Alice C. Quillen | University of Rochester (original) (raw)
Papers by Alice C. Quillen
Astrophysical Journal Supplement Series, 2003
This paper introduces a continuing survey of galaxies in the local universe. Consistent deep imag... more This paper introduces a continuing survey of galaxies in the local universe. Consistent deep images are being acquired for a representative sample of 321 galaxies in the Uppsala General Catalogue down to 21.7 mag arcsec~2 at Ks (2.16 km) and 22.4 mag arcsec~2 at J (1.25 km) using a NICMOS camera with a Ðeld of view attached to the 61 inch (1.5 m) telescope on Mount Bigelow. We provide some 3@ .8 ] 3@ .8 examples of the results being obtained by employing 64 deep images of a subset of 44 galaxies. Bulge-todisk ratios are tabulated for 30 galaxies. The brightness of the central region of 44 galaxies declines approximately 5 mag from Hubble type S0 to Sm. An exponential vertical scale height at Ks is found to be 500 pc for the disk of UGC 5173. Arm amplitudes of four nearly face-on spiral galaxies are found to range between 11% and 88% compared to the interarm region. There is some evidence that the arm amplitude is larger at Ks than it is at J. Color gradients are measured for 15 galaxies with only one showing a signiÐcant nonzero result. A measurement of galactic symmetry applied to 64 deep images reveals an average asymmetry of 7.6% (p \ 4.6%) for these galaxies.
We simulate planet migration caused by interactions between planets and a planetesimal disk. We u... more We simulate planet migration caused by interactions between planets and a planetesimal disk. We use an N-body integrator optimized for near-Keplerian motion that runs in parallel on a video graphics card, and that computes all pair-wise gravitational interactions. We find that the fraction of planetesimals found in mean motion resonances is reduced and planetary migration rates are on average about
Monthly Notices of The Royal Astronomical Society, 2008
We introduce a differential equation for star formation in galaxies that incorporates negative fe... more We introduce a differential equation for star formation in galaxies that incorporates negative feedback with a delay. When the feedback is instantaneous, solutions approach a self-limiting equilibrium state. When there is a delay, even though the feedback is negative, the solutions can exhibit cyclic and episodic solutions. We find that periodic or episodic star formation only occurs when two conditions
Astrophysical Journal, 2003
The star S0-2, which is orbiting Sgr A* with a 15 yr period, almost certainly did not form in sit... more The star S0-2, which is orbiting Sgr A* with a 15 yr period, almost certainly did not form in situ. We propose that it was injected into this close orbit by the tidal disruption of a massive-star binary, whose primary was more massive than S0-2 and at least 60Msolar. From numerical integrations we find that 1%-2% of incoming binaries with
Monthly Notices of the Royal Astronomical Society
We searched the light curves of over 40000 stars in the 2MASS calibration database, spanning appr... more We searched the light curves of over 40000 stars in the 2MASS calibration database, spanning approximately 4 years, for objects that have significant day long dimming events. We also searched the multi-color light curves for red dimming events that could be due to transient extinction. In the color independent sigma-limited search, we found 46 previously unknown eclipsing binaries, 6 periodic variable stars likely to be intrinsic pulsators and 21 young stellar objects in the rho\rhorho Ophiucus star formation region previously studied by Parks et al. 2013. An additional 11 objects exhibited dimming events and most of these are unclassified. The search for red dimming events primarily reveals a population of low luminosity active galaxies that become bluer when they are brighter, and variable young stellar objects exhibiting high cross-correlation coefficients between color and brightness. The young stellar objects exhibit brightness and color variations in the direction of interstellar ...
