Catalogue Search | MBRL
Are you sure you want to remove the book from the shelf?
{{itemTitle}}
28
result(s) for
"Bridge, Carrie R"
Sort by:
The star formation and merger evolution of interacting galaxies
Hierarchical models and observations show that galaxy mergers and interactions play a key role in galaxy assembly and star formation, but to what extent is still unclear. This thesis attempts to quantify their contribution to galaxy evolution by probing the number of interactions and mergers, along with their star forming properties as a function of redshift. The presence of long tidal tails and bridges are robust signatures of recent merger activity. This completely dynamical phenomenon was used to develop a new classification scheme to identify interacting galaxies and probe the interaction fraction and merger rate. We applied this new technique to large area, multi-band imaging obtained via the Canada France Hawaii Telescope Legacy Survey (CFHTLS-Deep), yielding the first statistically secure, lower limit of the galaxy interaction fraction between 0.1 < z < 1.0. Optically, the fraction of galaxies undergoing an interaction evolves moderately with redshift as (1 + z)2.24±0.24 . The Spitzer 24μm coverage of both the Extragalactic First Look Survey (XFLS) and CFHTLSDeep Survey were used to carry out one of the first and largest merger studies of IR bright galaxies. Within the ACS component of the XFLS, interactions were identified over the full merger sequence using traditional techniques, finding a merger rate increase for 24µm galaxies of (1 + z)∼2. This result implies that merging is an increasingly important process in the evolution of luminous IR galaxies (LIRGs), contributing 40–60% of the IR luminosity density and at least 30–40% of the star formation rate density at z ∼ 1. Galaxy interactions at all stages are found to have elevated star formation rates greater than a factor of two-four (on average) and a higher incidence of AGN activity compared to non-interacting field galaxies. This result supports a causal connection between galaxy merging, induced star formation, and AGN activity. Ultimately, major mergers provide a moderate contribution to the evolution of the cosmic star formation rate density and IR luminosity density to z ∼ 1, with an increasing trend suggesting that merging plays a larger role at higher redshifts (z > 1). It is also clear that merging plays a significant role in triggering the processes that power the IR emission of LIRG galaxies at z > 0.5.
Dissertation
A close-pair analysis of damp mergers at intermediate redshifts
We have studied the kinematics of ~2800 candidate close pair galaxies at 0.1
Paper
Half of the Most Luminous Quasars May Be Obscured: Investigating the Nature of WISE-Selected Hot, Dust-Obscured Galaxies
The WISE mission has unveiled a rare population of high-redshift (\\(z=1-4.6\\)), dusty, hyper-luminous galaxies, with infrared luminosities \\(L_{\\rm IR} > 10^{13}~L_{\\odot}\\), and sometimes exceeding \\(10^{14}~L_{\\odot}\\). Previous work has shown that their dust temperatures and overall far-IR SEDs are significantly hotter than expected for star-formation. We present here an analysis of the rest-frame optical through mid-IR SEDs for a large sample of these so-called \"Hot, Dust-Obscured Galaxies\" (Hot DOGs). We find that the SEDs of Hot DOGs are generally well modeled by the combination of a luminous, yet obscured AGN that dominates the rest-frame emission at \\(\\lambda > 1\\mu\\rm m\\) and the bolometric luminosity output, and a less luminous host galaxy that is responsible for the bulk of the rest optical/UV emission. Even though the stellar mass of the host galaxies may be as large as \\(10^{11}-10^{12}~M_{\\odot}\\), the AGN emission, with luminosities comparable to those of the most luminous QSOs known, require that either Hot DOGs have black hole masses significantly in excess of the local relations, or that they radiate significantly above the Eddington limit. We show that, while rare, the number density of Hot DOGs is comparable to that of equally luminous but unobscured (i.e., Type 1) QSOs. This is inconsistent with the trend of a diminishing fraction of obscured objects with increasing luminosity found for less luminous QSOs, possibly indicating a reversal in this relation at high luminosity, and that Hot DOGs are not the torus-obscured counterparts of the known optically selected, largely unobscured Hyper-Luminous QSOs. Hot DOGs may represent a different type of galaxy and thus a new component of the galaxy evolution paradigm. Finally, we discuss the environments of Hot DOGs and show that these objects are in regions as dense as those of known high-redshift proto-clusters.(Abridged)
Paper
The CFHTLS Deep Catalog of Interacting Galaxies I. Merger Rate Evolution to z=1.2
We present the rest-frame optical galaxy merger fraction between 0.24sigma level of confidence. A mild trend, where massive galaxies with M>10^10.7 M_sun are undergoing fewer mergers than less massive systems M~10^10 M_sun), consistent with the expectations of galaxy assembly downsizing is observed. Our results also show that interacting galaxies have on average SFRs double that found in non-interacting field galaxies. We conclude that (1) the optical galaxy merger fraction does evolve with redshift, (2) the merger fraction depends mildly on stellar mass, with lower mass galaxies having higher merger fractions at z<1, and (3) star formation is triggered at all phases of a merger, with larger enhancements at later stages, consistent with N-body simulations.
