Outflow Kinematics Research Articles

The Correlation of Outflow Kinematics with Star Formation Rate. VI. Gas Outflows in AGNs

Abstract We investigate the connection between ionized gas outflows and star formation activity using a large sample of type 1 and 2 active galactic nuclei (AGNs) with far-infrared detections or star formation rate (SFR) estimates. The strength of ionized gas outflows, measured by the velocity dispersion and velocity shift of the [O iii] emission line, clearly shows a correlation with SFR. The connection between specific star formation rate (sSFR) and [O iii] gas velocity dispersion indicates that AGNs with stronger outflows are hosted by galaxies with higher SFR. Compared with star-forming galaxies in the main sequence, both type 1 and type 2 AGNs show sSFRs similar to that of non-AGN galaxies, indicating no instantaneous AGN feedback, while sSFR is higher (lower) for AGNs with stronger (weaker) outflows than that of main-sequence galaxies. These results are consistent with a delayed AGN feedback scenario. However, it is also possible that a decease/increase of gas fraction may cause the correlation without AGN feedback.

Protostellar Outflows at the EarliesT Stages (POETS)

Context. Although recent observations and theoretical simulations have pointed out that accretion disks and jets can be essential for the formation of stars with a mass of up to at least 20 M⊙, the processes regulating mass accretion and ejection are still uncertain. Aims. The goal of the Protostellar Outflows at the EarliesT Stages (POETS) survey is to image the disk-outflow interface on scales of 10–100 au in a statistically significant sample (36) of luminous young stellar objects (YSO), targeting both the molecular and ionized components of the outflows. Methods. The outflow kinematics is studied at milliarcsecond scales through very long baseline interferometry (VLBI) observations of the 22 GHz water masers, which are ideal test particles to measure the three-dimensional (3D) motion of shocks owing to the interaction of winds and jets with ambient gas. We employed the Jansky Very Large Array (JVLA) at 6, 13, and 22 GHz in the A- and B-Array configurations to determine the spatial structure and the spectral index of the radio continuum emission, and address its nature. Results. In about half of the targets, the water masers observed at separation ≤1000 au from the YSOs trace either or both of these kinematic structures: (1) a spatially elongated distribution oriented at close angle with the direction of collimation of the maser proper motions (PM), and (2) a linear local standard of rest (LSR) velocity (VLSR) gradient across the YSO position. The kinematic structure (1) is readily interpreted in terms of a protostellar jet, as confirmed in some targets via the comparison with independent observations of the YSO jets, in thermal (continuum and line) emissions, reported in the literature. The kinematic structure (2) is interpreted in terms of a disk-wind (DW) seen almost edge-on on the basis of several pieces of evidence: first, it is invariably directed perpendicular to the YSO jet; second, it agrees in orientation and polarity with the VLSR gradient in thermal emissions (when reported in the literature) identifying the YSO disk at scales of ≤1000 au; third, the PMs of the masers delineating the VLSR gradients hint at flow motions at a speed of 10–20 km s−1 directed at large angles with the disk midplane. In the remaining targets, the maser PMs are not collimated but rather tend to align along two almost perpendicular directions. To explain this peculiar PM distribution, and in light of the observational bias strongly favoring masers moving close to the plane of sky, we propose that, in these sources, the maser emission could originate in DW-jet systems slightly inclined (≤30°) with respect to edge-on. Magneto-centrifugally driven DWs could in general account for the observed velocity patterns of water masers.