Quillen et al. and O'Dea et al. carried out a Spitzer study of a sample of 62 brightest clust... more Quillen et al. and O'Dea et al. carried out a Spitzer study of a sample of 62 brightest cluster galaxies (BCGs) from the ROSAT Brightest Cluster Sample chosen based on their elevated H-alpha flux. We present Hubble Space Telescope Advanced Camera for Surveys (ACS) far ultraviolet (FUV) images of the Ly-alpha and continuum emission of the luminous emission-line nebulae in
EPJ Web of Conferences, 2012
Disc non-axisymmetrc components, such as spirals and central bars, are nowadays known to play an ... more Disc non-axisymmetrc components, such as spirals and central bars, are nowadays known to play an important role in shaping galactic discs. Here we use Tree-SPH Nbody simulations to examine the effect of these perturbers on two aspects: the occurrence of multiple patterns in discs and the effects of radial migration on disc thickening. We find that, in addition to a central bar, multiple spiral patterns and lopsided modes develop in all models. Interaction among these asymmetric features results in a large scale stellar migration. However, we show that, despite the strong radial mixing, discs cannot be thickened sufficiently to match observed thick discs. We relate this to the adiabatic cooling as stars migrate radially outwards. We also find that the bulge contribution to a thick-disc component for an Sa-type galaxy at ∼ 2.5 disc scale-lengths is less than 1% and zero in the case of a Milky Way-like, Sb-type. Our findings cast doubt on the plausibility of thick disc formation via stellar radial migration. a
With funding from the National Science Foundation, the University of Delaware (UD) in partnership... more With funding from the National Science Foundation, the University of Delaware (UD) in partnership with the New Castle County Vocational Technical School District (NCCoVoTech) in Delaware has initiated a GK-12 Program. In each of year this program, nine full time UD graduate students in the sciences, who have completed all or most of their coursework, will be selected to serve as fellows. Participation in the GK-12 program benefits the graduate fellows in many ways. In addition to gaining general insight into current issues of science education, the fellows enhance their experience as scientific researchers by directly improving their ability to effectively communicate complex quantitative and technical knowledge to an audience with multiple and diverse learning needs. In the first year of this project, fellows have been paired with high school science teachers from NCCoVoTech. These pairs, along with the principal investigators (PIs) of this program have formed a learning community ...
With 2D hydrodynamical simulations of disks perturbed externally by stars, brown dwarfs or planet... more With 2D hydrodynamical simulations of disks perturbed externally by stars, brown dwarfs or planets we investigate possible scenarios that can account for the spiral structure in circumstellar disks. We consider two scenarios, spiral structure driven by an external bound planet or low mass star and that excited by a previous stellar close encounter or flyby. We find that both scenarios produce morphology similar to that observed in the outer disks of HD 141569A and HD 100546; moderately open 2-armed outer spiral structure. The outer two-armed spiral structure observed in the disk of HD 141569A is qualitatively reproduced with tidal perturbations from its companion binary HD 141569B,C on a prograde orbit near periapse. Our simulation accounts for the outer spiral arms, but is less successful than the secular model of Augereau and Papaloizou at matching the lopsidedness or asymmetry of the disk edge at 300AU. The disk has been previously truncated by the tidal force from the binary. A ...
The Astrophysical Journal, 2005
Outflows from young stellar objects have been identified as a possible source of turbulence in mo... more Outflows from young stellar objects have been identified as a possible source of turbulence in molecular clouds. To investigate the relationship between outflows, cloud dynamics and turbulence, we compare the kinematics of the molecular gas associated with NGC 1333, traced in 13 CO(1-0), with the distribution of young stellar objects (YSOs) within. We find a velocity dispersion of ∼ 1 − 1.6km/s in 13 CO that does not significantly vary across the cloud, and is uncorrelated with the number of nearby young stellar outflows identified from optical and submillimeter observations. However, from velocity channel maps we identify about 20 depressions in the 13 CO intensity of scales 0.1 − 0.2pc and velocity widths 1 − 3km/s. The depressions exhibit limb brightened rims in both individual velocity channel maps and position velocity diagrams, suggesting that they are slowly expanding cavities. We interpret these depressions to be remnants of past YSO outflow activity: If these cavities are presently empty, they would fill in on time scales of ∼ 10 6 yr. This can exceed the lifetime of a YSO outflow phase, or the transit time of the central star through the cavity, explaining the absence of any clear correlation between the cavities and YSO outflows. We find that the momentum and energy deposition associated with the expansion of the cavities is sufficient to power the turbulence in the cloud. In this way we conclude that the cavities are an important intermediate step between the conversion of YSO outflow energy and momentum into cloud turbulent motions.
The Astrophysical Journal, 2004
Spitzer observations of the young star CoKuTau/4 reveal a disk with a 10 AU hole that is most lik... more Spitzer observations of the young star CoKuTau/4 reveal a disk with a 10 AU hole that is most likely caused by a newly formed planet. Assuming that the planet opened a gap in the viscous disk, we estimate that the planet mass is greater than 0.1 Jupiter masses. This estimate depends on a lower limit to the disk viscosity derived from the time scale needed to accrete the inner disk, creating the now detectable hole. The planet migration time scale must at least modestly exceed the time for the spectrally inferred hole to clear. The proximity of the planet to the disk edge implied by our limits suggests that the latter is perturbed by the nearby planet and may exhibit a spiral pattern rotating with the planet. This pattern might be resolved with current ground based mid-infrared cameras and optical cameras on the Hubble Space Telescope. The required sub-Myr planet formation may challenge core accretion formation models. However, we find that only if the planet mass is larger than about 10 Jupiter masses, allowing for a high enough surface density without inducing migration, would formation by direct gravitational instability be possible.
