arXiv subjects

C. J. Conselice

Publications and source records attributed to C. J. Conselice.

359 records · Page 20Linked to original sources

arXiv2005

AGN Host Galaxies at z~0.4-1.3 : Bulge-dominated and Lacking Merger-AGN Connection

We investigate morphological structure parameters and local environments of distant moderate-luminosity active galactic nucleus (AGN) host galaxies in the overlap between the HST/ACS observations of the Great Observatories Origins Deep Survey (GOODS) and the two Chandra Deep Fields. We compute near-neighbor counts and BViz asymmetry (A) and concentration (C) indices for ~35,500 GOODS/ACS galaxies complete to z_850 ~ 26.6, including the resolved hosts of 322 X-ray-selected AGNs. Distributions of (1) z_850 asymmetry for 130 AGN hosts at z_850 < 23 and (2) near-neighbor counts for 173 AGN hosts at z_850 < 24 are both consistent with non-AGN control samples. This implies no close connection between recent galaxy mergers and moderate-luminosity AGN activity out to appreciable look-back times (z < 1.3), approaching the epoch of peak AGN activity in the universe. The distribution of z_850 concentrations for the AGN hosts is offset by +0.5 compared to the non-AGN, a 6.4-sigma discrepancy much larger than can be explained by the possible influence of unresolved emission from the AGN or a circumnuclear starburst. The local universe association between AGN and bulge-dominated galaxies thus persists to substantial look-back time. We discuss implications in the context of the low-redshift supermassive central black hole mass correlation with host galaxy properties, including concentration.

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arXiv2005

The Mass Assembly Histories of Galaxies of Various Morphologies in the GOODS Fields

We present an analysis of the growth of stellar mass with cosmic time partitioned according to galaxy morphology. Using a well-defined catalog of 2150 galaxies based, in part, on archival data in the GOODS fields, we assign morphological types in three broad classes (Ellipticals, Spirals, Peculiar/Irregulars) to a limit of z_AB=22.5 and make the resulting catalog publicly available. We combine redshift information, optical photometry from the GOODS catalog and deep K-band imaging to assign stellar masses. We find little evolution in the form of the galaxy stellar mass function from z~1 to z=0, especially at the high mass end where our results are most robust. Although the population of massive galaxies is relatively well established at z~1, its morphological mix continues to change, with an increasing proportion of early-type galaxies at later times. By constructing type-dependent stellar mass functions, we show that in each of three redshift intervals, E/S0's dominate the higher mass population, while spirals are favored at lower masses. This transition occurs at a stellar mass of 2--3 times 10^{10} Msun at z~0.3 (similar to local studies) but there is evidence that the relevant mass scale moves to higher mass at earlier epochs. Such evolution may represent the morphological extension of the ``downsizing'' phenomenon, in which the most massive galaxies stop forming stars first, with lower mass galaxies becoming quiescent later. We infer that more massive galaxies evolve into spheroidal systems at earlier times, and that this morphological transformation may only be completed 1--2 Gyr after the galaxies emerge from their active star forming phase. We discuss several lines of evidence suggesting that merging may play a key role in generating this pattern of evolution.

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arXiv2004

The Structural Properties of Isolated Galaxies, Spiral-Spiral Pairs, and Mergers: The Robustness of Galaxy Morphology During Secular Evolution

We present a structural analysis of nearby galaxies in spiral-spiral pairs in optical BVRI bands and compare with the structures of isolated spiral galaxies and galaxies in ongoing mergers. We use these comparisons to determine how galaxy structure changes during galaxy interactions and mergers. We analyze light concentration (C), asymmetry (A), and clumpiness (S) parameters, and use the projections of CAS parameter space to compare these samples. We find that the CAS parameters of paired galaxies are correlated with the projected separations of the pair. For the widest and closest pairs, the CAS parameters tend to be similar to those of isolated and ongoing major mergers (ULIRGs), respectively. Our results imply that galaxy CAS morphology is a robust quantity that only changes significantly during a strong interaction or major merger. The typical time-scale for this change in our paired sample, based on dynamical friction arguments, is short, t ~ 0.1 - 0.5 Gyr. We find average enhancement factors for the spiral pair asymmetries and clumpiness values of ~2.2 and 1.5. The S parameter, which is related to star formation activity, has a moderate level of enhancement suggesting that this activity in modern spirals depends more on internal processes than on external conditions. We furthermore test the statistical criterion for picking up interacting galaxies in an automated way by using the A-S projection plane. The diversity of our spiral pair sample in the CAS space suggests that structural/SF/morphological properties of interacting galaxies change abruptly only when the interaction becomes very strong and that the criteria for finding galaxies involved in major mergers from Conselice (2003) is effective.