Properties of ionized outflows in MaNGA DR2 galaxies

ABSTRACT We present the results from a systematic search and characterization of ionized outflows in nearby galaxies using the data from the second Data Release of the Mapping Nearby Galaxies at Arecibo Point Observatory (MaNGA) Survey (DR2; >2700 galaxies, z ≤ 0.015). Using the spatially resolved spectral information provided by the MANGA data, we have identified ∼5200 H α-emitting regions across the galaxies and searched for signatures of ionized outflows. We find evidence for ionized outflows in 105 regions from 103 galaxies, roughly 7 per cent of all the H α-emitting galaxies identified in this work. Most of the outflows are nuclear, with only two cases detected in off-nuclear regions. Our analysis allows us to study ionized outflows in individual regions with star formation rates (SFRs) down to ∼0.01 M⊙ yr−1, extending the ranges probed by previous works. The kinematics of the outflowing gas is strongly linked to the type of ionization mechanism: regions characterized by low-ionization emission region emission (LIER) host the outflows with more extreme kinematics (FWHMbroad ∼ 900 km s−1), followed by those originated in active galactic nuclei (550 km s−1), ‘Intermediate’ (450 km s−1), and star-forming (350 km s−1) regions. Moreover, in most of the outflows we find evidence for gas ionized by shocks. We find a trend for higher outflow kinematics towards larger stellar masses of the host galaxies but no significant variation as a function of star formation properties within the SFR regime we probe (∼0.01–10 M⊙ yr−1). Our results also show that the fraction of outflowing gas that can escape from galaxies decreases towards higher dynamical masses, contributing to the preservation of the mass–metallicity relation by regulating the amount of metals in galaxies. Finally, assuming that the extensions of the outflows are significantly larger than the individual star-forming regions, as found in previous works, our results also support the presence of star formation within ionized outflows, as recently reported by Maiolino et al. (2017) and Gallagher et al. (2018).

MAGiiCAT VI. The Mg ii Intragroup Medium Is Kinematically Complex

Abstract By comparing Mg ii absorption in the circumgalactic medium (CGM) of group environments to isolated galaxies, we investigated the impact of environment on the CGM. An Mg ii absorber is associated with a group if there are two or more galaxies at the absorption redshift within a projected distance of D = 200 kpc from a background quasar and a line-of-sight velocity separation of 500 km s−1. We compiled a sample of 29 group environments consisting of 74 galaxies (two to five galaxies per group) at . The group absorber median equivalent width ( Å) and covering fraction ( ) are larger than isolated absorbers (1.27σ and 2.2σ, respectively), but median column densities are statistically consistent. A pixel-velocity two-point correlation function analysis shows that group environment kinematics are statistically comparable to isolated environments (0.8σ), but with more power for high velocity dispersions similar to outflow kinematics. Group absorbers display more optical depth at larger velocities. A superposition model in which multiple galaxies contribute to the observed gas matches larger equivalent width group absorbers but significantly overpredicts the kinematics owing to large velocity separations between member galaxies. Finally, galaxy–galaxy groups (similar member galaxy luminosities) may have larger absorber median equivalent widths (1.7σ) and velocity dispersions (2.5σ) than galaxy–dwarf groups (disparate luminosities). We suggest that the observed gas is coupled to the group rather than individual galaxies, forming an intragroup medium. Gas may be deposited into this medium by multiple galaxies via outflowing winds undergoing an intergalactic transfer between member galaxies or from tidal stripping of interacting members.

The Redshift Evolution of Rest-UV Spectroscopic Properties in Lyman-break Galaxies at z ∼ 2–4

Abstract We present the first comprehensive evolutionary analysis of the rest-frame UV spectroscopic properties of star-forming galaxies at z ∼ 2–4. We match samples at different redshifts in UV luminosity and stellar mass, and perform systematic measurements of spectral features and stellar population modeling. By creating composite spectra grouped according to Lyα equivalent width (EW) and various galaxy properties, we study the evolutionary trends among Lyα, low- and high-ionization interstellar (LIS and HIS) absorption features, and integrated galaxy properties. We also examine the redshift evolution of Lyα and LIS absorption kinematics, and fine-structure emission EWs. The connections among the strengths of Lyα, LIS lines, and dust extinction are redshift independent, as is the decoupling of the Lyα and HIS line strengths, and the bulk outflow kinematics as traced by the LIS lines. Stronger Lyα emission is observed at higher redshift at fixed UV luminosity, stellar mass, SFR, and age. Much of this variation in the average Lyα strength with redshift, and the variation in Lyα strength at fixed redshift, can be explained in terms of variations in the neutral gas covering fraction and/or dust content in the ISM and CGM. However, based on the connection between Lyα and C iii] emission strengths, we additionally find evidence for variations in the intrinsic production rate of Lyα photons at the highest Lyα EWs. The challenge now is to understand the observed evolution of the neutral gas covering fraction and dust extinction within a coherent model for galaxy formation, and make robust predictions for the escape of ionizing radiation at z > 6.

What Sets the Line Profiles in Tidal Disruption Events?