The Astrophysical Journal, 2010
carried out a Spitzer study of a sample of 62 brightest cluster galaxies (BCGs) from the ROSAT br... more carried out a Spitzer study of a sample of 62 brightest cluster galaxies (BCGs) from the ROSAT brightest cluster sample, which were chosen based on their elevated Hα flux. We present Hubble Space Telescope Advanced Camera for Surveys far-ultraviolet (FUV) images of the Lyα and continuum emission of the luminous emission-line nebulae in seven BCGs found to have an infrared (IR) excess. We confirm that the BCGs are actively forming stars which suggests that the IR excess seen in these BCGs is indeed associated with star formation. Our observations are consistent with a scenario in which gas that cools from the intracluster medium fuels the star formation. The FUV continuum emission extends over a region ∼7-28 kpc (largest linear size) and even larger in Lyα. The young stellar population required by the FUV observations would produce a significant fraction of the ionizing photons required to power the emission-line nebulae. Star formation rates estimated from the FUV continuum range from ∼3 to ∼14 times lower than those estimated from the IR, however, both the Balmer decrements in the central few arcseconds and detection of CO in most of these galaxies imply that there are regions of high extinction that could have absorbed much of the FUV continuum. Analysis of archival Very Large Array observations reveals compact radio sources in all seven BCGs and kpc scale jets in A-1835 and RXJ 2129+00. The four galaxies with archival deep Chandra observations exhibit asymmetric X-ray emission, the peaks of which are offset from the center of the BCG by ∼10 kpc on average. A low feedback state for the active galactic nucleus could allow increased condensation of the hot gas into the center of the galaxy and the feeding of star formation.
The Astrophysical Journal, 2009
In this paper we explore the relationship between protostellar outflows and turbulence in molecul... more In this paper we explore the relationship between protostellar outflows and turbulence in molecular clouds. Using 3-D numerical simulations we focus on the hydrodynamics of multiple outflows interacting within a parsec scale volume. We explore the extent to which transient outflows injecting directed energy and momentum into a sub-volume of a molecular cloud can be converted into random turbulent motions. We show that turbulence can readily be sustained by these interactions and show that it is possible to broadly characterize an effective driving scale of the outflows. We compare the velocity spectrum obtained in our studies to that of isotropically forced hydrodynamic turbulence finding that in outflow driven turbulence a power law of the form E(k) ∝ k −β is indeed achieved. However we find a steeper spectrum β ∼ 3 is obtained in outflow driven turbulence models than in isotropically forced simulations β ∼ 2.0. We discuss possible physical mechanisms responsible for these results as well and their implications for turbulence in molecular clouds where outflows will act in concert with other processes such as gravitational collapse.
The Astrophysical Journal, 2009
The link between turbulence in star formatting environments and protostellar jets remains controv... more The link between turbulence in star formatting environments and protostellar jets remains controversial. To explore issues of turbulence and fossil cavities driven by young stellar outflows we present a series of numerical simulations tracking the evolution of transient protostellar jets driven into a turbulent medium. Our simulations show both the effect of turbulence on outflow structures and, conversely, the effect of outflows on the ambient turbulence. We demonstrate how turbulence will lead to strong modifications in jet morphology. More importantly, we demonstrate that individual transient outflows have the capacity to re-energize decaying turbulence. Our simulations support a scenario in which the directed energy/momentum associated with cavities is randomized as the cavities are disrupted by dynamical instabilities seeded by the ambient turbulence. Consideration of the energy power spectra of the simulations reveals that the disruption of the cavities powers an energy cascade consistent with Burgers'-type turbulence (E(k) ∝ k −2 ) and produces a driving scale-length associated with the cavity propagation length. We conclude that fossil cavities interacting either with a turbulent medium or with other cavities have the capacity to sustain or create turbulent flows in star forming environments. In the last section we contrast our work and its conclusions with previous studies which claim that jets can not be the source of turbulence.
