does not. This supports the suggestion that extra light Es are made in wet mergers with starbursts whereas core Es are made in dry mergers. After dry mergers, cores are believed to be scoured by BH binaries that fling stars away as their orbits decay or by BHs that sink back to the center after recoiling from anisotropic gravitational radiation emitted when they merge. Direct evidence for these mechanisms has been elusive. We interpret the new correlations as the "smoking gun" that connects cores with BHs. Together, the M(center dot) - sigma and M(center dot) - L(def) correlations give us two independent ways to estimate BH masses in core Es.Item Discovery of a Dynamical Cold Point in the Heart of the Sagittarius dSph Galaxy With Observations from the APOGEE Project(2013-11) Majewski, Steven R.; Hasselquist, Sten; Lokas, Ewa L.; Nidever, David L.; Frinchaboy, Peter M.; Garcia Perez, Ana E.; Johnston, Kathryn V.; Meszaros, Szabolcs; Shetrone, Matthew; Allende Prieto, Carlos; Beaton, Rachael L.; Beers, Timothy C.; Bizyaev, Dmitry; Cunha, Katia; Damke, Guillermo; Ebelke, Garrett; Eisenstein, Daniel J.; Hearty, Fred; Holtzman, Jon; Johnson, Jennifer A.; Law, David R.; Malanushenko, Viktor; Malanushenko, Elena; O'Connell, Robert W.; Oravetz, Daniel; Pan, Kaike; Schiavon, Ricardo P.; Schneider, Donald P.; Simmons, Audrey; Skrutskie, Michael F.; Smith, Verne V.; Wilson, John C.; Zasowski, Gail; Shetrone, MatthewThe dynamics of the core of the Sagittarius (Sgr) dwarf spheroidal (dSph) galaxy are explored using high-resolution (R similar to 22,500), H-band, near-infrared spectra of over 1000 giant stars in the central 3 deg(2) of the system, of which 328 are identified as Sgr members. These data, among some of the earliest observations from the Sloan Digital Sky Survey III/Apache Point Observatory Galactic Evolution Experiment (APOGEE) and the largest published sample of high resolution Sgr dSph spectra to date, reveal a distinct gradient in the velocity dispersion of Sgr from 11 to 14 km s(-1) for radii > 0 degrees.8 from center to a dynamical cold point of 8 km s(-1) in the Sgr center-a trend differing from that found in previous kinematical analyses of Sgr over larger scales that suggests a more or less flat dispersion profile at these radii. Well-fitting mass models with either cored and cusped dark matter distributions can be found to match the kinematical results, although the cored profile succeeds with significantly more isotropic stellar orbits than required for a cusped profile. It is unlikely that the cold point reflects an unusual mass distribution. The dispersion gradient may arise from variations in the mixture of populations with distinct kinematics within the dSph; this explanation is suggested (e. g., by detection of a metallicity gradient across similar radii), but not confirmed, by the present data. Despite these remaining uncertainties about their interpretation, these early test data (including some from instrument commissioning) demonstrate APOGEE's usefulness for precision dynamical studies, even for fields observed at extreme airmasses.Item A Dozen New Galaxies Caught In The Act: Gas Stripping And Extended Emission Line Regions In The Coma Cluster(2010-12) Yagi, Masafumi; Yoshida, Michitoshi; Komiyama, Yutaka; Kashikawa, Nobunari; Furusawa, Hisanori; Okamura, Sadanori; Graham, Alister W.; Miller, Neal A.; Carter, David; Mobasher, Bahram; Jogee, Sharadha; Jogee, SharadhaWe present images of extended H alpha clouds associated with 14 member galaxies in the Coma cluster obtained from deep narrowband imaging observations with the Suprime-Cam at the Subaru Telescope. The parent galaxies of the extended H alpha clouds are distributed farther than 0.2 Mpc from the peak of the X-ray emission of the cluster. Most of the galaxies are bluer than g - r approximate to 0.5 and they account for 57% of the blue ( g - r < 0.5) bright ( r < 17.8 mag) galaxies in the central region of the Coma cluster. They reside near the red- and blueshifted edges of the radial velocity distribution of Coma cluster member galaxies. Our findings suggest that most of the parent galaxies were