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arXiv2004

Bar Evolution Over the Last Eight Billion Years: A Constant Fraction of Strong Bars in GEMS

One third of present-day spirals host optically visible strong bars that drive their dynamical evolution. However, the fundamental question of how bars evolve over cosmological times has yet to be addressed, and even the frequency of bars at intermediate redshifts remains controversial. We investigate the frequency of bars out to z~1.0 drawing on a sample of 1590 galaxies from the GEMS survey, which provides morphologies from HST ACS two-color images, and highly accurate redshifts from the COMBO-17 survey. We identify spiral galaxies using the Sersic index, concentration parameter, and rest-frame color. We characterize bars and disks by fitting ellipses to F606W and F850LP images, taking advantage of the two bands to minimize bandpass shifting. We exclude highly inclined (i>60 deg) galaxies to ensure reliable morphological classifications, and apply completeness cuts of M_v <= -19.3 and -20.6. More than 40% of the bars that we detect have semi major axes a<0.5" and would be easily missed in earlier surveys without the small PSF of ACS. The bars that we can reliably detect are fairly strong (with ellipticities e>=0.4) and have a in the range ~1.2-13 kpc. We find that the optical fraction of such strong bars remains at ~(30% +- 6%) from the present-day out to look-back times of 2-6 Gyr (z~0.2-0.7) and 6-8 Gyr (z~0.7-1.0); it certainly shows no sign of a drastic decline at z>0.7. Our findings of a large and similar bar fraction at these three epochs favor scenarios in which cold gravitationally unstable disks are already in place by z~1, and where on average bars have a long lifetime (well above 2 Gyr). The distributions of structural bar properties in the two slices are, however, not statistically identical and therefore allow for the possibility that the bar strengths and sizes may evolve over time.

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arXiv2004

X-ray Properties of Lyman Break Galaxies in the Great Observatories Origins Deep Survey

We constrain the X-ray emission properties of Lyman break galaxies (LBGs) at z ~ 3-6 using the 2 Ms Chandra Deep Field-North and 1 Ms Chandra Deep Field-South. Large samples of LBGs were discovered using HST as part of the Great Observatories Origins Deep Survey (GOODS). Deep optical and X-ray imaging over the GOODS fields have allowed us to place the most significant constraints on the X-ray properties of LBGs to date. Mean X-ray properties of 449, 1734, 629, and 247 LBGs with z ~ 3, 4, 5, and 6, respectively, were determined using stacking techniques. When stacked, we detect X-ray emission from LBGs at z ~ 3 (7 sigma) and from an optically bright subset (brightest 25%) of LBGs at z ~ 4 (3 sigma); the latter is the highest redshift detection yet for "normal" galaxies in the X-ray band. The effective exposure times for these stacked observations are 0.7 and 0.5 Gs, respectively. The derived average rest-frame 2.0-8.0 keV luminosities are 1.5 and 1.4 x 10^41 erg s^-1, respectively. X-ray emission from these LBGs is likely due to high mass X-ray binaries (HMXBs) and Type II supernovae; the corresponding star formation rates are 85-240 M_sol yr^-1. The X-ray to B-band mean luminosity ratio (Lx/LB) at z~3 is somewhat elevated with respect to that measured for starburst galaxies in the local Universe. When stacking full samples of LBGs at z ~ 4, 5, and 6 we do not obtain significant detections and derive rest-frame 2.0-8.0 keV luminosity upper limits of 0.9, 2.8, and 7.1 x 10^41 erg s^-1, respectively. These upper limits constrain any widespread AGN activity in these objects to be modest at best. Furthermore, we find that ~ 0.5% of our LBGs from z ~ 3-6 are detected individually in the X-ray band. Continued ...