The Astrophysical Journal, 2006
Spitzer Space Telescope mid-infrared images of the radio galaxy Centaurus A reveal a shell-like, ... more Spitzer Space Telescope mid-infrared images of the radio galaxy Centaurus A reveal a shell-like, bipolar, structure 500 pc to the north and south of the nucleus. This shell is seen in 5.8, 8.0 and 24µm broad-band images. Such a remarkable shell has not been previously detected in a radio galaxy and is the first extragalactic nuclear shell detected at mid-infrared wavelengths. We estimate that the shell is a few million years old and has a mass of order million solar masses. A conservative estimate for the mechanical energy in the wind driven bubble is 10 53 erg. The shell could have created by a small few thousand solar mass nuclear burst of star formation. Alternatively, the bolometric luminosity of the active nucleus is sufficiently large that it could power the shell. Constraints on the shell's velocity are lacking. However, if the shell is moving at 1000 km s −1 then the required mechanical energy would be 100 times larger.
The Astrophysical Journal, 2007
We investigate isophotal properties and dust morphology in the nuclear regions of 84 radio galaxi... more We investigate isophotal properties and dust morphology in the nuclear regions of 84 radio galaxies, imaged in the optical and near-infrared as part of Hubble Space Telescope snapshot surveys. We present a sample-wide trend between host galaxy isophotal structure and the inclination of dusty circumnuclear disks at the centers of 13 of these objects. We find that galaxies containing edge-on disks are invariably seen to possess boxy isophotes, while round, face-on disks are seen exclusively in objects with round or elliptical isophotes. Dustrich sources with disky isophotes are observed only to possess dust in the form of extended filamentary lanes, and not in settled distributions like disks. As we do not expect that edge-on and face-on disks reside in different populations of galaxies, we conclude that perceived isophotal boxiness is dependent upon the angle at which the observer views the host galaxy's axis of symmetry. We discuss our results in the context of dissipative merger scenarios, and infer that dusty disks primarily reside in old, boxy remnants of gas-poor galaxy mergers, whereas filamentary dust lanes reside in younger disky remnants of gas-rich mergers.
The Astrophysical Journal, 2006
In the original version of this paper, we reported on a series of ultraviolet (UV) spectroscopic ... more In the original version of this paper, we reported on a series of ultraviolet (UV) spectroscopic observations of the dwarf Seyfert 1 galaxy NGC 4395, made with the Space Telescope Imaging Spectrograph on Hubble Space Telescope (HST). Unfortunately, a data processing error led to an incorrect flux calibration for these spectra. All STIS-based UV fluxes in the original paper are too high by a factor of 7.96 as a result of neglecting to adjust the flux-scaling algorithm from a diffuse source to a point source.
The Astrophysical Journal, 2006
We report the discovery of a new optical-IR synchrotron jet in the radio galaxy 3C 133 from our H... more We report the discovery of a new optical-IR synchrotron jet in the radio galaxy 3C 133 from our HST/NICMOS snapshot survey. The jet and eastern hotspot are well resolved, and visible at both optical and IR wavelengths. The IR jet follows the morphology of the inner part of the radio jet, with three distinct knots identified with features in the radio. The radio-IR SED's of the knots are examined, along with those of two more distant hotspots at the eastern extreme of the radio feature. The detected emission appears to be synchrotron, with peaks in the NIR for all except one case, which exhibits a power-law spectrum throughout.
The Astrophysical Journal, 2006
Spitzer mid-infrared images of the dusty warped disk in the galaxy Centaurus A show a parallelogr... more Spitzer mid-infrared images of the dusty warped disk in the galaxy Centaurus A show a parallelogram-shaped structure. We successfully model the observed mid-infrared morphology by integrating the light from an emitting, thin, and warped disk, similar to that inferred from previous kinematic studies. The models with the best match to the morphology lack dust emission within the inner 0.1 to 0.8 kpc, suggesting that energetic processes near the nucleus have disturbed the inner molecular disk, creating a gap in the molecular gas distribution.
![Research paper thumbnail of Erratum: “Multiwavelength Monitoring of the Dwarf Seyfert 1 Galaxy NGC 4395. I. A Reverberation‐based Measurement of the Black Hole Mass” (ApJ, 632, 799 [2005])](https://attachments.academia-assets.com/44112468/thumbnails/1.jpg)
](The Astrophysical Journal, 2006
In the original version of this paper, we reported on a series of ultraviolet (UV) spectroscopic ... more In the original version of this paper, we reported on a series of ultraviolet (UV) spectroscopic observations of the dwarf Seyfert 1 galaxy NGC 4395, made with the Space Telescope Imaging Spectrograph on the Hubble Space Telescope (HST ). Unfortunately, a data processing error led to an incorrect flux calibration for these spectra. All STIS-based UV fluxes in the original paper are too high by a factor of 7.96 as a result of neglecting to adjust the flux-scaling algorithm from a diffuse source to a point source.