recently captured by the Coma cluster potential and are now infalling toward the cluster center with their disk gas being stripped off and producing the observed H alpha clouds.Item Frequency And Properties Of Bars In Cluster And Field Galaxies At Intermediate Redshifts(2009-04) Barazza, F. D.; Jablonka, P.; Desai, V.; Jogee, S.; Aragon-Salamanca, A.; De Lucia, G.; Saglia, R. P.; Halliday, C.; Poggianti, B. M.; Dalcanton, J. J.; Rudnick, G.; Milvang-Jensen, B.; Noll, S.; Simard, L.; Clowe, D. I.; Pello, R.; White, S. D. M.; Zaritsky, D.; Jogee, S.We present a study of large-scale bars in field and cluster environments out to redshifts of similar to 0.8 using a final sample of 945 moderately inclined disk galaxies drawn from the EDisCS project. We characterize bars and their host galaxies and look for relations between the presence of a bar and the properties of the underlying disk. We investigate whether the fraction and properties of bars in clusters are different from their counterparts in the field. The properties of bars and disks are determined by ellipse fits to the surface brightness distribution of the galaxies using HST/ACS images in the F814W filter. The bar identification is based on quantitative criteria after highly inclined (> 60 degrees) systems have been excluded. The total optical bar fraction in the redshift range z = 0.4-0.8 (median z = 0.60), averaged over the entire sample, is 25% (20% for strong bars). For the cluster and field subsamples, we measure bar fractions of 24% and 29%, respectively. We find that bars in clusters are on average longer than in the field and preferentially found close to the cluster center, where the bar fraction is somewhat higher (similar to 31%) than at larger distances (similar to 18%). These findings however rely on a relatively small subsample and might be affected by small number statistics. In agreement with local studies, we find that disk-dominated galaxies have a higher optical bar fraction (similar to 45%) than bulge-dominated galaxies (similar to 15%). This result is based on Hubble types and effective radii and does not change with redshift. The latter finding implies that bar formation or dissolution is strongly connected to the emergence of the morphological structure of a disk and is typically accompanied by a transition in the Hubble type. The question whether internal or external factors are more important for bar formation and evolution cannot be answered definitely. On the one hand, the bar fraction and properties of cluster and field samples of disk galaxies are quite similar, indicating that internal processes are crucial for bar formation. On the other hand, we find evidence that cluster centers are favorable locations for bars, which suggests that the internal processes responsible for bar growth are supported by the typical interactions taking place in such environments.Item History Of Galaxy Interactions And Their Impact On Star Formation Over The Last 7 Gyr From GEMS(2009-06) Jogee, Shardha; Miller, Sarah H.; Penner, Kyle; Skelton, Rosalind E.; Conselice, Christopher J.; Somerville, Rachel S.; Bell, Eric F.; Zheng, Xian Zhong; Rix, Hans-Walter; Robaina, Aday R.; Barazza, Fabio D.; Barden, Marco; Borch, Andrea; Beckwith, Steven V. W.; Caldwell, John A. R.; Peng, Chien Y.; Heymans, Catherine; McIntosh, Daniel H.; Haeussler, Boris; Jahnke, Knud; Meisenheimer, Klaus; Sanchez, Sebastian F.; Wisotzki, Lutz; Wolf, Christian; Papovich, Casey; Jogee, Shardha; Miller, Sarah H.; Penner, KyleWe perform a comprehensive estimate of the frequency of galaxy mergers and their impact on star formation over z similar to 0.24-0.80 (lookback time T(b) similar to 3-7 Gyr) using similar to 3600 (M >= 1 x 10(9) M(circle dot)) galaxies with GEMS Hubble Space Telescope, COMBO-17, and Spitzer data. Our results are as follows. (1) Among similar to 790 high-mass (M >= 2.5 x 10(10) M(circle dot)) galaxies, the visually based merger fraction over z similar to 0.24-0.80, ranges from 9% +/- 5% to 8% +/- 2%. Lower limits on the major merger and minor merger fraction over this interval range from 1.1% to 3.5%, and 3.6% to 