Paper
Submillimetre observations of WISE-selected high-redshift, luminous, dusty galaxies
We present SCUBA-2 850um submillimetre (submm) observations of the fields of 10 dusty, luminous galaxies at z ~ 1.7 - 4.6, detected at 12um and/or 22um by the WISE all-sky survey, but faint or undetected at 3.4um and 4.6um; dubbed hot, dust-obscured galaxies (Hot DOGs). The six detected targets all have total infrared luminosities greater than 10^13 L_sun, with one greater than 10^14 L_sun. Their spectral energy distributions (SEDs) are very blue from mid-infrared to submm wavelengths and not well fitted by standard AGN SED templates, without adding extra dust extinction to fit the WISE 3.4um and 4.6um data. The SCUBA-2 850um observations confirm that the Hot DOGs have less cold and/or more warm dust emission than standard AGN templates, and limit an underlying extended spiral or ULIRG-type galaxy to contribute less than about 2% or 55% of the typical total Hot DOG IR luminosity, respectively. The two most distant and luminous targets have similar observed submm to mid-infrared ratios to the rest, and thus appear to have even hotter SEDs. The number of serendipitous submm galaxies (SMGs) detected in the 1.5-arcmin-radius SCUBA-2 850um maps indicates there is a significant over-density of serendipitous sources around Hot DOGs. These submm observations confirm that the WISE-selected ultra-luminous galaxies have very blue mid-infrared to submm SEDs, suggesting that they contain very powerful AGN, and are apparently located in unusual arcmin-scale overdensities of very luminous dusty galaxies.
Paper
Interferometric Follow-Up of WISE Hyper-Luminous Hot, Dust-Obscured Galaxies
WISE has discovered an extraordinary population of hyper-luminous dusty galaxies which are faint in the two bluer passbands (\\(3.4\\, \\mu\\)m and \\(4.6\\, \\mu\\)m) but are bright in the two redder passbands of WISE (\\(12\\, \\mu\\)m and \\(22\\, \\mu\\)m). We report on initial follow-up observations of three of these hot, dust-obscured galaxies, or Hot DOGs, using the CARMA and SMA interferometer arrays at submm/mm wavelengths. We report continuum detections at \\(\\sim\\) 1.3 mm of two sources (WISE J014946.17+235014.5 and WISE J223810.20+265319.7, hereafter W0149+2350 and W2238+2653, respectively), and upper limits to CO line emission at 3 mm in the observed frame for two sources (W0149+2350 and WISE J181417.29+341224.8, hereafter W1814+3412). The 1.3 mm continuum images have a resolution of 1-2 arcsec and are consistent with single point sources. We estimate the masses of cold dust are 2.0\\(\\times 10^{8} M_{\\odot}\\) for W0149+2350 and 3.9\\(\\times 10^{8} M_{\\odot}\\) for W2238+2653, comparable to cold dust masses of luminous quasars. We obtain 2\\(\\sigma\\) upper limits to the molecular gas masses traced by CO, which are 3.3\\(\\times 10^{10} M_{\\odot}\\) and 2.3\\(\\times 10^{10} M_{\\odot}\\) for W0149+2350 and W1814+3412, respectively. We also present high-resolution, near-IR imaging with WFC3 on the Hubble Space Telescope for W0149+2653 and with NIRC2 on Keck for W2238+2653. The near-IR images show morphological structure dominated by a single, centrally condensed source with effective radius less than 4 kpc. No signs of gravitational lensing are evident.
Paper
A Deep Hubble and Keck Search for Definitive Identification of Lyman Continuum Emitters at z~3.1
Narrow-band imaging of the rest-frame Lyman continuum (LyC) of galaxies at z~3.1 has produced a large number of candidate LyC-emitting galaxies. These samples are contaminated by galaxies at lower redshift. To better understand LyC escape, we need an uncontaminated sample of galaxies that emit strongly in the LyC. Here we present deep Hubble imaging of five bright galaxies at z~3.1 that had previously been identified as candidate LyC-emitters with ground-based images. The WFC3 F336W images probe the LyC of galaxies at z>3.06 and provide an order-of-magnitude increase in spatial resolution over ground-based imaging. The non-ionizing UV images often show multiple galaxies (or components) within ~1'' of the candidate LyC emission seen from the ground. In each case, only one of the components is emitting light in the F336W filter, which would indicate LyC escape if that component is at z>3.06. We use Keck/NIRSPEC near-IR spectroscopy to measure redshifts of these components to distinguish LyC-emitters from foreground contamination. We find that two candidates are low redshift contaminants, one candidate had a previously misidentified redshift, and the other two cannot be confirmed as LyC-emitters. The level of contamination is consistent with previous estimates. For the galaxies with z>3.06, we derive strong 1 sigma limits on the relative escape fraction between 0.07 and 0.09. We still do not have a sample of definitive LyC-emitters, and a much larger study of low luminosity galaxies is required. The combination of high resolution imaging and deep spectroscopy is critical for distinguishing LyC-emitters from foreground contaminants.