Astrophysical Journal Supplement Series, 2003
This paper introduces a continuing survey of galaxies in the local universe. Consistent deep imag... more This paper introduces a continuing survey of galaxies in the local universe. Consistent deep images are being acquired for a representative sample of 321 galaxies in the Uppsala General Catalogue down to 21.7 mag arcsec~2 at Ks (2.16 km) and 22.4 mag arcsec~2 at J (1.25 km) using a NICMOS camera with a Ðeld of view attached to the 61 inch (1.5 m) telescope on Mount Bigelow. We provide some 3@ .8 ] 3@ .8 examples of the results being obtained by employing 64 deep images of a subset of 44 galaxies. Bulge-todisk ratios are tabulated for 30 galaxies. The brightness of the central region of 44 galaxies declines approximately 5 mag from Hubble type S0 to Sm. An exponential vertical scale height at Ks is found to be 500 pc for the disk of UGC 5173. Arm amplitudes of four nearly face-on spiral galaxies are found to range between 11% and 88% compared to the interarm region. There is some evidence that the arm amplitude is larger at Ks than it is at J. Color gradients are measured for 15 galaxies with only one showing a signiÐcant nonzero result. A measurement of galactic symmetry applied to 64 deep images reveals an average asymmetry of 7.6% (p \ 4.6%) for these galaxies.
We simulate planet migration caused by interactions between planets and a planetesimal disk. We u... more We simulate planet migration caused by interactions between planets and a planetesimal disk. We use an N-body integrator optimized for near-Keplerian motion that runs in parallel on a video graphics card, and that computes all pair-wise gravitational interactions. We find that the fraction of planetesimals found in mean motion resonances is reduced and planetary migration rates are on average about
Monthly Notices of The Royal Astronomical Society, 2008
We introduce a differential equation for star formation in galaxies that incorporates negative fe... more We introduce a differential equation for star formation in galaxies that incorporates negative feedback with a delay. When the feedback is instantaneous, solutions approach a self-limiting equilibrium state. When there is a delay, even though the feedback is negative, the solutions can exhibit cyclic and episodic solutions. We find that periodic or episodic star formation only occurs when two conditions
Astrophysical Journal, 2003
The star S0-2, which is orbiting Sgr A* with a 15 yr period, almost certainly did not form in sit... more The star S0-2, which is orbiting Sgr A* with a 15 yr period, almost certainly did not form in situ. We propose that it was injected into this close orbit by the tidal disruption of a massive-star binary, whose primary was more massive than S0-2 and at least 60Msolar. From numerical integrations we find that 1%-2% of incoming binaries with
Monthly Notices of the Royal Astronomical Society
We searched the light curves of over 40000 stars in the 2MASS calibration database, spanning appr... more We searched the light curves of over 40000 stars in the 2MASS calibration database, spanning approximately 4 years, for objects that have significant day long dimming events. We also searched the multi-color light curves for red dimming events that could be due to transient extinction. In the color independent sigma-limited search, we found 46 previously unknown eclipsing binaries, 6 periodic variable stars likely to be intrinsic pulsators and 21 young stellar objects in the rho\rhorho Ophiucus star formation region previously studied by Parks et al. 2013. An additional 11 objects exhibited dimming events and most of these are unclassified. The search for red dimming events primarily reveals a population of low luminosity active galaxies that become bluer when they are brighter, and variable young stellar objects exhibiting high cross-correlation coefficients between color and brightness. The young stellar objects exhibit brightness and color variations in the direction of interstellar ...