7.5%, respectively. This is the first, albeit approximate, empirical estimate of the frequency of minor mergers over the last 7 Gyr. Assuming a visibility timescale of similar to 0.5 Gyr, it follows that over T(b) similar to 3-7 Gyr, similar to 68% of high-mass systems have undergone a merger of mass ratio > 1/10, with similar to 16%, 45%, and 7% of these corresponding respectively to major, minor, and ambiguous "major or minor" mergers. The average merger rate is similar to a few x 10(-4) galaxies Gyr(-1) Mpc(-3). Among similar to 2840 blue-cloud galaxies of mass M >= 1.0 x 10(9) M(circle dot), similar results hold. (2) We compare the empirical merger fraction and merger rate for high-mass galaxies to three. cold dark matter-based models: halo occupation distribution models, semi-analytic models, and hydrodynamic SPH simulations. We find qualitative agreement between observations and models such that the (major+minor) merger fraction or rate from different models bracket the observations, and show a factor of 5 dispersion. Near-future improvements can now start to rule out certain merger scenarios. (3) Among similar to 3698 M >= 1.0 x 10(9) M(circle dot) galaxies, we find that the mean star formation rate (SFR) of visibly merging systems is only modestly enhanced compared to non-interacting galaxies over z similar to 0.24-0.80. Visibly merging systems only account for a small fraction (< 30%) of the cosmic SFR density over T(b) similar to 3-7 Gyr. This complements the results of Wolf et al. over a shorter time interval of T(b) similar to 6.2-6.8 Gyr, and suggests that the behavior of the cosmic SFR density over the last 7 Gyr is predominantly shaped by non-interacting galaxies.Item The HST/ACS Coma Cluster Survey. VIII. Barred Disk Galaxies In The Core Of The Coma Cluster(2012-02) Marinova, Irina; Jogee, Shardha; Weinzirl, Tim; Erwin, Peter; Trentham, Neil; Ferguson, Henry C.; Hammer, Derek; den Brok, Mark; Graham, Alister W.; Carter, David; Balcells, Marc; Goudfrooij, Paul; Guzman, Rafael; Hoyos, Carlos; Mobasher, Bahram; Mouhcine, Mustapha; Peletier, Reynier F.; Peng, Eric W.; Kleijn, Gus V.; Marinova, Irina; Jogee, Shardha; Weinzirl, TimWe use high-resolution (similar to 0.'' 1) F814W Advanced Camera for Surveys (ACS) images from the Hubble Space Telescope ACS Treasury survey of the Coma cluster at z similar to 0.02 to study bars in massive disk galaxies (S0s), as well as low-mass dwarf galaxies in the core of the Coma cluster, the densest environment in the nearby universe. Our study helps to constrain the evolution of bars and disks in dense environments and provides a comparison point for studies in lower density environments and at higher redshifts. Our results are: (1) we characterize the fraction and properties of bars in a sample of 32 bright (M-V less than or similar to -18, M-* > 10(9.5) M-circle dot) S0 galaxies, which dominate the population of massive disk galaxies in the Coma core. We find that the measurement of a bar fraction among S0 galaxies must be handled with special care due to the difficulty in separating unbarred S0s from ellipticals, and the potential dilution of the bar signature by light from a relatively large, bright bulge. The results depend sensitively on the method used: the bar fraction for bright S0s in the Coma core is 50% +/- 11%, 65% +/- 11%, and 60% +/- 11% based on three methods of bar detection, namely, strict ellipse fit criteria, relaxed ellipse fit criteria, and visual classification. (2) We compare the S0 bar fraction across different environments (the Coma core, A901/902, and Virgo) adopting the critical step of using matched samples and matched methods in order to ensure robust comparisons. We find that the bar fraction among bright S0 galaxies does not show a statistically significant variation (within the error bars of +/- 11%) across environments which span two orders of magnitude in galaxy number density (n similar to 300-10,000 galaxies Mpc(-3)) and include rich and poor clusters, such as the core of Coma, the A901/902 cluster, and Virgo. We speculate that the bar fraction among S0s is not significantly enhanced in rich clusters