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arXiv2004

Large scale diffuse light in the Coma cluster: a multi-scale approach

We have obtained wide field images of the Coma cluster in the B, V, R and I bands with the CFH12K camera at CFHT. In order to search for large scale diffuse emission, we have applied to these images an iterative multi scale wavelet analysis and reconstruction technique which allowed to model all the sources (stars and galaxies) and subtract them from the original images. We found various concentrations of diffuse emission present in the central zone around the central galaxies NGC4874 and NGC4889. We characterize the positions, sizes and colors of these concentrations. Some sources do not seem to have strong star formation, while another one probably exhibits spiral-like color. One possible origin for the star forming diffuse emission sources is that in the region of the two main galaxies NGC4874 and NGC4889 spiral galaxies have recently been disrupted and star formation is still active in the dispersed material. We also use the characteristics of the sources of diffuse emission to trace the cluster dynamics. A scenario in which the group around NGC 4874 is moving north is consistent with our data.

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arXiv2003

The Recent Cluster Formation Histories of NGC 5253 and NGC 3077: Environmental Impact on Star Formation

We present multicolor photometry of bright star cluster candidates in the nearby starburst galaxies NGC 3077 and NGC 5253, observed with the Hubble Space Telescope Wide Field and Planetary Camera 2 in both broadband (F300W, F547M and F814W) and narrowband (F487N and F656N) filters. By comparing the photometry with theoretical population synthesis models, we estimate the age and mass of each star cluster, which provides constraints on the recent star formation histories of the host galaxies. We compare the star cluster populations in these dwarf starburst galaxies to those of the nuclear starburst in the barred spiral M 83, and discuss implications for our understanding of the nature and evolution of starburst events.

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arXiv2003

The Nature of Near-UV Selected Objects in the Chandra Deep Field South

We present the first results of the pure parallel near-UV observations with WFPC2 in the Chandra Deep Field South. The main goal is to search for the population of objects that contribute to the rise in the volume-averaged star formation rate at intermediate redshifts (z<1). A total of 34 objects, were identified in the WFPC2 images and their counterparts found in the ACS GOODS images. We use template fitting of the spectral energy distributions to classify the objects and found that 17 are starbursts, 9 are late-type, 2 are early-type galaxies, and 6 are stars; two of the late-types and one of the starbursts are X-ray sources. The colors of the starbursts were reproduced by the stellar evolutionary synthesis code Starburst99 which shows a mixed population of bursts with ages < 1 Gyr. Analysis of the light concentration, asymmetry and clumpiness, shows that this sample is a mixed bag, containing dwarf ellipticals, early and late-spirals and peculiar objects which resemble mergers in progress.

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arXiv2003

The relationship between the optical Halpha filaments and the X-ray emission in the core of the Perseus cluster

NGC 1275 in the centre of the Perseus cluster of galaxies, Abell 426, is surrounded by a spectacular filamentary Halpha nebula. Deep Chandra X-ray imaging has revealed that the brighter outer filaments are also detected in soft X-rays. This can be due to conduction and mixing of the cold gas in the filaments with the hot, dense intracluster medium. We show the correspondence of the filaments in both wavebands and draw attention to the relationship of two prominent curved NW filaments to an outer, buoyant radio bubble seen as a hole in the X-ray image. There is a strong resemblance in the shape of the hole and the disposition of the filaments to the behaviour of a large air bubble rising in water. If this is a correct analogy, then the flow is laminar and the intracluster gas around this radio source is not turbulent. We obtain a limit on the viscosity of this gas.