Quillen et al. and O'Dea et al. carried out a Spitzer study of a sample of 62 brightest clust... more Quillen et al. and O'Dea et al. carried out a Spitzer study of a sample of 62 brightest cluster galaxies (BCGs) from the ROSAT Brightest Cluster Sample chosen based on their elevated H-alpha flux. We present Hubble Space Telescope Advanced Camera for Surveys (ACS) far ultraviolet (FUV) images of the Ly-alpha and continuum emission of the luminous emission-line nebulae in
EPJ Web of Conferences, 2012
Disc non-axisymmetrc components, such as spirals and central bars, are nowadays known to play an ... more Disc non-axisymmetrc components, such as spirals and central bars, are nowadays known to play an important role in shaping galactic discs. Here we use Tree-SPH Nbody simulations to examine the effect of these perturbers on two aspects: the occurrence of multiple patterns in discs and the effects of radial migration on disc thickening. We find that, in addition to a central bar, multiple spiral patterns and lopsided modes develop in all models. Interaction among these asymmetric features results in a large scale stellar migration. However, we show that, despite the strong radial mixing, discs cannot be thickened sufficiently to match observed thick discs. We relate this to the adiabatic cooling as stars migrate radially outwards. We also find that the bulge contribution to a thick-disc component for an Sa-type galaxy at ∼ 2.5 disc scale-lengths is less than 1% and zero in the case of a Milky Way-like, Sb-type. Our findings cast doubt on the plausibility of thick disc formation via stellar radial migration. a
With funding from the National Science Foundation, the University of Delaware (UD) in partnership... more With funding from the National Science Foundation, the University of Delaware (UD) in partnership with the New Castle County Vocational Technical School District (NCCoVoTech) in Delaware has initiated a GK-12 Program. In each of year this program, nine full time UD graduate students in the sciences, who have completed all or most of their coursework, will be selected to serve as fellows. Participation in the GK-12 program benefits the graduate fellows in many ways. In addition to gaining general insight into current issues of science education, the fellows enhance their experience as scientific researchers by directly improving their ability to effectively communicate complex quantitative and technical knowledge to an audience with multiple and diverse learning needs. In the first year of this project, fellows have been paired with high school science teachers from NCCoVoTech. These pairs, along with the principal investigators (PIs) of this program have formed a learning community ...
With 2D hydrodynamical simulations of disks perturbed externally by stars, brown dwarfs or planet... more With 2D hydrodynamical simulations of disks perturbed externally by stars, brown dwarfs or planets we investigate possible scenarios that can account for the spiral structure in circumstellar disks. We consider two scenarios, spiral structure driven by an external bound planet or low mass star and that excited by a previous stellar close encounter or flyby. We find that both scenarios produce morphology similar to that observed in the outer disks of HD 141569A and HD 100546; moderately open 2-armed outer spiral structure. The outer two-armed spiral structure observed in the disk of HD 141569A is qualitatively reproduced with tidal perturbations from its companion binary HD 141569B,C on a prograde orbit near periapse. Our simulation accounts for the outer spiral arms, but is less successful than the secular model of Augereau and Papaloizou at matching the lopsidedness or asymmetry of the disk edge at 300AU. The disk has been previously truncated by the tidal force from the binary. A ...
The Astrophysical Journal, 2005
Outflows from young stellar objects have been identified as a possible source of turbulence in mo... more Outflows from young stellar objects have been identified as a possible source of turbulence in molecular clouds. To investigate the relationship between outflows, cloud dynamics and turbulence, we compare the kinematics of the molecular gas associated with NGC 1333, traced in 13 CO(1-0), with the distribution of young stellar objects (YSOs) within. We find a velocity dispersion of ∼ 1 − 1.6km/s in 13 CO that does not significantly vary across the cloud, and is uncorrelated with the number of nearby young stellar outflows identified from optical and submillimeter observations. However, from velocity channel maps we identify about 20 depressions in the 13 CO intensity of scales 0.1 − 0.2pc and velocity widths 1 − 3km/s. The depressions exhibit limb brightened rims in both individual velocity channel maps and position velocity diagrams, suggesting that they are slowly expanding cavities. We interpret these depressions to be remnants of past YSO outflow activity: If these cavities are presently empty, they would fill in on time scales of ∼ 10 6 yr. This can exceed the lifetime of a YSO outflow phase, or the transit time of the central star through the cavity, explaining the absence of any clear correlation between the cavities and YSO outflows. We find that the momentum and energy deposition associated with the expansion of the cavities is sufficient to power the turbulence in the cloud. In this way we conclude that the cavities are an important intermediate step between the conversion of YSO outflow energy and momentum into cloud turbulent motions.
The Astrophysical Journal, 2004
Spitzer observations of the young star CoKuTau/4 reveal a disk with a 10 AU hole that is most lik... more Spitzer observations of the young star CoKuTau/4 reveal a disk with a 10 AU hole that is most likely caused by a newly formed planet. Assuming that the planet opened a gap in the viscous disk, we estimate that the planet mass is greater than 0.1 Jupiter masses. This estimate depends on a lower limit to the disk viscosity derived from the time scale needed to accrete the inner disk, creating the now detectable hole. The planet migration time scale must at least modestly exceed the time for the spectrally inferred hole to clear. The proximity of the planet to the disk edge implied by our limits suggests that the latter is perturbed by the nearby planet and may exhibit a spiral pattern rotating with the planet. This pattern might be resolved with current ground based mid-infrared cameras and optical cameras on the Hubble Space Telescope. The required sub-Myr planet formation may challenge core accretion formation models. However, we find that only if the planet mass is larger than about 10 Jupiter masses, allowing for a high enough surface density without inducing migration, would formation by direct gravitational instability be possible.