compared to low-density environments for two reasons. First, S0s in rich clusters are less prone to bar instabilities as they are dynamically heated by harassment and are gas poor as a result of ram pressure stripping and accelerated star formation. Second, high-speed encounters in rich clusters may be less effective than slow, strong encounters in inducing bars. (3) We also take advantage of the high resolution of the ACS (similar to 50 pc) to analyze a sample of 333 faint (MV > -18) dwarf galaxies in the Coma core. Using visual inspection of unsharp-masked images, we find only 13 galaxies with bar and/or spiral structure. An additional eight galaxies show evidence for an inclined disk. The paucity of disk structures in Coma dwarfs suggests that either disks are not common in these galaxies or that any disks present are too hot to develop instabilities.Item Hunting for Supermassive Black Holes in Nearby Galaxies With the Hobby-Eberly Telescope(2015-05) van den Bosch, Remco C. E.; Gebhardt, Karl; Gultekin, Kayhan; Yildirim, Akin; Walsh, Jonelle L.; Gebhardt, Karl; Walsh, Jonelle L.We have conducted an optical long-slit spectroscopic survey of 1022 galaxies using the 10 m Hobby-Eberly Telescope (HET) at McDonald Observatory. The main goal of the HET Massive Galaxy Survey (HETMGS) is to find nearby galaxies that are suitable for black hole mass measurements. In order to measure accurately the black hole mass, one should kinematically resolve the region where the black hole dominates the gravitational potential. For most galaxies, this region is much less than an arcsecond. Thus, black hole masses are best measured in nearby galaxies with telescopes that obtain high spatial resolution. The HETMGS focuses on those galaxies predicted to have the largest sphere-of-influence, based on published stellar velocity dispersions or the galaxy fundamental plane. To ensure coverage over galaxy types, the survey targets those galaxies across a face-on projection of the fundamental plane. We present the sample selection and resulting data products from the long-slit observations, including central stellar kinematics and emission line ratios. The full data set, including spectra and resolved kinematics, is available online. Additionally, we show that the current crop of black hole masses are highly biased toward dense galaxies and that especially large disks and low dispersion galaxies are under-represented. This survey provides the necessary groundwork for future systematic black hole mass measurement campaigns.Item Insights On The Formation, Evolution, And Activity Of Massive Galaxies From Ultracompact And Disky Galaxies At Z=2-3(2011-12) Weinzirl, Tim; Jogee, Shardha; Conselice, Christopher J.; Papovich, Casey; Chary, Ranga-Ram; Bluck, Asa; Grutzbauch, Ruth; Buitrago, Fernando; Mobasher, Bahram; Lucas, Ray A.; Dickinson, Mark; Bauer, Amanda E.; Weinzirl, Tim; Jogee, ShardhaWe present our results on the structure and activity of massive galaxies at z = 1-3 using one of the largest (166 with M-star >= 5 x 10(10) M-circle dot) and most diverse samples of massive galaxies derived from the GOODS-NICMOS survey: (1) Sersic fits to deep NIC3 F160W images indicate that the rest-frame optical structures of massive galaxies are very different at z = 2-3 compared to z similar to 0. Approximately 40% of massive galaxies are ultracompact (r(e) <= 2 kpc), compared to less than 1% at z similar to 0. Furthermore, most (similar to 65%) systems at z = 2-3 have a low Sersic index n <= 2, compared to similar to 13% at z similar to 0. We present evidence that the n <= 2 systems at z = 2-3 likely contain prominent disks, unlike most massive z similar to 0 systems. (2) There is a correlation between structure and star formation rates (SFRs). The majority (similar to 85%) of non-active galactic nucleus (AGN) massive galaxies at z = 2-3, with SFR high enough to yield a 5 sigma (30 mu Jy) 24 mu m Spitzer detection, have low n <= 2. Such n <= 2 systems host the highest SFR. (3) The frequency of AGNs is similar to 40% at z = 2-3. Most (similar to 65%) AGN hosts have disky (n <= 2) morphologies. Ultracompact