Abstract We investigate line formation in gas that is outflowing and optically thick to electron scattering, as may be expected following the tidal disruption of a star by a supermassive black hole. Using radiative transfer calculations, we show that the optical line profiles produced by expanding TDE outflows most likely are primarily emission features, rather than the P-Cygni profiles seen in most supernova spectra. This is a result of the high line excitation temperatures in the highly irradiated TDE gas. The outflow kinematics cause the emission peak to be blueshifted and have an asymmetric red wing. Such features have been observed in some TDE spectra, and we propose that these may be signatures of outflows. We also show that non-coherent scattering of hot electrons can broaden the emission lines by ∼10,000 km s−1, such that the line width in some TDEs may be set by the electron scattering optical depth rather than the gas kinematics. The scattering-broadened line profiles produce distinct, wing-shaped profiles that are similar to those observed in some TDE spectra. The narrowing of the emission lines over time in these observed events may be related to a drop in density rather than a drop in line-of-sight velocity.

Do galaxies that leak ionizing photons have extreme outflows?

To reionize the early universe, high-energy photons must escape the galaxies that produce them. It has been suggested that stellar feedback drives galactic outflows out of star-forming regions, creating low density channels through which ionizing photons escape into the inter-galactic medium. We compare the galactic outflow properties of confirmed Lyman continuum (LyC) leaking galaxies to a control sample of nearby star-forming galaxies to explore whether the outflows from leakers are extreme as compared to the control sample. We use data from the Cosmic Origins Spectrograph on the Hubble Space Telescope to measure the equivalent widths and velocities of Si II and Si III absorption lines, tracing neutral and ionized galactic outflows. We find that the Si II and Si III equivalent widths of the LyC leakers reside on the low-end of the trend established by the control sample. The leakers' velocities are not statistically different than the control sample, but their absorption line profiles have a different asymmetry: their central velocities are closer to their maximum velocities. The outflow kinematics and equivalent widths are consistent with the scaling relations between outflow properties and host galaxy properties -- most notably metallicity -- defined by the control sample. Additionally, we use the Ly\alpha\ profiles to show that the Si II equivalent width scales with the Ly\alpha\ peak velocity separation. We determine that the low equivalent widths of the leakers are likely driven by low metallicities and low H I column densities, consistent with a density-bounded ionization region, although we cannot rule out significant variations in covering fraction. While we do not find that the LyC leakers have extreme outflow velocities, the low maximum-to-central velocity ratios demonstrate the importance of the acceleration and density profiles for LyC and Ly\alpha\ escape. [abridged]

Outflow Kinematics Manifested by the Hα Line: Gas Outflows in Type 2 AGNs. IV.

Abstract Energetic ionized gas outflows driven by active galactic nuclei (AGNs) have been studied as a key phenomenon related to AGN feedback. To probe the kinematics of the gas in the narrow-line region, [O iii] λ5007 has been utilized in a number of studies showing nonvirial kinematic properties due to AGN outflows. In this paper, we statistically investigate whether the Hα emission line is influenced by AGN-driven outflows by measuring the kinematic properties based on the Hα line profile and comparing them with those of [O iii]. Using the spatially integrated spectra of ∼37,000 Type 2 AGNs at z < 0.3 selected from the Sloan Digital Sky Survey DR7, we find a nonlinear correlation between Hα velocity dispersion and stellar velocity dispersion that reveals the presence of the nongravitational component, especially for AGNs with a wing component in Hα. The large Hα velocity dispersion and velocity shift of luminous AGNs are clear evidence of AGN outflow impacts on hydrogen gas, while relatively smaller kinematic properties compared to those of [O iii] imply that the observed outflow effect on the Hα line is weaker than the case of [O iii].

Delayed or No Feedback? Gas Outflows in Type 2 AGNs. III.

Abstract We present gas kinematics based on the [O iii]λ5007 line and their connection to galaxy gravitational potential, active galactic nucleus (AGN) energetics, and star formation, using a large sample of ∼110,000 AGNs and star-forming (SF) galaxies at z < 0.3. Gas and stellar velocity dispersions are comparable to each other in SF galaxies, indicating that the ionized gas kinematics can be accounted by the gravitational potential of host galaxies. In contrast, AGNs clearly show non-gravitational kinematics, which is comparable to or stronger than the virial motion caused by the gravitational potential. The [O iii] velocity–velocity dispersion (VVD) diagram dramatically expands toward high values as a function of AGN luminosity, implying that the outflows are AGN-driven, while SF galaxies do not show such a trend. We find that the fraction of AGNs with a signature of outflow kinematics, steeply increases with AGN luminosity and Eddington ratio. In particular, the majority of luminous AGNs presents strong non-gravitational kinematics in the [O iii] profile. AGNs with strong outflow signatures show on average similar specific star formation rates (sSFRs) to those of star-forming galaxies. In contrast, AGNs with weak or no outflows have an order of magnitude lower sSFRs, suggesting that AGNs with current strong outflows do now show any negative AGN feedback and that it may take dynamical time to impact on star formation over galactic scales.