The Astrophysical Journal, 2010
carried out a Spitzer study of a sample of 62 brightest cluster galaxies (BCGs) from the ROSAT br... more carried out a Spitzer study of a sample of 62 brightest cluster galaxies (BCGs) from the ROSAT brightest cluster sample, which were chosen based on their elevated Hα flux. We present Hubble Space Telescope Advanced Camera for Surveys far-ultraviolet (FUV) images of the Lyα and continuum emission of the luminous emission-line nebulae in seven BCGs found to have an infrared (IR) excess. We confirm that the BCGs are actively forming stars which suggests that the IR excess seen in these BCGs is indeed associated with star formation. Our observations are consistent with a scenario in which gas that cools from the intracluster medium fuels the star formation. The FUV continuum emission extends over a region ∼7-28 kpc (largest linear size) and even larger in Lyα. The young stellar population required by the FUV observations would produce a significant fraction of the ionizing photons required to power the emission-line nebulae. Star formation rates estimated from the FUV continuum range from ∼3 to ∼14 times lower than those estimated from the IR, however, both the Balmer decrements in the central few arcseconds and detection of CO in most of these galaxies imply that there are regions of high extinction that could have absorbed much of the FUV continuum. Analysis of archival Very Large Array observations reveals compact radio sources in all seven BCGs and kpc scale jets in A-1835 and RXJ 2129+00. The four galaxies with archival deep Chandra observations exhibit asymmetric X-ray emission, the peaks of which are offset from the center of the BCG by ∼10 kpc on average. A low feedback state for the active galactic nucleus could allow increased condensation of the hot gas into the center of the galaxy and the feeding of star formation.
The Astrophysical Journal, 2009
In this paper we explore the relationship between protostellar outflows and turbulence in molecul... more In this paper we explore the relationship between protostellar outflows and turbulence in molecular clouds. Using 3-D numerical simulations we focus on the hydrodynamics of multiple outflows interacting within a parsec scale volume. We explore the extent to which transient outflows injecting directed energy and momentum into a sub-volume of a molecular cloud can be converted into random turbulent motions. We show that turbulence can readily be sustained by these interactions and show that it is possible to broadly characterize an effective driving scale of the outflows. We compare the velocity spectrum obtained in our studies to that of isotropically forced hydrodynamic turbulence finding that in outflow driven turbulence a power law of the form E(k) ∝ k −β is indeed achieved. However we find a steeper spectrum β ∼ 3 is obtained in outflow driven turbulence models than in isotropically forced simulations β ∼ 2.0. We discuss possible physical mechanisms responsible for these results as well and their implications for turbulence in molecular clouds where outflows will act in concert with other processes such as gravitational collapse.
The Astrophysical Journal, 2009
The link between turbulence in star formatting environments and protostellar jets remains controv... more The link between turbulence in star formatting environments and protostellar jets remains controversial. To explore issues of turbulence and fossil cavities driven by young stellar outflows we present a series of numerical simulations tracking the evolution of transient protostellar jets driven into a turbulent medium. Our simulations show both the effect of turbulence on outflow structures and, conversely, the effect of outflows on the ambient turbulence. We demonstrate how turbulence will lead to strong modifications in jet morphology. More importantly, we demonstrate that individual transient outflows have the capacity to re-energize decaying turbulence. Our simulations support a scenario in which the directed energy/momentum associated with cavities is randomized as the cavities are disrupted by dynamical instabilities seeded by the ambient turbulence. Consideration of the energy power spectra of the simulations reveals that the disruption of the cavities powers an energy cascade consistent with Burgers'-type turbulence (E(k) ∝ k −2 ) and produces a driving scale-length associated with the cavity propagation length. We conclude that fossil cavities interacting either with a turbulent medium or with other cavities have the capacity to sustain or create turbulent flows in star forming environments. In the last section we contrast our work and its conclusions with previous studies which claim that jets can not be the source of turbulence.