galaxies appear quiescent in terms of both AGN activity and star formation. (4) Large stellar surface densities imply massive galaxies at z = 2-3 formed via rapid, highly dissipative events at z > 2. The large fraction of n <= 2 disky systems suggests cold mode accretion complements gas-rich major mergers at z > 2. In order for massive galaxies at z = 2-3 to evolve into present-day massive E/S0s, they need to significantly increase (n, r(e)). Dry minor and major mergers may play an important role in this process.Item Integral Field Unit Spectroscopy of the Stellar Disk Truncation Region of NGC 6155(2010-06) Yoachim, Peter; Roskar, Rok; Debattista, Victor P.; Roskar, RokLike the majority of spiral galaxies, NGC 6155 exhibits an exponential surface brightness profile that steepens significantly at large radii. Using the VIRUS-P integral field unit spectrograph, we have gathered spatially resolved spectra of the system. Modifying the GANDALF spectral fitting routine for use on the complex stellar populations found in spirals, we find that the average stellar ages increase significantly beyond the profile break radius. This result is in good agreement with recent simulations that predict the outskirts of disk galaxies are populated through stellar migration. With the ability to bin multiple fibers, we are able to measure stellar population ages down to mu(V) similar to 24 mag arcsec(-2).Item Interacting Galaxies In The A901/902 Supercluster With Stages(2009-11) Heiderman, Amanda; Jogee, Shardha; Marinova, Irina; van Kampen, Eelco; Barden, Marco; Peng, Chien Y.; Heymans, Catherine; Gray, Meghan E.; Bell, Eric F.; Bacon, David; Balogh, Michael; Barazza, Fabio D.; Boehm, Asmus; Caldwell, John A. R.; Haeussler, Boris; Jahnke, Knud; Lane, Kyle; McIntosh, Daniel H.; Meisenheimer, Klaus; Sanchez, Sebastian F.; Somerville, Rachel S.; Taylor, Andy; Wisotzki, Lutz; Wolf, Christian; Zheng, Xianzhong; Heiderman, Amanda; Jogee, Shardha; Marinova, IrinaWe present a study of galaxy mergers and the influence of environment in the Abell 901/902 supercluster at z similar to 0.165, based on 893 bright (R(Vega) <= 24) intermediate-mass (M(*) >= 10(9) M(circle dot)) galaxies. We use HST ACS F606W data from the Space Telescope A901/902 Galaxy Evolution Survey, COMBO-17, Spitzer 24 mu m, and XMM-Newton X-ray data. Our analysis utilizes both a physically driven visual classification system and quantitative CAS parameters to identify systems which show evidence of a recent or ongoing merger of mass ratio >1/10 (i.e., major and minor mergers). Our results are (1) after visual classification and minimizing the contamination from false projection pairs, we find that the merger fraction f(merge) is 0.023 +/- 0.007. The estimated fractions of likely major mergers, likely minor mergers, and ambiguous cases are 0.01 +/- 0.004, 0.006 +/- 0.003, and 0.007 +/- 0.003, respectively. (2) All the mergers lie outside the cluster core of radius R < 0.25 Mpc: the lack of mergers in the core is likely due to the large galaxy velocity dispersion in the core. The mergers, instead, populate the region (0.25 Mpc < R <= 2 Mpc) between the core and the cluster outskirt. In this region, the estimated frequency of mergers is similar to those seen at typical group overdensities in N-body simulations of accreting groups in the A901/902 clusters. This suggests the ongoing growth of the clusters via accretion of group and field galaxies. (3) We compare our observed merger fraction with those reported in other clusters and groups out to z similar to 0.4. Existing data points on the merger fraction for L <= L* galaxies in clusters allow for a wide spectrum of scenarios, ranging from no evolution to evolution by a factor of similar to 5 over z similar to 0.17-0.4. (4) In A901/902, the fraction of interacting galaxies, which lie on the blue cloud is 80% +/- 18% (16/20) versus 34% +/- 7% or (294/866) for non-interacting galaxies, implying that interacting galaxies are preferentially blue. (5) The average star formation rate (SFR), based on UV or a combination of UV+IR data, is enhanced by a factor of similar to 1.5-2 in mergers compared