Paper
The Space Density Evolution of Wet and Dry Mergers in the Canada-France-Hawaii Telescope Legacy Survey
We analyze 1298 merging galaxies with redshifts up to z=0.7 from the Canada-France-Hawaii Telescope Legacy Survey, taken from the catalog presented in Bridge et al. (2010). By analyzing the internal colors of these systems, we show that so-called wet and dry mergers evolve in different senses, and quantify the space densities of these systems. The local space density of wet mergers is essentially dentical to the local space density of dry mergers. The evolution in the total merger rate is modest out to z ~ 0.7, although the wet and dry populations have different evolutionary trends. At higher redshifts dry mergers make a smaller contribution to the total merging galaxy population, but this is offset by a roughly equivalent increase in the contribution from wet mergers. By comparing the mass density function of early-type galaxies to the corresponding mass density function for merging systems, we show that not all the major mergers with the highest masses (M_stellar > 10^11 M_solar) will end up with the most massive early-type galaxies, unless the merging timescale is dramatically longer than that usually assumed. On the other hand, the usually-assumed merging timescale of ~ 0.5-1 Gyr is quite consistent with the data if we suppose that only less massive early-type galaxies form via mergers. Since low-intermediate mass ellipticals are 10 --100 times more common than their most massive counterparts, the hierarchical explanation for the origin of early-type galaxies may be correct for the vast majority of early-types, even if incorrect for the most massive ones.
Paper
A New Population of High-z, Dusty Lyman-alpha Emitters and Blobs Discovered by WISE: Feedback Caught in the Act?
By combining data from the NASA Wide-field Infrared Survey Explorer (WISE) mission with optical spectroscopy from the W. M. Keck telescope, we discover a mid-IR color criterion that yields a 78% success rate in identifying rare, typically radio-quiet, 1.6 approx. < z approx. < 4.6 dusty Ly-alpha emitters (LAEs). Of these, at least 37% have emission extended on scales of 30-100 kpc and are considered Ly-alpha \"blobs\" (LABs). The objects have a surface density of only approx.. 0.1 deg(exp -2), making them rare enough that they have been largely missed in deep, small area surveys. We measured spectroscopic redshifts for 92 of these galaxies, and find that the LAEs (LABs) have a median redshift of 2.3 (2.5). The WISE photometry coupled with data from Herschel (Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA) reveals that these galaxies are in the Hyper Luminous IR galaxy regime (L(sub IR) approx. > 10(exp 13)-10(exp 14) Solar L) and have warm colors. They are typically more luminous and warmer than other dusty, z approx.. 2 populations such as submillimeter-selected galaxies and dust-obscured galaxies. These traits are commonly associated with the dust being illuminated by intense active galactic nucleus activity. We hypothesize that the combination of spatially extended Ly-alpha, large amounts of warm IR-luminous dust, and rarity (implying a short-lived phase) can be explained if the galaxies are undergoing brief, intense \"feedback\" transforming them from an extreme dusty starburst/QSO into a mature galaxy.
Journal Article
Spitzer Photometry of WISE-Selected Brown Dwarf and Hyper-Lumninous Infrared Galaxy Candidates
We present Spitzer 3.6 and 4.5 micrometer photometry and positions for a sample of 1510 brown dwarf candidates identified by the Wide-field Infrared Survey Explorer (WISE) all-sky survey. Of these, 166 have been spectroscopically classified as objects with spectral types M(1), L(7), T(146), and Y(12). Sixteen other objects are non-(sub)stellar in nature. The remainder are most likely distant L and T dwarfs lacking spectroscopic verification, other Y dwarf candidates still awaiting follow-up, and assorted other objects whose Spitzer photometry reveals them to be background sources. We present a catalog of Spitzer photometry for all astrophysical sources identified in these fields and use this catalog to identify seven fainter (4.5 m to approximately 17.0 mag) brown dwarf candidates, which are possibly wide-field companions to the original WISE sources. To test this hypothesis, we use a sample of 919 Spitzer observations around WISE-selected high-redshift hyper-luminous infrared galaxy candidates. For this control sample, we find another six brown dwarf candidates, suggesting that the seven companion candidates are not physically associated. In fact, only one of these seven Spitzer brown dwarf candidates has a photometric distance estimate consistent with being a companion to the WISE brown dwarf candidate. Other than this, there is no evidence for any widely separated (greater than 20 AU) ultra-cool binaries. As an adjunct to this paper, we make available a source catalog of 7.33 x 10(exp 5) objects detected in all of these Spitzer follow-up fields for use by the astronomical community. The complete catalog includes the Spitzer 3.6 and 4.5 m photometry, along with positionally matched B and R photometry from USNO-B; J, H, and Ks photometry from Two Micron All-Sky Survey; and W1, W2, W3, and W4 photometry from the WISE all-sky catalog.
Journal Article