The Astrophysical Journal, 2006
Spitzer Space Telescope mid-infrared images of the radio galaxy Centaurus A reveal a shell-like, ... more Spitzer Space Telescope mid-infrared images of the radio galaxy Centaurus A reveal a shell-like, bipolar, structure 500 pc to the north and south of the nucleus. This shell is seen in 5.8, 8.0 and 24µm broad-band images. Such a remarkable shell has not been previously detected in a radio galaxy and is the first extragalactic nuclear shell detected at mid-infrared wavelengths. We estimate that the shell is a few million years old and has a mass of order million solar masses. A conservative estimate for the mechanical energy in the wind driven bubble is 10 53 erg. The shell could have created by a small few thousand solar mass nuclear burst of star formation. Alternatively, the bolometric luminosity of the active nucleus is sufficiently large that it could power the shell. Constraints on the shell's velocity are lacking. However, if the shell is moving at 1000 km s −1 then the required mechanical energy would be 100 times larger.
The Astrophysical Journal, 2007
We investigate isophotal properties and dust morphology in the nuclear regions of 84 radio galaxi... more We investigate isophotal properties and dust morphology in the nuclear regions of 84 radio galaxies, imaged in the optical and near-infrared as part of Hubble Space Telescope snapshot surveys. We present a sample-wide trend between host galaxy isophotal structure and the inclination of dusty circumnuclear disks at the centers of 13 of these objects. We find that galaxies containing edge-on disks are invariably seen to possess boxy isophotes, while round, face-on disks are seen exclusively in objects with round or elliptical isophotes. Dustrich sources with disky isophotes are observed only to possess dust in the form of extended filamentary lanes, and not in settled distributions like disks. As we do not expect that edge-on and face-on disks reside in different populations of galaxies, we conclude that perceived isophotal boxiness is dependent upon the angle at which the observer views the host galaxy's axis of symmetry. We discuss our results in the context of dissipative merger scenarios, and infer that dusty disks primarily reside in old, boxy remnants of gas-poor galaxy mergers, whereas filamentary dust lanes reside in younger disky remnants of gas-rich mergers.
The Astrophysical Journal, 2006
In the original version of this paper, we reported on a series of ultraviolet (UV) spectroscopic ... more In the original version of this paper, we reported on a series of ultraviolet (UV) spectroscopic observations of the dwarf Seyfert 1 galaxy NGC 4395, made with the Space Telescope Imaging Spectrograph on Hubble Space Telescope (HST). Unfortunately, a data processing error led to an incorrect flux calibration for these spectra. All STIS-based UV fluxes in the original paper are too high by a factor of 7.96 as a result of neglecting to adjust the flux-scaling algorithm from a diffuse source to a point source.
The Astrophysical Journal, 2006
We report the discovery of a new optical-IR synchrotron jet in the radio galaxy 3C 133 from our H... more We report the discovery of a new optical-IR synchrotron jet in the radio galaxy 3C 133 from our HST/NICMOS snapshot survey. The jet and eastern hotspot are well resolved, and visible at both optical and IR wavelengths. The IR jet follows the morphology of the inner part of the radio jet, with three distinct knots identified with features in the radio. The radio-IR SED's of the knots are examined, along with those of two more distant hotspots at the eastern extreme of the radio feature. The detected emission appears to be synchrotron, with peaks in the NIR for all except one case, which exhibits a power-law spectrum throughout.
The Astrophysical Journal, 2006
Spitzer mid-infrared images of the dusty warped disk in the galaxy Centaurus A show a parallelogr... more Spitzer mid-infrared images of the dusty warped disk in the galaxy Centaurus A show a parallelogram-shaped structure. We successfully model the observed mid-infrared morphology by integrating the light from an emitting, thin, and warped disk, similar to that inferred from previous kinematic studies. The models with the best match to the morphology lack dust emission within the inner 0.1 to 0.8 kpc, suggesting that energetic processes near the nucleus have disturbed the inner molecular disk, creating a gap in the molecular gas distribution.
The Astrophysical Journal, 2006
In the original version of this paper, we reported on a series of ultraviolet (UV) spectroscopic ... more In the original version of this paper, we reported on a series of ultraviolet (UV) spectroscopic observations of the dwarf Seyfert 1 galaxy NGC 4395, made with the Space Telescope Imaging Spectrograph on the Hubble Space Telescope (HST ). Unfortunately, a data processing error led to an incorrect flux calibration for these spectra. All STIS-based UV fluxes in the original paper are too high by a factor of 7.96 as a result of neglecting to adjust the flux-scaling algorithm from a diffuse source to a point source.