MICROLENSING CONSTRAINTS ON BROAD ABSORPTION AND EMISSION LINE FLOWS IN THE QUASAR H1413+117

We present new integral field spectroscopy of the gravitationally lensed broad absorption line (BAL) quasar H1413+117, covering the ultraviolet restframe spectral range. We observe strong microlensing signatures in lensed image D, and we use this microlensing to simultaneously constrain both the broad emission and broad absorption line gas. The wavelength independence of image D magnifications across the broad emission lines (BELs) indicates a lower limit on the broad emission line region (BELR) size equal to the Einstein radius (ER) of the system: ≳11 lt-day for a lens redshift of 1.4 and ≳15 lt-day for zL = 0.94. Lensing simulations verify that the observed wavelength independence is very unlikely for BELRs with significant velocity stratification at size scales below an ER. We perform spectral decomposition to derive the intrinsic BEL and continuum spectrum, subject to BAL absorption. We reconstruct the intrinsic BAL absorption profile, whose features allow us to constrain outflow kinematics in the context of a disk-wind model. We find a very sharp, blueshifted onset of absorption of 1500 km s−1 in both C iv and N v, which may correspond to an inner edge of a disk-wind's radial outflow. The lower ionization Si iv and Al iii have higher-velocity absorption onsets, consistent with a decreasing ionization parameter with radius in an accelerating outflow. There is evidence of strong absorption in the BEL component, which indicates a high covering factor for absorption over two orders of magnitude in outflow radius.

KECK SPECTROSCOPY OF GRAVITATIONALLY LENSEDz≃ 4 GALAXIES: IMPROVED CONSTRAINTS ON THE ESCAPE FRACTION OF IONIZING PHOTONS

The fraction of ionizing photons that escape from young star-forming galaxies is one of the largest uncertainties in determining the role of galaxies in cosmic reionization. Yet traditional techniques for measuring this fraction are inapplicable at the redshifts of interest due to foreground screening by the Lyman alpha forest. In an earlier study, we demonstrated a reduction in the equivalent width of low-ionization absorption lines in composite spectra of Lyman break galaxies at z=4 compared to similar measures at z=3. This might imply a lower covering fraction of neutral gas and hence an increase with redshift in the escape fraction of ionizing photons. However, our spectral resolution was inadequate to differentiate between several alternative explanations, including changes with redshift in the outflow kinematics. Here we present higher quality spectra of 3 gravitationally lensed Lyman break galaxies at z=4 with a spectral resolution sufficient to break this degeneracy of interpretation. We present a method for deriving the covering fraction of low-ionization gas as a function of outflow velocity and compare the results with similar quality data taken for galaxies at lower redshift. We find a significant trend of lower covering fractions of low-ionization gas for galaxies with strong \Lya emission. In combination with the demographic trends of \Lya emission with redshift from our earlier work, our results provide new evidence for a reduction in the average H I covering fraction, and hence an increase in the escape fraction of ionizing radiation from Lyman break galaxies, with redshift.

CARMA OBSERVATIONS OF PROTOSTELLAR OUTFLOWS IN NGC 1333

We present observations of outflows in the star-forming region NGC 1333 using the Combined Array for Research in Millimeter-Wave Astronomy (CARMA). We combined the 12CO and 13CO (1-0) CARMA mosaics with data from the 14-m Five College Radio Astronomy Observatory (FCRAO) to probe the central, most dense and active region of this protostellar cluster at scales from 5'' to 7' (or 1000 AU to 0.5 pc at a distance of 235 pc). We map and identify 12CO outflows, and along with 13CO data we estimate their mass, momentum and energy. Within the 7'x7' map, the 5'' resolution allows for a detailed study of morphology and kinematics of outflows and outflow candidates, some of which were previously confused with other outflow emission in the region. In total, we identify 22 outflow lobes, as well as 9 dense circumstellar envelopes marked by continuum emission, of which 6 drive outflows. We calculate a total outflow mass, momentum and energy within the mapped region of 6 Msun, 19 Msun km/s, and 7x10^44 erg, respectively. Within this same region, we compare outflow kinematics with turbulence and gravitational energy, and we suggest that outflows are likely important agents for the maintenance of turbulence in this region. In the earliest stages of star formation, outflows do not yet contribute enough energy to totally disrupt the clustered region where most star formation is happening, but have the potential to do so as the protostellar sources evolve. Our results can be used to constrain outflow properties, such as outflow strength, in numerical simulations of outflow-driven turbulence in clusters.