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arXiv2002

An HST Survey of the mid-UV Morphology of Nearby Galaxies

(Abbreviated) We present an imaging survey of 37 nearby galaxies observed with HST/WFPC2 in the mid-UV F300W filter and in F814W. 11 galaxies were also imaged in F255W. These galaxies were selected to be detectable with WFPC2 in one orbit, and cover a wide range of Hubble types and inclinations. The mid-UV spans the gap between our groundbased optical/NIR images and far-UV images available from the Astro/UIT missions. Our first qualitative results are: (1) Early-type galaxies show a significant decrease in surface brightness going from the red to the mid-UV, and in some cases the presence of dust lanes. Some galaxies would be classified different when viewed in the mid-UV, some become dominated by a blue nuclear feature or point source. (2) Half of the mid-type spiral and star-forming galaxies appear as a later morphological type in the mid-UV, as Astro/UIT also found in the far-UV. Some- times these differences are dramatic. The mid-UV images show a considerable range in the scale and surface brightness of individual star-forming regions. Almost all mid-type spirals have their small bulges bi-sected by a dust-lane. (3) Most of the heterogeneous subset of late-type, irregular, peculiar, and merging galaxies display F300W morphologies that are similar to those seen in F814W, but with differences due to recognizable dust features absorbing the bluer light, and due to UV-bright hot stars, star-clusters, and star-forming ridges. In the rest-frame mid-UV, early- to mid-type galaxies are more likely to be misclassified as later types than vice versa. This morphological K-correction explains only part of the excess faint blue galaxies seen in deep HST fields.

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arXiv2001

Young Clusters in the Nuclear Starburst of M 83

We present a photometric catalog of 45 massive star clusters in the nuclear starburst of M 83 (NGC 5236), observed with the Hubble Space Telescope WFPC2, in both broad-band (F300W, F547M, and F814W) and narrow-band (F656N and F487N) filters. By comparing the photometry to theoretical population synthesis models, we estimate the age and mass of each cluster. We find that over 75% of the star clusters more massive than 2*10^4 Msun in the central 300 pc of M 83 are less than 10 Myr old. Among the clusters younger than 10 Myr and more massive than 5*10^3 Msun, 70% are between 5 and 7 Myr old. We list an additional 330 clusters that are detected in our F300W images, but not in the shallower F547M and F814W images. The clusters are distributed throughout a semicircular annulus that identifies the active region in the galaxy core, between 50 and 130 pc from the optical center of M 83. Clusters younger than 5 Myr are preferentially found along the perimeter of the semicircular annulus. We suggest that the 5-7 Myr population has evacuated much of the interstellar material from the active ringlet region, and that star formation is continuing along the edges of the region.

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arXiv2000

Patterns of Super Star Cluster Formation in `Clumpy' Starburst Galaxies

We present preliminary results from a Hubble Space Telescope (HST) WFPC2 investigation of spatial and temporal distributions of star clusters in the clumpy irregular galaxy NGC 7673 and the starburst spirals NGC 3310 and Haro 1. We compare the spectral energy distributions of star clusters in the large clumps in NGC 7673 to model calculations of stellar clusters of various ages. We also propose that the presence of super star clusters in clumps seems to be a feature of intense starbursts.

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arXiv2000

Physical morphology and triggers of starburst galaxies

We present a method of determining the likely triggering mechanisms for luminous, nearby starbursts based on their optical asymmetry and (B-V) color -- what we term as indices of `physical morphology.' By comparing the starbursts' locations in a color-asymmetry diagram to an independent, nearby galaxy sample, we identify which starbursts are likely triggered by an interaction/merger. We confirm our morphological interpretation based on a comparison to 20% and 50% HI velocity-width ratios. We further explain how this use of physical morphology can put constraints on the dynamical history of other galaxies, including star-forming galaxies at high redshifts.

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arXiv1999

Structure and Evolution of Nearby UV-bright Starburst Galaxies

Nearby (D < 100 Mpc) luminous blue starburst galaxies frequently show morphological evidence for recent involvement in mild collisions, or minor mergers where the disk survives. As a consequence UV-bright starbursts are preferentially seen in near face-on galaxies, and the postburst systems may become star-forming late-type galaxies. If this starburst evolutionary channel is important at moderate redshifts, then descendants of the faint blue galaxies could be the very common Sm-Sd field galaxies.