to non-interacting galaxies. However, mergers in the A901/902 clusters contribute only a small fraction (between 10% and 15%) of the total SFR density, while the rest of the SFR density comes from non-interacting galaxies.Item The L Proportional To Sigma(8) Correlation for Elliptical Galaxies With Cores: Relation With Black Hole Mass(2013-05) Kormendy, John; Bender, Ralf; Kormendy, JohnWe construct the Faber-Jackson correlation between velocity dispersion sigma and total galaxy luminosity L-V separately for elliptical galaxies with and without cores. The coreless ellipticals show the well-known, steep relationship d log sigma/d log L-V = 0.268 or L-V proportional to sigma(3.74). This corresponds to d log sigma/d log M = 0.203, where M is the stellar mass and we use M/L proportional to L-0.32. In contrast, the velocity dispersions of core ellipticals increase much more slowly with L-V and M: d log sigma/d log L-V = 0.120, L-V proportional to sigma(8.33), and d log sigma/d log M = 0.091. Dissipationless major galaxy mergers are expected to preserve sigma according to the simplest virial-theorem arguments. However, numerical simulations show that sigma increases slowly in dry major mergers, with d log sigma/d log M similar or equal to +0.15. In contrast, minor mergers cause sigma to decrease, with d log sigma/d log M similar or equal to -0.05. Thus, the observed relation argues for dry major mergers as the dominant growth mode of the most massive ellipticals. This is consistent with what we know about the Formation of cores. We know no viable way to explain galaxy cores except through dissipationless mergers of approximately equal-mass galaxies followed by core scouring by binary supermassive black holes. The observed, shallow sigma proportional to L-V(+ 0.12) relation for core ellipticals provides further evidence that they formed in dissipationless and predominantly major mergers. Also, it explains the observation that the correlation of supermassive black hole mass with velocity dispersion, M-circle proportional to sigma(4), "saturates" at high M-circle such that M-circle becomes almost independent of sigma.Item Nuclear Star Clusters From Clustered Star Formation(2011-03) Agarwal, Meghann; Milosavljevic, Milos; Agarwal, MeghannPhotometrically distinct nuclear star clusters (NSCs) are common in late-type disk and spheroidal galaxies. The formation of NSCs is inevitable in the context of normal star formation in which a majority of stars form in clusters. A young, mass-losing cluster embedded in an isolated star-forming galaxy remains gravitationally bound over a period determined by its initial mass and the galactic tidal field. The cluster migrates radially toward the center of the galaxy and becomes integrated in the NSC if it reaches the center. The rate at which the NSC grows by accreting young clusters can be estimated from empirical cluster formation rates and dissolution times. We model cluster migration and dissolution and find that the NSCs in late-type disks and in spheroidals could have assembled from migrating clusters. The resulting stellar nucleus contains a small fraction of the stellar mass of the galaxy; this fraction is sensitive to the high-mass truncation of the initial cluster mass function (ICMF). The resulting NSC masses are consistent with the observed values, but generically, the final NSCs are surrounded by a spatially more extended excess over the inward-extrapolated exponential (or Sersic) law of the outer galaxy. We suggest that the excess can be related to the pseudobulge phenomenon in disks, though perhaps not all of the pseudobulge mass assembles this way. Comparison with observed NSC masses can be used to constrain the truncation mass scale of the ICMF and the fraction of clusters suffering prompt dissolution. We infer truncation mass scales of less than or similar to 10(6) M-circle dot (greater than or similar to 10(5) M-circle dot) without (with 90%) prompt dissolution. Since the NSC assembly is collisionless and non-dissipative, no relation to the process responsible for central black hole assembly in more massive galaxies is expected.