NEUTRAL GAS OUTFLOWS AND INFLOWS IN INFRARED-FAINT SEYFERT GALAXIES

Previous studies of the Na I D interstellar absorption line doublet have shown that galactic winds occur in most galaxies with high infrared luminosities. However, in infrared-bright composite systems where a starburst coexists with an active galactic nucleus (AGN), it is unclear whether the starburst, the AGN, or both are driving the outflows. The present paper describes the results from a search for outflows in 35 infrared-faint Seyferts with 10^9.9 < L_IR/L_sun < 10^11, or, equivalently, star formation rates (SFR) of ~0.4 -- 9 solar masses per year, to attempt to isolate the source of the outflow. We find that the outflow detection rates for the infrared-faint Seyfert 1s (6%) and Seyfert 2s (18%) are lower than previously reported for infrared-luminous Seyfert 1s (50%) and Seyfert 2s (45%). The outflow kinematics of infrared-faint and infrared-bright Seyfert 2 galaxies resemble those of starburst galaxies, while the outflow velocities in Seyfert 1 galaxies are significantly larger. Taken together, these results suggest that the AGN does not play a significant role in driving the outflows in most infrared-faint and infrared-bright systems, except the high-velocity outflows seen in Seyfert 1 galaxies. Another striking result of this study is the high rate of detection of inflows in infrared-faint galaxies (39% of Seyfert 1s, 35% of Seyfert 2s), significantly larger than in infrared-luminous Seyferts (15%). This inflow may be contributing to the feeding of the AGN in these galaxies, and potentially provides more than enough material to power the observed nuclear activity over typical AGN lifetimes.

Beam models for gamma-ray bursts sources: outflow structure, kinematics and emission mechanisms

The variety of γ-ray burst phenomenology could be largely attributable to differences in the opening angle of an isotropic outflow or to a standard type of event viewed from different orientations. Motivated by this currently popular idea, we study the effects of varying the energy per unit solid angle in the unsteady expelled outflow by an increase either in the bulk Lorentz factor or in the baryon loading. We apply these models to interpret the observed correlations between variability, luminosity and spectral peak energy and find that while the latter scenario fails to provide a good description, bursts produced by collisions between similar mass shells but with increasingly large Lorentz factors are both more variable and have larger peak spectral energies. We present detailed internal shock calculations confirming this interpretation and discuss the roles various timescales, radii and the optical thickness of the wind play in determining this wide range of behaviors. Finally, we discuss the variety of scenarios in which large variations of the source expansion velocity are naturally expected.

Velocity-Resolved Echo Mapping

AbstractWe probe the structure and kinematics of Seyfert broad-line regions by using a velocity-delay map to fit simultaneously the observed variations in the continuum and the emission-line profiles. The velocity-delay map of C IVλ1550 emission constructed from 44 IUE spectra of NGC 4151 suggests virial motions, with 107M⊙ inside two light days. Pure inflow and outflow kinematics are ruled out by the approximate symmetry of the map. A stronger redshifted response at small delays suggests either a component with free-fall kinematics, or an outflow with CIV being emitted inward by optically thick gas clouds.