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arXiv1999

Dwarf Elliptical Galaxies in the Perseus Cluster

Dwarf ellipticals have the lowest stellar densities of any galaxies, but paradoxically are most common in the densest regions of the universe, and are especially frequent in rich clusters of galaxies. Simple estimates suggest that low luminosity dwarf ellipticals should be subject to substantial tidal heating in rich clusters if most of their mass is in the form of normal stars. We have therefore undertaken a program to image dwarfs in clusters with the 3.5-m high performance WIYN, ARC and smaller, wide field telescopes. Our objectives include testing for evidence of tidal disruption in the form of asymmetries and searching for evidence of recent star formation which might be associated with the production of elliptical dwarfs from in-falling field galaxies.

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arXiv1999

Panchromatic Study of Nearby UV-Bright Starburst Galaxies: Implications for Massive Star Formation and High Redshift Galaxies

We present a panchromatic study of nearby starburst galaxies from the ultraviolet to the visible, including narrow band H(alpha) using WIYN and HST data, to determine how star formation processes affect the morphology and integrated fluxes of nearby starbursts. We find the UV/H(alpha) morphology of starbursts tend to differ, although not in a standard or predictable manner. From our sample of six nearby starbursts, three systems show a good correlation between UV and H(alpha) fluxes, but we find differences in UV and H(alpha) morphology between the other three. Occasionally we find systems with well defined H II regions without the corresponding brightness in the UV, and vice-versa. We discuss the likely mechanisms behind these differences which include: starburst ages, dust absorption, stellar energy ejecta through SNe and winds, as well as leakage of UV photons from stellar clusters. We conclude that the large scale morphological features in starbursts are primarily due to both age and absorption from a `picket fence' dust distribution. We further demonstrate the similarity and differences between these nearby starbursts and high redshift star forming galaxies. The overall morphology of our sample of starbursts changes little between UV and visible wavelengths. If high redshift galaxies are similar to these starbursts, their morphologies should change little between rest-frame UV and optical. We also show that FIR and UV spectral energy distributions and slopes can be used to determine large scale morphological features for extreme starbursts, with the steepest FIR slopes correlating with the most disturbed galaxies.

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arXiv1999

The Structure and Morphology of the Ionized Gas in Starburst Galaxies: NGC5253/5236

(Abridged) We investigate the interplay between starbursts and host galaxies by studying the structure and physical characteristics of the ionized gas surrounding the central starbursts in the two nearby galaxies NGC5253 and NGC5236. The two systems represent very different galactic environments, NGC5253 being a metal-poor dwarf, and NGC5236 being a metal-rich, massive spiral. We present images of the starburst regions in these two galaxies in the line emission [OIII], H-alpha, and [SII], and in continuum U, V, R. For NGC5253, line ratio maps [OIII]/H-beta and [SII]/H-alpha show that in the outer regions the diffuse ionized gas (DIG) is partially excited by a non-photoionization process (`shocks'). The `shocked' gas is mostly concentrated south-west of the galaxy's center, in coincidence with the position of H-alpha bubbles and with extended soft X-ray emission. The H-alpha emission from the shock-excited gas is ~1-2% of the total. About 80-90% of the DIG is consistent with being photoionized, requiring that about 10% of the ionizing photons escape from the starburst site. The starburst in NGC5253 appears to be fed by gas infalling along the galaxy's optical minor axis, while hot gas expanding from the starburst has a preferential direction along the major axis. The results for NGC5236 are less clear than for NGC5253, as the images are not as deep. The emission line ratio maps show very little or no evidence for presence of shock excitation and very little or no ionized gas appears expanding from the center of the galaxy outward along the disk plane. The starburst in NGC5236 is thus more strongly confined than that in NGC5253, probably due to the deeper gravitational potential well of the more massive galaxy.

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