Outflows from young stellar objects in BOK globules: Maps

view Abstract Citations (82) References (20) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Outflows from Young Stellar Objects in BOK Globules: Maps Yun, Joao Lin ; Clemens, Dan P. Abstract We have obtained (12)CO J = 1-0 spectral line maps of high-velocity gas outflows from a sample of 14 small Bok globules containing low-mass young stellar objects (YSOs). The observations were performed using the new 15 beam receiver (QUARRY) of the Five College Radio Astronomy Observatory. Morphologically, the outflows in our sample exhibit small angular extents, and relatively wide angular lobes with the majority exhibiting low apparent degrees of collimation. The presence of an outflow was found to be correlated with the value of the Infrared Astronomical Satellite (IRAS)- based spectral index (between 12 and 25 micrometers) of the YSOs. Outflows were more frequently detected in those globules with the reddest IRAS point sources. These spectral indices are consistent with emission from objects in fairly early stages of the star formation process which are still deeply embedded in gas and dust. Energetically, the outflows in our sample may be among the weakest and least massive found to date. Nevertheless, both the outflow kinematics and energetics indicate that they may play an important role in cloud support and evolution. Publication: The Astrophysical Journal Supplement Series Pub Date: May 1994 DOI: 10.1086/191963 Bibcode: 1994ApJS...92..145Y Keywords: Astronomical Maps; Carbon Monoxide; Ejecta; Globules; Interstellar Matter; Line Spectra; Mapping; Molecular Clouds; Radio Astronomy; Radio Spectra; Star Formation; Stellar Evolution; Stellar Mass Ejection; Antennas; Astronomical Spectroscopy; Data Integration; Microwave Spectrometers; Stellar Envelopes; Astrophysics; ISM: JETS AND OUTFLOWS; ISM: MOLECULES; RADIO LINES: ISM; STARS: FORMATION; STARS: PRE--MAIN-SEQUENCE full text sources ADS | data products SIMBAD (34)

High-resolution spectra of the 6300-Å region of Comet P/Halley

A series of high resolution spectra of the 6300-Å region of Comet P/Halley were taken with the echelle/reticon system on the 61-in. telescope at the Harvard-Smithsonian Oak Ridge Observatory from 23 October 1985 through 5 January 1986. Relative contributions of various rotational lines within the (0,8,0) band of NH 2 and of the cometary and airglow contributions of O( 1D) were clearly spectrally separated. Measurements were taken both centered on the nucleus as well as offset by various displacements in different directions. A number of important implications have resulted from the analysis of these data. (1) The relative fluxes of different rotational members of the NH 2 (0,8,0) band vary not only from day-to-day, as previously reported, but also with radial distance within the coma. Indications are that the vib-rotational structure of the band could be useful as a diagnostic for coma temperatures and/or outflow kinematics. (2) Deviations from circular symmetry were negligible for NH 2 but detectable for O( 1D), having only a small (0–10%) average sunward asymmetry. (3) The inner radial brightness distribution for O( 1D) is consistent with its production from the photodissociation of its parent (H 2O). (4) The inner radial brightness distributions for NH 2 were reasonably consistent with previously published results found for Halley and other comets. (5) Some inconsistencies were found in the comparison of the cometary NH 2 line wavelengths with the standard laboratory values.

Relics of an eruptive starburst in NGC 1569

view Abstract Citations (101) References (41) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Relics of an Eruptive Starburst in NGC 1569 Waller, William H. Abstract Hα, A, and I band CCD images of the "posteruptive" irregular galaxy NGC 1569 are presented. The discovery of two arclike structures of diffuse Hα emission located more than 1 kpc beyond the star- forming bar is reported. These features are used to estimate an age for the near-nuclear starburst that created them along with other filamentary and armlike structures previously seen in Ha photographs. Considerations of likely outflow geometries and kinematics lead to an estimated age range of 10-60 Myr, in rough accord with the 10-20 Myr age that Israel and de Bruyn derive based on considerations of synchrotron losses in the nonthermal radio spectrum. The gravitational and kinematic energies associated with the Hα arcs are estimated to be orders of magnitude higher than can be provided by a single supernova explosion. Coherent outbursts involving thousands of supernovae each could explain the diffuse Hα features without exceeding the starbirth rate inferred from the total Hα luminosity of the galaxy. Comparisons between the line and continuum imagery show the inner bar to be populated with H II regions of high Hα equivalent width and blue color. These regions are located on opposite sides of the brightest continuum emission which, in turn, is offset from the dynamical nucleus as defined by the outer B and V isophotes. A starburst history incorporating these observations is proposed and discussed. Publication: The Astrophysical Journal Pub Date: March 1991 DOI: 10.1086/169799 Bibcode: 1991ApJ...370..144W Keywords: Galactic Evolution; Galactic Structure; Irregular Galaxies; Star Formation; Starburst Galaxies; Charge Coupled Devices; Emission Spectra; Galactic Nuclei; H Alpha Line; H Ii Regions; Spectral Line Width; Astrophysics; GALAXIES: EVOLUTION; GALAXIES: INDIVIDUAL NGC NUMBER: NGC 1569; GALAXIES: INTERSTELLAR MATTER; GALAXIES: STELLAR CONTENT; GALAXIES: STRUCTURE full text sources ADS | data products SIMBAD (22) NED (15)